Spark plug

Abstract

To provide a spark plug capable of reducing occurrence of cracking in a chip.SOLUTION: A spark plug comprises an insulator in which an axis hole extending in an axis line is provided, a center electrode which is disposed in the axis hole, a main body fitting which is disposed in an outer periphery of the insulator, and a ground electrode which is connected to the main body fitting. At least one of the center electrode and the ground electrode includes a chip containing Ru as a main component, and a porosity of the chip is from 0.1 ppm or more to 100,000 ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a prior art in which at least one of the center electrode and the ground electrode includes a tip made of simple Ru or a Ru alloy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-54955 Summary of the Invention [Problem to be solved by the invention]

[0004] Chips containing Ru as the main component generally have poor ductility, so there is a risk of cracks occurring in the chips due to vibrations from the engine, etc.

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

[0006] A first aspect for achieving this object includes an insulator having an axial hole extending along an axis, a center electrode disposed in the axial hole, a metallic shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metallic shell, wherein at least one of the center electrode and the ground electrode includes a tip containing Ru as a main component, and the porosity of the tip is 0.1 ppm or more and 100,000 ppm or less.

[0007] In a second aspect, in the first aspect, the amount of hydrogen contained in the chip is 0.1 ppm or more and 4 ppm or less.

[0008] In a third aspect, in the first or second aspect, the tip comprises Pt.

[0009] A fourth aspect is the third aspect, wherein the proportion of Pt in the tip is 0.1 mass % or more and 30 mass % or less.

[0010] A fifth aspect is any one of the first to fourth aspects, wherein the tip has a Vickers hardness of 190 HV or more. [Effects of the Invention]

[0011] According to the present invention, by setting the porosity of the chip to 0.1 ppm or more and 100,000 ppm or less, the pores can relieve stress and reduce the occurrence of cracks. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a half cross-sectional view of a spark plug according to an embodiment; [Figure 2] 2 is a cross-sectional view of a portion where a center electrode and a ground electrode of a spark plug face each other. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 one embodiment, taken along axis X. 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.

[0014] As shown in Fig. 1, a spark plug 10 includes an insulator 11, a center electrode 13, a metallic shell 15, and a ground electrode 16. The insulator 11 is a substantially cylindrical member made of a ceramic such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 has an axial hole 12 that penetrates along the axis X. The center electrode 13 is a rod-shaped electrode that is disposed in the axial hole 12 along the axis X.

[0015] The terminal fitting 14 is a rod-shaped member 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 14 is electrically connected to the center electrode 13 in the axial hole 12.

[0016] The metal shell 15 is a substantially cylindrical metal member that is fixed to a screw hole (not shown) of an internal combustion engine. The metal shell 15 is made of a conductive metal material (such as low-carbon steel). The metal shell 15 is fixed to the outer periphery of the insulator 11. A ground electrode 16 is connected to the metal shell 15.

[0017] 2 is a cross-sectional view of the portion of the spark plug 10 where the center electrode 13 and the ground electrode 16 face each other. The center electrode 13 includes a base material 17 and a tip 20 provided at the tip of the base material 17.

[0018] A core material 18 having excellent thermal conductivity is embedded in the base material 17. The material of the base material 17 is, for example, Ni or an alloy containing Ni as a main component, and the material of the core material 18 is, for example, Cu or an alloy containing Cu as a main component. The core material 18 can be omitted.

[0019] The tip 20 is joined to the base material 17 by a fusion zone 19. The tip 20 and the base material 17 are melted together in the fusion zone 19. The fusion zone 19 is formed by laser welding, resistance welding, diffusion bonding, or the like. The tip 20 includes a tip surface 21 in the thickness direction of the tip 20 and a side surface 22 connected to the tip surface 21.

[0020] The ground electrode 16 includes a base material 23 connected to the metallic shell 15 and a tip 25 provided in the base material 23. A core material (not shown) with excellent thermal conductivity is embedded in the base material 23. The base material 23 is made of an alloy containing Ni as its main component, and the core material is made of Cu or an alloy containing Cu as its main component. The core material can be omitted. An intermediate member protruding toward the center electrode 13 may be provided in the base material 23, and the tip 25 may be joined to the intermediate member. The intermediate member is a part of the base material 23.

