Robust handling improvement of four-wheel steering vehicles

This paper presents coprime factors and LFT based feedforward and feedback H_∞ control of four wheel steering vehicle handling improvement. Control synthesis uses a linear vehicle model which includes the yaw motion and disturbance input with road adhesion variations. The synthesis procedure allows the separate processing of the robust yaw damping, disturbance rejection and side slip angle minimization or model matching. The control is applied to the rear wheels by combination of the driver input and feedback of the yaw rate. The synthesized controller is tested on a nonlinear model in both disturbance rejection and driver imposed yaw reference tracking maneuvers.