JPS62204137A - Pressure detector - Google Patents

Abstract

PURPOSE:To detect variation on static pressure accurately and to obtain a relatively small-sized pressure detector for high pressure by providing two electrostrictive elements for pressure detection and temperature compensation in a housing. CONSTITUTION:An electrostrictive element 1 is arranged in the housing 11 whose inside is formed in a bag shape and an electrostrictive element 2, on the other hand, is arranged opposite the top surface side of the element 1 while made of the same material with the element 1 and having the same temperature coefficient. A diaphragm 9 seals the entrance part of the housing 1 and a rod 10 as a pressure medium is arranged between the diaphragm 9 and element 1. Consequently, pressure applied to the diaphragm 9 is transmitted to the element 1 through the rod 10 and the element 1 varies in electrostatic capacity C with the pressure because of reverse electostriction effect. The element 2 also varies equally in capacity C with temperature and the both cancel each other, so that the variation in the capacity C is compensated. Further, while the pressure is applied, the value of the capacity C corresponding to it is maintained because of the properties of the electrostrictive elements and static pressure variation is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detector, and more particularly, to a pressure detector for high pressure such as brake oil of an automobile or combustion pressure in an engine cylinder.

[Conventional technology]

Conventional pressure detectors include those that utilize piezoresistive effects and those that utilize metal strain gauges. In addition, as a sensor using a piezoelectric element, Japanese Patent Application Laid-Open No. 52-12328
There are some that are shown in Publication No. 3, etc.

[Problems to be solved by the present invention]

However, when using the above-mentioned piezoresistance effect to make a pressure detector for high pressure, it is not possible to directly detect high pressure, so high pressure is detected as low pressure corresponding to the value. Therefore, a device is required to convert high pressure to low pressure.

This results in a complicated structure, which poses problems in terms of cost and reliability. In the case of using a metal strain gauge, the field of application is limited because an amplifier with a high amplification degree is required. In addition, sensors using piezoelectric elements have a problem in that they are easy to detect dynamic pressure changes due to the properties of the piezoelectric elements, but are difficult to detect static pressure changes.

Therefore, the present invention was devised in view of the above problems, and has a relatively simple structure and can be manufactured at low cost.
Moreover, it is an object of the present invention to provide a relatively compact high-pressure pressure detector that can accurately detect static pressure changes.

[Means for solving problems]

To achieve the above object, the pressure sensor of the present invention includes a housing having a bag-shaped inner shape, a first electrostrictive element for pressure detection disposed inside the housing, and a first electrostrictive element for detecting pressure disposed inside the housing.
a second electrostrictive element for temperature compensation, which is disposed opposite to the upper surface side or the lower surface side of the electrostrictive element, and is made of the same material as the first electrostrictive element and has the same temperature coefficient; and a bag of the housing. It is composed of a diaphragm that seals the inlet portion of the shape, and a rod serving as a pressure medium disposed between the diaphragm and the first electrostrictive element.

[Effect]

With the above configuration, the pressure applied to the diaphragm is
The electrostatic charge is transmitted to the first electrostrictive element via the rod, and in the first electrostrictive element, an electrostatic charge is generated in response to the pressure due to the reverse electrostrictive effect (the dielectric constant of the electrostrictive material changes when force is applied). There is a change in capacity. Here, the dielectric constant of the electrostrictive element has temperature characteristics, and the capacitance of the first electrostrictive element changes depending on the temperature, but the capacitance of the second electrostrictive element also changes depending on the temperature. Since the two cancel each other out, the change in capacitance due to temperature has been compensated for. Furthermore, due to the nature of the electrostrictive element, while pressure is applied, it continues to maintain a corresponding capacitance value, so static pressure changes can also be detected.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings.

FIG. 1 shows a sectional view of a first embodiment of the pressure detector of the present invention. In FIG. 1, 1 is a first electrostrictive element for detecting pressure having an electrostrictive effect, and has a donut-shaped structure with a through hole in the center. The material (composition) is P b (Mg
+7z, Nbzzx)03-P bTie, system, P
b (Mg+73.Nbzz:+)03-P bT
i 03-B a (Z n 111. N bz/
+) Ceramics such as 03 series or a fired mixture thereof. 1a+ib is A6. An electrode made of Ag etc.
It is attached to both sides of the first electrostrictive element 1 by means of printing, vapor deposition, or the like. Reference numeral 2 denotes a second electrostrictive element for temperature compensation, which is arranged to face the first electrostrictive element across a part of the sensor body 12, and is installed in a position where no pressure is applied. It has the same material and configuration as the electrostrictive element, and has the same temperature characteristics. 2a and 2b are A6. These electrodes are made of Ag or the like, and are attached to both sides of the second electrostrictive element 2.

