Spark plug with

Abstract

To provide a spark plug capable of improving pull-out strength of a terminal fitting while suppressing a temperature rise of the terminal fitting.SOLUTION: The spark plug includes a center electrode disposed on a front end side in an axial hole of an insulator, a metal terminal disposed on a rear end side in the axial hole, a resistance material provided in the axial hole, a first conductive material in contact with the resistance material and the center electrode, and a second conductive material in contact with the resistance material and the metal terminal. When the front side of the first range is defined as a second range, the porosity of the first range is smaller than that of the second range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a spark plug having a built-in resistor material. [Background technology]

[0002] To reduce noise generated during discharge, a spark plug is known that includes a resistor provided within an axial bore of an insulator, a first conductive material in contact with the center electrode and the resistor, and a second conductive material in contact with the resistor and a terminal fitting.Patent Document 1 discloses a prior art technique for improving the pull-out strength of a terminal fitting by setting the dimensions of the resistor portion and setting the porosity of the resistor to 5.0% or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5401606 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, when the porosity of the resistor material is high, the tensile strength of the resistor material decreases, so when a tensile load is applied to the terminal fitting, the resistor material joined to the terminal fitting via the second conductive material may break with a relatively small force. On the other hand, when the porosity of the resistor material is low, the thermal conductivity of the resistor material increases, causing the temperature of the terminal fitting to rise.

[0005] The present invention has been made to solve this problem, and has as its object to provide a spark plug that can improve the pull-out strength of the terminal metal fittings while suppressing the temperature rise of the terminal metal fittings. [Means for solving the problem]

[0006] A first aspect for achieving this object includes an insulator having an axial hole extending from the front end to the rear end along an axis, a metallic shell arranged on the outer periphery of the insulator, a center electrode arranged on the front end side within the axial hole, a terminal fitting arranged on the rear end side within the axial hole, a resistor material arranged in the axial hole, a first conductive material in contact with the resistor material and the center electrode, and a second conductive material in contact with the resistor material and the terminal fitting, wherein, in a cross section including the axis, when 10% of the axial length of the resistor material from the rear end side is defined as a first range and the range from the first range to the front end side is defined as a second range, the porosity of the first range is smaller than the porosity of the second range.

[0007] A second embodiment is the first embodiment, wherein the porosity in the first range is 0.8% or less.

[0008] In the third aspect, in the first or second aspect, when the leading 10% of the axial length of the resistance material is defined as a third range and the trailing side of the third range is defined as a fourth range, the porosity of the third range is greater than the porosity of the fourth range.

[0009] A fourth embodiment is the third embodiment, wherein the porosity in the third range is 1.5% or more. [Effects of the Invention]

[0010] According to the present invention, a center electrode, a first conductive material, a resistor, a second conductive material, and a terminal fitting are arranged in an axial hole of an insulator in this order from the tip, and the porosity of a first region on the rear end side of the resistor is smaller than the porosity of a second region on the tip side of the first region. The tensile strength of the first region in contact with the second conductive material can be increased, thereby improving the pull-out strength of the terminal fitting joined to the first region via the second conductive material. Meanwhile, the porosity of the second region is greater than the porosity of the first region, thereby suppressing an increase in thermal conductivity in the second region and suppressing a rise in temperature of the terminal fitting. [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. [Figure 3] 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-sectional view of a spark plug 10 according to one embodiment, combining an outline view and a full cross-sectional view along axis X. The lower side of Fig. 1 is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10 (the same applies to Figs. 2 and 3). The spark plug 10 includes an insulator 11, a center electrode 13, a metal terminal 17, and a metal shell 18.

[0013] The insulator 11 is a cylindrical member having an axial hole 12 extending along the axis X, and is made of ceramic such as alumina, which has excellent insulating properties and mechanical properties at high temperatures. The axial hole 12 is connected from the rear end to the front end of the insulator 11.

[0014] A center electrode 13 is disposed at the tip end of the axial hole 12 of the insulator 11. The center electrode 13 is a rod-shaped conductor, and a core material with excellent thermal conductivity is embedded in a base material. Examples of the material of the base material include a Ni-based alloy or a metal made of Ni. Examples of the material of the core material include copper or an alloy mainly composed of copper. The core material can be omitted. A tip containing a precious metal such as Pt, Ir, or Ru can be provided at the tip of the center electrode 13, or the tip can be omitted.

