JP3564088B2 - Diagnostic device for exhaust gas purification device - Google Patents

Diagnostic device for exhaust gas purification device Download PDF

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JP3564088B2
JP3564088B2 JP2001266268A JP2001266268A JP3564088B2 JP 3564088 B2 JP3564088 B2 JP 3564088B2 JP 2001266268 A JP2001266268 A JP 2001266268A JP 2001266268 A JP2001266268 A JP 2001266268A JP 3564088 B2 JP3564088 B2 JP 3564088B2
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air
fuel ratio
catalyst
exhaust gas
ratio sensor
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JP2002155735A (en
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豊 高久
俊夫 石井
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Hitachi Ltd
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Hitachi Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

【０００１】
【産業上の利用分野】
本発明は、広い空燃比範囲で空燃比を計測するためのいわゆる広域空燃比センサ、あるいは、理論空燃比付近で急激に出力が変化し２値的な出力を発生するいわゆるＯ２センサ（以下、両者をまとめて”空燃比センサ”という）や触媒を使用するエンジンの排気ガス浄化装置の診断装置に関する。
【０００２】
【従来の技術】
エンジンの排気ガスを浄化する装置として、触媒と空燃比フィードバック制御装置とからなるものが広く公知である。触媒は、排気中に含まれるＨＣ、ＮＯｘ、ＣＯを除去するため排気幹部に設置するものである。また、空燃比フィードバック制御装置は、触媒の機能を充分に発揮させるために空燃比を所定の値に保つため、触媒の上流に空燃比センサを設置して空燃比を計測しつつ制御する装置である。このような排気ガス浄化装置では、空燃比を計測するための空燃比センサに性能劣化を生ずると、空燃比が所定の値からずれたりするため排気ガス中の有害ガス成分の量が増加したり、触媒が性能を発揮できる空燃比から外れてしまうため有害ガスの除去効率（転換効率）が低下してしまう。また、触媒そのものに性能劣化を生じた場合、触媒が性能を発揮できる空燃比に制御されていても有害ガスの転換効率が低下してしまう。このように空燃比センサや触媒の性能劣化は結果として大気に放出される有害ガスの量を増加させてしまう。このためこれらの性能劣化を運転中に診断し、運転者に警告したりするための排気浄化装置の診断装置が考案されている。この様な診断装置としては、例えば触媒の上下流に空燃比センサを設けて、少なくとも触媒上流側の空燃比センサの出力に基づき比空燃比フィードバック制御を行ない、触媒下流側の空燃比センサの出力等により触媒の劣化を検出するがある。このような従来技術として、特開平２−９１４４０号公報や特開平３−２８６１６０号公報記載のものがある。
【０００３】
【発明が解決しようとする課題】
空燃比フィードバック制御中、触媒下流側の空燃比センサの出力により触媒の劣化を検出する方法では、当然のことながら空燃比フィードバック制御が停止している間は触媒の劣化検出は不可能である。また、触媒が活性化していないような場合には、触媒が劣化していなくても劣化していると誤検出する可能性が高いため、例えばエンジンの回転速度や負荷等の運転状態により触媒の劣化検出を許可したり、禁止したりする必要がある。これらについては特開平２−９１４４０号公報記載の従来技術においても考慮されている。また、触媒上流側の空燃比センサが劣化した場合には、劣化の程度や内容によっては触媒の劣化検出に影響を与えるため、検出結果に対する補正や触媒の劣化検出を禁止したりする必要がある。このため、特開平３−２８６１６０号公報記載の従来技術においては触媒上流側の空燃比センサが劣化した場合には、触媒の劣化検出を禁止している。
【０００４】
ところで、エンジンの燃焼行程で失火が発生すると、未燃焼ガスとともに空気中の酸素が排気管内に流れていくので、触媒上流の空燃比センサがリーンスパイク状の信号を発生したり、触媒下流の空燃比センサが、実際よりもリーン側の信号を発生したりする。このため触媒の劣化検出精度が低下するという問題がある。この点については従来技術では考慮されていない。
【０００５】
本発明の目的は、失火が発生しても、触媒の劣化検出精度を低下させないことである。
【０００６】
【課題を解決するための手段】
本発明の一態様としての診断装置は、
触媒の上流側における排気ガスの空燃比を検出する第１の空燃比センサと、
前記触媒の下流側における排気ガスの空燃比を検出する第２の空燃比センサと、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算する触媒劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定する触媒劣化判定手段と、
エンジンの燃焼状態を該エンジンの回転速度変動に基づいて検出し失火の発生を検出する失火検出手段と、
前記失火検出手段により失火が検出されたときに前記触媒劣化判定手段の判定を中断する触媒劣化判定中断手段と、
を備えていることを特徴とするものである。
【０００７】
本発明の他の態様としての診断装置は、
排気ガスの空燃比を検出する空燃比センサと、
前記空燃比センサの出力信号から空燃比センサの劣化状態を示す空燃比センサ劣化指標を計算する空燃比センサ劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記空燃比センサ劣化指標とを比較することによって空燃比センサの劣化状態を判定する空燃比センサ劣化判定手段と、
エンジンの燃焼状態を該エンジンの回転速度変動に基づいて検出し失火の発生を検出する失火検出手段と、
前記失火検出手段により失火が検出されたときに前記空燃比センサ劣化判定手段の判定を中断する空燃比センサ劣化判定中断手段と、
を備えていることを特徴とするものである。
【０００８】
本発明のさらに他の態様としての診断装置は、
触媒の上流側における排気ガスの空燃比を検出する第１の空燃比センサと、
前記触媒の下流側における排気ガスの空燃比を検出する第２の空燃比センサと、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算する触媒劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定する触媒劣化判定手段と、
エンジンの失火の発生を該エンジンの回転速度変動に基づいて検出する失火検出手段と、
少なくとも一定気筒の連続的な失火が発生したときに前記触媒劣化判定手段の判定を中断する触媒劣化診断中断手段と、
を備えていることを特徴とするものである。
【０００９】
【作用】
本発明による構成によれば、触媒の劣化検出精度を低下させるような失火が発生した場合には、失火検出手段によりこれを検出し、触媒の劣化状態の判定を中断する。従って、失火が発生しても、触媒の劣化状態を誤って判定してしまうことがない。
【００１０】
【実施例】
以下、本発明の実施例を図面により説明する。
【００１１】
図１は本発明の一実施例である診断装置および該診断装置を適用するエンジンシステムの構成を示す図である。
【００１２】
まず、前提となるエンジンシステムの概要を説明する。但し、本発明の診断装置適用の対象は、該エンジンシステムに限定されるものではない。
【００１３】
エンジン１に吸入される空気の量Ｑａは空気流量計２により計量される。また、図示しない回転速度計測手段により回転速度Ｎｅが計測される。空燃比フィードバック制御手段３は吸入空気量Ｑａと回転速度Ｎｅとから下記数１に従って燃料の基本噴射量Ｆ０を求める。
【００１４】
【数１】
Ｆ０＝ｋＱａ／Ｎｅ
ｋ：係数
空燃比センサ７はエンジン１から排出された排気ガスの空燃比を計測する。なお、上述したとおり、本明細書において”空燃比センサ”といった場合、酸素濃度を二値的に検知する（理論空燃比付近で出力が急激に変化する。）ものと、酸素濃度をリニアに検出するいわゆる広域空燃比センサと、の両方を含んでいる。空燃比フィードバック制御手段３は空燃比センサ７の出力に応じて補正係数αを求め、前述の基本噴射量を下記数２により補正し、噴射量Ｆを求める。
【００１５】
【数２】
Ｆ＝Ｆ０（１＋α）
さらにこの噴射量Ｆに対応した幅のパルス信号をインジェクタ４に印加することによって燃料供給量をフィードバック制御する。このような制御により、混合気の空燃比は理論空燃比付近に保持される。触媒５では、排気ガス中の有害成分である未燃ガス成分（以下ＨＣと記す。）やＣＯ２を酸化すると同時に、ＮＯｘを還元することによって、これらを減少させている。このような触媒を三元触媒と言うが、該三元触媒による酸化反応と、還元反応とを同時に行なうためには空燃比を理論空燃比付近に保持する必要が有る。そして、そのためには、前述の空燃比フィードバック制御が正確に行なわれることが必要である。
【００１６】
２次空気系６は、混合気の燃料濃度が理論空燃比より濃い状態（以下リッチと記す。）としなくてはならないような運転状態（例えば、エンジン始動時）において、ポンプ６０によって排気管１００内に空気を導入し、排気管１００内に排出された余剰分のＨＣを燃焼し低減するためのものである。
【００１７】
以下、本実施例の診断装置を説明する。
【００１８】
本実施例の診断装置は、図１に示したとおり、失火検出手段９と、２次空気系故障検出手段１０と、触媒劣化指標計算手段１１と、触媒劣化判定手段１２と、触媒劣化指標補正手段１３と、触媒劣化判定中断手段１４と、を含んで構成される。
【００１９】
触媒劣化指標計算手段１１は、触媒５の劣化状態を検出するためのものである。本実施例の触媒劣化指標計算手段１１は、触媒５の上流側に設置された空燃比センサ７と、触媒５の下流側に設置された空燃比センサ８の信号の相関を利用して触媒５の劣化検出を行う。つまり、触媒５が劣化していない状態においては、空燃比センサ８の出力信号は、空燃比センサ７の出力信号と類似した変動をとらないが、触媒５が劣化するにつれて空燃比センサ８の出力信号は空燃比センサ７の出力信号と類似した変動をするようになってくることを利用して劣化検出を行っている。以下、該劣化検出方法の概要を説明する。
【００２０】
触媒劣化指標Φｃ計算手段１１は、まず、空燃比センサ７、８の出力信号を同期して計測する。そして、高周波通過型フィルタを用いて、該計測した信号から劣化検出の外乱となる直流成分を除去する。図２にこれらの信号の例を示す（以下、空燃比センサ７の出力信号から直流成分を除去した信号をｘ、空燃比センサ８の出力信号から直流成分を除去した信号をｙで示す）。
【００２１】
そして、ｘの自己相関関数φｘｘおよび、ｘとｙとの相互相関関数φｘｙを計算する（下記数３、数４参照）。
【００２２】
【数３】

Figure 0003564088
【００２３】
【数４】
Figure 0003564088
【００２４】
φｘｘ（τ）はτ＝０のとき最大値φｘｘ（０）となるので、下記数５の関係が成り立つ。
【００２５】
【数５】
（φｘｘ）ｍａｘ＝φｘｘ（０）
更に、位相τを相互相関関数の積分区間内で変えて、φｘｙ（τ）の最大値を求める。τ＝τ０で最大値となるとすると、下記数６が得られる。
【００２６】
【数６】
（φｘｙ）ｍａｘ＝φｘｙ（τ０）
これらの値より、触媒劣化指標Φｃを下記数７により求める。
【００２７】
【数７】
Φｃ＝（φｘｙ）ｍａｘ／（φｘｘ）ｍａｘ
図３に、φｘｙ（τ）／（φｘｘ）ｍａｘと触媒劣化度との関係を示す。触媒５の劣化度が大きい場合には、空燃比センサ７の出力信号と空燃比センサ８の出力信号の相関度が高く、大きなピーク（最大値）を示す。一方、触媒５の劣化度が小さい場合（あまり劣化していない場合）には、両出力信号の相関度は低く、小さなピーク（最大値）しか示さない。したがって、触媒劣化指標Φｃの大小により触媒５の劣化度を検出することができる。
