JP2016184571A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deposition of carbon on an insulator.SOLUTION: The main body metal fitting of a spark plug forms an annular gap between the outer peripheral surface of the leg of an insulator and itself. Between the reduced outer diameter portion of the insulator and the reduced inner diameter portion of the main body metal fitting, a packing is disposed. The position of the contact part of the packing and main body metal fitting, closest to the tip side, is the contact end position, the distance in the radial direction between the outer peripheral surface of the leg of an insulator and the inner peripheral surface of the main body metal fitting is the gap distance, and the position of the rear end of a maximum part where the gap distance is maximum out of the annular gaps is the maximum end position. The gap distance at the tip of the main body metal fitting is larger than the distance of the gap between the center electrode and ground electrode. The main body metal fitting includes an enlarged inner diameter portion where the inner diameter increases toward the rear end side in the axial direction, on the side closer to the tip than the contact end position. The maximum end position is located closer to the rear end side than the middle position, where the distance between the contact end position and the tip of the main body metal fitting in the axial direction is divided equally into two parts.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a spark plug.

  Conventionally, spark plugs have been used in internal combustion engines. As the spark plug, for example, a spark plug having an insulator that forms a through hole and a metal shell that is disposed around the radial direction of the insulator is used. When such an insulator is exposed to combustion gas, carbon may adhere to the surface of the insulator. In some cases, such carbon causes problems. For example, an unintended discharge may occur inside the metal shell through carbon. As a technique for suppressing such inconvenience, for example, the volume of the space formed by the surface of the insulator leg and the inner wall surface of the metal shell is reduced to prevent the invasion of combustion gas, thereby preventing the resistance of the insulator leg. Technologies that improve fouling properties have been proposed.

Japanese Patent Laid-Open No. 9-45457 JP 63-216282 A Japanese Patent No. 4187654

  However, the fact is that no sufficient contrivance has been made to suppress the deposition of carbon on the insulator.

  The present disclosure discloses a technique capable of suppressing the deposition of carbon on an insulator.

  For example, the present disclosure discloses the following application examples.

[Application Example 1]
A through-hole having a reduced outer diameter portion whose outer diameter decreases toward the distal end in the direction of the axis, and a leg portion that is a portion on the distal end side from the reduced outer diameter, and extending in the direction of the axis An insulator to be formed;
A central electrode at least a part of which is inserted on the tip side of the through hole;
A metal shell that is disposed around the insulator in the radial direction, has a reduced inner diameter portion that decreases in inner diameter toward the tip side, and forms an annular gap with the outer peripheral surface of the leg portion;
A ground electrode electrically connected to the metal shell and forming a gap with the center electrode;
A packing disposed between the reduced outer diameter portion of the insulator and the reduced inner diameter portion of the metal shell;
A spark plug comprising:
Of the contact portion between the packing and the metal shell, the position on the most distal side is the contact end position,
The radial distance between the outer peripheral surface of the leg portion of the insulator and the inner peripheral surface of the metal shell is a gap distance,
When the position of the rear end of the maximum portion of the annular gap where the gap distance is the maximum is the maximum end position,
The gap distance at the tip of the metal shell is larger than the gap distance between the center electrode and the ground electrode,
The metal shell includes an enlarged inner diameter portion whose inner diameter increases toward the rear end side in the direction of the axis on the tip side than the contact end position,
The maximum end position is located on the rear end side from a center position that is a position that bisects the distance in the direction of the axis between the contact end position and the front end of the metal shell.
Spark plug.

  According to this configuration, the gap distance of the annular gap can be increased as compared with the case where the expanded inner diameter portion of the metal shell is omitted, so that the ease of gas flow inside the annular gap can be improved. Therefore, since carbon contained in the combustion gas can be suppressed from remaining inside the annular gap, it can be suppressed that carbon is deposited on the insulator.

[Application Example 2]
The spark plug according to application example 1,
On the cross section including the axis, the front end surface of the metallic shell and the inner peripheral surface of the metallic shell, the portion on the distal end side from the enlarged inner diameter portion forms one or more corners,
Each of the one or more corners is an obtuse angle.
Spark plug.

  According to this configuration, it is possible to suppress the occurrence of discharge at any one or more corners of the metal shell instead of the ground electrode.

[Application Example 3]
The spark plug according to application example 1,
The enlarged inner diameter portion of the metal shell includes a portion whose inner diameter increases from the front end of the metal shell toward the rear end side.
Spark plug.

  According to this configuration, the combustion gas that has flowed into the annular gap easily flows out of the annular gap, so that it is possible to suppress carbon from remaining inside the annular gap. Therefore, it is possible to suppress the deposition of carbon on the insulator.

[Application Example 4]
The spark plug according to any one of Application Examples 1 to 3,
The metal shell includes a portion whose inner diameter becomes smaller along a convex curve toward the outer side in the radial direction toward the rear end side on the rear end side than the maximum end position.
Spark plug.

  According to this configuration, since the gap distance can be increased from the maximum end position inside the annular gap from the rear end side, the ease of gas flow can be improved from the maximum end position to the rear end side. Therefore, since carbon can be suppressed from remaining at the rear end side from the maximum end position inside the annular gap, it is possible to suppress carbon deposition on the insulator.

  The technology disclosed in the present specification can be realized in various modes, for example, in a mode of a spark plug, an internal combustion engine equipped with the spark plug, or the like.

It is sectional drawing of one Embodiment of a spark plug. 2 is a schematic view showing a part of a spark plug 100 on the front direction Df side. FIG. It is the schematic of the spark plug 100B of a 1st reference example. It is a graph which shows the test result of the sample of embodiment. It is a graph which shows the test result of the sample of the 1st reference example. It is the schematic of the spark plug 100C of the 2nd reference example. It is a graph which shows the measurement result of a heat value. It is a graph which shows the test result of the sample of the spark plug 100. FIG. It is a graph which shows the test result of the sample of spark plug 100D. It is the schematic which shows a part of the front direction Df side of the spark plug 100E of another embodiment. It is the schematic which shows a part of the front direction Df side of the spark plug 100F of another embodiment.

A. Embodiment:
FIG. 1 is a cross-sectional view of one embodiment of a spark plug. In the drawing, the center axis CL of the spark plug 100 is shown (also referred to as “axis line CL”). The illustrated cross section is a cross section including the central axis CL. 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 central axis CL is also simply referred to as “radial direction”, and the circumferential direction of the circle centered on the central 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 electrodes 20 and 30. 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 an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, a metal shell 50, a conductive first seal portion 60, a resistor 70, and a conductive second. The seal portion 80, the front end side packing 8, the talc 9, the first rear end side packing 6, and the second rear end side packing 7 are provided.

  The insulator 10 is a substantially cylindrical member having a through hole 12 (hereinafter also referred to as “shaft hole 12”) extending along the central axis CL and penetrating the insulator 10. The insulator 10 is formed by firing alumina (other insulating materials can also be used). The insulator 10 includes a leg portion 13, a first reduced outer diameter portion 15, a distal end side trunk portion 17, a third reduced outer diameter portion 14, and a collar portion, which are arranged in order from the distal end side toward the rear direction Dfr. 19, a second reduced outer diameter portion 11, and a rear end side body portion 18. The flange portion 19 is a portion having the largest outer diameter in the insulator 10 (also referred to as a large diameter portion 19). The outer diameter of the first reduced outer diameter portion 15 gradually decreases from the rear end side toward the front end side. In the vicinity of the first reduced outer diameter portion 15 of the insulator 10 (the front end side body portion 17 in the example of FIG. 1), the first reduced inner diameter portion 16 gradually decreases in inner diameter from the rear end side toward the front end side. Is formed. The outer diameter of the second reduced outer diameter portion 11 gradually decreases from the front end side toward the rear end side. The outer diameter of the third reduced outer diameter portion 14 gradually decreases from the rear end side toward the front end side.

