JP4294332B2

JP4294332B2 - Spark plug

Info

Publication number: JP4294332B2
Application number: JP2003019921A
Authority: JP
Inventors: 健一熊谷; 誠山口; 宏昭九鬼
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2002-02-27
Filing date: 2003-01-29
Publication date: 2009-07-08
Anticipated expiration: 2023-01-29
Also published as: JP2003323962A

Description

【０００１】
【発明の属する技術分野】
この発明は、内燃機関の点火用に使用されるスパークプラグに関する。
【０００２】
【従来の技術】
近年、自動車エンジン等の内燃機関の性能改良、あるいはは排ガス規制の強化や燃焼効率向上を目的としてエンジンのリーンバーン化に伴い、その着火に使用されるスパークプラグの電極温度も上昇する傾向にある。特に、接地電極は中心電極よりも燃焼室内側に位置するため温度上昇が激しく、特に直噴型エンジンなどに使用されるスパークプラグは、接地電極の温度上昇が特に生じやすい。上記のような過酷な条件下においては、電極の火花消耗も進みやすくなるので、火花放電ギャップの拡大率を抑制するために、接地電極の火花放電ギャップに面する部位に貴金属チップを溶接したスパークプラグが普及している。
【０００３】
接地電極の温度が上昇した場合、貴金属チップが溶接される電極母材の高温酸化が問題となる。従来、接地電極の母材は、高温耐酸化性を確保するために例えばインコネル６００（インコネルは、英国Ｉｎｃｏ社の商標名）等のＮｉ基耐熱合金で構成されることが多い。しかし、Ｎｉ基耐熱合金の熱伝導率は一般にそれほど高くないので、いわゆる熱引きが悪く、高速運転時等においては電極温度が特に上昇しやすい難点がある。熱引きが悪化して電極温度が上昇すると、電極母材に接合した金属チップの温度も上昇し、異常消耗による寿命低下の原因となる。そこで、熱引き改善を促進するために、Ｃｕ系金属からなる芯材（Ｃｕ系伝熱促進部）を電極母材中に配置して、電極の温度上昇を抑制する方法が提案されている（例えば特許文献１、特許文献２）。
【０００４】
【特許文献１】
特開平５−１５９８５７号公報
【特許文献２】
特公平６−４８６２９号公報
【０００５】
【発明が解決しようとする課題】
しかしながら、燃焼温度がさらに上昇し、前記した直噴エンジンなどのように、発火部が燃焼室の中心にさらに近づくと、接地電極の温度上昇がさらに著しくなる。その結果、インコネル６００程度の合金性能では電極母材の高温酸化を抑えきれなくなる問題が生ずる。この場合、電極母材の材質を、より高温耐酸化性の優れたものに置換することが考えられる。例えば、従来使用されていたインコネル６００に代え、Ｃｒ及びＦｅの含有量を増加させることにより、高温耐酸化性を向上させたインコネル６０１を用いる提案もなされている。しかしながら、この材質置換は、Ｃｕ系伝熱促進部の埋設を選定とする場合、大きな障害が存在する。
【０００６】
すなわち、Ｃｕ系伝熱促進部を有する電極は、電極母材となるＮｉ合金素材中にＣｕ系伝熱促進部となるＣｕ素材を組み付けて組立体を作り、この組立体を引き抜きや鍛造、あるいは圧延により冷間加工してクラッド線材を作ることにより製造される。ところが、インコネル６０１等のＣｒ含有率を高めたニッケル基耐熱合金は、高合金化により強度向上を図った金属材料の常として、インコネル６００等と比較して変形抵抗が高く、延性も低い。従って、上記のような加工によりＣｕ系伝熱促進部とのクラッド線材を製造しようとすると、割れ等のトラブルが発生しやすく、製造歩留まりの大幅な低下を来たす問題がある。また、Ｎｉを主体とする電極母材にＣｕ系伝熱促進部を有するスパークプラグをエンジンで使用すると、電極母材とＣｕ系伝熱促進部との間で成分拡散をさせた拡散層が形成される。そして、両者の熱膨張差に起因する繰返し荷重を受けることによって、この拡散層から剥離を生じることがある。この結果、電極母材からＣｕ系伝熱促進部に対して、熱伝導が十分に行われなくなる可能性がある。他方、Ｃｕ系伝熱促進部を省略すると、電極母材の高温酸化は抑制できても、貴金属チップの温度上昇は抑制できないので、異常消耗の問題は解決できない。
【０００７】
本発明の課題は、接地電極の電極母材に十分な高温耐酸化性を付与でき、また、Ｃｕ系伝熱促進部を埋設した構造を冷間加工により問題なく製造でき、ひいては電極母材に接合された貴金属チップの異常消耗を防止できるスパークプラグを提供することにある。
【０００８】
【課題を解決するための手段及び作用・効果】
上記の課題を解決するために、本発明のスパークプラグは、筒状の主体金具と、その主体金具の内側に嵌め込まれた絶縁体と、該絶縁体の内側に設けられた中心電極と、主体金具に一端が溶接等により結合されるとともに他端側において中心電極との間に火花放電ギャップを形成する接地電極とを備え、接地電極が、電極母材と、該電極母材中に埋設されるとともにＣｕを主成分として構成されるＣｕ系伝熱促進部と、火花放電ギャップに面する位置において電極母材に溶接された貴金属チップとを有し、さらに、電極母材が、Ｃｒを１４〜１７質量％、Ｍｏを０．８〜３．５質量％、Ｎｉを６８〜８５．２質量％含有するＮｉ合金からなることを特徴とする。なお、本明細書において「主成分」とは、最も質量含有率の高い成分のことをいう。
