JP3721263B2

JP3721263B2 - Oxygen sensor with heater

Info

Publication number: JP3721263B2
Application number: JP21107198A
Authority: JP
Inventors: 正二赤塚; 聡石川; 孝水草
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 1998-07-27
Filing date: 1998-07-27
Publication date: 2005-11-30
Anticipated expiration: 2018-07-27
Also published as: JP2000046787A

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中の酸素濃度を検出するための酸素センサ、あるいは所定のガス中の酸素を検出するための酸素センサに関し、特に短時間に酸素センサを活性化温度まで加熱するヒータを備えた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知素子と、その酸素検知素子の中空部内に配置されてその酸素検知素子を加熱する軸状の発熱体とを備えた構造のものが知られている（例えば特開平４−１５７３５８号公報）。この種の酸素センサでは、酸素検知素子の内部空間に対し、軸状（棒状）の発熱体（ヒータ）をその先端内面に達するまで同心的に差し入れた構造のものが一般的であったが、特開平１０−５４８２２号公報には新しいタイプのセンサとして、先端の発熱部の近傍において発熱体の中心軸線が、酸素検知素子の中空部の中心軸線に対して片側に寄るように偏心した状態で位置決めされた構造のものが提案されている。
【０００３】
上記センサにおいて、例えば発熱部が酸素検知素子と接触するいわば横当て構造を採用することで、発熱部で発生する熱が酸素検知素子へ直接的に熱伝導してセンサの活性化に要する時間が短縮される。これにより、例えば車両の始動時やアイドル時などの、排気ガス温度が低い場合でも酸素センサを有効に作動させることができる。また発熱体の発熱部が酸素検知素子の中空部内壁面に側方から接触した構造であれば、発熱部や酸素検知素子の熱膨張が生じても、発熱部の先端を酸素検知素子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、発熱体や酸素検知素子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り、センサ特性のばらつきを少なく抑さえることができる。
【０００４】
【発明が解決しようとする課題】
ところで、上記特開平１０−５４８２２号公報に開示されたセンサでは、酸素検知素子内において発熱体を上記偏心状態で固定するために端子金具が使用されている。端子金具の実例として、公報図１には、発熱体（３）を周方向に包囲するとともに酸素検知素子（２）の内側の電極層に接触する内部電極接続部（２６）を有し、その内部電極接続部（２６）の基端側に発熱体（３）を把持する発熱体把持部（２７）が結合される一方、先端側には発熱体（３）を素子内壁面に弾性的に付勢するガイド部（２８）が連結された構造のものが開示されている。他方、同公報図８には、内部電極接続部（２６）の基端側と先端側との両方に発熱体把持部（２７ａ，２７ｂ）を結合し、それら発熱体把持部（２７ａ，２７ｂ）の中心軸線同士を互いに偏心させた構造のものが開示されている。
【０００５】
しかしながら、これらの構成では、内部電極接続部の両側に発熱体把持部やガイド部が連結されるため、（発熱体把持部＋内部電極接続部＋発熱体把持部（あるいはガイド部））の部分、ひいてはセンサの全長が長くなり、近年高まりつつあるコンパクト化の要求を満たす上で不利となる。また、２ケ所の把持部（あるいは１ケ所の把持部とガイド部）により、横方向に強い曲げ力が作用した状態で発熱体が把持される形となるので、例えば端子金具を装着した発熱体を酸素検知素子の中空部内に挿入してセンサを組み立てる際に、端子金具を介して過剰な横方向の力が発熱体に作用し、折損等の不具合が生じる心配がある。
【０００６】
本発明の課題は、中空軸状の酸素検知素子の内部に発熱体を偏心固定することにより短時間で効果的にセンサ活性化温度に加熱でき、かつ全長を短くしてコンパクト化を図ることができるヒータ付き酸素センサを提供することにある。
【０００７】
【課題を解決するための手段及び作用・効果】
上述の課題を解決するために、本発明のヒータ付き酸素センサ（以下、単に酸素センサともいう）は、先端部が閉じた中空軸状をなし、それの内外面に電極層を有する酸素検知素子と、
該酸素検知素子の中空部内に配置されて該酸素検知素子を加熱する軸状の発熱体と、
発熱体を周方向に包囲するように形成され、酸素検知素子の内面に直接又は他部材を介して間接的に接触する固定部と、その固定部に対し発熱体の軸方向において少なくとも一方の側に連結されて発熱体を把持する発熱体把持部とを有し、固定部により発熱体を酸素検知素子の内側に固定する固定金具とを備え、
発熱体把持部は固定部に対し、該固定部の軸線に対して傾斜した状態で結合されており、これに把持される発熱体の中心軸線が酸素検知素子の中空部の中心軸線に対して傾斜することにより、該発熱体はその発熱部の近傍において片側に寄るように偏心した状態で位置決めされていることを特徴とする。なお、固定部の軸線とは、該固定部に内接する最大直円筒の中心軸線として定義する。
【０００８】
ここで、上記のような偏心（オフセット）の結果として、発熱体の発熱部の表面が、酸素検知素子の中空部内壁面に接触していることが望ましい（請求項２）。この場合は、酸素検知素子の中空部の中心軸線に対して発熱体の発熱部の近傍において該発熱体の中心軸線が偏心していることにより、該発熱体の発熱部の表面が、該酸素検知素子の中空部内壁面に接触する構成となる。
【０００９】
例えば発熱部が酸素検知素子と接触する横当て構造を採用することで、発熱体の発熱部で発生する熱がその接触に基づき、その発熱部から酸素検知素子へ直接的に熱伝導するとともに、その接触点近傍の輻射熱も酸素検知素子に効果的に作用して、その酸素検知素子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。また発熱体の発熱部が酸素検知素子の中空部内壁面に側方から接触した構造であれば、発熱部や酸素検知素子の熱膨張が生じても、発熱部の先端を酸素検知素子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、発熱体や酸素検知素子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のである。
【００１０】
また、発熱部を側方から酸素検知素子の中空部内壁面に当てるようにすれば、接触による直接的な熱伝導並びに輻射熱の効果により、先端同士で当てる構造よりも全体としての熱伝達効率は高くなる。そして、上記のように、酸素センサにおける酸素検知素子と発熱体の発熱部との接触状態を安定に保証できることにより、酸素検知素子の加熱状態のばらつきが減少し、このことが酸素センサとしての特性のばらつきを減少させる効果につながる。
【００１１】
また、上記構成によれば、酸素検知素子内において発熱体を、発熱部の近傍において片側に寄るように偏心させた構造が、固定部の軸線に対して傾斜した状態で発熱体把持部を結合した固定金具の構成により簡単に実現される。さらに、発熱体把持部が１カ所にのみ設けられるので、端子金具の発熱体軸線方向における長さを短くでき、ひいては酸素センサの上記軸線方向の長さを減じてこれをコンパクトに構成できるようになる。また、発熱体が１ケ所の把持部により把持される形としたから、例えば固定金具を装着した発熱体を酸素検知素子の中空部内に挿入してセンサを組み立てる際に、固定金具を介した過剰な横方向の力が発熱体に作用しにくくなり、ひいては組立時の発熱体の折損等を防止することができる。
【００１２】
固定部と発熱体把持部とは、発熱体の周囲において対向する端面同士が周方向の一部区間にて上記連結部により一体化された構造とすることができる。この場合、発熱体把持部は固定部に対し、上記対向する端面の、連結部が形成されているのとは反対側の端縁同士が互いに近づく向きに傾斜して結合されていても、逆に遠ざかる向きに傾斜して結合されていてもいずれでもよい。
【００１３】
