JPH10197369A - Torque sensor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a torque sensor in which a change in a zero point is suppressed to be small and which obtains a good sensor characteristic by a method wherein a high-frequency quenching and tempering treatment is executed to a worked part at a knurled groove. SOLUTION: When a high-frequency quenching and tempering treatment is executed to a sensor shaft 1 and, especially, to magnetically anisotropic parts 2A, 2B, a hardened layer is formed. The surface hardness of the hardened layer is at an Hv 400 to 600, and a hardening depth amounts to 2.5 to 3.5mm when the shaft diameter of a sensor shaft is, e.g. 13.7mm. Then, the hardened layer becomes a martensite texture whose surface texture is stable as different from a carbonization protective layer formed in a carburizing treatment. As a result, its uniform hardness is obtained in regions of groove parts at the magnetically anisotropic parts 2A, 2B, the hardened layer which is thick is obtained, and a good sensor characteristic can be obtained. Even when especially a torque which is larger than a rated torque is applied, a change in a zero point can be suppressed to be small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a torque sensor and a method of manufacturing the same, and more particularly to a magnetostrictive torque sensor having a sensor axis provided with magnetic anisotropy and a method of manufacturing the same.

[0002]

2. Description of the Related Art A magnetostrictive torque sensor in which magnetic anisotropy is provided by a knurling groove on an outer periphery of a sensor shaft is known. In this groove type magnetostrictive torque sensor, SN having a large Ni content is used as a shaft material of the sensor shaft.
CM materials are generally used, and in particular, SNCM815 materials are often used. In order to use the shaft as a structural member of the torque transmitting portion, heat treatment is generally performed for the purpose of imparting a required shaft strength.

[0003] In this case, since the SNCM material has a low carbon content, carburizing, quenching and tempering are usually performed as heat treatment. At this time, if the knurling groove is carburized, the hardness increases and the amount of carbon increases to decrease the magnetic permeability. Therefore, the groove is carburized to prevent this.

[0004]

However, as described above, S
When carburizing, quenching and tempering are performed on the knurling groove of the shaft material made of NCM material and then carburizing, quenching and tempering, when a torque more than twice the rated torque is applied to the torque sensor composed of this shaft material, There is a problem that the zero point of is greatly changed. In addition, there is a problem that a large variation in zero point and sensitivity occurs when a large number of sensors are produced. Furthermore, if the surface of the shaft material is not subjected to shot peening after the heat treatment, the static performance of the sensor such as hysteresis, linearity and reproducibility will not be good, and specifically, these hysteresis, linearity and reproducibility will not be improved. There is also a problem that it does not fall below 1% FS.

Therefore, the present invention solves such a problem, and does not cause a significant change in the zero point even when a torque larger than the rated torque is applied, so that the variation in the zero point and sensitivity during production is small. It is another object of the present invention to improve the static performance of a sensor without performing shot peening after heat treatment.

[0006]

According to the present invention, there is provided a magnetostrictive torque sensor in which magnetic anisotropy is provided on the outer periphery of a sensor shaft by a knurling groove. It has been tempered.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes a sensor shaft constituting a torque sensor, which is formed of a JIS SNCM material, for example, an SNCM815 material. This sensor axis 1
A pair of magnetic anisotropic parts 2A and 2B are formed on the outer periphery of the pair at a distance in the axial direction. These magnetic anisotropic parts 2
A and 2B are formed by knurling grooves which are inclined in directions opposite to each other with respect to the axial direction of the sensor shaft 1.

Since the SNCM815 material has a low carbon content, it is generally used only as a carburizing material. However, in the present invention, the sensor shaft 1 using this material, particularly the magnetic anisotropic parts 2A and 2B, is used. And induction hardening and tempering.
A hardened layer is formed in the portion subjected to the induction hardening and tempering treatment, and the hardened layer has a surface hardness of Hv 420 to 600.
When the shaft diameter of the sensor shaft 1 is 13.7 mm, the curing depth reaches 2.5 to 3.5 mm. The hardening depth is 0.4 mm of the axial radius in the magnetic anisotropic parts 2A and 2B.
The optimal value is from 0 to 0.45 times.

The hardened layer formed by this induction hardening and tempering treatment has a martensitic structure with a stable surface structure, unlike the carbon preventing layer formed during the carburizing treatment. For this reason, uniform hardness is obtained in the groove area of the magnetic anisotropic parts 2A and 2B, and a thick cured layer is obtained, so that good sensor characteristics can be obtained.

In the present invention, as described above, S
When the NCM material is used, the Ni content is particularly 4.
0 to 6.0%, and the content of C is 0.1 to 0.5%.
% Is preferred. Of these, Ni is a component for imparting magnetism to the shaft, and its content affects the magnetic properties of the sensor. C has an effect on the hardness, that is, the strength, of the shaft material.
%, It is possible to impart sufficient strength necessary for the torque transmission sensor shaft of the torque sensor to the shaft material.