[0021] The tip 25 is joined to the base material 23 by a fusion zone 24. The tip 25 and the base material 23 are melted to form the fusion zone 24. The fusion zone 24 is formed by laser welding, resistance welding, diffusion bonding, or the like. The tip 25 includes a front end surface 26 in the thickness direction of the tip 25 and a side surface 27 connected to the front end surface 26. In this embodiment, the front end surface 21 of the tip 20 of the center electrode 13 and the front end surface 26 of the tip 25 of the ground electrode 16 face each other, and a spark gap is provided between the front end surface 21 and the front end surface 26.

[0022] At least one of the chips 20, 28 has Ru as its main component. "Having Ru as its main component" means that Ru is the element with the largest content among the elements constituting the chips 20, 28. The Ru content is preferably 50% by mass or more, more preferably 60% by mass or more or 70% by mass or more, of the total amount of components constituting the chips 20, 28.

[0023] When the tip 20 of the center electrode 13 is primarily composed of Ru, or when the tip 25 of the ground electrode 16 is primarily composed of Ru, the elements other than Ru that make up the tips 20, 28 can be one or more selected from Rh, Pd, Os, Ir, Pt, Ta, W, Mo, Nb, Re, Cr, Mn, Fe, Co, Ni, V, Ti, Zr, Hf, Al, and Sc.

[0024] When the tip 20 of the center electrode 13 is mainly composed of Ru, the ground electrode 16 is either one that includes a tip 25 mainly composed of Ru, one that includes a tip 25 mainly composed of one or more platinum group elements other than Ru (Rh, Pd, Os, Ir, Pt), or one in which the fusion zone 24 and the tip 25 are not provided in the base material 23.

[0025] When the tip 25 of the ground electrode 16 is mainly composed of Ru, the center electrode 13 is either one that includes a tip 20 mainly composed of Ru, one that includes a tip 20 mainly composed of one or more platinum group elements other than Ru (Rh, Pd, Os, Ir, Pt), or one in which the fusion zone 19 and the tip 20 are not provided in the base material 17.

[0026] 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 14 is inserted into the axial hole 12 to ensure electrical continuity between the metal terminal 14 and the center electrode 13, and then the metal shell 15, to which the ground electrode 16 is previously connected, is assembled to the outer periphery of the insulator 11. The ground electrode 16 is bent to form a spark gap between the center electrode 13 and the ground electrode 16, and the spark plug 10 is obtained.

[0027] The chips 20, 25, which are primarily composed of Ru, are made by sintering a compact of metal powder containing Ru (powder or metallurgical method), punching a metal plate containing Ru, cutting a metal wire containing Ru, etc. The shape of the chips 20, 25 is not limited and may be a disk, a truncated cone, an elliptical cylinder, or a polygonal prism such as a triangular prism or a square prism.

[0028] When the tip 20 of the center electrode 13 is mainly composed of Ru, the porosity of the tip 20 is 0.1 ppm or more and 100,000 ppm or less. The pores in the tip 20 relieve stress and reduce the occurrence of cracks in the tip 20. If the porosity is low, stress tends to be less relieved, and if the porosity is high, the mechanical strength of the tip 20 tends to decrease.

[0029] The porosity of the tip 20 is measured by Archimedes' method after cutting the tip 20 and separating the fused portion 19. When the tip 20 is produced by powder metallurgy, the porosity of the tip 20 can be set by adjusting the particle size distribution of the metal powder and the sintering temperature. When the tip 20 is produced by punching a metal plate or cutting a wire, the porosity can be set by adjusting the processing conditions, such as forging or rolling the plate or wire.

[0030] The amount of hydrogen contained in the tip 20 is preferably 0.1 ppm or more and 4 ppm or less. The hydrogen contained in the tip 20 is released at temperatures at which the spark plug 10 is used, and gaps where the hydrogen has escaped are formed in the tip 20. These gaps relieve stress, further reducing the occurrence of cracks in the tip 20. If the amount of hydrogen is small, stress tends to be less relieved, while if the amount of hydrogen is large, there tends to be more defects in the metal bonding of the tip 20, reducing the mechanical strength of the tip 20.

[0031] The amount of hydrogen contained in the chip 20 is measured by cutting the chip 20 and separating the fused portion 19 using an atmospheric pressure ionization mass spectrometer. The chip 20 is heated from room temperature to 900°C at a rate of 10°C / min in an argon atmosphere, and the amount of hydrogen released is measured.

