JP3768259B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

【００３７】
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。
【００３８】
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。
【００３９】
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。
【００４０】
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。
【００４１】
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。
【００４２】
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。
【００４３】
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。
【００４４】
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。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。
【００４５】
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。
【００４６】
【数２】

【００４７】
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。
【００４８】
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。
【００４９】
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、
【００５０】
【数３】

【００５１】
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。
【００５２】
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。
【００５３】
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。
【００５４】
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。
【００５５】
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。
【００５６】
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、「切替ＳＷ」で示す切替機構を備え、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。
【００５７】
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。
【００５８】
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。
【００５９】
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、
【００６０】
【数４】

【００６１】
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）。
【００６２】
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、
【００６３】
【数５】

【００６４】
と求める。
【００６５】
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。
【００６６】
【数６】

【００６７】
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。
【００６８】
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。
【００６９】
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プラントを例にとった。ここでのｋは時刻、より具体的には、制御サイクルを示す。
【００７０】
【数７】

【００７１】
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。
【００７２】
【数８】

【００７３】
【数９】

【００７４】
【数１０】

【００７５】
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。
【００７６】
【数１１】

【００７７】
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。
【００７８】
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。
【００７９】
【数１２】

【００８０】
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。
【００８１】
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。
【００８２】
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。
【００８３】
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。
【００８４】
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、サンプリング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。
【００８５】
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。
【００８６】
【数１３】

【００８７】
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。
【００８８】
【数１４】

【００８９】
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。
【００９０】
【数１５】

【００９１】
【数１６】

【００９２】
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。
【００９３】
【数１７】

【００９４】
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。
【００９５】
【数１８】

【００９６】
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。
【００９７】
また、その状態方程式は数１９のようになる。
【００９８】
【数１９】

【００９９】
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。
【０１００】
【数２０】

【０１０１】
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。
【０１０２】
【数２１】

【０１０３】
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。
【０１０４】
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。
【０１０５】
【数２２】

【０１０６】
【数２３】

【０１０７】
【数２４】

【０１０８】
これよりＡ−ＫＣを求めると、数２５のようになる。
【０１０９】
【数２５】

【０１１０】
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。
【０１１１】
【数２６】

【０１１２】
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。
【０１１３】
【数２７】

【０１１４】
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。
【０１１５】
【数２８】

【０１１６】
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。
【０１１７】
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。
【０１１８】
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。
【０１１９】
【数２９】

【０１２０】
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（２回微分に相当する）＃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。
【０１２１】
【数３０】

【０１２２】
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、
【０１２３】
【数３１】

【０１２４】
で求められる（ｎは気筒）。
【０１２５】
以上、サンプリング動作ブロックsel-Ｖとオブザーバ及び第３のフィードバック系との基本原理を述べた。
更に、図１９に示すように、第３のフィードバック系には、始動後リーンバーン制御時に、排気ガスの浄化効率の向上を図るための適切な気筒別フィードバック制御を行う適正制御部ＲＥＦが、各ＰＩＤブロックに対して併設されている。かかる適正制御部ＲＥＦの機能の詳細は図２１のフローチャートと共に後述するので、ここでは概略を述べる。
【０１２６】
先ず、始動後リーンバーン制御時でないとき（内燃機関１０が通常の運転状態にあるとき）には、ＰＩＤ制御則により求められた気筒別空燃比補正係数＃ｎKLAFを数３２に基づいて学習処理し、図２６に示す如き機関回転数Ｎｅと吸気圧力Ｐｂで決められる所定の記憶領域に、その学習データ＃ｎKLAFREF を逐一記憶すると共に、新規の学習データ＃ｎKLAFREF に順次更新するという繰り返し処理を行う。したがって、内燃機関１０が停止された場合には、直近に求められた学習データ＃ｎKLAFREF がその記憶領域に記憶されて保持される。
【０１２７】
【数３２】