  As shown in FIG. 1, a center electrode 20 is inserted on the distal end side of the shaft hole 12 of the insulator 10. The center electrode 20 has a rod-shaped shaft portion 27 extending along the center axis CL, and a first tip 29 joined to the tip of the shaft portion 27. The shaft portion 27 includes a leg portion 25, a flange portion 24, and a head portion 23 that are arranged in order from the distal end side toward the rear direction Dfr. The first tip 29 is joined to the tip of the leg portion 25 (that is, the tip of the shaft portion 27) (for example, laser welding). In the present embodiment, at least a part of the first chip 29 is exposed outside the shaft hole 12 on the distal end side of the insulator 10. The surface on the front direction Df side of the flange portion 24 is supported by the first reduced inner diameter portion 16 of the insulator 10. The shaft portion 27 includes an outer layer 21 and a core portion 22. The outer layer 21 is formed of a material (for example, an alloy containing nickel) that has better oxidation resistance than the core portion 22. The core part 22 is formed of a material (for example, pure copper, copper alloy, etc.) having a higher thermal conductivity than the outer layer 21. Further, the first chip 29 is made of a material that is more resistant to discharge than the shaft portion 27 (for example, at least one selected from precious metals such as iridium (Ir) and platinum (Pt), tungsten (W), and those metals. Alloy containing seeds).

  A part of the terminal fitting 40 is inserted into the rear end side of the shaft hole 12 of the insulator 10. The terminal fitting 40 is formed using a conductive material (for example, a metal such as low carbon steel).

In the shaft hole 12 of the insulator 10, a substantially cylindrical resistor 70 for suppressing electrical noise is disposed between the terminal fitting 40 and the center electrode 20. The resistor 70 includes, for example, a conductive material (for example, carbon particles), ceramic particles (for example, ZrO ₂ ), and glass particles (for example, SiO ₂ —B ₂ O ₃ —Li ₂ O—BaO-based glass particles). ). A conductive first seal portion 60 is disposed between the resistor 70 and the center electrode 20, and a conductive second seal portion 80 is disposed between the resistor 70 and the terminal fitting 40. Yes. The seal portions 60 and 80 are formed using a material including, for example, the same glass particles as those included in the material of the resistor 70 and metal particles (for example, Cu). The center electrode 20 and the terminal fitting 40 are electrically connected via the resistor 70 and the seal portions 60 and 80.

  The metal shell 50 is a substantially cylindrical member having a through hole 59 extending along the central axis CL and penetrating the metal shell 50. The metal shell 50 is formed using a low carbon steel material (other conductive materials (for example, metal materials) can also be used). The insulator 10 is inserted into the through hole 59 of the metal shell 50. The metal shell 50 is fixed to the outer periphery of the insulator 10. On the front direction Df side of the metal shell 50, the tip of the insulator 10 (in this embodiment, the portion on the tip side of the leg portion 13) is exposed outside the through hole 59. That is, the tip of the insulator 10 is located on the front direction Df side with respect to the tip of the metal shell 50. On the rear end side of the metal shell 50, the rear end of the insulator 10 (in this embodiment, the portion on the rear end side of the rear end side body portion 18) is exposed outside the through hole 59.

  The metal shell 50 includes a body portion 55, a seat portion 54, a deformation portion 58, a tool engaging portion 51, and a caulking portion 53, which are arranged in order from the front end side to the rear end side. Yes. The seat part 54 is a bowl-shaped part. The trunk portion 55 is a substantially cylindrical portion extending from the seat portion 54 along the central axis CL toward the front direction Df. A thread 52 for screwing into the mounting hole of the internal combustion engine is formed on the outer peripheral surface of the body portion 55. An annular gasket 5 formed by bending a metal plate is fitted between the seat portion 54 and the screw thread 52.

  The metal shell 50 has a reduced inner diameter portion 56 disposed on the front direction Df side with respect to the deformable portion 58. The inner diameter of the reduced inner diameter portion 56 gradually decreases from the rear end side toward the front end side. The front end packing 8 is sandwiched between the reduced inner diameter portion 56 of the metal shell 50 and the first reduced outer diameter portion 15 of the insulator 10. The front end packing 8 is an iron-shaped O-shaped ring (other materials (for example, metal materials such as copper) can also be used).

  The tool engaging part 51 is a part for engaging with a tool (for example, a spark plug wrench) for tightening the spark plug 100. The caulking portion 53 is disposed on the rear end side of the second reduced outer diameter portion 11 of the insulator 10 and forms the rear end of the metal shell 50 (that is, the end on the rear direction Dfr side). The caulking portion 53 is bent toward the inner side in the radial direction. On the front direction Df side of the caulking portion 53, the first rear end side packing 6, the talc 9, and the second rear end side packing 7 are disposed between the inner peripheral surface of the metal shell 50 and the outer peripheral surface of the insulator 10. In this order toward the front direction Df. In this embodiment, these rear end side packings 6 and 7 are iron-made C-shaped rings (other materials are also employable).

  When the spark plug 100 is manufactured, the crimping portion 53 is crimped so as to be bent inward. And the crimping part 53 is pressed to the front direction Df side. Thereby, the deformation | transformation part 58 deform | transforms and the insulator 10 is pressed toward the front end side in the metal shell 50 through the packings 6 and 7 and the talc 9. The front end side packing 8 is pressed between the first reduced outer diameter portion 15 and the reduced inner diameter portion 56 and seals between the metal shell 50 and the insulator 10. Thus, the metal shell 50 is fixed to the insulator 10.

  In the present embodiment, the ground electrode 30 has a rod-shaped shaft portion 37 and a second tip 39 joined to the tip portion 31 of the shaft portion 37. The rear end of the shaft portion 37 is joined (for example, resistance welding) to the surface of the front end 57 of the metal shell 50 (that is, the front side Df side surface 57, also referred to as “front end surface 57”). The shaft portion 37 extends from the front end surface 57 of the metal shell 50 toward the front direction Df, bends toward the central axis CL, and reaches the front end portion 31. The distal end portion 31 is disposed on the front direction Df side of the center electrode 20. The second tip 39 is joined to the surface on the center electrode 20 side of the surface of the tip portion 31 (for example, laser welding). The second chip 39 is made of a material having higher durability against discharge than the shaft portion 37 (for example, noble metal such as iridium (Ir) and platinum (Pt), tungsten (W), and at least one selected from these metals. Alloy). The first tip 29 of the center electrode 20 and the second tip 39 of the ground electrode 30 form a gap g for spark discharge. The ground electrode 30 faces the tip of the center electrode 20 with a gap g therebetween.

  The shaft portion 37 of the ground electrode 30 has an outer layer 35 that forms at least a part of the surface of the shaft portion 37, and a core portion 36 embedded in the outer layer 35. The outer layer 35 is formed using a material excellent in oxidation resistance (for example, an alloy containing nickel and chromium). The core portion 36 is formed using a material (for example, pure copper) having a higher thermal conductivity than the outer layer 35.

  FIG. 2 is a schematic view showing a part of the spark plug 100 on the front direction Df side. In the figure, the central axis CL is shown. On the left side of the central axis CL, the cross section of the metal shell 50 and the insulator 10 and the appearance of the ground electrode 30 are shown. In the drawing, the illustration of the structure of the through hole 12 of the insulator 10 and the inside of the through hole 12 is omitted. The appearance of the spark plug 100 is shown on the right side of the central axis CL.

  A gap 310 is formed between the inner peripheral surface 55 i of the body portion 55 of the metal shell 50 and the outer peripheral surface 13 o of the leg portion 13 of the insulator 10 on the front direction Df side with respect to the front end side packing 8. The gap 310 is an annular gap centered on the central axis CL. Hereinafter, the radial distance 802 of the annular gap 310, that is, the radial distance 802 between the inner peripheral surface 55 i of the metal shell 50 and the outer peripheral surface 13 o of the insulator 10 is referred to as “gap distance 802”. The gap distance 802 can change according to the position in the direction parallel to the central axis CL. A tip clearance distance 812 in the figure is a clearance distance at the tip 57 of the metal shell 50 (that is, the opening 310o of the gap 310). In the embodiment of FIG. 2, the tip clearance distance 812 is larger than the distance 811 of the gap g formed by the center electrode 20 and the ground electrode 30. The distance 811 of the gap g is the shortest distance of the gap g.

