JP4075137B2

JP4075137B2 - Spark plug

Info

Publication number: JP4075137B2
Application number: JP15784698A
Authority: JP
Inventors: 憲端無; 啓二金生
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1998-06-05
Filing date: 1998-06-05
Publication date: 2008-04-16
Anticipated expiration: 2018-06-05
Also published as: JPH11354251A

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の燃焼室等に設置されるスパークプラグに関し、特に、接地電極に設けられる貴金属チップの耐久性向上に関する。
【０００２】
【従来の技術】
一般に、スパークプラグは、取付金具内に絶縁体を介して絶縁保持された中心電極と、取付金具に接合された接地電極とを備える。そして、中心電極の絶縁体から露出した部分と接地電極とを対向させ、この対向部（火花放電部）に、火花放電が行われる放電ギャップを形成する。さらに、プラグの長寿命、高性能化のために、放電ギャップにおいて中心電極及び接地電極の少なくとも一方に、火花放電部電極材としての貴金属チップを溶接する。
【０００３】
このチップ構成材料としては、従来より、Ｐｔを主成分とするＰｔ合金が使用されてきたが、Ｐｔ合金では、将来のより厳しいエンジン仕様に対し、耐消耗性の不足が予想されるため、近年、Ｐｔ合金よりも高融点であるＩｒを主成分とするＩｒ合金の使用が検討されている。このようなＩｒ合金チップを用いたものとしては、例えば、特開平９−７７３３号公報に記載のものある。これは、高温耐熱性及び耐消耗性に優れたＩｒ−Ｒｈ合金をチップに用いたものである。
【０００４】
【発明が解決しようとする課題】
ところで、Ｐｔ合金チップにおいては、チップと中心電極及び接地電極との溶接は、一般的に製造性及びコストの面から抵抗溶接により行われている。しかし、Ｉｒ合金は、Ｐｔ合金よりも電極母材（Ｎｉを主成分とするＮｉ基合金）との線膨張係数差が大きいため、抵抗溶接による溶接では、高温の燃焼室内での使用中に、Ｉｒ合金チップとチップ接合部との接合部分に、両合金の線膨張差に起因する熱応力が発生し、接合部に亀裂・剥離が生じ、最悪チップの脱落を招く。
【０００５】
そこで、本発明者等は、両者を直接溶接するにあたり、剥離を防止するためには、両者の溶融を十分に行うことが可能なレーザ溶接を用いることとした。このレーザ溶接によれば、接地電極とＩｒ合金チップとの溶融により、接合界面を挟んで接地電極内及びＩｒ合金チップ内の両側に、Ｎｉ及びＩｒを含む合金よりなる溶融部が十分に形成され、それによって上記熱応力を低減でき、接合が強固なものとできると考えられる。
【０００６】
しかし、レーザ溶接では、形成される溶融部が局所的に偏りやすく、熱応力に対する接合信頼性が劣る場合がしばしばある。特に、接地電極については、例えば、中心電極の外周の取付金具から中心電極の先端と対向させるために曲がり形状を有する等の構成上の理由から、固定されたレーザ照射部に対して回転させながら効率よく全周に渡って接合することは困難である。また、接地電極を取付金具に溶接等により固定した後、チップをレーザ溶接する場合も同様である。
【０００７】
そこで、本発明は上記問題点に鑑みて、Ｉｒを主成分とするＩｒ合金チップと接地電極及び／又は中心電極とをレーザ溶接により溶融接合してなるスパークプラグにおいて、熱応力に対する接合信頼性の高い溶融部構成を接地電極において提供することを第１の目的とし、熱応力に対する接合信頼性の高い溶融部構成を中心電極において提供することを第２の目的とする。
【０００８】
【課題を解決するための手段】
本発明者等は、上記目的を達成するため、レーザ溶接により形成された溶融部の形状寸法、特にＩｒ合金チップと接地電極及び／又は中心電極（以下、母材電極という）との接合界面に占める溶融部の長さと、母材電極への溶融部の溶け込み度合とに着目し、鋭意検討を行なった。ここで、これら長さを図３に示す。図３は、接地電極にＩｒ合金チップを接合した例を示す。
【０００９】
図３に示す様に、接合界面に占める溶融部の長さは、接合界面（６０）の中心電極（３）側端部（６１）と、溶融部（７０）の接合界面（６０）における中心電極（３）とは反対側端部（７２）とを結ぶ直線の最大寸法をＡとし、この最大寸法Ａのうち溶融部（７０）の占める長さＢとする。図３では長さＢは、溶融部（７０）の接合界面（６０）における中心電極（３）側端部（７１）と上記反対側端部（７２）との直線長さである。
【００１０】
そして、ＡとＢの比Ｂ／Ａについて検討した。また、溶融部の溶け込み度合は、図３に示す様に、接合界面（６０）から突出するチップ（５２）の突出長さをｔとし、この突出長さｔと溶融部（７０）の接合界面（６０）から接地電極（４）への最大溶け込み長さとの合計長さをｄとしたときのｄとｔの比ｄ／ｔで、検討した。
【００１１】
そして、プラグをエンジンの燃焼室に設置し、高温燃焼雰囲気下における、上記各比Ｂ／Ａ及びｄ／ｔと、チップの剥離度合との関係を調査した。その結果、比Ｂ／Ａについて、Ｂ／Ａ≧０．５を満足することにより、接合界面（６０）において熱応力によりチップ（５２）が接地電極（４）から剥離するのを防止できる（後述の図６参照）ことを見出した。
【００１２】
また、比ｄ／ｔについて、２≦ｄ／ｔ≦４を満足することにより、熱応力によるチップ（５２）と溶融部（７０）との剥離、及び溶融部（７０）と接地電極（４）との剥離を防止できる（後述の図５参照）ことを見出した。請求項１〜４記載の発明は、上記知見に基づいて、上記第１の目的を達成すべく、母材電極を接地電極とした場合についてなされたものである。
【００１３】
すなわち、請求項１記載の発明では、チップ（５２）側からレーザを照射したレーザ溶接によって接合界面（６０）を介してチップ（５２）内及び接地電極（４）内の両側に溶け込んで形成された溶融部（７０）は、比Ｂ／Ａが０．５以上であり、比ｄ／ｔが２以上４以下であることを特徴としている。それによって、レーザ溶接によりチップ（５２）内を接地電極（４）に接合した場合の、熱応力に対する接合信頼性の高い溶融部構成を実現できる。
【００１４】
また、請求項２記載の発明のように、上記チップ（５２）を構成するＩｒ合金は、ＩｒとＲｈとを含むＩｒ−Ｒｈ合金を用いることができる。また、請求項１記載の寸法関係を満足するＮｉ及びＩｒを含む合金よりなる溶融部（７０）の組成は、請求項３記載の発明のように、ＩｒとＮｉとの合計を１００重量％としたとき、Ｉｒが２０重量％〜８０重量％含有されているものが好ましい。
