JP2004239652A - Magnetostrictive torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain satisfactory detection accuracy by suppressing both the occurrence of large plastic deformation in a steering shaft and the exfoliation of magnetostrictive films even in the case that excessive torque acts on the steering shaft. <P>SOLUTION: A shaft 6 constituting this magnetostrictive torque sensor 1 is made of a chrome molybdenum steel material or the like. The magnetostrictive films 8 and 9 are previously deposited onto the shaft 6 made of the chrome molybdenum steel material. Then by applying heat treatments such as quenching to the steel material, the Rockwell hardness of the shaft 6 is set within the range of HRC 40-65. The shaft 6 may be formed by applying case-hardening treatments to the surface of the chrome molybdenum steel material by carburizing and quenching. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetostrictive torque sensor which is mounted on an electric power steering device such as an automobile and is optimally used as a detection device for magnetically detecting a steering torque applied to a shaft via a steering shaft.
[0002]
[Prior art]
2. Description of the Related Art Generally, an electric power steering device mounted on an automobile or the like detects a torque applied to a shaft from a steering shaft by a driver's steering operation using a torque sensor. Then, in response to the detection signal from the torque sensor, the motor for assisting the power of the driver (applying an auxiliary steering force) to the driver's steering operation is controlled to reduce the driver's steering force to provide a comfortable steering feeling. I am trying to give a ring.
[0003]
As such a conventional torque sensor, a magnetostrictive torque sensor is known (for example, see Patent Document 1). In this magnetostrictive torque sensor, a magnetostrictive film (for example, a Ni—Fe alloy film) having magnetic anisotropy is applied to the surface of a shaft. When a torque is applied to the shaft from the outside, a change in the magnetic characteristics (permeability) of the magnetostrictive film according to the torsion generated in the shaft is magnetically detected by contact.
[0004]
[Patent Document 1]
JP-A-2002-257648 (paragraph numbers [0002] and [0003], FIG. 6)
[0005]
Therefore, an example in which this type of conventional magnetostrictive torque sensor is used in an electric power steering device of an automobile will be described with reference to FIGS. FIG. 7 is a schematic diagram showing a conventional electric power steering device, and FIG. 8 is an explanatory diagram showing a relationship between a steering torque and a pinion torque according to a conventional technology. FIG. 9 is an enlarged longitudinal sectional view of a conventional magnetostrictive torque sensor, FIG. 10 is a characteristic diagram showing a relationship between steering torque and impedance according to the conventional technology, and FIG. 11 shows a conventional magnetostrictive torque sensor. It is a circuit diagram.
[0006]
As shown in FIG. 7, the electric power steering apparatus 101 includes a magnetostrictive torque sensor 103 that detects a steering torque from a steering wheel 102, a motor 104 that applies an auxiliary steering force to the operation of the steering wheel 102, and the motor 104. A speed reduction device 105 for increasing the rotational torque of the vehicle, an ECU (Electrical Control Unit) 107 for controlling the drive of the motor 104 in accordance with detection signals from the magnetostrictive torque sensor 103, the vehicle speed sensor 106, and the like, and a tire 108 for rotating the motor 104. , 108 and a rack shaft 109 for changing the direction of the tire 108 and a pinion 110. As shown in FIG. 8, the speed reducer 105 includes a worm 105A and a worm wheel 105B.
[0007]
In this prior art, a steering torque when a driver performs a steering operation is detected using a magnetostrictive torque sensor 103, and a detection signal (torque signal) from the magnetostrictive torque sensor 103 and a detection signal from a vehicle speed sensor 106 are detected by an ECU 107. The drive of the motor 104 is controlled in accordance with a signal (vehicle speed signal) or the like, and the torque of the motor 104 at this time is increased by the reduction gear 105 and transmitted to the tires 108 via the rack shaft 109 and the pinion 110.
