JP3890775B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Air-fuel ratio control device for internal combustion engine Download PDF

Info

Publication number
JP3890775B2
JP3890775B2 JP29072398A JP29072398A JP3890775B2 JP 3890775 B2 JP3890775 B2 JP 3890775B2 JP 29072398 A JP29072398 A JP 29072398A JP 29072398 A JP29072398 A JP 29072398A JP 3890775 B2 JP3890775 B2 JP 3890775B2
Authority
JP
Japan
Prior art keywords
air
fuel ratio
state
internal combustion
combustion engine
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP29072398A
Other languages
Japanese (ja)
Other versions
JP2000120477A (en
Inventor
隆行 出村
直秀 不破
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyota Motor Corp
Original Assignee
Toyota Motor Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyota Motor Corp filed Critical Toyota Motor Corp
Priority to JP29072398A priority Critical patent/JP3890775B2/en
Publication of JP2000120477A publication Critical patent/JP2000120477A/en
Application granted granted Critical
Publication of JP3890775B2 publication Critical patent/JP3890775B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Landscapes

  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、多気筒内燃機関の空燃比を制御する内燃機関の空燃比制御装置に関する。
【０００２】
【従来の技術】
ある気筒群の空燃比と他の気筒群の空燃比とが異なるように多気筒内燃機関の空燃比状態を制御する空燃比制御装置があり、このような空燃比制御装置としては特開平8-61052号公報に記載のものなどが知られている。特開平8-61052号公報に記載の空燃比制御装置は、ある気筒群の空燃比と他の気筒群の空燃比とが異なるように制御することによって排気通路上の排気浄化触媒を昇温させることなどを目的としている。
【０００３】
【発明が解決しようとする課題】
しかし、多気筒内燃機関の空燃比状態は、通常、全気筒が同一の空燃比となるように制御されており、ある気筒群の空燃比と他の気筒群の空燃比とが異なるような制御への切替時に気筒群毎の出力トルクに差が生じ、切替時における内燃機関全体での出力トルクが不安定になってしまう傾向がある。上述した特開平8-61052号公報に記載の制御装置なども、この点に関しては十分な配慮がなされていないものであり、更なる改善が望まれていた。
【０００４】
また、例えば燃料噴射弁や空燃比センサ、燃焼室のデポジット付着量により気筒群毎に機関個体差や経時変化が発生する。この影響を考慮しないで気筒群毎に空燃比を相違させると、各気筒群の空燃比が目標の空燃比からずれて、結果的に排気エミッションが悪化する場合があった。
【０００５】
従って、本発明の目的は、出力トルクを安定な状態に維持しすると共に、排気エミッションの悪化も抑止しつつ、空燃比状態を、ある気筒群の空燃比と他の気筒群の空燃比とが異なる空燃比相違状態に円滑に切り替えることのできる内燃機関の空燃比制御装置を提供することにある。
【０００６】
【課題を解決するための手段】
請求項１に記載の発明は、オープンループ制御により全気筒が同じ空燃比で運転される空燃比同一状態と、気筒群毎の空燃比が異なる状態で運転される空燃比相違状態とを切り替える空燃比状態切替手段を備えた内燃機関の空燃比制御装置において、多気筒内燃機関の排気通路上に設けられた排気浄化触媒と、排気浄化触媒の温度を上昇させるか否かを判断する触媒昇温判定手段と、多気筒内燃機関の排気通路上に設けられた空燃比センサとをさらに備え、空燃比同一状態で内燃機関が運転している際、触媒昇温判定手段により排気浄化触媒の昇温が必要であると判断したときに、空燃比状態切替手段が、空燃比を空燃比同一状態から空燃比相違状態に切り替える切替を行い、切替を行うにあたり、空燃比センサの出力に基づいて機関空燃比を所定の目標空燃比となるようにフィードバック制御する状態を経由させた後に空燃比相違状態に切り替えることを特徴とする。
【０００７】
請求項１に記載の発明によれば、空燃比状態が、空燃比制御切替手段によって、オープンループ制御を行っている空燃比同一状態から空燃比センサの出力に基づいて機関空燃比を所定の目標空燃比となるようにフィードバック制御する状態を経由して空燃比相違状態に切り替えられる。このフィードバック制御する状態は、排気ガス中の有害物質の浄化率を高く維持しつつ、十分な出力トルクを高く維持するために、空燃比センサの出力に基づいて機関空燃比を所定の目標空燃比となるようにフィードバック制御する状態であるため、オープンループ制御を行っている空燃比同一状態から空燃比相違状態への切替時に出力トルクを大きく変動させることなく、かつ、排気ガス中の有害物質を効率良く浄化しつつ、円滑に空燃比状態を切り替えることができる。そして、触媒昇温判定手段によって、排気浄化触媒の温度を昇温させる必要があると判定したときに、空燃比相違状態に切り替えることによって、排気浄化触媒を昇温させることができる。排気浄化触媒を昇温させれば、排気浄化触媒をより早期に活性状態とさせることができたり、排気浄化触媒に吸蔵された有害物質を浄化させたりすることなどができる。
また、空燃比センサの出力に基づくフィードバック制御を行うので、内燃機関の空燃比を高精度に制御でき、空燃比制御状態をより高次元に安定させることができる。この結果、空燃比状態が、このフィードバック制御を行う状態を経由して空燃比相違状態に切り替えられる際に、より円滑に切替が行われるようにできる。
【００１０】
請求項２に記載の発明は、請求項１に記載の発明において、目標空燃比が理論空燃比であることを特徴とする。
【００１１】
請求項２に記載の発明によれば、上記フィードバック制御時の目標空燃比を理論空燃比とするので、排気ガス中の有害物質を最も効率良く浄化しつつ、十分な出力トルクを安定して出力することができる。この結果、空燃比状態が上記フィードバック制御を行う状態を経由して空燃比相違状態に切り替えられる際に、その切替を円滑に行うことができ、このときの排気ガス中の有害物質の浄化と十分な出力トルクの安定出力とをバランス良く実現することができる。
【００１２】
また、上記フィードバック制御を行う状態における機関空燃比を理論空燃比とするので、空燃比相違状態での各気筒群の空燃比がどのようなものでも、その切替前後の空燃比のギャップを平均的な大きさとすることができ、空燃比状態を空燃比相違状態に安定的かつ円滑に切り替えることができる。即ち、ある気筒群の空燃比状態を、理論空燃比よりリーンな状態に切り替える場合であっても、理論空燃比よりリッチな状態へと切り替える場合であっても、その切替前後の空燃比のギャップは、リーンな状態からリッチな状態に一気に切り替えるような場合のように大きくなることはない。
【００１３】
請求項３に記載の発明は、請求項１に記載の発明において、空燃比センサの出力に基づくフィードバック制御によって得られる空燃比フィードバック補正値から空燃比制御値を学習する空燃比学習手段を備えたことを特徴とする。
【００１４】
請求項３に記載の発明によれば、空燃比学習手段によって、上記フィードバック制御を行う状態で空燃比制御値を学習することができる。空燃比制御値は、内燃機関の個体差や経時変化を反映させるためのものである。この空燃比制御値を上記フィードバック制御中に学習し、これを空燃比制御に反映させることによって、より高精度の空燃比制御を行うことができる。この結果、上記フィードバック制御を行う状態を経由させて空燃比相違状態に切り替える際に、より円滑に空燃比状態を切り替えることができる。
【００１５】
請求項４に記載の発明は、請求項３に記載の発明において、排気通路が、各気筒群毎に設けられた上流排気通路と上流排気通路の下流側で合流された合流排気通路とからなり、空燃比センサが、上流排気通路上に配置されており、空燃比学習手段が、各上流排気通路毎に得られた空燃比フィードバック補正値から各気筒群毎に空燃比制御値を学習することを特徴とする。
【００１６】
請求項４に記載の発明によれば、各気筒群毎に空燃比センサを配置して、各気筒群毎に空燃比フィードバック補正値を用い、かつ、学習した空燃比制御値を反映させて、フィードバック制御を行う。各気筒群毎にフィードバック制御を行うため、空燃比制御の精度をより一層高精度にすることができ、空燃比状態が上記フィードバック制御を行う状態を経由して空燃比相違状態に切り替えられる際に、さらにきめ細かく制御を行って、より一層円滑に空燃比状態を切り替えることができる。
【００１７】
請求項５に記載の発明は、請求項３に記載の発明において、空燃比制御値を空燃比相違状態でのフィードバック制御に反映させる学習値反映手段を備えることを特徴とする。
【００１８】
請求項５に記載の発明によれば、空燃比制御値を、学習値反映手段によって、空燃比相違状態でのフィードバック制御に反映させるので、空燃比相違状態でのフィードバック制御を高精度に行うことができる。空燃比相違状態では気筒群毎に異なる空燃比で運転されるため、空燃比の学習を行えなかったり、精度良く行えない場合もあり、上記フィードバック制御を行う状態で学習した最新の空燃比制御値を反映させることによって、空燃比相違状態でのフィードバック制御を高精度に行うことができる。この結果、空燃比相違状態への切替時のみならず、空燃比相違状態に切り替えられた後のトルク変動抑止や排気ガス浄化も好適に行うことができる。
【００１９】
また、請求項６に記載の発明は、請求項１に記載の発明において、空燃比状態切替手段が、空燃比状態を空燃比相違状態から空燃比同一状態に切り替える際に、内燃機関全体の空燃比制御状態が全気筒の機関空燃比を理論空燃比とするように運転される全気筒理論空燃比状態を経由させた後に空燃比同一状態に切り替えることを特徴とする。
【００２０】
請求項６に記載の発明によれば、空燃比状態が、空燃比制御切替手段によって、空燃比相違状態から全気筒理論空燃比状態を経由して空燃比同一状態に切り替えられる。全気筒理論空燃比状態は、出力トルクと排気ガス中の有害物質除去とを安定した状態に維持できる理論空燃比で全気筒が運転されるため、空燃比相違状態から空燃比同一状態への切替時に出力トルクを大きく変動させることなく、かつ、排気ガス中の有害物質を効率良く浄化しつつ、円滑に空燃比状態を切り替えることができる。
【００２１】
請求項７に記載の発明は、請求項６に記載の発明において、多気筒内燃機関の排気通路上に設けられた空燃比センサと、空燃比センサの出力に基づくフィードバック制御によって得られる空燃比フィードバック補正値から空燃比制御値を学習する空燃比学習手段とを備え、全気筒理論空燃比状態において、空燃比状態切替手段によって、予め学習された空燃比制御値に基づくオープンループ制御を行った後に、空燃比センサの出力に基づくフィードバック制御を行う
【００２２】
請求項７に記載の発明によれば、空燃比相違状態から全気筒理論空燃比状態に移行した直後に、予め学習した空燃比制御値を用いてオープンループ制御することによって、より早期に機関空燃比を理論空燃比にすることができる。また、全気筒理論空燃比状態において、上述したオープンループ制御を行った後は、空燃比センサの出力に基づくフィードバック制御に移行することによって、より早期に理論空燃比にした機関空燃比を、より高精度に理論空燃比に維持することができる。この結果、空燃比状態を空燃比相違状態から全気筒理論空燃比状態への切替を円滑に行うことができると共に、空燃比相違状態以後のトルク変動抑止や排気ガス浄化も好適に行うことができる。
【００２５】
請求項８に記載の発明は、請求項１記載の発明において、触媒昇温判定手段は、排気浄化触媒の温度が触媒活性化温度よりも低いときに、排気浄化触媒の昇温が必要であると判断することを特徴とする。
【００２６】
請求項８に記載の発明によれば、排気浄化触媒の温度が触媒活性化温度より低い温度であり、排気浄化触媒が排気ガス中の有害物質を充分に浄化できないような状態である時ときに、触媒昇温判定手段が、排気浄化触媒を昇温させる必要があると判定する。この結果、排気浄化触媒は、空燃比相違状態によって早期に昇温されるので、より早期に排気ガス中の有害物質を充分に浄化できる状態になる。
【００２７】
請求項９に記載の発明は、請求項１に記載の発明において、排気浄化触媒がNOx吸蔵還元触媒であり、触媒昇温判定手段は、排気浄化触媒のSOx被毒量が所定量以上となったときに、排気浄化触媒の昇温が必要であると判断することを特徴とする。
【００２８】
請求項９に記載の発明によれば、排気浄化触媒であるNOx吸蔵還元触媒のSOx被毒量が所定量以上となったときは、NOx吸蔵還元触媒のSOx被毒を解消するために、触媒昇温判定手段が、排気浄化触媒を昇温させる必要があると判定する。この結果、NOx吸蔵還元触媒は、空燃比相違状態によって早期に昇温されるので、SOx被毒を解消することができ、NOx吸蔵能力を低下させることなく、排気ガス中の有害物質を浄化することができる。
【００２９】
【発明の実施の形態】
図１は本発明の空燃比制御装置の一実施形態を備えた内燃機関の構成を示している。エンジン１は、四気筒エンジンであり、希薄燃焼も可能である。エンジン１の#1気筒と#4気筒とで一つの気筒群を構成し、#2気筒と#3気筒とでもう一つの気筒群を構成している。各気筒からの排気通路は、各気筒群毎にそれぞれ第一上流排気通路２ａ１及び第二上流排気通路２ａ１にまとめられた後、さらにその下流側で合流排気通路２ｂとして一本にまとめられている。
【００３０】
各上流排気通路２ａ１，２ａ２上には、排気浄化触媒である第一スタートキャタリスト３ａ１及び第二スタートキャタリスト３ａ２がそれぞれ配設されている。そして、各上流排気通路２ａ１，２ａ２上の各スタートキャタリスト３ａ１，３ａ２の上流側には、排気ガス中の酸素濃度から各気筒群の空燃比を検出する空燃比センサである第一酸素センサ４ａ１及び第二酸素センサ４ａ２が配設されている。一方、合流排気通路２ｂ上には、排気浄化触媒であるNOx吸蔵還元触媒３ｂが配設されている。そして、合流排気通路２ｂ上のNOx吸蔵還元触媒３ｂの上流側にも空燃比センサである第三酸素センサ４ｂが配設されている。これらの酸素センサ４ａ１，４ａ２，４ｂは、理論空燃比を跨いで空燃比がリッチ側かリーン側かで出力電圧が変化するものであり、理論空燃比を境に、空燃比がリッチであるかリーンであるかをオン-オフ的に検出する。
【００３１】
第一スタートキャタリスト３ａ１及び第二スタートキャタリスト３ａ２には、それぞれの触媒温度（即ち排気温度）を検出する第一温度センサ５ａ１及び第二温度センサ５ａ２がそれぞれ取り付けられている。また、NOx吸蔵還元触媒３ｂにも、触媒温度（即ち排気温度）を検出する第三温度センサ５ｂが取り付けられている。さらに、エンジン１の各気筒の燃焼室内には燃料噴射弁６がそれぞれ配設されており、燃料噴射弁６によって各気筒内に直接燃料噴射（筒内噴射）を行うことができる。酸素センサ４ａ１，４ａ２，４ｂ、温度センサ５ａ１，５ａ２，５ｂ及び燃料噴射弁６は、電子制御コントロールユニット（ECU）７に接続されている。酸素センサ４ａ１，４ａ２、４ｂ及び温度センサ５ａ１，５ａ２，５ｂによる検出結果はECU７に送られ、燃料噴射弁６はECU７からの信号に基づいて燃料を噴射する。
【００３２】
ECU７は、CPU,ROM,RAMなどで構成されるマイクロコンピュータであり、イグニッションキーをオフにした後もバッテリにより記憶内容が消去されずに保持されるバックアップRAMも備えている。また、ECU７には、吸入空気量に相当する吸気管圧力を検出する吸気管圧センサ８、エンジン回転数センサ９、アクセル開度センサ１０及びその他のエンジン制御に必要な各種センサが接続されている。ECU７は、エンジン制御全般を司っており、空燃比状態切替手段、空燃比学習手段、学習値反映手段及び触媒温判定手段としても機能する。
【００３３】
上述したエンジン１は、下記の五つの燃焼モードによって運転される。
(1)成層燃焼
(2)弱成層燃焼
(3)均質リーン燃焼
(4)均質ストイキ燃焼
(5)均質リッチ燃焼
上述したモードの内の何れのモードで燃焼を行うかは、各種センサによって検出された機関運転状態（運転者の出力要求値）に基づいて決定される。
【００３４】
(1)の成層燃焼は、気筒内の点火プラグ近傍の空燃比をリッチとすると同時にその周囲に空気層を形成させて筒内全体では超希薄燃焼をさせるものである。(3)の均質リーン燃焼は、機関空燃比を気筒内全域で均質で、かつ、理論空燃比よりもリーンな空燃比にして希薄燃焼をさせるものである。(2)の弱成層燃焼は、成層燃焼と均質リーン燃焼との中間状態で、１サイクル中において吸気行程と圧縮行程で計二回、燃料噴射を行う。(4)の均質ストイキ燃焼は、機関空燃比を気筒内全域で均質で、かつ、理論空燃比にして燃焼をさせるものである。(5)の均質リッチ燃焼は、機関空燃比を気筒内全域で均質で、かつ、理論空燃比よりもリッチな空燃比にして燃焼をさせるものである。
【００３５】
均質ストイキ燃焼時及び均質リッチ燃焼時には、吸気管圧センサ８の出力から得られる吸入空気量とエンジン回転数センサ９により検出されたエンジン回転数から基本燃料噴射量ＱALLが決定される。成層燃焼時、弱成層燃焼時及び均質リーン燃焼時には、アクセル開度センサ１０により検出されたアクセル開度とエンジン回転数センサ９により検出されたエンジン回転数から基本燃料噴射量ＱALLが決定される。
【００３６】
第一スタートキャタリスト３ａ１、第二スタートキャタリスト３ａ２及びNOx吸蔵還元触媒３ｂについて詳述する。
【００３７】
