A spark plug having a connection portion disposed in the axial hole and between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member disposed between the magnetic substance and the conductor, and an inner peripheral surface of the insulator and having lower electrical conductivity than the conductor. The conductor includes a base and a conductive layer disposed on an outer periphery of the base and having higher electrical conductivity than the base, and the conductive layer has a thickness of larger than 0.1 m and equal to or smaller than 25 m.

A spark plug having a connection portion disposed in the axial hole and between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member disposed between the magnetic substance and the conductor, and an inner peripheral surface of the insulator and having lower electrical conductivity than the conductor. The conductor includes a base and a conductive layer disposed on an outer periphery of the base and having higher electrical conductivity than the base, and the conductive layer has a thickness of larger than 0.1 m and equal to or smaller than 25 m.

A problem exists in that, as a loop through which high frequency energy conducts is long, it is difficult to suppress noise generated from the loop and suppress an influence thereof on peripheral equipment. A high frequency discharge ignition device according to this invention is a structure integrally constituted by a second housing into which a high frequency energy supply circuit is built and a first housing into which an output circuit is built, wherein the high frequency energy supply circuit is connected to the output circuit by a connection terminal so as to be connected to a spark plug which is mounted on a grounded object. Further, the high frequency energy supply circuit is grounded via a conducting member disposed in a through hole provided in the first housing.

A problem exists in that, as a loop through which high frequency energy conducts is long, it is difficult to suppress noise generated from the loop and suppress an influence thereof on peripheral equipment. A high frequency discharge ignition device according to this invention is a structure integrally constituted by a second housing into which a high frequency energy supply circuit is built and a first housing into which an output circuit is built, wherein the high frequency energy supply circuit is connected to the output circuit by a connection terminal so as to be connected to a spark plug which is mounted on a grounded object. Further, the high frequency energy supply circuit is grounded via a conducting member disposed in a through hole provided in the first housing.

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.

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.

Spark plug connector with a connector body, which has a first end portion for inserting an end of a high-tension lead and a second end portion for receiving an end of a spark plug, wherein an electrical wiring section for transmitting a sparking voltage from the high-tension lead to the spark plug is arranged between the first end portion and the second end portion, and wherein the electrical wiring section has, adjacent to the first end portion, at least one inductor; internal combustion engine with at least one arrangement consisting of a spark plug and such a spark plug connector; and arrangement with a device to be driven mechanically and at least one such internal combustion engine for driving the device to be driven mechanically.

Spark plug connector with a connector body, which has a first end portion for inserting an end of a high-tension lead and a second end portion for receiving an end of a spark plug, wherein an electrical wiring section for transmitting a sparking voltage from the high-tension lead to the spark plug is arranged between the first end portion and the second end portion, and wherein the electrical wiring section has, adjacent to the first end portion, at least one inductor; internal combustion engine with at least one arrangement consisting of a spark plug and such a spark plug connector; and arrangement with a device to be driven mechanically and at least one such internal combustion engine for driving the device to be driven mechanically.

A spark plug having a connection portion disposed in the axial hole and between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member disposed between the magnetic substance and the conductor, and an inner peripheral surface of the insulator and having lower electrical conductivity than the conductor. The conductor includes a base and a conductive layer disposed on an outer periphery of the base and having higher electrical conductivity than the base, and the conductive layer has a thickness of larger than 0.1 m and equal to or smaller than 25 m.

A spark plug having a connection portion disposed in the axial hole and between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member disposed between the magnetic substance and the conductor, and an inner peripheral surface of the insulator and having lower electrical conductivity than the conductor. The conductor includes a base and a conductive layer disposed on an outer periphery of the base and having higher electrical conductivity than the base, and the conductive layer has a thickness of larger than 0.1 m and equal to or smaller than 25 m.