Abstract: A sparkplug having ground and/or center electrodes that include a firing tip formed by reflowing of an end of wire having an opposite end carried by a feed mechanism. The present invention also includes methods of manufacturing an ignition device and electrodes therefore having a firing tip, including providing a metal electrode having a firing tip region; providing a wire having a free end and another end carried by a feed mechanism; and reflowing the free end to form a firing tip.

Abstract: A spark plug in which a distal end portion (60) of a crimp portion (53) of a metallic shell (50) is crimped by bending the distal end portion inward, whereby the metallic shell (50) and an insulator (10) are fixed together with a first packing (6), a second packing (7), and talc (9) being present therebetween. The first packing (6) assumes an annular shape and has a circular cross section. A minimum diameter portion of the crimp portion (53), which portion is closest to the outer circumferential surface (17) of a trunk portion (18), is located at the position of the center line of the first packing (6) or inward thereof with respect to the axis O. The crimp portion (53) does not come into contact with the insulator (10), and the first packing (6) comes into contact with the insulator (10). Furthermore, the first packing (6) has a hardness that is lower than that of the crimp portion (53).

Abstract: A spark plug including: a center electrode; an insulator which holds the center electrode therein in a state where a tip end portion of the center electrode protrudes therefrom; a metal shell which holds the insulator therein; a ground electrode which is fixed to the metal shell, the ground electrode having an inner side face having a width that is smaller as it advances toward a tip end side, in a portion of the inner side face positioned between a pair of tapered faces; and a discharge portion which is bonded to the inner side face of the ground electrode by laser welding so as to attain a diameter of 0.8 mm or less and a height of 0.5 mm or more, and a discharge gap being formed between the discharge portion and the tip end portion of said center electrode.

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 plasma jet spark plug and a manufacturing method therefor are disclosed. In a state in which a noble-metal chip having a flange-like outwardly projecting portion is disposed in a communication section of a ground electrode, an electrode base metal of the ground electrode is disposed in a stepped engagement portion of a metallic shell, which retains an insulator therein. While being pressed against a front end portion of the insulator, the noble-metal chip is joined to the electrode base metal, whereby a clearance between the ground electrode (electrode base metal) and the front end portion of the insulator can be closed. Therefore, energy of plasma generated within the cavity does not leak.

Abstract: A spark plug comprising a housing, a ceramic insulator and a sleeve is provided. The housing has an inner cavity while the ceramic insulator encloses a central electrode. The ceramic insulator is disposed inside the inner cavity and maintain from the housing with a gap. The sleeve is provided enclosing an inner wall of the housing and corresponds to an opening of the inner cavity. The level of an edge surface of the housing corresponding to the opening of the inner cavity is disposed higher than the level of an edge surface of the central electrode, and the level of the center electrode is also higher than the level of the edge surface of the ceramic insulator.

Abstract: A spark plug including a center electrode; an insulator; and a metal shell, wherein the metal shell includes: a mounting portion; a cylindrical portion; a seal portion; a crimping portion; and a buckled portion all as defined herein, and a relationship A<B is satisfied, in which A is a length in the axial direction of an external thread formed on the mounting portion, and B is a length of the cylindrical portion in the axial direction.

Abstract: A spark plug assembly (10) for engine applications where the combustion chamber is difficult to access when servicing or replacing a spark plug. The spark plug assembly (10) includes a fairly traditional spark plug component (28) to which an elongated tubular conduit (12) is attached, such as by welding, to a portion of the metallic shell (32). The conduit (12) contains an upper ceramic insulator (52) adjacent its top end (14) disposed in end-to-end abutting contact with an outer elastomeric insulator (58). The ceramic insulator of the spark plug component (28), herein referred to as a lower ceramic insulator (30), is surrounded by the outer elastomeric insulator (58) and held securely within the conduit (12) thereby. An inner elastomeric insulator (62) is disposed in a continuous passageway formed between aligned central bores formed in the respective upper ceramic (52) and outer elastomeric (58) insulators.

Abstract: A spark plug for an internal combustion engine is provided which includes a hollow cylindrical metal shell with an open end portion to be exposed to a combustion chamber of the engine, a ground electrode joined to the metal shell, a center electrode disposed in the metal housing to define a spark gap between itself and the ground electrode. The spark plug also includes a stream shaper or a stream reflector geometrically formed on the metal shell and/or the porcelain insulator to shape a vortex steam of air-fuel mixture into a stream thereof which is oriented outside the spark plug or serves to decrease the amount of the air-fuel mixture into a pocket between the metal shell and the porcelain insulator. This ensures the stability of ignition of the air-fuel mixture.

