Spark plug

Abstract

To improve both the separation resistance and spark consumption resistance of a fusion part.SOLUTION: A spark plug includes a base material and a fusion part in which the base material is fused. The fusion part contains a noble metal and includes a first electrode in which a discharge surface formed of a curved surface or a flat surface is formed on a surface of the base material, and a second electrode facing the discharge surface. In a cross section perpendicular to a surface including a center of gravity of the discharge surface, inside a triangle whose bottom side is a line segment connecting two points expressing a border between the discharge surface and the surface and two oblique lines are line segments connecting the two points and a top point of the fusion part, a part of the base material exists between the fusion part and at least one of the oblique lines. A value obtained by dividing a length A of a perpendicular line from the top point to the bottom line of the triangle by a length B of the bottom line is 0.2 or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a spark plug. [Background technology]

[0002] Patent Document 1 discloses a prior art spark plug in which a molten portion, formed by melting a member containing a precious metal and a base material, is included in the discharge surface of an electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-45049 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the prior art can ensure the peeling resistance and spark wear resistance of the fusion zone, there is room for improvement.

[0005] The present invention has been made in response to this demand, and has an object to provide a spark plug capable of improving the peeling resistance and spark wear resistance of the fusion zone. [Means for solving the problem]

[0006] To achieve this object, the spark plug of the present invention comprises a base material and a fusion zone formed by melting the base material, the fusion zone containing a precious metal and comprising a first electrode forming a curved or flat discharge surface on the surface of the base material, and a second electrode facing the discharge surface. In a cross section perpendicular to the surface of the base material including the center of gravity of the discharge surface, a triangle is defined with a base that is a line segment connecting two points indicating the boundary between the discharge surface and the surface of the base material, and two hypotenuses that are line segments connecting the two points and the apex of the fusion zone, respectively, and a part of the base material is present between the fusion zone and at least one of the hypotenuses inside the triangle. The value obtained by dividing the length A of the perpendicular line drawn from the apex to the base of the triangle by the length B of the base is 0.2 or more. Effect of the Invention

[0007] According to the present invention, in a cross section perpendicular to the surface of the base metal including the center of gravity of the discharge surface, a triangle having a line segment connecting two points indicating the boundary between the discharge surface and the surface of the base metal as the base and a line segment connecting each of the two points and the apex of the molten part as the hypotenuse is a value obtained by dividing the length A of the perpendicular line from the apex to the base by the length B of the base is 0.2 or more, so that the length of the interface joining the molten part to the base metal can be secured and the peeling resistance of the molten part can be improved. Furthermore, since a part of the base metal is present inside the triangle between at least one of the hypotenuses and the molten part, the size of the molten part can be limited and the proportion of the precious metal in the molten part can be secured. Therefore, the spark wear resistance of the molten part can be improved. [Brief description of the drawings]

[0008] [Figure 1] 1 is a half-sectional view of a spark plug according to a first embodiment. [Diagram 2] FIG. 4 is a cross-sectional view of a ground electrode. [Diagram 3] FIG. 11 is a cross-sectional view of a ground electrode of a spark plug according to a second embodiment. [Figure 4] FIG. 11 is a cross-sectional view of a ground electrode of a spark plug according to a third embodiment. [Diagram 5] FIG. 11 is a cross-sectional view of a ground electrode of a spark plug according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 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 the axis X. 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 trailing end side of the spark plug 10 (the same applies to Figs. 2 to 5). As shown in Fig. 1, the spark plug 10 has a first electrode and a second electrode at which spark discharge occurs. In this embodiment, the ground electrode 20 is the first electrode, and the center electrode 13 is the second electrode.

[0010] 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 is provided with an axial hole 12 along the axis X.

[0011] The center electrode 13 is a rod-shaped member disposed in the axial hole 12 of the insulator 11. The center electrode 13 has a core material mainly composed of copper covered by a cylindrical base material 14 with a bottom. It is possible to omit the core material. The base material 14 is made of, for example, a Ni-based alloy, but is not limited to this material. A tip 15 is joined to the tip of the base material 14. The tip 15 protrudes from the tip of the insulator 11 toward the tip side. The tip 15 contains one or more of precious metals, such as Pt, Rh, Ir, Ru, etc. The tip 15 is possible to omit.

[0012] The center electrode 13 is electrically connected to a terminal fitting 16 in the axial hole 12. The terminal fitting 16 is a rod-shaped member to which a high-voltage cable or an ignition coil (neither of which are shown) is connected, and is made of a conductive metal material (such as low carbon steel). The terminal fitting 16 is fixed to the rear end side of the insulator 11 with its tip side inserted into the axial hole 12.

