Patent ID: 8648519
Filing Date: 2014-02-11
Classification: H01T

Abstract:
1. A spark plug for use in an internal-combustion engine, comprising: an insulator having an axial bore extending in an axial direction; a rod-like center electrode disposed in the axial bore; a cylindrical metal shell formed on an outer circumference of the insulator; a ground electrode extending from a front end portion of the metal shell and bent towards the center electrode; a plate-like relieving layer tip embedded in and joined to a front end portion of the ground electrode by resistance welding; and a noble metal tip having one end surface which is in contact with, and joined by resistance welding to, both a portion of the relieving layer tip on the center electrode side and to a portion of the ground electrode which corresponds to an outer circumference of the portion of the relieving layer tip on the center electrode side, and the noble metal tip further having the other end surface forming a gap with a front end portion of the center electrode, wherein the noble metal tip is made of a platinum alloy containing platinum as a principal component, wherein the relieving layer tip is made of a platinum alloy and has a linear expansion coefficient between that of the platinum alloy constituting the noble metal tip and a metal material constituting the ground electrode, wherein a portion of the relieving layer tip to which the noble metal tip is joined has an area smaller than an area of the one end surface of the noble metal tip, and wherein a melted bond formed by melting at least the noble metal tip and the ground electrode by laser welding is provided on an entire outer circumference of a boundary portion between the ground electrode and the noble metal tip.