Spark plug

Abstract

To provide a spark plug which can improve the visibility of a mark on an insulator while reducing the damage to the insulator.SOLUTION: A spark plug includes a ceramic insulator, and the insulator includes a fusion zone formed by melting a surface of a base material. In a cross section of the insulator, a value obtained by dividing the length of an interface between the base material and the fusion zone by the length of a line segment connecting both ends of the interface is 1.1 to 1.5. In a cross section of the insulator, the interface between the base material and the fusion zone preferably includes two or more protrusions protruding in a direction away from the surface of the fusion zone.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a prior art technique for providing marks on spark plugs in which, instead of providing marks on a metal shell arranged around the outer periphery of a ceramic insulator, a mark is provided on the surface of the insulator by irradiating the insulator with a laser beam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-252441 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, when the beam intensity of the laser beam is reduced, the visibility of the mark tends to decrease, and when the beam intensity is increased, the insulator tends to be easily destroyed. The prior art has room for improvement in terms of achieving both improved visibility of the mark and reduced destruction of the insulator.

[0005] The present invention has been made to meet this demand, and an object of the present invention is to provide a spark plug that can improve the visibility of the mark while reducing the breakdown of the insulator. [Means for solving the problem]

[0006] To achieve this object, the spark plug of the present invention includes a ceramic insulator including a fusion zone formed by melting the surface of a base material, and in a cross section of the insulator, the value obtained by dividing the length of the interface between the base material and the fusion zone by the length of a line segment connecting both ends of the interface is 1.1 to 1.5. [Effects of the Invention]

[0007] According to the present invention, in a cross section of an insulator including a molten portion where the surface of the base material is melted, the value obtained by dividing the length of the interface between the base material and the molten portion by the length of the line segment connecting both ends of the interface is 1.1 or more and 1.5 or less, thereby achieving both improved visibility of the molten portion as a mark and reduced destruction of the insulator. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a half-sectional view of a spark plug according to a first embodiment. [Figure 2] 2 is a cross-sectional view of the insulator taken along the line II-II of FIG. 1. [Figure 3] FIG. 10 is a cross-sectional view of an insulator of a spark plug according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to a first embodiment, taken along an axis O. The lower side of Fig. 1 is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10. The spark plug 10 includes an insulator 11.

[0010] The insulator 11 is a cylindrical member having an axial hole 12 extending along the axis O, and is made of a ceramic such as alumina, which has excellent insulating properties and mechanical properties at high temperatures. The insulator 11 has a first end 13 including the axial front end and a second end 14 including the axial rear end, and an annular protruding portion 15 that protrudes radially outward is provided in the axial center between the first end 13 and the second end 14. The insulator 11 has a glass layer 16 and a mark 17 on the outer peripheral surface of the insulator 11, closer to the second end 14 (rear end) than the protruding portion 15, in a portion including the second end 14. The surface of the glass layer 16 is less susceptible to dirt and easily removable.

[0011] The mark 17 may be, for example, a letter, a figure, a number, a code, a symbol, or a design. Examples of information indicated by the mark 17 include the manufacturer or seller of the spark plug 10, the country of production of the spark plug 10, the trademark associated with the spark plug 10, the type of the spark plug 10, an identification mark for the engine to which the spark plug 10 is to be fitted, and the lot number and manufacturing history of the spark plug 10, the insulator 11, etc. The mark 17 may include a one-dimensional code (barcode) or a two-dimensional code. In this embodiment, the mark 17 is the letters "NGK," a registered trademark. FIG. 1 shows a portion of the mark 17.

[0012] A rod-shaped center electrode 18 is disposed at the tip end of the axial hole 12 of the insulator 11. The center electrode 18 has a core material with excellent thermal conductivity embedded in a base material. The base material is formed of a Ni-based alloy or a metal material made of Ni. The core material is formed of copper or an alloy mainly composed of copper. The core material can be omitted. The center electrode 18 is electrically connected to a terminal fitting 19 in the axial hole 12. The terminal fitting 19 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is formed of a conductive metal material (such as low-carbon steel).

[0013] The metallic shell 20 is a substantially cylindrical member made of a conductive metal material (such as low-carbon steel). The metallic shell 20 is disposed on the outer periphery of the insulator 11 and mainly surrounds the insulator 11 from the first end 13 to the protruding portion 15. The ground electrode 21 is a rod-shaped metallic member (such as a nickel-based alloy) connected to the metallic shell 20. A plurality of ground electrodes 21 may be provided.

