JP2009187721A - Method of manufacturing spark plug, and spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a spark plug and the spark plug, capable of reducing bending stress applied to a welding part between a ground electrode and an electrode tip. <P>SOLUTION: In the method of manufacturing the spark plug 100, before a tip welding process in which the electrode tip 95 is welded on the tip part 31 of the ground electrode 30, a preliminary bending process to preliminarily bend the ground electrode 30 is carried out. After that, the electrode tip 95 is welded in the tip welding process, and in a final bending process, the ground electrode 30 applying a bending habit is finally bent. In the final bending process, since the ground electrode 30 is bent centering around a part applying the bending habit, the tip part 31 to which the electrode tip 95 is welded is not bent. Accordingly, the bending stress applied to the welding part between the ground electrode 30 and the electrode tip 95 can be reduced. Then, since welding strength between the ground electrode 30 and the electrode tip 95 is retained, the spark plug 100 capable of sufficiently resistant to high temperature and vibrations can be provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spark plug manufacturing method and a spark plug that are assembled in an internal combustion engine to ignite an air-fuel mixture.

  Conventionally, spark plugs for ignition are used in internal combustion engines. In this spark plug, generally, one end of the ground electrode is joined to the front end surface on the combustion chamber side of the metal shell holding the insulator in which the center electrode is inserted, and the other end side is the front end of the center electrode. It is bent toward. A needle-like electrode tip is welded to the other end of the ground electrode. A spark discharge gap is formed between the electrode tip and the tip of the center electrode. Thereby, since spark discharge is actively performed in the spark discharge gap, the ignitability is improved. Further, in the initial stage of the growth process of the flame kernel, it is possible to prevent the flame kernel from contacting the ground electrode and taking heat away.

As a method for manufacturing this type of spark plug, for example, there is known a method for manufacturing a spark plug in which a ground electrode side tip (electrode tip) is welded to a rod-shaped ground electrode, bent, and then joined to a metal shell. (For example, refer to Patent Document 1). According to this method, since an axial shift does not occur between the electrode tip of the ground electrode and the center electrode, an accurate spark discharge gap can be formed.
JP 2003-229231 A

  However, in recent years, it has been required to reduce the diameter of the plug in order to free the design around the engine. When the diameter of the plug is reduced, the distance between the bent portion of the ground electrode and the tip welded portion is reduced, so that the bending stress applied to the tip welded portion inevitably increases. Therefore, when it is attached to an automobile and vibrates at a high temperature, there is a possibility that the tip weld portion is cracked and the electrode tip falls off. In order to solve this fear, for example, a method of separating the distance between the bent portion and the tip welded portion by tightening the degree of bending can be considered. However, since the stress applied to the bent portion is further increased, the bent portion may be damaged.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug manufacturing method and a spark plug that can reduce bending stress applied to a welded portion between a ground electrode and an electrode tip. To do.

  In order to achieve the above object, a spark plug manufacturing method according to a first aspect of the present invention has a center electrode and an axial hole extending along the axial direction, and holds the central electrode inside the axial hole. An insulator, a metal shell that surrounds and holds the periphery of the insulator in the circumferential direction, and one end portion is joined to the tip surface of the metal shell, and the other end portion is bent toward the tip portion of the center electrode. A spark plug manufacturing method comprising: a ground electrode that is formed; and a projecting first electrode tip that is joined to the other end portion of the ground electrode and forms a spark discharge gap with the tip end portion of the center electrode. The electrode bending step of bending the ground electrode, and the chip bonding step of bonding the first electrode chip to the other end portion of the ground electrode after the electrode bending step.

  According to a second aspect of the invention, there is provided a spark plug manufacturing method according to the first aspect of the present invention, in addition to the configuration of the first aspect of the invention, before the electrode bending step, the one end of the ground electrode on the tip surface of the metal shell. A fitting joining step for joining the parts.

  According to a third aspect of the present invention, there is provided a method for manufacturing a spark plug according to the second aspect of the present invention, wherein the insulation for holding the center electrode is performed after the metal fitting joining step and before the electrode bending step. An insulator holding step of holding the insulator on the metal shell;

  According to a fourth aspect of the present invention, there is provided a spark plug manufacturing method according to any one of the first to third aspects, wherein the ground electrode is provided after the electrode bending step and before the chip joining step. A chip disposing step of disposing the first electrode chip at a position corresponding to the position of the tip end portion of the center electrode at the other end.

  According to a fifth aspect of the present invention, there is provided a spark plug manufacturing method according to any one of the first to third aspects, wherein the ground electrode is provided after the electrode bending step and before the chip joining step. A positioning portion forming step of forming a positioning portion at a position corresponding to the position of the tip portion of the center electrode at the other end portion of the center electrode, and the other end portion of the ground electrode in the tip bonding step. The first electrode chip is bonded to the formed positioning portion.

  According to a sixth aspect of the present invention, there is provided a spark plug manufacturing method according to any one of the first to fifth aspects, wherein the ground electrode is further bent after the chip joining step, and the first An electrode rebending step of aligning the position of the electrode tip with the tip of the center electrode;

  According to a seventh aspect of the present invention, there is provided a spark plug manufacturing method according to any one of the first to sixth aspects, wherein, in the electrode bending step, the other end of the ground electrode is Bending toward the side surface of the tip portion of the center electrode or the side surface of the protruding second electrode chip joined to the tip portion of the center electrode.

