A corona comprises a central electrode surrounded by an insulator, which is surrounded by a conductive component. The conductive component includes a shell and an intermediate part both formed of an electrically conductive material. The intermediate part is a layer of metal which brazes the insulator to the shell. An outer surface of the insulator presents a lower ledge, and the layer of metal can be applied to the insulator above the lower ledge prior to or after inserting the insulator into the shell. The conductive inner diameter is less than an insulator outer diameter directly below the lower ledge such the insulator thickness increases toward the electrode firing end. The insulator outer diameter is also typically less than the shell inner diameter so that the corona igniter can be forward-assembled.

A corona comprises a central electrode surrounded by an insulator, which is surrounded by a conductive component. The conductive component includes a shell and an intermediate part both formed of an electrically conductive material. The intermediate part is a layer of metal which brazes the insulator to the shell. An outer surface of the insulator presents a lower ledge, and the layer of metal can be applied to the insulator above the lower ledge prior to or after inserting the insulator into the shell. The conductive inner diameter is less than an insulator outer diameter directly below the lower ledge such the insulator thickness increases toward the electrode firing end. The insulator outer diameter is also typically less than the shell inner diameter so that the corona igniter can be forward-assembled.

A spark plug including a center electrode that has a large-diameter portion having an outside diameter that is largest in the center electrode. The large-diameter portion is retained at a rear facing surface in an axial hole of an insulator. A metal shell has a diameter increased portion on a rear end side with respect to the center electrode, the diameter increased portion having an inside diameter that is increased toward the rear end side. The insulator has a first portion which is a portion of the insulator in a region from a rear end of the rear facing surface to a front end of the diameter increased portion. The first portion has a thickness that is the largest in the region, and is disposed at least on an outer periphery of the large-diameter portion.

An insulator for a spark plug including a first portion; a second portion located on the rear side of the first portion, an outer diameter F at a front end of the second portion being smaller than an outer diameter of the first portion; a third portion located on the front side of the first portion, an outer diameter D at a rear end of the third portion being smaller than the outer diameter of the first portion and the outer diameter F at the front end of the second portion; a first slope portion connecting the first portion and the second portion; and a second slope portion connecting the first portion and the third portion. A length A of the second slope portion and a length B of the first slope portion satisfy 2.0≤A/B≤3.9, and 0.50≤D/F≤0.88 is satisfied.

A spark plug is provided that ensures that a ground electrode is positioned in a predefined, precise orientation when installed in a spark plug hole of an engine head. The spark plug is configured for axial insertion into the plug hole, and has a non-axisymmetric ground shield that fits into the plug hole, wherein the ground shield has an outer shield surface with a non-axisymmetric shape and the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the spark plug includes a jamb nut which is rotatable to fix the spark plug in position in a predefined orientation. Preferably, an outer surface of the insulator and an inner surface of the ground shield have complementary shapes wherein the ground shield fits closely on the insulator. For example, the outer insulator surface and the inner shield surface may have a complementary axisymmetric shape, such as cylindrical, or a non-axisymmetric shape, which may conform to the non-axisymmetric shape of the outer shield surface.

A spark plug is provided that ensures that a ground electrode is positioned in a predefined, precise orientation when installed in a spark plug hole of an engine head. The spark plug is configured for axial insertion into the plug hole, and has a non-axisymmetric ground shield that fits into the plug hole, wherein the ground shield has an outer shield surface with a non-axisymmetric shape and the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the spark plug includes a jamb nut which is rotatable to fix the spark plug in position in a predefined orientation. Preferably, an outer surface of the insulator and an inner surface of the ground shield have complementary shapes wherein the ground shield fits closely on the insulator. For example, the outer insulator surface and the inner shield surface may have a complementary axisymmetric shape, such as cylindrical, or a non-axisymmetric shape, which may conform to the non-axisymmetric shape of the outer shield surface.

A spark plug is provided, including a housing, an insulator situated within a housing, the insulator having a longitudinal axis, an insulator foot, body, head, and seat. Inside the housing is a housing seat which is in contact with the insulator seat of the insulator. An inner seal is situated between the housing seat and the insulator seat, so that the inner seal, the housing seat, and the insulator seat form a sealing system. The insulator seat includes a step that has a first section and a second section having an angle γ to one another that is greater than 0° and the first section being parallel to the insulator longitudinal axis. The inner seal is in contact with this first section, so that a radial sealing surface is formed at the insulator.

A spark plug is provided, including a housing, an insulator situated within a housing, the insulator having a longitudinal axis, an insulator foot, body, head, and seat. Inside the housing is a housing seat which is in contact with the insulator seat of the insulator. An inner seal is situated between the housing seat and the insulator seat, so that the inner seal, the housing seat, and the insulator seat form a sealing system. The insulator seat includes a step that has a first section and a second section having an angle γ to one another that is greater than 0° and the first section being parallel to the insulator longitudinal axis. The inner seal is in contact with this first section, so that a radial sealing surface is formed at the insulator.

A spark plug has a housing, an insulator, a central electrode and a ground electrode. A projection part is formed projecting radially from the housing. The spark plug has a structure which satisfies a relationship of t2/t1≤0.85, s1≤0.5, and s1≥1.05−t2/t1. A leg part of the insulator has a first end and a second end in an axial direction thereof. The second end is located opposite to the first end in the axial direction. In the relationship, t1 represents a first radial thickness of the first end in a radial direction of the leg part, t2 represents a center radial thickness in the radial direction at a middle position of the leg part, and s1 represents a first gap width in the radial direction of the housing between the projection part of the housing and the first end of the leg part.

A spark plug has a housing, an insulator, a central electrode and a ground electrode. A projection part is formed projecting radially from the housing. The spark plug has a structure which satisfies a relationship of t2/t1≤0.85, s1≤0.5, and s1≥1.05−t2/t1. A leg part of the insulator has a first end and a second end in an axial direction thereof. The second end is located opposite to the first end in the axial direction. In the relationship, t1 represents a first radial thickness of the first end in a radial direction of the leg part, t2 represents a center radial thickness in the radial direction at a middle position of the leg part, and s1 represents a first gap width in the radial direction of the housing between the projection part of the housing and the first end of the leg part.