JP6169751B2

JP6169751B2 - Spark plug

Info

Publication number: JP6169751B2
Application number: JP2016085620A
Authority: JP
Inventors: 研悟藤村; 治樹吉田
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 2015-07-15
Filing date: 2016-04-21
Publication date: 2017-07-26
Anticipated expiration: 2036-04-21
Also published as: JP2017027929A

Description

本発明は、内燃機関等において燃料ガスに点火するためのスパークプラグに関する。 The present invention relates to a spark plug for igniting fuel gas in an internal combustion engine or the like.

内燃機関等において着火に用いられるスパークプラグは、絶縁体によって互いに絶縁された中心電極と接地電極とに電圧が印加されることによって、中心電極の先端部と接地電極の先端部との間に形成された火花ギャップに、火花を発生させる（例えば、特許文献１）。 A spark plug used for ignition in an internal combustion engine or the like is formed between the tip of the center electrode and the tip of the ground electrode by applying a voltage to the center electrode and the ground electrode insulated from each other by an insulator. Sparks are generated in the generated spark gap (for example, Patent Document 1).

特開２０１３−２０６７４０号公報JP 2013-206740 A

しかしながら、スパークプラグの小径化、小型化に伴って、絶縁体の肉厚はより薄く、端子金具の外径はより細くなる傾向にある。この結果、端子金具の振動などによって絶縁体の割れが発生しやすくなる傾向にあった。このために、絶縁体の割れに対する耐性の確保が困難になる可能性があった。 However, as the diameter of the spark plug is reduced and the size is reduced, the thickness of the insulator is thinner and the outer diameter of the terminal fitting tends to be thinner. As a result, there was a tendency for the insulator to be easily cracked by the vibration of the terminal fitting. For this reason, there is a possibility that it is difficult to ensure resistance to the cracking of the insulator.

本明細書は、スパークプラグの絶縁体の割れに対する耐性を向上できる技術を開示する。 This specification discloses the technique which can improve the tolerance with respect to the crack of the insulator of a spark plug.

本明細書に開示される技術は、以下の適用例として実現することが可能である。 The technology disclosed in this specification can be implemented as the following application examples.

［適用例１］軸線に沿って延びる軸孔を有する絶縁体と、
前記軸線に沿って延び、後端が前記軸孔内に位置する中心電極と、
前記軸孔内に配置され、先端が前記中心電極の後端より後端側に位置する胴部と、前記胴部より後端側に位置し、前記絶縁体より後端側で外部に露出する頭部と、を備える端子金具と、
前記軸孔内において前記端子金具の先端に接触する導電性のシール材と、
を備えるスパークプラグであって、
前記絶縁体は、
前記端子金具の前記胴部の先端が配置され、第１の内径を有する円筒状の第１部と、
前記絶縁体の後端から先端側に１ｍｍ以上離れた部分を含み、前記第１の内径より大きな第２の内径を有する円筒状の第２部と、
前記第１部と前記第２部との間に位置し、前記第１の内径より大きく前記第２の内径より小さな第３の内径を有する円筒状の第３部と、を備え、
前記端子金具の前記胴部は、先端を含む円筒状の先端胴部と、前記先端胴部より後端側に位置し、前記先端胴部の外径より大きな外径を有する円筒状の後端胴部と、を備え、
前記第３部の後端は、前記後端胴部の先端より後端側に位置することを特徴とする、スパークプラグ。 Application Example 1 An insulator having an axial hole extending along the axis,
A central electrode extending along the axis and having a rear end located in the shaft hole;
A body portion disposed in the shaft hole and having a front end located on the rear end side from the rear end of the center electrode, and located on the rear end side from the body portion, and exposed to the outside on the rear end side from the insulator. A terminal fitting comprising a head,
A conductive sealing material in contact with the tip of the terminal fitting in the shaft hole;
A spark plug comprising:
The insulator is
A cylindrical first portion having a first inner diameter, the tip of the body portion of the terminal fitting being disposed;
A cylindrical second portion including a portion separated from the rear end of the insulator by 1 mm or more on the front end side and having a second inner diameter larger than the first inner diameter;
A cylindrical third part located between the first part and the second part and having a third inner diameter that is larger than the first inner diameter and smaller than the second inner diameter;
The body portion of the terminal fitting includes a cylindrical front end body portion including a front end, and a cylindrical rear end located on a rear end side from the front end body portion and having an outer diameter larger than an outer diameter of the front end body portion. A torso, and
The spark plug according to claim 1, wherein a rear end of the third part is located on a rear end side with respect to a front end of the rear end body part.

上記構成によれば、例えば、端子金具が振動した場合に、胴部は、前記絶縁体の後端から比較的離れた第３部と接触しやすく、第２部とは接触し難い。この結果、端子金具から絶縁体に付加される衝撃を低減できるので、絶縁体の割れを抑制することができる。 According to the said structure, when a terminal metal fitting vibrates, for example, a trunk | drum is easy to contact the 3rd part comparatively separated from the rear end of the said insulator, and is hard to contact with a 2nd part. As a result, since the impact applied to the insulator from the terminal fitting can be reduced, cracking of the insulator can be suppressed.

［適用例２］適用例１に記載のスパークプラグであって、
前記絶縁体の前記第３部の径方向の厚さは、６．１ｍｍ以下であることを特徴とする、スパークプラグ。 [Application Example 2] The spark plug according to Application Example 1,
The spark plug according to claim 1, wherein a radial thickness of the third portion of the insulator is 6.1 mm or less.

上記構成によれば、第３部の径方向の厚さが比較的薄い絶縁体の割れを効果的に抑制することができる。 According to the said structure, the crack of the insulator whose radial thickness of the 3rd part is comparatively thin can be suppressed effectively.

［適用例３］適用例１または２に記載のスパークプラグであって、
前記第１の内径は、２．９ｍｍ以下であることを特徴とする、スパークプラグ。 [Application Example 3] The spark plug according to Application Example 1 or 2,
The spark plug according to claim 1, wherein the first inner diameter is 2.9 mm or less.

上記構成によれば、端子金具の胴部の外径が比較的細いために振動しやすいにも拘わらずに、効果的に絶縁体１０の割れを抑制することができる。 According to the said structure, although the outer diameter of the trunk | drum of a terminal metal fitting is comparatively thin, although it is easy to vibrate, the crack of the insulator 10 can be suppressed effectively.

なお、本発明は、種々の態様で実現することが可能であり、例えば、スパークプラグやスパークプラグ用の絶縁体、スパークプラグを搭載する内燃機関や、そのスパークプラグを用いた点火装置、該点火装置を搭載する内燃機関等の態様で実現することができる。 The present invention can be realized in various modes. For example, a spark plug, an insulator for the spark plug, an internal combustion engine equipped with the spark plug, an ignition device using the spark plug, the ignition This can be realized in an aspect of an internal combustion engine or the like equipped with the device.

本実施形態のスパークプラグ１００の断面図。Sectional drawing of the spark plug 100 of this embodiment. 図１における端子金具４０の近傍の拡大図。The enlarged view of the vicinity of the terminal metal fitting 40 in FIG. 比較形態のスパークプラグ１００ｂの端子金具４０近傍の構成を示す図。The figure which shows the structure of the terminal metal fitting 40 vicinity of the spark plug 100b of a comparison form. 比較形態のスパークプラグ１００ｃの端子金具４０近傍の構成を示す図。The figure which shows the structure of the terminal metal fitting 40 vicinity of the spark plug 100c of a comparison form. 変形例のスパークプラグの絶縁体１０ｄの断面図。Sectional drawing of the insulator 10d of the spark plug of a modification. 変形例のスパークプラグの端子金具４０の近傍の構成を示す第１の図。The 1st figure which shows the structure of the vicinity of the terminal metal fitting 40 of the spark plug of a modification. 変形例のスパークプラグの端子金具４０の近傍の構成を示す第２の図。The 2nd figure which shows the structure of the vicinity of the terminal metal fitting 40 of the spark plug of a modification.

Ａ．実施形態：
Ａ−１．スパークプラグの構成：
以下、本明細書に開示される技術を実施形態に基づいて説明する。図１は本実施形態のスパークプラグ１００の断面図である。図１の一点破線は、スパークプラグ１００の軸線ＣＯを示している。軸線ＣＯを中心とする円の径方向を、単に「径方向」とも呼び、軸線ＣＯを中心とする円の周方向を、単に「周方向」とも呼ぶ。図１における下方向を先端方向ＦＤと呼び、上方向を後端方向ＢＤとも呼ぶ。図１における下側を、先端側と呼び、図１における上側を後端側と呼ぶ。スパークプラグ１００は、絶縁体１０と、中心電極２０と、接地電極３０と、端子金具４０と、主体金具５０と、を備える。 A. Embodiment:
A-1. Spark plug configuration:
Hereinafter, the technology disclosed in the present specification will be described based on embodiments. FIG. 1 is a cross-sectional view of a spark plug 100 of the present embodiment. The dashed line in FIG. 1 indicates the axis CO of the spark plug 100. The radial direction of the circle centered on the axis CO is simply referred to as “radial direction”, and the circumferential direction of the circle centered on the axis CO is also simply referred to as “circumferential direction”. The lower direction in FIG. 1 is referred to as a front end direction FD, and the upper direction is also referred to as a rear end direction BD. The lower side in FIG. 1 is called the front end side, and the upper side in FIG. 1 is called the rear end side. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50.

絶縁体（絶縁碍子）１０は、アルミナ等を焼成して形成されている。絶縁体１０は、軸線ＣＯに沿って延び、絶縁体１０を貫通する軸孔１２を有する略円筒形状の部材である。絶縁体１０は、鍔部１９と、後端側胴部１８と、先端側胴部１７と、段部１５と、脚長部１３とを備えている。後端側胴部１８は、鍔部１９より後端側に位置し、鍔部１９の外径より小さな外径を有している。先端側胴部１７は、鍔部１９より先端側に位置し、鍔部１９の外径より小さな外径を有している。脚長部１３は、先端側胴部１７より先端側に位置し、先端側胴部１７の外径よりも小さな外径を有している。脚長部１３は、スパークプラグ１００が内燃機関（図示せず）に取り付けられた際には、その燃焼室に曝される。段部１５は、脚長部１３と先端側胴部１７との間に形成されている。 The insulator (insulator) 10 is formed by firing alumina or the like. The insulator 10 is a substantially cylindrical member having an axial hole 12 extending along the axis CO and penetrating the insulator 10. The insulator 10 includes a flange part 19, a rear end side body part 18, a front end side body part 17, a step part 15, and a leg length part 13. The rear end side body portion 18 is located on the rear end side of the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The distal end side body portion 17 is located on the distal end side from the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The long leg portion 13 is positioned on the distal end side from the distal end side body portion 17 and has an outer diameter smaller than the outer diameter of the distal end side body portion 17. The leg portion 13 is exposed to the combustion chamber when the spark plug 100 is attached to an internal combustion engine (not shown). The step portion 15 is formed between the leg long portion 13 and the distal end side body portion 17.

主体金具５０は、導電性の金属材料（例えば、低炭素鋼材）で形成され、内燃機関のエンジンヘッド（図示省略）にスパークプラグ１００を固定するための円筒状の金具である。主体金具５０は、軸線ＣＯに沿って貫通する挿入孔５９が形成されている。主体金具５０は、絶縁体１０の外周に配置される。すなわち、主体金具５０の挿入孔５９内に、絶縁体１０が挿入・保持されている。絶縁体１０の先端は、主体金具５０の先端より先端側に突出している。絶縁体１０の後端は、主体金具５０の後端より後端側に突出している。 The metal shell 50 is formed of a conductive metal material (for example, a low carbon steel material) and is a cylindrical metal fitting for fixing the spark plug 100 to an engine head (not shown) of an internal combustion engine. The metal shell 50 is formed with an insertion hole 59 penetrating along the axis CO. The metal shell 50 is disposed on the outer periphery of the insulator 10. That is, the insulator 10 is inserted and held in the insertion hole 59 of the metal shell 50. The tip of the insulator 10 protrudes from the tip of the metal shell 50 toward the tip side. The rear end of the insulator 10 protrudes toward the rear end side from the rear end of the metal shell 50.

