Abstract: A spark plug includes a metallic shell having a stepped portion an insulator disposed inside the metallic shell, while being engaged with the stepped portion of the metallic shell, and having an axially extending through hole; a center electrode fixed within the through hole of the insulator; and a ground electrode having a tip end portion bent toward the center electrode to thereby form a spark discharge gap. The insulator is formed such that the outer diameter of the insulator decreases toward the tip end side from an engagement position at which the insulator engages the stepped portion and such that the diameter decreases stepwise at an axial position between the engagement position and the tip end of the insulator. The diameter reduction ratio Y1=D1/d1 is 0.

Abstract: A heater 1 has a seal structure formed by inserting a shaft-like member 4 into a stepped bore 8 formed in a tubular member 2, and setting an O-ring 16 on an upper surface of a stepped portion of the stepped bore 8, a clearance 15 between the shaft-like member 4 and tubular member 2 being thereby sealed with this seal structure. A seal region 17 is formed on the upper surface of the stepped portion of the stepped bore 8, and a conical introduction port portion 18 extending divergently in the rearward direction from the seal region toward an opening of the stepped bore 8 is provided. Moreover, a cone angle &agr; of the introduction port portion 18 with respect to an axis L of the tubular member 2 is set to not larger than 35°.

Abstract: A spark plug having a ceramic insulator, which contains a precious-metal center electrode in a cylindrical, axial opening, at the end on the side of the combustion chamber. A contact pin is arranged in the cylindrical opening, downstream from the precious-metal center electrode, in the direction of the insulator end away from the combustion chamber. To reduce corrosion, the surface of the contact pin is provided with a layer of one or more metal aluminides.

Abstract: A ceramic sheathed-element glow plug is proposed in which a metallic tubular holder holds a ceramic U-shaped heating device in a cantilevered fashion at its combustion chamber side end and has a terminal stud for applying a voltage to the ceramic heating device on the end remote from the combustion chamber. At its end enclosed by the holder, the ceramic heating device has a segment of greatest diameter and is coated with an insulating layer which has recesses for an electrical contacting. One recess is provided at the end of the ceramic heating device remote from the combustion chamber and a second recess is provided on the external wall of the ceramic heating device. A for an electrically conductive sealing compound is provided between the external wall of the ceramic heating device and the internal wall of the holder.

Abstract: A spark plug configured such that a metallic shell is joined to an insulator through hot-crimping. The metallic shell is firmly joined to the insulator by means of a sufficient fastening force even when the diameter of the spark plug is reduced, to thereby enhance gastightness and vibration resistance. A rear end portion of a metallic shell (1) is hot-crimped toward an insulator (2) to form a curved, crimped portion (1d). The inside diameter of an insulator insertion hole (40) of the metallic shell (1) is 8-12 mm.

Abstract: The spark plug has a top end portion of a main metal shell that is almost cylindrical on an outer circumferential face without having a plug attaching external thread screwed into the cylinder head. Further, the plug hole formed in the cylinder head has a top end counterpart corresponding to the top end portion of the main metal shell. And in the mounting structure of the spark plug into the cylinder head (plug hole), the clearance amount (&phgr;D−&phgr;d) satisfies a relation &phgr;D−&phgr;d≦0.15 (unit: mm) where the outer diameter of the top end portion of the main metal shell is &phgr;d and the hole diameter of the top end counterpart of the plug hole is &phgr;D.

Abstract: A spark plug configured such that a metallic shell is joined to an insulator through crimping. The metallic shell is firmly joined to the insulator by means of a sufficient fastening force even when the diameter of the spark plug is reduced, to thereby enhance gastightness and vibration resistance. A rear end portion of a metallic shell (1) is crimped toward an insulator (2) to thereby be formed into a curved, crimped portion (1d). The inside diameter of an insulator insertion hole (40) of the metallic shell (1) is 8-12 mm.

Abstract: In an ignition device, especially a spark plug (10), having a housing (12) that is provided with a screw-in thread (14), a permanent sticking or contact corrosion of the spark plug in the cylinder head is to be prevented. For this purpose, it is provided that the housing, at least in the region of the screw-in thread, include a coating (26) of a varnish provided with nonstick pigments.