【００１５】
また、請求項４記載の発明は、上記チップ（５２）の具体的形状を提供するものであり、柱状のチップ（５２）が、柱の側面にて接地電極（４）と対面して接合界面（６０）を形成しているものにすることができる。また、請求項５記載の発明は、上記各比Ｂ／Ａ及びｄ／ｔに関する知見に基づいて、母材電極を中心電極とした場合についてなされたものであり、中心電極について請求項１記載の発明と同様の効果を得、上記第２の目的を達成することが出来る。
【００１６】
なお、上記した括弧内の符号は、後述する実施形態記載の具体的手段との対応関係を示す一例である。
【００１７】
【発明の実施の形態】
以下、本発明を図に示す実施形態について説明する。本実施形態は例えば内燃機関の点火栓として用いられる。図１に本実施形態のスパークプラグ１００の全体構成を示す半断面図である。
スパークプラグ１００は、円筒形状の取付金具１を有しており、この取付金具１は、図示しないエンジンブロックに固定するための取付ネジ部１ａを備えている。取付金具１の内部には、アルミナセラミック（Ａｌ₂Ｏ₃）等からなる絶縁体２が固定されており、この絶縁体２の先端部２ａは、取付金具１から露出するように設けられている。
【００１８】
絶縁体２の軸孔２ｂには中心電極３が固定されており、この中心電極３は取付金具１に対して絶縁保持されている。中心電極３は、内材がＣｕ等の熱伝導性に優れた金属材料、外材がＮｉ基合金等の耐熱性および耐食性に優れた金属材料により構成された円柱体で、図１に示すように、その先端部３ａが絶縁体２の先端部２ａから露出するように設けられている。
【００１９】
一方、接地電極４は、一端側の固定部４ａにて取付金具１の一端に溶接により固定され、途中で略Ｌ字に曲げられて、固定部４ａとは反対の対向部４ｂにおいて中心電極３の先端部３ａと放電ギャップ６を隔てて対向している。ここで、図２は（ａ）は接地電極４の対向部４ｂ近傍の拡大斜視図、（ｂ）は（ａ）のＹ矢視図、（ｃ）は（ａ）のＸ矢視図である。接地電極４は、Ｎｉを主成分とするＮｉ基合金（例えばインコネル（登録商標））より構成され、全長が例えば１０ｍｍの断面偏平（図２中、例えば幅Ｗが２．８ｍｍ、厚さＨが１．６ｍｍ）の角柱が、略Ｌ字に曲げられた形状を成す。
【００２０】
そして、中心電極３の先端部３ａには、貴金属チップ５１がレーザ溶接により固定されている。このチップ５１は円盤状であり、中心電極３の先端部３ａの円柱端面に接合されている。一方、接地電極４の対向部４ｂの側面４ｃには、略円柱状をなす貴金属チップ５２がレーザ溶接により固定されている。これら両チップ（火花放電部電極材に相当）５１、５２は、Ｉｒを主成分とするＩｒ合金（例えばＩｒが９０重量％、Ｒｈが１０重量％のＩｒ−１０Ｒｈ合金）からなる。ここで、上記の放電ギャップ６は両チップ５１、５２の隙間であり、例えば約１ｍｍである。
【００２１】
ここで、本発明の要部である接地電極４側のチップ５２について、図２を参照して更に詳細に述べる。チップ５２は柱状をなすものであり、図示例では長さが接地電極４の厚さＨと略同等の円柱体（例えば直径０．７ｍｍ、長さ１．６ｍｍ）としている。そして、その円柱長手方向の側面の一部が、対向部４ｂの側面４ｃに沈み込んだ形となっている。従って、チップ５２の円柱側面とこれに対面する対向部４ｂの側面４ｃとの境界面が接合界面６０となっている。
【００２２】
この接合界面６０におけるチップ５２と接地電極４との溶接状態を、図３を参照して述べる。図３は図２（ｂ）のａ−ａ断面図すなわちチップ５２の円柱長手方向の中心軸を通る断面図である。図３において上側が中心電極３側である。また図３では、接合界面６０にて示される直線の長さは、チップ５２をなす円柱体の長さすなわち接地電極４の厚さＨ（例えば１．６ｍｍ）と同等である。
【００２３】
チップ５２と接地電極４とはレーザ溶接されるため、図３の半楕円状ハッチングに示す様に、両者が溶融した溶融部７０が、チップ５２内から接合界面６０を挟んで接地電極４内に渡って溶け込んで形成されている。ここで、上述のようにチップ５２はＩｒ合金、接地電極４はＮｉ基合金であるため、溶融部７０はＩｒとＮｉとの合金（Ｉｒ−Ｎｉ合金）よりなる。
【００２４】
また、図２（ｂ）、（ｃ）及び図３の白抜き矢印Ｒに示す様に、レーザ溶接においてレーザは、対向部４ｂの側面４ｃに略垂直、且つチップ５２の円柱長手方向の中心軸を通るように照射される。そのため、図３は、この中心軸と平行な方向において、レーザのエネルギーが最も多くかかる方向に沿った断面、つまり接合界面６０において溶融部７０が最も広く形成された断面に相当する。
【００２５】
そのため、図３に示す寸法Ａ、すなわち、接合界面６０の中心電極３側端部６１と、溶融部７０の接合界面６０における中心電極３とは反対側の端部７２とを結ぶ直線寸法のうちの最大寸法（以下、最大寸法Ａという）となる。そして、上記最大寸法Ａのうち溶融部７０の占める長さ、すなわち図３において、溶融部７０の中心電極３側端部７１とその反対側端部７２との間の長さをＢ（以下、溶融部長さＢという）としている。
【００２６】
ここで、図３では、接合界面６０のうち、溶融部７０の中心電極３とは反対側端部７２と、接合界面６０の中心電極３側とは反対側端部６２との間では、チップ５２は溶融しておらず未溶融部となっている。つまり、図３では、最大寸法Ａは接合界面６０の端部６１と端部６２とを結ぶ直線のうち、未溶融部を除いた長さである。なお、この未溶融部はなくてもよい。
【００２７】
また、上述のように、図３においては、レーザのエネルギーが最も多くかかる方向に沿った断面であるため、接合界面６０から接地電極４内への溶融部７０の溶け込み長さは、最大溶け込み長さとなっている。
図３においては、接合界面６０から垂直方向に突出するチップの突出長さをｔ（以下、突出長さｔという）としている。本例では突出長さｔはチップ５２の直径と同等（例えば０．７ｍｍ）である。また、突出長さｔと、接合界面６０から接地電極４の対向部４ｂ内への溶融部７０の最大溶け込み長さとの合計長さをｄ（以下、合計長さｄという）としている。ちなみに、突出長さｔは、最大溶け込み長さ（ｄ−ｔ）の延長線上にて接合界面６０から突出する長さである。
【００２８】
そして、本実施形態では、チップ５２と接地電極４との接合信頼性を高めるために、上記各寸法（Ａ、Ｂ、ｄ、ｔ）を以下のように規定したことを主たる特徴としている。すなわち、最大寸法Ａと溶融部長さＢとの比Ｂ／Ａを０．５以上とし、突出長さｔと合計長さｄとの比ｄ／ｔを２以上４以下としている。
