VEHICLE STEERING CONTROL SYSTEM USING DESIRED VEHICLE MODEL

A vehicle steering control system has a steering wheel angle sensor, a vehicle speed sensor, a control unit and an actuator for steering either (or both) of front and rear wheel pairs of a controlled vehicle. The control unit determines desired values of yaw rate and lateral acceleration corresponding to the sensed steering wheel angle and vehicle speed by using at least one desired mathematical vehicle model having desired vehicle response characteristics. Then, the control unit determines a desired value of a front or rear wheel steer angle (or both of the front and rear wheel angles) theoretically required to achieve the desired value of the yaw rate, and another desired value of the steer angle theoretically required to achieve the desired value of the lateral acceleration. Finally, the control unit determines a weighted average of two desired values of the steer angle by using weights which are functions of vehicle speed and/or steering wheel angular speed. The actuator steers the front or rear wheel pair so that an actual steer angle is maintained equal to the weighted average.