Abstract: A spark plug (1) for an internal combustion engine includes: a cylindrical insulator (2) having an axial hole (4) penetrating in a direction of an axis (C1); a center electrode (5) partially inserted in the axial hole (4); a metal shell (3) surrounding an outer periphery of the insulator (2) and which is fixed to the insulator (2) by means of a crimped portion (20) provided at a rear end portion of the metal shell (3); and a ground electrode (27) joined to the metal shell (3) such that a portion of the ground electrode (27) opposes a leading end portion of the center electrode (5) via a spark discharge gap (33), wherein the insulator (2) has an annular groove portion (23) which opposes an inner edge of the crimped portion (20).

Abstract: A spark plug including: a center electrode including an electrode base member and a core member; an electrode tip joined to the center electrode via a molten bond; an insulator holding the center electrode; a metal shell holding the insulator; and a ground electrode joined to the metal shell. Relationships d?2.1 [mm] and ?0.09×d+0.33<Vb/(Va+Vb)<?0.2×d+0.75 are satisfied, where d is an outer diameter of the center electrode at a position 4 mm closer to the base end of the center electrode from the base end of the molten bond in the axial direction, and Va and Vb are volumes of the electrode base member and the core member, respectively, at a region between the base end of the molten bond and the position in the axial direction.

Abstract: There is provided a spark plug of an internal combustion engine, including a cylindrical metal shell, an insulator retained in the metal shell and having a through hole in an axial direction of the spark plug and a center electrode fitted in the through hole of the insulator. The insulator includes a rear body portion, a middle body portion and a large-diameter portion located between and protruded radially outwardly from the rear and middle body portions to define a rear shoulder section connected to the rear body portion and a front shoulder section connected to the middle body portion. For strength improvements, the insulator has a first glaze layer extending over the rear body portion and the rear shoulder section of the large-diameter portion and a second glaze layer extending over at least part of the middle body portion from some point on the front shoulder section of the large-diameter portion.

Abstract: A spark plug including: a center electrode including an electrode base member and a core member; an electrode tip joined to the center electrode via a molten bond; an insulator holding the center electrode; a metal shell holding the insulator; and a ground electrode joined to the metal shell. Relationships d?2.1 [mm] and ?0.09×d+0.33<Vb/(Va+Vb)<?0.2×d+0.75 are satisfied, where d is an outer diameter of the center electrode at a position 4 mm closer to the base end of the center electrode from the base end of the molten bond in the axial direction, and Va and Vb are volumes of the electrode base member and the core member, respectively, at a region between the base end of the molten bond and the position in the axial direction.

Abstract: A spark plug is provided with a metal shell and a ceramic insulator to support therein a center electrode. The ceramic insulator includes a front portion with a stepped outer surface, a middle portion, a rear portion and a shoulder portion defined between the middle and rear portions. A difference between the outer diameters of the middle and rear portions of the ceramic insulator is 1.8 mm or smaller. The metal shell includes a radially inward protrusion to retain thereon the stepped outer surface of the ceramic insulator and a rear end portion crimped onto the shoulder portion of the ceramic insulator. An inner circumferential surface of the crimped shell portion has a region held in contact with the insulator shoulder portion with a radially innermost point of the crimped shell portion being spaced radially apart from the ceramic insulator and axially apart from the insulator shoulder portion.

Abstract: There is provided a spark plug of an internal combustion engine, including a cylindrical metal shell, an insulator retained in the metal shell and having a through hole in an axial direction of the spark plug and a center electrode fitted in the through hole of the insulator. The insulator includes a rear body portion, a middle body portion and a large-diameter portion located between and protruded radially outwardly from the rear and middle body portions to define a rear shoulder section connected to the rear body portion and a front shoulder section connected to the middle body portion. For strength improvements, the insulator has a first glaze layer extending over the rear body portion and the rear shoulder section of the large-diameter portion and a second glaze layer extending over at least part of the middle body portion from some point on the front shoulder section of the large-diameter portion.

Abstract: A spark plug (1) for an internal combustion engine includes: a cylindrical insulator (2) having an axial hole (4) penetrating in a direction of an axis (C1); a center electrode (5) partially inserted in the axial hole (4); a metal shell (3) surrounding an outer periphery of the insulator (2) and which is fixed to the insulator (2) by means of a crimped portion (20) provided at a rear end portion of the metal shell (3); and a ground electrode (27) joined to the metal shell (3) such that a portion of the ground electrode (27) opposes a leading end portion of the center electrode (5) via a spark discharge gap (33), wherein the insulator (2) has an annular groove portion (23) which opposes an inner edge of the crimped portion (20).

Abstract: A spark plug is provided with a metal shell and a ceramic insulator to support therein a center electrode. The ceramic insulator includes a front portion with a stepped outer surface, a middle portion, a rear portion and a shoulder portion defined between the middle and rear portions. A difference between the outer diameters of the middle and rear portions of the ceramic insulator is 1.8 mm or smaller. The metal shell includes a radially inward protrusion to retain thereon the stepped outer surface of the ceramic insulator and a rear end portion crimped onto the shoulder portion of the ceramic insulator. An inner circumferential surface of the crimped shell portion has a region held in contact with the insulator shoulder portion with a radially innermost point of the crimped shell portion being spaced radially apart from the ceramic insulator and axially apart from the insulator shoulder portion.