A spark plug for an internal combustion engine is provided which has a center electrode and a ground electrode. The ground electrode includes an upright portion extending in a lengthwise direction of the spark plug and an extension bent from the upright portion in a radial direction of the spark plug. The extension has a slant surface which is shaped to be inclined away from the center electrode downstream in a flow of air-fuel mixture within a combustion chamber when the spark plug is mounted in the engine. This results in an increase in in distance by which a starting point on the ground electrode where a spark is created is moved on the slant surface, thereby increasing a length of time the spark is moved downstream and then blown out to increase the probability of successful ignition of the air-fuel mixture.

An ignition plug such as a spark plug or a glow plug configured to ignite an air-fuel mixture in an internal combustion engine includes a mark that is formed of an oxide film generated on the surface of a metal member or is formed of the metal member and the oxide film. The mark is formed by promoting formation of the oxide film on the surface of the metal member or removing the oxide film through radiation of a laser beam onto the surface of the metal member.

An ignition plug such as a spark plug or a glow plug configured to ignite an air-fuel mixture in an internal combustion engine includes a mark that is formed of an oxide film generated on the surface of a metal member or is formed of the metal member and the oxide film. The mark is formed by promoting formation of the oxide film on the surface of the metal member or removing the oxide film through radiation of a laser beam onto the surface of the metal member.

A corona igniter assembly 20 comprises an ignition coil assembly 22, a firing end assembly 24, and a metal tube 26 connecting the ignition coil assembly 22 to the firing end assembly 24. A rubber boot 28 is disposed in the metal tube 26 and compressed symmetrically between a coil output member 30 of the ignition coil assembly 22 and an insulator 42 of the firing end assembly 24. Thus, the rubber boot 28 fills any air gaps and provides a hermetic seal between the ignition coil assembly 22 and the firing end assembly 24 to prevent unwanted corona discharge from forming from those air gaps.

A corona igniter assembly 20 comprises an ignition coil assembly 22, a firing end assembly 24, and a metal tube 26 connecting the ignition coil assembly 22 to the firing end assembly 24. A rubber boot 28 is disposed in the metal tube 26 and compressed symmetrically between a coil output member 30 of the ignition coil assembly 22 and an insulator 42 of the firing end assembly 24. Thus, the rubber boot 28 fills any air gaps and provides a hermetic seal between the ignition coil assembly 22 and the firing end assembly 24 to prevent unwanted corona discharge from forming from those air gaps.

An engine ignition coil assembly disclosed herein provides an ignition coil housing that may be mounted on an engine block assembly and that is isolated from engine vibrations. The engine ignition coil assembly comprises an ignition coil housing. The ignition coil housing contains an ignition coil apparatus. An electrical connector for the ignition coil apparatus is mounted to the ignition coil housing. An elastomeric boot supports the ignition coil housing and may be disposed on an engine block assembly such that ignition coil housing is spaced apart from the engine block assembly by the elastomeric boot. A single fastener extends through a fastener opening in the ignition coil housing parallel with the elastomeric boot. An elastomeric isolator is disposed on the ignition coil housing at the fastener opening around the single fastener. A proximal end of the single fastener may be fixed to the engine block assembly.

A spark plug assembly includes a spark plug, where the spark plug includes a high voltage connector, an insulator body, a metallic shell, and an electrical conductor at least partly disposed in the insulator body and the metallic shell. The spark plug assembly includes a detection unit having a transmitter device and a receiver device. The transmitter device is coupled to the spark plug and is electrically disposed between the high voltage connector and the electrical conductor. Further, the transmitter device is configured to draw an excitation current from the electrical conductor. The transmitter device includes an optical signal generator that is configured to generate an optical signal in response to the drawn excitation current. The receiver device is disposed in optical communication with the transmitter device and configured to receive the optical signal from the transmitter device.

A spark plug assembly includes a spark plug, where the spark plug includes a high voltage connector, an insulator body, a metallic shell, and an electrical conductor at least partly disposed in the insulator body and the metallic shell. The spark plug assembly includes a detection unit having a transmitter device and a receiver device. The transmitter device is coupled to the spark plug and is electrically disposed between the high voltage connector and the electrical conductor. Further, the transmitter device is configured to draw an excitation current from the electrical conductor. The transmitter device includes an optical signal generator that is configured to generate an optical signal in response to the drawn excitation current. The receiver device is disposed in optical communication with the transmitter device and configured to receive the optical signal from the transmitter device.

An ignition coil for an internal combustion engine includes a coil main body portion, a connecting portion, and a conducting member. A convex surface forming portion, which is a portion constituting an inner peripheral convex surface, is disposed in the connecting portion. The convex surface forming portion has an outer peripheral concave surface. The connecting portion has a boundary portion which is a boundary between the convex surface forming portion and other portions in the axial direction. In the convex surface forming portion, at least a part of a region where the outer peripheral concave surface is formed has a portion having an area, in a cross-section orthogonal to the axial direction, equal to or smaller than that of the boundary portion. A thickness of the convex surface forming portion is equal to or thicker than that of the boundary portion.

An ignition coil for an internal combustion engine includes a coil main body portion, a connecting portion, and a conducting member. A convex surface forming portion, which is a portion constituting an inner peripheral convex surface, is disposed in the connecting portion. The convex surface forming portion has an outer peripheral concave surface. The connecting portion has a boundary portion which is a boundary between the convex surface forming portion and other portions in the axial direction. In the convex surface forming portion, at least a part of a region where the outer peripheral concave surface is formed has a portion having an area, in a cross-section orthogonal to the axial direction, equal to or smaller than that of the boundary portion. A thickness of the convex surface forming portion is equal to or thicker than that of the boundary portion.