主体金具５０は、スパークプラグレンチが係合する六角柱形状の工具係合部５１と、内燃機関に取り付けるための取付ネジ部５２と、工具係合部５１と取付ネジ部５２との間に形成された鍔状の座部５４と、を備えている。取付ネジ部５２の呼び径は、例えば、Ｍ８（８ｍｍ（ミリメートル））、Ｍ１０、Ｍ１２、Ｍ１４、Ｍ１８のいずれかとされている。 The metal shell 50 is formed between a hexagonal column-shaped tool engagement portion 51 with which a spark plug wrench engages, an attachment screw portion 52 for attachment to an internal combustion engine, and the tool engagement portion 51 and the attachment screw portion 52. And a bowl-shaped seat portion 54. The nominal diameter of the mounting screw portion 52 is, for example, one of M8 (8 mm (millimeters)), M10, M12, M14, and M18.

主体金具５０の取付ネジ部５２と座部５４との間には、金属板を折り曲げて形成された環状のガスケット５が嵌挿されている。ガスケット５は、スパークプラグ１００が内燃機関に取り付けられた際に、スパークプラグ１００と内燃機関（エンジンヘッド）との隙間を封止する。 An annular gasket 5 formed by bending a metal plate is fitted between the mounting screw portion 52 and the seat portion 54 of the metal shell 50. The gasket 5 seals a gap between the spark plug 100 and the internal combustion engine (engine head) when the spark plug 100 is attached to the internal combustion engine.

主体金具５０は、さらに、工具係合部５１の後端側に設けられた薄肉の加締部５３と、座部５４と工具係合部５１との間に設けられた薄肉の圧縮変形部５８と、を備えている。主体金具５０における工具係合部５１から加締部５３に至る部位の内周面と、絶縁体１０の後端側胴部１８の外周面との間に形成される環状の領域には、環状のパッキン６，７が配置されている。当該領域における２つのパッキン６、７の間には、タルク（滑石）９の粉末が充填されている。加締部５３の後端は、径方向内側に折り曲げられて、絶縁体１０の外周面に固定されている。主体金具５０の圧縮変形部５８は、製造時において、絶縁体１０の外周面に固定された加締部５３が先端側に押圧されることにより、圧縮変形する。圧縮変形部５８の圧縮変形によって、パッキン６、７およびタルク９を介し、絶縁体１０が主体金具５０内で先端側に向け押圧される。これによって、金属製の環状の板パッキン８を介して、主体金具５０の取付ネジ部５２の内周に形成された段部５６（金具側段部）によって、絶縁体１０の段部１５（絶縁碍子側段部）が押圧される。この結果、内燃機関の燃焼室内のガスが、主体金具５０と絶縁体１０との隙間から外部に漏れることが、板パッキン８によって防止される。 The metal shell 50 further includes a thin caulking portion 53 provided on the rear end side of the tool engaging portion 51, and a thin compression deformation portion 58 provided between the seat portion 54 and the tool engaging portion 51. And. An annular region formed between the inner peripheral surface of the portion of the metal shell 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10 has an annular shape. Packings 6 and 7 are arranged. Between the two packings 6 and 7 in the said area | region, the powder of the talc (talc) 9 is filled. The rear end of the crimping portion 53 is bent radially inward and fixed to the outer peripheral surface of the insulator 10. The compression deformation portion 58 of the metal shell 50 is compressed and deformed when the crimping portion 53 fixed to the outer peripheral surface of the insulator 10 is pressed toward the distal end side during manufacture. By the compression deformation of the compression deformation portion 58, the insulator 10 is pressed toward the front end side in the metal shell 50 through the packings 6, 7 and the talc 9. Accordingly, the step portion 15 (insulation) of the insulator 10 is formed by the step portion 56 (metal step portion) formed on the inner periphery of the mounting screw portion 52 of the metal shell 50 through the metal annular plate packing 8. The insulator side step) is pressed. As a result, the gas in the combustion chamber of the internal combustion engine is prevented by the plate packing 8 from leaking outside through the gap between the metal shell 50 and the insulator 10.

中心電極２０は、軸線ＣＯに沿って延びる棒状の中心電極本体２１と、中心電極本体２１の先端に接合された円柱状の中心電極チップ２９と、を備えている。中心電極本体２１は、絶縁体１０の軸孔１２の内部の先端側の部分に配置されている。中心電極本体２１は、例えば、ニッケルまたはニッケルを主成分とする合金で形成されている。また、中心電極本体２１は、軸線方向の所定の位置に設けられた鍔部２４と、鍔部２４よりも後端側の部分である頭部２３と、鍔部２４よりも先端側の部分である脚部２５と、を備えている。鍔部２４は、絶縁体１０の軸孔１２に形成された段部１２Ｓに支持されている。脚部２５の先端、すなわち、中心電極本体２１の先端は、絶縁体１０の先端より先端側に突出している。頭部２３の後端、すなわち、中心電極本体２１の後端は、絶縁体１０の軸孔１２内に位置している。中心電極チップ２９は、例えば、高融点の貴金属材料で形成され、中心電極本体２１の先端に接合されている。 The center electrode 20 includes a rod-shaped center electrode main body 21 extending along the axis CO, and a columnar center electrode tip 29 joined to the tip of the center electrode main body 21. The center electrode main body 21 is disposed at a tip side portion inside the shaft hole 12 of the insulator 10. The center electrode body 21 is made of, for example, nickel or an alloy containing nickel as a main component. The center electrode main body 21 includes a flange portion 24 provided at a predetermined position in the axial direction, a head portion 23 that is a portion on the rear end side of the flange portion 24, and a portion on the front end side of the flange portion 24. And a certain leg portion 25. The flange portion 24 is supported by a step portion 12 S formed in the shaft hole 12 of the insulator 10. The distal end of the leg 25, that is, the distal end of the center electrode main body 21 protrudes from the distal end of the insulator 10 toward the distal end side. The rear end of the head 23, that is, the rear end of the center electrode main body 21 is located in the shaft hole 12 of the insulator 10. The center electrode tip 29 is made of, for example, a noble metal material having a high melting point, and is joined to the tip of the center electrode body 21.

接地電極３０は、主体金具５０の先端に接合された接地電極本体３１と、円柱状の接地電極チップ３９と、を備えている。接地電極本体３１の後端は、主体金具５０の先端面に接合されている。接地電極本体３１は、耐腐食性の高い金属、例えば、ニッケル合金を用いて形成されている。接地電極チップ３９は、高融点の貴金属材料で形成され、接地電極本体３１の先端部分の中心電極２０を向いた面に接合されている。 The ground electrode 30 includes a ground electrode body 31 joined to the tip of the metal shell 50 and a cylindrical ground electrode tip 39. The rear end of the ground electrode main body 31 is joined to the front end surface of the metal shell 50. The ground electrode main body 31 is formed using a metal having high corrosion resistance, for example, a nickel alloy. The ground electrode tip 39 is made of a high melting point noble metal material, and is joined to the surface of the tip portion of the ground electrode body 31 facing the center electrode 20.

接地電極チップ３９の後端面と、中心電極チップ２９の先端面とは、火花放電が発生する間隙（ギャップとも呼ぶ）を形成している。ギャップの近傍をスパークプラグ１００の発火部とも呼ぶ。 The rear end surface of the ground electrode tip 39 and the front end surface of the center electrode tip 29 form a gap (also referred to as a gap) in which spark discharge occurs. The vicinity of the gap is also called the ignition part of the spark plug 100.

端子金具４０は、軸線ＣＯに沿って延びる棒状の部材である。端子金具４０は、導電性の金属材料（例えば、低炭素鋼）で形成されている。端子金具４０は、先端が中心電極２０の後端より後端側に位置する胴部４３と、胴部４３より後端側に位置する頭部４５と、を備えている。胴部４３は、絶縁体１０の軸孔１２内に配置され、頭部４５は、絶縁体１０より後端側で外部に露出している。胴部４３は、鍔部４２（端子顎部）と、鍔部４２より後端側に位置するキャップ装着部４１と、を備えている。 The terminal fitting 40 is a rod-shaped member that extends along the axis CO. The terminal fitting 40 is made of a conductive metal material (for example, low carbon steel). The terminal fitting 40 includes a body portion 43 whose front end is located on the rear end side from the rear end of the center electrode 20, and a head portion 45 located on the rear end side from the body portion 43. The body 43 is disposed in the shaft hole 12 of the insulator 10, and the head 45 is exposed to the outside on the rear end side of the insulator 10. The body part 43 includes a collar part 42 (terminal jaw part) and a cap mounting part 41 located on the rear end side of the collar part 42.

絶縁体１０の軸孔１２内において、端子金具４０の先端と中心電極２０の後端との間には、火花発生時のノイズを低減するための抵抗体７０が配置されている。軸孔１２内において、抵抗体７０と中心電極２０との隙間は、導電性のシール部材６０によって埋められている。また、抵抗体７０と端子金具４０の胴部４３との隙間は、導電性のシール部材８０によって埋められている。したがって、胴部４３の先端（すなわち、端子金具４０の先端）は、軸孔１２内において、導電性のシール部材８０に接触している。 In the shaft hole 12 of the insulator 10, a resistor 70 is disposed between the front end of the terminal fitting 40 and the rear end of the center electrode 20 to reduce noise when a spark occurs. In the shaft hole 12, a gap between the resistor 70 and the center electrode 20 is filled with a conductive seal member 60. Further, the gap between the resistor 70 and the body 43 of the terminal fitting 40 is filled with a conductive seal member 80. Therefore, the distal end of the body portion 43 (that is, the distal end of the terminal fitting 40) is in contact with the conductive seal member 80 in the shaft hole 12.

このスパークプラグ１００は、自動車等の内燃機関に取り付けて使用される。具体的には、端子金具４０と主体金具５０との間に、例えば、約２０ｋＶの直流電圧が印加されることによって、中心電極２０と接地電極３０と間のギャップに火花放電が発生する。該火花放電のエネルギーによって、内燃機関において、燃料ガスへの着火が行われる。 The spark plug 100 is used by being attached to an internal combustion engine such as an automobile. Specifically, for example, when a DC voltage of about 20 kV is applied between the terminal fitting 40 and the metal shell 50, a spark discharge is generated in the gap between the center electrode 20 and the ground electrode 30. The fuel gas is ignited in the internal combustion engine by the energy of the spark discharge.

Ａ−２.端子金具４０の近傍の構成
次に、端子金具４０の近傍の構成について、さらに、詳しく説明する。図２は、図１における端子金具４０の近傍の拡大図である。絶縁体１０の軸孔１２は、第１の孔１２Ａと、第１の孔１２Ａより後端側に位置する第２の孔１２Ｅと、第１の孔１２Ａと第２の孔１２Ｅとの間に位置する第３の孔１２Ｃと、を含んでいる。そして、第１の孔１２Ａと第３の孔１２Ｃとの間には、先端側から後端側に向かって拡径する拡径孔１２Ｂが形成され、第３の孔１２Ｃと第２の孔１２Ｅとの間には、先端側から後端側に向かって拡径する拡径孔１２Ｄが形成されている。換言すれば、軸孔１２の観点から見ると、絶縁体１０は、第１の孔１２Ａが形成された円筒状の第１部１０Ａと、第２の孔１２Ｅが形成された円筒状の第２部１０Ｂと、第３の孔１２Ｃが形成された円筒状の第３部１０Ｃと、を備えている。そして、第２部１０Ｂの内径Ｒｂ（すなわち、第２の孔１２Ｅの孔径Ｒｂ）は、第１部１０Ａの内径Ｒａ（すなわち、第１の孔１２Ａの孔径Ｒａ）より大きい（Ｒａ＜Ｒｂ）。また、第３部１０Ｃの内径Ｒｃ（すなわち、第３の孔１２Ｃの孔径Ｒｃ）は、第１部１０Ａの内径Ｒａより大きく第２部１０Ｂの内径Ｒｂより小さい（Ｒａ＜Ｒｃ＜Ｒｂ）。そして、第１部１０Ａと第３部１０Ｃとの間には、拡径孔１２Ｂが形成された段部が配置され、第３部１０Ｃと第２部１０Ｂとの間には、拡径孔１２Ｄが形成された段部が配置されている。 A-2. Configuration in the vicinity of the terminal fitting 40 Next, the configuration in the vicinity of the terminal fitting 40 will be described in more detail. FIG. 2 is an enlarged view of the vicinity of the terminal fitting 40 in FIG. The shaft hole 12 of the insulator 10 is formed between the first hole 12A, the second hole 12E located on the rear end side of the first hole 12A, and the first hole 12A and the second hole 12E. And a third hole 12C located therein. And between the 1st hole 12A and the 3rd hole 12C, the diameter expansion hole 12B which expands from the front end side toward the rear end side is formed, and the 3rd hole 12C and the 2nd hole 12E are formed. Is formed with a diameter-enlarging hole 12D that increases in diameter from the front end side toward the rear end side. In other words, from the viewpoint of the shaft hole 12, the insulator 10 includes a cylindrical first part 10A in which the first hole 12A is formed and a cylindrical second part in which the second hole 12E is formed. A portion 10B, and a cylindrical third portion 10C in which a third hole 12C is formed. The inner diameter Rb of the second portion 10B (that is, the hole diameter Rb of the second hole 12E) is larger than the inner diameter Ra of the first portion 10A (that is, the hole diameter Ra of the first hole 12A) (Ra <Rb). The inner diameter Rc of the third portion 10C (that is, the hole diameter Rc of the third hole 12C) is larger than the inner diameter Ra of the first portion 10A and smaller than the inner diameter Rb of the second portion 10B (Ra <Rc <Rb). And the step part in which the enlarged diameter hole 12B was formed is arrange | positioned between 10A of 1st parts and the 3rd part 10C, and 12D of enlarged diameter holes are provided between the 3rd part 10C and the 2nd part 10B. A step portion in which is formed is arranged.

