Spark plug

Abstract

To provide a spark plug capable of reducing the overheating of a ground electrode.SOLUTION: A spark plug includes: a metal shell that has a cylindrical tip extending along a straight line toward a tip side and that is provided with a through hole penetrating in a direction that intersects the straight line, at the tip; and a ground electrode having a fixing portion disposed in the through hole. The through hole includes a counterbore portion and a penetrating portion that extends from the counterbore portion to an inner circumferential surface of the tip and that is thinner than the counterbore portion. The fixing portion includes a first portion disposed in the counterbore portion and a second portion that is disposed in the penetrating portion and that is thinner than the first portion. There is a gap between the second portion and an edge of the penetrating portion connected to the inner circumferential surface of the tip.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a spark plug having a ground electrode connected to a metallic shell. [Background technology]

[0002] In a spark plug that ignites fuel gas, a technology is known in which a ground electrode is disposed in a through hole that penetrates a metal shell. In the technology disclosed in Patent Document 1 (FIG. 5), the portion of the ground electrode that is disposed in the through hole is in contact with the through hole over the entire circumference. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-46660 A Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of spark plug, if the ground electrode overheats, it can become a spark that causes pre-ignition.

[0005] The present invention has been made to solve this problem, and has an object to provide a spark plug which is capable of reducing overheating of the ground electrode. [Means for solving the problem]

[0006] To achieve this object, the spark plug of the present invention comprises a metallic shell having a cylindrical tip portion extending along a straight line toward the tip side, and a through hole formed in the tip portion that penetrates in a direction intersecting the straight line, and a ground electrode having a fixing portion disposed in the through hole, the through hole comprising a countersunk portion and a through portion extending from the countersunk portion to the inner surface of the tip portion and narrower than the countersunk portion, the fixing portion comprising a first portion disposed in the countersunk portion and a second portion disposed in the through portion and narrower than the first portion, and there is a gap between the edge of the through portion connecting to the inner surface of the tip portion and the second portion. Effect of the Invention

[0007] According to the first aspect, the through hole penetrating the tip end of the metal shell includes a countersunk portion and a through portion that extends from the countersunk portion to the inner circumferential surface of the tip end and is thinner than the countersunk portion. The fixing portion of the ground electrode has a first portion disposed in the countersunk portion and a second portion thinner than the first portion disposed in the through portion. Since there is a gap between the edge of the through portion that is connected to the inner circumferential surface of the tip end and the second portion, the second portion of the ground electrode is cooled by the fuel gas that has entered the gap. This makes it possible to reduce overheating of the ground electrode.

[0008] According to the second aspect, when the gap is divided into two, a first gap located on the leading end side of the center of the through-hole and a second gap located on the rear end side of the center of the through-hole, as viewed from the inner peripheral surface side along the axis of the through-hole, the area of ​​the first gap is larger than the area of ​​the second gap. Since the fuel gas can easily enter the first gap, in addition to the effect of the first aspect, overheating of the ground electrode can be further reduced.

[0009] According to the third aspect, a part of the second part is in contact with the edge of the through-hole, and when the edge of the through-hole is divided into a first edge on the leading side of the center of the through-hole and a second edge on the rear side of the center of the through-hole, the first edge is not in contact with the second part, or the length of contact between the second edge and the second part is longer than the length of contact between the first edge and the second part. Since fuel gas can easily enter between the first edge and the second part, in addition to the effect of the first or second aspect, overheating of the ground electrode can be further reduced.

[0010] According to the fourth aspect, the area of ​​the second gap on the rear end side of the center of the through-hole is larger than the area of ​​the first gap on the tip side of the center of the through-hole, so that the second portion of the ground electrode can be disposed closer to the tip side by that amount. Since the second portion disposed on the tip side is easily cooled by the fuel gas, in addition to the effect of the first aspect, overheating of the ground electrode can be further reduced.