【０００９】
上記本発明のスパークプラグによると、接地電極をなす電極母材にＣｕ系伝熱促進部が埋設されることにより、その熱引きが促進され温度上昇が抑制される結果、接地電極の寿命向上を図ることができる。また、電極母材に溶接された貴金属チップの温度上昇も抑制されるので、異常消耗が防止され、耐久性を確保することができる。そして、本発明においては、電極母材を構成するＮｉ合金として、上記特有の組成を有するものを採用する。これにより、従来問題の多かったインコネル６０１等を採用する場合と比較して、以下の利点がある。まず、本発明のように、Ｃを含有するＮｉ合金を採用する場合、Ｃｒとともに一定量のＭｏを含有させることで、合金の高温耐酸化性を著しく向上させることができる。従って、Ｃｕ系伝熱促進部の採用と相俟って、より過酷な条件下でスパークプラグを使用する場合においても、接地電極の耐久性を十分に確保でき、寿命向上を図ることができる。
【００１０】
この場合、特にＣが含有されるＮｉ合金については、Ｍｏ添加による高温耐食性改善効果が高い。該Ｃは不純物として含有される場合と、炭化物形成による析出強化を図るため、積極添加される場合（いわゆる弱析出型合金）との両方があり、０．３質量％以下に調整される。特に後者の場合、Ｃ含有量は例えば０．０３〜０．３質量％の範囲で調整される。しかし、過度の添加は多量の炭化物形成により冷間加工性を低下させるため、０．１０質量％以下とすることが望ましい。いずれにしろ、含有されるＣは、Ｍｏが添加されない場合は、主にＣｒとの間で炭化物を形成する。このようなＣｒ炭化物が多量に形成されると、耐酸化性付与元素であるＣｒ成分が炭化物析出の形で目減りし、不働態酸化被膜の形成が不十分となって耐酸化性の低下につながる。特にＣｒ炭化物が粒界に形成されると、粒界付近にＣｒ欠乏層が形成され、局部電池効果なども加わって粒界腐食が進みやすくなり、電極母材の耐久性に一層の悪影響を及ぼす。
【００１１】
しかしながら、適量のＭｏを添加すると、Ｍｏ炭化物が優先的に形成されてＣｒ炭化物の析出が抑制され、不働態酸化被膜形成に寄与する有効Ｃｒ含有量を増加させることができる。その結果、同じＣｒ含有量であっても、より強固な不働態酸化被膜を形成可能となり、高温耐食性の向上に寄与する。また、Ｍｏ炭化物は一般に粒界析出を起こしにくいためＣｒ欠乏層も生じにくく、粒界腐食抑制という観点においても有利に作用する。
【００１２】
その結果、Ｍｏ添加による上記効果に基づき、Ｃｒ含有量を比較的低い１４〜１７質量％に設定しても、より高Ｃｒ組成を有するインコネル６０１等と同等又はそれ以上の高温耐食性が実現できる。従って、Ｃｒ含有量が減じられた分だけ冷間加工性が改善されるので、接地電極の素材となる、Ｃｕ系伝熱促進部を埋設したクラッド材の加工も問題なく行なうことができるようになる。
【００１３】
また、Ｍｏ添加によって、エンジンで長時間使用されても、電極母材とＣｕ系伝熱促進部との境界に形成される拡散層の厚みの増大を抑えることができるため、この拡散層における剥離を防止することができる。この剥離の発生は、この拡散層の主成分であるＣｕとＮｉとの合金の特徴である低延性が影響しているものと推察される。
【００１４】
電極母材をなすＮｉ合金のＣｒ含有量が１４質量％未満になると、電極母材の高温耐酸化性が不足することにつながり、電極寿命が低下する問題を生ずる。他方、１７質量％を超えると加工性が悪化し、接地電極素材となる、Ｃｕ系伝熱促進部を埋設したクラッド材を製造する際に、割れ等の発生を招きやすくなる。
【００１５】
また、Ｍｏの含有量が０．８質量％未満では、Ｍｏ添加による高温耐酸化性改善効果及び長時間使用時の拡散層における剥離防止効果が乏しくなる。また、３．５質量％を超えると合金の硬さが増して変形抵抗が増大し、加工性を悪化させることにつながる。さらに、Ｎｉの含有量が６８質量％未満では、副成分の含有量が高くなりすぎ、加工性の低下等を招きやすくなる。
他方、Ｎｉの含有量が８５．２質量％を超えると、Ｃｒ及びＭｏの必要な含有量を確保できなくなり、高温耐酸化性が悪化することにつながる。
【００１６】
電極母材をなすＮｉ合金は、接地電極を主体金具に溶接接合する際に、その溶接性ひいては溶接接合強度を確保する観点から、Ａｌの含有率を１質量％未満とするのがよい。Ａｌの含有率が１質量％以上になると、酸化アルミニウムの生成が過剰となり、溶接性ないし溶接接合強度が損なわれる場合がある。他方、高温耐酸化性を向上させる目的にて、Ａｌを上記範囲にて積極添加することも可能である。
【００１７】
電極母材をなすＮｉ合金には、Ｆｅを添加することができる。ＦｅはＮｉ基のマトリックスに固溶してこれを強化し、高温強度を向上させる働きをなす。該Ｆｅの含有量は、６〜１０質量％の範囲で調整するのがよい。Ｆｅの含有量が６質量％未満では高温強度向上効果に乏しく、１０質量％を超えると高温耐酸化性が十分に確保できなくなる場合がある。
【００１８】
【発明の実施の形態】
