Multi-objective control synthesis: an application to 4WS passenger vehicles

The vehicle dynamics and control play an important role in an automated hig hway system for passenger cars. This study addresses the problem of designi ng active controllers for four-wheel-steering (4WS) vehicles. We first obta in a set of linear maneuvering equations representing the four-wheel steeri ng motions and independent wheel torques for lateral/directional plus roll dynamics. We then formulate simultaneous H-2 and H-infinity (sub)-optimal c ontrols with a desired pole assignment via linear matrix inequalities (LMIs ). The steering angles are actively controlled by steering wheel commands t hrough the actuator mechanisms for the lateral/directional and roll motions . Further the wheel power and braking are directly controlled by independen t torques. Numerical simulations are performed on a complex vehicle model i n order to evaluate the vehicle performance (noise and disturbance attenuat ion), stability, and robustness under a given class of uncertainty. Finally , the presented autopilot controller provides greater maneuverability and i mproved directional stability for passenger vehicles. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.