JP2005181184A - Pressure-measuring sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure-measuring sensor of a high response speed, with respect to pressure changes in a pressure-measuring atmosphere. <P>SOLUTION: This pressure measuring sensor is provided with a rectangular-parallelopiped-shaped piezoelectric element 2 with at least one portion of an under face 2A serving as a pressure-receiving part 3; a pair of electrodes 4, arranged to contact with the piezoelectric element 2 sandwiching the piezoelectric element 2 therebetween; and a protective member 5 covering the piezoelectric element 2 and the pair of electrodes 4 under the condition, where the pressure receiving part 3 is exposed in the measuring atmosphere. The area of the pair of electrodes 4 is preferably larger than that of the pressure-receiving part 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pressure measurement sensor used in a combustion chamber of an internal combustion engine.

As a pressure measurement sensor for measuring the combustion pressure in a combustion chamber of an internal combustion engine, a piezoelectric element that converts a mechanical load into an analog signal using a piezoelectric element is provided, and a continuous pressure is obtained by measuring the converted analog signal. Those that measure change are known.
By inserting the piezoelectric element portion of such a pressure measuring sensor directly into the internal combustion engine and measuring the pressure and comparing the combustion waveform between the abnormal time and the normal time (hereinafter referred to as knock detection), exhaust is performed. It is possible to control the gas recirculation (hereinafter referred to as EGR) and the minimum approach angle for maximum torque (hereinafter referred to as MBT), thereby realizing the optimum fuel / air mixing ratio. And lean burn control becomes possible and the fuel consumption of an internal combustion engine can be improved significantly.

Conventionally, as such a pressure measuring sensor, a diaphragm made of a metal film, a piezoelectric element substrate placed on the diaphragm and having an electrode having a terminal on the upper part, and a piezoelectric element substrate placed on the piezoelectric element substrate There has been proposed one including an insulating member that exposes at least a part of the terminal and covers the electrode (see, for example, Patent Document 1).
This pressure measuring sensor applies a pressure applied to the diaphragm as a mechanical load to the piezoelectric element, and when the piezoelectric element is compressed by the diaphragm, an electric charge is generated by piezoelectric conversion. And the pressure applied to the sensor for pressure measurement is measured by detecting this electric charge with an electrode.
Japanese Patent No. 3256799 (FIG. 3)

  However, the following problems remain in the conventional pressure measurement sensor. That is, in the conventional pressure measurement sensor, the diaphragm is a pressure receiving portion, and the pressure applied to the diaphragm becomes a mechanical load and is transmitted to the piezoelectric element to generate an electric charge. For this reason, there exists a problem that the response speed of the piezoelectric element with respect to the pressure change of pressure measurement atmosphere is slow.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a pressure measurement sensor that has a quick response speed to a pressure change in a pressure measurement atmosphere.

  The present invention employs the following configuration in order to solve the above problems. That is, the pressure measurement sensor of the present invention includes a piezoelectric element having at least a part of a flat surface as a pressure receiving portion, and a pair of electrodes disposed so as to be in contact with the piezoelectric element with the piezoelectric element interposed therebetween. And a protective member that covers the piezoelectric element and the pair of electrodes in a state where the pressure receiving part is exposed to a measurement atmosphere.

  In the pressure measurement sensor according to the present invention, the pressure applied to the pressure receiving portion becomes a direct mechanical load on the piezoelectric element by forming at least a part of one surface of the piezoelectric element as a pressure receiving portion exposed in the measurement atmosphere. In addition, electric charges are generated by piezoelectric conversion, and the electric charges are detected by the pair of electrodes. Therefore, the sensitivity to the pressure change of the measurement atmosphere can be improved, and the response speed to the pressure change can be improved.

In the pressure measurement sensor according to the present invention, it is preferable that the area of the electrode is larger than the area of the pressure receiving portion.
In the pressure measurement sensor according to the present invention, since the electric flux density of the electric charge generated in the piezoelectric element by the piezoelectric conversion is proportional to the pressure applied to the pressure receiving portion, the generated electric charge can be detected efficiently and measured. Sensitivity to atmospheric pressure changes is further improved.

