Patent ID: 7550906
Filing Date: 2009-06-23
Classification: H01T

Abstract:
1. A spark plug comprising: a center electrode; an insulator having an axial hole, and holding the center electrode with a front end portion of the center electrode protruding from the axial hole; a metallic shell holding the insulator therein; a ground electrode having a first end portion joined to the metallic shell and a second end portion opposed to a front end portion of the center electrode; and a cylindrical noble-metal chip having a proximal end surface joined to at least either the front end portion of the center electrode or the second end portion of the ground electrode, and a facing end surface opposite the proximal end surface, wherein the noble-metal chip is made of iridium or an alloy that contains iridium in an amount of 70% by weight or more, and crystal grains constituting the noble-metal chip are longer in length along an axial direction of the noble-metal chip than along a direction perpendicular to the axial direction; said noble metal chip having an edge-removed portion along a circumferential edge of said facing end surface, an edge removal length of 0.01 mm or more, and a ratio of the edge removal length to a radius of the noble-metal chip of less than 0.3.