spark plug

Abstract

Spark plug (10), having: a point (26, 46) extending in a first direction from a rear end to a front end; and an electrode base metal (22, 41) with an extension section (23, 43) extending in the first direction, the front end section of which is connected to a rear end section of the tip (26, 46) by a melt zone (25, 45, 71), wherein in a section taken along the first direction and containing a central axis (C) of the tip (26, 46) extending in the first direction, A and B satisfy a comparison expression B / A ≥ 1,2, wherein in a case where two ends (51, 52, 61, 62, 72, 73) of a line indicating an interface (50, 60, 72) between the extension section (23, 43) and the melting zone (25, 45, 71) are arranged at the same position with respect to the first direction, A is a linear distance between the two ends, or, In a case where one of the two ends (51, 52, 61, 62, 72, 73) is positioned in front of the other end with respect to the first direction, A is a distance on a straight line (55, 67, 83) passing through one end and extending perpendicularly to the central axis (C), from one end to an intersection point (56, 84) between the straight line (55, 83) and an outline (25a, 71a) of the melting zone (25, 71) on one side towards the other end, B is the length of the line that indicates the interface, wherein the line indicating the boundary surface (50, 60, 72) has at least one projection (53, 63, 65, 75, 77, 79, 81) that projects towards the front end face, and wherein a first vertex (54, 64, 76) located furthest forward below the vertices of the projections (53, 63, 65, 75, 77, 79, 81) is present in a first region (58, 68) of the line indicating the interface (50, 60, 72), the first region being arranged in the direction of one end with respect to the central axis (C), or in a second region (59, 69) of the line indicating the interface (50, 60, 72), the second region being arranged in the direction of the other end with respect to the central axis (C).

Description

Scope of the invention

[0001] The present invention relates to a spark plug, particularly to a spark plug in which a tip is bonded to an electrode base metal. Background of the invention

[0002] Spark plugs are known in which a tip is connected to an electrode base metal via a melting zone (see e.g. JP 2017 - 228 430 A, DE 692 25 686 T2, DE 102011 077 279 A1).

[0003] Such a spark plug is required to apply a separation restriction technique at the interface between an electrode base metal and a molten zone to prevent peeling of a tip from the electrode base metal even when cracking occurs at one end of the interface between the electrode base metal and the molten zone.

[0004] The present invention is designed to meet the above-mentioned requirement. One advantage of the invention is a spark plug capable of preventing separation at the interface between an electrode base metal and a molten zone. Summary of the invention

[0005] According to claim 1 of the present invention, there is provided a spark plug comprising a tip extending in a first direction directed from a rear end side to a front end side, and an electrode base metal having an extension portion extending in the first direction, the front end portion of which is connected to a rear end portion of the tip through a fusion zone.In a section extending along the first direction and including a central axis of the tip extending in the first direction, A and B satisfy a relational expression B / A ≥ 1.2 when, in a case where two ends of a line indicating an interface between the extension section and the melting zone are located at the same position with respect to the first direction, A is a linear distance between the two ends, or in a case where one of the two ends is located in front of the other end with respect to the first direction, A is a distance on a straight line passing one end and extending perpendicular to the central axis from one end to an intersection point between the straight line and an outline of the melting zone on one side to the other end, and B is a length of the line indicating the interface.

[0006] According to the spark plug described above, in a section including the tip center axis, the length B of the line indicating the interface between the electrode base metal and the molten zone and the length A of the line segment perpendicular to the center axis including the ends of the interface satisfy the relational expression B / A ≥ 1.2. Therefore, the probability of cracks developing from one end to the other of the interface between the electrode base metal and the molten zone is reduced, which can contain separation at the interface.

[0007] According to claim 1, there is provided a spark plug as described above, wherein the interface indicating line includes at least one protrusion toward the front end side. Since the protrusion(s) can reduce the degree of cracking from one end or the other end along a direction perpendicular to the central axis, the effect of the first aspect of the invention can be achieved, and the separation at the interface between the electrode base metal and the molten zone can be further restricted.

