Patent ID: 9000658
Filing Date: 2015-04-07
Classification: H01T

Abstract:
1. A spark plug for an internal-combustion engine, comprising: a rod-like center electrode extending in an axis direction; an insulator having an axial bore in the axis direction in which the center electrode is inserted; a generally cylindrical metal shell provided on an outer circumference of the insulator; a ground electrode extending from a front end portion of the metal shell and disposed so that a front end thereof is bent toward the center electrode; a noble metal portion provided on the front end of the ground electrode which faces a front edge of the center electrode; and a gap formed between the ground electrode and the center electrode, wherein an entire front end portion of the ground electrode including the bent portion thereof is positioned outside of a virtual outer circumferential face that is formed by extending a front end outer circumferential face of the center electrode in the axis direction, and a terminating face of the ground electrode is positioned on a front end side in the axis direction with respect to a virtual face formed by extending a front end face of the center electrode, and wherein the following equation is satisfied: where “a” ( where “b” (