[0008]
In such an electric power steering apparatus 101, as shown in FIG. 8, the steering torque of the driver is TH, the torque transmitted to the pinion 110 is TP, and the constant related to the magnitude of the assist torque by the motor 104 is KA. Then, a relationship of TH = TP / (1 + KA) is established, and the steering torque of the driver can be reduced by the assist torque of the motor 104.
[0009]
Next, the magnetostrictive torque sensor 103 will be described. As shown in FIG. 9, the magnetostrictive torque sensor 103 is housed in a sensor housing case 111 including an upper case 111A and a lower case 111B. The magnetostrictive torque sensor 103 is connected to a steering shaft 102A of the steering wheel 102 (see FIG. 7), and is rotatably supported by a sensor housing case 111 via bearings 112 and 113. Coil 115, 115, which is detection means provided on the inner peripheral side of the portion 111 </ b> A and vertically separated from each other, and provided on the outer peripheral surface (outer surface) of the shaft 114 so as to face the coil 115. The first and second magnetostrictive films 116 and 117 each have a property.
[0010]
Here, the magnetostrictive films 116 and 117 are formed using a magnetostrictive material made of, for example, a Ni—Fe alloy film or the like, and are plated on the outer peripheral surface of the shaft 114. The magnetostrictive torque sensor 103 includes a primary coil 119 connected to an AC power supply 118 and a secondary coil provided opposite to the primary coil 119 with the magnetostrictive films 116 and 117 interposed therebetween, as shown in FIG. 120, 120 are provided.
[0011]
Then, when torque from the handle 102 acts on the shaft 114, changes in the magnetic characteristics of the magnetostrictive films 116 and 117 according to the torsion generated in the shaft 114 are electrically detected on the secondary coils 120 and 120 side, respectively. As a result, for example, two substantially convex magnetostrictive characteristic curves as shown by solid lines A and B in FIG. 10 are obtained, and the steering torque applied to the shaft 114 is calculated by calculating the difference between the two magnetostrictive characteristic curves. Direction and size are detected.
[0012]
[Problems to be solved by the invention]
By the way, when the conventional magnetostrictive torque sensor rotates clockwise or counterclockwise until the handle 102 is locked, one of the left and right ends 109A and 109A of the rack shaft 109 causes the rack shaft 109 to move. The end portion 121A (see FIG. 7) of the rack accommodating case 121 to be accommodated (collides), the impact torque at this time increases, and the shaft 114 (see FIG. 9) is plastically deformed. 117 may separate from the shaft 114. Here, the collision torque of the magnetostrictive torque sensor is compared with the collision torque of the torsion bar type torque sensor. The collision torque T acting on the torsion bar is T = E × (2 / θ) (E: collision energy, θ: torsion angle when E is applied) (Equation 1), whereas the magnetostrictive torque is The impact torque Tm acting on the sensor shaft is Tm = E × (2 / θm) (θm: torsion angle of the magnetostrictive torque sensor shaft when E is applied) (Equation 2). From the relationship of (Equation 1) and (Equation 2), the relationship of Tm = (θ / θm) × T (Equation 3) is established. In Equation 3, since θm≪θ, Tm≫T.
[0013]
When the shaft 114 is plastically deformed or the magnetostrictive films 116 and 117 are peeled off as described above, as shown in FIG. 12, a hysteresis occurs in the detected value of the steering torque, and as a result, the steering feeling is deteriorated. is there.
[0014]
Further, when the shaft 114 is plastically deformed, as shown by a dashed line in FIG. 10, the protruding portions (tops of the hills) of the magnetostrictive characteristic curves A ′ and B ′ are offset within the steering torque detection range. , The detection sensitivity of the magnetostrictive torque sensor 103 decreases. That is, as shown in FIG. 10, in the case of the magnetostrictive characteristic curves A and B, the steering torque can be detected within the steering torque detection range using only the linear portion, so that the steering torque can be accurately detected. is there. However, if the magnetostrictive characteristic curves A and B are offset like the magnetostrictive characteristic curves A 'and B', the peak side (non-linear side) of the peak is included in the steering torque detection range, and the magnetostrictive equation There is a problem that the detection accuracy by the torque sensor 103 is reduced.
