Spark plug

Abstract

The present invention provides a spark plug capable of improving stability when generating a flame nucleus by inter-electrode discharge. A spark plug is provided with: a center electrode which includes 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, and which extends in the axial direction; and a ground electrode facing the discharge surface of the tip in the axial direction. The projection drawing is obtained by projection in a direction perpendicular to the axis. Theta is an angle formed by the discharge surface and a straight line passing through a first boundary between tips located at both ends of an outer line of the molten portion and the molten portion and a second boundary between the molten portion and the base material, and A is a distance in the axial direction between the first boundary and the discharge surface. When the distance between the first boundary and the second boundary in the vertical direction perpendicular to the axial direction is represented by B, 0 < A / B < = 1 and theta < = 70 DEG are satisfied.

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 Art

[0002] Patent Document 1 discloses a prior art spark plug comprising a center electrode, comprising a tip made of a different material than the base metal, welded to the base metal, the center electrode extending along the axial direction; and a ground electrode, axially facing the discharge surface of the tip. This prior art reduces the electric field intensity at the weld of the center electrode by adjusting the distance between the discharge surface of the tip and the weld, as well as the shape of the weld. This reduces the likelihood of discharge starting at the weld.

[0003] Prior art literature

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-71976 Summary of the Invention

[0005] Problems to be solved by the invention

[0006] In the prior art, there is a problem of lack of stability when using discharge to generate flame core.

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

[0008] Means for solving problems

[0009] A first aspect of the present invention for achieving this object comprises: a center electrode comprising a base material, a tip formed of a material different from the base material, and a molten portion connecting the tip to the base material, the center electrode extending in the axial direction; and a ground electrode facing the discharge surface of the tip in the axial direction, wherein, in a projection image projected perpendicularly to the axial direction, when θ is the angle formed by 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 at both ends of the outer line of the molten portion, and the discharge surface, A is the distance in the axial direction between the first boundary and the discharge surface, and B is the distance in the perpendicular direction between the first boundary and the second boundary, the following conditions are satisfied: 0 < A / B ≤ 1, and θ ≤ 70°.

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

[0011] The third aspect is the first or second aspect, wherein when the distance between the discharge surface and the ground electrode in the axial direction is G and the length of the discharge surface in the vertical direction is C, G≤C.

[0012] Effects of the Invention

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

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

[0015] Figure 2 It will Figure 1 FIG. 2 is a partially enlarged single-side sectional view of a spark plug. FIG.

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

[0017] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a one-side cross-sectional view of the spark plug 10 in one embodiment, which is a combination of an outer shape view and a full cross-sectional view, with the axis O as the boundary. Figure 1 In the figure, 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 to ).

[0018] like Figure 1 As shown, the spark plug 10 includes an insulator 11, a center electrode 13 held by the insulator 11, a metallic shell 15 that holds the insulator 11 from the outer periphery, and a ground electrode 17 connected to the metallic shell 15. The insulator 11 is a generally cylindrical member made of a ceramic such as alumina, which has excellent mechanical properties and insulation properties at high temperatures. The insulator 11 is provided with an axial hole 12 extending along the axis O.

[0019] 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 core material of the center electrode 13, primarily composed of copper, is covered by a bottomed cylindrical metal. The core material can be omitted. Examples of the metal primarily constituting the center electrode 13 include a Ni-based alloy. The front end 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 within the axial hole 12. The terminal fitting 14 is a rod-shaped component that is connected to an ignition device (not shown) and is made of a conductive metal material (e.g., mild 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.

[0021] A metallic shell 15 is fixed to the outer periphery of the insulator 11. The metallic shell 15 is a cylindrical component made of a metal material (e.g., mild steel). The metallic shell 15 has external threads 16 that engage with the internal threads of a plug hole in the engine (not shown). A ground electrode 17 is connected to the front end of the metallic shell 15.

[0022] The ground electrode 17 is a conductor extending from the metallic shell 15 toward the axis O. The ground electrode 17 exemplifies a structure in which a core material composed primarily of copper is embedded in a metal composed primarily of Ni. The core material can be omitted. In this embodiment, the ground electrode 17 curves from the metallic shell 15 toward the center electrode 13.