Abstract: A spark plug for igniting gases in an internal combustion engine is disclosed. The spark plug has a center electrode, an insulator, a one-piece shell, and a terminal. The center electrode is in communication with an energy source. The insulator surrounds the center electrode. The one-piece shell surrounds and contacts the insulator for securing the insulator within the shell, wherein the shell has a plurality of threads near a first end and a ground electrode attached to the shell and aligned with a tip of the center electrode at a second end to define a spark gap. Further, a seat is formed in the shell between the plurality of threads and the ground electrode for sealing the shell against the engine. The terminal has a first end in communication with the center electrode and a second end which has a connector portion for connecting to the energy source.

Abstract: A spark plug including a ground electrode which has an excellent heat sinking ability. The ground electrode includes a core material therein. Heat received from a combustion chamber during a drive of an internal-combustion engine can be conducted to the core material. More effective heat sinking ability can be achieved because of the core material.

Abstract: A spark plug and method of construction thereof is provided. The spark plug includes a metal shell having a through cavity, a lower insulator and a plastic upper insulator. The lower insulator is received in the through cavity and has a through passage with a center electrode received therein. A ground electrode is operatively attached to the shell in spaced relation from the ground electrode to provide a spark gap. The plastic upper insulator has a distal end received in the through cavity of the shell and a terminal end extending axially outwardly from the shell. The upper insulator has a through passage extending between the terminal end and the distal end. An elongate conductive member is received in the through passage of the upper insulator and is configured for electrical communication with the center electrode.

Abstract: An extension-type spark plug (10) is disclosed for igniting the air-fuel mixture in an internal combustion engine. The spark plug (10) includes an installation conduit (12), a contact button (34), an electrode extension (20), a firing electrode (60), a ground plate (66), a sleeve insulator (22), an upper insulator (90) and a lower insulator (50). The electrode extension (20) is axially aligned with and in communication with the firing electrode (60). The ground plate (66) is proximate the firing electrode (60) to define a spark gap between the firing electrode (60) and a first end of the ground plate (66). The sleeve insulator (22) surrounds the electrode extension (20). The upper insulator (90) surrounds an upper portion of the electrode extension (20) and is in contact with the sleeve insulator (22). The lower insulator (50) surrounds the lower portion of the electrode extension (20) and is in contact with the sleeve insulator (22).

Abstract: A spark plug for an internal combustion engine is provided which includes a hollow cylindrical metal shell with an open end portion to be exposed to a combustion chamber of the engine, a ground electrode joined to the metal shell, a center electrode disposed in the metal housing to define a spark gap between itself and the ground electrode. The spark plug also includes a stream shaper geometrically formed on an outer periphery of the open end portion of the metal shell to shape tumble vortexes of air-fuel mixture into vortex streams oriented toward a central portion of the combustion chamber. This ensures the stability of orientation of the tumble vortexes to control a flow of sparks, thereby enhancing the ignitability of the air-fuel mixture in the combustion chamber.

Abstract: A spark plug including a center electrode; an insulator; a metal shell; a ground electrode; and an annular packing, all as defined herein, wherein the packing has a hardness greater than or equal to a hardness of the stepped portion of the metal shell or has a Vickers hardness of not less than 300 Hv. Preferably, a difference between the hardness of the packing and the hardness of the stepped portion of the metal shell is from 120 Hv to 160 Hv, and the packing has a Vickers hardness of not more than 500 Hv.

Abstract: A dual-electrode spark igniter (spark plug), which has two electrodes extending from the plug body. During a spark event, electricity flows across a first spark gap from a first electrode to a second electrode. Electricity also flows across a second spark gap from the second electrode to ground.

Abstract: A spark plug including an insulator and a metallic shell having an outer surface and an inner surface. The outer surface has a taper portion which comes into contact with a peripheral region around a mounting hole of an internal combustion engine, a tool engagement portion, and a trunk portion formed between the tool engagement portion and the taper portion. The inner surface has an annular step portion projecting toward the insulator and an internal trunk portion extending from the base of the step portion toward the rear end of the metallic shell. When the insulator and the metallic shell are fixed to each other by one of either cold and hot crimping, the projected area of the taper portion is at least two times or at least 1.5 times that of the step portion, respectively.

