JP6653672B2 - Spark plug - Google Patents

Description

  The present specification relates to a spark plug for igniting fuel gas in an internal combustion engine or the like.

  The spark plug is attached to an internal combustion engine or the like, and is used for igniting fuel gas in a combustion chamber. Patent Literature 1 discloses an ignition plug having a high voltage electrode to which a high voltage is applied, a ground electrode grounded, and a floating electrode insulated from the high voltage electrode and the ground electrode. In this spark plug, the ground electrode and the floating electrode function as one capacitor, and the floating electrode and the high-voltage electrode function as another capacitor. In this spark plug, when a voltage is applied between the high-voltage electrode and the ground electrode, discharge is generated between the floating electrode and the high-voltage electrode or between the floating electrode and the ground electrode due to the voltage divided by the two capacitors. appear. In this spark plug, only the electric charge stored in the capacitor is discharged at the time of discharge, so that ignition can be performed efficiently.

International Publication No. 2012/072895

  This type of spark plug does not function as a spark plug unless insulation between a first electrode (for example, a high-voltage electrode) and a second electrode (for example, a floating electrode) to be insulated from each other cannot be ensured. . For this reason, a technique capable of improving the insulation between the first electrode and the second electrode has been required.

  In this specification, the first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated. Disclosed is a technique for improving the insulation between a first electrode and a second electrode in a plug.

The technology disclosed in this specification can be realized as the following aspects or application examples.
[Aspect 1]
A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a portion of the gap on the first end side from a portion where the second electrode is disposed is filled with an insulating seal member over the entire circumference,
The ignition plug is characterized in that the seal member is formed of a thermosetting resin material.
[Aspect 2]
A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a portion of the gap on the first end side from a portion where the second electrode is disposed is filled with an insulating seal member over the entire circumference,
The outer peripheral surface of the inner insulator is located on the first end side of the second electrode, on the first end side of the second electrode, and on the inner end of the first electrode. An ignition plug including a portion located on the second end side of a portion disposed on a first end side and a portion located radially outward over at least one of the ends.
[Aspect 3]
A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side with respect to the inner insulator, and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a part of the gap on the first end side from a portion where the second electrode is arranged is filled with an insulating seal member over the entire circumference,
A spark plug, wherein a distance from an end on the first end side of the second electrode to an end on the first end side of the inner insulator is 10 mm or less.

[Application Example 1] A cylindrical outer insulator having a shaft hole extending from a first end side to a second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
An ignition plug, wherein at least a part of the gap closer to the first end than a part where the second electrode is arranged is filled with an insulating sealing member over the entire circumference. .

  According to the above configuration, in the gap between the inner peripheral surface of the outer insulator and the outer peripheral surface of the inner insulator, at least a part on the first end side of the portion where the second electrode is disposed over the entire circumference. And an insulating sealing member is filled. As a result, it is possible to prevent the insulation between the first electrode and the second electrode from being broken at the gap. Therefore, in the ignition plug, the first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated. The insulating property between the first electrode and the second electrode can be improved.

Application Example 2 The spark plug according to application example 1,
Wherein among the sealing member, wherein the axial length of the rear end portion of the rear end of the second electrode is 1mm or more, the spark plug.

  According to the above configuration, the insulation between the first electrode and the second electrode can be further improved.

Application Example 3 The spark plug according to application example 1 or 2,
The outer peripheral surface of the inner insulator is located on the first end side of the second electrode, on the first end side of the second electrode, and on the inner end of the first electrode. An ignition plug including a portion located on the second end side of a portion disposed on a first end side and a portion located radially outward over at least one of the ends.

  According to the above configuration, the insulation between the first electrode and the second electrode can be further improved.

Application Example 4 The spark plug according to any one of Application Examples 1 to 3,
In the axial direction range in which the seal member is filled over the entire circumference, the outer peripheral surface of the inner insulator has a protrusion protruding radially outward over the entire circumference, An ignition plug, wherein at least one of a concave portion that is concave inward in the radial direction is formed.

  According to the above configuration, the insulation between the first electrode and the second electrode can be further improved.

Application Example 5 The spark plug according to any one of Application Examples 1 to 4,
A spark plug, wherein a distance from an end on the first end side of the second electrode to an end on the first end side of the inner insulator is 10 mm or less.

  According to the above configuration, it is possible to prevent the spark plug from being excessively long in the axial direction while securing insulation between the first electrode and the second electrode.

  The technology disclosed in the present specification can be realized in various modes, for example, an ignition plug, an ignition device using the ignition plug, an internal combustion engine equipped with the ignition plug, and an ignition plug It can be realized in the form of an internal combustion engine equipped with an ignition device using the same, electrodes of a spark plug, and the like.

It is a sectional view of spark plug 100 of a 1st embodiment. FIG. 2 is a perspective view schematically illustrating an external shape of the floating electrode 20 of the first embodiment. It is an expanded sectional view near the rear end of inner insulator 70 of a 1st embodiment. It is the 1st explanatory view of the ignition plug of a modification. It is a 2nd explanatory view of the ignition plug of a modification. It is the 3rd explanatory view of the ignition plug of a modification. It is sectional drawing of 100M of ignition plugs of 2nd Embodiment. It is an expanded sectional view near the tip of 70 M of inner insulators of a 2nd embodiment.

A. First embodiment:
A-1. Configuration of spark plug:
FIG. 1 is a sectional view of a spark plug 100 according to the first embodiment. 1 indicates an axis CL of the ignition plug 100. A direction parallel to the axis CL (the vertical direction in FIG. 1) is also referred to as an axis direction. The radial direction of a circle centered on the axis CL and perpendicular to the axis CL is also simply referred to as “radial direction”, and the circumferential direction of the circle is also simply referred to as “circumferential direction”. The downward direction in FIG. 1 is referred to as a leading direction Df, and the upward direction is also referred to as a trailing direction Dr. The lower side in FIG. 1 is referred to as the front end side of the spark plug 100, and the upper side in FIG. Note that the rear end side in the first embodiment corresponds to the first end side in the claims, and the front end side in the first embodiment corresponds to the second end side in the claims.