【００２８】
なお、ここで述べた劣化度検出の方法については特願平３−３３８２２０号において既に提案しているものである。
【００２９】
触媒の劣化検出方法は該方法に限定されるものではない。例えば、空燃比センサ７，８の出力信号の変動幅、位相差や周波数等からから検出する方法等を用いてもよい。この他にも数多くの公知例があり、これらいずれの方法を用いるようにしてもよい。但し、その方法に応じて以下に述べる補正方法等を変更する必要がある。
【００３０】
触媒劣化判定手段１２は、触媒劣化指標計算手段１１の求めた劣化状態を判定し、排気浄化装置が故障しているか否かの判定を行うものである。本実施例においては、前述の触媒劣化指標Φｃを、予め設定された所定の値（注：該所定の値が、特許請求の範囲においていう”しきい値”に該当する。）と比較することによって、該判定を行っている。例えば、触媒劣化指標Φｃが上記が所定値より大きい時には故障と判定する。故障していた場合には、図示しない警告灯を点灯して、運転者に警告したりする。
【００３１】
失火検出手段９は、エンジンのシリンダ内で燃焼が行なわれる毎に失火の発生の有無を検出する働きをするものである。該失火検出方法としては、例えば特開平３−２０６３４２号公報に回示されているエンジンの回転速度の変動から検出する方法がある。これは、燃焼行程中の回転速度変動波形か燃焼状態を検出する方法である。回転速度の変動に基づいて燃焼状態を検出する方法としては、この他にもＵＳＰ４６２７３９９に記載がある。他の方法として、燃焼室内の燃焼圧力、温度等から検出する方法、排気ガス圧力の脈動、温度から検出する方法がある。さらに、ＵＳＰ４６４８３６７に開示されているように燃焼室内にイオンギャップを設けてその間を流れるイオン電流から検出する方法や、燃焼室内の燃焼光を測定し検出する方法、あるいは点火コイルを流れる電流波形等から検出する方法等、数多くの公知の方法がある。本実施例の失火検出手段９としては、これらいずれの方法を用いるようにしてもよい。
【００３２】
２次空気系故障検出手段１０は、２次空気系６の故障や劣化を検出する働きをするものである。これは、例えば２次空気系６の空気通路の途中に流量計を設けて実際の空気流量を検出し、ポンプ６０への制御量（電圧や電流値）から推定される流量と実流量との差に基づいて検出する方法がある。他にも２次空気系を作動したときに空燃比センサ７では酸素を検出するため前述の空燃比フィードバック制御をそのまま行なうと供給燃料を増加するように補正係数αが増加することを利用して、例えばポンプ６０を作動しても補正係数αが増加しないような場合には、２次空気が流れていないとして２次空気系の故障を検出する方法等、数多くの公知の方法があり、これらいずれの方法を用いるようにしてもよい。
【００３３】
触媒劣化指標補正手段１３は、失火検出手段９または、２次空気系故障検出手段１０により、失火または２次空気系の故障や劣化が検出されたとき、前述の触媒劣化指標を補正し、補正後の触媒劣化指標を触媒劣化判定手段１２に出力するものである。なお、補正の方法は後述する動作説明と併せて行う。
【００３４】
触媒劣化判定中断手段１４は、判定を中断するか否かの基準となる、失火や２次空気系の故障や劣化についての、予め定められた頻度（あるいは程度）を備えている。そして、失火検出手段９あるいは、２次空気系故障検出手段１０により、該予め定められた頻度（あるいは程度）を越えて検出されたときには、前述の触媒劣化判定手段１２による触媒の劣化判定を中断するための信号を発生するものである。なお、該頻度（あるいは程度）は、後述するとおり、温度等に応じて変更するようにしてもよい。
【００３５】
失火が発生したときの動作を説明する
図４は、失火していない場合と失火が発生しているときの触媒上流側空燃比センサ７の出力信号の例を示している。
【００３６】
失火が発生すると、排気管内に未燃焼ＨＣと空気が流入するため、失火に同期して排気ガスの空燃比が薄い（酸素が多いということ）ということを示すスパイク状の信号が発生している。このように失火が発生すると触媒５内では通常の浄化反応とともに未燃焼ＨＣの酸化反応も進が、反応し切れなかった分のＨＣと酸素とが触媒５の後流にも流れるため、空燃比センサ８は以下のような影響を受ける。
【００３７】
空燃比センサ８が２値的な出力を示すＯ２センサの場合、出力信号は空燃費が薄い（以下、”リ−ン”）ということを示す側にシフトすると同時に振幅が減少してくる。このため前述の触媒劣化指標Φｃは図５に示すよう失火の頻度に応じて変化し、低めの値となってしまう。すなわち、この場合には本来は触媒が劣化していても失火が発生すると、劣化度を低く評価してしまう。従って、触媒劣化指標補正手段１３では、例えば、図６に示すような係数Ｋｃをかけることにより失火の頻度に応じて触媒劣化指標Φｃを大きくするような補正をすればよい。また、当然のことながら触媒劣化判定手段１２で触媒劣化指標Φｃと比較するための所定値を失火の頻度に応じて小さくするような補正をしてもよい。例えば６気筒エンジンで１気筒が連続して失火しているような場合には、本来燃焼により過不足なく反応するはずの酸素とＨＣとが排気管内及び触媒５内で反応仕切れないため、大量の酸素が触媒の下流にまで流れていく。このため空燃比センサ８は触媒５の劣化度に係わらず空燃比が理論空燃比より薄い（以下リーンと記す。）という出力信号を示し、特に空燃比センサ８が空燃比を二値的に検出するタイプの場合、一定値となってしまう。その結果、触媒劣化指標Φｃも触媒の劣化度に係わらず、出力信号はリ−ンで一定の値（振幅がほぼゼロ）となってしまうため、補正することもできなくなってしまう。したがって、失火発生頻度が所定値よりも低い場合にはその頻度に応じて触媒劣化指標Φｃを補正し、頻度が所定値よりも高い場合には触媒の劣化判定を失火が発生または頻度が所定値を超えている間は中断するようにすることが好ましい。
【００３８】
なお、触媒の温度やエンジン負荷等によって、補正量や、補正可能な失火の頻度が変化するため、触媒５の温度やエンジンの運転状態に応じて、補正係数や、判定を中断する失火の頻度を、例えば図６に示すとおり、変えることが好ましい。これは、例えば触媒５の温度によってＨＣの酸化反応の速度が変化するからである（注：触媒が通常とりうる温度範囲においては、温度が高いほど反応速度が速い）。実際の失火は、点火系の故障等でいずれかの１気筒以上がほぼ連続的に失火するようなことが多い。そして、この場合には一気に補正不可能な頻度の失火が検出される。従って、失火が触媒の劣化検出に影響を与えるような頻度で発生したら、補正することなく、ただちに触媒の劣化判定を中断するようにしても十分なことが多い。なお、この場合多くの公知例では失火検出手段９は失火の発生を運転者に警告するようになっているので、警告に基づいて修理が終了した後に触媒の劣化判定を再会するようにすれば実用的には問題がないことが多い。
【００３９】
一方、空燃比センサ８がいわゆる広域空燃比センサの場合には、失火時に前述の空燃比センサ７のスパイク状の出力信号にほぼ同期して空燃比センサ８もリ−ンを示す信号を出力する。このため、図７に示すように、失火の頻度が低いときには、触媒劣化指標Φｃはわずかではあるが高めの値となる。また、失火の頻度がある程度高くなると、触媒５が劣化していなくとも正常に反応しなくなるため、空燃比センサ７と８とが近似した信号波形を出力するようになり、触媒劣化指標Φｃ大きな値を示すようになる。従って、例えば図８に示すように失火の頻度が低い場合には、係数Ｋｃをかける補正を行い、失火の頻度が高い場合には劣化判定を禁止するようにすれば良い。
【００４０】
なお、前述の場合と同様、失火が触媒の劣化検出に影響を与えるような頻度で発生したら、補正することなく、ただちに触媒の劣化判定を中断するようにしても十分なことが多い。さらに、この場合には、触媒の劣化判定で劣化指標Φｃがが大きめの値となるため、劣化していない触媒を劣化していると誤判定してしまっている可能性もあるので、直前の触媒の劣化判定結果を廃棄する等の手段を設けることが好ましい。
【００４１】
また、逆に、触媒劣化判定中断手段１４を設けることなく、触媒劣化指標Φｃ補正手段１３による補正のみを行う構成としても構わない。
【００４２】
次に２次空気系６が故障または劣化した場合について説明する。
【００４３】
上述したとおり、２次空気系６は、一般的には、混合気の空燃比をリッチとしなくてはならないような運転状態（例えば、エンジン始動時）において、ポンプ６０によって排気管１００内に空気を導入し、排気管１００内に排出された余剰分のＨＣを燃焼し低減するためのものである。通常の場合、空燃比フィードバック制御中は２次空気系６は作動していない。従って、本実施例の触媒劣化検出方法においては、空燃比センサ７，８によるデ−タサンプリング中に２次空気系６から空気が流れてしまうような故障が特に問題となる。
【００４４】
このような故障が生じた場合の影響については、２次空気系６の排気管への導入口６２と空燃比センサ７との位置関係等により異なる。
【００４５】
導入口６２よりも後流側に空燃比センサ７が位置している場合には、空燃比センサ７が２次空気系６から流入した酸素を検出することによってリーンであると判定し、燃料をリッチ側にフィードバック制御してしまう。その結果、２次空気系６から流入した酸素に対応する分以上に燃料の量を増量してしまい、結果として触媒５の位置ではリッチとなってしまう。このため触媒下流の空燃比センサ８の出力信号もリッチ側にシフトしてしまう。
【００４６】
空燃比センサ８が空燃比を２値的に検出するタイプの場合、空燃比が出力変化空燃比からずれてしまうため、出力波形の振幅が小さくなってしまう。そのため、漏れ空気量に応じて、図５の場合と同様、触媒劣化指標Φｃは低めの値となる。さらに漏れ空気量が多くなると、空燃比センサ８の出力信号は、一定状態（リッチ状態）になってしまうため、触媒劣化指標Φｃはほぼゼロとなり、補正できなくなる。従って、図９に示すように、空気の漏れ量が少ない場合には、触媒劣化指標Φｃに係数Ｋｃをかけて補正し、漏れ量が多い場合には劣化検出を中断するようにすればよい。
【００４７】
なお、一般的には、２次空気系故障検出手段１０は、漏れ量を正確に検出しようとするとコストが高くなるため、精度があまり高くないことが多い。このため、２次空気系６に故障があると判定された場合には、既に触媒の劣化判定が不可能となっていることもある。従って、補正することなく、一気に劣化判定を中断するようにしてもよい。また、逆に、触媒劣化判定中断手段１４を設けることなく、触媒劣化指標Φｃ補正手段１３による補正のみを行う構成としても構わない。
【００４８】
空燃比センサ８が広域空燃比センサの場合、空気の漏れがあると、触媒５が酸化還元反応を効率良く行なえる範囲を越えて空燃比が変動し、空燃比センサ８の出力信号の振幅も大きくなる。その結果、漏れ空気量に応じて触媒劣化指標Φｃは高めの値となる。漏れ空気量が多くなると触媒５の劣化度とは係わりなく空燃比センサ８の出力信号が振れて、補正ができなくなる。従って、図１０に示すように、２次空気系６の漏れ量が少ない場合には、触媒劣化指標Φｃに係数Ｋｃをかけて補正する。漏れ量が多いときには、劣化検出を中断するようにすればよい。 前述の場合と同様、この場合も２次空気系に故障があると判定された場合には、補正することなく、一気に劣化判定を中断するようにしてもよい。さらに、この場合には、触媒の劣化判定で触媒劣化指標Φｃが大きめの値となるため、劣化していない触媒を劣化していると誤判定してしまっている可能性もあるので、直前の触媒の劣化判定結果を廃棄するなどの手段を設けることが好ましい。また、逆に、触媒劣化判定中断手段１４を設けることなく、触媒劣化指標Φｃ補正手段１３による補正のみを行う構成としても構わない。
【００４９】
以上のように漏れ空気量が少ない場合には触媒劣化指標補正手段１３により触媒劣化指標Φｃを補正する。この場合、空燃比センサ８の種類等により補正の方向等が異なる。漏れ空気量が多い場合には触媒劣化判定中断手段１４により触媒劣化判定を中断するようにすることが好ましい。
【００５０】
なお、補正可能な漏れ空気量は触媒の温度等によって変化するため、触媒５の温度またはエンジンの運転状態に応じて、補正量や、判定を中断する漏れ空気量を変えるようにすることが好ましい。一般的には、失火の場合と同様に、負荷が高いほど、補正量を少なくする。また、判定を中断する漏れ空気量については、漏れが多い側に変える。
【００５１】
次に第２の実施例として、空燃比センサの劣化判定を行う診断装置を説明する。
【００５２】