以下、本発明の実施の形態を、図面を用いて説明する。図１は本発明の一例たるスパークプラグ１００の縦断面図を示すものであり、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、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において中心電極３との間に火花放電ギャップｇを形成する接地電極４を備えている。本実施形態のスパークプラグ１００は、いわゆる平行電極型と称されるもので、接地電極４の先端側が側方に曲げ返され、その側面と主体金具１の先端面との間に火花放電ギャップｇが形成されている。また、接地電極４及び中心電極３の、火花放電ギャップｇに面する位置には、それぞれＰｔ合金あるいはＩｒ合金よりなる貴金属チップ３１，３２が溶接されている。
【００１９】
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及び端子金具８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。
【００２０】
図２に示すように、接地電極４は、外表面部をなす電極母材４ａと、該電極母材４ａ中に埋設されるＣｕ系伝熱促進部４ｃとを有する。電極母材４ａは、Ｃｒを１４〜１７質量％、Ｍｏを０．８〜３．５質量％、Ｎｉを６８〜８５．２質量％含有するＮｉ合金からなる。また、Ｃｕ系伝熱促進部４ｃは純Ｃｕ又はＣｕ合金にて構成される。本実施例においてＣｕ系伝熱促進部４ｃは、接地電極４の長手方向に配置されている。Ｃｕ系伝熱促進部４ｃは先細り形態とされ、かつその先端は火花放電ギャップｇの位置から外れるように位置設定がなされている。これは、火花放電ギャップｇの位置する接地電極４の先端部は特に昇温が激しく、この部分にＣｕ系伝熱促進部４ｃが入り込んでいると、電極母材４ａとの間の線膨張係数差に基づいて電極の膨らみや層間剥離といった不具合を生じる場合があるためである。
【００２１】
なお、本実施形態においては、中心電極３も、電極母材３ａとこれに埋設されたＣｕ系伝熱促進部３ｃを有するものとして構成している。上記電極母材３ａも接地電極４側と同じＮｉ合金にて構成可能であるが、接地電極４よりは温度上昇しにくいことから、接地電極４側の電極母材４ａよりはＭｏ含有量を低く（あるいはＭｏを含有しないもの）、Ｃｒ含有量は電極母材４ａと同等もしくはそれ以下の含有量となるものを使用することもできる。
【００２２】
図４は、接地電極４の製造方法の一例を示すものである。すなわち、図４（ａ）に示すように、電極母材４ａの構成素材となるＮｉ合金により、空隙１０４ｈを有したＮｉ系成形体１０４ａを切削あるいは深絞り等の塑性加工により作製する。他方、Ｃｕ系伝熱促進部４の構成素材となる純Ｃｕ（たとえば無酸素銅素材）又はＣｕ合金により、前記空隙１０４ａに対応する形状のＣｕ系成形体１０４ｃを作製する。そして、このＣｕ系成形体１０４ｃをＮｉ系成形体１０４ａの空隙１０４ｈに嵌め入れて、図４（ｂ）の組立体１０４を作製する。
【００２３】
次いで、図４（ｃ）に示すように、該組立体１０４に対し、室温にてダイス引き抜き、鍛造、あるいは圧延を施すことにより減面・延伸してクラッド線材４’を作る。これによりＣｕ系成形体１０４ｃはＣｕ系伝熱促進部４ｃとなり、Ｎｉ系成形体１０４ａは電極母材４ａとなる。該クラッド線材４’のＣｕ系伝熱促進部４ｃの露出端側を主体金具１（図２）の端面に溶接し、曲げ加工を施すことにより、接地電極４が完成する。
【００２４】
Ｎｉ系成形体１０４ａをなすＮｉ合金は、前述のようにＣｒ含有量が減じられているので加工性が良好であり、室温での冷間加工、もしくは９００℃以下に昇温して行なうことにより、割れ等の不具合を生ずることなくクラッド材４’を問題なく得ることができる。そして、Ｃｒ含有量が減じられる代わりに、前記範囲内のＭｏが含有されていることから、Ｃｒ含有量の高いインコネル６０１等のＮｉ基耐熱合金と比較しても高温耐食性において遜色なくなり、接地電極の寿命を大幅に伸ばすことができる。また、Ｃｕ系伝熱促進部４ｃの配置が容易となり、さらに、エンジンでの長時間使用されても拡散層における剥離が発生しないので、貴金属チップ３２の温度上昇ひいては異常消耗が抑制され、耐久性を確保することができる。
【００２５】
なお、接地電極４を冷間加工で製造する場合、図４（ｄ）に示すように、その電極母材４ａには、結晶粒が電極長手方向に延伸した組織が観察される。なお、クラッド線材４’を加工上がりの状態から焼鈍を行なうと、Ｃｕ系伝熱促進部４ｃとＮｉ合金からなる電極母材４ａとの間で成分拡散が生じ、両者の結合力を向上させることができる。この焼鈍は、加工後に行っても、加工前に行ってもいずれでもよいが、加工後に行う焼鈍の温度が高い場合、図４（ｄ）に示す結晶粒の延伸した組織が、結晶粒成長した組織に変化することがある。
【００２６】
なお、図３に示すように、Ｃｕ系伝熱促進部４ｃのさらに内側に、純Ｎｉ又はＮｉ合金からなるＮｉ系膨張調整層４ｄを配置してもよい。Ｎｉ合金からなる電極母材４ａとＣｕ系伝熱促進部４ｃとは線膨張係数差が大きく、特に過酷な冷熱サイクルが加わると電極膨らみや層間剥離等を起こしやすくなる懸念がある。しかしながら、上記のようなＮｉ系膨張調整層４ｄを形成することにより、Ｃｕ系伝熱促進部４ｃの厚みを減ずるとともに、Ｃｕ系伝熱促進部４ｃをＮｉ系金属により挟み込む形とすることにより、上記不具合を生じにくくすることができる。
【００２７】
【実施例】
本発明の効果を確認するために、以下の実験を行った。
