JP2011253826A

JP2011253826A - Spark plug

Info

Publication number: JP2011253826A
Application number: JP2011174442A
Authority: JP
Inventors: Yasushi Sakakura; 靖坂倉; Yosuke Imai; 庸介今井; Yoshinori Doi; 義規土井
Original assignee: NGK Spark Plug Co Ltd; Ishifuku Metal Industry Co Ltd
Current assignee: Ishifuku Metal Industry Co Ltd; Niterra Co Ltd
Priority date: 2011-08-10
Filing date: 2011-08-10
Publication date: 2011-12-15

Abstract

PROBLEM TO BE SOLVED: To suppress peeling of a noble metal chip member in a spark plug which uses a noble metal chip member in a spark discharge portion.SOLUTION: The spark plug includes a center electrode extending in an axial direction of the spark plug, an earth electrode having an end portion which faces an end portion of the center electrode and forming a spark gap with the center electrode. At least one end portion, from among the end portions of the center electrode and the earth electrode, includes a noble metal chip member having a welding surface and an intermediate member. One surface of the intermediate member is welded to the welding surface of the noble metal chip member by resistance welding, and the other surface is welded to an electrode base material by resistance welding. When thickness of the noble metal chip member in a direction perpendicular to the welding surface is set as Ta and thickness of the intermediate member in a direction perpendicular to the one surface is set as Tb, Tb>Ta is satisfied.

Description

本発明は、スパークプラグに関する。 The present invention relates to a spark plug.

スパークプラグには、メンテナンスフリー達成のための長寿命化のみならず、電極の小型化による着火性の向上や燃焼効率の向上が求められ、こうした要求に応えるため、中心電極や接地電極における火花放電部位に貴金属チップ部材を接合したスパークプラグが知られている。このようなスパークプラグにおいて、貴金属チップ部材と電極母材との間に、貴金属チップ部材の線膨張係数と電極母材の線膨張係数との中間の値の線膨張係数を有する中間部材を配置する技術が知られている。（例えば、特許文献１）。 Spark plugs are required not only to have a long life to achieve maintenance-free, but also to improve ignitability and combustion efficiency by miniaturizing the electrodes. To meet these demands, spark discharge at the center electrode and ground electrode is required. A spark plug in which a noble metal tip member is joined to a part is known. In such a spark plug, an intermediate member having a linear expansion coefficient that is an intermediate value between the linear expansion coefficient of the noble metal tip member and the linear expansion coefficient of the electrode base material is disposed between the noble metal tip member and the electrode base material. Technology is known. (For example, patent document 1).

このような構成を採用することにより、貴金属チップ部材の電極母材からの剥離を抑制している。 By adopting such a configuration, peeling of the noble metal tip member from the electrode base material is suppressed.

特開昭６０−２６２３７４号公報JP 60-262374 A 特開昭５９−９４３９１号公報JP 59-94391 A 特開平６−６０９５９号公報JP-A-6-60959

しかしながら、さらに、貴金属チップ部材の剥離を抑制することが求められている。例えば、上記の従来の構成では、貴金属チップ部材が中間部材から剥離するおそれがあった。
本発明は、火花放電部位において貴金属チップ部材を用いるスパークプラグにおいて、貴金属チップ部材の剥離を抑制することを目的とする。 However, it is further required to suppress peeling of the noble metal tip member. For example, in the conventional configuration described above, the noble metal tip member may be peeled off from the intermediate member.
An object of the present invention is to suppress peeling of a noble metal tip member in a spark plug using the noble metal tip member at a spark discharge site.

本発明は、上述の課題の少なくとも一部を解決するために、以下の形態または適用例を取ることが可能である。 In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.

［適用例１］スパークプラグであって、
前記スパークプラグの軸線方向に延在する中心電極と、
前記中心電極との間で火花ギャップを形成する接地電極と、
を備え、
前記中心電極と前記接地電極のうち少なくとも一方は、
貴金属チップ部材と、
第１の面が前記貴金属チップ部材と抵抗溶接され、前記第１の面と反対側の第２の面が電極母材と抵抗溶接された中間部材と、
を備え、
前記貴金属チップ部材の端面に垂直な方向の厚さをＴａとし、
前記中間部材における前記第１の面に垂直な方向の厚さをＴｂとした場合において、
Ｔｂ＞Ｔａ
を満たす、スパークプラグ。
こうすれば、抵抗溶接された中間部材と貴金属チップ部材との間に発生する応力を抑制することができる。この結果、貴金属チップ部材と中間部材との剥離を抑制することができる。 [Application Example 1] A spark plug,
A center electrode extending in the axial direction of the spark plug;
A ground electrode that forms a spark gap with the center electrode;
With
At least one of the center electrode and the ground electrode is
A precious metal tip member;
An intermediate member in which a first surface is resistance-welded with the noble metal tip member, and a second surface opposite to the first surface is resistance-welded with an electrode base material;
With
The thickness in the direction perpendicular to the end face of the noble metal tip member is Ta,
When the thickness of the intermediate member in the direction perpendicular to the first surface is Tb,
Tb> Ta
Meet the spark plug.
If it carries out like this, the stress which generate | occur | produces between the intermediate member and the noble metal tip member which were resistance-welded can be suppressed. As a result, peeling between the noble metal tip member and the intermediate member can be suppressed.

［適用例２］適用例１に記載のスパークプラグにおいて、
前記中間部材のヤング率は、前記貴金属チップ部材のヤング率および前記電極母材のヤング率より小さい、スパークプラグ。
こうすれば、中間部材のヤング率が貴金属チップ部材のヤング率および電極母材のヤング率より小さいので、中間部材と貴金属チップ部材との間、および、中間部材と電極母材との間に発生する応力を抑制することができる。この結果、中間部材と貴金属チップ部材と剥離、および、中間部材と電極母材との剥離を抑制することができる。 [Application Example 2] In the spark plug according to Application Example 1,
The spark plug has a Young's modulus of the intermediate member smaller than that of the noble metal tip member and Young's modulus of the electrode base material.
By doing so, the Young's modulus of the intermediate member is smaller than the Young's modulus of the noble metal tip member and the Young's modulus of the electrode base material, so that it occurs between the intermediate member and the noble metal tip member and between the intermediate member and the electrode base material. Stress to be suppressed. As a result, separation between the intermediate member and the noble metal tip member and separation between the intermediate member and the electrode base material can be suppressed.

［適用例３］適用例１または適用例２のいずれかに記載のスパークプラグであって、
前記中間部材の線膨張係数は、前記貴金属チップ部材の線膨張係数より大きく、前記電極母材の線膨張係数より小さい、スパークプラグ。
こうすれば、中間部材の線膨張係数は、貴金属チップ部材の線膨張係数より大きく、電極母材の線膨張係数より小さいので、中間部材と貴金属チップ部材との間、および、中間部材と電極母材との間に発生する応力を抑制することができる。この結果、中間部材と貴金属チップ部材と剥離、および、中間部材と電極母材との剥離を抑制することができる。 [Application Example 3] The spark plug according to either Application Example 1 or Application Example 2,
A spark plug in which a linear expansion coefficient of the intermediate member is larger than a linear expansion coefficient of the noble metal tip member and smaller than a linear expansion coefficient of the electrode base material.
In this case, the linear expansion coefficient of the intermediate member is larger than the linear expansion coefficient of the noble metal tip member and smaller than the linear expansion coefficient of the electrode base material, and therefore, between the intermediate member and the noble metal tip member, and between the intermediate member and the electrode base member. The stress which generate | occur | produces between materials can be suppressed. As a result, separation between the intermediate member and the noble metal tip member and separation between the intermediate member and the electrode base material can be suppressed.