端子金具４０の胴部４３は、胴部４３の先端を含む円筒状の先端胴部４３Ａと、先端胴部４３Ａより後端側に位置する円筒状の後端胴部４３Ｃと、先端胴部４３Ａと後端胴部４３Ｃとの間に位置する段部４３Ｂと、を備える。後端胴部４３Ｃの外径Ｒｅは、先端胴部４３Ａの外径Ｒｄより大きい。段部４３Ｂの外周面は、先端側から後端側に向かって拡径している。 The body 43 of the terminal fitting 40 includes a cylindrical front end body 43A including the front end of the body 43, a cylindrical rear end body 43C located on the rear end side from the front end body 43A, and a front end body 43A. And a stepped portion 43B located between the rear end barrel portion 43C. The outer diameter Re of the rear end body part 43C is larger than the outer diameter Rd of the front end body part 43A. The outer peripheral surface of the stepped portion 43B increases in diameter from the front end side toward the rear end side.

先端胴部４３Ａの先端（すなわち、胴部４３の先端）は、第１部１０Ａの第１の孔１２Ａ内に配置されている。 The distal end of the distal body portion 43A (that is, the distal end of the body portion 43) is disposed in the first hole 12A of the first portion 10A.

第３部１０Ｃの後端Ｐ１は、後端胴部４３Ｃの先端Ｐ２より後端側に位置している。このために、絶縁体１０の第２部１０Ｂの内部と、第３部１０Ｃのうち、後端側の部分の内部と、には、後端胴部４３Ｃが位置する。 The rear end P1 of the third portion 10C is located on the rear end side with respect to the front end P2 of the rear end barrel portion 43C. For this reason, the rear end body portion 43C is located inside the second portion 10B of the insulator 10 and inside the portion of the third portion 10C on the rear end side.

また、第１部１０Ａの後端Ｐ３は、後端胴部４３Ｃの先端Ｐ２より先端側に位置している。このために、絶縁体１０の第１部１０Ａの内部には、先端胴部４３Ａが位置している。 Further, the rear end P3 of the first portion 10A is located on the front end side with respect to the front end P2 of the rear end trunk portion 43C. For this reason, the front end barrel portion 43 A is located inside the first portion 10 A of the insulator 10.

また、図２に示すように、胴部４３の段部４３Ｂの軸線方向の位置と、絶縁体１０の拡径孔１２Ｂの軸線方向の位置は、ほぼ同じである。このために、胴部４３の外周面（拡径面）と、拡径孔１２Ｂを形成する絶縁体１０の内周面（拡径面）とは、対向している。 As shown in FIG. 2, the position in the axial direction of the stepped portion 43 B of the trunk portion 43 and the position in the axial direction of the enlarged diameter hole 12 B of the insulator 10 are substantially the same. For this reason, the outer peripheral surface (expansion surface) of the trunk | drum 43 and the inner peripheral surface (expansion surface) of the insulator 10 which forms the diameter expansion hole 12B have opposed.

端子金具４０の胴部４３と、絶縁体１０の第２部１０Ｂとは、周方向の全周に亘って、非接触である。すなわち、胴部４３の後端胴部４３Ｃの外周面と、第２部１０Ｂの内周面とは、離れている。また、端子金具４０の胴部４３と、絶縁体１０の第３部１０Ｃとは、図２に示すように、周方向の全周に亘って、非接触である。後端胴部４３Ｃの外周面と第２部１０Ｂの内周面との間の隙間ΔＲ１は、後端胴部４３Ｃの外周面と第３部１０Ｃの内周面との間の隙間ΔＲ２より大きい。 The trunk | drum 43 of the terminal metal fitting 40 and the 2nd part 10B of the insulator 10 are non-contact over the perimeter of the circumferential direction. That is, the outer peripheral surface of the rear end barrel portion 43C of the trunk portion 43 is separated from the inner peripheral surface of the second portion 10B. Moreover, the trunk | drum 43 of the terminal metal fitting 40 and the 3rd part 10C of the insulator 10 are non-contact over the perimeter of the circumferential direction, as shown in FIG. The clearance ΔR1 between the outer peripheral surface of the rear end barrel portion 43C and the inner peripheral surface of the second portion 10B is larger than the clearance ΔR2 between the outer peripheral surface of the rear end barrel portion 43C and the inner peripheral surface of the third portion 10C. .

ここで、第３部１０Ｃの径方向の厚さ（肉厚）をＴとする。また、絶縁体１０の後端側部分の外径、すなわち、第３部１０Ｃおよび第２部１０Ｂの外径をＲｆとする。第３部１０Ｃの厚さＴは、第３部１０Ｃの外径Ｒｆと、第３部１０Ｃの内径Ｒｃと、を用いて、Ｔ＝｛（Ｒｆ−Ｒｃ）／２｝と表すことができる。 Here, T is the thickness (wall thickness) in the radial direction of the third portion 10C. Further, the outer diameter of the rear end portion of the insulator 10, that is, the outer diameters of the third portion 10C and the second portion 10B is Rf. The thickness T of the third part 10C can be expressed as T = {(Rf−Rc) / 2} by using the outer diameter Rf of the third part 10C and the inner diameter Rc of the third part 10C.

ここで、絶縁体１０の後端Ｐｅから第３部１０Ｃの後端Ｐ１までの軸線方向の長さをＬｄとする。また、絶縁体１０の後端Ｐｅから第１部１０Ａの後端Ｐ３までの軸線方向の長さをＬｂとする。絶縁体１０の後端Ｐｅ（すなわち、胴部４３の後端）から胴部４３の先端Ｐｓまでの軸線方向の長さをＬａとする。絶縁体１０の後端Ｐｅ（すなわち、胴部４３の後端）から後端胴部４３Ｃの先端Ｐ２までの軸線方向の長さをＬｃとする。 Here, the length in the axial direction from the rear end Pe of the insulator 10 to the rear end P1 of the third portion 10C is Ld. Further, the length in the axial direction from the rear end Pe of the insulator 10 to the rear end P3 of the first portion 10A is Lb. The length in the axial direction from the rear end Pe of the insulator 10 (that is, the rear end of the body 43) to the front end Ps of the body 43 is defined as La. The length in the axial direction from the rear end Pe of the insulator 10 (that is, the rear end of the body portion 43) to the front end P2 of the rear end body portion 43C is defined as Lc.

Ｂ．第１評価試験：
スパークプラグのサンプルを用いて、衝撃に対する耐性を評価する耐衝撃性試験が実行された。第１評価試験では、表１に示すように、５種類のスパークプラグ１００のサンプルＡ１〜Ａ５を作成した。各サンプルに共通な寸法は、以下の通りである。
絶縁体１０の後端Ｐｅから胴部４３の先端Ｐｓまでの長さＬａ：４１ｍｍ
絶縁体１０の後端Ｐｅから第１部１０Ａの後端Ｐ３までの長さＬｂ：１９．２ｍｍ
絶縁体１０の後端Ｐｅから後端胴部４３Ｃの先端Ｐ２までの長さＬｃ：７．０ｍｍ
第１部１０Ａの内径Ｒａ：３ｍｍ
第２部１０Ｂの内径Ｒｂ：３．９ｍｍ
第３部１０Ｃの内径Ｒｃ：３．４ｍｍ
先端胴部４３Ａの外径Ｒｄ：２．８５ｍｍ
後端胴部４３Ｃの外径Ｒｅ：３．２ｍｍ
第３部１０Ｃの外径Ｒｆ：９．０ｍｍ B. First evaluation test:
An impact resistance test was performed to evaluate impact resistance using a spark plug sample. In the first evaluation test, as shown in Table 1, samples A1 to A5 of five types of spark plugs 100 were created. The dimensions common to each sample are as follows.
Length La from the rear end Pe of the insulator 10 to the front end Ps of the body 43: 41 mm
Length Lb from the rear end Pe of the insulator 10 to the rear end P3 of the first part 10A: 19.2 mm
Length Lc from the rear end Pe of the insulator 10 to the front end P2 of the rear end body portion 43C: 7.0 mm
Inner diameter Ra of the first part 10A: 3 mm
Inner diameter Rb of second part 10B: 3.9 mm
Inner diameter Rc of the third part 10C: 3.4 mm
Outer diameter Rd of the tip body 43A: 2.85 mm
The outer diameter Re of the rear end barrel portion 43C: 3.2 mm
Third part 10C outer diameter Rf: 9.0 mm

５種類のサンプルＡ１〜Ａ５では、絶縁体１０の後端Ｐｅから第３部１０Ｃの後端Ｐ１までの軸線方向の長さＬｄが、それぞれ異なり、０．５ｍｍ、０．９ｍｍ、１ｍｍ、３ｍｍ、５ｍｍとされている。なお、サンプルＡ１〜Ａ５において、絶縁体１０は、アルミナを用いて形成され、端子金具４０は、低炭素鋼を用いて形成された。 In the five types of samples A1 to A5, the lengths Ld in the axial direction from the rear end Pe of the insulator 10 to the rear end P1 of the third portion 10C are different, and are 0.5 mm, 0.9 mm, 1 mm, 3 mm, It is 5 mm. In samples A1 to A5, the insulator 10 was formed using alumina, and the terminal fitting 40 was formed using low carbon steel.

耐衝撃性試験は、ＪＩＳＢ８０３１：２００６（内燃機関−スパークプラグ）の７．４に規定された条件で、各サンプルに衝撃を加えた。試験後のサンプルの絶縁体１０を目視で確認して、絶縁体１０の割れの発生の有無を調べた。試験では、１種類のサンプルについて、１０個ずつサンプルの試験を行った。 In the impact resistance test, an impact was applied to each sample under the conditions specified in 7.4 of JIS B8031: 2006 (internal combustion engine-spark plug). The insulator 10 of the sample after the test was visually checked to determine whether the insulator 10 was cracked. In the test, 10 types of samples were tested for one type of sample.

そして、１０個の全てで割れの発生が認めらなかったサンプルの評価を「Ａ」とし、１０個のうちの１個以上３個以下で割れの発生が認められたサンプルの評価を「Ｂ」とし、１０個のうちの４個以上６個以下で割れの発生が認められたサンプルの評価を「Ｃ」とし、１０個のうちの７個以上で割れの発生が認められたサンプルの評価を「Ｄ」とした。 And the evaluation of the sample in which the occurrence of cracking was not recognized in all 10 pieces was “A”, and the evaluation of the sample in which occurrence of cracking was observed in 1 to 3 of the 10 pieces was “B”. The evaluation of the sample in which cracking was observed in 4 to 6 out of 10 was “C”, and the evaluation of the sample in which cracking was observed in 7 or more of 10 “D”.