第一スタートキャタリスト３ａ１及び第二スタートキャタリスト３ａ２は、表面にアルミナの薄膜層がコーティングされた担体上に、白金やパラジウムやロジウムなどの貴金属を担持させた三元触媒であり、排気ガス内の炭化水素HC、一酸化炭素CO、窒素酸化物NOxを浄化する。HC,CO,NOxの浄化は、理論空燃比近傍で燃焼されたときに最も効率良く行われる。第一スタートキャタリスト３ａ１及び第二スタートキャタリスト３ａ２は、エンジン１本体に近い位置に設置されており、エンジン１の始動後、排気ガスによってより早期に触媒活性化温度に達する。
【００３８】
NOx吸蔵還元触媒３ｂは、基本的には、上述した三元触媒であるが、アルミナコーティング層上に、アルカリ金属（カリウム，ナトリウム，リチウム，セシウムなど）、アルカリ土類金属（バリウム，カルシウムなど）又は希土類元素（ランタン，セシウム，イットリウムなど）などをもさらに担持させ、空燃比がリーンのときにNOxを吸蔵させることができるようにしたものである。
【００３９】
このため、NOx吸蔵還元触媒３ｂは、通常の三元触媒としての機能、即ち、理論空燃比近傍で燃焼されたときの排気ガス内のHC,CO,NOxを浄化する機能に加えて、排気ガス中に含まれる還元されないNOxを吸蔵することができる。理論空燃比よりもリーンな空燃比で燃焼された排気ガス中には還元剤となるHC,COがほとんど含まれないためNOxは還元されにくく、この還元されないNOxがNOx吸蔵還元触媒３ｂに一時的に吸蔵される。
【００４０】
NOx吸蔵還元触媒３ｂに吸蔵されたNOxは、理論空燃比よりもリッチな空燃比（あるいは理論空燃比近傍）で燃焼されたときの排気ガス中のHC,COによって還元されて浄化される（このときHC,COは同時に酸化される）。このために、NOx吸蔵還元触媒３ｂにある程度NOxが吸蔵されたと判断されたときは、理論空燃比よりもリッチな空燃比で短時間エンジン１を運転して吸蔵されたNOxを還元させる、いわゆるリッチスパイク運転を行う。
【００４１】
また、上述したようなNOx吸蔵還元触媒３ｂは、NOxの吸蔵と同様に、排気ガス中に硫黄酸化物SOxが存在するとこのSOxも吸蔵する性質を有している。しかも、SOxはNOxに比べてNOx吸蔵還元触媒３ｂに安定的に吸蔵されてしまうため、NOxよりも還元されにくく、通常のリッチスパイク運転では還元することができずに、NOx吸蔵還元触媒３ｂに吸蔵され続けてしまうという傾向がある。この結果、NOx吸蔵還元触媒３ｂに吸蔵されるSOx量が増加し、その分NOxを吸蔵できなくなり（以下、この現象をSOx被毒という）、NOxがNOx吸蔵還元触媒３ｂによって浄化されなくなる場合がある。
【００４２】
NOx吸蔵還元触媒３ｂに吸蔵されたSOxを放出させるには、NOx吸蔵還元触媒３ｂの温度をNOx還元時よりも高温（例えば600〜850℃）とし、かつ、周囲雰囲気を還元雰囲気として還元させれば良い。このため、NOx吸蔵還元触媒３ｂの温度を昇温させつつ、理論空燃比よりもややリッチな空燃比で燃焼された後の排気ガスと同等な還元雰囲気中でSOxを還元させて、NOx吸蔵還元触媒３ｂをSOx被毒から回復させる。
【００４３】
NOx吸蔵還元触媒３ｂを昇温するために、#1,#4気筒側気筒群を理論空燃比よりもリーンな空燃比で燃焼させると共に#2,#3気筒側気筒群を理論空燃比よりもリッチな空燃比で燃焼（あるいはこの逆）させる。このようにすることにより、#1,#4気筒側気筒群からの排気ガス中には酸素が含まれ、#2,#3気筒側気筒群からの排気ガス中にはHC,COが含まれるので、合流排気通路２ｂ上のNOx吸蔵還元触媒３ｂにおいてHC,COが酸化され、その酸化反応熱によってNOx吸蔵還元触媒３ｂが昇温される。このとき、酸素をHC,COの酸化反応後に若干のHC,COが排気ガス中に残存して還元雰囲気が形成されれば、SOxを還元させる上で好ましい。
【００４４】
また、上述したSOx被毒からの回復のみならず、NOx吸蔵還元触媒３ｂの温度を早期に触媒活性化温度に昇温させたいような場合など、NOx吸蔵還元触媒３ｂを積極的に昇温させる必要がある場合にも、一部の気筒群を理論空燃比よりもリーンな空燃比で燃焼させると共に他の気筒群を理論空燃比よりもリッチな空燃比で燃焼させることは有用である。このように、多気筒内燃機関の空燃比状態を、ある気筒群と他の気筒群とが異なる空燃比となるように制御すること、即ち、空燃比状態を空燃比相違状態に切り替えることは種々の利点がある。本発明は、この空燃比相違状態への切替時のトルク変動を抑止すると共に、空燃比相違状態時における排気ガス中の有害物質の排出をも抑止する。
【００４５】
ここで、空燃比のフィードバック制御について簡単に説明する。
【００４６】
機関を運転する際の燃料噴射量TAUは、次のように決定される。
TAU←α・ＱALL・EFTOTAL+β・・・・(I)
ここで、ＱALLは吸気管圧力及びエンジン回転数から決定される基本燃料噴射量であり（上述したように、アクセル開度とエンジン回転数から決定される場合もある）、この基本燃料噴射量ＱALLを機関運転状態に応じて補正することにより、燃料噴射量TAUを決定する。また、EFTOTALは、空燃比反映トータル値である。空燃比反映トータル値EFTOTALは、空燃比を目標空燃比とするために基本燃料噴射量ＱALLを補正する成分であり、この値によって空燃比のフィードバック制御が行われる。α及びβは、始動直後の暖気増量補正値や加速時の加速増量補正値などの他の補正成分である。このEFTOTALは、例えば、空燃比フィードバック補正値FAFと空燃比学習値KGとの和で表される。即ち、この場合、(I)式は次のようになる。
TAU←α・ＱALL・(FAF+KG)+β・・・・(II)
【００４７】
空燃比フィードバック補正値FAFは、酸素センサの出力を基に実際の空燃比を検出して、この空燃比が目標空燃比になるようにフィードバック補正するためのものである。例えば、空燃比を理論空燃比とする際には、図２(a)及び図２(b)に示されるように、酸素センサによって検出された空燃比が理論空燃比よりもリッチである間は、空燃比フィードバック補正値FAFに対して、燃料噴射量を徐々に減量する値が与えられ、酸素センサによって検出された空燃比がリッチからリーンに変わったときには、応答性向上を考慮して燃料噴射量を増量する値がスキップ的に与えられる。
【００４８】
逆に、酸素センサによって検出された空燃比が理論空燃比よりもリーンである間は、空燃比フィードバック補正値FAFに対して、燃料噴射量を徐々に増量する値が与えられ、酸素センサによって検出された空燃比がリーンからリッチに変わったときには、応答性向上を考慮して燃料噴射量を減量する値がスキップ的に与えられる。このようにして、機関空燃比を常に目標空燃比である理論空燃比に維持すべく、空燃比フィードバック補正値FAFが生成されるのである。
【００４９】
なお、酸素センサの検出遅れを考慮して、空燃比フィードバック補正値FAFに図２(c)に示されるような遅れ時間DT1,DT2を設定する場合もある。また、ECUにおいて酸素センサの出力からリーン-リッチをオン-オフ的に判定した判定信号を生成し、この判定信号に基づいてFAF信号を生成する場合もある。
【００５０】
一方、空燃比学習値KGは、空燃比制御値の一つであり、空燃比フィードバック補正値FAFを平均化した空燃比フィードバック補正平均値FAFAVから生成される。なお、空燃比フィードバック補正平均値FAFAVも空燃比制御値の一つである。空燃比学習値KGは、燃料噴射弁や空燃比センサなどの機関の個体差や経時変化を反映させるための補正値であり、所定の機関負荷領域毎に定められる。空燃比のフィードバック制御が行われずにオープンループ制御されているような場合（例えばFAF=1.0に固定して制御する場合）であっても、機関の個体差や経時変化により生じる空燃比のズレを吸収するために、この空燃比学習値KGを用いて補正する。
【００５１】
空燃比フィードバック補正値FAFを用いて空燃比のフィードバック制御を行っていれば、機関空燃比は、このような空燃比学習値KGを用いなくても酸素センサの出力に基づく空燃比フィードバック補正値FAFによって目標空燃比に補正される。しかし、機関の個体差や経時変化を反映させてより精度の高い制御を行うため、オープンループ制御中のみならずフィードバック制御中も空燃比学習値KGが反映される。なお、この空燃比学習値KGは、ECU内のバックアップRAM内に記憶され、必要時に取り出される。
【００５２】
上述した空燃比フィードバック補正値FAFや空燃比制御値（空燃比フィードバック補正平均値FAFAVや空燃比学習値KGなど）は、ECU７内のROMに格納されたプログラムによって数ミリ秒毎に演算・更新される。また、ECU７において演算された空燃比フィードバック補正値FAFや空燃比制御値に基づいて、燃料噴射量TAUが決定され、燃料噴射弁６を用いて燃料が噴射される。ECU７においては、燃料噴射量TAU以外に、点火時期やバルブタイミング、ＥＧＲ量、スロットル弁開度も演算・決定される。
【００５３】
次に、上述した内燃機関の空燃比状態を、#1,#4気筒側気筒群と#2,#3気筒側気筒群とを異なる空燃比で燃焼させる状態、即ち、空燃比相違状態に切り替える行程について、図３に示す空燃比制御状態の説明図と図４に示すフローチャートを参照しつつ説明する。
【００５４】
エンジン１は、通常、全気筒の空燃比が同一の空燃比となるような空燃比同一状態で運転されている。ここでは、図３に示されるように、空燃比同一状態として全気筒が成層燃焼されている状態から、全気筒が均質ストイキ燃焼される空燃比制御安定状態▲１▼を経由して、#1,#4気筒側気筒群が均質リッチ燃焼され、かつ、#2,#3気筒側気筒群が均質リーン燃焼される空燃比相違状態▲２▼に切り替えられる。その後さらに、空燃比相違状態▲２▼の終了後に、全気筒が均質ストイキ燃焼される全気筒理論空燃比状態▲３▼に切り替えられる。以下に、空燃比同一状態−空燃比制御安定状態▲１▼−空燃比相違状態▲２▼−全気筒理論空燃比状態▲３▼と切り替える行程を順に説明する。
【００５５】
なお、ここに言う空燃比制御安定状態とは、排気ガス中の有害物質の浄化率を高く維持しつつ、十分な出力トルクを維持することのできる状態をいう。空燃比制御安定状態の一例としては、機関空燃比がある所定の目標空燃比となるようにフィードバック制御される状態がある。このようにフィードバック制御を行えば、空燃比制御上、目標空燃比を基準にして各種外乱によるズレを求めることができ、各種制御値を学習できるので、さらに空燃比の制御状態を安定させることができる。ここでは、上述した目標空燃比が特に理論空燃比とされた場合である。
【００５６】
図３においては、上述した制御過程の種々の状態が時間軸に沿って示されている。図３(a)はエンジン１の各気筒の燃焼状態を示す模式図、図３(b)はエンジン１の各気筒の制御目標となる空燃比を示す模式図、図３(c)は空燃比フィードバック補正値の状態を示す模式図である。なお、図３(b)の縦軸は空燃比の大きさを示す。また、図３(c)では空燃比制御安定状態▲１▼及び全気筒理論空燃比状態▲３▼-2においては気筒群毎の各酸素センサ４ａ１，４ａ２の出力でフィードバック制御しているので、便宜的に各気筒群に対応する空燃比フィードバック補正値FAF1,FAF2を図示している。
【００５７】
図４に示されるように、ECU７は、接続された各種センサの検出結果に基づいて、排気浄化触媒の昇温制御が必要であるかどうかを常時監視している。本実施形態では、例えば、燃料噴射量の噴射積算値が所定値以上になったとき、NOx吸蔵還元触媒３Ｂが所定量のSOxの被毒を受けていると判断する。このSOx被毒を回復するために、NOx吸蔵還元触媒３ｂの昇温制御が必要であると判断される。
【００５８】
ECU７によって、排気浄化触媒の昇温制御が必要と判断される（ステップ１００）と、燃料噴射弁６の噴射モードが切り替えられ、図３に示されるように、エンジン１が理論空燃比運転以外の運転状態、例えば成層燃焼されている状態（空燃比同一状態）であれば、空燃比制御安定状態▲１▼に切り替えられる（ステップ１０１）。なお、昇温制御が必要なときに理論空燃比運転であれば、そのまま空燃比安定状態▲１▼に切り替えられる。
【００５９】
このとき、出力トルク変動などを円滑にするため、短時間の弱成層燃焼及び均質リーン燃焼を経てから、空燃比制御安定状態▲１▼であるストイキ燃焼に切り替えられる。空燃比制御安定状態▲１▼以前の成層燃焼から均質リーン燃焼までは、空燃比のフィードバック制御は行われておらず、アクセル開度（運転者による機関要求負荷）及び機関回転数から定まる燃料噴射量でオープンループ制御されている。
【００６０】
空燃比制御安定状態▲１▼に移行した後、空燃比のフィードバック制御が開始される。このとき、各気筒群毎の第一上流排気通路２ａ１及び第二上流排気通路２ａ２上の第一スタートキャタリスト３ａ１及び第二スタートキャタリスト３ａ２の上流側の第一酸素センサ４ａ１及び第二酸素センサ４ａ２の出力に基づいて、上述した空燃比反映トータル値が各気筒群毎に形成され、これに基づいて空燃比のフィードバック制御が各気筒群毎に行われる。
【００６１】
以下、説明のために、#1,#4気筒側気筒群の空燃比反映トータル値をEFTOTAL1とし、#2,#3気筒側気筒群の空燃比反映トータル値をEFTOTAL2とする。同様に、#1,#4気筒側気筒群の第一酸素センサ４ａ１に基づく空燃比フィードバック補正値をFAF1とし、この空燃比フィードバック補正値FAF1から得られる空燃比フィードバック補正平均値をFAFAV1、空燃比学習値をKG1とする。同様に、#2,#3気筒側気筒群の第二酸素センサ４ａ２に基づく空燃比フィードバック補正値をFAF2とし、この空燃比フィードバック補正値FAF2から得られる空燃比フィードバック補正平均値をFAFAV2、空燃比学習値をKG2とする。
【００６２】
即ち、空燃比制御安定状態▲１▼では、EFTOTAL1=FAF1+KG1となり、
TAU1←α・ＱALL・EFTOTAL1+β=α・ＱALL・(FAF1+KG1)+β
で基本燃料噴射量ＱALLをフィードバック制御によって補正し、#1,#4気筒側気筒群の燃料噴射量TAU1を決定する。同様に、EFTOTAL2=FAF2+KG2となり、
TAU2←α・ＱALL・EFTOTAL2+β=α・ＱALL・(FAF2+KG2)+β
で基本燃料噴射量ＱALLをフィードバック制御によって補正し、#2,#3気筒側気筒群の燃料噴射量TAU2を決定する。
【００６３】
均質ストイキ燃焼が行われる空燃比制御安定状態▲１▼は、理論空燃比での燃焼であるため、排気浄化触媒（三元触媒）での排気ガス中の有害物質の除去率が高く、かつ十分な出力トルクを維持できる。また、このとき、空燃比フィードバック補正平均値FAFAV1,FAFAV2や空燃比学習値KG1,KG2などの空燃比制御値も学習され、その時点での機関状態を反映させた精度の高いフィードバック制御を行うことができる。
【００６４】
空燃比制御安定状態▲１▼は、空燃比状態が一旦安定するまで所定時間行われるため、ECU７によって、空燃比制御安定状態▲１▼に移行してからの時間がカウントされており、所定時間が経過したか否かが判定されている（ステップ１０２）。空燃比制御安定状態▲１▼に移行してから所定時間が経過していないと判定されている間は、所定時間が経過するまで空燃比制御安定状態▲１▼が継続される。一方、ステップ１０２において、空燃比制御安定状態▲１▼に移行してから所定時間が経過したと判定された場合は、空燃比フィードバック制御が、第一酸素センサ４ａ１及び第二酸素センサ４ａ２に基づく制御から、第三酸素センサ４ｂに基づく制御に切り替えられて（ステップ１０３）、空燃比相違状態▲２▼に移行する。
【００６５】
即ち、空燃比制御安定状態▲１▼で空燃比フィードバック制御が所定時間実行された後、ECU７によって、空燃比相違状態▲２▼となるように、各気筒群毎の空燃比が所定の空燃比変化速度で徐々に切り替えられる。空燃比相違状態▲２▼では、#1,#4気筒側気筒群を均質リッチ燃焼させ、#2,#3気筒側気筒群を均質リーン燃焼させる。そして、合流排気通路２ｂ上のNOx吸蔵還元触媒３ｂに流入される合流後の排気ガスが、理論空燃比（あるいは、これよりもややリッチな空燃比）で燃焼されたときの排気ガスと同等となるように、第三酸素センサ４ｂの出力に基づいてフィードバック制御される。
【００６６】
このように空燃比相違状態▲２▼に切り替える条件、即ち排気浄化触媒の温度を昇温させる必要がある条件とは、上述したように、NOx吸蔵還元触媒３ｂのSOx被毒量が所定量以上となったと判定されたときなどが考えられる。機関空燃比を、空燃比制御安定状態▲１▼を経由させて空燃比相違状態▲２▼に切り替える判定条件については、追ってさらに詳述する。
【００６７】
このとき、第一上流排気通路２ａ１及び第二上流排気通路２ａ２を通過する排気ガスは、その一方が理論空燃比よりもリッチで他方が理論空燃比よりもリーンな空燃比で燃焼された後のものであるため、理論空燃比を境にしてリッチであるかリーンであるかをオン-オフ的に検出する第一酸素センサ４ａ１及び第二酸素センサ４ａ２によっては、高精度に空燃比のフィードバック制御を行うことが困難な場合もある。このため、空燃比相違状態▲２▼においては、合流排気通路２ｂ上のNOx吸蔵還元触媒３ｂの上流側の第三酸素センサ４ｂの出力に基づいて、合流された排気ガスが理論空燃比（あるいは、これよりもややリッチな空燃比）で燃焼されたときの排気ガスと同等となるように空燃比のフィードバック制御を行う。
【００６８】
両気筒群から排出されて合流後にNOx吸蔵還元触媒３ｂに流入される排気ガスを、理論空燃比（あるいはこれよりもややリッチな空燃比）で燃焼された場合の排気ガスと同等となるようにフィードバック制御が行われるので、NOx吸蔵還元触媒３ｂ上でリッチな排気とリーンな排気が酸化反応を起こして、NOx吸蔵還元触媒３ｂの温度が上昇される。その上、NOx吸蔵還元触媒３ｂに流入する排気ガスのトータルの空燃比が理論空燃比（あるいはこれよりもややリッチな空燃比）とされるので、上述したように、NOx吸蔵還元触媒３ｂをSOx被毒から回復させることができる。以下、説明のために、合流排気通路２ｂ上の第三酸素センサ４ｂに基づく空燃比フィードバック補正値をFAF3とする。
【００６９】
ここで、空燃比相違状態▲２▼における空燃比フィードバック補正値FAF3の初期値FAF3(S)として、空燃比制御安定状態▲１▼終了時の空燃比フィードバック補正平均値FAFAV1(E),FAFAV2(E)を用いた以下の値を用いる（ステップ１０４）。
FAF3(S)=[FAFAV1(E)+FAFAV2(E)]/2
また、空燃比相違状態▲２▼における空燃比反映トータル値EFTOTAL1,EFTOTAL2の初期値EFTOTAL1(S),EFTOTAL2(S)としては、空燃比制御安定状態▲１▼終了時の空燃比学習値KG1(E),KG2(E)と上述したFAFAV1(E),FAFAV2(E)を用いた以下の値を用いる（ステップ１０５）。

