JP2000009558A - Magnetostrictive torque sensor - Google Patents

Abstract

(57) [Problem] To provide a magnetostrictive torque sensor capable of ideally reducing hysteresis to zero. SOLUTION: A torque sensor shaft and a hysteresis canceling means are provided. The torque sensor shaft 11 includes a portion having a first hysteresis characteristic and a portion having a second hysteresis characteristic having a polarity opposite to that of the first hysteresis characteristic. The hysteresis canceling means 16 is connected to the torque sensor shaft 11.
In the portion having the first hysteresis characteristic and the hysteresis generated in the portion having the second hysteresis characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetostrictive torque sensor.

[0002]

2. Description of the Related Art As one type of torque sensor, a magnetostrictive torque sensor disclosed in U.S. Pat. Nos. 4,933,580 and 5520059 is known. The magnetostrictive torque sensor includes a torque sensor shaft having a magnetic anisotropic portion whose magnetic permeability changes when a torque to be detected is transmitted, and an exciting unit that excites the torque sensor shaft. This exciting means is usually constituted by a solenoid coil or a magnetic head disposed around the magnetic anisotropic part, and the magnetic permeability of the magnetic anisotropic part which is in an excited state by this exciting means. By detecting the change with a detecting means such as a solenoid coil or a magnetic head, the magnitude of the torque can be detected.

As a field to which such a magnetostrictive torque sensor can be applied, there is a field of automobile power steering. In this field, various steering controls are performed by installing a magnetostrictive torque sensor on a power steering shaft and detecting a torque acting on the power steering shaft. In this power steering shaft, the measured rated torque is generally about 10 Nm.

However, when a running car rides on a curb or the like, an overload torque of 10 times or more of the measured rated torque generally acts on the power steering shaft. For this reason, the shaft material of the power steering shaft is required to have a structure that has a strength to withstand such severe overload torque. Accordingly, the torque sensor interposed in the power steering shaft is also required to withstand an overload torque of 10 times or more the measured rated torque.

For this reason, usually, a torque sensor having a torque capacity (allowable overload torque) capable of withstanding the assumed maximum overload torque is installed, and a light load of 1/10 or less of the allowable overload torque is used. It is the rated torque at the time of measurement.

[0006]

Here, for example, while the measured rated torque during use is 10 Nm,
When designing a torque sensor that can withstand overload torque of 0 Nm, the aforementioned U.S. Pat.
In a magnetostrictive torque sensor such as No. 0, since a normal structural steel (SCM, SNCM material, etc.) is used for the sensor shaft, an overload torque of 150 Nm is applied in consideration of the strength of the structural steel. In order to guarantee that the sensor is within the elastic range even when the overload torque of 150 Nm is applied, the surface stress of the magnetically anisotropic portion of the sensor shaft should be about 10 kg / mm ^2. Is desirable. At this time, the hysteresis peculiar to the magnetostrictive torque sensor is such that when a technique such as U.S. Pat. No. 4,933,580 is used, when the overload torque of 150 Nm is applied and unloaded, the sensor when the overload torque of 150 Nm is applied. It can be about 0.3% of the output.

However, when the overload torque of 150 Nm is applied, the hysteresis of the torque sensor is 15
Even if the sensor output is 0.3% of the sensor output when 0 Nm is applied, if the measured rated torque is 10 Nm and 1/15 of the applied overload torque, the hysteresis at the time of overload application is the measured rated torque. For 10 Nm which is (FS), there is a problem that 0.3 × (150/10) = 4.5% (FS).

Accordingly, the present invention provides a large-capacity torque sensor capable of withstanding a required overload torque, such as a magnetostrictive torque sensor used for controlling the power steering of an automobile, for example. When a load is used as a measured rated torque, it is an object of the present invention to ideally reduce the hysteresis to zero so that the hysteresis can be greatly reduced.

The present invention also makes it possible to ideally reduce the hysteresis to zero for magnetostrictive torque sensors used for ordinary applications other than those used for special applications such as power steering control of automobiles. The purpose is also to do so.

[0010]

To achieve this object, the present invention comprises a torque sensor shaft and a hysteresis canceling means, wherein the torque sensor shaft has a portion having a first hysteresis characteristic and a first hysteresis characteristic. A portion having a second hysteresis characteristic having a polarity opposite to that of the first hysteresis characteristic, and the hysteresis canceling means is provided with a hysteresis and a second hysteresis characteristic generated in a portion of the torque sensor shaft having the first hysteresis characteristic. This is configured to offset the hysteresis generated in the holding portion.

According to such a configuration, since the polarity of the hysteresis, that is, the polarity of the portion having the first hysteresis characteristic and the portion having the second hysteresis characteristic in the torque sensor shaft are reversed, the hysteresis canceling means makes these parts different. By canceling the hysteresis generated in the portion having the hysteresis characteristic of the opposite polarity, the hysteresis of the sensor can be made substantially zero.

When the embodiment of this configuration is viewed in more detail, the hysteresis canceling means is constituted by exciting means for exciting the torque sensor shaft, and the torque sensor shaft has a positive value under the first exciting condition. And a second hysteresis characteristic having a negative value under a second excitation condition, wherein the excitation means generates a first hysteresis characteristic of the first excitation condition. A third excitation frequency band between a first excitation frequency band and a second excitation frequency band that creates the second excitation condition, wherein the third excitation frequency band can substantially reduce the hysteresis of the sensor. Is configured to perform excitation.

That is, according to the findings of the present inventors, the torque sensor shaft exhibits a first hysteresis characteristic of a positive value under a first excitation frequency band that creates a first excitation condition, In a case where a second hysteresis characteristic having a negative value is provided under the second excitation frequency band that creates the second excitation condition, the excitation frequency band as the excitation condition is changed. The hysteresis of the torque sensor constituted by the torque sensor shaft can be varied between a positive value and a negative value. Therefore, the specific third
, The hysteresis of the sensor can be set to be substantially zero between the above-mentioned positive value and negative value.

