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 particles having an aspect ratio of 1.1 or more, which is obtained by dividing the length of the longest line segment connecting two points on the contour of the particle by the distance between the parallel lines when the contour is sandwiched between the two parallel lines parallel to the line segment, and having an angle of 45° or less between the line segment and the second side.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 appearing in the specific range contain 30% or more particles having an aspect ratio of 1.1 or more, calculated by dividing the length of the longest line segment connecting two points on the particle's contour by the distance between two parallel lines parallel to the line segment when the contour is sandwiched between them, and an angle between the line segment and the second side of the particle of 45° or less.

[0007] In the second embodiment, in the first embodiment, the particles appearing in the specific range include 25% or more particles in which the angle formed by the line segment and the second side is 30° or less.

[0008] In a third embodiment, in the first or second embodiment, the particles appearing in the specific range contain 18% or more particles in which the angle formed between the line segment and the second side is 15° or less. [Effects of the Invention]

[0009] According to the present invention, 30% or more of the glass particles appearing in a specific area of ​​the resistive material have an aspect ratio of 1.1 or more, calculated by dividing the length of the longest line segment connecting two points on the particle's outline by the distance between two parallel lines when the outline is sandwiched between the line segment, and the angle between the line segment and the second side is 45° or less. This allows the current path between particles present in the specific area to be bypassed, thereby lengthening the current path and 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. 2 is a cross-sectional view of a 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 clarified, after which the lengths L1 (see FIG. 4) and distances L2 of all particles 29 appearing in range 26 (see FIG. 2) are determined.

[0026] 4 is a cross-sectional view of particle 32. Particle 32 is a particle among particles 29 that has an aspect ratio of 1.1 or more. The aspect ratio is L1 / L2, which is the value obtained by dividing the length L1 of the longest line segment 34 connecting two points on the outline 33 of particle 32 by the distance L2 between two parallel lines 35 and 36 that are parallel to line segment 34 and sandwich outline 33 between them.

[0027] Furthermore, image analysis software is used to determine the angle θ between line segment 34 and second side 25 of all particles 32 (particles with an aspect ratio of 1.1 or more) appearing in range 26 (see Figure 2), and the number of particles 32 with an angle θ of 45° or less, the number of particles 32 with an angle θ of 30° or less, and the number of particles 32 with an angle θ of 15° or less is determined. The angle θ between line segment 34 and second side 25 refers to the angle between line segment 34 and an arbitrary straight line parallel to second side 25 set for each particle 32. A specific range 28 where the proportion (by number) of particles 32 with an angle θ of 45° or less to the particles 29 appearing in the cross section is 30% or more is found from the image of range 26.

[0028] When manufacturing the spark plug 10, elongated glass particles with an aspect ratio of 1.1 or more are added to the raw material powder of the resistor material 15, the raw material powder is filled into the axial hole 12, and the raw material powder is compressed using the terminal fitting 17, whereby the raw material powder is rearranged as the terminal fitting 17 moves. As a result, a specific area 28 is formed mainly near the terminal fitting 17.

[0029] In the present 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 that define the specific area 28 may be two sides parallel to the second side 25 (including the case where one of the two sides coincides with the second side 25), and may be two line segments whose distance between the two sides is 10% or more of the distance between the first side 22 and the second side 25. When the raw material powder filled in the axial hole 12 is pre-compressed using a compression rod (not shown), the raw material powder is rearranged, and the position and size of the specific area 28 can be set as desired.

[0030] Because the particles 29 are insulators, when the spark plug 10 discharges, a current flows through the mixture containing the ceramic particles 30 and the conductor 31 filled between the particles 29. If the resistive material 15 has a specific region 28 in which the proportion (by number) of particles 32 with an aspect ratio of 1.1 or more and an angle θ of 45° or less is 30% 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 particles 32 can be bypassed, and the current path in the specific region 28 can be lengthened. This increases the noise reduction effect.

