JPS6255537A - Pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a stable output against positional deviation due to a heat cycle and an impact, by building up a member contacting a soft magnetic body and an amorphous magnetic alloy disc using non-magnetic material. CONSTITUTION:A pressure sensor is provided with a spacer 3 made up of a non-magnetic disc between a soft magnetic body 1 and an amorphous magnetic alloy disc 2. The soft magnetic body 1, the amorphous magnetic alloy disc 2 and the non-magnetic disc 3 are covered with a cylindrical non-magnetic body 8 on the side thereof to keep a magnetic circuit from leaking a magnetic flux. Then, when an oil pressure is applied at an oil pressure introduction port, it is applied to the amorphous magnetic alloy disc 2 through a through-hole 6 to be forced down with a groove of the soft magnetic body 1. This generates a stress in the disc 2 to reduce the magnetic permeability of the disc 2 with a magnetostrictive effect by the resulting internal stress, a change which is detected with a coil 10 in the form of inductance to measure the oil pressure. Here, the magnetic circuit is separated by a magnetic container 9 and the non- magnetic body 8 and thus, there is no leakage of magnetic flux, thereby enabling highly accurate detection of oil pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a pressure sensor using the magnetostrictive effect of an amorphous magnetic alloy.

BACKGROUND OF THE INVENTION In recent years, pressure sensors using the magnetostrictive effect of amorphous magnetic alloys have been proposed. For example, Japanese Patent Application No. 58-195239,
No. 58-195240, etc.

FIG. S shows the former embodiment.

31 is a cylindrical soft magnetic body provided with an annular groove;
2 is an amorphous magnetic alloy disk having magnetostriction, 33 is a coil wound around the groove of the soft magnetic material, and 34 has one end in contact with the bottom of the groove and the other end flush with the opening surface of the soft magnetic material. The non-magnetic ring, 36 is a container for storing these, and 36 is a lid having a through hole 3 for transmitting pressure to the amorphous magnetic alloy. When hydraulic pressure is applied to the hydraulic pressure inlet 38, pressure is applied to the amorphous magnetic alloy disk 32 through the through hole 37, pushing it down in the soft magnetic groove and generating stress within the amorphous magnetic alloy disk. Due to the generation of this internal stress, the magnetic permeability of the amorphous magnetic alloy decreases due to the magnetostrictive effect.

This change is detected in the form of inductance using a coil 33 to measure the oil pressure.

Because of the problem that the invention attempts to solve, it is necessary to use a magnetic iron-based container, and this also helps to reduce the cost. However, although such a configuration poses no problem in low-precision measurements, leakage of magnetic flux has become a problem as sensors become more precise. For example, Figure 6 shows the change in inductance value of a conventional sensor during a heat cycle test from -30°C to 80''C. The positional relationship between the disk and the container changes, the state of the magnetic flux leaking into the container changes, and the inductance value becomes unstable.

Similarly, when the container is dropped, the inductance value becomes unstable because the positional relationship between the soft magnetic material and the amorphous magnetic alloy disc and the container changes. FIG. 7 shows the relationship between the number of drops and the inductance value when the sensor is dropped from a height of about 1 m. The results of the impact test show that the inductance value is also unstable.

Means for Solving the Problem In order to completely shield the magnetic circuit, the members in contact with the soft magnetic material and the amorphous magnetic alloy disk are constructed using non-magnetic materials.

By configuring the members in contact with the soft magnetic material and the amorphous magnetic alloy disc using non-magnetic materials, the magnetic circuit can be completely shielded, and the magnetic circuit can be completely shielded. The inductance value remains stable even if the positional relationship with the container changes. As a result, the sensor output becomes stable during heat cycle tests and the impact of the falling ring of the container, making it possible to perform highly accurate measurements.

Embodiment FIG. 1 is a sectional view of an embodiment of this patent. 1 is a cylindrical soft magnetic material provided with an annular groove, 2 is an amorphous magnetic alloy disk having magnetostriction, and 3 is placed between the soft magnetic material 1 and the amorphous magnetic alloy disk 20. The spacer is made of a non-magnetic disk and has an elongated groove in a portion corresponding to the soft magnetic groove.

These three constitute one closed magnetic path. 4 has a through hole 6 that transmits hydraulic pressure and prevents oil from entering. It is a non-magnetic lid part on which a ring 5 is arranged, and 7 is a non-magnetic metal bottom plate arranged on the soft magnetic bottom part. 8 is a cylindrical non-magnetic material provided to cover the sides of the soft magnetic material 1, the amorphous magnetic alloy disk 2, and the non-magnetic disk 3, and is arranged so that there is no leakage of the magnetic flux of the magnetic circuit mentioned above. has been done. 9 is a container, which includes a lid portion 4 and a non-magnetic metal bottom plate 7;
It also houses and holds the aforementioned magnetic circuit. Reference numeral 10 denotes a coil provided in the soft magnetic groove, which is used to measure the inductance of the magnetic circuit described above. 11 is a detection circuit.

