JP3642171B2 - Diesel engine exhaust purification system - Google Patents

Description

ただし、Ｒ ： 気体定数
Ｋvol ： １シリンダ容積／吸気系容積
Ｋpm、Ｏpm ： 定数
の式（理論式）により吸気圧Ｐmを計算する。なお、Ｐmの初期値はＲＯＭに記憶させておく。
【００５８】
図６は排気圧（ＥＧＲ取り出し口）の演算フローである。
【００５９】
ステップ１ではシリンダから排出される排気量Ｑexh、排気温度Ｔexh、エンジン回転数Ｎeを読み込む。ただし、排気量Ｑexhと排気温度Ｔexhの各パラメータの演算については、別のフローにより後で詳しく説明する。
【００６０】
ステップ２では排気圧Ｐexhを
Ｐexh＝（Ｑexh×Ｎe／Ｋcon）²×Ｔexh×Ｋpexh＋Ｏpexh … （２）
ただし、Ｋcon、Ｋpexh、Ｏpexh：定数
の式（次元解析より求めた実験式）により計算する。なお、Ｐexhの初期値はＲＯＭに記憶させておく。
【００６１】
次に上記した各パラメータの演算方法について説明する。
【００６２】
まず、図７はシリンダ吸入新気量Ｑacを演算するフローである。ステップ１ではエアフローメータＡＭＦの出力電圧を読み込み、ステップ２でこの出力電圧からテーブル変換により吸気量を演算する。ステップ３では吸気脈動の影響をならすためこの吸気量演算値に対して加重平均処理を行う。
【００６３】
ステップ４ではエンジン回転数Ｎeを読み込み、ステップ５においてこの回転数Ｎeと前記した吸気量の加重平均値Ｑas0とから、１シリンダ当たりの吸気量Ｑac0を、
Ｑac0＝（Ｑas0／Ｎe）×ＫＣＯＮ ＃
ただし、ＫＣＯＮ ＃： 定数
の式により計算する。
【００６４】
ステップ６ではこのＱac0のｎ回演算分のディレイ処理を行い、このディレイ処理後の値Ｑac0・Ｚ^-nをコレクタ５２ａ入口の新気量Ｑacｎとして算出する。これはエアフローメータ５５からコレクタ５２ａ入口までの吸入空気の遅れを考慮したものである。
【００６５】
ステップ７では容積比Ｋvolと体積効率相当値Ｋinを用い、上記のコレクタ５２ａ入口の新気量Ｑacｎから
Ｑac＝Ｑac_n-1×（１−Ｋvol×Ｋin）＋Ｑacｎ×Ｋvol×Ｋin … （３）
ただし、Ｑac_n-1：Ｑacの前回値
の式により遅れ処理を行ってシリンダ吸入新気量（シリンダに吸入される新気量）Ｑacを求める。これはコレクタ５２ａ入口からシリンダまでの吸入空気の遅れを考慮したものである。
【００６６】
図８はシリンダ吸入ＥＧＲ量Ｑecを演算するフローである。
【００６７】
この演算内容は上記図７に示したシリンダ吸入新気量Ｑacの演算方法と同様である。ステップ１で後述（図１６参照）のようにして求めるＥＧＲ量Ｑeを読み込み、ステップ２でエンジン回転数Ｎeを読み込む。ステップ３でＱeに対して加重平均処理を行い、ステップ４ではＱeの加重平均値であるＱes0とＮeと定数ＫＣＯＮ ＃ とからコレクタ５２ａ入口かつ１シリンダ当たりの吸入ＥＧＲ量Ｑecｎを計算する。さらに、ステップ５でこのコレクタ５２ａ入口かつ１シリンダ当たりの吸入ＥＧＲ量Ｑecｎと容積比Ｋvol、体積効率相当値Ｋinを用いて、
Ｑec＝Ｑec_n-1×（１−Ｋvol×Ｋin）＋Ｑecｎ×Ｋvol×Ｋin … （４）
ただし、Ｑec_n-1：Ｑecの前回値
の式により遅れ処理を行ってシリンダ吸入ＥＧＲ量Ｑecを計算する。これはコレクタ５２ａ入口からシリンダまでのＥＧＲガスの遅れを考慮したものである。
【００６８】
図９は吸入新気温度Ｔaを演算するフローである。ステップ１では吸気圧の前回値Ｐm_n-1と吸気温度検出値Ｔa0を読み込み、この吸気圧の前回値Ｐm_n-1に基づいてステップ２で圧力補正係数Ｋtmpiを、Ｋtmpi＝Ｐm_n-1×ＰＡ ＃ の式より計算する。ただし、ＰＡ ＃ は定数である。
【００６９】
そして、ステップ３ではこの圧力補正係数Ｋtmpiに基づいてコレクタ５２ａ入口での吸入新気温度Ｔaを、Ｔa＝Ｔa0×Ｋtmpi＋ＴＯＦＦ ＃ の式（近似式）により計算する。ただし、ＴＯＦＦ ＃ は定数である。ＴＯＦＦ ＃ は水温や車速等により補正してもよい。
【００７０】
図１０はコレクタ５２ａ入口のＥＧＲガス温度Ｔeを演算するフローである。ステップ１で排気温度ＴexhとＥＧＲ通路内での排気温度降下係数ＫＴＬＯＳ ＃を読み込み、コレクタ入口５２ａのＥＧＲガス温度Ｔeを、Ｔe＝Ｔexh×ＫＴＬＯＳ ＃ の式により計算する。これはＥＧＲ取り出し口よりコレクタ入口までの温度降下を考慮したものである。なお排気温度Ｔexhの演算については後述する。
【００７１】
図１１は上記した体積効率相当値Ｋinを演算するフローである。ステップ１でシリンダ吸入新気量Ｑac、主噴射の目標燃料噴射量（以下単に燃料噴射量という）Ｑf、エンジン回転数Ｎeを読み込む（ただし、燃料噴射量Ｑfについては図１９により後述する）。ステップ２、３ではシリンダ吸入新気量Ｑacと回転数Ｎeとから図１２を内容とするマップを検索して体積効率基本値ＫinＨ１を、また燃料噴射量Ｑfと回転数Ｎeから図１３を内容とするマップを検索して体積効率負荷補正値ＫinＨ２を求め、ステップ４においてこれらＫinＨ１とＫinＨ２を乗算して体積効率相当値Ｋinを求める。
