Patent ID: 7710006
Filing Date: 2010-05-04
Classification: H01T

Abstract:
1. A spark plug having a front-end side and a rear-end side, comprising: a center electrode; a ground electrode forming a spark gap at a front-end side of the spark plug between the center electrode and the ground electrode; an insulator having an intermediate trunk portion, a rear trunk portion provided rearwards of the intermediate trunk portion, and an axial hole extending along an axis of the insulator, the insulator holding the center electrode within the axial hole at the front end thereof; and a metallic shell accommodating the intermediate trunk portion of the insulator and having a crimp portion at the rear end thereof, wherein the intermediate trunk portion of the insulator includes: a shoulder portion pressed forward by means of the crimp portion, a maximum diameter portion disposed frontward of the shoulder portion and having a maximum outer diameter among those portions constituting the intermediate trunk portion, and an intermediate diameter portion connecting the shoulder portion and the maximum diameter portion, the entire intermediate portion having a smaller diameter than the maximum diameter portion, and having a groove portion arranged between the shoulder portion and the maximum diameter portion extending at least in a circumferential direction on an outer surface of the intermediate diameter portion, and wherein a glaze layer covers a surface of the insulator extending from a rear trunk portion to a portion located between the shoulder portion and the groove portion.