JPH1197153A - Spark plug with pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug equipped with a pressure sensor, which can decrease heat conduction to a piezoelectric element by a high temp. combustion gas and in which the pyroelectric characteristics and thermal characteristics of the piezoelectric element are improved. SOLUTION: A spark plug A equipped internally with a pressure sensor is composed of an insulator 1, a center electrode 2 fitted in a shaft hole 10 and fixed, a main metal piece 3 with which a seat case 30 is welded consolidatedly and which has a hexagonal part 31, a flange 34 an intermediate cylinder 33, and a front cylinder 32, and a pressure sensor 4 which is located in a ring-shaped space 400, wherein radiation fins 306 are provided on the outside surface of the seat case 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug with a pressure sensor in which a pressure sensor using a piezoelectric element is provided in a mounting bracket of the spark plug.

[0002]

2. Description of the Related Art In order to measure the combustion pressure of an internal combustion engine,
Conventionally, a spark plug with a pressure sensor has been used (Japanese Unexamined Patent Publication (Kokai) No. Hei 6-290853, Japanese Unexamined Utility Model Publication No. Hei2-1829)
No. 1). Note that a single crystal or a sintered body that exhibits a piezoelectric effect when pressure is applied is used for the built-in piezoelectric element.

[0003]

The above prior art has the following problems. [A] Piezoelectric elements have characteristics that are susceptible to thermal changes, such as generation of pyroelectricity due to thermal changes (pyroelectric characteristics) and increase in output due to temperature rise (temperature characteristics). [A] Since the metal case for protecting the piezoelectric element is welded to the mounting seat of the metal shell, it takes a lot of time to manufacture and may fall off when a mechanical shock is applied.

[0004] It is an object of the present invention to provide a spark plug with a pressure sensor with reduced pyroelectric characteristics and temperature characteristics of a piezoelectric element, which can reduce the conduction of heat to a piezoelectric element due to high-temperature combustion gas.

[0005]

In order to solve the above-mentioned problems,
The present invention employs the following configuration. (1) A spark plug with a pressure sensor in which a pressure sensor using a piezoelectric element is provided in a mounting bracket of the spark plug for mounting the spark plug to a cylinder head, wherein A heat dissipating part was provided between the mounting brackets.

(2) A spark plug with a pressure sensor has the configuration described in (1) above, and includes both a mounting seat surface of the mounting bracket and an outer peripheral surface of the mounting bracket excluding the mounting seat surface, or mounting of the mounting bracket. The heat radiating portion was provided on one of the seat surface and the outer peripheral surface of the mounting bracket excluding the mounting seat surface.

(3) A spark plug with a pressure sensor has the configuration of (1) or (2) above, and the shape of the heat radiating portion is a fin shape having irregularities.

(4) The spark plug with a pressure sensor has any one of the above constitutions (1) to (3), and has an insulator with a shaft hole and a center electrode fitted and fixed in the shaft hole. A hexagonal portion provided on the rear end side, a cylindrical portion provided on the distal end side, and a thick flange portion provided between the hexagonal portion and the cylindrical portion, and the insulator is fitted therein. An inner metal shell to be fixed at, a front cylinder portion formed with an engine-provided screw on the outer periphery, a large-diameter rear cylinder portion having a longer axial length than the flange portion, and a combination of the rear cylinder portion and the front cylinder portion. An outer metal shell provided between the outer cylindrical metal part having the same inner diameter as the front cylindrical part and having the same inner diameter as the inner cylindrical metal shell from the cylindrical part to the flange part; A pressure sensor using a piezoelectric element was disposed in a space formed between the end face and the inner end face of the flange.

(5) The spark plug with a pressure sensor has the configuration of (4) above, wherein the outer metallic shell and the inner metallic shell are formed on a part of the inner peripheral surface of the rear cylinder portion and the outer peripheral surface of the flange portion. Are screwed together, and are integrated by welding the tips of the forward tubular portion and the tubular portion.

