Robust stabilization of vehicle dynamics by active front wheel steering control

The study of designing steering control systems for vehicles has attracted much attention, with the purpose of improving maneuverability and stability. Most of the vehicles models used to represent the dynamics were linear ones. Because of this, the control has to be restricted, at least theoretically, within a small range of steering angle, and may not be enough to compensate stability in critical motions. The purpose of this paper is to present a control strategy of the active front wheel steering system to protect the vehicle from spin and to realize the improved cornering performance. For this, the mechanism of vehicle spin behavior is analyzed and explained using concepts of bifurcation theory. The vehicle destabilization is shown to be caused by a saddle-node bifurcation and it depends heavily on a rear tire side force saturation. Based on these observations, the saturation characteristics of rear tires are modeled by a linear function with uncertainty terms of a special structure. Then the linear H^∞ control theory is applied to design a front wheel steering controller which compensates the instability against the nonlinear uncertainty