JP2004151018A - Laminated gas sensing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated gas sensing element highly accurately detecting a specific gas concentration by reducing the effect of oxygen coexisting in a measuring-object gas chamber. <P>SOLUTION: In a pump electrode 21 facing to the measuring-object gas chamber of an oxygen pump cell, the total length G of the width directional lengths orthogonally crossing with the longitudinal direction of clearance portions between the side faces 211 and 212 of the pump electrode 21 along the longitudinal direction of this laminated gas sensing element and the inside faces 111 and 112 of the measuring-object gas chamber 11 opposed to the side faces 211 and 212 is not more than 0.5mm. When the area of the pump electrode facing to the measuring-object gas chamber is taken as Se and the total of the area of the clearance portions between the side faces of the pump electrode along the longitudinal direction of the laminated gas sensing element and the inside faces of the measuring-object gas chamber opposed to the sides is taken as Sg, these values are set to satisfy the relationship of Sg/Se≤0.3. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【技術分野】
本発明は，自動車用内燃機関の排気系等に使用され，ＮＯｘ濃度等の検出に利用できる積層型ガスセンサ素子に関する。
【０００２】
【従来技術】
自動車用内燃機関等から排出される排気ガスを原因とする大気汚染は現代社会に深刻な問題を引き起こしており，排気ガス中の公害物質であるＮＯｘ等に対する浄化基準法規が年々厳しくなっている。
排気ガス中のＮＯｘ濃度を検出し，検出結果をエンジン燃焼制御モニタ，触媒モニタ等にフィードバックすれば，より効率よく排気ガス浄化を行うことができると考えられる。このような背景から，排気ガス中のＮＯｘ濃度を精度高く検出可能な積層型ガスセンサ素子が求められていた。
【０００３】
ところで，従来よく知られた積層型ガスセンサ素子として，図１６に示す構成の素子が挙げられる。
図１６に示す積層型ガスセンサ素子９は，第１被測定ガス室１１と対面するよう酸素ポンプセル９２が配置され，該酸素ポンプセル９２に電圧を印加することで，第１被測定ガス室１１内にある酸素を素子外部ヘポンピングする。または，第１被測定ガス室１１内へ素子外部の酸素をポンピングする。
そして，第１被測定ガス室１１内の酸素濃度を検知可能な酸素モニタセル９３を設け，この酸素モニタセル９３が検出する第１被測定ガス室１１内の酸素濃度が定常状態となるように，酸素ポンプセル９２がフィードバック制御される。
【０００４】
第１被測定ガス室１１と連通する第２被測定ガス室１２には，ＮＯｘを電極上で分解して生成した酸素イオンによるイオン電流を測定することで，ＮＯｘ濃度を測定するよう構成したセンサセル９４を設けておく。
上述したごとく第１被測定ガス室１１内の酸素濃度は定常状態となるよう制御されているため，第２被測定ガス室１２内の酸素濃度も一定となる。従って，センサセル９４における電極間を移動する酸素イオンの量，即ちセンサセル９４における酸素イオン電流の大きさはＮＯｘ濃度に対応する。
このように，第１及び第２被測定ガス室１１，１２に導入した被測定ガス中のＮＯｘ濃度を，素子外の雰囲気中の酸素濃度増減にかかわらず，精度高く測定することができる。
【０００５】
【特許文献１】
特許第２８８５３３６号公報
【０００６】
【解決しようとする課題】
ところで，被測定ガス中の酸素濃度が％のオーダーで存在し，ＮＯｘがｐｐｍのオーダーで存在する場合，非常に微量なＮＯｘを精度よく測定するために，ＮＯｘ検出に影響のでないレベルまで酸素を酸素ポンプセルによって排出し，被測定ガス室の酸素濃度を非常に少なくする必要がある。また，この問題はＮＯｘ以外の特定ガスを検出する際にも生じることがある。
【０００７】
本発明は，かかる従来の問題点に鑑みてなされたもので，被測定ガス室に共存する酸素による影響を小さくし，高い精度で特定ガス濃度を検出可能な積層型ガスセンサ素子を提供しようとするものである。
【０００８】
【課題の解決手段】
第１の発明は，所定の拡散抵抗の下に被測定ガスを導入する被測定ガス室と，酸素イオン導電性の固体電解質板の表面に，一方のポンプ電極が上記被測定ガス室に面するように設けた一対のポンプ電極を有し，これら一対のポンプ電極へ通電することにより上記被測定ガス室に酸素を導入または排出し，上記被測定ガス室の酸素濃度を調整する酸素ポンプセルと，
酸素イオン導電性の固体電解質板の表面に，一方のセンサ電極が上記被測定ガス室に面するように設けた一対のセンサ電極を有し，これら一対のセンサ電極間に生じる酸素イオン電流に基づいて，上記被測定ガス室内の特定ガス濃度を検出するセンサセルとを有する積層型ガスセンサ素子であって，
上記酸素ポンプセルの上記被測定ガス室に面するポンプ電極において，
上記積層型ガスセンサ素子の長手方向に沿った上記ポンプ電極の側面と，該側面と対向する上記被測定ガス室の内側面とのクリアランス部の上記長手方向と直交する幅方向の長さの総計Ｇの最小値は０．５ｍｍ以下であることを特徴とする積層型ガスセンサ素子にある（請求項１）。
【０００９】
第１の発明にかかる積層型ガスセンサ素子は，被測定ガス室に面するポンプ電極の側面と，該側面と対向する被測定ガス室の内側面とのクリアランス部の幅方向長さの総計Ｇの最小値が０．５ｍｍ以下と，十分小さくなっている。
【００１０】
また，第２の発明は，所定の拡散抵抗の下に被測定ガスを導入する被測定ガス室と，
酸素イオン導電性の固体電解質板の表面に，一方のポンプ電極が上記被測定ガス室に面するように設けた一対のポンプ電極を有し，これら一対のポンプ電極へ通電することにより上記被測定ガス室に酸素を導入または排出し，上記被測定ガス室の酸素濃度を調整する酸素ポンプセルと，
酸素イオン導電性の固体電解質板の表面に，一方のセンサ電極が上記被測定ガス室に面するように設けた一対のセンサ電極を有し，これら一対のセンサ電極間に生じる酸素イオン電流に基づいて，上記被測定ガス室内の特定ガス濃度を検出するセンサセルとを有する積層型ガスセンサ素子であって，
上記被測定ガス室に対し被測定ガスを導入する導入部よりガス流れ下流における上記酸素ポンプセルにおける上記被測定ガス室に面するポンプ電極の形成範囲において，
上記被測定ガス室に面するポンプ電極の面積をＳｅ，上記積層型ガスセンサ素子の長手方向に沿った上記ポンプ電極の側面と該側面と対向する上記被測定ガス室の内側面との間のクリアランス部の面積の総計をＳｇとした場合，Ｓｇ／Ｓｅ≦０．３であることを特徴とする積層型ガスセンサ素子である（請求項３）。
【００１１】
第２の発明にかかる積層型ガスセンサ素子は，ポンプ電極の面積とクリアランス部の面積との間にＳｇ／Ｓｅ≦０．３なる関係が成立し，ポンプ電極の面積と比較してクリアランス部の面積が十分小さくなっている。
【００１２】
ところで被測定ガス室においてポンプ電極の表面付近を流れる被測定ガス（後述する図３の矢線１１８）は上記ポンプ電極により含まれる酸素のイオン化が生じやすい。ここで発生した酸素イオンは一対のポンプ電極の間を酸素イオン電流となって流れ，被測定ガス室の外部に容易に排出される。
しかしながら，ポンプ電極の側面と該側面と対向する被測定ガス室の内側面との間を流れる被測定ガス（後述する図３の矢線１１９）はポンプ電極との距離が遠く，ここに含まれる酸素はポンプ電極によってイオン化され難い。
【００１３】
ところでセンサセルにおける特定ガス濃度検出は，被測定ガス室に面するセンサ電極上で特定ガスを分解し，この分解により発生した酸素イオンから生じる一対のセンサ電極間に流れる酸素イオン電流に基づいて行う。
仮にセンサ電極上で被測定ガス室に含まれる酸素が分解された場合，特定ガスに由来する酸素イオンと酸素に由来する酸素イオンとが混じって，正確に特定ガス濃度が検出なくなるおそれある。
【００１４】
第１の発明にかかる積層型ガスセンサ素子は，ポンプ電極の側面と被測定ガス室の内側面とのクリアランス部の総計が十分小さく（請求項１），または第２の発明にかかる積層型ガスセンサ素子は，ポンプ電極の面積に比べてクリアランス部の面積が十分小さく（請求項３），より多くの被測定ガスを酸素ポンプセルのポンプ電極上を通過させることができる。
従って，被測定ガス室の酸素濃度をより薄くして，特定ガス濃度検出に対する酸素の影響をより小さくし，精度の高い特定ガス濃度の測定が可能となる。
【００１５】
以上，本発明によれば，被測定ガス室に共存する酸素による影響を小さくし，高い精度で特定ガス濃度を検出可能な積層型ガスセンサ素子を提供することができる。
【００１６】
【発明の実施の形態】
第１の発明（請求項１），第２の発明（請求項３）における積層型ガスセンサ素子において，酸素ポンプセルのポンプ電極形状は，後述する図３に示すように長手方向と直交する幅方向に略均一な幅を備えた長方形，幅が不均一な形状（図５），長方形の４つの頂点を丸めた略楕円形（図１２）等の各種の形状に構成することができる。
また，被測定ガス室の形状は，ポンプ電極と同様に長方形や略楕円形等に構成することができるが，内側面とポンプ電極の側面との間のクリアランス部をより小さくするために，ポンプ電極の形状と略同形状に構成することが好ましい。
【００１７】
ここに第１の発明におけるクリアランス部の総計Ｇについて，積層型ガスセンサ素子をポンプ電極の表面を含む平面で切断した断面の模式図である図４を用いて説明する。
Ｓは被測定ガス室の内側面，Ｔはポンプ電極の側面を示す曲線で，Ｕ０１とＵ０２はそれぞれポンプ電極の長手方向における端部を通過する直線，Ｕ１〜Ｕ３はポンプ電極を横切る直線で，Ｕ０１，Ｕ０２，Ｕ１〜Ｕ３は全て積層型ガスセンサ素子の長手方向と直交する幅方向と平行な直線である。
各直線Ｕ０１，Ｕ０２，Ｕ１〜Ｕ３がＳやＴと交わる交点がＳ０１〜Ｓ０４，Ｓ１１〜Ｓ１６，Ｔ１１〜Ｔ１６である。
【００１８】
図４において，Ｇは，同一の直線Ｕ１上における距離Ｓ１１−Ｔ１１，距離Ｓ１２−Ｔ１２を足した値，Ｕ２上におけるＳ１３−Ｔ１３，Ｓ１４−Ｔ１４を合計した値等となる。または，Ｓ０１−Ｓ０２，Ｓ０３−Ｓ０４の長さとなる。
そして，ポンプ電極の側面全体のいずれかにおいてＧが０．５ｍｍ以下となれば第１の発明が成立する。
図４にかかるポンプ電極の場合は，直線Ｕ２上のＳ１３−Ｔ１３とＴ１４−Ｓ１４にかかるＧが最小の部分となり，他の部分はこれより大きいため，この部分の距離が０．５ｍｍ以下であれば第１の発明が成立する。
なお，ポンプ電極の側面を示す曲線が複数ある場合も同様の方法でＧを考えることができる。
【００１９】