【００７２】
図１４は排気温度Ｔexhを演算するフローである。ステップ１、２では燃料噴射量のサイクル処理値Ｑf0とシリンダ吸気温度のサイクル処理値Ｔn0を読み込む（ただし、いずれも図１８により後述する）。さらに、ステップ３で排気圧の前回値Ｐexh_n-1を読み込む。
【００７３】
ステップ４では燃料噴射量のサイクル処理値Ｑf0から図１５を内容とするテーブルを検索して排気温度基本値Ｔexhbを求める。
【００７４】
ステップ５で前記した吸気温度のサイクル処理値Ｔn0から排気温度の吸気温度補正係数Ｋtexh1を、Ｋtexh1＝（Ｔn0／ＴＡ ＃ ）^KN # の式により計算する。ただし、ＴＡ ＃、 ＫＮ ＃ は定数である。
【００７５】
次に、ステップ６で排気温度の排気圧力補正係数Ｋtexh2を、排気圧の前回値Ｐexh_n-1から、Ｋtexh2＝（Ｐexh_n-1／ＰＡ ＃ ）⁽ # ^Ke-1)/ # ^Keの式により計算する。ただし、ＰＡ ＃、＃ Ｋeは定数である。
【００７６】
そして、ステップ７では、排気温度基本値Ｔexhbに各補正係数Ｋtexh1、Ｋtexh2を乗じて排気温度Ｔexhを計算する。
【００７７】
図１６はＥＧＲ量Ｑeを演算するフローである。ステップ１では上記した吸気圧Ｐm、排気圧Ｐexh、ＥＧＲ弁実開度としてのＥＧＲ弁実リフト量Ｌiftsを読み込む。あるいは、ステップモータのように目標値を与えれば実際のＥＧＲ弁リフト量が一義に決まる場合は、目標ＥＧＲ弁リフト量でもよい。
【００７８】
ステップ２では、このＥＧＲ弁実リフト量Ｌiftsから図１７を内容とするテーブルを検索して、ＥＧＲ弁流路面積Ａveを求める。
【００７９】
そして、ステップ３において、ＥＧＲ流量Ｑeを、これら吸気圧Ｐmと排気圧Ｐexh、ＥＧＲ弁流路面積Ａveとから、Ｑe＝Ａve×（Ｐexh−Ｐm）^1/2×ＫＲ ＃ の式により計算する。ただし、ＫＲ ＃ は定数で、ほぼ２× ρ （ρは排気密度）に等しい。
【００８０】
図１８はシリンダ吸入新気量、燃料噴射量、シリンダ吸気温度のサイクル処理のフローである。ステップ１でシリンダ吸入新気量Ｑac、燃料噴射量Ｑf、シリンダ吸気温度Ｔnを読み込む。なお、シリンダ吸気温度Ｔnは、シリンダに吸入される新気とＥＧＲガスとの混合ガスの平均温度、つまりＴn＝（Ｑac×Ｔa＋Ｑec×Ｔe）／（Ｑac＋Ｑec）の式により計算している（図２８により後述する）。
【００８１】
ステップ２ではこれらＱac、Ｑf、Ｔnを用いてＱexh＝Ｑac・Ｚ^-(CYLN#^-1)、Ｑf0＝Ｑf・Ｚ^-(CYLN#^-2)、Ｔn0＝Ｔn・Ｚ^-(CYLN#^-1)の式によりサイクル処理を施すが、これらはエアフローメータの読み込みタイミングに対しての位相差に基づく補正を行うものである。ただし、ＣＹＬＮ＃はシリンダ数である。たとえば４気筒エンジンでは、燃料の噴射は、エアフローメータの読み込みタイミングに対して１８０ＣＡ×（気筒数−２）ずれるので、シリンダ数から２引いた分だけディレイ処理を行う。
【００８２】
図１９は燃料噴射量Ｑfを演算するフローである。ステップ１でエンジン回転数Ｎeとコントロールレバー開度（アクセルペダル開度により定まる）ＣＬを読み込み、ステップ２でこれらＮeとＣＬから図２０を内容とするマップを検索して基本燃料噴射量Ｍqdrvを求める。
【００８３】
ステップ３ではこの基本燃料噴射量に対してエンジン冷却水温等に基づいて各種の補正を行い、この補正後の値Ｑf1に対してさらにステップ４で図２１を内容とするマップに基づいて、燃料噴射量の最大値Ｑf1MAXによる制限を行い、制限後の値を燃料噴射量Ｑfとして演算する。
【００８４】
これで先願装置と同様の部分の説明を終える。
【００８５】
次に、図２２はＥＧＲ弁指令開度としてのＥＧＲ弁指令リフト量Ｌifttを演算するフローである。ステップ１では吸気圧Ｐm、排気圧Ｐexh、要求ＥＧＲ量Ｔqe（図２４により後述する）を読み込む。ステップ２ではＥＧＲ弁要求流路面積Ｔavを、Ｔav＝ ｛ （Ｐexh−Ｐm）×ＫＲ ＃｝ ^1/2の式（流体力学の法則）で計算する。ただし、ＫＲ ＃ は補正係数である。ステップ３ではこのＥＧＲ弁要求流路面積Ｔavより図２３を内容とするテーブルを検索して目標ＥＧＲ弁開度としてのＥＧＲ弁目標リフト量Ｍliftを求め、この目標リフト量Ｍliftに対して、ステップ４において、ＥＧＲ弁の作動遅れ分の進み処理を行い、その進み処理後の値をＥＧＲ弁指令リフト量Ｌifttとして求める。
【００８６】
このようにして求められたＥＧＲ弁指令リフト量Ｌifttが図示しないフローによりステップモータ５７ａへと出力され、ＥＧＲ弁５７が駆動される。
【００８７】
