Spark plug

Abstract

To provide a spark plug capable of improving stability of generation of a flame kernel due to a discharge between electrodes.SOLUTION: A spark plug comprises: a center electrode that contains a base material, a chip made of a material that is different from the base material, and a welding part for connecting the base material to the chip, and is extended to a shaft direction; and a ground electrode that is opposite to a discharge surface of the chip and the shaft direction. In a projection drawing formed by vertically projecting it to the shaft direction, when an angle formed by a straight line passing through a first boundary of the chip and the welding part that is positioned on both ends of an outer line of the welding part and a second boundary of the welding part and the base material and the discharge surface is θ, a distance of the shaft direction between the first boundary and the discharge surface is A, and a distance of a vertical direction that is vertical to the shaft direction between the first boundary and the second boundary is B, 0<A / B≤1 and θ≤70°.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a spark plug in which a center electrode and a ground electrode face each other. [Background technology]

[0002] A prior art related to a spark plug including a center electrode in which a tip made of a material different from the base metal is welded to the base metal and extends in the axial direction, and a ground electrode that faces the discharge surface of the tip in the axial direction, is disclosed in Patent Document 1. The prior art reduces the electric field strength at the welded part of the center electrode by setting the distance between the discharge surface of the tip and the welded part and the shape of the welded part, thereby reducing discharges originating from the welded part. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-71976 A Summary of the Invention [Problem to be solved by the invention]

[0004] The prior art has a problem in that the generation of the flame kernel by discharge is unstable.

[0005] The present invention has been made to solve this problem, and has an object to provide a spark plug which can improve the stability of the generation of a flame kernel by the discharge between the electrodes. [Means for solving the problem]

[0006] A first aspect of the present invention for achieving this object is a welding arc welding tool comprising a base metal, a tip made of a material different from the base metal, a fusion zone connecting the tip to the base metal, a central electrode extending in an axial direction, and a ground electrode facing the discharge surface of the tip in the axial direction, wherein, in a projection view projected perpendicular to the axial direction, an angle formed by the discharge surface and a straight line passing through a first boundary between the tip and the fusion zone and a second boundary between the fusion zone and the base metal, which are located at both ends of the outline of the fusion zone, is θ, the axial distance between the first boundary and the discharge surface is A, and the vertical distance between the first boundary and the second boundary, which is perpendicular to the axial direction, is B, and

[0007] In the second aspect, in the first aspect, 0

[0008] The third aspect is the first or second aspect, in which, when the axial distance between the discharge surface and the ground electrode is G and the vertical length of the discharge surface is C, G≦C. Effect of the Invention

[0009] 0 at the tip and fusion part of the center electrode [Brief description of the drawings]

[0010] [Figure 1] 1 is a half-sectional view of a spark plug according to an embodiment; [Diagram 2] FIG. 2 is a half-sectional view of the spark plug, showing an enlarged portion indicated by II in FIG. [Diagram 3] FIG. 2 is a half-sectional view of a center electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] ​​​A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view combining an outline view and a full cross-sectional view of a spark plug 10 according to an embodiment, with the boundary being the axis O. In Fig. 1, the lower side of the page is the rear end side of the spark plug 10, and the upper side of the page is the front end side of the spark plug 10 (the same applies to Figs. 2 and 3).

[0012] 1, a spark plug 10 includes an insulator 11, a center electrode 13 held by the insulator 11, a metal shell 15 that holds the insulator 11 from the outer periphery, and a ground electrode 17 connected to the metal shell 15. The insulator 11 is a substantially cylindrical member made of ceramic such as alumina that 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.

[0013] The center electrode 13 is a rod-shaped conductor disposed in the axial hole 12 of the insulator 11 and extending along the axis O. The center electrode 13 has a core material mainly composed of copper covered with a cylindrical metal with a bottom. It is possible to omit the core material. An example of the metal mainly constituting the center electrode 13 is a Ni-based alloy. The tip side of the center electrode 13 protrudes from the tip of the insulator 11 along the axis O.

[0014] The center electrode 13 is electrically connected to a terminal fitting 14 in the axial hole 12. 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 side of the insulator 11 with its front end inserted into the axial hole 12 and its rear end protruding from the insulator 11.

