JP4267837B2

JP4267837B2 - Spark plug and manufacturing method thereof

Info

Publication number: JP4267837B2
Application number: JP2001093802A
Authority: JP
Inventors: 昌幸瀬川; 渉松谷; 聡子伊藤
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 2001-03-28
Filing date: 2001-03-28
Publication date: 2009-05-27
Anticipated expiration: 2021-03-28
Also published as: JP2002299005A

Description

【０００１】
【発明の属する技術分野】
本発明は内燃機関に使用されるスパークプラグ及びその製造方法に関する。
【０００２】
【従来の技術】
上述のようなスパークプラグにおいては、耐火花消耗性向上のために電極の先端にＰｔやＩｒ等を主体とする貴金属チップを溶接して耐消耗部を形成したタイプのものが多数提案されている。特に、火花放電時に負極性に設定されることの多い中心電極側の耐消耗部は、火花の強いアタックを受けて消耗しやすいことから、貴金属化の効果が特に大きい。このような貴金属耐消耗部は、Ｐｔ系金属で構成されることも多かったが、高温での耐火花消耗性に優れたIr系のものの使用が拡大しつつある。
【０００３】
一方、高出力エンジンあるいはリーンバーンエンジンへの適用が進むにつれ、接地電極側の耐消耗部についても耐消耗性が求められるようになってきており、従来、主にＰｔ系金属がその材質として採用されてきた。このようなＰｔ系金属による耐消耗部は、Ｐｔ系金属からなるチップを接地電極の母材に抵抗溶接を用いて接合することにより形成される。
【０００４】
しかしながら、スパークプラグの適用環境がますます厳しくなりつつある近年では、接地電極側の耐消耗部でさえ、Ｐｔ系金属では耐久性の不足が指摘されており、Ｉｒ系金属への転換が検討されている。しかし、Ｉｒ系金属はＰｔ系金属と比べて融点が相当に高く、抵抗溶接では接合強度を十分に確保することが困難になる問題がある。その原因は、一見、Ｉｒ系金属の高融点に起因した溶け不足にあるものと思われるが、本発明者らが検討したところによると、本質的な原因はこのような溶け不足によるものではなく、Ｉｒ系金属と接地電極の母材を構成するＮｉ系金属との、線膨張係数の不一致に起因したものであることが明らかになってきた。
【０００５】
すなわち、Ｎｉの高温での線膨張係数は、８００Ｋ（５２７℃）で１６．８×１０^−６／℃であるのに対し、Ｉｒは８．１×１０^−６／℃とかなり小さい。従って、溶接後に冷却する際に、あるいは、エンジンに取り付けて使用するときの冷熱サイクル付加により、耐消耗部と母材との接合面に収縮差に基づく応力が集中し、剥離等につながりやすくなるのである。
【０００６】
そこで、特開２０００−２７７２３１号公報には、Ｉｒ系金属からなる耐消耗部とＮｉ系金属からなる電極母材との間に、両者の中間の線膨張係数を有する緩和層を挿入し、接合界面への熱的な力集中を緩和して耐剥離性を向上させる提案がなされている。緩和層の材質としては、Ｐｔ−２０質量％Ｉｒ合金、Ｐｔ−２０質量％Ｉｒ−２質量％Ｎｉ合金、あるいはＰｔ−１０質量％Ｎｉ合金など、Ｐｔを主成分とした金属が用いられている。また、上記公報中では、耐消耗部となる貴金属チップを緩和層に食い込ませ、接合界面を曲面状となすことで、耐剥離性をさらに向上させる提案もなされている（公報図２、図１０等）。
【０００７】
【発明が解決しようとする課題】
しかしながら、上記公報のスパークプラグにおいては、次のような問題が生じやすくなる。すなわち、ガソリンエンジンの燃料の無鉛化が遅れている一部の国や地域では、アンチノック剤として四メチル鉛などを添加した有鉛ガソリンが現在でも使用されている。そして、これらの国や地域でも、高級車等においては貴金属チップを使用したスパークプラグが使用され始めているが、本発明者らの検討によると、有鉛ガソリンを使用するエンジンにおいては、Ｐｔ系の耐消耗部を使用したスパークプラグを適用すると、ガソリン中に含まれるＰｂ（鉛）成分の影響により耐消耗部が異常腐食することが判明した。従って、上記公報のように緩和層を使用するタイプのスパークプラグにおいても、その緩和層がＰｔ系金属で構成されている場合、特に、公報図２や図１０等のように、緩和層の表面が一部雰囲気中に露出する形になっている場合は、Ｐｂ成分のアタックにより緩和層が急速に腐食し、耐消耗部の剥離・脱落等につながる懸念が生ずる。この鉛腐食の問題は、電極温度の上がりやすい接地電極側にてより生じやすく、極端な場合、接地電極側の耐消耗部だけが鉛腐食の影響を大きく受けるといったこともありうる。なお、本願出願人は、特公平７−１１９７４号公報において、接地電極側ではなく、中心電極側の貴金属耐消耗部及び緩和層を、それぞれ耐鉛腐食性に優れたＩｒ−Ｎｉ系合金で構成するスパークプラグを提案している。しかし、本発明者等の検討によると、貴金属耐消耗部及び緩和層がいずれもＩｒ−Ｎｉ系合金で構成される該公報の構造を、より温度上昇の激しい接地電極側に適用した場合、貴金属耐消耗部と緩和層との接合界面でＩｒの酸化による界面腐食が著しくなり、貴金属耐消耗部の剥離・脱落が生じやすくなる問題があることがわかった。
【０００８】
本発明は、貴金属耐消耗部と接地電極母材との間に緩和金属部を設けるとともに、特に鉛腐食及び酸化腐食の進行しやすい環境下でも、貴金属耐消耗部と緩和金属部との界面の剥離耐久性に優れたスパークプラグと、その製造方法とを提供することにある。
【０００９】
【課題を解決するための手段及び作用・効果】
本発明に係るスパークプラグは、接地電極の側面に固着された貴金属耐消耗部を中心電極の先端面と対向させることにより火花放電ギャップを形成したスパークプラグにおいて、
接地電極の少なくとも側面部がニッケル合金からなる電極母材とされ、
貴金属耐消耗部は、Ｉｒ及びＲｈの一方又は双方を合計にて８０質量％以上含有し、かつＩｒの含有量が９７質量％以下であって、Ｐｔ、Ｒｈ、Ｒｕ及びＲｅから選ばれる１種又は２種以上の含有率が３質量％以上である金属にて構成されるとともに、電極母材と貴金属耐消耗部との中間の線膨張係数を有する金属からなる緩和金属部を介して電極母材に接合され、
また、緩和金属部は、ＩｒとＲｈとの合計が３０質量％以上であり、かつＲｈとＮｉとの合計が２０質量％以上である金属にて構成され、さらに、
貴金属耐消耗部と中心電極との対向方向を基準として見たときに、緩和金属部は、側周面の少なくとも一部を電極母材中に埋没させる形で該電極母材に接合される一方、その緩和金属部の中心電極との対向側の端面外周縁部を接地電極の側面に露出させた形態にて、貴金属耐消耗部が、側周面の少なくとも一部を緩和金属部中に埋没させる形で該緩和金属部に接合されたことを特徴とする。
【００１０】
上記本発明のスパークプラグにおいては、接地電極母材を周知のＮｉ系合金にて構成する場合、該接地電極側の貴金属耐消耗部を、その側周面の少なくとも一部を緩和金属部中に埋没させる形で貴金属耐消耗部に接合した構造となし、かつ、貴金属耐消耗部と緩和金属部とを各々上記の組成にて構成することにより、鉛腐食及び酸化腐食の双方を考慮しなければならない過酷な環境下においても、それら貴金属耐消耗部と緩和金属部との接合界面の剥離耐久性を大幅に向上させることができる。
【００１１】
また、上記本発明のスパークプラグは、緩和金属部を形成するための第一金属チップを接地電極の側面に重ね合わせて加圧しつつ通電加熱することにより、該第一金属チップを電極母材に接合する第一接合工程と、緩和金属部を形成するための第一金属チップに対し、貴金属耐消耗部を形成するための、第一金属チップよりも径小の第二金属チップを重ね合わせて加圧しつつ通電加熱することにより、該第一金属チップを第二金属チップに接合する第二接合工程とを含む本発明のスパークプラグの製造方法により製造できる。なお、第一接合工程と第二接合工程は、この順序で実施してもよいし、実施順序を逆としてもよい。なお、本明細書でいう貴金属耐消耗部及び緩和金属部の各組成は、接合されたチップのうち、溶接時に生ずる溶融部あるいは拡散部を除いた部分の組成を指すものとする。この意味において、第一金属チップは得るべき緩和金属部と同一組成のものが、また、第二金属チップは貴金属耐消耗部と同一組成のものが、それぞれ使用されることとなる。
【００１２】
【発明の実施の形態】
以下、本発明の、いくつかの実施の形態を、図面を用いて説明する。
図１に示す本発明の一例たるスパークプラグ１００は、筒状の主体金具１、先端部２１が突出するようにその主体金具１の内側に嵌め込まれた絶縁体２、先端に形成された中心電極側貴金属耐消耗部３１を突出させた状態で絶縁体２の内側に設けられた中心電極３、及び主体金具１に一端が溶接等により結合されるとともに他端側が側方に曲げ返されて、その側面が中心電極３の先端部（ここでは、先端面）と対向するように配置された接地電極４等を備えている。また、接地電極４には上記中心電極側貴金属耐消耗部３１に接地電極側貴金属耐消耗部３２が形成されており、それら中心電極側貴金属耐消耗部３１と、接地電極側貴金属耐消耗部３２との間の隙間が火花放電ギャップｇとされている。
【００１３】
絶縁体２は、例えばアルミナあるいは窒化アルミニウム等のセラミック焼結体により構成され、その内部には自身の軸方向に沿って中心電極３を嵌め込むための孔部６を有している。また、主体金具１は、低炭素鋼等の金属により円筒状に形成されており、スパークプラグ１００のハウジングを構成するとともに、その外周面には、プラグ１００を図示しないエンジンブロックに取り付けるためのねじ部７が形成されている。
【００１４】
中心電極３及び接地電極４は、少なくとも表層部をなす電極母材部分４ｍがＮｉ合金で構成されている。このうち、図２（ａ）に示すように、中心電極３の先端部３ａはテーパ状に縮径されるとともにその先端面が平坦に構成され、ここに中心電極側貴金属耐消耗部３１の上記合金組成が得られるように組成調整された円板状のチップを重ね合わせ、さらにその接合面外縁部に沿ってレーザー溶接、電子ビーム溶接、抵抗溶接等により溶接部Ｂを形成してこれを固着することにより中心電極側貴金属耐消耗部３１が形成される。接地電極側貴金属耐消耗部（以下、単に貴金属耐消耗部という）３２の形成方法については、後に詳述する。
