Abstract: A spark plug according to the invention includes a metal shell that has a threaded portion with an outer diameter of 10 mm or less, or equal to 12 mm, an insulator, a center electrode, and a ground electrode. The spark plug has an improved structure in which an end portion of the insulator tapers toward an end thereof that protrudes from an end of the metal shell, and dimensional parameters, including a space G of the spark gap in the spark plug, a taper degree of the end portion of the insulator that is represented by an outer diameter difference (D?D0) in the end portion, and a size T0 of the air pocket formed in the spark plug, each have an effective range determined based on the experimental investigation results from the inventors. The structure ensures high insulation properties and high ignition capability of the spark plug.

Abstract: A spark plug according to the present invention includes a metal shell, an insulator, a cylindrical center electrode, a first ground electrode, and a second ground electrode. The first ground electrode is aligned with the center electrode in the axial direction of the center electrode to form a first spark gap, across which normal sparks are discharged when the insulator is not fouled with carbon. The second ground electrode is aligned with the center electrode in the radial direction of the center electrode to form a second spark gap, across which side sparks are discharged when the insulator is fouled with carbon. The spark plug has an improved structure where dimensional parameters A, T, B, C, L, D, and E are specified to be in suitable ranges that are determined through experimental investigation. The improved structure ensures a high ignition capability and a long service life of the spark plug.

Abstract: A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. The metal shell has a threaded portion with an outer diameter of equal to or less than 10 mm, or equal to 12 mm for installing the spark plug in an internal combustion engine. The dimensional parameters in the structure of the spark plug, such as a clearance X between the center electrode and the insulator, a surface-creeping distance Y outside the metal shell, a protruding length Y1 of the insulator, an air pocket size Z, and a surface-creeping distance W inside the metal shell satisfy the dimensional relationships defined through experimental investigation in the invention. The structure ensures a high capability of the spark plug to ignite the air-fuel mixture even when the insulator thereof is fouled with carbon.

Abstract: A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. The insulator is retained in the metal shell. The center electrode is secured in the insulator and has an end portion that protrudes from the insulator and has an end edge. The ground electrode includes a base member fixed to the metal shell and a protruding member joined to the base member. The protruding member protrudes from a surface of the base member and has a hollow end face that faces the end portion of the center electrode through a spark gap. The end face of the protruding member has an inner edge and an outer edge, both of which face the end edge of the end portion of the center electrode. With the above configuration, the spark plug can induce spark discharges with a low discharge voltage while securing the ignition capability thereof.

Abstract: A spark plug according to the present invention includes a metal shell, an insulator retained in the metal shell, a center electrode secured in the insulator, and a ground electrode. The center electrode includes a base member and a thin member thinner the base member The ground electrode includes a base member fixed to the metal shell and a protruding member that protrudes from the base member and has an end face with an inner and an outer edge. When the insulator is clean, sparks can be discharged between the thin member and the inner edge. When the insulator is fouled with carbon, sparks can be discharged between the base member and the outer edge to self-clean the insulator. Dimensional parameters and relationships are specified in the spark plug, so that the spark plug can induce spark discharges with a low discharge voltage while securing an excellent self-cleaning capability thereof.

Abstract: A spark plug is composed of a main metal fitting having a cylindrical structure, an insulator disposed inside the cylindrical main metal fitting, a center electrode fitted in the insulator in a manner that a front end portion of the center electrode projects outward over one end of the insulator, and a grounding electrode mounted to the main metal fitting and having one end portion opposing to the front end portion of the center electrode through a discharge gap therebetween. The front end portion of the center electrode includes a conical portion having a tapered surface having a taper angle of less than 80°, and a columnar portion formed to a top end portion of the conical portion so as to have a diameter in a range of 0.4 mm to 0.8 mm.

