Spark plug

Abstract

To provide a spark plug capable of securing durability while maintaining effects of improvement of ignitability due to electric field strength increase or heat drawing suppression due to a recess.SOLUTION: A spark plug comprises: a center electrode extending along an axis; a main body metal fitting holding insulation of the center electrode; and a ground electrode connected to the main body metal fitting by a connection part. At least one of the center electrode and the ground electrode includes a projection. A discharge member joined to the projection via a fusion part forms a spark gap between the discharge member and the other electrode. A recess is provided at a position including the projection.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a spark plug having protrusions on electrodes. [Background technology]

[0002] In a spark plug having a projection on an electrode, the prior art disclosed in Patent Document 1 has a discharge member joined to the projection via a fusion zone, and a depression is formed in the fusion zone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-4932 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, the volume of the molten part is reduced by the amount of the depression, and the volume of the molten part is smaller than that of a spark plug that does not have a depression in the molten part.As a result, there is a risk that the combined part of the discharge member and the molten part will be worn out quickly by spark discharge, raising concerns about reduced durability.

[0005] The present invention has been made to solve this problem, and has as its object to provide a spark plug that can ensure durability while maintaining the effects of increasing electric field strength due to the recess and improving ignition performance due to heat dissipation suppression. [Means for solving the problem]

[0006] To achieve this object, a first aspect of the present invention comprises a center electrode extending along an axis, a metal shell that holds the center electrode via an insulator, and a ground electrode connected to the metal shell by a connection part, wherein the center electrode has a protrusion that protrudes from the tip of the insulator, and has a discharge member that is joined to the protrusion via a fusion part and forms a spark gap between the center electrode and the ground electrode, and a recess is provided at a position including the protrusion.

[0007] The second aspect comprises a center electrode extending along the axis, a metal shell that holds the center electrode via an insulator, and a ground electrode connected to the metal shell by a connecting part, in which the ground electrode has a protrusion at its tip and a discharge member that is joined to the protrusion via a fusion part and forms a spark gap between the ground electrode and the center electrode, and a recess is provided at a position including the protrusion.

[0008] The third aspect is the first or second aspect, wherein when viewed from the axial direction, a first sector is defined as a sector that has its center on the axis, has its radius equal to the length of a line segment connecting the axis and the center of gravity of the connection part, has a central angle of 90°, and is symmetrical with respect to the line segment, and when the area obtained by projecting the first sector in the axial direction is defined as a first range, the depression exists only outside the first range.

[0009] In the fourth aspect, when viewed from the axial direction in the third aspect, a second sector is defined as a sector that is symmetrical to the first sector with respect to a line segment and a straight line that is perpendicular to the axis and passes through the axis, and the area obtained by projecting the second sector in the axial direction is defined as a second range, and the depression exists only outside the second range.

[0010] The fifth aspect is the third aspect, in which, when viewed from the axial direction, a second sector is defined as a sector that is symmetrical to the first sector with respect to a line segment and a straight line that is perpendicular to the axis and passes through the axis, and the area obtained by projecting the second sector in the axial direction is defined as a second range, and the depression exists only within the second range. [Effects of the Invention]

[0011] According to the present invention, since the recess is provided at a position including the protrusion, the volume of the combined portion of the discharge member and the fusion zone can be secured. Since the amount of wear due to spark discharge in the combined portion of the discharge member and the fusion zone can be secured, durability can be secured while maintaining the effects of increasing the electric field strength due to the recess and improving ignition performance by suppressing heat dissipation. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a half-sectional view of a spark plug according to a first embodiment. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] 4(a) is a side view of the protrusion, and FIG. 4(b) is a cross-sectional view of the protrusion taken along line IVb-IVb in FIG. 4(a). [Figure 5] FIG. 2 is a plan view of the spark plug. [Figure 6] FIG. 2 is a plan view of the spark plug. [Figure 7] FIG. [Figure 8] FIG. 10 is a plan view of a spark plug according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to a first embodiment, taken along an axis O. In Fig. 1, the lower side of the page refers to the rear end side of the spark plug 10, and the upper side refers to the front end side of the spark plug 10 (the same applies to Figs. 2 and 3).