  A spark plug according to a seventh aspect of the invention is manufactured by the spark plug manufacturing method according to any one of the first to seventh aspects.

  In the spark plug manufacturing method according to the first aspect of the invention, after the ground electrode is bent in the electrode bending step, the first electrode chip is bonded to the other end of the ground electrode in the chip bonding step. Thereby, since the stress by a bending is not applied to the junction part of a 1st electrode tip and a ground electrode, it can prevent that a 1st electrode tip falls off.

  Moreover, in the spark plug manufacturing method of the invention according to claim 2, in addition to the effect of the invention of claim 1, the metal fitting joining step is performed before the electrode bending step. In the metal fitting joining step, one end of the ground electrode is joined to the front end surface of the metal shell. Thereby, since the one end part of a ground electrode is fixed, it can be made easy to bend the other end part of a ground electrode in an electrode bending process.

  Moreover, in the spark plug manufacturing method of the invention according to claim 3, in addition to the effect of the invention of claim 2, the insulator holding step is performed after the metal fitting joining step, and then the electrode bending step is conducted. In the insulator holding step, the insulator holding the center electrode is held by the metal shell. Thereby, in the electrode bending step, the other end of the ground electrode can be bent toward the tip of the center electrode held by the metal shell via the insulator.

  In addition, in the spark plug manufacturing method of the invention according to claim 4, in addition to the effect of the invention according to any one of claims 1 to 3, a chip placement process is performed after the electrode bending process, and then a chip bonding process is performed. . In the chip arrangement step, the first electrode chip is arranged at a position corresponding to the position of the tip of the center electrode at the other end of the ground electrode. Thus, in the tip welding process, the first electrode tip can be welded to a position corresponding to the position of the tip of the center electrode, and therefore, there is less misalignment between the axis of the center electrode and the axis of the first electrode tip in the spark discharge gap. it can.

  Further, in the spark plug manufacturing method of the invention according to claim 5, in addition to the effect of the invention according to any one of claims 1 to 3, a positioning portion forming step is performed after the electrode bending step, and then a chip joining step is performed. Do. In the positioning portion forming step, the positioning portion is formed at a position corresponding to the position of the tip portion of the center electrode at the other end portion of the ground electrode. In the chip bonding step, the electrode chip can be positioned at a position corresponding to the position of the tip of the center electrode by bonding the first electrode chip to the positioning portion formed at the other end of the ground electrode. . Thereby, the gap between the axis of the center electrode and the axis of the first electrode tip can be reduced in the spark discharge gap.

  Further, in the spark plug manufacturing method of the invention according to claim 6, in addition to the effect of the invention of any one of claims 1 to 5, the electrode rebending step is performed after the chip joining step. In the electrode re-bending step, the ground electrode is already bent by the electrode bending step, so that the first electrode tip can be easily aligned with the tip of the center electrode. Furthermore, since the ground electrode is bent around the already bent portion, the other end of the ground electrode to which the first electrode tip is bonded is not easily bent. Therefore, the bending stress applied to the joint between the other end of the ground electrode and the first electrode tip can be reduced as compared with the method of joining the first electrode tip before bending the ground electrode.

  Further, in the spark plug manufacturing method of the invention according to claim 7, in addition to the effect of the invention according to any of claims 1 to 6, the side surface of the center electrode from the tip portion in the protruding direction of the first electrode chip, or A so-called “lateral discharge type” spark plug that discharges toward the side surface of the second electrode tip can be provided.

  In addition, since the spark plug of the invention according to claim 8 is manufactured by the method for manufacturing a spark plug according to any one of claims 1 to 7, the joint portion between the first electrode tip and the ground electrode is bent. A spark plug that is not stressed can be provided.

  Hereinafter, a spark plug manufacturing method and a spark plug according to an embodiment of the present invention will be described with reference to the drawings. First, the structure of the spark plug 100 as an example will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view of a spark plug 100. FIG. 2 is an enlarged view of the vicinity of the tip 22 of the center electrode 20 shown in FIG. 1 and 2, the axis O direction of the spark plug 100 is the vertical direction in the drawings, the lower side is the front end side of the spark plug 100, and the upper side is the rear end side.

  As shown in FIG. 1, the spark plug 100 roughly includes an insulator 10 that holds the center electrode 20 on the front end side in its own shaft hole 12 and holds the terminal fitting 40 on the rear end side. Is surrounded and held by the metal shell 50. The ground electrode 30 is joined to the front end surface 57 of the metal shell 50, and the other end (the front end 31) side is bent so as to face the center electrode 20.

  First, the insulator 10 will be described. As shown in FIG. 1, the insulator 10 is formed by firing alumina or the like as is well known, and has a cylindrical shape in which an axial hole 12 extending in the direction of the axis O is formed at the center of the axis. A flange portion 19 having the largest outer diameter is formed at the approximate center in the direction of the axis O. A rear end side body 18 is formed on the rear end side (the upper side in FIG. 1). A front end side body portion 17 having a smaller outer diameter than the rear end side body portion 18 is formed on the front end side (lower side in FIG. 1) from the flange portion 19. Further, a leg length portion 13 having an outer diameter smaller than that of the distal end side body portion 17 is formed on the distal end side of the distal end side body portion 17. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head (not shown) of the internal combustion engine. A step portion 15 is formed between the long leg portion 13 and the front end side body portion 17.