また，クリアランス部の総計Ｇは最小で０．５ｍｍ以下となる条件を満たせば第１の発明の効果を得ることができるが，最小で０．２ｍｍ以下とすることで，より高い検出精度を備えた積層型ガスセンサ素子を得ることができる。
また，クリアランス部の総計Ｇが０である，すなわちポンプ電極の側面が被測定ガス室の内側面と接触した状態にある場合に，最も検出精度の高い積層型ガスセンサ素子を得ることができる。
また，積層型ガスセンサ素子の長手方向とは，略断面長方形で柱状の積層型ガスセンサ素子の長軸方向である。
【００２０】
次に，第１の発明において，上記クリアランス部の総計Ｇが０．５ｍｍ以下である部分の積層型ガスセンサ素子の長手方向に沿った長さがポンプ電極全体の上記長手方向に沿った長さに対して１／４以上を占めている時に，より検出精度の高い積層型ガスセンサ素子を得ることができる（請求項２）。
また，ポンプ電極全体の長さにおける１／２以上を，クリアランス部の総計Ｇが０．５ｍｍ以下である部分が占めている場合は，更に検出精度の高い優れた積層型ガスセンサ素子を得ることができる。
【００２１】
また，第２の発明におけるポンプ電極の面積等について，積層型ガスセンサ素子をポンプ電極の表面を含む平面で切断した断面の模式図である図７を用いて説明する。
Ｓは被測定ガス室の内側面，Ｔはポンプ電極の側面を示す曲線で，点Ｖは被測定ガス導入部の中心位置，Ｖ０は点Ｖを通る幅方向と平行な直線，Ｖ１はポンプ電極の長手方向における端部を通過し，幅方向と平行な直線である。
第２の発明におけるポンプ電極の面積Ｓｅとは，曲線Ｔと直線Ｖ０にて囲まれた領域の面積であり，クリアランス部の面積の総計Ｓｇとは，直線Ｖ０，Ｖ１曲線Ｔ，Ｓで囲まれた領域の面積である。
【００２２】
なお，後述する図１１に示すごとく，積層型ガスセンサ素子の端面から被測定ガスを導入する方式では，ポンプ電極全体がガス流れの下流側に含まれるため，電極全体の面積をＳｅとする。Ｓｇは電極の長手方向の両端を通る幅方向の直線間によって区切られる領域となる。
このクリアランス部の面積Ｓｇとポンプ電極の面積ＳｅとについてＳｇ／Ｓｅ≦０．３であれば，第２の発明にかかる効果を得ることができる。
また，Ｓｇ＝０である場合，すなわちポンプ電極の側面が被測定ガス室の内側面と接触した状態にある場合は，最も検出精度の高い積層型ガスセンサ素子を得ることができる。
【００２３】
また，第１，第２の発明にかかる積層型ガスセンサ素子は２セルまたはそれ以上のセルを備えた構成のＮＯｘセンサ素子やＣＯセンサ素子，ＨＣセンサ素子に適用することができる。
【００２４】
また，第１及び第２の発明において，酸素イオン導電性の固体電解質板の表面に，一方の電極が上記被測定ガス室に面するように設けた一対の電極を有し，これら一対の電極間に生じる電流値または起電力に基づいて，上記被測定ガス室内の酸素濃度を検出する酸素モニタセルを備えることが好ましい（請求項４）。
これにより被測定ガス室の酸素濃度を監視することができる。
【００２５】
そして，例えば被測定ガス室の酸素濃度が所定の範囲内に納まるように酸素ポンプセルの作動を制御する等の構成を加えて，センサセルの一対の電極間に流れる酸素イオン電流がより正確に測定したい特定ガス濃度に対応するように積層型ガスセンサ素子を構成することができる。
なお，電流値に基づいて酸素濃度を検出する酸素モニタセルは限界電流式の酸素センサとして機能し，起電力に基づいて酸素濃度を検出する酸素モニタセルは酸素濃淡起電力式の酸素センサとして機能するよう構成する（後述する図１，実施例１参照）。
【００２６】
【実施例】
以下に，図面を用いて第１の発明の実施例について説明する。
（実施例１）
本例にかかる積層型ガスセンサ素子について説明する。
本例の積層型ガスセンサ素子１は，図１に示すごとく，所定の拡散抵抗の下に被測定ガスを導入する被測定ガス室と，酸素イオン導電性の固体電解質板１６の表面に，一方のポンプポンプ電極２１が上記被測定ガス室１１に面するように設けた一対のポンプポンプ電極２１，２２を有し，これら一対のポンプポンプ電極２１，２２へ通電することにより上記被測定ガス室１１に酸素を導入または排出し，上記被測定ガス室１１の酸素濃度を調整する酸素ポンプセル２と，酸素イオン導電性の固体電解質板１４の表面に，一方のセンサセンサ電極４２が上記被測定ガス室１２に面するように設けた一対のセンサセンサ電極４１，４２を有し，これら一対のセンサセンサ電極４１，４２間に生じる酸素イオン電流に基づいて，上記被測定ガス室１２内の特定ガス濃度を検出するセンサセル４とを有する。
【００２７】
そして，図３に示すごとく，上記酸素ポンプセル２の上記被測定ガス室１１に面するポンプポンプ電極２１において，上記積層型ガスセンサ素子１の長手方向に沿った上記ポンプポンプ電極２１の側面２１１及び２１２と，該側面２１１及び２１２と対向する上記被測定ガス室１１の内側面１１１及び１１２とのクリアランス部の上記長手方向と直交する幅方向に沿った長さの総計Ｇ１＋Ｇ２＝Ｇは０．５ｍｍ以下である。
【００２８】
以下，詳細に説明する。
本例にかかる積層型ガスセンサ素子１は，酸素ポンプセル２を構成するシート状の固体電解質板１６と，酸素モニタセル３，センサセル４を構成するシート状の固体電解質板１４と，第１被測定ガス室１１及び第２被測定ガス室１２を構成するシート状のスペーサ１５と，基準ガス室１２１，１２２を形成するシート状のスペーサ１７，１３３，１３２と，各セル２，３，４を加熱するヒータ１９とを，図１や図２に示すごとく，順次積層して構成する。
【００２９】
第１被測定ガス室１１及び第２被測定ガス室１２は，素子外部から被測定ガスを導入する内室であり，図２に示すごとく，固体電解質板１４，１６との間に位置するスペーサ１５に設けた２つの抜き穴１１０，１２０にて形成する。上記抜き穴１１０，１２０間には抜き穴１１０，１２０よりも幅細の絞り部１０２を設け，該絞り部１０２を境として，積層型ガスセンサ素子１の先端部側（図１及び図２における左側）から順に，抜き穴１１０により第１被測定ガス室１１が，抜き穴１２０により第２被測定ガス室１２を構成する。
【００３０】
また，第１被測定ガス室１１は，固体電解質板１４を貫通する拡散抵抗手段としてのピンホール１０１を介して，素子の外部と連通する。
このピンホール１０１の穴径は，該ピンホール１０１を通過して第１被測定ガス室１１及び第２被測定ガス室１２に導入する被測定ガスの拡散速度が所定の速度となるよう適宜設定する。
【００３１】
また，固体電解質板１４には，素子外部側からピンホール１０１の開口端を覆うように多孔質アルミナ等よりなる多孔質保護層１３１を形成する。
これにより，第１被測定ガス室１１及び第２被測定ガス室１２内に位置するポンプ電極２１，３２，４２の被毒や，ピンホール１０１の目詰まりを防止する。
【００３２】
基準ガス室１２１，１２２は，一定の酸素濃度をもつ基準酸素濃度ガスとして大気を導入する内室である。
基準ガス室１２１は，固体電解質板１６の下方に積層したスペーサ１７に設けた抜き穴１２１０，基準ガス室１２２は，固体電解質板１４の上方に積層したスペーサ１３３に設けた抜き穴１２２０にて形成する。
この抜き穴１２１０，１２２０は，それぞれ積層型ガスセンサ素子１の長手方向に伸びる溝としての通路部１２１１，１２２１を有し，この通路部１２１１，１２２１を通して大気を導入することができる。
【００３３】
酸素ポンプセル２は，固体電解質板１６と，該固体電解質板１６を挟むように対向配置した一対のポンプ電極２１，２２とより構成する。
一対のポンプ電極２１，２２のうち，ポンプ電極２１は，第１被測定ガス室１１及び第２被測定ガス室１２におけるガス流れ上流側に位置する第１被測定ガス室１１に面して固体電解質板１６に接して設け，他方の電極２２は基準ガス室１２１に面して固体電解質板１６に接して設ける。
【００３４】
センサセル４は，固体電解質板１４と，該固体電解質板１４を挟むように対向配置した一対のセンサ電極４１，４２とより構成する。
一対のセンサ電極４１，４２のうち一方のセンサ電極４２は，第１被測定ガス室１１及び第２被測定ガス室１２におけるガス流れ下流側に位置する第２被測定ガス室１２に面して固体電解質板１４に接して設け，他方のセンサ電極４１は基準ガス室１２２に面して固体電解質板１４に接して設ける。
【００３５】
酸素モニタセル３は，固体電解質板１４と，固体電解質板１４を挟むように対向配置した一対のモニタ電極３１，３２とより構成する。
一対のモニタ電極３１，３２のうち一方のモニタ電極３２は，第１被測定ガス室１１及び第２被測定ガス室１２におけるガス流れ下流側に位置する第２被測定ガス室１２に面して固体電解質板１４に接して設け，他方のモニタ電極３１は基準ガス室１２２に面して固体電解質板１４に接して設ける。
【００３６】
また，図２に示すように，これら各電極２１，２２，３１，３２，４１，４２には，電気信号を取出したり，電源から電力を供給するために，電極リード部２１１，２２１，３１１，３２１，４１１，４２１が一体に形成されている。
また，固体電解質板１４，１６上のポンプ電極２１等以外の部位，特に電極リード部２１１等の形成部位には，固体電解質板１４，１６と電極リード部２１１，３２１，４２１等の間にアルミナ等の絶縁層を形成しておくことが好ましい（図示略）。
【００３７】
また，図２に示すように，各セル２，３，４の電極２１等は，それぞれ各リード部２２１等及び各スペーサ１７等に形成したスルーホール１８０を通して，積層型ガスセンサ素子１の外部に露出形成された外部端子部３１０，３２０，４１０，４２０，２１０，２２０に電気的に接続する。
外部端子部３１０等に適当なコネクタを介し圧着やろう付け等によりリード線を接続することで，外部に設けた回路（詳細は後述する）と各セル２，３，４との間で電気信号のやりとり等が可能となる。
また，符合３２２，４２２は電極リード部３２１，４２１と導通する内部端子である。
【００３８】
酸素ポンプセル２はポンプ電源２５１と電流計２５２を備えたポンプ回路２５０に，酸素モニタセル３は電源３５１と電流計３５２を備えたモニタ回路３５０に，センサセル４は電源４５１と電流計４５２を備えたセンサ回路４５０に上記外部端子部３１０等を介して接続する。
【００３９】
ヒータ１９は，発熱部１９１を外部電源（図示略）からの給電により発熱させ，各セル２，３，４を活性温度まで加熱するために設けてある。
上記ヒータ１９は，アルミナ製のヒータ基板１９５の上面に，通電発熱する発熱部１９１をパターニング形成し，この発熱部１９１の上面（スペーサ１７側の面）に，絶縁のため被覆板１９６を積層してなる。
なお，図２より明らかであるが，ヒータ端子部１９０，外部端子部２１０，２２０は積層型ガスセンサ素子１のヒータ１９側の表面（図面下方）に，外部端子部３１０，３２０，４１０，４２０は，スペーサ１３２側の表面（図面上方）に設けてある。
【００４０】
次に，酸素ポンプセル２にかかるポンプ電極２１と第１被測定ガス室１１との寸法等について以下に説明する。
図３に示すごとく，ポンプ電極２１，第１被測定ガス室１１はいずれも積層型ガスセンサ素子１長手方向と同一方向が長辺となる長方形である。ポンプ電極２１の一方の側面２１１の延長線がＭ１，該側面２１１と対向する内側面１１１の延長線がＮ１で，Ｍ１とＮ１との距離はポンプ電極２１の端部２１３から端部２１４の範囲において均一でＧ１となる。
また，ポンプ電極２１の他方の側面２１２の延長線がＭ２，対向する内側面１１２の延長線がＮ２で，Ｍ２とＮ２との距離はポンプ電極２１の端部２１３から端部２１４の範囲において均一でＧ２となる。
よって，ポンプ電極２１の側面２１１，２１２と，対向する内側面１１１，１１２とのクリアランス部の総計ＧはＧ１＋Ｇ２となり，本例にかかる積層型ガスセンサ素子１においてＧは０．５ｍｍ以下となるよう構成する。
【００４１】
次に，本例にかかる積層型ガスセンサ素子１の各部の組成について説明する。
各スペーサ１７，１５，１３３，１３２はアルミナ等の絶縁材料よりなる。
酸素ポンプセル２，酸素モニタセル３，センサセル４を構成するための固体電解質板１４，１６は，ジルコニアやセリア等の酸素イオン導電性を有するセラミックよりなる。
