SPARK PLUG

Abstract

A spark plug (10) includes: a metal shell (16); a center electrode (13) held by the metal shell (16) in an insulating manner; a ground electrode (17) having a first end portion (28) and a second end portion (29), the ground electrode (17) being connected to the metal shell (16) at the first end portion (28) and extending to the second end portion (29); and a chip (20) disposed on an opposing surface (22) in the ground electrode (17) opposite a tip end surface (14) of the center electrode (13). The opposing surface (22) includes an uneven surface (31) including an uneven portion (32) extending in a first direction (D1), and in the uneven surface (31), a maximum height (H), which is a distance between a highest portion and a lowest portion, is 3 µm or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a spark plug comprising a ground electrode with a plate. 2. Description of the technology in question

[0002] Document JP 2019 - 125569 A describes a spark plug comprising a ground electrode with a plate and further comprising a center electrode electrically insulated from the ground electrode, and a discharge occurs mainly between the plate of the ground electrode and the center electrode. SUMMARY OF THE INVENTION

[0003] When there is a gas flow in a combustion chamber, a discharge path extends downstream due to the gas flow, and the discharge cannot be maintained depending on the circumstances.

[0004] Accordingly, the present invention has been made to solve the above-mentioned problem, and it is an object of the present invention to provide a spark plug capable of facilitating the maintenance of discharge.

[0005] To achieve the object, a spark plug according to a first aspect comprises: a metal shell; a center electrode held by the metal shell in an insulating manner; a ground electrode having a first end portion and a second end portion, the ground electrode being connected to the metal shell at the first end portion and extending to the second end portion; and a chip disposed on an opposing surface in the ground electrode opposite to a tip end surface of the center electrode. The opposing surface includes an uneven surface including an uneven portion extending in a first direction, and in the uneven surface, a maximum height, which is a distance between a highest portion and a lowest portion, is 3 µm or more.

[0006] According to a second aspect, in the first aspect, the first direction is a longitudinal direction of the ground electrode.

[0007] According to a third aspect, the uneven surface in the first or second aspect also includes an uneven portion extending in a second direction intersecting the first direction.

[0008] According to a fourth aspect, the ground electrode in any one of the first to third aspects comprises a base material and a metal film covering the base material, wherein the thermal conductivity of the metal film is higher than the thermal conductivity of the base material, and the uneven surface is provided in a portion of the base material not covered with the metal film.

[0009] According to a fifth aspect, the maximum height of the uneven surface in any one of the first to fourth aspects is 53 µm or less.

[0010] According to a sixth aspect, in any one of the first to fifth aspects, when a length of the opposing surface is divided into three in a longitudinal direction of the opposing surface and the opposing surface is divided into a first portion, a second portion, and a third portion in this order from the second end portion to the first end portion of the ground electrode, the first portion, the second portion, and the third portion include the uneven surface, and a boundary of the uneven surface is available on the third portion.

[0011] According to a seventh aspect, in any one of the first to fifth aspects, when a length of the opposing surface is halved in a longitudinal direction of the opposing surface and the opposing surface is divided into a fourth portion and a fifth portion in this order from the second end portion to the first end portion of the ground electrode, the fourth portion includes the uneven surface, and a boundary of the uneven surface is present on the fourth portion.

[0012] According to an eighth aspect, in any one of the first to fifth aspects, when a length of the opposing surface is divided into three in a longitudinal direction of the opposing surface and the opposing surface is divided into a first portion, a second portion, and a third portion in this order from the second end portion to the first end portion of the ground electrode, the first portion includes the uneven surface, and a boundary of the uneven surface is present on the first portion.

[0013] According to a ninth aspect, in any one of the first to eighth aspects, the uneven surface is provided only on the opposite surface.

[0014] According to a tenth aspect, the uneven surface in any one of the first to ninth aspects includes a region in which five or more depressed portions are present and protruding portions are present that do not intersect.

[0015] According to the present invention, the chip is arranged on the opposite surface in the ground electrode opposite to the tip end surface of the center electrode, and the opposite surface has the uneven surface.

[0016] The maximum height, that is, the distance between the highest and lowest portions of the uneven surface, is 3 µm or more. Even if a discharge starting point of the ground electrode is moved downstream and located outside the wafer, since a discharge path extends downstream due to a flow, such a discharge starting point can easily form on the uneven portion of the uneven surface, and the discharge can be easily maintained. BRIEF DESCRIPTION OF THE CHARACTERS