本実施例の診断装置および適用対象となるエンジンシステムの全体構成を図１１に示した。エンジン１、空気流量計２、空燃比フィ−ドバック制御手段３、インジェクタ４、空燃比センサ７等は上記第１の実施例で説明したものと同じである。
【００５３】
該診断装置は、失火検出手段９と、２次空気故障検出手段１０と、空燃比センサ劣化指標計算手段２１と、空燃比センサ劣化判定手段２２と、空燃比センサ劣化指標補正手段２３と、空燃比センサ劣化判定中断手段２４とを含んで構成される。
【００５４】
空燃比センサ劣化指標計算手段２１は、空燃比センサ７の劣化状態を検出するものである。本実施例においては、劣化状態の検出を空燃比センサ７の出力信号の自己相関関数を用いて行っている。つまり、空燃比センサ７劣化指標計算手段２１は前述の触媒劣化指標計算手段１１の場合と同様にして、空燃比センサ７の出力信号から直流成分を除去した信号ｘから自己相関関数φｘｘ（０）を計算する。空燃比センサ７の応答性の劣化度を表わす劣化指標Φｓｒとしてこのφｘｘ（０）を採用すると、該劣化指標Φｓｒは空燃比センサ７は劣化していないときはに大きな値、劣化すると小さな値を示す。
【００５５】
なお、空燃比センサの劣化検出方法はこの方法に限定されるものではない。例えば空燃比センサの出力信号の微分値や所定電圧間を変化するのにかかる応答時間、あるいは周波数等から検出方法等数多くの公知例があり、これらいずれの方法を用いるようにしても構わない。以下に述べる補正方法等異なってくるだけである。
【００５６】
空燃比センサ劣化判定手段２２では、前述の空燃比センサ劣化指標Φｓｒを所定の値（注：該所定の値が特許請求の範囲においていう”しきい値”に該当する。）と比較することによって空燃比センサの劣化度を判定する。空燃比センサ劣化指標Φｓｒが所定値より高いときは故障と判定し、例えば図示しない警告灯を点灯して、運転者に警告したりする。
【００５７】
失火検出手段９及び２次空気系故障検出手段１０は、前記実施例と同様である。 空燃比センサ劣化指標補正手段２３は、失火検出手段９または、２次空気系故障検出手段１０により、失火または２次空気系の故障や劣化が検出されたとき、前述の空燃比センサ劣化指標を補正し、補正後の空燃比センサ劣化指標を空燃比センサ劣化判定手段２２に出力するものである。
【００５８】
空燃比センサ劣化判定中断手段２４は、判定を中断するか否かの基準となる、失火や２次空気系故障についての予め定められたの頻度（あるいは程度）を備えている。そして、該予め定められた頻度（あるいは程度）を越えて、失火や２次空気系の故障や劣化が検出されたときには、前述の空燃比センサ劣化判定手段２２による空燃比センサの劣化判定を中断するための信号を発生するものである。
次に失火が発生したときの動作について説明する。
【００５９】
失火が発生すると、スパイク状のリ−ン信号が生じる（図４参照）。すると、空燃比劣化指標Φｓｒは、失火の発生頻度に応じて大きめの値となってしまう（図１２参照）。つまり、空燃比センサ７の応答性を実際よりもよい側に評価し、その劣化度を低く評価してしまう。これは、空燃比センサ７の種類によらず、同じことがいえる。従って、空燃比センサ劣化指標補正手段２３において、失火の頻度に応じて決められた係数Ｋｓｒ（図１３参照）を、空燃比劣化指標Φｓｒにかけることによって、空燃比劣化指標Φｓｒを小さくするような補正を行なう。失火の頻度が大きくなりすぎると空燃比劣化指標Φｓｒのばらつきが大きくなってくるので、空燃比センサ劣化判定中断手段２４により空燃比センサ劣化判定を中断するようにする。
【００６０】
次に２次空気系６に故障が発生したときの動作について説明する。
【００６１】
触媒の劣化検出の場合と同様に、空燃比センサがデ−タをサンプリングしている時に、空気が漏れて流れてしまうような故障が特に問題となる。このような故障が生じた場合の影響は、導入口６２と空燃比センサ７との間における、排気ガスと２次空気系６から流れてくる漏れ空気との混合状態等により異なる。
【００６２】
空燃比センサ７が空燃比を２値的に検出するタイプの場合、導入口６２からの漏れてくる空気（酸素）のためにリッチ側の信号が出にくくなる。そのため、漏れ空気量に応じて、空燃比センサ７の出力信号の振幅が小さくなり、空燃比センサ劣化指標Φｓｒも低めの値となる。漏れ空気量がさらに多くなるとΦｓｒほぼゼロとなり、補正できなくなる。従って、図１４に示すように、漏れ空気量が少ない場合には係数ｋｓｒをかける補正を行う。漏れ空気量が多い場合には劣化判定を中断する。
【００６３】
一方、空燃比センサ７が広域空燃比センサの場合には、漏れ量が少ない場合には、触媒劣化指標Φｓｒは低めの値となる。漏れ量がさらに多くなると出力が不安定になり、劣化判定が不可能となる。従って、図１４と同様の補正および劣化判定中断を行う。
【００６４】
なお、前述のように、一般には２次空気系故障検出手段１０は、精度があまり高くないことが多いため、２次空気系６に故障があると判定された場合には、既に空燃比センサの劣化判定が不可能となっていることもある。従って、２次空気系６に故障があると判定された場合には、一気に劣化判定を中断するようにしてもよい。逆に、空燃比センサ劣化判定中断手段２４を設けることなく、空燃比センサ劣化指標補正手段２３による補正のみを行う構成としても構わない。
【００６５】
以上は空燃比センサの応答性に関する劣化の判定について説明したが、他にも例えば出力電圧に関する劣化判定等もある。これは空燃比を所定値に保持して空燃比センサの出力を測定することによって検出するが、失火や２次空気系の故障によって空燃比が変動してしまうので、劣化指標の補正や劣化判定の中断が必要である。
【００６６】
例えば、空燃比をリッチ状態に保持して、空燃比センサのリッチ側信号出力電圧を判定するような場合、２次空気系６から空気が漏れていると、空燃比センサはリ−ン信号を発生する。その結果、空燃比センサが劣化しているものと誤判定してしまう。また、失火が発生しても同様で、失火の頻度がすくない場合には、リ−ンスパイク状の信号出力が生じる。失火頻度が高くなると、出力信号は一定値（リ−ン状態）を示したり（２値センサの場合）、出力信号が大きくばらついたり（広域空燃比センサ）してしまう。従って、このような劣化判定にも本発明は適用可能である。
【００６７】
また、上記実施例では触媒上流の空燃比センサの劣化検出について説明したが、触媒下流の空燃比センサの劣化検出等についても、失火や２次空気系の故障に応じ、劣化指標の補正や劣化判定の中断が必要であり、適用可能である。
【００６８】
以上述べたように空燃比センサの劣化検出についても、失火や２次空気系の故障に応じ、空燃比センサ劣化指標の補正や空燃比劣化判定の中断が必要であり、適用可能である。
【００６９】
さらに上記説明においては、触媒劣化指標を補正する場合について述べたが、劣化を判定するために触媒劣化指標と比較するためのしきい値の方を補正しても実質的には同じことである。
【００７０】
【発明の効果】
本発明によれば、失火が発生しても、触媒の劣化度を誤って判定してしまうことがなくなる。このため、劣化していないのに交換してしまったり、劣化しているのにそのまま走行してしまうようなことがなくなり、余分な出費や大気汚染の防止に役立つ。
【図面の簡単な説明】
【図１】本発明の一実施例の構成を示す図面である。
【図２】触媒上下流の空燃比センサ７，８の出力信号の一例を示す図である。
【図３】触媒劣化度と劣化指標との関係を説明する図である。
【図４】失火が空燃比センサの出力信号に与える影響を示す図である。
【図５】失火が、触媒の劣化指標に与える影響を示す図である。
【図６】補正係数および判定中断領域を示す図である。
【図７】失火が、触媒の劣化指標に与える影響を示す図である。
【図８】補正係数および判定中断領域を示す図である。
【図９】補正係数および判定中断領域を示す図である。
【図１０】補正係数および判定中断領域を示す図である。
【図１１】本発明の他の実施例を示す図である。
【図１２】失火が、空燃比センサ劣化指標に与える影響を示す図である。
【図１３】補正係数および判定中断領域を示す図である。
【図１４】補正係数および判定中断領域を示す図である。
【符号の説明】
１……エンジン、２……空気流量計、３……空燃比フィ−ドバック制御手段、４……５……触媒、６……２次空気系、７……空燃比センサ、８……空燃比センサ、９……失火検出手段、１０……２次空気系故障検出手段、１１……触媒劣化指標計算手段、１２……触媒劣化判定手段、１３……触媒劣化指標補正手段、１４……触媒劣化判定中断手段、２１……空燃比センサ劣化指標計算手段、２２……空燃比センサ劣化判定手段、２３……空燃比センサ劣化指標補正手段、２４……空燃比センサ劣化判定中断手段[0001]
[Industrial applications]
The present invention relates to a so-called wide-range air-fuel ratio sensor for measuring an air-fuel ratio in a wide air-fuel ratio range, or a so-called O2 sensor (hereinafter, referred to as both O2 sensors) whose output rapidly changes near a stoichiometric air-fuel ratio to generate a binary output. Collectively referred to as an “air-fuel ratio sensor”) and a diagnostic device for an exhaust gas purifying device of an engine using a catalyst.
[0002]
[Prior art]
2. Description of the Related Art As a device for purifying exhaust gas of an engine, a device comprising a catalyst and an air-fuel ratio feedback control device is widely known. The catalyst is installed in the exhaust trunk to remove HC, NOx, and CO contained in the exhaust. The air-fuel ratio feedback control device is a device that controls the air-fuel ratio by installing an air-fuel ratio sensor upstream of the catalyst and measuring the air-fuel ratio in order to maintain the air-fuel ratio at a predetermined value in order to sufficiently exert the function of the catalyst. is there. In such an exhaust gas purifying apparatus, when the performance of the air-fuel ratio sensor for measuring the air-fuel ratio is deteriorated, the air-fuel ratio deviates from a predetermined value, so that the amount of the harmful gas component in the exhaust gas increases. In addition, since the catalyst deviates from the air-fuel ratio at which the catalyst can exhibit its performance, the harmful gas removal efficiency (conversion efficiency) decreases. Further, when the performance of the catalyst itself deteriorates, the conversion efficiency of the harmful gas is reduced even if the air-fuel ratio is controlled so that the catalyst can exhibit its performance. As described above, performance degradation of the air-fuel ratio sensor and the catalyst results in an increase in the amount of harmful gas released to the atmosphere. For this reason, a diagnostic device of an exhaust gas purifying device for diagnosing such performance deterioration during driving and warning a driver has been devised. As such a diagnostic device, for example, an air-fuel ratio sensor is provided upstream and downstream of the catalyst, and a specific air-fuel ratio feedback control is performed based on at least the output of the air-fuel ratio sensor on the upstream side of the catalyst. For example, the deterioration of the catalyst may be detected. As such prior art, there are those described in JP-A-2-91440 and JP-A-3-286160.
