Patent ID: 9266555
Filing Date: 2016-02-23
CPC Classification: B62D,F16H,Y10T

Claim Text:
1. An electric power steering apparatus of a ball screw type, the electric power steering apparatus comprising: a rack bar having a spiral outer peripheral screw groove on an outer peripheral surface of the rack bar; a ball nut coupled to the rack bar via a ball and having an end cap coupled to the inner surface of the ball nut and having a ball moving passage, wherein one side of the ball moving passage passes through the ball circulation passage and other side of the ball moving passage passes through the spiral outer peripheral screw groove and the inner screw groove, wherein a first distance from a central axis of the ball nut to an outermost of the inner screw groove gradually increases from a center of the ball nut to two end sides of the ball nut, wherein the inner screw groove has a hollow shaped groove which contains a lubricant, and wherein a radial cross-sectional area of the hollow shaped groove formed in a section where a second distance from the central axis of the ball nut to the center of ball on the inner screw groove gradually increases, gradually decreases toward an inlet of the ball moving passage.