EP-4741260-A1 - ELECTRIC POWER STEERING DEVICE AND METHOD FOR MANUFACTURING ELECTRIC POWER STEERING DEVICE

EP4741260A1EP 4741260 A1EP4741260 A1EP 4741260A1EP-4741260-A1

Abstract

In order to suppress breakage of a permanent magnet used in a torque sensor, an electric power steering device 10 includes: an input shaft 13 having an input-shaft-side hole 13a inside; an output shaft 16 having an output-shaft-side hole 16a inside; a torsion bar 17 with one end side disposed inside the input-shaft-side hole 13a and the other end side disposed inside the output-shaft-side hole 16a on the other end side, and couples the input shaft 13 and the output shaft 16; and a torque sensor 30 including a magnet member 31 that includes a permanent magnet 32 and is connected to an outer peripheral surface 13b of the input shaft 13, in which the input shaft 13 has a press-fitting portion 14 where the torsion bar 17 is press-fitted into the input-shaft-side hole 13a, and a connecting portion 15, which is a portion of the input shaft 13 to which the magnet member 31 is connected, is located at a position different from a position of the press-fitting portion 14 in an axial direction.

Inventors

SHIGEYAMA, Tomofumi

Assignees

NSK Steering & Control, Inc.

Dates

Publication Date: 20260513
Application Date: 20240228

Claims (10)

An electric power steering device comprising: an input shaft having an input-shaft-side hole inside; an output shaft having an output-shaft-side hole inside; a torsion bar with one end side disposed inside the input-shaft-side hole and another end side disposed inside the output-shaft-side hole, the torsion bar coupling the input shaft and the output shaft; and a torque sensor including a magnet member that includes a permanent magnet and is connected to an outer peripheral surface of the input shaft, wherein the input shaft has a press-fitting portion where the torsion bar is press-fitted into the input-shaft-side hole, and a connecting portion, which is a portion of the input shaft to which the magnet member is connected, is located at a position different from a position of the press-fitting portion in an axial direction of the input shaft.
The electric power steering device according to claim 1, wherein the magnet member includes a magnet sleeve on which the permanent magnet is disposed, and the magnet sleeve is connected to the connecting portion of the input shaft.
The electric power steering device according to claim 1, wherein the permanent magnet included in the magnet member is connected to the connecting portion of the input shaft.
The electric power steering device according to claim 2 or 3, wherein the magnet member has a separating portion that extends from the position of the connecting portion to a side where the press-fitting portion is located in the axial direction and is separated from the outer peripheral surface of the input shaft, and at least a part of the press-fitting portion is located inside the separating portion in a radial direction of the input shaft.
The electric power steering device according to any one of claims 1 to 4, wherein the position of the press-fitting portion in the axial direction is located closer to the output shaft than the position of the connecting portion.
The electric power steering device according to any one of claims 1 to 5, wherein a torsion bar sleeve is disposed between the output-shaft-side hole and the torsion bar disposed inside the output-shaft-side hole.
The electric power steering device according to claim 6, further comprising: a housing in which the input shaft and the output shaft are disposed; and a bearing that rotatably supports the output shaft with respect to the housing, at least a part of the bearing being disposed at a same position as a position of the torsion bar sleeve in the axial direction.
The electric power steering device according to any one of claims 1 to 7, wherein a key lock collar included in a lock device, which restricts rotation of the input shaft, is disposed on the outer peripheral surface of the input shaft, and the key lock collar is disposed at a position different from the position of the press-fitting portion in the axial direction.
The electric power steering device according to any one of claims 1 to 8, wherein a coupling pin, which couples the output shaft and the torsion bar disposed inside the output-shaft-side hole, is disposed on the output shaft.
A method for manufacturing an electric power steering device, the electric power steering device including: an input shaft having an input-shaft-side hole inside; an output shaft having an output-shaft-side hole inside; a torsion bar with one end side disposed inside the input-shaft-side hole and another end side disposed inside the output-shaft-side hole, the torsion bar coupling the input shaft and the output shaft; and a torque sensor including a magnet member connected to an outer peripheral surface of the input shaft, the input shaft having a press-fitting portion where the torsion bar is press-fitted into the input-shaft-side hole, the method comprising: performing forging to form the press-fitting portion of the input shaft; and forming a connecting portion, which is a portion of the input shaft to which the magnet member is connected, to be located at a position different from a position of the press-fitting portion in an axial direction of the input shaft.