固定金具は、具体的には、固定部が酸素検知素子の内側の電極層に接触する内部電極接続部とされた端子金具とすることができる。固定部が酸素検知素子からの出力取出し用の内部電極接続部を兼ねることにより、部品点数が削減されるので、センサをより安価に構成することが可能となり、組立工程も簡略化される。
【００１４】
上記構成では、内部電極接続部と発熱体把持部とを、発熱体の周囲において対向する端面同士が周方向の一部区間にて連結部により一体化し、内部電極接続部の発熱体把持部が接続されているのと反対側の端部は、内部電極接続部の周方向において、該内部電極接続部と発熱体把持部とを連結する連結部に対応する位置に、発熱体の軸線方向に延びる接続線部の一端を一体化することができる。この場合、発熱体把持部は内部電極接続部に対し、対向する端面の、連結部が形成されているのとは反対側の端縁同士が互いに遠ざかる向きに傾斜して結合されていることが望ましい。このようにすれば、端子金具に対して、内部電極接続部側から発熱体把持部に発熱体を挿入してこれに組み付ける際に、接続線部と発熱体とが干渉しにくくなり、組付けをスムーズに行うことができる。
【００１５】
【発明の実施の形態】
以下、図面に示すいくつかの実施例を参照しつつ、本発明の実施の形態を説明する。図１に示すヒータ付き酸素センサ（以下、単に酸素センサあるいはセンサとも称する）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知素子２と、軸状のセラミックヒータである発熱体３とを備え、それらの外殻を構成する各種部材の組立体として構成される。酸素検知素子２は酸素イオン伝導性を有する固体電解質により構成されている。そのような固体電解質としては、Ｙ_２Ｏ_３ないしＣａＯを固溶させたＺｒＯ_２が代表的なものであるが、それ以外のアルカリ土類金属ないし希土類金属の酸化物とＺｒＯ_２との固溶体を使用してもよい。また、ベースとなるＺｒＯ_２にはＨｆＯ_２が含有されていてもよい。
【００１６】
この酸素検知素子２の中間部外側には、絶縁性セラミックから形成されたインシュレータ６，７、並びにタルクから形成されたセラミック粉末８を介して金属製の筒部材であるハウジング９が設けられ、酸素検知素子２はハウジング９と電気的に絶縁された状態で貫通している。また、図２に示すように、酸素検知素子２の内面及び外面には、そのほぼ全面を覆うように一対の電極層２ｂ，２ｃが設けられている。これら電極層２ｂ，２ｃはいずれも、酸素検知素子２を構成する固体電解質へ酸素を注入するための酸素分子の解離反応、及び該固体電解質から酸素を放出させるための酸素の再結合反応に対する可逆的な触媒機能（酸素解離触媒機能）を有する多孔質電極、例えばＰｔ多孔質電極として構成されている。
【００１７】
次に、ハウジング９の一方の開口部には、酸素検知素子２の先端側を所定の空間を隔てて覆うようにプロテクタ１１が設けられ、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が形成され、これにより排気ガス中の酸素が酸素検知素子２の先端側表面に接触可能となっている。ハウジング９の他方の開口部には、第１のスリーブ１４がインシュレータ６との間にリング１５を介してかしめられ、このスリーブ１４にさらに第２のスリーブ１６が外側から嵌合・固定されている。このスリーブ１６の図中上端側の開口は栓体１７で封止され、またこれに続いてさらに内方に栓体１８、及び１９が設けられている。そして栓体１７，１８を貫通するようにリード線２０，２１が配置されている。
【００１８】
一方のリード線２０は、端子金具（固定金具）２３のコネクタ部２４及びこれに続く引出し線部２５（絶縁管２５ａで覆われている）、並びに端子金具２３の内部電極接続部（固定部）２６を経て、前述の酸素検知素子２の図示しない内側の電極層と電気的に接続されている。他方のリード線２１は、別の端子金具３３のコネクタ部３４及びこれに続く引出し線部３５並びに外部電極接続部３５ｂを経て、酸素検知素子２の図示しない外側の電極層と電気的に接続されている。また前述の発熱体３に通電するためのプラス側及びマイナス側の一対のヒータ端子部４０が、発熱体３の基端部（図１において上端部）に固定され、これらヒータ端子部４０を経て、発熱体３内に埋設された後述の発熱用抵抗回路に通電されるようになっている。なお図１で図示はしないが、一対のヒータ端子部４０は、栓体１７，１８等を貫通して設けられたヒータ用の一対のリード線にそれぞれ接続される。
【００１９】
このように構成された酸素センサ１は、酸素検知素子２の内側空間に対し、例えばリード線２０，２１の被覆部２０ａ，２１ａと芯線２０ｂ，２１ｂとの間に形成された空隙を介して基準ガスとしての大気が導入される一方、酸素検知素子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、該酸素検知素子２にはその内外面で生ずる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からリード線２１，２０を介して取り出す。ここで、酸素検知素子２は、排気ガス温が十分高温となっている場合には当該排気ガスで加熱されて活性化されるが、エンジン始動時など排気ガス温が低温である場合には前述の発熱体３で強制的に加熱することで活性化される。
【００２０】
発熱体３は、通常はセラミックヒータであり、例えばアルミナを主とするセラミック棒４５を芯材とし、図３に示すようにこのセラミック棒４５の表面に例えば蛇行状に形成された抵抗線部（抵抗パターン）４１からなる発熱部４２を備える。これはシート状の外層セラミック部４３に抵抗ペーストを所定のパターンで印刷し、これをセラミック棒４５に巻き付けるように丸めて焼成したものである。セラミック棒４５は外層セラミック部４３の先端から若干突出しており、また抵抗パターン４１にヒータ端子部４０から延びる図示しない通電路を経て、発熱のための通電が行われる。このような発熱部４２は発熱体３の先端側に偏って設けられ、その先端部で局部的に発熱するようになっている。
【００２１】
そして、図４に示すように、発熱体３の発熱部４２の近傍における中心軸線Ｏ1は、酸素検知素子２の中心軸線Ｏ2に対して片側に寄るように一定量δだけ偏心（オフセット）している。それによって、発熱体３の発熱部４２の先端部表面が酸素検知素子２の中空部内壁面（以下、素子内壁面ともいう）２ａに所定の面圧で押し付けられた状態で接触している。この接触位置は、図１から明らかなように酸素検知素子２の閉塞側先端からやや中間側へ寄ったところ、より好ましくは前述のプロテクタ１１のガス透過口１２にほぼ対応する位置にあたるとよい。
【００２２】
上述のように発熱体３の中心軸線Ｏ1を酸素検知素子２の中空部の中心軸線Ｏ2から偏心させ、かつ発熱部４２を素子内壁面２ａに弾性的に押し付ける機能を果たしているのは端子金具２３である。図５に端子金具２３の単体状態を、図６に端子金具２３を発熱体３に組み付けた状態を示す。これらの図から明らかなように、前述の内部電極接続部２６に関して発熱体３の先端側（すなわち発熱部４２に近い側）に発熱体把持部２７が形成されている。発熱体把持部２７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を把持するものである。
【００２３】
内部電極接続部２６は、左右両側の縁に鋸刃状の接触部２６ａ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。そして、その外周面と酸素検知素子２の中空部内壁面２ａとの間の摩擦力によって発熱体３を該中空部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側の電極層２ｃ（図２）と接触・導通するようになっている。また、発熱体３との間には所定の隙間が形成されている。なお、これら両側の接触部２６ａは、鋸刃の山に相当する部分と谷に相当する部分とが、左右両側で互い違いに形成されており、例えばセンサ組立時において内部電極接続部２６を酸素検知素子２の内側に挿入する際に、左右の接触部２６ａが同時に酸素検知素子２の開口縁に引っ掛かったりする等のトラブルが生じにくくなり、ひいては内部電極接続部２６の酸素検知素子２に対する組み付けが容易となる効果を有している。また、鋸刃状の各接触部２６ａの高さをやや大きく設定することにより、上記板状部分を筒状に曲げて内部電極接続部２６を形成する際に、その曲げ方向の幅が増大して加工が行いやすくなる効果も合わせて達成される。
【００２４】