【０１２８】
尚、数３２は、前回（ｋ−１）求められて記録領域の格子点（ｉ，ｊ）に格納されていた学習データ＃ｎKLAFREF _i,j (k-1) に係数（β−１）を乗算して得られる値と、ＰＩＤ制御則により今回（ｋ）求められた気筒別空燃比補正係数＃ｎKLAF(k) に係数βを乗算して得られる値とを加算することによって学習データ＃ｎKLAFREF _i,j (k) を求めるようになっている。
【０１２９】
また、図２６に示す記憶領域は、ＲＡＭ７４中に予め気筒＃ｎ（＝１〜４）毎に割り当てられている。更に、いずれの記憶領域も、内燃機関１０が作動し得る機関回転数Ｎｅの範囲を複数分割する（この実施例ではｉ＝１〜４の４分割）と共に、吸気圧力Ｐｂも同様に複数分割する（この実施例ではｊ＝１〜４の４分割）ことによって、機関回転数Ｎｅと吸気圧力Ｐｂで規定される運転状態を１６個の格子点（ｉ，ｊ）に設定し、各格子点（ｉ，ｊ）の範囲内に該当する学習データ＃ｎKLAFREF _i,j (k) を数３２に基づいて演算し、逐次記憶するようになっている。
【０１３０】
また、始動後リーンバーン制御時か否かの判断、及びＬＡＦセンサ５４が活性化しているか否かの判断を行い、ＬＡＦセンサ５４が活性化しているとき又は始動後リーンバーン制御時でないときは、ＰＩＤ制御則による気筒別空燃比補正係数＃ｎKLAFの演算を行わせることにより、通常の気筒別フィードバック制御を継続させ、一方、ＬＡＦセンサ５４が活性化していないときは、ＰＩＤ制御則による気筒別空燃比補正係数＃ｎKLAFの演算を停止すると共に、上記の記憶領域の学習データを、機関回転数Ｎｅと吸気圧力Ｐｂをパラメータとしてマップ検索し、その検索した学習データを気筒別空燃比補正係数＃ｎKLAFと置換えて、気筒別の出力燃料噴射量＃Ｔout を補正する。即ち、ＬＡＦセンサ５４が活性化していないときに得られる検出空燃比KACTに基づいて通常の気筒別フィードバック制御を行ったのでは、排気ガスの浄化効率を向上させることができないが、この実施例のように、学習しておいた気筒別空燃比補正係数＃ｎKLAFの学習データに基づいて気筒別の出力燃料噴射量＃Ｔout を補正することとすると、燃料性状やインジェクタ２２のバラツキ等の要因を抑制して、均一な気筒別空燃比を設定することができる。
【０１３１】
更に、内燃機関１０の運転状態に応じて、気筒別空燃比補正係数＃ｎKLAFを所定値（例えば、１．０）に固定することにより、実質的に気筒別フィードバック制御を停止して、第１，第２のフィードバック系のみによる出力燃料噴射量＃Ｔout を得るようにしている。
【０１３２】
次に、サンプリング動作ブロックsel-Ｖと第３のフィードバック系の具体的な動作を図２０及び図２１のフローチャートと共に説明する。
【０１３３】
先ず、図２０のフロー・チャートに基づいて、サンプリング動作ブロックsel-Ｖが排気系集合部の空燃比（即ち、KACT）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。
【０１３４】
図２０において、ステップ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、次いでステップ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。 図２２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、ＬＡＦセンサ５４の反応時間を一定と仮定すれば、図２３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２２に示すように設定した。
【０１３５】
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。
【０１３６】
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２４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、かかる正確な空燃比に基づいて図５中のステップＳ７００とＳ８００に示すフィードバック制御が行われることになる。
【０１３７】
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の動作を図２１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、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、気筒別フィードバック補正係数＃ｎKLAFを求めるようになっている。
【０１３８】
図２１のステップＳ８０２では、適正制御部ＲＥＦによりＬＡＦセンサ５４が活性化されているか否か判断される。例えば、ＬＡＦセンサ５４が活性化されていないときの出力値LAF を予め計測してＲＡＭ７４等に記憶しておき、実測値がこの記憶値に該当するときは、ＬＡＦセンサ５４が未だ活性化していないと判断する。そして、活性化していると判断したときには、ステップＳ８１６以降の処理へ移り、活性化していないと判断したときは、ステップＳ８０４の処理へ移行する。
【０１３９】
ステップＳ８０４及びＳ８０６においては、冷却水温ＴｗがＴ_L ≦Ｔｗ≦Ｔ_H の所定温度範囲内にあるか否かの判断と、スロットル弁１６の開度θ_THが所定値θ_L 以下であるか否かの判断を行う。この実施例では、温度をＴ_L ＝０℃、Ｔ_H ＝３０℃に設定することにより、内燃機関１０が作動するための適正温度の可否を判断することにより始動後リーンバーン制御実行温度を設定し、更にθ_L を３°に設定している。そして、これらの条件を満足するときは、ステップＳ８０８に処理が移行し、条件を満足しないときは始動後リーンバーン制御を許可し、ステップＳ８１０へ移行する。
【０１４０】
ステップＳ８０８では、始動後リーンバーン制御が許可されているので、空燃比の基本値ＫＢＳに対してリーン補正係数０．８９を乗算することでその基本値を補正する。
【０１４１】
ステップＳ８１０では、機関回転数Ｎｅと吸気圧力Ｐｂをパラメータとして図２６に示した記憶領域を検索することにより、該当気筒＃ｎについての学習データ＃ｎKLAFREF を求め、次いでステップＳ８１２において、この検索した学習データ＃ｎKLAFREF を気筒別空燃比補正係数＃ｎKLAFに置換して保持する。更に、ＰＩＤ制御則による気筒別空燃比補正係数＃ｎKLAFの算出を停止させる。したがって、図５に示したステップＳ９００において、気筒別の出力燃料噴射量＃ｎＴout を演算するときには、上記の学習データ＃ｎKLAFREF に置き換えられた気筒別空燃比補正係数＃ｎKLAFによって補正することとなる。
【０１４２】
このように、始動後リーンバーン制御期間中であってＬＡＦセンサ５４が未だ活性化していないときは、学習データ＃ｎKLAFREF により出力燃料噴射量＃ｎＴout を補正するので、燃料性状やインジェクタ２２のバラツキ等の要因を抑制して、均一な気筒別空燃比を設定することができる。
【０１４３】
一方、前記ステップＳ８０２において、ＬＡＦセンサ５４が活性化していると判断した場合には、ステップ８１６〜Ｓ８２２の処理により、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。運転状態が予め決められた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。
【０１４４】
ここで、気筒別フィードバック領域とは、図２５のグラ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、ステップＳ８１４の処理によって気筒別空燃比補正係数＃ｎKLAFを固定値（１．０）にすることで、実質的に気筒別フィードバック制御を停止し、この領域内に該当するときは、通常の気筒別フィードバック制御を行うべく、ステップＳ８２４〜Ｓ８２６の処理へ移行する。
【０１４５】
即ち、図２５において、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。
【０１４６】
かかる条件判断を行うために、ステップＳ８１６とＳ８１８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Ｓ８２０へ移行し、１つでも条件を満足しない場合には、ステップＳ８１４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。
【０１４７】
ステップＳ８２０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Ｓ８２２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Ｓ８１４へ移行して全ての気筒別フィードバック補正係数＃１KLAF〜＃ｎKLAFの値を１．０に設定する。一方、ステップＳ８２２において肯定される場合はステップＳ８２４へ処理が移行する。
【０１４８】
ステップＳ８２４では、数３０，３１により、目標値KCMDOBSV及び気筒別空燃比補正＃ｎKLAFを算出する。したがって、各気筒別のフィードバック経路に設けられている加減算器が、オブザーバ０ＢＳＶで推定された気筒別空燃比＃ｎＡ／Ｆとこの目標値KCMDOBSVとの偏差を減少させるように作動し、そして、図５に示したステップＳ９００において気筒別の出力燃料噴射量＃ｎＴout が求められる。更に、ステップＳ８２６においては、前述した如く、数３２に従って学習データ＃ｎKLAFREF _i,j (k) を演算して、図２６に示した記憶領域に記憶させる。
【０１４９】
このようにこの実施例によれば、機関始動直後からＬＡＦセンサ５４が活性化するまでの期間中では、機関が停止される直前に求められていた学習データ＃ｎKLAFREF に基づいて気筒別の出力燃料噴射量＃ｎＴout を補正する第１の処理を行うことにより、たとえＬＡＦセンサ５４が不活性であっても、インジェクタ２２のバラツキを補償して排気ガスの清浄効率を向上することができる。特に、従来技術のように、目標空燃比を或る幅を持った許容範囲に設定しないので、インジェクタ２２のバラツキによる空燃比のバラツキを大幅に低減して、排気ガスの清浄効率を向上することができる。
【０１５０】
そして、触媒装置２８，３０が活性化した後は、通常の気筒別フィードバック制御により、排気ガスの清浄効率を向上させることができる。
【０１５１】
尚、この実施例では、気筒別空燃比補正係数＃ｎKLAFを学習して、この学習により得られた学習データに基づいてフィードバック制御を行うようにしたが、オブザーバＯＢＳＶで推定される気筒別空燃比＃ｎＡ／Ｆを学習し、この学習データをＰＩＤ制御則に適用してもよい。即ち、図２１中のステップＳ８２４及びＳ８２６において、気筒別空燃比＃ｎＡ／Ｆを学習及び所定の記憶領域に記憶し、始動後リーンバーン制御中にＬＡＦセンサ５４が未だ活性化していないときには、ステップＳ８１０及びＳ８１２において、気筒別空燃比＃ｎＡ／Ｆを適用してＰＩＤ制御則による気筒別空燃比＃ｎKLAFを求めるようにする。
【０１５２】
更に、排気系に設けられるＬＡＦセンサ５４とＯ₂ センサ５６及び触媒装置２８，３０の配置を図１及び図４に示す場合に限定されるものではない。
【０１５３】
例えば、図２７に示すように、触媒装置２８，３０の間にＨＣトラップキャタライザＴＲを設けてもよい。即ち、触媒装置２８，３０が活性化するまでの間、炭化水素（ＨＣ）をトラップしておき、触媒装置２８，３０が活性化した後に、トラップしておいたＨＣを触媒装置２８，３０で清浄化させる。この構成によれば、始動後リーンバーン制御期間中に気筒別空燃比のバラツキを補正しつつ、ＨＣトラップキャタライザＴＲによるＨＣのトラップを行うことになるので、ＨＣトラップキャタライザＴＲのトラップ効率を向上させることが可能となり、排気ガスの清浄効率を更に向上させることができる。
【０１５４】
また、図２８に示すように、主触媒装置ＣＡＴの前に、ライトオフキャタライザＬＣＡＴとエレクトリック・ヒート・キャタライザＥＨＣを設けるようにしても、上記の始動後リーンバーン制御期間中に気筒別空燃比のバラツキを補正することとの相乗効果が得られることから、排気ガスの清浄効率の更なる向上を図ることができる。
【０１５５】
また、図２９に示すように、主触媒装置ＣＡＴの前に、ライトオフキャタライザＬＣＡＴとエレクトリック・ヒート・キャタライザＥＨＣを設けると共に、更にエレクトリック・ヒート・キャタライザＥＨＣの前方にＨＣトラップキャタライザＴＲを配置するようにしても、同様に、排気ガスの清浄効率の更なる向上を図ることができる。
【０１５６】
更にまた、図３０に示すように、主触媒装置ＣＡＴの前に、ライトオフキャタライザＬＣＡＴとエレクトリック・ヒート・キャタライザＥＨＣを設けると共に、更にエレクトリック・ヒート・キャタライザＥＨＣの前方に、ＨＣトラップキャタライザＴＲと別個の触媒装置ＣＡＴを配置しても同様に、排気ガスの清浄効率の更なる向上を図ることができる。
【０１５７】
このように、本発明の、始動後リーンバーン制御期間中に気筒別空燃比のバラツキを補正する制御を行うと、各種の触媒装置の機能を十分に発揮させて排気ガスの清浄効率を向上させることができるという、優れた相乗効果をも発揮させることができる。
【０１５９】
【発明の効果】
請求項１の内燃機関の燃料噴射量制御装置にあっては、各気筒毎に割り当てられ多気筒内燃機関のエンジン回転数及び吸気圧力に基づいて決められる所定の記憶領域に、気筒別空燃比補正係数を学習・記憶しておき、始動後リーンバーン中に空燃比センサが未だ活性化されていないと判断すると、記憶されている気筒別空燃比補正係数の学習値に基づいて気筒別燃料噴射量を補正するので、空燃比センサが未だ活性化されず正確な空燃比を検出することができないときでも、炭化水素の低減等排気ガスの浄化を図ることができる。
