JPH0963746A - Spark plug - Google Patents

Abstract

(57) An object of the present invention is to provide a spark plug 1 capable of quickly radiating heat of a center electrode 5 to a ceramic 15 on a tip side of an insulator 4. SOLUTION: The spark plug 1 has a split type insulator 4 and a tip side ceramic 15 made of aluminum nitride on the spark discharge side. An adhesive 23 mainly composed of a silicon varnish having a thermal conductivity of 4 W / m · k or more and a heat resistance of 400 ° C. or more is filled in a gap between the tip side ceramic 15 and the center electrode 5. The heat of the center electrode 5 is transferred through the adhesive 23 to the tip side ceramic 1 having excellent thermal conductivity.
5, the temperature of the center electrode 5 is lowered and the heat resistance of the spark plug 1 is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for performing spark discharge in an internal combustion engine or the like, and more particularly to heat dissipation technology for a center electrode.

[0002]

2. Description of the Related Art Spark plugs often employ an insulator mainly composed of alumina. Since alumina has a low thermal conductivity, the tip (spark discharge side) of the insulator becomes high in temperature when heat is drawn from the center electrode, and that portion becomes a hot point, and preignition easily occurs. Therefore, there has been proposed a spark plug in which aluminum nitride, which is more excellent in heat resistance and thermal conductivity than alumina, is used on the ignition side of an insulator that becomes high temperature to improve preignition resistance.

However, since the center electrode has a structure that is inserted into the shaft hole of the insulator, a gap is created between the center electrode and the insulator, and as a result, heat of the insulator is generated. It was difficult to reach the center electrode, and as a result, preignition could not be sufficiently suppressed.

[0004]

As a technique for solving this problem, an inorganic adhesive such as Sumiceram, Aron ceramic, or a phosphate-based adhesive is filled in the gap between the center electrode and the insulator. However, a technique has been proposed in which the heat of the center electrode is released to the insulator by filling the gap.

However, these inorganic adhesives have poor thermal conductivity (the thermal conductivity of SUMISERAM is 1.25 W / m.multidot.m).
k, the thermal conductivity of Aron ceramic is 0.79W / m
k, three bond 2.55 W / m · k, aluminum hydroxide adhesive 1.25 W / m · k), the heat of the center electrode cannot be quickly released to the insulator, leading to the occurrence of preignition. In addition, the heat stored in the insulator cannot be quickly released to the center electrode, resulting in a high temperature of the insulator, which causes a problem of preignition.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a spark plug capable of radiating heat from a center electrode to an insulator with high conductivity.

[0007]

The spark plug of the present invention employs the following technical means. [Means of Claim 1] A spark plug comprises a tubular metallic shell, a tubular insulator fixed in the metallic shell and having a shaft hole therein, and a rod-shaped insulator inserted into the shaft hole. A center electrode is provided, and an adhesive having a thermal conductivity of 4 W / m · k or more is filled in at least a part of a gap between the insulator and the center electrode.

[Means for Claim 2] In the spark plug according to claim 1, the adhesive is a silicon-based resin and Al.
₂ O ₃ , MgO, SiO ₂ , ZnO ₂ , BaO, Sr
It is characterized by comprising at least one kind of insulating metal oxide powder such as O, CaO, Y ₂ O ₃ and the like and good heat conductive powder such as BN and AlN.

[Means for Claim 3] In the spark plug according to claim 2, the adhesive contains 2 parts of the metal oxide powder.
It is characterized in that 0 to 40% by weight, the good thermal conductive powder is 0.5 to 5% by weight, and the balance is the silicon resin.

[0010]

The operation and effect of the present invention is such that at least a part of the gap between the insulator and the center electrode is filled with an adhesive having a thermal conductivity of 4 W / m · k or more, so that the heat conductivity between the center electrode and the insulator is improved. Improved, if the center electrode is warmer than the insulator,
The heat of the center electrode is quickly transferred to the insulator, and conversely, when the temperature of the insulator is higher than that of the center electrode, the heat of the insulator is quickly transferred to the center electrode.

As described above, since the thermal conductivity between the center electrode and the insulator is improved, the heat of the center electrode can be quickly released to the insulator and the heat of the insulator can be quickly released to the center electrode. The heat of the center electrode or the insulator falls faster than before. As a result, the temperature on the spark discharge side can be quickly dissipated, and the heat resistance of the spark plug can be improved.

