JP3729282B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

【００４１】
により、定常運転状態時の有効開口面積Ａと過渡運転状態時の有効開口面積Ａ_DELAY との比RATIO-A を演算する。
【００４２】
ステップＳ５２０においては、燃料噴射量ＴiMに比RATIO-A を乗算することによって、定常運転状態時及び過渡運転状態時に適応する燃料噴射量ＴiM-F’を求める。即ち、比RATIO-A の値は、定常運転状態では１となり、過渡運転状態では１を除く或る値になるので、定常運転状態と過渡運転状態との両者に対応するものである。よって、燃料噴射量ＴiMに比RATIO-A を乗算することによって、定常運転状態時及び過渡運転状態時に適応する燃料噴射量ＴiM-F’が求まる。
【００４３】
ステップＳ５２２においては、機関回転数Ｎｅと吸気圧力Ｐｂ、吸気温度及び冷却水温度Ｔｗ、パージガス濃度ＰＵＧ、排気ガスの還流率等のパラメータに基づいて、ＲＯＭ７６の所定マップを検索することにより補正係数KTOTALを求め、更に、燃料噴射量ＴiM-F’に補正係数KTOTALを乗算することにより、ＥＧＲ機構１００とキャニスタパージ機構２００の影響を補償した基本燃料噴射量ＴiM-Fを決定する。
【００４４】
このように、このフィードフォワード制御系は、運転状態の変化に伴ってシリンダ流入空気量が変動しても、スロットル開度θ_THと吸気圧力Ｐｂからそのシリンダ流入空気量に対応する最適な基本燃料噴射量ＴiM-Fを決定する。
【００４５】
次に、第１のフィードバック系を説明する。このフィードバック系は、図４中の「ＫＣＭＤ」と「ＫＣＭＤ補正」及び「ＫＣＭＤＭ］で示す機能ブロックを備え、図８に示すフローチャート（図５のステップＳ６００に対応する）に従って演算処理を行う。
【００４６】
先ず、図８のステップＳ６０２において、機関回転数Ｎｅと吸気圧力ＰｂをパラメータとしてＲＯＭ７６の所定マップを検索することにより、空燃比の基本値ＫＢＳを求める。即ち、この基本値ＫＢＳは、機関回転数Ｎｅと吸気圧力Ｐｂをパラメータとして、定常運転状態時にＯ₂ センサ５６の出力から求めることができる空燃比のデータであり、予めＲＯＭ７６に格納されている。尚、このマップにはアイドル運転状態時に対応する基本値も格納されている。更に、機関の低負荷時にその機関へ供給する空燃比を大きく（当量比で言えば小さく）して燃焼特性を向上させるための所謂リーンバーン機関にあっては、リーンバーン用の基本値も格納されている。
【００４７】
ステップＳ６０４においては、内蔵されているタイマ回路（図示せず）の値を参照することにより、機関始動後のリーンバーン制御が実行されているか否かを判定し、リーンバーン制御期間であれば、リーン補正係数を例えば０．８９、そうでない場合には１．０とする。
【００４８】
かかる判定を行うのは次の理由による。本実施例に係る内燃機関１０には可変バルブタイミング機構３００が設けられており、始動後のクランキング期間（始動期間）では、各気筒の吸気弁の一方の動作を休止させることによって、目標空燃比を理論空燃比よりもややリーン側に設定するリーンバーン制御を行い、この結果、触媒装置が未だ活性化していない始動期間であっても、炭化水素（ＨＣ）の増加を抑制することができるという効果を発揮させるようにしているからである。尚、気筒毎に２個の吸気弁を有している通常の内燃機関（可変バルブタイミング機構を備えない内燃機関）にあっては、機関始動後に目標空燃比をリーン側に設定すると、機関内の燃焼が不安定となって失火を招来することとなるが、かかる可変バルブタイミング機構３００を備えた本実施例の内燃機関にあっては、吸気弁の一方を休止させることに伴って燃焼室内に所謂スワールと呼ばれる渦流ができるので、機関の始動直後にリーン化を行っても安定した燃焼が得られる。
【００４９】
ステップＳ６０６において、スロットル開度が全開（ＷＯＴ）であるか否か判定し、この判定結果に応じて全開増量補正値を算出し、更にステップＳ６０８において、冷却水温度Ｔｗが高いか否か判定し、この判定結果に応じて増量補正係数KTWOT を演算する。尚、この増量補正係数KTWOT には、高水温時の機関保護のための補正係数値も含まれる。
【００５０】
ステップＳ６１０では、補正係数KTWOT を基本値ＫＢＳに乗算することによってその基本値ＫＢＳを補正すると共に、数２に示す演算によって目標空燃比KCMDを決定する。即ち、図３に示す如く、理論空燃比近傍のＯ₂ センサ５６の出力が線形特性を備える範囲内（縦軸に破線で示す）において、空燃比の微小制御を行うためのウインドウ（以下、DKCMD-OFFSETとする）を設定した後、補正後の上記基本値ＫＢＳにこのウインドウ値DKCMD-OFFSETを加算することにより、目標空燃比KCMDを求める。
【００５１】
【数２】

【００５２】
次に、ステップＳ６１２において、目標空燃比KCMD(k) （ここで、ｋは時刻）のリミット処理を行った後、ステップＳ６１４において、その目標空燃比KCMD(k) が１ないしその付近の値にあるか否かを判断し、肯定されるときはステップＳ６１６において、Ｏ₂ センサ５４の活性化判断を行う。尚、この活性化判断は、図示しない別ルーチンで実行され、Ｏ₂ センサ５６の検出信号の電圧変化を検出することで行う。
【００５３】
次に、ステップＳ６１８において、ＭＩＤＯ₂ 制御用の値DKCMD を演算する。ここで、ＭＩＤＯ₂ 制御とは、三元触媒装置２８の下流側のＯ₂ センサ５６の出力により上流側のＬＡＦセンサ５４の目標空燃比KCMD(k) を可変とする作業を意味する。詳しくは図３に示す如く、所定の比較電圧ＶrefMとＯ₂ センサ５６の出力電圧ＶO2Ｍの偏差にＰＩＤ制御則を用いて値DKCMD を算出することで行う。尚、比較電圧ＶrefMは、大気圧Ｐａ、水温Ｔｗ、排気ボリューム（機関回転数Ｎｅおよび吸気圧力Ｐｂより求めることが可能）などに応じて求められる。
【００５４】
更に、上記のウインドウ値DKCMD-OFFSETは、三元触媒装置２８，３０の浄化率を最適状態に維持するために付加されるオフセット値であり、触媒装置固有の特性に起因して相違するので、三元触媒装置２８の特性を勘案して決定される。また、ウインドウ値DKCMD-OFFSETは、触媒装置２８，３０の経年劣化によっても変化することから、値DKCMD の毎回の算出値を用いて加重平均により学習する。具体的には、
【００５５】
【数３】

【００５６】
の演算式により求められる。ここで、Ｗは重み係数、ｋは時刻であり、より具体的には制御サイクルを示す。即ち、目標空燃比KCMDをウインドウ値DKCMD-OFFSETの前回算出値で学習演算することにより、触媒装置２８，３０の経年劣化の影響を受けることなく、それらの浄化率が最適となる空燃比にフィードバック制御するようにしている。
【００５７】
次に、ステップＳ６２０において、上記算出した値DKCMD(k)に目標空燃比KCMD(k) を加算して、新たな目標空燃比KCMD(k) を設定（更新）し、次に、ステップＳ６２２において、更新後の目標空燃比KCMD(k) に基づいてＲＯＭ７６中の所定テーブルを検索することにより、補正係数KETCを求める。補正係数KETCは、気化熱で吸入空気の充填効率が相違するのを補償するためにある。具体的には、求めた補正係数KETCに目標空燃比KCMD (k)を乗算することにより、補正された（更新された）目標空燃比補正係数KCMDM(k)を算出する。即ち、この制御においては目標空燃比を当量比で示すと共に、それに充填効率補正を施した値を目標空燃比補正係数KCMDM(k)としている。
【００５８】
尚、上記ステップＳ６１４で否定されるときは、制御すべき目標空燃比KCMD (k) が理論空燃比に対して大きくずれているときであり、例えばリーンバーン運転状態時であることから、直ちにステップＳ６２２へジャンプする。
【００５９】
最後にステップＳ６２４において、目標空燃比補正係数KCMD(k) のリミット処理を行い、そして、図４に示すように、フィードフォワード制御系からの基本燃料噴射量ＴiM-Fに目標空燃比補正係数KCMDM(k)を乗算することにより、要求燃料噴射量Ｔcyl を算出する。
【００６０】
このように、第１のフィードバック系の機能は、定常運転状態における空燃比の基本値ＫＢＳについてＯ₂ センサ５６の出力に基づく上記所定の補正処理を行うことによって、目標空燃比KCMDと目標空燃比補正係数KCMDM を求めると共に、基本燃料噴射量ＴiM-Fに目標空燃比補正係数KCMDM を乗算することにより、触媒装置に対する理想的な空燃比を設定し得る要求燃料噴射量Ｔcyl を算出する。
【００６１】
次に、第２のフィードバック系を説明する。このフィードバック系は、図４中の「ＳＴＲ」で示す適応型制御器と、「ＰＩＤＣ」で示すＰＩＤ制御器と、「切換ＳＷ」で示す切換機構を備え、以下に述べるこれらの機能は、ＣＰＵコア６４による所定アプリケーションプログラムの実行によって実現される。尚、このフィードバック系は、特願平６−３４００２１号に詳細に開示されているので、ここではその概略を説明する。
【００６２】
このフィードバック系は、前記フィードフォワード系で演算された基本燃料噴射量ＴiMに目標空燃比補正係数KCMDM を乗算することにより要求燃料噴射量Ｔcyl を求めただけでは、内燃機関１０の応答遅れ等に起因して目標空燃比KCMDが鈍された空燃比となってしまうので、目標空燃比KCMDから空燃比の応答を動的に補償する目的で、適応制御器ＳＴＲを用いてフィードバック補正係数KSTRを求め、このフィードバック補正係数KSTRにより要求燃料噴射量Ｔcyl を更に補正するようにしている。更に、適応制御器ＳＴＲは制御の応答性が比較的高いので、運転状態に応じて目標空燃比KCMDが大きく変動するような場合には却って制御量が発振して制御の安定性が低下するという問題を招来することから、制御が不安定となるような場合には、ＰＩＤ制御器ＰＩＤＣにより求めたフィードバック補正係数KLAFで要求燃料噴射量Ｔcyl を補正する。そして、運転状態に応じてこれらのフィードバック補正係数KSTRとKLAFを切換えて適用するために、切換機構が設けられている。更に、異なる制御則に基づいて決定されたフィードバック補正係数を切り換えるときは、それぞれの特性が異なることから、補正係数に段差が生じて操作量が急変し、制御量が不安定となって制御の安定性が低下する恐れがあるので、切換機構は、その切り換えを滑らかに実行することによって、フィードバック補正係数に不連続を生じないようにしている。
【００６３】
先ず、ＰＩＤ制御器ＰＩＤＣは、サンプリング動作ブロック（図中に「sel-Ｖ」と示す）で推定される排気系集合部の空燃比（以下、検出空燃比KACTと呼ぶ）に基づいて目標空燃比KCMDを動的に補償する。ここで、サンプリング動作ブロックsel-Ｖは、ＬＡＦセンサ５４の検出信号から上記検出空燃比KACTを演算する機能を有しており、後述する第３のフィードバック系においても、この検出空燃比KACTを用いて所定のフィードバック制御を行うようになっている。尚、サンプリング動作ブロックsel-Ｖの詳細は第３のフィードバック系と共に説明することとする。
【００６４】
ＰＩＤ制御器ＰＩＤＣの処理を述べると、先ず、目標空燃比KCMDと検出空燃比KACTの制御偏差DKAFを、
【００６５】
【数４】

【００６６】
と求める。尚、ｄ’はKCMDがKACTに反映されるまでの無駄時間を示す。よって、KCMD(k-d')は無駄時間制御周期前の目標空燃比を示す。KACT(k) は今回制御周期の検出空燃比を示す。また、この明細書での空燃比は、目標値KCMDも検出値KACTも実際には当量比、即ち、Ｍst／Ｍ＝１／λで示している（Ｍstは理論空燃比、Ｍは空気消費量Ａと燃料消費量Ｆの比Ａ／Ｆ、λは空気過剰率）。
【００６７】
次いで、それに所定の係数を乗じてＰ項KLAFP(k)、Ｉ項KLAFI(k)、及びＤ項KLAFD(k)を、
【００６８】
【数５】

【００６９】
と求める。
【００７０】
このように、Ｐ項は偏差DKAF(k) に比例ゲインKPを乗じて求め、Ｉ項は偏差に積分ゲインKIを乗じて得た値をフィードバック補正係数の前回値KLAF(k) に加算することによって求め、Ｄ項は偏差の今回値DKAF(k) と前回値DKAF(k-1) の差に微分ゲインKDを乗じることによって求める。尚、各ゲインKP，KI，KDは、機関回転数Ｎｅと吸気圧力Ｐｂをパラメータとして所定のマップ検索により求められる。更に、数６に示す如く、これらの値を合算し、更にオフセット分１．０を加算することにより、ＰＩＤ制御器ＰＩＤＣのＰＩＤ制御則によるフィードバック補正係数の今回値KLAF(k) を求める。
【００７１】
【数６】

【００７２】
次に、適応制御器ＳＴＲの機能を図９に基づいて説明する。適応制御器ＳＴＲは、ＳＴＲコントローラとパラメータ調整機構とを有し、ＳＴＲコントローラは、第１のフィードバック系からの目標空燃比KCMD(k) と前記サンプリング動作ブロック（ｓｅｌ−Ｖ）からの検出空燃比KACT(k) とを入力すると共に、ランダウらの提案したパラメータ調整則（機構）によって同定された係数ベクトルを受け取って適応デジタル信号処理を行うことにより、フィードバック補正係数KSTR(k) を算出する。換言すれば、漸化式を用いてフィードバック補正係数KSTR(k) を算出する。
【００７３】
この手法によれば、いわゆる適応システムを線形ブロックと非線形ブロックとから構成される等価フィードバック系に変換し、非線形ブロックについては入出力に関するポポフの積分不等式が成立し、線形ブロックは強正実となるように調整則を決めることによって、適応システムの安定が保証されることとなる。尚、かかる手法は、例えば、「コンピュートロール」（コロナ社刊）Ｎｏ．２７．２８頁〜４１頁、ないし「自動制御ハンドブック」（オーム社刊）７０３頁〜７０７頁に記載されている。
【００７４】
このランダウらの調整則を用いた適応制御技術を以下説明すると、ランダウらの調整則では、離散系の制御対象の伝達関数Ａ（Ｚ^-1）／Ｂ（Ｚ^-1）の分母分子の多項式を数７で▲１▼▲２▼のようにおいたとき、適応パラメータθハット (k)および適応パラメータ調整機構への入力ζ(k) は、数７で▲３▼▲４▼のように定められる。数７では、ｍ＝１，ｎ＝１，ｄ＝３の場合、即ち、１次系で３制御サイクル分の無駄時間を持つブランドを例にとった。ここでのｋは時刻、より具体的には、制御サイクルを示す。
【００７５】
【数７】

【００７６】
ここで適応パラメータθハット (k)は、数８で表される。また数８中のΓ(k) およびｅアスタリスク(K) は、それぞれゲイン行列および同定誤差信号であり、数９および数１０のような漸化式で表される。
【００７７】
【数８】

【００７８】
【数９】

【００７９】
【数１０】

【００８０】
また数９中のλ1(k)，λ2(k)の選び方により、種々の具体的なアルゴリズムが与えられる。λ1(k)＝１，λ2(k)＝λ（０＜λ＜２）とすると漸減ゲインアルゴリズム（λ＝１の場合には最小自乗法）、λ1(k)＝λ１（０＜λ１＜１）、λ2(k)＝λ２（０＜λ２＜λ) とすると可変ゲインアルゴリズム（λ２＝１の場合には重み付き最小自乗法）、λ1(k)／λ2(k)＝σとおき、λ３が数１１のように表されるとき、λ1(k)＝λ３とおくと固定トレースアルゴリズムとなる。またλ1(k)＝１，λ2(k)＝０のとき固定ゲインアルゴリズムとなる。この場合は数９から明らかな如く、Γ(k) ＝Γ(k-1) となり、よってΓ(k) ＝Γの固定値となる。
【００８１】
【数１１】

