JP2020053173A - Ignition plug - Google Patents

Abstract

To enhance performance of attenuating radio noise caused by a connection portion containing a coil, and reduce cracks in the connection portion.SOLUTION: An ignition plug includes an insulator having a through-hole extending in an axial direction, a center electrode which is at least partially inserted at least at a tip end of the through-hole, a terminal fitting which is at least partially inserted at a rear end of the through-hole, and a connection portion for electrically connecting the center electrode and the terminal fitting inside the through-hole. The connection portion includes a helical coil formed of a conductive material, a rod-shaped core portion that is in contact with the coil and disposed radially inside of the coil and contains one or more kinds of iron-containing oxides, and a cylindrical outer barrel portion that is in contact with the coil, covers the radial outside of the coil, and contains one or more kinds of iron-containing oxides. When the diameter of the core portion is represented by D1 and the thickness of the outer barrel portion in the radial direction is represented by D2, 0.15≤(D2/D1)≤0.92 is satisfied.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a spark plug.

  Conventionally, an ignition plug has been used in an internal combustion engine. In addition, in order to suppress radio noise generated by ignition, a technology has been proposed in which a connection portion including a coil is provided between a center electrode and a terminal in a through hole of an insulator (for example, Patent Document 1). ).

WO 2015/099081 JP-A-2005-225793

  However, it cannot be said that the structure around the coil has been sufficiently devised. For this reason, there is room for improving the attenuation performance of radio wave noise and reducing cracks in the connection portion.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for improving the attenuating performance of radio noise by a connection portion including a coil in an ignition plug and reducing a crack in the connection portion.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples.

[Application Example 1] An insulator having a through hole extending in an axial direction,
A center electrode at least partially inserted at the tip side of the through-hole,
Terminal fittings at least partially inserted on the rear end side of the through hole,
In the through-hole, a connection portion for electrically connecting the center electrode and the terminal fitting,
A spark plug comprising:
The connection unit is
A helical coil formed of a conductive material,
A rod-shaped core portion that is arranged in contact with the coil and radially inside the coil and contains one or more iron-containing oxides,
A cylindrical outer cylinder portion that contacts the coil and covers the outside in the radial direction of the coil, and contains one or more iron-containing oxides,
With
When the diameter of the core is D1 (unit: mm) and the thickness of the outer cylinder in the radial direction is D2 (unit: mm),
A spark plug characterized by satisfying 0.15 ≦ (D2 / D1) ≦ 0.92.

  According to this configuration, the diameter D1 of the core portion formed of the iron-containing oxide and the thickness D2 of the outer cylindrical portion formed of the iron-containing oxide satisfy 0.15 ≦ (D2 / D1) ≦ 0. .92, it is possible to improve the attenuating performance of the radio noise by the connecting portion including the coil. Further, since the connection portion includes the core portion and the outer cylinder portion, it is possible to suppress the occurrence of cracks in the connection portion at the time of manufacturing as compared with the case where the core portion and the outer cylinder portion are formed of one member. Therefore, it is possible to improve the attenuating performance of the radio noise by the connecting portion including the coil and reduce the crack in the connecting portion.

Application Example 2 The spark plug according to application example 1,
The porosity of the outer cylinder portion is higher than the porosity of the core portion.

  According to this configuration, it is possible to further suppress the occurrence of cracks in the connection portion during manufacturing.

Application Example 3 The spark plug according to application example 2,
The porosity of the outer cylindrical portion is not more than 20%.

  According to this configuration, it is possible to suppress a decrease in the overall strength of the outer cylindrical portion and the strength of the microstructure, and to suppress a decrease in the durability and impact resistance of the connection portion.

Application Example 4 The spark plug according to any one of Application Examples 1 to 3,
The coil is characterized by comprising a wire formed of a material containing at least one material selected from carbon and a carbon compound as a main component, and a metal covering portion that covers the wire. Spark plug.

  According to this configuration, the contact of the wire with oxygen can be suppressed, so that the deterioration of the wire can be suppressed, so that the durability of the wire and, consequently, the durability of the connection portion can be improved.

Application Example 5 The spark plug according to application example 4, wherein
The spark plug according to claim 1, wherein the covering portion is formed of a material mainly containing at least one material selected from Ni and NiB.

  According to this configuration, due to the magnetism of Ni, the attenuation performance of radio wave noise by the connection portion can be further improved.

Application Example 6 The spark plug according to any one of application examples 1 to 3,
The spark plug according to claim 1, wherein the coil is formed of a material mainly containing at least one material selected from Ni and NiB.

  According to this configuration, due to the magnetism of Ni, the attenuation performance of radio wave noise by the connection portion can be further improved.

Application Example 7 The spark plug according to any one of Application Examples 1 to 6,
The spark plug according to claim 1, wherein the content of Cu in at least one of the core and the outer cylinder is 0.5% by weight or more and 7% by weight or less in terms of oxide (CuO).

  According to this configuration, by adding 0.5% by weight or more of Cu, it is possible to densify the core and the outer cylinder even if the firing temperature during production is lowered. By lowering the firing temperature at the time of manufacturing, the deterioration of the coil is suppressed, so that the attenuation performance of radio noise can be improved. When an excessively large amount of Cu is added, the magnetic permeability of the core and the outer cylinder decreases, and the attenuation performance of radio wave noise decreases. However, when the Cu content is 7% by weight or less, the magnetic permeability decreases. Can be suppressed. Therefore, by setting the content of Cu to be 0.5% by weight or more and 7% by weight or less, the attenuation performance of the radio noise by the connection portion can be further improved.

  The present invention can be realized in various aspects, for example, in an aspect of an ignition plug, an ignition device using the ignition plug, an internal combustion engine equipped with the ignition plug, and the like.

It is a sectional view of spark plug 100 of a 1st embodiment. FIG. 3 is a cross-sectional view of the noise filter 200. It is a flowchart of a manufacturing method. It is explanatory drawing of a manufacturing method.

A. First embodiment:
A-1. Configuration of spark plug:
FIG. 1 is a cross-sectional view of a spark plug 100 according to the first embodiment. The cross section of FIG. 1 is a cross section including the axis AX of the spark plug 100. The direction parallel to the axis AX is also referred to as “axial direction”. The radial direction of the circle about the axis AX is also simply referred to as “radial direction”, and the circumferential direction of the circle about the axis AX is also called “circumferential direction”. Of the directions parallel to the axis AX, the downward direction in FIG. 1 is referred to as a front end direction DF, and the upward direction is also referred to as a rear end direction DR. The tip direction DF is a direction from the terminal fittings 40 to be described later toward the electrodes 20 and 30. 1 is referred to as the front end side of the spark plug 100, and the rear end direction DR side in FIG. 1 is referred to as the rear end side of the spark plug 100.

  The ignition plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, a metal shell 50, a first seal portion 60, a resistor 70, a second seal portion 75, The filter includes a filter 200, a third seal portion 80, a front packing 8, talc 9, a first rear packing 6, and a second rear packing 7.

