MAGNETOSTRICTIVE TORQUE SENSOR AND ELECTRIC POWER STEERING APPARATUS

Abstract

The magnetostrictive torque sensor is a magnetostrictive torque sensor 10 having a rotating shaft 11 on which at least one magnetostrictive film 14A or 14B is formed, and has such a structure that the rotating shaft 11 has small diameter portions 11e and 11f and large diameter portions 11b, 11c and 11d positioned on both end sides of the small diameter portions, and a length in an axial direction of the small diameter portion is determined in relation to a coil width of an induction heating coil RC to be used at a high frequency heating step and one magnetostrictive film is formed in the small diameter portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional side view showing an exemplary embodiment of a magnetostrictive torque sensor according to the invention,

FIG. 2 is a side view conceptually showing a basic structure of the magnetostrictive torque sensor according to the exemplary embodiment,

FIG. 3 is a partial side view showing a characteristic shape of a rotating shaft of the magnetostrictive torque sensor according to the exemplary embodiment,

FIG. 4 is a longitudinal sectional view showing a main part of a specific structure in which the magnetostrictive torque sensor according to the exemplary embodiment is incorporated as a steering torque detecting portion in a steering shaft of an electric power steering apparatus,

FIG. 5 is a graph showing a magnetostrictive characteristic curve related to each detecting coil in the magnetostrictive torque sensor according to the exemplary embodiment and a sensor detecting characteristic,

FIG. 6 is a diagram showing a method of manufacturing the magnetostrictive torque sensor according to the exemplary embodiment of the invention, illustrating steps of a process for manufacturing a rotating shaft,

FIG. 7 is a flowchart showing a magnetic anisotropy adding step,

FIG. 8 is a longitudinal sectional view showing a positional relationship based on respective shapes of the rotating shaft and an induction heating coil at the magnetic anisotropy adding step,

FIG. 9 is a view showing a temperature distribution (1) and a distortion distribution (2) in a radial direction in the rotating shaft at respective steps (a) to (d) of the magnetic anisotropy adding step,

FIG. 10 is a chart showing an impedance characteristic of the magnetostrictive torque sensor immediately after a magnetostrictive material plated portion is formed and an impedance characteristic of the magnetostrictive torque sensor using a magnetostrictive film after adding a magnetic anisotropy in the magnetostrictive torque sensor according to the exemplary embodiment,

FIG. 11 is a graph showing a comparison between the impedance characteristic of the magnetostrictive torque sensor according to the exemplary embodiment and a conventional one,

FIG. 12 is a longitudinal sectional view for explaining a problem in respect of a relationship between the rotating shaft and the induction heating coil at the magnetic anisotropy adding step, in a related art,

FIG. 13 is a graph showing a temperature distribution in heating of the magnetostrictive film in order to explain the problem, and

FIG. 14 is a graph showing a sensitivity characteristic of the magnetostrictive torque sensor for a heating temperature of the magnetostrictive film in order to explain the problem.

Claims

1. A magnetostrictive torque sensor comprising: a rotating shaft on which at least one magnetostrictive film is formed,wherein the rotating shaft has a small diameter portion and large diameter portions positioned on both end sides of the small diameter portion,a length in an axial direction of the small diameter portion is determined in relation to a coil width of an induction heating coil used at a high frequency heating step, andthe magnetostrictive film is provided on the small diameter portion.

2. The magnetostrictive torque sensor according to claim 1, wherein diameters of the two large diameter portions positioned on the both end sides of the small diameter portion are equal to each other.

3. The magnetostrictive torque sensor according to claim 1, wherein distances between the two respective large diameter portions and corresponding portions of the induction heating coil are equal to each other.

4. An electric power steering apparatus comprising: a motor for adding an auxiliary torque to a steering system;a steering torque sensor for detecting a steering torque of the steering system; anda controller for controlling a driving operation of the motor based on at least a steering torque signal sent from the steering torque sensor,wherein the steering torque sensor is set to be the magnetostrictive torque sensor according to claim 1.

5. A rotating shaft comprising: a first portion having a first diameter;a second portion being adjacent to the first portion in an axial direction and having a second diameter, wherein the second diameter is smaller than the first diameter;a third portion being adjacent to the second portion in the axial direction in an opposite side of the first portion and having the first diameter;a fourth portion being adjacent to the third portion in the axial direction in an opposite side of the second portion and having the second diameter;a fifth portion being adjacent to the fourth portion in the axial direction in an opposite side of the third portion and having the first diameter;a first magnetostrictive film provided on the second portion; anda second magnetostrictive film provided on the fourth portion.