JP2004225684A - Oxygen sensor abnormality detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen sensor abnormality-detecting device capable of accurately detecting the abnormality of a downstream oxygen sensor installed downstream of catalyst. <P>SOLUTION: The catalyst is provided in an exhaust passage of an internal combustion engine. The downstream oxygen sensor is installed downstream of the catalyst. As the output of the downstream oxygen sensor (Fig. B) changes from the rich output to the lean output, the exhaust air fuel ratio upstream of the catalyst (Fig. A) is made to change from the lean air fuel ratio to the rich air fuel ratio. As the output of the downstream oxygen sensor changes from the lean output to the rich output, the exhaust air fuel ratio upstream of the catalyst is made to change from the rich air fuel ratio to the lean air fuel ratio (time T1 or T2). While the air fuel ratio control is carried out, the abnormality of the downstream oxygen sensor is determined according to the output of the downstream oxygen sensor (indicated by a solid line or a broken line in Fig. B). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０１０９】
また、上流触媒２８は、触媒前空燃比Ａ／Ｆが理論空燃比Ａ／Ｆ_{ｓｔｏｉｃｈｉ}よりリーンである場合、つまり、Ａ／Ｆ＞Ａ／Ｆ_{ｓｔｏｉｃｈｉ}である場合に、酸素の過剰分を吸蔵する。この場合、内燃機関１０に対する燃料供給量をＦとすると、過剰な酸素量ＱＯ_２は、やはり上記（１）式により表すことができる。
【０１１０】
本実施形態において、ＥＣＵ４０は、空燃比センサ３２により触媒前空燃比Ａ／Ｆを検出することができる。また、ＥＣＵ４０は、燃料噴射量自体を制御しているため、単位時間当たりの燃料供給量Ｆを検知することができる。このため、ＥＣＵ４０は、それらのＡ／ＦおよびＦを上記（１）式に代入することにより、単位時間当たりの不足或いは過剰酸素量ＱＯ_２を算出することができる。そして、ＥＣＵ４０は、アクティブ空燃比制御の実行に伴って下流酸素センサ３４の出力Ｖｓが反転する環境下で、その反転を起点および終点として酸素量ＱＯ_２を積分することにより、上流触媒２８の酸素吸蔵容量を算出することができる。
【０１１１】
ところで、本実施形態の装置は、上述した他の実施形態の装置と同様に、下流酸素センサ３４の異常検出の際にもアクティブ空燃比制御を実行する。アクティブ空燃比制御は、強制的に触媒前空燃比を変動させて、上流触媒２８の下流にリッチまたはリーンな排気ガスを吹き抜けさせる制御であるから、ドライバビリティやエミッション特性の悪化を避ける意味で、その実行頻度は低いことが望ましい。そこで、本実施形態の装置は、上流触媒２８の酸素吸蔵容量を検知するためのアクティブ空燃比制御と、下流酸素センサ３４の異常検出のためのアクティブ空燃比制御とを兼用するため、それら両者の制御を同時に進行させることとした。
【０１１２】
また、上述した酸素吸蔵容量の算出手法は、下流酸素センサ３４が正常であることを前提としている。このため、下流酸素センサ３４に異常が生じている場合、上記の算出手法では、酸素吸蔵容量が正確に算出できない事態が生じ得る。そして、不正確な酸素吸蔵容量に基づいて上流触媒２８の状態が判断されると、誤った異常或いは正常判定がなされ得る。そこで、本実施形態の装置は、下流酸素センサ３４の異常検出処理と、上流触媒２８の酸素吸蔵容量の算出処理とを同時に進行させながら、上流触媒２８の異常判定は、下流酸素センサ３４の異常検出処理の終了後に実行することとした。
【０１１３】
図１１は、上記の機能を実現すべく、本実施形態においてＥＣＵ４０が実行する制御ルーチンのフローチャートである。尚、図１１において、上記図５または図８に示すステップと同一のステップについては、同一の符号を付してその説明を省略または簡略する。
【０１１４】
図１１に示すルーチンは、ステップ１３４と１３６の間にステップ１７０〜１７４が挿入されている点、ステップ１４２と１４３の間にステップ１７６〜１８０が挿入されている点、ステップ１４６の後にステップ１８２が挿入されている点、およびステップ１４８の後にステップ１８４〜１８８が挿入されている点を除き、図８に示すルーチンと同一である。
【０１１５】
すなわち、図１１に示すルーチンでは、ステップ１３０の条件が成立する場合に、つまり、下流酸素センサ３４がリッチ出力を発している場合に、出力最大値Ｖｍａｘを更新する処理（ステップ１３２および１３４）に次いで、上流触媒２８の酸素吸蔵容量を算出する処理が実行される。ここでは、先ず、空燃比差ΔＡ／Ｆが検出される（ステップ１７０）。
空燃比差ΔＡ／Ｆは、上記（１）式に含まれる値、すなわち、空燃比センサ３２により検出される触媒前空燃比Ａ／Ｆと理論空燃比Ａ／Ｆ_{ｓｔｏｉｃｈｉ}との差（│Ａ／Ｆ_{ｓｔｏｉｃｈｉ}−Ａ／Ｆ│）である。
【０１１６】
ＥＣＵ４０は、次に、単位時間当たり（本ステップの実行周期当たり）の燃料噴射量Ｆを算出する（ステップ１７２）。
そして、算出された燃料噴射量Ｆと上記の空燃比差ΔＡ／Ｆとを上記（１）式に代入して単位時間当たりの過剰酸素量ＱＯ_２＝ｋ・ΔＡ／Ｆ・Ｆを算出し、更に、その酸素量ＱＯ_２の積分値（上記ステップ１３０の条件が成立した後の積分値）を、上流触媒２８の酸素吸蔵容量（ＯＳＣ）の最新値として算出する（ステップ１７４）。
【０１１７】
酸素吸蔵量の算出処理（上記ステップ１７０〜１７４の処理）は、出力最大値Ｖｍａｘの更新処理（上記ステップ１３２，１３４の処理）と同様に、ステップ１３６において、Ｖｓ≦ＶＬが成立すると判別されるまで繰り返し実行される。このため、上述した一連の処理によれば、センサ出力Ｖｓがリッチ出力に反転した後、その出力Ｖｓが再びリーン出力に反転するまでの期間中に生じた過剰な酸素量ＱＯ_２の積算値を、上流触媒２８の酸素吸蔵容量として算出することができる。
【０１１８】
図１１に示すルーチンでは、ステップ１３８の条件が成立する場合に、つまり、下流酸素センサ３４がリーン出力を発している場合に、出力最小値Ｖｍｉｎを更新する処理（ステップ１４０および１４２）に次いで、上流触媒２８の酸素吸蔵容量を算出する処理が実行される。ここでは、実質的に、上記ステップ１７０〜１７４の場合と同様の手順で酸素吸蔵容量が算出される（ステップ１７６〜１８０）。これらの処理によれば、センサ出力Ｖｓがリーン出力に反転した後、その出力Ｖｓが再びリッチ出力に反転するまでの期間中に生じた過小な酸素量ＱＯ_２の積算値を、上流触媒２８の酸素吸蔵容量として算出することができる。
【０１１９】
上記ステップ１３２〜１３６の処理が繰り返されることにより算出される過剰な酸素量ＱＯ_２の積算値、および、上記ステップ１４０〜１４３の処理が繰り返されることにより算出される過小な酸素量ＱＯ_２の積算値は、下流酸素センサ３４が正常である場合は、上流触媒２８の酸素吸蔵容量と精度良く一致する。従って、下流酸素センサ３４が正常である場合は、それらの一連の処理により、上流触媒２８の酸素吸蔵容量を精度良く算出することができる。
【０１２０】
図１１に示すルーチンでは、ステップ１４６において下流酸素センサ３４の劣化が判定された場合、上記の如く算出された酸素吸蔵容量のデータが破棄される（ステップ１８２）。
そして、この場合は、酸素吸蔵容量に基づく上流触媒２８の異常判定が行われることなく、今回の処理サイクルが終了される。このため、図１１に示すルーチンによれば、下流酸素センサ３４に異常が生じている場合に、異常なセンサ出力Ｖｓを基礎として算出された不正確な酸素吸蔵容量に基づいて、上流触媒２８の状態が誤って判断されるのを確実に防止することができる。
【０１２１】
また、図１１に示すルーチンでは、ステップ１４８において下流酸素センサ３４が正常であると判別された場合、上述した手順で算出された酸素吸蔵容量（ＯＳＣ）が、正常値であるか否かが判別される（ステップ１８４）。
その結果、酸素吸蔵容量が正常値であると判別された場合は、上流触媒２８が正常であるとの判定がなされる（ステップ１８６）。
一方、酸素吸蔵容量が正常値でないと判別された場合は、上流触媒２８が劣化しているとの判定がなされる（ステップ１８８）。
【０１２２】
上記の処理によれば、下流酸素センサ３４が正常である場合に限り、酸素吸蔵容量に基づく上流触媒２８の劣化判定を実行することができる。このため、図１１に示すルーチンによれば、上流触媒２８の劣化判定を、常に正常な酸素吸蔵容量に基づいて精度良く実行することができる。
【０１２３】
以上説明した通り、図１１に示すルーチンによれば、アクティブ空燃比制御の実行中に、上流触媒２８の酸素吸蔵容量の算出と、出力最大値Ｖｍａｘまたは出力最小値Ｖｍｉｎの算出とを同時に実行することができる。更に、このルーチンによれば、上流触媒２８の異常判定を、下流酸素センサ３４の異常検出処理の終了後に限り、より具体的には、下流酸素センサ３４の正常判定がなされた場合にのみ実行することができる。このため、本実施形態の装置によれば、ドライバビリティやエミッションの悪化を最小限に抑えつつ、下流酸素センサ３４の異常、および上流触媒２８の異常を、常に正確に判定することができる。
【０１２４】
ところで、上述した実施の形態４においては、下流酸素センサ３４の異常を判定する手法として実施の形態２の手法を用いているが、本発明はこれに限定されるものではなく、その判定手法は、実施の形態１の手法であってもよい。また、上述した実施の形態４においては、アクティブ空燃比制御の振幅を変動させないこととしているが、本発明はこれに限定されるものではなく、実施の形態３の場合と同様に、アクティブ空燃比制御の振幅を変動させることとしてもよい。
【０１２５】
尚、上述した実施の形態４においては、ＥＣＵ４０が、上記ステップ１７４または１８０の処理を実行することにより前記第５の発明における「酸素吸蔵容量算出手段」が、上記ステップ１８４並１８８の処理を実行することにより前記第５の発明における「劣化状態判断手段」が、それぞれ実現されている。更に、上述した実施の形態４においては、ＥＣＵ４０が、上記ステップ１４６に次いで、触媒の劣化判定を実行することなく処理サイクルを終了させることにより前記第６の発明における「劣化判定禁止手段」が実現されている。
【０１２６】
実施の形態５．
次に、図１２および図１３を参照して、本発明の実施の形態５について説明する。本実施形態の装置は、実施の形態１の場合と同様に、図１に示すシステム構成を用いて実現することができる。
【０１２７】
既述した通り、実施の形態１の装置は、アクティブ空燃比制御、つまり、下流酸素センサ３４の出力がリッチからリーンに反転した際に、触媒前空燃比をリーンからリッチに反転させ、また、下流酸素センサ３４の出力がリーンからリッチに反転した際に、触媒前空燃比をリッチからリーンに反転させる制御を実行する。この制御の実行中、触媒前空燃比がリッチに維持されている間は、上流触媒２８の内部において、上流側の領域から下流側の領域に向かって順次酸素が吸蔵されていくのが通常である。この場合、上流触媒２８の下流には、上流触媒２８の内部全域に酸素が一杯に吸蔵された後に空燃比のリーンな排気ガスが流出する。そして、このような通常の流れに従う場合、触媒後空燃比は、上流触媒２８に酸素が一杯に吸蔵された後、理論空燃比近傍値から大きくリーンに偏った値に変化する。
【０１２８】
実施の形態１の装置は、アクティブ空燃比制御の実行中に、上流触媒２８に酸素が一杯に吸蔵されるまではその下流にリーンな排気ガスが流出してこないことを前提として下流酸素センサ３４の異常判定を行っている。つまり、実施の形態１では、触媒後空燃比が理論空燃比近傍値からリーンに偏った値に変化する際には、常に大きな変化が生ずることが前提とされている。
【０１２９】
しかしながら、上流触媒２８の下流には、上流触媒２８の全域に酸素が一杯に吸蔵されていない状況下でも、空燃比のリーンな排気ガスが流出することがある。このような現象は、例えば、吸入空気量Ｇａが少なく、上流触媒２８の状態が不安定である場合、吸入空気量Ｇａが多量であり上流触媒２８下流に未処理ガスが吹き抜けるような場合、或いは、上流触媒２８の温度が低く上流触媒２８が正規の酸素吸蔵能力を発揮しない場合などにおいて生じ得る。
【０１３０】
上流触媒２８に酸素が一杯に吸蔵されていない状況下で上流触媒２８の下流にリーンな排気ガスが流出する場合は、上流触媒２８に酸素が一杯に吸蔵された後にその下流にリーンな排気ガスが流出する場合に比して、触媒後空燃比はより理論空燃比に近い値となる。つまり、上流触媒２８に酸素が一杯に吸蔵されていない状況下でその下流にリーンな排気ガスが流出する場合は、触媒後空燃比が、通常時のリーン空燃比にまで至らず、中途半端にリーンな値となる。
【０１３１】
図１２は、アクティブ空燃比制御の実行に伴って上流触媒２８の下流に中途半端にリーンな排気ガスが流出する状況と、その実行に伴って上流触媒２８の下流に十分にリーンな排気ガスが流出する状況とを対比して説明するためのタイミングチャートである。より具体的には、図１２（Ａ）は、アクティブ空燃比制御の実行中における触媒前空燃比の目標値および実測値の波形を示す。図１２（Ｂ）は、アクティブ空燃比制御の実行中における触媒後空燃比の実測値、つまり、下流酸素センサ３４の出力の波形を示す。また、図１２（Ｃ）は、アクティブ空燃比制御の実行中に算出された酸素吸蔵容量ＯＳＣの値を示す。
【０１３２】
アクティブ空燃比制御の実行中は、図１２（Ａ）および図１２（Ｂ）に示すように、触媒後空燃比がリーン判定値ＶＬを下回ることにより触媒前空燃比の目標値がリッチ空燃比に反転され、また、触媒後空燃比がリッチ判定値ＶＲを上回ると触媒前空燃比の目標値がリーン空燃比に反転される。図１２に示すタイミングチャートは、このような処理が繰り返される過程で、下流酸素センサ３４の出力（触媒後空燃比）が、時刻ｔ１以前は十分にリーン化せず、時刻ｔ１以降において正常なリーン値に到達するようになった場合を例示している。下流酸素センサ３４の出力（触媒後空燃比）がこのような変化を示すのは、時刻ｔ１以前において、上流触媒２８の下流に中途半端にリーンな排気ガスが流出する現象が生じていたからであり、下流酸素センサ３４に異常が生じていたからではない。
【０１３３】
しかしながら、時刻ｔ１以前の下流酸素センサ３４の出力を見ると、正常時に比してその応答性は悪く、出力も縮小されている。従って、実施の形態１または２の手法で下流酸素センサ３４の異常判定が行われた場合、時刻ｔ１以前においては、その異常が誤判定される事態が生ずる。このため、異常判定の精度を高めるべく、上流触媒２８の下流に中途半端な空燃比を伴う排気ガスが流出してくるような状況下では、下流酸素センサ３４の異常判定の実行を禁止することが望ましい。
【０１３４】
図１２（Ｃ）に示す波形は、実施の形態４の場合と同様の手法で算出された酸素吸蔵容量ＯＳＣの変化を示す。酸素吸蔵容量ＯＳＣは、下流酸素センサ３４の出力Ｖｓがリーン判定値ＶＬを下回った後その値Ｖｓがリッチ判定値ＶＲを上回るまでの間、上流触媒２８に流入した排気ガス中の酸素不足量を積算することにより、或いは、下流酸素センサ３４の出力Ｖｓがリッチ判定値ＶＲを上回った後その値Ｖｓがリーン判定値ＶＬを下回るまでの間、上流触媒２８に流入した過剰な酸素量を積算することにより算出することができる（図１１中、ステップ１７０〜１７４、ステップ１７６〜１８０参照）。
【０１３５】
時刻ｔ１以前のように、上流触媒２８の下流に中途半端な空燃比の排気ガスが流出してくる状況下では、上流触媒２８に酸素が一杯に吸蔵される以前に下流酸素センサ３４の出力Ｖｓがリーン判定値ＶＬを下回る事態が生ずる。上記の算出手法によれば、酸素吸蔵容量ＯＳＣは、下流酸素センサ３４の出力Ｖｓがリーン判定値ＶＬを下回った時点で一端確定される。従って、上流触媒２８の下流に中途半端な空燃比の排気ガスが流出してくる状況下では、酸素吸蔵容量ＯＳＣは、上流触媒２８が有する本来の酸素吸蔵能力に対して過小な値となる。
【０１３６】
また、下流酸素センサ３４の出力Ｖｓが、上記の如く上流触媒２８に酸素が一杯に吸蔵される以前にリーン判定値ＶＬを下回ると、その後、触媒前空燃比の目標値がリッチ空燃比に反転されると共に、上流触媒２８内に酸素の吸蔵余力が残された状態を起点として次回の酸素吸蔵容量ＯＳＣの算出が開始される。そして、以後、下流酸素センサ３４の出力がリッチ判定値ＶＲを上回るまでに上流触媒２８から放出された酸素量の積算値に相当する値が酸素吸蔵容量ＯＳＣとして算出される。この場合、下流酸素センサ３４の出力が、上流触媒２８内の全ての酸素が放出された時点で正しくリッチ判定値ＶＲを上回ったとしても、酸素吸蔵容量ＯＳＣは、上流触媒２８が有する本来の酸素吸蔵能力に対して過小な値となる。
【０１３７】
図１２（Ｃ）において、破線で示す基準値は、上流触媒２８が有する本来の酸素吸蔵能力に対応する酸素吸蔵容量ＯＳＣとみなすべき下限の値を示す。図１２（Ｃ）は、上流触媒２８内に酸素が一杯に吸着される以前に下流酸素センサ３４の出力がリーン判定値ＶＬを下回るような状況下（時刻ｔ１以前）では、酸素吸蔵容量ＯＳＣが、その基準値より小さな値となることを示している。
【０１３８】
図１２（Ｃ）に示す関係は、換言すると、酸素吸蔵容量ＯＳＣが基準値を下回るような状況下（時刻ｔ１以前）では、アクティブ空燃比制御の実行に伴って、上流触媒２８の下流に中途半端な空燃比を有する排気ガスが流出している可能性が高いこと、つまり、上流触媒２８内に酸素が一杯に吸蔵される以前にセンサ出力Ｖｓがリーン判定値ＶＬを下回った可能性（或いは、上流触媒２８内の酸素が全て放出される以前にセンサ出力Ｖｓがリッチ判定値ＶＲを上回った可能性）が高いことを意味している。そして、酸素吸蔵容量ＯＳＣが上記の基準値を下回る状況下で下流酸素センサ３４の異常判定を禁止することとすれば、時刻ｔ１以前において、下流酸素センサ３４の異常が誤判定されるのを防ぐことができる。
【０１３９】
上記の基準値は、既述した通り、正規の酸素吸蔵容量ＯＳＣとみなすことのできる下限の値である。このような基準値としては、例えば、上流触媒２８が示す酸素吸蔵容量ＯＳＣの定常的な値を用いることができる。そして、そのような定常的な値は、ある程度の期間に渡って酸素吸蔵容量ＯＳＣの学習を継続することで得ることができる。そこで、本実施形態では、アクティブ空燃比制御の実行中に、酸素吸蔵容量ＯＳＣの学習値を作成し、その学習値より小さな酸素吸蔵容量ＯＳＣが算出された際には、そのＯＳＣの算出期間中に発せられたセンサ出力Ｖｓに基づいて下流酸素センサ３４の異常を判定するのを禁止することとした。
【０１４０】
図１３は、上記の機能を実現するために、本実施形態においてＥＣＵ４０が実行する制御ルーチンのフローチャートを示す。
図１３に示すルーチンにおいては、先ず、アクティブ制御が実施中であるか否かが判別される（ステップ１９０）。
【０１４１】
次に、下流酸素センサ出力処理が実施される（ステップ１９２）。
下流酸素センサ出力処理では、具体的には、下流酸素センサ３４のセンサ出力Ｖｓの検出、酸素吸蔵容量ＯＳＣの更新処理、および異常判定パラメータの更新処理などが実行される。酸素吸蔵容量ＯＳＣの更新処理は、空燃比センサ３２のセンサ出力に基づいて、図１１に示すステップ１７０〜１７４、或いはステップ１７６〜１８０の処理と同様の手順で行われる。また、異常判定パラメータとは、実施の形態１におけるカウンタＣの計数値、或いは、実施の形態２における最大値Ｖｍａｘまたは最小値Ｖｍｉｎを意味し、その更新処理は、図５におけるステップ１０８または１１４と同様の手順で、或いは図８におけるステップ１３２−１３４または１４０−１４２と同様の手順で実行される。
【０１４２】
図１３に示すルーチンでは、次に、前回の処理サイクルから今回の処理サイクルにかけて、下流酸素センサ３４のセンサ出力Ｖｓがリーン判定値ＶＬを上回る値から、その値ＶＬ以下に低下したか、或いは、センサ出力Ｖｓがリッチ判定値ＶＲを下回る値からその値ＶＲ以上に上昇したかが判別される。つまり、下流酸素センサ３４の出力Ｖｓが、今回の処理サイクルにおいてリーン出力、或いはリッチ出力に反転したと認められるか否かが判別される（ステップ１９４）。
【０１４３】
その結果、センサ出力Ｖｓの反転が認められないと判別された場合は、以後、速やかに今回の処理サイクルが終了される。一方、センサ出力Ｖｓの反転が認められると判別された場合は、先ず、現時点で算出されている酸素吸蔵容量ＯＳＣが、今回の反転周期における酸素吸蔵容量ＯＳＣとして確定される（ステップ１９６）。
【０１４４】
図１３に示すルーチンでは、上記ステップ１９６の処理が終了した後、ステップ１９８以降の処理と、ステップ２０２以降の処理とが並列して実行される。
すなわち、上記ステップ１９６の処理が終了すると、一方では、先ず、酸素吸蔵容量ＯＳＣの学習条件が成立しているか否かが判別される（ステップ１９８）。
ここでは、具体的には、▲１▼吸入空気量Ｇａが、下限判定値ＧａＬ以上、かつ、上限判定値ＧａＨ以下であるか、および▲２▼上流触媒２８の温度が下限判定値ＴｃＬ以上、かつ、上限判定値ＴｃＨ以下であるかが判別される。
【０１４５】
