Spark plug

Abstract

To provide a spark plug capable of reducing cracks in a discharge member.SOLUTION: A spark plug includes a first electrode having a discharge member joined to a base material mainly composed of Ni via a fusion zone, and a second electrode facing the discharge member via a spark gap. The discharge member is mainly composed of Ru, and a value obtained by dividing the Vickers hardness of the fusion zone by the Vickers hardness of the discharge member is equal to 0.25 or more and equal to 2.8 or less. The discharge member may contain one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, W, Au, Al, Co, Ni, Cr, and Si.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a spark plug having a discharge member containing Ru. [Background technology]

[0002] Patent Document 1 discloses a prior art spark plug having a first electrode including a discharge member and a second electrode facing the discharge member across a spark gap, in which the material of the discharge member is a metal containing Ru as a main component. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-512551 Summary of the Invention [Problem to be solved by the invention]

[0004] The crystal structure of Ru is a hexagonal close-packed lattice, which has high resistance to displacement under external forces and is difficult to deform. Therefore, the prior art has a problem in that discharge members containing Ru as the main component are prone to cracking.

[0005] The present invention has been made to solve this problem, and has as its object to provide a spark plug that can reduce cracking of the discharge member. [Means for solving the problem]

[0006] To achieve this object, a first aspect of the present invention comprises a first electrode having a discharge member joined to a base material primarily composed of Ni via a fusion zone, and a second electrode facing the discharge member via a spark gap, wherein the discharge member is primarily composed of Ru, and the value obtained by dividing the Vickers hardness of the fusion zone by the Vickers hardness of the discharge member is 0.25 or more and 2.8 or less.

[0007] In the second aspect, in the first aspect, the discharge member contains one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, W, Au, Al, Co, Ni, Cr, and Si.

[0008] In a third aspect, in the first aspect, the value obtained by dividing the Vickers hardness of the fusion zone by the Vickers hardness of the discharge member is 1.05 or more and 2.8 or less.

[0009] A fourth aspect is the third aspect, wherein the discharge member contains one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, and W. [Effects of the Invention]

[0010] According to the present invention, the Vickers hardness of the fusion zone joining the discharge member mainly composed of Ru and the base material mainly composed of Ni divided by the Vickers hardness of the discharge member is 0.25 or more and 2.8 or less, so that deformation of the fusion zone assists deformation of the discharge member, thereby reducing cracking of the discharge member. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a half cross-sectional view of a spark plug according to an embodiment; [Figure 2] FIG. 2 is a half-sectional view of the spark plug, showing an enlarged portion indicated by II in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half cross-sectional view of a spark plug 10 according to one embodiment, taken along an axis O. In Fig. 1, the lower side of the drawing is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10.

[0013] As shown in FIG. 1, a spark plug 10 includes a center electrode 13 (first electrode) and a ground electrode 19 (second electrode). An insulator 11 insulates the center electrode 13 from the ground electrode 19. The ground electrode 19 is connected to a metal shell 18. The insulator 11 is a substantially cylindrical member made of ceramic such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 is provided with an axial hole 12 that penetrates along an axis O. The center electrode 13 (first electrode) is a rod-shaped conductor that is disposed in the axial hole 12 along the axis O.

[0014] FIG. 2 is a half-side cross-sectional view of the spark plug 10, enlarging the portion indicated by II in FIG. 1. The center electrode 13 includes a base material 14, a discharge member 15 provided at the tip of the base material 14, and a fusion zone 16 formed by the melting of the base material 14 and the discharge member 15. A core material having excellent thermal conductivity is embedded in the base material 14. The base material 14 is made of a metal containing Ni as its main component, and the core material is made of, for example, Cu or an alloy containing Cu as its main component. The core material can be omitted. The base material 14 being made of a metal containing Ni as its main component means that Ni accounts for 50% or more by mass of the metal.

[0015] The material of the discharge member 15 is a metal whose main component is Ru. Ru being the main component means that the mass ratio of Ru to the mass of the discharge member 15 is 50% or more. In this embodiment, the shape of the discharge member 15 is disk-shaped. The discharge member 15 is fixed to the base material 14 via a fusion zone 16 formed by laser welding, resistance welding, or the like.

[0016] Returning to Fig. 1, the terminal fitting 17 is a rod-shaped conductor to which an ignition device (not shown) is connected, and its tip side is disposed in the axial hole 12 of the insulator 11. The terminal fitting 17 is electrically connected to the center electrode 13 in the axial hole 12.

[0017] The metallic shell 18 is a substantially cylindrical member that is fixed to a threaded hole in a spark plug hole of an internal combustion engine (not shown). The metallic shell 18 is made of a conductive metal material (such as low-carbon steel). The metallic shell 18 is fixed to the outer periphery of the insulator 11. A ground electrode 19 (second electrode), which is a rod-shaped conductor, is connected to the metallic shell 18. The ground electrode 19 is bent from the metallic shell 18 toward the axis O.

