Patent ID: 7906893
Filing Date: 2011-03-15
Classification: H01T

Abstract:
1. A spark plug of an internal combustion engine, comprising: an insulator having a through hole in an axial direction of the spark plug, the insulator including a rear body portion, a middle body portion and a large-diameter portion located between the rear and middle body portions and protruding radially outwardly from the rear and middle body portions, the large-diameter portion having a rear shoulder section connected at a rear end thereof to a front end of the rear body portion and a front shoulder section connected at a front end thereof to a rear end of the middle body portion; a cylindrical metal shell retaining the middle body portion and the large-diameter portion of the insulator therein; a center electrode fitted in the through hole of the insulator; a ground electrode joined to the metal shell and having a given portion facing a front end of the center electrode to define a spark gap between the front end of the center electrode and the given portion of the ground electrode; a first glaze layer formed on an outer surface of the insulator and extending over the rear body portion and the rear shoulder section of the large-diameter portion; and a second glaze layer formed on the outer surface of the insulator and extending over at least part of the middle body portion from some point on the front shoulder section of the large-diameter portion, wherein the first glaze layer includes a first corner glaze section to cover a corner between the front end of the rear body portion and the rear end of the rear shoulder section of the large-diameter portion and a first body glaze section to cover the rear body portion; and the first corner glaze section is larger in thickness than the first body glaze section.