JPH02281586A - Spark plug for use in internal combustion engine - Google Patents

Abstract

PURPOSE:To maintain both the durability and electrical conductivity of a spark plug at a high level by sealing a ceramic powder having its surface covered with metal in a space between a glass seal sealed inside a shaft hole provided through the inside portion of an insulator and the upper portion of a spark plug portion so that the space is filled therewith. CONSTITUTION:A spark plug 1 for use in an internal combustion engine is equipped with an end terminal 12 which is sealed together with a glass seal 11 inside a shaft hole 13 provided between a spark discharge portion 6 joined to the end of an insulator 2 and a glass seal 11. A ceramic powder 10 of alumina having its surface covered with a metal 9 via wet plating method is sealed as intermediate electrode in an axial hole 8 provided between the spark discharge portion 6 joined to the end of the insulator 2 and the glass seal 11 and thus the hole 8 is filled therewith. The ceramic powder 10 put therein as intermediate electrode reduces the difference in coefficient of linear expansion generated between the powder and ceramic forming the insulator 2 to a minimum, and so cracking of the insulator 2 that may be caused by thermal stress caused by heat generated by burning inside a burning chamber is prevented, and, since the ceramic powder 10 is covered with the metal 9 of high corrosion resistance such as Ni and the like, oxidation expansion of the insulator 2 is prevented.

Description

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

(Prior Art) Conventionally, in spark plugs used in internal combustion engines,
Electrodes are required to have high thermal conductivity and strength at high temperatures to efficiently conduct heat generated by combustion, so nickel alloys with a copper core sealed inside are generally used. Furthermore, in consideration of workability, etc., it has been proposed to use nickel or tungsten powder as the intermediate electrode.

(Problem to be Solved by the Invention) However, in the above-mentioned conventional device, when a nickel alloy or the like is used for the electrode, it is subject to high-temperature oxidation due to the heat generated by combustion of combustion gas in the combustion chamber, making it difficult to use for a long time. The spark gap is likely to increase due to spark consumption, deformation of the electrode shaft, etc. Furthermore, in the case of an intermediate electrode filled with nickel or tungsten powder, a heat load test conducted by repeated combustion and cooling shows that the insulator and the nickel or tungsten powder filled in the intermediate electrode are different from each other. Thermal stress is generated due to the difference in the linear expansion coefficient of This may cause problems such as damage to the insulator, resulting in a lack of reliability. Therefore, the present invention aims to improve the drawbacks of the conventional type described in E, and aims to prevent damage to the insulator due to heat generated by an internal combustion engine.

(Means for solving the problem) For this purpose, a spark discharge part made of a precious metal and an insulator are closely joined, and a glass seal sealed in a shaft hole provided inside the insulator and an upper part of the spark discharge part are bonded together. the surface between
For example, it is filled and sealed with ceramic powder coated with a metal such as nickel, chromium, or cobalt.

(Function) With the above configuration, the metal covering the surface of the ceramic powder can be filled as an intermediate electrode while maintaining electrical conductivity.
The encapsulated ceramic powder can minimize the difference in coefficient of linear expansion that conventionally occurs between metal and the ceramic that makes up the insulator, preventing cracks in the insulator caused by thermal stress. In addition, since the spark discharge part made of precious metal and the insulator are tightly bonded, combustion gas does not enter due to the expansion of the metal in the spark discharge part at the tip of the insulator, and insulation caused by oxidation expansion is prevented. It can also prevent cracks caused by mechanical stress on the body.

(Example) This invention will be further explained with reference to an example shown in the drawings. (1) is a spark plug for an internal combustion engine which is an example of the invention. A spark discharge part (6) consisting of is tightly bonded and joined, and an insulator (2) of alumina or nitride ceramic (AIN, 5F3N4) and a screw part (4) used for attachment to an internal combustion engine are provided on the outer periphery. , and further the spark discharge section (6).
The metal shell (
3) and a terminal electrode (12) sealed in a shaft hole (13) in an insulator (2) together with a glass seal (11). Then, a metal (9) is placed on the surface as an intermediate electrode by wet plating in the shaft hole (8) between the spark discharge part (6) and the glass seal (11), which are joined to the tip of the insulator (2). Alumina coated with A
IN , S l 3 N 4 , B N , T i
N or BeO is used. ) of ceramic powder (10
) is filled and enclosed. This lick minimizes the difference in linear expansion coefficient between the ceramic powder (10) filled and enclosed as the intermediate electrode and the ceramic constituting the insulator (2), so that the combustion inside the combustion chamber is minimized. Insulators ( caused by thermal stress due to heat generated by
2) can be prevented from cracking, and since the tip of the insulator (2) and the spark discharge part (6) made of precious metal are closely joined, combustion gas will not enter the shaft hole (8) due to thermal expansion. Moreover, since the ceramic powder (10) is coated with a highly corrosion-resistant metal, such as nickel, chromium, or cobalt, mechanical damage to the insulator (2) caused by oxidative expansion may occur. It also prevents the loading of physical stress.
Moreover, the increase in cost can be minimized.

