Vehicle dynamics and control synthesis for four-wheel steering passenger cars

This paper is concerned with the active robust autopilot design of a four-w heel steering vehicle against external disturbances. Firstly, the effect of four-wheel steering and independent wheel torques for lateral/directional and roll motions is modelled by a set of linear models under proper manoeuv ring conditions. To enhance the dynamic performance of an automobile system , a mixed H-2/H-infinity, synthesis with pole constraint is designed on the basis of full state feedback applying linear matrix inequality (LMI) theor y. For lateral/directional and roll motions, the steering angles are active ly controlled by steering wheel angles through the actuator dynamics. The w heel power and braking are also controlled by independent wheel torques. Si mulation results indicate that the proposed control approach can achieve pr edetermined performance (or acceptable level of disturbance attenuation) an d stability as well as robustness even when external disturbances are sever e. The active 4WS car along with steering and wheel torque control algorith ms allows greater manoeuvrability and improved stability in a wide range of uncertainty.