Abstract: A spark plug having a metal shell, the metal shell having a tool engagement portion, a trunk portion and a cylindrical groove disposed between the tool engagement portion and the trunk portion, wherein the following relationship is satisfied: Z1<=Z2, where “Z1” represents a section modulus of a first groove end of the groove, and where “Z2” represents a section modulus of a second groove end of the groove.

Abstract: The present invention provides a spark plug that includes a center electrode extending in an axial direction, a ceramic insulator having an axial hole formed in the axial direction to retain the center electrode in a front side of the axial hole and thereby form an assembly unit of the center electrode and the ceramic insulator, a metal shell surrounding an outer circumference of the ceramic insulator to retain therein the assembly unit, and a ground electrode having one end portion joined to a front end face of the metal shell and the other end portion facing the center electrode to define a spark gap therebetween, wherein the spark plug satisfies the following conditions: H?1 mm, Vc?17 mm3 and Ra?1.

Abstract: A spark plug includes a ceramic insulator extending in the direction of an axis (CL1) and a metallic shell provided around the ceramic insulator. Talc is pressed charged between the ceramic insulator and the metallic shell and a crimp portion is formed for fixing the metallic shell and the ceramic insulator while the metallic shell having the ceramic insulator inserted thereinto is supported by a tubular receiving member. The receiving member is made movable in relation to a pressing jig in its radial direction. Thus, at the time of pressing of the talc, etc., the eccentricity between the center axis (CL2), (CL3) of the pressing jig and the axis (CL1) in the radial direction can be reduced, whereby the misalignment between the axis (CL1) and the center axis of the metallic shell or the like assembly error can be suppressed.

Abstract: A spark plug includes a ceramic insulator having a tapered rear end stepped portion whose diameter decreases from front to rear and a metal shell having a crimp portion which crimps the rear end stepped portion from the rear end. An area defined by an outer edge of the rear end stepped portion and an inner edge of the crimp portion is 5-25 mm2 when the spark plug is projected on a plane perpendicular to an axial line. An angle formed by a tapered surface of the rear end stepped portion and a plane perpendicular to the axial line is 20-60 degrees. A distance along the axial line from a front end of a proximal portion of the crimp portion to a frontmost position of a contact portion between an inner surface of the crimp and the rear end stepped portion is 0.4-1.8 mm.

Abstract: A spark plug having an insulator with improved breakage resistance. The spark plug has a cross-section that satisfies the following relationship: 0.6 mm<=L, where “A” represents a connection point between a support portion of the insulator and an insulator trunk portion formed at a front end side with respect to the support portion, where “B” represents a position closer to the outer circumference side among the positions of (a) an innermost position of a contact portion where the support portion and a packing are in contact with each other and (b) an intersection of the support portion and a virtual straight line that is parallel to an axial line of the spark plug and extends from an innermost circumferential end of a stepped portion of a metal shell, and where “L” represents a length of a path from point “A” to point “B” along a surface of the insulator.

Abstract: A spark plug having a metal shell, the metal shell having a tool engagement portion, a trunk portion and a cylindrical groove disposed between the tool engagement portion and the trunk portion, wherein the following relationship is satisfied: Z1<=Z2, where “Z1” represents a section modulus of a first groove end of the groove, and where “Z2” represents a section modulus of a second groove end of the groove.

Abstract: Disclosed is a spark plug having an insulator with good breakage resistance. A spark plug 1 contains a ceramic insulator 2, a plate packing 22 and a metal shell 3. The ceramic insulator 2 has, on an outer circumferential surface thereof, a step portion 14, a leg portion 13 and a curved surface portion 31 between the step portion 14 and the leg portion 13. The metal shell 3 has, on an inner circumferential surface thereof, a taper portion 21. The ceramic insulator 2 is fixed in the metal shell 3 with the step portion 14 retained on the taper portion 21 via the plate packing 22. Herein, 50% or more of an inner circumferential edge portion IP of the plate packing 22 is in contact with a part of the ceramic insulator 2 located front of a middle region CP of the curved surface portion 31.

Abstract: A spark plug capable of preventing breakage of a ground electrode. The spark plug is comprised of a ground electrode having a base end portion fixed to a metal shell, a bend portion integrally formed with the base end portion and being bent and a front end portion integrally formed with the bend portion and forming a spark discharge gap “g” with a center electrode. The ground electrode is comprised of a core extending from the base end portion towards the front end portion through the bend portion; and an outer layer disposed outside the core and extending from the base end portion up to the front end portion through the bend portion. The core is made of Hastelloy C serving as a first metal, and the outer layer is made of Inconel 601 serving as a second metal. Hardness of Hastelloy C is higher than that of Inconel 601.

Abstract: A spark plug having a front end of an insulating member which projects 2 mm or more from a front end face of a metal shell and a volume of the insulating member which lies within a range from a front end of the insulating member to a position lying 1 mm towards a rear end side is 11 mm3 or smaller. When the positions PA, PB, PC and PD are as defined herein, a parallel displacement amount E by which the straight line BC is displaced parallel until it contacts PD is 0.75 mm or larger. In this manner, the occurrence of lateral spark and inside spark can be suppressed effectively.