  Next, the center electrode 20 will be described. As shown in FIGS. 1 and 2, the center electrode 20 is formed in a base material made of nickel such as Inconel (trade name) 600 or 601 or an alloy containing nickel as a main component, rather than the base material. This is a rod-like electrode having a structure in which a core material 25 made of copper or an alloy containing copper as a main component having excellent thermal conductivity is embedded. The center electrode 20 is held on the distal end side in the shaft hole 12 of the insulator 10, and the distal end portion 22 protrudes further toward the distal end side than the distal end of the insulator 10. The distal end portion 22 of the center electrode 20 is formed so as to have a smaller diameter toward the distal end side, and an electrode tip 90 made of a noble metal for improving spark wear resistance is joined to the distal end surface.

  Further, a slight gap is provided between the inner peripheral surface of the shaft hole 12 near the tip of the insulator 10 and the outer peripheral surface of the center electrode 20 facing the inner peripheral surface (see FIG. 2). By generating a corona discharge in this gap at the time of turning, the carbon adhering to the vicinity of the tip of the insulator 10 is burned out and the insulation resistance is restored. Further, the center electrode 20 extends toward the rear end side in the shaft hole 12 of the insulator 10, and passes through the seal body 4 and the ceramic resistor 3, and is located at the rear (upper side in FIG. 1) terminal. It is electrically connected to the metal fitting 40. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage is applied.

  Next, the metal shell 50 will be described. A metal shell 50 shown in FIG. 1 is a cylindrical metal fitting for fixing the spark plug 100 to an engine head (not shown) of an internal combustion engine, and is formed of a low carbon steel material. The metal shell 50 inserts and holds the insulator 10 so as to surround a portion from a part of the rear end body part 18 to the leg long part 13. Further, the metal shell 50 includes a tool engaging portion 51 into which a spark plug wrench (not shown) is fitted, and a mounting screw portion 52 in which a screw thread that is screwed into a mounting hole (not shown) of the engine head is formed. ing.

  Further, a hook-shaped seal portion 54 is formed between the tool engagement portion 51 and the mounting screw portion 52. Further, an annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the attachment screw portion 52 and the seal portion 54. The gasket 5 is deformed by being crushed between the seat surface 55 of the seal portion 54 and the opening peripheral edge of the attachment hole when the spark plug 100 is attached to the attachment hole (not shown) of the engine head. Thereby, since the space between the seat surface 55 and the opening peripheral edge of the mounting hole is sealed, airtight leakage in the engine via the mounting hole is prevented.

  Further, a thin caulking portion 53 is provided on the rear end side of the tool engaging portion 51. A thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51 in the same manner as the caulking portion 53. Further, annular ring members 6 and 7 are interposed between the inner peripheral surface from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10. Yes. Between the ring members 6 and 7, powder of talc (talc) 9 is filled.

  In such a metal shell 50, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6, 7 and the talc 9 by crimping the caulking portion 53 inwardly. Is done. Thus, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8. The insulator 10 is integrated. Moreover, since the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, the outflow of combustion gas is prevented. Further, the buckling portion 58 is configured to bend outwardly and deform as the compressive force is applied during caulking. Moreover, the compression length of the talc 9 in the direction of the axis O is increased to improve the airtightness in the metal shell 50.

  Next, the ground electrode 30 will be described. The ground electrode 30 shown in FIG. 2 is formed of a metal having high corrosion resistance. As an example, a nickel-based alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially rectangular cross section perpendicular to the longitudinal direction of the ground electrode 30 and is formed in a square bar shape bent into a substantially L shape. The ground electrode 30 includes a distal end portion 31 to which an electrode tip 95 described later is joined, a proximal end portion 32 that is resistance-welded to the distal end surface 57 of the metal shell 50, and the distal end portion 31 and the proximal end portion 32. And a bent portion 35 that is bent substantially in an L shape.

An electrode tip 95 that protrudes in a needle shape and faces the electrode tip 90 joined to the tip 22 of the center electrode 20 on the inner surface 33 of the tip 31 is formed by resistance welding. Has been. The electrode tip 95 is made of a noble metal having a high resistance to spark consumption, such as Pt, Ir, or Rh. The shape is a columnar shape having a cross-sectional area (cross-sectional area of a cross section orthogonal to the axial direction of the electrode tip 95) of 0.12 to 1.13 mm ² and a height (projection height from the inner surface 33) of 0.5 mm or more. Is formed. Then, by causing the electrode tip 90 to protrude from the center electrode 20 and the electrode tip 95 to protrude from the ground electrode 30, spark discharge is actively performed in the spark discharge gap G. Then, since a flame nucleus is formed in the spark discharge gap G, it is suppressed that the flame nucleus contacts the ground electrode 30 and heat is taken away in the initial stage of the growth process of the flame nucleus. The electrode tip 95 shown in FIG. 2 corresponds to the “first electrode tip” of the present invention.

