JPH0566165A - Detection shaft for torque sensor and manufacture thereof - Google Patents

Abstract

(57) [Summary] [Purpose] To increase the mechanical strength of the shaft. [Structure] After the magnetostrictive material 12 is deposited on the peripheral surface of the shaft body 10, a part of the magnetostrictive material 12 is removed to provide a plurality of grooves 14 to form magnetic anisotropy. After that, the surface layer portion of the shaft including at least the groove portion is subjected to heat treatment and mechanical processing for improving the yield strength to enhance the mechanical strength of the shaft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor which detects a torque by forming a groove on a peripheral surface of a shaft to provide a magnetic anisotropic portion and utilizing a magnetostrictive effect generated in the magnetic anisotropic portion. In particular, the present invention relates to a detection shaft for a torque sensor, which is suitable for a heavy-duty shaft material for large-scale construction machines and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, not only mechanical strength is expected of a shaft portion of a construction machine but also functional characteristics such as a detection function for torque and load are required. For example, an engine output shaft in a construction machine is also used as a torque sensor detection shaft for detecting load and output.

As the detection axis of the torque sensor, the first patent
There is one related to No. 69326. The detection axis has a magnetic anisotropy portion formed by providing a groove on the surface of a rotating shaft made of a ferromagnetic material. When detecting torque, the magnetic anisotropy is generated by the torque acting on the rotating shaft of the ferromagnetic material. The magnetostriction generated in the
It is performed by detecting with a detection coil. The torque sensor detection shaft is a high-strength material having a high yield stress, and it is desired that the magnetostrictive characteristics linearly change to the high stress side. Usually, carburized steel and hardened steel are often used. (RABeth et al .: "The Review of Scientific In
struments "25 (1954) 603, W. Winterhoff et al.:"Tech
nisches Messen "50 (1983) 461).

On the other hand, in order to improve the magnetostrictive characteristic of the detection axis, a padding, plasma powder welding (PP)
W), TIG welding, brazing, adhesion, etc. to fix a member having excellent magnetostrictive properties such as permalloy on the surface of the shaft material,
It is considered to improve the magnetostrictive property, and it has been proposed to form a film having excellent magnetostrictive property on the surface of the shaft material by physical vapor deposition (PVD) or the like (for example, Japanese Patent Laid-Open No. 61-195323). Publication or Japanese Patent Laid-Open No. 1-1234
87 publication). Further, it has been proposed to attach an amorphous alloy having a magnetostrictive property by adhesion, plating or the like (Harada, Theory of Electricity 11 (1981) 22).

As described above, the detection shaft having the surface of the shaft covered with the magnetostrictive material detects a change in the magnetic permeability of the magnetostrictive film. Therefore, the magnetostrictive film has a spiral concave-convex groove inclined by 45 degrees with respect to the axis of the shaft. By forming a magnetic anisotropy part and exciting this magnetic anisotropy part at high frequency, the magnetic flux is concentrated on the upper part of the convex part of the groove, the change in the magnetic flux is detected by the coil, and the stress in that part is detected. To detect. In the case of forming a groove in the magnetostrictive material coated on the shaft material, conventionally, cost-effective rolling has been used (Japanese Patent Laid-Open No. 63-117230).

[0006]

However, when the magnetostrictive material is coated on the surface of the shaft material by overlaying, PPW, thermal spraying or the like as described above, the strength of the shaft body is lowered due to the heat history during the coating process. Therefore, if the shaft of a construction machine under high load is coated with a magnetostrictive material, the strength of the shaft material is reduced and the reliability of the construction machine is reduced. In particular, in a shaft such as a construction machine where a high load acts, it is necessary to improve the reliability of strength even if the functional characteristics are sacrificed to some extent.

Therefore, in order to improve the strength of the shaft, it is considered that the surface of the shaft material is hardened by carburizing or the like. However, a soft magnetostrictive material such as Permalloy, which is a Ni alloy, tends to return to its original shape when plastically worked to form a groove by rolling or the like, and deforms after processing to fill the groove. Therefore, even if a hardening process such as carburizing, quenching, tempering, heat treatment such as subzero is performed after the groove is filled with deformation, the magnetostrictive material acts as a carbon-proof material that prevents the infiltration of carbon, and Carbon does not permeate and the shaft strength cannot be improved. Moreover, the steel material to be carburized is basically low-carbon steel, usually called case-hardened steel, so it has basically low rigidity, and if there is a groove where stress concentration occurs, it is not hardened and the strength is high. Cause shortage problems. Of course, since the amount of C is low, even if it is hardened by tempering treatment, sufficient strength cannot be reached.