[0010]

[Action and effect of the invention]

A spark plug with a pressure sensor provided with a pressure sensor using a piezoelectric element is mounted on a cylinder head via a mounting bracket for the spark plug. For this reason, the heat of the high-temperature combustion gas (high temperature) is transmitted to the pressure sensor, which affects the pyroelectric characteristics and temperature characteristics of the piezoelectric element.

The following two types of heat conduction can be considered. Receiving heat from the cylinder head on the mounting surface of the mounting bracket → Piezoelectric element of the pressure sensor Receiving heat due to combustion of the air-fuel mixture on the mounting bracket facing the combustion chamber → Screw neck → Mounting bracket near the mounting seat →
Piezoelectric element of pressure sensor

However, a heat radiating portion is provided on a mounting bracket between the spark plug mounting bracket for mounting the spark plug to the cylinder head and the pressure sensor. Because of this,
Because it can reduce the conduction of heat to the piezoelectric element,
The influence on the pyroelectric characteristics and the temperature characteristics can be prevented.

[0013] [Claim 2] Specifically, the heat radiating portion is provided with a mounting seat surface (a part of the mounting seat surface) of the mounting plug of the spark plug, or a mounting bracket excluding the mounting seat surface (of the mounting bracket). Partly). still,
If the heat radiating portions are provided on both the mounting seat surface (a part of the mounting seat surface) and the mounting bracket excluding the mounting seat surface (a part of the mounting bracket may be provided), the heat to the piezoelectric element can be more effectively heated. Can be reduced, so that the influence on pyroelectric characteristics and temperature characteristics can be further prevented.

[Claim 3] When the heat radiating portion is formed into a fin shape having irregularities, the heat radiating portion can effectively dissipate heat into the air and significantly reduce heat conduction to the piezoelectric element. it can. Therefore, the influence on the pyroelectric characteristics and the temperature characteristics can be largely prevented.

[Invention 4] The inner metal shell has a hexagonal portion, a cylindrical portion, and a thick flange portion, and fixes an insulator in which a center electrode is fitted into a shaft hole. The outer metal shell is formed by a front cylinder having an engine-arranged screw formed on the outer periphery, a large-diameter rear cylinder having an axial length longer than the flange, and a front cylinder provided between the rear cylinder and the front cylinder. A thick cylindrical portion having the same inner diameter as the portion is provided, and an inner metal shell from the cylindrical portion to the flange portion is externally fitted.

The metallic shell of the spark plug has a double structure, and a piezoelectric element is provided in a space formed between the inner end surface of the thick cylindrical portion of the outer metallic shell and the inner end surface of the flange of the inner metallic shell. Since the used pressure sensor is provided, the pressure sensor is not easily damaged, and the pressure sensor can be prevented from falling off.

[Claim 5] A screw formed on a part of the inner peripheral surface of the rear cylinder portion and the outer peripheral surface of the flange portion in a state where the rear end surface of the pressure sensor is temporarily fixed or fixed to the inner end surface of the flange portion of the inner metal shell. Then, the inner metal shell and the outer metal shell are screwed together with the screw formed in the step (1) to dispose the pressure sensor in the space. And
The outer metal shell and the inner metal shell are integrated by seam-welding the tip of the front tubular part and the tip of the tubular part.
For this reason, it is easy to manufacture the spark plug with the pressure sensor, and it is difficult for the pressure sensor to be damaged by a mechanical impact, and it is possible to prevent the pressure sensor from falling off. Before the inner metal shell and the outer metal shell are screwed together, an insulator is fitted into the inner metal shell and fixed, or the outer metal shell and the inner metal shell are integrated and then the inner metal shell is insulated. Insert insulator and fix.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First and second embodiments of the present invention (corresponding to claims 1, 2 and 3) will be described with reference to FIGS. 5 will be described with reference to FIG. Spark plug A with built-in pressure sensor,
B is an insulator 1 having a shaft hole 10 as shown in FIGS.
And a center electrode 2 fitted and fixed in the shaft hole 10.
A metal shell 3 to which a seat case 30 described later is welded;
And a piezoelectric pressure sensor 4 disposed in the annular space 400.

