JP3123796B2 - Piezoelectric sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a piezoelectric sensor for detecting physical quantities such as pressure, vibration and acceleration, such as changes in the cylinder internal pressure of an internal combustion engine, using a piezoelectric element.

[0002]

2. Description of the Related Art A detection element such as a piezoelectric element and a pressure transmission rod is housed in a metal shell mounted in a screw hole for mounting a sensor provided in a cylinder block of an internal combustion engine, and a lower end face located in a cylinder. A diaphragm is sealed to the piezoelectric element through the diaphragm and the pressure transmission rod, and an electric signal proportional to the magnitude of the pressure in the cylinder is taken out from the element. Such a piezoelectric sensor is known.

In general, a piezoelectric element made of a ceramic material such as lead zirconate titanate or lead titanate is used as the piezoelectric element.

[0004]

However, such a piezoelectric sensor is exposed to a high combustion temperature (500 ° C.) together with the internal pressure of the cylinder, like a spark plug. Its Curie point is about 250 ° C for lead zirconate titanate and about 350 ° C for lead titanate.
° C and lower than the combustion temperature.
The temperature of the element part becomes extremely high (around 400 ° C.), which degrades the piezoelectric characteristics due to depolarization and the like, and cannot be used. Therefore, usually, a cooling means for maintaining the piezoelectric element at an appropriate temperature is used after being added. For this reason, there were drawbacks in that the structure was complicated, large, and the price was high. Therefore, a piezoelectric sensor including a piezoelectric element having excellent heat resistance and requiring no cooling means has been desired. Further, it is also desired to improve the reduction of the S / N ratio due to the pyroelectric effect of the piezoelectric element.

As described above, a piezoelectric sensor which detects not only the internal pressure of the cylinder of an internal combustion engine but also physical quantities such as pressure, vibration and acceleration by a piezoelectric element is also excellent in heat resistance and S / N. What has a high ratio is desired. An object of the present invention is to provide a piezoelectric sensor that can satisfy such a demand.

[0006]

According to the present invention, a metal shell mounted on a cylinder of an internal combustion engine is provided with a shaft hole having a detection opening located in the cylinder, and a piezoelectric element is provided inside the shaft hole.
In a device in which a detection element such as a pressure transmission rod is housed and the opening end of the shaft hole is sealed with a metal diaphragm, a Curie having a temperature of 500 ° C. or more is used as the piezoelectric element.
Niobium having a point and a Z-axis component of the polarization direction of 20 ° or less
It uses a circular or square plate-shaped piezoelectric element made of a Y-cut single crystal piezoelectric material of lithium oxide and having an outer dimension of 0.3 mm to 1.5 mm.

[0007]

[0008]

[Function] The Curie point of LiNbO ₃ is about 1200 ° C.
The Curie point of LiTaO ₃ is about 650 ° C., and the Curie temperature is higher than 500 ° C. in each case. Therefore, a piezoelectric element made of such a single-crystal piezoelectric material has excellent heat resistance and does not deteriorate the piezoelectric characteristics.

Further, these single crystal materials have poor mechanical strength and may be broken by ordinary cutting methods such as diamond cutter, ultrasonic cutter, laser beam, etc., but the thickness is limited to 0.3 mm to 1.5 mm. This solves such a problem. Here, if it is less than 0.3 mm, it cannot withstand mechanical shock at the time of cutting. If it exceeds 1.5 mm, cracking will occur due to thermal shock during cutting. Therefore preferably 1.0m
m or less is good. Further, in such a piezoelectric sensor, accuracy and parallelism of the pressure receiving surface are required, and usually, the surface is polished in many cases. From this point, 0.3 mm or more is required.

When the Z-axis component of the polarization direction is set to 20 ° or less, a decrease in the S / N ratio due to the pyroelectric effect of the piezoelectric element can be improved.

[0011] Furthermore , X-cut products, Y
After preparing and examining each product,
The piezoelectric material has better piezoelectric characteristics than the X-cut material.
In addition, the mechanical strength is good.

