Abstract: A spark plug for an internal combustion engine includes a ground electrode, an insulator held inside the ground electrode, and a center electrode held inside the insulator. When a segment of a line extending in a plug radial direction to connect an arbitrary start point on a surface of the ground electrode and an outer peripheral surface of the insulator is a line segment H, a point of intersection between the line segment H and the outer peripheral surface of the insulator is an intersection point K, a length of the line segment H is L1, and an axial distance between the intersection point K and the distal end of the insulator is L2, the ground electrode is provided on the surface thereof with a shortest discharge forming portion as the start point along a plug circumferential direction at which a value of (L1+L2) becomes minimum.

Abstract: A spark plug 1 includes a housing 2, an insulator 3, a center electrode 4 held inside the insulator 3 such that a distal end portion 41 protrudes, a ground electrode 5 including a standing portion 51 and an opposing portion 52, and a guide member 22 that has a guide surface 221 facing the standing portion 51 of the ground electrode 5 and functions to guide a flow of an air-fuel mixture in a combustion chamber of an internal combustion engine to a spark discharge gap G formed between the center electrode 4 and the opposing portion 52 of the ground electrode 5. The opposing portion 52 of the ground electrode 5 has an opposing surface 521 that opposes the center electrode 4, a back surface 522 on the opposite axial side to the opposing surface 521, and a pair of side surfaces 523 and 524 that connect the opposing surface 521 and the back surface 522.

Abstract: In an ignition device, a base section of a discharge chamber is formed by a part of a central dielectric body. A front section of a ground electrode and a front end section of the central dielectric body are projected toward a combustion chamber of a head cylinder of an internal combustion engine by a predetermined height which is measured from a top ceiling wall of the head cylinder. The predetermined height of the front end section of the central dielectric body projected into the inside of the head cylinder is the same or higher than the predetermined height of the front end section of the ground electrode projected into the inside of the head cylinder. The predetermined height of the front end section of the ground electrode is within a range of 3 mm to 25 mm.

Abstract: A spark plug for an internal combustion engine has a housing, an insulator, a center electrode, a ground electrode, and a tip projecting portion. The tip projecting portion has an air guiding surface. In the spark plug, when viewed from a plug axial direction, a straight line that connects the center, in the plug circumferential direction, of the erect portion of the ground electrode and a center point of the center electrode is a straight line. An extension line of the air guiding surface is a straight line. A distance between an intersection, between the straight line and the straight line, and the center point of the center electrode is a (positive towards the side moving away from the erect portion. An angle formed by the straight line and the straight line is b. A diameter of the housing is D. At this time, all of b??67.8×(a/D)+27.4, b?123.7×(a/D)+64.5, ?0.4?(a/D)?0.4, and 0°<b?90° are satisfied.

Abstract: An ignition device includes a center electrode, a center dielectric covering the center electrode, a ground electrode disposed so as to form a discharge space with the center dielectric, and a high energy source for applying an AC voltage between the center electrode and the ground electrode to generate a streamer discharge. A distal end portion of the center electrode projects beyond a distal end of the ground electrode to an inside of the combustion chamber of an internal combustion engine to make a dielectric discharge portion. The ground electrode is formed with an airflow inlet and en airflow outlet at a lateral portion thereof for enabling an in-cylinder airflow to be introduced into the discharge space. A distal end portion of the ground electrode projects radially inward to make a ground electrode projecting portion so that a discharge space narrow portion is formed with the dielectric discharge portion.

Abstract: A spark plug for internal combustion engines is provided, where the spark plug includes a cylindrical housing, a cylindrical insulation porcelain part, a center electrode, and a ground electrode. The insulation porcelain is housed in the housing and the center electrode is held inside the insulation porcelain. The ground electrode protrudes from a top end portion of the housing. A spark discharge gap is left between the ground and center electrodes. Further, first to third projections are formed on the top end portion. The first projection is opposed to the ground electrode with the center electrode therebetween. The second projection is closer to the ground electrode than to the first projection. The third projection is closer to the first projection than to the ground electrode.

Abstract: An ignition system for an internal combustion engine includes a discharge portion of the center electrode in which a part thereof is surrounded by a bottom portion and a tubular tip portion of the center dielectric, the part of the discharge portion and the tubular tip portion are projected into a combustion chamber of the internal combustion engine from a substantially annular tip portion of the ground electrode that opens to the combustion chamber at a distal end of the ground electrode, a diameter-changing portion formed by reducing a diameter of a part of the tubular tip portion in a radial direction gradually as approaching toward a tip thereof, and a thin-walled portion formed by reducing a thickness of the tip of the tubular tip portion.