Abstract: A noble metal tip of a grounding electrode is inclinedly disposed with respect to a noble metal chip of a central electrode by an angle &agr; so that a discharging gap is narrow at a side closer to one end of the grounding electrode and wide at the opposite side closer to the other side of the grounding electrode. When the discharging gap has expanded to a certain extent due to exhaustion of the noble metal tips of the electrodes, the re-gapping adjustment is performed to decline or push the noble metal tip of the grounding electrode toward the noble metal tip of the central electrode so as to decrease the angle &agr;. Thus, the discharging gap can be adjusted to an adequate value.

Abstract: In a spark plug, whose shell is provided with an eccentrically positioned, full-length, longitudinal bore designed to hold an insulating element, parts of the shell having varying wall thicknesses and a pressure measuring device being located in a part of greater wall thickness. In order to simplify connection with the ignition cable or coil, respectively, and to avoid breakage of the insulator, the spark plug insulator is configured as a multi-piece element and comprise at least an upper piece carrying the high voltage connector, a lower piece adjacent to the combustion chamber, and an insulating intermediate element of flexible material, which is placed between the upper and the lower piece of the insulator.

Abstract: A spark plug comprising: a center electrode; a metal shell; and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, wherein the glaze layer comprises: 1 mol % or less of a Pb component in terms of PbO; 30 to 60 mol % of a Si component in terms of SiO2; 20 to 50 mol % of a B component in terms of B2O3; 0.5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 2 to 12 mol % in total of at least two alkaline metal components of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein K and Li is essential; and 0.1 to 10 mol % of a F component in terms of F2.

Abstract: A spark plug having a glaze layer on the insulator thereof, wherein the glaze layer has a reduced Pb content, is capable of being fired at a relatively low temperature, exhibits excellent insulation properties, and can have a smooth surface.

Abstract: A spark plug comprising: a center electrode; a metal shell; and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, the glaze layer comprising: 1 mol % or less of a Pb component in terms of PbO; 40 to 60 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 0.5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 2 to 12 mol % in total of at least one alkaline metal component of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein K is essential; and 0.

Abstract: Spark plugs having a center electrode and surrounding ground electrode configurations that allow the spark to selectively fire across the path of least resistance are disclosed. In one embodiment the plug has a cylindrical ground electrode with plural inverted V-shaped projections at its outer end that face outwardly from the end of the electrode. The side wall of the ground electrode may be provided with apertures to facilitate radial gas flow. In another embodiment the ground electrode has plural spherical projections at its outer end. In another embodiment the ground electrode is a cylindrical foraminous configuration with inverted V-shaped projections at its outer end. In another embodiment the center electrode has a spherical outer end encircled by and a cylindrical ground electrode. In another embodiment the center electrode has a spherical outer end surrounded by a hemispherical foraminous dome-shaped ground electrode.

Abstract: Spark plug with an electrically insulating ceramic insulator (1), a metallic spark plug body (2), a ground electrode (3) and a middle electrode (4) which is located centrally in a hole (5) of the ceramic insulator (1), around the ignition-side end area on the periphery of the middle electrode (4) a peripheral tip (10) being formed which encompasses the middle electrode (4) in an annular manner.

Abstract: A spark plug with a metallic housing (10) is proposed, which has an insulator (11) embedded in the housing (10), in which a rod-shaped internal conductor device is disposed. The internal conductor device has a contact pin (13), a current-limiting erosion resistor (17), and a central electrode (14). A sealing material (16) secures the central electrode (14) in a sealed fashion in the insulator (11). The temperature resistant sealing material (16) essentially contains at least one metallic component and at least one ceramic component with a low thermal expansion, wherein the metallic component has a melting temperature that is higher than the operating temperature.

Abstract: In a spark plug 100, the outer diameter of a tool engaging portion 1e formed on a main metal member 1 is not larger than 14 mm. An insulator 2 is provided with a expanded diameter portion (2e) positioned within the main metal member 1 and projecting radially outward from an outer circumferential surface of the insulator, and an intermediate trunk portion (2g) adjacent to an axial front side of the expanded diameter portion (2e) and having a cylindrical outer circumferential surface. The inclined portion (2j) has a linearly inclined outer circumferential surface formed in a position so as to connect the expanded diameter portion (2e) and intermediate trunk portion (2g), and formed so that in orthogonal projections with respect to a plane of projection parallel to an axis O, the diameters become smaller from the side of the expanded diameter portion (2e) toward that of the intermediate trunk portion (2g).