請求項２の内燃機関の燃料噴射量制御装置にあっては、始動後リーンバーン制御期間中に空燃比センサの活性と判断すると、多気筒内燃機関の運転状態を表すパラメータが所定の領域内にあるか否かを判別し、パラメータが前記所定の領域内にないときは、空燃比補正係数算出手段に気筒別空燃比補正係数の算出を停止させ、且つ気筒別空燃比補正係数を予め決められた所定値に置換して気筒別燃料噴射量を補正させるので、空燃比センサが活性化されたときでも気筒別フィードバック制御を実行することができない運転状態であるときは、気筒別空燃比補正係数を予め決められた所定値に置換することにより実質的に気筒別フィードバック制御を停止させ、もって炭化水素の低減等排気ガスの浄化を図ることができる。
請求項３の内燃機関の燃料噴射量制御装置にあっては、パラメータは多気筒内燃機関のエンジン回転数及び吸気圧力からなり、所定の領域は、エンジン回転数及び吸気圧力に基づいて予め定められるので、炭化水素の低減等排気ガスの確実な浄化を図ることができる。
【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線図である。
【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３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】第３のフィードバック系（気筒別フィードバック系）の動作を説明するフローチャートである。
【図２２】図２１のフローチャートで使用されるタイミングマップの特性を示す説明図である。
【図２３】図２１のフローチャートで使用されるタイミングマップの特性を更に示す説明図である。
【図２４】サンプリング動作ブロック（sel-Ｖ）のサンプリング動作を説明するためのタイミングチャートである。
【図２５】気筒別フィードバック領域を説明する説明図である。
【図２６】学習データを記憶する記憶領域のマップ構成を説明するための説明図である。
【図２７】排気系に設けられる排気ガス浄化機構の変形例を示す説明図である。
【図２８】排気系に設けられる排気ガス浄化機構の他の変形例を示す説明図である。
【図２９】排気系に設けられる排気ガス浄化機構の更に他の変形例を示す説明図である。
【図３０】排気系に設けられる排気ガス浄化機構の更に他の変形例を示す説明図である。
【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、ＲＥＦ…適正制御部。[0001]
[Industrial application fields]
The present invention relates to a fuel injection control device for an internal combustion engine, and in particular, estimates the air-fuel ratio of each cylinder based on the detection output of an air-fuel ratio sensor installed at a collection portion of an exhaust system, and based on the air-fuel ratio of each cylinder. The present invention relates to a fuel injection control device that feedback-controls the fuel injection amount for each cylinder supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce variation in the air-fuel ratio of each cylinder.
[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 of 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 technique, it is possible not only to set an accurate air-fuel ratio for each cylinder, but also to provide a simple structure because it is not necessary to provide a plurality of air-fuel ratio sensors independently for each cylinder. . 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, the latter technique is provided in the exhaust system to clean the exhaust gas during the start mode period of the multi-cylinder internal combustion engine, that is, during a certain period immediately after the start of the internal combustion engine. The internal combustion engine is equipped with a mechanism that performs lean control after starting to reduce the concentration of hydrocarbons (HC) because the three-way catalyst device and the air-fuel ratio sensor are not yet activated. However, there has been a problem that the exhaust gas cannot be effectively purified by the feedback control for each cylinder.
[0005]
For example, since the effective air-fuel ratio cannot be detected until the air-fuel ratio sensor is activated, the cylinder-by-cylinder feedback control is substantially stopped, and the fuel injection amount of each cylinder remains lean in an open loop. Thus, after the air-fuel ratio sensor is activated, it is necessary to take measures to start cylinder-by-cylinder feedback control.
[0006]
However, according to such means, during this open loop control period, unavoidable factors such as fuel properties and characteristic variations of the injectors are damaged, and the air-fuel ratios for lean control (for example, the air-fuel ratio of all cylinders) 17: 1) is difficult to achieve, and the expected HC purification efficiency cannot be obtained.
[0007]
Further, the cylinder-by-cylinder feedback control is performed during the period until the air-fuel ratio sensor is activated, and the cylinders are set to a predetermined target air-fuel ratio (air-fuel ratio for lean control). There is also an idea that HC purification efficiency can be improved by feedback control of the air-fuel ratio. However, when such a predetermined target air-fuel ratio is applied, the air-fuel ratio of each cylinder cannot be made uniform because of variations in fuel properties and injector characteristics, and a sufficient effect can be obtained. There wasn't. In other words, the cylinder-by-cylinder air-fuel ratio must be feedback-controlled to the target air-fuel ratio while preventing problems such as the engine being stopped during lean control. Therefore, the target air-fuel ratio is set to a single value (17: 1). This is because it is difficult to fix the air-fuel ratio for each cylinder to the target air-fuel ratio having a certain allowable range. Therefore, even if such cylinder-by-cylinder feedback control is performed, the air-fuel ratio of a certain cylinder varies such that the air-fuel ratio of another cylinder is 16: 1, the air-fuel ratio of other cylinders is 17: 1, and so on. It is extremely difficult to make it uniform to 1.
[0008]
The present invention has been made in view of such problems, and improves the exhaust gas purification efficiency after the engine is started until the air-fuel ratio sensor for detecting the air-fuel ratio and the three-way catalyst device are activated. It is an object of the present invention to provide an injection fuel control apparatus for an internal combustion engine that can be made to operate.
[0010]
[Means for Solving the Problems]
