Spark plug with

Abstract

To provide a spark plug capable of increasing noise reduction effect.SOLUTION: The resistance material of the spark plug includes a range surrounded by a first side passing through a position on the most rear end side in the axial direction in a boundary between the first conductive material and the resistance material, and a second side passing through a position on the most front end side in the axial direction in a boundary between the second conductive material and the resistance material, in a cross section including the axial line. The range includes a specific range which is surrounded by two sides parallel to the second side and in which a distance between the two sides is 10% or more of a distance between the first side and the second side. The glass particles appearing in the specific range include 30% or more of large particles having a cross-sectional area of 50000 μ m2 or more, and the large particles include 40% or more of angular particles having a length of 100 μm or more.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] Spark plugs with built-in resistors are known to reduce noise generated during discharge. Patent Document 1 discloses a technology in which 50% or more by mass of the glass particles contained in the resistors are spherical. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-153393 Summary of the Invention [Problem to be solved by the invention]

[0004] This type of spark plug is required to further reduce noise.

[0005] The present invention has been made to meet this demand, and has as its object to provide a spark plug that can achieve a greater noise reduction effect. [Means for solving the problem]

[0006] A first aspect to achieve this object includes an insulator having an axial hole extending from a front end to a rear end along an axis, a metallic shell disposed on the outer periphery of the insulator, a center electrode disposed at the front end of the axial hole, a terminal metal member disposed at the rear end of the axial hole, a resistive material containing glass particles disposed within the axial hole, a first conductive material in contact with the resistive material and the center electrode, and a second conductive material in contact with the resistive material and the terminal metal member, wherein, in a cross section including the axis, the resistive material includes an area surrounded by a first side of the boundary between the first conductive material and the resistive material that is located at the rear end side in the axial direction and perpendicular to the axis, and a second side of the boundary between the second conductive material and the resistive material that is located at the front end side in the axial direction and perpendicular to the axis. The area includes a specific area surrounded by two sides parallel to the second side, where the distance between the two sides is 10% or more of the distance between the first side and the second side. The particles that appear in the specific range have a cross-sectional area of ​​50,000 μm 2 The large particles contain 30% or more large particles having a length of 100 μm or more, the length of the longest line segment connecting two points on the outline of the large particle minus the diameter of the circle inscribed in the outline being 100 μm or more.

[0007] In the second embodiment, in the first embodiment, the proportion of angular particles among the large particles is 80% or less.

[0008] In a third embodiment, in the first or second embodiment, the large particles have a line segment length of 100 μm or more and an aspect ratio of 1.5 or less. [Effects of the Invention]

[0009] According to the present invention, the glass particles appearing in the specific area of ​​the resistive material have a cross-sectional area of ​​50,000 μm 2 The large particles contain 30% or more large particles having a length of 100 μm or more, calculated by subtracting the diameter of a circle inscribed in the outline from the length of the longest line segment connecting two points on the outline of the large particles. The large particles contain 40% or more angular particles having a length of 100 μm or more, calculated by subtracting the diameter of a circle inscribed in the outline from the length of the longest line segment connecting two points on the outline of the large particles. The current path between large particles containing angular particles can be bypassed, thereby lengthening the current path between particles, thereby enhancing the noise reduction effect. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a half cross-sectional view of a spark plug according to an embodiment; [Figure 2] FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the resistor material of a portion indicated by III in FIG. 2. [Figure 4] FIG. 1 is a cross-sectional view of an angular particle. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 Fig. 2). The spark plug 10 includes an insulator 11, a center electrode 13, a metal terminal 17, and a metal shell 18.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 at a speed of 1 mm / sec to 30 mm / sec while heating the raw material powder to a temperature higher than the softening point of the glass component contained in the raw material powder (e.g., 800°C to 900°C). 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.

[0021] FIG. 2 is a cross-sectional view of the resistive material 15 including the axis X. In FIG. 2, portions of the insulator 11, the first conductive material 14, and the second conductive material 16 are omitted from the illustration. The cross-section of the resistive material 15 includes an area 26 surrounded by the first side 22, the second side 25, and the insulator 11. The first side 22 is a line segment including the rear end 21, which is located at the rearmost end of the boundary 20 between the first conductive material 14 and the resistive material 15. The second side 25 is a line segment including the front end 24, which is located at the frontmost end of the boundary 23 between the second conductive material 16 and the resistive material 15. The first side 22 and the second side 25 are perpendicular to the axis X (see FIG. 1). In this embodiment, the rear end 21 is located at the left end of the boundary 20, and the front end 24 is located at the center of the boundary 23. However, this is merely an example. The rear end 21 and the front end 24 may be selected appropriately depending on the shapes of the boundaries 20 and 23.