［適用例４］適用例１ないし適用例３のいずれかに記載のスパークプラグであって、
前記中間部材は、
i）パラジウム（Ｐｄ）
ii）金（Ａｕ）
iii）金パラジウム合金（ＡｕＰｄ合金）
のうちのいずれかを主成分とする材料で形成されている、スパークプラグ。
こうすれば、上記ヤング率の条件と、線膨張係数の条件を満たす中間部材を形成することができる。 [Application Example 4] The spark plug according to any one of Application Examples 1 to 3,
The intermediate member is
i) Palladium (Pd)
ii) Gold (Au)
iii) Gold palladium alloy (AuPd alloy)
A spark plug formed of a material mainly comprising any one of the above.
In this way, an intermediate member that satisfies the conditions of the Young's modulus and the linear expansion coefficient can be formed.

［適用例５］適用例１ないし適用例４のいずれかに記載のスパークプラグであって、
前記中心電極と前記接地電極は、前記スパークプラグの軸線方向に火花ギャップを形成する、スパークプラグ。
こうすれば、縦放電型のスパークプラグにおいて、貴金属チップ部材の剥離を抑制することができる。 [Application Example 5] The spark plug according to any one of Application Examples 1 to 4,
The spark plug, wherein the center electrode and the ground electrode form a spark gap in an axial direction of the spark plug.
If it carries out like this, peeling of a noble metal tip member can be suppressed in a longitudinal discharge type spark plug.

［適用例６］適用例１ないし適用例４のいずれかに記載のスパークプラグであって、
前記中心電極と、前記接地電極は、前記スパークプラグの軸線方向と垂直な方向に火花ギャップを形成する、スパークプラグ。
こうすれば、横放電型のスパークプラグにおいて、貴金属チップ部材の剥離を抑制することができる。 [Application Example 6] The spark plug according to any one of Application Example 1 to Application Example 4,
The spark plug, wherein the center electrode and the ground electrode form a spark gap in a direction perpendicular to an axial direction of the spark plug.
If it carries out like this, peeling of a noble metal tip member can be suppressed in a transverse discharge type spark plug.

［適用例７］適用例１ないし適用例６記載のいずれかにのスパークプラグであって、
前記貴金属チップ部材は、厚さ方向と垂直な断面が直径Ｄａの円である円筒形状を有し、
前記中間部材は、厚さ方向と垂直な断面が直径Ｄｂの円である円筒形状を有し、
Ｄｂ＞Ｄａ
を満たす、スパークプラグ。
こうすれば、貴金属チップ部材は、中間部材より小さく、円筒形上の底面全体で中間部材と抵抗溶接されるので、貴金属チップ部材の中間部材からの剥離を抑制することができる。 [Application Example 7] The spark plug according to any one of Application Examples 1 to 6,
The noble metal tip member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle with a diameter Da,
The intermediate member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle having a diameter Db,
Db> Da
Meet the spark plug.
In this way, the noble metal tip member is smaller than the intermediate member and is resistance-welded to the intermediate member over the entire bottom surface on the cylindrical shape, so that peeling of the noble metal tip member from the intermediate member can be suppressed.

［適用例８］スパークプラグであって、
前記スパークプラグの軸線方向に延在する中心電極と、
前記中心電極との間で火花ギャップを形成する接地電極と、
を備え、
前記中心電極と前記接地電極のうち少なくとも一方は、
貴金属チップ部材と、
第１の面が前記貴金属チップ部材と抵抗溶接され、前記第１の面と反対側の第２の面面が電極母材と抵抗溶接された中間部材と、
を備え、
前記中間部材における前記第１の面の面積をＳｂとし、
前記中間部材における前記第１の面に垂直な方向の厚さをＴｂとした場合において、
２５πＴｂ²＞Ｓｂ（πは円周率）
を満たす、スパークプラグ。
こうすれば、円筒形状の中間部材と貴金属チップ部材との間に発生する応力を抑制することができる。この結果、貴金属チップ部材と円筒形状の中間部材との剥離を抑制することができる。 [Application Example 8] Spark plug,
A center electrode extending in the axial direction of the spark plug;
A ground electrode that forms a spark gap with the center electrode;
With
At least one of the center electrode and the ground electrode is
A precious metal tip member;
An intermediate member in which a first surface is resistance welded to the noble metal tip member, and a second surface opposite to the first surface is resistance welded to an electrode base material;
With
The area of the first surface of the intermediate member is Sb,
When the thickness of the intermediate member in the direction perpendicular to the first surface is Tb,
25πTb ² > Sb (π is the circumference)
Meet the spark plug.
If it carries out like this, the stress which generate | occur | produces between a cylindrical intermediate member and a noble metal tip member can be suppressed. As a result, peeling between the noble metal tip member and the cylindrical intermediate member can be suppressed.

［適用例９］前記中間部材は、厚さ方向と垂直な断面が直径Ｄｂの円形である円筒形状を有し、
１０Ｔｂ＞Ｄｂ
を満たす、スパークプラグ。
こうすれば、円筒形状の中間部材と貴金属チップ部材との間に発生する応力を抑制することができる。この結果、貴金属チップ部材と円筒形状の中間部材との剥離を抑制することができる。 Application Example 9 The intermediate member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle having a diameter Db.
10Tb> Db
Meet the spark plug.
If it carries out like this, the stress which generate | occur | produces between a cylindrical intermediate member and a noble metal tip member can be suppressed. As a result, peeling between the noble metal tip member and the cylindrical intermediate member can be suppressed.

［適用例１０］適用例８または適用例９に記載のスパークプラグであって、
前記貴金属チップ部材の端面に垂直な方向の厚さをＴａとした場合において、
Ｔｂ＞Ｔａ
を満たす、スパークプラグ。
こうすれば、抵抗溶接された中間部材と貴金属チップ部材との間に発生する応力をより抑制することができる。この結果、貴金属チップ部材と中間部材との剥離をより抑制することができる。 [Application Example 10] The spark plug according to Application Example 8 or Application Example 9,
When the thickness in the direction perpendicular to the end face of the noble metal tip member is Ta,
Tb> Ta
Meet the spark plug.
If it carries out like this, the stress which generate | occur | produces between the intermediate member resistance-welded and the noble metal tip member can be suppressed more. As a result, peeling between the noble metal tip member and the intermediate member can be further suppressed.

