Abstract: A method and an apparatus for manufacturing a spark plug. A bending apparatus includes a bending unit having a preliminary bending unit and a main bending unit, and a gap adjusting unit. The main bending unit including pressing unit for pressing a distal end of a ground electrode toward a center electrode, and a gap adjusting unit configured to adjust a relative height position of the distal end of the ground electrode relative to a distal end of the center electrode in an axis line direction. The gap adjusting unit includes a gap adjusting unit for relatively moving the distal end of the ground electrode relative to the center electrode in a direction substantially perpendicular to the axis line direction, and a restricting unit for restricting relative movement of the distal end of the ground electrode relative to the center electrode in the axis direction.

Abstract: A spark plug provides a reduced production cost by forming a tip from a metallic material containing Ni that exhibits excellent erosion resistance. The spark plug comprises an insulator having an axial hole extending in an axial direction; a center electrode inserted into the axial hole at a front end thereof; a metallic shell provided around the insulator; a ground electrode whose proximal end portion is fixed to a front end portion of the metallic shell; and a tip bonded to a distal end portion of the ground electrode such that a spark discharge gap is formed between the tip and a front end portion of the center electrode. The tip is formed of a metallic material containing Ni in an amount of 93 mass % or more, and has a Vickers hardness of 163 Hv or less.

Abstract: A ground electrode of an igniter plug has inlets for supplying cooling fluid therethrough to a first space formed between an insulator and the ground electrode, and first outlets located forward of the inlets and radially outward of the inner circumference of a ground electrode forward-end portion and adapted to discharge the cooling fluid therethrough. A second space communicating with the first space and having a second outlet for discharging the cooling fluid therethrough is formed between a forward end surface of the insulator and a surface of the ground electrode which faces the forward end surface.

Abstract: A spark ignition device, ground electrode therefor, and methods of construction thereof are provided. The spark ignition device includes a generally annular ceramic insulator with a metal shell surrounding at least a portion of the ceramic insulator. A center electrode is received at least in part in the ceramic insulator and a ground electrode extends from the shell to a free end portion. A firing tip is attached adjacent the free end portion of the ground electrode to provide a spark gap between the center electrode and the firing tip. The free end portion is at least partially bounded by at least one “as laser cut” peripheral side extending adjacent the firing tip.

Abstract: A method of making a spark plug includes providing a metal shell, an insulator at least partially disposed in the metal shell, a ground electrode coupled to the metal shell, and a center electrode disposed within the insulator. The method also includes depositing a tip substance on the spark plug to form an electrode tip.

Abstract: A spark plug includes an electrode tip assembly located at an axially-facing free end surface of an electrode body. The electrode tip assembly includes an electrode tip body and a firing tip and has a longitudinal axis that is generally perpendicular to a longitudinal axis of the electrode body. The electrode tip body may be a Ni-alloy piece and is attached to the electrode body, and the firing tip may be an Ir-alloy piece with a sparking surface that faces a spark gap. The electrode body may include a groove formed in the axially-facing free end surface that is useful to help position the electrode tip assembly for attachment. The spark gap can be formed between opposing electrode tip assemblies, and the size of the spark gap can be adjusted during assembly without the need for bending the electrode body.

Abstract: Provided are a spark plug in which the occurrence of spark blowout or the like is restrained for improvement of ignition performance, and a method of manufacturing the spark plug. A ground electrode (27 ) of the spark plug has a protrusion (28 ) which faces a center electrode (5). The distal end surface of the protrusion (28) has a noble metal tip (32) provided at the center thereof and includes an annular fusion portion (33) adjacent to the periphery of the noble metal tip (32), and an annular electrode base metal surface located externally of the annular fusion portion (33). A spark discharge gap (35) is formed between the center electrode (5) and the distal end of the protrusion (28) including the noble metal tip (32).

