Abstract: A spark plug for an internal combustion engine has a cylindrical insulator, a center electrode held inside of the insulator, and, a terminal portion held inside of the insulator and electrically connected to the center electrode. The insulator has a insertion portion arranged closer to the base end side than the housing is, the insertion portion being inserted into a cylindrical plug cap. The insertion portion has a non-fit portion formed at the base end of the insulator, and, a fit portion formed to the head end side of the non-fit portion, an outer diameter of the non-fit portion being equal to or smaller than an inner diameter of the plug cap, the fit portion being fitted in the inner periphery surface of the plug cap.

Abstract: A spark plug includes a main fitting having a first, second, and third portions adjacent to each other. The spark plug further includes an insulator having a first opposing portion with a predetermined portion opposed to the first portion with a first interval, a second opposing portion with a second portion opposing the second portion with a second interval, and a third opposed portion opposed to the third portion. A connecting portion between the second opposing portion is supported by a support portion, and a value obtained by dividing the first interval by a length from the support portion to a rear end portion of the predetermined portion is configured to be smaller than a value obtained by dividing the second interval by a length from the support portion to a rear end portion of the second opposed portion.

Abstract: A spark plug includes a main fitting having a first, second, and third portions adjacent to each other. The spark plug further includes an insulator having a first opposing portion with a predetermined portion opposed to the first portion with a first interval, a second opposing portion with a second portion opposing the second portion with a second interval, and a third opposed portion opposed to the third portion. A connecting portion between the second opposing portion is supported by a support portion, and a value obtained by dividing the first interval by a length from the support portion to a rear end portion of the predetermined portion is configured to be smaller than a value obtained by dividing the second interval by a length from the support portion to a rear end portion of the second opposed portion.

Abstract: The spark plug has a configuration satisfying the relationships of B?0.7A and 0.3 mm?A?0.6 mm, where B is an axial thickness along the central axis line Q of the weld portion formed between the base material electrode and the noble-metal chip, and A is an axial distance along the central axis line Q between the intersection points P3 and X. The intersection point P3 is a point at which a phantom axis line radially distant from the central axis line Q by D/2 (D being a diameter of the noble-metal chip) intersects with the boundary line between the weld portion and the noble-metal chip. The intersection point X is a point at which an extension of the contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line between the weld portion and the base material electrode.

Abstract: The spark plug has a configuration satisfying the relationships of B?0.7A and 0.3 mm?A?0.6 mm, where B is an axial thickness along the central axis line Q of the weld portion formed between the base material electrode and the noble-metal chip, and A is an axial distance along the central axis line Q between the intersection points P3 and X. The intersection point P3 is a point at which a phantom axis line radially distant from the central axis line Q by D/2 (D being a diameter of the noble-metal chip) intersects with the boundary line between the weld portion and the noble-metal chip. The intersection point X is a point at which an extension of the contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line between the weld portion and the base material electrode.

Abstract: A spark plug for an internal combustion engine has a cylindrical insulator, a center electrode held inside of the insulator, and, a terminal portion held inside of the insulator and electrically connected to the center electrode. The insulator has a insertion portion arranged closer to the base end side than the housing is, the insertion portion being inserted into a cylindrical plug cap. The insertion portion has a non-fit portion formed at the base end of the insulator, and, a fit portion formed to the head end side of the non-fit portion, an outer diameter of the non-fit portion being equal to or smaller than an inner diameter of the plug cap, the fit portion being fitted in the inner periphery surface of the plug cap.

Abstract: A method of manufacturing a spark plug having an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to attachment fitting 2, earth electrode 5 has a convex part 510 formed by projecting a part of an opposed surface 51 toward center electrode 4, and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 passes through the area in which the concave part 520 is formed. The relation S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug for an internal-combustion engine comprises an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to the attachment fitting 2, the earth electrode 5 has a convex part 510 formed by projecting toward the center electrode 4 a part of the opposed surface 51, which faces the center electrode 4, of the earth electrode and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52 which is the reverse side of the opposed surface 51 of the earth electrode 5. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 may pass through the area in which the concave part 520 is formed. A relation of S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A method of manufacturing a spark plug having an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to attachment fitting 2, earth electrode 5 has a convex part 510 formed by projecting a part of an opposed surface 51 toward center electrode 4, and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 passes through the area in which the concave part 520 is formed. The relation S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug for an internal-combustion engine comprises an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5 . While fixed to the attachment fitting 2, the earth electrode 5 has a convex part 510 formed by projecting toward the center electrode 4 a part of the opposed surface 51, which faces the center electrode 4, of the earth electrode and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52 which is the reverse side of the opposed surface 51 of the earth electrode 5 . The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 may pass through the area in which the concave part 520 is formed. A relation of S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug has a compact structure where a threaded portion of a metal shell has a size of M10 or M12 and the width between any two opposite side surfaces of a polygonal prism-shaped portion of the metal shell is no greater than 14 mm. In the spark plug, a thickness A of the polygonal prism-shaped portion of the metal shell, a thickness B of a crimped portion of the metal shell, and a thickness C of a buckled portion of the metal shell are subject to a dimensional relationship of A>B>C. Through specifying such a relationship, the crimped portion of the metal shell exerts a large constricting force on sealing members provided in a gap between the inner surface of the polygonal prism-shaped portion of the metal shell and the outer surface of an insulator, thereby securing high gas tightness of the spark plug.

Abstract: In producing a spark plug including a central electrode having a first chip including noble metal and an earth electrode having a second chip including the noble metal, a spark gap being disposed between the first and second chips, a chip including the noble metal. The chip is welded to an end of the central electrode and to an end of the earth electrode. The welded chip is cut to form the first and second chips and the spark gap.

Abstract: An improved structure of a spark plug is provided for improving heat dissipation from an Ir-alloy chip attached to a ground electrode. The Ir-alloy chip works to a sequence of sparks between itself and the tip of a center electrode mounted in a metal shell and is embedded in a center electrode-facing surface of the ground electrode, thereby enhancing the transmission of heat produced in the Ir-alloy chip to the metal shell through the ground electrode.

Abstract: In producing a spark plug including a central electrode having a first chip including noble metal and an earth electrode having a second chip including the noble metal, a spark gap being disposed between the first and second chips, a chip including the noble metal. The chip is welded to an end of the central electrode and to an end of the earth electrode. The welded chip is cut to form the first and second chips and the spark gap.

Abstract: An improved structure of a spark plug is provided for improving heat dissipation from an Ir-alloy chip attached to a ground electrode. The Ir-alloy chip works to a sequence of sparks between itself and the tip of a center electrode mounted in a metal shell and is embedded in a center electrode-facing surface of the ground electrode, thereby enhancing the transmission of heat produced in the Ir-alloy chip to the metal shell through the ground electrode.