発熱体把持部２７と内部電極接続部２６との間には両者を接続する連結部３０が形成されているが、該発熱体把持部２７を内部電極接続部２６に対し、該内部電極接続部２６の軸線Ｏd（内部電極接続部２６の最大内接直円筒の中心軸線として定義する）に対し発熱体把持部２７の軸線Ｏfが傾斜した状態となるように接続している。
【００２５】
具体的には、内部電極接続２６部の発熱体把持部２７が接続されているのと反対側の端部に、内部電極接続部２６の周方向において連結部３０に対応する位置に、発熱体３の軸線方向に延びる接続線部２５の一端が一体化されており、連結部３０は、発熱体把持部２７を内部電極接続部２６に対し、接続線部２５の側に傾くように連結している。
【００２６】
また、連結部３０は、発熱部４２と酸素検知素子２の内壁面２ａとの当接により生ずる反作用により押し戻される形で弾性変形しており、該連結部３０はその弾性復帰力により発熱部４２を、酸素検知素子２の内壁面２ａに対して押しつける向きに付勢している。
【００２７】
図５に示す端子金具２３の単体状態では、内部電極接続部２６の軸線Ｏdと発熱体把持部２７の軸線Ｏfとのなす角度θfは、図１の組付け状態よりも大きくなっている。図６に示すように、発熱体３は、内部電極接続部２６の側から発熱体把持部２７に挿通することで端子金具２３に対し組み付けられる。ここで、発熱体把持部２７は内部電極接続部２６に対し接続線部２５の側に傾くように連結されていることから、発熱体把持部２７に発熱体３を挿入する際に、接続線部２５と発熱体３との干渉が生じにくく、組付けをスムーズに行うことができる。
【００２８】
酸素センサ１の製造工程では、発熱体３に端子金具２３を固定した後、このアッセンブリを酸素検知素子２に挿入するのが普通である。ここで、発熱体３に対する酸素検知素子２の壁部からの拘束力が存在しないと仮定した場合に、発熱体把持部２７の内部電極接続部２６に対する半径方向の連結位置関係は、発熱体把持部２７によって該発熱体３の中心軸線Ｏ1が酸素検知素子２の中空部の中心軸線Ｏ2に対し、発熱部４２側が該中心軸線Ｏ2から遠ざかるように少し傾いた状態で保持されるように定められている。これにより、上記アッセンブリの挿入の際に、発熱体３の先端部は素子内壁面２ａに弾性的に接触した状態でここを滑りつつ内部に挿入され、その中心軸線Ｏ1 が中空部の中心軸線Ｏ2に近づく向きにその傾斜状態が矯正されつつ該検知素子２に対して装着されることとなる。また、発熱体把持部２７と内部電極接続部２６との間の連結部３０は、両側から周方向にＵ字状の切欠を形成することによりくびれた形態で形成されている。そして、発熱体３の検知素子２への装着時には、これが内向きに弾性変形し、その弾性復帰力によって発熱体３の発熱部４２を検知素子２の中空部内壁面２ａに押し付け、図１のような横当たり形態を生じさせる。
【００２９】
この状態で発熱体３には、素子内壁面２ａが発熱体３に及ぼす応力と発熱体把持部２７において発熱体３に作用する応力とによって、これらの合成による曲げモーメントが生じるが、その曲げモーメントにより発熱体３が折れないように、言い換えれば発熱体３の許容強度範囲以上の応力が生じないようにされている。このような応力ひいては曲げモーメントの調整を図るのは、内部電極接続部２６に隣接するくびれ形態の連結部３０である。
【００３０】
すなわち、連結部３０は、上記挿入工程で発熱体把持部２７を介して発熱体３に付与される曲げ力を吸収・緩和してその折損等を防止する役割も果たす。そして、その弾性力の調整は、くびれ部分の幅調整により可能となる。換言すれば、連結部３０のくびれ幅を適切に設定することで、上記弾性力を適度な値に調整でき、図１の発熱体３の横当たり構造において、素子内壁面２ａに対する弾性的な押付力を必要十分な値に確保できるのである。
【００３１】
以下、上記酸素センサ１の作用について説明する。
上記酸素センサ１においては、発熱体３の素子内壁面２ａに対する横当たり構造を採用することにより、発熱部４２で生じた熱が上記接触に基づく熱伝導により速やかに酸素検知素子２に伝わってこれを加熱し、また発熱部４２の上記接触部近傍の局部的に発熱した部分の熱輻射によっても酸素検知素子２が加熱される。そして、その熱伝導及び熱輻射による相乗的な熱伝達が、酸素検知素子２を急速に加熱し、活性化温度までの上昇時間を短縮する。
【００３２】
ここで、図２に示すように酸素検知素子２は、その素子内壁面２ａに横当て状態で配置された発熱部４２により局所加熱されるのであるが、センサの立ち上がり時間は従来構成のセンサと同等レベルに維持されるか、あるいは却って短縮される。その要因としては、次のようなことが考えられる。すなわち、酸素イオン伝導性固体電解質により形成された酸素検知素子２に十分な濃淡電池起電力が生じるためには、酸素検知素子２の電気抵抗値が十分小さくなることのほかに、酸素分子の解離ないし再結合反応に対する電極層２ｂ，２ｃの触媒活性が十分に高められている必要がある。そして、センサの検出出力レベルは、酸素検知素子２の電気抵抗値と上記２ｂ，２ｃの触媒活性の兼ね合いで決まる。
【００３３】
ここで、酸素検知素子２が発熱部４２により局所加熱されると、固体電解質の活性化による酸素検知素子２の電気抵抗減少は、従来の構成ほどには進まないが、図２に示すように、その局所加熱された部分２ｄはより高温まで加熱されるので、当該部分で電極層２ｂ，２ｃの触媒活性が高めらる。そして、電極層２ｂの触媒活性が向上すると被測定ガス中の酸素分子の解離が促進され、その効果により固体電解質の濃淡電池起電力ひいてはセンサの検出出力レベルが補われ、結果としてセンサの活性化時間（立ち上がり時間）が短縮されるものと推測される。
【００３４】
また、図１に示すように、端子金具２３において、発熱体把持部２７が内部電極接続部２６に対し発熱体３の発熱部４２に近い側にのみ連結されているので、端子金具２３の発熱体３の軸線方向における長さが短くなり、ひいては酸素センサ１は、その軸線方向の長さが減じられてコンパクトに構成されている。また、発熱体３が１ケ所の把持部２７により把持される形としたから、端子金具２３を装着した発熱体３を酸素検知素子２の中空部内に挿入してセンサ１を組み立てる際に、前述の通り、端子金具２３を介した過剰な横方向の力が発熱体に作用しにくくなり、ひいては組立時の発熱体３の折損等を防止することができる。
【００３５】
以下、上記酸素センサ１のいくつかの変形例について説明する。なお、上記酸素センサ１と共通する部分には同一の符号を付与して説明は省略し、主にその相違点について以下に説明する。図７に示す酸素センサ２００は、端子金具２３に代えて、内部電極接続金具１２０と、固定金具１２３とを設けた例である。内部電極接続金具１２０は、酸素検知素子２の中空部に対し、その開口側端部に嵌め込まれる筒状の内部電極接続部１２１を備え、その内部電極接続部１２１の後端側に、図１の酸素センサ１の端子金具２３の、コネクタ部２４及びこれに続く引出し線部２５（絶縁管２５ａで覆われている）とを結合した構造を有している。
【００３６】
図８に示すように、内部電極接続部１２１は、軸方向のスリット１２１ｂを有するＣ字状断面を有する略円筒状に形状を有し、自由状態において酸素検知素子２の開口側端部よりも少し大きい外径を有する。また、その後端面には、引出し線部２５の一端がスリット１２１ｂと反対側の位置に一体化されている。図７に示すように、内部電極接続部１２１は、酸素検知素子２内に押し込まれることにより、スリット１２１ｂを縮小させつつ径方向に圧縮され、その弾性復帰力による摩擦で酸素検知素子２の内面に固定されるとともに、素子２の内面側の電極層２ａ（図２）と接し、引出し線部２５を経て素子２からの出力電圧を取り出す役割を果たす。なお、内部電極接続部１２１の後端側開口縁には、外向きに突出する係止用凸部１２１ａが周方向に沿って複数形成されている。これら係止用凸部１２１ａは素子２の中空部の開口内縁と係合し、該素子２内において内部電極接続部１２１を軸線方向に位置決めする。
【００３７】
一方、固定金具１２３は、図１の端子金具２３からコネクタ部２４及び引出し線部２５を取り除いたものと略等価な形態を有する。発熱体把持部２７は、発熱体３を把持する。他方、固定部１２６は、図１の端子金具２３の内部電極接続部２６に対応するものであり、形態もこれとほぼ同様である。そして、該固定金具１２３は内部電極接続部１２１内に押し込まれ、その外周面と内部電極接続部１２１の内壁面との間の摩擦力によって発熱体３を素子２の中空部に対し軸線方向に位置決めする役割を果たす。なお、固定部１２６は、内部電極接続部１２１を介して間接的に酸素検知素子２の内面に接する形となっている。
