Abstract: A spark plug includes an insulator and a center electrode. The insulator includes: a first cylindrical portion; a truncated cone-shaped portion whose outer diameter reduces toward a front end side; and a second cylindrical portion formed at a front end side of the truncated cone-shaped portion. A diameter C of the center electrode is not larger than 2.2 mm. A total I of a volume of the truncated cone-shaped portion and a volume of the second cylindrical portion, a volume E of the center electrode from a position at a rear end of the truncated cone-shaped portion to a position at a front end of the second cylindrical portion, and the diameter C satisfy I/E?4.2333C2?19.79C+24.869.

Abstract: A spark plug includes an insulator and a center electrode. The insulator includes: a first cylindrical portion; a truncated cone-shaped portion whose outer diameter reduces toward a front end side; and a second cylindrical portion formed at a front end side of the truncated cone-shaped portion. A diameter C of the center electrode is not larger than 2.2 mm. A total I of a volume of the truncated cone-shaped portion and a volume of the second cylindrical portion, a volume E of the center electrode from a position at a rear end of the truncated cone-shaped portion to a position at a front end of the second cylindrical portion, and the diameter C satisfy I/E?4.2333C2?19.79C+24.869.

Abstract: The ignitability of a spark plug configured without a noble metal for a center electrode and a ground electrode is improved. The spark plug comprises a center electrode, an insulator, a metal shell, and a ground electrode including a discharge surface. The ground electrode forms a spark gap between the discharge surface and the center electrode. The center electrode and the ground electrode both do not include a noble metal. The ground electrode comprises a proximal end portion combined with the metal shell and positioned above, the discharge surface and a distal end portion including the discharge surface and positioned below the proximal end portion while continued from the proximal end portion. A width Da of the center electrode viewed from a first direction and a width Db of the proximal end portion viewed from the first direction satisfy Db/Da?0.92. The first direction is perpendicular to the axial direction and directing from the proximal end portion to the center electrode.

Abstract: A spark plug includes: a metal shell having a mounting thread formed with a nominal diameter of M12 or smaller; a ground electrode consisting of a first structural member and at least one ith structural member (i=2, 3, 4, 5) laminated to cover an outer surface thereof, the length of protrusion of the ground electrode from a front end face of the metal shell being 4.5 mm or larger, the ground electrode having a bent portion with a curvature radius of 2.3 mm or smaller; and an electrode tip joined thereto at a position facing the front end of the center electrode and having a protrusion length of 0.5 mm or larger and a cross sectional area of 0.20 to 1.13 mm2. The ground electrode has a total thermal conductivity of 35 W/(m·K) or higher at 20° C.

Abstract: A sealing member for a cylindrical spark plug having a metal shell with threaded ridges thereon to be screwed into a mounting hole of a combustion engine, the sealing member comprised of a piece of annular sheet material made of austenitic stainless steel or ferritic stainless steel that is folded back in a radial direction so as to form a region where at least two or more layers of the sheet material are overlapped in an axial direction.

Abstract: The ignitability of a spark plug configured without a noble metal for a center electrode and a ground electrode is improved. The spark plug comprises a center electrode, an insulator, a metal shell, and a ground electrode including a discharge surface. The ground electrode forms a spark gap between the discharge surface and the center electrode. The center electrode and the ground electrode both do not include a noble metal. The ground electrode comprises a proximal end portion combined with the metal shell and positioned above, the discharge surface and a distal end portion including the discharge surface and positioned below the proximal end portion while continued from the proximal end portion. A width Da of the center electrode viewed from a first direction and a width Db of the proximal end portion viewed from the first direction satisfy Db/Da?0.92. The first direction is perpendicular to the axial direction and directing from the proximal end portion to the center electrode.

Abstract: A spark plug of the present invention is designed as a small-diameter spark plug, which includes: a metal shell having a mounting thread formed with a nominal diameter of M12 or smaller based on JIS standard; a ground electrode consisting a first structural member extending from one end toward the other end thereof and at least one ith structural member (i=2, 3, 4, 5) laminated to cover an outer surface of the first structural member, the length of protrusion of the other end of the ground electrode from a front end face of the metal shell being 4.5 mm or larger, the ground electrode having a bent portion formed between the one end to the other end thereof with a curvature radius of 2.3 mm or smaller; and an electrode tip joined to the other end of the ground electrode at a position facing the front end of the center electrode and having a protrusion length of 0.5 mm or larger and a cross sectional area of 0.20 to 1.13 mm2.

Abstract: A sealing member for a cylindrical spark plug having a metal shell with threaded ridges thereon to be screwed into a mounting hole of a combustion engine, the sealing member comprised of a piece of annular sheet material made of austenitic stainless steel or ferritic stainless steel that is folded back in a radial direction so as to form a region where at least two or more layers of the sheet material are overlapped in an 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.

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.