JPH06132066A - Park plug with built-in pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a pressure sensor-built in spark plug of high detecting accuracy with small generation of a pyroelectron while excellent in durability with a high Curie point of a piezoelectric element. CONSTITUTION:A piezoelectric element is arranged in a main unit metal fixture 1 having a through hole 11, insulator 2, center electrode 3, between the main unit metal fixture and a gasket, in a through hole 12 provided in the main unit metal fixture 1 and sealed while positioning a detection opening in a cylinder, or between the main unit metal fixture and the insulator 2. In a spark plug 100 with a built-in pressure sensor 4 having the piezoelectric element 5 for converting a change of pressure, received by the relative displacement in the axial direction between these members, into an electric signal, the piezoelectric element 5 is formed of monocrystal piezoelectric material of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). In the piezoelectric element 5, a flat plate shape of 0.3mm to 1.5mm thickness is presented from a view point of manufacture, further with a 20 deg. or less deflection preferable in a Z-axis direction in a polarization direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug incorporating a pressure sensor for detecting combustion pressure in a cylinder of an engine.

[0002]

2. Description of the Related Art In order to improve fuel efficiency and purify exhaust gas, the engine is operated stably at a lean air-fuel ratio, or the exhaust gas recirculation amount is increased to improve fuel efficiency in the stoichiometric air-fuel ratio range.
It is necessary to detect the combustion pressure in the cylinder and keep the torque fluctuation below a certain value. Therefore, a spark plug with a built-in pressure sensor, which incorporates a pressure sensor for detecting combustion pressure fluctuations in the cylinder, is used to detect engine torque fluctuations and knocking.

[0003]

A conventional spark plug with a built-in pressure sensor uses a lead zirconate titanate-based or lead titanate-based ceramic as a piezoelectric element.
These piezoelectric elements have a low Curie point and inferior heat resistance and durability, and the output floats (drifts) due to the action of pyroelectrons generated at high temperatures, and the ratio of the noise component N to the signal component S of the output S / There is a drawback that the measurement accuracy cannot be increased because the N ratio is large. An object of the present invention is to provide a spark plug with a built-in pressure sensor, in which the piezoelectric element has a high Curie point and is excellent in durability, and the generation of pyroelectrons is small and the detection accuracy is high.

[0004]

The spark plug with a built-in pressure sensor according to the present invention is such that a center electrode is fitted in the shaft hole of an insulator with a shaft hole, and the insulator is used as a metal shell provided with a through hole. An electric signal is applied to the fitted spark plug between the pressure receiving member that receives the combustion pressure in the cylinder of the spark plug and a member adjacent to the member, and the pressure change that is caused by the relative axial displacement between these members. In a spark plug with a built-in pressure sensor that incorporates a piezoelectric element for conversion, the piezoelectric element is lithium niobate (LiNbO ₃ )
Alternatively, it is characterized by being made of a single crystal piezoelectric material of lithium tantalate (LiTaO ₃ ).

The piezoelectric element is provided, for example, between the metal shell and a gasket mounted on the metal shell, the detection opening is located in the cylinder, and the detection opening is sealed with a metal diaphragm. It is disposed between the pressure receiving member and the metal shell in the through hole, or between the metal shell and the insulator. From the viewpoint of manufacturing, the piezoelectric element preferably has an annular plate shape with a thickness of 0.3 mm to 1.5 mm. The piezoelectric element can reduce the output drift to the minimum when the Z-axis component of the polarization direction is zero, and the deflection of the polarization direction in the Z-axis direction is preferably 20 ° or less from the viewpoint of reducing the output drift. .

[0006]

According to the present invention, since the piezoelectric element made of a single crystal piezoelectric material of lithium niobate or lithium tantalate has a Curie point of 500 ° C. or higher, it has sufficient heat resistance even when incorporated in a spark plug. And
Excellent in durability because thermal deterioration of piezoelectric characteristics hardly occurs. Further, by setting the Z-axis component of the polarization direction to be 20 ° or less, the pyroelectric effect is less likely to occur, and the floating output and the S / N ratio can be reduced, so that the detection accuracy can be increased. The thickness of the plate-shaped piezoelectric element is set to 0.3 mm to 1.5 mm because the above-mentioned single crystal material has poor mechanical strength. If it is less than 0.3 mm, it is easily damaged when cut, and if it exceeds 1.5 mm. This is due to a manufacturing constraint that cracks occur due to thermal shock during cutting.