[0017] Embodiments are described with reference to the figures, without being limited thereto. Fig. 1 is a half-sectional view of a spark plug according to a first embodiment. Fig. 2 is a sectional view of a center electrode and a ground electrode. Fig. 3 is a perspective view of the ground electrode. Fig. 4 is a plan view of the ground electrode, with the Fig. 3 The part marked IV is enlarged. Fig. 5 is a sectional view of the ground electrode along the line VV in Fig. 4. Fig. 6 is a perspective view of a ground electrode of a spark plug according to a second embodiment. Fig. 7 is a plan view of the ground electrode, with the Fig. 6 part marked VII is enlarged. Fig. 8 is a partial sectional view of a spark plug according to a third embodiment. Fig. 9 is a front view of the ground electrode when it is in the direction of arrow IX in Fig. 8 is considered. Fig. 10 is a partial sectional view of a spark plug according to a fourth embodiment. Fig. 11 is a partial sectional view of a spark plug according to a fifth embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 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 an embodiment, wherein the axial line X represents the boundary. The lower side on the paper sheet of Fig. 1 is called the front end side of the spark plug 10, and the upper side on the paper sheet of Fig. 1 is called the rear end side of the spark plug 10 (the same applies to the Fig. 2, 3 and 8 to 11).

[0019] How Fig. As shown in Figure 1, the spark plug 10 includes an insulator 11, a center electrode 13 held by the insulator 11, a metal shell 16 disposed on an outer periphery of the insulator 11, and a ground electrode 17 connected to the metal shell 16. The insulator 11 is a substantially cylindrical member made of ceramics such as alumina, with excellent mechanical properties and excellent high-temperature insulation performance. The insulator 11 has an axial hole 12 along the axial line X.

[0020] The center electrode 13 is a rod-shaped conductor disposed in the axial hole 12 of the insulator 11 and extending along the axial line X. The center electrode 13 includes a core material containing copper as a main component and a cylindrical metal with a bottom covering the core material. The core material may be omitted. As an example of the metal forming the center electrode 13, a Ni-based alloy is cited. A tip end of the center electrode 13 protrudes from the insulator 11. Although a tip containing a noble metal is disposed in the tip end of the center electrode 13 in the present embodiment, the tip may be omitted.

[0021] In the axial hole 12, the center electrode 13 is electrically connected to a metal terminal 15. The metal terminal 15 is a rod-shaped member to which an ignition system (not shown) is connected, and the metal terminal 15 is made of a conductive metallic material (e.g., low-carbon steel). The front end of the metal terminal 15 is inserted into the axial hole 12, and the metal terminal 15 is fixed to the rear end of the insulator 11, with a rear end of the metal terminal 15 protruding from the insulator 11.

[0022] The metal shell 16 is fixed to the outer periphery of the insulator 11. An external thread, which connects to a plug hole of an engine (not shown), is provided on the metal shell 16. The ground electrode 17 is connected to the metal shell 16. The ground electrode 17 is a conductor extending from the metal shell 16 to the axial line X. A core material containing copper as a main component is embedded in the ground electrode 17. The core material may be omitted.

[0023] Fig. 2 is a sectional view of the center electrode 13 and the ground electrode 17. Fig. 2 shows a section of the center electrode 13 and a section of the ground electrode 17. Fig. 3 is a perspective view of the ground electrode 17. Fig. 3 shows a part of the spark plug 10 without the center electrode 13, the metal shell 16 and other parts.

[0024] How Fig. As shown in FIG. 2, the ground electrode 17 includes a base material 18 made of a metal, a chip 20 made of a different metal than the base material 18, and a welding portion 21 that joins the chip 20 to the base material 18. In the present embodiment, the base material 18 is a bent rod whose section has a quadrilateral shape, and the chip 20 has a disk shape. A part of the welding portion 21 is provided between an outer periphery of the chip 20 and the base material 18.

[0025] A first element of the elements contained in the base material 18, which has the highest content, is different from a second element of the elements contained in the platelet 20, which has the highest content. The first element contained in the base material 18 is, for example, Ni, and the second element contained in the platelet 20 is, for example, a type of precious metal such as Pt, Ir, and Ru. The welding portion 21, into which the base material 18 and the platelet 20 are fused, contains the first element and the second element.

[0026] How Fig. 3, the ground electrode 17 includes an opposing surface 22 corresponding to a tip end surface 14 of the center electrode 13 (see Fig. 2), a rear surface 23 arranged on the other side of the opposite surface 22, a side surface 24 connecting the opposite surface 22 and the rear surface 23, a side surface 25 arranged on the other side of the side surface 24 and connecting the opposite surface 22 and the rear surface 23, and a distal end surface 26 connected to the opposite surface 22, the rear surface 23, and the side surfaces 24 and 25. The opposite surface 22, the rear surface 23, and the side surfaces 24 and 25 extend from the distal end surface 26 to an end surface 27. The end surface 27 is connected to the metal housing 16 (see Fig. 1).

[0027] The ground electrode 17 includes a first end portion 28 which is connected to the metal housing 16 (see Fig. 1) and has a linear shape, and a second end portion 29 containing the distal end surface 26 and having a linear shape. In the present embodiment, an arcuately bent portion 30 is provided between the first end portion 28 and the second end portion 29. The plate 20 is arranged on the second end portion 29 on the opposite surface 22.