[0003]
[Problems to be solved by the invention]
In the method of detecting the deterioration of the catalyst by the output of the air-fuel ratio sensor on the downstream side of the catalyst during the air-fuel ratio feedback control, it is naturally impossible to detect the deterioration of the catalyst while the air-fuel ratio feedback control is stopped. Further, when the catalyst is not activated, there is a high possibility that the catalyst is erroneously detected as deteriorated even if it is not deteriorated. It is necessary to permit or prohibit deterioration detection. These are also considered in the prior art described in JP-A-2-91440. Further, if the air-fuel ratio sensor on the upstream side of the catalyst deteriorates, it affects the detection of deterioration of the catalyst depending on the degree and content of the deterioration, so it is necessary to correct the detection result and prohibit detection of deterioration of the catalyst. . For this reason, in the prior art described in JP-A-3-286160, when the air-fuel ratio sensor on the upstream side of the catalyst has deteriorated, detection of deterioration of the catalyst is prohibited.
[0004]
By the way, when a misfire occurs in the combustion stroke of the engine, oxygen in the air flows into the exhaust pipe together with unburned gas, so that the air-fuel ratio sensor upstream of the catalyst generates a lean spike-like signal or the air downstream of the catalyst. The fuel ratio sensor generates a signal leaner than the actual one. For this reason, there is a problem that the detection accuracy of the catalyst deterioration is reduced.You. This pointIs not considered in the prior art.
[0005]
The purpose of the present invention is toThe fireEven if it occurs, TouchThat is, the accuracy of detecting the deterioration of the medium is not reduced.
[0006]
[Means for Solving the Problems]
A diagnostic device according to one embodiment of the present invention,
A first air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on the upstream side of the catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas downstream of the catalyst;
Catalyst deterioration index calculating means for calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
A catalyst deterioration determining unit that has a predetermined threshold value and compares the threshold value with the catalyst deterioration index to determine a deterioration state of the catalyst;
Misfire detection means for detecting the combustion state of the engine based on the rotation speed fluctuation of the engine and detecting the occurrence of misfire;
Catalyst degradation determination suspending means for suspending the determination of the catalyst degradation determining means when misfire is detected by the misfire detecting means,
It is characterized by having.
[0007]
A diagnostic device according to another aspect of the present invention includes:
An air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas,
Air-fuel ratio sensor deterioration index calculation means for calculating an air-fuel ratio sensor deterioration index indicating the deterioration state of the air-fuel ratio sensor from the output signal of the air-fuel ratio sensor,
An air-fuel ratio sensor deterioration determining unit that includes a predetermined threshold value and compares the threshold value with the air-fuel ratio sensor deterioration index to determine the deterioration state of the air-fuel ratio sensor;
Misfire detection means for detecting the combustion state of the engine based on the rotation speed fluctuation of the engine and detecting the occurrence of misfire;
Air-fuel ratio sensor deterioration determination interruption means for interrupting the determination of the air-fuel ratio sensor deterioration determination means when misfire is detected by the misfire detection means,
It is characterized by having.
[0008]
A diagnostic device according to still another aspect of the present invention includes:
A first air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on the upstream side of the catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas downstream of the catalyst;
Catalyst deterioration index calculating means for calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
A catalyst deterioration determining unit that has a predetermined threshold value and compares the threshold value with the catalyst deterioration index to determine a deterioration state of the catalyst;
Misfire detection means for detecting occurrence of engine misfire based on fluctuations in engine speed;
Catalyst deterioration diagnosis interrupting means for interrupting the determination of the catalyst deterioration determining means when at least continuous misfire of a certain cylinder occurs,
It is characterized by having.