[0015]
Further, when the shaft 114 is plastically deformed and the magnetostrictive films 116 and 117 are peeled as described above, the waveforms (shapes) of the magnetostrictive characteristic curves A and B are disturbed, and the detection accuracy of the magnetostrictive torque sensor 103 is further reduced. There is a problem of doing.
[0016]
Therefore, according to the present invention, even when an excessive torque (maximum torque) acts on the shaft, large plastic deformation of the shaft or peeling of the magnetostrictive film can be suppressed, and the detection accuracy can be kept good. It is an object of the present invention to provide a magnetostrictive torque sensor that can be used.
[0017]
[Means for Solving the Problems]
A magnetostrictive torque sensor according to the present invention that solves the above-mentioned problem includes a shaft rotatably supported by a bearing, and a magnetostrictive film provided on a surface of the shaft and having a magnetostrictive characteristic that changes according to a torque applied to the shaft. And a detecting means for detecting a change in magnetostriction characteristics occurring in the magnetostrictive film.
[0018]
A feature of the configuration adopted by the first aspect of the invention is that the Rockwell hardness of the shaft is set to 40 to 65 HRC. With this configuration, even if an excessive torque (for example, about 30 kgf · m (294 N · m)) is applied to the shaft and the shaft is greatly twisted, plastic deformation (permanent deformation) of the shaft is suppressed. be able to. Therefore, the shaft can be elastically deformed, and the magnetostrictive film can be prevented from peeling off from the shaft. Thereby, the magnetostrictive film can be stably applied to the shaft, and the detection accuracy of the magnetostrictive torque sensor can be improved.
[0019]
A feature of the structure adopted by the invention according to claim 2 is that anisotropy is imparted to the surface of the magnetostrictive film after the magnetostrictive film is attached to the shaft in advance. With such a configuration, for example, it is not necessary to quench the shaft after giving the anisotropy to the magnetostrictive film, and it is possible to stably provide the anisotropy to the magnetostrictive film, and to have high linearity. The torque detection performance (see the magnetostrictive characteristic curves A and B in FIG. 10) can be obtained.
[0020]
A third aspect of the present invention is characterized in that the shaft provided with the magnetostrictive film is applied to an electric power steering device that applies an auxiliary steering force to a steering mechanism of a vehicle. With this configuration, the detection accuracy of the steering torque can be enhanced by the magnetostrictive film provided on the shaft, and the performance, reliability, and the like of the electric power steering device can be enhanced.
[0021]
Further, a feature of the configuration adopted by the invention according to claim 4 is that both of them collide between an end of a rack shaft constituting the electric power steering device and an end of a rack housing case housing the rack shaft. The configuration is such that an elastic member is provided to alleviate the impact force when doing so. With this configuration, the elastic member can absorb an impact force generated when the end of the rack shaft collides with the end of the rack housing case during operation of the electric power steering device.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment)
An example in which the magnetostrictive torque sensor according to the first embodiment of the present invention is applied to an electric power steering device (see FIG. 7) will be described in detail with reference to FIGS.
[0023]
FIG. 1 is an enlarged longitudinal sectional view of a magnetostrictive torque sensor according to the present embodiment, and FIG. 2 is a characteristic diagram illustrating a relationship between a torsion angle and a steering torque according to the present embodiment.
FIG. 3 is a characteristic diagram showing a relationship between the hardness of the shaft and the hysteresis according to the present embodiment.
[0024]
As shown in FIG. 1, a magnetostrictive torque sensor 1 according to the present embodiment includes a bearing 3, 4, 5 and the like in a sensor housing case 2 including an upper case portion 2A and a lower case portion 2B, in substantially the same manner as the related art. A shaft 6 rotatably supported via a shaft, coils 7, 7 serving as detecting means provided vertically spaced apart on the inner peripheral side of the upper case portion 2A, and a shaft facing the coils 7, 7 6 has first and second magnetostrictive films 8 and 9 having anisotropy in directions opposite to each other, which are adhered to the outer peripheral surface (outer surface). The magnetostrictive films 8 and 9 are formed using a magnetostrictive material made of, for example, a Ni—Fe alloy film. The lower case portion 2B of the sensor housing case 2 is provided with a motor 10, a speed reducer 11, a rack shaft 12, a pinion 13, and the like. The speed reducer 11 has a worm 11A, a worm wheel 11B, and the like.
