| 摘要 |
<p>A spark plug is such that a front end portion of an insulating member projects 2 mm or larger from a front end face of a metal shell and a volume of a portion of the insulating member which lies within a range from a front end of the insulating member to a position lying 1 mm towards a rear end side from the front end is 11 mm 3 or smaller. When assuming that a corner portion where a front end face of the insulating member intersects a side surface of an axial hole is referred to as a position PA, a position on a center electrode where a straight-line distance from the position PA to the center electrode within the axial hole is referred to as a position PB, a position where the insulating member first contacts the metal shell from the front end face of the insulating element along a surface of the insulating element is referred to as a position PC, and a position on the insulating element where a straight line BC which connects the position PB with the position PC contacts the surface of the insulating member when the straight line BC is displaced parallel towards an outside of an axis is referred to as a position PD, a parallel displacement amount E by which the straight line BC is displaced parallel until it contacts the position PD is 0.75 mm or larger. According to the spark plug configured in this way, even though the spark plug is shaped small, the occurrence of lateral spark and inside spark can be suppressed effectively.</p> |
