Patent ID: 8115371
Filing Date: 2012-02-14
Classification: H01T

Abstract:
1. A spark plug comprising: a rod-shaped center electrode; a substantially cylindrical insulating member which has an axial hole extending along a direction of an axis of the center electrode and holds the center electrode within the axial hole while allowing a front end portion of the center electrode to be exposed; a substantially cylindrical metal shell which is provided around an outer circumference of the insulating member; and a ground electrode which is joined to a front end face of the metal shell and which forms a spark gap with a front end portion of the center electrode, wherein a front end portion of the insulating member projects 2 mm or more from the front end face of the metal shell, and a volume of a portion of the insulating member which lies within a range from a front end to a position lying 1 mm towards a rear end of the insulating member from the front end is 11 mm wherein when assuming in a section of the spark plug which passes through the axis that: a parallel displacement amount E by which the straight line BC is displaced parallel so as to contact the position PD is 0.75 mm or more.