JP2018152310A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug which suppresses discharge through a surface of an insulator and suppresses temperature of the insulator from becoming excessively high.SOLUTION: An insulator of a spark plug has a stepped portion whose outer diameter decreases toward the distal end side. A main fitting of the spark plug has a supporting portion that is a portion whose inner diameter decreases when tracing toward the distal end side, and that directly or indirectly supports the stepped portion as well. The insulator includes: a first portion which is a portion on the inner peripheral side; a second portion which is a portion on the outer peripheral side; and a third portion which is a portion between the first portion and the second portion and is recessed toward the rear end side from either the tip of the first portion and the tip of the second portion. In the second portion, at least a part of a portion closer to the tip side than the stepped portion is directly or indirectly connected to the main fitting.SELECTED DRAWING: Figure 1

Description

  The present specification relates to a spark plug.

  Conventionally, spark plugs have been used in internal combustion engines. Examples of the spark plug include a cylindrical insulator having an axial hole extending in the direction of the axis, a metal shell disposed on the outer periphery of the insulator, a center electrode disposed in the shaft hole of the insulator, and a metal shell. There is used a spark plug including a ground electrode connected to the.

JP-A-9-219273

  During operation of the internal combustion engine, the temperature of the insulator of the spark plug rises due to heat received from the combustion gas. When the amount of heat transferred from the combustion gas to the insulator is small, such as when the output of the internal combustion engine is small, the temperature of the insulator continues to be low. When the temperature of the insulator is low, carbon can be deposited on the surface of the insulator. Due to such carbon, discharge can occur along unintended paths through the surface of the insulator. Here, if the spark plug is configured so that the heat value becomes small, the burning of the carbon can be promoted by the temperature rise of the insulator, so that the discharge through the surface of the insulator can be suppressed. However, if the amount of heat transferred from the combustion gas to the insulator increases due to an increase in the output of the internal combustion engine or the like, erroneous ignition such as pre-ignition may occur due to abnormal overheating of the insulator. It has not been easy to achieve both suppression of discharge passing through the surface of the insulator and suppression of an excessive increase in the temperature of the insulator.

  This specification discloses the technique which can suppress the discharge which passes along the surface of an insulator and can suppress that the temperature of an insulator becomes high too much.

  This specification discloses the following application examples, for example.

[Application Example 1]
A cylindrical insulator having an axial hole extending from the front end side to the rear end side along the direction of the axis, and a step portion whose outer diameter is reduced toward the front end side,
A cylindrical metal shell having a support portion that is disposed on the outer periphery of the insulator and has a support portion that directly or indirectly supports the stepped portion as well as a portion having a smaller inner diameter when traced toward the tip side.
A central electrode disposed in the axial hole of the insulator;
A ground electrode connected to the metal shell and facing the tip of the center electrode;
A spark plug comprising:
The insulator includes a first portion that is an inner peripheral portion, a second portion that is an outer peripheral portion, a tip of the first portion and the first portion between the first portion and the second portion. A third portion recessed to the rear end side from any of the two portions of the tip, and
Of the second part, at least a part of the tip side of the step part is directly or indirectly connected to the metal shell,
Spark plug.

  According to this configuration, since the path from the center electrode to the metal shell through the surface of the insulator becomes long, discharge through the surface of the insulator can be suppressed. In addition, at least a part of the portion of the second portion of the insulator that is closer to the tip than the stepped portion is directly or indirectly connected to the metal shell. Therefore, the second portion of the insulator can easily transfer heat to the metal shell. Moreover, it is suppressed that a combustion gas enters between an insulator and a metal shell. As described above, it is possible to suppress the temperature of the tip portion of the insulator from becoming excessively high. Thereby, misfires, such as preignition, can be controlled.

[Application Example 2]
The spark plug according to application example 1,
The metal shell includes a protruding portion that protrudes toward the inner peripheral side at the distal end side of the second portion of the insulator,
Spark plug.

  According to this configuration, the combustion gas is suppressed from coming into contact with the second portion of the insulator, and the combustion gas is suppressed from entering between the insulator and the metal shell. Therefore, it can suppress that the temperature of the front-end | tip part of an insulator becomes high too much.

[Application Example 3]
The spark plug according to application example 2,
The protruding portion extends to the inner peripheral side from the tip surface of the second portion of the insulator,
Spark plug.

  According to this configuration, the combustion gas is suppressed from coming into contact with the second portion of the insulator, and the combustion gas is suppressed from entering between the insulator and the metal shell. Therefore, it can suppress that the temperature of the front-end | tip part of an insulator becomes high too much.

[Application Example 4]
The spark plug according to any one of Application Examples 1 to 3,
The first portion of the insulator extends from the rear end side to the front end side from the front end of the metal shell.
Spark plug.

  According to this configuration, since the discharge path passing through the surface of the insulator becomes long, the discharge passing through the surface of the insulator can be suppressed.

[Application Example 5]
The spark plug according to any one of Application Examples 1 to 4,
The center electrode extends from the rear end side to the front end side from the front end of the first portion of the insulator.
Spark plug.

  Even in this configuration, the discharge passing through the surface of the tip of the insulator can be suppressed.

[Application Example 6]
The spark plug according to any one of Application Examples 1 to 5,
The second portion of the insulator includes a portion in which the inner diameter of the inner peripheral surface on the third portion side becomes smaller toward the tip side.
Spark plug.

  According to this configuration, since the combustion gas hardly enters between the first portion and the second portion of the insulator, it is possible to suppress the temperature of the tip portion of the insulator from becoming excessively high.

  The technology disclosed in the present specification can be realized in various modes. For example, a spark plug, an ignition device using the spark plug, an internal combustion engine equipped with the spark plug, and the spark plug are provided. This can be realized in an aspect of an internal combustion engine or the like equipped with the used ignition device.

It is sectional drawing of the spark plug 100 as one Embodiment. FIG. 2 is a cross-sectional view and an enlarged view of a tip portion of a spark plug 100. It is sectional drawing which shows 2nd Embodiment of a spark plug. It is sectional drawing which shows 3rd Embodiment of a spark plug. It is sectional drawing which shows 4th Embodiment of a spark plug. It is sectional drawing which shows 5th Embodiment of a spark plug. It is sectional drawing which shows 6th Embodiment of a spark plug.

A. First embodiment:
A-1. Spark plug 100 configuration:
FIG. 1 is a cross-sectional view of a spark plug 100 as one embodiment. In the drawing, a center axis CL (also referred to as “axis line CL”) of the spark plug 100 and a flat cross section including the center axis CL of the spark plug 100 are shown. Hereinafter, the direction parallel to the central axis CL is also referred to as “direction of the axis CL”, or simply “axis direction” or “front-rear direction”. The radial direction of the circle centered on the axis CL is also referred to as “radial direction”. The radial direction is a direction perpendicular to the axis CL. The circumferential direction of the circle centered on the axis CL is also referred to as “circumferential direction”. Of the directions parallel to the central axis CL, the lower direction in FIG. 1 is referred to as the front end direction Df or the front direction Df, and the upper direction is also referred to as the rear end direction Dfr or the rear direction Dfr. The tip direction Df is a direction from the terminal fitting 40 described later toward the center electrode 20. 1 is referred to as the front end side of the spark plug 100, and the rear end direction Dfr side in FIG. 1 is referred to as the rear end side of the spark plug 100.