  The spark plug 100 generates a discharge in a gap formed between the floating electrode 20 and the ground electrode 30, which will be described in detail later. The spark plug 100 is attached to an internal combustion engine and is used to ignite fuel gas in a combustion chamber of the internal combustion engine. The spark plug 100 includes an outer insulator 10, a floating electrode 20, a ground electrode 30, a center electrode 40, a metal shell 50, and an inner insulator 70.

  The outer insulator 10 is a cylindrical member formed by firing a ceramic material such as alumina. The outer insulator 10 insulates the metal shell 50 from the center electrode 40 and insulates the metal shell 50 from the floating electrode 20. The outer insulator 10 includes a flange portion 19, a rear end body portion 18, a front end side body portion 17, a first step portion 15, and a leg length portion 13. The rear end side body 18 is located on the rear end side of the flange 19 and has an outer diameter smaller than the outer diameter of the flange 19. The distal-side body 17 is located on the distal side of the flange 19 and has an outer diameter smaller than the outer diameter of the flange 19. The leg long portion 13 is located on the distal side from the distal side trunk portion 17 and has an outer diameter smaller than the outer diameter of the distal side trunk portion 17. When the spark plug 100 is attached to an internal combustion engine (not shown), the leg portion 13 is exposed to a combustion chamber of the internal combustion engine (not shown). The first step portion 15 is formed between the leg length portion 13 and the front trunk portion 17. The first step portion 15 is reduced in diameter from the rear end side to the front end side.

  The outer insulator 10 has a first hole 11 and a second hole 12. The first hole 11 is a hole extending from the rear end side to the front end side along the axis CL. The second hole 12 is a hole extending from the front end side to the rear end side. The first hole 11 is formed between the rear end of the rear end body 18 and a part of the front end body 17. The second hole 12 is formed between the distal end of the leg 13 and a part of the distal trunk 17. The rear end of the second hole 12 communicates with the front end of the first hole 11. That is, the first hole 11 and the second hole 12 can be regarded as one shaft hole. In the present embodiment, the second holes 12 are provided around the axis CL by the number of floating electrodes 20 described later (for example, 2 to 4).

  The metal shell 50 is a cylindrical metal fitting that is disposed on the outer periphery of the outer insulator 10 and extends from a part of the rear end body 18 to the leg 13, and holds the outer insulator 10. The distal end of the outer insulator 10 protrudes more distally than the distal end of the metal shell 50. The rear end of the outer insulator 10 protrudes rearward from the rear end of the metal shell 50. The metal shell 50 is formed of, for example, a conductive metal material (for example, low-carbon steel), and is entirely plated with nickel or zinc.

  The metal shell 50 includes a tool engaging part 51, a seat part 54, and a mounting screw part 52 in order from the rear end side. A tool for attaching the spark plug 100 to the engine head of the internal combustion engine is fitted into the tool engagement portion 51. A screw thread to be screwed into a mounting screw hole of the engine head is formed on the outer periphery of the mounting screw portion 52. The seat portion 54 is formed in a flange shape at the base of the mounting screw portion 52.

  An annular gasket 65 formed by bending a metal plate is fitted between the mounting screw portion 52 and the seat portion 54 of the metal shell 50. The gasket 65 seals a gap between the spark plug 100 and the engine head when the spark plug 100 is attached to the engine head.

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 from the tool engaging portion 51. Further, between the seat portion 54 and the tool engagement portion 51, a compression deformation portion 58 having a small thickness is provided similarly to the caulking portion 53. Annular ring members 66 and 67 are interposed between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the rear end side body portion 18 of the outer insulator 10. The space between the two ring members 66 and 67 is filled with talc (talc) 69 powder. At the time of manufacturing the spark plug 100, the compression deforming portion 58 is compressed and deformed by bending the caulking portion 53 inward and pressing the crimping portion 53 toward the distal end, and the ring member 66, 67 and The outer insulator 10 is pressed toward the distal end in the metal shell 50 via the talc 69. Due to this pressing, the talc 69 is compressed in the direction of the axis CL, and the first step 15 of the outer insulator 10 is pressed via the second step 56 (described later) of the metal shell 50 and the packing 68 (described later). Thus, the airtightness between the outer insulator 10 and the metal shell 50 is enhanced.

  The metal shell 50 has a second step 56 on the inner periphery thereof, with which the first step 15 of the outer insulator 10 contacts. The second step portion 56 is formed on the inner periphery of the mounting screw portion 52, and is reduced in diameter from the rear end to the front end. The first step 15 and the second step 56 are in contact via an annular packing 68. The packing 68 is a member that maintains airtightness between the metal shell 50 and the outer insulator 10, and prevents the outflow of combustion gas.

  The inner insulator 70 is a cylindrical member formed by firing a ceramic material such as alumina. The inner insulator 70 insulates between the floating electrode 20 and the center electrode 40. The tip of the inner insulator 70 is closed. That is, the inner insulator 70 is formed with a bottomed hole 74 having an opening at the rear end and a bottom 73 disposed at the front end. The inner insulator 70 is disposed inside the first hole 11 of the outer insulator 10. On the outer peripheral surface 70S of the inner insulator 70, a groove 72 corresponding to the shape of the first plate-shaped portion 24 of the floating electrode 20, which will be described later, is formed.

  The center electrode 40 is a metal rod-shaped member extending along the axis CL. The center electrode 40 is formed of a conductive metal material (for example, low-carbon steel), and the surface of the center electrode 40 is plated with, for example, Ni or the like for corrosion protection. The center electrode 40 includes a flange 42 abutting on the rear end of the outer insulator 10, a cap mounting portion 41 located on the rear end side of the flange 42, a large-diameter leg 43 on the distal end side of the flange 42, And a small-diameter leg 44 on the distal end side of the large-diameter leg 43. The small-diameter leg 44 has a smaller outer diameter than the large-diameter leg 43. The cap mounting portion 41 of the center electrode 40 is exposed on the rear end side of the outer insulator 10. A plug cap to which a high-voltage cable (not shown) is connected is mounted on the cap mounting section 41, and a high voltage for generating a discharge is applied. The large-diameter leg 43 is disposed on the rear end side of the inner insulator 70 in the first hole 11 of the outer insulator 10. The small-diameter leg portion 44 is located in the bottomed hole 74 of the inner insulator 70. Since the length of the small diameter leg 44 in the axial direction is substantially equal to the length of the bottomed hole 74 in the axial direction, the tip of the small diameter leg 44 reaches the vicinity of the bottom 73 of the bottomed hole 74.

  FIG. 2 is a perspective view schematically illustrating the appearance of the floating electrode 20. The floating electrode 20 is formed using a conductive metal material, for example, a metal having high corrosion resistance and heat resistance, Ni or an alloy containing Ni as a main component (for example, NCF600, NCF601). The floating electrode 20 includes a first plate portion 24, a second plate portion 25, and a rod portion 26. The first plate-shaped portion 24 is a strip-shaped thin plate member extending along the axis. The second plate-like portion 25 is a substantially rectangular thin plate member extending in a direction perpendicular to the axis. The tip of the first plate-shaped portion 24 and the radially outer end of the second plate-shaped portion 25 are connected to form an L-shape. The rod portion 26 is a round rod-shaped member extending from the distal end surface of the second plate-shaped portion 25 to the distal end side along the axial direction.

  The rod portion 26 is arranged in the second hole 12 of the outer insulator 10. The tip of the rod-like portion 26 protrudes from the leg 13 of the outer insulator 10 toward the tip. The second plate-shaped portion 25 is arranged in a gap between the distal end surface of the inner insulator 70 and the bottom surface of the first hole 11 of the outer insulator 10. That is, the second plate-like portion 25 and the bar-like portion 26 are arranged on the tip side of the inner insulator 70.

  The first plate-shaped portion 24 is disposed in a gap between the outer peripheral surface 70S of the inner insulator 70 and the inner peripheral surface 11S of the outer insulator 10 where the first hole 11 is formed. Specifically, the first plate-shaped portion 24 is curved along the inner peripheral surface 11S forming the first hole 11, and fits into the groove 72 formed on the outer peripheral surface 70S of the inner insulator 70. are doing. The radial depth of the groove 72 is slightly larger than the radial thickness of the first plate-shaped portion 24. For this reason, the entire first plate-shaped portion 24 is housed inside the groove 72. The rear end of the first plate-shaped portion 24 is located near the center of the rear end body 18 in the axial direction, on the rear end side of the rear end of the metal shell 50.

  The plurality of floating electrodes 20 are arranged at equal intervals around the axis CL. The number of floating electrodes 20 is, for example, 2 to 4, and is 2 in the present embodiment. In the present embodiment, the respective floating electrodes 20 are insulated from each other.

  The ground electrode 30 is an electrode member fixed to the distal end portion 57 of the metal shell 50. Like the floating electrode 20, the ground electrode 30 is formed using a conductive metal material, for example, Ni or an alloy containing Ni as a main component. The ground electrode 30 has a rod shape, and has a distal end bent toward the axis CL. A surface on the rear end side near the front end of the ground electrode 30 forms a gap for discharge with the front end surface 27 of the floating electrode 20. The number of ground electrodes 30 is the same as the number of floating electrodes 20.

  In the spark plug 100 described above, the center electrode 40 and the floating electrode 20 that are insulated by the inner insulator 70 function electrically as a capacitor and have a certain capacitance (hereinafter, referred to as “first capacitance”). ). In addition, the floating electrode 20 and the metal shell 50 (including the ground electrode 30) insulated by the outer insulator 10 also electrically function as a capacitor, and have a certain capacitance (hereinafter, referred to as “second capacitance”). Or "parasitic capacitance"). When a voltage is applied between the cap mounting portion 41 of the center electrode 40 and the metal shell 50 (ground electrode 30), the voltage divided by the first capacitance and the second capacitance causes the floating electrode 20 and the ground electrode Discharge is performed in the gap between the first and the second. The current that flows through the gap in one discharge is only the charge stored in the center electrode 40 and the floating electrode 20 functioning as a capacitor. For this reason, in the spark plug 100 of the present embodiment, the discharge is completed in a very short time of several microseconds or less. Can be discharged again. Therefore, if a pulsed voltage is applied to the center electrode 40 to repeatedly perform discharge, discharge in a low-temperature plasma state (streamer discharge) becomes possible, and ignition can be performed efficiently.

  The configuration of the ignition plug 100 will be further described with reference to FIG. FIG. 3 is an enlarged cross-sectional view near the rear end of the inner insulator 70. FIG. 3 is an enlarged view of a region RA indicated by a dashed line in FIG. A gap between the inner peripheral surface 11S of the outer insulator 10 and the outer peripheral surface 70S of the inner insulator 70 (hereinafter, also referred to as a gap between insulators) is filled with a seal member 80. In the present embodiment, the seal member 80 is filled over the entire circumference in the circumferential direction. The seal member 80 is formed of a rubber member, for example, a thermosetting silicone rubber. In the present embodiment, liquid silicone rubber “TSE3331” manufactured by Momentive Performance Materials Japan GK is used. The sealing member 80 inserts the inner insulator 70 into the first hole 11 of the outer insulator 10 in a state where the liquid rubber is applied to the outer peripheral surface 70S of the inner insulator 70, and heats the liquid after the insertion. It is formed by curing rubber.

