A spark plug that can reduce variation in a discharge point. The spark plug includes: a center electrode; a metal shell insulating and holding the center electrode; and a ground electrode including a base material having one end portion connected to the metal shell, and a tip connected to another end portion of the base material. The tip has a discharge surface opposed to the center electrode with a spark gap therebetween. The discharge surface has a quadrangular shape and is chamfered at four sides thereof. Only a first side which is one of the four sides is provided with a C chamfer.

A spark plug for an internal combustion engine includes a cylindrical insulator, a center electrode, a cylindrical housing, and a plug cover. On a tip side of the insulator, an auxiliary combustion chamber is formed which is surrounded by at least the plug cover. The plug cover is provided with nozzle holes that communicate between the auxiliary combustion chamber and the outside of the auxiliary combustion chamber. A central axis of the nozzle hole is inclined with respect to a plug radial direction when viewed in a plug axial direction. At least a part around an outer opening of the nozzle hole is provided with a concave portion that is adjacent to the outer opening. The concave portion is recessed from the outside to the inside of the plug cover.

A spark plug for an internal combustion engine includes a cylindrical insulator, a center electrode, a cylindrical housing, and a plug cover. On a tip side of the insulator, an auxiliary combustion chamber is formed which is surrounded by at least the plug cover. The plug cover is provided with nozzle holes that communicate between the auxiliary combustion chamber and the outside of the auxiliary combustion chamber. A central axis of the nozzle hole is inclined with respect to a plug radial direction when viewed in a plug axial direction. At least a part around an outer opening of the nozzle hole is provided with a concave portion that is adjacent to the outer opening. The concave portion is recessed from the outside to the inside of the plug cover.

A metallic shell for a spark plug which metallic shell achieves suppressed elution of hexavalent chromium, and a spark plug including the metallic shell. The spark plug has a metallic shell. The metallic shell includes a tubular metallic shell body; a metal plating layer provided on a surface of the metallic shell body; and a chromium-containing chemical conversion coating layer provided to cover the metal plating layer. The chemical conversion coating layer has a zirconium component content of 0.1 mass % or more.

A metallic shell for a spark plug which metallic shell achieves suppressed elution of hexavalent chromium, and a spark plug including the metallic shell. The spark plug has a metallic shell. The metallic shell includes a tubular metallic shell body; a metal plating layer provided on a surface of the metallic shell body; and a chromium-containing chemical conversion coating layer provided to cover the metal plating layer. The chemical conversion coating layer has a zirconium component content of 0.1 mass % or more.

One example provides a spark plug having an insulative core extending along an axial centerline between a terminal and a firing end and including a central bore extending there through, and an insulative nose at the terminal end having an end surface. A center electrode includes an electrode head having an outer edge extending about a perimeter of the electrode head beyond a perimeter of the end surface of the insulative nose and forming a spark gap with a side electrode. The electrode includes an electrode plate, at least a portion of which is positioned axially beyond the end surface of the insulative nose and has cross-sectional which is at least greater than a cross-sectional area of the central bore. An electrode wire extends from the electrode plate into the central bore, wherein the electrode plate and electrode wire are a contiguous piece of material.

One example provides a spark plug having an insulative core extending along an axial centerline between a terminal and a firing end and including a central bore extending there through, and an insulative nose at the terminal end having an end surface. A center electrode includes an electrode head having an outer edge extending about a perimeter of the electrode head beyond a perimeter of the end surface of the insulative nose and forming a spark gap with a side electrode. The electrode includes an electrode plate, at least a portion of which is positioned axially beyond the end surface of the insulative nose and has cross-sectional which is at least greater than a cross-sectional area of the central bore. An electrode wire extends from the electrode plate into the central bore, wherein the electrode plate and electrode wire are a contiguous piece of material.

A spark plug housing. The spark plug housing includes an inner side, an outer side, and a longitudinal axis, which extends from an end of the spark plug housing facing toward the combustion chamber up to an end of the spark plug housing facing away from the combustion chamber. The spark plug housing includes a circumferential shoulder on its inner side, which is designed so that a spark plug insulator rests thereon, and a corrosion protection layer on its inner side, which is formed on a section of the inner side of the spark plug housing, the section extending from the end of the spark plug housing facing toward the combustion chamber to at least over the shoulder and along the inner circumference of the spark plug housing.

A spark plug housing. The spark plug housing includes an inner side, an outer side, and a longitudinal axis, which extends from an end of the spark plug housing facing toward the combustion chamber up to an end of the spark plug housing facing away from the combustion chamber. The spark plug housing includes a circumferential shoulder on its inner side, which is designed so that a spark plug insulator rests thereon, and a corrosion protection layer on its inner side, which is formed on a section of the inner side of the spark plug housing, the section extending from the end of the spark plug housing facing toward the combustion chamber to at least over the shoulder and along the inner circumference of the spark plug housing.

A prechamber spark plug for an internal combustion engine with the following features: a body with an external thread at its front end for screwing the spark plug into the engine; the external thread has a center line and begins with a thread start at the front end; the body has a passage in which an insulator is fastened and a center electrode protrudes from the front end of this insulator; at the front end of the body, a prechamber-forming cap is provided, which delimits a prechamber and shields the center electrode from a combustion chamber of the engine after the spark plug has been installed in the engine; the cap has at least one opening, which has a predefined orientation in relation to the thread start and is oriented obliquely to the center line of the external thread so as to permit a gas exchange between the prechamber and the space outside the prechamber.