Since the adhesive is composed of a silicon resin, an insulating metal oxide powder, and a good thermal conductive powder, the adhesive has excellent heat resistance and a thermal conductivity of 4 W / m · k or more. It can be an agent.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a spark plug of the present invention will be described with reference to the drawings. [Structure of First Embodiment] FIG. 1 is a cross-sectional view of the front end side of a spark plug showing a first embodiment.

The spark plug 1 has a main structure as follows.
A split-type insulator 4 having a substantially cylindrical metal shell 2 that is fastened to an internal combustion engine such as a gasoline engine, and a hole (hereinafter, shaft hole 3) fixed in the metal shell 2 and extending in the axial direction.
A center electrode 5 fixed to the tip side (combustion chamber side) of the insulator 4 in the shaft hole 3; and an outer electrode 6 joined to the end of the metal shell 2.

In the shaft hole 3 of the insulator 4, in addition to the center electrode 5, a terminal electrode 7, which is fixed to the rear end side (anti-combustion chamber side) of the insulator 4, the center electrode 5 and the terminal electrode 7, a monolithic resistor 8 disposed between the central electrode 5, the terminal electrode 7 and the monolithic resistor 8 is fixed by a conductive glass seal 9 enclosed in the shaft hole 3 of the insulator 4. Has been done.

The metal shell 2 is grounded to the engine by being fastened to an internal combustion engine (not shown), around which the screw portion 11 screwed into the internal combustion engine and the metal shell 2 are fastened. A hexagonal part 12 into which a tool is fitted is formed. Also, on the inner circumference of the metal shell 2,
An annular pedestal 14 for receiving the packing 13 is provided. The packing 13 is a ring made of a metal such as nickel or iron, and is pressed between the pedestal 14 of the metal shell 2 and the insulator 4 (outer peripheral step 21 described later) to make the metal shell 2 and the insulator The heat of the insulator 4 is guided to the metal shell 2 while closing the gap with the metal shell 4.

The insulator 4 is composed of a front end side ceramic 15 held on the front end side of the metallic shell 2 and a rear end side ceramic 16 held on the rear end side of the metallic shell 2.
The tip side ceramic 15 is exposed to the combustion gas in the combustion chamber, and is made of aluminum nitride having excellent heat resistance and thermal conductivity. The rear end side ceramic 16 is made of alumina having excellent mechanical strength.

At the front end of the tip side ceramic 15, there is formed a tapered leg long portion 17 which forms a gas volume with the metal shell 2. The rear end of the front side ceramic 15 is provided with a recess 18 into which the rear side ceramic 16 is fitted. In addition, the rear end surface 1 of the front side ceramic 15
Reference numeral 9 denotes a ring-shaped flat surface, which firmly contacts the rear end side ceramic 16 when the metal shell 2 is caulked. An annular outer peripheral step 21 is formed on the outer periphery of the tip side ceramic 15 so as to abut the packing 13. The heat of the tip side ceramic 15 is quickly transmitted to the metal shell 2 through the packing 13.

On the inner periphery of the tip side ceramic 15, a tip side shaft hole 22 is formed to pass through the tip side of the center electrode 5. The inner diameter of the tip-side shaft hole 22 is set to be slightly larger than the outer diameter of the center electrode 5 in order to insert the tip side of the center electrode 5. An adhesive 23 for quickly transmitting the heat of the center electrode 5 to the tip side ceramic 15 is filled in a gap between the tip side shaft hole 22 in the tip side ceramic 15 and the center electrode 5. This adhesive 23 is an adhesive mainly composed of a silicon varnish having a thermal conductivity of 4 W / m · k or more and a heat resistance of 400 ° C. or more, which will be described in detail later.

At the front end of the rear end side ceramic 16, there is provided a convex portion 24 which is fitted into the recess 18 at the rear end of the front end side ceramic 15. The annular flat surface portion 25 on the outer side of the convex portion 24 firmly contacts the rear end side ceramic 16 at the time of caulking. A step 26 that receives the crimping force of the metal shell 2 is provided on the outer periphery of the rear end side ceramic 16.
Two rings 27, 28 and a ceramic filling powder 29 are interposed between the swaged portion of the metal shell 2 and the step 26.

A rear end side axial hole 31 in which the rear end side of the center electrode 5, the terminal electrode 7, the monolithic resistor 8 and the glass seal 9 are arranged is formed on the inner periphery of the rear end side ceramic 16. . The inner diameter of the rear end side axial hole 31 is set slightly larger than the outer diameter of the center electrode 5 in order to insert the center electrode 5. The rear end side axial hole 31 has a small diameter on the front end side, and the flange portion 33 of the center electrode 5 is pressed against the step portion 32 between the large diameter portion and the small diameter portion so that the center electrode 5 is locked. It is provided in. The terminal electrode 7, the monolithic resistor 8 and the glass seal 9 are arranged in the large diameter portion of the rear end side axial hole 31, and the rear end side of the center electrode 5 is inserted into the small diameter portion of the rear end side axial hole 31. To be done.

The outer electrode 6 is made of nickel or nickel alloy (for example, Inconel), which is made by bending a rod-shaped metal having a substantially rectangular cross section into a substantially L shape and has excellent heat resistance and corrosion resistance. Is joined by.
The end of the outer electrode 6 is disposed so as to face the tip of the center electrode 5, and a predetermined spark discharge gap G is formed between the end of the outer electrode 6 and the tip of the center electrode 5.

The center electrode 5 is fixed to the combustion chamber side in the shaft hole 3 (front end side shaft hole 22, rear end side shaft hole 31) of the insulator 4 (front end side ceramic 15, rear end side ceramic 16). It is rod-shaped and has a tip protruding from the end of the insulator 4.
On the periphery of the rear end side of the center electrode 5, the above-mentioned flange portion 33 which is engaged with the step portion 32 of the insulator 4 and which projects in the radial direction is provided. The center electrode 5 is a composite electrode in which copper or copper alloy having excellent thermal conductivity is arranged inside a nickel alloy having excellent heat resistance and corrosion resistance.

The terminal electrode 7 includes an ignition device (not shown) for generating a high voltage at ignition timing and a high voltage cord (not shown).
It is connected through. Also, the glass seal 9
The monolithic resistor 8 prevents noise from being generated when a high voltage is applied, and when assembled, is softened and solidified to fix the center electrode 5 and the terminal electrode 7 in the shaft hole 3 of the insulator 4. To do.

The adhesive 23 filled in the gap between the tip side ceramic 15 and the center electrode 5 has a thermal conductivity of 4 W.
In order to achieve a heat resistance of 400 ° C. or higher and a heat resistance of 400 m / k or more, a silicon resin, an insulating metal oxide powder, and a good heat conductive powder are mixed. Specifically, the adhesive 23
Is Al ₂ O ₃ , MgO, SiO ₂ , ZnO ₂ , Ba
20 to 40% by weight of at least one insulating metal oxide powder such as O, SrO, CaO and Y ₂ O ₃ , BN,
It is a mixture of 0.5 to 5% by weight of good thermal conductive powder such as AlN and the balance of silicon-based resin, and has a thermal conductivity of 4
It becomes ~ 6 W / m · k.

[Experimental data] Various mixing ratios of silicon varnish (silicon resin), Al ₂ O ₃ powder (metal oxide powder), and BN powder (good thermal conductive powder) which constitute the adhesive 23 were changed. The heat resistance of the spark plug 1 was measured by using the adhesive 23 that was manufactured as a prototype and was used for the spark plug 1 (type in which the length of the leg portion 17 is 20 mm). The experimental method was to use the spark plug 1 with the adhesive 23 manufactured as a prototype.
The cylinder was mounted on a cylinder internal combustion engine, and the ignition advance was sequentially advanced during operation at 5000 rpm to generate preignition, and heat resistance was evaluated by the advance (ignition timing) at which the preignition occurred. The results of this heat resistance test are shown in Table 1 below.

