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UBC Theses and Dissertations

Improving the dynamic performance of multiply-articulated vehicles Rempel, Michael R.

Abstract

Current heavy vehicles having two or more trailers suffer from unique dynamic characteristics which limit both their stability and maneuverability at speed. The control of these characteristics in A-train vehicles is the objective of this work; specifically, the attenuation of rearward amplification and high-speed offtracking. Control is attained is through automatic steering of the A-dolly axle; the control system is localized entirely on the A-dolly, creating a modular and easily-implemented unit. The equations of motion were derived for a reference A-train vehicle, and the results simulated and compared to literature. A nonlinear two-dimensional yaw plane model with semi-static load transfer in the pitch and roll modes was found to adequately display the intended system characteristics. To apply control, a second linear state space model was created, based on the behavior of the A-dolly and the second semitrailer only. For high-speed, low amplitude maneuvers under feasible input frequencies, the results corresponded to the nonlinear simulation. Control was achieved using a state variable feedback controller to steer the dolly wheels; the gains were determined by moving the plant eigenvalues via Ackermann's method to the critically-damped locations of the "faster" mode. The controller was shown as to be robust to parameter estimation errors and to balance performance and required control inputs well. An Extended Kalman Filter (EKF) was employed to estimate the unknown tire cornering properties and states not measurable direcdy from the A-dolly. Through simulation, it was found that the controller was effective in reducing both the observed rearward amplification and the dynamic offtracking, although the effectiveness decreased with increasing forward velocity. At the nominal velocity for interstate highways in the United States (24.6 m/s), the peak improvement in rearward amplification under control was reduced to a minimum of 25 percent of the uncontrolled value; the peak value of offtxacking was reduced up to 50 percent.

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