JPH0560643A - Piezoelectric pressure sensor - Google Patents

Abstract

PURPOSE:To improve the temperature characteristic of a sensor by providing a temperature compensating capacitor of the same material as a piezoelectric device inside the sensor, and using the capacitor as a feedback capacitor for a charge amplifier. CONSTITUTION:This sensor uses a charge amplifier as a signal amplifying circuit. A temperature compensating capacitor 15 is made of the same material as a piezoelectric element 13 without being subjected to polarization. The temperature is compensated by using the capacitor 15 as a feedback capacitor of the charge amplifier. The length of the temperature compensating capacitor 15 in the thicknesswise direction is made easily changeable, whereby the gain of the amplifier can be easily changed.

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. 3 shows the basic configuration of a piezoelectric pressure sensor that has been conventionally used. This figure is a vertical cross-sectional view of the sensor. The piezoelectric element 34 installed inside the sensor box 31 is pressed against the back surface of the pressure receiving surface 32 processed into a diaphragm shape by the upper fixing screw 35 via the pressure transmission member 33. Fixed and prestressed. This prestress is also necessary to measure the negative pressure, especially when measuring the combustion pressure in the cylinder of the internal combustion engine.

Next, the operation will be described. Sensor box 3
The pressure applied to the pressure receiving surface 32 from the outside of 1 is transmitted via the pressure transmitting member 33 so as to push up the inner peripheral portion of the piezoelectric element 34. Here, since the outer peripheral portion of the upper end of the piezoelectric element 34 is pressed downward by the upper fixing screw 35, a shearing force is applied to the piezoelectric element 34. 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. Electrodes for collecting charges generated in the piezoelectric element are provided on the inner side surface and the outer side surface of the cylindrical piezoelectric element 34. The outer electrode is grounded to the sensor box,
In order to detect the electric charge of the inner electrode, the signal extraction fitting 36
Is taking out the signal. Further, this charge was input to a signal amplification circuit (not shown) and converted into a voltage.

When the sensor using such a piezoelectric element is used for measuring the combustion pressure of an engine whose temperature changes drastically, the temperature characteristic of the piezoelectric element has a great influence. Therefore, a method of newly installing a thermistor or the like in the sensor for temperature compensation (see Japanese Patent Laid-Open No. 1-213535) and a method of using a temperature compensating capacitor (see Japanese Patent Laid-Open No. 61-209334) have been considered.

[0006]

The current engine is mainly a four-valve engine for high output, and the portion where the sensor can be attached to the cylinder head is extremely limited. Therefore, the sensor used for the above purpose is required to have a smaller mounting portion.

However, in order to perform temperature compensation by newly using components such as the thermistor as in the conventional example, there is a drawback that it is difficult to downsize the sensor. In addition, the increase in the number of parts causes a problem of reliability of the sensor. Further, in the method disclosed in Japanese Patent Laid-Open No. 61-209334, the temperature characteristics of the temperature compensating capacitor and the piezoelectric element need to exhibit opposite characteristics, but it is very difficult to select such a capacitor. Accurate temperature compensation is not possible.

[0008]

In order to solve the above-mentioned problems, the present invention provides a cylindrical box body having a pressure receiving surface, and an inner surface of the box body, one end of which is substantially the back surface of the pressure receiving surface. A pressure transmitting member in contact with the center, a polarized cylindrical piezoelectric element provided inside the box body, and a signal take-out member provided inside the box body for taking out charges generated by the piezoelectric element to the outside of the box body. , A cylindrical capacitor that is provided inside the box and is made of the same material as the piezoelectric element and is not polarized,
A signal extracting member, a pressure transmitting member, and a fixing member that fixes the capacitor by applying pressure,
The signal extracting member, the piezoelectric element, and the capacitor are arranged between the fixing member and the pressure transmitting member, and the pressure transmitting member, the signal extracting member, the piezoelectric element, the capacitor, and the fixing member are arranged substantially coaxially, and the capacitor and the piezoelectric element are arranged. Is a piezoelectric type pressure sensor that constitutes a capacitor that electrically connects in series.

Furthermore, in the piezoelectric pressure sensor, a charge amplifier is used as an amplifier when the output of the piezoelectric element is detected, and the capacitor is used as a feedback capacitor of the charge amplifier.

[0010]

With the above construction, the present invention comprises the temperature compensating capacitor as the same material as the piezoelectric element and not polarized, so that the piezoelectric element and the temperature compensating capacitor exhibit the same temperature characteristic. By using this temperature compensating capacitor as the feedback capacitor of the charge amplifier, the temperature of the sensor output can be easily and accurately compensated. Furthermore, the gain of the charge amplifier can be easily changed by changing the axial thickness of the temperature compensating capacitor.

