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

Abstract

This paper is concerned with the active robust autopilot design of a four-wheel 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 manoeuvring conditions. To enhance the dynamic performance of an automobile system, a mixed H2/H∞ synthesis with pole constraint is designed on the basis of full state feedback applying linear matrix inequality (LMI) theory. For lateral/directional and roll motions, the steering angles are actively controlled by steering wheel angles through the actuator dynamics. The wheel power and braking are also controlled by independent wheel torques. Simulation results indicate that the proposed control approach can achieve predetermined performance (or acceptable level of disturbance attenuation) and stability as well as robustness even when external disturbances are severe. The active 4WS car along with steering and wheel torque control algorithms allows greater manoeuvrability and improved stability in a wide range of uncertainty.