  The spark plug 100 includes a cylindrical insulator 10 having a through hole 12 (also referred to as an axial hole 12) extending along the axis CL, a center electrode 20 held on the tip side of the through hole 12, and the through hole 12. The terminal metal fitting 40 held on the rear end side, the resistor 73 disposed between the center electrode 20 and the terminal metal fitting 40 in the through-hole 12, and the center electrode 20 and the resistor 73 are brought into contact with these. A conductive first seal portion 72 that electrically connects the members 20 and 73, and a conductive second seal that contacts the resistor 73 and the terminal fitting 40 to electrically connect the members 73 and 40. Part 74, cylindrical metal shell 50 fixed to the outer peripheral side of insulator 10, one end is joined to front end surface 55 of metal shell 50, and the other end faces center electrode 20 through gap g. A ground electrode 30 arranged in a manner .

  A large-diameter portion 14 having the largest outer diameter is formed at the approximate center in the axial direction of the insulator 10. A rear end side body portion 13 is formed on the rear end side from the large diameter portion 14. A front end side body portion 15 having an outer diameter smaller than that of the rear end side body portion 13 is formed on the front end side of the large diameter portion 14. A further reduced diameter portion 16 and a leg portion 19 are formed in this order toward the distal end side further on the distal end side than the distal end side body portion 15. The outer diameter of the reduced outer diameter portion 16 gradually decreases toward the front direction Df. A groove 390 that is recessed toward the rear direction Dfr is formed on the distal end surface of the leg portion 19 (details will be described later). In the vicinity of the reduced outer diameter portion 16 (in the example of FIG. 1, the front end side body portion 15), a reduced inner diameter portion 11 is formed in which the inner diameter gradually decreases in the front direction Df. The insulator 10 is preferably formed in consideration of mechanical strength, thermal strength, and electrical strength. For example, the insulator 10 is formed by firing alumina (other insulating materials can also be used). is there).

  The center electrode 20 is a metal member, and is disposed at the end on the front direction Df side in the through hole 12 of the insulator 10. The center electrode 20 has a substantially cylindrical rod portion 28 and a first tip 29 joined to the tip of the rod portion 28 (for example, laser welding). The rod portion 28 includes a head portion 24 that is a portion on the rear direction Dfr side, and a shaft portion 27 that is connected to the front direction Df side of the head portion 24. The shaft portion 27 extends in the forward direction Df parallel to the axis line CL. A portion on the front direction Df side of the head portion 24 forms a flange portion 23 having an outer diameter larger than the outer diameter of the shaft portion 27. The surface on the front direction Df side of the flange portion 23 is supported by the reduced inner diameter portion 11 of the insulator 10. The shaft portion 27 is connected to the front direction Df side of the flange portion 23. The first chip 29 is joined to the tip of the shaft portion 27.

  The rod portion 28 includes an outer layer 21 and a core portion 22 disposed on the inner peripheral side of the outer layer 21. The outer layer 21 is formed of a material (for example, an alloy containing nickel as a main component) that has better oxidation resistance than the core portion 22. Here, the main component means a component having the highest content rate (weight percent (wt%)). The core portion 22 is formed of a material having higher thermal conductivity than the outer layer 21 (for example, pure copper, an alloy containing copper as a main component, etc.). The first chip 29 is formed using a material (for example, a noble metal such as iridium (Ir) or platinum (Pt)) that is more durable against discharge than the shaft portion 27. A part of the center electrode 20 on the tip side including the first tip 29 is exposed from the shaft hole 12 of the insulator 10 to the front direction Df side. The core portion 22 may be omitted. Further, the first chip 29 may be omitted.

  The terminal fitting 40 is a rod-shaped member extending in parallel with the axis CL. The terminal fitting 40 is formed using a conductive material (for example, a metal containing iron as a main component). The terminal fitting 40 includes a cap mounting portion 49, a flange portion 48, and a shaft portion 41, which are arranged in order in the front direction Df. The shaft portion 41 is inserted into a portion on the rear direction Dfr side of the shaft hole 12 of the insulator 10. The cap mounting portion 49 is exposed outside the shaft hole 12 on the rear end side of the insulator 10.

  In the shaft hole 12 of the insulator 10, a resistor 73 for suppressing electrical noise is disposed between the terminal fitting 40 and the center electrode 20. The resistor 73 is formed using a conductive material (for example, a mixture of glass, carbon particles, and ceramic particles). A first seal portion 72 is disposed between the resistor 73 and the center electrode 20, and a second seal portion 74 is disposed between the resistor 73 and the terminal fitting 40. These seal portions 72 and 74 are formed using a conductive material (for example, a mixture of metal particles and the same glass as that included in the material of the resistor 73). The center electrode 20 is electrically connected to the terminal fitting 40 by the first seal portion 72, the resistor 73, and the second seal portion 74.

  The metal shell 50 is a cylindrical member having a through hole 59 extending along the axis CL. The insulator 10 is inserted into the through hole 59 of the metal shell 50, and the metal shell 50 is fixed to the outer periphery of the insulator 10. The metal shell 50 is formed using a conductive material (for example, a metal such as carbon steel containing iron as a main component). A part of the insulator 10 on the rear direction Dfr side is exposed outside the through hole 59.

  The metal shell 50 has a tool engaging portion 51 and a front end side body portion 52. The tool engaging portion 51 is a portion into which a spark plug wrench (not shown) is fitted. The front end side body portion 52 is a portion including the front end surface 55 of the metal shell 50. On the outer peripheral surface of the front end side body portion 52, a screw portion 57 for screwing into a mounting hole of an internal combustion engine (for example, a gasoline engine) is formed. The screw part 57 is a part in which a male screw extending in the direction of the axis CL is formed.

  On the outer peripheral surface between the tool engaging portion 51 and the front end side body portion 52 of the metal shell 50, a flange-shaped middle body portion 54 that projects outward in the radial direction is formed. The outer diameter of the middle body portion 54 is larger than the maximum outer diameter of the screw portion 57 (that is, the outer diameter of the top of the screw thread). A surface 300 on the front direction Df side of the middle body portion 54 is a seating surface that forms a seal with a mounting portion (for example, an engine head) that is a portion that forms a mounting hole in the internal combustion engine.

  An annular gasket 90 is disposed between the screw portion 57 of the front end side body portion 52 and the seat surface 300 of the middle body portion 54. The gasket 90 is formed, for example, by bending a metal plate member. The gasket 90 is crushed and deformed when the spark plug 100 is attached to the internal combustion engine. Due to the deformation of the gasket 90, a gap between the seat surface 300 of the inner body portion 54 of the spark plug 100 and a mounting portion (for example, engine head) of an internal combustion engine (not shown) is sealed, and leakage of combustion gas is suppressed. The The gasket 90 may be omitted. In this case, the seat surface 300 of the middle body portion 54 directly contacts the attachment portion of the internal combustion engine, thereby sealing a gap between the seat surface 300 and the attachment portion of the internal combustion engine.

  The front end side body portion 52 of the metal shell 50 is formed with a reduced inner diameter portion 56 whose inner diameter gradually decreases toward the front end side. The front end side packing 8 is sandwiched between the reduced inner diameter portion 56 of the metal shell 50 and the reduced outer diameter portion 16 of the insulator 10. In this embodiment, the front end side packing 8 is, for example, a plate ring made of iron (other materials (for example, metal materials such as copper) can also be used).

