Patent ID: 8975809
Filing Date: 2015-03-10
Classification: H01T

Abstract:
1. An ignition plug comprising: an insulator having an axial bore extending in a direction of an axis; a center electrode inserted into a forward end portion of the axial bore; a terminal electrode having a rod-shaped leg portion inserted into a rear end portion of the axial bore, and a head portion projecting from a rear end of the insulator; and a tubular metallic shell disposed around the insulator such that a portion of the insulator projects from a rear end of the metallic shell, a length L of the portion of the insulator projecting from the rear end of the metallic shell measured along the axis being not less than 28 mm but not greater than 34 mm, wherein, a thickness t of a thinnest portion of the insulator is 1.0 mm or greater within a region which extends 5.5 mm from the rear end of the insulator toward the forward end side with respect to the direction of the axis; a forward end surface of the head portion and a rear end surface of the insulator have respective flat portions; and when the flat portion of the rear end surface of the insulator and the flat portion of the forward end surface of the head portion are projected along the axis onto a plane orthogonal to the axis, an area D of a region where a projected area of the flat portion of the rear end surface overlaps with a projected area of the flat portion of the forward end surface is set to 8 mm