酸素ポンプセル２及び酸素モニタセル３の一方の電極２１，３２には，第１被測定ガス室１１及び第２被測定ガス室１２におけるＮＯｘの分解を抑制するため，ＮＯｘ分解活性の低い電極を用いることが好ましく，具体的には，ＰｔとＡｕを含有する多孔質サーメット電極を好適に用いることができる。この場合，上記多孔質サーメット電極において，金属成分中のＡｕの含有量は，１〜１０重量％程度とすることが好ましい。
【００４２】
また，センサセル４の第２被測定ガス室１２に面したセンサ電極４２は，被測定ガス中のＮＯｘを分解するために，ＮＯｘの分解活性の高い電極を用いることが好ましく，具体的には，ＰｔとＲｈを含有する多孔質サーメット電極を好適に用いることができる。この場合，上記多孔質サーメット電極において，金属成分中のＲｈの含有量は１０〜５０重量％程度とすることが好ましい。
【００４３】
固体電解質板１４，１６，スペーサ１５，１７，１３３，１３２，アルミナ絶縁板１９６及びヒータシート１９５は，ドクターブレード法や押し出し成形法等により，シート形状に成形することができる。
また，上記の各ポンプ電極２１等，リード２１１等及び端子部２１０等は，スクリーン印刷等により形成することができる。そして，各シートは積層して焼成することにより，一体化される。
【００４４】
また，酸素ポンプセル２，酸素モニタセル３，センサセル４の基準ガス室１２１，１２２と対面する電極２２，３１，４１には，例えば，Ｐｔ多孔質サーメット電極を用いることが好ましい。
そして，発熱部１９１及びヒータリード部１９２は，Ｐｔとアルミナ含有セラミックとからなるサーメット材料より構成する。
【００４５】
次に，上記構成の積層型ガスセンサ素子の動作原理を説明する。
被測定ガスは多孔質保護層１３１，ピンホール１０１を通過して第１被測定ガス室１１に導入される。このとき導入されるガス量は多孔質保護層１３１，ピンホール１０１の拡散抵抗により定まる。その後，被測定ガスは絞り部１０２を通過して第２被測定ガス室１２に導入される。
【００４６】
酸素ポンプセル２の一対のポンプ電極２１，２２に基準ガス室１２１側の電極２２が＋極となるようにポンプ電源にて電圧を印加した場合，上記第１被測定ガス室１１側のポンプ電極２１上で被測定ガス中の酸素が還元されて酸素イオンとなり，ポンピング作用により電極２２側に排出される。
【００４７】
逆に，第１被測定ガス室１１側のポンプ電極２１が＋極となるように電圧を印加した場合，基準ガス室１２１側の電極２２上で酸素が還元されて酸素イオンとなり，ポンピング作用によりポンプ電極２１側に排出される。
この酸素ポンプ作用を利用して第１被測定ガス室１１，これと連通した第２被測定ガス室１２の酸素濃度を制御することができる。
なお，このとき，ポンプ電極２１の上を通過する矢線１１８のような被測定ガスの酸素は充分イオン化されるが，矢線１１９を通過する被測定ガスからはあまり酸素がイオン化しない。
【００４８】
酸素モニタセル３の一対のモニタ電極３１，３２に，基準ガス室１２２側のモニタ電極３１が＋極となるように所定の電圧（例えば０．４０Ｖ）を印加することで，上記第２被測定ガス室１２側のモニタ電極３２上で被測定ガス中の酸素が還元されて酸素イオンとなり，ポンピング作用によりモニタ電極３１側に排出される。
モニタ電極３２はＮＯｘの分解に不活性なＰｔ−Ａｕサーメット電極であるため，モニタ電極３１，３２間に流れる酸素イオン電流は，多孔質保護層１３１，ピンホール１０１，第１被測定ガス室１１等を通過して，モニタ電極３２に到達する被測定ガス中の酸素量に依存し，ＮＯｘ量には依存しない。
従って，このモニタ電極３１，３２間の電流値が所定の一定値（例えば，０．２μＡ）となるように，酸素ポンプセル２のポンプ電極２１，２２間の印加電圧を制御すれば，第２被測定ガス室１２を常に一定の酸素濃度となるよう制御できる。
【００４９】
センサセル４の一対のセンサ電極４１，４２に，基準ガス室１２２側のセンサ電極４１が＋極となるように所定の電圧（例えば０．４０Ｖ）を印加する。センサ電極４２は，ＮＯｘの分解に活性なＰｔ−Ｒｈサーメット電極であるため，上記第２被測定ガス室１２側のセンサ電極４２上で被測定ガス中の酸素やＮＯｘが還元されて酸素イオンとなり，ポンピング作用によりセンサ電極４１側に排出される。
【００５０】
そして，図１に示すごとく，本例にかかる積層型ガスセンサ素子１では，酸素モニタセル３のモニタ電極３１，３２間の電流値が一定値（例えば０．２μＡ）となるように，酸素ポンプセル２を制御する。
このとき，被測定ガス中にＮＯｘが存在しなければ，センサセル４のセンサ電極４１，４２間の電流値も一定値（例えば０．２μＡ）となる。一方，被測定ガス中にＮＯｘが存在すると，ＮＯｘ濃度に応じて電流値が増加する。これにより，被測定ガス中のＮＯｘ濃度が検出可能となる。
【００５１】
次に，本例の作用効果について説明する。
本例の積層型ガスセンサ素子１は，図３に示すごとく，被測定ガス室１１に面するポンプ電極２１の側面２１１，２１２と，対向する内側面１１１，１１２とのクリアランス部の総計Ｇが０．５ｍｍ以下と，十分小さくなっている。
よって，より多くの被測定ガスを酸素ポンプセル２のポンプ電極２１上を矢線１１８に示すように通過させることができる。
従って，被測定ガス室１１，１２の酸素濃度をより薄くして，ＮＯｘ濃度検出に対する酸素の影響をより小さくし，精度の高い特定ガス濃度の測定が可能となる。
【００５２】
以上，本発明によれば，被測定ガス室に共存する酸素による影響を小さくし，高い精度で特定ガス濃度（本例はＮＯｘ）を検出可能な積層型ガスセンサ素子を提供することができる。
【００５３】
また，図４は不定形のポンプ電極２１及び第１の被測定ガス室１１を持つ場合についての説明図である。
図４では，ＧはＳ０１−Ｓ０２，Ｓ１１−Ｔ１１の距離＋Ｔ１２−Ｓ１２の距離・・・等といった具合に場所ごとに異なる。
このような場合，最も小さなＧが０．５ｍｍ以下であれば本例にかかる効果を得ることができる。
【００５４】
（実施例２）
本例は，場所によってクリアランス部の総計Ｇが異なるポンプ電極２１を備えた積層型ガスセンサ素子について説明する。
図５に示すごとく，本例のポンプ電極２１は，図面左方の側面２１１と対向する内側面１１１との距離は右方より広くてＧ１’，右方はＧ１，図面左方の側面２１２と対向する内側面１１２との距離は右方より広くてＧ２’，右方はＧ２である。Ｇ１，Ｇ２にかかる部分の幅太のポンプ電極２１の長手方向に沿った長さはＬで，ポンプ電極２１全体の長さはＬｅである。
【００５５】
本例にかかる積層型ガスセンサ素子において，図面左方のクリアランス部の総計はＧ１’＋Ｇ２’＝０．８ｍｍ，図面右方のクリアランス部の総計はＧ１＋Ｇ２＝０．４ｍｍ，Ｌｅ＝６ｍｍ，Ｌ＝４ｍｍである。
【００５６】
従って，クリアランス部の総計Ｇが０．５ｍｍ以下である部分の長さは，ポンプ電極全体の長さに対して１／４以上を占めており，より精度の高い積層型ガスセンサ素子を得ることができる（詳細は実施例４の測定参照）。
なお，本例の積層型ガスセンサ素子のその他の構成は実施例１と同様である。
【００５７】
（実施例３）
本例は，実施例１と同様の構成で，ポンプ電極の面積に関して以下に示す条件を満たした積層型ガスセンサ素子について説明する。
図６に示すごとく，本例のポンプ電極２１は，実施例１と同形である。被測定ガスの導入路となるピンホール１０１（実施例１の図１参照）の中心位置を図６に投影した位置がＶで，該Ｖを通り幅方向に平行な直線がＶ０となる。また，ポンプ電極２１において，長手方向の第２被測定ガス室１２側の端部を通る幅方向に平行な直線がＶ１となる。
【００５８】
本例にかかる積層型ガスセンサ素子は，Ｖ０よりも図面右方のポンプ電極２１の表面積（図６において斜線のハッチングを付した面積）がＳｅで１０ｍｍ^２，被測定ガス室の内側面１１１，１１２，ポンプ電極２１の側面２１１，２１２，直線Ｖ０及びＶ１で囲まれた面積（図６において点々のハッチングを付した面積）Ｓｇが１．５ｍｍ^２で，Ｓｇ／Ｓｅ≦０．３である。
【００５９】
本例の積層型ガスセンサ素子１は，図６に示すごとく，被測定ガス室１１に面するポンプ電極２１のＶ０より右側の破線のハッチングを付した面積Ｓｅに比べて，内側面１１１と側面２１１等に囲まれて点々のハッチングを付した面積Ｓｇが充分小さくなって，Ｓｇ／Ｓｅ≦０．３となっている。
よって，より多くの被測定ガスを酸素ポンプセルのポンプ電極２１上を通過させることができる。
従って，被測定ガス室１１，１２の酸素濃度をより薄くして，ＮＯｘ濃度検出に対する酸素の影響をより小さくし，精度の高い特定ガス濃度の測定が可能となる。
その他，積層型ガスセンサ素子の詳細な構成は実施例１と同様である。
【００６０】
また，図７は不定形のポンプ電極２１及び第１の被測定ガス室１１を持つ場合についての説明図である。
この場合も図６と同様に，ポンプ電極のＶ０より右側の面積Ｓｅに比べて，Ｖ０，Ｖ１，Ｔ及びＳで囲まれた面積Ｓｇが充分小さくなって，Ｓｇ／Ｓｅ≦０．３であれば，本例と同様の効果を得ることができる。
【００６１】
（実施例４）
本例は各種積層型ガスセンサ素子について検出誤差を測定して，それぞれ性能評価を行った。
実施例１に示すごとき積層型ガスセンサ素子において，Ｇを違えた試料をいくつか準備して，それぞれについて検出誤差についての測定を行った。
すなわち，Ｇ＝０の場合の検出誤差を１として，Ｇが異なる他の積層型ガスセンサ素子についても同様に検出誤差を測定し，まとめて図８に記載した。
【００６２】
検出誤差の測定方法について説明する。
Ｇの異なる積層型ガスセンサ素子を準備し，１００ｐｐｍのＮＯを含有する被測定ガス中にさらし，被測定ガス中の酸素濃度を１０ｐｐｍ〜２０％まで変化させたときのＮＯｘ濃度の検出誤差を測定した。これは，クリアランスが大きくなる（すなわちＧが大きくなる）と，酸素ポンプセルで排出できない酸素が多くなるため，酸素濃度による検出誤差が大きくなることに基づく。
図８より，Ｇが大きくなると検出誤差が大きくなり，高い検出精度を得るにはＧ≦０．５以下（好ましくは０．２以下）であることが必要だと判明した。
【００６３】
また，同様の試験を，実施例２に示すごとき積層型ガスセンサ素子において，Ｌ／Ｌｅを違えた試料をいくつか準備して検出誤差を測定した。
Ｌ／Ｌｅ＝１の時の検出誤差を１として，Ｌ／Ｌｅが異なる他の積層型ガスセンサ素子についても同様に検出誤差を測定して，まとめて図９に記載した。
図９より，Ｌ／Ｌｅが小さくなると検出誤差が増大するため，Ｇ≦０．５ｍｍとした上で，より高い検出精度を得るためにＬ／Ｌｅを０．２５以上とすることが望ましいことが分かった。
【００６４】
また，同様の試験を，実施例３に示すごとき積層型ガスセンサ素子において，Ｓｇ／Ｓｅを違えた試料をいくつか準備して検出誤差を測定した。
Ｓｇ／Ｓｅ＝０の時の検出誤差を１として，Ｓｇ／Ｓｅが異なる他の積層型ガスセンサ素子についても同様に検出誤差を測定して，まとめて図１０に記載した。
図１０より，Ｓｇ／Ｓｅが大きくなると検出誤差が増大するため，高い検出精度を得るためにＳｇ／Ｓｅを０．３以下であることが必要だと判明した。
【００６５】
（実施例５）
本例は，図１１に示すごとく，端面１５０に第１被測定ガス室１１に抜けるピンホール１０３を設け，ここから被測定ガスを第１被測定ガス室１１に導入するよう構成した積層型ガスセンサ素子である。
このような構成にかかる積層型ガスセンサ素子であっても，実施例１〜実施例３に示すような条件でポンプ電極２１や第１被測定ガス室１１を構成することで，実施例１〜実施例３と同様の効果が得られることが分かった。
なお，この構成の場合にかかる実施例３に示したＳｅはポンプ電極２１の表面積となる。ポンプ電極２１全体が被測定ガスのガス流れ下流に含まれるためである。
【００６６】
（実施例６）
本例は，図１２，図１３に示すごとく，ポンプ電極２１，第１被測定ガス室１１が共に楕円である積層型ガスセンサ素子１である。
図１２に示すごとく，長手方向に沿ったポンプ電極２１の側面２１１や２１２と，該側面２１１や２１２と対向する内側面１１１や１１２との幅方向の長さの総計Ｇ１＋Ｇ２＝Ｇを０．５ｍｍ以下とすることで，実施例１と同様の作用効果を得ることができる。
【００６７】