【００８２】
ここで、図９にあっては、前記したＳＴＲコントローラ（適応制御器）と適応パラメータ調整機構とは燃料噴射量演算系の外におかれ、検出空燃比KACT（k)が目標空燃比KCMD(k-d')（ここでｄ’は前述の如くKCMDがKACTに反映されるまでの無駄時間）に適応的に一致するように動作してフィードバック補正係数KSTR(k) を演算する。即ち、ＳＴＲコントローラは、適応パラメータ調整機構によって適応的に同定された係数ベクトルθハット(k) を受け取って目標空燃比KCMD(k-d')に一致するようにフィードバック補償器を形成する。
【００８３】
このように、フィードバック補正係数KSTR(k) および検出空燃比KACT(k) が求められて適応パラメータ調整機構に入力され、そこで適応パラメータθハット (k) が算出されてＳＴＲコントローラに入力される。ＳＴＲコントローラには入力として目標空燃比KCMD(k) が与えられ、検出空燃比KACT(k) が目標空燃比KCMD(k) に一致するように漸化式を用いて数１２に示すフィードバック補正係数KSTR(k) を算出する。
【００８４】
【数１２】

【００８５】
演算されたフィードバック補正係数KSTR(k) は、切換機構を介して要求燃料噴射量Ｔcyl に乗算され、その補正された燃料噴射量Ｔcyl ’が更に後述する第３のフィードバック制御系の気筒別空燃比補正係数＃ｎKLAFで補正されることにより、気筒別出力燃料噴射量＃ｎＴout が求められる。
【００８６】
尚、切換機構は、所定の切換えフラグFKSTR に同期して切換え処理し、目標空燃比KCMDが大きく変動するような運転状態にあっては、フィードバック補正係数KLAF(k) を切換え選択して要求燃料噴射量Ｔcyl に乗算し、目標空燃比KCMDが大きく変動しない運転状態にあっては、フィードバック補正係数KSTR(k) を切換え選択して、要求燃料噴射量Ｔcyl に乗算する。即ち、要求燃料噴射量Ｔcyl は、フィードバック補正係数KSTR又はKLAFにより補正される。
【００８７】
次に、第３のフィードバック系を説明する。このフィードバック系は基本的には、サンプリング動作ブロック「sel-Ｖ」が推定する排気系集合部の空燃比、即ち、検出空燃比KACTにオブザーバ（図４中にＯＢＳＶと示す）を適用することにより、気筒別空燃比＃ｎKACTを求め、更に、ＰＩＤ制御則（図４中にＰＩＤと示す）により気筒別空燃比＃ｎKACTから気筒毎の空燃比補正係数＃ｎKLAFを算出する。尚、添字＃ｎは各気筒を示す。そして、気筒別空燃比補正係数＃ｎKLAFを燃料噴射量Ｔcyl ’に乗算することによって、各気筒の空燃比を均一化することができる出力燃料噴射量＃ｎＴout を設定し、ひいては三元触媒２８，３０の排気ガス清浄効率の向上を図るようにしたものである。即ち、この第３のフィードバック系は、空燃比が各気筒でバラツクのをフィードバック補正するものである。まず、このフィードバック系の動作を説明する前に、サンプリング動作ブロック「sel-Ｖ」及びオブザーバについて説明する。
【００８８】
排気ガスは排気行程で排出されることから、多気筒内燃機関１０の排気系集合部において空燃比の挙動をみると、明らかに空燃比はＴＤＣに同期する。従って、排気系の集合部に単一のＬＡＦセンサ５４を設けて空燃比をサンプリングするときもＴＤＣに同期して行う必要があることとなる。しかし、ＬＡＦセンサ５４の検出出力を処理する制御ユニット（ＥＣＵ）３６のサンプルタイミングによっては空燃比の挙動を正確に捉えられない場合が生じる。即ち、例えば、ＴＤＣに対して排気系集合部の空燃比が図１０のようであるとき、制御ユニット３６で認識する空燃比は図１１に示す如く、サンプルタイミングによっては全く違った値となってしまう。更に、その空燃比の変化は、排気ガスがＬＡＦセンサ５４に到達するまでの時間やＬＡＦセンサ５４の反応時間によっても相違する。その内、ＬＡＦセンサ５４までの到達時間は排気ガス圧力、排気ガスボリュームなどに依存して変化する。更に、ＴＤＣに同期してサンプリングすることはクランク角度に基づいてサンプリングすることになるので、必然的に機関回転数Ｎｅの影響を受けざるを得ない。このように、空燃比の検出値は機関の運転状態に依存するところが大きい。このような課題を解決するために、サンプリング動作ブロックsel-ＶとオブザーバＯＢＳＶが設けられている。
【００８９】
排気系集合部に設けられた単一のＬＡＦセンサ５４の検出信号から各気筒の空燃比を精度良く分離抽出するためには、ＬＡＦセンサ５４の検出応答遅れを正確に解明する必要がある。そこで、図１２に示すように、この遅れを擬似的に１次遅れ系でモデル化すると、その状態方程式は数１３で示すことができる。
【００９０】
【数１３】

【００９１】
これを周期ΔＴで離散化すると、数１４で示すようになる。図１３は数１４をブロック線図で表したものである。
【００９２】
【数１４】

【００９３】
従って、数１４を用いることによってＬＡＦセンサ５４の検出出力から真の空燃比を求めることができる。即ち、数１４を変形すれば数１５に示すようになるので、時刻ｋのときの値から時刻ｋ−１のときの値を数１６のように逆算することができる。
【００９４】
【数１５】

【００９５】
【数１６】

【００９６】
具体的には数１５をＺ変換を用いて伝達関数で示せば数１７のようになるので、その逆伝達関数を今回のＬＡＦセンサ５４の検出出力ＬＡＦ(k) に乗じることによって前回の入力空燃比をリアルタイムに推定することができる。図１４にそのリアルタイムのＡ／Ｆ推定器のブロック線図を示す。
【００９７】
【数１７】

【００９８】
続いて、上記の如く求めた真の空燃比に基づいて各気筒の空燃比を分離抽出する手法について説明すると、排気系の集合部の空燃比を各気筒の空燃比の時間的な寄与度を考慮した加重平均であると考え、時刻ｋのときの値を、数１８のように表した。尚、Ｆ（燃料量）を制御量としたため、ここでは『燃空比Ｆ／Ａ』を用いているが、後の説明においては理解の便宜のため、支障ない限り「空燃比」を用いる。尚、空燃比（ないしは燃空比）は、先に数１７で求めた応答遅れを補正した真の値を意味する。
【００９９】
【数１８】

【０１００】
即ち、集合部の空燃比は、気筒ごとの過去の燃焼履歴に重みＣ（例えば直近に燃焼した気筒は４０％、その前が３０％．．．など）を乗じたものの合算で表した。このモデルをブロック線図であらわすと、図１５のようになる。
【０１０１】
また、その状態方程式は数１９のようになる。
【０１０２】
【数１９】

【０１０３】
また集合部の空燃比をｙ(k) とおくと、出力方程式は数２０のように表すことができる。
【０１０４】
【数２０】

【０１０５】
上記において、ｕ(k) は観測不可能のため、この状態方程式からオブザーバを設計してもｘ(k) は観測することができない。そこで４ＴＤＣ前（即ち、同一気筒）の空燃比は急激に変化しない定常運転状態にあると仮定してｘ(k＋1 ) ＝ｘ(k-3) とすると、数２１のようになる。
【０１０６】
【数２１】

【０１０７】
そして、かかるモデルについてシミュレーションすると、モデル出力値がＬＡＦセンサ５４出力の実測値に対して良好に追従するという結果が得られ、上記モデルが多気筒内燃機関の排気系を良くモデル化していることを検証することができた。
【０１０８】
よって、数２２で示される状態方程式と出力方程式（数２０）にてｘ(k) を観察する通常のカルマンフィルタの問題に帰着する。その荷重行列Ｑ，Ｒを数２３のように置いてリカッチの方程式を解くと、ゲイン行列Ｋは数２４のようになる。
【０１０９】
【数２２】

【０１１０】
【数２３】

【０１１１】
【数２４】

【０１１２】
これよりＡ−ＫＣを求めると、数２５のようになる。
【０１１３】
【数２５】

【０１１４】
ところで、一般的なオブザーバの構成は図１６に示されるようになるが、今回のモデルでは入力ｕ(k) がないので、図１７に示すようにｙ(k) のみを入力とする構成となり、これを数式で表すと数２６のようになる。
【０１１５】
【数２６】

【０１１６】
ここで、ｙ(k) を入力するとオブザーバ、即ちカルマンフィルタのシステム行列は数２７のように表される。
【０１１７】
【数２７】

【０１１８】
今回のモデルで、リカッチ方程式の荷重配分Ｒの要素：Ｑの要素＝１：１のとき、カルマンフィルタのシステム行列Ｓは、数２８で与えられる。
【０１１９】
【数２８】

【０１２０】
図１８に上記したモデルとオブザーバを組み合わせたものを示す。シミュレーションの結果によれば、集合部空燃比より各気筒の空燃比を的確に抽出することができることが検証された。
【０１２１】
このように、オブザーバによって、集合部空燃比Ａ／Ｆ（即ち、Ａ／ＦとはKACTと等価である）より各気筒空燃比＃ｎＡ／Ｆを推定することができたことから、ＰＩＤ制御則を用いて空燃比を気筒別に制御するための気筒別空燃比補正係数＃ｎKLAFを演算することが可能となる。
【０１２２】
具体的には、図１９に示すように、排気系集合部の空燃比（即ち、KACT）を気筒毎の空燃比補正係数＃ｎ気筒別空燃比の全気筒についての平均値の前回演算値で除算して求めた目標値と、上記オブザーバの気筒毎の推定値＃ｎＡ／Ｆと、の偏差を解消するようにＰＩＤ制御則を用いて求める。即ち、数２９に示す如く、ＰＩＤ制御則に適用する上記目標値KCMDOBSVは、前回ＴＤＣ時に推定された各気筒の空燃比補正係数＃１KLAF〜＃４KLAFの平均値で、今回求められた検出空燃比KACTを除算することによって求められる。
【０１２３】
【数２９】

【０１２４】
一方、気筒別空燃比補正係数＃ｎKLAFは、数３０に示すように、各気筒＃ｎ毎に、検出空燃比＃ｎKACT(m) と目標値KCMDOBSVとの偏差＃ｎDKACT(m)を求めると共に、今回求められた偏差＃ｎDKACT(m)と前回求められた偏差＃ｎDKACT(m-1)との偏差＃ｎDDKACTを求め、更に、これらの演算結果を適用することによって、各気筒＃ｎに該当するＰＩＤ制御則のＫＰ項とＫＩ項及びＫＤ項を求め、最後に、これらのＫＰ項とＫＩ項及びＫＤ項を適用して、気筒別空燃比補正係数＃ｎKLAFを求める。尚、＃ｎは各気筒＃１〜＃４を示し、ｍは、４ＴＤＣ毎の時点を示す。即ち、気筒別空燃比補正係数＃ｎKLAFは、それぞれ４ＴＤＣに１回演算される。尚、次式中、基準ゲインであるＫＰOBSV項とＫＩOBSV項及びＫＤOBSV項は、機関がアイドリング動作のときと、それ以外の動作時とでは、それぞれ異なった値に設定され、ＲＯＭ７６に予めデータマップとして格納されているので、かかる演算の際に運転状態に応じてマップ検索されるようになっている。
【０１２５】
【数３０】

【０１２６】
これにより、各気筒の空燃比は集合部空燃比に収束し、集合部空燃比は目標空燃比に収束することとなって、結果的に全ての気筒の空燃比が目標空燃比に収束する。ここで、各気筒の出力燃料噴射量＃ｎＴout （インジェクタの開弁時間で規定される）は、
【０１２７】
【数３１】

