Control apparatus for electric power steering system

A control apparatus for an electric power steering system, said control apparatus comprising:

• steering torque detecting means for detecting a steering torque caused at a steering shaft;
• steering force assist command value calculating means for calculating a steering force assist command value which is a target value for controlling a steering assist force caused at the power steering system at least based on the detected steering torque;
• and
• motor controlling means for controlling a current value of a motor for assisting a steering operation based on the calculated steering force assist command value;
• wherein the steering force assist command value calculating means comprises digital calculation means having a bit number larger than a bit number of the motor controlling means, calculates the steering force assist command value based on data of the steering torque sampled at predetermined time intervals and outputs the calculated steering force assist command value to the motor controlling means in which the steering force assist command value is calculated by adding lower bits data of the steering force assist command value that is omitted in outputting the steering force assist command value to the motor controlling means, to data of the steering torque that is sampled at a next time.