Moreover, in order to improve the magnetostrictive characteristics of the torque sensor detection shaft, the surface of the shaft is coated with a magnetostrictive material as described above, but the strength of the coating material itself is taken into consideration. It has not been.

For example, as described in JP-A-62-113037, when a magnetostrictive material made of amorphous is coated on the groove formed in the shaft, the amorphous has a large strength and yield stress. Since it is expensive, there is basically no problem except for special cases such as delayed fracture. However, many magnetostrictive materials such as permalloy have low strength, and when they are coated on the shaft, they become a factor that reduces the strength of the shaft. Even if you sacrifice some characteristics,
It is highly desirable to ensure the mechanical strength of the shaft.

The present invention has been made in view of the above requirements, and an object of the present invention is to provide a detection shaft for a torque sensor having high mechanical strength and a method for manufacturing the detection shaft.

[0011]

In order to achieve the above object, the first of the detection shafts for a torque sensor according to the present invention is to provide a groove-like unevenness on the peripheral surface to form a magnetic anisotropic portion. In the formed detection shaft for torque sensor, a magnetostrictive material adhered to the peripheral surface of the shaft body and a plurality of groove portions provided to remove a part of the magnetostrictive material and form a magnetic anisotropic portion are provided. However, the surface layer portion including at least the groove portion is characterized by being subjected to a heat treatment and a mechanical processing treatment for improving the yield strength.

A second aspect of the torque sensor detecting shaft according to the present invention is a magnetic sensor formed by providing a groove portion on the circumferential surface of the torque sensor detecting shaft having a magnetic anisotropic portion on the surface of the shaft. In order to improve the strength of the anisotropic portion and the entire shaft, the surface layer portion of the shaft is heat-treated and machined to improve the yield stress.

A method of manufacturing a detection shaft for a torque sensor according to the present invention is the method of manufacturing a detection shaft for a torque sensor having a magnetic anisotropy portion on the surface of the shaft, wherein a magnetostrictive material is coated on the peripheral surface of the shaft body. Including a step of adhering, a step of cutting the magnetostrictive material to provide a plurality of groove portions to form a magnetic anisotropic portion, and a heat treatment or machining treatment step for improving at least the yield strength of the groove portions. Is characterized by. In addition, when forming the groove portion, in addition to the excision, Japanese Patent Laid-Open No. 64-25
As described in Japanese Patent No. 490, trimming by a laser or the like may be used.

In the torque sensor detection shaft of the present invention constructed as described above, after the groove is formed, the surface including at least the groove is subjected to heat treatment or machining for improving the yield strength, and therefore occurs in the groove. It is possible to avoid damage to the shaft due to stress concentration, and it is possible to obtain a detection shaft for a torque sensor that has a high mechanical strength that can withstand a high load, and improve the reliability of strength. Moreover, the groove is formed by removing a part of the magnetostrictive material by machining such as a hob or an end mill, etching, or the like, and the groove may be closed after the processing as in the case of plastically processing the magnetostrictive material. Therefore, it is possible to surely perform the hardening treatment of the groove portion.

The magnetostrictive material may be adhered to the shaft body by adhesion with an adhesive material, padding, thermal spraying, PPW, TIG welding, brazing, or the like. In recent years, the overlay technology has advanced, and various heat treatments can be performed after overlay without causing defects such as cracks between the base material and the overlay member. Therefore, as the hardening treatment for improving the yield strength, various heat treatments utilizing phase transformation such as carburizing, nitriding, austempering and subzero can be carried out. In addition, rolls, shot peening, and the like are examples of mechanical hardening treatments that can obtain work hardening.

As the magnetostrictive material, a ferromagnetic material containing Ni as a main component such as permalloy can be used. Of course, F
Various magnetostrictive materials such as e-Al may be used. When a magnetostrictive material is provided on the shaft body, the magnetic flux tends to collect more in the magnetostrictive material than in the shaft body, and due to the effect of the eddy current generated in the magnetostrictive material, the magnetic flux is less likely to enter the groove and the characteristics as a detection axis are improved To do. Therefore, it is not necessary to perform highly accurate groove processing, the groove depth can be reduced, and the processing cost can be reduced.
Moreover, even if the corners of the groove bottom are rounded so as to reduce the stress concentration coefficient, the deterioration of the characteristics as the detection axis is small. Further, in order to further improve the characteristics, it is possible to plate the groove portion with copper having high electric conductivity so that eddy current does not enter the shaft main body and the signal from the groove portion is not detected.

