Patent ID: 7290638

Claim:
An electric power steering system comprising: a steering shaft disposed to a steering wheel; a torque sensor disposed to said steering shaft to detect a steering torque generated by said steering shaft; a first pinion disposed to said steering shaft; a rack shaft in mesh with said first pinion and connected with said steering shaft to change a rotational motion of said steering shaft to an axial motion of said rack shaft and to be operated in relation to said steering shaft; a first motor connected with said first pinion to generate a steering assist torque in accordance with the steering torque detected by said torque sensor; a second pinion disposed to be separate from said first pinion and in mesh with said rack shaft; a second motor connected with said second pinion to generate a steering assist torque in accordance with the steering torque; a first control board provided with said first motor; a first control circuit for drivingly controlling said first motor, said first control circuit being provided on said first control board; a second control board provided with said second motor; and a second control circuit for drivingly controlling said second motor, said second control circuit being provided on said second control board; wherein the first control circuit monitors an abnormality in control state of the second control circuit, and the second control circuit monitors an abnormality in control state of the first control circuit.