Patent ID: 8418573

Claim:
A ball-screw spline, comprising: a screw shaft having an outer peripheral surface provided with a helical ball rolling groove; a ball-screw nut formed into a substantially cylindrical shape and threadedly engaged with the screw shaft through intermediation of a first plurality of balls; and a spline nut assembled outside of the ball-screw nut through intermediation of a second plurality of balls, and including an infinite circulation path for the second plurality of balls to freely reciprocate over the entire length of an axial direction of the ball-screw nut, wherein the ball-screw nut comprises a screw portion and an extended portion which are formed integrally with each other with the same outer diameter, wherein the screw portion has an inner peripheral surface comprising a load-rolling groove facing the helical ball rolling groove on the screw shaft side so as to form a load path for the first plurality of balls together with the helical ball rolling groove; and a ball return path coupling adjacent valley portions of the load-rolling groove so as to form an infinite circulation path for the first plurality of balls, corresponding to one loop around the screw shaft, wherein the ball-screw nut has an outer peripheral surface provided with a ball rolling groove for the spline nut, the ball rolling groove for the spline nut being formed over a portion of the ball-screw nut corresponding to the screw portion and the extended portion, and wherein the ball rolling groove for the spline nut is formed at a position which does not overlap the ball return path, in a circumferential direction of the ball-screw nut.