Patent ID: 7154404

Claim:
An electric power steering system comprising: a three-phase brushless DC motor; a steering torque detection means for detecting a steering torque generated on a steering shaft; and a resolver for detecting a resolver rotation angle of the brushless DC motor, characterized by a rotation angle conversion means for converting the resolver rotation angle into a motor rotation angle corresponding to the number of poles employed in the brushless DC motor; a rotational direction command value computation means for computing a rotational direction command value of the brushless DC motor; a command current value computation means for computing a command current value for driving the brushless DC motor; a MOS driving computation means for driving the brushless DC motor based on the command current value; a failure detection apparatus connected to be capable of communicating with the command current value computation means for determining whether a computation carried out by the command current value computation means is normal, wherein the failure detection apparatus determines whether a computation operation is normal based on the motor rotation angle and the rotational direction command value.