  Further, the spark plug 100 having the above structure is manufactured as a small-diameter spark plug in which the nominal diameter of the thread formed on the mounting screw portion 52 of the metal shell 50 is M12 or less. In such a spark plug 100, the distance between the center electrode 20 and the ground electrode 30 in the radial direction is smaller. For this reason, since the portion extending along the axis O direction of the ground electrode 30 is ensured and bent at the tip side as much as possible, the radius of curvature at the bent portion 35 is the nominal diameter of the commonly used thread M14. It is smaller than the spark plug.

  Next, the manufacturing process of the spark plug 100 characterized by the above configuration will be described. FIG. 3 is a diagram showing a process from the metal fitting joining process to the preliminary bending process. FIG. 4 is a diagram illustrating a chip bonding process to a main bending process. FIG. 5 is a diagram showing how the ground electrode 30 is pre-bent in the pre-bending step. FIG. 6 is a diagram showing the contents of the chip bonding step. FIG. 7 is a diagram showing the contents of the laser welding process. FIG. 8 is a diagram showing resistance welding of the electrode tip 95. FIG. 9 is a diagram showing how the ground electrode 30 is finally bent in the final bending step.

  First, the manufacturing process of the spark plug 100 is divided into a “preparation process” in which the components of the spark plug 100 are produced and prepared, and an “assembly process” in which the components produced in the preparation process are assembled together. . Hereinafter, each process is demonstrated in order. The preparation process is the same as that of the conventional method, and will be described schematically.

  The preparation process will be described. In the preparation step, the insulator 10, the center electrode 20, and the ground electrode 30 are respectively produced. Alumina is used as the main raw material for the insulator 10. And the insulator 10 is produced by cutting etc. so that it may become a predetermined shape, and baking at high temperature. The center electrode 20 and the ground electrode 30 are made in a rod shape using the nickel-based alloy described above. A core material 25 made of copper or an alloy containing copper as a main component is inserted into the base material of the center electrode 20, which is superior in thermal conductivity to the base material.

  Next, the center electrode 20, the seal body 4, the resistor 3, the terminal fitting 40 previously produced by plastic working or the like are sequentially inserted into the produced insulator 10, and a heating compression process called a glass seal is performed. These are integrally formed. On the other hand, a steel material is used for the metal shell 50. Then, the metal shell 50 is manufactured by performing plastic working, cutting, thread forming process, and the like so as to have a predetermined shape. The metal fitting 50 is formed with the above-described tool engaging portion 51, seal portion 54, and the like.

  Next, the assembly process will be described. As shown in FIGS. 3 and 4, the assembling process is composed of five processes, a metal fitting welding process in which the ground electrode 30 is welded to the front end surface 57 of the metal shell 50, and the insulator 10 is inserted and held in the metal shell 50. An insulator holding step, a pre-bending step of pre-bending the ground electrode 30, a tip joining step of welding the electrode tip 95 to the tip 31 of the pre-bent ground electrode 30, and the electrode tip 95 welded And a main bending step of performing the main bending of the ground electrode 30. Hereinafter, each process is demonstrated in order.

  First, the metal fitting joining process will be described. As shown in FIG. 3, in the metal fitting joining step, the base end portion 32 of the ground electrode 30 is joined to the front end surface 57 of the metal shell 50 before the insulator 10 is assembled by resistance welding. The ground electrode 30 is in a rod-like state before being bent. That is, the ground electrode 30 is in a state extending in parallel to the axial direction of the metal shell 50. After this, a plating process is performed. In the plating step, the metal shell 50 is plated with the ground electrode 30 joined. At the time of plating, the ground electrode 30 is masked or the like, or the metal shell 50 is plated without masking, and then the plating attached to the ground electrode 30 is peeled off. Thereby, it is possible to prevent the plating from adhering to the position where the electrode tip 95 of the ground electrode 30 is welded and the welding strength of the electrode tip 95 from being lowered. Thus, the metal fitting assembly 200 is formed.

  Next, the insulator holding process will be described. As shown in FIG. 3, in the insulator holding step, first, the insulator 10 in which the center electrode 20 is integrated with a glass seal is inserted inside the metal fitting assembly 200. Next, the crimping portion 53 (see FIG. 1) is crimped so as to be bent inward. Then, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9 (see FIG. 1). As a result, insulation is provided to the stepped portion 56 (see FIG. 1) formed at the position of the mounting screw portion 52 (see FIG. 1) on the inner periphery of the metal shell 50 via the annular plate packing 8 (see FIG. 1). The step portion 15 of the insulator 10 is supported. The insulator 10 is integrally held by the metal shell 50 with the tip of the center electrode 20 protruding from the tip side of the metal shell 50.

