Abstract: This invention has an object to provide a spark plug exhibiting high withstand voltage characteristics and high strength at high temperature, formed by an alumina-based sintered body prepared with excellent processability and high productivity, and a method for manufacturing the spark plug. This invention relates to a spark plug 1 including an insulator 3, wherein the insulator 3 includes a dense alumina-based sintered body having an average crystal particle diameter of 1.50 ?m or more, and the alumina-based sintered body contains Si, a Group 2 element component containing Ba and a Group 2 element other than those, and a rare earth element component, such that a ratio of a content S of the Si component to a total content of the content S and a content A of the Group 2 element component is 0.60 or more, and a method for manufacturing the spark plug 1 prepared through a grinding-shaping process in which the insulator 3 is ground before burning to shape the same.

Abstract: A spark plug for an internal combustion engine, having an insulator including an insulator shoulder designed for mounting a tensioning nut or a housing and having a first outer diameter, an insulator head which is situated farther from the combustion chamber and adjoins the insulator shoulder, and which has a second outer diameter which is smaller than the first outer diameter, and a continuous cavity, a composition including a first contact composition, a second contact composition, and a composition resistor situated between the first contact composition and the second contact composition, a connecting pin which contacts the first contact composition, a center electrode which contacts the second contact composition, and a ground electrode. The connecting pin, the composition, and the center electrode are situated in the cavity, and the composition resistor has a third outer diameter, and a ratio of the third outer diameter to the second outer diameter is between 0.35 and 0.7.

Abstract: A spark plug includes an insulator having an axial hole extending in the direction of an axis, and a terminal electrode disposed at a rear end portion of the axial hole. An identifier bearing externally visible identification information is joined to the rear end surface of the terminal electrode. The identifier has a thickness of 0.03 mm or greater along the direction of the axis.

Abstract: An ignition part (80) of a ground electrode (30) includes a fused part (85) in which construction materials of a base portion (82) and a noble metal member (81) are fused and mixed by performing laser welding on the two. In the fused part (85), an average ratio P of components originated from the noble metal member (81) at points K1, L1, and M1 is equal to or greater than 80%, and an average ratio Q of components originated from the base portion at points K3, L3, and M3 is equal to or higher than 20%, and P+Q is equal to or higher than 160%. Accordingly, it is possible to obtain joining strength in the parts in the ignition part (80), thereby sufficiently preventing the generation of cracks, separation, and the like due to thermal stress.

Abstract: A spark plug for an internal combustion engine is provided which is equipped with an inward top end protrusion. The inward top end protrusion extends inwardly from a top end of a cylindrical housing within which a porcelain insulator is disposed. The porcelain insulator has a center electrode disposed therein. The inward top end protrusion is at least partially located to be closer to the top of the spark plug than a top end of the porcelain insulator is in an axial direction of the spark plug. This enhances the strength of an electric field surrounding the center electrode, which facilitates the ease with which an electron is emitted by the center electrode and thus permits an initial required voltage at the spark plug to be decreased, thereby resulting in an increase in service life of the spark plug.

Abstract: A spark plug for an internal combustion engine, including an electrical connecting arrangement on a connection-side end, an end on the combustion-chamber side pointing toward a combustion chamber, an insulator and a housing having a thread for attaching the spark plug to an engine component, a first sealing area and a second sealing area being provided between the insulator and the housing, the first sealing area being situated closer to the connection-side end and the second sealing area being situated closer to the end on the combustion-chamber side, a tool engagement area for transmitting a torque to the spark plug for fitting or removing the spark plug being situated in an area of the spark plug which lies between the connection-side end and the first sealing area.

Abstract: A spark plug comprises a shell having a substantially cylindrical threaded portion for threadable engagement in a cylinder head of an internal combustion engine, an insulator disposed coaxially in the shell, a center electrode disposed coaxially in the insulator, a side ground electrode having a first end coupled to the shell and a second end facing an end of the center electrode to define a spark discharge gap therebetween, and an electrode tip portion secured to either the side ground electrode or the center electrode proximate the spark discharge gap. The tip portion is formed from an alloy comprising from about 60 to about 70 percent by weight iridium, from about 30 to about 35 percent by weight rhodium, from 0 to about 10 percent by weight nickel, from about 3500 to about 4500 parts per million tantalum, and from about 100 to about 200 parts per million zirconium.

