Power steering apparatus and method of manufacturing power steering apparatus

A power steering apparatus comprising:

• a wheel turning shaft arranged to move in an axial direction in response to rotation of a steering wheel to steer a steered wheel;
• a housing including a wheel turning shaft housing portion accommodating the wheel turning shaft movably in the axial direction, and a reduction mechanism housing portion disposed at an intermediate position in the axial direction of the wheel turning shaft housing portion so as to surround the wheel turning shaft;
• a wheel turning shaft-side ball screw groove provided on an outer periphery of the wheel turning shaft in a spiral groove configuration;
• a nut which is a rotary element provided in the reduction mechanism housing portion, the rotary element being formed annularly so as to surround the wheel turning shaft by a die forging process in which, when an axis of rotation of the rotary element is defined as a first reference axis, a die used for the die forging process is released in a direction along a direction of the first reference axis;
• a bearing provided between an inner wall of the reduction mechanism housing portion and the nut in a radial direction radial to a central axis defined by the axis of rotation of the nut, the bearing configured to surround the nut to rotatably support the nut relative to the housing;
• a nut-side ball screw groove provided on an inner periphery of the nut in a spiral groove configuration to configure a ball recirculation groove in combination with the wheel turning shaft-side ball screw groove;
• a plurality of balls provided in the ball recirculation groove;
• an output pulley abutting surface provided on the nut at a position closer to the ball recirculation groove than the bearing in the direction of the first reference axis, the output pulley abutting surface being formed by a surface substantially perpendicular to the first reference axis;
• a circular cylindrical output pulley secured to the nut in a state where the output pulley is positioned relative to the nut in the direction of the first reference axis by abutting against the output pulley abutting surface, the output pulley overlapping a region of the ball recirculation groove where the plurality of balls recirculate but not overlapping the bearing in the direction of the first reference axis;
• a circular cylindrical input pulley disposed such that a second reference axis defined by an axis of rotation of the input pulley is offset from the first reference axis in the radial direction;
• a transmitting member provided to extend over the output pulley and the input pulley to transmit rotation of the input pulley to the output pulley;
• an electric motor arranged to rotationally drive the input pulley to rotationally drive the nut through the transmitting member and the output pulley, so that rotation of the nut is converted into axial motion of the wheel turning shaft, thereby applying steering force to the wheel turning shaft;
• and
• a recirculation member provided to connect one end and other end of the ball recirculation groove so that the plurality of balls are recirculatable in either direction between the one end and other end of the ball recirculation groove.