図１に示すスパークプラグ１００の種々の試作品を製造した。接地電極４は、図４の方法により製造した。すなわち、表１に示す種々の組成のＮｉ合金を電極母材用素材として準備し、電極母材４ａとなるＮｉ系成形体１０４ａを、外径４．５ｍｍ、長さ５．４ｍｍの寸法にて作製した。また、Ｃｕ系伝熱促進部４ｃとなるＣｕ系成形体１０４ｃを、無酸素銅を素材として、基端部外径２．９ｍｍ、長さ５ｍｍにて作製した。そして、これをＮｉ系成形体１０４ａに形成した空隙１０４ｈにはめ込み、組立体１０４とした。この組立体１０４を、１パス当たりの減面率が５５％となるように冷間押出加工して、断面が縦１．５ｍｍ、横２．８ｍｍの長方形状であって、長さが１９ｍｍの線材を得た。なお、比較のため、番号１の組成の接地電極については、Ｃｕ系伝熱促進部４ｃを省略したものも作製した（番号１３）。
【００２８】
上記の各接地電極は、加工性評価を以下の基準にて行った。
良（○）：電極母材４ａとＣｕ系伝熱促進部４ｃとの間にクラックや剥離などが見られず、問題なく冷間加工できたもの。
可（△）：電極母材４ａとＣｕ系伝熱促進部４ｃとの間にクラックないし剥離が見られたが、組立体を９３０℃で１時間焼鈍してから冷間加工を行なうと、不具合が解消されたもの。
不可（×）：組立体を９３０℃で１時間焼鈍しても、不具合が解消されなかったもの（不具合のない接地電極を、別途、温度７３０℃での温間押出加工により得ている）。
【００２９】
また、得られた接地電極の高温疲労試験を以下の条件にて行っている。すなわち、試験機は軸荷重疲労試験を用い、温度を６００℃に、応力振幅条件を±９００Ｎの引張り／圧縮に、繰返し速度を１０Ｈｚにそれぞれ設定して行った。そして、疲労強度は、ＪＩＳ：Ｚ２２７３に規定された方法に準拠して、試験品数Ｎ＝２とし、疲労寿命を１０^６回に設定したときの時間強度を求め、以下の基準にて評価した（高温折損性の確認）。
良（○）：時間強度が２２０ＭＰａ以上のもの。
可（△）：時間強度が２００ＭＰａ以上２２０ＭＰａ未満のもの。
不可（×）：時間強度が２００ＭＰａ未満のもの。
【００３０】
次に、中心電極３については、電極母材３ａをインコネル６００により、Ｃｕ系伝熱促進部３ｃを無酸素銅により構成する形で、接地電極４と同様の冷間押出加工により、断面が外径２．５ｍｍの円状となり、長さが２４ｍｍとなるように製造した。
【００３１】
そして、接地電極４に対しては、材質がＰｔ−１０質量％Ｎｉ合金であり、直径０．９ｍｍ、厚さ０．４ｍｍの円板状の貴金属チップ３２を抵抗溶接により接合した。また、中心電極３に対しては、材質がＰｔ−１３質量％Ｉｒ合金であり、直径０．８ｍｍ、厚さ０．６ｍｍの円板状の貴金属チップ３２をレーザー溶接により接合した。そして、中心電極３はアルミナ製の絶縁体２に組み付け、その絶縁体２に、接地電極４を溶接した主体金具１を組み付けて該接地電極４に曲げ加工を施すことにより、貴金属チップ３１，３２間に間隔０．９ｍｍの火花放電ギャップｇを形成した。
【００３２】
上述した製造方法により得られた接地電極を用いた各スパークプラグの試験品に対し、以下の試験を行った。なお、下記のエンジンによる試験を行った接地電極には予め、９３０℃で１時間の焼鈍を行い、Ｃｕ系伝熱促進部４ｃと電極母材４ａとの間に拡散層を１０〜２０μｍ形成してある。
スパークプラグを４気筒ガソリンエンジン（排気量２０００ｃｃ）に取り付け、スロットル全開状態、エンジン回転数６０００ｒｐｍにて２５０時間連続運転する実機試験を行った（接地電極側の貴金属チップ３２の推定温度：約１０００℃）。試験後に接地電極４の断面を走査型電子顕微鏡により観察し、形成された酸化スケール層の厚さを測定し、以下の基準にて評価した（接地電極の高温耐酸化性の確認）。
良（○）：酸化スケール層厚さが０．０５ｍｍ未満のもの。
可（△）：酸化スケール層厚さが０．０５ｍｍ以上０．１５ｍｍ未満のもの。
不可（×）：酸化スケール層厚さが０．１５ｍｍ以上のもの。
【００３３】
さらに、試験終了後の接地電極側の貴金属チップの、ギャップ間隔方向の消耗厚さを測定し、以下の基準にて評価した（貴金属チップの耐久性確認）。
良（○）：消耗厚さが０．３ｍｍ未満のもの。
可（△）：消耗厚さが０．３ｍｍ以上０．３５ｍｍ未満のもの。
不可（×）：消耗厚さが０．３５ｍｍ以上のもの。
【００３４】
また、接地電極４と主体金具１との溶接強度を以下のようにして行った。強度試験は、主体金具１と接地電極４（曲げ前）の先端部（先端より５ｍｍの位置）とを把持して接地電極４の軸線方向に引張りを行なう引張試験と、主体金具１を片持ち把持し、接地電極４に対し、金具端面より５ｍｍの位置にて、接地電極４の軸線方向と直交する向きに一定の折り曲げ荷重を、破断が生ずるまで反復付加する折曲試験とを行った。そして、以下の条件にて評価した（溶接性の確認）。
良（○）：引張試験及び折曲試験のいずれにおいても溶接部で破断しない。
可（△）：引張試験のみ溶接部で破断しない。
不可（×）：引張試験及び折曲試験のいずれにおいても溶接部で破断する。
【００３５】
さらに、試験後に接地電極４のＸ線による観察及び断面を走査型電子顕微鏡により観察することにより、拡散層における剥離の発生及び拡散層の厚さを測定し、以下の基準にて評価した（接地電極の伝熱促進部剥離性の確認）。
良（○）：Ｃｕ系伝熱促進部４ｃと電極母材４ａとは剥離しておらず、かつ拡散層の幅が５０μｍ以下のもの。
可（△）：Ｃｕ系伝熱促進部４ｃと電極母材４ａとは剥離していないが、拡散層の幅が５０μｍ以上のもの。
不可（×）：Ｃｕ系伝熱促進部４ｃと電極母材４ａとの間に剥離が発生しているもの。
【００３６】
以上の結果を表１に示す。
【００３７】
【表１】