  The insulator 10 is a substantially cylindrical member having a through hole 12 extending along the axis AX and penetrating the insulator 10. The insulator 10 is formed by firing an insulating ceramic such as alumina. The insulator 10 is arranged in order from the front end side to the rear end side. The leg portion 13, the first reduced outer diameter portion 15, the distal side trunk portion 17, the flange portion 19, and the second reduced outer diameter portion 11 and a rear end body 18.

  The flange 19 is a maximum outer diameter portion of the insulator 10. The outer diameter of the first reduced outer diameter portion 15 on the distal end side from the flange portion 19 gradually decreases from the rear end side to the distal end side. In the vicinity of the first reduced outer diameter portion 15 of the insulator 10 (in the example of FIG. 1, the distal side trunk portion 17), a reduced inner diameter portion 16 whose inner diameter gradually decreases from the rear end side toward the distal end side is formed. Have been. The outer diameter of the second reduced outer diameter portion 11 on the rear end side from the flange portion 19 gradually decreases from the front end side to the rear end side.

  A center electrode 20 is inserted into the insulator 10 at the end of the through hole 12. The center electrode 20 is a rod-shaped member extending along the axis AX. The center electrode 20 has an electrode base material 21 and a core material 22 embedded inside the electrode base material 21. The electrode base material 21 is formed using, for example, an alloy containing nickel as a main component (for example, NCF600, NCF601). The core member 22 is formed of a material having a higher thermal conductivity than the electrode base member 21 (for example, an alloy containing copper).

  Focusing on the outer shape of the center electrode 20, the center electrode 20 includes a leg 25 forming an end on the tip direction DF side, a flange 24 provided on the rear end side of the leg 25, and a flange 24. And a head 23 provided on the rear end side. The head 23 and the flange 24 are disposed in the through-hole 12, and the surface of the flange 24 on the tip direction DF side is supported by the reduced inner diameter portion 16 of the insulator 10. A portion on the tip end side of the leg portion 25 is exposed outside the through hole 12 on the tip end side of the insulator 10.

  At the rear end side of the through hole 12 of the insulator 10, a terminal fitting 40 is inserted. The terminal fitting 40 is formed using a conductive material (for example, metal such as low carbon steel). A metal layer for anticorrosion may be formed on the surface of the terminal fitting 40. For example, a Ni layer is formed by plating. The terminal fitting 40 has a flange portion 42, a cap mounting portion 41 forming a portion on the rear end side from the flange portion 42, and a leg portion 43 forming a portion on the distal end side from the flange portion 42. The cap mounting portion 41 is exposed outside the through hole 12 on the rear end side of the insulator 10. The leg 43 is inserted into the through-hole 12 of the insulator 10.

  In the through hole 12 of the insulator 10, a resistor 70 for suppressing electrical noise is disposed between the terminal fitting 40 and the center electrode 20. The resistor 70 has, for example, a resistance value of 1 KΩ or more (for example, 5 KΩ), and has a function of reducing radio noise at the time of spark generation together with a noise filter 200 described later. The resistor 70 is formed of, for example, a composition containing glass particles as a main component, ceramic particles other than glass, and a conductive material.

  In the through hole 12 of the insulator 10, a noise filter 200 for reducing radio noise is disposed between the resistor 70 and the terminal fitting 40. Details of the noise filter 200 will be described later.

In the through hole 12, between the resistor 70 and the center electrode 20, a conductive first seal portion 60 that is in contact with the resistor 70 and the center electrode 20 is arranged. Between the resistor 70 and the noise filter 200, a conductive second seal portion 75 that is in contact with the resistor 70 and the noise filter 200 is arranged. Between the noise filter 200 and the terminal fitting 40, a conductive third seal portion 80 that is in contact with the noise filter 200 and the terminal fitting 40 is arranged. Seal unit 60,75,80 is made of a material having conductivity, for example, B ₂ O ₃ -SiO ₂ system like glass particles and metal particles (Cu, Fe, etc.) are formed with a composition comprising a.

  The center electrode 20 and the terminal fitting 40 are electrically and physically connected via the resistor 70, the noise filter 200, and the seal portions 60, 75, 80. Hereinafter, the entirety of the plurality of members 60, 70, 75, 200, 80 that connect the center electrode 20 and the terminal fittings 40 in the through-hole 12 is also referred to as a “connection part CT”.

  The metal shell 50 is a substantially cylindrical member having a through hole 59 extending along the axis AX and penetrating the metal shell 50. The metal shell 50 is formed using, for example, a metal material such as a low carbon steel material. A metal layer for corrosion protection such as Ni plating may be formed on the surface of the metal shell 50. The insulator 10 is inserted into the through hole 59 of the metal shell 50, and the metal shell 50 is fixed to the outer periphery of the insulator 10. On the distal end side of the metal shell 50, the distal end of the insulator 10 (the distal end portion of the leg 13 in the present embodiment) is exposed outside the through hole 59. On the rear end side of the metal shell 50, the rear end of the insulator 10 (the rear end side portion of the rear end body 18 in the present embodiment) is exposed outside the through hole 59.

  The metal shell 50 includes a body 55, a seat 54, a deformable part 58, a tool engaging part 51, and a caulking part 53, which are arranged in order from the front end side to the rear end side. I have. The seat 54 is a flange-shaped portion. The outer diameter of the body portion 55 on the tip direction DF side of the seat portion 54 is smaller than the outer diameter of the seat portion 54. A screw portion 52 for screwing into a mounting hole of an internal combustion engine (for example, a gasoline engine) is formed on the outer peripheral surface of the body portion 55. An annular gasket 5 formed by bending a metal plate is fitted between the seat portion 54 and the screw portion 52.

  The metal shell 50 has a reduced inner diameter portion 56 disposed closer to the distal direction DF than the deformed portion 58. The inner diameter of the reduced inner diameter portion 56 gradually decreases from the rear end side to the front end side. The tip side packing 8 is sandwiched between the reduced inner diameter portion 56 of the metal shell 50 and the first reduced outer diameter portion 15 of the insulator 10. The tip-side packing 8 is, for example, an O-ring formed using a metal material such as iron.

  The deformed portion 58 of the metal shell 50 is deformed such that the central portion protrudes radially outward (in a direction away from the axis AX). The tool engaging portion 51 is provided on the rear end side of the deforming portion 58. The shape of the tool engagement portion 51 is a shape (for example, a hexagonal prism) with which a plug wrench is engaged. On the rear end side of the tool engaging portion 51, a caulking portion 53 having a smaller thickness than the tool engaging portion 51 is provided. The caulking part 53 is arranged on the rear end side of the second reduced outer diameter part 11 of the insulator 10 and forms the rear end of the metal shell 50 (that is, the end on the rear end direction DR side). The caulking portion 53 is bent inward in the radial direction.