次に、接地電極４とチップ５２との接合方法について述べる。なお、本実施形態のスパークプラグの製造方法について、他の部分の製造工程については、周知であるため説明を省略する。通常は、取付金具１に接地電極４を固定した状態でチップ５２をレーザ溶接するが、接地電極４単独の状態で行ってもよい。
【００２９】
まず、レーザ溶接を行う前に、レーザ溶接時にチップ５２が動かないように、接地電極４の対向部４ｂ側面４ｃにチップ５２を抵抗溶接にて仮止めする。この仮止めの段階で、チップ５２は対向部４ｂ側面４ｃに沈み込む。なお、チップの設置を容易とするために予め接地電極４のチップ接合部に溝等の加工をしてもよい。続いて、上記白抜き矢印Ｒ方向から、レーザ溶接を行う。
【００３０】
ここで、レーザ溶接条件は、例えばエネルギーが３３Ｊ（パルス幅が１５ｍｓｅｃ、充電電圧が３６０Ｖ）、デフォーカスが＋２ｍｍ（つまりレーザの焦点がチップ５２の照射面よりも２ｍｍ奥にある）、レーザのビーム径がφ０．４ｍｍとした。例えばこのような条件にて連続照射（例えば３発）することにより、上記溶融部７０が形成される。なお、チップ５２の径（本例では突出長さｔに相当）は、チップ単体と溶接後とで変化せず一定である。
【００３１】
このように、数回に分けて連続照射する理由は次のようである。レーザ溶接は、上記白抜き矢印Ｒのようにチップ５２側から照射するため、エネルギーが弱いと母材である接地電極４の溶融が少なくＩｒ成分が多くなる。また強すぎるとＩｒ合金と接地電極４が飛散してしまい、適切な条件が出にくい。そこで、ある程度抑えたエネルギーを連続照射することで、１発ごとに溶融部分におけるＩｒ成分の減少及びＮｉ成分の増加を行い、チップ５２と接地電極４の中間的物性をもつ溶融部７０を形成させることとしている。
【００３２】
ここで、レーザ溶接条件及び照射回数は、予めレーザ溶接条件等と溶融部７０形状との関係を確認しておくことで求められる。溶融部７０の確認は、レーザ溶接後、接地電極４及びチップ５２を削って上記図３に示す切断面を出す。そして、金属顕微鏡などの観察により、溶融部７０の各寸法（Ａ、Ｂ、ｄ、ｔ）を把握する。また組成については、ＥＤＳ等のエネルギー分散分析装置を用いた分析により組成比を求めることができる。
【００３３】
図４に、溶融部７０状態の確認の一例を示す。上記レーザ溶接条件例にて、レーザ照射回数と比ｄ／ｔとの関係（図４（ａ）参照）、レーザ照射回数と溶融部７０においてＩｒとＮｉとの合計を１００重量％としたときのＮｉ及びＩｒの組成比（重量％）との関係（図４（ｂ）参照）を調べた。レーザ照射回数を多くするにつれ、比ｄ／ｔが大きくなり、また、溶融部７０におけるＮｉ量が増加しＩｒ量が減少することがわかる。
【００３４】
次に、チップ５２と接地電極４との接合部において、各寸法（Ａ、Ｂ、ｄ、ｔ）を上述のように規定した根拠を述べる。この根拠は実験的データに基づくものであり、Ｉｒ−１０Ｒｈ合金のチップ５２において、突出長さ（すなわちチップ５２の直径）ｔ＝０．７ｍｍ、最大寸法Ａ＝１．６ｍｍ、溶融部長さＢ＝１．０ｍｍとして、比Ｂ／ＡをＢ／Ａ＝０．６３と一定の状態になるようにし、レーザ照射回数を変化させて溶け込み長さ（ｄ−ｔ）を変化させ接合性を検討した。
【００３５】
接合性は、以下の耐久テストにて調査した。テストは、６気筒２０００ｃｃエンジンで実施し、運転条件はアイドル状態（例えば約３００℃）で１分保持した後、スロットル全開状態（例えば約９００℃で）６０００ｒｐｍ、１分保持を１００時間繰り返した。そして、比ｄ／ｔが１．５〜５の範囲における剥離状態を調べ、接合性を評価した。その結果を図５に示す。
【００３６】
図５（ａ）に示す様に、長さＬ１を有する接地電極４と溶融部７０との界面（電極母材−溶融部界面）と、長さＬ２を有するチップ５２と溶融部７０との界面（チップ−溶融部界面）とにおいて、剥離率を調べた。各界面において剥離した部分は顕微鏡で確認できるため、各界面に占める剥離部分の長さＬ３が求められる。そして剥離率は、電極母材−溶融部界面では（Ｌ１−Ｌ３）／Ｌ１×１００（％）で表され、チップ−溶融部界面では（Ｌ２−Ｌ３）／Ｌ２×１００（％）で表される。
【００３７】
図５（ｂ）は、各界面において、この剥離率と比ｄ／ｔとの関係を示したものである。電極母材−溶融部界面を黒丸、チップ−溶融部界面を白丸で表してある。電極母材−溶融部界面では、比ｄ／ｔが２以上で、ほぼ亀裂及び剥離なく良好な接合性を示す。一方、チップ−溶融部界面では、比ｄ／ｔが４以下で、ほぼ亀裂及び剥離なく良好な接合性を示す。従って、比ｄ／ｔは、２≦ｄ／ｔ≦４がよい。
【００３８】
これは、上記図４に示す様に、ｄ／ｔ＝１．５では、溶融部７０でのＩｒ成分が多すぎる（約８５重量％）ため、溶融部７０と接地電極４の電極母材との線膨張係数差が大きくて剥離が発生したと考える。またｄ／ｔ＝５では、Ｉｒ成分が少なすぎる（約１５重量％）ため、溶融部とＩｒ合金チップの線膨張係数差が大きくて剥離が発生したと考える。そして比ｄ／ｔの上記範囲において、溶融部７０中のＩｒが、ＩｒとＮｉとの合計を１００重量％としたとき、２０重量％〜８０重量％の組成範囲を有すれば、接合性向上のために好ましいと考えられる。
【００３９】
次に比ｄ／ｔをｄ／ｔ＝３と一定にし、比Ｂ／Ａを変えて上記と同様の耐久テストを実施した。その結果を図６に示す。ここで接合性は、図６（ａ）に示す様に、接合界面６０からチップ５２が剥離した時の角度θを用いて評価した。図６（ｂ）に示す様に、比Ｂ／Ａが０．５以上でチップ５２の傾斜がなくなり、良好な接合性を示す。比Ｂ／Ａが小さすぎると、抵抗溶接のみで接合（仮止め）されている部分が多いので、熱応力によりチップ５２が接地電極４から剥離、傾斜していき、中心電極との放電ギャップを適正に保てなくなる。
【００４０】
このように、本実施形態によれば、溶融部７０の形状寸法が、Ｂ／Ａ≧０．５を満足することにより、接合界面６０において熱応力によりチップ５２が接地電極４から剥離するのを防止でき、且つ２≦ｄ／ｔ≦４を満足することにより、熱応力によるチップ５２と溶融部７０との剥離、及び溶融部７０と接地電極４との剥離を防止でき、熱応力に対する接合信頼性の高い溶融部構成を実現できる。
【００４１】
また、本実施形態によれば、上記接合信頼性の高い溶融部構成のため、プラグ交換時間の大幅拡大が図れ、長寿命のスパークプラグを実現でき、さらには、熱負荷の厳しい環境で使用されるスパークプラグを提供できる。また、本実施形態によれば、抵抗溶接に比べ加圧が不要となる等、非常に容易な製造法であるレーザ溶接にて、接合を行うことができ、製造面から低コスト化が図れる。
【００４２】
本発明の参考例として図７及び図８は、接地電極４へのチップ５２の接合位置および中心電極３との位置関係を変えたものである。図７（ａ）において、チップ５２は、その円柱長手方向の側面の一部が、接地電極４の対向部４ｂのうち中心電極３の先端部３ａとの対向面にレーザ溶接されている。ここで、図７及び後述の図８及び図９では、実際は外観上、溶融部７０は見えないが、図中にハッチングで示してある。