下限判定値ＧａＬは、上流触媒２８が安定した状態を維持することのできる下限の吸入空気量Ｇａとして定められた値である。そして、吸入空気量Ｇａが下限判定値ＧａＬを下回っている場合は、上流触媒２８が正常な浄化能力を発揮せず、上流触媒２８が浄化能力を有する状況下でもその下流に未浄化の排気ガスが吹き抜けてくる可能性があると判断できる。また、上限判定値ＧａＨは、上流触媒２８が、未浄化の排気ガスを吹き抜けさせることなく処理することのできる吸入空気量Ｇａの上限値である。従って、吸入空気量Ｇａが上限判定値ＧａＨを超えている場合は、上流触媒２８が浄化能力を有する状況下でもその下流に未浄化の排気ガスが吹き抜けてくる可能性があると判断できる。更に、下限判定値ＴｃＬは、上流触媒２８が、正常な浄化能力を発揮することのできる最低の温度である。従って、上流触媒２８の温度が下限判定値ＴｃＬを下回っている場合も、上流触媒２８の下流には、上流触媒２８が浄化能力を有しているにも関わらず未浄化の排気ガスが吹き抜けてくる可能性があると判断できる。
【０１４６】
つまり、上記ステップ１９８において判定される▲１▼および▲２▼の条件の何れかが成立しない場合は、触媒後空燃比（下流酸素センサ３４の出力Ｖｓ）がリーン判定値Ｖｓ以下、或いはリッチ判定値ＶＲ以上に反転した段階で、上流触媒２８に、未だに酸素吸蔵余力、或いは酸素放出余力が残っている可能性があると判断できる。換言すると、上記▲１▼および▲２▼の条件の何れかが成立しない場合は、上記ステップ１９６において算出された酸素吸蔵容量ＯＳＣが、上流触媒２８が本来有する酸素吸蔵能力に対応した値でない可能性があると判断できる。
【０１４７】
このため、図１３に示すルーチンでは、上記ステップ１９８において、▲１▼および▲２▼の学習条件の少なくとも一方が不成立であると判別された場合は、以後、今回算出された酸素吸蔵容量ＯＳＣを学習値に反映させることなく、今回の処理サイクルが終了される。一方、それらの学習条件▲１▼および▲２▼が何れも成立すると判別された場合は、今回算出された酸素吸蔵容量ＯＳＣを学習値に反映させた後（ステップ２００）、今回の処理サイクルが終了される。
尚、酸素吸蔵容量ＯＳＣを学習値に反映させる手法は、公知の如何なる手法であってもよい。例えば、過去所定回数にわたる有効な酸素吸蔵容量ＯＳＣを単純平均して学習値としても、或いは、今回以前に得られた複数の酸素吸蔵容量ＯＳＣに適当な重み付けを施したうえで、それらの平均を取って学習値としてもよい。
【０１４８】
図１３に示すルーチンによれば、上記ステップ１９６の処理に次いで、上記ステップ１９８以降の処理と並行して、酸素吸蔵容量ＯＳＣの学習値と今回得られたＯＳＣとの差が、判定値ΔＯＳＣ_０より小さいか否かが判別される（ステップ２０２）。
判定値ΔＯＳＣ_０は、今回得られた酸素吸蔵容量ＯＳＣが、ＯＳＣの学習値、つまり上流触媒２８の定常的な酸素吸蔵容量ＯＳＣと同視できるものであるか否かを判断するための値である。
【０１４９】
従って、上記ステップ１９８において、今回得られたＯＳＣと、ＯＳＣの学習値との差が、判定値ΔＯＳＣ_０より小さくないと判別された場合は、今回得られた酸素吸蔵容量ＯＳＣは、異常な値であると判断できる。そして、この場合は、その酸素吸蔵容量ＯＳＣが算出される過程において発せられていた下流酸素センサ３４の出力Ｖｓは、上流触媒２８の下流に吹き抜けてきた空燃比の中途半端な排気ガスの影響を受けている可能性があると判断できる。このため、図１３に示すルーチンでは、上記ステップ１９８の条件が成立しない場合、以後、下流酸素センサ３４の異常判定処理を行うことなく今回の処理サイクルが終了される。
【０１５０】
一方、上記ステップ１９８において、今回得られた酸素吸蔵容量ＯＳＣが、ＯＳＣの学習値と同視できると判断された場合は、その酸素吸蔵容量ＯＳＣが算出される過程において出力されていたセンサ出力Ｖｓは、上流触媒２８下流における空燃比が正しく変化する過程において発せられた正しい値であると判断できる。このため、図１３に示すルーチンでは、この場合、以後、下流酸素センサ３４の異常判定処理が実行される（ステップ２０６）。
本ステップ２０６では、具体的には、上記ステップ１９２において更新された異常判定パラメータ（実施の形態１におけるカウンタＣの計数値、或いは、実施の形態２における最大値Ｖｍａｘまたは最小値Ｖｍｉｎ）が正常値と見なせるか否かが判別される。この処理は、図５におけるステップ１１８、或いは図８におけるステップ１４４と同様の手順で行うことができる。
【０１５１】
次いで、上記ステップ２０４の判別により、異常判定条件の成立が認められたか否かが判別される（ステップ２０６）。
具体的には、カウンタＣの計数値が判定値Ｃ０以上であると認められるか、或いは、最大値Ｖｍａｘが判定値αより小さいか、または最小値Ｖｍｉｎが判定値β大きいかが判別される。
【０１５２】
その結果、異常判定条件の成立が認められないと判別された場合は、下流酸素センサ３４の異常を判定することなく、今回の処理サイクルが終了される。一方、異常判定条件の成立が認められると判別された場合は、下流酸素センサ３４の異常が判定された後（ステップ２０８）、今回の処理サイクルが終了される。
【０１５３】
以上説明した通り、図１３に示すルーチンによれば、アクティブ空燃比制御の実行中に、下流酸素センサ３４が中途半端な空燃比の排気ガスに影響された出力Ｖｓを発するような状況下では、その出力Ｖｓに基づく異常判定の実行を禁止することができる。そして、アクティブ空燃比制御の実行に伴い、触媒後空燃比が適正に大きく変化している場合に限り、下流酸素センサ３４の異常判定を許可することができる。このため、本実施形態の装置によれば、不安定なセンサ出力Ｖｓが発せられる状況下で誤った異常判定がなされるのを有効に防止して、下流酸素センサ３４の異常判定を高精度に行うことが可能である。
【０１５４】
ところで、上述した実施の形態５においては、実施の形態１または２で用いた異常判定の手法に、その判定の実行を禁止する処理を組み合わせることとしているが、その組み合わせの対象は、実施の形態１または２に限定されるものではない。すなわち、異常判定の実行を禁止する処理は、実施の形態３または４の処理と組み合わせることとしてもよい。
【０１５５】
また、上述した実施の形態５においては、ある処理サイクルにおいて算出された酸素吸蔵容量ＯＳＣが、ＯＳＣの学習値から乖離している場合に、そのＯＳＣの算出期間中に発せられたセンサ出力Ｖｓに基づく異常判定の実行を禁止することとしているが、その禁止の判断の基礎は、酸素吸蔵容量ＯＳＣと学習値との乖離に限定されるものではない。すなわち、既述した通り、吸入空気量Ｇａが下限判定値ＧａＬを下回る場合や上限判定値ＧａＨを上回る場合、或いは、上流触媒２８の温度が下限判定値ＴｃＬを下回るような場合には、上流触媒２８の下流に中途半端な空燃比の排気ガスが流出し易い。そして、その場合は、下流酸素センサ３４のセンサ出力Ｖｓが不適正な値となり易く、その出力Ｖｓに基づく異常判定の精度が低下し易い。このため、センサ出力Ｖｓに基づく異常判定の実行可否は、吸入空気量Ｇａや上流触媒２８の温度が適正な値であるか否かに基づいて判断することとしてもよい。
【０１５６】
尚、上述した実施の形態５においては、ＥＣＵ４０が、上記ステップ１９２において酸素吸蔵容量ＯＳＣの更新処理を行うことにより前記第７の発明における「酸素吸蔵容量算出手段」が、上記ステップ２０２の処理を実行することにより前記第７の発明における「判定禁止手段」が、それぞれ実現されている。
また、上述した実施の形態５においては、ＥＣＵ４０が、上記ステップ２００の処理を実行することにより前記第８の発明における「学習値更新手段」が、上記ステップ１９８の処理を実行することにより前記第９の発明における「学習値更新禁止手段」が、それぞれ実現されている。
更に、上述した実施の形態５においては、ＥＣＵ４０に、吸入空気量Ｇａ、或いは上流触媒２８の温度に基づいて異常判定の実行可否を判断させることにより、前記第１０の発明における「判定禁止手段」を実現することができる。
【０１５７】
【発明の効果】
この発明は以上説明したように構成されているので、以下に示すような効果を奏する。
第１の発明によれば、アクティブ空燃比制御を実行することにより、触媒の下流における排気空燃比を的確にリッチ空燃比とリーン空燃比の間で反転させることができる。従って、その制御の実行中に下流酸素センサから発せられるセンサ出力を基礎とすれば、下流酸素センサの異常を正確に判断することができる。
【０１５８】
第２の発明によれば、アクティブ空燃比制御の実行中に、下流酸素センサの出力が、適正な変化速度でその出力を変化させているか否かを見ることで、下流酸素センサの応答性異常を正確に判断することができる。
【０１５９】
第３の発明によれば、アクティブ空燃比制御の実行中に、下流酸素センサの出力が、変化の過程で適正な値に到達しているか否かを見ることで、下流酸素センサの応答性異常および出力縮小異常を正確に判断することができる。
【０１６０】
第４の発明によれば、小さな振幅巾で排気空燃比を振幅させることにより、ドライバビリティやエミッションを悪化させることなく、下流酸素センサの異常を仮判定することができる。そして、異常の発生が仮判定された場合にのみ、大きな振幅で、異常として捕らえるべき劣化が下流酸素センサに生じているのかを確認することができる。このため、本発明によれば、ドライバビリティやエミッションの悪化を最小限に抑制しつつ、下流酸素センサの異常を正確に検出することができる。
【０１６１】
第５の発明によれば、下流酸素センサの異常を検出するためのアクティブ空燃比の実行中に、その下流酸素センサの出力変化を利用しつつ触媒の酸素吸蔵容量を算出することができる。そして、下流酸素センサに異常が生じていないことが確認された状態で、その酸素吸蔵容量に基づいて触媒の劣化状態を判断することができる。このため、本発明によれば、アクティブ空燃比制御の実行を最小限に抑制しつつ、下流酸素センサの異常判定と、触媒の劣化判定とを共に正確に行うことができる。
【０１６２】
第６の発明によれば、下流酸素センサに異常が認められる場合には、触媒の劣化判定の実行を禁止することができる。触媒の劣化判定の基礎となる酸素吸蔵容量は、下流酸素センサのセンサ出力を利用して算出されている。従って、下流酸素センサに異常が生じている場合は、酸素吸蔵容量が正しくない可能性がある。本発明によれば、そのような不正確な酸素吸蔵容量に基づく劣化判定を禁止することで、触媒状態の誤判定を防止することができる。
【０１６３】
第７の発明によれば、下流酸素センサの異常を検出するためのアクティブ空燃比の実行中に、その下流酸素センサの出力変化を利用しつつ触媒の酸素吸蔵容量を算出することができる。そして、算出された酸素吸蔵容量が基準値から大きく乖離している場合には、異常判定の実施を禁止することができる。酸素吸蔵容量の算出値が基準値から大きく乖離しているときは、その算出の期間中に下流酸素センサが一時的に異常な出力を発したと判断できる。そして、その場合、下流酸素センサ自身に異常が生じているよりは、むしろ、そのセンサを取り巻く環境に異常が生じていた可能性が高いと判断できる。本発明によれば、そのような環境下で発せられたセンサ出力に基づいて、下流酸素センサの異常判定が誤って行われるのを有効に防ぐことができる。
【０１６４】
第８の発明によれば、酸素吸蔵容量の学習値を基準値として、順次算出される酸素吸蔵容量が適正な値であるか否かを判断することができる。このため、本発明によれば、酸素吸蔵容量が算出される毎に、その算出期間中におけるセンサ出力が、その時点における下流酸素センサの状態に適合した通常の値であったのか、或いは、異常な環境に起因する異常値であったのかを精度良く判断することができる。
【０１６５】
第９の発明によれば、吸入空気量および触媒温度の少なくとも一方が所定範囲から外れている場合に、つまり、触媒の下流に、中途半端にリッチ或いはリーンなガスが吹き抜けてくる可能性が高い場合に、酸素吸蔵容量の学習値が更新されるのを禁止することができる。このため、本発明によれば、その学習値の精度を十分に高く維持することができる。
【０１６６】
第１０の発明によれば、吸入空気量および触媒温度の少なくとも一方が所定範囲から外れている場合に、つまり、触媒の下流に、中途半端にリッチ或いはリーンなガスが吹き抜けてくる可能性が高い場合に、下流酸素センサの異常判定が行われるのを禁止することができる。このため、本発明によれば、触媒の下流に中途半端なガスが流出してきた際に、そのガスを受けて下流酸素センサの異常状態が誤判定されるのを有効に防ぐことができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１の構成を説明するための図である。
【図２】本発明の実施の形態１の装置が実行するアクティブ空燃比制御の内容を説明するためのタイミングチャートである。
【図３】本発明の実施の形態１において、アクティブ空燃比制御の実行中に、触媒後空燃比の反転に伴って下流酸素センサの出力に生ずる変化の様子を説明するための図である。
【図４】図２に示すタイミングチャートに、下流酸素センサの応答性が劣化した場合に実現されるタイミングチャートを重ねて表した図である。
【図５】本発明の実施の形態１において実行される劣化検出ルーチンのフローチャートである。
【図６】図１に示す構成において下流酸素センサに生ずる劣化のモードを説明するための図である。
【図７】図１に示す構成においてアクティブ空燃比制御の実行中に発せられる下流酸素センサの出力の詳細な波形である。
【図８】本発明の実施の形態２において実行される劣化検出ルーチンのフローチャートである。
【図９】本発明の実施の形態３の装置が実行するアクティブ空燃比制御の内容を説明するためのタイミングチャートである。
【図１０】本発明の実施の形態３において実行される劣化検出ルーチンのフローチャートである。
【図１１】本発明の実施の形態４において実行される劣化検出ルーチンのフローチャートである。
【図１２】本発明の実施の形態５の特徴的動作を説明するためのタイミングチャートである。
【図１３】本発明の実施の形態５において実行されるルーチンのフローチャートである。
【符号の説明】
１０ 内燃機関
１２ 吸気通路
１４ 排気通路
２８ 上流触媒
３０ 下流触媒
３２ 空燃比センサ
３４ 下流酸素センサ
Ｖｓ 下流酸素センサのセンサ出力
ＶＲ リッチ判定値
ＶＬ リーン判定値
Ｖｍａｘ 出力最大値
Ｖｍｉｎ 出力最小値
ＯＳＣ 酸素吸蔵容量[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an abnormality detection device for an oxygen sensor, and more particularly to an abnormality detection device suitable for detecting an abnormality in an oxygen sensor located downstream of a catalyst disposed in an exhaust passage of an internal combustion engine.
[0002]
[Prior art]
BACKGROUND ART Conventionally, as disclosed in, for example, Japanese Patent No. 3134698, a configuration in which an oxygen sensor is provided in an exhaust passage of an internal combustion engine is known. The oxygen sensor is provided for detecting the concentration of oxygen contained in the exhaust gas and detecting the exhaust air-fuel ratio from the oxygen concentration. The oxygen sensor disposed in the exhaust passage is an important element for controlling the air-fuel ratio of the internal combustion engine. For this reason, it is necessary to detect abnormality of the oxygen sensor promptly.
[0003]
More specifically, the conventional internal combustion engine described above includes an oxygen sensor upstream of a catalyst disposed in an exhaust passage. The system forcibly changes the air-fuel ratio of the exhaust gas flowing out of the internal combustion engine, that is, the air-fuel ratio of the exhaust gas reaching upstream of the catalyst, between the rich air-fuel ratio and the lean air-fuel ratio. In this case, an abnormality of the oxygen sensor is detected.
[0004]
In the conventional internal combustion engine, when the exhaust air-fuel ratio upstream of the catalyst is forcibly changed, if the oxygen sensor is normal, the output of the sensor indicates a change following the change in the exhaust air-fuel ratio. Therefore, in this system, the oxygen sensor operates normally by forcibly changing the exhaust air-fuel ratio upstream of the catalyst and checking whether an appropriate change corresponding to the change occurs in the output of the oxygen sensor. It is possible to accurately determine whether or not they are performing.
[0005]
[Patent Document 1]
Japanese Patent No. 3134698
[Patent Document 2]
JP 2001-329832 A
[Patent Document 3]
Japanese Patent Publication No. 7-42884
[0006]
[Problems to be solved by the invention]
Incidentally, an oxygen sensor may be arranged in the exhaust passage of the internal combustion engine also on the downstream side of the catalyst. Specifically, for example, in an exhaust passage of an internal combustion engine, an upstream catalyst for improving emission characteristics at the time of starting and warming-up and a downstream catalyst for securing emission characteristics during normal operation are connected in series. May be placed in In such a configuration, an oxygen sensor may be arranged upstream of the downstream catalyst, that is, downstream of the upstream catalyst, in order to accurately control the air-fuel ratio of the exhaust gas flowing into the downstream catalyst. Further, even when there is no downstream catalyst, the output characteristics of the upstream oxygen sensor vary depending on the exhaust gas component, and accurate detection of the air-fuel ratio may not be performed by the upstream oxygen sensor. In such a case, an oxygen sensor may be disposed downstream of the catalyst in order to control the air-fuel ratio with high accuracy, and the air-fuel ratio may be feedback-controlled using the two sensors. Hereinafter, such an oxygen sensor is referred to as a “downstream oxygen sensor”.
[0007]
The exhaust air-fuel ratio downstream of the catalyst is substantially the stoichiometric air-fuel ratio during the period when the catalyst exerts a purifying action, regardless of the value of the exhaust air-fuel ratio upstream of the catalyst. In this case, even if the downstream oxygen sensor is normal, the sensor output does not show a change following the exhaust air-fuel ratio upstream of the catalyst. For this reason, the abnormality detection method used by the above-described conventional system cannot accurately detect the abnormality of the downstream oxygen sensor disposed downstream of the catalyst.
