JP2018195412A - Spark plug - Google Patents

Abstract

To provide a spark plug which allows improvement in heat dissipation.SOLUTION: A spark plug comprises: an insulator having a locking part; and a cylindrical main metal fitting which is arranged on the outer periphery of the insulator. The main metal fitting has: a shelf part which protrudes to the radially inner side so as to lock, from the tip side, the locking part directly or via another member; and a screw part formed on an outer periphery surface. The nominal diameter of the screw part is 8 mm. A portion, of the screw part, on the further rear end side than the shelf part has a length of 10 mm or longer in the axial direction of the screw. The portion has a thickness of 1.1 mm or thinner at a valley bottom. The minimum value of the cross sectional area defined by cutting the portion from the valley bottom along a direction perpendicular to the axis is 13 mmor larger.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spark plug, and more particularly to a spark plug excellent in heat dissipation.

  As a spark plug to be attached to an internal combustion engine, there is known a spark plug that fastens a screw portion formed on a metal shell that holds an insulator to a screw hole of the internal combustion engine. From the viewpoint of improving the degree of freedom in design of an internal combustion engine, the spark plug has been reduced in size (smaller diameter) (Patent Document 1).

JP 2014-41700 A

  However, since the heat capacity becomes smaller as the spark plug is made smaller, such as when the nominal diameter of the threaded portion is 8 mm, the temperature of the spark plug tends to rise, and pre-ignition (pre-ignition) can occur if heat dissipation is poor. It tends to occur. Therefore, there is a demand for improvement in heat dissipation in a spark plug having a nominal diameter of the threaded portion of 8 mm.

  The present invention has been made to meet the above-described demand, and an object thereof is to provide a spark plug that can improve heat dissipation.

In order to achieve this object, the spark plug of the present invention is disposed on the outer periphery of the insulator having an engaging portion extending in the axial direction from the front end side to the rear end side and projecting outward in the radial direction. And a shelf that protrudes inward in the radial direction and locks the locking portion directly from the front end side or via another member, and a cylindrical metal shell provided with a screw portion formed on the outer peripheral surface. . The nominal diameter of the threaded portion is 8 mm, and the portion of the threaded portion on the rear end side of the shelf portion has a length in the axial direction of the threaded portion of 10 mm or more, and the thickness of the valley bottom portion is 1.1 mm or less. The minimum value of the cross-sectional area when cut in the direction perpendicular to the axis from the valley bottom is 13 mm ² or more.

According to the spark plug of the first aspect, the heat of the insulator is transmitted to the portion of the metallic shell closer to the rear end side than the shelf through the engaging portion and the rear end side portion from the engaging portion. After that, it is transmitted to the internal combustion engine via the screw portion. Of the screw part, the part on the rear end side of the shelf part has a length in the axial direction of the screw of 10 mm or more, and the wall thickness of the valley bottom part is 1.1 mm or less, thus securing the area of the part where heat moves. However, the radial distance through which heat moves can be shortened. As a result, the amount of heat flowing through the metallic shell per unit time can be secured, so that heat dissipation can be improved. Furthermore, since the cross-sectional area when cut in the direction perpendicular to the axis from the valley bottom is 13 mm ² or more, it is possible to suppress a reduction in axial force due to elongation of the threaded portion and breakage of the threaded portion.

  According to the spark plug of claim 2, the axial length of the threaded portion is 24.5 mm or more. As a result, the contact area between the metal shell and the internal combustion engine via the threaded portion, that is, the area of the portion where the heat moves can be secured. Therefore, in addition to the effect of Claim 1, heat dissipation can be further improved.

It is a half sectional view of the spark plug in one embodiment of the present invention. It is the one side sectional view of the spark plug which expanded a part of FIG. It is a figure which shows the relationship between the thickness of the part of a valley bottom, and ignition timing. It is a figure which shows the relationship between the length of a thread part, and ignition timing.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-side sectional view with an axis O as a boundary of a spark plug 10 according to an embodiment of the present invention. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10 (the same applies to FIG. 2). As shown in FIG. 1, the spark plug 10 includes an insulator 11 and a metal shell 40.

