JP2015064987A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a spark plug.SOLUTION: A spark plug comprises: a center electrode extending in an axial line direction; an insulator that has a shaft hole extending in the axial line direction and in which the center electrode is arranged on a tip side of the shaft hole; a resistor arranged nearer a rear end than the center electrode in the shaft hole; and a seal part arranged at least at one part between the resistor and the center electrode in the shaft hole. Here, a rear end of a face directed to a tip side of the resistor at a portion away from an inner periphery of the insulator is designated as a second rear end, and a rear end of the seal part on a cross section including the axial line and the second rear end at a portion contacting the inner periphery of the insulator is designated as a first rear end. The second rear end is arranged nearer the rear end than the first rear end. A shortest distance in a radial direction between the second end and the inner periphery of the insulator is 0.5 mm or more.

Description

  The present invention relates to a spark plug.

  Conventionally, spark plugs have been used in internal combustion engines. As the spark plug, a central electrode extending in the axial direction, an insulator having an axial hole extending in the axial direction and having the central electrode inserted on the tip side of the axial hole, a resistor disposed in the axial hole, A spark plug having a conductive seal layer provided between a resistor in a shaft hole and a center electrode is known. Here, in order to increase the area of the joint surface between the conductive seal layer and the resistor, a technique for forming the joint surface in a curved shape protruding toward the center electrode side has been proposed.

JP 2009-245716 A JP 58-102481 A

  A current flows through a member (for example, a seal layer) inside the shaft hole during discharge. Due to this current, the conductive performance of the member can be reduced. For example, the heat generated by the current can cause a decrease in the conductive performance of the member (for example, the resistance value increases). Further, when the current is concentrated on a partial region of the member, the conductive performance of the member may be locally reduced. Such a decrease in the conductive performance of the member is one of the factors that limit the durability of the spark plug.

  The main advantage of the present invention is to improve the durability of the spark plug.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples.

[Application Example 1]
A central electrode extending in the direction of the axis;
An insulator having an axial hole extending in the direction of the axial line, and the central electrode disposed on a tip side of the axial hole;
A resistor disposed on the rear end side of the center electrode in the shaft hole;
A seal portion disposed at least in part between the resistor and the center electrode in the shaft hole;
A spark plug comprising:
The seal portion on the cross section including the axis and the second rear end, with the rear end of a portion of the surface facing the front end side of the resistor away from the inner peripheral surface of the insulator as the second rear end When the rear end of the portion in contact with the inner peripheral surface of the insulator is the first rear end,
The second rear end is disposed closer to the rear end side than the first rear end, and the shortest radial distance between the second rear end and the inner peripheral surface of the insulator is 0.5 mm or more. is there,
Spark plug.

  According to this configuration, since the vicinity of the second rear end of the front end face of the resistor is easily used as a current path during discharge, it is possible to suppress the current from being concentrated in a part of the region. Therefore, durability can be improved.

[Application Example 2]
The spark plug according to application example 1,
A spark plug, wherein a distance in a direction of the axis between the first rear end and the second rear end is 0.5 mm or more.

  According to this configuration, since the vicinity of the first rear end of the seal portion and the vicinity of the second rear end of the resistor are easily used as a current path at the time of discharging, the current is concentrated in a part of the region. Can be further suppressed. Therefore, durability can be further improved.

[Application Example 3]
The spark plug according to application example 1 or 2,
The minimum value of the length along a straight line passing through the center of gravity of the portion surrounded by the resistor in a cross section perpendicular to the direction of the axis at a position where the distance in the direction of the axis from the second rear end is 0.2 mm Is a spark plug which is 1 mm or more.

  According to this configuration, compared with the case where the minimum value of the length is less than 1 mm, a wide portion including the second rear end of the front end surface of the resistor is easily used as a current path during discharge. Therefore, it can suppress that an electric current concentrates on a one part area | region. Therefore, durability can be improved.

[Application Example 4]
The spark plug according to any one of Application Examples 1 to 3,
A spark plug, wherein a radial thickness of a portion of the insulator that accommodates the seal portion is 1.1 mm or more.

  According to this structure, compared with the case where the thickness is less than 1.1 mm, the vicinity of the seal portion is difficult to cool, and thus the temperature of the seal portion is likely to increase. Even under such conditions, it is possible to improve the durability because the current is suppressed from being concentrated in a part of the region.

[Application Example 5]
The spark plug according to any one of Application Examples 1 to 4,
The spark plug has a maximum diameter of 3.0 mm or less.

  According to this configuration, compared to the case where the maximum diameter of the seal portion exceeds 3.0 mm, the current is less likely to be dispersed during discharge, and the durability of the seal portion is likely to be reduced. Even under such conditions, it is possible to improve the durability because the current is suppressed from being concentrated in a part of the region.

[Application Example 6]
The spark plug according to any one of Application Examples 1 to 5,
A spark plug, wherein a rear end of the center electrode is covered with the seal portion.

  According to this configuration, since the adhesion between the center electrode and the seal portion can be improved, durability against vibration can be improved.

  It should be noted that the present invention can be realized in various aspects, for example, in aspects such as a spark plug and an internal combustion engine equipped with the spark plug.

It is sectional drawing of the spark plug 100 of 1st Embodiment. 2 is a partial cross-sectional view showing an insulator 10, a resistor 70, a first seal portion 60, and a center electrode 20. FIG. It is a fragmentary sectional view of spark plug 100R of a reference example, and a fragmentary sectional view of spark plug 100 of an embodiment. It is explanatory drawing of the spark plug 100x of 2nd Embodiment. It is explanatory drawing of the spark plug 100z of 3rd Embodiment.

A. First embodiment:
A1. Spark plug configuration:
FIG. 1 is a cross-sectional view of the spark plug 100 of the first embodiment. The illustrated line CL indicates the central axis of the spark plug 100. The illustrated cross section is a cross section including the central axis CL. Hereinafter, the central axis CL is also referred to as “axis line CL”, and the direction parallel to the central axis CL is also referred to as “axis direction” or simply “axial 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”. The downward direction in FIG. 1 is referred to as a leading end direction D1, and the upward direction is also referred to as a trailing end direction D2. 1 is referred to as the front end side of the spark plug 100, and the rear end direction D2 side in FIG. 1 is referred to as the rear end side of the spark plug 100. These directions D1 and D2 are both parallel to the central axis CL. The tip direction D1 is a direction from the terminal fitting 40 described later toward the electrodes 20 and 30.

  The spark plug 100 includes an insulator 10 (also referred to as “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 resistance The body 70, the electroconductive 2nd seal | sticker part 80, the front end side packing 8, the talc 9, the 1st rear end side packing 6, and the 2nd rear end side packing 7 are provided.

  The insulator 10 is a substantially cylindrical member having a through hole 12 (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 body portion 17, a flange portion 19, and a second reduced outer diameter portion, which are arranged in order from the front end side to the rear end side. 11 and a rear end side body portion 18.

  The flange portion 19 is a portion located approximately at the center in the axial direction of the insulator 10, and is the maximum outer diameter portion of the insulator 10. A front end side body portion 17 is provided on the front end side of the flange portion 19. A first reduced outer diameter portion 15 is provided on the distal end side of the distal end side body portion 17. The outer diameter of the first reduced outer diameter portion 15 gradually decreases from the rear end side toward the front end side. A leg portion 13 is provided on the distal end side of the first reduced outer diameter portion 15. With the spark plug 100 attached to an internal combustion engine (not shown), the leg 13 is exposed to the combustion chamber. Further, 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 reduced inner diameter portion 16 whose inner diameter gradually decreases from the rear end side toward the front end side. Is formed.