[0014] 1, a spark plug 10 includes an insulator 11, a center electrode 13 held by the insulator 11, a metal shell 16 disposed on the outer periphery of the insulator 11, and a ground electrode 18 connected to the metal shell 16. The insulator 11 is a substantially cylindrical member made of ceramic such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 has an axial hole 12 formed along an axis O.

[0015] The center electrode 13 is a rod-shaped conductor disposed in the axial hole 12 of the insulator 11 and extending along the axis O. The center electrode 13 has a copper-based core covered by a cylindrical metal with a bottom. The core can be omitted. An example of the metal constituting the center electrode 13 is a Ni-based alloy. The center electrode 13 includes a protrusion 14 protruding from the tip of the insulator 11. The protrusion 14 is provided on the axis O.

[0016] The center electrode 13 is electrically connected to a metal terminal 15 in the axial hole 12. The metal terminal 15 is a rod-shaped member to which an ignition device (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel). The metal terminal 15 is fixed to the rear end of the insulator 11 with its front end inserted into the axial hole 12 and its rear end protruding from the insulator 11.

[0017] A metal shell 16 is fixed to the outer periphery of the insulator 11. The metal shell 16 is provided with a male thread 17 that is coupled to a female thread of a spark plug hole of an engine (not shown). A ground electrode 18 is connected to the tip of the male thread 17.

[0018] The ground electrode 18 is a conductor extending from the metallic shell 16 toward the axis O. A core material mainly composed of copper is embedded in the ground electrode 18. The core material can be omitted. In this embodiment, the ground electrode 18 is a curved rod with a rectangular cross section.

[0019] The ground electrode 18 includes a connection portion 19 connected to the metallic shell 16 and a tip portion 20 facing the protrusion 14 of the center electrode 13. The connection portion 19 is the surface of the portion connected to the metallic shell 16 by means of welding, diffusion bonding, or the like that comes into contact with the weld metal or the joint interface, and is also the base of the ground electrode 18.

[0020] A protrusion 21 is provided on the tip end 20. In this embodiment, the protrusion 21 is provided on the axis O. A spark gap 22 is provided between the tip end 20 of the ground electrode 18 and the center electrode 13.

[0021] FIG. 2 is a perspective view of the center electrode 13. FIG. 2 illustrates a portion of the center electrode 13 including the protrusion 14 protruding from the tip of the insulator 11. The protrusion 14 is the portion protruding from the tip of the insulator 11. The protrusion 14 has a conical first portion 14a whose diameter decreases toward the tip, and a cylindrical second portion 14b integrated with the tip of the conical first portion 14a. The second portion 14b partially protrudes from the first portion 14a. The second portion 14b is formed on the protrusion 14 by means of welding, diffusion bonding, plastic processing, or the like.

[0022] The discharge member 23 is joined to the tip (second portion 14b) of the projection 14 via a fusion zone 26. The fusion zone 26 is formed by melting the projection 14 and the discharge member 23. The discharge member 23 is made of an alloy containing a large amount of a second element different from a first element contained in a large amount in the projection 14. The first element contained in the projection 14 is, for example, Ni, and the second element contained in the discharge member 23 is, for example, one of precious metals such as Pt, Ir, and Ru.

[0023] In this embodiment, the discharge member 23 has a circular disk-like tip surface 24. In Fig. 2, the axis O passes through the center of gravity 25 of the tip surface 24 of the discharge member 23. The center of gravity 25 of the tip surface 24 is the geometric center, calculated by known means, when the tip surface 24 is considered as a plane figure.

[0024] The molten zone 26 is exposed around the entire circumference between the projection 14 and the discharge member 23. The molten zone 26 is formed between the projection 14 and the discharge member 23 by, for example, laser welding. The molten zone 26 may also be formed between the projection 14 and the discharge member 23 by resistance welding. There is no limit to the axial distance from the edge of the tip surface 24 of the discharge member 23 to the molten zone 26, but it is, for example, 0.25 mm or less.