【０１２８】
で求められる（ｎは気筒）。
【０１２９】
次に、図２０のフロー・チャートに基づいて、ＬＡＦセンサ５４の検出出力をサンプリングして気筒毎の空燃比の推定値＃ｎＡ／Ｆを求めるまでの動作を説明する。尚、この処理は、実際には、図５に示すルーチン中のステップＳ４００の中で予め実行されることにより、ステップ７００及びステップＳ８００の処理で検出空燃比KACT及び推定値＃ｎＡ／Ｆを用いることができるようになっている。
【０１３０】
図２０において、Ｓ４０２では、機関回転数Ｎｅ、吸気圧力Ｐｂ、バルブタイミングV/T を読み出し、次いでＳ４０４とＳ４０６に進んでＨｉＶ／ＴとＬｏＶ／Ｔ用のタイミングマップを検索し、ステップＳ４０８に進んでＬＡＦセンサ５４の出力をＨｉＶ／ＴとＬｏＶ／Ｔ用にサンプリングすることにより、ＨｉＶ／Ｔ用の検出空燃比KACTとＬｏＶ／Ｔ用の検出空燃比KACT求める。
【０１３１】
図２１はそのタイミングマップの特性を示す説明図であり、図示の如く特性は、機関回転数Ｎｅが低くないしは吸気圧力（負圧）Ｐｂが高いほど早いクランク角度でサンプリングされた値を選択するように設定される。ここで、「早い」とは前のＴＤＣ位置により近い位置でサンプリングされた値（換言すれば古い値）を意味する。逆に、機関回転数Ｎｅが高くないしは吸気圧力Ｐｂが低いほど遅いクランク角度、即ち、後のＴＤＣ位置に近いクランク角度でサンプリングされた値（換言すれば新しい値）を選択するように設定する。即ち、ＬＡＦセンサ出力は図１１に示したように、実際の空燃比の変局点に可能な限り近い位置でサンプリングするのが最良であるが、その変局点、例えば最初のピーク値は、センサの反応時間を一定と仮定すれば、図２２に示すように、機関回転数Ｎｅが低くなるほど早いクランク角度で生じる。また、負荷が高いほど排気ガス圧力や排気ガスボリュームが増加し、従って排気ガスの流速が増してＬＡＦセンサ５４への到達時間が早まるものと予想される。その意味から、サンプルタイミングを図２１に示すように設定した。
【０１３２】
更に、バルブタイミングに関しては、機関回転数の任意の値Ｎe1をＬｏ側についてＮe1-Lo 、Ｈｉ側についてＮe1-Hi とし、吸気圧力についてもその任意の値をＬｏ側についてＰb1-Lo 、Ｈｉ側についてＰb1-Hi とすると、マップ特性は、
Ｐb1-Lo ＞Ｐb1-Hi
Ｎe1-Lo ＞Ｎe1-Hi
とする。即ち、ＨｉＶ／Ｔにあっては排気弁の開き時点がＬｏＶ／Ｔのそれより早いため、機関回転数ないし吸気圧力の値が同一であれば、早期のサンプリング値を選択するように、マップ特性が設定される。
【０１３３】
以上のステップＳ４０２〜Ｓ４０８の処理が、サンプリング動作ブロックsel-Ｖに相当する。従って、図２３下部に示すように、ＣＰＵコア６４はセンサ出力の最大値と最小値を正確に認識することができる。そして、この構成によりオブザーバを用いて各気筒の空燃比を推定するときも、実際の空燃比の挙動に近似する値を使用することができてオブザーバの推定精度が向上し、次ぎの図２４乃至図２６に関して述べる気筒別の空燃比フィードバック制御を行うときの精度も向上する。
【０１３４】
次に、図５中のステップＳ８００における気筒別フィードバック制御を図２４ないし図２５のフローチャートに基づいて説明する。尚、本実施例の内燃機関１０にはバルブタイミング機構３００が設けられているので、図２４の処理において、バルブタイミングＨｉＶ／ＴとＬｏＶ／Ｔに応じて気筒別の空燃比＃ｎＡ／Ｆを推定した後、図２５に示す気筒別空燃比補正係数＃ｎKLAFを求めるようになっている。
【０１３５】
図２４において、ステップＳ８０２では、図２０中のステップＳ４０８において求められたＨｉＶ／Ｔ用の検出空燃比（排気系集合部の空燃比）KACTをオブザーバ行列の演算に適用することにより、ＨｉＶ／Ｔ用の気筒別空燃比＃ｎＡ／Ｆを求め、続いてステップＳ８０４に進んで、ＬｏＶ／Ｔ用の検出空燃比（排気系集合部の空燃比）KACTをオブザーバ行列の演算に適用することにより、ＬｏＶ／Ｔ用の気筒別空燃比＃ｎＡ／Ｆ（＃ｎKACT）を求める。続いてＳ８０６に進んで現在のバルブタイミングV/T を判断し、判断結果に応じてステップＳ８０８または８１０に進んで、ＨｉＶ／Ｔ用またはＬｏＶ／Ｔ用のいずれかの気筒別空燃比＃Ａ／Ｆを選択する。このように、ステップＳ８０２〜Ｓ８１０においては、バルブタイミングV/T に応じた気筒別空燃比＃ｎＡ／Ｆを求めるために、オブザーバによる気筒別空燃比推定処理が行われる。
【０１３６】
次ぎに、図２５に示すフローチャートに従って、本発明の課題である制御の安定性等を確保するための判断処理を行うと共に、ＰＩＤ制御則による気筒別空燃比補正係数＃ｎKLAFを求め、最後にかかる補正係数＃ｎKLAFを燃料噴射量Ｔcyl ’に乗算することによって、気筒別のインジェクタ開弁時間を決定するための出力燃料噴射量＃ｎＴout を決定する。
【０１３７】
先ず、図２５のステップＳ８１２では、気筒別空燃比＃ｊＡ／Ｆ（ここで、＃ｊは各気筒を示しｊ＝１〜ｎ）について、夫々の値が所定の基準最低値KACT_LMTLと基準最高値KACT_LMTHとの範囲内に存在するか否かを判断する。より具体的には、ｎ＝４気筒内燃機関の場合には、
第１の気筒について； KACT_LMTL＜＃１Ａ／Ｆ≦KACT_LMTH
第２の気筒について； KACT_LMTL＜＃２Ａ／Ｆ≦KACT_LMTH
第３の気筒について； KACT_LMTL＜＃３Ａ／Ｆ≦KACT_LMTH
第４の気筒について； KACT_LMTL＜＃４Ａ／Ｆ≦KACT_LMTH
の条件を満足しているか否かの判断を行う。即ち、過渡運転時の目標空燃比の変化に対応して推定空燃比が急変した場合に、該所定範囲も目標空燃比の変化に対応して変化するので、推定空燃比が所定範囲外となり空燃比制御を停止する期間が長くなる。そこで、気筒別空燃比が異常にバラツク場合に該当する気筒を判定するために所定範囲を目標空燃比に基づいて設定している。
【０１３８】
ステップＳ８１２において、ひとつでも上記条件を満足しない気筒別空燃比が検出されると、ステップＳ８１４へ処理が移行し、全気筒についての気筒別空燃比＃１〜ｎＡ／Ｆが上記条件を満足する場合には、ステップＳ８１６の処理へ移行する。
【０１３９】
ステップＳ８１４では、所定のタイマー回路（図示せず）に所定時間τをプリセット（計数値ｔ_ACTST をτにプリセット）して、時間計測を開始させた後、ステップＳ８２０の処理へ移行する。このタイマー設定は、フィードバック制御再開時の安定性を考慮して、時間調整を行うためにある。
【０１４０】
ステップＳ８１６では、上記タイマー回路がプリセットされた時間τの計測を完了したか否か判断する。即ち、ｔ_ACTST ＝０となったか否か判断する。
【０１４１】
そして、肯定される場合は、ステップＳ８１８へ移行して、各気筒について割り振られている判断フラグ＃１FOBFB 〜＃ｎFOBFB の全てを“１”に設定した後、ステップＳ８２２へ移行する。一方、ステップＳ８１６において否定される場合には、ステップＳ８２０に移行し、判断フラグ＃１FOBFB 〜＃ｎFOBFB の内、上記条件を満足しない気筒についての判断フラグ＃ｊFOBFB を“０”にセットする。即ち、判断フラグ＃１FOBFB 〜＃ｎFOBFB は、上記条件を満足する気筒別空燃比と満足しない気筒別空燃比に関係する気筒を識別するためにある。
【０１４２】
次に、ステップＳ８２２においては、各判断フラグが“１”の場合と“０”の場合とで以降の処理内容を相違させるための判断を行い、判断フラグが“１”に該当する気筒についての処理は（Ａ）へ、判断フラグが“０”に該当する気筒についての処理は（Ｂ）へ移行させる。
【０１４３】
（Ｂ）に続く処理においては、ステップＳ８２４で、判断フラグが“０”に該当する気筒＃ｊの補正係数＃ｊKLAFを強制的に１．０の値にする。換言すれば、判断フラグが“１”に該当する残余の気筒の補正係数については、後述する更なる条件を満足すると、通常のＰＩＤ制御則により求められる。
【０１４４】
（Ａ）に続く処理においては、ステップＳ８２６〜Ｓ８３２において、運転状態を表す機関回転数Ｎｅと吸気圧力Ｐｂが所定の気筒別フィードバック領域内に在るか否かの判断を行う。ここで、気筒別フィードバック領域とは、図２６のグルフ中の斜線領域にて示すように、気筒別フィードバック制御を実行することができる条件を設定するものであり、この領域を外れる場合は、気筒別フィードバック制御を停止する。即ち、機関回転数Ｎｅが、上限値Ｎ_OBSVH と下限値０との間に在り、且つ吸気圧力Ｐｂが、機関回転数に応じて設定されている所定下限値Ｐ_OBSVL と上限値Ｐ_OBSVH との間に在る場合には、気筒別フィードバック制御を実行することができる。尚、同図中のΔＮ_OBSVの領域とΔＰ_OBSVは、気筒別フィードバック制御を停止から実行又は実行から停止へ変更する際に、制御の安定性を確保するために設けられたヒステリシスである。また、この気筒別フィードバック領域のデータはマップ検索することができるように予めＲＯＭ７６に格納されている。
【０１４５】
かかる条件判断を行うために、ステップＳ８２６とＳ８２８において、機関回転数Ｎｅが上限値Ｎ_OBSVH より低く且つ吸気圧力Ｐｂが上限値Ｐ_OBSVH より低いか否か判断する。両方の条件を満足する場合に限りステップＳ８３０へ移行し、１つでも条件を満足しない場合には、ステップＳ８３６へ移行して全ての気筒別空燃比補正係数＃１KLAF〜＃ｎKLAFの値を１．０に設定する。
【０１４６】
ステップＳ８３０においては、機関回転数Ｎｅに対応する吸気圧力の下限値Ｐ_OBSVL をマップ検索し、続いてステップＳ８３２において、吸気圧力Ｐｂがその下限値Ｐ_OBSVL より大きいか否か判断する。ここで否定される場合はステップＳ８３６へ移行して全ての気筒別空燃比補正係数＃１KLAF〜＃ｎKLAFの値を１．０に設定する。一方、ステップＳ８３２において肯定される場合はステップＳ８３４へ処理が移行する。
【０１４７】
ステップＳ８３４では、判断フラグ＃１FOBFB 〜＃ｎFOBFB の内の設定値が “１”となっている気筒についての気筒別空燃比補正係数をＰＩＤ制御則により求める。
【０１４８】
尚、上記のステップＳ８２４とＳ８３６において、強制的に気筒別空燃比補正係数を１に設定した場合であっても、オブザーバによる気筒別空燃比＃ｎＡ／Ｆの推定処理は継続して行うようになっている。即ち、気筒別空燃比＃ｎＡ／Ｆを推定するためには過去の履歴情報が必要であるからであり、もし仮に、強制的に気筒別空燃比補正係数を１に設定した場合にこの推定処理をも停止させることとすれば、空燃比が正常状態に復帰等した場合に、迅速的確に次の気筒別空燃比＃ｎＡ／Ｆを推定することができなくなる恐れがあるからである。逆言すれば、気筒別空燃比＃ｎＡ／Ｆの推定処理を継続することによって、空燃比が正常状態に復帰等した場合に、次の気筒別空燃比＃ｎＡ／Ｆを迅速的確に推定することができる。
【０１４９】
そして、ステップＳ８２４、Ｓ８３４、Ｓ８３６の処理が完了すると、図５に示したメインルーチン中のステップＳ９００の処理が成されて、各気筒の出力燃料噴射量＃ｎＴout が決定される。
【０１５０】
このように、この実施例によれば、第３のフィードバック系による気筒別フィードバック制御を行うことにより、各気筒相互間での空燃比のバラツキを補正し、触媒装置による排気ガスの清浄効率を向上させることができる。
【０１５１】
更に、気筒別フィードバック制御を行うべきでない状況を運転状態を表すパラメータＮｅとＰｂに基づいて判断し、この状況においては、全ての気筒別空燃比補正係数＃ｎKLAFを強制的に１．０にすることによって、実質的に気筒別フィードバック制御を停止するので、全体のフィードバック制御に悪影響を与えるのを防止し、正常に戻った場合には、再び気筒別フィードバック制御を開始して、オブザーバＯＢＳＶを活かした気筒別空燃比制御を行うことができる。
【０１５２】
更に、気筒別フィードバック制御を行うことができる状況下であっても、気筒別空燃比＃ｎＡ／Ｆのいずれかが所定値の範囲から外れる場合には、それに該当する気筒についての気筒別空燃比補正係数についてのみ強制的に１．０に設定し、残余の気筒別空燃比補正係数については通常のＰＩＤ制御則により継続して演算するので、全体のフィードバック制御に悪影響を与えるのを防止し、正常に戻った場合には、再び全ての気筒別フィードバック制御を開始して、オブザーバＯＢＳＶを活かした気筒別空燃比制御を行うことができる。
【０１５３】
尚、この実施例の以上の説明では、図２５中のステップＳ８２４及びＳ８３６において、制御の不安定性等を回避するために、該当する気筒別空燃比補正係数を強制的に１．０に設定することによって、該当する気筒への出力燃料噴射量Ｔout を実質的に補正しないようにしているが、この１．０の値に限定しなくともよい。例えば、前回以前に推定された正常時での気筒別空燃比＃ｎＡ／Ｆの値を、該当する気筒別空燃比補正係数に使用してもよい。このようにすると、空燃比のバラツキをより迅速に収束させることが期待できる。
【０１５４】
（第２実施例）
次に、第２の実施例を図２７のフローチャートと共に説明する。尚、この実施例は、前記第３のフィードバック系による気筒別フィードバック制御に関するものであり、第１の実施例に示したフィードフォワード系及び第１，第２のフィードバック系の構成は同一又は同等であるので、第１の実施例との相違点について対比しつつ説明することとする。また、この実施例の特徴を示す図２７中で、第１の実施例における処理内容と同一または相当する部分については、同一符号にて示すものとする。
【０１５５】
第１の実施例で説明した図２５中のステップＳ８２４〜Ｓ８３６の処理では、気筒別フィードバック制御に支障をきたす場合に当該する気筒別空燃比補正係数を選んで強制的に１．０等の定数値に固定しているが、この実施例では、気筒別空燃比＃ｎＡ／Ｆの１つでも、制御に支障をきたす値となった場合には、全ての気筒別空燃比補正係数＃ｎKLAFを強制的に１．０に設定することによって、空燃比が正常に戻るまでの期間中は実質的に気筒別フィードバック制御を停止したり、又は、前回推定時に得られた正常時での気筒別空燃比補正係数＃ｎKLAFを用いて出力燃料噴射量＃Ｔout の補正処理を継続することで、全体のフィードバック制御に悪影響を与えるのを防止し、正常に戻った場合には、再び全ての気筒別フィードバック制御を開始して、オブザーバＯＢＳＶを活かした気筒別空燃比制御を行うことができるようにしたものである。
【０１５６】
即ち、図２５中のステップＳ８２２の振分け処理が終了すると、図２７中の処理（Ａ）と処理（Ｂ）のいずれかへ継続される。処理（Ｂ）に継続する場合は、少なくとも１つの気筒別空燃比（例えば＃１Ａ／Ｆ等）が所定値を越えた場合であり、ステップＳ１０００において、全ての気筒別空燃比補正係数＃１KLAF〜＃ｎKLAFを１．０に設定する。尚、ここで、前回推定時に得られた正常時での気筒別空燃比補正係数＃ｎKLAFに設定してもよい。
【０１５７】
処理（Ａ）に継続する場合は、推定された気筒別空燃比＃ｎＡ／Ｆが正常な場合である。したがって、ステップＳ８２６〜Ｓ８３２の処理により、運転状態が気筒別フィードバック補正領域（図２６参照）に適合するか否か判断される。そして、完全に上記条件を満足（肯定）する場合には、ステップＳ８３４へ移行して、ＰＩＤ制御則による気筒別空燃比補正係数＃ｎKLAFが演算され、それに続いてステップＳ９００で各気筒の出力燃料噴射量＃ｎＴout の補正が成される。一方、ステップＳ８２６〜Ｓ８３２の処理において否定された場合には、ステップＳ１０００へ移行し、全ての気筒別空燃比補正係数＃１KLAF〜＃ｎKLAFを１．０、又は上記した正常時での気筒別空燃比補正係数＃ｎKLAFに設定する。
【０１５８】
（第３実施例）
次に、第３の実施例を図２８のフローチャートと共に説明する。尚、この実施例は、第１実施例で説明した、第３のフィードバック系による気筒別空燃比制御に関するものであり、第１の実施例に示したフィードフォワード系及び第１，第２のフィードバック系の構成は同一又は同等であるので、第１の実施例との相違点について対比しつつ説明することとする。また、この実施例の特徴を示す図２８中で、第１の実施例における処理内容と同一または相当する部分については、同一符号にて示すものとする。
【０１５９】
第１の実施例で説明した図２５中のステップＳ８１２〜Ｓ８２２の処理では、気筒別フィードバック制御に支障をきたす場合に当該する気筒別空燃比＃ｎＡ／Ｆを判定し、その判定結果に基づいて、該当する気筒別空燃比補正係数の値を１．０等の定数値に決定しているが、この第３の実施例は、更に、検出空燃比KACTの時間変化と目標空燃比補正係数KLAFの時間変化が共に大きく変化する場合にも、気筒別フィードバック制御を実質的に停止するようにしたものである。
【０１６０】
即ち、図２７において、気筒別空燃比＃ｎＡ／Ｆが求められた後に、ステップＳ２０００において、最新の検出空燃比KACT(k) とその前に求められた検出空燃比KACT(k-1) との差の絶対値ΔKACT＝｜KACT(k) −KACT(k-1) ｜が、予め決められた上限値ΔKACT_LMTHより小さいか否か判断し、肯定されるときはステップＳ２００２へ処理が移行し、否定されるときはステップＳ８１４へ処理が移行する。
【０１６１】
ステップＳ２００２では、最新の目標空燃比補正係数KLAF(k) とその前に求められた目標空燃比補正係数KLAF(k-1) との差の絶対値ΔKLAF＝｜KLAF(k) −KLAF(k-1) ｜が、予め決められた上限値ΔKLAF_LMTHより小さいか否か判断し、肯定されるときはステップＳ８１２へ処理が移行し、否定されるときはステップＳ８１４へ処理が移行する。
【０１６２】
したがって、検出空燃比KACTの変動と目標空燃比補正係数KLAFの変動の両者共に大きくない場合に限り、ステップＳ８１２へ移行する。一方、少なくとも検出空燃比KACTの変動と目標空燃比補正係数KLAFの変動の一方が大きいときはステップＳ８１４へ移行する。
【０１６３】
次に、第１の実施例で説明した如く、ステップＳ８１２〜Ｓ８２２の処理を行うことにより、気筒別空燃比が所定値範囲外にある場合に該当する処理については処理（Ｂ）へ、気筒別空燃比が所定値範囲内にある場合に該当する処理については処理（Ａ）へ、移行する。続いて、図２５中に示すステップＳ８２６〜Ｓ８３６の処理により、気筒別空燃比補正係数＃１KLAF〜＃ｎKLAFが決定さた後、気筒毎の出力燃料噴射量＃ｎＴout が演算される。
【０１６４】
この実施例によれば、制御の安定性の有無を検出空燃比KACTと目標空燃比補正係数KLAFの各変化量から判断することとなるので、すくなくとも１つの気筒の異常に起因する気筒別空燃比制御の安定性の低下を防止することができる。
【０１６５】
尚、この実施例では、検出空燃比KACTと目標空燃比補正係数KLAFの両者の変化分から制御の安定性等を判断することとしているが、いずれか一方の変化分に基づいてかかる判断制御を行うようにしても良い。
【０１６６】
更にまた、上記説明では、図２８に示す処理の後に、図２５に示す第１の実施例の処理（Ａ）と（Ｂ）に継続する場合を述べたが、図２７に示す第２の実施例の処理（Ａ）と（Ｂ）に継続しても良い。
【０１６７】
【発明の効果】
請求項１と請求項２にあっては、オブザーバにより推定される気筒毎の推定空燃比が所定範囲外となった該当気筒に対する気筒別フィードバック制御を停止するので、他の気筒に対するフィードバック制御への影響を低減することができる。更に、オブザーバによる気筒毎の空燃比の推定を継続するので、気筒フィードバック制御を再開する時、オブザーバを用いて過去の気筒毎の空燃比推定値の履歴情報に基づいて直ちに再開直後の気筒別空燃比補正係数を求めることができ、該気筒別空燃比補正係数に基づきフィードバック制御再開直後における応答性の優れた気筒別フィードバック制御を可能にする。
【０１６８】
請求項３にあっては、気筒別空燃比が異常にバラツク場合に該当する気筒を判定するための所定範囲を目標空燃比に基づいて設定したことにより、過渡運転時の目標空燃比の変化に対応して推定空燃比が急変した場合に、該所定範囲も目標空燃比の変化に対応して変化するので、推定空燃比が所定範囲外となり空燃比制御を停止する期間が長くなることを防止することができる。
【０１６９】
請求項４にあっては、少なくとも１つの気筒の異常を検出空燃比（混合気の空燃比）の変化量から判断して、気筒別フィードバック制御を実質的に停止するので、他の気筒に対するフィードバック制御への影響を低減することができる。更に、オブザーバによる気筒毎の空燃比の推定を継続するので、気筒フィードバック制御を再開する時、オブザーバを用いて過去の気筒毎の空燃比推定値の履歴情報に基づいて直ちに再開直後の気筒別空燃比補正係数を求めることができ、該気筒別空燃比補正係数に基づきフィードバック制御再開直後における応答性の優れた気筒別フィードバック制御を可能にする。
【０１７０】
請求項５にあっては、少なくとも１つの気筒の異常を目標空燃比補正係数の変化量から判断して、気筒別フィードバック制御を実質的に停止するので、他の気筒に対するフィードバック制御への影響を低減することができる。更に、オブザーバによる気筒毎の空燃比の推定を継続するので、気筒フィードバック制御を再開する時、オブザーバを用いて過去の気筒毎の空燃比推定値の履歴情報に基づいて直ちに再開直後の気筒別空燃比補正係数を求めることができ、該気筒別空燃比補正係数に基づきフィードバック制御再開直後における応答性の優れた気筒別フィードバック制御を可能にする。
【図面の簡単な説明】
【図１】実施例に係わる内燃機関の燃料噴射装置の全体構成を示す概略構成図である。
【図２】図１中の制御ユニットの構成を示すブロック図である。
【図３】図１中のＯ₂ センサ出力特性を示す説明図である。
【図４】実施例に係わる内燃機関の燃料噴射装置の機能を示すブロック図である。
【図５】燃料噴射装置の動作を説明するためのフローチャートである。
【図６】フィードフォワード系の動作を説明するためのフローチャートである。
【図７】フィードフォワード系の機能を説明するためのブロック図である。
【図８】第１のフィードバック系の動作を説明するためのフローチャートである。
【図９】第２のフィードバック系の機能を説明するためのブロック図である。
【図１０】多気筒内燃機関のＴＤＣと排気系集合部の空燃比との関係を示す説明図である。
【図１１】実際の空燃比に対するサンプルタイミングの良否を示す説明図である。
【図１２】ＬＡＦセンサの検出動作をモデル化して示すブロック図である。
【図１３】図１２のモデルのＺ変換表示モデルを示すブロック図である。
【図１４】空燃比センサの検出挙動をモデル化した空燃比推定器を示すブロック線図である。
【図１５】内燃機関の排気系の挙動をモデル化したブロック線図である。
【図１６】一般的なオブザーバを示すブロック線図である。
【図１７】実施例に係わるオブザーバの構成を示すブロック線図である。
【図１８】空燃比推定器とオブザーバとを組合わせた構成を示すブロック線図である。
【図１９】第３のフィードバック系の機能を示すブロック線図である。
【図２０】サンプリング動作ブロック（sel-Ｖ）における検出空燃比のサンプリング動作を示すフローチャートである。
【図２１】サンプリング動作ブロック（sel-Ｖ）のサンプリング動作で使用するタイミングマップの特性を示す説明図である。
【図２２】機関回転数と機関負荷に対するＬＡＦセンサ出力特性を示す説明図である。
【図２３】サンプリング動作ブロック（sel-Ｖ）のサンプル動作を説明するタイミングチャートである。
【図２４】オブザーバの動作に関し、気筒別空燃比を機関タイミングに対応して発生する動作を示すフローチャートである。
【図２５】第３のフィードバック系（気筒別フィードバック制御系）において気筒別空燃比補正係数を求めるための判断動作を説明するフローチャートである。
【図２６】図２５の判断動作に使用される気筒別フィードバック領域を示す説明図である。
【図２７】第２の実施例に関し、第３のフィードバック系（気筒別フィードバック制御系）において気筒別空燃比補正係数を求めるための判断動作を説明するフローチャートである。
【図２８】第３の実施例に関し、第３のフィードバック系（気筒別フィードバック制御系）において気筒別空燃比補正係数を求めるための判断動作を説明するフローチャートである。
【符号の説明】
１０…内燃機関、１２…吸気管、１４…エアクリーナ、１６…スロットル弁、
１８…サージタンク、２０…吸気マニホールド、２２…インジェクタ、２４…排気マニホールド、２６…排気管、２８，３０…触媒装置、３２…電磁弁、３４…バイパス路、３６…エンジン制御ユニット、３８…燃料タンク、４０…クランク角検出センサ、４２…スロットル開度検出センサ、４４…絶対圧センサ、４６…吸気温度センサ、４８…大気圧センサ、５０…水温センサ、５２…タイミング検出センサ、５４…空燃比検出センサ（ＬＡＦセンサ）、５６…Ｏ₂ センサ、
５８，６０…ローパスフィルタ、６２…マイクロプロセッサ、６４…ＣＰＵコア、６６…検出回路、６８…マルチプレクサ、７０…検出回路、７２…Ａ／Ｄ変換器、７４…ＲＡＭ、７６…ＲＯＭ、７８…波形整形回路、８０…カウンタ、８２〜８８…駆動回路、１００…ＥＧＲ機構、１０２…電磁弁、２００…キャニスタパージ機構、２０２…電磁弁、３００…バルブタイミング機構。[0001]
[Industrial application fields]
The present invention relates to a fuel injection control device for an internal combustion engine, and in particular, matches a detected air-fuel ratio with a target air-fuel ratio based on a detection output of a wide-range air-fuel ratio sensor installed upstream of a catalyst provided in an exhaust system. The present invention relates to a fuel injection control device that adaptively controls the fuel injection amount.
[0002]
[Prior art]
Conventionally, in a fuel injection control device for an internal combustion engine, focusing on the fact that the exhaust gas purification rate by the catalyst device provided in the exhaust system is maximized at the theoretical air-fuel ratio, an air-fuel ratio sensor (oxygen concentration) provided in the exhaust system is used. The air-fuel ratio is detected by a sensor), and the fuel injection amount is feedback-controlled so that the detected value becomes the stoichiometric air-fuel ratio (Japanese Patent Laid-Open No. 59-101562).
[0003]
Further, even if only one air-fuel ratio sensor is provided in the exhaust system collection portion of a multi-cylinder internal combustion engine and the air-fuel ratio is detected, the air-fuel ratio for each cylinder cannot be accurately detected. Since only the mixed value of the fuel ratio is detected, there is a problem that if the air-fuel ratio is feedback-controlled based on this detected value, the emission is deteriorated. In order to solve this problem, a theoretical model of the exhaust system is constructed, and the air-fuel ratio for each cylinder is estimated by applying the detection value of one air-fuel ratio sensor to this theoretical model. There is a technique for performing feedback control on a cylinder-by-cylinder basis by setting the air-fuel ratio of each cylinder to a target value based on the value (Japanese Patent Laid-Open No. 5-180040). According to this technology, it is possible not only to set an accurate air-fuel ratio for each cylinder but also to realize a simple structure because it is not necessary to provide a plurality of air-fuel ratio sensors independently for each cylinder. it can. Further, if a plurality of air-fuel ratio sensors are provided, it is necessary to consider the characteristic variation due to secular change or the like. However, as a result of applying one air-fuel ratio sensor, it is necessary to consider such a characteristic variation. Has no effect.
[0004]
[Problems to be solved by the invention]
However, in the latter technique, when the estimated value of the cylinder-by-cylinder air-fuel ratio falls outside the predetermined upper and lower limit range, the cylinder-by-cylinder feedback control is performed using the upper and lower limit values as the estimated value. There is a problem that the air-fuel ratio responsiveness deteriorates due to the divergence of the fuel ratio.
[0005]
For example, when the estimated value of the cylinder-by-cylinder air-fuel ratio for one or more specific cylinders of a multi-cylinder internal combustion engine falls outside the upper and lower limit range, the estimated value is held at the upper and lower limit values at that time, Since the feedback control is continued, feedback is performed with a control air-fuel ratio different from the control target value, resulting in deterioration of air-fuel ratio responsiveness and emission.
[0006]
The present invention has been made in view of such a problem of the prior art, and is an internal combustion engine capable of performing cylinder-by-cylinder feedback control so that the cylinder-by-cylinder air-fuel ratio does not deviate outside a predetermined feedback range according to the operating state. An object of the present invention is to provide a fuel injection amount control device.
[0007]
[Means for Solving the Problems]
  In order to achieve such an object, according to claim 1, the air-fuel ratio of the air-fuel mixture disposed in the exhaust system collection portion of the multi-cylinder internal combustion engine and discharged from each cylinder of the multi-cylinder internal combustion engine is detected. Based on a model that defines the air-fuel ratio behavior in the exhaust system of the multi-cylinder internal combustion engine and setting an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system,Based on past history information of estimated air-fuel ratio for each cylinderAir-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder, and supply to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine comprising an air-fuel ratio correction coefficient calculating means for calculating a cylinder-by-cylinder air-fuel ratio correction coefficient for correcting a cylinder-by-cylinder fuel injection amount, when the estimated air-fuel ratio becomes a value outside a predetermined range An air-fuel ratio control stop means for stopping the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient for the cylinder, and an air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped. It was set as the structure which comprises.
[0008]
  According to claim 2, an air-fuel ratio detecting means that is disposed in an exhaust system collecting portion of a multi-cylinder internal combustion engine and detects an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and the multi-cylinder Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the internal combustion engine, setting the observer that inputs the air-fuel ratio and observes the internal state of the exhaust system,Based on past history information of estimated air-fuel ratio for each cylinderAir-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder, and supply to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine comprising an air-fuel ratio correction coefficient calculating means for calculating a cylinder-by-cylinder air-fuel ratio correction coefficient for correcting a cylinder-by-cylinder fuel injection amount, when the estimated air-fuel ratio becomes a value outside a predetermined range Air-fuel ratio control stop means for stopping calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient for all cylinders; air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped; It was set as the structure which comprises.
[0009]
According to a third aspect of the present invention, there is provided a predetermined range setting means for setting the predetermined range of the first or second aspect based on a target air-fuel ratio supplied to the multi-cylinder internal combustion engine.
[0010]
  According to a fourth aspect of the present invention, an air-fuel ratio detecting means that is disposed in an exhaust system collecting portion of a multi-cylinder internal combustion engine and detects an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and the multi-cylinder Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the internal combustion engine, setting the observer that inputs the air-fuel ratio and observes the internal state of the exhaust system,Based on past history information of estimated air-fuel ratio for each cylinderAir-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder, and supply to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine comprising an air-fuel ratio correction coefficient calculating means for calculating a cylinder-by-cylinder air-fuel ratio correction coefficient for correcting a cylinder-by-cylinder fuel injection amount, the amount of change in the air-fuel ratio detection value of the collective portion is large An air-fuel ratio control stop means for stopping the calculation of the air-fuel ratio correction coefficient, and an air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped. did.
[0011]
  According to a fifth aspect of the present invention, an air-fuel ratio detecting means that is disposed in an exhaust system collecting portion of a multi-cylinder internal combustion engine and detects an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and the multi-cylinder Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the internal combustion engine, setting the observer that inputs the air-fuel ratio and observes the internal state of the exhaust system,Based on past history information of estimated air-fuel ratio for each cylinderAir-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder; first air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for correcting the fuel injection amount so that the air-fuel ratio matches the target air-fuel ratio; A cylinder-by-cylinder air-fuel ratio correction coefficient that corrects the cylinder-by-cylinder fuel injection amount supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder. In a fuel injection amount control apparatus for an internal combustion engine comprising second air-fuel ratio correction coefficient calculation means for calculating the first air-fuel ratio correction coefficient, when the amount of change in the first air-fuel ratio correction coefficient is large, And an air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped.
[0012]
[Action]
In the fuel injection amount control apparatus for an internal combustion engine according to claim 1, the air-fuel ratio of each cylinder is estimated by applying the detected air-fuel ratio of the air-fuel mixture to the observer, and based on the estimated air-fuel ratio of each cylinder. Thus, the cylinder specific air-fuel ratio correction coefficient is obtained to correct the cylinder specific fuel injection amount. When the estimated air-fuel ratio of each cylinder estimated by the observer is outside the predetermined range and the control stability is reduced, the correction of the fuel injection amount for each cylinder for the cylinder outside the range is corrected. Although the control is substantially stopped, the cylinder-by-cylinder air-fuel ratio estimation process by the observer continues.
[0013]
In the fuel injection amount control device for an internal combustion engine according to claim 2, when the estimated air-fuel ratio of each cylinder estimated using the observer is outside a predetermined range and the control stability is lowered, However, the cylinder-by-cylinder air-fuel ratio estimation process by the observer continues.
[0014]
The fuel injection amount control device for an internal combustion engine according to claim 3, wherein the target for determining whether or not the estimated air-fuel ratio of each cylinder is within a predetermined range is supplied to the multi-cylinder internal combustion engine. Set based on air-fuel ratio.
[0015]
5. The fuel injection amount control apparatus for an internal combustion engine according to claim 4, wherein the calculation of the air-fuel ratio correction coefficient for each cylinder is stopped when the change amount of the air-fuel ratio detection value of the air-fuel mixture detected by the air-fuel ratio detection means is large. However, the cylinder-by-cylinder air-fuel ratio estimation process by the observer continues.
In the fuel injection amount control apparatus for an internal combustion engine according to claim 5, the first air-fuel ratio correction coefficient calculating means calculates an air-fuel ratio correction coefficient for making the air-fuel ratio coincide with the target air-fuel ratio, The air-fuel ratio correction coefficient calculating means calculates an air-fuel ratio correction coefficient for correcting variation in the air-fuel ratio of each cylinder. When the change amount of the air-fuel ratio correction coefficient calculated by the first air-fuel ratio correction coefficient calculation means becomes large, the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient by the second air-fuel ratio correction coefficient calculation means is stopped. The cylinder-by-cylinder air-fuel ratio estimation process by the observer continues.
[0016]
【Example】
(First embodiment)
A fuel injection control device for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings. A typical example will be described which is applied to a four-cylinder internal combustion engine.
[0017]
FIG. 1 is a schematic diagram showing the overall configuration of this fuel injection control device. In the figure, intake air introduced from an air cleaner 14 provided at the tip of an intake pipe 12 passes through a surge tank 18 and an intake manifold 20 while being adjusted in flow rate by a throttle valve 16, and further, an intake valve (not shown) for each cylinder. ) Through each cylinder of the four-cylinder internal combustion engine 10.
[0018]
An injector 22 for fuel injection is provided in the vicinity of the intake valve of each cylinder, and an air-fuel mixture of intake air and injected fuel is ignited by an ignition plug (not shown) provided for each cylinder and burned. Then, each piston (not shown) is driven.
[0019]
Exhaust gas after combustion is discharged to an exhaust manifold 24 through an exhaust valve (not shown) of each cylinder, and further through an exhaust pipe 26 connected to a collecting portion of the exhaust manifold 24, the first three-way catalyst device. 28 and the second three-way catalyst device 30 are cleaned and discharged outside the engine.
[0020]
The throttle valve 16 is driven and controlled by a pulse motor M that rotates in accordance with the operating condition such as the amount of depression of the accelerator pedal. Secondary air is provided near the throttle valve 16 of the intake pipe 12 in accordance with the opening / closing amount of the electromagnetic valve 32. A bypass path 34 for controlling the amount is also provided. The throttle valve 16 may be mechanically interlocked with the accelerator pedal, as in a generally known mechanism.
[0021]
Further, the internal combustion engine 10 is generated in an exhaust gas recirculation mechanism (EGR mechanism) 100 that recirculates part of the exhaust gas to the intake system by controlling the opening / closing amount of a solenoid valve (not shown), and the fuel tank 38. A canister purge mechanism 200 is provided for supplying evaporated fuel (purge gas) to the intake system in accordance with the opening / closing amount of a solenoid valve (not shown).
[0022]
Further, the internal combustion engine 10 is provided with a so-called variable valve timing mechanism 300 disclosed in Japanese Patent Laid-Open No. 2-275043 and the like, and indicates an operating state such as the engine speed Ne and the intake pressure Pb in the intake system. Depending on the parameter, the valve timing V / T of the internal combustion engine 10 is variably controlled between two types of timing characteristics LoV / T and HiV / T.
[0023]
Further, a crank angle detection sensor 40 for detecting a crank angle position of a piston (not shown) is provided in a distributor (not shown) of the internal combustion engine 10, and the throttle opening θ is provided in the vicinity of the throttle valve 16._THA throttle opening detection sensor 42 for detecting the intake pressure is provided. The intake pipe 12 has an absolute pressure sensor 44 for detecting an intake pressure (absolute pressure) Pb downstream of the throttle valve 16 and an intake air temperature upstream of the throttle valve 16. An intake air temperature sensor 46 for detection is provided. At an appropriate position of the internal combustion engine 10, an atmospheric pressure sensor 48 for detecting the atmospheric pressure Pa and a water temperature sensor 50 for detecting the temperature Tw of the engine cooling water are provided. Although not shown in FIG. 1, the variable valve timing mechanism 300 is provided with a detection sensor 52 that detects a selected valve timing characteristic. The detection signals from these sensors 40 to 52 are supplied to the control unit 36 one by one.
[0024]
In the exhaust pipe 26, a wide area air-fuel ratio sensor 54 as a first air-fuel ratio detection means is attached to a portion upstream of the three-way catalyst device 28, and a second air-fuel ratio sensor 54 is provided between the three-way catalyst devices 28 and 30. O as air-fuel ratio detection means₂A sensor 56 is attached.
[0025]
As the wide area air-fuel ratio sensor 54, the LAF sensor disclosed in Japanese Patent Application Laid-Open No. 2-11842 previously applied by the applicant of the present patent application is applied. The LAF sensor 54 is an exhaust gas in a wide range from lean to rich. It has a wide-range characteristic that can detect the oxygen concentration in it linearly. And this LAF sensor 54 and O₂Each detection signal of the sensor 56 is supplied to the control unit 36 via low-pass filters 58 and 60 set to a predetermined cutoff frequency.
[0026]
Next, the system configuration of the control unit 36 will be described based on the circuit block diagram of FIG. The control unit 36 includes a microprocessor 62 and various input / output ports, and a central control unit (hereinafter referred to as a CPU core) 64 executes various application programs that are firmwareized by a ROM 76 to be described later. Feedforward control and feedback control are performed.
[0027]
The detection signal of the LAF sensor 54 is input to the first detection circuit 66 through the low-pass filter 58, and the detection circuit 66 performs a predetermined linearization process on the detection signal, thereby exhaust gas in a wide range from lean to rich. A linear air-fuel ratio (A / F) proportional to the oxygen concentration inside is obtained and output to the multiplexer 68. O₂A detection signal from the sensor 56 is input to the second detection circuit 70 through the low-pass filter 60, and the detection circuit 70 applies the detection signal value to a characteristic curve as shown in FIG. A signal indicating whether the air-fuel ratio of the supplied air-fuel mixture is rich or lean with respect to the theoretical air-fuel ratio (λ = 1) is generated and output to the multiplexer 68. Detection signals from the sensors 42 to 52 are also supplied to the multiplexer 68. Each signal is time-division-transferred to the A / D converter 72 through a multiplexer 68 that performs channel switching in synchronization with a predetermined switching timing, converted into digital data, and stored in a random access memory (RAM) 74. The data is stored in a predetermined buffer area or used for calculation by the CPU core 64. In this embodiment, the A / D converter 72 A / D converts the detection signal from the second detection circuit 70 every predetermined crank angle (for example, 15 degrees).
[0028]
Further, the detection signal from the crank angle sensor 40 is shaped into a binary logic rectangular signal by the waveform shaping circuit 78 and then counted by the counter 80, and the count value is also stored in a predetermined buffer area of the RAM 74. It is used for the calculation of the CPU core 64.
[0029]
The read-only memory (ROM) 76 stores in advance the above-described various application programs, the above-described timing characteristics LoV / T and HiV / T map data, and various search map data to be described later. The application program is executed while applying various data in the RAM 74 and the ROM 76 to obtain the optimum fuel injection control condition according to the operation state, and the injector 22, the electromagnetic valve 32, the exhaust gas recirculation through the drive circuits 82 to 88. The electromagnetic valve 102 of the mechanism (EGR mechanism) 100 and the electromagnetic valve 202 of the canister purge mechanism 200 are controlled.
[0030]
FIG. 4 is a block diagram showing the function of the fuel injection control apparatus according to this embodiment, which is provided with a feedforward control system for compensating the characteristics of the intake system for the internal combustion engine 10 and three feedback control systems. By executing the various application programs, a control function equivalent to the block diagram is exhibited.
[0031]
That is, as shown in the main flowchart of FIG. 5, in step S400, the engine speed Ne, the intake pressure Pb, the throttle opening θ_THThe latest various sensor outputs such as the cooling water temperature Tw are read into the RAM 74, and the basic fuel injection amount TiM-F is determined by performing calculation processing of the feedforward control system in step S500, and the first feedback is performed in step S600. The target air-fuel ratio KCMD, the target air-fuel ratio correction coefficient KCMDM, etc. are obtained by performing the arithmetic processing of the system, and the correction coefficient KSTR for adaptive feedback control is performed by performing the second feedback system arithmetic processing in step S700. And KLAF, etc. are obtained, and the third feedback system calculation process is performed in step S800 to obtain the cylinder specific air-fuel ratio correction coefficient #nKLAF. And each correction coefficient KSTR or KLAF multiplied by #nKLAF And drives the injector 22 determines the cylinder of the output fuel injection quantity #nTout. The subscript #n indicates each cylinder, and the output fuel injection amount #nTout defines the valve opening time of the injector 22 of each cylinder. Further, the processing of this main flowchart is performed in synchronization with TDC.
[0032]
Next, functions will be described for each block. First, the feedforward control system (shown as “FFC” in FIG. 4) is disclosed in Japanese Patent Application No. Hei 6-1972238 previously proposed by the present applicant. Therefore, a throttle valve in the intake system will be briefly described. A fluid dynamic model (mathematical model) for all effective volumes (a chamber including the corresponding portion of the intake pipe 12 and the surge tank 18) from the downstream of 16 to the intake port of each cylinder is constructed, and the throttle opening θ_THAnd the intake pressure Pb are applied to the hydrodynamic model to determine the optimum basic fuel injection amount TiM-F in all operating states including not only the steady operating state but also the transient operating state.
[0033]
FIG. 6 is a flowchart showing a calculation routine for basic fuel injection amount TiM-F (corresponding to step S500 in FIG. 5), and FIG. 7 is a block diagram for explaining this calculation routine. The function of the forward control system will be described.
[0034]
In step S502, it is determined whether or not the engine is in a starting state. If the determination is affirmative, the basic fuel injection amount TiM-F corresponding to the starting mode is set in step S504. If the determination is negative, the fuel cut state is determined in step S506. It is judged whether it is in. When the result is affirmative, a basic fuel injection amount TiM-F (= 0) for fuel cut is set at step S508, and when the result is negative, a step is performed to set the basic fuel injection amount corresponding to the normal operation state. The process proceeds to S510 and subsequent steps.
[0035]
In step S510, a predetermined map in the ROM 76 is searched using the engine speed Ne and the intake pressure Pb as parameters to obtain the fuel injection amount (reference value) TiM in the steady operation state. That is, the fuel injection amount TiM using the engine speed Ne and the intake pressure Pb as parameters based on the speed density method is obtained in advance, and the fuel injection amount TiM is stored in the ROM 76 as map data.
[0036]
In step S512, the throttle opening θ_THIs applied to the first-order lag transfer function (1-B) / (Z-B)._THFirst-order lag value θ_TH-DIs calculated. That is, in the transient operation state, the throttle opening θ_THThe first-order lag value θ does not directly correspond to the intake air amount of the intake port._TH-DIt is decided to approximate with. Note that B in the transfer function is a coefficient.
[0037]
In step S514, as shown in FIG. 7, the throttle opening θ is retrieved by searching a map stored in the ROM 76 in advance._THThrottle projection area (slottle projection area in the longitudinal direction of the intake pipe) S and throttle opening θ_THAnd the correction coefficient (product of the flow coefficient α and the gas expansion correction coefficient ε) C corresponding to the intake pressure Pb and multiplying the throttle projection area S by the correction coefficient C, the throttle effective opening area in the steady operation state A is calculated.
[0038]
In step S516, the primary delay value θ of the throttle opening is obtained by searching a map stored in advance in the ROM 76, as shown in FIG._TH-DThrottle projection area S corresponding to the first-order lag value θ_TH-DAnd a correction coefficient C corresponding to the intake pressure Pb, and multiplying the throttle projection area S by the correction coefficient C, the throttle effective opening area A in the transient operation state_DELAYIs calculated.
[0039]
In step S518, the opening cross section A of the bypass passage 34 is shown._BYPASSTaking into account
[0040]
[Expression 1]