  Of the body portion 55 of the metal shell 50, the portion on the front direction Df side of the reduced inner diameter portion 56 is divided into three portions 511, 512, and 513 arranged from the front direction Df side toward the rear end direction Dfr. The first portion 511 is a portion including the tip 57. The inner diameter of the first portion 511 gradually increases from the front end 57 of the metal shell 50 toward the rear direction Dfr (hereinafter, the first portion 511 is also referred to as “expanded inner diameter portion 511”). In the embodiment of FIG. 2, the inner peripheral surface of the first portion 511 is represented by a straight line on the cross section including the central axis CL.

  The inner diameter of the second portion 512 gradually decreases toward the rear direction Dfr. In the embodiment of FIG. 2, the inner diameter of the second portion 512 decreases along a convex curve toward the outer side in the radial direction. In other words, on the cross section including the center axis CL, the absolute value of the ratio of the change amount of the inner diameter to the change amount of the position in the direction parallel to the center axis CL (that is, the inclination of the inner peripheral surface 55i with respect to the center axis CL) is It gradually increases toward the rear direction Dfr. Here, when the inner peripheral surface 55i is parallel to the central axis CL, the inclination of the inner peripheral surface 55i with respect to the central axis CL is zero degrees. When the inner peripheral surface 55i is perpendicular to the central axis CL, the inclination of the inner peripheral surface 55i with respect to the central axis CL is 90 degrees. In the embodiment of FIG. 2, the inclination of the inner peripheral surface 55i with respect to the central axis CL in the second portion 512 increases from an angle of less than 45 degrees to an angle of more than 45 degrees toward the rear direction Dfr. .

  The inner diameter of the third portion 513 is constant regardless of the position in the direction parallel to the central axis CL. A reduced inner diameter portion 56 is connected to the rear direction Dfr side of the third portion 513. Hereinafter, like the third portion 513, a portion having a constant inner diameter regardless of the position in the direction parallel to the central axis CL is also referred to as a “constant inner diameter portion”.

  The leg portion 13 of the insulator 10 is divided into four portions 111, 112, 113, and 114 that are aligned from the front direction Df side toward the rear end direction Dfr. The first portion 111 is a portion including the tip of the insulator 10. The outer diameter of the first portion 111 is constant regardless of the position in the direction parallel to the central axis CL, except for the corner of the tip.

  The outer diameter of the second portion 112 gradually increases toward the rear direction Dfr. In the embodiment of FIG. 2, the outer peripheral surface of the second portion 112 is represented by a straight line on the cross section including the central axis CL. Further, the second portion 112 of the insulator 10 faces the first portion 511 of the metal shell 50. The outer peripheral surface of the second portion 112 is parallel to the inner peripheral surface of the first portion 511 of the metal shell 50.

  The outer diameter of the third portion 113 gradually increases toward the rear direction Dfr. Further, the third portion 113 faces the second portion 512 of the metal shell 50.

  The outer diameter of the fourth portion 114 is constant regardless of the position in the direction parallel to the central axis CL. The fourth portion 114 of the insulator 10 faces the third portion 513 of the metal shell 50. A first reduced outer diameter portion 15 is connected to the rear direction Dfr side of the fourth portion 114.

  A portion 315 in the drawing is a portion having the maximum gap distance 802 in the gap 310. Hereinafter, this portion 315 is also referred to as a maximum gap portion 315. In the embodiment of FIG. 2, the maximum gap portion 315 is a portion sandwiched between the first portion 511 of the metal shell 50 and the second portion 112 of the insulator 10. A position 317 in the figure indicates the position of the rear end of the maximum gap portion 315 (hereinafter also referred to as “maximum end position 317”).

  Three positions 711, 712, and 713 in the figure each indicate a position in a direction parallel to the central axis CL. The first position 711 indicates the position of the tip 57 of the metal shell 50. The third position 713 is a position on the most front direction Df side in the contact portion between the metal shell 50 and the front end side packing 8 (hereinafter also referred to as “contact end position 713”). The second position 712 is a position that bisects the distance in the direction parallel to the central axis CL between the first position 711 and the third position 713 (also referred to as “intermediate position 712”). In the embodiment of FIG. 2, the rear end 317 of the maximum gap portion 315 is located on the rear direction Dfr side with respect to the intermediate position 712. The maximum gap portion 315 extends from the front direction Df side of the intermediate position 712 of the gap 310 to the rear direction Dfr side of the intermediate position 712. Hereinafter, in the gap 310, a portion on the front direction Df side from the intermediate position 712 is referred to as a “front portion gap 311”, and a portion on the rear direction Dfr side from the intermediate position 712 is also referred to as a “rear portion gap 312”.

B. First evaluation test:
A first evaluation test using a sample of the spark plug 100 will be described. In the first evaluation test, the fouling resistance was evaluated. In this evaluation test, in addition to the sample of the spark plug 100 (FIGS. 1 and 2), the sample of the spark plug of the first reference example was also evaluated. FIG. 3 is a schematic view of a spark plug 100B of the first reference example. In the drawing, as in FIG. 2, a cross section and an appearance of a part of the spark plug 100 </ b> B on the front direction Df side are shown. A center axis CL in the figure is the center axis of the spark plug 100B. On the left side of the central axis CL, the cross section of the metal shell 50B and the insulator 10B and the appearance of the ground electrode 30 are shown. In the drawing, the illustration of the internal structure of the insulator 10B is omitted. On the right side of the central axis CL, the appearance of the spark plug 100B is shown. The difference from the embodiment of FIGS. 1 and 2 is that the cross-sectional shape of the inner peripheral surface 55Bi of the body portion 55B of the metal shell 50B and the cross-sectional shape of the outer peripheral surface 13Bo of the leg portion 13B of the insulator 10B are as shown in FIG. It is different from the corresponding shape. The structure of the other parts of the spark plug 100B is the same as the structure of the corresponding parts of the spark plug 100 of FIGS. 1 and 2 (the same elements as the corresponding elements are denoted by the same reference numerals and the description thereof is omitted). To do).

  On the front direction Df side with respect to the front end side packing 8, an annular centering on the central axis CL is provided between the inner peripheral surface 55Bi of the trunk portion 55B of the metal shell 50B and the outer peripheral surface 13Bo of the leg portion 13B of the insulator 10B. The gap 320 is formed. The tip gap distance 822 at the tip of the metal shell 50B (that is, the gap distance at the opening 320o of the gap 320) is larger than the gap distance 821 formed by the center electrode 20 and the ground electrode 30. The tip clearance distance 822 of the sample of the first reference example was the same as the tip clearance distance 812 (FIG. 2) of the sample of the embodiment.

  Of the body 55B of the metal shell 50B, the portion on the front direction Df side with respect to the reduced inner diameter portion 56 is divided into five portions 521, 522, 523, 524, and 525 arranged from the front direction Df side to the rear end direction Dfr. Is done. The first portion 521 is a portion including the tip surface 57B. The inner diameter of the first portion 521 is constant regardless of the position in the direction parallel to the central axis CL. Thus, the metal shell 50B of the first reference example has the constant inner diameter portion 521 that forms the tip portion.

  The inner diameter of the second portion 522 gradually increases toward the rear direction Dfr. On the cross section including the central axis CL, the inner peripheral surface of the second portion 522 is represented by a straight line. The inner diameter of the third portion 523 is constant regardless of the position in the direction parallel to the central axis CL. The inner diameter of the fourth portion 524 gradually decreases toward the rear direction Dfr. On the cross section including the central axis CL, the inner peripheral surface of the fourth portion 524 is represented by a straight line. The inner diameter of the fifth portion 525 is constant regardless of the position in the direction parallel to the central axis CL. A reduced inner diameter portion 56 is connected to the rear direction Dfr side of the fifth portion 525.

  The leg portion 13B of the insulator 10B is divided into three portions 121, 122, 123 arranged in the direction from the front direction Df toward the rear end direction Dfr. The first portion 121 is a portion including the tip of the insulator 10B. The outer diameter of the first portion 121 is constant regardless of the position in the direction parallel to the central axis CL, except for the corner of the tip. The first portion 121 faces the entirety of the first portion 521 and the second portion 522 of the metal shell 50B and a portion of the third portion 523 on the front direction Df side. The outer diameter of the second portion 122 gradually increases toward the rear direction Dfr. On the cross section including the central axis CL, the outer peripheral surface of the second portion 122 is represented by a straight line. The second portion 122 opposes a part of the third portion 523 of the metal shell 50B on the rear direction Dfr side and the entire fourth portion 524. The outer diameter of the third portion 123 is constant regardless of the position in the direction parallel to the central axis CL. The third portion 123 faces the fifth portion 525 of the metal shell 50B.