本発明の一実施例としてのスパークプラグ１００の部分断面図である。It is a fragmentary sectional view of the spark plug 100 as one Example of this invention. 第１実施例におけるスパークプラグ１００の中心電極２０の先端付近の拡大図である。It is an enlarged view near the front-end | tip of the center electrode 20 of the spark plug 100 in 1st Example. 接地電極３０の先端部３１を軸線方向ＯＤに見た図である。It is the figure which looked at the front-end | tip part 31 of the ground electrode 30 in the axial direction OD. 中間部材３２０と貴金属チップ部材３１０との間（抵抗溶接部）に発生する応力を示すグラフである。It is a graph which shows the stress which generate | occur | produces between the intermediate member 320 and the noble metal tip member 310 (resistance welding part). 第２実施例におけるスパークプラグ１００Ａの中心電極２０の先端付近の拡大図である。It is an enlarged view near the front-end | tip of the center electrode 20 of the spark plug 100A in 2nd Example. 第３実施例におけるスパークプラグ１００Ｂの中心電極２０Ｂの先端付近の拡大図である。It is an enlarged view near the front-end | tip of the center electrode 20B of the spark plug 100B in 3rd Example.

Ａ．第１実施例：
以下、本発明の実施の形態を実施例に基づいて説明する。図１は本発明の一実施例としてのスパークプラグ１００の部分断面図である。なお、図１において、スパークプラグ１００の軸線方向ＯＤを図面における上下方向とし、下側をスパークプラグ１００の先端側、上側を後端側として説明する。 A. First embodiment:
Hereinafter, embodiments of the present invention will be described based on examples. FIG. 1 is a partial cross-sectional view of a spark plug 100 as an embodiment of the present invention. In FIG. 1, the axial direction OD of the spark plug 100 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side as the rear end side.

図１に示すように、スパークプラグ１００は、絶縁体としての絶縁碍子１０と、この絶縁碍子１０を保持する主体金具５０と、絶縁碍子１０内に軸線方向ＯＤに保持された中心電極２０と、接地電極３０と、絶縁碍子１０の後端部に設けられた端子金具４０とを備える。 As shown in FIG. 1, the spark plug 100 includes an insulator 10 as an insulator, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the insulator 10 in the axial direction OD, A ground electrode 30 and a terminal fitting 40 provided at the rear end of the insulator 10 are provided.

絶縁碍子１０は周知のようにアルミナ等を焼成して形成され、軸中心に軸線方向ＯＤへ延びる軸孔１２が形成された筒形状を有する。軸線方向ＯＤの略中央には外径が最も大きな鍔部１９が形成されており、それより後端側（図１における上側）には後端側胴部１８が形成されている。鍔部１９より先端側（図１における下側）には、後端側胴部１８よりも外径の小さな先端側胴部１７が形成され、さらにその先端側胴部１７よりも先端側に、先端側胴部１７よりも外径の小さな脚長部１３が形成されている。脚長部１３は先端側ほど縮径され、スパークプラグ１００が内燃機関のエンジンヘッド２００に取り付けられた際には、その燃焼室に曝される。脚長部１３と先端側胴部１７との間には段部１５が形成されている。 As is well known, the insulator 10 is formed by firing alumina or the like, and has a cylindrical shape in which an axial hole 12 extending in the axial direction OD is formed at the axial center. A flange portion 19 having the largest outer diameter is formed substantially at the center in the axial direction OD, and a rear end side body portion 18 is formed on the rear end side (upper side in FIG. 1). A front end side body portion 17 having a smaller outer diameter than the rear end side body portion 18 is formed on the front end side from the flange portion 19 (lower side in FIG. 1), and further, on the front end side from the front end side body portion 17, A leg length portion 13 having an outer diameter smaller than that of the distal end side body portion 17 is formed. The long leg portion 13 is reduced in diameter toward the tip side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head 200 of the internal combustion engine. A step portion 15 is formed between the long leg portion 13 and the front end side body portion 17.

主体金具５０は、内燃機関のエンジンヘッド２００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、絶縁碍子１０を、その後端側胴部１８の一部から脚長部１３にかけての部位を取り囲むようにして内部に保持している。主体金具５０は低炭素鋼材より形成され、図示しないスパークプラグレンチが嵌合する工具係合部５１と、内燃機関の上部に設けられたエンジンヘッド２００の取付ネジ孔２０１に螺合するネジ山が形成された取付ネジ部５２とを備えている。本実施例では、この取付ネジ部５２を、その外径Ｍ（呼び径）が標準的な外径であるＭ１４、或いは、Ｍ１０〜Ｍ１８とした。 The metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to the engine head 200 of the internal combustion engine. The metal shell 50 holds the insulator 10 inside so as to surround a portion from a part of the rear end side body part 18 to the leg long part 13. The metal shell 50 is formed of a low carbon steel material, and has a thread engaging with a tool engaging portion 51 into which a spark plug wrench (not shown) is fitted and a mounting screw hole 201 of the engine head 200 provided at the upper part of the internal combustion engine. And a formed mounting screw portion 52. In this embodiment, the mounting screw portion 52 is M14 whose outer diameter M (nominal diameter) is a standard outer diameter, or M10 to M18.

主体金具５０の工具係合部５１と取付ネジ部５２との間には、鍔状のシール部５４が形成されている。取付ネジ部５２とシール部５４との間のネジ首５９には、板体を折り曲げて形成し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をエンジンヘッド２００に取り付けた際に、シール部５４の座面５５と取付ネジ孔２０１の開口周縁部２０５との間で押し潰されて変形する。このガスケット５の変形により、スパークプラグ１００とエンジンヘッド２００間が封止され、取付ネジ孔２０１を介したエンジン内の気密漏れが防止される。 Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a bowl-shaped seal portion 54 is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the mounting screw portion 52 and the seal portion 54. When the spark plug 100 is attached to the engine head 200, the gasket 5 is crushed and deformed between the seat surface 55 of the seal portion 54 and the opening peripheral edge portion 205 of the attachment screw hole 201. Due to the deformation of the gasket 5, the gap between the spark plug 100 and the engine head 200 is sealed, and airtight leakage in the engine through the mounting screw hole 201 is prevented.

主体金具５０の工具係合部５１より後端側には薄肉の加締部５３が設けられている。また、シール部５４と工具係合部５１との間には、加締部５３と同様に薄肉の座屈部５８が設けられている。工具係合部５１から加締部５３にかけての主体金具５０の内周面と絶縁碍子１０の後端側胴部１８の外周面との間には、円環状のリング部材６，７が介在されており、さらに両リング部材６，７間にタルク（滑石）９の粉末が充填されている。加締部５３を内側に折り曲げるようにして加締めることにより、リング部材６，７およびタルク９を介し、絶縁碍子１０が主体金具５０内で先端側に向け押圧される。これにより、主体金具５０の内周で取付ネジ部５２の位置に形成された段部５６に、環状の板パッキン８を介し、絶縁碍子１０の段部１５が支持されて、主体金具５０と絶縁碍子１０とが一体にされる。このとき、主体金具５０と絶縁碍子１０との間の気密性は、板パッキン８によって保持され、燃焼ガスの流出が防止される。座屈部５８は、加締めの際に、圧縮力の付加に伴い外向きに撓み変形するように構成されており、タルク９の軸線方向ＯＤの圧縮長を長くして主体金具５０内の気密性を高めている。なお、段部５６よりも先端側における主体金具５０と絶縁碍子１０との間には、所定寸法のクリアランスが設けられている。 A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. Further, a thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engagement portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Further, talc (talc) 9 powder is filled between the ring members 6 and 7. By crimping the crimping portion 53 so as to be bent inward, the insulator 10 is pressed toward the front end side in the metal shell 50 via the ring members 6, 7 and the talc 9. As a result, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8 so as to be insulated from the metal shell 50. The insulator 10 is integrated. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, and the outflow of combustion gas is prevented. The buckling portion 58 is configured to bend outwardly and deform as the compression force is applied during caulking. The compression length in the axial direction OD of the talc 9 is increased to increase the airtightness in the metal shell 50. Increases sex. A clearance having a predetermined dimension is provided between the metal shell 50 and the insulator 10 on the tip side of the step portion 56.