[0013] A metal shell 17 is fixed to the outer periphery of the insulator 11. The metal shell 17 is a substantially cylindrical member made of a metallic material (such as low carbon steel) having electrical conductivity. The metal shell 17 has a seat portion 18 that protrudes radially outward like a brim, and a threaded portion 19 provided on the outer periphery surface on the tip side of the seat portion 18. The metal shell 17 is fixed by fastening the threaded portion 19 to a screw hole (not shown) provided in a plug hole of the engine (cylinder head).

[0014] The ground electrode 20 is connected to the metallic shell 17. The ground electrode 20 is a curved rod-shaped member made of a conductive metal material. The ground electrode 20 includes a base material 21 joined to the metallic shell 17 and a fusion portion 24 formed by melting the base material 21. A spark gap is provided between the fusion portion 24 and the center electrode 13.

[0015] The material of the base material 21 is, for example, a Ni-based alloy, but is not limited to this. It is of course possible to embed a core material mainly composed of copper in the base material 21. The fusion zone 24 has a chemical composition containing one or more of precious metals such as Pt, Rh, Ir, and Ru. To ensure spark wear resistance, the fusion zone 24 preferably has a chemical composition containing 20 wt% or more of precious metals. The proportion of precious metals in the fusion zone 24 can be determined, for example, by analysis using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDS).

[0016] 2 is a cross-sectional view of the ground electrode 20, taken parallel to the longitudinal direction in which the ground electrode 20 extends. In FIG. 2, the vicinity of the fusion zone 24 of the ground electrode 20 is shown, and other portions are omitted from the illustration (the same applies to FIGS. 3 to 5). The base material 21 includes a first surface 22 facing the rear end side, and a second surface 23 connected to the first surface 22. The second surface 23 is a surface perpendicular to the first surface 22. The first surface 22 and the second surface 23 are part of the surface of the base material 21.

[0017] The molten portion 24 appears on the first surface 22. The molten portion 24 has a spherical crown-shaped portion that is raised relative to the first surface 22. The boundaries 25, 26 of the molten portion 24 where the molten portion 24 and the first surface 22 intersect are substantially circular in shape. The inner surfaces of the boundaries 25, 26 are the discharge surface 27 of the molten portion 24. The discharge surface 27 is a smoothly curved surface without any corners.

[0018] The center of gravity 28 of the discharge surface 27 is the geometric center, calculated by known means, of a plane figure obtained by projecting the discharge surface 27 onto a plane parallel to the first surface 22. Since Fig. 2 is a cross-sectional view perpendicular to the first surface 22 including the center of gravity 28 of the discharge surface 27, two boundaries 25, 26 of the fusion zone 24 appear.

[0019] The ground electrode 20 is made, for example, by the following method. After placing a disk-shaped member containing a precious metal on the first surface 22 of the base material 21, the member is fixed to the base material 21 by resistance welding in which an electric current is passed between the member and the base material 21 while pressing the member against the base material 21. Next, the vicinity of the member and the base material 21 are melted by laser welding in which a laser beam is irradiated toward the member from a processing head facing the first surface 22. This results in a ground electrode 20 in which a molten portion 24 containing a precious metal is provided in the base material 21. In this embodiment, the member containing a precious metal is entirely melted in the molten portion 24, so that the distribution of the precious metal in the molten portion 24 is uniform.

[0020] The shape and depth of the molten zone 24 are set depending on the shape of the component, the shape of the portion of base material 21 that contacts the component, the direction of the laser beam, the range to which the laser beam is irradiated, the spatial intensity distribution of the laser beam, the settings of the beam intensity, etc. The proportion of the precious metal in the molten zone 24 is set depending on the amount of precious metal contained in the component, the size of the component, the amount of melted base material 21, etc.

[0021] The molten portion 24 includes an interface 30 connecting the apex 29 of the molten portion 24 and the boundary 25, and an interface 31 connecting the apex 29 and the boundary 26. The apex 29 is the deepest point of the molten portion 24 with respect to the first surface 22, and the distance between the apex 29 and the first surface 22 (the length of a perpendicular line drawn from the apex 29 to a line segment connecting the boundaries 25, 26) is longer than the distance between any point of the molten portion 24 other than the apex 29 and the first surface 22. The apex 29 is located at a corner where the interface 30 and the interface 31 are connected.