Figure 0003890775
【００７０】
FAF3,EFTOTAL1,EFTOTAL2は、空燃比相違状態▲２▼における初期値として上述したFAF3(S),EFTOTAL1(S),EFTOTAL2(S)が用いられた後は、第三酸素センサ４ｂの出力に基づいて、以下の式によって演算され、空燃比相違状態▲２▼が継続して行われる（ステップ１０６）。
EFTOTAL1=FAF3+KG1(E)
EFTOTAL2=FAF3+KG2(E)
即ち、空燃比相違状態▲２▼においては、空燃比フィードバック補正値FAF3としては、合流排気通路２ｂ上の第三酸素センサ４ｂの出力に基づくものが両気筒群に対して用いられ、空燃比制御安定状態▲１▼終了時の空燃比学習値KG1(E),KG2(E)（それぞれ固定値）が各気筒群に対してそれぞれ用いられる。
【００７１】
上述したように、空燃比相違状態▲２▼では、EFTOTAL1=FAF3+KG1(E)であるから、
TAU1←α・ＱALL1・EFTOTAL1+β=α・ＱALL1・[FAF3+KG1(E)]+β
で基本燃料噴射量ＱALL1をフィードバック制御によって補正し、#1,#4気筒側気筒群の燃料噴射量TAU1を決定する。同様に、EFTOTAL2=FAF3+KG2(E)であるから、
TAU2←α・ＱALL2・EFTOTAL2+β=α・ＱALL2・[FAF3+KG2(E)]+β
で基本燃料噴射量ＱALL2をフィードバック制御によって補正し、#2,#3気筒側気筒群の燃料噴射量TAU2を決定する。
【００７２】
なお、上述したように、#1,#4気筒側気筒群を均質リッチ燃焼させるので、#1,#4気筒側の基本燃料噴射量ＱALL1はリッチ寄りの噴射量とされている。同様に、#2,#3気筒側気筒群を均質リーン燃焼させるので、#2,#3気筒側の基本燃料噴射量ＱALL2はリーン寄りの噴射量とされている。
【００７３】
上述したように、ステップ１０４において算出した初期値FAF3(S)は、各気筒群の空燃比フィードバック補正値FAF1,FAF2をそれぞれ平均化した空燃比フィードバック補正平均値FAFAV1,FAFAV2の空燃比制御安定状態▲１▼終了時の値FAFAV1(E),FAFAV2(E)を、さらに平均したものである。空燃比相違状態▲２▼における空燃比フィードバック補正値FAF3の初期値としては、平均値を平均したこの初期値FAF3(S)を用いている。
【００７４】
これは、空燃比制御安定状態▲１▼において各気筒群がそれぞれ別個の空燃比フィードバック補正値FAF1,FAF2で独立してフィードバック制御されていたものを、空燃比相違状態▲２▼において単一の空燃比フィードバック補正値FAF3によるフィードバック制御に移行させるのに、両気筒群の空燃比フィードバック補正値のズレを吸収しつつフィードバック制御をバランス良く円滑に移行させるためである。また、フィードバック制御をバランス良く円滑に移行させることができるので、排気ガス中の有害物質の浄化率も高くすることができ、切替時のトルク変動も抑止することができる。
【００７５】
同様に、ステップ１０５において算出した初期値EFTOTAL1(S),EFTOTAL2(S)には、空燃比制御安定状態▲１▼終了時の空燃比学習値KG1(E),KG2(E)が反映されている。これは、空燃比相違状態▲２▼においては単一の空燃比フィードバック補正値FAF3によるフィードバック制御に移行する結果、空燃比相違状態▲２▼においては各気筒群毎に空燃比制御値（空燃比学習値KG1,KG2）の正確な学習を行えないため、最も信頼できる最新の空燃比学習値KG1(E),KG2(E)を反映させて高精度のフィードバック制御を行うためである。
【００７６】
また、ここで、EFTOTAL1(S),EFTOTAL2(S)に対して、それぞれ<FAFAV1(E)-[FAFAV1(E)+FAFAV2(E)]/2>,<FAFAV2(E)-[FAFAV1(E)+FAFAV2(E)]/2>の項を加えたのは、空燃比制御安定状態▲１▼において各気筒群がそれぞれ別個の空燃比フィードバック補正値FAF1,FAF2で独立してフィードバック制御されていたものを、空燃比相違状態▲２▼において単一の空燃比フィードバック補正値FAF3によるフィードバック制御に移行させる際に、FAF1,FAF2からFAF3への各気筒群毎のズレを吸収させてフィードバック制御をバランス良く円滑に移行させるためである。
【００７７】
上述したように、空燃比状態が空燃比制御安定状態▲１▼を経由させてから空燃比相違状態▲２▼に切り替えられるため、気筒群毎の出力トルクが異なる空燃比相違状態▲２▼に移行する際に、トルク変動を極力抑止できる。また、このとき、空燃比状態が空燃比制御安定状態▲１▼を経由させてから空燃比相違状態▲２▼に切り替えられるため、排気ガス中の有害物質の浄化率を高く維持でき、有害物質の排出を抑止することもできる。
【００７８】
ところで、従来のように空燃比制御安定状態▲１▼を経由させずに空燃比相違状態▲２▼に切り替えると、成層燃焼からリーン燃焼に切り替えられる気筒群においては、切替前後の空燃比差が小さいので短時間で移行できるが、成層燃焼からリッチ燃焼に切り替えられる気筒群においては、切替前後の空燃比差が大きいので、リーン燃焼に切り替えられる気筒群に比べて時間を要する。この結果、空燃比制御安定状態▲１▼を経由させずに空燃比相違状態▲２▼に切り替えると、空燃比相違状態▲２▼に完全に移行するまでの過渡期が長くなり、トルク変動が大きくなる。一方、本実施形態においては、空燃比制御安定状態▲１▼を全気筒が理論空燃比となるように制御される状態とし、この空燃比制御安定状態▲１▼を経由させてから空燃比相違状態▲２▼に切り替えるので、過渡期を短くすることができ、トルク変動を抑制することができる。
【００７９】
特に、上述した空燃比制御安定状態▲１▼が、第一酸素センサ４ａ１及び第二酸素センサ４ａ２の出力に基づいて、機関空燃比が所定の目標空燃比となるようにフィードバック制御を行う状態であるため、空燃比を制御する上で、空燃比制御値（空燃比学習値KG1,KG2など）を学習でき、機関状態を反映させた最新のこの空燃比制御値に基づいて、空燃比制御安定状態▲１▼及び空燃比相違状態▲２▼における空燃比のフィードバック制御を行えるため、高精度のフィードバック制御ができる。この結果、トルクの変動を抑止しつつ、円滑に空燃比制御安定状態▲１▼を経由して空燃比相違状態▲２▼に切り替えることができる。また、高精度のフィードバック制御ができるので、排気ガス中の有害物質も効率良く浄化させることができる。
【００８０】
さらに、ここで上述した目標空燃比が理論空燃比であるため、空燃比制御安定状態▲１▼で、トルク変動の変動抑止及び排気ガス中の有害物質の排出抑止を高次元にバランスさせた後に空燃比相違状態▲２▼に切り替えるので、その移行を非常に円滑に行うことができる。また、空燃比制御安定状態▲１▼においては、均質ストイキ燃焼が行われるので、空燃比のフィードバック制御も非常に高精度に行うことができる。
【００８１】
そして、NOx吸蔵還元触媒３ｂに吸蔵されてしまったSOxが還元され、NOx吸蔵還元触媒３ｂがSOx被毒から回復し、NOx吸蔵還元触媒３ｂの昇温が必要なくなったたとECU７によって判定された場合は、空燃比相違状態▲２▼が終了され（ステップ１０７）、全気筒理論空燃比状態▲３▼に切り替えられる。
【００８２】
全気筒理論空燃比状態▲３▼に切り替えられた直後は、均質リッチ燃焼あるいは均質リーン燃焼されていた各気筒群をより早期に均質ストイキ燃焼となるように制御する。ここで、全気筒理論空燃比状態▲３▼への切替直後から第一酸素センサ４ａ１及び第二酸素センサ４ａ２の出力に基づく空燃比フィードバック補正値FAF1,FAF2によるフィードバック制御を行うと、切替直後の各気筒毎の空燃比がリッチとリーンとで大きく異なっているので、全気筒を均質ストイキ燃焼に完全に移行するまでに時間がかかる。即ち、空燃比フィードバック補正値FAF1,FAF2によるフィードバック制御は、理論空燃比近傍に制御されている空燃比を維持するには非常に好適な制御方法であるが、理論空燃比よりもリッチあるいはリーンな空燃比で燃焼されていたものを、より早期に理論空燃比による燃焼に移行させるには、必ずしも最適な制御方法ではない。
【００８３】
そこで、全気筒理論空燃比状態▲３▼への切替直後は、空燃比フィードバック補正値FAF1,FAF2を、それぞれ上述した空燃比制御安定状態▲１▼終了時の空燃比フィードバック補正平均値FAFAV1(E),FAFAV2(E)に固定してしまい、空燃比がより早期に理論空燃比近傍となるように所定時間オープンループ制御する［図３(a)における▲３▼-1］（ステップ１０８）。また、このときも、より高精度な制御のため、空燃比制御安定状態▲１▼終了時の空燃比学習値KG1(E),KG2(E)も反映させる。
【００８４】
即ち、全気筒理論空燃比状態▲３▼に移行した直後の▲３▼-1の期間では、EFTOTAL1=FAFAV1(E)+KG1(E)となり、
TAU1←α・ＱALL・EFTOTAL1+β=α・ＱALL・[FAFAV1(E)+KG1(E)]+β
でオープンループ制御し、#1,#4気筒側気筒群の燃料噴射量TAU1を決定する。同様に、EFTOTAL2=FAFAV2(E)+KG2(E)であるから、
TAU2←α・ＱALL・EFTOTAL2+β=α・ＱALL2・[FAFAV2(E)+KG2(E)]+β
でオープンループ制御し、#2,#3気筒側気筒群の燃料噴射量TAU2を決定する。
【００８５】
全気筒理論空燃比状態▲３▼に移行して所定時間（▲３▼-1）が経過し、各気筒群の期間空燃比がほぼ理論空燃比近傍となったら、各スタートキャタリスト３ａ１，３ａ２の上流側の第一酸素センサ４ａ１及び第二酸素センサ４ａ２の出力に基づく空燃比フィードバック補正値FAF1,FAF2を用いて、各気筒群が理論空燃比で燃焼されるようにフィードバック制御に移行する［図３(a)中▲３▼-2］（ステップ１０９）。また、これ以降は、空燃比制御値も学習し、空燃比フィードバック補正値FAF1,FAF2から得られる空燃比学習値KG1,KG2も反映させる。
【００８６】
即ち、全気筒理論空燃比状態▲３▼に移行して所定時間（▲３▼-1）が経過した後の▲３▼-2の期間では、空燃比制御安定状態▲１▼と同様に、EFTOTAL1=FAF1+KG1となり、
TAU1←α・ＱALL・EFTOTAL1+β=α・ＱALL・(FAF1+KG1)+β
で基本燃料噴射量ＱALLをフィードバック制御によって補正し、#1,#4気筒側気筒群の燃料噴射量TAU1を決定する。同様に、EFTOTAL2=FAF2+KG2となり、
TAU2←α・ＱALL・EFTOTAL2+β=α・ＱALL・(FAF2+KG2)+β
で基本燃料噴射量ＱALLをフィードバック制御によって補正し、#2,#3気筒側気筒群の燃料噴射量TAU2を決定する。
【００８７】
なお、上述したように、空燃比相違状態▲２▼に切り替えると種々の利点があるが、どのようなときに切り替えるか、即ち、切替が必要であると判定される場合としては、排気浄化触媒（NOx吸蔵還元触媒３ｂ）の温度を上昇させる必要がある場合が考えられる。このとき、排気浄化触媒の温度は、第一温度センサ５ａ１、第二温度センサ５ａ２及び第三温度センサ５ｂによって検出され、この検出結果と車輌状態とに基づいて、排気触媒を昇温させる必要があるかどうかがECU７によって判定される。なお、上記実施形態では温度センサを使用したが、温度センサの代わりに、機関負荷、回転数、空燃比、燃焼状態から排気浄化触媒の温度を推定しても良い。
【００８８】
そして、排気浄化触媒（NOx吸蔵還元触媒３ｂ）の温度を上昇させる必要がある場合としては、上述したように、NOx吸蔵還元触媒３ｂに対してリッチスパイク運転を行う場合やNOx吸蔵還元触媒３ｂのSOx被毒量が所定量を超え、SOx被毒から回復させる必要がある場合がある。
【００８９】
NOx吸蔵量やSOx被毒量は、エンジン１の運転状況からECU７によって推定でき、推定されたNOx吸蔵量やSOx被毒量を随時ECU７内で演算記憶し、ECU７内のRAMに保存しておく。演算記憶されたNOx吸蔵量やSOx被毒量が所定量に達したときには、ECU７によって、エンジン１の空燃比状態を空燃比相違状態▲２▼に切り替える、即ち、NOx吸蔵還元触媒３ｂを昇温させる必要があると判定される。このように判定されたときは、ECU７によって、SOx吸蔵還元触媒３ｂを昇温させるべく、空燃比制御安定状態▲１▼を経由させて空燃比相違状態▲２▼に切り替えられる。
【００９０】
あるいは、排気浄化触媒の温度を上昇させる必要がある場合としては、排気浄化触媒（NOx吸蔵還元触媒３ｂ）の温度が触媒活性化温度以下であり、排気ガス中の有害物質を十分に浄化できない場合がある。このときは、排気浄化触媒の温度を触媒活性化温度以上にすべく、排気浄化触媒を昇温させる。
【００９１】
排気浄化触媒は、その温度がある一定の触媒活性化温度以上とならないと、触媒としての機能を十分に発揮しない。このため、エンジン１が始動直後や長時間のアイドル運転後あるいは長時間の成層燃焼運転後である場合などは、排気浄化触媒が触媒活性化温度以下であり、排気ガス中の有害物質を十分に浄化することができない。このような場合は、ECU７によって、エンジン１の空燃比状態を空燃比相違状態▲２▼に切り替える、即ち、排気浄化触媒を昇温させる必要があると判定される。このように判定されたときは、ECU７によって、排気浄化触媒を触媒活性化温度にまで昇温させるべく、空燃比制御安定状態▲１▼を経由させて空燃比相違状態▲２▼に切り替えられる。
【００９２】
このように、排気浄化触媒の昇温が必要であると判定されたときに、空燃比相違状態▲２▼に切り替えることによって排気浄化触媒を昇温することができるので、二次空気供給装置や、排気噴射弁などを配設することなく排気浄化触媒の昇温を行える。即ち、エンジン１に複雑な構成を採用することなく、簡易な構成で排気浄化触媒を昇温させることができる。
【００９３】
本発明の内燃機関の空燃比制御装置は、上述した実施形態のものに限定されない。例えば、上述した実施形態においては、#1気筒と#4気筒により一つの気筒群を構成し、#2気筒と#3気筒とで他の気筒群を構成したが、ある一気筒により一つの気筒群を構成し、残りの三気筒で他の気筒群を構成するようにしても良い。また、全気筒数は必ずしも四気筒に限られるものではなく、直列六気筒やＶ型八気筒のような多気筒エンジンにも適用可能である。また、全気筒群数も必ずしも二つに限られるものではない。さらに、上述した実施形態においては、空燃比センサとして酸素センサ４ａ１，４ａ２，４ｂを用いたが、空燃比センサとしてリニア空燃比センサなど、空燃比を検出する他の種類の空燃比センサを用いても良いことは言うまでもない。
【００９４】
【発明の効果】
本発明の内燃機関の空燃比制御装置は、多気筒内燃機関の空燃比状態を、空燃比状態切替手段によって、空燃比制御安定状態を経由させた後に空燃比相違状態に切り替える。空燃比制御安定状態は、出力トルク及び排気ガス中の有害物質の除去を安定した状態に維持できる状態であるので、本発明の内燃機関の空燃比制御装置によれば、空燃比相違状態への切替時に出力トルクを大きく変動させることなく、かつ、排気ガス中の有害物質を効率良く浄化しつつ、円滑に空燃比状態を切り替えることができる。
【図面の簡単な説明】
【図１】本発明の内燃機関の空燃比制御装置の一実施形態を示す概略構成図である。
【図２】空燃比センサ（酸素センサ）の出力信号と生成される空燃比フィードバック補正値の信号との関係を示す説明図である。
【図３】本発明の内燃機関の空燃比制御装置の一実施形態による空燃比制御の種々の状態を示しており、(a)はエンジンの各気筒の燃焼状態を示す模式図、(b)はエンジンの各気筒の制御目標となる空燃比を示す模式図、(c)は空燃比フィードバック補正値の状態を示す模式図である。
【図４】本発明の内燃機関の空燃比制御装置の一実施形態による空燃比制御を示すフローチャートである。
【符号の説明】
１…エンジン、２ａ１…第一上流排気通路（上流排気通路、排気通路）、２ａ２…第二上流排気通路（上流排気通路、排気通路）２ｂ…合流排気通路（排気通路）、３ａ１…第一スタートキャタリスト（排気浄化触媒）、３ａ２…第二スタートキャタリスト（排気浄化触媒）、３ｂ…NOx吸蔵還元触媒（排気浄化触媒）、４ａ１…第一酸素センサ（空燃比センサ）、４ａ２…第二酸素センサ（空燃比センサ）、４ｂ…第三酸素センサ（空燃比センサ）、６…燃料噴射弁、７…ECU（空燃比切替手段、空燃比学習手段、学習値反映手段、触媒昇温判定手段）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio of a multi-cylinder internal combustion engine.
[0002]
[Prior art]
There is an air-fuel ratio control device that controls the air-fuel ratio state of a multi-cylinder internal combustion engine so that the air-fuel ratio of a certain cylinder group differs from the air-fuel ratio of another cylinder group. Those described in Japanese Patent No. 61052 are known. The air-fuel ratio control apparatus described in Japanese Patent Application Laid-Open No. 8-61052 raises the temperature of the exhaust purification catalyst on the exhaust passage by controlling the air-fuel ratio of a certain cylinder group to be different from the air-fuel ratio of the other cylinder group. The purpose is to.
[0003]
[Problems to be solved by the invention]
However, the air-fuel ratio state of a multi-cylinder internal combustion engine is normally controlled so that all cylinders have the same air-fuel ratio, and the control is such that the air-fuel ratio of one cylinder group differs from the air-fuel ratio of another cylinder group. When switching to, there is a difference in output torque for each cylinder group, and the output torque of the entire internal combustion engine at the time of switching tends to become unstable. The control device described in JP-A-8-61052 described above has not been sufficiently considered in this regard, and further improvement has been desired.
[0004]
Further, for example, individual engine differences and changes with time occur for each cylinder group due to the deposit amount of fuel injection valves, air-fuel ratio sensors, and combustion chambers. If the air-fuel ratio is made different for each cylinder group without taking this effect into account, the air-fuel ratio of each cylinder group may deviate from the target air-fuel ratio, and as a result, exhaust emission may deteriorate.
[0005]
Therefore, an object of the present invention is to maintain the output torque in a stable state and suppress the deterioration of exhaust emission, while changing the air-fuel ratio state between the air-fuel ratio of one cylinder group and the air-fuel ratio of another cylinder group. An object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that can be smoothly switched to different air-fuel ratio different states.
[0006]
[Means for Solving the Problems]
  The invention described in claim 1Open loop controlAir-fuel ratio control of an internal combustion engine provided with air-fuel ratio state switching means for switching between the same air-fuel ratio state in which all cylinders are operated at the same air-fuel ratio and the air-fuel ratio different state in which the air-fuel ratio is different for each cylinder group In the apparatus, an exhaust purification catalyst provided on an exhaust passage of a multi-cylinder internal combustion engine, and a catalyst temperature increase determination means for determining whether or not to raise the temperature of the exhaust purification catalystAn air-fuel ratio sensor provided on the exhaust passage of the multi-cylinder internal combustion engine,And when the internal combustion engine is operating in the same air-fuel ratio state, the air-fuel ratio state switching means reduces the air-fuel ratio when the catalyst temperature increase determination means determines that the exhaust purification catalyst needs to be heated. When switching from the same air-fuel ratio to a different air-fuel ratio,The feedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio based on the output of the air-fuel ratio sensorIt is characterized by switching to the air-fuel ratio different state after passing through.
[0007]
  According to the invention described in claim 1, the air-fuel ratio state is determined by the air-fuel ratio control switching means.Open loop controlFrom the same air-fuel ratioState in which feedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio based on the output of the air-fuel ratio sensorIs switched to an air-fuel ratio difference state.This feedback controlThe state isFeedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio based on the output of the air-fuel ratio sensor in order to maintain a sufficient output torque while maintaining a high purification rate of harmful substances in the exhaust gas.Because it is in a stateOpen loop controlWhen switching from the same air-fuel ratio state to the different air-fuel ratio state, the air-fuel ratio state can be smoothly switched without greatly changing the output torque and efficiently purifying harmful substances in the exhaust gas. When it is determined by the catalyst temperature increase determination means that the temperature of the exhaust purification catalyst needs to be raised, the exhaust purification catalyst can be raised in temperature by switching to the air-fuel ratio difference state. If the temperature of the exhaust purification catalyst is raised, the exhaust purification catalyst can be activated earlier, or harmful substances occluded in the exhaust purification catalyst can be purified.
Further, since feedback control based on the output of the air-fuel ratio sensor is performed, the air-fuel ratio of the internal combustion engine can be controlled with high accuracy, and the air-fuel ratio control state can be stabilized at a higher level. As a result, when the air-fuel ratio state is switched to the air-fuel ratio different state via the state where the feedback control is performed, the switching can be performed more smoothly.
[0010]
  Claim2The invention described in claim 11The target air-fuel ratio is the stoichiometric air-fuel ratio.
[0011]
  Claim2According to the invention described inthe aboveSince the target air-fuel ratio at the time of feedback control is the stoichiometric air-fuel ratio, it is possible to stably output a sufficient output torque while purifying the harmful substances in the exhaust gas most efficiently. As a result, the air-fuel ratio state isPerform the above feedback controlWhen switching to a different air-fuel ratio state via the state, the switching can be performed smoothly, and at this time, the purification of harmful substances in the exhaust gas and the stable output of sufficient output torque are realized in a balanced manner be able to.
[0012]
  Also,State to perform the above feedback controlSince the engine air-fuel ratio is the stoichiometric air-fuel ratio, whatever the air-fuel ratio of each cylinder group in the air-fuel ratio difference state, the air-fuel ratio gap before and after the switching can be set to an average size, The air-fuel ratio state can be switched to the air-fuel ratio different state stably and smoothly. That is, whether the air-fuel ratio state of a certain cylinder group is switched to a state leaner than the stoichiometric air-fuel ratio or to a state richer than the stoichiometric air-fuel ratio, the air-fuel ratio gap before and after the switching is changed. Is not as large as when switching from a lean state to a rich state at once.
[0013]
  Claim3The invention described in claim 11Obtained by feedback control based on the output of the air-fuel ratio sensor.SkyAn air-fuel ratio learning means for learning an air-fuel ratio control value from the fuel-fuel ratio feedback correction value is provided.
[0014]
  Claim3According to the invention described in the above, by the air-fuel ratio learning means,State to perform the above feedback controlThus, the air-fuel ratio control value can be learned. The air-fuel ratio control value is for reflecting individual differences and changes with time of the internal combustion engine. This air-fuel ratio control valueDuring the above feedback controlThus, the air-fuel ratio control can be performed with higher accuracy by reflecting this in the air-fuel ratio control. As a result,State to perform the above feedback controlThe air-fuel ratio state can be switched more smoothly when switching to the air-fuel ratio different state via the.
[0015]
  Claim4The invention described in claim 13The exhaust passage is composed of an upstream exhaust passage provided for each cylinder group and a merged exhaust passage merged downstream of the upstream exhaust passage, and an air-fuel ratio sensor is disposed on the upstream exhaust passage. The air-fuel ratio learning means learns the air-fuel ratio control value for each cylinder group from the air-fuel ratio feedback correction value obtained for each upstream exhaust passage.
[0016]
  Claim4According to the invention, the air-fuel ratio sensor is arranged for each cylinder group, the air-fuel ratio feedback correction value is used for each cylinder group, and the learned air-fuel ratio control value is reflected to perform feedback control. Do. Since feedback control is performed for each cylinder group, the accuracy of the air-fuel ratio control can be further increased, and the air-fuel ratio state isState to perform the above feedback controlWhen switching to the air-fuel ratio different state via the control, the air-fuel ratio state can be switched more smoothly by performing finer control.
[0017]
  Claim5The invention described in claim 13In the invention described in,SkyA learning value reflecting means for reflecting the fuel ratio control value to the feedback control in the air-fuel ratio difference state is provided.
[0018]
  Claim5According to the invention described in,SkySince the fuel ratio control value is reflected in the feedback control in the air-fuel ratio different state by the learned value reflecting means, the feedback control in the air-fuel ratio different state can be performed with high accuracy. In the air-fuel ratio difference state, since the operation is performed with different air-fuel ratios for each cylinder group, the air-fuel ratio may not be learned or may not be accurately performed.State to perform the above feedback controlBy reflecting the latest air-fuel ratio control value learned in step 1, feedback control in the air-fuel ratio difference state can be performed with high accuracy. As a result, not only the switching to the air-fuel ratio difference state but also the torque fluctuation suppression and the exhaust gas purification after switching to the air-fuel ratio difference state can be suitably performed.
[0019]
  Claims6According to the invention described in claim 1, when the air-fuel ratio state switching means switches the air-fuel ratio state from the air-fuel ratio different state to the same air-fuel ratio state, the air-fuel ratio control state of the entire internal combustion engine is all set. It is characterized in that the air-fuel ratio is switched to the same state after passing through the all-cylinder theoretical air-fuel ratio state in which the engine air-fuel ratio of the cylinder is operated to be the stoichiometric air-fuel ratio.