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 method of manufacturing a spark plug, the method including the step of: securing an electrode tip to at least one of a side ground electrode or a center electrode of the spark plug, the electrode tip comprising a platinum-based alloy comprising 20 to 35% by weight of palladium, from greater than 0 to 15% by weight iridium, and the balance of the alloy being platinum, all % by weight being based on the total weight of the alloy.

Abstract: The present invention relates to a spark plug having good combustible-gas ignitability even when the spark plug is downsized and to a method for high-yield manufacturing of a spark plug with good combustible-gas ignitability. There is provided according to one aspect of the present invention a spark plug 1 having a center electrode 2, an insulator 3 and a metal shell 4 and satisfying the following conditions (1) to (5). There is provided according to another aspect of the present invention a manufacturing method of a spark plug including the step of producing an insulator by preparing a raw material powder in such a manner that the particle size distribution ratio (90% volume diameter/10% volume diameter) between particles of 10% volume diameter and particles of 90% volume diameter in the raw material powder is 3.6 to 5.2, and then, press-forming and sintering the prepared raw material powder. Condition (1): The insulator has a wall thickness T of 0.3 to 1.

Abstract: One of an electric wiring substrate and a retaining member includes a section having an absorptance with respect to a laser beam, and the other one of the electric wiring substrate and the retaining member includes a section having a transmittance with respect to the laser beam. The electric wiring substrate and the retaining member are welded to each other by irradiation with a laser beam. At this time, the electric wiring substrate and the retaining member are welded to each other at least at a part of an outer peripheral section of the electric wiring substrate.

Abstract: A spark plug is provided having a resistor. The resistor is made from resistor glass material containing an alkali free barium alumino-silicate glass mixed with mullite. In one embodiment, the resistor is a 15 to 30 wt % alkali free barium alumino-silicate glass and 10 to 25 wt % mullite. The resistor material provides for a greater processing kiln temperature range with reduced resistor variability and improved durability performance.

Abstract: The invention relates to a pre-chamber spark plug with a housing which, at its forward end, comprises a pre-chamber with a plurality of openings, an insulator arranged in the housing, a center electrode which is surrounded by the insulator and supports an ignition electrode arranged in the pre-chamber which comprises a plurality of electrode arms, wherein the electrode arms each comprise a rear section which extends in a transverse direction in relation to the longitudinal direction of the center electrode and a forward section which extends along a pre-chamber wall and forms a spark gap between itself and the pre-chamber wall. It is provided according to the invention that the electrode arms are embedded in the center electrode and project from a lateral surface of the center electrode. Furthermore, the invention relates to a method according to the invention.

Abstract: A method for producing a spark plug is provided, which includes a ground electrode fixed to a housing, and a center electrode insulated electrically from the housing by an insulator, the ground electrode having a ground electrode base and a ground electrode section, which ground electrode section including an electrode base and a noble metal section. In order to produce the spark plug, the ground electrode base is connected to the ground electrode section, in which, in a first step, the electrode base is connected to the noble metal section to form the ground electrode section, and in a second step, the ground electrode section is connected to the ground electrode base.

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 corona igniter 20 includes an insulator 28 surrounding a central electrode 24 and a shell 30 surrounding the insulator 28. The shell 30 presents a shell gap 38 having a shell gap width ws between a shell lower end 34 and a shell inner surface 90 or shell outer surface 92. The shell 30 has a shell thickness is decreasing toward the shell lower end 34 allowing the shell gap width ws to increase toward the shell lower end 34. The shell gap 38 is open at the shell lower end 34 allowing air to flow therein, and the shell gap width ws is greatest at the shell lower end 34. The increasing shell gap width ws enhances corona discharge 22 along the insulator 28 between the central electrode 24 and shell 30.