Abstract: It is an object of the present invention to provide a spark plug that can be produced at low cost and secure compatibility between ignition performance and durability. The spark plug according to the present invention includes a center electrode and a ground electrode having an inner surface facing the center electrode, characterized in that; the ground electrode has a protrusion and a hole; the protrusion protrudes from the inner surface by a protruding length A of 0.4 to 1 mm and has a first straight portion with a projected first straight portion area S1 of 1.5 to 3 mm2; the hole has an opening at an outer surface of the ground electrode, a second straight portion, a bottom portion and a transition portion; the opening is formed in such a manner that the ratio (S2/S1) of a projected opening area S2 of the opening to the projected first straight portion area S1 is not less than 1.2; and the transition portion is in the form of a taper portion.

Abstract: Provided is a spark plug that is excellent not only in salt resistance but also in stress corrosion cracking resistance. The spark plug includes a metal shell covered by a composite layer including a nickel plating layer and a chromate layer formed on the nickel plating layer. The chromate layer has a film thickness of 2 to 45 nm and Cr element concentration of not more than 60 at % and contains Ni in addition to Cr.

Abstract: A spark plug casing includes a single-piece shell having a nut portion, first and second tubular portions and a converging shell portion, which are configured to be removed from a cylinder head as an integral device. The first tubular portion extends from the nut portion and has a first cross-sectional size. The second tubular portion has a second cross-sectional size less than the first cross-sectional size. The converging shell portion is coupled between the first and second tubular portions. The casing further includes a ground strap having a third cross-sectional size less than the second cross-sectional size. The ground strap is received within an end portion of the second tubular portion opposite the converging shell portion, such that the ground strap and the cylinder head are in a spaced relationship with respect to each other for preventing carbon buildup from binding the ground strap to the cylinder head.

Abstract: A spark plug may include a first electrode, an insulator positioned radially outside the first electrode, and a housing positioned radially outside the insulator. The spark plug may also include a second electrode electrically coupled to the housing. The second electrode may form a spark gap with the first electrode. The spark plug may further include an ignition electrode coupled to at least one of the first electrode and the second electrode. The ignition electrode may include fibers of Nb—Ti within a matrix material.

Abstract: A spark plug is provided. The spark plug has an insulative sleeve with a central axial bore and an exterior surface of a shaped tip portion. A coating is disposed on the exterior surface of the shaped tip portion and the coating comprises a transition metal compound or a combination of transition metal compounds, and an alkali metal compound. A center electrode extends through the central axial bore of the insulative sleeve. A metal sleeve is provided, wherein the insulating sleeve is positioned within, and secured to, the metal shell. A ground electrode is coupled to the metal shell and positioned in a spaced relationship relative to the center electrode so as to define a spark gap.

Abstract: A spark plug with excellent vibration resistance performance and resistor load life-span characteristics, and a reduced diameter which is achieved by strengthening adhesion between a resistor and a conductive glass sealing layer.

Abstract: A spark plug (100) has a resistor (15) between a center electrode 3 and a metal terminal (13). The resistor (15) contains glass, ceramic powder, an electrically conductive material, and metal. An average of two or more particles of the metal are present in an arbitrary region measuring 300 (?m)×300 (?m) on an arbitrary section of the resistor (15), and the total sectional area of the metal present in the region accounts for less than 1.6% of the region.

Abstract: A spark member (70) is formed by joining a noble metal member (71) and an intermediate member (75) and is provided in a spark discharge gap between a center electrode and a ground electrode (30). A bottom surface (80) of the intermediate member (75) is resistance-welded to an inner surface (33) of the ground electrode (30), and a weld metal zone (73) is formed in the region of joint therebetween. As viewed on the section of the spark member (70) which contains a centerline (Q), the weld metal zone (73) is reliably formed within the range of the length (D) of a columnar portion (76) as measured along a direction orthogonal to the projecting direction of the spark member (70) and has a length (d) of at least 0.1 times (10% of) the length (D).