Abstract: The glaze layer 2d of the spark plug 100 includes oxides of: 15 to 60 mol % of a Si component in terms of SiO2; 22 to 50 mol % of a B component in terms of B2O3; 10 to 30 mol % of a Zn component in terms of ZnO; 0.5 to 35 mol % of Ba and/or Sr components in terms of BaO or SrO; 1 mol % or less of an F component; 0.1 to 5 mol % of an Al component in terms of Al2O3; and 5 to 10 mol % in total of at least one of alkaline metal components of Na, K and Li, in terms of Na2O, K2O, and Li2, respectively, wherein Li is essential, and the amount of the Li component is 1.1 to 6 mol % in terms of Li2O.

Abstract: An insulator for spark plug comprises an alumina-based sintered body comprising: Al2O3 as a main component; and at least one component (hereinafter referred to as “&bgr; component”) selected from the group consisting of Ca component, Sr component and Ba component, wherein the alumina-based sintered body comprises particles comprising a compound comprising the &bgr; component and Al component, the compound having a molar ratio of the Al component to the &bgr; component of 4.5 to 6.7 as calculated in terms of oxides thereof, and has a relative density of 90% or more.

Abstract: A spark plug having a tubular metallic housing has an internal conductor arrangement including a refractory erosion. The refractory erosion resistor is designed either as a wound wire resistor or a filament-like thin-layer resistor.

Abstract: A composition for forming an electrode for use in a torch jet spark plug is provided. The composition comprises a ceramic material, ceramic particles, and an electrically conductive material. The ceramic particles are dispersed within the ceramic material. At least some of the ceramic particles have a predetermined size. This predetermined size is at least as large as the thickness of the finally formed electrode. The electrically conductive material is capable of being manipulated to form ribbons around the ceramic particles and of being sintered to form the electrode. The resultant electrode has good resistance to explosive erosion mechanisms, which consequently increases the life of the torch jet spark plug.

Abstract: A spark plug is disclosed, in which a center electrode has, at the end thereof which forms a spark discharge gap, a noble metal chip which has a straight rod portion of 1.0 mm or less in diameter and 0.2 mm or more in length; width of coverage K of a ground electrode on which a rectangular noble metal chip is welded satisfies a relation of −d≦K≦0.5 mm (where, d represents the diameter of the end face of the center electrode); and width w of a portion of the discharge plane 111A which falls within a range corresponded to the axial extension of the end face 22B of the noble metal chip 22 provided on the center electrode 2 satisfies a relation of w<2.1−K (in mm), where K is the foregoing width of coverage.

Abstract: A spark plug has a tubular fitting which is assembled with a center electrode, a ground electrode and an insulator. The fitting has a reach length of at least 12 mm for use in high output-type engines. The fitting is formed with a thread part and a taper part so that the fitting is thread engaged with an engine head and seals a combustion chamber from an outside by a contact between the taper part and a seat surface of the engine head. The fitting is made by cold-forging a low carbon steel to provide the taper surface of a surface roughness of less than 10 &mgr;m and a column part. The column part is machine-cut to provide the thread part thereon. The deflection between the axes of the thread part and the taper part is limited to be less than 0.15 mm.

Abstract: In a spark plug, an annular seal packing is arranged in a gap defined between an insulator and a fitting. Electrically insulating oil is filled in an oil-retaining section of the gap that is located on the distal side of the packing. The oil-retaining section of the gap is the continuous section having a width ranging from 0.05 mm to 0.3 mm and an axial length of 2 mm or more from the packing. The filled insulating oil is retained within the oil-retaining section of the gap by its surface tension while it is in a liquid state.

Abstract: A sparking plug for a combustion engine, includes a metal shell with an externally threaded end part for screwing into a tapped hole in a cylinder head. The shell supports, on the inside, an insulating body, through which there passes a central electrode capable of being connected to a high tension. An annular chamber is delimited by an interior surface in the region of the threaded end part of the shell and the exterior surface of the end of the insulating body. The sparking plug also has at least one pressure sensor, and is designed to subject this sensor to the pressure of an associated combustion chamber when the sparking plug is in place. The pressure sensor is installed in the threaded end part of the shell delimiting the annular chamber radially out from the internal surface of this end part such that the geometry of the annular chamber is not altered by the presence of the sensor.

