Abstract: A spark plug includes a center electrode, a tubular metallic shell which holds the center electrode therein in an insulated state, and a ground electrode which faces a forward end portion of the center electrode. The metallic shell has a penetration hole which penetrates the metallic shell in a direction intersecting an axial direction. The ground electrode has a press-fitted portion inserted into the penetration hole and fixed to the metallic shell, a projecting portion projecting toward an inner side of the metallic shell, and an insertion portion disposed between the press-fitted portion and the projecting portion, inserted into the penetration hole, and forming a space between the insertion portion and an inner surface of the penetration hole. An angle ? formed between the inner surface of the penetration hole and an outer surface of the insertion portion falls within a range of 0°<?<90°.

Abstract: A spark plug capable of generating a sufficient volume of jet with an increased range is provided. The spark plug includes a metal shell having a tubular shape; a center electrode retained in the metal shell in an insulated manner; a ground electrode that is electrically connected to the metal shell and that defines a spark gap between the center electrode and an end portion of the ground electrode; and a cap portion that covers the center electrode and the end portion of the ground electrode from the front in a region in front of the metal shell and in which a through hole is formed. The cap portion includes a plurality of projections on an inner surface of the through hole. The projections extend in an extending direction in which the through hole extends.

Abstract: A spark plug includes a center electrode, a tubular metallic shell which holds the center electrode therein in an insulated state, and a ground electrode which faces a forward end portion of the center electrode. The metallic shell has a penetration hole which penetrates the metallic shell in a direction intersecting an axial direction. The ground electrode has a press-fitted portion inserted into the penetration hole and fixed to the metallic shell, a projecting portion projecting toward an inner side of the metallic shell, and an insertion portion disposed between the press-fitted portion and the projecting portion, inserted into the penetration hole, and forming a space between the insertion portion and an inner surface of the penetration hole. An angle ? formed between the inner surface of the penetration hole and an outer surface of the insertion portion falls within a range of 0°<?<90°.

Abstract: A spark plug includes a metal shell and a cap member joined to the metal shell to define a pre-chamber. The cap member includes an overlapping surface that overlaps the metal shell along the axial line direction, an inner facing surface positioned closer to the pre-chamber than is the overlapping surface, the inner facing surface facing the metal shell in the axial line direction, and an outer facing surface positioned closer to an outer periphery than is the overlapping surface, the outer facing surface facing the metal shell in the axial line direction. A portion of the cap member that is closer to the pre-chamber than is the overlapping surface s spaced from the metal shell. The metal shell and the cap member are joined together at at least one of the outer facing surface and the overlapping surface.

Abstract: A spark plug capable of generating a sufficient volume of jet with an increased range is provided. The spark plug includes a metal shell having a tubular shape; a center electrode retained in the metal shell in an insulated manner; a ground electrode that is electrically connected to the metal shell and that defines a spark gap between the center electrode and an end portion of the ground electrode; and a cap portion that covers the center electrode and the end portion of the ground electrode from the front in a region in front of the metal shell and in which a through hole is formed. The cap portion includes a plurality of projections on an inner surface of the through hole. The projections extend in an extending direction in which the through hole extends.

Abstract: A spark plug includes a metal shell and a cap member joined to the metal shell to define a pre-chamber. The cap member includes an overlapping surface that overlaps the metal shell along the axial line direction, an inner facing surface positioned closer to the pre-chamber than is the overlapping surface, the inner facing surface facing the metal shell in the axial line direction, and an outer facing surface positioned closer to an outer periphery than is the overlapping surface, the outer facing surface facing the metal shell in the axial line direction. A portion of the cap member that is closer to the pre-chamber than is the overlapping surface s spaced from the metal shell. The metal shell and the cap member are joined together at at least one of the outer facing surface and the overlapping surface.

Abstract: A spark plug that improves the heat resistance performance of an ignition plug.

Abstract: A spark plug includes a plug cap having a plurality of through holes. In a cross section including an axial line, the plug cap includes an enlarging portion in a portion of a region between a first imaginary straight line and a second imaginary straight line, the first imaginary straight line extending through a front end of the end portion of a ground electrode and being perpendicular to the axial line, the second imaginary straight line extending through a back end of one of inner open ends of the through holes that is closest to a front end of the spark plug and being perpendicular to the axial line. The enlarging portion being a portion in which a minimum distance from an outer surface to an inner surface of the plug cap increases with increasing distance in a direction from back to front.

Abstract: A spark plug that improves the heat resistance performance of an ignition plug.

Abstract: A spark plug that can suppress pre-ignition of a combustible air-fuel mixture that has flowed into the sub-chamber. The spark plug includes a ground electrode that joins to a metal shell and forms a spark gap; and a cap member that covers a center electrode and the ground electrode and forms a sub-chamber. A first fused portion that joins the metal shell and the cap member is located on the front-end side relative to the spark gap. At least a part of a first facing portion at which the metal shell and the cap member face each other is located on the sub-chamber side relative to the first fused portion. The first fused portion is not formed in an inner peripheral surface of the metal shell and an inner peripheral surface of the cap member.