The terminal electrode 5 has a terminal portion 51 projecting from the head end surface 120 of the insulator 1 and a sealing portion (not shown).
Are sealed in the shaft hole 10 and are electrically connected to the center electrode 2. And spark plugs A and B with built-in pressure sensors
Is screwed into a plug mounting hole (not shown) of the cylinder head of the engine via a copper plate-like gasket (not shown) disposed on the front end surface 301 of the seat case 30, and fitted into the terminal portion 51. A high voltage is applied to the terminal electrode 5 via the plug cap (not shown).

The insulator 1 is formed of a ceramic sintered body mainly composed of alumina, and has a leg portion 11 located on the front side.
And a head 12 having a corrugation 121 formed on the outer periphery and located on the rear side, and a large-diameter portion 13 located between the leg length 11 and the head 12. The insulator 1 is fitted and fixed in the metal shell 3 (before welding the seat case 30), and then the pressure sensor 4 is attached and the seat case 30 is welded.

The center electrode 2 includes a sheath material made of a nickel alloy,
Core material (good thermal conductive metal such as copper) enclosed in this sheath material
, And fitted into the shaft hole 10 so that the tip portion 21 protrudes from the insulator tip surface 111, and a base (not shown) is sealed in the shaft hole 10 via a seal glass (not shown). Have been.

The metal shell 3 (made of low-carbon steel) includes a hexagonal portion 31 provided on the rear end side, a front cylindrical portion 32 having an external thread 321 for arranging the engine formed on the outer periphery, and an outer periphery of the external thread 321. An intermediate cylindrical portion 33 having substantially the same outer circumference and located behind the forward cylindrical portion 32 and a hexagonal portion 31-provided between the intermediate cylindrical portion 33 and having a male screw 341 for fitting the seat case 30 on the outer circumference. And a thick flange portion 34.

The seat case 30 made of a good heat conductive metal (copper alloy or the like) is substantially the same as the rear tube portion 302 having a female screw screwed to the male screw 341 formed on the rear inner periphery, and the intermediate tube portion 33. And a seam weld 304, 305
With this, it is integrated with the metal shell 3.

In the spark plug A with a built-in pressure sensor (first embodiment) shown in FIG.
An uneven radiating fin 306 is formed on the outer peripheral surface of No. 03 (corresponding to the outer peripheral surface of the mounting bracket excluding the mounting seat surface). or,
In the spark plug B with a built-in pressure sensor shown in FIG. 3 (second embodiment), uneven heat radiating fins 306 are provided on the mounting seat surface of the forward cylindrical portion 303 of the seat case 30 (corresponding to the mounting seat surface of the mounting bracket). Has formed.

Electrode plate 42 (annular plate shape) and plate packing 43
(Annular plate shape) sandwiching the piezoelectric element 41 (annular plate shape), an insulating plate 44 (annular plate shape) is arranged between the arrangement surface 342 of the flange portion 34 and the electrode plate 42.

The insulating shrink tube 40 includes a piezoelectric element 41
Further, the pressure sensor 4 (piezoelectric element 41, piezoelectric element 41,
The electrode plate 42 and the insulating plate 44) are fitted. The coated lead wire 45 electrically connected to the electrode plate 42 outputs an electric signal that changes in response to a change in the tightening load of the spark plug A with a built-in pressure sensor (a change due to a change in the combustion pressure). ).

Spark plugs A and B with built-in pressure sensor
Is manufactured through the following steps. (1) The insulator 1 in which the terminal electrode 5 and the center electrode 2 are glass-sealed in the shaft hole 10 is fitted and fixed in the metal shell 3.

(2) An insulating shrink tube 40 having a length substantially equal to the total thickness of the insulating plate 44, the electrode plate 42, and the piezoelectric element 41 is attached to one end of the insulating shrink tube 40. Is inserted into the intermediate cylindrical portion 33 so as to abut against.
The pressure sensor 4 (the piezoelectric element 41, the electrode plate 42, and the insulating plate 4) is fitted to the intermediate cylindrical portion 33 in which the insulating contraction tube 40 is inserted.
4) Fit.