[0011] According to the fifth aspect, a part of the second part is in contact with the edge of the through-hole, and the second edge on the rear end side of the center of the through-hole is not in contact with the second part of the ground electrode, or the length of contact between the first edge on the tip side of the center of the through-hole and the second part is longer than the length of contact between the second edge and the second part, so that the second part of the ground electrode can be disposed closer to the tip side by that amount. The second part disposed closer to the tip side is more likely to be cooled by the fuel gas, and thus overheating of the ground electrode can be further reduced in addition to the effects of the first or fourth aspect. [Brief description of the drawings]

[0012] [Figure 1] 1 is a partial cross-sectional view of a spark plug according to a first embodiment. [Diagram 2] 2(a) is an enlarged cross-sectional view of a spark plug of a portion indicated by IIa in FIG. 1, and FIG. 2(b) is a cross-sectional view of the spark plug taken along line IIb-IIb in FIG. 2(a) as viewed from the inner peripheral surface side of the tip portion. [Diagram 3] 3(a) is a cross-sectional view of a spark plug in a second embodiment, and FIG. 3(b) is a cross-sectional view of the spark plug taken along line IIIb-IIIb in FIG. 3(a) as viewed from the inner peripheral surface side of the tip portion. [Figure 4] 4(a) is a cross-sectional view of a spark plug in a third embodiment, and FIG. 4(b) is a cross-sectional view of the spark plug taken along line IVb-IVb in FIG. 4(a) as viewed from the inner peripheral surface side of the tip portion. [Diagram 5] 5(a) is a cross-sectional view of a spark plug in a fourth embodiment, and (b) is a cross-sectional view of the spark plug taken along line Vb-Vb in FIG. 5(a) as viewed from the inner peripheral surface side of the tip portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a partial cross-sectional view of a spark plug 10 in a first embodiment. In Fig. 1, the lower side of the paper refers to the leading end side of the spark plug 10, and the upper side of the paper refers to the rear end side of the spark plug 10 (the same applies to Figs. 2(a) to 5(b)). Fig. 1 shows a cross section including a straight line O of the leading end side of the spark plug 10. The spark plug 10 includes a metal shell 20 arranged on the outer periphery of an insulator 11, and a ground electrode 40 connected to the metal shell 20.

[0014] The insulator 11 is a substantially cylindrical member having an axial hole 12 along a straight line O, and is made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. A center electrode 13 is disposed in the axial hole 12 of the insulator 11. The center electrode 13 is a rod-shaped member having electrical conductivity. A portion of the center electrode 13 protrudes from the insulator 11 toward the front end. The center electrode 13 is electrically connected to a terminal fitting 14 within the axial hole 12. The terminal fitting 14 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel). The terminal fitting 14 is fixed to the rear end of the insulator 11.

[0015] The metal shell 20 is a substantially cylindrical member made of a conductive metal material (such as low carbon steel). The metal shell 20 has a cylindrical tip portion 21 provided with a male thread 22, and a seat portion 23 adjacent to the rear end side of the tip portion 21. The male thread 22 of the tip portion 21 screws into a threaded hole of an engine (not shown). The outer diameter of the seat portion 23 is larger than the outer diameter of the male thread 22. The seat portion 23 receives an axial force when the male thread 22 is tightened into the threaded hole of the engine.

[0016] A cap 24 is connected to the tip portion 21 of the metallic shell 20 on the tip side of the male thread 22. The cap 24 is a cylindrical or semispherical member with a bottom, and is formed of a metal material containing one or more of Fe, Ni, Cu, etc. as a main component. The tip portion 21 of the metallic shell 20 is closed by the cap 24. In this embodiment, the cap 24 is a semispherical member, and is joined to the tip portion 21 by a welded portion (not shown). An auxiliary chamber 25 is formed by being surrounded by the tip portion 21 and the cap 24. The cap 24 is provided with an injection hole 26 that penetrates the cap 24 in the thickness direction. The injection hole 26 communicates between the combustion chamber of the engine (not shown) and the auxiliary chamber 25.

