JPH11258077A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque sensor with good sensitivity and small hysteresis of output characteristic. SOLUTION: This torque sensor 1 comprises a part 5 to be detected externally fitted to a shaft 2 and a detecting part 6 for detecting a magnetic change due to distortion of the part 5 to be detected. A magnetostrictive material 8 composing the part 5 to be detected cylindrically formed and integrally rotatably fitted to the shaft 2 through an intermediate sleeve 7. A cylindrical yoke 10 is disposed relatively rotatable in relation to the shaft 2, and an exciting coil 11 and a detecting coil 12 are arranged inside the yoke 10. The magnetostrictive material 8 is formed in 0.5-3 mm thick, and 8 is formed by a crystalline magnetostrictive material. An Fe-Ni alloy containing 30-80 wt.% Ni added with several wt.% Cr is used as the magnetostrictive material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor for detecting a torque acting on a shaft to be detected by utilizing a change in the magnetic permeability of a magnetostrictive material.

[0002]

2. Description of the Related Art In a magnetostrictive torque sensor of this type, a magnetostrictive material fixed to an outer peripheral surface of a shaft is twisted and distorted by a torque acting on the shaft, so that its magnetic permeability changes in accordance with the torque. The torque is detected from the induced electromotive force induced in the detection coil based on the magnetic flux change corresponding to the magnetic susceptibility change. If the detected shaft itself is made of a magnetostrictive material as a magnetostrictive torque sensor, it is difficult to achieve both the magnetic characteristics and mechanical strength of the detected shaft and machining is difficult. Is provided with a magnetostrictive material.

[0003] Japanese Patent Application Laid-Open No. 7-55603 discloses the configuration shown in FIGS. In this torque sensor, as shown in FIG. 5, a high magnetostrictive alloy (FeAl alloy) layer 52
Are formed in a belt-like manner by being metallically fused. Further, at a position corresponding to the high magnetostrictive alloy layer 52 of the steel shaft raw material 51, groove forming portions 54a and 54b in which a plurality of partial spiral grooves 53a and 53b are formed symmetrically are provided. At positions corresponding to the groove forming portions 54a and 54b, coils 55a and 55b functioning as exciting and detecting means are provided.
6 are arranged inside.

[0004] The high magnetostrictive alloy layer 52 is formed as a belt-like overlay layer by TIG welding, plasma powder welding, plasma spraying, or the like. If the build-up layer is too thick, a crack may occur in the build-up layer. Therefore, the build-up thickness is preferably set to 3 mm or less, and when the FeAl alloy layer is used as the high magnetostrictive alloy layer 52, In order to effectively detect the magnetostriction phenomenon caused by the layer, it is desirable that the build-up thickness be 0.1 mm or more. Further, a hardened layer is formed at least over the depth of the high magnetostrictive alloy layer 52 by the induction hardening treatment of the surface of the steel shaft material 51.

As shown in FIG. 6, the circuit configuration of the magnetostriction detecting section includes coils 55a and 55b and resistors 57a and 57b.
To form a bridge circuit, and one of the opposing connection points C-
D is the supply side Vin of the AC power supply 58 and both coils 55
A constant voltage of alternating current is applied to a and 55b, and the output between the other opposing connection points AB is connected to the differential amplifier 59. The torque T is applied to the steel shaft blank 51 shown in FIG.
Is added, an output corresponding to the torque is generated from the differential amplifier 59.

Japanese Unexamined Patent Publication No. Sho 59-228140 discloses an axle in which a cylindrical magnetostrictive material is fitted to an axle (a shaft to be detected). In this magnetostrictive torque sensor, two annular regions are formed on the surface of a magnetostrictive material such that a large number of grooves are formed at an angle of 45 degrees and -45 degrees in the axial direction. Then, two sets of excitation coils and detection coils are arranged outside the magnetostrictive material corresponding to the respective annular regions, the excitation coils are connected to an AC power supply, and the detection coils are connected to a processing circuit. . Then, a detection signal corresponding to the torque acting on the axle is output from both the detection coils, and the processing circuit calculates the torque.

