JP3756005B2

JP3756005B2 - Oxygen sensor and method for manufacturing oxygen sensor

Info

Publication number: JP3756005B2
Application number: JP37386298A
Authority: JP
Inventors: 聡石川
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 1998-12-28
Filing date: 1998-12-28
Publication date: 2006-03-15
Anticipated expiration: 2018-12-28
Also published as: JP2000193631A

Description

【０００１】
【発明の属する技術分野】
この発明は、例えば内燃機関の排気ガスなど、被測定ガス中の酸素を検出するための酸素センサに関する。
【０００２】
【従来の技術】
上記のようなヒータ付き酸素センサの一形態として、先端部が閉じた中空軸状をなし、それの内壁面に電極層を有する酸素検出素子を備えたものが知られている。このようなタイプのセンサは、酸素検出素子の中空部内に軸状のヒータが配置され、例えばエンジン始動直後など排気ガス温度が低いときに、固体電解質で構成された酸素検出素子をそのヒータで加熱・活性化させるようにしている。そして、その酸素検出素子からのセンサ出力は、素子の内外面に形成された電極層を介してリード線により取り出される。
【０００３】
ところで、近年は自動車産業の隆盛に伴い酸素センサに対する需要も増え、かつ価格低下に対する要望も年々強まりつつある。酸素センサは、自動車用電装部品の中でも部品点数が多く、組立工程の簡略化を如何にして図るかが製造コスト削減の重要な鍵を握っている。そのためには、組立工程の自動化など生産設備側の技術改良も必要であるが、工数削減に有利なセンサ構造を工夫することも重要である。
【０００４】
例えば、上記タイプの酸素センサにおいては、中空の酸素検出素子の内面に形成される内部電極層からの出力を、素子の中空部に嵌入される筒状の接続金具を介してリード線により取り出すようにしている。リード線は、接続金具の後方に配置されたセラミックセパレータを貫いて、ケーシング末端から外部に引き出される。
【０００５】
【発明が解決しようする課題】
ところで、一般の多くの酸素センサにおいては、酸素検出素子を収容するケーシングの後端側（検出部と反対側）に、基準ガスとしての大気をケーシング内に導入するための気通部を有したカバー部材が組み付けられる。リード線は、カバー部材の後端開口部に嵌め込まれたシール用のゴムグロメットを貫いて引き出される。また、接続金具の端部に一端がつながる形で一体形成された引出し線部をセラミックセパレータ内に導き、コネクタを介してその引出し線部にリード線を接続するようにしている。
【０００６】
ここで、カバー部材の内側にセラミックセパレータと接続金具とを予め組み付けておき、酸素検出素子が配置されたケーシングに後方側からカバー部材を差し込みつつ、検出素子の中空部への接続金具の押込・装着を同時に行う（すなわち、セパレータと接続金具とを一体化した形で検出素子に組み付ける）ことができれば、工数削減上有利である。しかしながら、従来の酸素センサでは接続金具は、長く延びる引出し線部により、セラミックセパレータの端面からかなり離れた位置において、いわばぶら下げられる形で組み付けられている。そのため、カバー部材とともにセラミックセパレータを酸素検出素子に対し接近させ、接続金具の素子の中空部内への嵌め込みを行おうとすると、細い引出し線部がセラミックセパレータと接続金具との間で挫屈して嵌め込みがうまく行えないばかりでなく、引出し線部の破断等のトラブルも引き起こしかねない。
【０００７】
そのため、従来は、まず手作業により接続金具の酸素検出素子への嵌め込みを行い、セラミックセパレータを酸素検出素子の後方側にて指等で保持しながらカバー部材をその外側に静かに被せ、その後、カバー部材をケーシングに対し加締めや溶接等により接合して組み付けていた。しかしこれでは、接続金具の取付けを挟む前後の一連の工程が手作業中心にならざるを得ず、工数も増えるので能率の低下が甚しかった。
【０００８】
本発明の課題は、セラミックセパレータと接続金具との酸素検出素子に対する一体組付けを容易に行うことができ、ひいては高能率な製造が可能な構造を有する酸素センサと、その構造を利用した酸素センサ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】
上記課題を解決するために、本発明の酸素センサは、
先端部が閉じた中空軸状をなし、その中空部の内外面に電極層を有する酸素検出素子と、
その酸素検出素子を収容するケーシングと、
そのケーシング内において酸素検出素子の後方側に配置され、該酸素検出素子の内面に形成された内部電極層と、同じく外面に形成された外部電極層とのそれぞれに電気的に導通するリード線を挿通するための複数のリード線挿通孔が軸線方向に貫通して形成されたセラミックセパレータとを備え、
酸素検出素子の中空部の開口端部内側には、内部電極層に導通する筒状の内部電極接続金具が挿入されるとともに、その内部電極接続金具の後端縁をセラミックセパレータの前端面に当接配置し、
酸素検出素子の中空部には軸状の発熱体が挿入され、
セラミックセパレータは、リード線挿通孔が、該セラミックセパレータの中心軸線を取り囲む形態で複数形成され、
また、セラミックセパレータの軸線方向前端側には、内径が発熱体の外径よりも大きく設定されてセラミックセパレータの前端面に開口し、底面がセラミックセパレータの軸方向中間部に位置するとともに、発熱体の後端部を収容する発熱体端部収容孔が、各リード線挿通孔に対し内側から重なりを生ずるように、該セラミックセパレータの中央部を切り欠いた形態で形成されており、
内部電極接続金具の後端は、セラミックセパレータの発熱体端部収容孔の開口側の端面において、隣接するリード線挿通孔の間に形成される隔壁部の端面に当接してなり、
筒状の内部電極接続金具には、その後端周縁から外向きに突出する形態でセパレータ受け部が形成されており、セラミックセパレータの隔壁部の端面は、そのセパレータ受け部に当接していることを特徴とする。
【００１０】
この構造の採用により、以下の本発明の酸素センサの製造方法が実現される。すなわち、酸素検出素子の中空部開口側に内部電極接続金具を位置決めし、その状態でセラミックセパレータの前端面に該内部電極接続金具の後端縁を当接させつつセラミックセパレータと酸素検出素子とを軸線方向において相対的に接近させることにより、酸素検出素子の中空部に内部電極接続金具を嵌入させてこれを組み付ける。
【００１１】
これによれば、セラミックセパレータの前端面に内部電極接続金具の後端縁を当接させているので、接続金具を検出素子に対し軸線方向に相対接近させてその外側に嵌め込む際に、例えば外部電極接続金具からリード線側に引出し線部が延びている場合にもその挫屈等が起こらない。その結果、セパレータを一体化した形での、酸素検出素子に対する内部電極接続金具の組付けを支障なく行うことができる。
【００１２】
例えば、酸素検出素子を覆うケーシングの後端側にカバー部材を組み付ける場合、カバー部材の内側にセラミックセパレータと内部電極接続金具とを予め組み付けておき、酸素検出素子が配置されたケーシングに後方側からカバー部材を差し込みつつ、内部電極接続金具の検出素子の中空部への押込を同時に行う工程を問題なく行うことができる。このように、上記本発明の酸素センサの構造及び製造方法の採用により、酸素センサの大幅な組立工数の削減を図ることができ、ひいては酸素センサの製造能率の向上とコストダウンとが実現する。
【００１３】
なお、上記酸素センサは、ケーシングの後方側においてこれと一体的に設けられ、ケーシング内に外気を導くための第一気体導入孔が形成された第一フィルタ保持部と、その第一フィルタ保持部の内側又は外側に設けられ、ケーシング内に外気を導くための第二気体導入孔が形成された第二フィルタ保持部と、それら第一及び第二フィルタ保持部の間において第一及び第二気体導入孔を塞ぐ形態で配置され、液体の透過は阻止し気体の透過は許容するフィルタとを備え、第一フィルタ保持部が、ケーシングとは別体の筒状体として該ケーシングに対し後方側から連結されるものとして構成できる。この場合、本発明の製造方法を以下のようにして実施できる。まず、ケーシングに組付ける前の状態で、第一フィルタ保持部の外側にフィルタ及び第二フィルタ保持部をこの順序で配置し、その状態で加締め部を形成することにより、第二フィルタ保持部及びフィルタを第一フィルタ保持部に組み付けてフィルタアセンブリとなす。そして、セラミックセパレータと内部電極接続金具とを予め組み付けておき、そのフィルタアセンブリの第一フィルタ保持部の内側に、ケーシングの後端部を該フィルタアセンブリの組付けのために挿入するとともに、その挿入に際して、内部電極接続金具の酸素検出素子の中空部への嵌入・組付けを同時に行うようにする。
【００１４】
上記のセンサ構成の要旨は、フィルタを含む気通構造部をフィルタアセンブリとしてケーシングとは独立に構成し、これをケーシングに連結・一体化した構成を有する点にある。これにより、その製法上、次のような効果が達成される。
▲１▼フィルタアセンブリの組立てを、酸素検出素子などのケーシング内への組付けとは独立に行うことができるので、例えば検出素子のリード線が邪魔になったりせず、組立作業を極めて能率的に行うことができる。