[0009]
[Action]
According to the configuration of the present invention,MediumLoss that reduces the detection accuracyFire breaks outIf a misfire is detected,Step by stepTwisterTheDetect and touchMediumSuspends the determination of the activation status. Therefore,Fire breaks outEven if you are born,MediumThere is no possibility of erroneously determining the activation state.
[0010]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is a diagram showing a configuration of a diagnostic device according to an embodiment of the present invention and an engine system to which the diagnostic device is applied.
[0012]
First, the outline of the premise engine system will be described. However, the target to which the diagnostic device of the present invention is applied is not limited to the engine system.
[0013]
The amount Qa of air taken into the engine 1 is measured by the air flow meter 2. The rotation speed Ne is measured by a rotation speed measurement unit (not shown). The air-fuel ratio feedback control means 3 calculates the basic fuel injection amount F from the intake air amount Qa and the rotational speed Ne according to the following equation (1).0Ask for.
[0014]
(Equation 1)
F0= KQa / Ne
k: coefficient
The air-fuel ratio sensor 7 measures the air-fuel ratio of the exhaust gas discharged from the engine 1. As described above, in the case of the “air-fuel ratio sensor” in this specification, the oxygen concentration is detected in a binary manner (the output sharply changes near the stoichiometric air-fuel ratio), and the oxygen concentration is detected linearly. And a so-called wide-range air-fuel ratio sensor. The air-fuel ratio feedback control means 3 obtains a correction coefficient α in accordance with the output of the air-fuel ratio sensor 7, corrects the aforementioned basic injection amount by the following equation 2, and obtains the injection amount F.
[0015]
(Equation 2)
F = F0(1 + α)
Further, the fuel supply amount is feedback-controlled by applying a pulse signal having a width corresponding to the injection amount F to the injector 4. By such control, the air-fuel ratio of the air-fuel mixture is maintained near the stoichiometric air-fuel ratio. In the catalyst 5, unburned gas components (hereinafter referred to as HC), which are harmful components in the exhaust gas, and CO2These are reduced by simultaneously oxidizing and reducing NOx. Such a catalyst is called a three-way catalyst. To simultaneously perform an oxidation reaction and a reduction reaction by the three-way catalyst, it is necessary to maintain an air-fuel ratio near a stoichiometric air-fuel ratio. For that purpose, it is necessary that the above-described air-fuel ratio feedback control is accurately performed.
[0016]
The secondary air system 6 is operated by the pump 60 by the exhaust pipe 100 in an operating state (for example, when the engine is started) in which the fuel concentration of the air-fuel mixture must be higher than the stoichiometric air-fuel ratio (hereinafter, referred to as rich). This is for introducing air into the inside and burning and reducing excess HC discharged into the exhaust pipe 100.
[0017]
Hereinafter, the diagnostic device of the present embodiment will be described.
[0018]
As shown in FIG. 1, the diagnostic apparatus of the present embodiment includes a misfire detection unit 9, a secondary air system failure detection unit 10, a catalyst deterioration index calculation unit 11, a catalyst deterioration determination unit 12, a catalyst deterioration index correction Means 13 and catalyst deterioration determination interruption means 14.
[0019]
The catalyst deterioration index calculating means 11 is for detecting the deterioration state of the catalyst 5. The catalyst deterioration index calculating means 11 of the present embodiment utilizes the correlation between the signals of the air-fuel ratio sensor 7 installed on the upstream side of the catalyst 5 and the air-fuel ratio sensor 8 installed on the downstream side of the catalyst 5 to make use of the catalyst 5. Is performed for deterioration detection. That is, when the catalyst 5 is not deteriorated, the output signal of the air-fuel ratio sensor 8 does not fluctuate similarly to the output signal of the air-fuel ratio sensor 7, but as the catalyst 5 deteriorates, the output signal of the air-fuel ratio sensor 8 becomes smaller. The deterioration detection is performed by utilizing the fact that the signal fluctuates similarly to the output signal of the air-fuel ratio sensor 7. Hereinafter, an outline of the deterioration detection method will be described.
[0020]
First, the catalyst deterioration index Φc calculating means 11 measures the output signals of the air-fuel ratio sensors 7 and 8 in synchronization. Then, using a high-frequency pass filter, a DC component which is a disturbance for deterioration detection is removed from the measured signal. FIG. 2 shows examples of these signals (hereinafter, a signal obtained by removing the DC component from the output signal of the air-fuel ratio sensor 7 is represented by x, and a signal obtained by removing the DC component from the output signal of the air-fuel ratio sensor 8 is represented by y).
[0021]
Then, an auto-correlation function φxx of x and a cross-correlation function φxy of x and y are calculated (see the following Expressions 3 and 4).
[0022]
(Equation 3)
Figure 0003564088
[0023]
(Equation 4)
Figure 0003564088
[0024]
Since φxx (τ) becomes the maximum value φxx (0) when τ = 0, the relationship of the following equation 5 holds.
[0025]
(Equation 5)
(Φxx) max = φxx (0)
Further, the maximum value of φxy (τ) is obtained by changing the phase τ within the integration interval of the cross-correlation function. τ = τ0Assuming that the maximum value is obtained, the following Expression 6 is obtained.
[0026]
(Equation 6)
(Φxy) max = φxy (τ0)
From these values, the catalyst deterioration index Φc is determined by the following equation (7).
[0027]
(Equation 7)
Φc = (φxy) max / (φxx) max
FIG. 3 shows the relationship between φxy (τ) / (φxx) max and the degree of catalyst deterioration. When the degree of deterioration of the catalyst 5 is large, the correlation between the output signal of the air-fuel ratio sensor 7 and the output signal of the air-fuel ratio sensor 8 is high and shows a large peak (maximum value). On the other hand, when the degree of deterioration of the catalyst 5 is small (when the degree of deterioration is small), the correlation between the two output signals is low, and only a small peak (maximum value) is shown. Therefore, the degree of deterioration of the catalyst 5 can be detected from the magnitude of the catalyst deterioration index Φc.
[0028]
The method of detecting the degree of deterioration described above has already been proposed in Japanese Patent Application No. 3-338220.
[0029]
The method for detecting the deterioration of the catalyst is not limited to this method. For example, a method of detecting from the fluctuation width of the output signals of the air-fuel ratio sensors 7 and 8, the phase difference, the frequency, and the like may be used. There are many other publicly known examples, and any of these methods may be used. However, it is necessary to change the correction method described below according to the method.
[0030]
The catalyst deterioration determining means 12 determines the deterioration state obtained by the catalyst deterioration index calculating means 11 and determines whether or not the exhaust gas purification device has failed. In the present embodiment, the above-mentioned catalyst deterioration index Φc is compared with a predetermined value set in advance (note: the predetermined value corresponds to a “threshold” in the claims). Is used to make the determination. For example, when the catalyst deterioration index Φc is larger than a predetermined value, it is determined that a failure has occurred. If a failure has occurred, a warning light (not shown) is turned on to warn the driver.
[0031]
The misfire detection means 9 functions to detect the occurrence of misfire every time combustion is performed in the cylinder of the engine. As a misfire detection method, for example, there is a method for detecting a misfire based on fluctuations in the rotation speed of an engine disclosed in Japanese Patent Application Laid-Open No. 3-206342. This is a method of detecting the combustion state or the rotational speed fluctuation waveform during the combustion stroke. Another method for detecting the combustion state based on the fluctuation of the rotation speed is described in US Pat. No. 4,627,399. As other methods, there are a method of detecting from the combustion pressure and temperature in the combustion chamber, and a method of detecting from the pulsation and temperature of the exhaust gas pressure. Further, as disclosed in US Pat. No. 4,648,367, a method of providing an ion gap in a combustion chamber and detecting from an ion current flowing therebetween, a method of measuring and detecting combustion light in the combustion chamber, or a method of measuring a current waveform flowing through an ignition coil and the like. There are many known methods, such as a detection method. Either of these methods may be used as the misfire detecting means 9 of the present embodiment.
[0032]
The secondary air system failure detecting means 10 functions to detect a failure or deterioration of the secondary air system 6. This is because, for example, a flow meter is provided in the middle of the air passage of the secondary air system 6 to detect the actual air flow rate, and the flow rate estimated from the control amount (voltage or current value) to the pump 60 is compared with the actual flow rate. There is a method of detecting based on the difference. In addition, since the air-fuel ratio sensor 7 detects oxygen when the secondary air system is operated, the correction coefficient α increases so as to increase the supplied fuel if the above-described air-fuel ratio feedback control is directly performed. For example, when the correction coefficient α does not increase even when the pump 60 is operated, there are a number of known methods such as a method of detecting a secondary air system failure assuming that the secondary air is not flowing. Either method may be used.
[0033]
The catalyst deterioration index correction means 13 corrects and corrects the above-mentioned catalyst deterioration index when the misfire detection means 9 or the secondary air system failure detection means 10 detects misfire or failure or deterioration of the secondary air system. The latter catalyst deterioration index is output to the catalyst deterioration determination means 12. Note that the correction method is performed in conjunction with the operation described below.
[0034]
The catalyst deterioration determination suspending means 14 has a predetermined frequency (or degree) of misfire or failure or deterioration of the secondary air system, which serves as a criterion for suspending the determination. If the misfire detection means 9 or the secondary air system failure detection means 10 detects the frequency exceeding the predetermined frequency (or degree), the above-mentioned catalyst deterioration determination means 12 interrupts the catalyst deterioration determination. To generate a signal for performing the operation. The frequency (or degree) may be changed according to the temperature or the like as described later.
