Spark plug

Abstract

Provided is a spark plug capable of improving stability when generating a flame kernel by discharge between electrodes. The spark plug includes: a center electrode including a base material, a tip made of a material different from the base material, a melting portion connecting the tip to the base material, and extending in an axial direction; and a ground electrode facing a discharge surface of the tip in the axial direction. In a projection view obtained by projecting in a direction perpendicular to the axial direction, an angle formed by a straight line connecting a first boundary between the tip and the melting portion at both ends of an outline of the melting portion and a second boundary between the melting portion and the base material and the discharge surface is set to θ, a distance in the axial direction between the first boundary and the discharge surface is set to A, and a distance in a perpendicular direction perpendicular to the axial direction between the first boundary and the second boundary is set to B, then 0 < A / B ≤ 1 and θ ≤ 70°.

Description

TECHNICAL FIELD

[0001] The present application relates to a spark plug in which a center electrode faces a ground electrode. BACKGROUND

[0002] Patent Document 1 discloses a conventional technique of a spark plug provided with a center electrode in which a tip made of a material different from a base material is welded to the base material, the center electrode extending in an axial direction, and a ground electrode facing a discharge surface of the tip in the axial direction. The conventional technique reduces the electric field intensity at the welded portion of the center electrode and reduces discharge from the welded portion as a starting point by setting the distance between the discharge surface of the tip and the welded portion and the shape of the welded portion.

[0003] PRIOR ART DOCUMENTS

[0004] Patent Document 1: Japanese Patent Application Publication No. 2014-71976 SUMMARY

[0005] PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In the conventional technique, there is a problem that stability is lacking when a flame kernel is generated by discharge between electrodes.

[0007] The present application has been made to solve the problem, and has an object to provide a spark plug capable of improving stability when a flame kernel is generated by discharge between electrodes.

[0008] MEANS FOR SOLVING THE PROBLEMS

[0009] A first aspect of the present application for achieving the object is provided with a center electrode including a base material, a tip made of a material different from the base material, and a fused portion connecting the tip to the base material, the center electrode extending in an axial direction, and a ground electrode facing a discharge surface of the tip in the axial direction, in a projection view obtained by projecting in a direction perpendicular to the axial direction, when an angle formed by a straight line connecting a first boundary between the tip and the fused portion at both ends of an outline of the fused portion and a second boundary between the fused portion and the base material and the discharge surface is set to θ, a distance in the axial direction between the first boundary and the discharge surface is set to A, and a distance in the perpendicular direction between the first boundary and the second boundary is set to B, then 0 < A / B ≤ 1 and θ ≤ 70°.

[0010] A second aspect is based on the first aspect, and 0 < A / B ≤ 0.77.

[0011] A third aspect is based on the first or second aspect, and when a distance in the axial direction between the discharge surface and the ground electrode is set to G, and a length in the perpendicular direction of the discharge surface is set to C, then G ≤ C.

[0012] EFFECTS OF THE INVENTION

[0013] Since the tip of the center electrode and the molten portion have a relationship of 0 < A / B ≤ 1 and θ ≤ 70°, the stability at the time of generating a flame kernel by the discharge between the electrodes can be improved by the electric field intensity of the molten portion. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a single cross-sectional view of a spark plug according to an embodiment.

[0015] Figure 2 is a single cross-sectional view of a spark plug according to an embodiment. Figure 1 is a single cross-sectional view of a spark plug according to an embodiment.

[0016] Figure 3 is a single cross-sectional view of a center electrode. DETAILED DESCRIPTION

[0017] Hereinafter, a preferred embodiment of the present application will be described with reference to the drawings. Figure 1 is a single cross-sectional view of a spark plug 10 according to an embodiment, in which an outline view and a full cross-sectional view are combined with the axis O as a boundary. In Figure 1 , the lower side of the paper is referred to as the rear end side of the spark plug 10, and the upper side of the paper is referred to as the front end side of the spark plug 10 (in Figure 2 and Figure 3 , the same applies).