Description

Field The present disclosure relates to an electric power steering device and a method for manufacturing an electric power steering device. Background An electric power steering device includes a torque sensor that detects steering torque when a steering wheel is steered, and an electric motor that generates an assist force, and can assist a steering force of a driver as the electric motor generates the assist force based on the steering torque detected by the torque sensor. In such an electric power steering device, an input shaft and an output shaft are coupled via a torsion bar, and the torque sensor can detect the steering torque by detecting a change in a relative rotation angle between the input shaft and the output shaft due to slight twisting of the torsion bar when the steering torque is transmitted from the input shaft to the output shaft via the torsion bar. For example, in an electric power steering device described in Patent Literature 1, a proximal end of a torsion bar is press-fitted and fixed to an input shaft, a distal end of the torsion bar is fixed to an output shaft by a fixing pin, and a torque sensor unit is provided on a vehicle rear side of the output shaft. Further, in a steering device described in Patent Literature 2, a torsion bar is fitted into a hole provided at the center of an input shaft and fixed to the input shaft via a pin, and with respect to an output shaft, the torsion bar is press-fitted into a hole provided at the center of the output shaft and is fixed to the output shaft. Further, in the steering device described in Patent Literature 2, a torque sensor includes a magnet and a yoke, the magnet is attached to the input shaft via a first sleeve, and the yoke is attached to the output shaft via a second sleeve. Citation List Patent Literature Patent Literature 1: JP 2006-27350 APatent Literature 2: WO 2019/059230 A Summary Technical Problem A permanent magnet is used in a torque sensor used in an electric power steering device, and the permanent magnet is disposed on an input shaft or an output shaft. However, since the permanent magnet has low ductility, it is conceivable that the permanent magnet is broken when a shaft to which the permanent magnet is attached is elastically deformed. For example, when a torsion bar is press-fitted to the input shaft in a state where the permanent magnet is attached directly or via a sleeve to an outer peripheral surface of a portion of the input shaft to which the torsion bar is press-fitted, the input shaft slightly swells due to the press-fitting of the torsion bar, and slightly expands in diameter. In this case, there is a possibility that the permanent magnet attached to the outer peripheral surface of the input shaft directly or via the sleeve cannot follow the swelling of the input shaft and breaks. When the permanent magnet is broken in this manner, the torque sensor cannot detect steering torque. Thus, the electric power steering device including the torque sensor has room for improvement from the viewpoint of the way of disposing the permanent magnet. The present disclosure has been made in view of the above, and an object thereof is to provide an electric power steering device capable of suppressing breakage of a permanent magnet used in a torque sensor, and a method for manufacturing the electric power steering device. Solution to Problem A electric power steering device according to an aspect of the present disclosure includes: an input shaft having an input-shaft-side hole inside; an output shaft having an output-shaft-side hole inside; a torsion bar with one end side disposed inside the input-shaft-side hole and the other end side disposed inside the output-shaft-side hole, the torsion bar coupling the input shaft and the output shaft; and a torque sensor including a magnet member that includes a permanent magnet and is connected to an outer peripheral surface of the input shaft, wherein the input shaft has a press-fitting portion where the torsion bar is press-fitted into the input-shaft-side hole, and a connecting portion, which is a portion of the input shaft to which the magnet member is connected, is located at a position different from a position of the press-fitting portion in an axial direction of the input shaft. According to this configuration, a position in an axial direction of a connecting portion to which a magnet member is connected is different from a press-fitting portion in an input shaft. Thus, even when a diameter of the input shaft slightly increases at a position of the press-fitting portion when a torsion bar is press-fitted into an input-shaft-side hole, the magnet member having a permanent magnet can be attached to the input shaft without being affected by the expansion in the diameter of the input shaft. Therefore, the permanent magnet having low ductility can be attached to the input shaft while avoiding the expansion in the diameter of the input shaft due to press-fitting of the torsion bar.