Abstract: A spark plug is described that includes a housing, an insulator nose attached to the housing, a center electrode inserted through the insulator nose and projecting over the insulator nose tip, an intermediate electrode separated from the center electrode by a first spark gap, and a ground electrode attached to the housing. A solid-state insulating body, which forms a second spark gap in the form of a surface gap passing over the solid-state insulating body, is provided between the intermediate electrode and the ground electrode.

Abstract: A spark plug 100 is configured such that an insulator 2 is formed of alumina ceramic, and the diameter of a through-hole 6 is not greater than 4 mm as measured at a position where conductive seal materials 16 and 17 are disposed. The coefficient of linear expansion of the conductive seal materials 16 and 17 is adjusted to not greater than 6.5×10−6/° C.

Abstract: In a glow plug and a spark plug, the surface of a main metal shell is coated with a chromate film in which the quantity of trivalent chrome is 95 wt % or more of the contained chrome components and which has a thickness of 0.2 &mgr;m to 0.5 &mgr;m.

Abstract: In a creeping discharge type spark plug, the firing surface forming portions of a center electrode and a ground electrode are made of a metallic material containing a corrosion impeding component consisting of one or more of Fe, Cr and Cu. The spark plug is attached to an internal combustion engine. When it is operated under conditions of a predetermined high speed and high load, a corrosion impeding layer containing a corrosion impeding component is formed on the surface of the top end of an insulating member, with progression of spark discharge in spark discharge gaps. The corrosion impeding layer thus formed protects the center electrode from the attack by the creeping discharge spark. Therefore, the channeling is considerably effectively prevented or restricted.

Abstract: Encapsulated spark plugs improve combustion control in spark ignited engines. The present invention improves reliability and life of an encapsulated spark plug. A spark plug shell has a connection region and an orificed region, and a tip portion. The present invention provides improved heat transfer from the tip portion through the orificed region to the connection region. An access orifice provides access to set an electrode gap.

Abstract: A spark plug in which the diameter of a front end portion 2i of an insulator 2 is reduced due to a circumferentially extending stepped portion thereof to form the stepped portion into an insulator-side locking portion 2h, and the insulator is inserted into a main metal member 1 from a rear opened portion thereof. The insulator-side locking portion 2h engages a metal member-side locking portion 1c projecting from an inner circumferential surface of the main metal member 1, and an outer circumferential surface (clearance-forming outer circumferential surface) 2k of the portion 2i positioned ahead of the locking portion 2h of the insulator 2 is opposed to an inner circumferential surface (clearance-forming inner circumferential surface) 52 of the metal member-side locking portion 1c so as to form a predetermined clearance Q in a locking position.

Abstract: In a glow plug and a spark plug, the surface of a main metal shell is coated with a chromate film in which the quantity of trivalent chrome is 95 wt % or more of the contained chrome components and which has a thickness of 0.2 &mgr;m to 0.5 &mgr;m.

Abstract: A ceramic sheathed element glow plug has a tubular metal casing holding a ceramic U-shaped heating device cantilevered at its end facing the combustion chamber, and on the end remote from the combustion chamber, it has a terminal pin for applying a voltage to the ceramic heating device. In the metal casing, a ceramic bushing and a ring follow the ceramic heating device at the end remote from the combustion chamber.

Abstract: A spark plug according to this invention includes an insulator having a center through-hole formed therein, a center electrode held in the center through-hole, a metallic shell holding the insulator by swaging, and a ground electrode electrically connected to the metallic shell and defining a spark discharge gap in cooperation with the center electrode. The metallic shell has a male-threaded portion formed on the outer circumferential surface of a front end portion of the metallic shell, and a tightening portion formed on the outer circumferential surface of the metallic shell, located at a rear side with respect to the male-threaded portion. The tightening portion has a width-across-flats W of not greater than 14 mm. A cushion material is filled into a space defined by the metallic shell and an insulator to form a cushion-material charged portion. The cushion-material charged portion has an axial length L of from 0.5 mm to 10.0 mm inclusive and a thickness M of from 0.5 mm to 1.3 mm inclusive.

Abstract: A spark plug includes a partially cylindrical insulator element, including a bore hole and a central electrode located in an opening in the base part of the insulator element. The insulator element and the central electrode are connected by at least one metallic soldered connection and/or one metallic welded connection and/or one friction-locked connection aligned in the radial direction.