[0020]
  Claim6According to the present invention, the air-fuel ratio state is switched from the air-fuel ratio different state to the same air-fuel ratio state via the all-cylinder theoretical air-fuel ratio state by the air-fuel ratio control switching means. In the all cylinders theoretical air-fuel ratio state, all cylinders are operated at a theoretical air-fuel ratio that can maintain stable output torque and removal of harmful substances in the exhaust gas. It is possible to smoothly switch the air-fuel ratio state while efficiently purifying harmful substances in the exhaust gas without sometimes greatly changing the output torque.
[0021]
  Claim7The invention described in claim 16The air-fuel ratio control value is learned from an air-fuel ratio sensor provided on the exhaust passage of the multi-cylinder internal combustion engine and an air-fuel ratio feedback correction value obtained by feedback control based on the output of the air-fuel ratio sensor. Learning means, and in the all-cylinder theoretical air-fuel ratio state, the air-fuel ratio state switching means performs open loop control based on the air-fuel ratio control value learned in advance, and then performs feedback control based on the output of the air-fuel ratio sensor.
[0022]
  Claim7According to the invention described in the above, the engine air-fuel ratio is theoretically determined earlier by performing open-loop control using the air-fuel ratio control value learned in advance immediately after shifting from the air-fuel ratio difference state to the all-cylinder stoichiometric air-fuel ratio state. The air-fuel ratio can be set. In addition, after performing the above-described open loop control in the all-cylinder stoichiometric air-fuel ratio state, the engine air-fuel ratio that has been brought to the stoichiometric air-fuel ratio earlier can be increased by shifting to feedback control based on the output of the air-fuel ratio sensor. The stoichiometric air-fuel ratio can be maintained with high accuracy. As a result, the air-fuel ratio state can be smoothly switched from the air-fuel ratio different state to the all-cylinder theoretical air-fuel ratio state, and torque fluctuation suppression and exhaust gas purification after the air-fuel ratio different state can be suitably performed. .
[0025]
  Claim8In the invention described in claim 1, in the invention described in claim 1, the catalyst temperature increase determination means determines that the temperature increase of the exhaust purification catalyst is necessary when the temperature of the exhaust purification catalyst is lower than the catalyst activation temperature. It is characterized by that.
[0026]
  Claim8According to the invention described in the above, when the temperature of the exhaust purification catalyst is lower than the catalyst activation temperature and the exhaust purification catalyst is in a state in which it cannot sufficiently purify harmful substances in the exhaust gas, The temperature determining means determines that it is necessary to raise the temperature of the exhaust purification catalyst. As a result, the temperature of the exhaust purification catalyst is raised at an early stage due to the difference in air-fuel ratio, so that the harmful substances in the exhaust gas can be sufficiently purified earlier.
[0027]
  Claim9In the invention described in claim 1, in the invention described in claim 1, the exhaust purification catalyst is a NOx occlusion reduction catalyst, and the catalyst temperature increase determination means is configured to detect when the SOx poisoning amount of the exhaust purification catalyst becomes a predetermined amount or more. The exhaust purification catalyst is judged to need to be heated.
[0028]
  Claim9According to the invention described in the above, when the SOx poisoning amount of the NOx occlusion reduction catalyst that is the exhaust purification catalyst is equal to or greater than a predetermined amount, the catalyst temperature increase determination is performed in order to eliminate the SOx poisoning of the NOx occlusion reduction catalyst. It is determined that the means needs to raise the temperature of the exhaust purification catalyst. As a result, the NOx occlusion reduction catalyst is heated up early due to the difference in air-fuel ratio, so SOx poisoning can be eliminated, and harmful substances in the exhaust gas are purified without reducing the NOx occlusion capacity. be able to.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of an internal combustion engine provided with an embodiment of an air-fuel ratio control apparatus of the present invention. The engine 1 is a four-cylinder engine and can perform lean combustion. The # 1 cylinder and # 4 cylinder of the engine 1 constitute one cylinder group, and the # 2 cylinder and # 3 cylinder constitute another cylinder group. The exhaust passages from the respective cylinders are grouped into a first upstream exhaust passage 2a1 and a second upstream exhaust passage 2a1 for each cylinder group, and then are combined into a single merged exhaust passage 2b on the downstream side. .
[0030]
On each upstream exhaust passage 2a1, 2a2, a first start catalyst 3a1 and a second start catalyst 3a2 which are exhaust purification catalysts are respectively arranged. A first oxygen sensor 4a1, which is an air-fuel ratio sensor for detecting the air-fuel ratio of each cylinder group from the oxygen concentration in the exhaust gas, is upstream of each start catalyst 3a1, 3a2 on each upstream exhaust passage 2a1, 2a2. And a second oxygen sensor 4a2. On the other hand, a NOx occlusion reduction catalyst 3b, which is an exhaust purification catalyst, is disposed on the combined exhaust passage 2b. A third oxygen sensor 4b, which is an air-fuel ratio sensor, is also arranged upstream of the NOx storage reduction catalyst 3b on the merged exhaust passage 2b. These oxygen sensors 4a1, 4a2 and 4b are those in which the output voltage changes depending on whether the air-fuel ratio is rich or lean across the stoichiometric air-fuel ratio, and is the air-fuel ratio rich with respect to the stoichiometric air-fuel ratio? Whether it is lean or not is detected on-off.
[0031]
A first temperature sensor 5a1 and a second temperature sensor 5a2 are attached to the first start catalyst 3a1 and the second start catalyst 3a2, respectively. Further, the NOx occlusion reduction catalyst 3b is also provided with a third temperature sensor 5b for detecting the catalyst temperature (that is, the exhaust gas temperature). Further, a fuel injection valve 6 is disposed in the combustion chamber of each cylinder of the engine 1, and fuel injection (in-cylinder injection) can be performed directly into each cylinder by the fuel injection valve 6. The oxygen sensors 4a1, 4a2, 4b, temperature sensors 5a1, 5a2, 5b and the fuel injection valve 6 are connected to an electronic control unit (ECU) 7. Detection results from the oxygen sensors 4a1, 4a2, 4b and the temperature sensors 5a1, 5a2, 5b are sent to the ECU 7, and the fuel injection valve 6 injects fuel based on a signal from the ECU 7.
[0032]
The ECU 7 is a microcomputer composed of a CPU, ROM, RAM, and the like, and also includes a backup RAM that retains the stored contents without being erased by the battery even after the ignition key is turned off. The ECU 7 is connected to an intake pipe pressure sensor 8 that detects an intake pipe pressure corresponding to the intake air amount, an engine speed sensor 9, an accelerator opening sensor 10, and other various sensors necessary for engine control. . The ECU 7 is responsible for overall engine control, and also functions as air-fuel ratio state switching means, air-fuel ratio learning means, learned value reflecting means, and catalyst temperature determining means.
[0033]
The engine 1 described above is operated in the following five combustion modes.
(1) Stratified combustion
(2) Weak stratified combustion
(3) Homogeneous lean combustion
(4) Homogeneous stoichiometric combustion
(5) Homogeneous rich combustion
Which of the modes described above is used for combustion is determined based on the engine operation state (driver's output request value) detected by various sensors.
[0034]
In the stratified combustion of (1), the air-fuel ratio in the vicinity of the spark plug in the cylinder is made rich, and at the same time, an air layer is formed around the air-fuel ratio to cause ultra lean combustion in the entire cylinder. In the homogeneous lean combustion (3), lean combustion is performed with the engine air-fuel ratio being uniform throughout the cylinder and leaner than the stoichiometric air-fuel ratio. The weak stratified combustion (2) is an intermediate state between stratified combustion and homogeneous lean combustion, in which fuel injection is performed twice in total in the intake stroke and the compression stroke in one cycle. In the homogeneous stoichiometric combustion (4), combustion is performed with the engine air-fuel ratio being uniform throughout the cylinder and the stoichiometric air-fuel ratio. In the homogeneous rich combustion (5), combustion is performed with the engine air-fuel ratio being homogeneous throughout the cylinder and richer than the stoichiometric air-fuel ratio.
[0035]
During homogeneous stoichiometric combustion and homogeneous rich combustion, the basic fuel injection amount QALL is determined from the intake air amount obtained from the output of the intake pipe pressure sensor 8 and the engine speed detected by the engine speed sensor 9. During stratified combustion, weak stratified combustion, and homogeneous lean combustion, the basic fuel injection amount QALL is determined from the accelerator opening detected by the accelerator opening sensor 10 and the engine speed detected by the engine speed sensor 9.
[0036]
The first start catalyst 3a1, the second start catalyst 3a2, and the NOx storage reduction catalyst 3b will be described in detail.
[0037]
The first start catalyst 3a1 and the second start catalyst 3a2 are three-way catalysts in which a noble metal such as platinum, palladium or rhodium is supported on a carrier whose surface is coated with a thin film layer of alumina. Purifies hydrocarbons HC, carbon monoxide CO, and nitrogen oxides NOx. The purification of HC, CO, and NOx is most efficiently performed when burned near the stoichiometric air-fuel ratio. The first start catalyst 3a1 and the second start catalyst 3a2 are installed at positions close to the main body of the engine 1 and reach the catalyst activation temperature earlier by the exhaust gas after the engine 1 is started.
[0038]
The NOx occlusion reduction catalyst 3b is basically the above-described three-way catalyst, but an alkali metal (potassium, sodium, lithium, cesium, etc.), an alkaline earth metal (barium, calcium, etc.) on the alumina coating layer. Alternatively, a rare earth element (such as lanthanum, cesium, yttrium, etc.) is further carried so that NOx can be occluded when the air-fuel ratio is lean.
[0039]
Therefore, the NOx occlusion reduction catalyst 3b functions as an ordinary three-way catalyst, that is, a function of purifying HC, CO, NOx in the exhaust gas when burned near the stoichiometric air-fuel ratio, It is possible to occlude unreduced NOx contained therein. The exhaust gas burned at an air / fuel ratio leaner than the stoichiometric air / fuel ratio hardly contains HC and CO as reducing agents, so NOx is difficult to be reduced, and this non-reduced NOx is temporarily stored in the NOx occlusion reduction catalyst 3b. Occluded.
[0040]
The NOx occluded in the NOx occlusion reduction catalyst 3b is reduced and purified by HC and CO in the exhaust gas when burned at an air-fuel ratio richer than the stoichiometric air-fuel ratio (or near the stoichiometric air-fuel ratio) (this When HC and CO are oxidized simultaneously). Therefore, when it is determined that the NOx occlusion / reduction catalyst 3b has occluded NOx to some extent, the engine 1 is operated for a short time at an air / fuel ratio richer than the stoichiometric air / fuel ratio to reduce the occluded NOx. Perform spike operation.
[0041]
Further, the NOx occlusion reduction catalyst 3b as described above has a property of occlusion of SOx when sulfur oxide SOx is present in the exhaust gas, similarly to NOx occlusion. Moreover, since SOx is stably stored in the NOx occlusion reduction catalyst 3b as compared with NOx, it is less likely to be reduced than NOx, and cannot be reduced in the normal rich spike operation, and the NOx occlusion reduction catalyst 3b. There is a tendency to continue being occluded. As a result, the amount of SOx occluded in the NOx occlusion reduction catalyst 3b increases, and accordingly, NOx cannot be occluded (hereinafter this phenomenon is referred to as SOx poisoning), and NOx may not be purified by the NOx occlusion reduction catalyst 3b. is there.
[0042]
In order to release the SOx stored in the NOx storage reduction catalyst 3b, the temperature of the NOx storage reduction catalyst 3b can be reduced to a higher temperature (for example, 600 to 850 ° C.) than during NOx reduction, and the ambient atmosphere can be reduced as a reduction atmosphere. It ’s fine. For this reason, while raising the temperature of the NOx occlusion reduction catalyst 3b, SOx is reduced in a reducing atmosphere equivalent to the exhaust gas after being burned at an air / fuel ratio slightly richer than the stoichiometric air / fuel ratio. The catalyst 3b is recovered from SOx poisoning.
[0043]
In order to raise the temperature of the NOx storage reduction catalyst 3b, the # 1, # 4 cylinder side cylinder group is burned at an air fuel ratio leaner than the stoichiometric air fuel ratio, and the # 2, # 3 cylinder side cylinder group is made to burn more than the stoichiometric air fuel ratio. Burn with rich air-fuel ratio (or vice versa). By doing so, oxygen is contained in the exhaust gas from the # 1, # 4 cylinder side cylinder group, and HC, CO is contained in the exhaust gas from the # 2, # 3 cylinder side cylinder group Therefore, HC and CO are oxidized in the NOx occlusion reduction catalyst 3b on the combined exhaust passage 2b, and the NOx occlusion reduction catalyst 3b is heated by the oxidation reaction heat. At this time, it is preferable to reduce SOx if a reduction atmosphere is formed by leaving some HC and CO in the exhaust gas after the oxidation reaction of oxygen and HC and CO.
[0044]
In addition to recovery from the SOx poisoning described above, the NOx storage reduction catalyst 3b needs to be actively heated, for example, when it is desired to raise the temperature of the NOx storage reduction catalyst 3b to the catalyst activation temperature at an early stage. Even in such a case, it is useful to burn some cylinder groups at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and to burn other cylinder groups at an air-fuel ratio richer than the stoichiometric air-fuel ratio. As described above, there are various ways of controlling the air-fuel ratio state of a multi-cylinder internal combustion engine so that a certain cylinder group and another cylinder group have different air-fuel ratios, that is, switching the air-fuel ratio state to an air-fuel ratio different state. There are advantages. The present invention suppresses torque fluctuation at the time of switching to the different air-fuel ratio state and also suppresses emission of harmful substances in the exhaust gas when the air-fuel ratio is different.
[0045]
Here, the feedback control of the air-fuel ratio will be briefly described.
[0046]
The fuel injection amount TAU when operating the engine is determined as follows.
TAU ← α ・ QALL ・ EFTOTAL + β ・ ・ ・ ・ (I)
Here, QALL is a basic fuel injection amount determined from the intake pipe pressure and the engine speed (as described above, it may be determined from the accelerator opening and the engine speed), and this basic fuel injection amount QALL. Is corrected according to the engine operating state to determine the fuel injection amount TAU. EFTOTAL is an air-fuel ratio reflecting total value. The air-fuel ratio reflecting total value EFTOTAL is a component for correcting the basic fuel injection amount QALL in order to set the air-fuel ratio to the target air-fuel ratio, and the air-fuel ratio feedback control is performed by this value. α and β are other correction components such as a warm-air increase correction value immediately after start-up and an acceleration increase correction value during acceleration. This EFTOTAL is represented, for example, by the sum of the air-fuel ratio feedback correction value FAF and the air-fuel ratio learning value KG. That is, in this case, the formula (I) is as follows.
TAU ← α ・ QALL ・ (FAF + KG) + β ・ ・ ・ ・ (II)
[0047]
The air-fuel ratio feedback correction value FAF is for detecting the actual air-fuel ratio based on the output of the oxygen sensor and performing feedback correction so that this air-fuel ratio becomes the target air-fuel ratio. For example, when the air-fuel ratio is set to the stoichiometric air-fuel ratio, as shown in FIGS. 2 (a) and 2 (b), while the air-fuel ratio detected by the oxygen sensor is richer than the stoichiometric air-fuel ratio. When a value that gradually decreases the fuel injection amount is given to the air-fuel ratio feedback correction value FAF, and the air-fuel ratio detected by the oxygen sensor changes from rich to lean, the fuel injection is taken into account to improve responsiveness A value to increase the amount is given in a skipping manner.
[0048]