  A second reduced outer diameter portion 11 is provided on the rear end side of the flange portion 19. The outer diameter of the second reduced outer diameter portion 11 gradually decreases from the front end side toward the rear end side. A rear end side body portion 18 is provided on the rear end side of the second reduced outer diameter portion 11.

  A center electrode 20 is inserted on the distal end side of the through hole 12 of the insulator 10. The center electrode 20 is a rod-shaped member extending along the center axis CL. The center electrode 20 includes an electrode base material 21 and a core material 22 embedded in the electrode base material 21. The electrode base material 21 is formed using, for example, Inconel (“INCONEL” is a registered trademark) which is an alloy containing nickel as a main component. The core material 22 is formed of a material (for example, an alloy containing copper) having a higher thermal conductivity than the electrode base material 21.

  Focusing on the external shape of the center electrode 20, the center electrode 20 includes a head portion 23 that forms an end on the rear end direction D 2 side, a flange portion 24 provided on the distal end side of the head portion 23, and a flange portion 24. And a leg portion 25 provided on the distal end side. The shape of the head 23 is a substantially cylindrical shape centered on the central axis CL. The outer diameter of the collar portion 24 is larger than the outer diameter of the head portion 23 and the outer diameter of the leg portion 25. The head portion 23 and the flange portion 24 are disposed in the through hole 12, and the surface of the flange portion 24 on the tip direction D 1 side is supported by the reduced inner diameter portion 16 of the insulator 10. A portion on the distal end side of the leg portion 25 is exposed outside the through hole 12 on the distal end side of the insulator 10.

  A terminal fitting 40 is inserted on the rear end side of the through hole 12 of the insulator 10. The terminal fitting 40 is a rod-shaped member that extends along the central axis CL. The terminal fitting 40 is formed using low carbon steel (however, other conductive materials (for example, metal materials) can also be used). The terminal fitting 40 includes a flange portion 42, a cap mounting portion 41 that forms a portion on the rear end side from the flange portion 42, and a leg portion 43 that forms a portion on the front end side from the flange portion 42. The cap mounting portion 41 is exposed outside the through hole 12 on the rear end side of the insulator 10. The leg 43 is inserted into the through hole 12 of the insulator 10.

A resistor 70 is disposed between the terminal fitting 40 and the center electrode 20 in the through hole 12 of the insulator 10. The resistor 70 is formed of a composition including glass particles as a main component, ceramic particles other than glass, and a conductive material. As the material of the glass particles, for example, B ₂ O ₃ —SiO ₂ type, BaO—B ₂ O ₃ type, SiO ₂ —B ₂ O ₃ —CaO—BaO type, etc. can be adopted. As a material of the ceramic particles, for example, TiO ₂ , ZrO ₂ or the like can be adopted. As the conductive material, for example, non-metallic conductive materials such as carbon particles (carbon black and the like), TiC particles and TiN particles, and metals such as Al, Mg, Ti, Zr and Zn can be employed. The resistance value of the resistor 70 is, for example, preferably from 0.1 kΩ to 30 kΩ, and more preferably from 1 kΩ to 20 kΩ.

  In the through hole 12, the first seal portion 60 is disposed at least at a part between the resistor 70 and the center electrode 20. A second seal portion 80 is disposed at least partly between the resistor 70 and the terminal fitting 40. As a result, the center electrode 20 and the terminal fitting 40 are electrically connected through the resistor 70 and the seal portions 60 and 80. The seal portions 60 and 80 include, for example, the above-described various glass particles and metal particles (Cu, Fe, etc.) at a ratio of about 1: 1. The seal portions 60 and 80 have material characteristics between the material characteristics of the center electrode 20 and the terminal fitting 40, which are metal, and the material characteristics of the resistor 70 whose main component is glass. As a result, by interposing the seal portions 60, 80, the contact resistance between the stacked members 20, 60, 70, 80, 40 is stabilized, and the resistance value between the center electrode 20 and the terminal fitting 40 is stabilized. Can be made. In addition, as the seal portions 60 and 80, a member having a smaller electrical resistivity (electrical resistivity (unit: “Ωm”)) than that of the resistor 70 is employed.

  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, and the metal shell 50 is fixed to the outer periphery of the insulator 10. The tip of the insulator 10 (that is, the end on the tip direction D1 side) is exposed outside the through hole 59 on the tip side of the metal shell 50. The rear end of the insulator 10 (that is, the end on the rear end direction D2 side) is exposed outside the through hole 59 on the rear end side of the metal shell 50.

  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. A body portion 55 is provided on the distal end side of the seat portion 54. The outer diameter of the trunk portion 55 is smaller than the outer diameter of the seat portion 54. A threaded portion 52 is formed on the outer peripheral surface of the body portion 55 to be screwed into a mounting hole of the internal combustion engine. An annular gasket 5 formed by bending a metal plate is fitted between the seat portion 54 and the screw portion 52.

  The trunk portion 55 of the metal shell 50 has a reduced inner diameter portion 56. The reduced inner diameter portion 56 is disposed on the tip side of the flange portion 19 of the insulator 10. 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 side packing 8 is an iron O-ring (other materials (for example, metal materials such as copper) can also be used).

  On the rear end side of the seat portion 54, a deformed portion 58 that is thinner than the seat portion 54 is provided. The deformed portion 58 is deformed so that the center portion protrudes outward in the radial direction (in a direction away from the central axis CL). A tool engagement portion 51 is provided on the rear end side of the deformation portion 58. The shape of the tool engaging portion 51 is a shape (for example, a hexagonal column) with which the spark plug wrench is engaged. On the rear end side of the tool engaging portion 51, a caulking portion 53 that is thinner than the tool engaging portion 51 is provided. 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 end direction D2 side). The caulking portion 53 is bent toward the inner side in the radial direction.

  The inner peripheral surface of the rear end side portion (in this embodiment, the caulking portion 53 and the tool engagement portion 51) including the caulking portion 53 of the metal shell 50, the second reduced outer diameter portion 11 of the insulator 10, and An annular space SP is formed between the rear end side body portion 18 and the outer peripheral surface. A first rear end side packing 6 is disposed on the rear end side in the space SP, and a second rear end side packing 7 is disposed on the front end side in the space SP. In this embodiment, these rear end side packings 6 and 7 are iron C-rings (other materials are also employable). Between the two rear end side packings 6 and 7 in the space SP, powder of talc (talc) 9 is filled.

  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 end direction D1 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. As a result, the gas in the combustion chamber of the internal combustion engine is prevented from leaking outside through the metal shell 50 and the insulator 10.

  The ground electrode 30 is joined to the tip of the metal shell 50 (that is, the end on the tip direction D1 side). In the present embodiment, the ground electrode 30 is a rod-shaped electrode. The ground electrode 30 extends from the metal shell 50 in the distal direction D1, bends toward the central axis CL, and reaches the distal end portion 31. The distal end portion 31 forms a gap g with the distal end surface 20s1 (surface 20s1 on the distal end direction D1 side) of the center electrode 20. The ground electrode 30 is joined to the metal shell 50 so as to be electrically connected (for example, laser welding). The ground electrode 30 has a base material 35 that forms the surface of the ground electrode 30 and a core portion 36 embedded in the base material 35. The base material 35 is formed using, for example, Inconel. The core part 36 is formed using a material (for example, pure copper) whose thermal conductivity is higher than that of the base material 35.

A2. Configuration in the vicinity of the first seal portion 60:
FIG. 2 is a partial cross-sectional view showing the insulator 10, the resistors 70 and 72, the first seal portions 60 and 60, and the center electrode 20 accommodated in the through hole 12 of the insulator 10. 2A shows a case where a distance Dc described later is relatively large, and FIG. 2B shows a case where the distance Dc is relatively small. In the drawing, the vicinity of the first seal portions 60 and 62 is shown. The illustrated cross section is a cross section including the central axis CL. In the drawing, the cross section of the center electrode 20 is shown without distinguishing the electrode base material 21 (FIG. 1) and the core material 22.

  First, the structure in FIG. 2A will be described. As shown in the drawing, the end of the resistor 70 on the tip end direction D1 side has a substantially cylindrical wall portion 70w protruding toward the tip end direction D1, and a bottom portion 70b surrounded by the wall portion 70w. Yes. The wall portion 70w is in contact with the inner peripheral surface 10i of the insulator 10 over the entire circumference. The bottom portion 70b is disposed on the rear end direction D2 side with respect to the front end surface 70ws1 of the wall portion 70w (that is, the surface 70ws1 on the front end direction D1 side). The shape of the surface 70bs1 (surface on the front end direction D1 side) of the bottom portion 70b is a concave shape (substantially bowl shape) recessed toward the rear end direction D2 side. In the region surrounded by the bottom portion 70b and the wall portion 70w, an end portion (here, a part of the head portion 23) on the rear end direction D2 side of the center electrode 20 is disposed. The wall portion 70w is disposed between the outer peripheral surface of the center electrode 20 (here, the head portion 23) and the inner peripheral surface 10i of the insulator 10. The front end surface 70ws1 of the wall 70w of the resistor 70 is located at a position away from the flange 24 of the center electrode 20 in the rear end direction D2.

  In the space between the outer peripheral surface of the center electrode 20 and the inner peripheral surface 10i of the insulator 10, a portion of the wall portion 70w on the side of the distal end direction D1 with respect to the distal end surface 70ws1 is a portion of the first seal portion 60. A certain outer seal portion 60a is arranged. The first rear end E1 in the drawing indicates the rear end (the end on the most rear end direction D2 side) of the portion where the first seal portion 60 is in contact with the inner peripheral surface 10i of the insulator 10 in the illustrated cross section. ing. In the embodiment of FIG. 2 (A), the position of the first rear end E1 is the tip of the portion of the resistor 70 in contact with the inner peripheral surface 10i of the insulator 10 in the cross section shown in the figure. It is the same as the position on the tip direction D1 side).

  On the end surface 23s2 on the rear end direction D2 side of the center electrode 20 (here, the surface 23s2 on the rear end direction D2 side of the head 23), an inner seal portion 60b that is a part of the first seal portion 60 is disposed. ing. The shape of the inner seal portion 60b is a convex shape (substantially dome shape) protruding from the end face 23s2 toward the rear end direction D2. That is, the substantially central portion of the inner seal portion 60b protrudes more toward the rear end direction D2 than the peripheral edge portion of the inner seal portion 60b. The inner seal portion 60 b is surrounded by the end surface 23 s 2 of the center electrode 20 and the surface 70 bs 1 (surface on the tip direction D 1 side) of the bottom portion 70 b of the resistor 70. The second rear end E2 in the drawing indicates the rear end (the end on the most rear end direction D2 side) of the surface 70bs1 of the bottom 70b of the resistor 70. The position of the second rear end E2 is the same as the position of the rear end (the end closest to the rear end direction D2) of the inner seal portion 60b. In the present embodiment, the second rear end E2 is disposed closer to the rear end direction D2 than the first rear end E1. 2A is a cross section including the central axis CL and the second rear end E2. In the embodiment of FIG. 2, the second rear end E2 is located at a position away from the central axis CL. When the second rear end E2 is located on the central axis CL, a plurality of cross sections including the central axis CL are candidates for a cross section including the central axis CL and the second rear end E2. In this case, as the first rear end E1, the first rear end on the cross section in which a distance Dd (a distance parallel to the central axis CL between the first rear end E1 and the second rear end E2) to be described later is minimized. E1 may be adopted.

  The surface 70bs1 of the bottom 70b of the resistor 70 and the inner peripheral surface 70wi and the tip surface 70ws1 of the wall 70w form a surface 70s1 facing the tip direction D1 side of the resistor 70 (hereinafter referred to as “tip surface”). 70s1 "). Said 2nd rear end E2 respond | corresponds to the rear end (end on the most back end direction D2 side) of the part away from the inner peripheral surface 10i of the insulator 10 among the front end surfaces 70s1 of the resistor 70. Here, the surface 70s1 facing the front end direction D1 side of the resistor 70 faces the rear end direction D2 from the position on the central axis CL on the front end direction D1 side of the resistor 70 in the surface of the resistor 70. When observing, the surface which can be observed is shown. In the present embodiment, the surface of the resistor 70 is in contact with the inner peripheral surface 10 i of the insulator 10 over the entire circumference. Accordingly, the entire portion of the surface of the portion on the tip direction D1 side of the resistor 70 that is away from the inner peripheral surface 10i of the insulator 10 corresponds to the tip surface 70s1. In other words, the remaining part excluding the part in contact with the inner peripheral surface of the insulator 10 from the surface of the part on the tip direction D1 side of the resistor 70 corresponds to the tip surface 70s1. Note that the surface of the resistor 70 facing the tip direction D1 side has no relation to the normal direction of a micro surface (for example, a surface of several tens of nanometers) that can be observed by a scanning electron microscope or the like. Specified. Similarly, the surface of the other member facing the front end direction D1 side and the surface facing the rear end direction D2 side can also be specified. For example, the end surface 23 s 2 of the head 23 of the center electrode 20 is a part of the surface facing the rear end direction D 2 side of the center electrode 20.

Further, in the figure, five parameters Dc to Dg described below are shown.
1) The distance Dc is the shortest distance between the second rear end E2 and the inner peripheral surface 10i of the insulator 10 (hereinafter also referred to as “shortest distance Dc”). The cross section of FIG. 2A is a cross section including the central axis CL and the second rear end E2, so the shortest distance between the second rear end E2 and the inner peripheral surface 10i on this cross section is the shortest distance. Corresponds to Dc.
2) The distance Dd is a distance parallel to the central axis CL between the first rear end E1 and the second rear end E2 (hereinafter also referred to as “end-to-end distance Dd”).

3) The length De is a minimum value of a length along a straight line passing through the center of gravity of an offset portion 70o described later (hereinafter also referred to as “minimum length De”). Here, the offset portion 70o is a portion of the front end surface 70s1 of the resistor 70 at a position where the distance parallel to the central axis CL from the second rear end E2 is Dw. In other words, the offset portion 70o is a portion (namely, region) surrounded by the resistor 70 in a cross section perpendicular to the central axis CL at a position where the distance parallel to the central axis CL from the second rear end E2 is Dw. Outline is shown. Hereinafter, 0.2 mm is adopted as the distance Dw. An example of the offset portion 70o viewed from the front end direction D1 is shown on the right side of FIG. As shown in the figure, the offset portion 70o forms a closed loop. As shown in FIG. 2A, the shape of the offset portion 70o may be a substantially circular shape. The center of gravity 70 oc in the drawing indicates the center of gravity of the offset portion 70 o, that is, the center of gravity of the region surrounded by the offset portion 70 o. The center of gravity of the region is the position of the center of gravity when it is assumed that the mass is evenly distributed in the region. The center of gravity 70 oc of the offset portion 70 o can be disposed at a position away from the central axis CL. The minimum length De is the minimum value of the length of the offset portion 70o along a straight line passing through the center of gravity 70oc. In other words, the minimum length De is the minimum value of the distance between two intersections of the straight line passing through the center of gravity 70oc and the offset portion 70o. Note that a straight line defining the minimum length De (that is, a straight line passing through the center of gravity 70 oc) may be different from a straight line on the cross section including the central axis CL and the second rear end E2.