  On the rear end side of the metal shell 50, an annular space SP is formed between the inner peripheral surface of the metal shell 50 and the outer peripheral surface of the insulator 10. In the present embodiment, the space SP is surrounded by the caulking portion 53 and the tool engaging portion 51 of the metal shell 50, the second reduced outer diameter portion 11 of the insulator 10, and the rear end side trunk portion 18. Space. A first rear end packing 6 is arranged on the rear end side in the space SP, and a second rear end packing 7 is arranged on the front end side in the space SP. In the present embodiment, these rear end side packings 6 and 7 are, for example, C-rings formed using a metal material such as iron. The space between the two rear end packings 6 and 7 in the space SP is filled with talc (talc) 9 powder.

  When the spark plug 100 is manufactured, the caulking portion 53 is caulked so as to bend inward. Then, the caulking portion 53 is pressed toward the distal end direction DF. As a result, the deformable portion 58 is deformed, and the insulator 10 is pressed toward the distal end side in the metal shell 50 via the packings 6 and 7 and the talc 9. The distal end packing 8 is pressed between the first reduced outer diameter portion 15 and the reduced inner diameter portion 56, and seals between the metal shell 50 and the insulator 10. As described above, the gas in the combustion chamber of the internal combustion engine is prevented from leaking outside through the space between the metal shell 50 and the insulator 10. Further, the metal shell 50 is fixed to the insulator 10.

  The ground electrode 30 is joined to the tip of the metal shell 50 (that is, the end on the tip direction DF side). In the present embodiment, the ground electrode 30 is a rod-shaped electrode. The ground electrode 30 extends from the metal shell 50 in the distal direction DF, bends toward the axis AX, and reaches the distal end 31. The tip portion 31 forms a gap g with the tip surface 20s1 of the center electrode 20 (the surface 20s1 on the tip direction DF side). The ground electrode 30 is joined to the metal shell 50 so as to be electrically connected (for example, laser welding). The ground electrode 30 has a base material 35 that forms the surface of the ground electrode 30, and a core 36 embedded in the base material 35. The base material 35 is formed using, for example, Inconel. The core portion 36 is formed using a material having a higher thermal conductivity than the base material 35 (for example, pure copper).

A-2. FIG. 2 is a sectional view of the noise filter 200. The cross section of FIG. 2 is a cross section including the axis line AX similarly to FIG. The noise filter 200 includes a spiral coil 220, a rod-shaped core 210 disposed radially inside the coil 220, and a cylindrical outer tube 230 covering the coil 220 radially outside. I have. The core part 210, the coil 220, and the outer cylinder part 230 are separate members.

The coil 220 is formed of a conductive wire 222 wound around a spiral castle from the front end to the rear end of the core 210 along the outer peripheral surface of the core 210. The wire 222 is, for example, any of a pure metal, an alloy, carbon, a carbon compound, and an oxide conductive material. For example, as a metal or an alloy, a metal or an alloy containing one or more elements of Pt, Zn, Fe, Ni, Ag, Cr, Sn, and Cu, specifically, pure Pt, stainless steel (for example, SUS304), Permalloy (Fe-Ni alloy), Inconel (Ni-Cr-Fe alloy), Sendust (Fe-Si-Al alloy), pure Ni or NiB, or an alloy of Ni and NiB is used. As the carbon or the carbon compound, for example, pure carbon (C), TiC, WC, SiC, TaC is used. As the oxide conductive material, for example, SrCoO ₃ or (La, Sr) MnO ₃ is used.

  When the wire 222 is formed using carbon or a carbon compound, the wire 222 can be covered with a metal covering portion 221 (FIG. 2) such as a pure metal or an alloy. The covering portion 221 is made of, for example, a metal or alloy containing one or more elements of Pt, Au, Ag, Cr, and Ni. In particular, pure Ni, NiB, or an alloy of Ni and NiB can be used for the covering portion 221. The coating 221 is formed by electroless plating or electrolytic plating. The film thickness of the covering portion 221 is, for example, in a range from 5 μm to 10 μm. When the wire 222 is formed of any of a pure metal, an alloy, and an oxide conductive material, the covering portion 221 may not be provided.

  The diameter d (also referred to as a wire diameter) of the wire 222 is, for example, in a range from 0.1 mm to 0.5 mm. The pitch of the coils 220 is, for example, in a range from 0.2 mm to 0.5 mm.

  The tip of the wire 222 is exposed at the tip of the noise filter 200, and is in contact with the second seal 75 (FIG. 1). The rear end of the wire 222 is exposed at the rear end of the noise filter 200, and is in contact with the third seal portion 80 (FIG. 1). Thus, the distal end of the wire 222 is electrically connected to the center electrode 20 via the second seal 75, the resistor 70, and the first seal 60. The rear end of the wire 222 is electrically connected to the terminal fitting 40 via the third seal 80.

The core part 210 and the outer cylinder part 230 are magnetic materials, and both are formed using an iron-containing oxide. The iron-containing oxide is, for example, ferrite in a broad sense, specifically, NiFe ₂ O ₄ , (Ni, Zn) Fe ₂ O ₄ , CaFe ₂ O ₄ , (Mn, Zn) Fe ₂ O ₄ , MnFe ₂ O ₄ , CoFe ₂ O ₄ , BaFe ₁₂ O ₁₉ , MgFe ₂ O ₄ , (Co, Zn) Fe ₂ O ₄ , Y ₃ Fe ₅ O ₁₂ , (Ni, Zn, Cu) Fe ₂ O ₄ , (Ni, Cu _{) Fe 2 O 4, (Mn} , Zn, Cu) Fe 2 O 4, (Ca, Zn) of _Fe 2 _{O 4,} oxides of one or more kinds are used. The material forming the core portion 210 and the material forming the outer cylindrical portion 230 may be the same or different.

  The core part 210 has a columnar shape extending along the axis AX. The outer peripheral surface of the core 210 is in contact with the coil 220. The core part 210 is a porous body. The ratio of the porosity to the entire volume of the core 210 is defined as a porosity ARi (unit:%).

  The outer cylinder 230 has a cylindrical shape extending along the axis AX. The outer peripheral surface of the outer cylinder 230 is in contact with the coil 220. The outer cylinder part 230 is a porous body. The ratio of the porosity to the entire volume of the outer cylindrical portion 230 is defined as a porosity ARo (unit:%).

  The axial length of the core 210 and the axial length of the outer cylinder 230 are substantially equal. The axial length of the core 210 and the outer cylinder 230 (the length of the noise filter 200) is, for example, in a range of 5 mm or more and 40 mm or less.

  When the materials exemplified for the coil 220 (the wire 222 and the covering portion 221), the core 210, and the outer cylinder 230 are used, it is not always necessary to form 100% of the exemplified materials, and impurities and the like may be used. May be included. It is preferable that the coil 220 (the wire rod 222 and the covering part 221), the core part 210, and the outer cylinder part 230 are formed of a material whose main component is the exemplified material. Maintaining the exemplified material as the main component means that the content of the exemplified material (unit is% by weight) is the largest. For example, in the present embodiment, Cu and CuO may be added to the core 210 and the outer cylinder 230 in order to lower the firing temperature as described later.