[0041]
The effective opening area A in the steady operation state and the effective opening area A in the transient operation state_DELAYThe ratio RATIO-A is calculated.
[0042]
In step S520, by multiplying the fuel injection amount TiM by the ratio RATIO-A, the fuel injection amount TiM-F 'adapted to the steady operation state and the transient operation state is obtained. That is, the value of the ratio RATIO-A is 1 in the steady operation state and a certain value excluding 1 in the transient operation state, and thus corresponds to both the steady operation state and the transient operation state. Therefore, by multiplying the fuel injection amount TiM by the ratio RATIO-A, the fuel injection amount TiM-F ′ that is adapted in the steady operation state and the transient operation state can be obtained.
[0043]
In step S522, the correction coefficient KTOTAL is searched by searching a predetermined map in the ROM 76 based on parameters such as the engine speed Ne, the intake pressure Pb, the intake air temperature and the cooling water temperature Tw, the purge gas concentration PUG, the exhaust gas recirculation rate, and the like. Further, by multiplying the fuel injection amount TiM-F ′ by the correction coefficient KTOTAL, the basic fuel injection amount TiM-F that compensates for the effects of the EGR mechanism 100 and the canister purge mechanism 200 is determined.
[0044]
In this way, this feedforward control system is able to control the throttle opening θ even if the cylinder inflow air amount fluctuates as the operating state changes._THThen, an optimum basic fuel injection amount TiM-F corresponding to the cylinder inflow air amount is determined from the intake pressure Pb.
[0045]
Next, the first feedback system will be described. This feedback system includes functional blocks indicated by “KCMD”, “KCMD correction”, and “KCMDM” in FIG. 4, and performs arithmetic processing according to the flowchart shown in FIG. 8 (corresponding to step S600 in FIG. 5).
[0046]
First, in step S602 in FIG. 8, the basic value KBS of the air-fuel ratio is obtained by searching a predetermined map in the ROM 76 using the engine speed Ne and the intake pressure Pb as parameters. That is, the basic value KBS is obtained when the engine speed Ne and the intake pressure Pb are used as parameters.₂This is air-fuel ratio data that can be obtained from the output of the sensor 56 and is stored in the ROM 76 in advance. This map also stores basic values corresponding to the idling operation state. Furthermore, in a so-called lean burn engine for improving the combustion characteristics by increasing the air-fuel ratio supplied to the engine at low load (in terms of equivalent ratio), the basic value for lean burn is also stored. Has been.
[0047]
In step S604, it is determined whether or not lean burn control after engine start is being executed by referring to the value of a built-in timer circuit (not shown). The lean correction coefficient is set to 0.89, for example, and 1.0 otherwise.
[0048]
This determination is performed for the following reason. The internal combustion engine 10 according to the present embodiment is provided with a variable valve timing mechanism 300, and during the cranking period (starting period) after starting, the operation of one of the intake valves of each cylinder is suspended to thereby achieve target emptying. Lean burn control is performed in which the fuel ratio is set slightly leaner than the stoichiometric air-fuel ratio. As a result, an increase in hydrocarbons (HC) can be suppressed even during the start-up period in which the catalyst device is not yet activated. This is because the effect is demonstrated. In a normal internal combustion engine having two intake valves for each cylinder (internal combustion engine not equipped with a variable valve timing mechanism), if the target air-fuel ratio is set to the lean side after engine startup, However, in the internal combustion engine of this embodiment provided with such a variable valve timing mechanism 300, the combustion chamber is deactivated when one of the intake valves is deactivated. In addition, a so-called swirl called a swirl is generated, so that stable combustion can be obtained even if leaning is performed immediately after the engine is started.
[0049]
In step S606, it is determined whether or not the throttle opening is fully open (WOT), and a full opening increase correction value is calculated in accordance with the determination result. In step S608, it is determined whether or not the coolant temperature Tw is high. The increase correction coefficient KTWOT is calculated according to the determination result. The increase correction coefficient KTWOT includes a correction coefficient value for engine protection at high water temperature.
[0050]
In step S610, the basic value KBS is corrected by multiplying the basic coefficient KBS by the correction coefficient KTWOT, and the target air-fuel ratio KCMD is determined by the calculation shown in Equation 2. That is, as shown in FIG.₂Within the range in which the output of the sensor 56 has a linear characteristic (indicated by a broken line on the vertical axis), after setting a window for minute control of the air-fuel ratio (hereinafter referred to as DKCMD-OFFSET), the above-mentioned basic after correction The target air-fuel ratio KCMD is obtained by adding the window value DKCMD-OFFSET to the value KBS.
[0051]
[Expression 2]

