Robust two degree-of-freedom vehicle steering controller design

Robust steering control based on a specific two degree-of-freedom control structure is used here for improving the yaw dynamics of a passenger car. The usage of an auxiliary-steering actuation system for imparting the corrective action of the steering controller is assumed. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the boundary of the operating domain of the vehicle. The design is carried out by finding the region in controller parameter plane where Hurwitz stability and a mixed-sensitivity frequency-domain constraint are simultaneously satisfied. A velocity-based gain scheduling type implementation is used. Moreover, the steering controller has a fading effect that leaves the low-frequency driving task to the driver, intervening only when necessary. The effectiveness of the final design is demonstrated with linear simulations and nonlinear simulations using a highly realistic model of an actual car.