Appeal No. 96-1087
Application 08/068,700
BACKGROUND
The invention is directed to a spark plug for an internal combustion engine which
has a long service life using a very small amount of noble metal. A narrowed portion of the
tip of the center electrode has a metal chip formed of a noble metal firmly attached to the
end of the narrowed projection. The electrode is formed of a nickel base and the metal
chip is formed of a platinum-iridium alloy. The diameter of the narrowed portion of the
electrode, the length of the narrowed portion of the electrode, and the thickness of the
noble metal chip are set forth in specified relationships. The invention arises from an
appreciation that the bonding between the platinum chip and the center electrode is
influenced by 2 factors. First, the difference between the thermal expansion of the chip
and base material and second, the difference between the thermal capacity of the chip and
the base material of the electrode. In the embodiment of claim 2, the invention is further
directed to additionally including a relaxing layer having a thickness not less than 0.05 mm
between the noble chip and the center electrode.
Independent claim 1 (first embodiment) is reproduced as follows:
1. A spark plug for an internal combustion engine comprising:
an insulator;
2
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