[0015] A terminal fitting 17 is disposed at the rear end side within the axial hole 12 of the insulator 11. The terminal fitting 17 is a rod-shaped metal member to which an ignition device (not shown) is connected. The material of the terminal fitting 17 is, for example, low carbon steel. The front end side of the terminal fitting 17 is disposed within the axial hole 12 of the insulator 11, and the rear end side of the terminal fitting 17 protrudes from the insulator 11. A first conductive material 14, a resistive material 15, and a second conductive material 16 are disposed within the axial hole 12 of the insulator 11 between the center electrode 13 and the terminal fitting 17, in this order from the front end side.

[0016] The first conductive material 14 functions to fix the center electrode 13 to the insulator 11 and to close the axial hole 12. The second conductive material 16 functions to fix the terminal fitting 17 to the insulator 11. The first conductive material 14 and the second conductive material 16 are conductive. The first conductive material 14 contacts the center electrode 13 and the resistor material 15, and the second conductive material 16 contacts the resistor material 15 and the terminal fitting 17.

[0017] The first conductive material 14 and the second conductive material 16 are, for example, a mixture containing glass particles and conductor (particles) in a ratio of about 1:1. Examples of glass particle materials include B2O3-SiO2, BaO-B2O3, SiO2-B2O3-BaO, and SiO2-ZnO-B2O3. Examples of conductor materials include metals such as Cu and Fe. A plurality of these materials may be mixed.

[0018] The resistive material 15 is a member for reducing noise generated during discharge. The resistive material 15 is a mixture containing glass particles, ceramic particles other than glass, and conductor (particles). Examples of glass particle materials include B2O3-SiO2, BaO-B2O3, SiO2-B2O3-BaO, and SiO2-ZnO-B2O3. Examples of ceramic particle materials include oxides such as TiO2 and ZrO2. Examples of conductor materials include carbon (carbon black, etc.), non-metallic conductive materials such as TiC and TiN, and metals such as Al, Mg, Ti, Zr, and Zn.

[0019] The ratio of glass particles in resistive material 15 is, for example, 60-90 mass %, the ratio of ceramic particles is 5-30 mass %, and the ratio of conductor is 0.5-10 mass %. When the ratios of particles, ceramic particles, and conductor are within these ranges, resistive material 15 can be set to an appropriate resistance value, thereby ensuring the noise reduction effect of resistive material 15.

[0020] The metallic shell 18 is a substantially cylindrical member made of a conductive metal material (such as low-carbon steel). The metallic shell 18 is disposed on the outer periphery of the insulator 11. The ground electrode 19 is a rod-shaped conductor connected to the metallic shell 18. A spark gap is formed between the ground electrode 19 and the center electrode 13. The ground electrode 19 may be omitted, or multiple ground electrodes 19 may be connected to the metallic shell 18.

[0021] The spark plug 10 is manufactured, for example, by the following method. First, the center electrode 13 is inserted into the axial bore 12 from the rear end of the insulator 11. Next, raw material powder of the first conductive material 14 is placed in the axial bore 12, and the raw material powder is packed around the center electrode 13. After that, the raw material powder is pre-compressed using a compression rod (not shown). Next, raw material powder of the resistor material 15 is packed on top of the raw material powder of the first conductive material 14, and the raw material powder is pre-compressed using a compression rod. Finally, raw material powder of the second conductive material 16 is packed on top of the raw material powder of the resistor material 15, and the raw material powder is pre-compressed using a compression rod.

[0022] A terminal fitting 17 is inserted into the axial hole 12 from the rear end of the insulator 11 so that the tip of the terminal fitting 17 comes into contact with the raw material powder of the second conductive material 16. The terminal fitting 17 is then pressed into the raw material powder while heating it to a temperature higher than the softening point of the glass component contained in the raw material powder. An axial load is applied to the raw material powder by the terminal fitting 17, compressing and solidifying the raw material powder to form the first conductive material 14, the resistance material 15, and the second conductive material 16 within the axial hole 12. Next, a metallic shell 18 to which a ground electrode 19 is connected is assembled to the outer periphery of the insulator 11. The ground electrode 19 is then bent to set a spark gap between the ground electrode 19 and the center electrode 13, thereby completing the spark plug 10.