In the pressure measurement sensor according to the present invention, it is preferable that the piezoelectric element is made of a langasite single crystal or a langate single crystal.
In the pressure measurement sensor according to the present invention, a langasite (La ₃ Ga ₅ SiO ₁₄ ) single crystal or langate that does not have a Curie temperature up to 1470 ° C. and can stably maintain the same crystal structure even at a high temperature inside the internal combustion engine. By using a single crystal (La ₃ Ta _0.5 Ga _5.5 O ₁₄ ) as a piezoelectric element, it is possible to directly measure pressure by putting it in an internal combustion engine without any material deterioration of the piezoelectric element.
In addition, when Langatate is used, temperature stability similar to that of α-quartz is maintained, so that the internal pressure can be accurately measured even if it is directly inserted at a high temperature such as the internal combustion engine.

In the pressure measurement sensor according to the present invention, the one surface is preferably a surface according to the coordinate axis Y on the crystal optics.
In the pressure measuring sensor according to the present invention, the pressure applied to the surface according to the coordinate axis Y on the crystal optics of the langasite single crystal generates electric charges on the surface according to the coordinate axis X on the crystal optics by piezoelectric conversion. . That is, more efficient pressure measurement is possible by arranging the pressure receiving portion and the pair of electrodes vertically.

  According to the pressure measurement sensor of the present invention, a pressure change in the measurement atmosphere can be directly applied to the piezoelectric element by setting at least a part of one surface of the piezoelectric element as a pressure receiving portion in contact with the measurement atmosphere. Therefore, since a pressure transmission medium for transmitting pressure to the piezoelectric element is not required, it is possible to improve the sensitivity to the pressure change in the measurement atmosphere and improve the response speed to the pressure change. Further, by not using the pressure transmission medium, the pressure measurement sensor can be reduced in size and the manufacturing cost can be reduced.

Hereinafter, a first embodiment of a pressure measuring sensor according to the present invention will be described with reference to FIG.
A combustion pressure sensor (pressure measurement sensor) 1 according to the present embodiment measures a combustion pressure in an internal combustion engine such as a vehicle engine, and has a rectangular parallelepiped shape and a part of the lower surface (one surface) 2A is measured. The piezoelectric element 2 that is the pressure receiving portion 3 in contact with the atmosphere, the pair of electrodes 4 disposed on the side surfaces 2B facing each other, the pressure receiving portion 3 is exposed to the measurement atmosphere, and the piezoelectric element 2 and the pair of electrodes 4 are covered. A protective member 5 and lead wires 6 electrically connected to the pair of electrodes 4 are provided.

  The piezoelectric element 2 is formed of a langasite single crystal formed in a rectangular parallelepiped shape by cutting along the crystal axes X, Y and Z, and the lower surface 2A including the pressure receiving portion 3 has a Y plane. The side surface 2B on which the pair of electrodes 4 that are thin film electrodes formed of silver is disposed is the X plane.

  The protective member 5 is a box-shaped member in which the piezoelectric element 2 and the pair of electrodes 4 are installed. The protective member 5 includes an insulating ceramic 11 formed of an insulating member such as alumina and a conductive member such as stainless steel. And a metal casing 12 that covers the insulating ceramic 11.

The insulating ceramic 11 is hollow and has a substantially rectangular parallelepiped shape, and includes a box portion 13 in which the piezoelectric element 2 and the pair of electrodes 4 are disposed, and a lid portion 14.
The box portion 13 has a pair of electrodes 4 formed on a pair of inner side surfaces 13 </ b> A facing the X surface of the piezoelectric element 2, and the upper ends of the pair of electrodes 4 from the insulating ceramics 11 when the lid portion 14 is attached. It is configured to be exposed.
Further, a rectangular opening 13C is formed on the bottom surface 13B of the box portion 13 so that the pressure receiving portion 3 of the piezoelectric element 2 is exposed in the measurement atmosphere.

