JP6880469B2 - Manufacturing method of shaft for magnetostrictive torque sensor - Google Patents

Description

The present invention relates to a shaft for a magnetostrictive torque sensor and a method for manufacturing the same.

Conventionally, a magnetostrictive torque sensor is known. The magnetostrictive torque sensor uses a shaft with magnetostrictive characteristics that changes the magnetic permeability when stress is applied, and detects changes in the magnetic permeability of the shaft when torque is applied and the shaft is twisted. Changes in coil inductance The torque applied to the shaft is detected by detecting as (see, for example, Patent Document 1).

JP-A-2002-340701

By the way, it is known that the steel material used for the shaft contains a non-magnetic structure called austenite. Austenite is a solid solution of other elements in γ-iron having a face-centered cubic lattice structure.

If the shaft contains a large amount of non-magnetic austenite, the change in magnetic permeability when torque is applied becomes small, leading to a decrease in the sensitivity of the magnetostrictive torque sensor.

However, if the amount of austenite in the entire shaft is reduced by adjusting the heat treatment conditions or the like, the toughness of the shaft is lowered and the shaft is liable to crack.

Further, since hysteresis causes an error (linearity error, hereinafter referred to as hysteresis error), it is desired to be as small as possible.

The present invention, while still ensuring the toughness, and to provide a method for producing improved and hysteresis error reduction is available magnetostrictive shafts preparative torque sensor of the sensor sensitivity.

The present invention is a shaft for a magnetostrictive torque sensor to which a sensor portion of the magnetostrictive torque sensor is attached, for the purpose of solving the above problems, and the shaft for the magnetostrictive torque sensor made of chrome steel or chrome molybdenum steel. The sensor unit is partially attached, and the peak values of the X-ray diffraction intensities of the magnetostrictive torque sensor shafts Martensite (200) and Martensite (211) at the attachment portion of the sensor portion are not attached to the sensor portion. Provided is a shaft for a magnetostrictive torque sensor, which is 1.15 times or more each of the peak values of the X-ray diffraction intensities of Martensite (200) and Martensite (211) of the shaft for the magnetostrictive torque sensor in the portion. ..
Further, for the purpose of solving the above problems, the present invention is a shaft for a magnetostrictive torque sensor to which a sensor portion of a magnetostrictive torque sensor is attached, and is for the magnetostrictive torque sensor made of chrome steel or chrome molybdenum steel. The sensor unit is attached to a part of the shaft, and the peak value of the X-ray diffraction intensity of austenite (200) of the magnetostrictive torque sensor shaft is the X-ray diffraction of martensite (200) in the non-attached portion of the sensor unit. The peak value of the X-ray diffraction intensity of austenite (200) of the shaft for the magnetostrictive torque sensor is the peak of the X-ray diffraction intensity of martensite (200) at the mounting portion of the sensor portion, which is larger than the peak value of the intensity. A shaft for a magnetostrictive torque sensor, which is smaller than the value, is provided.
Further, the present invention is a method for manufacturing a shaft for a magnetic strain type torque sensor to which a sensor portion of the magnetic strain type torque sensor is attached, for the purpose of solving the above problems, and the shaft material made of chrome steel or chrome molybdenum steel is used. A heat treatment step of performing a carburizing, quenching and quenching treatment, and a shot peening step of performing shot peening at least at a position where the sensor portion of the shaft material after the heat treatment step is attached are provided. In the shot peening step, the particle size is 0. A method for manufacturing a shaft for a magnetic strain type torque sensor, which uses a shot material of 6 mm or more and 0.8 mm or less and a rockwell hardness of 60 or more, an injection pressure of 0.4 MPa or more and 0.6 MPa or less, and an injection time of 2 minutes or more. I will provide a.

According to the present invention, even while securing the toughness, it can provide a method for producing improved and hysteresis error reduction is available magnetostrictive shafts preparative torque sensor of the sensor sensitivity.

