Appeal No. 96-1087
Application 08/068,700
a center electrode supported by said insulator;
a housing secured to an outer periphery of said insulator;
an earth electrode arranged on said housing and facing to said
center electrode; and
a narrowed portion disposed on a tip of an electrode material of at
least one of said center electrode and said earth electrode, said
narrowed portion including a projection formed by extending said
electrode material and a noble metal chip firmly connected to a
terminal end of said projection;
wherein said electrode material is made of a nickel-base heat-
resisting alloy, said noble metal chip being made of a platinum-
iridium alloy essentially consisting, by weight, of 90-100% Pt and 0 -
10% Ir, or made of an alloy obtained by dispersing 0.01 - 2% zirconia
or yttria in said Pt-Ir alloy of 98 to 99.99%; a diameter D of said
narrowed portion being in a range of 0.6 - 1.2 mm, a length L of said
narrowed portion being in a range of 0.8 - 1.5 mm, the relationship
among a thickness of said noble metal chip t, said diameter D and
said length L being made to satisfy
0.4L # t # 0.8 mm when 0.6 mm # D < 0.8 mm,
0.3L # t # 0.8 mm when 0.8 mm# D < 1.0 mm, and
0.2L # t # 0.8 mm when 1.0 mm # D # 1.2 mm.
Independent claim 2 (second embodiment) is reproduced as follows:
2. A spark plug for an internal combustion engine comprising:
an insulator;
3
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