Spark plug

Abstract

To provide a spark plug that can reduce the generation of a gap at an interface.SOLUTION: A spark plug includes a first electrode including a base material and a chip bonded to the base material through a fusion part, and a second electrode facing a discharge surface of the chip in a direction of an axial line. When a line parallel to the axial line is drawn at a cross section that is parallel to the axial line and includes the chip, the fusion part, and the base material, there exists a first uneven part having three or more intersections between the line and a first border between the base material and the fusion part or a second uneven part having three or more intersections between the line and a second border between the chip and the fusion part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a spark plug having an electrode that includes a tip. [Background technology]

[0002] Some spark plug electrodes have a tip joined to a base material via a fusion zone, as disclosed in Patent Document 1. The fusion zone buffers thermal stress on the electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-119818 Summary of the Invention [Problem to be solved by the invention]

[0004] The interface between the base material and the fusion zone, and the interface between the fusion zone and the tip, should be tightly adhered, so if thermal stress causes cracks at the interface and gaps form, defects can occur. Therefore, technology to reduce the occurrence of gaps at the interface is needed.

[0005] The present invention has been made to meet this demand, and has an object to provide a spark plug that can reduce the occurrence of gaps at the interface. [Means for solving the problem]

[0006] To achieve this objective, a first aspect of the present invention comprises a first electrode including a base material and a tip joined to the base material via a fusion zone, and a second electrode facing the discharge surface of the tip in the axial direction, wherein when a straight line parallel to the axis is drawn on a cross section parallel to the axis and including the tip, fusion zone, and base material, a first uneven portion exists where the first boundary between the base material and the fusion zone intersects with the line at three or more points, or a second uneven portion exists where the second boundary between the tip and the fusion zone intersects with the line at three or more points.

[0007] In the second embodiment, in the first embodiment, a first uneven portion and a second uneven portion are present in the cross section.

[0008] In the third aspect, in the first or second aspect, the axis in the cross section includes the center of gravity of the discharge surface, and a first uneven portion or a second uneven portion is present in two adjacent regions of the cross section separated by the axis.

[0009] In the fourth embodiment, in the third embodiment, the first uneven portion and the second uneven portion are present in each of the two regions.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the fusion zone is continuous across the axis from one end of the tip to the other in cross section. [Effects of the Invention]

[0011] According to the present invention, a first uneven portion exists at a first boundary between the base material and the fusion zone, or a second uneven portion exists at a second boundary between the tip and the fusion zone. Even if a crack occurs at the interface, the first uneven portion catches the fusion zone, making it difficult for the tip to rise above the base material, and the second uneven portion catches the tip, making it difficult for the tip to rise above the fusion zone. Because the first uneven portion and the second uneven portion act like hooks, the occurrence of gaps at the interface can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a half-sectional view of a spark plug according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a spark plug. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the spark plug showing a portion indicated by III in FIG. 2. [Figure 4] 4 is an enlarged cross-sectional view of the spark plug showing a portion indicated by IV in FIG. 2. FIG. [Figure 5] 3 is an enlarged cross-sectional view of the spark plug showing a portion indicated by V in FIG. 2. [Figure 6]FIG. 6 is a cross-sectional view of a spark plug according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to a first embodiment, combining an outline view and a full cross-sectional view along the axis O. In Fig. 1, the lower side of the page refers to the rear end of the spark plug 10, and the upper side refers to the front end of the spark plug 10 (the same applies to Figs. 2 to 6).

[0014] 1, a spark plug 10 includes an insulator 11, a center electrode 13 disposed at the center of the insulator 11, a metal shell 15 disposed on the outer periphery of the insulator 11, and a ground electrode 16 connected to the metal shell 15. The insulator 11 is a cylindrical member made of a 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 extending along an axis O.

[0015] The center electrode 13 (first electrode) is a rod-shaped conductor disposed in the axial hole 12 of the insulator 11 and extending along the axis O. The tip of the center electrode 13 protrudes from the tip of the insulator 11 along the axis O. The center electrode 13 is electrically connected to a terminal fitting 14 in the axial hole 12.

[0016] The terminal fitting 14 is a rod-shaped member to which an ignition device (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel). The terminal fitting 14 is fixed to the rear end of the insulator 11 with its front end inserted into the axial hole 12 and its rear end protruding from the insulator 11.

[0017] A metal shell 15 is fixed to the outer periphery of the insulator 11. The metal shell 15 is a cylindrical member made of a metal material (for example, low carbon steel). A ground electrode 16 (second electrode) is connected to the tip of the metal shell 15.