[0017] A ground electrode 40 is connected to the tip 21 of the metallic shell 20. The ground electrode 40 is a rod-shaped metal member whose main component is, for example, one or more of Pt, Ni, Ir, etc. The material of the ground electrode 40 is different from the material of the metallic shell 20. A spark gap is provided between the center electrode 13 and the ground electrode 40. In this embodiment, a spark gap is provided on the axial tip side of the center electrode 13. It is of course possible to place a tip on the center electrode 13 or the ground electrode 40 in contact with the spark gap.

[0018] When the spark plug 10 is attached to an engine (not shown), operation of the engine valves and pistons causes fuel gas to flow from the engine's combustion chamber through the nozzle hole 26 into the pre-chamber 25. The spark plug 10 generates a flame kernel in the spark gap by discharging between the center electrode 13 and the ground electrode 40. As the flame kernel grows, it ignites the fuel gas in the pre-chamber 25 and the fuel gas burns. Due to the expansion pressure generated by this combustion, the spark plug 10 injects a gas flow containing a flame from the nozzle hole 26 into the combustion chamber. The fuel gas in the combustion chamber is combusted by the flame jet.

[0019] Fig. 2(a) is a cross-sectional view of the spark plug 10 in which a portion indicated by IIa in Fig. 1 is enlarged. As shown in Fig. 2(a), a through hole 30 is provided in the tip portion 21 of the metallic shell 20, penetrating from the outer peripheral surface 27 to the inner peripheral surface 28 of the tip portion 21. In this embodiment, the through hole 30 is provided at the position of the male thread 22 in the tip portion 21. The through hole 30 includes a countersunk portion 31 and a through portion 32, in this order from the outer peripheral surface 27 to the inner peripheral surface 28 of the tip portion 21.

[0020] The countersunk portion 31 opens to the outer peripheral surface 27 of the tip portion 21. The depth of the countersunk portion 31 is deeper than the valley 29 of the male thread 22. The through portion 32 is a hole narrower than the countersunk portion 31, and extends from the countersunk portion 31 to the inner peripheral surface 28 of the tip portion 21. In this embodiment, the countersunk portion 31 and the through portion 32 are cylindrical surfaces with circular cross-sectional shapes, and an annular step 33 is provided between the countersunk portion 31 and the through portion 32.

[0021] The ground electrode 40 has a fixing portion 41 arranged in the through hole 30. The fixing portion 41 has a first portion 42 arranged in the counterbore portion 31 and a second portion 43 arranged in the through portion 32 along the axis C of the through portion 32. The second portion 43 is thinner than the first portion 42. In this embodiment, the first portion 42 and the second portion 43 are cylindrical. The fit between the counterbore portion 31 and the first portion 42 is a clearance fit. The first portion 42 is in contact with the step 33, and the first portion 42 and the tip portion 21 are joined by the fusion portion 44. The first portion 42 is arranged radially inside the valley 29 of the male thread 22.

[0022] There is a gap 35 between the edge 34 of the through portion 32 connected to the inner circumferential surface 28 of the tip portion 21 and the second portion 43. Since fuel gas before combustion can enter the gap 35, the second portion 43 is cooled by the fuel gas that has entered the gap 35. Since the second portion 43 is cooled by the fuel gas, overheating of the ground electrode 40 can be reduced compared to when there is no gap 35. This makes it possible to reduce the occurrence of pre-ignition, in which an overheated ground electrode 40 becomes a source of fire.

[0023] When the second portion 43 is cooled, the thermal expansion of the second portion 43 is suppressed, and this, together with the gap 35 between the edge 34 of the through portion 32 and the second portion 43, reduces the tensile stress acting on the through portion 32 due to the thermal expansion of the second portion 43. Therefore, the occurrence of cracks in the through portion 32 can be reduced.

