JP2580115B2 - Pressure detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detector suitable for directly detecting, for example, the pressure in a combustion chamber of an internal combustion engine. The present invention relates to a mounting structure of a piezoelectric element for temperature compensation for compensating for a change in output characteristics in a detection process.

[Conventional technology]

Conventionally, in a piezoelectric pressure detector of this type, as shown in an electric circuit diagram of FIG. 4, an output from a piezoelectric element 1a is input to an impedance conversion circuit to obtain an output signal.

[Problems to be solved by the invention]

However, when this type of piezoelectric element is used in places where the temperature changes rapidly, such as in an engine control system, the charge generated by the pyro effect of the piezoelectric element is also output, causing temperature drift and accurate pressure detection. There is a problem that is not done.

Therefore, an object of the present invention is to provide a pressure detector capable of performing temperature compensation by minimizing a change in output characteristics due to a temperature change in a pressure detection process of a piezoelectric element.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a cylindrical housing, a first piezoelectric element disposed in the housing, for detecting pressure, and a first piezoelectric element in the housing, in the axial direction of the housing. The first piezoelectric element is disposed at a predetermined distance from the piezoelectric element, has a polarization direction opposite to the polarization direction of the first piezoelectric element, and is connected in parallel with the first piezoelectric element. A pressure transmission interposed between a piezoelectric element and the first and second piezoelectric elements to prevent transmission of pressure received by the first piezoelectric element to the second piezoelectric element. And a prevention member.

According to the structure of the present invention, a charge due to the piezoelectric effect and a charge due to the pyro effect caused by a temperature change are generated in the first piezoelectric element, but a charge due to the pyro effect is also generated in the second piezoelectric element. Since the two piezoelectric elements are connected in parallel in such a manner that the polarization directions of the two piezoelectric elements are opposite to each other, the charges due to the pyro effect of the two elements cancel each other, and the influence of the pyro effect can be sufficiently suppressed.

Further, in the present invention, the first piezoelectric element and the second
Since the pressure transmission preventing member is interposed between the first piezoelectric element and the second piezoelectric element, the second piezoelectric element hardly receives the pressure applied to the first piezoelectric element. Therefore, the temperature compensation of the first piezoelectric element can be reliably performed by the second piezoelectric element.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a main part showing the configuration of a first embodiment of a pressure detector of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit of the pressure detector of the present invention, and FIG. FIG. 3 is an enlarged schematic view of a first piezoelectric element or a second piezoelectric element and respective electrodes in the illustrated pressure detector of the present invention. The pressure detector of the present invention is a broken line portion of FIG. It is about structure.

In FIG. 1, a diaphragm 5 is welded all around a housing 7 made of a metal member such as SUS (stainless steel), and when the diaphragm 5 is deformed by receiving a detected pressure such as a combustion pressure of an internal combustion engine, a rod 6 is formed. Is pushed up to the top. The first pressure detecting ring formed in a ring shape
The upper and lower silver electrodes 11b and 11a are provided on the upper and lower piezoelectric elements 1a, respectively, and the second piezoelectric element 1b for temperature detection which is also formed in a ring shape and has the same temperature characteristics as the first piezoelectric element 1a. Are provided with silver electrodes 11d and 11c, respectively. Further, to ensure electrical connection, electrode plates 9b and 9a are provided outside silver electrodes 11b and 11a, respectively, and 9d and 9c are provided outside silver electrodes 11d and 11c, respectively. Electrode plate on output side
To insulate 9a and 9d from the driving ring 12 which is a pressure transmission preventing member, ring-shaped insulators 3a and 3b made of Teflon or the like are arranged on the side surfaces of the piezoelectric elements 1a and 1b, respectively. An insulator 10 also made of Teflon or the like is arranged on the inner surface of the housing 7 so as to insulate the electrode plate 9a and the lead wire 8 from the driving ring 12. The screw portion 7a is for fixing the pressure detector main body to the engine main body or the like. An insulator 2a made of alumina or the like insulates the electrode plate 9a from the rod 6, and insulates the rod 6 from heat. An insulator 2b also made of alumina or the like fixes the electrode plate 9d, insulates the driving ring 12, and fixes the metal fixing ring 13 to the housing 7 by spot welding. The driving ring 12 is made of, for example, a metal member such as SUS. When the driving ring 12 is pressed into the housing 7, a preload is applied to the insulating pair 2 a and the first piezoelectric element 1 a by the elastic force of the preload cover 4. Is adjusted so as to have a predetermined value. Electrode plates 9a and 9d are spot-welded or brazed to the lead wire 8, and as shown in FIG. 2, electric charges generated from the first piezoelectric element 1a and the second piezoelectric element 1b are output from a terminal S1. , To the impedance conversion circuit.
The electrode plates 9b and 9c are in pressure contact with the driving ring 12, and are electrically connected to, for example, an engine body or the like via the housing 7 (terminal S2 in FIG. 2) and are electrically grounded. In FIG. 2, the arrows in the figure indicate the polarization direction of each piezoelectric element, and the polarization direction is obtained by applying a voltage to the electrodes on both surfaces of the piezoelectric element during the manufacturing process of each piezoelectric element. A predetermined polarization direction is given. As shown in the enlarged view of the first piezoelectric element portion in FIG. 3 (a) and the enlarged view of the second piezoelectric element portion in FIG. 3 (b), respective silver electrodes 11a, 11b and 11c are shown.
The area of 11d is adjusted by changing the size so that the amount of charge generated by the pyro effect caused by the temperature change is the same. Here, the amount of electric charge generated by the pyro effect from the piezoelectric elements 1a and 1b is basically determined by the area of the silver electrodes 11a to 11d formed on the surface of the piezoelectric element, and is hardly affected by the size and shape of the piezoelectric element. Therefore, as described above, if the temperatures of the two piezoelectric elements 1a and 1b are always substantially the same, the two electrode areas may be substantially the same, but in the case of a structure in which a predetermined temperature difference occurs between the two piezoelectric elements, This is because it is necessary to make the electrode areas different in consideration of the temperature difference and to adjust the charge amounts generated by the pyro effect so as to be substantially the same.