[0022] 2, when a triangle 35 is provided on the ground electrode 20, with the line segment connecting two points indicating the boundaries 25, 26 of the discharge surface 27 as the base 32 and the line segments connecting the two points and the vertex 29 as the hypotenuses 33, 34, respectively, the fusion zone 24 is formed so that a part of the base material 21 exists inside the triangle 35 at least on one side between the hypotenuse 33 and the interface 30 and between the hypotenuse 34 and the interface 31. The value A / B obtained by dividing the length A of the perpendicular line from the vertex 29 to the base 32 by the length B of the base 32 is 0.2 or more and 0.43 or less.

[0023] Because A / B≧0.2, the length of interfaces 30, 31 joining fusion zone 24 to base material 21 can be ensured, improving the peeling resistance of fusion zone 24. Furthermore, because at least a portion of interfaces 30, 31 are present inside triangle 35, the size of fusion zone 24 can be limited. Because the proportion of precious metal in fusion zone 24 can be ensured, the spark ablation resistance of fusion zone 24 can be improved. Furthermore, because A / B≦0.43, the size of fusion zone 24 is further limited, further improving the spark ablation resistance of fusion zone 24.

[0024] In this embodiment, the vicinity of the boundary 25 and the vicinity of the vertex 29 of the interface 30 overlap with the hypotenuse 33, the central portion of the interface 30 is away from the hypotenuse 33 and located inside the triangle 35, and the vicinity of the boundary 26 and the vicinity of the vertex 29 of the interface 31 overlap with the hypotenuse 34, and the central portion of the interface 31 is away from the hypotenuse 34 and located inside the triangle 35. In other words, the interfaces 30, 31 are located on the hypotenuses 33, 34 of the triangle 35 or inside the triangle 35. Since the size of the fusion zone 24 can be further limited, the spark ablation resistance can be further improved.

[0025] Since interfaces 30, 31 are on hypotenuses 33, 34 of triangle 35 or inside triangle 35, the area of ​​the portion of fusion zone 24 surrounded by interface 30 and hypotenuse 33 is zero, and the area of ​​the portion of fusion zone 24 surrounded by interface 31 and hypotenuse 34 is also zero. Since part of base material 21 exists between hypotenuse 33 and interface 30 inside triangle 35, and part of base material 21 exists between hypotenuse 34 and interface 31, it is possible to lengthen interfaces 30, 31 and further limit the size of fusion zone 24. Therefore, the peeling resistance and spark wear resistance of fusion zone 24 can be further improved.

[0026] The combined area of ​​the portion of base material 21 surrounded by interface 30 and oblique side 33 and the portion of base material 21 surrounded by interface 31 and oblique side 34 is greater than the combined area (zero in this embodiment) of the portion of fusion zone 24 surrounded by interface 30 and oblique side 33 and the portion of fusion zone 24 surrounded by interface 31 and oblique side 34. This is advantageous in improving the spark wear resistance of fusion zone 24, as the size of fusion zone 24 can be further limited.

[0027] A second embodiment will be described with reference to Fig. 3. In the first embodiment, a case where the member containing the precious metal is completely melted into the melted portion 24 during laser welding is described. In contrast, in the second embodiment, a case where a part of the member containing the precious metal remains unmelted during laser welding is described. In the second embodiment, the same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted.

[0028] FIG. 3 is a cross-sectional view of a ground electrode 40 of a spark plug in the second embodiment. The ground electrode 40 is disposed in the spark plug 10 in place of the ground electrode 20 in the first embodiment. The ground electrode 40 includes a base material 21, a molten portion 41 formed by melting the base material 21, and a precious metal portion 42 having a higher proportion of precious metal than the proportion of precious metal in the molten portion 41. The precious metal portion 42 is a part of a member containing precious metal that remains unmelted during laser welding to create the molten portion 41. The precious metal portion 42 is in contact with the molten portion 41. The area of ​​the precious metal portion 42 is smaller than the area of ​​the molten portion 41. In this embodiment, the surface of the precious metal portion 42 that is not in contact with the molten portion 41 appears on the surface of the ground electrode 40.

[0029] The fusion zone 41 appears on the first surface 22 of the base material 21. The fusion zone 41 has a spherical crown-shaped portion that is raised relative to the first surface 22. The shape of the boundaries 43, 44 of the fusion zone 41 where the fusion zone 41 and the first surface 22 intersect is approximately circular. The inner surface of the boundaries 43, 44 is the discharge surface 45 of the fusion zone 41. The discharge surface 45 is a smooth curved surface without corners. The discharge surface 45 is an annular surface, and the inner outline of the discharge surface 45 is in contact with the surface of the precious metal portion 42, and the outer outline of the discharge surface 45 is in contact with the first surface 22. Since FIG. 3 is a cross-sectional view perpendicular to the first surface 22 including the center of gravity 46 of the discharge surface 45, two points appear as the boundaries 43, 44 of the fusion zone 41. The center of gravity 46 is the geometric center when the outer outline of the discharge surface 45 is taken as a plane figure.

