UBC Theses and Dissertations

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UBC Theses and Dissertations

The synthesis of a free-piston power saw Fandrich, Helmut Edward 1970

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THE  SYNTHESIS OF A F R E E - P I S T O N POWER SAW  by HELMUT EDWARD FANDRICH B.A.Sc., U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1960 M.A.Sc., U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1962 ENGINEER, S t a n f o r d U n i v e r s i t y , 1964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department of MECHANICAL ENGINEERING  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e required standard:  UNIVERSITY OF BRITISH COLUMBIA F e b r u a r y , 1970  In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l requirements  f u l f i l m e n t of  the  f o r an advanced degree a t the U n i v e r s i t y  of  B r i t i s h C o l u m b i a , I agree t h a t the L i b r a r y s h a l l make  it  freely  a v a i l a b l e f o r r e f e r e n c e and s t u d y a f t e r May 1, 1973  unless t h i s  d i r e c t i o n i s countermanded by me and the Head  o f the Department of M e c h a n i c a l E n g i n e e r i n g b e f o r e t h a t d a t e . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of  this  t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head of my Department o r by h i s r e p r e s e n t a t i v e s a f t e r May 1, 1973. It  i s understood t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s  for financial  thesis  g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n  permission.  HELMUT EDWARD FANDRICH  Department o f M e c h a n i c a l E n g i n e e r i n g The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8 , Canada  ABSTRACT The  o b j e c t o f t h i s s t u d y was t o a p p l y t h e t e c h n i q u e  o f s y n t h e s i s t o t h e d e s i g n o f a s m a l l power saw.  The s t u d y  produced e x p e r i m e n t a l d a t a on optimum c h a i n speeds,  engine  v i b r a t i o n s , n o i s e l e v e l s , and h e a t t r a n s f e r c o e f f i c i e n t s f o r r e c i p r o c a t i n g c y l i n d e r heads, and l e d t o a s i m p l e f r e e - p i s t o n c o n f i g u r a t i o n i n w h i c h a p i s t o n o s c i l l a t e d between a m i x t u r e o f a i r and f u e l i n one end o f a c l o s e d c y l i n d e r and a s p r i n g i n the other.  The f e a s i b i l i t y o f d e v e l o p i n g t h e c o n f i g u r a t i o n  i n t o a p r a c t i c a l r e c i p r o c a t i n g engine was v e r i f i e d by d e s i g n ing,  b u i l d i n g and t e s t i n g a p r o t o t y p e . The p r o t o t y p e i n c o r p o r a t e d such n o v e l f e a t u r e s as  i n s t a n t , e f f o r t l e s s s t a r t i n g and s t o p p i n g , a u t o m a t i c ing,  s e l f - c o o l i n g , compression  i g n i t i o n of a carbureted a i r -  f u e l m i x t u r e , and a b a l a n c e d e n g i n e . t i m i n g reduced  Uncontrolled i g n i t i o n  engine e f f i c i e n c y , and t h e l a c k o f i n e r t i a  made e n g i n e s t a l l i n g easy and c a r b u r e t o r a d j u s t m e n t The  throttl-  difficult.  computed r e s u l t s suggest t h a t a d e v e l o p e d  3lb  f r e e - p i s t o n power saw w i l l produce 1.0 hp a t 6,400 cpm and have a s p e c i f i c f u e l consumption o f .9 l b / s h p - h r .  iii  TABLE OF CONTENTS Chapter  1.  Page  FORMULATION  1  1.1  Introduction  1  1.2  S p e c i f i c a t i o n f o r the Design Envelope  2.  26  SYNTHESIS  63  2.1  Wood C u t t i n g  Devices  . ;  2.2 2.3  Evaluation o f E x i s t i n g Engines Synthesis of A l t e r n a t i v e s  2.4  Synthesis  of the Free-piston  63  power  Saw 3.  107  DETAILING  118  3.1  Dimensional Analysis  118  3.2  Automatic T h r o t t l i n g  145  3.3  D e s i g n o f Components  156  3.3.1  General Considerations  156  3.3.2  Bounce S p r i n g  158  3.3.3  Synchronizing  3.3.4  A r r e s t i n g Mechanism  184  3.3.5  Cooling  190  3.3.6  Combustion  3.4 4.  77 91  Mechanism  System System  F a b r i c a t i o n of Parts  EVALUATION 4.1  Performance C h a r a c t e r i s t i c s o f the F r e e - p i s t o n Saw  172  197 206 216  216  .iv Page 4.2  Conclusions  4.3  Summary  . .  237 241  REFERENCES  247  APPENDICES I II III IV  Cutting  Speed T e s t D a t a  C h a i n Saw V i b r a t i o n  257  Test Data  258  C h a i n Saw N o i s e T e s t D a t a Data  from t h e Q u e s t i o n n a i r e  259 o n t h e Use  o f Power Saws V VI VII  Typical  260  Power Saw P e r f o r m a n c e  Data f o r Heat T r a n s f e r from Heads FPS P r o t o t y p e T e s t D a t a .  Data  . . . .  261  Reciprocating 262 263  V  LIST OF TABLES Table I II III IV  V VI VII VIII  Page S p e c i f i c a t i o n s f o r a s m a l l power saw  61  C h a r a c t e r i s t i c s o f t h e c o n v e n t i o n a l and Wankel e n g i n e s  81  Scaling characteristics f o r similar engines Size of m a t e r i a l  required  to store  129 175  i n - l b o f energy  166  C a p a c i t y and optimum s i z e o f bands  179  M a t e r i a l s s u i t a b l e f o r c y l i n d e r heads and b l o c k s Materials suitable f o r pistons  197 202  Performance c h a r a c t e r i s t i c s o f t h e f r e e p i s t o n power saw  237  vi L I S T OF  FIGURES  Figure 1.1  1.2  1.3  1.4  Page O u t l i n e of the engineers task Cutting with c h a i n saws  comprehensive  one  of  the  design ,  original  one-man 17  Sketches of the tooth chains  c h i s e l - t o o t h and  Typical l i s t  chain  circ.  10  of  chipper1^  saw  specifications,  1950  1  9  1.5  T y p i c a l t r e e h a r v e s t i n g machine  24  1.6 1.7  A p p a r a t u s used i n c h a i n speed t e s t s Schematic r e p r e s e n t a t i o n of m u f f l e r e l e c t r i c a l equivalent  33  1.8 1.9  Accidents reported Paper A s s o c i a t i o n Results of  saw  t o Quebec P u l p  and ">3  and ^6  of q u e s t i o n n a i r e  on  the  importance  characteristics  ^0  2.1  Diagrams  illustrating  2.2  Stirling  thermal engine  2.3  Sketches of  the  unbalanced  2.4  A  the  oscillating  sketch  of  hot-gas c y c l e schematic drawing l e v e r engine  85 . . . . . . .  88 9  ^  free-piston  engine  101  2.5  T y p i c a l r e c i p r o c a t i n g - b l a d e saws  115  2.6 3.1  Existing free-piston configurations F r e e body d i a g r a m o f t h e f r e e - p i s t o n power saw  117  3.2  3.3  Photographs of heat t r a n s f e r apparatus Free-piston  power saw  157  test  assembly  19 5 sketch  207  vii Figure  Page  3.4  Photograph o f t h e t r a n s f e r p o r t m a c h i n i n g operation  209  3.5  Photographs o f s y n c h r o n i z i n g and a r r e s t i n g mechanism a s s e m b l i e s  212  3.6  Photographs o f FPS components .  214  3.7  P h o t o g r a p h o f a l l FPS p a r t s  215  4.1  Photographs o f t h e i n s t r u m e n t e d  4.2  Photographs o f t h e FPS, w i t h a f i x e d - t h r o w crankshaft  222  4.3  Photographs o f t h e FPS w i t h an o s c i l l a t ing crankshaft  2 30  4.4  Subassembly photographs o f a c o n v e n t i o n a l power saw and t h e FPS  2 39  FPS  222  viii  LIST OF GRAPHS Graph  Page  1.1  Power saw performance t r e n d s  22  1.2  Optimum power as a f u n c t i o n o f t r e e size  31  1.3  Importance o f s p r o c k e t s i z e on c u t t i n g rates  - 35  1.4  Importance o f j o i n t on c u t t i n g r a t e s  35  1.5  Cutting  35  1.6 1.7  rate variations  -Importance o f b a r l e n g t h on c u t t i n g rates Importance o f wood s p e c i e s on c u t t i n g rates  .  1.8  Gear d r i v e c u t t i n g r a t e s  1.9  S p e c i f i c energy as a f u n c t i o n o f c h a i n speed V i b r a t i o n damage l e v e l s as a f u n c t i o n of frequency V i b r a t i o n amplitude while c u t t i n g versus counterweight s i z e  1.10 1.11 1.12  35 36 36 36 40 44  V i b r a t i o n a m p l i t u d e w h i l e c u t t i n g and w h i l e unloaded  44  1.13  E f f e c t o f b a r on a m p l i t u d e w i t h d i f f e r e n t counterweights  45  1.14  E f f e c t o f b a r on v i b r a t i o n a m p l i t u d e  46  1.15  E f f e c t o f speed on v i b r a t i o n a m p l i t u d e . . . .  46  1.16  E f f e c t o f r u b b e r i n s u l a t i o n on v i b r a t i o n amplitude  47  1.17  Noise saws  50  several  l e v e l r e a d i n g s o f t y p i c a l power  ix Graph  Page  1.18  S t a t e o f Washington s t a n d a r d t r i a l noise  1.19  T e n t a t i v e Swedish n o i s e l e v e l l i m i t s f o r power saws  52  S p e c i f i c energy r e q u i r e d by v a r i o u s wood c u t t i n g d e v i c e s  77  2.2  Power o f a Wankel e n g i n e compared w i t h c o n v e n t i o n a l engines  82  2.3  Computed p i s t o n p o s i t i o n f o r t h e unbalanced l e v e r engine  98  2.4  B l a d e and p i s t o n p o s i t i o n as a f u n c t i o n of c o m p r e s s i o n r a t i o  2.1  3.1  f o r indus-  51  103  Power as a f u n c t i o n o f p i s t o n a r e a f o r t y p i c a l power saws  122  3.2  S p e c i f i c power as a f u n c t i o n o f bore s i z e . .  125  3.3  S p e c i f i c w e i g h t as a f u n c t i o n o f b o r e size S p e c i f i c power as a f u n c t i o n o f p i s t o n speed  3.4 3.5  125 133  S p e c i f i c power as a f u n c t i o n o f e n g i n e speed  133  3.6  P o r t a r e a s o f t y p i c a l power saws v e r s u s stroke/bore r a t i o s  135  3.7  Port heights versus bore r a t i o s  137  3.8  square r o o t o f s t r o k e /  S p e c i f i c power and BMEP v e r s u s p o r t  area  ratios  141  3.9  Flow a r e a v e r s u s  3.10  P i s t o n s t r o k e s as a f u n c t i o n o f t i m e f o r i d e a l FPS S t r o k e v a r i a t i o n caused by sudden l o a d changes  3.11  s t r o k e f o r i d e a l FPS . . . .  149 152 163  X  Graph  Page  3.12  Maximum l o a d t r a n s m i t t e d by bands  181  3.13  Heat t r a n s f e r c u r v e f o r r e c i p r o c a t i n g c y l i n d e r heads  196  3.14  C a l c u l a t e d thermal b u s t i o n chambers  200  4.1  Prototype  4.2  Prototype engine t r a c e s without (computed)  4.3  E f f e c t of leakage,  l o s s e s from com-  engine t r a c e s  (experimental).  . . .  combustion  223 224  f r i c t i o n and damping  on t r a c e s  (computed)  225  4.4  Prototype  engine t r a c e s w i t h combustion . . .  226  4.5  Crank e n g i n e performance ( e x p e r i m e n t a l and computed) Experimental engine p o s i t i o n t r a c e s (experimental)  4.6 4.7  Experimental (computed)  229 2 32  engine p o s i t i o n t r a c e s 233  ACKNOWLEDGEMENTS  Of the  author would  special Stainsby and  like  recognition:  thesis,  Mr. A.F.B. M i l l i g a n a n d Mr. J . C . Saw  G. Dueck f o r c o n t i n u i n g  Fellowship  the f i n a n c i a l  D r . E.G. Hauptmann f o r s u p e r v i s i o n o f t h e p r o j e c t ;  C. B r o c k l e y ,  Prof.  this  to s i n g l e out the following f o r  f o r s e t t i n g up t h e C a n a d i e n C h a i n  G r a n t ; Mr. P e t e r  support; Dr.  t h e many p e o p l e a s s o c i a t e d w i t h  W.O.  D r . J . P . D u n c a n , D r . N. E p s t e i n , a n d  Richmond  A proofreading  f o r a c t i n g on t h e s u p e r v i s o r y  s p e c i a l t h a n k s t o my w i f e the t h e s i s .  committee  f o r her help i n  1  1. 1.1  FORMULATION  Introduction This  study evolved a c o n f i g u r a t i o n f o r a s m a l l  prime mover t o be used i n a c l a s s o f a p p l i c a t i o n s such as power saws.  Starting with a formulation  of the basic  power saw r e q u i r e m e n t s , t h e s t u d y c o n t i n u e d w i t h a s y n t h e s i s of s e v e r a l a l t e r n a t i v e s t o t h e c o n v e n t i o n a l engine.  Synthesis  reciprocating  was f o l l o w e d w i t h an o p t i m i z a t i o n o f  the most p r o m i s i n g a l t e r n a t i v e and a d e t a i l d e s i g n o f t h e components.  The s t u d y c o n c l u d e d w i t h a v e r i f i c a t i o n o f  the i d e a by t e s t i n g an a c t u a l p r o t o t y p e .  The end r e s u l t  was a l i g h t - w e i g h t , v i b r a t i o n l e s s , q u i c k - s t a r t i n g , s e l f t h r o t t l i n g , f r e e - p i s t o n machine t h a t d e p a r t e d  "radically"  from e x i s t i n g power saws. In the c o n f i g u r a t i o n optimized  and b u i l t , a p i s t o n  bounces between a s p r i n g i n one end o f a c l o s e d and  cylinder  a volume o f f u e l and a i r i n t h e o t h e r end. A b l a d e i s  attached  d i r e c t l y t o the o s c i l l a t i n g p i s t o n .  the m i x t u r e d u r i n g  By i g n i t i n g  the compression s t r o k e , a simple  prime mover i s t h e o r e t i c a l l y p o s s i b l e . Engineering process applying  d e s i g n i s an i t e r a t i v e d e c i s i o n - m a k i n g  s c i e n t i f i c p r i n c i p l e s and u t i l i z i n g  t i c a l techniques i n order t o define a device,  prac-  a process, or  a system i n s u f f i c i e n t d e t a i l t o p e r m i t i t s p h y s i c a l  real-  2 ization  [ 1 . 1 , 1.2]  *  t h e most e c o n o m i c a l  .  A good d e s i g n  and r e s u l t s  i n a functional,  that  n o t o n l y meets t h e s t i p u l a t e d a e s t h e t i c appeal  creatively-designed combination device  product  of engineering principles  very broad  behaviour. creative his  concepts  ability  [1.8]  will  called  this  f a m i l i a r with  thought  and  He u n d e r s t a n d s  the  a delicate  each d e s i g n common  between  and t o e v a l u a t e .  and s e r v i c e d .  a "comprehensive  Arnold designer".  p r o j e c t h a s i t s own  history,  t o a l l p r o j e c t s forms a  pattern  t h a t c a n be s t u d i e d p r o f i t a b l y .  pattern  engineers  have o b t a i n e d  methodology o f d e s i g n  balance  the environment i n which h i s  used  generalist  t o be  who i s m o t i v a t e d  o f human a c t i v i t y ,  He m a i n t a i n s  sequence o f events  likely  The  1.7].  i s a generalist  be made, s o l d ,  Although the  [1.6,  startling  I t s a t i s f i e s the  to synthesize, t o analyze,  He i s t h o r o u g h l y product  and v e r y  He c o m m u n i c a t e s w e l l .  process.  often  A good  and known d a t a .  s p e c t a c u l a r and newsworthy.  A good d e s i g n e r  product  conditions but also  i s a unique,  maker and f a s c i n a t e s t h e u s e r  by  often patentable  [ 1 . 3 , 1.4, 1 . 5 ] ,  i s u s e f u l and b e n e f i c i a l  dramatic,  m a n u f a c t u r e by  method and i n t h e s h o r t e s t p o s s i b l e  time  incorporates  permits  By e x a m i n i n g  an i n s i g h t  by w h i c h t h o u g h t s  this  into the  about needs a r e  * end  References i n parenthesis r e f e r of this thesis.  to Bibliography at  3 projected  into  The theorize, recipe  results  cially  and  not  process  following  steps  4.  store  of  The  solution  necessarily  the  recipe.  - gathering  - thinking  use  of  that  is  this usually  best  one  finan-  possible.  solution,, e s p e c i a l l y to  add  a creative  The  inventive  1.14,  1.15]:  skills  and  process  or has  formulating  - a period  deliberate  thinking  i n s p i r a t i o n - the i s the  verification  As  scope of  knowledge, the and  and  to  has  after  failed,  sudden i d e a  his  or  reorganization  and  through with  generaliza-  elaborations.  creative  progressive  work d e p e n d s upon d e s i g n e r endeavours  enlarge his viewpoints  observation.  e m o t i o n a l b l o c k s and  of mental r e s t  - following  evaluations  perceptive  intensely  solution,  tions, the  d e l i b e r a t e l y and  problem,  incubation  experience,  the  i t i s necessary  [1.12, 1.13,  perspiration  which 5.  [1.11].  analyze,  problem,  about the 3.  to  preparation the  2.  modify  1.10].  standard recipe:  a r r i v e a t a more o p t i m a l  a complex p r o b l e m ,  1.  the  in a conventional  f e a s i b l e but  inventive  be  leads to  [1.9,  r e a l i z a b l e , e c o n o m i c a l l y w o r t h w h i l e , and  To  the  pattern  delineate  physically  to  ideas about t h i n g s  By  conscious of  being  through  aware o f  to  study,  his  his predisposition  his  to  4  p a r t i c u l a r images, methods or way his  o f t h i n k i n g , he overcomes  b i g g e s t o b s t a c l e t o o r i g i n a l i t y because a b i l i t y t o  r e c a l l the r i g h t images and the a b i l i t y t o m o d i f y images e f f e c t i v e l y a r e two e s s e n t i a l i n g r e d i e n t s of [1.12,  creativity  1.16]. In c o n t r a s t t o the c r e a t i v e m e n t a l p r o c e s s e s  these non-creative processes  are  [1.15]:  1. o b s e r v a t i o n - s t u d y i n g p e r c e i v e d o b j e c t s and  circum-  stances , 2. r e f l e c t i o n - r e v i e w i n g the c o n t e n t o f the mind, 3. remembering - r e c a l l i n g p a s t e x p e r i e n c e s  and  pre-  v i o u s l y acquired ideas, 4. r e a s o n i n g - d e t e r m i n i n g  the consequences o f assumed  c o n d i t i o n s and c o u r s e s o f a c t i o n , 5. judgment - f o r m u l a t i n g d e c i s i o n s . But no new  s o l u t i o n s are p o s s i b l e without s t i m u l a t i o n .  What s t i m u l a t e s us? a new  Niemann [1.17] suggests  phenomenon, a new  r e a l i z a t i o n , a new  f r u i t f u l anger over an i n c o m p l e t e  excitement  requirement,  t h i n g o r the l i v e l y  ence o f o p i n i o n w i t h o t h e r e x p e r i e n c e d  over  people.  the differ-  Less  i n f l u e n t i a l , but n e v e r t h e l e s s s a t i s f a c t o r y , i s the s t i m u l a t i o n t h a t comes through r e a d i n g w i t h an a l e r t a t t i t u d e and u n r e s t t h a t comes t h r o u g h c r i t i c i s m o f the p r e s e n t , p r e s e n t a t i o n o f new express t h e i r  p o i n t s of v i e w and by h e a r i n g  wishes.  the  by  others  5  C r e a t i v i t y i s only a f a i r l y recent i n c l u s i o n i n engineering  courses.  Perhaps t h e e a r l i e s t f o r m u l a t i o n o f  the c r e a t i v e d e s i g n p r o c e s s was f o r G e n e r a l E l e c t r i c Company's " C r e a t i v e E n g i n e e r i n g 1937  [1.18, 1.19]. 1. 2. 3. 4.  Program" e s t a b l i s h e d i n  The f o l l o w i n g s t e p s were  formulated:  D e f i n i t i o n o f the problem, M a n i p u l a t i o n o f elements b e a r i n g on s o l u t i o n . Period r e s u l t i n g i n the i n t u i t i v e idea, The i d e a i s shaped t o p r a c t i c a l u s e f u l n e s s . [1.19, p. 9] From about 1940 t o 1960,  c r e a t i v i t y was emphasized i n  the hope t h a t b e t t e r t e c h n o l o g i c a l d e s i g n s would r e s u l t . Roadblocks by d e s i g n e r s  t o c r e a t i v e a c t i v i t y were i n v e s t i g a t e d n o t o n l y b u t by a u t h o r s g e n e r a l l y .  c l e a r l y demonstrates t h a t although  E r i c h Fromm [1.20]  each p e r s o n has a s t r o n g  need f o r s e c u r i t y , t o be a member o f a g r o u p , t o b e l o n g t o s o m e t h i n g , he e x p r e s s e s t h i s need p o s i t i v e l y o r n e g a t i v e l y . He becomes a f r e e p r o d u c t i v e l o g i c a l blocks.  i n d i v i d u a l o r he forms psycho-  These b l o c k s form f i l t e r s t h a t d i s t o r t t h e  i n f o r m a t i o n he r e c e i v e s from t h e o u t s i d e w o r l d ,  inhibit  f r e e a s s o c i a t i o n w i t h i n h i s b r a i n , and p r e v e n t c l e a r communication to others. In t h e l a t e f i f t i e s and e a r l y s i x t i e s ,  thoughtful  i n d i v i d u a l s began t o r e a l i z e t h a t t h e r e was c o n s i d e r a b l y more t o t h e d e s i g n p r o c e s s t h a n a n a l y s i s o r even c r e a t i v i t y . O b s e r v i n g t h e a c t i o n s o f h i s f e l l o w man, T i e l h a r d de C h a r d i n [1.21] f e l t t h a t man i s o b s e s s e d by t h e need t o d e p e r s o n a l -  6 ize  a l l that  he  most  admires,  partly  because  of  analysis, that marvellous instrument of scientific r e s e a r c h t o w h i c h we owe a l l our advances but w h i c h , b r e a k i n g down s y n t h e s i s a f t e r s y n t h e s i s , a l l o w s one s o u l a f t e r a n o t h e r t o e s c a p e , l e a v i n g us c o n f r o n t e d w i t h a p i l e o f d i s m a n t l e d machinery. [1.21, p. 283]  Arnold engineers view  of  to  the  topics  as  theory  and  [1.7,  1.18]  recognize design  rapidly  changing  when  in  included  of  the  and  mind,  research view of  has  a  flexibility  yet  the  time  engineer  alternatives,  choose  uration  rational  using  continually  challenges  process  an  not  solution but  a  "open  environment  [1.22].  increases required.  the The  dynamic  number result  The of  problems  of  to  approach.  arrive  at  achieve  concrete  generate  several  then  optimize  the  Information  loop"  system the  system  where  of  the  skill  design  where  the  environment, the  design,  feedback  config-  feedback  the  affect  "the  a  To  the  to  v a r i a b l e s and  i s that  important  complex  interaction dynamic  an  to  h i s d e c i s i o n s , making  not  design.  solution  techniques.  information  such  The  and  " s o c i o - t e c h n i c a l feedback" the  of  become  flexible  best,  h y p o t h e t i c a l l y does  anticipates  now  i s encouraged  the  theory  design.  requires  he  aesthetics, decision  increasingly  same  19 59  in his  design  the  first  process  engineering  solution,  the  comprehensive  philosophy  at  of  f o r a more  comprehensive  i n the  one  need  operations  concept  perhaps  the  psychology  This  was  solution  man  and  system  greatly  number  of  of  the  decisions  designer  is  7  measured by h i s a b i l i t y p r i a t e compromises"  t o i d e n t i f y l i m i t s and t o make appro-  [1.21, p. 9],  Even as o p t i m i z a t i o n t e c h n i q u e s , d e c i s i o n systems a n a l y s i s , o p e r a t i o n s a t i o n , value engineering,  research,  reliability  theory,  cybernetic engineering  imaginand program  e v a l u a t i o n r e v i e w t e c h n i q u e s a r e b e i n g i n v e s t i g a t e d and a p p l i e d , some s o c i a l s c i e n t i s t s a r e c o n s i d e r i n g  the e f f e c t  t h a t t o o much .emphasis on methods has on t h e i n d i v i d u a l because t h e p r o c e s s o f s y n t h e s i s istic.  Jacques E l l u l  i sessentially individual-  [1.23] s u g g e s t s t h a t  optimization  t e c h n i q u e s when a p p l i e d t o m a n a g e r i a l o r g a n i z a t i o n s  lead  t o s t a n d a r d i z a t i o n and r a t i o n a l i z a t i o n o f economic and administrative l i f e .  He quotes A n t o i n e Mas t o expand h i s  point: s t a n d a r d i z a t i o n means r e s o l v i n g i n advance a l l the problems t h a t might p o s s i b l y impede t h e f u n c t i o n i n g o f an o r g a n i z a t i o n . I t i s not a matter of leaving i t t o i n s p i r a t i o n , ingenuity, nor even i n t e l l i g e n c e t o f i n d a s o l u t i o n a t t h e moment some d i f f i c u l t y a r i s e s ; i t i s r a t h e r i n some way t o a n t i c i p a t e b o t h t h e d i f f i c u l t y and i t s r e s o l u t i o n . From t h e n on s t a n d a r d i z a t i o n c r e a t e s i m p e r s o n a l i t y , i n t h e sense t h a t o r g a n i z a t i o n r e l i e s more on methods and i n s t r u c t i o n s t h a n on i n d i v i d u a l s . [1.23, P. 11] But  some e n g i n e e r i n g  e d u c a t o r s a r e o p t i m i s t i c about  the c h a n g i n g n a t u r e o f e n g i n e e r i n g believes  design.  Thimm [1.22]  that:  s y s t e m a t i c t r a i n i n g i n o p e r a t i o n s r e s e a r c h and d e c i s i o n t h e o r y w i l l improve o v e r a l l e n g i n e e r i n g p e r f o r m a n c e ; i t might even save t h e w o r l d from t e c h n o l o g i c a l p o l l u t i o n and e c o l o g i c a l c a t a s t r o p h e . [1.22, p. 12]  8 S o c i e t y i s e x p e c t i n g t h e d e s i g n e r t o t a k e more responsibility  not only against errors but a l s o f o r e f f l u -  e n t s o f an u n h e a l t h y  nature.  A t t h e t h i r d annual McMaster  U n i v e r s i t y d e s i g n s e m i n a r , F.R. Duncan [1.24] c l o s e d h i s remarks on t h e l e g a l r e s p o n s i b i l i t y o f t h e d e s i g n e r w i t h t h e remark t h a t , " I t s j u s t n o t s a f e t o l e a v e d e s i g n e r r o r s f l o a t i n g around any more" seminar A l l c u t  [1.24, p. 3 6 ] . A t t h e same  [1.25] mentioned t h a t w h i l e e t h i c s r e l a t e  e n t i r e l y t o people  and d e s i g n d e a l s o n l y w i t h t h i n g s , t h e  r e l a t i o n s h i p between t h e two i s e s s e n t i a l l y t h a t o f cause and e f f e c t and " c o n s i d e r a b l e judgment based on e x p e r i e n c e i s r e q u i r e d t o combine t h e s e two f a c t o r s i n t h e r i g h t proportions" The  [1.25, p. 3 8 ] , emphasis on c r e a t i v i t y i s a s s o c i a t e d w i t h t h e  G e s t a l t t h e o r y o f p e r c e p t i o n developed [1.26].  around t h e 1920's  The c r u x o f t h e t h e o r y i s t h a t i t i s i m p o r t a n t t o  examine t h e t o t a l i t y o f a p r o b l e m , n o t m e r e l y i t s components. I n p e r c e p t i o n t h e whole i s g r e a t e r t h a n t h e sum o f i t s parts.  To p e r c e i v e t h e t o t a l i t y o r i m p l i c a t i o n o f t h e  s o l u t i o n r e q u i r e s a " t o t a l " approach t o p r o b l e m s o l v i n g . What i s c a l l e d t h e " t o t a l " approach i s an a l l i a n c e between i n t e l l e c t and i n t u i t i o n , between v e r t i c a l t h i n k i n g based on l o g i c l e a d i n g t o a c o n v e n t i o n a l s o l u t i o n and l a t e r a l t h i n k i n g based on i n t u i t i v e awareness l e a d i n g t o r a d i c a l solutions.  T h i s approach i n t e g r a t e s what C P . Snow c a l l s  the "two c u l t u r e s " [1.27] and l e a d s t o new d i s c o v e r i e s ,  9  unusual  s o l u t i o n s , and comprehensive u n d e r s t a n d i n g  of the  problems. I n the " t o t a l " approach t o c r e a t i v e d e s i g n , t r a t e d on F i g u r e 1.1, [1.28,  t h e e n g i n e e r goes t h r o u g h  illus-  five  stages  1.2]:  1. Problem f o r m u l a t i o n , 2. Concept s y n t h e s i s , 3. C o n f i g u r a t i o n o p t i m i z a t i o n , 4. Element d e s i g n ,  and  5. Performance e v a l u a t i o n . I f i t i s i n i t i a t e d a f t e r the problem i s c l e a r l y understood  and the d e s i g n e n v e l o p e i s e x p l i c i t l y  s y n t h e s i s can l e a d t o a number of c o n c e p t s s a t i s f y the r e q u i r e m e n t s economy.  formulated,  which t e n t a t i v e l y  o f f u n c t i o n , environment and  Each o f t h e c o n c e p t s  i s subjected to  critical  s c i e n t i f i c a n a l y s i s and judged on sound e n g i n e e r i n g ciples.  F o r t h e most p r o m i s i n g c o n c e p t ,  prin-  an optimum c o n f i -  g u r a t i o n i s d e v i s e d and the elements o f the c o n f i g u r a t i o n are designed  u s i n g the b e s t e n g i n e e r i n g p r a c t i c e .  Finally  a w o r k i n g model i s c o n s t r u c t e d and the performance e v a l u a t e d . Throughout the d e s i g n , feedback i s used t o c o r r e c t d e c i s i o n s made a t any o f the e a r l i e r  stages.  I n a p p l y i n g the f i v e s t e p s , c o n f l i c t s o c c u r between c r e a t i v e s y n t h e s i s and l o g i c a l a n a l y s i s .  One  difficulty is  t h a t t h e c r e a t i v e s t e p r e q u i r e s a b r e a d t h o f knowledge and understanding  and an a b i l i t y t o r e l a t e d i v e r s e e l e m e n t s ,  10 Experimental  General Knowledge  Personal Experience  Field Study  1  J  S t e p 1. Formulation  Formulation of Design Envelope  Scientific Principles  Concept  7E  1  Creative^ Ability  Concept  2 S t e p 2. Synthesis  Engineering Judgment  Scientific Knowledge New  fl  Information  S t e p 3. Optimization Engineering Judgment  General facts principles, techniques  h  New  Step 4 . Delineation  Information Proposed Design C o n s t r u c t i o n and T e s t i n g of |_J Working Model  | Figure  1.1  O u t l i n e of the Comprehensive Design  S t e p 5. Evaluation  Engineer's  Task  11 whereas the a n a l y t i c s t e p r e q u i r e s a depth o f  specialized  knowledge, an a b i l i t y t o use m a t h e m a t i c s , and an  ability  t o r e c o g n i z e and remember s p e c i f i c f a c t s .  effective  To be  t h e c r e a t i v e e n g i n e e r must be a b l e t o o s c i l l a t e  freely  between the c r e a t i v e s t e p and a n a l y t i c a l s t e p , between i m a g i n a t i o n and r e a s o n .  I m a g i n a t i o n e v o l v e s new  a t i o n s o f i d e a s and r e a s o n e v a l u a t e s each  combin-  combination.  I n o r d e r t o be c r e a t i v e and e v o l v e new  i d e a s the  mind must be f r e e t o a l t e r n a t e between a l l a s p e c t s o f the problem  whereas i n o r d e r t o e v a l u a t e l o g i c a l l y  must n o t d e p a r t from a s y s t e m a t i c s t e p - b y - s t e p  the mind sequence.  T h i s c o n f l i c t between c r e a t i v e s y n t h e s i s and l o g i c a l a n a l y s i s i s r e s o l v e d by a l l o w i n g the mind complete freedom t o produce i d e a s , s o l u t i o n s , p o s s i b i l i t i e s and guess work a t any w h i l e employing  time  a system o f n o t a t i o n t o r e c o r d a l l d e s i g n  information f o r l o g i c a l analysis.  Thus i m a g i n a t i o n i s  u n r e s t r i c t e d i n the mind and l o g i c i s p r e s e r v e d on paper. Once s t a r t e d , t h e system o f n o t a t i o n must be used  flexibly  as a g u i d e , n o t d o g m a t i c a l l y as a r i t u a l . One generate  e n g i n e e r i n g h e u r i s t i c s t e c h n i q u e used t o  s o l u t i o n s t o problems i s t o p o s t u l a t e a g e n e r a l -  i z e d model o f the d e s i g n p r o c e s s i n the form o f a " t r e e " [1.28].  Each s o l u t i o n t o some d e s i g n concept w i l l , i n  g e n e r a l , g i v e r i s e t o a s e r i e s o f s u b s i d i a r y problems each o f w h i c h has  ( u s u a l l y ) more than one p o s s i b l e s o l u t i o n .  12 The This  design  i s c o m p l e t e when a l l b r a n c h e s o f  h a p p e n s when t h e  1.  2.  3.  Factor which attempts  to  are  terminate.  followed:  solve  the  vertically. listed  a table  features  54]  i s another  analysis with creative  concerned with  or  basic  i n t e r e s t i n g technique  difficulty  thought  other  combining 1.30].  functions  desired  achieving to  are  the  functions. solutions  to give  several  a l t e r n a t i v e whole s o l u t i o n s .  reverse  which a  single  details  b e i n g worked out As  of  are  t h e n combined  conventional  solution i s conceived  the  function  conflicting  partial  i s the  This  listed  each  The  procedure  log-  o r m a t r i x where a l l p a r a m e t e r s  A l l p o s s i b l e means o f  the  of  [1.28, 1.29,  h o r i z o n t a l l y with reference  demands o f  tion  [1.28, p.  analysis  technique requires  are  rules  tree  When a number o f a l t e r n a t i v e s o l u t i o n s a r e p r e s e n t e d , any one may be a c c e p t e d and t h e r e s t ignored. A l l t h e p r o b l e m s d e p e n d e n t on t h e c h o i c e o f a p a r t i c u l a r a l t e r n a t i v e s o l u t i o n , must, however, be solved. A p a r t i c u l a r b r a n c h o f t h e t r e e must be followed u n t i l a s o l u t i o n i s r e a c h e d w h i c h d o e s n o t have a dependent problem. Provided that t h i s solution i s t h e p r e f e r r e d one a t t h i s p o i n t , t h e b r a n c h  terminates.  ical  following  the  as  permutaThis  d e s i g n methods a "whole w i t h  in  the  later.  work p r o c e e d s , many more i d e a s  Incomplete, questionable  by  or  stantiated  by  a literature  persons or  by  performing  conflicting search,  by  experiments.  are  added.  information  consulting New  ideas  is  sub-  experienced are  encour-  aged b y l o o k i n g a t e x i s t i n g  designs, viewing  a new v i e w p o i n t ,  comparing  identifying  the object being designed,  ideal  with  solution,  design  occurs  t o him a f t e r  solutions,  and b r a i n s t o r m i n g  T h i s l a t t e r method i s b e s t  uncritically  suited  r e c o r d s any i d e a o r s o l u t i o n  being  confronted with  the problem,  l o o k i n g a t e x a m p l e s , d r a w i n g s and r e p o r t s o f  existing  designs. R e l a t i o n s h i p s between s o l u t i o n s  trend plots  o r new s o l u t i o n  plots.  c a n be  is  with  the reason  f o r the changes.  a means o f c o m p a r i n g  new p r o p o s a l s  p l o t s c a n be u s e d  to find  ful  thought  solutions  i s given  and  no s o l u t i o n  ing  procedure:  plot  s o l u t i o n s , or These  a r e a s where new c o m b i n a t i o n s  to aspects  have a p p e a r e d .  A new s o l u t i o n  t o shape o r p e r f o r m a n c e .  s h a p e and p e r f o r m a n c e c a n be s o u g h t .  shows  the years t o -  the range of e x i s t i n g  i n relation  clarified  A trend plot  how s h a p e and p e r f o r m a n c e h a v e c h a n g e d o v e r gether  to a  and o c c u r s  or a f t e r  with  from  f a n t a s i z i n g an  team w i t h w e l l d e f i n e d r e s p o n s i b i l i t i e s  when e a c h p e r s o n that  the problem with other  using free association,  [1.14, 1.28, 1 . 3 1 ] .  the problem  More l o g i c a l  of  and c a r e -  o f t h e p r o b l e m where no  I f t h e i m a g i n a t i o n comes t o a h a l t  seems p o s s i b l e ,  Jones  suggests  the f o l l o w -  1. W r i t e down t h e c o n d i t i o n s w h i c h w o u l d make a solution possible, 2. W r i t e down a p h r a s e d e s c r i b i n g t h e d i f f i c u l t y and s u b s t i t u t e a l t e r n a t i v e s f o r e a c h w o r d , 3. W r i t e down t h e c o n s e q u e n c e s o f n o t f i n d i n g a Solution. n oo CAI  [1.28, p . 64]  14 Because i t safeguards not  feasible  against wasting  in parallel  able  solution  with  are indeed  a l l other design  are blended  sketches  The  for  synthesized the best  stability  facts  of l i f e  and i n g e n u i t y  initially  calculations  i n a mass-production  o f new c o n c e p t s  very costly  and t o s e e k i t .  and  and t h e involves finally  economy make  and r i s k y . This  I ti s  preference  means t h a t i n n o v a t i o n s and i n v e n t i o n s , i f t h e y  a r e t o become p r o d u c t i o n i t e m s , w i l l c u r r e n t market c a p a b i l i t i e s  available  have t o f i t i n w i t h t h e  and t h e e s t a b l i s h e d means o f p r o -  d u c t i o n , m a i n t e n a n c e and s e r v i c i n g  as w e l l as f i n a n c i a l r e -  {1.4, 1 . 3 2 ] .  Where i t i s p o s s i b l e t o v a r y  the p r o p e r t i e s of the  e l e m e n t s o r o f i n p u t s o r some a s p e c t s o f e n v i r o n m e n t effect  The  analysis.  to prefer stability  sources  designing.  This blending  and o r d e r - o f - m a g n i t u d e  introduction  natural  i s kept  unaccept-  with design philosophy, material selection  uses d e t a i l e d  the  I f an  i s o n l y a c h i e v e d when e x p e r i e n c e  p r o d u c t i o n methods a v a i l a b l e . rough  continuous  i s d e t e c t e d work on i t c e a s e s .  i s c h o s e n f o r o p t i m i z a t i o n and d e t a i l  optimum d e s i g n  a  acceptable  activity.  F r o m among t h e a l t e r n a t i v e s one  on a s y s t e m t h a t i s  o r goes o u t s i d e t h e d e s i g n e n v e l o p e ,  check t h a t t h e p o s s i b l e s o l u t i o n s up  time  so a s t o  t h e p r o p e r t i e s o f t h e system, i t i s p o s s i b l e t o choose  a combination mance. connects  o f v a r i a b l e s which y i e l d  F o r the case overall  the best  i n which a mathematical  c o s t and t h e v a r i a b l e s  system p e r f o r -  relationship  t o be o p t i m i z e d , c a l -  15 cuius,  linear  possible. other  p r o g r a m m i n g o r d y n a m i c p r o g r a m m i n g methods  Where v a r i a b l e s a r e n o t m a t h e m a t i c a l l y  techniques  i s , the  to f i n d  the b e s t  p a t t e r n o f moves l i k e l y  summit, a r e u s e d The  d e t e r m i n e how  search",  are  identified can  crucial  and  an  attempt  be m o d i f i e d  to yield  result will  a hierarchy of p o s s i b l e designs,  t h e m o s t f a v o u r a b l e and  e l e m e n t s c a n n o t be  proceeding  no  alternative  is  available  feasibility  where a c e r t a i n  realizations  i n the  experimental  event  work i s i n i t i a t e d of  this  element.  of  work on  some b r a n c h e s o f t h e  the whole d e s i g n  while  there are  still  The  starting  with  alter-  This  element proves  i s to safeguard  design  few  of  retreat  the  against  I t i s unwise  t r e e to the p o i n t of  unresolved although obtained  or  unavailable  to demonstrate  at a l a t e r date.  be  e l e m e n t has  adequate path  i n order  i s , more a b s t r a c t ) l e v e l ,  i n f o r m a t i o n r e q u i r e d may  actual  realized.  favourable  crucial  so t h a t no  t h a t the  failure  the  a workable  arrangements. In cases  (that  to less  the  i s made t o  the  detail  the  u n c e r t a i n f e a t u r e s of  system i n case  native  that  t o l e a d most q u i c k l y t o  e l e m e n t s and  the d e s i g n  be  connected,  [1.33].  crucial  optimum s o l u t i o n  "strategy of  are  problems a t a  to  fine  'higher'  f o r small projects, from t e s t s  on  an  prototype. The be  design  design  can  design  courses.  t r e e and  profitably Typical  other  s t u d i e d and  approaches to  systematic  applied i n engineering  of the c r e a t i v e d e s i g n  p r o j e c t s under-  16 t a k e n on a g r a d u a t e of  a Machine:  level  i s de P e n d e r * s  A P r o d u c t i o n Paper  Ph.D. t h e s i s ,  C u t t e r [1.34].  Genesis  In h i s t h e s i s  he d e s c r i b e s t h e e v o l u t i o n o f t h e m a c h i n e f r o m an i d e a  t o an  operating prototype:  The e m p h a s i s i s o n t h e d e c i s i o n s , m e t h o d s , c r i t e r i a , and r e s u l t s i n c o r p o r a t e d i n t h e m a c h i n e r a t h e r t h a n on a n a l y t i c a l a s p e c t s o f t h e d e s i g n . The p r i m a r y c r i t e r i a g u i d i n g t h e d e s i g n was t o p r o v i d e a m a c h i n e more e c o n o m i c a l f o r u s e r s t o own. [Abstract,  The sign are  approach  i s n o t s y s t e m a t i c b u t by t r i a l sought  totality to  usual industrial  o n l y t o urgent problems  of the design.  get specific  solutions  t o small engine de-  and e r r o r .  Solutions  without a study o f the  immediately.  c a s e w i t h t h e development  first  (1.34)]  P r e s s u r e i s e x e r t e d on t h e d e s i g n e r  c h a n g e s l o w l y and b r e a k t h r o u g h s the  ref.  seldom  Consequently occur.  Such has been  o f t h e power saw.  German saws were i m p o r t e d  into  British  When t h e  Columbia  12 0 l b s a n d p r o d u c e d  8 hp).  War I I c u t t h e s u p p l y o f saws a n d s p a r e  parts  and t h e d e a l e r , D . J . Smith  necessary In  t o make h i s own u n i t s ,  1943 he b r o u g h t  Industrial formed, chain  Engineering Limited,  and V a n c o u v e r  saw i n d u s t r y .  (rated a t  Equipment, found i t he c o p i e d t h e i m p o r t e d saw.  o u t a 90 l b v e r s i o n  number o f one-man c h a i n saws.  5 hp  i n 1937,  they weighed about When W o r l d  about  concepts  By 19 45  and then a  limited  the dealer  h a d become  Power M a c h i n e r y  L i m i t e d had  was t h e c e n t e r o f t h e N o r t h  American  17 When they b r o u g h t o u t t h e s u c c e s s f u l one-man c h a i n saw shown on F i g u r e 1.2, Power M a c h i n e r y L i m i t e d became a s t r o n g competitor with I n d u s t r i a l Engineering saw market.  L i m i t e d f o r t h e power  W i t h c o m p e t i t i o n came more r a p i d p r o g r e s s .  The  problem a r e a s on e x i s t i n g saws were i n v e s t i g a t e d by b o t h  F i g u r e 1.2  C u t t i n g w i t h one o f t h e o r i g i n a l one man power saws  companies i n d e p e n d e n t l y .  The manual rope and p u l l e y s t a r t i n g  system was r e p l a c e d w i t h an a u t o m a t i c i n 1946.  r e c o i l rewind  mechanism  18 When t h e Cox c h i p p e r c h a i n came on t h e market i n 1948, i t s v a l u e i n r e d u c i n g f r i c t i o n and saw b l a d e immediately  recognized.  l o a d i n g was  Whereas t h e s t a n d a r d  an e x t e r n a l f o r c e t o feed t h e t e e t h  chain required  much l i k e t h e f o r c e  r e q u i r e d t o c u t w i t h t h e c o n v e n t i o n a l t a b l e saw, t h e c h i p p e r c h a i n r e q u i r e d no such f o r c e , because t h e s e l f - f e e d i n g a c t i o n o r i g i n a t e d from t h e shape o f t h e t e e t h , as shown on F i g u r e  F i g u r e 1.3  1.3.  S k e t c h e s o f t h e c h i s e l - t o o t h ( l e f t ) and t h e chipper-tooth (right) chains  Because t h e s e l f - f e e d i n g reduced b a r and c h a i n  t h e need f o r a f o o l p r o o f a u t o m a t i c  friction,  o i l i n g system, i n use  s i n c e about 1946, was n o t as c r i t i c a l . The  s e l f - e n e r g i z i n g c e n t r i f u g a l c l u t c h was added t o  the saws i n 1949. T h i s c l u t c h a u t o m a t i c a l l y engaged when the engine speed reached a p r e d e t e r m i n e d l e v e l when t h e speed dropped below t h i s  level;  and d i s e n g a g e d  t h e amount o f p r e -  compression of  the  determined  engagement  the  springs acting against centrifugal  By t h i s As w e l l  time  as b e i n g p a i n t e d f o r  s y s t e m s , as shown by of  speed.  some a t t e n t i o n  shaped more a t t r a c t i v e l y . the  the  Also  last  specifications, Figure  force  first  was g i v e n t o time,  the  units  emphasized were the  four  items of  aesthetics. were  automatic  a typical  list  1.4.  SPECIFICATIONS Motor  Single cylinder, 2 cycle, air cooled  Power  4 H.P. at 4000 R.P.M.  Cylinder  Main Bearings ...Ball and needle - Standard malces Connecting Rod Bearings  Aluminum, chrome plated and honed  Crankshaft  Guide Bar  Forged alloy steel, machined, heattreated and precision ground.  Connecting Rod  Cutting Chain. Alloy steel, heat treated, chipper type  Same as above  Piston  Aluminum - 3 ring  Carburetor Ignition Lubrication  Figure  Starting Mechanism  Automatic recoil ^  Flywheel type - Wico  Clutch  Automatic ^  Chain Oiler  Automatic  Typical list 1950 *  keep the  Cast Magnesium  Drive  The G i l m e r used to  General Construction  Float type - Tillotson  Oil and gasoline mixed  1.4  belt  of  c h a i n saw s p e c i f i c a t i o n s ,  was one o f  c h a i n speed  Gilmer Belt - no lubrication necessary </  low.  several  Not u n t i l  Industrial  Engineering L i m i t e d advanced the  technology  far  tical.  Needle and Bronze  Alloy steel, heat treated, hard tipped  e n o u g h t o make a d i r e c t - d r i v e  circ.  speed r e d u c e r s 1953  had  chain-cutter  bar  c h a i n saw p r a c -  By u s i n g a h i g h - s p e e d c h a i n and s t e l l a r - t i p p e d  bar  * Specifications ref.  [1.35].  for  the  P.M. "Rocket"  c h a i n saw,  V  they e l i m i n a t e d t h e need f o r G i l m e r b e l t s , c h a i n d r i v e s , b e v e l g e a r s , spur g e a r s o r o t h e r speed When I n d u s t r i a l E n g i n e e r i n g  reducers.  L i m i t e d brought out  t h e i r d i r e c t d r i v e c h a i n s a w , Power M a c h i n e r y L i m i t e d was behind  i n t h e i r chain technology,  having  supported t h e  development o f a T i l l o t s o n a l l - p o s i t i o n c a r b u r e t o r .  The  l e a d gave I n d u s t r i a l E n g i n e e r i n g L i m i t e d a name and a market w h i c h t h e i r c o m p e t i t i o n c o u l d n o t match even w i t h t h e i n t r o d u c t i o n o f an a l l - p o s i t i o n c a r b u r e t o r a y e a r The  later.  a l l p o s i t i o n diaphragm c a r b u r e t o r w i t h a b u i l t -  i n diaphragm f u e l pump ended many f u e l m e t e r i n g  problems.  When t h e T i l l o t s o n diaphragm f u e l pump became a v a i l a b l e i n June 19 54, Power M a c h i n e r y L i m i t e d [1.36] announced t h a t the new c a r b u r e t o r would be s o l d a t t h e o p t i o n o f t h e b u y e r . By November t h e new c a r b u r e t o r was s t a n d a r d The  equipment.  q u i c k changeover can be b e t t e r u n d e r s t o o d i f one con-  s i d e r s t h e problems e n c o u n t e r e d w i t h t h e two t y p e s o f o l d e r carburetors—the  f l o a t t y p e u s i n g g r a v i t y f e e d and t h e  diaphragm t y p e u s i n g a p r e s s u r i z e d f u e l t a n k . type c a r b u r e t o r operated  The f l o a t  o n l y when u p r i g h t ; i n one d e s i g n  t h i s r e q u i r e m e n t was met by m a n u a l l y s w i v e l l i n g t h e c a r b u r e t o r when t h e engine was t u r n e d f o r b u c k i n g ,  and i n t h e o t h e r  d e s i g n by m a n u a l l y s w i v e l l i n g t h e b l a d e and c h a i n w h i l e keeping  the engine u p r i g h t .  The p r e s s u r i z e d t a n k  type  c a r b u r e t o r r e q u i r e d c o n t i n u a l a d j u s t m e n t because t h e i n l e t and o u t l e t check v a l v e s c o n t r o l l i n g t h e tank p r e s s u r e f r e -  21 quently plugged or f a l l  or  l e a k e d , c a u s i n g the p r e s s u r e to  below the p r o p e r working Since  the  occurred, although  of design, materials, the weight  engine.  I n 1945  weighed about  34  pressure.  i n t r o d u c t i o n o f the a l l p o s i t i o n c a r b u r e t o r  no m a j o r c h a n g e h a s  reduced  exceed  continual  and m a n u f a c t u r i n g  o f t h e saw  and  refinement  techniques  have  i n c r e a s e d the speed  of  the  when t h e y were i n t r o d u c e d , t h e one-man saws l b s and  produced  about  displacement.  Ten  2 1/2  hp  a t 3800  3 rpm  from  saw  produced  I n 1963 5.8  a 4.5  a  in  produce  16  in  4 hp  a t 6000 rpm  l b saw  produced  displacement. 2 hp  a t 9000 rpm  These t r e n d s , p l o t t e d increased ing  4 1/2  a  6,2  hp  a t 7500 rpm  i n 1969  from  a 2.8  on G r a p h 1.1,  in  the 3  o p e r a t i n g speed  mean e f f e c t i v e  pressure.  saws were i n t r o d u c e d ,  a 22  in  lb  displacement. from  s m a l l 6 1/2  a  l b saws  displacement.  show t h a t e n g i n e e r s  t h e power p e r u n i t d i s p l a c e m e n t by  the r e l i a b l e  brake  Now  from  years l a t e r 3  gradually  have rais-  a l t h o u g h a t the expense of Nevertheless, since  t h e method o f c u t t i n g  has  t h e power  not  changed. Although  the  introduction  o f t h e power saw  l a n d s o p e r a t i o n i n E a s t e r n Canada d a t e s  from  4 hp  tested,  German m a c h i n e w e i g h i n g  until  t h e one-man saw  the use  during  the  l b s was  became c o m m e r c i a l l y  o f t h e power saw  [1.37] r e p o r t s t h a t  80  became g e n e r a l .  