【００３８】
また、図９の酸素センサ２０１のように、発熱体把持部２７を内部電極接続部２６に対し接続線部２５と反対側に傾くように連結するようにしてもよい。この場合、発熱体３の傾斜方向は、図１とは逆向きとなる。また、図１０は、その端子金具２３の単体状態を示す。内部電極接続部２６の軸線Ｏdと発熱体把持部２７の軸線Ｏfとのなす角度θfは、図９の組付け状態よりも大きくなっている。他方、図１１は、発熱体３を組み付けた状態を示す。発熱体３は、内部電極接続部２６の後端において引出し線部２５側の内縁Ｕと、発熱体把持部２７の前端において上記引出し線部２５とは反対側の内縁Ｖとにそれぞれ当接するとともに、連結部３０を、発熱体把持部２７の傾斜方向と逆向きに弾性変形させる形で内部電極接続部２６及び発熱体把持部２７に挿通されている。
【００３９】
なお、図１２の酸素センサ２０２は、図９の酸素センサ２０１の端子金具２３を、図７の酸素センサ２００と同様に、内部電極接続金具１２０と固定金具１２３とで置き換えた例である。
【００４０】
以上、図面に示す実施例を参照しながら説明したが、本発明は以上の実施例の記載により限定的に解釈されるものでは決してなく、特許請求の範囲の趣旨を逸脱しない限りにおいて、当業者の知識に基づく種々なる変更・改良が可能であることは言うまでもない。
【図面の簡単な説明】
【図１】本発明の一実施例たるヒータ付き酸素センサの縦断面図。
【図２】図１の発熱部と酸素検知素子との接触部付近を拡大して示す断面図。
【図３】図１の発熱部の一例を示す図。
【図４】図１の発熱部近傍を概念化して示す部分断面図。
【図５】図１の端子金具を単体状態で示す図。
【図６】図５の端子金具に発熱体を組み付ける工程を説明する図。
【図７】図１の酸素センサの第一の変形例の縦断面図。
【図８】その内部電極接続金具と固定金具とを示す分解斜視図。
【図９】図１の酸素センサの第二の変形例の縦断面図。
【図１０】図９の端子金具を単体状態で示す図。
【図１１】図１０の端子金具に発熱体を組み付けたアッセンブリを示す図。
【図１２】図９の酸素センサの変形例の縦断面図。
【符号の説明】
１，２００〜２０２酸素センサ
２酸素検知素子
２ａ中空部内壁面（素子内壁面）
３発熱体
２３端子金具（固定金具）
２６内部電極接続部（固定部）
２７発熱体把持部
３０連結部
４２発熱部
１２３固定金具
１２６固定部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen sensor for detecting, for example, an oxygen concentration in exhaust gas of an internal combustion engine, or an oxygen sensor for detecting oxygen in a predetermined gas, and in particular, heating the oxygen sensor to an activation temperature in a short time. The present invention relates to an oxygen sensor provided with a heater.
[0002]
[Prior art]
As one form of the oxygen sensor with a heater as described above, a hollow shaft with a closed tip is formed, an oxygen sensing element having an electrode layer on its inner wall surface, and the oxygen sensing element disposed in the hollow part of the oxygen sensing element A structure having a shaft-like heating element for heating the oxygen sensing element is known (for example, JP-A-4-157358). This type of oxygen sensor generally has a structure in which an axial (bar-shaped) heating element (heater) is inserted concentrically into the inner space of the oxygen sensing element until it reaches the inner surface of the tip. In Japanese Patent Laid-Open No. 10-54822, as a new type sensor, the central axis of the heating element is decentered so as to be closer to one side with respect to the central axis of the hollow part of the oxygen sensing element in the vicinity of the heating part at the tip. A positioned structure has been proposed.
[0003]
In the sensor described above, for example, by adopting a so-called horizontal structure in which the heat generating part comes into contact with the oxygen detecting element, the heat generated in the heat generating part is directly conducted to the oxygen detecting element and the time required for activation of the sensor is obtained. Shortened. As a result, the oxygen sensor can be effectively operated even when the exhaust gas temperature is low, such as when the vehicle is started or when the vehicle is idling. In addition, if the heat generating portion of the heating element is in contact with the inner wall surface of the hollow portion of the oxygen sensing element from the side, the tip of the heat generating portion is connected to the inner surface of the tip of the oxygen sensing element even if thermal expansion of the heat generating portion or the oxygen sensing element occurs. Compared to the structure applied to, it is less susceptible to thermal expansion. In other words, by adopting such a lateral structure, it is easy to maintain a good contact state between the heating element and the oxygen sensing element even when receiving heat history, and the variation in sensor characteristics can be suppressed to a small extent.
