Ball screw and electric power steering system including ball screw

摘要

There are provided a ball screw that makes it possible to prevent a situation where a large load is applied to a part of a plurality of balls, and an electric power steering system including the ball screw. The ball nut is a component that surrounds a part of the male thread groove, and has a nut inner surface and a female thread groove. The female thread groove is formed in the nut inner surface, and forms a part of the rolling path. A female thread diameter varies according to a position in an axial direction of the ball nut. The female thread diameter is larger at each axial end of the ball nut than at an axially intermediate portion of the ball nut, and the female thread diameter is larger at one axial end than at the other axial end.

主权项

1. A ball screw comprising:
a ball screw shaft; a ball nut; a plurality of balls; and a rolling path, wherein the ball screw shaft has a screw shaft outer surface and a male thread groove, the ball nut is a component that surrounds a part of the male thread groove or the entire male thread groove, the ball nut having a nut inner surface and a female thread groove, the balls are disposed in the rolling path, the rolling path is formed between the ball screw shaft and the ball nut, the male thread groove is formed in the screw shaft outer surface and forms a part of the rolling path, the female thread groove is formed in the nut inner surface and forms a part of the rolling path, and a female thread diameter that is a diameter of the female thread groove varies according to a position in an axial direction of the ball nut, the female thread diameter being larger at each axial end of the ball nut than at an axially intermediate portion of the ball nut, and the female thread diameter being larger at one axial end than at the other axial end.