【００１５】
接地電極４は、少なくとも側面部、ここでは全体がニッケル合金からなる電極母材４ｍとされている。貴金属耐消耗部３２は、Ｉｒ及びＲｈの一方又は双方を合計にて８０質量％以上含有し、かつＩｒの含有量が９７質量％以下であって、Ｐｔ、Ｒｈ、Ｒｕ及びＲｅから選ばれる１種又は２種以上の含有率が３質量％以上である金属にて構成されている。そして、図２（ｂ）に示すように、電極母材４ｍと貴金属耐消耗部３２との中間の線膨張係数を有する金属からなる緩和金属部３３を介して電極母材４ｍに接合されている。緩和金属部３３は、ＩｒとＲｈとの合計が３０質量％以上であり、かつＲｈとＮｉとの合計が２０質量％以上である金属にて構成されている。なお、緩和金属部３３はＮｉを必須成分として含有していると、Ｎｉを主体に構成する電極母材４ｍとの線膨張係数の差をさらに縮めることができるので、より望ましい。
【００１６】
そして、貴金属耐消耗部３２と中心電極３との対向方向（即ち、中心電極３の軸線方向）Ｏを基準として見たときに、緩和金属部３３は、側周面３３ｓの少なくとも一部を電極母材４ｍ中に埋没させる形で該電極母材４ｍに接合されている。また、貴金属耐消耗部３２は、緩和金属部３３の中心電極３との対向側の端面外周縁部３３ｐを接地電極４の側面４ｃに露出させた形態にて、側周面３２ｓの少なくとも一部を緩和金属部３３中に埋没させる形で該緩和金属部３３に接合されている。
【００１７】
接地電極４側の貴金属耐消耗部３２の周辺構造及び各部の組成を上記のように構成することで、有鉛ガソリンを使用した高速・高負荷条件下でスパークプラグ１００を使用する場合など、鉛腐食及び酸化腐食の双方を考慮しなければならない過酷な環境下において、それら貴金属耐消耗部３２と緩和金属部３３との接合界面ＢＤの剥離耐久性を大幅に向上させることができる。以下、その理由について詳細に説明する。
【００１８】
貴金属耐消耗部３２の組成は、高温での耐火花消耗性及び耐酸化消耗性を抑制することを一つの観点として設定されたものであるが、ＲｈやＩｒがリッチな組成であるから、高温（例えば８００Ｋ）での線膨張係数の値はおおむね９〜１０（×１０^−６／℃:以下、煩雑であるので、線膨張係数の値を示すとき、「×１０^−６／℃」の部分を省略して示す）程度の値となるのに対し、電極母材４ｍはＮｉリッチであり、線膨張係数の値は１５〜１６と大きい。そこで、両者の収縮差を緩和するために両者の間に、それらの中間の線膨張係数を有する緩和金属部３３が配置される。
【００１９】
しかしながら、図６（ａ）に示すように、貴金属耐消耗部３２の側周面３２ｓが電極母材４ｍと直接接する界面ＢＤＤが形成されている場合、この区間には緩和金属部３３の効果が及ばないので、冷熱サイクルが加わったとき、貴金属耐消耗部３２と電極母材４ｍとの膨張差により界面ＢＤＤを開く向きの応力が強く作用する。特に、前記した公報のごとく、接地電極４側において、鉛腐食及び酸化腐食への耐久性を両立させるための各部の組成条件を十分に考慮していない構成を採用したときは、図６（ｂ）に示すように、貴金属耐消耗部３２の側周面３２ｓから緩和金属層３３ｒの周側面を経て底面３３ｂ側に回り込む亀裂Ｃが急速に進展し、貴金属耐消耗部３２が緩和金属層３３ｒもろとも剥離しやすくなることがわかった。また、昇温時の膨張差により界面ＢＤＤに亀裂Ｃが生じたとき、応力集中する亀裂先端部での腐食が助長されると、いわゆる応力腐食割れと類似の現象により亀裂進展が促される可能性もありうる。
【００２０】
そこで、図６（ｃ）に示すように、貴金属耐消耗部３２の側周面３２ｓを緩和金属部３３中に埋没させた構造にすると、側周面３２ｓと電極母材４ｍとの間にも緩和金属部３３が挟まって応力緩和効果を生ずるので、図６（ｄ）に示すように、貴金属耐消耗部３２の側周面３２ｓにおける亀裂Ｃの進展速度は減少する。また、該亀裂Ｃは、貴金属耐消耗部３２の底面３２ｂには回り込まず、緩和金属層３３を横切って電極母材４ｍに到達する形で進展し、結果的に貴金属耐消耗部３２の剥離が生じにくくなることもわかった。なお、この効果を高めるには、図２（ｃ）に示すように、貴金属耐消耗部３２の側周面３２ｓの全面を緩和金属部３３に埋没させた構造とすることが望ましい。図６（ｂ）のような構成では、緩和金属部３３の底面外周縁が、比較的大きな曲率半径を有した形状になりやすく、その丸みを帯びた縁に沿ってクラックが底面３２ｂ側に回り込みやすくなるなるのに対し、図６（ｄ）の構成では、貴金属耐消耗部３２の底面外縁までクラックが進行しても、該外縁が比較的先鋭な形状となっているため、クラックが底面３２ｂ側に回り込まず、直進しやすくなると考えられる。
【００２１】
しかし、接合界面ＢＤＤの剥離耐久性を十分に確保するためには、それだけでは十分でなく、貴金属耐消耗部３２及び緩和金属部３３の組成を上記の範囲に調整することが不可欠である。まず、貴金属耐消耗部３２は、先にも説明した通り、高温での耐火花消耗性を確保する観点から、Ｉｒ及びＲｈの一方又は双方を合計にて８０質量％以上含有したものとする必要がある。例えば、高温での火花消耗を抑制する観点では融点のより高いＩｒを使用することが有効であるが、Ｉｒは高温では酸化揮発消耗を生じやすいので、これを抑制するために、Ｉｒの含有量は９７質量％以下とし、かつ、Ｐｔ、Ｒｈ、Ｒｕ及びＲｅから選ばれる１種又は２種以上の含有率を３質量％以上とする必要がある。後者の元素群は、Ｉｒが含有される場合には、その酸化揮発を抑制する効果を有する。ただし、合計含有量が３質量％未満では、十分な効果が得られない。また、酸化揮発消耗抑制をより優先させたい場合には、８０質量％以上確保されるＲｈ＋Ｉｒの合計含有量において、Ｒｈ含有量を優位とし、Ｉｒ含有量を低減することが有効となる。もちろん、Ｉｒを全く含有させない組成を採用することも可能であり、この場合は、Ｉｒの酸化揮発消耗が生じなくなることが自明である。なお、Ｒｈ含有量を増大させることは、耐鉛腐食性を向上させる観点においても効果があり、特に、Ｒｈの含有量を５０質量％以上としたときに顕著である。他方、鉛腐食抑制を考慮しつつ、高温での耐火花消耗性抑制効果をより高めたい場合には、Ｉｒ含有量を３０〜８０質量％とするのがよい。
【００２２】
次に、緩和金属部３３は、ＩｒとＲｈとの合計が４０質量％以上（１００質量％含む）であり、かつＲｈとＮｉとの合計が２０質量％以上（１００質量％含む）である金属にて構成する必要がある。緩和金属部３３は、貴金属耐消耗部３２が、Ｉｒ及び／又はＲｈを主体に構成されるので、ＩｒとＲｈとの合計含有量を４０質量％以上確保しないと、応力緩和効果が十分に達成されなくなる。他方、ＲｈとＮｉとは、耐鉛腐食性を改善する効果があり、両者の一方又は双方を合計にて２０質量％以上含有させることで、鉛腐食による緩和金属部３３自体の消耗抑制、及び貴金属耐消耗部３２との界面での、鉛腐食に起因した亀裂進展助長を抑制することができる。ここでも、鉛腐食の影響を緩和するためには、Ｒｈの含有量を増加させることがより有効であり、例えば、Ｒｈの含有量を５０質量％以上（１００質量％含む）とすると、鉛腐食の影響をさらに劇的に改善することができる。
【００２３】
そして、重要な点は、前記した貴金属耐消耗部３２の組成と上記の緩和金属部３３の組成とを組み合わせて採用した場合に限り、接地電極４側において、貴金属耐消耗部３２と緩和金属部３３との界面における、酸化腐食に起因した亀裂進展助長を抑制する効果も同時に達成することが可能になることである。すなわち、貴金属耐消耗部３２側では、Ｉｒを含有しない場合も含め、Ｉｒの酸化消耗が問題となりにくい組成が採用されているが、これが、結果としては緩和金属部３３との界面での亀裂進展をも効果的に抑制することにつながる（特に、酸化腐食に起因した応力腐食割れ的な機構が関与している場合は、亀裂進展抑制はより顕著になるものと考えられる）。そして、鉛腐食と酸化腐食の双方が問題となるスパークプラグの使用環境下では、これらのいずれの構成が欠けても、結果的に貴金属耐消耗部３２の耐剥離性を十分に確保することができなくなってしまうのである。
【００２４】
なお、緩和金属部３３の組成は、当然に、線膨張係数が貴金属耐消耗部３２と電極母材４ｍとの中間となることも考慮して選択されなければならないが、これは、採用する電極母材４ｍ及び貴金属耐消耗部３２の具体的な組成に応じて、適宜調整されなければならない。しかし、貴金属耐消耗部３２は、前述した通り、ＩｒとＲｈとの合計含有量が８０質量％以上であり、その８００Ｋでの線膨張係数は８〜１１程度の範囲にある。他方、接地電極４の電極母材４ｍの材質としては、Ｎｉ含有量が６０質量％以上（高温強度及び耐酸化性確保の関係から、上限は９５質量％程度である）であり、かつＮｉ以外の残部が主にＣｒ又はＣｒ及びＦｅからなるＮｉ合金とされることが多い。例えば、電極母材４ｍの材質として多用されるインコネル６００（商標名）は、Ｎｉ：７６質量％、Ｃｒ：１５．５質量％、Ｆｅ：８質量％（残部微量添加元素もしくは不純物）であり、インコネル６０１（商標名）は、Ｎｉ：６０．５質量％、Ｃｒ：２３質量％、Ｆｅ：１４質量％（残部微量添加元素もしくは不純物）である。Ｆｅ及びＣｒの８００Ｋでの線膨張係数がそれぞれ１６.２及び１１．８であることを考慮すれば、上記の組成の電極母材４ｍの８００Ｋでの線膨張係数は、１４〜１６程度の範囲にあると見積もられる。
【００２５】
そこで、緩和金属部３３は、前記した緩和金属部の効果が損なわれない範囲での副成分の含有を考慮して、Ｉｒ、Ｒｈ及びＮｉの合計含有量を９０質量％以上に定めたとき、Ｉｒ、Ｒｈ及びＮｉの合計を１００質量％に換算したときの、Ｉｒ、Ｒｈ及びＮｉの組成が、図３に示すＩｒ−Ｎｉ−Ｒｈ三成分系組成正三角形上において、
Ａ点：Ｉｒ＝８０質量％、Ｎｉ＝２０質量％、Ｒｈ＝０質量％
Ｂ点：Ｉｒ＝８０質量％、Ｎｉ＝０質量％、Ｒｈ＝２０質量％
Ｃ点：Ｉｒ＝０質量％、Ｎｉ＝０質量％、Ｒｈ＝１００質量％
Ｄ点：Ｉｒ＝０質量％、Ｎｉ＝７０質量％、Ｒｈ＝３０質量％
Ｅ点：Ｉｒ＝３０質量％、Ｎｉ＝７０質量％、Ｒｈ＝０質量％
の各点を順次結んで得られる閉組成領域の内部（境界含む）に設定されていることが、緩和金属部３３による応力緩和効果を十分に確保する上で望ましい。図３には、各組成にて推定される８００Ｋでの線膨張係数の値を等高線により示している（括弧内は線膨張係数の数値である）。これからもわかる通り、上記の閉組成領域は、線膨張係数の値がおおむね略９〜１５となる範囲に対応している。