  A caulking portion 53 that is a thin portion is formed on the rear end side of the metal fitting 50 from the tool engaging portion 51. Further, a buckled portion 58 that is a thin portion is formed between the middle barrel portion 54 and the tool engaging portion 51. Annular ring members 61 and 62 are inserted between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the rear end side body portion 13 of the insulator 10. ing. Further, a talc 70 powder is filled between the ring members 61 and 62. In the manufacturing process of the spark plug 100, when the crimping portion 53 is bent inward and crimped, the buckling portion 58 is deformed outward (buckling) with the addition of the compressive force. And the insulator 10 are fixed. The talc 70 is compressed during the caulking process, and the airtightness between the metal shell 50 and the insulator 10 is improved. The packing 8 is pressed between the reduced outer diameter portion 16 of the insulator 10 and the reduced inner diameter portion 56 of the metal shell 50, and seals between the metal shell 50 and the insulator 10.

  Thus, the reduced outer diameter portion 16 of the insulator 10 forms a step portion whose outer diameter decreases toward the front direction Df side. The reduced inner diameter portion 56 of the metal shell 50 is a portion whose inner diameter decreases when the inner peripheral surface is traced toward the front direction Df side, and the reduced outer diameter portion 16 of the insulator 10 is replaced with the front end side packing 8. The support part supported indirectly via is formed.

  The ground electrode 30 is a metal member and is composed of a rod-shaped main body portion 37. One end portion 33 (also referred to as a base end portion 33) of the main body portion 37 is joined to the distal end surface 55 of the metal shell 50 (for example, resistance welding). The main body portion 37 extends from the base end portion 33 joined to the metal shell 50 in the distal direction Df, bends toward the central axis CL, and reaches the distal end portion 34. The tip 34 of the ground electrode 30 and the first tip 29 of the center electrode 20 form a gap g. That is, the tip 34 of the ground electrode 30 is disposed on the front electrode Df side of the first tip 29 of the center electrode 20 and faces the first tip 29 via the gap g.

  The main body portion 37 includes an outer layer 31 and an inner layer 32 disposed on the inner peripheral side of the outer layer 31. The outer layer 31 is made of a material (for example, an alloy containing nickel as a main component) that has better oxidation resistance than the inner layer 32. The inner layer 32 is formed of a material having higher thermal conductivity than the outer layer 31 (for example, pure copper, an alloy containing copper as a main component, etc.). The inner layer 32 may be omitted.

  Alternatively, the second tip may be joined to the rear direction Dfr side of the tip 34 (for example, laser welding), and the second tip and the first tip 29 of the center electrode 20 may form a gap g. The second chip is preferably formed using a material (for example, a noble metal such as iridium (Ir) or platinum (Pt)) that is more durable against discharge than the main body portion 37.

A-2. About the tip of the spark plug 100:
FIG. 2A shows a cross section of the tip of the spark plug 100. This cross section shows a part of a flat cross section including the axis CL. In the drawing, illustration of the internal configuration of the center electrode 20 and the internal configuration of the ground electrode 30 is omitted.

  As shown in FIG. 2A, in this embodiment, the insulator 10 includes a first portion 310 that is an inner peripheral portion, a second portion 320 that is an outer peripheral portion, and a first portion 310. 3rd part 330 which is a part between 2nd part 320 is included. The first portion 310 forms the inner peripheral surface of the shaft hole 12. The shape of the first portion 310 is substantially cylindrical with the axis CL as the center. The center electrode 20 is disposed on the inner peripheral side of the portion of the first portion 310 on the front direction Df side.

  The second portion 320 forms the outer peripheral surface of the insulator 10. The shape of the second portion 320 is a substantially cylindrical shape centering on the axis CL. The outer peripheral surface 323 of the portion of the second portion 320 on the front direction Df side is covered with the inner peripheral surface of the metal shell 50 (in this embodiment, the front end side body portion 52).

  A portion 510 on the front direction Df side of the metal shell 50 in the drawing is a portion of the front end side body portion 52 of the metal shell 50 connected to the front direction Df side of the reduced inner diameter portion 56 (the front portion 510). Called). In addition, a portion 328 on the front direction Df side of the second portion 320 of the insulator 10 is a portion on the front direction Df side of the reduced outer diameter portion 16 in the second portion 320 (referred to as a front portion 328). In the present embodiment, at least a portion of the tip portion 328 of the second portion 320 is directly connected to the metal shell 50 (here, the tip portion 510) (that is, at least a portion of the tip portion 328 is It is in direct contact with the tip 510 of the metal shell 50). Specifically, the insulator 10 is formed such that the outer diameter of the tip portion 328 of the insulator 10 is approximately the same as the inner diameter of the tip portion 510 of the metal shell 50. In this case, due to the manufacturing tolerance of parameters such as the position of the insulator 10 with respect to the metal shell 50, the inner diameter of the tip portion 510 of the metal shell 50, the outer diameter of the tip portion 328 of the insulator 10, etc. At least a part of the ten front portions 328 is in direct contact with the metal shell 50.

  The third portion 330 of the insulator 10 is a portion between the first portion 310 and the second portion 320. In the present embodiment, the third portion 330 is recessed to the rear direction Dfr side from both the tip of the first portion 310 and the tip of the second portion 320. A cylindrical groove 390 that is recessed toward the rear direction Dfr is formed between the first portion 310 and the second portion 320. A front surface Df-side surface 331 (also referred to as a front end surface 331) of the third portion 330 forms a bottom of the groove 390 on the rearward direction Dfr side. In the embodiment of FIG. 2A, the tip surface 331 of the third portion 330 is located on the front direction Df side with respect to the reduced outer diameter portion 16 of the insulator 10.

  A protruding portion 400 that protrudes toward the inner peripheral side is formed at the tip of the metal shell 50. The protruding portion 400 is disposed on the distal end side of the second portion 320 of the insulator 10. The protrusion 400 is an annular part centered on the axis CL, and is provided over the entire circumference in the circumferential direction. Such a protrusion 400 covers the front surface Df-side surface 321 (also referred to as the front end surface 321) of the second portion 320 over the entire circumference in the circumferential direction.

  The spark plug 100 described above has various advantages as described below. When the internal combustion engine equipped with the spark plug 100 is operated, the insulator 10 receives heat from the combustion gas. If the temperature of the insulator 10 becomes excessively high, erroneous ignition such as pre-ignition may occur. As described above, in the present embodiment, at least a part of the tip portion 328 of the second portion 320 of the insulator 10 is directly connected to the metal shell 50 (here, the tip portion 510). Therefore, the second portion 320 (particularly, the tip portion 328) can easily transfer heat to the metal shell 50. As a result, it is possible to suppress an increase in the temperature of the tip portion 328 of the second portion 320 (and hence the temperature of the tip portion of the insulator 10). As a result, misfires such as pre-ignition can be suppressed.

  Further, when at least a part of the tip portion 328 of the second portion 320 of the insulator 10 is directly connected to the metal shell 50, an increase in the gap between the tip portion 328 and the metal shell 50 is suppressed. . Therefore, the combustion gas is prevented from entering the gap between the tip portion 328 of the insulator 10 and the metal shell 50. As a result, it is possible to suppress an increase in the temperature of the tip portion 328 of the insulator 10 (and hence the temperature of the tip portion of the insulator 10). As a result, misfires such as pre-ignition can be suppressed.