[0012]

FIG. 1 shows an embodiment of the present invention, in which 1 is a male screw 2 screwed to a cylinder block on the outer periphery of a lower end 1a, and a hexagonal portion 3 on the outer periphery of an upper end 1b which is compatible with a tightening tool such as a spanner. And a metal shell having a bolt structure formed with a shaft hole 4 formed therein. This shaft hole 4 has a lower end 1
It consists of connecting holes of different diameter holes 4a, 4b penetrating through the side a and large diameter holes 4c penetrating through the upper end 1b side. The different diameter hole 4
a, 4b, the electric insulating ring 5, the first terminal member 6,
A piezoelectric element 7 having electrodes 7a and 7b on the front and back surfaces,
Are sequentially arranged in layers, and are insulated from the metal shell 1 by an insulating material covering the periphery of these laminates.
In addition, a connecting hand 6 a for connecting to a signal carrying cable 12 described later protrudes from the upper surface of the first terminal member 6 through the insulating ring 5.

Further, the pressure transmitting rod 1 is provided in the hole 4a on the larger diameter side.
0 is inserted, and one end thereof is pressed against the second terminal member 8,
The other end is bonded to a metal diaphragm 11 joined so as to seal the lower end 1a end face of the metal shell 1 secretly. The metal diaphragm 11 needs to have heat resistance, and is preferably made of, for example, a heat-resistant metal material such as Inconel or SUS630.

On the inner surface of the large-diameter hole 4c on the hexagonal portion 3 side,
A stepped seat 4c 'is formed, a metal sleeve 9 having a flange 9a seated thereon is fitted therein, and the annular thin piece 3a protruding from the upper end of the hexagonal portion 3 is crimped by bending inward. I have.

One end of a signal-carrying cable 12 is inserted and fixed inside the metal sleeve 9, and a core wire 12 a protruding from the cable 12 is connected to the first terminal member 6 via a relay conductor 13 covered with insulation. It is connected. However, one electrode of the piezoelectric element 7 is connected to the core wire 12a of the cable 12 through the first terminal member 6 and the relay conductor 13, and the other electrode is connected to the metal shell 1 through the second terminal member 8 and the transmission rod 10. Connected to ground.

Although the configuration described above is conventionally known, the feature of the configuration of the present invention is that the first terminal member 6
The piezoelectric element 7 disposed between the first and second terminal members 8 is made of lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or a single crystal piezoelectric material having the same effect as these single crystal materials. A circular (see FIG. 2) or square (see FIG. 3) plate-like piezoelectric element having an outer dimension of 0.3 mm to 1.5 mm is used.

The piezoelectric element 7 made of a single crystal may be a circular plate, but is preferably a rectangular plate as shown in FIG. 3 in terms of economy and mass productivity. In this case, as shown in FIG. By applying a grid-shaped cutting line t to one large single crystal substrate s, a large number of piezoelectric elements 7, 7... Can be manufactured at once without waste.

Further, the electrodes 7a and 7b to be adhered to the front and back surfaces of the piezoelectric element 7 can be formed by plating, vapor deposition, or the like. However, in order to enhance the adhesion to the piezoelectric element, a metal such as nickel or silver is used. An organic metal ink dispersed in an organic solvent may be used, and this may be formed and printed by printing. In this case, the first and second terminal members 6 and 8 are laminated after printing the organic metal ink. By integrally baking, the adhesion between the piezoelectric element and the electrode and between the electrode and the terminal member is increased, and there is an advantage that the contact failure during use is reliably prevented.

The piezoelectric element 7 is made of lithium niobate and subjected to ultrasonic cutting to the outer diameter as shown in Table 1 below. The inner and outer diameters of the diaphragm were also changed as shown in Table 1. Note that only Sample No. 4 is made of a single crystal piezoelectric material of lithium tantalate. Here, sample No. 2, No. 4,
No. 15 is square and the others are circular. Also, outer diameter φmm
In the samples marked with “H” in the column of, the thickness of the diaphragm
The thickness is 0.1 mm, and the others are 0.2 mm thick.

[Table 1] In the above table, the cylinder volume of the piezoelectric sensor 2000cc, rotation speed 6000 rpm, mounted on an internal combustion engine of a motor vehicle having a nominal specification of the maximum cylinder pressure 70 kg / cm ^2, after testing for 100 hours, investigate the breakage of the piezoelectric element did. Next, when the generated electric charge was examined with respect to the change in the cylinder pressure, Sample No. 1, Sample No. 4 and Sample No. 7 showed slightly poor pressure dependence.
In addition, the temperature dependency was investigated by heating with a band heater, and it was found that Sample No. 1 and Sample No. 7 showed large temperature dependency, and the degree of partial pressure at the diaphragm was largely due to this. did. This is probably because sample No. 4 had poor piezoelectric properties of lithium tantalate.