Similar to the insulating ceramic 11, the metal housing 12 is hollow and has a substantially rectangular parallelepiped shape, and includes a box portion 15 in which the insulating ceramic 11 is disposed and a lid portion 16.
Similar to the insulating ceramic 11, a rectangular opening 15 </ b> B is formed on the bottom surface 15 </ b> A of the box portion 15 so that the pressure receiving portion 3 of the piezoelectric element 2 comes into contact with the measurement atmosphere.
In addition, a gap 17 is formed between the inner side surface of the box portion 15 and the insulating ceramic 11, and the pressure from the side surface side of the piezoelectric element 2 is relieved by the gap 17 so that the piezoelectric element 2 does not receive pressure. It is made into the composition.
The lid portion 16 has a pair of lead wires 6 that are electrically connected to the pair of electrodes 4 at the approximate center of the portion of the insulating ceramic 11 that contacts the pair of inner side surfaces 13A. A lead wire opening 16A is formed.
The metal casing 12 and the insulating ceramic 11 are sealed with glass so that the measurement atmosphere does not enter the inside.

The lead wire 6 is electrically connected to the upper ends of the pair of electrodes 4 and is disposed in the insulating tube 18 so as not to be in electrical contact with the lid portion 16 of the metal housing 12. It is installed so that the generated charges do not leak except for the pair of electrodes 4 and lead wires 6.
As shown in FIG. 2, one of the pair of lead wires 6 is connected to the charge amplifier 20 and the other is connected to the ground G. The charge amplifier 20 is configured to output an analog voltage signal that is easy to handle from the charge generated by the piezoelectric element 2.

A method for manufacturing the combustion pressure sensor 1 of the present invention configured as described above will be described below.
First, the langasite is processed so that the size of the X plane is, for example, 3.5 mm × 3.5 mm and the side surfaces are the Y plane and the Z plane, thereby forming the piezoelectric element 2.
Next, a pair of electrodes 4 is formed by applying silver paste to the pair of inner side surfaces 13A of the box portion 13 of the insulating ceramic 11 and drying at 150 ° C. for 1 hour. Then, the piezoelectric element 2 is placed in the box portion 13 so that the X surface of the piezoelectric element 2 is in contact with the pair of electrodes 4, and the lid portion 14 is placed on the piezoelectric element 2. The side surface parallel to the X plane of the element 2 is pressed with a load of 1 kg.

Next, the insulating ceramic 11 and the piezoelectric element 2 are placed on a porous zirconia substrate, subjected to binder removal treatment at 300 ° C. for 48 hours using an electric furnace, and further fired at 850 ° C. for 2 hours. Then, the lead wire 6 and the insulating tube 18 are attached to the upper ends of the pair of electrodes 4 exposed from the insulating ceramic 11.
Finally, the assembly thus assembled is placed in the box portion 15 of the metal housing 12 so that the side surface of the insulating ceramic 11 and the inner side surface of the box portion 15 do not contact each other, and the lid portion 16 is further mounted. The insulating ceramics 11 are accommodated by placing them.
At this time, the insulating ceramics 11 and the metal casing 12 are sealed with glass so that the measurement atmosphere does not enter the inside.

Next, a method for using the combustion pressure sensor 1 according to the present embodiment will be described.
First, as shown in FIG. 3, the combustion pressure sensor 1 is inserted into the combustion chamber 33 so as to expose the pressure receiving part 3 from, for example, a position near the ignition plug 31 and the intake port 32 of the gasoline engine 30. Then, the crown shaft 34 is rotated to move the piston 36 connected to the connecting rod 35 up and down. At this time, the gasoline fuel inserted into the combustion chamber 33 burns to generate a pressure F shown in FIG. 2, and this pressure F displaces the pressure receiving portion 3 of the combustion pressure sensor 1. At this time, since the pressure receiving portion 3 is the Y plane on the crystal optics of the piezoelectric element 2, charges generated by the piezoelectric conversion are generated on the side surface 2B which is the X plane on the crystal optics of the piezoelectric element.

