Patent ID: 7909131

Claim:
An electric power steering apparatus applied to a steering system that transmits a steering operation of a driver to a steerable wheel, the electric power steering apparatus comprising: a steering force assist device provided with a motor as a driving source, the steering force assist device applying an assist force for assisting the steering operation to the steering system by rotating a steering shaft that couples a steering wheel operated by the driver to the steerable wheel using the motor; control means for controlling an actuation of the steering force assist device by feeding a driving power to the motor; a speed reducing mechanism provided with first and second gears meshed with each other; and frequency extracting means for extracting, from a signal indicating a state of the steering system, a frequency component corresponding to a vibration that increases rattling noise generated at the meshed part of the first and second gears, wherein the motor is drivingly coupled to the steering shaft via the speed reducing mechanism, the control means controls the actuation of the steering force assist device to suppress rattling noise generated in a meshed part of the first and second gears based on a frequency analysis of a vibration generated in the steering system, and when an effective value of the extracted frequency component is equal to or more than a predetermined threshold value, the control means reduces the assist force applied to the steering system.