Abstract: A side electrode for a spark plug is provided. The side electrode includes a side wire having a first end and a second end; an opening proximate to the first end, the opening extending from a first surface of the side wire to a second surface of the side wire, wherein the first surface has a flared portion proximate to the opening; and an electrode tip secured to the first end of the side wire, the electrode tip having a tip portion and a shaft portion, wherein the tip portion is located on the second surface and the shaft portion is secured to the side wire by engaging the flared portion.

Abstract: A spark plug comprising: a cylindrical metal shell; a cylindrical insulator provided in an inner hole of said metal shell; a center electrode provided in a leading end side inner hole of said insulator; and a ground electrode having one end bonded to a leading end side of said metal shell and having another end face forming a spark discharge gap with said center electrode, wherein said ground electrode comprises an electrode material containing from 0.5 to 1.5 wt. % of Si, from 0.5 to 1.5 wt. % of Al, from 0.02 to 1.0 wt. % of at least one of Ti, V, Zr, Nb and Hf, from 0.03 to 0.09 wt. % of C and 95.5 wt. % or more of Ni, and having a specific resistance at 20° C. of 25 tincm or less.

Abstract: A spark plug (20) includes a center electrode (24) and a ground electrode (22). The electrodes (22, 24) include a core (26) formed of a copper (Cu) alloy and a clad (28) formed of a nickel (Ni) alloy enrobing the core (26). The Cu alloy includes Cu in an amount of at least 98.5 weight percent, and at least one of Zr and Cr in an amount of at least 0.05 weight percent. The Cu alloy includes a matrix of the Cu and precipitates of the Zr and Cu dispersed in the Cu matrix. The Ni alloy of the clad (28) includes Ni in an amount of at least 90.0 weight percent. The Ni alloy also includes at least one of a Group 3 element, a Group 4 element, a Group 13 element, chromium (Cr), silicon (Si), and manganese (Mn) in a total amount sufficient to affect the strength of the Ni alloy.

Abstract: The object of the invention is to provide a spark plug including a central electrode and/or a ground electrode with a gap, which can suppress generation of corrosion-like generated foreign substances while maintaining high thermal conductivity and high strength. The gap between the central electrode and the ground electrode with at least one of the central electrode and the ground electrode formed from an electrode material including 96% by mass or more of Ni, in which the electrode material includes a total content of from 0.05% by mass to 0.45% by mass of at least one selected from a group consisting of Y and rare earth elements, 0.05% by mass or more of Mn, and a total content of 0.01% by mass or more of at least one selected from a group consisting of Ti, V, and Nb, and the ratio (a/b) of the total content (a) of Ti, V, and Nb to the content (b) of Mn is from 0.02 to 0.40.

Abstract: A spark plug exhibits a satisfactory withstand voltage characteristic and sufficient mechanical strength in a high temperature environment exceeding 700° C. The spark plug has a center electrode, an insulator, and a ground electrode, characterized in that the insulator is formed of an alumina-based sintered material containing an Si component, a Group 2 element (2A) component, and a rare earth element (RE) component; that the alumina-based sintered material has an RE-?-alumina crystal phase; and that the mean crystal grain size DA(RE) of the RE-?-alumina crystal phase and that of alumina DA(Al) satisfy the following relationship (1): 0.2?DA(RE)/DA(Al)?3.0.

Abstract: A device including two plasma generation electrodes, a series resonator having a resonant frequency above 1 MHz and including a capacitor with two terminals, and an induction coil surrounded by a screen, the capacitor and the coil being placed in series, the electrodes being connected to the respective terminals of the capacitor. The ratio of the spark plug to the radius of the screen is equal to 0.56. The device can optimize the Q-factor of such a device by adjusting the radius of the coil to that of the screen.

Abstract: A spark plug electrode material that may be used in spark plugs and other ignition devices including industrial plugs, aviation igniters, glow plugs, or any other device that is used to ignite an air/fuel mixture in an engine. According to an exemplary embodiment, the electrode material includes a refractory metal (for example, tungsten (W), molybdenum (Mo), rhenium (Re), ruthenium (Ru) and/or chromium (Cr)) and a precious metal (for example, rhodium (Rh), platinum (Pt), palladium (Pd) and/or iridium (Ir)), where the refractory metal is present in an amount that is greater than that of the precious metal. This includes, but is certainly not limited to, electrode materials including tungsten-based alloys such as W—Rh and ruthenium-based alloys such as Ru—Rh. Other combinations and embodiments are also possible.

