Patent ID: 7328677
Filing Date: 2008-02-12
Classification: F02P,H01T

Abstract:
1. A plasma-jet spark plug, comprising: a metal shell; an electrical insulator retained in the metal shell and formed with an axial hole; a center electrode held in the axial hole of the electrical insulator so as to define a discharge cavity by a front end face of the center electrode and an inner circumferential surface of the axial hole in a front end part of the electrical insulator; and a ground electrode formed in a plate shape with an opening, fitted to a front end face of the electrical insulator to allow communication between the discharge cavity and the outside of the spark plug via the opening and connected electrically with the metal shell, the spark plug satisfying the following dimensional relationships on the condition of d≦D≦3d: where D is a diameter of the opening of the ground electrode; L1 is a thickness of the ground electrode; d is a diameter of the discharge cavity; and L2 is an axial distance between the front end face of the electrical insulator and the front end face of the center electrode.