また，図１３に示すごとく，Ｓは第１被測定ガス室１１の内側面，Ｔはポンプ電極２１の側面を示す曲線で，点Ｖは被測定ガス導入部となるピンホール（図示略）の中心位置，Ｖ０は点Ｖを通る幅方向と平行な直線，Ｖ１はポンプ電極２１の長手方向における端部を通過し，幅方向と平行な直線とした場合，曲線Ｔと直線Ｖ０にて囲まれた部分がポンプ電極の面積Ｓｅ，直線Ｖ０，Ｖ１曲線Ｔ，Ｓで囲まれた部分がクリアランス部の面積の総計Ｓｇとなる。
これについてＳｅ／Ｓｇ≦０．３とすることで，実施例３と同様の作用効果を得ることができる。
【００６８】
（実施例７）
本例にかかる積層型ガスセンサ素子１は，図１４に示すごとく，素子の各部構成は実施例１と略同じであるが回路構成が異なる。
すなわち，ポンプ回路２５０は電源２５１と電流計２５２とを備え，予め求めておいた酸素ポンプセル２に対する印加電圧と酸素ポンプセル２に流れる電流の関係に基づいて，酸素ポンプ電流が限界電流と一致するように，酸素濃度に応じた電圧を印加する。
これにより，第１被測定ガス室１１と第２被測定ガス室１２の酸素濃度を所定の低濃度に制御することができる。
【００６９】
この方法で第１被測定ガス室１１，第２被測定ガス室１２の酸素濃度を制御すると，実施例１にかかる酸素モニタセルに基づいた制御に比べて，第２被測定ガス室１２内の酸素濃度は変動しやすく，したがってセンサセル４のセンサ電極４１，４２間に流れる電流をそのままセンサ信号とするとＮＯｘの検出精度が悪化する。
そこで，センサセル４のセンサ電極４１，４２間に流れる電流と酸素モニタセル３のモニタ電極３１，３２間に流れる電流との差を電流差検出回路４５９において検出し，この値をセンサ信号とすることにより，第２被測定ガス室１２内の酸素濃度変動の影響を減らして，被測定ガス中の酸素濃度に依存しないより正確なＮＯｘ濃度にかかるセンサセル出力を得ることができる。
【００７０】
このような積層型ガスセンサ素子１に，図３，図５，図７，図１１〜図１３にかかるポンプ電極２１を設けることで，他の実施例と同様に，測定精度の高い素子を得ることができる。
【００７１】
（実施例８）
本例にかかる積層型ガスセンサ素子６は，図１５に示すごとく，第２の酸素ポンプセル５を設けた４セル構成素子である。
本例の積層型ガスセンサ素子１は，実施例１と同様のヒータ１９に基準ガス室６４０用のスペーサ６４，酸素モニタセル３とセンサセル４を設けた固体電解質板６３，第１被測定ガス室１１，第２被測定ガス室１２用のスペーサ６２，酸素ポンプセル２と第２酸素ポンプセル５用の固体電解質板６１を積層して構成した。
【００７２】
酸素ポンプセル２は，第１被測定ガス室１１に面したポンプ電極２１と，多孔質保護層１３１で覆われて素子外部の被測定ガスにさらされた電極２２を有し，電源２５１を備えたポンプ回路２５０に接続される。
モニタセル３は，第１被測定ガス室１１に面したモニタ電極３２と基準ガス室６４０に面したモニタ電極３１を有し，電圧計３５７を備えた回路３５０に接続される。
センサセル４は，第２被測定ガス室１２に面したセンサ電極４２と基準ガス室６４０に面したセンサ電極４１を有し，電流計４５７を備えた回路４５０に接続される。
また，モニタ電極３１，４１は一体の電極である。
電圧計３５７と電源２５１との間には，電圧計３５７で検出した電圧値に基づいて酸素ポンプセル２の電源２５１を制御する制御回路２５５が接続される。
【００７３】
第２酸素ポンプセル５は，第１酸素ポンプセル２の電極２２と一体に形成した電極５１と，第２被測定ガス室１２にさらされる電極５２を有し，電源５５１を備えた回路５５０に接続される。
【００７４】
実施例１では，第２被測定ガス室１２の酸素濃度を酸素モニタセル３に流れる電流値により検出したが，本例は，酸素モニタセル３のモニタ電極３１，３２間に発生する起電力から検出する。
この場合の作動の一例を図９に基づいて説明する。
酸素モニタセル３のモニタ電極３２は第１被測定ガス室１１に面し，モニタ電極３１は大気が導入される基準ガス室６４０に面している。モニタ電極３１，３２間には，第１被測定ガス室１１と基準ガス室６４０との酸素濃度の違いにより，ネルンストの式に基づいた起電力が発生する。
【００７５】
基準ガス室６４０の酸素濃度は一定であるので，モニタ電極３１，３２間に発生する起電力は第１被測定ガス室１１の酸素濃度を反映する事になる。したがって，モニタ電極３１，３２間に発生する起電力が所定の一定値（例えぱ０．２０Ｖ）になるように酸素ポンプセル２のポンプ電極２１，２２間の印加電圧を制御すれぱ，第２被測定ガス室１２へ流れ込む酸素濃度を一定に制御できる。
【００７６】
さらに，本例では，第２酸素ポンプセル５が形成してあり，酸素ポンプセル２で排出できずに第２被測定ガス室１２に流入した酸素を外部に排気する。
これにより，第２被測定ガス室１２内の酸素濃度はほぽ０となり，センサセル４により，高精度なＮＯｘ濃度測定が可能となる。
【００７７】
このような積層型ガスセンサ素子１に，図３，図５，図７，図１１〜図１３にかかるポンプ電極２１を設けることで，他の実施例と同様に，測定精度の高い素子を得ることができる。
【図面の簡単な説明】
【図１】実施例１における，（ａ）積層型ガスセンサ素子の長手方向の断面説明図，（ｂ）幅方向の断面説明図（図１（ａ）のＡ−Ａ矢視断面説明図）。
【図２】実施例１における，積層型ガスセンサ素子の斜視展開図。
【図３】実施例１における，ポンプ電極と第１被測定ガス室とにおいて，側面と内側面とのクリアランス部の総計を示す平面図（図１（ａ）のＢ−Ｂ矢視断面説明図）。
【図４】実施例１における，不定形のポンプ電極及び第１の被測定ガス室におけるクリアランス部の総計についての説明図。
【図５】実施例２における，ポンプ電極の幅が部分的に異なる積層型ガスセンサ素子の断面説明図。
【図６】実施例３における，被測定ガス室に面するポンプ電極の面積とクリアランス部の面積総計とを示す積層型ガスセンサ素子の断面説明図。
【図７】実施例３における，不定形のポンプ電極及び第１の被測定ガス室におけるポンプ電極の面積とクリアランス部の面積総計についての説明図。
【図８】実施例４における，積層型ガスセンサ素子においてクリアランス部の長さの総計Ｇと検出誤差との関係を示す線図。
【図９】実施例４における，積層型ガスセンサ素子においてＬ／Ｌｅと検出誤差との関係を示す線図。
【図１０】実施例４における，積層型ガスセンサ素子において，被測定ガス室に面するポンプ電極の面積Ｓｅとクリアランス部の面積の総計Ｓｇとの間の比Ｓｇ／Ｓｅと検出誤差との関係を示す線図。
【図１１】実施例５における，端面から被測定ガスを被測定ガス室に導入するよう構成した積層型ガスセンサ素子の断面説明図。
【図１２】実施例６における，ポンプ電極が楕円の積層型ガスセンサ素子についてＧ１及びＧ２を図示した断面説明図。
【図１３】実施例６における，ポンプ電極が楕円の積層型ガスセンサ素子についてＳｅ及びＳｇを図示した断面説明図。
【図１４】実施例７における，酸素ポンプセルに対する印加電圧と酸素ポンプセルに流れる電流に基づいて制御する構成の積層型ガスセンサ素子の（ａ）長手方向の断面説明図，（ｂ）幅方向の断面説明図（図１４（ａ）のＣ−Ｃ矢視断面説明図）。
【図１５】実施例８における，第１と第２の酸素ポンプセルを備えた積層型ガスセンサ素子の説明図。
【図１６】従来における，積層型ガスセンサ素子の説明図。
【符号の説明】
１．．．積層型ガスセンサ素子，
１１，１２．．．第１及び第２被測定ガス室，
１４，１６．．．固体電解質板，
２．．．酸素ポンプセル，
２１，２２．．．ポンプ電極，
３．．．酸素モニタセル，
３１，３２．．．モニタ電極，
４．．．センサセル，
４１，４２．．．センサ電極，[0001]
【Technical field】
The present invention relates to a stacked gas sensor element used for an exhaust system of an internal combustion engine for a vehicle and used for detecting NOx concentration and the like.
[0002]
[Prior art]
Air pollution caused by exhaust gas emitted from automobile internal combustion engines and the like causes serious problems in modern society, and purification standards and regulations for NOx, etc., which are pollutants in exhaust gas, are becoming stricter every year.
If the NOx concentration in the exhaust gas is detected and the detection result is fed back to an engine combustion control monitor, a catalyst monitor, etc., it is considered that the exhaust gas can be more efficiently purified. From such a background, a stacked gas sensor element capable of detecting the NOx concentration in exhaust gas with high accuracy has been demanded.
[0003]
Meanwhile, as a conventionally well-known stacked gas sensor element, an element having a configuration shown in FIG. 16 is exemplified.
In the stacked gas sensor element 9 shown in FIG. 16, an oxygen pump cell 92 is arranged so as to face the first measured gas chamber 11, and by applying a voltage to the oxygen pump cell 92, the oxygen gas is supplied into the first measured gas chamber 11. Some oxygen is pumped outside the device. Alternatively, oxygen outside the element is pumped into the first measured gas chamber 11.
An oxygen monitor cell 93 capable of detecting the oxygen concentration in the first measured gas chamber 11 is provided. The oxygen monitor cell 93 detects the oxygen concentration in the first measured gas chamber 11 so that the oxygen concentration in the first measured gas chamber 11 becomes a steady state. The pump cell 92 is feedback-controlled.
[0004]
A sensor cell configured to measure a NOx concentration by measuring an ion current due to oxygen ions generated by decomposing NOx on an electrode is provided in a second measured gas chamber 12 communicating with the first measured gas chamber 11. 94 is provided.