[0018] As shown in Figure 1 , the spark plug 10 includes an insulator 11, a center electrode 13 held to the insulator 11, a main body fitting 15 holding the insulator 11 from the outer peripheral side, and a ground electrode 17 connected to the main body fitting 15. The insulator 11 is a substantially cylindrical member made of a ceramic such as alumina, which has excellent mechanical properties and insulation properties at high temperatures. An axial hole 12 extending along the axis O is provided in the insulator 11.

[0019] The center electrode 13 is a rod-shaped conductor disposed in the axial hole 12 of the insulator 11, which extends along the axis O. A core material mainly composed of copper of the center electrode 13 is covered with a bottomed cylindrical metal. The core material can be omitted. The metal mainly constituting the center electrode 13 can be exemplified by a Ni-based alloy. The front end side of the center electrode 13 protrudes from the front end of the insulator 11 along the axis O.

[0020] 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 that connects a sparking device (not shown), and is made of a metal material (for example, low carbon steel or the like) having electrical conductivity. The terminal fitting 14 is fixed to the rear end side of the insulator 11 in a state in which the front end side is inserted into the axial hole 12 and the rear end side protrudes from the insulator 11.

[0021] A main body fitting 15 is fixed to the outer periphery of the insulator 11. The main body fitting 15 is a cylindrical member made of a metal material such as mild steel. An external thread 16 is provided in the main body fitting 15 to be combined with an internal thread of a hole of an engine (not shown). A ground electrode 17 is connected to the front end of the main body fitting 15.

[0022] The ground electrode 17 is a conductor extending from the main body fitting 15 toward the axis O. The ground electrode 17 is exemplified as a structure in which a core material having copper as a main component is embedded in a metal having Ni as a main component. The core material can be omitted. In the present embodiment, the ground electrode 17 is bent from the main body fitting 15 toward the center electrode 13.

[0023] Figure 2 is an enlarged view of a portion indicated by II in Figure 1 . An end 18 toward the rear end side is provided in the ground electrode 17 at a portion intersecting the axis O. The material of the end 18 can be exemplified as a material containing one or more selected from among precious metal elements such as Pt, Ir, Ru, and Rh. The end 18 can be omitted.

[0024] The center electrode 13 includes a base material 20, an end 21 made of a material different from the base material 20, and a fusion portion 22 connecting the end 21 to the base material 20. The base material 20 is a metal to which the end 21 is joined, and the material can be exemplified as a material having Ni as a main component and containing Cr, Fe, or the like. The outer shape of the base material 20 is tapered toward the front end side.

[0025] The material of the end 21 can be exemplified as a material containing one or more selected from among precious metal elements such as Pt, Ir, Ru, and Rh. In the present embodiment, the shape of the end 21 is a circular plate shape, but is not limited thereto. A discharge surface 23 of the end 21 faces the ground electrode 17 (the end 18 in the present embodiment) in the axis direction. A distance in the axis direction between the discharge surface 23 and the ground electrode 17 is set as G.

[0026] The fusion portion 22 is formed by melting the base material 20 and the end 21. In the present embodiment, the fusion portion 22 is made by laser welding. Of course, the fusion portion 22 can be provided by resistance welding or the like. The outer shape of the fusion portion 22 is tapered toward the front end side, and thus an outer shape line 24 indicating the shape of the fusion portion 22 is closer to the axis O on the front end side than on the rear end side. Thereby, the end 21 can be made thinner than the base material 20, and thus the heat capacity of the end 21 can be reduced compared to the base material 20. Therefore, the energy of a flame kernel generated by spark discharge between the center electrode 13 and the ground electrode 17 is not easily taken away by the end 21.