It is a figure which shows an example of the sensor part of a magnetostriction type torque sensor, (a) is a side view when it is attached to a shaft, and (b) is a sectional view taken along line AA. It is a top view which shows the state which expanded the bobbin schematically, (a) is a figure explaining the 1st detection coil and 4th detection coil, (b) is a figure explaining the 2nd detection coil and 3rd detection coil. It is a figure. It is a circuit diagram which shows an example of the measuring part which measures the torque applied to a shaft by the detection signal of a torque sensor. It is a figure explaining sensitivity and hysteresis error. It is a graph which shows the test result when chrome steel (SCr420) was used as a shaft material, (a) is the measurement result of the sensor sensitivity for each shot peening condition, and (b) is the hysteresis error for each shot peening condition. It is a graph which shows the measurement result of. (A) to (c) are graphs showing the results of the X-ray diffraction test of the sample of P5M10 in FIG. 5 and the sample not subjected to shot peening. It is a graph which shows the test result when the chrome molybdenum steel (SCM420) was used as a shaft material, (a) is the measurement result of the sensor sensitivity for each shot peening condition, and (b) is the hysteresis for each shot peening condition. It is a graph which shows the measurement result of an error. (A) to (c) are graphs showing the results of the X-ray diffraction test of the sample of P5M10 in FIG. 7 and the sample not subjected to shot peening.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Explanation of magnetostrictive torque sensor)
First, a magnetostrictive torque sensor (hereinafter, simply referred to as a torque sensor) will be described with reference to FIGS. 1 to 3. 1A and 1B are views showing an example of a sensor unit of a torque sensor, FIG. 1A is a side view when the torque sensor is attached to a shaft, and FIG. 1B is a sectional view taken along line AA thereof. 2A and 2B are plan views schematically showing a state in which the bobbin is deployed. FIG. 2A is a diagram illustrating a first detection coil and a fourth detection coil, and FIG. 2B is a second detection coil and a third detection coil. It is a figure explaining the coil. FIG. 3 is a circuit diagram showing an example of a measuring unit that measures the torque applied to the shaft by the detection signal of the torque sensor.

As shown in FIGS. 1A and 1B, the sensor unit 2 of the torque sensor 1 is attached around a magnetostrictive torque sensor shaft (hereinafter, simply referred to as a shaft) 101 having a magnetostrictive characteristic. The torque sensor 1 measures the torque (rotational torque) applied to the shaft 100.

The shaft 100 is made of a material having magnetostrictive characteristics and is formed in a columnar shape (rod shape). The shaft 100 is, for example, a shaft used for torque transmission of a vehicle power train system or a shaft used for torque transmission of a vehicle engine.

The sensor unit 2 includes a coil 21 and a magnetic ring 22. The magnetic ring 22 is made of a magnetic material (ferromagnetic material) and is formed in a hollow cylindrical shape. The coil 21 is inserted into the hollow portion of the magnetic ring 22. The magnetic ring 22 plays a role of suppressing the magnetic flux generated in the detection coil 3 of the coil 21 from leaking to the outside and lowering the sensitivity.

The coil 21 has a bobbin 23 made of a non-magnetic resin, and a plurality of detection coils 3 formed by winding an insulated wire around the bobbin 23. The bobbin 23 is provided coaxially with the shaft 100 and is formed in a hollow cylindrical shape. On the outer peripheral surface of the bobbin 23, a plurality of first inclined grooves 4 inclined by a predetermined angle (here, +45 degrees) with respect to the axial direction of the shaft 100, and a predetermined direction opposite to the first inclined groove 4 with respect to the axial direction. A plurality of second inclined grooves 5 inclined at an angle (here, −45 degrees) are formed. The first inclined groove 4 and the second inclined groove 5 are formed by grooves recessed in the radial direction of the bobbin 23.

As shown in FIGS. 2A and 2B, the coil 21 has first to fourth detection coils 31 to 34 as the detection coil 3. The first detection coil 31 and the fourth detection coil 34 are formed by winding an insulated wire around the bobbin 23 along the first inclined groove 4. The second detection coil 32 and the third detection coil 33 are formed by winding an insulated wire around the bobbin 23 along the second inclined groove 5.

In FIG. 2A, reference numerals 31a and 31b indicate input ends and output ends for one layer of the first detection coil 31, respectively, and reference numerals 34a and 34b are inputs for one layer of the fourth detection coil 34, respectively. Indicates the end and the output end. In FIG. 2B, reference numerals 32a and 32b indicate input ends and output ends for one layer of the second detection coil 32, respectively, and reference numerals 33a and 33b are inputs for one layer of the third detection coil 33, respectively. Indicates the end and the output end. Note that FIGS. 2 (a) and 2 (b) show the winding of the insulated wire for one turn, and each detection coil 31 to 34 is formed by repeating the winding of the target turn insulated wire. Further, the method of winding the insulated wire shown in FIGS. 2A and 2B is an example, and the detection coils 31 to 34 may be formed by using another winding method.