  Claim1In this case, an air-fuel ratio detecting means that is disposed in an exhaust system collecting portion of the 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; An air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder by setting an observer for inputting the air-fuel ratio and observing the internal state of the exhaust system based on a model that defines the behavior of the air-fuel ratio in the exhaust system; The cylinder-by-cylinder air-fuel ratio correction 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 an air-fuel ratio correction coefficient calculation means for calculating a coefficient, the latest learning value is obtained by learning the cylinder-by-cylinder air-fuel ratio correction coefficient calculated by the air-fuel ratio correction coefficient calculation means. Memorize sequentially And it has a learning storage means, the air-fuel ratio and the after-start lean-burn control periodDetection meansThe air-fuel ratio is detected during the lean burn control period after the start.Detection meansIs determined to be inactive, the air-fuel ratio correction coefficient calculating means stops calculating the cylinder-by-cylinder air-fuel ratio correction coefficient, and the cylinder-by-cylinder air-fuel ratio correction coefficient is replaced with a learning value stored in the learning storage means. Correction control for correcting the fuel injection amount for each cylinderStepEquippedThe learning storage means stores the latest learning value of the cylinder-by-cylinder air-fuel ratio correction coefficient in a predetermined storage area assigned to each cylinder and determined based on the engine speed and intake pressure of the multi-cylinder internal combustion engine. It is characterized by memorizing sequentially.
  According to claim 2, in the fuel injection control device for an internal combustion engine according to claim 1, the correction control means determines that the air-fuel ratio detection means is active during the after-start lean burn control period. It is determined whether or not a parameter representing the operating state of the multi-cylinder internal combustion engine is within a predetermined region, and when the parameter is not within the predetermined region, the air-fuel ratio correction coefficient calculation means is provided with a cylinder-by-cylinder air-fuel ratio. The calculation of the correction coefficient is stopped, and the cylinder-by-cylinder air-fuel ratio correction coefficient is replaced with a predetermined value to correct the cylinder-by-cylinder fuel injection amount..
  Further, according to claim 3, in the fuel injection control device for an internal combustion engine according to claim 2, the parameter includes an engine speed and an intake pressure of the multi-cylinder internal combustion engine, and the predetermined region is the engine It is predetermined based on the rotation speed and the intake pressure.
[0012]
[Action]
  Claim1In the internal combustion engine fuel injection amount control device ofIn a predetermined storage area assigned to each cylinder and determined based on the engine speed and intake pressure of the multi-cylinder internal combustion engineIf the air-fuel ratio correction coefficient for each cylinder is learned and stored, and it is determined that the air-fuel ratio sensor is not yet activated during the lean burn after starting, it is based on the stored learning value of the air-fuel ratio correction coefficient for each cylinder. Then, the fuel injection amount for each cylinder is corrected.
  Further, in the fuel injection amount control apparatus for an internal combustion engine according to claim 2, if it is determined that the air-fuel ratio sensor is active during the lean burn control period after the start, the parameter indicating the operating state of the multi-cylinder internal combustion engine has a predetermined range. If the parameter is not within the predetermined range, the air-fuel ratio correction coefficient calculation means stops calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient, and the cylinder-by-cylinder air-fuel ratio correction coefficient is set in advance. The cylinder-specific fuel injection amount is corrected by substituting the determined predetermined value.
Further, in the fuel injection amount control apparatus for an internal combustion engine according to claim 3, the parameter is composed of the engine speed and the intake pressure of the multi-cylinder internal combustion engine, and the predetermined region is determined in advance based on the engine speed and the intake pressure. Determined.
[0013]
【Example】
An embodiment of a fuel injection control device for an internal combustion engine according to 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.
[0014]
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.
[0015]
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.
[0016]
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.
[0017]
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.
[0018]
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).
[0019]
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.
[0020]
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.
[0021]
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.
[0022]
As the wide area air-fuel ratio sensor 54, the LAF sensor disclosed in Japanese Patent Laid-Open No. 2-11842 previously applied by the applicant of this 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.
[0023]
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.
[0024]
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).
[0025]
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.
[0026]
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.
[0027]
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.
[0028]
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 and the like, and the third feedback system calculation process is performed in step S800 to obtain the cylinder specific air-fuel ratio correction coefficient #nKLAF. In step S900, the basic fuel injection amount TiM-F is set to the target air-fuel ratio correction coefficient KCMDM. 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.
[0029]
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.
[0030]
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. 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.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
In step S518, the opening cross section A of the bypass passage 34 is shown._BYPASSTaking into account
[0036]
[Expression 1]