【００３８】
番号３，４，５，８，９，１０は本発明品のスパークプラグであり、電極母材として、Ｃｒを１４〜１７質量％、Ｍｏを０．８〜３．５質量％、Ｎｉを６８〜８５．２質量％含有するＮｉ合金を用いている。いずれもＣｒの含有量を減少させる代わりに、Ｍｏを上記範囲で添加しているので、Ｃを含有しているにもかかわらず、耐高温酸化性はＣｒの多い番号１の比較例と遜色ない程度に確保できていることがわかる。そして、Ｃｒの含有量が比較的低いので、番号１の比較例よりも電極の加工性が良好であり、Ｃｕ系伝熱促進部の埋設も支障なく行うことができる。該埋設により、熱引きが改善される結果、貴金属チップの耐久性も良好である。また、Ｍｏの添加により高温強度が著しく向上し、耐高温折損性も良好である。さらに、エンジンで長時間使用しても拡散層の厚みの増大を抑えることができ、この拡散層における剥離がない。これに対し、Ｍｏを添加しない番号１の比較例は冷間加工性が悪く、Ｃｕ系伝熱促進部の埋設には面倒な温間加工が必要である。また、耐高温折損性もあまり良好でなく、拡散層における剥離が発生している。そして、番号１２のようにＣｕ系伝熱促進部の埋設を省略すると、高温耐酸化性及び貴金属チップの耐久性が著しく低下する結果を招いている。
【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縦断面図。
【図２】図１のスパークプラグの要部を拡大して示す断面図。
【図３】図１のスパークプラグの変形例を示す要部断面図。
【図４】図１のスパークプラグの接地電極の製造工程説明図。
【図５】図３のスパークプラグの接地電極の製造工程説明図。
【符号の説明】
１主体金具
２絶縁体
２１先端部
３中心電極
３２貴金属チップ
４接地電極
４ａ電極母材
４ｃＣｕ系伝熱促進部
１００スパークプラグ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug used for ignition of an internal combustion engine.
[0002]
[Prior art]
In recent years, with the aim of improving the performance of internal combustion engines such as automobile engines, or the lean burn of engines for the purpose of strengthening exhaust gas regulations and improving combustion efficiency, the electrode temperature of spark plugs used for ignition tends to increase. . In particular, since the ground electrode is located on the combustion chamber side with respect to the center electrode, the temperature rises rapidly. In particular, a spark plug used for a direct injection engine or the like is particularly likely to cause a temperature rise of the ground electrode. Under the above severe conditions, the sparks of the electrode can easily be consumed. Therefore, in order to suppress the expansion rate of the spark discharge gap, a spark in which a noble metal tip is welded to the portion of the ground electrode facing the spark discharge gap is used. Plugs are popular.
[0003]
When the temperature of the ground electrode rises, high temperature oxidation of the electrode base material to which the noble metal tip is welded becomes a problem. Conventionally, the base material of the ground electrode is often made of a Ni-base heat-resistant alloy such as Inconel 600 (Inconel is a trade name of Inco, UK) in order to ensure high-temperature oxidation resistance. However, since the heat conductivity of Ni-base heat-resistant alloys is generally not so high, so-called heat sinking is bad, and the electrode temperature is particularly likely to rise during high-speed operation. When the heat pulling deteriorates and the electrode temperature rises, the temperature of the metal tip bonded to the electrode base material also rises, causing a decrease in life due to abnormal wear. Therefore, a method has been proposed in which a core material made of a Cu-based metal (Cu-based heat transfer accelerating portion) is arranged in the electrode base material to suppress the temperature rise of the electrode in order to promote improvement in heat dissipation ( For example, Patent Document 1 and Patent Document 2).
[0004]
[Patent Document 1]
JP-A-5-159857 [Patent Document 2]
Japanese Examined Patent Publication No. 6-48629
[Problems to be solved by the invention]
However, when the combustion temperature further rises and the ignition part gets closer to the center of the combustion chamber as in the direct injection engine described above, the temperature rise of the ground electrode becomes more significant. As a result, there arises a problem that the high temperature oxidation of the electrode base material cannot be suppressed with an alloy performance of about Inconel 600. In this case, it is conceivable to replace the material of the electrode base material with a material having better high-temperature oxidation resistance. For example, instead of the conventionally used Inconel 600, a proposal has been made to use Inconel 601 with improved high-temperature oxidation resistance by increasing the content of Cr and Fe. However, this material replacement presents a major obstacle when the embedding of the Cu-based heat transfer promoting portion is selected.
[0006]
That is, an electrode having a Cu-based heat transfer promoting portion is assembled by assembling a Cu material serving as a Cu-based heat transfer promoting portion into a Ni alloy material serving as an electrode base material, and this assembly is drawn or forged, or Manufactured by cold working by rolling to make a clad wire. However, nickel-base heat-resistant alloys with increased Cr content such as Inconel 601 have higher deformation resistance and lower ductility than conventional Inconel 600 and the like as a metal material whose strength has been improved by high alloying. Therefore, when it is going to manufacture a clad wire with a Cu system heat transfer promotion part by the above processes, troubles, such as a crack, are easy to occur and there is a problem which brings about a significant fall of a manufacturing yield. In addition, when a spark plug having a Cu-based heat transfer promoting portion is used in an engine for a Ni-based electrode base material, a diffusion layer in which components are diffused between the electrode base material and the Cu-based heat transfer promoting portion is formed. Is done. In addition, peeling may occur from this diffusion layer by receiving a repeated load due to the difference in thermal expansion between the two. As a result, heat conduction may not be sufficiently performed from the electrode base material to the Cu-based heat transfer promoting portion. On the other hand, if the Cu-based heat transfer promoting portion is omitted, even if the high-temperature oxidation of the electrode base material can be suppressed, the temperature increase of the noble metal tip cannot be suppressed, so the problem of abnormal consumption cannot be solved.
[0007]
The object of the present invention is to provide sufficient resistance to high-temperature oxidation to the electrode base material of the ground electrode, and to be able to manufacture a structure in which a Cu-based heat transfer promoting portion is embedded without any problem by cold working. It is an object of the present invention to provide a spark plug that can prevent abnormal consumption of bonded noble metal tips.
[0008]
[Means for solving the problems and actions / effects]
In order to solve the above problems, a spark plug according to the present invention includes a cylindrical metal shell, an insulator fitted inside the metal shell, a center electrode provided inside the insulator, One end of the bracket is joined by welding or the like and a ground electrode is formed on the other end side to form a spark discharge gap with the center electrode. The ground electrode is embedded in the electrode base material and the electrode base material. And a Cu-based heat transfer promoting portion composed mainly of Cu, and a noble metal tip welded to the electrode base material at a position facing the spark discharge gap. It consists of a Ni alloy containing ˜17% by mass, Mo of 0.8 to 3.5% by mass, and Ni of 68 to 85.2% by mass. In the present specification, “main component” refers to a component having the highest mass content.
[0009]