長さＬｄが１ｍｍ未満であるサンプルＡ１、Ａ２の評価は、「Ｄ」であり、長さＬｄが１ｍｍ以上であるサンプルＡ３〜Ａ５の評価は、「Ｂ」であった。この理由は、以下のように考えられる。スパークプラグ１００に衝撃が加えられると、絶縁体１０の軸孔１２内にて、端子金具４０は、シール部材８０によって絶縁体１０内に固定された先端胴部４３Ａの先端Ｐｓ（図２参照）を支点として振動すると考えられる。スパークプラグ１００の場合には、第３部１０Ｃの後端Ｐ１が、振動時に、端子金具４０の胴部４３と接触する接触点となる。すなわち、振動時には、第３部１０Ｃの後端Ｐ１と、胴部４３と、が衝突して、端子金具４０から絶縁体１０に径方向に衝撃が加えられる。したがって、スパークプラグ１００では、振動の支点Ｐｓから衝撃の作用点Ｐ１までの距離は、（Ｌａ−Ｌｄ）となる。 The evaluation of samples A1 and A2 having a length Ld of less than 1 mm was “D”, and the evaluation of samples A3 to A5 having a length Ld of 1 mm or more was “B”. The reason is considered as follows. When an impact is applied to the spark plug 100, the terminal fitting 40 is inserted into the insulator body 10 by the seal member 80 in the shaft hole 12 of the insulator 10 (see FIG. 2). It is thought that it vibrates with fulcrum. In the case of the spark plug 100, the rear end P1 of the third portion 10C serves as a contact point that contacts the body portion 43 of the terminal fitting 40 during vibration. That is, at the time of vibration, the rear end P1 of the third portion 10C and the body portion 43 collide, and an impact is applied from the terminal fitting 40 to the insulator 10 in the radial direction. Therefore, in the spark plug 100, the distance from the vibration fulcrum Ps to the impact application point P1 is (La−Ld).

図３は、比較形態のスパークプラグ１００ｂの端子金具４０近傍の構成を示す図である。図３のスパークプラグ１００ｂの絶縁体１０ｂのように、第３部１０Ｃが設けられていない場合を考える。この絶縁体１０ｂは、第３部１０Ｃが設けられていないので、第１部１０Ａの後端側の拡径孔１２Ｂの後端側において、図２の第２部１０Ｂと第３部１０Ｃとが配置されている位置に、内径Ｒｂを有する第２部１０Ｂｂが位置している。この場合には、第２部１０Ｂｂの後端Ｐｅ（すなわち、絶縁体１０の後端Ｐｅ）が、振動時に、端子金具４０の胴部４３と接触する接触点となる。したがって、スパークプラグ１００ｂでは、振動の支点Ｐｓから衝撃の作用点Ｐｅまでの距離は、Ｌａとなる。 FIG. 3 is a view showing a configuration in the vicinity of the terminal fitting 40 of the spark plug 100b of the comparative form. Consider a case where the third portion 10C is not provided as in the insulator 10b of the spark plug 100b of FIG. Since the insulator 10b is not provided with the third portion 10C, the second portion 10B and the third portion 10C in FIG. 2 are connected to each other at the rear end side of the enlarged diameter hole 12B on the rear end side of the first portion 10A. The second portion 10Bb having the inner diameter Rb is located at the position where it is disposed. In this case, the rear end Pe of the second part 10Bb (that is, the rear end Pe of the insulator 10) serves as a contact point that contacts the body 43 of the terminal fitting 40 during vibration. Therefore, in the spark plug 100b, the distance from the vibration fulcrum Ps to the impact application point Pe is La.

以上の説明から解るように、実施形態のスパークプラグ１００では、振動の支点Ｐｓから衝撃の作用点Ｐ１までの距離（Ｌａ−Ｌｄ）が、比較形態のスパークプラグ１００ｂの振動の支点Ｐｓから衝撃の作用点Ｐｅまでの距離Ｌａより短くなるので、端子金具４０によって絶縁体１０に付加される衝撃（モーメント）を小さくすることができる。この結果、絶縁体１０の耐衝撃性を向上することができる。 As can be seen from the above description, in the spark plug 100 according to the embodiment, the distance (La−Ld) from the vibration fulcrum Ps to the impact application point P1 is equal to the vibration fulcrum Ps of the comparative spark plug 100b. Since the distance La is shorter than the distance La to the action point Pe, the impact (moment) applied to the insulator 10 by the terminal fitting 40 can be reduced. As a result, the impact resistance of the insulator 10 can be improved.

しかしながら、長さＬｄが過度に短い場合には、振動の支点Ｐｓから衝撃の作用点Ｐ１までの距離（Ｌａ−Ｌｄ）を十分に短くすることができないので、耐衝撃性を十分に向上できない場合があると考えられる。第１評価試験の結果から、長さＬｄは、１ｍｍ以上であれば、振動の支点Ｐｓから衝撃の作用点Ｐ１までの距離（Ｌａ−Ｌｄ）を短くすることによって、耐衝撃性を向上できることが解った。図２のスパークプラグ１００において、第２部１０Ｂの軸線方向の長さが、１ｍｍ以上となるように、第３部１０Ｃを形成すれば、長さＬｄを１ｍｍ以上に設定できる。換言すれば、第２部１０Ｂが、絶縁体１０の後端から先端側に１ｍｍ以上離れた部分を含むように、第３部１０Ｃを形成すれば、絶縁体１０の耐衝撃性を向上することができることが解った。 However, when the length Ld is excessively short, the distance (La-Ld) from the vibration fulcrum Ps to the impact application point P1 cannot be sufficiently shortened, and therefore the impact resistance cannot be sufficiently improved. It is thought that there is. From the result of the first evaluation test, if the length Ld is 1 mm or more, the impact resistance can be improved by shortening the distance (La−Ld) from the vibration fulcrum Ps to the impact application point P1. I understand. In the spark plug 100 of FIG. 2, the length Ld can be set to 1 mm or more by forming the third part 10C so that the length of the second part 10B in the axial direction is 1 mm or more. In other words, if the third portion 10C is formed so that the second portion 10B includes a portion 1 mm or more away from the rear end of the insulator 10 toward the front end side, the impact resistance of the insulator 10 is improved. I understand that I can do it.

Ｃ．第２評価試験：
さらに、耐衝撃性を向上できる構成を確かめるべく、第２評価試験を行った。第２評価試験では、表２に示すように、５種類のサンプルＢ１〜Ｂ５を作成した。各サンプルに共通な寸法は、以下の通りである。
絶縁体１０の後端Ｐｅから胴部４３の先端Ｐｓまでの長さＬａ：４１ｍｍ
絶縁体１０の後端Ｐｅから第１部１０Ａの後端Ｐ３までの長さＬｂ：１９．２ｍｍ
絶縁体１０の後端Ｐｅから後端胴部４３Ｃの先端Ｐ２までの長さＬｃ：１０ｍｍ
第１部１０Ａの内径Ｒａ：３ｍｍ
第２部１０Ｂの内径Ｒｂ：３．９ｍｍ
第３部１０Ｃの内径Ｒｃ：３．４ｍｍ
先端胴部４３Ａの外径Ｒｄ：２．８５ｍｍ
後端胴部４３Ｃの外径Ｒｅ：３．２ｍｍ、
第３部１０Ｃの外径Ｒｆ：９.０ｍｍ
なお、絶縁体１０や端子金具４０などの各部材の材質は、上記第１評価試験と同じである。また、各サンプルに対する耐衝撃性試験の内容および評価基準は、上述した第１評価試験と同じである。 C. Second evaluation test:
Further, a second evaluation test was conducted in order to confirm the configuration capable of improving the impact resistance. In the second evaluation test, as shown in Table 2, five types of samples B1 to B5 were prepared. The dimensions common to each sample are as follows.
Length La from the rear end Pe of the insulator 10 to the front end Ps of the body 43: 41 mm
Length Lb from the rear end Pe of the insulator 10 to the rear end P3 of the first part 10A: 19.2 mm
Length Lc from the rear end Pe of the insulator 10 to the front end P2 of the rear end body portion 43C: 10 mm
Inner diameter Ra of the first part 10A: 3 mm
Inner diameter Rb of second part 10B: 3.9 mm
Inner diameter Rc of the third part 10C: 3.4 mm
Outer diameter Rd of the tip body 43A: 2.85 mm
The outer diameter Re of the rear end barrel part 43C: 3.2 mm,
Third part 10C outer diameter Rf: 9.0 mm
The material of each member such as the insulator 10 and the terminal fitting 40 is the same as that in the first evaluation test. Further, the contents and evaluation criteria of the impact resistance test for each sample are the same as those in the first evaluation test described above.

５種類のサンプルＢ１〜Ｂ５では、絶縁体１０の後端Ｐｅから第３部１０Ｃの後端Ｐ１までの軸線方向の長さＬｄが、それぞれ異なり、５ｍｍ、９ｍｍ、１０ｍｍ、１１ｍｍ、１５ｍｍとされている。なお、絶縁体１０の後端Ｐｅから後端胴部４３Ｃの先端Ｐ２までの長さＬｃは、１０ｍｍに固定されている。この結果、２個のサンプルＢ１、Ｂ２では、（Ｌｃ−Ｌｄ）は、０より大きな値となり、図２のスパークプラグ１００のように、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部４３Ｃの先端Ｐ２より後端側に位置している。 In the five types of samples B1 to B5, the lengths Ld in the axial direction from the rear end Pe of the insulator 10 to the rear end P1 of the third portion 10C are different, and are 5 mm, 9 mm, 10 mm, 11 mm, and 15 mm, respectively. Yes. The length Lc from the rear end Pe of the insulator 10 to the front end P2 of the rear end barrel portion 43C is fixed to 10 mm. As a result, in the two samples B1 and B2, (Lc−Ld) is a value larger than 0, and the rear end P1 of the third portion 10C of the insulator 10 is not the rear as in the spark plug 100 of FIG. It is located on the rear end side from the front end P2 of the end barrel portion 43C.

これに対して、サンプルＢ４、Ｂ５は、（Ｌｃ−Ｌｄ）は、０未満の値となる。この場合には、図２のスパークプラグ１００とは異なり、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部の先端Ｐ２より先端側に位置している。サンプルＢ３は、（Ｌｃ−Ｌｄ）＝０である。この場合には、図２のスパークプラグ１００とは異なり、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部の先端Ｐ２と、同じである。 On the other hand, in samples B4 and B5, (Lc−Ld) is a value less than zero. In this case, unlike the spark plug 100 of FIG. 2, the rear end P1 of the third portion 10C of the insulator 10 is located on the front end side of the front end P2 of the rear end body portion. Sample B3 has (Lc−Ld) = 0. In this case, unlike the spark plug 100 of FIG. 2, the rear end P1 of the third portion 10C of the insulator 10 is the same as the front end P2 of the rear end barrel portion.

以上の説明から解るように、２個のサンプルＢ１、Ｂ２は、図２の実施形態のスパークプラグのサンプルであり、３個のサンプルＢ３〜Ｂ５は、図２とは異なる比較形態のスパークプラグのサンプルである。 As understood from the above description, the two samples B1 and B2 are the spark plug samples of the embodiment of FIG. 2, and the three samples B3 to B5 are the spark plugs of the comparative form different from FIG. It is a sample.

（Ｌｃ−Ｌｄ）が０より大きな値となる２個のサンプルＢ１、Ｂ２の評価は、「Ｂ」であった。これに対して、（Ｌｃ−Ｌｄ）＝０であるサンプルＢ３の評価は、「Ｃ」であり、
（Ｌｃ−Ｌｄ）が０未満である２個のサンプルＢ４、Ｂ５の評価は、「Ｄ」であった。この理由は、以下のように考えられる。（Ｌｃ−Ｌｄ）が０より大きい場合、すなわち、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部４３Ｃの先端Ｐ２より後端側に位置している場合には、第３部１０Ｃの後端Ｐ１は、比較的大きな外径Ｒｅを有する後端胴部４３Ｃと、径方向に対向する。この結果、振動時には、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが、担保できる。この結果、絶縁体１０の耐衝撃性を向上することが十分にできると考えられる。 The evaluation of the two samples B1 and B2 in which (Lc−Ld) is greater than 0 was “B”. On the other hand, the evaluation of the sample B3 in which (Lc−Ld) = 0 is “C”,
The evaluation of two samples B4 and B5 in which (Lc−Ld) is less than 0 was “D”. The reason is considered as follows. When (Lc−Ld) is greater than 0, that is, when the rear end P1 of the third portion 10C of the insulator 10 is located on the rear end side with respect to the front end P2 of the rear end barrel portion 43C, the third The rear end P1 of the portion 10C faces the rear end barrel portion 43C having a relatively large outer diameter Re in the radial direction. As a result, at the time of vibration, it can be ensured that the rear end P1 of the third portion 10C serves as a contact point that contacts the trunk portion 43 of the terminal fitting 40. As a result, it is considered that the impact resistance of the insulator 10 can be sufficiently improved.