[0037]
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.
[0038]
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.
[0039]
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 coolant temperature Tw, the purge gas concentration PUG, and the exhaust gas recirculation rate. 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.
[0040]
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.
[0041]
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).
[0042]
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.
[0043]
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.
[0044]
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. 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.
[0045]
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.
[0046]
[Expression 2]

[0047]
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.
[0048]
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.
[0049]
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,
[0050]
[Equation 3]

[0051]
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.
[0052]
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).
[0053]
Note that the negative result in step S614 is when the target air-fuel ratio KCMD (k) to be controlled is greatly deviated from the stoichiometric air-fuel ratio. Jump to S622.
[0054]
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.
[0055]
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 state.₂By 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.
[0056]
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 “switching 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.
[0057]
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.
[0058]
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.
[0059]
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:
[0060]
[Expression 4]

[0061]
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).
[0062]
Next, multiply it by a predetermined coefficient to obtain P-term KLAFP (k), I-term KLAFI (k), and D-term KLAFD (k),
[0063]
[Equation 5]

[0064]
I ask.
[0065]
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.
[0066]
[Formula 6]

[0067]
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.
[0068]
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.
[0069]
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 plant 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.
[0070]
[Expression 7]

[0071]
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.
[0072]
[Equation 8]

[0073]
[Equation 9]

[0074]
[Expression 10]

[0075]
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.
[0076]
## EQU11 ##

[0077]
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 ′).
[0078]
In this way, 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).
[0079]
[Expression 12]

[0080]
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.
[0081]
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.
[0082]
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.
[0083]
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.
[0084]
That is, for example, when the air-fuel ratio of the exhaust system collecting portion is as shown in FIG. 10 with respect to TDC, the air-fuel ratio recognized by the control unit 36 becomes a completely different value depending on the sampling 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 inevitably is affected 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.
[0085]
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.
[0086]
[Formula 13]

[0087]
When this is discretized with a period ΔT, it is as shown in Equation 14. FIG. 13 is a block diagram of Equation 14.
[0088]
[Expression 14]

[0089]
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.
[0090]
[Expression 15]

[0091]
[Expression 16]

[0092]
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.
[0093]
[Expression 17]

[0094]
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 air-fuel ratio of the exhaust system collecting portion is expressed as the time contribution of the air-fuel ratio of each cylinder. 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. Incidentally, the air-fuel ratio (or fuel-air ratio) means a true value obtained by correcting the response delay previously obtained by Equation 17.
[0095]
[Formula 18]

[0096]
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.
[0097]
Further, the equation of state is as shown in Equation 19.
[0098]
[Equation 19]

[0099]
Further, if the air-fuel ratio of the collecting portion is y (k), the output equation can be expressed as in Expression 20.
[0100]
[Expression 20]

[0101]
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.
[0102]
[Expression 21]

[0103]
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.
[0104]
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.
[0105]
[Expression 22]

[0106]
[Expression 23]

[0107]
[Expression 24]

[0108]
From this, A-KC is obtained as shown in Equation 25.
[0109]
[Expression 25]

[0110]
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.
[0111]
[Equation 26]

[0112]
Here, when y (k) is inputted, the system matrix of the observer, that is, the Kalman filter, is expressed as in Expression 27.
[0113]
[Expression 27]

[0114]
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.
[0115]
[Expression 28]

[0116]
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.
[0117]
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.
[0118]
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 cylinder-by-cylinder air-fuel ratio. 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 Expression 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.
[0119]
[Expression 29]