Conversely, while the air-fuel ratio detected by the oxygen sensor is leaner than the stoichiometric air-fuel ratio, a value that gradually increases the fuel injection amount is given to the air-fuel ratio feedback correction value FAF, which is detected by the oxygen sensor. When the air-fuel ratio is changed from lean to rich, a value for reducing the fuel injection amount is given in a skipping manner in consideration of improvement in response. In this way, the air-fuel ratio feedback correction value FAF is generated so as to always maintain the engine air-fuel ratio at the theoretical air-fuel ratio that is the target air-fuel ratio.
[0049]
In consideration of the detection delay of the oxygen sensor, delay times DT1 and DT2 as shown in FIG. 2C may be set in the air-fuel ratio feedback correction value FAF. In some cases, the ECU generates a determination signal that determines lean-rich on-off from the output of the oxygen sensor, and generates a FAF signal based on the determination signal.
[0050]
On the other hand, the air-fuel ratio learning value KG is one of the air-fuel ratio control values, and is generated from the air-fuel ratio feedback correction average value FAFAV obtained by averaging the air-fuel ratio feedback correction value FAF. Note that the air-fuel ratio feedback correction average value FAFAV is also one of the air-fuel ratio control values. The air-fuel ratio learning value KG is a correction value for reflecting individual differences between engines, such as fuel injection valves and air-fuel ratio sensors, and changes with time, and is determined for each predetermined engine load region. Even when air-fuel ratio feedback control is not performed and open-loop control is performed (for example, when FAF is fixed to 1.0), the deviation of the air-fuel ratio caused by individual differences or changes with time In order to absorb, it correct | amends using this air-fuel-ratio learning value KG.
[0051]
If air-fuel ratio feedback control is performed using the air-fuel ratio feedback correction value FAF, the air-fuel ratio feedback correction value FAF based on the output of the oxygen sensor can be used as the engine air-fuel ratio without using such an air-fuel ratio learning value KG. To correct the target air-fuel ratio. However, since highly accurate control is performed by reflecting individual differences and changes with time of the engine, the air-fuel ratio learning value KG is reflected not only during open loop control but also during feedback control. The air-fuel ratio learning value KG is stored in the backup RAM in the ECU and is taken out when necessary.
[0052]
The above-described air-fuel ratio feedback correction value FAF and air-fuel ratio control value (air-fuel ratio feedback correction average value FAFAV, air-fuel ratio learning value KG, etc.) are calculated and updated every few milliseconds by a program stored in the ROM in the ECU 7. The Further, the fuel injection amount TAU is determined based on the air-fuel ratio feedback correction value FAF calculated in the ECU 7 and the air-fuel ratio control value, and fuel is injected using the fuel injection valve 6. In the ECU 7, in addition to the fuel injection amount TAU, ignition timing, valve timing, EGR amount, and throttle valve opening are also calculated and determined.
[0053]
Next, the above-described air-fuel ratio state of the internal combustion engine is switched to a state in which the # 1, # 4 cylinder side cylinder group and the # 2, # 3 cylinder side cylinder group are burned at different air-fuel ratios, that is, an air-fuel ratio different state. The stroke will be described with reference to the explanatory diagram of the air-fuel ratio control state shown in FIG. 3 and the flowchart shown in FIG.
[0054]
The engine 1 is normally operated in the same air-fuel ratio state in which the air-fuel ratios of all cylinders are the same. Here, as shown in FIG. 3, from the state in which all the cylinders are stratified combustion with the same air-fuel ratio, the air-fuel ratio control stable state (1) in which all the cylinders are homogeneously stoichiometrically combusted, # 1 , The # 4 cylinder side cylinder group is homogeneously rich burned, and the # 2, # 3 cylinder side cylinder group is switched to the air-fuel ratio difference state (2) where the # 2 cylinder side cylinder group is homogeneously lean burned. Thereafter, after completion of the air-fuel ratio difference state (2), the engine is switched to the all-cylinder theoretical air-fuel ratio state (3) in which all cylinders are subjected to homogeneous stoichiometric combustion. The process of switching from the same air-fuel ratio state-air-fuel ratio control stable state (1) -air-fuel ratio different state (2) -all cylinder theoretical air-fuel ratio state (3) will be described in order.
[0055]
The air-fuel ratio control stable state here refers to a state in which a sufficient output torque can be maintained while maintaining a high purification rate of harmful substances in the exhaust gas. As an example of the air-fuel ratio control stable state, there is a state in which feedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio. If feedback control is performed in this way, deviation due to various disturbances can be obtained with reference to the target air-fuel ratio in air-fuel ratio control, and various control values can be learned, so that the control state of the air-fuel ratio can be further stabilized. it can. In this case, the above-described target air-fuel ratio is particularly set to the stoichiometric air-fuel ratio.
[0056]
In FIG. 3, various states of the above-described control process are shown along the time axis. 3 (a) is a schematic diagram showing the combustion state of each cylinder of the engine 1, FIG. 3 (b) is a schematic diagram showing the air-fuel ratio as a control target of each cylinder of the engine 1, and FIG. 3 (c) is the air-fuel ratio. It is a schematic diagram which shows the state of a feedback correction value. In addition, the vertical axis | shaft of FIG.3 (b) shows the magnitude | size of an air fuel ratio. In FIG. 3C, in the air-fuel ratio control stable state (1) and the all-cylinder theoretical air-fuel ratio state (3) -2, feedback control is performed by the outputs of the oxygen sensors 4a1 and 4a2 for each cylinder group. For convenience, air-fuel ratio feedback correction values FAF1, FAF2 corresponding to each cylinder group are shown.
[0057]
As shown in FIG. 4, the ECU 7 constantly monitors whether the temperature raising control of the exhaust purification catalyst is necessary based on the detection results of the various sensors connected. In the present embodiment, for example, when the integrated injection value of the fuel injection amount becomes a predetermined value or more, it is determined that the NOx storage reduction catalyst 3B is poisoned by a predetermined amount of SOx. In order to recover this SOx poisoning, it is determined that the temperature increase control of the NOx occlusion reduction catalyst 3b is necessary.
[0058]
When the ECU 7 determines that the temperature raising control of the exhaust purification catalyst is necessary (step 100), the injection mode of the fuel injection valve 6 is switched, and as shown in FIG. If the operation state is, for example, the state in which stratified combustion is performed (the same air-fuel ratio state), the air-fuel ratio control stable state (1) is switched (step 101). If the stoichiometric air-fuel ratio operation is required when temperature increase control is required, the air-fuel ratio stable state (1) is switched as it is.
[0059]
At this time, in order to make output torque fluctuation smooth, the engine is switched to stoichiometric combustion which is in the stable state of air-fuel ratio control (1) after short-time weak stratified combustion and homogeneous lean combustion. Air-fuel ratio control stable state (1) From the previous stratified combustion to homogeneous lean combustion, air-fuel ratio feedback control is not performed, and fuel injection determined by the accelerator opening (the engine required load by the driver) and the engine speed Open loop control with quantity.
[0060]
After shifting to the air-fuel ratio control stable state (1), the air-fuel ratio feedback control is started. At this time, the first oxygen sensor 4a1 and the second oxygen sensor upstream of the first start catalyst 3a1 and the second start catalyst 3a2 on the first upstream exhaust passage 2a1 and the second upstream exhaust passage 2a2 for each cylinder group. Based on the output of 4a2, the air-fuel ratio reflecting total value described above is formed for each cylinder group, and based on this, the air-fuel ratio feedback control is performed for each cylinder group.
[0061]
Hereinafter, for the sake of explanation, the total air-fuel ratio reflecting value for the # 1, # 4 cylinder side cylinder group is EFTOTAL1, and the total air-fuel ratio reflecting value for the # 2, # 3 cylinder side cylinder group is EFTOTAL2. Similarly, the air-fuel ratio feedback correction value based on the first oxygen sensor 4a1 of the # 1, # 4 cylinder group is FAF1, and the air-fuel ratio feedback correction average value obtained from this air-fuel ratio feedback correction value FAF1 is FAFAV1, the air-fuel ratio The learning value is KG1. Similarly, the air-fuel ratio feedback correction value based on the second oxygen sensor 4a2 of the # 2, # 3 cylinder side cylinder group is FAF2, the air-fuel ratio feedback correction average value obtained from this air-fuel ratio feedback correction value FAF2 is FAFAV2, and the air-fuel ratio The learning value is KG2.
[0062]
That is, in the stable state of air-fuel ratio control (1), EFTOTAL1 = FAF1 + KG1 and
TAU1 ← α ・ QALL ・ EFTOTAL1 + β = α ・ QALL ・ (FAF1 + KG1) + β
The basic fuel injection amount QALL is corrected by feedback control to determine the fuel injection amount TAU1 of the # 1, # 4 cylinder side cylinder group. Similarly, EFTOTAL2 = FAF2 + KG2
TAU2 ← α ・ QALL ・ EFTOTAL2 + β = α ・ QALL ・ (FAF2 + KG2) + β
The basic fuel injection amount QALL is corrected by feedback control to determine the fuel injection amount TAU2 for the # 2, # 3 cylinder side cylinder group.
[0063]
Air-fuel ratio controlled stable state (1) in which homogeneous stoichiometric combustion is performed is combustion at the stoichiometric air-fuel ratio, so the exhaust purification catalyst (three-way catalyst) has a high removal rate of harmful substances in the exhaust gas, and is sufficiently Can maintain a stable output torque. At this time, air-fuel ratio control values such as air-fuel ratio feedback correction average values FAFAV1, FAFAV2 and air-fuel ratio learning values KG1, KG2 are also learned, and highly accurate feedback control reflecting the engine state at that time is performed. Can do.
[0064]
Since the air-fuel ratio control stable state (1) is performed for a predetermined time until the air-fuel ratio state is once stabilized, the ECU 7 counts the time since the transition to the air-fuel ratio control stable state (1). Whether or not has elapsed has been determined (step 102). While it is determined that the predetermined time has not elapsed since the transition to the air-fuel ratio control stable state (1), the air-fuel ratio control stable state (1) is continued until the predetermined time has elapsed. On the other hand, when it is determined in step 102 that the predetermined time has elapsed since the transition to the air-fuel ratio control stable state (1), the air-fuel ratio feedback control is based on the first oxygen sensor 4a1 and the second oxygen sensor 4a2. The control is switched to the control based on the third oxygen sensor 4b (step 103), and the state shifts to the air-fuel ratio difference state (2).
[0065]
That is, after the air-fuel ratio feedback control is executed for a predetermined time in the air-fuel ratio control stable state (1), the air-fuel ratio for each cylinder group is set to the predetermined air-fuel ratio so that the ECU 7 enters the air-fuel ratio different state (2). It is gradually switched at the changing speed. In the air-fuel ratio difference state (2), the # 1, # 4 cylinder side cylinder group is subjected to homogeneous rich combustion, and the # 2, # 3 cylinder side cylinder group is subjected to homogeneous lean combustion. The combined exhaust gas flowing into the NOx occlusion reduction catalyst 3b on the combined exhaust passage 2b is equivalent to the exhaust gas when burned at the stoichiometric air fuel ratio (or a slightly richer air fuel ratio). Thus, feedback control is performed based on the output of the third oxygen sensor 4b.
[0066]
As described above, the condition for switching to the air-fuel ratio difference state (2), that is, the condition for raising the temperature of the exhaust purification catalyst, is that the SOx poisoning amount of the NOx occlusion reduction catalyst 3b is a predetermined amount or more. When it is determined that it has become. The determination condition for switching the engine air-fuel ratio to the air-fuel ratio different state (2) via the air-fuel ratio control stable state (1) will be described in further detail later.
[0067]
At this time, after the exhaust gas passing through the first upstream exhaust passage 2a1 and the second upstream exhaust passage 2a2 is burned at an air-fuel ratio, one of which is richer than the stoichiometric air-fuel ratio and the other is leaner than the stoichiometric air-fuel ratio. Therefore, depending on the first oxygen sensor 4a1 and the second oxygen sensor 4a2 that detect whether the engine is rich or lean on the boundary of the theoretical air-fuel ratio, feedback control of the air-fuel ratio is performed with high accuracy. It may be difficult to do. For this reason, in the air-fuel ratio different state (2), the combined exhaust gas is converted to the stoichiometric air-fuel ratio (or the other) based on the output of the third oxygen sensor 4b upstream of the NOx storage reduction catalyst 3b on the combined exhaust passage 2b. The air-fuel ratio feedback control is performed so as to be equivalent to the exhaust gas when burned at a slightly richer air-fuel ratio.
[0068]
The exhaust gas discharged from both cylinder groups and flowing into the NOx occlusion reduction catalyst 3b after merging is equivalent to the exhaust gas when burned at the stoichiometric air fuel ratio (or a slightly richer air fuel ratio). Since feedback control is performed, rich exhaust gas and lean exhaust gas are caused to oxidize on the NOx storage reduction catalyst 3b, and the temperature of the NOx storage reduction catalyst 3b is raised. In addition, since the total air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 3b is the stoichiometric air-fuel ratio (or an air-fuel ratio slightly richer than this), as described above, the NOx occlusion reduction catalyst 3b is converted into the SOx. Can recover from poisoning. Hereinafter, for the sake of explanation, the air-fuel ratio feedback correction value based on the third oxygen sensor 4b on the merged exhaust passage 2b is assumed to be FAF3.
[0069]
Here, as the initial value FAF3 (S) of the air-fuel ratio feedback correction value FAF3 in the air-fuel ratio difference state (2), the air-fuel ratio feedback correction average values FAFAV1 (E), FAFAV2 ( The following values using E) are used (step 104).
FAF3 (S) = [FAFAV1 (E) + FAFAV2 (E)] / 2
The initial values EFTOTAL1 (S) and EFTOTAL2 (S) of the air-fuel ratio reflected total values EFTOTAL1, EFTOTAL2 in the air-fuel ratio difference state (2) are the air-fuel ratio learning value KG1 at the end of the air-fuel ratio control stable state (1). The following values using E) and KG2 (E) and FAFAV1 (E) and FAFAV2 (E) described above are used (step 105).
Figure 0003890775
[0070]
FAF3, EFTOTAL1, and EFTOTAL2 are based on the output of the third oxygen sensor 4b after the above-described FAF3 (S), EFTOTAL1 (S), and EFTOTAL2 (S) are used as initial values in the air-fuel ratio difference state (2). Thus, the air-fuel ratio difference state (2) is continuously calculated by the following equation (step 106).
EFTOTAL1 = FAF3 + KG1 (E)
EFTOTAL2 = FAF3 + KG2 (E)
That is, in the air-fuel ratio difference state (2), the air-fuel ratio feedback correction value FAF3 is based on the output of the third oxygen sensor 4b on the combined exhaust passage 2b, and is used for both cylinder groups. The air-fuel ratio learning values KG1 (E) and KG2 (E) (respectively fixed values) at the end of the stable state (1) are used for each cylinder group.
[0071]
As described above, in the air-fuel ratio difference state (2), EFTOTAL1 = FAF3 + KG1 (E).
TAU1 ← α ・ QALL1 ・ EFTOTAL1 + β = α ・ QALL1 ・ [FAF3 + KG1 (E)] + β
The basic fuel injection amount QALL1 is corrected by feedback control to determine the fuel injection amount TAU1 of the # 1, # 4 cylinder side cylinder group. Similarly, since EFTOTAL2 = FAF3 + KG2 (E),
TAU2 ← α ・ QALL2 ・ EFTOTAL2 + β = α ・ QALL2 ・ [FAF3 + KG2 (E)] + β
The basic fuel injection amount QALL2 is corrected by feedback control to determine the fuel injection amount TAU2 of the # 2, # 3 cylinder side cylinder group.
[0072]
As described above, since the # 1, # 4 cylinder side cylinder group is subjected to homogeneous rich combustion, the basic fuel injection amount QALL1 on the # 1, # 4 cylinder side is set to an injection amount close to rich. Similarly, since the # 2, # 3 cylinder side cylinder group is subjected to homogeneous lean combustion, the basic fuel injection amount QALL2 on the # 2, # 3 cylinder side is set to an lean lean injection amount.
[0073]
As described above, the initial value FAF3 (S) calculated in step 104 is the air-fuel ratio feedback correction average value FAFAV1, FAFAV2 in which the air-fuel ratio feedback correction values FAF1, FAF2 of the respective cylinder groups are averaged. (1) The values FAFAV1 (E) and FAFAV2 (E) at the end are further averaged. As an initial value of the air-fuel ratio feedback correction value FAF3 in the air-fuel ratio difference state (2), this initial value FAF3 (S) obtained by averaging the average values is used.