  FIG. 2B shows an enlarged view of a portion including the tip side packing 8 in the cross section of FIG. As shown in the drawing, the front end side packing 8 is sandwiched between the reduced inner diameter portion 56 of the metal shell 50 and the reduced outer diameter portion 16 of the insulator 10. In the present embodiment, the tip portion 510 of the metal shell 50 covers the outer peripheral surface 323 of the tip portion 328 of the second portion 320 of the insulator 10. The distance d1 in the drawing is a radial direction perpendicular to the axis CL between the inner peripheral surface 512 of the tip portion 510 of the metal shell 50 and the outer peripheral surface 323 of the tip portion 328 of the second portion 320 of the insulator 10. Is the distance.

  When the distance d <b> 1 is small, the tip portion 328 of the insulator 10 can easily transfer heat to the tip portion 510 of the metal shell 50. Therefore, it is possible to suppress an increase in the temperature of the tip portion 328 (and consequently the temperature of the tip portion of the insulator 10). The distance d1 can vary depending on the position of the front direction Df (that is, the position in the direction parallel to the axis CL). Further, the distance d1 can vary depending on the position in the circumferential direction centered on the axis CL. Here, in order to suppress the temperature rise of the insulator 10, the minimum value of the distance d1 is preferably 0.2 mm or less, and particularly preferably 0.1 mm or less. Here, the tip portion 510 of the metal shell 50 and the tip portion 328 of the insulator 10 may include a portion where the distance d1 exceeds 0.2 mm. In order to further suppress the temperature rise of the insulator 10, the distance d1 (that is, the maximum value of the distance d1) is provided over the entire gap between the tip portion 510 of the metal shell 50 and the tip portion 328 of the insulator 10. ) Is preferably 0.2 mm or less, and particularly preferably 0.1 mm or less. In any case, the distance d1 is zero mm or more.

  In the partial cross section of FIG. 2B, a gap is formed between the outer peripheral surface 323 of the tip portion 328 of the insulator 10 and the inner peripheral surface 512 of the tip portion 510 of the metal shell 50 for explanation. (That is, the distance d1 is larger than zero in the partial cross section of FIG. 2B). However, in the present embodiment, at least a part of the outer peripheral surface 323 of the tip portion 328 of the insulator 10 is in direct contact with the inner peripheral surface 512 of the tip portion 510 of the metal shell 50. This contact portion may be a portion included in the partial cross section shown in FIG. 2 (B), or may be another portion of the spark plug 100 different from the portion shown in FIG. 2 (B). Good.

  Further, the connection portion C1 between the inner peripheral surface of the reduced inner diameter portion 56 of the metal shell 50 and the inner peripheral surface of the tip portion 510 can be rounded. In this case, the boundary between the reduced inner diameter portion 56 and the tip portion 510 may be specified as follows. In the cross section of FIG. 2B, the portion 56 </ b> L closest to the tip portion 510 among the straight portions representing the inner peripheral surface of the reduced inner diameter portion 56, and the innermost reduced portion among the straight portions representing the inner peripheral surface of the tip portion 510. An intersection P1 of two straight lines obtained by extending the portion 52L close to the portion 56 can be adopted as the boundary position. It is preferable that the minimum value of the distance d1 is in the above-described preferable range on the front direction Df side from the intersection P1, and further, the distance d1 (that is, the maximum value of the distance d1) is in the above-described preferable range. It is preferable.

  Further, at least a part of the tip portion 328 which is a portion on the front direction Df side of the reduced outer diameter portion 16 in the second portion 320 of the insulator 10 is directly or indirectly with the metal shell 50 (that is, , Preferably via other members). For example, a member that connects the tip portion 328 and the metal shell 50 may be disposed in at least a part of the gap between the tip portion 328 of the insulator 10 and the metal shell 50 (referred to as a connecting material). As the connecting material, any member that can withstand heat during operation of the internal combustion engine with the spark plug 100 attached and can transfer heat from the tip portion 328 to the metal shell 50 can be employed. For example, cement containing alumina as a main component may be employed (also referred to as alumina cement). In this case, the tip portion 328 is indirectly connected to the metal shell 50 via cement. As the alumina cement, various members containing alumina can be used. For example, a member containing alumina as a main component and silica can be used. As a method of arranging such a connecting material in the gap between the tip portion 328 of the insulator 10 and the metal shell 50, any method can be adopted. For example, a connecting material is applied to at least one of the outer peripheral surface of the tip portion 328 of the insulator 10 and the inner peripheral surface of the metal shell 50 (particularly, the tip portion 510), and then the insulator 10 is attached to the metal shell 50. You may adopt the method of attaching to.

  Note that the connection portion C2 between the outer peripheral surface of the reduced outer diameter portion 16 and the outer peripheral surface of the tip portion 328 of the insulator 10 (FIG. 2B) can be rounded. In this case, the boundary between the reduced outer diameter portion 16 and the tip portion 328 may be specified as follows. In the cross section of FIG. 2B, the portion 16L closest to the tip portion 328 among the straight portions representing the outer peripheral surface of the reduced outer diameter portion 16 and the outermost reduced diameter of the straight portions representing the outer peripheral surface of the tip portion 328. An intersection P2 of two straight lines obtained by extending the portion 328L close to the portion 16 can be adopted as the boundary position. Here, at least a part of the second portion 320 on the front direction Df side from the intersection P2 (that is, the tip portion 328) is connected to the metal shell 50 directly or indirectly. It is preferable.

  In the right part of FIG. 2A, the discharge path Pth is indicated by a bold line. This discharge path Pth is a path when an unintended discharge occurs along the outer surface of the insulator 10 between the metal shell 50 and the center electrode 20 (also referred to as a creeping path Pth). In the present embodiment, the creeping path Pth extends from the metal shell 50 (here, the inner peripheral surface of the protruding portion 400) to the inner peripheral surface 322 of the second portion 320, the distal end surface 331 of the third portion 330, and the first surface. The center electrode 20 is reached through the outer peripheral surface 313 of the portion 310 and the tip surface 311 of the first portion 310. The inner peripheral surface 322 of the second portion 320 is a radially inner surface centering on the central axis CL of the outer surface of the second portion 320, and is a surface on the third portion 330 side. The outer peripheral surface 313 of the first portion 310 is a radially outer surface around the central axis CL of the outer surface of the first portion 310, and is a surface on the third portion 330 side. In the present embodiment, both the outer peripheral surface 313 and the inner peripheral surface 322 are parallel to the axis line CL.

  If the groove 390 is filled and the groove 390 is omitted, the creeping path is shorter than the creeping path Pth in FIG. In the present embodiment, since the groove 390 is formed at the tip of the insulator 10, the creeping path Pth becomes long. Accordingly, unintended discharge passing through the surface of the tip of the insulator 10 can be suppressed. And the appropriate discharge in the gap g between the center electrode 20 and the ground electrode 30 can be accelerated | stimulated.

  In the present embodiment, the center electrode 20 extends from the rear direction Dfr side to the front direction Df side with respect to the front end 319 of the first portion 310 of the insulator 10 (that is, the center electrode 20 has the first portion 310). A portion located on the front direction Df side of the front end 319. Further, a portion on the front direction Df side of the center electrode 20 is exposed on the front direction Df side of the shaft hole 12). If the end of the center electrode 20 on the front direction Df side is located on the rear side Dfr side of the front end 319 of the first portion 310, that is, the entire center electrode 20 is disposed in the shaft hole 12. Assume. In this case, the creeping path Pth includes a portion passing on the inner peripheral surface of the shaft hole 12, and therefore the creeping path Pth becomes longer correspondingly. In the present embodiment, the portion of the center electrode 20 on the front direction Df side is exposed on the front direction Df side of the shaft hole 12. In this case, since the creeping path Pth cannot include a portion passing on the inner peripheral surface of the shaft hole 12, the creeping path Pth is shortened accordingly. As described above, even in a configuration in which the creeping path Pth can be shortened, the creeping path Pth is lengthened by the groove 390, so that unintended discharge passing through the surface of the tip portion of the insulator 10 can be suppressed.