【００２６】
なお、緩和金属部３３の組成は、より望ましくは、
Ａ’点：Ｉｒ＝７０質量％、Ｎｉ＝３０質量％、Ｒｈ＝０質量％
Ｂ’点：Ｉｒ＝０質量％、Ｎｉ＝１０質量％、Ｒｈ＝９０質量％
Ｄ点：Ｉｒ＝０質量％、Ｎｉ＝７０質量％、Ｒｈ＝３０質量％
Ｅ点：Ｉｒ＝３０質量％、Ｎｉ＝７０質量％、Ｒｈ＝０質量％
の各点を順次結んで得られる閉組成領域の内部（境界含む：線膨張係数の値が略１１〜１４に対応）に設定されていること、さらには望ましくは、
Ａ”点：Ｉｒ＝６０質量％、Ｎｉ＝４０質量％、Ｒｈ＝０質量％
Ｂ”点：Ｉｒ＝０質量％、Ｎｉ＝２０質量％、Ｒｈ＝８０質量％
Ｄ’点：Ｉｒ＝０質量％、Ｎｉ＝６０質量％、Ｒｈ＝４０質量％
Ｅ’点：Ｉｒ＝４０質量％、Ｎｉ＝６０質量％、Ｒｈ＝０質量％
の各点を順次結んで得られる閉組成領域の内部（境界含む：線膨張係数の値が略１２〜１４に対応）に設定されているのがよい。緩和金属部３３中のＮｉ含有量を増加させることは、電極母材４ｍとの線膨張係数差を縮小する上でより有効である。
【００２７】
上記スパークプラグ１００の貴金属耐消耗部３２は、図４に示すような、一般的な抵抗溶接を用いた工程により形成することができる。まず、（ａ）に示すように、緩和金属部３３を形成するための第一金属チップ３３’を接地電極４の側面４ｃに重ね合わせて加圧しつつ、電極ＥＬ，ＥＬ間に挟み付けて通電加熱することにより、該第一金属チップ３３’を電極母材４ｍに食い込ませながら接合する（第一接合工程）。次に、（ｂ）に示すように、緩和金属部３３を形成するための第一金属チップ３３’に対し、貴金属耐消耗部３２を形成するための、第一金属チップ３３’よりも径小の第二金属チップ３２を重ね合わせて加圧しつつ通電加熱することにより、該第一金属チップ３３’を第二金属チップ３２’に食い込ませながら接合する（第二接合工程）。これらの工程により、（ｃ）に示すように、第一金属チップ３３’と第二金属チップ３２’とは、それぞれ緩和金属部３３及び貴金属耐消耗部３２となる。
【００２８】
第一金属チップ３３’及び第二金属チップ３２’が、厚さ方向に重ね合される円板状とされる場合、第二金属チップ３２’の直径を０．２〜２ｍｍに設定するとともに、第一金属チップ３３’の直径を第二金属チップ３２’の直径の１０４〜２００％に設定するのがよい。第二金属チップ３２’の直径が０．２ｍｍ未満では、形成される貴金属耐消耗部３２が、高温ですぐに火花消耗し、寿命を十分に確保できなくなる。他方、第二金属チップ３２’の直径が２ｍｍを超えると、接合界面に働く熱応力が大きくなりすぎて、耐剥離性を十分に確保できなくなる。また、第一金属チップ３３’の直径が第二金属チップ３２’の直径の１０４％未満になると、緩和金属部３３を、貴金属耐消耗部３２の側周面３２ｓ側に十分回り込ませた構造を実現できなくなる。他方、２００％を超えると、得られる緩和金属部３３による応力緩和効果が飽和し、不要なコストアップを招く。第一金属チップ３３’の直径は、これらを考慮して０．３〜２．５ｍｍとする。
【００２９】
さらに、第二金属チップ３２’の厚さは０．１〜１．０ｍｍとするのがよく、第一金属チップ３３’の厚さは第二金属チップ３２’の厚さの２０〜３００％とするのがよい。第二金属チップ３２’の厚さが０．１ｍｍ未満では、得られる貴金属耐消耗部３２の厚さが不足し、十分な寿命を確保できなくなる。また、機械的な剛性も不足するので、熱応力による貴金属耐消耗部３２の変形も起こりやすくなる。第二金属チップ３２’の厚さが１．０ｍｍを超えると、抵抗溶接時における電極母材４ｍへの埋没量が大きくなりすぎ、電極母材４ｍの変形が甚だしくなる。他方、第一金属チップ３３’の厚さが第二金属チップ３２’の厚さの２０％未満になると、得られる緩和金属部３３の厚さが薄くなり過ぎ、応力緩和機能が不十分となる。また、３００％を超えると、得られる緩和金属部３３による応力緩和効果が飽和し、不要なコストアップを招く。
【００３０】
さらに、図４（ｄ）に示すように、接地電極４の側面４ｃの幅をＷ、第一チップ３３’の直径をｄ１としたとき、寸法差Ｌ＝Ｗ−ｄ１が０．１ｍｍ以上確保されていることが望ましい。Ｌが０．１ｍｍ未満になると、抵抗溶接時において、第一チップ３３’を電極母材４ｍ中に十分に埋没させることが困難となる。
【００３１】
なお、図２（ｃ）に示すように、貴金属耐消耗部３２及び緩和金属部３３との双方を、対向方向Ｏにおいて繊維状に引き延ばされた結晶組織を有するものとして構成すると、図６（ｃ）に示す、貴金属耐消耗部３２の底面３２ｂ側への亀裂の進展が一層進みにくくなり、耐剥離性をより高めることができる。組織をこのようなものとするには、合金を熱間鍛造、熱間圧延及び熱間伸線の１種又は２種以上の組合せにより線状あるいはロッド状の素材に加工した後、これを長さ方向に所定長に切断して形成したチップ（後述する第一チップ３３’及び第二チップ３２’）を用いて貴金属耐消耗部３２及び緩和金属部３３を形成することが有効である。なお、繊維状に引き延ばされた結晶組織とは、組織延伸方向と平行な断面に観察される結晶粒子の平均的なアスペクト比（図２（ｄ）：Ｗ１／Ｗ２）が５以上となっているものをいう。
【００３２】
なお、円板状の第一金属チップ３３’及び第二金属チップ３２’を用いたとき、図５に示すように、前記した対向方向Ｏにおいて、貴金属耐消耗部３２の緩和金属部３３への接合端面３２ｂを平坦に形成し、緩和金属部３３の電極母材４ｍへの接合端面（底面）３３ｂが、中央部が外縁部よりも突出する凸曲面状に形成することができる。このようにすると、接合面積が増大して貴金属耐消耗部３２の接合強度が高められるほか、接合端面３３ｂの中央部において緩和金属部３３の厚みが増すので、該中央部での応力緩和効果が高められ、接合端面３３ｂの中央部への亀裂進展を抑制することができる。その結果、貴金属耐消耗部３２の耐剥離性をさらに向上させることができる。なお、上記のような構造を得るには、用いる第一チップ３３’の厚さｔ１と、第二チップ３２’の厚さｔ２との比ｔ１／ｔ２を０．５〜２．０に設定することが有効である。
【００３３】
さらに、図７（ｄ）に示すように、緩和金属部３３の側周面３３ｓを、対向方向Ｏにおける中央部が両端部よりも半径方向に膨出する凸型に形成することもできる。このようにすると、緩和金属部３３の凸状の側周面３３ｓが、対応する凹状に形成された電極母材４ｍ側の孔内側面４ｓと係合して、緩和金属部３３の抜け落ちが生じにくくなる。このような緩和金属部３３を形成するには、図７（ａ）に示すように、球状の第一チップ１３３を用い、これを抵抗溶接時の加熱圧縮によりつぶしながら電極母材４ｍに食い込ませればよい。なお、この実施形態では、球状の第一チップ１３３は、図７（ｂ）に示すように、抵抗溶接時の電極の先端面に対応して、上面が平坦化される形で電極母材４ｍに食い込んでおり、図７（ｃ）に示すように、ここに円板状の第二チップ３２’を重ねて、図４と同様に抵抗溶接することにより、図７（ｄ）に示すように、貴金属耐消耗部３２を形成している。これによると、貴金属耐消耗部３２の緩和金属部３３への接合端面３２ｂを平坦に形成できる一方、緩和金属部３３の電極母材４ｍへの接合端面（底面）３３ｂは、図５と同様に、中央部が外縁部よりも突出する凸曲面状に形成することができる。
【００３４】
なお、図８に示すように、１つの緩和金属部３３に対し、複数の貴金属耐消耗部３２を分散させる形で接合することもできる。
【００３５】
【実施例】
本発明の効果を確認するために、以下の実験を行なった。
（実施例１）
接地電極側の緩和金属層及び貴金属耐消耗部を形成するための第一チップ及び第二チップを、以下のように作製した。まず、貴金属耐消耗部用の第二チップは、所定量のＩｒとＲｈとを配合・溶解することにより、Ｉｒ−４０質量％Ｒｈの組成を有する合金を作製した。この合金を、１５００℃にて熱間鍛造し、次いで１３００℃で熱間圧延及び熱間スエージングし、さらに１２００℃にて熱間伸線することにより、直径１ｍｍの合金線材を得た。これを長手方向に切断することで直径１ｍｍ、厚さ０．２ｍｍの円板状のチップとした。また、緩和金属層用の第一チップは、種々の比率にてＩｒとＮｉとを配合・溶解することにより、表１に示す各種Ｎｉ含有量を有するＩｒ−Ｎｉ合金を作製した。そして、第二チップと同様の方法により直径１．２ｍｍ、厚さ０．２ｍｍの円板状のチップとした。これらチップを用いて、インコネル６００製の接地電極母材の側面（幅２．５ｍｍ）に、図４に示す方法により抵抗溶接し、図２に示す形態の接地電極側の接合構造を完成させた。なお、抵抗溶接の条件は、通電電流値６５０Ａ、加圧荷重３５ｋｇ／ｃｍ^２に設定した。
【００３６】
一方、中心電極３側については、組成がＩｒ−５質量％Ｐｔであり、直径０．６ｍｍ厚さ０．８ｍｍの寸法を有する貴金属チップを、上記第二チップと同様の方法により作製し、インコネル６００製の中心電極母材の先端面に全周レーザー溶接することにより接合した。そして、これら接地電極及び中心電極を用いて図１に示す形態のスパークプラグ試験品を作成し（ただし、ギャップ間隔１．１ｍｍ）、接地電極側の貴金属耐消耗部の耐剥離性と耐鉛腐食性とを評価した。
【００３７】
まず、耐剥離性の評価は以下の通りである。まず、スパークプラグの火花放電ギャップ側の先端部をガスバーナーにより１０００℃に２分間加熱し、次いで１分空冷するサイクルを１０００回繰り返す。次に、試験品を、接地電極の貴金属耐消耗部の中心軸線を通る面にて切断・研磨して顕微鏡にて拡大観察するとともに、貴金属耐消耗部と緩和金属層部との界面の亀裂もしくは酸化スケールの進展長を観察視野上にて測定し、界面の全長で割った値を剥離進展率として算出する。そして、その剥離進展率が５０％を超えたものを不良（×）、５０％以下のものを良好（○）として評価する。
【００３８】
他方、耐鉛腐食性の評価は以下のようにして行なった。すなわち、各スパークプラグを、６気筒ガソリンエンジン（排気量２０００ｃｃ）に取り付け、４メチル鉛を０．０４質量％含有する有鉛ガソリンを燃料として、スロットル全開状態、エンジン回転数５０００ｒｐｍにて、中心電極側が負となる極性にて１００時間運転を行なった。運転終了後、試験品を、接地電極の貴金属耐消耗部と緩和金属層との中心軸線を通る面にて切断・研磨して顕微鏡にて拡大観察するとともに、緩和金属層の貴金属耐消耗部の周囲を取り囲む部分の残留率が８０％以上のものを優良（◎）、６０％以上８０％未満のものを良好（○）、６０％未満のものを不良（×）として評価する。以上の結果を表１に示す。
【００３９】
【表１】

