Motor-driven power steering system and method of controlling same

Abstract

The maximum rotational speed of an electric motor upon returning motion of a steering mechanism to its neutral position is limited below a preset value dependent on the speed of travel of an automotive vehicle incorporating the steering mechanism. A motor-driven power steering system comprises the steering mechanism, the electric motor for applying assistive power to the steering mechanism, steering torque detecting means for producing signals representative of a steering torque, steering rotation detecting means for producing signals indicative of steering rotation, and a control unit. The control unit includes returning motion detecting means for detecting returning motion of the steering mechanism to its neutral position, vehicle speed detecting means for producing a signal representing the speed of travel of the automotive vehicle, correcting means for limiting a signal indicating the speed of steering rotation below a preset value based on the signal from the vehicle speed detecting means when returning motion of the steering mechanism is detected, and motor control means for determining a motor control signal based on the signals from the steering torque detecting means and the signal indicating the speed of steering rotation, or the signals from the steering torque detecting means and the limited signal from the correcting means when returning motion of the steering mechanism is detected, and for controlling the electric motor with the determined motor control signal.

Dependencies are inferred from the claim text.