Patent ID: 9234491
Filing Date: 2016-01-12
CPC Classification: F02P,H01T

Claim Text:
1. A spark plug for an internal combustion engine, the spark plug comprising: a tubular housing: a tubular insulator retained in the housing; a center electrode secured in the insulator with a distal end portion of the center electrode protruding outside the insulator; a ground electrode having a standing portion that stands distalward from a distal end of the housing and an opposing portion that opposes the distal end portion of the center electrode in an axial direction of the spark plug through a spark gap formed therebetween; and a guide member configured to guide the flow of an air-fuel mixture in a combustion chamber of the internal combustion engine to the spark gap, the guide member protruding distalward from the distal end of the housing at a different circumferential position from the ground electrode, the guide member having a guide surface that faces the ground electrode in a circumferential direction of the spark plug, wherein on a projection plane which is defined to extend perpendicular to the axial direction of the spark plug through the spark gap and on which the above components of the spark plug are projected, the following dimensional relationships are satisfied: where a is a distance between a center point of the center electrode and an intersection point between straight lines L and M, the straight line L extending through both a center of the standing portion of the ground electrode in the circumferential direction of the spark plug and the center point of the center electrode, the straight line M extending through the guide surface of the guide member, the distance a being positive on the side of the center point of the center electrode away from the standing portion of the ground electrode and negative on the side of the center point of the center electrode approaching the standing portion of the ground electrode, b is an angle between the straight lines L and M, and D is an outer diameter of the housing, wherein a first reference plane P a second reference plane P a third reference plane P the oblique angle θ is positive when the third reference plane P with the oblique angle θ being in a range of 0 to 30° and projecting on the projection plane a cross section of the ground electrode and a cross section of the guide member both of which are taken along the third reference plane P where r is a distance on the projection plane between the central axis of the center electrode and an outer side of the cross section of the ground electrode, and R is a distance on the projection plane between the central axis of the center electrode and a guide surface-side outer corner of the cross section of the guide member.