[0018] As shown in Fig. 2, the ground electrode 19 includes a base material 20 connected to the metallic shell 18, a discharge member 21 provided on the base material 20, and a fusion zone 22 formed by the base material 20 and the discharge member 21 melting together. A core material with excellent thermal conductivity is embedded in the base material 20. The material of the base material 20 is, for example, an alloy containing Ni as its main component, and the material of the core material is Cu or an alloy containing Cu as its main component. The core material can be omitted.

[0019] Examples of materials for the discharge member 21 include precious metals such as Pt, Ir, Ru, and Rh, W, or alloys mainly composed of precious metals or W, which have higher resistance to spark consumption than the base material 20. The discharge member 21 is fixed to the base material 20 via a fusion zone 22 made by laser welding, resistance welding, or the like. The discharge member 15 of the center electrode 13 has a discharge surface 23 facing the tip side that faces the ground electrode 19 via a spark gap 24.

[0020] The spark plug 10 is manufactured, for example, by the following method. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11. Next, the metal terminal 17 is inserted into the axial hole 12 to ensure electrical continuity between the metal terminal 17 and the center electrode 13. Then, the metal shell 18, to which the ground electrode 19 is previously connected, is assembled to the outer periphery of the insulator 11. The ground electrode 19 is bent to form a spark gap 24 between the center electrode 13 and the discharge member 21 of the ground electrode 19, and the spark plug 10 is obtained.

[0021] The center electrode 13 has a value M / D obtained by dividing the Vickers hardness M of the fusion zone 16 by the Vickers hardness D of the discharge member 15, which is 0.25 or more and 2.8 or less. The test surface for measuring the Vickers hardness M and D is a polished cross section including a straight line 26 (a straight line 26 perpendicular to the discharge surface 23) passing through the center of gravity 25 of the discharge surface 23 of the discharge member 15. The center of gravity 25 of the discharge surface 23 is the geometric center calculated by a known method when the discharge surface 23 is considered as a plane figure.

[0022] Vickers hardness is calculated based on JIS Z2244-1:2020 by dividing the test force applied by pressing an indenter into the test surface by the surface area of ​​the indentation made by the indenter on the test surface. Taking into account variations, the average of the Vickers hardnesses at 30 arbitrary points on the test surface of the fusion zone 16 is taken as the Vickers hardness of the fusion zone 16, and the average of the Vickers hardnesses at 30 arbitrary points on the test surface of the discharge member 15 is taken as the Vickers hardness of the discharge member 15.

[0023] The discharge member 15 is produced by compressing and molding powder containing Ru, followed by sintering at high temperatures (sintering method). By using the sintering method, the Vickers hardness of the discharge member 15 can be increased or decreased by adjusting the temperature and pressure during sintering. By using the sintering method, the discharge member 15 can be formed into any shape, such as a disk, a truncated cone, an elliptical cylinder, or a polygonal cylinder such as a triangular prism or a square prism.

[0024] The discharge member 15 can also be produced by hot or cold forging, rolling, swabbing, punching, wire drawing, or other plastic processing of an ingot of a metal material containing Ru. By using plastic processing, the Vickers hardness of the discharge member 15 can be adjusted by processing strain (work hardening) and grain refinement.

[0025] The fusion zone 16 is produced by laser welding. With laser welding, the Vickers hardness of the fusion zone 16 can be increased or decreased by changing the ratio of the base material 14 and the discharge member 15 in the fusion zone 16 through the laser output and the irradiation position of the laser beam. The fusion zone 16 can also be produced by resistance welding. With resistance welding, the Vickers hardness of the fusion zone 16 can be adjusted by the welding current, current flow time, pressure, etc.

[0026] The crystal structure of Ru is a hexagonal close-packed lattice, which has high resistance to shear against external forces and is difficult to deform, so there is a problem that the discharge member 15, which is mainly composed of Ru, is prone to cracking. If the value M / D obtained by dividing the Vickers hardness M of the fusion zone 16 by the Vickers hardness D of the discharge member 15 is set to be 0.25 or more and 2.8 or less, the deformation of the fusion zone 16 will assist the deformation of the discharge member 15, so that cracking of the discharge member 15 joined to the base material 14 via the fusion zone 16 can be reduced.

[0027] The Vickers hardness of the fusion zone 16 is preferably 100 HV or more and 650 HV or less, and more preferably 120 HV or more and 630 HV or less. This is to ensure the tensile strength and toughness of the fusion zone 1622 so as to reduce cracking of the discharge member 15.

