JPH05248981A - Piezoelectric pressure sensor - Google Patents

Abstract

PURPOSE:To make accurate pressure sensing by avoiding influence of the pyroe lectric effect in the atmosphere where the piezo element temp. varies. CONSTITUTION:Signal takeout electrodes 15, 16 having the same area as the oversurface and undersurface of a piezo element are drawn out from the electric charge gathering electrodes installed on the outer and inner side faces of the piezo element, and the electric charges generated on the signal takeout electrodes are set off, and thereby accurate pressure sensing is established even under varying temp. which can be done free from influence of the pyroelectric effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric pressure sensor suitable for detecting pressure such as combustion pressure in a cylinder of an internal combustion engine.

[0002]

2. Description of the Related Art Piezoelectric pressure sensors that utilize the piezoelectric effect of applying stress to generate electric charge have been used more frequently than before. In particular, recently, a pressure sensor suitable for detecting the combustion pressure in the cylinder of an internal combustion engine has been actively developed. FIG. 2 shows the basic structure of the piezoelectric pressure sensor described in Japanese Patent Application No. 3-54499. The figure is a vertical sectional view of the sensor.
The piezoelectric element 23 installed inside the sensor housing 21 is connected to the signal extraction fitting 25 and the pressure transmission member 2 by the upper fixing screw 22.
It is pressed and fixed to the back surface of the pressure receiving surface 29 processed into a diaphragm shape via 8, and a pre-stress is given. This prestress is also necessary to measure the negative pressure, especially when measuring the combustion pressure in the cylinder of the internal combustion engine. 3 is an electrode layout diagram of the piezoelectric element 23 shown in FIG.

Next, the operation will be described. Sensor housing 2
The pressure applied to the pressure receiving surface 29 from the outside of 1 is transmitted via the pressure transmitting member 28 and the signal extracting metal fitting 25 so as to push up the inner peripheral portion of the piezoelectric element 23. Here, since the upper end outer peripheral portion of the piezoelectric element 23 is pressed downward by the upper fixing screw 22, a shearing force is applied to the piezoelectric element 23.
The electric charge generated in response to this stress is detected as an electric signal.

Now, a structure for detecting the generated charges will be described. As shown in FIG. 3, the cylindrical piezoelectric element 23 is provided with charge collecting electrodes 32 and 34 on the outer side surface and the inner side surface to collect electric charges generated in the piezoelectric element, and the electric charges generated according to stress are generated by these electrodes. Collected on top. Charge collection electrode 3
The electric charge of 2 is grounded to the sensor housing 21 through the upper fixing screw 22 which is in contact with the signal extraction electrode 31. Further, the charge of the charge collecting electrode 34 is guided to the connector section 20 by the signal extracting metal fitting 25 which is in contact with the signal extracting electrode 33, and the signal is taken out by the cable.

[0005]

However, when the signal extraction electrode as shown in FIG. 3 is used, when the piezoelectric element changes in temperature, a part of the electric charge due to the pyroelectric effect is collected in the signal extraction electrode. Since the electric charge due to this pyroelectric effect is superimposed and detected on the electric charge generated by the pressure application,
It was difficult to detect pressure with high accuracy while the temperature changed.

It is an object of the present invention to provide a piezoelectric pressure sensor capable of highly accurate pressure detection even when the temperature of the piezoelectric element changes.

[0007]

According to the present invention, a signal is taken out from each of the charge collecting electrodes on the side of the piezoelectric element on the signal detection side and on the ground side so that the amounts of electric charges due to the pyroelectric effect are equal on the upper and lower surfaces of the piezoelectric element. Each of the electrodes is drawn out, and the electric charge as a pressure signal is taken out from the signal taking-out electrode.

[0008]

In the signal extracting electrodes attached to both end surfaces of the piezoelectric element according to the present invention, the amount of electric charges generated by the pyroelectric effect on the opposing electrodes is equal on the upper and lower surfaces, and the opposing electrodes are side surface charge collecting electrodes. Since they are connected through, the charges generated by the pyroelectric effect are canceled out, and an error in pressure detection due to a temperature change can be avoided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the piezoelectric pressure sensor of the present invention will be described below with reference to the drawings.

