JP2012221656A - Spark plug manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique, by which a filler can be easily filled in an annular clearance formed between an insulator and a main body metal fitting in a spark plug manufacturing step.SOLUTION: A filler is annular, and is formed prior to a filling step so that it has a shape having an inside diameter approximately identical to an inside diameter of an annular clearance and an outside diameter larger than an outside diameter of the annular clearance. The filling step is performed using a jig having a through hole extending in an axial direction. A taper part, whose inside diameter is reduced to be approximately identical to the outside diameter of the clearance as it approaches to an axial tip, is formed on an inner periphery of the through hole of the jig. The filling step includes a step of arranging the annular filler inside the through hole of the jig, and a step of pressurizing the annular filler arranged inside the through hole of the jig in a direction of the taper part to fill the annular clearance with the filler.

Description

  The present invention relates to a method for manufacturing a spark plug.

  As a spark plug used in an internal combustion engine, a center electrode extending in the axial direction, an insulator (insulator) that holds the center electrode, and a cylindrical metal shell that surrounds the insulator and holds the insulator Spark plugs are known. In such a spark plug, talc (talc) as a filler (sealing material) is filled in an annular gap formed between the insulator and the metal shell.

JP 2003-257582 A

  However, as the spark plug is reduced in size, there is a problem that it is difficult to fill the filler when the annular gap formed between the insulator and the metal shell becomes small.

  The present invention has been made to solve at least a part of the above-described conventional problems, and in the spark plug manufacturing process, a filler is provided in an annular gap formed between the insulator and the metal shell. An object of the present invention is to provide a technique that can be easily filled.

  In order to solve at least a part of the above problems, the present invention can be realized as the following forms or application examples.

[Application Example 1]
A central electrode extending in the axial direction;
An insulator having an axial hole extending in the axial direction and holding the center electrode on the axial tip side of the axial hole;
A method of manufacturing a spark plug having a cylindrical metal shell surrounding the insulator and holding the insulator;
A filling step of filling a filler into an annular gap formed between the insulator and the metal shell;
Prior to the filling step, the filler is annular and has an inner diameter substantially equal to an inner diameter of the annular gap and an outer diameter larger than the outer diameter of the annular gap. And
The filling step is performed using a jig having a through hole extending in the axial direction,
The inner periphery of the through hole of the jig is formed with a tapered portion whose inner diameter decreases as it approaches the tip end in the axial direction until the inner diameter is substantially equal to the outer diameter of the gap.
The filling step includes
Disposing the annular filler inside the through hole of the jig;
Filling the annular gap with the filler by pressing the annular filler disposed inside the through-hole of the jig in the direction of the tapered portion. To
Spark plug manufacturing method.
According to this manufacturing method, since the jig in which the tapered portion is formed is used, it is possible to easily fill the annular gap with the annular filler formed thicker than the annular gap.

  Further, according to this manufacturing method, since the annular filler formed thicker than the annular gap formed between the insulator and the metal shell can be used, the annular filler is cured. Before being placed on the tool, it can be prevented from being damaged due to insufficient strength.

[Application Example 2]
A spark plug manufacturing method according to Application Example 1,
Of the inner periphery of the through-hole of the jig used in the filling step, on the rear end side in the axial direction of the taper portion, the outer diameter of the filler formed in an annular shape is substantially the same. A method for manufacturing a spark plug, characterized in that a cylindrical portion having an equal inner diameter is formed.
According to this manufacturing method, since the jig in which the cylindrical portion is formed is used, it is possible to suppress the filler that has been pressed and crushed from falling out of the jig.

[Application Example 3]
A method for manufacturing a spark plug according to Application Example 1 or Application Example 2,
Of the angles formed by the tapered portion of the jig used in the filling step and the radial direction of the insulator, an acute angle is 45 ° or more,
Spark plug manufacturing method.
If a jig having such a shape is used, a filler can be easily filled into an annular gap formed between the insulator and the metal shell.

[Application Example 4]
A method for manufacturing a spark plug according to any one of Application Example 1 to Application Example 3,
Of the angles formed by the tapered portion of the jig used in the filling step and the radial direction of the insulator, an acute angle is 85 ° or less,
Spark plug manufacturing method.
In this way, the dimension of the jig in the axial direction can be reduced.

[Application Example 5]
A method for manufacturing a spark plug according to any one of Application Examples 1 to 4,
The radial thickness of the annular filler used in the filling step is 1.0 mm or more,
Spark plug manufacturing method.
The filler formed in such a shape has high strength. Therefore, if it does in this way, it can control that an annular filler will be damaged by lack of intensity, before being arranged in a jig.