[0028] The Vickers hardness of the discharge member 15 is preferably 180 HV or more and 550 HV or less, and more preferably 200 HV or more and 530 HV or less, in order to ensure the tensile strength and toughness of the discharge member 15.

[0029] In addition to Ru, the discharge member 15 preferably contains one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, W, Au, Al, Co, Ni, Cr, and Si. The atomic radii of these elements are in the range of 111-144 pm, which is close to the atomic radius of Ru, 134 pm, and therefore the mechanical strength of the fusion zone 16 formed by the fusion of the base material 14 and the discharge member 15 can be increased by solid solution strengthening.

[0030] It is more preferable that the discharge member 15 contains, in addition to Ru, one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, and W. The atomic radii of these elements are in the range of 130-139 pm, which is closer to the atomic radius of Ru, 134 pm, and therefore the mechanical strength of the fusion zone 16 can be further increased by solid solution strengthening.

[0031] The discharge member 21 may contain oxides such as Y2O3 and Al2O3 in addition to Ru. The oxide content is, for example, 8% by mass or less. The total proportion of elements other than Ru (excluding impurities) and oxides in the discharge member 21 is preferably 40% by mass or less. This is to prevent a decrease in the melting point of the discharge member 21. Examples of impurities include Na, K, Fe, Sn, Mn, Cu, Ag, and Th. The proportion of impurities in the discharge member 21 is, for example, less than 1% by mass. [Example]

[0032] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0033] (Production of Discharge Member) The researchers vacuum-melted a mixture of metals such as Ru, Ir, and Rh, and Y2O3 in various ratios, and then used inert gas atomization to obtain various powders with different Ru ratios. The powder was placed in a mold and compressed to obtain cylindrical compacts, which were then sintered at approximately 2000°C in a reducing atmosphere. By varying the sintering temperature and time, various discharge members with different Vickers hardness were obtained. The discharge members were cylindrical, with a base diameter of 0.6 mm and a height of 0.55 mm. The density of the discharge members (according to the Archimedes method) was over 95%. The chemical composition of the discharge members was measured using a wavelength-dispersive X-ray spectrometer (WDS). The measurement conditions were an acceleration voltage of 20 kV, a beam diameter of 20 μm, and a measurement time of 10 seconds at peak top.

[0034] (Preparation of test specimens) The tester performed laser welding with the bottom of the discharge member in contact with the edge of the bottom of a rectangular base material with a bottom width of 2.7 mm and a height of 1.3 mm, and obtained a test piece for Sample No. 1-68 in which the discharge member was joined to the base material via the fusion zone. The base material was a nickel-based alloy NCF601. For example, the laser welding conditions for Sample No. 61 were a laser power range of 10-50 W. By varying the laser power and the laser beam irradiation position, the Vickers hardness of the fusion zone of the test piece was varied. This resulted in two test pieces for Sample No. 1-68, each containing a discharge member and fusion zone with different Vickers hardnesses.

[0035] Each test piece of sample No. 1-68 was embedded in epoxy resin and hardened, and then a cross section including a line passing through the center of gravity of the bottom surface of the discharge member (a line perpendicular to the bottom surface) was polished to prepare a test surface. The presence or absence of cracks in the discharge member and fusion zone on the test surface was confirmed using a metallurgical microscope.

[0036] (Vickers hardness measurement) For the test pieces that had been confirmed to have cracks, an indenter was pressed into the test surfaces of the fusion zone and the discharge member with a test force of 500 N for 10 seconds to determine their Vickers hardness in accordance with JIS Z2244-1:2020. The average of the Vickers hardnesses at 30 arbitrary points on the test surface of the fusion zone was taken as the Vickers hardness M of the fusion zone, and the average of the Vickers hardnesses at 30 arbitrary points on the test surface of the discharge member was taken as the Vickers hardness D of the discharge member. The Vickers hardness M of the fusion zone was divided by the Vickers hardness D of the discharge member to determine M / D.

[0037] (heat cycle test) A metal shell connected to a ground electrode was assembled around the outer periphery of an insulator on which a center electrode and a metal terminal, each connected to one of the test pieces of Sample No. 1-68, were arranged, and the ground electrode was then bent to provide a spark gap between the ground electrode and the discharge member of the center electrode. The materials and dimensions of the parts of the spark plug samples other than the test pieces were the same.

[0038] The testers attached the sample to a 2-liter, four-cylinder, direct-injection turbocharged engine and conducted a thermal cycle test in which the engine was operated at 5,000 rpm for one minute, then at 800 rpm for one minute, repeating this cycle for a total of 100 hours.

[0039] After the thermal cycle test, the sample specimen was embedded in epoxy resin and hardened. Then, a cross section including a line passing through the center of gravity of the bottom surface of the discharge member (a line perpendicular to the bottom surface) was polished, and the presence or absence of cracks in the discharge member and the molten part was confirmed using a metallurgical microscope.