[0028] The ground electrode 17 is provided with a metal film 19 covering a portion of the base material 18 (see Fig. 2). The metal material from which the metal film 19 is formed is different from the metal material from which the base material 18 is formed. The metal film 19 contains at least one or more types selected from elements such as Zn, Cr, Fe, Cu, and Ag. The thermal conductivity of the metal film 19 is higher than the thermal conductivity of the base material 18. There is no metal film 19 on the opposite surface 22. The metal film 19 is entirely located on the side surfaces 24 and 25 and the back surface 23 of the ground electrode 17.

[0029] Fig. 4 is a plan view of the opposite surface 22 of the ground electrode 17, while the Fig. 3 is enlarged. The opposing surface 22 includes an uneven surface 31 having uneven portions 32. The uneven portions 32 extend in a first direction D1 and are spaced apart in a second direction D2 orthogonal to the first direction D1. In the present embodiment, the uneven portions 32 are entirely provided in the opposing surface 22 except for locations where the chip 20 and the welding portion 21 are provided. The first direction D1 is a longitudinal direction of the ground electrode 17, and the second direction D2 is a transverse direction of the ground electrode 17. The longitudinal direction of the ground electrode 17 is the same as a direction in which a line connecting the center of the first end portion 28 and the center of the second end portion 29 along the bent portion 30 extends.The expression “the uneven portion 32 extends in the first direction D1” means that an angle of the uneven portion 32 relative to the line connecting the center of the first end portion 28 and the center of the second end portion 29 and extending along the bent portion 30 is smaller than 45°.

[0030] Fig. 5 is a sectional view of the ground electrode 17 (the base material 18) taken along the line VV in Fig. 4. The uneven portion 32 includes a depressed portion 33 and a projecting portion 34 extending in the first direction D1 (the direction perpendicular to the paper sheet of Fig. 5), and the recessed portion 33 and the projecting portion 34 are adjacent to each other. The uneven surface 31 (see Fig. 4) contains an area (area IV in Fig. 3), in which there are five or more recessed portions 33 and protruding portions 34 which do not intersect.

[0031] On the uneven surface 31 (see Fig. 5) The maximum height, which is a distance H between the highest portion (the highest protruding portion 34) and the lowest portion (the lowest depressed portion 33) of the uneven portions 32, is 3 μm or more and 53 μm or less. The maximum height is a value prescribed in JIS B 0601:2013 and is the sum of a maximum peak height value and a maximum valley depth value of the contour curve of the uneven surface 31 in a reference length (e.g., 2.5 mm) in the second direction D2. The contour curve of the uneven surface 31 can be obtained by a surface roughness meter. A width W between adjacent ones of the uneven portions 32 is preferably 50 μm or less.

[0032] A method for manufacturing the spark plug 10 will be described by way of example. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11, and the axial hole 12 is then filled with powder of a raw material such as conductive glass. The metal terminal 15 is inserted into the axial hole 12, and while heating the insulator 11, the raw material powder is then axially compressed by the metal terminal 15. Thus, the center electrode 13 and the metal terminal 15 are electrically connected. Next, the metal shell 16, to which the ground electrode 17 has been connected in advance, is mounted on the insulator 11, and the ground electrode 17 is then bent to obtain the spark plug 10.

[0033] Before assembly with the insulator 11, the metal shell 16 to which the ground electrode 17 is connected undergoes barrel plating treatment, primarily to improve corrosion resistance. The metal film 19 is formed on the metal shell 16 and the ground electrode 17 by the barrel plating treatment. Before the plate 20 is welded to the opposing surface 22 of the ground electrode 17 and before the ground electrode 17 is bent, the opposing surface 22 is irradiated with a laser beam in the form of a flat surface to remove the metal film 19 located on the opposing surface 22.

[0034] For example, after the irradiation position of the laser beam is continuously moved in the first direction D1 from one end to the other end of the opposing surface 22 (from the distal end surface 26 to the end surface 27), the irradiation position of the laser beam is shifted in the second direction D2 at the end of the opposing surface 22 by an amount corresponding to one beam diameter, and this continuous movement of the irradiation position of the laser beam in the first direction D1 is repeated again to remove the metal film 19. As marks indicating the irradiation of the laser beams onto the ground electrode 17, the uneven portions 32 extending in the first direction D1 are formed in a surface of the base material 18 of the opposing surface 22.

[0035] The weld portion 21 is formed, for example, by laser welding or resistance welding, on the opposite surface 22 from which the metal film 19 has been removed, and the chip 20 is bonded thereto. The uneven portions 32 near the location where the chip 20 is disposed are fused into the weld portion 21, and the weld portion 21 formed in the uneven surface 31 is adjacent to the respective uneven portions 32. After assembling the metal shell 16 with the insulator 11, the ground electrode 17 is bent to position the chip 20 opposite the tip end surface 14 of the center electrode 13.

