JP2000171317A - Fluid pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid pressure sensor capable of precisely measuring the value of fluid for a long period even under acondition that dew condensation occurs inside the sensor. SOLUTION: The fluid pressure sensor is provided with flexible thin film 6 receiving fluid pressure on the front surface, a pressure receiving board 10 placed along the rear surface of the flexible thin film 6, and an electric resistor connected to the pressure receiving part 10. The electric resistor changes its electric resistance according to the distortion generated when the pressure receiving board 10 bends. The fluid pressure sensor detects fluid pressure based on the change of the resistance value of the electric resistor. Moisture absorbing members 8, 9 absorbing moisture are placed behind the flexible thin film 6 in the pressure sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fluid pressure sensor for detecting a pressure of a fluid.

[0002]

2. Description of the Related Art A fluid pressure sensor used for detecting the pressure of a refrigerant in a refrigeration cycle or the like generally includes a pressure receiving plate disposed along a back surface of a diaphragm which receives a fluid pressure on a front surface side. An electric resistor whose electric resistance changes according to a strain generated when the electric resistor is bent is joined, and the fluid pressure is detected from a change in the resistance of the electric resistor.

[0003]

In order for a fluid pressure sensor having such a structure to perform correct pressure detection, it is essential that the electric resistor be accurately distorted in accordance with the deflection of the pressure receiving plate.

However, if dew condensation occurs inside the fluid pressure sensor due to a change in temperature or the like, the adhesive for joining the electric resistor and the pressure receiving plate is hydrolyzed and deteriorated, and the joining force is weakened and the electric resistor receives the pressure. Since the distortion does not accurately correspond to the deflection of the board, the measured value of the fluid pressure may be inaccurate.

Accordingly, an object of the present invention is to provide a fluid pressure sensor capable of accurately measuring a fluid value over a long period of time even under conditions where dew condensation occurs inside.

[0006]

In order to achieve the above object, a fluid pressure sensor according to the present invention is provided on a pressure receiving plate arranged along a back surface of a flexible thin film which receives a fluid pressure on a front surface side. In a fluid pressure sensor in which an electric resistor whose electric resistance changes according to a strain generated when the board is bent is joined, and the fluid pressure is detected based on a change in the resistance of the electric resistor, water A moisture absorbing member that absorbs water is disposed at a position on the back side of the flexible thin film.

[0007] The moisture absorbing member may be arranged in the vicinity of the pressure receiving plate and at a position not directly touching a joint between the pressure receiving plate and the electric resistor.

[0008]

FIG. 1 shows a fluid pressure sensor according to an embodiment of the present invention, which is used, for example, to detect the pressure of a refrigerant in a refrigeration cycle of a car air conditioner.

At the tip of the metal pressure receiving housing 1,
A connection hole 2 connected to the refrigerant flow path is formed, and the connection hole 2 and the pressure receiving space 4 inside the pressure receiving portion housing 1 communicate with each other through the communication hole 3.

An electric housing 11 made of plastic is connected and fixed by caulking the pressure receiving housing 1, and a diaphragm supporting member 5a sandwiched and fixed between the housings 1 and 11 is provided with a flexible thin film. The diaphragm 6 is disposed so as to face the pressure receiving space 4 on the entire surface to receive the refrigerant pressure, and the outer edge of the diaphragm 6 is formed by an O-ring 7 sandwiched between the pressure receiving portion housing 1 and the diaphragm support member 5a. It is pressed and fixed airtight over the entire circumference.

An electrically insulating pressure-receiving plate 10 made of, for example, a ceramic disk and having a diameter slightly smaller than the diameter of the diaphragm 6 is disposed along the back surface of the diaphragm 6.

The surface of the pressure receiving plate supporting member 5b, which is supported by being sandwiched between the back surface of the diaphragm supporting member 5a and the electrical unit housing 11, is formed in a donut-shaped projection. An intermediate portion between the center of the back surface side of 10 and the outer edge portion abuts. Therefore, the pressure receiving plate 10 is pressed by the diaphragm 6 from the entire surface on the front surface side, and the intermediate portion on the rear surface side is supported in a state of being in contact with the pressure receiving plate support member 5b.

An electric resistance piece is bonded and fixed to the surface of the pressure receiving plate 10 so as to deform together with the pressure receiving plate 10.
As shown in FIG. 1, four electric resistance pieces 21 to 24 whose electric resistance values change with distortion are fixed to the surface of the pressure receiving plate 10.

Since the two electric resistance pieces 21 and 22 of the four electric resistance pieces 21 to 24 are fixed to the center position of the pressure receiving plate 10, they contract when the pressure receiving plate 10 is bent by the fluid pressure. The other two electric resistance pieces 23 and 24 are
Since it is fixed at an intermediate position between the center of 0 and the outer edge,
It extends when the pressure receiving plate 10 is bent by the fluid pressure. In FIG. 2, each of the electric resistance pieces 2 is shown for easy viewing.
1 to 24 are hatched.