[0040] Samples in which cracks were found in the test piece after laser welding were rated C. Samples in which no cracks were found in the test piece after laser welding but cracks were found after the thermal cycle test were rated B. Samples in which no cracks were found after laser welding or the thermal cycle test were rated A.

[0041] The chemical composition, Vickers hardness M, D, value M / D, and judgment of the discharge member of Sample No. 1-68 are shown in Tables 1 and 2. The chemical composition of each sample is shown in Tables 1 and 2, with Ru as the balance (balance) and the proportion (mass%) of added elements excluding impurities other than Ru.

[0042] [Table 1]

[0043] [Table 2]

[0044] As shown in Tables 1 and 2, sample No. 1 with an M / D value of 0.24 and sample No. 68 with an M / D value of 2.90 were judged to be C. It is presumed that the deformation of the fusion zone was unable to assist the deformation of the discharge member, and that the discharge member cracked due to the tensile stress of the discharge member caused by the rapid heating and cooling during welding and the contraction of the fusion zone.

[0045] In contrast, sample No. 2-67, which had an M / D value of 0.25 or more and 2.80 or less, was judged to be A or B. It is estimated that the tensile stress of the discharge material caused by the rapid heating and cooling during welding and the shrinkage of the molten part was reduced by the molten part, which is why the discharge material and the molten part did not crack during welding.

[0046] In particular, sample No. 34-67, which had an M / D value of 1.05 or more and 2.80 or less, was rated A. It became clear that when the M / D value is in this range, cracks do not occur in the discharge material or fusion zone even when subjected to thermal shock during the thermal cycle test.

[0047] Sample No. 34-67, which was graded A, contained elements selected from the group consisting of Ir, Pt, Rh, Re, and Pd in ​​addition to Ru. It is presumed that the grade was A because the strength of the fusion zone was improved by solid solution strengthening due to these elements.

[0048] 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.

[0049] In the embodiment, the center electrode 13 is exemplified as the first electrode and the ground electrode 19 is exemplified as the second electrode, but this is not necessarily limited to this. It is of course possible to use the ground electrode 19 as the first electrode and the center electrode 13 as the second electrode. In this case, the discharge member 21, which is mainly composed of Ru, is fixed to the base material 20, which is mainly composed of Ni, of the ground electrode 19 via the fusion zone 22, and the value obtained by dividing the Vickers hardness of the fusion zone 22 by the Vickers hardness of the discharge member 21 is set to be 0.25 or more and 2.8 or less.

[0050] In the embodiment, the base material 20 of the ground electrode 19 is bent, but this is not necessarily limited to this. Naturally, it is possible to use a straight base material instead of the bent base material 20. In this case, the tip end of the metallic shell 18 is extended in the axial direction, and the straight base material is connected to the metallic shell 18, so that the ground electrode 19 faces the center electrode 13. The number of ground electrodes 19 is also set appropriately.

[0051] In the embodiment, the ground electrode 19 is disposed so that the discharge member 15 faces the ground electrode 19 in the axial direction. However, this is not necessarily limited to this, and the positional relationship between the ground electrode 19 and the center electrode 13 can be set as appropriate. As another positional relationship between the ground electrode 19 and the center electrode 13, for example, the ground electrode 19 may be disposed so that the side surface of the discharge member 15 of the center electrode 13 faces the ground electrode 19.

[0052] In the embodiment, the discharge member 21 is fixed to the surface of the base material 20 of the ground electrode 19 facing the rear end, but this is not necessarily limited to this. As long as a spark gap 24 is provided between the discharge member 21 and the center electrode 13, the discharge member 21 may be fixed to any surface of the base material 20. It is of course possible to omit the discharge member 21 from the ground electrode 19. [Explanation of symbols]

[0053] 10 Spark Plugs 13 Center electrode (1st electrode) 14 Base material 15 Discharge member 16 Welding section 19 Ground electrode (second electrode) 24 Spark Gap

Claims

1. a first electrode including a discharge member joined to a base material mainly composed of Ni via a fusion zone; a second electrode facing the discharge member across a spark gap, The discharge member is a spark plug containing Ru as a main component, A spark plug in which the value obtained by dividing the Vickers hardness of the fusion zone by the Vickers hardness of the discharge member is 0.25 or more and 2.8 or less.

2. 2. The spark plug according to claim 1, wherein the discharge member contains one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, W, Au, Al, Co, Ni, Cr, and Si.

3. 2. The spark plug according to claim 1, wherein said value is equal to or greater than 1.05 and equal to or less than 2.

8.

4. 4. The spark plug according to claim 3, wherein said discharge member contains one or more elements selected from the group consisting of Ir, Pt, Rh, Re, Pd, Mo, and W.

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