[0036] When the spark plug 10 is installed in the engine (not shown), the tip end face 14 of the center electrode 13 and the ground electrode 17 are exposed in a combustion chamber. Discharge occurs between the center electrode 13 and the ground electrode 17 when insulation formed by a gap between the center electrode 13 and the ground electrode 17 is broken. In the ground electrode 17, a portion a short distance from the center electrode 13 or a protruding portion is likely to be a starting point of discharge, and thereby a discharge path is likely to be formed between the tip end face 14 of the center electrode 13 and the chip 20.

[0037] During gas flow in the combustion chamber, a discharge starting point of the ground electrode 17 can move from the chip 20 to the vicinity of the chip 20 positioned downstream in the gas flow because the discharge path extends downstream due to the gas flow. Since the opposing surface 22 includes the uneven surface 31 near the chip 20 and the maximum height of the uneven surface 31 is 3 μm or more, a discharge starting point located outside the chip 20 is held on the uneven portions 32 of the uneven surface 31 and thus hardly moves therefrom. A discharge starting point is easily formed on the uneven portions 32, and the discharge can thereby be easily maintained.

[0038] The maximum height of the uneven surface 31 is preferably 53 μm or less. This is because the mechanical strength of the ground electrode 17 can be ensured by preventing the deepest portion of the uneven portions 32 from becoming a starting point for the destruction of the ground electrode 17.

[0039] The gas flow moving from the first end portion 28 to the second end portion 29 of the ground electrode 17 is likely to be obstructed by the first end portion 28 and the bent portion 30 of the ground electrode 17, and the flow velocity of the gas flow decreases as a result. On the other hand, a gas flow moving from the side surface 24 toward the side surface 25 of the ground electrode 17 is not obstructed by anything, and the flow velocity of such a gas flow hardly decreases as a result. Therefore, when a gas flow moves from the side surface 24 toward the side surface 25 of the ground electrode 17, a discharge starting point of the ground electrode 17 is located outside the plate 20 and is slightly moved on the uneven surface 31 in the transverse direction of the opposite surface 22 toward the side surface 25.Since the uneven portions 32 extend in the longitudinal direction of the ground electrode 17, a discharge starting point can be easily maintained on the uneven portions 32 when moving in the transverse direction of the opposing surface 22. A discharge starting point is easily formed on the uneven portions 32, and the discharge can therefore be more easily maintained.

[0040] Since the metal film 19 is completely present on the side surfaces 24 and 25 and the back surface 23 of the ground electrode 17 and continuously from the second end portion 29 to the first end portion 28 of the ground electrode 17, compared with the case where no metal film 19 is present, the heat of the second end portion 29 heated by the discharge or by the combustion of fuel is easily transferred from the first end portion 28 through the metal case 16 due to the heat conduction of the base material 18 and the metal film 19. Fig. 1) to the engine (not shown). The second end portion 29 is slightly cooled, which can reduce overheating of the plate 20, which can lead to an improvement in the wear resistance of the plate 20.

[0041] A second embodiment is described with reference to the Fig. 6 and Fig. 7. In the first embodiment, the ground electrode 17 is described, which includes the uneven surface 31 including the uneven portions 32 extending in the first direction D1. In contrast, in the second embodiment, a ground electrode 40 is described, which includes an uneven surface 41 with uneven portions 42 that also extend in the second direction D2 intersecting the first direction D1. The same parts as in the first embodiment are denoted by the same reference numerals, and the description of these parts will be omitted below.

[0042] Fig. Fig. 6 is a perspective view of the ground electrode 40 of a spark plug 10 according to the second embodiment. The ground electrode 40 is arranged in place of the ground electrode 17 of the spark plug 10 described in the first embodiment. The ground electrode 40 is provided with a metal film 19 covering a portion of a base material 18 (see Fig. 2). The metal film 19 is completely applied to a rear surface 23 of the ground electrode 40. No metal film 19 is provided on an opposite surface 22 and the side surfaces 24 and 25.

[0043] Fig. 7 is a plan view of the opposite surface 22 of the ground electrode 40, wherein the Fig. 6, the part labeled VII is shown enlarged. The opposite surface 22 contains the uneven surface 41 including the uneven sections 42. The side surfaces 24 and 25 also each contain the uneven surface 41 with the uneven sections 42. The uneven sections 42 extend in the first direction D1 and in the second direction D2 perpendicular to the first direction D1. The uneven sections 42 are also markings that indicate the irradiation of the laser beams onto the opposite surface 22.

[0044] In the present embodiment, the uneven portions 42 are entirely provided in the opposing surface 22 and the side surfaces 24 and 25, except for the positions where a chip 20 and a weld portion 21 are provided. The expression "the uneven portions 42 extend in the first direction D1 and the second direction D2" means that an angle formed by the intersecting uneven portions 42 is 45° or more and 135° or less. The maximum height of the uneven surface 41 is 3 μm or more.