  A portion 325 in the figure is a portion having the maximum gap distance in the gap 320. Hereinafter, this portion 325 is also referred to as a maximum gap portion 325. In the first reference example of FIG. 3, the maximum gap portion 325 is a portion sandwiched between the third portion 523 of the metal shell 50B and the first portion 121 of the insulator 10B. A position 327 in the drawing indicates the position of the rear end of the maximum gap portion 325.

  In the figure, three positions 721, 722, and 723 in a direction parallel to the central axis CL are shown. The 1st position 721 has shown the position of the tip of metallic shell 50B. The third position 723 is a position on the most front direction Df side in the contact portion between the metal shell 50 </ b> B and the front end side packing 8. The second position 722 is a position that bisects the distance in the direction parallel to the central axis CL between the first position 721 and the third position 723 (also referred to as “intermediate position 722”). In the first reference example of FIG. 3, the rear end 327 of the maximum gap portion 325 is located on the front direction Df side with respect to the intermediate position 722. Thus, the entire maximum gap portion 325 is located on the front direction Df side with respect to the intermediate position 722 of the gap 320. On the rear direction Dfr side with respect to the intermediate position 722, the gap distance is shorter than the gap distance of the maximum gap portion 325. In the first reference example, the gap distance decreases from the position on the front direction Df side with respect to the intermediate position 722 toward the rear direction Dfr. Hereinafter, in the gap 320, a portion on the front direction Df side from the intermediate position 722 is referred to as a “front portion gap 321”, and a portion on the rear direction Dfr side from the intermediate position 712 is also referred to as a “rear portion gap 322”.

  4 (A) and 4 (B) are graphs showing the test results of the sample of the embodiment, and FIGS. 5 (A) and 5 (B) show the test results of the sample of the first reference example. It is a graph. 4A and 5A, the horizontal axis represents the cycle number NC of the test operation, and the vertical axis represents the insulation resistance Ra (unit: MΩ). The scale on the vertical axis is a logarithmic scale. The insulation resistance Ra is an electrical resistance between the terminal fitting 40 and the metallic shells 50 and 50B. In the graph, the scale of 10,000 MΩ indicates that the insulation resistance Ra is 10,000 MΩ or more. In FIGS. 4B and 5B, the horizontal axis indicates the cycle number NC of the test operation, and the vertical axis indicates the leak occurrence rate RT (unit:%). Note that the upward direction of the vertical axis is the direction in which the leak rate RT decreases.

  In this evaluation test, the leak discharge is not a gap g between the electrodes 20 and 30, but a discharge passing through a path from the center electrode 20 through the outer peripheral surfaces of the insulators 10 and 10B to the inner peripheral surfaces of the metal shells 50 and 50B. is there. The leak occurrence rate RT is a ratio of the number of times of occurrence of leak discharge with respect to high voltage application. In this evaluation test, the four samples of the embodiment and the four samples of the first reference example were tested. The insulation resistance Ra is the minimum value among the insulation resistances of the four samples. The leak occurrence rate RT is the maximum value among the leak occurrence rates of the four samples.

  The test operation is as follows. A test vehicle having a 4-cylinder engine with a displacement of 1500 cc was placed on a chassis dynamometer in a low temperature test chamber at -10 degrees Celsius. Four samples of spark plugs were assembled to the engine of this test car corresponding to each cylinder. And the driving | operation comprised by the 1st driving | operation and the 2nd driving | running following a 1st driving | operation was performed as 1 cycle test driving | operation. The first operation consists of “three idlings”, “running for 40 seconds at 3 speed, 35 km / h”, “idling for 90 seconds”, and “40 seconds at 3 speed, 35 km / h” This is an operation in which “travel”, “engine stop”, and “cooling of the automobile until the temperature of the cooling water reaches −10 degrees Celsius” are performed in this order. The second operation consists of “three empty blows”, “running three times for 15 seconds at 15 km / h in 1st speed with 30 seconds of engine stop” and “engine stop” And “cooling the automobile until the temperature of the cooling water reaches −10 degrees Celsius” in this order. The first operation is a high-load operation compared to the second operation. In the first operation, the temperature of the spark plug is likely to be higher than in the second operation.

  Such a test operation composed of the first operation and the second operation was repeated 10 times (10 cycles). Then, at the end of the first operation and the end of the second operation of each cycle, the spark plug sample was removed from the engine, and the insulation resistance Ra was measured. Further, the leak occurrence rate RT in the first operation and the leak occurrence rate RT in the second operation of each cycle were measured. The leak occurrence rate RT in the first operation is as follows. Analyzing the voltage waveform when all the high voltages are applied in the first operation, the ratio of the number of abnormal waveform discharges (that is, leak discharge) to the total number of discharges as the leak occurrence rate RT in the first operation Calculated. Similarly, the leak occurrence rate RT in the second operation is the ratio of the number of abnormal waveform discharges (that is, leak discharge) to the total number of discharges in the second operation.

  In the graph in the figure, the data on the left side of each cycle number NC indicates the measurement result of the insulation resistance Ra at the end of the first operation and the leak occurrence rate RT in the first operation, and the data on the right side of each cycle number NC. The data shows the measurement results of the insulation resistance Ra at the end of the second operation and the leak occurrence rate RT in the second operation. As shown in the figure, the insulation resistance Ra decreases at the end of the second operation, but the insulation resistance Ra recovers at the end of the next first operation. The reason for this is as follows. In the second operation, since the engine speed is low, the temperature in the combustion chamber of the engine is low, and carbon tends to adhere to the outer peripheral surfaces of the insulators 10 and 10B. In the first operation, since the engine speed is high, the temperature in the combustion chamber is high, and the carbon attached to the outer peripheral surfaces of the insulators 10 and 10B is burned out.

  As shown in FIG. 4A, when the spark plug 100 of the embodiment is used, the insulation resistance Ra is reduced to 10,000 MΩ or more by the first operation, although the insulation resistance Ra is reduced by the second operation. Such recovery of the insulation resistance Ra by the first operation progressed constantly over 10 cycles. Similarly, when the number of cycles NC exceeds 10, it is similarly estimated that the insulation resistance Ra can be recovered to 10000 MΩ or more by the first operation.

  As shown in FIG. 5 (A), when the spark plug 100B of the first reference example was used, the recovery of the insulation resistance Ra of 10000 MΩ or more by the first operation could not be continued. Further, the insulation resistance Ra gradually decreased as the number of cycles NC increased.

  Further, as shown in FIG. 4B, when the spark plug 100 of the embodiment is used, the leak occurrence rate RT was zero% over 10 cycles. On the other hand, as shown in FIG. 5B, when the spark plug 100B of the first reference example is used, the leak rate RT in the first operation tends to be higher than the leak rate RT in the second operation. It was. The reason for this is as follows. During the second operation, the amount of carbon attached to the outer peripheral surface of the insulator 10B gradually increases. Therefore, at the start of the next first operation, the amount of carbon attached is large, so that leak discharge is likely to occur. Further, during the first operation, the amount of carbon adhering to the outer peripheral surface of the insulator 10B gradually decreases due to burning or the like. Therefore, at the start of the next second operation, the amount of carbon attached is small, so that leak discharge hardly occurs. Further, since the first operation is a high load operation, leak discharge is likely to occur in the first operation. On the other hand, since the second operation is a low-load operation, leak discharge hardly occurs in the second operation. As described above, when the first operation and the second operation are repeated, the leak occurrence rate RT in the first operation can be high, and the leak occurrence rate RT in the second operation can be low.

  A high leak rate RT in the first operation indicates that the outer peripheral surface of the insulator is easily soiled, and a low leak rate RT in the first operation indicates that the outer peripheral surface of the insulator is not easily polluted. It is shown that. Comparing FIG. 4B and FIG. 5B, the leak rate RT in the first operation of the spark plug 100 of the embodiment (FIG. 4B) is the spark plug 100B of the first reference example ( The leak occurrence rate RT in the first operation in FIG. 5 (B) was lower.

