JPH05198425A - Magnetic body of rotation sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance the holding force in the radial direction by heat-treating the outer surface part under the state, wherein the inner surface part of a ring-shaped magnetic body is cooled, and growing the crystal grains in the radial direction of the magnetic body. CONSTITUTION:A ring-shaped magnetic body 7 having the composition of Fe-31Cr-23Co is coupled with a pipe 8. Cooling water at the temperature of 60 deg.C is made to flow in the pipe 8. The pipe is held in the atmosphere of the temperature of 800-950 deg.C for four hours, and heat treatment is performed. After the heat treatment, the magnetic body 7 is cooled. Thus, the magnetic body 7 having the required surface hardness is obtained. The heat treatment is performed so that the temperature gradient is provided in the radial direction of the magnetic body. Thus, the crystal grains are grown in the magnetic body 7 in the radial direction. In this way, the holding force in the radial direction can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet body for a sensor which generates a magnetic signal by relative displacement with a detection head and a method for manufacturing the magnet body.

[0002]

2. Description of the Related Art Conventionally, in order to detect the number of rotations of a rotary shaft with high accuracy, a magnet body magnetized in multiple poles is used as a rotor as disclosed in, for example, Japanese Patent Application Laid-Open No. 62-218814. There is known a magnetic signal detection sensor which is mounted on a rotary shaft and has a detection head provided on the fixed portion side in the vicinity of the rotor.

In such a rotation sensor, the rotor for detecting the rotational speed of a shaft rotating at high speed has a mechanical strength sufficient to withstand tensile stress caused by a centrifugal force and an excellent impact resistance against vibration. In addition, FeCrCo-based permanent magnets have been conventionally used.

[0004]

However, since this magnet material has a low coercive force by nature, when iron powder or the like adheres to this magnet material, it causes a significant demagnetization, and there is a problem that the signal output decreases. ..

Further, although the above-mentioned magnet material is hardened by heat treatment after molding, it has a mechanically fragile property, so that when it is press-fitted into a shaft, problems such as cracking and chipping may occur.

In view of the above problems, it is an object of the present invention to provide a ring-shaped magnet body having an improved holding force and capable of preventing the occurrence of cracks during press fitting into a shaft, and a method for manufacturing the ring-shaped magnet body. To do.

[0007]

A ring-shaped magnet body according to the present invention is provided with crystal grains that have been heat-treated on the outer peripheral portion thereof and have grown in the radial direction of the magnet body, and are press-fitted and fixed to a rotary shaft. It is characterized by

Further, in the method for manufacturing a ring-shaped magnet body according to the present invention, heat treatment is applied to the outer peripheral portion of the ring-shaped magnet body while the inner peripheral portion of the ring-shaped magnet body is cooled, so that crystal grains are grown in the radial direction of the magnet body. Characterize.

The heat treatment temperature of the outer peripheral portion is selected within the range of 800 to 950 ° C.

[0010]

FUNCTION AND EFFECT Since the magnet body according to the present invention is provided with the crystal grains grown in the radial direction of the magnet body by the heat treatment of the outer peripheral portion, the holding force in the radial direction is increased.

In the method of manufacturing a magnet body according to the present invention,
Since the outer peripheral portion is heat-treated while the inner peripheral portion is cooled, the inner peripheral portion is kept in a plastically workable state before the heat treatment, so that cracking can be prevented when pressure is applied to the shaft.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an axle portion of an automobile equipped with a magnet body according to the present invention as a rotor of a rotation sensor.
In FIG. 1, 1 is an axle, 2 is a knuckle that rotatably supports the axle 1 via a bearing 3, 4 is a ring-shaped permanent magnet rotor press-fitted to the axle 1, and 5 is opposed to the rotor 4. Sensor head fixed to the knuckle 2 and 6
Is a brake disc mounting portion fixed to the axle.

FIG. 2 is an explanatory view schematically showing a heat treatment apparatus used for manufacturing the ring-shaped magnet body according to the present invention.
The ring-shaped magnet body 7 has a composition of Fe-31Cr-23Co, and its dimensions are an outer diameter of 70 mm, an inner diameter of 60 mm, and a width of 10 mm. The ring-shaped magnet body 7 is fitted on the pipe 8 and
Cooling water with a temperature of 60 ° C is passed inside the
Heat treatment is carried out by holding in an atmosphere of 950 ° C. for 4 hours. After this heat treatment, the magnet body 7 is rapidly cooled to obtain the magnet body 7 having a required surface hardness.

This heat treatment is performed with a temperature gradient in the radial direction of the magnet body 7 as described above, so that the crystal grains grown in the radial direction grow in the magnet body 7 and thereby the holding force is increased. An increase is brought about.

FIG. 3 shows the heat treatment temperature from 700 ° C to 1050 ° C.
Aspect ratio of crystal grains in the radial direction with respect to heat treatment temperature (length of major axis / length of 8 samples shifted by 50 ° C)
It is the figure which showed the relationship of the length of the minor axis. As is clear from FIG. 3, the heat treatment at a temperature of 800 to 950 ° C. has an aspect ratio of 5 or more.

FIG. 4 is a diagram showing the relationship between the heat treatment temperature and the radial holding force (oersted). From FIG. 4, an increase in the radial holding force is recognized for the heat-treated product at a temperature of 800 to 950 ° C. Therefore, it can be said from FIGS. 3 and 4 that the preferential growth of the crystal grains in the radial direction by the heat treatment by the method of the present invention resulted in an increase in the holding force in the radial direction.

Next, the hardness distribution in the radial direction of the ring-shaped magnet body 7 when heat-treated at a temperature of 800 ° C. is shown in Table 1 below.

[0019]

[Table 1]

As is apparent from Table 1, the inner peripheral portion of the magnet body 7 has a hardness of about Hv160 and a hardness before heat treatment,
As a result, cracks are less likely to occur during press fitting into the shaft. By the way, in the case of the magnet body subjected to the usual heat treatment, a defect of 4% (n = 100) occurred at the time of press fitting into the shaft, whereas the defect rate of the magnet body subjected to the heat treatment at 800 ° C. according to the present invention. Was reduced to 1% (n = 100).

[Brief description of drawings]

FIG. 1 is a sectional view of an axle portion of an automobile equipped with a ring-shaped magnet body according to the present invention as a rotor of a rotation sensor.

FIG. 2 is an explanatory view schematically showing a heat treatment apparatus used for manufacturing a ring-shaped magnet body according to the present invention.

FIG. 3 is a graph showing the relationship between heat treatment temperature and the aspect ratio of crystal grains.

FIG. 4 is a graph showing the relationship between heat treatment temperature and holding power.

[Explanation of symbols]

 1 axle 2 knuckle 3 bearing 4 permanent magnet rotor 5 detection head 6 ring-shaped magnet body 7 pipe

Claims (3)

[Claims] 1. A rotation sensor comprising a ring-shaped magnet body and a detection head for detecting a magnetic signal, wherein the ring-shaped magnet body is heat-treated at its outer peripheral portion and is a crystal grown in the radial direction of the magnet body. A magnet body for a rotation sensor, which comprises particles and is press-fitted and fixed to a rotation shaft. 2. A method for manufacturing a magnet body for a rotation sensor, comprising heat-treating an outer peripheral portion of an inner peripheral portion of a ring-shaped magnet body in a cooled state to grow crystal grains in a radial direction of the magnet body. .. 3. The method for manufacturing a magnet body according to claim 2, wherein a heat treatment temperature for heat treating the outer peripheral portion is selected within a range of 800 to 950 ° C.