[0045] Since the uneven portions 42 provided in the opposing surface 22 of the ground electrode 40 extend in the longitudinal direction and the transverse direction of the ground electrode 40, a discharge starting point can be easily maintained on the uneven portions 42 even when a discharge starting point moves from the wafer 20 to any location on the opposing surface 22 due to a flow in the combustion chamber. A discharge starting point is easily formed on the uneven portions 42, and the discharge can thereby be more easily maintained.

[0046] Since the uneven portions 42 are also present in the side surfaces 24 and 25 of the ground electrode 40, a discharge easily occurs even between a high portion of the uneven portions 42 in the side surfaces 24 and 25 and a center electrode 13. A starting point of the discharge is easily formed at the uneven portions 42 in the side surfaces 24 and 25, and the discharge can therefore be more easily maintained.

[0047] Since the metal film 19 in the ground electrode 40 is provided entirely on the back surface 23 and continuously from a second end portion 29 to a first end portion 28 of the ground electrode 40, the second end portion 29 is easily cooled due to heat conduction between the base material 18 and the metal film 19, compared to the case where no metal film 19 is provided. Overheating of the chip 20 can be reduced, and the wear resistance of the chip 20 can be improved.

[0048] The third to fifth embodiments are described with reference to the Fig. 8 to 11. In the first and second embodiments, the case where each of the uneven surfaces 31 and 41 is entirely provided in the opposing surface 22 of a corresponding ground electrode 17 and 40, except for the locations of the chip 20 and the welding portion 21, is described. In contrast, in the third to fifth embodiments, the case where an uneven surface 31 is provided in a portion of an opposing surface 22 is described. In the third embodiment, the same parts as in the first embodiment or the second embodiment are denoted by the same reference numerals, and their description will be omitted below.

[0049] Fig. 8 is a partial sectional view of a spark plug 50 according to the third embodiment. In Fig. 8, the rear end side of an insulator 11, a center electrode 13 and a metal case 16 is not shown (the same applies to the Fig. 10 and Fig. 11). A ground electrode 51 of the spark plug 50 is connected to the metal shell 16 via a welded portion 52. The ground electrode 51 contains the uneven surface 31 only in the opposite surface 22. In a rear surface 23 (see Fig. 3) and the side surfaces 24 and 25 of the ground electrode 51, a metal film 19 completely covers a base material 18.

[0050] When a creepage distance of the opposing surface 22 of the ground electrode 51 (the length of the opposing surface 22 in the longitudinal direction) between a corner 53 where the opposing surface 22 intersects a distal end surface 26 and an end 54 of the welding portion 52 is divided into three, and the opposing surface 22 is divided into a first portion 55, a second portion 56, and a third portion 57 in this order from the corner 53 toward the end portion 54, a chip 20 is provided on the first portion 55. The first portion 55, the second portion 56, and the third portion 57 each include the uneven surface 31. A boundary 58 of the uneven surface 31 is present on the third portion 57. In the present embodiment, the metal film 19 is provided on the third portion 57 adjacent to the uneven surface 31 and is in contact with the boundary 58 of the uneven surface 31 and with the end 54.

[0051] Fig. 9 is a front view of the ground electrode 51 in the direction of arrow IX in Fig. 8. In Fig. 9, the distal end side of the ground electrode 51 is not shown, but a portion of the metal shell 16. In the boundary 58 of the uneven surface 31, an end closer to the side surface 24 is positioned closer to the welding portion 52 than an end closer to the side surface 25. The expression "the boundary 58 of the uneven surface 31 is present on the third portion 57 (see Fig. 8)” means that a portion in the boundary 58 of the uneven surface 31 closest to the welding portion 52 is present on the third portion 57.

[0052] The description is again made with reference to Fig. 8. Since the first portion 55, the second portion 56, and the third portion 57 of the opposing surface 22 include the uneven surface 31, when a discharge starting point of the ground electrode 51 moves from the chip 20 to the vicinity of the chip 20 due to a gas flow in the combustion chamber, such a discharge starting point is easily formed on the uneven surface 31. Thus, the discharge can be easily maintained.

[0053] Since the boundary 58 of the uneven surface 31 is present at the third portion 57, the length from the corner 53 of the opposing surface 22 to the boundary 58 of the uneven surface 31 can be shortened compared to the case where the uneven surface 31 is present up to the end 54 of the weld portion 52. This can reduce the bending stress acting on the boundary 58 due to the load applied to the ground electrode 51 by the ignition and combustion of fuel, thereby improving the durability of the ground electrode 51.

[0054] Since the metal film 19 is present on the third portion 57 of the opposing surface 22, the first portion 55 is slightly cooled due to the heat conduction of the base material 18 and the metal film 19, compared to the case where no metal film 19 is present on the opposing surface 22. Overheating of the chip 20 can be reduced, and the wear resistance of the chip 20 can thereby be improved.