[0011]

FIG. 2 shows how the zero point fluctuates when a torque higher than the rated torque is applied. In the drawing, the + mark indicates a shaft diameter of 1.
The measurement results of a torque sensor having a sensor shaft obtained by subjecting a 6.2 mm SNCM815 material to induction hardening and tempering according to the present invention are shown. In addition, □ mark,
The measurement result about the torque sensor provided with the sensor shaft obtained by subjecting the sensor shaft of the same material and shaft diameter as described above to a carburizing treatment having a carburized portion as in the prior art is shown. Note that both the axes were subjected to shot peening under the same conditions after the heat treatment.

The rated torques of the torque sensor shafts of the product of the present invention and the conventional product were both 10 kgm. As is clear from FIG. 2, in the case of the product of the present invention, even when a torque larger than the rated torque was applied, the zero point fluctuation was smaller than that of the conventional product. For example, even when a torque three times the rated torque is applied, the zero-point variation is 2% FS or less, and when a torque six times the rated torque is applied, the zero-point variation is less than 20% FS. . As shown in the figure, according to the product of the present invention, the effect was particularly remarkable when a torque larger than 5 times the rated torque was applied.

According to the present invention, when a large number of torque sensors are manufactured, the variation of the zero point of each torque sensor is 40% FS or less, and the variation of the sensitivity is 10% FS or less.

FIG. 3 shows an example of the static performance of the torque sensor according to the present invention. That is, it shows the change in the output voltage of the sensor when a clockwise and counterclockwise torque is applied to the torque sensor of the present invention having a rated torque of 0.8 kgm. The sensor shaft of this torque sensor was subjected to the induction hardening and tempering as described above, but was not subjected to the shot peening after the heat treatment. As shown in the figure, the measurement data changed linearly, and the nonlinearity was 0.5% FS or less. From this measurement data, the hysteresis and reproducibility of the sensor, that is, the repeatability, were similarly obtained, but these were also 0.5% FS or less. That is, such good static performance was obtained without performing the shot peening treatment after the heat treatment, which was essential in the conventional sensor shaft.

FIG. 4 shows an example of the dynamic range of the torque sensor according to the present invention. That is,
FIG. 6 shows changes in the output voltage of the sensor when a clockwise and counterclockwise torque is applied to the torque sensor of the present invention having a rated torque of 6 kgm. As shown in the figure, even when a torque up to about 2.5 times the rated torque was applied, the sensor output linearly changed in proportion to the applied torque, and it was confirmed that the dynamic range was wide.

[0016]

As described above, according to the present invention, in a magnetostrictive torque sensor in which magnetic anisotropy is imparted to the outer periphery of a sensor shaft by a knurling groove, high-frequency quenching and tempering is performed on a processed portion of the knurling groove. Configuration
The hardened layer formed by this induction quenching and tempering treatment can be a martensite structure having a stable surface structure, unlike the carbon-prevention layer formed during the carburizing process,
For this reason, it is possible to obtain a thick hardened layer having a uniform hardness in the knurling groove of the magnetic anisotropic part, and it is possible to obtain good sensor characteristics, particularly when a torque larger than the rated torque is applied. Can also keep the fluctuation of the zero point small.

[Brief description of the drawings]

FIG. 1 is a front view showing an example of a torque transmission shaft for a torque sensor according to the present invention.

FIG. 2 is a diagram illustrating a zero point fluctuation of the torque sensor according to the embodiment of the present invention.

FIG. 3 is a diagram showing static characteristics of the torque sensor according to the embodiment of the present invention.

FIG. 4 is a diagram showing a dynamic range of the torque sensor according to the embodiment of the present invention.

[Explanation of symbols]

 1 sensor axis 2A magnetic anisotropic part 2B magnetic anisotropic part

Claims (3)

[Claims] 1. A torque sensor of a magnetostrictive type in which magnetic anisotropy is provided on the outer periphery of a sensor shaft by a knurling groove, wherein a high frequency quenching and tempering is performed on a processed portion of the knurling groove. Sensor. 2. The sensor shaft material is an SNCM material having a Ni content of 4.0 to 6.0% and a C content of 0.1 to 0.1%.
2. The torque sensor according to claim 1, wherein the value is 5%. 3. A knurling groove is machined in the sensor shaft, and a processed portion of the knurling groove is subjected to induction hardening and tempering to obtain a surface hardness of Hv 420-600 and a hardening depth of 0.40-0. A method of manufacturing a torque sensor, wherein the torque sensor is set to 45 times.