  The insulator 11 is a substantially cylindrical member formed of alumina or the like that is excellent in insulation at high temperatures and mechanical properties. The insulator 11 passes through the shaft hole 12 along the axis O. On the distal end side of the shaft hole 12, a step portion 13 that is reduced in diameter toward the distal end side is formed. The insulator 11 has a large-diameter portion 14 formed in the center in the direction of the axis O. The large diameter portion 14 is a portion having the largest outer diameter in the insulator 11. A small-diameter portion 15 having an outer diameter smaller than that of the large-diameter portion 14 is connected to the distal end side of the large-diameter portion 14. The outer diameter of the small diameter portion 15 is substantially the same over the entire length of the small diameter portion 15 in the axis O direction. A distal end portion 16 having an outer diameter smaller than that of the small diameter portion 15 is connected to the distal end side of the small diameter portion 15. On the outer periphery of the boundary between the distal end portion 16 and the small diameter portion 15, a locking portion 17 that is reduced in diameter toward the distal end side is formed. The step portion 13 is provided on the inner periphery of the small diameter portion 15.

  The center electrode 20 is a rod-shaped electrode that is inserted into the distal end side of the shaft hole 12 and is held by the insulator 11 along the axis O. The center electrode 20 is connected to a shaft portion 21 extending in the direction of the axis O and a head portion 22 projecting in a direction perpendicular to the shaft portion 21. The head portion 22 is locked to the step portion 13, and the shaft portion 21 is disposed in the shaft hole 12 with the tip protruding from the insulator 11. The center electrode 20 has a core material excellent in thermal conductivity embedded in the electrode base material. The electrode base material is made of an alloy mainly composed of Ni or a metal material made of Ni, and the core material is made of copper or an alloy mainly composed of copper.

  The terminal fitting 30 is a rod-like member to which a high voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel). The terminal fitting 30 includes a shaft portion 31 inserted into the shaft hole 12 and a protruding portion 34 that protrudes in the direction of the axis O with respect to the insulator 11.

  In the terminal fitting 30, a fixing portion 32 inserted into the shaft hole 12 and a flange portion 33 that abuts against an end surface in the axial direction of the insulator 11 are formed between the protruding portion 34 and the shaft portion 31. . Since the outer diameter of the shaft portion 31 is smaller than the outer diameter of the fixing portion 32, the terminal metal 30 has the fixing portion 32 in close contact with the shaft hole 12 of the insulator 11 and the flange portion 33 in close contact with the end surface of the insulator 11. A metal shell 40 is fixed to the front end side of the outer periphery of the insulator 11 with a space in the direction of the axis O from the protruding portion 34.

  The metal shell 40 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel). The metal shell 40 has a front end 41 positioned on the outer side in the radial direction of the front end portion 16 of the insulator 11, and a rear end 42 in the radial direction of a portion of the insulator 11 on the rear end side relative to the large diameter portion 14. Located outside. The metal shell 40 is connected to the body portion 43 surrounding the distal end portion 16 and the small diameter portion 15 of the insulator 11, the seat portion 46 connected to the rear end side of the body portion 43, and the rear end side of the seat portion 46. A connecting portion 47, a tool engaging portion 48 connected to the rear end side of the connecting portion 47, and a rear end portion 49 connected to the rear end side of the tool engaging portion 48 are provided.

  The body portion 43 has a screw portion 44 that is screwed into a screw hole of an internal combustion engine (not shown) on the outer periphery, and a shelf portion 45 that locks the locking portion 17 of the insulator 11 from the front end side. It is formed around the circumference. The inner diameter of the portion of the trunk portion 43 on the rear end side of the shelf portion 45 is substantially the same over the entire length of the trunk portion 43 in the axis O direction. A packing 50 is interposed between the shelf portion 45 and the locking portion 17. The packing 50 is an annular plate formed of a metal material such as a mild steel plate that is softer than the metal material constituting the metal shell 40.

  In the present embodiment, the screw portion 44 has a nominal diameter of 8 mm, and the length L in the axis O direction of the screw portion 44 is set to 24.5 mm or more. The length L of the threaded portion 44 refers to the length in the direction of the axis O from the beginning of threading to the end of threading.

  The seat portion 46 is a portion for closing a gap between a screw hole of an internal combustion engine (not shown) and the screw portion 44, and has an outer diameter larger than the outer diameter of the body portion 43. The seat portion 46 surrounds a boundary portion between the small diameter portion 15 and the large diameter portion 14. In the present embodiment, a gasket 52 is attached to the tip of the seat 46. A gasket 52 sandwiched between the seat portion 46 and the internal combustion engine seals a gap between the screw portion 44 and a screw hole (not shown).