[0023] FIG. 2 is a cross-sectional view of the resistive material 15 including the axis X (see FIG. 1). In FIG. 2, the insulator 11, the first conductive material 14, and a portion of the second conductive material 16 are omitted (the same applies to FIG. 3). The leading end 21 of the resistive material 15 is the portion located most distally of the boundary 20 between the first conductive material 14 and the resistive material 15. The rear end 23 of the resistive material 15 is the portion located most proximal of the boundary 22 between the second conductive material 16 and the resistive material 15. The axial length L of the resistive material 15 is equal to the distance in the axial direction between the leading end 21 and the rear end 23 of the resistive material 15.

[0024] The first range 25 is a range defined by a line segment 24 perpendicular to the axis X (see FIG. 1 ), the boundary 22, and the insulator 11. The distance between the rear end 23 of the resistor material 15 and the line segment 24 is 1 / 10 of the length L of the resistor material 15. In other words, the first range 25 is a range extending 10% of the length L of the resistor material 15 toward the rear end. The second range 26 is a range of the resistor material 15 that is closer to the tip end than the first range 25. The second range 26 is defined by the line segment 24, the boundary 20, and the insulator 11.

[0025] The porosity of the first region 25 is smaller than the porosity of the second region 26. This increases the tensile strength of the first region 25, which is in contact with the second conductive material 16, thereby improving the pull-out strength of the terminal fitting 17 joined to the first region 25 via the second conductive material 16. Meanwhile, the porosity of the second region 26 is larger than that of the first region 25, thereby reducing the thermal conductivity of the second region 26 compared to when the porosity of the first region 25 and the porosity of the second region 26 are the same. This reduces the heat transfer from the center electrode 13 to the rear end side via the first conductive material 14 and the second region 26. This suppresses the temperature rise of the terminal fitting 17, thereby reducing thermal deterioration of, for example, a synthetic resin portion of a plug cap (not shown) connected to the terminal fitting 17.

[0026] The porosity of the first region 25 is preferably 0.8% or less. This can reduce the reduction in strength of the first region 25 due to tensile stress concentration in the pores, and further improve the pull-out strength of the terminal fitting 17.

[0027] The porosity of the first region 25 and the second region 26 is determined from an image of the cross section of the resistor material 15 taken with a scanning electron microscope (SEM). First, a cross section of the spark plug 10 including the axis X is polished to a mirror finish, and then the entire cross section of the resistor material 15 is divided into multiple sections, and a secondary electron image (image) is obtained for each divided section using the SEM. Next, using known image editing software (e.g., Photoshop (registered trademark)), the acquired images are joined to form a single image of the resistor material 15. Next, using known image analysis software (e.g., WinROOF (registered trademark)), a threshold is set to binarize the pores and other areas, and the boundaries of the pores are clearly defined. After that, the area of ​​all pores appearing in the resistor material 15 is determined for each pore.

[0028] The porosity of the first region 25 is the value obtained by dividing the sum of the areas of the pores appearing in the first region 25 by the area of ​​the first region 25. The porosity of the second region 26 is the value obtained by dividing the sum of the areas of the pores appearing in the second region 26 by the area of ​​the second region 26. If there are pores that overlap with the line segment 24, the pores are divided into a portion that exists in the first region 25 and a portion that exists in the second region 26, with the line segment 24 as the boundary, and the porosity of each is calculated.

[0029] To make the porosity of the first region 25 smaller than the porosity of the second region 26, for example, when manufacturing the spark plug 10, the raw material powder filled in the axial bore 12 of the insulator 11 is heated to, for example, 800°C or higher and 900°C or lower, while the terminal fitting 17 is pressed into the raw material powder at a speed of 1 mm / sec or higher and 30 mm / sec or lower. By slowly compressing the raw material powder using the terminal fitting 17, the raw material powder of the second conductive material 16 in contact with the terminal fitting 17 and the raw material powder of the resistor material 15 near the second conductive material 16 are rearranged, thereby increasing the packing density of the raw material powder. Because the first region 25 is denser than the second region 26, the porosity of the first region 25 becomes smaller than the porosity of the second region 26.