[0008]
The present invention has been made in order to solve the above-described problems, and has as its object to provide an oxygen sensor abnormality detection device capable of accurately detecting an abnormality of a downstream oxygen sensor disposed downstream of a catalyst. And
[0009]
[Means for Solving the Problems]
A first invention is a device for detecting an abnormality of a downstream oxygen sensor located downstream of a catalyst disposed in an exhaust passage of an internal combustion engine, in order to achieve the above object,
Exhaust air-fuel ratio control means for controlling the exhaust air-fuel ratio upstream of the catalyst,
In response to the output of the downstream oxygen sensor changing from the rich output to the lean output, the exhaust air-fuel ratio upstream of the catalyst is changed from the lean air-fuel ratio to the rich air-fuel ratio, and the output of the downstream oxygen sensor is changed from the lean output to the rich output. Active air-fuel ratio control means for executing active air-fuel ratio control for changing the exhaust air-fuel ratio upstream of the catalyst from a rich air-fuel ratio to a lean air-fuel ratio in response to a change in output,
Abnormality determining means for determining abnormality of the downstream oxygen sensor based on a sensor output issued from the downstream oxygen sensor during execution of the active air-fuel ratio control;
It is characterized by having.
[0010]
According to a second aspect, in the first aspect, the abnormality determining means determines an abnormality of the downstream oxygen sensor based on a change speed of an output of the downstream oxygen sensor.
[0011]
In a third aspect based on the first aspect, the abnormality determining means determines an abnormality of the downstream oxygen sensor based on a maximum value or a minimum value of the output of the downstream oxygen sensor.
[0012]
Further, a fourth invention is the invention according to any one of the first to third inventions,
Air-fuel ratio amplitude width changing means for changing the amplitude width of the air-fuel ratio generated in the exhaust air-fuel ratio upstream of the catalyst during the execution of the active air-fuel ratio control,
The abnormality determining means includes:
A small-amplitude active control command means for executing the active air-fuel ratio control with a first amplitude width;
First abnormality determination command means for causing the abnormality determination means to perform abnormality determination with respect to execution of the active air-fuel ratio control at the first amplitude width;
When it is determined that the downstream oxygen sensor is abnormal with respect to the execution of the active air-fuel ratio control at the first amplitude width, the active air-fuel ratio control is performed at a second amplitude width larger than the first amplitude width. Large-amplitude active control command means for executing fuel ratio control;
A second abnormality determination command unit that causes the abnormality determination unit to perform abnormality determination with respect to the execution of the active air-fuel ratio control at the second amplitude width;
An abnormality occurrence determining means for determining the abnormality of the downstream oxygen sensor definitely only when the abnormality of the downstream oxygen sensor is determined with respect to the execution of the active air-fuel ratio control at the second amplitude width. It is characterized by the following.
[0013]
According to a fifth aspect of the present invention, in any one of the first to fourth aspects,
During the execution of the active air-fuel ratio control, a process in which the sensor output changes from a rich output to a lean output in parallel with the abnormality determination means taking in the sensor output generated from the downstream oxygen sensor, or In the process where the output changes from the lean output to the rich output, oxygen storage capacity calculation means for calculating the oxygen storage capacity of the catalyst,
A deterioration state determination unit that determines a deterioration state of the catalyst based on the oxygen storage capacity when no abnormality of the downstream oxygen sensor is recognized by the abnormality determination unit;
It is characterized by having.
[0014]
In a sixth aspect based on the fifth aspect, a deterioration determination prohibiting means for prohibiting a deterioration determination of the catalyst based on the oxygen storage capacity when the abnormality determining means detects an abnormality in the downstream oxygen sensor. It is characterized by having.
[0015]
Further, a seventh invention is the liquid crystal display device according to any one of the first to sixth inventions,
During the execution of the active air-fuel ratio control, a process in which the sensor output of the downstream oxygen sensor changes from a rich output to a lean output in parallel with the abnormality determination unit taking in the sensor output emitted from the downstream oxygen sensor, Alternatively, in a process in which the sensor output changes from the lean output to the rich output, oxygen storage capacity calculation means for calculating the oxygen storage capacity of the catalyst,
When the difference between the oxygen storage capacity and the reference value is equal to or larger than a determination value, a determination prohibition unit that prohibits the determination by the abnormality determination unit based on the sensor output issued during the calculation period of the oxygen storage capacity,
It is characterized by having.
[0016]
In an eighth aspect based on the seventh aspect,
Each time the oxygen storage capacity is calculated, a learning value updating unit that updates a learning value of the oxygen storage capacity so that the value is reflected,
The reference value is a learned value of the oxygen storage capacity.
[0017]
In a ninth aspect based on the eighth aspect, a learning value update prohibiting means for prohibiting updating of the learning value of the oxygen storage capacity when at least one of the intake air amount and the catalyst temperature is out of a predetermined range. It is characterized by having.
[0018]
Further, in a tenth aspect based on any of the first to sixth aspects, when at least one of the intake air amount and the catalyst temperature is out of a predetermined range, the determination by the abnormality determining means is prohibited. Means is provided.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.
[0020]
Embodiment 1 FIG.
[Description of Configuration of First Embodiment]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. The configuration shown in FIG. 1 includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. An air filter 16 is arranged at an end of the intake passage 12. Downstream of the air filter 16, an air flow meter 18 for detecting the amount of air flowing through the intake passage 12, that is, the amount of intake air Ga is arranged.
[0021]
A throttle valve 20 is provided downstream of the air flow meter 18. Near the throttle valve 20, a throttle sensor 22 for detecting the throttle opening TA and an idle switch 24 that is turned on when the throttle valve 20 is fully closed are arranged. The intake passage 12 is further provided with a fuel injection valve 26 for injecting fuel to an intake port of the internal combustion engine 10.
[0022]
In the exhaust passage 14, an upstream catalyst 28 and a downstream catalyst 30 are arranged in series. These catalysts can exhibit a function of purifying exhaust gas by reaching a predetermined activation temperature after the internal combustion engine 10 is started. The main purpose of the upstream catalyst 28 is to reduce exhaust emissions immediately after the start of the internal combustion engine 10 and during the warm-up process. The main purpose of the downstream catalyst 30 is to improve exhaust emissions during normal operation.
[0023]
The upstream catalyst 28 and the downstream catalyst 30 each have an oxygen storage capacity (OSC: O ₂ Storage Capacitor) and can store oxygen within its capacity range. When unburned components such as HC and CO are contained in the exhaust gas, these catalysts 28 and 30 oxidize the unburned components by releasing the occluded oxygen. If the gas contains a large amount of oxygen, NOx, or the like, excess oxygen can be stored, and the catalyst atmosphere can be maintained at the stoichiometric air-fuel ratio. The upstream catalyst 28 and the downstream catalyst 30 purify the exhaust gas according to the above principle.
[0024]
An air-fuel ratio sensor 32 is arranged upstream of the upstream catalyst 28. The air-fuel ratio sensor 32 is a sensor that outputs an output according to the oxygen concentration in the exhaust gas. The oxygen concentration in the exhaust gas has a correlation with the exhaust air-fuel ratio. Therefore, the air-fuel ratio sensor 32 can detect the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 28, that is, the exhaust gas immediately after being discharged from the internal combustion engine 10.
[0025]
A downstream oxygen sensor 34 is arranged downstream of the upstream catalyst 28, that is, upstream of the downstream catalyst 30. The downstream oxygen sensor 34 is a sensor that largely changes its output depending on whether or not oxygen exists in the exhaust gas. Oxygen does not remain in the exhaust gas when the exhaust air-fuel ratio is rich. On the other hand, when the exhaust air-fuel ratio is lean, oxygen in the exhaust gas remains. Therefore, the downstream oxygen sensor 34 can accurately detect whether the exhaust gas flowing out of the upstream catalyst 28 is rich or lean.