図２は、第１実施例におけるスパークプラグ１００の中心電極２０の先端付近の拡大図である。中心電極２０は、インコネル（商標名）６００等のニッケルまたはニッケルを主成分とする合金から形成された電極母材２１の内部に、電極母材２１よりも熱伝導性に優れる銅または銅を主成分とする合金からなる芯材２５を埋設した構造を有する棒状の電極である。通常、中心電極２０は、有底筒状に形成された電極母材２１の内部に芯材２５を詰め、底側から押出成形を行って引き延ばすことで作製される。芯材２５は、胴部分においては略一定の外径をなすものの、先端側においては先細り形状に形成される。 FIG. 2 is an enlarged view of the vicinity of the tip of the center electrode 20 of the spark plug 100 in the first embodiment. The center electrode 20 is mainly made of copper or copper having higher thermal conductivity than the electrode base material 21 inside the electrode base material 21 formed of nickel such as Inconel (trade name) 600 or an alloy containing nickel as a main component. It is a rod-shaped electrode having a structure in which a core material 25 made of an alloy as a component is embedded. Usually, the center electrode 20 is produced by filling a core material 25 inside an electrode base material 21 formed in a bottomed cylindrical shape, and performing extrusion molding from the bottom side and stretching it. The core member 25 has a substantially constant outer diameter at the body portion, but is formed in a tapered shape at the distal end side.

中心電極２０、詳しくは、電極母材２１は、その先端部分に、先端に向かって小径となるテーパ状の電極母材台座２２と溶融部２３と電極チップ９０とを備え、この電極チップ９０を含む電極母材台座２２よりも先端側の部分は絶縁碍子１０の先端部１１よりも突出されている。電極チップ９０は、耐火花消耗性を向上するために、高融点の貴金属を主成分として形成されている。この電極チップ９０としては、例えば、イリジウム（Ｉｒ）や、Ｉｒを主成分として、白金（Ｐｔ）、ロジウム（Ｒｈ）、ルテニウム（Ｒｕ）、パラジウム（Ｐｄ）、レニウム（Ｒｅ）のうち、１種類あるいは２種類以上を添加したＩｒ合金によって形成され、Ｉｒ−５Ｐｔ合金（５質量％の白金を含有したイリジウム合金）などが多用される。 The center electrode 20, more specifically, the electrode base material 21, includes a tapered electrode base material base 22, a melting portion 23, and an electrode tip 90 having a small diameter toward the front end. The portion on the tip side of the electrode base material pedestal 22 is protruded from the tip portion 11 of the insulator 10. The electrode tip 90 is formed with a high melting point noble metal as a main component in order to improve spark wear resistance. Examples of the electrode chip 90 include iridium (Ir) and one type of platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), and rhenium (Re) mainly containing Ir. Alternatively, an Ir alloy to which two or more kinds are added is used, and an Ir-5Pt alloy (iridium alloy containing 5% by mass of platinum) or the like is frequently used.

溶融部２３は、電極母材台座２２への電極チップ９０の溶接、例えばレーザを照射してその熱により電極母材台座２２と電極チップ９０とを溶融させるレーザ溶接を経て形成される。つまり、電極母材台座２２の先端面に電極チップ９０を配置した状態で、電極母材台座２２と電極チップ９０との境界面を狙ってレーザを照射しつつ、その照射箇所を境界面全周に亘って一周させる。このレーザ溶接では、レーザの照射により両材料（電極母材台座２２の構成材と電極チップ９０の貴金属）が溶融して混ざり合うため、電極チップ９０と電極母材台座２２とが強固に接合されると共に、電極母材台座２２と電極チップ９０とを繋ぐ溶融部２３が形成される。この溶融部２３は、上記両材料の溶融により両材料の合金として形成される。 The melting part 23 is formed through welding of the electrode tip 90 to the electrode base material pedestal 22, for example, laser welding that irradiates a laser and melts the electrode base material base 22 and the electrode tip 90 by the heat. That is, in a state where the electrode tip 90 is disposed on the tip surface of the electrode base material pedestal 22, while irradiating a laser aiming at the boundary surface between the electrode base material base 22 and the electrode tip 90, the irradiated portion is arranged around the entire boundary surface. Make one round. In this laser welding, since both materials (the constituent material of the electrode base material base 22 and the noble metal of the electrode tip 90) are melted and mixed by laser irradiation, the electrode tip 90 and the electrode base material base 22 are firmly joined. At the same time, a melting portion 23 that connects the electrode base material base 22 and the electrode tip 90 is formed. The melting portion 23 is formed as an alloy of both materials by melting the both materials.

中心電極２０は軸孔１２内を後端側に向けて延設され、シール体４およびセラミック抵抗３（図１参照）を経由して、後方（図１における上方）の端子金具４０に電気的に接続されている。端子金具４０には高圧ケーブル（図示外）がプラグキャップ（図示外）を介して接続され、高電圧が印加される。 The center electrode 20 extends in the shaft hole 12 toward the rear end side, and is electrically connected to the terminal fitting 40 on the rear side (upper side in FIG. 1) via the seal body 4 and the ceramic resistor 3 (see FIG. 1). It is connected to the. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied.

接地電極３０の電極母材は耐腐食性の高い金属から構成され、一例として、ニッケル合金が用いられる。本実施例では、インコネル（商標名）６００（ＩＮＣ６００）と呼ばれるニッケル合金が用いられている。この接地電極３０は、自身の長手方向と直交する方向における横断面が略長方形を有している。接地電極３０の基端部（一端部）３２は、主体金具５０の先端面５７に溶接にて接合されている。接地電極３０の先端部（他端部）３１の一側面は、中心電極２０の電極チップ９０と、軸線Ｏ上で軸線方向ＯＤに対向するように屈曲されている。そして、この接地電極３０の先端部３１の一側面と電極チップ９０の先端面との間には火花ギャップが形成される。この火花ギャップは、例えば、０．２〜０．６ｍｍ程度である。 The electrode base material of the ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel alloy is used. In this embodiment, a nickel alloy called Inconel (trade name) 600 (INC600) is used. The ground electrode 30 has a substantially rectangular cross section in a direction orthogonal to its longitudinal direction. A proximal end portion (one end portion) 32 of the ground electrode 30 is joined to the distal end surface 57 of the metal shell 50 by welding. One side surface of the tip (other end) 31 of the ground electrode 30 is bent so as to face the electrode tip 90 of the center electrode 20 on the axis O in the axial direction OD. A spark gap is formed between one side surface of the tip 31 of the ground electrode 30 and the tip surface of the electrode tip 90. This spark gap is, for example, about 0.2 to 0.6 mm.

