Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Reexamination Certificate
1999-01-14
2001-10-16
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
C313S118000, C445S001000
Reexamination Certificate
active
06304022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spark plug used in an internal combustion engine.
2. Description of the Related Art
In recent years, there have been proposed many variations of a spark plug in which a noble metal chip containing, as a main component, Pt, Ir, or the like is welded to the tip end of an electrode in order to improve spark consumption resistance.
However, in recent years, the temperature within a combustion chamber has tended to become higher with an improvement in the performance of an internal combustion engine. Also, more and more engines have been equipped with a spark plug having a spark discharge portion projecting into the interior of a combustion chamber in order to improve ignition performance. Under these circumstances, the spark discharge portion of a spark plug is exposed to high temperature, with the result that consumption of the noble metal chip of the spark discharge portion proceeds more readily. This tendency is especially significant in spark plugs using an Ir chip, which is susceptible to oxidation/volatilization at high temperature.
The consumption of such a chip at high temperature is considered to occur as follows. The chip undergoes a sputtering-like phenomenon caused by sparks as well as oxidation/corrosion or oxidation/volatilization, so that grain boundaries become fragile, and detachment of grains proceeds due to action of sparks. In this connection, Laid-Open Japanese Patent Applications Nos. 8-37082 and 8-45643 propose methods in which the microstructure of the noble metal chip is controlled such that flat crystal grains are layered in a direction perpendicular to a spark discharge surface, thereby increasing the length of the path along which corrosion of grain boundaries proceeds. As a result, the detachment of the grains of chip is suppressed. However, corrosion and grain detachment cannot be effectively prevented through mere control of the crystal grain morphology of a noble metal chip.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a spark plug having a spark discharge portion formed through attachment of a noble metal chip, in which durability of the spark discharge portion is improved through control of the alloy structure of the spark discharge portion from a point of view other than crystal grain morphology.
To achieve the above-mentioned object, the spark plug according to the present invention includes a center electrode; an insulator provided outside the center electrode; a metallic shell provided outside the insulator; a ground electrode disposed to face the center electrode; and a spark discharge portion fixed on at least one of the center electrode and the ground electrode for defining a spark discharge gap. To solve the above-mentioned problems, the spark discharge portion is formed from a noble metal alloy containing a main component element selected from among Ir, Pt, and Rh, and at least one additional component element differing from the main component element. In the noble metal alloy, the additional component element is distributed such that stripes of high concentration regions and low concentration regions extend in a direction perpendicular to the direction of voltage application.
The spark discharge portion is formed through welding of a chip made of the above-mentioned noble metal alloy to a ground electrode and/or a center electrode. In the present specification, the “spark discharge portion” denotes a portion of a welded chip that is free from variations in composition caused by welding (i.e. a portion other than the portion of the welded chip which has alloyed with a material of the ground electrode or center electrode due to welding).
REFERENCES:
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patent: 4670684 (1987-06-01), Kagawa et al.
patent: 4743793 (1988-05-01), Toya et al.
patent: 4786267 (1988-11-01), Toya et al.
patent: 5990602 (1999-11-01), Katoh et al.
patent: 6121719 (2000-09-01), Matsutani et al.
patent: 61-124082 (1986-06-01), None
patent: 61-237385 (1986-10-01), None
patent: 62-88287 (1987-04-01), None
patent: 62-226592 (1987-05-01), None
patent: 61-124083 (1989-06-01), None
patent: 3-176978 (1991-07-01), None
patent: 8-45643 (1996-02-01), None
patent: 8-37082 (1996-02-01), None
Brinks Hofer Gilson & Lione
Day Michael H.
Gerike Matthew J.
NGK Spark Plug Co. Ltd.
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