[0026]
The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 40. The ECU 40 is supplied with sensor outputs from the various sensors described above. Further, the ECU 40 can calculate a fuel amount to be supplied to the internal combustion engine 10 based on the sensor outputs, and control the fuel injection valve 26 so that the fuel amount is injected.
[0027]
The system according to the present embodiment executes control of the exhaust air-fuel ratio, that is, control of the fuel injection amount, based on the output of the air-fuel ratio sensor 32 and the output of the downstream oxygen sensor 34. Therefore, it is desirable that abnormality of the air-fuel ratio sensor 32 and the downstream oxygen sensor 34 can be detected promptly.
[0028]
Regarding the abnormality of the air-fuel ratio sensor 32, after forcibly changing the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 10, it is determined whether or not a change following the change appears in the output of the air-fuel ratio sensor 32. You can judge it accurately by looking. In other words, the ECU 40 determines the fuel injection amount so that the air-fuel ratio A / F varies with respect to the intake air amount Ga detected by the air flow meter 18, and changes the air-fuel ratio sensor 32 according to the variation. It can be determined whether or not the air-fuel ratio sensor 32 is normal depending on whether or not it appears in the output.
[0029]
However, the abnormality of the downstream oxygen sensor 34 cannot be detected by the above method. That is, even if the fuel injection amount is controlled with respect to the intake air amount Ga as described above, and as a result, the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 28 is forcibly changed, What is guided is the exhaust gas that has passed through the upstream catalyst 28. Exhaust gas after passing through the upstream catalyst 28 is maintained at the stoichiometric air-fuel ratio as long as the upstream catalyst 28 exhibits a purifying ability. Therefore, depending on whether or not a correlation is found between the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 10 and the sensor output of the downstream oxygen sensor 34, it is determined whether or not the downstream oxygen sensor 34 is normal. I can't judge. Therefore, in the present embodiment, when the abnormality detection of the downstream oxygen sensor 34 is required, the active air-fuel ratio control described below is executed to forcibly change the exhaust air-fuel ratio around the downstream oxygen sensor 34. It was decided to.
[0030]
[Explanation of Principle of Abnormal Detection of Downstream Oxygen Sensor]
FIG. 2 is a timing chart for explaining the contents of the active air-fuel ratio control executed by the ECU 40. More specifically, FIG. 2A shows a waveform indicating whether the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 28 (hereinafter, referred to as “the air-fuel ratio before the catalyst”) is rich or lean. . FIG. 2B shows a sensor output waveform of the downstream oxygen sensor 34. FIG. 2C shows a change in the air-fuel ratio of the exhaust gas flowing out of the upstream catalyst 28 and guided around the downstream oxygen sensor 34 (hereinafter, referred to as a post-catalyst air-fuel ratio).
[0031]
During execution of the active air-fuel ratio control, first, the air-fuel ratio before the catalyst is maintained at a predetermined rich air-fuel ratio or lean air-fuel ratio. FIG. 2A shows a state in which the pre-catalyst air-fuel ratio is maintained at the rich air-fuel ratio before time t1. When the pre-catalyst air-fuel ratio is maintained at the rich air-fuel ratio, the upstream catalyst 28 releases stored oxygen to oxidize unburned components (HC, CO) in the exhaust gas. While the stored oxygen remains in the upstream catalyst 28, the exhaust gas purified to the stoichiometric air-fuel ratio flows downstream thereof. Therefore, during that time, the post-catalyst air-fuel ratio is maintained substantially at the stoichiometric air-fuel ratio.
[0032]
As a result of maintaining the pre-catalyst air-fuel ratio to be rich, when all the stored oxygen in the upstream catalyst 28 is consumed, then rich exhaust gas containing unburned components starts to flow downstream of the upstream catalyst 28. FIG. 2C shows a state in which all the stored oxygen in the upstream catalyst 28 has been consumed immediately before the time t1, and as a result, the post-catalyst air-fuel ratio has changed from the stoichiometric air-fuel ratio to the rich air-fuel ratio.
[0033]
When the air-fuel ratio after the catalyst changes from the stoichiometric air-fuel ratio to the rich air-fuel ratio, the sensor output of the downstream oxygen sensor 34 changes from the lean output to the rich output as shown in FIG. The ECU 40 uses the lean determination value VL and the rich determination value VR to determine whether the sensor output is a rich output or a lean output. More specifically, when the output of the downstream oxygen sensor 34 exceeds the rich determination value VR, the ECU 40 determines that the sensor output has changed to a rich output, while the output of the downstream oxygen sensor 34 has a lean determination value. If the output falls below VL, it is determined that the sensor output has changed to a lean output. Time t1 shown in FIG. 2 is a time at which it is determined that the output of the downstream oxygen sensor 34 has changed to a rich output according to the above criteria.
[0034]
When the ECU 40 determines that the output of the downstream oxygen sensor 34 has changed to the rich output during the execution of the active air-fuel ratio control, the ECU 40 determines that the stored oxygen of the upstream catalyst 28 has been used up at that time. After that, the ECU 40 changes the ratio of the fuel injection amount to the intake air amount Ga so that the pre-catalyst air-fuel ratio reverses lean. As a result, after time t1, the pre-catalyst air-fuel ratio is inverted from rich to lean as shown in FIG.
[0035]
The period from when the pre-catalyst air-fuel ratio is inverted from rich to lean until the exhaust gas affected by the inversion flows downstream of the upstream catalyst 28 (hereinafter, referred to as “gas transport delay period”) is Thus, the air-fuel ratio after the catalyst is maintained rich. After the elapse of the gas transport delay period (after time t2 in FIG. 2), the air-fuel ratio flows into the upstream catalyst 28 after the air-fuel ratio is reversed to lean, and the exhaust gas treated inside the upstream catalyst 28 Spills downstream.
[0036]
At time t1, the upstream catalyst 28 has released all stored oxygen. In this state, when lean exhaust gas with an air-fuel ratio flows into the upstream catalyst 28, the upstream catalyst 28 stores excess oxygen in the exhaust gas to maintain the catalyst atmosphere at the stoichiometric air-fuel ratio and purify the exhaust gas. . For this reason, the air-fuel ratio of the exhaust gas flowing downstream of the upstream catalyst 28 after the elapse of the gas transport delay period, that is, after the time t2 shown in FIG. 2, becomes a value close to the stoichiometric air-fuel ratio again. .
[0037]
During execution of the active air-fuel ratio control, the air-fuel ratio before the catalyst is maintained lean thereafter. During the period in which the pre-catalyst air-fuel ratio is maintained lean, the upstream catalyst 28 continues to store oxygen until it has completely stored oxygen. Then, when the oxygen is fully stored in the upstream catalyst 28, the oxygen-lean exhaust gas begins to flow downstream of the upstream catalyst 28.
[0038]
At time t3 shown in FIG. 2, the time at which lean exhaust gas starts to flow downstream of the upstream catalyst 28 is shown. At time t4, the output of the downstream oxygen sensor 34 falls below the lean determination value VL. This is the time when the exhaust gas was recognized to be lean. The period during which the post-catalyst air-fuel ratio is maintained in the vicinity of the stoichiometric air-fuel ratio is a period during which the upstream catalyst 28 properly exhibits its purification ability, and its length corresponds to the oxygen storage capacity of the upstream catalyst 28.
[0039]
Thereafter, as long as the execution of the active control is continued, the above-described process, that is, the process of forcibly inverting the air-fuel ratio before the catalyst in response to the output inversion of the downstream oxygen sensor 34 is repeatedly executed. As a result, during execution of the active control, the air-fuel ratio after the catalyst periodically becomes the rich air-fuel ratio and the lean air-fuel ratio as shown in FIG. Under such circumstances, if the downstream oxygen sensor 34 is normal, its output repeats a periodic change between a rich output and a lean output, as shown in FIG. Therefore, according to the system of the present embodiment, it is determined whether or not the output of the downstream oxygen sensor 34 normally outputs the rich output and the lean output alternately with the execution of the active air-fuel ratio control. An abnormality of the oxygen sensor 34 can be accurately detected.
[0040]
[Effect of responsiveness of downstream oxygen sensor]
Next, how the responsiveness of the downstream oxygen sensor 34 affects the sensor output during execution of the active air-fuel ratio control will be described.
FIG. 3 is a diagram for explaining a state of a change occurring in the output of the downstream oxygen sensor 34 due to the inversion of the air-fuel ratio after the catalyst during the execution of the active air-fuel ratio control. In FIG. 3, the waveform shown by the solid line is a waveform when the downstream oxygen sensor 34 shows normal response, while the waveform shown by the broken line is the output waveform of the downstream oxygen sensor 34 whose response has deteriorated.
[0041]
As shown in FIG. 3, the output of the downstream oxygen sensor 34 during execution of the active air-fuel ratio control has a gradual rise and fall at the time of inversion due to deterioration of its response. Therefore, in the system according to the present embodiment, the response of the downstream oxygen sensor 34 can be determined by observing the rising or falling speed of the downstream oxygen sensor 34 generated during execution of the active air-fuel ratio control.
[0042]
FIG. 4 is a timing chart of the timing chart shown in FIG. 2 (a timing chart realized in an environment in which the downstream oxygen sensor 34 shows a normal response) when the response of the downstream oxygen sensor 34 is deteriorated. It is the figure which expressed the chart in piles. The timing chart shown by the solid line in FIG. 4 is a chart at the time of normality, while the chart shown by the broken line is a chart at the time of responsiveness deterioration.
[0043]
In FIG. 4, before time T1, the air-fuel ratio before the catalyst is maintained rich. The time T1 is a time when the air-fuel ratio after the catalyst changes from the stoichiometric air-fuel ratio to the rich air-fuel ratio. In the process in which the post-catalyst air-fuel ratio changes in this manner, the output of the downstream oxygen sensor 34 changes at a speed according to its own responsiveness. Therefore, as shown in FIG. 2B, when the response is normal, the output of the downstream oxygen sensor 34 exceeds the rich determination value VR at time T1, but the response deteriorates. If there is, the output of the downstream oxygen sensor 34 is maintained at or below the rich determination value VR until time T2, which is later than time T1.
[0044]
As described above, the ECU 40 detects the inversion of the air-fuel ratio after the catalyst based on the output of the downstream oxygen sensor 34, and aims to invert the air-fuel ratio before the catalyst. Accordingly, if the time when the output of the downstream oxygen sensor 34 exceeds the rich determination value VR is delayed from T1 to T2, a delay occurs when the air-fuel ratio before the catalyst is reversed from rich to lean as shown in FIG. . The post-catalyst air-fuel ratio changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio after the gas transport delay period has elapsed after the pre-catalyst air-fuel ratio has been reversed. Therefore, when the responsiveness of the downstream oxygen sensor 34 is degraded, as shown in FIG. 4C, the period during which the air-fuel ratio after the catalyst is maintained rich is lower than when the responsiveness is normal. As a result, the time becomes longer by the time caused by the response delay of the sensor.
[0045]
The period from when the pre-catalyst air-fuel ratio is reversed from rich to lean and before the lean exhaust gas with the air-fuel ratio flows out downstream of the upstream catalyst 28, as described above, depends on the oxygen storage capacity of the upstream catalyst 28. Determined accordingly. Therefore, the period is substantially constant without being affected by the response of the downstream oxygen sensor 34. For this reason, the time lag due to the response delay of the downstream oxygen sensor 34 (the lag between T1 and T2) is caused by the lag in the time when the lean exhaust gas with the air-fuel ratio starts to flow downstream of the upstream catalyst 28 (the time in FIG. 4). (Shift between T3 and T4).
[0046]
When the downstream oxygen sensor 34 shows appropriate responsiveness, the output of the downstream oxygen sensor 34 becomes lower than the lean determination value VL at a point in time after the time T3 when the time due to the normal responsiveness has elapsed. On the other hand, when the response is deteriorated, after the time T4, the downstream oxygen sensor 34 is turned off until a time equal to the sum of the time caused by the normal response and the time caused by the sensor response delay elapses. The output is maintained at or above the lean determination value VL. Therefore, comparing the case where the downstream oxygen sensor 34 shows normal responsiveness and the case where the responsiveness is deteriorated, the time when the air-fuel ratio before the catalyst is switched from lean to rich after the time T3 or T4 is compared. Is a difference between the time T1 and the time T2 (the time caused by the initial sensor response delay) and the time obtained by adding the time caused by the sensor response delay. Thereafter, as long as the active air-fuel ratio control is continued, if the responsiveness of the downstream oxygen sensor 34 is degraded, the time lag due to the sensor response delay is changed every time the sensor output is inverted. Are superimposed on the inversion cycle of.
[0047]
As described above, the reversal operation during the execution of the active air-fuel ratio control is not completely the same between when the downstream oxygen sensor 34 shows normal responsiveness and when the responsiveness is deteriorated. These can be distinguished based on, for example, a change speed when the output of the downstream oxygen sensor 34 changes from an output corresponding to the stoichiometric air-fuel ratio to a rich output or a lean output. Therefore, in the present embodiment, when the output of the downstream oxygen sensor 34 changes with execution of the active air-fuel ratio control, the response speed of the downstream oxygen sensor 34 is checked by checking whether or not the change speed is normal. It is determined whether or not is deteriorated.
[0048]
FIG. 5 shows a flowchart of a control routine executed by the ECU 40 in the present embodiment to realize the above functions.
In the routine shown in FIG. 5, first, it is determined whether the execution condition of the active air-fuel ratio control is satisfied (step 100).
As a result, if it is determined that the above-mentioned execution condition is not satisfied, a command to stop the active air-fuel ratio control is issued (step 102), and then the current processing cycle is ended.
[0049]
On the other hand, when it is determined that the above-mentioned execution condition is satisfied, an execution command of the active air-fuel ratio control is issued (step 104).
When the execution command is issued by the processing of step 104, the ECU 40 starts controlling the fuel injection amount and the like so as to realize the above-described active air-fuel ratio control.
[0050]
In the routine shown in FIG. 5, next, from the previous processing cycle to the current processing cycle, whether the output Vs of the downstream oxygen sensor 34 has changed from a value below the lean determination value VL to a value equal to or greater than the determination value VL. It is determined whether or not it is (step 106).
[0051]
As a result, when it is determined that the sensor output Vs has changed to the lean determination value VL or more, it can be determined that the output Vs of the downstream oxygen sensor 34 has started to change from the lean output to the rich output. . In this case, the counter C is incremented in order to count the required change time of the sensor output Vs (step 108).
[0052]
Next, it is determined whether or not the output Vs of the downstream oxygen sensor 34 has reached the rich determination value VR (Step 110).
Until it is determined in this step 110 that Vs ≧ VR, the processing of step 108 is repeatedly executed. Then, when it is determined that Vs ≧ VR holds, the process of step 118 described later is executed. According to the above processing, in the process where the output Vs of the downstream oxygen sensor 34 changes from the lean output to the rich output, the time required for the value Vs to change from the lean determination value VL to the rich determination value VR is determined by the counter C. Can be counted.
[0053]
In the routine shown in FIG. 5, in step 106, it is determined that the output Vs of the downstream oxygen sensor 34 has not changed from a value lower than VL to a value equal to or higher than VL from the previous processing cycle to the current processing cycle. Then, from the previous processing cycle to the current processing cycle, it is determined whether or not the sensor output Vs has changed from a value exceeding the rich determination value VR to a value equal to or less than the rich determination value VR. (Step 112).
[0054]
As a result, when it is determined that the sensor output Vs has changed below the rich determination value VR, it can be determined that the output Vs of the downstream oxygen sensor 34 has started to change from the rich output to the lean output. . In this case, next, the counter C is incremented to count the required change time of the sensor output Vs (step 114).
[0055]
Next, it is determined whether or not the output Vs of the downstream oxygen sensor 34 has reached the lean determination value VL (step 116).
Until it is determined in this step 116 that Vs ≦ VL, the processing of step 114 is repeatedly executed. Then, when it is determined that Vs ≦ VL is satisfied, the process of step 118 described later is executed. According to the above processing, in the process where the output Vs of the downstream oxygen sensor 34 changes from the rich output to the lean output, the time required for the value Vs to change from the rich determination value VR to the lean determination value VL is determined by the counter C. Can be counted.
[0056]
When the processing in step 110 or the processing in step 116 ends, it is next determined whether or not the count value of the counter C is equal to or greater than the determination value C0 (step 118).