[0014]

FIG. 1 shows a schematic configuration of a magnetostrictive torque sensor according to the present invention. Here, reference numeral 11 denotes a torque sensor shaft, which is formed of a material having both required strength and magnetostriction characteristics, and specifically formed of JIS SNCM815 material or the like. This torque sensor shaft 11
On the outer peripheral surface of a pair of positions spaced apart in the axial direction,
Magnetic anisotropic parts 12 and 13 having characteristics opposite to each other and formed in directions of ± 45 degrees with respect to the axial direction are provided. These magnetic anisotropic parts 12 and 13 are preferably formed by knurling grooves.
The magnetic anisotropic part 12 and the magnetic anisotropic part 13 are configured such that the knurling grooves are inclined in directions opposite to each other by ± 45 degrees with respect to the axial direction. More specifically, these knurling grooves can be formed by cutting the outer peripheral surface of the shaft 11 or rolling the outer peripheral surface of the shaft 11.

Exciting coils 14 and 14 for exciting the magnetic anisotropic parts 12 and 13 respectively are provided around the magnetic anisotropic parts 12 and 13 and torque is applied to the shaft 11 in an excited state. Detection coils 15, 15 for detecting a change in the magnetic permeability of each of the magnetic anisotropic parts 12, 13 at the time are arranged concentrically. Excitation coils 14, 14
Are connected to an AC power supply 16. Each detection coil 1
Outputs V1 and V2 appear at 5 and 15. These outputs V1 and V2 are formed into V1-V2 by a subtractor 17 and a rectifier circuit 18, and then output to an output terminal 19. I have. T represents the torque applied to the shaft 11.

The torque sensor shaft 11 exhibits a positive value of the first hysteresis characteristic under the first excitation condition and a negative value of the second hysteresis characteristic under the second excitation condition. It is configured to present. That is, the torque sensor constituted by the torque sensor shaft 11 has a positive value hysteresis under the first excitation condition and a negative value hysteresis under the second excitation condition. It is characterized as occurring. Hereinafter, this point will be described in detail.

Generally, magnetic materials usually have a positive hysteresis characteristic. That is, FIG. 2 conceptually shows the output voltage of the ideal torque sensor having the configuration shown in FIG. 1 when torque is applied. The horizontal axis represents the torque T, and the vertical axis represents the output voltage V. is there. Output voltage V
Is given by V = V1-V2 from the torque sensor of FIG. As shown, when the torque T is gradually applied from zero, the output voltage V gradually increases from zero correspondingly. When the torque T decreases at a certain time, the output voltage V decreases accordingly. However, in this decreasing stage, even if the applied torque T becomes zero, the output voltage V does not become zero, but becomes a constant positive value. That is, a positive hysteresis 21 occurs.

Here, the polarity of the hysteresis is defined as follows. That is, generally, when a torque is applied clockwise or counterclockwise from the state of zero torque, and then returned to the state of zero torque again, the output of the torque sensor or the output of the detection coil is changed from the original value (V0) at zero torque. After changing in the increasing direction or the decreasing direction, another value (VH) different from the original value (V0)
Return to Here, when the output is increased from the original value (V0) by application of the torque and then returns to the direction of decreasing to another value (VH), if VH> V0, "positive hysteresis" has occurred. If VH <V0, it is defined that "negative hysteresis" has occurred.

The "positive hysteresis" characteristic which is a characteristic of general magnetic materials can be considered to be caused by the following causes. That is, the material magnetized by the excitation undergoes a change in the state of magnetization when a torque is applied, and performs domain wall movement or magnetization rotation. However, at this time, impurities such as impurities and crystal grain boundaries inside the material have a micro magnetic pin center.
Since the applied torque is unloaded, the state of magnetization cannot be restored even when the applied torque is unloaded. Thus, it can be considered that the hysteresis 21 occurs. Here, this phenomenon can be referred to as “hysteresis due to the magnetic effect”.

This phenomenon will be described in detail. When a clockwise (CW) torque T is applied to the torque sensor shaft 11 shown in FIG. 1 as shown in the figure, the output from the magnetically anisotropic portion 12 in which a knurling groove is formed in a +45 degree direction with respect to the axial direction. V1 is as shown in FIG. 3, and the output V2 from the magnetic anisotropic portion 13 in which the knurling groove is formed in the direction of -45 degrees with respect to the axial direction is as shown in FIG. ΔV1 is the positive hysteresis in FIG. 3, and ΔV2 is the positive hysteresis in FIG. That is, ΔV1 and ΔV2 both show that when the output increases due to the application of torque from the state of zero torque (the output is not always zero) and when the state returns to the state of zero torque again, the output becomes the original value. It is larger than the value.

As a result, if the torque sensor output V is set to V = V1−V2 by the circuit configuration of FIG.
Is obtained. At this time, since the magnitude of the positive hysteresis 21 is “positive hysteresis” having the same polarity in both ΔV1 and ΔV2, | ΔV1 | + | ΔV
2 |.

Torque sensor shaft 1 made of magnetic material
FIG. 1 shows that the hysteresis phenomenon due to the presence of the micro magnetic pin center becomes dominant when the micro magnetic pin center does not have a mechanical defect larger than that of the micro magnetic pin center.
It is considered that the positive hysteresis 21 as shown in FIG. 2 is generated in the torque sensor shown in FIG.

On the other hand, it is also possible to provide the magnetostrictive torque sensor with a negative hysteresis characteristic as shown in FIG. For example, if the magnetically anisotropic parts 12 and 13 of the torque sensor shaft 11 shown in FIG. 1 are formed by rolling, and then this part is subjected to a heat treatment such as carburizing, quenching and tempering, the torque obtained thereby can be obtained. The sensor exhibits the negative hysteresis characteristic shown in FIG. Furthermore, in order to improve the sensor characteristics, when the sensor axis after the heat treatment is subjected to shot peening with shot particles having a particle size smaller than the radius at the bottom of the knurling groove of the magnetically anisotropic part, the hysteresis is also reduced. Have a small hysteresis characteristic, though they have a small size. It is considered that this causes a negative hysteresis 22 as shown in FIG.