[0004]
[Problems to be solved by the invention]
By the way, in the sensor disclosed in Japanese Patent Laid-Open No. 10-54822, a terminal fitting is used to fix the heating element in the eccentric state in the oxygen sensing element. As an example of the terminal fitting, FIG. 1 has an internal electrode connection portion (26) that surrounds the heating element (3) in the circumferential direction and contacts the electrode layer inside the oxygen sensing element (2). A heating element gripping part (27) for gripping the heating element (3) is coupled to the proximal end side of the internal electrode connection part (26), while the heating element (3) is elastically attached to the inner wall surface of the element at the distal end side. A structure in which a biasing guide portion (28) is connected is disclosed. On the other hand, in FIG. 8 of the same publication, heating element gripping portions (27a, 27b) are coupled to both the proximal end side and the distal end side of the internal electrode connection portion (26), and these heating element gripping portions (27a, 27b). A structure in which the central axes of each other are eccentric from each other is disclosed.
[0005]
However, in these configurations, since the heating element gripping part and the guide part are coupled to both sides of the internal electrode connection part, the part of (heating element gripping part + internal electrode connection part + heating element gripping part (or guide part)) As a result, the total length of the sensor becomes longer, which is disadvantageous in meeting the demand for compactness that is increasing in recent years. In addition, since the heating element is gripped by two gripping parts (or one gripping part and a guide part) in a state where a strong bending force is applied in the lateral direction, for example, a heating element equipped with a terminal fitting. When an oxygen sensor is inserted into the hollow portion of the oxygen sensing element to assemble the sensor, excessive lateral force acts on the heating element via the terminal fitting, and there is a concern that problems such as breakage may occur.
[0006]
The object of the present invention is to heat the sensor to the sensor activation temperature effectively in a short time by fixing the heating element eccentrically inside the hollow shaft-shaped oxygen sensing element, and to shorten the overall length and achieve compactness. The object is to provide a heater-equipped oxygen sensor.
[0007]
[Means for solving the problems and actions / effects]
In order to solve the above-mentioned problems, an oxygen sensor with a heater according to the present invention (hereinafter also simply referred to as an oxygen sensor) has a hollow shaft shape with a closed tip, and has an electrode layer on the inner and outer surfaces thereof. When,
An axial heating element that is disposed in the hollow portion of the oxygen sensing element and heats the oxygen sensing element;
A fixing portion that is formed so as to surround the heating element in the circumferential direction and is in direct contact with the inner surface of the oxygen sensing element directly or indirectly through another member, and at least one side in the axial direction of the heating element with respect to the fixing portion A heating element gripping part connected to the heating element and holding the heating element, and a fixing bracket for fixing the heating element to the inside of the oxygen detection element by the fixing part,
The heating element gripping part is coupled to the fixing part in an inclined state with respect to the axis of the fixing part, and the central axis of the heating element gripped by this is relative to the central axis of the hollow part of the oxygen sensing element. By being inclined, the heating element is positioned in an eccentric state so as to be closer to one side in the vicinity of the heating part. The axis of the fixed part is defined as the central axis of the largest right cylinder that is inscribed in the fixed part.
[0008]
Here, as a result of the above-described eccentricity (offset), it is desirable that the surface of the heat generating portion of the heating element is in contact with the inner wall surface of the hollow portion of the oxygen detecting element. In this case, since the central axis of the heating element is decentered in the vicinity of the heating part of the heating element with respect to the central axis of the hollow part of the oxygen sensing element, the surface of the heating part of the heating element is It becomes a structure which contacts the hollow part inner wall face of an element.
[0009]
For example, by adopting a lateral support structure in which the heat generating part comes into contact with the oxygen detecting element, heat generated in the heat generating part of the heating element is directly conducted from the heat generating part to the oxygen detecting element based on the contact, The radiant heat in the vicinity of the contact point also effectively acts on the oxygen sensing element, so that the oxygen sensing element can be raised in a short time, and the sensor activation time is shortened. In addition, if the heat generating portion of the heating element is in contact with the inner wall surface of the hollow portion of the oxygen sensing element from the side, the tip of the heat generating portion is connected to the inner surface of the tip of the oxygen sensing element even if thermal expansion of the heat generating portion or the oxygen sensing element occurs. Compared to the structure applied to, it is less susceptible to thermal expansion. In other words, by adopting such a lateral support structure, it is easy to maintain a good contact state between the heating element and the oxygen sensing element even when the heating element or the oxygen sensing element receives a thermal history.
[0010]
Also, if the heat generating part is applied from the side to the inner wall surface of the hollow part of the oxygen sensing element, the heat transfer efficiency as a whole is higher than the structure applied by the tips due to the effect of direct heat conduction and radiant heat by contact. Become. As described above, the stable contact state between the oxygen sensing element and the heat generating portion of the heating element in the oxygen sensor reduces the variation in the heating state of the oxygen sensing element, which is a characteristic of the oxygen sensor. This leads to an effect of reducing the variation of the.
[0011]
Further, according to the above configuration, the heating element gripping part is coupled with the structure in which the heating element is decentered so as to be closer to one side in the vicinity of the heating part in the oxygen sensing element in an inclined state with respect to the axis of the fixed part. This is easily realized by the structure of the fixing bracket. Furthermore, since the heating element gripping portion is provided only at one location, the length of the terminal fitting in the axial direction of the heating element can be shortened, and by extension, the length of the oxygen sensor in the axial direction can be reduced so that it can be made compact. Become. In addition, since the heating element is gripped by a single gripping portion, for example, when the heating element with the mounting bracket is inserted into the hollow portion of the oxygen sensing element and the sensor is assembled, excess heat is passed through the mounting bracket. This makes it difficult for the lateral force to act on the heating element, and as a result, breakage of the heating element during assembly can be prevented.
[0012]
The fixing part and the heating element gripping part may have a structure in which end surfaces facing each other around the heating element are integrated by the connecting part in a partial section in the circumferential direction. In this case, the heating element gripping portion is connected to the fixed portion in such a manner that the opposite end surfaces of the opposing end surfaces are inclined in the direction in which they approach each other. It may be either inclined or coupled in a direction away from the center.
[0013]
Specifically, the fixing fitting can be a terminal fitting in which the fixing portion is an internal electrode connecting portion that contacts the electrode layer inside the oxygen sensing element. Since the fixing portion also serves as the internal electrode connection portion for taking out the output from the oxygen sensing element, the number of parts can be reduced, so that the sensor can be configured at a lower cost and the assembly process is simplified.
[0014]
In the above configuration, the internal electrode connection portion and the heating element gripping portion are integrated by a connecting portion in a circumferential section of the end surfaces facing each other around the heating element, and the heating element gripping portion of the internal electrode connection portion is The end on the opposite side of the connection is in the circumferential direction of the internal electrode connection portion at a position corresponding to the connecting portion connecting the internal electrode connection portion and the heating element gripping portion in the axial direction of the heating element. One end of the extending connection line portion can be integrated. In this case, the heating element gripping part may be coupled to the internal electrode connection part so that the opposite end faces on the opposite side of the connecting part are inclined to each other in a direction away from each other. desirable. In this way, when the heating element is inserted into the heating element gripping part from the internal electrode connecting part side and assembled to the terminal fitting, the connecting wire part and the heating element are less likely to interfere with each other. Can be done smoothly.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to some examples shown in the drawings. An oxygen sensor with a heater (hereinafter also simply referred to as an oxygen sensor or a sensor) 1 shown in FIG. 1 includes an oxygen sensing element 2 that is a hollow shaft-shaped solid electrolyte member with a closed tip, and a heating element that is a shaft-shaped ceramic heater. 3 and an assembly of various members constituting the outer shell. The oxygen sensing element 2 is composed of a solid electrolyte having oxygen ion conductivity. A typical example of such a solid electrolyte is ZrO _{2 in} which Y ₂ O ₃ or CaO is dissolved, but a solid solution of an oxide of other alkaline earth metal or rare earth metal and ZrO ₂ is used. May be used. Moreover, HfO ₂ may be contained in ZrO _{2 serving as} a base.