[0052]
Next, in step S612, after the target air-fuel ratio KCMD (k) (where k is time) is limited, in step S614, the target air-fuel ratio KCMD (k) is set to 1 or a value in the vicinity thereof. It is determined whether or not there is, and if affirmative, in step S616, O₂The activation determination of the sensor 54 is performed. This activation determination is executed by another routine (not shown), and O₂This is performed by detecting a voltage change in the detection signal of the sensor 56.
[0053]
Next, in step S618, MIDO₂Calculate the control value DKCMD. Where MIDO₂Control refers to the O downstream of the three-way catalyst device 28.₂This means that the output of the sensor 56 makes the target air-fuel ratio KCMD (k) of the upstream LAF sensor 54 variable. Specifically, as shown in FIG. 3, predetermined comparison voltages VrefM and O₂This is done by calculating the value DKCMD using the PID control law for the deviation of the output voltage VO2M of the sensor 56. The comparison voltage VrefM is obtained according to the atmospheric pressure Pa, the water temperature Tw, the exhaust volume (which can be obtained from the engine speed Ne and the intake pressure Pb), and the like.
[0054]
Furthermore, the window value DKCMD-OFFSET is an offset value added to maintain the purification rate of the three-way catalyst devices 28 and 30 in an optimal state, and is different due to the characteristics unique to the catalyst device. It is determined in consideration of the characteristics of the three-way catalyst device 28. Further, since the window value DKCMD-OFFSET also changes due to aging of the catalyst devices 28 and 30, it is learned by a weighted average using the calculated value of the value DKCMD every time. In particular,
[0055]
[Equation 3]