[0025] A depression 27 is provided at a position including the protrusion 14. In this embodiment, one elliptical depression 27 is provided at the boundary between the second portion 14b of the protrusion 14 and the molten portion 26. The depression 27 is formed at a position including the protrusion 14 by cutting or plastic processing. Examples of cutting include using a blade or cutting tool, and laser processing.

[0026] 3 is a side view of the protrusion 14. There is no limit to the axial length L of the depression 27 provided in the protrusion 14, and the length L may be any length. The depression 27 provided at a position including the protrusion 14 provides an edge 28 of the depression 27 on the protrusion 14 and the fusion zone 26.

[0027] The depth D of the depression 27 is 10 μm or more. The depth D is the distance from an imaginary line on the outer periphery of the protrusion 14 to the bottom of the depression 27 when it is assumed that the depression 27 does not exist. Because the protrusion 14 has the depression 27, the cross-sectional area of ​​the protrusion 14 perpendicular to the axis O can be reduced by the amount of the depression 27 compared to when the protrusion 14 does not have the depression 27. As a result, compared to when the protrusion 14 does not have the depression 27, the thermal conductivity from the discharge member 23 to the protrusion 14 is reduced and the temperature of the discharge member 23 is maintained higher, making it harder for the discharge member 23 to take away the energy of the flame kernel generated by the spark discharge, and making it easier for the flame kernel to grow. As a result, ignition performance is improved.

[0028] Providing depressions 27 in the discharge member 23 or the fusion zone 26 to reduce the cross-sectional area of ​​the discharge member 23 or the fusion zone 26 can also reduce the thermal conductivity from the discharge member 23 to the protrusion 14. However, when depressions 27 are provided in the discharge member 23 or the fusion zone 26, the volume of the discharge member 23 or the fusion zone 26 is reduced by the amount of the depressions 27, and therefore the amount of wear that can be tolerated before the discharge member 23 or the fusion zone 26 is worn by spark discharge and the protrusion 14 begins to wear out is reduced, raising concerns about reduced durability.

[0029] In this embodiment, the depression 27 is provided at a position including the protrusion 14, so it is possible to ensure the volume of the combined part of the discharge member 23 and the fusion zone 26. Since it is possible to ensure the amount of wear due to spark discharge in the combined part of the discharge member 23 and the fusion zone 26, it is possible to ensure durability.

[0030] 4(a) is a side view of the protrusion 14. There is no limit to the width W of the recess 27 in the circumferential direction of the protrusion 14, and the width W can be as short as desired. The width W of the recess 27 is the length of the longest line segment formed when a straight line 29 parallel to the tip surface 24 of the discharge member 23 is cut off by the edge 28 of the recess 27.

[0031] FIG. 4(b) is a cross-sectional view of the protrusion 14 taken along line IVb-IVb in FIG. 4(a). Line IVb-IVb is equal to line 29. FIG. 4(b) shows only the vicinity of depression 27 in the cross-section of the protrusion 14. When line 29 is set so that the two distances from the two edges 28 of depression 27 to line 29 are equal as shown in FIG. 4(b), the ratio ((d2-d1) / W) of the difference (d2-d1) between the longest distance d2 between line 29 and depression 27 and the shortest distance d1 between line 29 and depression 27 to the width W of depression 27 is preferably less than 0.09. This is to prevent depression 27 from becoming a sharp notch and from becoming a starting point for fracture of the protrusion 14.

[0032] Fig. 5 is a plan view of the spark plug 10 as seen from the front end side. When the spark plug 10 is viewed from the front end side, the projection 14 is hidden by the shadow of the ground electrode 18, and even if the ground electrode 18 is omitted, the depression 27 provided on the outer periphery of the projection 14 may not be visible. Therefore, in Fig. 5, the ground electrode 18 other than the connection portion 19 is not shown, and the depression 27 is exaggerated (the same applies to Figs. 6 and 8).

[0033] When it is assumed that the axis O passes through the center of gravity 25 of the discharge member 23, the recess 27 provided in the projection 14 exists outside the first range obtained by projecting the first sector 32 in the axial direction. Since the shape of the first range is a columnar shape with the first sector 32 as its base and extending parallel to the axis O, when the spark plug 10 is viewed from the tip side, the first range overlaps the first sector 32. Therefore, the same reference numeral as the first sector 32 is used for the first range.