[0015] 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 (e.g., low carbon steel). The metal shell 15 is provided with a male thread 16 that is coupled to a female thread of a spark plug hole of an engine (not shown). A ground electrode 17 is connected to the tip of the metal shell 15.

[0016] The ground electrode 17 is a conductor extending from the metallic shell 15 toward the axis O. The ground electrode 17 is, for example, an electrode in which a core material mainly composed of copper is embedded in a metal mainly composed of Ni. The core material can be omitted. In this embodiment, the ground electrode 17 is bent from the metallic shell 15 toward the center electrode 13.

[0017] Fig. 2 is an enlarged half-sectional view of the spark plug 10 showing a portion II in Fig. 1. A tip 18 facing toward the rear end is provided at a portion of the ground electrode 17 that intersects with the axis O. Examples of materials for the tip 18 include materials containing one or more precious metal elements such as Pt, Ir, Ru, and Rh. The tip 18 may be omitted.

[0018] The center electrode 13 includes a base material 20, a tip 21 made of a material different from the base material 20, and a fusion zone 22 connecting the tip 21 to the base material 20. The base material 20 is a metal to which the tip 21 is joined, and examples of the material include a material containing Ni as a main component and containing Cr, Fe, etc. The outer shape of the base material 20 becomes thinner toward the tip side.

[0019] The material of the tip 21 is, for example, one containing at least one selected from precious metal elements such as Pt, Ir, Ru, and Rh. In this embodiment, the tip 21 has a disk shape, but is not limited to this. The discharge surface 23 of the tip 21 faces the ground electrode 17 (tip 18 in this embodiment) in the axial direction. The axial distance between the discharge surface 23 and the ground electrode 17 is designated as G.

[0020] The fusion zone 22 is formed by melting the base material 20 and the tip 21. In this embodiment, the fusion zone 22 is formed by laser welding. It is of course possible to provide the fusion zone 22 by resistance welding or the like. The outer shape of the fusion zone 22 becomes thinner toward the tip side, so that the outer shape line 24 representing the shape of the fusion zone 22 is closer to the axis O at the tip side than at the rear end side. This allows the tip 21 to be thinner than the base material 20, so that the heat capacity of the tip 21 can be smaller than that of the base material 20. Therefore, the tip 21 is less likely to take away the energy of the flame kernel generated by the spark discharge between the center electrode 13 and the ground electrode 17.

[0021] 3 is a half-side cross-sectional view including the axis O of the center electrode 13. An outline 24 of the fusion zone 22 in a projection (equivalent to the outline drawing on the left side of the axis O in FIG. 3) obtained by projecting the center electrode 13 perpendicularly to the axis O connects a first boundary 25 between the tip 21 and the fusion zone 22 and a second boundary 26 between the base material 20 and the fusion zone 22. In this embodiment, the axial length of the outline 24 is longer than the axial distance A between the first boundary 25 and the discharge surface 23. Since the volume of the fusion zone 22 can be secured, the joining strength of the tip 21 by the fusion zone 22 can be secured.

[0022] The angle θ (acute angle) between a straight line 27 passing through the first boundary 25 and the second boundary 26 and a straight line 28 perpendicular to the axis O is 70° or less. In this embodiment, the line indicating the discharge surface 23 overlaps part of the straight line 28, but this is not limited to this. This is because even if the line indicating the discharge surface 23 is not perpendicular to the axis O, it may be included in the tolerance range of the spark plug 10.

[0023] In the spark plug 10, when the distance between the first boundary 25 and the second boundary 26 in the vertical direction perpendicular to the axis O is B, the relationship between the distances A, B, and θ is 0.

[0024] Because the spark plug 10 can improve the stability of flame kernel generation through discharge between electrodes, it is suitable not only for gasoline engines in which the spark plug 10 ignites a mixture of air and a liquid fuel such as gasoline, but also for hydrogen engines that use hydrogen as fuel, and gas engines in which the spark plug 10 ignites gaseous fuels such as coal gas, city gas, natural gas, and biogas.