Abstract: A spark plug in which the rising of a ground electrode is more reliably restrained. The spark plug includes a ground electrode having a core portion extending from a proximal end section toward a distal end section via a bent section, a heat transfer portion extending from the proximal end section toward the distal end section via the bent section, and an external layer located externally of the core portion and the heat transfer portion and extending from the proximal end section to the distal end section via the bent section. As viewed on a section of the ground electrode taken orthogonally to a direction along which the ground electrode extends, at least at an intermediate position of the bent section with respect to the direction, the center of the core portion is offset toward a center electrode from the center of the heat transfer portion.

Abstract: Provided is a technique for limiting the radial displacement between a metal shell and an insulator in a spark plug. At the time of manufacturing a spark plug with a metal shell and an insulator, the metal shell and the insulator are assembled together by, while allowing relative positional displacement between the metal shell and the insulator in an axial direction (O-O), limiting relative positional displacement between the metal shell and the insulator in a radial direction intersecting with the axial direction in such a manner that the amount of deviation between an axis of the metal shell and an axis of the insulator becomes less than or equal to a predetermined level.

Abstract: [Objective] To provide a spark plug which is configured such that an insulation member, from which a center electrode projects, is pressed frontward and held in a metallic shell, and is fixed by means of crimping the rear end of the metallic shell, and which can prevent a drop in gas tightness between the metallic shell and the insulation member due to a difference in thermal expansion therebetween. [Means for Solution] In a spark plug in which a mating shaft portion (10) of an insulation member (1) is loose-fitted into a mating hole portion (30) of a metallic shell (21), a filler (41) for maintaining gas tightness is charged between the outer circumferential surface of the mating shaft portion (10) and the inner circumferential surface of the mating hole portion (30). Despite the thermal expansion difference, the gas tightness is maintained, because the filler (41) for maintaining gas tightness is charged between the inner and outer circumferential surfaces.

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 capable of preventing breakage of a ground electrode. The spark plug is comprised of a ground electrode having a base end portion fixed to a metal shell, a bend portion integrally formed with the base end portion and being bent and a front end portion integrally formed with the bend portion and forming a spark discharge gap “g” with a center electrode. The ground electrode is comprised of a core extending from the base end portion towards the front end portion through the bend portion; and an outer layer disposed outside the core and extending from the base end portion up to the front end portion through the bend portion. The core is made of Hastelloy C serving as a first metal, and the outer layer is made of Inconel 601 serving as a second metal. Hardness of Hastelloy C is higher than that of Inconel 601.

Abstract: A spark plug is such that a front end portion of an insulating member projects 2 mm or larger from a front end face of a metal shell and a volume of a portion of the insulating member which lies within a range from a front end of the insulating member to a position lying 1 mm towards a rear end side from the front end is 11 mm3 or smaller.

Abstract: The present invention provides a spark plug that includes a center electrode extending in an axial direction, a ceramic insulator having an axial hole formed in the axial direction to retain the center electrode in a front side of the axial hole and thereby form an assembly unit of the center electrode and the ceramic insulator, a metal shell surrounding an outer circumference of the ceramic insulator to retain therein the assembly unit, and a ground electrode having one end portion joined to a front end face of the metal shell and the other end portion facing the center electrode to define a spark gap therebetween, wherein the spark plug satisfies the following conditions: H?1 mm, Vc?17 mm3 and Ra?1.

Abstract: A spark plug in which a glaze is applied to a rear trunk portion (245), a shoulder portion (240), and a portion of a intermediate diameter portion (230) of an insulator (200), and glaze firing is performed. Even when the glaze (shown by dots in the drawings) softened by heating flows downwards, the glaze is accommodated within a groove portion (235) formed between the shoulder portion (240) and the maximum diameter portion (210), and does not reach the maximum diameter portion (210). Such structure facilitates assembly of the insulator (200) to a metallic shell in a spark plug manufacturing process.

Abstract: A spark plug in which the rising of a ground electrode is more reliably restrained. The spark plug includes a ground electrode having a core portion extending from a proximal end section toward a distal end section via a bent section, a heat transfer portion extending from the proximal end section toward the distal end section via the bent section, and an external layer located externally of the core portion and the heat transfer portion and extending from the proximal end section to the distal end section via the bent section. As viewed on a section of the ground electrode taken orthogonally to a direction along which the ground electrode extends, at least at an intermediate position of the bent section with respect to the direction, the center of the core portion is offset toward a center electrode from the center of the heat transfer 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 for an internal combustion engine includes: a cylindrical insulator as defined herein; a center electrode as defined herein; a cylindrical metal shell as defined herein; and a ground electrode as defined herein, an annular gasket receiving portion projecting radially outward being provided on a rear end side of the externally threaded portion of the metal shell, and a metallic gasket capable of abutting against the gasket receiving portion being provided on the outer periphery of the metal shell, wherein the gasket has a solid annular shape, an inside diameter of the gasket is smaller than an outside diameter of the externally threaded portion, and a groove portion whose depth coincides with the direction of the axis is provided over an entire circumference of the gasket.