Here, when the displacement of the pressure receiving portion 3 is in the direction in which the piezoelectric element 2 is compressed, a negative charge is generated on one side surface of the piezoelectric element 2 and a positive charge is generated on the other side surface. On the other hand, when the displacement of the pressure receiving portion 3 is in the direction in which the piezoelectric element 2 is pulled, a positive charge is generated on one side surface of the piezoelectric element 2 and a negative charge is generated on the other side surface. The charge thus generated is input to the charge amplifier 20 via the electrode 4 and the lead wire 6 in any case, and is converted into an electric signal.
In addition, by providing the gap 17, it is possible to prevent the piezoelectric element 2 from converting the pressure from the side of the piezoelectric element 2 into piezoelectric. Thereby, the pressure only from the pressure receiving part 3 can be measured.

The output analog signal is converted into a pressure value and displayed by an external circuit (not shown) provided in the vehicle.
Thus, by directly detecting the engine torque fluctuation from the measured combustion pressure, it is possible to control EGR, MBT, etc., and to realize the optimum mixture ratio of fuel and air. And lean burn control becomes possible and the fuel consumption of an internal combustion engine can be improved significantly.

In the combustion pressure sensor 1 configured in this way, since the pressure receiving part 3 is exposed in the measurement atmosphere, the pressure applied to the pressure receiving part 3 becomes a mechanical load directly and is applied to the piezoelectric element to charge. generate. Thereby, the pressure transmission loss is reduced, so that the sensitivity can be improved, and the response speed to the pressure change of the measurement atmosphere can be improved.
In addition, since the pair of electrodes 4 are separated from the measurement atmosphere, the pair of electrodes 4 can be prevented from being deteriorated due to corrosion caused by repeated exposure to pressure or high temperature, and deterioration of measurement accuracy can be suppressed.

Further, by using a langasite single crystal for the piezoelectric element 2 that does not have a Curie temperature up to 1470 ° C. and can stably maintain the same crystal structure even in a high temperature state inside the internal combustion engine, the internal combustion engine is free from material deterioration. It is possible to measure pressure directly in
In addition, since the pressure receiving portion 3 is a surface according to the coordinate axis Y on the crystal optics, electric charges are generated on the surface according to the coordinate axis X on the crystal optics, so that the pressure receiving portion 3 and the pair of electrodes 4 are perpendicular to each other. Therefore, more efficient pressure measurement is possible.
In addition, since the area of the pair of electrodes 4 is larger than the area of the pressure receiving portion 3, the generated charges can be detected efficiently, and the sensitivity is improved. The ratio between the pair of electrodes 4 and the area of the pressure receiving portion 3 is desirably 2.0 or more.

Next, a second embodiment of the pressure measurement sensor according to the present invention will be described with reference to FIG. In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
The difference between the second embodiment and the first embodiment is that in the combustion pressure sensor 1 according to the first embodiment, the piezoelectric element 2 is placed in the insulating ceramic 11, and the insulating ceramic 11 is further connected to the metal housing. In contrast to being placed in the body 12, the combustion pressure sensor 40 in the second embodiment is that the piezoelectric element 2 is placed directly in the metal casing 41 as a protective member.

That is, in the combustion pressure sensor 40 in the present embodiment, a pair of electrodes 4 are formed on the side surfaces 2B facing each other as the X surface of the piezoelectric element 2, and the piezoelectric element 2 is the bottom surface of the box portion 42 of the metal casing 41. 42A.
The pair of electrodes 4 is not formed on the end side of the side surface 2B on the bottom surface 41A side so as to be electrically separated from the metal housing 41. In addition, a gap 17 is provided between the piezoelectric element 2 and the inner side surface of the metal housing 41. Similarly to the above, the pressure from the side surface side of the piezoelectric element 2 is relieved by the gap 17, and the piezoelectric element receives pressure. The configuration is such that it does not. In addition, the piezoelectric element 2, the bottom surface 42A, and the lid portion 43 are sealed with glass so that the measurement atmosphere does not enter the interior, as described above.

