Vehicle Handling Improvement by Active Steering

This paper first analyses some stability aspects of vehicle lateral motion, then a coprime factors and linear fractional transformations (LFT) based feedforward and feedback H1 control for vehicle handling improvement is presented. The control synthesis procedure uses a linear vehicle model which includes the yaw motion and disturbance input with speed and road adhesion variations. The synthesis procedure allows the separate processing of the driver reference signal and robust stabilization problem or disturbance rejection. The control action is applied as an additional steering angle, by combination of the driver input and feedback of the yaw rate. The synthesized controller is tested for different speeds and road conditions on a nonlinear model in both disturbance rejection and driver imposed yaw reference tracking maneuvers. NOMENCLATURE G vehicle center of gravity (CG) m; J mass and inertia (991 kg, 1574 kg m2) lf distance from CG to front axle (1.00 m) lr distance from CG to rear axle (1.46 m) sb wheel-base (1.40 m) R steering gear ratio (21) cf front cornering stiffness (41.6 kN/rad) cr rear cornering stiffness (47.13 kN/rad) road adhesion (scaling factor 0; 1 ) nt tire-road length contact (1.3 cm) fxi; fyi longitudinal and lateral forces of the ith tire fxf; fyf total front longitudinal and lateral force