JPH067077B2 - Pressure detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detector, and more particularly to a pressure detector with high accuracy suitable for detecting the pressure of a high-pressure fluid.

[Prior Art] As a pressure detector of this type, a sensing body composed of a tubular body with one end closed is inserted through a tubular detector housing, and the closed end of the sensing body serves as a pressure receiving diaphragm. A semiconductor strain gauge is generally attached and fixed to the back surface.

The pressure introduced into the inside of the sensing body from the opening and acting on the pressure receiving diaphragm is measured by detecting the strain amount of the diaphragm with a strain gauge.

[Problems to be Solved by the Invention] By the way, the contact portion between the sensing body and the housing is usually tightly fixed by welding. However, the sealability deteriorates due to corrosion of the weld, or high pressure is applied to the entire sensing body, especially when measuring high-pressure fluid, so if the weld is damaged and the sensing body is misaligned, or if there is a serious problem. Since the sensing body may come off, the pressure sensor for high pressure, which requires high reliability in terms of sealing property and safety, cannot be said to be satisfactory.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pressure detector that reliably fixes a sensing body in close contact with a housing and has high reliability for high pressure.

[Means for Solving the Problems] The structure of the present invention will be described. A thin-walled pressure receiving diaphragm is provided at the closed end of the cylindrical body, which is inserted and disposed in the cylindrical housing 1 and whose one end is closed. In a pressure detector having a pressure-resistant alloy sensing body 2 in which a pressure gauge 21 is formed and a semiconductor strain gauge 3 which is closely fixed to an end surface of the diaphragm 21 opposite to the pressure receiving surface, a cylinder inner circumference of the housing 1 has a different diameter. Stopper part 11 protruding as a step
In addition, the sensing body 2 has a stepped small diameter on the closed end side so that the stepped portion 22 is brought into close contact with the stopper portion 11 and at least a part of the outer circumference from the stepped portion 22 to the closed end is formed. The entire circumference is recessed so as to form a gap S with the small-diameter inner peripheral surface of the housing 1.

[Effect] In the pressure detector having such a structure, the sensing body 2
Since the paragraph 22 is provided on the outer circumference and is brought into close contact with the stopper portion 11 protruding from the inner circumferential surface of the housing 1, even if a high pressure is introduced from the pressure introducing portion, the sensing body 2 is not displaced.

At this time, due to the compressive load due to the application of high pressure, the stepped portion 22 of the sensing body 2 that abuts the stopper portion 11 may be distorted and transmitted to the diaphragm 21 at the closed end. Since a gap S is formed between the inner peripheral surface of the diaphragm and the inner peripheral surface thereof, the strain is absorbed in this portion and is not transmitted to the diaphragm. Thus, a pressure detector having high reliability for high pressure can be realized.

[Embodiment] In FIG. 1, the housing 1 of the pressure detector is a cylindrical body having a through hole in the center, and the outer circumference of the upper half of a large diameter is made into a hexagonal surface and the mounting screw is attached to the outer circumference of the lower half. The part 12 is formed.

A sensing body 2 is inserted through the through hole of the housing 1. The sensing body 2 is a cylinder whose upper end is closed and whose lower end is open, and the inside of the cylinder serves as a pressure introducing passage. On the outer circumference of the sensing body 2, a step portion 22 is provided near the center portion so that the upper half portion of the sensing body 2, that is, the closed end side has a smaller diameter than the lower half portion. Further, a stopper portion 11 is provided on the inner periphery of the upper end of the housing 1, and the step portion 22 is closely attached to the stopper portion 11. And the sensing body 2 with a large diameter
The lower half is closely fixed to the inner circumference of the housing 1 by interposing the nickel braze layer 5 on the outer circumference. Further, the upper half portion of the small-diameter sensing body 2 has its entire outer circumference retreated with respect to the inner peripheral surface of the housing 1 to form a predetermined gap S with the inner peripheral surface.

The sensing body 2 is made of a Fe-Ni-Co alloy having a small coefficient of thermal expansion and excellent pressure resistance, and the upper end surface of the sensing body 2 has a thin central portion as a pressure receiving diaphragm 21 (Fig. 2). The entire upper surface of the diaphragm 21 is oxidized to form an oxide layer 23. Then, the oxide layer 23
The semiconductor strain gauge 3 is bonded to the upper side of the low melting point glass layer 24.

The semiconductor gauge 3 is connected by a wire 6 to an electrode on a ring-shaped ceramic substrate 4 provided on the upper surface of the housing 1 so as to surround it. A ceramic substrate 7 on which an IC circuit for signal processing is formed is arranged above the semiconductor strain gauge 3, and the signal processing circuit is connected to an electrode on the substrate 4 via a pin 71 that supports the substrate 7. .