[0014] The spark plug 10 is manufactured, for example, by the following method. First, a cylindrical compact obtained by molding ceramic powder is fired to obtain a sintered body. A glaze is applied to the outer surface of the sintered body, and then the sintered body is fired to obtain the insulator 11 provided with the glass layer 16. The center electrode 18 is placed in the axial hole 12 of the insulator 11, and the center electrode 18 and a metal terminal 19 are electrically connected. After that, the metal shell 20, to which the ground electrode 21 has been previously connected, is assembled to the insulator 11, and a spark gap is formed between the center electrode 18 and the ground electrode 21.

[0015] A laser beam is irradiated onto a portion of the insulator 11 including the second end 14, melting the glass layer 16 on the surface of the insulator 11 and the base material 22 (see FIG. 2) inside the glass layer 16. The melted portion becomes the mark 17. The laser beam is appropriately selected from a CW laser (continuous wave) and a pulsed laser depending on the type of mark 17, etc.

[0016] Figure 2 is a cross-sectional view of the insulator 11 taken along the line II-II of the arrow in Figure 1. Figure 2 shows an enlarged view of a portion of the insulator 11, in a cross section perpendicular to the axis O, where a mark 17 (see Figure 1) is attached, and the other portions are not shown (the same applies to Figure 3). The insulator 11 includes a base material 22 having a sintered structure and a fusion zone 24 formed by melting a surface 23 of the base material 22. The fusion zone 24 is adjacent to a glass layer 16 provided on the surface 23 of the base material 22. The fusion zone 24, which is visually recognized as being a different color from the glass layer 16 and the base material 22, constitutes the mark 17.

[0017] The fusion zone 24 includes a surface 25 and an interface 26 between the base material 22 and the fusion zone 24. The value obtained by dividing the length of the interface 26 of the fusion zone 24 by the length of a line segment 29 connecting both ends 27, 28 of the interface 26 is 1.1 or more and 1.5 or less. Both ends 27, 28 of the interface 26 are the intersections of the surface 25 of the fusion zone 24 and the interface 26.

[0018] If the value obtained by dividing the length of interface 26 of fusion zone 24 by the length of line segment 29 is less than 1.1, the area where fusion zone 24 is bonded to base material 22 is small, making fusion zone 24 more likely to peel off from base material 22, and the distance between surface 25 of fusion zone 24 and interface 26 is short, reducing the visibility of mark 17 (fusion zone 24). If the value obtained by dividing the length of interface 26 of fusion zone 24 by the length of line segment 29 exceeds 1.5, fusion zone 24 acts as a notch in base material 22, reducing the strength of insulator 11. On the other hand, if the value obtained by dividing the length of interface 26 of fusion zone 24 by the length of line segment 29 is 1.1 or more and 1.5 or less, the peel strength of mark 17 (fusion zone 24), the visibility of mark 17, and the mechanical strength of insulator 11 can be ensured.

[0019] The interface 26 of the molten portion 24 includes a plurality of (ten in this embodiment) protrusions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 that protrude in a direction away from the surface 25 of the molten portion 24. The positions of the protrusions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 correspond to the position of the beam axis of the laser beam irradiated onto the insulator 11 to create the molten portion 24, for example.

[0020] Convex portion 30 is a portion of interface 26 cut off by straight line 49 passing through valley 40 between adjacent convex portions 30, 31. Valley 40 is the point of the recessed portion between convex portions 30, 31 that is closest to line segment 29. Straight line 49 is a straight line parallel to line segment 29. The value D / W obtained by dividing the depth D of convex portion 30 from straight line 49 by the width W of convex portion 30 (the length of the line segment cut by convex portion 30 from straight line 49) is 0.1 or more. A portion with a value D / W of 0.1 or more is called a convex portion. Convex portions 31, 32, 33, 34, 35, 36, 37, 38, and 39 also have values ​​D / W of 0.1 or more. A portion of interface 26 with a value D / W of less than 0.1 is not a convex portion.

[0021] The convex portion 31 is a portion of the interface 26 cut off by a straight line 50 passing through the valley 40 between the adjacent convex portions 30, 31 and the valley 41 between the adjacent convex portions 31, 32 that is farther from the line segment 29. The valley 41 is the point closest to the line segment 29 in the recessed portion between the convex portions 31, 32. The straight line 50 is a straight line parallel to the line segment 29.