Abstract: A spark plug include an insulator, a central electrode, which is in the form of a bar received in the insulator, a metal case, which surrounds the insulator and is grounded, and a ground elbow fixed to the metal case. The central electrode includes a discharge terminal exposed outside the insulator and defining an extension line as an imaginary line extending from the discharge terminal along a central axis of the central electrode. The ground elbow has a connection end and an opposite, sharp-tip-like receiving end. The connection end is fixed to the metal case. The receiving end is set close to but spaced from the discharge terminal and is locate by one side of the extension line.

Abstract: An ignition plug that maintains excellent ignition performance over a long period of time through effective prevention of channeling. The ignition plug includes an insulator having an axial bore, a center electrode inserted into the axial bore, a metallic shell disposed externally of the outer circumference of the insulator, and a ground electrode fixed to a front end portion of the metallic shell. A cavity is defined by the wall surface of the axial bore and the front end surface of the center electrode. The ground electrode includes a body whose distal end portion is disposed away from the front end of the insulator, and a protrusion protruding from the body.

Abstract: A spark plug includes a tubular metal shell, an insulator, a cylindrical center electrode, and a ground electrode. The ground electrode has an inclined portion, a straight portion, and a bend between the inclined and straight portions. The inclined portion extends obliquely with respect to the axial direction of the center electrode from a base end of the ground electrode, which is joined to an end of the metal shell, to the bend that is positioned closer to the center electrode in the radial direction of the center electrode than the base end. The straight portion extends substantially parallel to the axial direction of the center electrode from the bend to a tip end of the ground electrode. The straight portion has an inner side surface facing the side surface of an end portion of the center electrode through a spark gap in the radial direction of the center electrode.

Abstract: A method for manufacturing an ignition plug is provided. The method includes: preparing an insulator having a cavity provided at a leading end portion thereof by disposing a leading end of a center electrode more inwards in an axial hole than a leading end of the insulator; building the insulator in an interior of a metal shell; disposing a ground electrode at a leading end portion of the metal shell; positioning a center of a through hole of the ground electrode and a center of the cavity of the insulator; and welding the ground electrode and the metal shell together after the positioning step.

Abstract: A spark plug has a center electrode, a ceramic insulator having an axial hole to support the center electrode therein, a metal shell holding the ceramic insulator, and a ground electrode, one end portion of which is fixedly connected with the metal shell, the other end portion of which is located apart from an outer circumferential surface of a top end portion of the center electrode for defining a spark discharge gap therebetween. The ceramic insulator is provided with recesses at an edge portion between a top end surface of the ceramic insulator and an inner circumferential surface of the axial hole. When defining first and second imaginary circles with the axis being their respective centers as circles passing through portions of the recesses whose radial distances from the axis are a maximum and a minimum respectively, a difference of diameters of the first and second imaginary circles is 0.08 mm or less.

Abstract: There is provided an ignition plug whereby an electrical configuration for discharge and an electrical configuration for guiding and radiating microwaves are provided concomitantly, within dimensions permitting installation in an installation space for an ordinary ignition plug, and adapted to efficiently guide and transmit microwaves into a combustion chamber. The ignition plug comprises a center electrode and a ground electrode for spark discharge; a center wire and an outside conductor forming a coaxial electromagnetic wave transmission line; and a microwave radiation antenna that is electrically integrated with the center wire; the microwave radiation antenna having a profile that defines part of a sphere or arc including a plurality of locations substantially equidistant from the center electrode.

Abstract: Provided is a spark plug that includes a center electrode extending in an axial direction, a cylindrical insulator that holds the center electrode, and a cylindrical main metal fitting, which has a ground electrode at a tip portion thereof. The cylindrical main metal fitting includes a tool engagement portion for mounting the spark plug to an engine and a metal fitting-side fitting portion provided at a rear side of the main metal fitting opposite from the tip portion. The metal fitting-side fitting portion holds the insulator in a tightly fitted state in a radial direction.