FIG. 1 is an electrode layout diagram of a piezoelectric element according to an embodiment of the present invention. The piezoelectric element has a cylindrical shape and is polarized in the axial direction. Charge collecting electrodes 12 and 14 are attached to the outer surface and the inner surface of the piezoelectric element, respectively. Further, a signal extraction electrode 1 is provided on the upper end surface of the piezoelectric element.
1, 15 are attached to the lower end faces of the signal extraction electrodes 13 and 16, and the signal extraction electrodes 11 and 16 are connected to the charge collection electrodes 12 on the outer side of the signal extraction electrodes 15 and 1.
3 is connected to the charge collecting electrode 14 on the inner surface.

FIG. 2 is a sectional view of a piezoelectric pressure sensor using the piezoelectric element according to the embodiment of the present invention shown in FIG. In the figure, reference numeral 21 denotes a sensor housing made of metal, and a pressure receiving surface 2 formed on one surface of the sensor housing 21 in a diaphragm shape.
9 is provided. The pressure receiving surface 29 is installed in the measured region, for example, in the cylinder of the internal combustion engine. Inside the sensor housing 21, one end of a pressure transmission member 28 formed of an insulating material (for example, ceramic) is provided in contact with the back surface of the pressure receiving surface 29, and a cylindrical piezoelectric element 23 is provided at the other end. ing. The lower inner peripheral portion of the cylindrical piezoelectric element 23 is held by a pressure transmitting member 28 via a signal extracting fitting 25. Further, the outer peripheral portion of the upper end of the piezoelectric element 23 is pressed by the upper fixing screw 22. The tightening force of the upper fixing screw 22 presses the piezoelectric element 23, the signal extracting fitting 25, and the pressure transmitting member 28 against the pressure receiving surface 29 to fix each member and apply pre-stress to the piezoelectric element 23. At this time, the convex portion 2 of the signal extraction fitting 25
6 is fitted in the recess 27 of the pressure transmission member 28, and the signal extraction metal fitting 25 and the pressure transmission member 28 are positioned with high precision. Further, since the piezoelectric element 23 and the pressure transmitting member 28 are positioned with high accuracy on the inner wall of the sensor housing 21, the piezoelectric element 23 and the signal extracting fitting 25 are positioned with high accuracy. The rod-shaped portion 24 of the signal extraction fitting 25 is directly connected to the connector portion 20.

FIG. 4 shows the state of electric charge generation when a load is applied to the piezoelectric element and the temperature changes. (A) shows the case of a conventional type element, and (B) shows the case of the present invention. There is.

Next, the operation of the piezoelectric pressure sensor of this embodiment will be described. When the pressure in the measured region is applied to the pressure receiving surface 29, the force is transmitted to the lower inner peripheral portion of the piezoelectric element 23 through the pressure transmitting member 28 and the signal extracting metal fitting 25. On the other hand, since the upper outer peripheral portion of the piezoelectric element 23 is pressed by the upper fixing screw 22, a shearing force is applied to the piezoelectric element 23, and an electric charge according to the applied force is generated in the piezoelectric element 23, and the outer surface And inner surface charge collecting electrode 1
Collected on 2,14. External charge collecting electrode 12
The upper charge is applied to the signal extraction electrode 11 at the upper end of the piezoelectric element,
The charges on the charge collecting electrode 14 on the inner surface are respectively guided to the signal extracting electrodes 13 at the lower end of the piezoelectric element. Since the upper fixing screw 22 is in contact with the signal extraction electrode 11, the electric charge of the signal extraction electrode 11 is grounded through the sensor housing 21. On the other hand, the signal extraction electrode 13 has
Since the signal take-out metal fitting 25 is in contact with the signal take-out electrode 13, the electric charge of the signal take-out electrode 13 is transmitted through the rod-like portion 24.
And is taken out as a pressure signal by a cable.