i n the pulpwood l i m i t s  1950-51 s e a s o n  less  than  4%  1929  t o woodwhen a  i t was  available  not  that  F o r example,  Brown  o f E a s t e r n Canada  o f t h e wood was  cut  ,  22  9000.  SPEED (RPM)  3000 50iBMEP (PSI)  40 30 j  20  i  i  ^  120r • TWO  DRY WEIGHT (LBS)  MAN  60 *  .  \  /ONE  MAN  LIGHTWEIGHTS—• OB—  1935  Graph  1.1  1945  1955 YEAR  Power Saw P e r f o r m a n c e  1965  Trends  1975  w i t h power saws.  T h i s i n c r e a s e d t o 55% d u r i n g t h e 1954-55  season and t o 97% d u r i n g t h e 1957-58 s e a s o n .  Over t h e  same e i g h t y e a r p e r i o d t h e p r o d u c t i o n went up from 1.67  to  2.44 c o r d s per man per day, l a r g e l y due t o t h e extended use of  t h e power saw. Now because t h e t o t a l i t y o f t h e wood c u t t i n g  o p e r a t i o n i s b e i n g c o n s i d e r e d ^ a new r e v o l u t i o n i s sweeping the  pulpwood l o t s o f E a s t e r n Canada.  Instead of f e l l i n g  pulpwood t r e e s and t h e n b u c k i n g them i n t o 8 f o o t l e n g t h s w i t h a p o r t a b l e power saw, t h e o p e r a t o r s a r e t u r n i n g t o a semi-mechanized o r t o t a l l y mechanized h a r v e s t i n g system. the  semi-mechanized system t h e t r e e s a r e f e l l e d and topped  w i t h power saws; f u r t h e r p r o c e s s i n g i s done by machines. the  In  In  t o t a l l y mechanized system s h e a r s mounted on t r a c t o r s o r  s p e c i a l h a r v e s t i n g machines d e l i m b , c u t , and buck t h e t r e e s . The speed a t w h i c h t h e t o t a l l y mechanized system i s e x p e c t e d t o be i n t r o d u c e d i n t h e l i m i t e d pulpwood a r e a s i n E a s t e r n Canada, i s shown by t h e f o l l o w i n g s t a t i s t i c s  [1.38]:  whereas  o n l y 8% o f t h e pulpwood produced i n 1966 was h a r v e s t e d by t h e t o t a l l y mechanized system, by 1970 t h i s p r o p o r t i o n i s f o r e c a s t t o be 20% and by 1975 i t i s t o be 75%. As an example o f t h e f u l l y mechanized c u t t i n g system, the  t r e e h a r v e s t e r of F i g u r e 1.5 w a l k s up t o a t r e e , wraps  a d e l i m b i n g head around t h e t r u n k and sends t h e d e l i m b i n g head f l y i n g up t h e t r e e r i d i n g on a t e l e s c o p i n g mast. the  As  head moves up i t removes a l l branches and s h e a r s t h e t o p  24 The operator places open bottom shear on the tree at ground level. He then encircles the tree with the delimbing arms.  As the tree decreases in diameter, cutting edges follow. When the top diameter measures about three inches, operator tops the tree by actuating the hydraulically operated topping shear.  After trunk is sheared at the bottom, the tree ( rests on the shears cupped by the curved , shoe that holds it in position while the operator r swings it to bunching position. The operator i tilts the mast forward, opens the delimber grapple jaws and the tree drops to the ground.  F i g u r e 1.5  Typical tree harvesting  machine [1.39]  i  25 off  a t any  and  holds  off  a t ground  tree  on  cycle  desired point. the  the  while  level.  ground  per  man-day.  The  h e a d and  Although t h i s  This  production  figures could the  technology of  s y s t e m s were n o t  timberjack  suggest the  were c o n s i d e r e d  as  one  concept.  One  before  introduced  logger.  Would t h e  was  power saw  of  the  the  now  cords  per  cords  per  pro-  "total"  Even though  the  harvesting requirements  approach been to the  the  cords  w o n d e r s what t h e  "total"  be  tree  of  These  a l l harvesting  the  power saw  way  the  22  1.67  wood.  new,  come w o u l d h a v e b e e n had the  and  2.6  1.41].  value  c u t t i n g i s not until  and  averaged  compares w i t h  [1.37, 1.40,  developed  pattern  machine i s c a p a b l e  problem of h a r v e s t i n g  shear  part  bottom shears d e p o s i t  day, i n p r a c t i c e i t has  man-day f o r a g o o d axeman  approach to  then r e t u r n s  some l a r g e r s h e a r s s n i p t h e  man-day f o r a g o o d power saw  duction  head  in a pre-established  i s complete.  80-100 c o r d s per  trunk  The  out-  applied  professional  relegated  t o the  casual  user? The harvesting How  the  value  of  i s evident  formulation  e n g i n e was  based  subject  the  of  applying  on  next  the  from the  of the  a design  brief  a p p r o a c h t o wood  history just  envelope of  "totality"  section.  "total"  of  the  given.  a power  problem  is  saw the  26 1.2  Specifications  for  An a c c u r a t e light real any  of  all  life  the  is  stated,  is it  complex  incomplete,  in  the  to  be p a r t  of  of  what  list  has  of  speed and  power,  2.  environmental  3.  allowable  noise  4.  allowable  vibration  5.  spark  6.  safety  7.  importance  always  suggest  shown t o  be  of  the  correctly  And b e f o r e  description  the  of  the  must  be  given.  expect  in  a  and e n f o r c e , important,  chain  and resulted  which were  considered  envelope:  levels, levels,  regulations,  precautions, of  cost,  ease of  maintenance, operating  consider  solutions.  of  solving  stage not  the  control,  arrestor  Wallace  are  characteristics  1.  long  first  saw o p e r a t o r s  guidelines  design  of  creatively  posed,an exact  the  weight,  in  in  requirements  and imposed c o n d i t i o n s  experience  following  step  proffer  requirements  factors  first  problems  expected  what  design problem  and the  c a n be c o r r e c t l y  what government  the  as the  problems  saw,  of  As long  u s e l e s s to  The a n a l y s i s  Envelope  and c o n f l i c t i n g  problem.  is  Design  formulation  an i m p o r t a n t  technical  analysis  the  [1.11] the  appearance,  starting, low  fuel  ease of and o i l  reliability, handling,  ease  consumption,  and  life. suggests  worst  set  of  that  the  designer  should  circumstances which  can  occur  27 -and d e s i g n a c c o r d i n g l y because "sooner o r l a t e r any machinery may be l o a d e d t o t h e l i m i t o f i t s c a p a b i l i t i e s " . [1.11, p. 2 3 ] . Even though t h e w o r s t s e t o f c i r c u m s t a n c e s  s h o u l d be con-  s i d e r e d , a good f o r m u l a t i o n o f t h e d e s i g n envelope w i l l i n sure a g a i n s t overdesigning. B e f o r e u n d e r t a k i n g a new d e s i g n p r o j e c t i t i s o f course necessary item.  I f t h e i t e m i s t o compete w i t h e x i s t i n g u n i t s , i t must  possess  some u n i q u e c h a r a c t e r i s t i c h i g h l y d e s i r e d by p r o s -  pective users. for  t o know i f a market e x i s t s f o r t h e proposed  Not o n l y must t h i s c h a r a c t e r i s t i c be s u i t a b l e  t h e environment i n w h i c h i t w i l l o p e r a t e , b u t i t must  a l s o be e c o n o m i c a l l y and a e s t h e t i c a l l y a t t r a c t i v e .  In addi-  t i o n t o p o s s e s s i n g a u n i q u e c h a r a c t e r i s t i c , t h e new i t e m must compare f a v o u r a b l y w i t h f e a t u r e s and c h a r a c t e r i s t i c s o f existing units.  I f t h e market i s v e r y c o m p e t i t i v e , i t may  be n e c e s s a r y t o d e s i g n a u n i t f o r a s p e c i f i c  application  b e f o r e i t becomes s a l e a b l e . To a c h i e v e a l o w - c o s t p r o d u c t , t h e d e s i g n always be r e l a t e d t o m a s s - p r o d u c t i o n  techniques.  should A simple,  mass-produced p a r t w i l l c o s t l e s s t o make than a m a n u a l l y machined  part.  I f i t c a n be made and assembled on an a u t o -  m a t i c assembly l i n e , a new saw can have a b r i g h t f u t u r e . Because how and where t h e p r o d u c t i s used many o f t h e r e q u i r e m e n t s ,  determines  a d e c i s i o n t o d e s i g n t h e saw f o r  the c a s u a l u s e r was made e a r l y i n t h e d e s i g n s t u d y . machine was t o be o f s p e c i f i c i n t e r e s t t o  4  groups  The of  28 p e o p l e who  require a small portable  device:  1. t r e e p r u n e r s such as o r c h a r d i s t s , g a r d e n e r s , 2. c o n s t r u c t i o n w o r k e r s such as c a r p e n t e r s ,  plumbers,  electricians, 3. d e m o l i t i o n  crews,  4..casual operators  such as campers, f a r m e r s ,  hunters. By assuming t h a t the t i m e between c u t s i s independent of the s i z e o f the c u t and power, and by u s i n g average o f c o s t , wages, s p e c i f i c c u t t i n g r a t e s , and t i n g t i m e - t o - i d l e t i m e , i t was  r a t i o s of  p o s s i b l e t o s e t up an  l i n k i n g c o s t t o t h e s i z e o f c u t and  power s u p p l i e d .  values cut-  equation More  s p e c i f i c a l l y , the f o l l o w i n g a s s u m p t i o n s were used: 1. a c a p i t a l c o s t o f s i x t y d o l l a r s per horsepower a w o r k i n g l o a d of "N" a t i o n i n "W" =  days per y e a r , and  w o r k i n g days w i t h (60) (hp) W  2. an o p e r a t i n g  |  6%  (hp),*  a depreci-  annual i n t e r e s t ,  (.06) (60) (hp) N  c o s t e q u a l t o 1.3  times the  annual  d e p r e c i a t i o n c o s t 11.42] (1.3)(60)(hp) ] W ' 2 3. an average s p e c i f i c c u t t i n g r a t e  (SCR)  of 3 i n /  sec-hp {1.43] . *Based on the l i s t p r i c e f o r C a n a d i a n 270 w i t h i n c h bar and c h a i n , A p r i l 1, 1964.  30  4. a 1:3 r a t i o o f c u t t i n g t i m e - t o - i d l e time f o r a 5 hp machine i n 14 i n d i a m e t e r t i m b e r t i m e = (|^;) A,  [1.44],  i d l e time = g ^ P 3  jcutting  = 40J ,  ) A  5. an o p e r a t o r ' s wage o f t h i r t y d o l l a r s a day. A d d i n g t h e d e p r e c i a t i o n , i n t e r e s t , o p e r a t i n g expenses and wages, t h e f o r m u l a f o r t h e d a i l y c o s t i s :  COST  =  30. + * 3  6  h N  P +  1 3 8  P  h w  [$/day]  T a k i n g t h e c y c l e t i m e t o be e q u a l t o t h e sum o f c u t t i n g based on t h e assumed s p e c i f i c c u t t i n g r a t e and i d l e  time  time  w h i c h i s assumed t o be c o n s t a n t , t h e p r o d u c t i o n r a t e e q u a t i o n is: RATE  =  jArea/cycle) (time/cycle)  A  =  3Tp  where  A  {  a  +  4  inf. sec  0  i s t h e a r e a i n sq i n p e r c u t .  The c o s t o f g e n e r a t i n g a s u r f a c e i s o b t a i n e d by d i v i d i n g t h e c o s t by p r o d u c t i o n r a t e :  PRODUCTION COST - 4™ +  +  1.6 W  +  r  i£L  +  $ 1000 i n  ^ 1  2  +  I ^ J E  30 The e q u a t i o n f o r optimum power based on minimum c o s t i s o b t a i n e d by d i f f e r e n t i a t i n g t h e above e q u a t i o n and s e t t i n g the r e s u l t e q u a l t o z e r o :  optimum  14.4 NA  +  552 WA  F o r t r e e s and round wood t h e e q u a t i o n becomes > ^"optimum  _  diameter Jl8.3. T N  702 W  T h i s e q u a t i o n i s p l o t t e d on Graph 1.2. I f t h e p r u n e r c u t s branches t h a t average 3 i n d i a m e t e r , o r i f t h e c a r p e n t e r c u t s boards t h a t average  1 x 8  2  i n , o r i f t h e f a r m e r averages 7 i n between c u t s , a 1 hp saw w i l l be t h e l e a s t e x p e n s i v e s i z e .  then  As w e l l as  c o s t i n g more t o purchase and o p e r a t e , a l a r g e r machine i s l e s s f l e x i b l e t o h a n d l e and h a r d e r t o c o n t r o l . Below 1 hp a c h a i n saw  may become more o f a t o y  than a t o o l , e s p e c i a l l y s i n c e 50% o f t h e b r a k e  horsepower  never r e a c h e s t h e c u t t i n g p o i n t b u t i s absorbed by t h e s p r o c k e t , c h a i n and g u i d e - b a r [1.43].' The need f o r e n s u r i n g t h a t t r a n s m i s s i o n l o s s e s on a s m a l l saw a r e k e p t t o a minimum and t h a t t h e maximum amount o f engine power i s a v a i l a b l e f o r a c t u a l l y c u t t i n g t h e wood, i s e v i d e n t from t h e s e c o n s i d e r a t i o n s .  31  0  ,  5  10 TREE DIAMETER  Graph 1.2  15  (iN)  Optimum power as a f u n c t i o n o f t r e e  size  The e n g i n e speed s h o u l d be as low as c o n v e n i e n t and the t o r q u e as h i g h as p r a c t i c a l .  In a d d i t i o n a curve o f  t h e power as a f u n c t i o n o f speed s h o u l d be f l a t .  The  flat  power c u r v e e n s u r e s t h a t t h e saw c u t s a t a c o n s t a n t r a t e o v e r a wide speed range.  This specif ication'^ i s e s p e c i a l l y  s i g n i f i c a n t f o r c a s u a l u s e r s who l a c k t h e e x p e r i e n c e r e q u i r e d t o keep t h e saw r u n n i n g a t a c o n s t a n t speed even i f t h e y knew what t h e optimum speed was. U s u a l l y c a s u a l u s e r s do n o t c u t wood i n extremes o f weather.  E x c e p t i n s p e c i f i c a r e a s and i s o l a t e d c a s e s t h e  saw w i l l n o t be used i f t h e t e m p e r a t u r e drops below 0° F or  goes above 100°  r a i n w i l l be q u i t e  F.  L i k e w i s e i t s use i n snow, o r heavy  limited.  Optimum power i s n o t t h e o n l y performance  specifi-  c a t i o n r e q u i r e d ; t h e c h a i n speed o r t h e s h a f t t o r q u e must a l s o be s p e c i f i e d .  The v a l u e s s p e c i f i e d w i l l depend on t h e  k i n e m a t i c r a t i o s o f t h e c h a i n and s p r o c k e t , t h e c o n s t r u c t i o n of  the c h a i n and o f t h e t e e t h , and t h e p h y s i c a l p r o p e r t i e s  of  t h e wood. To approach  t h e optimum c o m b i n a t i o n o f f a c t o r s ,  the a u t h o r s e t up a s e r i e s o f t e s t s on t y p i c a l c h a i n saws. The d a t a f o r each t e s t i n c l u d e d t h e t i m e r e q u i r e d by cut,  each  t h e a r e a o f t h e c u t , t h e t y p e o f work, t h e engine  and t h e s p e c i f i c a t i o n o f t h e c h a i n , b a r and s p r o c k e t . was  o b t a i n e d from engine performance  f o l l o w i n g v a r i a b l e s were i n v e s t i g a t e d :  1. t y p e s o f wood - maple, hemlock, and 2. c h a i n p i t c h e s - .375,  .404, and  cedar,  .500 i n ,  3. s p r o c k e t s i z e s - 7, 8, and 9 t o o t h 4. j o i n t s - .025,  .030, and  The  and t h e d a t a i s i n Appendix  I. The  Power  c u r v e s drawn from  dynamometer d a t a t a k e n b e f o r e and a f t e r the t e s t . a p p a r a t u s i s shown on F i g u r e 1.6  speed,  .040 i n ,  5. b a r l e n g t h s - 15 i n and 2 4 i n , 6. t y p e s o f saw - d i r e c t d r i v e and gear d r i v e , 7. speed range - 4,500 - 7,000 rpm.  F i g u r e 1.6  A p p a r a t u s used i n t h e c h a i n speed t e s t s  The r e s u l t s , drawn on Graphs 1.3 t o 1.9, l e d t o t h e f o l l o w ing  conclusions: 1. The minimum s p e c i f i c energy r e q u i r e d t o c u t hemlock 2 was 1,600 i n - l b / i n 3,700 i n - l b / i n  2  and t o c u t maple  (Graph 1.3).  i t  was  The minimum  energy o c c u r r e d a t the l o w e s t speed t e s t e d and c o i n c i d e d w i t h t h e speed f o r most r a p i d  cutting  (Graph 1.5). 2. When c u t t i n g hemlock, the s p e c i f i c energy was  not  a f f e c t e d v e r y much by t h e s p r o c k e t s i z e b u t when c u t t i n g maple, t h e s p e c i f i c energy was the s m a l l e r s p r o c k e t  (Graph 1 . 3 ) .  lower f o r  3. B e c a u s e i t p r e c e d e s t h e c u t t e r . t o o t h kerf,  t h e d e p t h gauge t o o t h d e t e r m i n e s t h e  depth of c u t or " b i t e " t h e d e p t h gauge t e e t h is  i n t o the  known a s j o i n t .  minimum j o i n t  (Figure  1.3).  The  distance  a r e below the c u t t e r  The t e s t s  produced  showed  teeth  that the  t h e most e f f i c i e n t  cuts  (Graph 1 . 4 ) . 4. The s h o r t e r b a r c u t s  faster  t h a n t h e l o n g e r one  (Graph 1 . 6 ) . 5. The c u t t i n g than t h a t maple  rate  f o r c e d a r was  only-slightly  f o r hemlock b u t about d o u b l e  less  that f o r  (Graph 1 . 7 ) .  6. F o r t h e g e a r d r i v e  saw,  the c u t t i n g  rate  depended c  on t h e number o f t e e t h p a s s i n g a g i v e n p o i n t (Graph 1 . 8 ) . 7. A l t h o u g h t h e g e a r d r i v e w i t h a 24 i n b a r c u t s l i g h t l y faster bar,  than the d i r e c t  i t c u t 15% s l o w e r t h a n t h e d i r e c t  a 15 i n b a r Vibration ensure that vibration  d r i v e w i t h t h e same  l e v e l s must a l s o be s p e c i f i e d  the operator w i l l  l e v e l s when h a n d l i n g t h e saw.  fingers".  with  to  n o t e x p e r i e n c e damaging  produces  Prolonged  a vascular  t h e h a n d s known a s Raynaud's phenomenon, "white  drive  (Graph 1 . 9 ) .  to excessive v i b r a t i o n  or  length  exposure  disturbance of  air-hammer  disease,  During a vascular disturbance blood  35 5000 B—  5000  X 4000  4000  30001—  3000  2000  2000 HEMLOCK  .025 .375 PITCH  15  10001  5000  Graph 1 3  6000  IN BAR  7000  S P E E D (RPH)  Impdrtance o f s p r o c k e t size  1000'  5000  Graph 1.4  6000 S P E E D (RPH)  Importance o f j o i n t  7 TOOTH ,375 PITCH ,040 JOINT  10  15"  BAR  3000 Graph 1.5  6000 SPEED (RPI'i)  Cutting rates  7000  5000  6000  SPEED (P.PC)  7000 .  Graph 1.6 Importance o f b a r length '  36 ,  10  8 TOOTH .404 P I T C H .025 J O I M T 24 I N BAR  7 TOOTH -.500 P I T C H 24 IN BAR  9 TOOTH .404 P I T C H 2 4 IN BAR  7 TOOTH . 404 PITCH! 15 I N BAR  I  8 TOOTO .375 P I T C H .040 J O I N T 15 I N BAR  •••  5000 •  .  Graph 1.7  1 """"  „„.  •  MAPLE  6000  HEMLOCK. . 0 3 0 J'JI 3:1 CLA;RLDUC:  7000  60M  .. SPEED (RPil)  Importance o f wood species  Graph 1.9  7000 SPEED (P\PM)  Graph 1.8 S p e c i f i c rate  S p e c i f i c energy as a f u n c t i o n  cutting  o f c h a i n speed  37 circulation fingers  decreases s i g n i f i c a n t l y  turn white,  become s t i f f , [1.45].  although  a r e damaged t h e  be n o r m a l other  they  and t h e  than  vibration,  During of  British  location porary  cient  to  of  or  these  in  20 c a s e s , they  the  hunting  in  of  the  to  return  of  vibration  authorities  driving  3 1/2  aware o f  only  this  two  the is  Not  saws.  the  be  suffi-  the  [1.46]  In  chain all  from  Once  saws,  but  1 to  one 6  afflicted,  painful working  pallor or  football.  disease after  but  from  using  them.  are  tem-  normal.  indicative  danger,  the  will  cars, while  only  areas  particular  away  intermittent  their  of  a  occurred  chain  again  coastal  by Grounds  20 o f  temporary,  conditions  Due t o  when w a t c h i n g  years  problem.  in  fellers  trouble  experienced  91% i n c i d e n c e only  study  in  using  or  to  feeling,  never  conditions  22 t i m b e r  first  cold weather,  This exposure  of  started  fingers, while  a day o r  weather  phenomenon o c c u r r e d  after  the  in  loggers  the  cold.  phenomenon.  a medical  a group  t h e s e men t y p i c a l l y of  this  fingers  Australia,  showed t h a t Raynaud's  the  is  by  to  that  their  hands w i l l  triggered  the  condition  a change  allow In  the  lose  a n d damp d a y s o n t h e  C o l u m b i a , 25%* o f  nature saw,  years  some c o o l  extent  condition  such as exposure  may e x p e r i e n c e  power  of  s p a s m s may b e  the  ache,  and become u s e l e s s once  This  to  of  an  the  average severity  medical  loggers  themselves  * U n o f f i c i a l s t a t i s t i c from the Workman's Board O f f i c e , Vancouver, B r i t i s h Columbia.  Compensation  are  beginning  to r e a l i z e  the  p e r m a n e n t damage t h a t c a n especially  the  powerful  group of  loggers  test  use  the  In g e n e r a l vibration  of  occur  of  the  disabling  from h a n d l i n g  l i g h t w e i g h t ones.  saws t h e y  felt  incidence of  and  chain  saws  1968,  a  strike  were v i b r a t i n g  is a relationship  the  the  I n May  i n W a s h i n g t o n S t a t e went on  there and  extent  to  pro-  excessively.  between the  nature  of  disease:  The e v i d e n c e i n g e n e r a l s u g g e s t s t h a t i f any t o o l produces h i g h amplitudes a t the lower f r e q u e n c i e s o f , f o r e x a m p l e , 40 t o 125 c y c l e s p e r s e c o n d (2,400 t o 7,500 rpm) , i t i s l i k e l y t o p r o d u c e Rayn a u d ' s phenomenon, p a r t i c u l a r l y i f i t i s i n c o n t i n u a l u s e . . . t h e s a l i e n t f a c t o r i s n o t so much t h e t o o l , as t h e h e a v i n e s s o f t h e work e x p r e s s e d i n t e r m s o f s p e e d o f w o r k i n g e x e r t i o n , and g r i p required. [1.46, p. 272] Ground  states that:  t h e damage done t o t h e v a s c u l a t u r e o f t h e h a n d s b e a r s some r e l a t i o n t o t h e e n e r g y a b s o r b e d . The e n e r g y E o f a wave m o t i o n o f f r e q u e n c y F and amp l i t u d e A i s g i v e n by t h e e q u a t i o n E = K A 2 F 2 w h e r e K i s a constant. On t h i s a s s u m p t i o n , t h e n o x i o u s e f f e c t s of a v i b r a t i n g t o o l w i l l increase g r e a t l y with i n c r e a s i n g frequency, u n t i l a l i m i t i s r e a c h e d beyond which t h e s k i n w i l l f a i l t o c o n d u c t the v i b r a t i o n , a n d i f the handles are a p p r o p r i a t e l y i n s u l a t e d t h i s l i m i t w i l l be l o w e r . [ 1 . 4 6 , p. 272]  The forces to out  engine v i b r a t i o n s are  a c t i n g on  the  mass o f  l i g h t w e i g h t saws has decreasing  quently should  the  the  result  the machine.  decreased  the  But  i s t h a t the  because the  of p e r i o d i c  The  present  vibrating  p e r i o d i c f o r c e to the  expectation  increase.  the  mass  same e x t e n t .  amplitude  of  newer saws a r e  trend  withConse  vibration designed  to  operate  at  creased while has.  higher the  This  the  Thompson  health.  1.  2. 3.  energy  the  amplitude  imparted  energy u l t i m a t e l y  damage done t o  vestigated  speeds,  the  vasculature  [1.44]  effects  at of  to  the  may n o t  machine  determines  of  the  the  in  probably amount  of  hands.  McCulloch Corporation chain  have  saw v i b r a t i o n  on  also  in-  operators  He c o n c l u d e d :  There i s danger of p h y s i c a l i n j u r y to the hands a n d arms f r o m l a r g e a m p l i t u d e saw v i b r a t i o n s at f r e q u e n c i e s above 10,00 0 rpm. H i g h s p e e d v i b r a t i o n c a n be t o l e r a t e d f r o m a h e a l t h s t a n d p o i n t i f the amplitude i s low enough. D i s a g r e e a b l e v i b r a t i o n s and i n j u r i o u s vibrations a r e n o t n e c e s s a r i l y t h e same . . .  The r e a s o n saws have n o t c a u s e d more i n j u r y a p p e a r s t o b e b e c a u s e (1) t h e r e l a t i v e l y l o w s p e e d o f m o s t s a w s a n d (2) t h e f a c t t h a t t h e o p e r a t o r i s c o n t i n u a l l y c h a n g i n g h i s g r i p , a l t e r i n g h i s body p o s i t i o n a n d o p e r a t i n g t h e saw i n t e r m i t t e n t l y . [ 1 . 4 4 , p . 8]  He s u g g e s t e d t h a t s h o u l d be below permissible to  the  5,500  for .75  ips;  amplitude  at  would  Russian permissible cpm w i t h  45-50 min  of  limit  and the  drawn  on G r a p h  a mandatory continuous  the  .001  limit 5-10  for  operation  10,000  be  work.  damage l i m i t  cpm in.  which min  velocity  the He c o m p a r e d  is  rest  This  the  .0032 period  limit,  continuous  in  this  at after  Thompson's  operation  is  1.10.  The n e c e s s i t y for  continuous  lightweight  for  saws  rest as  periods they  are  is run  imperative for  a  greater  portion used  o f a working  at high  speeds;  o p e r a t o r may  • D •  day.  Then a l s o ,  they  f o r example d u r i n g  open  are frequently  limbing, the  t h e t h r o t t l e w i d e and u s e t h e m a c h i n e  A M P L I T U D E OF SAWS T E S T E D AT  IDLING  SPEED  - D  D  g  A M P L I T U D E OF SAWS TESTED AT  D  • D  OPERATING  S"EED  *  :  °  R  Co  /v'f7w,','*''''i... ou  1,Ju  s  •  L I M I T S E T IN R U S S I A  £••'•> ^io BR  N  LIMIT  4000  2000  ^  m  SUGGESTED BY THOMPSON.  "™^ooT™l^B^ooo  ^ , ,  ^  10000  FREQUENCY (CPM)  Graph 1 . 1 0  as  an a x e .  require  less  V i b r a t i o n damage l e v e l s frequency  as a f u n c t i o n o f  N o t o n l y do t h e saws r u n f a s t e r time  for a cut.  but they  T h i s means t h a t t h e o p e r a t o r  makes more c u t s p e r d a y and more c u t s r e q u i r e more and  pressure  on t h e h a n d l e s .  also  control  No s t u d y out  at  power  least  of  piston  facturing  engine v i b r a t i o n  a cursory  saw m o s t  balance,  of  the  a n a l y s i s of vibrations  of  but  the  the  unbalance  along  direction on the  unbalance  in  direction.  the  c a u s e d by cutting  can be l a r g e l y  a plane Thus the of  of  the  But  this  perpendicular addition  vibration  piston  of  clearances  is  an  inherent  engine.  s e t s up  adding  counterweight to  Manu-  The u n b a l a n c e by  the  a  on one p l a n e b u t  an in  counter-  sets  original  counterweights  a  un-  chains.  piston  eliminated  withIn  engine  two-stroke  centerline.  crankshaft.  amplitude  cylinder  motion  piston  causes.  engine unbalance  single  The r e c i p r o c a t i n g  the  are  and d e s i g n t o l e r a n c e s d e t e r m i n e  characteristic  weight  vibration  c l e a r a n c e s , and rough  and c h a i n o p e r a t i o n ,  this  would be c o m p l e t e  up  an  piston  decreases  increases it  in  another. A s e r i e s of determine  the  on v i b r a t i o n vertical the  of  levels.  were performed  a change i n  In  one t e s t ,  c y l i n d e r s were u s e d ;  they  the 4 were  c o u n t e r b a l a n c i n g mass w h i c h v a r i e d  24 8 g r a m s . cating  tests  In  another  root-mean-square the  without  by  the  saw c u t t i n g a bar  to  similar  saws  identical  size with  except  f r o m 197 g r a m s the  6 saws were  vibration  and w i t h  it  level  compared.  recipro-  From the  data obtained  the  For  r e a d i n g s were  unloaded either  for  to  2 4 9 g r a m m a s s b a l a n c e d 76% o f  test  and c h a i n .  author  counterweight  T h e 1 9 7 g r a m m a s s b a l a n c e d 53% o f  u n b a l a n c e and t h e  unbalance.  with  effect  tests  with  both  taken or  (shown  in  42 Appendix  I I ) , Graphs 1.10 - 1.16 were drawn and t h e f o l l o w -  i n g c o n c l u s i o n s were made: 1. The v i b r a t i o n a m p l i t u d e v a r i e s from .013 t o .030 i n and i s i n t h e a r e a where damage t o t h e hands w i l l o c c u r i f saws a r e used uously without the p r o t e c t i o n gloves  contin-  a f f o r d e d by  (Graph 1.10) .  2. The e f f e c t o f l a r g e r c o u n t e r w e i g h t s i s t o l o w e r p e r p e n d i c u l a r v i b r a t i o n s i n t h e r e a r h a n d l e , and t o r a i s e b o t h h o r i z o n t a l and v e r t i c a l i n the f r o n t handle  (Graph  vibrations  1.11).  3. The c u t t i n g a c t i o n c o n t r i b u t e s t o t h e v i b r a t i o n amplitudes i n both planes but e s p e c i a l l y t o the h o r i z o n t a l component (Graph  1.12).  4. The g u i d e b a r l o w e r s t h e h o r i z o n t a l component o f c y l i n d e r v i b r a t i o n b u t does n o t a f f e c t t h e v e r t i c a l component, p r o b a b l y because by moving the c e n t e r o f g r a v i t y f o r w a r d , t h e a d d i t i o n a l mass i n c r e a s e s t h e r a d i u s from t h e c e n t e r o f r o t a t i o n to the center of the accelerometer, negating the e f f e c t o f t h e i n c r e a s e d mass (Graph 1.13). i n t h e v i b r a t i o n i s more pronounced  The change than  indicated  because t h e v i b r a t i o n s caused by t h e c u t t i n g a c t i o n were n o t a c c o u n t e d f o r . 5. Whereas i n t h e c y l i n d e r t h e v e r t i c a l v i b r a t i o n i s independent o f i n i t i a l p i s t o n u n b a l a n c e , i n t h e  h a n d l e the p e r p e n d i c u l a r v i b r a t i o n i s dependent on the amount o f p i s t o n u n b a l a n c e .  I f the  piston  i s l i g h t l y o v e r b a l a n c e d so t h a t the u n b a l a n c e i s m a i n l y h o r i z o n t a l , the a d d i t i o n of the bar duces the p e r p e n d i c u l a r a m p l i t u d e , and  re-  i f the  pis-  t o n i s b a l a n c e d n o r m a l l y so t h a t the v e r t i c a l h o r i z o n t a l i m b a l a n c e are n e a r l y does not change the a m p l i t u d e 6. V i b r a t i o n 6,000 rpm  e q u a l , the  and  bar  (Graph 1.14).  l e v e l s r e a c h a minimum v a l u e around and  p o s s i b l y due  are v e r y h i g h d u r i n g e n g i n e i d l e , t o e r r a t i c combustion (Graph 1.15).  7. C o n t r a r y t o e x p e c t a t i o n s , the v i b r a t i o n i n s u l a t i o n r u b b e r on the h a n d l e s a c t u a l l y the v i b r a t i o n a m p l i t u d e s  increased  (Graph 1.16).  I t i s o b v i o u s t h a t the optimum c o u n t e r w e i g h t w i l l a compromise between k e e p i n g e i t h e r the h o r i z o n t a l o r v e r t i c a l v i b r a t i o n s low. t h a t the  The  be  the  f o r e g o i n g r e s u l t s suggest  l a r g e s t u n b a l a n c e s h o u l d be  i n a plane with  the  h i g h e s t i n e r t i a o r i n a p l a n e where the v i b r a t i o n i s l e a s t disturbing.  In a c h a i n saw  a p p l i c a t i o n the h i g h e s t  i s u s u a l l y i n the d i r e c t i o n of the bar  and  the  t u r b i n g v i b r a t i o n s are p e r p e n d i c u l a r t o the No  c h a i n saw  a l l e x h i b i t a rocking  inertia  least dis-  arm.  exhibits only t r a n s l a t i o n a l vibrations; m o t i o n as w e l l .  unbalanced f o r c e i s l o c a t e d  Indeed when the  a t some d i s t a n c e  from  the  44  MASS BALANCED (%)  Graph 1.11  Graph 1.12  -  '  I1ASS BALANCED  V i b r a t i o n amplitude w h i l e c u t t i n g versus weight s i z e  Vibration unloaded  (%)  counter-  a m p l i t u d e w h i l e c u t t i n g and r u n n i n g  50  60  70  w 5  60  0  70  HASS BALANCED  MASS BALANCED (%)'  .03  1  (%)  1  REAR HANDLE VERTICAL  ?  CUTTING  02 L U 1=1  LiJ  S=  50 Graph  1.13  60  70  MASS BALANCED (I) E f f e c t of adding counterweights  .02 -  NOT CUTTING^ CUTTING *m -  01 .0 50  60  70  MAGS BALANCED (%) b a r on t h e a m p l i t u d e  with several  .03  ijj  CYLINDER  46  •03|—  VERTICAL  LONGITUDINAL  .021-  .02 E  ra  A G E .  ca I—  G H A  .01  H  UJ  1  _  •  CX-  WITHOUT  C U T T I N G V.'ITH  BAR  BAR  J  01  *  r  CU I IlilG  WITHOUT BAR  0  '  A H  FRONT  HANDLE  RESULTANT OF V E R T • WITHOUT B A R  CUTTING  WITHOUT BAR  Graph 1.14  CUTTING  E f f e c t o f t h e b a r on v i b r a t i o n  'REAR HANDLE  amplitude  l CYLINDER  1  AND LONG  I i VERTICAL  PERPENDICULAR  .02  —  0 2  "  dm  4  S P E E D  .061]  •  •— -—  —fi  6 (RPM x  S P E E D  10" ) 3  .oc  "ILI"  CYLINDER  (RPM x  10" ) J  LONGITUDINAL  .04 .02 0 !i P L L J (RPM / 10 ) J  Graph 1.15  4  6  S P E E D (RPM x 10~ )  E f f e c t o f speed on v i b r a t i o n  J  amplitude  center This is  of i n e r t i a ,  fact  large  a point  a large  c a n be u s e d  rocking  t o a d v a n t a g e when t h e u n b a l a n c e d  i n o n l y one p l a n e . which undergoes v e r y  .03  1-  c o u p l e may be s e t u p .  REAR  In such a s i t u a t i o n little  there  translational  HANDLE  force exists  motion„  -  PERPENDICULAR TO GRIP  -  ~ J)2 Q_ < NO BAR  mBB-  E f f e c t of rubber amplitude  Finding with  tribution. can  vertical  o f t h e mode o f v i b r a t i o n s  I t i s then necessary  be r e d u c e d  handle a t a v i b r a t i o n  that the  location  location.  certainly and w e i g h t  t o c h e c k where  u n b a l a n c e and t h e n  begins dis-  vibrations  locate  one  mode and t h e o t h e r h a n d l e a t a low  but p a r a l l e l  to the largest  component a t  The w e i g h t must be d i s t r i b u t e d  to result i n  o v e r a l l minimum v i b r a t i o n  vibrations  of vibration  o r , i f i t i s advantageous, t o have o n l y a  or a horizontal  amplitude  insulation  t h e optimum h a n d l e p o s i t i o n  an a n a l y s i s  s  WITH RUBBER  WITHOUT INSULATION G r a p h 1.16  a»««*'  levels.  No f a c t o r  a s much a s p o o r w e i g h t and l o a d  accentuates  distribution  and no system a b s o r b s v i b r a t i o n as much as s p e c i a l shock a b s o r b i n g g l o v e s , u s u a l l y made o f foam and l e a t h e r .  Also,  f l e e c e g l o v e s keep t h e hand warm and d r y and a l l o w f o r c r i m p i n g i n t h e palm o f t h e hand where t h e v i b r a t i o n i n s u l a t i n g m a t e r i a l i s most e f f e c t i v e l y used. Instead of l i n i n g  a  glove  c o u l d be wrapped around t h e h a n d l e .  the i n s u l a t i n g m a t e r i a l Because h i g h  pressure  i s e x e r t e d on t h e h a n d l e , t h i s method i s n o t always as e f f e c t i v e as i t c o u l d be. A t h i r d method o f r e d u c i n g v i b r a t i o n t r a n s m i s s i o n i s t o a t t a c h t h e h a n d l e n o t s o l i d l y t o t h e e n g i n e frame b u t f l e x i b l y t o some i n s u l a t i n g m a t e r i a l . supposedly hand.  The f l e x i b l e h a n d l e  reduces the v i b r a t i o n l e v e l s t r a n s m i t t e d t o the  Observations  during a series of v i b r a t i o n l e v e l  t e s t s v e r i f i e d t h i s e x p e c t a t i o n ; when comparing t h e l e v e l s o f two s i m i l a r saws,  t h e v i b r a t i o n i n t h e machine w i t h t h e  f l e x i b l e h a n d l e was lower than o r e q u a l t o t h e v i b r a t i o n i n t h e machine w i t h t h e s o l i d h a n d l e . * Exposure t o h i g h l e v e l i n d u s t r i a l n o i s e " l i m i t s speech communication, changes a t t i t u d e s  and b e h a v i o u r , and  impairs hearing."** I f t h e o p e r a t o r i s exposed t o h i g h l e v e l n o i s e f o r a c o n s i d e r a b l e l e n g t h o f time n o t o n l y w i l l t h e n o i s e c o n t r i b u t e t o f a t i g u e b u t i t may p e r m a n e n t l y damage t h e e a r . *  Author's u n o f f i c i a l observations during v i b r a t i o n l e v e l t e s t s a t Pe E l , Washington, June 22, 1967. ** From a t a l k by B.P. C a r t o n p r e s e n t e d t o T r u c k L o g g e r s ' C o n v e n t i o n , Vancouver, J a n u a r y 20, 19 67.  49 What we a r e c o n c e r n e d workman's a b i l i t y  with  here  i s the impairment o f the  t o h e a r and u n d e r s t a n d  normal speech.  d e g r e e o f i m p a i r m e n t d e p e n d s on many f a c t o r s , type of  of noise, the i n t e n s i t y  ithemic  sound  ratio  the energy  level  o f t h e n o i s e , and t h e d u r a t i o n  threshold  i n a standard  140 dB r e p r e s e n t s  long-term  reduce  as t h e l o g a r -  i n t h e measured p r e s s u r e  wave  p r e s s u r e wave, u s u a l l y t h e  a t 1000 c p s .  of hearing,  To  i s g e n e r a l l y expressed  o f the energy  threshold of hearing  and  i n c l u d i n g the  exposure. The  to  The  Thus  60 dB r e p r e s e n t s  0 dB r e p r e s e n t s t h e c o n v e r s a t i o n a l speech,  the threshold of pain.  the p o s s i b i l i t y  exposure t o high  level  of hearing  impairment  from  n o i s e , t h e Workman's  Compensation Board o f B r i t i s h Columbia  adopted  Prevention  This regulation states  in  part  Regulation  12.28 i n 1966.  Accident  that  where t h e n o i s e l e v e l s e x c e e d t h e B o a r d c r i t e r i a , and t h e c i r c u m s t a n c e s a r e s u c h t h a t a h a z a r d t o h e a r i n g e x i s t s , t h e n o i s e s h a l l be r e d u c e d t o a c c e p t a b l e l e v e l s by e n g i n e e r i n g means. Where r e d u c t i o n by e n g i n e e r i n g means i s n o t p r a c t i c a l , a d e q u a t e e a r p r o t e c t i o n s h a l l be p r o v i d e d and  s h a l l be worn. The  [1.47, p . 4]  broad-band n o i s e  level  a d o p t e d by t h e Workman's suggested  by B a r a n e k  readings  at the operator's The d a t a  f o r hearing  conservation  C o m p e n s a t i o n B o a r d , t h e damage  criteria  G r a p h 1.17.  criteria  [1.48] and t h e n o i s e  ear of t y p i c a l  f o r the noise  level  risk  level  saws a r e shown i n readings  shown i n  i n Appendix I I I . The from  t h e saw.  noise intensity  decreases  with  distance  F o r e x a m p l e , where t h e o p e r a t o r  an i n t e n s i t y  to  82 dBA a n d a t 50 f t he i s e x p o s e d t o 75 dBA [ 1 . 4 9 ] .  1  1  I  I  an o b s e r v e r  i s exposed  to  120  o f 105 dBA,  I  away  a t 23 f t i s e x p o s e d  I I I J  1  1  1  M  M  M  WITHOUT BAR OH DYNAMOMETER  a  BARAMEK 100  o  CO  B . CV W6 RKMTI^ CO M P E^ ,,  '  801 100  I  I  I  ,,,  ,  ,  ,  T  ,  11111  I  I  1000  I  I  1111  10000  FREQUENCY (CPS)  Graph  1.17  Noise  level  readings  Because the e x t e n t the  l e n g t h o f exposure,  varying  of typical  of hearing  The  saws  i m p a i r m e n t d e p e n d s on  the noise c r i t e r i a  amounts o f e x p o s u r e .  power  should  accommodate  S t a t e of Washington  51  100  1000  10000  FREQUENCY (CPS)  Graph 1.18  S t a t e o f Washington s t a n d a r d  Graph 1.19  for industrial  T e n t a t i v e Swedish n o i s e l e v e l  limits  noise  Occupational ing  Health  the n o i s e  level  p e r week w i t h o u t the  length of  operator  the  given  exposure does not v a r y  noise  the  type  as  fibreglass  when t h e  lost,  Since  the  the  ported  backpressure,  muffler of e i t h e r  the r e a c t i v e  the  significantly.  exhaust noise  saw.  quencies  energy r e l e a s e d  when e x h a u s t  i s the  engine  a power  type  reactive muffler  below i t s r e s o n a n t  reducing  But  the  material  particles  silencing flow  i s very  effective-  i s increased.  sensitive  to  a small i n c r e a s e i n flow r e s i s t a n c e produces  suitable  The  flow r e s i s t i v e  to absorb  only  two-stroke  This  in  1.19.  r e s i s t a n c e to exhaust  a l a r g e power d r o p . on  from  pro-  or asbestos  ness  a great deal  amount o f  reduces  the p e r f o r a t i o n s , not  because  i n terms o f the  e a r , Graph  clog  But  i n hours  saws  exhaust p o r t s open.  but  exposure  specify-  for chain  d i s s i p a t i v e muffler contains  such  by  Swedish c r i t e r i a  levels  to the  or d i s s i p a t i v e  does t h i s  e a r p r o t e c t i o n , G r a p h 1.18.  A p r o p e r l y designed  The  criteria  i n terms of a l l o w a b l e  to operator,  specifies tection  Standards  noise  level  of m u f f l e r then,  i s timed  possible.  E f f e c t i v e n e s s can  electrical  analogue  to pass only  frequency.  i s limited  (low p a s s  be  by  the  very  fre-  Its effectiveness the volume o r  understood  filter)  i s not  as  size  i n terms o f  shown on  an  Figure  1.7. The the  source  current into  (volume o f g a s  the c a p a c i t o r  exhausted)  flows  ( m u f f l e r v o l u m e ) and  from is dis-  charged t h r o u g h t h e i n d u c t a n c e c o i l  (tailpipe).  To be  e f f e c t i v e a t low f r e q u e n c i e s , t h e c a p a c i t o r and i n d u c t a n c e must be l a r g e .  The optimum volume f o r a power saw i s i n  t h e o r d e r o f 10 t i m e s t h e e n g i n e d i s p l a c e m e n t and t h e optimum l e n g t h o f t h e t a i l p i p e i s i n t h e o r d e r o f 12 f t [1.44, 1.50].  O b v i o u s l y a compromise between s i z e and  e f f e c t i v e n e s s i s necessary. I t i s g e n e r a l l y assumed t h a t e n g i n e n o i s e comes from e x h a u s t . picture.  But exhaust n o i s e s a r e o n l y p a r t o f t h e n o i s e  M c C u l l o c h ' s e x p e r i e n c e [1.44] shows t h a t w i t h o u t  t h e exhaust n o i s e t h e accumulated  aerodynamic n o i s e o f t h e  c o o l i n g a i r f a n and t h e m e c h a n i c a l n o i s e o f b e a r i n g s , t h r u s t  L  V= V o l u m e o f C a v i t y - c m  5  H=Ambient P r e s s u r e - U I O ' d y n e s / c m ' P = D e n s i t y of A i r - L Z I x l O ^ g m / c m i - L e n g t h of T u b e A -Area  of  1  -cm  Tube-cm'  Frequency  F i g u r e 1.7  Schematic r e p r e s e n t a t i o n o f m u f f l e r and e l e c t r i c a l e q u i v a l e n t [1.50]  washers,  gears,  vibrating  sprocket  noises  are  Better of  engine  this  or  dynamically  around  reduces  the  reductions  c a n be  to  sparks  impinge  baffle,  or  surface  must  carbon deposits  [1.51].  80% r e t e n t i o n in)  ways  accepts  level  is  and  achieved  purpose.  prevents substances if  the  may b e a w a l l ,  the  large  up b e f o r e  used as the  from  aero-  quietness.  and o t h e r  such a fashion  line  by  and by  for  and b r e a k  Automotive  they a  impingement that  port  to  of  particles the  that  o n a n ASTM#16  similar  specifies a muffler  to  the  (.047  the  if  pine  muffler  c a n be r e t a i n e d  in)  SAE-PSMA,  90% r e t e n t i o n  conjunction  Association,drafted  To be a c c e p t a b l e particles  Engineers,in  s c r e e n a n d a 100% r e t e n t i o n  be r e t a i n e d  [1.52]  is  surface  P o w e r Saw M a n u f a c t u r e r s  standard  most  in  a straight  panels  some  exhaust.  the  (.023  surface  Whatever  The S o c i e t y o f with  Retention  saw.  can reduce  saw h a s a d u a l  an a c c e p t a b l e  be p o s i t i o n e d in  power  the  and  accomplished  and c o w l i n g  The s o l i d  a screen.  travel  muffler  fan  on a s o l i d  muffler.  vibrating  on t h e  cause a f i r e .  the  cannot  the  to  sparks,  likely  leave  noise  the  chain  from  Other  designing  escape of  3 ft  tolerances  insulating  the  100 dB a t  slap,  and c l o s e r  The m u f f l e r It  piston  balance  noise.  stiffening  panels,  in  of  muffler  have  an  o n a n ASTM#30  particles  screen. the  must  a  that  Although  California  both  categories.  needles with  6% m o i s t u r e  can in  standard Australia content  do n o t for  ignite  after  30 s e c d u r i n g  test  [1.53].  impinge  on  In  the  or  2 perforated  .030  muffler  in  or  if  .080  must  more  baffle  than  require that  in  a muffler  will  not  PSMA s t a n d a r d  but  the  cleaning  is  required  is  the  to  or  equal  be  one  less  periphery,  or  h o l e s must  Most  be  standards  850°  a minimum of  n e c e s s a r y and have a l i f e  in  Maine, only  a  F.  8 hours  also  material  temperatures;  temperature  for  baffles,  .187  d e s i g n e d a n d made o f  this  muffler,  h o l e s must  [1.55].  must  l e s s than  and the  excessive shell  operate  gas  solid  of  spaced around  muffler  engine  the  than  holes  required  that  limits  should  less  state  diameter  allow  arrester  holes  the  and  from  staggered  the  load  exhaust  In  diameter  .030  two  screens with  [1.54]. is  the  with  no  exhausting  with  screens are used,3 are  less  contact  open t h r o t t l e ,  contain  baffles  2 or  in  in  Washington State  diameter,  perforated than  a wide  held  3 surfaces before  or  diameter  being  the SAEThe before  expectancy of  50  hours. No e l e c t r i c , dangerous  pneumatic,  as one w i t h  sharply  And y e t  no  has as  guards.  imagination  can occur  is  to  required  Pulp  in  is  tool  required  a m i s h a p and  accept accident  A breakdown of  power  moving,  saw.  much i n j u r y  engine  rapidly  such as a power Little  or  the  to  tool filed  few  as  teeth,  protective  visualize  little  is  how  persuasion  statistics.  accidents  and P a p e r S a f e t y A s s o c i a t i o n i s  reported  to  given  Figure  in  the  Quebec 1.8.  to  TYPE OF ACCIDENT  1455  Branching ;  1957  1956  While clearing, saw kicked back^ or defected, ^s.-.c-^s"-' ' : 1 Branching '• with- saw, kicked/ : back, cut through or deflected. 1 Branch hit accelerator startutg saw, i 1  .  8  31 .1  0  %-. TPoetraclentage  Saw kicked back or chain jumped due to touching branch 5 Saw cut through log striking worker. 2 Foot slipped and leg hit saw. .3 Placed foot on tree, beside. saw, chain jumped. -,  8  5  :  1956  1957  29  73  35 16  45 3  1  1.19*  Total Percentage  40 6.92%  13 2.34*  3  "ll  4.36%  82 14.80%  123 : 21.28%  Miscellaneous  Felling  Preparing, adjusting or repair-' ingsaw. )  Saw kicked back' o r saw chain • ; jumped due to touching branch, tree log, other obstruction or punching. .. : 53 As tree fell it pushed,saw chain' which hit operator. . ; 7 Falling branch hit saw or opcr-' ator causing fall on saw. {10 Pushing tree, with one hand • while holding saw with other, j 4 H i t by companion's saw while i helping by pushing tree. i 10 After, felling, hit by saw while i cutting hinge, attached to j ....-. stump. . .-;'•)' i 12 H i t chain saw while getting away; . from falling tree. ! 2 • '  1955  Bucking  ' •  130  41  36  :  i 98  .Total •' : Percentage  131  ! 38.88%  11  6  10  6  13.  10  2  2  7  5  215 38.80%  Starting motor.' •.• I Hit chain acadentally while : handling. Cham broke striking operator. • Burns, gasoline spilled on ^ . clothing ignited. j* Working too close to com com-; panion, hitby saw; . Foreign body in eye. ^ .  195 33.73% .. Kick-back (felling).  C h a n g i n g Position :  . Total Percentage  15 . 1 2 . .13  To •  ••  17 9 8  17.,  4  18  10  1 0  17 • 1  9  0  2  0 6  i 5  **  • 3 45 7.78%  55 9.92%  37 14 68"%  58(4 x) 10 46%  71 (4x) 12.88%  73x 28.96%,  91x 16.42%  70x 12.11%  554fx>  578(5x)  Total Fall with chain at rest, hit saw . ! -4 • teeth. ': 7 Fell with chain in motion. 5 Hit self with saw in motion.  11  14 5.557o  Total Percentage  ."Hit by companion's tree. ;  3  252x  Note: (xy Indicates mat figures include fuui! accident  34 5.88%  40  6.34%  POWER SAW K I C K - B A C K , HIT B Y COMPANION'S T R E E 1955  Age of Injured Employees 20 vears old and under 21 to 25 26 to 30 •• 31 to 35 36 to 45 46 to 70 Unknown ,r . Total  64 71 46 .. 26 30 -• 13x 2  •  .  252x  •  1956  1957  Nature of Injury  1955  .143 • • 142 (2x) 96 56 61 x 47(2x) 9  I48x 154x 23x 59x 79x 43 12  Cut Laceration Amputation Bruise Fracture Foreign body in eye Strain Sprain  ,554(5x)  578(5x)  106 26 1 , 15 29x 5 16 54  .. ._ ,—  Part of Body Injured 10 11 18  Finger Hand Arm Elbow Torso Head Eye Multiple Foot Leg Knee Toe  . 30 21x 14 15 72 48 1 Total  F i g u r e 1.8  252.x  30 41 30 10 56x 21 1\ • 11 23 2.6 147 138 8 554 5xi 1  :  .'..-V-.-  1956 291 76 1 105 30(5x1 4 31 . 16  1957 •/  .f  108 295 1 38 . 3S(5x' 5 23 : 25 :  .578(5x' 2 5 2 X . , „ , A ..554:5x.i I.engthT of o t aTl i m e E m p l o y e d Before Accident.;  Less than 1 week 41 43 1 to 2 weeks 34 2 to 4 " 4 Over 4 Uhknown 43 34 (4 x) 7 Total 43 34 146x 135 14  '•  ' •' 30 13 . . 68 78 45x  '90x 88 98 19! 8VM\:  96 104 136 137(2* 105(3?  • 252x  554i5i,-i  578 (5>  —  -  578(5x1 / Note: (x) Indicates that lii'ures include: fatal accident.  A c c i d e n t s r e p o r t e d t o Quebec P u l p and Paper A s s o c i a t i o n [1.37]  An a n a l y s i s o f t h e s e s t a t i s t i c s c h a i n was  r e s p o n s i b l e f o r two  t h i r d of the f a t a l i t i e s . 