これに対して、（Ｌｃ−Ｌｄ）が０以下である場合、すなわち、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部４３Ｃの先端Ｐ２より先端側に位置している場合には、第３部１０Ｃの後端Ｐ１は、比較的小さな外径Ｒｄを有する先端胴部４３Ａと、径方向に対向する。この結果、振動時には、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが、担保できず、第２部１０Ｂの後端Ｐｅが、胴部４３と接触する接触点となってしまう可能性が高くなる。この結果、絶縁体１０の耐衝撃性を向上することが十分にできないと考えられる。 On the other hand, when (Lc−Ld) is 0 or less, that is, when the rear end P1 of the third portion 10C of the insulator 10 is located on the front end side with respect to the front end P2 of the rear end barrel portion 43C. In addition, the rear end P1 of the third portion 10C is opposed to the distal end barrel portion 43A having a relatively small outer diameter Rd in the radial direction. As a result, at the time of vibration, it cannot be ensured that the rear end P1 of the third portion 10C is a contact point that comes into contact with the body portion 43 of the terminal fitting 40, and the rear end Pe of the second portion 10B is the body portion 43. There is a high possibility that the contact point will come into contact. As a result, it is considered that the impact resistance of the insulator 10 cannot be sufficiently improved.

図４は、比較形態のスパークプラグ１００ｃの端子金具４０近傍の構成を示す図である。図４の例では、後端胴部４３Ｃｃの軸線方向の長さが比較的短く、先端胴部４３Ａｃの軸線方向の長さが比較的長いために、絶縁体１０の第３部１０Ｃの後端Ｐ１は、後端胴部４３Ｃｃの先端Ｐ２より先端側に位置している。このような場合には、第３部１０Ｃの後端Ｐ１は、比較的小さな外径Ｒｄを有する先端胴部４３Ａｃと、径方向に対向するので、絶縁体１０の第３部１０Ｃの後端Ｐ１と、胴部４３ｃと、の間隔ΔＲ２ｂは、図２のΔＲ２ｂより広くなってしまう。この結果、振動時に、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３ｃと接触する接触点となることが、担保しがたくなることが解る。 FIG. 4 is a view showing a configuration in the vicinity of the terminal fitting 40 of the spark plug 100c of the comparative form. In the example of FIG. 4, the rear end barrel portion 43Cc has a relatively short length in the axial direction, and the tip barrel portion 43Ac has a relatively long length in the axial direction. P1 is located on the front end side with respect to the front end P2 of the rear end body portion 43Cc. In such a case, the rear end P1 of the third portion 10C is opposed to the front end barrel portion 43Ac having a relatively small outer diameter Rd in the radial direction, so that the rear end P1 of the third portion 10C of the insulator 10 And the space | interval (DELTA) R2b of the trunk | drum 43c will become wider than (DELTA) R2b of FIG. As a result, it is understood that it is difficult to ensure that the rear end P1 of the third portion 10C is a contact point that contacts the trunk portion 43c of the terminal fitting 40 during vibration.

これに対して、（Ｌｃ−Ｌｄ）が０である場合、すなわち、絶縁体１０の第３部１０Ｃの後端Ｐ１は、比較的大きな外径Ｒｅを有する後端胴部４３Ｃと径方向に対向しているが、Ｒｅより小さな外径を有する段部４３Ｂとも対向している。このために、（Ｌｃ−Ｌｄ）が０より大きい場合と比較すると、振動時には、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが十分に担保できず、第２部１０Ｂの後端Ｐｅが、胴部４３と接触する接触点となってしまう可能性もある、と考えられる。この結果、絶縁体１０の耐衝撃性を向上することが十分にできないと考えられる。 On the other hand, when (Lc−Ld) is 0, that is, the rear end P1 of the third portion 10C of the insulator 10 is opposed to the rear end barrel portion 43C having a relatively large outer diameter Re in the radial direction. However, it is also opposed to the stepped portion 43B having an outer diameter smaller than Re. For this reason, as compared with the case where (Lc−Ld) is greater than 0, it is sufficiently ensured that the rear end P1 of the third portion 10C becomes a contact point that contacts the body portion 43 of the terminal fitting 40 during vibration. It is considered that the rear end Pe of the second part 10 B may become a contact point in contact with the body part 43. As a result, it is considered that the impact resistance of the insulator 10 cannot be sufficiently improved.

以上の説明から解るように、第２評価試験から、（Ｌｃ−Ｌｄ）が０より大きければ、すなわち、絶縁体１０の第３部１０Ｃの後端Ｐ１が、後端胴部４３Ｃの先端Ｐ２より後端側に位置していれば、絶縁体１０の耐衝撃性を向上することができることが解った。 As understood from the above description, from the second evaluation test, if (Lc−Ld) is larger than 0, that is, the rear end P1 of the third portion 10C of the insulator 10 is more than the front end P2 of the rear end barrel portion 43C. It was found that the impact resistance of the insulator 10 can be improved if it is located on the rear end side.

このように、第１評価試験と第２評価試験の結果から、第２部１０Ｂは、絶縁体１０の後端から先端側に１ｍｍ以上離れた部分を含み、かつ、第３部１０Ｃの後端Ｐ１が、後端胴部４３Ｃの先端Ｐ２より後端側に位置していることが好ましいことが解った。こうすれば、端子金具４０が振動した場合に、胴部４３は、絶縁体１０の後端から比較的離れた第３部１０Ｃと接触しやすく、第２部１０Ｂとは接触し難い。この結果、端子金具４０から絶縁体１０に付加される衝撃を低減できるので、絶縁体１０の割れを抑制することができる。 Thus, from the results of the first evaluation test and the second evaluation test, the second part 10B includes a portion that is 1 mm or more away from the rear end of the insulator 10 toward the front end side, and the rear end of the third part 10C. It was found that P1 is preferably located on the rear end side with respect to the front end P2 of the rear end body portion 43C. In this way, when the terminal fitting 40 vibrates, the trunk portion 43 easily comes into contact with the third portion 10C that is relatively far from the rear end of the insulator 10, and hardly comes into contact with the second portion 10B. As a result, since the impact applied to the insulator 10 from the terminal fitting 40 can be reduced, cracking of the insulator 10 can be suppressed.

Ｄ．第３評価試験：
さらに、耐衝撃性を向上できる構成を確かめるべく、第３評価試験を行った。第３評価試験では、表３に示すように、スパークプラグ１００の８種類のサンプルＣ１〜Ｃ８を作成した。各サンプルに共通な寸法は、以下の通りである。
絶縁体１０の後端Ｐｅから胴部４３の先端Ｐｓまでの長さＬａ：４１ｍｍ
絶縁体１０の後端Ｐｅから第１部１０Ａの後端Ｐ３までの長さＬｂ：１９.２ｍｍ
絶縁体１０の後端Ｐｅから後端胴部４３Ｃの先端Ｐ２までの長さＬｃ：１０ｍｍ
絶縁体１０の後端Ｐｅから第３部１０Ｃの後端Ｐ１までの長さＬｄ：５．０ｍｍ
第１部１０Ａの内径Ｒａ：３ｍｍ
第２部１０Ｂの内径Ｒｂ：４．１ｍｍ
第３部１０Ｃの内径Ｒｃ：４．０ｍｍ
先端胴部４３Ａの外径Ｒｄ：２．８５ｍｍ
後端胴部４３Ｃの外径Ｒｅ：３．８ｍｍ
なお、絶縁体１０や端子金具４０などの各部材の材質は、上記第１評価試験と同じである。また、各サンプルに対する耐衝撃性試験の内容および評価基準は、上述した第１評価試験と同じである。 D. Third evaluation test:
Furthermore, a third evaluation test was conducted in order to confirm the configuration capable of improving the impact resistance. In the third evaluation test, as shown in Table 3, eight types of samples C1 to C8 of the spark plug 100 were created. The dimensions common to each sample are as follows.
Length La from the rear end Pe of the insulator 10 to the front end Ps of the body 43: 41 mm
Length Lb from the rear end Pe of the insulator 10 to the rear end P3 of the first portion 10A: 19.2 mm
Length Lc from the rear end Pe of the insulator 10 to the front end P2 of the rear end body portion 43C: 10 mm
Length Ld from the rear end Pe of the insulator 10 to the rear end P1 of the third portion 10C: 5.0 mm
Inner diameter Ra of the first part 10A: 3 mm
Inner diameter Rb of second part 10B: 4.1 mm
Inner diameter Rc of the third part 10C: 4.0 mm
Outer diameter Rd of the tip body 43A: 2.85 mm
The outer diameter Re of the rear end barrel portion 43C: 3.8 mm
The material of each member such as the insulator 10 and the terminal fitting 40 is the same as that in the first evaluation test. Further, the contents and evaluation criteria of the impact resistance test for each sample are the same as those in the first evaluation test described above.

８種類のサンプルＣ１〜Ｃ８では、絶縁体１０の第３部１０Ｃを含む後端部分の外径Ｒｆ（図２）が互いに異なっており、２０ｍｍ、１８ｍｍ、１７ｍｍ、１６.４ｍｍ、１６.２ｍｍ、１４ｍｍ、９ｍｍ、７．５ｍｍのいずれかとされている。これによって、８種類のサンプルＣ１〜Ｃ８の第３部１０Ｃの肉厚Ｔ＝｛（Ｒｆ−Ｒｃ）／２｝（図２）は互いに異なっており、８ｍｍ、７ｍｍ、６．５ｍｍ、６．２ｍｍ、６．１ｍｍ、５ｍｍ、２．５ｍｍ、１．７５ｍｍとされている。 In the eight types of samples C1 to C8, the outer diameters Rf (FIG. 2) of the rear end portion including the third portion 10C of the insulator 10 are different from each other, and are 20 mm, 18 mm, 17 mm, 16.4 mm, 16.2 mm, 14 mm, 9 mm, or 7.5 mm. Accordingly, the thickness T = {(Rf−Rc) / 2} (FIG. 2) of the third part 10C of the eight types of samples C1 to C8 is different from each other, and is 8 mm, 7 mm, 6.5 mm, 6.2 mm. 6.1 mm, 5 mm, 2.5 mm, and 1.75 mm.

第３部１０Ｃの肉厚Ｔが、８ｍｍであるサンプルＣ１の評価は、「Ａ」であり、第３部１０Ｃの肉厚Ｔが、７ｍｍ以下のサンプルＣ２〜Ｃ８の評価は、「Ｂ」であった。ここで、第３部１０Ｃの肉厚Ｔが、７ｍｍ以下のサンプルＣ２〜Ｃ８において、肉厚Ｔが小さくなっても、耐衝撃性の低下が認められないのは、絶縁体１０に第３部１０Ｃと第２部１０Ｂとが設けられることによって、上述したように、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが担保されているからであると考えられる。 The evaluation of the sample C1 in which the thickness T of the third part 10C is 8 mm is “A”, and the evaluation of the samples C2 to C8 in which the thickness T of the third part 10C is 7 mm or less is “B”. there were. Here, in the samples C2 to C8 in which the thickness T of the third portion 10C is 7 mm or less, even if the thickness T is reduced, the decrease in impact resistance is not recognized. By providing 10C and the second part 10B, as described above, it is ensured that the rear end P1 of the third part 10C is a contact point that contacts the body part 43 of the terminal fitting 40. It is believed that there is.