[0034] The first sector 32 has its center on the axis O, its radius is the length of a line segment 31 connecting the axis O and the center of gravity 30 of the connection part 19, and its central angle θ including the center of gravity 30 is 90°, and the sector is symmetrical with respect to the line segment 31. The center of gravity 30 of the connection part 19 is the geometric center calculated by known means when the connection part 19 is represented as a plane figure.

[0035] In the spark plug 10, the edge 28 of the recess 27, which is located at a position including the projection 14, has a higher electric field strength than the portion of the projection 14 other than the recess 27. As the electric field strength at the edge 28 of the recess 27 increases, the electric field strength at the portion 24a (see FIG. 3 ) of the tip surface 24 of the discharge member 23 located on the tip side of the recess 27 also increases, making the portion 24a more likely to become the starting point of a spark discharge. In an engine with a high-intensity flow field, the edge 28 of the recess 27 may also become the starting point of a spark discharge. Since the portion 24a and the edge 28 of the recess 27 are located outside the first range 32, which is less affected by the ground electrode 18, the energy of a flame kernel generated by a spark discharge between the portion 24a or the edge 28 of the recess 27 and the ground electrode 18 is less likely to be taken away by the ground electrode 18. Furthermore, the flame kernel grows and the ignited mixture is more likely to diffuse, improving ignition performance.

[0036] FIG. 6 is a plan view of the spark plug 10. Assuming that the axis O passes through the center of gravity 25 of the discharge member 23, the recess 27 formed in the projection 14 is outside the first range 32 formed when the first sector 32 is projected in the axial direction, and is also outside the second range formed when the second sector 34 is projected in the axial direction. The second sector 34 is symmetrical to the first sector 32 with respect to the line segment 31 and a straight line 33 that is perpendicular to the axis O and passes through the axis O. Since the shape of the second range is a columnar shape extending parallel to the axis O with the second sector 34 as its base, the second range overlaps the second sector 34 when the spark plug 10 is viewed from the tip side. Therefore, the second range is denoted by the same reference numeral as the second sector 34.

[0037] The spark plug 10 (see FIG. 1) generates a flame kernel in the spark gap 22 by spark discharge between the center electrode 13 and the ground electrode 18. As the flame kernel grows, the air-fuel mixture (gas) is ignited and combusted. The spark discharge continues until the energy of the coil of the ignition device (not shown) is consumed. When the discharge path connecting the discharge member 23 of the center electrode 13 and the tip 20 of the ground electrode 18 is extended downstream by the gas flow, ignition performance improves. In the ranges excluding the first range 32 and the second range 34, the ground electrode 18 is not present in the gas flow (gas flow parallel to the straight line 33), so the gas flows easily. Since the portion 24a of the discharge member 23, which is likely to be the starting point of a spark discharge, is present in these ranges, the discharge path is more likely to extend, improving ignition performance.

[0038] When the discharge path extends, the voltage between the electrodes increases, causing a short circuit in the discharge path or a re-discharge. If a discharge path is formed between the protrusion 14 and the ground electrode 18 when a short circuit or re-discharge occurs in the discharge path, the length of the discharge path extending downstream is shorter by the thickness of the discharge member 23 and the fused portion 26 than when a discharge occurs between the tip surface 24 of the discharge member 23 and the ground electrode 18. However, because the portion 24a of the discharge member 23, where the electric field strength is high, is likely to become the starting point of a spark discharge, it becomes difficult for a discharge to occur between the protrusion 14 and the ground electrode 18, and the length of the discharge path extending downstream can be secured. As a result, ignition performance is improved.

[0039] FIG. 7 is a perspective view of the tip portion 20 of the ground electrode 18 (see FIG. 1). The tip portion 20 of the ground electrode 18 includes a first surface 35 facing the rear end of the spark plug 10, second surfaces 36 connected to both sides of the first surface 35, a third surface 37 located behind the first surface 35, and a rectangular end surface 38 connected to the first surface 35, the second surface 36, and the third surface 37. In this embodiment, a cylindrical protrusion 21 is provided on the first surface 35 of the tip portion 20 at a position including the axis O. The protrusion 21 is provided on the tip portion 20 by means of welding, diffusion bonding, plastic working, or the like. Examples of plastic working include bringing a die (not shown) into contact with the first surface 35 of the tip portion 20 and pressing a punch (not shown) into the third surface 37 to raise the protrusion 21 on the first surface 35.