[0030] The fusion zone 41 includes an interface 48 connecting the vertex 47 of the fusion zone 41 and the boundary 43, and an interface 49 connecting the vertex 47 and the boundary 44. The vertex 47 is located on a curve connecting the interface 48 and the interface 49. In the fusion zone 41, a part of the base material 21 exists between the hypotenuse 34 and the interface 49 inside a triangle 35 having a base 32 as a line segment connecting two points indicating the boundaries 43 and 44, and hypotenuses 33 and 34 as line segments connecting the two points and the vertex 47. The interface 48 is outside the triangle 35 except for the boundary 43 and the vertex 47. A / B, which is the length A of a perpendicular line drawn from the vertex 47 to the base 32 divided by the length B of the base 32, is 0.2 or more and 0.43 or less.

[0031] Because A / B≧0.2, the length of interfaces 48, 49 that join fusion zone 41 to base material 21 can be ensured, improving the peeling resistance of fusion zone 41. Furthermore, because part of interface 49 is present inside triangle 35, the size of fusion zone 41 can be limited. Because the proportion of precious metal in fusion zone 41 can be ensured, the spark ablation resistance of fusion zone 41 can be improved. Furthermore, because A / B≦0.43, the size of fusion zone 41 is further limited, further improving the spark ablation resistance of fusion zone 41.

[0032] Since there is a precious metal portion 42 where the material remains unmelted during laser welding, the proportion of the precious metal in the molten portion 41 is smaller by the amount of the precious metal portion 42 than when all the material has melted and there is no precious metal portion 42. However, since the area of ​​the precious metal portion 42 is smaller than the area of ​​the molten portion 41, the proportion of the precious metal in the molten portion 41 can be increased to a certain extent. Therefore, it is possible to prevent the spark wear resistance of the molten portion 41 from decreasing.

[0033] Precious metal portion 42 is in contact with fusion zone 41, and since precious metal portion 42 has a higher proportion of precious metal than fusion zone 41, precious metal portion 42 can improve spark ablation resistance. Since interfaces 48, 49 of fusion zone 41 are separated from precious metal portion 42, precious metal portion 42 can prevent the bonding area between fusion zone 41 and base material 21 from being reduced. Precious metal portion 42 can prevent the peeling resistance of fusion zone 41 from being reduced.

[0034] A third embodiment will be described with reference to Fig. 4. In the first and second embodiments, the case where the fusion zones 24, 41 protrude in one direction in the cross-sectional view is described. In contrast, in the third embodiment, the case where the fusion zone 51 protrudes in two directions in the cross-sectional view is described. In the third embodiment, the same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted.

[0035] FIG. 4 is a cross-sectional view of a ground electrode 50 of a spark plug in a third embodiment. The ground electrode 50 is disposed in the spark plug 10 in place of the ground electrode 20 in the first embodiment. The ground electrode 50 includes a base material 21 and a fusion zone 51 formed by melting the base material 21. The fusion zone 51 appears on the first surface 22 of the base material 21. The fusion zone 51 has a spherical crown-shaped portion that is raised with respect to the first surface 22. The shape of the boundaries 52, 53 of the fusion zone 51 where the fusion zone 51 and the first surface 22 intersect is substantially circular. The inner surface of the boundaries 52, 53 is a discharge surface 54. The discharge surface 54 is a smooth curved surface without corners. Since FIG. 4 is a cross-sectional view perpendicular to the first surface 22 including the center of gravity 55 of the discharge surface 54, the boundaries 52, 53 of the fusion zone 51 appear at two points.

[0036] The fusion zone 51 includes an interface 57 connecting the apex 56 of the fusion zone 51 and the boundary 52, and an interface 59 connecting the apex 56 and the boundary 53. The interface 57 includes a vertex 58 protruding in a direction away from the first surface 22. The apex 56 is located at the corner where the interface 57 and the interface 59 are connected.