As described above, since the oxygen concentration in the first measured gas chamber 11 is controlled to be in a steady state, the oxygen concentration in the second measured gas chamber 12 is also constant. Therefore, the amount of oxygen ions moving between the electrodes in the sensor cell 94, that is, the magnitude of the oxygen ion current in the sensor cell 94 corresponds to the NOx concentration.
As described above, the NOx concentration in the gas to be measured introduced into the first and second gas-to-be-measured chambers 11 and 12 can be measured with high accuracy irrespective of the increase or decrease in the oxygen concentration in the atmosphere outside the element.
[0005]
[Patent Document 1]
Japanese Patent No. 2885336
[0006]
[Problem to be solved]
By the way, when the oxygen concentration in the gas to be measured is on the order of% and NOx is on the order of ppm, in order to accurately measure a very small amount of NOx, the oxygen is reduced to a level that does not affect the NOx detection. It is necessary to discharge the gas by an oxygen pump cell and to make the oxygen concentration in the gas chamber to be measured extremely low. This problem may also occur when a specific gas other than NOx is detected.
[0007]
The present invention has been made in view of such a conventional problem, and aims to provide a stacked gas sensor element capable of reducing the influence of oxygen coexisting in a gas chamber to be measured and detecting a specific gas concentration with high accuracy. Things.
[0008]
[Means for solving the problem]
According to a first aspect of the present invention, a measured gas chamber for introducing a measured gas under a predetermined diffusion resistance, and a surface of an oxygen ion conductive solid electrolyte plate, and one pump electrode faces the measured gas chamber. An oxygen pump cell having a pair of pump electrodes provided as described above, and introducing or discharging oxygen into or from the measured gas chamber by applying a current to the pair of pump electrodes to adjust the oxygen concentration of the measured gas chamber;
On the surface of the oxygen ion conductive solid electrolyte plate, there is provided a pair of sensor electrodes provided so that one sensor electrode faces the gas chamber to be measured, and based on an oxygen ion current generated between the pair of sensor electrodes. A gas sensor element for detecting a specific gas concentration in the gas chamber to be measured.
In the pump electrode facing the measured gas chamber of the oxygen pump cell,
The total length G of the clearance in the width direction orthogonal to the longitudinal direction of the clearance between the side surface of the pump electrode along the longitudinal direction of the stacked gas sensor element and the inner surface of the gas chamber to be measured facing the side surface. Has a minimum value of 0.5 mm or less in the laminated gas sensor element (claim 1).
[0009]
The stacked gas sensor element according to the first invention is characterized in that the total length G in the width direction of the clearance between the side surface of the pump electrode facing the measured gas chamber and the inner side surface of the measured gas chamber facing the side surface. The minimum value is 0.5 mm or less, which is sufficiently small.
[0010]
Further, a second invention provides a measured gas chamber for introducing a measured gas under a predetermined diffusion resistance,
A pair of pump electrodes is provided on the surface of the oxygen-ion conductive solid electrolyte plate so that one pump electrode faces the gas chamber to be measured. An oxygen pump cell for introducing or discharging oxygen into the gas chamber and adjusting the oxygen concentration in the gas chamber to be measured;
On the surface of the oxygen ion conductive solid electrolyte plate, there is provided a pair of sensor electrodes provided so that one sensor electrode faces the gas chamber to be measured, and based on an oxygen ion current generated between the pair of sensor electrodes. A gas sensor element for detecting a specific gas concentration in the gas chamber to be measured.
In the formation range of the pump electrode facing the measured gas chamber in the oxygen pump cell downstream of the gas flow from the inlet for introducing the measured gas into the measured gas chamber,
The area of the pump electrode facing the measured gas chamber is Se, and the clearance between the side surface of the pump electrode along the longitudinal direction of the stacked gas sensor element and the inner surface of the measured gas chamber facing the side surface. When the total area of the parts is Sg, the laminated gas sensor element is characterized by Sg / Se ≦ 0.3 (claim 3).
[0011]
In the stacked gas sensor element according to the second aspect of the present invention, a relationship of Sg / Se ≦ 0.3 is established between the area of the pump electrode and the area of the clearance, and the area of the clearance is compared with the area of the pump electrode. Is small enough.
[0012]
By the way, in the gas to be measured (the arrow 118 in FIG. 3 described later) flowing near the surface of the pump electrode in the gas to be measured, ionization of oxygen contained by the pump electrode is likely to occur. The oxygen ions generated here flow between the pair of pump electrodes as an oxygen ion current, and are easily discharged to the outside of the gas chamber to be measured.
However, the gas to be measured flowing between the side surface of the pump electrode and the inner surface of the gas chamber to be measured opposing the side surface (arrow 119 in FIG. 3 described later) is far from the pump electrode and is included here. Oxygen is not easily ionized by the pump electrode.
[0013]
The detection of the specific gas concentration in the sensor cell is performed based on an oxygen ion current flowing between a pair of sensor electrodes generated from oxygen ions generated by decomposition of the specific gas on the sensor electrode facing the gas chamber to be measured.
If oxygen contained in the measured gas chamber is decomposed on the sensor electrode, oxygen ions derived from the specific gas and oxygen ions derived from oxygen may be mixed, and the specific gas concentration may not be detected accurately.
[0014]
The stacked gas sensor element according to the first invention has a sufficiently small total clearance between the side surface of the pump electrode and the inner surface of the gas chamber to be measured (claim 1), or the stacked gas sensor element according to the second invention. The area of the clearance portion is sufficiently smaller than the area of the pump electrode (claim 3), so that more gas to be measured can pass through the pump electrode of the oxygen pump cell.
Accordingly, the oxygen concentration in the gas chamber to be measured is made thinner, the influence of oxygen on the detection of the specific gas concentration is made smaller, and the measurement of the specific gas concentration with high accuracy becomes possible.
[0015]
As described above, according to the present invention, it is possible to provide a stacked gas sensor element capable of reducing the influence of oxygen coexisting in a measured gas chamber and detecting a specific gas concentration with high accuracy.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
In the stacked gas sensor element according to the first invention (claim 1) and the second invention (claim 3), the shape of the pump electrode of the oxygen pump cell is in the width direction orthogonal to the longitudinal direction as shown in FIG. Various shapes such as a rectangle having a substantially uniform width, a shape having an uneven width (FIG. 5), and a substantially elliptical shape having four rounded vertexes (FIG. 12) can be used.
The shape of the gas chamber to be measured can be rectangular or substantially elliptical, as with the pump electrode. However, in order to make the clearance between the inner surface and the side surface of the pump electrode smaller, It is preferable to configure the electrode to have substantially the same shape as that of the electrode.
[0017]
Here, the total G of the clearance portions in the first invention will be described with reference to FIG. 4 which is a schematic view of a cross section of the stacked gas sensor element cut along a plane including the surface of the pump electrode.
S is the inner surface of the gas chamber to be measured, T is a curve showing the side surface of the pump electrode, U01 and U02 are straight lines passing through the ends in the longitudinal direction of the pump electrode, U1 to U3 are straight lines crossing the pump electrode, U01, U02, U1 to U3 are all straight lines parallel to the width direction orthogonal to the longitudinal direction of the stacked gas sensor element.
The intersections where the straight lines U01, U02, U1 to U3 intersect S and T are S01 to S04, S11 to S16, and T11 to T16.
[0018]
In FIG. 4, G is a value obtained by adding the distances S11-T11 and S12-T12 on the same straight line U1, a value obtained by summing S13-T13 and S14-T14 on U2, and the like. Alternatively, the length is S01-S02 and S03-S04.
The first invention is established when G is 0.5 mm or less on any of the side surfaces of the pump electrode.
In the case of the pump electrode shown in FIG. 4, the G on S13-T13 and T14-S14 on the straight line U2 is the smallest part, and the other parts are larger than this. Therefore, even if the distance of this part is 0.5 mm or less. Thus, the first invention is established.
Note that G can be considered in the same manner when there are a plurality of curves indicating the side surfaces of the pump electrode.
[0019]
The effect of the first invention can be obtained by satisfying the condition that the total amount G of the clearance portion is 0.5 mm or less at the minimum. A stacked gas sensor element can be obtained.
In addition, when the total G of the clearances is 0, that is, when the side surface of the pump electrode is in contact with the inner surface of the gas chamber to be measured, a stacked gas sensor element with the highest detection accuracy can be obtained.
The longitudinal direction of the stacked gas sensor element is the long axis direction of the columnar stacked gas sensor element having a substantially rectangular cross section.
[0020]
Next, in the first invention, the length of the portion in which the total G of the clearances is 0.5 mm or less along the longitudinal direction of the multilayer gas sensor element is equal to the length of the entire pump electrode along the longitudinal direction. On the other hand, when it accounts for １ ／ or more, it is possible to obtain a stacked gas sensor element with higher detection accuracy.
In addition, when a portion where the total G of the clearances is 0.5 mm or less occupies more than 1/2 of the entire length of the pump electrode, it is possible to obtain an excellent stacked gas sensor element having higher detection accuracy. it can.
[0021]
The area and the like of the pump electrode in the second invention will be described with reference to FIG. 7, which is a schematic cross-sectional view of the stacked gas sensor element cut along a plane including the surface of the pump electrode.
S is an inner surface of the gas chamber to be measured, T is a curve showing the side surface of the pump electrode, point V is the center position of the gas introduction part to be measured, V0 is a straight line parallel to the width direction passing through point V, and V1 is the pump electrode. Is a straight line that passes through the end in the longitudinal direction and is parallel to the width direction.
The area Se of the pump electrode in the second invention is the area of the region surrounded by the curve T and the straight line V0, and the total area Sg of the clearance is surrounded by the straight lines V0 and V1 curves T and S. The area of the region.
[0022]
Note that, as shown in FIG. 11, which will be described later, in the method in which the gas to be measured is introduced from the end face of the stacked gas sensor element, the entire pump electrode is included on the downstream side of the gas flow. Sg is an area delimited by a line in the width direction passing through both ends in the longitudinal direction of the electrode.
If the area Sg of the clearance and the area Se of the pump electrode are Sg / Se ≦ 0.3, the effect according to the second invention can be obtained.
When Sg = 0, that is, when the side surface of the pump electrode is in contact with the inner surface of the gas chamber to be measured, a stacked gas sensor element with the highest detection accuracy can be obtained.
[0023]
Further, the stacked gas sensor element according to the first and second aspects of the invention can be applied to a NOx sensor element, a CO sensor element, and an HC sensor element having a configuration including two or more cells.
[0024]
In the first and second inventions, a pair of electrodes is provided on the surface of the oxygen-ion-conductive solid electrolyte plate such that one electrode faces the gas chamber to be measured. It is preferable that an oxygen monitor cell for detecting the oxygen concentration in the measured gas chamber be provided based on a current value or an electromotive force generated therebetween (claim 4).
Thus, the oxygen concentration in the measured gas chamber can be monitored.
[0025]
Then, for example, by adding a configuration for controlling the operation of the oxygen pump cell so that the oxygen concentration in the gas chamber to be measured falls within a predetermined range, it is desired to more accurately measure the oxygen ion current flowing between the pair of electrodes of the sensor cell. The stacked gas sensor element can be configured to correspond to a specific gas concentration.
The oxygen monitor cell that detects the oxygen concentration based on the current value functions as a limiting current type oxygen sensor, and the oxygen monitor cell that detects the oxygen concentration based on the electromotive force functions as an oxygen concentration electromotive force type oxygen sensor. (See FIG. 1 and Example 1 to be described later).
[0026]
【Example】
Hereinafter, embodiments of the first invention will be described with reference to the drawings.
(Example 1)
The stacked gas sensor element according to this example will be described.