  The combustion pressure sensor 40 configured in this way has the same operation and effect as the combustion pressure sensor 1 in the first embodiment, but the number of parts is reduced by directly covering the piezoelectric element 2 with the metal casing 41. It can be reduced and the size can be reduced.

Next, a third embodiment of the pressure measurement sensor according to the present invention will be described with reference to FIG. In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
The difference between the third embodiment and the first embodiment is that, in the combustion pressure sensor 1 in the first embodiment, a part of the lower surface 2A of the piezoelectric element 2 is the pressure receiving portion 3, whereas the first embodiment is different from the first embodiment. In the combustion pressure sensor 50 according to the third embodiment, the entire lower surface of the piezoelectric element 2 is the pressure receiving portion 3.

That is, in the combustion pressure sensor 50 according to the present embodiment, the pair of electrodes 4 are arranged on the side surface 2B of the piezoelectric element 2, the pressure receiving portion 3 is exposed by the protective member 51, and the piezoelectric element 2 and the pair of electrodes 4 are covered. Yes.
The protection member 51 is composed of an insulating ceramic 52 and a metal housing 12. The insulating ceramic 52 includes a rectangular cylinder portion 53 and a lid portion 54, and a pair of electrodes 4 are formed on a pair of inner side surfaces 53 </ b> A where the cylinder portion 53 faces the X surface of the piezoelectric element 2. The upper ends of the pair of electrodes 4 are exposed from the insulating ceramic 52 when the lid portion 54 is attached.
The pair of electrodes 4 are not formed on the lower end side of the inner side surface 53A so as not to contact the pressure receiving portion 3, and are protected by the glass 55 so as not to be exposed to the measurement atmosphere.

  The combustion pressure sensor 50 configured as described above has the same operation and effect as the combustion pressure sensor 1 in the first embodiment, but the entire lower surface of the piezoelectric element 2 is the pressure receiving portion 3, so that the measurement atmosphere The accuracy with respect to the pressure change is improved.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, the pressure measurement sensor of the present invention is not limited to being used as a combustion pressure sensor as described above, and may be used for pressure measurement in a high temperature environment.
Moreover, although langasite was used as the piezoelectric element 2, a langamate may be used. Langatate maintains temperature stability comparable to α-quartz, so that the internal pressure can be accurately measured even if it is directly inserted into a high temperature inside the internal combustion engine or the like.
The conductive substance used for the pair of electrodes may be formed of a conductive substance such as silver, platinum, or gold, or a mixture thereof.

It is sectional drawing which shows the combustion pressure sensor in 1st Embodiment concerning this invention. It is a figure which shows the cross section of the combustion pressure sensor in 1st Embodiment concerning this invention, and the structure of charge amplifier. It is sectional drawing which shows the state which attached the combustion pressure sensor in 1st Embodiment concerning this invention to the gasoline engine. It is sectional drawing which shows the combustion pressure sensor in 2nd Embodiment concerning this invention. It is sectional drawing which shows the combustion pressure sensor in 3rd Embodiment concerning this invention.

Explanation of symbols

1, 40, 50 Combustion pressure sensor (pressure measurement sensor)
2 Piezoelectric element 2A Lower surface (one surface)
3 Pressure receiving part 4 Electrodes 5, 51 Protective member

Claims (4)

A piezoelectric element in which at least a part of one flat surface is a pressure receiving portion;
A pair of electrodes disposed so as to be in contact with the piezoelectric element with the piezoelectric element interposed therebetween;
A pressure measurement sensor comprising: a protective member that covers the piezoelectric element and the pair of electrodes in a state where the pressure receiving portion is exposed to a measurement atmosphere.   The pressure measurement sensor according to claim 1, wherein an area of the pair of electrodes is larger than an area of the pressure receiving portion.   The pressure measuring sensor according to claim 1 or 2, wherein the piezoelectric element is composed of a langasite single crystal or a langate single crystal.   The pressure measuring sensor according to claim 3, wherein the one surface is a surface according to a coordinate axis Y on crystal optics.

Images