40% of the a c c i d e n t s  The  i n d i c a t e s t h a t the moving  t h i r d s o f the i n j u r i e s and three f a t a l i t i e s  a  as w e l l as  (1957) were caused b.y k i c k b a c k ;  this  r e a c t i o n o c c u r s when the t o p o f the moving c h a i n a c c i d e n t a l l y h i t s a f o r e i g n o b j e c t and causes t h e whole machine t o k i c k back out of c o n t r o l .  The  r e m a i n d e r o f the  accidents  o c c u r r e d when the c h a i n jumped o u t of the g u i d e b a r ,  or  when the o p e r a t o r o r a s s i s t a n t a c c i d e n t a l l y h i t t h e  chain  i n t r y i n g t o escape from f a l l i n g branches o r t r e e s o r were pushed i n t o the c h a i n by the b r a n c h o r t r e e , o r when the o p e r a t o r o r a s s i s t a n t were too c a r e l e s s . I t i s o b v i o u s t h a t i n t h e hands o f an o p e r a t o r the c h a i n saw maiming.  The  inexperienced  has a h i g h p o t e n t i a l f o r h u r t i n g and  statistics  show t h a t 75% of the  accidents  o c c u r w i t h i n 4 weeks a f t e r t h e o p e r a t o r s t a r t s work w i t h a c h a i n saw. saw,  Though somewhat s a f e r  the bow  cumbersome. saw  t h a n the b a r t y p e  chain  type i s u n p o p u l a r because i t i s e x p e n s i v e A l s o c o n s i d e r a b l y s a f e r than the c h a i n  and  type  because t h e r e i s p r a c t i c a l l y no chance of k i c k b a c k ,  r e c i p r o c a t i n g b l a d e saw  the  i s u n p o p u l a r because i t does n o t  f e e d as e a s i l y as does the c h i p p e r t o o t h c h a i n nor does i t remove t h e sawdust as q u i c k l y .  Consequently, the  operator  must e x e r t c o n s i d e r a b l e e f f o r t t o keep the saw c u t t i n g rapidly.  The  e f f o r t causes f a t i g u e w h i c h i n t u r n makes him  more prone t o a c c i d e n t s .  58  It forcibly  properly  handles.  fatigue hand  the  location  during v e r t i c a l of  the  hand  The  cutting  the  are  as  faster  power f o r cutting  gravity.  chain  accidentally  or  saw  cuts  the be  less  the  he  maintained  that  especially  control  hand as  a  so  control.  that  a minimum, finger  and  and thumb  cut-off.  the  higher  fatigue.  But  the with  spends l e s s to  saw  cut.  power, more time  Because  more.  vibration  w e i g h t d e c r e a s e s . O t h e r means o f  f o u n d b e c a u s e most e x p e r t s  the  removed.  agree t h a t  levels reducing fatigue  the  Therefore i t  a high-power-to-weight r a t i o i f the  be  the  r e d u c e power when  that  the  the  handlebar  ignition  operator  must c o n t r o l  the  and  good  grouped  and  more t i m e m o v i n g f r o m c u t  fatigue, saw  the  a g i v e n w e i g h t , the  faster  c a n n o t be less  cut,  shape o f  front  index  purposely  think  minimum b a c k  and  kept to  automatically  designing  guide bar  rear  must be  oiler,  be  t h i s arrangement  the  the  when  can  properly  the  the  In  and  movements o f  must a l s o  the  that  f i n g e r movements a r e  the  and  with  require  Some o p e r a t o r s the  back f a t i g u e Fatigue  and  Good b a l a n c e  a pivot  throttle,  controls  fingers  saw  conforms to  engine c o n t r o l s  quick natural  control  the  l i n e s up  gravity.  i s used  unintentional  grip  center of  The  that  avoid  Maximum o p e r a t o r c o m f o r t and  engine center of  front  balancing  r e s u l t when t h e  and  forward  to  c o n t r o l l i n g a v i b r a t i n g machine.  r e d u c e d by the  i s always d i f f i c u l t  means  increase fatigue is a  as must  prime  59 cause  of  accidents. To d e t e r m i n e  the  saw c h a r a c t e r i s t i c s , number but  of  were  Queen C h a r l o t t e tionnaire stated  them  according  0 to  by  appearance, loggers  him,  much,  totalling  a value  how  each category (7  for  an i m p o r t a n c e mentioned  the  The o r i g i n a l  data  lot, 3,  2,  1  and  professional  factor  and the  evaluate  a  of  ques-  the  or  quite  few,  the  The  He w a s a s k e d t o  responses  1.9.  loggers  low weight  was  deter-  results  is  shown  considered easy s t a r t i n g ,  as 'the  smell  most  important  and n o i s e  expressed personal  existing  saws,  keep out  sawdust.  filter,  ments  of  area.  what extent  affected  very  a  Responses were  local to  be.  to  obtained in  IV. The  air  by  controllable  New B r u n s w i c k ,  By a s s i g n i n g  pulpwood),  shown on F i g u r e  to  or  degrees:  a l l .  number  indicate  them  The c h a r a c t e r i s t i c s  Appendix  and  four at  from the  bothered  degrees,  the  cutting  mined. are  and n o t these  dividing logger  to  to  of  was d i s t r i b u t e d  from O n t a r i o , and  user  he c o n s i d e r e d  somewhat, and  Islands,  characteristics  important  a number  and c a s u a l u s e r s .  received  asked the  of  a questionnaire  professional  replies  importance  and  Both  least  suggestions  suggestions  chain,  important.  for  Two  improvements  filtering included  tinkerproof  and  system  a more  carburetor  to to  rugged adjust-  self-cleaning ports .  Even though important,  characteristics,  suggested a fuel  Other  a better  as the  reliability  if  other  users things  did are  not  consider  equal  or  appearance to  unknown,  they  are  be  Not Imp > o r t a n t  Characteristics  Easy  Very  starting  9  Reliability Low w e i g h t Long,  9 and  size  9  trouble-free  Low i n i t i a l Low f u e l Easy  life  9  cost  i  consumption  Low o i l  >  9  maintenance  Low u p k e e p  Neat  9  cost  9  consumption  9  appearance  9  •  Weight 5  Vibration  9  Smell  9  Noise  9  Figure  1.9  R e s u l t s of q u e s t i o n n a i r e saw c h a r a c t e r i s t i c s  more  likely  than  an u n a t t r a c t i v e  to  often  buy  an a t t r a c t i v e ,  is  other  c a s u a l saws t h a t  .saw s h o u l d  be  for  sell  the  convinced  the  one.  price  than  Im p o r t a n t  For  below  sell  the  the  for  100  200 d o l l a r s . saw,  the  saw's merits  importance  functionally  In  the  to  200 d o l l a r s ,  If  the  price  before  he p a y s  is  will the  saw  purchase  comparison  casual user  of  arranged  casual user,  main, c o n s i d e r a t i o n .  conventional of  on t h e  with  a  new  higher have  to  extra  price. To s u m m a r i z e a power  saw s h o u l d  be  what  the  like,  operating  one  can  characteristics  say t h a t  the  casual  of user  r e q u i r e s and carried  wants a simple one-handed t o o l t h a t  i n t o a t r e e , pushed i n t o a t i g h t c o r n e r or  long d i s t a n c e s . to be  can  For  safety  and  perched oh  f a s t s t o p p i n g because i n  such as when a t r e e pruner i s  the  overhang of a r o o f , hand s t a r t i n g  and  dangerous.  to h i s h e a l t h so t h a t  amplitudes must be machine must be  low.  o p e r a t o r wants  fatigue  and  the maximum  n o i s e l e v e l s and  vibration  To make i t easy to handle,  l i g h t i n weight and  be  i n e x p e n s i v e to own  and  be  safe,  readily  r e l i a b l e and  cutting  i s essentially, d i f f i c u l t  w i t h a l l hand t o o l s , the  to e x p e r i e n c e the minimum amount of protection  precariously  a branch or a c a r p e n t e r i s a c c u r a t e l y  As  carried  convenience, he wants i t  p o w e r f u l , s e l f - s t a r t i n g and  awkward s i t u a t i o n s  be  operate.  small i n s i z e .  the I t should  I t s source o f power must  available.  Table 1 Specifications 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.  f o r a Small Power  Saw  power - 1 hp, c h a i n speed - l e s s than 2000 fpm i f a c h a i n i s used, weight - l e s s than 4 l b s , c o s t - l e s s than 2:00 d o l l a r s , v i b r a t i o n amplitude - l e s s than .002 i n at 7000 rpm, n o i s e l e v e l - below 110 dBA, s a f e t y - automatic s t o p p i n g i f t r i g g e r i s r e l e a s e d , appearance - a e s t h e t i c a l l y p l e a s i n g , s p e c i f i c f u e l consumption - l e s s than 1.2 lb/bhp-hr, f u e l tank c a p a c i t y - 7 in-3 - enough f o r 10 min continuous f u l l power c u t t i n g , o i l - i f mixed w i t h f u e l , r a t e s should be a t l e a s t 50:1, starter - self-starting.  The been  summarized  cations  step  desired  step,  the  cutting  in  constitutes  The n e x t the  specifications  is  to  output,  analysis  devices,  is  Table only  for  I.  The  the  first  ascertain within of  the  subject  design  formulation  all  suitable  the  the  step  in  possible  specified power of  of  the  the  limitations. and  following  have  specifi-  design  means o f  sources  the  envelope  process.  achieving This  possible chapter.  63  2.  2.1  Wood C u t t i n g Finding  device  required  The t a s k more  of  Devices the  best  source of  an e v a l u a t i o n  eliminating  the  of  less  power  the  liable,  the  safe,  machine  i n e x p e n s i v e and  Solar is  e n e r g y was t h e  Not  only  its  conversion into  this  p o s s i b l e to  1.  to  source  heat  to  boilers,  to  it  as  power  available.  help  of  power  the  following  must  be  re-  portable. first  source to  in  evaluated.  available,  water  following  or  energy  ways:  absorbing  (especially  algae)  and  then  and then  burn  the  hydrogen  and  and  an energy  sun i s  reaching  a horizontal  1/10  2  hp/ft .  converter  and then  use  the  Because  at  the  plate  zenith  at  conversion  the  solar  sea l e v e l  is  efficiency  power about  is  only  2 about  10%,  but  r e c e i v e d much s t u d y .  the  heaters  be  electricity. When t h e  the  fuel,  photolyze  to  cutting  and a c c e p t i n g  and u n i v e r s a l l y  air  wood  directly,  oxygen produced, 4.  the  source of  energy  grow v e g e t a t i o n  burn 3.  free  the  many s o u r c e s  work has r e c e n t l y  use s o l a r  materials 2.  and i t s  for  desirable  r e a s o n a b l e was e x p e d i a t e d w i t h  criteria:  is  SYNTHESIS  a collector  area of  100  ft  is  required  to  It  produce 1 hp. day  According  t o T h i r r i n g [ 2 . 1 ] , d u r i n g a sunny  t h e t o t a l d a i l y energy r e a c h i n g  t h e e a r t h a t t h e 50th  p a r a l l e l v a r i e s from a peak o f 570 g r a m - c a l o r i e s i n June t o a low o f 100 g r a m - c a l o r i e s The c a p r i c e c l o u d c o v e r p r e v a l e n t  per sq cm  p e r sq cm i n December  i n many a r e a s r e d u c e s t h e  r a d i a t i o n and makes s o l a r power u n r e l i a b l e . The drawbacks o f c a p r i c e c l o u d c o v e r can be o v e r come when t h e c l o u d y  i n t e r v a l s are short.  Thermal energy  can be s t o r e d i n m e l t e d s a l t o r , i f f i r s t c o n v e r t e d i n t o e l e c t r i c a l energy, i n b a t t e r i e s .  One hp-hr  can be  s t o r e d i n 25 l b s o f Na SO .10H O [ 2 . 1 ] , i n a 20 l b z i n c - a i r 2  battery  4  2  [2.2] o r i n 70 l b s o f l e a d - a c i d s t o r a g e b a t t e r i e s .  A l t h o u g h i t would n o t be v e r y p o r t a b l e , even w i t h o u t an i n t e g r a t e d s t o r a g e d e v i c e , s o l a r power i s f e a s i b l e f o r a s t a t i o n a r y power p l a n t , as was shown by t h e s m a l l p i s t o n engine b u i l t i n I t a l y t o pump i r r i g a t i o n w a t e r .  Using a  f l a t p l a t e as a c o l l e c t o r and s u l p h u r d i o x i d e as a w o r k i n g m a t e r i a l , i t c o n v e r t e d s o l a r energy i n t o work a t an e f f i c i e n c y o f 10%.  Because s o l a r power i s n o t p o r t a b l e , i t d i d  not meet t h e d e s i g n  r e q u i r e m e n t s so no f u r t h e r a n a l y s i s  was u n d e r t a k e n . A l t h o u g h f e a s i b l e i n windy a r e a s and p r a c t i c a l i n undeveloped c o u n t r i e s , l a c k i n g a more s u i t a b l e s o u r c e , wind power i s n o t r e l i a b l e and n o t p o r t a b l e  [2.3],  Power from  t i d e s and waves and from h y d r a u l i c p o t e n t i a l i s a l s o n o t portable.  N u c l e a r energy i s n o t o n l y t o o e x p e n s i v e b u t a l s  65 too  heavy;  the  performance  10A  reactor-thermoelectric  target unit  [2.4].  Consequently windpower,  nuclear  energy were It  power  is  over  the  heat  power  the  commercial market. expensive per  temperature  ment  but  fuel  cells.  per  fuel  voltaic high  zinc-air  verter  weighs  converters  has a  is  too  weight  are  2 lbs  less  such as  H  source  weigh  weigh  fuel,  per  e  <  weigh  [2.5]. a 5 lb  3  u  i  x  100  e  lbs  High per  commercial  develop-  than  lbs  20 l b s  per  kilowatt-  per  may a p p r o a c h 5  lbs  Lithium[2.8].  thermionic  generate  Besides  and  thermo-  electricity.  15% e f f i c i e n c i e s  supply  as the  heavier  200  kilowatt-hour  a production  a radio-isotope  r  the  70 -  batteries  with to  for  2~°2  expensive but  photovoltaic,  operating  advantage  expensive  for  to  [2.6],  c a n be u s e d t o  heat  and  and b a t t e r i e s  a n d a new e x p e r i m e n t a l  can be c o m p a c t ;  using  kilowatt-hour  potential,  and e x p e n s i v e  batteries  and b a t t e r i e s ,  temperature  it  cells  difficult  [2.7],  converters  converters  cell  organic-electrolyte  battery  cells  electric  fuel  batteries  kilowatt-hour  Tellurium  cells  s h o w some p r o m i s e is  S.N.A.P.-  and an e f f i c i e n c y  Conventional batteries  [2.2],  per  such as a l k a l i - h a l o g e n w i t h  containment  kilowatt-hour, hour  the  battery  The room t y p e  rating  Storage  lbs  a n d a c h i e v e 50% e f f i c i e n c i e s  cells  kilowatt-hour  500 w a t t  hydraulic  Although  electro-catalysts,  kilowatt-hour  200  use f u e l  saw.  storage  engine,  is  the  analyzed.  possible to  an e l e c t r i c  advantage over  not  for  radiant type  source of  require  energy.  10 0 w a t t heat  Photo-  can  The conbe  a  housed  in  a 2 in  converter  diameter  transforms  by u t i l i z i n g  the  of  and the  temperature  energy  thermal  thermionic  iencies  utilizing  sphere  [2.9,  energy  the  into  electrical  at  The m a g n e t o - h y d r o d y n a m i c  5p00°  F  plasma jets  fuel,  and the  voltages tal  [2.13, All  in  50,000  the  themselves  volts  heavy  and  in  further  increases the  lbs  the  [2.15],  power  saws,  they  to  compare  do n o t  assuming  pressure,  the  meet  suitable in  using  magnetic  the  for  experimen-  sizes  or  an 8 i n  and f u e l  cells  cumbersome design  shown  energy,  below:  which  reciproca-  blade, with  than  weighs an  8  electric  existing  requirements.  as p o t e n t i a l  ability  are  work,  electric  energy strain  chemical energy.  storing as  and b a t t e r i e s  produce  A typical  as k i n e t i c  energy,  cells  such as a motor  the  stored  or  energy  typical  a  device  and more  E n e r g y may b e  thermal  2-10%  a device  to  Because b a t t e r i e s be h e a v i e r  internal  fuel  1 hp W e l l s a w 4 0 0 , w i t h  would  or  of  order  weight.  motor  gravity  s t i l l  generator  thermal  in  generator  both  above mentioned  an e l e c t r o m e c h a n i c a l  saw,  materials  2.14].  require  ting  converts  electricity  are  Effic-  on the  generator,  electro-gas-dynamic  above  stage  conduct  energy  electrons.  efficienciences  [2.12].  to  thermionic  A thermoelectric  principle,  energy  A  electrical  depending  [2.11].  thermocouple  into  emission of  4-19% c a n be o b t a i n e d used  2.10].  It  on a w e i g h t  due  to  energy, is  possible  basis  by  67 1.  K i n e t i c energy: K. E .  .=  1/2 (RCO)  2  for  R = radius = 3 inch oj - speed = 9,000 rpm  K.E. = 860 f t - l b / l b mass  2.  S t r a i n energy: S.E.  2Ep for  s t e e l rods,  S  P  S.E. for  steel springs,  S.E.  for  rubber,  S.E.  = s t r e s s = 200,000 p s i 7 = modulus = 10 p s i 3 = d e n s i t y = .28 l b / i n = 240 f t - l b / l b mass = 100 f t - l b / l b mass = 4,000 f t - l b / l b mass  3.  Gravity potential: F o r 100 f t above datum,  4.  P.E.  = 100 f t - l b / l b mass  Compressed a i r p o t e n t i a l :  where  Wk  =  work o u t i n expanding a volume o f gas from P t o Pa a c c o r d i n g t o law pVY = c o n s t a n t  Pa  =  pressure  pa  =  d e n s i t y o f atmosphere  o f atmosphere  '  Y  =  r a t i o o f s p e c i f i c h e a t s = 1.4  r  =  compression r a t i o = 9  Energy based on a i r w e i g h t o n l y :  Wk = 80,000 f t - l b / l b a i r  I f s t o r e d i n aluminum s p h e r e , ( s t r e s s / p r e s s = 2 3 0 ) : Wk = 2,600 f t - l b / l b mass.  5.  Thermal energy i n s a l t : For Na S0 .10H O, 2  4  Heat o f F u s i o n = 104 B t u / l b  2  Energy = 80,000 f t - l b / l b mass  6.  Hydrocarbon  fuel:  Heat o f Combustion  = 18,000 B t u / l b  W i t h 20% e f f i c i e n c y ,  Wk = 2,800,000 f t - l b / l b mass  Of a l l t h e energy s t o r i n g d e v i c e s c o n s i d e r e d , f u e l has t h e h i g h e s t e n e r g y - t o - w e i g h t r a t i o only a small storage  the hydrocarbon and  requires  volume.  The fundamental o b j e c t i v e o f t h e d e v i c e i s t o c u t a p i e c e o f wood w i t h a minimum e x p e n d i t u r e the s h o r t e s t p o s s i b l e t i m e . t o exceed t h e r u p t u r e  o f energy and i n  By a p p l y i n g a f o r c e l a r g e enough  s t r e n g t h o f t h e wood f i b r e s a p i e c e o f  wood c a n be b r o k e n , by a p p l y i n g a shear l o a d l a r g e enough t o exceed t h e shear s t r e s s a t f a i l u r e t h e p i e c e c a n be c u t , by a p p l y i n g an a b r a s i v e m a t e r i a l t h e wood can be e r o d e d , and by a p p l y i n g a h o t w i r e o r flame t h e p i e c e can be burned.  Wood  69 exhibits  pronounced v i s c o - e l a s t i c c h a r a c t e r i s t i c s .  suddenly  applied  approximating by  is  the  a logarithmic  istic  means t h a t  made,  the  specific  loads  there  is  an immediate  c l a s s i c a l deformation increase with the  faster  higher  the  energy w i l l  time  the  deformation  patterns,  [2.16].  load  stress will  is  i n c r e a s e as the  This  applied  be.  Under  or  followed characterthe  Consequently  cutting  speed  cut the  is  increased. Under the  outer  fibres  moment  is  varies  with  given  the  large the  influence  in  a piece of  The as  bending  wood c a n be b r o k e n  For round  wood t h e  diameter  cubed and f o r  moment, if  required  Douglas  fir  it  the moment is  by:*  the  diameter  amount the  of  lever  increases. lever  an a p p l i e d  enough.  M  where  of  work  is  400 d  given  required  arm between t h e The r e l a t i o n s h i p  arm f o r  Douglas f i r  Specific and the  (d)  =  required  Work force  = is  is  to  [in-lb]  3  in  inches.  break  point  a given  of  application  between work given  .39 I given  tree  per  unit  increases and  ground  area  and  by:  [in-lb/in ] 2  by:  * For dense s t r u c t u r a l wood, e . g . Douglas f i r , southern p i n e , M a r k s Handbook [ 2 . 1 6 ] , g i v e s t h e f o l l o w i n g v a l u e s : S = 2000 p s i , S i m p a c t = 4000 p s i , E = 1.76 x 106 p s i .  =  P  <oodi  I l b ]  I  where the l e v e r arm  (Z) i s g i v e n i n i n c h e s .  When a f o r c e i s a p p l i e d 8 1/2  f t from the ground on a 10 i n  d i a m e t e r Douglas f i r t r e e the f o l l o w i n g w i l l be r e q u i r e d  to  f e l l the t r e e : b e n d i n g moment force  =  = ,400,000  in-lb,  4,000 l b , 2  s p e c i f i c energy  =  39  xn-lb/xn  Because l i t t l e energy i s r e q u i r e d and  the t y p e of  s u r f a c e produced i s u n i m p o r t a n t , f e l l i n g t r e e s by them i s an a t t r a c t i v e way i c a l l y by p u l l i n g two and heavy s t e e l b a l l .  long chains attached Two  a p a r t , p u l l the f r e e end between them. is  The  ground clearance), and t o p r e v e n t the c h a i n s breaking  T h i s i s done mechan to a very  large  t r a c t o r s , t r a v e l l i n g some d i s t a n c e  of the c h a i n s  and  t o p p l e the  trees  r e a s o n f o r h a v i n g the b a l l d i a m e t e r l a r g e  t o keep the f o r c e s  and  to c l e a r land.  breaking  low  (by m a i n t a i n i n g  suitable  the r e a s o n f o r h a v i n g the b a l l heavy i s from r i d i n g a l o n g t h e t o p s o f the  o f f only the t r e e t o p s .  a t the P o r t a g e M o u n t a i n Dam  Such a d e v i c e was  s i t e where two  385  trees used  hp t r a c t o r s  t r a v e l l i n g 75-8 0 f t a p a r t p u l l e d an 8 f t d i a m e t e r , 9 t o n s t e e l b a l l and to 4  ft  c l e a r e d 9 a c r e s of f o r e s t per hour.  d i a m e t e r were t o p p l e d  [2.17].  Trees  up  Because the energy  a p p l i e d t o the t r e e i s d i s t r i b u t e d o v e r a l a r g e v o l u m e , i t  is  not  s u r p r i s i n g t h a t many r a g g e d  parting  surface  of  t h e wood.  of  a low g r a d e .  and many m i n u t e c r a c k s  becomes b r i t t l e  of  Yu  against  and d i s i n t e g r a t e s .  friction  Columbia.  wood t o i t s i g n i t i o n by  attrition.  ignition by  He f o u n d  does n o t g e n e r a t e  burning  as w e l l  I t i s by t h i s  that  a t low f e e d  sufficient  temperature;  i s reached,  heat  a t high so t h a t  rates  to r a i s e the  therefore  as by a t t r i t i o n .  2 4 i n / m i n , Yu r e q u i r e d  method  experiments a t the U n i v e r s i t y  He c a l c u l a t e d t h a t  temperature  i s therefore  a r o t a t i n g d i s c , wood h e a t s up,  [2.18] c u t wood d u r i n g  British  o c c u r on t h e i n s i d e  The wood b r o k e n by t h i s method  When h e l d  that  s p l i n t e r s p r o t r u d e on t h e  wood  feed  i s removed  rates the  t h e wood  A t a feed  i s removed  rate of  ic  f o r c e o f 5 l b s and a s p e c i f 2 2 c u t t i n g e n e r g y o f 100,000 i n - l b / i n . A t 16 i n / m i n ,  he  required  a force  a loading  o f 7 0 l b s and a s p e c i f i c  energy o f  2 300,000 i n - l b / i n the  grain  .  of a f i r board  of  72%.  is  smooth, p o l i s h e d  clean.  These v a l u e s  The s u r f a c e  are f o r cutting  across  1 i n thick, with a moisture  content  o f t h e wood p r o d u c e d by a f r i c t i o n and s t r a i g h t .  But t h e f r i c t i o n  disc  The k e r f  i s practical  disc  i s n a r r o w and only  i f ample  power i s a v a i l a b l e . The the  k i n e t i c energy o f a water  v e l o c i t y i s high  their  rupture  j e t c a n c u t wood i f  enough t o s t r e s s t h e wood t i s s u e s  strengths.  beyond  Because the water j e t r e c e i v e s i t s  k i n e t i c energy as i t passes through  a very small nozzle, th  u s a b l e energy i s i n a h i g h l y c o n f i n e d and c o n t r o l l e d The  form.  j e t i s a c u t t e r t h a t i s n o t l i a b l e t o wear, does not  r e q u i r e d a i l y maintenance by h i g h l y s k i l l e d p e r s o n n e l ,  and  produces h i g h q u a l i t y s u r f a c e s w i t h a n e g l i g i b l e l o s s o f material. advantage.  But c u t t i n g w i t h w a t e r j e t s has one major d i s U n l i k e the bending method of b r e a k i n g wood and  l i k e t h e f r i c t i o n d i s c method, the h i g h v e l o c i t y j e t method c a u s e s a complete breakdown o f the m a t e r i a l b e i n g removed. Because i t r e q u i r e s energy i n p r o p o r t i o n t o the amount o f breakdown, the j e t - c u t t i n g method i s h i g h l y i n e f f i c i e n t . Bryan [2.19] a t the U n i v e r s i t y of M i c h i g a n energy r e q u i r e d by t h i s method was  found t h a t the  a t l e a s t 50 t i m e s  t h a n n o r m a l l y o b t a i n e d w i t h the c o n v e n t i o n a l power  higher saw.  T h i s p u t s the s p e c i f i c energy r e q u i r e d a t about 100,000 2 2 i n - l b / i n . A t a feed r a t e o f about 5 i n /min and w i t h a p r e s s u r e of 30,000 p s i he was a b l e t o p e n e t r a t e 1 i n o f 2 maple and g e n e r a t e 2 0 i n o f s u r f a c e a r e a per min. At a 2 f e e d r a t e of about 100 i n /min, the .010 i n d i a m e t e r j e t 2 generated  6 0 i n /min  but the p e n e t r a t i o n was  o n l y .3 i n .  E x t r a p o l a t i n g from the r e s u l t s produced by the p r e d i c t e d t h a t a .040  .010  j e t , he  j e t would c u t 16 i n s t o c k .  A number o f o t h e r r e s e a r c h e r s have i n v e s t i g a t e d c u t t i n g w i t h water j e t s  [2.20, 2.21].  f i n d i n g s a r e l i s t e d below:  Some o f  their  73 1. The d e p t h o f p e n e t r a t i o n i s i n v e r s e l y p r o p o r t i o n a l to  the feeding  speed; t h e a r e a o f c u t f i r s t  with  i n c r e a s e d f e e d i n g speed, reaches  then  at a certain  p o i n t begins  2. When t h e j e t p a s s e s a  "critical  kinetic by  depth"  through  the water pressure  reaches  1/10 o f t h e s u p p l y  pressure.  supply  be c o m p l e t e l y  "water  pressure  exhausted  cushion".  a t depths g r e a t e r than  4. The maximum p r e s s u r e  times,  against the walls of the  and a g a i n s t t h e so c a l l e d holes  decrease.  a t which p o i n t the  energy o f the j e t s w i l l  3. I n b l i n d  a maximum, a n d  t h e same c u t many  i s reached  the forces of f r i c t i o n  cut  to  increases  10 h o l e  a constant  value  diameters,  o f about  on a t a r g e t p l a t e i s h a l f  a t a d i s t a n c e o f about  of the  350 n o z z l e  diameters. 5. The p r e s s u r e radically  distribution  from p o i n t o f impact  2.6 j e t r a d i i  the pressure  6. The d e s t r u c t i v e c a p a b i l i t y increasing when is  reduced  tissues,  decreases  at a radius of  i s zero. of j e t s drops  slowly  with  and s a m p l e ;  i s moved 5-25 cms, t h e d e s t r u c t i v e e f f e c t 15-20%.  o f k e r f i n wood  the diameter As  until  d i s t a n c e between h e a d p i e c e  sample  7. T h e w i d t h  on a t a r g e t p l a t e  of the nozzle  w e l l a s by b r e a k i n g  o r wearing  particles  i s approximately  equal to  opening.  the f i b r e s ,  crushing the  away, wood c a n be c u t by  shear-  ing  the  that the  fibres  most  of  cutting  sharp blades.  pruning  limbing  carried  angle  required. at  the  felling,  system i s  with  a cutting  affects  angle  gardens  and c u t t i n g  out.  Johnston  in  in  is  cutting found  [2.22] 45°  this  latter  method  and most  a mechanized  harvesting  of  force that  required  by  and o r c h a r d s  The t h i c k n e s s the  of  It  the  blade  and  and s p e c i f i c  a  .250  in  of  its  energy  thick  knife and  a force  of  5,06 0 l b s  to  a  4.6  a  2 specific  energy  cant.  .750  A  of  in  817  in-lb/in  thick  knife  cut  required  in  spruce  a maximum f o r c e  of  2 9,470  lbs  and a s p e c i f i c  cut  a similar  45°  was i n s i g n i f i c a n t .  Johnston the  cant.  range  where  of  3-6  ins  Force  =  t  is  knife  ing  3,400  lbs  diameter.  to  diameter  the  1 1/4  trees.  cut  The  At  angle  experimental design  below  results,  formula  spruce  shearing the  and d  is  speed of crawler  sec per  diameter  thick  3,400 t  a commercial  pressure of  12  cutting  fresh  d -  (inch)  from 5-10  in  to  in  which the  gives  diameter  2.24]:  example of  A 6 in  a maximum o p e r a t i n g force  to  e x c l u s i v e of  varies  the  following  thickness  [2.25].  tree  of  3,000 + 2,300 t  Shear  mounted,  the  [2.23,  Tree  1,520 i n - l b / i n  Based on h i s  required  A typical  is  of  The e f f e c t  came up w i t h  maximum f o r c e  energy  log  hydraulic  shear  is  (inch).  the  Roanoke  Model TF-10,  weigh-  on w h i c h  d e p e n d i n g on cylinder  2^100-2^00 p s i  a 25 i n  diameter  tractor  tree  blade which  sec for  [lb]  the  working  supplies  o p e n s up t o diameter  on  the  cut  tree,  it  26  the  in  .75 feed  rate  68,000  is  2,500 i n  2  /min  maximum c u t t i n g  cutting  methods  fast.  an a x e ,  used by man,  one o f  is  very  An e x p e r i e n c e d lumberjack pine  log  in  31.3  sec  .4  in hp  and  [2.27],  if  his  the  [2.26].  At  power d u r i n g  specific  energy  first  efficient  . /min  the  can cut  2 300  force  is  lbs. Chopping w i t h  white  and the  . this  for  and  a 14  this  wood  in  diameter  rate  . time  quite  he  cuts  averages  chopping  is  530  2 in-lb/in the  .  Even  though  axeman c a n n o t m a i n t a i n  he m u s t  take  no r e s t  periods.  a rest.  Another information holes.  the  hole  forward  this  of  was a v a i l a b l e )  Instead  of  by  thrust  rate  is  the  rate;  cutting is  and r e d u c e  the  power  the  is  used to  potential  stress  produce  wood i s  The method amount  of  external  yet of  fibres  a rupture.  push screws i n t o in  time,  hand,  require  (for  which  closely  the  cutters  required  to  be  Even  is  though  [2.29],  a  give  added  [2.28]. cut  wood.  tool  beyond t h e i r  could  tensile ultrasonics  its  cutting  determined.  wood c u t t i n g  energy  spaced  perimeter  to  a vibrating  plastics  little  removed as w i t h  c o u l d p o s s i b l y be used t o  be  periods,  a short  c a n be p r e s s e d a g a i n s t  produced by  and t h u s  wood  by d r i l l i n g  The m e c h a n i c a l f r i c t i o n  limit  short  other  special wing-and-spur  to  for  after  shavings being  they  Ultrasonics  sufficient  high  Machines on the  method  conventional bit, of  his  burning.  requiring  the  Once the  smallest ignition  t e m p e r a t u r e of the wood i s r e a c h e d w i t h the a i d of a flame o r hot band, the c u t t i n g a c t i o n can be s e l f s u s t a i n i n g . I f r a p i d combustion i s m a i n t a i n e d  w i t h a length of  hot  w i r e o r s t e e l band and a c o n t r o l l e d s u p p l y of oxygen, the c u t can be completed b e f o r e combustion i n the v i c i n i t y the c u t becomes s e l f - s u s t a i n i n g . m e n t a l l y proved f e a s i b l e by  T h i s c o n c e p t was  cutting  of  experi-  w i t h an oxygen-  acetylene torch. The most p o p u l a r method o f c u t t i n g wood i s w i t h a saw  because the s p e c i f i c energy r e q u i r e d i s low and  the  c u t t i n g r a t e i s d i r e c t l y p r o p o r t i o n a l t o the power available. J o h n s t o n [2.30] found t h a t f o r f e e d r a t e s from 2 600-2,300 i n /min he r e q u i r e d a s p e c i f i c energy o f about 2 1460  in-lb/in  to cross-cut white  r e q u i r e d t o c u t w h i t e p i n e was y e l l o w b i r c h i t was  s p r u c e lumber.  The  energy  18% l o w e r , w h i l e t o c u t  23% h i g h e r .  As has been shown i n C h a p t e r  1, the energy r e q u i r e d t o c u t wood w i t h a c h a i n saw  depends  on the j o i n t o f the c h a i n , the c h a i n speed, t h e r a t e o f c u t t i n g and the s p e c i e s of t r e e . s p e c i f i c energy r e q u i r e d was 2 o f 700  i n /min.  1,650  F o r hemlock the minimum 2 i n - l b / i n at a feed r a t e  T h i s s p e c i f i c energy i s shown on Graph  w i t h the s p e c i f i c energy  r e q u i r e d by the o t h e r c u t t i n g  devices. B e f o r e the c h o i c e of a wood c u t t i n g d e v i c e f i n a l i z e d , the e x i s t i n g e n g i n e s were e v a l u a t e d . e v a l u a t i o n i s the s u b j e c t of t h e n e x t s e c t i o n .  This  was  2.1,  77  G r a p h 2.1  2.2  S p e c i f i c energies cutting devices  Evaluation In  gas  the e v o l u t i o n  t o the conventional  turbine,  designer  wood  of the i n t e r n a l combustion  and S t i r l i n g  as c o n c e p t s t h a t  h a v e emerged  power u n i t s .  Other  as p o s s i b l e  r e c i p r o c a t i n g engine. engines,  engine alterna-  The W a n k e l ,  f a m i l i a r to the engine  h a v e o v e r c o m e some o f t h e d i s a d -  v a n t a g e s o f r e c i p r o c a t i n g e n g i n e s were small  by v a r i o u s  of E x i s t i n g Engines  many t y p e s and c o n f i g u r a t i o n s tives  required  evaluated  as  possible  t y p e s p r o p o s e d by i n v e n t o r s  such  as T s c h u d i ,  Mercer, L l e w e l l y n ,  Gursted, Virmel, considered  D o t t o , L i m , James, Y o t o ,  Kauretz, Unsin,  but not evaluated  R a j a k a r u n a and  Selwood  were  as none o f them a p p e a r e d  promising. The constant a high  gas  turbine  has  the advantages o f a  torque a t a l l speeds, v i b r a t i o n l e s s o p e r a t i o n  power-to-weight  ratio.  weight per horsepower  cies deteriorate  v a r i e s w i t h the square r o o t  r a p i d l y below  i n weight p e r horsepower  Disadvantages of t h i s and  and  500 hp  compressor  so t h a t  of the efficien-  the promised  t e n d s t o be c a n c e l l e d  engine are the high  fuel  out.  consumption  the slow r a t e o f a c c e l e r a t i o n . A number o f s m a l l  are  and  Although i n p r i n c i p l e the  h o r s e power, i n p r a c t i c e t h e t u r b i n e  gain  relatively  proposed.  gas  turbines  Sollar's feasibility  study of small  turbines  indicated that  rpm  will  have  a specific  and w i l l  cost  $1,400 i n q u a n t i t i e s o f 2,000  [2.31].  An  to  rpm  2,000  driven  Volvo's  fuel  80 hp t u r b i n e weighs  by m e r c u r y  hermetically weighs  a 20 hp g a s  have b e e n b u i l t  sealed  consumption  turning  o f 1.04  A  u n i t s per year  two-stage  package  7 i n d i a m e t e r by  lbs [2.34J.  a t 3,600  trucks  are to cost  F o r d ' s 400 hp g a s  1 0 - 1 5 $/hp.  [2.35].  turbine  rpm  in a  [2.33].  transmission,  turbines  These  gear  18 i n l o n g ,  250 hp a u t o m o t i v e g a s t u r b i n e , i n c l u d i n g 800  a t 100,000 lb/shp-hr  and d r i v i n g an a l t e r n a t o r  60 l b s and p r o d u c e s 4 k i l o w a t t  weighs  gas  i n a tractor with a reduction  90 l b s [ 2 . 3 2 ] .  vapour  turbine  or  for  examples  i n d i c a t e t h a t t h e gas t u r b i n e i s n o t c o m p e t i t i v e with the conventional  costwise  r e c i p r o c a t i n g engine.  Of t h e numerous r o t a r y e n g i n e s proposed d u r i n g t h e l a s t decade o n l y t h e Wankel has emerged as a p r a c t i c a l a l t e r n a t i v e t o the p i s t o n engine.  F a c t o r i e s i n Japan and  Germany a r e p r o d u c i n g them on an assembly l i n e b a s i s , and companies i n I t a l y , F r a n c e and E n g l a n d a r e p l a n n i n g  t o do  the same. Some r e c e n t d e s i g n  changes found n e c e s s a r y t o  improve t h e performance and r e l i a b i l i t y  [2.36] show up  some weaknesses o f t h e Wankel: 1.  i n t a k e p o r t s were moved t o t h e s i d e s so t h a t t h e o v e r l a p between i n t a k e and e x h a u s t p o r t s was reduced, thereby improving f u e l consumption,  2.  t h e t r o i c h o i d a l t r a c k was s p r a y e d w i t h s p e c i a l m a t e r i a l and s e a l s were made o f more s u i t a b l e m a t e r i a l s t o reduce apex s e a l c h a t t e r i n g ( N i t r i t e d c a s t i r o n , molybdenum s p r a y and chromep l a t i n g had p r e v i o u s l y been t r i e d ) ,  3.  t h e h e a t f l o w p a t h from t h e  unsymmetrically  h e a t e d r o t o r and t r a c k was changed t o r e d u c e distortion. To e v a l u a t e  t h e f e a s i b i l i t y o f u s i n g t h e Wankel  e n g i n e i n a power saw, t h e performance c h a r a c t e r i s t i c s o f an i n d u s t r i a l Wankel e n g i n e p r o d u c i n g 6.6 hp a t 5,500 rpm  80 was  compared w i t h an i n d u s t r i a l two-stroke engine p r o d u c i n g  3 hp a t 5,000 rpm and a c o n v e n t i o n a l power saw producing 5.8  hp a t 7,000 rpm.  The i n f o r m a t i o n on the Wankel and  i n d u s t r i a l engines was  o b t a i n e d from Go-Power C o r p o r a t i o n  [2.37] and the i n f o r m a t i o n on the power saw, Machinery L i m i t e d . was  from  The Wankel engine used i n t h i s  Power comparison  the f i r s t p r o d u c t i o n v e r s i o n of a s i n g l e r o t o r a i r c o o l e d  F i c h t l and Sachs KM37 i n d u s t r i a l u n i t .  The scavenging  charge i n t h i s engine heats up as i t passes through the r o t o r b e f o r e e n t e r i n g the c y l i n d e r , t o keep the temperatures down to acceptable l e v e l s  [2.38].  The governor, a l t h o u g h v e r y  n e c e s s a r y on the Wankel, i s an u n a t t r a c t i v e f e a t u r e f o r loggers.  The two-cycle i n d u s t r i a l u n i t used i n the compar-  i s o n s was  an a i r c o o l e d , d i e c a s t , r e e d - v a l v e - p o r t e d M c C u l l o c h  S e r i e s 49 i n d u s t r i a l engine, a type commonly used i n c h a i n saws, s c o o t e r s and outboard motors.  The c h a i n saw was  a sand  c a s t , p i s t o n - p o r t e d Canadien 275 complete w i t h bar and c h a i n . The c h a r a c t e r i s t i c s of the t h r e e engines are l i s t e d i n T a b l e II.  The p o s i t i v e f e a t u r e s of the Wankel engine,when used  i n a power saw, would be: 1. lower v i b r a t i o n  levels,  2. smoother torque, 3. lower f u e l  consumption,  4. lower o i l consumption, 5. lower s t a r t i n g t o r q u e , 6. lower n o i s e l e v e l .  81 Table Characteristics  Displacement  (in  Maximum power  Weight  3  the  )  (lb/hp)  price  C h a i n Saw  4.9  6.6  7.4  3.0 @ 5,000 r p m  6.6 @ 5.8 @ 5,500 rpm 7,000 r p m  4.0  5.2  3.7  1.1  0.7  1.0  33  ratio  6 at  R a t i o o f maximum t o torque [2.39]  mean  Number o f n o i s e per c y c l e  60  60  8.5  .017 (typical)  5.7 .014  .0025  7.0  3.5  7.0  1  3  1  pulses  The n e g a t i v e  features  1.  higher  2.  more  3.  greater  complexity,  4.  reduced  reliability*  on t h e  Wankel  consumption  V i b r a t i o n amplitude 4000 rpm [ 2 . 3 8 ]  last  Industrial  ($/hp)  Compression  The  C o n v e n t i o n a l and Wankel E n g i n e s  (shp)  Specific fuel (lbs/shp-hr) List  of  II  would  be:  cost,  weight,  feature  c a n be  sealing, cooling  i m p r o v e d by more d e v e l o p m e n t and c o m b u s t i o n  systems.  work  Graph  2.2  82 shows t h a t t h e power-speed c h a r a c t e r i s t i c o f t h e Wankel engine i s q u i t e c l o s e t o t h a t o f a c h a i n saw e n g i n e , a l t h o u g h the  power i n t h e Wankel drops f a s t e r as t h e e n g i n e slows  down.  As t h e o p e r a t o r c o n t r o l s t h e engine speed by t h e  amount o f l o a d he a p p l i e s t o t h e saw, t h e Wankel engine, as p o r t e d , would be h a r d e r t o keep a t t h e optimum speed, especi a l l y s i n c e t h e governor c u t s i n as t h e e n g i n e d e v e l o p s maximum power.  As t h e n e g a t i v e f a c t o r s  are important t o a  power saw o p e r a t o r , o t h e r e n g i n e s were e v a l u a t e d .  .SPEED  Graph 2.2  (RPM)  Power o f a Wankel e n g i n e compared w i t h conv e n t i o n a l engines  A l t h o u g h i n v e n t e d by S t i r l i n g i n 1816, t h e q u i e t h o t - a i r c y c l e engine was n o t a p r a c t i c a l h i g h speed u n t i l very r e c e n t l y . concept p r a c t i c a l a r e :  engine  The i n n o v a t i o n s w h i c h made t h e o l d  83 1. use o f hydrogen o r h e l i u m as t h e w o r k i n g g a s , 2. i n c r e a s e d knowledge o f compact heat 3. i n v e n t i o n o f t h e rhombic  drive,  4. i n v e n t i o n o f " r o l l s o c k " p o s i t i v e Philips  exchanges,  seals.  [2.40] b u i l t a 440 l b hot-gas engine t h a t  d e v e l o p e d 50 hp a t 2,500 rpm.  By u s i n g l i g h t - w e i g h t m a t e r i a l s ,  by o p e r a t i n g t h e engine a t h i g h speeds, and by d e s i g n i n g f o r low w e i g h t and h i g h power, one would e x p e c t t h e w e i g h t t o power r a t i o o f t h e h o t gas engine  t o be  competitive with  e x i s t i n g two-stroke engines. The i n h e r e n t c h a r a c t e r i s t i c s o f t h e e x t e r n a l comb u s t i o n engine g i v e t h e S t i r l i n g engine t h e f o l l o w i n g  positive  features: 1. smokefree combustion w i t h a g r e a t v a r i e t y o f f u e l s , 2. exhaust t e m p e r a t u r e s o n l y a few degrees above t h e incoming a i r t e m p e r a t u r e , 3. low s p e c i f i c f u e l consumption  (.52 l b / s h p - h r ) ,  4. low peak t o r q u e (3.5 t i m e s mean o u t p u t t o r q u e r e s u l t i n g p a r t l y from two p u l s e s p e r r e v o l u t i o n ) , 5. low p i s t o n v e l o c i t i e s 6. low n o i s e l e v e l s  (750-800 f p s ) ,  ( i n a u d i b l e a t 100-300 f t ) ,  7. low v i b r a t i o n l e v e l s  (rhombic d r i v e r e s u l t i n g i n a  balanced engine). Some o f t h e n e g a t i v e c h a r a c t e r i s t i c s  that  produce a h e a v i e r and more e x p e n s i v e e n g i n e a r e :  84 1. more c o m p l i c a t e d mechanisms such as s e a l s , power and speed c o n t r o l d e v i c e s , r e g e n e r a t o r , o i l pump and an a u x i l i a r y compressor  f o r the working gas,  2. h i g h e r f o r c e s i n the d r i v e mechanism and c y l i n d e r , 3. long d e l a y i n s t a r t i n g c o l d engine 4. l a r g e r c o o l i n g system  (1-2 m i n ) ,  (approximately double con-  v e n t i o n a l engine r e q u i r e m e n t s ) . The hot-gas engine i s based on the w e l l known p r i n c i p l e o f compressing gas a t a low temperature and expanding  i t a t a h i g h temperature  (Figure 2.IB)  (Figure 2.ID).  When  a h i g h temperature i s r e q u i r e d , the gas i s f o r c e d i n t o a hot region  (Figure 2.1C)  into a cold region  and when a low temperature i s r e q u i r e d ,  (Figure 2.1A).  What makes the modern  engine work so w e l l i s an e f f e c t i v e r e g e n e r a t o r s i t u a t e d between the h o t and c o l d r e g i o n s .  This regenerator stores  most o f the heat r e j e c t e d a t the end o f the expansion s t r o k e and r e t u r n s i t t o the gas a t the end o f the compression stroke. In order t o g e t the most work out of a c y c l e , the power p i s t o n s t r o k e and the d i s p l a c e r p i s t o n s t r o k e must o v e r l a p , and the c o l d volume must go t o z e r o .  At a given  r a t i o between the hot and c o l d space temperatures and the r a t i o between the maximum hot and maximum c o l d volumes, t h e r e e x i s t optimum v a l u e s o f p i s t o n phase angle and swept volume. These c o n d i t i o n s were a n a l y z e d by K i r k l e y  [2.41],  Creswick  [2.42] a n a l y z e d t h e h e a t and mass f l o w i n  the i d e a l i s o t h e r m a l S t i r l i n g c y c l e and made t h e f o l l o w i n g observations: 1. Heat must be r e j e c t e d from a l l s u r f a c e s d u r i n g compression and added everywhere  during expansion  to m a i n t a i n a constant temperature.  A F i g u r e 2.1  B  C  Diagrams i l l u s t r a t i n g  D t h e hot-gas  cycle  2. Because more mass i s i n t h e e x p a n s i o n space d u r i n g e x p a n s i o n t h a n d u r i n g c o m p r e s s i o n , more h e a t i s added t h a n i s r e j e c t e d . compression  The r e v e r s e i s t r u e f o r t h e  space.  3. The dead spaces r e j e c t as much h e a t as t h e y t a k e i n , t h u s t h e y have no u s e f u l f u n c t i o n i n t h e i d e a l thermal c y c l e .  iso-  86  4.  The peak h e a t heat  flux  addition;  far  therefore,  s h o u l d be d e s i g n e d t o heat  addition  exceeds the  rates  heat  average rate  transfer  accommodate the  rather  than  the  of  surfaces instantaneous  average  net  rate. 5.  The t o t a l in  one  amount  "blow"  greater  than  environment  At  least  opposed,  Vee, o i l  [2.43].  In  pressures  the  must  pressure  in  crankcase pistons  acting  five  engine  (in  but  In  the  power  each of  the  and a power  affects  to  piston another  a limit  to  of  drive  high 100  Vee arrangement dead space  thermodynamic  with  a column the  In  oil  the  alternately,as  the  gas  variation  must  of is  regenerator; in  efficiencies.  hot In  and the  of be  double  work  the  the  between  the  the  atmo-  average  performs  through  thermodynamic  the  reduce  pistons  pistons  the  possible:  a high  these d e f i c i e n c i e s but  four  from  are  order  large  symmetry  times  and r h o m b i c  introducing  flow the  the  up  several  transferred  acting  crankcase.  of  picked  configuration,  pistons  compact,  is  arrangements  column, double  Driving  arrangement  volumes  amount  cycle.  lack  from one c y l i n d e r this  net  or  c o o l e d , d e g a s s e d and f i l t e r e d .  engine  displacer  the per  o v e r c o m e s some o f  circulated,  regenerator  large  and the  efficiencies. oil  the  on t h e  more  deposited  of  be b a l a n c e d by  the  is  heat  opposed p i s t o n  acting  spheres)  of  a forced in  cold rhombic  87 drive  configuration,  crankcase easily is  is  p o s s i b l e because the  sealed with  of  a hot-gas  its  application. the  designing of  wall.  smaller  a coarse wire the  spirals  sprayed with through  the  incoming  .001  the  efficiency. admitting  in  diameter  gauze  [2.44].  the  on t h e  burner.  atomized inside  of  the  components  the  the  of  were saw  is  shown  regenerator.  annular  space  continuous  with  the  can be o b t a i n e d  with  a  p a c k e d mass o f by  2 in  The a i r outside  of  ignited,  hot-air  used i n  the  copper  long, arranged  and r e t a i n e d  Once i n  fuel,  appealing  a power  course,  chambers not  compressed paper  the  on the  wires between  ends  engine  the  hot  air  ducts  The c o n t r o l  and w i t h d r a w i n g  the  air  is  and t h e  hot  gas  leaves  duct  to  be  the  affecting  system c o n s i s t s of gas  and  burner  mean p r e s s u r e o f  output without  by  combustion  insulated  by  air.  Altering controls  is,  a randomly  preheater  into  for  is  configuration  these components  Best performance  c o n s i s t i n g of  sleeves of  this  can be a v o i d e d by d i v i d i n g of  piston  basic  them  of  stress  pressurized  configuration  The m a i n component  approximately  the  to  the  2.2.  cylinder  enters  a view  of  drive  The a r r a n g e m e n t  a number  matrix  All  a rhombic  a  and t e c h n i c a l l y  schematic diagram Figure  Thermal into  in  displacer  diaphraphm;  favourable  simplicity.  engine  evaluated with  two  a rolling  thermodynamically  because  in  a balanced engine without  from the  working the  thermal  a method  working  gas  cycle  for and  a thermostat t o c o n t r o l the heater temperature.  An a u x i l i a r y  compressor f o r c e s gas i n t o t h e w o r k i n g c y c l e and a low p r e s sure r e c e i v e r tank a c c e p t s excess g a s .  (below t h e l o w e s t maximum c y c l e p r e s s u r e ) By u s i n g a low d e n s i t y gas such as h y d r o -  gen, f l o w l o s s e s a r e r e l a t i v e l y s m a l l , h e a t t r a n s f e r  coeffic-  i e n t s a r e h i g h , and t h e r e s p o n s e t o t h r o t t l e i s f a s t .  I Schematic diagram of rhombic drive mechanism. J = power pistonT 6 — displacer piston. 5-5' = cranks in two shafts rotating in opposite senses and coupled by gears 10-10'. 4-4' c con-rods pivoted from ends of yoke 3 fixed to the hollow power-piston rod 2. 9-9' = con-rods pivoted from ends of yoke 8 fixed to displacer-piston rod, which runs through the hollow power-piston rod, 11 and 12= gas-tight stuffing-boxes. /.'