  Here, as shown in FIG. 2, the diameter of the core part 210 is D1 (unit: mm), and the radial thickness of the outer cylindrical part 230 is D2 (unit: mm). The measuring method of the diameter D1 of the core part 210 and the thickness D2 of the outer cylinder part 230 is as follows.

  The noise filter 200 is cut at a plane including the axis AX. Of the cut surface, the central portion CP (the central portion (FIG. 2) of length (L / 3)) into which the noise filter 200 is divided into three in the axial direction is mirror-polished. From the mirror-polished central portion CP, an area EA that can be observed in one field of view is photographed using an SEM (scanning electron microscope) to obtain an SEM image. The region EA is set such that the cross section of the wire 222 is 20 or more. By analyzing the SEM image of the area EA, the area S1 of the core 210 in the area EA and the axial length L1 (FIG. 2) of the area EA are calculated. For the image analysis, Analysis Five manufactured by Soft imaging System GmbH was used. The diameter D1 of the core 210 is calculated by dividing the calculated area S1 by the length L1 (D1 = (S1 / L1)).

The area S of the entire noise filter 200 in the area EA is calculated. By dividing the calculated area S by the above-described length L1, the overall diameter D (FIG. 2) of the noise filter 200 is calculated (D = (S / L1)). Further, the diameter d of the wire 222 is calculated as follows. First, the number n (n is an integer of 2 or more) of the wires 222 in the area EA and the entire area S2 of the wires 222 in the area EA are calculated by image analysis. By dividing S2 by n, the average cross-sectional area S3 per wire 222 is determined. The diameter d is calculated using the equation of S3 = π × (d / 2) ² . The diameter d is a diameter including the covering portion 221 when the wire rod 222 is covered with the covering portion 221. Using the overall diameter D of the noise filter 200, the diameter D1 of the core part 210, and the diameter d of the wire 222, according to the formula of D2 = {D−D1− (2 × d)} / 2, the outer cylindrical part 230 is used. Is calculated.

  The method for measuring the porosity ARi of the core 210 described above is as follows. Using the SEM (scanning electron microscope), a rectangular region of 200 μm × 200 μm in the core 210 is photographed at ten locations from the mirror-polished central portion CP to obtain ten SEM images. Imaging is performed under the conditions of an acceleration voltage of 15 kV and a working distance of 10 to 12 mm. An SEM image is subjected to image analysis using Analysis Five manufactured by Soft imaging System GmbH to create a binarized image for distinguishing a dense portion from a pore portion. Specifically, the secondary electron image and the backscattered electron image in the SEM image are confirmed, and a line is drawn on a portion (dark boundary) indicating a crystal grain boundary in the backscattered electron image to clarify the position of the crystal grain boundary. To The reflection electron image is subjected to a smoothing process at a level at which the edge of the crystal grain boundary of the reflection electron image is maintained. Each pixel of the smoothed backscattered electron image is counted for each pixel brightness, and a histogram is created in which the horizontal axis represents brightness and the vertical axis represents the number of pixels (frequency). Since a peak corresponding to the dense portion and a peak corresponding to the pore portion appear in the histogram, the intermediate brightness between the two peaks is set as the threshold for binarization. Using the set threshold, the backscattered electron image is binarized to obtain a binarized image. In the binarized image, the area Sm of the dense part and the area Sa of the pore are calculated, and the area Sa of the pore occupying the area (Sm + Sa) of the entire image is calculated as the porosity ARi of the core 210 (ARi). = {Sa / (Sm + Sa)} × 100).

  The porosity ARo of the outer cylinder 230 is calculated in the same manner as the porosity ARi of the core 210.

  The material (for example, the type of the iron-containing oxide) and the Cu content (unit:% by weight) of the outer cylindrical portion 230 constitute the outer cylindrical portion 230 on the surface of the above-mentioned mirror-polished central portion CP. The types and amounts of the elements are measured by analyzing them by electron beam micro analysis (Electron Probe Micro Analysis: EPMA). The Cu content (unit:% by weight) of the core 210 is measured by the same method.

  Whether or not the wire 222 is covered with the metal covering portion 221 is determined by, for example, determining the type and amount of the element constituting the surface portion of the wire 222 in the above-mentioned mirror-polished central portion CP by the energy dispersive X The determination can be made by performing analysis using a line analysis (EDS).

A-3. Manufacturing Method A method of manufacturing the spark plug 100 will be described with reference to FIGS. FIG. 3 is a flowchart of the manufacturing method. FIG. 4 is an explanatory diagram of the manufacturing method.

  In S10, a rod is formed using an iron-containing oxide powder produced by a known method. Specifically, a mixture obtained by mixing the powder of the iron-containing oxide and the binder is formed into a rod-shaped body using a mold. At this time, the porosity ARi of the completed core portion 210 decreases as the iron-containing oxide powder occupying the mixture increases.

  In S20, the rod is fired at a temperature corresponding to the type of the iron-containing oxide. For firing, for example, an electric furnace is used. At this time, as the firing temperature is higher, the porosity ARi of the completed core portion 210 is lower.

  In S30, the fired rod is polished to form a core 210 having a predetermined size (FIG. 4A).

  In S40, the wire 220 is wound around the outer peripheral surface to form the coil 220 that is in contact with the outer peripheral surface of the core 210 (FIG. 4B).

  In S50, a sheet of the iron-containing oxide is wound around the coil 220 in a tubular shape. The iron-containing oxide sheet is obtained by molding a mixture obtained by mixing the iron-containing oxide powder and the binder by a known method such as a doctor blade method. At this time, the higher the powder of the iron-containing oxide in the mixture, the lower the porosity ARo of the completed outer cylinder portion 230 becomes.

  In S60, the iron-containing oxide sheet is fired by heating the iron-containing oxide sheet together with the coil 220 and the core 210 around which the iron-containing oxide sheet is wound. Thus, the noise filter 200 is completed (FIG. 4C). For firing, for example, an electric furnace is used. At this time, the higher the firing temperature, the lower the porosity ARi, ARo of the completed core portion 210 and outer cylinder portion 230.

  In S70, the noise filter 200 is arranged in the through hole 12 of the insulator 10 together with other members (FIG. 4D). Specifically, first, the center electrode 20 is inserted from the opening 14 on the rear end direction DR side of the through hole 12 of the insulator 10. As described with reference to FIG. 1, the center electrode 20 is disposed at a predetermined position in the through hole 12 by being supported by the reduced inner diameter portion 16 of the insulator 10. Next, the material powders 60P, 70P, and 75P of the first seal portion 60, the resistor 70, and the second seal portion 75 are sequentially injected into the through-hole 12 from the opening 14. The charged powder material is compression-molded using a rod inserted through the opening 14. Next, the noise filter 200 and the powder material 80P of the third seal portion 80 are sequentially injected into the through-hole 12 from the opening 14.