[0031] The average cross-sectional area of ​​particles 32 with an aspect ratio of 1.1 or more appearing in the specific range 28 is 50,000 μm 2 Since the current path detours along the particles 32, the average cross-sectional area of ​​the particles 32 is preferably 50,000 μm or more. 2 This is because it is easy to lengthen the current path in the specific area 28. The average cross-sectional area of ​​the particles 32 having an aspect ratio of 1.1 or more appearing in the specific area 28 is 400,000 μm 2This is because the current path that detours along the particles 32 becomes complicated.

[0032] The ratio (by number) of particles 32 having an aspect ratio of 1.1 or more and an angle θ of 30° or less to the particles 29 appearing in the specific range 28 is preferably 25% or more. This is to further detour the current path between the particles 32 and further increase the noise reduction effect.

[0033] The ratio (by number) of particles 32 having an aspect ratio of 1.1 or more and an angle θ of 15° or less to the particles 29 appearing in the specific range 28 is preferably 18% or more. This is to further detour the current path between the particles 32 and further increase the noise reduction effect. [Example]

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

[0035] (Test 1) Samples Nos. 1-5 were produced, each having the same basic configuration as the spark plug 10 exemplified in the embodiment. Samples Nos. 1-5 were identical in terms of the dimensions of each part, the materials constituting the resistor 15, and the proportions of the particles 29, ceramic particles 30, and conductor 31. When producing the resistor 15 of each sample, a resistor material powder (hereinafter referred to as "powder A") containing spherical glass particles as disclosed in Patent Document 1 (JP 2010-153393 A) was filled into the axial hole 12, and then a resistor material powder (hereinafter referred to as "powder B") containing crushed glass particles was filled into the axial hole 12 using a stirring mill.

[0036] After filling the container with Powder A and Powder B in a volume ratio of 8:2, the heating temperature (800°C to 900°C) when the raw powder was pressed into the container with the metal terminal 17 and the pressing speed (1 mm / sec to 30 mm / sec) of the metal terminal 17 were varied to change the degree of rearrangement of Powder A, thereby producing samples with various embedded resistor materials 15. For Samples Nos. 4 and 5, the time for crushing the glass using a stirring mill was changed to vary the shapes of the particles 29 contained in the resistor material 15. The tester measured the radio noise characteristics of the produced samples in accordance with JASO D002-2.

[0037] After measuring the radio noise characteristics, the tester cut each sample at a position including the axis X, polished the cut surface of the resistance 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 stitched together into a single image using image editing software Photoshop (registered trademark), and then a binarized image of the particle 29 was created using image analysis software WinROOF2021 (WinROOF is a registered trademark). The area including the second side 25, where the distance between the two sides 25, 27 is 10% of the distance between the first side 22 and the second side 25, was defined as a specific range 28, and the angle θ between the line segment 34 and the second side 25 was calculated for each particle 29 appearing in the specific range 28.

[0038] The tester determined the length L1 and distance L2 of the line segments 34 of all particles 29 appearing in the specific range 28, calculated the aspect ratio L1 / L2 of the particles 29, and determined the minimum value of the aspect ratio of the particles 29 appearing in the specific range 28. The minimum value of the aspect ratio was rounded to one decimal place.

[0039] The tester further determined the proportion of particles 32 with an aspect ratio of 1.1 or more and an angle θ of 45° or less, the proportion of particles 32 with an aspect ratio of 1.1 or more and an angle θ of 30° or less, and the proportion of particles 32 with an aspect ratio of 1.1 or more and an angle θ of 15° or less (all proportions are based on the number of particles) to the particles 29 appearing in the specific range 28. The proportions (%) were rounded to one decimal place.

[0040] The results of judging the percentage (%) of particles 32 with an angle θ of 15° or less, the percentage (%) of particles 32 with an angle θ of 30° or less, the percentage (%) of particles 32 with an angle θ of 45° or less, the minimum value of L1 / L2 (aspect ratio), and the radio noise characteristics of Samples No. 1-5 are shown in Table 1. With regard to the radio noise characteristics, samples whose radio noise characteristics were 1.1 times or more compared to the radio noise characteristics of Sample No. 1 were judged as A, samples whose radio noise characteristics were 1.05 times or more but less than 1.1 times were judged as B, and samples whose radio noise characteristics were less than 1.05 times were judged as C.

