An insulator arrangement for a spark plug arrangement, in particular for a prechamber spark plug, with an elongated body that has an insulator arrangement longitudinal bore for accommodating a center electrode arrangement and has a front end. A sealing shoulder is formed on an outer circumferential section of the body. An axial transition section is formed between the sealing shoulder and the front end of the body. The front end of the body is designed such that at least 50% of a gas flow impinging thereon in a first direction is deflected in a direction opposite to the first direction.

A spark plug has a housing, an insulator, a central electrode and a ground electrode. At least one projection part is formed on an outer peripheral surface of the insulator at a location facing a distal end cylindrical surface of the insulator in a radial direction of the spark plug so that at least one projection part has a minimum distance measured from a plug central axis of the spark plug, which is longer than a distance of another part of the insulator measured from the plug central axis. On a cross section of the spark plug, at least one projection part is formed on the outer peripheral surface of the insulator in a direction between at least one projection part and the plug central axis which crosses to a direction between a rod-shaped part and the plug central axis.

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

A method for manufacturing a spark plug that includes preparing an assembly fitted with a cylindrical insulator, and a main metal fitting disposed on an outer periphery of the insulator; photographing the assembly by using a camera disposed on the axis while turning on a first lighting equipment disposed; photographing the assembly by using the camera while turning on a second lighting equipment; specifying a position of an outer peripheral surface of the insulator by using one of photographed images; specifying a position of an inner peripheral surface of the main metal fitting by using the other of the photographed images; and specifying a size of a clearance between the insulator and the main metal fitting by using the position of the outer peripheral surface of the insulator and the position of the inner peripheral surface of the main metal fitting.

A method for manufacturing a spark plug that includes preparing an assembly fitted with a cylindrical insulator, and a main metal fitting disposed on an outer periphery of the insulator; photographing the assembly by using a camera disposed on the axis while turning on a first lighting equipment disposed; photographing the assembly by using the camera while turning on a second lighting equipment; specifying a position of an outer peripheral surface of the insulator by using one of photographed images; specifying a position of an inner peripheral surface of the main metal fitting by using the other of the photographed images; and specifying a size of a clearance between the insulator and the main metal fitting by using the position of the outer peripheral surface of the insulator and the position of the inner peripheral surface of the main metal fitting.

A spark plug including a tubular insulator extending in the direction of an axial line from a forward end side to a rear end side; and a tubular metallic shell fixed to an outer circumference of the insulator, the tubular metallic shell having a male thread formed on part of an outer circumferential surface thereof. The insulator has a groove formed in a region of an outer circumference thereof, the region overlapping the male thread of the metallic shell in the direction of the axial line. At least part of a heat transfer member is disposed in the groove. In a cross section passing through the axial line and extending along the axial line, the depth of the groove decreases toward at least one of a forward opening end of the groove and a rear opening end thereof.

A spark plug including a tubular insulator extending in the direction of an axial line from a forward end side to a rear end side; and a tubular metallic shell fixed to an outer circumference of the insulator, the tubular metallic shell having a male thread formed on part of an outer circumferential surface thereof. The insulator has a groove formed in a region of an outer circumference thereof, the region overlapping the male thread of the metallic shell in the direction of the axial line. At least part of a heat transfer member is disposed in the groove. In a cross section passing through the axial line and extending along the axial line, the depth of the groove decreases toward at least one of a forward opening end of the groove and a rear opening end thereof.

A corona igniter assembly which is designed to reduce the amount of air gaps between insulating components and thus reduce electrical fields concentrated in those air gaps and the associated unwanted corona discharge. The assembly includes a high voltage center electrode surrounded by a ceramic insulator and a high voltage insulator. A dielectric compliant insulator is disposed between the ceramic insulator and the high voltage insulator. A layer of metal is applied to at least one of the insulators, for example the ceramic insulator. A compliant collet formed of a partially resistive material covers a sharp edge of the layer of metal to reduce the electric field and smooth the electric field distribution at the sharp edge of the metal layer.

A corona igniter assembly which is designed to reduce the amount of air gaps between insulating components and thus reduce electrical fields concentrated in those air gaps and the associated unwanted corona discharge. The assembly includes a high voltage center electrode surrounded by a ceramic insulator and a high voltage insulator. A dielectric compliant insulator is disposed between the ceramic insulator and the high voltage insulator. A layer of metal is applied to at least one of the insulators, for example the ceramic insulator. A compliant collet formed of a partially resistive material covers a sharp edge of the layer of metal to reduce the electric field and smooth the electric field distribution at the sharp edge of the metal layer.

An ignition plug comprising: an insulator having a through hole extending from a rear-end side toward a forward-end side; a center electrode inserted at least partially into a portion of the through hole on the forward-end side; a metal terminal member inserted at least partially into a portion of the through hole on the rear-end side; and a seal disposed within the through hole and in contact with the center electrode and an inner circumferential surface of the insulator. The seal contains a glass and an electrically conductive substance, and the glass contained in the seal contains Si in an amount of 50 mass % or more as reduced to SiO.sub.2 and Na in an amount of 0.1 mass % or more and less than 1 mass % as reduced to Na.sub.2O.