Patent ID: 6215235
Filing Date: 2001-04-10
Classification: H01T

Abstract:
A spark plug for an internal combustion engine, comprising an insulator having a through hole, a central electrode disposed at least at one end of said through hole, a housing holding said insulator, a grounded electrode provided on said housing in a confronting relationship with said central electrode to form a spark gap between said central electrode and said grounded electrode, anda noble metallic firing tip bonded on at least one confronting surface of said central electrode and said grounded electrode, said noble metallic firing tip being laser welded to a base electrode member of said confronting surface so as to form a fused junction layer at the boundary between said noble metallic firing tip and said base electrode member in which said noble metallic firing tip and said base electrode member are fused together and then hardened,wherein said fused junction layer contains 40.about.70 wt % noble metallic firing tip component,said noble metallic firing tip has a non-fused portion axially extending from its top to an upper end of said fused junction layer by an axial length ""L"", where 0.2 mm .ltoreq.L.ltoreq.0.7 mm,said fused junction layer axially extends from the upper end to its lower end by an axial length ""M"", where 0.2 mm .ltoreq.M.ltoreq.0.7 mm, andthe relationship B.gtoreq.1.3A is established when ""A"" represents the diameter of said noble metallic firing tip and ""B"" represents the diameter of a contact area at the boundary between said fused junction layer and said base electrode member, where 0.3 mm .ltoreq.A.ltoreq.0.6 mm.