[0041] [Table 1]

[0042] According to Table 1, samples Nos. 3 and 4, which had a minimum aspect ratio of 1.1 and a proportion of particles with an angle θ of 45° or less of 30% or more, were judged A or B for their radio noise characteristics, whereas samples Nos. 2 and 5, which had a minimum aspect ratio of 1.0 or a proportion of particles with an angle θ of 45° or less of less than 30%, were judged C for their radio noise characteristics. It was revealed that the noise reduction effect can be increased when the proportion of particles with an aspect ratio of 1.1 or more and an angle θ of 45° or less is 30% or more of the number of particles appearing in specific range 28.

[0043] In samples Nos. 3 and 4, the heating temperature when the raw material powder was pressed into the terminal fitting 17 during sample production was lower than that of sample No. 2, and the pressing speed of the terminal fitting 17 was slower than that of sample No. 2. It is presumed that the heating temperature of the raw material powder and the pressing speed of the terminal fitting 17 affected the arrangement of the particles 29.

[0044] In samples Nos. 3 and 4, the proportion of particles with a minimum aspect ratio of 1.1 and an angle θ of 30° or less was 25% or more. It was revealed that the noise reduction effect can be increased when the proportion of particles with an aspect ratio of 1.1 or more and an angle θ of 30° or less is 25% or more relative to the number of particles appearing in specific range 28.

[0045] Sample No. 4, which had a minimum aspect ratio of 1.1 and a proportion of particles with an angle θ of 15° or less of 18% or more, was judged as an A for radio noise characteristics, whereas sample No. 3, which had a minimum aspect ratio of 1.1 and a proportion of particles with an angle θ of 15° or less of less than 18%, was judged as a B for radio noise characteristics. It was revealed that the noise reduction effect can be further increased when the proportion of particles with an aspect ratio of 1.1 or more and an angle θ of 15° or less to the number of particles appearing in specific range 28 is 18% or more.

[0046] (Test 2) Samples Nos. 6-10 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. 6-10 were the same as those of Samples Nos. 1-5.

[0047] For Samples Nos. 6-10, when filling the axial hole 12 of the insulator 11 with the raw material powder of the resistive material 15, first Powder A was filled, and then the raw material powder of the resistive material 15 used in producing Sample No. 4 (hereinafter referred to as "Powder C") was filled. By varying the ratio of Powder A to Powder C, the ratio of the specific area 28 made by Powder C to the area 26 made by Powders A and C was changed. The tester measured the radio noise characteristics of the produced samples in accordance with JASO D002-2.

[0048] After measuring the radio noise characteristics, the tester calculated the aspect ratio and angle θ of all particles 29 appearing in area 26 of resistor material 15 in the same manner as in Test 1, and determined the percentage (%) of specific area 28 in which 30% or more of particles had an aspect ratio of 1.1 or more and an angle θ of 45° or less existed relative to area 26. The percentage (%) of specific area 28 and the results of the radio noise characteristics evaluation for Samples No. 6-10 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.

[0049] [Table 2]

[0050] 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.

[0051] 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.

[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 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 33 Contour 34 line segments 35,36 Parallel Lines L1 Length of the line segment L2 Distance between parallel lines X axis θ angle

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 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 spark plug contains 30% or more of the particles that appear in the specific range, and the particles have an aspect ratio of 1.1 or more, which is calculated by dividing the length of the longest line segment connecting two points on the outline of the particle by the distance between two parallel lines that are parallel to the line segment and sandwich the outline, and the angle between the line segment and the second side is 45° or less.

2. 2. The spark plug according to claim 1, wherein 25% or more of the particles appearing in the specific range have an angle of 30 degrees or less between the line segment and the second side.

3. 2. The spark plug according to claim 1, wherein the particles appearing in the specific range include particles in which the angle formed between the line segment and the second side is 15 degrees or less in an amount of 18% or more.

Images