Patent ID: 7305902

Claim:
A ball screw device comprising: a screw shaft having substantially one turn of at least one thread groove provided in an outer peripheral surface thereof; a nut externally mounted on the screw shaft and having a thread groove provided in an inner peripheral surface thereof at an angle substantially identical to that of the thread groove; and a plurality of balls interposed between the respective thread grooves, wherein a ball circulation groove for coupling downstream and upstream sides of the thread groove of the screw shaft are provided on the screw shaft so that the balls are returned from the downstream side to the upstream side to be thereby circulated in the thread groove of the screw shaft, the ball circulation groove has an intermediate region in a direction of rolling balls having such a curved shape as to sink radially inward and both end side regions positioned on both sides of the intermediate region and having a predetermined shape, and the ball circulation groove configured in the manner in that a centrode of the balls rolling in the both end side regions and a centrode of the balls rolling in the thread groove of the screw shaft satisfy predetermined conditions with respect to the circulation of the balls, wherein the predetermined conditions are that an angle, at which a first tangent line obtained at an intersection point of a small arc formed by the centrode of the balls rolling in the both end regions of the ball circulation groove with respect to a large arc formed by the centrode of the balls rolling in the thread groove of the screw shaft intersects with a second tangent line obtained at the intersection point with respect to the small arc, is set at a degree larger than 0 degree and at most 30 degrees.