As shown in FIG. 1, the laminated gas sensor element 1 of the present embodiment has a gas chamber to be measured into which a gas to be measured is introduced under a predetermined diffusion resistance and a surface of a solid electrolyte plate 16 having oxygen ion conductivity. The pump electrode 21 has a pair of pump electrodes 21 and 22 provided so as to face the gas chamber 11 to be measured. Oxygen pump cell 2 for introducing or discharging oxygen to adjust the oxygen concentration in the gas chamber 11 to be measured, and one sensor electrode 42 on the surface of the solid electrolyte plate 14 having oxygen ion conductivity. And a pair of sensor electrodes 41 and 42 provided to face the sensor gas electrode 12 based on an oxygen ion current generated between the pair of sensor electrodes 41 and 42. And a sensor cell 4 to detect a specific gas concentration in the.
[0027]
Then, as shown in FIG. 3, at the pump pump electrode 21 facing the measured gas chamber 11 of the oxygen pump cell 2, the side surfaces 211 and 212 of the pump pump electrode 21 along the longitudinal direction of the stacked gas sensor element 1. And the total length G1 + G2 = G of the clearance along the width direction orthogonal to the longitudinal direction of the clearance between the inner surfaces 111 and 112 of the measured gas chamber 11 facing the side surfaces 211 and 212 is 0.5 mm or less. It is.
[0028]
The details are described below.
The laminated gas sensor element 1 according to the present embodiment includes a sheet-like solid electrolyte plate 16 constituting the oxygen pump cell 2, a sheet-like solid electrolyte plate 14 constituting the oxygen monitor cell 3 and the sensor cell 4, and a first gas chamber to be measured. 11 and the sheet-shaped spacer 15 forming the second measured gas chamber 12, sheet-shaped spacers 17, 133, 132 forming the reference gas chambers 121, 122, and heaters for heating the cells 2, 3, 4 1 and 2 are sequentially laminated as shown in FIGS.
[0029]
The first gas chamber 11 to be measured and the second gas chamber 12 to be measured are inner chambers for introducing a gas to be measured from outside the element, and as shown in FIG. 2, spacers located between the solid electrolyte plates 14 and 16 are provided. 15 are formed by two punched holes 110 and 120. A narrowed portion 102 narrower than the holes 110 and 120 is provided between the holes 110 and 120, and a front end portion of the stacked gas sensor element 1 (the left side in FIGS. ), The first measured gas chamber 11 is constituted by the hole 110, and the second gas chamber 12 is constituted by the hole 120.
[0030]
In addition, the first measured gas chamber 11 communicates with the outside of the element via a pinhole 101 as a diffusion resistance means penetrating through the solid electrolyte plate 14.
The hole diameter of the pinhole 101 is appropriately set so that the diffusion rate of the gas to be measured which is introduced into the first gas chamber 11 and the second gas chamber 12 through the pinhole 101 becomes a predetermined speed. I do.
[0031]
In addition, a porous protective layer 131 made of porous alumina or the like is formed on the solid electrolyte plate 14 so as to cover the opening end of the pinhole 101 from the outside of the element.
This prevents poisoning of the pump electrodes 21, 32, and 42 located in the first measured gas chamber 11 and the second measured gas chamber 12 and clogging of the pinhole 101.
[0032]
The reference gas chambers 121 and 122 are internal chambers for introducing the atmosphere as a reference oxygen concentration gas having a constant oxygen concentration.
The reference gas chamber 121 is formed by a hole 1210 provided in the spacer 17 stacked below the solid electrolyte plate 16, and the reference gas chamber 122 is formed by a hole 1220 provided in the spacer 133 stacked above the solid electrolyte plate 14. I do.
The holes 1210 and 1220 have passages 1211 and 1221 as grooves extending in the longitudinal direction of the multilayer gas sensor element 1, respectively, and the atmosphere can be introduced through the passages 1211 and 1221.
[0033]
The oxygen pump cell 2 is composed of a solid electrolyte plate 16 and a pair of pump electrodes 21 and 22 disposed so as to sandwich the solid electrolyte plate 16 therebetween.
Of the pair of pump electrodes 21 and 22, the pump electrode 21 is a solid facing the first measured gas chamber 11 located upstream of the gas flow in the first measured gas chamber 11 and the second measured gas chamber 12. The other electrode 22 is provided in contact with the electrolyte plate 16 and is provided in contact with the solid electrolyte plate 16 so as to face the reference gas chamber 121.
[0034]
The sensor cell 4 includes a solid electrolyte plate 14 and a pair of sensor electrodes 41 and 42 opposed to each other with the solid electrolyte plate 14 interposed therebetween.
One sensor electrode 42 of the pair of sensor electrodes 41 and 42 faces the second measured gas chamber 12 located downstream of the gas flow in the first measured gas chamber 11 and the second measured gas chamber 12. The other sensor electrode 41 is provided in contact with the solid electrolyte plate 14 and is provided in contact with the solid electrolyte plate 14 so as to face the reference gas chamber 122.
[0035]
The oxygen monitor cell 3 includes a solid electrolyte plate 14 and a pair of monitor electrodes 31 and 32 opposed to each other with the solid electrolyte plate 14 interposed therebetween.
One monitor electrode 32 of the pair of monitor electrodes 31 and 32 faces the second measured gas chamber 12 located downstream of the gas flow in the first measured gas chamber 11 and the second measured gas chamber 12. The monitor electrode 31 is provided in contact with the solid electrolyte plate 14, and the other monitor electrode 31 is provided in contact with the solid electrolyte plate 14 so as to face the reference gas chamber 122.
[0036]
As shown in FIG. 2, the electrodes 21, 22, 31, 32, 41, and 42 are connected to electrode leads 211, 221 and 311, respectively, for extracting electric signals and supplying power from a power source. 321, 411 and 421 are formed integrally.
In addition, the portions of the solid electrolyte plates 14 and 16 other than the pump electrodes 21 and the like, particularly the portions where the electrode leads 211 and the like are formed, are provided between the solid electrolyte plates 14 and 16 and the electrode leads 211, 321, 421 and the like. It is preferable to form an insulating layer (not shown).
[0037]
As shown in FIG. 2, the electrodes 21 of the cells 2, 3, and 4 are exposed to the outside of the multilayer gas sensor element 1 through through holes 180 formed in the lead portions 221 and the spacers 17 and the like. The external terminals 310, 320, 410, 420, 210, and 220 are electrically connected.
By connecting a lead wire to the external terminal section 310 or the like via a suitable connector by crimping, brazing, or the like, an electric signal is transmitted between an external circuit (to be described in detail later) and each of the cells 2, 3, and 4. Exchange etc. becomes possible.
Reference numerals 322 and 422 denote internal terminals electrically connected to the electrode lead portions 321 and 421.
[0038]
The oxygen pump cell 2 is a pump circuit 250 having a pump power supply 251 and an ammeter 252, the oxygen monitor cell 3 is a monitor circuit 350 having a power supply 351 and an ammeter 352, and the sensor cell 4 is a sensor having a power supply 451 and an ammeter 452. It is connected to the circuit 450 via the external terminal 310 and the like.
[0039]
The heater 19 is provided to heat the heat generating portion 191 by power supply from an external power supply (not shown) and heat each of the cells 2, 3, and 4 to an activation temperature.
The heater 19 is formed by patterning a heat generating portion 191 for generating and supplying electricity on the upper surface of a heater substrate 195 made of alumina. It becomes.
As is apparent from FIG. 2, the heater terminal portion 190 and the external terminal portions 210 and 220 are provided on the surface (downward in the drawing) of the multilayer gas sensor element 1 on the heater 19 side, and the external terminal portions 310, 320, 410 and 420 are provided. , On the side of the spacer 132 (above the drawing).
[0040]
Next, dimensions and the like of the pump electrode 21 and the first measured gas chamber 11 according to the oxygen pump cell 2 will be described below.
As shown in FIG. 3, each of the pump electrode 21 and the first measured gas chamber 11 is a rectangle whose long side is in the same direction as the longitudinal direction of the multilayer gas sensor element 1. The extension of one side surface 211 of the pump electrode 21 is M1, the extension of the inner side surface 111 facing the side surface 211 is N1, and the distance between M1 and N1 is in the range from the end 213 to the end 214 of the pump electrode 21. Is uniform and G1.
The extension of the other side surface 212 of the pump electrode 21 is M2, and the extension of the opposing inner surface 112 is N2, and the distance between M2 and N2 is uniform in the range from the end 213 to the end 214 of the pump electrode 21. And G2.
Therefore, the total G of the clearances between the side surfaces 211 and 212 of the pump electrode 21 and the opposing inner surfaces 111 and 112 is G1 + G2. In the multilayer gas sensor element 1 according to this example, G is 0.5 mm or less. I do.
[0041]
Next, the composition of each part of the multilayer gas sensor element 1 according to the present embodiment will be described.
Each spacer 17, 15, 133, 132 is made of an insulating material such as alumina.
The solid electrolyte plates 14, 16 for constituting the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 are made of a ceramic having oxygen ion conductivity such as zirconia or ceria.
The electrodes 21 and 32 of the oxygen pump cell 2 and the oxygen monitor cell 3 use electrodes having low NOx decomposition activity in order to suppress the decomposition of NOx in the first measured gas chamber 11 and the second measured gas chamber 12. More specifically, a porous cermet electrode containing Pt and Au can be suitably used. In this case, in the porous cermet electrode, the content of Au in the metal component is preferably about 1 to 10% by weight.
[0042]
Further, as the sensor electrode 42 facing the second measured gas chamber 12 of the sensor cell 4, it is preferable to use an electrode having a high NOx decomposition activity in order to decompose NOx in the measured gas. A porous cermet electrode containing Pt and Rh can be suitably used. In this case, in the porous cermet electrode, the content of Rh in the metal component is preferably about 10 to 50% by weight.
[0043]
The solid electrolyte plates 14, 16, the spacers 15, 17, 133, 132, the alumina insulating plate 196, and the heater sheet 195 can be formed into a sheet shape by a doctor blade method, an extrusion method, or the like.
Further, the above-described pump electrodes 21 and the like, the leads 211 and the like, and the terminal portions 210 and the like can be formed by screen printing or the like. Then, the respective sheets are laminated and fired to be integrated.
[0044]
Further, it is preferable to use, for example, a Pt porous cermet electrode as the electrodes 22, 31, 41 facing the reference gas chambers 121, 122 of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4.
The heat generating portion 191 and the heater lead portion 192 are made of a cermet material composed of Pt and alumina-containing ceramic.
[0045]
Next, the operation principle of the laminated gas sensor element having the above configuration will be described.
The measured gas passes through the porous protective layer 131 and the pinhole 101 and is introduced into the first measured gas chamber 11. The amount of gas introduced at this time is determined by the diffusion resistance of the porous protective layer 131 and the pinhole 101. Thereafter, the measured gas passes through the throttle unit 102 and is introduced into the second measured gas chamber 12.
[0046]
When a voltage is applied to the pair of pump electrodes 21 and 22 of the oxygen pump cell 2 by a pump power supply so that the electrode 22 on the reference gas chamber 121 side becomes a positive electrode, the pump electrode 21 on the first gas chamber 11 side to be measured is applied. Above, oxygen in the gas to be measured is reduced to oxygen ions, and is discharged to the electrode 22 side by a pumping action.
[0047]
Conversely, when a voltage is applied so that the pump electrode 21 on the first measured gas chamber 11 side becomes a positive electrode, oxygen is reduced on the electrode 22 on the reference gas chamber 121 side to become oxygen ions, and the oxygen ions are reduced by the pumping action. It is discharged to the pump electrode 21 side.
The oxygen concentration of the first measured gas chamber 11 and the second measured gas chamber 12 communicating with the first measured gas chamber 11 can be controlled by using the oxygen pumping action.
At this time, oxygen of the gas to be measured as indicated by an arrow 118 passing over the pump electrode 21 is sufficiently ionized, but oxygen from the gas to be measured passing through the arrow 119 is not so ionized.
[0048]
By applying a predetermined voltage (for example, 0.40 V) to the pair of monitor electrodes 31 and 32 of the oxygen monitor cell 3 so that the monitor electrode 31 on the reference gas chamber 122 side becomes a positive electrode, the second gas to be measured is applied. Oxygen in the measured gas is reduced to oxygen ions on the monitor electrode 32 on the chamber 12 side, and is discharged to the monitor electrode 31 side by a pumping action.