【００４３】
また、図７（ｂ）では、中心電極３を延長し、中心電極の先端部３ａの両側面に、取付金具１に固定された２つの接地電極４が対向している。そして、両接地電極４の対向部４ｂに、チップ５２がレーザ溶接されている。
【００４４】
ここで、図７（ａ）及び（ｂ）は、上記未溶融部が存在しない例であるが、更に図８（ａ）及び（ｂ）に示す様に、上記未溶融部が存在していてもよい。また、図９に示すスパークプラグは、本発明の他の実施形態であり、図７（ｂ）の中心電極と接地電極の配置関係において、母材電極を中心電極３とした例を示すものである。中心電極３の先端部３ａには、柱状のチップ５１ａがレーザ溶接されている。ここで、図９において、（ｂ）は（ａ）のチップ５１ａの溶接部拡大図、（ｃ）は（ｂ）の上視図である。
【００４５】
図９（ｂ）の例では、上記実施形態における寸法Ａ及びＢは、図９（ａ）における右側の接地電極４（以下、右側接地電極４という）との関係において示してある。すなわち、最大寸法Ａは、接合界面６０の右側接地電極４側の端部６３と、溶融部７０の接合界面６０における右側接地電極４とは反対側の端部７３とを結ぶ直線の最大寸法であり、溶融部長さＢは、この最大寸法Ａのうち溶融部７０が占める長さである。
【００４６】
これら寸法ＡとＢの関係は、図９（ａ）における左側の接地電極４との関係においても同様である。そして、図９に示すスパークプラグでは、各寸法（Ａ、Ｂ、ｄ、ｔ）は、上記実施形態と同様の寸法関係に規定されており、中心電極３において、熱応力に対する接合信頼性の高い溶融部構成を実現できる。また、図９に示される構成は、上記図８（ｂ）の構成と組み合わせてもよい。
【００４７】
また、母材電極３、４にレーザ溶接されるチップ５１、５１ａの形状は、円柱だけでなく、角柱状、円盤状であってもよい。ただし、レーザ溶接をするためには、適当な厚さ、すなわち接合界面からの突出長さｔが、溶融部７０を形成するに十分な大きさを持つものが好ましい。さらに、チップを構成するＩｒ合金は、Ｉｒが９０重量％、Ｒｈが１０重量％のＩｒ−１０Ｒｈ合金だけでなく、Ｉｒを主成分とするＩｒ合金であればよい。
【図面の簡単な説明】
【図１】本発明の実施形態に係るスパークプラグの全体構成を示す半断面図である。
【図２】（ａ）は図１における接地電極の対向部近傍の拡大斜視図、（ｂ）は（ａ）のＹ矢視図、（ｃ）は（ａ）のＸ矢視図である。
【図３】図２（ｂ）のａ−ａ断面図である。
【図４】（ａ）はレーザ照射回数と比ｄ／ｔとの関係を示すグラフ、（ｂ）はレーザ照射回数と溶融部におけるＮｉ及びＩｒの組成比との関係を示すグラフである。
【図５】比ｄ／ｔに対する接地電極及びチップの接合性の評価結果を示す図である。
【図６】比Ｂ／Ａに対する接地電極及びチップの接合性の評価結果を示す図である。
【図７】本発明の第１の参考例を示す図である。
【図８】本発明の第２の参考例を示す図である。
【図９】本発明の他の実施形態を示す図である。
【符号の説明】
１…取付金具、３…中心電極、４…接地電極、４ｂ…接地電極の対向部、６…放電ギャップ、５２…チップ、６０…接合界面、６１…接合界面の中心電極側端部、６３…接合界面の接地電極側端部、７０…溶融部、７２…溶融部の接合界面における中心電極とは反対側の端部、７３…溶融部の接合界面における接地電極とは反対側の端部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug installed in a combustion chamber or the like of an internal combustion engine, and more particularly to improving the durability of a noble metal tip provided on a ground electrode.
[0002]
[Prior art]
In general, a spark plug includes a center electrode that is insulated and held in an attachment fitting through an insulator, and a ground electrode that is joined to the attachment fitting. And the part exposed from the insulator of a center electrode and the ground electrode are made to oppose, and the discharge gap in which spark discharge is performed is formed in this opposing part (spark discharge part). Further, in order to improve the life and performance of the plug, a noble metal tip as a spark discharge part electrode material is welded to at least one of the center electrode and the ground electrode in the discharge gap.
[0003]
Conventionally, a Pt alloy containing Pt as a main component has been used as this chip constituent material. However, since the Pt alloy is expected to have insufficient wear resistance with respect to future stricter engine specifications, The use of Ir alloys whose main component is Ir, which has a higher melting point than Pt alloys, has been studied. An example of using such an Ir alloy chip is disclosed in JP-A-9-7733. This is an Ir—Rh alloy excellent in high-temperature heat resistance and wear resistance used for a chip.
