Patent ID: 7772752
Filing Date: 2010-08-10
Classification: H01T

Abstract:
1. A plasma-jet spark plug, comprising: a center electrode having a front end face; an insulator having an axial bore which extends in an axial direction, said insulator accommodating said front end face of the center electrode therein and holding the center electrode; a cavity formed at the front end side of the insulator said cavity having a shape defined by an inner circumference face of the axial bore and either a front end face of the center electrode or a plane surface including the front end face; a metal shell holding the insulator by surrounding a radial circumference of the insulator; and a ground electrode joined to the metal shell to provide electrical connection thereto, the ground electrode being disposed at the front end side with respect to the insulator and having an opening portion for providing communication between the cavity and the outside of the spark plug, wherein a plasma can be produced in the cavity along with a spark discharge between the center electrode and the ground electrode, wherein the insulator and the ground electrode are disposed apart from each other in the axial direction, and wherein the following relations are satisfied: where “a” is a dimension of a clearance between the insulator and the ground electrode in the axial direction; and “S” is a volume of the cavity (