The determination value C0 changes when the downstream oxygen sensor 34 shows normal response, when the sensor output Vs changes from the lean determination value VL to the rich determination value VR, or when the sensor output Vs changes from the rich determination value VR to the lean determination value VL. This is equivalent to a time obtained by adding a margin to the time required for the operation. Therefore, if it is determined in this step 118 that C ≧ C0 is satisfied, it can be determined that the downstream oxygen sensor 34 does not show normal responsiveness. On the other hand, if it is determined that the count value C is not equal to or greater than the determination value C0, it can be determined that the downstream oxygen sensor 34 shows normal responsiveness.
[0057]
In the routine shown in FIG. 5, if it is determined in step 118 that C ≧ C0 is satisfied, then it is determined that the responsiveness of the downstream oxygen sensor 34 has deteriorated (step 120).
On the other hand, if it is determined in step 118 that C ≧ C0 is not satisfied, it is determined that the downstream oxygen sensor 34 is normal (step 122).
[0058]
As described above, according to the system of the present embodiment, by executing the active air-fuel ratio control, the post-catalyst air-fuel ratio can be periodically changed between rich and lean. Then, it is accurately determined whether or not the downstream oxygen sensor 34 shows normal responsiveness based on whether or not the change occurring in the sensor output Vs due to the change in the air-fuel ratio has a regular change speed. can do.
[0059]
In the first embodiment, the ECU 40 controls the fuel injection amount so that the pre-catalyst air-fuel ratio becomes the desired air-fuel ratio, so that the “exhaust air-fuel ratio control means” in the first invention is described above. The “active air-fuel ratio control means” in the first invention controls the fuel injection amount to execute the active air-fuel ratio control, and the “active air-fuel ratio control means” in the first invention executes the processing in steps 106 to 122 to “ Abnormality determining means "are each realized.
[0060]
Embodiment 2 FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.
The device of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 8 described later in the system shown in FIG.
[0061]
The above-described device of the first embodiment detects deterioration of the responsiveness of the downstream oxygen sensor 34 based on the sensor output Vs of the downstream oxygen sensor 34 during execution of the active air-fuel ratio control. By the way, the downstream oxygen sensor 34 may be deteriorated not only in response but also in its output value.
[0062]
FIG. 6 is a diagram for explaining a mode of deterioration that occurs in the downstream oxygen sensor 34. The waveforms indicated by the solid line and the broken line in FIG. 6 indicate the sensors generated by the normal downstream oxygen sensor 34 or the downstream oxygen sensor 34 whose responsiveness has deteriorated during the execution of the active air-fuel ratio control, similarly to those shown in FIG. It is a waveform of the output Vs. The waveform shown by the dashed line in FIG. 6 is the output waveform of the downstream oxygen sensor 34 (hereinafter, referred to as “output reduction sensor”) that has been deteriorated so as to reduce the output value on the rich side.
[0063]
If the output characteristics of the downstream oxygen sensor 34 degrade to such an extent that the output Vs does not exceed the rich determination value VR, the system of the present embodiment cannot maintain normal air-fuel ratio control. Therefore, it is desirable that the degradation that reduces the output of the downstream oxygen sensor 34 can be detected with high accuracy, similarly to the degradation that reduces the response. On the other hand, the output reduction sensor may exhibit characteristics similar to those of a normal sensor with respect to responsiveness. Therefore, it is not possible to detect the deterioration of the output reduction sensor by the method used in the first embodiment, that is, the method of detecting the deterioration by focusing on the change speed of the sensor output Vs.
[0064]
By the way, the output Vs of the downstream oxygen sensor 34 during the execution of the active air-fuel ratio control changes strictly as shown in FIG. 7 (provided that the response is good). That is, the output Vs of the downstream oxygen sensor 34 shows the highest value during the period when the actual post-catalyst air-fuel ratio is rich after the rich exhaust gas starts flowing downstream of the upstream catalyst 28. Then, when the post-catalyst air-fuel ratio becomes the stoichiometric air-fuel ratio due to the purifying action of the upstream catalyst 28, the sensor output Vs becomes a value slightly lower than the rich output Vs. Further, the output Vs of the downstream oxygen sensor 34 shows the smallest value during a period in which the actual post-catalyst air-fuel ratio is lean after the lean exhaust gas starts flowing downstream of the upstream catalyst 28. Thereafter, when the post-catalyst air-fuel ratio becomes the stoichiometric air-fuel ratio due to the purifying action of the upstream catalyst 28, the sensor output Vs becomes a value slightly higher than the lean output Vs.
[0065]
The output change shown in FIG. 7 is based on the premise that the value of the air-fuel ratio after the catalyst is promptly reflected on the sensor output Vs. On the other hand, when the response of the downstream oxygen sensor 34 is poor and the value of the air-fuel ratio after the catalyst is not immediately reflected in the sensor output Vs, the waveform of the sensor output Vs differs from the waveform shown in FIG. It will be.
[0066]
In other words, when the response of the downstream oxygen sensor 34 is degraded, after the rich exhaust gas starts flowing downstream of the upstream catalyst 28, the sensor output during the period when the post-catalyst air-fuel ratio is actually rich A situation occurs where Vs cannot reach the maximum value. Similarly, in such a case, after the lean exhaust gas starts to flow downstream of the upstream catalyst 28, the sensor output Vs decreases to the minimum value during a period in which the air-fuel ratio after the catalyst is actually lean. The situation that cannot be obtained occurs. If the post-catalyst air-fuel ratio changes to the stoichiometric air-fuel ratio before the sensor output Vs reaches the maximum value, the sensor output Vs converges to a value corresponding to the stoichiometric air-fuel ratio without reaching the maximum value. Also, if the post-catalyst air-fuel ratio changes to the stoichiometric air-fuel ratio before the sensor output Vs reaches the minimum value, the sensor output Vs converges to a value corresponding to the stoichiometric air-fuel ratio without reaching the minimum value.
[0067]
For the above-described reason, the maximum value of the output Vs of the downstream oxygen sensor 34 becomes smaller as the response of the sensor deteriorates. Further, the minimum value of the output Vs of the downstream oxygen sensor 34 increases as the response of the sensor deteriorates. Therefore, in the system of the present embodiment, whether the response of the downstream oxygen sensor 34 has deteriorated is determined by checking whether the maximum value of the sensor output Vs is a normal value or the minimum value of the sensor output Vs is a normal value. Can also be determined.
[0068]
The above-described deterioration that reduces the sensor output Vs can also be determined by checking whether or not the maximum value of the output Vs of the downstream oxygen sensor 34 is a normal value. Therefore, in the system of the present embodiment, the execution of the active air-fuel ratio control determines whether or not the maximum value or the minimum value of the sensor output Vs reaches the normal value. Diagnosis of both responsiveness degradation and output reduction degradation is made at the same time.
[0069]
FIG. 8 shows a flowchart of a control routine executed by the ECU 40 in the present embodiment to realize the above functions. In FIG. 8, steps that are the same as the steps shown in FIG. 5 are given the same reference numerals, and descriptions thereof will be omitted or simplified.
[0070]
In the routine shown in FIG. 8, when execution of the active air-fuel ratio control is instructed by the process of step 104, it is then determined whether or not the output Vs of the downstream oxygen sensor 34 is equal to or greater than the rich determination value VR (see FIG. 8). Step 130).
[0071]
As a result, when it is determined that the sensor output Vs is equal to or greater than the rich determination value VR, it can be determined that the downstream oxygen sensor 34 is generating a rich output. In this case, first, the output maximum value Vmax is cleared (step 131).
Next, it is determined whether or not the current sensor output Vs is larger than the maximum output value Vmax (step 132).
As a result, when it is determined that Vs> Vmax holds, the sensor output Vs is stored as the output maximum value Vmax (step 134).
On the other hand, if it is determined that Vs> Vmax is not satisfied, the process of step 134 is jumped.
[0072]
In the routine shown in FIG. 8, it is next determined whether or not the sensor output Vs has dropped below the lean determination value VL (step 136).
If it is determined in step 136 that Vs ≦ VL is not established, the processes in and after step 132 are executed again. Then, the processing of steps 132 and 134 is repeated until it is determined in this step 136 that Vs ≦ VL is satisfied.
[0073]
If it is determined in step 136 that Vs ≦ VL, it can be determined that the sensor output Vs has changed from a rich output to a lean output. That is, in this case, it can be determined that the maximum value Vmax of the sensor output Vs has been determined at the present time. In this case, in the routine shown in FIG. 8, the process of step 144 described later is executed.
[0074]
In the routine shown in FIG. 8, when it is determined in step 130 that the output Vs of the downstream oxygen sensor 34 is not equal to or greater than the rich determination value VR, it is determined whether the sensor output Vs is equal to or less than the lean determination value VL. (Step 138).
[0075]
As a result, when it is determined that the sensor output Vs is equal to or less than the lean determination value VL, it can be determined that the downstream oxygen sensor 34 is generating a lean output. In this case, first, the output minimum value Vmin is cleared (step 139).
Next, it is determined whether or not the current sensor output Vs is smaller than the minimum output value Vmin (step 140).
As a result, if it is determined that Vs <Vmin holds, the sensor output Vs is stored as the minimum output value Vmin (step 142).
On the other hand, if it is determined that Vs <Vmin is not established, the process of step 142 is jumped.
[0076]
In the routine shown in FIG. 8, it is next determined whether or not the sensor output Vs has risen above the rich determination value VR (step 143).
If it is determined in step 143 that Vs ≧ VR is not satisfied, the processing in step 140 and subsequent steps is executed again. Then, the processing of steps 140 and 142 is repeated until it is determined in this step 143 that Vs ≧ VR is satisfied.
[0077]
If it is determined in step 143 that Vs ≧ VR holds, it can be determined that the sensor output Vs has changed from a lean output to a rich output. That is, in this case, it can be determined that the minimum value Vmin of the sensor output Vs has been determined at this time. In this case, in the routine shown in FIG. 8, the process of step 144 described later is executed.
[0078]
When the condition of the step 136 or the condition of the step 143 is satisfied, it is next determined whether or not the output maximum value Vmax is smaller than the judgment value α and whether or not the output minimum value Vmin is larger than the judgment value β. (Step 144).
The determination value α is a value obtained by subtracting a margin from the maximum value reached by the sensor output Vs when the downstream oxygen sensor 34 shows normal output characteristics (responsivity and output value). Therefore, when it is determined in this step 144 that Vmax <α is satisfied, it can be determined that the downstream oxygen sensor 34 does not show the normal output characteristics. The determination value β is a value obtained by adding a margin to the maximum value reached by the sensor output Vs when the downstream oxygen sensor 34 has a normal output characteristic (response and output value). Therefore, if it is determined in this step 144 that Vmax> β is satisfied, it can be determined that the downstream oxygen sensor 34 does not show the normal output characteristics. On the other hand, if it is determined in step 144 that neither of these two conditions is satisfied, it can be determined that the downstream oxygen sensor 34 has a normal output characteristic.
[0079]
In the routine shown in FIG. 8, if it is determined in step 144 that either Vmax <α or Vmax> β is satisfied, it is determined that the downstream oxygen sensor 34 has deteriorated (responsiveness deterioration or output reduction deterioration). (Step 146).
On the other hand, if it is determined in step 144 that neither Vmax <α nor Vmax> β holds, the downstream oxygen sensor 34 is determined to be normal (step 148).
[0080]
As described above, according to the system of the present embodiment, the maximum value Vmax and the minimum value Vmin of the sensor output Vs are detected while performing the active air-fuel ratio control, and whether the values Vmax and Vmin are normal values is determined. By determining whether or not the downstream oxygen sensor 34 has deteriorated in responsiveness or in output reduction, it can be accurately determined.
[0081]
In the first embodiment, the ECU 40 controls the fuel injection amount so that the pre-catalyst air-fuel ratio becomes the desired air-fuel ratio, so that the “exhaust air-fuel ratio control means” in the first invention is described above. The “active air-fuel ratio control means” in the first aspect of the present invention controls the fuel injection amount to execute the active air-fuel ratio control. Abnormality determining means "are each realized.
[0082]
Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIGS.
The apparatus of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 10 described later in the system shown in FIG.
[0083]
In the above-described first and second embodiments, the air-fuel ratio before the catalyst is varied with a constant amplitude during the active air-fuel ratio control. On the other hand, the device of the present embodiment is characterized in that the active air-fuel ratio control is executed by changing the amplitude width of the air-fuel ratio before the catalyst as needed.
[0084]
FIG. 9 shows a comparison between the operation when the air-fuel ratio before the catalyst is varied with a large amplitude during the execution of the active air-fuel ratio control and the operation when the air-fuel ratio before the catalyst is varied with a small amplitude. It is a timing chart shown. The waveforms shown in FIGS. 9A to 9C are, specifically, a waveform of the air-fuel ratio before the catalyst, an output waveform of the downstream oxygen sensor 34, and a waveform of the air-fuel ratio after the catalyst.
[0085]
In FIG. 9A, the waveform shown by the solid line indicates that the air-fuel ratio before the catalyst is changed with a large amplitude during the execution of the active air-fuel ratio control. 9 (B) and 9 (C), the waveforms indicated by solid lines respectively indicate the change appearing in the output Vs of the downstream oxygen sensor 34 and the change occurring in the air-fuel ratio after the catalyst corresponding to the large amplitude width. I have.
In FIG. 9A, the waveform shown by a broken line indicates that the air-fuel ratio before the catalyst is changed with a small amplitude during the execution of the active air-fuel ratio control. 9 (B) and 9 (C), the waveforms indicated by broken lines respectively indicate changes appearing in the output Vs of the downstream oxygen sensor 34 and changes occurring in the air-fuel ratio after the catalyst corresponding to the small amplitude width. I have.
[0086]
As shown in FIG. 9C, the amplitude width of the air-fuel ratio after the catalyst increases as the amplitude width of the air-fuel ratio before the catalyst increases. The output Vs of the downstream oxygen sensor 34 shows a sharp and large change as the post-catalyst air-fuel ratio increases in amplitude. Therefore, as shown in FIG. 9 (B), the output Vs of the downstream oxygen sensor 34 shows a large and sharp change as the amplitude width of the pre-catalyst air-fuel ratio increases.
[0087]
Even if the responsiveness of the downstream oxygen sensor 34 is deteriorated, if the air-fuel ratio after the catalyst shows a large and sudden change, the sensor output Vs also tends to show a sudden change. Further, even if the downstream oxygen sensor 34 has a reduced output and deteriorated, if the air-fuel ratio after the catalyst shows a large change, a large change is likely to occur in the sensor output Vs. For this reason, the output behavior of the normal downstream oxygen sensor 34 and the output behavior of the deteriorated downstream oxygen sensor 34 are more difficult to distinguish as the air-fuel ratio after the catalyst changes in a large range and the change is sharper. It becomes. Therefore, in detecting the deterioration of the downstream oxygen sensor 34 with high sensitivity, the air-fuel ratio after the catalyst (FIG. 9C) shows a small and gradual change (broken line) rather than a large and sharp change (solid line). It is desirable. Focusing on this point, it is desirable that the amplitude width of the air-fuel ratio before the catalyst accompanying the active air-fuel ratio control is larger (solid line) and smaller (dashed line).
[0088]
Further, when the air-fuel ratio before the catalyst is changed in accordance with the active air-fuel ratio control, a torque change occurs due to the change in the air-fuel ratio. In order to maintain good drivability of the vehicle, it is desirable that such a torque fluctuation is as small as possible. At this point, the amplitude width of the pre-catalyst air-fuel ratio associated with the active air-fuel ratio control is preferably larger (solid line) but smaller (broken line).
[0089]
Furthermore, in order to maintain good exhaust emission of the vehicle, it is desirable that the air-fuel ratio after the catalyst be controlled as close to the stoichiometric air-fuel ratio as possible during the execution of the active air-fuel ratio control. As described above with reference to FIG. 9C, the air-fuel ratio after the catalyst increases as the amplitude of the air-fuel ratio before the catalyst increases. Therefore, from the viewpoint of emission, it is desirable that the amplitude width of the air-fuel ratio before the catalyst accompanying the active air-fuel ratio control is large (solid line) and smaller (dashed line).
[0090]
As described above, the amplitude width of the pre-catalyst air-fuel ratio accompanying the active air-fuel ratio control is such that deterioration of the downstream oxygen sensor 34 is detected with high sensitivity, good drivability is ensured, and good emission characteristics are maintained. In view of this, it is desirable that the size be as small as possible. However, reducing the amplitude width of the pre-catalyst air-fuel ratio accompanying the active air-fuel ratio control has the following disadvantages.
