Ball screw

Abstract

Provided is a ball screw where a three-dimensionally formed recirculation trajectory of a recirculation groove can be connected to a helical trajectory in such a manner that the tangential directions thereof are substantially continuous. A ball screw () includes: a ball screw shaft () including a helical groove (); a ball nut () including a helical groove; and a plurality of balls () placed between the helical groove () of the ball screw shaft () and the helical groove of the ball nut (). The ball nut () is provided with a recirculation groove that is connected to one end and the other end of the helical groove of the ball nut () to recirculate the balls (). A recirculation trajectory () of the recirculation groove is formed on the basis of a groove cross-sectional trajectory curve representing a trajectory along which the balls () are recirculated in a groove cross-section of the ball screw shaft (), and a longitudinal trajectory curve representing a trajectory along which the balls () are recirculated in a virtual plane where a trajectory length ω of the groove cross-sectional trajectory curve is an H-axis and a helical trajectory length F(ω) is a V-axis.