Abstract: A spark plug having excellent ignitability including a rod-shaped center electrode; a ground electrode that includes a facing portion facing a front end portion of the center electrode and forms a discharge gap between the facing portion and the front end portion of the center electrode; an insulator; a metal shell; and a cover portion that covers, from a front end side of the spark plug, the front end portion of the center electrode and the facing portion of the ground electrode to form a pre-chamber and includes injection holes that are through holes.

Abstract: A spark plug having excellent ignitability including a rod-shaped center electrode; a ground electrode that includes a facing portion facing a front end portion of the center electrode and forms a discharge gap between the facing portion and the front end portion of the center electrode; an insulator; a metal shell; and a cover portion that covers, from a front end side of the spark plug, the front end portion of the center electrode and the facing portion of the ground electrode to form a pre-chamber and includes injection holes that are through holes.

Abstract: A spark plug includes: a center electrode; a ground electrode that is provided such that a gap for spark discharge is formed between the center electrode and the ground electrode; and a plug cover covering the center electrode and the ground electrode from a front side. The plug cover has a through hole, wherein the plug cover includes a diameter reduction portion formed in a range of 0.1 mm or less from an outer open end of the through hole in a direction along a central axis of the through hole and having a diameter gradually decreasing from the outer open end toward an inner open end of the through hole. A relationship of 0 mm<x?y<0.2 mm is satisfied, where x is a diameter at the outer open end, and y is a diameter at an inner end of the diameter reduction portion.

Abstract: A spark plug includes a plug cap having a plurality of through holes. In a cross section including an axial line, the plug cap includes an enlarging portion in a portion of a region between a first imaginary straight line and a second imaginary straight line, the first imaginary straight line extending through a front end of the end portion of a ground electrode and being perpendicular to the axial line, the second imaginary straight line extending through a back end of one of inner open ends of the through holes that is closest to a front end of the spark plug and being perpendicular to the axial line. The enlarging portion being a portion in which a minimum distance from an outer surface to an inner surface of the plug cap increases with increasing distance in a direction from back to front.

Abstract: A spark plug wherein the occurrence of pre-ignition and misfires is suppressed. The spark plug includes a cover portion that covers a front end portion of a center electrode and a facing portion of a ground electrode from a front end side of the spark plug to form a pre-chamber space. The cover portion has injection holes that are through-holes. A total area A (mm2) of inner peripheral surfaces of the injection holes and a thermal conductivity B (W/mK) of a material of the cover portion satisfy a formula (1): 10<A×B<4000.

Abstract: A spark plug that can suppress pre-ignition of a combustible air-fuel mixture that has flowed into the sub-chamber. The spark plug includes a ground electrode that joins to a metal shell and forms a spark gap; and a cap member that covers a center electrode and the ground electrode and forms a sub-chamber. A first fused portion that joins the metal shell and the cap member is located on the front-end side relative to the spark gap. At least a part of a first facing portion at which the metal shell and the cap member face each other is located on the sub-chamber side relative to the first fused portion. The first fused portion is not formed in an inner peripheral surface of the metal shell and an inner peripheral surface of the cap member.

Abstract: A spark plug includes a center electrode; a metal shell that retains the center electrode at an outer periphery of the center electrode in an insulating manner; a ground electrode disposed such that a spark gap is formed between the center electrode and an end portion of the ground electrode; and a plug cap connected to the metal shell, the plug cap covering the center electrode and the end portion of the ground electrode from front and having a through hole in a region in front of the ground electrode. An inner surface of the plug cap has at least one ridge in a first region that is in front of an inner open end of the through hole.

Abstract: A spark plug capable of facilitating the growth of a flame kernel. The spark plug including a metal shell; a center electrode retained in the metal shell in an insulated manner; a ground electrode disposed such that a spark gap is formed between the center electrode and an end portion of the ground electrode; and a plug cap that covers the center electrode and the end portion of the ground electrode from the front in a region in front of the metal shell and in which a through hole is formed. An inner surface of the plug cap in a region in front of a back end of the end portion of the ground electrode and an inner surface of the through hole each have an arithmetical mean roughness of less than or equal to 6.3 ?m.

Abstract: In an ignition plug, since a ground electrode is formed in a thin-rod-shape or a mesh-like shape, sufficiently strong radicals are locally generated by a barrier discharge, an anti-inflammation effect by the electrode is small, and the growth of a flame is hardly hindered. Furthermore, by making the thickness dimension of a second dielectric facing a discharge region uniform, the barrier discharge is spread over the surface of the second dielectric, the generation of the radicals is maintained, and combustibility after ignition is promoted. Furthermore, because an end portion of a high voltage electrode and a ground electrode are disposed to face each other within a combustion chamber, a fuel gas introduced into the combustion chamber is liable to flow into the discharge region, and is easily ignited by the radicals generated due to the discharge.

Abstract: An ignition system that uses a technique capable of restraining radiation of noise caused by discharge of a spark plug in the ignition system. The ignition system includes a spark plug and a power supply section. The spark plug is attached to an engine head. The power supply section has a battery having a ground terminal, and an ignition coil which transforms a voltage of the battery and supplies a transformed voltage to the spark plug. In the ignition system, a metallic shell of the spark plug is fixed to the engine head while being electrically insulated from the engine head through an insulator; an electrically conductive path is connected to the metallic shell; and the electrically conductive path is electrically connected to the ground terminal of the battery while being electrically insulated from the engine head.