[0023] Figure 2 It will Figure 1 FIG2 is an enlarged, one-side cross-sectional view of the spark plug 10, shown in FIG2 . A tip 18 is provided at the portion of the ground electrode 17 that intersects the axis O, facing the rear end. Examples of materials for tip 18 include materials containing one or more noble metal elements selected from Pt, Ir, Ru, and Rh. Tip 18 can be omitted.

[0024] 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 bonded, and examples thereof include materials primarily composed of Ni and containing Cr, Fe, and the like. The outer shape of the base material 20 tapers toward the distal end.

[0025] The material of tip 21 can include, for example, one or more materials selected from precious metal elements such as Pt, Ir, Ru, and Rh. In this embodiment, tip 21 is disk-shaped, but is not limited to this. The discharge surface 23 of tip 21 faces the ground electrode 17 (in this embodiment, tip 18) in the axial direction. The axial distance between the discharge surface 23 and the ground electrode 17 is denoted by G.

[0026] The molten zone 22 is formed by melting the base material 20 and the tip 21. In this embodiment, the molten zone 22 is formed by laser welding. Of course, the molten zone 22 can also be formed by resistance welding or other methods. The outer shape of the molten zone 22 tapers toward the front end, so the front end of the outer line 24 representing the shape of the molten zone 22 is closer to the axis O than the rear end. This allows the tip 21 to be thinner than the base material 20, thereby reducing the heat capacity of the tip 21 compared to the base material 20. Therefore, the energy of the flame kernel generated by the spark discharge between the center electrode 13 and the ground electrode 17 is less likely to be dissipated by the tip 21.

[0027] Figure 3This is a sectional view of the center electrode 13 from one side including the axis O. The projection diagram obtained by projecting the center electrode 13 perpendicular to the axis O (equivalent to Figure 3 The outline 24 of the molten zone 22 (shown to the left of the axis O in the outer diagram) connects the first boundary 25 between the tip 21 and the molten zone 22 and the second boundary 26 between the base material 20 and the molten 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. This ensures the volume of the molten zone 22, thereby ensuring the bonding strength of the molten zone 22 to the tip 21.

[0028] The angle θ (acute angle) formed 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 representing the discharge surface 23 partially overlaps with the straight line 28, but this is not the only limitation. This is because even if the line representing the discharge surface 23 is not perpendicular to the axis O, it may still be within the tolerance range of the spark plug 10.

[0029] In the spark plug 10, the relationship between the distance A, B, and θ, where B is the distance between the first boundary 25 and the second boundary 26 in the direction perpendicular to the axis O, 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 zone 22 of the center electrode 13 is close to the ground electrode 17. This increases the electric field intensity near the tip 21. The concentrated electric field at the molten zone 22 facilitates discharge between the center electrode 13 and the ground electrode 17, thereby improving the stability of the flame kernel generated by inter-electrode discharge.

[0030] The spark plug 10 can improve the stability when generating a flame core by discharge between electrodes. Therefore, the spark plug 10 is suitable for gasoline engines that ignite a mixture of liquid fuel such as gasoline and air, as well as hydrogen engines that use hydrogen as fuel, and gas engines that use the spark plug 10 to ignite gaseous fuels such as coal gas, city gas, natural gas, and biogas.

[0031] If a portion satisfying 0 < A / B ≤ 1 and θ ≤ 70° exists in the center electrode 13, it is easy to generate discharge between the center electrode 13 and the ground electrode 17 using the electric field strength of the molten zone 22. Therefore, the distances A, B, and angle θ can also be measured based on a projection diagram obtained by projecting the spark plug 10 perpendicular to the axis O from any direction. However, it is preferable to use a projection diagram prepared so that the portion of the ground electrode 17 connected to the metal shell 15 is located at the right end of the projection diagram (see Figure 2), the measurement is performed with the outer contour line 24 of the left end of the fusion zone 22 as a reference. This is because the tip 21 and the fusion zone 22 are not cast as shadows by the ground electrode 17 in the projection view, so the length C and the distance G can also be measured in the projection view in which the distances A and B and the angle θ are measured.