The first detection coil 31 and the fourth detection coil 34 are for detecting a change in the magnetic permeability of the shaft 100 in the first direction inclined by a predetermined angle (here, +45 degrees) with respect to the axial direction of the shaft 100. .. Further, the second detection coil 32 and the third detection coil 33 are transparent to the shaft 100 in the second direction inclined by a predetermined angle (here, −45 degrees) on the side opposite to the first direction with respect to the axial direction of the shaft 100. This is for detecting a change in magnetic coefficient.

As shown in FIG. 3, the measuring unit 41 measures the torque applied to the shaft 100 by detecting the change in the inductance of the first to fourth detection coils 31 to 34.

The measuring unit 41 includes a bridge circuit 42 formed by connecting the first detection coil 31, the second detection coil 32, the fourth detection coil 34, and the third detection coil 33 in an annular shape in this order, and the first detection coil 33. The transmitter 43 that applies an AC voltage between the contact a between the second detection coil 32 and the contact b between the third detection coil 33 and the fourth detection coil 34, and the first detection coil 31. The voltage measuring circuit 44 that detects the voltage between the contact c between the third detection coil 33 and the contact d between the second detection coil 32 and the fourth detection coil 34, and the voltage measured by the voltage measuring circuit 44. A torque calculation unit 45 for calculating the torque applied to the shaft 100 is provided. The bridge circuit 42 is configured by arranging the first detection coil 31 and the fourth detection coil 34 on one opposite side, and arranging the second detection coil 32 and the third detection coil 33 on the other side facing each other. ..

In the measuring unit 41, when no torque is applied to the shaft 100, the inductances L1 to L4 of the first to fourth detection coils 31 to 34 become equal, and the voltage detected by the voltage measuring circuit 44 becomes substantially 0.

When torque is applied to the shaft 100, the magnetic permeability in the direction of +45 degrees with respect to the axial direction decreases (or increases), and the magnetic permeability in the direction of −45 degrees with respect to the axial direction increases (or decreases). Therefore, when torque is applied to the shaft 100 while the AC voltage is applied from the transmitter 43, the inductance of the first detection coil 31 and the fourth detection coil 34 decreases (or increases), and the second detection coil 32 and Inductance increases (or decreases) in the third detection coil 33. As a result, the voltage detected by the voltage measuring circuit 44 changes, and the torque calculation unit 45 calculates the torque applied to the shaft 100 based on the change in the voltage.

Since the first detection coil 31 and the fourth detection coil 34 and the second detection coil 32 and the third detection coil 33 have exactly the same configuration except that the winding directions are different, the bridge circuit 42 as shown in FIG. 3 is used. As a result, it is possible to cancel the influence of temperature and the like on the inductance of the first to fourth detection coils 31 to 34, and the torque applied to the shaft 100 can be detected with high accuracy. Further, in the torque sensor 1, if the inductance of the first detection coil 31 and the fourth detection coil 34 increases (or decreases), the inductance of the second detection coil 32 and the third detection coil 33 decreases (or increases). By using the bridge circuit 42 as shown in FIG. 3, the detection sensitivity can be further improved.

(Explanation of shaft 100 and its manufacturing method)
In the present embodiment, as the shaft 100, a shaft material made of chrome steel (SCr) or chrome molybdenum steel (SCM) is subjected to carburizing, quenching and tempering, and then shot peening.

That is, in the method for manufacturing the shaft 100 according to the present embodiment, a heat treatment step of performing a carburizing, quenching and tempering treatment on a shaft material made of chrome steel or chrome molybdenum steel, and at least a sensor portion 2 of the shaft material after the heat treatment step are attached. It is provided with a shot peening process for performing shot peening at the position where it is to be used.

By carburizing, quenching, and tempering the entire shaft material, the mechanical strength including the toughness of the shaft 100 can be increased.