Furthermore, ceramic powder (10
) is too large, the spark discharge part at the tip (6
) Since a sufficient contact area cannot be ensured, poor conductivity is likely to occur, so the particle size of the ceramic powder is preferably 10 to 120 μm.

In addition, the upper part of the spark discharge part (6) made of noble metal is bonded to the tip so as to be in close contact with the insulator (2), that is, the shaft hole (
By arranging the flange (7) on the side 8), a contact area with the ceramic powder (10) filled as an intermediate electrode is ensured, and damage caused by stress caused by thermal expansion is prevented. The diameter of the axial hole in which the ceramic powder (10) is filled and enclosed is preferably 1.5 mm or less.

On the other hand, by using iridium as a noble metal in the spark discharge part (6) joined to the tip of the insulator (2), it has a high melting point, has high thermal durability, and can reduce spark consumption. It is possible. In addition, when molding the spark discharge part (6) using iridium, after press-molding the iridium powder with a mold, the molded body is placed in a non-oxidizing atmosphere, for example, in order to improve impact resistance during combustion. hydrogen, nitrogen atmosphere), 1400-200
The firing is performed at 0°C for 1 to 6 hours so that the firing density becomes 90% or more, and this is to prevent cost increases due to damage such as cracks that occur when header processing is performed on melted iridium products. Furthermore, this spark discharge part (6)
Alternatively, a cermet electrode manufactured by coating alumina powder with platinum and then sintering it may be used.

Note that the spark discharge part (
6), the spark discharge part (6) is inserted into the small tip diameter hole (14) of the shaft hole (8) in the insulator (2) before sintering, and the insulator (2) is heated for 1500 min in an atmospheric atmosphere. ~1700℃
By sintering the insulator (2), the insulator (2) is joined together by the heat shrinkage force. Furthermore, the ceramic powder (10) is filled and enclosed as an intermediate electrode in the shaft hole (8) of the insulator (2), which is formed by joining the spark discharge part (6) made of a noble metal to the tip of the ceramic powder (10). Add 50w of nickel to the same alumina spray granulated powder as the insulator (2) by weight.
It is formed as an intermediate electrode by sequentially press-filling the material coated with t% in several steps,
By press-filling the ceramic powder (10) coated with the metal (9) in several steps in this way, no voids are generated in the shaft hole (8) and sufficient conductivity is ensured. become something that can be done.

Therefore, a spark plug for an internal combustion engine (1) which is an embodiment of the present invention, and a spark plug for an internal combustion engine in which the intermediate electrode is filled with a Kovar sphere or a platinum-coated tungsten powder as a comparative product. , in an actual machine, that is, a 2000cc, 6-cylinder engine, 500
A thermal cycle test was conducted for 3000 cycles in which one cycle was 0 rpm (fully open) x 1 minute → idle link x 1 minute, and the degree of damage to the insulator (2) was compared, and it was found that this is an example of the present invention. Spark plugs for internal combustion engines (
In 1), while the comparative product easily cracked after 10 to 50 cycles, no cracking occurred at all, and the effect was sufficiently recognized (Table). Furthermore, a desktop accelerated spark discharge test (200 times/second, spark energy x induction time: 50 m)
J x 200 hours), ceramic powder (
It was confirmed that there was no deterioration in the metal nickel layer (9) coated with 10), and that spark discharge was performed stably.

Table (Effects of the Invention) As described above, even if a metal or cermet electrode that cannot be welded is used for the ignition part electrode, there is no need to bond it to the intermediate electrode, so it has high reliability and durability. This has the excellent effect of ensuring electrical conductivity and improving mass productivity.

[Brief explanation of drawings]

FIG. 1 is an enlarged partial cross-sectional view of a spark plug for an internal combustion engine according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of a main part thereof, and FIG. 3 is a partial cross-sectional view of a powder material. 1...Spark plug for internal combustion engine 2...Insulator 6
...Spark discharge part 7...Flame part 8, 13...Shaft hole 9...Gold 8.10...Ceramic powder 11...
Glass seal 14...-Tip small diameter hole patent applicant Agent Patent attorney Miyuki Fujiki 2, jJ/

Claims (4)

[Claims] (1) A spark discharge part made of a precious metal and an insulator are closely bonded, and the surface is coated with metal between the glass seal enclosed in the shaft hole provided inside the insulator and the upper part of the spark discharge part. A spark plug for internal combustion engines that is filled and sealed with ceramic powder. (2) The ceramic powder to be filled and enclosed between the glass seal and the upper part of the spark discharge part has a surface coated with nickel,
coated with either chromium or cobalt, and
The spark plug for an internal combustion engine according to claim 1, wherein the ceramic powder has a particle size of 10 to 120 μm. (3) A flange is provided on the axial hole insertion side of the precious metal spark discharge part that is tightly bonded to the insulator, and the diameter of the axial hole in which the ceramic powder is filled and enclosed is 1.5 mm or less. The spark plug for an internal combustion engine according to (1) or (2). (4) Claims (1), (2) or (4), wherein the spark discharge part is made of iridium, and its shape is formed by powder press molding and then firing to a firing density of 90% or more.
3), the spark plug for an internal combustion engine as described.