Patent ID: 6566793
Filing Date: 2003-05-20
Classification: H01T

Abstract:
A spark plug comprising:a center electrode disposed on an axial center in axial direction of said spark plug; an axial insulator which covers the outside of said center electrode and secures said center electrode at a forward side thereof; a metal shell which is shaped like a barrel that is open at both ends and disposed outside said electrode; a ground electrode which forms a spark discharge gap with respect to said electrode, being connected to said metal shell; a screw portion whose thread reach in 25 mm or greater, formed on an outside circumferential surface of the forward end portion of said metal shell; a peripheral flange portion which protrudes outward at a portion of said insulator located within said metal shell half way in the axial direction; a middle trunk portion which is adjacent to a forward side of said flange portion, wherein the middle trunk portion includes a connecting section where axial sectional size changes to have a largest diameter at the forward side of said flange portion and a middle trunk main section having a substantially uniform axial sectional size adjacent to a forward side of the connecting section; a terminal is secured at a backward side of said insulator, wherein a bottom end edge of said terminal protrudes from the backward side of said insulator; a portion which defines a through hole formed in the axial direction of said insulator; and an electrically conductive binder layer is disposed between said terminal and said center electrode within said through hole, wherein the forward side is defined as the side where said spark discharge gap is located in an axial direction of said insulator, a backward side is defined as the opposite side, and a top end edge of said terminal penetrates through said connecting section in said middle trunk portion of said insulator.