[0022] Area 26 includes specific area 28 surrounded by two sides 25, 27 parallel to second side 25 and insulator 11. The distance between side 25 and side 27 defining specific area 28 is 10% or more of the distance between first side 22 and second side 25 defining area 26. In this embodiment, one of the sides defining specific area 28 coincides with second side 25, and therefore specific area 28 is in contact with boundary 23.

[0023] FIG. 3 is an enlarged cross-sectional view of the resistive material 15 of the portion indicated by III in FIG. 2 (part of the specific area 28). The resistive material 15 includes glass particles 29, ceramic particles 30, and conductors 31. The particles 29 are densely distributed in the specific area 28, but FIG. 3 shows only a portion of the particles 29, so the particles 29 are sparsely distributed. The proportion of the particles 29 in the resistive material 15 is, for example, 60-90% by mass, the proportion of the ceramic particles 30 is 5-30% by mass, and the proportion of the conductors 31 is 0.5-10% by mass. When the proportions of the particles 29, ceramic particles 30, and conductors 31 are within these ranges, the resistive material 15 can be set to an appropriate resistance value, thereby ensuring a noise reduction effect.

[0024] To determine where the specific region 28 exists within region 26, 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. For each of the divided sections, a backscattered electron composition image (COMPO image) showing contrast dependent on atomic number is obtained using a scanning electron microscope (SEM). Next, using known image editing software (e.g., Photoshop (registered trademark)), the multiple obtained COMPO images are joined together to form a single COMPO image of the resistor material 15.

[0025] Next, using known image analysis software (e.g., WinROOF (registered trademark)), a threshold is set so that glass particles 29 and other particles are binarized, and the boundaries of the particles 29 are clearly defined. Then, the cross-sectional area, length L1 (see FIG. 4), diameter L2, and distance L3 of all particles 29 appearing in range 26 (see FIG. 2) are determined. Large particles 32 are a type of particle 29, and only those particles 29 with a cross-sectional area of ​​50,000 μm 2 That's all.

[0026] FIG. 4 is a cross-sectional view of an angular particle 33. An angular particle 33 is a type of large particle 32, and is a large particle 32 in which the length L1 of the longest line segment 35 connecting two points on the outline 34 minus the diameter L2 of the largest circle 36 inscribed in the outline 34 is 100 μm or more. An angular particle 33 is a particle whose outline 34 is not rounded and has angular edges. A specific range 28 is found within the image of range 26 in which the proportion (by number) of large particles 32 among the particles 29 appearing in the cross section is 30% or more, and the proportion (by number) of angular particles 33 among the large particles 32 is 40% or more.

[0027] When manufacturing the spark plug 10, the cross-sectional area is 50,000 μm 2The specific area 28 is created within the area 26 of the resistor material 15 by including angular glass particles having a size equal to or larger than the above-mentioned size in the raw material powder of the resistor material 15, filling the axial hole 12 with the raw material powder, and compressing the raw material powder using the terminal fitting 17. In this embodiment, the case where the side 25 of the specific area 28 coincides with the second side 25 (the specific area 28 is in contact with the boundary 23) has been described, but this is not necessarily limited to this. The two sides defining the specific area 28 may be two lines parallel to the second side 25 (including the case where one of the two sides coincides with the second side 25), and the distance between the two sides may be 10% or more of the distance between the first side 22 and the second side 25. By filling the axial hole 12 with raw material powder of the resistor material 15, in which the particle size distribution of the glass particles has been adjusted, the position and size of the specific area 28 can be set as desired.

[0028] Because the particles 29 are insulators, when the spark plug 10 discharges, a current flows through the mixture containing the ceramic particles 30 and conductors 31 filled between the particles 29. If the resistor material 15 has a specific region 28 in which the ratio of large particles 32 among the particles 29 is 30% or more and the ratio of angular particles 33 among the large particles 32 is 40% or more, the axial length of the specific region 28 is 10% or more of the axial length of the region 26, and therefore the current path between the large particles 32 containing the angular particles 33 can be bypassed, and the current path in the specific region 28 can be lengthened. This can enhance the noise reduction effect.

[0029] The proportion (by number) of angular particles 33 among the large particles 32 appearing in the specific area 28 is preferably 80% or less. Since the current path in the specific area 28 can be prevented from becoming too long, energy loss due to Joule heat in the specific area 28 can be reduced. As a result, the amount of electrical energy supplied to the center electrode 13 during discharge can be secured, thereby ensuring the ignition performance of the spark plug 10 due to discharge.

[0030] The cross-sectional area of ​​large particle 32 is 400,000 μm 2 This is because a complex circuitous current path is provided between the large particles 32.