Abstract: A power-saving type of ignition apparatus is provided with a spark plug of which electrodes (30, 40) are regulated in their shapes to lower an amount of energy required for its ignition. To face to a tip (31) of a center electrode (30) extending from a mounting bracket (10), a cylindrical protrusion (41) is built on one surface (43) of an earth electrode (40). The protrusion extends toward the center electrode to form a discharge gap (50) between the protrusion and the tip of the center electrode. Both of the tip of the center electrode and the protrusion of the earth electrode are 2.3 [mm] or less in each diameter (D1, D2), thus an amount of energy required for ignition being limited to 17 [mJ] or less.

Abstract: A spark plug according to the present invention includes a metal shell, an insulator, a cylindrical center electrode, a first ground electrode, and a second ground electrode. The first ground electrode is aligned with the center electrode in the axial direction of the center electrode to form a first spark gap, across which normal sparks are discharged when the insulator is not fouled with carbon. The second ground electrode is aligned with the center electrode in the radial direction of the center electrode to form a second spark gap, across which side sparks are discharged when the insulator is fouled with carbon. The spark plug has an improved structure where dimensional parameters A, T, B, C, L, D, and E are specified to be in suitable ranges that are determined through experimental investigation. The improved structure ensures a high ignition capability and a long service life of the spark plug.

Abstract: A spark plug according to the invention includes a metal shell, a hollow insulator, a center electrode, and a ground electrode. The insulator has a first end protruding into a combustion chamber of an engine and a second end opposite to the first end in the lengthwise direction of the insulator. The insulator increases in outer diameter from the edge of the inner surface thereof at the first end to a reference plane that is defined to extend perpendicular to the lengthwise direction of the insulator and away 0.1 mm from the edge of the inner surface of the insulator toward the second end of the same in the lengthwise direction. Further, a first volume V1, which is the volume of a portion of the insulator between the edge of the inner surface of the insulator and the reference plane, is in the range of 0.15 to 0.38 mm3.

Abstract: A spark plug according to the invention includes a metal shell that has a threaded portion with an outer diameter of 10 mm or less, or equal to 12 mm, an insulator, a center electrode, and a ground electrode. The spark plug has an improved structure in which an end portion of the insulator tapers toward an end thereof that protrudes from an end of the metal shell, and dimensional parameters, including a space G of the spark gap in the spark plug, a taper degree of the end portion of the insulator that is represented by an outer diameter difference (D?D0) in the end portion, and a size T0 of the air pocket formed in the spark plug, each have an effective range determined based on the experimental investigation results from the inventors. The structure ensures high insulation properties and high ignition capability of the spark plug.

Abstract: A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. The metal shell has a threaded portion with an outer diameter of equal to or less than 10 mm, or equal to 12 mm for installing the spark plug in an internal combustion engine. The dimensional parameters in the structure of the spark plug, such as a clearance X between the center electrode and the insulator, a surface-creeping distance Y outside the metal shell, a protruding length Y1 of the insulator, an air pocket size Z, and a surface-creeping distance W inside the metal shell satisfy the dimensional relationships defined through experimental investigation in the invention. The structure ensures a high capability of the spark plug to ignite the air-fuel mixture even when the insulator thereof is fouled with carbon.

Abstract: A spark plug includes a metal shell, an insulator, a center electrode, a ground electrode, a first noble metal chip, and a second noble metal chip. The metal shell has a threaded portion with an outer diameter of equal to or less than 14 mm for installing the spark plug to an internal combustion engine. The parameters in the structure of the spark plug, such as an end surface area S of the first noble metal chip, a length A of the first noble metal chip, an end surface area Q of the second noble metal chip, a length B of the second noble metal chip, an air pocket size L, a space G of a spark gap, a ratio L/G, and a thickness T of the insulator, have suitable dimensional ranges determined through experimental investigation. The structure ensures high performance and a long service life for the spark plug.