[0040] The discharge member 39 is joined to the tip of the projection 21 via a fusion zone 42. The fusion zone 42 is formed by melting the projection 21 and the discharge member 39. The discharge member 39 is made of an alloy containing a large amount of a second element different from a first element contained in a large amount in the projection 21. The first element contained in the projection 21 is, for example, Ni, and the second element contained in the discharge member 39 is, for example, one of precious metals such as Pt, Ir, or Ru. In this embodiment, the discharge member 39 has a circular disk-shaped tip surface 40. FIG. 8 shows the axis O passing through the center of gravity 41 of the tip surface 40 of the discharge member 39. The center of gravity 41 of the tip surface 40 is the geometric center calculated by known means when the tip surface 40 is considered as a planar figure.

[0041] The center of gravity 41 of the tip surface 40 of the discharge member 39 of the ground electrode 18 and the center of gravity 25 of the tip surface 24 of the discharge member 23 of the center electrode 13 do not have to be located on the same axis O. The center of gravity 41 of the tip surface 40 of the discharge member 39 and the center of gravity 25 of the tip surface 24 of the discharge member 23 may be misaligned with respect to the same axis O within a tolerance of, for example, about 0.2 mm.

[0042] The molten portion 42 is exposed around the entire circumference between the projection 21 and the discharge member 39. The molten portion 42 is formed between the projection 21 and the discharge member 39 by, for example, laser welding. The molten portion 42 may also be formed between the projection 21 and the discharge member 39 by resistance welding.

[0043] A depression 43 is provided on the outer periphery of the protrusion 21. In this embodiment, a plurality of rectangular depressions 43 are provided in the protrusion 21. The depressions 43 are formed at positions that include the protrusion 21 by cutting or plastic processing. Examples of cutting include using a blade or cutting tool, and laser processing.

[0044] The length L, depth D, width W, ratio (d2-d1) / W of the recess 43, and the presence of the recess 43 outside the first range 32 and the second range 34 are similar to those of the recess 27 provided in the projection 14, and therefore a description thereof will be omitted. The recess 43 provided in the projection 21 of the ground electrode 18 can improve ignition ability and durability, similar to the improvement of ignition ability and durability achieved by the recess 27 of the projection 14 of the center electrode 13.

[0045] A second embodiment will be described with reference to Figure 8. In the first embodiment, a case was described in which the recess 27 formed on the projection 14 exists outside the first range 32 and the second range 34. In contrast, in the second embodiment, a case will be described in which the recess 27 formed on the projection 14 exists in the second range 34, unlike in the first embodiment. The same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted. Figure 8 is a plan view of the spark plug 10 according to the second embodiment, as viewed from the tip side.

[0046] Assuming that axis O passes through center of gravity 25 of discharge member 23, depression 27 provided in projection 14 exists in second range 34 obtained by projecting second sector 34 in the axial direction. Portion 24a and edge 28 of depression 27 exist in second range 34, which is least affected by ground electrode 18. Therefore, energy of the flame kernel generated by spark discharge between portion 24a or edge 28 of depression 27 and ground electrode 18 is less likely to be taken away by ground electrode 18. Furthermore, as the flame kernel grows, the ignited air-fuel mixture is more likely to diffuse, improving ignition performance.

[0047] If at least one of the plurality of recesses 43 provided on the protrusion 21 of the ground electrode 18 is located within the second range 34, a portion that is likely to become the starting point of a spark discharge can be located within the second range 34, thereby contributing to improved ignition performance. If all of the plurality of recesses 43 are located only within the second range 34, the effect of contributing to improved ignition performance is greater, which is preferable.