  As shown in FIG. 3, the sealing member 80 is filled in a portion of the floating electrode 20 located in the gap between the insulators on the rear end side of the rear end of the first plate-shaped portion 24. As a result, for example, it is possible to prevent the insulation between the center electrode 40 and the floating electrode 20 from being destroyed in the gap between the insulators by a leak current flowing along the outer peripheral surface 70S of the inner insulator 70. it can. Therefore, in the spark plug 100, the insulation between the center electrode 40 and the floating electrode 20 can be improved.

  Further, it is preferable that the axial length L2 (FIG. 3) of a portion of the sealing member 80 closer to the rear end than the rear end of the first plate portion 24 of the floating electrode 20 is 1 mm or more. In this case, the insulation between the center electrode 40 and the floating electrode 20 can be further improved.

  The seal member 80 is further filled in a portion closer to the front end than the rear end of the first plate-shaped portion 24 arranged in the gap between the insulators. In the circumferential position where the first plate-shaped portion 24 is arranged, the portion is located between the radial outer surface of the first plate-shaped portion 24 and the inner circumferential surface 11S of the outer insulator 10. Is filled. The front end of the seal member 80 is located, for example, on the front end side with respect to the rear end of the metal shell 50 (not shown). Thereby, the insulation between the center electrode 40 and the floating electrode 20 can be further improved.

  In the outer peripheral surface 70S of the inner insulator 70, a concave portion 75 that is concave inward in the radial direction is formed over the entire circumference in a range in the axial direction that is in contact with the seal member 80. A projection 85 that projects radially inward and fits into the recess 75 is formed on the entire inner circumference of the seal member 80. As a result, the occurrence of creeping discharge in the gap between the outer peripheral surface 70S of the inner insulator 70 and the seal member 80 can be more effectively suppressed, so that the insulation between the center electrode 40 and the floating electrode 20 is further improved. it can.

  The depth D of the concave portion 75 in the radial direction (FIG. 3, substantially equal to the radial height of the protrusion 85) is preferably 0.1 mm or more, for example, 0.25 mm. Thereby, the insulation between the center electrode 40 and the floating electrode 20 can be more effectively improved.

  The outer peripheral surface 70S of the inner insulator 70 is located on the rear end side of the first plate-shaped portion 24 of the floating electrode 20, and is the tip of the portion of the center electrode 40 arranged on the rear end side of the inner insulator 70, that is, It is located radially outward over the entire circumference from the rear end of the large diameter leg 43. That is, as shown by ΔS in FIG. 3, the outer peripheral surface 70S of the rear end portion of the inner insulator 70 is located radially outside the outer peripheral surface of the large-diameter leg 43. Thereby, the insulation between the center electrode 40 and the floating electrode 20 can be further improved.

  In the present embodiment, the first plate portion 24 of the floating electrode 20 is fitted in a groove 72 formed on the outer peripheral surface 70S of the inner insulator 70. Since the radial depth of the groove 72 is slightly larger than the radial thickness of the first plate portion 24, the outer peripheral surface 70 </ b> S of the inner insulator 70 is located at the rear end of the first electrode 24 of the floating electrode 20. On the side, the floating electrode 20 is located radially outward over the entire circumference from the rear end (that is, the first plate-shaped portion 24). That is, in FIG. 3, the outer peripheral surface 70 </ b> S of the rear end portion of the inner insulator 70 is positioned radially outward from the radially outer surface of the first plate-shaped portion 24, as shown in the wavy line area CA. are doing. Thereby, the insulation between the center electrode 40 and the floating electrode 20 can be further improved.

  In the spark plug 100 of the present embodiment, the distance L1 (see FIG. 1) from the rear end of the floating electrode 20 to the rear end of the inner insulator 70 is 10 mm or less, for example, 8 mm. As described above, even if the distance L1 is relatively short, the insulating property between the center electrode 40 and the floating electrode 20 can be ensured by arranging the seal member 80. In other words, it is possible to prevent the spark plug 100 from becoming excessively long while ensuring insulation between the center electrode 40 and the floating electrode 20. Furthermore, since the distance L1 can be set to 10 mm or less, the rear end of the first plate-shaped portion 24 of the floating electrode 20 can be positioned closer to the rear end, so that the length of the first plate-shaped portion 24 is increased. can do. When the length of the first plate portion 24 is increased, the area where the first plate portion 24 of the floating electrode 20 and the small-diameter leg portion 44 of the center electrode 40 face each other with the inner insulator 70 interposed therebetween increases. Thereby, the above-described first capacitance of the center electrode 40 and the floating electrode 20 functioning as a capacitor can be increased. By increasing the first capacitance, the amount of charge flowing between the gaps by one discharge increases, so that the ignitability can be improved. In addition, by increasing the first capacitance, even if the voltage applied between the ground electrode 30 and the center electrode 40 is the same, the voltage generated between the ground electrode 30 and the floating electrode 20 ( That is, since the voltage between the gaps can be increased, the ignitability can be improved.

A-2. Modifications of First Embodiment FIGS. 4 to 6 are explanatory diagrams of a spark plug according to a modification. 4 to 6 show enlarged cross-sectional views of the vicinity of the rear end of the inner insulator similarly to FIG. In the spark plug 100a of FIG. 4A, the concave portion 75 (FIG. 3) is not provided on the outer peripheral surface 70aS of the inner insulator 70a. For this reason, the protrusion 85 (FIG. 3) is not provided on the seal member 80a. Other configurations are the same as those of the spark plug 100 of the first embodiment.

  In the spark plug 100b of FIG. 4B, the outer diameter of the large-diameter leg portion 43b of the center electrode 40b is larger than the outer diameter of the inner insulator 70a. As a result, the outer peripheral surface 70aS of the rear end portion of the inner insulator 70a is located radially inward of the outer peripheral surface of the large-diameter leg 43b. The other configuration is the same as that of the ignition plug 100a in FIG.

  In the spark plug 100c of FIG. 5A, a groove 72 for fitting the first plate-shaped portion 24 is not provided on the outer peripheral surface 70cS of the inner insulator 70c. For this reason, the first plate-shaped portion 24 is located radially outward from the outer peripheral surface 70cS of the inner insulator 70c. Therefore, the outer peripheral surface 70cS of the rear end portion of the inner insulator 70 is located radially inward from the radially outer surface of the first plate-shaped portion 24. The other configuration is the same as that of the ignition plug 100a in FIG.

  In the spark plug 100d of FIG. 5B, the center electrode 40b of FIG. 4B is employed as the center electrode. For this reason, the outer diameter of the large-diameter leg 43b is larger than the outer diameter of the inner insulator 70c. As a result, the outer peripheral surface 70cS of the rear end portion of the inner insulator 70c is located radially inward of the outer peripheral surface 70cS of the large-diameter leg 43b. Other configurations are the same as those of the ignition plug 100c in FIG. That is, in the spark plug 100d of FIG. 5B, the inner insulator 70c without the groove 72 is employed as the inner insulator. For this reason, in the spark plug 100d of FIG. 5B, the outer peripheral surface 70cS of the rear end portion of the inner insulator 70c is located radially inward from the radially outer surface of the first plate-shaped portion 24. I have.

  The outer peripheral surface 70eS of the inner insulator 70e of the ignition plug 100e of FIG. 6 has a diameter within the axial range in contact with the seal member 80e instead of the concave portion 75 of the inner insulator 70 of the first embodiment. A protrusion 75e protruding outward in the direction is formed over the entire circumference. A concave portion 85e is formed on the inner peripheral surface of the seal member 80e so as to be depressed outward in the radial direction and fitted with the protrusion 75e over the entire circumference. As a result, similarly to the ignition plug 100 of the first embodiment, the occurrence of creeping discharge in the gap between the outer peripheral surface 70eS of the inner insulator 70e and the seal member 80e can be more effectively suppressed. The insulating property between the floating electrode 20 and the floating electrode 20 can be further improved.

B. Evaluation test B-1. First Evaluation Test In the first evaluation test, as shown in Table 1 below, 42 samples of the ignition plug 100d in FIG. 5B were prepared. In the 42 samples, at least one of the interval t and the length L2 is different from each other. The interval t is the interval (FIG. 5B) between the outer peripheral surface 70cS of the inner insulator 70c and the inner peripheral surface 11S of the outer insulator 10 (the rear end body 18). It can also be said that the interval t is the radial thickness of the seal member 80. The length L2 is a length in the axial direction of a portion of the sealing member 80 closer to the rear end than the rear end of the first plate portion 24 of the floating electrode 20 (FIG. 5B). As a comparative sample, a sample in which the sealing member 80 was removed from the ignition plug 100d in FIG. 5B was prepared. In the comparative sample, the interval t was set to 0.2 mm.

  As shown in Table 1, in the 42 samples, the interval t is any one of 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, and 0.3 mm. The length L2 is any one of 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and 3.5 mm. The interval t was changed by fixing the inner diameter of the first hole 11 of the outer insulator 10 to 6.3 mm and changing the outer diameter of the inner insulator 70c.

Items common to each sample are as follows.
Inner diameter of first hole 11 of outer insulator 10: 6.3 mm
Distance L1: 8 mm from the rear end of floating electrode 20 to the rear end of inner insulator 70
Number of floating electrodes 20: 2

  In this test, a DC voltage V is applied between the ground electrode 30 (metal shell 50) and the center electrode 40 in a state where the ground electrode 30 and the floating electrode 20 are short-circuited, so that the center A voltage was applied between the electrode 40. Then, it was examined whether or not dielectric breakdown occurred between the floating electrode 20 and the center electrode 40 during the application of the DC voltage V for 10 seconds. If dielectric breakdown did not occur, the DC voltage V was increased by 1 kV, and the above test was repeated to check the minimum voltage at which dielectric breakdown occurred (also referred to as leak voltage).

  The results of this test are as shown in Table 1. The unit of the leak voltage shown in Table 1 is “kV”. The leak voltage of the comparative sample was 12 kV. As shown in Table 1, the leak voltage of all 42 samples was 13 kV or more. From this result, it was confirmed that, by filling the seal member 80, the insulation (voltage resistance) between the ground electrode 30 and the floating electrode 20 can be improved.

  Furthermore, in all the sample groups with the interval t, the sample having the length L2 of 1 mm or more had a leak voltage higher by 2 kV or more than the sample having the length L2 of 0.5 mm at the same interval t. From this result, it was confirmed that when the length L2 was 1 mm or more, the insulation between the center electrode 40 and the floating electrode 20 could be further improved.

  In addition, when comparing samples having the same length L2, it was confirmed that as the interval t (the thickness of the sealing member 80) increases, the leak voltage tends to increase. For example, among the six samples having a length L2 of 1 mm, a sample having an interval t of 0.2 mm or less has a leak voltage of 16 kV, whereas a sample having an interval t of 0.25 mm or more has a leak voltage of 16 kV. The voltage was 17 kV. Also, among the six samples having a length L2 of 1.5 mm, the sample having an interval t of 0.15 mm or less has a leak voltage of 17 kV, whereas the sample having an interval t of 0.2 mm or more has a leak voltage of 17 kV. And the leak voltage was 18 kV. Thus, it was confirmed that as the thickness of the seal member 80 was larger, the insulating property between the center electrode 40 and the floating electrode 20 tended to be improved.

  Further, when comparing samples having the same interval t, it was confirmed that the leak voltage tended to increase as the length L2 increased. For example, in the seven samples in which the interval t is 0.2 mm, as the length L2 becomes longer as 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and 3.5 mm, the leakage increases. It was confirmed that the voltage gradually increased to 14 kV, 16 kV, 18 kV, 18 kV, 19 kV, 20 kV, and 20 kV. Thus, it was confirmed that the longer the length L2, the better the insulation between the center electrode 40 and the floating electrode 20.

  Also, it was confirmed that a leak voltage of 20 kV could be secured if at least the interval t (the thickness of the sealing member 80) was 0.1 mm or more and the length L2 was 3 mm or more.

B-2. Second Evaluation Test In the second evaluation test, as shown in Table 2 below, samples of four types of spark plugs 100a, 100b, 100c, and 100d shown in FIGS. 4 and 5 were prepared.

  In the samples of the spark plugs 100a and 100c, the outer peripheral surfaces 70aS and 70cS on the rear end side of the inner insulators 70a and 70c are located radially outward by 0.1 mm from the outer peripheral surface of the large-diameter leg 43 of the center electrode 40. (ΔS = 0.1 mm). In the samples of the ignition plugs 100b and 100d, the outer peripheral surfaces 70aS and 70cS on the rear end side of the inner insulators 70a and 70c are located 0.1 mm radially inward from the outer peripheral surface of the large-diameter leg 43b of the center electrode 40b. (ΔP = 0.1 mm).

Items common to each sample are as follows.
Inner diameter of first hole 11 of outer insulator 10: 6.3 mm
Distance L1: 8 mm from the rear end of floating electrode 20 to the rear end of inner insulator 70
Number of floating electrodes 20: 2 Interval t between outer peripheral surfaces 70aS, 70cS of inner insulators 70a, 70c and inner peripheral surface 11S of outer insulator 10: 0.2 mm
The axial length L2 of the portion of the sealing member 80 on the rear end side of the first plate portion 24 with respect to the rear end is 3.5 mm.

  In this test, the same test as the above-described first evaluation test was performed, and the leak voltage of each sample was examined. The results of this test are as shown in Table 2. The leak voltage (22 kV) of the sample of the ignition plug 100c was 2 kV higher than the leak voltage (20 kV) of the sample of the ignition plug 100d. From this result, as shown by ΔS in FIG. 3, by positioning the outer peripheral surface 70S of the rear end portion of the inner insulator 70 radially outside the outer peripheral surface of the large-diameter leg 43, the center electrode 40 It has been confirmed that the insulation between the electrode and the floating electrode 20 can be further improved.

  Further, the leak voltage (24 kV) of the sample of the ignition plug 100b was higher by 4 kV than the leak voltage (20 kV) of the sample of the ignition plug 100d. From this result, as shown in the wavy line area CA in FIG. 3, the outer peripheral surface 70S of the rear end portion of the inner insulator 70 is positioned more radially outward than the radially outer surface of the first plate-shaped portion 24. It has been confirmed that the position between the center electrode 40 and the floating electrode 20 can further improve the insulating property.

  The leak voltage (26 kV) of the sample of the ignition plug 100a was higher than the leak voltage (26 kV) of the sample of the ignition plugs 100c and 100b by 2 kV or more. According to this result, the outer peripheral surface 70S of the rear end portion of the inner insulator 70 is positioned radially outward from the outer peripheral surface of the large-diameter leg portion 43, and the outer peripheral surface 70S of the first plate-shaped portion 24 is radially outward. Also, it was confirmed that the insulating property between the center electrode 40 and the floating electrode 20 can be particularly improved by being positioned on the outside in the radial direction.

B-3. Third Evaluation Test In the third evaluation test, as shown in Table 3 below, four samples of the ignition plug 100 of FIG. 1 were prepared. The four samples of the spark plug 100 are different from the sample of the spark plug 100a in the second evaluation test in that a concave portion 75 is formed in the outer peripheral surface 70S of the inner insulator 70, and the seal member 80 is fitted in the concave portion 75. A mating projection 85 is formed. Other configurations of the four samples of the spark plug 100 are the same as those of the sample of the spark plug 100a in the second evaluation test.

  In the four samples of the spark plug 100, the radial depth D of the concave portion 75 of the inner insulator 70 (FIG. 3, substantially equal to the radial height of the protrusion 85) is different from each other. Specifically, the depth D of the four samples is 0.05 mm, 0.1 mm, 0.15 mm, and 0.2 mm.

  In this test, the same tests as the first and second evaluation tests described above were performed, and the leak voltage of each sample was examined. The results of this test are as shown in Table 3. The leak voltage (27 kV, 30 kV, 31 kV) of the four samples of the spark plug 100 was 1 kV or more higher than the leak voltage (26 kV) of the sample of the spark plug 100 a in the second evaluation test. From this result, it is possible to improve the insulation between the center electrode 40 and the floating electrode 20 by forming the concave portion 75 on the outer peripheral surface 70S of the inner insulator 70, as compared with the case where the concave portion 75 is not formed. It could be confirmed.

  Also, the leak voltage (30 kV, 31 kV) of the sample whose depth D is 0.1 mm or more is 3 kV or more higher than the leak voltage (27 kV) of the sample whose depth D is 0.05 mm. Was. From this result, it was confirmed that the insulating property between the center electrode 40 and the floating electrode 20 can be particularly improved by setting the radial depth D of the concave portion 75 to 0.1 mm or more.

C. Second Embodiment FIG. 7 is a cross-sectional view of a spark plug 100M according to a second embodiment. The spark plug 100M includes a center electrode 40M, an inner insulator 70M, and a floating electrode 20M instead of the center electrode 40, the inner insulator 70, and the floating electrode 20 of the spark plug 100 of the first embodiment. Other configurations of the spark plug 100M are the same as those of the spark plug 100 of the first embodiment. Note that the rear end side in the second embodiment corresponds to the second end side in the claims, and the front end side in the first embodiment corresponds to the first end side in the claims.

  The rear end of the inner insulator 70M opposite to the inner insulator 70 of the first embodiment is closed. That is, the inner insulator 70M is formed with a bottomed hole 74M having an opening at the front end and a bottom 73M arranged at the rear end. The inner insulator 70M is disposed inside the first hole 11 of the outer insulator 10. On the outer peripheral surface 70MS of the inner insulator 70M, a groove 72M corresponding to the shape of a plate-like leg 44M of the center electrode 40M described later is formed.

  The center electrode 40M is a metal member extending along the axis CL. The center electrode 40M includes a flange portion 42 and a cap mounting portion 41, similarly to the center electrode 40 of the first embodiment. The center electrode 40M includes a columnar leg 43M and a plate-like leg 44M instead of the large-diameter leg 43 and the small-diameter leg 44 of the center electrode 40. The columnar leg 43M has an outer diameter slightly smaller than the inner diameter of the first hole 11 of the outer insulator 10, and is arranged on the rear end side of the inner insulator 70M inside the first hole 11. .

  The plate leg portion 44M is a strip-shaped thin plate member extending along the axis. The plate-shaped leg portion 44M is disposed in a gap between the outer peripheral surface 70MS of the inner insulator 70M and the inner peripheral surface 11S forming the first hole 11 of the outer insulator 10. Specifically, the plate-like leg 44M is curved along the inner peripheral surface 11S forming the first hole 11, and fits into the groove 72M formed on the outer peripheral surface 70MS of the inner insulator 70M. ing. Instead, the plate-shaped leg 44M may be a cylindrical member formed of a thin plate. Then, the rear end side of the inner insulator 70M may be inserted into the inside of the tubular plate-like leg 44M.

  The floating electrode 20M includes one large-diameter rod portion 24M on the rear end side, a plate-shaped portion 25M, and two rod-shaped portions 26. The large-diameter rod portion 24M extends from the rear end surface of the plate portion 25M toward the rear end. The large-diameter rod portion 24M is located in the bottomed hole 74M of the inner insulator 70M. The rear end in the axial direction of the large-diameter rod portion 24M reaches near the bottom 73M of the bottomed hole 74M.

  The plate-like portion 25M is disposed in a gap between the surface on the tip end side of the inner insulator 70M and the bottom surface of the first hole 11 of the outer insulator 10. The plate-like portion 25M and the rod-like portion 26 are disposed on the tip side of the inner insulator 70M. The rod-shaped portion 26 extends from the surface on the distal end side of the plate-shaped portion 25M toward the distal end side. The configuration of the bar portion 26 is the same as the bar portion 26 of the first embodiment. The rod portion 26 is disposed in the second hole 12 of the outer insulator 10 as in the first embodiment, and the distal end of the rod portion 26 protrudes from the leg 13 of the outer insulator 10 toward the distal end.

  FIG. 8 is an enlarged cross-sectional view near the tip of the inner insulator 70M. FIG. 8 is an enlarged view of the area RAM indicated by the dashed line in FIG. A gap between the inner peripheral surface 11S of the outer insulator 10 and the outer peripheral surface 70MS of the inner insulator 70M (also referred to as a gap between insulators) is filled with a seal member 80M. The seal member 80M is filled over the entire circumference in the circumferential direction. The seal member 80M is formed of a rubber member, like the seal member 80 of the first embodiment. Similar to the seal member 80 of the first embodiment, the seal member 80M is configured such that the inner insulator 70M is placed in the first hole 11 of the outer insulator 10 in a state where liquid rubber is applied to the outer peripheral surface 70MS of the inner insulator 70M. The liquid rubber is formed by curing the liquid rubber by inserting the liquid rubber and heating after the insertion.

  As shown in FIG. 8, the seal member 80M includes a portion closer to the tip than the tip of the plate-like leg 44M of the center electrode 40M disposed in the gap between the insulators. As a result, it is possible to prevent the insulation between the center electrode 40M and the floating electrode 20M from being broken in the gap between the insulators. Therefore, in the spark plug 100M, the insulation between the center electrode 40M and the floating electrode 20M can be improved. It is preferable that the axial length L2M of the portion of the seal member 80M closer to the distal end than the distal end of the plate-like leg portion 44M is 1 mm or more.

  The seal member 80M further includes a portion closer to the rear end than the front end of the plate-like leg portion 44M arranged in the gap between the insulators. This portion is filled between the radially outer surface of the plate-like leg 44M and the inner peripheral surface 11S of the outer insulator 10 at the circumferential position where the plate-like leg 44M is arranged. ing. Thereby, the insulation between the center electrode 40M and the floating electrode 20M can be further improved.

  The outer peripheral surface 70MS of the inner insulator 70M is located on the distal end side of the plate-shaped leg portion 44M, the rear end of the portion of the floating electrode 20 that is located on the distal end side of the inner insulator 70M, that is, the plate-shaped portion 25M. Is located radially outward over the entire circumference from the rear end. That is, as shown by ΔS in FIG. 8, the outer peripheral surface 70MS of the tip portion of the inner insulator 70M is located radially outside the outer peripheral surface of the plate-shaped portion 25M. Thereby, the insulation between the center electrode 40M and the floating electrode 20M can be further improved.

  Further, the outer peripheral surface 70MS of the inner insulator 70M is located radially outward over the entire circumference from the tip of the center electrode 40 (that is, the plate-like leg 44M) on the tip side of the plate-like leg 44M. I have. That is, in FIG. 8, as shown in the region CA of the wavy line, the outer peripheral surface 70MS of the tip portion of the inner insulator 70M is located radially outward from the radially outer surface of the plate-like leg 44M. I have. Thereby, the insulation between the center electrode 40M and the floating electrode 20M can be further improved.

  In the spark plug 100M of the present embodiment, the distance L1M (FIG. 7) from the tip of the plate-like leg 44M to the tip of the inner insulator 70 is 10 mm or less, for example, 8 mm. As described above, even when the distance L1M is relatively short, the insulation between the center electrode 40M and the floating electrode 20M can be ensured by disposing the seal member 80M.