Silicon varnish and Al ₂ O ₃ in the table
The numerical values of the powder and the BN powder show% by weight. A crank angle ▲ indicates that pre-ignition has occurred, and a circle indicates that pre-ignition has not occurred. A rating of ◯ indicates extremely excellent heat resistance, and a rating of Δ indicates that the heat conductivity of the adhesive 23 is 4 or more and the heat resistance is improved as compared with the conventional product, but the heat resistance is inferior to the evaluation ◯. , × indicate the sample in which sufficient heat resistance was not obtained as in the case of sample number 12 (using the inorganic adhesive 23 as the adhesive 23), and XX indicates the sample in which the adhesive 23 was not mixed well. In addition,
When BN is less than 0.5% by weight, sufficient thermal conductivity cannot be obtained. When it exceeds 5% by weight, or when Al ₂ O ₃ is 40% by weight.
If it exceeds 5% by weight, the mixture does not mix well and the adhesive 23 cannot be formed. In addition to Al ₂ O ₃ , the metal oxide powders include MgO, SiO ₂ , ZnO ₂ , BaO, SrO, and C.
Similar effects can be obtained when aO and Y ₂ O ₃ powders are used, or when two or more kinds thereof are mixed and used. In addition, the good heat-electricity powder is AlN instead of BN.
The same effect can be obtained by using powder.

[0028]

[Table 1]

[Effects of the Embodiment] As is clear from the above experimental results, the insulator 4 (the tip side ceramic 15),
By filling the gap with the center electrode 5 with the adhesive 23 having a thermal conductivity of 4 W / m · k or more, heat resistance is improved as compared with the conventional case. This is because the heat of the center electrode 5 is quick,
This is to prevent the preignition from occurring because the temperature of the central electrode 5 is reduced more quickly than in the conventional case by being transferred to the adhesive 23 → insulator 4 (ceramic 15 on the tip side) → packing 13 → metal shell 2 → internal combustion engine.

[Second Embodiment] FIG. 2 is a cross-sectional view of the spark plug 1 at the tip side showing a second embodiment. In the above-described first embodiment, the example in which the adhesive 23 is filled in the entire gap between the tip end side axial hole 22 of the tip end side ceramic 15 and the center electrode 5 is shown. The adhesive 23 is filled only in the gap between the rear end side and the center electrode 5, and the front end side axial hole 2
The adhesive 23 is not filled in the gap between the tip side of 2 and the center electrode 5.

When the adhesive 23 is filled up to the spark discharge side, the adhesive 23 may be exposed to combustion gas and oxidatively expanded to crack the insulator 4. However, the adhesive 23 is not filled up on the spark discharge side. As a result, it is possible to avoid the problem that the adhesive 23 expands and damages the insulator 4.

[Third Embodiment] FIG. 3 is a sectional view of the spark plug 1 on the front end side showing a third embodiment. First, above
In the second embodiment, an example in which the insulator 4 is a split type is shown, but the insulator 4 of this embodiment is a single body made of alumina. Alumina has a lower thermal conductivity than aluminum nitride, and heat is accumulated near the rear end side of the center electrode 5 and becomes higher in temperature than the center electrode 5. Therefore, in this embodiment, the adhesive 23 is filled between the rear end side of the center electrode 5 and the insulator 4 to quickly release the heat stored in the insulator 4 to the center electrode 5, resulting in a spark plug. The heat of 1 is reduced to improve heat resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a front end side of a spark plug (first
Example).

FIG. 2 is a sectional view of a tip side of a spark plug (second
Example).

FIG. 3 is a cross-sectional view of a tip side of a spark plug (third part)
Example).

[Explanation of symbols]

 1 Spark plug 2 Metal shell 3 Shaft hole 4 Insulator 5 Center electrode 23 Adhesive

Claims (3)

[Claims] 1. A cylindrical metallic shell, a cylindrical insulator fixed in the metallic shell and having a shaft hole therein, and a rod-shaped center electrode inserted into the shaft hole. In the spark plug, at least a part of the gap between the insulator and the center electrode is filled with an adhesive having a thermal conductivity of 4 W / m · k or more. 2. The spark plug according to claim 1, wherein the adhesive is a silicon-based resin, Al ₂ O ₃ and Mg.
O, SiO ₂ , ZnO ₂ , BaO, SrO, CaO, Y
A spark plug comprising at least one insulating metal oxide powder such as ₂ O ₃ and a good thermal conductive powder such as BN and AlN. 3. The spark plug according to claim 2, wherein the adhesive is 20 to 40% by weight of the metal oxide powder, 0.5 to 5% by weight of the good thermal conductive powder, and the balance is the silicon-based material. A spark plug characterized by being made of resin.