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A nonlinear “bicycle model” of an automobile was used to investigate both conventional front wheel (FWS) and four wheel steering (4WS) automobiles during emergency maneuvers combining braking with steering commands. The model includes a comprehensive, nonlinear tire model. Two different 4WS control laws were used. The first was an open loop law where the commanded rear wheel steer angle was based on the instantaneous front wheel steer angle. The second, a closed loop law, required a signal comprised of a comparison of yaw rate and front wheel steer angle to command the rear wheel steer angle. Simulated results of the response to combined hard steering and braking inputs the potential benefits of 4WS in these types of maneuvers - among these are faster and more stable response and improved maneuverability.

Decreasing the propensity for rollover during steady state cornering of tractor semi-trailers is a key advantage to the trucking industry. This will be referred to as “increasing the lateral stability during steady state cornering” and may be accomplished by changes in design and loading variables which influence the behavior of a vehicle. To better understand the effects of such changes, a computer program was written to optimize certain design variables and thus maximize the lateral acceleration where an incipient loss of lateral stability occurs. The vehicle model used in the present investigation extends that developed by Law [1] and presented in Law and Janajreh [2]. The original model included the effects of tire flexibility, nonlinear roll-compliant suspensions, and fifth wheel lash. This model was modified to include (a) additional effects of displacement due to both lateral and vertical tire flexibility, and (b) provisions for determining “off-tracking”.

Tuning a race car for good handling requires accurate prediction of the tire normal loads and tire orientation as specified by steer and camber angles. This paper describes the development and examples of the application of computer models which have been developed to predict suspension geometry characteristics and wheel loads for Winston Cup cars running on banked tracks. Example cases are presented illustrating the effects of roll center movement front spring split different rates right to left), and cross weight percentage (wedge).