▲２▼ケーシング内への部品の組付けと、フィルタアセンブリの組立てとを並行して行えるので、生産性が飛躍的に向上する。また、フィルタの組付け不良などが生じても、フィルタアセンブリの段階で不良が発見できれば、センサ完成品に該不良の影響は及ばず、部品等の無駄等が生じにくい。
▲３▼フィルタアセンブリのケーシングへの組付けと同時に、内部電極接続金具の酸素検出素子の中空部への篏入・組付けも同時に完了するので、極めて能率的である。
【００１５】
【発明の実施の形態】
以下、本発明の実施の形態を図面に示す実施例に基づき説明する。
図１は本発明のガスセンサの一実施例たる酸素センサの内部構造を示している。該酸素センサ１は、先端が閉じた中空軸状の固体電解質部材である酸素検出素子２と、発熱体３とを備える。酸素検出素子２は、ジルコニア等を主体とする酸素イオン伝導性固体電解質により中空に形成されている。また、この酸素検出素子２の外側には金属製のケーシング１０が設けられている。
【００１６】
ケーシング１０は、酸素センサ１を排気管等の取付部に取り付けるためのねじ部９ｂを有する主体金具９、その主体金具９の一方の開口部に内側が連通するように結合された主筒１４、該主筒１４とは反対側から主体金具９に取り付けられたプロテクタ１１等を備える。図２に示すように、酸素検出素子２の外面及び中空部２ａの内面には、そのほぼ全面を覆うように、例えばＰｔあるいはＰｔ合金により多孔質に形成された外部電極層２ｂと内部電極層２ｃとが設けられている。
【００１７】
図１に戻り主体金具９の後方側の開口部には、前述の主筒１４が絶縁体６との間にリング１５を介して加締められ、この主筒１４に筒状のフィルタアセンブリ１６（カバー部材）が外側から嵌合・固定されている。このフィルタアセンブリ１６の後端側開口部はゴム等で構成されたグロメット１７で封止され、またこれに続いてさらに内方にセラミックセパレータ１８が設けられている。そして、それらセラミックセパレータ１８及びグロメット１７を貫通するように、酸素検出素子２用のリード線２０，２１及び発熱体３用のリード線（図示していない）が配置されている。
【００１８】
次に、図４に示すように、セラミックセパレータ１８には、各リード線２０，２１を挿通するための複数のセパレータ側リード線挿通孔７２が軸方向に貫通して形成されており、その軸方向中間位置には、外周面から突出する形態でフランジ状のセパレータ側支持部７３が形成されている。そして、図３に示すように、該セラミックセパレータ１８は、セパレータ側支持部７３よりも前方側に位置する部分を主筒１４の後端部内側に入り込ませた状態で、該セパレータ側支持部７３において主筒１４の後端面に当接するとともに、セパレータ側支持部７３よりも後方側に位置する部分を主筒１４の外側に突出させた状態で配置される。
【００１９】
図１に戻り、酸素検出素子２用の一方のリード線２０は、互いに一体に形成されたコネクタ２３ａ、引出し線部２３ｂ金具本体２３ａ及び発熱体把持部２３ｄからなる内部電極接続金具２３を経て前述の酸素検出素子２の内部電極層（以下、内部電極層という）２ｃ（図２）と電気的に接続されている。一方、他方のリード線２１は、互いに一体に形成されたコネクタ３３ａ、引出し線部３３ｂ及び金具本体部３３ｃとを有する外部電極接続金具３３を経て、酸素検出素子２の外部電極層（以下、外部電極層という）２ｂ（図２）と電気的に接続されている。酸素検出素子２は、その内側に配置された発熱体３で加熱することで活性化される。発熱体３は棒状のセラミックヒータであり、抵抗発熱線部（図示せず）を有する発熱部４２（図２）がリード線１９，２２（図１）を経て通電されることにより、酸素検出素子２の先端部（検出部）を加熱する。
【００２０】
図７に示すように、外部電極接続金具３３は、筒状の金具本体部３３ｃを有するとともに、前記した引出し線部３３ｂの一端が周方向の１ケ所に接続する形で一体化されている。他方、その中心軸線を挟んで引出し線部３３ｂの接続点と反対側には、軸線方向のスリット３３ｅが形成されている。このような金具本体部３３ｃの内側に、酸素検出素子２の後端部がこれを弾性的に押し広げる形で内側から挿入されている。具体的には、酸素検出素子２の外周面後端部には外部側出力取出部としての導電層２ｆが、周方向に沿って帯状に形成されている。外部電極層２ｂは、例えば無電解メッキ等により、酸素検出素子２の係合フランジ部２ｓよりも前端側の要部全面を覆うものとされている。他方、導電層２ｆは、例えば金属ペーストを用いたパターン形成・焼き付けにより形成されるもので、同様に形成される軸線方向の接続パターン層２ｄを介して外部電極層２ｂと電気的に接続されている。
【００２１】
一方、内部電極接続金具２３は、発熱体３の先端側に形成された発熱体把持部２３ｄにおいて発熱体２３を把持するとともに、金具本体２３ｃにより酸素検出素子２の内面にこれを固定する役割を果たす。発熱体把持部２３ｄは、発熱体３の周囲を包囲するＣ字状の横断面形状を有している。そして、発熱体３を未挿入の状態では該発熱体３の外径よりは少し小さい内径を有し、発熱体３の挿入にともない弾性的に拡径してその摩擦力により該発熱体３を把持する。
【００２２】
また、金具本体２３ｃは、左右両側の縁に鋸刃状の接触部２３ｅがそれぞれ複数形成された板状部分を円筒状に曲げ加工することにより、発熱体３を包囲する形態で形成されている（すなわち、発熱体３が挿通される）。そして、図２に示すように、その外周面と酸素検出素子２の中空部２ａの内壁面との間の摩擦力によって発熱体３を該中空部２ａに対し軸線方向に位置決めする役割を果たすとともに、上記複数の接触部２６ａの各先端部において内部電極層２ｃと接触・導通するようになっている。
【００２３】
次に、図３に示すように、フィルタアセンブリ１６は、主筒１４（ケーシング１０）に対し後方外側からほぼ同軸的に連結される筒状形態をなすとともに、内部が主筒１４の外部と連通し、かつ壁部に複数の気体導入孔５２が形成された第一フィルタ保持部５１を備える。そして、その第一フィルタ保持部５１の外側には、上記気体導入孔５２を塞ぐ筒状のフィルタ５３が配置され、さらに、そのフィルタ５３の外側には、壁部に１ないし複数の気体導入孔５５が形成されるとともに、フィルタ５３を第一フィルタ保持部５１との間で挟み付けて保持する第二フィルタ保持部５４が配置される。
【００２４】
図６は、フィルタアセンブリ１６の組立状態を示している。気体導入孔５２及び気体導入孔５５は、第一フィルタ保持部５１及び第二フィルタ保持部５４に対し、各軸方向中間部において互いに対応する位置関係で周方向に沿って所定の間隔で形成されており、フィルタ５３は、第一フィルタ保持部５１を周方向に取り囲むように配置されている。なお、フィルタ５３は、例えばポリテトラフルオロエチレンの多孔質繊維構造体（商品名：例えばゴアテックス（ジャパンゴアテックス（株）））等による撥水性フィルタとして構成されている。
【００２５】
また、第二フィルタ保持部５４には、補助気体導入孔５５の列を挟んでその軸方向両側に、フィルタ５３を介して該第二フィルタ保持部５４を第一フィルタ保持部５１に対して結合する環状のフィルタ加締め部５６，５７（以下、単に加締め部５６，５７ともいう）が形成されており、第一フィルタ保持部５１の外面とフィルタ５３との間には隙間５８が形成されている。他方、第一フィルタ保持部５１は、自身の軸方向中間部に形成された段付き部６０により、該段付き部６０に関して軸方向前方側を第一部分６１、同じく軸方向後方側を第二部分６２として、該第二部分６２が第一部分６１よりも径小となるように構成されており、気体導入孔５２はその第二部分６２の壁部に形成されている。さらに、第二フィルタ保持部５４は第一フィルタ保持部５１の第一部分６１の外径よりも小さい内径を有する。
【００２６】
図３に戻り、第一フィルタ保持部５１は、セラミックセパレータ１８の突出部分を第二部分６２の内側まで進入させてこれを覆うとともに、段付き部６０においてセパレータ側支持部７３に対し、主筒１４とは反対側から金属弾性部材７４（例えば、リング状の波形座金にて構成される）を介して当接するように配置される。他方、該第一フィルタ保持部５１の先端側、すなわち第一部分６１において主筒１４（ケーシング１０）に対し外側からこれに重なりを生じるように配置され、その重なり部には、第一フィルタ保持部５１を主筒１４に対し気密状態となるように連結するケーシング加締め部７６が形成されている。
【００２７】
第二フィルタ保持部５４の外側には、筒状の防護カバー６４がこれを覆うように設けられている。この防護カバー６４は、第二フィルタ保存部５４との間に気体滞留空間６５を生じるように配置され、第一フィルタ保持部５１に対し、加締め部６６，６７により接合されている。なお、図６に示すように、第一フィルタ保持部５１の第一部分６１の外周面には、上記防護カバー内への気体導入部となる溝部６９が周方向に沿って所定の間隔で複数形成されている。
【００２８】
図３に戻り、セラミックセパレータ１８はセパレータ側支持部よりも前方側が主筒１４（ケーシング１０）の内側に入り込むように配置され、各リード線２０，２１等がセパレータ側リード線挿通孔７２において軸方向に挿通される。一方、グロメット１７は、第一フィルタ保持部５１の後方側開口部に対しその内側に弾性的にはめ込まれ、各リード線２０，２１等を挿通するためのシール側リード線挿通孔９１を有するとともに、それらリード線２０，２１等の外面と第一フィルタ保持部５１の内面との間をシールする。
【００２９】
セラミックセパレータ１８の後端面は、軸方向において気体導入孔５２よりも後方側に位置するとともに、グロメット１７とセラミックセパレータ１８との間には所定量の隙間９８が形成されている。また、第一フィルタ保持部５１の内周面とセラミックセパレータ１８の外周面との間にも隙間９２が形成されている。そして、気体導入孔５２からの気体は該隙間９２内に供給され、さらにセパレータ側リード線挿通孔７２とリード線との間に形成された隙間Ｋを通ってケーシング１０内に導かれる。
