JPS6348296B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a piezoelectric pressure sensor that utilizes the piezoelectric effect of a ferroelectric material, and in particular to a piezoelectric pressure sensor that applies a load to a pressure-sensitive element in advance so that negative pressure can also be measured. This relates to a pressure detector covered with a load cover.

A conventional pressure detector with a preloading cover is shown in Figs. 1 and 3. Fig. 1 is a vertical cross-sectional view showing the overall structure of the pressure sensor, and Fig. 3 shows the sensitivity of the pressure sensor. FIG. 3 is a partial vertical cross-sectional view showing the detailed configuration of the pressure element portion. 1 is a pressure detector, 14 is a pressure sensitive element, and its piezoelectric portion 140 is generally made of magnetic material such as crystal, lead titanate, lead zirconia porcelain, etc., and output electrodes 141 and grounding electrodes 142 are provided on both upper and lower end surfaces. is formed, and electrical continuity with the pressure detector main body, diaphragm 15, etc. is maintained by pressing with the preload cover 16, diaphragm 15, etc. A lead wire 17 connects the output electrode 141 and the electrode 11. 12 is an insulator, and 13 is a housing.

FIG. 2 shows a state in which the conventional pressure detector is used to measure the pressure of combustion gas in the cylinder of an internal combustion engine, and the pressure detector 1 is screwed onto the cylinder head 2. As shown in FIG. 3 is a sealing sleeve, and 4 is a combustion chamber of the cylinder. In this state of use, the pressure detector measures the pressure of high-temperature fluid such as combustion gas pressure of an internal combustion engine, and the pressure-sensitive element 14 comes into direct contact with the high-temperature fluid. When a large amount of heat flows into the piezoelectric element, the electrodes of the piezoelectric pressure-sensitive element 14 become separated, causing problems such as zero point movement and sensitivity deterioration due to floats, etc., and when the temperature becomes extremely high, the piezoelectric material stops exhibiting the piezoelectric effect. arise. Further, as mentioned above, the pressure sensitive element 14 is made of porcelain, while the preload cover 16 is made of metal, so the coefficients of thermal expansion are different between the pressure sensitive element and the preload cover. Since elongation differs depending on temperature, when the temperature rises, the value of the load previously applied to the pressure sensitive element changes or the load is no longer applied.
Furthermore, the grounding electrode 142 of the pressure-sensitive element may become separated from the preloading cover 16, resulting in unstable electrical continuity.

As described above, the present invention prevents a large amount of heat from flowing into the pressure sensitive element from the high temperature fluid to be measured.
In order to eliminate problems caused by the pressure-sensitive element as well as problems caused by differences in thermal expansion coefficients, the preload cover is structured to be easily expanded and contracted.

The pressure detector according to the present invention will be explained below with reference to the drawings. FIG. 4 shows a first embodiment of the pressure detector of the present invention, in which a pressure-sensitive element 14 made of a piezoelectric material is provided on the bottom of a bag-shaped body formed inside the pressure detector main body, and the pressure-sensitive element 14 is covered. A preloading cover 16 is provided which is pressed to apply a preload to the pressure sensitive element,
A pressure receiving plug 18 made of a thin rod-like body is inserted between the lower end surface of the preload cover 16 and the diaphragm 15 that seals the bag-shaped entrance. It has the function of a pressure medium that transmits the received combustion gas pressure from the combustion chamber to the pressure sensing element 14. and the preload cover 1
The side surface of 6 is formed into a bellows shape 161.
191 is a flange portion formed on the housing 13;
192 is a threaded portion for attachment.

Next, the operation of the pressure detector of the present invention having the above structure will be explained. A large amount of heat is transferred from the combustion chamber of the cylinder to the diaphragm 15, but since the pressure receiving plug 18, which is the pressure medium, is formed into a thin rod-shaped body, a large amount of heat is difficult to transfer and is transferred to the pressure sensitive element 14 via the preload cover 16. The amount of heat transmitted is reduced, and the pressure-sensitive element 14 made of piezoelectric material is prevented from being damaged by a large amount of heat as described above.