[0091]
First, in the device of the present embodiment, in order to determine the deterioration state of the downstream oxygen sensor 34, a known air-fuel ratio is forcibly introduced around the downstream oxygen sensor 34 along with the execution of the active air-fuel ratio control. is necessary. Then, according to the method of the present embodiment, as the error superimposed on the air-fuel ratio increases, the deterioration detection accuracy of the downstream oxygen sensor 34 deteriorates. It becomes more difficult to maintain the control accuracy of the air-fuel ratio as the amplitude width becomes smaller. Therefore, in the present embodiment, when the amplitude width of the air-fuel ratio before the catalyst accompanying the active air-fuel ratio control is reduced, there is a disadvantage that the deterioration determination is likely to vary.
[0092]
Second, in the device of the present embodiment, the smaller the amplitude width of the air-fuel ratio before the catalyst accompanying the active air-fuel ratio control, the longer the inversion period of the air-fuel ratio after the catalyst (see FIG. 9). That is, in the device of the present embodiment, during the execution of the active air-fuel ratio control, the exhaust gas having a rich or lean air-fuel ratio continuously flows into the upstream catalyst 28, and the transfer of oxygen corresponding to the oxygen storage capacity is performed. At this point, the inversion of the air-fuel ratio after the catalyst occurs. Therefore, the reversal period becomes longer as the amplitude width of the pre-catalyst air-fuel ratio is smaller and the amount of transferred oxygen per unit time is smaller. In a situation where the operating state of the internal combustion engine greatly changes during the inversion period of the post-catalyst air-fuel ratio, the deterioration state of the downstream oxygen sensor 34 cannot be accurately determined. The operating state of the internal combustion engine is more likely to change significantly during the reversal period as the above-described reversal period becomes longer. For this reason, in the device of the present embodiment, there is a disadvantage that the smaller the amplitude width of the pre-catalyst air-fuel ratio associated with the active air-fuel ratio control, the lower the frequency with which the deterioration state of the downstream oxygen sensor 34 can be accurately determined is reduced. easy.
[0093]
As described above, in the apparatus according to the present embodiment, the setting for decreasing the amplitude width of the air-fuel ratio before the catalyst accompanying the execution of the active air-fuel ratio control and the setting for increasing the amplitude have respective advantages and disadvantages. Therefore, in the present embodiment, the amplitude width of the air-fuel ratio before the catalyst during the execution of the active air-fuel ratio control is set as necessary so that the respective advantages can be used to the maximum and the respective disadvantages can be suppressed to the minimum. It is decided to switch between large and small stages.
[0094]
FIG. 10 is a flowchart for explaining the specific contents of the deterioration detection routine executed by the ECU 40 in the present embodiment. In FIG. 10, steps that are the same as the steps shown in FIG. 5 or FIG. 8 are given the same reference numerals, and descriptions thereof will be omitted or simplified.
[0095]
In the routine shown in FIG. 10, if it is determined in step 100 that the execution condition of the active control is satisfied, then a predetermined small amplitude is set as the amplitude width of the air-fuel ratio before the catalyst (step 150).
After the process of step 150 is executed, the ECU 40 thereafter executes active air-fuel ratio control such that the pre-catalyst air-fuel ratio fluctuates at the small amplitude.
[0096]
In the routine shown in FIG. 10, next, processing for detecting the deterioration of the downstream oxygen sensor 34, specifically, the processing of steps 106 to 122 shown in FIG. 5 or the processing of steps 130 to 148 shown in FIG. Processing is executed. By performing these processes, the deterioration state of the downstream oxygen sensor 34 is determined in an environment where the active air-fuel ratio control using the small amplitude is performed.
[0097]
Next, it is determined whether an abnormality (deterioration) of the downstream oxygen sensor 34 has been determined by the above-described deterioration detection processing using the small amplitude (step 152).
As a result, when it is determined that no abnormality has been determined, it is determined that the downstream oxygen sensor 34 has not deteriorated, and the normal determination of the downstream oxygen sensor 34 is determined (step 160).
[0098]
On the other hand, if it is determined in step 152 that the downstream oxygen sensor 34 has been determined to be abnormal, then a predetermined large amplitude is set as the amplitude width of the pre-catalyst air-fuel ratio (step 154).
After the process of step 154 is executed, the ECU 40 thereafter executes active air-fuel ratio control such that the pre-catalyst air-fuel ratio fluctuates at the above-described large amplitude.
[0099]
Next, in the routine shown in FIG. 10, the deterioration detection processing of the downstream oxygen sensor 34 is executed again. More specifically, the processing of steps 106 to 122 shown in FIG. 5 or the processing of steps 130 to 148 shown in FIG. 8 is executed again. By performing these processes, it is determined whether or not the downstream oxygen sensor 34 has deteriorated in an environment where the active air-fuel ratio control using the large amplitude is performed.
[0100]
Next, it is determined whether or not abnormality (deterioration) of the downstream oxygen sensor 34 is determined by the above-described deterioration detection processing using the large amplitude (step 156).
As a result, when it is determined that the abnormality has been determined, the deterioration of the downstream oxygen sensor 34 is definitely determined (step 158).
On the other hand, if it is determined that the abnormality determination has not been made, it is determined that the downstream oxygen sensor 34 has not deteriorated, and the processing of step 160 is executed to determine the normal determination of the downstream oxygen sensor 34. .
[0101]
As described above, according to the routine shown in FIG. 10, when detecting the deterioration of the downstream oxygen sensor 34, first, the active air-fuel ratio control with a small amplitude can be executed to determine the deterioration state. Then, when a normal judgment is obtained by the judgment, the normal judgment of the downstream oxygen sensor 34 can be determined without executing the large-amplitude active air-fuel ratio control thereafter. As described above, active air-fuel ratio control with a small amplitude is superior to active air-fuel ratio control with a large amplitude in maintaining good drivability and emission characteristics of a vehicle. According to the routine shown in FIG. 10, when the downstream oxygen sensor 34 is normal, the active air-fuel ratio control with a large amplitude is prevented from being executed, and the frequency at which the drivability deteriorates and the emission characteristic deteriorates is generated. Can be effectively lowered.
[0102]
Further, according to the routine shown in FIG. 10 described above, when the abnormality of the downstream oxygen sensor 34 is provisionally determined by the deterioration detection process accompanied by the small-amplitude active air-fuel ratio control, the downstream oxygen sensor 34 In order to determine whether or not this has occurred, a deterioration detection process involving active air-fuel ratio control with a large amplitude can be executed. As described above, the large-amplitude active air-fuel ratio control is superior to the small-amplitude active air-fuel ratio control in accurately determining whether or not the downstream oxygen sensor 34 has deteriorated without variation. I have. Therefore, according to the routine shown in FIG. 10, the deterioration of the downstream oxygen sensor 34 can be accurately detected while minimizing the frequency of deterioration of drivability and emission.
[0103]
In the third embodiment, the ECU 40 executes the processes of steps 150 and 154 so that the “air-fuel ratio amplitude width changing unit” in the fourth invention is set to the small value set in step 150. By executing the active air-fuel ratio control with the amplitude, the “small amplitude active control command means” in the fourth aspect of the present invention performs the steps 106 to 122 under the environment where the active air-fuel ratio control with the small amplitude is executed. Alternatively, by executing the processes of 130 to 148, the “first abnormality determination command means” in the fourth invention causes the active air-fuel ratio control with the large amplitude set in the step 154 to be executed to execute the fourth abnormality determination. The active air-fuel ratio control at the large amplitude is executed by the "large amplitude active control command means" according to the invention. By executing the processing of steps 106 to 122 or 130 to 148 under the boundary, the “second abnormality determination command means” in the fourth invention executes the processing of step 158 to execute the processing of the fourth invention. Are implemented, respectively.
[0104]
Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG.
The device of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 11 described later in the system configuration shown in FIG.
[0105]
In order for the device of the present embodiment to function properly, the upstream catalyst 28 and the downstream catalyst 30 need to have appropriate oxygen storage capacities. For this reason, in this device, it is desirable that the oxygen storage capacity of each of the catalysts 28 and 30 is detected, and if the capacity is too small, the deterioration of the catalyst can be determined.
[0106]
The device of the present embodiment executes active air-fuel ratio control similarly to the devices of the other embodiments described above. Here, as described above, the active air-fuel ratio control means that the exhaust gas flowing into the upstream catalyst 28 flows every time the output Vs of the downstream oxygen sensor 34 is inverted from the lean output to the rich output or from the rich output to the lean output. , Ie, the air-fuel ratio before the catalyst is inverted from rich to lean or from lean to rich (see FIG. 2).
[0107]
The output Vs of the downstream oxygen sensor 34 is inverted from the lean output to the rich output when all the oxygen stored in the upstream catalyst 28 has been consumed (time t1 in FIG. 2), and the upstream catalyst 28 has full oxygen storage capacity. When the oxygen is occluded, the output is inverted from rich output to lean (time t4 in FIG. 2). Therefore, the oxygen storage capacity of the upstream catalyst 28 is determined by the amount of oxygen stored in the upstream catalyst 28 between the time when the output Vs of the downstream oxygen sensor 34 is inverted to the rich output and the time when the output is inverted to the lean output. It is detected as an integrated value or as an integrated value of the amount of oxygen released from the upstream catalyst 28 from the time when the output Vs of the downstream oxygen sensor 34 is inverted to the lean output until the output is inverted to the rich output. It is possible.
[0108]
The upstream catalyst 28 has a pre-catalyst air-fuel ratio A / F with a stoichiometric air-fuel ratio A / F. _stoichi If it is richer, that is, A / F <A / F _stoichi If, release oxygen to make up for the oxygen deficiency. In this case, assuming that the fuel supply amount to the internal combustion engine 10 is F, the insufficient oxygen amount QO ₂ Are the above A / F and A / F _stoichi And can be expressed as: Here, in the following equation, the count k is the oxygen ratio (0.23) contained in the air.

[0109]
The upstream catalyst 28 has a stoichiometric air-fuel ratio A / F before the catalyst. _stoichi When leaner, that is, A / F> A / F _stoichi In this case, the excess oxygen is stored. In this case, assuming that the fuel supply amount to the internal combustion engine 10 is F, the excess oxygen amount QO ₂ Can also be expressed by the above equation (1).
[0110]
In the present embodiment, the ECU 40 can detect the pre-catalyst air-fuel ratio A / F by the air-fuel ratio sensor 32. Further, since the ECU 40 controls the fuel injection amount itself, the ECU 40 can detect the fuel supply amount F per unit time. For this reason, the ECU 40 substitutes the A / F and F into the above equation (1) to obtain the shortage or excess oxygen amount QO per unit time. ₂ Can be calculated. Then, in an environment in which the output Vs of the downstream oxygen sensor 34 is inverted with execution of the active air-fuel ratio control, the ECU 40 sets the oxygen amount QO with the inversion as a starting point and an ending point. ₂ Is integrated, the oxygen storage capacity of the upstream catalyst 28 can be calculated.
[0111]
By the way, the device of the present embodiment executes the active air-fuel ratio control also when the abnormality of the downstream oxygen sensor 34 is detected, similarly to the devices of the other embodiments described above. The active air-fuel ratio control is a control for forcibly changing the air-fuel ratio before the catalyst to blow a rich or lean exhaust gas downstream of the upstream catalyst 28. It is desirable that the execution frequency is low. Therefore, the device of the present embodiment combines active air-fuel ratio control for detecting the oxygen storage capacity of the upstream catalyst 28 and active air-fuel ratio control for detecting an abnormality of the downstream oxygen sensor 34. It was decided that the control would proceed simultaneously.
[0112]
The above-described calculation method of the oxygen storage capacity is based on the premise that the downstream oxygen sensor 34 is normal. Therefore, when an abnormality occurs in the downstream oxygen sensor 34, a situation may occur in which the oxygen storage capacity cannot be accurately calculated by the above calculation method. When the state of the upstream catalyst 28 is determined based on the incorrect oxygen storage capacity, an erroneous abnormality or normal determination may be made. Therefore, the apparatus of the present embodiment determines the abnormality of the upstream catalyst 28 while simultaneously performing the abnormality detection processing of the downstream oxygen sensor 34 and the calculation processing of the oxygen storage capacity of the upstream catalyst 28. It is to be executed after the end of the detection processing.
[0113]
FIG. 11 is a flowchart of a control routine executed by the ECU 40 in the present embodiment to realize the above functions. In FIG. 11, steps that are the same as the steps shown in FIG. 5 or FIG. 8 are given the same reference numerals, and descriptions thereof will be omitted or simplified.
[0114]
In the routine shown in FIG. 11, steps 170 to 174 are inserted between steps 134 and 136, steps 176 to 180 are inserted between steps 142 and 143, and step 182 is added after step 146. 8 is the same as the routine shown in FIG. 8 except that it is inserted and that steps 184 to 188 are inserted after step 148.
[0115]
That is, in the routine shown in FIG. 11, when the condition of step 130 is satisfied, that is, when the downstream oxygen sensor 34 is generating a rich output, the processing for updating the output maximum value Vmax (steps 132 and 134) is performed. Next, a process of calculating the oxygen storage capacity of the upstream catalyst 28 is executed. Here, first, the air-fuel ratio difference ΔA / F is detected (step 170).
The air-fuel ratio difference ΔA / F is a value included in the above equation (1), that is, the air-fuel ratio A / F before the catalyst detected by the air-fuel ratio sensor 32 and the stoichiometric air-fuel ratio A / F. _stoichi Difference (| A / F _stoichi -A / F |).
[0116]
Next, the ECU 40 calculates the fuel injection amount F per unit time (per execution cycle of this step) (step 172).
Then, the calculated fuel injection amount F and the above-described air-fuel ratio difference ΔA / F are substituted into the above equation (1) to obtain the excess oxygen amount QO per unit time. ₂ = K · ΔA / F · F, and the oxygen amount QO ₂ (The integrated value after the condition of step 130 is satisfied) is calculated as the latest value of the oxygen storage capacity (OSC) of the upstream catalyst 28 (step 174).
[0117]
In the calculation process of the oxygen storage amount (the processes in steps 170 to 174), it is determined in step 136 that Vs ≦ VL is satisfied in the same manner as the update process of the output maximum value Vmax (the processes in steps 132 and 134). It is repeatedly executed until. Therefore, according to the series of processes described above, after the sensor output Vs is inverted to the rich output, the excess oxygen amount QO generated during the period until the output Vs is again inverted to the lean output. ₂ Can be calculated as the oxygen storage capacity of the upstream catalyst 28.
[0118]
In the routine shown in FIG. 11, when the condition of step 138 is satisfied, that is, when the downstream oxygen sensor 34 emits a lean output, following the processing of updating the output minimum value Vmin (steps 140 and 142), Processing for calculating the oxygen storage capacity of the upstream catalyst 28 is executed. Here, the oxygen storage capacity is calculated in substantially the same procedure as in steps 170 to 174 (steps 176 to 180). According to these processes, after the sensor output Vs is inverted to the lean output, the excessive oxygen amount QO generated during the period until the output Vs is again inverted to the rich output. ₂ Can be calculated as the oxygen storage capacity of the upstream catalyst 28.
[0119]
Excessive oxygen amount QO calculated by repeating steps 132 to 136 ₂ And an oxygen amount QO calculated by repeating the processing of steps 140 to 143 described above. ₂ When the downstream oxygen sensor 34 is normal, the integrated value of accurately matches the oxygen storage capacity of the upstream catalyst 28. Therefore, when the downstream oxygen sensor 34 is normal, the oxygen storage capacity of the upstream catalyst 28 can be accurately calculated by a series of these processes.
[0120]
In the routine shown in FIG. 11, when the deterioration of the downstream oxygen sensor 34 is determined in step 146, the data of the oxygen storage capacity calculated as described above is discarded (step 182).
Then, in this case, the current processing cycle is ended without performing the abnormality determination of the upstream catalyst 28 based on the oxygen storage capacity. Therefore, according to the routine shown in FIG. 11, when the downstream oxygen sensor 34 is abnormal, the upstream catalyst 28 is determined based on the incorrect oxygen storage capacity calculated based on the abnormal sensor output Vs. The state can be reliably prevented from being erroneously determined.
[0121]
In the routine shown in FIG. 11, when it is determined in step 148 that the downstream oxygen sensor 34 is normal, it is determined whether the oxygen storage capacity (OSC) calculated in the above-described procedure is a normal value. Is performed (step 184).