[0011]

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 shows a sectional view of a piezoelectric pressure sensor according to an embodiment of the present invention. 1 in the figure
1 is a sensor box body made of metal, and this sensor box body 1
A pressure-receiving surface 17 processed in a diaphragm shape is provided at one end of the pressure sensor 1. The pressure receiving surface 17 is installed in the measured region, for example, in the cylinder of the internal combustion engine. A pressure transmitting member 16 made of an insulating material (for example, ceramic) is provided inside the sensor box body 11 so that one end is in contact with the back surface of the pressure receiving surface 17, and the other end is for temperature compensation via an electrode plate 18. The capacitor 15 is in contact. This temperature compensating capacitor 15
As the element, an element that is made of the same material as the cylindrical piezoelectric element 13 and is not polarized is used. Further, a signal extracting fitting 14 is located on the side of the temperature compensating capacitor 15 opposite to the pressure transmitting member 16. The signal take-out fitting 14 electrically connects the electrode provided on the inner circumference of the cylindrical piezoelectric element 13 and the electrode provided on the upper surface of the temperature compensating capacitor 15, and leads to the charge amplifier by a lead wire. .. As the piezoelectric element 13 of cylindrical shape, for example, lead titanate and is used plus the M _n and L _a like as a main component, it is subjected to axially polarized. Further, the upper end outer peripheral portion of the piezoelectric element 13 is pressed by the upper fixing screw 12. Due to the tightening force of the upper fixing screw 12, the piezoelectric element 13, the signal extracting fitting 14, the temperature compensating capacitor 15, the electrode plate 18 and the pressure transmitting member 16 are pressed against the pressure receiving surface 17, and each member is fixed and the piezoelectric element 13 is spared. Applying stress.

Next, the operation of the piezoelectric type pressure sensor of this embodiment will be described. When the pressure in the measured region is applied to the pressure receiving surface 17, the force is transmitted to the lower inner peripheral portion of the piezoelectric element 13 through the pressure transmitting member 16, the electrode plate 18, the temperature compensating capacitor 15, and the signal extracting fitting 14. On the other hand, since the upper outer peripheral portion of the piezoelectric element 13 is pressed by the upper fixing screw 12, a shearing force is applied to the piezoelectric element 13, and an electric charge corresponding to the applied force is generated in the piezoelectric element 13, and the inner and outer peripheral parts Are collected on electrodes (not shown) formed on the substrate. The outer peripheral electrode is in contact with the inner side surface of the sensor box 11 and is grounded. Further, the inner peripheral electrode is in contact with the signal extraction metal fitting 14,
The electric charge is taken out through.

FIG. 2 is a schematic diagram of the present invention. The part surrounded by the broken line is the inside of the sensor, and the part surrounded by the alternate long and short dash line is the charge amplifier 20. In such a charge amplifier, the output voltage E _a is represented by E _a = −Q / C _f , all the charges Q generated in the piezoelectric element 22 are transferred to the capacitance C _{f of the} feedback capacitor, and the output gain is C _f. It has the feature that it is determined by the size of. That is, since the temperature compensation capacitor 23 is connected as the feedback capacitor of the charge amplifier 20, all the charges generated in the piezoelectric element 22 are transferred to the temperature compensation capacitor 23.
Here, since the temperature compensation capacitor 23 is made of the same material as the piezoelectric element 22 and placed in the same temperature state, the output of the charge amplifier can be corrected. Furthermore, since the capacity of the temperature compensating capacitor 23 is determined by the electrode area and the distance between the electrodes, it is possible to easily change the interelectrode distance of the temperature compensating capacitor in the configuration of the embodiment. It is possible to easily change the gain of the charge amplifier.

[0014]

As described above, according to the present invention, the temperature compensating capacitor, which is made of the same material as the piezoelectric element and is not polarized, is used between the pressure transmitting member and the signal extracting fitting. Temperature compensation is performed by using a feedback capacitor of a charge amplifier that is a signal amplification circuit.

This enables temperature compensation easily and accurately. Further, it is possible to easily change the capacitance of the temperature compensating capacitor, and it is possible to easily change the gain of the charge amplifier.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of the present invention.

FIG. 3 is a sectional view of a piezoelectric pressure sensor in a conventional example.

[Explanation of symbols]

 10 Connector Part 11 Sensor Box Body 12 Upper Fixing Screw 13 Piezoelectric Element 14 Signal Extraction Fitting 15 Temperature Compensating Capacitor 16 Pressure Transmitting Member 17 Pressure Receiving Surface 18 Electrode Plate 20 Charge Amplifier 21 Sensor 22 Piezoelectric Element 23 Temperature Compensating Capacitor 61 Sensor Box Body 62 Pressure Receiving Section 63 Pressure Transmission Member 64 Piezoelectric Element 65 Upper Fixing Screw 66 Electrode Extraction Metal Fitting

Claims (3)

[Claims] 1. A cylindrical box body having a pressure receiving surface, a pressure transmitting member provided inside the box body, and having one end in contact with substantially the center of a surface on the back side of the pressure receiving surface, and the inside of the box body. A polarized cylindrical piezoelectric element, a signal extraction member provided inside the box body for extracting charges generated in the piezoelectric element to the outside of the box body, and a signal extraction member provided inside the box body. , The same material as the piezoelectric element, which is not polarized, and includes the piezoelectric element, the signal extracting member, the pressure transmitting member, and a fixing member that fixes the capacitor while applying pressure. The member, the piezoelectric element, and the capacitor are arranged between the fixing member and the pressure transmitting member, and the pressure transmitting member, the signal extracting member, the piezoelectric element, the capacitor, and the fixing portion. The substantially coaxially position, piezoelectric pressure sensors, characterized by connecting the said capacitor piezoelectric element electrically in series. 2. The piezoelectric pressure sensor according to claim 1, wherein a charge amplifier is used as an amplifier when the output of the piezoelectric element is detected, and the capacitor is used as a feedback capacitor of the charge amplifier. 3. The capacitor has an electrode, is disposed between the pressure transmitting member and the signal extracting member, and is electrically connected to the electrode provided on the piezoelectric element by the signal extracting member. The piezoelectric pressure sensor according to claim 1 or 2, characterized in that.