4) The thickness Df is a radial thickness of a portion of the insulator 10 that houses the first seal portion 60.
5) The outer diameter Dg is the maximum diameter of the first seal portion 60. In the present embodiment, the outer diameter Dg of the first seal portion 60 is the same as the inner diameter of the through hole 12 of the insulator 10.

  These parameters Dc, Dd, De, Df, Dg can be measured as follows, for example. First, the shapes of the first seal portion 60 and the resistor 70 are specified using an X-ray CT scanner, and the rear end E2 on the front end surface 70s1 is specified. Next, the spark plug 100 is cut along a plane including the central axis CL and the specified rear end E2. The first rear end E1 is specified from the cross section obtained as a result. Then, on this cross section, the shortest distance Dc, the end-to-end distance Dd, the thickness Df, and the outer diameter Dg are measured. The minimum length De can be calculated based on the specified shape by specifying the shape of the offset portion 70o using an X-ray CT scanner. Instead, the spark plug 100 may be further cut along a plane that includes the offset portion 70o and is perpendicular to the central axis CL. The shape of the offset part 70o is specified from the cross section obtained in this way, and the minimum length De can be calculated based on the specified shape.

  Next, the structure of FIG. 2B will be described. In the configuration of FIG. 2B, the resistor 70 of the configuration of FIG. 2A is replaced with a resistor 72 having a slightly different shape, and the first seal portion 60 is replaced with a first seal portion 62 having a slightly different shape. Has been replaced. The resistor 72 has a wall portion 72w and a bottom portion 72b, similarly to the resistor 70 of FIG. The first seal portion 62 has an outer seal portion 62a and an inner seal portion 62b, similarly to the first seal portion 60 of FIG. The other structure in FIG. 2B is the same as the structure in FIG. 2B, the same elements as those in FIG. 2A are denoted by the same reference numerals, and description thereof is omitted.

  In the configuration shown in FIG. 2B, the first rear end E1, the second rear end E2, and the parameters Dc, Dd, De, Df, and Dg can be specified as in the configuration in FIG. is there. In FIG. 2B, the second rear end E2 is closer to the inner peripheral surface 10i of the insulator 10 than in FIG. Thereby, the shape of the inner seal portion 62 b is a convex shape that is biased toward the second rear end E <b> 2, and protrudes more outward than the outer peripheral surface of the head 23 of the center electrode 20. The shape of the bottom portion 72b of the resistor 72 is a shape that matches the shape of the inner seal portion 62b.

  The shape of the wall portion 72w is the same as the shape of the wall portion 70w in FIG. The shape of the outer seal portion 62a is the same as the shape of the outer seal portion 60a in FIG. The front surface 72bs1 of the bottom 72b, the inner peripheral surface 72wi and the front end surface 72ws1 of the wall 72w form a front end surface 72s1 of the resistor 72.

  An example of the offset portion 72o viewed from the front end direction D1 is shown on the right side of FIG. The specifying method of the offset unit 72o is the same as the method of FIG. As illustrated, the shape of the offset portion 72o may be a shape having an outwardly convex part and an inwardly convex part. Also in such a case, the minimum value of the length of the offset portion 72o along the straight line passing through the center of gravity 72oc of the offset portion 72o is calculated as the minimum length De.

  In addition, as a manufacturing method of the spark plug 100 having the configuration shown in FIGS. 1, 2A, and 2B, any method can be adopted. For example, the following manufacturing method can be employed. First, the insulator 10, the center electrode 20, the terminal fitting 40, the material powder of the first seal portions 60 and 62, the material powder of the resistors 70 and 72, and the material powder of the second seal portion 80. prepare. Next, the center electrode 20 is inserted from the opening on the rear end direction D2 side of the through hole 12 of the insulator 10 (hereinafter referred to as “rear opening 12o2”). As described with reference to FIG. 1, the center electrode 20 is supported by the reduced inner diameter portion 16 of the insulator 10. As a result, the center electrode 20 is disposed at a predetermined position in the through hole 12.

  Next, the material powder of the first seal portions 60 and 62 is charged from the rear opening 12o2 of the through hole 12 toward the center electrode 20. Next, preliminary compression is performed on the material powder of the first seal portions 60 and 62. Pre-compression is a process of compressing the material powder using the first rod. When manufacturing a spark plug having a large shortest distance Dc as shown in FIG. 2A, a rod having an end having substantially the same shape as the tip surface 70s1 of the resistor 70 is used as the first rod. Thus, the material powder is formed into substantially the same shape as the shape of the first seal portion 60. When manufacturing a spark plug with a shortest distance Dc as shown in FIG. 2 (B), a rod having an end portion close to the shape of the distal end surface 72s1 of the resistor 72 is used as the first rod. The material powder is formed into a shape close to the shape of the first seal portion 62.

  Next, the material powder of the resistors 70 and 72 is charged from the rear opening 12o2 of the through hole 12 toward the material powder of the first seal portions 60 and 62. Next, the material powder of the resistors 70 and 72 is molded by pre-compressing the material powder of the resistors 70 and 72. For example, in this preliminary compression, a second rod having a flat end surface on the front end direction D1 side is used, and the ends of the resistor powders 70 and 72 on the rear end direction D2 side are in a plane substantially perpendicular to the central axis CL. Molded.

  Next, the material powder of the second seal portion 80 is charged from the rear opening 12o2 of the through hole 12 toward the material powder of the resistors 70 and 72. Next, the material powder of the second seal portion 80 is molded by pre-compressing the material powder of the second seal portion 80. This pre-compression is performed in the same manner as the pre-compression of the material powder of the resistors 70 and 72.

  Next, the insulator 10 is heated to a predetermined temperature higher than the softening point of the glass component contained in each material powder, and in the state heated to the predetermined temperature, the terminal fitting 40 is penetrated from the rear opening 12o2 of the through hole 12. Insert into hole 12. As a result, the respective material powders are compressed and sintered to form the first seal portions 60 and 62, the resistors 70 and 72, and the second seal portion 80, respectively. In the compression and sintering, the shape of each material powder formed by the pre-compression can be changed. For example, even when the second rear end E2 is formed on the central axis CL by pre-compression, the second rear end E2 after sintering is separated from the central axis CL as shown in FIG. Get away. Moreover, the structure of FIG. 2 (B) can be implement | achieved by the shape of each material powder changing by compression and sintering.

  Next, the metal shell 50 is assembled to the outer periphery of the insulator 10, and the ground electrode 30 is fixed to the metal shell 50. Next, the ground electrode 30 is bent to complete the spark plug.

A3. Evaluation test:
An evaluation test using a spark plug sample will be described. This evaluation test is a load life test of the spark plug. In this evaluation test, in addition to the spark plug sample of the embodiment, the spark plug sample of the reference example is also evaluated.

  3A shows a partial cross-sectional view of a spark plug 100R of a reference example, and FIG. 3B shows a partial cross-sectional view of the same configuration as FIG. 2A of the spark plug 100 of the embodiment. . Each partial cross-sectional view is a cross-sectional view including the central axis CL, and shows an internal configuration of the through hole 12 of the insulator 10. The difference between the reference example and the embodiment is that in the spark plug 100R of the reference example, the shape of the tip surface 70Rs1, which is a surface facing the tip direction D1 side of the resistor 70R, is a convex shape protruding toward the tip direction D1. A point that is (substantially dome-shaped), a point that the resistor 70R and the center electrode 20 are separated from each other, and a point that the entire space between the resistor 70R and the center electrode 20 is filled with the first seal portion 60R. And only. Other configurations of the spark plug 100R of the reference example are the same as the spark plug 100 of the embodiment. Among the elements of the spark plug 100R of the reference example, the same elements as those of the spark plug 100 of the embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 3A, the estimated current path EPr at the time of discharge is indicated by a bold line. According to the experiments by the inventors, in the spark plug 100R of the reference example, the decrease in the conductive performance is not uniform on the tip surface 70Rs1 of the resistor 70R. Specifically, in the annular edge portion 70Rr in contact with the inner peripheral surface 10i of the insulator 10, the conductive performance is likely to be lower than that of the central portion 70Rc of the tip surface 70Rs1 (for example, the resistor 70R and the first seal). The contact resistance with the portion 60R increases). One of the causes of the decrease in the conductive performance is heat generated by current during discharge. Therefore, in the spark plug 100R of the reference example, it is estimated that the current at the time of discharging is concentrated on the edge portion 70Rr. The estimated current path EPr in the figure is a path from the leg portion 43 of the terminal fitting 40 to the edge portion 70Rr through the resistor 70R. The estimated current path EPr is a path that connects the vicinity of the terminal fitting 40 (leg portion 43) of the resistor 70R and the edge portion 70Rr with the shortest distance (that is, with a straight line).

  In FIG. 3B, the estimated current path EP at the time of discharging is indicated by a bold line. In the spark plug 100 of the embodiment, the second rear end E2 is disposed on the rear end direction D2 side with respect to the edge portion 70r (first rear end E1). Therefore, the vicinity of the terminal metal fitting 40 in the resistor 70 and the vicinity of the second rear end E2 are more than the path (not shown) connecting the vicinity of the terminal metal fitting 40 in the resistor 70 and the first rear end E1. The connecting path has a shorter path length, that is, a smaller electric resistance. As a result, in the spark plug 100 according to the embodiment, the current at the time of discharge is a region including the second rear end E2 and the vicinity thereof in the front end surface 70s1 of the resistor 70 as in the estimated current path EP in the drawing. It is estimated that the distribution can be made (for example, a region surrounded by the offset portion 70o in FIG. 2A). In addition, since the current is dispersed in this manner, the heat generated by the current can be prevented from being concentrated in a part of the region, so that a decrease in the conductive performance in the resistor 70 and the first seal portion 60 can be suppressed. The above advantages can be similarly realized in the configuration shown in FIG.

  Table 1 shown below shows the configuration of each sample and the evaluation results of the operation time. As samples of the spark plug 100, 36 samples in which at least one of the shortest distance Dc, the end-to-end distance Dd, the minimum length De, the thickness Df, and the outer diameter Dg is different from each other were used ( Sample numbers 1-36). The first row of Table 1 shows data of one sample of the reference example. Each adjustment of the shortest distance Dc, the end-to-end distance Dd, and the minimum length De was performed by adjusting the shape of the first seal portions 60 and 62 during the above-described preliminary compression. The outer diameter Dg is adjusted by adjusting the inner diameter of the front end side body portion 17 of the insulator 10, and the thickness Df is adjusted at least between the inner diameter and the outer diameter of the front end side body portion 17 of the insulator 10. Done by adjusting one. Other configurations (for example, the configuration of the center electrode 20) are the same among the 37 samples.

  In the table, the sample number, the shortest distance Dc, the end-to-end distance Dd, the minimum length De, the thickness Df, the outer diameter Dg, and the operation time evaluation result R are shown ( The unit of Dc, Dd, De, Df, and Dg is “millimeter”). The operation time evaluation result R indicates the result of the load life test. The load life test was performed based on the test conditions specified in 7.14 of JIS B8031: 2006 (internal combustion engine-spark plug). However, when the load life test based on JIS regulations was performed as it was, good evaluation results (resistance value change rate of 50% or less) were obtained for all the samples. Therefore, in this evaluation test, a test operation was performed in which discharge was repeated at a constant cycle under conditions stricter than those of JIS by increasing temperature, discharge frequency, and applied voltage. Then, the test operation was performed until the change rate of the resistance value exceeded 50%, and the evaluation was performed using the operation time of the test operation when the change rate of the resistance value exceeded 50%. The resistance value is an electric resistance value between the terminal fitting 40 and the center electrode 20, and was measured in accordance with the provisions of JIS B8031: 2006 7.13. Further, the rate of change in resistance value is the ratio of the difference between the resistance value before and after the test to the resistance value before the test.

The operation time evaluation result R represents the above operation time in 10 stages from 1 to 10, and is set so as to increase as the operation time increases, that is, as the service life increases. Specifically, it is as follows.
Evaluation result R: Range of operation time 1: Less than 150 hours 2: 150 hours or more, less than 200 hours 3: 200 hours or more, less than 250 hours 4: 250 hours or more, less than 300 hours 5: 300 hours or more, less than 350 hours 6 : 350 hours or more and less than 400 hours 7: 400 hours or more and less than 450 hours 8: 450 hours or more and less than 500 hours 9: 500 hours or more and less than 550 hours 10: 550 hours or more

A3-1. Shortest distance Dc:
The shortest distances Dc are different between the first to seventh samples, and the other parameters Dd, De, Df, and Dg are the same (Dd = 0.50, De = 1.00, Df = 1.10, Dg = 3.90). As the evaluation results R of these samples indicate, the longer the shortest distance Dc, the better the evaluation results R. The reason is estimated that the longer the shortest distance Dc is, the farther away the first path EPa and the second path EPb described in FIG. 3B are, that is, the current can be distributed over a wide range. . In addition, the evaluation results R of the first to seventh samples were all better than the evaluation results of the samples of the reference examples. Further, the evaluation results R (8 or more) of the samples No. 2 to No. 7 whose shortest distance Dc is 0.50 mm or more are the evaluation results R (2) of the No. 1 sample whose shortest distance Dc is 0.25 mm. It was especially good compared.

  Thus, the configuration of the embodiment can improve the durability of the spark plug as compared to the configuration of the reference example. In particular, the durability of the spark plug can be greatly improved by setting the shortest distance Dc to 0.50 mm or more. In addition, the shortest distance Dc of No. 2 to No. 7 at which a particularly favorable evaluation result R (8 or more) was obtained as compared with the reference example is 0.50, 0.85, 1.00, 1.25, 1. 45 and 1.95 (unit: mm). Any value among these values can be adopted as the lower limit of the preferable range (the lower limit and the upper limit) of the shortest distance Dc. The upper limit of the shortest distance Dc is half the outer diameter of the resistors 70 and 72 (same as the outer diameter Dg).

  As shown by other samples different from No. 1 to No. 7, even when at least one of the parameters Dd, De, Df, Dg is changed, the shortest distance Dc is set to 0.50 mm or more for reference. The evaluation result R (2 or more evaluation results R) favorable compared with the example was able to be obtained. Therefore, the above-described preferable range of the shortest distance Dc is estimated to be applicable regardless of the parameters Dd, De, Df, and Dg.

A3-2. End-to-end distance Dd:
Between the samples No. 2 and No. 9 to No. 15, the end-to-end distances Dd are different from each other, and the other parameters Dc, De, Df, and Dg are the same (Dc = 0.50, De = 1.00, Df = 1.10, Dg = 3.90). As the evaluation result R of these samples shows, the longer the end-to-end distance Dd, the better the evaluation result R. The reason for this is presumed that the longer the end-to-end distance Dd, the farther away the first path EPa and the second path EPb described in FIG. 3B are, that is, the current can be distributed over a wide range. The The evaluation results R (8 or more) of the samples No. 2, No. 10 to No. 15 with the end-to-end distance Dd of 0.50 mm or more are the evaluation results R of the No. 9 sample with the end-to-end distance Dd of 0.25 mm It was particularly good compared to (5).

  Thus, the durability of the spark plug can be greatly improved by setting the end-to-end distance Dd to 0.50 mm or more. Note that the end-to-end distances Dd of No. 2, No. 10 to No. 15 at which particularly favorable evaluation results R (8 or more) were obtained compared to the reference example were 0.50, 0.75, 1.00, 1. 50, 1.75, 2.00, 2.30 (unit: mm). Any value of these values can be adopted as the lower limit of the preferable range (the lower limit and the upper limit) of the end-to-end distance Dd. In addition, any value that is equal to or greater than the lower limit of these values can be used as the upper limit of the preferable range of the end-to-end distance Dd. As shown in the sample No. 9, when the shortest distance Dc is 0.5 mm or more, even if the end-to-end distance Dd is less than 0.50 mm (here, 0.25 mm), The evaluation result R (here, 5) which is better than that is obtained. Therefore, when the shortest distance Dc is 0.5 mm or more, the lower limit of the preferable range of the end-to-end distance Dd may be less than 0.50 mm, for example, 0.25 mm may be adopted.

  As shown by other samples different from No. 2 and No. 9 to No. 15, even when at least one of the parameters Dc, De, Df, and Dg is changed, the end-to-end distance Dd is set to 0.50 mm or more. By setting, it was possible to obtain a favorable evaluation result R (evaluation result R of 2 or more) compared to the reference example (however, the shortest distance Dc is 0.50 mm or more). Accordingly, it is estimated that the above-described preferable range of the end-to-end distance Dd is applicable regardless of the parameters Dc, De, Df, and Dg when the shortest distance Dc is 0.50 mm or more.

A3-3. Minimum length De:
The minimum length De is different between the samples No. 2 and No. 16 to No. 21, and the other parameters Dc, Dd, Df, and Dg are the same (Dc = 0.50, Dd = 0.50, Df = 1.10, Dg = 3.90). As the evaluation results R of these samples indicate, the longer the minimum length De, the better the evaluation results R. The reason is estimated as follows. That is, when the minimum length De is long, the portions 70s1, 72s1 of the resistors 70, 72 (FIG. 2) are located in the vicinity of the second rear end E2 (specifically, the second rear end). The portion within the range of the distance Dw from E2) is large. The portion located in the vicinity of the second rear end E2 can realize the second route EPb in FIG. Accordingly, the longer the minimum length De, the larger the portion of the tip surfaces 70s1 and 72s1 that can realize the second path EPb. Therefore, the current during discharge can be distributed over a wide range. As a result, it is possible to suppress a decrease in conductive performance in the resistors 70 and 72 and the first seal portions 60 and 62.

  In addition, the evaluation results R (8 or more) of the samples No. 2 and No. 17 to No. 21 whose minimum length De is 1.00 mm or more are the evaluation results of the No. 16 sample whose minimum length De is 0.75 mm. It was particularly good compared to R (6).

  Thus, the durability of the spark plug can be greatly improved by setting the minimum length De to 1.00 mm or more. In addition, the minimum length De of No. 2, No. 17 to No. 21 for which a particularly good evaluation result R (8 or more) was obtained as compared with the reference example is 1.00, 1.27, 1.61, 1. 83, 2.40, and 3.00 (unit: mm). Any value among these values can be adopted as a lower limit of a preferable range (a range not less than the lower limit and not more than the upper limit) of the minimum length De. Further, an arbitrary value equal to or higher than the lower limit of these values can be adopted as the upper limit of the preferable range of the minimum length De. As shown in the sample No. 16, when the shortest distance Dc is 0.5 mm or more, even if the minimum length De is less than 1.00 mm (here, 0.75 mm), The evaluation result R (6 here) is better than that. Therefore, when the shortest distance Dc is 0.5 mm or more, the lower limit of the preferable range of the minimum length De may be less than 1.00 mm, for example, 0.75 mm may be adopted.

  As shown in other samples different from No. 2 and No. 16 to No. 21, even when at least one of parameters Dc, Dd, Df, and Dg is changed, the minimum length De is set to 1.00 mm or more. By setting, it was possible to obtain a favorable evaluation result R (evaluation result R of 2 or more) compared to the reference example (however, the shortest distance Dc is 0.50 mm or more). Therefore, it is estimated that the above-mentioned preferable range of the minimum length De is applicable regardless of the parameters Dc, Dd, Df, and Dg when the shortest distance Dc is 0.50 mm or more.

A3-4. Thickness Df:
The thicknesses Df are different between the samples No. 1, No. 23 and No. 26, and the other parameters Dc, Dd, De and Dg are the same (Dc = 0.25, Dd = 0). .50, De = 1.00, Dg = 3.90). The evaluation results R of these samples are as follows.
No. 23: Df = 1.00, evaluation result R = 4
No. 1: Df = 1.10, evaluation result R = 2
26th: Df = 4.20, evaluation result R = 1
Thus, the thinner the thickness Df, the better the evaluation result R. The reason for this is estimated as follows. That is, when the thickness Df of the insulator 10 is thin, the heat of the members (for example, the first seal portions 60 and 62 and the resistors 70 and 72) in the through hole 12 is larger than when the thickness Df is thick. Is easy to escape (easy to cool). Therefore, it is presumed that the lower the thickness Df, the lower the conductive performance in the resistors 70 and 72 and the first seal portions 60 and 62 can be suppressed.

The configurations of the samples No. 2, 24, and 27 are the configurations in which the shortest distance Dc of the samples No. 1, 23, and 26 is increased from 0.25 mm to 0.50 mm. The evaluation results R of these six samples are as follows.
No. 23: Dc = 0.25, Df = 1.00, evaluation result R = 4
No. 24: Dc = 0.50, Df = 1.00, evaluation result R = 8
No. 1: Dc = 0.25, Df = 1.10, evaluation result R = 2
No. 2: Dc = 0.50, Df = 1.10, evaluation result R = 8
26th: Dc = 0.25, Df = 4.20, evaluation result R = 1
27th: Dc = 0.50, Df = 4.20, evaluation result R = 6
Thus, regardless of the thickness Df, by increasing the shortest distance Dc from 0.25 mm to 0.50 mm, it was possible to realize a better evaluation result R (here, 6 or more) compared to the reference example. . In particular, when the thickness Df is 1.10 mm or more, the shortest distance Dc is increased to 0.50 mm even though the evaluation result R of the sample with Dc = 0.25 mm is 2 or less. As a result, an evaluation result R of 6 or more was realized. As described above, when the thickness Df is 1.10 mm or more, the shortest distance Dc is set to 0.50 mm or more despite the fact that the temperature of the first seal portions 60 and 62 tends to increase. Evaluation result R could be improved appropriately.

Here, the improvement dR of the evaluation result R by changing the shortest distance Dc from 0.25 mm to 0.50 mm (that is, the difference between the evaluation results R) is shown below.
Df = 1.00: dR = 4 (23rd and 24th)
Df = 1.10: dR = 6 (No. 1, No. 2)
Df = 4.20: dR = 5 (26th and 27th)
Thus, when the thickness Df is 1.10 mm or more, the improvement amount dR of the evaluation result R is 5 or more. On the other hand, when the thickness Df is 1.00 mm, the improvement amount dR of the evaluation result R is 4. Thus, when the thickness Df is 1.10 mm or more, the evaluation result R can be significantly improved.

  As described above, when the thickness Df is 1.10 mm or more, the temperature of the first seal portions 60 and 62 tends to be high, but even under such conditions, the shortest distance Dc is 0.50 mm or more. By setting to, the deterioration of the conductive performance in the resistors 70 and 72 and the first seal portions 60 and 62 can be suppressed. Note that the thicknesses Df of No. 2, No. 23, No. 24, and No. 27 for which favorable evaluation results R (4 or more) were obtained compared to the reference examples were 1.00, 1.10, and 4.20. (Unit is mm). Any value of these values can be adopted as the lower limit of the preferred range (the range above the lower limit and below the upper limit) of the thickness Df. In addition, any value that is equal to or greater than the lower limit of these values can be used as the upper limit of the preferable range of the thickness Df.

A3-5. Outer diameter Dg:
The outer diameter Dg is different between the samples No. 1, No. 29, No. 31, and No. 34, and the other parameters Dc, Dd, De, and Df are the same (Dc = 0.25, Dd = 0.50, De = 1.00, Df = 1.10). The evaluation results R of these samples are as follows.
34th: Dg = 2.00, evaluation result R = 1
No. 31: Dg = 3.00, evaluation result R = 1
No. 29: Dg = 3.50, evaluation result R = 2
No. 1: Dg = 3.90, evaluation result R = 2
Thus, the evaluation result R was slightly better when the outer diameter Dg was larger than when the outer diameter Dg was small. This is because the larger the outer diameter Dg of the first seal portions 60 and 62 is, the larger the first seal portions 60 and 62 are, so that the current during discharge is easily dispersed on the first seal portions 60 and 62. It is estimated to be.

Samples Nos. 2, 30, 32, and 36 have configurations in which the shortest distance Dc of the samples No. 1, 29, 31, and 34 is increased from 0.25 mm to 0.50 mm, respectively. Have. The evaluation results R of these eight samples are as follows.
No. 34: Dc = 0.25, Dg = 2.00, evaluation result R = 1
No. 35: Dc = 0.50, Dg = 2.00, evaluation result R = 8
No. 31: Dc = 0.25, Dg = 3.00, evaluation result R = 1
No. 32: Dc = 0.50, Dg = 3.00, evaluation result R = 8
No. 29: Dc = 0.25, Dg = 3.50, evaluation result R = 2
No. 30: Dc = 0.50, Dg = 3.50, Evaluation result R = 8
No. 1: Dc = 0.25, Dg = 3.90, evaluation result R = 2
No. 2: Dc = 0.25, Dg = 3.90, evaluation result R = 8
Thus, regardless of the outer diameter Dg, by increasing the shortest distance Dc from 0.25 mm to 0.50 mm, it was possible to realize a better evaluation result R (here, 8 or more) compared to the reference example. .

Here, the improvement dR of the evaluation result R by changing the shortest distance Dc from 0.25 mm to 0.50 mm (that is, the difference between the evaluation results R) is shown below.
Dg = 2.00: dR = 7 (34th and 35th)
Dg = 3.00: dR = 7 (31 and 32)
Dg = 3.50: dR = 6 (29th and 30th)
Dg = 3.90: dR = 6 (No. 1, No. 2)
Thus, when the outer diameter Dg is 3.00 mm or less, the improvement amount dR of the evaluation result R is “7”. On the other hand, when the outer diameter Dg exceeds 3.00 mm, the improvement amount dR of the evaluation result R is “6”. Thus, when the outer diameter Dg is 3.00 mm or less, the evaluation result R can be greatly improved as compared with the case where the outer diameter Dg exceeds 3.00 mm. Therefore, even when a thin spark plug having an outer diameter Dg of 3.00 mm or less is used, durability can be improved.

  As described above, when the outer diameter Dg is 3.00 mm or less, the current is difficult to be dispersed during discharge, but even under such conditions, by setting the shortest distance Dc to 0.50 mm or more, It is possible to suppress a decrease in conductive performance in the resistors 70 and 72 and the first seal portions 60 and 62. The outer diameters Dg of No. 2, No. 30, No. 32, and No. 35, which gave favorable evaluation results R (8 or more) compared to the reference examples, were 2.00, 3.00, 3.50, 3 .90 (unit: mm). Any value among these values can be adopted as the lower limit of the preferred range (the lower limit and the upper limit) of the outer diameter Dg. In addition, any value that is equal to or greater than the lower limit of these values can be adopted as the upper limit of the preferable range of the outer diameter Dg.

B. Second embodiment:
FIG. 4 is an explanatory diagram of the spark plug 100x according to the second embodiment. In the figure, a partial cross-sectional view similar to FIG. 2 is shown. The difference from the first embodiment shown in FIG. 2 is that the shape of the tip surface 70xs1, which is the surface facing the tip direction D1 of the resistor 70x, is a concave shape (substantially bowl shape) recessed toward the rear end direction D2. A continuous first seal portion 60x is disposed between a certain point, a point where the resistor 70x is not in contact with the center electrode 20 and away from the center electrode 20, and a space between the resistor 70x and the center electrode 20. It is only a point. Other configurations of the spark plug 100x are the same as the configuration of the spark plug 100 of the first embodiment shown in FIG. Among the elements of the spark plug 100x of the second embodiment, the same elements as those of the spark plug 100 of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The second rear end E2x in the drawing indicates the rear end (the end on the most rear end direction D2 side) of the distal end surface 70xs1 of the resistor 70x that is away from the inner peripheral surface 10i of the insulator 10. In the present embodiment, the position of the second rear end E2 is the same as the position of the rear end (the end on the most rear end direction D2 side) of the first seal portion 60x. The cross section of FIG. 4 is a cross section including the central axis CL and the second rear end E2x.

  The first rear end E1x in the drawing indicates the rear end (the end on the most rear end direction D2 side) of the portion where the first seal portion 60x contacts the inner peripheral surface 10i of the insulator 10 in the illustrated cross section. ing. In the present embodiment, the position of the first rear end E1 is the tip of the portion of the resistor 70x in contact with the inner peripheral surface 10i of the insulator 10 in the illustrated cross section (most in the tip direction D1 side). It is the same as the position of (end). Also in the present embodiment, the second rear end E2x is disposed closer to the rear end direction D2 than the first rear end E1x.

  As shown in FIG. 4, in the second embodiment, parameters Dc, Dd, De, Df, and Dg are defined as in the first embodiment of FIG. In the second embodiment, the shape of the distal end surface 70xs1 of the resistor 70x is the same as the shape of the distal end surfaces 70s1 and 72s1 of the resistors 70 and 72 (FIG. 2) of the first embodiment on the rear end direction D2 side. It has a concave shape that dents toward it. Therefore, if the values in the preferred ranges described in the first embodiment are adopted as the parameters Dc, Dd, De, Df, and Dg, the current during discharge is advanced as in the spark plug 100 of the first embodiment. It is estimated that it can be distributed on the surface 70xs1. It is estimated that the durability of the spark plug 100x can be improved.