[0025] ​ 0

[0026] In the spark plug 10, when the vertical length of the discharge surface 23 is C, the length C is preferably equal to or greater than the distance G (see FIG. 2). If the length C is less than the distance G, the electric field strength between the center electrode 13 and the ground electrode 17 becomes small, and discharge tends to be difficult to occur. EXAMPLES

[0027] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0028] Example 1 The tester produced sample Nos. 1-11 of the spark plug 10, each of which had different distances A, B and angle θ of the center electrode 13. In sample Nos. 1-11, the dimensions and materials of each part were constant except for the distances A, B and angle θ, and for example, the nominal diameter of the male thread 16 of the metal shell 15 was 12 mm, the length C of the discharge surface 23 of the tip 21 was 0.6 mm, and the distance G between the discharge surface 23 and the ground electrode 17 was 0.8 mm.

[0029] ​The tester connected an ignition device (not shown) to the terminal fitting 14 of each sample attached to a gasoline engine, and measured the voltage of the secondary coil (required voltage) when the sample broke down (spark discharge occurred). The operating conditions of the engine were a rotational speed of 2000 rpm and a load of indicated mean effective pressure (NMEP) of 1200 kPa, and the compression ratio, intake pressure, air-fuel ratio, etc. were kept constant.

[0030] For each sample, the required voltage was measured 1000 times, and the average of the 1000 required voltages was calculated. Compared with the average of the required voltage of Sample No. 11, samples with an average required voltage 1.0 kV or more lower were judged as A, samples with an average required voltage 0.5 kV or more and less than 1.0 kV lower were judged as B, samples with an average required voltage exceeding 0 kV and less than 0.5 kV lower were judged as C, and samples with no difference or a higher average in the average required voltage were judged as D. The results were recorded in Table 1.

[0031]

Table 1

[0032] As shown in Table 1, Samples No. 1 - 6 were judged as A or B, and compared with Sample No. 11, the average required voltage was reduced by 0.5 kV or more. Samples No. 7 - 10 were judged as C or D, and compared with Sample No. 11, the average required voltage was reduced by a maximum of less than 0.5 kV. The fact that the required voltage was reduced by 0.5 kV or more indicates that Samples No. 1 - 6 can ignite the fuel at a discharge voltage 0.5 kV or more lower than that of Sample No. 11, that is, the stability of the generation of flame kernels by discharge is high.

[0033] When comparing Samples No. 1 - 6 and Samples No. 7 - 10, Samples No. 1 - 6 satisfy 0 < A / B ≤ 1 and θ ≤ 70°, while Samples No. 7, 8 have A / B > 1, and Samples 9, 10 have θ > 70°. Therefore, it became clear that when 0 < A / B ≤ 1 and θ ≤ 70°, the stability of the generation of flame kernels by discharge between the electrodes can be improved.

[0034] In particular, sample No. 1-4 was judged to be A, and the average required voltage was reduced by 1.0 kV or more compared to sample No. 11.

[0035] Example 2 The tester produced Sample No. 12-15 of the spark plug 10, which differed in distance G, following Sample No. 6 of Example 1. Sample No. 12-15 had constant dimensions and materials for each part except for distance G, and for example, the nominal diameter of the male thread 16 of the metallic shell 15 was 12 mm, the distance A of the center electrode 13 was 0.16 mm, the distance B was 0.16 mm, A / B=1.00, the angle θ was 70°, and the length C of the discharge surface 23 was 0.6 mm.

[0036] The tester connected an ignition device to the terminal fittings 14 of each sample, which was attached to a container of a fixed volume filled with air, and measured the required voltage of each sample. Since the required voltage is proportional to the product (P·G) of the pressure inside the container (P) and the distance G between the electrodes according to Paschen's law, the tester measured the required voltage when P·G = 1.32 MPa·mm using sample No. 14, and then measured the required voltage of samples No. 12, 13, and 15 while keeping the environmental temperature constant and changing the pressure P according to the distance G so that the product of P and G satisfies 1.32 MPa·mm.

[0037] The required voltage was measured 1000 times for each sample, and the average of the 1000 required voltages was calculated. Samples with a lower average required voltage compared to the average required voltage of sample No. 14 were judged as E, and samples with no difference in the average required voltage or with a higher average were judged as P. The results are shown in Table 2.

