Active controls used for the enhancement of maneuverability and handling predictability of automobiles.

摘要

Active controls are used on automobiles to alter their dynamics for the enhancement of maneuverability and handling predictability. Anti-lock braking systems are a good example of this. They avoid wheel lock up, which enables steerability to be maintained and usually provides improved stopping distances in emergency maneuvers. Some more recent developments are yaw rate control systems. These systems produce much more predictable vehicle behavior despite fairly large changes in the vehicle parameters. Yaw rate control systems have been proposed to be actuated by augmented steering, driving and braking torque at each wheel, and active suspensions. Because the steering and torque control inputs seem intuitively to have stronger affects on yaw rate than the suspension, their individual performances in yaw rate control systems were compared through simulation. Unexpectedly, yaw rate control with active suspension input alone is quite effective. In fact, it is more effective in rejecting yaw disturbance than is steering augmentation near the limits of tire adhesion. The individual wheel torque control, however, is shown to be by far the most effective input for yaw rate control.; Active suspensions conventionally improve ride comfort and minimize body motion. In this study, the active suspension is proposed to affect yaw rate as discussed above, and further, to improve "road holding", which is commonly considered a direct result of minimizing the dynamic tire normal force variation. Theoretically, the reduction of tire normal force variation will be shown to be possible with active suspension. However, it will also be shown to be realistically impractical.; When a driver saturates both the braking and steering inputs, it is inferred that he or she desires to maximize the vehicle lateral acceleration and deceleration simultaneously. Active controls are studied for use in controlling the resultant cornering and braking force direction of all four tires in order to respond logically to conflicting driver desires. A very logical response is to minimize the average path radius of curvature. This is accomplished through nonlinear optimal control theory and a simple point mass vehicle model. The improved maneuverability and realistic feasibility of this control is validated through full vehicle simulation.