これによると、Ｉｒ−Ｎｉ合金からなる緩和金属部の場合、Ｎｉ量が２０〜７０質量％の範囲内において、耐剥離性及び耐鉛腐食性のいずれも良好となっていることがわかる。
【００４０】
（実施例２）
貴金属耐消耗部用の第二チップをＩｒ−４０質量％Ｒｈの組成とし、緩和金属層用の第一チップを、種々の比率のＲｈ−Ｎｉ合金とした以外は、実施例１と同様のスパークプラグ試験品を作製し、同様の評価を行なった。以上の結果を表２に示す。
【００４１】
【表２】

これによると、Ｒｈ−Ｎｉ合金からなる緩和金属部の場合、Ｎｉ量が７０質量％以下の範囲（１００質量％Ｒｈを含む）において、耐剥離性及び耐鉛腐食性のいずれも良好となっていることがわかる。
【００４２】
（実施例３）
貴金属耐消耗部用の第二チップを種々の比率のＩｒ−Ｐｔ合金とし、緩和金属層用の第一チップを、Ｉｒ−４０質量％Ｎｉの組成とした以外は、実施例１と同様のスパークプラグ試験品を作製し、同様の評価を行なった。ただし、耐鉛腐食性の評価は、貴金属耐消耗部の残留率が８０％以上のものを優良（◎）、６０％以上８０％未満のものを良好（○）、６０％未満のものを不良（×）として評価する。以上の結果を表３に示す。
【００４３】
【表３】

これによると、Ｉｒ−Ｐｔ合金からなる貴金属耐消耗部の場合、Ｐｔ量が３〜２０質量％の範囲において、耐剥離性及び耐鉛腐食性のいずれも良好となっていることがわかる。
【００４４】
（実施例４）
貴金属耐消耗部用の第二チップを種々の比率のＩｒ−Ｒｈ合金とし、緩和金属層用の第一チップを、Ｉｒ−４０質量％Ｎｉの組成とした以外は、実施例１と同様のスパークプラグ試験品を作製し、同様の評価を行なった。ただし、耐鉛腐食性の評価は、貴金属耐消耗部の残留率が８０％以上のものを優良（◎）、６０％以上８０％未満のものを良好（○）、６０％未満のものを不良（×）として評価する。以上の結果を表４に示す。
【００４５】
【表４】

これによると、Ｉｒ−Ｒｈ合金からなる貴金属耐消耗部の場合、Ｒｈ量が１０質量％以上の範囲において、耐剥離性及び耐鉛腐食性のいずれも良好となっていることがわかる。
【００４６】
（実施例５）
貴金属耐消耗部用の第二チップをＩｒ−４０質量％Ｒｈ合金とし、緩和金属層用の第一チップを、Ｉｒ−４０質量％Ｎｉの組成として、実施例１と同様に作製した。ここで、第一チップの寸法は直径ｄ１を１．２ｍｍ、厚さを０．２ｍｍに固定したが、第二チップは厚さ０．２ｍｍに固定し、直径ｄ２を０．９〜１．１８ｍｍの種々の寸法に形成した。これらのチップを用いて、実施例１と同様のスパークプラグ試験品を作製し、耐剥離性の評価を実施例１と同様に行なった。以上の結果を表５に示す。
【００４７】
【表５】

これによると、ｄ１／ｄ２が１０４％以上で耐剥離性がいずれも良好となっていることがわかる。
【００４８】
（実施例６）
貴金属耐消耗部用の第二チップをＩｒ−４０質量％Ｒｈ合金とし、緩和金属層用の第一チップを、Ｉｒ−４０質量％Ｎｉの組成として、実施例１と同様に作製した。ここで、第一チップの直径ｄ１と第二チップの直径ｄ２との比ｄ１／ｄ２を１２０％に固定し（いずれも厚さ０．２ｍｍ）、かつ第二チップの直径ｄ２を０．２〜１．５ｍｍの種々の寸法に設定した。これらのチップを用いて、実施例１と同様のスパークプラグ試験品を作製し、耐火花消耗性試験を以下の条件にて行った。すなわち、プラグを試験用チャンバに取り付けるとともにフルトランジスタ型イグナイタに接続し、チャンバ内空気圧０．４ＭＰａ（約４気圧）、最大電圧３０ｋＶにて周波数１００Ｈｚの交流電圧を１００時間印加するとともに、試験後に同様の断面観察を行い、貴金属耐消耗部の厚さが７０％以上残留していたものを良好（○）、７０％未満であったものを不良（×）として評価する。結果を表６に示す。
【００４９】
【表６】

【００５０】
これによると、ｄ２が０．３ｍｍ以上で耐消耗性が良好となっていることがわかる。
【００５１】
（実施例７）
貴金属耐消耗部用の第二チップをＩｒ−４０質量％Ｒｈ合金とし、緩和金属層用の第一チップを、Ｉｒ−４０質量％Ｎｉの組成として、実施例１と同様に作製した。ここで、第一チップの直径ｄ１を、接地電極の幅Ｗ（２．５ｍｍ）を基準として、Ｌ＝Ｗ−ｄ１の値が０〜０．４ｍｍの種々の値となるように設定した。これらのチップを、実施例１と同様に接地電極に溶接するとともに、溶接後の同様の断面観察により、チップ厚みの９０％以上が埋没していたものを良好（○）、９０％未満であったものを不良（×）として評価する。結果を表７に示す。
【００５２】
【表７】