[0031] The large particles 32 appearing in the specific area 28 preferably have a line segment 35 length L1 of 100 μm or more and an aspect ratio of 1.5 or less. This is to ensure a stable length of the current path in the specific area 28. The aspect ratio is L1 / L3, which is the value obtained by dividing the length L1 of the line segment 35 by the distance L3 between two parallel lines 37, 38 that are parallel to the line segment 35 and sandwich the outline 34 between them.

[0032] Large particles 32 with line segment 35 length L1 of 100 μm or more and aspect ratio of 1.5 or less represent particles with contours 34 that are nearly circular. If elongated particles with aspect ratios greater than 1.5 exist in specific range 28 and are aligned along axis X, it becomes difficult for the current path between particles to detour, resulting in a short current path and a low-resistance area. Because current flows through areas with low resistance, the noise reduction effect of resistor material 15 may be reduced. In contrast, if line segment 35 length L1 of large particles 32 is 100 μm or more and the aspect ratio is 1.5 or less, it becomes difficult for a short current path to be created in specific range 28, thereby reducing the variation in the noise reduction effect of resistor material 15.

[0033] It is preferable that the length obtained by subtracting the diameter L2 of the circle 36 from the length L1 of the line segment 35 of the angular particle 33 is 500 μm or less. This is because it reduces the possibility that elongated particles whose length obtained by subtracting the diameter L2 from the length L1 exceeds 500 μm are lined up in the specific range 28, thereby reducing the variation in the noise reduction effect. [Example]

[0034] The present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples.

[0035] (Test 1) Samples No. 1-11 were fabricated having the same basic configuration as the spark plug 10 exemplified in the embodiment. Samples No. 1-11 were identical in terms of the dimensions of each part, the materials constituting the resistor material 15, and the proportions of the particles 29, ceramic particles 30, and conductor 31, but the degree of glass crushing was varied to vary the particle size distribution of the particles 29 contained in the resistor material 15. The tester measured the radio noise characteristics of the fabricated samples in accordance with JASO D002-2.

[0036] After measuring the radio noise characteristics, the tester cut each sample at a position including the axis X, polished the cut surface of the resistive material 15 to a mirror finish, and then obtained multiple COMPO images by dividing the polished surface using an SEM. The multiple COMPO images were joined together to form a single image using image editing software Photoshop (registered trademark), and then a binary image of the particles 29 was created using image analysis software WinROOF2021 (WinROOF is a registered trademark). The cross-sectional areas of all particles 29 appearing within the range 26 of the resistive material 15 were calculated, and a cross-sectional area of ​​50,000 μm was obtained. 2 The distribution of the large particles 32 was investigated. The large particles 32 were found to be distributed almost uniformly throughout the entire range 26.

[0037] The tester determined the percentage (%) of large particles 32 based on the number of all particles 29 appearing in a rectangular area (hereinafter referred to as "area S") whose axial length is 10% of the axial length of area 26 and is in contact with boundary 23, the length L1 of all large particles 32 appearing in area S, and the diameter L2 and distance L3 of a circle 36 inscribed in the outline 34 of all large particles 32 appearing in area S. Next, the tester determined the number of angular particles 33 among the large particles 32 whose length, calculated by subtracting diameter L2 from length L1, was 100 μm or more, and calculated the percentage (%) of angular particles 33 based on the number of all large particles 32. The tester also determined the minimum value (μm) of length L1 of all large particles 32 appearing in area S, and the maximum value L1 / L3 (aspect ratio) obtained by dividing length L1 by distance L3 of all large particles 32 appearing in area S.

[0038] The results of judging the proportion (%) of large particles 32, the proportion (%) of angular particles 33, the minimum length L1 (μm), the maximum L1 / L3 (aspect ratio), and the radio noise characteristics of Samples No. 1-11 are shown in Table 1. Compared with the radio noise characteristics of Sample No. 1, samples whose radio noise characteristics were 1.1 times or more were rated A, samples whose radio noise characteristics were 1.05 times or more but less than 1.1 times were rated B, and samples whose radio noise characteristics were less than 1.05 times were rated C.

[0039] [Table 1]

[0040] According to Table 1, sample No. 5-11, in which the proportion of large particles 32 among particles 29 appearing in range S was 30% or more and the proportion of angular particles 33 among large particles 32 was 40% or more, was evaluated as A or B for radio noise characteristics, whereas sample No. 2-4, in which the proportion of large particles 32 was less than 30% or the proportion of angular particles 33 was less than 40%, was evaluated as C for radio noise characteristics. For sample No. 5-11, the entire range 26 was specific range 28 in which the proportion of large particles 32 was 30% or more and the proportion of angular particles 33 was 40% or more. According to sample No. 5-11, it was revealed that when the proportion of large particles 32 among particles 29 appearing in range S (equivalent to specific range 28) having an axial length 10% of the axial length of range 26 was 30% or more and the proportion of angular particles 33 among large particles 32 was 40% or more, the noise reduction effect could be enhanced.