According to the spark plug of the present invention, the Cu-based heat transfer promoting portion is embedded in the electrode base material that forms the ground electrode, thereby promoting the heat dissipation and suppressing the temperature rise, thereby improving the life of the ground electrode. Can be planned. Moreover, since the temperature rise of the noble metal tip welded to the electrode base material is also suppressed, abnormal wear is prevented and durability can be ensured. And in this invention, what has the said specific composition is employ | adopted as Ni alloy which comprises an electrode base material. As a result, there are the following advantages compared to the case of employing Inconel 601 or the like, which has been problematic in the past. First, when a Ni alloy containing C is employed as in the present invention, the high temperature oxidation resistance of the alloy can be remarkably improved by containing a certain amount of Mo together with Cr. Therefore, combined with the adoption of the Cu-based heat transfer promoting part, even when the spark plug is used under more severe conditions, the durability of the ground electrode can be sufficiently ensured and the life can be improved.
[0010]
In this case, particularly for the Ni alloy containing C, the effect of improving the high temperature corrosion resistance by adding Mo is high. There are both cases where the C is contained as an impurity and cases where it is positively added (so-called weak precipitation type alloy) in order to enhance precipitation strengthening by carbide formation, and is adjusted to 0.3% by mass or less. Particularly in the latter case, the C content is adjusted within a range of, for example, 0.03 to 0.3% by mass. However, excessive addition reduces the cold workability due to the formation of a large amount of carbide, so it is desirable to make it 0.10% by mass or less. In any case, the contained C mainly forms carbides with Cr when Mo is not added. When a large amount of such Cr carbide is formed, the Cr component, which is an oxidation resistance imparting element, decreases in the form of carbide precipitation, resulting in insufficient formation of a passive oxide film, leading to a decrease in oxidation resistance. . In particular, when Cr carbide is formed at the grain boundary, a Cr-deficient layer is formed near the grain boundary, and the interfacial corrosion is facilitated due to the local battery effect and the like, which further adversely affects the durability of the electrode base material. .
[0011]
However, when an appropriate amount of Mo is added, Mo carbides are preferentially formed and the precipitation of Cr carbides is suppressed, and the effective Cr content contributing to passive oxide film formation can be increased. As a result, even with the same Cr content, a stronger passive oxide film can be formed, which contributes to the improvement of high temperature corrosion resistance. In addition, since Mo carbides generally do not easily cause grain boundary precipitation, a Cr-deficient layer is also unlikely to occur, which is advantageous in terms of suppressing grain boundary corrosion.
[0012]
As a result, high-temperature corrosion resistance equivalent to or higher than that of Inconel 601 and the like having a higher Cr composition can be realized even if the Cr content is set to a relatively low value of 14 to 17% by mass based on the above effect due to the addition of Mo. Accordingly, the cold workability is improved by the amount of Cr content reduced, so that the processing of the clad material in which the Cu-based heat transfer promoting portion is embedded can be performed without any problem. Become.
[0013]
In addition, the addition of Mo can suppress an increase in the thickness of the diffusion layer formed at the boundary between the electrode base material and the Cu-based heat transfer promoting portion even if the engine is used for a long time. Can be prevented. The occurrence of this peeling is presumed to be due to the low ductility that is characteristic of the alloy of Cu and Ni, which is the main component of this diffusion layer.
[0014]
When the Cr content of the Ni alloy constituting the electrode base material is less than 14% by mass, the high temperature oxidation resistance of the electrode base material is insufficient, which causes a problem that the electrode life is reduced. On the other hand, when it exceeds 17 mass%, workability deteriorates, and when a clad material having a Cu-based heat transfer promoting portion embedded therein, which is a ground electrode material, is produced, cracking or the like is likely to occur.
[0015]
If the Mo content is less than 0.8% by mass, the effect of improving the high-temperature oxidation resistance due to the addition of Mo and the effect of preventing peeling in the diffusion layer during long-time use become poor. On the other hand, if it exceeds 3.5 mass%, the hardness of the alloy increases and the deformation resistance increases, leading to deterioration of workability. Furthermore, if the Ni content is less than 68% by mass, the content of subcomponents becomes too high, which tends to cause deterioration in workability.
On the other hand, if the Ni content exceeds 85.2% by mass, the necessary Cr and Mo contents cannot be ensured, leading to deterioration in high-temperature oxidation resistance.
[0016]
The Ni alloy constituting the electrode base material should have an Al content of less than 1% by mass from the viewpoint of securing the weldability and thus the weld joint strength when the ground electrode is welded to the metal shell. When the Al content is 1% by mass or more, the production of aluminum oxide becomes excessive, and weldability or weld joint strength may be impaired. On the other hand, Al can be positively added in the above range for the purpose of improving high-temperature oxidation resistance.
[0017]
Fe can be added to the Ni alloy that forms the electrode base material. Fe functions as a solid solution in a Ni-based matrix to strengthen and strengthen high temperature strength. The Fe content is preferably adjusted in the range of 6 to 10% by mass. If the Fe content is less than 6% by mass, the effect of improving the high-temperature strength is poor, and if it exceeds 10% by mass, sufficient high-temperature oxidation resistance may not be ensured.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a longitudinal cross-sectional view of a spark plug 100 as an example of the present invention. A cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip 21 protrudes, A center electrode 3 provided inside the insulator 2 and a ground electrode 4 having one end coupled to the metal shell 1 by welding or the like and forming a spark discharge gap g between the other end and the center electrode 3 are provided. ing. The spark plug 100 according to the present embodiment is a so-called parallel electrode type, and the front end side of the ground electrode 4 is bent back to the side, and a spark discharge gap g is formed between the side surface and the front end surface of the metal shell 1. Is formed. Further,

