A spark plug, including a housing, an insulator situated in the housing, a center electrode situated in the insulator and a ground electrode situated on the housing, the ground electrode and the center electrode being situated relative to one another in such a way that the ground electrode and the center electrode form a spark gap, and the ground electrode including a core and a sheath surrounding the core, the core being made of a material which has a higher thermal conductivity than the material of the sheath, and a cross sectional area of the ground electrode being not greater than 2.76 mm.sup.2, the sheath having a wall thickness c of not greater than 0.4 mm in a first region of the ground electrode.

A spark plug, including a housing, an insulator situated in the housing, a center electrode situated in the insulator and a ground electrode situated on the housing, the ground electrode and the center electrode being situated relative to one another in such a way that the ground electrode and the center electrode form a spark gap, and the ground electrode including a core and a sheath surrounding the core, the core being made of a material which has a higher thermal conductivity than the material of the sheath, and a cross sectional area of the ground electrode being not greater than 2.76 mm.sup.2, the sheath having a wall thickness c of not greater than 0.4 mm in a first region of the ground electrode.

An electrode tip assembly for a spark plug includes an electrode tip that is formed on an electrode base using an additive manufacturing process, such as a powder bed fusion technique, after which the electrode base is welded to an electrode body. The electrode base includes a welding side and an additive manufacturing side, and the electrode tip includes a plurality of laser deposition layers built on the additive manufacturing side of the electrode base.

An electrode tip assembly for a spark plug includes an electrode tip that is formed on an electrode base using an additive manufacturing process, such as a powder bed fusion technique, after which the electrode base is welded to an electrode body. The electrode base includes a welding side and an additive manufacturing side, and the electrode tip includes a plurality of laser deposition layers built on the additive manufacturing side of the electrode base.

In a cross section including a central axis, a value L/D obtained by dividing an axial length L of an overlap portion where a metal contact surface located on a metal shell and on which a packing is in contact with the metal shell overlaps a projection plane located on the metal shell and on which a contact surface located on an insulator and on which the packing is in contact with the insulator is projected in a direction orthogonal to the central axis by a difference D between a radius of an outer circumference of a tube portion at a connection position to a step portion and a radius of an outer circumference of a leg portion at a connection position to the step portion is 1.2 or more. This ensures the force of constraint in the radial direction provided by the packing on the insulator.

A plasma jet plug includes a rod-shaped central electrode, an insulator having an axial hole, a metal shell disposed around the insulator, an orifice electrode electrically connected to the metal shell and located at a distal end side of the insulator, and a gasket that contacts an outer surface of the insulator and an inner surface of the metal shell. The insulator includes a first member, a second member and an inorganic seal layer. The first member has the axial hole and includes a large-diameter portion and a small-diameter portion. The second member has a through hole into which the small-diameter portion is inserted. The second member has an outer surface that contacts the gasket. The inorganic seal layer seals a gap between the first member and the second member. In a section including the axis, the sum of seal lengths is greater than or equal to 3 mm.

A plasma jet plug includes a rod-shaped central electrode, an insulator having an axial hole, a metal shell disposed around the insulator, an orifice electrode electrically connected to the metal shell and located at a distal end side of the insulator, and a gasket that contacts an outer surface of the insulator and an inner surface of the metal shell. The insulator includes a first member, a second member and an inorganic seal layer. The first member has the axial hole and includes a large-diameter portion and a small-diameter portion. The second member has a through hole into which the small-diameter portion is inserted. The second member has an outer surface that contacts the gasket. The inorganic seal layer seals a gap between the first member and the second member. In a section including the axis, the sum of seal lengths is greater than or equal to 3 mm.

A spark plug having an insulator with a leg portion whose outer circumferential surface has an arithmetic mean roughness Ra of 0.5 μm or less. The leg portion has a first section, a second section, and a third section. The first section has an outer diameter that decreases toward the forward end of the first section. The second section is located forward of and adjacent to the first section and its outer diameter decreases toward the forward end of the second section. The outer circumferential surface of the second section is located inward of a first straight line passing through the base and forward ends of the outer circumferential surface of the first section. The third section is located forward of and adjacent to the second section. The outer diameter of the third section is equal to or less than a forward end outer diameter Ds of the second section over the entire third section.

A batch of spark plugs. Each spark plug has a longitudinal axis, a central electrode oriented in the direction of the longitudinal axis, a ground electrode oriented at an angle to the longitudinal axis, such that a spark gap is formed between a tip of the central electrode and a tip of the ground electrode, and an outer thread for screwing the spark plug in the longitudinal direction into an inner thread of a cylinder head of a combustion chamber of an internal combustion engine, and has an annular contact surface oriented perpendicularly to the longitudinal axis and intended for bringing the spark plug to rest against the cylinder head. After the spark plugs have been screwed into the inner thread of the cylinder head, the ground electrodes have the same orientation with regard to a rotation about the longitudinal axis of the spark plug relative to the combustion chamber.

A pre-chamber spark plug that includes a shell, and an end cap attached to the shell. Additionally, the pre-chamber spark plug includes an insulator disposed within the shell. In a particular embodiment, a center electrode has a first portion surrounded by the insulator, and a second portion that extends from the insulator into a pre-chamber. The pre-chamber defined by the shell and end cap. In a further embodiment, a ground electrode is attached to the shell. In particular embodiments, the ground electrode is tubular in shape and includes an inner spark surface ring spaced in surrounding relation to the center electrode to create a spark gap, an outer ring attached to the shell, and a plurality of rounded spokes connecting the inner and outer rings. In a particular embodiment, the ground and center electrodes accommodate attachment of precious metal alloys to increase electrode surface life.