[Application Example 6]
A method for manufacturing a spark plug according to any one of Application Examples 1 to 5,
The metal shell has a polygonal tool engaging portion,
The distance between opposite sides between two opposite sides of the polygonal shape of the tool engaging portion is 12 mm or 14 mm,
Spark plug manufacturing method.
In the spark plug having such a configuration, an annular gap formed between the insulator and the metal shell is particularly small. Therefore, in the spark plug having such a configuration, the effect of the application example is particularly remarkable.

[Application Example 7]
The spark plug manufacturing method according to any one of Application Example 1 to Application Example 6,
The metal shell has a mounting screw portion used for mounting to the internal combustion engine,
The screw diameter of the mounting screw portion is M12 or less,
Spark plug manufacturing method.
In the spark plug having such a configuration, an annular gap formed between the insulator and the metal shell is particularly small. Therefore, in the spark plug having such a configuration, the effect of the application example is particularly remarkable.

  Note that the present invention can be realized in various modes. For example, it can be realized in the form of a spark plug manufacturing method, manufacturing apparatus, or a spark plug manufactured by these manufacturing method or manufacturing apparatus.

It is a fragmentary sectional view showing an example of spark plug 100 manufactured by applying the present invention. 3 is a flowchart showing a spark plug assembly process which is a part of the manufacturing process of the spark plug 100. It is explanatory drawing which shows the mode of the assembly | attachment process of a spark plug. It is explanatory drawing which shows roughly the process of filling the talc 9 in the cyclic | annular clearance gap C formed between the insulator 10 and the main metal fitting base member 50a. It is sectional drawing which expanded the broken-line part of FIG. It is explanatory drawing which shows the mode of the process of crimping to the metal shell base member 50a among the assembly | attachment processes of assembling the insulator 102 with a center shaft to the metal shell base member 50a. It is explanatory drawing which shows the experimental result of the experiment example regarding the angle (alpha) in the taper part 538t in a tabular form. It is explanatory drawing about the evaluation criteria of an experimental result. It is explanatory drawing which shows the mode of the experiment example regarding the wall thickness T of the cyclic | annular talc 9r. It is explanatory drawing which shows the experimental result of the experiment example regarding the thickness T of the cyclic | annular talc 9r in a tabular form. It is explanatory drawing which shows the cross section in the radial direction of the tool engaging part 51 of the metal shell 50. FIG.

A. First embodiment:
A1. Spark plug structure:
FIG. 1 is a partial cross-sectional view showing an example of a spark plug 100 manufactured by applying the present invention. In the following description, the axial direction OD of the spark plug 100 in FIG. 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug and the upper side is the rear end side. In FIG. 1, an external appearance of the spark plug 100 is shown on the right side of the axis OO, and a cross section obtained by cutting the spark plug 100 on the left side of the axis OO along a plane passing through the axis OO (that is, the central axis). Show.

  The insulator 10 is an insulator formed by firing alumina or the like. The insulator 10 is a cylindrical insulator in which an axial hole 12 extending in the axial direction OD is formed along the central axis. The insulator 10 is formed with a flange portion 19 having the largest outer diameter in the approximate center of the axial direction OD, and a rear end side body portion 18 is formed on the rear end side. The rear end side body portion 18 is formed with a flange portion 11 for increasing the surface length and enhancing the insulation. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side from the flange portion 19. A long leg portion 13 having an outer diameter smaller than that of the front end side body portion 17 is formed further on the front end side than the front end side body portion 17. The long leg portion 13 has a smaller outer diameter toward the distal end side. The leg portion 13 is exposed to the combustion chamber of the internal combustion engine when the spark plug 100 is attached to the engine head 200 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.

  The center electrode 20 is held in a shaft hole 12 provided in the insulator 10. The center electrode 20 extends along the central axis OO from the front end side of the insulator 10 toward the rear end side, and is exposed on the front end side of the insulator 10. The center electrode 20 is a rod-shaped electrode having a structure in which a core material 25 is embedded in an electrode base material 21. The electrode base material 21 is formed of nickel of Inconel 600, Inconel 601 or the like (“Inconel” is a trade name) or an alloy containing nickel as a main component. The core material 25 is made of copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the electrode base material 21. Usually, the center electrode 20 is produced by filling a core material 25 inside an electrode base material 21 formed in a bottomed cylindrical shape, and performing extrusion molding from the bottom side and stretching it. The core member 25 has a substantially constant outer diameter at the body portion, but is formed in a tapered shape at the distal end side. In the shaft hole 12, the center electrode 20 is electrically connected to a terminal fitting 40 provided on the rear end side of the insulator 10 through the seal body 4 and the ceramic resistor 3. The center electrode 20, the seal body 4, the ceramic resistor 3, and the terminal fitting 40 are collectively referred to as “middle shaft”. Therefore, hereinafter, the insulator 10 to which the center electrode 20, the seal body 4, the ceramic resistor 3, and the terminal fitting 40 (medium shaft) are attached is also referred to as “insulator 102 with a middle shaft”.