[0008] According to claim 1, there is provided a spark plug as described above, wherein a first vertex located furthest forward of the vertices of the projection is present in a first portion of the line indicating the interface located toward the one end with respect to the central axis, or a second portion of the line indicating the interface located toward the other end with respect to the central axis. Thus, compared with the case where the first vertex is present on the central axis, the degree of cracking from one end or the other end along a direction perpendicular to the central axis can be further reduced. This can achieve the effect of the second aspect of the invention and further restrict separation at the interface between the electrode base metal and the molten zone.

[0009] According to a second aspect of the present invention, there is provided a spark plug as described above, wherein the line indicating the interface has two or more protrusions. In the first region or the second region where the first vertex is missing, a second vertex is provided which is located at the same position with respect to the first direction as the first vertex or which is the second foremost one next to the first vertex. By the second vertex, the degree of cracking from one end or the other end along a direction perpendicular to the central axis can be reduced. Moreover, compared with the case where the second vertex is provided on the central axis, the degree of cracking from one end or the other end along a direction perpendicular to the central axis can be further reduced.Thereby, the effect of the third aspect of the invention can be achieved and the separation at the interface can be further restricted.

[0010] According to a third aspect of the present invention, there is provided a spark plug as described above, wherein the relational expression B / A ≥ 1.2 is satisfied in each section including the central axis. This can achieve the effect of any of the aforementioned aspects of the invention, and the separation at the interface between the electrode base metal and the molten zone can be further restricted. Brief description of the drawings Fig. 1 is a half section through a spark plug according to a first embodiment. Fig. 2 is a sectional view of a center electrode including the center axis of a tip. Fig. 3 is a sectional view of a ground electrode including the central axis of a tip. Fig. 4 is a sectional view of a center electrode including the center axis of a tip in a spark plug according to a second embodiment. Fig. 5A is a side view of an electrode base metal and a tip, and Fig. Figure 5B is a correlation diagram showing the relationship between B / A and the percentage of crack length in an interface. Detailed description of the invention

[0011] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. Fig. 1 is a half section, bounded by an axial line O, of a spark plug 10 according to a first embodiment. In Fig. 1, the lower side is referred to as the front end side of the spark plug 10 and the upper side is referred to as the rear end side of the spark plug 10. As in Fig. 1, the spark plug 10 has a center electrode 20 and a ground electrode 40.

[0012] An insulator 11 is a roughly cylindrical member with an axial hole 12 along the axial line O and is made of ceramic, such as alumina, which exhibits excellent mechanical properties and high-temperature insulation performance. The insulator 11 has a rearward-facing surface 13 or a rearward-facing annular surface formed on the front end side of the inner peripheral surface of the axial hole 12. The rearward-facing surface 13 decreases in diameter toward the front end side.

[0013] The center electrode 20 is a rod-shaped member mounted on the rearward-facing surface 13. The front end of the center electrode 20 protrudes forward from the front end of the insulator 11. The center electrode 20 is configured such that a core 21 containing copper as the main component is covered with a closed-bottom cylindrical electrode base metal 22. The electrode base metal 22 has a chemical composition containing Ni in an amount of 50 wt% or more. The core 21 may be omitted.

[0014] The electrode base metal 22 has an extension portion 23 whose front end portion 24 protrudes from the front end of the insulator 11. The extension portion 23 is a portion of the electrode base metal 22 and is formed into a circular columnar shape extending in the axial direction. A rear end portion 27 of a disk-shaped tip 26 is connected to the front end portion 24 of the extension portion 23 through a fusion zone 25. In the present embodiment, the tip 26 has a chemical composition containing one or more noble metals of Pt, Rh, Ir, Ru, etc. in an amount of 50 wt% or more. A discharge surface 28 of the tip 26 faces the ground electrode 40. The center electrode 20 is electrically connected to a metal terminal 29 in the axial hole 12.

[0015] The metal clamp 29 is a rod-shaped member for connecting to a high-voltage cable (not shown) and is made of an electrically conductive metal material (e.g., low-carbon steel). The metal clamp 29 is attached to the rear end of the insulator 11, while a front end thereof is inserted into the axial hole 12.