Consider a case where a temperature change occurs in the piezoelectric element while a shear load is applied to the element. As shown in FIG. 4, charges 41 and 42 are generated on the charge collecting electrodes 32 and 34 due to the shear load. In FIG. 4A, in addition to the electric charge due to the shearing, the electric charges 44 and 43 due to the pyroelectric effect due to the temperature change of the piezoelectric element are generated on the signal extraction electrodes 31 and 33. The charges 44 and 43 due to the pyroelectric effect are superimposed on the charges 41 and 42 generated by the application of the shear load, respectively, and are detected as a pressure signal. However, as shown in FIG. 4 (B), if the signal extraction electrodes 13 and 15 have the same area and the signal extraction electrodes 11 and 16 have the same area, the signal extraction electrodes 13 and 15 have the same absolute value. Charges 43 and 44 having opposite signs are generated, and the same occurs at the signal extraction electrodes 11 and 16. Here, since the signal extraction electrodes 11 and 16 are connected through the charge collection electrode 12 and the signal extraction electrodes 13 and 15 are connected through the charge collection electrode 14, the charges 43 and 44 due to the pyroelectric effect are offset, and Only the electric charge generated by the shear load remains. Therefore, even if the temperature of the piezoelectric element changes, accurate pressure detection can be realized without being affected by the pyroelectric effect.

Although shear stress is used in this embodiment, the present invention can be applied to the case where pressure is detected by using the piezoelectric lateral effect using compressive stress.

In this embodiment, the signal extraction electrodes having the same area are provided on the upper and lower surfaces, but the areas of the signal extraction electrodes on the upper and lower surfaces are set so that the signal extraction electrodes have the same amount of charges generated by the pyroelectric effect. Is determined, it is not necessary that the areas of the signal extraction electrodes on the upper and lower surfaces are equal.

Although not particularly described in this embodiment, the pyroelectric effect is particularly related to the polarization direction of the piezoelectric element,
The polarization direction of the piezoelectric element is the vertical direction in this embodiment.

[0018]

As described above, according to the present invention, two signal extraction electrodes having the same area are provided on the upper and lower end surfaces of each of the charge collection electrodes attached to the side surface of the piezoelectric element, and the pressure signal is extracted therefrom. That is, it is possible to realize a piezoelectric pressure sensor that can accurately detect pressure even when the temperature changes without being affected by the pyroelectric effect.

[Brief description of drawings]

FIG. 1 is an electrode layout diagram of a piezoelectric element according to an embodiment of the present invention.

FIG. 2 is a sectional view of a piezoelectric pressure sensor in a conventional example and an example of the present invention.

FIG. 3 is an electrode layout diagram of a piezoelectric element in a conventional example.

FIG. 4 is a charge distribution diagram on a piezoelectric element electrode in a conventional example and an example of the present invention.

[Explanation of symbols]

 11 Signal Extraction Electrode (Outer Upper) 12 Charge Collecting Electrode (Outer) 13 Signal Extracting Electrode (Inner Lower) 14 Charge Collecting Electrode (Inner) 15 Signal Extracting Electrode (Inner Upper) 16 Signal Extracting Electrode (Outer Lower) 20 Connector Part 21 Sensor housing 22 Upper fixing screw 23 Piezoelectric element 24 Rod-shaped portion 25 Signal extraction metal fitting 26 Convex portion 27 Recessed portion 28 Pressure transmission member 29 Pressure receiving surface 31 Signal extraction electrode (outside) 32 Charge collection electrode (outside) 33 Signal extraction electrode (inside) 34 Charge collection electrode (inside) 41 Charge due to shear load 42 Charge due to shear load 43 Charge due to pyroelectric effect 44 Charge due to pyroelectric effect

Claims (1)

[Claims] 1. A housing having a pressure receiving surface, a pressure transmitting member provided inside the housing and having one end in contact with a surface on the back side of the pressure receiving surface, and a pressure transmitting member provided inside the housing and other than the pressure transmitting member. A piezoelectric element provided at an end, one of the side surfaces of the piezoelectric element is provided with a signal detection charge collecting electrode, and the other side surface of the piezoelectric element is provided with a ground side charge collecting electrode, Signal extraction electrodes drawn from the signal detection charge collection electrode are provided on the upper surface and the lower surface of the piezoelectric element from the signal detection charge collection electrode, and the ground side charge collection electrode is provided on the upper surface and the lower surface of the piezoelectric element, respectively. A piezoelectric pressure sensor, characterized in that another signal extraction electrode drawn from the ground side charge collection electrode is provided.