【００３０】
図５（ａ）に示すように、セラミックセパレータ１８には、４つのリード線挿通孔７２が、該セラミックセパレータ１８の中心軸線Ｏを中心とするピッチ円Ｃに沿って略９０°間隔で形成されている。また、同図（ｃ）及び（ｄ）に示すように、セラミックセパレータ１８の軸線方向前端側（図面では下端側）には、発熱体端部収容孔１８ａが軸線方向に形成されている。発熱体端部収容孔１８ａは、内径が発熱体３の外径よりも大きく設定されてセラミックセパレータ１８の前端面に開口し、底面１８ｅがセラミックセパレータ１８の軸方向中間部に位置し、ここに発熱体３の後端部を収容する形となっている。これにより、センサ１の全長がが短くなり、センサ寸法のコンパクト化が実現されている。また、発熱体端部収容孔１８ａは、各リード線挿通孔７２に対し内側から重なりを生ずるように、セラミックセパレータ１８の中央部を切り欠いた形態で形成されている。また、隣接するリード線挿通孔７２，７２の間には、隔壁部１８ｂが形成されている。
【００３１】
そして、図５（ｅ）及び図９に示すように、外部電極接続金具３３の金具本体部３３ｃの後端縁は、セラミックセパレータ１８の発熱体端部収容孔１８ａの開口側の端面において、上記隔壁部１８ｂの端面に当接している。また、内部電極接続金具２３の金具本体部２３ｃの後端縁は、外部電極接続金具３３の金具本体部３３ｃよりも内側にて、上記隔壁部１８ｂの端面に当接している。
【００３２】
図５（ｄ）に示すように、発熱体３の後端部と、発熱体端部収容孔１８ａの内面との間には一定量の隙間ｈｇが形成されるとともに、図１に示すように、発熱体３は酸素検出素子２の中空部２ａ内に傾けて配置されている。この傾斜配置状態は、内部電極接続金具２３において、発熱体把持部２３ｄと金具本体部２３ｃとのくびれ形態の接続部２３ｍを少し曲げて発熱体把持部２３ｄを傾斜させることにより実現されている。これにより、図２に示すように、発熱体３は、その先端部に形成された発熱部４２の近傍において、該発熱体３の中心軸線Ｏ1が酸素検出素子２の中空部２ａの中心軸線Ｏ2に対して片側に寄る形で偏心し、発熱部４２が発熱体３の内壁面に近づく形となっている（この実施例では、発熱部４２が発熱体３の内壁面に対し、いわば横当り形態で当接している）。
【００３３】
このような構造を採用することで、発熱部４２で発生する熱の酸素検出素子２への熱伝達が促進され、例えば発熱部４２が発熱体３の内壁面に当接する場合には、その接触点近傍の輻射熱も酸素検出素子２に効果的に作用して、酸素検出素子２を短時間で昇温させることができ、センサ活性化時間が短縮される。また発熱部４２や酸素検出素子２の熱膨張が生じても、発熱部４２の先端を酸素検出素子２の先端内面に当てる構造に比べて、その熱膨張の影響を受けにくい。言い換えれば、そのような横当て構造をとることにより、発熱体３や酸素検出素子４２が熱履歴を受けても、両者の接触状態を良好に保ち易くなる。また、酸素センサ１の特性のばらつきも減少できる。
【００３４】
なお、発熱体３の傾斜により、発熱部４２側すなわち先端側が、酸素検出素子２の中空部の中心軸線に対し偏心するということは、図５（ｄ）にやや誇張して描いているように、発熱体３の後端部が発熱体端部収容孔１８ａ内において、これと逆向きに偏心することを意味する。従って、前記した隙間ｈｇは、発熱体３の後端部の偏心を吸収する役割を果たしているということができる。このような隙間ｈｇを過不足なく確保することで、発熱体３を酸素検出素子２内に組み付ける際に、発熱体３が発熱体端部収容孔１８ａの内縁と当接しにくくなり、ひいてはこれを支点とした強い曲げ力が作用しにくくなって、発熱体３の折損等を効果的に防止できるようになる。
【００３５】
なお、上記隙間ｈｇを十分な大きさで形成するには、図５（ｅ）に示すように、発熱体端部収容孔１８ａの内面を形成する隔壁部１８ｂと、発熱体３との間に十分な距離が形成されるよう、発熱体端部収容孔１８ａの半径方向における、隔壁部１８ｂの突出量をある程度小さくしなければならない。そこで、筒状の内部電極接続金具２３（の金具本体部３３ｃ）に、その後端周縁から外向きに突出する形態でセパレータ受け部２３ｋを形成し、セラミックセパレータ１８の隔壁部１８ｂの端面を、そのセパレータ受け部２３ｋに当接させる形とすれば、隔壁部１８ｂの突出量が小さくとも、セラミックセパレータ１８と内部電極接続金具２３との当接状態を確実に得ることができる。
【００３６】
図１１に示すように、この実施例では、セパレータ受け部２３ｋは、筒状の内部電極接続金具２３（の金具本体部３３ｃ）の後端周縁から放射状に延びる複数の爪部として形成されている。セパレータ受け部２３ｋをこのような爪部として構成すれば、金具本体部３３ｃの後端開口部に、軸線方向の切れ目を周方向に沿って所定の間隔で形成し、切れ目の間に位置する舌状部を外向きに曲げることで、セパレータ受け部２３ｋを形成する各爪部を簡単に形成できる。なお、これら爪部は、各隔壁部１８ｂに対応した形で形成することで、セラミックセパレータ１８と内部電極接続金具２３との間に、より安定な当接状態を形成できる。
【００３７】
なお、図１３に示すように、筒状の内部電極接続金具２３（の金具本体部３３ｃ）は、その軸線方向中間部に形成された周方向の段付き部２３ｊにより後端部を拡径することができ、その拡径された後端部の端面においてセラミックセパレータ１８の前端面に当接させる形とすることもできる。この場合、後端部の拡径のみでラミックセパレータ１８の例えば隔壁部１８ｂの前端面との当接状態を確保できるのであれば、セパレータ受け部２３ｋを省略してもよい。ただし、この場合もセパレータ受け部２３ｋを形成すれば、セラミックセパレータ１８と内部電極接続金具２３との当接状態をさらに安定化させることができる。
【００３８】
さて、内部電極接続金具２３（の金具本体部３３ｃ）の後端部に上記のようなセパレータ受け部２３ｋを形成すると、セパレータ受け部２３の突出方向先端と外部電極接続金具３３の後端部内面との間の距離が縮まり、例えば組付けの際の位置ずれや金具の寸法ばらつきなどの影響により両者が接触して短絡等の不具合を生ずることが考えられる。そこで、図１１に示すように、外部電極接続金具３３（の金具本体部３３ｃ）の後端開口部を、内部電極接続金具２３に形成されたセパレータ受け部２３と干渉しない位置まで拡径する構成とすれば、上記のような短絡等の不具合を生じにくくすることができる。
【００３９】
図１１に示す例では、外部電極接続金具３３の金具本体部３３ｃの後端部を、軸線方向中間位置に形成された周方向の段付部３３ｊにより拡径された拡径部３３ｋとすることで、上記構成を実現している。この場合、金具本体部３３ｃの段付部３３ｊよりも前方側部分は、酸素検出素子２の後端部よりも少し小さい内径となるようにしておき、ここに酸素検出素子２を圧入・嵌合させるようにすればよい。
【００４０】
他方、図１２に示すように、金具本体部３３ｃ全体の内径寸法を酸素検出素子２よりも大きく形成しておき、例えば酸素検出素子２が嵌め込まれる前端部分の内面に把持突出部３３ｔを形成し、その把持突出部３３ｔにより酸素検出素子２を把持させるようにしてもよい（図１０はその組立状態を示している）。把持突出部３３ｔは金具本体部３３ｃの内面周方向に沿って所定の間隔で複数形成することで、酸素検出素子２をより安定的に把持できる。なお、この実施例では、金具本体部３３ｃにＣ字状の切れ目を形成し、その切れ目の内側に位置する舌状部分を内側に曲げ起こすことにより各把持突出部３３ｔを形成しているが、金具本体部３３ｃの外面をプレス加工等により凹ませ、対応する内面位置にダボ状の凸部を形成してこれを把持突出部としてもい。
【００４１】
図１に戻り、主体金具９の前方側開口部には筒状のプロテクタ装着部９ａが形成され、ここに、酸素検出素子２の先端側（検出部）を所定の空間を隔てて覆うようにキャップ状のプロテクタ１１が装着されている。プロテクタ１１には、排気ガスを透過させる複数のガス透過口１２が貫通形態で形成されている。
【００４２】
上記酸素センサ１においては、前述の通り外筒部材５４のフィルタ５３を介して基準ガスとしての大気が導入される一方、酸素検出素子２の外面にはプロテクタ１１のガス透過口１２を介して導入された排気ガスが接触し、該酸素検出素子２には、その内外面の酸素濃度差に応じて酸素濃淡電池起電力が生じる。そして、この酸素濃淡電池起電力を、排気ガス中の酸素濃度の検出信号として電極層２ｂ，２ｃ（図２）からリード線２１，２０を介して取り出すことにより、排気ガス中の酸素濃度を検出できる。
【００４３】
以下、酸素センサ１の製造方法について説明する。まず、図８（ａ）に示すように、セラミックセパレータ１８に金属弾性部材７４を外挿する。一方、フィルタアセンブリ１６は図６に示すように予め組み立てておき、その内側にセラミックセパレータ１８、外部電極接続金具３３、内部電極接続金具２３、発熱体３及びグロメット１７等を組み付ける。なお、リード線２０，２１等は両金具３３，２３のコネクタ３３ａ，２３ａに接続するとともに、セラミックセパレータ１８のセパレータ側リード線挿通孔７２（図３）に通し、さらにフィルタ保持部５１の後端側開口部に嵌め込まれたグロメット１を経て外側に延出した状態にしておく。他方、酸素検出素子２は主筒１４内に予め組み付けておく。
【００４４】