  In S80, the terminal fitting 40 is inserted into the through hole 12 from the opening 14 while heating the insulator 10. The insulator 10 is heated to a predetermined temperature higher than the softening point of the glass component contained in each material powder. The terminal fitting 40 is inserted with the insulator 10 heated to a predetermined temperature. As a result, each material powder is compressed and sintered to form the seal portions 60, 75, 80 and the resistor 70. Further, the noise filter 200 is fixed between the third seal 80 and the second seal 75.

  Thereafter, the metal shell 50 is attached to the outer periphery of the insulator 10, and the ground electrode 30 is fixed to the metal shell 50. Further, the ground electrode 30 is bent to form a gap g, thereby completing the spark plug.

  In the spark plug 100 of the present embodiment, the diameter D1 of the core portion 210 and the radial thickness D2 of the outer cylindrical portion 230 satisfy 0.15 ≦ (D2 / D1) ≦ 0.92. As a result, the performance of attenuating radio noise by the noise filter 200 including the coil 220 can be improved. Further, since the noise filter 200 includes the core portion 210 and the outer cylinder portion 230, cracks are generated in the noise filter 200 at the time of manufacturing, compared to the case where the core portion 210 and the outer cylinder portion 230 are formed by one member. Can be suppressed. Therefore, it is possible to improve the attenuating performance of radio noise by the noise filter 200 and to reduce cracks in the noise filter 200.

  More specifically, when an iron-containing oxide, which is a magnetic substance, exists inside and outside the coil 220, the reactance of the coil 220 increases, so that the attenuation performance of radio noise is improved. The larger the diameter D1 of the core portion 210 and the radial thickness D2 of the outer cylindrical portion 230 are, the more the attenuation performance of radio noise is improved. However, the noise filter 200 is disposed in the through hole 12 of the insulator 10. Is done. Therefore, (D1 + 2 × D2) cannot exceed the diameter of the through hole 12. For this purpose, an evaluation test described later is performed to evaluate how much the ratio between D1 and D2 should be set, and the range in which the attenuation performance of radio noise can be improved (D2 / D1) is 0. .15 ≦ (D2 / D1) ≦ 0.92. If (D2 / D1) is less than 0.15, it is considered that the outer cylinder 230 cannot improve the radio noise attenuation performance because the thickness D2 of the outer cylinder 230 is excessively small. When (D2 / D1) is larger than 0.95, the diameter D1 of the core portion 210 is excessively small, so that it is not expected that the core portion 210 can improve the radio wave noise attenuation performance. On the other hand, when 0.15 ≦ (D2 / D1) ≦ 0.92 is satisfied, it is considered that the attenuation performance of radio noise is improved by the contribution of both the core 210 and the outer cylinder 230.

  In the spark plug 100 of the present embodiment, the porosity ARo of the outer cylinder 230 is preferably higher than the porosity ARi of the core 210. As a result, it is possible to further suppress the occurrence of cracks in the connection portion during manufacturing. For example, at the time of firing in S60 of FIG. 3, due to the difference between the coefficient of thermal expansion of the outer cylinder 230 and the coefficient of thermal expansion of the coil 220 (wire 222), the coil 220 and the outer cylinder 230 may Cracks can occur at the boundaries. Further, at the time of compression and sintering of the seal portions 60, 75, and 80 in S 80 of FIG. 3, the boundary between the coil 220 and the outer cylindrical portion 230 and the outer Cracks may occur inside the cylindrical portion 230. By increasing the porosity ARo of the outer cylinder portion 230, it is possible to absorb the stress generated in the boundary between the coil 220 and the outer cylinder portion 230 and the inside of the outer cylinder portion 230, so that the occurrence of cracks can be suppressed. If the porosity ARi of the core portion 210 is also increased, the volume of the magnetic substance disposed in the coil 220 may be reduced and the attenuation performance of radio wave noise may be reduced, but only the porosity ARo of the outer cylinder portion 230 is increased. By doing so, it is possible to suppress a decrease in the attenuation performance of radio noise.

  In the spark plug 100 of the present embodiment, the porosity ARo of the outer cylinder 230 is higher than the porosity ARi of the core 210, and the porosity ARo of the outer cylinder 230 is 20% or less. Is preferred. If the porosity ARo of the outer cylinder portion 230 is excessively large, the overall strength of the outer cylinder portion 230 and the strength of the microstructure are reduced, and the durability and impact resistance of the noise filter 200 are reduced. If the porosity ARo of the outer cylindrical portion 230 is 20% or less, the overall strength of the outer cylindrical portion 230 and the strength of the fine structure are suppressed, and the durability and the impact resistance of the noise filter 200 are suppressed. Can be suppressed.

  Further, in the spark plug 100 of the present embodiment, when the wire 222 is formed of a material mainly containing at least one material selected from carbon and a carbon compound, a metal coating that covers the wire 222 is used. It is preferable to include the part 221 (FIG. 2). Carbon and carbon compounds are oxidized and deteriorated when exposed to oxygen. When the wire 222 (coil 220) deteriorates, the attenuation performance of radio wave noise decreases. When the wire 222 is covered with the covering portion 221, the contact of the wire 222 with oxygen can be suppressed, and thus the deterioration of the wire 222 can be suppressed. Therefore, the durability of the wire 222 and, consequently, the durability of the noise filter 200 are improved. it can.

  Furthermore, in the spark plug 100 of the present embodiment, when the coating portion 221 is provided, the coating portion 221 is formed of a material mainly containing at least one material selected from Ni and NiB. Is preferred. In this case, the magnetic property of Ni can further improve the attenuation performance of radio noise by the noise filter 200.

  Furthermore, in the spark plug 100 of the present embodiment, it is preferable that the coil 220 (wire 222) is formed of a material mainly composed of at least one material selected from Ni and NiB. In this case, the magnetic property of Ni can further improve the attenuation performance of radio noise by the noise filter 200.

  Further, in the spark plug 100 of the present embodiment, the content of Cu in at least one of the core portion 210 and the outer cylindrical portion 230 is 0.5% by weight or more and 7% by weight or less in terms of oxide (CuO) conversion value. It is preferred that By adding 0.5% by weight or more of Cu, the core 210 and the outer cylinder 230 can be densified even if the firing temperature in S60 of FIG. 3 is lowered. By lowering the firing temperature at the time of manufacturing, the deterioration of the coil 220 (wire 222) is suppressed, and thus the attenuation performance of radio noise by the noise filter 200 can be improved. When an excessively large amount of Cu is added, the magnetic permeability of the core portion 210 and the outer cylindrical portion 230 is reduced, and the attenuation performance of radio noise is reduced. However, if the Cu content is 7% by weight or less, Permeability can be suppressed. Therefore, by setting the content of Cu to be 0.5% by weight or more and 7% by weight or less, the attenuation performance of radio noise by the noise filter 200 can be further improved.

B. Evaluation test:
B-1. Configuration of ignition plug sample An evaluation test using a plurality of types of ignition plug samples will be described. Tables 1 and 2 below show the respective configurations of each sample.

