BALL SCREW MECHANISM

PROBLEM TO BE SOLVED: To provide a ball screw mechanism suppressing noise and vibration, and ensuring smooth operation. SOLUTION: Lead-in parts 4b having a center axis X2 (between a point A and a point B) agreeing with a center axis X1 of a rolling passage, i.e., an internal thread groove 2a, are formed in both ends of a circulating groove 4a connected to one end of the internal thread groove 2a forming the rolling passage when a nut 2 and a piece 4 are viewed from the radially inside, that is, the center P of a circular arc with a radius Rf described by the centerline of the circulating groove 4a is in a position axially overlapping the point B. This means that force in the axial direction of the nut 2 is not applied to the ball 3 discharged from the rolling passage. Thus, there is little possibility of causing catching of the ball 3, and there is no need to enlarge the width of a lead-in part 4b in relation to the width of the rolling passage. The ball 3 is thereby restrained from coming in abutting contact with a groove wall to suppress noise and vibration. COPYRIGHT: (C)2007,JPO&INPIT