[0022] The convex portion 32 is a portion of the interface 26 cut off by a straight line 51 passing through the valley 41 between the adjacent convex portions 31, 32 and the valley 42 between the adjacent convex portions 32, 33 that is farther from the line segment 29. The valley 42 is the point closest to the line segment 29 in the recessed portion between the convex portions 32, 33. The straight line 51 is a straight line parallel to the line segment 29.

[0023] The convex portion 33 is a portion of the interface 26 cut off by a straight line 52 passing through the valley 42 between adjacent convex portions 32, 33 and the valley 43 between adjacent convex portions 33, 34 that is farther from the line segment 29. The valley 43 is the point closest to the line segment 29 in the recessed portion between the convex portions 33, 34. The straight line 52 is a straight line parallel to the line segment 29.

[0024] The convex portion 34 is a portion of the interface 26 cut off by a straight line 53 passing through the valley 43 between the adjacent convex portions 33, 34 and the valley 43 between the adjacent convex portions 34, 35 that is farther from the line segment 29. The valley 44 is the point closest to the line segment 29 in the recessed portion between the convex portions 34, 35. The straight line 53 is a straight line parallel to the line segment 29.

[0025] The convex portion 35 is a portion of the interface 26 cut off by a straight line 54 passing through the valley 44 between the adjacent convex portions 34, 35 and the valley 45 between the adjacent convex portions 35, 36 that is farther from the line segment 29. The valley 45 is the point closest to the line segment 29 in the recessed portion between the convex portions 35, 36. The straight line 54 is a straight line parallel to the line segment 29.

[0026] The convex portion 36 is a portion of the interface 26 cut off by a straight line 55 passing through the valley 45 between the adjacent convex portions 35, 36 and the valley 46 between the adjacent convex portions 36, 37 that is farther from the line segment 29. The valley 46 is the point closest to the line segment 29 in the recessed portion between the convex portions 36, 37. The straight line 55 is a straight line parallel to the line segment 29.

[0027] The convex portion 37 is a portion of the interface 26 cut off by a straight line 56 that passes through the valley 46 between the adjacent convex portions 36, 37 and the valley 46 between the adjacent convex portions 37, 38 that is farther from the line segment 29. The valley 47 is the point closest to the line segment 29 in the recessed portion between the convex portions 37, 38. The straight line 56 is a straight line parallel to the line segment 29.

[0028] The convex portion 38 is a portion of the interface 26 cut off by a straight line 57 passing through the valley 47 between adjacent convex portions 37, 38 and the valley 48 between adjacent convex portions 38, 39 that is farther from the line segment 29. The valley 48 is the point closest to the line segment 29 in the recessed portion between the convex portions 38, 39. The straight line 57 is a straight line parallel to the line segment 29.

[0029] The convex portion 39 is a portion of the interface 26 cut off by a straight line 58 that passes through the valleys 48 of the adjacent convex portions 38, 39. The straight line 58 is a straight line that is parallel to the line segment 29.

[0030] When a crack originating from edge 27 of interface 26 of fusion zone 24 propagates along interface 26, the direction of crack propagation changes from a direction away from surface 23 to a direction approaching surface 23 at the apex of protrusion 30, where the crack first reaches, and the propagation of the crack is impeded. Protrusions 31, 32, 33, and 34 similarly impede the propagation of the crack, thereby reducing damage to interface 26.

[0031] Similarly, when a crack originating at edge 28 of interface 26 propagates along interface 26, the direction of crack propagation changes from a direction away from surface 23 to a direction approaching surface 23 at the apex of protrusion 39, which the crack first reaches, and the propagation of the crack is impeded. Protrusions 38, 37, 36, and 35 similarly impede crack propagation, thereby reducing destruction of interface 26. Interface 26 of fusion zone 24 includes two or more protrusions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39, which reduces the propagation of the crack along interface 26 and reduces peeling of fusion zone 24 from base material 22.

[0032] Convex portions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 are located away from a straight line 60 that passes through a midpoint 59 of line segment 29. Straight line 60 is a straight line perpendicular to line segment 29. Convex portions located away from straight line 60 mean that there are convex portions that do not intersect with straight line 60. Because convex portions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 are located away from straight line 60, when a crack propagates from ends 27 and 28 of interface 26 along interface 26, the crack reaches convex portions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 earlier than when the convex portions intersect with straight line 60. The protrusions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 prevent the crack from progressing, so that the crack can be suppressed from progressing while it is still short, compared to when there are protrusions that intersect with the straight line 60. Therefore, damage to the interface 26 can be further reduced.