Since the magnetostrictive material containing Ni as a main component such as permalloy is relatively soft, when it comes into contact with a detection portion such as a detection coil due to vibration or the like, galling is likely to occur. Therefore, it is preferable that the magnetostrictive material contains one or more precipitation hardening elements such as Ti, Al, Co, Mo, and Nb to improve the galling resistance and the sliding resistance. With regard to the addition amounts of these precipitation hardening elements, hardness and cost are the upper limit determining factors, and
Is 10 wt% or less, Co is 10 wt% or less, Ti is 1 wt% or less, Mo is 8 wt% or less, and Nb is 1 wt% or less.

When a heat treatment such as carburizing is applied after depositing the magnetostrictive material, the surface layer portion is often modified. Further, the curing treatment by shot peening increases the roughness of the surface and causes deterioration of detection characteristics. Therefore, it is desirable to finish the surface by polishing or etching. When polishing the surface, it is desirable to process slowly while cooling so that the residual stress becomes uniform. This is because it is most important that the surface of the sensor part that detects the torque is smooth and the surface residual stress is uniform. The residual stress is sufficient by heat treatment, and does not require high residual stress such as shot peening. ..

When the magnetostrictive material is simply applied and used, the shaft material should have a higher content of C, Mo and Cr than the case-hardened steel so that the strength can be satisfied only by quenching. .. The reason is that the strength of alloy steel mainly depends on the amount of C,
Further, Mo and Cr increase the temper softening resistance and prevent the deterioration due to the thermal influence when the magnetostrictive material is applied. It should be noted that the strength of the shaft material is selected if it is too hard, because the workability decreases, so a balance with the machinability is taken into consideration.

As the shaft material, a base material composition having a C content of 0.1 to 0.5% by weight before heat treatment is used, and the C content of the surface layer portion is 0.3 to 2 by normal or high carbon carburizing treatment. 0.5% by weight. Mo is preferably 1% by weight or less. Mo is
It is an element that improves the strength of steel most and is important. Then, the case-hardening steel has improved strength by the addition of Mo, but if the amount of Mo is too large, the notch toughness decreases and the cost of the shaft increases. The amount of Cr added is
It is preferably 6% by weight or less. If the amount of addition of Cr is increased, the strength of the shaft is improved, but if the amount of addition exceeds 6% by weight, the steel becomes austenitic.

In the carburizing treatment which is one of the heat treatments for steel, an oxide layer remains on the surface of the steel material. Conventionally, in the detection axis for a torque sensor, no attention has been paid to this oxide layer and it has been ignored. However, according to the research conducted by the inventors, the oxide layer existing on the surface of the shaft material greatly affects the magnetostriction detection characteristics. In particular, when the crystal grain boundaries are oxidized, the strength is remarkably lowered and the yield stress is lowered. Therefore, the linear relationship between the stress generated in the shaft and the magnetostriction locally deviates with low stress, resulting in a large hysteresis.
At this time, performing high carbon carburization in which the amount of surface carbon is 2% by weight or more can improve the yield stress, and in particular, improve the characteristics.

Further, if compression unevenness occurs in the oxide layer on the shaft surface, the magnetic flux is affected and the sensor output signal becomes unstable. Therefore, it is conceivable to apply a large stress to the surface layer of the shaft to make the surface compression unevenness uniform, but this is difficult to apply to a shaft used for a large structure. Therefore, the oxide layer on the surface layer of the shaft must be removed. However, the oxide layer cannot be removed sufficiently by shot peening,
It needs to be removed by polishing or etching. As a result, the residual stress on the shaft surface can be made uniform.

By smoothing the upper surface of the convex portion of the groove forming the magnetic anisotropy after the mechanical surface processing, the disturbance of the magnetic flux due to the minute irregularities on the upper surface of the convex portion can be eliminated. The detection accuracy of can be improved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a torque sensor detection shaft and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

Using SNCM 220 of low alloy steel as the shaft material, as shown in FIG. 1 (A), after the carved cylindrical shaft body 10 is carburized, the peripheral surface of the shaft body 10 is made of permalloy. The magnetostrictive material 12 was deposited by 0.3 mm by submerged arc welding. Thereafter, as shown in FIGS. 1B and 2, the spiral groove 14 inclined by 45 degrees with respect to the axis of the shaft body 10 is formed, and the four magnetic anisotropic portions 16a to 16d are formed. Provided. The groove 14 has a width of 1 mm and a depth of 1
It was formed in millimeters with a pitch of 1 millimeter. The groove 14
The bottom corner 15 has a radius of curvature of 0.06 mm.
Further, the width (length in the axial direction) of each of the magnetic anisotropic portions 16a to 16d was set to 5 mm.