これを確かめるために、さらに、表４に示すように、図３の比較形態のスパークプラグ１００ｂの８種類のサンプルＤ１〜Ｄ８を作成して、同じように、耐衝撃性試験を行った。これらの８種類のサンプルＤ１〜Ｄ８は、図３に示すように、絶縁体１０ｂにおいて、第３部が設けられていないので、第１部１０Ａの後端側の拡径孔１２Ｂの後端側において、図２の第２部１０Ｂと第３部１０Ｃとが配置されている位置に、内径Ｒｂを有する第２部１０Ｂｂが位置している。これらの８種類のサンプルＤ１〜Ｄ８は、第３部が設けられていない点を除く部分の寸法は、表３のサンプルＣ１〜Ｃ８の末尾の数字が同じサンプルと同じである。すなわち、８種類のサンプルＤ１〜Ｄ８では、絶縁体１０ｂの第２部１０Ｂｂを含む後端部分の外径Ｒｆ（図３）が互いに異なっており、２０ｍｍ、１８ｍｍ、１７ｍｍ、１６.４ｍｍ、１６.２ｍｍ、１４ｍｍ、９ｍｍ、７．５ｍｍとされている。これによって、８種類のサンプルＤ１〜Ｄ８の第２部１０Ｂｂの肉厚ｔ＝｛（Ｒｆ−Ｒｂ）／２｝（図３）は互いに異なっており、７．９５ｍｍ、６．９５ｍｍ、６．４５ｍｍ、６．１５ｍｍ、６．０５ｍｍ、４．９５ｍｍ、２．４５ｍｍ、１．７ｍｍとされている。 In order to confirm this, as shown in Table 4, eight types of samples D1 to D8 of the spark plug 100b of the comparative form of FIG. 3 were prepared, and the impact resistance test was conducted in the same manner. As shown in FIG. 3, these eight types of samples D1 to D8 are not provided with the third part in the insulator 10b, so the rear end side of the diameter-enlarged hole 12B on the rear end side of the first part 10A In FIG. 2, the second portion 10Bb having the inner diameter Rb is located at the position where the second portion 10B and the third portion 10C in FIG. 2 are arranged. These eight types of samples D1 to D8 have the same dimensions as the samples having the same numbers at the end of samples C1 to C8 in Table 3 except that the third part is not provided. That is, in the eight types of samples D1 to D8, the outer diameters Rf (FIG. 3) of the rear end portion including the second portion 10Bb of the insulator 10b are different from each other, and are 20 mm, 18 mm, 17 mm, 16.4 mm, 16. They are 2 mm, 14 mm, 9 mm, and 7.5 mm. Accordingly, the thickness t = {(Rf−Rb) / 2} (FIG. 3) of the second part 10Bb of the eight types of samples D1 to D8 is different from each other, and is 7.95 mm, 6.95 mm, 6.45 mm. 6.15 mm, 6.05 mm, 4.95 mm, 2.45 mm, and 1.7 mm.

第２部１０Ｂｂの肉厚ｔが、７．９５ｍｍであるサンプルＤ１の評価は、「Ａ」であり、第２部１０Ｂｂの肉厚ｔが、６．１５ｍｍ以上６．９５ｍｍ以下のサンプルＤ２〜Ｄ４の評価は、「Ｂ」であった。そして、第２部１０Ｂｂの肉厚ｔが、６．０５ｍｍであるサンプルＤ５の評価は、「Ｃ」であり、第２部１０Ｂｂの肉厚ｔが、４．９５ｍｍ以下のサンプルＤ６〜Ｄ８の評価は、「Ｄ」であった。 The evaluation of the sample D1 in which the thickness t of the second part 10Bb is 7.95 mm is “A”, and the samples D2 to D4 in which the thickness t of the second part 10Bb is 6.15 mm or more and 6.95 mm or less. Was evaluated as “B”. And evaluation of sample D5 whose thickness t of 2nd part 10Bb is 6.05 mm is "C", and evaluation of sample D6-D8 whose thickness t of 2nd part 10Bb is 4.95 mm or less. Was "D".

このように、第２部１０Ｂｂの肉厚ｔが６．１ｍｍ以下のサンプルＤ５〜Ｄ８では、肉厚ｔが小さくことに伴って、耐衝撃性の低下が認められた。以上のことから、図２のスパークプラグ１００では、絶縁体１０に第３部１０Ｃと第２部１０Ｂとが設けられることによって、特に、絶縁体１０の後端側部分の肉厚Ｔ（すなわち、第３部１０Ｃの肉厚Ｔ）が、６．１ｍｍ以下である場合に、耐衝撃性の低下を抑制する効果が顕著であることが解った。 As described above, in samples D5 to D8 in which the thickness t of the second part 10Bb is 6.1 mm or less, a decrease in impact resistance is observed as the thickness t is reduced. From the above, in the spark plug 100 of FIG. 2, the third portion 10C and the second portion 10B are provided in the insulator 10, and in particular, the thickness T (that is, the rear end side portion of the insulator 10 (that is, It was found that when the thickness T) of the third part 10C is 6.1 mm or less, the effect of suppressing the reduction in impact resistance is significant.

この理由は、以下のように考えられる。絶縁体１０の後端側部分の肉厚が小さくなるに連れて、絶縁体１０の径方向に加えられる衝撃に対する耐性が低下していき、端子金具４０の振動に対する耐性が低下すると考えられる。この結果、絶縁体１０の後端側部分の肉厚が小さくなるに連れて、端子金具４０の振動による絶縁体１０の割れが、主に発生する割れとなると考えられる。このときに、図２の実施形態のスパークプラグ１００では、上述したように、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが担保されているので、端子金具４０の振動によって絶縁体１０に加えられる衝撃を抑制できる。この結果、絶縁体１０の後端側部分の肉厚が小さくなっても、具体的には、第３部１０Ｃの肉厚Ｔが、６．１ｍｍ以下であっても、絶縁体１０の割れを抑制できる、と考えられる。これに対して、図３の比較形態のスパークプラグ１００ｂでは、上述したように、第２部１０Ｂｂの後端Ｐｅ（すなわち、絶縁体１０の後端Ｐｅ）が、振動時に、端子金具４０の胴部４３と接触する接触点となってしまう。この結果、端子金具４０の振動によって絶縁体１０に加えられる衝撃を十分に抑制できない。この結果、絶縁体１０の後端側部分の肉厚が小さくなると、具体的には、第２部１０Ｂｂの肉厚ｔが、６．１ｍｍ以下になると、絶縁体１０の割れが発生しやすくなる、と考えられる。 The reason is considered as follows. As the thickness of the rear end portion of the insulator 10 becomes smaller, the resistance to the impact applied in the radial direction of the insulator 10 decreases, and the resistance to vibration of the terminal fitting 40 is considered to decrease. As a result, as the thickness of the rear end portion of the insulator 10 becomes smaller, it is considered that the crack of the insulator 10 due to the vibration of the terminal fitting 40 becomes a mainly generated crack. At this time, in the spark plug 100 of the embodiment of FIG. 2, as described above, it is ensured that the rear end P1 of the third portion 10C serves as a contact point that contacts the trunk portion 43 of the terminal fitting 40. Therefore, the impact applied to the insulator 10 by the vibration of the terminal fitting 40 can be suppressed. As a result, even if the thickness of the rear end portion of the insulator 10 is reduced, specifically, even if the thickness T of the third portion 10C is 6.1 mm or less, the insulator 10 is cracked. It can be suppressed. On the other hand, in the spark plug 100b of the comparative form of FIG. 3, as described above, the rear end Pe of the second portion 10Bb (that is, the rear end Pe of the insulator 10) is It will be a contact point which contacts the part 43. As a result, the impact applied to the insulator 10 due to the vibration of the terminal fitting 40 cannot be sufficiently suppressed. As a result, when the thickness of the rear end portion of the insulator 10 is reduced, specifically, when the thickness t of the second portion 10Bb is 6.1 mm or less, the insulator 10 is easily cracked. ,it is conceivable that.

以上の結果から、実施形態のスパークプラグ１００では、絶縁体１０の第３部１０Ｃの肉厚Ｔ、すなわち、径方向の厚さＴは、６．１ｍｍ以下である場合に、効果的であることが解った。すなわち、この場合に、第３部１０Ｃの径方向の厚さＴが比較的薄い絶縁体１０の割れを効果的に抑制することができる。 From the above results, the spark plug 100 of the embodiment is effective when the thickness T of the third portion 10C of the insulator 10, that is, the radial thickness T is 6.1 mm or less. I understand. That is, in this case, it is possible to effectively suppress the cracking of the insulator 10 in which the radial thickness T of the third portion 10C is relatively thin.

Ｄ．第４評価試験：
さらに、耐衝撃性を向上できる構成を確かめるべく、第４評価試験を行った。第４評価試験では、表５に示すように、スパークプラグ１００の９種類のサンプルＥ１〜Ｅ９を作成した。各サンプルに共通な寸法は、以下の通りである。
絶縁体１０の後端Ｐｅから胴部４３の先端Ｐｓまでの長さＬａ：４１ｍｍ
絶縁体１０の後端Ｐｅから第１部１０Ａの後端Ｐ３までの長さＬｂ：１９．２ｍｍ
絶縁体１０の後端Ｐｅから後端胴部４３Ｃの先端Ｐ２までの長さＬｃ：１０ｍｍ
絶縁体１０の後端Ｐｅから第３部１０Ｃの後端Ｐ１までの長さＬｄ：５．０ｍｍ
第２部１０Ｂの内径Ｒｂ：４．１ｍｍ
第３部１０Ｃの内径Ｒｃ：４．０ｍｍ
後端胴部４３Ｃの外径Ｒｅ：３．８ｍｍ
なお、絶縁体１０や端子金具４０などの各部材の材質は、上記第１評価試験と同じである。また、各サンプルに対する耐衝撃性試験の内容および評価基準は、上述した第１評価試験と同じである。 D. Fourth evaluation test:
Further, a fourth evaluation test was conducted to confirm the configuration capable of improving the impact resistance. In the fourth evaluation test, as shown in Table 5, nine types of samples E1 to E9 of the spark plug 100 were created. The dimensions common to each sample are as follows.
Length La from the rear end Pe of the insulator 10 to the front end Ps of the body 43: 41 mm
Length Lb from the rear end Pe of the insulator 10 to the rear end P3 of the first part 10A: 19.2 mm
Length Lc from the rear end Pe of the insulator 10 to the front end P2 of the rear end body portion 43C: 10 mm
Length Ld from the rear end Pe of the insulator 10 to the rear end P1 of the third portion 10C: 5.0 mm
Inner diameter Rb of second part 10B: 4.1 mm
Inner diameter Rc of the third part 10C: 4.0 mm
The outer diameter Re of the rear end barrel portion 43C: 3.8 mm
The material of each member such as the insulator 10 and the terminal fitting 40 is the same as that in the first evaluation test. Further, the contents and evaluation criteria of the impact resistance test for each sample are the same as those in the first evaluation test described above.

９種類のサンプルＥ１〜Ｅ９では、絶縁体１０の第１部１０Ａの内径Ｒａ（図２）が互いに異なっており、２．７ｍｍ、２．９ｍｍ、３ｍｍのいずれかとされている。ここで、胴部４３の先端胴部４３Ａの外径Ｒｄ（図２）は、先端胴部４３Ａが位置する第１部１０Ａの内径Ｒａに応じて調整されている。具体的には、先端胴部４３Ａの外径Ｒｄは、第１部１０Ａの内径Ｒａより０．２ｍｍだけ小さな値に設定されている（Ｒｄ＝Ｒａー０．２ｍｍ）。 In the nine types of samples E1 to E9, the inner diameter Ra (FIG. 2) of the first portion 10A of the insulator 10 is different from each other, and is set to either 2.7 mm, 2.9 mm, or 3 mm. Here, the outer diameter Rd (FIG. 2) of the distal end barrel portion 43A of the trunk portion 43 is adjusted according to the inner diameter Ra of the first portion 10A where the distal end barrel portion 43A is located. Specifically, the outer diameter Rd of the distal end body portion 43A is set to a value smaller by 0.2 mm than the inner diameter Ra of the first portion 10A (Rd = Ra−0.2 mm).

また、サンプルＥ１〜Ｅ９では、絶縁体１０の第３部１０Ｃを含む後端部分の外径Ｒｆ（図２）が互いに異なっており、２０ｍｍ、１８ｍｍ、１７ｍｍ、１２ｍｍ、９ｍｍ、７．５ｍｍのいずれかとされている。これによって、９種類のサンプルＥ１〜Ｅ９の第３部１０Ｃの肉厚Ｔ＝｛（Ｒｆ−Ｒｃ）／２｝（図２）は互いに異なっており、８ｍｍ、７ｍｍ、６．５ｍｍ、４ｍｍ、２．５ｍｍ、１．７５ｍｍのいずれかとされている。 In Samples E1 to E9, the outer diameters Rf (FIG. 2) of the rear end portion including the third portion 10C of the insulator 10 are different from each other, and any of 20 mm, 18 mm, 17 mm, 12 mm, 9 mm, and 7.5 mm. It has been heeled. Accordingly, the thickness T = {(Rf−Rc) / 2} (FIG. 2) of the third portion 10C of the nine types of samples E1 to E9 are different from each other, and are 8 mm, 7 mm, 6.5 mm, 4 mm, 2 .5 mm or 1.75 mm.