  The metal shell 50 is a cylindrical metal fitting made of a low carbon steel material, and holds the insulator 10 inside. A portion from a part of the rear end side body portion 18 of the insulator 10 to the long leg portion 13 is surrounded by a metal shell 50.

  The metal shell 50 includes a tool engaging portion 51 and a mounting screw portion 52. The tool engaging part 51 is a part into which a spark plug wrench (not shown) is fitted. The mounting screw portion 52 of the metal shell 50 is a portion where a screw thread is formed, and is screwed into a mounting screw hole 201 of the engine head 200 provided in the upper part of the internal combustion engine. Thus, the spark plug 100 is fixed to the engine head 200 of the internal combustion engine by screwing the mounting screw portion 52 of the metal shell 50 into the mounting screw hole 201 of the engine head 200 and tightening. In addition, the screw diameter of the attachment screw part 52 in this embodiment is M12.

  Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a flange-like flange portion 54 that bulges radially outward is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the mounting screw portion 52 and the flange portion 54. When the spark plug 100 is attached to the engine head 200, the gasket 5 is crushed and deformed between the seat surface 55 of the flange portion 54 and the opening peripheral edge portion 205 of the attachment screw hole 201. Due to the deformation of the gasket 5, the gap between the spark plug 100 and the engine head 200 is sealed, and leakage of combustion gas through the mounting screw hole 201 is suppressed.

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 from the tool engaging portion 51. In addition, a thin buckled portion 58 is provided between the flange portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Annular ring members 6, 7 are inserted between the inner peripheral surface of the metal shell 50 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. Has been. Further, between the ring members 6 and 7, powder of talc (talc) 9 as a filler (sealant) is filled. The metal shell 50 and the insulator 10 are fixed by caulking the caulking portion 53 inwardly. The airtightness between the metal shell 50 and the insulator 10 is determined by the annular plate packing 8 interposed between the step portion 56 formed on the inner peripheral surface of the metal shell 50 and the step portion 15 of the insulator 10. Is retained, and combustion gas leakage is prevented. The buckling portion 58 is configured to bend outwardly and deform as the compression force is applied during caulking. The buckling portion 58 secures the compression length of the talc 9 and increases the airtightness in the metal shell 50. ing.

  A ground electrode 30 bent from the distal end portion of the metallic shell 50 toward the central axis OO is joined to the distal end portion of the metallic shell 50. The ground electrode 30 can be formed of a nickel alloy having high corrosion resistance such as Inconel 600 or the like (“Inconel” is a trade name). The ground electrode 30 and the metal shell 50 can be joined by welding. The tip 33 of the ground electrode 30 faces the center electrode 20.

  A high voltage cable (not shown) is connected to the terminal fitting 40 of the spark plug 100 via a plug cap (not shown). A spark discharge is generated between the ground electrode 30 and the center electrode 20 by applying a high voltage between the terminal fitting 40 and the engine head 200.

  Although not shown in FIG. 1, each of the center electrode 20 and the ground electrode 30 has an electrode chip formed mainly of a high melting point noble metal in order to improve spark wear resistance. It is attached. Specifically, for example, iridium (Ir) or iridium as a main component, platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), An electrode tip formed of an Ir alloy to which one or more of rhenium (Re) is added is attached. Further, platinum or an electrode chip mainly composed of platinum is attached to the surface of the tip 33 of the ground electrode 30 facing the center electrode 20.

A2. Spark plug manufacturing process:
FIG. 2 is a flowchart showing an assembling process of the spark plug, which is a part of the manufacturing process of the spark plug 100. FIG. 3 is an explanatory diagram showing the state of the spark plug assembly process. In step S100 of FIG. 2, the insulator 102 with the middle shaft and the metal shell base member 50a are prepared. The metal shell base member 50a has cylindrical tubular portions 53a and 58a that are the bases of the crimped portion 53 and the buckling portion 58 of the metal shell 50 (FIG. 1) (FIG. 3A).

  In step S200, the plate packing 8 and the intermediate shaft-equipped insulator 102 are inserted in this order in the axial direction OD with respect to the metal shell base member 50a (FIG. 3A). In step S300, the ring member 7 is inserted into an annular gap formed between the insulator 102 with the middle shaft and the metal shell base member 50a.

  In step S400, the talc 9 is pressed and filled into an annular gap formed between the insulator 102 with the middle shaft and the metal shell base member 50a (FIG. 3B). Thus, when the ring member 7 and the talc 9 are pressed toward the axial direction OD, the insulator 102 with the middle shaft is pressed toward the front end side in the metal shell base member 50a, and the metal shell base member 50a. Assembled into. The step of filling talc 9 will be described in detail later.

