Spark plug having the center electrode sheath with a nickel alloy

Claim 1

A SPARK PLUG COMPRISING A METAL SHELL, A GROUND ELECTRODE SECURED TO THE BASE OF SAID SHELL, AN INSULATOR SURROUNDED AND SUPPORTED BY SAID SHELL AND HAVING A CENTERBORE THEREIN, AND A COMPOSITE ELECTRODE INSERTED IN SAID CENTERBORE, SUPPORTED AND RETAINED BY SAID INSULATOR AND HAVING A FIRING END IN SPACED RELATIONSHIP TO SAID GROUND ELECTRODE TO FORM A SPARK GAP THEREBETWEEN, SAID COMPOSITE ELECTRODE COMPRISING A ROD HAVING A METAL CORE, A TUBULAR METAL SHEATH OF SUBSTANTIALLY UNIFORM DIAMETER THROUGHOUT ITS LENGTH ENCOMPASSING SAID CORE FOR A SUBSTANTIAL DISTANCE OF ITS LENGTH, AND, AT SAID FIRING END, AN ESSENTIALLY PLANAR METAL CAP CENTRALLY ABUTTING SAID CORE, PERIPHERALLY WELDED TO AND ABUTTING SAID SHEATH, AND FORMING WITH SAID SHEATH AN ESSENTIALLY GAS-TIGHT SEAL, THE CAP-ABUTTING END OF SAID CORE TERMINATING IN A FLAT SURFACE, SAID CORE HAVING A HIGHER HEAT CONDUCTIVITY THAN SAID SHEATH AND SAID CAP, SAID SHEATH AND SAID CAP HAVING A SUBSTANTIALLY GREATER RESISTANCE TO EROSION AND CORROSION THAN SAID CORE.