Power steering apparatus

A power steering apparatus comprising:

• a wheel turning shaft configured to turn a wheel to be steered by axially moving according to a rotation of a steering wheel;
• a wheel turning shaft side ball screw groove formed on an outer circumferential side of the wheel turning shaft, and shaped into a spiral groove;
• a nut having a main body portion annularly formed so as to surround the wheel turning shaft, and provided rotatably relative to the wheel turning shaft;
• a nut side ball screw groove formed on an inner circumferential side of the nut, shaped into a spiral groove, and forming a ball circulation groove together with the wheel turning shaft side ball screw groove;
• a plurality of balls loaded in the ball circulation groove;
• an output pulley attachment portion formed on a one end side in an axial direction relative to the main body portion, assuming that the axial direction is a direction along a rotational axis of the nut, and formed so as to have a larger diameter than an outer diameter of the main body portion;
• an output pulley attached to the output pulley attachment portion so as to face the one end side of the nut in the axial direction, and formed into a cylindrical shape so as to surround the wheel turning shaft;
• a cylindrically formed input pulley having a rotational axis located offset from the rotational axis of the nut in a radial direction, in which the rotational axis of the nut is defined as a first reference axis and the rotational axis of the input pulley is defined as a second reference axis;
• a transmission member provided so as to extend over the output pulley and the input pulley, and configured to transmit a rotation of the input pulley to the output pulley;
• an electric motor configured to rotationally drive the nut via the transmission member and the output pulley by rotationally driving the input pulley, and provide a steering force to the wheel turning shaft through conversion of the rotation of the nut into an axial motion of the wheel turning shaft;
• a flat surface portion formed on an outer side of the nut in the radial direction over a predetermined range in a circumferential direction, assuming that the radial direction is a radial direction of the first reference axis and the circumferential direction is a circumferential direction of the first reference axis, and formed in a region other than a region where the output pulley attachment portion is formed in the axial direction of the nut and extend substantially in parallel with the first reference axis;
• a ball circulation groove one end side opening provided in communication with an one end of the ball circulation groove, and formed so as to be at least partially opened to the flat surface portion in the region where the output pulley attachment portion is formed in a range of the nut in the axial direction;
• a ball circulation groove opposite end side opening provided in communication with an opposite end of the ball circulation groove, and formed so as to be opened to the flat surface portion;
• a circulation member escape portion provided so as to surround the ball circulation groove one end side opening in the region where the output pulley attachment portion is formed in the axial direction on the outer side of the nut in the radial direction, and formed so as to become a same plane continuous from the flat surface portion;
• and
• a circulation member connecting the one end and the opposite end of the ball circulation groove so that the plurality of balls can circulate from the one end to the opposite end of the ball circulation groove or the opposite end from the one end of the ball circulation groove.