[0016] A metallic shell 30 is crimped onto the outer periphery of a front end portion of the insulator 11. The metallic shell 30 is an approximately cylindrical member formed of an electrically conductive metal material (e.g., low-carbon steel). The metallic shell 30 has a seat portion 31 projecting radially outward in a collar-like shape and a screw portion 32 formed on an outer peripheral surface located forward of the seat portion 31. The metallic shell 30 is fixed by screwing the screw portion 32 into a threaded hole (not shown) of an engine (cylinder head). The ground electrode 40 is connected to a front end portion of the metallic shell 30.

[0017] The ground electrode 40 is a rod-shaped member formed of an electrically conductive metal material. The ground electrode 40 includes an electrode base metal 41 bonded to the metallic shell 30 and a tip 46. The electrode base metal 41 includes a support portion 42 whose end portion is bonded to the metallic shell 30, and an extension portion 43 bonded to the support portion 42 by resistance welding, laser welding, or the like. The support portion 42 and the extension portion 43 have a chemical composition containing Ni in an amount of 50 wt% or more.

[0018] The extension portion 43 is formed into a circular columnar shape extending in the axial direction. A rear end portion 47 of a disk-shaped tip 46 is connected to a front end portion 44 of the extension portion 43 through a fusion zone 45. In the present embodiment, the tip 46 has a chemical composition containing one or more noble metals selected from Pt, Rh, Ir, Ru, and so on in an amount of 50 wt% or more. A discharge surface 48 of the tip 46 faces the center electrode 20. A spark gap is formed between the discharge surface 48 of the tip 46 and the center electrode 20.

[0019] Specifically, in order to coincide the front end side and the rear end side of the extending portion 43 and the tip 46 of the ground electrode 40 with the front end side and the rear end side of the extending portion 23 and the tip 26 of the center electrode 20, other than the front end side and the rear end side of the spark plug 10, a part of the extending portion 43 connected to the supporting portion 42 is referred to as a rear end, and the discharge surface 48 of the tip 46 is referred to as a front end.

[0020] Fig. 2 is a sectional view of the center electrode 20 with the center axis C of the tip 26. The center axis C passes through the centroid of the discharge surface 28 of the tip 26 and extends in the direction in which the extension section 23 extends. The arrow F indicates a first direction directed from the rear end section 27 to the discharge surface 28 of the tip 26. In the present embodiment, the center axis C coincides with the axial line O (see Fig. 1) of the spark plug 10. The tip 26 is connected to the extension portion 23 by the fusion zone 25. In the fusion zone 25, the tip 26 and the extension portion 23 are fused together. The line indicating an interface 50 between the fusion zone 25 and the extension portion 23 is divided into a first region 58 located on one side toward one end 51 of the interface 50 with respect to the central axis C, and a second region 59 located on one side toward the other end 52 of the interface 50 with respect to the central axis C.

[0021] In the present embodiment, the fusion zone 25 is formed by laser welding. The one end 51 and the other end 52 (two ends of the interface 50) at which the line indicating the interface 50 and an outline 23a of the extension portion 23 intersect are configured such that the one end 51 is located in front of the other end 52 with respect to the direction of the arrow F (first direction). In this case, the relational expression B / A ≥ 1.2 is satisfied, where A is a distance on a straight line 55 passing through the one end 51 and extending perpendicular to the central axis C, from an intersection point 56 between the straight line 55 and an outline 25a of the fusion zone 25 to the one end 51, and B is the length of the interface 50 (length along the interface 50 from the one end 51 to the other end 52).

[0022] In particular, the straight line 55 also intersects the contour of the melting zone 25 at an intersection point 57 in addition to the intersection point 56. However, an intersection point used to obtain the distance A from the one end 51 is the intersection point 56 with the outline 25a, which indicates an externally visible shape of the melting zone 25, not the intersection point 57, which is only visible in a section (invisible from the outside). This is due to the following: Since the length B along the interface 50 lies from the intersection (the other end 52) between the outline 23a of the extension section 23 and the interface 50 to the one end 51, the intersection point 56 between the straight line 55 and the outline 25a is used to obtain the distance A for reasons of consistency with the length B.