  Thus, the stain resistance of the spark plug 100 of the embodiment is better than the stain resistance of the spark plug 100B of the first reference example. The reason is estimated as follows. In the spark plug 100 of the embodiment, the tip clearance distance 812 of the gap 310 (FIG. 2) is larger than the distance 811 of the gap g of the electrodes 20 and 30. Further, the metal shell 50 includes a first portion 511 whose inner diameter increases toward the rear direction Dfr on the front direction Df side with respect to the contact end position 713. Further, the rear end 317 of the maximum gap portion 315 is located on the rear direction Dfr side with respect to the intermediate position 712, that is, the maximum gap portion 315 extends on the rear direction Dfr side with respect to the intermediate position 712. As a result, the easiness of the flow of the combustion gas in the rear part gap 312 and thus the gap 310 is improved. This suppresses the combustion gas from staying in the rear part gap 312. Accordingly, the accumulation of carbon in the rear partial gap 312 and consequently in the gap 310 is suppressed. Further, since the high-temperature combustion gas easily flows in the gap 310, the burning of carbon adhering to the outer peripheral surface of the insulator 10 can be promoted. Further, when the combustion gas flows into the rear partial gap 312, the combustion gas can easily flow out from the rear partial gap 312 and thus from the gap 310. Therefore, it is possible to suppress the deposition of carbon on the outer peripheral surface 13o of the insulator 10. Moreover, the burning of carbon adhering to the outer peripheral surface 13o of the insulator 10 can be promoted. As a result, leak discharge can be suppressed. Moreover, the fall of insulation resistance can be suppressed.

  On the other hand, in the first reference example (FIG. 3), the rear end 327 of the maximum gap portion 325 is located on the front direction Df side with respect to the intermediate position 722. Therefore, in the rear portion gap 322, the gap distance is shortened, and the combustion gas tends to stay. As a result, carbon easily deposits on the outer peripheral surface of the insulator 10B in the rear portion gap 322. Further, since carbon is deposited on the outer peripheral surface of the insulator 10B in the rear partial gap 322 having a short gap distance, leak discharge is likely to occur.

C. Second evaluation test:
In the second evaluation test, a constant inner diameter portion (for example, the first portion 521 in FIG. 3) formed at the front end portion of the metal shell and reducing the inner diameter of the metal shell at the front end portion, and the flow of combustion gas in the annular gap. The relationship with ease was evaluated. FIG. 6 is a schematic view of a spark plug 100C of the second reference example. In the second evaluation test, the sample of the spark plug 100B of the first reference example shown in FIG. 3 and the sample of the spark plug 100C of the second reference example shown in FIG. 6 were evaluated.

  The metal shell 50C of the spark plug 100C of FIG. 6 replaces the portions 521 to 524 on the front direction Df side of the fifth portion 525 of the metal shell 50B of FIG. 3 with the first portion 531 and the second portion 532 of FIG. Is obtained. The first portion 531 extends from the front end surface 57C to the vicinity of the fifth portion 525. The inner diameter of the first portion 531 is constant regardless of the position in the direction parallel to the central axis CL. The inner diameter of the first portion 531 is larger than the inner diameter of the first portion 521 of the metal shell 50B of FIG. Further, the tip gap distance 832 at the tip of the metal shell 50C (that is, the gap distance at the opening 330o of the gap 330) is larger than the gap distance 821 formed by the center electrode 20 and the ground electrode 30.

  The inner diameter of the second portion 532 gradually decreases toward the rear direction Dfr. In the cross section including the central axis CL, the inner peripheral surface of the second portion 532 is represented by a straight line. A fifth portion 525 is connected to the rear direction Dfr side of the second portion 532. The radial width of the front end surface 57C of the metal shell 50C is smaller than the radial width of the front end surface 57B of the metal shell 50B in FIG. The thickness of the shaft portion 37C of the ground electrode 30C is adjusted to be small according to the width of the front end surface 57C of the metal shell 50C. The configuration of other parts of the spark plug 100C in FIG. 6 is the same as the configuration of the corresponding part of the spark plug 100B in FIG. 3 (the same elements as the corresponding elements are denoted by the same reference numerals and description thereof is omitted). To do). For example, the structure of the insulator 10B is the same between the spark plug 100B of FIG. 3 and the spark plug 100C of FIG.

  FIG. 7 is a graph showing the measurement result of the heat value. In the drawing, the heat value of the sample of the spark plug 100B of FIG. 3 and the heat value of the sample of the spark plug 100C of FIG. 6 are shown. The horizontal axis represents the heat value (the heat value increases toward the right). The heat value indicates the ease of heat release. A large heat value indicates that the type of the spark plug is “cold type”, that is, the spark plug is easily cooled, and the temperature rise of the spark plug is suppressed. A small heat value indicates that the type of spark plug is “burnt type”, that is, cooling of the spark plug is suppressed and the temperature of the spark plug tends to be high. A range R7 in the figure indicates a range corresponding to the No. 7 heat value.

  As shown in the drawing, the heat value of the sample of the spark plug 100B of the first reference example was smaller than the heat value of the sample of the spark plug 100C of the second reference example. That is, in the sample of the spark plug 100B, the temperature drop was suppressed compared to the sample of the spark plug 100C.

  The spark plug is heated by the high-temperature combustion gas that has flowed into the gap between the metal shell and the insulator (for example, the gaps 320 and 330 in FIGS. 2 and 6). When the high-temperature combustion gas in the gap is prevented from flowing out of the gap, the spark plug is continuously heated by the combustion gas, so that the spark plug is difficult to cool and the heat value is reduced. When the high-temperature combustion gas in the gap tends to flow out of the gap, the spark plug is easily cooled and the heat value is increased. Between the first reference example (FIG. 3) and the second reference example (FIG. 6), the shapes of the inner peripheral surfaces of the body portions 55B and 55C of the metal shells 50B and 50C are different. Due to such a difference in shape, there is a difference in the ease of the outflow of the combustion gas from the gaps 320 and 330. It is estimated that the difference in heat value shown in FIG. 7 is caused by the difference in easiness of the flow of combustion gas from the gaps 320 and 330.

  Specifically, when the inner peripheral surface 55Bi of the metal shell 50B of the spark plug 100B of FIG. 3 is traced from the rear direction Dfr side toward the front direction Df, the inner diameter is reduced by the second portion 522, and the first The portion 521 maintains a small inner diameter. The gap 320 is narrowed down in a portion including the opening 320o (portion formed by the first portion 521). Therefore, it is presumed that the combustion gas that has flowed in the rearward direction Dfr from the second portion 522 is suppressed from flowing out of the gap 320 through the narrow gap formed by the first portion 521. As described above, when the outflow of the combustion gas from the gap 320 is suppressed, the spark plug is difficult to cool (the heat value becomes small). In the spark plug 100B of the first reference example, the estimation that the outflow of the combustion gas from the gap 320 is matched with the small heat value of the spark plug 100B shown in FIG. When the outflow of the combustion gas from the gap 320 is suppressed, carbon contained in the combustion gas tends to remain in the gap 320. Therefore, in the spark plug 100B of FIG. 3, it is estimated that the outer peripheral surface of the insulator 10B is easily damaged as compared with the spark plug 100C of FIG.

  In the spark plug 100C in FIG. 6, a portion (for example, the first portion 521 in FIG. 3) for reducing the inner diameter of the metal shell 50C in the vicinity of the opening 330o of the gap 330 is omitted. Therefore, it is estimated that the combustion gas flowing into the gap 330 can easily flow out of the gap 330. As described above, when the combustion gas can easily flow out from the gap 330, the spark plug is easily cooled (the heat value is increased). In the spark plug 100C of the second reference example, the estimation that the combustion gas easily flows out from the gap 330 is consistent with the large heat value of the spark plug 100C shown in FIG. When the combustion gas easily flows out from the gap 330, the carbon contained in the combustion gas can be suppressed from remaining in the gap 320. Therefore, in the spark plug 100C in FIG. 6, it is presumed that the outer peripheral surface of the insulator 10B is less contaminated than the spark plug 100B in FIG.