Since the monitor electrode 32 is a Pt-Au cermet electrode which is inactive for decomposition of NOx, the oxygen ion current flowing between the monitor electrodes 31 and 32 flows through the porous protective layer 131, the pinhole 101, and the first gas chamber 11 to be measured. And the like, and depends on the amount of oxygen in the gas to be measured reaching the monitor electrode 32, and does not depend on the amount of NOx.
Therefore, if the voltage applied between the pump electrodes 21 and 22 of the oxygen pump cell 2 is controlled so that the current value between the monitor electrodes 31 and 32 becomes a predetermined constant value (for example, 0.2 μA), the second voltage The measurement gas chamber 12 can be controlled so as to always have a constant oxygen concentration.
[0049]
A predetermined voltage (for example, 0.40 V) is applied to the pair of sensor electrodes 41 and 42 of the sensor cell 4 so that the sensor electrode 41 on the reference gas chamber 122 side becomes a positive electrode. Since the sensor electrode 42 is a Pt-Rh cermet electrode that is active in decomposing NOx, oxygen and NOx in the measured gas are reduced to oxygen ions on the sensor electrode 42 on the second measured gas chamber 12 side. Is discharged to the sensor electrode 41 side by the pumping action.
[0050]
As shown in FIG. 1, in the multilayer gas sensor element 1 according to the present embodiment, the oxygen pump cell 2 is controlled so that the current value between the monitor electrodes 31 and 32 of the oxygen monitor cell 3 becomes a constant value (for example, 0.2 μA). Control.
At this time, if NOx does not exist in the gas to be measured, the current value between the sensor electrodes 41 and 42 of the sensor cell 4 also becomes a constant value (for example, 0.2 μA). On the other hand, when NOx is present in the gas to be measured, the current value increases according to the NOx concentration. Thereby, the NOx concentration in the gas to be measured can be detected.
[0051]
Next, the operation and effect of this example will be described.
As shown in FIG. 3, the multilayer gas sensor element 1 of this example has a total clearance G of 0 between the side surfaces 211 and 212 of the pump electrode 21 facing the gas chamber 11 to be measured and the inner surfaces 111 and 112 facing each other. 0.5 mm or less, which is sufficiently small.
Therefore, more gas to be measured can be passed over the pump electrode 21 of the oxygen pump cell 2 as shown by the arrow 118.
Therefore, the oxygen concentration in the gas chambers 11 and 12 to be measured is made thinner, the influence of oxygen on the NOx concentration detection is made smaller, and the specific gas concentration can be measured with high accuracy.
[0052]
As described above, according to the present invention, it is possible to provide a laminated gas sensor element capable of reducing the influence of oxygen coexisting in the gas chamber to be measured and detecting the specific gas concentration (NOx in this example) with high accuracy.
[0053]
FIG. 4 is an explanatory view of the case where the pump electrode 21 and the first gas chamber 11 to be measured are provided.
In FIG. 4, G is different for each location, such as S01-S02, S11-T11 distance + T12-S12 distance...
In such a case, if the smallest G is 0.5 mm or less, the effect according to the present example can be obtained.
[0054]
(Example 2)
In this example, a stacked gas sensor element including a pump electrode 21 having a total clearance G different from place to place will be described.
As shown in FIG. 5, in the pump electrode 21 of this example, the distance between the inner side surface 111 facing the left side surface 211 on the left side of the drawing is wider than the right side G1 ′, the distance on the right side is G1, and the left side surface 212 on the left side of the drawing The distance from the opposing inner side surface 112 is wider than the right side and G2 ', and the right side is G2. The length along the longitudinal direction of the wide pump electrode 21 at the portion corresponding to G1 and G2 is L, and the entire length of the pump electrode 21 is Le.
[0055]
In the laminated gas sensor element according to the present example, the total clearance at the left side of the drawing is G1 ′ + G2 ′ = 0.8 mm, the total clearance at the right side of the drawing is G1 + G2 = 0.4 mm, Le = 6 mm, L = 4 mm. It is.
[0056]
Therefore, the length of the portion where the total G of the clearance is 0.5 mm or less occupies 1/4 or more of the entire length of the pump electrode, so that a more accurate laminated gas sensor element can be obtained. (For details, refer to the measurement in Example 4.)
Other configurations of the stacked gas sensor element of this embodiment are the same as those of the first embodiment.
[0057]
(Example 3)
In this embodiment, a laminated gas sensor element having the same configuration as that of the first embodiment and satisfying the following conditions regarding the area of the pump electrode will be described.
As shown in FIG. 6, the pump electrode 21 of this embodiment has the same shape as that of the first embodiment. The position where the center position of the pinhole 101 (see FIG. 1 of the first embodiment) serving as the introduction path of the gas to be measured is projected on FIG. 6 is V, and a straight line passing through V and parallel to the width direction is V0. In the pump electrode 21, a straight line parallel to the width direction passing through the end on the side of the second measured gas chamber 12 in the longitudinal direction is V1.
[0058]
In the stacked gas sensor element according to the present example, the surface area of the pump electrode 21 on the right side of the drawing with respect to V0 (the area hatched in FIG. 6) is 10 mm in Se. ² The area Sg (the area indicated by hatching in FIG. 6) surrounded by the inner surfaces 111 and 112 of the gas chamber to be measured, the side surfaces 211 and 212 of the pump electrode 21, and the straight lines V0 and V1 is 1.5 mm. ² And Sg / Se ≦ 0.3.
[0059]
As shown in FIG. 6, the laminated gas sensor element 1 of the present embodiment has an inner side surface 111 and a side surface 211 which are smaller than the area Se with a broken line on the right side of V0 of the pump electrode 21 facing the measured gas chamber 11. The area Sg surrounded by dots and hatched with dots is sufficiently small to satisfy Sg / Se ≦ 0.3.
Therefore, more gas to be measured can be passed over the pump electrode 21 of the oxygen pump cell.
Therefore, the oxygen concentration in the gas chambers 11 and 12 to be measured is made thinner, the influence of oxygen on the NOx concentration detection is made smaller, and the specific gas concentration can be measured with high accuracy.
Otherwise, the detailed configuration of the stacked gas sensor element is the same as that of the first embodiment.
[0060]
FIG. 7 is an explanatory diagram of a case where the pump electrode 21 and the first gas chamber 11 to be measured are provided.
Also in this case, similarly to FIG. 6, the area Sg surrounded by V0, V1, T, and S is sufficiently smaller than the area Se on the right side of V0 of the pump electrode, and Sg / Se ≦ 0.3. For example, the same effect as in the present embodiment can be obtained.
[0061]
(Example 4)
In this example, detection errors were measured for various stacked gas sensor elements, and the performance of each was evaluated.
In the stacked gas sensor element as shown in Example 1, several samples having different G were prepared, and the measurement of the detection error was performed for each of them.
That is, assuming that the detection error in the case of G = 0 is 1, the detection errors were similarly measured for other stacked gas sensor elements having different Gs, and the results are collectively shown in FIG.
[0062]
A method for measuring the detection error will be described.
A stacked gas sensor element having a different G was prepared, exposed to a gas to be measured containing 100 ppm of NO, and the detection error of the NOx concentration when the oxygen concentration in the gas to be measured was changed from 10 ppm to 20% was measured. . This is based on the fact that when the clearance increases (that is, G increases), the amount of oxygen that cannot be exhausted by the oxygen pump cell increases, and the detection error due to the oxygen concentration increases.
From FIG. 8, it has been found that as G increases, the detection error increases, and it is necessary to satisfy G ≦ 0.5 or less (preferably 0.2 or less) in order to obtain high detection accuracy.
[0063]
In a similar test, in a stacked gas sensor element as shown in Example 2, several samples having different L / Le were prepared and the detection error was measured.
Assuming that the detection error when L / Le = 1 is 1, detection errors were similarly measured for other stacked gas sensor elements having different L / Le, and the results are collectively shown in FIG.
From FIG. 9, since the detection error increases as L / Le decreases, it is desirable that G ≦ 0.5 mm and that L / Le be 0.25 or more in order to obtain higher detection accuracy. Do you get it.
[0064]
In a similar test, in a laminated gas sensor element as shown in Example 3, several samples having different Sg / Se were prepared, and the detection error was measured.
Assuming that the detection error when Sg / Se = 0 is 1, the detection errors were similarly measured for other stacked gas sensor elements having different Sg / Se, and the results are collectively shown in FIG.
From FIG. 10, it has been found that the detection error increases as Sg / Se increases, so that Sg / Se needs to be 0.3 or less in order to obtain high detection accuracy.
[0065]
(Example 5)
In this embodiment, as shown in FIG. 11, a pinhole 103 is provided on the end face 150 to pass through the first measured gas chamber 11, and the gas to be measured is introduced into the first measured gas chamber 11 from there. Element.
Even in the stacked gas sensor element having such a configuration, the pump electrode 21 and the first gas chamber 11 to be measured are configured under the conditions shown in the first to third embodiments, so that the first to the third embodiments can be implemented. It was found that the same effect as in Example 3 was obtained.
In this case, Se shown in the third embodiment is the surface area of the pump electrode 21. This is because the entire pump electrode 21 is included downstream of the gas flow of the gas to be measured.
[0066]
(Example 6)
In this example, as shown in FIGS. 12 and 13, the pump gas 21 and the first measured gas chamber 11 are both elliptical gas sensors.
As shown in FIG. 12, the total length G1 + G2 = G of the side surfaces 211 and 212 of the pump electrode 21 along the longitudinal direction and the inner surfaces 111 and 112 facing the side surfaces 211 and 212 is 0.5 mm. The following operation and effect can be obtained as in the first embodiment.
[0067]
Further, as shown in FIG. 13, S is a curve showing the inner surface of the first gas chamber 11 to be measured, T is a curve showing the side surface of the pump electrode 21, and point V is a pinhole (not shown) serving as a gas introduction part to be measured. The center position, V0 is a straight line parallel to the width direction passing through the point V, and V1 is a straight line parallel to the width direction passing through the end of the pump electrode 21 in the longitudinal direction and surrounded by a curve T and a straight line V0. The area surrounded by the pump electrode area Se and the straight lines V0 and V1 curves T and S is the total area Sg of the clearance.
By setting Se / Sg ≦ 0.3, the same operation and effect as in the third embodiment can be obtained.
[0068]
(Example 7)
As shown in FIG. 14, the multilayer gas sensor element 1 according to the present embodiment has substantially the same configuration as that of the first embodiment, but has a different circuit configuration.
That is, the pump circuit 250 includes a power supply 251 and an ammeter 252 so that the oxygen pump current matches the limit current based on the relationship between the applied voltage to the oxygen pump cell 2 and the current flowing through the oxygen pump cell 2 determined in advance. Is applied with a voltage corresponding to the oxygen concentration.
Thereby, the oxygen concentration in the first measured gas chamber 11 and the second measured gas chamber 12 can be controlled to a predetermined low concentration.
[0069]
When the oxygen concentration in the first measured gas chamber 11 and the second measured gas chamber 12 is controlled by this method, the oxygen concentration in the second measured gas chamber 12 is smaller than the control based on the oxygen monitor cell according to the first embodiment. The concentration tends to fluctuate. Therefore, if the current flowing between the sensor electrodes 41 and 42 of the sensor cell 4 is used as a sensor signal as it is, the detection accuracy of NOx deteriorates.
Therefore, the difference between the current flowing between the sensor electrodes 41 and 42 of the sensor cell 4 and the current flowing between the monitor electrodes 31 and 32 of the oxygen monitor cell 3 is detected by a current difference detection circuit 459, and this value is used as a sensor signal. Thus, the effect of the fluctuation of the oxygen concentration in the second measured gas chamber 12 can be reduced, and a more accurate sensor cell output concerning the NOx concentration independent of the oxygen concentration in the measured gas can be obtained.
[0070]
By providing the pump electrode 21 according to FIGS. 3, 5, 7, 11 to 13 in such a stacked gas sensor element 1, an element having high measurement accuracy can be obtained as in the other embodiments. Can be.
[0071]
(Example 8)
The stacked gas sensor element 6 according to the present embodiment is a four-cell element provided with the second oxygen pump cell 5, as shown in FIG.