* ** buffer space containing gas at high buffer pressure.  F i g u r e 2. 2  S t i r l i n g t h e r m a l engine s c h e m a t i c d r a w i n g  [2.40]  89  The r o l l i n g efficiency positive  of  seal  no w o r k i n g diaphragm confined working only  is to  modern h o t - g a s  between  supported  above  a pressure in  the  stroke,  pressure rolling the  diaphrams  diaphragm  about  high  surface atures  and  piston  Across  of  about  (50-100  seal.  oil  its  This  seal  is  in  suitable  the  there  the  by  the in  independent the  pressure  rubber  real  and  The e n d u r a n c e  thickness,  is  oil  piston  orifices,  inversely  (Polyurethane  The  becomes  on the  the  the  carried  separates  c u s h i o n volume  on  from  is  space containing  steps  that  the  5 atmospheres.  from the  designing  so  diaphragm  atmospheres)  a  function  cushion  the  the  walls As  depends d i r e c t l y  clearance;  of  the  across  temperature  diaphragms  last  a year) [2.46] .  cooling  saw e n g i n e rate  are  not  kept  are  low,  laws  blower  be a i r - c o o l e d .  a hot-gas  required.  efficiency  and power  to  maintained,  that  for  displacement. then  the  To  engine,  are  indicate  proportional  speed i s  should  required<in  a r e a and a l a r g e  Scaling weights  the  and by  A power the  piston.  the  c a n b e made s e l f - r e g u l a t i n g .  and p i s t o n for  in  fluid  By d e s i g n i n g  wall,  cylinder.  the  to  maintains  and c y l i n d e r  cushion,  diaphragm  mechanism.  cylinder the  the  It  on an o i l  pressures  cushion under  of  engine.  piston  difference  second conventional  the  the  separating  gas  driving  has added g r e a t l y  gas can escape from the  difference a  the  diaphragm  If is  similar If  a  a  the  achieve large temper-  low. engines, constant  power-to-weight  ratio  90 goes  up  surface will  as the  area-to-volume  have  desired  displacement  the  hot  Based a  small  engine  clearances 40 h p  engine  gas  would  as  a cylinder  5 in  when t h e to  burn  be  pumps  or  timed  it  should  be  complicated malfunction,  lbs by  the  the  characteristic  and w i t h  saw i s  and  present  very  rugged  run  volume  exhaust. and  would  its  operate  high  start-  be v e r y  such as to  heavier  in  short ability  at  a  pressure  fuel  some a d v a n t a g e s , power  and  a p r e s s u r i z e d gas  but  speed  system  disadvantages.  often  and  running  quietly,  a cool  complicated  cost  (if  Philips  same  complex  delay  without  of  ratio  The d e l a y  efficiently,  seals,  the  saw w o u l d  the  that  long.  engine.  fuel  expected  a 5 hp e n g i n e  and be more  requirement  controls  of  cylinders  on the  and occupy 12 i n  but  fuels  ignite  simple,  is  Secondary factors  maintenance  A chain  it  .36),  power  more  special  and the  present  m =  magnetos, would  such as  ratio  small  (a  Based  two-stroke  of  speed and t o  would  cycle  saw was h o t .  controls,  20  inconvenient,  lower  factors  factor  cost  a variety  the  power-to-weight  vibrationless  a conventional would  transfer  a high  diameter  nearly  The m a c h i n e w o u l d  ing  heat  very  observations,  weigh  A Stirling smoke-free,  so t h a t  s c a l e d down.)  rpm w o u l d  Also,  engine.)  have  (scaling  4,500  high  on t h e s e  c a n be  at  than  g o e s up  a relatively  in  goes down.  abused.  foolproof.  or  seals  on the  engine  would  not  run  hot-gas  For If  this  any o f  engine  and would  reason the  were  require  to a  competent mechanic f o r r e p a i r s .  Because the saw would c o s t  a t l e a s t t w i c e as much as the c o n v e n t i o n a l  e n g i n e and  weigh  about 50% more, i t i s d o u b t f u l t h a t i t would be a c c e p t e d i n the g e n e r a l c o m p e t i t i v e market.  Nevertheless,  m a r k e t s , where m u l t i f u e l c a p a c i t y and  for limited  freedom from n o i s e  and v i b r a t i o n i s paramount, the S t i r l i n g c y c l e power m i g h t be the answer.  But f o r the purpose of t h i s p r o j e c t ,  the S t i r l i n g c y c l e engine d i d not meet the d e s i g n ments so t h a t the a n a l y s i s was  2.3  saw  require-  discontinued.  S y n t h e s i s of A l t e r n a t i v e s As the e v a l u a t i o n of the gas t u r b i n e , Wankel and  S t i r l i n g e n g i n e s f a i l e d t o i n d i c a t e an engine t h a t would  be  c o m p e t i t i v e w i t h the t w o - s t r o k e c y c l e engine p r e s e n t l y used e x t e n s i v e l y i n p o r t a b l e power saws, the n e x t s t a g e i n the d e s i g n program was ments.  The  t o s y n t h e s i z e some new  engine arrange-  synthesis s t a r t e d with a c o n s i d e r a t i o n of  b a s i c problem a r e a s i n the e x i s t i n g power saws and with a f e a s i b i l i t y  concluded  check.  No p a r t i n h i g h - s p e e d e n g i n e s i s as i m p o r t a n t the c o n n e c t i n g  the  rod bearings.  And  as  y e t no. p a r t f a i l s as o f t e n .  To produce as much power as p o s s i b l e from a g i v e n w e i g h t , designers  have gone t o h i g h e r and h i g h e r speeds, u n t i l  f a t i g u e l i f e of the c o n n e c t i n g  rod bearings  w i t h i n the u s e f u l l i f e of t h e saw.  The  engine to stop.  An engine w i t h o u t  i s o f t e n reached  high loadings  l a r g e number of c y c l e s cause the b e a r i n g s  the  t o f a i l and  a c r a n k would be  and the  ideal.  92 The c r a n k l e s s  r o t a t i n g f r e e p i s t o n engine c o n c e p t ,  based on t h e i d e a t h a t a w e i g h t a t t h e end o f a h o r i z o n t a l l e v e l causes an u n b a l a n c e d moment, meets t h i s r e q u i r e m e n t . I f t h e l e v e r were a l l o w e d t o r o t a t e and i f t h e w e i g h t were moved up whenever t h e w e i g h t r e a c h e s i t s l o w e s t  point  ( i . e . when t h e l e v e r i s v e r t i c a l ) , t h e n t h e l e v e r would continue to rotate.  By u s i n g a p i s t o n as t h e w e i g h t and a  c y l i n d e r as a l e v e r , an e n g i n e i s t h e o r e t i c a l l y p o s s i b l e . An a n a l y s i s o f t h e energy p r e s e n t i n such a system y i e l d e d the f o l l o w i n g e q u a t i o n f o r t h e k i n e t i c energy:  K.E.  Where  0  =  (Ic + 1 p + M pR ) 2  I c  2  +  M V  2  ? 2P  i s t h e i n e r t i a o f t h e c y l i n d e r about 1  center of r o t a t i o n , I  P  i s t h e i n e r t i a o f t h e p i s t o n about center of r o t a t i o n ,  Vp  i s the v e l o c i t y of the p i s t o n ,  M  i s t h e mass o f t h e p i s t o n ,  P  R  i s the distance  from t h e p i s t o n  center  of g r a v i t y , to  i s the angular v e l o c i t y of c y l i n d e r .  Assuming t h a t t h e p i s t o n e x p e r i e n c e d o n l y a c e n t r i f u g a l force  ( g r a v i t a t i o n a l f o r c e and gas f o r c e  then the d i f f e r e n t i a l equation i s :  negligible)  93  2M Ru> = _ _J2 d  This the up  equation  I  t  + 1  C  V  P  + M R< p p  i n d i c a t e s t h a t t h e c y l i n d e r w o u l d s l o w down a s  p i s t o n moved away f r o m t h e c e n t e r  o f r o t a t i o n and speed  a s t h e p i s t o n moved t o w a r d s t h e c e n t e r .  work o u t , a p l a n e t a r y the  g e a r a n d a one-way c l u t c h  cylinder to accelerate  accelerated  In order  only  was p o s t u l a t e d .  that  On c l o s e r e x a m i n a t i o n i t became unless the  work p u t i n t o t h e s y s t e m t h r o u g h c o m b u s t i o n c o u l d cylinder.  energy i n v o l v e d force.  This  realization  a r r a n g e d so t h a t w h i l e center  the c e n t r i f u g a l  was made t h a t i f t h e s y s t e m c o u l d  o f r o t a t i o n t h e c y l i n d e r r o t a t e d more s l o w l y  p i s t o n was m o v i n g t o w a r d t h e c e n t e r  out  could  be p o s s i b l e .  t h a n when  o f r o t a t i o n , n e t work  C o m b u s t i o n m u s t o c c u r when t h e p i s t o n  was f u r t h e s t f r o m t h e c e n t e r released  be  t h e p i s t o n was m o v i n g away f r o m t h e  the  o f r o t a t i o n , so t h a t t h e e n e r g y  i n c o m b u s t i o n w o u l d move t h e p i s t o n a g a i n s t t h e  centrifugal  force.  But t h i s arrangement lacked  f o r c e a n d w i t h o u t one no s y s t e m c o u l d s t e p was t o p o s t u l a t e give  accelerate  l e d t o an a n a l y s i s o f t h e  i n moving t h e p i s t o n a g a i n s t  The o b s e r v a t i o n  allowed  i f t h e o u t p u t arm a l s o  o b v i o u s t h a t t h e s y s t e m w o u l d s l o w down a n d s t o p  the  to get  the required  work.  a reaction  Therefore the next  an a r r a n g e m e n t w h e r e b y g r a v i t y w o u l d  reaction force.  ment t h e p i s t o n moved a g a i n s t  In this  simple  arrange-  a g r a v i t y f o r c e , as i n  Figure  94 2.3. the  As long center  as the  of  piston  rotation,  r e m a i n e d on t h e  the  output  torque  left  was  side  of  positive.  e  a  Figure  2.3  Sketches  In the  this At  principle  cylinder  piston  moved t o w a r d  end of  "A"  ignited  But  the  passed pull  rotated  position  the  shaft.  the  unbalanced lever  engine  end  " A " as weight  the  stroke  the  and t h e  piston the  pressure  was a l s o  the  center  of  the  earth's  ted  by  the  cylinder  e n g i n e was t h e o r e t i c a l l y  as f o l l o w s :  shaft  "0",  Figure  2.3.  in  a c c e l e r a t e d towards so when t h e  rotation,  the  gravitational about  possible.  another  the In  end  end"B'.' piston  had  gravitational  a positive  o n e n d "B" a s  as  cylinder.  compressed mixture  continued  " A " , and i f  engine  a c c e l e r a t e d the  rotating,  end  swinging  shown i n  again exerted  cycle  operated  c o u n t e r c l o c k w i s e on  piston  through  If  the  the  cylinder  on the  of  torque it  pull  on  the  had done was  center,  on  augmena  compact  95 A simple c a l c u l a t i o n assembly center ation  of  the  at  1,000  cylinder  a distance rpm,  of  1 in  a 4 cylinder  the  equations; other  the  150 g . and  If if  the  engine would  An a n a l y s i s of eous  rpm a b o u t  rotation,  was a p p r o x i m a t e l y  piston 6,000  rotating  showed t h a t  the  an a x i s  a  cylinder  6 in  from  centrifugal combustion  raised  cylinders produce  cylinder  piston  the  accelera  rotated  about  s y s t e m p r o d u c e d two  one d e s c r i b e d the  d e s c r i b e d the  for  1  lb  at  10  hp.  simultan-  acceleration  and  acceleration:  2 ri  R  = A(P»-P  2 2 dR ) + Leo c o s 9 + R(CO+(JO ) ± y[2 ~  dt  (co+co )+  Lu  2 O  -  =  (  dt  C  (Leo s i n e  2  dT  \  ± u[RW+R+Lu  cos8])=—*• dt^  + L w s i n 8 ] [cose  ^+U )  2  Q  + A (P - P » ) r £  Where  r\ A  0  sine  -  R  =  R  =  r  is  piston  s  is  reference  T  [R + RW + LW is  I/ [ I W 1/ \ °  + ~ + 5_  + I  W  + ^  dimensionless piston position  sine]  y  +-S.-R  q  cos6][cos8  ±  + _  ±  of  d8 angular  speed of  cylinder  6  is  angular  position  of  rotating  arm),  sin6]  rotation),  stroke  is  u  position,  (from c e n t e r  co  )  i  = ^  cylinder  , (from  sin9]  96  de OJ  i s angular  speed  of rotating  arm =  °  dt  I L  = —  i s dimensionless  length of rotating  I  i s length of rotating  t  i s time,  W  = —°-  arm,  arm,  OJ  i s dimensionless  angular  speed  ratio,  OJ  u  i s c o e f f i c i e n t of  A  = A'P.  friction,  i s piston  area  ratio,  Mps A  1  i s piston  area,  P^  i s atmospheric  Mp  i s mass o f  P  P ' = —— P a r  r  p  pressure,  piston,  i s pressure  ratio i n right  i s pressure  ratio i n left  cylinder,  1  L P  p L  = P L  Tout Mps  I' = — °(— j LMps"  I  q  Because  a  — 3 — LMps  2  i s output  torque  cylinder,  ratio,  i s inertia  of rotating  i s inertia  of cylinder-piston  the gas f o r c e s present  non-linear,  the equations  integration  using  were  i n these  arm  equations  s o l v e d by s t e p - w i s e  the Runge-Kutta  subroutine.  assembly,  are  assembly.  highly  computer  97 The engineer  is  equations  number  of  reflected  as w e l l  design choices available  in  the  as the  number  of  combustion  parameters  conditions.  appropriate  parameters,  trends  qualitative  predictions  b a s e d on e x i s t i n g  changes within were  were  used.  practical  investigated,  would  rotating meant  final  engine  that  the  resulting  Duhammel s 1  R  =  where  ~2 2 P -oo  following  the  results  drawn  step before  2  to  choosing  results  of  and force  were  varied  combinations  discovered.  energy  head would on G r a p h  abandoning linearize  of  piston  be b l o w n  the  off,  crankless  system.  a linear  were  the  The  2.3.  the  was r e p l a c e d by equations  the  and e x p e c t e d  number  kinetic  the  in In  parameters  c y c l e s were  cylinder  differential  solved  This  spring. using  give:  (cosuJt^-costot-^)  k = rr— Mp  k  The  the  force  Integral  P  stable  c o n c e p t was t o gas  all  and a l a r g e  indicated  typical  The  The  no  increase until  shown by  even a f t e r  limits  computed r e s u l t s  as  But  from previous  to  (OJ+CO ) o  = spring  are  results  2  '  rate  of  the  linear  system:  2 1.  If  (OJ+CO ) O  unstable,  is  greater  than  k/m^,  the  system  is  98  Graph 2.3  Computed p i s t o n p o s i t i o n s - u n b a l a n c e d l e v e r  engine  2.  If  (o)+to )  = k/nip,  o  the  cycle  is  then  p = 0 and R =  sinusoidal. 2  3.  If  p =  OJ  of  the  piston  the  4.  and k/m^  solution  +  ( R . + 4)  If  p = OJ,  l  the  cycle.  cycle  for  of  achieve increase piston  is  It  is  the  cycle  must at  p o s s i b l e to  top  be  only  ignition  to  the  work  practice.  piston  sinut  The c o n c e p t o f  e n g i n e was t h e r e f o r e  removed not  is  from a  stable p<oj  i n c r e a s e d when  from  and  opens.  at  least  3 are  not  a suitable  solution. and  the  impossible,  To  pressure  position  required  when  the  angular pressure cycle. to  a crankless, rotating, abandoned.  a  remaining  The optimum  depends on t h e  is  obtain  for  timing  increase  if  port  cylinder  dead c e n t e r .  difficult,  p  workable  speed and t h e  in  R = —  the  2 and  depends on the  are  V.  is  gas p r e s s u r e ,  stable  conditions  c y c l e the  be r e l a t e d  the  position  requirements  cylinder;  p a n d OJ i f  of  exhaust  c y c l e must speed,  of  value  suddenly r a i s e s  the in  value  the  4 becomes the  the  the  frequency  decreasing  a n d p>oj f o r  d e c r e a s e d when t h e  a stable  of  cycle  displacement  i n c r e a s i n g or  an e n g i n e  combustion  and c o n d i t i o n  , the  integration  a particular  In  variation  OJ  same a s t h a t  maximum p i s t o n  to  Since  +  O  by d o u b l e  cycle  is  2  (OJ+OJ )  the  function  part  =  COSOJt.  2  part.  small  is  periodic  for  L(l-cosojt)  These  achieve free-  100 As has been shown, the p u r s u i t o f a p r a c t i c a l r o t a t i n g f r e e - p i s t ' o n engine r e q u i r e d decision  tree.  many b r a n c h e s o f t h e  Some l e d t o dead ends b u t o t h e r s opened  up a l t e r n a t e p o s s i b i l i t i e s .  When i t became o b v i o u s  that  s t a b l e c y c l e s were d i f f i c u l t t o a c h i e v e i n t h e r o t a t i n g free c y l i n d e r engine, the a l t e r n a t e p o s s i b i l i t y of using r e c i p r o c a t i n g m o t i o n d i r e c t l y was i n v e s t i g a t e d . had  shown t h a t a p i s t o n b o u n c i n g i n a c l o s e d  Experience  cylinder  could  be made i n t o a w o r k a b l e engine i f t h e p i s t o n and c y l i n d e r were s y n c h r o n i z e d and i f a u t o m a t i c t h r o t t l i n g were ated.  No major problem w i t h  incorpor-  s e a l i n g and combustion was  e n v i s i o n e d as l o n g as c o n v e n t i o n a l p i s t o n s , c y l i n d e r s and r i n g s were t o be u s e d . A number o f a l t e r n a t e s  f o r automatic  throttling  were c o n c e i v e d b u t d i s c a r d e d because t h e y were t o o c o m p l i c a t e d or too u n r e l i a b l e . •  Connecting the t h r o t t l e d i r e c t l y t o the  p i s t o n was n o t s u i t a b l e because t h e d i f f e r e n c e l o a d and f u l l l o a d s t r o k e s  was s m a l l .  v a l v e complicated the engine.  between no  A wedge o r a r o t a t i n g  A device s e n s i t i v e t o the  s c a v e n g i n g chamber p r e s s u r e was t o o u n r e l i a b l e .  Finally a  l e v e r arrangement t h a t was s i m p l e and s e n s i t i v e t o s t r o k e was  conceived.  A d e s c r i p t i o n o f t h i s arrangement w i t h  r e f e r e n c e t o F i g u r e 2.4 f o l l o w s . In t h e p o s i t i o n drawn, the the the  t o p c y l i n d e r from t h e t o p  s c a v e n g i n g charge e n t e r s  s c a v e n g i n g chamber, w h i l e  i n t a k e charge e n t e r s t h e bottom s c a v e n g i n g chamber from  Figure  2.4  A s k e t c h of the o s c i l l a t i n g  free-piston  engine  102 the  intake  cylinder. cylinder  The gas  motion  throttle  passage. the  port  to  The m o t i o n  the  ports.  continues  the  gases.  the  cycle  piston  the  Then i t  until  all  top  occurs  the  kinetic  in  the  the  rod  top  port.  in  the  cylinder  is  angle  less  than  (8) 45°,  between  the  connecting  a s m a l l movement  in  larger  movement  Because  it  is  of  blade,  an i n h e r e n t  c o u l d be d e s i g n e d t o c y c l e when t h e  Graph  the  compression  a corresponding but  piston  pression  uncovers  and  energy  in  the  intake  throttle  results  of  the  uncovers  of  and  repeats. When t h e  the  and  intake  has been a b s o r b e d by  Combustion then  into  the  The  and c y l i n d e r  closes the  bottom pushes  a load  charge  the  the  assembly up.  piston  and t h e n  in  cylinder  against  a fresh  of  occurs  bottom  blade  admit  port  and c y l i n d e r  piston  in  motion  exhaust  transfer  piston  force  moves t h e  Further  bottom  bottom  and combustion  a s s e m b l y down and t h e  resulting the  passage,  2.4.  remain  piston  stroke  ratio  part  movement  illustrates  the  piston  stops  at  the  piston  stroke  closed for  and b l a d e  For example,  the  the  the  load  is  a compression r a t i o  portion  i n c r e a s e s 13% a n d t h e  the  suddenly  of  50  blade  blade.  throttle  as a f u n c t i o n  s e n s i t i v i t y , of  and  piston  the  becomes l a r g e r .  stroke  when t h e  the  in  a greater  rod  of  A  plot  of  the  com-  arrangement, removed,  instead stroke  of  10,  increases  57%. After using  the  the  c o n c e p t was r e f i n e d , a c o m p u t e r  Runge-Kutta subroutine  was  set  up t o  program  solve  and  the  two  Graph 2.4  Blade and p i s t o n p o s i t i o n as a f u n c t i o n of compression r a t i o  coupled e q u a t i o n s d e r i v e d from a f o r c e a n a l y s i s friction.  without  The a n a l y s i s r e s u l t e d i n the f o l l o w i n g  dY  equations  2  2  dX  v  (Pr -P») A £  2  —2 at Where  = <W Y  A m  i s the d i m e n s i o n l e s s blade p o s i t i o n  (=  , s  X  i s the d i m e n s i o n l e s s c y l i n d e r p o s i t i o n  L  i s the connecting rod length  s  i s a reference  I'  (= — ) ,  stroke, A P. (= ^^~) i  A  i s t h e reduced p i s t o n a r e a  F  i s t h e n e t l o a d on t h e saw (= rr^—) , M s ' P  P (=p—) , 1  i s t h e gas p r e s s u r e i n r i g h t c y l i n d e r P  p  JC  i s t h e gas p r e s s u r e i n t h e l e f t i  p  cylinder  3.  JL  (= |T-> , a m m m P  i s t h e mass r a t i o  P c a  (=  m m  c  ,  is is i s the atmospheric pressure.  The p r e s s u r e s i n t h e c y l i n d e r s were c a l c u l a t e d the  with  i s e n t r o p i c equation:  P  r  =  Where CR SF  4.74 ( S F ) ( C R )  1 , 4  i s the compression r a t i o  (function o f x+y),  i s t h e scavenging f a c t o r .  The f o l l o w i n g o b s e r v a t i o n s were made from t h e computed r e s u l t s : 1. When no t h r o t t l i n g , no bounce and no was used and t h e a p p l i e d load:  synchronization  l o a d was below t h e f u l l  105 (a) t h e engine s t a l l e d when t h e a p p l i e d exceeded t h e f u l l  load  load,  (b) t h e c y c l e s were q u i t e s t a b l e f o r a v e r y heavy c y l i n d e r , e.g. c y l i n d e r mounted t o heavy base. 2. When t h e combustion p r e s s u r e depended on t h e b l a d e stroke: (a) t h e c y c l e s s t a b i l i z e d compression r a t i o s applied  f o r a heavy c y l i n d e r a t  t h a t depended on t h e l o a d  ( f o r no l o a d t h e l e f t c o m p r e s s i o n  ratio  was 55 and t h e r i g h t was 8 7 ) , (b) t h e c y c l e s were u n s t a b l e when t h e c y l i n d e r and p i s t o n w e i g h t s were e q u a l , (c) t h e c o m p r e s s i o n r a t i o f l u c t u a t e d f o r a medium w e i g h t c y l i n d e r and a heavy l o a d . 3. When a u t o m a t i c t h r o t t l i n g and a u x i l i a r y  bounce  chambers were used: (a) t h e c y c l e was u n s t a b l e f o r c y l i n d e r w e i g h t s l e s s than 10 t i m e s t h e p i s t o n w e i g h t , (b) t h e a d d i t i o n o f t h e bounce chamber made t h e c y c l e s more u n s t a b l e . 4. When t h e c y l i n d e r and p i s t o n were s y n c h r o n i z e d b u t no t h r o t t l i n g was used: (a) f o r a l a r g e l o a d t h e c y c l e s were s t a b l e , (b) f o r a s m a l l l o a d t h e c o m p r e s s i o n kept i n c r e a s i n g .  ratio  106  When t h e to  a practical  quired  for  1.  the  of  the  the  ideal  following  cycle are  two  applied  conditions  are  re-  cycles:  cylinder  heavy 2.  engine,  stable  the  results  frame  intake  must or  be v e r y  heavy,  synchronized with  must  be t h r o t t l e d  fastened the  during  to  a  piston, part  load  operation. These piston  and c y l i n d e r  A detailed for  the  ,2 t  force  with  V  a rack  the  A(P,-P  f,=— 1 ms  the  V  f '2 ~ = -ms  and f. '3 f = 3 ms  is and  F  F' =— ms  the  following  the  the  arrangement. equation  F  f  r— ^ ! )  — 1  2  +  d  d + d ) - 1  sum o f  and  7  f  piston  frame is  the  gear  = ti+d]  is  synchronizing  and p i n i o n  -  0  ) + r  by  piston:  f =  2  Where  were met  analysis yielded  a c c e l e r a t i o n of  2-1 d  requirements  the  friction  and c y l i n d e r ,  force  between  and between  the  cylinder,  friction  force  between  the  blade  force  between  the  c  frame, the  friction  piston  frame,  is  the  load  is  the  ratio  diameters  on  blade,  of c y l i n d e r - t o - p i s t o n gear m (= —£• f o r b a l a n c e d e n g i n e ) , m c  107 m The  m m mass. (= —P— ) . m +m p c  i s the reduced  normal f o r c e a g a i n s t the bladeguide  i s given  by: F - f F n  When the p i s t o n i s a t the end o f i t s s t r o k e so that  (6) approaches 90°, the normal f o r c e on the guide i s  v e r y high i f the saw l o a d i s h i g h .  But 9 o n l y approaches  90° when the saw i s unloaded, so the normal f o r c e i s n o t as h i g h as might f i r s t the s t r o k e  be expected.  i s short.  The  When the f o r c e i s h i g h ,  blade makes two c u t t i n g  s t r o k e s f o r every p i s t o n c y c l e and i s connected t o the p i s t o n with a connecting  r o d c o n t a i n i n g two b e a r i n g s .  I t was s u r -  mised t h a t i f these two b e a r i n g s c o u l d be e l i m i n a t e d , t h e arrangement would have even fewer moving p a r t s .  Consequently  b a s i c engine requirements  i n hopes  of  were again c o n s i d e r e d  a c h i e v i n g even a s i m p l e r  2.4  design.  S y n t h e s i s o f the F r e e - P i s t o n Power Saw (FPS) The  simple concept concept filled  s y n t h e s i s o f the new power saw s t a r t e d w i t h a and ended w i t h a p r a c t i c a l arrangement.  The  was based on a p i s t o n bouncing i n a c l o s e d c y l i n d e r w i t h gas.  By adding  bounce can be maintained  energy t o the gas, the p i s t o n  and work removed.  By p r o v i d i n g  108 the  cylinder  exhaust  with  intake  pulses to  combustion  and e x h a u s t  scavenge the  engine  is  practice, to  the  idea of  scavenge the  and  low  air  used.  without  i n c r e a s i n g the  cylinder  other  is as  free  accelerate by for  stable  mount  With the  is  high. to  allowing mass. rack  of  not  rapidly load.  moving  the  the  within  when t h e  into  parts  piston  gas  manifolds  manifolds a  scavenging  the if  design  one end  and p i n i o n ,  cylinder  cylinder  motion force  force,  the  cutting  c a u s e d by  the  the  gas p r e s s u r e s  mass t o  and c y l i n d e r  This  high  problem  c a n be or  required  the  is  the loading  force. small  is  force  overcome the  by  piston  sychronized with connecting  but  still  reaction  is  counter-balance  and p u l l e y ,  arrangement.  the  to  impeded  feeding  c a u s e d by  that  is  force,  b e n d i n g moment  suggests  the  so t h a t  the  belt  of  the  and  is  teeth,  cylinder  The p i s t o n  the  cylinder,  c o u l d be mounted  b e n d i n g moment  force  the  a reaction  an u n b a l a n c e d mass.  crankshaft  long  possible if  connected to  Because  Inversion  the  in  chamber.  reciprocate  self-feeding  reaction  due  is  cycles,  and t h e  the  very  to  transmits  force,  are  incorporated  number  the  internal  and e x h a u s t  associated with  a combustion it  more  an e x t e r n a l  simple  and a t t a i n a b l e  intake  flows  using  d e s i g n e d as a s c a v e n g i n g chamber w h i l e  Since is  the  and by  possible.  theory  A pump c a n b e  remains  piston  is  Higher  pump i s  the  in  tuning  cylinder  flows.  cylinder,a  theoretically  Though p o s s i b l e  ports  rod  and  a  109 I f r i g i d l y a t t a c h e d t o the moving c y l i n d e r , carburetor  makes f u e l m e t e r i n g d i f f i c u l t .  to eliminate  o v e r the  I t i s possible  t h i s problem by mounting the c a r b u r e t o r  the s t a t i o n a r y base and  then a l l o w i n g  j e t on  the v e n t u r i t o move  j e t , o r by mounting the complete c a r b u r e t o r  the base and  the  on  c o n n e c t i n g i t t o the i n t a k e m a n i f o l d w i t h  f l e x i b l e or t e l e s c o p i c I f the saw  a  tube.  b l a d e i s c o n n e c t e d t o the  piston  i n s t e a d of t o the c y l i n d e r , the w e i g h t s are b r o u g h t c l o s e r t o g e t h e r , so t h a t s m a l l e r  counterweights are  T h i s arrangement has s c a v e n g i n g , good c a r b u r e t i o n ,  required.  a potential for efficient and v i b r a t i o n l e s s  operation.  I t l a c k s , however, a s a t i s f a c t o r y t h r o t t l i n g system. the amount o f energy added d u r i n g  each c y c l e j u s t e q u a l s  the amount of work removed, the c y c l e i s s t a b l e . amount added exceeds the amount removed, the acceleration increases causes so much gas  (1/30  When the  piston-cylinder  u n t i l the e x t r e m e l y h i g h gas  pressure  t o l e a k from the c y l i n d e r t h a t the  i m p a c t s the c y l i n d e r head. 2 or 3 c y c l e s  When  piston  Because f a i l u r e can o c c u r w i t h i n  sec) manual t h r o t t l i n g i s too slow  the engine must be d e s i g n e d t o t h r o t t l e i t s e l f  and  instantaneously.  To a l i m i t e d e x t e n t the arrangement i s i n h e r e n t l y s e l f - t h r o t t l i n g , because the  l e n g t h of time the p o r t s  open i s i n v e r s e l y p r o p o r t i o n a l v e l o c i t y which increases work removed.  t o the p i s t o n  cylinder  when the energy added exceeds  As the v e l o c i t y i n c r e a s e s ,  remain  the p o r t s  the  remain  110 open f o r s h o r t e r d u r a t i o n s , so t h a t l e s s charge e n t e r s .  Also  more energy i s d i s s i p a t e d t h r o u g h f r i c t i o n and l o s t t h r o u g h increased heat t r a n s f e r .  The end r e s u l t of i n c r e a s e d  t h r o t t l i n g , f r i c t i o n , and heat t r a n s f e r i s t h a t t h e r e i s an upper l i m i t t o t h e p i s t o n v e l o c i t y even throttling. at  without external  Maximum t o r q u e i n c o n v e n t i o n a l e n g i n e s o c c u r s  about 4,500 rpm and f r e e w h e e l i n g speed o c c u r s a t 9,500  rpm.  This o b s e r v a t i o n concurs  with a calculated  result  based on the assumptions t h a t t h e energy r e l e a s e d v a r i e s i n v e r s e l y w i t h mean p i s t o n speed and f r i c t i o n removes 10% of  k i n e t i c energy.  A t the upper speed l i m i t  (2.2 t i m e s  h i g h e r t h a n a t maximum t o r q u e ) t h e i d e a l gas e q u a t i o n f o r i s e n t r o p i c c o m p r e s s i o n p r e d i c t s t h a t the maximum c o m p r e s s i o n r a t i o w i l l be 180 and t h a t t h e maximum p r e s s u r e w i l l be atmospheres.  800  The upper speed l i m i t and t h e r e f o r e t h e  maximum p r e s s u r e s can be reduced by i n c r e a s i n g t h e s e n s i t i v i t y o f t h r o t t l i n g t o speed, the f r i c t i o n a t h i g h e r speeds, and t h e heat t r a n s f e r a t h i g h e r speeds.  Of the t h r e e means  l i s t e d , o n l y t h r o t t l i n g l i m i t s the speed  efficiently.  The s t r o k e becomes more s e n s i t i v e t o the k i n e t i c energy i n t h e p i s t o n - c y l i n d e r assembly i f t h e bounce chamber i s r e p l a c e d by a spring^, s i n c e t h e energy absorbed by t h e s p r i n g i s p r o p o r t i o n a l to the d e f l e c t i o n squared.  For  example, t o i n c r e a s e t h e energy absorbed t o 5 t i m e s the o r i g i n a l v a l u e , a s p r i n g w i l l d e f l e c t 123% more, whereas ' t h e s t r o k e of an i d e a l gas w i l l  i n c r e a s e o n l y 16%.  The  engine becomes s e l f - t h r o t t l i n g  i f the p i s t o n s k i r t can cover  the t r a n s f e r p o r t s when the s t r o k e i s l o n g .  T h i s means t h a t  f o r long s t r o k e s the p o r t s w i l l be open o n l y f o r a s h o r t time.  F o r very long s t r o k e s , the p i s t o n can uncover an  a u x i l i a r y b l e e d p o r t t o r e c i r c u l a t e the scavenging i n t o the c a r b u r e t o r and so reduce the scavenging flow and i n c r e a s e the f u e l - a i r r a t i o . bleed port created confidence  charge charge  The s y n t h e s i s o f the  i n the concept because i t was  reasoned t h a t even i f the p i s t o n s k i r t f a i l e d t o t h r o t t l e the i n t a k e properly, the b l e e d p o r t would a c t as a s a f e t y valve. A f o r c e a n a l y s i s o f the arrangement y i e l d e d the following d i f f e r e n t i a l  AP - £  Y  equation:  + r( f e  2  i s the d i m e n s i o n l e s s  Where Y  F±yN  + (  1+d  p i s t o n p o s i t i o n (= —) ,  s A  ) ,  P  i s the r e s u l t a n t p r e s s u r e  m  i s the reduced mass (=  m m  P c  r a t i o on p i s t o n  i s the mass o f p i s t o n assembly, i s the mass o f c y l i n d e r assembly,  k  is  the  spring  rate,  r  is  the  damping  r' s —^~)i F e x t e r n a l l o a d o n s a w (= — ) , ms n o r m a l l o a d o n s a w (= — ) , coefficient  (=  1  F  is  the  N  is  the  ms u  is  the  coefficient  d  is  the  ratio  of  friction,  of c y l i n d e r - t o - p i s t o n d (= — ) .  gear  1  diameters This solve  for  the  sures  during  isentropic  equation piston  was u s e d  position  in  a computer  as a f u n c t i o n  compression were  calculated  of  using  program  to  time.  Pres-  the  following  equation:  1 4  1 4  (cR r-* -  (CR r-  r  Where CR^  is  the  4  £  compression  ratio  in  the  combustion  ratio  in  the  scavenging  chamber, CR  is  £  the  compression  chamber. C o m b u s t i o n was in  the  combustion  and u n t i l  the  calculated  P  assumed t o  =  chamber  exhaust  according  4.74  occur  reached  port to  (SF)  when  the  7.4.  compression After  was u n c o v e r e d , t h e  the  isentropic  (CR ) r  Y  -  1  4  time  pressures  equation:  (CR ) * £  this  ratio  were  113 Where y  1  SF  S  the r a t i o o f s p e c i f i c heats and  i s the scavenging f a c t o r .  The scavenging f a c t o r was i n s e r t e d so t h a t the combustion c o u l d be r e l a t e d t o the scavenging and combustion  efficiencies.  When the t h r o t t l e was c o m p l e t e l y open and a l l the exhaust gases were scavenged, the scavenging f a c t o r was 1.0 and the c y l i n d e r pressure, when the exhaust p o r t opened, was 69.6 p s i a . When the t h r o t t l e was c o m p l e t e l y c l o s e d so t h a t no f r e s h charge was admitted t o the c y l i n d e r , o r when combustion d i d not o c c u r , the scavenging f a c t o r was 0.211.  The l o a d on the  blade was e i t h e r a p p l i e d g r a d u a l l y o r h e l d c o n s t a n t . The f r i c t i o n and damping f o r c e s were added  a f t e r the program was  debugged. V a l u e s o f s p r i n g s i z e s f o r the program were based  3 on the assumed output o f a 0.8 i n engine stroke).  (1 i n bore by 1 i n  When the mean e f f e c t i v e p r e s s u r e was 50 p s i , each  c y c l e of the engine r e l e a s e d  40 i n - l b o f energy.  Assuming  t h a t the compression of the f r e s h charge r e q u i r e s one f o u r t h of the energy r e l e a s e d  and t h a t t h i s energy i s s t o r e d i n  the s p r i n g , the s p r i n g r a t e should be 20 p p i .  When i t  d e f l e c t s t o 1.5 i n , t h e s p r i n g w i l l absorb 22 i n - l b o f energy. The f r e e l e n g t h o f a t y p i c a l s p r i n g w i r e diameter) i s 2 1/2 i n .  (.95 i n O.D., .10 i n  I f a short overload  spring  (.62 i n O.D., .12 i n w i r e , f r e e l e n g t h 1.33 i n , r a t e 400 ppi)  i s i n s e r t e d i n s i d e the main one, a l l o f the combustion  energy r e l e a s e d  i n one c y c l e can be absorbed d u r i n g a  1 p i s t o n s t r o k e o f 1.5 i n . optimum s p r i n g  But an e v a l u a t i o n showed t h a t t h e  (minimum w e i g h t ) would have no p r e - c o m p r e s s i o n  but would be l o n g enough t o remain i n c o n t a c t w i t h t h e piston. The f o l l o w i n g t y p e s o f t h r o t t l i n g were i n v e s t i g a t e d (a) d i r e c t l y p r o p o r t i o n a l t o s t r o k e , (b) d i r e c t l y p r o p o r t i o n a l t o s t r o k e w i t h random combustion pressure  v a r i a t i o n s (because combustion  i n t w o - s t r o k e e n g i n e s i s q u i t e e r r a t i c as shown by t h e r e s u l t s o f an e a r l i e r t h e s i s  [2.47],)  (c) p r o p o r t i o n a l t o a r e a o f p o r t open w i t h random  pres-  sure v a r i a t i o n s . The f o l l o w i n g c o n c l u s i o n s  were drawn from t h e  computed r e s u l t s : (a) t h e e x a c t s p r i n g r a t e i s n o t c r i t i c a l , (b) t h e f r i c t i o n f o r c e s a r e n o t c r i t i c a l , (c) o v e r l o a d i n g  immediately s t a l l s the engine,  (d) t h e e n g i n e i s s e l f - s t a r t i n g even under f u l l (e) t h e e x a c t t h r o t t l i n g r a t e and e r r a t i c  load,  combustion  are not c r i t i c a l , (f) c o n d i t i o n s a r e more c r i t i c a l i f t h e saw c u t s on the r e t u r n  stroke,  (g) a bounce chamber i s n o t n e c e s s a r y , (h) a s y n c h r o n i z i n g mechanism i s r e q u i r e d , ( i ) s t i f f e r s p r i n g s produce h i g h e r  speeds  115 (j)  t h e speed  i s nearly  (k)  the engine  c a n go  independent  through  of load  a number  (or  stroke),  of cycles  before  starting.  blade the  saw  The  results  was  theoretically  commercial  (Figure  2.5)  showed  Of  t h e ones  is  completely  the  that  portable. j i g saw,  a cord  hydraulic  blade  types  Figure  and  a power  2.5  a  free-piston  possible saws  available saw  on  could  and  supply  a hose  Typical  and a  competitive.  two-stroke  power  types  reciprocating  while  with  the market  be  electric-powered saw  reciprocating  and a comparison  the Wright  The  sabre  require  that  t h e new  available,only  electric  require  power  showed  such  blade  the pneumatic  blade  as saws  or the  tank.  reciprocating  saw  saws  116 A engines  large  number  are available;  of publications  the National  Bibliography  on F r e e - P i s t o n  references.  The s t a n d a r d  has  a stationary  come  together  during been  t h e power  used  fluid  used  i n a pile  pile  driver  able  Motorborr  the  two-stroke piston  [2.52],  engine  of the engine  proximity  plug  Although  the free  starting  piston  i t sa p p l i c a t i o n  many  of the free-piston  engine  free  operation,  starting  capacity, cation  has a  more  used  of the  of the  piston  crankshaft,  as a  passes  port-  i s connected  refrigerant  i s pivoted  mass.  engine  to a reciprocating  t h e saw v e r y  concept  The head  so  that  through the  I t uses  on t h e f i r s t  features  concept  blade  fuel  stroke  and  such  unique.  i snot  saw i s .  Indeed  as v i b r a t i o n -  and s t o p p i n g ,  and s i m p l i c i t y a r e p r e s e n t  a n d make  apart  ignition.  new,  instant  This  which  saw i t h a s b e ^ n  assembly  compressor  forpositive  a n d move  r o d and  has been  o f t h e suspended  for satisfactory  pistons  t o t h e head  connecting  The c y l i n d e r  of percussion  injection  blade  2.6 [ 2 . 5 0 ] .  i n many w a y s  engine  configuration  rockdrill,but the r o c k d r i l l  The f r e e  centerline  center  a  i s similar  282  a linear generator,  In another  Figure  lists  free-piston  2.6 [ 2 . 9 9 ] .  Figure  an a i rcompressor,  driver,  1964)  stroke  to the reciprocating  a conventional  compressor,  (April,  piston  Council's  a n d two r e c i p r o c a t i n g  and a t u r b i n e .  related  [2.51].  Engines  the compression  stroke,  to drive  pump,  closely  to  during  Research  conventional  cylinder  on t h e f r e e  multifuel  i n the blade  saw  appli-  How  piston a n d h a m m e r o p e r a t e s  W h e n the e x p l o s i o n takes p l a c e , the p i s t o n is d r i v e n u p w a r d s ; i t goes t h r o u g h its c y c l e at c o n s t a n t speed. T h e h a m m e r is d r i v e n d o w n w a r d s at the same t i m e , a n d strikes the d r i l l . "When the p i s t o n m o v e s u p w a r d s , i t u n c o v e r s t h e gas d u c t , a n d gas f r o m t h e c o m b u s t i o n c h a m b e r f l o w s i n t o t h e space b e l o w t h e h a m m e r flange. T h e gas pressure a c t i n g here o n the u n d e r s i d e o f t h e h a m m e r flange, t o g e t h e r w i t h t h e r e c o i l f r o m the d r i l l , t h r o w s the h a m m e r b a c k u p to its s t a r t i n g p o s i t i o n . T h e m e a n pressure i n t h e gas c h a m b e r b e l o w the h a m m e r flange is a u t o m a t i c a l l y r e g u l a t e d b y a s p r i n g - l o a d e d v a l v e so t h a t t h e h a m m e r is a l w a y s k e p t i n t i m e w i t h the p i s t o n .  COMPRESSOR INLET  —  MECHANICAL  BOUNCE , \ CYLINDER  B -  EXHAUST  r  g  A-  DRIVE  GAS COLLECTOR  -COMPRESSOR DISCHARGE  DIESELCYLINDER 1  COMPRESSOR CYLINDER  "Free- -head" Free- piston  C -  Pile  D -  Freon  rockdrill turbo  set  driver compressor  POWER CYLINDER  COMPRESSION TANK  BOUNCE CHAMBER VENT  COUNTER CHAMBER  LIFTING FINGER MECHANISM  BOUNCE CHAMBER  PISTON COMPRESSOR  DRIVING HEAD  Figure  2.6  Existing  free-piston  configurations  118  3.  3.1  Dimensional  the mechanisms  facilitates the  range  The  i t contributes taking  place  engines  i n terms  two-stroke  engine  designer  2.  stroke/bore  3.  exhaust  4.  intake  5.  exhaust  port  6.  exhaust  height/stroke  7.  transfer  8.  intake  to the  an  uses  (specified  understanding  engine,  similitude  r e s u l t s and  scaled  of dimensionless  scaling factor  1.  inside  c a n be  1.  He  little  the interpretation of test  of sizes  performance  COMPONENTS  Analysis  Although of  DETAILING  extends  by c o r r e l a t i n g  variables  and  the following  bore/reference  ratios:  bore)  m s/b  port part  area/piston area/piston  area  Ae/Ap  area  area/transfer  Ai/Ap  port  area  Ae/At ExHt/s  height/stroke  TrHt/s  height/stroke  determines  observing  ratios.  how  what  size  InHt/s  sizes  t o use by:  v a r i a t i o n a f f e c t s engine  perfor-  mance, 2.  c o r r e l a t i n g performance variables  3.  deducing will  give  that from rise  c a n be  i n terms  of  extrapolated  t h e c o r r e l a t i o n new to the required  dimensionless t o new  sizes,  dimensions  performance.  that  In  small  are  engine  usually  an a c t u a l less  warranted  performance  b e c a u s e by  e n g i n e more  accurate  A family  similar  building  results  are  predictions and  testing  obtained  at  cost.  bore/stroke deduction for  not  design,elaborate  ratio,  that  similar  of  e n g i n e s has  mean p i s t o n  the  volumetric  engines  can be  the  same  speed and g e o m e t r y . efficiency  shown t o  remains  be v a l i d ,  The  the  same  provided  the  * inlet  and exhaust  Flow/cycle  conditions  f  = K  remain  ^ P y j ^  the  same.  = K^A  = ^At  J (ExHt) (width)  = K  Under  S_ m  — = K ( K s ) (K TTb) m 3  4  5  m  = K, s b b 2  TT  T  Vol.  TH.CC  Eff.  m  /  K, s b b = — Trb^ 2  i  Flow/cycle = — Displacement  P —  Where  AP  is  pressure  p  is  density  t  is  across  = Ky T r  3  port,  upstream,  time,  is  the  mean p i s t o n  A  is  port  K's  are  s  is  piston  b  is  cylinder  area  constants stroke bore  speed,  ,s, (g-)  =  , , constant  120 such c o n d i t i o n s  the r a t i o of the amount of gas  trapped i n  the c y l i n d e r to the amount e n t e r i n g remains c o n s t a n t . a constant  pressure  drop across  the p o r t s and  a  o r i f i c e c o e f f i c i e n t , the mass of charge f l o w i n g p o r t i s p r o p o r t i o n a l to the  through a  (valid  volumetric  efficiency =  so  that  constant  weight of gas d i s p l a c e d per c y c l e and  f o r e the weight of f r e s h charge s u p p l i e d the engine d i s p l a c e m e n t .  At a c o n s t a n t  mean p i s t o n v e l o c i t y stroke  so  the weight of the mixture s u p p l i e d , as w e l l as the s u p p l i e d per u n i t time  there-  i s p r o p o r t i o n a l to  the engine speed v a r i e s i n v e r s e l y w i t h the  constant),  for  the l e n g t h of time the p o r t remains open  i s p r o p o r t i o n a l to the l e n g t h of the s t r o k e  The  constant  l e n g t h of time the p o r t i s open.  When the mean p i s t o n v e l o c i t y remains constant s i m i l a r engines),  For  that  energy  ( i f the combustion e f f i c i e n c y remains  v a r i e s w i t h the bore diameter squared so  that  2* Energy s u p p l i e d a m where m i s the any  two  s c a l i n g f a c t o r and  i s defined  as the r a t i o  s i m i l a r dimensions.  *  2 Weicfht time  Energy cycle  =  =  Vf_ 1/N  (  H  e  a  t  =  b s  2  fm 2s  6  i  n  g  8  v a l u e ) ( E f f . ) (Weight/time)  = K '(Kgbs) = K b s g  =  9  of  If pressure engine be  the  air/fuel  and v o l u m e t r i c  size  similar  is  friction  efficiency  changed,  and the  ratio,  then  brake  the  are  mean  effective  unaltered  indicator  mean e f f e c t i v e  as  the  diagrams  will  pressure w i l l  be  constant: bmep = Power w i l l diameters  squared  constant.  be p r o p o r t i o n a l  so  engines  is  the  shaft  plotted  the  ratio  of  the  that 2* a m .  shp On G r a p h 3 . 1  to  as  horsepower  of  a function  of  typical piston  p o w e r saw ** area.  * , shp =  (BMEP) (Vd) (N) . 2 , .... — —-—- = k , ( B M E P ) ( b s ) (N) 33000 n  = K  Where  1 Q  (BMEP)  Vd  is  b  2  ^  engine  BMEP i s  brake  N  engine  is  =  K  i ; L  b  2  displacement, mean e f f e c t i v e  pressure,  and  speed  ** Unpublished data in Appendix V.  from  Power M a c h i n e r y L t d . ,  shown  122  2  3  PISTON  Graph 3.1  AREA  (SQ  IN)  Power as a f u n c t i o n o f p i s t o n a r e a f o r t y p i c a l power saws  When c o n s i d e r e d on a d i s p l a c e m e n t b a s i s , t h e power of a g e o m e t r i c a l l y  s i m i l a r engine i s i n v e r s e l y  proportional  to the bore: Vd  a  -m *  When compared on a w e i g h t b a s i s , a s m a l l e n g i n e p e r f o r m s b e t t e r t h a n a b i g one because t h e w e i g h t o f an engine i s p r o p o r t i o n a l t o 3 d i m e n s i o n s  (volume), whereas  power i s p r o p o r t i o n a l t o o n l y two d i m e n s i o n s  Sh£  Vd  K  ll ' b  TT,  4  b  2 s  K  13  (area).  This  123 means t h a t t h e w e i g h t p e r u n i t horsepower  f o r a geometrically  s i m i l a r engine v a r i e s d i r e c t l y w i t h t h e b o r e : Wt shp a m Though i t i s p o s s i b l e i n medium and l a r g e bore e n g i n e s , t h e i d e a o f r e d u c i n g t h e w e i g h t - t o - p o w e r r a t i o by d e c r e a s i n g t h e bore d i a m e t e r cannot always be u t i l i z e d f o r b o r e s l e s s than 2 i n .  Such s m a l l e n g i n e s a r e i n e f f i c i e n t  for the f o l l o w i n g four reasons: 1. V e r y s m a l l c y l i n d e r s have a h i g h r e l a t i v e h e a t l o s s because t h e r a t i o o f exposed s u r f a c e  area  t o volume i s v e r y h i g h d u r i n g c o m b u s t i o n .  Con-  sequently a l a r g e percentage o f heat i s t r a n s f e r r e d t o t h e c y l i n d e r head and b l o c k . 2. The i n l e t m a n i f o l d i s s h o r t .  As i t can mix w i t h  the a i r f o r o n l y a s h o r t t i m e , much o f t h e f u e l goes t h r o u g h t h e e n g i n e u n e v a p o r a t e d and unburned. 3. The c y l i n d e r w a l l t e m p e r a t u r e s w i l l be l o w e r . This r e s u l t s i n higher o i l v i s c o s i t y .  The h i g h  v i s c o s i t y o i l and h i g h r e l a t i v e t o l e r a n c e s cont r i b u t e t o an a b n o r m a l l y h i g h f r i c t i o n mean effective  Wt shp  pressure.  4. The e f f e c t i v e Reynolds number c o r r e s p o n d i n g t o gas f l o w s may be so low t h a t v i s c o u s f o r c e s add an i n c r e ment t o f o r c e s r e s i s t i n g gas f l o w  [3.1].  Because s m a l l bore e n g i n e s a r e i n e f f i c i e n t , the power p e r u n i t d i s p l a c e m e n t of t y p i c a l power saws bore s i z e (Graph 3.2)  does n o t depend on  and t h e w e i g h t p e r horsepower a c t u a l l y  i n c r e a s e s as the c y l i n d e r b o r e s a r e made s m a l l e r  (Graph 3.3).  S t r e s s e s due t o gas p r e s s u r e and i n e r t i a o f p a r t s w i l l be the same a t s i m i l a r p i s t o n p o s i t i o n s p r o v i d e d the mean p i s t o n speeds a r e t h e same, the i n d i c a t o r diagrams a r e the same, and no s e r i o u s feedback o f v i b r a t o r y f o r c e s occurs.  Under t h e s e c o n d i t i o n s mechanical s t r e s s = constant  S t r e s s due t o gas  =  K  forces  *  gas f o r c e area  15  S t r e s s due t o a c c e l e r a t i n g f o r c e s =  (mass)(acc)  125 ro  £  9 CL. X CQ  LU 5:  LU O <  .8  A  a  _J  D_ CO  LU  3:  •  o  \  CL.  \—  X ID t—i  LU  .7  o  eh  .6 —ms -A_ , _ l .  .4  BORE (IN  Graph 3.2  1.8  .8  2.2  BORE  )  S p e c i f i c ' p o w e r as a f u n c t i o n o f bore  Graph 3.3  2J5  (IN)  S p e c i f i c w e i g h t as a f u n c t i o n o f bore  Even though t h e a p p l i e d s t r e s s e s remain c o n s t a n t ,  higher  s t r e s s r a t i n g s a r e p o s s i b l e f o r s m a l l c y l i n d e r s i z e s because the one p i e c e c o n s t r u c t i o n and t h i n n e r s e c t i o n s have allowable  higher  working s t r e s s e s . The gas s i d e heat t r a n s f e r c o e f f i c i e n t v a r i e s  i n v e r s e l y w i t h t h e bore when t h e Reynolds number remains c o n s t a n t [3.1] . ha  h  =  K Nu( ) r  K = Ki Re( > 6  z  — * m 1  K 16 = -j-  (if  R e y n o l d s number  creases,  the  coefficient  will  and c o o l i n g  hold  this  heat  be  to  the  so  that  hot  larger.)  transfer  low,it  coefficient  to  d e s i g n changes are  short,  the  gases w i l l  the  To k e e p t h e  system c a p a c i t y  Unless paths  piston  N u s s e l t number and t h e r e f o r e  high  flow  increases because the  is  in-  transfer efficiency  desirable  to  a minimum.  incorporated  of  rise  cylinder  T  heat  thermal  temperature as the  speed  the  parts  (  size  T w  to  keep  )  exposed  is  increased  a m . w  Wall  temperatures  are  limited  by  and d u r a b i l i t y  of  the m a t e r i a l  cylinder  by  the  surface does the  bore, free  the  from  wall  across the  K  16  Z **  (T  g  -T  Conduction  i  w  T  =  w  through ^  Z  T —T = K , _ — w c 17 K  =  T  n  wall  = K  g  wall  K, b 18  bore  - K ,£  16 n  of a  strength the  bearing Not  only  increases  but  also increases:  **  = Q  wall  ) ;  am  case  and w e a r .  go up as t h e  difference  to  the  maintaining  excessive friction  T -T w c  Convection  and i n  n e c e s s i t y of  temperature  temperature  c o n s i d e r a t i o n s of  =  17  also  = h(T  K _b 17 n  = £ = K' = £ A 17 Z  (T - T ) w c  g  -T  w  )  Given t h a t the s t r e s s e s due to thermal expansion i n the solid  body of a g i v e n m a t e r i a l are p r o p o r t i o n a l t o the  d i f f e r e n c e i n temperature between two p o i n t s i n a body, the thermal s t r e s s w i l l v a r y w i t h the bore: thermal s t r e s s a m . Lower w a l l temperatures a l s o mean lower compression tempera t u r e s and c o n s e q u e n t l y lower compression p r e s s u r e s as w e l l as lower l o c a l hot spot temperatures.  The lower  temperature  and s h o r t e r flame t r a v e l l e n g t h w i l l reduce the tendency for  the mixture i n the c y l i n d e r to d e t o n a t e .  Smaller  c y l i n d e r s can thus be operated a t a h i g h e r compression  ratio  b e f o r e s e l f - i g n i t i o n occurs, so t h a t compression r a t i o a — m c  C e n t r i f u g a l f o r c e s i n r o t a t i n g p a r t s such as the crankshaft  are i n v e r s e l y p r o p o r t i o n a l to engine  size,  2 **  c e n t r i f u g a l force a  m  D e f l e c t i o n s of p a r t s due t o mechanical f o r c e s a r e p o r p o r t i o n a l t o s t r e s s e s and p a r t  length, deflection a m  Thermal s t r e s s **  ***  W W  C e n t r i f u g a l f o r c e = mrw  =  2  =  mv  K  ***  x9 18  2  K  K  b  =  K  19  20  s/2  D e f l e c t i o n = £(strain) = — ( s t r e s s ) = K„,£ hi  Z  x  b  128 Natural to  the  frequency length  of  of  vibration  the  depth  of  Wear  in  engines  and  in  some c a s e s ,  corrosive  wear  bearing  size.  ated  proportional  is  is  to  bore  ratio)  the  performance  are  For list  of  stroke 1.  the  size  on engine  of  similar  summarized  a constant  of in  the  part  engines  III.  displacement  in  can be  K„„ / 22 /  ~~T m  3 3 m m .  the toler-  question:  size  on  the  effect  stroke/ engine  following  of  the  bore/  performance: engine  will  at  have  a short-stroke  the  vibration  the  beginning  of  of4 u n i f o r m  a higher engine.  thermal The  extremely the  power  beam = C  K m  22  amount  high  gas  stroke  /gEI  'w£ =  The  of  (constant  engine  summarizes the  area exposed to  of  contact.  wear which  Table  of  Frequency  matter,  independent  cylinder  than  temperature  is  the  efficiency surface  metallic  time  of  foreign  damage a — .  effect  A long-stroke  direct  depth  of  characteristics ratio  proportional  1 * —  c a u s e d by  the  wear  a family  a  per. u n i t  However,  For  inversely  part  frequency  corrosion,  is  3  129 Table I I I Scaling Characteristics f o rSimilar  Engines  energy s u p p l i e d  a  2  shp, f h p w e i g h t p e r shp  m a 2 m a m  d e f l e c t i o n of p a r t s w a l l temperature  a m a m  temperature across w a l l thermal stress  a m a m  fmep, bmep  = est  bearing pressures mechanical stresses  est = est  power p e r u n i t d i s p l a c e m e n t maximum c o m p r e s s i o n r a t i o  a 1/m a 1/m a 1/m a 1/m  wear damage heat t r a n s f e r  coefficient  n a t u r a l v i b r a t i o n frequency c e n t r i f u g a l force  a 1/m a 1/m  depends l a r g e l y on t h e p i s t o n f o r c e and c y l i n d e r head a r e a s and c o n t r o l s much o f t h e h e a t t r a n s m i s s i o n from t h e combustion volume.  The p i s t o n a r e a t o c y l i n d e r  displacement r a t i o varies i n v e r s e l y with the stroke: combustion s u r f a c e a r e a  .  a  1  _  d isplacement The a d v i s a b i l i t y o f u s i n g a low b o r e / s t r o k e r a t i o t o d e c r e a s e s u r f a c e a r e a i s o b v i o u s , b u t what i s n o t so o b v i o u s i s t h e advantage g a i n e d t h r o u g h a s h o r t e r  130 flame t r a v e l d i s t a n c e .  Because combustion  i s com-  p l e t e d sooner and t h e r e f o r e c l o s e r t o t h e optimum c r a n k a n g l e , combustion p r e s s u r e s a r e h i g h e r . H i g h e r p r e s s u r e s and lower heat t r a n s m i s s i o n r e s u l t in  higher thermal e f f i c i e n c i e s .  t e c h n i q u e s o f u s i n g a domed  (The c o n v e n t i o n a l  or c o n i c a l  combustion  chamber t o reduce t h e s u r f a c e - t o - v o l u m e r a t i o and t o s h o r t e n t h e flame t r a v e l d i s t a n c e , and u s i n g a s q u i s h a r e a t o promote t u r b u l e n t combustion be used i n t h e f r e e - p i s t o n  cannot  engine.)  2. A s m a l l bore e n g i n e w i l l o p e r a t e w i t h a c o o l e r p i s t o n than one w i t h a l a r g e b o r e .  The h e a t f l o w p a t h from  the p i s t o n crown t o t h e n e a r e s t c o o l e d s u r f a c e s h o r t e n s as t h e bore d e c r e a s e s so t h a t t h e temperature d i f f e r e n c e also decreases: T, - T a b h c For a d e t o n a t i o n l i m i t e d  spark i g n i t i o n e n g i n e , t h e  c o o l e r p i s t o n and c y l i n d e r , and t h e s h o r t e r flame t r a v e l d i s t a n c e , a l l o w the engine t o run a t a h i g h e r compression r a t i o .  For a compression i g n i t i o n  engine,  the c o o l e r c y l i n d e r n e c e s s i t a t e s a h i g h e r c o m p r e s s i o n r a t i o before i g n i t i o n occurs. 3. The f o r c e s due t o gas p r e s s u r e s w i l l be l o w e r f o r a s m a l l bore t h a n f o r a l a r g e b o r e .  Since force i s  proportioned t o area, a smaller piston area r e s u l t s  131  in a smaller force.  In terms o f s t r o k e , the r e l a t i o n -  ship i s force  -, a -  displacement  '  S  4. I f the s t r o k e i s i n i t i a l l y v e r y s h o r t , more f u e l w i l l probably be trapped stroke i s increased.  i n the c y l i n d e r as the  S i n c e the charge i s d e f l e c t e d  upwards i n t o the chamber, the l o n g e r s t r o k e p r o duces a l o n g e r flow path so i t seems probable a long s t r o k e w i l l and decrease  that  i n c r e a s e f u e l - r e s i d u e mixing  short c i r c u i t i n g .  5. As the b o r e / s t r o k e r a t i o d e c r e a s e s , h i g h e r p i s t o n speeds w i l l be r e q u i r e d t o m a i n t a i n the same output.  I f the displacement  and brake mean e f f e c -  t i v e p r e s s u r e remain the same, the rpm must a l s o remain c o n s t a n t .  A longer s t r o k e a t a c o n s t a n t  speed means the average p i s t o n v e l o c i t y w i l l be higher. rpm,  Because i t depends on v e l o c i t y and not on  the f r i c t i o n mean e f f e c t i v e p r e s s u r e and the  heat generated  by the r i n g f r i c t i o n w i l l be h i g h e r .  I f the p i s t o n v e l o c i t y i s a l r e a d y c r i t i c a l , the h i g h e r v e l o c i t y may cause the l u b r i c a t i o n between the r i n g s and c y l i n d e r t o break down.  But i f the  mean p i s t o n v e l o c i t y remains c o n s t a n t , the power of a long s t r o k e , c o n s t a n t brake mean e f f e c t i v e sure engine w i l l decrease  pres-  as the s t r o k e i n c r e a s e s :  bhp V, d  1  s.  A p l o t o f s p e c i f i c power as a f u n c t i o n o f s t r o k e f o r t y p i c a l power saws d i d n o t v e r i f y relationship.  this  This i s not s u r p r i s i n g since the  b r a k e mean e f f e c t i v e p r e s s u r e and mean p i s t o n speed v a r i e s from m a n u f a c t u r e r t o m a n u f a c t u r e r and  from engine t o e n g i n e .  The power o f t y p i c a l  saws as a f u n c t i o n o f t h e mean p i s t o n speed and the rpm i s shown on Graph 3.4 and 3.5. curves  These  a l s o i n c l u d e a s m a l l model a i r c r a f t engine 3  (.10 i n , .14 hp) and a s m a l l u t i l i t y (1.26  i n ^ , .5 h p ) .  A longer stroke permits areas.  engine  the design of l a r g e r port  As a l o n g s t r o k e e n g i n e has a h i g h  w a l l surface/volume r a t i o , the usable area f o r ports i s also large. width/circumference  When t h e r a t i o s o f t h e p o r t and p o r t h e i g h t / s t r o k e remain  constant, the r a t i o of the port area/piston i s a f u n c t i o n of the stroke/bore  ratio,  area  .MEAN PISTON SPEED  ( F P M ) •'  Graph  3.4  Specific  power as a f u n c t i o n  of p i s t o n  speed  Graph  3.5  Specific  power a s a f u n c t i o n  o f engine  speed  134 port  area  piston A plot bore the  of  the  ratios,  exhaust  areas as a f u n c t i o n  verified  transfer  port  area  the  above  areas did  of  the  supposition  not  verify  but  it,  as  mining  a function  the  of  factors  flow  through  influencing  ports  flow.  a plot  Graph  A n u n s u c c e s s f u l a t t e m p t was made t o power  stroke/  by  of  3.6.  correlate first  The d e r i v e d  deterrelation-  ship,  was  then .set  equal  to  a constant  so  that:  Define I port width width + bridge  _ w ~ w+y  port width + bridge circumference ' port width ' ' circumference port area .: „ j - ~ _ ~ . piston area  **  Ratio  V  f  A  VT  d  =  a ^  K~T  of  flow  t  =  p  where  §  (  ,A A  p  (  a C  ' )  n  =  ,Ht , s~ *  K  r P  —  (V ) f  24  .  ^  to  (Ht)  (  )  y  \  K  v  displacement  ,s Ht>2,a C (  (w) , s , w b lbu ')  o  w  26 b  I±i\ -  R  24 _  «  v  =  A.  K  23  „  2/r r  K  orifice  )  m  _ w+y irb  _ w_ _ Trb  s  (  23  A _ w (Ht)  through  w )  A ~  2 5 <l>  (V^)  .  )  m  (continued page )  on  next  135:  <  LU CC  <  in < x  X LU  CC  < CC  LU LL. CO  <  LU  T  = .35 (§•)-*** Ap b>  <  v  D  < .2  o CO  9  ^ A i Ap  =  (g)  .28  a • PORTED  & o  REED  VALVE  • A SPECIAL JL  .8  1.0  12  STROKE/BORE RATIO  Graph  3.6  Port bore  areas of ratio  typical  power  saws v e r s u s  stroke/  136 1. when p i s t o n v e l o c i t y  ( ) c  1  S  m  constant,  2. when rpm i s c o n s t a n t ,  Ht s These v a r i a b l e s were used  t o c o r r e l a t e the p o r t h e i g h t s of  t y p i c a l saws as shown on Graph 3.7. i s t h a t the p o r t h e i g h t decreases  What t h i s graph  as the bore/stroke  verifies ratio  decreases. The next step i n the p o r t d e s i g n was t o a s c e r t a i n the shape and s i z e s o f the i n t a k e , t r a n s f e r and exhaust ports.  F o r e f f e c t i v e scavenging,  the d e s i g n o b j e c t i v e should  be to secure h i g h v a l u e s o f flow c o e f f i c i e n t and scavenging  *(continued  *  from  last  page)  a  i s v e l o c i t y o f sound = 49v T ~  r^  i s pressure r a t i o across port  C  i s mean p i s t o n ^  /  m  v  f  s  V  (b) when  f d  then — s  1  a  (a) when ^ — = d then Ht  velocity  and ^— = K^g m V  = 27\/F K  = K^  7  and N =  = K-^/b 30  -  A  r  r-  X  ID I—I  LU X  cc  LU LL. co  <  CC r-  X CD  ht.  1—1  LU X  LU  LU  CC  < — I  ^ O  25 .lb'  «,  «0  I—  x.  CO  1.1  12  1.3  BORE 'STROKE  Graph 3.7  T y p i c a l port heights versus the square root of bore/stroke r a t i o  14  efficiency. large.  o b j e c t i v e r e q u i r e s t h a t the port areas  But f o r expansion  objective the  This  should  expansion  portion  ratio  stroke  ratio,  objectives stroke  stroke  stroke  and a low v a l u e giving rise  c y l i n d e r port design  promise between e f f i c i e n t  efficiency,  The the  effect  of the exhaust p o r t  of the intake port port areas.  involves a great  scavenging  This  height/  height/ Since  these  deal  and a h i g h  o f com-  power/dis-  a  than  high  ratio. c o m p r o m i s e c a n be more e a s i l y ratio  on p o r t  c a n be more e a s i l y  total  width of a set of ports w i l l  is  small  t o q u i t e a d e g r e e , t h e two-  ratio  devoted  and a  process.  o b j e c t i v e was t o a c h i e v e  of stroke/bore  circumference  process,  B u t s i n c e power was more i m p o r t a n t  the design  power/weight  a small portion of  to the charging  to small  oppose each o t h e r  placement r a t i o .  only  t o the scavenging  r e q u i r e s a low v a l u e  stroke  u t i l i z a t i o n , the design  be t o s a c r i f i c e  of the intake  objective  stroke  be  predicted  and t o t h e f r a c t i o n  to porting.  I  -  K  s  K  area  assume t h a t t h e  be p r o p o r t i o n a l t o t h e of this  s  circumference  assumption  height/bore  <r> !-  areas/piston  i f we  B a s e d on t h i s  p r o p o r t i o n a l to the port  u n d e r s t o o d and  the area  rati  ratio.  <"><!>  P It the to  i s evident port  that  f o r a fixed  area/piston  the stroke/bore  area  ratio  ratio  ratio  of port  height/stroke,  t e n d s t o be p r o p o r t i o n a l  as a l r e a d y  shown on G r a p h  3.6.  139 Based on the c o n s i d e r a t i o n s p r e v i o u s l y d i s c u s s e d , the b o r e / s t r o k e b l a d e engine was  r a t i o f o r the f r e e - p i s t o n r e c i p r o c a t i n g chosen as ^ =  1.35  s When the b o r e i s 1.250 0.9 3 i n .  i n the s t r o k e s h o u l d be e q u a l  For t h i s b o r e / s t r o k e  r a t i o , Graph 3.7  t h a t the e x h a u s t h e i g h t / s t r o k e r a t i o s h o u l d ExHt . s =  Graph 3.6 should  to  suggests  be  3 0  s u g g e s t s t h a t the e x h a u s t a r e a / p i s t o n a r e a  ratio  be  The  e x h a u s t gases f l o w out t h r o u g h the p o r t s  not  o n l y d u r i n g the blowdown p e r i o d but a l s o d u r i n g the scavenging period.  Scavenging s h o u l d s t a r t when the p r e s s u r e  the c y l i n d e r has dropped t o the p r e s s u r e chamber.  i n the  scavenging  I f the t r a n s f e r p o r t s open t o o soon, b u r n t  w i l l r u s h i n t o the chamber and p r e v e n t  proper  in  gases  scavenging.  As most o f the b u r n t gases w i l l have e x h a u s t e d by the time the t r a n s f e r p o r t s a r e u n c o v e r e d , t h e f r e s h charge f o r c e s out o n l y a f r a c t i o n of the o r i g i n a l mass o f burnt gases.  On the c o m p r e s s i o n s t r o k e the c y l i n d e r p r e s -  sure w i l l b u i l d up and exceed the c r a n k c a s e  pressure  i f the  140 t r a n s f e r p o r t s a r e t o o h i g h ; when t h i s h a p p e n s t h e g a s w i l l flow from the c y l i n d e r i n t o the crankcase scavenging  efficiency.  I f the t r a n s f e r port area  small, the c y l i n d e r w i l l  n o t be c o m p l e t e l y  time the t r a n s f e r port i s c l o s e d . ments o f h i g h conflict  and reduce t h e  f l o w and h i g h  scavenged by t h e  Here a g a i n  scavenging  the require-  efficiency  u n i t displacement  G r a p h 3.8.  r a t i o a s shown  The g r a p h i n d i c a t e d t h a t a s t h e e x h a u s t  i n c r e a s e d , t h e bmep and h o r s e p o w e r p e r c u b i c A similar the  t r e n d was o b s e r v e d b y T a y l o r  ~ = A  t  area  inch decreased.  [ 3 . 1 ] when he r e d u c e d  exhaust area r a t i o of a loop-scavenged engine  A  o f power  a n d bmep w e r e p l o t t e d a s a f u n c t i o n  of the exhaust port a r e a / t r a n s f e r port area in  arei n  and a c o m p r o m i s e m u s t be made. A t r e n d was o b s e r v e d when t y p i c a l v a l u e s  per  i stoo  from  A 1.2  to r ^ = A  0.6.  .  t  Based on t h e s e  observations,  a s u i t a b l e area  ratio  was assumed t o be A A  By  combining t h i s  t  choice with the previous  the t r a n s f e r a r e a / p i s t o n area  ratio  t -— = 30 A ' ^  A  P  becomes  exhaust area  ratio,  141  and t h e reduced a r e a r a t i o  A  r  1  becomes  A  e  1  The p e r i o d o f t i m e a f t e r t h e e x h a u s t p o r t s open and b e f o r e t h e t r a n s f e r p o r t s open i s c a l l e d blowdown.  the exhaust  A p l o t o f t h e blowdown/stroke r a t i o v e r s u s t h e  square r o o t o f bore i n d i c a t e d t h a t t h e blowdown r a t i o i s independent o f t h e bore when t h e r a t i o i s v a r i e d from  .094  142 to  .140, Graph 3.7.  T h i s graph suggested  ^  that:  = .20  Combining t h i s c h o i c e w i t h the r a t i o o f the exhaust p o r t height  yields Blowdown _  In d e s i g n i n g f o r the i n t a k e p o r t area and h e i g h t , a compromise must be made between a l a r g e flow and minimum amount of blowback.  A l a r g e flow i s achieved  by making  the p o r t s l a r g e ; blowback through the c a r b u r e t o r i s minimi z e d by making p o r t areas  s m a l l and p o r t h e i g h t s low. I f  the areas a r e too, s m a l l e x c e s s i v e t h r o t t l i n g w i l l take  place  a t h i g h speeds; i f the areas a r e too l a r g e , e x c e s s i v e blowback through the c a r b u r e t o r w i l l occur a t slow speeds.  The  optimum area and h e i g h t w i l l r e s u l t i n the maximum q u a n t i t y of mixture  being trapped The  a t the o p e r a t i n g  areas can be made l a r g e without  blowback i f a one-way reed v a l v e i s used. fail,  c o s t money, add complexity  the bmep o n l y s l i g h t l y . of a h i g h e r torque disadvantages  speed. sacrificing  But reed v a l v e s  t o the engine and i n c r e a s e  F o r a s m a l l power saw the advantage  (bmep) probably w i l l n o t outweigh the  o f i n c r e a s e d engine complexity  and decreased  reliability. With the d e c i s i o n made t o use p o r t s i n s t e a d of  143 r e e d v a l v e s , t h e r e remains the q u e s t i o n of what i n t a k e p o r t a r e a and h e i g h t t o use.  As a p l o t o f s p e c i f i c power v e r s u s  a r e a i n d i c a t e d no t r e n d s , the a r e a chosen was the  1.25  i n diameter  the same as  engine: A.  F o r a b o r e / s t r o k e r a t i o of 1.35, InHt  =  Graph 3.7  gives  .28  s The p o r t shape c o n t r o l s the r a t e o f p o r t The  r a t e f o r squared  opening.  p o r t s i s h i g h e r t h a n t h a t f o r round  p o r t s , but a square h o l e i s more d i f f i c u l t t o machine and tends t o snag the ends o f the p i s t o n r i n g s u n l e s s the r i n g s are pinned  so t h a t the r i n g ends a r e always s u p p o r t e d  the c y l i n d e r w a l l .  by  S i n c e round h o l e s have the w i d t h e q u a l t o  the h e i g h t , the r e q u i r e d s m a l l p o r t h e i g h t n e c e s s i t a t e s a l a r g e number o f s m a l l h o l e s w h i c h r e s u l t i n a l a r g e p e r i m e t e r / a r e a r a t i o and a h i g h f r i c t i o n  loss.  To reduce the p e r i m e t e r / a r e a r a t i o of round h o l e s , two t e c h n i q u e s were c o n s i d e r e d .  One  t e c h n i q u e was  o n l y a p o r t i o n of a l a r g e r h o l e and the second was  to d r i l l  the h o l e a t an a n g l e .  The  t o expose  technique  f i r s t technique i s  s t a n d a r d p r a c t i c e on many e n g i n e s w i t h round exhaust p o r t s . The p o r t s a r e d r i l l e d so t h a t the t o p edge i s a t the r e q u i r e d h e i g h t ; the d r i l l  s i z e chosen i s one t o g i v e the r e q u i r e d  144  c r o s s - s e c t i o n a l area  (when the p o r t i s uncovered  s p e c i f i e d height) without exceeding of the c y l i n d e r c i r c u m f e r e n c e . used  t o the  the a l l o w a b l e p o r t i o n  The second  technique, o f t e n  f o r the t r a n s f e r p o r t , i s t o d r i l l h o l e s a t an angle  so t h a t e l o n g a t e d h o l e s r e s u l t . As w e l l as having a h i g h p e r i m e t e r - t o - a r e a  ratio,  an e l o n g a t e d h o l e imparts a d i r e c t i o n a l momentum t o the charge moving through  it.  T h i s can be used  t o advantage i n  the t r a n s f e r p o r t by d i r e c t i n g the f r e s h charge of the c y l i n d e r .  t o the back  The t r a n s f e r p o r t i s so p l a c e d t h a t the  flows from two opposing  h o l e s meet and a r e d e f l e c t e d  upward.  When t h e flows meet, the h o r i z o n t a l v e l o c i t y components c a n c e l and the r e s u l t i n g p r e s s u r e wave a i d s c y l i n d e r  scavenging.  The d i r e c t i o n a l momentum may a l s o be c r e a t e d i n a square p o r t by s l a n t i n g the t o p edge of the p o r t so t h a t the p o r t i s uncovered charge  g r a d u a l l y from the back t o the f r o n t , c a u s i n g the  t o flow toward the back o f the c y l i n d e r . Because round  h o l e s can be e a s i l y d r i l l e d  c a s t c y l i n d e r s , they were s p e c i f i e d f o r a l l p o r t s . squared  p o r t s been s p e c i f i e d , the machining  i n sandHad  o p e r a t i o n would  have i n v o l v e d a more complex m i l l i n g procedure.  Had the  c y l i n d e r been d i e c a s t i n s t e a d of sandcast, the c l o s e r  toler-  ances p o s s i b l e would have allowed any shape o f p o r t t o be integrally cast. Drilled  holes  were used  large perimeter/area r a t i o holes.  i n t h i s d e s i g n t o produce Based on the s p e c i f i c a t i o n s  d e t e r m i n e d e a r l i e r , the l i m i t a t i o n s o f space around circumference,  and the r e q u i r e m e n t of e f f i c i e n t  the  scavenging,  the f o l l o w i n g h o l e s were s p e c i f i e d : 1. e x h a u s t p o r t s - two t o a h e i g h t of .28  .406  i n d i a m e t e r h o l e s exposed  i n t o g i v e an exposed a r e a  of  .19 i n , 2  2. t r a n s f e r p o r t s - two s i d e d r i l l e d 45° a h e i g h t o f .18  .281  i n d i a m e t e r h o l e s on each  t o the r a d i a l l i n e and exposed t o i n t o g i v e an exposed a r e a of  .24  . 2 in . 3. i n t a k e p o r t - e i g h t .172 t o a h e i g h t of .12 2 in  .  i n d i a m e t e r h o l e s , exposed  i n t o g i v e an exposed a r e a of  .15  ( I t s h o u l d be p o i n t e d out t h a t the exposed  h e i g h t o f the i n t a k e p o r t i s s m a l l because the  rel-  a t i v e s t r o k e between the mount c o n t a i n i n g the  holes  and  the cap e x p o s i n g  them i s h a l f o f the  relative  s t r o k e between the c y l i n d e r c o n t a i n i n g the t r a n s f e r and e x h a u s t p o r t s and  the p i s t o n e x p o s i n g  S t r e n g t h and mount c i r c u m f e r e n c e  them.)  size considerations  i n f l u e n c e d the c h o i c e o f the number of h o l e s f o r the i n t a k e p o r t . 3.2  Automatic T h r o t t l i n g The  f l o w o f a i r and f u e l t h r o u g h the e n g i n e i s  caused by p r e s s u r e v a r i a t i o n s i n the s c a v e n g i n g  chamber i  under the p i s t o n ( a l s o c a l l e d p r e c o m p r e s s i o n chamber).  In  moving towards t h e c y l i n d e r the  h e a d on i t s c o m p r e s s i o n  p i s t o n expands t h e scavenging  lowering  t h e chamber p r e s s u r e .  decrease  until  holes  the c y l i n d e r  i n the circumference  These h o l e s connect carburetor. scavenging  with  The  a i r continues  pressure power  decreases through  during  pressure  a i r rushes  the f u e l ,  i s higher through  and f l o w s  mount.  the p o r t .  t h e power  Since  than the  the  into  t h e chamber t h r o u g h  t h e chamber the intake  reaches  t h e c a p on t h e c y l i n d e r ,  stroke, covers  to  a passageway l e a d i n g t o t h e  t h e chamber p r e s s u r e  or u n t i l  continues  of the s t a t i o n a r y r o l l e r  to enter  either  thereby  c a p u n c o v e r s a row o f i n t a k e  chamber p r e s s u r e ,  port u n t i l  The p r e s s u r e  I f the atmospheric  c a r b u r e t o r , mixes w i t h  chamber v o l u m e ,  stroke,  atmospheric  r e t u r n i n g on t h e  t h e chamber v o l u m e  s t r o k e , some c h a r g e may  the intake p o r t .  See F i g u r e  escape  3.3.  On t h e t o p s i d e o f t h e p i s t o n t h e c y l i n d e r v o l u m e expands d u r i n g  t h e power  s t r o k e and t h e c y l i n d e r  drops n e a r l y i s e n t r o p i c a l l y exhaust p o r t to s t a r t in  cylinder  until  pressure  reaches  and  process.  associated with  atmospheric  gases have escaped transfer  still  t h e blowdown  the p i s t o n uncovers the  through  burnt  pressure.  gases w i l l  the pressure flow  port  into  or u n t i l  the  I f n o t enough  i n the scavenging  burnt  time  i n the c y l i n d e r  t h e chamber.  drop  continues  t h e e x h a u s t p o r t s by t h e  p o r t s open, t h e p r e s s u r e  be g r e a t e r t h a n  The r a p i d  t h e blowdown  the p i s t o n uncovers the t r a n s f e r  pressure  the  until  pressure  will chambe  This action  147 reduces  scavenging  blowdown t i m e  efficiency.  i s too  long  so  that  reaches atmospheric pressure part of  of  the  sion the  the  stroke  as  f r e s h charge w i l l  the  are  While ports  are  transfer  to  closing. port area  auxiliary will  be  pletely to  I f the  properly designed scavenging  i n t o the  equals  the  at the  throttle  optimum  the  port  stroke  throttle i s long  but  long  scavenging  chamber b e f o r e  The  and  the  the  c y l i n d e r , i n t o the are  At  bleed  the  to create  scavenging  remain  of  be  the  a very  long  already  causing  chamber. entered  s o o n as  Consequently, only i n the  com-  piston  a vacuum i n t h e  chamber as  port  f r e s h charge  have e s c a p e d ,  c h a r g e w h i c h had  uncovered.  charge w i l l  end  to  the  throttle  the  the  continue  port w i l l  allows  f r e s h charge w i l l  stroke  draws some o f  the  the  continues  enough and  p o r t opens soon enough, the  throttle  If  port w i l l  port  amount o f  chamber  area.  open b l e e d  ports  porting  opening, the  open.  throttle  compres-  c y l i n d e r f o r as  closed  compression  open,  percentage  subsequent  completely  s t r o k e most o f  the  the  i s r e a c h e d when  r e a c h e s bottom dead c e n t e r .  This  and  Optimum s t r o k e  power s t r o k e  escape from the  the  transfer ports  are  stop  bleed  pressure  transfer ports  i t s power s t r o k e ,  close.  cylinder  the  from the and  hand, i f the  open. the  p i s t o n does not move on  flow  other  the  during  For  transfer ports  ports  the  remains u n u t i l i z e d  i s increased.  through the  the  before  f r e s h charge escaping  stroke  On  c y l i n d e r , so  a  the small  that  the  148 i n t a k e i s e f f e c t i v e l y and a u t o m a t i c a l l y t h r o t t l e d . A u t o m a t i c t h r o t t l i n g must a c c o m p l i s h  two t h i n g s :  1. a l l o w t h e maximum q u a n t i t y o f f u e l - a i r m i x t u r e t o e n t e r t h e c y l i n d e r when t h e p i s t o n s t r o k e ends a t the maximum power p o s i t i o n , 2. t h r o t t l e t h e m i x t u r e  a c c o r d i n g t o t h e amount o f  energy r e q u i r e d . The  i n t a k e , e x h a u s t , and t r a n s f e r p o r t d i m e n s i o n s , t o s a t i s f y  the f i r s t requirement, were o b t a i n e d by s c a l i n g e x i s t i n g e n g i n e s as d e s c r i b e d i n t h e p r e v i o u s s e c t i o n . p o r t s i z e and shape, t o s a t i s f y t h e second c o u l d n o t be o b t a i n e d  The t h r o t t l e  requirement,  from e x i s t i n g e n g i n e s ,  so a computer  program was s e t up t o p r e d i c t t h e engine r e s p o n s e as t h e s i z e s and shapes o f t h e t h r o t t l e p o r t  were changed.  I n t h e f i r s t computer t r i a l s ,  a hypothetical  r e l a t i o n s h i p between t h e s t r o k e and energy r e l e a s e d was u s e d . T h i s r e l a t i o n s h i p was based on t h e a s s u m p t i o n t h a t t h r o t t l i n g was d i r e c t l y p r o p o r t i o n a l t o t h e p i s t o n p o s i t i o n a t t h e bottom dead c e n t e r .  No t h r o t t l i n g o c c u r r e d when t h e dead  c e n t e r c o i n c i d e d w i t h t h e maximum power p o s i t i o n  a n t  ^  full  t h r o t t l i n g o c c u r r e d when t h e dead c e n t e r reached a p r e s e t position.  F o r example, i n one s e r i e s o f t e s t s no t h r o t t l i n g  o c c u r r e d when t h e d i m e n s i o n l e s s  stroke  (at dead c e n t e r ) was  1.2 and f u l l t h r o t t l i n g o c c u r r e d when t h e s t r o k e was 2.7. These two p o i n t s were c o n n e c t e d by a s t r a i g h t l i n e as shown  on  G r a p h 3.9.  curve  b a s e d on  variations. area  graph  values  i s p l o t t e d the  ports  and  computer-calculated  time curve  1.0  by  port bleed  o n l y by  1.5 /  port  amount o f  changing  the  throttling  2.0  STROKE AT BDC  size  the  3.9  Flow-area versus  and  shape o f of bleed  2.5  \  stroke  for ideal  The  straight  EFFECTIVE STROKE  Graph  size  curve.  a hypothetical  I t i s p o s s i b l e t o change the  not  area-time  measuring  position-time  c a l c u l a t i o n s were b a s e d on  position.  three  were o b t a i n e d  r e l a t i o n s h i p between the  piston area  this  rectangular  The  under the  computer line  On  FPS  the the port  150 areas  as  shown, but  by m o d i f y i n g  the  After graphically, the  still  shown by  piston high  port  area-time  computer  the  factors  Throttling  port  intake  near  port,  as  Because  also  top  for  were  the  straight  and  for  in  the  to  integrate was  relationship.  to  throttling  integration.  shorter  obtained  program  line  contributes  area-time  reflected  spring  a stiffer  bottom  the  timing  Because  periods  when  the  the  accelerations,  integration,  as  is  the  not  long. The  near  port  p r o g r a m was m o d i f i e d  hypothetical  intake  the  compression pressure produces high  open as  the  rate  spring  affects results  dead c e n t e r , the  spring  depicts for  altering  shape.  directly.  the  dwells  intake  as  the  b a s e d on t h e The  is  port  the  area-time  a l s o by  rate  plot  3 values of  the  piston  spring  port  The t o p stroke  rate.  acceleration area decreases  curve  on G r a p h  as a f u n c t i o n  more spring  (k/m =  40,000), t h e t h i r d s t r o k e i s h i g h e r t h a n t h e  second  shorter  c a n be e x p l a i n e d as amount  of  absorbed long,  throttling by  the  follows: was l e s s  spring  causing too  than  so t h a t  the for than the  much t h r o t t l i n g .  the  time  weak  is  For  3.10  of  The c y c l e s become  increases.  area.  as the  fourth  rate  a higher  port  stable  and t h e  spring  the  in  integrated  integrated  increases.  of  the  effective the  first  the  stroke. stroke  amount  of  second stroke The t h i r d  This the  energy was  too  stroke  was  too  151 short  and c o n s e q u e n t l y d i d  unstable  cycles continued  increasing energy could  the  spring  not  cause enough t h r o t t l i n g .  until  the  stiffness,  engine  the  and p r o d u c e d more u n i f o r m  stalled.  spring  cycles.  have been p r o d u c e d by d e c r e a s i n g the  By  absorbed  (The  more  same  rate  The  effect  of  throttling.) The the  end of  second* c u r v e d e p i c t s  the  power  integrated  port  area.  assumed t o  vary  at  calculated. stiffness; 4 ,250 cpm,  stroke  for  piston  when t h r o t t l i n g  Again combustion  random b u t  The o p e r a t i n g for  the  a weak  less  than  position  at  depends on  an  pressures  were  ±10% f r o m  the  speed depended on the  spring,  the  piston  spring  oscillated  a medium s p r i n g , 5,150 cpm, and  values  for  a  at  about  stiff  s p r i n g , 6 , 00.0 c p m . The e f f e c t position weight also  is  illustrated  piston  be n o t e d  5% h i g h e r  engine  the  that  engine  at  the no  load curve  not  proportion  stall to  earlier  the  the  what  port  It  load  effect  should  is  it  did  only  cpm). throttling  Although  stability  linearly,  when t h e  medium  v e r s u s 5,700  stability.  affect  integrated  full  piston  The  cycles.  speed at  indicates  on t h e  curve.  stable  (6 , 0 0 0 c p m  e n g i n e was t h r o t t l e d  to  third  most  c o m b u s t i o n have on  combustion did  when t h e  by  piston weight  the  The b o t t o m  erratic  the  produces  than  and e r r a t i c  of  the  significantly cause  e n g i n e was t h r o t t l e d area.  the in  Graph 3.10  P i s t o n s t r o k e s as a f u n c t i o n of time f o r i d e a l o s c i l l a t i n g power saw  the  The  next stage  p o r t s i z e was model.  i n the o p t i m i z a t i o n o f the  throttle  t o c a l c u l a t e the f l o w r a t e u s i n g an i d e a l  By employing the t e c h n i q u e s  gas  used by London [3.2]  in  h i s s o l u t i o n of a r e c e i v e r blowdown p r o b l e m , more e x a c t equations  were o b t a i n e d  charge e x p e r i e n c e s  f o r the amount of t h r o t t l i n g  i n f l o w i n g t h r o u g h the p o r t s .  a t u r e s i n the c y l i n d e r and  scavenging  the  The  temper-  chamber depend on  the  amount and t e m p e r a t u r e of the gases e n t e r i n g and l e a v i n g , and on the amount of c o m p r e s s i o n t a k i n g p l a c e . gas  f l o w i n g t h r o u g h a p o r t was  equation  suggested by T a y l o r dM  = 5Bf  W  c Where  = AC  ap  dt  K  0  r  ' °  [3.1]:  P, , d 2> —  p ,, d, y+ll — - (—) * (p-)Y Y u u A  A  i s the p o r t  area,  C  i s the p o r t  coefficient,  a  i s t h e speed of sound,  P^  i s the downstream p r e s s u r e ,  P^  i s the upstream  p  i s the d e n s i t y , 1 S  r a t e of  c a l c u l a t e d from the f o l l o w i n g  A  Y  The  pressure,  the r a t i o o f s p e c i f i c  heats.  The d e r i v e d t e m p e r a t u r e e q u a t i o n used an  ideal  f l o w r a t e e q u a t i o n f o r each p o r t and assumed t h a t c o m p r e s s i o n took p l a c e i s e n t r o p i c a l l y . t h r o u g h the i n t a k e p o r t s and  F o r example, when the f l o w l e a v e s t h r o u g h the  p o r t and b l e e d p o r t , the scavenging  enters  scavenging  chamber t e m p e r a t u r e v a r i e s  Where  R  i s t h e gas c o n s t a n t ,  m  i s the molecular weight,  c T  i s the specific  v  heat a t c o n s t a n t volume,  i s the temperature  a  o f charge e n t e r i n g  through  intake, Tp  i s t h e temperature  Wj  i s the flow rate  through  w  i s the flow rate  through bleed  i s the flow rate  through scavenging  D  i n scavenging intake  chamber, port,  port,  13  w  g  14^  i s t h e mass o f g a s i n s i d e  X  i s the piston displacement,  x  i s the piston  L  i s t h e maximum e f f e c t i v e  Q  i s heat t r a n s f e r r e d  When t h e f l o w r e v e r s e d though  similar  flow o f f u e l computation  and  assumed t o i n c r e a s e  m  _ m  c "  g  piston  position,  out of cylinder.  Also  a different  equations f o r the  a i r were l a t e r  ratios  When c o m b u s t i o n was  velocity,  used.  and f r e s h  of air-fuel  s c a v e n g i n g volume,  t h r o u g h any o f t h e p o r t s ,  equation,was  port,  added  to allow  throughout the engine.  occurred, the cylinder  temperature  according to the following equation:  + E. A 9 ,800\ ^ r C  y  JM  c  155 Where  is  the  temperature  in  cylinder  prior  to  combustion,  F — M  r  M  is  the  fuel-air  ratio  of  is  the  mass o f  fresh  is  the  mass o f  mixture  mixture  mixture in  c The  specific  charge  present  in  calculations  the  chamber  calculations  were  temperature,  and an e q u a t i o n  The engine to  design,  ensure  was  the  were  port  the  maximum  same a s t h e  spaced so t h a t ,  amount  the  volume.  The  volume,  chosen for  of  pressure  the  chamber  diameter.  optimum the  the  throttling  actual  throttle  port  uncovered  same a s  the  transfer  port  uncovered.  the  throttle  port  is  partly  or  completely  the  transfer  port  is  partly  or  completely  the  two  are  in  series,  When t h e  both ports  the the  need  would  The  stroke,  the  ports  mass  d i s c u s s e d and the  of  port  is  the  state.  factors  transfer at  of  2  b a s e d on  specific  diameter  based on the  that  and i t s  b a s e d on t h e  throttle  were  trapped,  cylinder. .  volume  entering,  occur,  holes portion  portion  stroke  is  of of  longer,  covered,whereas open.  control  Because the  flow  rate. By 1/8  in,the  specifying total  a width  of  cross-sectional  1/8 area  in for  and a d e p t h two  of  bleed  ports  area).  By  2 would  be  .03  in  (or  1/6  of  specifying  a height/stroke  bleed  should  hole  be  the ratio  similar  to  transfer of that  1.8,  port the  effect  shown on G r a p h  of  the  3.9.  156 3.3 3.3.1  Design of Components General  Considerations  In the preceding  step, concept f e a s i b i l i t y and  performance o p t i m i z a t i o n were d e s i g n c o n s i d e r a t i o n s . the p r e s e n t  step s t r e n g t h , c o s t , m a t e r i a l  and manufacturing c a p a b i l i t y were g e n e r a l  In  availability considerations.  More s p e c i f i c a l l y , the f o l l o w i n g p r a c t i c e s were f o l l o w e d i n designing  the p a r t s c o n s t i t u t i n g the f r e e p i s t o n r e c i p r o -  c a t i n g blade power saw: 1. r i g h t and l e f t hand p a r t s were e l i m i n a t e d wherever possible, 2. as few p a r t s as p o s s i b l e were used, 3. s i z e and weight of p a r t s were kept a t a minimum, except f o r the p i s t o n which had t o have the same mass as the c y l i n d e r , 4. wherever p r a c t i c a l , at  the machine shop  facilities  the U n i v e r s i t y o f B r i t i s h Columbia were  used, 5. ease of assembly and appearance determined the shape o f the p a r t s where s t r e n g t h was not important. A 1 hp engine o s c i l l a t i n g  a t 6,000 cpm w i t h a  .93 i n s t r o k e w i l l produce about 65 i n - l b o f work per c y c l e . A  1.25 i n diameter p i s t o n and c y l i n d e r (bmep = 57 p s i )  e x e r t a combined c u t t i n g f o r c e o f 140 l b s on the b l a d e .  This  f o r c e must be matched by an e q u a l f o r c e on t h e h a n d l e . operator  applying  t h i s force also exerts a feeding  The  force  whose magnitude depends on t h e shape and c o n d i t i o n o f t h e teeth  (assumed  t o be 40 l b s as shown on F i g u r e 3.1), and a  t w i s t i n g moment. I f t h e f o r c e a p p l i e d i s 2.3 i n ( X ) above 2  the s p e c i f i e d c u t t i n g f o r c e and 8 i n (X^) back from t h e feeding  force,no  bending moment i s r e q u i r e d .  I f forces are  a p p l i e d on t h e bottom h a n d l e ( X = -3.5 i n and X^ - -4.0 i n ) 2  t h e n t h e r e q u i r e d t w i s t i n g moment e q u a l s 950 i n - l b ) .  Because  the t w i s t i n g moment i s s m a l l e s t when t h e t o p h a n d l e i s used t o l o a d t h e saw, t h e bottom h a n d l e w i l l be used m a i n l y t o c o n t r o l the cut.  F i g u r e 3.1  F r e e body diagram o f t h e r e c i p r o c a t i n g power saw  The b e n d i n g the  magnitude  sawing  force  changing (If  of  the  to  the  distance  X^ v a r i e s  so  that  the  be  less  than  moment forces,  blade  from  1-7  in  bending ± 120  occurs  not  as c a l c u l a t e d  If  the  feeding  force  of  the  feeding  force,  return  steel,of stress and  pin  psi  Bounce  of  and t o tling  power  a direct  the  combustion  of  energy  length).  the  shear  4 in, the  cutting  psi.)  above but at  stress  in  in  (X^). .86  stroke  a  .12x.64  in  maximum  during  the  return  and f r i c t i o n 29,000  of  safety,  the  lug  slightly  stress stroke.  is  in-lb  20% during  with AISI  and the  in,  will  the  equals  a factor  frame  But  40 l b s  stress  the  constantly  X ^ s h o u l d be  stress  c r o s s - s e c t i o n are  it  was d e t e r m i n e d  that  the  a n a n a l y s i s was made o f Its  a means o f  amount  of  correlation  in  16,000  remains  spring.  provide to  to  the  1040  bending  lower  at  28,000  respectively.  reasonable,  the  force  from  on  Spring  Once were  feeding  during  depends  distance and the  and the  giving  The  the  27,000  3.3.2  stroke,  2.7.  at  than  blade  (X^),  moment  be  the  preset  and a v e r a g e s  blade w i l l  the  the  in  centroid  the  in-lb  less  acting  When t h e  relating  the  the  amount  The  ideal  between  the  amount  the  throttle)  to  by  work  amount  of  (controlled work  is  forces  requirements  compress  work.  (controlled  converted  p u r p o s e was t o  overall  of  the the  relationship of  by  energy  reduced by  throtrequired  released  and the load  charge  and  amount stroke  removing  159  some o f t h e l o a d from t h e b l a d e , t h e s t r o k e l e n g t h t o absorb more energy.  increases  The i n c r e a s e d s t r o k e must t h r o t t l e  the i n t a k e more, so t h a t t h e subsequent power s t r o k e s r e l e a s e l e s s energy.  will  The c o r r e c t amount o f t h r o t t l i n g  will  r e l e a s e j u s t as much energy as i s r e q u i r e d by t h e work t a k e n out so t h a t t h e l e n g t h o f subsequent s t r o k e s w i l l n o t change. I f t h e amount o f t h r o t t l i n g i s n o t c o r r e c t , t h e s t r o k e length w i l l continue  t o change u n t i l t h e q u a n t i t y o f energy  r e l e a s e d and t h e amount o f work p e r f o r m e d i s b a l a n c e d . The e q u a t i o n  governing the length of s t r o k e ,  d e r i v e d from an energy b a l a n c e t a k e n o v e r one c y c l e , i s as follows:  N (x ) + f(x ) = W 1  ±  i  k  + f(x) + E  f  Where N ( x ^ ) i s t h e energy r e l e a s e d i n c o m b u s t i o n , 1  f(x)  i s t h e energy s t o r e d i n t h e s t o r i n g  W. k  i s t h e work removed, and  device,  i s t h e energy l o s t i n f r i c t i o n .  When a m e c h a n i c a l s p r i n g w i t h a l i n e a r t h r o t t l e r a t e i s u s e d , the e q u a t i o n  can be s o l v e d f o r x and e x p r e s s e d a s :  160  {  -F+!/F +  Where  X  N +  2  X  2 ±  i s the p i s t o n p o s i t i o n a t BDC  (= — ) , o p o s i t i o n a t BDC (= ——) x  X. 1  i s the i n i t i a l  1  XQ  i s a reference p o s i t i o n , F  1  F  i s the l o a d on blade  (=  )  k  i s the s p r i n g r a t e ,  N  i s the work r e l e a s e d d u r i n g  the power  stroke  minus energy l o s t i n f r i c t i o n i n dimension(N (x. )-E ) l e s s u n i t s (N = 2N* = 2 - ) kx o 1  f  z  T h i s e q u a t i o n can be used t o study the e f f e c t o f t h r o t t l i n g on the s t a b i l i t y o f the c y c l e s . ment f o r s t a b i l i t y  A general  i s t h a t a suddenly a p p l i e d f u l l  a suddenly removed f u l l For example; c o n s i d e r  l o a d should  not s t a l l  a t y p i c a l engine:  require-  load or  the engine.  i t r e c i p r o c a t e s with  a s t r o k e o f 1 i n , r e l e a s e s 100 i n - l b s d u r i n g  the power s t r o k e ,  performs 60 i n - l b s o f work and s t o r e s 40 i n - l b s o f energy i n the s p r i n g  (k=80 p p i ) .  When the l o a d i s suddenly removed the  s p r i n g w i l l d e f l e c t 1.6 i n t o absorb a l l the energy (e.g.,  100 i n - l b s l e s s 5% f r i c t i o n ) and the t h r o t t l e  a l l o w no more charge t o e n t e r .  released should  In t h i s example the e q u a t i o n  f o r the energy r e l e a s e d i s g i v e n by: * Assumptions: 1. amount o f t h r o t t l i n g v a r i e s l i n e a r l y w i t h the s t r o k e and r e l e a s e s 60 i n - l b s o f energy when Xj_=l and r e l e a s e s no energy when the s p r i n g has absorbed 60 i n - l b s o f energy, 2. a l i n e a r s p r i n g i s used, 3. work out v a r i e s w i t h f o r c e and d i s t a n c e , 4. f r i c t i o n l o s s i s p r o p o r t i o n a l to maximum energy r e l e a s e d , 5. e f f e c t i v e s t r o k e does not change.  161 N* =  2.04  X.  - 1.25  l  and the  equation X  for  the  = -  F + ^"V F "  s u d d e n l y removed  setting  the  load X  n  (F)  obtained  equal to  = Jx. i i  is  suddenly  giving  = - .75 +  tegrated  port  of  when t h e  load  from the  latter  equation  by  length  when  4.08  the  stroke  capacity  is  obtained  by  the setting  by  Jx.  The s e c o n d e q u a t i o n representation  2 ±  zero:  F=.75 a n d c a n b e r e p r e s e n t e d  X„  X  length  i  loaded to  - 1.25  stroke  - 2.5 X . +  2  The e q u a t i o n engine  the  is  + 4 .08  2  giving  is  position  + + XX,±  2  The e q u a t i o n is  piston  throttling  - 2.5 X . +  2  o n G r a p h 3.11 because i t  a r e a more c l o s e l y .  If  N = 1.94  -  - 1.19  X. 1  is  a more  approximates  this  0  accurate the  equation,  (X -.9) 0  4.64  0  7  5  3  i  is  substituted  suddenly  into  removed,the X  n  the  piston  = W X. 1  stroke  l  2  + N  equation  stroke  is  and t h e  given  by  load  in-  162 and when the load i s suddenly a p p l i e d  (F=.49) the p i s t o n  stroke i s :  X  £  =  - .49 + ^ ( . 4 9 )  2  + X  2 i  +  N~  Note on t h i s graph what happens t o the p i s t o n when the  l o a d i s suddenly removed.  Assume t h a t d u r i n g  c y c l e the p i s t o n had stopped when Xj_=1.30. .41 u n i t occurs  Graph 3.11).  the next power s t r o k e ,  The next combustion  cycle  the will  .07 u n i t s o f energy, and d e f l e c t the s p r i n g t o  No energy w i l l be r e l e a s e d  during  f r i c t i o n reduces the s t r o k e  subsequent  cycles  1.62.  until  t o i t s steady s t a t e , no-load  1.6. I f the l o a d i s suddenly i n c r e a s e d  F=.75 the s t r o k e w i l l decrease t o 1.0, The next combustion of  on  I f the load i s then removed so t h a t no work i s  s p r i n g w i l l d e f l e c t 1.56.  value of  combustion  the N=2 .04-1.25X^ c u r v e ,  taken out of the engine d u r i n g  release  T h i s means t h a t  of energy i s added t o the engine when  ( t h r o t t l i n g follows  the p r e v i o u s  from F=.31  to  on the c u r v e .  