[0055] Since the ground electrode 51 includes the uneven surface 31 only in the opposing surface 22, the cross-sectional area of the ground electrode 51 can be increased compared to the case where the rear surface 23 and the side surfaces 24 and 25 of the ground electrode 51 also include the uneven surface 31. The bending stress of the ground electrode 51 can be reduced, thus improving the service life of the ground electrode 51.

[0056] Fig. 10 is a partial sectional view of a spark plug 60 according to the fourth embodiment. In the fourth embodiment, the same parts as in the first, second, or third embodiments are denoted by the same reference numerals, and their descriptions will be omitted below.

[0057] A ground electrode 61 of the spark plug 60 contains the uneven surface 31 only on the opposite surface 22. Both on the rear surface 23 (see Fig. 3) as well as on the side surfaces 24 and 25 of the ground electrode 61, a metal film 19 completely covers the base material 18. When a creepage distance of the opposing surface 22 of the ground electrode 61 (the length of the opposing surface 22 in the longitudinal direction) between a corner 53 of the opposing surface 22 and an end 54 of a welding portion 52 is halved, and the opposing surface 22 is divided into a fourth portion 62 and a fifth portion 63 in this order from the corner 53 to the end 54, the fourth portion 62 is provided with a plate 20 and includes the uneven surface 31. A boundary 64 of the uneven surface 31 is present on the fourth portion 62. In the present embodiment, the metal film 19 is provided on the fourth portion 62 and the fifth portion 63 adjacent to the uneven surface 31 and is in contact with the boundary 64 of the uneven surface 31 and with the end 54.

[0058] Since the fourth portion 62 of the opposing surface 22 includes the uneven surface 31, when a discharge starting point of the ground electrode 61 moves from the chip 20 to the vicinity of the chip 20 due to a flow in the combustion chamber, such a discharge starting point is easily formed on the uneven surface 31. Thus, the discharge can be easily maintained.

[0059] Since the boundary 64 of the uneven surface 31 is provided on the fourth portion 62, the bending stress acting on the boundary 64 due to the load applied to the ground electrode 61 by ignition and combustion of fuel can be reduced compared to the case where the boundary 64 is provided on the fifth portion 63. This can improve the durability of the ground electrode 61.

[0060] Since the metal film 19 is present on the fourth portion 62 and the fifth portion 63 of the opposing surface 22, the fourth portion 62 is easily cooled due to heat conduction between the base material 18 and the metal film 19, compared to the case where no metal film 19 is present on the opposing surface 22. Overheating of the chip 20 can be reduced, and the wear resistance of the chip 20 can thereby be improved.

[0061] Fig. 11 is a partial sectional view of a spark plug 70 according to the fifth embodiment. In the fifth embodiment, the same parts as those described in the first embodiment, the second embodiment, or the third embodiment are denoted by the same reference numerals, and the description thereof will be omitted below.

[0062] A ground electrode 71 of the spark plug 70 has the uneven surface 31 only in the opposite surface 22. Both in the rear surface 23 (see Fig. 3) and the side surfaces 24 and 25 of the ground electrode 71, a metal film 19 completely covers a base material 18. A first portion 55 of the ground electrode 71 includes the uneven surface 31. A boundary 72 of the uneven surface 31 is present on the first portion 55. In the present embodiment, the metal film 19 is provided on the first portion 55, a second portion 56, and a third portion 57 adjacent to the uneven surface 31 and is in contact with the boundary 72 of the uneven surface 31 and with one end 54.

[0063] Since the first portion 55 of the opposing surface 22 includes the uneven surface 31, a discharge starting point of the ground electrode 71, when moved from a plate 20 to the vicinity of the plate 20 due to a flow in the combustion chamber, can be easily formed on the uneven surface 31. Thus, the discharge can be easily maintained.

[0064] Since the boundary 72 of the uneven surface 31 is present on the first portion 55, the bending stress acting on the boundary 72 due to the load applied to the ground electrode 71 by ignition and combustion of fuel can be reduced compared to the case where the boundary 72 is present on the second portion 56 or the third portion 57. Thus, the durability of the ground electrode 71 can be improved.

[0065] Since the metal film 19 is present on the first portion 55, the second portion 56, and the third portion 57 of the opposing surface 22, the first portion 55 is easily cooled due to the heat conduction of the base material 18 and the metal film 19, compared to the case where no metal film 19 is present on the opposing surface 22. Overheating of the chip 20 can be reduced, thereby improving the wear resistance of the chip 20.

[0066] Although the present invention has been described so far with reference to the embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that various improvements and modifications can be made without departing from the spirit of the present invention.