[0018] The ground electrode 16 is a conductor extending from the metallic shell 15 toward the axis O. The ground electrode 16 is, for example, made of a metal mainly composed of Ni with a core material mainly composed of copper embedded therein. The core material may be omitted. In this embodiment, the ground electrode 16 is bent from the metallic shell 15 toward the center electrode 13.

[0019] 2 is a cross-sectional view of the spark plug 10 including the axis O, showing an enlarged view of the tip portion of the center electrode 13. The cross section of the center electrode 13 is divided into a first region 17 and a second region 18 adjacent to each other with the axis O as the boundary. The center electrode 13 includes a base material 19, a fusion zone 20, and a tip 21. The rear end side of the base material 19 is not shown in FIG. 2.

[0020] A copper-based core (not shown) is embedded in the base material 19 to improve thermal conductivity. The core may be omitted. An example of the material for the base material 19 is a Ni-based alloy. A tip 21 is joined to the base material 19 via a fusion zone 20. An example of the material for the tip 21 is a material containing at least one selected from precious metal elements such as Pt, Ir, Ru, and Rh. The fusion zone 20 is formed by melting the base material 19 and the tip 21. The fusion zone 20 is formed by, for example, laser welding. A first boundary 22 between the base material 19 and the fusion zone 20 is at least partially bent. A second boundary 23 between the fusion zone 20 and the tip 21 is also at least partially bent. The fusion zone 20 is continuous across the axis O and extends across the first region 17 and the second region 18.

[0021] The discharge surface 24 of the tip 21 faces the ground electrode 16 (see FIG. 1) in the direction of axis O. A spark gap is formed between the discharge surface 24 of the tip 21 and the ground electrode 16, and discharge occurs mainly in the spark gap. The shape of the discharge surface 24 can be a circle, an ellipse, a polygon, or the like, but there is no limitation on the shape. The cross-sectional view of FIG. 2 includes the center of gravity 25 of the discharge surface 24 and the axis O. The center of gravity 25 is the geometric center of the discharge surface 24.

[0022] The first boundary 22 includes bent first uneven portions 26, 27, and the second boundary 23 includes bent second uneven portions 28, 29. The first uneven portion 26 and the second uneven portion 28 exist in the first region 17, and the first uneven portion 27 and the second uneven portion 29 exist in the second region 18. The first uneven portions 26, 27 and the second uneven portions 28, 29 can be formed by setting the laser welding conditions.

[0023] 3 to 5, the order of identifying the first uneven portion 26 and the second uneven portion 28 will be described. First, among elements not contained in the base material 19 but contained in the chip 21, the element (hereinafter referred to as the "specific element") that is contained in the chip 21 in the largest amount is analyzed by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). The specific element is, for example, one of precious metal elements such as Pt, Ir, Ru, or Rh.

[0024] FIG. 3 is a cross-sectional view of the spark plug 10, enlarging the portion indicated by III in FIG. 2. By SEM-EDX line analysis, the concentration distribution 31 of a specific element on a specified line 30 on the cross section (SEM image) is analyzed. The line 30 coincides with the axis O. The line analysis acquires concentration data at intervals of 1 / 300 mm.

[0025] In the fusion zone 20, the base material 19 and the tip 21 are melted. The concentration of a specific element in the base material 19 is 0%. If the concentration of the specific element in the tip 21 is 100%, the concentration distribution 31 of the specific element is greater than 0% in the fusion zone 20 and 100% in the tip 21. A point 33 is determined where the distance 32 between the point where the concentration of the specific element becomes greater than 0% and the point where the concentration becomes 100% is half.

[0026] By SEM-EDX line analysis, the concentration distribution of the specific element on a line passing through point 34, which is obtained by superimposing point 33 on the SEM image, and which is perpendicular to axis O, is analyzed. In the line analysis, concentration data is obtained at intervals of 1 / 300 mm, and the average is taken as the concentration of the specific element in the fusion zone 20. In this embodiment, the concentration (average) of the specific element in the fusion zone 20 is taken as 50% for convenience.

[0027] FIG. 4 is an enlarged cross-sectional view of the spark plug 10 showing the portion indicated by IV in FIG. 2. By SEM-EDX line analysis, the concentration distribution 36 of a specific element on a specified line 35 on the SEM image is analyzed. The line 35 is a line parallel to the axis O. The line analysis on the line 35 acquires concentration data at intervals of 1 / 300 mm, and the concentration distribution 36 is plotted by averaging the data within a range of 1 / 100 mm sections. The concentration distribution 36 is plotted by averaging the data in order to reduce noise in the analysis results.