[0048] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0049] In the embodiment, the case where the protrusions 14, 21 are provided on both the center electrode 13 and the ground electrode 18, and the protrusions 14, 21 are provided with the recesses 27, 43, respectively, has been described, but this is not necessarily limited to this. For example, it is of course possible to omit one of the recesses and provide a recess on either the protrusions 14, 21, or to omit one of the protrusions and provide a protrusion on either the center electrode 13 or the ground electrode 18.

[0050] In the embodiment, the case where the recess 27 is provided at the boundary between the protrusion 14 and the fusion zone 26 and the recess 43 is provided in the protrusion 21 has been described, but this is not necessarily limited to this. As long as the recess is provided at a position that includes the protrusions 14 and 21, the recess may be located anywhere.

[0051] In the above embodiment, the distal end surfaces 24, 40 of the discharge members 23, 39 are circular and the protrusions 21 are cylindrical, but this is not necessarily limited to this. The shape of the distal end surfaces 24, 40 may be set appropriately, such as a square, a polygonal prism other than a square, or a truncated cone. The shape of the protrusions 21 may also be set appropriately, such as a square prism, a polygonal prism other than a square prism, or a truncated cone.

[0052] In the embodiment, the protrusion 14 of the center electrode 13 is described as being formed by integrating the conical first portion 14a and the cylindrical second portion 14b, and the discharge member 23 is joined to the second portion 14b, but this is not necessarily limited to this. It is of course possible to provide a protrusion having only the first portion 14a without the second portion 14b, join the discharge member 23 to the tip of the protrusion, and provide a recess 27 in the protrusion.

[0053] In the embodiment, the protrusion 14 of the center electrode 13 includes a conical portion (first portion 14a) whose diameter decreases toward the tip, but this is not necessarily limited to this. The protrusion 14 refers to the portion protruding from the tip of the insulator 11, so it is of course possible to make a cylindrical protrusion 14 with a constant diameter protrude from the tip of the insulator 11 and join the discharge member 23 to the tip of the protrusion 14.

[0054] In the embodiment, the case where the recess 27 is provided at one location on the protrusion 14 has been described, but this is not necessarily limited to this. It is of course possible to provide recesses 27 at multiple locations on the protrusion 14. When recesses 27 are provided at multiple locations on the protrusion 14, it is sufficient that one of the multiple recesses 27 is located outside the first range 32, outside the second range 34, or within the second range 34. This is because if even one recess 27 is present in that range, a portion that is likely to become a starting point for spark discharge can be located in that range, which contributes to improving ignition performance.

[0055] When recesses 27 are provided in multiple locations on protrusion 14, it is of course possible for all of the recesses 27 to be located only outside first range 32 or only outside second range 34, or only within second range 34. This is because if all of the recesses 27 are located within that range, the effect of contributing to improved ignition performance is greater.

[0056] In the embodiment, an example has been described in which the protrusion 14 is provided with an elliptical depression 27 and the protrusion 21 is provided with a rectangular depression 43, but this is not necessarily limited to this. The shape of the depressions 27, 43 may be set appropriately, such as a circle, a triangle, a rhombus, a pentagon, or a hexagon. It is of course possible to provide a continuous annular depression around the entire circumference of the protrusions 14, 21, or a continuous linear depression along part of the outer periphery of the protrusions 14, 21.

[0057] When a continuous linear depression is provided on part of the outer periphery of the protrusions 14, 21, it is sufficient that part of the depression is outside the first range 32 or outside the second range 34, or inside the second range 34. If part of the depression is present in that range, a part that is likely to become the starting point of spark discharge can be located in that range, which contributes to improving ignition performance.

[0058] When a continuous linear depression is provided on part of the outer periphery of the protrusions 14, 21, it is of course possible for the entire depression to be located only outside the first region 32 or only outside the second region 34, or only within the second region 34. This is because if the entire depression is located within that region, the effect of contributing to improved ignition performance is greater.

[0059] In the embodiment, the case where the tip 20 of the ground electrode 18 is disposed on the axis O has been described, but this is not necessarily limited to this. It is of course possible to dispose the tip 20 of the ground electrode 18 at a position that does not intersect with the axis O, for example, radially outward from the protrusion 14 of the center electrode 13 and spaced apart from the protrusion 14.