Next, the shafts on which the magnetic anisotropy parts 16a to 16d are formed are subjected to a hardening treatment by carburization for improving the yield strength, and then a hardening (surface treatment) such as a sub-zero treatment which is a normal hardening treatment. A heat treatment was performed with a C content of 0.7% by weight and tempering at 170 ° C.). Carburizing depth is 2.0m
set to m. Reference numeral 20 shown in FIG. 2 is a detection coil arranged around the detection axis.

When the example in which the hardening treatment by carburization was performed as described above was compared with the conventional example in which the hardening treatment was not carried out, the results shown in FIG. 3 were obtained. That is, in the example, not only the fatigue strength was 1.8 times higher than in the conventional example, but also the detection sensitivity as a sensor was improved. And when the example was cut and observed with a microscope,
The shaft main body 10 and the magnetostrictive material 12 were melted at the interface, and even if the SNCM 220 forming the shaft main body 10 entered the lower portion of the magnetostrictive material 12 by carburization, problems such as cracks did not occur.

Further, in order to work-harden the above-mentioned embodiment, the portion of the groove 14 of the shaft was subjected to shot peening to impart a mechanical residual stress.
It was possible to improve by more than%. However, when the sensor output characteristic (detection characteristic) with respect to the load torque was obtained, a history curve as shown in FIG. 4 was obtained, and the detection characteristic was lower than before the shot peening. Therefore, when the example in which the groove portion was shot peened was polished by about 0.1 mm and the output characteristics were examined, it was found that the linearity was extremely excellent as shown in FIG.

Next, when shot peening was applied to the groove to improve the residual stress, the fatigue strength could be improved by 10% or more. Therefore, when arranging the shaft strength, the strength of the permalloy-coated shaft <the strength of the permalloy-coated + grooved shaft <the strength of the permalloy-coated + grooved + carburized shaft (A) <
Permalloy coating + Grooving + Carburizing shaft + Shot peening shaft strength (B) <Permalloy coating + Grooving + Carburizing shaft + Shot peening + Polishing shaft strength (C) where (B) is (A) As a result, the fatigue strength was improved by about 10%, but the sensor characteristics were deteriorated. Also,
The sensor characteristics of (C) are improved by about 10% as compared with (A), and the fatigue strength is equivalent to that of (B).

It should be noted that permalloy contains 0.1% of Ti and Al.
When added in a weight percentage, the hardness of the magnetostrictive material 12 is about 30.
% (HRC30) was confirmed to be improved. For this reason, when a precipitation hardening type element such as Ti or Al is added to permalloy, a detection shaft having excellent galling resistance and good slidability can be obtained. However, when about 0.1% by weight of Ti or Al was added to permalloy, the sensor output decreased by about 20%.

The cooling condition after the magnetostrictive material 12 is built up has a great influence on the strength of the shaft. That is, the conditions for hardening the steel are such that the precipitation of elements and crystals changes depending on the cooling rate at the time of cooling the material during quenching, and the normal precipitation is annealing at 300 to 400 ° C. However, in the case of the example, when annealing is performed, the shaft base material itself is softened. Therefore, in the examples, there is no choice but to use the cooling after the heat treatment such as the padding or the carburizing of the groove portion to achieve the hardening. That is, gradual cooling at the time of cooling is used for build-up, and for carburizing or the like, cooling is performed as slowly as possible for quenching. In this case, the amount of Mo in the shaft material is set to about 1% by weight so that the shaft can be quenched even if slowly cooled. When the annealing temperature and time were properly controlled, the strength and magnetic properties of the shaft were improved by 15%. As described above, the fact that the axial strength and the magnetic properties can be improved is based on the data of maraging steel and JP-A-63-25.
No. 2487.

FIG. 6 is a characteristic diagram of an embodiment in which the magnetostrictive material is not adhered to the peripheral surface of the shaft body 10. That is, the detection shaft having the characteristics shown in FIG. 6 is provided with a spiral groove on the peripheral surface of the SNCM 220 to form a magnetic anisotropic portion, and thereafter the surface of the shaft is hardened by carburization to improve the yield strength. It has been processed. In this embodiment, the detection characteristics are significantly inferior to those in which the magnetostrictive material is provided. However, since the magnetostrictive material is not provided, the manufacturing is easy and the cost can be reduced, and the fatigue strength is about the same as the case where the magnetostrictive material is provided.