[0074]
This is because each cylinder group is independently feedback-controlled with separate air-fuel ratio feedback correction values FAF1 and FAF2 in the air-fuel ratio control stable state (1), but in a single air-fuel ratio difference state (2). This is because the shift to the feedback control based on the air-fuel ratio feedback correction value FAF3 is made to smoothly shift the feedback control in a well-balanced manner while absorbing the deviation of the air-fuel ratio feedback correction values of both cylinder groups. In addition, since the feedback control can be smoothly transferred in a balanced manner, the purification rate of harmful substances in the exhaust gas can be increased, and torque fluctuation at the time of switching can be suppressed.
[0075]
Similarly, the initial values EFTOTAL1 (S) and EFTOTAL2 (S) calculated in step 105 reflect the air-fuel ratio learning values KG1 (E) and KG2 (E) at the end of the air-fuel ratio control stable state (1). Yes. This is because, in the air-fuel ratio difference state (2), the control shifts to feedback control with a single air-fuel ratio feedback correction value FAF3. In the air-fuel ratio difference state (2), the air-fuel ratio control value (air-fuel ratio) is set for each cylinder group. This is because accurate learning of the learning values KG1, KG2) cannot be performed, and the most reliable latest air-fuel ratio learning values KG1 (E), KG2 (E) are reflected to perform highly accurate feedback control.
[0076]
Also, here, for EFTOTAL1 (S) and EFTOTAL2 (S), <FAFAV1 (E)-[FAFAV1 (E) + FAFAV2 (E)] / 2>, <FAFAV2 (E)-[FAFAV1 (E ) + FAFAV2 (E)] / 2> is added because each cylinder group is independently feedback-controlled with separate air-fuel ratio feedback correction values FAF1, FAF2 in the stable state of air-fuel ratio control (1). When shifting to a feedback control with a single air-fuel ratio feedback correction value FAF3 in the air-fuel ratio difference state (2), the deviation control for each cylinder group from FAF1, FAF2 to FAF3 is absorbed and feedback control is performed. This is to make a smooth transition with good balance.
[0077]
As described above, since the air-fuel ratio state passes through the air-fuel ratio control stable state (1) and then is switched to the air-fuel ratio different state (2), the output torque for each cylinder group is changed to a different air-fuel ratio different state (2). When shifting, torque fluctuation can be suppressed as much as possible. At this time, since the air-fuel ratio state is switched to the air-fuel ratio difference state (2) after passing through the air-fuel ratio control stable state (1), the purification rate of harmful substances in the exhaust gas can be maintained high, Can also be suppressed.
[0078]
By the way, when switching to the air-fuel ratio difference state (2) without going through the air-fuel ratio control stable state (1) as in the prior art, in the cylinder group that is switched from stratified combustion to lean combustion, the air-fuel ratio difference before and after the switching is Since it is small, it can be transferred in a short time. However, in the cylinder group that can be switched from stratified combustion to rich combustion, the air-fuel ratio difference before and after the switching is large, so that it takes more time than the cylinder group that can be switched to lean combustion. As a result, when switching to the air-fuel ratio difference state (2) without going through the air-fuel ratio control stable state (1), the transition period until the transition to the air-fuel ratio difference state (2) is completed becomes longer, and torque fluctuations growing. On the other hand, in this embodiment, the air-fuel ratio control stable state (1) is set to a state in which all cylinders are controlled to the stoichiometric air-fuel ratio, and after passing through the air-fuel ratio control stable state (1), the air-fuel ratio difference Since the state (2) is switched, the transition period can be shortened and the torque fluctuation can be suppressed.
[0079]
In particular, the air-fuel ratio control stable state (1) described above is a state in which feedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio based on the outputs of the first oxygen sensor 4a1 and the second oxygen sensor 4a2. Therefore, when controlling the air-fuel ratio, the air-fuel ratio control value (air-fuel ratio learning value KG1, KG2, etc.) can be learned, and based on the latest air-fuel ratio control value reflecting the engine state, the air-fuel ratio control is stable. Since the air-fuel ratio feedback control can be performed in the state (1) and the air-fuel ratio difference state (2), highly accurate feedback control can be performed. As a result, it is possible to smoothly switch to the air-fuel ratio difference state (2) via the air-fuel ratio control stable state (1) while suppressing fluctuations in torque. Moreover, since highly accurate feedback control can be performed, harmful substances in the exhaust gas can be efficiently purified.
[0080]
In addition, since the target air-fuel ratio described above is the stoichiometric air-fuel ratio, after balancing the fluctuation suppression of torque fluctuation and the discharge suppression of harmful substances in the exhaust gas at a high level in the air-fuel ratio control stable state (1). Since the air-fuel ratio difference state (2) is switched, the transition can be performed very smoothly. Further, in the air-fuel ratio control stable state (1), homogeneous stoichiometric combustion is performed, so that air-fuel ratio feedback control can be performed with very high accuracy.
[0081]
When the ECU 7 determines that the SOx occluded in the NOx occlusion reduction catalyst 3b is reduced, the NOx occlusion reduction catalyst 3b recovers from the SOx poisoning, and the temperature rise of the NOx occlusion reduction catalyst 3b is no longer necessary. The air-fuel ratio difference state {circle around (2)} is terminated (step 107) and is switched to the all-cylinder theoretical air-fuel ratio state {circle around (3)}.
[0082]
Immediately after switching to the all-cylinder theoretical air-fuel ratio state (3), control is performed so that each cylinder group that has been subjected to homogeneous rich combustion or homogeneous lean combustion is subjected to homogeneous stoichiometric combustion at an earlier stage. Here, immediately after switching to the all-cylinder theoretical air-fuel ratio state (3), if feedback control is performed using the air-fuel ratio feedback correction values FAF1, FAF2 based on the outputs of the first oxygen sensor 4a1 and the second oxygen sensor 4a2, Since the air-fuel ratio for each cylinder is greatly different between rich and lean, it takes time to completely shift all cylinders to homogeneous stoichiometric combustion. That is, the feedback control using the air-fuel ratio feedback correction values FAF1, FAF2 is a very suitable control method for maintaining the air-fuel ratio controlled near the stoichiometric air-fuel ratio, but is richer or leaner than the stoichiometric air-fuel ratio. It is not always an optimal control method to shift the combustion at the air-fuel ratio to combustion at the stoichiometric air-fuel ratio at an earlier stage.
[0083]
Therefore, immediately after switching to the all-cylinder theoretical air-fuel ratio state (3), the air-fuel ratio feedback correction values FAF1 and FAF2 are set to the air-fuel ratio feedback correction average value FAFAV1 (E ), FAFAV2 (E) is fixed, and open-loop control is performed for a predetermined time so that the air-fuel ratio becomes closer to the theoretical air-fuel ratio earlier [(3) -1 in FIG. 3 (a)] (step 108). At this time, the air-fuel ratio learning values KG1 (E) and KG2 (E) at the end of the air-fuel ratio control stable state (1) are also reflected for more accurate control.
[0084]
That is, in the period of (3) -1 immediately after the transition to the all cylinder theoretical air-fuel ratio state (3), EFTOTAL1 = FAFAV1 (E) + KG1 (E),
TAU1 ← α ・ QALL ・ EFTOTAL1 + β = α ・ QALL ・ [FAFAV1 (E) + KG1 (E)] + β
To open-loop control to determine the fuel injection amount TAU1 of the # 1, # 4 cylinder side cylinder group. Similarly, since EFTOTAL2 = FAFAV2 (E) + KG2 (E)
TAU2 ← α ・ QALL ・ EFTOTAL2 + β = α ・ QALL2 ・ [FAFAV2 (E) + KG2 (E)] + β
To open-loop control to determine the fuel injection amount TAU2 of the # 2, # 3 cylinder side cylinder group.
[0085]
When a predetermined time ((3) -1) elapses after the transition to the all-cylinder theoretical air-fuel ratio state (3) and the period air-fuel ratio of each cylinder group is substantially close to the theoretical air-fuel ratio, each start catalyst 3a1, 3a2 The air-fuel ratio feedback correction values FAF1, FAF2 based on the outputs of the first oxygen sensor 4a1 and the second oxygen sensor 4a2 on the upstream side of the engine are used to shift to feedback control so that each cylinder group is burned at the stoichiometric air-fuel ratio [ In FIG. 3A, (3) -2] (step 109). Thereafter, the air-fuel ratio control value is also learned, and the air-fuel ratio learning values KG1, KG2 obtained from the air-fuel ratio feedback correction values FAF1, FAF2 are also reflected.
[0086]
That is, during the period of (3) -2 after the predetermined time ((3) -1) has passed since the transition to the all-cylinder theoretical air-fuel ratio state (3), as in the air-fuel ratio control stable state (1), EFTOTAL1 = FAF1 + KG1,
TAU1 ← α ・ QALL ・ EFTOTAL1 + β = α ・ QALL ・ (FAF1 + KG1) + β
The basic fuel injection amount QALL is corrected by feedback control to determine the fuel injection amount TAU1 of the # 1, # 4 cylinder side cylinder group. Similarly, EFTOTAL2 = FAF2 + KG2
TAU2 ← α ・ QALL ・ EFTOTAL2 + β = α ・ QALL ・ (FAF2 + KG2) + β
The basic fuel injection amount QALL is corrected by feedback control to determine the fuel injection amount TAU2 for the # 2, # 3 cylinder side cylinder group.
[0087]
As described above, there are various advantages when switching to the air-fuel ratio different state (2). When it is determined when switching is necessary, that is, when it is necessary to switch, the exhaust purification catalyst. It is conceivable that the temperature of the (NOx storage reduction catalyst 3b) needs to be raised. At this time, the temperature of the exhaust purification catalyst is detected by the first temperature sensor 5a1, the second temperature sensor 5a2, and the third temperature sensor 5b, and it is necessary to raise the temperature of the exhaust catalyst based on the detection result and the vehicle state. The ECU 7 determines whether or not there is. Although the temperature sensor is used in the above embodiment, the temperature of the exhaust purification catalyst may be estimated from the engine load, the rotational speed, the air-fuel ratio, and the combustion state instead of the temperature sensor.
[0088]
And as mentioned above, when it is necessary to raise the temperature of the exhaust gas purification catalyst (NOx storage reduction catalyst 3b), when the rich spike operation is performed with respect to the NOx storage reduction catalyst 3b, or the NOx storage reduction catalyst 3b. The SOx poisoning amount may exceed a predetermined amount and may need to be recovered from SOx poisoning.
[0089]
The NOx occlusion amount and SOx poisoning amount can be estimated by the ECU 7 from the operating state of the engine 1, and the estimated NOx occlusion amount and SOx poisoning amount are calculated and stored in the ECU 7 as needed and stored in the RAM in the ECU 7. . When the stored NOx storage amount or SOx poisoning amount reaches a predetermined amount, the ECU 7 switches the air-fuel ratio state of the engine 1 to the air-fuel ratio different state (2), that is, raises the temperature of the NOx storage reduction catalyst 3b. It is determined that it is necessary to do so. When determined in this way, the ECU 7 switches to the air-fuel ratio difference state (2) via the air-fuel ratio control stable state (1) in order to raise the temperature of the SOx storage reduction catalyst 3b.
[0090]
Alternatively, when the temperature of the exhaust purification catalyst needs to be raised, the temperature of the exhaust purification catalyst (NOx storage reduction catalyst 3b) is lower than the catalyst activation temperature, and the harmful substances in the exhaust gas cannot be sufficiently purified. There is. At this time, the temperature of the exhaust purification catalyst is raised so that the temperature of the exhaust purification catalyst becomes equal to or higher than the catalyst activation temperature.
[0091]
The exhaust purification catalyst does not sufficiently function as a catalyst unless the temperature exceeds a certain catalyst activation temperature. For this reason, when the engine 1 is immediately after starting, or after a long idle operation or after a long stratified combustion operation, the exhaust purification catalyst is below the catalyst activation temperature, and the harmful substances in the exhaust gas are sufficiently removed. It cannot be purified. In such a case, the ECU 7 determines that it is necessary to switch the air-fuel ratio state of the engine 1 to the air-fuel ratio difference state (2), that is, to raise the temperature of the exhaust purification catalyst. When determined in this way, the ECU 7 switches to the air-fuel ratio difference state (2) via the air-fuel ratio control stable state (1) in order to raise the exhaust purification catalyst to the catalyst activation temperature.
[0092]
As described above, when it is determined that the temperature of the exhaust purification catalyst needs to be increased, the temperature of the exhaust purification catalyst can be increased by switching to the air-fuel ratio difference state (2). In addition, the temperature of the exhaust purification catalyst can be increased without providing an exhaust injection valve or the like. That is, it is possible to raise the temperature of the exhaust purification catalyst with a simple configuration without adopting a complicated configuration for the engine 1.
[0093]
The air-fuel ratio control apparatus for an internal combustion engine of the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, # 1 cylinder and # 4 cylinder constitute one cylinder group, and # 2 cylinder and # 3 cylinder constitute another cylinder group, but one cylinder constitutes one cylinder. A group may be formed, and the remaining three cylinders may form another cylinder group. Further, the total number of cylinders is not necessarily limited to four cylinders, and is applicable to multi-cylinder engines such as in-line six cylinders and V-type eight cylinders. Further, the total number of cylinder groups is not necessarily limited to two. Further, in the above-described embodiment, the oxygen sensors 4a1, 4a2, 4b are used as the air-fuel ratio sensors, but other types of air-fuel ratio sensors that detect the air-fuel ratio, such as linear air-fuel ratio sensors, are used as the air-fuel ratio sensors. It goes without saying that it is also good.
[0094]
【The invention's effect】
The air-fuel ratio control apparatus for an internal combustion engine according to the present invention switches the air-fuel ratio state of the multi-cylinder internal combustion engine to an air-fuel ratio different state after passing the air-fuel ratio control stable state by the air-fuel ratio state switching means. Since the air-fuel ratio control stable state is a state in which the removal of harmful substances in the output torque and exhaust gas can be maintained in a stable state, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, It is possible to smoothly switch the air-fuel ratio state without effectively changing the output torque at the time of switching and while efficiently purifying harmful substances in the exhaust gas.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention.
FIG. 2 is an explanatory diagram showing a relationship between an output signal of an air-fuel ratio sensor (oxygen sensor) and a generated signal of an air-fuel ratio feedback correction value.
FIG. 3 shows various states of air-fuel ratio control according to an embodiment of the air-fuel ratio control apparatus for an internal combustion engine of the present invention, (a) is a schematic diagram showing the combustion state of each cylinder of the engine, and (b) Is a schematic diagram showing an air-fuel ratio as a control target of each cylinder of the engine, and (c) is a schematic diagram showing a state of an air-fuel ratio feedback correction value.
FIG. 4 is a flowchart showing air-fuel ratio control according to an embodiment of the air-fuel ratio control apparatus for an internal combustion engine of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2a1 ... First upstream exhaust passage (upstream exhaust passage, exhaust passage), 2a2 ... Second upstream exhaust passage (upstream exhaust passage, exhaust passage) 2b ... Merged exhaust passage (exhaust passage), 3a1 ... First start Catalyst (exhaust purification catalyst), 3a2 ... second start catalyst (exhaust purification catalyst), 3b ... NOx occlusion reduction catalyst (exhaust purification catalyst), 4a1 ... first oxygen sensor (air-fuel ratio sensor), 4a2 ... second oxygen Sensor (air-fuel ratio sensor), 4b ... third oxygen sensor (air-fuel ratio sensor), 6 ... fuel injection valve, 7 ... ECU (air-fuel ratio switching means, air-fuel ratio learning means, learning value reflecting means, catalyst temperature rise determination means) .