[0016]
Outside the intermediate part of the oxygen sensing element 2, there are provided insulators 6 and 7 made of insulating ceramic, and a housing 9 which is a metal cylinder member through ceramic powder 8 made of talc. The detection element 2 penetrates the housing 9 while being electrically insulated. As shown in FIG. 2, a pair of electrode layers 2b and 2c are provided on the inner and outer surfaces of the oxygen sensing element 2 so as to cover almost the entire surface. These electrode layers 2b and 2c are both reversible with respect to the dissociation reaction of oxygen molecules for injecting oxygen into the solid electrolyte constituting the oxygen sensing element 2 and the recombination reaction of oxygen for releasing oxygen from the solid electrolyte. A porous electrode having a typical catalytic function (oxygen dissociation catalytic function), for example, a Pt porous electrode.
[0017]
Next, a protector 11 is provided at one opening of the housing 9 so as to cover the front end side of the oxygen sensing element 2 with a predetermined space therebetween, and the protector 11 has a plurality of gas permeation ports through which exhaust gas permeates. 12 is formed, so that oxygen in the exhaust gas can come into contact with the front surface of the oxygen sensing element 2. A first sleeve 14 is caulked to the other opening of the housing 9 via a ring 15 between the insulator 6 and a second sleeve 16 is fitted and fixed to the sleeve 14 from the outside. . An opening on the upper end side of the sleeve 16 in the figure is sealed with a plug body 17, and subsequently, plug bodies 18 and 19 are provided further inward. Lead wires 20 and 21 are arranged so as to penetrate the plug bodies 17 and 18.
[0018]
One lead wire 20 includes a connector portion 24 of a terminal metal fitting (fixing metal fitting) 23 and a lead wire portion 25 (covered by an insulating tube 25a) following the connector portion 24, and an internal electrode connecting portion (fixing portion) of the terminal metal fitting 23. 26 and electrically connected to an inner electrode layer (not shown) of the oxygen sensing element 2 described above. The other lead wire 21 is electrically connected to an outer electrode layer (not shown) of the oxygen sensing element 2 through a connector portion 34 of another terminal fitting 33, a lead wire portion 35 and an external electrode connection portion 35b following the connector portion 34. ing. A pair of plus and minus heater terminal portions 40 for energizing the heating element 3 is fixed to the base end portion (upper end portion in FIG. 1) of the heating element 3, and passes through the heater terminal portions 40. The heating resistor circuit, which will be described later, embedded in the heating element 3 is energized. Although not shown in FIG. 1, the pair of heater terminal portions 40 is connected to a pair of heater lead wires provided through the plug bodies 17, 18 and the like.
[0019]
The oxygen sensor 1 configured as described above has a reference to the inner space of the oxygen sensing element 2 through a gap formed between the covering portions 20a and 21a of the lead wires 20 and 21 and the core wires 20b and 21b, for example. While the atmosphere as gas is introduced, the exhaust gas introduced through the gas permeation port 12 of the protector 11 is in contact with the outer surface of the oxygen sensing element 2, and oxygen generated on the inner and outer surfaces of the oxygen sensing element 2. Oxygen concentration cell electromotive force is generated according to the concentration difference. The oxygen concentration cell electromotive force is taken out from the electrode layers 2b and 2c through the lead wires 21 and 20 as a detection signal of the oxygen concentration in the exhaust gas. Here, when the exhaust gas temperature is sufficiently high, the oxygen sensing element 2 is heated and activated by the exhaust gas. However, when the exhaust gas temperature is low, such as when the engine is started, the oxygen detection element 2 is activated. It is activated by forcibly heating with the heating element 3.
[0020]
The heating element 3 is usually a ceramic heater. For example, a ceramic rod 45 mainly composed of alumina is used as a core material, and a resistance wire portion (for example, meandering) formed on the surface of the ceramic rod 45 as shown in FIG. A heating pattern 42 comprising a resistance pattern 41). This is one in which a resistance paste is printed in a predetermined pattern on the sheet-like outer layer ceramic portion 43 and then rolled and fired so as to be wound around the ceramic rod 45. The ceramic rod 45 slightly protrudes from the front end of the outer layer ceramic portion 43, and energization for heat generation is performed through a current path (not shown) extending from the heater terminal portion 40 to the resistance pattern 41. Such a heat generating part 42 is provided in a biased manner toward the front end side of the heat generating element 3, and heat is generated locally at the front end part.
[0021]
As shown in FIG. 4, the central axis O1 in the vicinity of the heat generating portion 42 of the heating element 3 is decentered (offset) by a certain amount δ so as to be closer to one side with respect to the central axis O2 of the oxygen sensing element 2. Yes. As a result, the surface of the tip of the heat generating portion 42 of the heat generating element 3 is in contact with the hollow portion inner wall surface (hereinafter also referred to as element inner wall surface) 2a of the oxygen sensing element 2 in a state of being pressed with a predetermined surface pressure. As is apparent from FIG. 1, this contact position is located slightly closer to the middle side from the front end of the oxygen sensing element 2, more preferably a position substantially corresponding to the gas permeation port 12 of the protector 11 described above.
[0022]
As described above, it is the terminal fitting 23 that functions to decenter the central axis O1 of the heating element 3 from the central axis O2 of the hollow portion of the oxygen sensing element 2 and to elastically press the heating part 42 against the inner wall surface 2a of the element. It is. FIG. 5 shows a single state of the terminal fitting 23, and FIG. 6 shows a state where the terminal fitting 23 is assembled to the heating element 3. As is apparent from these drawings, a heating element gripping portion 27 is formed on the distal end side of the heating element 3 (that is, the side close to the heating portion 42) with respect to the internal electrode connection portion 26 described above. The heating element gripping portion 27 has a C-shaped cross section 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. To grip.
[0023]
The internal electrode connecting portion 26 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 26a are formed on both left and right edges into a cylindrical shape. . The heating element 3 is positioned in the axial direction with respect to the hollow portion by a frictional force between the outer peripheral surface and the hollow inner wall surface 2a of the oxygen sensing element 2, and each tip of the plurality of contact portions 26a. In this part, contact / conduction with the inner electrode layer 2c (FIG. 2) is achieved. A predetermined gap is formed between the heating element 3 and the heating element 3. The contact portions 26a on both sides are formed so that a portion corresponding to a crest of a saw blade and a portion corresponding to a trough are alternately formed on both the left and right sides. For example, when the sensor is assembled, the internal electrode connection portion 26 is detected with oxygen. When inserted inside the element 2, troubles such as the left and right contact portions 26 a being simultaneously hooked on the opening edge of the oxygen detection element 2 are less likely to occur, and as a result, the assembly of the internal electrode connection portion 26 to the oxygen detection element 2 is prevented. It has the effect of facilitating. In addition, by setting the height of each of the saw blade-like contact portions 26a to be slightly larger, when the internal electrode connecting portion 26 is formed by bending the plate-like portion into a cylindrical shape, the width in the bending direction increases. The effect of facilitating processing is also achieved.