As is apparent from FIG. 1, the first piezoelectric element 1a and the second piezoelectric element 1b are arranged at a predetermined distance from each other in the axial direction of the housing 7. Therefore, it is clear that the pressure acting on the housing 7, that is, the pressure acting on the rod 6, acts on the first piezoelectric element 1a, but does not act on the second piezoelectric element 1b.

Therefore, according to the above configuration, when the diaphragm 5 is deformed by receiving pressure, the rod 6 is pushed upward, stress is transmitted to the first piezoelectric element 1a, and electric charges corresponding to the stress are generated by the piezoelectric effect. Furthermore, although the charge is generated by the pyro effect, the same amount of charge is generated by the pyro effect at the same time in the second piezoelectric element 1b. Only the charge generated in the first piezoelectric element 1a due to the effect is output,
The signal is input to the impedance conversion circuit through the lead wire 8.

Incidentally, the mounting structure of the second pressure element 1b is not limited to the above embodiment, but can be variously modified as follows.

(1) As shown in FIG. 5 (a) and FIG. 5 (b) which are a longitudinal sectional view of an essential part of the second embodiment and an enlarged view (b) of the second piezoelectric element portion, the silver electrode 11d of the second piezoelectric element 1b and the electrode The plate 9d, the silver electrode 11c, and the driving ring 12 may be respectively bonded with a conductive adhesive 14, and then the upper portion may be filled with a potting material 15.

(2) The second piezoelectric element 1b and the insulating pair 2b may be held down by a tightening ring 16 and fixed by screwing, as shown in the vertical sectional view of the main part of the third embodiment of FIG.
Further, as shown in the figure, the welded portion between the electrode plate 9a and the lead wire 8 may be insulated by an insulating tube 17.

(3) The second piezoelectric element 1b and the insulator 2b can be fixed by welding the fixed cover 18 to the driving ring 12 as shown in the vertical sectional view of the main part of the fourth embodiment of FIG. Good.
Also, two lead wires 8a and 8b are provided, and
And 9d may be connected and insulated by an insulating tube 17. Note that the lead wires 8a and 8b are electrically connected.

(4) The shape of the second piezoelectric element 1b is not limited to a ring shape but may be a disk shape or the like. This is the same for the first piezoelectric element 1a.

(5) The size and thickness of the second piezoelectric element 1b and the first piezoelectric element 1a may be different as shown in the first embodiment, or may be the same.

〔The invention's effect〕

As described above, in the pressure detector of the present invention,
Since the second piezoelectric element is electrically connected in parallel with the first piezoelectric element so as not to be affected by the Pyro effect, and the second piezoelectric element is arranged in a place where external pressure is not applied. In addition, the second piezoelectric element is prevented from generating an extra charge due to the piezoelectric effect, so that more accurate temperature compensation can be performed.

According to the present invention, the first piezoelectric element for detecting pressure and the second piezoelectric element for temperature compensation are arranged at a predetermined distance from each other in the axial direction of the housing. On the other hand, there is an effect that the pressure transmission can be reliably shut off. In addition, the first in the axial direction of the housing
In addition, since the second piezoelectric element is disposed, it is possible to solve problems such as a decrease in pressure detection accuracy due to pressure distribution and temperature distribution and an increase in the radial dimension of the housing as in the case where both piezoelectric elements are disposed in parallel. There is also an effect.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part showing a configuration of a first embodiment of a pressure detector of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit of the pressure detector of the present invention, and FIG. FIG. 1B is an enlarged view of a first piezoelectric element portion of the first embodiment, and FIG.
FIG. 4 is an electric circuit diagram showing the prior art, FIG. 5 (a) is a longitudinal sectional view of a main part of the second embodiment, FIG. 4 (b) is an enlarged view of the second piezoelectric element, and FIG. Main part longitudinal sectional view of the third embodiment, FIG.
The figure is a longitudinal sectional view of a main part of the fourth embodiment. 1a: a first piezoelectric element for pressure detection, 1b: a second piezoelectric element for temperature compensation, 2a, 2b ... insulator, 3a, 3b, 10 ... insulator, 4 ... preload cover, 5 ... Diaphragm, 6 ... Rod, 7 ... Housing, 8 ... Lead wire, 9a, 9b, 9c, 9d ...
Electrode plate, 11a, 11b, 11c, 11d: Silver electrode, 12: Driving ring, 13: Fixing ring.

Claims (1)

(57) [Claims] 1. A cylindrical housing, a first piezoelectric element disposed in the housing and for detecting pressure, and an axial direction of the housing in the housing.
The first piezoelectric element is disposed at a predetermined distance from the first piezoelectric element, has a polarization direction opposite to the polarization direction of the first piezoelectric element, and is connected in parallel with the first piezoelectric element for temperature compensation. A second piezoelectric element, interposed between the first piezoelectric element and the second piezoelectric element, for preventing transmission of pressure received by the first piezoelectric element to the second piezoelectric element; And a pressure transmission preventing member.