Claims (9)

オープンループ制御により全気筒が同じ空燃比で運転される空燃比同一状態と、気筒群毎の空燃比が異なる状態で運転される空燃比相違状態とを切り替える空燃比状態切替手段を備えた内燃機関の空燃比制御装置において、
多気筒内燃機関の排気通路上に設けられた排気浄化触媒と、前記排気浄化触媒の温度を上昇させるか否かを判断する触媒昇温判定手段と、多気筒内燃機関の排気通路上に設けられた空燃比センサとをさらに備え、
前記空燃比同一状態で内燃機関が運転している際、前記触媒昇温判定手段により前記排気浄化触媒の昇温が必要であると判断したときに、前記空燃比状態切替手段が、空燃比を前記空燃比同一状態から前記空燃比相違状態に切り替える切替を行い、前記切替を行うにあたり、前記空燃比センサの出力に基づいて機関空燃比を所定の目標空燃比となるようにフィードバック制御する状態を経由させた後に前記空燃比相違状態に切り替えることを特徴とする内燃機関の空燃比制御装置。An internal combustion engine provided with air-fuel ratio state switching means for switching between an air-fuel ratio identical state where all cylinders are operated with the same air-fuel ratio by open loop control and an air-fuel ratio different state operated with different air-fuel ratios for each cylinder group In the air-fuel ratio control apparatus of
An exhaust purification catalyst provided on the exhaust passage of the multi-cylinder internal combustion engine, a catalyst temperature increase determination means for determining whether or not to increase the temperature of the exhaust purification catalyst, and provided on the exhaust passage of the multi-cylinder internal combustion engine An air-fuel ratio sensor ,
When the internal combustion engine is operating in the same air-fuel ratio state, when the catalyst temperature increase determination means determines that the exhaust purification catalyst needs to be heated, the air-fuel ratio state switching means When switching from the same air-fuel ratio state to the different air-fuel ratio state, and performing the switching, a state in which feedback control is performed so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio based on the output of the air-fuel ratio sensor. An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio is switched to the air-fuel ratio difference state after passing through. 前記目標空燃比が理論空燃比である、請求項１に記載の内燃機関の空燃比制御装置。The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 , wherein the target air-fuel ratio is a stoichiometric air-fuel ratio. 前記空燃比センサの出力に基づく前記フィードバック制御によって得られる空燃比フィードバック補正値から空燃比制御値を学習する空燃比学習手段を備えた、請求項１に記載の内燃機関の空燃比制御装置。Wherein with the air-fuel ratio learning means for learning the air-fuel ratio control value from the air-fuel ratio feedback correction value that is obtained by the feedback control based on the output of the air-fuel ratio sensor, the air-fuel ratio control apparatus for an internal combustion engine according to claim 1. 前記排気通路が、前記各気筒群毎に設けられた上流排気通路と前記上流排気通路の下流側で合流された合流排気通路とからなり、前記空燃比センサが、前記上流排気通路上に配置されており、前記空燃比学習手段が、前記各上流排気通路毎に得られた空燃比フィードバック補正値から前記各気筒群毎に前記空燃比制御値を学習する、請求項３に記載の内燃機関の空燃比制御装置。The exhaust passage is composed of an upstream exhaust passage provided for each cylinder group and a combined exhaust passage joined downstream of the upstream exhaust passage, and the air-fuel ratio sensor is disposed on the upstream exhaust passage. The internal combustion engine according to claim 3 , wherein the air-fuel ratio learning means learns the air-fuel ratio control value for each cylinder group from an air-fuel ratio feedback correction value obtained for each upstream exhaust passage. Air-fuel ratio control device. 前記空燃比制御値を前記空燃比相違状態でのフィードバック制御に反映させる学習値反映手段を備える、請求項３に記載の内燃機関の空燃比制御装置。 The air-fuel ratio control apparatus for an internal combustion engine according to claim 3 , further comprising learning value reflecting means for reflecting the air-fuel ratio control value to feedback control in the air-fuel ratio difference state. 前記空燃比状態切替手段が、空燃比状態を前記空燃比相違状態から前記空燃比同一状態に切り替える際に、内燃機関全体の空燃比制御状態が全気筒の機関空燃比を理論空燃比とするように運転される全気筒理論空燃比状態を経由させた後に前記空燃比同一状態に切り替える、請求項１に記載の内燃機関の空燃比制御装置。  When the air-fuel ratio state switching means switches the air-fuel ratio state from the air-fuel ratio difference state to the air-fuel ratio same state, the air-fuel ratio control state of the entire internal combustion engine is set so that the engine air-fuel ratio of all cylinders becomes the stoichiometric air-fuel ratio. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio is switched to the same air-fuel ratio after passing through the all-cylinder stoichiometric air-fuel ratio operated at the same time. 多気筒内燃機関の排気通路上に設けられた空燃比センサと、前記空燃比センサの出力に基づくフィードバック制御によって得られる空燃比フィードバック補正値から空燃比制御値を学習する空燃比学習手段とを備え、前記全気筒理論空燃比状態において、前記空燃比状態切替手段によって、予め学習された前記空燃比制御値に基づくオープンループ制御を行った後に、前記空燃比センサの出力に基づくフィードバック制御を行う、請求項６に記載の内燃機関の空燃比制御装置。An air-fuel ratio sensor provided on an exhaust passage of a multi-cylinder internal combustion engine; and air-fuel ratio learning means for learning an air-fuel ratio control value from an air-fuel ratio feedback correction value obtained by feedback control based on an output of the air-fuel ratio sensor. In the all-cylinder theoretical air-fuel ratio state, after the open-loop control based on the air-fuel ratio control value learned in advance by the air-fuel ratio state switching unit, feedback control based on the output of the air-fuel ratio sensor is performed. The air-fuel ratio control apparatus for an internal combustion engine according to claim 6 . 前記触媒昇温判定手段は、前記排気浄化触媒の温度が触媒活性化温度よりも低いときに、前記排気浄化触媒の昇温が必要であると判断する、請求項１に記載の内燃機関の空燃比制御装置。2. The internal combustion engine air conditioner according to claim 1, wherein the catalyst temperature increase determination means determines that the temperature increase of the exhaust purification catalyst is necessary when the temperature of the exhaust purification catalyst is lower than the catalyst activation temperature. Fuel ratio control device. 前記排気浄化触媒がNOx吸蔵還元触媒であり、前記触媒昇温判定手段は、前記排気浄化触媒のSOx被毒量が所定量以上となったときに、前記排気浄化触媒の昇温が必要であると判断する、請求項１に記載の内燃機関の空燃比制御装置。The exhaust purification catalyst is a NOx occlusion reduction catalyst, and the catalyst temperature increase determination means needs to increase the temperature of the exhaust purification catalyst when the SOx poisoning amount of the exhaust purification catalyst exceeds a predetermined amount. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein
JP29072398A 1998-10-13 1998-10-13 Air-fuel ratio control device for internal combustion engine Expired - Fee Related JP3890775B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP29072398A JP3890775B2 (en) 1998-10-13 1998-10-13 Air-fuel ratio control device for internal combustion engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP29072398A JP3890775B2 (en) 1998-10-13 1998-10-13 Air-fuel ratio control device for internal combustion engine