As a result, when it is determined that the oxygen storage capacity is a normal value, it is determined that the upstream catalyst 28 is normal (step 186).
On the other hand, when it is determined that the oxygen storage capacity is not a normal value, it is determined that the upstream catalyst 28 has deteriorated (step 188).
[0122]
According to the above processing, the deterioration determination of the upstream catalyst 28 based on the oxygen storage capacity can be executed only when the downstream oxygen sensor 34 is normal. Therefore, according to the routine shown in FIG. 11, it is possible to always accurately determine the deterioration of the upstream catalyst 28 based on the normal oxygen storage capacity.
[0123]
As described above, according to the routine shown in FIG. 11, during the execution of the active air-fuel ratio control, the calculation of the oxygen storage capacity of the upstream catalyst 28 and the calculation of the maximum output value Vmax or the minimum output value Vmin are simultaneously executed. be able to. Further, according to this routine, the abnormality determination of the upstream catalyst 28 is executed only after the abnormality detection processing of the downstream oxygen sensor 34 is completed, more specifically, only when the normal determination of the downstream oxygen sensor 34 is made. be able to. For this reason, according to the device of the present embodiment, it is possible to always accurately determine the abnormality of the downstream oxygen sensor 34 and the abnormality of the upstream catalyst 28 while minimizing deterioration of drivability and emission.
[0124]
By the way, in the above-described fourth embodiment, the method of the second embodiment is used as a method of determining abnormality of the downstream oxygen sensor 34, but the present invention is not limited to this, and the determination method is Alternatively, the method of the first embodiment may be used. Further, in the above-described fourth embodiment, the amplitude of the active air-fuel ratio control is not changed, but the present invention is not limited to this, and similarly to the third embodiment, the active air-fuel ratio The amplitude of the control may be varied.
[0125]
In the fourth embodiment described above, the “oxygen storage capacity calculating means” in the fifth aspect of the present invention executes the processing of steps 184 and 188 by the ECU 40 executing the processing of step 174 or 180. Thereby, the “deterioration state determination means” in the fifth invention is realized. Further, in the above-described fourth embodiment, the “deterioration determination prohibiting means” in the sixth aspect of the present invention is realized by the ECU 40 terminating the processing cycle without executing the catalyst deterioration determination after step 146. Have been.
[0126]
Embodiment 5 FIG.
Next, a fifth embodiment of the present invention will be described with reference to FIGS. The device of the present embodiment can be realized using the system configuration shown in FIG. 1 as in the case of the first embodiment.
[0127]
As described above, the device of the first embodiment performs active air-fuel ratio control, that is, when the output of the downstream oxygen sensor 34 reverses from rich to lean, the pre-catalyst air-fuel ratio reverses from lean to rich. When the output of the downstream oxygen sensor 34 is inverted from lean to rich, control is performed to invert the pre-catalyst air-fuel ratio from rich to lean. During the execution of this control, while the pre-catalyst air-fuel ratio is maintained rich, it is normal for oxygen to be sequentially stored inside the upstream catalyst 28 from the upstream region to the downstream region. is there. In this case, after the oxygen is fully stored in the entire area inside the upstream catalyst 28, the exhaust gas lean in the air-fuel ratio flows downstream of the upstream catalyst 28. Then, when following such a normal flow, the after-catalyst air-fuel ratio changes from a value near the stoichiometric air-fuel ratio to a value that is largely leaned to lean after oxygen is fully stored in the upstream catalyst 28.
[0128]
The apparatus according to the first embodiment is based on the premise that lean exhaust gas does not flow downstream of the upstream catalyst 28 until oxygen is fully stored during active air-fuel ratio control. Is determined. That is, in the first embodiment, it is assumed that a large change always occurs when the post-catalyst air-fuel ratio changes from a value near the stoichiometric air-fuel ratio to a value biased toward lean.
[0129]
However, a lean exhaust gas with an air-fuel ratio may flow downstream of the upstream catalyst 28 even in a situation where oxygen is not fully stored in the entire area of the upstream catalyst 28. Such a phenomenon occurs, for example, when the intake air amount Ga is small and the state of the upstream catalyst 28 is unstable, when the intake air amount Ga is large and the untreated gas blows downstream of the upstream catalyst 28, or This may occur when the temperature of the upstream catalyst 28 is low and the upstream catalyst 28 does not exhibit the normal oxygen storage capacity.
[0130]
When lean exhaust gas flows downstream of the upstream catalyst 28 in a situation where oxygen is not fully stored in the upstream catalyst 28, lean exhaust gas is generated downstream of the upstream catalyst 28 after oxygen is fully stored in the upstream catalyst 28. The air-fuel ratio after the catalyst becomes a value closer to the stoichiometric air-fuel ratio as compared with the case where the water flows out. In other words, when lean exhaust gas flows downstream of the upstream catalyst 28 under a situation where oxygen is not fully stored, the post-catalyst air-fuel ratio does not reach the normal lean air-fuel ratio and is halfway It is a lean value.
[0131]
FIG. 12 shows a state in which lean exhaust gas flows out halfway downstream of the upstream catalyst 28 with execution of the active air-fuel ratio control, and a sufficiently lean exhaust gas flows downstream of the upstream catalyst 28 with the execution. It is a timing chart for explaining in contrast with the situation of outflow. More specifically, FIG. 12A shows waveforms of a target value and an actually measured value of the air-fuel ratio before the catalyst during execution of the active air-fuel ratio control. FIG. 12B shows the measured value of the air-fuel ratio after the catalyst during execution of the active air-fuel ratio control, that is, the waveform of the output of the downstream oxygen sensor 34. FIG. 12C shows the value of the oxygen storage capacity OSC calculated during the execution of the active air-fuel ratio control.
[0132]
During execution of the active air-fuel ratio control, as shown in FIGS. 12 (A) and 12 (B), the target value of the air-fuel ratio before the catalyst becomes the rich air-fuel ratio when the air-fuel ratio after the catalyst falls below the lean determination value VL. When the air-fuel ratio after the catalyst exceeds the rich determination value VR, the target value of the air-fuel ratio before the catalyst is inverted to the lean air-fuel ratio. The timing chart shown in FIG. 12 shows that in the process of repeating such processing, the output of the downstream oxygen sensor 34 (the air-fuel ratio after the catalyst) does not sufficiently become lean before time t1, and becomes normal after time t1. The case where the value has been reached is illustrated. The output of the downstream oxygen sensor 34 (the air-fuel ratio after the catalyst) shows such a change because a phenomenon occurs in which the lean exhaust gas flows out halfway before the time t1 downstream of the upstream catalyst 28. This is not because an abnormality has occurred in the downstream oxygen sensor 34.
[0133]
However, looking at the output of the downstream oxygen sensor 34 before the time t1, the response is poor compared to the normal time, and the output is also reduced. Therefore, when the abnormality determination of the downstream oxygen sensor 34 is performed by the method of the first or second embodiment, there is a case where the abnormality is erroneously determined before the time t1. For this reason, in order to increase the accuracy of the abnormality determination, the execution of the abnormality determination of the downstream oxygen sensor 34 should be prohibited in a situation where exhaust gas with an incomplete air-fuel ratio flows out downstream of the upstream catalyst 28. Is desirable.
[0134]
The waveform shown in FIG. 12C shows a change in the oxygen storage capacity OSC calculated by a method similar to that in the fourth embodiment. The oxygen storage capacity OSC is determined by the amount of oxygen deficiency in the exhaust gas flowing into the upstream catalyst 28 after the output Vs of the downstream oxygen sensor 34 falls below the lean determination value VL until the value Vs exceeds the rich determination value VR. By integrating, or until the output Vs of the downstream oxygen sensor 34 exceeds the rich determination value VR and the value Vs falls below the lean determination value VL, the excess oxygen amount flowing into the upstream catalyst 28 is integrated. (Steps 170 to 174 and Steps 176 to 180 in FIG. 11).
[0135]
In a situation in which exhaust gas having a halfway air-fuel ratio flows out downstream of the upstream catalyst 28 as before time t1, the output Vs of the downstream oxygen sensor 34 before oxygen is fully stored in the upstream catalyst 28. Is below the lean determination value VL. According to the above calculation method, the oxygen storage capacity OSC is once determined when the output Vs of the downstream oxygen sensor 34 falls below the lean determination value VL. Therefore, in a situation where exhaust gas having a halfway air-fuel ratio flows out downstream of the upstream catalyst 28, the oxygen storage capacity OSC becomes an excessively small value with respect to the original oxygen storage capacity of the upstream catalyst 28.
[0136]
If the output Vs of the downstream oxygen sensor 34 falls below the lean determination value VL before oxygen is fully stored in the upstream catalyst 28 as described above, then the target value of the pre-catalyst air-fuel ratio is inverted to the rich air-fuel ratio. At the same time, the next calculation of the oxygen storage capacity OSC is started from the state where the oxygen storage capacity remains in the upstream catalyst 28. Thereafter, a value corresponding to the integrated value of the amount of oxygen released from the upstream catalyst 28 until the output of the downstream oxygen sensor 34 exceeds the rich determination value VR is calculated as the oxygen storage capacity OSC. In this case, even if the output of the downstream oxygen sensor 34 correctly exceeds the rich determination value VR at the time when all the oxygen in the upstream catalyst 28 has been released, the oxygen storage capacity OSC is equal to the original oxygen that the upstream catalyst 28 has. The value is too small for the storage capacity.
[0137]
In FIG. 12C, a reference value indicated by a broken line indicates a lower limit value which should be regarded as the oxygen storage capacity OSC corresponding to the original oxygen storage capacity of the upstream catalyst 28. FIG. 12 (C) shows that the oxygen storage capacity OSC is lower in a situation in which the output of the downstream oxygen sensor 34 falls below the lean determination value VL before oxygen is fully absorbed in the upstream catalyst 28 (before time t1). , Is smaller than the reference value.
[0138]
In other words, the relationship shown in FIG. 12C indicates that, under the condition that the oxygen storage capacity OSC is lower than the reference value (before time t1), the active air-fuel ratio control is performed, and the relationship is halfway downstream of the upstream catalyst 28. The possibility that exhaust gas having an odd air-fuel ratio is flowing out is high, that is, the possibility that the sensor output Vs falls below the lean determination value VL before oxygen is fully stored in the upstream catalyst 28 (or This means that the possibility that the sensor output Vs has exceeded the rich determination value VR before all the oxygen in the upstream catalyst 28 is released is high. If the abnormality determination of the downstream oxygen sensor 34 is prohibited in a situation where the oxygen storage capacity OSC is lower than the reference value, it is possible to prevent the abnormality of the downstream oxygen sensor 34 from being erroneously determined before time t1. be able to.
[0139]
As described above, the reference value is a lower limit value that can be regarded as the normal oxygen storage capacity OSC. As such a reference value, for example, a steady value of the oxygen storage capacity OSC indicated by the upstream catalyst 28 can be used. Such a steady value can be obtained by continuing learning of the oxygen storage capacity OSC for a certain period. Therefore, in the present embodiment, during execution of the active air-fuel ratio control, a learning value of the oxygen storage capacity OSC is created, and when an oxygen storage capacity OSC smaller than the learning value is calculated, during the calculation period of the OSC. It is prohibited to determine the abnormality of the downstream oxygen sensor 34 based on the sensor output Vs issued in the above.
[0140]
FIG. 13 shows a flowchart of a control routine executed by the ECU 40 in the present embodiment to realize the above functions.
In the routine shown in FIG. 13, first, it is determined whether or not the active control is being performed (step 190).
[0141]
Next, a downstream oxygen sensor output process is performed (step 192).
In the downstream oxygen sensor output processing, specifically, detection of the sensor output Vs of the downstream oxygen sensor 34, update processing of the oxygen storage capacity OSC, update processing of the abnormality determination parameter, and the like are executed. The process of updating the oxygen storage capacity OSC is performed based on the sensor output of the air-fuel ratio sensor 32 in the same procedure as the process of steps 170 to 174 or steps 176 to 180 shown in FIG. The abnormality determination parameter refers to the count value of the counter C in the first embodiment, or the maximum value Vmax or the minimum value Vmin in the second embodiment, and the update processing is performed in step 108 or 114 in FIG. It is executed in a similar procedure or in a procedure similar to steps 132-134 or 140-142 in FIG.
[0142]
In the routine shown in FIG. 13, next, from the previous processing cycle to the current processing cycle, the sensor output Vs of the downstream oxygen sensor 34 has decreased from a value exceeding the lean determination value VL to the value VL or less, or It is determined whether the sensor output Vs has risen from a value below the rich determination value VR to the value VR or more. That is, it is determined whether or not the output Vs of the downstream oxygen sensor 34 is recognized as being inverted to the lean output or the rich output in the current processing cycle (step 194).
[0143]
As a result, when it is determined that the inversion of the sensor output Vs is not recognized, the current processing cycle is immediately terminated thereafter. On the other hand, if it is determined that reversal of the sensor output Vs is recognized, first, the oxygen storage capacity OSC calculated at the present time is determined as the oxygen storage capacity OSC in the current reversal cycle (step 196).
[0144]
In the routine shown in FIG. 13, after the processing of step 196 is completed, the processing of step 198 and thereafter and the processing of step 202 and thereafter are executed in parallel.
That is, when the process of step 196 is completed, first, it is determined whether the learning condition of the oxygen storage capacity OSC is satisfied (step 198).
Here, specifically, (1) whether the intake air amount Ga is equal to or greater than the lower limit determination value GaL and equal to or less than the upper limit determination value GaH, and (2) the temperature of the upstream catalyst 28 is equal to or greater than the lower limit determination value TcL; And it is determined whether it is equal to or less than the upper limit determination value TcH.
[0145]
The lower limit determination value GaL is a value determined as a lower limit intake air amount Ga that allows the upstream catalyst 28 to maintain a stable state. When the intake air amount Ga is smaller than the lower limit determination value GaL, the upstream catalyst 28 does not exhibit a normal purification ability, and even if the upstream catalyst 28 has the purification ability, the unpurified exhaust gas is downstream therefrom. Can be determined to blow through. The upper limit determination value GaH is an upper limit value of the intake air amount Ga that the upstream catalyst 28 can process without blowing unpurified exhaust gas. Therefore, when the intake air amount Ga exceeds the upper limit determination value GaH, it can be determined that there is a possibility that unpurified exhaust gas may flow downstream of the upstream catalyst 28 even in a situation where the upstream catalyst 28 has a purifying ability. Further, the lower limit determination value TcL is a minimum temperature at which the upstream catalyst 28 can exhibit a normal purification ability. Therefore, even when the temperature of the upstream catalyst 28 is lower than the lower limit determination value TcL, unpurified exhaust gas blows downstream of the upstream catalyst 28 despite the fact that the upstream catalyst 28 has a purification ability. It can be determined that there is a possibility.
[0146]
That is, if any of the conditions (1) and (2) determined in step 198 does not hold, the after-catalyst air-fuel ratio (output Vs of the downstream oxygen sensor 34) is equal to or less than the lean determination value Vs, or the rich determination is made. At the stage where the value is reversed to the value VR or more, it can be determined that there is a possibility that the upstream catalyst 28 may still have the remaining oxygen storage capacity or the remaining oxygen release capacity. In other words, if any of the above conditions (1) and (2) is not satisfied, the oxygen storage capacity OSC calculated in step 196 may not be a value corresponding to the oxygen storage capacity that the upstream catalyst 28 originally has. You can judge that there is.
[0147]
For this reason, in the routine shown in FIG. 13, when it is determined in step 198 that at least one of the learning conditions (1) and (2) is not satisfied, the oxygen storage capacity OSC calculated this time is thereafter determined. The current processing cycle is ended without reflecting it on the learning value. On the other hand, when it is determined that both of the learning conditions (1) and (2) are satisfied, the currently calculated oxygen storage capacity OSC is reflected on the learning value (step 200), and then the current processing cycle is started. Will be terminated.
The method of reflecting the oxygen storage capacity OSC in the learning value may be any known method. For example, the effective oxygen storage capacity OSC over a predetermined number of times in the past may be simply averaged to obtain a learning value, or a plurality of oxygen storage capacities OSC obtained before this time may be appropriately weighted, and the average may be calculated. It may be taken as a learning value.
[0148]
According to the routine shown in FIG. 13, following the processing of step 196, the difference between the learned value of the oxygen storage capacity OSC and the OSC obtained this time is determined in parallel with the processing of step 198 and thereafter. ₀ It is determined whether or not it is smaller (step 202).