[0023] The length B can be obtained as follows: a section containing the central axis C is imaged; 100 equal division points of the interface 50 (obtained by projecting equal division points of the straight line 55 onto the interface 50) are recorded by image processing; then, linear distances between the adjacent points are summed.

[0024] Since the spark plug 10 is repeatedly heated and cooled within an engine, thermal stress is likely to cause cracks to develop in the interface 50 between the extension portion 23 and the fusion zone 25. Cracks from one end 51 and the other end 52 of the interface 50 are generated by contact with high-temperature combustion gas. In the spark plug 10, in a portion containing the central axis C of the tip 26, since A and B satisfy the relational expression B / A ≥ 1.2, where B is the length of the interface 50 and A is the length of a line segment containing one end 51 of the interface 50 and extending perpendicular to the central axis C, cracks are unlikely to develop from one end 51 to the other end 52 of the interface 50 or from the other end 52 to one end 51. Therefore, fracture of the interface 50, which might otherwise be caused by cracking, can be avoided.

[0025] The interface 50 has a protrusion 53 protruding toward the front end side. A first vertex 54, located at the frontmost point on the protrusion 53, is located at a different position from that of one end 51 and the other end 52 of the interface 50. Since the first vertex 54 is present on the protrusion 53, the inclination direction of the protrusion 53 with respect to the central axis C changes at the first vertex 54. Therefore, the protrusion 53 can reduce the degree of cracking in a direction perpendicular to the central axis C. This can further restrict separation at the interface 50.

[0026] The first vertex 54 of the protrusion 53 is located in the second region 59 of the interface 50, which is located toward the other end 52 with respect to the central axis C. As a result, the degree of cracking from the other end 52 in a direction perpendicular to the central axis C can be further reduced compared to the case where the first vertex 54 is present on the central axis C. As a result, the separation at the interface 50 can be further restricted compared to the case where the first vertex 54 is present on the central axis C.

[0027] Specifically, it is preferable that the condition of B / A ≥ 1.2, which the interface 50 of the fusion zone 25 satisfies, holds in each section including the central axis C. Each section including the central axis C can be obtained by image processing. The method is as follows. First, the center electrode 20 is gradually ground perpendicular to the central axis C, and the resulting section is repeatedly imaged. The resulting images are processed to obtain a three-dimensional structure of the interface 50. Then, the length B of the interface 50 and the distance A are measured in each section including the central axis C of the obtained three-dimensional structure, whereby it can be judged whether the relational expression B / A ≥ 1.2 is satisfied or not in the section including the central axis C.By satisfying the relation B / A ≥ 1.2 in each section containing the central axis C, the separation at the interface 50 can be further restricted.

[0028] Fig. 3 is a sectional view of the ground electrode 40 with the central axis C of the tip 46. The central axis C passes through the centroid of the discharge surface 48 of the tip 46 and extends in the direction in which the extension section 43 extends. The arrow F indicates a first direction directed from the rear end section 47 to the discharge surface 48 of the tip 46. In the present embodiment, the central axis C coincides with the axial line O (see Fig. 1) of the spark plug 10. The tip 46 is connected to the extension portion 43 by the fusion zone 45. The line indicating an interface 60 between the fusion zone 45 and the extension portion 43 is divided into a first region 68 located on one side toward one end 61 of the interface 60 with respect to the central axis C, and a second region 69 located on one side toward the other end 62 of the interface 60 with respect to the central axis C.