  In this evaluation test, 30 types of samples having different configurations were evaluated. As shown in Tables 1 and 2, at least one of the configuration of the coil 220, the core portion 210, and the outer cylinder portion 230 differs among the 30 types of samples. Samples 1 to 25 are samples of the above embodiment, and samples 26 to 30 are comparative samples for comparison.

The material of the wire 222 of the coil 220, Pt, SUS304, C, TiC, SrCoO 3, (La, Sr) MnO 3, Inconel, Mo, SiC, WC, TiC , TaC, either Ni was used. The diameter d (wire diameter) of the wire 222 was set to any of 0.1 mm, 0.2 mm, 0.3 mm, and 0.5 mm. In Samples 15 to 21, the wire 222 was formed using carbon or a carbon compound, and the wire 222 was covered with the coating portion 221 having a thickness of 8 μm. Any of Pt, Au, Ag, Cr, and Ni was used as the material of the covering portion 221. In other samples, the covering portion 221 is not provided.

As shown in Tables 1 and 2, any of the iron-containing oxides described above was used as the material of the core 210. However, in sample 30 for comparison, Al ₂ O ₃ (alumina), which is not a magnetic material, was used as the material of core portion 210. The porosity ARi of the core 210 was set to any of 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, and 13%. The porosity ARi was changed by adjusting the ratio of the powder of the iron-containing oxide in the mixture (rod) used in S10 of FIG. 3 and the firing temperature in S20. The porosity ARi was measured by the method described above. In Samples 23 to 25, Cu was added to the core 210. The Cu content of Samples 23 to 25 was 0.5% by weight, 7% by weight, and 2.5% by weight in terms of oxide (CuO). In other samples, Cu is not added to the core 210. The Cu content was measured by the above-mentioned EPMA analysis. The diameter D1 of the core 210 was set to any of 1.2 mm, 1.3 mm, 1.5 mm, 1.7 mm, and 2 mm. The diameter D1 of the core part 210 was adjusted by the polishing in S30 of FIG. The diameter D1 of the core 210 was measured by the method described above.

As shown in Tables 1 and 2, any of the iron-containing oxides described above was used as the material of the outer cylindrical portion 230. However, in Sample 29 for comparison, Al ₂ O ₃ (alumina), which is not a magnetic material, was used as the material of the outer cylindrical portion 230. The porosity ARo of the outer cylinder part 230 is 5%, 7%, 9%, 11%, 12%, 13%, 14%, 16%, 17%, 18%, 20%, 22%, 24%, 25% %, 27%, 29%, or 31%. The porosity ARo was changed by adjusting the ratio of the powder of the iron-containing oxide in the mixture (sheet) used in S50 of FIG. 3 and the firing temperature in S60. The porosity ARo was measured by the method described above. In samples 23 to 25, Cu was added to the outer cylinder 230. The Cu content of Samples 23 to 25 was 0.5% by weight, 7% by weight, and 2.5% by weight in terms of oxide (CuO). In other samples, Cu is not added to the outer cylinder 230. The Cu content was measured by the above-mentioned EPMA analysis. The thickness D2 of the outer cylinder portion 230 is any one of 0.15 mm, 0.2 mm, 0.4 mm, 0.45 mm, 0.65 mm, 0.7 mm, 0.9 mm, 1 mm, 1.15 mm, and 1.2 mm Was set to The thickness D2 of the outer cylinder 230 was adjusted according to the thickness of the mixture (sheet) used in S50 of FIG. The thickness D2 of the outer cylinder 230 was measured by the method described above.

  Tables 1 and 2 further show a value (D2 / D1) obtained by dividing the radial thickness D2 of the outer cylindrical portion 230 by the diameter D1 of the core portion 210.

  In each sample, the diameter of the through hole 12 of the insulator 10 was adjusted to a size that allows the noise filter 200 to be inserted according to the diameter {D1 + (2 × D2)} of the noise filter 200. In the sample, the length L in the axial direction of the noise filter 200 was set to 17 mm, and the pitch of the coil 220 was set to about 0.4 mm.

  In samples 23 to 25 in which Cu is added to the core 210 and the outer cylinder 230, the firing temperatures in S20 and S60 in FIG. 3 are lower than those of the other samples. As described above, by adding Cu, the core portion 210 and the outer cylindrical portion 230 can be formed densely even when the firing temperature is lowered, as compared with the case where Cu is not added. For example, the firing temperature of samples 23 to 25 was 1000 degrees Celsius or lower, and the firing temperature of the other samples was 1100 degrees Celsius or higher.

B-2. Test contents and results As an evaluation test, a noise test, an impact resistance test, and confirmation of a crack occurrence rate were performed. The results are as shown in Table 3 for each of the samples 1 to 30.

  In the noise test, the noise of each sample was measured in accordance with the box method described in "Automobile-Radio noise characteristics-Part 2: Measurement method of preventer" of JASO D002-2 (Transmission Standard D-002-2 of the Japan Automobile Engineers Association). (In dB) was measured. Note that a network analyzer was used as a signal generator and a voltmeter in the box method. At a voltage of 150 mV, the amount of noise attenuation was measured at three frequencies of 30 MHz, 60 MHz, and 100 MHz. The numerical values in Table 3 are the absolute values of the noise attenuation. The larger the absolute value, the larger the amount of noise attenuation, and the better the noise attenuation performance.

  “Before endurance” indicates the result of a noise test before the endurance test described below, and “after endurance” indicates the result of the noise test after the endurance test. The durability test is a test in which a spark plug sample is discharged for 200 hours at a discharge voltage of 10 kV at room temperature. Such a durability test may cause the deterioration of the noise filter 200 to proceed, thereby reducing the amount of noise attenuation.

  The reference values of the attenuation of the noise of 30 MHz, 60 MHz, and 100 MHz before the endurance are 25 dB, 30 dB, and 35 dB, respectively, and the reference values of the attenuation of the noise of 30 MHz, 60 MHz, and 100 MHz after the endurance are 15 dB, 20 dB, and 25 dB, respectively. The amount of noise attenuation was evaluated.

  As shown in Tables 1 and 2, sample 1 of the embodiment using an iron-containing oxide as the material of the core portion 210 and the outer cylindrical portion 230 and satisfying 0.15 ≦ (D2 / D1) ≦ 0.92 The noise attenuation of の 25 exceeded the standard for all frequencies before and after endurance. The noise attenuation amount of Samples 1 to 25 is the same, regardless of the material and wire diameter of the wire 222, the porosity and the Cu content of the core 210 and the outer cylinder 230, both before and after endurance. Above standard for all frequencies.

On the other hand, the noise attenuation amount of the comparative sample 30 using Al ₂ O ₃ as the material of the core portion 210 satisfies 0.15 ≦ (D2 / D1) ≦ 0.92, Before and after endurance, the frequency was below the standard for all frequencies. Further, the noise attenuation of the sample 29 using Al ₂ O ₃ for the outer cylinder 230 satisfies 0.15 ≦ (D2 / D1) ≦ 0.92. Both later, significantly below the norm for all frequencies.