[0007]

1 shows a spark plug 100 with a built-in pressure sensor according to a first embodiment of the present invention. This spark plug 100 has a through hole 11 for a spark plug inside.
And a metal shell 1 in which a pressure sensor through hole 12 is provided in parallel.
Have. The through hole 11 and the through hole 12 are inclined at a predetermined angle, and both of them are open to a recess 13 formed at the tip of the metal shell 1. The metal shell 1 has a substantially L-shaped ground electrode 14 welded to its tip, an attachment screw 15 to the engine is formed on the outer periphery of the tip, and the through hole 1 is formed at the rear end.
A thin-walled cylinder portion 16 having an edge 1 protruding rearward is provided, and a hexagonal head 17 is formed on the outer periphery of the middle portion of the thin-walled cylinder portion 16.

The through hole 11 is composed of a small tip portion 111, an intermediate middle diameter portion 112, and a large rear end portion 113.
Insulator 2 with 1 is fitted. The insulator 2
Has a front end 22 protruding into the recess 13, a rear part 23 protruding rearward from the metal shell 1, and a middle-sized body 24 having a slightly larger diameter, which is held by caulking the thin-walled cylinder 16 inward. Has been done. The center electrode 3 is inserted into and fixed to the shaft hole 21. A tip portion 31 of the center electrode 3 projects from the tip of the insulator 2, and a rear end thereof is connected to a terminal 32 via a conductive glass 34 with a resistor 33 sandwiched in a shaft hole 21 of the insulator 2. .

As shown in FIGS. 1 and 2, the through hole 12
Is composed of a tip middle diameter portion 121, a middle small diameter portion 122, and a rear end large diameter portion 123, and a thin-walled tubular caulking portion 124 is extended from the rear end edge to form the middle small diameter portion 122 and the rear end large diameter portion. 1
A step 125 is provided between the steps 23 and 23. Pressure sensor 4
Is provided in the through hole 12, and has a pressure receiving rod 42 with a screw hole 41 fitted in the tip middle diameter portion 121;
Inserted from the large rear end diameter portion 123, the small intermediate diameter portion 12
2 and a screw 43 screwed into the screw hole 41. At the tip of the pressure receiving rod 42, a thin plate portion 44 having a large diameter and a disc shape
The outer periphery of the thin plate portion 44 is laser-welded to the wall surface of the tip opening 126 of the through hole 12. This laser welding keeps the cylinder and the through hole 12 airtight, and the thin plate portion 44 acts as a diaphragm whose surface serves as a pressure receiving surface for combustion pressure. A tube 45 made of heat resistant insulation is covered on the upper part of the screw 43.

Between the head portion (pressure-receiving member) 46 of the screw 43 and the step (member adjacent to the pressure-receiving member) 125 of the through hole 12, the piezoelectric element unit 5 is fixed with a constant tightening torque.
0 has been concluded. In this piezoelectric element unit 50, an annular electrode plate 52 with a lead wire 51 is arranged in the middle of the annular plate piezoelectric elements 5 and 5, and the outer surfaces of the piezoelectric elements 5 and 5 are annular plate metal packings 53 and 53. It is sandwiched. A sleeve sleeve 54 for holding the insulating coating of the lead wire 51 is fixed to the tubular caulking portion 124 by crimping the edge of the tubular caulking portion 124.

As shown in FIG. 3, the piezoelectric element 5 is an annular plate strip having a thickness of 0.5 mm, an inner diameter of 2.0 mm and an outer diameter of 4.0 mm, and is made of a lithium niobate or lithium tantalate single crystal piezoelectric material. Has been formed. The piezoelectric element 5 is polarized in the plane direction of the plate thickness (X and Y directions),
There is no component in the Z direction (plate thickness direction), or the polarization direction is set to 20 ° or less.

