Robust control of cars with front and rear wheel steering

A steering performance enhancement system for a 4WS car designed to improve the ability of the driver to keep the vehicle on the desired path is described. The system is commanded by the driver to control the front and rear wheel steering. The system is developed on the basis of a single-gain design approach having three goals: first, to guarantee that the lateral acceleration follows the driver´s command, second to achieve robust relaxation of the sideslip angle, and third to preserve robust stability. The system designed is independent of the major uncertainties of the car model, namely the car´s mass and the road characteristics. The system utilises the general robust triangular decoupling controller, achieving robust decoupling of the front lateral acceleration from the yaw dynamics, and a prefilter that activates the yaw dynamics according to the driver´s commands guaranteeing the robust relaxation (reduction) of the sideslip angle.