[0029] In the present embodiment, the fusion zone 45 is formed by laser welding. The one end 61 and the other end 62 (two ends of the interface 60) where the line indicating the interface 60 and the outlines 43a and 45a of the extension portion 43 and the fusion zone 45 intersect are located at the same position with respect to the direction of arrow F (first direction). In this case, the linear distance A (length of a line segment) between the one end 61 and the other end 62 and the length B of the interface 60 satisfy the relational expression B / A ≥ 1.2. The length B of the interface 60 is obtained in a similar manner to the length B of the interface 50. By satisfying the relation B / A ≥ 1.2, cracks are unlikely to develop from one end 61 to the other end 62 of the interface 60 or from the other end 62 to one end 61.Therefore, separation at the interface 60, which might otherwise occur due to crack formation, can be suppressed.

[0030] The interface 60 has a plurality of protrusions 63 and 65 projecting toward the front end side. A first vertex 64, which is located furthest forward on the protrusion 63, is located in the first region 68 of the interface 60 (excluding one end 61 and the central axis C), which is located toward one end 61 with respect to the central axis C. A second vertex 66, which is located furthest forward on the protrusion 65, is located in the second region 69 of the interface 60 (excluding the other end 62 and the central axis C), which is located toward the other end 62 with respect to the central axis C. The second vertex 66 is located furthest forward next to the first vertex 64 with respect to the first direction (direction of arrow F).

[0031] Since the second vertex 66 is present on the protrusion 65, the inclination direction of the protrusion 65 with respect to the central axis C changes at the second vertex 66. In addition to the first vertex 64, the second vertex 66 can reduce the degree of cracking from the other end 62 to one end 61 of the interface 60 in a direction perpendicular to the central axis C. Thus, the action and effect on the interface 50 of the fusion zone 25 of the center electrode 20 can be achieved, and the separation at the interface 60 can be further restricted.

[0032] A second embodiment will be described below with reference to Fig. 4. The first embodiment was described with reference to interfaces 50 and 60 having one or two protrusions. In contrast, the second embodiment will be described with reference to an interface 72 having a larger number of protrusions. In particular, similar structural features of the first and second embodiments are designated by like reference numerals, and repetitive description is avoided. Fig. 4 is a sectional view of a center electrode 70 including the center axis C of the tip 26 in a spark plug according to the second embodiment.

[0033] The tip 26 is connected to the extension portion 23 via a fusion zone 71. In the present embodiment, the fusion zone 71 is also formed by laser welding. One end 73 and the other end 74 (two ends of the interface 72) at which the line indicating the interface 72 between the fusion zone 71 and the extension portion 23 and the outline 23a of the extension portion 23 intersect are arranged such that one end 73 is located in front of the other end 74 with respect to the direction of the arrow F (first direction). In this case, the relational expression B / A ≥ 1.2 is satisfied, where A is a distance on a straight line 83 passing one end 73 and extending perpendicular to the central axis C, from an intersection point 84 between the straight line 83 and an outline 71a of the melt zone 71 to one end 73, and B is the length of the interface 72 (length along the interface 72 from one end 73 to the other end 74).

[0034] The interface 72 has a plurality of protrusions 75, 77, 79, and 81 projecting toward the front end side. A first vertex 76, located forwardmost on the protrusion 75, is located at the same position with respect to the first direction (direction of arrow F) as the second vertex 78, located forwardmost on the protrusion 77. A third vertex 80, located forwardmost on the protrusion 79, and a fourth vertex 82, located forwardmost on the protrusion 81, are located rearward of the first vertex 76 and the second vertex 78 with respect to the first direction (direction of arrow F). The second vertex 78 is located in the first region 58 of the interface 72 (except for the one end 73 and the central axis C), which extends towards the one end 73 with respect to the central axis C.The first apex 76 is located in the second region 59 of the interface 72 (excluding the other end 74 and the central axis C), which is located toward the other end 74 with respect to the central axis C. According to the present spark plug, a result and effect similar to those of the ground electrode 40 described in the first embodiment can be achieved. Example

[0035] The present invention will be described in more detail using an example; however, the present invention is not limited to the example. Fig. 5A is a side view showing an electrode base metal (extending portion 23) of a center electrode and the tip 26 used for preparing samples of a spark plug in the example.

