Patent ID: 8072125
Filing Date: 2011-12-06
Classification: H01T

Abstract:
1. A spark plug for use in an internal-combustion engine, comprising: a center electrode; an insulator at least partially surrounding the center electrode; a cylindrical metal shell at least partially surrounding the insulator; a ground electrode so disposed that one end thereof is joined to a front-end face of the metal shell and the other end thereof faces the front-end face of the center electrode; and a spark discharge gap formed between the front-end face of the center electrode and a front-end portion of the ground electrode, wherein the ground electrode has a width between 1.3 mm and 1.7 mm at least in the front-end portion thereof located forward of a center of the spark discharge gap, wherein at least a portion of the ground electrode where sparks are discharged has an outer layer made of a nickel alloy selected from the group consisting of a nickel alloy having the following chemical composition: or a nickel alloy having the following chemical composition: wherein a ratio of a cross-sectional area of the inner layer to the entire cross-sectional area of the ground electrode is 10% or more to 28.4% or less, and said ratio is selected such that spring-back of said ground electrode during use of said spark plug is prevented.