Patent ID: 8432092
Filing Date: 2013-04-30
Classification: H01T

Abstract:
1. A spark plug comprising: an insulator having an axial hole which extends along an axis; a center electrode which is inserted into a front end portion of the axial hole and which has a front end placed further forwards than a front end of the insulator; and a cylindrical shell which is provided around an outer circumference of the insulator; the center electrode including a shoulder portion which increases in diameter as it extends from a rear end of a front end portion of the center electrode towards a rear end side and a main body portion which extends from a rear end of the shoulder portion towards the rear end side along the axis, the center electrode having a multi-layer construction configured of an outer layer and an inner layer which is provided in an interior of the outer layer and which contains a material having higher thermal conductivity than that of the outer layer, characterized in that: a front end face, which is connected to an outer circumferential surface of the insulator and the axial hole and slopes towards the rear end side, is formed at a front end portion of the insulator, the front end of the insulator is placed further forwards than a boundary between the shoulder portion and the main body portion of the center electrode, a front end portion of the inner layer is placed further forwards along the axis than the boundary between the shoulder portion and the main body portion of the center electrode, and regarding a cross-section which includes the axis, when angles A where, the angle A the angle A the angle A the angle A the angle A