JPH02152183A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To permit heat to be diffused sufficiently, and thereby contrive to enhance withstand voltage property which is in need by making up an insulating body out of ceramics in a nitride family, concurrently holding a spark discharge section made of a specified material in a specified shape by means of its sinter contracting force at the time of sintering, and thereby arranging an intermediate electrode made of a specified material. CONSTITUTION:An insulating body 2 is made up out of ceramics excellent in heat conductivity such as aluminum nitride and the like, and it is formed into a stepped cylindrical shape with a small diameter section smaller than 1.5mm in diameter by means of sinter contracting force at the time of sintering so that a spark discharge section 6 is held wherein the section is made of a noble material such as an iridium alloy and the like with a melting point equal to or more than 2000 deg.C which is made up by sintering a powdered press body. An intermediate electrode 7 is arranged between the discharge section 6 and a glass seal section 8 at the tip end of a terminal electrode 9, and the electrode is made up from the press body of conductive powder made of the simple substance or mixture of respective W, Mo, Ti, Cr, Zr, Ta, Nb and the like or respective carbide and/or silicide of these, or the surface of these substance is plated with the other metal excellent in acid resistance so that high performance is thereby maintained for the long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a spark plug used in an internal combustion engine.

(Prior Art) Conventionally, insulators constituting spark plugs used in internal combustion engines are generally made mainly of A I 203 (alumina).

(Problem to be Solved by the Invention) However, in the above conventional product, the insulator has A1
When using Al203 (alumina) as a main component, it has a low thermal conductivity, so when used in internal combustion engines, which have become more efficient in recent years, it is difficult to burn due to the low thermal conductivity of Al203 (alumina) itself. The combustion heat generated inside the room cannot be dissipated outwards sufficiently smoothly, and problems such as pre-ignition occur due to the heated insulator. Therefore, it has been proposed that the insulator be made of nitride-based ceramics, which have higher thermal conductivity, and that this high thermal conductivity allows the insulator to efficiently dissipate heat received from the combustion chamber to the outside. Since the system ceramic itself lacks voltage resistance, it has the disadvantage that it is not possible to apply a higher voltage to strengthen the spark discharge to ignite the fuel. In order to improve the voltage resistance, it is conceivable to increase the thickness of the insulator, but this would significantly increase the cost. Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional products, and aims to construct an insulator using nitride ceramics having excellent heat dissipation, and to improve the insufficient voltage resistance.

(Means for solving the problem) To this end, an insulator is constructed of nitride ceramics, and the sintering shrinkage force during firing of the nitride ceramics is applied to noble metal materials (for example, iridium alloys, etc.) with a melting point of 2000°C or higher. ), and this spark discharge part is formed into a stepped cylindrical shape consisting of a small diameter part and a large diameter part, and the diameter of the small diameter part is 5 mm or less,
Alternatively, it may be formed by sintering a pressed powder body.

Further, conductive powder (for example, linear expansion coefficient is 9.OX 106/°C or less) is pressed between the spark discharge part made of a noble metal material obtained by sintering the powder press body and the glass seal part at the tip of the terminal electrode. An intermediate electrode of the conductive powder body is arranged, and the powder of this conductive powder press body contains W, Mo, Ti, Cr, Z.
r, Ta, Nb, etc., or their carbides, silicides, alone or in mixtures, and furthermore, W, Mo, T.
The surface of primary particles such as i, Cr, Zr, Ta, N+) or granulated powders thereof is coated with other metals having excellent oxidation resistance.

(Function) With the above configuration, by making the diameter of the intermediate electrode small, it is possible to relatively increase the thickness of the insulator using nitride-based ceramics whose withstand voltage decreases at high temperatures. In addition, precious metal materials (
(For example, sintered iridium alloy or pressed powder body)
By using this, consumption due to spark discharge can be minimized, so the voltage applied to the insulator due to the increase in discharge voltage can be suppressed, and penetration of the insulator, which is likely to occur under high voltage, can be prevented.

(Example) This invention will be further explained with reference to embodiments shown in the drawings.

(1) is a spark plug for an internal combustion engine, which is an embodiment of the present invention. 5) is composed of a main metal fitting (3) for arranging the main body (3) and an insulator (2) made of nitride-based ceramics,
A terminal electrode (9) and a glass seal (
8), and an intermediate electrode (7) are enclosed,
Due to the sintering contraction force during firing of this insulator (2), a spark discharge part (6) made of a noble metal material (for example, iridium or iridium alloy) with a melting point of 2000°C or higher is formed at the tip of the intermediate electrode (7). It is something to keep.

Moreover, this spark discharge part (6) has a small diameter part (11) and a large diameter part (
12) with a stepped cylindrical shape, and a small diameter part (1
1) The diameter of 1) can be made to be 1.5 mm or less, but since the noble metal materials used (for example, iridium and iridium alloys) are difficult to process as headers, powder pressing of precious metal materials is required in consideration of mass production. Shaping the body, sintering can be used.