Publications (2)

Publication Number Publication Date
JP2000120477A JP2000120477A (en) 2000-04-25
JP3890775B2 true JP3890775B2 (en) 2007-03-07

Family

ID=17759699

Family Applications (1)

Application Number Title Priority Date Filing Date
JP29072398A Expired - Fee Related JP3890775B2 (en) 1998-10-13 1998-10-13 Air-fuel ratio control device for internal combustion engine

Country Status (1)

Country Link
JP (1) JP3890775B2 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4254819B2 (en) 2006-07-25 2009-04-15 トヨタ自動車株式会社 Control device for internal combustion engine
JP6737156B2 (en) * 2016-12-06 2020-08-05 トヨタ自動車株式会社 Control device for internal combustion engine

Also Published As

Publication number Publication date
JP2000120477A (en) 2000-04-25

Similar Documents

Publication Publication Date Title
EP1167726B1 (en) Air-fuel ratio control apparatus of internal combustion engine
US6148612A (en) Engine exhaust gas control system having NOx catalyst
EP0971104B1 (en) An exhaust gas purification device for an internal combustion engine
JP3067685B2 (en) Exhaust purification system for spark ignition type direct injection type internal combustion engine
JP3966014B2 (en) Exhaust gas purification device for internal combustion engine
US7127883B1 (en) Exhaust gas purifying apparatus of internal combustion engine
US8205435B2 (en) Deterioration determination device for catalyst, catalyst deterioration determining method, and engine control unit
JP4186259B2 (en) Exhaust gas purification device for internal combustion engine
JPH11148338A (en) Method to regenerate trap for nitrogen oxides of exhaust system of internal combustion engine
JP2000130223A (en) Exhaust emission control system of multi-cylinder internal combustion engine
JP4475117B2 (en) Engine air-fuel ratio control device
JPH10274085A (en) Exhaust emission control device for inter-cylinder injection type internal combustion engine
JP3890775B2 (en) Air-fuel ratio control device for internal combustion engine
JP4389141B2 (en) Exhaust gas purification device for internal combustion engine
JP2004308526A (en) Exhaust emission cleaning device for internal combustion engine
JP3509482B2 (en) Exhaust gas purification device for internal combustion engine
JPH09112308A (en) Air-fuel ratio controller for internal combustion engine
JP3680237B2 (en) Exhaust gas purification device for internal combustion engine
JP4345202B2 (en) Exhaust gas purification device for internal combustion engine
JP3633312B2 (en) Exhaust gas purification device for internal combustion engine
JP2000080914A (en) Internal combustion engine
JPH11107828A (en) Air-fuel ratio controller for internal combustion engine
GB2380425A (en) A method and system for controlling an internal combustion engine.
JP2005083205A (en) Control device for internal combustion engine
JP2002235585A (en) Exhaust emission control device of internal combustion engine

Legal Events

Date Code Title Description
A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20060517

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20060523

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20060720

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20060815

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20061006

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20061114

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20061127

LAPS Cancellation because of no payment of annual fees