  The connecting portion 47 is a portion for plastically deforming (bending) and fixing by caulking when the metal shell 40 is assembled to the insulator 11. The connecting portion 47 surrounds the distal end side of the large diameter portion 14. The tool engaging portion 48 is a portion for engaging a tool such as a wrench when the screw portion 44 is tightened in a screw hole of an internal combustion engine (not shown). The tool engaging portion 48 surrounds a portion of the insulator 11 on the rear end side with respect to the large diameter portion 14 and a rear end side of the large diameter portion 14. The rear end portion 49 is bent toward the inside in the radial direction, and is located on the rear end side with respect to the large diameter portion 14.

  A filler 51 such as talc is disposed inside the tool engaging portion 48 and the rear end portion 49 in the radial direction, on the front end side of the rear end portion 49 and on the rear end side of the large diameter portion 14. A portion of the metal shell 40 from the rear end portion 49 to the locking portion 17 applies a load that presses the insulator 11 in the direction of the axis O to the large diameter portion 14 and the locking portion 17 via the filler 51. As a result, the metal shell 40 is fixed to the outer periphery of the insulator 11. Since the packing 50 and the filler 51 are compressed in the axial direction, airtightness can be ensured.

  The ground electrode 60 is a rod-shaped metal member (for example, a nickel-base alloy member) joined to the tip 41 of the metal shell 40. The tip of the ground electrode 60 is opposed to the center electrode 20 via a gap (spark gap). In the present embodiment, the ground electrode 60 is bent.

  A resistor 61 is disposed in the shaft hole 12 of the insulator 11 between the head portion 22 of the center electrode 20 and the shaft portion 31 of the terminal fitting 30. The conductive seal 62 electrically connects the head 22 and the resistor 61, and the conductive seal 63 electrically connects the resistor 61 and the shaft portion 31. Thereby, the terminal fitting 30 is electrically connected to the center electrode 20 in the shaft hole 12.

  FIG. 2 is a side sectional view of the spark plug 10 in which a part of FIG. 1 is enlarged. In FIG. 2, illustration of one side with the axis O as a boundary and illustration of both ends in the direction of the axis O are omitted. In the spark plug 10, the length M of the screw in the axis O direction of the portion 64 on the rear end side (upper side in FIG. 2) of the shelf 45 in the screw portion 44 (see FIG. 1) is 10 mm or more. The length M refers to the length in the direction of the axis O from the end on the rear end side (upper side in FIG. 2) of the shelf 45 to the rear end of the screw portion 44 (start of screw cutting).

In the spark plug 10, the wall thickness T of the valley bottom 65 of the portion 64 on the rear end side of the shelf 45 in the screw portion 44 (see FIG. 1) is 1.1 mm or less. The cross-sectional area when cut in a direction perpendicular to is set to 13 mm ² or more.

  Further, a portion 64 of the screw portion 44 on the rear end side with respect to the shelf portion 45 is close to the small diameter portion 15 (insulator 11). In the present embodiment, the size in the radial direction of the gap G between the small-diameter portion 15 and the portion 64 on the rear end side of the shelf 45 in the screw portion 44 is set to 0.2 mm at the maximum.

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 20 is inserted into the shaft hole 12 of the insulator 11 and disposed so that the tip of the shaft portion 21 is exposed to the outside from the shaft hole 12. Next, while the conductive seals 62 and 63 and the resistor 61 are formed in the shaft hole 12, the shaft portion 31 of the terminal fitting 30 is inserted into the shaft hole 12 and the fixing portion 32 is disposed in the shaft hole 12. Thereby, the terminal metal fitting 30 is fixed to the rear end of the insulator 11 while ensuring the conduction between the terminal metal fitting 30 and the center electrode 20. Next, the insulator 11 is inserted into the metal shell 40 to which the ground electrode 60 is bonded in advance, the connecting portion 47 and the rear end portion 49 are bent, and the metal shell 40 is assembled to the insulator 11. Next, the ground electrode 60 is bent so that the tip of the ground electrode 60 faces the center electrode 20, and the gasket 52 is attached to obtain the spark plug 10.