On the other hand, the nitride-based ceramics used for this insulator (2) include aluminum nitride and silicon nitride, which have good thermal conductivity. Since the firing temperature is extremely high, for example, after a powder press body made of iridium powder into a stepped cylindrical shape with a mold press is attached to the raw material obtained through the cutting process, under a nitrogen atmosphere, 1850 ~ It is sintered at 2000°C, and the spark discharge part (6) is held by the sintering contraction force generated in the green base of the insulator (2) during sintering. Furthermore, a spark discharge part (
6) and the glass seal (8) at the tip of the terminal electrode (9). In order to alleviate the occurrence, for example, the coefficient of linear expansion from 0 to 100°C is 9.OX 10-6/°C or less, preferably 6.OX 1
It is 0-6/℃ or less. ) By using a pressed body, the close contact with the spark discharge part (6) is improved. In addition to MoSi2, the conductive powder used for the intermediate electrode (7) includes W, Mo, T, i,
Cr, Zr, Ta, Nb, etc. can be used, and in order to prevent oxidation by combustion gas, carbides and silicides thereof may be used alone or in combination, and further W, Mo,
The surface of primary particles such as Ti, Cr, Zr, Ta, Nb, etc., or their granulated powders, is coated with other oxidation-resistant N! , C
A material coated with a metal such as r, Pd or PT may also be used. Moreover, as shown in Figure 3,
The intermediate electrode (7) is coated with these different conductive powders 1'
! (7'), (7'') by making it a laminated structure,
A more stable structure can be obtained.

Since the embodiment of the present invention has the above configuration, by making the diameter of the intermediate electrode (7) small, it is possible to use the nitride ceramic insulator (2), which has a relatively low withstand voltage at high temperatures.
), and by using a noble metal material (for example, an iridium alloy or a sintered powder press) for the spark discharge part (6), wear due to spark discharge can be minimized. Therefore, the voltage applied to the insulator (2) due to the increase in discharge voltage can be suppressed, and penetration of the insulator, which is likely to occur under high voltage, can be prevented.

Therefore, when comparing the embodiment of the present invention with the conventional one, it was found that while the withstand voltage performance was equivalent to that of an insulator made of Al2O3, the discharge voltage was 20 to 30% lower. It has been confirmed that it sufficiently prevents body penetration, and it has also been tested in a 2000cc turbo engine for 500 hours of cold and hot cyclic operation (10 minutes full throttle → 10 minutes off)? As a result, spark consumption is also suppressed and similar problems do not occur.

(Effects of the invention) As described above, by using electrodes that improve withstand voltage performance and minimize spark consumption that leads to an increase in discharge voltage, the performance of the spark plug itself is improved as performance increases. It has the excellent effect of being able to be maintained for a long period of time and further simplifying maintenance for the user to a minimum.

[Brief explanation of the drawing]

FIG. 1 shows an internal combustion engine 8! which is an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the main part of the leap spark plug, and FIG. 3 is an enlarged cross-sectional view of the main part of another embodiment. 1...Spark plug for internal combustion engine 2...Insulator 3
... Metal shell 4 ... Threaded part 5 ... Outer electrode 6
...Spark discharge part 7...Intermediate electrode? '7"・
...Coating layer 8...Glass seal 9...Terminal electrode lO...Shaft hole 11...Small diameter portion 12...Large diameter portion Patent applicant Agent Patent attorney Yukihiro Fujiki San! Figure diagram

Claims (7)

[Claims] (1) A spark for an internal combustion engine in which the insulator is composed of nitride ceramics, and a spark discharge part made of a noble metal material with a melting point of 2000°C or higher is maintained by the sintering contraction force of the nitride ceramics during firing. plug. (2) The spark plug for an internal combustion engine according to claim (1), wherein the noble metal material of the spark discharge portion, which is held by the sintering contraction force during firing of the nitride-based ceramic constituting the insulator, is an iridium alloy. (3) The spark for an internal combustion engine according to claim (1) or (2), wherein the spark discharge part has a stepped cylindrical shape consisting of a small diameter part and a large diameter part, and the diameter of the small diameter part is 1.5 mm or less. plug. (4) Claim (1), (2) or (3), wherein the precious metal material constituting the spark discharge part is made by sintering a pressed powder body.
) Spark plugs for internal combustion engines. (5) Claim (1) wherein an intermediate electrode made of a conductive pressed powder body is arranged between a spark discharge part made of a noble metal material obtained by sintering a pressed powder body and a glass seal part at the tip of the terminal electrode.
, (2), (3) or (4). (6) Claim (1) wherein the powder of the conductive powder press constituting the intermediate electrode is made of W, Mo, Ti, Cr, Zr, Ta, Nb, etc., or their carbides or silicides alone or in mixtures.
), (2), (3), (4), or (5). (7) The powder of the conductive powder press body constituting the intermediate electrode contains primary particles such as W, Mo, Ti, Cr, Zr, Ta, and Nb, or the surface of these granulated powders is coated with other oxidation-resistant materials. Claims (1), (2), (3), (4), (5) covered with a metal having excellent properties or having a laminated structure in the axial direction.
), or the spark plug for an internal combustion engine according to (6).