[0120]
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, By calculating the deviation (corresponding to the second derivative) #nDDKACT of the deviation #nDKACT (m) obtained this time and the previously obtained deviation #nDKACT (m-1), and applying these calculation results Then, the KP term, KI term, and KD term of the PID control law corresponding to each cylinder #n are obtained, and finally, by applying these KP term, KI term, and KD term, the cylinder-specific air-fuel ratio correction coefficient #nKLAF is obtained. Ask. 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.
[0121]
[30]

[0122]
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
[0123]
[31]

[0124]
(N is a cylinder).
[0125]
The basic principle of the sampling operation block sel-V, the observer, and the third feedback system has been described above.
Further, as shown in FIG. 19, the third feedback system includes an appropriate control unit REF that performs appropriate cylinder-by-cylinder feedback control for improving exhaust gas purification efficiency at the time of lean burn control after startup. It is attached to the PID block. Details of the function of the appropriate control unit REF will be described later together with the flowchart of FIG.
[0126]
First, when it is not during lean burn control after start-up (when the internal combustion engine 10 is in a normal operating state), learning processing is performed on the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF obtained by the PID control law based on Equation 32. 26, the learning data #nKLAFREF is stored one by one in a predetermined storage area determined by the engine speed Ne and the intake pressure Pb as shown in FIG. 26, and is repeatedly updated to new learning data #nKLAFREF. Therefore, when the internal combustion engine 10 is stopped, the most recently obtained learning data #nKLAFREF is stored and held in the storage area.
[0127]
[Expression 32]