[0037] In the fusion zone 51, a line segment connecting two points indicating boundaries 52, 53 is defined as base 32, and lines connecting the two points and an apex 56 are defined as hypotenuses 33, 34. Inside the triangle 35, a part of the base material 21 exists between hypotenuse 33 and an interface 57, and a part of the base material 21 exists between hypotenuse 34 and an interface 59. The interface 59 is on the hypotenuse 34 or inside the triangle 35. The value A / B obtained by dividing the length A of the perpendicular line from the apex 56 to the base 32 by the length B of the base 32 is 0.2 or more and 0.43 or less.

[0038] Because A / B≧0.2, the length of interfaces 57, 59 joining fusion zone 51 to base material 21 can be ensured, improving the peeling resistance of fusion zone 51. Also, because parts of interfaces 57, 59 are present inside triangle 35, the size of fusion zone 51 can be limited. Because the proportion of precious metal in fusion zone 51 can be ensured, the spark ablation resistance of fusion zone 51 can be improved. Furthermore, because A / B≦0.43, the size of fusion zone 51 is further limited, further improving the spark ablation resistance of fusion zone 51.

[0039] Since the interface 57 includes the apex 58, the interface 57 can be made longer by the length of the apex 58. The interface 57 can further improve the peeling resistance of the fusion zone 51.

[0040] A fourth embodiment will be described with reference to Fig. 5. In the first to third embodiments, the cases where molten parts 24, 41, 51 appear on the first surface 22 of the base material 21 have been described. In contrast, in the fourth embodiment, a case where a molten part 61 appears on the first surface 22 and the second surface 23 of the base material 21 will be described. In the fourth embodiment, the same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description will be omitted.

[0041] 5 is a cross-sectional view of a ground electrode 60 of a spark plug in a fourth embodiment. The ground electrode 60 is disposed in the spark plug 10 in place of the ground electrode 20 in the first embodiment. The ground electrode 60 includes a base material 21 and a molten portion 61 formed by melting the base material 21. The molten portion 61 appears on a first surface 22 and a second surface 23 of the base material 21.

[0042] The discharge surface 64 of the fusion zone 61 is a curved surface that is smoothly connected to the first surface 22 and the second surface 23. The shape of the discharge surface 64 is such that the portion facing the same direction as the first surface 22 is approximately rectangular, and the portion facing the same direction as the second surface 23 is also approximately rectangular. The portion of the discharge surface 64 that faces the same direction as the first surface 22 is flat and at approximately the same height as the first surface 22, and the portion of the discharge surface 64 that faces the same direction as the second surface 23 is flat and at approximately the same height as the second surface 23. The corners of the discharge surface 64 where the portion facing the same direction as the first surface 22 and the portion facing the same direction as the second surface 23 intersect are rounded, and the two are connected by a smooth curved surface without corners.

[0043] The center of gravity 65 of the discharge surface 64 is the geometric center, calculated by known means, of a plane figure created by projecting the discharge surface 64 onto a plane parallel to the first surface 22. Since Figure 5 is a cross-sectional view perpendicular to the first surface 22 including the center of gravity 65 of the discharge surface 64, two boundaries 62 and 63 of the fusion zone 61 appear. The boundary 62 is the boundary between the discharge surface 64 and the first surface 22, and the boundary 63 is the boundary between the discharge surface 64 and the second surface 23.

[0044] The ground electrode 60 is made, for example, by the following method. A base material 21 having a recess at the corner where the first surface 22 and the second surface 23 intersect is prepared, and a rectangular plate-shaped member containing a precious metal is placed in the recess. The member is then fixed to the base material 21 by resistance welding in which a current is passed between the member and the base material 21 while pressing the member against the base material 21. Next, the vicinity of the member and the base material 21 are melted by laser welding in which a laser beam is irradiated from a processing head toward the member. This results in a ground electrode 60 in which a molten portion 61 containing a precious metal is provided in the base material 21. In this embodiment, the member containing a precious metal is entirely melted in the molten portion 61, so that the distribution of the precious metal in the molten portion 61 is uniform.

[0045] The fusion zone 61 includes an interface 67 connecting the vertex 66 of the fusion zone 61 and the boundary 62, and an interface 68 connecting the vertex 66 and the boundary 63. The vertex 66 is located at a corner where the interface 67 and the interface 68 are connected. In the fusion zone 61, a line segment connecting two points indicating the boundaries 62 and 63 is the base 32, and the line segments connecting the two points and the vertex 66 are the hypotenuses 33 and 34. Inside the triangle 35, a part of the base material 21 exists between the hypotenuse 33 and the interface 67, and a part of the base material 21 exists between the hypotenuse 34 and the interface 68. The interface 67 intersects with the hypotenuse 33, and the interface 68 intersects with the hypotenuse 34. The value A / B obtained by dividing the length A of the perpendicular line from the vertex 66 to the base 32 by the length B of the base 32 is 0.2 or more and 0.43 or less.