  The spark plug 10 is attached to the internal combustion engine by fastening the threaded portion 44 of the metal shell 40 to the screw hole of the internal combustion engine (not shown). When the internal combustion engine operates, the insulator 11 is heated. After the heat of the insulator 11 is transmitted to the portion 64 on the rear end side with respect to the shelf portion 45 of the metal shell 40 through the engagement portion 17 and the portion on the rear end side from the engagement portion 17, the screw portion 44 to the internal combustion engine.

  A portion 64 of the metal shell 40 on the rear end side from the shelf 45 is farther from the tip 41 of the metal shell 40 than a portion on the tip side of the shelf 45. Therefore, the portion 64 on the rear end side from the shelf 45 is less susceptible to the thermal influence of the combustion gas in the combustion chamber (not shown) of the internal combustion engine than the portion on the front end side from the shelf 45. Therefore, the portion 64 on the rear end side from the shelf 45 can be easily cooled by a cooling device (not shown) of the internal combustion engine as compared to the portion on the front end side from the shelf 45. Therefore, the spark plug 10 uses the portion 64 on the rear end side of the shelf 45 in the metal shell 40 to improve heat dissipation.

  In the spark plug 10, the portion 64 on the rear end side of the shelf portion 45 in the screw portion 44 has a length M in the direction of the axis O of the screw of 10 mm or more, and the thickness T of the valley bottom 65 portion is 1.1 mm. Since it is below, the area of the part 64 to which heat moves toward the outer side in the radial direction of the metal shell 40 can be secured, and the radial distance at which heat moves can be shortened. As a result, the amount of heat flowing through the metallic shell 40 toward the outside in the radial direction per unit time can be secured, so that heat dissipation can be improved.

  A portion 64 of the screw portion 44 on the rear end side of the shelf portion 45 is close to the small diameter portion 15, and specifically, the gap G with the insulator 11 is 0.2 mm or less. By narrowing the gap G, it is possible to prevent the gap G from becoming a rate-determining rate of heat transfer. Therefore, it is possible to easily transfer the heat from the engagement portion 17 to the rear end side of the insulator 11 to the metal shell 40. Therefore, the heat dissipating property of the portion 64 on the rear end side with respect to the shelf 45 can be further improved.

Furthermore, since the cross-sectional area of the portion 64 when it is cut from the valley bottom 65 in a direction perpendicular to the axis O is 13 mm ² or more, a reduction in axial force due to the extension of the screw portion 44 and a breakage of the screw portion 44 can be suppressed. The decrease in the axial force of the threaded portion 44 causes a decrease in the sealing performance of the gasket 52. However, the tightening pressure of the gasket 52 can be secured by setting the cross-sectional area of the portion 64 to 13 mm ² or more. Can be suppressed.

  Further, since the length L in the axis O direction of the screw portion 44 is 24.5 mm or more, a contact area between the metal shell 40 and the internal combustion engine (not shown) can be secured via the screw portion 44. As a result, heat dissipation can be improved by utilizing not only the portion 64 on the rear end side of the shelf 45 in the screw portion 44 but also the portion on the front end side of the shelf 45.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
The tester prepared samples of various spark plugs in which the length M in the axis O direction of the portion 64 on the rear end side of the shelf 45 in the screw portion 44 and the thickness T of the valley bottom 65 portion were different. Four samples were prepared for one condition. Each sample is the same as the spark plug 10 described in FIG. 1 except that the dimensions of each part are different. Each sample has a nominal diameter of the screw portion 44 of 8 mm, a cross-sectional area of 13.5 mm ² when cut in a direction perpendicular to the axis O from the valley bottom 65, and a length L of the screw portion 44 in the axis O direction of 24. 0.5 mm.

  The tester attached a sample to each cylinder of a 2.0-liter 4-cylinder gasoline engine, operated the engine, and fully opened the intake throttle valve. A voltage was applied to the sample so that the ignition timing was the MBT for each operation, and after the mixture was ignited, the ignition timing was gradually advanced until preignition (premature ignition) occurred. The tester examined the crank angle at which pre-ignition occurred for each sample.

  FIG. 3 is a diagram showing the relationship between the wall thickness T of the valley bottom 65 and the ignition timing (crank angle at which pre-ignition occurs). In FIG. 3, the horizontal axis represents the wall thickness T (mm) of the valley bottom 65, and the vertical axis represents the crank angle (°). It shows that preignition is less likely to occur as the crank angle is larger, that is, the heat dissipation property of the metal shell 40 is better (heat drawing is better). Numerical values 7 mm, 9 mm, 10 mm, and 13 mm attached to each graph in FIG. 3 indicate the length M of the sample.