接地電極３０の先端部３１において、電極チップ９０と対向する側面には、２層部材３００が電極母材に抵抗溶接されている。２層部材３００は、貴金属チップ部材３１０と、中間部材３２０とを有している。貴金属チップ部材３１０と中間部材３２０とは、電極チップ９０と対向する方向（第１実施例では、軸線方向ＯＤ）に積層されている。貴金属チップ部材３１０の下側の面と中間部材３２０の上側の面との間は、抵抗溶接されている。中間部材３２０の下側の面は、接地電極３０の電極母材と抵抗溶接されている。貴金属チップ部材３１０には、例えば、Ｐｔ（白金）または、Ｐｔを主成分とする合金が用いられる。本実施例では、Ｐｔ−２０Ｉｒ合金（２０質量％のイリジウムを含有した白金合金）が用いられている。中間部材３２０には、Ｐｄ（パラジウム）またはＰｄを主成分とする合金、Ａｕ（金）またはＡｕを主成分とする合金、ＡｕＰｄ合金、Ｐｔ合金が用いられる。本実施例では、Ｐｄや、Ｐｔ−２０Ｎｉ（２０質量％のニッケルを含有した白金合金）が用いられている。中間部材３２０は、中間部材３２０の下側が接地電極３０の電極母材に埋設されているのは、２層部材３００を電極母材に抵抗溶接する際に、中間部材３２０より融点の低い電極母材が溶けるため、中間部材３２０の下側部分が電極部材の内部に沈みこむためである。中間部材３２０の積層方向（第１実施例では、軸線方向ＯＤ）の厚さＴｂは、貴金属チップ部材３１０の積層方向の厚さＴａより大きい（Ｔｂ＞Ｔａ）。 A two-layer member 300 is resistance-welded to the electrode base material on the side surface facing the electrode tip 90 at the tip 31 of the ground electrode 30. The two-layer member 300 includes a noble metal tip member 310 and an intermediate member 320. The noble metal tip member 310 and the intermediate member 320 are stacked in a direction facing the electrode tip 90 (in the first embodiment, the axial direction OD). Resistance welding is performed between the lower surface of the noble metal tip member 310 and the upper surface of the intermediate member 320. The lower surface of the intermediate member 320 is resistance-welded to the electrode base material of the ground electrode 30. For the noble metal tip member 310, for example, Pt (platinum) or an alloy containing Pt as a main component is used. In this embodiment, a Pt-20Ir alloy (a platinum alloy containing 20% by mass of iridium) is used. For the intermediate member 320, Pd (palladium) or an alloy containing Pd as a main component, Au (gold) or an alloy containing Au as a main component, an AuPd alloy, or a Pt alloy is used. In this embodiment, Pd or Pt-20Ni (a platinum alloy containing 20% by mass of nickel) is used. The intermediate member 320 has the lower side of the intermediate member 320 embedded in the electrode base material of the ground electrode 30 when the two-layer member 300 is resistance welded to the electrode base material. This is because the lower part of the intermediate member 320 sinks into the electrode member because the material melts. The thickness Tb of the intermediate member 320 in the stacking direction (in the first embodiment, the axial direction OD) is larger than the thickness Ta of the noble metal tip member 310 in the stacking direction (Tb> Ta).

図３は、接地電極３０の先端部３１を、軸線方向ＯＤに見た図である。貴金属チップ部材３１０は、厚さ方向に垂直な方向の断面が直径Ｄａの円形である。中間部材３２０は、厚さ方向に垂直な方向の断面が直径Ｄｂの円形である。すなわち、貴金属チップ部材３１０および中間部材３２０は、円筒形状を有している。中間部材３２０の直径Ｄｂは、貴金属チップ部材３１０の直径Ｄａより大きく、貴金属チップ部材３１０と中間部材３２０の厚さ方向に垂直な方向の断面は、同心円である。したがって、中間部材３２０の外縁部は、厚さ方向から見て、貴金属チップ部材３１０の外縁より外側にはみ出している。 FIG. 3 is a view of the tip 31 of the ground electrode 30 as viewed in the axial direction OD. The noble metal tip member 310 has a circular cross section with a diameter Da in a direction perpendicular to the thickness direction. The intermediate member 320 has a circular shape with a diameter Db in a cross section perpendicular to the thickness direction. That is, the noble metal tip member 310 and the intermediate member 320 have a cylindrical shape. The diameter Db of the intermediate member 320 is larger than the diameter Da of the noble metal tip member 310, and the cross section in the direction perpendicular to the thickness direction of the noble metal tip member 310 and the intermediate member 320 is concentric. Therefore, the outer edge portion of the intermediate member 320 protrudes outside the outer edge of the noble metal tip member 310 when viewed from the thickness direction.

ここで本実施例では、中間部材３２０の直径Ｄｂと、中間部材３２０の厚さＴｂとは、１０Ｔｂ＞Ｄｂを満たす。なお、この式を、中間部材３２０の上側の面の面積Ｓｂは、Ｓｂ＝π（Ｄｂ／２）²であるので、１０Ｔｂ＞Ｄｂの式を、Ｓｂを用いて表すと、２５πｔｂ²＞Ｓｂとなる。 In this embodiment, the diameter Db of the intermediate member 320 and the thickness Tb of the intermediate member 320 satisfy 10Tb> Db. In addition, since the area Sb of the upper surface of the intermediate member 320 is Sb = π (Db / 2) ² in this expression, when the expression of 10Tb> Db is expressed using Sb, 25πtb ² > Sb Become.

以下に、接地電極３０の電極母材の材料（ＩＮＣ６００）と、貴金属チップ部材３１０の材料（Ｐｔ−２０Ｉｒ）と、中間部材３２０の材料（ＰｄまたはＰｔ−２０Ｎｉ）の特性を示す。 The characteristics of the electrode base material (INC 600) of the ground electrode 30, the material of the noble metal tip member 310 (Pt-20Ir), and the material of the intermediate member 320 (Pd or Pt-20Ni) are shown below.

表１から解るように、中間部材３２０のヤング率は、貴金属チップ部材３１０のヤング率および接地電極３０の電極母材のヤング率より小さい。そして、中間部材３２０の線膨張係数は、貴金属チップ部材３１０の線膨張係数より大きく、接地電極３０の電極母材の線膨張係数より小さい。 As can be seen from Table 1, the Young's modulus of the intermediate member 320 is smaller than the Young's modulus of the noble metal tip member 310 and the electrode base material of the ground electrode 30. The linear expansion coefficient of the intermediate member 320 is larger than the linear expansion coefficient of the noble metal tip member 310 and smaller than the linear expansion coefficient of the electrode base material of the ground electrode 30.

以上説明した本実施例によれば、中間部材３２０の積層方向の厚さＴｂは、貴金属チップ部材３１０の積層方向の厚さＴａより大きい（Ｔｂ＞Ｔａ）ので、貴金属チップ部材３１０と中間部材３２０との剥離が抑制される。 According to the embodiment described above, the thickness Tb of the intermediate member 320 in the stacking direction is larger than the thickness Ta of the noble metal tip member 310 in the stacking direction (Tb> Ta). Peeling is suppressed.

