Patent ID: 7676309

Claim:
A motor-driven power steering apparatus in which a driving force of an assist motor assists a steering force, comprising: a torque sensor detecting a steering torque; a vehicle speed sensor detecting a vehicle speed; a steering angle detecting means for detecting a steering angle; an angular velocity computing means for detecting a steering angle or an angular velocity of a motor rotating angle; a self-aligning torque computing means for computing a self-aligning torque on the basis of the steering angle detected by the steering angle detecting means and the vehicle speed detected by the vehicle speed sensor; a friction torque computing means computing a friction torque in accordance with a steering angle change from the steering angular velocity computed by the angular velocity computing means; an apparent steering torque computing means for computing an apparent steering torque from the friction torque computed by the friction torque computing means and the steering torque detected by the torque sensor; and a steering torque feedback control means for driving and controlling the assist motor in such a manner that a difference between the self-aligning torque computed by the self-aligning torque computing means and the apparent steering torque computed by the apparent steering torque computing means becomes 0, wherein the apparent steering torque is calculated by subtracting the friction torque from the steering torque, wherein the self-aligning torque is calculated to increase with an increase in the vehicle speed and a change rate of the calculated self-aligning torque to the vehicle speed decreases with an increase in the vehicle speed.