[0036] As in Fig. As shown in Figure 5A, the extending portion 23 has a truncated cone shape, and an end surface 24a of the front end portion 24 has a circular shape. The extending portion 23 is formed of a Ni alloy (NCF601). The tip 26 is formed of an Ir alloy (Ir: 68 wt%; Ru: 11 wt%; Rh: 20 wt%; and Ni: 1 wt%) and has a circular columnar shape. An end surface 27a of the rear end portion 27 of the tip 26 opposite the discharge surface 28 has a circular shape.

[0037] When the end surface 27a of the tip 26 was in contact with the end surface 24a of the extension portion 23, the workpiece was rotated around the central axis C, and the boundary between the tip 26 and the extension portion 23 was irradiated with a laser beam emitted from the work head of a laser welder (not shown). Various samples were prepared so that their melt zones contained a total content of Ir, Ru, and Rh (components of the tip 26) of 50 wt% or more and contained approximately the same total content of Ir, Ru, and Rh, and were fabricated to differ in B / A by changing the spot diameter of the laser beam, the laser power, etc.

[0038] A durability test was conducted on each of the prepared samples. In the durability test, a heat cycle of 2 minutes of heat application to the tips 26, extension sections 23, and fusion zones by a gas burner, followed by 1 minute of radiation cooling, was repeated 1000 times. During heating in each cycle, the temperature of the extension section 23 reached 1000°C. Each sample was cut to obtain a section containing the central axis C; the section was polished to prepare a polished surface; the polished surface was imaged using a metallograph; and the image was measured by image processing for the length B of the interface between the fusion zone and the extension section, the distance A, and the percentage (%) of the length of the crack in a direction perpendicular to the central axis C to the distance A.The length B was obtained by summing the linear distances between adjacent equally dividing points of 100 points equally dividing the interface.

[0039] Fig. Figure 5B is a correlation diagram illustrating the relationship between B / A and the crack length at the interface. The horizontal axis represents B / A, and the vertical axis represents the percentage (%) of the crack length. When the percentage (%) of the crack length is 100, this indicates a fracture of the interface. As shown in Fig.As shown in Figure 5B, it was found that when B / A was 1.2 or more, the percentage (%) of the crack length was significantly reduced. In some of the samples that satisfied the comparative expression B / A ≥ 1.2, the interface did not have a protrusion. From this example, it is obvious that by satisfying the comparative expression B / A ≥ 1.2, interface fracture, which might otherwise occur due to crack development, can be avoided.

[0040] The present example is the case where the melt zone contains the noble metal components of the tip 26 in an amount of 50 wt% or more. However, even in a case where the melt zone contained the noble metal components of the tip 26 in an amount of less than 50 wt%, a similar tendency to that in the present example was observed when the comparative expression B / A ≥ 1.2 was satisfied.

[0041] Although the present invention has been described with reference to the above embodiments, the present invention is not limited thereto, and various improvements and modifications are possible without departing from the gist of the invention.

[0042] The above embodiments were described with reference to the extension portions 23 and 43 and the tips 26 and 46 having a circular columnar shape or a truncated cone shape; however, the present invention is not limited thereto. The extension portion and the tip may have a polygonal columnar shape.

[0043] The above embodiments were described with reference to the case where the center axis C of the tips 26 and 46 coincides with the axial line O of the spark plug 10; however, the present invention is not limited thereto. The axial line O of the spark plug 10 and the center axis C of the tip need not coincide.

[0044] Although not described in the above embodiments, a great effect is achieved when the fused zone 25, 45, or 71 contains the noble metal components of the tip 26 or 46 in an amount of 50 wt% or more. This is because: Since the difference in the linear expansion coefficient between the fused zone 25, 45, or 71 and the extending portion 23 or 43 increases with the degree of fusion of the tip 26 or 46 to form the fused zone 25, 45, or 71, the thermal stress generated in the interface 50, 60, or 72 between the fused zone 25, 45, or 71 and the extending portion 23 or 43 increases. In particular, even when the amount of the noble metal components of the tip 26 or 46 contained in the fused zone is less than 50 wt%.-%, the effect described in the sections of the embodiments results because thermal stresses continue to be generated at the interface between the melting zone and the extension portion due to the presence of a difference in the linear expansion coefficient therebetween.