【００５３】
これによると、Ｌ＝Ｗ−ｄ１の値が０．１ｍｍ以上で溶接性が良好となっていることがわかる。
【図面の簡単な説明】
【図１】本発明のスパークプラグの一実施例を示す正面部分断面図。
【図２】その要部を示す拡大断面図。
【図３】緩和金属部の望ましい組成範囲を示す図。
【図４】接地電極側の貴金属耐消耗部の形成工程の一例を説明する図。
【図５】緩和金属部の第一の変形態様を示す断面図。
【図６】本発明のスパークプラグの作用を比較例とともに示す図。
【図７】緩和金属部の第二の変形態様を示す断面図。
【図８】貴金属耐消耗部の変形態様を示す斜視図。
【符号の説明】
３中心電極
４接地電極
４ｃ側面
４ｍ電極母材
３１ａ先端面
３２貴金属耐消耗部
３２ｂ接合端面
３２ｓ側周面
３２’ 第二金属チップ
３３緩和金属部
３３ｐ端面外周縁部
３３ｓ側周面
３３’ 第一金属チップ
ｇ火花放電ギャップ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug used for an internal combustion engine and a method for manufacturing the same.
[0002]
[Prior art]
Many spark plugs as described above have been proposed in which a wear-resistant portion is formed by welding a noble metal tip mainly composed of Pt, Ir or the like to the tip of an electrode in order to improve the spark wear resistance. . In particular, the wear resistant part on the side of the center electrode, which is often set to negative polarity at the time of spark discharge, is likely to wear due to a strong attack of the spark, so that the effect of precious metalization is particularly great. Such noble metal wear resistant parts are often composed of Pt-based metals, but the use of Ir-based ones that are excellent in spark wear resistance at high temperatures is expanding.
[0003]
On the other hand, as application to high-power engines or lean-burn engines progresses, wear resistance is also required for the wear-resistant part on the ground electrode side. Conventionally, Pt-based metals have been mainly used as the material. It has been. Such a wear resistant part made of Pt-based metal is formed by joining a chip made of Pt-based metal to the base material of the ground electrode using resistance welding.
[0004]
However, in recent years when the application environment of spark plugs is becoming increasingly severe, it has been pointed out that even the wear-resistant part on the ground electrode side is insufficient in durability with Pt-based metals, and conversion to Ir-based metals has been studied. ing. However, Ir-based metals have a considerably higher melting point than Pt-based metals, and there is a problem that it is difficult to ensure sufficient joint strength by resistance welding. The cause seems to be due to insufficient melting due to the high melting point of Ir-based metals. However, according to the study by the present inventors, the essential cause is not due to such insufficient melting. It has become clear that this is due to a mismatch in linear expansion coefficient between the Ir-based metal and the Ni-based metal constituting the base material of the ground electrode.
[0005]
That is, the linear expansion coefficient of Ni at a high temperature is 16.8 × 10 8 at 800 K (527 ° C.). ^-6 / ° C while Ir is 8.1 × 10 ^-6 / C and very small. Therefore, when cooling after welding, or by applying a thermal cycle when mounted on an engine and used, stress based on the shrinkage is concentrated on the joint surface between the wear resistant part and the base material, which easily leads to peeling. It is.
[0006]
Therefore, in Japanese Patent Application Laid-Open No. 2000-277231, a relaxation layer having a linear expansion coefficient intermediate between both of the wear resistant part made of Ir metal and the electrode base material made of Ni metal is inserted and bonded. Proposals have been made to improve the peel resistance by relaxing the thermal force concentration on the interface. As the material of the relaxation layer, a metal mainly composed of Pt, such as a Pt-20 mass% Ir alloy, a Pt-20 mass% Ir-2 mass% Ni alloy, or a Pt-10 mass% Ni alloy, is used. . Further, in the above publication, a proposal has been made to further improve the peeling resistance by causing a noble metal tip serving as a wear resistant portion to bite into the relaxation layer and making the bonding interface into a curved surface (see FIGS. 2 and 10). etc).
[0007]
[Problems to be solved by the invention]
However, the spark plug of the above publication tends to cause the following problems. That is, in some countries and regions where lead-free fuel for gasoline engines is delayed, leaded gasoline with tetramethyl lead added as an anti-knock agent is still used. In these countries and regions, spark plugs using precious metal chips have begun to be used in luxury cars, etc., but according to the study by the present inventors, in engines using leaded gasoline, Pt series It has been found that when a spark plug using a wear resistant part is applied, the wear resistant part is abnormally corroded by the influence of a Pb (lead) component contained in gasoline. Therefore, even in a spark plug using a relaxation layer as described in the above publication, when the relaxation layer is made of a Pt-based metal, the surface of the relaxation layer is particularly formed as shown in FIGS. Is partially exposed to the atmosphere, the Pb component attack may cause the mitigation layer to corrode rapidly, leading to a concern that the wear resistant part may be peeled off or dropped off. This problem of lead corrosion is more likely to occur on the ground electrode side where the electrode temperature is likely to rise. In an extreme case, only the wear-resistant part on the ground electrode side may be greatly affected by lead corrosion. In addition, in the Japanese Patent Publication No. 7-19744, the applicant of the present application is configured with an Ir-Ni alloy having excellent lead corrosion resistance in each of the noble metal wear resistant portion and the relaxation layer on the center electrode side, not on the ground electrode side. A spark plug is proposed. However, according to the study by the present inventors, when the structure of the publication in which the noble metal wear resistant portion and the relaxation layer are both made of an Ir-Ni alloy is applied to the ground electrode side where the temperature rises more rapidly, the noble metal It has been found that there is a problem that interfacial corrosion due to oxidation of Ir becomes remarkable at the joint interface between the wear resistant part and the relaxation layer, and the noble metal wear resistant part is likely to be peeled off and dropped off.
[0008]
The present invention provides a relaxed metal portion between the noble metal wear resistant portion and the ground electrode base material, and particularly in an environment where lead corrosion and oxidative corrosion tend to proceed, especially at the interface between the noble metal wear resistant portion and the relaxed metal portion. An object of the present invention is to provide a spark plug excellent in peeling durability and a manufacturing method thereof.
[0009]
[Means for solving the problems and actions / effects]
The spark plug according to the present invention is a spark plug in which a spark discharge gap is formed by making a noble metal wear resistant portion fixed to the side surface of the ground electrode face the tip surface of the center electrode.
At least a side surface portion of the ground electrode is an electrode base material made of a nickel alloy,
The noble metal wear resistant part contains one or both of Ir and Rh in a total of 80% by mass or more, and the Ir content is 97% by mass or less, and is selected from Pt, Rh, Ru and Re Alternatively, the electrode matrix is formed of a metal having a content rate of 2 or more and 3% by mass or more, and a relaxed metal portion made of a metal having an intermediate linear expansion coefficient between the electrode matrix and the noble metal wear resistant portion. Bonded to the material,
The relaxed metal portion is made of a metal having a total of Ir and Rh of 30% by mass or more and a total of Rh and Ni of 20% by mass or more,
When viewed from the direction in which the noble metal wear-resistant portion and the center electrode face each other, the relaxation metal portion is joined to the electrode base material in such a manner that at least a part of the side peripheral surface is buried in the electrode base material. The noble metal wear-resistant part is buried in at least a part of the side peripheral surface in the relaxed metal part, with the outer peripheral edge of the relaxed metal part facing the center electrode exposed on the side surface of the ground electrode. It is characterized in that it is joined to the relaxed metal part in a form that causes
[0010]
In the spark plug of the present invention, when the ground electrode base material is made of a well-known Ni-based alloy, the noble metal wear-resistant portion on the ground electrode side is at least part of the side peripheral surface in the relaxed metal portion. Both lead corrosion and oxidation corrosion must be taken into account by constructing the structure in which the noble metal wear resistant part and the relaxed metal part are each composed of the above-mentioned composition by being buried in the noble metal wear resistant part. Even in a severe environment that does not become necessary, it is possible to greatly improve the peeling durability of the joint interface between the noble metal wear resistant portion and the relaxed metal portion.
[0011]
In addition, the spark plug of the present invention is configured such that the first metal tip for forming the relaxed metal portion is superposed on the side surface of the ground electrode and heated while being energized, whereby the first metal tip is used as the electrode base material. A second metal tip having a diameter smaller than that of the first metal tip for forming the noble metal wear resistant portion is superimposed on the first joining step to be joined and the first metal tip for forming the relaxed metal portion. It can manufacture by the manufacturing method of the spark plug of this invention including the 2nd joining process of joining this 1st metal tip to the 2nd metal tip by carrying out energization heating while pressing. In addition, a 1st joining process and a 2nd joining process may be implemented in this order, and it is good also as an implementation order reverse. In addition, each composition of a noble metal wear-resistant part and a relaxation metal part as used in this specification shall point out the composition of the part except the fusion | melting part or spreading | diffusion part which arises at the time of the chip | tip joined. In this sense, the first metal tip has the same composition as the relaxation metal portion to be obtained, and the second metal tip has the same composition as the noble metal wear resistant portion.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Several embodiments of the present invention will be described below with reference to the drawings.
A spark plug 100 as an example of the present invention shown in FIG. 1 includes a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip 21 protrudes, and a center electrode formed at the tip. One end is coupled to the center electrode 3 provided inside the insulator 2 with the side noble metal wear resistant portion 31 protruding, and the metal shell 1 by welding or the like, and the other end is bent back to the side. The ground electrode 4 etc. arrange | positioned so that the side surface may oppose the front-end | tip part (here front-end | tip surface) of the center electrode 3 are provided. Further, the ground electrode 4 is provided with a ground electrode-side noble metal wear-resistant portion 32 in the center electrode-side noble metal wear-resistant portion 31, and the center electrode-side noble metal wear-resistant portion 31 and the ground electrode-side noble metal wear-resistant portion 32. Is a spark discharge gap g.
[0013]
The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a hole 6 for fitting the center electrode 3 along its own axial direction. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Part 7 is formed.
[0014]
In the center electrode 3 and the ground electrode 4, at least the electrode base material portion 4m constituting the surface layer portion is made of Ni alloy. Among these, as shown in FIG. 2 (a), the tip 3a of the center electrode 3 is reduced in diameter in a taper shape, and its tip is configured to be flat. Disc-shaped chips whose composition has been adjusted so as to obtain an alloy composition are stacked, and a weld B is formed along the outer edge of the joint surface by laser welding, electron beam welding, resistance welding, etc., and fixed. By doing so, the center electrode side noble metal wear resistant portion 31 is formed. A method for forming the ground electrode side noble metal wear resistant portion (hereinafter, simply referred to as a noble metal wear resistant portion) 32 will be described in detail later.
[0015]
The ground electrode 4 is at least a side surface portion, here an electrode base material 4m made of a nickel alloy. The noble metal wear resistant part 32 contains one or both of Ir and Rh in a total of 80% by mass or more, and the Ir content is 97% by mass or less, and is selected from Pt, Rh, Ru, and Re. It is comprised with the metal whose content rate of a seed | species or 2 or more types is 3 mass% or more. Then, as shown in FIG. 2B, the electrode base material 4m is joined via a relaxation metal portion 33 made of a metal having a linear expansion coefficient intermediate between the electrode base material 4m and the noble metal wear resistant portion 32. . The relaxed metal part 33 is made of a metal having a total of Ir and Rh of 30% by mass or more and a total of Rh and Ni of 20% by mass or more. In addition, it is more desirable that the relaxation metal portion 33 contains Ni as an essential component because the difference in linear expansion coefficient from the electrode base material 4m mainly composed of Ni can be further reduced.
[0016]
Then, when viewed from the reference direction O (ie, the axial direction of the center electrode 3) O between the noble metal wear-resistant portion 32 and the center electrode 3, the relaxation metal portion 33 has at least a part of the side peripheral surface 33s as an electrode. The electrode base material 4m is joined so as to be buried in the base material 4m. Further, the noble metal wear-resistant part 32 has at least a part of the side peripheral surface 32s in a form in which the outer peripheral edge part 33p on the side facing the center electrode 3 of the relaxing metal part 33 is exposed to the side face 4c of the ground electrode 4. Is bonded to the relaxation metal portion 33 in such a manner that it is buried in the relaxation metal portion 33.
[0017]
When the spark plug 100 is used under high-speed and high-load conditions using leaded gasoline, the peripheral structure of the noble metal wear-resistant part 32 on the ground electrode 4 side and the composition of each part are configured as described above. In a harsh environment where both corrosion and oxidative corrosion must be considered, the peeling durability of the joint interface BD between the noble metal wear resistant portion 32 and the relaxed metal portion 33 can be greatly improved. Hereinafter, the reason will be described in detail.
[0018]
The composition of the noble metal wear resistant portion 32 is set from the viewpoint of suppressing the spark wear resistance and the oxidation wear resistance at high temperatures. However, since the composition is rich in Rh and Ir, The value of the linear expansion coefficient at (for example, 800K) is about 9 to 10 (× 10 ^-6 / ° C: Hereinafter, since it is complicated, when the value of the linear expansion coefficient is indicated, “× 10 ^-6 The electrode base material 4m is Ni-rich and the value of the linear expansion coefficient is as large as 15-16. Therefore, in order to relieve the shrinkage difference between them, a relieving metal part 33 having a linear expansion coefficient between them is arranged between them.
[0019]
However, as shown in FIG. 6A, when the interface BDD in which the side peripheral surface 32s of the noble metal wear resistant portion 32 is in direct contact with the electrode base material 4m is formed, the effect of the relaxation metal portion 33 is present in this section. Therefore, when the cooling / heating cycle is applied, the stress in the direction of opening the interface BDD acts strongly due to the difference in expansion between the noble metal wear resistant portion 32 and the electrode base material 4m. In particular, as described in the above publication, when the ground electrode 4 side adopts a configuration in which the composition conditions of each part for achieving both durability against lead corrosion and oxidation corrosion are not sufficiently considered, FIG. ), The crack C that rapidly turns from the side peripheral surface 32s of the noble metal wear resistant portion 32 to the bottom surface 33b side through the peripheral side surface of the relaxed metal layer 33r rapidly develops, and the noble metal wear resistant portion 32 is loosened by the relaxed metal layer 33r. Both were found to be easily peeled off. In addition, when a crack C occurs in the interface BDD due to an expansion difference at the time of temperature rise, if the corrosion is promoted at the crack tip where stress concentrates, crack propagation may be promoted by a phenomenon similar to so-called stress corrosion cracking. There is also a possibility.
[0020]
Therefore, as shown in FIG. 6 (c), when the side peripheral surface 32s of the noble metal wear resistant portion 32 is buried in the relaxed metal portion 33, the side peripheral surface 32s and the electrode base material 4m are also interposed. Since the relaxation metal portion 33 is sandwiched to produce a stress relaxation effect, as shown in FIG. 6 (d), the growth rate of the crack C on the side peripheral surface 32s of the noble metal wear resistant portion 32 decreases. In addition, the crack C does not enter the bottom surface 32b of the noble metal wear resistant portion 32 but propagates in a form that reaches the electrode base material 4m across the relaxation metal layer 33. As a result, the noble metal wear resistant portion 32 is peeled off. I also found it difficult to occur. In order to enhance this effect, it is desirable to have a structure in which the entire side peripheral surface 32 s of the noble metal wear resistant portion 32 is buried in the relaxed metal portion 33 as shown in FIG. In the configuration as shown in FIG. 6 (b), the outer peripheral edge of the bottom surface of the relaxed metal portion 33 tends to have a shape having a relatively large radius of curvature, and the crack wraps around the bottom surface 32b along the rounded edge. On the other hand, in the configuration of FIG. 6D, even if the crack progresses to the outer edge of the bottom surface of the noble metal wear resistant portion 32, the outer edge has a relatively sharp shape. It will be easier to go straight without going around.
[0021]