[0007]

Conventionally, it has been desired to improve the detection sensitivity of a torque sensor. Incidentally, the effective magnetic flux passing through the magnetostrictive material depends on the ratio of the cross-sectional area occupied by the magnetostrictive material to the total cross-sectional area of the shaft to be detected and the magnetostrictive material (effective cross-sectional area). Accordingly, the effective magnetic flux passing through the magnetostrictive material can be increased by increasing the thickness of the magnetostrictive material. Further, in order to increase the sensitivity of the magnetostrictive material itself, it has been general to perform magnetic annealing for enlarging the crystal grains as in the case of the ordinary high magnetic permeability material.

However, the output and torque of the torque sensor have a hysteresis phenomenon as shown in FIG. The hysteresis of the sensor is due to the magnetic properties of the material. The magnetization process of the ferromagnetic material includes a domain wall movement process and a magnetization rotation process, and the magnetization characteristics cause hysteresis as shown in FIG. 7B. It is said that the hysteresis of the sensor occurs because the minor loop is unstable near the origin of the magnetic field H in the magnetized state of the material. As a result, the sensor output at zero torque becomes unstable.

The instability of the minor loop is shown in FIG.
Is steeper, the steeper the hysteresis curve (BH curve) is. Therefore, the instability of the minor loop can be reduced by laying down the BH curve. When the BH curve is in a lying state, the magnetic permeability decreases, and the output of the sensor also decreases. However, it is considered that the decrease in the output of the sensor can be improved under the excitation condition.

However, the inventor of the present application has formed a magnetostrictive layer on a shaft to be detected by thermal spraying (hereinafter referred to as a thermal sprayed material).
For the magnetostrictive material (hereinafter, referred to as bulk material) formed into a cylindrical shape by rolling and cutting after melting, the drift at the time of overload of 24 times the rated value (when applying a torque of 12 N · m) is used to determine the exciting current value. As a result of observation under different conditions, results as shown in FIGS. 8A and 8B were obtained. Here, the overload drift is defined as follows. The drift voltage after overload corresponds to Vd in FIG.

Overload drift (% FS) = (drift voltage after overload / output voltage at rated time) × 100 As a result, as shown in FIG.
By increasing the exciting current, overload drift can be significantly reduced. However, as shown in FIG. 8B, in the case of a bulk material, the effect of the exciting current is small, and it is very difficult to increase the exciting current value to reduce the overload drift (hysteresis) to a value that can be satisfied. It has been found.

In Japanese Patent Application Laid-Open No. 7-55603,
When the sensor hysteresis Hys (%) is defined as the following equation, the Al concentration of the FeAl alloy is set to 10 to 16% by weight, and the hardened layer is formed on the surface of the steel shaft material at a depth greater than the thickness of the magnetostrictive alloy layer. It is stated that satisfactory results are obtained when formed.

Hys = {2Vh / (V1 + V2)} × 10
Here, Vh is the difference between the sensor outputs at zero torque in the graph showing the relationship between the torque and the output voltage in FIG. 7 (a), V1 is the output voltage when the maximum torque on the plus side is applied, and V1 is
2 means the output voltage when the maximum torque on the negative side is applied.

However, by welding the magnetostrictive material to the shaft to be detected,
In a configuration formed as a layer that has been fused in a metallographic manner, it is necessary to perform heating processing on the shaft to be detected, which may cause problems such as deterioration of the characteristics of the shaft to be detected itself. Also, the detected shaft is larger (longer length) than the magnetostrictive material
In this case, there is also a problem that the size of the processing apparatus is increased.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 59-228140, in a configuration in which a magnetostrictive material formed separately from a shaft to be detected, ie, a bulk material, is fixed to the shaft to be detected later, No problem. However, unlike the thermal sprayed material, it is difficult to reduce the hysteresis by the excitation current, unlike the thermal sprayed material, so that a bulk material satisfying the requirements has not been obtained conventionally.