[0045] The above embodiments were described with reference to interfaces 50, 60, 72 with protrusions 53, 63, 65, 75, 77, 79, and 81; however, the present invention is not limited thereto. The presence of one or more protrusions at the interface is not essential. Even if the interface has no protrusions, if the relational expression B / A ≥ 1.2 is satisfied, the stress generated at the interface is released, thereby restraining the separation at the interface.

[0046] The above embodiments were described with reference to the radiation of a laser beam for forming the melting zones 25, 45, and 71; however, the present invention is not limited thereto. Of course, the melting zone may be formed by the radiation of other high-energy beams, such as an electron beam.

[0047] The above embodiments were described with reference to the case where both the center electrode 20 and the ground electrode 40 satisfy the relational expression B / A ≥ 1.2; however, the present invention is not limited to this. It is sufficient that either the center electrode or the ground electrode satisfies the above relational expression. This is because in the electrode that satisfies the above relational expression, separation at the interface can be restricted. Description of reference symbols 10 Spark plug 22, 41 Electrode base metal 23, 43 extension section 24, 44 front end section of the extension section 25, 45, 71 melting zone 25a, 45a, 71a outline 26, 46 peak 27, 47 rear end section of the tip 50, 60, 72 interface 51, 61, 73 an end (end) 52, 62, 74 the other end (end) 53, 63, 65, 75, 77, 79, 81 lead 54, 64, 76 first vertex 55, 67, 83 straight line 56, 84 intersection 58, 68 first area 59, 69 second area 66, 78 second vertex A Distance C Central axis

Claims

[1] Spark plug (10), comprising: a tip (26, 46) extending in a first direction directed from a rear end side to a front end side; and an electrode base metal (22, 41) having an extension portion (23, 43) extending in the first direction, the front end portion of which is connected to a rear end portion of the tip (26, 46) by a melting zone (25, 45, 71), wherein in a section taken along the first direction and including a central axis (C) of the tip (26, 46) extending in the first direction, A and B satisfy a relational expression B / A ≥ 1.2, wherein, in a case where two ends (51, 52, 61, 62, 72, 73) of a line indicating an interface (50, 60, 72) between the extending portion (23, 43) and the melting zone (25, 45, 71) are arranged at the same position with respect to the first direction, A is a linear distance between the two ends, or, in a case where one of the two ends (51, 52, 61, 62, 72, 73) is arranged in front of the other end with respect to the first direction, A is a distance on a straight line (55, 67, 83) passing the one end and extending perpendicular to the central axis (C), from the one end to an intersection point (56, 84) between the straight line (55, 83) and an outline (25a, 71a) of the melt zone (25, 71) on one side towards the other end, B is a length of the line indicating the interface, wherein the line indicating the boundary surface (50, 60, 72) has at least one projection (53, 63, 65, 75, 77, 79, 81) projecting toward the front end side, and wherein a first vertex (54, 64, 76) located furthest forward among the vertices of the projections (53, 63, 65, 75, 77, 79, 81) is present in a first region (58, 68) of the line indicating the interface (50, 60, 72), the first region being arranged towards one end with respect to the central axis (C), or in a second region (59, 69) of the line indicating the interface (50, 60, 72), the second region being arranged towards the other end with respect to the central axis (C). [2] Spark plug (10) according to claim 1, wherein the line indicating the interface (60, 72) has two or more projections (63, 65, 75, 77, 79, 81), and in the first region (58, 68) or the second region (59, 69) in which the first vertex (64, 76) is not present, there is a second vertex (66, 78) which is located at the same position as the first vertex (64, 76) with respect to the first direction or is located at the second foremost position next to the first vertex (64, 76) with respect to the first direction. [3] Spark plug (10) according to one of claims 1 or 2, wherein in each section containing the central axis (C), the relational expression B / A ≥ 1.2 is satisfied.

Images