This phenomenon will be described in detail. FIG. 2 above
As in the description of the hysteresis shown in FIG. 4, the torque sensor shaft 11 shown in FIG.
When the torque T is applied, the output V1 from the magnetic anisotropic portion 12 in which the knurling groove is formed in the direction of +45 degrees with respect to the axial direction becomes as shown in FIG. FIG. 7 shows the output V2 from the magnetically anisotropic portion 13 in which the knurling groove is formed in the direction. ΔV1 is the negative hysteresis in FIG. 6, and ΔV2 is the negative hysteresis in FIG. As a result, when the torque sensor output V is set to V = V1−V2 by the circuit configuration of FIG. 1, the output voltage of FIG. 5 is obtained. At this time, since the magnitude of the negative hysteresis 22 is “negative hysteresis” of the same polarity in both ΔV1 and ΔV2, | ΔV1 | + | ΔV
2 |.

The cause of the occurrence of the negative hysteresis shown in FIG. 5 can be considered as follows. That is,
When the surface of the sensor shaft 11 is cut or rolled to form the knurling groove, a large number of minute cracks, that is, mechanical defects are generated on the shaft surface at that portion. The depth of the defect reaches about twice the depth of the knurling groove from the shaft surface. Then, when the sensor shaft is manufactured in a situation where such a mechanical defect exists, and a torque is applied to a torque sensor formed by the sensor shaft, the defect causes domain wall movement and the like. The magnetization process of the magnetization rotation is hindered. As a result, when the applied torque is released, the domain wall motion and magnetization rotation, which had been hindered by mechanical defects, are dragged by the magnetization motion around where there are few mechanical defects. Will go back beyond the state. As a result, FIG.
It is considered that the negative hysteresis 22 shown in FIG. Therefore, this phenomenon can be referred to herein as "hysteresis due to the magneto-mechanical effect".

As described above, if a torque sensor shaft formed of a specific material and having a specific controlled mechanical defect is used, a positive hysteresis characteristic and a negative hysteresis characteristic can be combined. Can be expected to be possible.

The present invention has been made by paying attention to this point. As described above, in a case where both the positive hysteresis characteristic and the negative hysteresis characteristic are provided in one torque sensor shaft, one embodiment of the present invention is configured by this torque sensor shaft as shown in FIG. By arbitrarily changing the excitation frequencies f1 to f4 as the excitation conditions of the torque sensor to be applied, the sensor has a positive hysteresis h.
3, h4 and negative hysteresis h1, h2. At this time, the excitation frequency f
By changing 1 to f4, each hysteresis h
The size of 1 to h4 can be changed.

Therefore, if a specific excitation frequency f0 between the excitation frequencies f3 and f4 that generate the positive hysteresis h3 and h4 and the excitation frequencies f1 and f2 that generate the negative hysteresis h1 and h2 is selected, A state can be created in which neither positive nor negative hysteresis occurs. That is, the hysteresis of the sensor can be set to a value that is substantially zero between a positive value and a negative value.

In order to configure the torque sensor shaft so as to have both the positive and negative hysteresis characteristics in this manner, for example, the magnetic anisotropic portions 12 and 13 of the torque sensor shaft 11 shown in FIG. The direction of the hysteresis of the magnetostriction characteristic of the outermost surface layer and the direction of the hysteresis of the magnetostriction characteristic of the layer immediately below the outermost surface layer may be opposite to each other.

One of the techniques for this is to apply a two-stage shot peening process to the magnetically anisotropic portion formed by the knurling groove while changing the particle size of the shot grains. That is, in FIG. 9, reference numeral 24 denotes a knurling groove peak portion forming the magnetic anisotropic portions 12 and 13 of the torque sensor shaft. Now, it is assumed that a crack 25 has been generated in the crest 24 as a mechanical defect caused by machining the crest 24 or the like.

First, as a first stage, relatively large shot grains are used for the entire magnetic anisotropic portion including the ridge 24 of the knurling groove having a groove bottom radius R of 0.3 mm, for example. Specifically, for example, shot peening is performed using steel shot grains 26 having a center particle diameter of 250 μm. Then, by the shot peening process of the first stage, the crack 25, that is, the mechanical defect is improved as a whole in macro terms. In this way, by performing the shot peening process to improve mechanical defects as a whole from a macro perspective, the originally large negative hysteresis characteristic can be suppressed to a required negative hysteresis characteristic.

Next, as a second stage, shot peening is performed using shot grains 27 made of steel having a very small grain size, specifically, for example, a center grain size of 50 μm. Then, by using the shot grains 27 having such a small particle size, defects in the cracks 25, particularly at the shaft surface portion, are further improved.

Generally, when the torque sensor shaft on which the magnetically anisotropic part is formed is AC-excited by an exciting coil, when the excitation frequency is changed, the direction of the magnetic flux in the magnetically anisotropic part is as follows. Become like That is, due to the skin effect of the magnetic flux, when the excitation frequency is low, the magnetic flux penetrates deep from the surface of the shaft, and when the excitation frequency is high, the magnetic flux concentrates on the outermost surface layer of the shaft.

Therefore, the mechanical defect is improved as a whole by performing the two-stage shot peening, and in particular, a torque sensor shaft having a magnetically anisotropic part in which the defect on the shaft surface is significantly improved is provided. When excited, the magnetic flux passes through the above-described generally improved but partially mechanically defective portion if the excitation frequency is relatively low. Therefore, the sensor exhibits a negative hysteresis characteristic as shown in FIG. 5 (the above-mentioned "hysteresis due to the magneto-mechanical effect"). Its value varies with the excitation frequency. On the other hand, when the excitation frequency is relatively high, the above-mentioned defect is significantly improved, and the flux passes only through the almost defect-free outermost surface, so that the sensor has a positive hysteresis characteristic as shown in FIG. ("Hysteresis due to the magnetic effect" described above). Its value also varies with the excitation frequency.