[0027] Figure 3is a single-side sectional view of the center electrode 13 including the axis O. The projection drawing (equivalent to the outer shape drawing on the left side of the axis O in Figure 3 The outer shape line 24 of the molten portion 22 in the projection drawing (equivalent to the outer shape drawing on the left side of the axis O in

[0028] The angle θ (acute angle) formed by the straight line 27 of the first boundary 25 and the second boundary 26 and the straight line 28 perpendicular to the axis O is 70° or less. In the present embodiment, the line indicating the discharge surface 23 overlaps a part of the straight line 28, but is not limited thereto. This is because even if the line indicating the discharge surface 23 does not perpendicularly intersect the axis O, it is sometimes included in the range of the tolerance of the spark plug 10.

[0029] In the spark plug 10, the relationship of the distance A when the distance in the perpendicular direction perpendicular to the axis O between the first boundary 25 and the second boundary 26 is B, and B and θ is 0 < A / B ≤ 1 and θ ≤ 70°. More preferably, 0 < A / B ≤ 0.77 and θ ≤ 70° are satisfied. When 0 < A / B ≤ 1 and θ ≤ 70°, the molten portion 22 of the center electrode 13 approaches the ground electrode 17, and thus the electric field intensity in the vicinity of the tip 21 can be increased by the molten portion 22. Since the electric field is concentrated by the molten portion 22, discharge is easily generated between the center electrode 13 and the ground electrode 17, and thus the stability when a spark kernel is generated by the inter-electrode discharge can be improved.

[0030] The spark plug 10 can improve the stability when a spark kernel is generated by the inter-electrode discharge, and thus the spark plug 10 is applicable not only to a gasoline engine in which a mixture of a liquid fuel such as gasoline and air is ignited, but also to a hydrogen engine in which hydrogen is used as a fuel, a gas engine in which a gaseous fuel such as coal gas, city gas, natural gas, or biogas is ignited, and the like.

[0031] If the portion satisfying 0 < A / B ≤ 1 and θ ≤ 70° is present in the center electrode 13, discharge is easily generated between the center electrode 13 and the ground electrode 17 by the electric field intensity of the molten portion 22. Thus, the distance A, B, and the angle θ can also be measured based on the projection drawing obtained by projecting the spark plug 10 from an arbitrary direction perpendicular to the axis O. However, the distance A, B, and the angle θ are preferably measured based on the projection drawing in which the portion in which the ground electrode 17 is connected to the main body fitting 15 is located at the right end of the projection drawing (refer to FIG. 6). Figure 2), measured from the outer shape line 24 of the left end of the melting portion 22. This is because, in the projection view, the end 21 and the melting portion 22 do not become a shadow of the ground electrode 17, and thus the length C and the distance G can be measured in the projection view in which the distances A, B and the angle Θ are measured.

[0032] When the length C in the vertical direction of the discharge face 23 of the spark plug 10 is set to C, the length C is preferably the distance G (refer to Figure 2 ) or more. This is because, when the length C is less than the distance G, the electric field intensity between the center electrode 13 and the ground electrode 17 becomes small, and there is a tendency that it is difficult to generate discharge.

[0033] [Example]

[0034] The present application will be described in more detail by an example, but the present application is not limited to the example.

[0035] (Example 1)

[0036] The tester produced sample Nos. 1-11 of the spark plug 10 in which the distances A, B and the angle Θ of the center electrode 13 were different. The dimensions and the materials of each part of the sample Nos. 1-11 except for the distances A, B and the angle Θ were constant, for example, the nominal diameter of the external thread 16 of the body fitting 15 was 12 mm, the length C of the discharge face 23 of the end 21 was 0.6 mm, and the distance G between the discharge face 23 and the ground electrode 17 was 0.8 mm.

[0037] The tester connected an ignition device (not shown) to the terminal fitting 14 of each sample installed in a gasoline engine, and measured the voltage of the secondary coil (voltage required) at the time when the sample was broken down (spark discharge was generated). The operating conditions of the engine were that the rotation speed was 2000 rpm, the load was the indicated mean effective pressure (NMEP) of 1200 kPa, and the compression ratio, the intake pressure, the air-fuel ratio, and the like were constant.

