Spark plug for internal-combustion engine

Abstract

A spark plug for internal-combustion engines has a spark discharge gap defined between at least two electrodes opposing to each other, and a platinum-containing wear-resistant discharging layer provided on one of the electrodes. The spark plug has a thermal stress relieving layer disposed between the discharging layer and the base metal constituting the one eletrode. The thermal stress relieving layer is made of a platinum base alloy containing nickel, which constitutes the base metal. The discharging layer may be made of a material consisting essentially of 70 to 90 wt % platinum and 30 to 10 wt % iridium. The thermal stress relieving layer may be made of a material consisting essentially of 5 to 95 wt % platinum and 95 to 5 wt % nickel. Another platinum-containing wear-resistant layer may be provided on the other electrode, the wear-resistant layer being made of a material consisting essentially of 5 to 60 wt % nickel and 95 to 40 wt % platinum.

Dependencies are inferred from the claim text.