  As for the spark plug 100 in FIG. 2, it is also estimated that the outer peripheral surface of the insulator 10 is less contaminated than the spark plug 100 </ b> B in FIG. 3. The reason for this is as follows. The metal shell 50 of FIG. 2 has a first portion 511 whose inner diameter decreases toward the front direction Df, like the second portion 522 of the metal shell 50B of FIG. However, the metal shell 50 in FIG. 2 has a portion (for example, the first portion 521 in FIG. 3) that maintains a small inner diameter from the front end of the metal shell in the rear direction Dfr, as in the metal shell 50C in FIG. Not done. In the first portion 511 of the metal shell 50 in FIG. 2, the inner diameter increases from the front end 57 of the metal shell 50 toward the rear direction Dfr. Therefore, in the spark plug 100 of FIG. 2, it is estimated that the combustion gas flowing into the gap 310 is likely to flow out of the gap 310 as compared with the spark plug 100B of FIG. The Therefore, in the spark plug 100 of FIG. 2, it is estimated that carbon is suppressed from being deposited on the outer peripheral surface 13 o of the insulator 10.

D. Third evaluation test:
In the third evaluation test, the insulation resistance was measured in a state where carbon was adhered to the outer peripheral surface of the leg portion of the insulator by the test operation. In the third evaluation test, the sample of the spark plug 100 of the embodiment shown in FIG. 2 and the sample of the spark plug 100D of the reference example having the metal shell 50C and the ground electrode 30C shown in FIG. 6 were evaluated. The parts other than the metal shell 50C and the ground electrode 30C of the spark plug 100D of the reference example are the same as the corresponding parts of the spark plug 100 of FIGS. In the evaluation test, the engine in which the samples of the spark plugs 100 and 100D were assembled was operated under predetermined conditions. Thereafter, the insulator 10 of the spark plugs 100 and 100D was removed from the metal shells 50 and 50C. Then, the first probe was fixed to the terminal fitting 40, and the second probe was brought into contact with the outer peripheral surface of the leg portion 13 of the insulator 10. Electrical resistance between these probes, that is, from the second probe to the center electrode 20 through the outer peripheral surface of the leg 13, and from the center electrode 20 to the terminal fitting 40 through the through-hole 12 of the insulator 10. The electrical resistance of the route to reach was measured as the insulation resistance. As the contact position of the second probe on the outer peripheral surface of the leg portion 13, thirteen positions selected at intervals of 1 mm from the range from 0 mm to 12 mm in distance from the tip of the leg portion 13 were used.

  FIG. 8 is a graph showing the test result of the sample of the spark plug 100, and FIG. 9 is a graph showing the test result of the sample of the spark plug 100D. The horizontal axis indicates the position Dp in the rear direction Dfr with reference to the tip of the insulator 10. The position Dp is represented by the distance in the backward direction Dfr from the tip 10f of the insulator 10 (unit: mm). The vertical axis on the right indicates the insulation resistance Rb (unit: MΩ). The scale on the right vertical axis is a logarithmic scale. The infinite symbol indicates that the insulation resistance Rb is 10,000 MΩ or more. Data points ma and mb indicate the relationship between the position Dp of the contact position of the second probe and the measurement result of the insulation resistance Rb.

  The left vertical axis indicates the outer diameter Do and the inner diameter Di (unit: mm). The outer diameter Do is the outer diameter of the outer peripheral surface 13o of the leg portion 13, and the inner diameter Di is the inner diameter of the inner peripheral surfaces 55i and 55Ci of the metal shells 50 and 50C. 8 and 9 show the relationship between the position Dp and the outer diameter Do of the outer peripheral surface 13o of the leg portion 13, and the position Dp and the inner peripheral surfaces 55i and 55Ci of the metal shells 50 and 50C. The relationship with the inner diameter Di is shown. A gap 340 in FIG. 9 is a gap between the inner peripheral surface 55Ci of the metal shell 50C and the outer peripheral surface 13o of the insulator 10.

  As shown in FIG. 8, the second portion 512 having a curved inner peripheral surface that protrudes outward in the radial direction is disposed within a range of a position Dp from 8 mm to 9 mm. In both FIG. 8 and FIG. 9, the gap distance was less than 0.5 mm within the range of the position Dp of 9 mm or more. Therefore, it is estimated that the combustion gas flows mainly within the range of the position Dp of 9 mm or less. Moreover, although illustration is abbreviate | omitted, the contact end position (for example, contact end position 713 of FIG. 2) was arrange | positioned in the range of the position Dp from 11 mm to 12 mm.

  When the amount of carbon adhering to the outer peripheral surface 13o of the leg portion 13 is large, the electric resistance of the outer peripheral surface 13o is reduced. Therefore, a small insulation resistance Rb indicates that the amount of carbon attached to the outer peripheral surface 13o is large. Further, as illustrated, the insulation resistance Rb was smaller as the position Dp was closer to the tip 10f, that is, as the second probe was closer to the center electrode 20.

  According to the measurement result shown in FIG. 8, within the range of the position Dp of 4 mm or more and 9 mm or less, the insulation resistance Rb was smaller as the position Dp was closer to the tip 10f. Within the range of the position Dp of 4 mm or less, the insulation resistance Rb was approximately constant regardless of the position Dp. In addition, the insulation resistance Rb was greater than 10 MΩ within the range of the position Dp of 6 mm or more, and the insulation resistance Rb was greater than 100 MΩ within the range of the position Dp of 7 mm or more.

  According to the measurement results shown in FIG. 9, the insulation resistance Rb rapidly decreased from 10000 MΩ or more to less than 10 MΩ by approaching the tips 10 f and 10 Bf within the range of the position Dp of 8 mm or more and 9 mm or less. By moving the position Dp from the 8 mm position to the 5 mm position, the insulation resistance Rb was further reduced. Within the range of the position Dp of 5 mm or less, the insulation resistance Rb was approximately constant regardless of the position Dp.

  In this way, in the reference example of FIG. 9, the insulation resistance Rb rapidly decreased from 10000 MΩ to less than 10 MΩ by moving the position Dp from the 9 mm position to the 8 mm position. On the other hand, in the embodiment of FIG. 8, although the insulation resistance Rb is decreased by moving the position Dp from the 9 mm position to the 8 mm position, the insulation resistance Rb exceeding 500 MΩ can be maintained at the 8 mm position Dp. As described above, the behavior of the insulation resistance Rb between the two positions Dp of 8 mm and 9 mm is greatly different between the embodiment of FIG. 8 and the reference example of FIG. Further, between the embodiment of FIG. 8 and the reference example of FIG. 9, the shape of the insulator 10 is approximately the same, but between the two positions Dp of 8 mm and 9 mm, the inside of the metal shells 50 and 50C. The shapes of the peripheral surfaces 55i and 55Ci are different. Therefore, it is estimated that the difference in the behavior of the insulation resistance Rb is mainly caused by the difference in the shapes of the inner peripheral surfaces 55i and 55Ci of the metal shells 50 and 50C.

  A portion between the two positions Dp of 8 mm and 9 mm of the metal shell 50 </ b> C of the reference example of FIG. 9 is formed by the first portion 531. As described with reference to FIG. 5, the inner diameter of the first portion 531 is constant regardless of the position in the direction parallel to the central axis CL. Therefore, the gap distance is smaller between the two positions Dp of 8 mm and 9 mm than in the embodiment of FIG. Thereby, the flow of combustion gas is suppressed. Then, between the two positions Dp of 8 mm and 9 mm, and in the range of the position closer to the tip 10 f than 8 mm, the outer peripheral surface 13 o of the leg portion 13 of the insulator 10 is compared with the embodiment of FIG. Carbon is easy to deposit. The above description of the reference example of FIG. 9 is based on the measurement result of FIG. 9, when the position Dp moves from the position of 9 mm to the position of 8 mm, the insulation resistance Rb decreases rapidly, and the position Dp of 8 mm or less This is consistent with the fact that the insulation resistance Rb was small in the range.