[0025]
When a torque from the handle acts on the shaft 6, a change in the magnetic characteristics of the magnetostrictive films 8 and 9 according to the torsion generated in the shaft 6 is electrically detected using the coil 7 and the like. As a result, for example, two substantially convex magnetostrictive characteristic curves as shown by solid lines A and B in FIG. 10 are obtained, and by calculating the difference between these two magnetostrictive characteristic curves, the steering torque applied to the shaft 6 is calculated. The direction and the size are detected.
[0026]
Here, the shaft 6 according to the present embodiment is formed using a chromium molybdenum steel material (for example, SCM822). The shaft 6 is subjected to a heat treatment such as quenching in advance on the chromium molybdenum steel material, and then the magnetostrictive films 8 and 9 are coated by a PVD method such as sputtering or ion plating, a plating method, a plasma spraying method or the like. By wearing, the Rockwell hardness is set in the range of HRC 40 to 65. Further, the shaft 6 may be formed by subjecting the surface of the chromium molybdenum steel material to case hardening by carburizing and quenching. Further, the reason why the Rockwell hardness of the shaft 6 is set to be equal to or less than HRC65 is that if the Rockwell hardness is set to be larger than HRC65, the shaft 6 becomes brittle and breaks.
On the other hand, the reason why the Rockwell hardness of the shaft 6 is set to HRC 40 or more is to elastically deform the shaft 6 even when an excessive torque acts on the shaft 6 as described later.
[0027]
In the present embodiment configured as described above, the steering torque when the driver operates is detected using the magnetostrictive torque sensor 1, and the detection signal from the magnetostrictive torque sensor and the vehicle speed sensor (both are used) by the ECU. The drive of the motor 10 is controlled in accordance with a detection signal from the control unit 10 (see FIG. 7), and the torque of the motor 10 at this time is increased by the reduction gear 11 and the tire (not shown) is transmitted through the rack shaft 12 and the pinion 13. To tell.
[0028]
By the way, when the magnetostrictive torque sensor 1 according to the present embodiment rotates clockwise or counterclockwise until the handle is locked, as described in the related art, the end of the rack shaft 12 is connected to the rack housing case. When the end hits (collides) with an end (not shown), a large impact torque at this time is transmitted to the shaft 6, and the shaft 6 may be plastically deformed. When the amount of plastic deformation increases, the magnetostrictive films 8 and 9 on the surface of the shaft 6 peel off, and the peeling causes hysteresis in the sensor output.
[0029]
However, as a result of trial and error by an experiment, as shown in FIG. 2, by setting the Rockwell hardness of the shaft 6 to HRC 40 to 65 as shown in this embodiment, as shown in FIG. 2) Even when an excessively large steering torque is applied, the amount of plastic deformation a of the shaft 6 according to the present embodiment can be suppressed significantly (a <b) as compared with the amount of plastic deformation b in the prior art. It was found that the magnetostrictive films 8 and 9 did not peel off.
[0030]
Accordingly, since the Rockwell hardness of the shaft 6 is set to HRC 40 to 65, even if a large steering torque of, for example, 30 kgfm (294 Nm) or more is applied to the shaft 6 during the steering operation, FIG. As shown in the figure, it was found that the hysteresis caused by the plastic deformation of the shaft 6 at this time was significantly reduced to 5% or less, which is the allowable value.
[0031]
Thereby, it is possible to prevent the magnetostrictive films 8 and 9 from peeling off from the surface of the shaft 6, and it is possible to maintain good detection accuracy by the magnetostrictive torque sensor 1 even when an excessive steering torque acts on the shaft. As a result, the occurrence of hysteresis due to the peeling of the magnetostrictive films 8, 9 can be reduced, and the steering feeling can be enhanced.