  Further, the heat receiving area Ax is indicated by a thick line on the left side in FIG. A heat receiving area Ax indicates a portion of the outer surface of the insulator 10 that is easily heated by heat received from the combustion gas. Since the surface of the groove 390 is exposed to the combustion gas, the temperature of the portion of the insulator 10 where the groove 390 is formed tends to increase. However, as described above, in the present embodiment, since the tip portion 328 of the second portion 320 of the insulator 10 can easily transfer heat to the metal shell 50, the temperature rise of the second portion 320 is suppressed. . Therefore, the inner peripheral surface 322 of the second portion 320 among the portions forming the groove 390 is excluded from the heat receiving area Ax. As a result, the heat receiving area Ax is configured by the tip surface 311 and the outer peripheral surface 313 of the first portion 310, and the tip surface 331 of the third portion 330. Thus, since the temperature rise of the second portion 320 of the insulator 10 is suppressed, the temperature rise of the insulator 10 can be suppressed.

  In addition, as shown in FIG. 2A, the metal shell 50 includes a protruding portion 400. The protrusion 400 protrudes toward the inner peripheral side on the front direction Df side of the second portion 320 of the insulator 10. Therefore, it is suppressed that combustion gas contacts the front end surface 321 of the second portion 320. Further, the combustion gas is prevented from entering the gap between the insulator 10 and the metal shell 50. Therefore, the temperature rise of the second portion 320 of the insulator 10 (and hence the tip of the insulator 10) can be suppressed.

A-3. About the manufacturing method of the spark plug 100:
As a manufacturing method of the spark plug 100 described above, any method can be adopted. For example, the following manufacturing method can be employed. First, the insulator 10, the terminal fitting 40, the material powder of the resistor 73, the material powder of the seal portions 72 and 74, the center electrode 20, the metal shell 50, and the linear ground electrode 30 are included. Prepare the spark plug 100 parts. The insulator 10 is manufactured, for example, by molding a material powder such as alumina using a molding die and firing the molded member. Here, the groove 390 may be formed by performing processing such as cutting or polishing on the member before firing or the member after firing. Metal members such as the terminal fitting 40, the center electrode 20, and the linear ground electrode 30 are manufactured by a method such as forging or cutting.

  Next, an assembly including the insulator 10, the center electrode 20, and the terminal fitting 40 is produced. For example, the center electrode 20 is inserted from the opening on the rear direction Dfr side of the insulator 10. The center electrode 20 is disposed at a predetermined position in the through hole 12 by being supported by the reduced inner diameter portion 11 of the insulator 10. Next, the material powder of each of the first seal portion 72, the resistor 73, and the second seal portion 74 and the molding of the charged powder material are performed in the order of the members 72, 73, and 74. The powder material is put into the through hole 12 from the opening on the rear direction Dfr side of the insulator 10. Next, the insulator 10 is heated to a predetermined temperature higher than the softening point of the glass component contained in the material powder of the members 72, 73, and 74, and the insulator 10 is heated to the predetermined temperature in the rear direction Dfr side. The shaft portion 41 of the terminal fitting 40 is inserted into the through hole 12 from the opening. As a result, the material powders of the members 72, 73, 74 are compressed and sintered to form the members 72, 73, 74. Then, the terminal fitting 40 is fixed to the insulator 10. Further, the ground electrode 30 is joined to the metal shell 50 (for example, resistance welding).

  Next, the assembly including the insulator 10 is fixed to the metal shell 50. Specifically, the front end side packing 8, the assembly, the ring member 62, the talc 70, and the ring member 61 are inserted into the through hole 59 of the metal shell 50 from the opening on the rear direction Dfr side. The The tip portion 328 of the second portion 320 of the insulator 10 is inserted on the inner peripheral side of the tip portion 510 of the metal shell 50. Then, the insulator 10 is fixed to the metal shell 50 by crimping the caulking portion 53 of the metal shell 50 so as to be bent inward. Then, the distance of the gap g is adjusted by bending the rod-shaped ground electrode 30. Thus, the spark plug 100 is completed.

B. Second embodiment:
FIG. 3A is a cross-sectional view showing a second embodiment of the spark plug. In the drawing, a cross section similar to that of FIG. The difference from the spark plug 100 of FIG. 2A is that in the spark plug 100a of FIG. 3A, the protruding portion 400a extends to the inner peripheral side from the tip surface 321 of the second portion 320 of the insulator 10. It is only a point. The structure of other parts of the spark plug 100a is the same as the structure of the corresponding part of the spark plug 100 in FIG. 2A (the same elements as the corresponding elements are denoted by the same reference numerals, (Omitted). For example, the shape of the tip portion 510a of the front end side body portion 52a of the metal shell 50a is the same as the shape of the front portion 510 of the front end side body portion 52 of the metal shell 50 in FIG. It is. Such a spark plug 100a can realize various advantages similar to the spark plug 100 of FIG.

  Moreover, the shape of the protrusion part 400a is the same as the shape obtained by extending the protrusion part 400 of FIG. 2 (A) further toward the inner peripheral side. According to this configuration, the combustion gas is further suppressed from contacting the tip portion 328 of the second portion 320 of the insulator 10. Further, the combustion gas is further suppressed from entering the gap between the insulator 10 and the metal shell 50. Therefore, the temperature rise of the second portion 320 of the insulator 10 (and hence the tip of the insulator 10) can be suppressed.

  Note that the connection portion C3 between the distal end surface 321 and the inner peripheral surface 322 of the second portion 320 can be rounded. In this case, you may specify the boundary of the front end surface 321 and the internal peripheral surface 322 as follows. FIG. 3B shows an enlarged view of a portion including the connection portion C3 in the cross section of FIG. A direction Di in the drawing is a direction toward the inner side in the radial direction (also referred to as an inner peripheral direction Di), and a direction Do is a direction toward the outer side in the radial direction (also referred to as an outer peripheral direction Do). Both directions Di and Do are perpendicular to the axis CL (FIG. 3A).

  As illustrated, the connection portion C3 is rounded. In this case, in the cross section of FIG. 3B, the portion 321i closest to the inner peripheral surface 322 among the straight portions representing the tip surface 321 and the portion closest to the tip surface 321 among the straight portions representing the inner peripheral surface 322. An intersection P3 of two straight lines obtained by extending 322L can be adopted as the boundary position. When the protrusion 400 extends to the inner circumferential direction Di side from the intersection P3 (that is, when the inner end 402a of the protrusion 400a is located closer to the inner circumferential direction Di than the intersection P3) It can be said that the protruding portion 400 extends to the inner peripheral side with respect to the distal end surface 321 of the second portion 320 of the insulator 10.

C. Third embodiment:
FIG. 4 is a cross-sectional view showing a third embodiment of the spark plug. In the drawing, a cross section similar to that of FIG. The spark plug 100 of FIG. 2A differs from the spark plug 100b of FIG. 4 in that the first portion 310b of the insulator 10b is closer to the rear direction Dfr side than the front end surface 55 of the metal shell 50. It is a point that extends to. In other words, the first portion 310b extends from the vicinity of the front end surface 331 of the third portion 330 located on the rear direction Dfr side of the front end surface 55 of the metal shell 50 toward the front direction Df. A portion extending to the front direction Df side is included. The front end surface 311b of the first portion 310b is located on the front direction Df side with respect to the front end surface 55 of the metal shell 50.