  The metal shell 50 of the embodiment of FIG. 8 has a second portion 512 between two positions Dp of 8 mm and 9 mm. As described with reference to FIG. 2, the inner diameter of the second portion 512 gradually decreases toward the rear direction Dfr. Moreover, the internal diameter of the 2nd part 512 is small along the convex curve toward the outer side of radial direction. Therefore, the gap distance can be increased between the two positions Dp of 8 mm and 9 mm, as compared with the reference example of FIG. Thereby, the ease of flow of combustion gas can be improved. Further, since the inner peripheral surface of the second portion 512 is represented by a curve on the cross section including the central axis CL, the direction in which the combustion gas flows is compared to the case where the inner peripheral surface is represented by a straight line or a broken line. It can change smoothly along the inner peripheral surface. Therefore, the ease of flow of the combustion gas can be improved. The second portion 512 is provided on the rear side Dfr side with respect to the maximum end position 317 of the maximum gap portion 315 (FIG. 2). Therefore, the easiness of flow of the combustion gas can be improved on the rear side Dfr side with respect to the maximum end position 317. As described above, the combustion gas is suppressed from staying in the vicinity of the second portion 512 and thus in the gap 310. Therefore, in the vicinity of the second portion 512, and thus in the gap 310, it is possible to suppress the deposition of carbon on the outer peripheral surface 13o of the insulator 10 as compared with the reference example of FIG. The above description of the embodiment of FIG. 8 is based on the measurement result of FIG. 8, and between the two positions Dp of 8 mm and 9 mm, and thus within the range of the position Dp of 6 mm or more, a large insulation resistance Rb (for example, This is consistent with the fact that an insulation resistance Rb) of 10 MΩ or more can be realized.

E. Variations:
(1) The configuration of the metal shell is not limited to the above configuration, and various other configurations can be employed. For example, the portion forming the tip of the metallic shell may be a constant inner diameter portion that maintains a constant inner diameter in the rear direction Dfr. Moreover, the part which forms the front-end | tip of a metal shell may be a part where an internal diameter becomes small toward the back direction Dfr from the front-end | tip of a metal shell.

  Further, a maximum gap portion (for example, the maximum gap portion 315 in FIG. 2) and a portion (for example, the second portion 512 in FIG. 2) in which the inner diameter decreases along a convex curve outward in the radial direction. Other parts may be formed between them. For example, at least one of the constant inner diameter portion and the portion whose inner diameter decreases toward the rear direction Dfr may be formed.

  Further, as the shape of the inner peripheral surface of the portion where the inner diameter becomes smaller toward the rear direction Dfr on the rear direction Dfr side than the maximum gap portion, instead of the curved shape like the second portion 512 in FIG. Any other shape can be adopted. For example, a curved shape that is convex toward the inside in the radial direction may be adopted. Further, the shape of the inner peripheral surface on the cross section including the central axis CL may be a shape represented by at least one of a straight line, a broken line, and a curved line. Further, the inner diameter may change stepwise with respect to the change in the position in the rear direction Dfr.

  Further, the inner diameter may decrease from the rear end of the maximum gap portion perpendicularly to the central axis CL. FIG. 10 is a schematic view showing a part of the spark plug 100E of another embodiment on the front direction Df side. Differences from the spark plug 100 of FIG. 2 are as follows. Of the body portion 55E of the metal shell 50E, the portion on the front direction Df side with respect to the reduced inner diameter portion 56 is divided into three portions 551, 552, and 513 arranged from the front direction Df side toward the rear end direction Dfr. The first portion 551 is a portion obtained by extending the first portion 511 in FIG. 2 to a position facing the end of the third portion 513 on the front direction Df side. The second portion 552 is a surface perpendicular to the central axis CL, and connects the end of the first portion 551 on the rear direction Dfr side and the end of the third portion 513 on the front direction Df side. The structure of the other parts of the spark plug 100E is the same as the structure of the corresponding part of the spark plug 100 of FIGS. 1 and 2 (the same elements as the corresponding elements are denoted by the same reference numerals and description thereof is omitted). To do). The gap 350 is a gap between the inner peripheral surface 55Ei of the metal shell 50E and the outer peripheral surface 13o of the insulator 10. The maximum gap portion 355 is a portion having the maximum gap distance in the gap 350. The maximum end position 357 indicates the position of the rear end of the maximum gap portion 355. The maximum end position 357 is located on the rear side Dfr side with respect to the intermediate position 712. Further, the tip gap distance 812 at the tip 57 of the metal shell 50E (that is, the opening 350o of the gap 350) is the same as the tip gap distance 812 in FIG. 2, and is larger than the distance 811 of the gap g. It is estimated that such a spark plug 100E can also suppress the accumulation of carbon on the outer peripheral surface 13o of the insulator 10.

  Further, on the cross section including the central axis CL, the front end Df side of the front end surface of the metal shell and the inner diameter surface of the metal shell from the enlarged inner diameter portion, which is the portion whose inner diameter increases toward the rear direction Dfr, are provided. A portion may form one or more corners. FIG. 11 is a schematic view showing a part of the spark plug 100F of another embodiment on the front direction Df side. In the drawing, a flat cross section including the central axis CL is shown as in the cross section of FIG. The only difference from the spark plug 100 of FIG. 2 is that the chamfered portion 511a is formed by chamfering the corner portion formed by the front end surface 57 of the metal shell 50 and the inner peripheral surface of the enlarged inner diameter portion 511. An enlarged sectional view of the vicinity of the chamfered portion 511a is shown in the lower part of FIG. 11 is the same as the structure of the corresponding part of the spark plug 100 of FIGS. 1 and 2 (the same elements as the corresponding elements are denoted by the same reference numerals, (The explanation is omitted.)

  In the embodiment of FIG. 11, the inner diameter of the chamfered portion 511a gradually decreases toward the rear direction Dfr. On the cross section shown in FIG. 11, the inner peripheral surface of the chamfered portion 511a is represented by a straight line. An expanded inner diameter portion 511b is provided on the rear direction Dfr side of the chamfered portion 511a. The shape of the expanded inner diameter portion 511b is the same as the shape of the remaining portion excluding the portion corresponding to the chamfered portion 511a in FIG. 11 of the expanded inner diameter portion 511 in FIG. The configuration of the metal shell 50F other than the chamfered portion 511a is the same as that of the metal shell 50 in FIG. For example, the shape of the inner peripheral surface 55Fi of the body portion 55F of the metal shell 50F is the same as that of the inner peripheral surface 55i of the body portion 55 of the metal shell 50 in FIG. 2 except for the inner surface of the chamfered portion 511a. The shape is the same.

  As shown in FIG. 11, the front end surface 57F of the metal shell 50F and the inner peripheral surface of the chamfered portion 511a form a first corner portion C1, and the inner peripheral surface of the chamfered portion 511a and the inner diameter surface of the expanded inner diameter portion 511b. The peripheral surface forms the second corner C2. On the cross section of FIG. 11, the first angle Ang1 indicates the angle of the first corner C1 (the angle on the inner side of the metal shell 50F), and the second angle Ang2 indicates the angle of the second corner C2. . In the present embodiment, these angles Ang1 and Ang2 are both greater than 90 degrees (that is, an obtuse angle). Generally, discharge is likely to occur at sharp corners. If the inner peripheral surface of the metal shell forms a corner of 90 degrees or less, a discharge may occur between the corner of the metal shell and the center electrode 20 instead of between the ground electrode 30 and the center electrode 20. . In the embodiment of FIG. 11, the distal end surface 57F of the metal shell 50F and the portion of the inner peripheral surface of the metal shell 50F on the side in the distal direction Df from the enlarged inner diameter portion 511b (that is, the inner peripheral surface and the surface of the enlarged inner diameter portion 511b) Each of the angles Ang1 and Ang2 of the two corners C1 and C2 formed by the inner peripheral surface of the take part 511a is larger than 90 degrees. Therefore, it is possible to suppress discharge from occurring between the corners C1 and C2 of the metal shell 50F and the center electrode 20 instead of the gap g between the electrodes 20 and 30.

  Further, the configuration of the spark plug 100F in FIG. 11 is the same as the configuration of the spark plug 100 in FIGS. 1 and 2 except that a chamfered portion 511a is formed. For example, the shape of the gap 360 between the inner peripheral surface 55Fi of the trunk portion 55F of the metal shell 50F and the outer peripheral surface 13o of the leg portion 13 of the insulator 10 is excluding the portion formed by the chamfered portion 511a. The shape of the gap 310 in FIG. 2 is the same. The tip clearance distance 812F at the tip 57F of the metal shell 50F (that is, the opening 360o of the gap 360) is larger than the distance 811 of the gap g. From the above, it is presumed that the spark plug 100F in FIG. 11 can suppress the accumulation of carbon on the outer peripheral surface 13o of the insulator 10 in the same manner as the spark plug 100 in FIGS. Note that the chamfered portion 511a in FIG. 11 may be applied to the metal shell of the other embodiment (for example, the metal shell 50E in FIG. 10).