Abstract: A spark plug having a center electrode 2 formed from an electrode base material 2n, which is made of an Ni alloy containing an alloy component (e.g., Cr) capable of forming an oxide semiconductor having a resistivity of negative temperature coefficient. Thus, a corrosion suppression layer originating from the components of the electrode base material is formed on the surface of a tip end portion of the insulator 3, so that corrosion (channeling) of the surface of the tip end portion of the insulator 3 due to creeping spark discharge can be effectively suppressed. In addition, when the constituent metal of the electrode base material 2n has a coefficient of thermal conductivity of 17 to 30 W/m·K, the heat transfer performance of the electrode is enhanced, so that durability against electrode consumption can be greatly improved.

Abstract: In insulator including alumina as a main component, a Na component in the insulator is set in the range of 0.07 to 0.5 wt % as Na2O. While the Na component content is as high as to have conventionally been regarded to be beyond the common sense, with this range of the Na component content, insulation resistance, mechanical strength and the like at high temperature are unexpectedly not reduced and an insulator with performances comparable to those of an insulator from conventional low soda alumina lower in Na component content than the above described range can be obtained. As a result, medium soda alumina and regular soda alumina that are much lower in cost than conventionally used low soda alumina can be used instead of the low soda alumina, so that dramatic reduction in production costs of insulator 2 for a spark plug 100 and in addition, of the spark plug 100 using the insulator 2 are realized.

Abstract: A firing tip for a spark plug assembly comprises an iridium-rhodium alloy. The firing tip is resistance welded to an electrode for use with a long life spark plug. A thermal expansion dividing layer can be bonded between the electrode surface and iridium-rhodium firing tip to prevent peeling, cracking and/or spalling due to thermal stress fatigue. The thermal expansion dividing material can be a platinum-nickel alloy having a coefficient of thermal expansion compatible with both the electrode material and iridium-rhodium alloy.

Abstract: A spark plug is disclosed in which, in a cross-section of the metallic shell of the spark plug, a crimped portion of the metallic shell is curved such that an end-side part of the crimped portion approaches the insulator, such that an exterior outline of the crimped portion has an outwardly convex crimped curve portion at the end-side part, and such that a tangent to the exterior outline at a base point of the crimped curve portion and a radial line perpendicular to the axis of the insulator form an angle of 50°-110°. Accordingly, most of a crimping force is imposed in the axial direction of the metallic shell during crimping, and stress generated in the metallic shell in a radial direction is very small. Thus, the metallic shell can be thin-walled and can maintain its shape with high accuracy after crimping.

Abstract: A spark plug according to this invention includes an elongate center electrode, an insulator enclosing the center electrode, a metallic shell having open opposite ends and enclosing the insulator, the metallic shell having a male-threaded portion formed on a front-side outer circumferential surface of the metallic shell, and a tool engagement portion formed on the outer circumferential surface of the metallic shell at a rear side with respect to the male-threaded portion, the tool engagement portion projecting circumferentially outwardly, and a ground electrode connected to the metallic shell and defining a spark discharge gap in cooperation with the center electrode. The size of the tool engagement portion is reduced such that |A-E| is not greater than 1.5 mm, where A is an outside dimension of the tool engagement portion, and E is an effective diameter of a male-threaded portion of the metallic shell.

Abstract: The glaze layer 2d of the spark plug 100 includes oxides of: 15 to 60 mol % of a Si component in terms of SiO2; 22 to 50 mol % of a B component in terms of B2O3; 10 to 30 mol % of a Zn component in terms of ZnO; 0.5 to 35 mol % of Ba and/or Sr components in terms of BaO or SrO; 1 mol % or less of an F component; 0.1 to 5 mol % of an Al component in terms of Al2O3; and 5 to 10 mol % in total of at least one of alkaline metal components of Na, K and Li, in terms of Na2O, K2O, and Li2, respectively, wherein Li is essential, and the amount of the Li component is 1.1 to 6 mol % in terms of Li2O.

Abstract: A spark plug derives an extended lifetime because a large plurality of sharp edges are provided on the center electrode, the ground electrode, or both to enhance spark propagation. In a first embodiment, the ground electrode has a conventional cantilever shape, but the center electrode extends into coplanar relation to a distal surface of the electrode so that sparks propagate from the cylindrical side walls of the center electrode. In variations of the first embodiment, the number of cantilevered ground electrodes is increased, with the ground electrodes being circumferentially and equidistantly spaced about the center electrode. In another embodiment, the ground electrode has an annular configuration and includes a cylindrical annular wall spaced radially outwardly of the cylindrical sidewall of the center electrode, in concentric relation to the center electrode.