[0038] [Table 2]

[0039] ​ As shown in Table 2, samples No. 12 and 13 were judged to be E, and the average required voltage was lower than that of samples No. 14 and 15. The reduction in required voltage indicates that samples No. 12 and 13 are able to ignite the fuel at a lower discharge voltage than samples No. 14 and 15, i.e., the stability of flame kernel generation by discharge is high. Samples No. 12 and 13 satisfied G≦C, but samples No. 14 and 15 satisfied G>C. It is therefore clear that when G≦C, the stability of flame kernel generation by discharge between the electrodes can be further improved.

[0040] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention without departing from the spirit of the present invention.

[0041] In the embodiment, the case where the outline 24 of the fusion zone 22 overlaps a part of the straight line 27 has been described, but this is not necessarily limited to this. The outline 24 may be a curved line that is convex toward the axis O or a curved line that is convex toward the opposite side of the axis O, or the outline 24 may have irregularities.

[0042] In the embodiment, the ground electrode 17 is bent, but this is not necessarily limited to this. It is of course possible to arrange the straight ground electrode 17 at the tip of the metal shell 15 with the male thread 16 portion extended in the axial direction, and to make the ground electrode 17 face the discharge surface 23 of the center electrode 13. The straight ground electrode 17 may be arranged perpendicular to the axis O, or may be arranged to intersect the axis O obliquely. When the ground electrode 17 intersects the axis O obliquely, the distance G between the discharge surface 23 of the center electrode 13 and the ground electrode 17 refers to the shortest axial distance between the discharge surface 23 and the ground electrode 17.

[0043] In a spark plug in which a linear ground electrode 17 is disposed on a metallic shell 15, the tip 21 and fusion zone 22 of the center electrode 13 may be surrounded by the metallic shell 15. Even when such a spark plug is viewed in a direction perpendicular to the axis O, the tip 21 and fusion zone 22 may not be visible due to the shadow of the metallic shell 15. In this case, a part of the metallic shell 15 is cut out to set the outline 24 of the fusion zone 22 so that the tip 21 and fusion zone 22 of the center electrode 13 are visible when the spark plug is viewed in a direction perpendicular to the axis O, and the distances A, B, G, angle θ, and length C are determined.

[0044] In the embodiment, the spark plug 10 in which one ground electrode 17 is disposed on the metallic shell 15 has been described, but the present invention is not necessarily limited to this. It is of course possible to dispose one or more electrodes in addition to the ground electrode 17 on the metallic shell 15 and to have a part of the electrode face a side surface of the center electrode 13. As a result, discharge normally occurs between the ground electrode 17 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 to burn off the carbon, thereby reducing deterioration of insulation between the ground electrode 17 and the center electrode 13. [Explanation of symbols]

[0045] 10 Spark plug 11 Insulators 13 Center electrode 15 Metal fitting 17 Ground electrode 20 Base material 21 Chip 22 Welding section 23 Tip discharge surface 24 Outline of fusion zone 25 First Boundary 26 The Second Boundary 27 straight line 28 straight line O axis

Claims

1. a center electrode including a base material, a tip made of a material different from the base material, and a fusion portion connecting the tip to the base material, the center electrode extending in an axial direction; a cylindrical insulator that holds the center electrode from an outer periphery; a cylindrical metal shell that holds the insulator from an outer periphery; a ground electrode connected to the metallic shell and facing the discharge surface of the tip in the axial direction, In a projection view obtained by projecting perpendicularly to the axial direction, An angle between a straight line passing through a first boundary between the tip and the molten portion and a second boundary between the molten portion and the base material, the first boundary being located at both ends of an outline of the molten portion, and a straight line extending in a vertical direction perpendicular to the axial direction is defined as θ; A is a distance in the axial direction between the first boundary and the discharge surface, A spark plug, wherein when the distance in the vertical direction between the first boundary and the second boundary is B, 0<A / B≦1 and θ≦70°.

2. 2. The spark plug according to claim 1, wherein 0<A / B≦0.

77.

3. The distance in the axial direction between the discharge surface and the ground electrode is G, 3. The spark plug according to claim 1, wherein G≦C is satisfied, where C is the length of the discharge surface in the perpendicular direction.

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