図２４は上記の要求ＥＧＲ量Ｔqeの演算フローである。ステップ１でエンジン回転数Ｎe、目標ＥＧＲ率Ｍegr（図２５により後述する）、シリンダ吸入新気量Ｑac、燃料噴射量のサイクル処理値Ｑf0を読み込み、ステップ２でシリンダ吸入新気量Ｑacに目標ＥＧＲ率Ｍegrを乗ずることで目標吸入ＥＧＲ量Ｔqec0を計算する。
【００８８】
ステップ３ではこの目標吸入ＥＧＲ量Ｔqec0に対して
Ｔqec＝Ｔqec_n-1・（１−Ｋin・Ｋvol）＋Ｔqec0・Ｋin・Ｋvol … （５）
ただし、Ｔqec_n-1：Ｔqecｎの前回値
の式により吸気系容量分の進み処理を行って目標シリンダ吸入ＥＧＲ量Ｔqec（１シリンダ当たり）を求める。
【００８９】
ステップ４ではこの目標シリンダ吸入ＥＧＲ量Ｔqecと回転数Ｎeと定数ＫＣＯＮ＃とから要求ＥＧＲ流量Ｔqe（全気筒分）を、Ｔqe＝（Ｔqec／Ｎe）×ＫＣＯＮ＃の式により計算する。
【００９０】
図２５は上記の目標ＥＧＲ率Ｍegrを演算するフローである。ステップ１でエンジン回転数Ｎeと燃料噴射量Ｑfとシリンダ吸気温度Ｔn（図２８により後述する）を読み込み、このうちＮeとＱfとから図２６を内容とするマップを検索して、目標ＥＧＲ率基本値Ｍegr0を求める。
【００９１】
ステップ３ではシリンダ吸入ガス温度Ｔintから図２７を内容とするテーブルを検索して目標ＥＧＲ率補正値Ｈegr1を求め、この目標ＥＧＲ率補正値Ｈegr1を目標ＥＧＲ率基本値Ｍegr0に乗ずることによって目標ＥＧＲ率Ｍegrを計算する。
【００９２】
図２８は上記のシリンダ吸気温度Ｔnを演算するフローである。ステップ１でシリンダ吸入新気量Ｑacと吸入新気温度Ｔaとシリンダ吸入ＥＧＲ量ＱecとＥＧＲガス温度Ｔeを読み込み、これらからＴn＝（Ｑac×Ｔa＋Ｑec×Ｔe）／（Ｑac＋Ｑec）の式によりシリンダ吸入新気とシリンダ吸入ＥＧＲガスの平均温度を求めてこれをシリンダ吸気温度Ｔnとする。
【００９３】
次に、ＮＯｘ触媒１にＨＣを供給するための後噴射の時期と量の制御について説明する。
【００９４】
図３０はターボチャージャ２のタービン２ｂ出口温度相当値Ｔexhcbを演算するフローである。ステップ１で排気圧（タービン入口圧でもある）Ｐexhと排気温度（タービン入口温度でもある）Ｔexhと排気流量Ｑexhを読み込み、ステップ２において排気流量Ｑexhと排気温度Ｔexhから図３１を内容とするマップを検索して基準タービン回転数Ｎtを、また排気流量Ｑexhから図３２を内容とするテーブルを検索してタービン出口排気圧（＝触媒入口排気圧）Ｐexhcを求める。
【００９５】
ステップ３では排気圧Ｐexhとこのタービン出口排気圧Ｐexhcの圧力比であるＰexh／Ｐexhcとタービン回転数Ｎtから図３３を内容とするマップ（タービン単体の圧力比、効率性能図より設定する）を検索して効率相当値ηtを求める。
【００９６】
ステップ４ではこのようにして求めた効率相当値ηtを排気温度Ｔexhに乗じた値をタービン出口温度相当値Ｔexhcbとして求める。
【００９７】
図３４は触媒入口温度相当値Ｔexhcを演算するフローである。ステップ１で上記のタービン出口温度相当値Ｔexhcbと排気量Ｑexhと車速ＶＳＰとを読み込み、ステップ２において、車速ＶＳＰから図３５を内容とするテーブルを検索して、車速による排気管表面からの車速温度降下係数ＫＴＥＬＯＳ１を、また同じく排気量Ｑ exhから図３６を内容とするテーブルを検索して、排気流速による排気管面への伝熱割合を示す排気流量降下係数ＫＴＥＬＯＳ２を求める。
【００９８】
そして、ステップ３ではこれら係数ＫＴＥＬＯＳ１とＫＴＥＬＯＳ２をタービン出口温度相当値Ｔexhcbに乗じた値を触媒入口排気温度相当値Ｔexhcとして計算する。これは、タービン２ｂ出口より触媒１入口までの排気温度の低下を考慮するものである。
【００９９】
図３７は、目標後噴射時期（目標とする後噴射開始時期）ＩＴafterの演算フローである。ステップ１で上記の触媒入口温度相当値Ｔexhcを読み込み、ステップ２においてこの触媒入口温度相当値Ｔexhcから図３８を内容とするテーブルを検索して目標後噴射時期ＩＴafterを求める。図３８において触媒入口温度相当値Ｔexhcが小さい温度域（つまり低負荷域）が主に使う領域であり、触媒入口温度相当値Ｔexhcが大きくなる領域（つまり高負荷域）で遅角させているのは、Ｔexhcが大きいとＨＣが燃えてしまうので、これを避けるためである。
【０１００】
図３９は触媒ベッド温度相当値Ｔexhbdの演算フローである。ステップ１で上記の触媒入口温度相当値Ｔexhcを読み込み、ステップ２において、
Ｔexhbd＝Ｔexhbd_n-1×ＴＤＢＥＤ＃＋Ｔexhc×（１−ＴＤＢＥＤ＃）… （６）
ただし、Ｔexhbd_n-1：Ｔexhbdの前回値
ＴＤＢＥＤ＃：定数（昇温時定数相当値）
の式（一次遅れの式）より触媒ベッド温度相当値Ｔexhbdを計算する。これは、触媒入口温度に対して応答遅れをもって触媒ベッド温度が変化するので、これを考慮したものである。なお、Ｔexhbdの初期値は一定値でよい。
【０１０１】
