Patent ID: 9059572
Filing Date: 2015-06-16
Classification: H01T

Abstract:
1. A spark plug for an internal combustion engine comprising: a center electrode; an insulator holding the center electrode inserted thereinto; a housing holding the insulator inserted thereinto in a state that an proximal end portion of the insulator is exposed from the housing; and a ground electrode joined to the housing so as to form a spark discharge gap with the center electrode; wherein the center electrode includes a core member having a bar shape and a cover layer covering a surface of the core member, the core member includes a large-diameter portion made of a material having a thermal conductivity higher than a thermal conductivity of the cover layer, a small-diameter portion which is smaller in diameter than the large-diameter portion and extends from the large-diameter portion in an axial direction of the core member toward a distal end side of the core member, and a connecting portion formed so as to connect the large-diameter portion to the small-diameter portion, the cover layer is made of a material having a linear expansion coefficient lower than a linear expansion coefficient of the core member, and covers between at least part of the connecting portion and a distal end of the small-diameter portion, and a surface of the large-diameter portion is exposed without being covered by the cover layer.