[0028] According to concentration distribution 36, there is a portion 37 in molten zone 20 where the concentration (average) of the specific element is 50% and where the concentration of the specific element is 25% or less. If the length of portion 37 overlapping the SEM image of portion 37 where the concentration (average) of the specific element is half or less than that of molten zone 20 is 0.04 mm or more, it is determined to be base material 19. The reason for setting limits on the concentration and length of the specific element is to eliminate noise from the analysis results.

[0029] The presence of portion 37 as determined by SEM-EDX line analysis is said to indicate the presence of first uneven portion 26 at first boundary 22, where there are three intersections between first boundary 22 and line 35. If first uneven portion 26 is present, even if a crack occurs at the interface (first boundary 22) between base material 19 and molten portion 20 due to thermal stress, first uneven portion 26 will catch on it like a hook, making it difficult for molten portion 20 to rise up relative to base material 19. Therefore, the occurrence of gaps at first boundary 22 can be reduced.

[0030] If the molten zone 20 rises above the base material 19 in the direction of the axis O and the discharge surface 24 of the tip 21 approaches or comes into contact with the ground electrode 16, the spark gap narrows and discharge becomes difficult to generate, resulting in a decrease in ignition performance. In contrast, the spark plug 10 has the first uneven portion 26 at the first boundary 22, which reduces the decrease in ignition performance caused by the molten zone 20 rising above the base material 19.

[0031] Returning to Figure 2, the explanation will be made. At the first boundary 22, a first uneven portion 27 is present in the second region 18. The method for identifying the first uneven portion 27 is similar to the method for identifying the first uneven portion 26, and therefore the explanation will be omitted. Because the first uneven portion 26 is present in the first region 17 and the first uneven portion 27 is present in the second region 18, even if a crack occurs at the interface (first boundary 22) between the base material 19 and the molten portion 20, the molten portion 20 is even less likely to lift up.

[0032] FIG. 5 is an enlarged cross-sectional view of the spark plug 10 showing the portion indicated by V in FIG. 2. By SEM-EDX line analysis, the concentration distribution 39 of a specific element on a line 38 specified on the SEM image is analyzed. The line 38 is a line parallel to the axis O. The line analysis on the line 38 acquires concentration data at intervals of 1 / 300 mm, and the concentration distribution 39 is plotted by averaging the data within a range of 1 / 100 mm sections. The concentration distribution 39 is plotted by averaging the data in order to reduce noise in the analysis results.

[0033] According to concentration distribution 39, within chip 21 where the concentration of a specific element is 100%, there exists a portion 40 where the concentration of the specific element is 75% or less. The portion 40 where the concentration is less than half the combined concentration of the specific element in chip 21 and the average concentration of the specific element in molten zone 20 is determined to be molten zone 20 if the length of portion 40 overlapping the SEM image is 0.04 mm or more. The reason for setting limits on the concentration and length of the specific element is to eliminate noise from the analysis results.

[0034] The presence of portion 40 as determined by SEM-EDX line analysis is said to indicate the presence of second uneven portion 28 at second boundary 23, where there are three intersections between second boundary 23 and line 38. If second uneven portion 28 is present, even if a crack occurs at the interface (second boundary 23) between fusion zone 20 and tip 21 due to thermal stress, the tip 21 will be caught by second uneven portion 28 like a hook, making it difficult for the tip 21 to lift up relative to fusion zone 20. Therefore, the occurrence of gaps at second boundary 23 can be reduced.

[0035] Returning to Figure 2, the explanation will be made. At the second boundary 23, a second uneven portion 29 is present in the second region 18. The method for identifying the second uneven portion 29 is similar to the method for identifying the second uneven portion 28, and therefore the explanation will be omitted. Because the second uneven portion 28 is present in the first region 17 and the second uneven portion 29 is present in the second region 18, even if a crack occurs in the interface (second boundary 23) between the fusion zone 20 and the tip 21, the tip 21 is even less likely to lift up.

[0036] Since the fusion zone 20 is continuous across the first region 17 and the second region 18 across the axis O, lifting of the fusion zone 20 and the tip 21 can be reduced even if the number of first uneven portions 26, 27 and second uneven portions 28, 29 is small.

[0037] The center electrode 13 has the first uneven portions 26, 27 and the second uneven portions 28, 29 in one SEM image, which reduces both the lifting of the fusion zone 20 and the lifting of the tip 21. The center electrode 13 has the first uneven portion 26 and the second uneven portion 28 in the first region 17, and the first uneven portion 27 and the second uneven portion 29 in the second region 18, which further reduces the lifting of the fusion zone 20 and the lifting of the tip 21.