  In step S500, the ring member 6 is disposed at the upper end of the pressed talc 9 (FIG. 3C). In step S600, the metal shell base member 50a is crimped to form the crimped portion 53 and the buckling portion 58, and the metal shell base member 50a becomes the metal shell 50 (FIG. 3D). .

  FIG. 4 is an explanatory view schematically showing a step of filling talc 9 in an annular gap C formed between the insulator 10 and the metal shell base member 50a. FIG. 5 is a cross-sectional view further enlarging the broken line portion of FIG. 4. Hereinafter, the annular gap C formed between the insulator 10 and the metal shell base member 50a is also simply referred to as “annular gap C”. First, in the step of filling talc, as shown in FIG. 4, the metal shell base member 50 a into which the insulator 102 with the center shaft is inserted is arranged on the base 400. The detailed configuration of the pedestal 400 will be described later.

  Prior to the step of filling the talc 9, the annular talc 9r is obtained by press-molding powdery talc into a cylindrical shape. The annular talc 9r is annular and has an inner diameter that is substantially equal to the inner diameter of the annular gap C, and an outer diameter that is larger than the outer diameter of the annular gap C (cylindrical shape). As shown in FIG. 4, the annular talc 9 r is disposed inside the talc introduction jig 538. In addition, when forming cyclic | annular talc 9r from a powdery talc, it is good also as adding inorganic substances, such as water glass, colloidal silica, and aluminum phosphate, or silicon | silicones, such as silicon oil and a silicon varnish, as a binder.

  The talc introduction jig 538 is a jig that serves as a guide for introducing the talc 9 into the annular gap C. The talc introduction jig 538 has a through hole 538h extending in the axial direction OD, and a tapered portion 538t and a cylindrical portion 538p are formed on the inner periphery of the through hole 538h.

  The tapered portion 538t has a shape in which the inner diameter decreases as it approaches the distal end side in the axial direction OD until the inner diameter is approximately equal to the outer diameter of the annular gap C. The cylindrical portion 538p is formed on the rear end side of the taper portion 538t in the axial direction OD, and has a constant inner diameter that is substantially equal to the outer diameter of the annular talc.

  The press jig 520 is a jig for pulverizing the annular talc 9r disposed inside the talc introduction jig 538 and for compressing and filling the pulverized talc 9 into the annular gap C. The pressing jig 520 has a first cylindrical portion 520a and a second cylindrical portion 520b on the tip side in the axial direction OD.

  The first tubular portion 520a has an inner diameter that is substantially equal to the inner diameter of the annular gap C and an outer diameter that is substantially equal to the outer diameter of the annular gap C. The second cylindrical portion 520b is provided on the rear end side in the axial direction OD of the first cylindrical portion 520a, and has an inner diameter substantially equal to the inner diameter of the cylindrical portion 538p of the talc introduction jig 538, and a talc introduction jig. 538 having an outer diameter substantially equal to the outer diameter of the cylindrical portion 538p.

  As described above, in the talc 9 filling step, the annular talc 9r is disposed inside the through hole of the talc introduction jig 538. Specifically, the annular talc 9r is disposed inside the cylindrical portion 538p of the talc introduction jig 538. Then, the annular talc 9r disposed inside the through hole of the talc introduction jig 538 is pressed in the direction of the taper portion 538t by the press jig 520 and pulverized into powder, and the talc 9 is disposed in the annular gap C. Fill. Specifically, the powdery talc 9 introduced into the annular gap C is pressed and compressed by the first cylindrical portion 520a of the pressing jig 520.

  Here, since the tapered portion 538t is formed in the talc introduction jig 538, the annular talc 9r formed thicker than the annular gap C can be easily filled into the annular gap C. Further, since the annular talc 9r formed thicker than the annular gap C can be used, the annular talc 9r is damaged due to insufficient strength before being placed on the talc introduction jig 538. Can be suppressed. That is, even when a spark plug with a small annular gap C is manufactured, the annular talc 9r having a larger strength than the annular gap C can be used.

  Further, since the cylindrical portion 538p is formed in the talc introduction jig 538, it is possible to prevent the talc 9 that has been pulverized and powdered from falling out of the talc introduction jig 538. . However, the cylindrical portion 538p may be omitted, and only the tapered portion 538t may be formed.

  Here, the acute angle α among the angles formed by the tapered portion 538t of the talc introduction jig 538 and the radial direction of the insulator 10 is preferably 45 ° or more. By doing so, the talc 9 can easily enter the annular gap C along the tapered portion 538t, and therefore, the talc 9 can be appropriately filled. The reason for limiting the angle α to the above angle will be described in detail later. In the present embodiment, the angle α is 70 °.

  The acute angle α among the angles formed by the tapered portion 538t of the talc introduction jig 538 and the radial direction of the insulator 10 is preferably 85 ° or less. In this way, the dimension of the talc introduction jig 538 in the axial direction OD can be reduced.