[0056]
It is calculated by the following equation. Here, W is a weighting factor and k is time, and more specifically indicates a control cycle. That is, the target air-fuel ratio KCMD is learned and calculated with the previous value of the window value DKCMD-OFFSET, so that the purification rate is fed back to the optimal air-fuel ratio without being affected by the aging of the catalyst devices 28 and 30. I try to control it.
[0057]
Next, in step S620, the target air-fuel ratio KCMD (k) is added to the calculated value DKCMD (k) to set (update) a new target air-fuel ratio KCMD (k), and then in step S622. Then, the correction coefficient KETC is obtained by searching a predetermined table in the ROM 76 based on the updated target air-fuel ratio KCMD (k). The correction coefficient KETC is for compensating for the difference in the charging efficiency of the intake air due to the heat of vaporization. Specifically, the corrected (updated) target air-fuel ratio correction coefficient KCMDM (k) is calculated by multiplying the calculated correction coefficient KETC by the target air-fuel ratio KCMD (k). That is, in this control, the target air-fuel ratio is indicated by an equivalence ratio, and the value obtained by correcting the target air-fuel ratio is used as the target air-fuel ratio correction coefficient KCMDM (k).
[0058]
Note that when the result in step S614 is negative, the target air-fuel ratio KCMD (k) to be controlled is greatly deviated from the stoichiometric air-fuel ratio. Jump to S622.
[0059]
Finally, in step S624, the target air-fuel ratio correction coefficient KCMD (k) is limited, and the target air-fuel ratio correction coefficient KCMDM is added to the basic fuel injection amount TiM-F from the feedforward control system as shown in FIG. By multiplying (k), the required fuel injection amount Tcyl is calculated.
[0060]
As described above, the function of the first feedback system is that the OFC for the basic value KBS of the air-fuel ratio in the steady operation state₂By performing the predetermined correction process based on the output of the sensor 56, the target air-fuel ratio KCMD and the target air-fuel ratio correction coefficient KCMDM are obtained, and the basic fuel injection amount TiM-F is multiplied by the target air-fuel ratio correction coefficient KCMDM. Then, a required fuel injection amount Tcyl that can set an ideal air-fuel ratio for the catalyst device is calculated.
[0061]
Next, the second feedback system will be described. This feedback system includes an adaptive controller indicated by “STR” in FIG. 4, a PID controller indicated by “PIDC”, and a switching mechanism indicated by “switch SW”. This is realized by executing a predetermined application program by the core 64. Since this feedback system is disclosed in detail in Japanese Patent Application No. 6-340021, its outline will be described here.
[0062]
This feedback system is caused by a response delay of the internal combustion engine 10 only by obtaining the required fuel injection amount Tcyl by multiplying the basic fuel injection amount TiM calculated in the feedforward system by the target air-fuel ratio correction coefficient KCMDM. Since the target air-fuel ratio KCMD becomes a dull air-fuel ratio, the feedback correction coefficient KSTR is obtained using the adaptive controller STR for the purpose of dynamically compensating the air-fuel ratio response from the target air-fuel ratio KCMD, The required fuel injection amount Tcyl is further corrected by the feedback correction coefficient KSTR. Further, since the adaptive controller STR has a relatively high control responsiveness, the control amount oscillates and the control stability decreases when the target air-fuel ratio KCMD fluctuates greatly depending on the operating state. If the control becomes unstable due to a problem, the required fuel injection amount Tcyl is corrected by the feedback correction coefficient KLAF obtained by the PID controller PIDC. A switching mechanism is provided to switch and apply these feedback correction coefficients KSTR and KLAF according to the operating state. Furthermore, when switching the feedback correction coefficient determined based on different control laws, the characteristics differ from each other. Therefore, a step occurs in the correction coefficient, the manipulated variable changes suddenly, and the controlled variable becomes unstable. Since the stability may be lowered, the switching mechanism smoothly performs the switching so as not to cause discontinuity in the feedback correction coefficient.
[0063]
First, the PID controller PIDC determines the target air-fuel ratio based on the air-fuel ratio (hereinafter referred to as the detected air-fuel ratio KACT) of the exhaust system aggregate estimated in the sampling operation block (shown as “sel-V” in the figure). Compensate for KCMD dynamically. Here, the sampling operation block sel-V has a function of calculating the detected air-fuel ratio KACT from the detection signal of the LAF sensor 54, and this detected air-fuel ratio KACT is also used in a third feedback system described later. Thus, predetermined feedback control is performed. The details of the sampling operation block sel-V will be described together with the third feedback system.
[0064]
The processing of the PID controller PIDC will be described. First, the control deviation DKAF between the target air-fuel ratio KCMD and the detected air-fuel ratio KACT is calculated as follows:
[0065]
[Expression 4]

[0066]
I ask. Here, d 'indicates a dead time until KCMD is reflected in KACT. Therefore, KCMD (k−d ′) indicates the target air-fuel ratio before the dead time control period. KACT (k) indicates the detected air-fuel ratio in the current control cycle. In addition, the air-fuel ratio in this specification is the target value KCMD and the detected value KACT actually indicated by the equivalent ratio, that is, Mst / M = 1 / λ (Mst is the theoretical air-fuel ratio, and M is the air consumption). Ratio of A and fuel consumption F A / F, λ is the excess air ratio).
[0067]
Next, multiply it by a predetermined coefficient to obtain P-term KLAFP (k), I-term KLAFI (k), and D-term KLAFD (k),
[0068]
[Equation 5]

[0069]
I ask.
[0070]
As described above, the P term is obtained by multiplying the deviation DKAF (k) by the proportional gain KP, and the I term is obtained by adding the value obtained by multiplying the deviation by the integral gain KI to the previous value KLAF (k) of the feedback correction coefficient. The D term is obtained by multiplying the difference between the current value DKAF (k) and the previous value DKAF (k-1) of the deviation by the differential gain KD. The gains KP, KI, and KD are obtained by a predetermined map search using the engine speed Ne and the intake pressure Pb as parameters. Further, as shown in Equation 6, these values are added together and an offset of 1.0 is added to obtain the current value KLAF (k) of the feedback correction coefficient according to the PID control law of the PID controller PIDC.
[0071]
[Formula 6]

[0072]
Next, the function of the adaptive controller STR will be described with reference to FIG. The adaptive controller STR has a STR controller and a parameter adjustment mechanism, and the STR controller detects the target air-fuel ratio KCMD (k) from the first feedback system and the detected air-fuel ratio from the sampling operation block (sel-V). KACT (k) is input, and a coefficient vector identified by the parameter adjustment rule (mechanism) proposed by Landau et al. Is received to perform adaptive digital signal processing, thereby calculating a feedback correction coefficient KSTR (k). In other words, the feedback correction coefficient KSTR (k) is calculated using a recurrence formula.
[0073]
According to this method, a so-called adaptive system is converted into an equivalent feedback system composed of a linear block and a non-linear block, and Popov's integral inequality for input and output is established for the non-linear block, so that the linear block is strongly positive and real. By determining the adjustment rule, the stability of the adaptive system is guaranteed. Such a method is disclosed in, for example, “Compute Roll” (Corona) No. 27.28-41 or "Automatic Control Handbook" (Ohm Co., Ltd.) 703-707.
[0074]
The adaptive control technique using the Landau et al. Adjustment rule will be described below. In the Landau et al. Adjustment law, the transfer function A (Z^-1) / B (Z^-1) When the polynomial of the denominator numerator in Equation 7 is set as in (1) (2), the adaptive parameter θ hat (k) and the input ζ (k) to the adaptive parameter adjustment mechanism are expressed in Equation 7 as (3) ▲. It is determined as 4 ▼. In Equation 7, a case where m = 1, n = 1, and d = 3, that is, a brand having a waste time of three control cycles in the primary system is taken as an example. Here, k represents a time, more specifically, a control cycle.
[0075]
[Expression 7]

[0076]
Here, the adaptive parameter θ hat (k) is expressed by Equation 8. Further, Γ (k) and e asterisk (K) in Equation 8 are a gain matrix and an identification error signal, respectively, and are expressed by recurrence formulas such as Equation 9 and Equation 10.
[0077]
[Equation 8]

[0078]
[Equation 9]

[0079]
[Expression 10]

[0080]
Various specific algorithms are given depending on how λ1 (k) and λ2 (k) in Equation 9 are selected. If λ1 (k) = 1, λ2 (k) = λ (0 <λ <2), then a gradually decreasing gain algorithm (least square method when λ = 1), λ1 (k) = λ1 (0 <λ1 <1) ), Λ2 (k) = λ2 (0 <λ2 <λ), variable gain algorithm (weighted least square method when λ2 = 1), λ1 (k) / λ2 (k) = σ, and λ3 When λ1 (k) = λ3, the fixed trace algorithm is obtained. When λ1 (k) = 1 and λ2 (k) = 0, the fixed gain algorithm is used. In this case, as apparent from Equation 9, Γ (k) = Γ (k−1), and therefore, Γ (k) = Γ is a fixed value.
[0081]
## EQU11 ##

[0082]
Here, in FIG. 9, the STR controller (adaptive controller) and the adaptive parameter adjustment mechanism are outside the fuel injection amount calculation system, and the detected air-fuel ratio KACT (k) is the target air-fuel ratio KCMD ( k-d ') (where d' is the dead time until KCMD is reflected in KACT as described above), and the feedback correction coefficient KSTR (k) is calculated. That is, the STR controller receives the coefficient vector θ hat (k) adaptively identified by the adaptive parameter adjustment mechanism and forms a feedback compensator so as to match the target air-fuel ratio KCMD (k−d ′).
[0083]
Thus, the feedback correction coefficient KSTR (k) and the detected air-fuel ratio KACT (k) are obtained and input to the adaptive parameter adjustment mechanism, where the adaptive parameter θ hat (k) is calculated and input to the STR controller. The STR controller is provided with a target air-fuel ratio KCMD (k) as an input, and a feedback correction coefficient shown in Equation 12 using a recurrence formula so that the detected air-fuel ratio KACT (k) matches the target air-fuel ratio KCMD (k). Calculate KSTR (k).
[0084]
[Expression 12]

[0085]
The calculated feedback correction coefficient KSTR (k) is multiplied by the required fuel injection amount Tcyl through the switching mechanism, and the corrected fuel injection amount Tcyl ′ is further described in the third feedback control system for each cylinder as described later. By correcting with the correction coefficient #nKLAF, the cylinder specific output fuel injection amount #nTout is obtained.
[0086]
The switching mechanism performs switching processing in synchronization with a predetermined switching flag FKSTR, and in an operating state in which the target air-fuel ratio KCMD fluctuates greatly, the feedback correction coefficient KLAF (k) is switched to select the required fuel. By multiplying the injection amount Tcyl and in an operation state in which the target air-fuel ratio KCMD does not fluctuate significantly, the feedback correction coefficient KSTR (k) is selected by switching and multiplied by the required fuel injection amount Tcyl. That is, the required fuel injection amount Tcyl is corrected by the feedback correction coefficient KSTR or KLAF.
[0087]
Next, the third feedback system will be described. This feedback system basically applies an observer (shown as OBSV in FIG. 4) to the air-fuel ratio of the exhaust system aggregate estimated by the sampling operation block “sel-V”, that is, the detected air-fuel ratio KACT. Then, the cylinder-specific air-fuel ratio #nKACT is obtained, and further, the air-fuel ratio correction coefficient #nKLAF for each cylinder is calculated from the cylinder-specific air-fuel ratio #nKACT by the PID control law (shown as PID in FIG. 4). The suffix #n indicates each cylinder. Then, by multiplying the fuel injection amount Tcyl ′ by the cylinder specific air-fuel ratio correction coefficient #nKLAF, an output fuel injection amount #nTout that can equalize the air-fuel ratio of each cylinder is set. The exhaust gas cleaning efficiency of 30 is improved. In other words, the third feedback system feedback corrects fluctuations in the air-fuel ratio among the cylinders. First, before describing the operation of this feedback system, the sampling operation block “sel-V” and the observer will be described.
[0088]
Since the exhaust gas is discharged in the exhaust stroke, the air-fuel ratio clearly synchronizes with TDC when the behavior of the air-fuel ratio is observed in the exhaust system collection portion of the multi-cylinder internal combustion engine 10. Therefore, when the single LAF sensor 54 is provided in the exhaust system collecting portion and the air-fuel ratio is sampled, it is necessary to perform it in synchronization with the TDC. However, depending on the sample timing of the control unit (ECU) 36 that processes the detection output of the LAF sensor 54, the air-fuel ratio behavior may not be accurately captured. That is, for example, when the air-fuel ratio of the exhaust system collecting portion with respect to TDC is as shown in FIG. 10, the air-fuel ratio recognized by the control unit 36 is completely different depending on the sample timing as shown in FIG. End up. Further, the change in the air-fuel ratio differs depending on the time until the exhaust gas reaches the LAF sensor 54 and the reaction time of the LAF sensor 54. Among them, the arrival time to the LAF sensor 54 varies depending on the exhaust gas pressure, the exhaust gas volume, and the like. Furthermore, sampling in synchronism with the TDC results in sampling based on the crank angle, and therefore must be influenced by the engine speed Ne. As described above, the detected value of the air-fuel ratio largely depends on the operating state of the engine. In order to solve such a problem, a sampling operation block sel-V and an observer OBSV are provided.
[0089]
In order to accurately separate and extract the air-fuel ratio of each cylinder from the detection signal of the single LAF sensor 54 provided in the exhaust system assembly, it is necessary to accurately clarify the detection response delay of the LAF sensor 54. Therefore, as shown in FIG. 12, when this delay is modeled in a pseudo first-order lag system, the equation of state can be expressed by Equation 13.
[0090]
[Formula 13]

[0091]
When this is discretized with a period ΔT, it is as shown in Equation 14. FIG. 13 is a block diagram of Equation 14.
[0092]
[Expression 14]

[0093]
Therefore, the true air-fuel ratio can be obtained from the detection output of the LAF sensor 54 by using Equation 14. That is, if the equation 14 is modified, the equation 15 is obtained, so that the value at the time k−1 can be calculated back as the equation 16 from the value at the time k.
[0094]
[Expression 15]

[0095]
[Expression 16]

[0096]
More specifically, if Equation 15 is expressed as a transfer function using Z conversion, Equation 17 is obtained. Therefore, by multiplying the inverse transfer function by the detection output LAF (k) of the current LAF sensor 54, the previous input empty The fuel ratio can be estimated in real time. FIG. 14 shows a block diagram of the real-time A / F estimator.
[0097]
[Expression 17]

[0098]
Next, a method for separating and extracting the air-fuel ratio of each cylinder based on the true air-fuel ratio obtained as described above will be described. The value at the time k is considered as a weighted average in consideration, as shown in Equation 18. Since “F (fuel amount)” is a control amount, “fuel / air ratio F / A” is used here. However, in the following description, for convenience of understanding, “air / fuel ratio” is used as long as there is no problem. Note that the air-fuel ratio (or fuel-air ratio) means a true value obtained by correcting the response delay previously obtained by Equation 17.
[0099]
[Expression 18]

[0100]
That is, the air-fuel ratio of the collecting portion is represented by the sum of the past combustion history of each cylinder multiplied by a weight C (for example, 40% for the most recently burned cylinder, 30% before the cylinder, etc.). This model is represented by a block diagram as shown in FIG.
[0101]
Further, the equation of state is as shown in Equation 19.
[0102]
[Equation 19]

[0103]
Further, if the air-fuel ratio of the collecting portion is y (k), the output equation can be expressed as in Expression 20.
[0104]
[Expression 20]

[0105]
In the above, since u (k) cannot be observed, x (k) cannot be observed even if the observer is designed from this equation of state. Therefore, assuming that the air-fuel ratio before 4 TDC (that is, the same cylinder) is in a steady operation state in which the air-fuel ratio does not change abruptly, x (k + 1) = x (k−3) is obtained.
[0106]
[Expression 21]

