UBC Theses and Dissertations
Dynamic loads on spur gear teeth. Yeh, Benjamin Hsi-Lu
The load on gear teeth while in operation has long been an open question. So many variable and uncertain factors are involved that it is not surprising that many different formulas and rules have been proposed from time to time. Few, if any, systematic experiments were made to obtain data on this subject until about 1923, when the ASME Special Research Committee on the Strength of Gear Teeth was organized and the Lewis gear-testing machine was built. The results of this Committee's work were published in an ASME Research Publication, 1931, entitled "Dynamic Loads on Gear Teeth". For the experiment in this thesis, a gear testing machine was designed and built in order to investigate the dynamic loads on gear teeth. Strain gages were applied to one of the test gear teeth and the main shaft, and were calibrated to give an indication of tooth load and shaft torque respectively. A static tooth load calibration on a strain indicator was made by means of a load arm, a cable and dead weights. The static calibration helped to set the indicator so that the reading shown on it during the dynamic load test could be converted to the true load applied. During the dynamic load test of each test series, photographs of the oscillograph traces were taken at different machine speeds and at several different values of nominal torque. The principal object of these tests was to determine loads between gear teeth under operating conditions by using strain gages and electronic recordings at the present time, the experimental work is limited to involute spur gears only. It is suggested by most gear experts, that the dynamic tooth load may be considered as the sum of the static load and the increment load. The experiments show clearly that the precise gears have no increment loads on their teeth, and that the measured maximum tooth loads are almost the same at different test speeds. The formula for evaluating the dynamic load on spur gear teeth, developed by Earle Buckingham, gives slightly higher values than the measured loads at low speed (approximate pitch line velocity 90 fpm), but diverges widely from the present experimental results at high speed (approximate pitch line velocity 2800 fpm).
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