そして、発熱体３を先端側から酸素検出素子２内に挿入し、フィルタアセンブリ１６の第一フィルタ保持部６１を主筒１４に被せ、セラミックセパレータ１８を酸素検出素子２の後端部に向けて軸線方向に接近させる。これにより、外部電極接続金具３３の金具本体部３３ｃと、内部電極接続金具２３の金具本体部２３ｃとが、酸素検出素子２の開口部に位置決めされた形となる。そして、その状態でセラミックセパレータ１８の前端面（図５の隔壁部１８ｂの端面）に、外部電極接続金具３３の金具本体部３３ｃの後端縁と、内部電極接続金具２３のセパレータ受け部２３ｋとを当接させつつ、セラミックセパレータ１８と酸素検出素子２に向けて軸線方向にさらに接近させる。
【００４５】
これにより、図９に示すように、酸素検出素子２の後端部が金具本体部３３ｃの内側に相対的に押し込まれるとともに、金具本体部２３ｃは酸素検出素子２の内側に押し込まれる。このとき、各金具本体部３３ｃ，２３ｃの後端縁はセラミックセパレータ１８の端面に当接しているので、軸線方向の押込力による引出し線部３３ｂ，２３ｂの挫屈といった不具合を生じることなく、スムーズな組立てが可能となっている。なお、図７に示すように、金具本体部３３ｃの素子挿入側の開口部には、例えばその周方向に沿って外向きに開く挿入ガイド部３３ｆを形成しておけば、挿入時の引っ掛かり等が生じにくく、一層スムーズな組付けが可能となる。また、同様の目的で、酸素検出素子２の開口部外縁に面取部２ｇを形成することもできる。
【００４６】
そして、図８（ｂ）において、第一フィルタ保持部５１と主筒１４とを軸線方向に加圧して金属弾性部材７４を圧縮変形させ、その状態で第一フィルタ保持部５１と主筒１４とにケーシング加締部７６を形成して両者を結合することにより組立てが終了する。
【００４７】
なお、図３において、金属弾性部材７４は主筒１４（ケーシング１０）の後端開口端面とセパレータ側支持部７３（セパレータ側係合部）との間に配置することもできる。この場合、最終的なセンサの組立状態においては、金属弾性部材７４の弾性復帰により、セラミックセパレータ１８と内部電極接続金具２３の金具本体部２３ｃとの間に、金属弾性部材７４を軸線方向において弾性圧縮変形限度まで変形させたときの、その圧縮ストロークに対応する大きさ以下（換言すれば、弾性復帰量以下）の範囲内で、若干の隙間が形成されることがある。本発明では、この程度の小さな隙間形成状態も、広義に「当接」に属するものとみなす。
【図面の簡単な説明】
【図１】本発明の一実施例たる酸素センサの縦断面図。
【図２】酸素検出素子の内外面に形成された電極層を示す断面模式図。
【図３】図１の酸素センサの要部を示す縦断面図。
【図４】セラミックセパレータの一例を示す斜視図。
【図５】図４のセラミックセパレータを詳しく示す平面図、側面図、Ａ−Ａ縦断面図、Ｂ−Ｂ縦断面図及び底面図。
【図６】組立状態のフィルタアセンブリの部分縦断面図。
【図７】酸素検出素子への外部電極接続金具の組付け方法を示す分解斜視図。
【図８】図１の酸素センサの組立方法の一例を示す工程説明図。
【図９】図８において、内部電極接続金具及び外部電極接続金具の各金具本体部が、セラミックセパレータとともに酸素検出素子に対して一体組付けされる様子を示す縦断面図。
【図１０】図１の酸素センサの変形例の要部を示す縦断面図。
【図１１】図１の酸素センサに使用した外部電極接続及び内部電極接続金具の要部を示す斜視図。
【図１２】図１０の酸素センサに使用した外部電極接続の要部を示す斜視図。
【図１３】内部電極接続金具の変形例を示す斜視図。
【符号の説明】
１酸素センサ
２酸素検出素子
２ａ内部電極
２ｂ外部電極
３発熱体
１０ケーシング
１６フィルタアセンブリ
１８セラミックセパレータ
１８ａ発熱体端部収容孔
１８ｂ隔壁部
２０，２１リード線
２３内部電極接続金具
２３ｃ金具本体部
２３ｋセパレータ受け部
３３外部電極接続金具
３３ｂ引出し線部
３３ｃ金具本体部
５３フィルタ
５４第二フィルタ保持部
６１第一フィルタ保持部
７２リード線挿通孔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen sensor for detecting oxygen in a gas to be measured such as an exhaust gas of an internal combustion engine.
[0002]
[Prior art]
As one form of the oxygen sensor with a heater as described above, one having a hollow shaft shape with a closed tip and an oxygen detection element having an electrode layer on the inner wall surface thereof is known. In this type of sensor, a shaft-shaped heater is disposed in the hollow portion of the oxygen detection element, and when the exhaust gas temperature is low, for example, immediately after the engine is started, the oxygen detection element composed of a solid electrolyte is heated by the heater.・ I try to activate it. And the sensor output from the oxygen detection element is taken out by the lead wire through the electrode layer formed on the inner and outer surfaces of the element.
[0003]
By the way, in recent years, the demand for oxygen sensors has increased with the rise of the automobile industry, and the demand for price reduction has been increasing year by year. The oxygen sensor has a large number of parts among electric parts for automobiles, and how to simplify the assembly process is an important key for reducing the manufacturing cost. To that end, it is necessary to improve the technology on the production equipment side, such as automation of the assembly process, but it is also important to devise a sensor structure that is advantageous for man-hour reduction.
[0004]
For example, in the above type of oxygen sensor, the output from the internal electrode layer formed on the inner surface of the hollow oxygen detecting element is taken out by a lead wire through a cylindrical connecting fitting fitted into the hollow portion of the element. I have to. The lead wire passes through a ceramic separator disposed behind the connection fitting and is drawn out from the casing end.
[0005]
[Problems to be solved by the invention]
By the way, in many general oxygen sensors, the rear end side of the casing that houses the oxygen detection element (the side opposite to the detection unit) has an air passage part for introducing air as a reference gas into the casing. A cover member is assembled. The lead wire is drawn out through a rubber grommet for sealing that is fitted into the rear end opening of the cover member. In addition, a lead wire portion integrally formed with one end connected to the end portion of the connection fitting is led into the ceramic separator, and the lead wire is connected to the lead wire portion via the connector.
