Patent ID: 8813903

Claim:
An electric power steering system that applies assist force that assists an operation of a steering system of a vehicle to a rack shaft by transmitting driving force of a motor to the rack shaft, the system comprising: a cylindrical motor shaft through which the rack shaft of the vehicle is passed, and that is rotated by driving of the motor; a motion conversion mechanism that has an engaging portion engaged with the motor shaft, and that converts a rotational motion of the motor shaft into an axial linear motion of the rack shaft: a bearing that is arranged on an outer periphery of the motion conversion mechanism; and a restricting member that restricts a distance, to a predetermined distance, that the motion conversion mechanism is able to move relative to the motor shaft, wherein the motion conversion mechanism moves in a same direction in which the engaging portion becomes disengaged; the bearing is provided so as to be movable together with the motion conversion mechanism in the same direction in which the engaging portion becomes disengaged; the restricting member is formed of a member that is arranged to face the bearing with a predetermined clearance left between the restricting member and the bearing; and a length of the engaging portion is set longer than the predetermined distance.