Furthermore, by applying shot peening to the shaft material after heat treatment, martensitic transformation (non-diffusion transformation) occurs on the surface of the shaft 100 (region at a predetermined depth from the surface), reducing non-magnetic austenite and making it stronger. Magnetic martensite can be increased. As a result, the non-magnetic region on the surface of the shaft 100 is reduced and the magnetic region is increased, so that the change in magnetic permeability when torque is applied becomes large, and the sensitivity of the torque sensor 1 can be improved. .. Austenite is a solid solution of other elements in iron (γ-iron) having a face-centered cubic lattice structure. Martensite is a solid solution in which carbon has penetrated into the iron crystals of the body-centered square lattice.

Further, by applying shot peening to the shaft material after the heat treatment, the surface of the shaft material is work-hardened and the hysteresis characteristics are improved. More specifically, by applying shot peening to the shaft material after the heat treatment, the magnetic domains (areas in which the directions of the magnetic moments are aligned) on the surface of the shaft 100 are subdivided, and the movement of the domain wall, which is the boundary of the magnetic domains, is performed. Austenite, which is an obstructive pinning site, is reduced. As a result, when the applied torque is released, the magnetic domain and the domain wall are likely to return to the original state, and the hysteresis error is reduced.

As shown in FIG. 4, the sensitivity of the torque sensor 1 is obtained by dividing the sensor output V (mV) by the torque T (Nm) applied to the shaft 100, and V / T (mV / Nm). ). Assuming that the torque T applied to the shaft 100 is −T1 or more and + T1 or less, the sensor output corresponding to the torque −T1 is V1, and the sensor output corresponding to the torque + T1 is V2, the sensor sensitivity is (V2-V1) / (2 ×). It is represented by T1) = Vs / Ts. The hysteresis error is also called a linearity error, and is the ratio of the maximum value Vh of the sensor output difference at the same torque when the torque is increased and decreased with respect to the sensor output Vs (= V2-V1). It can be expressed in Vh / Vs (% FS, FS means full scale).

In the present embodiment, the optimum shot peening conditions are examined when chrome steel (SCr420) is used as the shaft material of the shaft 100 and when chrome molybdenum steel (SCM420) is used. Table 1 shows the composition table of the chrome steel (SCr420) and chrome molybdenum steel (SCM420) used. Table 2 shows the respective heat treatment conditions.

As shown in Table 2, in the present embodiment, the hardness of the shaft material after the heat treatment step is HRC59 or more and 62 or less. This is because if the hardness of the shaft material after the heat treatment step is low, the sensor sensitivity may decrease or the hysteresis error may increase. In order to suppress deterioration of sensor sensitivity and hysteresis error, it is desirable that the hardness of the shaft material after the heat treatment step is HRC58 or more. That is, in the heat treatment step, it is desirable to perform the heat treatment so that the hardness of the shaft material after the heat treatment step is HRC58 or more. However, if the hardness of the shaft material after the heat treatment step is too high, the toughness may decrease and the performance of the shaft 100 may deteriorate. Therefore, it is desirable that the hardness of the shaft material after the heat treatment step is HRC62 or less. , It is more desirable that the HRC is 59 or more and 62 or less.

In this embodiment, a shot material made of steel having a particle size of 0.6 mm and an HRC (Rockwell hardness) of 60 was used as the shot material for shot peening. The injection pressure in shot peening is 0.4 MPa (expressed as P4) or 0.55 MPa (expressed as P5), and the injection time is 2 minutes (expressed as M2), 5 minutes (expressed as M5), or 10 minutes. (Represented as M10).

In the test, the torque applied to the shaft 100 is 0, 10, 20, 30, 40, 50, 40, 30, 20, 10, 0, -10, -20, -30, -40, -50, -40, The relationship between the torque and the sensor output (see FIG. 4) was obtained by changing the values to -30, -20, -10, and 0 (unit: Nm), and the sensor sensitivity and hysteresis error were calculated from the relationship. Further, the same test was conducted at temperatures of 150 ° C., 20 ° C., and −40 ° C.

The test results when chrome steel (SCr420) is used as the shaft material are shown in FIGS. 5 (a) and 5 (b). On the horizontal axis of FIGS. 5A and 5B, for example, the notation P4M2 indicates that the injection pressure is 0.4 MPa and the injection time is 2 minutes. On the horizontal axis of FIGS. 5A and 5B, the shot peening injection energy increases from left to right.