  Also in the present embodiment, the center electrode 20b extends from the rear direction Dfr side to the front direction Df side with respect to the front end 319b of the first portion 310b of the insulator 10b (that is, a portion of the center electrode 20b on the front direction Df side). Is exposed to the front direction Df side of the shaft hole 12b of the insulator 10b). The ground electrode 30b is configured such that the tip 34b of the ground electrode 30b is disposed at a position away from the center electrode 20b toward the front direction Df. The structure of the other part of the spark plug 100b is the same as the structure of the corresponding part of the spark plug 100 in FIG. 2A (the same elements as the corresponding elements are denoted by the same reference numerals, (Omitted). For example, the configuration of the leg portion 19b of the insulator 10b is the same as the configuration of the leg portion 19 in FIG. 2A except for the configuration of the first portion 310b. A groove 390b that is recessed toward the rear end direction Dfr is formed at the front end of the insulator 10b. Such a spark plug 100b can realize various advantages similar to the spark plug 100 of FIG.

  In the figure, a creeping path Pthb indicated by a bold line is a path when an unintended discharge occurs along the outer surface of the insulator 10b between the metal shell 50 and the center electrode 20b. The creeping path Pthb extends from the metal shell 50 (here, the inner peripheral surface of the protrusion 400) to the inner peripheral surface 322 of the second portion 320, the tip surface 331 of the third portion 330, and the outer peripheral surface of the first portion 310b. The center electrode 20 is reached through 313b and the tip surface 311b of the first portion 310b. In the present embodiment, the outer peripheral surface 313b of the first portion 310b includes a portion on the front direction Df side with respect to the front end surface 55 of the metal shell 50, and therefore the creeping path Pthb becomes longer correspondingly. Therefore, it is possible to suppress the occurrence of unintended discharge passing through the surface of the tip of the insulator 10b. And the appropriate discharge in the gap g between the center electrode 20b and the ground electrode 30b can be accelerated | stimulated.

  In the present embodiment, the first portion 310b of the insulator 10b includes a portion on the front direction Df side of the front end surface 55 of the metal shell 50, and thus is exposed to the combustion gas on the outer surface of the insulator 10. The area of the portion is increased accordingly. Even in such a case, the second portion 320 can easily transfer heat to the metal shell 50. Therefore, the temperature rise at the tip of the insulator 10 can be suppressed.

D. Fourth embodiment:
FIG. 5 is a sectional view showing a fourth embodiment of the spark plug. In the figure, a cross section similar to that of FIG. The spark plug 100a shown in FIG. 3A differs from the spark plug 100a shown in FIG. 5 in the second portion 320c of the insulator 10c (here, the tip portion 328c on the front direction Df side of the reduced outer diameter portion 16). However, it is only a point including the reduced diameter portion 322x in which the inner diameter of the inner peripheral surface 322c on the third portion 330 side decreases toward the front direction Df side. The configuration of the remaining portion of the inner peripheral surface 322c excluding the portion formed by the reduced diameter portion 322x is the same as the configuration of the corresponding portion of the inner peripheral surface 322 in the embodiment of FIG. Moreover, the structure of the other part of the spark plug 100c is the same as the structure of the corresponding part of the spark plug 100a in FIG. 3A (the same elements as the corresponding elements are denoted by the same reference numerals, (The explanation is omitted.) Such a spark plug 100c can realize various advantages similar to the spark plug 100a of FIG.

  In the present embodiment, the reduced diameter portion 322x is provided at the distal end portion of the second portion 320c. That is, the reduced diameter portion 322x is connected to the inner peripheral side of the distal end surface 321c of the second portion 320c. Of the inner peripheral surface 322c of the second portion 320c, the shape of the portion on the rear direction Dfr side of the reduced diameter portion 322x is the same as the shape of the corresponding portion of the inner peripheral surface 322 in FIG.

  A creeping path Pthc indicated by a bold line in the right part of the drawing is a path when an unintended discharge occurs along the outer surface of the insulator 10c between the metal shell 50a and the center electrode 20. The creeping path Pthc extends from the metal shell 50a (here, the inner peripheral surface of the protruding portion 400a) to the inner peripheral surface 322c of the second portion 320c, the distal end surface 331 of the third portion 330, and the outer peripheral surface of the first portion 310. 313 and the tip surface 311 of the first portion 310 are passed to the center electrode 20.

  Of the inner peripheral surface 322c of the second portion 320c, the portion formed by the reduced diameter portion 322x is inclined obliquely with respect to the axis CL. Therefore, the creeping path Pthc is longer than when the entire inner peripheral surface 322c is parallel to the axis CL. Therefore, it is possible to suppress the occurrence of unintended discharge passing through the surface of the tip of the insulator 10c. And the appropriate discharge in the gap g between the center electrode 20 and the ground electrode 30 can be accelerated | stimulated.

  In the reduced diameter portion 322x, the inner diameter of the inner peripheral surface 322c of the second portion 320c decreases toward the front direction Df side. Accordingly, the radial width of the groove 390c is narrowed by the reduced diameter portion 322x, so that the combustion gas is suppressed from entering the groove 390c. As a result, the temperature rise at the tip of the insulator 10c can be suppressed.

  In the embodiment of FIG. 5, the reduced diameter portion 322x is provided at the distal end portion of the second portion 320c (that is, the inner peripheral surface of the reduced diameter portion 322x is connected to the distal end surface 321c of the second portion 320c. Have been). Accordingly, the opening 392c of the groove 390c is reduced. As a result, it is possible to appropriately suppress the combustion gas from entering the groove 390c. However, the reduced diameter portion 322x may be provided at a position away from the distal end surface 321c of the second portion 320c toward the rear direction Dfr.

E. Fifth embodiment:
FIG. 6 is a cross-sectional view showing a fifth embodiment of the spark plug. In the drawing, a cross section similar to that of FIG. The spark plug 100 of FIG. 2A differs from the spark plug 100d of FIG. 6 in that the outer peripheral surface 313d of the first portion 310d of the insulator 10d and the second portion 320d (here, from the reduced outer diameter portion 16). Also, only an internal thread is formed on the inner peripheral surface 322d of the front portion 328d) on the front direction Df side. The structure of the other part of the spark plug 100d is the same as the structure of the corresponding part of the spark plug 100 of FIG. 2A (the same elements as the corresponding elements are denoted by the same reference numerals, (Omitted). Such a spark plug 100d can realize various advantages similar to the spark plug 100 of FIG.

  Further, a creeping path Pthd indicated by a bold line in the figure is a path when an unintended discharge occurs along the outer surface of the insulator 10d between the metal shell 50 and the center electrode 20. The creeping path Pthd extends from the metal shell 50 (here, the inner peripheral surface of the protruding portion 400) to the inner peripheral surface 322d of the second portion 320d, the distal end surface 331 of the third portion 330, and the outer peripheral surface of the first portion 310d. The center electrode 20 is reached through 313d and the tip surface 311 of the first portion 310d.

  Unlike the embodiment of FIG. 2A, a large number of threads are formed on the outer peripheral surface 313d of the first portion 310d and the inner peripheral surface 322d of the second portion 320d. Therefore, the creeping path Pthd becomes longer correspondingly. As a result, it is possible to suppress the occurrence of unintended discharge passing through the surface of the tip of the insulator 10d.