However, in order to sufficiently secure the peeling durability of the bonding interface BDD, it is not sufficient, and it is essential to adjust the composition of the noble metal wear resistant portion 32 and the relaxed metal portion 33 within the above ranges. First, as described above, the noble metal wear resistant part 32 needs to contain one or both of Ir and Rh in a total of 80% by mass or more from the viewpoint of securing spark wear resistance at high temperatures. There is. For example, it is effective to use Ir having a higher melting point from the viewpoint of suppressing spark consumption at high temperatures. However, since Ir tends to cause oxidative volatilization at high temperatures, the content of Ir is restricted to suppress this. Is 97 mass% or less, and the content of one or more selected from Pt, Rh, Ru and Re needs to be 3 mass% or more. The latter element group has an effect of suppressing oxidative volatilization when Ir is contained. However, if the total content is less than 3% by mass, sufficient effects cannot be obtained. In order to give higher priority to the suppression of oxidative volatilization, it is effective to make the Rh content dominant and reduce the Ir content in the total content of Rh + Ir secured at 80 mass% or more. Of course, it is also possible to adopt a composition that does not contain Ir at all, and in this case, it is obvious that no oxidation and volatilization of Ir occurs. Increasing the Rh content is also effective from the viewpoint of improving the lead corrosion resistance, and is particularly remarkable when the Rh content is 50% by mass or more. On the other hand, if it is desired to further enhance the spark wear resistance suppressing effect at high temperatures while taking lead corrosion suppression into consideration, the Ir content is preferably 30 to 80% by mass.
[0022]
Next, the relaxation metal part 33 is a metal in which the total of Ir and Rh is 40% by mass or more (including 100% by mass), and the total of Rh and Ni is 20% by mass or more (including 100% by mass). It is necessary to configure with. In the relaxation metal part 33, the noble metal wear-resistant part 32 is mainly composed of Ir and / or Rh. Therefore, unless the total content of Ir and Rh is secured to 40% by mass or more, the stress relaxation effect is sufficiently achieved. It will not be done. On the other hand, Rh and Ni have the effect of improving the lead corrosion resistance. By containing one or both of them in a total of 20% by mass or more, the consumption of the mitigation metal part 33 itself due to lead corrosion is suppressed, and It is possible to suppress the promotion of crack propagation due to lead corrosion at the interface with the noble metal wear resistant portion 32. Again, in order to mitigate the effects of lead corrosion, it is more effective to increase the Rh content. For example, if the Rh content is 50 mass% or more (including 100 mass%), lead corrosion Can be dramatically improved.
[0023]
The important point is that the noble metal wear resistant portion 32 and the relaxed metal portion are arranged on the ground electrode 4 side only when the composition of the noble metal wear resistant portion 32 and the composition of the relaxed metal portion 33 are used in combination. It is also possible to simultaneously achieve the effect of suppressing the crack propagation promotion caused by the oxidative corrosion at the interface with 33. That is, on the noble metal wear resistant part 32 side, a composition that does not cause the problem of Ir oxidation consumption, including the case where Ir is not contained, is adopted. As a result, crack propagation at the interface with the relaxed metal part 33 occurs. (In particular, when a stress corrosion cracking mechanism due to oxidative corrosion is involved, it is considered that crack growth suppression becomes more remarkable). And in the use environment of the spark plug in which both lead corrosion and oxidative corrosion are problems, even if any of these configurations is lacking, as a result, sufficient peeling resistance of the noble metal wear resistant portion 32 can be secured. It will not be possible.
[0024]
It should be noted that the composition of the relaxed metal portion 33 must be selected in consideration of the fact that the linear expansion coefficient is intermediate between the noble metal wear resistant portion 32 and the electrode base material 4m. According to the specific composition of the base material 4m and the noble metal wear resistant part 32, it must be adjusted as appropriate. However, as described above, the noble metal wear resistant part 32 has a total content of Ir and Rh of 80% by mass or more, and its linear expansion coefficient at 800K is in the range of about 8-11. On the other hand, the electrode base material 4m of the ground electrode 4 has a Ni content of 60% by mass or more (the upper limit is about 95% by mass from the viewpoint of securing high-temperature strength and oxidation resistance), and other than Ni. In many cases, the balance of Ni is mainly Cr or a Ni alloy composed of Cr and Fe. For example, Inconel 600 (trade name) frequently used as the material of the electrode base material 4m is Ni: 76% by mass, Cr: 15.5% by mass, Fe: 8% by mass (the remaining trace additive element or impurity), Inconel 601 (trade name) is Ni: 60.5% by mass, Cr: 23% by mass, Fe: 14% by mass (the remaining trace added elements or impurities). Considering that the linear expansion coefficients of Fe and Cr at 800K are 16.2 and 11.8, respectively, the linear expansion coefficient at 800K of the electrode base material 4m having the above composition is in the range of about 14-16. It is estimated that
[0025]
Therefore, in consideration of the inclusion of subcomponents within the range in which the effect of the relaxed metal portion is not impaired, the relaxed metal portion 33, when the total content of Ir, Rh and Ni is set to 90% by mass or more, On the Ir-Ni-Rh ternary composition equilateral triangle shown in FIG. 3, the composition of Ir, Rh and Ni when the total of Ir, Rh and Ni is converted to 100% by mass,
Point A: Ir = 80 mass%, Ni = 20 mass%, Rh = 0 mass%
B point: Ir = 80 mass%, Ni = 0 mass%, Rh = 20 mass%
C point: Ir = 0 mass%, Ni = 0 mass%, Rh = 100 mass%
D point: Ir = 0 mass%, Ni = 70 mass%, Rh = 30 mass%
E point: Ir = 30 mass%, Ni = 70 mass%, Rh = 0 mass%
In order to sufficiently secure the stress relaxation effect by the relaxed metal portion 33, it is desirable that it is set within the closed composition region (including the boundary) obtained by sequentially connecting these points. In FIG. 3, the value of the linear expansion coefficient at 800 K estimated for each composition is shown by contour lines (the values in the parentheses are the values of the linear expansion coefficient). As can be seen, the closed composition region corresponds to a range in which the value of the linear expansion coefficient is approximately 9 to 15.
[0026]
The composition of the relaxed metal part 33 is more desirably,
A ′ point: Ir = 70 mass%, Ni = 30 mass%, Rh = 0 mass%
B ′ point: Ir = 0 mass%, Ni = 10 mass%, Rh = 90 mass%
D point: Ir = 0 mass%, Ni = 70 mass%, Rh = 30 mass%
E point: Ir = 30 mass%, Ni = 70 mass%, Rh = 0 mass%
It is set within the closed composition region obtained by sequentially connecting the points (including the boundary: the value of the linear expansion coefficient corresponds to approximately 11 to 14), more preferably,
A ″ point: Ir = 60 mass%, Ni = 40 mass%, Rh = 0 mass%
B ″ point: Ir = 0 mass%, Ni = 20 mass%, Rh = 80 mass%
D ′ point: Ir = 0 mass%, Ni = 60 mass%, Rh = 40 mass%
E ′ point: Ir = 40 mass%, Ni = 60 mass%, Rh = 0 mass%
It is preferable to set the inside of the closed composition region obtained by sequentially connecting these points (including the boundary: the value of the linear expansion coefficient corresponds to approximately 12 to 14). Increasing the Ni content in the relaxed metal portion 33 is more effective in reducing the difference in linear expansion coefficient from the electrode base material 4m.
[0027]
The noble metal wear resistant portion 32 of the spark plug 100 can be formed by a process using general resistance welding as shown in FIG. First, as shown in (a), the first metal tip 33 ′ for forming the relaxed metal portion 33 is superimposed on the side surface 4c of the ground electrode 4 and pressed, and is sandwiched between the electrodes EL and EL to be energized. By heating, the first metal tip 33 ′ is joined while biting into the electrode base material 4 m (first joining step). Next, as shown in (b), the diameter of the first metal tip 33 ′ for forming the relaxed metal portion 33 is smaller than that of the first metal tip 33 ′ for forming the noble metal wear resistant portion 32. The second metal chip 32 is superposed and pressurized while being energized to join the first metal chip 33 ′ while biting into the second metal chip 32 ′ (second bonding step). By these steps, as shown in (c), the first metal tip 33 ′ and the second metal tip 32 ′ become the relaxed metal portion 33 and the noble metal wear resistant portion 32, respectively.
[0028]
When the first metal tip 33 ′ and the second metal tip 32 ′ are formed in a disc shape that is overlapped in the thickness direction, the diameter of the second metal tip 32 ′ is set to 0.2 to 2 mm, The diameter of the first metal tip 33 ′ is preferably set to 104 to 200% of the diameter of the second metal tip 32 ′. If the diameter of the second metal tip 32 ′ is less than 0.2 mm, the formed noble metal wear resistant part 32 is quickly consumed by sparks at a high temperature, and a sufficient life cannot be secured. On the other hand, if the diameter of the second metal tip 32 ′ exceeds 2 mm, the thermal stress acting on the bonding interface becomes too large, and it becomes impossible to ensure sufficient peel resistance. Further, when the diameter of the first metal tip 33 ′ is less than 104% of the diameter of the second metal tip 32 ′, the structure in which the relaxation metal portion 33 is sufficiently wound around the side peripheral surface 32 s of the noble metal wear resistant portion 32. It cannot be realized. On the other hand, when it exceeds 200%, the stress relaxation effect by the obtained relaxation metal part 33 is saturated, and an unnecessary cost increase is caused. Considering these, the diameter of the first metal tip 33 ′ is set to 0.3 to 2.5 mm.
[0029]
Further, the thickness of the second metal tip 32 ′ is preferably 0.1 to 1.0 mm, and the thickness of the first metal tip 33 ′ is 20 to 300% of the thickness of the second metal tip 32 ′. It is good to do. If the thickness of the second metal tip 32 ′ is less than 0.1 mm, the thickness of the obtained noble metal wear resistant part 32 is insufficient, and a sufficient life cannot be secured. Further, since the mechanical rigidity is insufficient, deformation of the noble metal wear resistant portion 32 due to thermal stress is likely to occur. If the thickness of the second metal tip 32 'exceeds 1.0 mm, the amount of burying in the electrode base material 4m at the time of resistance welding becomes too large, and the deformation of the electrode base material 4m becomes serious. On the other hand, when the thickness of the first metal tip 33 ′ is less than 20% of the thickness of the second metal tip 32 ′, the thickness of the obtained relief metal portion 33 becomes too thin and the stress relaxation function becomes insufficient. . On the other hand, if it exceeds 300%, the stress relaxation effect by the obtained relaxation metal part 33 is saturated, and an unnecessary cost increase is caused.
[0030]
Further, as shown in FIG. 4D, when the width of the side surface 4c of the ground electrode 4 is W and the diameter of the first chip 33 ′ is d1, the dimensional difference L = W−d1 is ensured to be 0.1 mm or more. It is desirable that When L is less than 0.1 mm, it is difficult to sufficiently bury the first tip 33 ′ in the electrode base material 4 m during resistance welding.
[0031]
As shown in FIG. 2C, when both the noble metal wear resistant portion 32 and the relaxed metal portion 33 are configured to have a crystal structure that is stretched in a fiber shape in the facing direction O, FIG. As shown in (c), the progress of the crack toward the bottom surface 32b side of the noble metal wear resistant portion 32 becomes more difficult to proceed, and the peel resistance can be further improved. In order to make the structure like this, the alloy is processed into a linear or rod-shaped material by one or a combination of two or more of hot forging, hot rolling and hot wire drawing, and then the alloy is long. It is effective to form the noble metal wear resistant portion 32 and the relaxed metal portion 33 by using chips (first chip 33 ′ and second chip 32 ′ described later) formed by cutting to a predetermined length in the vertical direction. In addition, the crystal structure stretched in a fibrous form means that the average aspect ratio (FIG. 2 (d): W1 / W2) of crystal grains observed in a cross section parallel to the structure stretching direction is 5 or more. Say what you are.
[0032]
When the disk-shaped first metal tip 33 ′ and second metal tip 32 ′ are used, as shown in FIG. The joining end face 32b can be formed flat, and the joining end face (bottom face) 33b of the relaxing metal portion 33 to the electrode base material 4m can be formed in a convex curved shape with the center portion protruding from the outer edge portion. In this way, the bonding area is increased, the bonding strength of the noble metal wear resistant portion 32 is increased, and the thickness of the relaxation metal portion 33 is increased at the central portion of the bonding end surface 33b, so that the stress relaxation effect at the central portion is achieved. The crack growth to the central part of the joining end face 33b can be suppressed. As a result, the peel resistance of the noble metal wear resistant portion 32 can be further improved. In order to obtain the structure as described above, the ratio t1 / t2 between the thickness t1 of the first chip 33 ′ to be used and the thickness t2 of the second chip 32 ′ is set to 0.5 to 2.0. It is effective.
[0033]
Furthermore, as shown in FIG.7 (d), the side peripheral surface 33s of the relaxation metal part 33 can also be formed in the convex type by which the center part in the opposing direction O bulges in a radial direction rather than both ends. In this way, the convex side peripheral surface 33s of the relaxation metal part 33 engages with the corresponding hole inner side surface 4s on the electrode base material 4m side formed in a concave shape, and the relaxation metal part 33 falls off. It becomes difficult. In order to form such a relaxed metal portion 33, as shown in FIG. 7A, a spherical first tip 133 is used, and this is bitten into the electrode base material 4m while being crushed by heat compression during resistance welding. That's fine. In this embodiment, as shown in FIG. 7B, the spherical first tip 133 has an electrode base material 4m in a form in which the upper surface is flattened corresponding to the tip surface of the electrode during resistance welding. As shown in FIG. 7 (c), the disk-shaped second tip 32 'is overlapped thereon and resistance-welded in the same manner as in FIG. 4, as shown in FIG. 7 (c). The noble metal wear resistant portion 32 is formed. According to this, the joining end face 32b of the noble metal wear resistant part 32 to the relaxation metal part 33 can be formed flat, while the joining end face (bottom face) 33b of the relaxation metal part 33 to the electrode base material 4m is the same as in FIG. Further, it can be formed in a convex curved shape in which the central portion protrudes from the outer edge portion.
[0034]
In addition, as shown in FIG. 8, it can also join to the one relaxation metal part 33 in the form which disperse | distributes several noble metal wear-resistant parts 32. FIG.
[0035]
【Example】
In order to confirm the effect of the present invention, the following experiment was conducted.
Example 1
The first chip and the second chip for forming the relaxed metal layer and the noble metal wear resistant part on the ground electrode side were produced as follows. First, a second chip for a noble metal wear resistant part was prepared by mixing and dissolving a predetermined amount of Ir and Rh to produce an alloy having a composition of Ir-40% by mass Rh. This alloy was hot forged at 1500 ° C., then hot rolled and hot swaged at 1300 ° C., and further hot drawn at 1200 ° C. to obtain an alloy wire having a diameter of 1 mm. This was cut in the longitudinal direction to obtain a disk-shaped chip having a diameter of 1 mm and a thickness of 0.2 mm. Moreover, the 1st chip | tip for relaxation | moderation metal layers produced Ir-Ni alloy which has various Ni content shown in Table 1 by mix | blending and melt | dissolving Ir and Ni in various ratios. And it was set as the disk-shaped chip | tip of diameter 1.2mm and thickness 0.2mm by the method similar to a 2nd chip | tip. Using these tips, resistance welding was performed on the side surface (width 2.5 mm) of the ground electrode base material made of Inconel 600 by the method shown in FIG. 4 to complete the ground electrode side joint structure shown in FIG. . The resistance welding conditions were as follows: energization current value 650A, pressure load 35 kg / cm ² Set to.
[0036]
On the other hand, for the center electrode 3 side, a noble metal tip having a composition of Ir-5 mass% Pt and a diameter of 0.6 mm and a thickness of 0.8 mm was produced by the same method as the second tip, and Inconel It joined by carrying out the laser welding of the perimeter to the front end surface of 600 center electrode base materials. Then, a spark plug test product of the form shown in FIG. 1 is prepared using these ground electrode and center electrode (however, the gap interval is 1.1 mm), and the peel resistance and lead corrosion resistance of the noble metal wear resistant part on the ground electrode side Sexuality was evaluated.
[0037]
First, evaluation of peeling resistance is as follows. First, a cycle in which the tip of the spark plug on the spark discharge gap side is heated to 1000 ° C. for 2 minutes by a gas burner and then air-cooled for 1 minute is repeated 1000 times. Next, the test article is cut and polished on the surface passing through the central axis of the noble metal wear resistant portion of the ground electrode and magnified and observed with a microscope, and a crack at the interface between the noble metal wear resistant portion and the relaxation metal layer portion or The progress length of the oxide scale is measured in the observation field, and the value divided by the total length of the interface is calculated as the peeling progress rate. And the thing whose peeling progress rate exceeded 50% is evaluated as bad (x), and the thing below 50% is evaluated as favorable ((circle)).
[0038]
On the other hand, lead corrosion resistance was evaluated as follows. That is, each spark plug is attached to a 6-cylinder gasoline engine (displacement 2000 cc), fueled with leaded gasoline containing 0.04% by mass of 4-methyllead, and the center electrode at a throttle fully opened state at an engine speed of 5000 rpm. The operation was carried out for 100 hours with a negative polarity. After the operation is completed, the test product is cut and polished on the surface passing through the central axis of the noble metal wear-resistant part of the ground electrode and the relaxation metal layer, and magnified and observed with a microscope. A case where the surrounding ratio of the surrounding portion is 80% or more is evaluated as excellent (◎), a case where it is 60% or more and less than 80% is evaluated as good (◯), and a case where it is less than 60% is evaluated as bad (×). The results are shown in Table 1.
[0039]
[Table 1]