[0038] A second embodiment will be described with reference to Fig. 6. In the first embodiment, the center electrode 13 was described in which the fusion zone 20 was continuous across the first region 17 and the second region 18 across the axis O. In contrast, in the second embodiment, a center electrode 41 will be described that includes fusion zones 42, 43 that are discontinuous in the first region 17 and the second region 18. The center electrode 41 is disposed in place of the center electrode 13 of the spark plug 10 described in the first embodiment. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

[0039] FIG. 6 is a cross-sectional view of a spark plug including the axis O according to the second embodiment, showing an enlarged view of the tip portion of the center electrode 41. The center electrode 41 includes a base material 19, fusion zones 42 and 43, and a tip 21. The fusion zones 42 and 43 are formed by melting the base material 19 and the tip 21. The fusion zone 42 is provided in the first region 17, and the fusion zone 43 is provided in the second region 18. Because the fusion zones 42 and 43 are separated by the axis O, a boundary 44 appears between the tip 21 and the base material 19. Because the center electrode 41 has fusion zones 42 and 43 in two locations, it is necessary to determine the (average) concentration of a specific element in each of the fusion zones 42 and 43. The method for doing this is described below.

[0040] After determining the area 45 where the chip 21 and molten zone 42 overlap in the direction of the axis O from the SEM image, a straight line 46 is designated on the SEM image, dividing the length of the area 45 in the direction perpendicular to the axis O into two equal parts. The line 46 is parallel to the axis O. The concentration distribution of a specific element on the line 46 is analyzed by SEM-EDX line analysis. Line analysis acquires concentration data at intervals of 1 / 300 mm, and determines the point 47 where the distance between the point where the concentration of the specific element becomes greater than 0% and the point where the concentration becomes 100% is halfway.

[0041] SEM-EDX line analysis is used to analyze the concentration distribution within range 45 of a specific element on line 48 passing through point 47 superimposed on the SEM image. Line 48 is perpendicular to axis O. Line analysis acquires concentration data at intervals of 1 / 300 mm, and the average is taken as the concentration of the specific element in fusion zone 42. Based on the concentration (average) of the specific element in fusion zone 42, a first uneven portion 53 included in first boundary 22 and a second uneven portion 55 included in second boundary 23 are identified.

[0042] Similarly, after determining from the SEM image the area 49 where the chip 21 and the molten zone 43 overlap in the direction of the axis O, a line 50 is designated on the SEM image that bisects the length of the area 49 in the direction perpendicular to the axis O. The line 50 is parallel to the axis O. The concentration distribution of a specific element on the line 50 is analyzed by SEM-EDX line analysis, and a point 51 is determined where the distance between the point where the concentration of the specific element becomes greater than 0% and the point where the concentration becomes 100% is halfway.

[0043] SEM-EDX line analysis is used to analyze the concentration distribution within range 49 of a specific element on line 52 passing through point 51 superimposed on the SEM image. Line 52 is perpendicular to axis O. Line analysis acquires concentration data at intervals of 1 / 300 mm, and the average is taken as the concentration of the specific element in fusion zone 43. Based on the concentration (average) of the specific element in fusion zone 43, a first uneven portion 54 included in first boundary 22 and a second uneven portion 56 included in second boundary 23 are identified.

[0044] The center electrode 41 has the first uneven portion 53 in the fusion zone 42, which can reduce the lifting of the fusion zone 42 relative to the base material 19, and the second uneven portion 55 in the fusion zone 42 can reduce the lifting of the tip 21 relative to the fusion zone 42. Therefore, the occurrence of gaps at the first boundary 22 can be reduced.

[0045] Furthermore, since the center electrode 41 has the first uneven portion 54 in the fusion zone 43, it is possible to reduce the lifting of the fusion zone 43 relative to the base material 19, and since the fusion zone 43 has the second uneven portion 56, it is possible to reduce the lifting of the tip 21 relative to the fusion zone 43. Therefore, it is possible to reduce the occurrence of gaps at the second boundary 23.

[0046] 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.

[0047] In the embodiments, the first uneven portions 26, 27, 53, 54 and the second uneven portions 28, 29, 55, 56 have been described using the center electrodes 13, 41 as an example, but this is not necessarily limited to this. When the tip is joined to the base material of the ground electrode 16 via a fusion zone, it is naturally possible to provide the first uneven portion and the second uneven portion on the ground electrode 16, as with the center electrodes 13, 41 described in the embodiments. This is because, because discharge occurs between the center electrodes 13, 41 and the ground electrode 16, lifting of the fusion zone and tip due to thermal stress can be reduced on the ground electrode 16, as with the center electrodes 13, 41.