  Next, the preliminary bending process will be described. As shown in FIG. 5, in the preliminary bending step, a preliminary bending mechanism having a preliminary bending spacer 60 and a bending punch 70 is used. The rod-shaped ground electrode 30 is processed into a predetermined preliminary bending shape by this preliminary bending mechanism. The pre-bending spacer 60 is formed in a triangular shape in a side view extending at an acute angle toward the inner surface of the ground electrode 30. A reference surface 61, which is a flat surface facing the center electrode 20, is formed on the outer surface on the lower end side of the pre-bending spacer 60, and is pressed against the ground electrode 30 on the outer surface on the front end side. A bending die surface 62 having a curved surface corresponding to the shape is formed. Further, a protrusion 63 that protrudes downward from the reference surface 61 is formed at the tip of the pre-bending spacer 60, and the tip of the bending mold surface 62 extends to the lower edge of the protrusion 63. ing. An inclined surface 64 is formed on the rear side of the bending mold surface 62 so as to move away from the tip surface of the center electrode 20 toward the rear.

  On the other hand, the bending punch 70 is formed with a bending die surface 71 that is in contact with the outer surface of the ground electrode 30 and that corresponds to the preliminary bending shape of the ground electrode 30. The bending die surface 71 corresponds to the inclined surface 72 corresponding to the inclined surface 64 of the pre-bending spacer 60 and the distal end side of the bending die surface 62 of the pre-bending spacer 60, and the inclined surface 72 for guiding the bending of the ground electrode 30. And a slope 73 that is steeper than that.

  When the metal fitting assembly 200 is installed in such a pre-bending mechanism, the rod-shaped ground electrode 30 is disposed between the pre-bending spacer 60 and the bending punch 70. Here, the tip 22 (see FIG. 2) of the center electrode 20 has already protruded from the tip of the metal fitting assembly 200. That is, the direction in which the tip 31 of the ground electrode 30 is bent is clear. In this state, the bending punch 70 is moved toward the preliminary bending spacer 60. Then, the ground electrode 30 is sandwiched and pressed between the preliminary bending spacer 60 and the inclined surfaces 72 and 73 of the bending punch 70. Thereby, the tip 31 of the ground electrode 30 faces obliquely upward, and the portion pressed against the preliminary bending spacer 60 is bent into the shape of the bending die surface 62. Thus, the preliminary bending portion 34 is formed on the ground electrode 30.

  The preliminary bending portion 34 formed on the ground electrode 30 is a portion that becomes a bending portion 35 formed in a subsequent main bending step. That is, a bending ridge is first attached to the portion that becomes the bent portion 35 of the ground electrode 30 in the preliminary bending step. Therefore, in this bending process, the bending is performed around the pre-bending portion 34 with the bending ridge, so that the distal end portion 31 to which the electrode tip 95 is later welded is not bent. In addition, since the bending degree of the preliminary | backup bending part 34 is enough for a bending wrinkle to be attached to the ground electrode 30, it may be smaller than the bending degree in the main bending process mentioned later.

  Next, the chip bonding process will be described. As shown in FIG. 4, in the chip bonding step, the electrode chip 95 is bonded to the tip 31 of the ground electrode 30 that has been pre-bent. As shown in FIG. 6 and FIG. 7, the chip joining process is composed of three processes, the “chip placement process” in which the electrode tip 95 is placed at a predetermined position of the tip portion 31 of the ground electrode 30, and the tip portion 31. It consists of a “resistance welding process” for resistance welding the arranged electrode tips 95 and a “laser welding process” for laser welding the welded portion of the resistance-welded electrode tips 95.

  First, the chip placement process will be described. As shown in FIG. 6, a protrusion 98 protruding downward is provided on the lower surface of the electrode chip 95. On the other hand, a positioning hole 38 for fitting the projection 98 of the electrode tip 95 is provided in advance in a predetermined portion of the inner surface 33 of the tip 31 of the ground electrode 30. The position of the positioning hole 38 is a position facing the electrode tip 90 welded to the tip of the center electrode 20 when the ground electrode 30 is finally bent.

  The electrode tip 95 is transported by a pair of arm-shaped tip guides 81 and 82. The chip guides 81 and 82 are made of metal, and insulating films 85 and 86 (see FIGS. 6 and 8) are provided on the lower surfaces of the chip guides 81 and 82 that are in contact with the inner surface 33 of the ground electrode 30. These insulating films 85 and 86 can prevent current from flowing and joining between the lower surfaces of the tip guides 81 and 82 and the inner surface 33 of the ground electrode 30 during resistance welding. Further, gripping grooves 181 and 182 (see FIGS. 6 and 8) that are curved corresponding to the outer peripheral surface of the columnar electrode chip 95 are provided at the tip portions of the tip guides 81 and 82, respectively. The electrode tip 95 is transported in a state of being sandwiched by gripping grooves 181 and 182 from both sides. Here, since the ground electrode 30 is before being bent, the distance between the tip 31 and the electrode tip 90 of the center electrode 20 is sufficiently wide. Accordingly, the electrode tip 95 is smoothly transported by the tip guides 81 and 82. And the protrusion part 98 of the electrode tip 95 is inserted in the positioning hole 38 provided in the inner surface 33 of the front-end | tip part 31 of the ground electrode 30, and a chip | tip arrangement | positioning process is completed.