  Further, the radial thickness of the annular talc 9r is preferably 1.0 mm or more. In this way, since the annular talc 9r has sufficient strength, it is possible to prevent the annular talc 9r from being broken and damaged before being placed in the talc introduction jig 538 in the spark plug manufacturing process. It becomes possible to do.

  In the present embodiment, in the assembling process including the process of filling talc 9, while allowing the relative displacement of the metal shell base member 50a and the insulator 102 with the middle shaft in the axial direction OD, Relative in the radial direction that intersects the axial direction OD of the metal shell base member 50a and the insulator 102 with the center shaft so that the deviation amount between the shaft of the metal base member 50a and the axis of the insulator 102 with the center shaft becomes a predetermined value or less. Restricts the displacement of various positions. In this manner, restricting the displacement of the relative position in the radial direction intersecting the axial direction OD between the metal shell base member 50a and the insulator 102 with the middle shaft is also simply referred to as “displacement restriction” and is referred to as displacement restriction. Proactively performing this is also referred to as a “displacement regulating step”. Below, the apparatus for performing this displacement control is demonstrated with reference to FIG.5 and FIG.6.

  The pedestal 400 has a receiving die 410, a bottom 420, a metal fitting restricting portion 430, an outer spring 440 that biases the metal fitting restricting portion 430 upward, an insulator restricting portion 450, and an insulator restricting portion 450. And an inner spring 460 for biasing. Among these members, the receiving die 410, the bottom 420, the metal fitting restricting portion 430, the outer spring 440, and the inner spring 460 are formed of a metal having high strength such as tool steel. On the other hand, the insulator regulating portion 450 is in contact with the insulator 10 as will be described later. Therefore, in order to suppress contamination of the insulator 10, it is more preferable that the insulator restricting portion 450 is formed of resin.

  The receiving mold 410 of the pedestal 400 has two flange portions 417 and 418 having different outer diameters and a body portion 419 having an outer diameter smaller than that of the flange portion 418 in the axial direction OD. The receiving die 410 is fixed by using these flange portions 417 and 418. On the upper end side of the flange portion 417, a bracket receiver 412 having an inner diameter substantially the same as the flange portion 54 of the metal shell base member 50a and an insertion portion 414 larger than the outer diameter of the mounting screw portion 52 of the metal shell base member 50a are provided. It has been. The insertion portion 414 is provided from approximately the center of the flange portions 417 and 418 to the body portion 419. A guide hole 416 having a larger inner diameter than the insertion portion 414 is provided on the inner surface of the body portion 419.

  The bottom part 420 is a member for receiving the outer spring 440, and is a ring-shaped part 422 having substantially the same outer diameter as the body part 419 of the receiving die 410, and a plate-like shape extending inwardly from the annular part 422 at the lower end. Part 424. A through hole 426 having an inner diameter smaller than that of the inner spring 460 is provided at the center of the plate-like portion 424. By providing the through hole 426, an increase in the pressure inside the base 400 when the metal shell base member 50a is inserted and the insulator 102 with the middle shaft is assembled is suppressed. The bottom portion 420 is fixed to the receiving die 410 with screws or the like (not shown).

  The bracket restricting portion 430 has a tapered portion 432 whose outer diameter gradually increases toward the axial direction OD (downward in FIG. 5) on the metal shell base member 50a side (that is, the upper end side), and the outer diameter is a receiving type. The guide hole 416 has a body portion 434 that is substantially the same as the inner diameter of the guide hole 416. Thereby, the metal fitting restricting portion 430 is movable in the axis OO direction with respect to the receiving die 410. And since the upper end surface 436 of the trunk | drum 434 is a plane perpendicular | vertical to the axis OO, when the upper end surface 436 contacts the lower end surface 415 of the insertion part 414, the upper limit position of the metal fitting control part 430 is determined. Is done. In addition, the metal fitting restricting portion 430 is provided with a guide hole 438 along the axis OO for inserting the insulator restricting portion 450.

  The insulator regulating portion 450 is a cylindrical member, and is provided on the lower side of the cylindrical body 452 and the cylindrical body 452 whose outer diameter is substantially the same as the inner diameter of the guide hole 438 provided in the metal fitting regulating portion 430. It has a flange 454. Thus, by making the outer diameter of the body part 452 substantially the same as the inner diameter of the guide hole 438, the insulator restricting part 450 can move in the direction of the axis OO with respect to the metal fitting restricting part 430. Further, the upper limit position of the insulator regulating portion 450 relative to the metal fitting regulating portion 430 is determined by providing the flange portion 454 on the lower side of the body portion 452. The inner surface of the insulator regulating portion 450 has a tapered hole 456 whose inner diameter is gradually reduced toward the axial direction OD (downward in FIG. 5) on the middle shaft-equipped insulator 102 side (that is, the upper end side), and the inner diameter is A substantially constant through hole 458 is provided.

  The metal fitting restricting portion 430 has a tapered portion 432 whose outer diameter gradually increases toward the axial direction OD on the metal shell original member 50a side. Therefore, when assembling the insulator 102 with the intermediate shaft and the metal shell base member 50a, the inner diameter of the metal shell base member 50a is regulated in the radial direction by abutting against the taper portion 432 of the metal fitting regulating portion 430. The attached center is located on the axis OO. Further, the insulator restricting portion 450 has a tapered hole 456 whose inner diameter gradually decreases toward the axial direction OD on the side of the insulator 102 with the middle shaft. Therefore, when assembling the insulator 102 with the intermediate shaft and the metal shell base member 50a, the insulator 10 on the tip side of the insulator 102 with the intermediate shaft comes into contact with the tapered hole 456 and is regulated in the radial direction. The center is located on the axis OO.

  According to such a displacement regulating process, when the insulator 102 with the middle shaft and the metal shell base member 50a are assembled, the insulator 102 with the medium shaft and the metal shell base member 50a can move along the axis OO. In this state, the radial displacement is restricted. For this reason, the centers of the tip portions after assembly substantially coincide. That is, the center of the distal end portion of the insulator 10 and the center of the distal end portion of the metal shell 50 are maintained in a state of being substantially located on the axis OO. Since the center of the center electrode 20 is substantially the same as the center of the insulator 10, the center of the center electrode 20 is substantially coincident with the center of the tip of the metal shell 50, and the center electrode 20 and the tip of the metal shell 50 are aligned. The shortest distance is kept large enough. Therefore, it is possible to suppress the occurrence of spark discharge between the center electrode 20 and the inner diameter of the metal shell 50, and it is possible to more reliably perform ignition in the internal combustion engine. Furthermore, by making the insulator regulating portion 450 into a cylindrical shape, it is possible to suppress damage to the electrode tip attached to the tip side of the center electrode 20.

  As shown in FIG. 5, in this embodiment, the outer surface of the taper portion 432 of the metal fitting restricting portion 430 and the inner surface of the taper hole 456 of the insulator restricting portion 450 are both conical surfaces. If it does in this way, regulation of a diameter direction will become easy. However, the outer surface of the taper portion 432 has various shapes as long as the outer diameter increases in a predetermined direction (axial direction OD) and the inner surface of the taper hole 456 decreases in inner diameter in a predetermined direction. Is possible. For example, the tapered portion 432 may have a cylindrical surface that conforms to the shape of the distal end portion of the metal shell 50. In addition, a curved surface that conforms to the shape of the outer periphery of the tip of the insulator 10 can be provided on the inner surface of the tapered hole 456 on the conical surface.

  FIG. 6 is an explanatory diagram showing a state of a step of caulking the metal shell base member 50a in an assembly process of assembling the insulator 102 with the middle shaft to the metal shell base member 50a. This caulking step is performed by pressing the caulking tool 600 from above toward the axial direction OD against the metal shell base member 50a into which the insulator 102 with the middle shaft is inserted.

  The cylindrical caulking tool 600 is provided with a through hole 610 having an inner diameter larger than that of the rear end side body portion 18 of the insulator 10 (FIG. 1) constituting the insulator 102 with the center shaft. A curved surface portion 612 having a shape along the outer shape of the crimping portion 53 is provided on the lower end side (that is, the front end side) of the through-hole 610. Further, a contact portion 614 having a shape along the outer shape of the rear end side of the tool engaging portion 51 is provided on the outer edge of the curved surface portion 612.

  As shown in FIG. 6A, when the curved surface portion 612 abuts on the upper cylindrical portion 53a of the metal shell base member 50a, the metal shell base member 50a receives a load in the axial direction OD and receives the metal fitting regulating portion 430. Pressed against. The metal shell base member 50a moves downward while being pressed by the receiving die 410 while the position of the front end side of the metal shell base member 50a is regulated by the metal fitting regulating portion 430.

  If the caulking tool 600 is further pressed toward the axial direction OD in a state where the metal shell base member 50a is pressed against the receiving die 410, the tubular portion 53a is bent along the curved surface portion 612 of the caulking tool 600 to be added. A fastening portion 53 is formed. After the caulking portion 53 is formed, when the caulking tool 600 is further lowered and the abutting portion 614 on the outer edge of the curved surface portion 612 and the tool engaging portion 51 abut, a load is applied to the tool engaging portion 51. The cylindrical portion 58a on the lower side of the tool engaging portion 51 is buckled to form the buckled portion 58 (FIG. 6B).

  In this caulking step, a load in the axial direction OD is applied to the talc 9 and the ring members 6 and 7, whereby a load in the axial direction OD is applied from the flange portion 19 of the insulator 10 to the insulator 102 with the middle shaft. As described above, the load in the axial direction OD is applied to the insulator 102 with the middle shaft, so that it is pressed against the insulator regulating portion 450. The insulator 102 with the middle shaft moves downward while the position on the tip side is regulated by the insulator regulating part 450 and is fixed to the metal shell base member 50a.

  Thus, also in the caulking step, the center of the front end portion of the insulator 102 with the middle shaft and the center of the front end portion of the metal shell 50 are fixed in a state of being substantially located on the axis OO. Therefore, the center of the center electrode 20 (FIG. 1) substantially coincides with the center of the tip of the metal shell 50 (FIG. 1). As a result, the distance between the center electrode 20 and the front end of the metal shell 50 is kept sufficiently large, so that the occurrence of spark discharge between the center electrode 20 and the inner diameter of the metal shell 50 is suppressed, and the internal combustion It is possible to more reliably perform ignition in the engine and to reduce the consumption of the spark plug 100.

  As described above, according to the manufacturing method of the present embodiment, the talc introduction jig 538 is formed with the tapered portion 538t, so that the talc 9 can be easily filled into the annular gap C.

B. Experimental example:
B1. Experimental example regarding angle α at tapered portion 538t:
In order to investigate the relationship between the angle α (FIG. 4) at the tapered portion 538t and whether or not the talc 9 is properly filled, an experiment was performed using a plurality of talc introduction jigs 538 having different angles α.

  FIG. 7 is an explanatory diagram showing, in a tabular form, experimental results of an experimental example relating to the angle α at the tapered portion 538t. FIG. 8 is an explanatory diagram of the evaluation criteria for the experimental results. In this experimental example, it was evaluated whether or not the talc 9 was properly filled up to a predetermined reference surface of the annular gap C. Specifically, as shown in FIG. 8, the surface on the front end side by 1 mm in the axial direction OD from the upper end 50 u of the metal shell base member 50 a is defined as the reference plane R. The case where the deviation of the filling surface Z filled with talc 9 from the reference surface R is within 0.25 mm is indicated as “◎” as the highest evaluation, and the deviation of the filling surface Z from the reference surface R is The case where it is larger than 0.25 mm and within 0.50 mm is indicated by “◯” as the second highest evaluation, and the case where the deviation of the filling surface Z from the reference surface R is larger than 0.50 mm is indicated as “low evaluation”. △ ”

  As can be understood from FIG. 7, when the angle α is 40 °, the evaluation is “△”, and when it is 45 ° or more, “○” is the second highest evaluation, and “◎” is the highest evaluation at 70 °. Become. Therefore, the angle α is preferably 45 ° or more, and more preferably 70 °. The angle α can be larger than 85 °, but if the angle α is 85 ° or less, the dimension of the tapered portion 538t in the axial direction OD can be reduced.

B2. Experimental example of wall thickness T of annular talc 9r:
In order to examine the relationship between the thickness T and the strength of the annular talc 9r in the radial direction, an experiment was performed using a plurality of annular talcs 9r having the same density but different thicknesses T. The radial thickness T of the annular talc 9r is equal to half the difference between the outer diameter and the inner diameter of the annular talc 9r.

  FIG. 9 is an explanatory diagram showing a state of an experimental example regarding the wall thickness T of the annular talc 9r. In this experimental example, a load of 1.7 N was applied to the annular talc 9r from the radial direction, and it was examined whether or not the annular talc 9r was broken and damaged. The length of the annular talc 9r used in this experimental example in the axial direction is 10 mm.

  FIG. 10 is an explanatory diagram showing, in a tabular form, experimental results of an experimental example related to the wall thickness T of the annular talc 9r. Regarding the evaluation, the case where the cyclic talc 9r was broken and broken was shown as “x” as a low evaluation, and the case where the cyclic talc 9r was not broken was shown as “◯” as a high evaluation. As can be understood from FIG. 10, if the thickness T of the annular talc 9r is 1.0 mm or more, it can be understood that the strength of the annular talc 9r is sufficient and does not break. Therefore, the wall thickness T of the annular talc 9r is preferably 1.0 mm or more.

C. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

C1. Modification 1:
In the above-described embodiment, the spark plug with the mounting screw portion 52 having a screw diameter of M12 has been described as an example. However, the manufacturing method described in the above embodiment is applied to a spark plug having a screw diameter of the mounting screw portion 52 other than M12. It can also be applied to. In particular, the manufacturing method described in the above embodiment is effective for a spark plug having a small annular gap C, for example, a spark plug having a screw diameter of the mounting screw portion 52 of M12 or less.