The inventor of the present application has examined the relationship between the thickness of the magnetostrictive material and the crystal grain size and the hysteresis of the sensor. As a result, the full-scale sensitivity at the rated torque sensor and the deviation of the sensor output at the zero point ( 7 (a), the larger the thickness of the magnetostrictive material is, the larger the thickness is. However, the degree of the increase is different, and in order to obtain a sensor with good performance, the thickness and the crystal grain size of the magnetostrictive material are reduced. We found that there was a certain range in size. That is, if the thickness of the magnetostrictive material is simply increased in order to increase the sensitivity of the sensor, it has been found that the deviation of the sensor output at the zero point increases and the sensor performance decreases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a torque sensor having good sensitivity and small hysteresis in output characteristics.

[0018]

According to the first aspect of the present invention, there is provided a cylindrical magnetostrictive material fixed to an outer peripheral surface of a shaft to be detected, and a magnetic flux passing through the magnetostrictive material. A torque sensor comprising: a magnetic flux generating means for generating; and a detecting means for detecting a change in the magnetic flux due to distortion of the magnetostrictive material according to a torque acting on the shaft to be detected. And was formed in a cylindrical shape fitted externally to the shaft to be detected, with a thickness of 3 mm or less.

In the second aspect of the present invention, the magnetostrictive material has a crystal grain size of 1 to 100 μm. According to a third aspect of the present invention, in the first or second aspect of the present invention, the magnetostrictive member is formed to have a thickness of 0.5 mm or more, and has an outer peripheral surface on an axial direction of the detected shaft. An annular region having a large number of grooves at a predetermined angle is formed symmetrically with respect to a plane perpendicular to the axis.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the magnetostrictive material has a Ni content of 30 to 80% by weight.
An alloy obtained by adding Cr or Mo to the alloy by several weight% is used.

Therefore, according to the first to fourth aspects of the present invention, when the magnetostrictive material is distorted by the torque acting on the detected shaft, the magnetic flux is changed to a magnetic flux formed so as to pass through the magnetostrictive material by the magnetic flux generating means. Appears, and the change of the magnetic flux according to the torque applied to the detected shaft is detected by the detecting means. The magnetostrictive material is made of a crystalline magnetostrictive material and is formed in a cylindrical shape that is externally fitted to the shaft to be detected, and its thickness is set to 3 mm or less, so that the hysteresis of the output characteristics becomes smaller even with the same sensitivity. .

According to the second aspect of the present invention, the crystal grain size of the magnetostrictive material is set to 1 to 100 μm, so that the hysteresis after an overload is applied to the driven shaft becomes smaller.

According to the third aspect of the present invention, when torque is applied to the shaft to be detected, a compressive force acts on one of the two regions formed on the magnetostrictive material and a tensile force acts on the other. When a magnetostrictive material receives a compressive force, its magnetic permeability decreases, and when it receives a tensile force, its magnetic permeability increases. Therefore, the detection signal of the region receiving the compressive force is different from the detection signal of the region receiving the tensile force.

According to the invention of claim 4, according to claim 1,
The magnetostrictive material according to the present invention can be easily obtained.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view of a portion where the torque sensor 1 is mounted. Shaft 2 as shaft to be detected
Is rotatably supported by the housing 3 via a bearing 4 while being inserted into the housing 3 having a substantially cylindrical shape. The torque sensor 1 includes a detected part 5 having a magnetostrictive property fitted to the shaft 2 and a detecting part 6 for detecting a magnetic change due to the distortion of the detected part 5.

As shown in FIG. 2, the detected portion 5 includes an intermediate sleeve 7 externally fitted to the shaft 2 and a cylindrical magnetostrictive material 8 externally fitted to the intermediate sleeve 7. The magnetostrictive material 8 is attached to the shaft 2 via the intermediate sleeve 7 so as to be integrally rotatable. On the surface (outer peripheral surface) of the magnetostrictive material 8, a number of grooves 8a are formed at a predetermined angle with respect to the axial direction of the shaft 2.
Are formed symmetrically with respect to a plane perpendicular to the axis. A large number of grooves 8a are formed at equal intervals in the circumferential direction at 45 ° and −45 ° in the axial direction.

