Patent ID: 8791627
Filing Date: 2014-07-29
Classification: H01T

Abstract:
1. A spark plug, comprising: an insulator having an axial hole penetrating in an axial direction and a center electrode disposed at a tip end side of the axial hole; and a tubular metal shell disposed at an outer periphery of the insulator for holding the insulator, the metal shell including a shoulder formed to project from an inner peripheral surface of the metal shell inward in a radial direction, wherein the insulator includes: the shoulder of the metal shell includes: a first shoulder that has an inner diameter reduced from a rear end side toward the tip end side; and a second shoulder formed at the tip end side of the first shoulder, the second shoulder extending to face the trunk portion, wherein the tip end of the second shoulder is positioned at the tip end side with respect to the tip end of the trunk portion in the axial direction, a distance Da between the tip end of the second shoulder and the leg along the radial direction and a distance Db between the tip end of the trunk portion and the second shoulder along the radial direction satisfy a relationship in Expression 1, and a distance T and a distance L satisfy a relationship in Expression 2, the distance T being a distance between the rear end of the first shoulder and the tip end of the second shoulder along the axial direction, the distance L being a distance between the rear end of the first shoulder and a tip end face of the metal shell along the axial direction: