JP2017004933A - Method of manufacturing spark plug and spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a spark plug that can prevent an insulator from cracking during the manufacture or during use of the spark plug fitted with an internal combustion engine, and the spark plug.SOLUTION: A method of manufacturing a spark plug comprising an insulator which is a cylindrical body having an axial hole extending in an axial direction, and also has, as an outer peripheral surface, a diameter-reduced outer surface decreasing in outer diameter from a rear end side toward a tip side, cylindrical main body metal fittings extending in the axial direction and having a through hole into which the insulator is inserted, and a center electrode held on the tip side of the insulator so that a tip part project from the insulator includes the processes of: forming an annular projection part which projects from an opposite surface, opposed in the axial direction to the diameter-reduced outer surface when the insulator is inserted, of an inner peripheral surface of the main body metal fittings, on the opposite side; inserting the insulator from a rear end side of the main body metal fittings and making the diameter-reduced outer surface abuts on the projection part; and pressing the insulator and main body metal fittings in the axial direction to deform the projection part.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a spark plug manufacturing method and a spark plug used for an internal combustion engine such as an automobile engine.

  Conventionally, a spark plug that is attached to an internal combustion engine such as an automobile engine and used for ignition of the internal combustion engine is known. As such a spark plug, for example, a cylindrical body extending in the axial direction and having an axial hole, an insulator having a reduced diameter outer surface on the outer peripheral surface, the outer diameter of which decreases from the rear end side toward the front end side, and A cylindrical body that extends in the axial direction and has a through-hole into which an insulator is inserted, has a threaded portion for mounting on the outer periphery, and has a reduced diameter inner surface that decreases in inner diameter from the rear end side toward the front end side. The metal shell on the surface, the center electrode held by the insulator so that the tip protrudes from the insulator, and the ground which is disposed at the tip of the metal shell and whose tip is opposite the tip of the center electrode The thing of the structure equipped with the electrode is known.

  In the spark plug having the above configuration, a plate packing is provided between the outer diameter of the insulator and the inner surface of the metal shell, and the plate packing ensures airtightness between the insulator and the metal shell. is there. That is, in such a spark plug, when the insulator and the metal shell are fixed by caulking the rear end portion of the metal shell, the plate packing is crushed by the caulking load to ensure the airtightness between the insulator and the metal shell. It is supposed to be.

  When trying to secure the airtightness between the insulator and the metal shell using the plate packing as described above, the plate packing presses the insulator when the caulking load is applied and the plate packing is deformed. A so-called squeeze crack may occur that deforms and breaks the insulator.

  For this reason, a method of manufacturing a spark plug without using plate packing has been proposed. In this method, the angle of the reduced diameter inner surface of the metal shell is made smaller than that of the reduced diameter outer surface of the insulator, and the reduced diameter inner surface of the metal shell is deformed by applying a caulking load. (See, for example, Patent Document 1). That is, in this method, when an insulator is inserted into the metal shell, the inner peripheral side end of the reduced diameter inner surface of the metal shell is brought into contact with the reduced diameter outer surface of the insulator, and then the caulking load is applied to the main metal fitting. The inner diameter of the metal fitting is deformed to hermetically seal between them.

Japanese Patent Publication No. 48-26687

  However, in the above method, when the reduced diameter inner surface of the metal shell is deformed by applying a caulking load, the inner peripheral side end of the reduced diameter inner surface of the metal shell is deformed so as to protrude toward the insulator. For this reason, when a caulking load is applied, a portion deformed so as to protrude toward the insulator may press the insulator, and the insulator may be cracked. Further, when the spark plug is attached to the internal combustion engine and used, a portion deformed so as to protrude toward the insulator may press the insulator due to thermal expansion or the like, and the insulator may be cracked.

  The present invention has been made in response to the above-described conventional circumstances. SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug manufacturing method and a spark plug capable of preventing the insulator from being cracked during manufacturing or when used by being attached to an internal combustion engine.

  One aspect of the method for producing a spark plug of the present invention is a cylindrical body having an axial hole extending in the axial direction, and has an outer surface with a reduced diameter outer surface whose outer diameter decreases from the rear end side toward the front end side. A body, a cylindrical metal shell having a through-hole into which the insulator is inserted, and a center electrode held on the tip side of the insulator so that the tip protrudes from the insulator In the method for manufacturing a spark plug comprising: and protruding from the opposing surface to an opposing surface that faces the reduced diameter outer surface in the axial direction when the insulator is inserted among the inner peripheral surface of the metal shell. Forming an annular convex portion, inserting the insulator from the rear end side of the metal shell, bringing the reduced diameter outer surface into contact with the convex portion, and the insulator and the metal shell. The projection is deformed by pressing in the axial direction. And having a that step.

  In the spark plug manufacturing method of the present invention, a reduced diameter outer surface (packing surface) formed in the insulator and an airtight seal between the reduced diameter outer surface and the opposing surface (shelf) of the metal shell facing in the axial direction. When manufacturing a spark plug having a structure to be stopped, an annular convex portion protruding from the facing surface is formed on the facing surface. Next, an insulator is inserted from the rear end side of the metal shell, and the reduced diameter outer surface is brought into contact with the convex portion. And a convex part is deformed by pressing an insulator and a metal shell in the direction of an axis. The step of deforming the convex portion may be performed simultaneously with the step of fixing the insulator and the metal shell by caulking the rear end portion of the metal shell radially inward.

  Thus, airtightness can be ensured without using a plate packing by forming a protrusion protruding from the opposing surface and pressing and deforming the protrusion. That is, according to the present invention, compared to the case where the opposed surface and the reduced diameter outer surface are brought into contact with each other over the entire opposed surface without forming the convex portion, the portion in contact with the pressed state is formed. The surface pressure can be increased, and high airtightness can be obtained without using plate packing.

  Moreover, the convex part formed in the opposing surface deform | transforms in that position, when pressed, and does not shift | deviate by pressing force like the plate packing which is another member. Therefore, when pressed, it is possible to prevent the insulator from being damaged by being deformed so as to protrude from the portion of the facing surface facing the reduced diameter outer surface to the outer peripheral side or the inner peripheral side. In addition, when the insulator and the metal shell are pressed in the axial direction and a caulking load is applied, the corners of the reduced diameter outer surface of the insulator do not contact the metal shell, so no stress is applied to the corners and cracks occur. Can be prevented. Furthermore, since the deformed part does not protrude to the outer peripheral side or the inner peripheral side, even when heat is applied and thermal expansion occurs when the spark plug is attached to the internal combustion engine, the protruding part is insulated. It is possible to prevent the insulator from being cracked by pressing the body.

  In the step of forming the convex portion, it is preferable to form the annular convex portion so that the apex of the convex portion is positioned on the outer peripheral side from the center of the portion of the opposing surface that faces the reduced diameter outer surface. Thereby, it can prevent more reliably that a convex part deform | transforms so that it may protrude to an inner peripheral side. The inner peripheral side (front end side) of the outer diameter-reduced outer surface of the insulator is a leg long part, and is a part where more thermal expansion occurs because it is exposed to combustion gas and becomes hot. For this reason, when the site | part which deform | transformed to the inner peripheral side protrudes, possibility that the leg long part outer surface of an insulator will be pressed and damaged by thermal expansion etc. will become high. Therefore, it can prevent more reliably that an insulator is damaged by preventing that a convex part deform | transforms so that it may protrude to an inner peripheral side.

  Further, the spark plug of the present invention is a cylindrical body having an axial hole extending in the axial direction, the insulator having a reduced diameter outer surface on the outer peripheral surface, the outer diameter of which decreases from the rear end side toward the front end side, A cylindrical metal shell extending in the axial direction and having a through-hole into which the insulator is inserted; and a center electrode held on the tip side of the insulator so that a tip portion protrudes from the insulator. In the spark plug, the metal shell has an opposing surface that faces the reduced diameter outer surface in the axial direction on an inner peripheral surface, and at least one contact portion that is provided on the opposing surface and continues in an annular shape. The reduced diameter outer surface and the contact portion are in direct contact, and a gap is formed between the reduced diameter outer surface and the facing surface on at least one of the inner peripheral side and the outer peripheral side from the contact portion. Features.

  In the spark plug of the present invention configured as described above, the reduced diameter outer surface of the insulator and the facing surface of the metal shell are in direct contact with each other at the contact portion, and the reduced diameter outer surface is at least one of the inner peripheral side and the outer peripheral side from the contact portion. A gap is formed between the surface and the opposite surface. In this way, the outer diameter-reducing surface and the opposing surface are not in contact with each other on the entire opposing surface, but a gap is formed between the outer diameter-reducing surface and the opposing surface on at least one of the inner peripheral side and the outer peripheral side from the contact portion. The configuration is as follows. This makes it possible to increase the surface pressure of the contact portion and achieve high airtightness without using plate packing, as compared with the case where the outer surface of the reduced diameter and the opposing surface are in contact with the entire opposing surface. Can do.

  The gap is preferably formed on both the inner peripheral side and the outer peripheral side from the contact portion. Thereby, it can prevent that a contact part presses the side surface of an insulator and damages an insulator.

  In this case, it is more preferable that the gap on the inner peripheral side from the contact portion is wider than the gap on the outer peripheral side from the contact portion. The inner peripheral side (front end side) of the outer diameter-reduced outer surface of the insulator is a leg long part, and is a part where more thermal expansion occurs because it is exposed to combustion gas and becomes hot. For this reason, the possibility that the insulator is damaged can be further reduced by adopting a configuration in which the pressing force is hardly applied from the contact portion to the leg portion on the inner peripheral side.

  The contact part previously forms an annular continuous convex portion on the opposite surface of the metal shell, presses the insulator and the metal shell in the axial direction and applies a caulking load, and the rear end of the metal shell is in the radial direction. It can be formed by a method of deforming the convex portion by a pressing force when the insulator and the metal shell are fixed by caulking inward.

  There are a plurality of the contact portions, and the contact portions include a first contact portion provided on the radially inner side of the opposing surface, and a second contact portion provided on the radially outer side than the first contact portion. It can be set as the structure which has at least. Thus, airtightness further improves by having a plurality of contact parts. Further, the number of contact portions is not limited to two, and may be three or more.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent that a crack arises in an insulator in the middle of manufacture or when attaching and using to an internal combustion engine.

The figure which shows the whole schematic structure of the spark plug which concerns on one Embodiment of this invention. The figure which expands and shows the principal part structure of the spark plug of embodiment. The figure which expands and shows the principal part structure in the middle of manufacture of embodiment spark plug. The figure which expands the principal part structure of the spark plug of embodiment, and shows a manufacturing process. The figure which expands and shows the principal part structure of the spark plug of embodiment. The figure which expands and shows the principal part structure of the spark plug which concerns on the modification of a convex part. The figure which expands and shows the principal part structure of the spark plug which concerns on the other modification of a convex part. The figure which expands and shows the principal part structure of the spark plug which concerns on the further another modification of a convex part.

  Hereinafter, details of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an overall schematic configuration of a spark plug 100 according to an embodiment of the present invention, and FIG. 2 is an enlarged diagram illustrating a main configuration of the spark plug 100. In the following description, the axis O direction of the spark plug 100 is the vertical direction in the drawing, 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 includes a cylindrical metal shell 50 that is made of a metal such as low carbon steel and extends in the direction of the axis O. A cylindrical insulator (insulator) 10 is supported on the inner side of the metal shell 50, which is made of a ceramic sintered body such as alumina and has a tip portion 11 protruding from the end surface of the metal shell 50. Yes.

  The insulator 10 is a cylindrical insulating member formed by firing alumina or the like and having an axial hole 12 in the direction of the axis O. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 having an outer diameter smaller than that of the flange portion 19 is formed on the rear end side. Further, a distal end side body portion 17 having an outer diameter smaller than that of the flange portion 19 is formed on the distal end side from the flange portion 19, and an outer diameter smaller than that of the distal end side body portion 17 is formed further on the distal end side of the distal end side body portion 17. A long leg portion 13 is formed. A step portion 15 is formed between the front end side body portion 17 and the leg long portion 13, and this step portion 15 has a reduced diameter outer surface 14 that is reduced in diameter from the rear end side toward the front end side. ing. The long leg portion 13 is reduced in diameter toward the distal end side.

  In the shaft hole 12 of the insulator 10, the center electrode 20 is disposed so that the tip 22 protrudes from the end surface of the insulator 10. The center electrode 20 has a core made of copper or a copper alloy for promoting heat dissipation at the center of an electrode base material made of a nickel-based alloy such as Inconel 600 (trade name) or Inconel 601 (trade name). This is a rod-shaped electrode in which the material 23 is embedded.

  The center electrode 20 is held in the shaft hole 12 at the portion where the leg portion 13 of the insulator 10 is formed. The center electrode 20 is connected to the connecting terminal 40 held in the shaft hole 12 in the portion where the rear end side body portion 18 is formed via the seal body 4 and the resistor 3 provided in the shaft hole 12. Is electrically connected. The rear end portion 41 of the connection terminal 40 is exposed from the rear end of the insulator 10, and a high voltage cable (not shown) is connected to the rear end portion 41 via a plug cap (not shown). A voltage is applied.

  The metal shell 50 holds the insulator 10 so as to surround the flange portion 19, the distal end side trunk portion 17, and the leg length portion 13 from the rear end side barrel portion 18 in the vicinity of the flange portion 19 of the insulator 10. The metal shell 50 is formed of a low carbon steel material, and includes a tool engaging portion 51 for engaging a tool such as a hexagon wrench, and a screw portion 52 for screwing into an engine head provided at the upper part of the internal combustion engine. ing. On the rear end side of the tool engaging portion 51, a caulking portion 53 for fixing the insulator 10 and the metal shell 50 by bending toward the inner peripheral side is formed. On the rear end side of the screw portion 52, a seat portion 54 formed in a bowl shape is formed. Further, a compression deformation portion 55 is formed between the seat portion 54 and the tool engagement portion 51.

  On the inner peripheral side of the screw portion 52, a shelf 56 that projects toward the inner peripheral side is formed so as to be positioned on the front end side of the step portion 15 of the insulator 10, and the rear end of the shelf 56. A part of the side surface is a facing surface 57 that faces the reduced diameter outer surface 14 of the insulator 10 in the direction of the axis O. As shown in FIG. 2, the opposing surface 57 is formed with at least one contact portion 58 that protrudes from the opposing surface 57 and continues in an annular shape that directly contacts the reduced diameter outer surface 14 of the insulator 10. In the present embodiment, an outer peripheral side gap 80 is formed between the opposing surface 57 and the reduced diameter outer surface 14 on the outer peripheral side of the contact portion 58, and the opposing surface 57 is provided on the inner peripheral side of the contact portion 58. An inner circumferential gap 81 is formed between the outer circumferential surface 14 and the reduced diameter outer surface 14. Note that it is sufficient that at least one of the outer peripheral side gap 80 and the inner peripheral side gap 81 is formed.

  In this way, the opposing surface 57 and the reduced diameter outer surface 14 do not contact with each other over the entire opposing surface, but contact with the reduced diameter outer surface 14 only at a part of the contact portions 58, thereby reducing the surface pressure of the contacted portion. The required airtightness can be ensured without using plate packing. In the present embodiment, the outer peripheral side gap 80 and the inner peripheral side gap 81 are formed on both the outer peripheral side and the inner peripheral side of the contact part 58, so that when the thermal expansion or the like occurs, the contact part 58 is It is possible to prevent the side surface of the insulator 10 from being pressed and damaged.

  Furthermore, in the present embodiment, the inner circumferential side gap 81 is wider than the outer circumferential side gap 80. Here, the inner peripheral side (front end side) of the insulator 10 from the reduced diameter outer surface 14 is a leg long portion 13 and is exposed to the combustion gas, resulting in a high temperature. is there. For this reason, the possibility that the insulator 10 is damaged can be further reduced by adopting a configuration in which the pressing force is hardly applied to the inner leg side long portion 13.

  As shown in FIG. 1, annular ring members 6 and 7 are disposed between the tool engaging portion 51 of the metal shell 50 and the rear end side body portion 18 of the insulator 10. The talc (talc) 9 powder is filled between the members 6 and 7. At the time of manufacturing the spark plug 100, by applying a caulking load and caulking the caulking portion 53 on the rear end side of the tool engaging portion 51, the insulator 10 is brought into the metal shell 50 via the ring members 6, 7 and the talc 9. Is pressed toward the tip side. As a result, the compression deformation portion 55 is deformed, and the step portion 15 between the front end side body portion 17 and the leg length portion 13 of the insulator 10 is supported on the shelf portion 56 formed on the inner periphery of the metal shell 50. The metal shell 50 and the insulator 10 are integrated. A gasket 5 is inserted between the seat portion 54 and the screw portion 52 to prevent gas escape from the combustion chamber.

  The ground electrode 30 is fixed to the front end of the metal shell 50 by welding. The ground electrode 30 is configured by the above-described Inconel 600 (trade name), Inconel 601 (trade name), or the like. The ground electrode 30 has a substantially rectangular cross section perpendicular to the longitudinal direction of the ground electrode 30 and has a bent rectangular bar-like outer shape. The base 32 on the base end side of the square bar shape is welded to the front end surface of the metal shell 50 on the front end side in the axial direction. On the other hand, the tip 31 of the ground electrode 30 opposite to the base 32 is bent so as to face the tip 22 of the center electrode 20. A spark discharge gap is formed between the tip 22 of the center electrode 20 and the portion facing the tip 31 of the ground electrode 30.

  Next, a method for manufacturing the spark plug 100 will be described with reference to FIG.

  First, the insulator 10 provided with the center electrode 20 and the connection terminals is manufactured, and the metal material is subjected to cold forging or the like. As shown in FIG. The metal shell 50 extending to the side is manufactured.

  Next, the rear end side of the shelf portion 56 is processed by cutting or the like, and as shown in FIG. 4B, the reduced diameter inner peripheral surface including the opposed surface 57 on the rear end side of the shelf portion 56, and the opposed surface 57 A convex portion 59 protruding from is formed. The convex portion 59 is later pressed and deformed to become a contact portion 58. Further, as shown in FIG. 5, the convex portion 59 is formed in an annular shape over the entire circumference of the facing surface 57.

  Next, the insulator 10 is inserted from the rear end side of the metal shell 50, and as shown in FIG. 4C, the convex portion 59 and the reduced diameter outer surface 14 of the insulator 10 are brought into contact with each other. In this case, as shown in FIG. 3, the convex portion 59 is a portion of the facing surface 57 (see FIG. 3) that faces the reduced diameter outer surface 14 of the insulator 10 when the insulator 10 is inserted from the rear end side of the metal shell 50. 3 (between the middle dotted line and the dotted line), the apex 60 of the convex portion 59 (the contact position with the reduced diameter outer surface 14) is disposed.

  In the present embodiment, in the region where the reduced diameter outer surface 14 and the facing surface 57 are opposed (between the dotted line and the dotted line in FIG. 3), the contact between the apex 60 of the convex portion 59 and the reduced diameter outer surface 14. The position is set to be on the outer peripheral side from the center of the region. That is, the relationship between the distance D1 from the outer peripheral end of the region to the contact position and the distance D2 from the inner peripheral end of the region to the contact position is set so that D2> D1. Has been.

  Accordingly, when the convex portion 59 is pressed and deformed, the convex portion 59 can be more reliably prevented from protruding and deforming, and the protruding portion presses the insulator 10 to insulate. It can prevent more reliably that the insulator 10 is damaged. As described above, the inner peripheral side (front end side) of the insulator 10 from the outer diameter 14 of the reduced diameter is the long leg portion 13 and is exposed to the combustion gas, resulting in a high temperature, resulting in more thermal expansion. It is a part to do. For this reason, the possibility that the insulator 10 is damaged can be further reduced by adopting a configuration in which the pressing force is hardly applied to the inner leg side long portion 13.

  Next, the ring member 7, talc (talc) 9 and ring member 6 shown in FIG. 1 are arranged between the metal shell 50 and the insulator 10, and the caulking load 53 is applied to fold the caulking portion 53 inward. In addition, the metal shell 50 and the insulator 10 are pressed and caulked in the axial direction, and the convex portion 59 is deformed to form the contact portion 58 as shown in FIG. At this time, the compression deformation portion 55 is deformed, and the insulator 10 is moved to the front end side in the axial direction within the metal shell 50.

  As described above, the spark plug 100 is manufactured without using the plate packing. In this case, airtightness can be ensured without using plate packing by forming a convex portion 59 projecting from the facing surface 57 and pressing and deforming the convex portion 59. That is, the surface pressure of the abutting portion can be increased as compared with the case where the opposing surface 57 and the reduced diameter outer surface 14 are in direct contact with each other on the entire opposing surface without forming the convex portion 59. High hermeticity can be obtained without using.

  Further, the convex portion 59 formed on the facing surface 57 is deformed at that position when pressed, and is not displaced by a pressing force unlike a plate packing which is a separate member. It is possible to prevent the insulator 10 from being damaged by being deformed so as to protrude from the portion of the surface 57 facing the reduced diameter outer surface 14 to the outer peripheral side or the inner peripheral side. Further, when the insulator 10 and the metal shell 50 are pressed in the axial direction and a caulking load is applied, the corners of the reduced diameter outer surface 14 of the insulator 10 do not come into contact with the metal shell 50, so stress is applied to the corners. It is possible to prevent the insulator 10 from cracking without being hung. Further, since the convex portion 59 is not deformed so as to protrude to the outer peripheral side or the inner peripheral side, even when heat is applied and thermal expansion occurs when the spark plug 100 is attached to the internal combustion engine, the protrusion 59 also protrudes. It can prevent that the part which pressed the insulator 10 and the insulator 10 cracks.

  Further, in the present embodiment, in the step of forming the annular convex portion 59, the vertex 60 of the convex portion 59 is annular so that it is located on the outer peripheral side from the center of the portion of the facing surface 57 that faces the reduced diameter outer surface 14. The convex part 59 is formed. Thereby, it can prevent more reliably that the convex part 59 deform | transforms so that it may protrude to an inner peripheral side. The inner peripheral side (front end side) of the insulator 10 from the reduced diameter outer surface 14 is a leg long portion 13 and is a portion where thermal expansion occurs more because it is exposed to the combustion gas and becomes hot. For this reason, when the site | part which deform | transformed to the inner peripheral side protrudes, possibility that the part which protruded will press and damage the outer surface of the leg long part 13 of the insulator 10 by thermal expansion etc. will become high. Therefore, by preventing the convex portion 59 from being deformed so as to protrude toward the inner peripheral side, the insulator 10 can be more reliably prevented from being damaged.

  In addition, the convex part 59 formed in the opposing surface 57 of the metal shell 50 is not limited to the triangular shape shown in FIG. For example, as shown in FIG. 6, the cross-sectional shape may be a trapezoidal convex portion 59, and as shown in FIG. 7, the cross-sectional shape may be an arc-shaped convex portion 59. Moreover, the convex part 59 formed in the opposing surface 57 of the metal shell 50 is not limited to one, and a plurality of convex parts 59 may be provided. For example, in the example shown in FIG. 8, the first convex portion 59a provided on the radially inner side of the facing surface 57 and the second convex portion 59b provided on the radially outer side of the first convex portion 59a are formed. Has been. In this case, the finished spark plug has a structure having a first contact portion 58a corresponding to the first protrusion 59a and a second contact portion 58b corresponding to the second protrusion 59b. By adopting such a structure, the airtightness can be further improved. In addition, the number of the convex parts 59 and the contact parts 58 is good also as three or more.

  Further, in this embodiment, the convex portion 59 is deformed when a caulking load is applied in the caulking process. However, the present invention is not limited to this, and when a preload is applied when the insulator 10 is inserted before the caulking process. The convex portion 59 may be deformed.

  As mentioned above, although this invention was described about embodiment, this invention is not limited to embodiment, Of course, various deformation | transformation are possible.

  DESCRIPTION OF SYMBOLS 10 ... Insulator, 14 ... Outer diameter outer surface, 20 ... Center electrode, 30 ... Ground electrode, 50 ... Metal fitting, 57 ... Opposite surface, 58 ... Contact part, 59 ... Convex part, 100 ……Spark plug.

Claims (7)

An insulator having an axial hole extending in the axial direction, an outer surface having a reduced-diameter outer surface whose outer diameter decreases from the rear end side toward the front end side;
A cylindrical metal shell extending in the axial direction and having a through-hole into which the insulator is inserted,
A center electrode held on the tip side of the insulator so that a tip portion protrudes from the insulator;
In a method for manufacturing a spark plug comprising:
Forming an annular convex portion protruding from the facing surface on the facing surface facing the reduced diameter outer surface in the axial direction when the insulator is inserted among the inner peripheral surface of the metal shell;
Inserting the insulator from the rear end side of the metal shell, and abutting the reduced diameter outer surface with the convex portion;
A step of pressing the insulator and the metal shell in the axial direction to deform the convex portion. A method of manufacturing a spark plug, comprising: In the step of forming the convex portion, the annular convex portion is formed such that the apex of the convex portion is positioned on the outer peripheral side from the center of the portion facing the reduced diameter outer surface of the opposing surface. The method for producing a spark plug according to claim 1. An insulator having an axial hole extending in the axial direction, an outer surface having a reduced-diameter outer surface whose outer diameter decreases from the rear end side toward the front end side;
A cylindrical metal shell extending in the axial direction and having a through-hole into which the insulator is inserted,
A center electrode held on the tip side of the insulator so that a tip portion protrudes from the insulator;
A spark plug comprising:
The metal shell has an opposing surface that faces the reduced diameter outer surface in the axial direction on an inner peripheral surface, and at least one contact portion that is provided on the opposing surface and continues in an annular shape, and the reduced diameter outer surface; The spark plug is characterized in that the contact portion is in direct contact, and a gap is formed between the reduced-diameter outer surface and the facing surface on at least one of the inner peripheral side and the outer peripheral side from the contact portion. The spark plug according to claim 3, wherein the gap is formed on both the inner peripheral side and the outer peripheral side from the contact portion. The spark plug according to claim 4, wherein the gap on the inner peripheral side from the contact portion is wider than the gap on the outer peripheral side from the contact portion. The spark plug according to any one of claims 3 to 5, wherein the contact part is an annular continuous convex part. A plurality of the contact portions, wherein the contact portions are a first contact portion provided radially inward of the facing surface, and a second contact portion provided radially outward of the first contact portion. The spark plug according to any one of claims 3 to 6, characterized by comprising:

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