c y c l e w i l l r e l e a s e the maximum energy  .78 u n i t s and the engine w i l l be s t a b i l i z e d a t X = l . o .  I f the t h r o t t l i n g  follows  the N=l. 94-1. 19x - . 00075/ ( X ^ . 9 )  curve and the l o a d i s suddenly i n c r e a s e d strokes  w i l l gradually  are reached a t X = l . l l .  decrease u n t i l  3  ±  to F=.49, the  steady s t a t e  conditions  A typical coiled  s p r i n g w i t h a s p r i n g r a t e o f 87  p p i a b s o r b s 45 i n - l b when compressed t o 1.03 i n , 105 i n - l b when compressed t o 1.56 i n , and 175 i n - l b when compressed t o 2.0 0 i n .  The r a t e o f t h r o t t l i n g must t h e r e f o r e  l i n e a r l y from no t h r o t t l i n g throttling  vary  a t a s t r o k e o f 1.03 i n t o f u l l  a t a s t r o k e o f 1.56 i n .  REGION OF FULL THROTTLING  INITIAL  DEFLECTION  Graph 3.11  INITIAL  DEFLECTION  S t r o k e when l o a d s u d d e n l y changed  High c a r b o n s p r i n g s t e e l w i r e  (.156 i n d i a m e t e r ) ,  when made i n t o a 1.0 i n mean d i a m e t e r c o i l e d  spring, w i l l  r e q u i r e 10 a c t i v e c o i l s t o s t o r e 175 i n - l b o f energy d u r i n g a 2 i n deflection.  I t w i l l compress t o a s o l i d h e i g h t o f  3 1.56 i n , occupy a .80 i n , and weigh .17 l b s .  This  spring  can  store  1,000  in-lb/lb  The g a s u n d e r absorber work  and p i s t o n  required  suggests creases  that  to  the  energy  with  a  of  at  ratio  .652 of  in  7.6,  175  in-lb  at  the  throttle  1.  not  2.  stop in  3.  must  is  not  the  = = =  the  flow  gas  for  flow  of  volume. the  amount  the  For  the two  flow  in  engine  at  in  stores  105  195.  gas  is  energy  in-  .750  in,  a compresin-lb  of  .746  in  stores  For  this  example  things:  stroke  when t h e  an i s e n t r o p i c  is  stroke  .652 is  in,  .734  fashion  between  limits. this  is  a good means o f  very  difficult  storing  E l a s t i c l i m i t 120,000 Modulus of E l a s t i c i t y Density  -  to  energy.  gives the f o l l o w i n g (ASTM A 2 2 9 - 4 1 ) :  of  example,  of  when t h e  completely  the  energy  isentropically  and a s t r o k e of  an  longer,  * R e f e r e n c e [3.3] o i l tempered wire S E p  54,  .734  accomplish three  Because gas  of  a compression r a t i o  or  the  of  of  45 i n - l b  a stroke  restrict  vary  stroke  in.  can be used as  absorbing a b i l i t y  stores  a compression r a t i o  in-lb/cu  The e q u a t i o n  a decrease in  maximum p o s s i b l e  sion  piston  bounce.  when t h e stroke  220  compress an i d e a l  the  rapidly  mass o r  accomplish, Flat  springs  specifications  250,000 p s i , 30,000,000 p s i , .282 l b / c u i n .  for  or bands can be used as an energy absorber and They can  a l s o be used to synchronize  the p i s t o n , thereby s e r v i n g a d u a l  bounce.  the c y l i n d e r w i t h purpose.  S t e e l bands are more e f f i c i e n t on a weight b a s i s than a c o i l  s p r i n g , and make p o s s i b l e a v a r i a b l e s p r i n g  r a t e t h a t corresponds more c l o s e l y to a c t u a l requirements.  Bands are u s u a l l y long  throttle  (25 i n when the  2 c r o s s - s e c t i o n a l area attached  i s .010  to the c y l i n d e r and  force required S t o r i n g 175 volume of  must be  piston.  (The  securely  attachment  i s 2,000 l b s when the l e n g t h i s 25 i n ) .  i n - l b of energy  .25  i n ) and  in  3  (W^)  (Volume =  2 E  Bands of rubber and the r e q u i r e d energy and  i n a band r e q u i r e s a band  ^) S  and  nylon  a weight of  can be used t o  bounce the p i s t o n .  of rubber as a s p r i n g m a t e r i a l , s i l a s t i c  For  .07 0 l b . store  evaluation  rubber was  chosen  because i t i s e x c e p t i o n a l l y r e s i s t a n t to s o l v e n t s , j e t f u e l s and  o i l s and  i s r e l a t i v e l y strong as compared w i t h  f l u o r o s i l i c o n e rubber s t o c k s . unvulcanized  s t a t e and may  ing, extruding  or moulding  other  I t i s easy to handle i n the  be processed by m i l l i n g ,  calender  [3.4].  For a 2 i n s t r o k e and  175  lb  f o r c e , the  rubber  band must be .53 i n long and have a c r o s s - s e c t i o n a l area 2 3 of .13 i n . I t w i l l occupy .069 i n and weigh .0036 l b . 3 * ( I t can  s t o r e 50,000 i n - l b / l b mass and  2,500 i n - l b / i n )  * Reference [3.4] g i v e s the t y p i c a l p h y s i c a l p r o p e r t i e s of S i l a s t i c LS-2249V f l u o r o s i l i c o n e rubber as f o l l o w s : T e n s i l e s t r e n g t h - 1370 p s i Tear s t r e n g t h - 165 p s i E l o n g a t i o n - 480% S p e c i f i c g r a v i t y - 1.46  166 I t s e l a s t i c i t y and suitable material  high  f o r absorbing  s t r e n g t h make nylon  or s t o r i n g energy.  a In 3  s t r e t c h i n g 2 i n , a p i e c e of nylon volume) can  s t o r e 175  i n - l b and  5.7  i n long  (.035  w i l l weigh .0012  (It s t o r e s 150,000 i n - l b / l b mass and  in *  lb.  5,000 i n - l b / i n ) . 3  T a b l e IV summarizes the energy s t o r i n g a b i l i t y of the f o u r m a t e r i a l s c o n s i d e r e d , b y l i s t i n g the volume weights r e q u i r e d  to s t o r e 175  in-lb  Table  of energy.  IV  S i z e of M a t e r i a l Required to Store  175  i n - l b s of Energy  Volume Occupied (in )  Weight (lb).  3  .80  .17  S t e e l band  .25  .070  Silastic  .069  .0036  .035  .0012  Coil  spring  rubber  Nylon  A comparison shows t h a t on a per pound b a s i s , the s t o r i n g c a p a c i t y of nylon  i s 140  Reference [3.5] g i v e s the Extremultus b e l t i n g :  times g r e a t e r  energy  than a c o i l e d  following specifications for  T e n s i l e s t r e n g t h - 28,500 p s i a t 35% E - 78,230 p s i D e n s i t y - 30 i n / l b Heat r e s i s t a n c e to +160°F C o l d r e s i s t a n c e to -20°F 3  and  stretch  167 s p r i n g , r u b b e r i s 47 t i m e s g r e a t e r , and a s t e e l band i s 2 1/2 t i m e s g r e a t e r .  But i n s p i t e o f i t s poor r a t i n g , a  s t e e l c o i l e d s p r i n g was chosen t o bounce t h e p i s t o n f o r these reasons: 1. t h e d i f f e r e n c e i n w e i g h t between any o f t h e m a t e r i a l s i s l e s s t h a n 3 ounces, 2. s p r i n g d e f l e c t i o n s a r e p r o p o r t i o n a l t o t h e load, 3. t h e f a t i g u e l i f e i s v e r y h i g h f o r low s t r e s s e s ( n y l o n and r u b b e r have a s h o r t l i f e i f compressions are high), 4. s p r i n g s a r e easy t o d e s i g n . Even though t h e y a r e more e f f i c i e n t t h a n round w i r e in  t h e use o f space, r e c t a n g u l a r w i r e c o i l e d s p r i n g s  require  more e x p e n s i v e m a t e r i a l s and more complex m a n u f a c t u r i n g techniques.  Because i t . i s n o t produced i n  tonnage,rectangular  w i r e has n o t had t h e r e f i n i n g development g i v e n t o round w i r e , so t h a t t h e a v a i l a b l e q u a l i t y i s n o t e q u a l t o t h a t o f good grades o f round w i r e . Because t h e y must n o t f a i l under an i n f i n i t e number o f l o a d i n g s , t h e s p r i n g s must be g i v e n t h e b e s t i n d e s i g n , m a t e r i a l and m a n u f a c t u r e .  C o n s e q u e n t l y round w i r e  springs  were chosen. The  choice of m a t e r i a l f o r springs i s u s u a l l y  between s t r a i g h t c a r b o n (ASTM A230-47) and a l l o y  steels.  168 Carbon v a l v e s p r i n g m a t e r i a l i s p r e f e r r e d because i t s u l t i m a t e s t r e n g t h e q u a l s t h a t o f a l l o y s t e e l s and i t s d e p e n d a b i l i t y at o r d i n a r y temperatures i s g r e a t e r .  Exposing carbon s t e e l  t o t e m p e r a t u r e s i n e x c e s s o f 350°F w i l l cause heat s e t t i n g and l o s s o f l o a d .  A l l o y s t e e l s , on t h e o t h e r hand, u s u a l l y  a r e more s u b j e c t t o seams and have a g r e a t e r tendency t o quench-crack. Carbon v a l v e s p r i n g w i r e  (ASTM A230-47) has an  u l t i m a t e s t r e n g t h o f 200,000-230,000 p s i , chrome alloy steel  vanadium  (SAE 6150) has an u l t i m a t e s t r e n g t h o f 200,000-  250,000 p s i ( e l a s t i c l i m i t i s 180,000-230,000 p s i ) , chrome silicon alloy steel  (SAE 9254) has an u l t i m a t e s t r e n g t h o f  250,000-325,000 p s i ( e l a s t i c l i m i t i s 220,000-300,000 p s i ) , and o i l - t e m p e r e d  spring wire  (ASTM A229-41) which i s most  g e n e r a l l y u s e d , has an e l a s t i c l i m i t o f 120,000-250,000 p s i . In s p e c i f y i n g a m a t e r i a l f o r a p a r t i c u l a r p a r t , performance and c o s t a r e always c o n n e c t e d .  availability,  I n r e s e a r c h and  development, c o s t i s o f t e n o f secondary i m p o r t a n c e t o p e r formance and a v a i l a b i l i t y .  The d e s i r e f o r q u i c k d e l i v e r y  l i m i t e d the choice of wire materials to oil-tempered  wire  a v a i l a b l e l o c a l l y and chrome s i l i c o n a l l o y s t e e l a v a i l a b l e on a s h o r t o r d e r b a s i s .  Because i t r e s i s t s h e a t up t o  450°F w e l l , chrome s i l i c o n w i r e was chosen.  Shot b l a s t i n g  was s p e c i f i e d because t h e impact o f t h e s t e e l o r g l a s s b a l l s p r e s t r e s s e s and c o l d works t h e s u r f a c e and so r a i s e s t h e p h y s i c a l p r o p e r t i e s o f t h e m a t e r i a l on t h e s u r f a c e where t h e s t r e s s i s t h e h i g h e s t and where f a t i g u e f r a c t u r e s w i l l  start.  169 When t h e modified  to  two  The d i a m e t e r spring  springs,  of  the  design using  a better  than  the  m a c h i n e was p o s s i b l e .  design.  The c h o i c e o f  that  the  (b)  operated  over  (c)  had  s p e c i f i e d maximum  (d)  had  the  (e)  required  the  shaft  conditions  spring  materials  were  istics  were  so t h a t  a  to  by  the  the  desired, the  final  n e c e s s a r y and  reduced  a computer The  the  time  program sliderule  for  conditions  changed, whenever and whenever  number  sizes  and  rate.  were  considered, a large  heights,  deflections,  were  sizes  diameters,  of  were  required  selected.  for  optimizing  8 PDK  [3.6]  A to  new  characterwere sliderule aid  calculations  the  was b a s e d on t h e  formulas:  new  calculations  d e s i g n e d by A s s o c i a t e d S p r i n g C o r p o r a t i o n  required.  cylinder  diameters,  solid  same s p r i n g  engine  that  the  added c o m p l e x i t y  outside  same s p e c i f i e d  these  before  preset  preset  changed whenever  selection  was  springs  within  performed  diameter  d i m e n s i o n s was r e s t r i c t e d  operated  all  spring  resulted.  enclosing  piston This  (a)  Because  a single  arrangement  s c a v e n g i n g chamber  w a s made l a r g e r  shorter  fact  initial  size  was  following  size so  not two  170  Gd P  =  4  8D N 3  p  i s the l o a d on s p r i n g ,  D  i s the mean d i a m e t e r o f c o i l ,  d  i s the d i a m e t e r o f w i r e ,  S  i s the t o r s i o n a l s t r e s s ,  K  i s the Wahl c o r r e c t i o n f o r m u l a f o r s t r e s s caused by c u r v a t u r e  of wire  load, G  i s the t o r s i o n a l modulus,  N  i s the number o f a c t i v e c o i l s ,  6  i s the d e f l e c t i o n .  When s u b j e c t e d springs often shorten  t o above normal t e m p e r a t u r e s , ( or "set" )  and l o s e l o a d .  This  l o s s o f l o a d can be p r e d i c t e d and a l l o w a n c e s can be made i n *  c a s e s where t h e l o a d i s s t e a d y . d i c t a b l e and t h e s p r i n g d e s i g n  Where t h e l o a d i s u n p r e i s n o t f l e x i b l e enough, t h e  s p r i n g s may be p r e s e t by' e x p o s i n g them t o t e m p e r a t u r e s and s t r e s s e s above t h o s e e n c o u n t e r e d i n o p e r a t i o n . spring design  Since the  i s f l e x i b l e i n the present design,no c o r r e c -  t i o n f a c t o r f o r s e t was  specified.  On page 25, r e f e r e n c e [3.6] s t a t e s t h a t SAE 6150 l o s e s 4% l o a d when s t r e s s e d t o 80,000 p s i a t 350°F, 7% a t 100,000 p s i and 13% a t 120,000 p s i .  171  vibration  A characteristic  sometimes c r i t i c a l  frequency  spring.  spring w i l l  surge  the  natural  times  the  operating  have to  frequency  than  tion  showed t h a t  well  four  below  the  effect  due  deflection/free  for  the  to  in  spring it  is  the  ratio  is  .4  .5  (limit  increase in  diameter  for  spring  it  the is  low  the  to  with  can buckle.  the  is .72)  to  mean  is  A  by  limit  set  spring  in  by  The ratio  the 24].  is  The maximum .025  should  length  p.  calcula-  checking  and f o r  [3.6,  is  diameter  springs  .70)  as the  small.  spring  3.5  surging  length  Deflection/free  is  is  spring  free  designed  (limit  be  augmented.  spring  of  the  length  diameter  cylinder .011  which  free  too  T h i s was c o n f i r m e d  length  c a l c u l a t e d and found  piston  of  buckling.  spring The  was  ratio  natural  arise.  mean d i a m e t e r  Spring Corporation.  piston  cylinder  the  in  4 and t h e r e f o r e  the  Associated  problems  springs  the  be g r e a t l y  frequency,  the  fail  is  designed  times  not  it  the  be o b s e r v e d i f  more  If  of  Compression  is  the  and s t r e s s e s w i l l  Since  will  of  is  compressed increase  and f o r  the  in.  * R e f e r e n c e [ 3 . 6 ] , page 2 2 , s u g g e s t s t h a t the v i b r a t i o n s p e r min of a s p r i n g v i b r a t i n g b e t w e e n i t s own e n d s c a n b e g i v e n N = .21S where S i s the u n c o r r e c t e d s t r e s s (not i n c l u d i n g t h e Wahl correction factor) f o r a d e f l e c t i o n of 1 i n . For our case S was a p p r o x i m a t e l y 1 0 0 , 0 0 0 p s i so t h a t N i s 2 1 , 0 0 0 cpm.  by:  3.3.3  S y n c h r o n i z i n g Mechanism The p i s t o n  connecting and to  rods  and c r a n k s h a f t s  inexpensive cylinder  tolerances standard  to  bearings  bearings  and wear,  or  bearings  c a n be u s e d .  consists  of  a thin  with  a mixture  power  [3.7]  .  for  of  oil  to  layer  shafts,teflon  stroke  minimize  heat  self-lubricated  spherical  TFE f l u o r o c a r b o n  design  Either  self-lubricated of  with  suitable  held.  impregnated  A typical  to  piston  changed and  The F r e e - P i s t o n Company o f  oscillating  simple  c a n be e a s i l y  teflon  of  synchronized  are  The r a t i o  requiring  porous  nated  can be  which  can be e a s i l y  the  roller  generation  fabricate.  stroke for  and c y l i n d e r  bearing  bronze  resin  and  Kingston  impreglead  found  impregnated  bearings  showed t h a t  a 1 in  that  were  * better  than  roller  Design by  .5  lbs  long  calculations  bearing  without  2,000  psi.  can s a f e l y  carry  exceeding Garlock's The  service  average operating the  bearings.  suggested  cross-section  load  limit area  factor of  of  25  for  the  [3.7] for  lbs  24,000.  a shock  is  load  suggested  10,000 9,500  hours  of  the  1,000  limit at  and w e l l  Even though  connecting  diameter  of  an below  required  rod  is  quite  small  the  required  space  2 (.04  in  for  a stress  to  allow  oscillation  in  order  to  oscillate  of is  25,000 not.  freely,  psi),  The c y l i n d e r require  * Unofficial  discussions,  1965.  connecting  a s p a c e 2 1/2  x  rods, 1  173 x  5 in,  2 1/2  and the  x  1 x  1 1/2  In over  or  quires gear  less  the  and p i n i o n  coil  volume  service  the  of  than  factor  of  connecting  the  spring  restricts  the  maximum s t r e s s ,  higher  than  average operating  used  A rack first  design.  skirt  and on t h e  the  piston.  starting  and p i n i o n  The p i n i o n s cylinder,  After  the  gears  between the  drawings the  a divided  divided  a  spring  gear mated w i t h  stationary  on t h e the  frame  is  teeth  on the  In  stress  stopping  forces,  to  are  reThe  only the  ten  so the  times  gear  was u s e d  drawings  the  concept  on t h e  in  t e e t h on the  and a s i n g l e  spring of  of  the  first  the  piston  so t h a t  the  this  stopped, i s when t h e  blade.  piston  rod  arrangement  force  acting  transmitted teeth  on the  in  inside  assembly  design,  the In  and  pinion spite  the  original when  a more  new a r r a n g e m e n t  the  fitted  placing  showed t h a t  t e e t h on the In  largest  move  arrangement  significantly,  mated w i t h  arrangement  mount.  e n g i n e was  force  racks  s c r a p p e d a n d a new d e s i g n u n d e r t a k e n  e n g i n e was p o s s i b l e . the  and  the  s p r i n g was f o r m a l i z e d .  work performed  were  space  arrangement.  average  arrangement  layout  had been c o m p l e t e d ,  all  a  efficiently.  parts  of  rod  but  during  is  so the  a connecting  involved  material  require  arrangement,  forces  the  rods  in.  a rack  into  one-tenth  piston  compact  delineated, and r o t a t e d  in  the  latch  pivoted  the  latch  when  through latch  the  gear.  engage  the  The  174 When compared t o the s l i d i n g a c t i o n of the connecti n g rod b e a r i n g , the r o l l i n g a c t i o n of a gear on a rack generates l e s s heat and r e q u i r e s l e s s l u b r i c a t i o n .  Because  the load changes c o n t i n u a l l y from one t o o t h t o another  and  r e v e r s e s a t the end of each s t r o k e , the gears would be n o i s y u n l e s s c l o s e t o l e r a n c e s were m a i n t a i n e d .  The gears designed  f o r the r a c k and p i n i o n took i n t o account  tolerances,  geometry, l o a d d i s t r i b u t i o n , life,  temperature  s i z e , dynamic o v e r l o a d , s e r v i c e  e f f e c t s and p i t t i n g d u r a b i l i t y .  a n a l y s i s f o l l o w e d the American t i o n standards  [3.8, 3.9].  Gear M a n u f a c t u r e r s ' A s s o c i a -  The r e s u l t i n g gears  20° spur w i t h a p i t c h diameter  of  of 3/8  x 2 x 7/8 i n .  i n ) , occupy  a volume 3/4  The  3/4  (24 p i t c h ,  i n and a f a c e width  On completion of the d e s i g n and d e l i n e a t i o n , a manufacturer  f o r the s m a l l r a c k and p i n i o n gears was  None of the l o c a l companies v i s i t e d had the proper  sought. facilities  and most of the o u t s i d e companies c o n t a c t e d by m a i l were not i n t e r e s t e d i n the s m a l l j o b . was  The  t h e r e f o r e r e a p p r a i s e d and a new  s y n c h r o n i z i n g mechanism  arrangement  sought.  Again the continuous quest f o r a compact, s t r e s s e d d e s i g n r e s u l t e d i n a new i d e a was  adopted  even though  low-  and v a l u a b l e i d e a .  This  a g a i n i t meant s c r a p p i n g the  o l d mechanism and i n i t i a t i n g a new  arrangement.  new  mounted on the c y l i n d e r  arrangement the stop l a t c h was  In the  so t h a t i t t r a n s m i t t e d the s t o p p i n g f o r c e d i r e c t l y t o the c y l i n d e r and the i n i t i a l  s p r i n g compressing  mechanism  was  175 mounted load the of  on t h e  directly force  10.  piston to  the  acting  in  the  culations  rod  for  diameter  connecting  to  the  be o n l y  The and bands  3/16 load  be used  [3.10].  the  and b u s h i n g  is  the  higher  parts  pin  for  joint.  the  in  to  which  the  is  0.7  in  of  11/32  strength hp a t  belts  helically  10,000  of  wound  But  calthe  A 3/16  of  in would  10,000  1/4  pitch  875  lbs  in  1,250  quieter  belts roller  transcould  friction  between  at  rpm.  between  uses  wide lbs  high This  action  chain  timing  8 , 0 00 r p m  motion  7,000-9,000  are  at  a rolling  silent  pitch  reduced  already  life  articulates  chain  The M o r s e  tensile  Timing because  this  articulation  of  a Morse  strength  joint  be  [3.7].  c a u s e d by  as the  space  a service  example,  galling  factor  showed t h a t  a l s o made c h a i n s ,  tensile  a  impregnated)  Joint  A 3/16  capacity  (Teflon  .5 hp  a chain  action.  an u l t i m a t e ing  For  not  arrangement.  psi,  reduced  little.  into  4,00 0 rpm and  speed of  during  sliding  at  could  forces  fit  for  forces  an a v e r a g e  1.4' hp  could  700  starting  mechanism by  gears  smaller  wide  of  smaller  mitting  of  bearing  in  feasible.  chain with  limits  size  and p i n i o n  rod  the  These m o d i f i c a t i o n s  l o a d had changed v e r y  rack  and a u n i t  pin  the  arrangement  designed  transmitted  synchronizing  now b a s e d o n t h e  connecting  hours  the  service  it  cylinder.  Nevertheless,  because  have  so t h a t  limit  metal  rather such a  silent  speeds,  than  rocker-  chain  and a l o a d  a  has  carry-  rpm.  than  chains  load-carrying  or  cables  gears are  imbedded  176  in  a rubber  or a plastic  covering.  part  of the covering,  like  the teeth i n a rack.  wide,  engage a m a t i n g  recommended a rack  sprocket,  transmits  integral  and f u n c t i o n  in pitch,  a 12 t o o t h ,  3/8 i n .764  .34 hp a t a maximum  5,000 rpm, and o c c u p i e s t h e same v o l u m e  speed o f  and p i n i o n a s s e m b l y .  1.15 p i t c h d i a m e t e r  sprocket  The M o r s e 1/5  "XL" t i m i n g b e l t , when u s e d w i t h  p i t c h diameter  as  The t e e t h , an  sprocket,  When u s e d w i t h the b e l t  an 18 t o o t h ,  transmits  .95 hp a t  10,000 rpm. A helically can  be u s e d  the  roller  larger  t o c a r r y the load. a t an a n g l e ,  than  strands  wound w i r e  synchronize a.tension  Because t h e s t r a n d s  cross  band t h i c k n e s s .  o f .007 i n d i a m e t e r w i r e  Steel  a pulley  the diameter of the strands  the allowable  rope can transmit  rope t u r n i n g over  wound  F o r example  a 35 l b f o r c e .  or plastic  bands f l e x i n g  The t o t a l  over  equation  s t r e s s i n t h e band w i l l  s t r e s s due t o t h e l o a d .  of force i s :  F=S Wt —  Where  a . r o l l e r can  transmitting only  sum o f t h e f l e x u r e s t r e s s due t o b e n d i n g o v e r plus the t e n s i l e  40  i n a .060 i n d i a m e t e r  t h e p i s t o n and c y l i n d e r w h i l e  load.  c a n be  t  is  band  thickness  W  is  band  width,  be t h e  the r o l l e r ,  The d e r i v e d  177  The  F  is  tensile  d  is  roller  E  is  the  S  is  yield  equations  thickness equating  diameter,  modulus o f  elasticity,  stress.  f o r maximum l o a d c a p a c i t y  can the  load,  be  found  r e s u l t to  by  and  differentiating  optimum band  this  equation  and  zero:  t  F  max  These e q u a t i o n s when t h e  thickness  to h a l f of will  be  the  the S  show t h a t  with  (=—) •  elude  some p l a s t i c s  of  spring  The  also  the  strength-to-stiffness  highest  the  load  stress i s equal  that  materials and  while  a low  more l o a d  the  than  the  which best metals  the  best  band  istics,  poor  stability  a  hysteresis  The  meet t h i s  commonly u s e d s t r e s s and  h a v e a low  Consequently  steels.  plastic  yield  plastics  modulus.  advantage of  large  bending  i t s maximum  s t r e s s , and  s t e e l s have a h i g h  elasticity  but  the  carry  material  2  ratio  The  band c a n  i s such t h a t  yield  one  the  "creep", undesirable  loss.  in  a high  yield  do  modulus  stress can  have the  aging  in-  springs.  some p l a s t i c s  plastics  under changing  criterion  carry  dis-  character-  temperatures  and  often  178 To  fit  into  the  existing  was r e s t r i c t e d  to  about  3/4  limited  in  (the  power  as  the  to  1/4  return  stituted optimum  band).  into  the  is  S  t  =  .375  for  reliability  nylon  even though nylon in  bands were  contact  For  with  example,  return 16  its  lbs  zero blade.  dimensions are  maximum f o r c e  sub-  and  by:  materials,  band t h i c k n e s s  suggests that  high  its  thermal  first  melting  temperature  to the  rollers  3.8  (2.8% s t r e t c h )  lbs,  the  the  and the  (2.8% c o n t r a c t i o n )  when  based on t h e s e steel  as w e l l  was o n l y  all  load  band  load  r e t u r n band 64  lbs  two  prefernylon  were  its  the  400°F.  they  "Habasit F - l "  power  is and  as  used i n  so t h a t  during  of  capacity.  material  be p r e l o a d e d  values  stability  availability  was t h e  the  spring  load carrying  by p r e l o a d i n g  bands to  of  and h i g h  Because of capacity,  wide  |  a number  The t a b l e  for  as  was  E  and optimum  preferable  diameter  band w i d t h  be t w i c e  limiting the  roller  2  .0469 £ -  equations. for  given  =  maximum l o a d  able  is  the  power  b a n d was t o  above e q u a t i o n s  max  Table V l i s t s ,  and the  When t h e s e  band t h i c k n e s s  F  in  space,  would  load  design The remain  conditions. nylon  power  increased  load  to  decreased  applied  to  the  and  to  Table V C a p a c i t y and Optimum S i z e o f Bands Material  $7  Preformed H^var Havtir<80% CW.  t aged)  E  Fmax  320,000  30xl0  6  320,000  30xl0  6  200,000  30xl0  6  S p r i n g s t e e l e.g. SAE 1074  F i b e r g l a s s r e i n f o r c e d epoxy ; 200,000 57,000  Nylon type 8  200,000  Preformed sprir-2 s t e e l  7.5xl0  3*0  6  160,000 30xl0  6  t  &  .0^.1  .008  Kesurics Winter* mainspring s t e u l  2. n  160  .0107  .0040  Watch mainspring s t e e l  3.1  62  .0067  .0025  S p e c i t l mold f o r 9 5 0 °  3.3  350  .0100  V i b r a t i o n dumper  3.27  950  .134  M e l t s a t 400°F  3.29  124  .005  Preformed to l j i n c h ait-.  3.3  .136  Temp -20 to 160°F  3.5  Temp - 4 to 300°F  3.29  1  Extremultus n y l o n  <:8,000  78,000  490  Habasit nylon  57,000  45,000  3400  M y l a r 4 77°F  12,000  550,000  12  .0081  s.2e  392°F  1,000  50,000  . 1  .007  3.2a  Kupton S 77°F  14,000  430,000  28  .012  3.28  9,000  260,000  14  .013  High thermal s t a b i l i t y  '3.28  1.8xl0  24  .0063  Heat d i s t o r t i o n * 500°K  3.30  J  d  392°F  30,000  Nylon 6/6 g l a s s r e i n f o r c e d  6  U n l i k e nylon which has  .017  an  upper temperature  l i m i t a t i o n of about 300°F, some s t e e l a l l o y s such as SAE 1074 are  s u i t a b l e as bands even up t o 950°F, although the u s u a l  s p r i n g m a t e r i a l s are r e l i a b l e o n l y up t o 400°F. s t e e l with a y i e l d  SAE 1074  s t r e s s of 200,000 p s i r e q u i r e s a band  t h i c k n e s s o f .0025 i n t o c a r r y the maximum l o a d o f 250 l b s / i n width when f l e x i n g over a 3/4 i n diameter r o l l e r .  The f l a t  p o r t i o n of the band w i l l e x p e r i e n c e a d i s t r i b u t e d  s t r e s s of  100,000 p s i and the p o r t i o n i n c o n t a c t w i t h the r o l l e r  will  e x p e r i e n c e a bending s t r e s s of 100,000 p s i superimposed on the  distributed  stress.  T h i s i n t e r e s t i n g f a c t l e d t o the  d i s c o v e r y t h a t by prebending the band t o twice the diameter of  the r o l l e r ,  the band t h i c k n e s s and l o a d c o u l d be doubled  180 w i t h o u t exceeding the y i e l d  s t r e s s because  ened out the f l a t p o r t i o n of the band was  i n being s t r a i g h t s t r e s s e d i n one  d i r e c t i o n and by being bent t o conform w i t h the r o l l e r diameter, the  bent p o r t i o n was  Because  s t r e s s e d i n the o p p o s i t e d i r e c t i o n .  the s t r e s s a l t e r n a t e s from compression to t e n s i o n ,  e a r l y f a t i g u e f a i l u r e may Because the  result.  the f l e x i n g a c t i o n of the band  resembles  s t r e s s i n g a c t i o n of a watch m a i n s p r i n g , t h e m a t e r i a l s used  as watch s p r i n g s c o u l d p r o b a b l y be used as bands.  In t h i s  r e g a r d i t i s s i g n i f i c a n t to note t h a t not u n t i l the d e v e l o p ment o f the h i g h s t r e n g t h c o b a l t base a l l o y s such as did  unbreakable mainsprings become a v a i l a b l e .  t h a t Havar may  Havar  It i s possible  prove t o be the a l l o y b e s t s u i t e d f o r band  m a t e r i a l not o n l y because of i t s h i g h s t r e n g t h and h i g h temperature s t a b i l i t y above 1,000°F,)  (300,000 p s i )  ( s t r e n g t h remains h i g h even  but a l s o because of i t s r e s i s t a n c e t o " s e t "  and s t r e s s c o r r o s i o n  [3.11].  The bands most e a s i l y a v a i l a b l e were h i g h s t r e n g t h automotive f e e l e r gauges. s t r e s s , a .005  i n f e e l e r gauge was  diameter mandrel. the  yield  bent over a 3/4 i n  S i n c e the band d i d not deform  s t r e s s was  s u i t a b l e as a band. was  For a q u i c k check as t o the y i e l d  i n excess of 200,000 p s i and  therefore  Before the band t h i c k n e s s o f .004 i n  chosen, the l o a d c a r r i e d by the band was  f u n c t i o n of band t h i c k n e s s , Graph 3.12. t h a t the f l a t band  plastically,  (.004  p l o t t e d as a  The graph shows  in) can c a r r y 150  l b s without  181 exceeding the y i e l d  s t r e s s o f 200,000 p s i . A h i g h e r  load  w i l l permanently deform the band, but not u n t i l the load reaches 480 l b s i s there danger of f a i l u r e .  A .005 i n band  would permanently deform w i t h any load but the load a t f a i l u r e i s higher  (700 l b s ) .  0  .004 BAND T H I C K N E S S  Graph 3.12  .008  .012  (iN)  Maximum l o a d t r a n s m i t t e d  by bands  The l o a d c a r r y i n g c a p a c i t y of the bands can be increased band.  by combining s e v e r a l f l a t bands i n t o a composite  The equation governing the l o a d c a r r i e d by the com-  posite, derived  from a f o r c e a n a l y s i s , i s g i v e n by:  182 F = | (Wt) 2 '  Where  + " l+6y N  l+3y  v  2  N  i s number o f bands,  y  i s the c o e f f i c i e n t of f r i c t i o n ,  W  i s t h e band w i d t h , -  t  i s t h e band t h i c k n e s s ,  S  i s t h e y i e l d s t r e n g t h o f band.  I f each band i s s e p a r a t e d  by a l a y e r o f l o w - f r i c t i o n m a t e r i a l  such as t e f l o n o r g r e a s e , t h e maximum l o a d i s n e a r l y  directly  p r o p o r t i o n a l t o t h e number o f bands because t h e low c o e f f i c i e n t o f f r i c t i o n a l l o w s each band t o a c t n e a r l y of t h e o t h e r bands.  independently  But i f t h e f r i c t i o n i s h i g h , t h e com-  p o s i t e band a c t s as a s i n g l e t h i c k band and t h e l o a d c a p a c i t y may even be l e s s t h a n a s i n g l e t h i n n e r band. The r a t i o o f t h e r a t e o f h e a t g e n e r a t e d by f r i c t i o n t o t h e maximum power i s g i v e n by: Q'  =  Where F ' P  (4 F' P  +  F' 6  ) (£) s' y (J-1) D  i s t h e l o a d on blade/maximum a l l o w a b l e on  load  blade,  F^  i s t h e band pretension/maximum l o a d on b l a d e ,  s'  i s t h e s t r o k e / s t r o k e a t maximum l o a d ,  t/D  i s t h e band t h i c k n e s s / r o l l e r d i a m e t e r ,  y  i s the c o e f f i c i e n t of f r i c t i o n ,  J  i s t h e number o f bands.  183 When the bands a r e p r e s t r e s s e d r e t u r n band c a r r i e s no l o a d , F  The  =  1  P  so t h a t a t maximum l o a d  the  then:  i  8  amount of h e a t g e n e r a t e d v a r i e s from .1% t o .2% of  rated  power. Up  t o now  considered.  The  o n l y the f o r c e s a c t i n g on the b l a d e were  question  of what f o r c e s a r e p r e s e n t when  the c y l i n d e r assembly mass does not e q u a l the p i s t o n assembly mass was  answered a f t e r the a c c e l e r a t i o n of the p i s t o n  equated t o the a c c e l e r a t i o n s o f the c y l i n d e r .  This  was  yielded  the f o l l o w i n g e q u a t i o n f o r the f o r c e i n the band: (A ) F Where A P  P  Am  =  —2-  2  PAm  i s the p i s t o n  area,  i s the c y l i n d e r  pressure,  i s the r a t i o of w e i g h t d i f f e r e n c e t o sum M -M p i s t o n and c y l i n d e r w e i g h t s (Am = P ) p c  of  c  + M  The  e q u a t i o n showed t h a t a 3% d i f f e r e n c e i n w e i g h t between  the p i s t o n and  c y l i n d e r a s s e m b l i e s would cause a 36 l b f o r c e  t o a c t i n the band when the c y l i n d e r p r e s s u r e was psi.  2,000  T h i s d i f f e r e n c e i n w e i g h t can o c c u r as the r e s u l t o f  s h a r p e n i n g the t e e t h  (shortening  them by 1/4  in).  The  result-  i n g f o r c e w i l l be c a r r i e d by the s i n g l e r e t u r n band because the p i s t o n i s l i g h t e r t h a n the c y l i n d e r .  184 The ing  bands can be f a s t e n e d  hooks on each end o f the band.  t o the c y l i n d e r by formThe minimum r a d i u s f o r  a c o l d worked hook i s about 1/32 i n so the maximum f o r c e the hook can c a r r y i s 6.7 l b s .  To c a r r y a l a r g e r f o r c e , the  band can be heated and a s m a l l e r be clamped. welded  hook formed, o r the hook can  A l t e r n a t i v e s t o the hook a r e d r i l l e d  holes or  brackets. Among the methods o f a d j u s t i n g band t e n s i o n  s i d e r e d , one r e q u i r e d material  attaching  such as n y l o n ,  con-  the s t e e l band t o a f l e x i b l e  another r e q u i r e d adding some f l e x i b l e  m a t e r i a l on the r o l l e r s or under the hooks, and a t h i r d r e q u i r e d adding a s e t s c r e w - a d j u s t e d l i n k on the end o f the band.  Because o f i t s p o s i t i v e f a s t e n i n g and adjustment  p o s s i b i l i t i e s even under h i g h temperature o p e r a t i o n , the adjustable  3.3.4  l i n k was chosen.  A r r e s t i n g Mechanism In d e s i g n i n g  a s u i t a b l e device  t o stop and l o c k the  p i s t o n and c y l i n d e r , i t was necessary t o c o n s i d e r tude of the f o r c e s i n v o l v e d i n stopping  the magni-  the a s s e m b l i e s .  For  t h i s purpose the energy absorbed by the d e v i c e was equated to the energy r e l e a s e d by the s p r i n g i n expanding from the end  o f the s t r o k e t o the stopped p o s i t i o n .  e q u a t i o n became:  =  2Kx  1  +^~r_2— n  The f o r c e  185 Where  K  i s the spring  rate,  x  i s the spring  deflection,  6  i s the displacement  f r o m BDC t o p o i n t  latch  engages, Z n  i s t h e d e f l e c t i o n o f n t h member, '  F  i s the load  The  force  i s smallest  the  end o f t h e s t r o k e  on  when t h e d e v i c e (6=0).  possible  allows very  the A so  large  little force  locking  force  to unlock  latch or ratchet the force  device  motion before  c l u t c h t o engage o n l y  than  the piston a t  i s twice the steady  magnitude. A  very  locks  But because o f impact, t h e  magnitude of the i n s t a n t a n e o u s state  device.  allows  involved  i s a one-way c l u t c h .  locking  but i trequires  and a mechanism t h a t  i n stopping  f o r a one-way c l u t c h .  absorbing  member  flexible  By  c a l c u l a t i n g t h e d e f l e c t i o n o f e a c h member i n t e r m s o f  force  (assuming equation  F  =  a constant  involved  /(KX)  are not excessive,  s t r e s s - s t r a i n r e l a t i o n s h i p ) , the  becomes:  KX +  lock,  i s higher  is  stress  (Z >>0). t h e f o r c e s n i  stroke.  the teeth  the assemblies  I f t h e energy  a  will-allow  a t t h e end o f a s e l e c t e d some movement b e f o r e  It  2  +  2  -—-A  (  K  X  )  E n n  S  186 Where  L A E  i s t h e l e n g t h of n t h member,  n  i s the a r e a o f n t h member,  n  i s Young's modulus f o r n t h member.  n  T h i s e q u a t i o n can be used when the s i z e of members i s known but t h e s t r e s s e s are n o t . s t e e l r o d , 2.8  F o r example, when a 3/16  i n l o n g s t o p s t h e p i s t o n i n .10 i n (Kx=175),  t h e r o d w i l l d e f l e c t .005  i n , be loaded t o 1,380  e x p e r i e n c e a s t r e s s o f 50,000 p s i . on a 3/16  i n diameter  l b s , and  But i f the s t e e l r o d r e s t s  i n d i a m e t e r n y l o n r o d , .25 i n l o n g , the assembly  w i l l d e f l e c t .054  i n and each member w i l l be l o a d e d t o o n l y  990 l b s and e x p e r i e n c e a s t r e s s o f 36,000 p s i . When the s i z e of a l l members i s n o t known b u t a l l t h e maximum a l l o w a b l e s t r e s s e s a r e , t h e n t h e f o l l o w i n g r e a r r a n g e d e q u a t i o n can be used t o c a l c u l a t e t h e unknown dimension:  n  2Kx  - 1  F o r example, when used t o c a l c u l a t e t h e l e n g t h o f a n y l o n r o d so t h a t t h e s t r e s s i n t h e 3/16  i n d i a m e t e r by 2.8  i n long  s t e e l r o d w i l l n o t exceed  30,000 p s i , a n d t h e s t r e s s i n t h e  n y l o n r o d w i l l not exceed  20,000 p s i , the e q u a t i o n gave t h e  l e n g t h as 5/8  i n and t h e d i a m e t e r as 1/4  in.  I n t h i s example  the r o d s w i l l t r a n s m i t a f o r c e o f 830 l b s . In  the d e s i g n o f t h e t e e t h on the l a t c h , t h e f a c t  t h a t the c o e f f i c i e n t of s l i d i n g f r i c t i o n i s l e s s than the c o e f f i c i e n t o f s t a t i c f r i c t i o n was used t o advantage.  The  a n g l e s o f t h e t e e t h were chosen so t h a t t h e f o r c e o f f r i c t i o n h o l d s t h e l a t c h i n t h e l o c k e d p o s i t i o n when t h e l a t c h i s s t a t i o n a r y and h e l p s t o open t h e l a t c h when i t i s already  s t a r t i n g t o open.  The f o r c e o f f r i c t i o n w i l l  hold  o r r e l e a s e t h e l a t c h as r e q u i r e d when t a n g e n t o f t h e t o o t h a n g l e i s between t h e s t a t i c and s l i d i n g c o e f f i c i e n t o f friction:  y s l-,i d.i n•g  < tan 8 > y s t a.t i. c .  But t h e c o e f f i c i e n t o f f r i c t i o n depends on t h e t y p e and q u a n t i t y o f l u b r i c a t i o n used and on t h e s u r f a c e finish.  The c o e f f i c i e n t o f s t a t i c f r i c t i o n o f s t e e l - o n -  s t e e l i s .78 when d r y and .23 when l u b r i c a t e d  with a l i g h t  mineral o i l ; the c o e f f i c i e n t of s l i d i n g f r i c t i o n of s t e e l o n - s t e e l i s .42 when d r y and .080 when l u b r i c a t e d c a s t o r o i l o r grease [3.12].  with a  Therefore, the tooth angle  s h o u l d be between 23° and 38° when t h e t e e t h a r e d r y and between 4 1/2° and 13° when t h e t e e t h a r e l u b r i c a t e d oil.  Consequently,the latches designed f o r operation  with with  l u b r i c a t i o n w i l l r e q u i r e a l a r g e f o r c e t o open them when the t e e t h a r e not l u b r i c a t e d , a n d  latches designed f o r operation  w i t h no l u b r i c a t i o n w i l l f l y open by t h e m s e l v e s when t h e teeth receive  lubrication.  188 A force latch  with  force  is  is  lbs  This  to  lb  The  large  of  free  trigger  is  force  motion  the  once  it  is  through  an a r c ,  and p u l l s  thereby  freeing  the  the  coil  cylinder  through  teeth  on the  motion contour the  the  force  no  piston  the  rod,  teeth  lever  was  The c o i l  spring  required  to  the  107  same  in-lb  the  energy.  latch  (e.g.  difficult.  the  motion  the  latch  to  the  and t o  latch  slides  spring;  of  spring,  an  to  the  pulls  over  follow  impact  rod,  operator  t e e t h when  teeth  impart  flat  flat  slide  spring  piston  The  the  3.3.  flat  the  by r e l e a s i n g  coiled  latch  Figure  level,  and c y l i n d e r .  the  pre-  open the  away f r o m t h e  s l o t , the  As  spring,  l o c k e d by  pulls  tooth  of  engine  to  no lbs  moving.  spring,  and engages t h e  To a l l o w  rod  2.2  oiled and  b y p u l l i n g -a s m a l l  rod  forces  it  cylinders,  latch  in  the  a coil  longer  action  an  of  open the  extended  the  locks  an a r c ,  the  slider,  the  assembly extends  reverses. of  keep  to  contracts,  piston  spring  latch  lever  spring  stopping  flat  with  dissipate  engine  the  once  needed to  r e l e a s e d the  spring,  the  latch  required  of  break  A force  c o u l d make s t a r t i n g  starts  a slot;  initiates  moving.  a dry  to  locked position  was a v o i d e d by u s i n g  the  The o p e r a t o r  required  from the  latch w i l l  when d r y )  when t h e  is  keep i t  force  dry  difficulty  lbs  free  break  the  t e n s i o n e d by  out  teeth  a n d a 44  opens,  107  10  necessary to  required  angle it  10°  of  the  the the the  load  to  hinged. attached  overcome the  to  the  locking  hinge force  must and  supply keep  189 the  latch  latch,  the  geometry travel teeth  in  contact  inertia  will  from  time  touch.  (Z) d e p e n d s o n t h e  I A 1 lb  of  the For  rod  distance  teeth the  spring  tops  size  force  will  cause the  teeth  teeth  separated.  teeth of  6 ppi,  from  have  dead c e n t e r will  1 in  releasing  not  to  during  as  the  in,  thus  required  is  31,000  rod  stress  psi). long  impact  required psi in  safely  it  the  piston  and  used,  the  the cylinder  the  the  according to  distance  the  the  equation:  least  '.022  when  in  after  cylinder-piston  A coil of  .022  spring  energy  the  as  required  it  the the  reaches  in,  the  with  a  rate  shortens  force  and  energy. stresses in  the  slider  inside  the  109  rod  it  during the lb  is  and  piston  specifying  The maximum s t r e s s piston  bearing  the  n e c e s s i t y of  same l o c a t i o n  transmit  engage f u l l y  has t r a v e l l e d  giving  showed t h e  and i n  at  the  in-lb  material.  The t e f l o n to  a s s e m b l y , and  latch  to  engaged.  The c a l c u l a t e d rod  If  r e l e a s e 2.2  1/2  the  before  be f u l l y  will  of  on  [in]  assembly t r a v e l s  bottom  The f o r c e  separate u n t i l  (F)  cylinder-piston tops  teeth.  latch-slider  the  =  force  the  the  determine  the  flats  with  in  50,700  steel  the  slider  psi.  (The  full  load  is  29,300  slider  must  be  3/16  shock  load.  in  190 3.3.5  Cooling  System  In d e s i g n i n g e f f i c i e n t is and  as i m p o r t a n t air.  varies and  The h e a t  directly  with  transfer  the tangential  turbulent,  and w i t h  body [3.13],  surface f r i c t i o n  I f the surface  i n terms o f a i r v e l o c i t y ,  varies directly  no m e c h a n i s m  according t o Mackerle  the v e l o c i t y .  i s expressed  fins,  exchange between a s o l i d  transfer,  inversely with  force  the  as t h e h e a t  cooling  force  friction  the heat  w i t h t h e a i r v e l o c i t y when f l o w i s  t h e square  root of the v e l o c i t y  when  flow i s laminar:  Q  Where  Since  =  =1.5  f o r laminar  n  =2.0  f o r turbulent flow,  n  = 1.73 f o r p a r t t u r b u l e n t a n d p a r t  K  i s a constant,  V  i s t h e mean v e l o c i t y  transfer  transfer  layer,  turbulent  n _ 1  n  the heat  boundary  KV  per unit  the t r a n s i t i o n  the cylinder  by  the cooling  sliding speed  laminar to heat  heat w i l l be.  i n a high-speed air.  percent o f the heat two-stroke  The p u r p o s e o f c o o l i n g  s u r f a c e f o r the p i s t o n which  o f 40 f p s .  from  a turbulent  p l a c e , t h e b e t t e r t h e average  Twenty t o t w e n t y f i v e in  laminar,  of flow.  i s most i n t e n s e t h r o u g h  the sooner  flow takes  flow,  engine  released  i s removed  i s t o secure  i s m o v i n g a t an  a  average  T h i s s u r f a c e i s f l u s h e d by h o t g a s e s whose  191 maximum t e m p e r a t u r e 4,000°F. film be  a t the onset  The c o n d i t i o n s  f o r the formation  maintained  below  rings  from e x c e s s i v e  suffer  supply  becomes i r r e g u l a r  power saws w i t h  lubricating  engine  internally  h i s t e s t s on t h e h e a t  listed  1.  the surface  adequate  conclusions  transmission  coefficient  to cool  lubrication.  from t h e r e s u l t s  from a i r c o o l e d  o f heat  transfer  engines  (h) and a r e  below:  The h e i g h t on  of f i n s normally  the surface  heat  2.  The f i n t h i c k n e s s  3.  The f i n s p a c i n g according h but  one  influence.  Z  below  deteriorates considerably at  .060 i n . (V) i n f l u e n c e s t h e c o e f f i c i e n t  t o the approximate  w  V,  A matte  transfer coefficient.  (Z) i n f l u e n c e s t h e c o e f f i c i e n t ,  4. T h e a i r v e l o c i t y  h  h a s no i n f l u e n c e  h a s no s i g n i f i c a n t  the c o e f f i c i e n t  according  used  to the r e l a t i o n : a  spacings  5.  and t h e p i s t o n  I t i s a common p r a c t i c e  and t o p r o v i d e 1  concern  wear.  must  At elevated  a r i c h f u e l - a i r mixture  Some o f M a c k e r l e s of  of a  400°F f o r n o r m a l o p e r a t i o n .  lubrication  the  reach  a r e adverse/ so t h a t t h e temperature o f t h e w a l l s  temperatures  to  o f e x p a n s i o n may  a  relation:  7 3  V  surface  has d e f i n i t e  w h e r e a s a p u n c h marked  advantages over  surface  a glossy  (.020 i n d e e p ,  192 .070  in  one.  apart)  Although  coefficient, better by  has no a d v a n t a g e  it  not by In  the  surface,  air  is  c a u s e d by  not  unpunched  influences  heat  of  is  the  always  surface  large  than  pro-  increased resistance surface This  friction  to  but  by  type  of  resistance  the  coefficient  transfer. diameter ratio  the  laminar  and t u r b u l e n t  The a i r  stream d i r e c t i o n  because  if  the  of  influences  because  and  an  cast  case  head d i f f e r e n c e s .  The c y l i n d e r  stice  that  a roughly  on t h e  flow  quality  true  jections  rupted  8.  is  a machined one.  impedes heat  7.  surface  transmitted  pressure  6.  the  over  air  heat  Rapid vibration  of  flow  flow  intensive  results,  surface  areas  varies  with  influences between  transfer has  in  is  to  the  the  the  turbulence  fins  exposed  diameter.  coefficient  fins the  is  dis-  fin  inter-  considerably  little  influence  augmented. on  the  coefficient. The e x t e n t  to  flows  stationary  over  cylinders  which Mackerle's observations  moving  in  stationary  Even though in  a parabolic  practical cated  the  also air  fin  with  apply  is  yet  theoretically  shape t e r m i n a t i n g  compromise,  conical  cylinders  according rounded  in to  to  In  air  reciprocating be  ideal  Judge  steady  to  a sharp  edges.  on  determined.  fin  has  sides  edge,  the  best  a  trun-  [3.14]  is  practice,the  fin  193 thickness There  should  must be ing  i s c h o s e n as  large  air.  fins  are  smaller rapid  production  many f i n s  as  possible  small  .31  cowling.  as  as  enough t o  For  spacing of no  be  small  to  If a  .47  in for a  spaced.  than twice the  At  efficiency  an  of  But  ature this  reciprocating  search revealed type of  effects  heat  127  by  that  In  o s c i l l a t i o n s are  obtained  in practice i s an To  ation  of  amount o f  that  by  and  so on  outright  large a cost  in.  cylinder A  uses liter-  information on  on  the  But  the  that  transfer  c o n v e c t i o n when required  t h e y may  not  weight b a s i s ,  amplibe forced  winner.  