Patent ID: 6988027

Claim:
An electric power steering system comprising: a motor for assisting a driver with a steering operation; motor current detection means for detecting a current supplied to the motor; a main CPU for carrying out control so that the current detected by the motor current detection means coincides with a target current; a sub CPU configured to communicate with the main CPU so as to monitor the main CPU; a motor drive circuit for driving the motor, said motor drive circuit including switching elements; a switching element drive circuit for controlling the switching elements; and a motor drive disable circuit disposed between said switching element drive circuit and said main and sub CPUs, wherein said motor drive disable circuit disables drive of the motor in a predetermined condition, the main CPU and the sub CPU individually calculate an offset voltage of the motor current detection means in order to calibrate the motor current detection means, wherein the main CPU calculates the offset voltage and sends an offset voltage calculation request signal to the sub CPU, upon communication between the main CPU and the sub CPU, the sub CPU calculates the offset voltage and sends an offset voltage calculation completion signal to the main CPU, and a normal condition is determined when the time from the main CPU offset voltage calculation to the offset voltage calculation complete signal being received from the sub CPU by the main CPU, falls within a predetermined period of time set by a timer.