  Various methods can be adopted as a method of forming the female screw on the outer peripheral surface 313d and the inner peripheral surface 322d. For example, a female screw may be formed by screwing a screw mold into portions corresponding to the outer peripheral surface 313d and the inner peripheral surface 322d of the insulator before firing.

F. Sixth embodiment:
FIG. 7 is a cross-sectional view showing a sixth embodiment of the spark plug. In the drawing, a cross section similar to that of FIG. The difference from the spark plug 100 in FIG. 2A is that the protruding portion 400 is omitted from the tip portion 510e of the front end side body portion 52e of the metal shell 50e in the spark plug 100e in FIG. The portion 510e is a portion connected to the front direction Df side of the reduced inner diameter portion 56 of the front end side body portion 52e of the metal shell 50e). In the embodiment of FIG. 7, the position in the front direction Df of the front end surface 55 e of the metal shell 50 e is approximately the same as the position in the front direction Df of the front end surface 321 of the second portion 320 of the insulator 10. The ground electrode 30e is configured such that the tip 34e of the ground electrode 30e is disposed at a position away from the center electrode 20 toward the front direction Df. The structure of other parts of the spark plug 100e is the same as the structure of the corresponding part of the spark plug 100 in FIG. 2A (the same elements as the corresponding elements are denoted by the same reference numerals, (Omitted).

  Also in this embodiment, at least a part of the tip portion 328 of the second portion 320 of the insulator 10 is directly connected to the tip portion 510e of the metal shell 50e. Accordingly, the second portion 320 (particularly the tip portion 328) can directly transfer heat to the metal shell 50e. As a result, even when the protruding portion 400 is omitted, it is possible to suppress an increase in the temperature of the tip portion 328 of the second portion 320 (and hence the temperature of the tip portion of the insulator 10). As a result, misfires such as pre-ignition can be suppressed.

  Moreover, the structure of the spark plug 100e is the same as the structure of the corresponding part of the spark plug 100 of FIG. 2 (A) except that the protrusion 400 is omitted. Therefore, the spark plug 100e can realize various advantages similar to the spark plug 100 of FIG.

G. Variation:
(1) As a structure of the front-end | tip part of a spark plug, it can replace with the structure of embodiment of FIGS. 2-7, and can employ | adopt other various structures. For example, a protrusion that extends to the inner peripheral side of the tip surface of the second portion of the insulator, such as the protrusion 400a of FIG. 3, may be applied to the metal shell of another embodiment. Further, as in the first portion 310b of the insulator 10b of FIG. 4, the first portion extending from the rear direction Dfr side to the rear direction Dfr side from the tip of the metal shell is applied to the insulator of the other embodiment. Also good. Further, like the second portion 320c of the insulator 10c in FIG. 5, a second portion including a reduced diameter portion in which the inner diameter of the inner peripheral surface on the third portion side of the insulator decreases toward the front direction Df side, You may apply to the insulator of other embodiment. Moreover, you may apply the internal peripheral surface which forms several unevenness | corrugations on the cross section containing the axis line CL like the internal peripheral surface 322d of FIG. 6 to the 2nd part of the insulator of other embodiment. Moreover, you may apply the outer peripheral surface which forms several unevenness | corrugations on the cross section containing the axis line CL like the outer peripheral surface 313d of FIG. 6 to the 1st part of the insulator of other embodiment. Moreover, you may apply the metal shell from which the protrusion part located in the front end side of the 2nd part of an insulator was abbreviate | omitted to the spark plug of other embodiment like the metal shell 50e of FIG.

(2) On the cross section including the axis CL (also referred to as the axial cross section), the shape of the groove formed by the first portion, the second portion, and the third portion of the insulator is variously recessed toward the rear direction Dfr. It may be a shape. For example, on the axial cross section, the outer peripheral surface of the first portion of the insulator may include a portion inclined with respect to the axis CL, may include a portion parallel to the axis CL, and includes a portion represented by a curve. It's okay. On the axial cross section, the inner peripheral surface of the second portion of the insulator may include a portion inclined with respect to the axis CL, may include a portion parallel to the axis CL, and may include a portion represented by a curve. Good. On the axial cross section, the distal end surface of the third portion may include a portion inclined with respect to the axis CL, may include a portion perpendicular to the axis CL, and may include a portion represented by a curve. Further, the tip surface of the third portion (that is, the bottom of the groove on the most rearward direction Dfr side) is a reduced outer diameter portion of the insulator (a portion supported by the reduced inner diameter portion of the metal shell, for example, FIG. 2A). May be located on the rear side Dfr side of the reduced outer diameter portion 16).

(3) As a structure of the protrusion provided in the metal shell, instead of the structure of the protrusions 400 and 400a of the above-described embodiments, the protrusion protrudes toward the inner peripheral side at the distal end side of the second portion of the insulator. Various configurations can be employed. For example, in each of the embodiments described above, the protrusions 400 and 400a are provided on the inner peripheral side of the tips of the metal shells 50 and 50a, and the front surface Df side surface of the protrusions 400 and 400a is the metal shell 50, A part of the end face 55, 55a of 50a is formed. It may replace with this and the protrusion part may be provided in the back direction Dfr side rather than the front end surface of a metal shell. The position of the protrusion in the direction parallel to the axis CL may be an arbitrary position on the tip side of the second portion of the insulator.

  In order to prevent the combustion gas from entering the gap between the insulator and the metal shell, the distal end surface of the second portion of the insulator and the protruding portion of the metal shell face each other in a direction parallel to the axis CL. It is preferable that the distance in the direction parallel to the axis CL (for example, the distance d2 in FIG. 3B) between the tip surface of the second portion and the surface on the rearward direction Dfr side of the protruding portion is small. . Note that the distance d2 can vary depending on the circumferential position about the axis CL and the radial position. Here, in order to suppress the temperature rise of the insulator, the minimum value of the distance d2 is preferably 0.2 mm or less, and particularly preferably 0.1 mm or less. Here, the protrusion part of the metal shell and the second part of the insulator may include a part where the distance d2 exceeds 0.2 mm. In order to further suppress the temperature rise of the insulator 10, the distance d2 (that is, the maximum value of the distance d2) is set over the entire gap between the second portion of the insulator and the protruding portion of the metal shell. It is preferably 0.2 mm or less, and preferably 0.1 mm or less. In any case, the distance d2 is zero mm or more.

  When the connecting portion C3 between the tip surface 321 and the inner peripheral surface 322 of the second portion 320 is rounded as in the embodiment of FIG. 3B, of the outer surface on the front direction Df side of the second portion 320 A portion closer to the outer peripheral direction Do than the intersection point P3 described with reference to FIG. Moreover, the connection part C4 of the front end surface 321 and the outer peripheral surface 323 of the 2nd part 320 can also be rounded like embodiment of FIG. 3 (B). In this case, you may specify the boundary of the front end surface 321 and the outer peripheral surface 323 as follows. That is, in the cross section of FIG. 3B, a portion 321j closest to the outer peripheral surface 323 among the straight portions representing the front end surface 321 and a portion 323L closest to the front end surface 321 among the straight portions representing the outer peripheral surface 323; It is possible to adopt an intersection P4 of two straight lines obtained by extending as a boundary position. A portion of the outer surface of the second portion 320 on the front direction Df side that is closer to the inner circumferential direction Di than the intersection point P4 may be employed as the tip surface 321. It is preferable that the minimum value of the distance d2 is within the above-described preferable range in a portion where the tip surface 321 and the protruding portion of the metal shell face each other along the direction parallel to the axis CL. It is preferable that the distance d2 (that is, the maximum value of the distance d2) is within the above preferable range. Moreover, it is preferable that at least a part of the second portion of the insulator is connected directly or indirectly (that is, via another member) to the protruding portion of the metal shell. A connecting material (for example, alumina cement) that connects the second portion and the protruding portion may be disposed in the gap between the second portion of the insulator and the protruding portion of the metal shell.