heat t r a n s f e r  heat t r a n s f e r r e d  a  transfer,Richardson  gener'ate enough i n f o r m a t i o n ,  t h i s type of  are  that  .10  cylinder.  forced  and  cooling,  found  survey a r t i c l e heat  having  fin efficiencies  the  valuable  a mean v e l o c i t y b a s i s .  tudes of  convection  a  the  a  thickness,  some c i r c u m s t a n c e s ^ h e a t  o s c i l l a t i o n s would exceed  compared on  and  cooling  s o u n d on  under  layer  i n t e r s t i c e s below  little  transfer.  for  interstices  fps, Mackerle  motion of  very  o f v i b r a t i o n and  [3.15] s u r m i s e d  i f the  flow conditions  drops o f f r a p i d l y at  inherent  cool-  recommends  is available  laminar boundary  a i r speed of  interstices  f r e e l y exposed c y l i n d e r  T h e - s i m p l e s t method o f the  the  permit.  s a t i s f a c t o r y flow of  stronger a i r flow  deterioration  but  a i r v e l o c i t i e s Mackerle  more d e n s e l y  occurs.  ensure a  processes  and  for a valid to determine  from a r e c i p r o c a t i n g  evaluthe  cylinder  head, an experiment was s e t up and t e s t s were performed. apparatus c o n s i s t e d o f a h e a t e r element,  The  thermocouples,  standard and s p e c i a l c y l i n d e r heads, and a mechanism t o r e c i p r o c a t e the head a t v a r y i n g speeds and through s e v e r a l amplitudes.  Photographs  o f the t e s t apparatus a r e shown on  F i g u r e 3.2 and the d a t a i s g i v e n i n Appendix V I . C a l c u l a t i o n s f o r the heat t r a n s f e r  coefficient  (h) were based on the measured v a l u e s o f the power s u p p l i e d t o the h e a t e r , the f i n temperature, the a i r temperature, and the f i n a r e a .  The d a t a i s p l o t t e d on Graph 3.13.  the c o - o r d i n a t e s t r i e d , the ones used on the graph number  (Nu) v e r s u s the p r o d u c t o f the Reynolds  Of a l l (Nusselt  number  (Re)  and the square r o o t o f the f i n h e i g h t - t o - s t r o k e  ratio  (£/s)),best c o r r e l a t e d a l l the a v a i l a b l e d a t a .  The e q u a t i o n  o b t a i n e d from the p l o t i s g i v e n by:  Nu  =  Where  ,,.986  10.8 + .0862 hi  Nu  K Ns£  Re K  =  c o n d u c t i v i t y of a i r ,  v  =  kinematic v i s c o s i t y of cooling a i r .  The graph was then used t o c a l c u l a t e the expected of the designed c y l i n d e r . (frequency  F o r an ambient  (N)=6,000 cpm, s t r o k e  temperature  temperature  70°F,  (s)=.75 i n , f i n h e i g h t (£)=  195  •Figure 3.2  Photograph of heat transfer test apparatus: (A) Model 210 head with heating element and spacer, (B) Model 275 head, (C) 275 head and block with heating element (D) 210 head assembled on scotch yolk, (E) test set-up (F) special cylinder head and mating stationary fins assembled on scotch yolk  196 2 1.30 i n , f i n a r e a 100 i n ) t h e f i n t e m p e r a t u r e may go up t o 430°F.  T h i s means t h a t t h e f i n t e m p e r a t u r e i n t h e f r e e -  p i s t o n engine w i l l be a p p r o x i m a t e l y t h e same as i n t h e conv e n t i o n a l power saw.  Graph 3.13  Heat t r a n s f e r d a t a f o r r e c i p r o c a t i n g  cylinder  197 3.3.6  Combustion System The need f o r a l i g h t w e i g h t c y l i n d e r assembly t o  keep o v e r a l l w e i g h t low and o p e r a t i n g the c h o i c e  speed h i g h , l i m i t e d  o f t h e c y l i n d e r and f i n m a t e r i a l t o t h e aluminum  a l l o y s shown on T a b l e V I .  The f i n a l c h o i c e was M e a n 135  as i t was a v a i l a b l e l o c a l l y and g i v e s in conventional  satisfactory service  power saws.  Table VI M a t e r i a l s S u i t a b l e f o r C y l i n d e r Heads and B l o c k s Alcan  Heat  treatment  —3 Tensile  strength (xlO  )  —3 Compressive s t r e n g t h ( x l O Xleld  strength  Hardness  (xl0~ ) 3  (Brinell)  —3 S h e a r s t r e n g t h <xtO Fatique lield  limit  a t 400°F  Keference  )  U:o" ) 3  (xlO  - 3  )  Alcan  225  ivlcan 250  ASTi-1 C4A  iiSTM CG100A  Sand & P.Mold  Sand  Sand & P.Hold  T5  T6  T6  T5B  26  35  39  25  22  22  £5  19  27  28  60  70  80  75  18  27  30  il  ASTH  Form  135 SU70JI  7.5 ) (3.18,  8  6.5  10.5  9.5  3.19)  (3.18,  T5C  T6  37  36  «lcan 385 ASTM  4032  Forced  125  ASTM SC5L,  Alcur. <13 AaTK C.V....  Sand 4 P.fioi.^  T6  T5  T6  Ttl  23  40  T571 29  24  13  35  30  23  18  >0  115  110  65  70  85  30  29  22  ^1  .6  8  8  i l  20  9.5  8.5  10.0  16.5 3.19)  Aican  (3.18,  3.19)  (3.18,  3.19)  (3.18,  ii.  ..1  1<:.C 3.19)  U.17, (3.19)  Uses cylinder  heat  reciprocating  c y l i n d e r head  and bio  cit,  p a r t s i n en-  p i s t o n , bush-  axles,  wheels  gines,  ings  cranjc  pistons  c y l i n d e r head t i m i n g gear3  j/lir.-er  neiidj  case  Because t h e r i n g s r e q u i r e  r.euvy j u t y  a special sliding  s u r f a c e , t h e c y l i n d e r bore had t o be a n o d i z e d , chrome p l a t e d , metal sprayed o r l i n e d w i t h a c a s t i r o n sleeve.  To m i n i m i z e  198 weight of  and m a x i m i z e  .001  in  was o r i g i n a l l y  fabrication, plated,  a  a machining  .040  in  wall  a room t e m p e r a t u r e side  diameter  block  from  reaches liner  bore  is  the  the  circular and  plate,  simply  12,000 2,500  the  psi. psi  tration,  stress  and b e c a u s e t h e  to  l o a d on t h e  spring  the  load  farther  it  blade  piston  chamber  and p i s t o n  at  in  and  psi  and  the  .001  in  the  2,000  psi  fins  the the  process, undersize.  flat pressure  cylinder  of  was  stress  head.  (140  560 p s i  was  stress,  and w a l l s ,  walls  of  cylinder  as a  away f r o m t h e  top  the  removal  honing  in  For  temperature  act  the  be  out-  The c a l c u l a t e d  points  lbs)  to  cylinder  The  was  h e a d was 5,000  psi.  concen-  a c c e l e r a t e d mass d e c r e a s e d ,  was 800  reaches the  of  around  stress  the  stress  and due  due  to  psi.  To a c h i e v e a v e r y the  edge.  depth  on the  for  final  a uniform  s t r e s s was h i g h e r  lower  the  specified  effect  tensile  was  the  to  around  shear  stress the  was  in  1,150  To a l l o w  in  surface  cylinder is  a  during  liner  maximum s t r e s s  stiffening  and the  The t e n s i l e  the  subjected  The  the  to  specified.  .003  h e a d was assumed t o  supported  neglecting  of  pressure  diameter  cylinder  fit  smaller.  the  s l e e v e was  prevent  material  To e s t i m a t e walls,  iron  to  when,  destroyed  e v e n when t h e  in  thick  machined bore  error  contact  .0017  in  s p e c i f i e d but  cast  (specified  500°F)  chrome p l a t i n g  interference  separating  .0010-.0015 the  reliability,  high  compression r a t i o  mechanical limit,the  f a c e must  remain  flat.  In  before  combustion  an a t t e m p t  to  d e t e r m i n e how a d v e r s e l y t h i s r e q u i r e m e n t would a f f e c t t h e heat t r a n s m i s s i o n , t h e p r o d u c t o f t h e exposed a r e a and t h e c a l c u l a t e d t e m p e r a t u r e d i f f e r e n c e between t h e w a l l and the  gas was p l o t t e d as a f u n c t i o n o f t i m e f o r a c o n v e n t i o n a l  power saw w i t h a c o n i c a l combustion chamber and a f r e e p i s t o n saw w i t h a f l a t combustion chamber.  A l t h o u g h com-  b u s t i o n was assumed t o o c c u r i n s t a n t a n e o u s l y a t a c o m p r e s s i o n r a t i o o f 7.4 i n b o t h e n g i n e s , t h e maximum c o m p r e s s i o n r a t i o i n t h e f r e e - p i s t o n engine i s a f u n c t i o n o f l o a d .  Temperatures  were t a k e n from T a y l o r ' s [3.1] graphs o f thermodynamic p r o p e r t i e s o f g a s o l i n e - a i r m i x t u r e s o r p r o d u c t s o f combustion at  r e a l i s t i c a i r - f u e l r a t i o s and p r o p o r t i o n s o f unburned  fuel. The r e s u l t , p l o t t e d on Graph 3.14, i n d i c a t e s t h a t because o f h i g h e r p i s t o n speeds i n t h e f r e e - p i s t o n e n g i n e , l e s s h e a t t r a n s f e r w i l l t a k e p l a c e i n t h e f r e e - p i s t o n engine as t h e c o m p r e s s i o n r a t i o goes up.  F o r example, i f t h e h e a t  t r a n s f e r c o e f f i c i e n t remains c o n s t a n t , then a t a c o m p r e s s i o n r a t i o o f 7.4 t h e h e a t t r a n s m i s s i o n from t h e f r e e - p i s t o n e n g i n e w i l l be about t h e same as from t h e c o n v e n t i o n a l e n g i n e , b u t a t a c o m p r e s s i o n r a t i o o f 22.4 t h e t r a n s m i s s i o n i n t h e f r e e - p i s t o n e n g i n e w i l l be h a l v e d because t h e power s t r o k e w i l l be completed i n much l e s s t i m e .  So a t p a r t l o a d , t h e  h e a t t r a n s f e r from t h e f r e e - p i s t o n e n g i n e s h o u l d be c o n s i d e r a b l y l e s s than from t h e c o n v e n t i o n a l e n g i n e .  20.0  TIME AFTER IGNITION  Graph 3.14  (MILLISEC.)  C a l c u l a t e d t h e r m a l l o s s e s from t h e combustion chambers  T e s t s performed by t h e a u t h o r [3.16] on t h e convent i o n a l engine  y i e l d e d t h e f o l l o w i n g o b s e r v a t i o n s when t h e  c o n i c a l combustion chamber was r e p l a c e d w i t h a f l a t one: 1. power went down 5-12%, 2. e x h a u s t temperature dropped,  201 3.  cylinder at  4.  high  head temperature  From the  results  the  transmission  a conical  the  equal  iron  it  limited  steels  of  was A I S I gears,  the  to  the  of  or  6150,  liners  leads results  rings  cation  than  from  weigh  the  same  a tough and  high  material  in  free  insufficient erratic  [3.21].  also  (ASTM  strength  fabricate  strength  a material  iron  are  of  would for  the  cast  80-002),  alloy  steels.  d e s c r i b e d on T a b l e  VII.  the  in  the  alloys.  piston rod  and rod  limited  The f i n a l  commonly u s e d f o r  the  choice  shafts,  pistons.  existing  to  cast  requirement  high  stroke  such as n o d u l a r  these metals  piston  a c c e l e r a t i o n s and r a p i d  point  engines  higher  piston  choice of  malleable  strength to  the  heavy metals  ( c l a s s N)  metals  In high  on s t a n d a r d  head i s  (so t h a t  d e c i s i o n w a s made t o  one p i e c e , choice  detonation  down.  a s s e m b l y was t o  stroke),  The c h a r a c t e r i s t i c s  the  piston  (ASTM 1 0 0 - 7 5 - 0 4 ) ,  nitriding  This  from a f l a t  assembly  cylinder  was  When t h e  went  was c o n c l u d e d t h a t  the  cylinder the  piston  to  head. Since  as  (led  speeds),  scavenging efficiency  heat  went up  shorten  the  extremely  pressure changes near gas pressure under  "flutter"  High thermal ring  engines  life.  and e v e n t u a l  loading  the  top  rings.  breakage  and m a r g i n a l  The F o r d M o t o r  dead  of  lubri-  Company  202 Table V I I Materials Suitable for Pistons C^st. n l . ,-.lcn 14*  Foiled ..1.  Heriii. 1-IOJ.G ..lean 162  ..dTn i u 3 t - T o i (U)-35  TensiLe -.U:i:ngth (xio* )  Diecast i'JOOUiar .•iaile-ble hi tricing ftlcan I O U A C.i. N dOOOi .lid .oTri ai«.«,B 100-75-04 35  100-1^0  100  -  200-240  197-290  16  75-90  tiiO  190  315--8  180  «.70-108  U5  6Ci-ivl  3  stren tii  (x10~ )  6  8 .=. 500°F  lifeld strength  5.5 <i 500°F  80  149  <xl0~ ) 3  Density  .098  (lb/in ) 3  Uses  References  200-^40  95  HarullC:S3 (lirir.ell)  heavy uuty pistons & a i r cooled cylinder heads  pistons  3.17  3.19  pistons & cylinders  3.18  096  24I-269  .257  pistons con rods cylinders  gears, pistons  3.18  3.19  .265  .283  gears, diesel pistons  cylinder liners, bushings gears  3-19  3.19  shaf t i , i j tv !' J > 1  r  »::..!'t», b'-i:_i:. !i b  liners  [3.22] overcame t h i s problem o f r i n g f r a c t u r e and b u r n i n g by r e d u c i n g t h e p r e s s u r e  ( o r i g i n a l l y 4,000 p s i ) , c h a n g i n g  f u e l i n j e c t i o n t i m i n g , employing porous-chrome p l a t e d c y l i n d e r b o r e s , and u s i n g s t e e l i n s t e a d o f c a s t i r o n r i n g s . R i n g s c a n be made o f c a s t i r o n , s t e e l a l l o y s and compounded forms o f TFE f l u o r o c a r b o n .  C a s t i r o n r i n g s , used  e x t e n s i v e l y i n conventional p i s t o n engines, and  i f properly l u b r i c a t e d , give long t r o u b l e - f r e e s e r v i c e .  In t h e m a n u f a c t u r i n g oil  are inexpensive  process  t h e r i n g c a n be covered  w i t h an  a b s o r p t i v e c o a t i n g t h a t f a c i l i t a t e s r a p i d s e a t i n g and  203 retards  scoring  be p l a t e d scoring the  with  and  ring  tection  and tin  or  faces  For  scuffing made o f  have a low  require  lubrication.  no  the  with  they  tricities  of  bore  and i s  expander,  t e f l o n makes a good  leakage  to  without  a gap  thermal  expansion),  then  blowby.  This w i l l  reduce  the  air  metal to  a negligible  and i n c r e a s e the  contact  4,200  occurs.  showed t h a t  teflon  Sealing making the  the  this  at  rings with  headland  conventional  With to  the  change the  cylinder  head s e a l s  wall.  If  long  conforms against up t o the  iron  in  it  rings  part  of  the  Although  annulus the  Extending  for  into  metal-toat  1,800  [3.23] practical.  improved head  piston  ring  piston the  by and  ring.  [3.24]  the  the  L-shape permits  gas  reduce  tests  piston  top  between  metal  allow  before  S e a l e d Power C o r p o r a t i o n 50%.  eccen-  pollutants  c a n be  the  and  c a n b e made  seal w i l l  the  dry)  and r e d u c e s  g a s o l i n e engines were rings  are  a  Du P o n t L a b o r a t o r y  iron  compounded  the by  to  100 h o u r  area between  by  molybdenum  (0.4 to  ring  compression r a t i o  the  pro-  life,  500°F  discharge of  of  abrasion,  (teflon)  friction  continuous  the  ring),  have d e c r e a s e d blowby piston  seal  cast  the  cast  (the  top  forced  A number  rpm p e r f o r m e d  it  amount.  (necessary in  of  for  can  retard  for  sprayed with  materials  coefficient  and  against  chromium and  c a n be  Because  cylinder  seating  a TFE f l u o r o c a r b o n  s p e c i a l wear r e s i s t a n t  expensive,  induce  added p r o t e c t i o n  can be p l a t e d  against  A l t e r n a t e l y , the  cadmium t o  scuffing.  Rings with  scuffing.  claims up  to  and  compression-  204 gas  pressure  which the  the pressure  direct  ring  to effect acts  contact with  the l a r g e r area  over  increases the f r i c t i o n  f o r c e , and  high  raises the  temperature  gases  temperature. The  pre-tension design. not  a better seal,  gas p r e s s u r e  under  combine t o e f f e c t  To k e e p t h e r i n g  pressure smaller  drop  across  a good  and t h e i n t e r n a l i n the conventional  low s o t h a t s e t d o e s  the conventional  ring  i s placed  t h e h o t g a s a n d t o g e t an e q u a l  each r i n g ,  than the s k i r t  seal  temperature  remove t h e p r e t e n s i o n ,  some d i s t a n c e away f r o m  the ring  diameter.  the land diameter These  i s made  conventional practices  were f o l l o w e d  i n designing  t h e f r e e - p i s t o n power saw.  For  satisfactory  combustion  t o occur,  c h a r g e must be w e l l m i x e d , i n t h e c o r r e c t r a t i o stoichiometric  charge),  (14.6 f o r a  a n d b r o u g h t up t o i g n i t i o n  a t u r e by a f l a m e , a s p a r k , a h o t s p o t , pressure.  the a i r - f u e l  or a high  A lean mixture requires a higher  temper-  compression  ignition  temper-  ature. When t h e i n t a k e entering and  i s throttled,  the c y l i n d e r mixes w i t h  i s diluted.  the a i r - f u e l  the residual  F o r r a p i d and complete  or the i g n i t i o n  high.  engine  is the  enriched, charge  i n the s t r a t i f i e d  i n the v i c i n i t y  e n e r g y must be  the o v e r a l l  charge  mixture  engine the p o r t i o n o f  o f the spark plug  i s enriched  [ 3 . 2 5 ] , and i n t h e f r e e - p i s t o n e n g i n e t h e c o m p r e s s i o n is  automatically  increased.  gases  combustion, the  c h a r g e e n t e r i n g must be r i c h In the conventional  exhaust  charge  ratio  205 The type its  with  carburetor  a 3/8  pressure  specified  i n diameter v e n t u r i .  pulses  from the  i t s fuel  through a tube i n the  frame.  during  chamber was when t h e  was  given  the  engine.  the  fuel  stroke  increased  to designing In t h i s  [3.26].  a standard  a special  carburetor  But  the  hole  pick-up  flocking  restricts  t h e m u f f l e r was The  in.  the  fall  entrance  filter  onto the  designed  cap  device  between the and  screen  must  shop.  the  e x p o s e d p a r t s and  inside  the  hot  surface.  As  up  the  l a r g e carbon p a r t i c l e s ,  meter  initial  into by  the  the  carburetor retards  covered  and  flow  the  with  a  foreign  horizontally,  1010/1015 s t e e l  twigs  a purpose of  and  leaves  from  the m u f f l e r  t h e m u f f l e r was  sheet,  machining  r e c i p r o c a t i n g m o t i o n moves c o o l i n g a i r  on  the  filter.  f o r an A I S I  prevents  the  best.  carburetor  of d i r t  to  could  the  made o f aluminum, t o f a c i l i t a t e  the  handle-  Consideration  t a n k draws f u e l  placed  a  the c y l i n d e r  fitting  during  made o f w i r e  the  a i r e n t e r i n g the  Although  opening  t r a n s f e r to carburetor  air filter  so m a t e r i a l c a n n o t  i n the  t h o u g h t t o be  into  insulator block  An  3/4  carburetor  i n the  receives  through  c l o s e d by  a fluidic  c a r b u r e t o r was  felt  An  vapour-lock.  material;  tank  diaphragm  the magnitude of  for r e l i a b i l i t y  frame r e d u c e s h e a t  rayon  limit  to about  f r o m where i t i s pumped  diaphragm. and  To  carburetor  chamber  from the  part-load operation,  The lines  The  l o c a t e d so t h a t i t w o u l d be  cap  tests  a conventional  scavenging  t u b e i n t h e mount,and  pulses  was  in  over settling  i s to  break  constructed  so t h a t t h e escape o u t l e t was a t r i g h t angles port opening.  Carbon sparks  t o the exhaust  impinge d i r e c t l y a g a i n s t the  s i d e and t o p w a l l of the m u f f l e r and then work through the p e r f o r a t i o n s i n the screen t o the second chamber where they again  impinge on the w a l l o f the m u f f l e r b e f o r e working  through t h e second group of p e r f o r a t i o n s .  These impinge-  ments b r e a k the carbon p a r t i c l e s i n t o s i z e s t h a t w i l l n o t start a f i r e .  T h i r t y - s i x holes  (3/32 i n diameter) gave a  2 p e r f o r a t i o n area of .25 i n . T h i s completed the d e s i g n o f the important ponents.  I t was o f course  necessary  com-  t o d e s i g n the small  elements b u t t h e i r d e l i n e a t i o n was s t r a i g h t - f o r w a r d and w i l l not be d e s c r i b e d . F i g u r e 3.3 shows the f i n a l assembly l a y o u t . 3.4  F a b r i c a t i o n of Parts In t h e development o f a new concept as complex as  a two-stroke engine, m o d i f i c a t i o n s a r e n o t l i m i t e d t o the t h e o r e t i c a l design  stages.  Even d u r i n g the f a b r i c a t i o n  p r o c e s s many v a l i d m o d i f i c a t i o n s suggest themselves, some t o be  i n c o r p o r a t e d immediately and o t h e r s t o be i n c o r p o r a t e d i n  f u t u r e models.  The m o d i f i c a t i o n s can be grouped as f o l l o w s :  R - r e v i s i o n s t h a t s i m p l i f y f a b r i c a t i o n or improve performance, C - c o r r e c t i o n s t o d e s i g n or drawings, T - temporary changes t o make r e v i s e d p a r t s f i t e x i s t i n g components, t o accept machining and  208 c a s t i n g e r r o r s , and t o a l l o w f o r t h e i n s t r u m e n t a t i o n of t h e u n i t . 1.  (T) To g i v e t h e r i n g s a good b e a r i n g s u r f a c e w h i l e keepi n g t h e w e i g h t low, t h e i n i t i a l d e s i g n chrome p l a t i n g on t h e c y l i n d e r b o r e .  specified When an under-  c u t was a c c i d e n t a l l y made i n t h e b o r e so t h a t p l a t i n g was  no l o n g e r p o s s i b l e , t h e c y l i n d e r was m o d i f i e d t o  accept a c a s t i r o n sleeve. 2.  (T) The d i s t a n c e s from t h e tops o f t h e e x h a u s t h o l e s t o the t o p s o f t h e t r a n s f e r h o l e s  (blowdown) were  machined .050 and .085 i n i n s t e a d o f .100 i n . Because t h e t r a n s f e r p o r t s opened t o o soon, the- e x h a u s t gases f l o w e d i n t o t h e s c a v e n g i n g e f f i c i e n t scavenging.  volume and p r e v e n t e d  To c o r r e c t t h i s m a c h i n i n g  e r r o r , t h e low t r a n s f e r p o r t h e i g h t s and t h e e x h a u s t p o r t s were r a i s e d .080 t o g i v e a .100 blowdown.  The  m a c h i n i n g o p e r a t i o n i s shown on F i g u r e 3.4. 3.  (T) Because t h e p i s t o n s k i r t was t h e same w i d t h as t h e exhaust p o r t width, a small misalignment i n the angular  l o c a t i o n of the s k i r t r e s u l t e d i n a hole  between t h e s c a v e n g i n g  chamber and m u f f l e r .  s t e e l was used t o f i l l  the hole.  Plastic  4. (T) Because they a l l o w e d t h e i n s p e c t i o n o f t h e t r a n s f e r p o r t s , temporary removable  p l a t e s were s u b s t i t u t e d  f o r expansion plugs i n the t r a n s f e r port holes. the p r o c e s s  of d r i l l i n g the t r a n s f e r holes  the  In  d r i l l came t h r o u g h the m a t e r i a l so the a r e a b u i l t up w i t h w e l d m a t e r i a l .  was  A comparison of  the  wooden p a t t e r n w i t h the d r a w i n g r e v e a l e d an e r r o r i n the p a t t e r n .  F i g u r e 3.4  (C)  Photograph operation  When the mount was  of t r a n s f e r p o r t m a c h i n i n g  lengthened  by  d e s i g n change,the c o r r e s p o n d i n g i n a d v e r t e n t l y l e f t unchanged.  .050  rod length  blade.  Because p r o p e r s u r f a c e g r i n d i n g f a c i l i t i e s c o r r e c t i n g heat t r e a t m e n t a b l e , the p i s t o n r o d was  was  This error required  m a c h i n i n g c l e a r a n c e s l o t s f o r the (T)  i n during a  distortion accepted  for  were not  unhardened  avail(yield  s t r e s s 100,000 p s i i n s t e a d o f 200,000 p s i when hardened t o Rc 4 0 ) .  The  b l a d e s l o t was  machined  210 .132-.140 i n wide i n s t e a d o f t h e s p e c i f i e d t h e screw l o c a t i o n was o f f by about  .125 i n ,  .020 i n , and  t h e b l a d e s p i g o t was .120 i n d i a m e t e r and t a p e r e d i n s t e a d o f .125 i n and p a r a l l e l t o t h e b l a d e .  Con-  s e q u e n t l y , the saw b l a d e was n o t p a r a l l e l t o t h e p i s t o n r o d ( v a r i e d 1/2° t o 3°). from an e x i s t i n g saw b l a d e  The b l a d e was made  and screwed t o  a large  b a c k i n g p l a t e (made l a r g e t o b a l a n c e t h e w e i g h t o f the c y l i n d e r ) . 7.  (R) The o r i g i n a l d e s i g n f o r a t t a c h i n g t h e band t o t h e p i s t o n r o d c a l l e d f o r a m i l l e d s l o t on t h e r o d .  An  i n s p e c t i o n o f t h e completed r o d r e v e a l e d t h a t t h e s l o t s had n o t been machined p e r p e n d i c u l a r t o t h e r o d , t h e i n s i d e edge o f t h e s l o t had been machined convex and i r r e g u l a r , and t h e s l o t s were n o t c u t d i r e c t l y o p p o s i t e each o t h e r as s p e c i f i e d on t h e d r a w i n g . An a t t e m p t was made t o m a n u a l l y square t h e s l o t s b u t an i n s t a l l e d band f a i l e d a f t e r a few c y c l e s .  To r e c t i f y  t h e problem a new s l o t was m i l l e d a c r o s s t h e r o d b u t a g a i n t h e edge was n o t smooth, p e r p e n d i c u l a r n o r round.  Even an u n d e r c u t d i d n o t p r e v e n t a n o t h e r  band from f a i l i n g .  For the next attempt, spot faces  f o r dowels were e n d - m i l l e d a t t h e c e n t e r o f t h e s l o t . Even though t h e d r a w i n g s had s p e c i f i e d c l o s e  toler-  ances f o r t h e i m p o r t a n t s u r f a c e s t o p r e v e n t t h e p r e v i o u s problem from r e - o c c u r i n g , when c o m p l e t e d , one  spot  211 f a c e was machined i n a c c u r a t e l y .  The l o c a t i o n was  off  by .014 i n , t h e d i a m e t e r o f t h e same s p o t  was  l a r g e r by about .005 i n and t h e edge o f t h e  s p o t f a c e was 1° from t h e p e r p e n d i c u l a r . the p i s t o n , t h e d i a m e t e r o f t h e o f f e n d i n g f a c e was e n l a r g e d  t o t a k e a shim.  face  To s a l v a g e spot-  With t h i s m o d i f i -  c a t i o n , t h e attachment as shown on F i g u r e 3.5, p e r formed s a t i s f a c t o r i l y b u t t h e p i s t o n r o d had a number o f s h a r p edges and t h i n s e c t i o n s , s o i t f a i l e d when d r i v e n by a f i x e d - t h r o w 8. (R) A l t h o u g h  crankshaft.  t h e ends o f t h e f i r s t bands were bent i n t o  hooks w h i c h clamped o v e r t h e attachment p l a t e , most o f t h e l o a d was t o be c a r r i e d by f r i c t i o n when t h e band was squeezed between t h e a t t a c h m e n t p l a t e and the c y l i n d e r .  The r i v e t s l o c a t i n g t h e bands were  r e p l a c e d w i t h screws t o a l l o w d i s m a n t l i n g and t o i n c r e a s e c l e a r a n c e under t h e attachment p l a t e . 9. (R) When t h e n y l o n band was r e p l a c e d w i t h a s t e e l band, the r o l l e r d i a m e t e r was i n c r e a s e d t o g i v e a s m a l l c l e a r a n c e between t h e p i s t o n r o d and r o l l e r ( t o stop a  p i s t o n from t w i s t i n g ) and t o keep band  t e n s i o n constant throughout the s t r o k e . 10.  (T) When t h e f i r s t s p r i n g s were t e s t e d , t h e s p r i n g r a t e s , i n s t e a d o f b e i n g 175 p p i as s p e c i f i e d , were o n l y 147  t o 150 p p i and o v e r s i z e .  When t h e s p r i n g s were  ground down t o t h e s p e c i f i e d s i z e , t h e r a t e had  212  F i g u r e 3.5  Photographs o f t h e s y n c h r o n i z i n g and mechanism a s s e m b l i e s  arresting  213 decreased to 140 p p i .  Consequently two back-up  s p r i n g s were designed to f i t i n s i d e the o r i g i n a l ones and a new  s e t of s p r i n g s were o r d e r e d .  edges of the s p r i n g ends were rounded  The  sharp  so t h a t the  bands would not be c u t and the flow path would be smoother.  The f i n a l t e s t engine used a double  under the p i s t o n  (K=158 and K=32 p p i ) and a s i n g l e  s p r i n g i n the c y l i n d e r 11.  (R)  The new  (K=190 p p i ) .  a r r e s t i n g mechanism, d e v i s e d when the r a c k  and p i n i o n arrangement  was  and r o l l e r arrangement  a f t e r the cover had  been c a s t , r e q u i r e d pushed  spring  a new  replaced  by the band  t r i g g e r assembly  i n s t e a d of p u l l e d , a n d some minor  already which  modifications  to the e x i s t i n g cover so the mechanism would f i t . 12.  (T)  Not u n t i l the a r r e s t i n g mechanism had been and t r i e d out was  assembled  i t e s t a b l i s h e d t h a t the l e v e r arms  to the s l i d e r were .100  i n shorter  drawing c a l l e d f o r , so new  than  the  ones were made.  When i t  became obvious t h a t the t e f l o n tape c o u l d not be bonded t o the s l i d e r w i t h the a v a i l a b l e epoxy, a bronze bushing was  brazed i n t o the s l i d e r .  s p r i n g s which p u l l e d the s l i d e r were doubled i n s i d e the o t h e r to conserve space. l e v e r s was  The one  A guide f o r the  added so t h a t the l a t c h remained  t o the p i s t o n rod w h i l e the engine was  parallel  running.  214  13.  (T) Because the c o v e r as r e c e i v e d from the  foundry  d i d not have s u f f i c i e n t m a t e r i a l on the bar f o r the mount, the r e q u i r e d m a t e r i a l was welding  and a h o l e was  d r i l l e d through t h i s  welded m a t e r i a l t o c o n n e c t the the  added by  fuel line with  carburetor.  A f t e r the f a b r i c a t i o n and m o d i f i c a t i o n s had  been  c o m p l e t e d , the p a r t s were assembled i n t o the complete f r e e p i s t o n power saw.  F i g u r e s 3.6  and  3.7  show the f i n i s h e d  p a r t s and t h e i r r e l a t i o n s h i p s t o each o t h e r . saw was  instrumented  completed  and put on a t e s t bench f o r c o n c e p t  e v a l u a t i o n , as d e s c r i b e d i n the n e x t  F i g u r e 3.6  The  chapter.  Photograph of a l l FPS  parts  215  F i g u r e 3.7  Photographs o f FPS components  216  4. 4.1  EVALUATION  Performance C h a r a c t e r i s t i c s o f t h e F r e e - P i s t o n Power Saw W h i l e t h e engine was b e i n g f a b r i c a t e d and t h e t e s t s  were b e i n g performed, to  t h e computer program was b e i n g r e f i n e d  a l l o w more a c c u r a t e r e p r e s e n t a t i o n o f engine  thermodynamics  and t o p e r m i t more c o n d i t i o n s t o be i n v e s t i g a t e d . ments l e d t o t h e f o l 3 o w i n g  The r e f i n e -  assumptions:  1. The p r e s s u r e i n t h e f i r s t r i n g groove i s e q u a l t o t h e c y l i n d e r p r e s s u r e and i n t h e second  r i n g groove t h e  pressure i s equal t o h a l f of the c y l i n d e r pressure, [3.1].  In a d d i t i o n t o the pressure forces, a constant  r i n g p r e - t e n s i o n f o r c e a c t s on t h e r i n g s 2. The combustion .068  e f f i c i e n c y below a f u e l / a i r r a t i o o f  i s c o n s t a n t a t 95% and above .068 i t d e c r e a s e s  l i n e a r l y w i t h the f u e l / a i r r a t i o of  .100.  No combustion  t o 54% a t a r a t i o  t a k e s p l a c e when t h e m i x t u r e  r a t i o i s below .05 and above .143 [4.1]. 3. The c o e f f i c i e n t ' o f f r i c t i o n d o u b l e s when t h e v e l o c i t y drops below 10 i p s . 4. The minimum volume a t t h e t o p end o f t h e s t r o k e when t h e p i s t o n touches t h e c y l i n d e r head i n c l u d e s t h e volume under t h e f i r s t r i n g , h a l f o f t h e volume under t h e second r i n g , t h e a n n u l a r volume between t h e p i s t o n  h e a d - l a n d and c y l i n d e r , h a l f o f t h e volume between the r i n g s , and t h e volume i n s i d e t h e glow p l u g . The damping c o e f f i c i e n t v a r i e s i n v e r s e l y w i t h t h e temperature a c c o r d i n g t o the f o l l o w i n g  r  =  ref  (ref Where  e  (T^pf-T^.  ).00356  txn  r e r  relationship:  changed from 2. a t 100°F t o .5 a t 500°F)  T r  e  f  T^^  reference temperature,  =  n  =  f i n temperature.  The o v e r a l l e f f e c t i v e r i n g gap a r e a v a r i e s i n d i r e c t proportion t o the thermal expansion: A  A  1  n  = (GAP + .28 x 1 0 ~  4  (DDI + .89 x 1 0 ~  5  1 2 effective = . . A  A  ( T . -T ,))-'x f i n ref £  (T... -T .)) fin ref  A  l  +  A  f o r t h e two r i n g s .  2  ( I f an aluminum p i s t o n and an aluminum c y l i n d e r i s used,the c l e a r a n c e between t h e p i s t o n and c y l i n d e r . (DDI) does n o t change.) Combustion s t a r t s when t h e gas t e m p e r a t u r e i n t h e c y l i n d e r r e a c h e s a p r e - s e t v a l u e o r when t h e p i s t o n comes w i t h i n a p r e - s e t d i s t a n c e from t h e head, and continues a t a pre-set rate  (based on t h e speed and  218 the amount o f c o m b u s t i b l e m i x t u r e p r e s e n t ) u n t i l a l l a v a i l a b l e f u e l has i g n i t e d o r u n t i l t h e p r e - s e t d e t o n a t i o n temperature i s reached.  As soon as t h e  d e t o n a t i o n t e m p e r a t u r e i s exceeded, t h e t e m p e r a t u r e increases very r a p i d l y .  The r a t e o f t e m p e r a t u r e  i n c r e a s e d u r i n g d e t o n a t i o n was chosen t o g i v e complete combustion i n t h e c o n v e n t i o n a l e n g i n e d u r i n g a 3° c r a n k r o t a t i o n  [4.1].  8. J a k l i s h ' s heat t r a n s f e r e q u a t i o n s r e p r e s e n t t h e . amount o f h e a t t r a n s f e r r e d cylinder,  [ 4 . 2 , 3.13],  (1 + .0063 C a  from t h e gas t o t h e  )  =  3  .0001685 Q = a (2rr \ (52^1) « 2 Where  +  r )]  2 P  T C  TTBORE X )  *  ^  C  (Tcy-T f _. i n )/144 [ B t u / h r ]  C = mean  mean p i s t o n speed  BORE  =  p i s t o n diameter  (inch),  x  =  piston position  (inch),  =  cylinder pressure (psi),  =  c y l i n d e r gas t e m p e r a t u r e (°F).  T  9. The amount o f h e a t t r a n s f e r r e d  (fpm),  from t h e c y l i n d e r t o  the c o o l i n g a i r i s g i v e n by t h e f o l l o w i n g f o r m u l a w h i c h had been d e t e r m i n e d e x p e r i m e n t a l l y :  Q = A . f  n  (1.48 + .00257 ( S p e e d ) *  (T . -T ) [Btu/hr] t i n atm f  9 8 5  i^^) ' 1  4 7 1  )  219 Where  A Speed  2 = f i n area ( f t ), = e n g i n e speed (cpm),  X„ max  = pc i s t o n pc o s i t i o n a t BDC  f  T  atm  (inch),  ^ k i e n t t e m p e r a t u r e (°F),  =  T fin  = f i n t e m p e r a t u r e (°F).  10. The f i n t e m p e r a t u r e i s based on an energy b a l a n c e between t h e h e a t t r a n s f e r from t h e gases the  (including  h e a t produced by f r i c t i o n ) and t h e h e a t t r a n s -  f e r r e d t o the cooling a i r . 11. M a c k e r l e ' s [3.13] e x p e r i m e n t a l l y d e r i v e d f l o w c o e f f i c i e n t s are v a l i d f o r the flow through the p o r t s , (C=0.5).  P e r f e c t m i x i n g o c c u r s and t h e f l o w i s  g i v e n by t h e f o l l o w i n g e q u a t i o n s : (a)  for sub-critical  W  f  f  44  = .923 C A r e a  (b) f o r c r i t i c a l  W  flow  flow  I .58  = .923 C A r e a up,  Where s u b s c r i p t s "up" and "dn" r e f e r t o upstream and downstream 12. The f o l l o w i n g f o r c e s a c t on t h e p i s t o n and c y l i n d e r : (a) Gas f o r c e s due t o p r e s s u r e s i n t h e c y l i n d e r and i n t h e p r e c o m p r e s s i o n chamber (= A^ ^ c y ~ ^ p c ^ ^ *  220 (b) R i n g f r i c t i o n f o r c e due t o r i n g p r e t e n s i o n and gas p r e s s u r e under t h e r i n g s  (= y £  p C  y  A  {-^p~}  + r  K} r]>+F  (c) Load on t h e b l a d e  (= F ^ ) . F  (d) F r i c t i o n f o r c e due t o l o a d i n g f o r c e ,  l  (= yy-) •  (e) S p r i n g f o r c e (= k X ) . The  force equation i s : (P-P ) A - y (J P A + F + cy pc p 2 cy r r A P  —  P cy  p i s t o n area  I- F J 2  - kx  1  (in^),  c y l i n d e r gas p r e s s u r e  (psi),  =  precompression  =  c o e f f i c i e n t of f r i c t i o n ,  =  p i s t o n r i n g area  =  ring pretension force ( l b ) ,  =  l o a d on b l a d e ( l b ) ,  k  =  spring rate  X  =  piston stroke ( i n ) .  p y  pc  A F  r r  F  l  gas p r e s s u r e  (psi),  (in^),  (ppi),  Performance c h a r a c t e r i s t i c s d u r i n g p r e l i m i n a r y t e s t s were o b t a i n e d from t h e p r o t o t y p e w h i c h was i n s t r u m e n t e d w i t h a c r a n k c a s e p r e s s u r e t r a n s d u c e r , a c y l i n d e r head a c c e l e r o m e t e r , a c y l i n d e r head thermocouple, i n d i c a t i n g mechanism.  and a p h o t o - e l e c t r i c  position  T h i s mechanism c o n s i s t e d o f a l i g h t  s o u r c e and a p h o t o - e l e c t r i c c e l l and was mounted so t h a t t h e b l a d e p o s i t i o n determined  t h e amount o f l i g h t r e a c h i n g t h e  221 cell.  When t h e s t a r t - s t o p t r i g g e r was pressed, a c o n t a c t  s w i t c h t r i g g e r e d an o s c i l l o s c o p e w h i c h d i s p l a y e d t h e p i s t o n p o s i t i o n as a f u n c t i o n o f t i m e .  Photographs o f t h e i n s t r u -  mented assembly a r e shown on F i g u r e 4.1. T e s t s w i t h o u t f u e l b u t w i t h o i l on t h e c y l i n d e r w a l l i n d i c a t e d t h a t t h e c o e f f i c i e n t o f f r i c t i o n and r i n g l e a k a g e was h i g h .  E x p e r i m e n t a l p i s t o n p o s i t i o n s and  case p r e s s u r e t r a c e s  crank-  shown on Graph 4.1 were compared w i t h  t h e computer c a l c u l a t e d r e s u l t s shown on Graph 4.2. Computed r e s u l t s were o b t a i n e d by u s i n g measured engine whenever p o s s i b l e . determined  Parameters  parameters  n o t e a s i l y measured were  by r e p e a t e d l y comparing t h e computed r e s u l t w i t h  the t e s t r e s u l t s .  Some o f t h e parameter v a r i a t i o n s a r e  shown on Graph 4.3. The p r o c e d u r e  led t o the f o l l o w i n g  important observations: 1.  The amount o f l e a k a g e from t h e c y l i n d e r i n f l u e n c e d t h e f i n a l stopped p i s t o n p o s i t i o n . (An e f f e c t i v e 2 gap a r e a o f . 0005 i n c o r r e l a t e d t h e computed p i s t o n p o s i t i o n s with the f i r s t t e s t data. Since the 2 y  c a l c u l a t e d r i n g gap a r e a was .0001 i n t h e amount of  l e a k a g e over t h e r i n g s was f o u r t i m e s h i g h e r than  t h e amount o f l e a k a g e t h r o u g h t h e r i n g gaps.  As t h e  r i n g s wore i n , t h e e f f e c t i v e gap a r e a d e c r e a s e d ) . 2. The c o e f f i c i e n t o f f r i c t i o n i n f l u e n c e d t h e number of  c y c l e s b e f o r e t h e p i s t o n motion  stopped.  (A  f r i c t i o n c o e f f i c i e n t o f .55 c o r r e l a t e d t h e computed values"with the t e s t observation.)  222  Figure 4.2  Photograph of the FPS with a fixed-throw crankshaft  223  •  ( T h r o t t l e open, top curve-position bottom-cyl.acc. (ref.-20g/div)  DThr. p a r t l y open c y l i n d e r greased bot.-cyl. accel. (lOOg/div)  B T h r o t t l e open bot.-scav.press (ref.=5psi)  CThrottle closed bot.-scav.press. ref.=5psi)  E T h r . p a r t l y open cylinder greased bot.-cyl. accel. (lOOg/div)  pThrottle  Note:  HThrottle bot.-cyl.  R e f e r e n c e l i n e s fot increments. Time  Graph  4.1  Prototype  bot.-cyl. accel (lOOg/div)  IilNllll  P| G T h r . p a r t l y open cylinder greased bot.-scav. press  closed  JBMH Will fUf.  I closed accel.  | Thr. partly  bot.-cyl. accel. (lOOg/div)  p o s i t i o n t r a c e s a r e i n 1/4 = 20 m i l l s e c / d i v  engine  test  open  traces  in  224  Of iv i \ i \ f \ i i  co o  .58—f  o CO  CO  < U ^ Z <  DC O  o  LU  DC ZD CO CO  LU  (X  CL  *  °I  1  r  a.  o  20  40  60  TIME (MILLISEC) Graph 4.2  P r o t o t y p e engine t r a c e s combustion  (computed) w i t h o u t  G r a p h 4.3  Effect traces  of leakage, (computed)  friction  and damping  on  .Of •  TEST  TRACE  (GRAPH  4 .1-G)  •  TEST  TRACE  (GRAPH  4 .1-E)  A I R -•FUEL  IN  CYLINDER  AIR- FUEL  IN  PRECOMP. C H .  AIR- FUEL MIXTURE  (AF ) =  18 .8  C  SUPPLIED  (AF ) =  500  p  (AF ) S  =  8.5  u r =.05 A g a p =.0001 Aleak=.003 -TRANSFER  EXHAUST  4  Prototype engine combustion  position  traces  (computed)  with  227 3. The amount o f leakage from t h e p r e c o m p r e s s i o n  chamber  i n f l u e n c e d t h e chamber p r e s s u r e and t h e r a t e o f 2 decay. was  (The deduced l e a k a g e a r e a was .006 i n w h i c h  e q u i v a l e n t t o a c l e a r a n c e o f .001 i n on a l l s l i d -  ing surfaces.) 4. The amount o f damping i n f l u e n c e d t h e shape o f t h e stroke-time curve. (The deduced damping c o e f f i c i e n t 2 2 was .05 sec - l b / i n ) . O r i g i n a l l y o n l y a few combustion c y c l e s c o u l d be o b t a i n e d from t h e t e s t engine,as  shown e a r l i e r on Graph 4.1,  and t h e n o n l y when s t a r t i n g f l u i d was i n j e c t e d i n t o t h e cylinder prior to a start.  Nevertheless,important  deductions  were made by comparing t h e engine t r a c e s w i t h t h e computed r e s u l t s , as shown on Graph 4.4. as  Some o f t h e d e d u c t i o n s a r e  follows: 1. When t h e i g n i t e d a i r - f u e l r a t i o was a p p r o x i m a t e l y s t o i c h i o m e t r i c o r when t o o much energy was p u t i n t o the s p r i n g , the p i s t o n h i t the t o p o f the c y l i n d e r head,  Graph 4.1 E.  2. When t h e c y l i n d e r m i x t u r e was r i c h , two combustion c y c l e s o c c u r r e d ; when t h e m i x t u r e was v e r y r i c h , t h e second c y c l e r e l e a s e d more energy t h a n t h e f i r s t , Graph 4.1 H. 3. When t h e c r a n k c a s e c o n t a i n e d a l e a n m i x t u r e and t h e c y l i n d e r c o n t a i n e d a r i c h m i x t u r e , t h r e e combustion cycles occurred.  228 4. When t h e c r a n k c a s e c o n t a i n e d a r i c h m i x t u r e and the c y l i n d e r a l s o contained a r i c h m i x t u r e , four o r f i v e combustion c y c l e s o c c u r r e d . When i t became o b v i o u s t h a t i n o r d e r t o f i n d t h e c o r r e c t a i r - f u e l r a t i o t h e e n g i n e had t o be r e c i p r o c a t e d c o n t i n u a l l y , a t h r e e - t h r o w ' c r a n k s h a f t was d e s i g n e d and fabricated.  The c r a n k s h a f t a l l o w e d t h e engine t o be d r i v e n  w i t h an e l e c t r i c motor a t a f i x e d s t r o k e so t h a t t h e c a r b u r e t o r c o u l d be a d j u s t e d and t h e r i n g s c o u l d be worn i n . The mechanism i s shown on F i g u r e 4.2. A f t e r t h e c a r b u r e t o r had been a d j u s t e d t o produce a c o m b u s t i b l e m i x t u r e , combustion took p l a c e c o n t i n u a l l y b u t n o t u n t i l t h e e n g i n e was c o o l e d w i t h an e x t e r n a l b l o w e r d i d t h e e n g i n e become s e l f - s u s t a i n i n g i n d e f i n i t e l y .  The use o f  the e x t e r n a l b l o w e r t o keep t h e f i n t e m p e r a t u r e low came about because t h e computer r e s u l t s had shown t h a t t h e u n c o o l e d e n g i n e would a t t a i n a f i n t e m p e r a t u r e o f 567°F i f d r i v e n externally.  The h i g h f i n t e m p e r a t u r e caused a l a r g e r i n g  gap, a low charge d e n s i t y and e a r l y i g n i t i o n .  Above a f i n  t e m p e r a t u r e o f 250°F t h e i n d i c a t e d horsepower  was l e s s t h a n  t h e f r i c t i o n horsepower by i t s e l f .  so t h a t t h e e n g i n e would n o t r u n  The d i s t r i b u t i o n o f energy as t h e f i n t e m p e r a t u r e  changes i s shown on Graph 4.5. The computed charge f l o w was v e r i f i e d e x p e r i m e n t a l l y by measuring t h e a i r f l o w s and e s t i m a t i n g c y l i n d e r  tempera-  229  .50 — 1  1  r<  DC CD  ^.40  Tc^j  P  FIRING-TEST DATA  O  NOT FIRING-TEST DATA COMPUTED NOT FIRING .,  •  "~ ™" ^» "» O """"""a—ff •  CD LU > < CJ CO  •  I  .  ,  1  CYLINDER TEMPERATURE ( ° F )  G r a p h 4.5  tures. are  The d a t a  Crank engine t e s t  i s given  i n Appendix V I I I  results  and t h e r e s u l t s  i n c l u d e d on t h e g r a p h . After  t h e c a r b u r e t o r had b e e n a d j u s t e d  a combustible  mixture,  replaced with  an o s c i l l a t i n g  synchronized  the piston  the s p e c i a l  t o produce  c r a n k s h a f t was moved and  crankshaft.  to the cylinder  The new and l a t e r  crankshaft allowed  230  Figure 4.3  Photographs of FPS with an o s c i l l a t i n g crankshaft (A) with a fixed-throw d r i v e crankshaft (B) d e t a i l s of connecting rod (C) Prony brake free from crankshaft flywheel (D) Prony brake loaded (E) general view i n free-piston configuration (F) manual s t a r t i n g with wrench  the s p r i n g to be pre-compressed manually. the c r a n k s h a f t and  connecting  o p e r a t i n g frequency The  new  A s i d e e f f e c t of  rod masses was  from 4,200 cpm  c r a n k s h a f t was  to 2,500  to reduce the cpm.  o s c i l l a t e d with the  original  crankshaft-motor mechanism or precompressed manually w i t h a wrench  (Figure 4.3).  When the wrench was  suddenly removed  the s p r i n g was  f r e e to d r i v e the p i s t o n through i t s compres-  sion strokes.  Because the s t r o k e s were no  by a c r a n k s h a f t , t h e  longer c o n t r o l l e d  engine o s c i l l a t e d on the f r e e - p i s t o n  p r i n c i p l e as o r i g i n a l l y designed,  although  a t a lower  quency because the c r a n k s h a f t and  connecting  fre-  rods i n c r e a s e d  the o s c i l l a t i n g masses. A Prony brake w i t h a l e a t h e r f r i c t i o n s u r f a c e added to the frame so t h a t the o s c i l l a t i n g be  loaded  the blade  crankshaft  could  f o r power t e s t ,  as shown on F i g u r e 4.3.  i n an a c t u a l saw  would be loaded o n l y d u r i n g i t s  o u t s t r o k e , the Prony brake a p p l i e d a l o a d t o the flywheel  was  (diameter  = 2.5  i n , crank throw = .75  i n s t r o k e as w e l l as d u r i n g the Experimental  Although  crankshaft  in) d u r i n g  the  outstroke.  p o s i t i o n traces during  c o n d i t i o n s are shown on Graph 4.6.  l o a d and  no-load  Several t y p i c a l piston  p o s i t i o n s a t the end  of the s t r o k e and  shown on Graph 4.7.  The  the computed t r a c e s are  lower curve on the graph shows what  e f f e c t a i r - f u e l r a t i o v a r i a t i o n has on the p i s t o n p o s i t i o n . The  t e s t engine t r a c e s o f Graph 4.6  the engine s t a r t e d and ran when  indicate that  the e q u i v a l e n t of a 7.4  lb  232  A,NO  D. NO  LOAD  LOAD  G. LOAD  J.  NO  =  4.5 L B  LOAD  Note:  Graph  B. LOAD  =  1.6 L B  C . LOAD  =  13.7 L B  E . LOAD  = 1.6 L B  F . LOAD  =  4.2 L B  H. LOAD  = 7.4  I . LOAD  =  13.7 L B  K. NO  Reference Time base  4.6  LB  LOAD  L . NO  LOAD  l i n e s a r e i n 1/4 i n i n c r e m e n t s . = 50 m i l l i s e c / d i v  Experimental  engine  test  position  traces  233 ^  ^  ^  r  A  T E S T T R A C E (GRAPH 4 . 6 - j ] f / \ j p O LOAD YL~ II IIAAIIRR--FFUU E LL~ C Y L . " ( A F T = ""7.6 7 . 6 / 1 7.6 I _/ A I R - F U E L P.C. ( A F ) = 7.6 \ » M R - F U E L CARB ( A F ) = = 11 33..22 / I C  P  :  co o  ',/  \;  w  './  ^ HEAD-J  ^  | / |  INTAKE . J »  / /  | • \  W H- . , t Ei HA UST  O r— CO  r to I—I  .30 y r = .09 A g a p = .0001 A l e a k = .007  \  i  a II  o  y>—«  CO  o a. o  rCO  o — I I—t  co o  CL  —\ o  r— CO 1—4  1.0fr-  CL  0.1 TIME ( S E C ) Graph  4.7  Experimental  engine  position  traces  (computed)  234 load  (.05  bhp)  when a 13.7  was  a c t i n g on the saw  l b load  (.10  bhp)  was  blade but  acting.  were v e r i f i e d by the computed r e s u l t s .  stalled  These r e s u l t s  What the computed  r e s u l t s do not show i s the s p o r a d i c type of combustion i n g p l a c e d u r i n g the slow speed o s c i l l a t i o n . program assumed i d e a l c a r b u r e t i o n . o p e r a t i o n can be e x p l a i n e d 1. The with  operating  e t i o n was  poor:  i z a t i o n was  computer  sporadic  engine  as f o l l o w s :  speed was  the e x i s t i n g  The  The  tak-  j u s t above i d l i n g  so t h a t ,  large-throat carburetor, a i r - f u e l f l u c t u a t e d and  incomplete.  carbur-  vapor-  T y p i c a l power saw  engines 3  a t t h i s speed have s i m i l a r problems engine produced o n l y  .1 bhp  (A 4.2  a t 2,300 rpm,  in [2.47]).  2. A good combustion c y c l e r e l e a s e d enough energy to f o r c e the p i s t o n a g a i n s t the c y l i n d e r head.  