第３部１０Ｃの肉厚Ｔが、８ｍｍであり、かつ、第１部１０Ａの内径Ｒａが３ｍｍであるサンプルＥ１の評価は、「Ａ」であり、その他のサンプルＥ２〜Ｅ９の評価は、「Ｂ」であった。ここで第１部１０Ａの内径Ｒａが小さくなっても、耐衝撃性の低下が認められないのは、絶縁体１０に第３部１０Ｃと第２部１０Ｂとが設けられることによって、上述したように、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが担保されているからであると考えられる。 The evaluation of the sample E1 in which the thickness T of the third part 10C is 8 mm and the inner diameter Ra of the first part 10A is 3 mm is “A”, and the evaluation of the other samples E2 to E9 is “ B ". Here, even when the inner diameter Ra of the first part 10A is reduced, the reduction in impact resistance is not recognized as described above by providing the insulator 10 with the third part 10C and the second part 10B. In addition, it is considered that it is ensured that the rear end P1 of the third portion 10C serves as a contact point that contacts the body portion 43 of the terminal fitting 40.

これを確かめるために、さらに、表６に示すように、図３の比較形態のスパークプラグ１００ｂの９種類のサンプルＦ１〜Ｆ９を作成して、同じように、耐衝撃性試験を行った。これらの９種類のサンプルＦ１〜Ｆ９は、第３部が設けられていない点を除く部分の寸法は、表５のサンプルＥ１〜Ｅ９の末尾の数字が同じサンプルと同じである。すなわち、９種類のサンプルＦ１〜Ｆ９では、絶縁体１０の第１部１０Ａの内径Ｒａ（図３）は、２．７ｍｍ、２．９ｍｍ、３ｍｍのいずれかとされている。そして、胴部４３の先端胴部４３Ａの外径Ｒｄ（図３）は、Ｒｄ＝（Ｒａ−０．２ｍｍ）に設定されている。 In order to confirm this, as shown in Table 6, nine types of samples F1 to F9 of the spark plug 100b of the comparative form of FIG. 3 were prepared, and the impact resistance test was conducted in the same manner. These nine types of samples F1 to F9 are the same as the samples having the same numbers at the end of samples E1 to E9 in Table 5 except for the point where the third part is not provided. That is, in the nine types of samples F1 to F9, the inner diameter Ra (FIG. 3) of the first portion 10A of the insulator 10 is either 2.7 mm, 2.9 mm, or 3 mm. And the outer diameter Rd (FIG. 3) of the front-end | tip trunk | drum 43A of the trunk | drum 43 is set to Rd = (Ra-0.2mm).

また、サンプルＦ１〜Ｆ９では、絶縁体１０の第３部１０Ｃを含む後端部分の外径Ｒｆ（図３）が、２０ｍｍ、１８ｍｍ、１７ｍｍ、１２ｍｍ、９ｍｍ、７．５ｍｍのいずれかとされている。これによって、９種類のサンプルＦ１〜Ｆ９の第２部１０Ｂｂの肉厚ｔ＝｛（Ｒｆ−Ｒｂ）／２｝（図３）は、７．９５ｍｍ、６．９５ｍｍ、６．４５ｍｍ、３．９５ｍｍ、２．４５ｍｍ、１．７ｍｍのいずれかとされている。 In Samples F1 to F9, the outer diameter Rf (FIG. 3) of the rear end portion including the third portion 10C of the insulator 10 is any of 20 mm, 18 mm, 17 mm, 12 mm, 9 mm, and 7.5 mm. . Accordingly, the thickness t = {(Rf−Rb) / 2} (FIG. 3) of the second part 10Bb of the nine types of samples F1 to F9 is 7.95 mm, 6.95 mm, 6.45 mm, and 3.95 mm. 2.45 mm or 1.7 mm.

第１部１０Ａの内径Ｒａが、３ｍｍであるサンプルＦ１〜Ｆ３の評価は、「Ａ」または「Ｂ」であった。すなわち、第２部１０Ｂｂの肉厚ｔが、７．９５ｍｍであるサンプルＦ１の評価は、「Ａ」であり、第２部１０Ｂｂの肉厚ｔが、６.９５ｍｍ、６．４５ｍｍのサンプルＦ２、Ｆ３の評価は、「Ｂ」であった。そして、第１部１０Ａの内径Ｒａが、２．９ｍｍであるサンプルＦ４〜Ｆ６の評価は、第２部１０Ｂｂの肉厚ｔに拘わらずに、「Ｃ」であった。そして、第１部１０Ａの内径Ｒａが、２．７ｍｍであるサンプルＦ７〜Ｆ９の評価は、第２部１０Ｂｂの肉厚ｔに拘わらずに、「Ｄ」であった。 The evaluation of the samples F1 to F3 in which the inner diameter Ra of the first part 10A was 3 mm was “A” or “B”. That is, the evaluation of the sample F1 in which the thickness t of the second part 10Bb is 7.95 mm is “A”, and the sample F2 in which the thickness t of the second part 10Bb is 6.95 mm, 6.45 mm, The evaluation of F3 was “B”. The evaluation of the samples F4 to F6 in which the inner diameter Ra of the first part 10A was 2.9 mm was “C” regardless of the thickness t of the second part 10Bb. And evaluation of sample F7-F9 whose inner diameter Ra of 1st part 10A is 2.7 mm was "D" irrespective of the thickness t of 2nd part 10Bb.

このように、第１部１０Ａの内径Ｒａが、２．９ｍｍ以下のサンプルＦ４〜Ｆ９では、第１部１０Ａの内径Ｒａが小さくなることに伴って、耐衝撃性の低下が認められた。以上のことから、図２のスパークプラグ１００では、絶縁体１０に第３部１０Ｃと第２部１０Ｂとが設けられることによって、特に、絶縁体１０の第１部１０Ａの内径Ｒａが、２．９ｍｍ以下である場合に、耐衝撃性の低下を抑制する効果が顕著であることが解った。 Thus, in samples F4 to F9 in which the inner diameter Ra of the first part 10A was 2.9 mm or less, a decrease in impact resistance was observed as the inner diameter Ra of the first part 10A became smaller. From the above, in the spark plug 100 of FIG. 2, the insulator 10 is provided with the third portion 10C and the second portion 10B, and in particular, the inner diameter Ra of the first portion 10A of the insulator 10 is 2. It has been found that when the thickness is 9 mm or less, the effect of suppressing a decrease in impact resistance is significant.

この理由は、以下のように考えられる。第１部１０Ａの内径Ｒａが小さくなるに連れて、第１部１０Ａの内部に位置する端子金具４０の先端胴部４３Ａの外径Ｒｄを小さくせざるを得なくなる。先端胴部４３Ａの外径Ｒｄが小さくなると、先端胴部４３Ａの剛性が低下するので、振動の振幅が大きくなる。この結果、スパークプラグ１００が衝撃を受けたときに、端子金具４０の胴部４３が、絶縁体１０に径方向に接触する頻度が高くなる。この結果、絶縁体１０が割れやすくなり耐衝撃性が低下すると考えられる。この結果、第１部１０Ａの内径Ｒａが小さくなるに連れて、端子金具４０の振動による絶縁体１０の割れが、主に発生する割れとなると考えられる。このときに、図２の実施形態のスパークプラグ１００では、上述したように、第３部１０Ｃの後端Ｐ１が、端子金具４０の胴部４３と接触する接触点となることが担保されているので、端子金具４０の振動によって絶縁体１０に加えられる衝撃を抑制できる。この結果、第１部１０Ａの内径Ｒａが小さくなっても、具体的には、第１部１０Ａの内径Ｒａが、２．９ｍｍ以下であっても、絶縁体１０の割れを抑制できる、と考えられる。これに対して、図３の比較形態のスパークプラグ１００ｂでは、上述したように、第２部１０Ｂｂの後端Ｐｅ（すなわち、絶縁体１０の後端Ｐｅ）が、振動時に、端子金具４０の胴部４３と接触する接触点となってしまう。この結果、端子金具４０の振動によって絶縁体１０に加えられる衝撃を十分に抑制できない。この結果、第１部１０Ａの内径Ｒａが小さくなると、具体的には、第１部１０Ａの内径Ｒａが、２．９ｍｍ以下になると、絶縁体１０の割れが発生しやすくなる、と考えられる。 The reason is considered as follows. As the inner diameter Ra of the first portion 10A becomes smaller, the outer diameter Rd of the distal end barrel portion 43A of the terminal fitting 40 located inside the first portion 10A has to be reduced. When the outer diameter Rd of the distal end barrel portion 43A is reduced, the rigidity of the distal end barrel portion 43A is reduced, and therefore the amplitude of vibration is increased. As a result, when the spark plug 100 receives an impact, the frequency at which the body 43 of the terminal fitting 40 contacts the insulator 10 in the radial direction increases. As a result, it is considered that the insulator 10 is easily broken and the impact resistance is lowered. As a result, it is considered that the crack of the insulator 10 due to the vibration of the terminal fitting 40 mainly occurs as the inner diameter Ra of the first portion 10A decreases. At this time, in the spark plug 100 of the embodiment of FIG. 2, as described above, it is ensured that the rear end P1 of the third portion 10C serves as a contact point that contacts the trunk portion 43 of the terminal fitting 40. Therefore, the impact applied to the insulator 10 by the vibration of the terminal fitting 40 can be suppressed. As a result, even if the inner diameter Ra of the first part 10A is reduced, specifically, even if the inner diameter Ra of the first part 10A is 2.9 mm or less, it is considered that cracking of the insulator 10 can be suppressed. It is done. On the other hand, in the spark plug 100b of the comparative form of FIG. 3, as described above, the rear end Pe of the second portion 10Bb (that is, the rear end Pe of the insulator 10) is It will be a contact point which contacts the part 43. As a result, the impact applied to the insulator 10 due to the vibration of the terminal fitting 40 cannot be sufficiently suppressed. As a result, it is considered that when the inner diameter Ra of the first portion 10A is reduced, specifically, when the inner diameter Ra of the first portion 10A is 2.9 mm or less, the insulator 10 is easily cracked.

以上の結果から、実施形態のスパークプラグ１００では、第１部１０Ａの内径Ｒａが、２．９ｍｍ以下である場合に、効果的であることが解った。この場合には、端子金具４０の先端胴部４３Ａの外径Ｒｄが比較的細いために振動しやすいにも拘わらずに、効果的に絶縁体１０の割れを抑制することができる。 From the above results, it was found that the spark plug 100 of the embodiment is effective when the inner diameter Ra of the first portion 10A is 2.9 mm or less. In this case, although the outer diameter Rd of the distal end barrel portion 43A of the terminal fitting 40 is relatively thin, cracking of the insulator 10 can be effectively suppressed even though the insulator 10 is likely to vibrate.

Ｅ．変形例：
（１）図５は、変形例のスパークプラグの絶縁体１０ｄの断面図である。図５では、端子金具４０などの他の構成の図示は省略されている。図５に示すように、絶縁体１０ｄは、第２部１０Ｂより後端側に、座繰りＣＢが形成されている。このような座繰りＣＢは、絶縁体の製造上の理由などによって形成され得る。座繰りＣＢは、わずかに、第２部１０Ｂより内径が大きくなっている部分である。座繰りＣＢの軸方向の長さは、０．３〜０．６ｍｍである。座繰りＣＢの有無に拘わらずに、第２部１０Ｂは、絶縁体の後端から先端側に１ｍｍ以上離れた部分を含んでいればよい。そして、当該第１部１０Ａと、第１部１０Ａと、の間に、第１部１０Ａの内径より大きく第２部１０Ｂの内径より小さな内径を有する第３部１０Ｃが位置していれば良い。こうすれば、第１評価試験の結果からわかるように、端子金具４０から絶縁体に付加される衝撃を低減できるので、絶縁体の割れを抑制することができる。 E. Variations:
(1) FIG. 5 is a cross-sectional view of a modified spark plug insulator 10d. In FIG. 5, illustration of other structures, such as the terminal metal fitting 40, is abbreviate | omitted. As shown in FIG. 5, the insulator 10d has a counterbore CB formed on the rear end side of the second portion 10B. Such a counterbore CB can be formed for reasons of manufacturing an insulator. The counterbore CB is a part having an inner diameter slightly larger than that of the second part 10B. The axial length of the counterbore CB is 0.3 to 0.6 mm. Regardless of the presence or absence of the counterbore CB, the second portion 10B only needs to include a portion 1 mm or more away from the rear end of the insulator toward the front end. The third part 10C having an inner diameter larger than the inner diameter of the first part 10A and smaller than the inner diameter of the second part 10B may be positioned between the first part 10A and the first part 10A. In this way, as can be seen from the result of the first evaluation test, the impact applied from the terminal fitting 40 to the insulator can be reduced, so that cracking of the insulator can be suppressed.