[0004]
[Problems to be solved by the invention]
By the way, in the Pt alloy tip, the tip, the center electrode, and the ground electrode are generally welded by resistance welding in terms of manufacturability and cost. However, since the Ir alloy has a larger difference in linear expansion coefficient from the electrode base material (Ni-based alloy containing Ni as a main component) than the Pt alloy, welding by resistance welding is performed during use in a high-temperature combustion chamber. Thermal stress due to the difference in linear expansion between the two alloys occurs at the joint between the Ir alloy chip and the chip joint, causing cracks and peeling at the joint, leading to the worst chip falling off.
[0005]
Therefore, the inventors of the present invention decided to use laser welding capable of sufficiently melting both of them in order to prevent peeling when directly welding them. According to this laser welding, a melted portion made of an alloy containing Ni and Ir is sufficiently formed on both sides of the ground electrode and the Ir alloy tip across the joining interface by melting the ground electrode and the Ir alloy tip. Thus, it is considered that the thermal stress can be reduced and the bonding can be made strong.
[0006]
However, in laser welding, the formed melted portion tends to be locally biased, and the bonding reliability against thermal stress is often inferior. In particular, the ground electrode is rotated with respect to a fixed laser irradiation part for structural reasons such as having a bent shape so as to face the tip of the center electrode from the mounting bracket on the outer periphery of the center electrode, for example. It is difficult to join the entire circumference efficiently. The same applies to the case where the tip is laser welded after the ground electrode is fixed to the mounting bracket by welding or the like.
[0007]
Therefore, in view of the above problems, the present invention provides a spark plug in which an Ir alloy chip containing Ir as a main component and a ground electrode and / or a center electrode are melt-bonded by laser welding, and has high reliability in connection with thermal stress. A first object is to provide a high melting part configuration in the ground electrode, and a second object is to provide a melting part configuration having high bonding reliability against thermal stress in the center electrode.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have formed a shape of a melted portion formed by laser welding, particularly at a bonding interface between an Ir alloy tip and a ground electrode and / or a center electrode (hereinafter referred to as a base material electrode). Focusing on the length of the melted portion occupied and the degree of penetration of the melted portion into the base material electrode, intensive studies were conducted. Here, these lengths are shown in FIG. FIG. 3 shows an example in which an Ir alloy tip is bonded to the ground electrode.
[0009]
As shown in FIG. 3, the length of the melted portion in the joint interface is the center of the joint interface (60) at the end portion (61) on the side of the center electrode (3) and the joint interface (60) of the melted portion (70). The maximum dimension of the straight line connecting the end (72) opposite to the electrode (3) is A, and the length B occupied by the melted part (70) in the maximum dimension A is defined as A. In FIG. 3, the length B is a linear length between the end (71) on the side of the center electrode (3) and the end (72) on the opposite side at the joining interface (60) of the melting part (70).
[0010]
And the ratio B / A of A and B was examined. Further, as shown in FIG. 3, the melting degree of the melted portion is defined as t where the protruding length of the tip (52) protruding from the bonding interface (60) is t, and the bonding interface between the protruding length t and the melting portion (70). The ratio d / t of d and t, where d is the total length of the maximum penetration length from (60) to the ground electrode (4), was examined.
[0011]
Then, a plug was installed in the combustion chamber of the engine, and the relationship between the ratios B / A and d / t and the degree of chip peeling was investigated in a high-temperature combustion atmosphere. As a result, when the ratio B / A satisfies B / A ≧ 0.5, it is possible to prevent the chip (52) from being peeled off from the ground electrode (4) due to thermal stress at the bonding interface (60) (described later). (See FIG. 6).
[0012]
Further, when the ratio d / t satisfies 2 ≦ d / t ≦ 4, the chip (52) and the melted part (70) are peeled off due to thermal stress, and the melted part (70) and the ground electrode (4). It was found that the peeling can be prevented (see FIG. 5 described later). The inventions described in claims 1 to 4 have been made on the basis of the above knowledge and the case where the base electrode is a ground electrode in order to achieve the first object.
[0013]
That is, in the first aspect of the present invention, it is formed by melting into both sides of the tip (52) and the ground electrode (4) through the joining interface (60) by laser welding with laser irradiation from the tip (52) side. The melted portion (70) is characterized in that the ratio B / A is 0.5 or more and the ratio d / t is 2 or more and 4 or less. As a result, it is possible to realize a melted portion configuration with high bonding reliability against thermal stress when the inside of the tip (52) is bonded to the ground electrode (4) by laser welding.
[0014]
Further, as in the invention described in claim 2 , the Ir-Rh alloy containing Ir and Rh can be used as the Ir alloy constituting the chip (52). Further, the composition of the melted portion (70) made of an alloy containing Ni and Ir that satisfies the dimensional relationship according to claim 1 is such that the total of Ir and Ni is 100% by weight as in the invention according to claim 3. In this case, it is preferable that Ir is contained in an amount of 20 to 80% by weight.
[0015]
The invention according to claim 4 provides a specific shape of the chip (52), and the columnar chip (52) faces the ground electrode (4) on the side surface of the column and joins the interface. (60) can be formed. Further, the invention described in claim 5 is based on the knowledge about each ratio B / A and d / t, and is based on the case where the base electrode is used as the center electrode. The same effect as the invention can be obtained, and the second object can be achieved.
[0016]
In addition, the code | symbol in the above-mentioned parenthesis is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below. This embodiment is used, for example, as an ignition plug for an internal combustion engine. FIG. 1 is a half sectional view showing the overall configuration of the spark plug 100 of the present embodiment.
The spark plug 100 has a cylindrical mounting bracket 1, and the mounting bracket 1 includes a mounting screw portion 1 a for fixing to an engine block (not shown). An insulator ₂ made of alumina ceramic (Al ₂ O ₃ ) or the like is fixed inside the mounting bracket 1, and a distal end portion 2 a of the insulator 2 is provided so as to be exposed from the mounting bracket 1. .
[0018]
A center electrode 3 is fixed to the shaft hole 2 b of the insulator 2, and the center electrode 3 is insulated and held with respect to the mounting bracket 1. The center electrode 3 is a cylindrical body made of a metal material having excellent heat conductivity such as Cu as an inner material and a metal material having excellent heat resistance and corrosion resistance such as a Ni-based alloy as shown in FIG. The tip portion 3 a is provided so as to be exposed from the tip portion 2 a of the insulator 2.
[0019]
On the other hand, the ground electrode 4 is fixed to one end of the mounting bracket 1 by welding at a fixing portion 4a on one end side, bent to a substantially L shape in the middle, and the center electrode 3 at an opposite portion 4b opposite to the fixing portion 4a. The front-end | tip part 3a and the discharge gap 6 are opposed. 2A is an enlarged perspective view in the vicinity of the facing portion 4b of the ground electrode 4, FIG. 2B is a view as viewed from the arrow Y in FIG. 2A, and FIG. 2C is a view as viewed from the arrow X in FIG. . The ground electrode 4 is made of a Ni-based alloy (for example, Inconel (registered trademark)) containing Ni as a main component, and has a cross-sectional flatness having a total length of, for example, 10 mm (in FIG. 2, for example, a width W of 2.8 mm and a thickness H of 1.6 mm) prisms are bent into a substantially L shape.