[0024] Since the first portion 42 of the ground electrode 40 contacts the step 33 of the through hole 30, heat of the ground electrode 40 is transferred from the first portion 42 to the engine (not shown) via the tip portion 21 and the male thread 22. The ground electrode 40 is also cooled by thermal conduction between the first portion 42 and the tip portion 21.

[0025] Fig. 2(b) is a cross-sectional view of the spark plug 10 taken along line IIb-IIb in Fig. 2(a). Fig. 2(b) shows a cut surface of the second portion 43 taken along line IIb-IIb, and an edge 34 of the through portion 32 when the through portion 32 is viewed along the axis C of the through portion 32 from the inner peripheral surface 28 side of the tip portion 21 (see Fig. 2(a)) (the same applies to Figs. 3(b), 4(b) and 5(b)). The second portion 43 does not contact the edge 34 of the through portion 32 at any point, and the entire outer periphery of the second portion 43 is separated from the edge 34 of the through portion 32.

[0026] The edge 34 of the through portion 32 is divided into two parts: a first edge 36 located on the tip side of the axis C (center) of the through portion 32, and a second edge 37 located on the rear side of the center of the through portion 32. The first edge 36 is a portion located on the tip side of the plane P when the edge 34 is cut by the plane P that includes the axis C and is perpendicular to the straight line O (see FIG. 1). The second edge 37 is a portion of the edge 34 located on the rear side of the plane P. The gap 35 between the edge 34 of the through portion 32 and the second portion 43 is divided into two parts: a first gap 38 located on the tip side of the plane P, and a second gap 39 located on the rear side of the plane P. A part of the second gap 39 is in the shadow of the second portion 43 when viewed from the tip side.

[0027] Since the area of ​​the first gap 38 is larger than the area of ​​the second gap 39, the fuel gas can easily enter the first gap 38, which is located closer to the tip than the second portion 43, and the second portion 43 can be easily cooled. This further reduces overheating of the ground electrode 40.

[0028] A second embodiment will be described with reference to Figures 3(a) and 3(b). In the first embodiment, a ground electrode 40 in which the second portion 43 does not contact the edge 34 of the through portion 32 is described. In contrast, in the second embodiment, a ground electrode 50 in which the second portion 43 contacts a part of the edge 34 of the through portion 32 is described. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description will be omitted.

[0029] Fig. 3(a) is a cross-sectional view of a spark plug in a second embodiment. Fig. 3(a) is an enlarged cross-sectional view of the portion indicated by IIa in Fig. 1, similar to Fig. 2(a) (the same applies to Figs. 4(a) and 5(a)). Fig. 3(b) is a cross-sectional view of the spark plug taken along line IIIb-IIIb in Fig. 3(a). The ground electrode 50 described in the second embodiment is disposed in the same manner as the ground electrode 40 of the spark plug 10 in the first embodiment.

[0030] The fixed portion 41 of the ground electrode 50 disposed in the through hole 30 includes a first portion 42 and a second portion 43. The area of ​​the first gap 38 is larger than the area of ​​the second gap 39. The second portion 43 is in contact with the second edge 37 of the through hole 32, but is not in contact with the first edge 36. Therefore, the length of contact between the second edge 37 and the second portion 43 is longer than the length of contact between the first edge 36 and the second portion 43 (zero in this embodiment). As a result, the width of the first gap 38 is larger than the width of the second gap 39, so that the fuel gas can more easily enter the first gap 38, and the second portion 43 can be more easily cooled. Thus, overheating of the ground electrode 40 can be further reduced.

[0031] A third embodiment will be described with reference to Fig. 4(a) and Fig. 4(b). In the first and second embodiments, the second portion 43 of the ground electrode 40, 50 is cylindrical. In contrast, in the third embodiment, the second portion 63 of the ground electrode 60 is rectangular prism-shaped. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description will be omitted.