  In the second embodiment, the rear end of the center electrode 20 (the end on the rear end direction D2 side, here, the head portion 23 and the flange portion 24) is covered with the first seal portion 60x. More specifically, the entire surface 20s2 (also referred to as “rear end surface 20s2”) facing the rear end direction D2 side of the surface of the center electrode 20 is covered with the first seal portion 60x. Therefore, since the adhesiveness between the center electrode 20 and the first seal portion 60x can be improved, durability against vibration can be improved. In the embodiment of FIG. 4, the rear end surface 20 s 2 of the center electrode 20 includes a rear end surface 23 s 2 of the head portion 23, an outer peripheral surface 23 o of the head portion 23, and a surface 24 s 2 facing the rear end direction D 2 side of the flange portion 24. , Is composed of.

C. Third embodiment:
FIG. 5 is an explanatory diagram of the spark plug 100z of the third embodiment. In the drawing, a partial cross-sectional view similar to FIG. 2A is shown. The only difference from the first embodiment shown in FIG. 2 (A) is that the inner seal portion 60b is omitted. Other configurations of the spark plug 100z are the same as the configuration of the spark plug 100 of the first embodiment shown in FIG. Of the elements of the spark plug 100z of the third embodiment, the same elements as those of the spark plug 100 of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As illustrated, the surface 70zbs1 of the bottom 70zb of the resistor 70z is in contact with the rear end surface 23s2 of the head 23 of the center electrode 20. A surface 70zs1 indicated by a bold line in the drawing indicates a surface 70zs1 (referred to as “tip surface 70zs1”) facing the tip direction D1 side of the resistor 70z. The tip surface 70zs1 of the resistor 70z is formed by the surface 70zbs1 of the bottom 70zb of the resistor 70z, the inner peripheral surface 70wi and the tip surface 70ws1 of the wall 70w. In the present embodiment, any position on the surface 70zbs1 of the bottom 70zb is a candidate for the second rear end. In this case, in order to specify an appropriate shortest distance Dc, the position E2z closest to the inner peripheral surface 10i of the insulator 10 in the surface 70zbs1 is adopted as the second rear end E2z.

  As shown in FIG. 5, also in the third embodiment, the offset unit 70zo and the parameters Dc, Dd, De, Df, and Dg are specified as in the first embodiment of FIG. In the third embodiment, the shape of the front end surface 70zs1 of the resistor 70z is on the rear end direction D2 side in the same manner as the shapes of the front end surfaces 70s1 and 72s1 of the resistors 70 and 72 (FIG. 2) of the first embodiment. It has a concave shape that dents toward it. Therefore, by adopting the values in the preferred ranges described in the first embodiment as the parameters Dc, Dd, De, Df, and Dg, the current during discharge is changed as in the spark plug 100 of the first embodiment. It is estimated that it can be dispersed on the tip surface 70zs1. And it is estimated that the durability of the spark plug 100z can be improved.

D. Variation:
(1) It is considered that the improvement in the durability of the spark plug of the embodiment is mainly caused by the shortest distance Dc. Further, it is considered that the further improvement of the durability of the spark plug is mainly caused by the end-to-end distance Dd and the minimum length De. Therefore, the configuration other than these parameters Dc, Dd, and De can be variously changed. For example, in FIG. 2, the tip surfaces 70ws1 and 72ws1 of the wall portions 70w and 72w of the resistors 70 and 72 are shown as a plane perpendicular to the central axis CL. However, the tip surfaces 70ws1 and 72ws1 can be inclined with respect to the central axis CL and can be curved surfaces. In the embodiment shown in FIG. 4, the first rear end E1x is disposed on the rear end direction D2 side with respect to the rear end surface 23s2 of the head portion 23 of the center electrode 20. Instead of this, the first rear end E1x may be disposed closer to the front end direction D1 than the rear end surface 23s2 of the head 23.

  Further, a noble metal tip may be provided in a portion of the center electrode 20 where the gap g is formed. Further, a noble metal tip may be provided in a portion of the ground electrode 30 where the gap g is formed. As a material for the noble metal tip, an alloy containing a noble metal such as iridium or platinum can be employed. Further, the outer diameter of the head 23 of the center electrode 20 may be the same as the outer diameter of the flange 24.

  In each of the above embodiments, the tip 31 of the ground electrode 30 is opposed to the tip surface 20s1 that is the surface facing the tip direction D1 side of the center electrode 20 to form the gap g. Instead, the tip of the ground electrode 30 may be opposed to the outer peripheral surface of the center electrode 20 to form a gap.

  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 packing, 7 ... second rear end packing, 8 ... front end packing, 9 ... talc, 10 ... insulator (insulation) Insulator), 10i ... inner peripheral surface, 11 ... second reduced outer diameter part, 12 ... shaft hole (through hole), 13 ... leg part, 15 ... first reduced outer diameter part , 16 ... Reduced inner diameter part, 17 ... Front end side body part, 18 ... Rear end side body part, 19 ... Gutter part, 20 ... Center electrode, 20s1 ... Front end surface, 21 ... Electrode base material, 22 ... Core material, 23 ... Head, 23s2 ... Rear end face, 24 ... Gutter, 25 ... Leg, 30 ... Ground electrode, 31 ... tip part, 35 ... base material, 36 ... core part, 40 ... terminal fitting, 41 ... cap mounting part, 42 ... collar part, 43 ... leg part, 50 ... Metal fitting, 51 ... Tool engaging part, 52 ... Screw part, 53 ... Casting part, 54 ... Seat part, 55 ... Body part, 56 ... Reduced inner diameter Part, 58 ... deformation part, 59 ... through hole, 60, 62, 60R, 60x ... 1 seal part, 60a, 62a ... outer seal part, 60b, 62b ... inner seal part, 70ws1, 72ws1 ... tip surface, 70,72,70R, 70x ... resistor, 70s1,72s1, 70Rs1, 70xs1 ... tip surface, 70b, 72b ... bottom, 70o, 72o ... offset part, 70r ... edge part, 70w, 72w ... wall part, 70Rr ... edge part, 70oc , 72 oc ... center of gravity, 80 ... second seal, 100, 100R, 100x ... spark plug, g ... gap, CL ... central axis (axis)

Claims (6)

A central electrode extending in the direction of the axis;
An insulator having an axial hole extending in the direction of the axial line, and the central electrode disposed on a tip side of the axial hole;
A resistor disposed on the rear end side of the center electrode in the shaft hole;
A seal portion disposed at least in part between the resistor and the center electrode in the shaft hole;
A spark plug comprising:
The seal portion on the cross section including the axis and the second rear end, with the rear end of a portion of the surface facing the front end side of the resistor away from the inner peripheral surface of the insulator as the second rear end When the rear end of the portion in contact with the inner peripheral surface of the insulator is the first rear end,
The second rear end is disposed closer to the rear end side than the first rear end, and the shortest radial distance between the second rear end and the inner peripheral surface of the insulator is 0.5 mm or more. is there,
Spark plug. The spark plug according to claim 1,
A spark plug, wherein a distance in a direction of the axis between the first rear end and the second rear end is 0.5 mm or more. The spark plug according to claim 1 or 2,
The minimum value of the length along a straight line passing through the center of gravity of the portion surrounded by the resistor in a cross section perpendicular to the direction of the axis at a position where the distance in the direction of the axis from the second rear end is 0.2 mm Is a spark plug which is 1 mm or more. The spark plug according to any one of claims 1 to 3,
A spark plug, wherein a radial thickness of a portion of the insulator that accommodates the seal portion is 1.1 mm or more. The spark plug according to any one of claims 1 to 4,
The spark plug has a maximum diameter of 3.0 mm or less. The spark plug according to any one of claims 1 to 5,
A spark plug, wherein a rear end of the center electrode is covered with the seal portion.

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