図４０は触媒１表面積と触媒１を通過するガスの質量流量との比であるＳＶ比の演算フローである。ステップ１で排気量Ｑexhを読み込み、ステップ２においてＳＶ比＝Ｑexh×ρ／ＳＣＡＴ＃の式よりＳＶ比を計算する。ただし、ρは排気代表比重、ＳＣＡＴ＃は触媒総表面積である。
【０１０２】
図４１は触媒１を通過する排気中の酸素濃度ＥＸo2の演算フローである。ステップ１で排気量Ｑexh、シリンダ吸入ＥＧＲ量Ｑec、シリンダ吸入新気量Ｑac、エンジン回転数Ｎe、燃料噴射量Ｑfを読み込み、ステップ２で排気量Ｑexhと回転数Ｎeを用いて
Ｑdry＝Ｑexh／ ｛ ＭＯＬＡＩＲ＃×（Ｎe／2）×ＮＣＹＬ＃×60×1000 ｝… （７）
ただし、ＭＯＬＡＩＲ＃：空気の見かけの分子量
ＮＣＹＬ＃：気筒数
の式より乾燥空気流量Ｑdryを求め、ステップ３で燃料噴射量Ｑfを用いて

ただし、ＨＦ＃：Ｈの質量比
ＣＦ＃：Ｃの質量比
ＡＣ＃：Ｃの原子量
ＡＨ＃：Ｈの原子量
の式より要求酸素量Ｑoを計算し、これら乾燥空気流量Ｑdry、要求酸素量Ｑoを用い、ステップ４において

ただし、Ｏ２ＡＩＲ＃：大気の酸素濃度
の式により酸素濃度Ｃeo2を計算する。
【０１０３】
ステップ５では、シリンダ吸入ＥＧＲ量Ｑecとシリンダ吸入新気量Ｑacを用いて実ＥＧＲ率相当値Ｒegrを、Ｒegr＝（Ｑec／Ｑac）×100の式により計算し、この実ＥＧＲ率相当値Ｒegrと上記の酸素濃度Ｃeo2を用い、ステップ６において、

の式により排気中の酸素濃度ＥＸo2を計算する。
【０１０４】
図４２は排気中のＨＣ／ＮＯｘ比の演算フローである。ステップ１でシリンダ吸入新気量Ｑac、エンジン回転数Ｎe、燃料噴射量Ｑf、目標主噴射時期（目標とする主噴射の開始時期）ＩＴs、実ＥＧＲ率相当値Ｒegrを読み込み、ステップ２でシリンダ吸入新気量Ｑacと燃料噴射量Ｑfを用いて空燃比Ｌambdaを、Ｌambda＝Ｑac／（ＴＨＡＦ＃×Ｑf）の式より計算する。ただし、ＴＨＡＦ＃は定数である。
【０１０５】
ステップ３ではＱfとＮeから図４３と図４４を内容とするマップを検索して基準ＮＯｘ排出量ＭＮＯｘと基準ＨＣ排出量ＭＨＣを求める。
【０１０６】
ステップ４から７まではこれらに対する各種補正値を演算する部分である。すなわち、ステップ４で目標主噴射時期ＩＴsから図４５を内容とするテーブルを検索することにより、基準となる噴射時期に対して運転中の噴射時期がずれている分だけＭＮＯｘとＭＨＣを補正するための値ＫＩＴＮＯＸとＫＩＴＨＣを、ステップ５で空燃比Ｌambdaから図４６を内容とするテーブルの検索により、基準となる空燃比に対して、運転中の空燃比がずれている分だけＭＮＯｘとＭＨＣを補正するための値ＫＡＦＮＯＸとＫＡＦＨＣを、ステップ６で実ＥＧＲ率相当値Ｒegrから図４７を内容とするテーブルの検索により、基準となるＥＧＲ率に対して、運転中のＥＧＲ率がずれている分だけＭＮＯｘとＭＨＣを補正するための値ＫＥＧＲＮＯＸとＫＥＧＲＨＣを、ステップ７で冷却水温Ｔwから図４８を内容とするテーブルの検索により、基準となる冷却水温に対して、運転中の冷却水温がずれている分だけＭＮＯｘとＭＨＣを補正するための値ＫＴＷＮＯＸとＫＴＷＨＣをそれぞれ求める。
【０１０７】
ここで、基準となる噴射時期、基準となる空燃比、基準となるＥＧＲ率、基準となる冷却水温とは、標準状態（吸気温度、冷却水温、大気圧）において、エンジン回転数と負荷（燃料噴射量）で設定される定常運転時の制御目標の値のことである。
【０１０８】
これら補正値を用い、ステップ８では

の式により基本ＮＯｘ排出量ＮＯｘＢと基本ＨＣ排出量ＨＣＢを計算し、これら２つの値ＮＯｘＢとＨＣＢから、ステップ９で実際のＨＣ／ＮＯｘ比であるＩ ＨＮrを、Ｉ ＨＮr＝ＨＣＢ／ＮＯｘＢの式により計算する。
【０１０９】
図４９は要求ＨＣ量ＨＣ０の演算フローである。ステップ１で燃料噴射量Ｑfとエンジン回転数Ｎeを読み込み、ステップ２でＱfとＮeから図５０を内容とするマップを検索して目標ＨＣ／ＮＯｘ比であるＴ ＨＮrを求め、ステップ３では
ＨＣ０＝（Ｔ ＨＮr−Ｉ ＨＮr）×ＨＣＢ … （１３）
の式より要求ＨＣ量ＨＣ０を計算する。
【０１１０】
通常、目標ＨＣ／ＮＯｘ比であるＴ ＨＮrより実際のＨＣ／ＮＯｘ比であるＩ ＨＮrのほうが小さいので、その差に応じて要求ＨＣ量ＨＣ０を求め、この値に基づいて後噴射量を演算（図５３により後述する）することで、エンジン回転数とエンジン負荷からマップ検索により後噴射量を求めるだけの従来装置と比較して、必要なＨＣ量だけを精度良く供給できるのである。
【０１１１】
図５１はＮＯｘ触媒１の前方もしくは内部にＨＣ吸着剤を装着した場合に、そのＨＣ吸着剤におけるＨＣの吸着・脱離量の演算フローである。ステップ１で触媒入口温度相当値Ｔexhcを読み込み、このＴexhcからステップ２において図５２を内容とするテーブルを検索して、ＨＣの吸着・脱離ゲインＧＫＣＡＴを求め、ステップ３においては
ＨＣＡＢ＝ＨＣＡＢ_n-1＋ＧＫＣＡＴ … （１４）
ただし、ＨＣＡＢ_n-1：ＨＣＡＢの前回値
の式により総ＨＣ吸着量指数ＨＣＡＢを計算する。
【０１１２】
