Patent ID: 8132477

Claim:
A ball screw device, comprising: a plurality of balls; a screw shaft in which a rolling groove for the balls is spirally formed at a predetermined lead; and a nut member comprising: a through-hole into which the screw shaft is inserted, the through-hole having an inner peripheral surface provided with a load rolling groove which faces the rolling groove of the screw shaft, the load rolling groove and the rolling groove of the screw shaft cooperating with each other so as to form a spiral load ball path; and a no-load ball path which forms an infinite circulation path for the balls while both ends of the load ball path are communicatively coupled to each other, wherein the no-load ball path is constituted by a no-load ball groove spirally formed in the inner peripheral surface of the through-hole of the nut member and by a pair of direction change grooves which communicatively couple the load rolling groove and the no-load ball groove to each other so as to complete the infinite circulation path as a closed loop, and wherein the direction change grooves are formed to become gradually deeper from the load rolling groove to the no-load ball groove so as to continuously couple the load rolling groove and the no-load ball groove to each other without steps.