Abstract: A spark plug arrangement for an exhaust treatment device is disclosed. The spark plug arrangement may have a body, and a center electrode extending from an end of the body. The spark plug arrangement may further have a mounting member with a bore configured to receive the body, and a grounded electrode extending proximal the center electrode.

Abstract: A spark plug for an internal combustion engine is provided which includes a metal shell, a porcelain insulator, a center electrode, and a ground electrode. The center electrode is retained in the porcelain insulator to define a spark gap between itself and the ground electrode. The porcelain insulator has a nose made up of an upright portion and a tapered portion continuing from the upright portion toward a top end thereof. The tapered portion has a diameter decreasing toward the top end of the porcelain insulator. The upright portion has an outer wall extending substantially parallel to an inner wall of the metal shell, thereby inducing the formation of side sparks between the tapered portion and the metal shell before the insulation resistance between the center electrode and the metal shell drops, thereby giving a signal indicative of such an event to an operator.

Abstract: A spark plug comprising: an insulator shell; a center electrode inside the insulator shell such that one end of the center electrode protrudes from the insulator shell; a metal shell exterior to the insulator shell; a side ground electrode having one end coupled to the metal shell and the other end facing the protruding end of the center electrode to form a spark discharge gap between the center electrode and the side ground electrode; and a metal tip on at least one of the side ground electrode or the center electrode, located at the spark discharge gap, that is a platinum-based alloy including 23-35 weight percent palladium, greater than 0 to 10 weight percent iridium and the balance being platinum.

Abstract: The present invention provides a spark plug that includes a center electrode extending in an axial direction, a ceramic insulator having an axial hole formed in the axial direction to retain the center electrode in a front side of the axial hole and thereby form an assembly unit of the center electrode and the ceramic insulator, a metal shell surrounding an outer circumference of the ceramic insulator to retain therein the assembly unit, and a ground electrode having one end portion joined to a front end face of the metal shell and the other end portion facing the center electrode to define a spark gap therebetween, wherein the spark plug satisfies the following conditions: H?1 mm, Vc?17 mm3 and Ra?1.

Abstract: A plasma jet spark plug provides improved ignitability and durability by forming a part of a spark discharge gap outside the electric discharge space which generates plasma. An ignition system for the plasma jet spark plug is also disclosed. The plasma jet spark plug includes a center electrode, an insulator defining an axial bore which partially surrounds the center electrode, a cavity surrounded by an inner circumferential face of the axial bore which extends from an opening portion of a front end of the axial bore of the insulator and wherein a front end face of the center electrode is formed. A ground electrode is bent towards a front end portion of the insulator.

Abstract: A spark plug comprises: a spark plug housing; an axial core electrode disposed in a longitudinal direction in the spark plug housing; and a ground electrode having a terminal part spaced apart along the longitudinal direction from a distal end of the axial core electrode and disposed in a perpendicular relation with the axial core electrode, the terminal part having a circular through hole formed along an axis coaxial with the axial core electrode, the circular through hole having a tapered inner surface and including a plurality of spiral protrusions disposed on the tapered inner surface to induce a turbulent air flow in the combustion inflow.

Abstract: A spark plug having a multilayer firing tip that minimizes the amount of precious metal used and a method of assembling a spark plug with a multilayer firing tip. The firing tip includes a discharge end and a weld end, with the weld end being connected to a center electrode, and more specifically to a base electrode on the center electrode. The weld end has a coefficient of thermal expansion, which is not between the values for the coefficients of thermal expansion for the discharge end and the base electrode. More specifically, the weld end has a coefficient of thermal expansion which is greater than the coefficients of thermal expansion for the discharge end and base electrode. The weld end is formed from Nickel and Chromium with a limited amount of additional elements. The spark plug is assembled by providing a first elongated material formed from the material used for the discharge end and a second elongated material formed from a material used for the weld end.

Abstract: A spark plug having a ground electrode in the shape of a parabolic defined by a dish reflector and a hole at the center of the parabolic dish reflector. An ignitor electrode terminates at its distal end in a round tip disposed in the center hole in spaced-apart relationship with respect to the center hole. An insulative body supports the ignitor electrode with a conductive body supporting the ground electrode. The parabolic dish reflector is joined with the conductive body by a pair of posts so as to define a pair of slots for venting exhaust gasses from the ignition site.