3.4 and 5.6 are metal plates, 3 is disk-shaped, and 4 is a metal plate.
, 5.6 has a donut-shaped structure and is made of Kovar, Cu, etc. ? a, 7b, 7c, and 7d are lead wires.

The lower electrode 1a of the first electrostrictive element 1 is attached to a lead wire 7a through a metal plate 3 by soldering, welding, etc., and electrical continuity is maintained. Similarly, the upper electrode 1b is a metal plate 4
It is electrically connected to the sensor body 12 via the bank body 17, and electrical continuity is maintained with the lead wire 7b via the bank body 17. The lower mold i2a of the second electrostrictive element 2 is attached to the lead wire 7c via the metal plate 5 to maintain electrical continuity. Here, 8 is a spacer made of an insulator (AfzOi etc.), which connects the sensor body 12 and the second electrostrictive element 2.
The insulation of the lower electrode plate 5 is maintained. Similarly, the upper electrode 2b is attached to the lead wire 7d via the metal plate 6 to maintain electrical continuity. The first electrostrictive element 1 is provided on the bottom of the lower recess of the sensor body 12, and a rod 1 made of stainless steel, for example,
It is made of an insulator such as 0 and AlzOz, and an insulator 15 serving as a pressure medium is inserted therein. Reference numeral 14 denotes a guide insulator made of an insulator such as Teflon, which maintains insulation between the sensor body 12, the first electrostrictive element 1, and the metal plate 3.

The sensor subassembly is assembled using the following procedure. The guide insulator 14 is inserted into the lower concave portion of the sensor body 12, and the metal plate 4, first electrostrictive element 1, metal plate 3, insulator 15, and one end of the rod 10 are sequentially inserted, and these are connected to the spring ring 13. Fix it by. Note that the inner wall of the guide insulator 14 is designed to have a small gap with the outer periphery of one end of the first electrostrictive element 1, the insulator 15, and the rod 10 so that they are in close contact with each other. be. The spring ring outer circumference 13a and the outer circumference 12a of the sensor body 12 are firmly fixed by welding or the like.

Note that a preload is constantly applied to the first electrostrictive element 1 due to the elastic force of the spring ring 13. The other end of the rod 10 has a locking protrusion 10a for positioning, and the diaphragm 9 also has a locking hole 9a at its center. The sensor subassembly is press-fitted into the inner wall of the housing 11, and the diaphragm 9 is connected to the artificial part 11b of the housing 11.
The inlet portion 11b is sealed. At this time, by fitting the locking protrusion 10a at the tip of the rod 10 with the locking hole 9a of the diaphragm 9, the center of the rod 1G coincides with the center of the diaphragm 9, and the rod 10 is accurately positioned. Further, the joints between the locking protrusion 10a and the locking hole 9a, and between the diaphragm outer circumference 9b and the housing inlet flb are firmly fixed by welding or the like. An annular insulator 18 made of Teflon or the like and having a protrusion on the upper and lower sides is inserted into the upper recess of the sensor body 12. The lower protrusion is inserted up to the hole of the first electrostrictive element 1, and the center hole is inserted into the upper recess of the sensor body 12. lead cotton 7a
is passing through. Further, the upper protrusion of the insulator 18 includes a spacer 8, an electrode plate 5, and a second electrostrictive element 2.
) The metal plates 6 are sequentially inserted and fixed by press-fitting the sensor back body 17 into the sensor body 12 via the temperature compensator insulator 16 made of an insulator such as A#ZO3. The temperature compensator insulator 16 and the sensor back body 17 have one through hole in the center and two in the outer periphery, into which the lead wires 7a and 7 are inserted, respectively.
c, through 7d. In addition, the sensor back body 17
is fixed to the housing 11 by caulking the caulking portion 11a of the housing 11.