As shown in FIGS. 5A and 5B, in the chrome steel (SCr420), the longer the injection time and the higher the injection pressure, the more the sensor sensitivity is improved and the effect of reducing the hysteresis error is obtained. It turns out that it can be done. That is, the larger the shot peening injection energy, the better the sensor sensitivity and the hysteresis error.

When the same test was performed on a sample not subjected to shot peening, the sensor sensitivity was about 2 mV / Nm and the hysteresis error was about 6% FS. Therefore, when chrome steel is used as the shaft material and an HRC60 shot material with a particle size of 0.6 mm is used, the sensor sensitivity is improved by setting the injection pressure to at least 0.4 MPa or more and the injection time to 2 minutes or more. , And the effect of reducing the hysteresis error can be obtained.

In the torque sensor 1, it is desired that the sensor sensitivity is 4 mV / Nm or more and the hysteresis error is 3% or less. Therefore, the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 5 minutes or more, or the injection pressure is 0.55 MPa so that the sensor sensitivity is 4 mV / Nm or more and the hysteresis error is 3% or less. It is preferable that the injection time is 2 minutes or more.

Furthermore, in order to suppress the overall hysteresis error to 3% or less in consideration of noise and the influence of rotation of the shaft 100 (the influence of eccentricity of the rotating shaft), the hysteresis error in the absence of these influences should be 2% or less. It is more preferable that the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 10 minutes or more, or the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more. It can be said that. If the injection time is 10 minutes or more, it takes time to produce the shaft 100, which may reduce mass productivity. Therefore, from the viewpoint of improving mass productivity, it can be said that it is more preferable that the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more in the shot peening step.

As described above, the larger the injection energy, the better the sensor sensitivity and the hysteresis error. Therefore, it is desirable to use a shot material having as large a particle size as possible and a high hardness. From the test results of FIG. 5, by using a shot material having a particle size of at least 0.6 mm and HRC60 or more (HV700 or more), and performing shot peening under the conditions of an injection pressure of 0.4 MPa or more and an injection time of 2 minutes or more. , Sensor sensitivity and hysteresis error can be improved.

When the present inventor performed shot peening using a shot material having a particle size of 0.35 mm and an HV (Vickers hardness) of 1200, the hysteresis error was reduced, but the sensor sensitivity was not sufficiently improved. Further, when shot peening was performed using a shot material having a particle size of 0.8 mm and HRC60, almost the same result as in the case of using a shot material having a particle size of 0.6 mm and HRC60 was obtained. If the particle size of the shot material is too large, the unevenness of the surface of the shaft 100 becomes large, which may increase the error. Therefore, the particle size of the shot material should be 0.6 mm or more and 0.8 mm or less. Is desirable.

Further, if the injection pressure at the time of shot peening is too high, it becomes necessary to use a special shot peening device in order to ensure safety, and the cost increases. Considering the use of a general shot peening device, it is desirable that the injection pressure during shot peening is 0.4 MPa or more and 0.6 MPa or less from the viewpoint of ensuring safety.

Next, an X-ray diffraction test was performed using a material (P5M10) having an injection pressure of 0.5 MPa and an injection time of 2 minutes. In the X-ray diffraction test, a short columnar sample having a diameter of 20 mm and a thickness of 5 mm was used, and the sample was irradiated with CuKα rays to perform the test. The results of the X-ray diffraction test are shown in FIGS. 6 (a) to 6 (c). Note that FIGS. 6 (b) and 6 (c) are enlargements of a part of FIG. 6 (a). In addition, FIGS. 6 (a) to 6 (c) also show the results for the samples not subjected to shot peening for comparison.

As shown in FIGS. 6A to 6C, the sample of the present invention (P5M10 with shot peening) contains non-magnetic austenite as compared with the conventional sample without shot peening (without shot peening). It can be seen that there is a decrease and an increase in ferromagnetic martensite, which improves sensor sensitivity. The numbers in parentheses in FIGS. 6 (a) to 6 (c) represent the Miller index. The unit of diffraction intensity on the vertical axis of FIGS. 6 (a) to 6 (c) is cps (counts per second).

