JPH04246123A - Manufacture of magneto-striction type torque sensor shaft - Google Patents

Abstract

PURPOSE:To prevent the development of secular change in sensor characteristic and to reduce hysteresis of the sensor by making structure in particularly the most outer surface layer of sensor part in a magneto-striction type torque sensor shaft sound. CONSTITUTION:The sensor parts 4, 5 are formed with knurling work on the shaft body 1. Successively, heat treatment, which does not develop abnormal layer and remaining austenite in the sensor parts 4, 5, is applied to the shaft body 1. After that, shot peening treatment is applied at least to the sensor parts 4, 5. By the heat treatment, the outermost surface layer in the shaft is made to the sound structure and strength of the whole shaft is improved. By the shot peening after that, the hysteresis in the sensor is reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetostrictive torque sensor shaft.

0002

2. Description of the Related Art A knurling type sensor disclosed in Japanese Patent No. 169326 has been known as a magnetostrictive torque sensor that uses a torque transmission shaft having a magnetic anisotropy as a sensor shaft. In such a magnetostrictive torque sensor, when torque is applied to the sensor shaft, the magnetic permeability of the magnetic anisotropic part changes according to the torque, so this change in magnetic permeability can be detected using a detection coil, magnetic head, etc. By detecting it, the magnitude of the applied torque can be determined.

[0003] In addition, in order to improve the strength of the sensor shaft and stabilize the magnetic characteristics, US Patent No. 4,
No. 823,620, particularly in FIGS. 35 and 36 thereof, discloses that the sensor shaft is subjected to carburizing, quenching and tempering.

0004

[Problems to be Solved by the Invention] However, when the sensor shaft is manufactured by carburizing, quenching and tempering, it is difficult to use the SNCM420 (JIS
Nickel chromium molybdenum steel) and SAE9310 (S
When carburizing (AE nickel chromium molybdenum steel), an abnormal carburized layer is generated in a portion of about 20 μm on the outermost surface layer of the shaft. This abnormal carburized layer consists of a troostite structure, which is an incompletely quenched structure, instead of a martensitic structure. If stress is repeatedly applied to the sensor shaft where this abnormal carburized layer has formed, the outermost surface layer will become fatigued, microcracks will occur, and sensor characteristics will tend to change over time.

Furthermore, when a Ni-containing alloy is used for the sensor shaft, residual austenite is generated during carburizing and quenching, and when repeated stress is applied, this changes to ferromagnetic martensite, which also causes deterioration over time.

[0006]The present invention solves these problems, and in particular, aims to make the structure of the outermost surface layer of the sensor portion healthy to prevent the sensor characteristics from changing over time, and to reduce the hysteresis of the sensor. The aim is to obtain an ideal torque sensor axis.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention forms a sensor portion on a shaft by knurling, and performs the heat treatment described above to prevent the generation of an abnormal layer and residual austenite in the sensor portion. The shot peening treatment is applied to the shaft body, and then at least the sensor portion is subjected to shot peening treatment.

Further, according to the present invention, as a heat treatment that does not generate an abnormal layer and no retained austenite in the sensor portion, (a) a portion of the shaft other than the sensor portion is carburized, quenched and tempered, and the sensor portion is (b) applying non-oxidation quenching and tempering to the entire shaft; (c) applying induction hardening and tempering to the entire shaft.

[0009]

[Function] By doing this, by applying heat treatment that does not generate an abnormal layer or residual austenite in the sensor part, mainly the outermost surface layer of the shaft will have a healthy structure, and then the shaft will be quenched. Improves overall strength. Further, although the hysteresis of the sensor remains large in this state, the hysteresis is reduced by shot peening.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a torque sensor shaft. Here, 1 is a shaft body, and at both ends there are joint parts 2 with other shafts,
3 are formed respectively. A pair of sensor parts 4 and 5 are formed in the center of the shaft body 1, and these sensor parts 4 and 5 are
It is composed of a magnetically anisotropic part formed by knurling. Reference numerals 6 and 7 denote bearing mounting parts, which are used when supporting the shaft body 1 with bearings.

Next, a method of manufacturing a torque sensor shaft having such a structure will be explained. After the shaft body 1 is machined to have the structure shown, it is then subjected to heat treatment and shot peening treatment. The heat treatment is performed on the sensor parts 4 and 5.
The heat treatment is such that neither abnormal layers nor retained austenite are generated.

As one method of such heat treatment, the shaft body 1
The parts other than the sensor parts 4 and 5, that is, the joint part 2
, 3 and the bearing mounting portions 6 and 7 are subjected to carburizing, quenching, and tempering treatments. Then, the sensor parts 4 and 5 are subjected to carburization prevention heat treatment using copper plating or the like.