[0067] Although the case where the plate 20 has a disc shape is described in the embodiments, this is not the only option. The plate 20 can be suitably set in a shape such as a quadrangular prism, a polygonal prism other than a quadrangular prism, or a truncated cone.

[0068] Although the embodiments describe the case where the base material 18 of the ground electrodes 17, 40, 51, 61, and 71 is a curved rod whose cross-section has a quadrangular shape, this is not the only option. Examples of the shape of the base material 18 include, in addition to a curved shape, a linear shape. Examples of the cross-section shape of the base material 18 include, in addition to a quadrilateral, a circle, an ellipse, and a semicircle.

[0069] Although the embodiments describe the case where the welded portion 21 is provided between the outer periphery of the chip 20 and the base material 18, and a bottom surface of the chip 20 and the base material 18 are in contact with each other, this is not the only possibility. The welded portion 21 can be formed from the outer periphery to the bottom surface of the chip 20 by laser beam welding. Furthermore, when the welded portion 21 is formed by resistance welding, the welded portion 21 can be provided between the bottom surface of the chip 20 and the base material 18.

[0070] Although the embodiments describe the case where the uneven portions 32 extend in the longitudinal direction of each of the ground electrodes 17, 51, 61, and 71, this is not the only possibility. The first direction in which the uneven portions 32 extend may be the transverse direction of each of the ground electrodes 17, 51, 61, and 71. The expression "the uneven portions 32 extend in the transverse direction of each of the ground electrodes 17, 51, 61, and 71" means that the angle of each of the uneven portions 32 relative to a perpendicular drawn perpendicular to an edge of the opposing surface 22 extending in the longitudinal direction of each of the ground electrodes 17, 51, 61, and 71 is less than 45°.The flow moving in the longitudinal direction of each of the ground electrodes 17, 51, 61 and 71 tends to be slower in flow velocity than the flow moving in the transverse direction of each of the ground electrodes 17, 51, 61 and 71, but can facilitate the maintenance of the discharge because, when a discharge starting point is moved from the plate 20 to the vicinity of the plate 20 due to the flow, such a discharge starting point is easily formed on the uneven portions 32, and the discharge can thereby be easily maintained.

[0071] Although the first to third embodiments describe the case where, in each of the ground electrodes 17, 40, and 51, a corresponding type of the uneven portions 32 and the uneven portions 42 are provided entirely in the opposing surface 22 except for the locations where the chip 20 and the welding portion 21 are arranged, this is not the only possibility. The uneven surface 31 and / or the uneven surface 41 may be provided only in the second end portion 29 in the opposing surface 22, or only in a portion of the opposing surface 22 from the second end portion 29 to the bent portion 30 (a portion other than the first end portion 28). The metal film 19 may be provided on a portion of the opposing surface 22 other than the uneven surfaces 31 and 41.In this case, the uneven surface 31 and / or the uneven surface 41 may be adjacent to the metal film 19, or a part not including the uneven portion 32 or 42 may be provided between the uneven surface 31 and / or the uneven surface 41 and the metal film 19.

[0072] Although the case where the metal film 19 is provided on the back surface 23 and the side surfaces 24 and 25 of each of the ground electrodes 17, 51, 61, and 71 is described in the first embodiment, the third embodiment, the fourth embodiment, and the fifth embodiment, this is not the only possibility. For example, the metal film 19 on the back surface 23 and the side surfaces 24 and 25 may be omitted entirely, the metal film 19 on the back surface 23 may be omitted, or the metal film 19 on one or both of the side surfaces 24 and 25 may be omitted. That is, at least a portion of the metal film 19 of each of the ground electrodes 17, 51, 61, and 71 may be omitted.

[0073] Although the case where the metal film 19 is provided on the back surface 23 but not on the side surface 24 or 25 of the ground electrode 40 is described in the second embodiment, this is not the only possibility. The metal film 19 of the back surface 23 may be omitted, or the metal film 19 may be provided on one of the side surfaces 24 and 25 or on both side surfaces.

[0074] Although the second embodiment describes the case where the uneven portions 42 are entirely provided in the side surfaces 24 and 25 of the ground electrode 40, this is not the only possibility. Instead of the uneven portions 42, the uneven portions 32 may also be entirely provided in the side surfaces 24 and 25. Furthermore, the uneven surface 31 and / or the uneven surface 41 may be provided in the side surface 24, and the metal film 19 may be provided on the side surface 25. Alternatively, the metal film 19 may be provided on the side surface 24, and the uneven surface 31 and / or the uneven surface 41 may be provided in the side surface 25.When the uneven surface 31 and / or the uneven surface 41 is provided in one of the side surfaces 24 or 25, only the second end portion 29 in a corresponding one of the side surfaces 24 and 25 may be the uneven surface 31 and / or the uneven surface 41, or only a portion of a corresponding one of the side surfaces 24 and 25 from the second end portion 29 to the bent portion 30 may be the uneven surface 31 and / or the uneven surface 41. The metal film 19 may be provided on a portion of the side surfaces 24 and 25 other than the uneven surfaces 31 and 41. In this case, the uneven surface 31 and / or the uneven surface 41 may be adjacent to the metal film 19, or a part not including the uneven portion 32 or 42 may be provided between the uneven surface 31 and / or the uneven surface 41 and the metal film 19.