[0006]
Here, the ceramic separator and the connection fitting are assembled in advance inside the cover member, and the connection fitting is pushed into the hollow portion of the detection element while inserting the cover member from the rear side into the casing where the oxygen detection element is arranged. If mounting can be performed at the same time (that is, the separator and the connection fitting can be assembled to the detection element in an integrated manner), it is advantageous in terms of man-hour reduction. However, in the conventional oxygen sensor, the connection fitting is assembled so as to be hung at a position considerably away from the end face of the ceramic separator by a long extending lead wire portion. For this reason, when the ceramic separator is brought close to the oxygen detecting element together with the cover member, and the fitting of the connection fitting element is inserted into the hollow portion, the thin lead wire portion is tightly fitted between the ceramic separator and the fitting. Not only can it not be done well, it can also cause troubles such as breakage of the leader line.
[0007]
Therefore, in the prior art, first of all, by manually fitting the connection fitting into the oxygen detection element, while holding the ceramic separator with a finger or the like on the back side of the oxygen detection element, gently cover the cover member on the outside, then The cover member was assembled and joined to the casing by caulking or welding. However, in this case, a series of processes before and after the attachment of the connection fittings must be performed manually, and the man-hours are increased, so the efficiency is greatly reduced.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide an oxygen sensor having a structure capable of easily assembling a ceramic separator and a connection fitting to an oxygen detection element, and thus capable of highly efficient manufacturing, and an oxygen sensor using the structure. It is in providing a manufacturing method.
[0009]
[Means for solving the problems and actions / effects]
  In order to solve the above problems, the oxygen sensor of the present invention is
  A hollow shaft with a closed tip is formed, and an oxygen detecting element having an electrode layer on the inner and outer surfaces of the hollow portion;
  A casing that houses the oxygen sensing element;
  Inside the casing, lead wires are arranged on the rear side of the oxygen detection element, and electrically connected to the internal electrode layer formed on the inner surface of the oxygen detection element and the external electrode layer formed on the outer surface, respectively. A plurality of lead wire insertion holes for insertion through a ceramic separator formed through the axial direction;
  A cylindrical internal electrode connection fitting conducting to the internal electrode layer is inserted inside the open end of the hollow portion of the oxygen detection element, and the rear end edge of the internal electrode connection fitting is brought into contact with the front end face of the ceramic separator. Tangent arrangementAnd
A shaft-shaped heating element is inserted into the hollow portion of the oxygen detection element,
The ceramic separator is formed with a plurality of lead wire insertion holes in a form surrounding the central axis of the ceramic separator,
In addition, the ceramic separator has an inner diameter that is set larger than the outer diameter of the heating element at the front end side in the axial direction and opens to the front end face of the ceramic separator. The heating element end accommodating hole for accommodating the rear end portion is formed in a form in which the central portion of the ceramic separator is cut away so as to overlap each lead wire insertion hole from the inside,
The rear end of the internal electrode connection fitting is in contact with the end face of the partition formed between the adjacent lead wire insertion holes on the end face on the opening side of the heating element end accommodating hole of the ceramic separator,
  A separator receiving portion is formed on the cylindrical internal electrode connection fitting so as to protrude outward from the peripheral edge of the rear end, and the end face of the partition wall portion of the ceramic separator is in contact with the separator receiving portion.It is characterized by that.
[0010]
By adopting this structure, the following oxygen sensor manufacturing method of the present invention is realized. That is, the internal electrode connection fitting is positioned on the opening side of the hollow portion of the oxygen detection element, and in this state, the ceramic separator and the oxygen detection element are placed while the rear end edge of the internal electrode connection fitting is brought into contact with the front end face of the ceramic separator. By relatively approaching in the axial direction, the internal electrode fitting is fitted into the hollow portion of the oxygen detecting element and assembled.
[0011]
According to this, since the rear end edge of the internal electrode connection fitting is brought into contact with the front end surface of the ceramic separator, when fitting the connection fitting relative to the detection element in the axial direction, Even when the lead wire portion extends from the external electrode connection fitting to the lead wire side, the buckling or the like does not occur. As a result, it is possible to assemble the internal electrode connection fitting to the oxygen detection element in a form in which the separator is integrated.
[0012]
For example, when the cover member is assembled on the rear end side of the casing that covers the oxygen detection element, a ceramic separator and an internal electrode connection fitting are assembled in advance on the inside of the cover member, and the casing on which the oxygen detection element is arranged is arranged from the rear side. While inserting the cover member, the step of simultaneously pressing the detection element of the internal electrode fitting into the hollow portion can be performed without any problem. As described above, by adopting the structure and manufacturing method of the oxygen sensor of the present invention, it is possible to significantly reduce the number of assembling steps of the oxygen sensor, thereby realizing improvement in manufacturing efficiency and cost reduction of the oxygen sensor.
[0013]
The oxygen sensor is provided integrally with the oxygen sensor on the rear side of the casing, and has a first filter holding portion in which a first gas introduction hole for introducing outside air into the casing is formed, and the first filter holding portion. And a second filter holding part provided with a second gas introduction hole for introducing outside air into the casing, and a first and second gas between the first and second filter holding parts. The filter is disposed in a form that closes the introduction hole, and includes a filter that prevents the liquid from permeating and allows the gas to permeate, and the first filter holding portion is a cylindrical body separate from the casing from the rear side. It can be configured to be connected. In this case, the production method of the present invention can be carried out as follows. First, in a state before being assembled to the casing, the filter and the second filter holding portion are arranged in this order on the outside of the first filter holding portion, and the caulking portion is formed in this state, whereby the second filter holding portion And a filter is assembled | attached to a 1st filter holding part, and it is set as a filter assembly. Then, the ceramic separator and the internal electrode connection fitting are assembled in advance, and the rear end portion of the casing is inserted inside the first filter holding portion of the filter assembly for the assembly of the filter assembly. At this time, the internal electrode fitting is inserted into the hollow portion of the oxygen detection element and assembled at the same time.
[0014]
The gist of the sensor configuration described above is that the ventilation structure including the filter is configured as a filter assembly independently of the casing, and is connected to and integrated with the casing. Thereby, the following effects are achieved in the manufacturing method.
(1) Since the assembly of the filter assembly can be performed independently of the assembly of the oxygen detection element or the like into the casing, for example, the lead wire of the detection element does not get in the way, and the assembly work is extremely efficient. Can be done.
(2) Since the assembly of parts into the casing and the assembly of the filter assembly can be performed in parallel, the productivity is dramatically improved. Even if a filter assembly failure or the like occurs, if a failure can be found at the filter assembly stage, the sensor will not be affected by the failure, and parts will not be wasted.
(3) Since the insertion and assembly of the internal electrode connection fitting into the hollow portion of the oxygen detection element are completed simultaneously with the assembly of the filter assembly to the casing, it is extremely efficient.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings.
FIG. 1 shows the internal structure of an oxygen sensor as an embodiment of the gas sensor of the present invention. The oxygen sensor 1 includes an oxygen detection element 2 that is a hollow shaft-shaped solid electrolyte member with a closed tip, and a heating element 3. The oxygen detection element 2 is formed hollow with an oxygen ion conductive solid electrolyte mainly composed of zirconia or the like. A metal casing 10 is provided outside the oxygen detection element 2.
[0016]
The casing 10 includes a metal shell 9 having a threaded portion 9b for attaching the oxygen sensor 1 to an attachment portion such as an exhaust pipe, and a main cylinder 14 coupled so that the inside communicates with one opening of the metal shell 9. A protector 11 attached to the metal shell 9 from the opposite side to the main cylinder 14 is provided. As shown in FIG. 2, an outer electrode layer 2b and an inner electrode layer formed on the outer surface of the oxygen detecting element 2 and the inner surface of the hollow portion 2a so as to cover almost the entire surface, for example, porous with Pt or a Pt alloy. 2c.
[0017]
Returning to FIG. 1, the main cylinder 14 is caulked through a ring 15 between the main cylinder 14 and the insulator 6 in the opening on the rear side of the metal shell 9, and a cylindrical filter assembly 16 ( Cover member) is fitted and fixed from the outside. The opening on the rear end side of the filter assembly 16 is sealed with a grommet 17 made of rubber or the like, and a ceramic separator 18 is further provided inward. Then, lead wires 20 and 21 for the oxygen detecting element 2 and lead wires (not shown) for the heating element 3 are arranged so as to penetrate the ceramic separator 18 and the grommet 17.
[0018]
Next, as shown in FIG. 4, a plurality of separator-side lead wire insertion holes 72 for inserting the lead wires 20 and 21 are formed in the ceramic separator 18 so as to penetrate in the axial direction. A flange-like separator-side support portion 73 is formed at the middle position in the direction so as to protrude from the outer peripheral surface. Then, as shown in FIG. 3, the ceramic separator 18 has the separator-side support portion 73 in a state where a portion located on the front side of the separator-side support portion 73 is inserted inside the rear end portion of the main cylinder 14. In FIG. 2, the portion that is in contact with the rear end surface of the main tube 14 and that is located on the rear side of the separator-side support portion 73 is disposed so as to protrude outward from the main tube 14.
