Power steering device

A power steering device comprising:

• a steered shaft configured to be moved in an axial direction in accordance with a rotation of a steering wheel, and thereby to steer a steered wheel;
• a nut formed into a cylindrical shape surrounding the steered shaft, and configured to be rotated relative to the steered shaft;
• a ball circulation groove including a shaft side ball screw groove having a helical groove shape, and provided on an outer circumference of the steered shaft, and a nut side ball screw groove having a helical groove shape, and provided on an inner circumference of the nut;
• a plurality of balls disposed within the ball circulation groove to be rolled within the ball circulation groove;
• a first connection passage including one end side opened on an outer circumference surface of the nut, and the other end side opened on an inner circumference surface of the nut, and opened on the one end side of the ball circulation groove;
• a second connection passage including one end side opened on the outer circumference surface of the nut, and the other end side opened on the inner circumference surface of the nut, and opened on the other end side of the ball circulation groove;
• a connection member connecting the first connection passage and the second connection passage to circulate the balls between the first connection passage and the second connection passage;
• an electric motor configured to drive and rotate the nut, and thereby to provide a steering force to the steered shaft;
• a first load transition region provided in a first predetermined range in the nut side ball screw groove from the other end side opening of the first connection passage along the nut ball screw groove, formed so that a radial distance between a rotation axis of the nut and the nut side ball screw groove is gradually increased toward the other end side opening of the first connection passage, and formed so that the balls pass through a first no load region in which a load is not transmitted from the nut side to the steered shaft side, and then the balls pass through a first load region in which the load transmitted from the nut side to the steered shaft side is gradually increased, when the balls in the first predetermined range are moved from the other end side opening of the first connection passage along the nut side ball screw groove;
• and
• a second load transition region provided in a second predetermined range in the nut side ball screw groove from the other end side opening of the second connection passage along the nut side ball screw groove, formed so that a radial distance between the rotation axis of the nut and the nut side ball screw groove is gradually increased toward the other end side opening of the second connection passage, and formed so that the balls pass through a second no load region in which the load is not transmitted from the nut side to the steered shaft side, and then the balls pass through a second load region in which the load transmitted from the nut side to the steered shaft side is gradually increased, when the balls in the second predetermined range are moved from the other end side opening of the second connection passage along the nut side ball screw groove,
• wherein the first load transition region and the second load transition region are formed so that a length of a portion from an end portion of the first transition region on the first connection passage side through the ball circulation groove to an end portion of the second load transition region on the second connection passage side is non-integer multiple of a diameter of one of the balls.