(3) When the seat case 30 is screwed into the metal shell 3, an annular space 40 formed by the seat case 30 is formed.
The pressure sensor 4 is built in the area 0. (4) Seam welding 30 between the seat case 30 and the metal shell 3
When the steps 4 and 305 are performed, the metal shell 3 and the seat case 30 are integrated.

Next, a third embodiment of the present invention will be described.
5) will be described with reference to FIG. In the spark plugs A and B with a built-in pressure sensor, the annular space 400 is created by welding the metallic shell 3 to the seat case 30, but the spark plug C with a built-in pressure sensor in the third embodiment is used.
Uses the inner metal shell 6 and the outer metal shell 7 to form an annular space 400 for housing the pressure sensor 4.

The spark plug C with a built-in pressure sensor differs from the spark plugs A and B with a built-in pressure sensor in the following points. The inner metal shell 6 (made of low carbon steel) has a hexagonal portion 61 provided on the rear end side and a small-diameter cylindrical portion 6 provided on the front end side.
2 and a thick flange portion 63 provided between the hexagonal portion 61 and the cylindrical portion 62 and having an external thread 631 formed on the outer periphery. still,
The insulating shrink tube 40 is inserted into the rear end side of the tubular portion 62.

The outer metal shell 7 is a male screw 7 for arranging the engine.
A rear cylindrical portion 71 having an axial length longer than the flange portion 63 and having a female screw 721 formed in a part of the inner circumference, Forward cylinder 71
And a thick-walled cylindrical portion 73 having the same inner diameter as the front-end cylindrical portion 71. The inner metal shell 6 is externally fitted from the cylindrical portion 62 to the flange portion 63.

In the spark plug C having a built-in pressure sensor,
Irradiation fins 731 having irregularities are formed on the outer periphery of the thick cylindrical portion 73 of the outer metal shell 7. In addition, a radiation fin having an uneven shape may be formed on the mounting seat surface of the thick tube portion 73.

The spark plug C with a built-in pressure sensor is manufactured through the following steps. (1) The insulating shrink tube 4 having a length substantially equal to the total thickness of the insulating plate 44, the electrode plate 42, and the piezoelectric element 41
0, one end of the insulating shrink tube 40 is
Is inserted into the cylindrical portion 62 so as to abut the cylindrical portion 62.

(2) The pressure sensor 4 (piezoelectric element 41, electrode plate 4) is inserted into the cylindrical portion 62 in which the insulating contraction tube 40 is inserted.
2, and the insulating plate 44) is fitted.

(3) As shown in FIG. 4, when the outer metal shell 7 is screwed into the inner metal shell 6, the pressure sensor 4 is placed in the annular space 400 formed by the outer metal shell 7 and the inner metal shell 6. Built-in.

(4) When the outer metal shell 7 and the inner metal shell 6 are seam-welded 70, the metal shell 3, the outer metal shell 7 and the inner metal shell 6 are integrated.

(5) The terminal electrode 5 and the center electrode 2 are
The insulator 1 glass-sealed therein is fitted and fixed to the inner metal shell 6.

Next, advantages of the spark plugs A, B, and C having a built-in pressure sensor will be described. [A] In the spark plugs A and B with built-in pressure sensors, uneven radiation fins 306 are formed on the outer peripheral surface of the front tubular portion 303 of the seat case 30 and on the mounting seat surface. This allows
Even if the seat case 30 becomes hot by receiving the heat of the high-temperature combustion gas, the heat can be quickly dissipated into the air, and the temperature rise of the pressure sensor 4 (piezoelectric element 41) is suppressed. .

Therefore, even if the engine is operated for a long time or the output of the engine is increased, the output change rate and the output drift rate of the pressure sensor 4 are small, and an error occurs when measuring the temperature thermal combustion pressure. Can be prevented.

[A] Spark plug C with built-in pressure sensor
Even if the inner metal shell 6 and the outer metal shell 7 become hot due to the heat of the high-temperature combustion gas, the uneven radiating fins 731 are formed on the outer peripheral surface and the mounting seat surface of the thick cylindrical portion 73. Therefore, the heat can be quickly dissipated into the air, so that the temperature rise of the piezoelectric element 41 can be suppressed.