[0107]
When a simulation is performed on such a model, a result is obtained that the model output value follows the measured value of the LAF sensor 54 output well, and that the above model well models the exhaust system of the multi-cylinder internal combustion engine. I was able to verify.
[0108]
Therefore, this results in a problem of a normal Kalman filter in which x (k) is observed by the state equation and the output equation (Equation 20) expressed by Equation 22. When the weight matrices Q and R are placed as shown in Equation 23 and the Riccati equation is solved, the gain matrix K becomes as shown in Equation 24.
[0109]
[Expression 22]

[0110]
[Expression 23]

[0111]
[Expression 24]

[0112]
From this, A-KC is obtained as shown in Equation 25.
[0113]
[Expression 25]

[0114]
By the way, the configuration of a general observer is as shown in FIG. 16, but since there is no input u (k) in this model, it becomes a configuration in which only y (k) is input as shown in FIG. When this is expressed by a mathematical formula, it becomes as in Expression 26.
[0115]
[Equation 26]

[0116]
Here, when y (k) is inputted, the system matrix of the observer, that is, the Kalman filter, is expressed as in Expression 27.
[0117]
[Expression 27]

[0118]
In this model, when the element of load distribution R of the Riccati equation: element of Q = 1: 1, the system matrix S of the Kalman filter is given by Equation 28.
[0119]
[Expression 28]

[0120]
FIG. 18 shows a combination of the above model and an observer. According to the result of the simulation, it was verified that the air-fuel ratio of each cylinder can be accurately extracted from the collective part air-fuel ratio.
[0121]
As described above, since the observer can estimate each cylinder air-fuel ratio # nA / F from the collective part air-fuel ratio A / F (that is, A / F is equivalent to KACT), the PID control law Can be used to calculate the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF for controlling the air-fuel ratio for each cylinder.
[0122]
Specifically, as shown in FIG. 19, the air-fuel ratio (that is, KACT) of the exhaust system collecting portion is calculated by calculating the air-fuel ratio correction coefficient for each cylinder #n and the previously calculated value of the average value for all cylinders of the air-fuel ratio for each cylinder. A PID control law is used to eliminate the deviation between the target value obtained by division and the estimated value # nA / F for each cylinder of the observer. That is, as shown in Equation 29, the target value KCMDOBSV applied to the PID control law is an average value of the air-fuel ratio correction coefficients # 1KLAF to # 4KLAF of each cylinder estimated at the previous TDC, and is the detected air-fuel ratio obtained this time. Calculated by dividing KACT.
[0123]
[Expression 29]

[0124]
On the other hand, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF calculates the deviation #nDKACT (m) between the detected air-fuel ratio #nKACT (m) and the target value KCMDOBSV for each cylinder #n as shown in Equation 30, Deviation #nDDKACT of deviation #nDKACT (m) obtained this time and deviation #nDKACT (m-1) obtained last time is obtained, and further, by applying these calculation results, it corresponds to each cylinder #n. The KP term, the KI term, and the KD term of the PID control law are obtained, and finally, the KP term, the KI term, and the KD term are applied to obtain the cylinder specific air-fuel ratio correction coefficient #nKLAF. Here, #n indicates each cylinder # 1 to # 4, and m indicates a time point for every 4TDC. That is, each cylinder air-fuel ratio correction coefficient #nKLAF is calculated once every 4 TDC. In the following equation, the KPOBSV term, KIOBSV term, and KDOBSV term, which are reference gains, are set to different values when the engine is in idling operation and during other operations, and are previously stored in the ROM 76 as a data map. Since it is stored, a map search is performed according to the driving state during such calculation.
[0125]
[30]

[0126]
As a result, the air-fuel ratio of each cylinder converges to the collective air-fuel ratio, the collective air-fuel ratio converges to the target air-fuel ratio, and as a result, the air-fuel ratios of all cylinders converge to the target air-fuel ratio. Here, the output fuel injection amount #nTout (specified by the valve opening time of the injector) of each cylinder is
[0127]
[31]