Therefore, if the excitation frequency is adjusted with respect to the special torque sensor shaft described above, neither positive nor negative hysteresis occurs, that is, the hysteresis of the sensor is changed between a positive value and a negative value. It can be set to a point where it becomes substantially zero.

As described above, by performing the two-stage shot peening, that is, the range from the outermost surface layer of the shaft, that is, the shaft surface to a depth of about 10 μm, is regarded as a sound structure having almost no mechanical defects. Hysteresis due to the magnetic effect "is developed, and a portion immediately below the sound outermost surface layer, that is, a depth of 10 μm to 100 μm.
By making the hysteresis due to the magneto-mechanical effect appear as a controlled mechanical defect layer in the range up to about μm, the hysteresis of the sensor can be made substantially zero by selecting the excitation frequency. Can be.

As another method for obtaining such a structure having a sound outermost surface layer and a controlled mechanical defect layer immediately below the outermost surface layer, a rolling speed for forming a knurling groove is known. By controlling the rolling process, such as slowing down, simultaneously forming a controlled mechanical defect layer,
Thereafter, a sound outermost surface layer can be formed by performing shot peening using fine shot grains.

Generally, the controlled mechanical defect layer is:
It can be formed by an appropriate method other than the above-described method of improving the mechanical defect by shot grains having a large particle diameter, or the method of forming the knurling groove by controlled rolling. The sound outermost surface layer may be formed by a chemical forming method such as plating or CVD, or a physical forming method such as thermal spraying, PVD, or ion plating, in addition to the shot peening treatment using the shot particles having a small particle diameter. Alternatively, it can be formed by a forming method by heat treatment such as laser irradiation.

As a measure for making the torque sensor have both a positive hysteresis characteristic and a negative hysteresis characteristic, the immediately lower layer composed of the above-mentioned controlled mechanical defect layer and a sound outermost surface layer are formed. Alternatively, other techniques can be employed.

For example, it is possible to impart a positive hysteresis characteristic and a negative hysteresis characteristic by heat-treating the shaft. According to the findings of the inventor,
For example, the shaft material of the knurling groove type torque sensor is SN
In the case of CM815, if the heat treatment is not performed only by rolling the knurling groove, or if carbonitriding, quenching and tempering are performed after rolling, a positive sensor output (V = V1-V2) is obtained. Hysteresis characteristics can be provided. On the other hand, to the shaft material after rolling, carburizing and quenching and tempering, and carburizing and quenching followed by induction hardening and tempering,
When quenching and tempering to prevent carbonitriding or induction hardening and tempering are performed, a negative hysteresis characteristic can be given to the sensor output (V = V1−V2).

Therefore, for example, a first heat treatment capable of imparting a positive hysteresis characteristic and a second heat treatment capable of imparting a negative hysteresis characteristic are applied to respective portions of the shaft material having different depths from the surface. Thus, both positive and negative hysteresis characteristics can be provided.

As another method for realizing a state of zero hysteresis by heat treatment, for example, a pair of magnetic anisotropic parts 12, 1 in a torque sensor shaft 11 shown in FIG.
The heat treatment method may be changed in 3 so that one magnetically anisotropic part has a positive hysteresis characteristic and the other magnetically anisotropic part has a negative hysteresis characteristic.

For example, the knurling groove of one magnetic anisotropic portion 12 in the torque sensor shaft 11 of FIG. 1 is subjected to carbonitriding quenching and tempering treatment so as to impart a negative hysteresis characteristic and to provide the other magnetic anisotropic member. By applying a carbonitriding, quenching and tempering treatment to the knurling groove of the characteristic portion 13 to give a positive hysteresis characteristic, the hysteresis characteristic can be made substantially zero for the combined output of the same sensor as described above.

In order to perform a carbonitriding quenching and tempering treatment on a part of the torque sensor shaft 11, the part is subjected to a carbonitriding preventive plating or an aluminum metallikon treatment before the heat treatment. All you have to do is remove the material.

The torque T is applied to the torque sensor shaft 11 as described above.
FIG. 10 shows an example of the characteristic of the output V1 of the magnetic anisotropic part exhibiting the negative hysteresis characteristic in the case where is applied, and the characteristic example of the output V2 of the magnetic anisotropic part exhibiting the positive hysteresis characteristic at that time. Is shown in FIG. If the above-mentioned carbonitriding, quenching, and tempering treatment is performed in order to exhibit a positive hysteresis characteristic, the shaft surface at that portion becomes hard, so that the torque detection sensitivity decreases as shown in the figure. FIG. 12 shows the output V of the torque sensor, that is, the characteristic of V = V1-V2.

When a single shaft is subjected to different heat treatments to form a pair of magnetically anisotropic parts having hysteresis characteristics having different polarities as shown in FIG.
As shown in FIG. 11 and described above, the characteristics of the output V1 of one magnetically anisotropic part and the characteristics of the output V2 of the other magnetically anisotropic part may not be uniform. That is, FIG.
11 and FIG. 11, the magnitudes (absolute values) of the outputs V1 and V2 when the same torque is applied are different, and the slopes of the diagrams are also different from each other. In such a case,
By adjusting the characteristic of the subtractor 17 as the arithmetic circuit shown in FIG. 1, the hysteresis of the sensor can be made substantially zero as shown in FIG.

Further, a magnetically anisotropic portion is formed by externally fitting a magnetostrictive sleeve on the shaft, wherein the magnetostrictive sleeve comprises a first layer having a positive hysteresis characteristic and a negative hysteresis. Even in the case of a multi-layer structure having a second layer having characteristics, both hysteresis characteristics can be similarly provided.