ここで、吸着剤にＨＣが吸着されるときは、吸着・脱離ゲインＧＫＣＡＴが正となるため、総ＨＣ吸着量指数ＨＣＡＢがプラス側に増加し、この逆に吸着剤よりＨＣが脱離するときは、吸着・脱離ゲインＧＫＣＡＴが負となるため総ＨＣ吸着量指数ＨＣＡＢがマイナス側に減少する。つまり、ＨＣＡＢは吸着剤に吸着されているＨＣの総量に相当するわけである（ただし下限値は０）。
【０１１３】
ステップ４ではＧＫＣＡＴ ＜ ０（つまりＨＣの脱離モード）でかつ総ＨＣ吸着量指数ＨＣＡＢが０（つまりＨＣが全く吸着されていない）であるかどうか、また、ステップ５ではＧＫＣＡＴ ＞ ＨＣ（つまりＨＣの吸着モード）でかつ総ＨＣ吸着量指数ＨＣＡＢがＦＵＬＬ（つまり吸着剤へのＨＣ吸着量が満タン）であるかどうかみる。
【０１１４】
ＨＣ脱離モードでかつＨＣが全く吸着されていないときと、吸着モードでかつ吸着剤へのＨＣ吸着量が満タンのときとはステップ７に進んで、上記の要求ＨＣ量ＨＣ０をそのまま目標ＨＣ量であるＴ ＨＣとする。
【０１１５】
これに対して、上記２つのケース以外のとき（吸着剤への吸着量が満タンでなくＨＣが吸着されている状態や吸着剤にＨＣが存在し、そのＨＣが脱離している状態のとき）は、ステップ４、５よりステップ６に進んで、
Ｔ ＨＣ＝ＨＣ０＋ＧＫＣＡＴ×ＫＡＢ＃ … （１５）
ただし、ＫＡＢ＃：ＨＣ量への換算係数
の式により目標ＨＣ量Ｔ ＨＣを計算する。
【０１１６】
この（１５）式によれば、吸着剤にＨＣが吸着されるときは、吸着・脱離ゲインＧＫＣＡＴが正となって目標ＨＣ量Ｔ ＨＣが増量補正され、この逆に吸着剤よりＨＣが脱離するときは吸着・脱離ゲインＧＫＣＡＴが負となって目標ＨＣ量Ｔ ＨＣが減量補正される。これは、吸着剤にＨＣが吸着されるときは、その分のＨＣが触媒１に供給されない（つまり後噴射量が不足する）ことになり、また吸着剤からＨＣが脱離するときは、その分のＨＣが触媒１に余計に供給される（つまり後噴射量が多すぎる）ことになるので、これを修正するようにしたものである。
【０１１７】
図５３は後噴射量の演算フローである。ステップ１で触媒入口温度相当値Ｔexhc、触媒ベッド温度相当値Ｔexhbd、ＳＶ比、燃料噴射量Ｑf、エンジン回転数Ｎeを読み込む。
【０１１８】
ステップ２からステップ１３までは後噴射量を行う条件であるかどうかを判定する部分で、次の条件
〈１〉 フラグＦＴＥＸＨＣ＝１（つまり触媒入口温度相当値Ｔexhcがそのしきい値以上）である、
〈２〉 フラグＦＴＥＸＢＤ＝１（つまり触媒ベッド温度相当値Ｔexhbdがそのしきい値以上）である、
〈３〉 ＳＶ比がそのしきい値ＴＳＶ＃以下である（ステップ１２）、
〈４〉 回転数Ｎeがそのしきい値ＴＮＥ ＃ 以上かつ燃料噴射量Ｑfがそのしきい値ＴＱf＃以上である（ステップ１３）
の全てを満足するとき（後噴射条件の成立時）、ステップ１４以降に進んで後噴射量を算出し、上記いずれかの条件でも満足しないとき（後噴射条件の非成立時）にはステップ１８に進んで後噴射量を算出しない（後噴射量Ｑfaf＝０）。
【０１１９】
上記 〈１〉 と 〈２〉 は触媒１が活性化しているかどうかを確認するためのもので、触媒１が活性化していないのに後噴射を行ったのでは、燃費の悪化やＨＣの増大を招くので、これを防止するため、 〈１〉 と 〈２〉 を条件としたわけである。
【０１２０】
ここで、上記フラグＦＴＥＸＨＣとフラグＦＴＥＸＢＤは、触媒入口温度相当値Ｔexhcと触媒ベッド温度相当値Ｔexhbdに対するしきい値にヒステリシスを設けたために必要となるものである。２つのフラグＦＴＥＸＨＣとＦＴＥＸＢＤの設定方法は同様なので、フラグＦＴＥＸＨＣのほうで代表して述べると、フラグＦＴＥＸＨＣ＝１の状態で触媒入口温度相当値Ｔexhcが高い状態にあり、この状態から温度低下してきて第１温度しきい値Ｔtexhc1 ＃ を下回った段階ではフラグＦＴＥＸＨＣを “ ０ ” に切換えず、さらに温度低下して第２温度しきい値Ｔtexhc2 ＃ （Ｔtexhc2 ＃＜ Ｔtexhc1 ＃ ）を下回ったときやっとフラグＦＴＥＸＨＣを “ ０ ” に切換える（ステップ２、３、４）。この逆にフラグＦＴＥＸＨＣ＝０の状態で触媒入口温度相当値Ｔexhcが低く、この状態から温度上昇しても第２温度しきい値Ｔtexhc2 ＃ を上回った段階ではフラグＦＴＥＸＨＣを“ １ ” に切換えず、さらに温度上昇して第１温度しきい値Ｔtexhc1 ＃ を超えるとフラグＦＴＥＸＨＣを “ １ ” に切換える（ステップ２、５、６）のである。
【０１２１】
さて、後噴射条件の成立時は、ステップ１４で目標ＨＣ量であるＴ ＨＣと排気中の酸素濃度ＥＸo2を読み込み、このうち酸素濃度ＥＸo2からステップ１５において図５４を内容とするテーブルを検索して、ＨＣ量補正係数Ｋqfを求め、またステップ１６において図５５を内容とするテーブルを用いて目標ＨＣ量で有るＴ ＨＣを基本後噴射量Ｑfaf0に変換する。ステップ１７ではこの基本噴射量Ｑfaf0に上記のＨＣ量補正係数Ｋqfを乗じて目標後噴射量Ｑfaf1を算出する。
【０１２２】
