Patent ID: 8354782
Filing Date: 2013-01-15
Classification: H01T

Abstract:
1. A spark plug comprising: a rod-shaped center electrode extending in an axial direction thereof; an insulating body provided around an outer circumference of the center electrode; a metal shell provided around an outer circumference of the insulating body; a ground electrode extending from a distal end portion of the metal shell; and a noble metal tip joined to a distal end portion of the center electrode, and forming a gap between the ground electrode and the noble metal tip, wherein the center electrode and the noble metal tip are joined to each other through a molten portion which is fused with a component of the center electrode and a component of the noble metal tip; an area of an interface between the noble metal tip and the center electrode is set to be 5% or less with respect to a cross-sectional area of the noble metal tip which is perpendicular to an axial line of the nobel metal tip at a portion, which is nearest to the molten portion, of an outer surface of the noble metal tip; in a cross section including the axial line, supposing that a length of a portion, which is exposed to the outer surface is A (mm), of the molten portion along the axial line, and a width of the noble metal tip is B (mm), A≦0.6 and B/A≦6 are satisfied; and a portion of the molten portion, of which a length along the axial line is A/1.5, is located further outwards radially than a position which comes in by as much as B/4 from the outer circumference of the noble metal tip.