FIG. 13 shows an example of a torque sensor having a structure in which a two-layered magnetostrictive sleeve is fitted around a shaft.
The torque sensor shown in FIG.
No. 520059 is an improved version of the torque sensor.

The torque sensor disclosed in US Pat. No. 5520059, for example, has a magnetostrictive sleeve made of nickel maraging steel, which is a soft magnetic magnetostrictive material, fitted tightly to a non-magnetic stainless steel shaft serving as a sensor shaft. The sleeve is magnetized in the circumferential direction, and a pickup element such as a Hall element for detecting leakage magnetic flux from the magnetostrictive sleeve in proportion to the torque applied to the shaft is arranged outside the magnetostrictive sleeve. In such a configuration, in a no-load state where no torque is applied to the sensor shaft, the circumferential magnetization introduced into the magnetostrictive sleeve does not leak out. Therefore, in this state, no torque output is generated from the Hall element. However, when a torque is applied to the sensor axis, the circumferential magnetization induced in the magnetostrictive sleeve changes the direction of the magnetization in the +45 degree direction or the -45 degree direction in accordance with the direction of the applied torque. As a result, a leakage magnetic flux proportional to the magnitude of the torque is generated from the magnetostrictive sleeve, and the Hall element detects the leakage magnetic flux to generate a torque output.

In this case, when an overload torque is applied to the sensor, a hysteresis of the magnetostrictive phenomenon of the magnetostrictive sleeve occurs due to the applied overload torque, and a hysteresis occurs in the detection output based on the hysteresis, in other words, a zero error after overload occurs. Will do.

The torque sensor according to the embodiment of the present invention shown in FIG. 13 prevents such a zero error from occurring. That is, a first magnetostrictive sleeve 32 as a first layer is tightly fitted on a torque sensor shaft 31 formed of a nonmagnetic material, and the first sleeve 3
In FIG. 2, a second magnetostrictive sleeve 33 as a second layer is tightly fitted. Reference numeral 34 denotes a Hall element, which is provided near the outer surface of the second magnetostrictive sleeve 33.

The inner first magnetostrictive sleeve 32 and the outer second magnetostrictive sleeve 33 are configured such that the hysteresis of the magnetostrictive phenomenon is opposite in sign. By doing so, a positive hysteresis characteristic can be provided to one of the inner and outer magnetostrictive sleeves, and a negative hysteresis characteristic can be provided to the other. Reversing the hysteresis characteristics of the first magnetostrictive sleeve 32 and the second magnetostrictive sleeve 33 can be achieved by any means. That is, it does not matter what shot peening, heat treatment, machining, physical treatment, chemical treatment, or the like is performed. Further, instead of the two inner and outer sleeve structures, it is also possible to adopt a configuration in which the outermost surface layer of one sleeve and the layer immediately below the outermost layer have opposite hysteresis characteristics.

Instead of disposing the first magnetostrictive sleeve 32 and the second magnetostrictive sleeve 33 inside and outside as described above,
As in the case of the heat treatment described above, the first magnetostrictive sleeve 3 is located at a pair of positions spaced apart in the axial direction of the torque sensor shaft 31.
The hysteresis characteristic of the combined output of the sensor can be made substantially zero by tightly fitting each of the second and second magnetostrictive sleeves 33 and controlling the sign of the hysteresis characteristic.

FIG. 14 shows an embodiment using another principle. That is, the first magnetic anisotropic portion 42 and the second magnetic anisotropic portion 43 formed by the knurling groove are formed on the torque sensor shaft 41 at a pair of positions spaced apart in the axial direction. Have been. Then, the first magnetic anisotropic part 4
The angle of the knurl groove, that is, the angle formed by the knurl groove with the axis 44 of the torque sensor shaft 41 is α,
The knurling groove of the magnetic anisotropic part 43 of the torque sensor shaft 4
The angle formed between the first magnetic anisotropic portion 42 and the second magnetic anisotropic portion 43 is determined by setting the angle formed between the first magnetic anisotropic portion 42 and the second magnetic anisotropic portion 43 by setting the angle formed between the first magnetic anisotropic portion 43 and the angle α to β. Are configured such that the positive and negative characteristics of are reversed. The other members have the same configuration as that shown in FIG. 1, and thus the same reference numerals are given and the detailed description thereof will be omitted.

The principle of the torque sensor shown in FIG. 14 is as follows. That is, for example, a knurling groove is formed by rolling on the torque sensor shaft, then carburizing is performed, and further induction hardening and tempering are performed, and finally the surface is shot peened to form a magnetic anisotropic portion. When the angle formed by the knurling groove with respect to the axial direction of the sensor shaft is changed, the hysteresis characteristic of the magnetically anisotropic portion is as described in JP-A-4-50741. , As shown in FIG.

That is, as the angle of the knurling groove becomes smaller from 45 degrees, the negative hysteresis of the sensor (shown in FIG. 5) becomes smaller, and when the angle becomes 15 degrees, the sensor becomes positive hysteresis (see FIG. 5). 2).

Therefore, based on FIG. 15, for example, the angle α formed by the knurling groove of the first magnetic anisotropic portion 42 is increased by +1.
The angle β formed by the knurling groove is set to 5 degrees so that the second magnetic anisotropic portion 43 has the same magnitude as that of the first magnetic anisotropic portion 42, so that the hysteresis is opposite to that of the first magnetic anisotropic portion 42. When the angle is set to −33 degrees, the hysteresis of the composite output V = V1−V2 formed by the circuit of FIG. 14 can be made substantially zero.

As described above, one shaft member has its shaft center 4
In the case of forming a pair of magnetic anisotropic parts having angles α and β different from each other, as in the case of FIGS. 10 and 11, the characteristic of the output V1 of one magnetic anisotropic part and the other And the output V2 characteristic of the magnetic anisotropic portion may not be uniform. However, in that case, too, the hysteresis of the sensor can be made substantially zero by adjusting the characteristics of the circuit shown in FIG.

