Patent ID: 8487520
Filing Date: 2013-07-16
Classification: H01T

Abstract:
1. A spark plug which comprises: a tubular insulator having an axial hole extending therethrough in an axial direction of the spark plug; a center electrode inserted into a front end portion of the axial hole; a tubular metallic shell surrounding the insulator; a ground electrode disposed at a front end portion of the metallic shell; and a noble metal tip joined to a distal end portion of the ground electrode and forming a gap in cooperation with a front end portion of the center electrode, wherein a surface of the noble metal tip which forms the gap has an area of 0.9 mm the noble metal tip is joined to the ground electrode via a fusion zone formed through fusion of a portion of the ground electrode and a portion of the noble metal tip effected by irradiating at least one surface among a distal end surface and side surfaces of the ground electrode with a laser beam or an electron beam; as viewed on a projection plane orthogonal to a center axis of the noble metal tip and on which the noble metal tip and the fusion zone are projected along the center axis, an overlapping region between the noble metal tip and the fusion zone accounts for 70% or more of a projected region of the noble metal tip; wherein the fusion zone is formed by irradiating at least a first surface and a second surface different from the first surface among the distal end surface and the side surfaces of the ground electrode with the laser beam or the electron beam, and a first fusion region formed by irradiating the first surface with the laser beam or the electron beam and a second fusion region formed by irradiating the second surface with the laser beam or the electron beam overlap each other, thereby forming an overlap fusion region; and wherein, when the noble metal tip, the fusion zone, and a straight line intersecting the center axis of the noble metal tip and extending along a longitudinal direction of the ground electrode are projected on a projection plane along the center axis of the noble metal tip, the overlap fusion region overlaps the straight line in the projected region of the noble metal tip.