  The noise attenuation of the comparative samples 26 and 28 in which (D2 / D1) is smaller than 0.15 is higher than that before the endurance despite the fact that the core portion 210 and the outer cylindrical portion 230 are made of an iron-containing oxide. , Both after endurance, below the norm for at least one frequency. The noise attenuation of the sample 27 in which (D2 / D1) is greater than 0.95 is before and after endurance despite the fact that the core 210 and the outer tube 230 are made of an oxide containing iron. In both cases, below the norm for at least one frequency.

  From the above results, by using an iron-containing oxide as the material of the core portion 210 and the outer cylinder portion 230 and satisfying 0.15 ≦ (D2 / D1) ≦ 0.92, the radio noise of the noise filter 200 can be reduced. It has been found that the damping performance can be improved.

Further, as an evaluation value of the durability of the noise filter 200, a change amount ΔN (unit: dB) of the attenuation amount after the durability test and before the durability test was calculated. The change amount ΔN is defined as A30, A60, and A100, respectively, for the noise attenuation of 30 MHz, 60 MHz, and 100 MHz before endurance, and B30, B60, and A100 for the noise attenuation of 30 MHz, 60 MHz, and 100 MHz after endurance, respectively. Assuming B100, it is calculated by the following equation.
ΔN = {(B30-A30) + (B60-A60) + (B100-A100)} / 3
As shown in Tables 1 and 2, the variation ΔN is a negative value. This is because the noise filter 200 deteriorates and the noise attenuation decreases after the durability test. The smaller the absolute value of the change amount ΔN is, the smaller the decrease of the noise attenuation amount is, indicating that the durability of the noise filter 200 is high.

  As shown in Tables 1 and 2, among the samples 1 to 25 of the embodiment, the porosity ARo of the outer cylindrical portion 230 is higher than the porosity ARi of the core portion 210, and the porosity ARo of the outer cylindrical portion 230. Was 10% or less, the absolute value of the variation ΔN was 4.3 or less. On the other hand, of samples 1 to 25 of the embodiment, samples 1 to 5 in which the porosity ARo of the outer cylindrical portion 230 is equal to or less than the porosity ARi of the core portion 210, and the porosity ARo of the outer cylindrical portion 230 is In Samples 6 to 9 larger than 20%, the absolute value of the variation ΔN was 7.7 or more.

  From the above results, in the spark plug 100 of the embodiment, the porosity ARo of the outer cylinder 230 is higher than the porosity ARi of the core 210, and the porosity ARo of the outer cylinder 230 is 20% or less. As a result, it has been found that the durability of the noise filter 200 can be prevented from lowering.

  Furthermore, among Samples 10 to 25, in Samples 15 to 21 in which the wire 222 was covered with the metal covering portion 221, the absolute value of the variation ΔN was 1.3 or less. Further, among Samples 10 to 25, in Samples 22 to 25 in which wire 222 was formed of Ni, the absolute value of variation ΔN was 1.3 or less. On the other hand, among Samples 10 to 25, in Samples 10 to 14 in which the covering portion 221 was not provided and the wire 222 was formed of a material different from Ni, the absolute value of the variation ΔN was 4 or more. there were.

  From the above results, it was found that the durability of the noise filter 200 can be improved by covering the wire 222 with the metal covering portion 221. When the wire 222 is formed of Ni, it is considered that the reason why the wire 222 is excellent in durability even without the covering portion 221 is that Ni is unlikely to be deteriorated by oxidation.

  Further, as shown in Tables 1 and 2, of the samples 15 to 21 in which the wire 222 was covered with the metal covering portion 221, the noise attenuation of the samples 19 to 20 in which the covering portion 221 was formed of Ni was: Before and after endurance, the coating portion 221 was larger in all frequencies before and after endurance than the samples 15 to 18 in which the coating 221 was formed of a metal other than Ni. For example, the attenuation of 30 MHz noise before endurance was 38 or more in samples 19 to 20, whereas it was 33 or less in samples 15 to 18. Further, the attenuation of the 30 MHz noise after the durability was 36 or more in the samples 19 to 20, whereas it was 33 or less in the samples 15 to 18.

  From the above results, it was found that by forming the covering portion 221 with Ni, the attenuation performance of radio noise by the noise filter 200 can be further improved. The improvement in the damping performance is considered to be due to the magnetism of Ni. From this, it can be estimated that the covering portion 221 is not limited to pure Ni, and may be formed of a material mainly containing Ni, a material mainly containing NiB, or an alloy of Ni and NiB. That is, generally speaking, it can be presumed that the covering portion 221 can be formed of a material containing at least one material selected from Ni and NiB as a main component, so that the damping performance can be improved.

  Further, as shown in Tables 1 and 2, of the samples 22 to 25 in which the wire 222 was formed of Ni, 0.5% to 7% by weight of Cu was added to the core 210 and the outer cylinder 230. The amount of noise attenuation of Samples 23 to 25 was larger than Sample 22 in which Cu was not added to core portion 210 and outer cylinder portion 230 at all frequencies before and after endurance. For example, the attenuation of the 30 MHz noise before the endurance was 41 or more in samples 23 to 25, whereas it was 38 in sample 22. In addition, the amount of attenuation of the 30 MHz noise after the durability was 40 or more in samples 23 to 25, whereas it was 37 in sample 22.

  From the above results, it was found that the addition of 0.5% by weight or more and 7% by weight or less of Cu to the core portion 210 and the outer cylindrical portion 230 can further improve the attenuation performance of radio noise by the noise filter 200. It is considered that the improvement of the damping performance is caused by lowering the firing temperature of the core portion 210 and the outer cylindrical portion 230 by adding Cu. For this reason, the firing temperature of the core portion 210 and the outer cylindrical portion 230 is not limited to the case where the wire 222 is formed of Ni, and may be any case where the wire 222 is formed of any material. It is considered that the deterioration of the wire 222 can be suppressed. Therefore, by adding 0.5 wt% or more and 7 wt% or less of Cu to the core portion 210 and the outer cylindrical portion 230, even when the wire 222 is formed of any material, the radio noise attenuating performance can be obtained. Is considered to be able to be further improved.

  Next, the impact resistance test will be described. The impact resistance test was carried out in accordance with JIS B8031: 2006, 7.4. Specifically, each sample was attached to an impact resistance test apparatus, the impact (vibration amplitude) was set to 22 mm, and the impact was applied to the sample 400 times per minute for 60 minutes. Thereafter, electrical continuity between the center electrode 20 and the terminal fitting 40 of each sample was confirmed. An impact resistance test was performed on 20 samples for each sample, and the ratio (unit:%) of the samples for which conduction was not confirmed was calculated as the NG ratio. The impact resistance test was performed on samples 1 to 25 of the embodiment, and was not performed on comparative samples 26 to 30.