According to the present invention, when the positive hysteresis characteristic and the negative hysteresis characteristic are expressed, each characteristic can be expressed by performing the above-described treatments repeatedly. For example, when expressing either the positive or negative hysteresis characteristics, the heat treatment and the shot peening can be used in combination.

In addition, according to the present invention, in addition to the above-described structure constituted by the combination of the knurling groove and the solenoid coil, the structure may be constituted by a magnetic sensor shaft and a magnetic head.

[0061]

Embodiment (First Embodiment) Measured rated torque is 10N
In order to manufacture a torque sensor shaft with an overload torque of 150 Nm, a knurling groove is formed at an angle of 45 degrees as a magnetically anisotropic part on the outer periphery of a 15 mm diameter shaft machined with JIS SNCM815 material. Formed. The radius R of the groove bottom was 0.3 mm. Then, the shaft was heat-treated by induction hardening and tempering. next,
As the first stage shot peening treatment, treatment using steel shot grains having a center particle diameter of about 250 μm was performed. Further, as a second stage shot peening treatment, a treatment using steel shot grains having a center particle diameter of about 50 μm was performed.

An excitation coil and a detection coil are arranged around the magnetically anisotropic portion of the torque sensor shaft obtained in this way, and a magnetostrictive torque for a power steering shaft of an automobile having a measured rated torque of 10 Nm. The sensor was configured.

The excitation frequency of the excitation coil is set to 20, 30, 3
The output of the sensor when changing to 5, 45 kHz (V =
V1-V2) is shown in FIG. Here, the horizontal axis is the excitation frequency. The vertical axis represents 150 Nm with 10 Nm of the rated torque measured as the full scale (FS).
Is a percentage of the hysteresis or zero error with respect to this measurement rated full scale after the application of the overload. The upper side of this vertical axis represents positive hysteresis, and the lower side thereof represents negative hysteresis. This figure 1
As shown in FIG. 6, when the excitation frequency was 20 and 30 kHz, negative hysteresis characteristics were exhibited. When the excitation frequency was 35 kHz or 45 kHz, a positive hysteresis characteristic was exhibited. Then, as shown in the diagram of FIG. 16, when the excitation frequency is 32.5 kHz,
Hysteresis could be substantially reduced to zero.

FIG. 17 shows that the torque sensor has 150 Nm.
Shows the hysteresis characteristic when the overload torque of -150 Nm and the overload torque of -150 Nm are alternately and repeatedly applied. Here, the horizontal axis is time. The vertical axis is
Assuming that 10 Nm of the measured rated torque is a full scale (FS), the hysteresis for this full scale (FS), that is, a zero error is expressed in percentage. Also,
Black square marks indicate zero error, that is, overload
The hysteresis data after unloading is shown, black diamonds indicate the timing at which a 150 Nm overload torque is applied clockwise, and black triangles indicate -150 in the counterclockwise direction.
The timing at which Nm overload torque is applied is shown. As shown in FIG. 17, the measured rated torque is 10 Nm.
The hysteresis was able to be suppressed to less than 0.5% of the full scale of the rated torque of 10 Nm even after the application of the overload torque of 15 times of the above.

(Second Embodiment) As in the first embodiment, the measured rated torque is 10 Nm and the overload torque is 150
In order to manufacture a torque sensor shaft of Nm, a similar knurling groove was formed in the shaft material by rolling. The knurling groove portion of the shaft is subjected to a carburizing prevention treatment to improve the sensor characteristics, and the portion other than the knurling groove, particularly the shaft end, is provided with the strength and hardness required for coupling with other mechanical elements. The entire shaft was subjected to a carburizing, quenching and tempering heat treatment without performing a carburizing prevention treatment to impart a hardness.

Further, as a first stage shot peening treatment, a treatment using steel shot grains having a center particle size of about 250 μm is performed, and as a second stage shot peening treatment, a steel shot particle having a center particle size of about 50 μm is performed. Processing using shot grains was performed. That is, the required hysteresis characteristics were developed by using both the heat treatment and the shot peening treatment.

An excitation coil and a detection coil are similarly arranged around the torque sensor shaft obtained in this way, and the measured rated torque for the power steering shaft of the automobile is 1 unit.
A 0 Nm magnetostrictive torque sensor was constructed.

FIG. 18 shows the hysteresis characteristics with respect to the measured rated torque after the application of the overload and the unloading when the excitation frequency is changed for this torque sensor as in FIG. FIG. 19 shows a hysteresis characteristic when the same overload as in FIG. 17 is applied. As shown in FIGS. 18 and 19, FIGS.
The same result as in FIG. 17 was able to be achieved.

(Embodiment 3) As in Embodiment 1, the measured rated torque is 10 Nm and the overload torque is 150 Nm.
A similar knurling groove was formed in the shaft material by rolling in order to manufacture the torque sensor shaft of (1). As in the case of the second embodiment, the knurling groove portion of the shaft is subjected to a carburizing prevention treatment to improve the sensor characteristics, and the portion other than the knurling groove, particularly the shaft end, is connected to other mechanical elements. The entire shaft was subjected to a carburizing, quenching and tempering heat treatment without performing a carburizing prevention treatment in order to impart the strength and hardness required for bonding. Further, a shot peening treatment using a steel shot grain having a center particle diameter of about 50 μm was performed only once.

The excitation coil and the detection coil are similarly arranged around the torque sensor shaft obtained in this manner, and the rated torque for the power steering shaft of the automobile is 10 N.
m of the magnetostrictive torque sensor.

FIG. 20 shows the hysteresis characteristics with respect to the measured rated torque after the application of the overload and the unloading when the excitation frequency is changed for this torque sensor as in FIG. FIG. 21 shows a hysteresis characteristic when the same repetitive overload as in FIG. 17 is applied. As shown in FIGS. 20 and 21, FIGS.
The same result as in Example 7 could be achieved.

