Ball screw mechanism and electric power steering apparatus using such mechanism

摘要

An electric power steering apparatus comprises a rack-and-pinion mechanism and a ball screw mechanism. The ball screw mechanism comprises a shaft formed a screw groove and a nut formed a screw groove. A ball-roll path is created spirally by the screw grooves of the shaft and the nut being opposite each other. A plural number of balls are contained into the ball-roll path. A ball-return path is connecting both ends of the ball-roll path so that the balls go through. A circulation path consists of the ball-roll path and the ball-return path, in which the balls move endlessly. A plural number of separators is arranged between the balls respectively in order to prevent balls from contacting each other. A number of the balls is fewer from one ball to three balls than a maximum number of the balls which can be contained into the circulation path.