[0046] Because A / B≧0.2, the length of interfaces 67, 68 joining fusion zone 61 to base material 21 can be ensured, improving the peeling resistance of fusion zone 61. Also, because portions of interfaces 67, 68 are present inside triangle 35, the size of fusion zone 61 can be limited. Because the proportion of precious metal in fusion zone 61 can be ensured, the spark ablation resistance of fusion zone 61 can be improved. Furthermore, because A / B≦0.43, the size of fusion zone 61 is further limited, further improving the spark ablation resistance of fusion zone 61.

[0047] Since a part of the base material 21 exists between the hypotenuse 33 and the interface 67 inside the triangle 35, and a part of the base material 21 exists between the hypotenuse 34 and the interface 68, the interfaces 67, 68 can be lengthened and the size of the fusion zone 61 can be further limited. Therefore, the peeling resistance and spark consumption resistance of the fusion zone 61 can be further improved.

[0048] The combined area of ​​the portion of base material 21 surrounded by interface 67 and oblique side 33 and the portion of base material 21 surrounded by interface 68 and oblique side 34 is greater than the combined area of ​​the portion of fusion zone 61 surrounded by interface 67 and oblique side 33 and the portion of fusion zone 61 surrounded by interface 68 and oblique side 34. Since interfaces 67 and 68 can further limit the size of fusion zone 61, this is advantageous in improving the spark ablation resistance of fusion zone 61. EXAMPLES

[0049] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0050] (Sample Preparation) The tester irradiated a laser beam under different conditions to a disk placed on the first surface of the base metal of the ground electrode, melting the entire disk, and produced spark plug samples No. 1-7 with a ground electrode including a fused zone formed by melting the disk and base metal. The samples had a spark gap between the ground electrode connected to a metal shell with a nominal diameter of a male thread of 12 mm, and a center electrode insulated and held by the metal shell. The width and thickness of the base metal of the ground electrode of the samples were 2.7 mm and 1.3 mm, respectively, and the base material was a Ni-based alloy, and the material of the disk was an alloy containing 50 wt% or more of Pt. The tester conducted a test to examine the effect of lengths A and B of the fused zone on the peeling resistance and spark wear resistance. The dimensions and materials of each part of the samples were the same except for lengths A and B of the fused zone.

[0051] (Peel test) For the peel test, a sample was attached to a 1,600cc turbocharged inline 4-cylinder gasoline direct injection engine placed on a test bench, and the engine was operated at 3,500 rpm for 2 minutes and then stopped for 2 minutes, and this process was repeated for 300 hours.

[0052] After the test, the cut surface of the sample parallel to the longitudinal direction of the ground electrode and perpendicular to the first plane including the center of gravity of the discharge surface of the fusion part was observed under a microscope, and the length A, length B, the total length C of the interface of the fusion part, and the length D of the crack that developed along the interface from the edge of the interface of the fusion part were measured. Since the crack was oxidized, it was possible to distinguish between a bonded interface and a crack where the interface had been destroyed. A / B and D / C were calculated, and samples with a crack ratio (D / C) of 0% of the total interface length were judged to be E (excellent peel resistance), samples with a crack ratio of less than 25% were judged to be G (good), and samples with a crack ratio of 25% or more were judged to be F (poor). The results are shown in Table 1.

[0053] Observation of the cut surfaces of Samples No. 1-7 revealed that in all samples, a part of the base metal was present between one of the hypotenuses of a triangle with the base being a line segment connecting two points indicating the boundary of the discharge surface and the hypotenuses being line segments connecting the two points and the apex of the molten part, and that a part of the base metal was present between the other hypotenuse and the interface. In addition, in all samples, the area of ​​the part of the base metal surrounded by the interface and the hypotenuse was larger than the area of ​​the part of the molten part surrounded by the interface and the hypotenuse.

[0054] (Spark consumption test) Prior to the spark erosion test, the distance between the discharge surface of the molten part of the sample and the central electrode (spark gap size) was measured with a projector. For the spark erosion test, a sample with a previously measured spark gap size was attached to a 1600cc turbocharged in-line 4-cylinder gasoline direct injection engine installed on a test bench, and the engine was operated for 500 hours at 6000 rpm and WOT (intake throttle valve fully open).

[0055] The spark gap size of the samples after the test was measured with a projector. Samples with a value of less than 0.05 mm, calculated by subtracting the spark gap size before the test from the spark gap size after the test, were rated as E (excellent spark wear resistance), samples with a value between 0.05 mm and 0.1 mm were rated as G (good), and samples with a value exceeding 0.1 mm were rated as F (poor). The results are shown in Table 1.

[0056] [Table 1]

[0057] According to Table 1, when A / B≧0.20 (sample No. 2-7), the peel resistance was rated E or G. For sample No. 1, A / B was 0.18, and the length A of the perpendicular line dropped from the apex to the base of the triangle formed by the molten part was significantly shorter than the length B of the base. This shortened the total length of the interface of the molten part, reducing the bonding strength of the molten part and making it more likely to peel off.

[0058] When A / B≦0.43 (sample No. 1-6), the spark erosion resistance was rated E or G. For sample No. 7, A / B was 0.55, and the length A of the perpendicular line from the apex to the base of the triangle formed by the molten part was significantly longer than the length B of the base, so it can be inferred that the volume of the molten part increased, the proportion of precious metal in the molten part decreased, and the molten part became more susceptible to spark erosion.

[0059] When 0.20≦A / B≦0.43 (sample No. 2-6), the peeling resistance and spark ablation resistance were rated E or G, making it clear that both were possible.When 0.20≦A / B≦0.33 (sample No. 2, 3), the peeling resistance and spark ablation resistance were rated E, making it clear that both were excellent.

[0060] 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 without departing from the spirit of the present invention.

[0061] In the above embodiment, the ground electrodes 20, 40, 50, 60 are the first electrodes, the center electrode 13 is the second electrode, and the fusion zones 24, 41, 51, 61 are provided in the base metal 21 of the ground electrodes 20, 40, 50, 60, but this is not necessarily limited to the above. It is of course possible to use the center electrode 13 as the first electrode, the ground electrode 20 as the second electrode, and provide a fusion zone in the base metal 14 of the center electrode 13.

[0062] In the first to third embodiments, the fusion zone 24, 41, 51 includes a spherical crown-shaped portion protruding from the first surface 22 of the base material 21, and the discharge surface 27, 45, 54 is a curved surface, but this is not necessarily limited to the above. It is of course possible to make the discharge surface of the fusion zone flat and at approximately the same height as the first surface 22 of the base material 21. Such a discharge surface can be formed, for example, by providing a recess in the first surface 22 of the base material 21, placing a member containing a precious metal in the recess, and then irradiating the member with a laser beam.

[0063] In the fourth embodiment, a case has been described in which the portion of the discharge surface 64 of the fusion zone 61 facing the same direction as the first surface 22 of the base material 21 is planar and at approximately the same height as the first surface 22, and the portion of the discharge surface 64 facing the same direction as the second surface 23 is planar and at approximately the same height as the second surface 23, but this is not necessarily limited to this. It is of course possible to make the portion of the discharge surface 64 facing the same direction as the first surface 22 of the base material 21 a curved surface raised relative to the first surface 22, or to make the portion of the discharge surface 64 facing the same direction as the second surface 23 a curved surface raised relative to the second surface 23.

[0064] In the first to third embodiments, the boundaries of the fusion zones 24, 41, and 51 are circular, and in the fourth embodiment, the boundaries of the fusion zone 61 are rectangular, but this is not necessarily limited to this. The shape of the boundary of the fusion zone can be set appropriately. For example, it is of course possible to make the boundary of the fusion zone in the first to third embodiments rectangular, and to make the boundary of the fusion zone in the fourth embodiment circular.

[0065] Although not described in the embodiments, the discharge surfaces 27, 45, 54, 64 of the molten parts 24, 41, 51, 61 may have irregularities. In other words, the discharge surfaces include those with irregularities within the surface. This is because the shape of the discharge surface is rounded due to the influence of the surface tension of the molten metal when the molten metal solidifies to form the molten part, and therefore the irregularities of the discharge surface can be said to be smooth curved surfaces without corners.

[0066] In the second embodiment, a case has been described in which a part of the precious metal portion 42 appears on the surface of the ground electrode 40, but this is not necessarily limited to this. The precious metal portion 42 may be embedded in the molten portion 41. Since the proportion of precious metal in the precious metal portion 42 is greater than the proportion of precious metal in the molten portion 41, even when the precious metal portion 42 is embedded in the molten portion 41, the precious metal portion 42 can improve the spark wear resistance even if the molten portion 41 is worn.