[0035]
Explain the operation when a misfire occurs
FIG. 4 shows an example of an output signal of the catalyst upstream-side air-fuel ratio sensor 7 when a misfire has not occurred and when a misfire has occurred.
[0036]
When a misfire occurs, unburned HC and air flow into the exhaust pipe, and a spike-like signal indicating that the air-fuel ratio of the exhaust gas is thin (more oxygen) is generated in synchronization with the misfire. . When such a misfire occurs, the oxidation reaction of unburned HC proceeds in the catalyst 5 together with the normal purification reaction. However, the unreacted HC and oxygen also flow downstream of the catalyst 5, so that the air-fuel ratio The sensor 8 is affected as follows.
[0037]
The air-fuel ratio sensor 8 indicates a binary output O2In the case of the sensor, the output signal shifts to the side indicating that the air-fuel efficiency is low (hereinafter, "lean"), and at the same time, the amplitude decreases. Therefore, the above-described catalyst deterioration index Φc changes according to the frequency of misfire as shown in FIG. That is, in this case, if a misfire occurs even if the catalyst is originally deteriorated, the degree of deterioration is evaluated as low. Therefore, the catalyst deterioration index correction means 13 may make a correction so as to increase the catalyst deterioration index Φc according to the frequency of misfires, for example, by multiplying the coefficient Kc as shown in FIG. Further, as a matter of course, correction may be made such that the predetermined value for comparison with the catalyst deterioration index Φc is reduced by the catalyst deterioration determining means 12 according to the frequency of misfire. For example, in the case where one cylinder is continuously misfiring in a six-cylinder engine, a large amount of oxygen and HC, which are supposed to react by combustion without excess or deficiency, cannot be partitioned in the exhaust pipe and the catalyst 5, so that a large amount of Oxygen flows downstream of the catalyst. For this reason, the air-fuel ratio sensor 8 shows an output signal indicating that the air-fuel ratio is thinner than the stoichiometric air-fuel ratio (hereinafter, referred to as lean) regardless of the degree of deterioration of the catalyst 5. In particular, the air-fuel ratio sensor 8 detects the air-fuel ratio in a binary manner. In the case of this type, the value becomes constant. As a result, the output signal becomes lean and constant (the amplitude is almost zero) regardless of the degree of deterioration of the catalyst, and the catalyst deterioration index Φc cannot be corrected. Therefore, if the misfire occurrence frequency is lower than the predetermined value, the catalyst deterioration index Φc is corrected according to the frequency, and if the frequency is higher than the predetermined value, the catalyst deterioration determination is made to determine whether the misfire has occurred or the frequency is higher than the predetermined value. It is preferable to suspend the operation while the value exceeds.
[0038]
The correction amount and the correctable misfire frequency change depending on the temperature of the catalyst, the engine load, and the like. Therefore, according to the temperature of the catalyst 5 and the operating state of the engine, the correction coefficient and the misfire frequency for interrupting the determination are determined. Is preferably changed as shown in FIG. 6, for example. This is because, for example, the rate of the HC oxidation reaction changes depending on the temperature of the catalyst 5 (note: in a temperature range that the catalyst can normally take, the higher the temperature, the faster the reaction rate). In actual misfires, one or more of the cylinders often misfires almost continuously due to a failure of the ignition system or the like. In this case, a misfire with a frequency that cannot be corrected at once is detected. Therefore, if the misfire occurs at such a frequency as to affect the detection of the deterioration of the catalyst, it is often sufficient to immediately stop the determination of the deterioration of the catalyst without making any correction. In this case, in many known examples, the misfire detection means 9 warns the driver of the occurrence of a misfire, so if the catalyst deterioration determination is re-established after the repair is completed based on the warning, There are often no problems in practice.
[0039]
On the other hand, when the air-fuel ratio sensor 8 is a so-called wide-range air-fuel ratio sensor, the air-fuel ratio sensor 8 also outputs a signal indicating a lean at the time of misfire almost in synchronization with the spike-like output signal of the air-fuel ratio sensor 7. . For this reason, as shown in FIG. 7, when the frequency of misfire is low, the catalyst deterioration index Φc has a slightly high value. Also, if the frequency of misfires increases to some extent, the catalyst 5 does not react normally even if it has not deteriorated, so that the air-fuel ratio sensors 7 and 8 output signal waveforms that are close to each other, and the catalyst deterioration index Φc has a large value. Will be shown. Therefore, for example, when the frequency of misfire is low as shown in FIG. 8, correction by multiplying by the coefficient Kc may be performed, and when the frequency of misfire is high, the deterioration determination may be prohibited.
[0040]
As in the case described above, if the misfire occurs at such a frequency as to affect the detection of the deterioration of the catalyst, it is often sufficient to immediately stop the determination of the deterioration of the catalyst without making any correction. Further, in this case, since the deterioration index Φc is a relatively large value in the catalyst deterioration determination, there is a possibility that an undegraded catalyst may be erroneously determined to be deteriorated. It is preferable to provide means for discarding the catalyst deterioration determination result.
[0041]
Conversely, the configuration may be such that only the correction by the catalyst deterioration index Φc correction means 13 is performed without providing the catalyst deterioration determination interruption means 14.
[0042]
Next, a case where the secondary air system 6 has failed or deteriorated will be described.
[0043]
As described above, the secondary air system 6 generally supplies air into the exhaust pipe 100 by the pump 60 in an operating state (for example, when starting the engine) in which the air-fuel ratio of the air-fuel mixture must be made rich. To burn and reduce excess HC discharged into the exhaust pipe 100. In a normal case, the secondary air system 6 is not operating during the air-fuel ratio feedback control. Therefore, in the catalyst deterioration detecting method of the present embodiment, a problem that air flows from the secondary air system 6 during the data sampling by the air-fuel ratio sensors 7 and 8 is particularly problematic.
[0044]
The effect of such a failure depends on the positional relationship between the inlet 62 to the exhaust pipe of the secondary air system 6 and the air-fuel ratio sensor 7 and the like.
[0045]
When the air-fuel ratio sensor 7 is located on the downstream side of the inlet 62, the air-fuel ratio sensor 7 detects oxygen flowing from the secondary air system 6 to determine that the fuel is lean, and determines that the fuel is lean. Feedback control is performed on the rich side. As a result, the amount of fuel is increased more than the amount corresponding to the oxygen flowing from the secondary air system 6, and as a result, the position of the catalyst 5 becomes rich. Therefore, the output signal of the air-fuel ratio sensor 8 downstream of the catalyst also shifts to the rich side.
[0046]
In the case where the air-fuel ratio sensor 8 detects the air-fuel ratio in a binary manner, the air-fuel ratio deviates from the output change air-fuel ratio, so that the amplitude of the output waveform is reduced. Therefore, similarly to the case of FIG. 5, the catalyst deterioration index Φc has a lower value according to the amount of leaked air. If the amount of leaked air further increases, the output signal of the air-fuel ratio sensor 8 becomes constant (rich state), so that the catalyst deterioration index Φc becomes almost zero and cannot be corrected. Therefore, as shown in FIG. 9, when the amount of air leakage is small, the catalyst deterioration index Φc is corrected by multiplying by the coefficient Kc, and when the amount of leakage is large, the deterioration detection may be interrupted.
[0047]
In general, the secondary air system failure detecting means 10 is not so high in accuracy because the cost is high if the leak amount is to be accurately detected. Therefore, when it is determined that there is a failure in the secondary air system 6, it may not be possible to determine the deterioration of the catalyst. Therefore, the deterioration determination may be interrupted at once without correcting. Conversely, the configuration may be such that only the correction by the catalyst deterioration index Φc correction means 13 is performed without providing the catalyst deterioration determination interruption means 14.
[0048]
If the air-fuel ratio sensor 8 is a wide-range air-fuel ratio sensor, if air leaks, the air-fuel ratio fluctuates beyond the range where the catalyst 5 can efficiently perform the oxidation-reduction reaction, and the amplitude of the output signal of the air-fuel ratio sensor 8 also increases. growing. As a result, the catalyst deterioration index Φc becomes a higher value according to the amount of leaked air. When the amount of leaked air increases, the output signal of the air-fuel ratio sensor 8 fluctuates irrespective of the degree of deterioration of the catalyst 5, and correction cannot be performed. Therefore, as shown in FIG. 10, when the leakage amount of the secondary air system 6 is small, the correction is made by multiplying the catalyst deterioration index Φc by the coefficient Kc. When the leakage amount is large, the deterioration detection may be interrupted. As in the case described above, in this case as well, if it is determined that there is a failure in the secondary air system, the deterioration determination may be stopped at once without correction. Further, in this case, since the catalyst deterioration index Φc becomes a relatively large value in the catalyst deterioration determination, there is a possibility that the undegraded catalyst may be erroneously determined to be deteriorated. It is preferable to provide means for discarding the catalyst deterioration determination result. Conversely, the configuration may be such that only the correction by the catalyst deterioration index Φc correction means 13 is performed without providing the catalyst deterioration determination interruption means 14.
[0049]
As described above, when the amount of leaked air is small, the catalyst deterioration index correction means 13 corrects the catalyst deterioration index Φc. In this case, the direction of correction and the like differ depending on the type of the air-fuel ratio sensor 8 and the like. When the amount of leaked air is large, it is preferable that the catalyst deterioration determination interrupting means 14 interrupt the catalyst deterioration determination.
[0050]
Since the correctable leak air amount changes depending on the temperature of the catalyst or the like, it is preferable to change the correction amount or the leak air amount for which the determination is interrupted according to the temperature of the catalyst 5 or the operating state of the engine. . Generally, as in the case of misfire, the higher the load, the smaller the correction amount. In addition, the amount of leaked air for which the determination is interrupted is changed to the side with more leakage.
[0051]
Next, as a second embodiment, a diagnostic device for determining deterioration of the air-fuel ratio sensor will be described.
