Electric power steering apparatus

Patent metadata

Field	Value
Publication number	US-9744988-B2
Application number	US-201615056010-A
Country	US
Kind code	B2
Filing date	Feb 29, 2016
Priority date	Mar 6, 2015
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

An electric power steering apparatus is configured to provide steering assistance as rotary torque of a driving toothed-pulley fixedly fitted to a rotary shaft of an electric motor is transmitted through a toothed belt to a driven toothed-pulley that rotates together with a ball screw nut in an integrated manner. The electric power steering apparatus is configured such that the amount of axial travel of a rack shaft is limited when a rack end and a housing come into contact with each other in the axial direction. The electric power steering apparatus includes a tilt allowing portion configured to cause the ball screw nut to tilt relative to a ball screw shaft such that the distance between the center of rotation of the driven toothed-pulley and that of the driving toothed-pulley increases when the rack end and the housing come into contact with each other in the axial direction.

First claim

What is claimed is:

1. An electric power steering apparatus including:
a ball screw shaft that is integral with a rack shaft provided so as to be movable relative to a housing in a vehicle-width direction;
a ball screw nut rotatably mounted on the ball screw shaft, the ball screw nut being fitted at a portion of an outer periphery on one side in an axial direction, to the housing via a bearing such that the ball screw nut is rotatable relative to the housing and immovable in the axial direction relative to the housing;
a driven toothed-pulley fixedly fitted onto a portion of the outer periphery of the ball screw nut on the other side in the axial direction, the driven toothed-pulley being configured to rotate together with the ball screw nut in an integrated manner;
an electric motor mounted on the housing;
a driving toothed-pulley to which rotary torque generated by the electric motor is transmitted, the driving toothed-pulley and the driven toothed-pulley are located in a same plane in the axial direction; and
a toothed belt looped over the driving toothed-pulley and the driven toothed-pulley to transmit the rotary torque generated by the electric motor to the ball screw nut,
the electric power steering apparatus configured to provide steering assistance by using an axial driving force that is applied to the rack shaft when the rotary torque generated by the electric motor is transmitted to the ball screw nut, and
the electric power steering apparatus configured such that an amount of axial travel of the rack shaft is limited when a rack end provided at an end of the rack shaft and the housing come into contact with each other in the axial direction,
the electric power steering apparatus comprising a tilt allowing portion configured to cause the ball screw nut to tilt relative to the ball screw shaft such that a distance between a center of rotation of the driven toothed-pulley and a center of rotation of the driving toothed-pulley increases when the rack end and the housing come into contact with each other in the axial direction.

2. The electric power steering apparatus according to claim 1 , wherein:
in a case where the driven toothed-pulley, the driving toothed-pulley, and the toothed belt are disposed between the bearing and the rack end, the tilt allowing portion is included in the housing; and
in the tilt allowing portion, axial stiffness of a housing first stopper portion that restricts an axial displacement of the bearing on the driving toothed-pulley side of the bearing is set lower than axial stiffness of a housing second stopper portion that restricts the axial displacement of the bearing on the driven toothed-pulley side of the bearing.

3. The electric power steering apparatus according to claim 1 , wherein:
in a case where the driven toothed-pulley, the driving toothed-pulley, and the toothed belt are disposed between the bearing and the rack end, the tilt allowing portion is included in an outer race of the bearing; and
in the tilt allowing portion, axial stiffness of a first portion of the outer race, the first portion coming into contact with a housing first stopper portion that restricts an axial displacement of the bearing on the driving toothed-pulley side of the bearing, is set lower than axial stiffness of a second portion of the outer race, the second portion coming into contact with a housing second stopper portion that restricts the axial displacement of the bearing on the driven toothed-pulley side of the bearing.

Assignees

• Toyota Motor Co Ltd
• Jtekt Corp

Inventors

• Nitano Masahide
• Takahashi Masafumi
• Uchiyama Kiyoshi
• Yamaguchi Masashi

Classifications

• B62D5/0424 Primary

  the axes of motor and final driven element of steering gear, e.g. rack, being parallel · CPC title

• B62D5/0421 Primary

  Electric motor acting on or near steering gear · CPC title

• B62D5/0448

  Ball nuts · CPC title

• B62D3/08

  using intermediate balls or the like · CPC title