Patent ID: 8731775

Claim:
An electric power steering apparatus including a steering force control unit that causes an electric motor to generate an assisting steering torque when steering steerable road wheels in dependence on a steering of a steering wheel, the apparatus comprising: a steering angle sensor for detecting a steering angle of the steering wheel, a yaw rate sensor for detecting a yaw rate of a vehicle, and a steering torque sensor for detecting a steering torque; wherein: a steering direction is determined to be in a direction away from or toward a neutral position according to the steering angle and the steering torque, and the steering force control unit performs a return control for the steering wheel according to the detected steering angle and yaw rate when the steering wheel is being returned towards the neutral position, and includes a failure detection unit for detecting a failure of the steering angle sensor; upon detection of a failure in the steering angle sensor, the steering force control unit performs the return control in an amplified manner according to the yaw rate detected by the yaw rate sensor as compared to a case where the steering angle sensor is functioning normally; the return control comprises a control action to increase and decrease a returning force of the steering wheel, and upon detection of a failure in the steering angle sensor, the steering force control unit increases the returning force based on the yaw rate detected by the yaw rate sensor as compared to a case where the steering angle sensor is functioning normally; and when the steering angle sensor and the yaw rate sensor are both normal, and the yaw rate detected by the yaw rate sensor is below a prescribed value, the contribution of the returning force based on the steering angle detected by the steering angle sensor is substantially greater than that based on the yaw rate detected by the yaw rate sensor.