Abstract: A spark plug which exhibits high dielectric strength at high temperature and which is unlikely to be deteriorated in dielectric strength is provided. The spark plug includes a center electrode, an insulator, and a metallic shell. The insulator includes an alumina-based sintered body which contains a silicon component, a Group II element component, and a rare earth element component. The alumina-based sintered body is composed of a glass phase and an alumina crystal phase as observed through X-ray diffraction analysis. When the grain boundary phase of the alumina-based sintered body is observed under a transmission electron microscope, and the weight ratio between an alkali metal component and the rare earth element component as reduced to oxides thereof [alkali metal/rare earth element] is calculated at 30 circular spots, each having a diameter of 0.3 nm, selected arbitrarily in a field of observation, the average of the weight ratios of the 30 spots falls within a range of 0.01 to 1.0.

Abstract: Disclosed herein is a spark plug comprising an insulative sleeve having a central axial bore and an exterior surface and a center electrode extending through the central axial bore of the insulative sleeve. The insulating sleeve is positioned within, and secured to, a metal shell that serves as a mounting platform and interface to an internal combustion engine. The metal sleeve also supports a ground electrode that is positioned in a spaced relationship relative to the center electrode so as to generate a spark gap. The insulating sleeve includes a shaped tip portion that resides in a recessed end portion of the metal shell. A coating is disposed on the exterior surface of the insulative sleeve. The coating comprises a silicone resin, optionally in combination with a filler.

Abstract: A spark plug includes an insulator, a center electrode, a metal shell, a ground electrode, and a noble metal tip joined to at least one of the two electrodes. The noble metal tip is joined to the electrode via a melt portion formed by using a laser or electron beam from a side surface of the noble metal tip. In a predetermined section, including a central axis of the noble metal tip, ¾ or more of one end face of the noble metal tip is joined to the electrode. When the thickness of the melt portion is taken to be TX (mm), and the length in a direction of irradiation with the laser beam is taken to be LX (mm), TX and LX satisfy 1.5?LX/TX, and an angle ?X or angle ?Y, formed by two predetermined straight lines, satisfies ?15??X (?Y)?25.

Abstract: A spark plug in which the center electrode is formed by laser welding along the circumference of a joint surface between a center electrode base metal and a noble metal tip in excess of full circumference. When G represents a spark gap and A represents a shortest gap between a laser weld bead and a line drawn parallel with axis X, A?3G. Straight lines S1 and S2 which connect the center of the noble metal tip 1 and the circumferential center of a proximal end 52 of the ground electrode 51 and vertex 8 of a protrusion 7 formed at a final end portion 6e of a bead 6 formed by circumferential laser welding, respectively, form an angle ? of 45 degrees. Since the protrusion 7 of the bead is the angle ? away from the ground electrode 51, an abnormal discharge is unlikely to be generated.

Abstract: An ignitor assembly constructed in accordance with one aspect of the invention has an upper inductor subassembly coupled to a lower firing end subassembly for relative pivot movement between the subassemblies. The upper inductor subassembly includes a tubular housing with inductor windings received therein with an upper electrical connector adjacent an upper end of the housing and a lower electrical connector adjacent a lower end of the housing. The lower firing end subassembly includes a ceramic insulator and a metal housing surrounding at least a portion of the ceramic insulator. The ceramic insulator has an electrical terminal extending from a terminal end and an electrode extending from a firing end. A flexible tube couples the upper inductor subassembly to the lower firing end subassembly and maintains the electrical terminal of the lower firing end subassembly in electrical contact with the lower electrical connector of the upper at a pivot joint.

Abstract: A process of manufacturing the spark plug that includes a step in which a receiving die having an insertion hole and a taper portion is used, wherein a thread portion of the spark plug is inserted into the insertion hole and a seat portion of the spark plug is brought into contact with the taper portion, and a pressing force is applied to a rear end portion of a metallic shell of the spark plug so as to bend a rear end opening portion of the metallic shell, and to thereby form a crimped portion, whereby an insulator and the metallic shell are fixed together.