[0020]
A noble metal tip 51 is fixed to the tip 3a of the center electrode 3 by laser welding. The tip 51 is disk-shaped and is joined to the cylindrical end surface of the tip 3 a of the center electrode 3. On the other hand, a noble metal tip 52 having a substantially cylindrical shape is fixed to the side surface 4c of the facing portion 4b of the ground electrode 4 by laser welding. Both of these chips (corresponding to spark discharge part electrode materials) 51 and 52 are made of an Ir alloy containing Ir as a main component (for example, an Ir-10Rh alloy having 90% by weight of Ir and 10% by weight of Rh). Here, the discharge gap 6 is a gap between the two chips 51 and 52, and is about 1 mm, for example.
[0021]
Here, the chip 52 on the ground electrode 4 side, which is the main part of the present invention, will be described in more detail with reference to FIG. The chip 52 has a columnar shape, and in the illustrated example, the length is a cylindrical body (for example, a diameter of 0.7 mm and a length of 1.6 mm) substantially equal to the thickness H of the ground electrode 4. A part of the side surface in the longitudinal direction of the cylinder is sunk into the side surface 4c of the facing portion 4b. Therefore, the boundary surface between the cylindrical side surface of the chip 52 and the side surface 4c of the facing portion 4b facing the cylindrical side surface is a bonding interface 60.
[0022]
The welding state of the tip 52 and the ground electrode 4 at the joint interface 60 will be described with reference to FIG. 3 is a cross-sectional view taken along the line aa in FIG. 2B, that is, a cross-sectional view passing through the central axis of the chip 52 in the longitudinal direction of the cylinder. In FIG. 3, the upper side is the center electrode 3 side. In FIG. 3, the length of the straight line indicated by the bonding interface 60 is equal to the length of the cylindrical body forming the chip 52, that is, the thickness H (for example, 1.6 mm) of the ground electrode 4.
[0023]
Since the tip 52 and the ground electrode 4 are laser-welded, as shown in the semi-elliptical hatching of FIG. 3, the melted portion 70 in which both are melted enters the ground electrode 4 from the tip 52 with the bonding interface 60 interposed therebetween. It is formed by melting across. Here, since the tip 52 is an Ir alloy and the ground electrode 4 is a Ni-based alloy as described above, the melting portion 70 is made of an alloy of Ir and Ni (Ir—Ni alloy).
[0024]
2B and 2C and the white arrow R in FIG. 3, in laser welding, the laser is substantially perpendicular to the side surface 4c of the facing portion 4b and the center axis of the tip 52 in the longitudinal direction of the cylinder. Irradiated to pass through. Therefore, FIG. 3 corresponds to a cross section along the direction in which the laser energy is the largest in the direction parallel to the central axis, that is, the cross section in which the melted portion 70 is formed most widely at the bonding interface 60.
[0025]
Therefore, among the dimension A shown in FIG. 3, that is, the linear dimension connecting the end portion 61 on the side of the center electrode 3 of the bonding interface 60 and the end portion 72 on the opposite side of the center electrode 3 in the bonding interface 60 of the melting portion 70. The maximum dimension (hereinafter referred to as the maximum dimension A). The length occupied by the melted portion 70 in the maximum dimension A, that is, the length between the end portion 71 of the melted portion 70 on the side of the center electrode 3 and the end portion 72 on the opposite side thereof in FIG. It is referred to as the melted part length B).
[0026]
Here, in FIG. 3, in the bonding interface 60, the tip is between the end portion 72 opposite to the center electrode 3 of the melting portion 70 and the end portion 62 opposite to the center electrode 3 side of the bonding interface 60. 52 is not melted and is an unmelted portion. That is, in FIG. 3, the maximum dimension A is the length of the straight line connecting the end portion 61 and the end portion 62 of the bonding interface 60 excluding the unmelted portion. This unmelted portion may not be present.
[0027]
Further, as described above, in FIG. 3, since the cross section is along the direction in which the laser energy is most applied, the penetration length of the melted portion 70 from the bonding interface 60 into the ground electrode 4 is the maximum penetration length. It has become.
In FIG. 3, the protruding length of the chip protruding in the vertical direction from the bonding interface 60 is t (hereinafter referred to as the protruding length t). In this example, the protruding length t is equal to the diameter of the tip 52 (for example, 0.7 mm). Further, the total length of the protruding length t and the maximum penetration length of the melted portion 70 from the bonding interface 60 into the facing portion 4b of the ground electrode 4 is d (hereinafter referred to as the total length d). Incidentally, the protruding length t is a length protruding from the bonding interface 60 on the extension line of the maximum penetration length (dt).
[0028]
The main feature of the present embodiment is that the dimensions (A, B, d, t) are defined as follows in order to improve the bonding reliability between the chip 52 and the ground electrode 4. That is, the ratio B / A between the maximum dimension A and the melted part length B is 0.5 or more, and the ratio d / t between the protrusion length t and the total length d is 2 or more and 4 or less.
Next, a method for joining the ground electrode 4 and the chip 52 will be described. In addition, about the manufacturing method of the spark plug of this embodiment, since the manufacturing process of another part is known, description is abbreviate | omitted. Usually, the tip 52 is laser welded in a state where the ground electrode 4 is fixed to the mounting bracket 1, but may be performed in a state where the ground electrode 4 is alone.
[0029]
First, before performing laser welding, the tip 52 is temporarily fixed to the side surface 4c of the facing portion 4b of the ground electrode 4 by resistance welding so that the tip 52 does not move during laser welding. In this temporary fixing stage, the chip 52 sinks into the side surface 4c of the facing portion 4b. In addition, in order to facilitate the installation of the chip, a groove or the like may be processed in advance in the chip joint portion of the ground electrode 4. Subsequently, laser welding is performed from the direction of the white arrow R.
[0030]
Here, the laser welding conditions are, for example, energy of 33 J (pulse width is 15 msec, charging voltage is 360 V), defocus is +2 mm (that is, the focal point of the laser is 2 mm behind the irradiation surface of the chip 52), laser beam The diameter was φ0.4 mm. For example, the melting part 70 is formed by continuous irradiation (for example, three shots) under such conditions. Note that the diameter of the tip 52 (corresponding to the protruding length t in this example) is constant without changing between the single tip and after welding.