[0019]
Returning to FIG. 1, the one lead wire 20 for the oxygen detection element 2 passes through the internal electrode connection fitting 23 including the connector 23a, the lead wire portion 23b fitting main body 23a, and the heating element gripping portion 23d formed integrally with each other. The oxygen detection element 2 is electrically connected to an internal electrode layer (hereinafter referred to as an internal electrode layer) 2c (FIG. 2). On the other hand, the other lead wire 21 passes through an external electrode connection fitting 33 having a connector 33a, a lead wire portion 33b, and a fitting main body portion 33c that are integrally formed with each other, and then the external electrode layer of the oxygen detection element 2 (hereinafter referred to as an external electrode). 2b (FIG. 2) which is electrically connected to the electrode layer. The oxygen detection element 2 is activated by heating with the heating element 3 disposed inside thereof. The heating element 3 is a rod-shaped ceramic heater, and an oxygen detection element is formed by energizing a heating part 42 (FIG. 2) having a resistance heating line part (not shown) through lead wires 19 and 22 (FIG. 1). The tip part (detection part) of 2 is heated.
[0020]
As shown in FIG. 7, the external electrode connection fitting 33 has a cylindrical fitting main body 33c, and is integrated in such a manner that one end of the lead wire portion 33b is connected to one place in the circumferential direction. On the other hand, an axial slit 33e is formed on the side opposite to the connection point of the lead line portion 33b across the central axis. The rear end portion of the oxygen detection element 2 is inserted into the metal fitting main body portion 33c from the inside in such a manner as to elastically push it. Specifically, a conductive layer 2 f as an external output extraction portion is formed in a strip shape along the circumferential direction at the rear end portion of the outer peripheral surface of the oxygen detection element 2. The external electrode layer 2b covers the entire surface of the main part on the front end side of the engagement flange portion 2s of the oxygen detection element 2 by, for example, electroless plating. On the other hand, the conductive layer 2f is formed, for example, by pattern formation / baking using a metal paste, and is electrically connected to the external electrode layer 2b via the axially formed connection pattern layer 2d. Yes.
[0021]
On the other hand, the internal electrode connection fitting 23 serves to hold the heating element 23 in the heating element holding portion 23d formed on the distal end side of the heating element 3 and to fix the heating element 23 to the inner surface of the oxygen detecting element 2 by the fitting main body 23c. Fulfill. The heating element gripping portion 23d has a C-shaped cross-sectional shape that surrounds the periphery of the heating element 3. When the heating element 3 is not inserted, the heating element 3 has an inner diameter that is slightly smaller than the outer diameter of the heating element 3, and elastically expands with the insertion of the heating element 3, and the frictional force causes the heating element 3 to be expanded. Hold it.
[0022]
Moreover, the metal fitting body 23c is formed in a form surrounding the heating element 3 by bending a plate-like portion in which a plurality of saw blade-like contact portions 23e are formed on both left and right edges into a cylindrical shape. (That is, the heating element 3 is inserted). And as shown in FIG. 2, while having the role which positions the heat generating body 3 to this hollow part 2a in an axial direction with the frictional force between the outer peripheral surface and the inner wall face of the hollow part 2a of the oxygen detection element 2 In addition, the tip portions of the plurality of contact portions 26a are brought into contact / conduction with the internal electrode layer 2c.
[0023]
Next, as shown in FIG. 3, the filter assembly 16 has a cylindrical shape that is substantially coaxially connected to the main cylinder 14 (casing 10) from the rear outer side, and the inside communicates with the outside of the main cylinder 14. And a first filter holding part 51 having a plurality of gas introduction holes 52 formed in the wall part. A cylindrical filter 53 that closes the gas introduction hole 52 is disposed outside the first filter holding portion 51, and one or more gas introduction holes are formed in the wall portion outside the filter 53. 55 is formed, and a second filter holding portion 54 that holds the filter 53 between the first filter holding portion 51 and the first filter holding portion 51 is disposed.
[0024]
FIG. 6 shows the assembled state of the filter assembly 16. The gas introduction hole 52 and the gas introduction hole 55 are formed at predetermined intervals along the circumferential direction with respect to the first filter holding part 51 and the second filter holding part 54 in a positional relationship corresponding to each other in each axial direction intermediate part. The filter 53 is disposed so as to surround the first filter holding portion 51 in the circumferential direction. The filter 53 is configured as a water-repellent filter made of, for example, a porous fiber structure of polytetrafluoroethylene (trade name: Gore-Tex (Japan Gore-Tex Co., Ltd.)) or the like.
[0025]
In addition, the second filter holding portion 54 is coupled to the first filter holding portion 51 via the filter 53 on both sides in the axial direction across the row of auxiliary gas introduction holes 55. Annular filter caulking portions 56, 57 (hereinafter also simply referred to as caulking portions 56, 57) are formed, and a gap 58 is formed between the outer surface of the first filter holding portion 51 and the filter 53. ing. On the other hand, the first filter holding part 51 has a stepped part 60 formed in its own axially intermediate part, and a first part 61 on the front side in the axial direction with respect to the stepped part 60 and a second part on the rear side in the same axial direction. The second portion 62 is configured to have a diameter smaller than that of the first portion 61, and the gas introduction hole 52 is formed in the wall portion of the second portion 62. Further, the second filter holding part 54 has an inner diameter smaller than the outer diameter of the first part 61 of the first filter holding part 51.
[0026]
Returning to FIG. 3, the first filter holding portion 51 covers the projection portion of the ceramic separator 18 to the inside of the second portion 62 and covers the main portion with respect to the separator-side support portion 73 in the stepped portion 60. 14 from the opposite side to the metal elastic member 74 (for example, formed of a ring-shaped corrugated washer). On the other hand, the first filter holding part 51 is arranged so as to overlap the main cylinder 14 (casing 10) from the outside at the front end side of the first filter 61, that is, the first part 61. A casing caulking portion 76 that connects 51 to the main cylinder 14 so as to be in an airtight state is formed.
[0027]
A cylindrical protective cover 64 is provided outside the second filter holding portion 54 so as to cover it. The protective cover 64 is disposed so as to generate a gas retention space 65 between the second filter storage portion 54 and joined to the first filter holding portion 51 by caulking portions 66 and 67. As shown in FIG. 6, a plurality of groove portions 69 serving as gas introduction portions into the protective cover are formed at predetermined intervals along the circumferential direction on the outer peripheral surface of the first portion 61 of the first filter holding portion 51. Has been.
[0028]
Returning to FIG. 3, the ceramic separator 18 is arranged so that the front side of the separator-side support part enters the inside of the main cylinder 14 (casing 10), and the lead wires 20, 21, etc. are arranged in the separator-side lead wire insertion holes 72. It is inserted in the direction. On the other hand, the grommet 17 is elastically fitted inside the rear opening of the first filter holding portion 51 and has a seal-side lead wire insertion hole 91 for inserting each lead wire 20, 21 and the like. The space between the outer surfaces of the lead wires 20 and 21 and the inner surface of the first filter holding portion 51 is sealed.
[0029]
The rear end surface of the ceramic separator 18 is positioned behind the gas introduction hole 52 in the axial direction, and a predetermined amount of gap 98 is formed between the grommet 17 and the ceramic separator 18. A gap 92 is also formed between the inner peripheral surface of the first filter holding part 51 and the outer peripheral surface of the ceramic separator 18. Then, the gas from the gas introduction hole 52 is supplied into the gap 92 and further guided into the casing 10 through the gap K formed between the separator-side lead wire insertion hole 72 and the lead wire.
[0030]
As shown in FIG. 5A, four lead wire insertion holes 72 are formed in the ceramic separator 18 at substantially 90 ° intervals along a pitch circle C centering on the central axis O of the ceramic separator 18. ing. Further, as shown in FIGS. 2C and 2D, a heating element end accommodating hole 18a is formed in the axial direction on the front end side in the axial direction of the ceramic separator 18 (the lower end side in the drawing). The heating element end accommodating hole 18a has an inner diameter that is set larger than the outer diameter of the heating element 3 and opens to the front end surface of the ceramic separator 18, and the bottom surface 18e is positioned at an axially intermediate portion of the ceramic separator 18. The rear end of the heating element 3 is accommodated. As a result, the overall length of the sensor 1 is shortened, and the sensor size is reduced. Further, the heating element end accommodating hole 18a is formed in a form in which the central portion of the ceramic separator 18 is cut away so as to overlap each lead wire insertion hole 72 from the inside. In addition, a partition wall 18b is formed between the adjacent lead wire insertion holes 72, 72.
[0031]
As shown in FIGS. 5 (e) and 9, the rear end edge of the metal body 33c of the external electrode connection metal 33 is on the end surface of the ceramic separator 18 on the opening side of the heating element end accommodating hole 18a. It is in contact with the end face of the partition wall 18b. The rear end edge of the metal body part 23 c of the internal electrode connection fitting 23 is in contact with the end surface of the partition wall part 18 b on the inner side of the metal fitting body part 33 c of the external electrode connection metal part 33.
