Plasma-jet spark plug and ignition system

Abstract

A plasma-jet spark plug includes a metal shell, an electrical insulator retained in the metal shell, a center electrode held in an axial hole of the electrical insulator to define a cavity by a front end face of the center electrode and an inner circumferential surface of the insulator axial hole and a ground electrode fitted to a front end face of the electrical insulator and formed with an opening for communication between the cavity and the outside of the spark plug and satisfies the following dimensional relationships:

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half section view of a plasma-jet spark plug according to one exemplary embodiment of the present invention.

FIG. 2 is an enlarged section view of a front side of the plasma-jet spark plug, in the case of satisfying a dimensional relationship of D=d between a ground electrode opening D and a discharge cavity diameter d, according to one exemplary embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply unit of an ignition system according to one exemplary embodiment of the present invention.

FIG. 4 is an enlarged section view of a front side of the plasma-jet spark plug, in the case of satisfying a dimensional relationship of D=3d between the ground electrode opening D and the discharge cavity diameter d, according to one exemplary embodiment of the present invention.

FIGS. 5 and 6 are graphs showing experimental data on ignition probability and electrode consumption of the plasma-jet spark plug according one exemplary embodiment of the present invention.

Claims

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; anda 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: 0.5 mm≦d≦1.5 mm;L1≦1.5 mm;2d≦L2≦3.5 mm; andL2+{(D−d)/2}≦3.5 mm

2. A plasma-jet spark plug according to claim 1, satisfying a dimensional relationship of L1≧0.8 mm.

3. A plasma-jet spark plug according to claim 1, satisfying a dimensional relationship of d<E where E is an outer diameter of the center electrode.

4. An ignition system, comprising: a plasma-jet spark plug according to claim 1; anda power source having a capacity to supply 50 to 200 mJ of energy to the spark plug.

5. An ignition system according to claim 4, wherein the power source is of 160 mJ capacity.