Abstract: There is provided a method for producing a spark plug in which welding strength between a noble metal tip and an electrode joined by laser welding can be restrained from becoming weak. A noble metal tip (90) to be joined to a center electrode (2) or ground electrode of a spark plug to form a spark discharge gap is resistance-welded to each electrode containing no noble metal and then laser-welded. In the noble metal tip (90) exposed under a severe environment involving spark discharge, a molten portion (80) formed in such a manner that a portion of the noble metal tip (90) and a portion of the electrode are melted by laser welding and a non-molten portion (95) on the noble metal tip (90) side are apt to be peeled from each other in a boundary surface (83) between the molten portion (80) and the non-molten portion (95).

Abstract: A spark plug including: a cylindrical insulator having an axial hole extending through the insulator in an axial direction; a center electrode inserted in the axial hole; a metal shell provided around an outer periphery of the insulator and having a leading end surface, from which a leading end surface of the insulator protrudes; a ground electrode having a base end bonded to the leading end surface of the metal shell; and a noble metal tip disposed on a distal end of the ground electrode, an end of the noble metal tip protruding toward the center electrode in a radial direction, wherein: the spark plug forming a spark discharge path upon application of a discharging voltage between the protruding end of the noble metal tip and an end of the center electrode, the spark discharge path including an aerial discharge gap between a part of the protruding end of the noble metal tip and a part of the end of the insulator and a surface-creeping discharge path beginning at a part of the end of the insulator and a part

Abstract: A method and apparatus to maximize spark plug life in pre-chamber spark plugs operating with ultra-lean mixtures and/or elevated engine BMEP is presented. Electrode erosion is reduced by spreading discharge energy over a wider surface area, maintaining fuel concentration in the spark gap, controlling gas static pressure during discharge, and maintaining safe electrode temperature. Energy is spread via a swirling effect created by periphery holes in an end cap, resulting in a lower specific energy discharge at the electrodes. Divergently configured electrodes reduce the spark voltage at high operating pressures and the energy required for ignition. The flow field generated at the electrodes prevents electrical shorts due to water condensation and avoids misfire. The center electrode insulation provides an effective heat transfer path to prevent electrode overheating and preignition.

Abstract: A spark plug fitted to a cylinder head has a center electrode with a noble metallic tip portion having a sectional area S1 between 0.07 mm2 and 0.95 mm2 and a melting point of 2000° C. or more, and a ground electrode with a noble metallic tip portion having a sectional area S2 and a melting point of 1700° C. or more. The plug has a length H ranging from 6.5 mm and 10 mm between the head and the tip portion of the center electrode, a length G ranging from 1.1 mm and 2.0 mm between the tip portions, a length J between the head and a housing, a length F satisfying J?F?H?1.0 mm between the head and an insulator, and a pocket clearance P satisfying P?1.1×(G+0.0345×S1?1.2418+0.0327×S2?1.2418) between the housing and the insulator.

Abstract: A spark plug for an internal combustion engine of a motor vehicle; the spark plug is embodied with a generally essentially long shape and includes: an essentially capacitive lower part including two coaxial electrodes, one of which is a central electrode, and the other a threaded shell for screwing in the spark plug on the engine; and an essentially inductive upper part including a central winding including a plurality of coils wound around a coaxial mandrel, an envelope, and an insulator inserted between the envelope and the winding. The essentially capacitive part and the essentially inductive part are mechanically interconnected as to enable transmission of a clamping couple applied to the envelope to the essentially capacitive lower part. The mandrel can be elastically deformed as to compensate effects of dilation of the insulator.

Abstract: A method and apparatus to maximize spark plug life in pre-chamber spark plugs operating with ultra-lean mixtures and/or elevated engine BMEP is presented. Electrode erosion is reduced by spreading discharge energy over a wider surface area, maintaining fuel concentration in the spark gap, controlling gas static pressure during discharge, and maintaining safe electrode temperature. Energy is spread via a swirling effect created by periphery holes in an end cap, resulting in a lower specific energy discharge at the electrodes. Divergently configured electrodes reduce the spark voltage at high operating pressures and the energy required for ignition. The flow field generated at the electrodes prevents electrical shorts due to water condensation and avoids misfire. The center electrode insulation provides an effective heat transfer path to prevent electrode overheating and pre-ignition.

Abstract: An improved structure of a spark plug is provided to ensure a high strength of joint between a ground electrode and a metal shell. The ground electrode is resistance-welded to the metal shell so that it is embedded partially in an end surface of the metal shell to create a weld interface extending from the end surface to an inner periphery of the metal shell, thus resulting in an increased size of the weld interface to increase the joint strength. The resistance welding keeps the temperature of a weld between the ground electrode and the metal shell at a lower level during welding as compared with laser welding, thus minimizing solidification cracking in the weld.