As shown in FIG. 1, the detecting section 6
And a cylindrical yoke 10 supported at both ends via two bearings 9 and arranged to be relatively rotatable. A concave portion is formed on the inner peripheral surface of the yoke 10 at a position facing each of the regions A and B. Each recess has an exciting coil 11 inside and a detecting coil 12 outside.
The bobbin (not shown) in which is wound respectively is stored. Since the yoke 10 is supported by the shaft 2 via the bearing 9, even if the shaft 2 is eccentric with respect to the housing 3, the axes of the yoke 10 and the magnetostrictive material 8 are easily aligned. Note that the exciting coil 11 constitutes a magnetic flux generating means, and the detecting coil 12 constitutes a detecting means.

The exciting coil 11 is connected to an AC power supply 13, and an AC current having a predetermined frequency is supplied to the exciting coil 11. The detection coil 12 is connected to a known processing circuit 14. When an alternating current flows through the exciting coil 11, a magnetic circuit in which a magnetic flux passes through the yoke 10 → the magnetostrictive material 8 → the yoke 10 is formed for each of the regions A and B. The magnetic flux passing through the magnetostrictive member 8 is inclined by 45 degrees or −45 degrees with respect to the axial direction of the magnetostrictive member 8 so that each region divided by the groove 8a is along the groove 8a.

Each induced electromotive force output from the two detection coils 12 is proportional to the strain in the region A and the region B of the magnetostrictive material 8, that is, the torque of the shaft 2. When a torque acts on the shaft 2, a compressive force acts on one of the regions A and B and a tensile force acts on the other in the regions A and B in accordance with the rotation direction at that time. The magnetic permeability of the magnetostrictive material 8 increases when a tensile force acts, and decreases when a compressive force acts. For this reason, the induced electromotive force from each detection coil 12 is large on the side that detects the detected area where the tensile force is applied, and is small on the side that detects the detected area where the compressive force is applied.

The processing circuit 14 subtracts the induced electromotive force input from both detection coils 12 by a differential circuit (not shown),
The subtracted signal is rectified by a rectifying circuit or the like provided therein to obtain a torque value by a known circuit. The reason why the subtraction is performed by the differential circuit is to perform highly accurate torque detection by canceling and compensating for disturbance noise due to a temperature change or the like. The level of the output signal from the detection coil 12 is set so that the processing circuit 14 detects zero torque when no torque is applied to the shaft 2. Then, the processing circuit 14 detects the magnitude and direction of the torque based on how much the signal level of the detection signal takes on the positive side with respect to the zero level and how much the value takes on the negative side. It has become.

The magnetostrictive material 8 is formed of a crystalline magnetostrictive material,
The thickness is formed to a predetermined value of 0.5 mm or more and 3 mm or less. When the thickness is set to 3 mm or less, if the thickness exceeds 3 mm, the hysteresis suddenly deteriorates. Therefore, the upper limit of the thickness is 3 mm to obtain a satisfactory hysteresis.
Also, setting the thickness to 0.5 mm or more is 0.5 m
m, a satisfactory groove 8a cannot be formed,
This is because the desired output sensitivity cannot be obtained due to the small volume of the magnetic material. In this embodiment, for example, the magnetostrictive material 8 is formed to a thickness of 1.5 mm.

The magnetostrictive material has a Ni content of 30 to 80.
An iron-nickel-chromium alloy obtained by adding a few percent of Cr to a wt.% Fe-Ni alloy is used. In this embodiment, as the magnetostrictive material, for example, an Fe-containing material having a Ni content of 56% by weight is used.
An iron-nickel-chromium alloy obtained by adding 4% of Cr to a Ni alloy is used. Further, the average grain size of the crystal is 300 μm.
m.

Next, the operation of the torque sensor 1 will be described. During the operation of the torque sensor 1, an AC current having a constant amplitude and frequency is supplied from the AC power supply 13 to the exciting coil 11, and two magnetic circuits are formed in which the magnetic flux passes through the yoke 10, the magnetostrictive material 8, and the yoke 10. . When a torque is generated by applying a rotational force to the shaft 2, one of the regions A and B that separates the magnetostrictive material 8 in the axial direction receives a compressive force and the other receives a tensile force. For this reason, each of the detection coils 12 for detecting a change in the magnetic flux in the region A and the region B becomes large on the side of detecting the detection target region that has received the tensile force, and detects the detection target region that has received the compressive force. An induced electromotive force proportional to the torque of the shaft 2 that decreases on the side is generated.