  As shown in FIG. 3, a negative correlation was observed between the wall thickness T and the crank angle. Samples with length M of 7 mm and 9 mm had the same relationship (on the same line of the graph). However, as the length M increased to 9 mm, 10 mm, and 13 mm, the crank angle tended to increase.

  In addition, when the length M was 7 mm and 9 mm, the slope of the straight line in the graph when the thickness T was reduced from 1.20 mm to 1.10 mm was constant. However, at lengths M = 10 mm and 13 mm, the thickness T becomes thinner from 1.15 mm to 1.10 mm than the straight line slope of the graph when the thickness T becomes thinner from 1.20 mm to 1.15 mm. The slope of the straight line in the graph was significantly increased. Therefore, it has been clarified that when the length M is 10 mm or more and the thickness T is 1.1 mm or less, the angle can be greatly advanced, that is, the heat dissipation can be improved.

(Example 2)
The tester differs in the cross-sectional area when the thread portion 44 is cut in the direction perpendicular to the axis O from the valley bottom 65 of the portion 64 on the rear end side of the shelf portion 45 and the length L of the thread portion 44 is different. Various samples were prepared. Each sample is the same as the spark plug 10 described in FIG. 1 except that the dimensions of each part are different. In each sample, the nominal diameter of the screw portion 44 was 8 mm, and the length M of the portion 64 on the rear end side of the shelf portion 45 in the screw portion 44 was 10 mm.

  After placing the gasket 52 on the seat 46 of the sample, the tester fastened the screw portion 44 in the screw hole of the cylinder head so that a minimum tightening pressure at which gas in the combustion chamber does not leak is applied to the gasket 52. Thereafter, the screw portion 44 was loosened, the sample was removed from the cylinder head, and it was examined whether the screw portion 44 was damaged. Table 1 shows the test results.

表１に示すように、ねじ部４４の長さＬが２４．５ｍｍ及び３０ｍｍのサンプルは、断面積が１２．５ｍｍ^２以下の場合にねじ部４４が破損した。しかし、断面積が１３．０ｍｍ^２以上の場合に、ねじ部４４の長さＬが２４．５ｍｍ及び３０ｍｍのサンプルは、ねじ部４４が破損しなかった。従って、ねじ部４４のうち棚部４５より後端側の部分６４の谷底６５から軸線Ｏに対して垂直な方向に切断したときの断面積を１３．０ｍｍ^２以上にすることにより、ねじ部の伸びによる軸力の低下やねじ部の破断を抑制できることが明らかになった。

As shown in Table 1, in the samples with the length L of the screw portion 44 of 24.5 mm and 30 mm, the screw portion 44 was damaged when the cross-sectional area was 12.5 mm ² or less. However, in the case where the cross-sectional area is 13.0 mm ² or more, the screw portion 44 was not damaged in the samples having the length L of the screw portion 44 of 24.5 mm and 30 mm. Therefore, by making the cross-sectional area of the thread portion 44 cut from the valley bottom 65 of the portion 64 on the rear end side of the shelf portion 45 in the direction perpendicular to the axis O to be 13.0 mm ² or more, It has become clear that the axial force drop due to elongation and the breakage of the thread portion can be suppressed.

Example 3
The tester prepared samples of various spark plugs having different lengths L in the axis O direction of the thread portion 44. Four samples were prepared for one condition. Each sample is the same as the spark plug 10 described in FIG. 1 except that the dimensions of each part are different. In each sample, the nominal diameter of the screw portion 44 is 8 mm, the length M in the axis O direction of the portion 64 of the screw portion 44 on the rear end side from the shelf 45 is 10 mm, and the thickness T of the valley bottom 65 portion is 1. The cross-sectional area when cut in the direction perpendicular to the axis O from the valley bottom 65 was 13.5 mm ² .

  The tester attached a sample to each cylinder of a 2.0-liter 4-cylinder gasoline engine, operated the engine, and fully opened the intake throttle valve. A voltage was applied to the sample so that the ignition timing was the MBT of each operation, and after the mixture was ignited, the ignition timing was gradually advanced until preignition occurred. The tester examined the crank angle at which pre-ignition occurred for each sample.