  Next, the resistance welding process will be described. As shown in FIG. 6, the tip guides 81 and 82 also serve as resistance welding electrodes. Therefore, as shown in FIG. 8, current for resistance welding is passed through the tip guides 81 and 82 while the electrode tip 95 is held and pressed against the inner surface 33 of the tip 31 of the ground electrode 30. Then, the contact portion between the lower surface of the electrode tip 95 and the inner surface 33 of the ground electrode 30 is melted, so that the electrode tip 95 is temporarily welded to a predetermined position on the inner surface 33 of the tip 31 of the ground electrode 30.

  Since the resistance welding process is intended to be temporarily fixed, the current flowing through the tip guides 81 and 82 may be weaker than usual. Therefore, the chip guides 81 and 82 that also serve as resistance welding electrodes can be designed in a compact manner. Further, if the electrode tip 95 is also a nickel base of a composite tip which will be described later, since the surface to be welded is a nickel-based alloy, sufficient welding strength can be obtained even with weak resistance welding. In the present embodiment, the tip guides 81 and 82 are used as resistance welding electrodes. However, for example, a thin ring-shaped resistance welding electrode may be used. In this case, after the electrode tips 95 are arranged with the tip guides 81 and 82, the tip guides 81 and 82 are separated from the ground electrode 30, and resistance welding is performed while pressing the electrode tips 95 with the ring-shaped resistance welding electrodes. .

  Next, the laser welding process will be described. As shown in FIG. 7, since the electrode tip 95 is temporarily welded to the inner surface 33 of the tip 31 of the ground electrode 30, laser welding is performed obliquely from above toward the welded portion (two-dot chain line in FIG. 7). R). Since the laser R is emitted so that the laser R does not hit the metal shell 50, the insulator 10, and the center electrode 20, the laser R does not go around the outer periphery of the electrode tip 95. That is, only one side of the outer periphery of the electrode tip 95 is laser welded. Here, the welding strength of the electrode tip 95 becomes a problem.

  However, since the ground electrode 30 has already been bent in the preliminary bending step, the tip portion 31 to which the electrode tip 95 is welded is not bent in the subsequent main bending step. Therefore, since the bending stress applied to the electrode tip 95 after laser welding is extremely small, the welding strength can be sufficiently maintained without making one round of laser welding. In this way, as shown in FIG. 4, the welding of the electrode tip 95 to the inner surface 33 of the tip 31 of the ground electrode 30 is completed, and the tip welding process is completed.

  Next, the main bending process will be described. In the main bending process, a main bending apparatus (not shown) is used. The ground electrode 30 that has already been pre-bent is conveyed to the bending apparatus by a linear conveyor (not shown). As shown in FIG. 9, this bending apparatus is provided with a main bending punch 80 that contacts and separates the ground electrode 30 positioned in the apparatus by a driving mechanism (not shown). Then, the main bending punch 80 is pressed against the ground electrode 30 that has been pre-bent so that the tip is directed obliquely upward. In this way, the inner surface 33 of the distal end portion 31 of the ground electrode 30 is finally bent so as to be substantially parallel to the distal end surface of the center electrode 20, thereby forming a bent portion 35. This bending process is performed step by step while monitoring with the CCD camera 92. Thereby, the spark discharge gap G can be formed in a predetermined interval size. In this bending step, the spark discharge gap G is monitored by the CCD camera 92, but may be monitored from various angles using a plurality of CCD cameras. For example, the CCD camera 92 is installed so as to shoot from the direction facing the inner surface 33 of the ground electrode 30 with the axis O interposed therebetween, but in addition to this, the CCD camera 92 faces the side surface of the ground electrode 30 (paper surface in FIG. 9). You may install the CCD camera which image | photographs along a radial direction from a near side. As described above, when monitoring with a plurality of CCD cameras, the spark discharge gap G can be adjusted more accurately than when monitoring with one CCD camera.

  Here, the ground electrode 30 is bent around the pre-bending portion 34 formed in the pre-bending step. That is, since it bends around the bending rod attached to the ground electrode 30, the tip portion 31 side to which the electrode tip 95 is welded does not bend. Therefore, since the bending stress is hardly applied to the welded portion between the electrode tip 95 and the inner surface 33 of the ground electrode 30, it is possible to prevent the welding strength of the electrode tip 95 from being lowered. In addition, since the preliminary bending is already performed before the main bending, the ground electrode 30 can be easily bent into a predetermined shape.

  Furthermore, since the ground electrode 30 is bent around the pre-bending portion 34, the position of the tip portion 31 after the main bending can be easily predicted. Therefore, the position of the electrode tip 95 can be accurately and easily aligned with the electrode tip 90 of the center electrode 20. Thus, a series of manufacturing steps of the spark plug 100 is completed. In the spark plug 100 produced in this manufacturing process, since the bending stress applied to the welded portion of the electrode tip 95 is reduced, the welded portion is cracked even if it is attached to an automobile and vibrates at a high temperature. Thus, the electrode tip 95 can be prevented from falling off.

  As described above, in the method for manufacturing the spark plug 100 according to the present embodiment, the pre-bending step of pre-bending the ground electrode 30 is performed before the tip welding step of welding the electrode tip 95 to the tip portion 31 of the ground electrode 30. Do. Thereafter, the electrode tip 95 is welded in a tip welding process, and the ground electrode 30 with a bending rod is finally bent in the main bending process. In this bending process, since the ground electrode 30 bends around a portion with a bending ridge, the tip 31 where the electrode tip 95 is welded does not bend. Therefore, the bending stress applied to the welded portion between the ground electrode 30 and the electrode tip 95 can be reduced. And since the welding strength of the ground electrode 30 and the electrode tip 95 is maintained, the spark plug 100 which can fully endure high temperature and vibration can be provided.