Generally, in a piezoelectric element, a potential difference occurs on both surfaces due to a pyroelectric effect as the temperature rises, and an output drift occurs. As a result, if the temperature rises during measurement, the zero point floats, which makes it difficult to accurately measure the pressure in the cylinder of the engine. However, in the piezoelectric element 5 made of the single crystal piezoelectric material of lithium niobate or lithium tantalate of the above-mentioned embodiment, the generation of pyroelectrons is small, and the polarization is made completely in the plane direction of the plate-shaped piezoelectric element 5 as described above. If there is, the above potential difference hardly occurs. Also, the smaller the Z-direction component of the polarization direction due to the polarization process, the less the number of pyroelectrons, and the deflection of the polarization direction in the Z-direction is 2
If it is 0 ° or less, the combustion pressure of the cylinder is measured sufficiently accurately. FIG. 4 shows the drift rate of the zero point with respect to the temperature change in the first embodiment.

FIG. 5 shows a second embodiment. In this embodiment, the pressure sensor 4 is mounted on the large-diameter body portion (pressure receiving member) 61 of the metal shell 6 of the spark plug. A through hole 63 is provided in the large-diameter body portion 61 in the axial direction, and the front end surface and the outer periphery of the body portion 61 have an L-shaped cross section.
It's wrapped in 4. In the pressure sensor 4, the piezoelectric element 66 is fitted into the distal end portion of the through hole 63 via the annular plate packing 65, and the electrode plate 68 with the lead wire 67 is provided behind the piezoelectric element 66.
It has a structure fitted through 9. The piezoelectric element 66, the lead wire 67, and the electrode plate 68 are sealed with the through hole 63 and the adhesive 81, and the piezoelectric element 66 has a thickness of 1.0 m.
m, the outer diameter is 19.0 mm, and the inner diameter is 15.0 mm. FIG. 6 shows the drift rate of the zero point with respect to the temperature change in the first embodiment.

FIG. 7 shows a third embodiment. In this embodiment, the pressure sensor 4 is provided between the metal shell (pressure receiving member) 7 of the spark plug and the insulator (member adjacent to the pressure receiving member) 2.
I am wearing. The metallic shell 7 has a large-diameter body portion 71 formed with an internal screw 72, and the lid screw 7 screwed to the internal screw 72.
3 has been concluded. Similar to the first embodiment, the piezoelectric element unit 50 has an electrode plate 52 with a lead wire 51 in the middle, and two annular plate-shaped piezoelectric elements in which both outer surfaces are sandwiched by annular plate metal packings 53, 53. 5 and 5 are sandwiched. The piezoelectric element 5 in this embodiment has a thickness of 1.0 mm and an outer shape 1.
It has an annular plate shape of 5.0 mm and an inner diameter of 11.0 mm.

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug with a built-in pressure sensor according to a first embodiment.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a perspective view of a piezoelectric element.

FIG. 4 is a correlation diagram between the temperature of the piezoelectric element according to the first embodiment and the zero-point drift amount of output.

FIG. 5 is a sectional view of a spark plug with a built-in pressure sensor according to a second embodiment.

FIG. 6 is a correlation diagram between the temperature of the piezoelectric element and the zero-point drift amount of output according to the second example.

FIG. 7 is a sectional view of a spark plug with a built-in pressure sensor according to a third embodiment.

[Explanation of symbols]

 1, 6, 7 Metal shell 2 Insulator 3 Center electrode 4 Pressure sensor 5 Piezoelectric element 11 Spark plug through hole 12 Pressure sensor through hole 100 Spark plug

Claims (3)

[Claims] 1. A spark plug in which a center electrode is fitted in the shaft hole of an insulator with a shaft hole, and the insulator is fitted in a metal shell provided with a through hole, in a cylinder of the spark plug. In a spark plug with a built-in pressure sensor, between a member that receives the combustion pressure of and a member that is adjacent to the member, a piezoelectric element that incorporates a piezoelectric element that converts a pressure change received by the relative displacement in the axial direction between these members into an electric signal, The spark plug with a built-in pressure sensor, wherein the piezoelectric element is made of a single crystal piezoelectric material of lithium niobate or lithium tantalate. 2. The piezoelectric element according to claim 1, wherein the piezoelectric element has a thickness of 0.
A spark plug with a built-in pressure sensor, which has a plate shape of 3 mm to 1.5 mm. 3. The spark plug with a built-in pressure sensor according to claim 2, wherein the polarization of the plate-shaped piezoelectric element in the Z-axis direction is 20 ° or less.