When hydraulic pressure is applied from the hydraulic pressure inlet 11, pressure is applied to the amorphous magnetic alloy through the through hole 6, and the amorphous magnetic alloy is pushed down by the soft magnetic groove.

This generates stress within the amorphous magnetic alloy disc, and this internal stress reduces the magnetic permeability of the amorphous magnetic alloy due to the magnetostrictive effect. This change is detected in the form of inductance using a coil 9 to measure the oil pressure. As can be seen from the above detection principle, this sensor detects oil pressure in the form of a change in inductance value, and therefore, if there is a leakage of magnetic flux, the measurement accuracy will deteriorate.

FIG. 2 is an exploded perspective view showing a part of the periphery of the magnetic circuit in the embodiment shown in FIG. It can be seen that there is no leakage at all and the inductance value is stable, which means that oil pressure can be detected with high accuracy.

FIG. 3 shows the results of a heat cycle test under the same conditions as described in the prior art.

It can be seen that the change in inductance value becomes extremely small during the heat cycle from -30°C to 80''C.The magnitude of the change is approximately 0.0% compared to the inductance value.
1%, which is so small that it does not pose a problem even when performing high-precision oil pressure measurements.

This is because even if the positional relationship between the soft magnetic material 1 and the amorphous magnetic alloy disc 2 and the container 9 changes due to a slight difference in coefficient of thermal expansion, there is almost no magnetic flux leaking into the container, so the state of the magnetic flux does not change. As a result, the inductance value is extremely stable.

Figure 4 shows the results of an impact test showing the relationship between the number of drops and the inductance value when the sensor was dropped from a height of about 1 m under the same conditions as described in the conventional technology. It can be seen that the change in inductance value is extremely small. The magnitude of the change is approximately 0.2% of the inductance value, which is also not a problem when performing high-precision oil pressure measurement.

The above description is effective even when the spacer 3 does not have an elongated groove in the portion corresponding to the soft magnetic groove. That is, in order to increase the withstand voltage, for example, a stainless steel disk may be used as a spacer. Even in this case, the structure of the magnetic circuit is exactly the same, and by adopting the structure of the present invention, leakage of magnetic flux can be eliminated.

Effects of the Invention According to the present invention, the shielding of the magnetic circuit including the amorphous magnetic alloy disk becomes perfect, and a pressure sensor can be realized that can provide a stable output even against positional displacement due to heat cycles and impacts.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a pressure sensor according to an embodiment of the present invention, and FIG.
The figure is an exploded perspective view depicting the periphery of the magnetic circuit in the embodiment shown in Fig. 1, Figs. 3 and 4 are graphs showing the output changes of the same embodiment in response to heat cycles and impacts, respectively, and Fig. 6 is the conventional technology. 6 and 7 are graphs showing the output changes of the conventional example shown in FIG. 6 with respect to heat cycles and impact, respectively. 1...Soft magnetic material, 2...Amorphous magnetic alloy disk having magnetostriction, 3...Nonmagnetic disk, 4.
...Lid, 5...Q ring, 6...
...Through hole, 7...Nonmagnetic metal bottom plate, 8...
...Cylindrical non-magnetic material, 9...Container, 1o...
...Coil, 11...Detection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 0 / 234.5 Heat Buoy 7
Le depression huan (@small figure 4 shock @ number (time figure 6 figure 5

Claims (2)

[Claims] (1) A cylindrical soft magnetic body provided with an annular groove,
a non-magnetic disc in contact with a surface of the soft magnetic material having a groove;
an amorphous magnetic alloy disk having one or more magnetostrictions that is in contact with the non-magnetic disk on a side opposite to the soft magnetic material; a coil wound in the soft magnetic material groove; and the soft magnetic material; a non-magnetic disk, a non-magnetic cylinder disposed to cover the side surface of the amorphous magnetic alloy disk, a non-magnetic metal bottom plate in contact with the bottom of the soft magnetic material, a container holding these, and the amorphous magnetic alloy disk. It is characterized by comprising a means for contacting the magnetic alloy to prevent the pressure transmission medium from flowing out, and a non-magnetic lid portion corresponding to the soft magnetic groove and having means for transmitting pressure to the amorphous magnetic alloy disc. pressure sensor. (2) Claim 1, wherein the non-magnetic disk has an elongated groove in a portion corresponding to the soft magnetic groove.
Pressure sensor described in section.