[0032] When the length of the spark plug 10 in the vertical direction of the discharge surface 23 is denoted as C, the length C is preferably the distance G (see Figure 2 This is because, when the length C is smaller than the distance G, the electric field intensity between the center electrode 13 and the ground electrode 17 decreases, and discharge tends to be less likely to occur.

[0033] [Example]

[0034] The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0035] (Example 1)

[0036] Testers produced spark plug samples No. 1-11 with different distances A and B and angle θ of the center electrode 13. The dimensions and materials of all components other than the distances A and B and angle θ were constant for Samples No. 1-11. For example, the nominal diameter of the external thread 16 of the metallic 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.

[0037] The tester connected an ignition device (not shown) to the terminal fitting 14 of each gasoline engine sample and measured the voltage (required voltage) across the secondary coil when the sample broke down (generated a spark discharge). The engine was operated at a speed of 2000 rpm, a load of 1200 kPa (NMEP), and constant compression ratio, intake pressure, and air-fuel ratio.

[0038] The required voltage was measured 1000 times for each sample, and the average of these 1000 required voltages was calculated. Comparing this with the average required voltage of Sample No. 11, samples whose average required voltage dropped by 1.0 kV or more were rated A, samples whose average required voltage dropped by 0.5 kV or more but less than 1.0 kV were rated B, samples whose average required voltage dropped by more than 0 kV but less than 0.5 kV were rated C, and samples whose average required voltage showed no difference or had a higher average value were rated D. The results are shown in Table 1.

[0039]

[0040] As shown in Table 1, Samples No. 1-6 were rated A or B, and their average required voltage was reduced by at least 0.5 kV compared to Sample No. 11. Samples No. 7-10 were rated C or D, and their average required voltage was reduced by less than 0.5 kV compared to Sample No. 11. This reduction in required voltage by at least 0.5 kV indicates that Samples No. 1-6 can ignite the fuel at a discharge voltage that is at least 0.5 kV lower than that of Sample No. 11, indicating a higher degree of stability in generating a flame kernel through discharge.

[0041] Comparing Samples No. 1-6 with Samples No. 7-10, Samples No. 1-6 satisfy 0 < A / B ≤ 1 and θ ≤ 70°, while Samples No. 7 and 8 satisfy A / B > 1, and Samples No. 9 and 10 satisfy θ > 70°. Therefore, it can be seen that if 0 < A / B ≤ 1 and θ ≤ 70°, the stability of the flame kernel generated by inter-electrode discharge can be improved.

[0042] In particular, sample No. 1-4 received an A rating, showing an average reduction of more than 1.0 kV in the required voltage compared to sample No. 11. Sample No. 1-4 satisfied the conditions 0 < A / B ≤ 0.77 and θ ≤ 70°. Therefore, it can be seen that if 0 < A / B ≤ 0.77 and θ ≤ 70°, the stability of the flame kernel generated by inter-electrode discharge can be further improved.

[0043] (Example 2)

[0044] The testers imitated Sample No. 6 of Example 1 and produced Samples Nos. 12-15 of spark plugs 10 with different distances G. The dimensions and materials of all parts other than distance G were constant for Samples Nos. 12-15. For example, the nominal diameter of the external thread 16 of the metallic body 15 was 12 mm, the distance A and distance B of the center electrode 13 were 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.

[0045] The testers connected an ignition device to the terminal fitting 14 of each sample, mounted in a container of a certain volume filled with air, and measured the required voltage for each sample. The required voltage is proportional to the product of the pressure (P) within the container and the distance G between the electrodes (P·G), according to Paschen's law. Therefore, using sample No. 14, the required voltage was measured when P·G = 1.32 MPa·mm. Then, while maintaining a constant ambient temperature, the pressure P was varied according to the distance G so that the product of P and G remained at 1.32 MPa·mm. The required voltages for samples Nos. 12, 13, and 15 were measured simultaneously.

[0046] The required voltage was measured 1000 times for each sample, and the average of the 1000 required voltages was calculated. This was compared with the average required voltage of Sample No. 14. Samples with lower average required voltages were rated E, while samples with no difference in average required voltage or higher average required voltages were rated P. The results are shown in Table 2.