Abstract: A spark plug (20) for being threaded into a cylinder head (28) includes a shell (24) with threads (26) disposed at a predetermined angled relative to the ground electrode (34). The position of the threads (26) relative to the ground electrode (34) places the ground electrode (34) in a predetermined position in the combustion chamber (22) and relative to components of the engine, thus allowing the ground electrode (34) to provide a robust and reliable ignition. The threads (26) are formed by a thread forming apparatus (102) that includes an orientation tool (38) to position the ground electrode (34) relative to a thread forming apparatus (102), allowing the thread forming apparatus (102) to form the threads (26) at the desired angle (?).

Abstract: There is provided according to the present invention a manufacturing method of a spark plug that includes a cylindrical metal shell, a cylindrical ceramic insulator retained in the metal shell, a center electrode retained in the ceramic insulator and extending in an axial direction and a ground electrode having a rear end portion fixed to the metal shell and a front end portion formed with a protruding region facing a front end portion of the center electrode with a gap left therebetween and being of substantially uniform thickness except for an area where the protrusion is formed. The spark plug manufacturing method includes a press forming step for pressing the whole of a ground electrode material for constituting the ground electrode, so as to form a protruding region on a front end portion of the ground electrode material and a welding step for, after the press forming step, welding a rear end portion of the ground electrode material to the metal shell.

Abstract: A spark plug that is equipped with an insulator that has a stem portion on a front end side, a center electrode, and a main metal member that retains the insulator at an engaging projection portion, wherein an inner diameter DIN of the engaging projection portion, the maximum outer diameter dOUT of the stem portion, which faces an inner circumferential surface of the engaging projection portion, its inner diameter dIN, and dielectric constant ? of the insulator satisfy the condition of “(DIN?dOUT)/2?0.40 (mm)”, “(dOUT?dIN)/2?1.65 (mm)”, and “??9.4”.

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 manufacturing method provides a reduction in the cost of raw material preparation and the cost of the disposal of unused powder by recycling powder not used in forming a filler layer of another spark plug. The method is used to make a spark plug that includes a metal shell having a through hole, and an insulating body held inside the through hole, and a filler layer containing talc in a space surrounded by an inner peripheral surface of the through hole and an outer peripheral surface of the insulating body. The powder not used in a process of forming a filler layer of another spark plug is recycled for forming the filler layer of the present spark plug, where the forming process is performed after talc and a binder are mixed.

Abstract: In joining a composite tip to an electrode, a method is used for properly adjusting the height of radiation of a laser beam to the height of the boundary between two tips used to form the composite tip. Further, a process for joining a first tip and a second tip together by use of a laser beam includes the steps of; (a) disposing the second tip on a support; (b) obtaining, after pressing downward at least the second tip by the use of a pressing jig, a correction value for correcting the height of radiation of a laser beam; (c) correcting the height of radiation of the laser beam on the basis of the correction value; and (d) joining the first and second tips together by use of the laser beam.

Abstract: A spark plug (10) includes an intermediate connecting pin (54) disposed in the central passage (28) of an the insulator body (12). The connecting pin (54) seats in an intermediate taper section (72) within the central passage (28), which is generally frustoconical and establishes a transition between a first larger diameter of the central passage (28) and a second smaller diameter. The intermediate tapered section (72) is located longitudinally above a filleted transition (26) feature of the insulator body (12) exterior. A pin head (53) of the connecting pin (54) has a complementary tapered under-cut and seats against the intermediate tapered section (72) to provide self-centering of the connecting pin (54) without trapping gas during the assembly process. The intermediate taper section (72) also provides an increase in insulator wall thickness which improves dielectric capacity and structural integrity of the insulator (12).

Abstract: A method for producing a spark plug which contains an inner conductor, an insulator surrounding the inner conductor, a spark plug body surrounding the insulator, and two electrodes forming an ignition gap. The first electrode is a center electrode connected to the inner conductor in an electrically conducting manner and the second electrode is a ground electrode connected to the spark plug body in an electrically conducting manner. An iridium component which contains more than 95 percent by weight of iridium is welded onto one of the electrodes. An iridium component that is punched out of an iridium sheet and has a thickness that is less in size than its diameter is also employed.