Judgment value ΔOSC ₀ Is a value for determining whether or not the oxygen storage capacity OSC obtained this time is a learning value of the OSC, that is, whether or not the oxygen storage capacity OSC of the upstream catalyst 28 can be regarded as a steady state.
[0149]
Therefore, in step 198, the difference between the OSC obtained this time and the learning value of the OSC is determined by the determination value ΔOSC ₀ When it is determined that it is not smaller, the oxygen storage capacity OSC obtained this time can be determined to be an abnormal value. In this case, the output Vs of the downstream oxygen sensor 34, which has been issued in the process of calculating the oxygen storage capacity OSC, reflects the influence of the halfway exhaust gas flowing through the downstream of the upstream catalyst 28. You can judge that you may have received it. For this reason, in the routine shown in FIG. 13, when the condition of step 198 is not satisfied, the current processing cycle is ended without performing the abnormality determination processing of the downstream oxygen sensor 34.
[0150]
On the other hand, if it is determined in step 198 that the oxygen storage capacity OSC obtained this time can be regarded as the same as the learned value of OSC, the sensor output Vs output in the process of calculating the oxygen storage capacity OSC is It can be determined that the air-fuel ratio is a correct value generated in the process of correctly changing the air-fuel ratio downstream of the upstream catalyst 28. Therefore, in the routine shown in FIG. 13, in this case, thereafter, the abnormality determination processing of the downstream oxygen sensor 34 is executed (step 206).
In this step 206, specifically, the abnormality determination parameter updated in step 192 (the count value of the counter C in the first embodiment, or the maximum value Vmax or the minimum value Vmin in the second embodiment) becomes a normal value. Is determined. This process can be performed in the same procedure as step 118 in FIG. 5 or step 144 in FIG.
[0151]
Next, it is determined whether or not the satisfaction of the abnormality determination condition is recognized by the determination in step 204 (step 206).
Specifically, it is determined whether the count value of the counter C is greater than or equal to the determination value C0, or whether the maximum value Vmax is smaller than the determination value α, or whether the minimum value Vmin is greater than the determination value β.
[0152]
As a result, if it is determined that the abnormality determination condition is not satisfied, the current processing cycle ends without determining that the downstream oxygen sensor 34 is abnormal. On the other hand, when it is determined that the abnormality determination condition is satisfied, the current processing cycle is ended after determining that the downstream oxygen sensor 34 is abnormal (step 208).
[0153]
As described above, according to the routine shown in FIG. 13, in the situation where the downstream oxygen sensor 34 emits the output Vs affected by the exhaust gas having the halfway air-fuel ratio during the execution of the active air-fuel ratio control, Execution of the abnormality determination based on the output Vs can be prohibited. Then, the abnormality determination of the downstream oxygen sensor 34 can be permitted only when the post-catalyst air-fuel ratio is appropriately and largely changed with the execution of the active air-fuel ratio control. For this reason, according to the device of the present embodiment, it is possible to effectively prevent the erroneous abnormality determination from being performed under the situation where the unstable sensor output Vs is generated, and to accurately determine the abnormality of the downstream oxygen sensor 34. It is possible to do.
[0154]
By the way, in the above-described fifth embodiment, the method of prohibiting the execution of the determination is combined with the abnormality determination method used in the first or second embodiment. It is not limited to 1 or 2. That is, the process of prohibiting the execution of the abnormality determination may be combined with the process of the third or fourth embodiment.
[0155]
Further, in the above-described fifth embodiment, when the oxygen storage capacity OSC calculated in a certain processing cycle deviates from the OSC learning value, the sensor output Vs generated during the OSC calculation period is used. Although the execution of the abnormality determination based on the determination is prohibited, the basis of the determination of the prohibition is not limited to the difference between the oxygen storage capacity OSC and the learning value. That is, as described above, when the intake air amount Ga falls below the lower limit determination value GaL, exceeds the upper limit determination value GaH, or when the temperature of the upstream catalyst 28 falls below the lower limit determination value TcL, Exhaust gas with an incomplete air-fuel ratio is likely to flow downstream of 28. In that case, the sensor output Vs of the downstream oxygen sensor 34 tends to be an inappropriate value, and the accuracy of abnormality determination based on the output Vs tends to decrease. Therefore, whether or not the abnormality determination based on the sensor output Vs can be performed may be determined based on whether or not the intake air amount Ga and the temperature of the upstream catalyst 28 are appropriate values.
[0156]
In the fifth embodiment, the ECU 40 performs the process of updating the oxygen storage capacity OSC in the step 192, whereby the “oxygen storage capacity calculation means” in the seventh invention performs the process of the step 202. By executing, the “judgment prohibition means” in the seventh invention is realized.
In the above-described fifth embodiment, the ECU 40 executes the process of step 200, and the “learning value updating unit” in the eighth invention executes the process of step 198. The "learning value update prohibiting means" in the ninth aspect of the present invention is realized.
Furthermore, in the above-described fifth embodiment, the ECU 40 is configured to determine whether or not to execute the abnormality determination based on the intake air amount Ga or the temperature of the upstream catalyst 28. Can be realized.
[0157]
【The invention's effect】
Since the present invention is configured as described above, it has the following effects.
According to the first aspect, by executing the active air-fuel ratio control, the exhaust air-fuel ratio downstream of the catalyst can be accurately reversed between the rich air-fuel ratio and the lean air-fuel ratio. Therefore, based on the sensor output generated from the downstream oxygen sensor during the execution of the control, it is possible to accurately determine the abnormality of the downstream oxygen sensor.
[0158]
According to the second aspect, during execution of the active air-fuel ratio control, it is checked whether or not the output of the downstream oxygen sensor is changing its output at an appropriate change speed, so that the response of the downstream oxygen sensor is abnormal. Can be accurately determined.
[0159]
According to the third aspect, during execution of the active air-fuel ratio control, it is checked whether or not the output of the downstream oxygen sensor has reached an appropriate value in the course of the change. In addition, the output reduction abnormality can be accurately determined.
[0160]
According to the fourth aspect, by oscillating the exhaust air-fuel ratio with a small amplitude width, it is possible to temporarily determine the abnormality of the downstream oxygen sensor without deteriorating drivability and emission. Then, only when the occurrence of the abnormality is provisionally determined, it is possible to confirm, with a large amplitude, whether the downstream oxygen sensor has deteriorated to be caught as an abnormality. For this reason, according to the present invention, it is possible to accurately detect an abnormality in the downstream oxygen sensor while minimizing deterioration of drivability and emission.
[0161]
According to the fifth aspect, during execution of the active air-fuel ratio for detecting an abnormality in the downstream oxygen sensor, the oxygen storage capacity of the catalyst can be calculated while utilizing the output change of the downstream oxygen sensor. Then, in a state where it is confirmed that no abnormality has occurred in the downstream oxygen sensor, the deterioration state of the catalyst can be determined based on the oxygen storage capacity. Therefore, according to the present invention, it is possible to accurately perform both the determination of the abnormality of the downstream oxygen sensor and the determination of the deterioration of the catalyst while minimizing the execution of the active air-fuel ratio control.
[0162]
According to the sixth aspect, when an abnormality is recognized in the downstream oxygen sensor, execution of the catalyst deterioration determination can be prohibited. The oxygen storage capacity, which is the basis for determining the deterioration of the catalyst, is calculated using the sensor output of the downstream oxygen sensor. Therefore, if an abnormality occurs in the downstream oxygen sensor, the oxygen storage capacity may be incorrect. According to the present invention, erroneous determination of the catalyst state can be prevented by prohibiting the deterioration determination based on such incorrect oxygen storage capacity.
[0163]
According to the seventh aspect, it is possible to calculate the oxygen storage capacity of the catalyst while utilizing the output change of the downstream oxygen sensor during execution of the active air-fuel ratio for detecting abnormality of the downstream oxygen sensor. Then, when the calculated oxygen storage capacity greatly deviates from the reference value, the execution of the abnormality determination can be prohibited. When the calculated value of the oxygen storage capacity greatly deviates from the reference value, it can be determined that the downstream oxygen sensor has temporarily generated an abnormal output during the calculation. Then, in that case, it can be determined that there is a high possibility that an abnormality has occurred in the environment surrounding the downstream oxygen sensor, rather than an abnormality has occurred in the downstream oxygen sensor itself. According to the present invention, it is possible to effectively prevent erroneous determination of an abnormality of the downstream oxygen sensor from being performed erroneously based on a sensor output generated under such an environment.
[0164]
According to the eighth aspect, it is possible to determine whether or not the sequentially calculated oxygen storage capacity is an appropriate value, using the learned value of the oxygen storage capacity as a reference value. For this reason, according to the present invention, every time the oxygen storage capacity is calculated, whether the sensor output during the calculation period is a normal value suitable for the state of the downstream oxygen sensor at that time, or It is possible to determine with high accuracy whether the value is an abnormal value due to an unusual environment.
[0165]
According to the ninth aspect, when at least one of the intake air amount and the catalyst temperature is out of the predetermined range, that is, there is a high possibility that a rich or lean gas blows in a halfway part downstream of the catalyst. In this case, it is possible to prohibit the learning value of the oxygen storage capacity from being updated. Therefore, according to the present invention, the accuracy of the learning value can be maintained sufficiently high.
[0166]
According to the tenth aspect, when at least one of the intake air amount and the catalyst temperature is out of the predetermined range, that is, there is a high possibility that a rich or lean gas blows in a halfway part downstream of the catalyst. In this case, it is possible to prohibit the abnormality determination of the downstream oxygen sensor from being performed. Therefore, according to the present invention, when a halfway gas flows out downstream of the catalyst, it is possible to effectively prevent the abnormal state of the downstream oxygen sensor from being erroneously determined by receiving the gas.
[Brief description of the drawings]
FIG. 1 is a diagram for describing a configuration according to a first embodiment of the present invention.
FIG. 2 is a timing chart for explaining details of active air-fuel ratio control executed by the device according to the first embodiment of the present invention.
FIG. 3 is a diagram for explaining how a change occurs in the output of a downstream oxygen sensor due to the reversal of the post-catalyst air-fuel ratio during execution of active air-fuel ratio control in the first embodiment of the present invention.
FIG. 4 is a diagram in which a timing chart realized when the response of the downstream oxygen sensor is deteriorated is superimposed on the timing chart shown in FIG. 2;
FIG. 5 is a flowchart of a deterioration detection routine executed in the first embodiment of the present invention.
FIG. 6 is a diagram for explaining a mode of deterioration occurring in the downstream oxygen sensor in the configuration shown in FIG. 1;
FIG. 7 is a detailed waveform of an output of a downstream oxygen sensor issued during execution of active air-fuel ratio control in the configuration shown in FIG. 1;
FIG. 8 is a flowchart of a deterioration detection routine executed in the second embodiment of the present invention.
FIG. 9 is a timing chart for explaining contents of active air-fuel ratio control executed by the device according to the third embodiment of the present invention.
FIG. 10 is a flowchart of a deterioration detection routine executed in Embodiment 3 of the present invention.
FIG. 11 is a flowchart of a deterioration detection routine executed in a fourth embodiment of the present invention.
FIG. 12 is a timing chart for explaining a characteristic operation of the fifth embodiment of the present invention.
FIG. 13 is a flowchart of a routine executed in a fifth embodiment of the present invention.
[Explanation of symbols]
10 Internal combustion engine
12 Intake passage
14 Exhaust passage
28 Upstream catalyst
30 Downstream catalyst
32 air-fuel ratio sensor
34 Downstream oxygen sensor
Vs Sensor output of downstream oxygen sensor
VR rich judgment value
VL lean judgment value
Vmax output maximum value
Vmin output minimum value
OSC oxygen storage capacity

Claims (10)

An apparatus for detecting an abnormality of a downstream oxygen sensor located downstream of a catalyst disposed in an exhaust passage of an internal combustion engine,
Exhaust air-fuel ratio control means for controlling the exhaust air-fuel ratio upstream of the catalyst,
In response to the output of the downstream oxygen sensor changing from the rich output to the lean output, the exhaust air-fuel ratio upstream of the catalyst is changed from the lean air-fuel ratio to the rich air-fuel ratio, and the output of the downstream oxygen sensor is changed from the lean output to the rich output. Active air-fuel ratio control means for executing active air-fuel ratio control for changing the exhaust air-fuel ratio upstream of the catalyst from a rich air-fuel ratio to a lean air-fuel ratio in response to a change in output,
Abnormality determining means for determining abnormality of the downstream oxygen sensor based on a sensor output issued from the downstream oxygen sensor during execution of the active air-fuel ratio control;
An oxygen sensor abnormality detection device, comprising: 2. The oxygen sensor abnormality detection device according to claim 1, wherein the abnormality determination unit determines an abnormality of the downstream oxygen sensor based on a change speed of an output of the downstream oxygen sensor. 3. 2. The oxygen sensor abnormality detection device according to claim 1, wherein the abnormality determination unit determines an abnormality of the downstream oxygen sensor based on a maximum value or a minimum value of an output of the downstream oxygen sensor. 3. Air-fuel ratio amplitude width changing means for changing the amplitude width of the air-fuel ratio generated in the exhaust air-fuel ratio upstream of the catalyst during the execution of the active air-fuel ratio control,
The abnormality determining means includes:
A small-amplitude active control command means for executing the active air-fuel ratio control with a first amplitude width;
First abnormality determination command means for causing the abnormality determination means to perform abnormality determination with respect to execution of the active air-fuel ratio control at the first amplitude width;
When it is determined that the downstream oxygen sensor is abnormal with respect to the execution of the active air-fuel ratio control at the first amplitude width, the active air-fuel ratio control is performed at a second amplitude width larger than the first amplitude width. Large-amplitude active control command means for executing fuel ratio control;
A second abnormality determination command unit that causes the abnormality determination unit to perform abnormality determination with respect to the execution of the active air-fuel ratio control at the second amplitude width;
An abnormality occurrence determining means for determining the abnormality of the downstream oxygen sensor definitely only when the abnormality of the downstream oxygen sensor is determined with respect to the execution of the active air-fuel ratio control at the second amplitude width. The oxygen sensor abnormality detection device according to claim 1, wherein: During the execution of the active air-fuel ratio control, a process in which the sensor output changes from a rich output to a lean output in parallel with the abnormality determination means taking in the sensor output generated from the downstream oxygen sensor, or In the process where the output changes from the lean output to the rich output, oxygen storage capacity calculation means for calculating the oxygen storage capacity of the catalyst,
A deterioration state determination unit that determines a deterioration state of the catalyst based on the oxygen storage capacity when no abnormality of the downstream oxygen sensor is recognized by the abnormality determination unit;
The oxygen sensor abnormality detection device according to any one of claims 1 to 4, further comprising: 6. The oxygen sensor according to claim 5, further comprising: a deterioration determination prohibition unit that prohibits a determination of deterioration of the catalyst based on the oxygen storage capacity when the abnormality determination unit determines that the downstream oxygen sensor is abnormal. Abnormality detection device. During the execution of the active air-fuel ratio control, a process in which the sensor output of the downstream oxygen sensor changes from a rich output to a lean output in parallel with the abnormality determination unit taking in the sensor output emitted from the downstream oxygen sensor, Alternatively, in a process in which the sensor output changes from the lean output to the rich output, oxygen storage capacity calculation means for calculating the oxygen storage capacity of the catalyst,
When the difference between the oxygen storage capacity and the reference value is equal to or larger than a determination value, a determination prohibition unit that prohibits the determination by the abnormality determination unit based on the sensor output issued during the calculation period of the oxygen storage capacity,
The oxygen sensor abnormality detection device according to any one of claims 1 to 6, further comprising: Each time the oxygen storage capacity is calculated, a learning value updating unit that updates a learning value of the oxygen storage capacity so that the value is reflected,
8. The oxygen sensor abnormality detecting device according to claim 7, wherein the reference value is a learned value of the oxygen storage capacity. 9. The oxygen sensor according to claim 8, further comprising a learning value update prohibiting unit that prohibits updating of the learning value of the oxygen storage capacity when at least one of the intake air amount and the catalyst temperature is out of a predetermined range. Abnormality detection device. The apparatus according to claim 1, further comprising a determination prohibition unit that prohibits the determination by the abnormality determination unit when at least one of the intake air amount and the catalyst temperature is out of a predetermined range. Oxygen sensor abnormality detection device.

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