Patent ID: 8746102

Claim:
A ball screw device comprising a screw shaft having a spiral screw groove in an outer peripheral surface, a nut having a spiral screw groove in its inner peripheral surface corresponding to the spiral screw groove of the screw shaft and to be screwed with the screw shaft, a number of balls rotatably loaded into a spiral path between the spiral screw grooves, and a circulating part to guide the ball rolling in the spiral path from one circular hole of a pair of circular holes drilled on a side of the nut in a direction substantially orthogonal to an axle line of the nut to the outside of the nut, in which respective ends of the circulating part are fit into respective circular holes, in order to form a ball circulation route inside to return back the ball from the one circular hole to the other circular hole to the spiral path, wherein the circulating part comprises a pair of legs having a tang on each end to scoop up the ball rolling in the spiral path in a direction substantially orthogonal to a tangential direction of the spiral path, and a body to connect the pair of the legs, and wherein a center path diameter Rb of the ball, an internal diameter Rn of the nut, and a distance Rt between a rotational axis of the screw shaft and an inner surface formed inside one of the pair of legs, the inner surface being opposite to the tang of the one of the pair of the legs, satisfy an equation (1): Rb≦Rt <Rn.