図４は、中間部材３２０と貴金属チップ部材３１０との間（抵抗溶接部）に発生する応力を示すグラフである。このグラフは、シミュレーションによって計算された値である。このシミュレーションでは、中間部材３２０の直径Ｄａを２．９ｍｍ、貴金属チップ部材３１０の直径Ｄｂを３．０ｍｍ、貴金属チップ部材３１０の厚さＴａを０．３ｍｍと設定している。そして、貴金属チップ部材３１０の材料特性はＰｔ−２０Ｉｒ、接地電極３０の電極母材の材料特性はＩＮＣ６００の特性値をそれぞれ用いている。また、このシミュレーションでは、中間部材３２０の材料としては、Ｐｄ（丸印）とＰｔ−２０Ｎｉ（四角印）の２種類について計算し、中間部材３２０の厚さＴｂとしては、０．２ｍｍ〜０．５ｍｍまで０．１ｍｍ刻みで計算した。このグラフの縦軸は、貴金属チップ部材と中間部材の間に発生する応力について、Ｔｂが０．２ｍｍのときの応力を１としたときの比を表す。 FIG. 4 is a graph showing the stress generated between the intermediate member 320 and the noble metal tip member 310 (resistance welding portion). This graph is a value calculated by simulation. In this simulation, the diameter Da of the intermediate member 320 is set to 2.9 mm, the diameter Db of the noble metal tip member 310 is set to 3.0 mm, and the thickness Ta of the noble metal tip member 310 is set to 0.3 mm. The material characteristic of the noble metal tip member 310 is Pt-20Ir, and the material characteristic of the electrode base material of the ground electrode 30 is the characteristic value of INC600. Further, in this simulation, two types of materials, Pd (circle) and Pt-20Ni (square), are calculated as the material of the intermediate member 320, and the thickness Tb of the intermediate member 320 is 0.2 mm to 0.2 mm. The calculation was performed in increments of 0.1 mm up to 5 mm. The vertical axis of this graph represents the ratio of the stress generated between the noble metal tip member and the intermediate member when the stress when Tb is 0.2 mm is 1.

図４に示すシミュレーション結果から解るように、Ｔｂ＞Ｔａが満たされる領域では、貴金属チップ部材３１０と中間部材３２０との間に発生する応力が、Ｔｂ≦Ｔａが満たされる領域より、顕著に抑制される。その結果、貴金属チップ部材３１０と中間部材３２０との剥離を抑制することができる。 As can be seen from the simulation results shown in FIG. 4, in the region where Tb> Ta is satisfied, the stress generated between the noble metal tip member 310 and the intermediate member 320 is significantly suppressed as compared with the region where Tb ≦ Ta is satisfied. The As a result, peeling between the noble metal tip member 310 and the intermediate member 320 can be suppressed.

また、本実施例では、中間部材３２０の積層方向の厚さＴｂと、中間部材３２０の上側の面の直径Ｄｂとの間は、１０Ｔｂ＞Ｄｂの関係式を満たすので、貴金属チップ部材３１０と中間部材３２０との剥離が抑制される。 In the present embodiment, the relationship between the thickness Tb of the intermediate member 320 in the stacking direction and the diameter Db of the upper surface of the intermediate member 320 satisfies the relational expression of 10Tb> Db. Separation from the member 320 is suppressed.

図４に示すシミュレーション結果から解るように、１０Ｔｂ＞Ｄｂが満たされる領域では、貴金属チップ部材３１０と中間部材３２０との間に発生する応力が、１０Ｔｂ≦Ｄｂが満たされる領域より、顕著に抑制される。その結果、貴金属チップ部材３１０と中間部材３２０との剥離を抑制することができる。 As can be seen from the simulation results shown in FIG. 4, in the region where 10Tb> Db is satisfied, the stress generated between the noble metal tip member 310 and the intermediate member 320 is significantly suppressed compared to the region where 10Tb ≦ Db is satisfied. The As a result, peeling between the noble metal tip member 310 and the intermediate member 320 can be suppressed.

中間部材３２０は、貴金属チップ部材３１０および接地電極３０の電極母材よりヤング率が低い、すなわち、弾性変形しやすい材料である。このような中間部材３２０が貴金属チップ部材３１０と接地電極３０の電極母材との間にクッションとして介在することによって、貴金属チップ部材３１０と接地電極３０の抵抗溶接面に発生する応力を緩和することができる。このような応力緩和能力が十分に発揮されるためには、中間部材３２０はある程度の厚さＴｂが必要になると考えられる。そして、この応力緩和能力が十分に発揮されるために厚さＴｂが満たすべき条件が、１０Ｔｂ＞Ｄｂや、Ｔｂ＞Ｔａであると考えられる。 The intermediate member 320 is a material having a lower Young's modulus than the electrode base material of the noble metal tip member 310 and the ground electrode 30, that is, a material that is easily elastically deformed. The intermediate member 320 is interposed as a cushion between the noble metal tip member 310 and the electrode base material of the ground electrode 30 to relieve stress generated on the resistance welding surface of the noble metal tip member 310 and the ground electrode 30. Can do. It is considered that the intermediate member 320 needs a certain thickness Tb in order to sufficiently exhibit such stress relaxation ability. And, it is considered that the conditions that the thickness Tb should satisfy in order to sufficiently exhibit the stress relaxation ability are 10Tb> Db and Tb> Ta.

また、本実施例では、中間部材３２０の線膨張係数は、貴金属チップ部材３１０の線膨張係数より大きく、接地電極３０の電極母材の線膨張係数より小さいので、温度変化により中間部材と貴金属チップ部材との間、および、中間部材と電極母材との間に発生する応力を抑制することができる。この結果、中間部材３２０と貴金属チップ部材３１０と剥離、および、中間部材３２０と接地電極３０の電極母材との剥離をより抑制することができる。 Further, in this embodiment, the linear member has a linear expansion coefficient larger than that of the noble metal tip member 310 and smaller than the linear expansion coefficient of the electrode base material of the ground electrode 30, so that the intermediate member and the noble metal tip are changed due to temperature change. Stress generated between the members and between the intermediate member and the electrode base material can be suppressed. As a result, separation between the intermediate member 320 and the noble metal tip member 310 and separation between the intermediate member 320 and the electrode base material of the ground electrode 30 can be further suppressed.

Ｂ．第２実施例：
図５は、第２実施例におけるスパークプラグ１００Ａの中心電極２０の先端付近の拡大図である。第２実施例におけるスパークプラグ１００Ａが、第１実施例におけるスパークプラグ１００と異なる点は、接地電極３０Ａの構成である。第２実施例の接地電極３０Ａの先端部３１Ａは、第１実施例と異なり、電極チップ９０の側面と対向するように形成されている。すなわち、先端部３１の端面は、電極チップ９０の側面と、軸線方向ＯＤと垂直な方向に対向する。そして、先端部３１の端面には、電極チップ９０との対向方向に２層部材３００Ａが抵抗溶接されている。２層部材３００Ａを構成する貴金属チップ部材３１０Ａおよび中間部材３２０Ａの構成は、積層方向が軸線方向ＯＤと垂直な方向であることを除いて、第１実施例と同じである。このように、本発明は、第１実施例のような軸線方向ＯＤに火花ギャップが設けられた縦放電タイプのスパークプラグだけでなく、第２実施例のような軸線方向ＯＤに垂直な方向に火花ギャップが設けられた横放電タイプのスパークプラグにも適用可能である。第２実施例においても、第１実施例と同様の作用・効果が得られる。 B. Second embodiment:
FIG. 5 is an enlarged view of the vicinity of the tip of the center electrode 20 of the spark plug 100A in the second embodiment. The spark plug 100A in the second embodiment is different from the spark plug 100 in the first embodiment in the configuration of the ground electrode 30A. Unlike the first embodiment, the tip 31A of the ground electrode 30A of the second embodiment is formed to face the side surface of the electrode tip 90. That is, the end surface of the tip portion 31 faces the side surface of the electrode chip 90 in a direction perpendicular to the axial direction OD. The two-layer member 300 A is resistance-welded to the end surface of the distal end portion 31 in the direction facing the electrode tip 90. The configuration of the noble metal tip member 310A and the intermediate member 320A constituting the two-layer member 300A is the same as that of the first embodiment except that the stacking direction is a direction perpendicular to the axial direction OD. As described above, the present invention is not limited to the longitudinal discharge type spark plug in which the spark gap is provided in the axial direction OD as in the first embodiment, but also in the direction perpendicular to the axial direction OD as in the second embodiment. The present invention can also be applied to a transverse discharge type spark plug provided with a spark gap. In the second embodiment, the same operation and effect as in the first embodiment can be obtained.