[0032]
As shown in FIG. 5 (d), a certain amount of gap hg is formed between the rear end of the heating element 3 and the inner surface of the heating element end accommodating hole 18a, as shown in FIG. The heating element 3 is disposed in an inclined manner in the hollow portion 2a of the oxygen detection element 2. This inclined arrangement state is realized by inclining the heating element gripping portion 23d by slightly bending the constricted connection portion 23m between the heating element gripping portion 23d and the bracket main body portion 23c in the internal electrode connection fitting 23. Thereby, as shown in FIG. 2, the heating element 3 has a central axis O1 of the heating element 3 in the vicinity of the heating part 42 formed at the tip thereof, and a central axis O2 of the hollow part 2a of the oxygen detecting element 2. In this embodiment, the heat generating portion 42 approaches the inner wall surface of the heating element 3 (in this embodiment, the heat generating portion 42 strikes the inner wall surface of the heating element 3 in a side-by-side manner. Abuts in form).
[0033]
By adopting such a structure, heat transfer from the heat generated in the heat generating portion 42 to the oxygen detecting element 2 is promoted. For example, when the heat generating portion 42 comes into contact with the inner wall surface of the heat generating body 3, the contact is made. Radiant heat in the vicinity of the point also effectively acts on the oxygen detection element 2, and the temperature of the oxygen detection element 2 can be raised in a short time, and the sensor activation time is shortened. Further, even when the heat generating portion 42 and the oxygen detecting element 2 are thermally expanded, the heat generating portion 42 and the oxygen detecting element 2 are less affected by the thermal expansion than the structure in which the tip of the heat generating portion 42 is brought into contact with the inner surface of the tip of the oxygen detecting element 2. In other words, by adopting such a lateral support structure, even when the heating element 3 and the oxygen detection element 42 receive a thermal history, it is easy to maintain a good contact state between them. In addition, variations in characteristics of the oxygen sensor 1 can be reduced.
[0034]
Note that the fact that the heat generating portion 42 side, that is, the tip end side is eccentric with respect to the central axis of the hollow portion of the oxygen detecting element 2 due to the inclination of the heat generating element 3 is slightly exaggerated in FIG. This means that the rear end portion of the heating element 3 is eccentric in the opposite direction in the heating element end accommodating hole 18a. Accordingly, it can be said that the gap hg described above plays a role of absorbing the eccentricity of the rear end portion of the heating element 3. By ensuring such a gap hg without excess or deficiency, when the heating element 3 is assembled into the oxygen detection element 2, the heating element 3 is less likely to come into contact with the inner edge of the heating element end accommodating hole 18a. A strong bending force as a fulcrum becomes difficult to act, and breakage of the heating element 3 can be effectively prevented.
[0035]
In order to form the gap hg with a sufficient size, as shown in FIG. 5 (e), between the heating element 3 and the partition wall 18 b that forms the inner surface of the heating element end accommodating hole 18 a. In order to form a sufficient distance, the protruding amount of the partition wall 18b in the radial direction of the heating element end accommodating hole 18a must be reduced to some extent. Therefore, a separator receiving portion 23k is formed on the cylindrical internal electrode connection fitting 23 (the fitting main body portion 33c) so as to protrude outward from the peripheral edge of the rear end thereof, and the end face of the partition wall portion 18b of the ceramic separator 18 is formed on the end face thereof. If the shape is made to abut against the separator receiving portion 23k, the abutting state between the ceramic separator 18 and the internal electrode connection fitting 23 can be reliably obtained even if the protruding amount of the partition wall portion 18b is small.
[0036]
As shown in FIG. 11, in this embodiment, the separator receiving portion 23k is formed as a plurality of claw portions extending radially from the rear end periphery of the cylindrical internal electrode connection fitting 23 (the fitting main body portion 33c). . If the separator receiving portion 23k is configured as such a claw portion, an axial cut is formed at a predetermined interval along the circumferential direction in the rear end opening of the metal fitting main body portion 33c, and the tongue positioned between the cuts. Each nail | claw part which forms the separator receiving part 23k can be easily formed by bending a shape part outward. In addition, these claw parts can form a more stable contact state between the ceramic separator 18 and the internal electrode connection fitting 23 by forming in a shape corresponding to each partition wall part 18b.
[0037]
As shown in FIG. 13, the cylindrical internal electrode connection fitting 23 (the fitting main body 33c) has a rear end portion whose diameter is increased by a circumferential stepped portion 23j formed at the intermediate portion in the axial direction. In addition, the end face of the expanded rear end portion may be in contact with the front end face of the ceramic separator 18. In this case, the separator receiving portion 23k may be omitted if the abutting state of the ceramic separator 18 with, for example, the front end surface of the partition wall portion 18b can be ensured only by increasing the diameter of the rear end portion. However, also in this case, if the separator receiving portion 23k is formed, the contact state between the ceramic separator 18 and the internal electrode connection fitting 23 can be further stabilized.
[0038]
Now, when the separator receiving portion 23k as described above is formed at the rear end portion of the internal electrode connection fitting 23 (the metal fitting main body portion 33c), the front end in the protruding direction of the separator receiving portion 23 and the inner surface of the rear end portion of the external electrode connection fitting 33 are provided. It is conceivable that the distance between the two will be reduced and, for example, due to the effects of positional deviation during assembly, dimensional variation of the metal fittings, etc., both may come into contact and cause a problem such as a short circuit. Therefore, as shown in FIG. 11, the configuration is such that the rear end opening of the external electrode connection fitting 33 (the metal fitting main body portion 33 c) is expanded to a position where it does not interfere with the separator receiving portion 23 formed in the internal electrode connection fitting 23. If so, it is possible to make it difficult to cause the above-described problems such as a short circuit.
[0039]
In the example shown in FIG. 11, the rear end portion of the metal fitting main body portion 33 c of the external electrode connecting metal fitting 33 is a diameter-expanded portion 33 k that has been diameter-expanded by a circumferential stepped portion 33 j formed at an intermediate position in the axial direction. Thus, the above configuration is realized. In this case, the front side part of the stepped part 33j of the metal fitting main body part 33c is set to have an inner diameter slightly smaller than the rear end part of the oxygen detecting element 2, and the oxygen detecting element 2 is press-fitted and fitted therein. You can make it.
[0040]
On the other hand, as shown in FIG. 12, the overall inner diameter dimension of the metal fitting body 33c is formed larger than that of the oxygen detection element 2, and for example, a grip protrusion 33t is formed on the inner surface of the front end portion into which the oxygen detection element 2 is fitted. The oxygen detecting element 2 may be gripped by the gripping protrusion 33t (FIG. 10 shows the assembled state). By forming a plurality of gripping protrusions 33t at predetermined intervals along the inner circumferential direction of the metal fitting main body 33c, the oxygen detection element 2 can be gripped more stably. In this embodiment, each gripping protrusion 33t is formed by forming a C-shaped cut in the metal fitting main body 33c and bending the tongue-like portion located inside the cut inward. The outer surface of the metal fitting main body portion 33c may be recessed by pressing or the like, and a dowel-shaped convex portion may be formed at the corresponding inner surface position, and this may be used as a gripping protrusion.
[0041]
Returning to FIG. 1, a cylindrical protector mounting portion 9 a is formed at the front opening of the metal shell 9, and covers the distal end side (detection portion) of the oxygen detection element 2 with a predetermined space therebetween. A cap-shaped protector 11 is attached. The protector 11 is formed with a plurality of gas permeation ports 12 through which exhaust gas permeates.
[0042]
In the oxygen sensor 1, the atmosphere as the reference gas is introduced through the filter 53 of the outer cylinder member 54 as described above, while introduced into the outer surface of the oxygen detection element 2 through the gas permeation port 12 of the protector 11. Oxygen concentration cell electromotive force is generated in the oxygen detecting element 2 in accordance with the oxygen concentration difference between the inner and outer surfaces. The oxygen concentration cell electromotive force is taken out from the electrode layers 2b and 2c (FIG. 2) through the lead wires 21 and 20 as a detection signal of the oxygen concentration in the exhaust gas, thereby detecting the oxygen concentration in the exhaust gas. it can.
[0043]
Hereinafter, a method for manufacturing the oxygen sensor 1 will be described. First, as shown in FIG. 8A, the metal elastic member 74 is extrapolated to the ceramic separator 18. On the other hand, the filter assembly 16 is assembled in advance as shown in FIG. 6, and the ceramic separator 18, the external electrode connection fitting 33, the internal electrode connection fitting 23, the heating element 3, and the grommet 17 are assembled therein. The lead wires 20, 21, etc. are connected to the connectors 33 a, 23 a of the metal fittings 33, 23, passed through the separator-side lead wire insertion hole 72 (FIG. 3) of the ceramic separator 18, and further the rear end of the filter holding portion 51. It is in a state of extending outward through the grommet 1 fitted in the side opening. On the other hand, the oxygen detection element 2 is assembled in the main cylinder 14 in advance.