[0031]
In this way, the reason for continuous irradiation in several times is as follows. In laser welding, irradiation is performed from the tip 52 side as indicated by the outlined arrow R. Therefore, if the energy is weak, the ground electrode 4 as a base material is less melted and the Ir component is increased. On the other hand, if it is too strong, the Ir alloy and the ground electrode 4 are scattered, and it is difficult to obtain appropriate conditions. Therefore, by continuously irradiating energy that is suppressed to some extent, the Ir component in the melted portion and the Ni component are increased for each shot to form the melted portion 70 having intermediate physical properties between the tip 52 and the ground electrode 4. I am going to do that.
[0032]
Here, the laser welding conditions and the number of irradiations are obtained by confirming the relationship between the laser welding conditions and the like and the shape of the melted portion 70 in advance. For confirmation of the melted portion 70, after the laser welding, the ground electrode 4 and the tip 52 are scraped to obtain the cut surface shown in FIG. And each dimension (A, B, d, t) of the fusion | melting part 70 is grasped | ascertained by observation with a metal microscope. As for the composition, the composition ratio can be determined by analysis using an energy dispersion analyzer such as EDS.
[0033]
FIG. 4 shows an example of confirmation of the melted part 70 state. In the above laser welding condition example, the relationship between the number of times of laser irradiation and the ratio d / t (see FIG. 4 (a)), when the total number of Ir and Ni in the melting portion 70 is 100% by weight. The relationship with the composition ratio (% by weight) of Ni and Ir (see FIG. 4B) was examined. It can be seen that as the number of times of laser irradiation is increased, the ratio d / t is increased, the amount of Ni in the melted portion 70 is increased, and the amount of Ir is decreased.
[0034]
Next, the grounds for defining the dimensions (A, B, d, t) as described above at the joint between the chip 52 and the ground electrode 4 will be described. This basis is based on experimental data. In the Ir-10Rh alloy tip 52, the protrusion length (that is, the diameter of the tip 52) t = 0.7 mm, the maximum dimension A = 1.6 mm, the melted portion length B = The ratio B / A was set to 1.0 mm, and the ratio B / A was kept constant at B / A = 0.63, and the weldability was examined by changing the number of laser irradiations and changing the penetration length (dt).
[0035]
The bondability was investigated by the following durability test. The test was conducted with a 6-cylinder 2000cc engine, and the operating condition was held for 1 minute in an idle state (for example, about 300 ° C.), and then the throttle was fully opened (for example, about 900 ° C.) at 6000 rpm for 1 hour. And the peeling state in ratio d / t in the range of 1.5-5 was investigated, and bondability was evaluated. The result is shown in FIG.
[0036]
As shown in FIG. 5A, the interface between the ground electrode 4 having the length L1 and the melting part 70 (electrode base material-melting part interface), and the interface between the chip 52 having the length L2 and the melting part 70 The peeling rate was examined with respect to (chip-melting portion interface). Since the part peeled off at each interface can be confirmed with a microscope, the length L3 of the peeled part occupying each interface is required. The peeling rate is represented by (L1-L3) / L1 × 100 (%) at the electrode base material-melting portion interface, and is represented by (L2-L3) / L2 × 100 (%) at the tip-melting portion interface. The
[0037]
FIG. 5B shows the relationship between the peeling rate and the ratio d / t at each interface. The electrode base material-melting part interface is represented by a black circle, and the tip-melting part interface is represented by a white circle. At the interface between the electrode base material and the melted part, the ratio d / t is 2 or more, and good bondability is exhibited with almost no cracks and peeling. On the other hand, at the interface between the chip and the melted part, the ratio d / t is 4 or less, and good bondability is exhibited with almost no cracks and peeling. Therefore, the ratio d / t is preferably 2 ≦ d / t ≦ 4.
[0038]
As shown in FIG. 4 above, when d / t = 1.5, the Ir component in the melting part 70 is too much (about 85 wt%), so that the melting part 70 and the electrode base material of the ground electrode 4 It is considered that peeling occurred due to a large difference in linear expansion coefficient. Further, when d / t = 5, the Ir component is too small (about 15% by weight), so that the difference in the linear expansion coefficient between the melted part and the Ir alloy tip is considered to be separated. In the above range of the ratio d / t, if Ir in the melted portion 70 has a composition range of 20 wt% to 80 wt% when the total of Ir and Ni is 100 wt%, the bondability is improved. Is considered preferred for.
[0039]
Next, the d / t ratio was kept constant at d / t = 3, and the same durability test as described above was performed with the ratio B / A changed. The result is shown in FIG. Here, the bondability was evaluated using the angle θ when the chip 52 peeled from the bonding interface 60 as shown in FIG. As shown in FIG. 6B, when the ratio B / A is 0.5 or more, the inclination of the chip 52 is eliminated, and good bonding property is exhibited. If the ratio B / A is too small, there are many portions that are joined (temporarily fixed) only by resistance welding, so that the tip 52 peels off from the ground electrode 4 due to thermal stress, and the discharge gap from the center electrode is increased. It cannot be maintained properly.
[0040]
As described above, according to the present embodiment, when the shape dimension of the melting portion 70 satisfies B / A ≧ 0.5, the chip 52 is peeled off from the ground electrode 4 due to thermal stress at the bonding interface 60. By satisfying 2 ≦ d / t ≦ 4, it is possible to prevent the chip 52 and the melted portion 70 from being peeled by the thermal stress and the melted portion 70 and the ground electrode 4 from being peeled off. It is possible to realize a highly melted structure.
[0041]
In addition, according to the present embodiment, because of the melting part configuration with high bonding reliability, the plug replacement time can be greatly extended, a long-life spark plug can be realized, and further, it can be used in an environment where heat load is severe. A spark plug can be provided. In addition, according to the present embodiment, joining can be performed by laser welding, which is a very easy manufacturing method, such as no need for pressurization as compared with resistance welding, and cost can be reduced from the manufacturing aspect.
[0042]
7 and 8 as reference examples of the present invention, the bonding position of the chip 52 to the ground electrode 4 and the positional relationship with the center electrode 3 are changed. In FIG. 7A, a part of the side surface of the chip 52 in the longitudinal direction of the cylinder is laser-welded to a surface facing the tip 3 a of the center electrode 3 among the facing portions 4 b of the ground electrode 4. Here, in FIG. 7 and FIGS. 8 and 9 to be described later, the melting part 70 is not actually visible in appearance, but is shown by hatching in the drawing.
[0043]
Moreover, in FIG.7 (b), the center electrode 3 is extended and the two ground electrodes 4 fixed to the attachment metal fitting 1 are facing the both side surfaces of the front-end | tip part 3a of a center electrode. The tip 52 is laser welded to the facing portion 4b of both ground electrodes 4 .