As is clear from FIGS. 16, 18 and 20, it is more preferable to perform a two-stage shot peening process by combining large-diameter shot grains and small-diameter shot grains as in the first and second embodiments. As compared with the case where the shot peening process is performed only once as in the third embodiment, the frequency at which the hysteresis can be made zero can be reduced.

[0073]

As described above, according to the present invention, there is provided a torque sensor shaft and a hysteresis canceling means, and the torque sensor shaft has a portion having a first hysteresis characteristic and the first hysteresis characteristic. A portion having a second hysteresis characteristic having a reverse polarity, wherein the hysteresis canceling means is provided with a hysteresis generated at a portion having the first hysteresis characteristic and a hysteresis generated at a portion having the second hysteresis characteristic on the torque sensor shaft. , The polarity of the hysteresis, that is, the polarity of the portion having the first hysteresis characteristic and that of the portion having the second hysteresis characteristic in the torque sensor axis are reversed. Cancels the hysteresis that occurs in the part with the opposite polarity hysteresis characteristics And, the hysteresis of the sensor can be substantially zero.

Therefore, for example, when used for power steering control of an automobile, a large-capacity torque sensor capable of withstanding a required overload torque is used when a light load during use is used as a measured rated torque. The hysteresis can be greatly reduced, and ideally can be made zero. Furthermore, the hysteresis can be ideally reduced to zero in a torque sensor used for a normal use other than the one used for a special use such as the power steering control of an automobile described above.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a magnetostrictive torque sensor according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a positive hysteresis characteristic of an output of the torque sensor.

FIG. 3 is a diagram for describing a positive hysteresis characteristic of one magnetic anisotropic portion in the torque sensor.

FIG. 4 is a diagram for explaining a positive hysteresis characteristic of the other magnetic anisotropic portion in the torque sensor.

FIG. 5 is a diagram for explaining a negative hysteresis characteristic of the output of the torque sensor.

FIG. 6 is a diagram for explaining a negative hysteresis characteristic of one magnetic anisotropic portion in the torque sensor.

FIG. 7 is a diagram for explaining a negative hysteresis characteristic of the other magnetic anisotropic portion in the torque sensor.

FIG. 8 is a diagram for explaining a relationship between an excitation frequency and hysteresis in the torque sensor.

FIG. 9 is a diagram for describing improvement of mechanical defects by performing two-stage shot peening on a sensor axis.

FIG. 10 is a diagram showing an example of a negative hysteresis characteristic of one magnetically anisotropic portion formed by a heat treatment.

FIG. 11 is a diagram illustrating an example of a positive hysteresis characteristic of the other magnetically anisotropic portion formed by the heat treatment.

FIG. 12 is a diagram showing an example of output characteristics of the torque sensor of the present invention having magnetically anisotropic portions formed by different heat treatments.

FIG. 13 is a perspective view of a magnetostrictive torque sensor according to another embodiment of the present invention.

FIG. 14 is a schematic configuration diagram of a magnetostrictive torque sensor according to still another embodiment of the present invention.

FIG. 15 is a diagram showing a relationship between a knurling angle and a hysteresis of a magnetic anisotropic portion of the torque sensor of FIG. 14;

FIG. 16 is a diagram showing the relationship between the excitation frequency and the hysteresis of the torque sensor according to the first embodiment of the present invention.

FIG. 17 is a diagram showing overload characteristics of the torque sensor according to the embodiment.

FIG. 18 is a diagram illustrating a relationship between an excitation frequency and hysteresis for a torque sensor according to a second embodiment of the present invention.

FIG. 19 is a diagram showing overload characteristics of the torque sensor according to the embodiment.

FIG. 20 is a diagram illustrating a relationship between an excitation frequency and hysteresis for a torque sensor according to a third embodiment of the present invention.

FIG. 21 is a diagram showing overload characteristics of the torque sensor according to the embodiment.

[Explanation of symbols]

 Reference Signs List 11 Torque sensor shaft 12 Magnetic anisotropic part 13 Magnetic anisotropic part 14 Excitation coil 16 AC power supply 21 Positive hysteresis 22 Negative hysteresis

Claims (17)