Abstract: A spark plug capable of increasing a welding strength between a leading end of a metal shell and a base end of a ground electrode to avoid fracture of a welded part due to vibrations and the like even when making the metal shell smaller. The spark plug satisfies a relation of S2?S wherein S2 is a sectional area of the welded part between the metal shell and the ground electrode, the sectional area S2 being cut off by a plane including a leading end surface of the metal shell, and S is a sectional area of the ground electrode, the sectional area S being cut off by a plane passing to the most axial leading end of a boundary between the ground electrode and the welded part and perpendicular to the axial direction.

Abstract: A spark plug and method of manufacturing the same. The spark plug includes a tubular insulator holding a center electrode, and a tubular metallic shell holding the insulator. The insulator is inserted into the metallic shell from the rear end side thereof until a portion of the insulator engages the metallic shell. In this state, the circumferential edge of the rear end portion of the metallic shell is crimped, whereby the insulator is unitarily fixed to the metallic shell. A talc charged layer is formed in a clearance portion between the insulator and the metallic shell, and a wire packing is placed on a rear end portion of the talc charged layer for engaging the crimp portion. A portion of the talc charged layer is interposed between the wire packing and the rear trunk portion of the insulator.

Abstract: Disclosed herein is a spark plug comprising an insulative sleeve having a central axial bore and an exterior surface and a center electrode extending through the central axial bore of the insulative sleeve. The insulating sleeve is positioned within, and secured to, a metal shell that serves as a mounting platform and interface to an internal combustion engine. The metal sleeve also supports a ground electrode that is positioned in a spaced relationship relative to the center electrode so as to generate a spark gap. The insulating sleeve includes a shaped tip portion that resides in a recessed end portion of the metal shell. A coating is disposed on the exterior surface of the shaped tip portion of the insulative sleeve. The coating comprises a metal oxide, a noble metal, late transition metal, or a combination comprising two or more of the foregoing metals.

Abstract: A spark plug 1 includes an insulator 2, a metal shell 3, a center electrode 5 and a ground electrode 27. A spark discharge gap 33 is formed between a front end portion 28 of the center electrode 5 and the ground electrode 27. The metal shell 3 has a through hole 29 therein and a metal convex portion 21 inwardly radially projecting in the through hole 29. The metal convex portion 21 includes a convex rearward face 30, a convex inner circumferential face 31 and a convex forward face 32. The through hole 29 has an inner diameter A (mm) at a front end side inner circumferential face 40, which is located at the front end side with respect to the convex forward face 32. The insulator 2 is inserted in the through hole 29 and has a first insulator taper portion 14, a second insulator taper portion 36 and a base 37 between the taper portions. The present invention satisfies the following representations: G?(A?B)/2; A?7.

Abstract: A method of producing a spark plug includes reducing the diameter of a center electrode while maintaining the heat dissipation property of the center electrode. A columnar member in which an outer skin member and a core member having a high thermal conductivity are clad, and which is columnarly extended, are configured by extrusion molding into a state where the thickness of the outer skin member is substantially uniform. A flange portion and a tip end portion are formed in the columnar member to obtain an electrode intermediate member. In a middle trunk portion of the electrode intermediate member, the thickness of the outer skin member is maintained. Then, the surface of the middle trunk portion is cut or polished to reduce the thickness, whereby the diameter of a center electrode is reduced while maintaining the outer diameter of the core member.

Abstract: An alumina-based sintered body for a spark plug having enhanced mechanical strength and a method of manufacturing the same, as well as a spark plug having the alumina-based sintered body for a spark plug and a method of manufacturing the same.

Abstract: A spark plug (100) includes: a center electrode (2); and a ground electrode (30) which is to be exposed in a combustion chamber of an internal combustion engine and which forms a spark discharge gap with the center electrode (2), wherein at least one of the center electrode (20) and the ground electrode (30) contains an electrode material whose principal component is Ni and in which an intermetallic compound is precipitated at least intergranularly and intragranularly.

Abstract: A high voltage resonator-amplifier for a radiofrequency ignition system that can be used in an internal combustion engine, the resonator-amplifier including at least two electrodes, a coil arranged in alignment with the electrodes along a longitudinal axis, and a linking mechanism retaining the coil and the electrodes in a relatively fixed position. The coil is wound around a closed bend which in turn wraps around the longitudinal axis.