[0032] When the chip 20 is produced by powder metallurgy, the amount of hydrogen contained in the chip 20 can be set by adjusting the hydrogen concentration in the atmosphere during sintering, annealing, etc. When the chip 20 is produced by punching a metal plate or cutting a wire, the amount of hydrogen in the chip 20 can be set by adjusting the hydrogen concentration in the atmosphere during production of the plate or wire, and the pressure during sintering.

[0033] When the tip 20 contains Pt, Pt has a high affinity for hydrogen and hydrogen is incorporated into the Pt crystal lattice, which is advantageous for increasing the amount of hydrogen contained in the tip 20. The proportion of Pr in the tip 20 is preferably 0.1% by mass or more and 30% by mass or less. This is to ensure the mechanical strength of the tip 20.

[0034] The Vickers hardness of the tip 20 is preferably 190 HV or higher. This is to ensure the mechanical strength of the tip 20. The Vickers hardness of the tip 20 is measured by pressing an indenter into the front end surface 21 or the cross section of the tip 20. The Vickers hardness can be adjusted by changing the conditions such as temperature and pressure during sintering and processing of the tip 20.

[0035] When the tip 25 of the ground electrode 16 is mainly composed of Ru, the porosity, amount of hydrogen, proportion of Pt, or Vickers hardness of the tip 25 is set within the same range as the porosity, amount of hydrogen, proportion of Pt, and Vickers hardness of the tip 20 of the center electrode 13. This reduces the occurrence of cracks in the tip 25. [Example]

[0036] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0037] The testers fabricated Nos. 1-50 chips using powder metallurgy, each cylindrical with a diameter of 0.6 mm and a height of 0.5 mm and varying porosity. Nos. 1-8 chips were made of a Ru-Pt alloy containing 0.1% Pt by mass and the remainder Ru. The hydrogen content of the chips was 0.1-0.2 ppm, and the Vickers hardness was 190-200 HV. Nos. 9-13 chips were made of a Ru-Pt alloy containing 0.1% Pt by mass and the remainder Ru. The Vickers hardness was 190-200 HV. Nos. 14-44 chips had a Vickers hardness of 190-200 HV.

[0038] The porosity of the tip was set by adjusting the particle size distribution of the metal powder and the sintering temperature. The amount of hydrogen in the tip was set by the amount of hydrogen gas used during sintering. The Vickers hardness of the tip was set by the pressure used during sintering. The tester created center electrodes by joining the tips to the base material, and then manufactured spark plugs in the same manner as in the above embodiment, and created multiple samples of each of No. 1-50 spark plugs in which a spark gap was provided between the front end surface of the center electrode tip and the ground electrode.

[0039] The testers separated chips from the samples and measured the porosity of the chips using the Archimedes method (10 samples) and the amount of hydrogen contained in the chips using an atmospheric pressure ionization mass spectrometer (10 samples). They also pressed an indenter into five locations on the chip cross section to measure Vickers hardness (5 samples). The average of the measurements was used as the representative value for porosity, hydrogen content, and Vickers hardness for each sample.

[0040] The testers mounted each of the samples No. 1-50 with the tips intact on an engine (Model L13A) and ran the engine at 5,000 rpm for one minute, followed by another minute at 800 rpm. This cycle was repeated alternately for 100 hours of continuous operation. After the test, a cross section parallel to the axis including the center of the tip end face was prepared and the tip cracks were observed using a metallurgical microscope. If a crack was present in the tip, it propagated in the direction of the tip end face extension, so the crack percentage was calculated by dividing the length of the crack in the direction of the tip end face extension by the length of the tip end face.

[0041] Samples with no cracks observed on the chip were rated A, and samples with a crack rate greater than 0% but less than 30% were rated B. Samples with a crack rate of 30% or more but less than 50% were rated C, samples with a crack rate of 50% or more but less than 90% were rated D, and samples with a crack rate of 90% or more were rated E. The results are shown in Table 1-4.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] [Table 4]

[0046] According to Table 1, samples No. 2-7, whose chip porosity was 0.1 ppm or more and 100,000 ppm or less, were rated B or C, whereas sample No. 1, whose porosity was less than 0.1 ppm, and sample No. 8, whose porosity was greater than 100,000 ppm, were rated E. This demonstrates that chip cracking can be reduced when the chip porosity is 0.1 ppm or more and 100,000 ppm or less.