[0032] Fig. 4(a) is a cross-sectional view of a spark plug according to a third embodiment. Fig. 4(b) is a cross-sectional view of the spark plug taken along line IVb-IVb in Fig. 4(a). The ground electrode 60 described in the third embodiment is disposed in the same manner as the ground electrode 40 of the spark plug 10 according to the first embodiment.

[0033] The fixed portion 61 of the ground electrode 60 disposed in the through hole 30 includes a first portion 62 disposed in the counterbore portion 31 and a second portion 63 disposed in the through hole 32 along the axis C of the through hole 32. The second portion 63 is thinner than the first portion 62. The first portion 62 is cylindrical, and the second portion 43 is rectangular prism-shaped with rounded corners. The first portion 62 is in contact with the step 33, and the first portion 62 and the tip portion 21 are joined by a fusion zone 64. The first portion 62 is disposed radially inside the valley 29 of the male thread 22.

[0034] There is a gap 35 between the edge 34 of the through-hole 32 and the second portion 63. The second portion 63 does not contact the edge 34 of the through-hole 32, and the entire outer periphery of the second portion 63 is separated from the edge 34 of the through-hole 32. Since the area of ​​the second gap 39 is larger than the area of ​​the first gap 38, the second portion 63 can be disposed correspondingly closer to the tip side (a position closer to the center of the engine's combustion chamber). The second portion 63 disposed on the tip side is more easily cooled by fuel gas, so overheating of the ground electrode 60 can be further reduced.

[0035] A fourth embodiment will be described with reference to Figures 5(a) and 5(b). In the third embodiment, a ground electrode 60 in which the second portion 63 does not contact the edge 34 of the through portion 32 is described. In contrast, in the fourth embodiment, a ground electrode 70 in which the second portion 63 contacts a part of the edge 34 of the through portion 32 is described. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description will be omitted.

[0036] Fig. 5(a) is a cross-sectional view of a spark plug according to a fourth embodiment. Fig. 5(b) is a cross-sectional view of the spark plug taken along line Vb-Vb in Fig. 5(a). The ground electrode 70 described in the fourth embodiment is disposed in the same manner as the ground electrode 40 of the spark plug 10 according to the first embodiment.

[0037] The fixed portion 61 of the ground electrode 70 disposed in the through hole 30 includes a first portion 62 and a second portion 63. The area of ​​the second gap 39 is larger than the area of ​​the first gap 38. The second portion 63 is in contact with the first edge 36 of the through hole 32, but is not in contact with the second edge 37. Therefore, the length of contact between the first edge 36 and the second portion 63 is longer than the length of contact between the second edge 37 and the second portion 63 (zero in this embodiment). This allows the second portion 63 to be disposed further toward the tip side (at a position closer to the center of the combustion chamber of the engine). The second portion 63 disposed on the tip side is easily cooled by the fuel gas, so that overheating of the ground electrode 60 can be further reduced.

[0038] Although the present invention has been described above based on the embodiment, the present invention is not limited to the above embodiment, and it can be easily assumed that various improvements and modifications are possible within the scope of the present invention. For example, the shape of the through hole 30 and the shapes of the ground electrodes 40, 50, 60, 70 can be appropriately set.

[0039] In the embodiment, the case where the tip of the metallic shell 20 is blocked by the cap 24 has been described, but the present invention is not necessarily limited to this. It is of course possible to omit the cap 24 to provide a spark plug 10 without the sub-chamber 25. In this case as well, a flame kernel is generated by discharge between the center electrode 13 and the ground electrodes 40, 50, 60, 70, and ignites the fuel gas. As the flame kernel grows, the fuel gas in the combustion chamber is burned. Even when the cap 24 is omitted, the fuel gas flows around the ground electrodes 40, 50, 60, 70 due to the operation of the engine valves and pistons, and the fuel gas enters the gap 35, thereby cooling the ground electrodes 40, 50, 60, 70.