  As shown in Tables 1 and 2, among the samples 1 to 25 of the embodiment, the porosity ARo of the outer cylindrical portion 230 is higher than the porosity ARi of the core portion 210, and the porosity ARo of the outer cylindrical portion 230. Was 10% or less, the NG ratio was 5% or less. On the other hand, of samples 1 to 25 of the embodiment, samples 1 to 5 in which the porosity ARo of the outer cylindrical portion 230 is equal to or less than the porosity ARi of the core portion 210, and the porosity ARo of the outer cylindrical portion 230 is In Samples 6 to 9 larger than 20%, the NG rate was 10% or more.

  From the above results, in the spark plug 100 of the embodiment, the porosity ARo of the outer cylinder 230 is higher than the porosity ARi of the core 210, and the porosity ARo of the outer cylinder 230 is 20% or less. As a result, it was found that the impact resistance of the noise filter 200 could be prevented from lowering.

  Next, the crack occurrence rate will be described. The prepared sample was cut along a cross section including the axis AX, and the cut surface was visually checked to determine whether or not cracks had occurred in the noise filter 200. Twenty cracks were confirmed for each sample, and the evaluation of the sample in which the percentage of cracked samples was less than 10% was defined as “A”, and the evaluation of the sample in which the percentage of cracked samples was less than 10% was evaluated. "B". Note that cracks were confirmed for Samples 1 to 25 of the embodiment, but not for Comparative Samples 26 to 30.

  As shown in Tables 1 and 2, among the samples 1 to 25 of the embodiment, the evaluation of the samples 6 to 25 in which the porosity ARo of the outer cylindrical portion 230 is higher than the porosity ARi of the core portion 210 is “A”. Met. On the other hand, among the samples 1 to 25 of the embodiment, the evaluation of the samples 1 to 5 in which the porosity ARo of the outer cylindrical portion 230 is equal to or less than the porosity ARi of the core portion 210 was “B”.

  From the above results, in the spark plug 100 of the embodiment, by setting the porosity ARo of the outer cylindrical portion 230 higher than the porosity ARi of the core portion 210, it is possible to further suppress the occurrence of cracks in the noise filter 200 during manufacturing. I understand what I can do.

C. Modification (1) In the spark plug 100 of FIG. 1, the connection part CT includes a resistor 70. Instead, the connection part CT does not have to include the resistor 70. In this case, the connection part CT includes the third seal part 80, the noise filter 200, and the second seal part 75. Then, the second seal portion 75 contacts the noise filter 200 and the center electrode 20.

(2) In the spark plug 100 of FIG. 1, the resistor 70 is located at the front end and the noise filter 200 is located at the rear end at the connection CT. Instead, the resistor 70 may be located on the rear end side, and the noise filter 200 may be located on the front end side.

(3) In the above embodiment, both the core 210 and the outer cylinder 230 are porous, but one or both of the core 210 and the outer cylinder 230 are dense (porosity is 0 or substantially 0). ).

(4) The configuration of the ignition plug 100 in FIG. 1 is an example, and various configurations can be adopted. For example, a noble metal tip may be provided in a portion of the center electrode 20 where the gap g is formed. Further, a noble metal tip may be provided in a portion of the ground electrode 30 where the gap g is formed. As a material of the noble metal tip, an alloy containing a noble metal such as iridium or platinum can be adopted.

  Further, in the spark plug 100 of FIG. 1, the distal end portion 31 of the ground electrode 30 faces the distal end surface 20s1 facing the distal direction D1 side of the center electrode 20 to form a gap g. Instead, the tip of the ground electrode 30 may face the outer peripheral surface of the center electrode 20 to form a gap.

  Further, instead of the ignition plug 100 of FIG. 1, a pre-chamber plug having a cap that covers the gap g and is provided with a through-hole at the tip end of the metal shell 50 may be employed.

  As described above, the present invention has been described based on the embodiment and the modified examples. However, the above-described embodiment of the present invention is for facilitating understanding of the present invention, and does not limit the present invention. The present invention can be modified and improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof.

    Reference Signs List 5 gasket, 6 first rear end packing, 7 second rear end packing, 8 front end packing, 9 talc, 10 insulator, 11 second reduced outer diameter portion, 12 through hole , 13 ... leg, 14 ... opening, 15 ... first reduced outer diameter part, 16 ... reduced inner diameter part, 17 ... tip side trunk, 18 ... rear end side trunk, 19 ... flange, 20 ... electrode, 20 ... center electrode, 21 ... electrode base material, 22 ... core material, 23 ... head, 24 ... flange, 25 ... leg, 30 ... ground electrode, 31 ... tip, 35 ... base material, 36 ... core Reference numerals 40: terminal fittings, 41: cap mounting portion, 42: flange portion, 43: leg portion, 50: metal shell, 51: tool engaging portion, 52: screw portion, 53: caulking portion, 54: seat portion, 55 ... Body part, 56 ... Reduced inner diameter part, 58 ... Deformed part, 59 ... Through hole, 60 ... First seal part, 75 ... Second seal part, 80 ... Third seal part, 100 ... Ignition plug , 200 ... noise filter 210 ... core, 220 ... coil, 221 ... covering portion, 222 ... wire, 230 ... outer cylinder portion

Claims (7)

An insulator having a through hole extending in an axial direction;
A center electrode at least partially inserted at the tip side of the through-hole,
Terminal fittings at least partially inserted on the rear end side of the through hole,
In the through-hole, a connection portion for electrically connecting the center electrode and the terminal fitting,
A spark plug comprising:
The connection unit is
A helical coil formed of a conductive material,
A rod-shaped core portion that is arranged in contact with the coil and radially inside the coil and contains one or more iron-containing oxides,
A cylindrical outer cylinder portion that contacts the coil and covers the outside in the radial direction of the coil, and contains one or more iron-containing oxides,
With
When the diameter of the core is D1 (unit: mm) and the thickness of the outer cylinder in the radial direction is D2 (unit: mm),
A spark plug characterized by satisfying 0.15 ≦ (D2 / D1) ≦ 0.92. The spark plug according to claim 1, wherein
The porosity of the outer cylinder portion is higher than the porosity of the core portion. The spark plug according to claim 2, wherein
The porosity of the outer cylindrical portion is not more than 20%. The spark plug according to claim 1,
The coil is characterized by comprising a wire formed of a material containing at least one material selected from carbon and a carbon compound as a main component, and a metal covering portion that covers the wire. Spark plug. The spark plug according to claim 4, wherein
The spark plug according to claim 1, wherein the covering portion is formed of a material mainly containing at least one material selected from Ni and NiB. The spark plug according to claim 1,
The spark plug according to claim 1, wherein the coil is formed of a material mainly containing at least one material selected from Ni and NiB. The spark plug according to any one of claims 1 to 6,
The spark plug according to claim 1, wherein the content of Cu in at least one of the core and the outer cylinder is 0.5% by weight or more and 7% by weight or less in terms of oxide (CuO).

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