The induced electromotive force induced by the two detection coils 12 is input to the processing circuit 14. The voltage from the two detection coils 12 input to the processing circuit 14 is subtracted by a differential circuit, and the subtracted signal is rectified by a rectification circuit or the like provided therein, and the value of the torque is calculated by a known circuit. Is required.

The full scale (FS) sensitivity of the torque sensor when 10 N · m was added as the rated torque was 60 mV (millivolt) as the output voltage. In this case, the hysteresis (rated hysteresis) is 2.1% FS
Met. Where hysteresis (rated hysteresis)
Is the output when the torque is reduced to zero after adding the rated torque, that is, Vh in FIG.
The output when the rated torque is applied, that is, V0 in FIG.
Is multiplied by 100, and is expressed by the following equation.

Hysteresis (% FS) = (Vh / V0) × 100 (1) Using the same magnetostrictive material, changing the thickness (sleeve thickness) of the magnetostrictive material 8 and changing the FS sensitivity under the same measurement conditions Are shown in Table 1 and FIG. 3 (a). The measurement results of the hysteresis are shown in Table 1 and FIG.

Here, the value of the hysteresis (% FS) indicated by the vertical axis of FIG.
The value is obtained by multiplying the value obtained by dividing the value of h by the FS sensitivity by 100. Hysteresis (% FS) = (Vh / FS sensitivity) × 100

[0039]

[Table 1] As is clear from FIGS. 3A and 3B, the FS sensitivity of the torque sensor increases at almost the same rate as the thickness of the magnetostrictive material 8 increases, whereas the hysteresis exceeds 3 mm. It turned out to increase suddenly. Therefore,
By setting the thickness of the magnetostrictive material 8 to 3 mm or less, the required FS
Sensitivity can be ensured and hysteresis can be reduced.
The following can be considered as a reason why the hysteresis is reduced when the thickness of the magnetostrictive material 8 is small.

Since the exciting coil 11 is arranged so as to be coaxial with the magnetostrictive material 8, when excited by the same magnetic field,
As the thickness of the magnetostrictive material 8 is smaller, the excitation magnetic flux concentrates on the surface layer (outer peripheral portion) of the magnetostrictive material 8. Therefore, when the thickness of the magnetostrictive material 8 is reduced, the thickness ratio of the eddy current caused by the magnetic flux passing through the magnetostrictive material 8 increases, and the AC magnetic permeability of the magnetostrictive material 8 is adjusted to be low. Therefore, the AC magnetization characteristic of the magnetostrictive material 8 does not have a steep BH curve. In the vicinity of the magnetization zero point of the high-permeability material, there is instability in which the magnetization characteristics of the AC-excited material rapidly fluctuate. Therefore, the hysteresis increases when the high-permeability material is used. Hysteresis is reduced by lowering the value.

This embodiment has the following effects. (A) By setting the thickness of the cylindrical magnetostrictive material 8 to 3 mm or less, the sensitivity is good and the hysteresis of the output characteristics can be reduced.

(B) The difference between the output signals corresponding to the two regions A and B formed on the outer peripheral surface of the magnetostrictive member 8 is used as the output of the torque sensor to increase the sensitivity. (C) Since the magnetostrictive material 8 has a thickness of 0.5 mm or more, the groove 8a can be formed without difficulty. Further, the required sensitivity can be obtained without making the magnetostrictive material 8 long.

(D) Ni content of the magnetostrictive material is 30
Since a material obtained by adding a few weight% of Cr to an 80-80 weight% Fe-Ni alloy is used, a magnetostrictive material is easily available. (E) Put the yoke 10 on the shaft 2 with the bearing 9
And supported so as to be relatively rotatable. Therefore, the shaft 2
The gap between the magnetostrictive material 8 and the yoke 10 externally fitted on the shaft 2 is independent of the eccentricity of the shaft 2 and the processing accuracy of the housing 3.
It can be kept constant at all times, and high detection accuracy of the torque sensor 1 can be ensured.