[0047]

[0048] As shown in Table 2, Samples No. 12 and 13 were rated E, indicating a lower average required voltage than Samples No. 14 and 15. This lower required voltage indicates that Samples No. 12 and 13 can ignite the fuel at a lower discharge voltage than Samples No. 14 and 15, indicating a higher stability in flame kernel generation through discharge. While Samples No. 12 and 13 satisfy G ≤ C, Samples No. 14 and 15 satisfy G > C. Therefore, it can be seen that when G ≤ C, the stability of flame kernel generation through inter-electrode discharge is further improved.

[0049] As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to the said embodiment at all, It can be easily estimated that various improvements and modifications can be made without departing from the scope of this invention.

[0050] In the embodiment, the outer line 24 of the fusion zone 22 partially overlaps the straight line 27, but the present invention is not necessarily limited to this. The outer line 24 may be a curve convex toward the axis O or a curve convex toward the opposite side of the axis O, and may have concavities and convexities.

[0051] While the embodiments describe a curved ground electrode 17, this is not necessarily limiting. A linear ground electrode 17 can be disposed at the distal end of the metallic shell 15, where the male thread 16 portion extends axially, with the ground electrode 17 facing the discharge surface 23 of the center electrode 13. The linear ground electrode 17 can be disposed perpendicular to the axis O or obliquely to the axis O. When the ground electrode 17 is oblique to the axis O, the distance G between the discharge surface 23 of the center electrode 13 and the ground electrode 17 is the shortest distance between the discharge surface 23 and the ground electrode 17 in the axial direction.

[0052] 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 are sometimes surrounded by the metallic shell 15. Even when such a spark plug is viewed from a direction perpendicular to the axis O, the tip 21 and fusion zone 22 may be hidden by the metallic shell 15. In this case, a portion of the metallic shell 15 is cut away so that the tip 21 of the center electrode 13 and the fusion zone 22 can be visually recognized when the spark plug is viewed from a direction perpendicular to the axis O. This is used to determine the outline 24 of the fusion zone 22 and the distances A, B, G, the angle θ, and the length C.

[0053] While the spark plug 10 has been described in the embodiments as having a single ground electrode 17 disposed on the metallic shell 15, this is not necessarily a limitation. In addition to the ground electrode 17, one or more electrodes may be disposed on the metallic shell 15, with portions of the electrodes facing the side surfaces of the center electrode 13. This allows for normal discharge between the ground electrode 17 and the center electrode 13. However, if carbon adheres to the insulator 11 due to soot fouling, discharge between the electrode and the center electrode 13 can occur, burning off the carbon. This reduces insulation degradation between the ground electrode 17 and the center electrode 13.

[0054] Description of Reference Numerals

[0055] 10 spark plugs

[0056] 11Insulator

[0057] 13 center electrode

[0058] 15Main accessories

[0059] 17 Grounding Electrode

[0060] 20 base material

[0061] 21 terminal

[0062] 22 Melting section

[0063] 23 terminal discharge surface

[0064] 24 Outline of the fusion zone

[0065] 25 The First Boundary

[0066] 26 Second Boundary

[0067] 27 straight line

[0068] 28 straight lines

[0069] O axis.

Claims

1. A spark plug comprising: A center electrode including a base material, a tip made of a material different from the base material, and a molten portion connecting the tip to the base material, and extending along the axial direction; a cylindrical insulator that holds the center electrode from the outer peripheral side; A cylindrical body member that holds the insulator from the outer peripheral side; and a ground electrode, facing the discharge surface of the end in the axial direction and connected to the main body fitting, In the projection diagram obtained by projecting perpendicularly to the axis direction, The angle formed by 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 at both ends of the outer shape line of the molten portion and a straight line extending in a direction perpendicular to the axial direction is θ, The distance between the first boundary and the discharge surface in the axial direction is set to A, When the distance between the first boundary and the second boundary in the vertical direction is set to 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: When the distance between the discharge surface and the ground electrode in the axial direction is G, When the length of the discharge surface in the vertical direction is set to C, Then G≤C.

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