DEVELOPMENT OF ACTIVE FRONT WHEEL STEERING CONTROL SYSTEM KEEPING STABLE REGION IN DRIVING PHASE DIAGRAM

This paper presents a new active steering control system based on driving phase diagram (beta(fr)-delta(f) diagram). In order to make state variables to follow those of nominal vehicle model that was developed under no consideration of disturbance, Quadratic Programming Problem (QPP) is formulated, where time varying objective function minimizes the differences between nominal and actual parameters. The steering characteristic in active steering control system changes when the vehicle faces disturbance such as crosswind and flat tire, and driver tries to counteract it after recognizing the change. The proposed method defines a stability region on beta(fr)-delta(f) diagram. In order to make beta(fr) and delta(f) remain in the stability region, a new model predictive controller is proposed. While conventional controllers are restrictive to satisfy the beta(fr)-delta(f) diagram based stability condition, the proposed controller ensures solution space and also plays a direct role to minimize the evaluation function in the constrained optimal control problem.