Ｃ．第３実施例：
図６は、第３実施例におけるスパークプラグ１００Ｂの中心電極２０Ｂの先端付近の拡大図である。第３実施例におけるスパークプラグ１００Ｂが、第１実施例におけるスパークプラグ１００と異なる点は、接地電極３０Ｂの構成と、中心電極２０Ｂの先端付近の構成である。第３実施例の接地電極３０Ｂの先端部３１Ｂは、第１実施例と異なり、２層部材３００が配置されていない。一方、第３実施例の中心電極２０Ｂの電極母材２１Ｂの先端部分には、第１実施例の溶融部２３および電極チップ９０に代えて、２層部材３００Ｂが形成されている。２層部材３００Ｂを構成する貴金属チップ部材３１０Ｂおよび中間部材３２０Ｂの構成は、電極母材２１Ｂが上側にあることに対応して、中間部材３２０Ｂが上側に貴金属チップ部材３１０Ｂが下側にあることを除いて、第１実施例と同じである。このように、本発明は、第１実施例および第２実施例の２層部材３００、３００Ａのように接地電極に適用されるだけでなく、第３実施例の２層部材３００Ｂのように中心電極にも適用可能である。中心電極に適用した場合においても、接地電極に適用した場合と同様の作用・効果が得られる。 C. Third embodiment:
FIG. 6 is an enlarged view of the vicinity of the tip of the center electrode 20B of the spark plug 100B in the third embodiment. The spark plug 100B in the third embodiment is different from the spark plug 100 in the first embodiment in the configuration of the ground electrode 30B and the configuration near the tip of the center electrode 20B. Unlike the first embodiment, the tip 31B of the ground electrode 30B of the third embodiment is not provided with the two-layer member 300. On the other hand, a two-layer member 300B is formed at the tip of the electrode base material 21B of the center electrode 20B of the third embodiment, instead of the melting portion 23 and the electrode tip 90 of the first embodiment. The configuration of the noble metal tip member 310B and the intermediate member 320B constituting the two-layer member 300B corresponds to the fact that the intermediate member 320B is on the upper side and the noble metal tip member 310B is on the lower side, corresponding to the electrode base material 21B being on the upper side. Except for this, it is the same as the first embodiment. Thus, the present invention is not only applied to the ground electrode as in the two-layer members 300 and 300A in the first and second embodiments, but also in the center as in the two-layer member 300B in the third embodiment. It can also be applied to electrodes. Even when applied to the center electrode, the same actions and effects as those applied to the ground electrode can be obtained.

Ｄ．変形例：
・第１変形例：
上記実施例では、２層部材３００、３００Ａ、３００Ｂは、接地電極か中心電極のいずれか一方に配置されているが、両方に配置しても良い。 D. Variations:
・ First modification:
In the above embodiment, the two-layer members 300, 300A, 300B are disposed on either the ground electrode or the center electrode, but may be disposed on both.

・第２変形例：
上記実施例では、２層部材３００、３００Ａ、３００Ｂを構成する貴金属チップ部材３１０、３１０Ａ、３１０Ｂ、および、中間部材３２０、３２０Ｂ、３２０Ａは、積層方向から見た形状が円形であるが、これに限られない。例えば、貴金属チップ部材３１０、３１０Ａ、３１０Ｂ、および、中間部材３２０、３２０Ｂ、３２０Ａは、四角形、六角形などの多角形であってもよいし、楕円形であっても良い。また、中間部材と貴金属チップ部材の形状が異なっていても良い。いずれの形状であっても、全周に亘って、中間部材の外縁部は、貴金属チップ部材の外縁より外側にあることが好ましい。また、中間部材の厚さＴｂと中間部材の積層方向の上面の面積Ｓｂは、２５πＴｂ²＞Ｓｂ（πは円周率）の関係式を満たしていることが好ましい。・ Second modification:
In the above embodiment, the noble metal tip members 310, 310A, 310B and the intermediate members 320, 320B, 320A constituting the two-layer members 300, 300A, 300B are circular in shape when viewed from the stacking direction. Not limited. For example, the noble metal tip members 310, 310 A, 310 B and the intermediate members 320, 320 B, 320 A may be a polygon such as a quadrangle, a hexagon, or an ellipse. Moreover, the shapes of the intermediate member and the noble metal tip member may be different. In any shape, it is preferable that the outer edge portion of the intermediate member is outside the outer edge of the noble metal tip member over the entire circumference. Moreover, it is preferable that the thickness Tb of the intermediate member and the area Sb of the upper surface in the stacking direction of the intermediate member satisfy the relational expression of 25πTb ² > Sb (π is the circumference).

・第３変形例：
上記実施例では、１０Ｔｂ＞Ｄｂの関係式と、Ｔｂ＞Ｔａの関係式の両方を満たしているが、いずれか一方を満たしているだけでも良い。・ Third modification:
In the above embodiment, both the relational expression of 10Tb> Db and the relational expression of Tb> Ta are satisfied, but only one of them may be satisfied.

・第４変形例：
上記実施例のように、中間部材３２０、３２０Ａ、３２０Ｂのヤング率は、貴金属チップ部材３１０、３１０Ａ、３１０Ｂのヤング率および電極母材２１、２１Ｂのヤング率より小さいことが好ましく、中間部材３２０、３２０Ａ、３２０Ｂの線膨張係数は、貴金属チップ部材３１０、３１０Ａ、３１０Ｂの線膨張係数より大きく、電極母材２１、２１Ｂの線膨張係数より小さいことが好ましい。貴金属チップ部材３１０、３１０Ａ、３１０Ｂが白金または白金を主成分とした合金であり、電極母材がニッケル合金である一般的な構成である場合、このような条件を満たす中間部材３２０、３２０Ａ、３２０Ｂの材料としては、i）パラジウム（Ｐｄ）、ii）金（Ａｕ）、iii）金パラジウム合金（ＡｕＰｄ合金）のうちのいずれかを主成分とする材料がある。 -Fourth modification:
As in the above embodiment, the Young members of the intermediate members 320, 320A, 320B are preferably smaller than the Young's modulus of the noble metal tip members 310, 310A, 310B and the Young's modulus of the electrode base materials 21, 21B. The linear expansion coefficient of 320A, 320B is preferably larger than the linear expansion coefficient of the noble metal tip members 310, 310A, 310B and smaller than the linear expansion coefficient of the electrode base materials 21, 21B. When the noble metal tip members 310, 310A, 310B are platinum or an alloy containing platinum as a main component and the electrode base material is a nickel alloy, the intermediate members 320, 320A, 320B satisfying such conditions are used. As the material, there is a material mainly comprising any one of i) palladium (Pd), ii) gold (Au), and iii) gold-palladium alloy (AuPd alloy).