[0128]
Note that Equation 32 is obtained by learning data #nKLAFREF stored at the lattice point (i, j) of the recording area previously obtained (k−1)._{i, j}The value obtained by multiplying (k-1) by the coefficient (β-1) and the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF (k) obtained this time (k) by the PID control law are multiplied by the coefficient β. Learning data #nKLAFREF by adding the obtained value_{i, j}(k) is requested.
[0129]
Further, the storage area shown in FIG. 26 is allocated in advance in the RAM 74 for each cylinder #n (= 1 to 4). Further, in any storage area, the range of the engine speed Ne in which the internal combustion engine 10 can operate is divided into a plurality of divisions (in this embodiment, i = 1 to 4 divisions), and the intake pressure Pb is similarly divided into a plurality of divisions. (In this embodiment, j = 1 to 4 is divided into four), thereby setting the operating state defined by the engine speed Ne and the intake pressure Pb to 16 lattice points (i, j). Learning data #nKLAFREF corresponding to the range of i, j)_{i, j}(k) is calculated based on Equation 32 and stored sequentially.
[0130]
Further, it is determined whether or not the lean burn control is performed after starting, and whether or not the LAF sensor 54 is activated. When the LAF sensor 54 is activated or not during the lean burn control after starting, By calculating the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF according to the PID control law, normal cylinder-by-cylinder feedback control is continued. On the other hand, when the LAF sensor 54 is not activated, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is continued. The calculation of the fuel ratio correction coefficient #nKLAF is stopped, the learning data in the storage area is searched for a map using the engine speed Ne and the intake pressure Pb as parameters, and the searched learning data is used as the cylinder specific air-fuel ratio correction coefficient #nKLAF. And the output fuel injection amount #Tout for each cylinder is corrected. That is, if the normal cylinder-by-cylinder feedback control is performed based on the detected air-fuel ratio KACT obtained when the LAF sensor 54 is not activated, the exhaust gas purification efficiency cannot be improved. As described above, when the output fuel injection amount #Tout for each cylinder is corrected based on the learned data of the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF, factors such as fuel properties and variations in the injector 22 are suppressed. Thus, a uniform cylinder-by-cylinder air-fuel ratio can be set.
[0131]
Further, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is fixed to a predetermined value (for example, 1.0) according to the operating state of the internal combustion engine 10, thereby substantially stopping the cylinder-by-cylinder feedback control. Therefore, the output fuel injection amount #Tout is obtained only by the second feedback system.
[0132]
Next, specific operations of the sampling operation block sel-V and the third feedback system will be described with reference to the flowcharts of FIGS.
[0133]
First, the operation until the sampling operation block sel-V obtains the air-fuel ratio (that is, KACT) of the exhaust system collecting portion 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.
[0134]
In FIG. 20, in step S402, the engine speed Ne, the intake pressure Pb, and the valve timing V / T are read out, and then the process proceeds to steps S404 and S406 to search the timing map for HiV / T and LoV / T, and in step S408. Then, the output of the LAF sensor 54 is sampled for HiV / T and LoV / T to obtain the detected air-fuel ratio KACT for HiV / T and the detected air-fuel ratio KACT for LoV / T. FIG. 22 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 LAF sensor 54 is constant, as shown in FIG. 23, 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.
[0135]
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 characteristic is 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.
[0136]
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. 24, the CPU core 64 can accurately recognize the maximum value and the minimum value of the sensor output. Then, feedback control shown in steps S700 and S800 in FIG. 5 is performed based on the accurate air-fuel ratio.
[0137]
Next, the operation of cylinder-by-cylinder feedback control in step S800 in FIG. 5 will be described based on the flowchart in FIG. Since the internal combustion engine 10 of the present embodiment is provided with the valve timing mechanism 300, after estimating the air-fuel ratio # nA / F for each cylinder according to the valve timings HiV / T and LoV / T, A feedback correction coefficient #nKLAF is obtained.
[0138]
In step S802 in FIG. 21, it is determined whether or not the LAF sensor 54 is activated by the appropriate control unit REF. For example, the output value LAF when the LAF sensor 54 is not activated is measured in advance and stored in the RAM 74 or the like, and when the measured value corresponds to this stored value, the LAF sensor 54 is not yet activated. Judge. If it is determined that it is activated, the process proceeds to step S816 and subsequent steps. If it is determined that it is not activated, the process proceeds to step S804.
[0139]
In steps S804 and S806, the cooling water temperature Tw is T_L≦ Tw ≦ T_HAnd whether the throttle valve 16 is within the predetermined temperature range and the opening θ of the throttle valve 16_THIs the predetermined value θ_LIt is determined whether or not: In this example, the temperature is T_L= 0 ° C, T_HBy setting to 30 ° C., the lean burn control execution temperature after starting is set by determining whether or not an appropriate temperature for operating the internal combustion engine 10 is determined._LIs set to 3 °. When these conditions are satisfied, the process proceeds to step S808. When the conditions are not satisfied, the lean burn control after the start is permitted, and the process proceeds to step S810.
[0140]
In step S808, since the lean burn control after the start is permitted, the basic value is corrected by multiplying the basic value KBS of the air-fuel ratio by the lean correction coefficient 0.89.
[0141]
In step S810, the storage area shown in FIG. 26 is searched by using the engine speed Ne and the intake pressure Pb as parameters to obtain learning data #nKLAFREF for the cylinder #n, and then in step S812, the searched learning is performed. Data #nKLAFREF is replaced with cylinder specific air-fuel ratio correction coefficient #nKLAF and held. Further, the calculation of the cylinder specific air-fuel ratio correction coefficient #nKLAF by the PID control law is stopped. Therefore, when the output fuel injection amount #nTout for each cylinder is calculated in step S900 shown in FIG. 5, it is corrected by the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF replaced with the learning data #nKLAFREF.
[0142]
In this way, when the LAF sensor 54 is not activated yet during the lean burn control period after start-up, the output fuel injection amount #nTout is corrected by the learning data #nKLAFREF, so that the fuel properties, variations in the injector 22, etc. Thus, a uniform cylinder-by-cylinder air-fuel ratio can be set.
[0143]
On the other hand, if it is determined in step S802 that the LAF sensor 54 is activated, the processing in steps 816 to S822 causes the engine speed Ne and the intake pressure Pb representing the operating state to be within a predetermined feedback range for each cylinder. Judgment whether or not there is. It is determined whether or not the operating state is within a predetermined feedback area for each cylinder.
[0144]
Here, the cylinder-by-cylinder feedback area sets conditions under which the cylinder-by-cylinder feedback control can be executed, as indicated by the hatched area in the graph of FIG. 25. The cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is set to a fixed value (1.0) by the process of S814, so that the cylinder-by-cylinder feedback control is substantially stopped. In order to perform control, the process proceeds to steps S824 to S826.
[0145]
That is, in FIG. 25, 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.
[0146]
In order to make such a condition determination, in steps S816 and S818, 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 when both conditions are satisfied, the process proceeds to step S820. When even one of the conditions is not satisfied, the process proceeds to step S814, and the values of all cylinder air-fuel ratio correction coefficients # 1KLAF to #nKLAF are set to 1. Set to 0.
[0147]
In step S820, the lower limit P of the intake pressure corresponding to the engine speed Ne._OBSVLIs retrieved, and in step S822, the intake pressure Pb is reduced to its lower limit value P._OBSVLJudge whether it is larger. If the determination is negative, the process proceeds to step S814, and the values of all cylinder feedback correction coefficients # 1KLAF to #nKLAF are set to 1.0. On the other hand, if the result is affirmative in step S822, the process proceeds to step S824.
[0148]
In step S824, the target value KCMDOBSV and the cylinder-by-cylinder air-fuel ratio correction #nKLAF are calculated from Equations 30 and 31. Therefore, the adder / subtracter provided in the feedback path for each cylinder operates so as to reduce the deviation between the cylinder-by-cylinder air-fuel ratio # nA / F estimated by the observer 0 BSV and the target value KCMDOBSV. In step S900 shown in FIG. 5, the output fuel injection amount #nTout for each cylinder is obtained. Further, in step S826, as described above, learning data #nKLAFREF is given according to Equation 32._{i, j}(k) is calculated and stored in the storage area shown in FIG.
[0149]
As described above, according to this embodiment, during the period from the start of the engine to the activation of the LAF sensor 54, the output fuel for each cylinder is determined based on the learning data #nKLAFREF obtained immediately before the engine is stopped. By performing the first process of correcting the injection amount #nTout, even if the LAF sensor 54 is inactive, it is possible to compensate for variations in the injector 22 and improve the exhaust gas cleaning efficiency. In particular, unlike the prior art, the target air-fuel ratio is not set within an allowable range having a certain width, so that the variation in the air-fuel ratio due to the variation in the injectors 22 is greatly reduced, and the exhaust gas cleaning efficiency is improved. Can do.
[0150]
Then, after the catalytic devices 28 and 30 are activated, the exhaust gas cleaning efficiency can be improved by normal cylinder-by-cylinder feedback control.
[0151]
In this embodiment, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is learned, and feedback control is performed based on the learning data obtained by this learning. However, the cylinder-by-cylinder air-fuel ratio estimated by the observer OBSV is used. # NA / F may be learned, and this learning data may be applied to the PID control law. That is, in steps S824 and S826 in FIG. 21, the cylinder-by-cylinder air-fuel ratio # nA / F is learned and stored in a predetermined storage area, and when the LAF sensor 54 is not yet activated during the lean burn control after the start, In S810 and S812, the cylinder-by-cylinder air-fuel ratio # nA / F is applied to obtain the cylinder-by-cylinder air-fuel ratio #nKLAF by the PID control law.
[0152]
Furthermore, the LAF sensor 54 provided in the exhaust system and the O₂The arrangement of the sensor 56 and the catalyst devices 28 and 30 is not limited to the case shown in FIGS.
[0153]
For example, as shown in FIG. 27, an HC trap catalyzer TR may be provided between the catalyst devices 28 and 30. That is, hydrocarbons (HC) are trapped until the catalyst devices 28 and 30 are activated, and after the catalyst devices 28 and 30 are activated, the trapped HC is trapped by the catalyst devices 28 and 30. Clean. According to this configuration, HC trapping by the HC trap catalyzer TR is performed while correcting the variation in the air-fuel ratio for each cylinder during the lean burn control period after starting, so that the trap efficiency of the HC trap catalyzer TR is improved. Therefore, the exhaust gas cleaning efficiency can be further improved.
[0154]
Further, as shown in FIG. 28, even if the light-off catalyzer LCAT and the electric heat catalyzer EHC are provided in front of the main catalyst device CAT, the air-fuel ratio of each cylinder is changed during the lean burn control period after starting. Since a synergistic effect with correcting the variation can be obtained, the exhaust gas cleaning efficiency can be further improved.
[0155]
Further, as shown in FIG. 29, a light-off catalyzer LCAT and an electric heat catalyzer EHC are provided in front of the main catalyst device CAT, and an HC trap catalyzer TR is further arranged in front of the electric heat catalyzer EHC. However, similarly, the exhaust gas cleaning efficiency can be further improved.
[0156]
Furthermore, as shown in FIG. 30, a light-off catalyzer LCAT and an electric heat catalyzer EHC are provided in front of the main catalyst device CAT, and further, separate from the HC trap catalyzer TR in front of the electric heat catalyzer EHC. Similarly, even when the catalyst device CAT is arranged, the exhaust gas cleaning efficiency can be further improved.
[0157]
As described above, when the control for correcting the variation in the air-fuel ratio for each cylinder is performed during the lean burn control period after the start of the present invention, the functions of various catalyst devices are fully exhibited and the exhaust gas cleaning efficiency is improved. It is possible to exhibit an excellent synergistic effect.
[0159]
【The invention's effect】
  Claim1In the internal combustion engine fuel injection amount control device ofIn a predetermined storage area assigned to each cylinder and determined based on the engine speed and intake pressure of the multi-cylinder internal combustion engine,If the air-fuel ratio correction coefficient for each cylinder is learned and stored, and it is determined that the air-fuel ratio sensor is not yet activated during the lean burn after starting, it is based on the stored learning value of the air-fuel ratio correction coefficient for each cylinder. Since the fuel injection amount for each cylinder is corrected, even when the air-fuel ratio sensor is not yet activated and an accurate air-fuel ratio cannot be detected, it is possible to purify the exhaust gas such as reducing hydrocarbons.
  In the fuel injection amount control apparatus for an internal combustion engine according to claim 2, if it is determined that the air-fuel ratio sensor is active during the lean burn control period after start-up, the parameter indicating the operating state of the multi-cylinder internal combustion engine is within a predetermined region. If the parameter is not within the predetermined range, the air-fuel ratio correction coefficient calculation means stops the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient, and the cylinder-by-cylinder air-fuel ratio correction coefficient is determined in advance. The cylinder-by-cylinder fuel injection amount is corrected by substituting the predetermined value. By substituting for a predetermined value, the cylinder-by-cylinder feedback control can be substantially stopped, thereby purifying exhaust gas such as reducing hydrocarbons.
  In the fuel injection amount control apparatus for an internal combustion engine according to claim 3, the parameter is composed of the engine speed and the intake pressure of the multi-cylinder internal combustion engine, and the predetermined region is predetermined based on the engine speed and the intake pressure. Therefore, it is possible to reliably purify the exhaust gas such as reducing hydrocarbons.
[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 third 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 a flowchart illustrating the operation of a third feedback system (cylinder feedback system).
FIG. 22 is an explanatory diagram showing characteristics of a timing map used in the flowchart of FIG.
FIG. 23 is an explanatory diagram further illustrating the characteristics of the timing map used in the flowchart of FIG. 21;
FIG. 24 is a timing chart for explaining the sampling operation of the sampling operation block (sel-V);
FIG. 25 is an explanatory diagram for explaining a feedback area for each cylinder;
FIG. 26 is an explanatory diagram for explaining a map configuration of a storage area for storing learning data.
FIG. 27 is an explanatory view showing a modification of the exhaust gas purification mechanism provided in the exhaust system.
FIG. 28 is an explanatory view showing another modified example of the exhaust gas purification mechanism provided in the exhaust system.
FIG. 29 is an explanatory view showing still another modified example of the exhaust gas purification mechanism provided in the exhaust system.
FIG. 30 is an explanatory view showing still another modified example of the exhaust gas purification mechanism provided in the exhaust system.
[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 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, REF ... proper control unit.