As mentioned above, by providing the pressure receiving plug 18, a large amount of heat is transferred to the preload cover 16 and the pressure sensitive element 14.
However, some heat is transmitted to the preload cover 16 and the pressure sensitive element 14, and the temperature rises. However, since the side surface of the preloading cover 16 is formed into a bellows shape, even if the temperature of the preloading cover 16 rises and expands, the expansion is absorbed by the bellows shape 161, and the preloading cover 16 and the pressure sensitive element 14 can be kept constant. FIG. 5 shows a second embodiment of the pressure detector according to the present invention, in which the lower end surface of the preloading cover is formed into a diaphragm shape 162, and a pressure medium is placed between the center of the diaphragm shape and the diaphragm 15. A rod-shaped pressure receiving plug 18 is inserted, and the preload cover is pressed by the pressure receiving plug 18.
In this embodiment, the diaphragm-shaped central portion of the preloading cover is pushed upward due to the rise in temperature, making it possible to maintain constant contact with the pressure sensitive element 14. Furthermore, if this preloading cover is made of a spring material, the durability will be increased and the load can be more stably applied to the pressure sensitive element. FIG. 6 shows a third embodiment of the pressure detector according to the present invention, in which the pressure sensitive element 14
and the diaphragm 15, a pressure receiving plug 18, which is a pressure medium and has a thin rod-shaped intermediate portion and flat plate portions having a diameter larger than the intermediate portion on both upper and lower end surfaces, is inserted, and the pressure receiving plug 18 on the pressure sensitive element side is inserted. A preloading cover with a diaphragm shape 162 on the lower end is arranged between the lower end of the flat plate and the bottom of the bag-shaped part of the pressure detector, and a spring receiver is installed on the inlet side of the bag-shaped part of the pressure detector. A portion 193 is integrally provided with the housing, and a spring is inserted between the lower end surface of the diaphragm shape 162 of the preloading cover and the spring receiving portion 193.

In this embodiment, since the diaphragm-shaped portion of the preloading cover is pressed by a spring, it is possible to prevent deterioration of pressure response sensitivity due to the difference in thermal expansion coefficient between the pressure sensitive element and the preloading cover. A large load can be easily applied to the pressure sensitive element.

The pressure receiving plug 18, which is the pressure medium shown in FIGS. 5 and 6, is formed of a thin rod-shaped body, so that less heat is transmitted to the pressure-sensitive element than from the combustion chamber of the cylinder, which generates a large amount of heat. However, it has a function of preventing the pressure sensitive element from being damaged by a large amount of heat.

As described above, in the pressure sensor of the present invention, a pressure receiving plug serving as a pressure medium is inserted between the preload cover covering the pressure sensitive element and the diaphragm, so that the high temperature fluid to be measured is It is possible to reduce the amount of heat that flows into the pressure-sensitive element, thereby eliminating the problems that tend to occur in pressure-sensitive elements made of piezoelectric materials due to high temperatures, and since the preload cover has a stretchable structure, it is possible to reduce the amount of heat flowing into the pressure-sensitive element. Even if the temperature of the cover and the pressure sensitive element rises, it is highly effective in eliminating problems such as changes in load values due to differences in elongation due to differences in thermal expansion coefficients, unstable electrical conduction, and the like.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing the overall configuration of a conventional pressure detector with a preload cover, and Figure 2 is a diagram showing how the pressure detector is used to measure combustion gas pressure in a cylinder of an internal combustion engine. A vertical cross-sectional view showing the condition,
FIG. 3 is a partial vertical sectional view showing the detailed structure of the pressure sensitive element portion of the conventional pressure detector shown in FIG. 1, and FIGS. FIG. 1 is a vertical cross-sectional view showing the first, second, and third embodiments, and the same reference numerals in the figures indicate the same or equivalent parts. 1...Pressure detector, 2...Cylinder bed, 4...
Combustion chamber, 11... Electrode, 141... Output electrode, 14
2... Grounding electrode, 140... Piezoelectric body, 14... Pressure sensitive element, 15... Diaphragm, 16... Preload cover, 161... Bellows shape, 162... Diaphragm shape, 17... Lead wire, 18... Pressure receiving plug as pressure medium , 20...Spring.

Claims (1)

[Claims] 1. The inner shape of the pressure detector body is a bag shape,
A pressure sensitive element made of a piezoelectric material is provided on the bottom surface of the bag shape, a diaphragm is provided to seal the entrance of the bag shape, and the pressure sensitive element is covered and pressed to apply a load to the pressure sensitive element in advance. In the pressure detector provided with a preload cover, a pressure receiving plug serving as a pressure medium is inserted between the diaphragm and the preload cover, and the preload cover has a structure that is elastic. A pressure detector characterized by: 2. The pressure detector according to claim 1, wherein the side surface of the preload cover is formed into a bellows shape. 3. The pressure detector according to claim 1, wherein the lower end surface of the preload cover is formed into a diaphragm shape. 4. The pressure detector according to claim 1, wherein the lower end surface of the preloading cover is formed into a diaphragm shape and is pressed by a spring. 5. The pressure detector according to claim 3 or 4, wherein the preload cover is made of a spring material.