[0033] A crack originating at edges 27, 28 of interface 26 propagates while releasing strain energy. A range 63 of interface 26, excluding portions 61, 62 extending inward along line segment 29 from edges 27, 28 of interface 26 by one-fifth the length of line segment 29, is reached when a crack originating at edges 27, 28 of interface 26 propagates beyond portions 61, 62. When the driving force for crack propagation of a crack that has reached range 63 is smaller than the driving force for a crack propagating through portions 61, 62, the presence of protrusions 32, 33, 34, 35, 36, and 37 in range 63 prevents crack propagation in range 63. This further reduces delamination of fusion zone 24 from base material 22.

[0034] A second embodiment will be described with reference to Fig. 3. In the first embodiment, the case where the interface 26 of the fusion zone 24 includes ten convex portions has been described. In contrast, in the second embodiment, the case where the interface 72 of the fusion zone 70 includes three convex portions will be described. In the second 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.

[0035] 3 is a cross-sectional view of insulator 11 of spark plug 10 according to the second embodiment. Insulator 11 includes fusion zone 70 formed by melting surface 23 of base material 22. Fusion zone 70 is adjacent to glass layer 16 provided on surface 23 of base material 22. Fusion zone 70, which has a different color from glass layer 16 and base material 22, constitutes mark 17.

[0036] The fusion zone 70 includes a surface 71 and an interface 72 between the base material 22 and the fusion zone 70. The value obtained by dividing the length of the interface 72 of the fusion zone 70 by the length of a line segment 75 connecting both ends 73, 74 of the interface 72 is 1.1 or more and 1.5 or less. This ensures the peel strength of the mark 17 (fusion zone 70), the visibility of the mark 17, and the mechanical strength of the insulator 11. The both ends 73, 74 of the interface 72 are the intersections of the surface 71 of the fusion zone 70 and the interface 72.

[0037] An interface 72 of the molten portion 70 includes a plurality of (three in this embodiment) protrusions 76, 78, 79 protruding in a direction away from the surface 71 of the molten portion 70. The positions of the protrusions 76, 78, 79 correspond to the position of the beam axis of the laser beam irradiated onto the insulator 11 to create the molten portion 70, for example.

[0038] Convex portion 76 is a portion of interface 72 cut off by a straight line 83 passing through a valley 80 between convex portion 76 and a raised portion 77 adjacent to convex portion 76. Valley 80 is the point in the recessed portion between convex portion 76 and raised portion 77 that is closest to line segment 75. Straight line 83 is a straight line parallel to line segment 75.

[0039] Convex portion 78 is a portion of interface 72 cut out by a straight line 84 passing through a valley 81 between protrusion 77 and convex portion 78 adjacent to convex portion 78 and the valley 82 between adjacent convex portions 78, 79 that is farther from line segment 75. Valley 82 is the point closest to line segment 75 in the recessed portion between convex portions 78, 79. Straight line 84 is a straight line parallel to line segment 75.

[0040] The convex portion 79 is a portion of the interface 72 cut off by a straight line 85 passing through the valleys 82 of the adjacent convex portions 78 and 79. The straight line 85 is a straight line parallel to the line segment 75.

[0041] The distance between the line segment 75 and the valley 80 between the protrusion 76 and the raised portion 77 is longer than the distance between the line segment 75 and the valley 81 between the protrusion 77 and the protrusion 78. The value D / W obtained by dividing the depth D of the raised portion 77 from a straight line 86 that is parallel to the line segment 75 and passes through the longer valley 80 by the length of the line segment where the straight line 86 is cut by the raised portion 77 (the width W of the raised portion 77) is less than 0.1. Therefore, the raised portion 77 protrudes from the interface 72 in a direction away from the surface 71 of the molten portion 70, but is not a convex portion.

[0042] When a crack originating from an edge 73 of the interface 72 of the fusion zone 70 propagates along the interface 72, the direction of the crack propagation changes from a direction away from the surface 23 to a direction approaching the surface 23 at the apex of the protrusion 76 where the crack first reaches, thereby preventing the crack from propagating. Therefore, damage to the interface 72 can be reduced.