(F) Since the magnetostrictive material 8 is fixed to the shaft 2 via the intermediate sleeve 7 so as to be integrally rotatable, the dimensional accuracy of the intermediate sleeve 7 is maintained at a certain level or more, so that the shaft 2 Even if the processing accuracy is not so severe, the magnetostrictive material 8 is centered on the shaft 2 and the detection accuracy of the torque sensor 1 is stabilized.

(Second Embodiment) Next, a second embodiment will be described. This embodiment is different from the above embodiment in that the average particle size of the crystal grains of the magnetostrictive material forming the magnetostrictive material 8 is changed, and the mechanical configuration of the torque sensor 1 itself is the same as in the above embodiment. is there. As a method for making the magnetostrictive material finer, for example, there is the following method. (1) The annealing temperature is lower than the conventional temperature (usually around 1100 ° C.), for example, 900 ° C. or less. (2) Add a small amount (several% by weight) of an additional element (for example, Ti, Al, Nb, etc.). (3) The workability is increased to change the cooling rate during annealing and to increase the number of crystal growth points. To increase the degree of processing,
This means that a large number of defective portions of crystal growth are actively formed by applying a non-uniform force partially when the material powder is compressed.

Table 2 shows the results of measuring the overload drift (% FS) of the coarse-grained product and the fine-grained product using the material A and the material B. Here, the overload drift means the output of the torque sensor when the torque is set to zero after application of the overload torque (corresponding to Vd in FIG. 4) and the output when the rated torque is applied (corresponding to V0 in FIG. 4). It is a value obtained by multiplying the value obtained by dividing by 100 by 100. In this embodiment, the rated torque is 3N ·
m, the overload torque was 250 N · m. Also,
The thickness of the magnetostrictive material 8 was 0.7 mm.

[0047]

[Table 2] For material A, Ti was added, and annealing was performed at 850 ° C. in a hydrogen atmosphere. For material B, annealing was performed in a hydrogen atmosphere at a temperature of 400 ° C. or less. In addition, both the materials A and B were obtained by annealing coarse particles at 1100 ° C.

As is evident from Table 2, it was confirmed that when the crystal grain size was reduced, the overload drift was reduced even if the composition of the magnetostrictive material or the method of reducing the size were different. The reason for this is that if the crystal grain size is increased, the residual stress is generated unevenly, so that the minor loop near the zero point becomes unstable. However, it is considered that by reducing the average grain size, a small crystal grain boundary is formed between the large crystal grains, and the crystal grain boundary hinders the domain wall movement and suppresses a sharp change in magnetic permeability. In addition, the increase in fine grains increases the electric resistance value, thereby preventing significant magnetic deterioration due to eddy current generated during use.

The appropriate crystal grain size varies depending on the material, but the average grain size is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 50 μm. When the thickness of the magnetostrictive material 8 is the same, the hysteresis is reduced by reducing the average particle size. Therefore, by setting the thickness of the magnetostrictive material 8 to 0.5 to 3 mm as in the embodiment, the hysteresis can be further reduced in addition to the effects (a) to (f) of the embodiment.

The embodiment is not limited to the above, and may be embodied as follows, for example. As the material of the magnetostrictive material 8, an iron-nickel-molybdenum alloy to which Mo is added in place of Cr of the iron-nickel-chromium alloy may be used. For example, when the Ni content is 30 to
80% by weight of Fe-Ni alloy containing several percents of Mo
Nickel-molybdenum alloy is used.

The materials for the magnetostrictive material 8 include iron / nickel / chromium alloy and iron / nickel / molybdenum alloy.
A high-permeability soft magnetic material such as an Fe-Al alloy or an Fe-Ni alloy is used.

The cylindrical magnetostrictive material 8 may be directly attached to the shaft 2 without providing the intermediate sleeve 7. In the case of forming the magnetostrictive material 8 made of a magnetostrictive material having a small crystal grain size, annealing may be omitted and only the cooling rate after sintering may be adjusted.