A cylindrical cover 8 is joined to the outer peripheral edge of the upper surface of the housing 1, and a lead holder 81 is tightly fitted in the upper opening of the cover 8. The lead wire 7 extending from the substrate 7
2 passes through the holder 81 and extends outside the detector.
In FIG. 1, 82 is a seal ring and 83 is a seal resin.

The semiconductor strain gauge 3 has boron (B) at four locations on the surface of the Si substrate.
3 to form P-type semiconductor strain gauge elements 31, 32, 33, and 34, which are located directly above the central portion of the diaphragm 21, and are formed as shown in FIG. , 34 are located directly above the peripheral edge of the diaphragm 21. And these elements 31-34 are Si
Electrode leads (not shown) formed on the substrate are connected to each other to form a full bridge as shown in FIG.

The sensing body 2 and the housing 1 and the semiconductor strain gauge 3 are joined to each other according to the procedure shown in FIG. First, the surface of the sensing body 2 is washed with acid to degrease it, and then the outer periphery of the sensing body 2 is plated with nickel.

The decarburization treatment of the sensing body 2 is performed by supplying water vapor into a reducing or weakly reducing atmosphere in which H ₂ and N ₂ are mixed, and is performed at 800 ° C. to 1100 ° C. for about 1 hour.

Next, the sensing body 2 is inserted and disposed in the housing 1, and these contact portions are brazed. The brazing is performed by sandwiching a nickel braze between the sensing body 2 and the housing 1 and in vacuum at 1000 ° C to 1100 ° C.

The sensing body 2 integrated with the housing 1 by brazing is then oxidized. Oxidation is carried out in an O ₂ atmosphere at 800 ° C. for 10 minutes or 1000
It is exposed at 0.5 ° C. for 0.5 minutes to form an oxide layer 23 at a depth of 1.5 μm to 5.5 μm.

The glass layer 24 is formed by printing a glass paste on the oxide layer 23 and calcining the glass paste (about 450 ° C.) so that the glass has a finished thickness of 40 μm to 60 μm. The glass paste is obtained by mixing glass powder into an organic melt. When the semiconductor strain gauge 3 is placed on the calcined glass layer 24 and main firing (about 450 ° C.) is performed, the semiconductor strain gauge 3 is firmly bonded onto the sensing body 2.

In the pressure detector having such a structure, when the diaphragm 21 is deformed by the introduction pressure, strain stress is generated in the semiconductor strain gauge 3 integrally joined thereto, and the resistance values of the strain gauge elements 31, 33 on the strain gauge 3 are increased. A linear and highly sensitive output signal corresponding to the measured pressure can be obtained. At this time,
A large load is applied to the joint between the sensing body 2 and the housing 1 by the high-pressure fluid, but according to the pressure detector having the above structure, the sensing body 2 is firmly and firmly fixed to the housing 1 by brazing. Moreover, since the sensing body 2 is supported by the stopper portion 11 of the housing 1 by the step portion 22, it is possible to prevent the sensing body 2 from slipping off or coming off.

Further, since the joining is performed by brazing, it is not necessary to extend the sensing body 2 to the pressure introducing passage inlet of the housing 1, and the cost can be reduced by downsizing the sensing body.

Due to the pressure of the high-pressure fluid, the step portion 22 of the sensing body 2
A large compressive load is applied to and the strain generated there is transmitted toward the upper diaphragm 21, but since a gap S is formed on the outer periphery of the upper half of the sensing body 2,
The strain is absorbed here and does not reach the diaphragm 21.

FIG. 6 shows a second embodiment of the present invention. In the figure,
At the upper end of the sensing body 2, a step portion 22 is provided on the outer circumference so that the closed end side has a small diameter, and the step portion 22 is fitted to a stopper portion 11 projecting on the inner circumference of the housing 1.

A groove 25 is formed on the outer circumference of the sensing body 2, and an O-ring 26 is provided in the groove 25 to seal the sensing body 2 and the housing 1. The lower end of the sensing body 2 extends to the opening end of the housing 1 and is aligned therewith. The sensing body 2 has a flange 27 formed by protruding the lower end opening peripheral edge, and the flange 27 is welded and fixed to the flange 13 provided on the opening peripheral edge of the housing 1.

According to the above structure, the sensing body 2 and the housing 1
Since the and are double-sealed with the O-ring 26 and welding,
Even if the welded part is damaged, the O-ring 26 seals the seal and ensures high reliability.