[0052]
FIG. 11 shows the overall configuration of the diagnostic apparatus of this embodiment and the engine system to which the diagnostic apparatus is applied. The engine 1, the air flow meter 2, the air-fuel ratio feedback control means 3, the injector 4, the air-fuel ratio sensor 7, etc. are the same as those described in the first embodiment.
[0053]
The diagnostic device includes a misfire detecting means 9, a secondary air failure detecting means 10, an air-fuel ratio sensor deterioration index calculating means 21, an air-fuel ratio sensor deterioration determining means 22, an air-fuel ratio sensor deterioration index correcting means 23, And a fuel ratio sensor deterioration determination suspending means 24.
[0054]
The air-fuel ratio sensor deterioration index calculating means 21 detects a deterioration state of the air-fuel ratio sensor 7. In the present embodiment, the deterioration state is detected using the autocorrelation function of the output signal of the air-fuel ratio sensor 7. That is, the air-fuel ratio sensor 7 deterioration index calculating means 21 calculates the autocorrelation function φxx (0) from the signal x obtained by removing the DC component from the output signal of the air-fuel ratio sensor 7 in the same manner as the above-described catalyst deterioration index calculating means 11. Is calculated. When this φxx (0) is adopted as the deterioration index Φsr representing the degree of deterioration of the response of the air-fuel ratio sensor 7, the deterioration index Φsr becomes a large value when the air-fuel ratio sensor 7 is not deteriorated, and a small value when the air-fuel ratio sensor 7 is deteriorated. Show.
[0055]
The method for detecting the deterioration of the air-fuel ratio sensor is not limited to this method. For example, there are a number of known examples such as a detection method based on a response time required to change a differential value of an output signal of the air-fuel ratio sensor or a predetermined voltage or a frequency, and any of these methods may be used. The only difference is the correction method described below.
[0056]
The air-fuel ratio sensor deterioration determination means 22 compares the air-fuel ratio sensor deterioration index Φsr with a predetermined value (note: the predetermined value corresponds to a “threshold” in the claims). The degree of deterioration of the air-fuel ratio sensor is determined. When the air-fuel ratio sensor deterioration index Φsr is higher than a predetermined value, it is determined that a failure has occurred, and, for example, a warning light (not shown) is turned on to warn the driver.
[0057]
The misfire detection means 9 and the secondary air system failure detection means 10 are the same as those in the above embodiment. The air-fuel ratio sensor deterioration index correction means 23, when the misfire detection means 9 or the secondary air system failure detection means 10 detects a misfire or a failure or deterioration of the secondary air system, uses the air-fuel ratio sensor deterioration index described above. The corrected air-fuel ratio sensor deterioration index is output to the air-fuel ratio sensor deterioration determination means 22.
[0058]
The air-fuel ratio sensor deterioration determination suspending means 24 has a predetermined frequency (or degree) of misfire or secondary air system failure as a reference for determining whether to suspend the determination. When the misfire or the failure or deterioration of the secondary air system is detected beyond the predetermined frequency (or degree), the determination of the deterioration of the air-fuel ratio sensor by the air-fuel ratio sensor deterioration determining means 22 is interrupted. To generate a signal for performing the operation.
Next, the operation when a misfire occurs will be described.
[0059]
When a misfire occurs, a spike-like lean signal is generated (see FIG. 4). Then, the air-fuel ratio deterioration index Φsr becomes a larger value in accordance with the frequency of occurrence of misfire (see FIG. 12). That is, the responsiveness of the air-fuel ratio sensor 7 is evaluated to be better than the actual one, and the degree of deterioration is evaluated to be lower. This is the same regardless of the type of the air-fuel ratio sensor 7. Accordingly, the air-fuel ratio deterioration index Φsr is reduced by multiplying the air-fuel ratio deterioration index Φsr by the coefficient Ksr (see FIG. 13) determined according to the frequency of misfires in the air-fuel ratio sensor deterioration index correcting means 23. Make corrections. If the frequency of misfires becomes too large, the variation of the air-fuel ratio deterioration index Φsr becomes large. Therefore, the air-fuel ratio sensor deterioration determination interrupting means 24 interrupts the air-fuel ratio sensor deterioration determination.
[0060]
Next, an operation when a failure occurs in the secondary air system 6 will be described.
[0061]
As in the case of detecting the deterioration of the catalyst, a problem in which air leaks and flows when the air-fuel ratio sensor is sampling data is particularly problematic. The effect of such a failure depends on the mixing state of the exhaust gas and the leaked air flowing from the secondary air system 6 between the inlet 62 and the air-fuel ratio sensor 7, and the like.
[0062]
In the case where the air-fuel ratio sensor 7 detects the air-fuel ratio in a binary manner, it is difficult to output a signal on the rich side due to air (oxygen) leaking from the inlet 62. Therefore, the amplitude of the output signal of the air-fuel ratio sensor 7 decreases according to the amount of leaked air, and the air-fuel ratio sensor deterioration index Φsr also has a lower value. When the amount of leaked air further increases, Φsr becomes substantially zero, and the correction cannot be performed. Therefore, as shown in FIG. 14, when the amount of leaked air is small, a correction by applying the coefficient ksr is performed. If the amount of leaking air is large, the deterioration determination is interrupted.
[0063]
On the other hand, when the air-fuel ratio sensor 7 is a wide-range air-fuel ratio sensor, the catalyst deterioration index Φsr has a lower value when the leakage amount is small. If the amount of leakage further increases, the output becomes unstable, making it impossible to determine deterioration. Therefore, the same correction and deterioration determination interruption as in FIG. 14 are performed.
[0064]
As described above, in general, the accuracy of the secondary air system failure detecting means 10 is often not so high. Therefore, when it is determined that the secondary air system 6 has a failure, the air-fuel ratio sensor In some cases, it may not be possible to determine the deterioration. Therefore, when it is determined that the secondary air system 6 has a failure, the deterioration determination may be interrupted at once. Conversely, a configuration may be adopted in which only the correction by the air-fuel ratio sensor deterioration index correction unit 23 is performed without providing the air-fuel ratio sensor deterioration determination interruption unit 24.
[0065]
In the above, the determination of the deterioration related to the responsiveness of the air-fuel ratio sensor has been described. This is detected by measuring the output of the air-fuel ratio sensor while maintaining the air-fuel ratio at a predetermined value. However, since the air-fuel ratio fluctuates due to misfiring or failure of the secondary air system, correction of the deterioration index or deterioration determination is performed. Need to be interrupted.
[0066]
For example, when the air-fuel ratio is held in a rich state and the rich-side signal output voltage of the air-fuel ratio sensor is determined, if air leaks from the secondary air system 6, the air-fuel ratio sensor outputs a lean signal. appear. As a result, it is erroneously determined that the air-fuel ratio sensor has deteriorated. The same is true even if a misfire occurs. If the misfire frequency is low, a lean spike signal output is generated. When the misfire frequency increases, the output signal shows a constant value (lean state) (in the case of a binary sensor), or the output signal fluctuates greatly (wide-range air-fuel ratio sensor). Therefore, the present invention is applicable to such a deterioration determination.
[0067]
Further, in the above embodiment, the detection of the deterioration of the air-fuel ratio sensor upstream of the catalyst has been described. However, the detection of the deterioration of the air-fuel ratio sensor downstream of the catalyst, etc. may be corrected or corrected according to the misfire or the failure of the secondary air system. Judgment of the judgment is necessary and applicable.
[0068]
As described above, the detection of the deterioration of the air-fuel ratio sensor is also applicable because it is necessary to correct the air-fuel ratio sensor deterioration index and interrupt the air-fuel ratio deterioration determination in response to misfire or a failure in the secondary air system.
[0069]
Further, in the above description, the case where the catalyst deterioration index is corrected has been described. However, even if the threshold value for comparison with the catalyst deterioration index is corrected in order to determine the deterioration, it is substantially the same. .
[0070]
【The invention's effect】
According to the present invention,Fire breaks outEven if you are born,MediumThe possibility of erroneously determining the degree of conversion is eliminated. For this reason, it is not necessary to replace the battery when it is not deteriorated, or to run the vehicle while it is deteriorated, which is useful for preventing extra expenses and air pollution.
[Brief description of the drawings]
FIG. 1 is a drawing showing a configuration of an embodiment of the present invention.
FIG. 2 is a diagram showing an example of output signals of air-fuel ratio sensors 7, 8 upstream and downstream of a catalyst.
FIG. 3 is a diagram illustrating a relationship between a catalyst deterioration degree and a deterioration index.
FIG. 4 is a diagram showing an influence of a misfire on an output signal of an air-fuel ratio sensor.
FIG. 5 is a diagram showing the effect of misfire on a catalyst deterioration index.
FIG. 6 is a diagram illustrating a correction coefficient and a determination interruption area.
FIG. 7 is a diagram showing the effect of misfire on a catalyst deterioration index.
FIG. 8 is a diagram illustrating a correction coefficient and a determination interruption area.
FIG. 9 is a diagram illustrating a correction coefficient and a determination interruption area.
FIG. 10 is a diagram illustrating a correction coefficient and a determination interruption area.
FIG. 11 is a diagram showing another embodiment of the present invention.
FIG. 12 is a diagram showing the influence of a misfire on an air-fuel ratio sensor deterioration index.
FIG. 13 is a diagram illustrating a correction coefficient and a determination interruption area.