According to this, in the case of a relaxed metal part made of an Ir—Ni alloy, it can be seen that both the peel resistance and lead corrosion resistance are good when the Ni content is in the range of 20 to 70 mass%.
[0040]
(Example 2)
A spark similar to that of Example 1 except that the second tip for the noble metal wear resistant portion has a composition of Ir-40% by mass Rh and the first tip for the relaxed metal layer is made of various ratios of Rh-Ni alloys. A plug test product was produced and evaluated in the same manner. The results are shown in Table 2.
[0041]
[Table 2]

According to this, in the case of a relaxed metal part made of an Rh—Ni alloy, both the peel resistance and lead corrosion resistance are good when the Ni content is in the range of 70 mass% or less (including 100 mass% Rh). I understand that.
[0042]
(Example 3)
The same spark as in Example 1 except that the second tip for the noble metal wear resistant portion is made of various proportions of Ir—Pt alloy and the first tip for the relaxed metal layer has a composition of Ir-40 mass% Ni. A plug test product was produced and evaluated in the same manner. However, the evaluation of lead corrosion resistance is excellent when the residual ratio of the precious metal wear-resistant part is 80% or more (◎), good when it is 60% or more and less than 80% (○), and poor if it is less than 60%. Evaluate as (x). The results are shown in Table 3.
[0043]
[Table 3]

