Patent ID: 8253312
Filing Date: 2012-08-28
Classification: F02P,H01T

Abstract:
1. A plasma jet spark plug, comprising: a cylindrical insulator having a front end, a rear end and an axial bore extending therethrough in an axial direction; a rod-shaped central electrode inserted into the axial bore so that a front end surface of the central electrode is located further to a rear end side in the axial direction than the front end of the insulator; a cylindrical metal shell disposed around an outer peripheral surface of the insulator; a ground electrode installed at a front end portion of the metal shell; and a cavity portion that is a substantially cylindrical space formed by the inner peripheral surface of the axial bore and the front end surface of the central electrode and opened toward a front end side of the plasma jet spark plug, wherein a tapered section having a reduced diameter toward a front end side in the axial direction is formed at a front end portion of the central electrode, and wherein the axial bore includes: a sidewall section forming the cavity portion; and a diameter-enlarged section extending from a rear end of the sidewall section and formed at a location corresponding to the tapered section of the central electrode in the axial direction, the diameter-enlarged section having an enlarged diameter toward a rear end side in the axial direction along an outer peripheral surface of the tapered section of the central electrode.