  Needless to say, the present invention can be modified in various ways. For example, welding in the tip welding process of the above embodiment is performed in two stages, a resistance welding process in which the electrode tip 95 is temporarily welded by resistance welding and a laser welding process in which laser welding is reinforced, as shown in FIG. In addition, the laser welding process can be omitted by using the composite tip 195. FIG. 10 is a diagram showing how the composite tip 195 is welded to the ground electrode 30 in the tip welding process.

  The composite tip 195 is a composite body including a columnar noble metal tip 196 and a nickel base 197 welded to the lower surface of the noble metal tip 196 by welding portions 199 and 199. The nickel base 197 is formed in a thin plate shape mainly composed of nickel. A projecting portion 198 projecting downward is provided on the lower surface.

  First, in the chip placement step, the composite chip 195 is held by the pair of chip guides 81 and 82 and is transported to the inner surface 33 of the distal end portion 31 of the ground electrode 30. And the protrusion part 198 of the composite chip | tip 195 is inserted and arrange | positioned with respect to the positioning hole 38 provided in the inner surface 33. FIG. Next, in the resistance welding process, resistance welding is performed by the tip guides 81 and 82. In this case, the contact portion between the nickel base 197 of the composite chip 195 and the inner surface 33 of the ground electrode 30 made of a nickel-based alloy is melted, so that the melted portion becomes thick. Thereby, compared with the case where the electrode tip 95 is welded alone, welding strength can be made higher. When the composite chip 195 is used, the nickel base 197 is preferably made of the same component as the ground electrode 30.

  In the above embodiment, the ground electrode 30 is bent in two stages, lightly bent at the first time and greatly bent at the second time, but on the contrary, it is bent largely at the first time and lightly bent at the second time. May be. In this case, in the second bending, the position of the electrode tip 95 can be finely adjusted with respect to the electrode tip 90 of the center electrode 20. Even in that case, since the electrode tip 95 is welded after the first bending, the bending stress applied to the welded portion between the electrode tip 95 and the ground electrode 30 is extremely small.

  Alternatively, the ground electrode 30 may be bent once, and then the electrode tip 95 may be welded. For example, as shown in FIG. 11, the main bending step may be performed without performing the preliminary bending of the ground electrode 30 after the insulator holding step. FIG. 11 is a diagram showing a manufacturing process when the ground electrode 30 is bent at a time.

  In this main bending step, the inner surface 33 of the tip 31 of the ground electrode 30 is bent so as to face the electrode tip 90 welded to the tip 22 (see FIG. 2) of the center electrode 20. Next, a “positioning hole forming step” is performed in which a positioning hole 38 is formed on the inner surface 33 of the tip 31 of the ground electrode 30 at a position facing the electrode tip 90 of the center electrode 20.

  In this positioning hole forming step, the position facing the tip 22 (see FIG. 2) of the center electrode 20 on the inner surface 33 of the ground electrode 30 is automatically determined by the computer (PC) using the CCD camera or the like. . And the positioning hole 38 is formed in the indexed position using a punch, a drill, or the like. That is, in the positioning portion forming step, since the ground electrode 30 is completely bent, the position of the center electrode 20 facing the electrode tip 90 is clear. Thereafter, in the chip bonding step, the protrusion 98 of the electrode chip 95 is inserted into the positioning hole 38 formed in the ground electrode 30. Thereby, the positional accuracy of the electrode tip 95 facing the electrode tip 90 is improved. Even with such a method, it is possible to obtain the same effects as in the above embodiment.

  Furthermore, in the above-described embodiment, in order to arrange the electrode tip 95 on the ground electrode 30 in the positioning portion forming step, the position facing the tip 22 (see FIG. 2) of the center electrode 20 is indexed by a computer, and the index position Although the positioning hole 38 is formed in the above, resistance welding may be performed by directly disposing the electrode tip 95 at the index position.

  Moreover, in the said embodiment, although it progresses in order of an insulator holding process, a pre-bending process, and a chip joining process after a metal fitting joining process, it advances in order of a pre-bending process, a chip joining process, and an insulator holding process after a metal fitting joining process. You may let them. That is, after the ground electrode 30 is welded to the front end surface 57 of the metal shell 50, the ground electrode 30 is pre-bent and the electrode tip 95 is welded. You may assemble | attach to the metal fitting 50.