Each of the electric resistance pieces 21 to 24 is printed on one surface side of the flexible substrate 20 by repeatedly curving an intermediate portion in a wavy shape in order to secure a sufficient length. As shown in FIG. 1, the amplifier 30 and the electric resistance pieces 21 to 24 attached to the other end of the flexible board 20 which is bent in a U-shape when viewed from the side, 20 are connected by wiring.

The four electric resistance pieces 21 to 24 constitute a Wheatstone bridge by alternately connecting central ones 21 and 22 and intermediate ones 23 and 24.
Every other four terminals between the electric resistance pieces 21 to 24 are an input terminal and an output terminal. A voltage is applied to the input terminal from an external DC power supply, and an output voltage is generated between the output terminals correspondingly.

Between the diaphragm 6 and the pressure receiving plate 10 (strictly, between the back surface of the diaphragm 6 and the flexible substrate 20), a thin sheet-shaped moisture absorbing member 8 having a hygroscopic property is sandwiched. A thick moisture absorbing member 9 is arranged in a space surrounded by a flexible substrate 20 formed in a U-shape at the back of the pressure receiving plate 10.

As a result, when water is generated in the internal space of the fluid pressure sensor, the water is absorbed by the moisture absorbing members 8 and 9 and the space can be kept in a dry state.
The adhesive for fixing the electric resistance pieces 21 to 24 and the pressure receiving plate 10 is deteriorated by hydrolysis, and the electric resistance pieces 2
The phenomenon that 1 to 24 peel off can be prevented beforehand.

To obtain such an effect more effectively,
The moisture absorbing members 8 and 9 are connected to the pressure receiving plate 10 and the electric resistance pieces 21 to 24.
Pressure plate 1 as far as possible without directly touching the joint
It is good to arrange near 0.

Three contact pins 12 are arranged in the electrical housing 11, and the wiring of the flexible board 20 is connected to the base of each contact pin 12. Two of the three contact pins 12 are, for example, 0 volt and 5 volt input voltage contacts, and the other one is, for example, 0-1.
It is an output contact that outputs a voltage of 0.2 to 4.8 volts corresponding to a pressure of 0 kg / cm ² .

In the fluid pressure sensor constructed as described above, the pressure of the refrigerant introduced into the pressure receiving space 4 from the connection hole 2 through the communication hole 3 is applied to the surface of the pressure receiving plate 10 via the diaphragm 6. The pressure is received, and the pressure receiving plate 10 is bent.

Then, the electric resistance pieces 21 and 22 on the center side of the pressure receiving plate 10 shrink to reduce the electric resistance value, and at the same time,
The electric resistance pieces 23 and 24 at an intermediate position between the center and the outer edge are extended to increase the electric resistance value. Then, the pressure of the refrigerant applied to the pressure receiving plate 10 can be detected based on the output voltage value from the contact pin 12 based on the voltage between the output terminals that changes accordingly.

The present invention is not limited to the above-described embodiment. For example, the pressure receiving plate 10 and the electric resistance pieces 21 to 21
The shape and the like of 24 may be any.
What is necessary is just to arrange | position the hygroscopic members 8 and 9 inside (namely, the position behind the diaphragm 6).

[0024]

According to the present invention, the moisture absorbing member for absorbing moisture is disposed at a position on the back side of the flexible thin film, so that moisture can be absorbed even under conditions where dew condensation occurs inside the fluid pressure sensor. Is absorbed by the moisture absorbing member, so that the joint between the electric resistor and the pressure receiving plate does not deteriorate due to hydrolysis, and the fluid value can be accurately measured over a long period of time.

By arranging the moisture absorbing member in a position near the pressure receiving plate and not in direct contact with the joint between the pressure receiving plate and the electric resistor, the effect is maximized.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a fluid pressure sensor according to an embodiment of the present invention.

FIG. 2 is a front view of the surface of the pressure receiving member according to the embodiment of the present invention.

[Explanation of symbols]

 6 Diaphragm (flexible thin film) 8, 9 Moisture absorbing member 10 Pressure receiving plate 21 to 24 Electric resistance piece

Claims (2)

[Claims] An electric resistance, the electric resistance value of which varies with a distortion generated when the pressure receiving plate bends, on a pressure receiving plate disposed along the back surface of a flexible thin film which receives fluid pressure on the front surface side. In a fluid pressure sensor in which a body is joined and the fluid pressure is detected from a change in the resistance value of the electric resistor, a moisture absorbing member that absorbs moisture is disposed at a position behind the flexible thin film. A fluid pressure sensor. 2. The fluid pressure sensor according to claim 1, wherein the moisture absorbing member is arranged near the pressure receiving plate and at a position not directly touching a joint between the pressure receiving plate and the electric resistor.