[0013] In this case, since the sensor sections 4 and 5 are not carburized, the inconveniences associated with the carburization do not occur, and the structure of the outermost surface layer becomes healthy. Moreover,
The sensor sections 4 and 5 are subjected to shot peening as will be described later, thereby improving sensor quality and shaft strength at the same time. On the other hand, in other parts, the strength is improved by carburizing. Therefore, the strength of the entire sensor shaft is improved.

As another method of heat treatment, the sensor parts 4 and 5
The entire shaft body 1 including the shaft body 1 is subjected to non-oxidation quenching and tempering treatment, that is, bright quenching and tempering treatment. When this treatment is performed in a non-oxidized state, no abnormal layer is generated due to grain boundary oxidation of the crystal structure, and a healthy outermost surface layer structure can be obtained. Of course, the strength of the entire sensor shaft is also ensured.

As yet another method of heat treatment, the entire shaft body 1 including the sensor parts 4 and 5 is subjected to induction hardening and tempering. Since the induction hardening and tempering process is a short-time operation, no abnormal layer is generated due to grain boundary oxidation of the crystal structure, and a healthy outermost surface layer structure can be obtained in this case as well.

By carrying out such heat treatment, as mentioned above, the structure of the outermost surface layer of the sensor parts 4 and 5 is made particularly healthy, the quality of the sensor shaft material is stabilized, and the sensor characteristics change over time. Change becomes less likely to occur. In addition, the strength of the shaft body 1, especially in parts other than the sensor parts 4 and 5, is improved by heat treatment. On the other hand, the strength of the sensor parts 4 and 5 is improved due to the above-mentioned healthy structure, and it is possible to improve the fatigue strength of the sensor shaft as a whole.

By the way, as mentioned above, the sensor section 4,
In a state where the tissue in No. 5 is only made healthy, the sensor still has a large hysteresis and cannot be used as a practical sensor.

Therefore, after the heat treatment, at least the sensor parts 4 and 5 are subjected to shot peening. This shot peening may be applied only to the sensor parts 4 and 5 as shown in the figure, or may be applied to the entire shaft body 1. The effect of shot peening treatment is described in U.S. Patent No. 4,933.
, No. 580, by performing this shot peening treatment, it is possible to reduce hysteresis and obtain high quality sensor characteristics with improved sensitivity. As a result, an ideal torque sensor shaft with a healthy structure and less hysteresis can be obtained.

FIG. 2 shows the experimental results graphically. Here, JIS SNCM815, which is equivalent to SAE9310, which is widely known as a material for magnetostrictive torque sensor shafts, is used as the shaft material. If carburized, quenched and tempered, then shot peened, (
3) The sensor part is quenched and tempered to prevent carburization.
The results are plotted after shot peening.

Compared to the case where the entire surface is carburized, the case where the shot peening process is added shows a greater improvement in both hysteresis and sensitivity. Furthermore, if shot peening is applied after quenching and tempering to prevent carburization of the sensor portion, the hysteresis and sensitivity are further improved, resulting in a torque sensor shaft with excellent characteristics.

[0021]

Effects of the Invention As described above, according to the present invention, the structure of the outermost surface layer of the sensor portion is improved by applying heat treatment to the shaft body that does not generate an abnormal layer or residual austenite in the sensor portion. This not only makes it possible to obtain a torque sensor shaft with little change in sensor characteristics over time, but also to reduce hysteresis since shot peening is applied to at least the sensor section after heat treatment. This makes it possible to manufacture high-quality, ideal torque sensor shafts.

[Brief explanation of the drawing]

FIG. 1 is an overall view of a shaft body for explaining a method of manufacturing a torque sensor shaft according to the present invention.

FIG. 2 is a diagram showing the characteristics of a torque sensor shaft obtained based on the present invention together with the characteristics of a conventional example.

[Explanation of symbols]

1 Shaft body 4 Sensor part 5 Sensor part

Claims (4)

[Claims] 1. A sensor portion is formed on the shaft by knurling, the shaft is subjected to heat treatment that does not generate an abnormal layer or residual austenite in the sensor portion, and then shot peening is applied to at least the sensor portion. A method for manufacturing a magnetostrictive torque sensor shaft, characterized by subjecting it to a treatment. 2. The magnetostrictive torque sensor shaft according to claim 1, wherein the heat treatment includes carburizing, quenching and tempering a portion of the shaft other than the sensor portion, and applying carburization prevention quenching and tempering to the sensor portion. manufacturing method. 3. The method of manufacturing a magnetostrictive torque sensor shaft according to claim 1, wherein the heat treatment includes performing non-oxidation quenching and tempering treatment on the entire shaft body. 4. The method of manufacturing a magnetostrictive torque sensor shaft according to claim 1, wherein the heat treatment includes performing induction hardening and tempering on the entire shaft.