[0048] In the embodiment, the first uneven portions 26, 27, 53, 54 and the second uneven portions 28, 29, 55, 56 are present in a cross section ( FIGS. 2 and 6 ) of the spark plug 10 that includes the axis O, but the present invention is not necessarily limited to this. When a cross section that is parallel to the axis O and includes the tip 21, the fusion zone 20, and the base material 19, a cross section that is parallel to the axis O and includes the tip 21, the fusion zone 42, and the base material 19, or a cross section that is parallel to the axis O and includes the tip 21, the fusion zone 43, and the base material 19 is observed and a line parallel to the axis O is drawn on the cross section, if there is a portion where the first boundary 22 intersects with three or more lines, the portion is a first uneven portion, and if there is a portion where the second boundary 23 intersects with three or more lines, the portion is a second uneven portion. In these cases, the first uneven portion and the second uneven portion also function as hooks, and the lift in the direction of the axis O can be reduced.

[0049] In the embodiment, the first uneven portions 26, 27, 53, 54 are present in both the first region 17 and the second region 18, and the second uneven portions 28, 29, 55, 56 are present in both the first region 17 and the second region 18, but this is not necessarily limited to this. This is because if the first uneven portions or the second uneven portions are present in either the first region 17 or the second region 18, it is possible to reduce the lifting of the molten zone or the chip.

[0050] In the embodiment, the case where the first uneven portions 26, 27, 53, and 54 exist at the first boundary 22 and the second uneven portions 28, 29, 55, and 56 exist at the second boundary 23 has been described, but the present invention is not necessarily limited to this. This is because the presence of either the first uneven portion or the second uneven portion can reduce the lifting of the molten portion and the chip.

[0051] In the embodiment, the first uneven portions 26, 27, 53, 54 have three intersections between a line parallel to the axis O and the first boundary 22, and the second uneven portions 28, 29, 55, 56 have three intersections between a line parallel to the axis O and the second boundary 23, but this is not necessarily limited to this. There may be four or more intersections between a line parallel to the axis O and the first boundary 22 in the first uneven portion, and there may be four or more intersections between a line parallel to the axis O and the second boundary 23 in the second uneven portion. This is because the first uneven portions and the second uneven portions also function like hooks in this case.

[0052] In the embodiment, the ground electrode 16 is bent, but this is not necessarily limited to this. It is of course possible to arrange a linear ground electrode 16 at the tip of the metallic shell 15 so that the ground electrode 16 faces the discharge surface 24 of the center electrode 13. The linear ground electrode 16 may be arranged perpendicular to the axis O or may be arranged so as to intersect the axis O at an angle.

[0053] In the embodiment described above, the spark plug 10 has one ground electrode 16 disposed on the metallic shell 15, but this is not necessarily limited to this. It is of course possible to dispose one or more electrodes in addition to the ground electrode 16 on the metallic shell 15, with a portion of the electrode facing a side surface of the center electrode 13. This allows discharge to normally occur between the ground electrode 16 and the center electrode 13, and when carbon adheres to the insulator 11 due to smoldering contamination, discharge occurs between the electrode and the center electrode 13, burning off the carbon, thereby reducing deterioration of insulation between the ground electrode 16 and the center electrode 13. [Explanation of symbols]

[0054] 10 Spark Plugs 13,41 Center electrode (1st electrode) 16 Ground electrode (second electrode) 17 First area 18 Second area 19 Base material 20, 42, 43 Welding zone 21 chips 22 First Boundary 23 The Second Boundary 24 Discharge surface 25 Center of gravity 26, 27, 53, 54 First uneven part 28, 29, 55, 56 Second uneven part O axis

Claims

1. a first electrode including a base material and a tip joined to the base material via a fusion zone; a second electrode facing the discharge surface of the tip in an axial direction, When a straight line parallel to the axis is drawn on a cross section that is parallel to the axis and includes the tip, the fusion zone, and the base material, a first uneven portion having three or more intersections between a first boundary between the base material and the fusion zone and the straight line, or a second uneven portion having three or more intersections between a second boundary between the tip and the fusion zone and the straight line.

2. 2. The spark plug according to claim 1, wherein the first uneven portion and the second uneven portion are present on the cross section.

3. In the cross section, the axis includes the center of gravity of the discharge surface, 2. The spark plug according to claim 1, wherein the first uneven portion is present in each of two regions of the cross section that are adjacent to each other across the axis, or the second uneven portion is present in each of two regions of the cross section that are adjacent to each other across the axis.

4. 4. The spark plug according to claim 3, wherein the first uneven portion and the second uneven portion are present in the two regions, respectively.

5. 5. The spark plug according to claim 1, wherein the fusion zone is continuous across the axis from one end of the tip to the other end of the tip in the cross section.

Images