Patent ID: 8294344
Filing Date: 2012-10-23
Classification: H01T

Abstract:
1. A spark plug comprising: a center electrode; an insulator which has an axial hole extending along an axial direction and holds the center electrode in the axial hole; a metallic shell which circumferentially surrounds and holds the insulator; a ground electrode whose one end portion is joined to the metallic shell and which is bent such that one surface of the other end portion thereof faces a front end portion of the center electrode so as to form a spark discharge gap therebetween; and a spark member which is provided on the one surface of the other end portion of the ground electrode at a position corresponding to the spark discharge gap, projects from the one surface toward the center electrode, and is configured such that a noble metal member disposed on a side toward the center electrode with respect to a projecting direction thereof and an intermediate member disposed between the noble metal member and the ground electrode are joined to each other; the intermediate member of the spark member having: a columnar portion including a top surface joined to the noble metal member and extending in the projecting direction and a flange portion including a bottom surface joined to the ground electrode and assuming such a flange-like shape as to be radially expanded as compared with the columnar portion; wherein the one surface of the ground electrode and the bottom surface of the intermediate member are resistance-welded to each other such that a weld metal zone is formed between the one surface and the bottom surface, and as viewed on a section of the intermediate member and the ground electrode taken along a plane which contains a centerline of the spark member extending along the projecting direction of the spark member, a relation d≧0.1D is satisfied, where d is a length occupied in a direction orthogonal to the projecting direction by a portion of the weld metal zone formed inside an imaginary plane which passes through a boundary between the columnar portion and the flange portion and extends along the projecting direction, and D is a length of the columnar portion as measured along a direction orthogonal to the projecting direction.