[0038] The voltage required was measured 1000 times for each sample, and the average of the 1000 voltage required was calculated. The sample in which the average of the voltage required was lowered by 1.0 kV or more was judged as A, the sample in which the average of the voltage required was lowered by 0.5 kV or more and less than 1.0 kV was judged as B, the sample in which the average of the voltage required was lowered by more than 0 kV and less than 0.5 kV was judged as C, and the sample in which the average of the voltage required was not different or was high was judged as D, in comparison with the average of the voltage required of sample No. 11. The results are described in Table 1.

[0039]

[0040] As shown in Table 1, samples No. 1-6 are classified as A or B, requiring an average voltage reduction of more than 0.5 kV compared to sample No. 11. Samples No. 7-10 are classified as C or D, requiring a maximum average voltage reduction of less than 0.5 kV compared to sample No. 11. A voltage reduction of more than 0.5 kV indicates that samples No. 1-6 can ignite fuel with a discharge voltage more than 0.5 kV lower than sample No. 11, meaning they exhibit high stability when using discharge to generate a flame nucleus.

[0041] When comparing samples No. 1-6 with samples No. 7-10, samples No. 1-6 satisfy 0 < A / B ≤ 1 and θ ≤ 70°, but samples No. 7 and 8 satisfy A / B > 1, and samples No. 9 and 10 satisfy θ > 70°. Therefore, it can be concluded that if 0 < A / B ≤ 1 and θ ≤ 70°, the stability of generating a flame nucleus using inter-electrode discharge can be improved.

[0042] In particular, samples No. 1-4 were classified as A, requiring an average voltage reduction of more than 1.0 kV compared to sample No. 11. Samples No. 1-4 satisfied 0 < A / B ≤ 0.77 and θ ≤ 70°. Therefore, it can be concluded that if 0 < A / B ≤ 0.77 and θ ≤ 70°, the stability of generating a flame nucleus using inter-electrode discharge can be further improved.

[0043] (Example 2)

[0044] The experimenter imitated sample No. 6 of Example 1 and produced samples No. 12-15 of spark plug 10 with different distances from G. The dimensions and materials of all parts of samples No. 12-15 except for distance G are constant. For example, the nominal diameter of the external thread 16 of the main body accessory 15 is 12 mm, the distance A of the center electrode 13 is 0.16 mm, the distance B is 0.16 mm, A / B = 1.00, the angle θ is 70°, and the length C of the discharge surface 23 is 0.6 mm.

[0045] The experimenter connected the ignition device to the terminal fittings 14 of each sample installed in a container of a certain volume filled with air, and measured the required voltage of each sample. The required voltage is proportional to the product of the pressure (P) inside the container and the distance G between the electrodes (P·G) according to Pascal's Law. Therefore, after measuring the required voltage of sample No. 14 when P·G = 1.32 MPa·mm, the ambient temperature was kept constant, and the pressure P was varied according to the distance G so that the product of P and G satisfies 1.32 MPa·mm. At the same time, the required voltages of samples No. 12, 13, and 15 were measured respectively.

[0046] The required voltage of each sample was measured 1000 times, and the average of the 1000 required voltages was calculated. The sample whose average of the required voltages was lower than that of sample No. 14 was determined as E, and the sample whose average of the required voltages was not different or higher than that of sample No. 14 was determined as P. The results are shown in Table 2.

[0047]

[0048] As shown in Table 2, the samples No. 12 and 13 were determined as E, and the average of the required voltages was lower than that of the samples No. 14 and 15. The decrease in the required voltage indicates that the samples No. 12 and 13 can ignite the fuel at a lower discharge voltage, i.e., the stability of generating the flame kernel by the discharge is high, compared to the samples No. 14 and 15. The samples No. 12 and 13 satisfy G ≤ C, but the samples No. 14 and 15 satisfy G > C. Therefore, it is known that the stability of generating the flame kernel by the discharge between the electrodes can be further improved when G ≤ C.