  In any case, in order to suppress the temperature rise of the insulator, when the spark plug is viewed in the rearward direction Dfr, the protruding portion of the metal shell is at least a part of the front end surface of the second portion of the insulator. It is preferable that the projection portion is configured to overlap with the projection portion (that is, the protruding portion hides at least a part of the distal end surface of the second portion). And in order to further suppress the temperature rise of the insulator, it is preferable that the protruding portion of the metal shell is configured to overlap the entire tip surface of the second portion of the insulator (that is, the protruding portion). Hiding the entire tip surface of the second part). In this case, in the cross section including the axis CL as shown in FIG. 3B, the position in the inner circumferential direction Di of the inner circumferential end of the projecting portion (for example, the end 402a of the projecting portion 400a) is the second position of the insulator. Same as the position in the inner circumferential direction Di of the inner peripheral side end (for example, the intersection point P3) of the distal end surface of the part (for example, the distal end surface 321 of the second portion 320), or more than the inner peripheral end of the distal end surface It is located on the inner circumferential direction Di side.

  Further, when the metal shell is provided with a protrusion, the protrusion is configured so that the shortest distance between the center electrode and the protrusion is longer than the distance of the discharge gap between the center electrode and the ground electrode. It is preferred that

(4) As a configuration of the metal shell, other various configurations can be adopted instead of the configurations of the above-described embodiments. For example, on the inner peripheral surface of a portion surrounding the outer peripheral side of the second part of the insulator of the metal shell (for example, the tip portion 510 in FIG. 2A), the inner metal member faces the inner peripheral side in order to contact the insulator. A protruding portion that protrudes in the direction may be provided. Further, the configuration of the support portion (for example, the reduced inner diameter portion 56 in FIG. 2A) that supports the step portion of the insulator may be various configurations in which the inner diameter decreases when tracing toward the distal end side. For example, the cross section including the axis line CL may be formed by a plane perpendicular to the axis line CL. That is, the support portion may be a portion whose inner diameter decreases stepwise when tracing toward the distal end side.

(5) As a configuration of the spark plug, other various configurations can be adopted instead of the configurations of the above-described embodiments. For example, the front end side packing 8 (FIG. 1) may be omitted. In this case, the reduced inner diameter portion of the metal shell (for example, the reduced inner diameter portion 56 in FIG. 2A) directly supports the reduced outer diameter portion of the insulator. Further, instead of the tip surface of the tip portion of the center electrode (for example, the surface on the front direction Df side of the first chip 29 in FIG. 1), the side surface (surface on the direction side perpendicular to the axis CL) of the tip portion of the center electrode. And the ground electrode may form a discharge gap. The total number of gaps for discharge may be 2 or more. The resistor 73 may be omitted. A magnetic body may be disposed between the center electrode in the through hole of the insulator and the terminal fitting.

  As mentioned above, although this invention was demonstrated based on embodiment and a modification, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

8 ... Front end side packing 10, 10b, 10c, 10d ... Insulator, 11 ... Reduced inner diameter part, 12, 12b ... Through hole (shaft hole), 13 ... Rear end side body part, 14 ... Large diameter part, 15 ... Front end side body part, 16 ... reduced outer diameter part, 16L ... part, 19, 19b ... leg part, 20, 20b ... center electrode, 21 ... outer layer, 22 ... core part, 23 ... collar part, 24 ... head part, 27 ... Shaft part, 28 ... Bar part, 29 ... First tip, 30, 30b, 30e ... Ground electrode, 31 ... Outer layer, 32 ... Inner layer, 33 ... Base end part, 34, 34b, 34e ... Tip part, 37 ... Main body , 40 ... terminal fitting, 41 ... shaft portion, 48 ... collar portion, 49 ... cap mounting portion, 50 ... metal fitting, 50a, 50e ... metal fitting, 51 ... tool engaging portion, 52 ... tip side body portion, 52L ... part, 52a, 52e ... front end side body part, 53 ... caulking part, 54 ... middle body part, 55, 55e ... front end surface, 6 ... Reduced inner diameter portion, 56L ... portion, 57 ... Screw portion, 58 ... Buckling portion, 59 ... Through hole, 61, 62 ... Ring member, 70 ... Talc, 72 ... First seal portion, 73 ... Resistor, 74 2nd seal part, 90 ... Gasket, 100, 100a to 100e ... Spark plug, 300 ... Seat surface, 310, 310b, 310d ... 1st part, 311, 311b ... Tip surface, 313, 313b, 313d ... Outer peripheral surface, 319, 319b ... tip, 320, 320c, 320d ... second part, 321, 321c ... tip surface, 321i, 321j ... part, 322, 322c, 322d ... inner peripheral surface, 322L ... part, 322x ... reduced diameter part, 323 ... outer peripheral surface, 323L ... portion, 328 ..., 328c, 328d ... tip portion, 328L ... portion, 330 ... third portion, 331 ... tip surface, 390, 390c ... groove, 92c: Opening, 400, 400a ... Projection, 402a ... End, 510, 510a, 510e ... Tip portion, 512 ... Inner circumferential surface, g ... Gap, Pth, Pthb, Pthc, Pthd ... Creeping path (discharge path), C1 C4: Connection portion, P1 to P4: Intersection, CL: Center axis (axis), Df: Front end direction (forward direction), Di ... Inner circumferential direction, Do ... Outer circumferential direction, Ax ... Heat receiving region, Dfr ... Rear end direction (Backward)

Claims (6)

A cylindrical insulator having an axial hole extending from the front end side to the rear end side along the direction of the axis, and a step portion whose outer diameter is reduced toward the front end side,
A cylindrical metal shell having a support portion that is disposed on the outer periphery of the insulator and has a support portion that directly or indirectly supports the stepped portion as well as a portion having a smaller inner diameter when traced toward the tip side.
A central electrode disposed in the axial hole of the insulator;
A ground electrode connected to the metal shell and facing the tip of the center electrode;
A spark plug comprising:
The insulator includes a first portion that is an inner peripheral portion, a second portion that is an outer peripheral portion, a tip of the first portion and the first portion between the first portion and the second portion. A third portion recessed to the rear end side from any of the two portions of the tip, and
Of the second part, at least a part of the tip side of the step part is directly or indirectly connected to the metal shell,
Spark plug. The spark plug according to claim 1,
The metal shell includes a protruding portion that protrudes toward the inner peripheral side at the distal end side of the second portion of the insulator,
Spark plug. The spark plug according to claim 2,
The protruding portion extends to the inner peripheral side from the tip surface of the second portion of the insulator,
Spark plug. The spark plug according to any one of claims 1 to 3,
The first portion of the insulator extends from the rear end side to the front end side from the front end of the metal shell.
Spark plug. The spark plug according to any one of claims 1 to 4,
The center electrode extends from the rear end side to the front end side from the front end of the first portion of the insulator.
Spark plug. The spark plug according to any one of claims 1 to 5,
The second portion of the insulator includes a portion in which the inner diameter of the inner peripheral surface on the third portion side becomes smaller toward the tip side.
Spark plug.

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