JPH031475A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a spark plug excellent in spark durability and having a long lifetime by molding iridium powder, defatting, and sintering under vacuum or non-oxidative or reductive atmosphere so that the sintering density will be over 90%, and thereby forming a firing part electrode. CONSTITUTION:Iridium powder is subjected to molding using a press, CIP molding, extrusion molding, or injection molding, followed by defatting and sintering under vacuum or a non-oxidating or reductive atmosphere so that the sintering density will be over 90%. Thus a firing part electrode 6 is yielded. The shape is flange-equipped 11, wherein the tip dia. (a) is 0.8mm, base dia. (b) 1.2mm, overall length C 2mm, base length (d) 0.5mm, and flange angle alpha 45deg. The sintering temp. under the sintering process shall preferably range between 1700-2200 deg.C. A sintering density of at least 90% is necessary, as too low density causes voids remaining much in the fabricated electrode material to localize the temp. rise due to the high energy of spark discharge, which should promote consumption of the electrode material.

Description

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

(Prior Art) In recent years, as the performance of internal combustion engines has improved, there has been an increasing demand for long-life spark plugs with excellent spark wear resistance from the viewpoint of maintenance-free performance. In order to extend the life of spark plugs, it is well known that the center electrode is made of a heat-resistant, corrosion-resistant metal such as a Ni alloy, and precious metals are used in the spark discharge part of the outer electrode. Therefore, it has been proposed to use rod-shaped chips or thin plate chips mainly made of noble metal materials such as Pt and Pt-Ir alloys by joining them by electric resistance welding, electron beam welding, or laser welding.

(Problem to be solved by the invention) However, the former method requires a large amount of expensive precious metal material, resulting in high costs, while the latter method involves punching disc-shaped chips from a precious metal plate.
Since these are to be bonded together, there are many parts other than the chips, which deteriorates the yield by 30% and causes high costs.

Moreover, the Pt-Ir alloy produced by the melting method has both elongation and brittleness, and has a high melting point of over 2300°C, making it difficult to process. Furthermore, when cutting the material, cracks tend to occur due to shearing force, making stable processing into complex shapes impossible. Further, there is a problem in that electric discharge machining takes time because the melting point of the pt-Ir alloy is high.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional devices, and uses a noble metal material as the chip of the spark discharge part, which does not waste precious metals, reduces costs, and has excellent spark consumption properties. This aims to extend the life of the plug.

(Means for solving the problem) To this end, the firing part electrode is made of iridium, and the iridium powder is molded by die press molding, CIP molding, extrusion molding, injection molding, etc., degreased, and molded in a vacuum or It is sintered in a non-oxidizing or reducing atmosphere so that the sintered density is 90% or more.

(Function) With the above configuration, there is no wastage of precious metals and mass production is possible, which reduces costs, and the ignition has a complex shape that is difficult to mold using the melting method and has excellent spark consumption. By using a partial electrode tip, it is possible to extend the life of the spark plug.

(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 a first embodiment of the present invention, and this spark plug for an internal combustion engine (1) has a spark plug [1] manufactured as described below to serve as a spark discharge part at the tip. (6) is the surrounding alumina or nitride ceramic (AIN, Sis N4) insulator (2).
) It is inserted into the tip hole of the shaft hole (8) and fired at the same time as the insulator (2). This insulator (2) consists of a metal shell (3) in which an outer electrode (4) is placed in a position facing the threaded part (5) used when attaching it to an internal combustion engine and the firing part electrode (6), and an insulator. A metal intermediate electrode (7) is electrically resistance welded to the firing part electrode (6) in the shaft hole (8) in (2).
), or an intermediate electrode (7) filled with conductive ceramic powder or ceramic powder coated with metal.
) is sealed with a glass seal (9).
10). And the firing part electrode (
6) is a molded resin made of iridium powder by mold press molding, CIP molding, extrusion molding, injection molding, etc.
Sintered in vacuum or in a non-oxidizing or reducing atmosphere to a sintered density of 90% or more, the diameter of the tip (a) is 0.811 m and the diameter of the base (b) is 0.811 m, as shown in Figure 3. )
1.2mm, total length (c) 2 cm, base length (d) 0.5m
m, and has a flange (11) with a flange angle α of 45°.

Table 1 shows the relationship between the press molding density ratio, the firing atmosphere, and the sintered density under the conditions. When creating the firing part electrode (6) material, if the firing atmosphere is air, iridium will be oxidized. The sintering process must be carried out under a non-oxidizing, preferably reducing atmosphere or vacuum, and the sintering temperature in the sintering process must be 170
The temperature is 0 to 2200°C, and more preferably 2000'C or higher. Furthermore, if the sintered density is low, many pores remaining in the created electrode material will localize the temperature rise due to the high energy of the spark discharge, accelerating the wear of the electrode material.
The sintered density is required to be at least 90% as shown in FIG. Moreover, at that time, by performing secondary firing as shown in Table 2, the sintered density can be further increased.

With the above configuration, commercially available iridium metal powder is press-molded as the firing part electrode (6) with a density ratio of 66.3%.
After pressing the mold, it was heated to 2200℃ in a hydrogen atmosphere so that
The sintered product was sintered for 60 minutes to reach a sintered density of 92.5%, then secondary fired at 1400°C for 60 minutes in an Ar atmosphere, and hot isostatically formed into the flanged shape shown in Figure 3. When we conducted a spark consumption test using sample K, we found that
It was possible to obtain excellent spark wear resistance equivalent to that of a Pt-Ir alloy made by the melting method.

FIG. 4 shows a spark plug (IA) showing a second embodiment of the present invention, in which the shape of the firing part electrode (6) is the same as that of the fifth embodiment.
As shown in the figure, diameter (e) 0.5m11+, length (f) 1
．． The firing part electrode (6) is placed in the recessed part (13) at the tip of the center electrode (12) made of a nickel alloy with copper sealed inside, and is subjected to electron beam welding. Alternatively, they are joined by laser welding (L). This center electrode (12) is inserted into the shaft hole (8) of the insulator (2), locked at the flange (14), and similarly heat-sealed with a glass seal (9).
This is a spark plug fixed to the inner cavity of the metal shell (3). Furthermore, the configuration of this ignition part electrode (6) is also useful in igniter plugs. In addition to being able to obtain a long-life plug, there is no wastage of materials, making it suitable for mass production, and reducing costs.

12...center electrode

Claims (1)

[Claims] A spark plug for an internal combustion engine having an ignition part electrode formed by molding iridium powder, degreasing it, and sintering it in a vacuum or in a non-oxidizing or reducing atmosphere to a sintering density of 90% or more.