Abstract: Peeling resistance of a noble metal chip is improved by reducing a difference in the thermal stress generated between the noble metal chip and a ground electrode. A spark plug 1 includes an insulator 2, a center electrode 5, a metal shell 3, and a ground electrode 27, wherein a spark discharge gap 33 is formed between the center electrode 5 and the noble metal chip 41 bonded to the ground electrode 27. The ground electrode 27 is provided with a concave hole portion 43, and 70% or more of the noble metal chip 41 is bonded to the hole portion 43 of the ground electrode 27 through a fusion portion 35 formed by fusing the noble metal chip and the ground electrode 27 to each other by emitting a laser beam or the like from the side surface of the noble metal chip. A gap 45 is formed between the noble metal chip 41 and at least a part of an inner wall surface 43 S of the hole portion 43 so as to be more than 0 mm and equal to or less than 1.

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 method of manufacturing a spark plug, the method including the step of: securing an electrode tip to at least one of a side ground electrode or a center electrode of the spark plug, the electrode tip comprising a platinum-based alloy comprising 20 to 35% by weight of palladium, from greater than 0 to 15% by weight iridium, and the balance of the alloy being platinum, all % by weight being based on the total weight of the alloy.

Abstract: A spark plug having improved durability having a ground electrode comprised of a ground electrode base member and a noble metal tip. A center axis of the noble metal tip slants in relation to the center axis of the ground electrode base member at angle ? which satisfies a relation 2°???25°.

Abstract: When a movable blade cuts a distal end portion of a ground electrode member and is pulled back along a cut surface formed at a distal end of the ground electrode member, the distal end portion may move in the pull-back direction of the movable blade due to friction generated between the movable blade and the cut surface. This movement could cause deflective deformation of the ground electrode member. In order to restrain such movement, a support part is provided on the movable blade via a spring located near the cut surface. During the pull back step, the support part presses and supports the portion of the cut ground electrode member near the distal end thereof. Therefore, even when friction is generated when the movable blade is pulled back, the ground electrode member does not undergo deflective deformation.

Abstract: A plasma jet ignition plug that reliably prevents current leakage with restraint on variation in the position of a ground electrode relative to an insulator and on overheat of the ground electrode, for stable generation of plasma. The plug includes an insulator having an axial bore extending in the direction of an axis CL1, a center electrode inserted in the axial bore, a metallic shell disposed externally of the outer circumference of the insulator, and a ground electrode fixed to the metallic shell, and has a cavity defined by the wall surface of the axial bore and the front end surface of the center electrode. Supports intervene between the insulator and the ground electrode. A space formed radially outward of the supports and a space formed radially inward of the support communicate with each other.

Abstract: A spark ignition device and method of construction is provided. The device includes a ceramic insulator and a metal shell surrounding at least a portion of the ceramic insulator. The metal shell extends along a central axis between an upper terminal end and a lower fastening end. The fastening end has a pair of projections diametrically opposite one another extending axially to free ends. A center electrode assembly is received at least in part in the ceramic insulator. In addition, the device includes an elongate ground electrode having opposite sides extending along a length of the ground electrode between opposite ends. The ground electrode has opposite faces with a sparking surface attached to one of the faces, wherein the face with the sparking surface attached thereto is sunk axially into the free ends of the projections with at least a portion of the opposite sides being surrounded by the projections.

Abstract: A method for manufacturing electrodes for a spark plug that reduces manufacturing time. The method includes a supply step of supplying a workpiece to a die for extrusion forming, wherein the die has a supply hole and an extrusion hole located adjacent to the supply hole for forming the workpiece to have a predetermined cross-sectional shape. The supply hole has a cross section greater than a cross section of the extrusion hole. The method also includes a forming step of pushing the workpiece, supplied to the supply hole, through the extrusion hole so as to form the workpiece into a shape corresponding to the cross section of the extrusion hole. In the supply step, the workpiece is supplied such that a plurality of workpieces form a vertical line in the die.

