Patent ID: 9568078
Date: 2017-02-14
CPC Classifications: F16H

Claim:
1. A screw device comprising: a screw shaft having a helical rolling-member rolling groove on an outer circumferential surface thereof; a nut having a helical loaded rolling-member rolling groove opposed to the rolling-member rolling groove on an inner circumferential surface thereof; a return path connecting one end and the other end of a helical loaded rolling-member rolling path formed by the rolling-member rolling groove of the screw shaft and the loaded rolling-member rolling groove of the nut; and a plurality of rolling members arranged in the loaded rolling-member rolling path and the return path, wherein when viewed in the axial direction of the nut, a curvature radius change section is provided in the return path the curvature radius change section is configured so that a curvature radius of a track centerline of the rolling members in the return path is equal to or larger than a curvature radius of a track centerline of the rolling members in the loaded rolling-member rolling path, and so that the curvature radius of the track centerline of the rolling members in the return path increases continuously or in a stepped manner by combining two or more arcs with increasing distance from the loaded rolling-member rolling path, and each of a sectional shape orthogonal to a longitudinal direction of the loaded rolling-member rolling groove of the nut and a sectional shape orthogonal to a longitudinal direction of an outer circumferential side of the curvature radius change section is formed into a gothic arch groove shape which comes into contact with balls at two points, the balls serving as the rolling members.