Abstract: A spark plug having a center electrode and a ground electrode wherein the spark portion of at least one of the center electrode and ground electrode includes a base material and a protective material that substantially prevents corrosion of the base material.

Abstract: An internal combustion engine radio frequency spark plug including two plasma-generating electrodes, separated by an insulator, that constitute respectively an outer shell enclosing the insulator and a central electrode housed in a central bore of the insulator. The spark plug includes a deep opening over the entire circumference of the shell, forming a heat-exchanger chamber inside the spark plug shell, opening outwards.

Abstract: A small diameter spark plug configuration is provided, the configuration has been found to provide additional volume for the insulator member. That is, by limiting the overall number of threads on the intermediate portion along with a limit of the overall diameter of the spark plug, additional volume of insulator material may be achieved in an interior cavity of a metal shell of the spark plug. This additional volume enables a portion of the insulator member to have a larger diameter and hence greater material thickness. The larger diameter of the insulator provides enhanced dielectric properties and protects internal components of the spark plug from high combustion chamber temperatures while simultaneously providing a robust attachment of the spark plug with an engine head.

Abstract: A spark plug is provided providing resistance to fouling. The spark plug includes a metal shell having a first end, a second end and an intermediate portion that collectively define a central cavity. The spark plug also includes an insulator that extends through the central cavity of the metal shell. The insulator includes a first end portion extending through an intermediate portion to a stepped tip portion having a first length. The stepped tip portion includes a first section and a substantially straight second section having a second length. The substantially straight second section includes a segment that extends beyond the second end of the metal shell to a third length. The second length of substantially straight portion is based upon at least one of the first length and the third length.

Abstract: A spark plug including: a center electrode (20); an insulator (10) having an axial hole (12) extending in an axial direction of the center electrode (20) and holding the center electrode (20) in the axial hole (12); a cylindrical metal shell (50) surrounding the insulator (10) and holding the insulator (10); and a ground electrode (30) having first and second end portions, an end face (35) of one end portion (32) being joined to a tip face (57) of the metal shell (50) and which is bent so that the other end portion (31) is opposed to the center electrode (20). An axial line (P) of the metal shell (50) and an axial line (O) of the insulator (10) deviate from one another so that a relationship A>B is satisfied for distances A and B as defined herein.

Abstract: A spark plug having a ground electrode with a precious metal pad welded to the ground electrode through a series of weld steps. The precious metal pad is a Pt-based pad which is attached to a side surface of the ground electrode via an attachment process that includes a resistance tack weld to initially secure the pad in place, a coining step to flatten the pad, a second resistance weld to form a permanent weld of the pad to the ground electrode, and a laser capping weld about the exposed periphery of the pad to seal the resistance weld. The laser capping weld comprises numerous overlapping weld spots that together form an annular weld bead located at or just below the discharge surface of the pad.

Abstract: A noble-metal chip (30, 90) joined to at least either a center electrode or a ground electrode, the center and ground electrodes forming a spark discharge gap, and having a circumferential edge of its facing end surface (31, 91) removed so as to form an edge-removed portion (32, 92). The edge-removal length is 0.01 mm or more and a ratio of the edge-removal length to a radius of the noble-metal chip is less than 0.3. The noble-metal chip is made of iridium or an alloy that contains iridium man amount of 70% by weight or more, and crystal grains constituting the noble-metal chip (30, 90) extends in the axial direction. Also disclosed is a method for manufacturing the spark plug.

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: There is provided a spark plug wherein an insulator and a metallic shell, when observed in a section made by a plane including an axis of a spark plug, have therebetween a gap of less than 0.45 mm at a more front end side than an engagement position of a packing and a first insulator stepped portion, and the gap is provided axially from a most front end side engagement position of the packing and a first insulator stepped portion as a starting point to a finishing point that is apart from the starting point by 1.2 mm or more toward the front end side while being apart from a front end surface of the metallic shell by 7.9 mm or more toward a rear end side.

Abstract: A spark plug 100, comprising a center electrode 3 which is extended in an axial direction, a cylindrical insulator 2 which holds the center electrode 3, and a cylindrical main metal fitting 1 which has a ground electrode 10 at a tip end portion and a tool engagement portion 8 for mounting on an engine, wherein the main metal fitting 1 has a part of a rear end side from the tool engagement portion 8 as a metal fitting-side fitting portion 9 and holds the insulator 2 in a tightly fitted state in a radial direction by the metal fitting-side fitting portion 9.