（２）図６は、変形例のスパークプラグの端子金具４０の近傍の構成を示す第１の図である。これらの変形例は、実施形態のスパークプラグ１００と同一の部材、例えば、絶縁体１０、端子金具４０、シール部材８０が用いられている。スパークプラグの製造時には、絶縁体１０の軸孔１２内に投入されたシール部材６０、抵抗体７０、シール部材８０の原料粉末を、端子金具４０の胴部４３の先端で圧縮するように、端子金具４０の胴部４３が、軸孔１２内に押し込まれる。このときに、端子金具４０には、軸線方向に圧縮する力が働くために、端子金具４０の変形が生じ得る。図６の例では、後端胴部４３Ｃが湾曲して、後端胴部４３Ｃの外周面が、絶縁体１０の第２部１０Ｂの内周面に接触している。 (2) FIG. 6 is a first view showing a configuration in the vicinity of the terminal fitting 40 of the spark plug of the modification. In these modifications, the same members as the spark plug 100 of the embodiment, for example, the insulator 10, the terminal fitting 40, and the seal member 80 are used. At the time of manufacturing the spark plug, the raw material powder of the seal member 60, the resistor 70, and the seal member 80 put in the shaft hole 12 of the insulator 10 is compressed at the tip of the body portion 43 of the terminal fitting 40. The body portion 43 of the metal fitting 40 is pushed into the shaft hole 12. At this time, the terminal metal fitting 40 may be deformed because a force compressing in the axial direction acts on the terminal metal fitting 40. In the example of FIG. 6, the rear end barrel portion 43 C is curved, and the outer peripheral surface of the rear end barrel portion 43 C is in contact with the inner peripheral surface of the second portion 10 B of the insulator 10.

図７は、変形例のスパークプラグの端子金具４０の近傍の構成を示す第２の図である。スパークプラグの製造時には、上述したように端子金具４０の胴部４３が軸孔１２内に押し込まれる際に、製造誤差によって、絶縁体１０の軸線ＣＬに対して、端子金具４０の軸線が傾斜する場合がある。図７の例では、端子金具４０の傾斜によって、後端胴部４３Ｃの外周面が、絶縁体１０の第２部１０Ｂの内周面に接触している。 FIG. 7 is a second view showing a configuration in the vicinity of the terminal fitting 40 of the spark plug of the modification. When manufacturing the spark plug, as described above, when the body 43 of the terminal fitting 40 is pushed into the shaft hole 12, the axis of the terminal fitting 40 is inclined with respect to the axis CL of the insulator 10 due to a manufacturing error. There is a case. In the example of FIG. 7, the outer peripheral surface of the rear end barrel portion 43 C is in contact with the inner peripheral surface of the second portion 10 B of the insulator 10 due to the inclination of the terminal fitting 40.

このように、製造時の端子金具４０の変形、および、傾斜の一方、あるいは、両方によって、端子金具４０の後端胴部４３Ｃの外周面が、周方向の一部において、絶縁体１０の第２部１０Ｂや第３部１０Ｃの内周面と、接触する場合がある。すなわち、端子金具４０の胴部４３と、絶縁体１０の内周面とは、一部で非接触であり、一部で接触していても良い。このような場合であっても、スパークプラグに衝撃が加えられたときに、端子金具４０の胴部４３が、絶縁体１０の第２部１０Ｂの後端のうち、通常時には非接触である部位（例えば、図６、図７の後端Ｐｅ）と接触することを抑制することができる。この結果、実施形態と同様に、絶縁体１０の割れを効果的に抑制することができる。 As described above, the outer peripheral surface of the rear end barrel portion 43C of the terminal fitting 40 is partly in the circumferential direction due to one or both of the deformation and / or the inclination of the terminal fitting 40 at the time of manufacture. In some cases, the inner surface of the second part 10B or the third part 10C may come into contact. In other words, the body 43 of the terminal fitting 40 and the inner peripheral surface of the insulator 10 are partly non-contact and may be partly in contact. Even in such a case, when the impact is applied to the spark plug, the body portion 43 of the terminal fitting 40 is a portion of the rear end of the second portion 10B of the insulator 10 that is normally non-contacting. For example, contact with the rear end Pe of FIGS. 6 and 7 can be suppressed. As a result, the crack of the insulator 10 can be effectively suppressed as in the embodiment.

一般的に言えば、端子金具４０の胴部４３と、絶縁体１０の内周面とは、少なくとも一部で非接触であることが好ましい。例えば、端子金具４０の後端胴部４３Ｃと、絶縁体１０の第２部１０Ｂの内周面とは、周方向の全周のうち、少なくとも一部で非接触であることが好ましい。同様に、端子金具４０の後端胴部４３Ｃと、絶縁体１０の第３部１０Ｃの内周面とは、周方向の全周のうち、少なくとも一部で非接触であることが好ましい。 Generally speaking, it is preferable that at least a part of the body 43 of the terminal fitting 40 and the inner peripheral surface of the insulator 10 are not in contact with each other. For example, it is preferable that the rear end body portion 43C of the terminal fitting 40 and the inner peripheral surface of the second portion 10B of the insulator 10 are not in contact with each other in at least a part of the entire circumference in the circumferential direction. Similarly, it is preferable that the rear end body portion 43C of the terminal fitting 40 and the inner peripheral surface of the third portion 10C of the insulator 10 are not in contact with each other in at least a part of the entire circumference in the circumferential direction.

（３）絶縁体１０の材料や、端子金具４０の材料は、一例であり、上述の材料に限られない。例えば、絶縁体１０は、アルミナ（Ａｌ_２Ｏ_３）を主成分とするセラミックスを用いて形成されているが、これに代えて、他の化合物（例えば、ＡｌＮ、ＺｒＯ_２、ＳｉＣ、ＴｉＯ_２、Ｙ_２Ｏ_３など）を主成分とするセラミックスを用いて形成されてもよい。 (3) The material of the insulator 10 and the material of the terminal fitting 40 are examples, and are not limited to the materials described above. For example, the insulator 10 is formed using ceramics mainly composed of alumina (Al ₂ O ₃ ). Instead, other compounds (for example, AlN, ZrO ₂ , SiC, TiO ₂ , Y ₂ O ₃ or the like) may be used.

（４）図２のスパークプラグ１００の具体的構成は、一例であり、これに限られない。例えば、抵抗体７０がないタイプのスパークプラグが採用されてもよい。また、中心電極や接地電極などの発火部の構成には、他のあらゆるタイプの構成、例えば、中心電極と接地電極とが径方向に対向するタイプの構成などが採用され得る。また、主体金具５０の材質や形状などは、適宜に変更可能である。 (4) The specific configuration of the spark plug 100 of FIG. 2 is an example, and is not limited thereto. For example, a type of spark plug without the resistor 70 may be employed. In addition, as the configuration of the firing part such as the center electrode and the ground electrode, any other type of configuration, for example, a configuration in which the center electrode and the ground electrode face each other in the radial direction can be adopted. In addition, the material and shape of the metal shell 50 can be changed as appropriate.

以上、実施形態、変形例に基づき本発明について説明してきたが、上記した発明の実施の形態は、本発明の理解を容易にするためのものであり、本発明を限定するものではない。本発明は、その趣旨並びに特許請求の範囲を逸脱することなく、変更、改良され得ると共に、本発明にはその等価物が含まれる。 As mentioned above, although this invention was demonstrated based on embodiment and a modification, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

５...ガスケット、６...パッキン、８...板パッキン、９...タルク、１０...絶縁体、１２...軸孔、１２Ａ...第１の孔、１２Ｂ...第２の孔、１２Ｃ...縮径孔、１３...脚長部、１５...段部、１７...先端側胴部、１８...後端側胴部、１９...鍔部、２０...中心電極、２１...中心電極本体、２３...頭部、２４...鍔部、２５...脚部、２９...中心電極チップ、３０度以上摂氏８０度以...摂氏、３０...接地電極、３１...接地電極本体、３９...接地電極チップ、４０...端子金具、４１...キャップ装着部、４２...鍔部、４３...脚部、５０...主体金具、５１...工具係合部、５２...取付ネジ部、５３...加締部、５４...座部、５６...段部、５８...圧縮変形部、５９...挿入孔、６０...導電性シール、７０...抵抗体、１００...スパークプラグ、２００...絶縁体支持部材、２１０...固定孔、３００...板状電極、３１０...電極孔、４００...電極支持部材、５００...棒状電極、５１０...大径部、５２０...小径部、５３０...縮外径部、５５０...絶縁部材、６００...油槽、６５０...オイル、７００...電源、１０００...検査装置 5 ... gasket, 6 ... packing, 8 ... plate packing, 9 ... talc, 10 ... insulator, 12 ... shaft hole, 12A ... first hole, 12B. 2nd hole, 12C ... reduced diameter hole, 13 ... long leg part, 15 ... step part, 17 ... front end side body part, 18 ... rear end side body part, 19. .. buttock, 20 ... center electrode, 21 ... center electrode body, 23 ... head, 24 ... buttock, 25 ... leg, 29 ... center electrode tip, 30 80 degrees Celsius or more ... Celsius, 30 ... ground electrode, 31 ... ground electrode body, 39 ... ground electrode tip, 40 ... terminal fitting, 41 ... cap mounting portion, 42 ... collar part, 43 ... leg part, 50 ... metal shell, 51 ... tool engaging part, 52 ... mounting screw part, 53 ... caulking part, 54 ... seat Part, 56 ... step part, 58 ... compression deformation part, 59 ... insertion hole, 60 ... conductive seal, 70 ... resistor, 100 ... spark plug, 200 ... Insulator support member, 210 ... Fixed hole, 300 ... plate electrode, 310 ... electrode hole, 400 ... electrode support member, 500 ... bar electrode, 510 ... large diameter part, 520 ... small diameter part, 530. .. Reduced outer diameter part, 550 ... Insulating member, 600 ... Oil tank, 650 ... Oil, 700 ... Power supply, 1000 ... Inspection device

Claims

An insulator having an axial hole extending along the axis;
A central electrode extending along the axis and having a rear end located in the shaft hole;
A body portion disposed in the shaft hole and having a front end located on the rear end side from the rear end of the center electrode, and located on the rear end side from the body portion, and exposed to the outside on the rear end side from the insulator. A terminal fitting comprising a head,
A conductive sealing material in contact with the tip of the terminal fitting in the shaft hole;
A spark plug comprising:
The insulator is
A cylindrical first portion having a first inner diameter, the tip of the body portion of the terminal fitting being disposed;
A cylindrical second portion including a portion separated from the rear end of the insulator by 1 mm or more on the front end side and having a second inner diameter larger than the first inner diameter;
A cylindrical third part located between the first part and the second part and having a third inner diameter that is larger than the first inner diameter and smaller than the second inner diameter;
The body portion of the terminal fitting includes a cylindrical front end body portion including a front end, and a cylindrical rear end located on a rear end side from the front end body portion and having an outer diameter larger than an outer diameter of the front end body portion. A torso, and
The spark plug according to claim 1, wherein a rear end of the third part is located on a rear end side with respect to a front end of the rear end body part.

The spark plug according to claim 1,
The spark plug according to claim 1, wherein a radial thickness of the third portion of the insulator is 6.1 mm or less.

The spark plug according to claim 1 or 2,
The spark plug according to claim 1, wherein the first inner diameter is 2.9 mm or less.