FIG. 2 shows the detection circuit of the pressure detector of this embodiment. 20
is an oscillation circuit, and 21 is a bridge circuit. The bridge circuit 21 includes a first electrostrictive element 1, a second electrostrictive element 2, and reference capacitors 21a and 21b. 22
is a rectifier circuit, and although the circuit is not shown, a publicly known one is used.

23 is an amplifier circuit, which includes an amplifier section 23a and a differential amplifier section 23.
b.

Next, the operation of the above configuration will be explained. diaphragm 9
When a pressure to be detected is applied to, the pressure is transmitted to the first electrostrictive element 1 via the rod 10 and the insulator 15. Here, since the diaphragm 9 and the rod 10 are accurately positioned by the locking hole 9a and the locking protrusion 10a, the rod 10 is in close contact with the first electrostrictive element 1 on a plane, and the rod 10 is in close contact with the first electrostrictive element 1 due to positional deviation and uneven contact. The output is proportional to pressure as shown in FIG. 3 without any non-linearity or hysteresis in the output. Then, when pressure is transmitted to the first electrostrictive element l, the electrostatic capacitance CO of the first electrostrictive element 1 changes by a value ΔC proportional to the pressure due to the reverse electrostrictive effect, and Co-Δ
It becomes C. Then, the detection circuit shown in FIG. 2 outputs a voltage ■ corresponding to ΔC. Here, the dielectric constant of the electrostrictive element has temperature characteristics, and the capacitance of the first electrostrictive element l also changes with temperature according to the temperature characteristics of the electrostrictive element shown in FIG. However, a similar change in capacitance occurs in the second electrostrictive element 2, and in FIG. The first electrostrictive element 1 and the second
The pressure is detected by comparing the potential at point a between the reference electrostrictive elements 21a and 21b, and the potential at point b between the reference electrostrictive elements 21a and 21b. Since it is determined by the ratio of the voltage difference between the two electrodes of the electrostrictive element 1 and the voltage difference between the two electrodes of the second electrostrictive element 2, changes in capacitance due to temperature characteristics can detect pressure. There was no actual effect, and temperature compensation was performed after all.

FIG. 5 shows the temperature characteristics at the zero point (state B where no pressure to be detected is applied). In the figure, the solid line is the characteristic of this example,
The dotted line shows the characteristics when the second electrostrictive element 2 for temperature compensation is not used. As is clear from the figure, according to this embodiment, the stability of the output (2) with respect to changes in ambient temperature is significantly improved, and the pressure detector can be used over a wide temperature range.

According to this embodiment, high pressure can be directly detected and a device for converting high pressure to low pressure corresponding to the value is not required, so the structure is relatively simple and can be manufactured at low cost. In addition, since an electrostrictive element is used instead of a piezoelectric element as a pressure detection element, when a predetermined pressure is applied to the pressure detection element ( In the same figure (al), in a piezoelectric element, a signal corresponding to the pressure is obtained as a change in the amount of charge, but it gradually attenuates with the passage of time, making it impossible to detect static changes in pressure (the same figure (b) )).However, as long as pressure is applied to the electrostrictive element, the capacitance ΔC continues to maintain the value corresponding to the pressure, so static changes in pressure can also be detected ((C) in the same figure). Furthermore, the first electrostrictive element 1 and the second
Since the electrostrictive elements 2 are arranged to face each other vertically, only a relatively small space is required when storing the elements in the housing 11, and there is an effect that miniaturization for pressure detection can be removed. .

FIG. 7 shows a second embodiment of the pressure detector according to the present invention.

In the first embodiment, the second electrostrictive element 2 was provided on the opposite side of the sensor body 12 to the first electrostrictive element 1, but in the second embodiment, the second electrostrictive element 2 was provided on the same side of the lower concave portion of the sensor body 31. It is set up in Assembly is performed in the following steps. A guide insulator 32 with a lead wire escape groove is inserted into the lower recess of the sensor body 31, and a metal plate 33 and a first
electrostrictive element 1, metal plate 34, insulating spacers 35, 36, etc. made of Alt02, etc. A rod 37, a second electrostrictive element 2) a metal plate 38, an insulating spacer 39 made of Al2O3, etc. are inserted, and a spring ring 40 is welded to the sensor body 31 in the same manner as in the first embodiment and fixed to form a sensor sub. form an assembly. After that, the sensor subassembly is press-fitted into the housing 41, and then the rod 37, the diaphragm 42, the diaphragm 42, and the housing 41 are connected to the first
Weld and fix in the same manner as in the example. Furthermore, 43a.