Abstract: A spark plug (10) having an elongated ceramic insulator (12) includes numerous design features in various strategic locations. At least the ground electrode (26) is fitted with a rimmed, hemispherical metallic sparking tip (56) which controls rogue electrical arcing (62) and facilitates attachment techniques due to increased surface contact with the ground electrode (26). The various features of the spark plug (10) cooperate with one another so that the physical dimensions of the spark plug (10) can be reduced to meet current demands of newer engines without sacrificing mechanical strength or performance.

Abstract: A plasma jet spark plug for internal combustion engines includes a center electrode, a shot channel defined by insulation material, and a ground electrode concentric with the shot channel. The center electrode has a conical shape and the ground electrode defines an outlet opening of the shot channel at a distal end of the spark plug. The shot channel has a tapered shape that forms an acceleration zone for plasma that is formed near the conical tip of the center electrode as the plasma moves toward the ground electrode.

Abstract: A spark plug configured such that a noble-metal tip is welded to each of a front end portion of a center electrode and a distal end portion of a ground electrode. The noble-metal tip of the center electrode or the ground electrode, whichever has a weld metal zone having a greater projected area where an electrode base metal and a metal of the noble metal tip are fused together, is made greater in exposed length of the noble-metal tip. In a preferred embodiment, the projected area of the weld metal zone and the exposed length of the noble-metal tip on the ground electrode side are made greater than those on the center electrode side.

Abstract: The invention describes a spark plug having an outer electrode (12), a central electrode (10), an inner conductor (2) connected to the central electrode (10) and an insulator (3) enclosing the inner conductor (2). It is provided according to the invention that the insulator (3) is produced by extrusion. The invention further relates to a method for production of a spark plug of that kind.

Abstract: A spark plug is provided with a metal shell and a ceramic insulator to support therein a center electrode. The ceramic insulator includes a front portion with a stepped outer surface, a middle portion, a rear portion and a shoulder portion defined between the middle and rear portions. A difference between the outer diameters of the middle and rear portions of the ceramic insulator is 1.8 mm or smaller. The metal shell includes a radially inward protrusion to retain thereon the stepped outer surface of the ceramic insulator and a rear end portion crimped onto the shoulder portion of the ceramic insulator. An inner circumferential surface of the crimped shell portion has a region held in contact with the insulator shoulder portion with a radially innermost point of the crimped shell portion being spaced radially apart from the ceramic insulator and axially apart from the insulator shoulder portion.

Abstract: A plurality of insulator samples of different dimensions are subjected to multiple regression analysis to thereby induce an expression for estimating the amount of unevenness in wall thickness of an insulator; specifically, 0.01 (17.527+0.141A?0.285B?6.124C?0.14D+1.105E), where A is an overall length of the insulator, B is the outside diameter of a rear trunk portion of the insulator, C is the diameter of a large diameter portion of the axial bore of the insulator, D is the length of the large diameter portion of the bore, and E is the diameter of a small diameter portion of the axial bore. The insulator is designed such that the amount of unevenness in wall thickness thereof estimated through calculation by this expression is less than 0.07 mm.

Abstract: A plasma jet spark plug and a manufacturing method therefor are disclosed. In a state in which a noble-metal chip having a flange-like outwardly projecting portion is disposed in a communication section of a ground electrode, an electrode base metal of the ground electrode is disposed in a stepped engagement portion of a metallic shell, which retains an insulator therein. While being pressed against a front end portion of the insulator, the noble-metal chip is joined to the electrode base metal, whereby a clearance between the ground electrode (electrode base metal) and the front end portion of the insulator can be closed. Therefore, energy of plasma generated within the cavity does not leak.

Abstract: A spark plug (30; 40) comprises an electrically-insulating sleeve (12), a first electrode (16), an electrically-conducting shell (20) surrounding said sleeve, and a second electrode (22) mounted on said shell. The electrodes (16 and 22) define a spark gap (G1) of the plug. The shell (20) has an end portion (20c) terminating at an end surface (20b) of the shell. The sleeve (12) extends past said end portion (20c) with a clearance therebetween and extends beyond said end surface (20b). The sleeve (12) has at least one projection (32) which projects from the sleeve (12) and reduces said clearance in the region of the end surface (20b), thereby forming a secondary spark gap (G2).