  FIG. 4 is a diagram showing the relationship between the length L of the screw portion 44 and the ignition timing (crank angle at which pre-ignition occurs). In FIG. 4, the vertical axis represents the crank angle (°). It shows that preignition is less likely to occur as the crank angle is larger, that is, the heat dissipation property of the metal shell 40 is better (heat drawing is better).

  As shown in FIG. 4, the crank angle tended to increase as the length L of the threaded portion 44 increased. In particular, it has been found that when the length L of the threaded portion 44 is 24.5 mm or more, the crank angle can be 42 ° or more. Referring to FIG. 3, it was found that according to the present embodiment, the crank angle can be made 42 ° or more under the condition of M = 10 mm or more.

  Therefore, it is clear that the length M can be greatly advanced by setting the length M to 10 mm or more, the thickness T to 1.1 mm or less, and the length L to 24.5 mm or more, that is, the heat dissipation can be remarkably improved. became.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  In the embodiment described above, the case where the packing 50 (other member) is interposed between the shelf 45 of the metal shell 40 and the locking portion 17 of the insulator 11 is not necessarily limited thereto. It is naturally possible to close the shelf 45 of the metal shell 40 and the locking portion 17 of the insulator 11 by omitting the packing 50. When the packing 50 is omitted, the shelf 45 of the metal shell 40 directly locks the locking portion 17 of the insulator 11.

  Although the case where the filler 51 is disposed between the rear end portion 49 of the metal shell 40 and the large diameter portion 14 of the insulator 11 has been described in the above embodiment, the present invention is not necessarily limited thereto. Of course, the filler 51 can be omitted.

  In the above embodiment, the spark plug 10 in which the gasket 50 is disposed in the seat portion 46 has been described, but the present invention is not necessarily limited thereto. When the spark plug 10 is a conical seal type, the gasket 50 can be omitted by making the front end side of the seat portion 46 a tapered surface.

  Although the description is omitted in the above embodiment, it is naturally possible to provide a tip containing a noble metal on the center electrode 20 or the ground electrode 60 in order to improve the spark wear resistance.

  In the above embodiment, the case where the center electrode 20 and the terminal fitting 30 are electrically connected by the conductive seals 62 and 63 with the resistor 61 interposed therebetween is described, but the present invention is not necessarily limited thereto. Of course, it is possible to omit the resistor 61.

  In the above embodiment, the case where the ground electrode 60 joined to the metal shell 40 is bent has been described. However, it is not necessarily limited to this. Naturally, instead of using the bent ground electrode 60, it is possible to use a linear ground electrode 60. In this case, the front end side of the metal shell 40 is extended in the direction of the axis O, the linear ground electrode 60 is joined to the metal shell 40, and the front end portion of the ground electrode 60 is opposed to the center electrode 20.

  In the above embodiment, the case where the ground electrode 60 is arranged so that the tip of the ground electrode 60 and the center electrode 20 face each other on the axis O has been described. However, the present invention is not necessarily limited to this, and the positional relationship between the ground electrode 60 and the center electrode 20 can be set as appropriate. Other positional relationships between the ground electrode 60 and the center electrode 20 include, for example, arranging the ground electrode 60 so that the side surface of the center electrode 20 and the tip of the ground electrode 60 face each other.

  In the above embodiment, the case where one ground electrode 60 is joined to the metal shell 40 has been described. However, the present invention is not necessarily limited to this, and it is a matter of course that a plurality of ground electrodes 60 are joined to the metal shell 40. Is possible.

DESCRIPTION OF SYMBOLS 10 Spark plug 11 Insulator 17 Locking part 40 Main metal fitting 44 Screw part 45 Shelf part 50 Packing (other members)
64 parts 65 valley bottom O axis

Claims (2)

An insulator including a locking portion extending in the axial direction from the front end side to the rear end side and projecting outward in the radial direction;
A shelf that is arranged on the outer periphery of the insulator, projects inward in the radial direction, and locks the locking portion directly from the distal end side or via another member, and a screw portion formed on the outer peripheral surface. A spark plug comprising a cylindrical metal shell,
The nominal diameter of the threaded portion is 8 mm,
The portion of the screw portion on the rear end side from the shelf portion has a screw axial length of 10 mm or more, a valley bottom thickness of 1.1 mm or less, and perpendicular to the axis from the valley bottom. A spark plug having a cross-sectional area of 13 mm ² or more when cut in the direction.   The spark plug according to claim 1, wherein a length of the screw portion in the axial direction is 24.5 mm or more.

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