A structure may be adopted in which the magnetostrictive material 8 is a smooth sleeve having no groove 8a on its surface, and the smooth sleeve is detected by a crosshead type pickup. The technical ideas (inventions) other than those described in the claims that can be understood from the above embodiments will be described below together with their effects.

(1) The torque sensor according to any one of claims 1 to 3, wherein the magnetostrictive material is Ni.
A few wt% of Cr is added to an Fe—Ni alloy having a content of 30 to 80 wt%, and additional elements for increasing the number of crystal growth points are added. In this case, it is easy to produce a magnetostrictive material having fine crystal grains.

(2) Al, T as additive elements in (1)
i and Nb are used, and the added amount thereof is several weight% or less. Also in this case, the same effect as (1) is exhibited. (3)
Fe-Ni alloy with 30-80 wt% Ni content
r using a magnetostrictive material to which a few percent by weight of
A magnetostrictive material formed in a cylindrical shape of up to 3 mm. By using this magnetostrictive material, a torque sensor having good sensitivity and output characteristics with small hysteresis can be obtained.

It should be noted that the term "hysteresis" as used herein does not only mean rated hysteresis but also includes overload drift (corresponding to overload hysteresis).

[0057]

As described in detail above, according to the first to fourth aspects of the present invention, it is possible to obtain a torque sensor having good sensitivity and output characteristics with small hysteresis.

According to the second aspect of the invention, the hysteresis of the output characteristics is further reduced. According to the third aspect of the present invention, since the detection signal is output based on the change in the magnetic permeability of the two regions formed in the magnetostrictive material, the torque can be reduced with a simple configuration as compared with the case where no groove is formed. Detection sensitivity is improved.

According to the fourth aspect of the invention, it is easy to obtain a magnetostrictive material having the above characteristics.

[Brief description of the drawings]

FIG. 1 is a partial schematic cross-sectional view of a torque sensor according to a first embodiment.

FIG. 2 is a perspective view showing a magnetostrictive material and a shaft.

3A is a graph showing the relationship between the thickness of the magnetostrictive material and output sensitivity, and FIG. 3B is a graph showing the relationship between the thickness of the magnetostrictive material and hysteresis.

FIG. 4 is a graph showing the relationship between the output of a torque sensor and torque.

FIG. 5 is a partial cross-sectional view of a conventional torque sensor.

FIG. 6 is a circuit diagram of a detection unit of the torque sensor.

7A is a graph showing a relationship between an output of a torque sensor and a torque, and FIG. 7B is a graph showing a magnetization curve.

8A is a graph showing a relationship between an exciting current value of a thermal sprayed material and an overload drift, and FIG. 8B is a graph showing a relationship between an exciting current value of a bulk material and an overload drift.

[Explanation of symbols]

1. Torque sensor, 2. Shaft constituting detected shaft,
8 ... magnetostrictive material, 8a ... groove, 11 ... exciting coil as magnetic flux generating means, 12 ... detecting coil as detecting means,
A, B ... area.

Claims (4)

[Claims] 1. A cylindrical magnetostrictive material fixed to an outer peripheral surface of a shaft to be detected, magnetic flux generating means for generating a magnetic flux passing through the magnetostrictive material, and the magnetostrictive material according to a torque acting on the shaft to be detected. Wherein the magnetostrictive material is formed of a crystalline magnetostrictive material into a cylindrical shape fitted around the shaft to be detected, and has a thickness A torque sensor having a length of 3 mm or less. 2. The crystal grain size of the magnetostrictive material is 1 to 100 μm.
The torque sensor according to claim 1, wherein m is m. 3. The magnetostrictive material is formed to have a thickness of 0.5 mm or more, and an annular region having a large number of grooves at a predetermined angle with respect to the axial direction of the detected shaft is formed on the outer peripheral surface thereof. The torque sensor according to claim 1 or 2, wherein the torque sensor is formed symmetrically with respect to a plane orthogonal to the plane. 4. The Ni content of the magnetostrictive material is 30 to 40.
4. An alloy comprising 80% by weight of Fe-Ni alloy and Cr or Mo added thereto by several% by weight.
The torque sensor according to claim 1.