43b and 43C are lead wires, each connected to the metal plate 34.
, sensor back body 44, and metal plate 38 to maintain electrical continuity. In the second embodiment, since the second electrostrictive element 2 is in the same atmosphere as the first electrostrictive element l, the characteristics due to the temperature difference between the second electrostrictive element 2 and the first electrostrictive element 1 are This eliminates variations in the number of images and enables more accurate detection.

FIG. 8 shows a third embodiment of the pressure detector according to the present invention.

In the first embodiment, the pressure receiving area of the diaphragm 9 and the pressure receiving area of the first electrostrictive element 1 are almost equal in FIG. 1, but in the third embodiment shown in FIG. The pressure receiving area of the electrostrictive element 1a is made small. In the figure, a guide insulator 53 is installed in the lower recess of the sensor body 52, and AI! 20. Insulating spacer 5 consisting of
4. The first electrostrictive element 1', the metal plates 55 and 56, and the upper end of the rod 57 are assembled, and these are fixed by caulking the lower end caulking portion 52a of the sensor body 52.

A diaphragm 51 is welded and fixed to the rod 57 and housing 58 by the same means as in the first embodiment. Also, 59a, 59b.

59c is a lead wire, and the lead wire 59a is connected to the metal plate 56.
Lead wire 59b is attached to the sensor back body 61 to maintain electrical continuity with the metal plate 55, and lead wire 59c is attached to the metal plate 62 to maintain electrical continuity. It's dripping. 63
By press-fitting the sensor hack body 61 into the sensor body 52 with a temperature compensation insulator made of Al2O2 or the like for fixing the second electrostrictive element 2,
The second electrostrictive element 2 is fixed. Note that 64 is an insulating spacer made of klzox.

In this third embodiment, since the pressure receiving area of the first electrostrictive element 1' is smaller than the pressure receiving area of the diaphragm 51, the pressure applied to the first electrostrictive element 1' is greater than the pressure applied to the diaphragm 51. , the sensitivity can be increased compared to the first embodiment, and the pressure detection accuracy can be improved.

Note that the present invention is not limited to the first to third embodiments above,
Various modifications can be made without departing from the spirit of the invention, for example as shown below.

(1) The first or second electrostrictive element may have a donut shape (or a disk shape), and its thickness can be adjusted arbitrarily.

(2) A structure without a sensor body may be used.

(3) The rods may have a coaxial double structure, and at least one of the rods may be made of a good thermal conductor.

〔Effect of the invention〕

As described above, the pressure detector of the present invention can directly detect high pressure, has a relatively simple structure, can be manufactured at low cost, and uses an electrostrictive element as the pressure detection element. Since the first electrostrictive element and the second electrostrictive element are arranged to face each other vertically, it is possible to detect a static value of pressure. It has the excellent effect of providing vessels.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a first embodiment of the pressure detector of the present invention, Fig. 2 is a detection circuit diagram of the pressure detector in the first embodiment, and Fig. 3 is a pressure sensor of the pressure detector in the first embodiment. Figure 4 is a graph showing the temperature characteristics of the electrostrictive element, Figure 5 is a graph showing the temperature characteristics at the zero point, and Figure 6 is the graph showing the characteristics of the pressure detection element with respect to static pressure. graph,
FIG. 7 is a cross-sectional view of a second embodiment of the pressure detector of the present invention, and FIG. 8 is a cross-sectional view of a third embodiment of the pressure detector of the present invention. 1... First electrostrictive element, 2... Second electrostrictive element, 9
...Diaphragm, 10...Rod, 11...Housing. Representative Patent Attorney Takashi Okabe 1o-11 Law, De Fig. 1 Pressure (Kgf/cm”) Fig. 3 Falseness (°C) Fig. 4 Temperature Fig. 5

Claims (2)

[Claims] (1) A housing having a bag-shaped inner side, a first electrostrictive element for pressure detection disposed in the housing, and facing the upper surface side or the lower surface side of the first electrostrictive element. a second electrostrictive element for temperature compensation, which is arranged as shown in FIG. and a rod serving as a pressure medium disposed between the first electrostrictive element and the first electrostrictive element. (2) The pressure detector according to claim 1, wherein the first electrostrictive element and the second electrostrictive element constitute a bridge circuit.