Patent ID: 6653766
Filing Date: 2003-11-25
Classification: H01T

Abstract:
A spark plug for an engine comprising:a mounting member made of a conductive material which is mounted to an engine; an insulator disposed inside the mounting member and formed with an axial hole; a center electrode formed of a metal material and disposed in the axial hole of the insulator in a manner insulated from the mounting member; and an earth electrode disposed so as to oppose to the center electrode, at least one of said center electrode and earth electrode being formed as a base material having one surface to which a tip composed, as a discharge member, of a noble metal or alloy thereof is welded and fixed thereto through a fused portion, wherein said fused portion between the tip and the base material has an area of a maximum sectional area portion of a size of not more than 1.5 times a sectional area of a portion of the tip positioned at a boundary portion to the fused portion, and the sectional area of the tip positioned at the boundary portion is not less than 2 mm2 and not more than 7 mm2.