[0044]
Here, FIGS. 7A and 7B are examples in which the unmelted portion is not present, but as shown in FIGS. 8A and 8B, the unmelted portion is present. Also good. The spark plug shown in FIG. 9 is another embodiment of the present invention, and shows an example in which the base electrode is the center electrode 3 in the arrangement relationship between the center electrode and the ground electrode in FIG. 7B. is there. A columnar tip 51 a is laser welded to the tip 3 a of the center electrode 3. Here, in FIG. 9, (b) is an enlarged view of the welded portion of the tip 51a of (a), and (c) is a top view of (b).
[0045]
In the example of FIG. 9B, the dimensions A and B in the above embodiment are shown in relation to the right ground electrode 4 (hereinafter referred to as the right ground electrode 4) in FIG. 9A. That is, the maximum dimension A is the maximum dimension of a straight line connecting the end 63 on the right ground electrode 4 side of the bonding interface 60 and the end 73 on the opposite side of the right ground electrode 4 in the bonding interface 60 of the melting part 70. The melted part length B is the length occupied by the melted part 70 in the maximum dimension A.
[0046]
The relationship between these dimensions A and B is the same as the relationship with the left ground electrode 4 in FIG. And in the spark plug shown in FIG. 9, each dimension (A, B, d, t) is prescribed | regulated to the same dimensional relationship as the said embodiment, and the center electrode 3 has high joining reliability with respect to a thermal stress. A melting part configuration can be realized. Further, the configuration shown in FIG. 9 may be combined with the configuration shown in FIG.
[0047]
Further, the shape of the chips 51 and 51a laser welded to the base material electrodes 3 and 4 may be not only a cylinder but also a prismatic shape or a disk shape. However, in order to perform laser welding, it is preferable that an appropriate thickness, that is, a protrusion length t from the joining interface is large enough to form the melted portion 70. Further, the Ir alloy constituting the chip is not limited to an Ir-10Rh alloy having 90% by weight of Ir and 10% by weight of Rh, but may be an Ir alloy having Ir as a main component.
[Brief description of the drawings]
FIG. 1 is a half sectional view showing an overall configuration of a spark plug according to an embodiment of the present invention.
2A is an enlarged perspective view in the vicinity of the facing portion of the ground electrode in FIG. 1, FIG. 2B is a view as viewed from the arrow Y in FIG. 1A, and FIG. 2C is a view as viewed from the arrow X in FIG.
FIG. 3 is a cross-sectional view taken along the line aa in FIG.
4A is a graph showing the relationship between the number of times of laser irradiation and the ratio d / t, and FIG. 4B is a graph showing the relationship between the number of times of laser irradiation and the composition ratios of Ni and Ir in the melted part.
FIG. 5 is a diagram showing the evaluation results of the bondability between the ground electrode and the chip with respect to the ratio d / t.
FIG. 6 is a diagram showing the evaluation results of the bonding properties of the ground electrode and the chip with respect to the ratio B / A.
FIG. 7 is a diagram showing a first reference example of the present invention.
FIG. 8 is a diagram showing a second reference example of the present invention.
9 is a diagram showing another embodiment form status of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Mounting bracket, 3 ... Center electrode, 4 ... Ground electrode, 4b ... Opposite part of ground electrode, 6 ... Discharge gap, 52 ... Tip, 60 ... Joining interface, 61 ... End side of center side of joining interface, 63 ... The ground electrode side end of the joint interface, 70... The melted portion, 72... The end opposite to the center electrode at the joint interface of the melted portion, 73.

Claims

A center electrode (3), a mounting bracket (1) for insulatingly holding the center electrode (3), and fixed to the mounting bracket (1), facing the center electrode (3) with a discharge gap (6) therebetween. A ground electrode (4) made of a Ni-based alloy having a facing portion (4b), and a chip (52) made of an Ir alloy is joined to the facing portion (4b) of the ground electrode (4). In the spark plug,
The facing portion of the ground electrode (4) (4b), said has parallel sides in the axial direction of the center electrode (3) (4c), said chip (52), said from said tip (52) side The center of the tip (52) in the longitudinal direction, the welding of the facing portion (4b) by laser welding that irradiates a laser toward the joining interface (60) where the tip (52) and the ground electrode (4) face each other. A melted part (70) made of an alloy containing Ni and Ir, which is bonded to the side surface (4c) and melted by the laser welding, is connected to the chip (52) and the ground electrode (4) from the chip (52). DOO via the bonding interface facing (60) is formed blend into the ground electrode (4) inside,
The end portion (61) on the side of the center electrode (3) of the bonding interface (60) and the end portion (72) on the opposite side to the center electrode (3) in the bonding interface (60) of the melting portion (70). The maximum dimension of the straight line connecting A and B is A, and the length occupied by the melted part (70) in the maximum dimension A is B. The ratio B / A of A and B is 0.5 or more, The projecting length of the tip (52) projecting from the joining interface (60) is t, and this projecting length t and the maximum from the joining interface (60) of the melting part (70) to the ground electrode (4). A spark plug, wherein a ratio d / t between d and t is 2 or more and 4 or less, where d is the total length of the penetration length.

The spark plug according to claim 1, wherein the Ir alloy constituting the tip (52) is an Ir-Rh alloy containing Ir and Rh.

3. The melt part (70) is characterized in that, when the total of Ir and Ni is 100 wt%, Ir is contained in an amount of 20 wt% to 80 wt%. Spark plug.

The chip (52) has a columnar shape, and a side surface of the column and the ground electrode (4) face each other to form the bonding interface (60). The spark plug according to one.

A center electrode (3), a mounting bracket (1) for insulatingly holding the center electrode (3), and fixed to the mounting bracket (1), facing the center electrode (3) with a discharge gap (6) therebetween. A spark plug comprising a ground electrode (4) made of a Ni-based alloy and having a tip (51a) made of an Ir alloy joined to a portion of the center electrode (3) facing the ground electrode (4) In
The chip (51a) is directed from the chip (51a) side toward the central axis in the longitudinal direction of the chip (51a) and the bonding interface (60) where the chip (51a) and the ground electrode (4) face each other. The laser beam is joined to the center electrode (3) by laser welding and protrudes from the tip (3a) of the center electrode (3) in the axial direction of the center electrode (3) and melted by the laser welding. The melted portion (70) made of an alloy containing Ni and Ir is melted into the center electrode (3) from the tip (51a) through the bonding interface (60), The end portion (63) on the ground electrode (4) side of the bonding interface (60) and the end portion (73) on the opposite side to the ground electrode (4) in the bonding interface (60) of the melting portion (70). The straight line connecting When the dimension is A and the length occupied by the melted part (70) in the maximum dimension A is B, the ratio B / A of A and B is 0.5 or more, and the bond interface (60) The protruding length of the protruding tip (51a) is t, and the total length of the protruding length t and the maximum penetration length from the joining interface (60) of the melting part (70) to the center electrode (3). A spark plug, wherein a ratio d / t between d and t is 2 or more and 4 or less, where d is t.