[0044]
Then, the heating element 3 is inserted into the oxygen detection element 2 from the front end side, the first filter holding portion 61 of the filter assembly 16 is covered on the main cylinder 14, and the ceramic separator 18 is directed toward the rear end portion of the oxygen detection element 2. Approach in the axial direction. Thereby, the metal fitting main body portion 33 c of the external electrode connecting metal fitting 33 and the metal fitting main body portion 23 c of the internal electrode connecting metal fitting 23 are positioned in the opening of the oxygen detection element 2. In this state, on the front end surface of the ceramic separator 18 (end surface of the partition wall portion 18b in FIG. 5), the rear end edge of the metal body portion 33c of the external electrode connection fitting 33, and the separator receiving portion 23k of the internal electrode connection fitting 23 Are brought closer to the ceramic separator 18 and the oxygen detection element 2 in the axial direction.
[0045]
As a result, as shown in FIG. 9, the rear end portion of the oxygen detection element 2 is relatively pushed into the inside of the metal fitting main body portion 33 c, and the metal fitting main body portion 23 c is pushed into the inside of the oxygen detection element 2. At this time, since the rear end edges of the respective metal fitting main body portions 33c and 23c are in contact with the end face of the ceramic separator 18, smoothness can be achieved without causing problems such as buckling of the lead wire portions 33b and 23b due to the pushing force in the axial direction. Assembly is possible. As shown in FIG. 7, if an insertion guide portion 33f that opens outward along the circumferential direction is formed in the opening portion on the element insertion side of the metal fitting main body portion 33c, for example, a hook at the time of insertion or the like Is less likely to occur, and smoother assembly is possible. For the same purpose, the chamfered portion 2g can be formed on the outer edge of the opening of the oxygen detecting element 2.
[0046]
And in FIG.8 (b), the 1st filter holding | maintenance part 51 and the main cylinder 14 are pressurized to an axial direction, the metal elastic member 74 is compressively deformed, and the 1st filter holding | maintenance part 51, the main cylinder 14, and The assembly is completed by forming the casing crimping portion 76 and joining them together.
[0047]
In FIG. 3, the metal elastic member 74 can also be disposed between the rear end opening end face of the main cylinder 14 (casing 10) and the separator-side support portion 73 (separator-side engagement portion). In this case, in the final assembled state of the sensor, the elastic metal member 74 elastically moves between the ceramic separator 18 and the metal fitting body 23c of the internal electrode connection metal fitting 23 in the axial direction by the elastic return of the metal elastic member 74. A slight gap may be formed within a range corresponding to the compression stroke when the deformation is made up to the compression deformation limit (in other words, an elastic recovery amount or less). In the present invention, such a small gap formation state is regarded as belonging to “contact” in a broad sense.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an oxygen sensor according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing electrode layers formed on the inner and outer surfaces of the oxygen detection element.
3 is a longitudinal sectional view showing a main part of the oxygen sensor in FIG. 1. FIG.
FIG. 4 is a perspective view showing an example of a ceramic separator.
5 is a plan view, a side view, an AA longitudinal sectional view, a BB longitudinal sectional view, and a bottom view showing the ceramic separator of FIG. 4 in detail.
FIG. 6 is a partial longitudinal sectional view of the filter assembly in an assembled state.
FIG. 7 is an exploded perspective view showing a method of assembling the external electrode connection fitting to the oxygen detection element.
FIG. 8 is a process explanatory view showing an example of a method for assembling the oxygen sensor of FIG. 1;
FIG. 9 is a longitudinal sectional view showing a state in which each metal fitting main body part of the internal electrode connecting metal fitting and the external electrode connecting metal fitting is integrally assembled to the oxygen detection element together with the ceramic separator in FIG. 8;
10 is a longitudinal sectional view showing a main part of a modified example of the oxygen sensor of FIG. 1. FIG.
11 is a perspective view showing a main part of an external electrode connection and an internal electrode connection fitting used in the oxygen sensor of FIG. 1. FIG.
12 is a perspective view showing a main part of external electrode connection used in the oxygen sensor of FIG.
FIG. 13 is a perspective view showing a modified example of the internal electrode connection fitting.
[Explanation of symbols]
1 Oxygen sensor
2 Oxygen detection element
2a Internal electrode
2b External electrode
3 Heating elements
10 Casing
16 Filter assembly
18 Ceramic separator
18a Heating element end receiving hole
18b Bulkhead
20, 21 Lead wire
23 Internal electrode connection bracket
23c bracket body
23k separator receiving part
33 External electrode connection bracket
33b Lead wire part
33c Bracket body
53 Filter
54 Second filter holder
61 First filter holder
72 Lead wire insertion hole

Claims

A hollow shaft with a closed tip is formed, and an oxygen detecting element having an electrode layer on the inner and outer surfaces of the hollow portion;
A casing that houses the oxygen sensing element;
A lead wire disposed in the casing on the rear side of the oxygen detection element and electrically conducting to an internal electrode layer formed on the inner surface of the oxygen detection element and an external electrode layer also formed on the outer surface. A plurality of lead wire insertion holes formed in the axial direction through the ceramic separator,
A cylindrical internal electrode connection fitting conducting to the internal electrode layer is inserted inside the opening end of the hollow portion of the oxygen detection element, and the rear end edge of the internal electrode connection fitting is connected to the ceramic separator. Abut the front end face ,
An axial heating element is inserted into the hollow portion of the oxygen detection element,
The ceramic separator is formed with a plurality of lead wire insertion holes so as to surround the central axis of the ceramic separator,
Further, on the front end side in the axial direction of the ceramic separator, the inner diameter is set larger than the outer diameter of the heating element and opens to the front end surface of the ceramic separator, and the bottom surface is located in the axial middle portion of the ceramic separator, The heating element end accommodating hole that accommodates the rear end of the heating element is formed in a form in which the central portion of the ceramic separator is cut away so as to overlap each lead wire insertion hole from the inside.
The rear end of the internal electrode connection fitting is in contact with the end face of the partition wall formed between adjacent lead wire insertion holes in the end face on the opening side of the heating element end accommodation hole of the ceramic separator,
A separator receiving portion is formed on the cylindrical internal electrode connection fitting so as to protrude outward from a peripheral edge of the rear end thereof, and an end surface of the partition wall portion of the ceramic separator is in contact with the separator receiving portion. oxygen sensor, characterized in that there.

A certain amount of gap is formed between the rear end of the heat generating element and the inner surface of the heat generating element end accommodating hole, and in the vicinity of the heat generating part formed at the front end of the heat generating element, 2. The oxygen sensor according to claim 1, wherein the heating element is inclined and arranged in the hollow portion so that the central axis of the heating element is decentered so as to approach one side with respect to the central axis of the hollow portion of the oxygen detecting element. .

3. The oxygen sensor according to claim 1, wherein the separator receiving portion includes a plurality of claw portions extending radially from a rear end peripheral edge of the cylindrical internal electrode connection fitting .

The cylindrical internal electrode connection fitting has a rear end portion whose diameter is enlarged by a stepped portion formed in an intermediate portion in the axial direction, and the front end surface of the ceramic separator at the end surface of the enlarged rear end portion. The oxygen sensor according to claim 1, which is in contact with the oxygen sensor.

At the rear end portion of the oxygen detection element, an external output extraction portion that conducts to the external electrode layer is formed, while an external electrode connection fitting is attached to the end portion of the corresponding lead wire, The external electrode connection fitting is formed in a cylindrical shape into which a rear end portion of the oxygen detection element is fitted inside, and a rear end opening of the external electrode connection fitting is formed in the internal electrode connection fitting. The oxygen sensor according to any one of claims 1 to 4, wherein the diameter is expanded to a position where the separator receiving portion does not interfere .

The oxygen sensor according to claim 5, wherein a rear end edge of the external electrode connection fitting is in contact with a front end surface of the ceramic separator .

A method for producing an oxygen sensor according to any one of claims 1 to 6,
The internal electrode connection fitting is positioned on the hollow opening side of the oxygen detection element, and in this state, the rear end edge of the internal electrode connection fitting is brought into contact with the front end surface of the ceramic separator and the oxygen separator by relatively close to the element in the axial direction, the manufacturing method of the oxygen sensor, characterized that you assembled this by fitting the internal electrode fitting to the hollow portion of said oxygen sensing element.

The gas sensor
A first filter holding portion provided integrally with the casing on the rear side of the casing and having a first gas introduction hole for guiding outside air into the casing;
A second filter holding portion provided outside the first filter holding portion and having a second gas introduction hole for guiding outside air into the casing;
A filter disposed between the first and second filter holding portions so as to block the first and second gas introduction holes, the first filter holding and the first filter holding filter including a filter that blocks liquid permeation and allows gas permeation. The part is connected to the casing from the rear side as a separate cylindrical body from the casing,
In a state before being assembled to the casing, the filter and the second filter holding part are arranged in this order outside the first filter holding part,
By forming a caulking portion in that state, the second filter holding portion and the filter are assembled to the first filter holding portion to form a filter assembly,
The ceramic separator and the internal electrode connection fitting are assembled in advance, the rear end of the casing is inserted into the first filter holding portion of the filter assembly for the assembly of the filter assembly, 8. The method of manufacturing an oxygen sensor according to claim 7, wherein the insertion and assembly of the internal electrode connection fitting into the hollow portion of the oxygen detection element are simultaneously performed during the insertion .