Patent ID: 7249533

Claim:
A ball screw device comprising: a nut having a nut thread groove in an inner peripheral surface thereof defining a ridge in the inner peripheral surface; a screw shaft having an outer peripheral surface and a plurality of screw shaft thread grooves each formed in a continuous first helical direction in the outer peripheral surface and axially adjacent to one another, each of said screw shaft thread grooves having an upstream end and a downstream end; a plurality of balls interposed between the screw shaft thread grooves and the nut thread groove; said screw shall having ball circulation grooves each adjoining and coupling the downstream end of one of the screw shaft thread grooves and the upstream end of the one of the screw shaft thread grooves so that the balls are returned to the upstream end from the downstream end so as to be thereby circulated, the ball circulation grooves being formed in the outer peripheral surface of the screw shaft and substantially in a common angular segment of the screw shaft defined by the upstream ends and the downstream ends of the screw shaft thread grooves, and the ball circulation grooves being axially adjacent to one another; and a retainer ring for rotatably retaining each of the balls in circumferentially spaced positions around a circumference of said screw shaft, said retainer ring being mounted to an outer periphery of the screw shaft so as to rotate relative said screw shaft and remain in an axially fixed position relative said screw shaft.