Patent ID: 7913804

Claim:
An electric power steering system, comprising: a steering mechanism for converting a rotational movement of a steering wheel to a steering movement of a road wheel; a steering torque sensor for detecting a steering torque applied to the road wheel; an electric motor for providing an assisting force for causing the steering movement of the road wheel; and a control unit for providing a control variable for the electric motor, the control unit comprising: a target control base value determining unit for determining a target control base value for the electric motor at least according to a steering torque applied to the steering wheel, a correction value determining unit that modifies the target control base value so as to determine a returning force that urges the steering wheel toward a neutral position, and forwards the modified target control base value to a drive unit for the electric motor, wherein the correction value determining unit modifies the target control base value so as to cause the electric motor to produce a relatively small returning force when a rotational direction of the steering wheel agrees with a direction of the steering torque applied to the road wheel, and a relatively large returning force when a rotational direction of the steering wheel disagrees from a direction of the steering torque applied to the road wheel; and wherein the returning force current computing unit is configured such that the returning force produced by the electric motor is reduced with an increase in a steering angle velocity of the steering wheel when a rotational direction of the steering wheel agrees with a direction of the steering torque applied to the road wheel at least in a range of the steering angle velocity.