The deterioration of the sensor characteristics in this embodiment is as follows.
This is probably because an oxide layer is formed on the surface when the shaft is taken out of the heating furnace. Then, after performing shot peening for the purpose of improving the groove strength on the entire axis, the upper surface of the convex portion of the groove portion forming the magnetic anisotropic portion was polished, and the detection characteristics became as shown in FIG. The detection characteristics could be improved significantly.

When high-carbon carburization of about 2% was performed on the surface of the shaft, it was possible to obtain a hysteresis equivalent to an output improvement of 10% as compared with normal carburization.

[0035]

As described above, according to the present invention, the mechanical strength of the shaft can be significantly improved by forming the groove portion and then hardening the groove portion, and the reliability is high. The detection axis is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method of manufacturing a torque sensor detection shaft according to an embodiment of the present invention.

FIG. 2 is a front view of a torque sensor detection shaft according to an embodiment.

FIG. 3 is a diagram showing a comparison result between a torque sensor detection shaft according to an embodiment and a conventional torque sensor detection shaft.

FIG. 4 is an output characteristic diagram of a detection shaft for a torque sensor according to an example in which carburizing treatment and shot peening treatment are performed after forming a groove portion.

FIG. 5 is an output characteristic diagram of an example in which carburizing treatment, shot peening treatment, and then polishing are performed after forming the groove portion.

FIG. 6 is an output characteristic diagram of an example in which a carburizing process is performed after forming a groove on a shaft having no magnetostrictive material.

FIG. 7 is an output characteristic diagram of an example in which a groove is formed on a shaft having no magnetostrictive material, carburizing and shot peening are performed, and then the upper surface of the groove convex is polished.

[Explanation of symbols]

 10 axis main body 12 magnetostrictive material 14 groove 16a-16d magnetic anisotropy part

Claims (8)

[Claims] 1. A magnetostrictive material adhered to the peripheral surface of a shaft body and a part of this magnetostrictive material in a detection shaft for a torque sensor in which a groove-shaped unevenness is formed on the peripheral surface to form a magnetic anisotropic portion. And a plurality of groove portions provided to form the magnetic anisotropy portion, and the surface layer portion including at least the groove portions has been subjected to heat treatment or machining treatment for improving the yield strength. Detecting shaft for torque sensor. 2. The magnetostrictive material is made of a ferromagnetic material containing Ni as a main component, and contains at least one precipitation hardening element such as Ti, Al, Co, Mo or Nb. The detection shaft for a torque sensor according to claim 1. 3. A torque sensor detection shaft having a magnetic anisotropy portion on the surface of the shaft, wherein the magnetic anisotropy portion formed by providing a groove portion on the peripheral surface of the shaft and the strength of the entire shaft are improved. Therefore, the torque sensor detection shaft is characterized in that the surface layer of the shaft is heat-treated and machined to improve the yield stress. 4. The heat treatment for improving the yield strength is performed on the upper surface of the convex portion of the groove portion forming the magnetic anisotropic portion,
The detection shaft for a torque sensor according to claim 3, wherein the smoothing process is performed after the machining process. 5. The torque sensor according to claim 3, wherein the groove portion forming the magnetic anisotropy portion is polished after heat treatment and mechanical processing for improving the yield strength. Detection axis. 6. A method of manufacturing a detection shaft for a torque sensor having a magnetic anisotropy portion on the surface of the shaft, the method comprising: applying a magnetostrictive material to the peripheral surface of the shaft body; A method of manufacturing a detection shaft for a torque sensor, comprising: a step of forming a groove portion to form a magnetic anisotropic portion; and a heat treatment and a machining processing step for improving the yield strength of at least the groove portion. 7. The heat treatment step is carburizing, nitriding, austempering, or subzero treatment utilizing phase transformation of the shaft body, and the machining treatment is roll or shot peening treatment. A method of manufacturing a detection shaft for a torque sensor according to item 1. 8. The method for manufacturing a detection shaft for a torque sensor according to claim 6, wherein the upper surface of the groove convex portion of the magnetostrictive material is smoothed after the heat treatment or machining processing step for improving the yield strength. A method for manufacturing a detection shaft for a torque sensor, the method comprising: