JP6333135B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

In the spark plug, when the center electrode is assembled to the metal shell through an insulator, an annular ring member is disposed between the outer peripheral surface of the insulator and the inner peripheral surface of the metal shell, and a sealing powder ( For example, what filled powder talc (talc) is known (for example, refer to patent documents 1 and 2). The ring member and the powder provided between the insulator and the metal shell hermetically seal between the insulator and the metal shell, and improve the holding power of the insulator against the metal shell.
In addition, it is known that a coil boot (also referred to as a plug cap) is attached to the rear end portion for supplying electricity to the spark plug (see, for example, Patent Document 3).

JP 2000-215964 A JP 2006-66385 A JP-A-8-34907

The holding force of the insulator with respect to the metal shell may be reduced by an external force applied to a portion of the spark plug disposed in the combustion chamber (for example, combustion pressure generated by gas combustion). In addition, although it is considered not to cause abnormal discharge (so-called flash over) between the head of the terminal electrode provided at the rear end of the spark plug and the metal shell, the performance to suppress the flash over (flash resistant) There was room for further improvement in (over performance).
Therefore, in view of such circumstances, the present invention aims to provide a spark plug that further improves the holding power of the insulator against the metal shell and the flashover resistance.

  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 forms.

(1) According to one aspect of the present invention, a spark plug is provided. This spark plug is a cylindrical insulator extending from the front end side to the rear end side about the axis, and a cylindrical metal shell that is caulked and fixed to the outer peripheral surface of the insulator. A metal fitting having a tool engaging portion projecting into a shape, and a caulking lid that is bent toward the outer peripheral surface of the insulator by caulking the rear end portion of the main metal fitting connected to the rear end side of the tool engaging portion, Powder is filled between the outer peripheral surface of the insulator and the inner peripheral surface of the caulking lid. In this spark plug, the caulking lid has an annular flat portion extending in the outer peripheral direction from its rear end. According to the spark plug of this form, when the caulking lid is bent by caulking, the caulking lid can be pushed with a jig through a flat portion that can easily transmit the caulking load. Even if it is difficult to bend for the reason, the caulking lid can be reliably bent and the insulator can be fixed to the metal shell. As a result, it can suppress that the retention strength of the insulator with respect to a metal shell falls. Also, when the coil boot (plug cap) is attached to the rear end of the spark plug, the annular flat surface comes into surface contact with the coil boot (plug cap), so that the coil boot (plug cap) and the caulking lid are in contact with each other. Increases area. Thereby, the anti-flashover performance can be improved.

(2) In the spark plug of the above aspect, when the filling region and the flat portion filled with powder between the metal shell and the insulator are projected on a plane perpendicular to the axis, the projection region of the flat portion is the filling region. It is good also as overlapping with the projection area. According to this form of the spark plug, a load can be more reliably applied to the talc by the flat portion. Thereby, a load can be more reliably applied to an insulator via a talc, and an insulator can be firmly fixed to a metal shell. As a result, it is possible to further suppress a decrease in the holding power of the insulator with respect to the metal shell.

(3) In the spark plug of the above aspect, an annular ring member is disposed between the rear end side of the filling region and the caulking lid, and the caulking lid protrudes in the inner circumferential direction on the inner circumferential side than the flat portion. It is good also as having at least one part of a cyclic | annular inner peripheral part to contact with a cyclic | annular ring member. According to the spark plug of this embodiment, the contact area between the caulking lid and the annular ring member is increased, so that it is possible to further suppress a decrease in the holding force of the insulator with respect to the metal shell.

(4) In the spark plug of the above aspect, the flat portion may be parallel to a direction orthogonal to the axis. According to the spark plug of this embodiment, since the caulking load can be transmitted more easily, the insulator can be more securely fixed to the metal shell.

It is explanatory drawing which shows the partial cross section of a spark plug. It is explanatory drawing which expands and shows the partial cross section of a spark plug. It is explanatory drawing which expands and shows the partial cross section of a crimping lid. It is a figure which shows the projection area | region of a filling area | region and a plane part. It is a table | surface which shows the result of a 1st evaluation test.

A. Embodiment:
A-1. Spark plug configuration:
FIG. 1 is an explanatory view showing a partial cross section of the spark plug 10. FIG. 1 illustrates the external shape of the spark plug 10 on the right side of the drawing with the axis CA1 being the axis of the spark plug 10 as a boundary, and the cross-sectional shape of the spark plug 10 on the left side of the drawing. In the description of the present embodiment, the lower side of the spark plug 10 in FIG. 1 is referred to as “front end side”, and the upper side of FIG. 1 is referred to as “rear end side”.

  The spark plug 10 includes a center electrode 100, an insulator 200, a metal shell 300, and a ground electrode 400. In the present embodiment, the axis CA1 of the spark plug 10 is also the axis of each member of the center electrode 100, the insulator 200, and the metal shell 300.

  The spark plug 10 has a gap SG formed between the center electrode 100 and the ground electrode 400 on the tip side. The gap SG of the spark plug 10 is also called a spark gap. The spark plug 10 is configured to be attachable to the internal combustion engine 90 in a state in which the front end side where the gap SG is formed protrudes from the inner wall 910 of the combustion chamber 920. When a high voltage is applied to the center electrode 100 with the spark plug 10 attached to the internal combustion engine 90, a spark discharge is generated in the gap SG. It is possible to ignite the air-fuel mixture in the combustion chamber 920 by the spark discharge generated in the gap SG.

  FIG. 1 shows XYZ axes orthogonal to each other. The XYZ axes in FIG. 1 correspond to the XYZ axes in other figures described later.

  Of the XYZ axes in FIG. 1, an axis along the axis CA <b> 1 is a Z axis. With respect to the Z-axis direction (axial direction) along the Z-axis, the + Z-axis direction from the rear end side to the front-end side of the spark plug 10 is set, and the opposite is the −Z-axis direction. The + Z-axis direction is a direction in which the center electrode 100 protrudes from the front end side of the metal shell 300 along the axis CA1 together with the insulator 200.

  Of the XYZ axes in FIG. 1, the axis along the direction in which the ground electrode 400 bends toward the axis CA1 is defined as the Y axis. With respect to the Y-axis direction along the Y-axis, the direction in which the ground electrode 400 bends toward the axis CA1 is the −Y-axis direction, and the opposite is the + Y-axis direction.

  Of the XYZ axes in FIG. 1, an axis orthogonal to the Y axis and the Z axis is taken as an X axis. With respect to the X-axis direction along the X-axis, the + X-axis direction is from the back of the sheet of FIG. 1 toward the front of the sheet, and the opposite is the −X-axis direction.

  The center electrode 100 of the spark plug 10 is a conductive electrode body. The center electrode 100 has a rod shape extending about the axis CA1. In the present embodiment, the center electrode 100 is made of a nickel alloy (for example, Inconel (registered trademark)) whose main component is nickel (Ni). The outer surface of the center electrode 100 is electrically insulated from the outside by an insulator 200. The distal end side of the center electrode 100 protrudes from the distal end side of the insulator 200. The rear end side of the center electrode 100 is electrically connected to the rear end side of the insulator 200. In the present embodiment, the rear end side of the center electrode 100 is electrically connected to the rear end side of the insulator 200 via the seal body 160, the ceramic resistor 170, the seal body 180, and the terminal fitting 190.

  The ground electrode 400 of the spark plug 10 is an electrode body having conductivity. The ground electrode 400 has a shape that once extends parallel to the axis CA1 from the metal shell 300 and then bends toward the axis CA1. The base end portion of the ground electrode 400 is joined to the metal shell 300. A gap SG is formed between the tip of the ground electrode 400 and the center electrode 100. In the present embodiment, the ground electrode 400 is made of a nickel alloy (for example, Inconel (registered trademark)) whose main component is nickel (Ni).

  The insulator 200 of the spark plug 10 is an insulator having electrical insulation. The thermal expansion coefficient of the insulator 200 is smaller than that of the metal shell 300. The insulator 200 has a cylindrical shape extending about the axis CA1. In this embodiment, the insulator 200 is formed by firing an insulating ceramic material (for example, alumina).

  The insulator 200 has a shaft hole 290 that is a through hole extending about the axis CA1. In the shaft hole 290 of the insulator 200, the center electrode 100 is held on the axis CA <b> 1 in a state where it protrudes from the tip side (+ Z axis direction side) of the insulator 200. On the outer side of the insulator 200, in order from the front end side to the rear end side, the first cylindrical portion 210, the second cylindrical portion 220, the third cylindrical portion 250, and the fourth cylindrical portion 270 are provided. Is formed.

  The first tubular portion 210 of the insulator 200 is a cylindrical portion that is tapered toward the distal end side, and the distal end side of the first tubular portion 210 protrudes from the distal end side of the metal shell 300. The second tubular portion 220 of the insulator 200 is a cylindrical portion having a larger diameter than the first tubular portion 210. The third cylindrical portion 250 of the insulator 200 is a cylindrical portion that protrudes in the outer peripheral direction from the second cylindrical portion 220 and the fourth cylindrical portion 270. The fourth cylindrical portion 270 of the insulator 200 is a cylindrical portion that forms the rear end side from the third cylindrical portion 250, and the rear end side of the fourth cylindrical portion 270 is the rear end side of the metal shell 300. Protruding from.

  The metal shell 300 of the spark plug 10 is a metal body having conductivity. The thermal expansion coefficient of the metal shell 300 is larger than that of the insulator 200. The metal shell 300 has a cylindrical shape extending about the axis CA1. In the present embodiment, the metallic shell 300 is a metal body obtained by applying nickel plating to a low carbon steel formed into a cylindrical shape. In other embodiments, the metallic shell 300 may be a metal body that is galvanized, or may be a metal body that is not plated (non-plated).

  The insulator 200 is held inside the metal shell 300 in a state of protruding together with the center electrode 100 from the front end side (+ Z-axis direction side) of the metal shell 300. Inside the metal shell 300, a metal fitting inner peripheral surface 392, an annular convex portion 394, and a metal fitting inner peripheral surface 396 are formed in order from the front end side to the rear end side.

  The metal inner peripheral surface 392 of the metal shell 300 is a portion of the inner peripheral surface of the metal shell 300 that is located on the tip side of the annular convex portion 394. The annular protrusion 394 of the metal shell 300 is an annular portion that protrudes inward from the metal inner peripheral surface 392 and the metal inner peripheral surface 396 that are the inner peripheral surface of the metal shell 300. The metal inner peripheral surface 396 of the metal shell 300 is a portion located on the rear end side of the inner peripheral surface of the metal shell 300 with respect to the annular convex portion 394.

  A gap between the metal inner peripheral surface 392 and the insulator 200 is larger than a gap between the annular convex portion 394 and the insulator 200 and a gap between the metal inner peripheral surface 396 and the insulator 200. When the insulator 200 is inserted from the rear end side of the metal shell 300 and assembled to the metal shell 300, the annular protrusion 394 and the metal inner peripheral surface 396 are used for positioning the insulator 200 with respect to the metal shell 300.

  The metal shell 300 is caulked and fixed to the outer surface of the insulator 200 while being electrically insulated from the center electrode 100. On the outer side of the metal shell 300, there are a front end portion 310, a screw portion 320, a body portion 340, a groove portion 350, a tool engagement portion 360, and a caulking lid 380 in order from the front end side to the rear end side. Is formed.

  The distal end portion 310 of the metallic shell 300 is a cylindrical portion that constitutes the distal end side (+ Z axial direction side) of the metallic shell 300. A ground electrode 400 is joined to the tip portion 310. From the center of the tip portion 310, the insulator 200 together with the center electrode 100 protrudes in the + Z-axis direction.

  The threaded portion 320 of the metal shell 300 is a cylindrical portion having a thread formed on the outer surface. In the present embodiment, the spark plug 10 can be attached to the internal combustion engine 90 by screwing the screw portion 320 of the metal shell 300 into the screw hole 930 of the internal combustion engine 90. In this embodiment, the nominal diameter of the screw part 320 is M12. In other embodiments, the nominal diameter of the threaded portion 320 may be smaller than M12 (for example, M8, M9, M10) or larger than M12 (for example, M14, M18).

  The body 340 of the metal shell 300 is a bowl-shaped portion that protrudes from the groove 350 in the outer circumferential direction. With the spark plug 10 attached to the internal combustion engine 90, the gasket 500 is compressed between the body 340 and the internal combustion engine 90.

  The groove portion 350 of the metal shell 300 is a cylindrical portion that is provided between the body 340 and the tool engaging portion 360 and bulges in the outer peripheral direction when the metal shell 300 is caulked and fixed to the insulator 200.

  The tool engagement portion 360 of the metal shell 300 is a bowl-shaped portion projecting in a polygonal shape in the outer peripheral direction from the groove portion 350 and engages with a tool (not shown) for attaching the spark plug 10 to the internal combustion engine 90. Make a shape. In the present embodiment, the outer shape of the tool engaging portion 360 is a hexagonal shape.

  The caulking lid 380 of the metal shell 300 is a part that is formed by bending the rear end side of the metal shell 300 toward the insulator 200 when the metal shell 300 is caulked and fixed to the insulator 200. The crimping is performed using a crimping jig. By applying a load while bringing a planar portion provided on the crimping jig into contact with the rear end portion of the metal shell 300, the rear end portion of the metal shell 300 is bent toward the insulator 200. An annular flat surface portion 370 extending in the outer peripheral direction is formed. Thus, even when it is difficult to bend due to the thickness of the caulking lid 380 being thick by applying a load while bringing the flat portion provided in the caulking jig into contact with the annular flat portion 370, Caulking can be performed reliably. The length in the radial direction of the flat portion 370 may be about 0.8 mm to 1.2 mm, and in this embodiment, it is 1 mm.

  Between the outer side of the third cylindrical part 250 and the fourth cylindrical part 270 of the insulator 200 and the inner side of the tool engaging part 360 and the caulking lid 380 of the metal shell 300, the ring member 610 is located on the rear end side. The ring members 620 are disposed on the distal end side, and the powder 650 is filled between the ring member 610 and the ring member 620. The ring members 610 and 620 are metal (for example, iron (Fe)) annular members. The powder 650 is a sealing powder (for example, powder talc).

The ring members 610 and 620 and the powder 650 seal the gap between the insulator 200 and the metal shell 300 and improve the holding force of the insulator 200 with respect to the metal shell 300. Here, the ring members 610 and 620 that are annular members may have an O-shape that is not cut in the circumferential direction when viewed in a cross section orthogonal to the axis CA1, or a C-shape that has a cut in a part of the circumferential direction. It may be.

  FIG. 2 is an explanatory view showing an enlarged partial cross section of the spark plug 10. In FIG. 2, the partial cross section around the tool engaging portion 360 in the spark plug 10 is illustrated in an enlarged manner as compared with FIG.

  As shown in FIG. 2, the caulking lid 380 of the metal shell 300 is formed by bending the end 388 of the metal shell 300 connected to the tool engaging portion 360 toward the outer peripheral surface 208 of the insulator 200 by caulking. 610, 620 and powder 650 are sealed. The sealing powder 650 includes an outer peripheral surface 208 from the third cylindrical portion 250 to the fourth cylindrical portion 270 in the insulator 200, and an inner peripheral surface 398 from the tool engaging portion 360 to the caulking lid 380 in the metal shell 300. It is filled between.

  The ring member 610 is pressed against the outer peripheral surface 208 of the insulator 200 by the caulking lid 380 of the metal shell 300, and the outer peripheral surface 208 of the fourth tubular portion 270 of the insulator 200 and the caulking lid 380 of the metal shell 300 are flat. It is in contact with the inner peripheral surface 398 of the annular inner peripheral portion 389 formed on the inner peripheral side with respect to the portion 370. The ring member 620 is disposed on the tip side of the ring member 610 and contacts the outer peripheral surface 208 of the third cylindrical portion 250 of the insulator 200 and the inner peripheral surface 398 of the tool engaging portion 360 of the metal shell 300. Yes.

  Except for the region where the ring members 610 and 620 are disposed, a region where the powder 650 is filled between the insulator 200 and the metal shell 300 along the axis CA1 is defined as a filling region FA. In the present embodiment, when the filling area FA and the plane part 370 are projected onto the plane PP perpendicular to the axis CA1 along the axis CA1, the projection area R1 of the plane part 370 overlaps the projection area R2 of the filling area FA. A flat portion 370 is formed.

  As described above, when the planar portion 370 is located at a position where the projection region R1 of the planar portion 370 overlaps the projection region R2 of the filling region FA, the planar portion 370 can apply a load to the talc more reliably. Thereby, a load can be more reliably applied to an insulator via a talc, and an insulator can be firmly fixed to a metal shell. As a result, it is possible to further suppress a decrease in the holding power of the insulator with respect to the metal shell.

  In addition, it is better if the flat surface portion 370 is located at a position where all the projection regions R1 of the flat surface portion 370 overlap with the projection region R2 of the filling region FA, because the insulator can be pressed more reliably through the talc. In the present embodiment, the plane portion 370 is a plane parallel to the direction orthogonal to the axis CA1. Thus, by forming the flat portion 370 so as to be parallel to the direction orthogonal to the axis CA1, it is possible to more reliably apply a load to the insulator via the talc.

  As shown in FIG. 2, the tool engagement portion 360 has an end surface 368 that is an end portion on the rear end side of the tool engagement portion 360. A caulking lid 380 is formed on the −Z axis direction side from a plane passing through the end surface 368 and parallel to the X axis and the Y axis.

  FIG. 3 is an explanatory diagram showing an enlarged partial cross section of the caulking lid 380. FIG. 3 shows a cross-section of a caulking lid 380 that is cut along a YZ plane that passes through the axis CA1 and is parallel to the Y axis and the Z axis.

  In FIG. 3, an annular inner peripheral portion 389 that protrudes in the inner peripheral direction is formed on the inner peripheral side of the crimping lid 380 with respect to the plane portion 370. As described above, since the annular inner peripheral portion 389 is provided on the inner peripheral side with respect to the flat portion 370, the contact area between the caulking 380 lid and the ring member 610 is increased, and the insulator 200 is more attached to the metal shell 300. It can be fixed securely.

  FIG. 4 is an explanatory diagram when the filling area FA and the plane portion 370 are projected onto the plane PP perpendicular to the axis CA1. As shown in FIG. 4, when the projection area R1 of the plane part 370 is projected onto the plane PP, the plane part 370 is formed so as to overlap the projection area R2 of the filling area FA.

A-2. First evaluation test:
FIG. 5 shows the results of evaluating the presence or absence of the occurrence of flashover between the head of the terminal electrode 190 and the metal shell 300 when a voltage is applied to the terminal electrode 190 of the spark plug 10. In the first evaluation test, 10 samples of the example having the flat portion 370 and 10 samples of the comparative example not having the flat portion 370 were prepared, and the flashover was performed when the applied voltage applied to the terminal electrode 190 was changed. It was investigated whether or not this occurred. Specifically, first, the center electrode 100 and the gap SG formed between the center electrode 100 and the ground electrode 400 and the center electrode 100 so that no discharge occurs between the insulator 200 and the metal inner peripheral surface 392 are described. Insulating oil was filled between the ground electrode 400 and between the insulator 200 and the metal fitting inner peripheral surface 392. Next, a plug cap is attached to the rear end portion of the spark plug 10, and the discharge is observed by synchronizing the discharge and the discharge waveform in a state where the caulking lid 380 and the plug cap are in contact with each other. The presence or absence was evaluated. In the first evaluation test, a voltage was applied at a period of 60 hertz while increasing the voltage by 0.5 kV per second. When no flashover occurred in any sample, it was determined as “◯”, and when there was a sample where flashover occurred even once, it was determined as “x”.

  As shown in FIG. 5, in the comparative example without the flat portion 370, flashover occurred when the applied voltage was increased, whereas in the example having the flat portion 370, the applied voltage was very high of 46 kV. However, the occurrence of flashover could be suppressed. This is because, when the flat portion 370 is not provided, the plug cap and the caulking lid are in line contact with each other, but by having the flat portion 370, when the plug cap is attached to the rear end portion of the spark plug, Since the flat portion is in surface contact with the plug cap, the contact area between the plug cap and the caulking lid is increased, and it is considered that the occurrence of flashover could be suppressed.