7 to 8 show a third embodiment of the present invention. 7th
In the figure, the sensing body 2 is a cylindrical body with an upper end closed, and a step portion 22 is provided on the outer circumference so that the closed end side has a small diameter. Most of the outer peripheral surface of the small-diameter portion is in contact with the inner peripheral surface of the housing 1, and the outer periphery of the closed end near the diaphragm 21 has a tapered cross-section on the entire periphery to have a smaller diameter, so that the inner peripheral surface between the housing 1 and A gap S is formed. The lower end portion 28 of the sensing body 2 has a tapered shape, and one end of the tapered portion 28 is connected to a detection target (not shown),
The other end of the pressure introducing pipe 9 having a tightening nut flare 91 (FIG. 8) arranged on the outer periphery is fitted in a tapered shape along the tapered portion 28. A screw for screwing the nut flare 91 is cut on the inner periphery of the lower end of the housing 1, and the nut flare 91 is attached to the housing 1.
The sensing body 2 is screwed from the lower end opening, and the sensing body 2 is tightened and fixed via the pipe 9. At the same time, the space between the sensing body 2 and the housing 1 is sealed.

According to the above structure, the sensing body 2 and the housing 1
Since the pipe 9 and the nut flare 91 are firmly and closely fixed to each other, it is not necessary to join the sensing body 2 and the housing 1 by welding or the like, and the structure is simple and high sealing performance can be secured.

The strain generated in the step portion 22 when the pressure of the high-pressure fluid is applied is absorbed by the gap S formed on the outer circumference of the closed end and is not transmitted to the diaphragm 21.

As described above, the gap S for absorbing strain does not necessarily have to be formed on the entire outer periphery of the small-diameter upper half portion of the sensing body 2, and the entire circumference is partially formed between the step portion 22 and the closed end provided with the diaphragm 21. Similar effects can be obtained by forming over.

[Brief description of drawings]

1 to 5 show an embodiment of the present invention, FIG. 1 is an overall cross-sectional view of a pressure detector, and FIG. 2 is a cross-sectional view of essential parts showing a joint structure between a sensing body and a semiconductor strain gauge element. FIG. 3 is a plan view of a semiconductor strain gauge, FIG. 4 is a connection diagram of a semiconductor strain gauge element, FIG. 5 is a schematic diagram showing a joining method, and FIG. 6 shows a second embodiment of the present invention. FIG. 7 is an overall sectional view of the pressure detector, FIGS. 7 to 8 show a third embodiment of the present invention, FIG. 7 is an overall sectional view of the pressure detector, and FIG. 8 shows a sensing body and a housing. It is a principal part sectional view which shows a joining structure. 1 ... Housing 2 ... Sensing body 3 ... Semiconductor strain gauge 9 ... Pressure introduction pipe 11 ... Stopper part 21 ... Pressure receiving diaphragm 22 ... Step part 26 ... O-ring 28 ... Tapered part 91 ... Nut flare S ... Gap

Front page continuation (72) Inventor Yoichi Kotaneda 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute, Inc. (56) Reference JP-A-52-143786 (JP, A)

Claims (4)

[Claims] Claims: 1. A pressure-resistant alloy sensing body, which is inserted and disposed in a tubular housing, and has a thin-walled pressure receiving diaphragm formed at its closed end with the inside of the cylindrical body serving as a pressure introducing portion, and the pressure receiving of said diaphragm. In a pressure detector having a semiconductor type strain gauge closely fixed to an end face opposite to the surface, a stopper portion protruding stepwise with the inner diameter of the cylinder of the housing having a different diameter is formed, and the sensing body is closed. The end side is stepped and has a small diameter, and the stepped portion is brought into close contact with the stopper portion, and at least part of the outer circumference from the stepped portion to the closed end is between the housing and the small diameter inner peripheral surface. A pressure detector characterized in that a concave portion is formed so as to form a predetermined gap with. 2. A pressure detector according to claim 1, wherein the sensing body has a large-diameter outer circumference fixed to the inner circumference of the housing by brazing. 3. An open end of the sensing body is welded and fixed to the housing, and an O-ring is arranged on a large-diameter outer circumference of the sensing body to seal between the sensing body and the housing. The pressure detector according to claim 1. 4. The outer periphery of the opening end of the sensing body is tapered, and the other end of the pressure introducing pipe, one end of which is connected to the object to be detected, is fitted into the tapered part by being tapered along the tapered part. The pressure detector according to claim 1, wherein the sensing flare is screwed into the housing and the sensing body is clamped and fixed to the housing through the pipe.