[0040] In the embodiment, the ground electrodes 40, 50, 60, 70 are disposed on the metallic shell 20 so as to provide a spark gap on the axial tip side of the center electrode 13, but this is not necessarily limited to this. It is of course possible to dispose the ground electrodes 40, 50, 60, 70 on the metallic shell 20 so as to provide a spark gap on the radial outer end side of the center electrode 13.

[0041] In the embodiment, the cross-sectional shape of the through hole 30 perpendicular to the axis C of the through portion 32 is described as a circle, but this is not necessarily limited to this. Examples of the cross-sectional shape of the through hole 30 include an ellipse and a polygon. Naturally, it is possible to round or chamfer the corners of the polygon.

[0042] In the embodiment, the case where the countersunk portion 31 has a cylindrical surface has been described, but this is not necessarily limited to this. It is of course possible to make at least the portion of the countersunk portion 31 connected to the through portion 32 a conical surface. In this case, the step 33 may be omitted and the through portion 32 may be connected to the countersunk portion 31, or the step 33 may be provided between the countersunk portion 31 and the through portion 32. It is of course possible to make the step 33 a conical surface.

[0043] In the embodiment, the first portion 42, 62 is cylindrical, but this is not necessarily limited to this. It is of course possible for the shape of the first portion 42, 62 to be, for example, a polygonal column, a polygonal pyramid, or a cone, depending on the shape of the countersunk portion 31.

[0044] In the embodiment, the fit between the countersunk portion 31 and the first portions 42, 62 is a clearance fit, but this is not necessarily limited to this. It is of course possible for the fit between the countersunk portion 31 and the first portions 42, 62 to be an interference fit. When the first portions 42, 62 are pressed into the countersunk portion 31 (interference fit), it is of course possible to omit the fusion portions 44, 64. This is because when the first portions 42, 62 are pressed into the countersunk portion 31, the ground electrodes 40, 50, 60, 70 are fixed to the through hole 30 without welding.

[0045] In the embodiment, the through hole 30 to which the ground electrodes 40, 50, 60, 70 are fixed is provided at the position of the male thread 22 of the tip portion 21, but this is not necessarily limited to this. For example, it is of course possible to provide a through hole to fix the ground electrodes 40, 50, 60, 70 in a portion of the tip portion 21 closer to the tip side than the male thread 22.

[0046] In the first and second embodiments, a case where a gap 35 is provided between the cylindrical second part 43 and the edge 34 of the through part 32 is described, and in the third and fourth embodiments, a case where a gap 35 is provided between the rectangular prism-shaped second part 63 and the edge 34 of the through part 32 is described, but this is not necessarily limited to this. It is of course possible to replace the second part 43 in the first and second embodiments with the second part 63 in the third and fourth embodiments. Even when the second parts 43, 63 are replaced, the same action and effect as before the second parts 43, 63 are replaced can be achieved.

[0047] In the second embodiment, a case has been described in which the second portion 43 contacts the second edge 37 of the through portion 32 and the second portion 43 does not contact the first edge 36, but the present invention is not limited to this. Depending on the shapes of the through portion 32 and the second portion 43, even in the case in which the second portion 43 contacts the second edge 37 and the second portion 43 contacts the first edge 36, the same effect as in the second embodiment can be achieved as long as the length over which the second portion 43 contacts the second edge 37 is longer than the length over which the second portion 43 contacts the first edge 36.