[0030] FIG. 3 is a cross-sectional view of the resistive material 15 including the axis X (see FIG. 1). The resistive material 15 can also be divided into a third region 28 and a fourth region 29 located rearward of the third region 28. The third region 28 is defined by a line segment 27 perpendicular to the axis X (see FIG. 1), the boundary 20, and the insulator 11. The distance between the tip 21 of the resistive material 15 and the line segment 27 is 1 / 10 of the length L of the resistive material 15. In other words, the third region 28 is a region extending 10% of the length L of the resistive material 15 from the tip side. The fourth region 29 is defined by the line segment 27, the boundary 22, and the insulator 11.

[0031] The porosity of the third region 28 is preferably greater than the porosity of the fourth region 29. This is because the pores in the third region 28 can reduce the thermal conductivity of the third region 28, thereby further reducing the heat transferred from the center electrode 13 to the rear end side via the first conductive material 14 and the third region 28, and further suppressing the temperature rise of the terminal fitting 17.

[0032] The porosity of the third region 28 is preferably 1.5% or more in order to improve the heat insulating properties of the third region 28. The porosity of the third region 28 is preferably 3.0% or less in order to ensure the mechanical strength of the third region 28. [Example]

[0033] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0034] (Test 1) Samples Nos. 1-3 were fabricated having the same basic configuration as the spark plug 10 exemplified in the embodiment. Samples Nos. 1-3 had the same dimensions of each part, the same material constituting the resistor material 15, and the same proportions of glass particles, ceramic particles, and conductor.

[0035] For Samples Nos. 1 and 2, raw material powder of the first conductive material 14 was placed in the axial hole 12 of the insulator 11 in which the center electrode 13 was disposed, and the raw material powder was then packed around the center electrode 13, after which the raw material powder was pre-compressed using a compression rod. Next, raw material powder of the resistor material 15 was half-filled on top of the raw material powder of the first conductive material 14, and the surface of the raw material powder was lightly pressed using a compression rod.

[0036] Next, the remaining half of the raw material powder of resistor material 15 was filled, and then the raw material powder was pre-compressed using a compression rod. Finally, the raw material powder of second conductive material 16 was filled on top of the raw material powder of resistor material 15, and then the raw material powder was pre-compressed using a compression rod. After the raw material powder was filled, the raw material powder was heated to a temperature of 800°C or higher and 900°C or lower, and then terminal fitting 17 was pressed into it at a speed of 1 mm / sec or higher and 30 mm / sec or lower, to produce 10 samples each of Sample Nos. 1 and 2.

[0037] For Sample No. 3, raw material powder of the first conductive material 14 was placed in the axial hole 12 of the insulator 11 in which the center electrode 13 was disposed, and the raw material powder was then packed around the center electrode 13, and then pre-compressed using a compression rod. Next, raw material powder of the resistor material 15 was packed on top of the raw material powder of the first conductive material 14, and then pre-compressed using a compression rod. Finally, raw material powder of the second conductive material 16 was packed on top of the raw material powder of the resistor material 15, and then pre-compressed using a compression rod.

[0038] After filling the raw material powder, the raw material powder was heated and then the terminal fitting 17 was pressed into the cavity to produce 10 samples of Sample No. 3. The temperature at which the raw material powder was heated when producing Sample No. 3 was set higher than the temperature at which the raw material powder was heated when producing Sample Nos. 1 and 2, and the speed at which the terminal fitting 17 was pressed into the cavity when producing Sample No. 3 was set higher than the speed at which the terminal fitting 17 was pressed into the cavity when producing Sample Nos. 1 and 2.

[0039] The tester cut five samples at a position including the axis X, polished the cut surface of the resistive material 15 of each sample to a mirror finish, divided the entire cross section of the resistive material 15 into multiple sections, and acquired secondary electron images (images) for each divided section using an SEM. After combining multiple images into a single image using image editing software Photoshop (registered trademark), a binary image of the pores was created using image analysis software WinROOF2021 (WinROOF is a registered trademark). The positions and areas of the pores in the binary image were identified, and the sum of the areas of the pores appearing in the first region 25 was divided by the area of ​​the first region 25 to determine the porosity (%) of the first region 25. The sum of the areas of the pores appearing in the second region 26 was divided by the area of ​​the second region 26 to determine the porosity (%) of the second region 26. The average porosity (%) of the first region 25 and the second region 26 of each sample was then calculated. The porosity was rounded to the first decimal place.

[0040] The tester used five uncut samples each other, excluding those for which the porosity of the resistance material 15 was measured, to measure the pull-out strength of the terminal fittings 17 in accordance with the terminal pull-out strength test of JIS B8031:2006, and calculated the average pull-out strength of each sample. Samples with a pull-out strength of 4.0 kN or more were rated A, and samples with a pull-out strength of less than 4.0 kN were rated B. The porosity (%) of the first range 25, the porosity (%) of the second range 26, and the pull-out strength ratings are shown in Table 1.

[0041] [Table 1]

[0042] According to Table 1, samples Nos. 1 and 2, in which the porosity of the first region 25 was smaller than the porosity of the second region 26, were evaluated as A in terms of pull-out strength, whereas sample No. 3, in which the porosity of the first region 25 was the same as the porosity of the second region 26, was evaluated as B in terms of pull-out strength. The porosity of the first region 25 of samples Nos. 1 and 2 was 0.8% or less. According to the examples, it was revealed that the terminal pull-out strength can be improved by making the porosity of the first region 25 smaller than the porosity of the second region 26. It was also revealed that samples Nos. 1 and 2, which had improved terminal pull-out strength, had a porosity of the first region 25 of 0.8% or less.

[0043] (Test 2) Samples Nos. 4-6 were fabricated having the same basic configuration as the spark plug 10 exemplified in the embodiment. Samples Nos. 4-6 had the same dimensions of each part, the same material constituting the resistor material 15, and the same proportions of glass particles, ceramic particles, and conductor.

[0044] For Samples Nos. 4 and 5, raw material powder of the first conductive material 14 was placed in the axial hole 12 of the insulator 11 in which the center electrode 13 was disposed, and the raw material powder was then packed around the center electrode 13, after which the raw material powder was pre-compressed using a compression rod. Next, raw material powder of the resistor material 15 was half-filled on top of the raw material powder of the first conductive material 14, and the surface of the raw material powder was lightly pressed using a compression rod.

[0045] Next, the remaining half of the raw material powder of resistor material 15 was filled, and then the raw material powder was pre-compressed using a compression rod. Finally, the raw material powder of second conductive material 16 was filled on top of the raw material powder of resistor material 15, and then the raw material powder was pre-compressed using a compression rod. After the raw material powder was filled, the raw material powder was heated to a temperature of 800°C or higher and 900°C or lower, and then terminal fitting 17 was pressed into it at a speed of 1 mm / sec or higher and 30 mm / sec or lower, to produce 10 samples each of Samples No. 4 and 5.

[0046] For sample No. 6, raw material powder of the first conductive material 14 was placed in the axial hole 12 of the insulator 11 in which the center electrode 13 was disposed, and the raw material powder was then packed around the center electrode 13, and then pre-compressed using a compression rod. Next, raw material powder of the resistor material 15 was packed on top of the raw material powder of the first conductive material 14, and then pre-compressed using a compression rod. Finally, raw material powder of the second conductive material 16 was packed on top of the raw material powder of the resistor material 15, and then pre-compressed using a compression rod.

[0047] After filling the raw material powder, the raw material powder was heated and then the terminal fitting 17 was pressed into the cavity to produce 10 samples of Sample No. 6. The temperature at which the raw material powder was heated when producing Sample No. 6 was set higher than the temperature at which the raw material powder was heated when producing Sample Nos. 4 and 5, and the speed at which the terminal fitting 17 was pressed into the cavity when producing Sample No. 6 was set higher than the speed at which the terminal fitting 17 was pressed into the cavity when producing Sample Nos. 4 and 5.