Abstract: A fuel injected, internal combustion engine that is protected from detrimental ignition due to pocket sparking. The engine includes one or more cylinders into which fuel is injected by an injector. A spark plug is used to ignite the fuel-air mixture within the cylinder. The spark plug is designed with a base and a shell extending from the base to define a hollow interior. A central electrode is disposed in an insulative core and extends through the hollow interior of the shell. The shell is connected to a secondary electrode. A gap is formed between the electrodes for promulgation of a spark to ignite the fuel-air mixture. The detrimental effects of pocket sparking are eliminated by placing a closure member between a terminal end of the shell and the nose of the insulative core. This closure member may be in the form of a lip that extends from the shell into proximity with the nose of the insulative core.

Abstract: In insulator including alumina as a main component, a Na component in the insulator is set in the range of 0.07 to 0.5 wt % as Na2O. While the Na component content is as high as to have conventionally been regarded to be beyond the common sense, with this range of the Na component content, insulation resistance, mechanical strength and the like at high temperature are unexpectedly not reduced and an insulator with performances comparable to those of an insulator from conventional low soda alumina lower in Na component content than the above described range can be obtained. As a result, medium soda alumina and regular soda alumina that are much lower in cost than conventionally used low soda alumina can be used instead of the low soda alumina, so that dramatic reduction in production costs of insulator 2 for a spark plug 100 and in addition, of the spark plug 100 using the insulator 2 are realized.

Abstract: The present invention is an improved igniter assembly for electrical ignition of a gas burner. The improved igniter assembly includes an electrode mantle that has a wavy surface.

Abstract: A spark plug includes a center electrode, a ground electrode opposing the center electrode in such a manner as to define a spark discharge gap between the center electrode and the ground electrode, and an igniter fixed to at least one of the center electrode and the ground electrode in such a manner as to face the spark discharge gap. The igniter is composed of a metallic material whose principal component is one of a platinum and an iridium. One type of the metallic material of the igniter contains an oxygen content of not more than 120 ppm. Another type of the metallic material of the igniter has a crystal grain of not less than 50 &mgr;m in mean diameter, and contains the oxygen content of not more than 300 ppm.

Abstract: The spark plug has a top end portion of a main metal shell that is almost cylindrical on an outer circumferential face without having a plug attaching external thread screwed into the cylinder head. Further, the plug hole formed in the cylinder head has a top end counterpart corresponding to the top end portion of the main metal shell.

Abstract: An iridium alloy firing tip, fixed to a center electrode, comprises a stem and a head. The firing tip head is integrally formed from one end of the stem. A distal end of the stem is opposed to an opponent electrode. The head is embedded in the opposing portion. The firing tip head is pointed or tapered in a direction opposite to the stem from a maximum diameter portion in such a manner that a cross-sectional area of the head continuously decreases with increasing distance from the maximum diameter portion. The maximum diameter portion is positioned deeply inside the opposing portion, and a base end of the stem extending from the maximum diameter portion is wrapped or surrounded by the opposing portion.

Abstract: A spark plug is provided which comprises a center electrode and a ground electrode having at a free end portion thereof a discharge surface which is opposite to an axial end surface of the center electrode to provide therebetween a spark gap, wherein the center electrode has a center electrode tip forming the axial end surface thereof, the center electrode tip being made of a material containing Ir as a major constituent, and wherein G≦2A+0.5 where G is a spark gap (mm) and A is the distance (mm) between a first imaginary line and a second marginal line.

Abstract: A noble metal tip of a grounding electrode is inclinedly disposed with respect to a noble metal chip of a central electrode by an angle &agr; so that a discharging gap is narrow at a side closer to one end of the grounding electrode and wide at the opposite side closer to the other side of the grounding electrode. When the discharging gap has expanded to a certain extent due to exhaustion of the noble metal tips of the electrodes, the re-gapping adjustment is performed to decline or push the noble metal tip of the grounding electrode toward the noble metal tip of the central electrode so as to decrease the angle &agr;. Thus, the discharging gap can be adjusted to an adequate value.