Claims (3)

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;
Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine, the air-fuel ratio is input and an observer that observes the internal state of the exhaust system is set to estimate the air-fuel ratio of each cylinder Air-fuel ratio estimating means for
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 device for an internal combustion engine comprising an air-fuel ratio correction coefficient calculating means for calculating
It has learning storage means for learning the cylinder-by-cylinder air-fuel ratio correction coefficient calculated by the air-fuel ratio correction coefficient calculation means and sequentially storing the latest learning value, and also includes a lean burn control period after starting and the activity of the air-fuel ratio detection means If the air-fuel ratio detection means is determined to be inactive during the after-start lean burn control period, the air-fuel ratio correction coefficient calculation means stops calculating the cylinder-by-cylinder air-fuel ratio correction coefficient, and is replaced with the learning value stored cylinder air-fuel ratio correction coefficient in the learning and memory means comprising a correction control hand stage to correct the cylinder fuel injection amount,
The learning storage means sequentially stores the latest learning value of the cylinder-by-cylinder air-fuel ratio correction coefficient in a predetermined storage area assigned to each cylinder and determined based on the engine speed and intake pressure of the multi-cylinder internal combustion engine. A fuel injection control device for an internal combustion engine, characterized by storing the fuel. When the correction control means determines that the air-fuel ratio detection means is active during the lean burn control period after starting, it determines whether or not a parameter indicating an operating state of the multi-cylinder internal combustion engine is within a predetermined region. When the parameter is not within the predetermined region, the air-fuel ratio correction coefficient calculating means stops calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient, and the cylinder-by-cylinder air-fuel ratio correction coefficient is set to a predetermined value. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the fuel injection amount for each cylinder is corrected by replacement . The internal combustion engine according to claim 2, wherein the parameter includes an engine speed and an intake pressure of the multi-cylinder internal combustion engine, and the predetermined region is determined in advance based on the engine speed and the intake pressure. Fuel injection control device.

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