According to this, in the case of a noble metal wear resistant part made of an Ir—Pt alloy, it can be seen that both the peel resistance and the lead corrosion resistance are good when the Pt amount is in the range of 3 to 20% by mass.
[0044]
(Example 4)
The same spark as in Example 1 except that the second tip for the noble metal wear resistant portion is made of various ratios of Ir—Rh alloy and the first tip for the relaxed metal layer has a composition of Ir-40 mass% Ni. A plug test product was produced and evaluated in the same manner. However, the evaluation of lead corrosion resistance is excellent when the residual ratio of the precious metal wear-resistant part is 80% or more (◎), good when it is 60% or more and less than 80% (○), and poor if it is less than 60%. Evaluate as (x). The results are shown in Table 4.
[0045]
[Table 4]

According to this, in the case of a noble metal wear resistant part made of an Ir—Rh alloy, it can be seen that both the peel resistance and the lead corrosion resistance are good when the Rh amount is 10% by mass or more.
[0046]
(Example 5)
The second tip for the noble metal wear resistant part was made of an Ir-40 mass% Rh alloy, and the first tip for the relaxed metal layer was produced in the same manner as in Example 1 with a composition of Ir-40 mass% Ni. Here, the dimensions of the first chip were fixed at a diameter d1 of 1.2 mm and a thickness of 0.2 mm, while the second chip was fixed at a thickness of 0.2 mm and a diameter d2 of 0.9 to 1.18 mm. It was formed in various dimensions. Using these chips, a spark plug test product similar to that in Example 1 was produced, and the peel resistance was evaluated in the same manner as in Example 1. The results are shown in Table 5.
[0047]
[Table 5]

According to this, it can be seen that d1 / d2 is 104% or more and that the peel resistance is good.
[0048]
(Example 6)
The second tip for the noble metal wear resistant part was made of an Ir-40 mass% Rh alloy, and the first tip for the relaxed metal layer was produced in the same manner as in Example 1 with a composition of Ir-40 mass% Ni. Here, the ratio d1 / d2 between the diameter d1 of the first chip and the diameter d2 of the second chip is fixed to 120% (both have a thickness of 0.2 mm), and the diameter d2 of the second chip is 0.2 to Various dimensions of 1.5 mm were set. Using these chips, a spark plug test product similar to that in Example 1 was produced, and a spark consumption test was performed under the following conditions. That is, the plug is attached to a test chamber and connected to a full transistor igniter, and an AC voltage of 100 Hz is applied for 100 hours at a chamber internal air pressure of 0.4 MPa (about 4 atm) and a maximum voltage of 30 kV. The cross-sectional observation is performed, and the case where the thickness of the noble metal wear resistant part remains 70% or more is evaluated as good (◯), and the case where it is less than 70% is evaluated as defective (×). The results are shown in Table 6.
[0049]
[Table 6]

[0050]
According to this, it is understood that the wear resistance is good when d2 is 0.3 mm or more.
[0051]
(Example 7)
The second tip for the noble metal wear resistant part was made of an Ir-40 mass% Rh alloy, and the first tip for the relaxed metal layer was produced in the same manner as in Example 1 with a composition of Ir-40 mass% Ni. Here, the diameter d1 of the first chip was set so that the value of L = W−d1 could be various values from 0 to 0.4 mm with reference to the width W (2.5 mm) of the ground electrode. These tips were welded to the ground electrode in the same manner as in Example 1, and by observation of the same cross section after welding, those in which 90% or more of the tip thickness was buried were good (◯), and less than 90%. Are evaluated as defective (×). The results are shown in Table 7.
[0052]
[Table 7]

[0053]
According to this, it can be seen that the weldability is good when the value of L = W−d1 is 0.1 mm or more.
[Brief description of the drawings]
FIG. 1 is a partial front sectional view showing an embodiment of a spark plug according to the present invention.
FIG. 2 is an enlarged sectional view showing the main part.
FIG. 3 is a view showing a desirable composition range of a relaxed metal part.
FIG. 4 is a diagram illustrating an example of a process for forming a noble metal wear resistant part on the ground electrode side.
FIG. 5 is a cross-sectional view showing a first modification of the relaxation metal portion.
FIG. 6 is a view showing the operation of the spark plug of the present invention together with a comparative example.
FIG. 7 is a cross-sectional view showing a second modification of the relaxation metal portion.
FIG. 8 is a perspective view showing a deformation mode of the noble metal wear resistant part.
[Explanation of symbols]
3 Center electrode
4 Ground electrode
4c side
4m electrode base material
31a Tip surface
32 Noble metal wear resistant part
32b Joint end face
32s side surface
32 'second metal tip
33 Relaxation metal part
33p Outer peripheral edge
33s side peripheral surface
33 '1st metal tip
g Spark discharge gap

Claims

A spark plug (a spark discharge gap (g) is formed by causing the noble metal wear resistant part (32) fixed to the side surface (4c) of the ground electrode (4) to face the tip surface (31a) of the center electrode (3). 100)
At least a side surface portion of the ground electrode (4) is an electrode base material (4m) made of a nickel alloy,
The noble metal wear-resistant part (32) contains one or both of Ir and Rh in a total of 80% by mass or more, and the Ir content is 97% by mass or less, and is obtained from Pt, Rh, Ru, and Re. It is configured in a disc shape with a metal having a content of 1 type or 2 types or more selected of 3% by mass or more, and is intermediate between the electrode base material (4m) and the noble metal wear resistant part (32). It is joined to the electrode base material (4m) via a relaxation metal part (33) made of a metal having a linear expansion coefficient,
The relaxed metal portion (33) is a metal in which Rh and Ni are essential , the total of Ir and Rh is 30% by mass or more, and the total of Rh and Ni is 20% by mass or more. In addition,
When viewed from the reference direction (O) between the noble metal wear resistant part and the center electrode, the relaxation metal part (33) has at least a part of the side peripheral surface (33s) formed on the electrode base material (4m). The outer peripheral edge portion (33p) on the opposite side of the relaxed metal portion (33) to the center electrode (3) is joined to the ground electrode while being bonded to the electrode base material (4m) so as to be buried in In the form exposed on the side surface (4c) of (4), the noble metal wear resistant portion (32) is configured to bury at least a part of the side peripheral surface (32s) in the relaxed metal portion (33). A spark plug (100), wherein the spark plug (100) is joined to the relaxation metal portion (33).

The electrode base material (4 m) is a Ni alloy having a Ni content of 60% by mass or more, and the balance other than Ni mainly composed of Cr or Cr and Fe,
The relaxed metal part (33) has a total content of Ir, Rh and Ni of 90% by mass or more, and Ir, Rh and Ni when the total of Ir, Rh and Ni is converted to 100% by mass. On the Ir-Ni-Rh ternary composition equilateral triangle shown in FIG.
Point A: (Ir = 80 mass%, Ni = 20 mass%, Rh = 0 mass%)
Point B: (Ir = 80 mass%, Ni = 0 mass%, Rh = 20 mass%)
C point: (Ir = 0 mass%, Ni = 0 mass%, Rh = 100 mass%)
Point D: (Ir = 0% by mass, Ni = 70% by mass, Rh = 30% by mass)
E point: (Ir = 30 mass%, Ni = 70 mass%, Rh = 0 mass%)
The spark plug (100) according to claim 1, wherein the spark plug (100) is set within a closed composition region obtained by sequentially connecting the points (including a boundary , except for a portion of Rh = 0 mass% and Ni = 0 mass% ). ).

The spark plug (100) according to claim 1 or 2, wherein the noble metal wear resistant part (32) and the relaxation metal part (33) have a crystal structure extended in a fiber shape in the facing direction (O). .

The spark plug (100) according to any one of claims 1 to 3, wherein an entire surface of the side peripheral surface (32s) of the noble metal wear resistant part (32) is buried in the relaxation metal part (33).

In the facing direction (O), a joining end surface (32b) of the noble metal wear resistant part (32) to the relaxation metal part (33) is formed flat, while the electrode mother of the relaxation metal part (33) is formed. The spark plug (100) according to any one of claims 1 to 4, wherein a joining end surface (33b) to the material (4m) is formed in a convex curved shape in which a central portion protrudes from an outer edge portion.

The side peripheral surface (33s) of the relaxation metal portion (33) is formed in a convex shape in which a central portion in the facing direction (O) bulges in a radial direction from both end portions. A spark plug (100) according to claim 1.

A method for manufacturing a spark plug (100) according to any of claims 1 to 6,
The first metal tip (33 ') for forming the relaxed metal portion (33) is superposed on the side surface (4c) of the ground electrode (4) and heated while being energized to thereby heat the first metal tip. A first joining step of joining (33 ′) to the electrode base material (4 m);
The diameter of the first metal tip (33 ′) for forming the relaxed metal portion (33) is smaller than that of the first metal tip (33 ′) for forming the noble metal wear resistant portion (32). A second joining step of joining the first metal tip (33 ′) to the second metal tip (32 ′) by applying and heating the second metal tip (32 ′) while being superposed and pressurized.
A method for manufacturing a spark plug, comprising:

The first metal tip (33 ′) and the second metal tip (32 ′) have a disk shape that is overlapped in the thickness direction, and the diameter of the first metal tip (33 ′) is 0.3. -2.5 mm, the diameter of the second metal tip (32 ') is 0.2-2 mm, and the diameter of the first metal tip (33') is the second metal tip (32 '). The method for manufacturing a spark plug according to claim 7, wherein the spark plug is set to 104 to 200% of the diameter of the spark plug.

The thickness of the second metal tip (32 ′) is 0.1 to 1.0 mm, and the thickness of the first metal tip (33 ′) is 20 times the thickness of the second metal tip (32 ′). The method for producing a spark plug according to claim 8, which is ˜300%.

The width of the side surface (4c) of the ground electrode (4) is W, and the diameter of the first tip (33 ') is d1, and W-d1 is secured to 0.1 mm or more. A method for producing the spark plug according to claim 1.