Patent ID: 8692447
Filing Date: 2014-04-08
Classification: H01T

Abstract:
1. A spark plug for an internal combustion engine, the spark plug comprising: a center electrode extending along an axis and having a leading end portion and an outer peripheral surface; an insulator of a cylindrical shape, the insulator provided about the outer peripheral surface of the center electrode and having an outer peripheral surface; a metal shell of a cylindrical shape, the metal shell provided about the outer peripheral surface of the insulator and having a leading end portion; a noble metal tip provided at the leading end portion of the center electrode, the noble metal tip including a leading end portion and a basal portion; a ground electrode, one end of the ground electrode fixed at the leading end portion of the metal shell, and the other end of the ground electrode forming a gap with the leading end portion of the noble metal tip; a stopper provided on at least one of the center electrode and the noble metal tip, the stopper preventing the noble metal tip from moving relative to the central electrode; a molten portion welding the center electrode and at least a part of the basal portion of the noble metal tip; and a closed space formed between a center part of the basal portion of the noble metal tip and the center electrode, wherein when the spark plug is viewed in a cross section including the axis, a width of the noble metal tip CO, a maximum width of the closed space SI, and a height of the closed space SH satisfy the following relationships: