Patent ID: 8424402
Filing Date: 2013-04-23
Classification: F16H,Y10T

Abstract:
1. A ball screw unit, comprising: a screw shaft including a groove; a nut that is fitted to the groove of the screw shaft via balls and that has an outer diameter which gradually decreases in a predetermined direction; a nut holding portion that disposed on an outer peripheral face of the nut, that holds the nut, and that has an inner diameter which gradually decreases in the predetermined direction in accordance with a gradual decrease in the outer diameter of the nut; and a nut biasing member that biases the nut in the predetermined direction in which the outer diameter of the nut and the inner diameter of the nut holding portion gradually decrease, wherein the outer diameter of the nut and the inner diameter of the nut holding portion gradually decrease in such a manner that when a force that proceeds in a direction opposite to a direction of the biasing force of the nut biasing member and that overcomes the biasing force is applied to the nut, a friction force between the outer peripheral face of the nut and an inner peripheral face of the nut holding portion decreases to allow relative movement between the nut and the nut holding portion, wherein the nut biasing member is disposed on an end of the nut, the end of the nut having an outer diameter greater than an outer diameter of an other end of the nut, and wherein the nut and nut holding portion are configured such that, when the nut reaches a movement limit position of the nut in the direction of the biasing force, the nut holding portion continues moving in the direction of the biasing force.