[0024]
A connecting portion 30 is formed between the heating element gripping portion 27 and the internal electrode connection portion 26, and the heating electrode gripping portion 27 is connected to the internal electrode connection portion 26 with respect to the internal electrode connection portion 26. The axis line Of of the heating element gripping part 27 is connected to be inclined with respect to the axis line Od of 26 (defined as the central axis line of the maximum inscribed straight cylinder of the internal electrode connecting part 26).
[0025]
Specifically, the heating element is located at a position corresponding to the connecting portion 30 in the circumferential direction of the internal electrode connection part 26 at the end of the internal electrode connection 26 part opposite to the side where the heating element gripping part 27 is connected. 3, one end of the connecting line portion 25 extending in the axial direction is integrated, and the connecting portion 30 connects the heating element gripping portion 27 to the internal electrode connecting portion 26 so as to be inclined toward the connecting line portion 25. ing.
[0026]
The connecting portion 30 is elastically deformed so as to be pushed back by a reaction caused by the contact between the heat generating portion 42 and the inner wall surface 2a of the oxygen detecting element 2, and the connecting portion 30 is heated by the elastic return force. Is urged in a direction to press against the inner wall surface 2a of the oxygen sensing element 2.
[0027]
In the single state of the terminal fitting 23 shown in FIG. 5, the angle θf formed by the axis Od of the internal electrode connecting portion 26 and the axis Of of the heating element gripping portion 27 is larger than that in the assembled state of FIG. As shown in FIG. 6, the heating element 3 is assembled to the terminal fitting 23 by being inserted into the heating element gripping part 27 from the internal electrode connection part 26 side. Here, since the heating element gripping part 27 is connected to the internal electrode connection part 26 so as to be inclined toward the connection line part 25, the connecting wire is inserted when the heating element 3 is inserted into the heating element gripping part 27. Interference between the portion 25 and the heating element 3 hardly occurs, and the assembly can be performed smoothly.
[0028]
In the manufacturing process of the oxygen sensor 1, it is common to fix the terminal fitting 23 to the heating element 3 and then insert this assembly into the oxygen sensing element 2. Here, assuming that there is no binding force from the wall of the oxygen sensing element 2 to the heating element 3, the radial connection position relationship of the heating element gripping part 27 to the internal electrode connection part 26 is as follows. The central axis O1 of the heating element 3 is determined by the portion 27 so as to be held in a state slightly inclined with respect to the central axis O2 of the hollow portion of the oxygen sensing element 2 so that the heating unit 42 side is away from the central axis O2. ing. As a result, when the assembly is inserted, the tip of the heating element 3 is inserted into the element while sliding on the inner wall surface 2a in a state of elastic contact with the inner wall surface 2a, and the center axis O1 is the center axis O2 of the hollow portion. The sensor is mounted on the detection element 2 while the inclination state is corrected in a direction approaching. Further, the connecting portion 30 between the heating element gripping portion 27 and the internal electrode connecting portion 26 is formed in a constricted form by forming U-shaped notches in the circumferential direction from both sides. Then, when the heating element 3 is mounted on the detection element 2, it is elastically deformed inward, and the heating part 42 of the heating element 3 is pressed against the hollow inner wall surface 2a of the detection element 2 by the elastic restoring force, as shown in FIG. Give a side-by-side form.
[0029]
In this state, a bending moment is generated in the heating element 3 by a combination of the stress exerted on the heating element 3 by the inner wall surface 2a of the element and the stress acting on the heating element 3 in the heating element gripping portion 27. Thus, the heating element 3 is prevented from being bent, in other words, the stress exceeding the allowable strength range of the heating element 3 is not generated. It is the constricted connecting portion 30 adjacent to the internal electrode connecting portion 26 that adjusts the stress and the bending moment.
[0030]
That is, the connecting part 30 also plays a role of preventing breakage and the like by absorbing / releasing the bending force applied to the heating element 3 through the heating element gripping part 27 in the insertion step. The elastic force can be adjusted by adjusting the width of the constricted portion. In other words, the elastic force can be adjusted to an appropriate value by appropriately setting the constriction width of the connecting portion 30, and in the lateral contact structure of the heating element 3 of FIG. The force can be secured at a necessary and sufficient value.
[0031]
Hereinafter, the operation of the oxygen sensor 1 will be described.
In the oxygen sensor 1, by adopting a lateral contact structure with respect to the element inner wall surface 2a of the heating element 3, the heat generated in the heating part 42 is quickly transferred to the oxygen sensing element 2 by heat conduction based on the contact. Further, the oxygen detecting element 2 is also heated by heat radiation of a portion of the heat generating portion 42 that is locally heated near the contact portion. And the synergistic heat transfer by the heat conduction and the heat radiation rapidly heats the oxygen sensing element 2 and shortens the rise time to the activation temperature.
[0032]
Here, as shown in FIG. 2, the oxygen sensing element 2 is locally heated by the heat generating part 42 disposed in a state of being horizontally applied to the inner wall surface 2a of the element, but the rise time of the sensor is the same as that of the conventional sensor. It is maintained at the same level or shortened. The following factors can be considered as the factor. That is, in order to generate a sufficient concentration cell electromotive force in the oxygen sensing element 2 formed of the oxygen ion conductive solid electrolyte, in addition to the electric resistance value of the oxygen sensing element 2 being sufficiently small, dissociation of oxygen molecules In addition, the catalytic activity of the electrode layers 2b and 2c for the recombination reaction needs to be sufficiently increased. The detection output level of the sensor is determined by the balance between the electric resistance value of the oxygen sensing element 2 and the catalytic activities of 2b and 2c.
[0033]
Here, when the oxygen sensing element 2 is locally heated by the heat generating portion 42, the electrical resistance reduction of the oxygen sensing element 2 due to the activation of the solid electrolyte does not proceed as much as the conventional configuration, but as shown in FIG. Since the locally heated portion 2d is heated to a higher temperature, the catalytic activity of the electrode layers 2b and 2c is enhanced in the portion. When the catalytic activity of the electrode layer 2b is improved, the dissociation of oxygen molecules in the gas to be measured is promoted, and the effect supplements the concentration electromotive force of the solid electrolyte and thus the detection output level of the sensor, resulting in the activation of the sensor. It is estimated that time (rise time) is shortened.
[0034]
Further, as shown in FIG. 1, in the terminal fitting 23, the heating element gripping portion 27 is connected to the internal electrode connection portion 26 only on the side close to the heating portion 42 of the heating element 3. The length of the body 3 in the axial direction is shortened, and thus the oxygen sensor 1 is configured to be compact by reducing the length in the axial direction. In addition, since the heating element 3 is gripped by the gripping part 27 at one place, when the sensor 1 is assembled by inserting the heating element 3 fitted with the terminal fitting 23 into the hollow part of the oxygen sensing element 2, As described above, excessive lateral force via the terminal fitting 23 is less likely to act on the heating element, and as a result, breakage of the heating element 3 during assembly can be prevented.