[0048] The tester cut five samples from each sample at a position including the axis X, and polished the cut surface of the resistance material 15 of each sample to a mirror finish. Then, in the same manner as in Test 1, the sum of the areas of the pores appearing in the third region 28 was divided by the area of ​​the third region 28 to determine the porosity (%) of the third region 28, and the sum of the areas of the pores appearing in the fourth region 29 was divided by the area of ​​the fourth region 29 to determine the porosity (%) of the fourth region 29. Next, the average of the porosity (%) of the third region 28 and the porosity (%) of the fourth region 29 for each sample was calculated. The porosity was rounded to one decimal place.

[0049] The tester attached five uncut samples each other, other than those for which the porosity of the resistor material 15 was measured, to a 1.6L four-cylinder engine, operated the engine at 8000 rpm, and measured the temperature of the terminal fitting 17. Samples whose terminal fitting 17 temperature was 180°C or less were rated A, and samples whose terminal fitting 17 temperature exceeded 180°C were rated B. The porosity (%) of the third range 28, the porosity (%) of the fourth range 29, and the temperature of the terminal fitting 17 are shown in Table 2.

[0050] [Table 2]

[0051] According to Table 2, samples Nos. 4 and 5, in which the porosity in the third region 28 was greater than the porosity in the fourth region 29, were judged to have a temperature of A, whereas sample No. 6, in which the porosity in the third region 28 was the same as the porosity in the fourth region 29, was judged to have a temperature of B. The porosity in the third region 28 of samples Nos. 4 and 5 was 1.5% or greater. According to the examples, it was revealed that the thermal insulation properties could be improved by making the porosity in the third region 28 greater than the porosity in the fourth region 29. It was also revealed that samples Nos. 4 and 5, which had improved thermal insulation properties, had a porosity in the third region 28 of 1.5% or greater.

[0052] 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.

[0053] In the embodiment, the spark plug 10 has been described in which the ground electrode 19 is exposed to the combustion chamber when the spark plug 10 is attached to an engine (not shown), but the present invention is not necessarily limited to this. It is of course possible to apply the configuration of the embodiment to a spark plug in which the ground electrode 19 is covered with a cap having a through hole (a spark plug in which an auxiliary chamber is provided in the combustion chamber).

[0054] In the embodiment, the spark plug 10 in which a spark discharge occurs between the center electrode 13 and the ground electrode 19 has been described, but the present invention is not necessarily limited to this. It is naturally possible to apply the configuration of the embodiment to a spark plug that utilizes non-equilibrium plasma generated around the center electrode 13. It is also naturally possible to apply the configuration of the embodiment to a spark plug in which a discharge occurs between the center electrode 13 and the metallic shell 18, omitting the ground electrode 19. [Explanation of symbols]

[0055] 10 Spark Plugs 11 Insulators 12 Shaft hole 13 Center electrode 14 First conductive material 15 Resistance material 16 Second conductive material 17 Terminal fittings 18 Metal body 25 First Range 26 Second Range 28 Third Range 29 Fourth Range L length X axis

Claims

1. an insulator having an axial hole extending from a front end side to a rear end side along an axis; a metallic shell disposed on the outer periphery of the insulator; a center electrode disposed on a tip side within the axial hole; a terminal fitting disposed at a rear end side within the axial hole; a resistance material provided in the axial hole; a first conductive material in contact with the resistor material and the center electrode; A spark plug comprising: a second conductive material in contact with the resistor material and the terminal metal fitting, In a cross section including the axis, When the rear 10% of the axial length of the resistance material is defined as a first range, and the tip side of the first range is defined as a second range, The porosity in the first range is smaller than the porosity in the second range.

2. 2. The spark plug according to claim 1, wherein said first range of porosity is 0.8% or less.

3. When a third range is defined as 10% of the length of the resistance material from the tip end side in the axial direction, and a fourth range is defined as a range from the third range to the rear end side, 3. The spark plug according to claim 1, wherein the porosity in the third range is greater than the porosity in the fourth range.

4. 4. The spark plug according to claim 3, wherein the third range of porosity is 1.5% or more.

Images