Therefore, even if the engine is operated for a long time or the output of the engine is increased, the output change rate or the output drift rate of the pressure sensor 4 is small, and an error occurs when measuring the temperature thermal combustion pressure. Can be prevented.

[C] Spark plug C with built-in pressure sensor
Is provided with the pressure sensor 4 in the annular space 400, seam-welding the outer metal shell 7 and the inner metal shell 6, and integrating the metal shell 30, the outer metal shell 7, and the inner metal shell 6 with each other. I have. Therefore, the pressure sensor 4 has excellent mechanical strength.
Can be prevented from falling off. Spark plug C with a built-in pressure sensor is a spark plug A with a built-in pressure sensor,
As compared with B, the inner diameter of the pressure sensor 4 is not limited to the outer diameter of the male screw 711 of the outer metal shell 7. Therefore, since the pressure receiving area can be made large, the output of the pressure sensor 4 is also large, and is hardly affected by noise.

[Brief description of the drawings]

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

FIG. 2 is an exploded view of a spark plug A with a built-in pressure sensor.

FIG. 3 is a partial sectional view of a spark plug B with a built-in pressure sensor according to a second embodiment of the present invention.

FIG. 4 is a partial sectional view of a spark plug C with a built-in pressure sensor according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulator 2 Center electrode 4 Pressure sensor 6 Inner metal shell 7 Outer metal shell 10 Shaft hole 41 Piezoelectric element 61 Hexagonal part 62 Cylindrical part 63 Flange part 70, 304, 305 Seam welding 71 Front cylinder part 72 Rear cylinder part 73 Meat Thick cylindrical part 306, 731 Radiation fin (radiation part) 321, 711 Male screw (engine installation screw) 400 Annular space (space) A, B, C Spark plug with built-in pressure sensor (spark plug with pressure sensor)

Claims (5)

[Claims] 1. A spark plug with a pressure sensor in which a pressure sensor using a piezoelectric element is disposed in a mounting bracket of the spark plug for mounting the spark plug to a cylinder head, wherein the mounting bracket and the pressure sensor are provided. A spark plug with a pressure sensor, wherein a heat radiating part is provided in a mounting bracket between the spark plug and the spark plug. 2. The spark plug with a pressure sensor according to claim 1, wherein both the mounting seat of the mounting bracket and the outer peripheral surface of the mounting bracket excluding the mounting seat, or the mounting seat of the mounting bracket or the mounting. A spark plug with a pressure sensor, wherein the heat radiating portion is provided on one of outer peripheral surfaces of a mounting bracket excluding a seat surface. 3. The spark plug with a pressure sensor according to claim 1, wherein the shape of the heat radiating portion is a fin shape having irregularities. 4. The spark plug with a pressure sensor according to claim 1, wherein the insulator has a shaft hole, a center electrode fitted and fixed in the shaft hole, and a rear end side. An inner main body that has a hexagonal portion provided at the front end, a cylindrical portion provided at the distal end side, and a thick flange portion provided between the hexagonal portion and the cylindrical portion, and in which the insulator is fitted and fixed. Metal fittings, a front cylinder portion formed with an engine disposition screw on the outer periphery, a large-diameter rear cylinder portion having a longer axial length than the flange portion, and a rear cylinder portion provided between the rear cylinder portion and the front cylinder portion. An outer metallic shell for externally fitting the inner metallic shell from the cylindrical portion to the flange portion, comprising a thick cylindrical portion having the same inner diameter as the forward cylindrical portion; an inner end surface of the thick cylindrical portion and the flange portion A pressure sensor using a piezoelectric element is disposed in the space formed between the Pressure spark plug with a sensor, wherein the door. 5. The spark plug with a pressure sensor according to claim 4, wherein the outer metallic shell and the inner metallic shell are screwed together with a screw formed on a part of an inner peripheral surface of a rear cylindrical portion and an outer peripheral surface of a flange portion. A spark plug with a pressure sensor, wherein the front end cylindrical portion and the distal end of the cylindrical portion are integrated by welding.