触媒１は排気中の酸素濃度（あるいは空気過剰率）に応じてＨＣを酸化してしまう作用があるため（図８４参照）、ＮＯｘを還元するためには排気中の酸素濃度に応じてＨＣが酸化される以上のＨＣを供給する必要があるのであるが、このように、排気中の酸素濃度ＥＸo2に応じて基本後噴射量Ｑfaf0を補正することで、触媒１が排気中の酸素濃度ＥＸo2に応じてＨＣを酸化する場合であっても、後噴射量を正確に算出できることになる。
【０１２３】
次に、図５６は主噴射時期の排気温度補正フローである。ステップ１で目標主噴射時期ＩＴsb、触媒入口温度相当値Ｔexhc、触媒ベッド温度相当値Ｔexhbdを読み込む。なお、目標主噴射時期ＩＴsbはエンジンの回転数と負荷より基本的に定まり、この基本値がＮＯｘ排出量や水温などにより補正されて求められる値である。
【０１２４】
ステップ２では、触媒活性排気温度しきい値Ｔ１＃と触媒入口温度相当値Ｔexhcの差ｄＴ１および触媒ベッド活性温度しきい値Ｔ２＃と触媒ベッド温度相当値Ｔexhbdの差ｄＴ２をそれぞれ計算し、ステップ３においてこれら温度差ｄＴ１とｄＴ２より図５７と図５８を内容とするテーブルを検索して主噴射時期の排気温度補正値ＩＴh1と主噴射時期の触媒表面温度補正値ＩＴh2を求める。ステップ４では目標主噴射時期ＩＴsbからこれら２つの補正値ＩＴh1とＩＴh2を差し引いた値を指令主噴射時期ＩＴsとすることによって、主噴射時期を遅角補正する。
【０１２５】
なお、ＩＴsという記号は、図５５までにおいては目標主噴射時期として述べているので紛らわしいが、図５５までにおいて述べた目標主噴射時期ＩＴsは図５６のＩＴsbとＩＴsのいずれであってもかまわない。
【０１２６】
ここで、主噴射時期が遅角補正されるのは、触媒活性排気温度しきい値Ｔ１＃に対して触媒入口温度相当値Ｔexhcがわずかに下回る場合や触媒ベッド活性温度しきい値Ｔ２＃に対して触媒ベッド温度相当値Ｔexhbdがわずかに下回る場合である。
【０１２７】
これを図５９を参照しながら具体的に説明すると、車速ＶＳＰの変化に対して、触媒入口温度相当値Ｔexhcのほうは応答良く変化するものの、触媒ベッド温度相当値Ｔexhbdのほうは遅れをもって変化している。この結果、両者がともに温度しきい値を超えるのは図示のＡ区間となり、図５３によればこのＡ区間でだけ後噴射が行われる（この後噴射によるＨＣのＮＯｘ触媒への供給によりＮＯｘの還元浄化が精度良く行われる）。
【０１２８】
この場合、Ａ区間に隣接するＢ区間やＣ区間は触媒ベッド温度相当値Ｔexhbdや触媒入口温度相当値Ｔexhcがこれに対応する温度しきい値を少し下回っているだけであるから、排気温度を少し高めてやりさえすれば、触媒ベッド温度相当値Ｔexhbdと触媒入口温度相当値Ｔexhcがともに温度しきい値を超えることになり（つまり後噴射条件が成立し）、後噴射が行われてＮＯｘ還元効率が高められる。
【０１２９】
そこで、触媒入口温度相当値Ｔexhcや触媒ベッド温度相当値Ｔexhbdがこれに対応する温度しきい値をわずかに下回る場合は、主噴射時期を遅角補正することにより、排気温度を上昇させて触媒１の活性域を拡大し、これによってＮＯｘ還元浄化を一段と進めるようにしたのである。
【０１３０】
このように、本発明の実施形態では、エンジンの回転数Ｎeとエンジンの負荷に基づいて基準ＨＣ排出量ＭＨＣと基準ＮＯｘ排出量ＭＮＯｘを演算し、これらに対して噴射時期補正値ＫＩＴＨＣ、ＫＩＴＮＯｘ、空燃比補正値ＫＡＦＨＣ、ＫＡＦＮＯＸ、水温補正値ＫＴＷＨＣ、ＫＴＷＮＯｘ、ＥＧＲ制御を行う場合はＥＧＲ補正値ＫＥＧＲＨＣ、ＫＥＧＲＮＯｘを演算し、これら補正値でこれに対応する前記基準値を補正して基本ＨＣ排出量ＨＣＢと基本ＮＯｘ排出量ＮＯｘＢを演算し、これらの比である実際のＨＣ／ＮＯｘ比Ｉ ＨＮrを演算し、この実際のＨＣ／ＮＯｘ比Ｉ ＨＮrと目標ＨＣ／ＮＯｘ比Ｔ ＨＮrの差に応じて要求ＨＣ量ＨＣ０を演算し、この要求ＨＣ量ＨＣ０に基づいて後噴射量Ｑfaf0を演算するので、運転中の主噴射時期、空燃比、水温、ＥＧＲ制御を行う場合はＥＧＲ率が基準となる主噴射時期、基準となる空燃比、基準となる水温、ＥＧＲ制御を行う場合は基準となるＥＧＲ率に対してそれぞれずれることがあっても、要求ＨＣ量を過不足なく求めることができ、これによってエンジン回転数とエンジン負荷からマップを検索して後噴射量を求めるものよりも、必要なＨＣ量だけを精度良く供給できる。
【０１３１】
この結果、図６０に示すように従来装置（図ではマップ制御で表示）に比べて後噴射による無駄なＨＣの供給を抑制できるとともに飛躍的に過渡運転時のＮＯｘ還元性能が向上することになった。
【０１３２】
また、特にＥＧＲ制御を行う場合に、ＮＯｘ転換率が低下するＳＶ比の大きい領域で後噴射を中止するので、この領域でも後噴射を実行することに伴うＨＣの過剰供給による白煙の発生や燃費の悪化を抑制することができる。
【０１３３】
図６１〜図８２は第２実施形態で、第１実施形態との関係は次の通りである。
【０１３４】
▲１▼図６１が図１に、図６２が図４に、図６３が図２５に、図７０が図２９に、図７１が図４２に、図７８〜図８１が図４９、図５０にそれぞれ対応する。