C2. Modification 2:
FIG. 11 is an explanatory view showing a cross section in the radial direction of the tool engaging portion 51 of the metal shell 50. As shown in FIG. 11, the metal shell 50 has a polygonal tool engaging portion 51. The distance between opposite sides between two opposing sides of the polygonal shape of the tool engaging portion 51 is L. Here, in the spark plug in which the distance L between opposite sides is 12 mm or 14 mm, the annular gap C is particularly small. Therefore, the manufacturing method described in the above embodiment is particularly effective for a spark plug having a distance L between opposite sides of 12 mm or 14 mm. However, the manufacturing method described in the above embodiment can also be applied to a spark plug in which the distance L between opposite sides is greater than 12 mm.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6, 7 ... Ring member 8 ... Plate packing 9 ... Talc 9r ... Cylindrical talc 10 ... Insulator 11 ... Girder part 12 ... Shaft hole 13 ... Leg long part 15 ... Step part 17 ... Front end side body part 18 ... Rear end side body part 19 ... Gutter part 20 ... Center electrode 21 ... Electrode base material 25 ... Core material 30 ... Ground electrode 33 ... Front end part 40 ... Terminal metal fitting 50 ... Main metal fitting 50a ... Main metal fitting original member DESCRIPTION OF SYMBOLS 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 53a ... Cylindrical part 54 ... Gutter part 55 ... Seat surface 56 ... Step part 58 ... Buckling part 58a ... Cylindrical part 59 ... Screw neck 100 ... Spark Plug 102 ... Insulator with medium shaft 200 ... Engine head 201 ... Mounting screw hole 205 ... Peripheral edge 400, 400b ... Base 410 ... Receiving die 412 ... Metal fitting 414 ... Insertion part 415 ... Lower end surface 416 ... Guide hole 41 , 418 ... collar part 419 ... trunk part 420 ... bottom part 422 ... annular part 424 ... plate-like part 426 ... through hole 430 ... metal fitting regulating part 432 ... taper part 434 ... trunk part 436 ... upper end surface 438 ... guide hole 440 ... outside Spring 450 ... Insulator restricting portion 452 ... trunk 454 ... collar 456 ... taper hole 458 ... through hole 460 ... inner spring 470 ... regulating member 472 ... taper 474 ... collar 476 ... trunk 480 ... spring 520 ... press cure Tool 520a ... first cylindrical portion 520b ... second cylindrical portion 538 ... talc introduction jig 538h ... through hole 538p ... cylindrical portion 538t ... tapered portion 600 ... caulking tool 610 ... through hole 612 ... curved surface portion 614 ... Contact part 624 ... curved surface part

Claims (7)

A central electrode extending in the axial direction;
An insulator having an axial hole extending in the axial direction and holding the center electrode on the axial tip side of the axial hole;
A method of manufacturing a spark plug having a cylindrical metal shell surrounding the insulator and holding the insulator;
A filling step of filling a filler into an annular gap formed between the insulator and the metal shell;
Prior to the filling step, the filler is annular and has an inner diameter substantially equal to an inner diameter of the annular gap and an outer diameter larger than the outer diameter of the annular gap. And
The filling step is performed using a jig having a through hole extending in the axial direction,
The inner periphery of the through hole of the jig is formed with a tapered portion whose inner diameter decreases as it approaches the tip end in the axial direction until the inner diameter is substantially equal to the outer diameter of the gap.
The filling step includes
Disposing the annular filler inside the through hole of the jig;
Filling the annular gap with the filler by pressing the annular filler disposed inside the through-hole of the jig in the direction of the tapered portion. To
Spark plug manufacturing method. It is a manufacturing method of the spark plug according to claim 1,
Of the inner periphery of the through-hole of the jig used in the filling step, on the rear end side in the axial direction of the taper portion, the outer diameter of the filler formed in an annular shape is substantially the same. A method for manufacturing a spark plug, characterized in that a cylindrical portion having an equal inner diameter is formed. A method of manufacturing a spark plug according to claim 1 or claim 2,
Of the angles formed by the tapered portion of the jig used in the filling step and the radial direction of the insulator, an acute angle is 45 ° or more,
Spark plug manufacturing method. It is a manufacturing method of the spark plug according to any one of claims 1 to 3,
Of the angles formed by the tapered portion of the jig used in the filling step and the radial direction of the insulator, an acute angle is 85 ° or less,
Spark plug manufacturing method. A method for manufacturing a spark plug according to any one of claims 1 to 4,
The radial thickness of the annular filler used in the filling step is 1.0 mm or more,
Spark plug manufacturing method. It is a manufacturing method of the spark plug according to any one of claims 1 to 5,
The metal shell has a polygonal tool engaging portion,
The distance between opposite sides between two opposite sides of the polygonal shape of the tool engaging portion is 12 mm or 14 mm,
Spark plug manufacturing method. It is a manufacturing method of the spark plug as described in any one of Claims 1-6, Comprising:
The metal shell has a mounting screw portion used for mounting to the internal combustion engine,
The screw diameter of the mounting screw portion is M12 or less,
Spark plug manufacturing method.

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