  Generally, the metal shell preferably includes a portion whose inner diameter increases toward the rear direction Dfr on the front direction Df side with respect to the contact end position (for example, the contact end position 713 in FIG. 2). Also called “inner diameter part”). When the metal shell includes the enlarged inner diameter portion, the gap distance can be increased, so that the ease of gas flow in the gap (for example, the gap 310 in FIG. 2) can be improved. Any shape can be adopted as the shape of the inner peripheral surface of the expanded inner diameter portion. For example, the shape of the inner peripheral surface on the cross section including the central axis CL may be a shape represented by at least one of a straight line, a broken line, and a curved line. Further, the inner diameter may change stepwise with respect to the change in the position in the rear direction Dfr.

  Moreover, it is preferable that the gap | interval distance in the front-end | tip of a metal fitting is larger than the distance of the gap between a center electrode and a ground electrode. According to this configuration, it is possible to suppress the possibility of occurrence of discharge through a path from the center electrode through the outer peripheral surface of the insulator to the metal shell. In addition, since the combustion gas can easily flow out of the gap between the inner peripheral surface of the metal shell and the outer peripheral surface of the insulator (for example, the gap 310 in FIG. 2), the outer peripheral surface of the insulator Carbon deposition can be suppressed.

  Further, the position of the end on the rear direction Dfr side of the maximum gap portion (for example, the maximum end position 317 of the maximum gap portion 315 in FIG. 2) is the distance in the axial direction between the contact end position and the tip of the metal shell. It is preferable to be located on the rear direction Dfr side with respect to a central position (for example, an intermediate position 712 between the first position 711 and the contact end position 713 in FIG. 2) that is a position that bisects. According to this configuration, since the ease of flow of the fuel gas in the gap can be improved, it is possible to suppress carbon from remaining in the gap.

  In addition, the metal shell is “a portion whose inner diameter increases from the front end to the rear end side of the metal shell as in the first portion 511 in FIG. 2” and “a second portion 512 in FIG. It is preferable to have at least one of “a portion whose inner diameter decreases along a convex curve toward the outer side in the radial direction toward the rear end side on the rear end side with respect to the end position”.

  In addition, various shapes can be adopted as the shape of the inner peripheral surface of the metal shell from the enlarged inner diameter portion to the tip side (also referred to as the front end side inner peripheral surface). For example, the shape of the inner peripheral surface on the front end side on the cross section including the central axis CL may be a shape represented by at least one of a straight line, a broken line, and a curved line. Further, on the cross section including the central axis CL, the front end surface and the front end side inner peripheral surface of the metal shell may form one or more corners. The corner portion is a portion where two straight lines are connected on the cross section including the central axis CL. The total number of corners may be one, two, or three or more. Here, on the cross section including the central axis CL, each angle of one or more corners formed by the front end surface of the metal shell and the inner peripheral surface of the metal tip (on the inner side, not the outer side of the metal shell) The angle) is preferably an obtuse angle. According to this configuration, it is possible to suppress discharge from occurring at the corners of the metal shell instead of the ground electrode.

(2) The configuration of the spark plug is not limited to the above configuration, and various other configurations can be employed. For example, another member may be disposed between the ground electrode and the metal shell. In general, the ground electrode may be electrically connected to the metal shell directly or via another member. Further, at least one of the first tip 29 of the center electrode 20 and the second tip 39 of the ground electrode 30 may be omitted. In addition, as the shape of the center electrode 20, various shapes different from the shapes described in FIG. Further, as the shape of the ground electrode 30, various shapes different from the shapes described in FIG. 1 can be adopted.

  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.

5 ... gasket, 6 ... first rear end side packing, 7 ... second rear end side packing, 8 ... front end side packing, 9 ... talc, 10, 10B ... insulator 10f ... tip, 11 ... second reduced outer diameter part, 12 ... through hole (shaft hole), 13, 13B ... leg part, 13o, 13Bo ... outer peripheral surface, 14 .... Third reduced outer diameter portion, 15 ... first reduced outer diameter portion, 16 ... first reduced inner diameter portion, 17 ... front end side barrel portion, 18 ... rear end side barrel portion, 19. .. Buttocks (large diameter part), 20 ... center electrode, 21 ... outer layer, 22 ... core, 23 ... head, 24 ... buttocks, 25 ... leg , 27 ... Shaft part, 29 ... First tip, 30, 30C ... Ground electrode, 31 ... Tip part, 35 ... Outer layer, 36 ... Core part, 37, 37C ... .Shaft portion, 39 ... second chip, 40 ... terminal fitting, 50, 50B, 50C, 50E, 50F ... main fitting, 51 ... tool engaging portion, 52 ... thread, 53 ... Clamping part, 54 ... Seat part, 5, 55B, 55E, 55F ... trunk, 55i, 55Bi, 55Ci, 55Ei, 55Fi ... inner peripheral surface, 56 ... reduced inner diameter part, 57, 57B, 57C, 57F ... tip (tip) Surface), 58 ... deformation part, 59 ... through hole, 60 ... first seal part, 70 ... resistor, 80 ... second seal part, 100, 100B, 100C, 100D, 100E, 100F ... Spark plug, 310, 320, 330, 340, 350, 360 ... Gap, 310o, 320o, 330o, 350o, 360o ... Opening, 311, 321 ... Front part gap, 312 322 ... rear part gap, 315, 325, 355 ... maximum gap part, 317, 327, 357 ... maximum end position (rear end), 511a ... chamfered part, 511, 511b. .Inner diameter part, 711, 721 ... 1st position, 712, 722 ... 2nd position (intermediate position) 713, 723 ... third position (contact end position), 802 ... gap distance, 811, 821 ... distance, 812, 822, 832 ... tip gap distance, g ... gap, CL. ..Center axis (axis), Df ... front end direction (forward direction), Dfr ... rear end direction (rear direction)

Claims (4)

A through-hole having a reduced outer diameter portion whose outer diameter decreases toward the distal end in the direction of the axis, and a leg portion that is a portion on the distal end side from the reduced outer diameter, and extending in the direction of the axis An insulator to be formed;
A central electrode at least a part of which is inserted on the tip side of the through hole;
A metal shell that is disposed around the insulator in the radial direction, has a reduced inner diameter portion that decreases in inner diameter toward the tip side, and forms an annular gap with the outer peripheral surface of the leg portion;
A ground electrode electrically connected to the metal shell and forming a gap with the center electrode;
A packing disposed between the reduced outer diameter portion of the insulator and the reduced inner diameter portion of the metal shell;
A spark plug comprising:
Of the contact portion between the packing and the metal shell, the position on the most distal side is the contact end position,
The radial distance between the outer peripheral surface of the leg portion of the insulator and the inner peripheral surface of the metal shell is a gap distance,
When the position of the rear end of the maximum portion of the annular gap where the gap distance is the maximum is the maximum end position,
The gap distance at the tip of the metal shell is larger than the gap distance between the center electrode and the ground electrode,
The metal shell includes an enlarged inner diameter portion whose inner diameter increases toward the rear end side in the direction of the axis on the tip side than the contact end position,
The maximum end position is located on the rear end side from a center position that is a position that bisects the distance in the direction of the axis between the contact end position and the front end of the metal shell.
Spark plug. The spark plug according to claim 1,
On the cross section including the axis, the front end surface of the metallic shell and the inner peripheral surface of the metallic shell, the portion on the distal end side from the enlarged inner diameter portion forms one or more corners,
Each of the one or more corners is an obtuse angle.
Spark plug. The spark plug according to claim 1,
The enlarged inner diameter portion of the metal shell includes a portion whose inner diameter increases from the front end of the metal shell toward the rear end side.
Spark plug. The spark plug according to any one of claims 1 to 3,
The metal shell includes a portion whose inner diameter becomes smaller along a convex curve toward the outer side in the radial direction toward the rear end side on the rear end side than the maximum end position.
Spark plug.

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