Further, as shown in FIG. 6 (c), the magnitude relationship between the peak values of austenite and martensite in the Miller index (200) is reversed between the present invention and the conventional example. That is, in the conventional example, the peak value of austenite (200) is larger than the peak value of martensite (200), but in the present invention, the peak value of austenite (200) is smaller than the peak value of martensite (200). It has become. As a result of the examination by the present inventor, it was found that the higher the peak value of martensite (200) and martensite (211), the more the hysteresis error at low temperature can be reduced. In order to reduce the hysteresis error at low temperature, it is desirable that the peak values of martensite (200) and martensite (211) are 1.15 times or more the peak values before shot peening.

Next, the test results of the chromium molybdenum steel (SCM420) are shown in FIGS. 7 (a) and 7 (b). The test conditions were the same as those for the chromium steel shown in FIG. As shown in FIGS. 7 (a) and 7 (b), in the case of chrome molybdenum steel, the sensor sensitivity is 4 mV / Nm or more and the hysteresis error is approximately 2% or less in any of P4M2, P5M2, and P5M10. ing. Therefore, by using a shot material having a particle size of at least 0.6 mm and HRC60 or more (HV700 or more), the injection pressure is 0.4 MPa or more, and the injection time is 2 minutes or more, the sensor sensitivity is improved and the hysteresis error is improved. The effect of reduction can be sufficiently obtained.

Further, the chrome molybdenum steel was also subjected to an X-ray diffraction test in the same manner as the chrome steel using a material (P5M10) having an injection pressure of 0.5 MPa and an injection time of 2 minutes. The results are shown in FIGS. 8 (a) to 8 (c). Note that FIGS. 8 (b) and 8 (c) are enlargements of a part of FIG. 8 (a). In addition, FIGS. 8 (a) to 8 (c) also show the results for the sample (SCM420) without shot peening for comparison.

As shown in FIGS. 8A to 8C, the sample of the present invention (P5M10 with shot peening) contains non-magnetic austenite as compared with the conventional sample without shot peening (without shot peening). It can be seen that the decrease and the increase of ferromagnetic martensite contribute to the improvement of sensor sensitivity. Further, the magnitude relationship between the peak values of austenite and martensite in the Miller index (200) is reversed between the present invention and the conventional example. Further, the peak values of martensite (200) and martensite (211) are 1.15 times or more the peak values before shot peening.

(Actions and effects of embodiments)
As described above, in the method for manufacturing the shaft 100 according to the present embodiment, a heat treatment step of carburizing, quenching and tempering a shaft material made of chrome steel or chrome molybdenum steel, and at least a sensor of the shaft material after the heat treatment step. A shot peening step of applying shot peening is provided at a position where the portion is attached. In the shot peening step, a shot material having a particle size of 0.6 mm or more and an HRC of 60 or more is used, the injection pressure is 0.4 MPa or more, and the injection time is set. It is set to 2 minutes or more.

By providing the shot peening step, it is possible to reduce non-magnetic austenite only on the surface of the shaft 100, and it is possible to suppress a decrease in the toughness of the shaft 100. Further, when a shaft material made of chrome steel or chrome molybdenum steel is used, a shot material having a particle size of 0.6 mm or more and HRC60 or more is used, and the injection pressure is 0.4 MPa or more and the injection time is 2 minutes or more. By performing shot peening in, the sensor sensitivity can be improved and the hysteresis error can be reduced.

Further, in the shot peening step, the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 5 minutes or more, or the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more. In a wide temperature range of 40 ° C. or higher and 150 ° C. or lower, a high sensor sensitivity of 4 mV / Nm or higher can be ensured, and a low hysteresis error of 3% FS or lower can be realized.

Further, in the shot peening step, the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 10 minutes or more, or the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more. Even when the error is set to 2% FS or less and the influence of noise and rotation of the shaft 100 is taken into consideration, a low hysteresis error of 3% FS or less can be realized as a whole.

Furthermore, in the shot peening step, by setting the injection pressure to 0.55 MPa or more and the injection time to 2 minutes or more, it is possible to shorten the time required for the shot peening step while maintaining a hysteresis error of 2% FS or less. Mass productivity can be increased.

Further, in the heat treatment step, by performing the heat treatment so that the hardness of the shaft material after the heat treatment step becomes HRC58 or more, deterioration of the sensor sensitivity and the hysteresis error due to the influence of the heat treatment can be suppressed.

Further, in the shot peening step, by performing shot peening so that the surface roughness Ra of the shaft surface after the shot peening step is 0.2 or less, the error due to the influence of the unevenness on the surface of the shaft 100 is suppressed, and the accuracy is improved. High torque detection is possible.