Abstract: A spark plug for internal combustion engines is provided, where the spark plug includes a cylindrical housing, a cylindrical insulation porcelain part, a center electrode, and a ground electrode. The insulation porcelain is housed in the housing and the center electrode is held inside the insulation porcelain. The ground electrode protrudes from a top end portion of the housing. A spark discharge gap is left between the ground and center electrodes. Further, first to third projections are formed on the top end portion. The first projection is opposed to the ground electrode with the center electrode therebetween. The second projection is closer to the ground electrode than to the first projection. The third projection is closer to the first projection than to the ground electrode.

Abstract: A barrier discharge ignition apparatus has a tip end exposed to a combustion chamber of an internal combustion engine and, when subjected to a high-frequency high-voltage AC burst, generates streamer discharges for igniting a fuel/air mixture in the combustion chamber. A central electrode of the apparatus, covered by a dielectric layer and coaxially enclosed in a ground electrode, extends into the combustion chamber to a greater distance than the ground electrode. An electrode portion close to the tip end of the inner periphery of the ground electrode protrudes towards the dielectric layer, for creating a localized high-density electric field. The streamer discharges thereby enter both the to combustion chamber and also a discharge chamber of the ignition apparatus.

Abstract: In an ignition device, a base section of a discharge chamber is formed by a part of a central dielectric body. A front section of a ground electrode and a front end section of the central dielectric body are projected toward a combustion chamber of a head cylinder of an internal combustion engine by a predetermined height which is measured from a top ceiling wall of the head cylinder. The predetermined height of the front end section of the central dielectric body projected into the inside of the head cylinder is the same or higher than the predetermined height of the front end section of the ground electrode projected into the inside of the head cylinder. The predetermined height of the front end section of the ground electrode is within a range of 3 mm to 25 mm.

Abstract: A spark plug for an internal combustion engine is provided which is equipped with a tip protrusion disposed on a top of a hollow cylindrical housing of the spark plug. The spark plug also includes a center electrode retained in a porcelain insulator disposed inside the housing and a ground electrode is joined to the housing so as to form a spark gap. The tip protrusion serves to direct a flow of gas to be ignited by a spark produced in the spark gap and is shaped to have a radial width extending in a radial direction of the housing and a circumferential width extending in a circumferential direction of the cylindrical housing. The radial width is greater than the circumferential width. This enhances the efficiency in guiding the flow of gas toward the spark gap.

Abstract: A spark plug for internal-combustion engines includes a housing, an insulator, a center electrode, and an earth electrode. A gas guiding sections equipped with slopes that slope inwardly as they approach toward a tip side from a circumference surface of the housing and guide surfaces that are disposed on both sides in a circumferential direction of the slopes are formed in a tip part of the housing. The gas guiding sections are formed in the circumferential direction within a 90-degree range measured relative to the center of the earth joint section, which is a junction of the housing and the earth electrode, in the circumferential direction. When the spark plug is mounted to the engine, it is constituted so that the gas guiding sections are projected into a combustion chamber.

Abstract: A spark plug for an internal combustion engine is provided which is equipped with a tip protrusion disposed on a top of a hollow cylindrical housing of the spark plug. The spark plug also includes a center electrode retained in a porcelain insulator disposed inside the housing and a ground electrode is joined to the housing so as to form a spark gap. The tip protrusion serves to direct a flow of gas to be ignited by a spark produced in the spark gap and is shaped to have a radial width extending in a radial direction of the housing and a circumferential width extending in a circumferential direction of the cylindrical housing. The radial width is greater than the circumferential width. This enhances the efficiency in guiding the flow of gas toward the spark gap.

Abstract: A spark plug for internal-combustion engines includes a housing, an insulator, a center electrode, and an earth electrode. A gas guiding sections equipped with slopes that slope inwardly as they approach toward a tip side from a circumference surface of the housing and guide surfaces that are disposed on both sides in a circumferential direction of the slopes are formed in a tip part of the housing. The gas guiding sections are formed in the circumferential direction within a 90-degree range measured relative to the center of the earth joint section, which is a junction of the housing and the earth electrode, in the circumferential direction. When the spark plug is mounted to the engine, it is constituted so that the gas guiding sections are projected into a combustion chamber.

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: There is provided a spark plug that includes a center electrode, an insulator, a housing, a ground electrode, an auxiliary ground electrode, and a projected portion in the housing. The housing has a though-hole which is formed in the housing along the longitudinal axis of the center electrode and has an opening of the through-hole at the first housing end. The ground electrode has a first end facing the end of the center electrode to form a first discharge gap. The auxiliary ground electrode has a first end facing an outer peripheral surface of the first end of the insulator to form a second discharge gap. The projected portion is formed in a hollow portion of the through-hole and is projected from an inner peripheral surface of the hollow portion of the housing.

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 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 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 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.