[0048] In the fourth embodiment, a case has been described in which the second portion 63 is in contact with the first edge 36 of the through portion 32, and the second edge 37 and the second portion 63 are not in contact with each other, but the present invention is not limited to this. Depending on the shapes of the through portion 32 and the second portion 63, even in the case in which the second portion 63 is in contact with the first edge 36 and the second portion 63 is in contact with the second edge 37, the same effect as in the fourth embodiment can be achieved as long as the length over which the second portion 63 is in contact with the first edge 36 is longer than the length over which the second portion 63 is in contact with the second edge 37. [Explanation of symbols]

[0049] 10 Spark plug 20 Metal fitting 21 Tip 28 Inner surface of tip 30 Through hole 31 Countersink 32 Penetration 34 Edge of penetration 35 Gap 36 First Edge 37 The Second Edge 38 First Gap 39 Second Gap 40,50,60,70 ground electrode 41,61 Fixed part 42,62 Part 1 43,63 Part 2 C Penetration shaft O straight line

Claims

1. a metallic shell having a cylindrical tip portion extending toward a tip side along a straight line, the tip portion being provided with a through hole passing through in a direction intersecting the straight line; a ground electrode having a fixing portion disposed in the through hole, The through hole includes a countersunk portion and a through portion that extends from the countersunk portion to an inner peripheral surface of the tip portion and is narrower than the countersunk portion, the fixing portion includes a first portion disposed in the countersunk portion and a second portion disposed in the through portion and narrower than the first portion, a gap is provided between an edge of the penetrating portion connected to the inner circumferential surface of the tip portion and the second portion; A spark plug in which, when the through portion is viewed from the inner surface side along the axis of the through portion and the gap is divided into two gaps, a first gap located toward the tip side of the center of the through portion and a second gap located toward the rear end side of the center, the area of ​​the first gap is larger than the area of ​​the second gap.

2. a metallic shell having a cylindrical tip portion extending toward a tip side along a straight line, the tip portion being provided with a through hole passing through in a direction intersecting the straight line; a ground electrode having a fixing portion disposed in the through hole, The through hole includes a countersunk portion and a through portion that extends from the countersunk portion to an inner peripheral surface of the tip portion and is narrower than the countersunk portion, the fixing portion includes a first portion disposed in the countersunk portion and a second portion disposed in the through portion and narrower than the first portion, a gap is provided between an edge of the penetrating portion connected to the inner circumferential surface of the tip portion and the second portion; A portion of the second portion is in contact with the edge, When the edge is divided into two, a first edge located on the tip side of the center of the through portion and a second edge located on the rear side of the center, the first edge and the second portion are not in contact with each other, or the length of contact between the second edge and the second portion is longer than the length of contact between the first edge and the second portion.

3. a metallic shell having a cylindrical tip portion extending toward a tip side along a straight line, the tip portion being provided with a through hole passing through in a direction intersecting the straight line; a ground electrode having a fixing portion disposed in the through hole, The through hole includes a countersunk portion and a through portion that extends from the countersunk portion to an inner peripheral surface of the tip portion and is narrower than the countersunk portion, the fixing portion includes a first portion disposed in the countersunk portion and a second portion disposed in the through portion and narrower than the first portion, a gap is provided between an edge of the penetrating portion connected to the inner circumferential surface of the tip portion and the second portion; A spark plug in which, when the through portion is viewed from the inner surface side along the axis of the through portion and the gap is divided into two gaps, a first gap located toward the tip side of the center of the through portion and a second gap located toward the rear end side of the center, the area of ​​the second gap is larger than the area of ​​the first gap.

4. a metallic shell having a cylindrical tip portion extending toward a tip side along a straight line, the tip portion being provided with a through hole passing through in a direction intersecting the straight line; a ground electrode having a fixing portion disposed in the through hole, The through hole includes a countersunk portion and a through portion that extends from the countersunk portion to an inner peripheral surface of the tip portion and is narrower than the countersunk portion, the fixing portion includes a first portion disposed in the countersunk portion and a second portion disposed in the through portion and narrower than the first portion, a gap is provided between an edge of the penetrating portion connected to the inner circumferential surface of the tip portion and the second portion; A portion of the second portion is in contact with the edge, When the edge is divided into two, a first edge located on the tip side of the center of the through portion and a second edge located on the rear side of the center, the second edge does not contact the second portion, or the length of contact between the first edge and the second portion is longer than the length of contact between the second edge and the second portion.

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