Abstract: The present invention provides a highly reliable spark plug used for an internal-combustion engine and including an insulator with a high withstand voltage, and a method for manufacturing the same. Namely, it provides a spark plug containing a cylindrical metal shell having an insulator holding hole, a cylindrical insulator including an axial hole therein which extends in an axial direction, and engaging with said insulator holding hole of said metal shell, and a center electrode held in said axial hole of said insulator, wherein said insulator has a texture in which one or more pores exposed in a judgment area with 50 ?m in diameter occupy 40% or less of said judgment area at any locations in an observation area, in the case where a predetermined mirror-finishing section of an enclosed portion surrounded by said metal shell is used as said observation area to observe pores exposed in said observation.

Abstract: When an insulator of a spark plug receives an external force in a bending direction perpendicular to an axis at a rear end side body portion, a position C where the insulator is supported by a crimping portion via a packing acts as a fulcrum, and a stress is applied between the position C and a position B where the insulator is supported by a ledge portion via a packing. When an insulator is designed in which the balance of size and modulus of section is adjusted so that ?A which denotes a proof strength against bending between a rear end position A of the insulator and the position C and ?B which denotes a proof strength against bending between the position B and the position C satisfy 0.71??A/?B?1.27, cracks can be prevented.

Abstract: The invention relates to a spark plug of an internal combustion engine, especially for use in Otto gas engines. Said spark plug comprises, supported by an insulating body (1), a preferably one-piece spark plug shell (2) and a center electrode (3), which is especially rod-shaped or has a plurality of electrode fingers, and at least one ground electrode (4), preferably a plurality of ground electrodes, the center electrode (3) and the at least one ground electrode (4) being surrounded by a chamber, especially a pre-chamber (5a) or a swirl chamber (5b) supported by the spark plug shell (2), or being located inside said chamber (5a, 5b).

Abstract: A spark plug has a central electrode and a plurality of peripheral electrodes. The central electrode has a proximal portion and a distal portion. The distal portion of the central electrode has a circular cross-section with a longitudinal axis and terminates in a distal end. Each peripheral electrode has a lower portion and an upper portion. Each upper portion has a distal-most point. Each distal-most point is disposed in a central plane within which the longitudinal axis of the distal portion of the central electrode is wholly disposed. The cross-section of each upper portion taken along its central plane defines a convex outer side and a non-convex inner side. Each convex outer side has a curved surface which is tangent to a plurality of tangent planes, all of which intersect the longitudinal axis of the distal portion of the central electrode at points at or above the distal end of the distal point of the central electrode.

Abstract: A spark plug for an internal combustion engine, includes: a cylindrical insulating body; a center electrode; a cylindrical metal shell; and a ground electrode, as defined herein, wherein the noble metal tip is bonded to the ground electrode via a molten bond, and when viewed in a cross-section including a center axis of the noble metal tip along a longitudinal direction of the ground electrode, a sum of a cross-sectional area of a base-end-side molten bond (A) positioned at a base end side of the ground electrode and a cross-sectional area of a front-end-side molten bond (B) positioned at a front end side of the ground electrode is equal to or greater than 4 mm2, and the cross-sectional area of the front-end-side molten bond (B) is 1.1 to 1.3 times greater than that of the base-end-side molten bond (A).

Abstract: A spark plug in which the rising of a ground electrode is more reliably restrained. The spark plug includes a ground electrode having a core portion extending from a proximal end section toward a distal end section via a bent section, a heat transfer portion extending from the proximal end section toward the distal end section via the bent section, and an external layer located externally of the core portion and the heat transfer portion and extending from the proximal end section to the distal end section via the bent section. As viewed on a section of the ground electrode taken orthogonally to a direction along which the ground electrode extends, at least at an intermediate position of the bent section with respect to the direction, the center of the core portion is offset toward a center electrode from the center of the heat transfer portion.

Abstract: An object of the invention is to provide a spark plug including an insulator which is difficult to cause breakdown and exhibits higher withstand voltage characteristics. This invention relates to a spark plug 1 including a center electrode 2, an insulator 3 and a grounding electrode 6, wherein the insulator is formed by an alumina-based sintered body which has a theoretical density ratio of 95.