Electric power steering apparatus and method for controlling the electric power steering apparatus

An electric power steering apparatus, comprising:

• a torque sensor that detects a steering torque which is applied by a steering operation of a driver's steering wheel;
• an electric motor that produces a steering assist torque used to assist the steering operation of the driver's steering wheel;
• an assist control unit that calculates a target assist torque based on at least the detected steering torque, and that executes drive control of the electric motor based on the calculated target assist torque;
• a vehicle speed detection unit that obtains vehicle-speed information concerning a vehicle speed at which a vehicle is moving;
• a malfunction determination unit that determines presence or absence of at least one of an abnormal torque fluctuation, which is a phenomenon in which a torque output from the electric motor abnormally fluctuates, and a torque clockwise/counterclockwise variation, which is a phenomenon in which the torque output from the electric motor varies between clockwise and counterclockwise turning operations of the driver's steering wheel that are performed with the same degree of steering torque;
• and
• a malfunction-time control unit that permits the drive control of the electric motor executed by the assist control unit when the vehicle speed is equal to or lower than a predetermined speed, and that prohibits the drive control of the electric motor executed by the assist control unit when the vehicle speed is higher than the predetermined speed, in a case where at least one of the abnormal torque fluctuation and the torque clockwise/counterclockwise variation is detected by the malfunction determination unit.