Abstract: An 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. The electrode material is a metal composite and includes a particulate component embedded or dispersed within a matrix component such that the metal composite has a multi-phase microstructure. In one embodiment, the metal composite includes a matrix component that includes a precious metal and makes up about 2-80% wt of the overall composite and a particulate component that includes a ruthenium-based material and makes up about 20-98% wt of the overall composite.

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: A method of manufacturing a spark plug having an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to attachment fitting 2, earth electrode 5 has a convex part 510 formed by projecting a part of an opposed surface 51 toward center electrode 4, and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 passes through the area in which the concave part 520 is formed. The relation S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug provides a reduced production cost by forming a tip from a metallic material containing Ni that exhibits excellent erosion resistance. The spark plug comprises an insulator having an axial hole extending in an axial direction; a center electrode inserted into the axial hole at a front end thereof; a metallic shell provided around the insulator; a ground electrode whose proximal end portion is fixed to a front end portion of the metallic shell; and a tip bonded to a distal end portion of the ground electrode such that a spark discharge gap is formed between the tip and a front end portion of the center electrode. The tip is formed of a metallic material containing Ni in an amount of 93 mass or more, and has a Vickers hardness of 163 Hv or less.

Abstract: A corona igniter (20) for emitting a radio frequency electric field and providing a corona discharge (24) includes a central electrode (22) at a positive voltage, a grounded metal shell (30), and an insulator (28) with an abruption (34) extending radially outward relative to the central electrode (22). The abruption (34) is typically an increase of at least 15% of a local thickness (t) of the insulator (28) over less than 25% of a nose length (1) of an insulator nose region (74). The abruption (34) is typically one flank (82) of a protrusion or a notch, and the flank (82) faces the shell (30). The abruption (34) reverses the electric field and voltage potential gradient along the insulator outer surface (32), repels charged ions away from the insulator (28), and thus prevents the formation of a conductive path between the central electrode (22) and the shell (22).

Abstract: There is provided a spark plug 100 with a ground electrode 30, wherein a protrusion amount A of a protruding portion 36 satisfies a relationship of 0.4 mm?A?1.0 mm and wherein a press recessed portion 37 extends to a front end surface 31 of the ground electrode 30.

Abstract: A spark ignition device has a ceramic insulator surrounded by a metal shell. The metal shell extends along a longitudinal axis to a distal end. A center electrode is received in the ceramic insulator and extends along the longitudinal axis. A ground electrode has an attachment end fixed by a weld joint to the distal end of the shell and a free end extending from the distal end to provide a spark gap. The weld joint includes a capacitive pulse discharge weld joint and a laser weld joint, which in combination inhibit material expulsion; provide a reliable, strong attachment of the ground electrode to the shell; provide an improved heat transfer path between the ground electrode and the shell, and facilitate repeatable and accurate positioning of the ground electrode to the shell. The weld joint includes a homogeneous mixture of the metal shell and the ground electrode.

Abstract: A corona igniter (20) includes an ignition coil (26) providing a high voltage energy to an electrode. The coil (26) is disposed in a housing (34) and electrically isolated by a coil filler (36) and a capacitance reducing component (38) which together improve energy efficiency of the system. The coil filler (36) includes an insulating resin permeating the coil (26). The capacitance reducing component (38) has a permittivity not greater than 6, for example ambient air, pressurized gas, insulating oil, or a low permittivity solid. The capacitance reducing compound (38) surrounds the coil (26) and other components and fills the remaining housing volume. The coil filler (36) has a filler volume and the capacitance reducing component (38) has a component volume greater than the filler volume.

