Patent ID: 9742157
Date: 2017-08-22
CPC Classifications: H01T

Claim:
1. A spark plug, comprising: an insulator having a front end part and a through hole formed in the direction of an axis of the spark plug; a rod-shaped center electrode inserted in the through hole and extending in the direction of the axis; a metal shell disposed around an outer circumference of the insulator; and a ground electrode electrically conducted with the metal shell and adapted to define a gap between the ground electrode and the center electrode, wherein the front end part of the insulator has a front end surface, an outer circumferential surface, and a curved surface region extending from the front end surface to the outer circumferential surface, wherein the outer circumferential surface is located rearward of the front end surface and extends rearwardly in the direction of the axis wherein, in a cross section including the axis, a front end of an inner circumferential surface of the metal shell is disposed opposite the curved surface region in a direction perpendicular to the axis, and wherein the curved surface region has a curvature radius in a range from 0.2 mm to 0.8 mm.