Spark plug and method of manufacturing spark plug

摘要

An ignition plug having a metallic shell with a through hole extending therethrough in an axial direction, an insulator fitted into the through hole of the metallic shell and having an axial hole extending in the axial direction, and a center electrode fitted into the axial hole of the insulator. The ignition plug further includes a cap member which covers a front end opening of the metallic shell, provided on a front end side thereof where the center electrode is disposed, to thereby form an ignition chamber at the front end portion of the metallic shell, and a ground electrode disposed within the ignition chamber and facing a circumferential surface of the center electrode directly or indirectly.

主权项

1. An ignition plug comprising:
a metallic shell having a through hole extending therethrough in an axial direction; an insulator fitted into the through hole of the metallic shell and having an axial hole extending in the axial direction; a center electrode fitted into the axial hole of the insulator; and a cap member which covers a front end opening of the metallic shell, provided on a front end side thereof where the center electrode is disposed, to thereby form an ignition chamber in a front end portion of the metallic shell; and a ground electrode disposed within the ignition chamber and facing a circumferential surface of the center electrode directly or indirectly, wherein the ground electrode has a rod-like shape; a proximal end portion of the ground electrode is fixed to the metallic shell such that the ground electrode is cantilevered and extends in a chord direction of the ignition chamber, and a distal end portion of the ground electrode faces the circumferential surface of the center electrode directly or indirectly via a gap G; and a metal fitting is disposed adjacent to the proximal end portion of the ground electrode, wherein the proximal end portion of the ground electrode is fixedly held between the metal fitting and the metallic shell, wherein the metal fitting has a cylindrical tubular shape; the metallic shell has, at its front end, a diameter-increased hole into which the metal fitting is fitted; and the metal fitting is joined to the metallic shell in a state in which the ground electrode is sandwiched between a step portion at the rear end of the diameter-increased hole and a rear end portion of the metal fitting; and wherein a clearance is formed between an outer circumferential surface of the metal fitting and a wall surface of the diameter-increased hole; and the step portion at the rear end of the diameter-increased hole and the rear end portion of the metal fitting are joined together through resistance welding.