noble metal tips

31 and 32 made of a Pt alloy or an Ir alloy are welded to the ground electrode 4 and the center electrode 3 at positions facing the spark discharge gap g, respectively.
[0019]
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 and the terminal fitting 8 along its own axial direction. Yes. 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.
[0020]
As shown in FIG. 2, the ground electrode 4 includes an electrode base material 4a forming an outer surface portion, and a Cu-based heat transfer promoting portion 4c embedded in the electrode base material 4a. The electrode base material 4a is made of a Ni alloy containing 14 to 17% by mass of Cr, 0.8 to 3.5% by mass of Mo, and 68 to 85.2% by mass of Ni. Further, the Cu-based heat transfer promoting portion 4c is composed of pure Cu or a Cu alloy. In the present embodiment, the Cu-based heat transfer promoting portion 4 c is disposed in the longitudinal direction of the ground electrode 4. The Cu-based heat transfer promoting portion 4c is tapered, and its tip is set so as to deviate from the position of the spark discharge gap g. This is because the temperature of the tip of the ground electrode 4 where the spark discharge gap g is located is particularly high, and when the Cu-based heat transfer promoting portion 4c enters this portion, the linear expansion coefficient with the electrode base material 4a is increased. This is because problems such as electrode swelling and delamination may occur based on the difference.
[0021]
In the present embodiment, the center electrode 3 is also configured to have an electrode base material 3a and a Cu-based heat transfer promoting portion 3c embedded therein. The electrode base material 3a can also be made of the same Ni alloy as that of the ground electrode 4 side. However, since the temperature is less likely to rise than the ground electrode 4, the Mo content is lower than that of the electrode base material 4a on the ground electrode 4 side. (Although it does not contain Mo), the Cr content can be the same as or lower than that of the electrode base material 4a.
[0022]
FIG. 4 shows an example of a method for manufacturing the ground electrode 4. That is, as shown in FIG. 4 (a), a Ni-based molded body 104a having a gap 104h is produced by plastic working such as cutting or deep drawing with a Ni alloy that is a constituent material of the electrode base material 4a. On the other hand, a Cu-based molded body 104c having a shape corresponding to the gap 104a is made of pure Cu (for example, oxygen-free copper material) or a Cu alloy as a constituent material of the Cu-based heat transfer promoting portion 4. Then, this Cu-based molded body 104c is fitted into the gap 104h of the Ni-based molded body 104a to produce the assembly 104 in FIG. 4B.
[0023]
Next, as shown in FIG. 4C, the assembly 104 is subjected to die drawing, forging, or rolling at room temperature to reduce and extend the clad wire 4 ′. Thereby, the Cu-based molded body 104c becomes the Cu-based heat transfer promoting portion 4c, and the Ni-based molded body 104a becomes the electrode base material 4a. The ground electrode 4 is completed by welding the exposed end of the Cu-based heat transfer promoting portion 4c of the clad wire 4 'to the end face of the metal shell 1 (FIG. 2) and bending it.
[0024]
The Ni alloy forming the Ni-based molded body 104a has good workability because the Cr content is reduced as described above, and is performed by cold working at room temperature or by raising the temperature to 900 ° C. or lower. Thus, the clad material 4 ′ can be obtained without any problems without causing defects such as cracks. And, instead of reducing the Cr content, Mo in the above range is contained, so even when compared with Ni-based heat-resistant alloys such as Inconel 601 having a high Cr content, the high temperature corrosion resistance is inferior, and the ground electrode Can greatly extend the service life. In addition, the Cu-based heat transfer promoting portion 4c can be easily arranged, and further, even if it is used for a long time in an engine, the diffusion layer does not peel off. Can be secured.
[0025]
When the ground electrode 4 is manufactured by cold working, as shown in FIG. 4D, a structure in which crystal grains extend in the longitudinal direction of the electrode is observed in the electrode base material 4a. When the clad wire 4 'is annealed from the finished state, component diffusion occurs between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a made of Ni alloy, thereby improving the binding force between the two. Can do. This annealing may be performed after processing or before processing, but when the temperature of annealing performed after processing is high, the stretched structure of crystal grains shown in FIG. May change to the organization.
[0026]
In addition, as shown in FIG. 3, you may arrange | position the Ni type expansion | swelling adjustment layer 4d which consists of pure Ni or Ni alloy further inside the Cu type heat transfer promotion part 4c. The electrode base material 4a made of an Ni alloy and the Cu-based heat transfer promoting portion 4c have a large difference in linear expansion coefficient, and there is a concern that electrode swelling, delamination, and the like are likely to occur particularly when a severe cooling / heating cycle is applied. However, by forming the Ni-based expansion adjustment layer 4d as described above, the thickness of the Cu-based heat transfer promoting portion 4c is reduced, and the Cu-based heat transfer promoting portion 4c is sandwiched between Ni-based metals, It is possible to make the above-mentioned problem difficult to occur.
[0027]
【Example】
In order to confirm the effect of the present invention, the following experiment was conducted.
Various prototypes of the spark plug 100 shown in FIG. 1 were manufactured. The ground electrode 4 was manufactured by the method shown in FIG. That is, Ni alloys having various compositions shown in Table 1 were prepared as electrode base material, and a Ni-based molded body 104a to be the electrode base material 4a was measured with an outer diameter of 4.5 mm and a length of 5.4 mm. Produced. Further, a Cu-based molded body 104c to be the Cu-based heat transfer promoting portion 4c was manufactured using oxygen-free copper as a material with a base end outer diameter of 2.9 mm and a length of 5 mm. Then, this was fitted into the gap 104h formed in the Ni-based molded body 104a to form an assembly 104. This assembly 104 was cold-extruded so that the area reduction rate per pass was 55%, and the cross-section was a rectangle with a length of 1.5 mm and a width of 2.8 mm, and the length was 19 mm. A wire was obtained. For comparison, a ground electrode having the composition of No. 1 was prepared by omitting the Cu heat transfer promoting portion 4c (No. 13).
[0028]
Each of the above ground electrodes was subjected to workability evaluation according to the following criteria.
Good (O): No cracks or peeling were observed between the electrode base material 4a and the Cu-based heat transfer promoting portion 4c, and cold working was possible without problems.
Possible (Δ): Cracks or peeling was observed between the electrode base material 4a and the Cu-based heat transfer promoting portion 4c. However, when the assembly was annealed at 930 ° C. for 1 hour, cold working was not possible. Is solved.
Impossibility (x): An assembly was annealed at 930 ° C. for 1 hour, but the failure was not eliminated (a ground electrode having no failure was obtained separately by warm extrusion at a temperature of 730 ° C.).
[0029]
Moreover, the high temperature fatigue test of the obtained ground electrode is performed on the following conditions. That is, the tester used an axial load fatigue test, setting the temperature to 600 ° C., the stress amplitude condition to ± 900 N tension / compression, and the repetition rate to 10 Hz. Then, the fatigue strength, JIS: Z2273 in compliance with the method defined in, a test number of goods N = 2, obtains the time-intensity at the time of setting the fatigue life of 10 ⁶ times, was evaluated by the following criteria ( Confirmation of high temperature breakability).
Good (◯): Time strength is 220 MPa or more.
Possible (Δ): Time strength is 200 MPa or more and less than 220 MPa.
Impossible (x): Time strength is less than 200 MPa.
[0030]
Next, with respect to the center electrode 3, the cross section of the center electrode 3 is externally formed by cold extrusion similar to the ground electrode 4 in the form in which the electrode base material 3 a is composed of Inconel 600 and the Cu-based heat transfer promoting portion 3 c is composed of oxygen-free copper. It was manufactured to have a circular shape with a diameter of 2.5 mm and a length of 24 mm.
[0031]
The ground electrode 4 was made of a Pt-10 mass% Ni alloy, and a disc-shaped noble metal tip 32 having a diameter of 0.9 mm and a thickness of 0.4 mm was joined by resistance welding. In addition, a disc-shaped noble metal tip 32 made of a Pt-13 mass% Ir alloy and having a diameter of 0.8 mm and a thickness of 0.6 mm was joined to the center electrode 3 by laser welding. The center electrode 3 is assembled to the insulator 2 made of alumina, and the metal shell 1 to which the ground electrode 4 is welded is assembled to the insulator 2, and the ground electrode 4 is bent, whereby the

