Patent ID: 6191525
Filing Date: 2001-02-20
Classification: H01T

Abstract:
A spark plug comprising:an insulator;a through hole formed along an axial direction of the insulator;a terminal inserted and fixed on one end side of the through hole;a center electrode inserted and fixed on a second end side of the through hole;a resistor placed between the terminal and the center electrode within the through hole;wherein a stem cross-section diameter of the center electrode is set smaller than a stem cross-section diameter of the resistor;wherein one side toward a tip end of the center electrode taken as a front side, the through hole of the insulator has a first portion which allows the center electrode to be inserted therethrough, and a second portion which is formed on a rear side of the first portion so as to be larger in diameter than the first portion and which accommodates the resistor therein;wherein the second portion is connected to the first portion via a connecting portion including a two-or more-stepped reduced-diameter portions; andan electrically conductive glass seal portion placed at a position corresponding to the connecting portion between the resistor and the center electrode, and wherein the electrically conductive glass of said glass seal portion is sealed into a narrow gap between an outer radial surface of said center electrode and said connecting portion of said through hole.