Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Reexamination Certificate
1999-12-21
2001-10-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
C313S118000, C313S141000
Reexamination Certificate
active
06307307
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority of Japanese Patent Applications No. H.10-363027 filed on Dec. 21, 1998 and No. H 11-324569 filed on Nov. 15, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spark plug for internal combustion engine provided with a ground electrode composed of an Ir alloy element and a Ni or Fe base alloy base element, in particular, applicable to the engine for a co-generation system, a delivery pump for pressurized gas and a vehicle.
2. Description of Related Art
A conventional spark plug has generally a center electrode fitted through an insulator into a housing and a ground electrode fixed to the housing. The center electrode partly exposed out of the end of the insulator faces the ground electrode.
To improve the life time and the performance of the spark plug, a noble metal chip is bonded to the ground electrode (generally, Ni base alloy) to constitute a spark discharge spot at the spark discharge gap.
Conventionally, a platinum (Pt) alloy has been widely used as material for the noble metal chip. However, the Pt alloy has a drawback that the consumption resistance thereof is considered not to be sufficient to meet more sever engine specifications for vehicles in future. Therefor, the use of the iridium (Ir) alloy having a melting point higher than that of the Pt alloy has been recently proposed, as shown in JP-A-8-298178.
For bonding an element made of Ir alloy including more than 50 weight percent Ir (hereinafter merely called Ir alloy) to the ground electrode, a resistance welding is not applicable to secure sufficient bonding strength and a laser beam welding is preferable because the chip and the electrode may be sufficiently molten due to the high density of its energy. However, the portion where Ni and Ir are molten is located near the spark discharge gap and, further, as the Ir content of the molten portion is less than that of the chip of Ir alloy, a spark consumption resistance of the molten portion is worse, compared to that of the chip of Ir alloy itself. Therefore, the molten portion tends to be more rapidly consumed so that the chip of Ir alloy may be left out of the ground electrode.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above mentioned problems, and an object of the present invention is to provide a spark having a construction that molten portions formed by bonding an Ir alloy element to a base element of a ground electrode made of Ni base alloy or Fe base alloy, where Ir alloy and Ni or Fe base alloy are mixed with each other, are located outside a region within which the spark is regularly discharged. As a result, the Ir alloy element can be hardly left out of the ground electrode so that a longer consumption life time of the spark plug may be assured.
To achieve the above object, the spark plug is composed of a center electrode, a housing holding and being insulated with the center electrode so as to expose a leading end of the center electrode out of an end of the housing, and a ground electrode composed of a base element made of Ni or Fe base alloy base and an Ir alloy element. A first leading end of the base element is fixed to the end of the housing at a horizontal side of the leading end of the center electrode. A second leading end of the base element is bonded to a first leading end of the Ir alloy element. Both of the Ir alloy element and the base element extend substantially perpendicular to an axis of the housing so that a second leading end of the Ir alloy element may face the leading end of the center electrode with the spark discharge gap therebetween.
Preferably, a shortest distance L between the center electrode and the molten portions is larger than, more preferably larger by more than 0.2 mm, than a shortest distance G of the spark discharge gap. When the shortest distance L is larger than the shortest distance G as mentioned above, the spark discharge may be prevented from being directed toward the molten portions located on a side of the center electrode so that a consumption of the molten portions may be remarkably limited.
Further, it is preferable to secure a higher bonding strength of the Ni or Fe base alloy base element and the Ir alloy element that a depth of the molten portion entered into the Ir alloy element is not thinner than 0.2 mm but the molten portion does not penetrate through the Ir alloy element. As a result, the Ir alloy element can be hardly left out of the ground electrode so that a longer consumption life time of the spark plug may be assured.
Furthermore, it is preferable to rigidly fix the Ir alloy element to the base element that the second leading end of the base element is provided with a cup shaped hole into which the first leading end of the Ir alloy element is inserted and bonded by welding at a portion where the base element is overlapped with the Ir alloy element.
The Ir alloy mentioned above is preferably more than 50 weight percent Ir including at least one of Rh, Pt, Ru, Pd and W.
REFERENCES:
patent: 4700103 (1987-10-01), Yamaguchi et al.
patent: 5461276 (1995-10-01), Matsutani et al.
patent: 5574329 (1996-11-01), Kagawa
patent: 6078129 (2000-06-01), Gotou et al.
patent: 567940 (1958-05-01), None
patent: 04-104491 (1992-04-01), None
patent: 08-298178 (1996-11-01), None
Clove Thelma Sheree
Denso Corporation
Patel Nimeshkumar D.
Pillsbury & Winthrop LLP
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