[0067] It is of course possible to provide the precious metal portion 42 described in the second embodiment in the fusion zone 24, 51, 61 in the first, third, and fourth embodiments. It is also of course possible to provide a plurality of precious metal portions 42 in the fusion zone 24, 41, 51, 61.

[0068] In the second embodiment, the area of ​​the portion of the base material 21 surrounded by the interface 49 and the oblique side 34 is smaller than the total area of ​​the portion of the fusion zone 41 surrounded by the interface 48 and the oblique side 33 and the portion of the fusion zone 41 surrounded by the interface 49 and the oblique side 34, but is not limited to this. It is of course possible to change the shape of the interface 49 by setting the laser welding conditions so that the area of ​​the portion of the base material 21 surrounded by the interface 49 and the oblique side 34 is larger than the total area of ​​the portion of the fusion zone 41 surrounded by the interface 48 and the oblique side 33 and the portion of the fusion zone 41 surrounded by the interface 49 and the oblique side 34. In this way, the size of the fusion zone 41 can be limited by the interfaces 48 and 49, which is advantageous for improving the spark wear resistance of the fusion zone 41.

[0069] In the embodiment, the first surface 22 of the base material 21 of the ground electrode 20, 40, 50, 60 is located on the tip side of the center electrode 13, and a spark gap is provided between the fusion zone 24, 41, 51, 61 provided on the first surface 22 and the center electrode 13, but this is not necessarily limited to this. It is naturally possible to arrange the second surface 23 of the base material 21 of the ground electrode 20, 40, 50, 60 on the tip side of the center electrode 13 and provide a spark gap between the fusion zone provided on the second surface 23 and the center electrode 13. It is also naturally possible to arrange the second surface 23 of the base material 21 of the ground electrode 20, 40, 50, 60 on the side of the center electrode 13 and provide a spark gap between the fusion zone provided on the second surface 23 and the center electrode 13. In this case, it is naturally possible to provide a plurality of ground electrodes.

[0070] In the above embodiment, the ground electrodes 20, 40, 50, 60 are curved rod-shaped members, but the present invention is not limited to this. It is of course possible to extend the threaded portion 19 of the metallic shell 17 in the axial direction to approximately the position of the tip of the center electrode 13, connect a linear ground electrode to the tip of the threaded portion 19, and set a spark gap between the center electrode 13 and the ground electrode. [Explanation of symbols]

[0071] 10 Spark plug 13 Center electrode (second electrode) 20,40,50,60 Ground electrode (1st electrode) 21 Base material 22 First side (front) 23 Second side (front) 24, 41, 51, 61 Welding section 25,26,43,44,52,53,62,63 boundary 27,45,54,64 Discharge surface 28,46,55,65 Center of gravity 29,47,56,66 Peak 30,31,48,49,57,59,67,68 interface 32 Bottom 33,34 Hypotenuse 35 triangle 42 Precious Metals Department

Claims

1. A base material and a fusion zone in which the base material is fused, the fusion zone including a first electrode that contains a noble metal and forms a discharge surface on a surface of the base material that is a curved or flat surface; A spark plug comprising: a second electrode facing the discharge surface, In a cross section perpendicular to the surface including the center of gravity of the discharge surface, a triangle is defined having a base that is a line segment connecting two points indicating a boundary between the discharge surface and the surface, and two hypotenuses that are line segments connecting the two points and the apex of the molten portion, respectively, and a part of the base material is present between at least one of the hypotenuses and the molten portion inside the triangle, A spark plug, wherein a value obtained by dividing a length A of a perpendicular line extending from the apex to the base by a length B of the base is 0.2 or more.

2. 2. The spark plug according to claim 1, wherein said first electrode is a ground electrode, said second electrode is a center electrode, and said cross section is a cross section parallel to a longitudinal direction of said ground electrode.

3. 3. The spark plug according to claim 1, wherein said value is equal to or greater than 0.2 and equal to or less than 0.

43.

4. 3. The spark plug according to claim 1, wherein said value is equal to or greater than 0.2 and equal to or less than 0.

33.

5. the first electrode further includes a precious metal portion having a ratio of precious metal greater than a ratio of precious metal in the fusion zone, 3. The spark plug according to claim 1, wherein the noble metal portion is in contact with the fusion portion.

6. 3. The spark plug according to claim 1, wherein in a cross section perpendicular to the surface and including a center of gravity of the discharge surface, an area of ​​a portion of the base material surrounded by an interface of the molten portion and the oblique side is larger than an area of ​​a portion of the molten portion surrounded by the interface and the oblique side.

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