The sample was stored in a tank containing water at 0 ° C.
The pyroelectric property was tested by alternately immersing the tank in a tank containing silicon oil at 50 ° C. At this time, the samples were No.3 and No.11
The measurements were performed on cut pieces of lithium niobate single crystal at various angles. The result was as shown in FIG. Here, the vertical axis indicates the charge generated by the temperature change, and the horizontal axis indicates the angle θ of the Z-axis component of the polarization direction. From this result, it was found that the smaller the Z-axis component, the better.
Here, the angle θ of the Z-axis component is defined as shown in FIG.
It refers to the angle of deviation of the polarization axis from the plane direction (X, Y directions) in the thickness direction (Z direction). That is, θ = 90 ° refers to one polarized in the same direction as the thickness direction, and θ = 0 ° refers to one polarized in the plane direction.

In order to make the pressure sensitivity equal to or less than 10 atm, it is preferable that the angle θ of the Z-axis component is equal to or less than 20 °, and it is more preferable that the angle θ be equal to or less than 5 atm. Becomes In these cuts, the piezoelectric properties were also sufficient.

As described above, the present invention has an effect that a small and inexpensive piezoelectric sensor having excellent heat resistance, durability or pyroelectricity can be provided on the market.

The above-described embodiment relates to a piezoelectric sensor which is screwed into a cylinder block and is used for detecting the internal pressure of the cylinder. In addition, the piezoelectric sensor which detects a physical quantity such as pressure, vibration, acceleration, etc. In addition, a piezoelectric element having a single crystal structure can be used.

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

According to the piezoelectric sensor of the present invention for detecting the pressure in the engine block, as described above, the piezoelectric element mounted inside the metallic shell has a LiNbO ₃ having a Curie point higher than the combustion temperature in the cylinder. , LiTaO _3, or a single crystal piezoelectric material having the same effect as above, there is no need to cool the piezoelectric element by a cooling means as in the prior art. Further, in the present invention, the thickness of the piezoelectric element is set to 0.3 mm to 1.5 mm.
By this, not only the manufacture is easy by assuming the area ratio with the diaphragm, but also there is no danger that the element is broken by the pressure in the cylinder during use. Therefore, such a configuration has an effect that a small-sized and inexpensive piezoelectric sensor having excellent heat resistance, durability or pyroelectricity can be provided to the market.

In another piezoelectric sensor using a piezoelectric element for converting a physical quantity such as pressure, vibration, acceleration or the like into an electric signal, the piezoelectric element is made of a single crystal piezoelectric material of lithium niobate. By setting the Z-axis component of the polarization direction to 20 ° or less, excellent heat resistance and pyroelectricity are obtained even at high temperatures, and stable characteristics are produced. As described above, the present invention has an effect that a small and inexpensive piezoelectric sensor having excellent heat resistance, durability or pyroelectricity can be provided to the market.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a piezoelectric sensor showing one embodiment of the present invention.

FIG. 2 is a perspective view of a piezoelectric element 7 formed in a circular shape.

FIG. 3 is a perspective view of a piezoelectric element 7 formed in a rectangular shape.

FIG. 4 is a perspective view showing a cutting means of the piezoelectric element 7;

FIG. 5 is a graph showing the influence of a pyroelectric effect on cut products of various angles of a lithium niobate single crystal.

FIG. 6 is a coordinate diagram showing the concept of the angle θ of the Z-axis component.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 4 Shaft hole 7 Piezoelectric element 11 Metal diaphragm

Continuation of the front page (56) References JP-A-1-174199 (JP, A) JP-A-2-59635 (JP, A) JP-A-62-181572 (JP, A) JP-A-62-219808 (JP) , A) Fully open 1988-84539 (JP, U) Fully open 1986-126620 (JP, U) Fully open 1987-35243 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB G01L 23/10 G01L 9/08 G01L 1/16

Claims (1)

(57) [Claims] 1. A metal shell mounted on a cylinder of an internal combustion engine has a shaft hole having a detection opening located in the cylinder.
A piezoelectric element within the axial bore, housing a sensing element such as a pressure transmission rod, further an open end of the axial bore, in which is formed by sealing a metal diaphragm, as the piezoelectric element, 50
It has a Curie point at a temperature of 0 ° C. or more, and has a Z
Lithium niobate single crystal piezoelectric material with an axial component of 20 ° or less
And a circular or square plate-like piezoelectric element having an outer dimension of 0.3 mm to 1.5 mm in thickness and made of a Y-cut product as described above .