[0075] Although the case where the uneven surface 31 is provided in the opposing surface 22 is described in the third, fourth, and fifth embodiments, this is not the only possibility. The uneven surface 41 may be provided in the opposing surface 22 in the third, fourth, and fifth embodiments.

[0076] Although the third, fourth, and fifth embodiments describe the case where the metal film 19 is adjacent to the uneven surface 31 located in the opposing surface 22, this is not the only possibility. The uneven surface 31 and / or the uneven surface 41 may be provided in the opposing surface 22 after the metal film 19 is removed, for example, with a peeling solution. Thus, the metal film 19 may be removed from the opposing surface 22, or a part not including the uneven portion 32 or 42 may be provided between the uneven surface 31 and / or the uneven surface 41 of the opposing surface 22 and the metal film 19. LIST OF REFERENCE SYMBOLS 10, 50, 60, 70 spark plug 13 Center electrode 14 Tip end face 16 metal housings 17, 40, 51, 61, 71 ground electrode 18 Base material 19 Metal film 20 tiles 22 opposite surface 28 first final section 29 second final section 31.41 uneven surface 32.42 uneven section 33 in-depth section 34 preceding section 55 first section 56 second section 57 third section 58,64,72 border 62 fourth section 63 fifth section D1 first direction D2 second direction H Distance (maximum height) QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2019 - 125569 A

[0002] Cited non-patent literature

[0000] JIS B 0601:2013

[0031]

Claims

[1] Spark plug (10), comprising: a metal housing (16); a center electrode (13) held by the metal casing (16) in an insulating manner; a ground electrode (17) including a first end portion (28) and a second end portion (29), the ground electrode (17) being connected to the metal housing (16) at the first end portion (28) and extending to the second end portion (29); and a plate (20) arranged on an opposite surface (22) of the ground electrode (17), the opposite surface (22) being opposite a tip end surface (14) of the center electrode (13), wherein the opposing surface (22) includes an uneven surface (31) including an uneven portion (32) extending in a first direction (D1), and, in the uneven surface (31) a maximum height (H), which is a distance between a highest portion and a lowest portion, is 3 µm or more. [2] Spark plug (10) according to claim 1, wherein the first direction (D1) is a longitudinal direction of the ground electrode (17). [3] Spark plug (10) according to claim 1 or 2, wherein the uneven surface (41) also includes an uneven portion (42) extending in a second direction intersecting the first direction (D1). [4] Spark plug (10) according to one of claims 1 to 3, wherein the ground electrode (17) contains a base material (18) and a metal film (19) covering the base material (18), a thermal conductivity of the metal film (19) is higher than a thermal conductivity of the base material (18), and the uneven surface (31) is provided in a portion of the base material (18) which is not covered with the metal film (19). [5] Spark plug (10) according to one of claims 1 to 4, wherein the maximum height (H) is 53 µm or less. [6] Spark plug (50) according to one of claims 1 to 5, wherein, when a length of the opposing surface (22) is divided into three in a longitudinal direction of the opposing surface (22) and the opposing surface (22) is divided into a first portion (55), a second portion (56) and a third portion (57) in this order from the second end portion (29) to the first end portion (28) of the ground electrode (51), the first section (55), the second section (56) and the third section (57) contain the uneven surface (31), and a boundary (58) of the uneven surface (31) is present on the third section (57). [7] Spark plug (60) according to one of claims 1 to 5, wherein, when a length of the opposing surface (22) is halved in a longitudinal direction of the opposing surface (22) and the opposing surface (22) is divided into a fourth section (62) and a fifth section (63) in this order from the second end section (29) to the first end section (28) of the ground electrode (61), the fourth section (62) contains the uneven surface (31), and a boundary (64) of the uneven surface (31) is present on the fourth section (62). [8] Spark plug (70) according to one of claims 1 to 5, wherein, when a length of the opposing surface (22) is divided into three in a longitudinal direction of the opposing surface (22) and the opposing surface (22) is divided into a first portion (55), a second portion (56) and a third portion (57) in this order from the second end portion (29) to the first end portion (28) of the ground electrode (71), the first section (55) contains the uneven surface (31), and a boundary (72) of the uneven surface (31) is present on the first section (55). [9] Spark plug (10) according to one of claims 1 to 8, wherein the uneven surface (31) is provided only in the opposite surface (22). [10] The spark plug (10) according to any one of claims 1 to 9, wherein the uneven surface (31) includes a region in which five or more recessed portions (33) are present and projecting portions (34) are present which do not intersect each other.

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