Abstract: Problem is to enhance the welding strength when a projecting shape section is resistance-welded to a around electrode. A ground electrode 30 includes a ground electrode base material 35 and a projecting shape section 36. The projecting shape section 36 is connected by resistance welding to an opposite surface 32 of the ground electrode 30 so as to be opposite and project towards the leading end of a center electrode 20. The ground electrode base material 35 and the projecting shape section 36 are formed from a material that is composed of the same metal (for example, nickel) as a main component and have a relation of formulas (1) and (2) described below. In formula (1), the specific resistance of the ground electrode base material 35 is R (??cm) and the specific resistance of the projecting shape section 36 is S (??cm). The specific resistance R>the specific resistance S . . . (formula 1), the specific resistance R? specific resistance S?20 . . . (formula 2).

Abstract: A method of forming a spark plug for an internal combustion engine is provided, the method including the steps of: separately securing a ground electrode to a ground shield, the ground shield having an elongated base section being configured to substantially surround a first insulator section of an insulator configured to substantially surround a center electrode, the insulator having a substantially cylindrical body with at least the first insulator section and a second insulator section, the first and second insulator sections having first and second diameters respectively and being separated by an insulator shoulder; and the elongated center electrode having a center electrode tip at one end and a terminal proximate another end of the center electrode, wherein the ground shield has a frustoconical flange protruding from a first end of the elongated base section, the frustoconical flange being configured to engage the insulator shoulder, and wherein the ground electrode extends from a second end of the elon

Abstract: A spark plug having sufficient durability for an internal combustion engine can restrain a sharp increase in resistance of a resistor in spite of its reduced size. The spark plug comprises an insulator having an axial hole, a metallic shell provided on the outer circumference of the insulator, a center electrode inserted into a front end portion of the axial hole, a terminal electrode inserted into a rear end portion of the axial hole, and a ground electrode. A circular columnar resistor is disposed within the axial hole between the center electrode and the terminal electrode, thereby electrically connecting the center electrode and the terminal electrode. The resistor is composed of carbon black that serves as a conductive material, a glass powder, and ceramic particles. Each of the ceramic particles has a maximum particle size of 0.5 ?m or less.

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: 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 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 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 includes a tubular metallic shell extending in the direction of an axis and having a tool engagement portion formed through extrusion. The tool engagement portion has a 12-point shape which is a sectional shape taken orthogonally to the axis and has a plurality of protrusions and recesses provided alternately. As viewed in a section taken orthogonally to the axis, when D (mm) represents the diameter of a circle which passes radially through the outermost positions on the protrusions, and d (mm) represents the diameter of a circle which passes radially through the innermost positions on the recesses, the relational expression 0.45?(D?d)/2?0.75 is satisfied. The spark plug can provide a more reliable restraint on the slippage of a tool at the time of mounting and enables the tool engagement portion to be reliably formed so as to form a desired shape.

Abstract: A generation of a stress corrosion cracking is prevented in a middle section. The spark plug 1 includes an insulator 2 that extends along an axis CL1 direction and a metal shell 3. The metal shell 3 includes a middle section 41 that is positioned between a collar section 16 and a tool engaging section 19. The middle section 41 has a bulged section 42 that bulges towards both the inside and the outside in the diametrical direction, a first slender section 43 that is the most slender at a portion that is positioned further to the rear end side in the axis CL1 direction than the bulged section 42 and a second slender section 44 that is the most slender at a portion that is positioned further to the leading end side in the axis CL1 direction than the bulged section 42 and the bulged section 42 has the most bulged section 42M that bulges toward the most inside of diametrical direction.

Abstract: A spark plug for use in an internal combustion engine. The spark plug is equipped with a metal shell, a ground electrode joined to the metal shell, and a center electrode disposed in the metal shell. The ground electrode has a protrusion formed on a top end thereof. The metal shell and the ground electrode are covered with a plated layer which has a thickness of 2 ?m to 18 ?m, which minimizes the possibility of peeling of the plated layer from the ground electrode while keeping the plated layer as thin as possible without sacrificing the resistance to corrosion on the ground electrode.