Electric power steering apparatus

An electric power steering apparatus for a vehicle, comprising:

• an electric motor for applying a steering assist torque to a steering system operatively connecting a steering wheel and steerable wheels of the vehicle;
• a steering torque sensor for detecting a steering torque of said steering system and outputting a steering torque signal corresponding to the detected steering torque;
• a target current calculating section for calculating, on the basis of at least said steering torque signal, a target current to be supplied to said electric motor and outputting a target current signal corresponding to the calculated target current;
• a motor current detector for detecting a current flowing in said electric motor and outputting a motor current signal corresponding to the detected current;
• an offset calculating section for calculating an offset between said target current signal and said motor current signal and outputting an offset signal corresponding to the calculated offset;
• a first drive control signal generating section for generating, on the basis of said offset signal, a first drive control signal to drive said electric motor;
• a fault detecting section for detecting abnormality in said electric power steering apparatus wherein said fault detecting section is capable of detecting a failure in said motor current detector;
• a second drive control signal generating section for generating on the basis of said target current signal a second drive control signal to drive said electric motor wherein the second drive control signal generating section generates the second drive control signal independently of the motor current signal at least when the fault detecting section detects a failure in said motor current detector, and
• a motor drive control mode switching section for changing over drive control modes of said electric motor such that when abnormality in said apparatus is not detected by said fault detecting section, operation of said electric motor is controlled on the basis of said first drive control signal, and when abnormality in said apparatus is detected by said fault detecting section, operation of said electric motor is controlled on the basis of said second drive control signal.