[0049] The present application has been described based on the embodiments, but the present application is not limited to the above-described embodiments, and various modifications can be easily conceived without departing from the spirit of the present application.

[0050] In the embodiments, the case where the outline 24 of the melting portion 22 overlaps a part of the straight line 27 has been described, but it is not necessarily limited thereto. The outline 24 can be a curve which is convex toward the axis O or a curve which is convex toward the opposite side of the axis O, or the like, and the outline 24 can have a concave-convex shape.

[0051] In the embodiments, the case where the ground electrode 17 is bent has been described, but it is not necessarily limited thereto. Of course, the straight line-shaped ground electrode 17 can be arranged at the front end of the main fitting 15 in which a part of the external thread 16 extends in the axial direction so that the ground electrode 17 faces the discharge surface 23 of the center electrode 13. The straight line-shaped ground electrode 17 can be arranged perpendicular to the axis O, or can be arranged obliquely to the axis O. In the case where the ground electrode 17 is arranged obliquely to the axis O, the distance G between the discharge surface 23 of the center electrode 13 and the ground electrode 17 refers to the shortest distance among the distances in the axial direction between the discharge surface 23 and the ground electrode 17.

[0052] In the spark plug in which the linear ground electrode 17 is provided to the main body fitting 15, the tip 21 and the melting portion 22 of the center electrode 13 are sometimes surrounded by the main body fitting 15. Even when such a spark plug is viewed from the direction perpendicular to the axis O, the tip 21 and the melting portion 22 are sometimes not visible due to the shadow of the main body fitting 15. In this case, the outer shape line 24 of the melting portion 22 is set in such a manner that the tip 21 and the melting portion 22 of the center electrode 13 can be visually confirmed when the spark plug is viewed from the direction perpendicular to the axis O, and the distances A, B, G, the angle Θ, and the length C are found by cutting a part of the main body fitting 15.

[0053] In the embodiment, the spark plug 10 in which one ground electrode 17 is provided to the main body fitting 15 is described, but it is not necessarily limited thereto. In addition to the ground electrode 17, one or more electrodes can be provided to the main body fitting 15 so that a part of the electrode faces the side surface of the center electrode 13. Thereby, discharge is generally made between the ground electrode 17 and the center electrode 13, and when carbon is attached to the insulator 11 due to soot contamination, discharge is made between the electrode and the center electrode 13 to burn off the carbon, so that reduction in insulation between the ground electrode 17 and the center electrode 13 can be reduced.

[0054] Reference Signs

[0055] 10 spark plug

[0056] 11 insulator

[0057] 13 center electrode

[0058] 15 main body fitting

[0059] 17 ground electrode

[0060] 20 base material

[0061] 21 tip

[0062] 22 melting portion

[0063] 23 discharge surface of tip

[0064] 24 outer shape line of melting portion

[0065] 25 first boundary

[0066] 26 second boundary

[0067] 27 straight line

[0068] 28 straight line

[0069] O axis

Claims

1. A spark plug, comprising: The center electrode includes a base material, an end made of a material different from the base material, and a molten portion connecting the end to the base material, and extends along the axial direction; A cylindrical insulator holds the central electrode from the outer peripheral side; The cylindrical main body component holds the insulator from the outer periphery; and The grounding electrode faces the discharge surface of the end in the axial direction and is connected to the main body component. In the projection diagram obtained by projecting perpendicular to the axis, Let θ be the angle formed by the straight line passing through the first boundary between the end points located at both ends of the outline of the molten part and the molten part, and the second boundary between the molten part and the base material, and the straight line extending in a direction perpendicular to the axis. Let A be the distance along the axial direction between the first boundary and the discharge surface. When the distance in the vertical direction between the first boundary and the second boundary is set as B, Then 0 < A / B ≤ 1 and θ ≤ 70°.

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

77.

3. The spark plug according to claim 1 or 2, wherein, Let G be the distance in the axial direction between the discharge surface and the grounding electrode. When the length of the discharge surface in the vertical direction is set as C, Then G≤C.

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