[0041] Among Samples No. 5-11, Samples No. 6 and 9, in which the minimum length L1 of the large particles 32 was 100 μm or more and the L1 / L3 (aspect ratio) was 1.5 or less, were evaluated as A for radio noise characteristics, whereas Samples No. 5, 7, 8, and 10, in which the minimum length L1 was less than 100 μm or the aspect ratio was greater than 1.5, were evaluated as B for radio noise characteristics. Furthermore, Sample No. 11, in which the minimum length L1 of the large particles 32 was 100 μm or more and the aspect ratio was 1.5 or less but the proportion of angular particles 33 was greater than 80%, was evaluated as B for radio noise characteristics. Samples No. 6 and 9 revealed that the noise reduction effect could be further enhanced when the minimum length L1 of the large particles 32 was 100 μm or more, the aspect ratio was 1.5 or less, and the proportion of angular particles 33 was 80% or less.

[0042] (Test 2) Samples Nos. 12-16 were fabricated having the same basic configuration as the spark plug 10 illustrated in the embodiment. The dimensions and materials of each part of Samples Nos. 1-11 were the same as those of Samples Nos. 1-11.

[0043] For samples Nos. 12-16, when filling the axial hole 12 of the insulator 11 with raw material powder of the resistive material 15, the raw material powder of the resistive material 15 used in producing sample No. 3 (hereinafter referred to as "powder A") was filled first, and then the raw material powder of the resistive material 15 used in producing sample No. 6 (hereinafter referred to as "powder B") was filled. The portion filled with powder B became the specific area 28. By varying the ratio of powder A to powder B, the ratio of the specific area 28 made by powder B to the area 26 made by powders A and B was changed. The tester measured the radio noise characteristics of the prepared samples in accordance with JASO D002-2.

[0044] After measuring the radio noise characteristics, the tester calculated the cross-sectional area of ​​all particles 29 appearing in range 26 of resistor material 15 in the same manner as in Test 1, and determined the proportion (%) of specific range 28, where 30% of large particles 32 and 40% of angular particles 33 existed, relative to range 26. The proportion (%) of specific range 28 and the results of judging the radio noise characteristics of samples Nos. 12-16 are shown in Table 2. Compared to the radio noise characteristics of sample No. 1 (see Test 1), samples whose radio noise characteristics were 1.1 times or more were rated A, samples whose radio noise characteristics were 1.05 times or more but less than 1.1 times were rated B, and samples whose radio noise characteristics were less than 1.05 times were rated C.

[0045] [Table 2]

[0046] According to Table 2, when the ratio of specific range 28 to range 26 was 10% or more, the judgment was A, which made it clear that the noise reduction effect could be increased. It became clear that in order to increase the noise reduction effect, it was sufficient to make the ratio of specific range 28 to range 26 10% or more.

[0047] In the embodiment, the specific area 28 is in contact with the boundary 23 between the resistive material 15 and the second conductive material 16, but the axial position of the specific area 28 is not limited to this. This is because if the specific area 28 exists somewhere in the resistive material 15, the current path can be diverted at the specific area 28.

[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 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).

[0050] 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]

[0051] 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 20 boundaries 22 First Side 23 Boundary 25 Second Side 26 Range 25,27 2 sides 28 Specific Range 29 Glass particles 30 ceramic particles 31 Conductors 32 Large particles 33 Square particles 34 Contour 35 line segments 36 yen L1 Length of the line segment L2 diameter 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 the tip side within the axial hole; a terminal fitting disposed at a rear end side within the axial hole; a resistive material including glass particles disposed 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, the resistive material includes an area surrounded by a first side of a boundary between the first conductive material and the resistive material that is located at the rear end side in the axial direction and perpendicular to the axis, and a second side of a boundary between the second conductive material and the resistive material that is located at the front end side in the axial direction and perpendicular to the axis, the range includes a specific range surrounded by two sides parallel to the second side, and the distance between the two sides is 10% or more of the distance between the first side and the second side, The particles appearing in the specific range have a cross-sectional area of ​​50,000 μm ２ Contains 30% or more large particles that are equal to or greater than 30% The spark plug contains 40% or more of the large particles being angular particles, the length of which, calculated by subtracting the diameter of a circle inscribed in the outline from the length of the longest line segment connecting two points on the outline of the large particle, being 100 μm or more.

2. 2. The spark plug according to claim 1, wherein the angular particles account for 80% or less of the large particles.

3. 3. The spark plug according to claim 1, wherein the large particles have a length of the line segments of 100 μm or more and an aspect ratio of 1.5 or less.

Images