The stacked gas sensor element 1 of the present embodiment has a heater 19 similar to that of the first embodiment, a spacer 64 for a reference gas chamber 640, a solid electrolyte plate 63 provided with an oxygen monitor cell 3 and a sensor cell 4, a first measured gas chamber 11, The spacer 62 for the second measured gas chamber 12 and the solid electrolyte plate 61 for the oxygen pump cell 2 and the second oxygen pump cell 5 are laminated.
[0072]
The oxygen pump cell 2 has a pump electrode 21 facing the first measured gas chamber 11, an electrode 22 covered with the porous protective layer 131 and exposed to the measured gas outside the element, and has a power supply 251. Connected to pump circuit 250.
The monitor cell 3 has the monitor electrode 32 facing the first measured gas chamber 11 and the monitor electrode 31 facing the reference gas chamber 640, and is connected to a circuit 350 having a voltmeter 357.
The sensor cell 4 has a sensor electrode 42 facing the second measured gas chamber 12 and a sensor electrode 41 facing the reference gas chamber 640, and is connected to a circuit 450 having an ammeter 457.
The monitor electrodes 31, 41 are integral electrodes.
A control circuit 255 that controls the power supply 251 of the oxygen pump cell 2 based on the voltage value detected by the voltmeter 357 is connected between the voltmeter 357 and the power supply 251.
[0073]
The second oxygen pump cell 5 has an electrode 51 formed integrally with the electrode 22 of the first oxygen pump cell 2 and an electrode 52 exposed to the second gas chamber 12 to be measured, and is connected to a circuit 550 having a power supply 551. You.
[0074]
In the first embodiment, the oxygen concentration in the second measured gas chamber 12 is detected based on the current value flowing through the oxygen monitor cell 3. In this embodiment, the oxygen concentration is detected from the electromotive force generated between the monitor electrodes 31 and 32 of the oxygen monitor cell 3. .
An example of the operation in this case will be described with reference to FIG.
The monitor electrode 32 of the oxygen monitor cell 3 faces the first measured gas chamber 11, and the monitor electrode 31 faces the reference gas chamber 640 into which the atmosphere is introduced. An electromotive force based on the Nernst equation is generated between the monitor electrodes 31 and 32 due to a difference in oxygen concentration between the first measured gas chamber 11 and the reference gas chamber 640.
[0075]
Since the oxygen concentration in the reference gas chamber 640 is constant, the electromotive force generated between the monitor electrodes 31 and 32 reflects the oxygen concentration in the first measured gas chamber 11. Therefore, by controlling the applied voltage between the pump electrodes 21 and 22 of the oxygen pump cell 2 so that the electromotive force generated between the monitor electrodes 31 and 32 becomes a predetermined constant value (for example, 0.20 V), The concentration of oxygen flowing into the measurement gas chamber 12 can be controlled to be constant.
[0076]
Further, in this example, the second oxygen pump cell 5 is formed, and oxygen that cannot be exhausted by the oxygen pump cell 2 and flows into the second measured gas chamber 12 is exhausted to the outside.
As a result, the oxygen concentration in the second measured gas chamber 12 becomes almost zero, and the sensor cell 4 enables highly accurate NOx concentration measurement.
[0077]
By providing the pump electrode 21 according to FIGS. 3, 5, 7, 11 to 13 in such a stacked gas sensor element 1, an element having high measurement accuracy can be obtained as in the other embodiments. Can be.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional explanatory views in a longitudinal direction of a laminated gas sensor element according to a first embodiment, and FIG. 1B is a cross-sectional explanatory view in a width direction (A-A cross-sectional explanatory view of FIG. 1A).
FIG. 2 is an exploded perspective view of the multilayer gas sensor element according to the first embodiment.
FIG. 3 is a plan view showing a total clearance portion between a side surface and an inner surface of a pump electrode and a first gas-to-be-measured chamber in Example 1 (a sectional view taken along the line BB in FIG. 1A); ).
FIG. 4 is an explanatory diagram of a total of an irregular-shaped pump electrode and a clearance portion in a first gas chamber to be measured in the first embodiment.
FIG. 5 is a cross-sectional explanatory view of a stacked gas sensor element in which the width of a pump electrode is partially different in Example 2.
FIG. 6 is a cross-sectional explanatory view of a multilayer gas sensor element showing an area of a pump electrode facing a gas chamber to be measured and a total area of a clearance portion in a third embodiment.
FIG. 7 is an explanatory diagram of an area of a pump electrode and a total area of a clearance portion in an irregular shaped pump electrode and a first gas chamber to be measured in a third embodiment.
FIG. 8 is a diagram showing the relationship between the total length G of the clearance portion and the detection error in the stacked gas sensor element according to the fourth embodiment.
FIG. 9 is a diagram showing a relationship between L / Le and a detection error in the laminated gas sensor element according to the fourth embodiment.
FIG. 10 is a graph showing the relationship between the ratio Sg / Se between the area Se of the pump electrode facing the gas chamber to be measured and the total area Sg of the clearance portion and the detection error in the stacked gas sensor element according to the fourth embodiment. FIG.
FIG. 11 is a cross-sectional explanatory view of a stacked gas sensor element configured to introduce a gas to be measured from an end face into a gas chamber to be measured in a fifth embodiment.
FIG. 12 is a cross-sectional explanatory diagram illustrating G1 and G2 in the stacked gas sensor element having an elliptical pump electrode in the sixth embodiment.
FIG. 13 is a cross-sectional explanatory diagram illustrating Se and Sg in a stacked gas sensor element having an elliptical pump electrode in a sixth embodiment.
14A and 14B are cross-sectional views in a longitudinal direction and a cross-sectional view in a width direction of a multilayer gas sensor element having a configuration in which control is performed based on a voltage applied to an oxygen pump cell and a current flowing through the oxygen pump cell in a seventh embodiment. FIG. 14 is an explanatory cross-sectional view taken along the line CC in FIG.
FIG. 15 is an explanatory view of a stacked gas sensor element provided with first and second oxygen pump cells in Example 8.
FIG. 16 is an explanatory view of a conventional laminated gas sensor element.
[Explanation of symbols]
1. . . Stacked gas sensor element,
11,12. . . First and second gas chambers to be measured,
14,16. . . Solid electrolyte plate,
2. . . Oxygen pump cell,
21, 22. . . Pump electrode,
3. . . Oxygen monitor cell,
31, 32. . . Monitor electrode,
4. . . Sensor cell,
41, 42. . . Sensor electrode,

Claims (4)

所定の拡散抵抗の下に被測定ガスを導入する被測定ガス室と，
酸素イオン導電性の固体電解質板の表面に，一方のポンプ電極が上記被測定ガス室に面するように設けた一対のポンプ電極を有し，これら一対のポンプ電極へ通電することにより上記被測定ガス室に酸素を導入または排出し，上記被測定ガス室の酸素濃度を調整する酸素ポンプセルと，
酸素イオン導電性の固体電解質板の表面に，一方のセンサ電極が上記被測定ガス室に面するように設けた一対のセンサ電極を有し，これら一対のセンサ電極間に生じる酸素イオン電流に基づいて，上記被測定ガス室内の特定ガス濃度を検出するセンサセルとを有する積層型ガスセンサ素子であって，
上記酸素ポンプセルの上記被測定ガス室に面するポンプ電極において，
上記積層型ガスセンサ素子の長手方向に沿った上記ポンプ電極の側面と，該側面と対向する上記被測定ガス室の内側面とのクリアランス部の上記長手方向と直交する幅方向の長さの総計Ｇの最小値は０．５ｍｍ以下であることを特徴とする積層型ガスセンサ素子。A measured gas chamber for introducing the measured gas under a predetermined diffusion resistance;
A pair of pump electrodes is provided on the surface of the oxygen-ion conductive solid electrolyte plate so that one pump electrode faces the gas chamber to be measured. An oxygen pump cell for introducing or discharging oxygen into the gas chamber and adjusting the oxygen concentration in the gas chamber to be measured;
On the surface of the oxygen ion conductive solid electrolyte plate, there is provided a pair of sensor electrodes provided so that one sensor electrode faces the gas chamber to be measured, and based on an oxygen ion current generated between the pair of sensor electrodes. A gas sensor element for detecting a specific gas concentration in the gas chamber to be measured.
In the pump electrode facing the measured gas chamber of the oxygen pump cell,
The total length G of the clearance in the width direction orthogonal to the longitudinal direction of the clearance between the side surface of the pump electrode along the longitudinal direction of the stacked gas sensor element and the inner surface of the gas chamber to be measured facing the side surface. Is a minimum value of 0.5 mm or less. 請求項１において，上記クリアランス部の総計Ｇが０．５ｍｍ以下である部分の積層型ガスセンサ素子の長手方向に沿った長さがポンプ電極全体の上記長手方向に沿った長さに対して１／４以上を占めていることを特徴とする積層型ガスセンサ素子。In Claim 1, the length along the longitudinal direction of the laminated gas sensor element at a portion where the total G of the clearances is 0.5 mm or less is 1/1 / the length of the entire pump electrode along the longitudinal direction. A stacked gas sensor element occupying at least four. 所定の拡散抵抗の下に被測定ガスを導入する被測定ガス室と，
酸素イオン導電性の固体電解質板の表面に，一方のポンプ電極が上記被測定ガス室に面するように設けた一対のポンプ電極を有し，これら一対のポンプ電極へ通電することにより上記被測定ガス室に酸素を導入または排出し，上記被測定ガス室の酸素濃度を調整する酸素ポンプセルと，
酸素イオン導電性の固体電解質板の表面に，一方のセンサ電極が上記被測定ガス室に面するように設けた一対のセンサ電極を有し，これら一対のセンサ電極間に生じる酸素イオン電流に基づいて，上記被測定ガス室内の特定ガス濃度を検出するセンサセルとを有する積層型ガスセンサ素子であって，
上記被測定ガス室に対し被測定ガスを導入する導入部よりガス流れ下流における上記酸素ポンプセルにおける上記被測定ガス室に面するポンプ電極の形成範囲において，
上記被測定ガス室に面するポンプ電極の面積をＳｅ，上記積層型ガスセンサ素子の長手方向に沿った上記ポンプ電極の側面と該側面と対向する上記被測定ガス室の内側面との間のクリアランス部の面積の総計をＳｇとした場合，Ｓｇ／Ｓｅ≦０．３であることを特徴とする積層型ガスセンサ素子。A measured gas chamber for introducing the measured gas under a predetermined diffusion resistance;
A pair of pump electrodes is provided on the surface of the oxygen-ion conductive solid electrolyte plate so that one pump electrode faces the gas chamber to be measured. An oxygen pump cell for introducing or discharging oxygen into the gas chamber and adjusting the oxygen concentration in the gas chamber to be measured;
On the surface of the oxygen ion conductive solid electrolyte plate, there is provided a pair of sensor electrodes provided so that one sensor electrode faces the gas chamber to be measured, and based on an oxygen ion current generated between the pair of sensor electrodes. A gas sensor element for detecting a specific gas concentration in the gas chamber to be measured.
In the formation range of the pump electrode facing the measured gas chamber in the oxygen pump cell downstream of the gas flow from the inlet for introducing the measured gas into the measured gas chamber,
The area of the pump electrode facing the measured gas chamber is Se, and the clearance between the side surface of the pump electrode along the longitudinal direction of the stacked gas sensor element and the inner surface of the measured gas chamber facing the side surface. Where the total area of the parts is Sg, Sg / Se ≦ 0.3. 請求項１〜３のいずれか１項において，酸素イオン導電性の固体電解質板の表面に，一方のモニタ電極が上記被測定ガス室に面するように設けた一対のモニタ電極を有し，これら一対のモニタ電極間に生じる電流値または起電力に基づいて，上記被測定ガス室内の酸素濃度を検出する酸素モニタセルを備えることを特徴とする積層型ガスセンサ素子。4. The method according to claim 1, further comprising a pair of monitor electrodes provided on the surface of the oxygen-ion conductive solid electrolyte plate such that one monitor electrode faces the gas chamber to be measured. A stacked gas sensor element comprising: an oxygen monitor cell that detects an oxygen concentration in the measured gas chamber based on a current value or an electromotive force generated between a pair of monitor electrodes.

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