The  impact o f t e n absorbed enough energy t o stop  the  engine. 3. The  f r i c t i o n and damping c o e f f i c i e n t s were h i g h .  4. The  amount of leakage p a s t the r i n g s was  (the gap  area a t room temperature was  whereas the designed  area was  very  .0001 2  high; 2  in  .00001 i n ).  5. I g n i t i o n d i d not s t a r t a t the optimum p i s t o n p o s i t i o n . The  p o i n t at which i g n i t i o n s t a r t e d depended on  c y l i n d e r head temperature, on the composition the f u e l  (mainly on the amount of s t a r t i n g  of  fluid  the  235 p r e s e n t and what f u e l was u s e d — e n g i n e  r a n on d i e s e l  f u e l , w h i t e g a s , r e g u l a r gas and g l o w - p l u g engine f u e l ) , and on the amount o f energy s u p p l i e d t o the glow-plug.  C o n s e q u e n t l y the i n d i c a t e d horsepower  v a r i e d from c y c l e t o c y c l e and from t e s t t o t e s t . Some o f the a f o r e m e n t i o n e d drawbacks t o good e n g i n e performance w i l l a l s o be p r e s e n t i n t h e r e d e s i g n e d e n g i n e . I t w i l l be d i f f i c u l t t o know what m i x t u r e the c a r b u r e t o r i s p r o d u c i n g u n l e s s t h e engine i s a l r e a d y r u n n i n g .  U n l i k e the  c o n v e n t i o n a l e n g i n e where q u i t e a few r e v o l u t i o n s o c c u r when the  e n g i n e i s s t a r t e d , t h e p r e s e n t f r e e - p i s t o n e n g i n e has a  maximum o f seven c h a r g i n g c y c l e s per s t a r t i n g a t t e m p t an i n i t i a l s t r o k e o f 1.9  i n ) . F o r example,with an  (from  initial  a i r / f u e l r a t i o of 100:1 and w i t h t h e c a r b u r e t o r c o r r e c t l y a d j u s t e d , a t l e a s t two s t a r t i n g a t t e m p t s w i l l be r e q u i r e d b e f o r e t h e m i x t u r e i n the c y l i n d e r i s i g n i t a b l e . the  But because  f r e e - p i s t o n engine always r u n s a t f u l l speed and t h e  b l e e d p o r t charge r e c i r c u l a t e s t h r o u g h t h e c a r b u r e t o r , t h e a i r v e l o c i t y i n t h e c a r b u r e t o r t h r o a t w i l l always be h i g h . C o n s e q u e n t l y m i x i n g and v a p o r i z a t i o n i n a p r o p e r l y matched c a r b u r e t o r w i l l be good. Initial  i g n i t i o n of a c o m b u s t i b l e charge s h o u l d  p r e s e n t no problem because t h e i n i t i a l c o m p r e s s i o n r a t i o i s very high.  F o r example, i f t h e e n g i n e i s s t a r t e d from an  i n i t i a l s t r o k e o f 1.90  i n , the f i r s t c o m p r e s s i o n r a t i o  be 55:1 and t h e gas t e m p e r a t u r e w i l l be 1,800°F.  will  I f the a i r  236 temperature sion  is  40°  temperature  below  will  Another  c a u s e d by  3 lb  oscillating  hand-held (57 will  the  vibration  lbs).  When h e l d  are  instead  used,the  of  60°F,  the  compres-  1200°F. of  the  prototype  unidirectional  at  against less.  of  .04  in  a bucking If  amplitude  two  saw w i l l  cutting  6 , 4 00 c p m w i l l  amplitude  be c o n s i d e r a b l y  blades  be  drawback  vibration unit  zero  have at  A  peak-to-peak  full  load  the  amplitude  counter-oscillating  c a n be r e d u c e d  the  action.  a  spike  be  to  a  saw  negligible  amount. The to  running  be  less  curve to  lack  the  blade  the  handle  is  less  is  from  although  a  these  number  concept.  of  or  the  has  if  the  more  excessive.  before  section.  store  engine  required  engine  engine  the  will  be  a flat frame  and the  energy.  stalling  or  blade  the  the  c a n be  fully  c o n c l u s i o n s c a n be drawn  These c o n c l u s i o n s  are  given  frame  will  about the  will  will on be  evaluated,  in  If  through  friction  work  designed  load.  The a c c e l e r a t i o n unless  will  is  applied  load,  More development  drawbacks  deterrant  power-versus-stroke  load  permissible  a  The d r a w b a c k  maximum p e r m i s s i b l e  object  than  protection  maximum p o w e r .  than  a solid  and  the  saw b l a d e  the  no more  hits  accelerate prevent  if  at  maximum p o w e r ,  transmit  the  overload  engine  critical  near  of  the next  the  4.2  Conclusions The performance d a t a of the t e s t engine, the p r e -  d i c t e d v a l u e s o f the p r o t o t y p e , and the p r e d i c t e d v a l u e s of a r e d e s i g n e d engine  are l i s t e d i n T a b l e V I I I .  The i n c r e a s e d  Table VIII Performance C h a r a c t e r i s t i c s o f FPS Computed  Data  Prototype  Test Engine  Values Redesigned  S h a f t horsepower (shp)  .05  .50  1.00  Maximum l o a d (lb)  ±7.4  35  57  U n i t weight (lb)  10  6  3  2500  4700  6400  F u e l consumption (lb/shp-hr)  -  0.95  0.90  P i s t o n diameter (in)  1.25  1.25  1.25  Blade s t r o k e (in)  .5-1.0  .5-1.0  .7-1.3  Speed  (cpm)  S p r i n g c o n s t a n t (ppi)  95  95  95  Overload p r o t e c t i o n  none  none  i f required  Ignition  glowplug  glowplug  proximity plug  Fuel  gasether  multifuel capacity  Oil  with fuel  with fuel  none  Throttle  open  none  none  Carburetor  floattype  conventional diaphragm  integrated diaphragm  Vibration Noise  levels  levels  Starting  below damage l e v e l i n range of t y p i c a l instantaneous,  saws  effortless  238  power o f speeds and  a  the  redesigned  engine  ( s m a l l e r p i s t o n mass), lower larger  area  The shown by  f o r the  simplicity  of  the  t h e p h o t o g r a p h s on  c o m p o n e n t s o f t h e FPS fan,  throttle  free  piston principle The following  1.  No  Figure  saw  will  i n less  the  starter  with  fewer assembly,  advantage of  the  saw. because of"  on  the  than  .01  top  and  to start an  starting  the  stopping  saw  the  and  will  motionless and  treacherous blade.  The  feature enables  after  awkward p o s i t i o n  A  a moving b l a d e  bottom o f the  n e c e s s i t y of handling  hazardous  sec.  a moving c h a i n w i t h  operator into  and  i s r e l e a s e d , the blade  i s o b v i o u s l y s a f e r than  effortless  the  system,  when s t a r t i n g  instant,  it  power saw,  safer to operate  trigger  much s a f e r t h a n  2.  be  is  characteristics:  motionless  teeth  temperatures,  When compared  show t h e  i n a power  Once t h e  blade  4.4.  blade  reed valves)  new  cylinder  operating  f r e e - p i s t o n power saw  (no i g n i t i o n  time-lag occurs  saw. be  and  to higher  intake port.  a conventional reciprocating  the  i s due  he  has  so  f r e e s him  the  manouvered from  a d a n g e r o u s weapon i n a  situation.  Throttling'is  automatic.  operator w i l l  not  be  T h i s means t h a t  concerned  about the  speed d u r i n g p a r t - l o a d o p e r a t i o n s .  the engine  239  conventional b l a d e saw  free-piston power saw  SUB  ASSEMBLIES  NOT REQUIRED reed  valve  starter throttle magneto spark plug fan ( c r a n k s h a f t and connecting rods n o t shown) - REQUIRED cover carburetor b l a d e , p i s t o n and c y l i n d e r assembly f u e l tank and  pickup  muffler igure 4.4  Photographs o f c o n v e n t i o n a l power saw and t h e FPS  3. I f t h e engine  s t a l l s suddenly d u r i n g an o v e r l o a d ,  some a c c i d e n t s w i l l be p r e v e n t e d A l t h o u g h t h e exhaust  o r reduced.  n o i s e l e v e l s from t h e f r e e -  p i s t o n engine w i l l be about t h e same as from a c o n v e n t i o n a l engine w i t h a s i m i l a r m u f f l e r , t h e n o i s e caused by s t r u c t u r a l v i b r a t i o n s w i l l be l o w e r f o r t h e f o l l o w i n g 1. S i n c e t h e engine  reasons:  i s balanced, the v i b r a t i o n ampli-  tude o f t h e frame w i l l be l o w e r . 2. S i n c e no c r a n k s h a f t i s u s e d , t h e amount o f p i s t o n s l a p and b e a r i n g n o i s e i s r e d u c e d . 3. S i n c e t h e c y l i n d e r i s s h o r t and s t i f f and t h e t r a n s mitted forces are mainly l o n g i t u d i n a l , lateral vibration w i l l  little  occur.  4. S i n c e no f a n i s r e q u i r e d , aerodynamic n o i s e i s reduced. 5. S i n c e a b l a d e and n o t a c h a i n i s u s e d , t h e c h a i n and s p r o c k e t n o i s e s a r e e l i m i n a t e d . A l t h o u g h t h e p r o t o t y p e engine  i s self-sustaining  and has produced a p o s i t i v e o u t p u t , more development work i s r e q u i r e d b e f o r e i t can produce t h e s p e c i f i e d power. The  f o l l o w i n g d e s i g n s t e p s c o u l d be f o l l o w e d : 1. R e d e s i g n at  p i s t o n head t o reduce t h e c l e a r a n c e volume  the top of the s t r o k e .  T h i s r e d u c t i o n can be  a c h i e v e d by u s i n g r i n g s w i t h s m a l l e r gaps and by  241 r e d u c i n g the volume under the r i n g s , between t h e p i s t o n headland and c y l i n d e r  l i n e r , and i n t h e glow  plug. 2. D e s i g n an i g n i t i o n system f o r a p r o x i m i t y - t y p e s p a r k plug. 3. R e d e s i g n t h e s y n c h r o n i z i n g and a r r e s t i n g to s i m p l i f y  mechanism  t h e d e s i g n , t o reduce t h e number o f  components, and t o p e r m i t the use o f a l i g h t aluminum piston. 4. D e s i g n a f u e l m e t e r i n g system f o r a s m a l l t a n k and so reduce t h e s p e c i f i c f u e l  propane  consumption  and t h e amount o f p o l l u t a n t s i n the e x h a u s t g a s e s . 5. R e d e s i g n engine t o i n c o r p o r a t e s p a r k i g n i t i o n , t o i n c o r p o r a t e a gaseous f u e l m e t e r i n g system, t o r e duce t h e frame w e i g h t , and t o a l l o w f o r e c o n o m i c a l manufacture.  4.3  Summary The d e s i g n e n v e l o p e f o r the power saw was  based  on e x p e r i m e n t s , p u b l i s h e d i n f o r m a t i o n , q u e s t i o n n a i r e s , and p r a c t i c a l experience. ing  E x p e r i m e n t s were performed on  saws t o d e t e r m i n e optimum c u t t i n g  vibration  and n o i s e l e v e l s .  a l l o w a b l e n o i s e and v i b r a t i o n and e n g i n e e r i n g p a p e r s .  speeds and  exist-  typical  These l e v e l s were compared w i t h levels published i n medical  The s p e c i f i c a t i o n s  f o r a spark  242 a r r e s t o r d e s i g n was  based on government r e g u l a t i o n s .  The  optimum s i z e and d e s i r e d o p e r a t i n g c h a r a c t e r i s t i c s were based on a q u e s t i o n n a i r e d i s t r i b u t e d t o power saw u s e r s and personal experience engineer  g a i n e d w h i l e employed as a r e s e a r c h  w i t h a c h a i n saw  with a logging The  on  company and as a c h a i n saw  operator  firm. c u t t i n g speed t e s t s produced d a t a on the  effect  o f c h a i n p i t c h , wood t y p e , s p r o c k e t s i z e , " b i t e " d e p t h , b a r l e n g t h , g e a r r e d u c t i o n and energy r e q u i r e d .  speed v a r i a t i o n on the  C a l c u l a t i o n s based on the  specific  experimental  r e s u l t s showed t h a t f o r hemlock the minimum s p e c i f i c energy 2 r e q u i r e d was 1,600 i n - l b / i n , and f o r maple the energy r e 2 q u i r e d was  3,700 i n - l b / i n . V i b r a t i o n l e v e l t e s t s showed t h a t the  amplitudes  o f e x i s t i n g saws v a r i e d from .013  that f o r continuous  saw  vibration  t o .030  i n , so  o p e r a t i o n the v i b r a t i o n c o u l d cause  damage t o the v a s c u l a t u r e o f the hands.  The  noise  t e s t s a l s o showed t h a t f o r l o n g term exposure  level  the n o i s e  cause h e a r i n g impairment ( t y p i c a l l e v e l s were about 105 The  dBA).  second d e s i g n stage c o n s i s t e d of an e v a l u a t i o n  of a v a i l a b l e energy s o u r c e s devices.  could  I t was  concluded  and an a n a l y s i s o f wood c u t t i n g t h a t of the e n g i n e s  considered,  the i n t e r n a l combustion e n g i n e b u r n i n g h y d r o c a r b o n f u e l s had one  o f the l o w e s t weight/power r a t i o s , and  that  had one  o f the l o w e s t s p e c i f i c power r e q u i r e m e n t s .  shears Although  q u i t e e f f i c i e n t , shears are n e v e r t h e l e s s heavy so t h a t t h e  243 conventional  saw  The  b l a d e was  chosen as the c u t t i n g  s y n t h e s i s o f new  device.  e n g i n e arrangements s t a r t e d  w i t h an a n a l y s i s o f problem a r e a s i n e x i s t i n g e n g i n e s produced t h r e e new  e n g i n e c o n f i g u r a t i o n s , one  t o produce r o t a r y m o t i o n and r e c i p r o c a t i n g motion.  The  and  of w h i c h  was  the o t h e r two were t o produce  rotary configuration  consisted  of a p i s t o n b o u n c i n g i n a r o t a t i n g c y l i n d e r so t h a t  the  w e i g h t of the p i s t o n caused the c y l i n d e r t o t u r n ; t h i s e n g i n e was  not d y n a m i c a l l y  stable.  The  reciprocating  configurations  c o n s i s t e d o f a p i s t o n b o u n c i n g i n an o s c i l l a t i n g c y l i n d e r ; t h e s e e n g i n e s were s t a b l e i f the p i s t o n and synchronized.  I t was  c y l i n d e r were  n e c e s s a r y t o r e p r e s e n t the dynamics  o f a l l t h r e e c o n f i g u r a t i o n s by two  coupled non-linear  e n t i a l e q u a t i o n s b e f o r e t h e i r s t a b i l i t y c o u l d be  differ-  checked  w i t h the a i d of a computer. I n the c o n f i g u r a t i o n f i n a l l y c h o s e n , the o s c i l l a t e d between gases i n one  end  m e c h a n i c a l s p r i n g i n the o t h e r .  o f the c y l i n d e r and  c o o l i n g and  self-cooling.  b a l a n c e d and  i t was  To d e t e r m i n e the amount o f  The  cylinder  data indicated that  h e a t t r a n s f e r from a c y l i n d e r head i n c r e a s e d 6 over f r e e convection  when a c y l i n d e r .was  a s t r o k e o f 1.375  1  (Re  self-  n e c e s s a r y t o o b t a i n heat t r a n s f e r  c o e f f i c i e n t s experimentally.  .082  was  the  the s i z e of f i n s r e q u i r e d t o p r e v e n t the  from o v e r h e a t i n g ,  a  Because the c y l i n d e r  a l s o f r e e t o o s c i l l a t e , the e n g i n e was c y l i n d e r was  piston  the  by a f a c t o r o f  reciprocated  i n a t a speed of 3,000 cpm  (Nu = 10.8  with +  244 The  i n f o r m a t i o n f o r t h e p i s t o n s i z e and p o r t dimen-  s i o n s was o b t a i n e d  from an a n a l y s i s o f e x i s t i n g engine  p e r f o r m a n c e s and d i m e n s i o n s .  The a v a i l a b l e d a t a was a s s e m b l e d ,  c o r r e l a t e d i n terms o f u s e f u l d i m e n s i o n l e s s  p a r a m e t e r s , and  used i n c o n j u n c t i o n w i t h d e r i v e d s c a l i n g f a c t o r s t o p r o v i d e the n e c e s s a r y  dimensions f o r the p o r t s i z e s .  f o r the scavenging was  obtained  and b l e e d p o r t s  (for automatic  throttling)  from an a n a l y s i s o f t h e dynamic and thermo-  dynamic b e h a v i o u r  o f t h e proposed e n g i n e i n c o n j u n c t i o n w i t h  a computer program.  The d e s i g n o f t h e machine components  followed conventional techniques t h a t was e v a l u a t e d The  The i n f o r m a t i o n  and d e l i n e a t e d a p r o t o t y p e  t h e o r e t i c a l l y as w e l l as e x p e r i m e n t a l l y .  f i r s t a t t e m p t s a t s t a r t i n g t h e engine, a f t e r t h e  p a r t s had been made and assembled, produced o n l y a maximum of 5 s u c c e s s i v e combustion c y c l e s .  When t h e e n g i n e was  driven with a fixed-throw crankshaft  i t was p o s s i b l e t o  b r e a k - i n t h e e n g i n e and a d j u s t t h e a i r - f u e l r a t i o so t h a t i t w o u l d become s e l f - s u s t a i n i n g . was  F o l l o w i n g t h i s adjustment i t  a simple matter t o disconnect  the connecting  r o d and r u n  the e n g i n e i n t h e f r e e - p i s t o n c o n f i g u r a t i o n . The porated  p r o t o t y p e o f t h e f r e e p i s t o n power saw i n c o r -  the f o l l o w i n g novel features:  1. The e n g i n e c a n be a c c u r a t e l y b a l a n c e d . c o r r e c t l y synchronized, p i s t o n i s balanced cylinder.  When  the a c c e l e r a t i o n of the  by t h e a c c e l e r a t i o n o f t h e  245 2. The  c y l i n d e r head i s s e l f - c o o l i n g . The  recipro-  c a t i n g m o t i o n of the c y l i n d e r moves the c o o l i n g a i r across 3. The  the  fins.  p i s t o n s t r o k e i s c o n t r o l l e d by gas  and  spring  f o r c e s and depends on an energy b a l a n c e between t h e amount r e l e a s e d and  the amount t a k e n out  during  the c y c l e . ,4. T h r o t t l i n g i s a u t o m a t i c . ^  Because the s t r o k e changes  when the l o a d i s changed, the l e n g t h of time t r a n s f e r and b l e e d p o r t s are open depends on  the the  load. 5. The  c o m p r e s s i o n r a t i o i n c r e a s e s when t h r o t t l i n g  increases.  As a r e s u l t , more energy i s a v a i l a b l e  f o r i g n i t i o n when t h e f r e s h charge i s more d i l u t e d w i t h r e s i d u a l gases. 6. The  carbureted  a i r - f u e l mixture i s i g n i t e d with  the energy of c o m p r e s s i o n . 7. The  spring i s automatically locked  s t a t e when the engine i s s t o p p e d .  i n a compressed This  feature  results i n instant, e f f o r t l e s s stop-start characteristics. 8. The  r e c i p r o c a t i n g m o t i o n of the p i s t o n i s used  d i r e c t l y s i n c e the b l a d e o f the saw  i s part of  the  piston. 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"News/Trends", M a c h i n e D e s i g n ,  V o l . 39,  2.8  "News/Trends", M a c h i n e D e s i g n ,  August  2.9  P.E. ical  2.10  A r v i n H. S m i t h , E n e r g e t i c s 5: P h o t o v o l t a i c Power", M e c h a n i c a l E n g i n e e r i n g , V o l . 88, No. 10, O c t o b e r , 1966.  2.11  J o h n M. H o u s t o n , " E n e r g e t i c s 4: T h e r m i o n i c Power", M e c h a n i c a l E n g i n e e r i n g , V o l . 88, No. 9, S e p t e m b e r ,  2.12  23, 1967.  No.  31,  12,  May  1967.  G l a s e r , " S o l a r Power: R e a l i t y o f V i s i o n " , Mechan E n g i n e e r i n g , V o l . 88, No. 3, M a r c h , 1966.  1966.  R.L. Klem and A.G.F. P i n g w a l l , " E n e r g e t i c s 3: Thermoe l e c t r i c Power", M e c h a n i c a l E n g i n e e r i n g , V o l . 88, No. August, 1966.  8,  2.13  A . C . J . M a t t s s o n , E . L . Ducharme, E.M. G o v a n i , I.B. Morrow J r . , and T.R. B r o g e n , " E n e r g e t i c s 6: M a g n e t o - H y d r o d y n a m i c Power", M e c h a n i c a l E n g i n e e r i n g , V o l . 88, No. 11, Novemb e r , 1966 .  2.14  William Tucker, J u l y 7, 1966.  2.15  W e l l s M a n u f a c t u r i n g Company, The S a w i n g M a g i c o f W e l l s a w 400, S a l e s B u l l e t i n , T h r e e R i v e r s , M i c h i g a n , 1962.  2.16  C a r l H. de Zeeuw, "Wood", M a r k s ' M e c h a n i c a l Engineers Handbook, e d . T h e o d o r e B a u m e i s t e r , New Y o r k , McGraw-  Hill,  "Power", R e p r i n t  from Machine  Design,  1958, S e c . 6, pp. 145-164.  2.17  F a g Company, B a l l and R o l l e r B e a r i n g E n g i n e e r i n g , Fag K u g e l f i s c h e r G e o r g S c h a f e r & Co., S c h w e i n f u r t , West Germany, 1967,No. 3.  2.18  Kewi Cho Yu, The F r i c t i o n B r i t i s h Columbia t h e s i s ,  2.19  E u g e n e L e e B r y a n , " H i g h E n e r g y J e t s as a New C o n c e p t i n Wood M a c h i n i n g " , F o r e s t P r o d u c t s J o u r n a l , V o l . 13, No. 8, A u g u s t , 1963.  2.20  V.G. Yugov and A . I . O s i p o v , "The Use o f H i g h Speed W a t e r j e t s i n Wood C u t t i n g and P r o c e s s i n g " , T r a n s a c t i o n s o f t h e C e n t r a l S c i e n t i f i c R e s e a r c h I n s t i t u t e o f Mechan i z a t i o n and E n e r g y R e q u i r e m e n t s o f t h e F o r e s t I n d u s t r y o f U.S.S.R., ( t r a n s l a t i o n No. 149, C a n a d a D e p a r t m e n t o f  Sawing o f Wood, U n i v e r s i t y o f 1967.  F o r e s t r y , 1 9 6 2 ) , V o l . 18, No. 6, Moscow, 1960.  252 2.21  S . J . L e a c h and G.L. W a l k e r , XXVI, "Some A s p e c t s o f Rock C u t t i n g b y H i g h Speed W a t e r J e t s " , P h i l . T r a n s . R o y a l S o c i e t y o f L o n d o n , S e r i e s A, ' V o l . 260, No. 28, J u l y , 1966.  2.22  J . S . J o h n s t o n , " C r o s s C u t t i n g o f Roundwood.by S h e a r i n g " , C a n a d i a n D e p a r t m e n t o f F o r e s t r y , P r o g r a m R e p o r t on P r o j e c t 0-209, No. 2, May, 1964.  2.23  Johnston, " S h e a r i n g " , Canadian Department o f F o r e s t r y , P r o g r a m R e p o r t on P r o j e c t 0-209, No. 4, M a r c h , 1966.  2.24  J . S . J o h n s t o n , "An E x p e r i m e n t i n S h e a r - b l a d e C u t t i n g o f S m a l l L o g s " , R e p r i n t e d f r o m P u l p and P a p e r M a g a z i n e o f Canada, V o l . 69, No. 3, F e b r u a r y 2, 1968.  2.25  "Roanoke T r e e F e l l e r L i n e " , R e p r i n t f r o m P u l p w o o d P r o d u c t i o n and Saw M i l l L o g g i n g , O c t o b e r , 1966.  2.26  "New W o r l d Champions Compete a t L u m b e r j a c k B o w l " , Saw A g e , November, 1 9 6 7 .  2.27  "Power M i s c e l l a n y " , M a r k s ' M e c h a n i c a l E n g i n e e r s Handbook, e d . T h e o d o r e B a u m e i s t e r , New Y o r k , M c G r a w - H i l l , 1958, S e c . 9, p p . 228-232.  2.28  "Power I n c r e m e n t B o r e r " , F o r e s t r y E q u i p m e n t News, No. A 30-63, F . a n d A.O., U n i t e d N a t i o n s , Rome, J u n e , 1963.  2.29  "Energy", 1965.  2.30  J . S . J o h n s t o n , " E x p e r i m e n t a l C u t - o f f Saw", R e p r i n t f r o m F o r e s t P r o d u c t s J o u r n a l , Canada Department o f F o r e s t r y , J u n e , 1962.  2.31  "20 hp Gas T u r b i n e " , Gas T u r b i n e D i v i s i o n ASME, V o l . 8, No. 1, F e b r u a r y , 19 67.  2.32  Farm E q u i p m e n t News B u l l e t i n , A p r i l , 1962.  2.33  "Mercury U n i t t e s t s i t s Stamina", T r e n d s , J u n e 8, 1 9 6 7 .  2.34  S.O. K r o n o g a r d , " A u t o m o t i v e Gas T u r b i n e b y V o l v o " , M e c h a n i c a l E n g i n e e r i n g , ( f r o m ASME p a p e r s , 6 2 - G 7 P - 8 ) , November, 1962.  2.35  A . L . L o n d o n , " C h a i r m a n , P r o f e s s o r A . L . L o n d o n Comments", Gas T u r b i n e D i v i s i o n N e w s l e t t e r , ASME, V o l . 8, No. 1, F e b r u a r y , 1967.  Product Design  and V a l u e  Chain  Engineering, July,  Newsletter,  Machine Design,  News/  253 2.36  W. F r o d e , R e c e n t D e v e l o p m e n t s i n t h e NSU Wankel E n g i n e , a d v a n c e c o p y o f James C l a y t o n ' s l e c t u r e , F e b r u a r y , 1966, p u b l i s h e d i n P r o c e e d i n g s , 1965-66, V o l . 180, P a r t 2A, I n s t . Mech. E n g i n e e r s .  2.37  Go-Power C o r p . , Go Power E n g i n e A n a l y s i s Power C o r p . , San F r a n c i s c o , 1967.  2.38  R.F. A n s d a l e , " A i r - c o o l e d E n g i n e e r , August, 1965.  2.39  C h a r l e s J o n e s , The E n g i n e s T o d a y , SAE  2.40  R . J . M e i j e r , "The P h i l i p s D r i v e Mechanism", P h i l i p s  1959.  Systems,  Wankel E n g i n e " ,  Curtiss-Wright Rotating p a p e r No. 8 86D, A u g u s t ,  Go  Automobile Combustion 19 64.  H o t - g a s E n g i n e w i t h Rhombic T e c h n i c a l R e v i e w , V o l . 20,  2.41  D.W. K i r k l e y , A Thermodynamic A n a l y s i s o f t h e S t i r l i n g C y c l e and a C o m p a r i s o n W i t h E x p e r i m e n t , SAE p a p e r No. 949B, J a n u a r y , 1965.  2.42  F . A . Creswick, Thermal Design of S t i r l i n g SAE p a p e r No. 949C, J a n u a r y , 1965.  2.43  A . A . D r o s , "An I n d u s t r i a l Gas with Hydraulic Piston Drive", V o l . 26, 1965.  2.44  G. W a l k e r , " O p e r a t i o n s C y c l e o f t h e S t i r l i n g E n g i n e w i t h P a r t i c u l a r Reference to the F u n c t i o n of the Generator", Journal of Mechanical Engineering Science, V o l . 3, No. 4, 1961.  2.45  G r e g o r y F l y n n J r . , W o r t h H. P e r c i v a l "G.M.C. S t i r l i n g T h e r m a l E n g i n e P a r t E n g i n e S t o r y , 1960 C h a p t e r " , R e p r i n t t i o n s , V o l . 68, 1960.  2.46  J . A . R i e t d i j k , , H . C . J , v a n B e u k e r i n g , H.H.M. v a n d e r Au, a n d R . J . M e i j e r , "A P o s i t i v e Rod o r P i s t o n S e a l f o r L a r g e P r e s s u r e D i f f e r e n c e s " , P h i l i p s T e c h n i c a l Review, V o l . 26, No. 10, 1965.  2.47  Helmut E. F a n d r i c h , S t r a t i f i e d Charge Scavenging o f a Two-Stroke Engine a t P a r t T h r o t t l e , Masters t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1962.  2.48  McCulloch Corp., Angeles.  2.49  A. B r a u n , "The P o t e n t i a l i n t h e F r e e - P i s t o n E n g i n e P r i n c i p l e " , The E n g i n e e r i n g J o u r n a l , J u l y , 1960.  Cycle  Machines,  R e f r i g e r a t i n g Machine P h i l i p s T e c h n i c a l Review,  Sales B u l l e t i n ,  and F. E a r l H e f f n e r , of the S t i r l i n g f r o m SAE T r a n s a c -  McCulloch Corp.,  Los  254 2.50  T.M. L e i g h , T h e S e l f - C o n t a i n e d D i e s e l p a p e r No. 900B, S e p t e m b e r , 1964.  2.51  Svenska Co., M o t o r b o r r , S a l e s B u l l e t i n , b o r r A k t i e b o l a g e t , S t o c k h o l m , Sweden.  2.52  J . H . M c N i c h , D.G. Mark and R . J . M c C r o r y , T h e F u e l a n d I g n i t i o n Systems o f a F r e e - P i s t o n R e f r i g e r a n t Compressor, SAE p a p e r No. 126B, F e b r u a r y , 1960.  3.1  C h a r l e s F a y e t t e T a y l o r , The I n t e r n a l Combustion i n T h e o r y and P r a c t i c e , New Y o r k , W i l e y , 1960.  3.2  A . L . L o n d o n , M.E. 233 C o u r s e n o t e s , F a l l Q u a r t e r , 1962.  3.3  A s s o c i a t e d S p r i n g C o r p . , S p r i n g D e s i g n and S e l e c t i o n i n B r i e f , B u l l e t i n o f A s s o c i a t e d Spring Corp., B r i s t o l , C o n n e c t i c u t , 1956.  3.4  Dow C o r n i n g Michigan.  3.5  E x t r e m u l t u s I n c . , E x t r e m u l t u s , t h e U l t i m a t e i n Power Transmission B e l t i n g , Sales B u l l e t i n , Extremultus T r a n s m i s s i o n s L t d . , 115 S i x t h A v e n u e , L a c h i n e , P.Q.  3.6  A s s o c i a t e d S p r i n g C o r p . , Handbook o f M e c h a n i c a l D e s i g n , B r i s t o l , C o n n e c t i c u t , 1950.  3.7  Garlock  3.8  AGMA, AGMA S t a n d a r d f o r S u r f a c e D u r a b i l i t y ( P i t t i n g ) o f S p u r G e a r T e e t h , AGMA 210.02, W a s h i n g t o n , J a n u a r y , 1965.  3.9  AGMA, AGMA S t a n d a r d f o r R a t i n g t h e S t r e n g t h o f S p u r Teeth, AGMA 220.02, W a s h i n g t o n , A u g u s t , 1966.  3.10  M o r s e C h a i n C o . , M o r s e M e c h a n i c a l Power T r a n s m i s s i o n S t o c k P r o d u c t s , SP-65, M o r s e C h a i n C o . , I t h a c a , New York, 1965.  3.11  M.S. Walmer, M a t e r i a l P r o p e r t i e s and T o l e r a n c e s i n R o l a m i t e B a n d s , B u l l e t i n H a m i l t o n Watch Company, L a n c a s t e r P a . , November, 1 9 6 8 .  3.12  D u d l e y D. F u l l e r , " F r i c t i o n " , M a r k s M e c h a n i c a l E n g i n e e r s Handbook, e d . T h e o d o r e B a u m e i s t e r , New Y o r k , M c G r a w - H i l l , 1958, S e c . 3, p p . 31-52.  Bulletin  Pile  Hammer, SAE  Svenska  Stanford  Motor-  Engine  University,  No. 09-081, J u n e , 1964, M i d l a n d ,  Inc., B u l l e t i n  Spring  BP-563, Camden, New J e r s e y .  Gear  255 3.13  J u l i u s Mackerle, A i r c o o l e d Motor Engines, C l e a v e r - H u m e , 1961.  3.14  A.W. Judge, Modern P e t r o l Hall, 1955.  3.15  P e t e r D. R i c h a r d s o n , " E f f e c t s o f Sound and V i b r a t i o n s on H e a t T r a n s f e r " , App. Mech. R e v i e w , V o l . 20, No. 3, M a r c h 1967.  3.16  Helmut E . F a n d r i c h , E v a l u a t i o n o f S e v e r a l C o m b u s t i o n Chamber S h a p e s , T e c h . R e p o r t No. 4, I n t e r n a l R e p o r t , Power M a c h i n e r y , L t d . , V a n c o u v e r , F e b r u a r y , 1966.  3.17  A l c o a , A l c o a A l u m i n u m Handbook, Aluminum Company America, P i t t s b u r g h , 1962.  3.18  A l c a n , Handbook o f Aluminum, S e c o n d E d i t i o n , Company o f C a n a d a , M o n t r e a l , 1961.  3.19  M a t e r i a l s i n Design I s s u e , V o l . 60, No.  3.20  A t l a s S t e e s Company, T e c h n i c a l D a t a Machinery S t e e l s , Welland, O n t a r i o .  3.21  A.W. J u d g e , S m a l l Gas T u r b i n e s and L o n d o n , Chapman and H a l l , 1960.  3.22  F.A. C r e s w i c k , R.W. K i n g and R . J . M c C r o r y , " F r e e - P i s t o n Engines" R e p r i n t from Advances i n Petroleum Chemistry and R e f i n i n g , e d . J o h n J . M c K e t t a , V o l . 7, I n t e r s c i e n c e , New Y o r k , 1963.  3.23  " T e f l o n E n g i n e - P i s t o n R i n g s Improve S e a l i n g " , M a c h i n e D e s i g n , V o l . 39, No. 3, F e b r u a r y 2, 1967, p . 32.  3.24  N e w s / T r e n d s , "New P i s t o n R i n g S o l v e s I.C. E n g i n e e r ' s P r o b l e m s " , M a c h i n e D e s i g n , V o l . 40, No. 18, A u g u s t 1,  Engines,  London,  L o n d o n , Chapman  Engineering, Materials 5, O c t o b e r , 1964.  and  of  Aluminum  Selection  Selectalloy Free Piston  Engines,  1968.  3.25  Helmut E . F a n d r i c h , A S t r a t i f i e d C h a r g e T w o - S t r o k e S p a r k I g n i t i o n Engine Performance C h a r a c t e r i s t i c s , T h e s i s , Stanford University, 1964.  3.26  N e w s / T r e n d s , " F l u i d i c A m p l i f i e r F e e d s Gas t o A u t o E n g i n e " , M a c h i n e D e s i g n , V o l . 39, No. 2, May 25, 1967, p . 12.  3.27  F i b e r g l a s s Canada L i m i t e d , F i b e r g l a s B u l l e t i n Book 1, A p r i l 1965.  3.28  N.W. T o d d , F.A. W o l f f , R.S. M a l l o u k , J.R. C o u r t r i g h t , " P o l y i m i d e s " , M a c h i n e D e s i g n , J u n e 16, 1966 (Plastics R e f e r e n c e I s s u e ) , pp. 81-83.  Reinforced  Plastics,  256  3.29-  H a b a s i t Canada L i m i t e d , P r o d u c t I n f o r m a t i o n Manual P I - 6 8 - 1 , H a b a s i t (Canada) L i m i t e d , O a k v i l l e , O n t a r i o , J a n u a r y , 1968.  3.30  D.D. C a r s w e l l , " N y l o n s " , Machine D e s i g n , June 6, 1966, pp. 68-71.  4.1  L e s t e r C. L i c h t y , I n t e r n a l Combustion E n g i n e s , Y o r k , M c G r a w - H i l l , 1951.  4.2  A. Stambuleanu, " C o n t r i b u t i o n t o t h e Study o f t h e D i s t r i b u t i o n o f Heat T r a n s f e r C o e f f i c i e n t s D u r i n g t h e Phase o f t h e Working C y c l e o f an I n t e r n a l Combustion E n g i n e " , P r o c e e d i n g s o f t h e T h i r d I n t e r n a t i o n a l Heat T r a n s f e r C o n f e r e n c e , A.I.Ch.E., New Y o r k , V o l . I , August 1966, pp. 339-353.  New  APPENDIX I CUTTING SPEED TESTS WITH CONVENTIONAL POWER SAW  Date & Type of Vood 24/4/67 maple (fresh) (center r o t 4" x 7")  24/4/67 maple (fresn)  Jaw S/N Sc S p e c s .  Speed (rpm)  .404 p i t c h .025 J o i n t 15" b a r direct drive  6400 6400 6300 7000 5800 5500 5500 5000 4500 5000 7000 4500 6000 5000 7000 6500 6000  26 *7 28 28  1770140 8 teeth .375 p i t c h .040 j o i n t  1770140  maple (fresn)  7 teeth .375 p i t c h .040 j o i n t 15" b a r  1/5/67 hemlock (semi-dry)  Suw S/N & Specs.  25 25  24/4/67  1/5/67 hemlock (3emi-dry)  Cutting Time (sec)  6000 tooo  6000  (semi-dry)  Forest  1770140 7 teeth  15" b a r  25/4/67 hemlock  p e r f o r m e d i n U.B.C. Endowment L a n d s  1770140 7 teeth .375 p i t c h .040 J o i n t 15" b a r  25 24 24 26 27 27 32 28 28 28  Date & Type of Wood  (in) 12 & 16 ( r o t 4x7)  24 25 30 26 27 2722 25 20 20 22  6000 5000 5000 6500  24 23 22 27  1/5/67 hemlock (aemi-dry) (difficult to l o a d Saw)  2/5/67 hemlock (fresh) 12 <ic 1 6 ( r o t 4x7)  2711,".b9^ 7  teeth  -404 p i t c h .030 j o i n t 15" b a r 3:1 g e a r reduction ^711069^ 9 teeth •404 p i t c h .030 j o i n t 24" b a r 3:1  29 26  6000 6000 7000 4500 6000 7000 5000 5500 6000 5000 5500 6500 7000 6000  6500 7000 7000 4500 5500 5500 6000 6000 6000 1770140 6000 6000 7 teeth .375 p i t c l T ^ O O O .025 J o i n t 7000 7000 15" b a r 5000 5000 5500 5500 6500 6500 6000 5000 5000 7000 5000 0000 7000 1770140 6000 8 teeth 6000 .375 p i t c h 7000 .025 j o i n t 7000 15" bar5000 5000 5500 5500 6500 6500 5000 bOOO 7000  Log Diameter  2/5/67 hemlock (fresh)  ^7110692 9 teeth .404 p i t c h .040 j o i n g 24" b a r 3:1  U j Sc 15 ( r o t 4x6) 11* & 1 5 ( r o t 4x6)  2/5/67 hemlock (fresh)  gear  27110692 7 teeth .500 p i t c h .030 j o i n t 24" b a r 3:1  11 4 15 ( r o t 2x3) 12 Sc 1 2 ;  gear  gear  Speed ( r . «)  Cuttin g Time (sec)  6500 6500  13i 15  6500 6500 6500 6500 6300 6200 7000 7000 6000 6500 7500 7500 7000 6500 6000 6000 7000 7000 6500 6500 6500 6500 7000 7000 7000 7000 6500 6500 6000 6000 7000  12 U s 12 12 11 11 *3 <\ 2L ' 21* *5 22* 21 20 *2* 20 ?  35*  14  hemlock  8  7000  43  13j 13 17  (fresh)  .404 p i t c h  7000  48  .025 j o i n g 24" b a r  6000 6000  32 30*  direct drive  6000 6000 5000 5000 5000 5500 5500 7000 6500 6500 6600 6500 6000 5000 6000 6000 6000 5000 6500  28j 30 i9j 31  132 18j 14 ' 14* 16 16 I82 19 18  12* & 1 2 13« & 13  2/5/67 cedar (3emi-6iy) (3mall r o t )  13a 12 U H i 14 Ui 14 12  ui  17* 10 102  d x w = 13 x 11  12* 11 11  G X V 14 x 12  13* 13 10 10  n  10j13 12 11 11 15  5  1770140 8 teeth .404 p i t c f t .025 j o i n t «_4» b a r direct drive  Power c h e c k S/N ± 7 7 6 1 4 0 14/4/67 scale bhp 4500 6.8 3.06 5000 6.5 3.25 5500 6.1 3.35 • 6000 3.36 5. 6 6500 5. 5 3.57 70U0 5.1 3.57 7500 3.30 4. 4 P o w e r c h e c k X/H ^711069* <5/4/67 6000 7.8 4.63 5500 8.0 4.40 8. J 5000 4.10 4500 8.3 3.73 8. 1 5000 4.05 5500 8. 0 4.40 4.68 OOOO 7. 8 6500 7. 3 4-74 o.8 4.76 Vuoo  20j 20  20 d i a .  21*  6500  17 18 18 16  d x w 2 14ixl2$ «.i d i a .  21s  1770140 teeth  d x w = 14 x 12  22  23 22J 20 2* ^0* 183 20 19 19i 19s 20  2/5/67  15  hOg Diameter (in)  19 & 1 9 *  -  3*  292 292 49* 31i 34j ift 44* 35* 352 43 46 38 37* 45  scale  self  feed  *0  24  SL  (4"  dia.  rot)  21 d i a . U" r o t )  10/5/67 bhp  7.0 6.4 t>.0 5.5 5.0 3.8 3.4  3.15  3.-0  . 3.30 3.30 3.25 2.66 2.55 3/5/67  8.1 8.2 8.5 8.6 8.5 8.~ 8.1 7.3 7.0  4.86 4.51 4.25 3.87 4.25 4.51 4.86 5.00 4.90  APPENDIX  II  VIBRATION L E V E L TEST  <A  •p  c-—j- i n  (v cv  o  H  cn cv to  oo O  to >n  in  H  to  rl r|  o  •£> o o  r| H  HO cn  r-i r-i CV  rH r l CV  O m  \ o - t cnCV cn £> r-i  r-i C\l r-i r-i r-i  cv  -4- to  vO  CV H H  r l r l —)  rH O rl  -4"  sf^OO H H m cn  m  r-i  o  rl r l rl  m m -1  rH O r | 00  t> r-i r-i r-i r-i  o m  cn  r-i r-i  o m cv  O f > - < t O l > H O rH H rH r-i  O  c*-  r i cv cn •>4 CV . V !  co  r-i r-i r-i r-i r-i  o  H H  -<f  , Noremec Meter APM 201)  CV CV r l  -4  H CV H  •>t vO O cn m r i r l H H (M  -.V  H  O CV O —i xO  rl  '.V t >  rl  —|  r i <n  H r|  r-i  <n  •  so fl o  m  oH o m cv cv cv  cv o  t o m c-  cv cn H o  •X> CV  H CV  cn  cn cv m to o sO m cv cv H cv m  m  to  o to  O r-i CV i V CV r l  -0 - 4  «  O  0  nj  io^ X>  o to to CV  sO CV —• £ >  36"  r-  7000  7000  o o o o o O  -35 o  rH CV  w>  c  $  -p o  m o  cn  in  Xi  o cn cn a  CO  o  :v  H  c>  cn  CV H  7000  r i cn O r l o m r-i CV rH -V r l  bar, cut, 30/5 7000 bar, cutting | | 7000 bar, not cutting 7000 bar, cutting 7000 bar, not cutting 7 0 0 0 I I bar, cutting | | 7000 bar, not cutting 7000  r-i r-i  36"  bar, cut, 29/5 36" bar, cutting  7200  6000  6000  —I  m cv cn CV  m cn m m i.V CV  V  V £> r-i  o O  t>  10 . f l  115" 15" 15" (23% balanced) 15" 115" B 15" 18500002 (20% balanced) 31/5/68 18" bar, cutting  O  O  -4/ m rH CV  CV r-i r-i  C  « t to  o o oo o o o o o o o oQ O O t> I> r- cv 3 1 >  -i  r-i O —i m CV H V r l  34001031 31/5/68  - o  r-i CO t O CV CV r-i H  rv O  rl rl  cn  E /rubber  ? cu  53% balanced)  •P Tf  O  r-i CV H r-i CV  29/5/68  7000  o o o o o  o  2400  CV CV rH r-i CV r-i  o  co -4 to  vO NO 50  rH  CV  63% balanced)  o H cv m  o  CV CV r-i r l  29/5/68  o  Cn rH  o cn  CV H <n CV - 4 —i cn rl r | rl r| H  28100006 (222 gm c'wt  Hrl  7000  cn H  no bar  H cn  cn  j> r- o  cn  F  to m  cv <n o -4- r-i  7000  CV rH r-i  in -4 •fl O to :V H ^ H rl rl  r-i  30/5/68  cv  to o to  cv to  H CV r-i  36" bar, cutting  o  to  CV O r-i H r-i  rH  53% balanced)  m r-  r-i  no bar 29/5/68  -4  -4 m  CV  G  m cv  CV CV rH r l CV H  o  V  CV r l -H  t>  m r-i  30/5/68  <n  7000  -4-  r-i cv rH H r-i r-i  rH  28100007 (207 gm c'wt  o tCV o  r-i r l r l  r l t> CV vO ^cr rH CV  cv H  1128940  cn '."v  28100005 (196 gm c'wt  MACHINE & S/N  DETAILS TEST DATE  SPEED  REAR HANDLE Rt. Vert. Long. Lat. Angle  0)  r-i  CV CV CV H  no bar  -P  H  FRONT HANDLE  <  cn rH  7000  O  m  :V - V  30/5/68  r-H  vO  36" bar, cutting  —  m H  no bar 29/5/68  8  Vertical II Horizontal! top bot. front backj  (Peek-to-peak v i b r a t i o n amplitude, inch xlO  DATA  •4i •l-J CJ  +> 3  m - -i  cn T)  co d crj  o  Q o  ;n xi H  o cc^cv cn—  F o r t y p i c a l power saws w i t h wide open t h r o t t l e taken on May 17, 1967, a t a d i s t a n c e o f 2.5 f e e t from microphone to s p r o c k e t c e n t e r l i n e u s i n g a B r u e l & K j a e r Sound M e t e r Type 2203 w i t h o c t a v e f i l t e r type 1613 and microphone type 4131. Readings taken on f l a t g r a s s y t e r r a i n i n Hew O r l e a n s , La. OCTAVE BAWD NOISE LEVEL IN DECIBELS Saw S/N  and Speed  dBA  dB Linear  GPS  K CP S  (H ) 2  63  125  250  500  1000  2  4  4-5  89  178  355  709  1.41  2.82  89  178  355  709  1410  2.82  5-63  (Kflg) 8  Freq. 16  Center  5.63  11.2  Lower  11.2  22.4  Upper  1760103 a t 7C00 rpm  109  110  82  97  102  107  110  103  102  94  88  A  109  110  73  96  97  103  107  100  102  94  86  110  111  85  94  99  107  108  100  96  92  93  104  105  75  94-  98  93  98  97  93  90  87  C  102  102  78  92  97  97  98  95  89  88  79  1760103 a t 7000 rpm  108  110  80  100  98  104  103  98  96  82  69  on e l e c t r i c dynamometer  110  110  80  98  104  108  99  99  86  8b  72  36001171 a t c u t t i n g rpm  B 3100-2-194-8 a t c u t t i n g rpm  operatorabsent operator present  APPENDIX IV RESULTS  OF  QUESTIONNAIRE  CHAIN  SAW  USERS  DISTRIBUTED  IN  TO  1967  Replies Received  Extent machine c h a r a c t e r i s t i c s bother operator (code: V-very much, Q-quite a b i t , S-somewhat, N-not at a l l )  Professional  1. viJbration  S  H  s  u  2. smell  S  a  s  N  3. nsaise  Q  N  Q  N  4. weight  V  6  V  Q  5. exasy s t a r t i n g  E  Q  E  • E.  6.  E;  E W Q  Casual Users  Loggers V  V  Q  N  Q  Q  S  s  N  s  V  V  V  s  Q  E  Q  E  E  E  E  E  Q  E  E  E  Q •  H  E  Q  Q  S ''  S  E  S  s  s  N  Q  Importance of s p e c i f i c items (code: E-extremely important, y-quite important, S-only s l i g h t l y important, H-unimportant)  reliability  N  7. easy maintenance 8. Imt  f u e l consumption  . E. :  9. neat appearance  $  s  s ;'•,;E • • •' s.'s  10. imm upkeep cost  N  Q  k-  11. low o i l consumption  Q  12. JEW f i r s t cost price  Q  13. low weight and small size  Q  Q  E  E  14.. long, troublefree  Q  Q  E  E  life  Area saw i s used  E  E  E  <i  £  •". y  Q  3  ' s;:. E  Q  Q  ; s  Q  E  • •' s E  E  E  Q  Q  E  E  E  s  Q  E  E  Q  Q  Q  E  E  Ont. Ont. Ont. Ont. Ont. N.B. N.B. B.C. Van. Van,  Average tree size cart (inch diameter)  7  8  6  6  8  Maximum tree size out (inch diameter)  16  15  15  12  26  40  18  18  24'.' 120  36  36  7  y / - y....  y  no  y  y  y  y  y  y  y  y  y  y  y  .." y  no  iy  y  y  y  y  no  y  y  y  no  no  no  y  y  y  y  y  y  y  Dumber of starts pesr day  20  20  20  5  20  50  50  25  6  Amount of wood cut — cords per day  U  50  u  12  12  6  3  30th  1  2800  3000  1188  6H  2  4000 200  2000 1000 10M  y  y:  y  y  y  y  y  y  y  .20° below  y  y  40° below  y  Saw used i n snow  y..  y  Saw used i n r a i n  y  Saw used where temperatures drop below 0°F •  Saw used where temperature goes above 110°F  cords per year  2800  ;  cords per saw Desired running tiaas on tankful of gas (minutes)  60  60  60  50  120  ;  90  90  40  15  2 6  45  261  APPENDIX V TYPICAL POWER SAW PERFORMANCE DATA  SAW SZMBOL  V  MAX bhp a. rpm BMEP  EXHA JST TRANSFER INTAKE Ht/S Ae/Ap Ht/S At/Ap Ht/S Ai/Ap  D  s/b  06  8.3  .60  60  .82  7000  .30  .123 .16  .108 Reed  valve  75  7.4  .53  53  .79 $ 6500  .36  .143 .23  .155  .38  .183  70  5.8  .60  55  .83 3 7000  .34  .143 .23  .195  .32  •  77  5.8  .60  41  .66  .35  .143 .24  .133 .32  75  5.5  .61  51  .69 3 7000  • 34  .135 .24  .110  21  5.0  .55  58  .82  7000  .35  .150 .25  .092 Reed  00  4.5  .72  55  .78 ai 6500  .31  .20  .21  .195 Reed  78  4*2  .60  55  .86  & 7000  .32  .108 .22  .136  .29  .132  PP  4.2  .60  49  .81 si 7000  .38  .173 .26  .175  .45  .087  42  4.1  .80  65  .93  7000  .30  .24 .21  .23 Reed  valve  U  3.6  .76  51  .71  6500  .30  .25  .21  .127 Reed  valve  10  3.3  .79  53  .75  6500  .31  .25  .175  .150  12  3.3  .79  53  .73  6000  -  -  10  3.3  .79  52  .73 & 6000  .28  .24  79  1.5 1.00  56  .78  & 7000  .27  .23  AS  1.3 1.00  56  .75  7000  -  -  OR  1.3  .83  35  .40  4500  .24  .20  0.1 jl.04  47  1.36  Model  «$  &  7500  11,400|  -  -  .14 .15 valve valve  .27  .191  Reed  valve  .165  .116 Reed  valve  .175  .200  -  .125  -  .13  -  .25  .19  -  -  Reed  valve  262  APPENDIX V I HEAT TRANSFERS FROM RECIPROCATING CYLINDER HEADS  Oscillating  Wattmeter 3/N 6E22 VT V o l t o e t o r S/H 6E83 S t r o b o t o c 3/N 6C20 Description of cylinder head Canadian 275 b l o c k and head  Teat ho.  Tims since change (min.)  1 2 3 4 5 6  mechanism - s c o t c h y o k e and c o n v e r t e d  Amplitude pk-to-pk  Frequency  (in.)  (cpm)  (w.ats)  • 25 .25 .25 .25 .25 .25  0 400 800 1600 2200 2550  216 216 212 213 216  Houter Power  215  c h a i n saw b a s e  Plug Temp.  Fin Temp.  Koom Temp.  Head Temp.  Block Temp.  millivolt  millivolt  0°F  millivolt  millivolt  8.10 7.8  7.80 7.6  7.55 6.90 5.85 4.85  7.3 6.15 5.50 4.45  70  7.95 7.65 7.35 .6.30 5.65 4.  7.85 7.55 7.15 6.15 5.95 4.50  E x t e r n a l c o o l i n g a i r s u p p l i e a by vacuum c l e a n e r bxower, no c o v e r o v e r n e a d . 0 0 106 0.42 7 0.10 70 0.41 8 0 0 106 0.36 0.02 70 0.33 106 0 0 0.35 70 9 0.33 0 0 Canadien 10 6 . 2 0 0 . 2 0 94 11 500 210 c y l . • 50 5.40 93 . 5.30 .50 1600 bead 12 89 3.80 3.83 .50 2000 3.50 13 91 '.. 3 . 4 5 U / S . . 5 0 2600 • 2.65 14 91 .50 3000 2.50 15 92 16 500 5.80 .25 92 1600 17 .25 . 5.60 92 . •-; A- • 18 2000 92 ;25 . 5.30 2600 92 . 4.80 19 .25 . 20 3000 92 ' 4.40 .25 21 3600 92 .25 4-1 Then&o c o u p l e t changed t o Chromel-alume! Canadian 22 0 0 6.8 SPACER 7.0 93 210 c y l . 500 6.2 .25 23 70 93 6.4 4.5 bead K i t h 1600 .25 24 93 : 5.4 5.2 69 3.9 oatching 2000 68 .25 ,4.7 . 25 93 4.9 3.5 spacer 26 2600 .25 : .4.0 . 68 93 4.2 .2.7 27 3000 .25 3.9 68 93 . ,3.7 -' 2 . 4 28 0 0 90 • 8.0 8.25 73 .4.45 80 29 .50 . 500 5.90 5 . 7 6 , . 75 . 92 3.4 30 90 0 0 . ' . 92 8.75 8.5 •76 4.8 .50 500 31 5 92 7.20 76 6.95 4.1 32 10 . .50 500 6.70 - 92 76 ,6.45 3.9 -50 500 92 33 15 6.20 6.45 ^ 77 • .3.8 ..  -  S p e c i a l head and m a t c h i n g spacer t o squeeze a i r Canadltui 210 head only  S p e c i a l h«ad una s p a c e r designed to a c t as a i r putsp  34 35 36 37 38 39 40  20 25 30 5 10  41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ti 73 74 75 70 77  25 30 35 40 5 10 3 5 7 3 7 9  79  .  15 20  5 5 5 3 20 5 10 5 5 5  -5 2 0 2 50 50 5 10 5 10 5 10  -  4  .50 .50 .50 .50 .50 .50 . .50 .50 .50 • .50 . • 50 • 50 .50 .50 • 50 .50 .50 .50 .50 .50 .50 .50 .50 .50 1.375 1.375 1.375 1.375 1.375 1.375 1.375 1.375 1.375 1.375 1.375 1.375 .50 .50 .50 .50 .50 .50 .50 .50 .50 .50  . 500 500 500 . 1600 1600 ltt» 1600 . 1600 1600 1600 • 1600 2000 . 2000 2600 . 2600 '•' 2600 3O00 3000 3000 0 400 1600 2000 2600 0 400 400 0 400 1600 2000 2600 2000 2600 2600 3000 0 50 400 400 1000 1000 1400 1400 0 400  92 6.33 " v6.08 • 9 2 - .'. . b . 2 0 - - 6.00 6.13 . 5.14 . 93 4.78 5 . 0 3 93 4.28 .4.50 -" 93 • •• 4 - 0 2 . 4.23 93 . 3.90 •4-10 . 93 3.82 . 4.02 . 9 3 " 4.02 • 3.82 . 93 .' 4 . 0 0 3.80 • . ' 92 3.90 3.73 91 3.60 3.38 90 3.28 3-48 90 2.82 90 3.13 3.02 2.80 90 2.80: 90 3.01 • 2.82 89i .• . 2 . 5 3 2.50 2.74 89j 2.74 2.51 89* 8.8 190 8.1 • 190 7.1 190 6.1 191 5.1 191 1 2.6 li.5 193 193 8.45 8.08 8.48 195 11.0 10.9 185 0/S 6.0 195 3.2 194 196 2.53 196 196 2.58 196 2.20 2.00 193 1.82 196 lod 10 10.6 193 193 9.85 196 9.50 198 8.35 197 7.7 197 6.8 197 6.43 9.7 193 193 B.5  78 ;*• 3 . 6 5 78 3.55 78 • 3.50 78 2.93 2.60 79 79 . : 2.40 80 ". 2 . 2 3 80 2.13' 79 2.15 78 2.08 iO.07 77 1.90 77 76 1.83 76 1.70 76 1.63 1.61 76 76 1.50 1.40 76 76 1.35  -  -  -  -  p l u g t / c broke  '• /  ." -  f u s e blew 24/11/67 c l e a r a n c e a t TDC between s p a c e r & head = . 0 5 "  29/11/67  Power o f f f o r f r a c U o n o f s e c . t e s t 42  Voltage suddenly d e c r e a s e d t o s t 51 C l e a r a n c e a t TDC between bead and s p a c e r = .02"  -  ---  1  lrt;. vibr. prsa-svoH" n r , top | root .3" i t O .2" .05° .2" .05"  4,'VtS  -  -  outlet l away 4' 423/11/67  13/11/67  I S / 1 / 6U 68 19/1/68  74 '  70  23/1/66  clearance .05* a c r e * bolea o n s p a c e r open T e s t 73 - o i l added T e a t 75 - o i l added T e a t 78 - ecrew h o l e s pluggedT e s t 79 - h e a t e r atortod  >-  263  APPENDIX V I I FPS PROTOTYPE TEST DATA A. Test Data f o r engine with fixed throw crankshaft- driven externally Date of Test 30/10/69  5/1/70  No. Speed (rpm)  10/1/70  2  Combustion Fuel Flow 10cc/ 2.48mii  Scavenging ratio 36.5  Air/ Fuel 10.2  1  3200  .010  350*  yes  1  2750  .008  100*  37.5  2  2910  .010  -  no no  40.0  3  3600  .018  100*  yes  43.0  4  3700  .016  200*  yes  40.0  5  3000  .012  100*  42.5  6  3600  .015  -  no yes  39.5  7  3400  .014  350*  yes  40.5  8  3400  .012  450*  yes  37.5  9  3430  .012  450*  yes  37.0  10  .007  350*  no  37.5 2.8cc/ .013 130-145 yes 36.5 3650 8.5 .56min 149-155 3700 .014 yes 7. cc/ 37.0 12.0 1,9min 4200 - s e l f - s u s t e i n i n g . Started to Blow down when f i n temp 230250 F. When motion ceased, f i n temp was 270 F.  1 2  6/1/70  Pree drop Fin temp (°F) (in H 0)  1  2620  2  3600 - s e l f - s u s t e i n i n g . Started to slow down when f i n temp 210°  3  3800 - s e l f - s u s t e i n i n g . Started to slow down when f i n temp 19020O F. When motion ceased, f i n temp was 240 F. Soak temp was^260 F.  1  3600 - With external cooling supplied by blower, f i n temp remained below 200 F and engine ran continuously •estimated temperature of piston  B. Test Data f o r free-piston test engine. Date  NoT Speed (rpm)  Length (cycles) 500  19/1/70  1  28/1/70  2  2500  100  5/2/70  3  2480  20  5/2/70  4  2460  6  Load =  L  Loading (out & i n )  Stroke  0#  \H  @ 8"  Fuel while gas, o i l  1.15  reg. gas, o i l  i# @ 19"  1.15  reg. gas, o i l ,  ether  1# @ 19"  1.05  reg. gas, o i l ,  ether  Load moment + lever arm moment 1.5  where lever arm moment = .26 x 9.7 M = c o e f f i c i e n t of f r i c t i o n , leather on C.I, = .56  

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