  As understood from the above description, in the spark plug 100 according to the first embodiment, the center electrode 40 corresponds to the first electrode in the claims, and the floating electrode 20 corresponds to the second electrode in the claims. Corresponding to In the spark plug 100M of the second embodiment, the center electrode 40M corresponds to a second electrode in the claims, and the floating electrode 20M corresponds to a first electrode in the claims.

C-2. Modifications of Second Embodiment (1) Similarly to the inner insulator 70 of the first embodiment, the outer peripheral surface 70MS of the inner insulator 70M of the second embodiment has an axial direction in contact with the seal member 80M. Within the range, a concave portion concaved inward in the radial direction may be formed over the entire circumference. In this case, the seal member 80M may include a projection that fits into the recess.

(2) Similarly to the inner insulator 70e (FIG. 6) of the modification of the first embodiment, the outer peripheral surface 70MS of the inner insulator 70M of the second embodiment has an axial direction in contact with the seal member 80M. Within the range, a protrusion protruding radially outward may be formed over the entire circumference. In this case, the seal member 80M may include a concave portion that fits into the protrusion.

(3) As in the modified examples of FIGS. 4 and 5 of the first embodiment, in the spark plug 100M of the second embodiment, the outer peripheral surface 70MS of the tip portion of the inner insulator 70M has the diameter of the plate-like leg 44M. It may be located radially inward of the outer surface in the direction. Further, the outer peripheral surface 70MS of the tip portion of the inner insulator 70M may be located radially inward of the outer peripheral surface of the plate-shaped portion 25M.

D. Modifications Common to Each Embodiment (1) In the above embodiment, the ignition plug includes a plurality of rod-shaped portions 26 of the floating electrodes 20 and 20M, but only one rod-shaped portion 26 may be provided. For example, the floating electrodes 20 and 20M may include only one columnar rod-shaped portion 26 on the axis CL.

(2) The material forming the seal members 80, 80a, 80c, and 80M may be another insulating material. For example, the seal members 80, 80a, 80c, and 80M may be formed of a resin material such as rubber or an elastomer different from silicone rubber. Further, the seal members 80, 80a, 80c, and 80M may be an inorganic material such as glass. In this case, for example, a slurry containing a glass powder and a liquid (for example, water) is applied to the outer peripheral surface of the inner insulator and inserted into the outer insulator 10, and then the slurry is heated and sintered. By doing so, a seal member is formed.

(3) The dimensions of each part in the above embodiment are examples, and are not limited to the dimensions described above, and various dimensions can be applied.

  As described above, the present invention has been described based on the embodiments and the modifications. However, the above-described embodiments and the modifications of the present invention are for facilitating the understanding of the present invention, and do not limit the present invention. Absent. The present invention can be modified and improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof.

  65 ... gasket, 10 ... outer insulator, 11 ... first hole, 12 ... second hole, 13 ... leg length, 15 ... first step, 17 ... tip side trunk, 18 ... back end trunk, 19 ... Flange, 20, 20M ... Floating electrode, 24 ... First plate, 24M ... Large bar, 25 ... Second plate, 25M ... Plate, 26 ... Bar, 27 ... Tip, Reference numeral 30: ground electrode, 40, 40b, 40M: center electrode, 41: cap mounting part, 42: flange, 43, 43b: large diameter leg, 43M: columnar leg, 44: small diameter leg, 44M: plate shape Legs, 50: metal shell, 51: tool engaging portion, 52: mounting screw portion, 53: caulking portion, 54: seat portion, 56: second step portion, 57: distal end portion, 58: compression deforming portion, 66: ring member, 68: packing, 69: talc, 70, 70a, 70c, 70M: inner insulator, 72, 72M: groove, 74, 4M ... bottomed hole, 75 ... recess, 75e ... protruding portion, 80, 80a, 80e ... sealing member, 85 ... protruding portion, 85e ... recess, 100,100A～100e, 100M ... spark plug

Claims (5)

A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a portion of the gap on the first end side from a portion where the second electrode is disposed is filled with an insulating seal member over the entire circumference ,
The ignition plug is characterized in that the seal member is formed of a thermosetting resin material . A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a portion of the gap on the first end side from a portion where the second electrode is disposed is filled with an insulating seal member over the entire circumference,
The outer peripheral surface of the inner insulator is located on the first end side of the second electrode, on the first end side of the second electrode, and on the inner end of the first electrode. An ignition plug including a portion located on the second end side of a portion disposed on a first end side and a portion located radially outward over at least one of the ends. A cylindrical outer insulator having an axial hole extending from the first end side to the second end side in the axial direction;
A cylindrical inner insulator in which a bottomed hole having a bottom disposed on the second end side is formed inside the shaft hole,
A metal shell disposed on the outer periphery of the outer insulator;
A first electrode having a portion arranged on the first end side of the inner insulator and a portion arranged inside the bottomed hole of the inner insulator;
A second electrode having a portion disposed on the second end side of the inner insulator and a portion disposed in a gap between an inner peripheral surface of the outer insulator and an outer peripheral surface of the inner insulator; With
The first electrode and the second electrode are insulated, and the first electrode and the second electrode and the metal shell are insulated spark plugs,
At least a portion of the gap on the first end side from a portion where the second electrode is disposed is filled with an insulating seal member over the entire circumference,
A spark plug, wherein a distance from an end on the first end side of the second electrode to an end on the first end side of the inner insulator is 10 mm or less. The spark plug according to claim 1, wherein:
Wherein among the sealing member, wherein the axial length of the rear end portion of the rear end of the second electrode is 1mm or more, the spark plug. The spark plug according to any one of claims 1 to 4 ,
In the axial direction range in which the seal member is filled over the entire circumference, the outer peripheral surface of the inner insulator has a protrusion protruding radially outward over the entire circumference, An ignition plug, wherein at least one of a concave portion that is concave inward in the radial direction is formed.

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