[0035]
Hereinafter, some modified examples of the oxygen sensor 1 will be described. In addition, the same code | symbol is attached | subjected to the part which is common in the said oxygen sensor 1, and description is abbreviate | omitted and the difference is mainly demonstrated below. An oxygen sensor 200 shown in FIG. 7 is an example in which an internal electrode connection fitting 120 and a fixing fitting 123 are provided in place of the terminal fitting 23. The internal electrode connection fitting 120 includes a cylindrical internal electrode connection portion 121 that is fitted into the opening-side end portion of the hollow portion of the oxygen sensing element 2, and a rear end side of the internal electrode connection portion 121 is shown in FIG. The oxygen sensor 1 has a structure in which a connector portion 24 and a lead wire portion 25 (covered by an insulating tube 25a) following the connector portion 24 are coupled.
[0036]
As shown in FIG. 8, the internal electrode connecting portion 121 has a substantially cylindrical shape having a C-shaped cross section having an axial slit 121b, and is in a free state than the opening side end portion of the oxygen sensing element 2. It has a slightly larger outer diameter. In addition, at the rear end face, one end of the leader line portion 25 is integrated at a position opposite to the slit 121b. As shown in FIG. 7, the internal electrode connecting portion 121 is compressed in the radial direction while being compressed into the oxygen detecting element 2 by being pressed into the oxygen detecting element 2, and the inner surface of the oxygen detecting element 2 is frictioned by the elastic restoring force. And is in contact with the electrode layer 2 a (FIG. 2) on the inner surface side of the element 2, and plays a role of taking out an output voltage from the element 2 through the lead wire portion 25. Note that a plurality of locking projections 121 a projecting outward are formed along the circumferential direction at the opening edge on the rear end side of the internal electrode connection portion 121. These locking convex portions 121 a engage with the inner edge of the opening of the hollow portion of the element 2 to position the internal electrode connection portion 121 in the axial direction in the element 2.
[0037]
On the other hand, the fixing bracket 123 has a form substantially equivalent to that obtained by removing the connector portion 24 and the lead wire portion 25 from the terminal fitting 23 of FIG. The heating element gripping part 27 grips the heating element 3. On the other hand, the fixing portion 126 corresponds to the internal electrode connecting portion 26 of the terminal fitting 23 of FIG. 1, and the form thereof is substantially the same. The fixing fitting 123 is pushed into the internal electrode connecting portion 121, and the heating element 3 is moved in the axial direction with respect to the hollow portion of the element 2 by the frictional force between the outer peripheral surface and the inner wall surface of the internal electrode connecting portion 121. Play a role in positioning. The fixing portion 126 is in contact with the inner surface of the oxygen sensing element 2 indirectly through the internal electrode connecting portion 121.
[0038]
Further, like the oxygen sensor 201 in FIG. 9, the heating element gripping part 27 may be coupled to the internal electrode connection part 26 so as to be inclined to the side opposite to the connection line part 25. In this case, the inclination direction of the heating element 3 is opposite to that in FIG. FIG. 10 shows a single state of the terminal fitting 23. The angle θf formed by the axis Od of the internal electrode connecting portion 26 and the axis Of of the heating element gripping portion 27 is larger than that in the assembled state of FIG. On the other hand, FIG. 11 shows a state in which the heating element 3 is assembled. The heating element 3 is in contact with the inner edge U on the lead wire portion 25 side at the rear end of the internal electrode connection portion 26 and the inner edge V on the opposite side of the lead wire portion 25 at the front end of the heating element grip portion 27. The connecting portion 30 is inserted into the internal electrode connecting portion 26 and the heating element gripping portion 27 in a form that is elastically deformed in the direction opposite to the inclination direction of the heating element gripping portion 27.
[0039]
Note that the oxygen sensor 202 in FIG. 12 is an example in which the terminal fitting 23 of the oxygen sensor 201 in FIG. 9 is replaced with an internal electrode connecting fitting 120 and a fixing fitting 123 in the same manner as the oxygen sensor 200 in FIG.
[0040]
Although the present invention has been described above with reference to the embodiments shown in the drawings, the present invention is not limited to the above description of the embodiments, and those skilled in the art will not depart from the spirit of the claims. It goes without saying that various modifications and improvements based on the knowledge of the above are possible.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an oxygen sensor with a heater according to an embodiment of the present invention.
2 is an enlarged cross-sectional view showing the vicinity of a contact portion between a heat generating portion and an oxygen detection element in FIG. 1;
FIG. 3 is a diagram showing an example of a heat generating part in FIG.
4 is a partial cross-sectional view conceptually showing the vicinity of a heat generating portion in FIG.
5 is a diagram showing the terminal fitting of FIG. 1 in a single state.
6 is a diagram illustrating a process of assembling a heating element to the terminal fitting of FIG.
7 is a longitudinal sectional view of a first modification of the oxygen sensor of FIG. 1. FIG.
FIG. 8 is an exploded perspective view showing the internal electrode connecting metal fitting and the fixing metal fitting.
9 is a longitudinal sectional view of a second modification of the oxygen sensor in FIG. 1. FIG.
10 is a diagram showing the terminal fitting of FIG. 9 in a single state.
11 is a view showing an assembly in which a heating element is assembled to the terminal fitting of FIG.
12 is a longitudinal sectional view of a modification of the oxygen sensor of FIG.
[Explanation of symbols]
1,200-202 Oxygen sensor 2 Oxygen sensing element 2a Hollow inner wall surface (element inner wall surface)
3 Heating element 23 Terminal bracket (fixing bracket)
26 Internal electrode connection (fixed part)
27 Heating element gripping part 30 Connecting part 42 Heating part 123 Fixing bracket 126 Fixing part

Claims

A hollow shaft with a closed tip, an oxygen sensing element having an electrode layer on the inner and outer surfaces thereof;
An axial heating element that is disposed in the hollow portion of the oxygen sensing element and heats the oxygen sensing element;
An internal electrode connecting portion that is formed so as to surround the heating element in the circumferential direction and is in contact with an electrode layer inside the oxygen sensing element, and is connected to the distal end side in the axial direction of the heating element with respect to the internal electrode connecting portion A heating element gripping part for gripping the heating element, and a fixing bracket for fixing the heating element inside the oxygen sensing element by the internal electrode connection part ,
The internal electrode connection part and the heating element gripping part are integrated by a connecting part in a partial section in the circumferential direction with the end faces facing each other around the heating element,
In the circumferential direction of the internal electrode connection portion, the internal electrode connection portion and the heating element gripping portion are connected to the end of the internal electrode connection portion opposite to the side where the heating element gripping portion is connected. One end of the connecting line portion extending in the axial direction of the heating element is integrated at a position corresponding to the connecting portion to be
In addition, the heating element gripping portion is coupled to the internal electrode connecting portion so that the opposite end surfaces of the opposing end faces away from the connecting portion are inclined in a direction away from each other. ,
When the central axis of the heating element gripped by the inclined heating element gripping part is inclined with respect to the central axis of the hollow part of the oxygen sensing element, the heating element approaches one side in the vicinity of the heating part. An oxygen sensor with a heater, which is positioned in an eccentric state as described above.

The oxygen sensor according to claim 1, wherein a surface of the heat generating portion of the heat generating element is in contact with an inner wall surface of the hollow portion of the oxygen detecting element.

In the fixing bracket, the connecting portion that connects the heating element gripping portion in an inclined state with respect to the internal electrode connecting portion is pushed back by a reaction caused by the contact between the heating portion and the inner wall surface of the oxygen sensing element. 3. The oxygen sensor according to claim 2, wherein the oxygen sensor is elastically deformed and the connecting portion urges the heat generating portion in a direction of pressing the heat generating portion against an inner wall surface of the oxygen detecting element by an elastic restoring force.