| 摘要 |
A ball screw nut of a ball screw device is fastened to a motor shaft (26) by engaging a male thread portion thereof with a female thread portion (34) of the motor shaft (26). In a case where, in a movement pathway for balls, an area where the balls roll under load from a rack shaft and the ball screw nut is set as a load area, an area that does not receive the load is set as a no-load area, and areas for transition from the load area to the no-load area are set as transition areas, the male thread portion is formed such that the transition area on the nut-side joint portion (75)-side closest to a seating surface (31) does not overlap phase ranges of cut portions (32) in a state where the ball screw nut is fastened to the motor shaft (26). |