[0032]
When the shaft 6 is manufactured, the chromium molybdenum steel material, which is the material of the shaft 6, is subjected to case hardening by carburizing and quenching, and then the magnetostrictive films 8, 9 are applied to the surface of the shaft 6. The bearings 3, 4, 5, the pinion 13, and the like can be subjected to heat treatment together with the shaft 6 in the same process, for example, to have a Rockwell hardness of HRC58 or more. Therefore, it is not necessary to heat-treat the bearings 3, 4, 5, and the pinion 13 in different steps, so that the steps can be shortened, and these members can be easily manufactured. Further, when heat-treating the bearings 3, 4, 5, the shaft 6, the pinion 13, and the like, it is possible to manage the process in consideration of the influence of distortion of these members, and to stabilize the quality. .
[0033]
Further, in the present embodiment, since the magnetostrictive films 8 and 9 are attached to the shaft 6, the detection sensitivity of the magnetostrictive torque 1 is reduced by 10 as compared with the case where the entire shaft 6 is formed using a magnetostrictive material. It can be increased up to about 100 times.
[0034]
Further, since the magnetostrictive torque sensor 1 is configured to be applied to an electric power steering device that applies an auxiliary steering force to a steering mechanism of an automobile, the detection accuracy of the steering torque can be increased by the magnetostrictive torque sensor 1. In addition, the performance and reliability of the electric power steering device can be improved.
[0035]
(Second embodiment)
Next, FIG. 4 shows a second embodiment of the present invention. The feature of this embodiment is that a shaft is subjected to a heat treatment so that the hardness becomes HRC 40 to 65, and then a magnetostrictive film is coated on the shaft. And then anisotropy is imparted to the magnetostrictive film.
[0036]
FIG. 4A is a perspective view showing a state in which a counterclockwise torque is applied to the shaft on which the magnetostrictive film according to the present embodiment is applied, and FIG. It is a perspective view showing the state where clockwise torque was given to the attached shaft.
[0037]
As shown in FIG. 4, the magnetostrictive torque sensor 21 is substantially vertically similar to the first embodiment in that a shaft 23 having a pinion 22 formed on the lower end side and an outer peripheral surface of the shaft 23 are vertically separated from each other. The first and second magnetostrictive films 24 and 25 are roughly formed.
[0038]
Next, a method of manufacturing the magnetostrictive torque sensor 21 will be described.
First, the shaft 23 is subjected to a heat treatment so that the Rockwell hardness becomes HRC 40 to 65, and then the magnetostrictive films 24 and 25 are attached to the outer peripheral surface of the shaft 23 while being vertically separated. Next, by twisting the shaft 23 in the directions indicated by the arrows P and S in FIG. 4A, a counterclockwise torque T (for example, 10 kgfm (98 Nm)) is applied to the first magnetostrictive film 24. In this state, the coil 26 is used to vibrate the magnetostrictive film 24 at a high frequency, so that the magnetostrictive film 24 is heated at about 300 ° C. for several seconds and cooled, and then the counterclockwise torque T is removed. The magnetostrictive film 24 is given anisotropy.
[0039]
Next, by twisting the shaft 23 in the directions indicated by arrows P and S in FIG. 4B, a clockwise torque T (for example, about 10 kgfm (98 Nm)) is applied to the second magnetostrictive film 25. ), And in this state, the magnetostrictive film 25 is heated at about 300 ° C. by vibrating the magnetostrictive film 25 at a high frequency using the coil 27 similarly to the magnetostrictive film 24. As a result, the magnetostrictive film 25 is given anisotropy in a direction opposite to that of the magnetostrictive film 24.
