Ball-screw spline

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.