FIG. 14 is a diagram illustrating a correction coefficient and a determination interruption area.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Air flow meter, 3 ... Air-fuel ratio feedback control means, 4 ... 5 ... Catalyst, 6 ... Secondary air system, 7 ... Air-fuel ratio sensor, 8 ... Air Fuel ratio sensor, 9 misfire detection means, 10 secondary air system failure detection means, 11 catalyst deterioration index calculation means, 12 catalyst deterioration judgment means, 13 catalyst deterioration index correction means, 14 ... Catalyst deterioration determination suspending means, 21: Air-fuel ratio sensor deterioration index calculating means, 22 ... Air-fuel ratio sensor deterioration determining means, 23 ... Air-fuel ratio sensor deterioration index correcting means, 24 ... Air-fuel ratio sensor deterioration determination suspending means

Claims (7)

排気ガス中の空燃比を所定値に保つように燃料噴射量を調整する空燃比制御装置を有するエンジンを対象とした、排気ガスを触媒により浄化するエンジンの排気ガス浄化装置の診断装置であって、
前記触媒の上流側における排気ガスの空燃比を検出する第１の空燃比センサと、
前記触媒の下流側における排気ガスの空燃比を検出する第２の空燃比センサと、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算する触媒劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定する触媒劣化判定手段と、
前記エンジンの燃焼状態を該エンジンの回転速度変動に基づいて検出し失火の発生を検出する失火検出手段と、
前記失火検出手段により失火が検出されたときに前記触媒劣化判定手段の判定を中断する触媒劣化判定中断手段と、
を備えていることを特徴とする排気ガス浄化装置の診断装置。A diagnostic device for an exhaust gas purifying device for an engine that purifies exhaust gas by using a catalyst for an engine having an air-fuel ratio control device that adjusts a fuel injection amount to maintain an air-fuel ratio in exhaust gas at a predetermined value. ,
A first air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas on the upstream side of the catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas downstream of the catalyst;
Catalyst deterioration index calculating means for calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
A catalyst deterioration determining unit that has a predetermined threshold value and compares the threshold value with the catalyst deterioration index to determine a deterioration state of the catalyst;
Misfire detecting means for detecting the combustion state of the engine based on the rotation speed fluctuation of the engine and detecting the occurrence of misfire,
Catalyst degradation determination suspending means for suspending the determination of the catalyst degradation determining means when misfire is detected by the misfire detecting means,
A diagnostic device for an exhaust gas purifying device, comprising: 排気ガス中の空燃比を所定値に保つように燃料噴射量を調整する空燃比制御装置を有するエンジンを対象とした、排気ガスを触媒により浄化するエンジンの排気ガス浄化装置の診断装置であって、
排気ガスの空燃比を検出する空燃比センサと、
前記空燃比センサの出力信号から空燃比センサの劣化状態を示す空燃比センサ劣化指標を計算する空燃比センサ劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記空燃比センサ劣化指標とを比較することによって前記空燃比センサの劣化状態を判定する空燃比センサ劣化判定手段と、
エンジンの燃焼状態を該エンジンの回転速度変動に基づいて検出し失火の発生を検出する失火検出手段と、
前記失火検出手段により失火が検出されたときに前記空燃比センサ劣化判定手段の判定を中断する空燃比センサ劣化判定中断手段と、
を備えていることを特徴とする排気ガス浄化装置の診断装置。A diagnostic device for an exhaust gas purifying device for an engine that purifies exhaust gas by using a catalyst for an engine having an air-fuel ratio control device that adjusts a fuel injection amount to maintain an air-fuel ratio in exhaust gas at a predetermined value. ,
An air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas,
Air-fuel ratio sensor deterioration index calculation means for calculating an air-fuel ratio sensor deterioration index indicating the deterioration state of the air-fuel ratio sensor from the output signal of the air-fuel ratio sensor,
An air-fuel ratio sensor deterioration determining unit that includes a predetermined threshold value and compares the threshold value with the air-fuel ratio sensor deterioration index to determine a deterioration state of the air-fuel ratio sensor;
Misfire detection means for detecting the combustion state of the engine based on the rotation speed fluctuation of the engine and detecting the occurrence of misfire;
Air-fuel ratio sensor deterioration determination interruption means for interrupting the determination of the air-fuel ratio sensor deterioration determination means when misfire is detected by the misfire detection means,
A diagnostic device for an exhaust gas purifying device, comprising: 排気ガス中の空燃比を所定値に保つように燃料噴射量を調整する空燃比制御装置を有すると共に、該排気ガスを触媒により浄化するエンジンの排気ガス浄化装置の診断装置であって、
前記触媒の上流側における排気ガスの空燃比を検出する第１の空燃比センサと、
前記触媒の下流側における排気ガスの空燃比を検出する第２の空燃比センサと、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算する触媒劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定する触媒劣化判定手段と、
前記エンジンの失火の発生を該エンジンの回転速度変動に基づいて検出する失火検出手段と、
少なくとも一定気筒の連続的な失火が発生したときに前記触媒劣化判定手段の判定を中断する触媒劣化診断中断手段と、
を備えていることを特徴とする排気ガス浄化装置の診断装置。A diagnostic device for an exhaust gas purifying device for an engine having an air-fuel ratio control device that adjusts a fuel injection amount so as to maintain an air-fuel ratio in exhaust gas at a predetermined value, and purifying the exhaust gas with a catalyst,
A first air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas on the upstream side of the catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas downstream of the catalyst;
Catalyst deterioration index calculating means for calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
A catalyst deterioration determining unit that has a predetermined threshold value and compares the threshold value with the catalyst deterioration index to determine a deterioration state of the catalyst;
Misfire detecting means for detecting the occurrence of misfire of the engine based on the rotation speed fluctuation of the engine;
Catalyst deterioration diagnosis interrupting means for interrupting the determination of the catalyst deterioration determining means when at least continuous misfire of a certain cylinder occurs,
A diagnostic device for an exhaust gas purifying device, comprising: 請求項３に記載の排気ガス浄化装置の診断装置において、
前記少なくとも一定気筒の連続的な失火は、点火系の失火であること、
を特徴とする排気ガス浄化装置の診断装置。The diagnostic device for an exhaust gas purifying device according to claim 3 ,
The continuous misfire of the at least certain cylinder is a misfire of an ignition system;
A diagnostic device for an exhaust gas purifying device, characterized in that: 排気ガス中の空燃比を所定値に保つように燃料噴射量を調整する空燃比制御装置を有すると共に、該排気ガスを触媒により浄化するエンジンの排気ガス浄化装置の診断装置において、
前記触媒の上流側における排気ガスの空燃比を検出する第１の空燃比センサと、
前記触媒の下流側における排気ガスの空燃比を検出する第２の空燃比センサと、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算する触媒劣化指標計算手段と、
予め定められたしきい値を備え、該しきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定する触媒劣化判定手段と、
少なくとも点火系の連続失火の検出を含む前記エンジンの失火の発生を該エンジンの回転速度変動に基づいて検出する失火検出手段と、
前記失火判定手段により失火が検出されたときに前記触媒劣化判定手段の判定を中断する触媒劣化診断中断手段と、
を備えていることを特徴とする排気ガス浄化装置の診断装置。A diagnostic device for an exhaust gas purifying device for an engine having an air-fuel ratio control device that adjusts a fuel injection amount so as to maintain an air-fuel ratio in exhaust gas at a predetermined value, and purifying the exhaust gas with a catalyst,
A first air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas on the upstream side of the catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas downstream of the catalyst;
Catalyst deterioration index calculating means for calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
A catalyst deterioration determining unit that has a predetermined threshold value and compares the threshold value with the catalyst deterioration index to determine a deterioration state of the catalyst;
Misfire detection means for detecting occurrence of misfire of the engine including detection of continuous misfire of at least the ignition system based on fluctuations in rotation speed of the engine;
Catalyst degradation diagnosis interruption means for interrupting the determination of the catalyst degradation determination means when misfire is detected by the misfire determination means,
A diagnostic device for an exhaust gas purifying device, comprising: 排気ガス中の空燃比を所定値に保つように燃料噴射量を調整すると共に、排気ガスを触媒により浄化するエンジンの排気ガス浄化装置の診断方法において、
前記触媒の上流側における排気ガスの空燃比を第１の空燃比センサで検出し、
前記触媒の下流側における排気ガスの空燃比を第２の空燃比センサで検出し、
前記第１の空燃比センサと前記第２の空燃比センサとの出力信号から前記触媒の劣化状態を示す触媒劣化指標を計算し、
予め定められたしきい値と前記触媒劣化指標とを比較することによって前記触媒の劣化状態を判定し、
エンジンの回転速度変動に基づいてエンジンの失火を検出し、
少なくとも一定気筒の連続的な失火が発生したときに前記触媒劣化の判定を中断する、
ことを特徴とする排気ガス浄化装置の診断方法。A method of diagnosing an exhaust gas purifying apparatus for an engine, which adjusts a fuel injection amount so as to maintain an air-fuel ratio in exhaust gas at a predetermined value and purifies exhaust gas by a catalyst,
The first air-fuel ratio sensor detects the air-fuel ratio of the exhaust gas on the upstream side of the catalyst,
The air-fuel ratio of the exhaust gas on the downstream side of the catalyst is detected by a second air-fuel ratio sensor,
Calculating a catalyst deterioration index indicating a deterioration state of the catalyst from output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor;
Determine the deterioration state of the catalyst by comparing a predetermined threshold value and the catalyst deterioration index,
Detects engine misfire based on engine speed fluctuations,
Suspending the determination of the catalyst deterioration when continuous misfire of at least a certain cylinder occurs,
A method for diagnosing an exhaust gas purifying device, comprising: 請求項６に記載の排気ガス浄化装置の診断方法において、
前記少なくとも一定気筒の連続的な失火は、点火系の失火である、
ことを特徴とする排気ガス浄化装置の診断方法。The method for diagnosing an exhaust gas purification device according to claim 6,
The continuous misfire of the at least one cylinder is a misfire of an ignition system;
A method for diagnosing an exhaust gas purifying device, comprising:
JP2001266268A 2001-09-03 2001-09-03 Diagnostic device for exhaust gas purification device Expired - Fee Related JP3564088B2 (en)

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