[0040]
In the present embodiment configured as described above, the magnetostrictive films 24 and 25 are integrally provided on the shaft 23 whose Rockwell hardness is set to HRC 40 to 65, and thereafter, the magnetostrictive films 24 and 25 are anisotropic. In the step of applying the torque T to the shaft 23 to impart anisotropy to the magnetostrictive films 24 and 25, the shaft 23 is not plastically deformed. Anisotropy can be imparted stably. Further, since the shaft 23 is not plastically deformed in this manner, a highly linear torque detection performance (see magnetostrictive characteristic curves A and B in FIG. 10) can be obtained.
[0041]
(Third embodiment)
Next, FIGS. 5 and 6 show a third embodiment of the present invention. The feature of this embodiment is that a rack accommodating case accommodating an end of a rack shaft and a rack shaft constituting an electric power steering apparatus. And an elastic member for reducing the impact force when the two collide with each other.
[0042]
Note that, in the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. FIG. 5 is an external view showing the rack shaft, the rack housing case, and the like in a partially broken state, and FIG. 6 is an enlarged cross-sectional view showing a part a in FIG. 5 in an enlarged manner.
[0043]
5 and 6, the rack shaft 31 has stepped ends 31A, 31A on both left and right sides thereof. The rack housing case 32 that houses the rack shaft 31 extends in the left-right direction, and is fitted on the left and right sides of the long tubular portion 32A into which the rack shaft 31 is inserted on the inner peripheral side. The short cylindrical portion 32B is formed with a stepped end 32C to which a buffer member 34 described later is attached on the inner peripheral side of the short cylindrical portion 32B.
[0044]
As shown in FIG. 6, the elastic member 33 is formed in an annular shape using an elastic material such as rubber, and a cushioning member 34 fixed to an end 32 </ b> C of the rack housing case 32 and an annular shape formed using a steel material. And a steel member 35 fixed to the inner peripheral side of the buffer member 34. A flange 34A is provided on the cushioning member 34 so as to project radially outward.
[0045]
In the present embodiment configured as described above, when the handle is rotated clockwise or counterclockwise until the handle is locked, one of the ends 31A of the rack shaft 31 becomes the end of the rack housing case 32. It collides with the flange 34A of the elastic member 33 (buffer member 34) provided on the 32C side, and the impact force at this time can be buffered by the buffer member 34. Therefore, a remarkable increase in the steering torque when the steering wheel is locked or the like can be suppressed by the elastic member 33, the magnetostrictive film can be prevented from peeling off from the shaft, and the hysteresis and durability of the magnetostrictive torque sensor 1 can be improved. And the steering feeling can be enhanced.
[0046]
In each of the above embodiments, the case where the magnetostrictive torque sensor is applied to an electric power steering device has been described as an example. However, the present invention is not limited to this, and can be applied to other various devices.
[0047]
Further, in the third embodiment, the case where the elastic member 33 is configured by the buffer member 34 made of rubber material or the like and the steel member 35 has been described as an example, but the present invention is not limited to this. For example, the elastic member may be formed by a member having elasticity such as a spring.
[0048]
Further, in the third embodiment, the case where the elastic member 33 is provided on the rack housing case 32 side of the rack shaft 31 and the rack housing case 32 has been described as an example. However, the present invention is not limited to this. For example, an elastic member may be provided on the rack shaft 31, or may be provided on both members of the rack shaft 31 and the rack housing case 32. Further, the present invention may be applied to a pinion assisted electric power steering device or a rack assisted electric power steering device.
[0049]
【The invention's effect】
As described in detail above, according to the first aspect of the present invention, the magnetostrictive film is provided on the surface of the shaft, and the Rockwell hardness of the shaft is set to HRC 40 to 65. (For example, about 30 kgf · m (294 N · m)), the plastic deformation of the shaft can be suppressed. Therefore, the shaft can be elastically deformed, the magnetostrictive film can be prevented from peeling off from the shaft, and the detection accuracy of the magnetostrictive torque sensor can be improved.