・第５変形例：
上記実施例では、横放電型と縦放電型を例として説明したが、接地電極の先端部と、中心電極２０の先端部との位置関係は、スパークプラグの用途や、必要とされる性能等に応じて適宜設定することが可能である。また、１つの中心電極に対して複数の接地電極が設けられても良い。 -5th modification:
In the above embodiment, the horizontal discharge type and the vertical discharge type have been described as examples. However, the positional relationship between the tip of the ground electrode and the tip of the center electrode 20 depends on the use of the spark plug, the required performance, etc. It is possible to set appropriately according to the situation. A plurality of ground electrodes may be provided for one central electrode.

以上、本発明の実施例および変形例について説明したが、本発明はこれらの実施例および変形例になんら限定されるものではなく、その要旨を逸脱しない範囲内において種々の態様での実施が可能である。 As mentioned above, although the Example and modification of this invention were demonstrated, this invention is not limited to these Example and modification at all, and implementation in a various aspect is possible within the range which does not deviate from the summary. It is.

３…セラミック抵抗
４…シール体
５…ガスケット
６…リング部材
８…板パッキン
９…タルク
１０…絶縁碍子
１１…先端部
１２…軸孔
１３…脚長部
１５…段部
１７…先端側胴部
１８…後端側胴部
１９…鍔部
２０、２０Ｂ…中心電極
２１、２１Ｂ…電極母材
２２…電極母材台座
２３…溶融部
２５…芯材
３０、３０Ａ、３０Ｂ…接地電極
４０…端子金具
５０…主体金具
５１…工具係合部
５２…取付ネジ部
５３…加締部
５４…シール部
５５…座面
５６…段部
５７…先端面
５８…座屈部
５９…ネジ首
９０…電極チップ
１００、１００Ａ、１００Ｂ…スパークプラグ
２００…エンジンヘッド
２０１…取付ネジ孔
２０５…開口周縁部
３００、３００Ａ、３００Ｂ…２層部材
３１０、３１０Ａ、３１０Ｂ…貴金属チップ部材
３２０、３２０Ａ、３２０Ｂ…中間部材 DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 11 ... Tip part 12 ... Shaft hole 13 ... Leg long part 15 ... Step part 17 ... Tip side trunk | drum 18 ... Rear end side body part 19 ... collar part 20, 20B ... center electrode 21, 21B ... electrode base material 22 ... electrode base material base 23 ... melting part 25 ... core material 30, 30A, 30B ... ground electrode 40 ... terminal fitting 50 ... Metal shell 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Caulking part 54 ... Sealing part 55 ... Seat surface 56 ... Step part 57 ... Tip face 58 ... Buckling part 59 ... Screw neck 90 ... Electrode tip 100, 100A , 100B ... Spark plug 200 ... Engine head 201 ... Mounting screw hole 205 ... Opening peripheral edge 300, 300A, 300B ... Two-layer member 310, 310A, 310B ... Precious metal tip member 320 320A, 320B ... the intermediate member

Claims

A spark plug,
A center electrode extending in the axial direction of the spark plug;
A ground electrode that forms a spark gap with the center electrode;
With
At least one of the center electrode and the ground electrode is
A precious metal tip member;
An intermediate member in which a first surface is resistance-welded with the noble metal tip member, and a second surface opposite to the first surface is resistance-welded with an electrode base material;
With
The thickness in the direction perpendicular to the end face of the noble metal tip member is Ta,
When the thickness of the intermediate member in the direction perpendicular to the first surface is Tb,
Tb> Ta
Meet the spark plug.

The spark plug according to claim 1, wherein
The spark plug has a Young's modulus of the intermediate member smaller than that of the noble metal tip member and Young's modulus of the electrode base material.

The spark plug according to claim 1 or 2, wherein
A spark plug in which a linear expansion coefficient of the intermediate member is larger than a linear expansion coefficient of the noble metal tip member and smaller than a linear expansion coefficient of the electrode base material.

The spark plug according to any one of claims 1 to 3,
The intermediate member is
i) Palladium (Pd)
ii) Gold (Au)
iii) Gold palladium alloy (AuPd alloy)
A spark plug formed of a material mainly comprising any one of the above.

The spark plug according to any one of claims 1 to 4, wherein
The spark plug, wherein the center electrode and the ground electrode form a spark gap in an axial direction of the spark plug.

The spark plug according to any one of claims 1 to 4, wherein
The spark plug, wherein the center electrode and the ground electrode form a spark gap in a direction perpendicular to an axial direction of the spark plug.

The spark plug according to any one of claims 1 to 6,
The noble metal tip member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle with a diameter Da,
The intermediate member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle having a diameter Db,
Db> Da
Meet the spark plug.

A spark plug,
A center electrode extending in the axial direction of the spark plug;
A ground electrode that forms a spark gap with the center electrode;
With
At least one of the center electrode and the ground electrode is
A precious metal tip member;
An intermediate member in which a first surface is resistance welded to the noble metal tip member, and a second surface opposite to the first surface is resistance welded to an electrode base material;
With
The area of the first surface of the intermediate member is Sb,
When the thickness of the intermediate member in the direction perpendicular to the first surface is Tb,
25πTb ² > Sb (π is the circumference)
Meet the spark plug.

The spark plug according to claim 8, wherein
The intermediate member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle having a diameter Db,
10Tb> Db
Meet the spark plug.

The spark plug according to claim 8 or 9, wherein
When the thickness in the direction perpendicular to the end face of the noble metal tip member is Ta,
Tb> Ta
Meet the spark plug.

The spark plug according to any one of claims 8 to 10,
The spark plug has a Young's modulus of the intermediate member smaller than that of the noble metal tip member and Young's modulus of the electrode base material.

A spark plug according to claim 8 or claim 11, wherein
A spark plug in which a linear expansion coefficient of the intermediate member is larger than a linear expansion coefficient of the noble metal tip member and smaller than a linear expansion coefficient of the electrode base material.

The spark plug according to any one of claims 8 to 12,
The intermediate member is
i) Palladium (Pd)
ii) Gold (Au)
iii) Gold palladium alloy (AuPd alloy)
A spark plug formed of a material mainly comprising any one of the above.

The spark plug according to any one of claims 8 to 13,
The spark plug, wherein the center electrode and the ground electrode form a spark gap in an axial direction of the spark plug.

The spark plug according to any one of claims 8 to 14,
The spark plug, wherein the center electrode and the ground electrode form a spark gap in a direction perpendicular to an axial direction of the spark plug.

The spark plug according to any one of claims 8 to 15,
The noble metal tip member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle with a diameter Da,
The intermediate member has a cylindrical shape whose cross section perpendicular to the thickness direction is a circle having a diameter Db,
Db> Da
Meet the spark plug.