(Summary of embodiments)
Next, the technical concept grasped from the above-described embodiment will be described with reference to the reference numerals and the like in the embodiment. However, the respective reference numerals and the like in the following description are not limited to the members and the like in which the components in the claims are specifically shown in the embodiment.

[1] A method for manufacturing a shaft (100) for a magnetic strain type torque sensor to which the sensor portion (2) of the magnetic strain type torque sensor (1) is attached. A heat treatment step of performing the treatment and a shot peening step of performing shot peening at least at a position where the sensor portion (2) of the shaft material after the heat treatment step is attached are provided. A method for manufacturing a shaft for a magnetic strain type torque sensor, which uses a shot material having a rockwell hardness of 60 or more and an injection pressure of 0.4 MPa or more and an injection time of 2 minutes or more.

[2] In the shot peening step, the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 5 minutes or more, or the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more. 1] The method for manufacturing a shaft for a magnetostrictive torque sensor according to.

[3] In the shot peening step, the injection pressure is 0.4 MPa or more and less than 0.55 MPa and the injection time is 10 minutes or more, or the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more. 1] The method for manufacturing a shaft for a magnetostrictive torque sensor according to.

[4] The method for manufacturing a magnetostrictive torque sensor shaft according to [1], wherein in the shot peening step, the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more.

[5] The method for manufacturing a shaft for a magnetostrictive torque sensor according to any one of [2] to [4], wherein the shaft material is made of chrome steel.

[6] The magnetostrictive torque according to any one of [1] to [5], wherein the heat treatment is performed so that the hardness of the shaft material after the heat treatment step is Rockwell hardness 58 or more. Manufacturing method of shaft for sensor.

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

The present invention can be appropriately modified and implemented without departing from the spirit of the present invention.

1 ... Torque sensor (magnetostrictive torque sensor)
2 ... Sensor unit 3 ... Detection coil 21 ... Coil 22 ... Magnetic ring 23 ... Bobbin 100 ... Shaft (magnetostrictive torque sensor shaft)

Claims (7)

It is a method of manufacturing a shaft for a magnetostrictive torque sensor to which the sensor part of the magnetostrictive torque sensor is attached.
A heat treatment process in which a shaft material made of chrome steel or chrome molybdenum steel is carburized, quenched and tempered.
A shot peening step of performing shot peening is provided at least at a position where the sensor portion of the shaft material after the heat treatment step is attached.
In the shot peening step, a shot material having a particle size of 0.6 mm or more and 0.8 mm or less and a Rockwell hardness of 60 or more is used, the injection pressure is 0.4 MPa or more and 0.6 MPa or less, and the injection time is 2 minutes or more.
A method for manufacturing a shaft for a magnetostrictive torque sensor. In the shot peening step, the injection pressure is 0.4 MPa or more and less than 0.55 MPa, and the injection time is 5 minutes or more.
The method for manufacturing a shaft for a magnetostrictive torque sensor according to claim 1. In the shot peening step, the injection pressure is 0.55 MPa or more and the injection time is 2 minutes or more.
The method for manufacturing a shaft for a magnetostrictive torque sensor according to claim 1. The shaft material is made of chrome steel.
The method for manufacturing a shaft for a magnetostrictive torque sensor according to any one of claims 1 to 3. In the heat treatment step, the heat treatment is performed so that the hardness of the shaft material after the heat treatment step is Rockwell hardness 58 or more.
The method for manufacturing a shaft for a magnetostrictive torque sensor according to any one of claims 1 to 4. The peak value of the X-ray diffraction intensity of martensite (200) and martensite (211) of the magnetostrictive torque sensor shaft is 1.15 times or more the peak value before the shot peening step is performed.
The method for manufacturing a shaft for a magnetostrictive torque sensor according to any one of claims 1 to 5. Before the shot peening step is performed, the peak value of the X-ray diffraction intensity of the austenite (200) of the shaft for the magnetostrictive torque sensor is larger than the peak value of the martensite (200).
After the shot peening step, the peak value of the X-ray diffraction intensity of the austenite (200) of the shaft for the magnetostrictive torque sensor becomes smaller than the peak value of the martensite (200).
The method for manufacturing a shaft for a magnetostrictive torque sensor according to any one of claims 1 to 6.

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