【０１３５】
▲２▼図２、図３、図５〜図２４、図２６〜図２８、図３０〜図４１、図５１〜図５９は第２実施形態でもそのまま用いる。図４３〜図４８は第２実施形態では用いない。
【０１３６】
▲３▼図６４〜図６９、図７２〜図７７を追加して設ける。
【０１３７】
さて、第１実施形態は、モデル規範制御によりＮＯｘ排出量を予測するものである。このため、系を物理則を用いて記述しているのであるが、その記述（モデル）が実際と合わない領域（たとえば、自動変速機付き車両によりモード走行を行わせる場合に車速を増すときシフトアップが行われるが、このシフトアップ時）があり、その領域で後噴射によるＨＣ量の過不足が生じ、ＨＣ排出量とＮＯｘ排出量がわずかながら増えることがわかっている。
【０１３８】
一方、従来、車両に適用できる小型で信頼性が高くかつ安価なＮＯｘ濃度センサがなかったため、ＮＯｘセンサを実車に適用した例がほとんどみあたらなかったが、近年のＮＯｘ濃度センサの研究、製造技術の発展により、実車に適用しうるセンサが開発されつつある（たとえば、ＳＡＥ９６０３４４で示される固体電解質タイプのＮＯｘ濃度センサや特開平７−３２５０５９号公報に示される単結晶様構造をもつ物質をＮＯｘ感応体としてＮＯｘ濃度を検出するものなど）。
【０１３９】
そこで、こうしたＮＯｘ濃度センサを用いてＮＯｘ排出量をフィードバック制御することが考えられる。
【０１４０】
この場合、制御したい量は触媒出口のＮＯｘ排出量であるから、ＮＯｘ濃度センサをＮＯｘ触媒１の下流に設け、このセンサ検出値に基づいてフィードバック制御しても、触媒自体が大きな遅れ要素となるので、フィードバック制御の制御ゲインを大きくとれない。このため、制御応答が悪くなるほか、制御精度もよくない。また、触媒により浄化されたガスを検出しなければならないため低濃度型のセンサが必要となり、検出精度の確保や生産バラツキの抑制、コスト抑制が困難である。
【０１４１】
そこで第２実施形態では、ＮＯｘ触媒１の上流にＮＯｘ濃度センサを設け、このセンサ検出値に基づいて実測ＮＯｘ排出量を演算し、この実測ＮＯｘ排出量を第１実施形態におけるＮＯｘ排出量の予測値に代えて用いるとともに、実測ＮＯｘ排出量が目標ＮＯｘ排出量と一致するように目標ＥＧＲ率をフィードバック制御することにより、モデルが実際と合わなくなる領域においても、後噴射によるＨＣ量の過不足を抑制して、ＨＣとＮＯｘの各排出量をさらに低減するとともに、ＮＯｘ濃度センサを用いていても、制御応答を高め、かつ高価な低濃度型のセンサを用いなくともよいようにしたものである。
【０１４２】
具体的には、まず触媒１の上流側に設けたＮＯｘ濃度センサ７２（図１参照）からのセンサ検出値を用いたＮＯｘ排出量のフィードバック制御について説明する。
【０１４３】
図６４は目標ＮＯｘ排出量ＴＮＯｘを演算するフローである。ステップ１で燃料噴射量Ｑfとエンジン回転数Ｎeを読み込み、これらから図６５を内容とするマップを検索して目標ＮＯｘ排出量ＴＮＯｘを求める。
【０１４４】
図６６は実測ＮＯｘ排出量ＲＮＯｘを演算するフローである。ステップ１でシリンダ吸入新気量Ｑacと燃料噴射量のサイクル処理値Ｑf0を読み込み、これらを用い、ステップ２において吸気乾燥モル流量Ｍ Ｑacを

ただし、ＭＯＬＡＩＲ＃：空気の見かけの分子量
ＨＦ＃：Ｈの質量比
ＣＦ＃：Ｃの質量比
ＡＨ＃：Ｈの原子量
の式により計算する。
【０１４５】
ステップ３ではエンジン回転数Ｎeを読み込む。ステップ４でＮＯｘ濃度センサ７２の出力電圧ＮＯｘ ioを読み込み、このセンサ出力電圧ＮＯｘ ioからステップ５においてセンサ出力電圧とＮＯｘ濃度の関係を与えたテーブルを検索して、ＮＯｘ濃度Ｃ ＮＯｘを求め、さらにステップ７では、このＮＯｘ濃度Ｃ ＮＯｘ、上記の吸気乾燥モル流量Ｍ Ｑac、エンジン回転数Ｎeを用いて、定常状態でのＮＯｘ排出量（質量流量）ＲＮＯｘ０を

ただし、ＡＮ：Ｎの分子量
ＡＯ：Ｏの分子量
ＮＣＹＬ＃：気筒数
の式により計算する。
【０１４６】
ステップ８では、ＮＯｘ濃度センサ７２の検出遅れを一次遅れとみなし、

ただし、ＲＮＯｘ_n-1：ＲＮＯｘの前回値
Ｋ ＮＯｘｉ＃：時定数相当値
の式により時定数相当値分だけの進み処理を行った値を実測ＮＯｘ排出量ＲＮＯｘとして求める。なお、ＲＮＯｘの初期値は固定値（ ≒ １）である。
【０１４７】
図６７は目標ＥＧＲ率のフィードバック補正量Ｈegr2を演算するフローである。ステップ１で上記の目標ＮＯｘ排出量ＴＮＯｘ、実測ＮＯｘ排出量ＲＮＯｘ、目標ＥＧＲ率基本値Ｍegr0を読み込み、ステップ２において実測ＮＯｘ排出量ＲＮＯｘと目標ＮＯｘ排出量ＴＮＯｘの差ｄＮＯｘ（＝ＴＮＯｘ−ＲＮＯｘ）を計算し、この差ｄＮＯｘからステップ３において図６８を内容とするテーブルを検索して、基本ＥＧＲ率フィードバック補正量ＫＥＧＲＨを求める。ステップ４では、図６９を内容とするテーブルを検索して、フィードバック補正ゲインＧＥＧＲＨを求め、ステップ５においてこの補正ゲインＧＥＧＲＨを基本ＥＧＲ率フィードバック補正量ＫＥＧＲＨに乗じて、目標ＥＧＲ率のフィードバック補正量Ｈegr2を計算する。