[0060] In the embodiment, the case where the tip portion 20 of the ground electrode 18 is disposed on the axis O and the protrusion 21 is provided on the first surface 35 of the tip portion 20 has been described, but this is not necessarily limited to this. When the tip portion 20 of the ground electrode 18 is provided radially outward of the protrusion 14 of the center electrode 13 with a gap therebetween, the protrusion 21 may be provided on the end surface 38 of the tip portion 20 and a discharge member may be joined to the protrusion 21. In this case as well, a spark discharge occurs between the discharge member of the ground electrode 18 and the center electrode 13.

[0061] In the embodiment, the ground electrode 18 is described as a curved rod with a rectangular cross section, but this is not necessarily limited to this. The shape of the ground electrode 18 can be a curved one or a linear one. The cross section of the ground electrode 18 can be a square one or a circle, an ellipse, a semicircle, or the like.

[0062] In the embodiment, the ground electrode 18, which has a rectangular cross section, is connected to the tip of the metallic shell 16 by welding or other means, and therefore the connection portion 19 of the ground electrode 18 is rectangular ( FIGS. 5 , 6 , and 8 ). The geometric center of the planar figure of the connection portion 19 is taken as the center of gravity 30 of the connection portion 19. However, this is not limited to this. The shape of the connection portion 19 is appropriately determined depending on the shape of the ground electrode 18, the connection state, and other factors, and the center of gravity of the connection portion is determined accordingly. For example, if a circular hole is drilled through the male thread 17 of the metallic shell 16 in the thickness direction, a ground electrode with a circular cross section is inserted into the hole, and an annular fusion zone is formed around the entire circumference of the ground electrode by laser welding, the shape of the connection portion of the ground electrode that contacts the fusion zone will be cylindrical. In this case, the center of gravity of the cylinder (solid) with a cylindrical outer surface is taken as the center of gravity of the connection portion. [Explanation of symbols]

[0063] 10 Spark Plugs 11 Insulators 13 Center electrode 14,21 protrusion 16 Metal body 18 Ground electrode 19 Connection 20 Tip 22 Spark Gap 23,39 Discharge members 26,42 Welding zone 27,43 recess 30 Center of gravity of connection 31 line segments 32 First sector, first range 33 straight line 34 Second sector, second range O axis θ central angle

Claims

1. a center electrode extending along an axis; a metallic shell that holds the center electrode via an insulator; a ground electrode connected to the metallic shell at a connection portion, a spark plug including a discharge member, the discharge member having a projection projecting from a tip end of the insulator and joined to the projection via a fusion zone to form a spark gap between the discharge member and the ground electrode, A spark plug in which a recess is provided in a portion of the outer periphery of the projection in the circumferential direction at a position including the projection.

2. a center electrode extending along an axis; a metallic shell that holds the center electrode via an insulator; a ground electrode connected to the metallic shell at a connection portion, a spark plug including a ground electrode having a projection at a tip end thereof, a discharge member joined to the projection via a fusion zone and forming a spark gap between the ground electrode and the center electrode, A spark plug in which a recess is provided in a portion of the outer periphery of the projection in the circumferential direction at a position including the projection.

3. a first sector is a sector that, when viewed from the axial direction, has a center on the axis, has a radius equal to the length of a line segment connecting the axis and the center of gravity of the connection portion, has a central angle of 90°, and is symmetrical with respect to the line segment; 3. The spark plug according to claim 1, wherein when a region obtained by projecting said first sector in said axial direction is defined as a first range, said recess exists only outside said first range.

4. When viewed from the axial direction, a sector that is symmetrical to the first sector with respect to the line segment and a straight line that is perpendicular to the axis and passes through the axis is defined as a second sector, 4. The spark plug according to claim 3, wherein when a region obtained by projecting said second sector in said axial direction is defined as a second range, said recess exists only outside said second range.

5. When viewed from the axial direction, a sector that is symmetrical to the first sector with respect to the line segment and a straight line that is perpendicular to the axis and passes through the axis is defined as a second sector, 4. The spark plug according to claim 3, wherein when a region obtained by projecting said second sector in said axial direction is defined as a second range, said recess exists only within said second range.

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