[0043] Similarly, when a crack originating at edge 74 of interface 72 propagates along interface 72, the direction of crack propagation changes from a direction away from surface 23 to a direction approaching surface 23 at the apex of protrusion 79, which the crack first reaches, and the propagation of the crack is hindered. Protrusion 78 similarly hinders crack propagation, thereby reducing destruction of interface 72. Interface 72 of fusion zone 70 includes two or more protrusions 76, 78, 79, which reduces the propagation of the crack along interface 72 and reduces peeling of fusion zone 70 from base material 22.

[0044] The convex portions 76, 78, and 79 are located away from a straight line 88 that passes through a midpoint 87 of the line segment 75. The straight line 88 is perpendicular to the line segment 75. Because the convex portions 76, 78, and 79 are located away from the straight line 88, when a crack propagates from the ends 73 and 74 of the interface 72 along the interface 72, the crack reaches the convex portions 76, 78, and 79 earlier than when the convex portions intersect the straight line 88. The convex portions 76, 78, and 79 hinder the propagation of the crack, and therefore the propagation of the crack can be suppressed while it is still short, compared to when a convex portion intersects the straight line 88. Therefore, damage to the interface 72 can be further reduced.

[0045] 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.

[0046] In the embodiment, the shapes of the interfaces 26, 72 of the fusion zones 24, 70 in a cross section perpendicular to the axis O of the insulator 11 have been described, but the shapes are not necessarily limited to this. Various cross sections can be used as long as they reveal the interfaces 26, 72 of the fusion zones 24, 70 provided in the insulator 11. Examples of the various cross sections include (1) a cross section including the axis O, (2) a cross section parallel to the axis O, and (3) a cross section intersecting the axis O other than a cross section perpendicular to the axis O.

[0047] In the embodiment, the spark plug 10 is described as being installed in an engine such that the tip of the center electrode 18 and the ground electrode 21 are exposed to the combustion chamber of the engine, but this is not necessarily limited to this. It is naturally possible to apply the insulator to other spark plugs. An example of such other spark plug is a spark plug in which a through-hole is provided in a cap that covers the tip of the center electrode 18 and the ground electrode 21 in order to provide a pre-combustion chamber in the engine. Furthermore, the present invention is not limited to spark plugs that generate spark discharge between the center electrode 18 and the ground electrode 21, and it is naturally possible to apply the insulator to spark plugs that ignite using barrier discharge or arc discharge.

[0048] In the first embodiment, the case where ten convex portions 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39 are present at positions away from the straight line 60 has been described, but this is not necessarily limited to this. It is sufficient that at least one convex portion is present at a position away from the straight line 60.

[0049] In the first embodiment, the case where six convex portions 32, 33, 34, 35, 36, and 37 exist in the range 63 has been described, but this is not necessarily limited to this. It is sufficient that at least one convex portion exists in the range 63. [Explanation of symbols]

[0050] 10 Spark Plugs 11 Insulators 22 Base material 23 Surface of base material 24 Welding zone 25 Surface of molten area 26 Interface 27,28 Interface Edge 29 line segments 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 Convex parts 40,41,42,43,44,45,46,47,48 valley 49,50,51,52,53,54,55,56,57,58 straight line 59 midpoint 60 straight line 61,62 parts 63 range 70 Welding zone 71 Surface of molten area 72 Interface 73,74 Interface Edge 75 line segments 76, 78, 79 Convex parts 80,82 valley 83,84,85 straight line 87 midpoint 88 straight line

Claims

1. an insulator including a ceramic sintered body; The insulator is a spark plug including a fusion portion formed by melting a surface of a base material, In a cross section of the insulator, a value obtained by dividing the length of the interface between the base material and the fusion zone by the length of a line segment connecting both ends of the interface is 1.1 or more and 1.5 or less.

2. In a cross section of the insulator, the interface includes two or more protrusions protruding in a direction away from the surface of the fusion zone, 2. The spark plug according to claim 1, wherein the convex portion is a portion where a straight line parallel to the line segment passing through the valleys of the adjacent convex portions cuts off the interface.

3. 3. The spark plug according to claim 2, wherein in a cross section of the insulator, at least one of the protrusions is located at a position away from a straight line passing through a midpoint of the line segment and perpendicular to the line segment.

4. 4. The spark plug according to claim 2, wherein at least one of the protrusions is present in a cross section of the insulator in a range excluding portions extending inward along the line segment from both ends of the interface by a length that is one-fifth of the length of the line segment.

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