Abstract: A small-sized spark plug is provided which ensures the stability in the location of production of sparks between center and ground electrodes. The center and ground electrodes have joined thereon cylindrical members such as noble metal chips which are opposed to each other through a spark gap. The cylindrical members are so oriented to have longitudinal center lines extend parallel in misalignment with each other. This orientation results in shorter and longer intervals between end surfaces of the cylindrical members. The sparks are concentrated between portions of edges of cylindrical members located apart the shorter interval, thereby resulting in the stability in the location of production of the sparks.

Abstract: A power-saving type of ignition apparatus is provided with a spark plug of which electrodes (30, 40) are regulated in their shapes to lower an amount of energy required for its ignition. To face to a tip (31) of a center electrode (30) extending from a mounting bracket (10), a cylindrical protrusion (41) is built on one surface (43) of an earth electrode (40). The protrusion extends toward the center electrode to form a discharge gap (50) between the protrusion and the tip of the center electrode. Both of the tip of the center electrode and the protrusion of the earth electrode are 2.3 [mm] or less in each diameter (D1, D2), thus an amount of energy required for ignition being limited to 17 [mJ] or less.

Abstract: At least one of a center electrode tip and a ground electrode tip is made of an iridium alloy. A discharge gap, formed between the center electrode tip and the ground electrode tip, is less than 1.1 mm. And, cross sections of the center electrode tip and the ground electrode tip are equal to or smaller than 0.95 mm2 in a spherical region where a distance from a midpoint of the discharge gap is within 0.6 mm.

Abstract: A bright surface structure formed on a member made from metal or resin. A first structure includes: (a) a resin film coated on the member, and (b) a thin metal film formed on the resin film. The thin metal film is made from any one of stainless steel, titanium alloy and nickel alloy. A second structure further includes (c) a clear protective film coated on the thin metal film. A third structure includes: (b′) a thin metal film formed on the resin film of (a), and (c′) a clear colored protective film coated on the thin metal film of (b′). The thin metal film of (b′) is made from any one of stainless steel, titanium alloy, nickel alloy, aluminum, titanium and chromium.

Abstract: A spark plug is composed of a main metal fitting having a cylindrical structure, an insulator disposed inside the cylindrical main metal fitting, a center electrode fitted in the insulator in a manner that a front end portion of the center electrode projects outward over one end of the insulator, and a grounding electrode mounted to the main metal fitting and having one end portion opposing to the front end portion of the center electrode through a discharge gap therebetween. The front end portion of the center electrode includes a conical portion having a tapered surface having a taper angle of less than 80°, and a columnar portion formed to a top end portion of the conical portion so as to have a diameter in a range of 0.4 mm to 0.8 mm.

Abstract: At least one of a center electrode tip and a ground electrode tip is made of an iridium alloy. A discharge gap, formed between the center electrode tip and the ground electrode tip, is less than 1.1 mm. And, cross sections of the center electrode tip and the ground electrode tip are equal to or smaller than 0.95 mm2 in a spherical region where a distance from a midpoint of the discharge gap is within 0.6 mm.

Abstract: At least one of a center electrode tip and a ground electrode tip is made of an iridium alloy. A discharge gap, formed between the center electrode tip and the ground electrode tip, is less than 1.1 mm. And, cross sections of the center electrode tip and the ground electrode tip are equal to or smaller than 0.95 mm2 in a spherical region where a distance from a midpoint of the discharge gap is within 0.6 mm.

Abstract: A power-saving type of ignition apparatus is provided with a spark plug of which electrodes (30, 40) are regulated in their shapes to lower an amount of energy required for its ignition. To face to a tip (31) of a center electrode (30) extending from a mounting bracket (10), a cylindrical protrusion (41) is built on one surface (43) of an earth electrode (40). The protrusion extends toward the center electrode to form a discharge gap (50) between the protrusion and the tip of the center electrode. Both of the tip of the center electrode and the protrusion of the earth electrode are 2.3 [mm] or less in each diameter (D1, D2), thus an amount of energy required for ignition being limited to 17 [mJ] or less.