[0047] According to Table 2, samples No. 10-12, in which the amount of hydrogen in the chip was between 0.1 ppm and 4.0 ppm, were graded C, while sample No. 9, in which the amount of hydrogen was less than 0.1 ppm, and sample No. 13, in which the amount of hydrogen was greater than 4.0 ppm, were graded D. This demonstrates that if the amount of hydrogen contained in the chip is between 0.1 ppm and 4.0 ppm, the occurrence of cracks in the chip can be further reduced.

[0048] According to Table 3, samples Nos. 18 and 20-34, which had chip porosities between approximately 4000 ppm and 6000 ppm and chip hydrogen contents between 0.1 ppm and 4.0 ppm, were graded B, whereas samples Nos. 14-17, which had hydrogen contents less than 0.1 ppm, and samples Nos. 36-44, which had hydrogen contents greater than 4.0 ppm, were graded C or D. This demonstrates that chip cracking can be further reduced when the amount of hydrogen contained in the chip is between 0.1 ppm and 4.0 ppm.

[0049] According to Table 3, samples Nos. 18 and 20-34, which had a hydrogen content of 0.1 ppm or more and 4.0 ppm or less and a Pt content of 0.1 mass% or more and 30 mass% or less, were rated B, whereas samples Nos. 19 and 35, which had a hydrogen content of 0.1 ppm or more and 4.0 ppm or less but a Pt content of more than 30 mass%, were rated C. This demonstrates that the occurrence of cracks in the chip can be further reduced when the Pt content is 0.1 mass% or more and 30 mass% or less.

[0050] According to Table 4, samples Nos. 46-48, which had chip porosity of 0.1 ppm or more and 100,000 ppm or less, chip hydrogen content of 0.1 ppm or more and 4.0 ppm or less, Pt content of 0.1 mass % or more and 30 mass % or less, and Vickers hardness of 190 HV or more, were rated A, while the other samples were rated B, C, or D.

[0051] 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.

[0052] In the embodiment, the ground electrode 16 is bent, but the present invention is not limited to this. Naturally, a straight ground electrode 16 can be used instead of the bent ground electrode 16. In this case, the tip end side of the metallic shell 15 is extended in the axial direction, and the straight ground electrode 16 is joined to the metallic shell 15. The number of ground electrodes 16 is also set appropriately.

[0053] In the embodiment, the center electrode 13 and the ground electrode 16 are arranged so that a spark gap is formed in the direction of the axis X between the front end surface 21 of the tip 20 of the center electrode 13 and the ground electrode 16, but this is not necessarily limited to this. The positional relationship between the center electrode 13 and the ground electrode 16 can be set as appropriate. Another positional relationship between the center electrode 13 and the ground electrode 16, for example, is that the side surface 22 of the tip 20 of the center electrode 13 and the ground electrode 16 are opposed to each other in a direction perpendicular to the axis X so that a spark gap is formed between the center electrode 13 and the ground electrode 16 in a direction perpendicular to the axis X. [Explanation of symbols]

[0054] 10 Spark Plugs 11 Insulators 12 Shaft hole 13 Center electrode 15 Metal body 16 Ground electrode 17 Base material 20.25 chips X axis

Claims

1. an insulator provided with an axial hole extending along an axis; a center electrode disposed in the axial hole; a metallic shell disposed on the outer periphery of the insulator; a ground electrode connected to the metallic shell, a spark plug in which at least one of the center electrode and the ground electrode includes a tip containing Ru as a main component, The porosity of the tip is 0.1 ppm or more and 100,000 ppm or less.

2. 2. The spark plug according to claim 1, wherein the amount of hydrogen contained in said tip is 0.1 ppm or more and 4 ppm or less.

3. 3. The spark plug according to claim 1, wherein the tip contains Pt.

4. 4. The spark plug according to claim 3, wherein the percentage of Pt in the tip is 0.1% by mass or more and 30% by mass or less.

5. 3. The spark plug according to claim 1, wherein the tip has a Vickers hardness of 190 HV or more.

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