[Claims] 1. A torque sensor shaft and a hysteresis canceling means, wherein the torque sensor shaft has a portion having a first hysteresis characteristic and a second hysteresis characteristic having a polarity opposite to that of the first hysteresis characteristic. With a part having
The hysteresis canceling means is configured to cancel hysteresis generated in a portion having a first hysteresis characteristic of the torque sensor shaft and hysteresis generated in a portion having a second hysteresis characteristic. Type torque sensor. 2. The hysteresis canceling means is constituted by exciting means for exciting a torque sensor shaft, wherein the torque sensor shaft exhibits a first hysteresis characteristic having a positive value under a first exciting condition. A second hysteresis characteristic having a negative value under the second excitation condition;
The excitation means is a specific frequency band between a first excitation frequency band for creating the first excitation condition and a second excitation frequency band for creating the second excitation condition, and includes a hysteresis of the sensor. 2. The magnetostrictive torque sensor according to claim 1, wherein the excitation is performed in a third excitation frequency band, which can substantially reduce the torque to zero. 3. A knurling groove is formed on the outer periphery of the torque sensor shaft, and the outermost surface layer of the shaft and a layer immediately below the knurling groove in a portion where the knurling groove is formed have opposite hysteresis characteristics. 3. The magnetostrictive torque sensor according to claim 1, wherein the magnetostrictive torque sensor is configured as follows. 4. The nearest lower layer has a mechanical defect for making the nearest lower layer have a required hysteresis characteristic, and the outermost surface layer has a hysteresis characteristic of the outermost surface layer. 4. The magnetostrictive torque sensor according to claim 3, wherein the magnetostrictive torque sensor is formed with few mechanical defects such that the hysteresis characteristic of the magnetic sensor is opposite to the positive and negative. 5. The magnetostrictive torque sensor according to claim 3, wherein the outermost surface layer has a hysteresis characteristic formed by performing a shot peening process on the surface of the shaft member. 6. The hysteresis characteristic of the immediately lower layer is formed by performing a shot peening process for improving the degree of a mechanical defect generated at the time of forming the knurling groove. The magnetostrictive torque sensor according to any one of claims 3 to 5. 7. The outermost surface layer is subjected to a shot peening process by a shot grain having a central grain size smaller than a shot grain for a shot peening process for forming a hysteresis characteristic of the immediately lower layer. 7. The magnetostrictive torque sensor according to claim 5, wherein a hysteresis characteristic is formed. 8. The magnetostrictive torque sensor according to claim 5, wherein the immediately lower layer is formed by a controlled mechanical defect layer such as a knurling groove rolled at a low speed. 9. An outermost surface layer is formed by heat treatment, plating or CV.
The magnetostrictive torque sensor according to claim 3, wherein the magnetostrictive torque sensor is formed by one of a chemical treatment such as D and a physical treatment such as thermal spraying or ion plating. 10. A portion having a first hysteresis characteristic is formed by a first heat treatment, and a portion having a second hysteresis characteristic is formed by a second heat treatment different from the first heat treatment. The magnetostrictive torque sensor according to claim 1, wherein: 11. A knurling groove is formed on an outer periphery of a torque sensor shaft, and a first heat treatment and a second heat treatment are performed on an outermost surface layer of the shaft and a layer immediately below the knurling groove at a portion where the knurling groove is formed. As a result, a portion having a first hysteresis characteristic and a portion having a second hysteresis characteristic are formed, and the hysteresis canceling means is a portion where the knurling groove is formed and the first and second heat treatments are performed. The portion where the knurling groove is formed and the first and second heat treatments are performed is constituted by exciting means for exciting
The excitation means is configured to exhibit a first hysteresis characteristic of a positive value under a first excitation condition and to exhibit a second hysteresis characteristic of a negative value under a second excitation condition. Is a specific frequency band between a first excitation frequency band that creates the first excitation condition and a second excitation frequency band that creates the second excitation condition, and substantially reduces the hysteresis of the sensor. 11. The magnetostrictive torque sensor according to claim 10, wherein excitation is performed in a third excitation frequency band that can be set to zero. 12. A first knurling groove is formed on the outer circumference of the torque sensor shaft, and a second knurling groove is formed on the outer circumference of the torque sensor shaft at a position spaced in the axial direction from the first knurling groove. The first heat treatment is applied to a portion where the first knurling groove is formed to form a portion having a first hysteresis characteristic, and a second heat treatment is applied to a portion where the second knurling groove is formed. Is performed, a portion having a second hysteresis characteristic is formed, and the hysteresis canceling means includes a first hysteresis component included in a first output obtained corresponding to the first knurling groove. , By adding / subtracting a second hysteresis component included in a second output obtained corresponding to the second knurling groove, the first hysteresis component and the second hysteresis component are added. 11. The magnetostrictive torque sensor according to claim 10, wherein the magnetostrictive torque sensor is configured to cancel out the hysteresis component of (2). 13. A magnetostrictive sleeve is fitted around a torque sensor shaft, and the outermost surface layer and a layer immediately below the outermost surface layer of the magnetostrictive sleeve are configured so that the positive and negative hysteresis characteristics are opposite to each other. 2. The magnetostrictive torque sensor according to claim 1, wherein a portion having a first hysteresis characteristic and a portion having a second hysteresis characteristic are formed. 14. A pair of magnetostrictive sleeves are fitted on the torque sensor shaft at an axial distance from each other, and the hysteresis characteristics of one sleeve and the other sleeve are offset by hysteresis canceling means. The magnetostrictive torque sensor according to claim 1, wherein the magnetostrictive torque sensor is configured. 15. When manufacturing a magnetostrictive torque sensor having a torque sensor shaft and an exciting means for exciting the torque sensor shaft, a knurling groove is formed on an outer periphery of a shaft material for manufacturing the torque sensor shaft. Then, the shaft material with the knurling groove is subjected to induction hardening and tempering,
Thereafter, a first shot peening process is performed on the knurling groove to improve a mechanical defect generated by processing the knurling groove, thereby providing a required hysteresis characteristic to a portion where the defect is improved. The second shot peening process is performed by using a shot grain having a smaller center grain size than the shot grain at the time of the first shot peening process on the axial surface of the portion where the defect is improved, A method of manufacturing a magnetostrictive torque sensor shaft, characterized in that the outermost surface layer of this portion is provided with a hysteresis characteristic in which the polarity is reversed to the hysteresis characteristic of a portion where the defect is improved, which is a layer immediately below the outermost surface layer. 16. The method for manufacturing a magnetostrictive torque sensor shaft according to claim 15, wherein the shaft material is subjected to a carburizing prevention quenching and tempering process before the induction hardening and tempering process is performed. 17. When manufacturing a magnetostrictive torque sensor having a torque sensor shaft and an exciting means for exciting the torque sensor shaft, a knurling groove is formed on an outer periphery of a shaft material for manufacturing the torque sensor shaft. Then, after performing the carburizing prevention quenching and tempering treatment on the shaft material on which the knurling groove is formed, and then performing the induction quenching and tempering treatment, and then performing the shot peening treatment on the knurling groove, By improving the defect of the outermost surface layer of the portion where the mechanical defect generated by the processing of the knurling groove is present and expressing the required hysteresis characteristic, the hysteresis characteristic of this outermost surface layer, A method of manufacturing a magnetostrictive torque sensor shaft, comprising: inverting the sign of the hysteresis characteristic of a portion where the defect is not improved, which is a layer immediately below the portion, in which the defect is not improved.