[0128]
(N is a cylinder).
[0129]
Next, an operation from sampling the detection output of the LAF sensor 54 to obtaining the estimated value # nA / F of the air-fuel ratio for each cylinder will be described based on the flowchart of FIG. Note that this processing is actually executed in advance in step S400 in the routine shown in FIG. 5, so that the detected air-fuel ratio KACT and the estimated value # nA / F are used in the processing in step 700 and step S800. Be able to.
[0130]
In FIG. 20, in S402, the engine speed Ne, the intake pressure Pb, and the valve timing V / T are read out, and then the process proceeds to S404 and S406 to search the timing map for HiV / T and LoV / T, and the process proceeds to step S408. Then, by sampling the output of the LAF sensor 54 for HiV / T and LoV / T, the detected air-fuel ratio KACT for HiV / T and the detected air-fuel ratio KACT for LoV / T are obtained.
[0131]
FIG. 21 is an explanatory diagram showing the characteristics of the timing map. As shown in the figure, the characteristics are selected such that the value sampled at an earlier crank angle is selected as the engine speed Ne is lower or the intake pressure (negative pressure) Pb is higher. Set to Here, “early” means a value sampled at a position closer to the previous TDC position (in other words, an old value). Conversely, the higher the engine speed Ne or the lower the intake pressure Pb, the slower the crank angle, that is, the value sampled at the crank angle close to the later TDC position (in other words, a new value) is selected. That is, as shown in FIG. 11, the LAF sensor output is best sampled at a position as close as possible to the actual air-fuel ratio inflection point, but the inflection point, for example, the first peak value is Assuming that the reaction time of the sensor is constant, as shown in FIG. 22, the lower the engine speed Ne, the faster the crank angle. Further, it is expected that the exhaust gas pressure and the exhaust gas volume increase as the load increases, so that the exhaust gas flow rate increases and the arrival time at the LAF sensor 54 is shortened. In that sense, the sample timing was set as shown in FIG.
[0132]
Further, regarding the valve timing, an arbitrary value Ne1 of the engine speed is set to Ne1-Lo for the Lo side and Ne1-Hi for the Hi side, and an arbitrary value of the intake pressure is set to Pb1-Lo for the Lo side and for the Hi side. Assuming Pb1-Hi, the map characteristics are
Pb1-Lo> Pb1-Hi
Ne1-Lo> Ne1-Hi
And That is, in HiV / T, since the exhaust valve opening time is earlier than that of LoV / T, if the engine speed or intake pressure value is the same, the map characteristic is selected so that an early sampling value is selected. Is set.
[0133]
The processes in steps S402 to S408 described above correspond to the sampling operation block sel-V. Therefore, as shown in the lower part of FIG. 23, the CPU core 64 can accurately recognize the maximum value and the minimum value of the sensor output. With this configuration, even when the air-fuel ratio of each cylinder is estimated using the observer, a value approximating the actual air-fuel ratio behavior can be used to improve the observer estimation accuracy. Accuracy when performing cylinder-by-cylinder air-fuel ratio feedback control described with reference to FIG. 26 is also improved.
[0134]
Next, the cylinder-by-cylinder feedback control in step S800 in FIG. 5 will be described based on the flowcharts in FIGS. Since the internal combustion engine 10 of this embodiment is provided with the valve timing mechanism 300, the air-fuel ratio # nA / F for each cylinder is set according to the valve timing HiV / T and LoV / T in the processing of FIG. After the estimation, the cylinder specific air-fuel ratio correction coefficient #nKLAF shown in FIG. 25 is obtained.
[0135]
In FIG. 24, in step S802, the detected air-fuel ratio for HiV / T (air-fuel ratio of the exhaust system collecting portion) KACT obtained in step S408 in FIG. 20 is applied to the calculation of the observer matrix, thereby obtaining the HiV / T By calculating the cylinder specific air-fuel ratio # nA / F, and then proceeding to step S804, applying the detected air-fuel ratio for LoV / T (the air-fuel ratio of the exhaust system collecting portion) KACT to the calculation of the observer matrix, The cylinder-by-cylinder air-fuel ratio # nA / F (#nKACT) for LoV / T is obtained. Subsequently, the flow proceeds to S806, where the current valve timing V / T is determined, and depending on the determination result, the flow proceeds to step S808 or 810, where either the HiV / T or LoV / T air-fuel ratio # A / Select F. As described above, in steps S802 to S810, the cylinder-by-cylinder air-fuel ratio estimation process by the observer is performed in order to obtain the cylinder-by-cylinder air-fuel ratio # nA / F corresponding to the valve timing V / T.
[0136]
Next, according to the flowchart shown in FIG. 25, determination processing for ensuring the control stability and the like, which is the subject of the present invention, is performed, and the cylinder-specific air-fuel ratio correction coefficient #nKLAF based on the PID control law is obtained. By multiplying the fuel injection amount Tcyl ′ by the correction coefficient #nKLAF, the output fuel injection amount #nTout for determining the injector valve opening time for each cylinder is determined.
[0137]
First, in step S812 of FIG. 25, each value is a predetermined reference minimum value KACT for each cylinder air-fuel ratio # jA / F (where #j represents each cylinder and j = 1 to n)._LMTLAnd standard maximum value KACT_LMTHIt is judged whether it exists in the range. More specifically, in the case of n = 4 cylinder internal combustion engine,
About the first cylinder; KACT_LMTL<# 1A / F ≦ KACT_LMTH
About the second cylinder; KACT_LMTL<# 2A / F ≦ KACT_LMTH
About the third cylinder; KACT_LMTL<# 3A / F ≦ KACT_LMTH
About the fourth cylinder; KACT_LMTL<# 4A / F ≦ KACT_LMTH
It is determined whether or not the above condition is satisfied. That is, when the estimated air-fuel ratio suddenly changes in response to a change in the target air-fuel ratio during transient operation, the predetermined range also changes in response to a change in the target air-fuel ratio. The period during which the fuel ratio control is stopped becomes longer. Therefore, a predetermined range is set based on the target air-fuel ratio in order to determine a cylinder corresponding to the case where the cylinder-by-cylinder air-fuel ratio varies abnormally.
[0138]
If at least one cylinder-by-cylinder air-fuel ratio that does not satisfy the above condition is detected in step S812, the process proceeds to step S814, and the cylinder-by-cylinder air-fuel ratios # 1 to nA / F for all the cylinders satisfy the above condition. In step S816, the process proceeds to step S816.
[0139]
In step S814, a predetermined time τ is preset (count value t) in a predetermined timer circuit (not shown)._ACTSTIs preset to τ) to start time measurement, and then the process proceeds to step S820. This timer setting is for adjusting the time in consideration of the stability when the feedback control is resumed.
[0140]
In step S816, it is determined whether or not the timer circuit has completed the measurement of the preset time τ. That is, t_ACTSTIt is determined whether or not = 0.
[0141]
If the determination is affirmative, the process proceeds to step S818, and all the determination flags # 1FOBFB to #nFOBFB assigned to each cylinder are set to “1”, and then the process proceeds to step S822. On the other hand, if the result is NO in step S816, the process proceeds to step S820, and among the determination flags # 1FOBFB to #nFOBFB, the determination flag #jFOBFB for the cylinder that does not satisfy the above condition is set to “0”. That is, the determination flags # 1FOBFB to #nFOBFB are for identifying cylinders related to the cylinder-by-cylinder air-fuel ratio satisfying the above-mentioned condition and the cylinder-by-cylinder air-fuel ratio not satisfied.
[0142]
Next, in step S822, a determination is made to make subsequent processing different depending on whether each determination flag is “1” or “0”. The process proceeds to (A), and the process for the cylinder corresponding to the determination flag “0” is shifted to (B).
[0143]
In the processing subsequent to (B), in step S824, the correction coefficient #jKLAF of the cylinder #j corresponding to the determination flag “0” is forcibly set to a value of 1.0. In other words, the remaining cylinder correction coefficients corresponding to the determination flag “1” can be obtained by a normal PID control law if the further condition described later is satisfied.
[0144]
In the processing subsequent to (A), in steps S826 to S832, it is determined whether or not the engine speed Ne representing the operating state and the intake pressure Pb are within a predetermined feedback area for each cylinder. Here, the cylinder-by-cylinder feedback area is for setting conditions under which the cylinder-by-cylinder feedback control can be executed, as indicated by the hatched area in the column of FIG. 26. Stop another feedback control. That is, the engine speed Ne is the upper limit value N._OBSVHAnd the lower limit value 0, and the intake pressure Pb is set to a predetermined lower limit value P according to the engine speed._OBSVLAnd upper limit P_OBSVHBetween the two cylinders, the cylinder-by-cylinder feedback control can be executed. In the figure, ΔN_OBSVRegion and ΔP_OBSVIs a hysteresis provided to ensure the stability of the control when the cylinder-by-cylinder feedback control is changed from stop to execution or from execution to stop. The cylinder-by-cylinder feedback area data is stored in advance in the ROM 76 so that the map can be searched.
[0145]
In order to make such a condition determination, in steps S826 and S828, the engine speed Ne is set to the upper limit value N._OBSVHLower and the intake pressure Pb is the upper limit P_OBSVHDetermine if it is lower. Only if both conditions are satisfied, the process proceeds to step S830. If even one of the conditions is not satisfied, the process proceeds to step S836 and the values of all cylinder air-fuel ratio correction coefficients # 1KLAF to #nKLAF are set to 1. Set to 0.
[0146]
In step S830, the lower limit P of the intake pressure corresponding to the engine speed Ne._OBSVLIs retrieved, and in step S832, the intake pressure Pb is reduced to its lower limit value P._OBSVLJudge whether it is larger. If the determination is negative, the routine proceeds to step S836, where the values of all cylinder air-fuel ratio correction coefficients # 1KLAF to #nKLAF are set to 1.0. On the other hand, if the result is affirmative in step S832, the process proceeds to step S834.
[0147]
In step S834, the cylinder-by-cylinder air-fuel ratio correction coefficient for the cylinder in which the set value of the determination flags # 1FOBFB to #nFOBFB is “1” is obtained by the PID control law.
[0148]
Note that, even when the cylinder-by-cylinder air-fuel ratio correction coefficient is forcibly set to 1 in steps S824 and S836, the estimation process of the cylinder-by-cylinder air-fuel ratio # nA / F by the observer is continuously performed. It has become. That is, in order to estimate the cylinder-by-cylinder air-fuel ratio # nA / F, past history information is necessary. If the cylinder-by-cylinder air-fuel ratio correction coefficient is forcibly set to 1, this estimation process is performed. This is because if the air-fuel ratio is returned to the normal state, the next cylinder-by-cylinder air-fuel ratio # nA / F cannot be estimated quickly and accurately. In other words, by continuing the estimation process of the cylinder-by-cylinder air-fuel ratio # nA / F, when the air-fuel ratio returns to the normal state, the next cylinder-by-cylinder air-fuel ratio # nA / F is quickly and accurately estimated. be able to.
[0149]
When the processes of steps S824, S834, and S836 are completed, the process of step S900 in the main routine shown in FIG. 5 is performed, and the output fuel injection amount #nTout of each cylinder is determined.
[0150]
As described above, according to this embodiment, by performing the cylinder-by-cylinder feedback control by the third feedback system, the variation in the air-fuel ratio among the cylinders is corrected and the exhaust gas cleaning efficiency by the catalyst device is improved. Can be made.
[0151]
Further, the situation where the cylinder-by-cylinder feedback control should not be performed is determined based on the parameters Ne and Pb representing the operating state. In this situation, all the cylinder-by-cylinder air-fuel ratio correction coefficients #nKLAF are forcibly set to 1.0. As a result, the cylinder-by-cylinder feedback control is substantially stopped, so that adverse effects on the overall feedback control are prevented, and when it returns to normal, the cylinder-by-cylinder feedback control is started again and the observer OBSV is utilized. It is possible to perform cylinder-by-cylinder air-fuel ratio control.
[0152]
Further, even in a situation where the cylinder-by-cylinder feedback control can be performed, if any of the cylinder-by-cylinder air-fuel ratio # nA / F falls outside the predetermined value range, the cylinder-by-cylinder air-fuel ratio for the corresponding cylinder Only the correction coefficient is forcibly set to 1.0, and the remaining cylinder-by-cylinder air-fuel ratio correction coefficient is continuously calculated according to the normal PID control law, thereby preventing adverse effects on the overall feedback control, When the engine returns to normal, all cylinder-by-cylinder feedback control is started again, and cylinder-by-cylinder air-fuel ratio control utilizing the observer OBSV can be performed.
[0153]
In the above description of this embodiment, the corresponding cylinder air-fuel ratio correction coefficient is forcibly set to 1.0 in steps S824 and S836 in FIG. 25 in order to avoid control instability and the like. Thus, the output fuel injection amount Tout to the corresponding cylinder is not substantially corrected, but the value need not be limited to 1.0. For example, the normal cylinder-by-cylinder air-fuel ratio # nA / F estimated before the previous time may be used as the corresponding cylinder-by-cylinder air-fuel ratio correction coefficient. In this way, it can be expected that the variation in the air-fuel ratio is converged more quickly.
[0154]
(Second embodiment)
Next, a second embodiment will be described with reference to the flowchart of FIG. This embodiment relates to cylinder-by-cylinder feedback control by the third feedback system, and the configurations of the feedforward system and the first and second feedback systems shown in the first embodiment are the same or equivalent. Therefore, the difference from the first embodiment will be described while being compared. In FIG. 27 showing the features of this embodiment, the same or corresponding parts as the processing contents in the first embodiment are denoted by the same reference numerals.
[0155]
In the processing of steps S824 to S836 in FIG. 25 described in the first embodiment, when the cylinder-by-cylinder feedback control is hindered, the relevant cylinder-by-cylinder air-fuel ratio correction coefficient is selected and forcibly set to 1.0 or the like. Although fixed to a numerical value, in this embodiment, if even one of the cylinder-by-cylinder air-fuel ratios # nA / F becomes a value that hinders control, all the cylinder-by-cylinder air-fuel ratio correction coefficients #nKLAF are set. By forcibly setting to 1.0, the cylinder-by-cylinder feedback control is substantially stopped during the period until the air-fuel ratio returns to normal, or the cylinder-by-cylinder empty at the normal time obtained during the previous estimation is performed. By continuing the correction process of the output fuel injection amount #Tout using the fuel ratio correction coefficient #nKLAF, it is possible to prevent the overall feedback control from being adversely affected. Start control Are those which make it possible to perform the cylinder air-fuel ratio control utilizing the observer obsv.
[0156]
That is, when the distribution process in step S822 in FIG. 25 is completed, the process is continued to either process (A) or process (B) in FIG. The process (B) is continued when at least one cylinder air-fuel ratio (for example, # 1 A / F) exceeds a predetermined value. In step S1000, all cylinder air-fuel ratio correction coefficients # 1KLAF˜ Set #nKLAF to 1.0. Here, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF at the normal time obtained at the previous estimation may be set.
[0157]
When the process (A) is continued, the estimated cylinder-by-cylinder air-fuel ratio # nA / F is normal. Accordingly, it is determined whether or not the operating state is suitable for the cylinder-by-cylinder feedback correction region (see FIG. 26) by the processing in steps S826 to S832. If the above condition is completely satisfied (affirmed), the process proceeds to step S834, where the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is calculated according to the PID control law. Subsequently, in step S900, the output fuel of each cylinder is calculated. The injection amount #nTout is corrected. On the other hand, if the result of step S826 to S832 is negative, the process proceeds to step S1000, where all the cylinder-by-cylinder air-fuel ratio correction coefficients # 1KLAF to #nKLAF are set to 1.0, or the above-described normal cylinder-by-cylinder sky. Set to fuel ratio correction coefficient #nKLAF.
[0158]
(Third embodiment)
Next, a third embodiment will be described with reference to the flowchart of FIG. This embodiment relates to the cylinder-by-cylinder air-fuel ratio control by the third feedback system described in the first embodiment, and the feedforward system and the first and second feedback shown in the first embodiment. Since the configuration of the system is the same or equivalent, the differences from the first embodiment will be described in comparison. In FIG. 28 showing the features of this embodiment, the same or corresponding parts as the processing contents in the first embodiment are denoted by the same reference numerals.
[0159]
In the processing of steps S812 to S822 in FIG. 25 described in the first embodiment, the cylinder-by-cylinder air-fuel ratio # nA / F is determined when the cylinder-by-cylinder feedback control is hindered, and based on the determination result. The corresponding cylinder-by-cylinder air-fuel ratio correction coefficient is determined to be a constant value such as 1.0. In the third embodiment, the time variation of the detected air-fuel ratio KACT and the target air-fuel ratio correction coefficient KLAF are further increased. The cylinder-by-cylinder feedback control is substantially stopped even when both the time changes greatly change.
[0160]
That is, in FIG. 27, after the cylinder specific air-fuel ratio # nA / F is obtained, in step S2000, the latest detected air-fuel ratio KACT (k) and the previously detected air-fuel ratio KACT (k-1) Absolute value ΔKACT = | KACT (k) −KACT (k−1) | is a predetermined upper limit value ΔKACT_LMTHThe process proceeds to step S2002 when the result is affirmed, and the process proceeds to step S814 when the result is negative.
[0161]
In step S2002, the absolute value ΔKLAF = | KLAF (k) −KLAF (k) of the difference between the latest target air-fuel ratio correction coefficient KLAF (k) and the previously obtained target air-fuel ratio correction coefficient KLAF (k−1). -1) | is a predetermined upper limit ΔKLAF_LMTHIt is determined whether or not it is smaller. If the result is affirmative, the process proceeds to step S812. If the result is negative, the process proceeds to step S814.
[0162]
Accordingly, the process proceeds to step S812 only when both the variation in the detected air-fuel ratio KACT and the variation in the target air-fuel ratio correction coefficient KLAF are not large. On the other hand, when at least one of the detected air-fuel ratio KACT and the target air-fuel ratio correction coefficient KLAF is large, the process proceeds to step S814.
[0163]
Next, as described in the first embodiment, the processing corresponding to the case where the cylinder air-fuel ratio is outside the predetermined value range is performed by performing the processing of steps S812 to S822. The processing corresponding to the case where the air-fuel ratio is within the predetermined value range shifts to processing (A). Subsequently, after the air-fuel ratio correction coefficients # 1KLAF to #nKLAF for each cylinder are determined by the processing in steps S826 to S836 shown in FIG. 25, the output fuel injection amount #nTout for each cylinder is calculated.
[0164]
According to this embodiment, since the presence or absence of control stability is determined from each change amount of the detected air-fuel ratio KACT and the target air-fuel ratio correction coefficient KLAF, the cylinder-by-cylinder air-fuel ratio caused by an abnormality in at least one cylinder is determined. A decrease in control stability can be prevented.
[0165]
In this embodiment, the stability of the control is determined from the change in both the detected air-fuel ratio KACT and the target air-fuel ratio correction coefficient KLAF. However, the determination control is performed based on either change. You may do it.
[0166]
Furthermore, in the above description, the case where the processing shown in FIG. 28 is followed by the processing (A) and (B) of the first embodiment shown in FIG. 25 is described, but the second embodiment shown in FIG. You may continue to the processing (A) and (B) of the example.
[0167]
【The invention's effect】
In the first and second aspects, the cylinder-by-cylinder feedback control for the corresponding cylinder in which the estimated air-fuel ratio for each cylinder estimated by the observer is outside the predetermined range is stopped. The influence can be reduced. Further, since the estimation of the air-fuel ratio for each cylinder by the observer is continued, when resuming the cylinder feedback control, the cylinder-by-cylinder air immediately after the restart is immediately used based on the history information of the past estimated air-fuel ratio for each cylinder using the observer. A fuel ratio correction coefficient can be obtained, and cylinder-by-cylinder feedback control with excellent responsiveness immediately after resuming feedback control is enabled based on the cylinder-by-cylinder air-fuel ratio correction coefficient.
[0168]
According to the third aspect of the present invention, the predetermined range for determining the cylinder corresponding to the case where the cylinder-by-cylinder air-fuel ratio varies abnormally is set based on the target air-fuel ratio. Correspondingly, when the estimated air-fuel ratio suddenly changes, the predetermined range also changes in response to the change in the target air-fuel ratio, preventing the estimated air-fuel ratio from being outside the predetermined range and extending the period during which the air-fuel ratio control is stopped. can do.
[0169]
According to the fourth aspect of the present invention, abnormality in at least one cylinder is judged from the amount of change in the detected air-fuel ratio (air-fuel ratio of the air-fuel mixture), and the cylinder-by-cylinder feedback control is substantially stopped. The influence on control can be reduced. Further, since the estimation of the air-fuel ratio for each cylinder by the observer is continued, when resuming the cylinder feedback control, the cylinder-by-cylinder air immediately after the restart is immediately used based on the history information of the past estimated air-fuel ratio for each cylinder using the observer. A fuel ratio correction coefficient can be obtained, and cylinder-by-cylinder feedback control with excellent responsiveness immediately after resuming feedback control is enabled based on the cylinder-by-cylinder air-fuel ratio correction coefficient.
[0170]
According to the fifth aspect, the abnormality in at least one cylinder is judged from the amount of change in the target air-fuel ratio correction coefficient, and the cylinder-by-cylinder feedback control is substantially stopped. Can be reduced. Further, since the estimation of the air-fuel ratio for each cylinder by the observer is continued, when resuming the cylinder feedback control, the cylinder-by-cylinder air immediately after the restart is immediately used based on the history information of the past estimated air-fuel ratio for each cylinder using the observer. A fuel ratio correction coefficient can be obtained, and cylinder-by-cylinder feedback control with excellent responsiveness immediately after resuming feedback control is enabled based on the cylinder-by-cylinder air-fuel ratio correction coefficient.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing the overall configuration of a fuel injection device for an internal combustion engine according to an embodiment.
FIG. 2 is a block diagram showing a configuration of a control unit in FIG.
FIG. 3 shows O in FIG.₂It is explanatory drawing which shows a sensor output characteristic.
FIG. 4 is a block diagram showing functions of a fuel injection device for an internal combustion engine according to an embodiment.
FIG. 5 is a flowchart for explaining the operation of the fuel injection device.
FIG. 6 is a flowchart for explaining the operation of the feedforward system.
FIG. 7 is a block diagram for explaining functions of a feedforward system.
FIG. 8 is a flowchart for explaining the operation of the first feedback system;
FIG. 9 is a block diagram for explaining a function of a second feedback system;
FIG. 10 is an explanatory diagram showing a relationship between TDC of a multi-cylinder internal combustion engine and an air-fuel ratio of an exhaust system collecting portion.
FIG. 11 is an explanatory diagram showing the quality of sample timing with respect to an actual air-fuel ratio.
FIG. 12 is a block diagram showing a modeled detection operation of a LAF sensor.
13 is a block diagram showing a Z-transform display model of the model of FIG.
FIG. 14 is a block diagram showing an air-fuel ratio estimator that models the detection behavior of the air-fuel ratio sensor.
FIG. 15 is a block diagram modeling the behavior of an exhaust system of an internal combustion engine.
FIG. 16 is a block diagram showing a general observer.
FIG. 17 is a block diagram illustrating a configuration of an observer according to an embodiment.
FIG. 18 is a block diagram showing a configuration in which an air-fuel ratio estimator and an observer are combined.
FIG. 19 is a block diagram showing functions of a third feedback system.
FIG. 20 is a flowchart showing a sampling operation of a detected air-fuel ratio in a sampling operation block (sel-V).
FIG. 21 is an explanatory diagram showing characteristics of a timing map used in the sampling operation of the sampling operation block (sel-V).
FIG. 22 is an explanatory diagram showing LAF sensor output characteristics with respect to engine speed and engine load.
FIG. 23 is a timing chart illustrating a sampling operation of the sampling operation block (sel-V).
FIG. 24 is a flowchart showing an operation for generating cylinder-by-cylinder air-fuel ratios corresponding to engine timing with respect to the operation of the observer.
FIG. 25 is a flowchart illustrating a determination operation for obtaining a cylinder-by-cylinder air-fuel ratio correction coefficient in a third feedback system (cylinder-by-cylinder feedback control system).
FIG. 26 is an explanatory diagram showing a cylinder-by-cylinder feedback region used in the determination operation of FIG. 25;
FIG. 27 is a flowchart illustrating a determination operation for obtaining a cylinder-by-cylinder air-fuel ratio correction coefficient in a third feedback system (cylinder-by-cylinder feedback control system) according to the second embodiment;
FIG. 28 is a flowchart illustrating a determination operation for obtaining a cylinder specific air-fuel ratio correction coefficient in a third feedback system (cylinder specific feedback control system) in the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake pipe, 14 ... Air cleaner, 16 ... Throttle valve,
DESCRIPTION OF SYMBOLS 18 ... Surge tank, 20 ... Intake manifold, 22 ... Injector, 24 ... Exhaust manifold, 26 ... Exhaust pipe, 28, 30 ... Catalyst apparatus, 32 ... Solenoid valve, 34 ... Bypass path, 36 ... Engine control unit, 38 ... Fuel Tank, 40 ... crank angle detection sensor, 42 ... throttle opening detection sensor, 44 ... absolute pressure sensor, 46 ... intake air temperature sensor, 48 ... atmospheric pressure sensor, 50 ... water temperature sensor, 52 ... timing detection sensor, 54 ... air-fuel ratio Detection sensor (LAF sensor), 56... O₂Sensor,
58, 60 ... Low-pass filter, 62 ... Microprocessor, 64 ... CPU core, 66 ... Detection circuit, 68 ... Multiplexer, 70 ... Detection circuit, 72 ... A / D converter, 74 ... RAM, 76 ... ROM, 78 ... Waveform Shaping circuit, 80 ... counter, 82-88 ... driving circuit, 100 ... EGR mechanism, 102 ... solenoid valve, 200 ... canister purge mechanism, 202 ... solenoid valve, 300 ... valve timing mechanism.

Claims (5)

An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and an air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine; Based on a model that defines the behavior of the engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and based on the history information of the past estimated air-fuel ratio for each cylinder, Air-fuel ratio estimation means for estimating the air-fuel ratio, and cylinder-by-cylinder fuel supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder An air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for each cylinder that corrects an injection amount, and when the estimated air-fuel ratio is outside a predetermined range, About cylinder Air-fuel ratio control stop means for stopping the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient; and air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped. A fuel injection control device for an internal combustion engine. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and an air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine; Based on a model that defines the behavior of the engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and based on the history information of the past estimated air-fuel ratio for each cylinder, Air-fuel ratio estimation means for estimating the air-fuel ratio, and cylinder-by-cylinder fuel supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder An air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for each cylinder that corrects the injection amount, and when the estimated air-fuel ratio is outside a predetermined range, About cylinder Air-fuel ratio control stop means for stopping the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient, and air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped. A fuel injection control device for an internal combustion engine.   3. The fuel injection control device for an internal combustion engine according to claim 1, further comprising predetermined range setting means for setting the predetermined range based on a target air-fuel ratio supplied to the multi-cylinder internal combustion engine. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and an air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine; Based on a model that defines the behavior of the engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and based on the history information of the past estimated air-fuel ratio for each cylinder, Air-fuel ratio estimation means for estimating the air-fuel ratio, and cylinder-by-cylinder fuel supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder An air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for each cylinder that corrects the injection amount, and when the amount of change in the air-fuel ratio detection value of the collective portion is large, The air-fuel ratio supplement An internal combustion engine comprising: an air-fuel ratio control stop unit that stops calculation of a coefficient; and an air-fuel ratio estimation process continuation unit that continues the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped Fuel injection control device. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, and an air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine; Based on a model that defines the behavior of the engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and based on the history information of the past estimated air-fuel ratio for each cylinder, Air-fuel ratio estimating means for estimating an air-fuel ratio; first air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for correcting the fuel injection amount so that the air-fuel ratio matches a target air-fuel ratio; Based on the air-fuel ratio of each cylinder, a cylinder-by-cylinder air-fuel ratio correction coefficient for correcting the cylinder-by-cylinder fuel injection amount supplied to each cylinder of the multi-cylinder internal combustion engine is calculated so as to reduce the variation in the air-fuel ratio of each cylinder. Second air-fuel ratio correction A fuel injection amount control apparatus for an internal combustion engine comprising: a number calculating means; and stopping the calculation of the second air-fuel ratio correction coefficient when the amount of change in the first air-fuel ratio correction coefficient is large And an air-fuel ratio estimation process continuation means for continuing the air-fuel ratio estimation process when the calculation of the air-fuel ratio correction coefficient is stopped.

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