[0050]
Further, the invention according to claim 2 has a configuration in which anisotropy is given to the surface of the magnetostrictive film after the magnetostrictive film is attached to the shaft in advance. It is no longer necessary to perform the above-described steps, and the anisotropy can be stably imparted to the magnetostrictive film, and a highly linear torque detection performance can be obtained. Further, for example, a pinion gear and the like provided on a shaft can be surface-treated in the same step, and members such as the shaft and the pinion gear can be easily manufactured, and quality can be stabilized.
[0051]
Furthermore, the invention according to claim 3 is configured such that the shaft provided with the magnetostrictive film is applied to an electric power steering device that applies an auxiliary steering force to a steering mechanism of a vehicle. Is improved, and the performance, reliability, and the like of the electric power steering device can be improved.
[0052]
Furthermore, according to the invention of claim 4, between the end of the rack shaft that constitutes the electric power steering device and the end of the rack housing case that houses the rack shaft, the impact force when the two collide with each other is reduced. Since the elastic member is provided, the elastic member can absorb an impact force generated when the end of the rack shaft collides with the end of the rack housing case when the electric power steering device is operated. As a result, the steering torque applied to the shaft can be prevented from significantly increasing, and the magnetostrictive film can be prevented from peeling off from the shaft.
[Brief description of the drawings]
FIG. 1 is an enlarged longitudinal sectional view showing a magnetostrictive torque sensor according to a first embodiment of the present invention.
FIG. 2 is a characteristic diagram illustrating a relationship between a torsion angle and a steering torque according to the first embodiment.
FIG. 3 is a characteristic diagram illustrating a relationship between hardness and hysteresis of a shaft according to the first embodiment.
FIG. 4A is a perspective view showing a state in which a counterclockwise torque is applied to a shaft according to a second embodiment of the present invention, and FIG. 4B is a shaft according to the second embodiment; FIG. 4 is a perspective view showing a state in which clockwise torque is applied to.
FIG. 5 is an external view showing a rack shaft, a rack housing case, and the like according to a third embodiment of the present invention in a partially broken state.
FIG. 6 is an enlarged cross-sectional view of a main part showing a part a in FIG. 5 in an enlarged manner.
FIG. 7 is a schematic diagram showing an electric power steering device according to the related art.
FIG. 8 is an explanatory diagram showing a relationship between a steering torque and a pinion torque according to the related art.
FIG. 9 is an enlarged longitudinal sectional view of a magnetostrictive torque sensor according to the related art.
FIG. 10 is a characteristic diagram showing a relationship between steering torque and impedance according to the related art.
FIG. 11 is a circuit diagram showing a magnetostrictive torque sensor according to the related art.
FIG. 12 is a characteristic diagram showing a relationship between a steering torque and a detection value of a magnetostrictive torque sensor according to the related art.
[Explanation of symbols]
1,21 Magnetostrictive torque sensor
3,4,5 bearing
6,23 shaft
7 coil (detection means)
8, 24 First magnetostrictive film
9,25 Second magnetostrictive film
10 Motor
11 Reduction gear
12,31 Rack axis
31A, 32C end
32 rack storage case
33 elastic member
101 Electric power steering device

Claims (4)

A shaft rotatably supported by a bearing, a magnetostrictive film provided on a surface of the shaft, the magnetostrictive characteristics of which change according to a torque applied to the shaft, and a detection for detecting a change in the magnetostrictive characteristics occurring in the magnetostrictive film A magnetostrictive torque sensor comprising:
A magnetostrictive torque sensor wherein the Rockwell hardness of the shaft is set to 40 to 65 HRC. The magnetostrictive torque sensor according to claim 1, wherein an anisotropy is given to a surface of the magnetostrictive film after the magnetostrictive film is attached to the shaft in advance. The magnetostrictive torque sensor according to claim 1 or 2, wherein the shaft provided with the magnetostrictive film is applied to an electric power steering device that applies an auxiliary steering force to a steering mechanism of a vehicle. An elastic member is provided between an end of a rack shaft that constitutes the electric power steering device and an end of a rack housing case that houses the rack shaft so as to reduce an impact force when the two collide. The magnetostrictive torque sensor according to claim 3, wherein:

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