  Furthermore, in the above-described embodiment, the manufacturing method of the so-called “longitudinal discharge type” spark plug 100 that discharges along the axial direction has been described. For example, the spark discharge gap is formed along the direction orthogonal to the axial direction. The present invention can also be applied to a so-called “lateral discharge type” spark plug manufacturing method. The spark plug 300 shown in FIG. 12 is a horizontal discharge type. In the spark plug 300, the distal end portion of the center electrode 120 integrated with the insulator 110 protrudes from the distal end side of the metal shell 150. A protruding electrode tip 190 (corresponding to the “second electrode tip” of the present invention) is welded to the tip of the center electrode 120. The ground electrode 130 bonded to the front end surface of the metal shell 150 is bent in an L shape, and the front end portion is directed to the side surface of the electrode tip 190. Furthermore, an electrode tip 295 is welded to the tip of the ground electrode 130, and a spark discharge gap G is formed in the lateral direction (direction perpendicular to the axial direction of the spark plug 300).

  In such a horizontal discharge type, since the electrode tip 295 is disposed horizontally, the space that can be used to form the bent portion 134 in the ground electrode 130 is limited as compared with the vertical discharge type. Therefore, the radius of curvature at the bent portion of the horizontal discharge type ground electrode is smaller than that of the vertical discharge type. Furthermore, regarding the small diameter spark plug having a nominal thread diameter of M12 or less, as described above, the radius of curvature at the bent portion is further smaller than that of the general spark plug (M14). That is, when manufacturing the horizontal discharge type spark plug 300 of M12 or less, the stress applied to the bent portion 134 of the ground electrode 130 increases. Therefore, as in the manufacturing method of the above embodiment, the ground electrode 130 is bent first, and then the electrode tip 295 is welded to the ground electrode 130. Thereby, even in the lateral discharge type spark plug 300, the stress applied to the bent portion 134 of the ground electrode 130 can be reduced.

  In addition, although the electrode tip 190 is welded to the front-end | tip part of the center electrode 120 of the spark plug 300, this invention is applicable also to the type in which the electrode tip is not welded to the front-end | tip part of a center electrode. The same applies to a so-called “longitudinal discharge type” (a type in which a spark discharge gap is formed along the axial direction) such as the spark plug 100 of the above embodiment.

1 is a partial cross-sectional view of a spark plug 100. FIG. FIG. 2 is an enlarged cross-sectional view of the vicinity of a tip 22 of a center electrode 20 shown in FIG. It is a figure which shows from a metal fitting joining process to a preliminary | backup bending process. It is a figure which shows from a chip | tip joining process to this bending process. It is a figure which shows a mode that the ground electrode 30 is pre-bent in a pre-bending process. It is a figure which shows the content of the chip | tip joining process. It is a figure which shows the content of the laser welding process. It is a figure which shows resistance welding of the electrode tip 95. FIG. It is a figure which shows a mode that the ground electrode 30 is finally bent in this bending process. It is a figure which shows a mode that the composite chip | tip 195 is welded to the ground electrode 30 in a chip welding process. It is a figure which shows the manufacturing process in the case of bending the ground electrode 30 at once. It is the elements on larger scale of the front end side of the spark plug 300 which is a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulator 20 Center electrode 22 Tip part 30 Ground electrode 31 Tip part 33 Inner surface 34 Preliminary bending part 35 Bending part 38 Positioning hole 50 Metal shell 57 Tip surface 95 Electrode tip 98 Projection part 100 Spark plug 300 Spark plug

Claims (8)

A central electrode, an insulator having an axial hole extending along the axial direction, the insulator holding the central electrode inside the axial hole, and a metal shell surrounding and holding the periphery of the insulator in the circumferential direction in the circumferential direction; One end portion is joined to the front end surface of the metal shell, and the other end portion is bent toward the front end portion of the center electrode, and the other end portion of the ground electrode is joined to the ground electrode. In a method for manufacturing a spark plug comprising a first electrode tip having a protruding shape that forms a spark discharge gap with the tip portion,
An electrode bending step for bending the ground electrode;
A spark plug manufacturing method comprising: a chip bonding step of bonding the first electrode chip to the other end portion of the ground electrode after the electrode bending process.   The spark plug manufacturing method according to claim 1, further comprising a fitting joining step of joining the one end of the ground electrode to the tip end surface of the metal shell before the electrode bending step. After the metal fitting joining process and before the electrode bending process,
The method for manufacturing a spark plug according to claim 2, further comprising an insulator holding step of holding the insulator holding the center electrode on the metal shell. After the electrode bending step and before the chip bonding step,
4. The chip placement step of placing the first electrode tip at a position corresponding to the position of the tip of the center electrode at the other end of the ground electrode. 5. A method for producing the spark plug according to claim 1. After the electrode bending step and before the chip bonding step,
A positioning portion forming step of forming a positioning portion at a position corresponding to the position of the tip portion of the center electrode at the other end portion of the ground electrode;
4. The spark plug according to claim 1, wherein, in the tip joining step, the first electrode tip is joined to the positioning portion formed at the other end of the ground electrode. 5. Production method. After the chip bonding step,
The spark plug according to any one of claims 1 to 5, further comprising an electrode rebending step of further bending the ground electrode and aligning the position of the first electrode tip with the tip of the center electrode. Manufacturing method. In the electrode bending step,
The other end portion of the ground electrode is bent toward a side surface of the tip portion of the center electrode or a side surface of a projecting second electrode chip joined to the tip portion of the center electrode. A method for manufacturing a spark plug according to any one of claims 1 to 6.   A spark plug manufactured by the method for manufacturing a spark plug according to any one of claims 1 to 7.

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