noble metal tips

31, 32 are assembled. A spark discharge gap g with a spacing of 0.9 mm was formed therebetween.
[0032]
The following tests were performed on the test pieces of each spark plug using the ground electrode obtained by the manufacturing method described above. In addition, the ground electrode which was tested by the following engine was previously annealed at 930 ° C. for 1 hour, and a diffusion layer of 10 to 20 μm was formed between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a. It is.
A spark plug was attached to a 4-cylinder gasoline engine (displacement 2000 cc), and an actual machine test was performed in which the throttle was fully opened and continuously operated at an engine speed of 6000 rpm for 250 hours (estimated temperature of the noble metal tip 32 on the ground electrode side: about 1000 ° C. ). After the test, the cross section of the ground electrode 4 was observed with a scanning electron microscope, and the thickness of the formed oxide scale layer was measured and evaluated according to the following criteria (confirmation of high temperature oxidation resistance of the ground electrode).
Good (O): Oxide scale layer thickness less than 0.05 mm.
Possible (Δ): Oxide scale layer thickness of 0.05 mm or more and less than 0.15 mm.
Impossible (x): Oxide scale layer thickness of 0.15 mm or more.
[0033]
Further, the wear thickness of the noble metal tip on the ground electrode side after the test was measured in the gap interval direction and evaluated according to the following criteria (confirmation of durability of the noble metal tip).
Good (O): Consumed thickness is less than 0.3 mm.
Possible (Δ): Consumed thickness is 0.3 mm or more and less than 0.35 mm.
Impossible (x): Consumed thickness is 0.35 mm or more.
[0034]
Further, the welding strength between the ground electrode 4 and the metal shell 1 was performed as follows. The strength test consists of a tensile test in which the metal shell 1 and the tip of the ground electrode 4 (before bending) (at a position 5 mm from the tip) are held and pulled in the axial direction of the ground electrode 4, and the metal shell 1 is cantilevered. A bending test was performed in which a fixed bending load was repeatedly applied to the ground electrode 4 in a direction orthogonal to the axial direction of the ground electrode 4 at a position 5 mm from the end surface of the metal fitting until breakage occurred. And it evaluated on the following conditions (confirmation of weldability).
Good (O): Does not break at the welded part in either the tensile test or the bending test.
Possible (Δ): Only the tensile test does not break at the weld.
Impossible (x): Breaks at the welded part in both the tensile test and the bending test.
[0035]
Furthermore, after the test, the observation of the ground electrode 4 by X-ray and the cross section thereof were observed with a scanning electron microscope, whereby the occurrence of peeling in the diffusion layer and the thickness of the diffusion layer were measured and evaluated according to the following criteria (grounding) Confirmation of peelability of electrode heat transfer promotion part).
Good (O): The Cu-based heat transfer promoting portion 4c and the electrode base material 4a are not separated and the width of the diffusion layer is 50 μm or less.
Possible (Δ): The Cu-based heat transfer promoting portion 4c and the electrode base material 4a are not separated, but the diffusion layer has a width of 50 μm or more.
Impossible (x): The peeling has occurred between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a.
[0036]
The results are shown in Table 1.
[0037]
[Table 1]

[0038]

Numbers

3, 4, 5, 8, 9, and 10 are spark plugs according to the present invention. As an electrode base material, Cr is 14 to 17% by mass, Mo is 0.8 to 3.5% by mass, and Ni is 68. Ni alloy containing ˜85.2% by mass is used. In either case, Mo is added in the above range instead of reducing the Cr content, so that the high-temperature oxidation resistance is comparable to the comparative example of No. 1 with a large amount of Cr even though it contains C. It can be seen that it has been secured to the extent. And since content of Cr is comparatively low, the workability of an electrode is better than the comparative example of No. 1, and embedding of a Cu type heat transfer promotion part can also be performed without trouble. As a result of improving the heat sinking by the burying, the durability of the noble metal tip is also good. Further, the addition of Mo significantly improves the high-temperature strength, and the high-temperature fracture resistance is also good. Further, even if the engine is used for a long time, an increase in the thickness of the diffusion layer can be suppressed, and there is no peeling in the diffusion layer. On the other hand, the comparative example of No. 1 in which Mo is not added has poor cold workability, and the embedding of the Cu-based heat transfer promoting portion requires troublesome warm working. Moreover, the high temperature fracture resistance is not very good, and peeling occurs in the diffusion layer. And if the embedding of the Cu-based heat transfer promoting part is omitted as in the case of No. 12, the result is that the high temperature oxidation resistance and the durability of the noble metal tip are remarkably lowered.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of a spark plug according to the present invention.
2 is an enlarged cross-sectional view showing a main part of the spark plug of FIG. 1. FIG.
FIG. 3 is a cross-sectional view of an essential part showing a modification of the spark plug of FIG.
4 is an explanatory diagram of a manufacturing process of the ground electrode of the spark plug of FIG. 1. FIG.
5 is an explanatory diagram of a manufacturing process of the ground electrode of the spark plug of FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main metal fitting 2 Insulator 21 Tip part 3 Center electrode 32 Noble metal tip 4 Ground electrode 4a Electrode base material 4c Cu system heat transfer promotion part 100 Spark plug

Claims

A cylindrical metal shell (1), an insulator (2) fitted inside the metal shell (1), a center electrode (3) provided inside the insulator (2), and the metal shell A ground electrode (4) having one end coupled to (1) by welding or the like and forming a spark discharge gap (g) with the center electrode (3) on the other end side;
The ground electrode (4) includes an electrode base material (4a), a Cu-based heat transfer promoting portion (4c) embedded in the electrode base material and mainly composed of Cu, and the spark discharge gap ( a noble metal tip (32) welded to the electrode base material (4a) at a position facing g), and
In the electrode base material (4a), Cr is 14 to 16 % by mass, Mo is 0.8 to 3 % by mass, Al is 1.1% by mass or less, C is 0.03 to 0.1% by mass, Fe is A spark plug comprising a Ni alloy containing 5 to 12% by mass, further containing Mn and Si, and the remaining 68 to 85.2% by mass of Ni .

A cylindrical metal shell (1), an insulator (2) fitted inside the metal shell (1), a center electrode (3) provided inside the insulator (2), and the metal shell A ground electrode (4) having one end coupled to (1) by welding or the like and forming a spark discharge gap (g) with the center electrode (3) on the other end side;
The ground electrode (4) includes an electrode base material (4a), a Cu-based heat transfer promoting portion (4c) embedded in the electrode base material and mainly composed of Cu, and the electrode base material ( 4a) and a diffusion layer formed at the boundary between the Cu-based heat transfer promoting portion (4c) and a noble metal tip (4a) welded to the electrode base material (4a) at a position facing the spark discharge gap (g) 32), and
In the electrode base material (4a), Cr is 14 to 16 % by mass, Mo is 0.8 to 3 % by mass, Al is 1.1% by mass or less, C is 0.03 to 0.1% by mass, Fe is A spark plug comprising a Ni alloy containing 5 to 12% by mass, further containing Mn and Si, and the remaining 68 to 85.2% by mass of Ni .

The spark plug according to claim 1 or 2, wherein the Ni alloy constituting the electrode base material has an Al content of less than 1 mass%.

The spark plug according to any one of claims 1 to 3, wherein the Ni alloy constituting the electrode base material has a Fe content of 6 to 10 mass%.

The spark plug according to any one of claims 1 to 4, wherein the position of the Cu-based heat transfer promoting part (4c) is set so that a tip of the Cu-based heat transfer promoting part (4c) is out of a position of the spark discharge gap (g) .

The spark according to any one of claims 1 to 5, wherein the Cu-based heat transfer promoting portion (4c) has a Ni-based expansion adjustment layer (4d) made of pure Ni or a Ni alloy disposed therein. plug.

The spark plug according to any one of claims 1 to 6, wherein the noble metal tip (32) is made of a Pt-Ni alloy .