A-4. effect:
According to the embodiment described above, when the caulking lid has an annular flat surface portion extending in the outer peripheral direction from the rear end of the caulking lid, when the caulking lid is bent by caulking, the planar portion that can easily transmit the caulking load is formed. The caulking lid can be pushed with a jig, so even if it is difficult to bend because the caulking lid is thick, be sure to bend the caulking lid and fix the insulator to the metal shell Can do. As a result, it can suppress that the retention strength of the insulator with respect to a metal shell falls. Also, when the coil boot (plug cap) is attached to the rear end of the spark plug, the annular flat surface comes into surface contact with the coil boot (plug cap), so that the coil boot (plug cap) and the caulking lid are in contact with each other. Increases area. Thereby, the anti-flashover performance can be improved.

  In addition, when the filling area filled with powder between the metal shell and the insulator and the plane part are projected onto a plane perpendicular to the axis, the projection area of the plane part overlaps the projection area of the filling area. In this case, a load can be applied to the talc more reliably by the flat surface portion, and the insulator can be firmly fixed to the metal shell by applying a load to the insulator more reliably through the talc.

  Further, when the caulking lid has an annular inner peripheral portion projecting in the inner peripheral direction on the inner peripheral side of the flat portion of the caulking lid, and at least a part of the annular inner peripheral portion is in contact with the annular ring member, Since the contact area between the lid and the annular ring member increases, it is possible to further suppress a decrease in the holding force of the insulator with respect to the metal shell.

  Further, when the flat portion is parallel to the direction orthogonal to the axis, the caulking load can be transmitted more easily, so that the insulator can be more securely fixed to the metal shell.

  In the present embodiment, the plane portion 370 is a plane parallel to the direction orthogonal to the axis CA1, but is not limited thereto, and may be a plane that is not parallel to the axis CA1.

B. Other embodiments:
The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above-described effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Spark plug 90 ... Internal combustion engine 100 ... Center electrode 160 ... Sealing body 170 ... Ceramic resistance 180 ... Sealing body 190 ... Terminal metal fitting 200 ... Insulator 208 ... Outer peripheral surface 210 ... 1st cylindrical part 220 ... 2nd cylindrical part 250 ... 3rd cylindrical part 270 ... 4th cylindrical part 290 ... shaft hole 300 ... metal shell 310 ... tip part 320 ... screw | thread part 340 ... trunk | drum 350 ... groove part 360 ... tool engaging part 370 ... plane part 368 ... end surface 380 ... Caulking lid 382 ... Contour 384 ... Contour 388 ... End 389 ... Annular inner peripheral part 392 ... Metal fitting inner peripheral surface 394 ... Ring convex part 396 ... Metal fitting inner peripheral surface 398 ... Inner peripheral surface 400 ... Ground electrode 500 ... Gasket 610 ... Ring member 620 ... Ring member 650 ... Powder 910 ... Inner wall 920 ... Combustion chamber 930 ... Screw hole FA ... Filling region SG ... Gap CA1 ... Shaft PP ... projection area of the projection area R2 ... filling region of a plane perpendicular R1 ... flat portion in the axial

Claims (3)

A cylindrical insulator extending from the front end side toward the rear end side about the axis,
A cylindrical metal shell fixed by caulking to the outer peripheral surface of the insulator,
A tool engaging portion projecting in a polygonal shape in the outer circumferential direction;
A metal shell having a caulking lid bent toward the outer peripheral surface of the insulator by caulking the rear end portion of the metal shell connected to the rear end side of the tool engaging portion,
A spark plug filled with powder between the outer peripheral surface of the insulator and the inner peripheral surface of the caulking lid,
An annular ring member is disposed between the rear end side of the filling region and the caulking lid,
The caulking lid has an annular flat surface portion extending in the outer peripheral direction from the rear end of the caulking lid, and has an annular inner peripheral portion projecting in the inner peripheral direction on the inner peripheral side from the flat surface portion. A spark plug characterized in that at least a part of an inner peripheral portion is in contact with the annular ring member . The spark plug according to claim 1,
When the filling region filled with the powder between the metal shell and the insulator and the planar portion are projected onto a plane perpendicular to the axis, the projection region of the planar portion is a projection region of the filling region. A spark plug characterized by overlapping. The spark plug according to claim 1 or 2, wherein
The spark plug according to claim 1, wherein the flat portion is parallel to a direction orthogonal to the axis .

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