【０１４８】
そして、図６３のステップ３に示したように、この目標ＥＧＲ率のフィードバック補正量Ｈegr2をＨegr1×Ｍegr0にさらに乗じることによって、目標ＥＧＲ率をフィードバック制御する。
【０１４９】
ここで、図６８に示したように、ＲＮＯｘがＴＮＯｘより少ない（つまりｄＮＯｘが正）ときは、基本ＥＧＲ率フィードバック補正量ＫＥＧＲＨに１．０を超える値を与えて目標ＥＧＲ率Ｍegrを大きく（ＮＯｘ排出量が増える側に補正）し、この逆にＲＮＯｘがＴＮＯｘより多い（つまりｄＮＯｘが負）ときは、基本ＥＧＲ率フィードバック補正量ＫＥＧＲＨに１．０を下回る値を与えて目標ＥＧＲ率Ｍegrを小さく（ＮＯｘ排出量が減る側に補正）するのである。なお、ＮＯｘ濃度センサ７２により保証されるＮＯｘ濃度検出範囲に図６８に示した不感帯を設けて、ＮＯｘ濃度センサ７２の検出精度以上での誤ったフィードバック制御の防止と、前述の目標ＥＧＲ率のフィードバック制御との干渉を回避している。
【０１５０】
また、図６９のように、目標ＥＧＲ率基本値Ｍegr0が小さくなるほどフィードバック補正ゲインＧＥＧＲＨを小さくしているのは、一般的にＥＧＲ量が少ない運転条件ほどＥＧＲ率の増減によるＮＯｘ排出量の変化感度が大きいので、ＥＧＲ量が少ない運転条件ではフィードバック制御の制御感度を鈍くすることで、ＮＯｘ排出量が大きく変化することがないようにするためである。
【０１５１】
次に、図７１は排気中の実測ＨＣ／ＮＯｘ比を演算するフローである。ステップ１で上記の実測ＮＯｘ排出量ＲＮＯｘ（ＮＯｘ濃度センサ７２に基づいて演算される）、実測ＨＣ排出量ＲＨＣ（ＨＣ濃度センサ７３（図１参照）に基づいて演算される）を読み込み、ステップ２で実測ＨＣ／ＮＯｘ比であるＩ ＨＮrをＩ ＨＮr＝ＲＨＣ／ＲＮＯｘの式により計算する。
【０１５２】
なお、エンジンの仕様によっては、ＨＣ濃度センサ７３なしでも、図７２に示すフローとこれに用いる図７３〜図７７の特性に従えばエンジンアウトのＨＣ排出量を予測することが可能である。なお、図７２〜図７７は図４２〜図４８より基本ＮＯｘ排出量ＮＯｘＢについての演算部分を削除して再構成したものであるため、説明は省略する。
【０１５３】
図７８は要求ＨＣ量ＨＣ０の演算フローである。ステップ１でエンジン回転数Ｎe、燃料噴射量Ｑf、空燃比Ｌambda、実ＥＧＲ率相当値Ｒegr、実測ＨＣ／ＮＯｘ比Ｉ ＨＮr、を読み込み、このうちＮeとＱfとからステップ２において図７９を内容とするマップを検索して、目標ＨＣ／ＮＯｘ比Ｔ ＨＮrを求める。
【０１５４】
ステップ３では空燃比Ｌambdaと実ＥＧＲ率相当値Ｒegrから図８０と図８１を内容とするテーブルを検索して、目標ＨＣ／ＮＯｘ比の空燃比補正値ＫＡＦＨＮとＥＧＲ補正値ＫＥＧＲＨＮを求め、これら補正値を上記の目標ＨＣ／ＮＯｘ比Ｔ ＨＮrに乗じた値を、ステップ４において改めて目標ＨＣ／ＮＯｘ比Ｔ ＨＮrとする。
【０１５５】
ここで、空燃比補正値ＫＡＦＨＮは図８０に示したように空燃比のリッチ側で小さくなる値である。これは、図７９の目標ＨＣ／ＮＯｘ比Ｔ ＨＮrをマッチングしたときの空燃比（基準空燃比）よりリッチ側の空燃比のとき、基準空燃比の場合よりＨＣ増加 ＞ ＮＯｘ増加となるので、空燃比補正値ＫＡＦＨＮによりＴ ＨＮrをＨＣの減量側に補正するためである。
【０１５６】
ＥＧＲ補正値ＫＥＧＲＨＮは図８１のように実ＥＧＲ率相当値Ｒegrの小さくなる側で大きくなる値である。これは、図７９の目標ＨＣ／ＮＯｘ比Ｔ ＨＮrをマッチングしたときのＥＧＲ率（基準ＥＧＲ率）より小さなＥＧＲ率のとき、基準ＥＧＲ率の場合よりＨＣ増加 ＜ ＮＯｘ増加となるので、ＥＧＲ補正値ＫＥＧＲＨＮによりＴ ＨＮrをＨＣの増量側に補正するためである。
【０１５７】
ステップ５では
ＨＣ０＝（Ｔ ＨＮr−Ｉ ＨＮr）×ＲＨＣ …（１９）
の式より要求ＨＣ量ＨＣ０を計算する。
【０１５８】
また、ＨＣ濃度センサ７３を設けることなく、前述の図７２に示すフローによりエンジンアウトのＨＣ排出量を予測するときは、（１９）に代えて
ＨＣ０＝（Ｔ ＨＮr−Ｉ ＨＮr）×ＨＣＢ … （２０）
を用いる。
【０１５９】
このように第２実施形態では、触媒１の上流にＮＯｘ濃度センサ７２を設け、このセンサ検出値に基づいて実測ＮＯｘ排出量ＲＮＯｘを演算し、この実測ＮＯｘ排出量ＲＮＯｘを第１実施形態におけるＮＯｘ排出量の予測値に代えて用いるとともに、実測ＮＯｘ排出量ＲＮＯｘが目標ＮＯｘ排出量ＴＮＯｘと一致するように目標ＥＧＲ率をフィードバック制御するようにしたので、モデルが実際と合わなくなる領域においても、後噴射によるＨＣ量の過不足を抑制して、ＨＣとＮＯｘの各排出量をさらに低減することができる。
【０１６０】
図８２は同一の走行モードで試験したときの排気特性である。図示のように、第２実施形態によれば、同じ走行モードで比較したとき、第１実施形態よりもさらにＨＣとＮＯｘの各排出量が低減されている。
【０１６１】
また、ＮＯｘ濃度センサを触媒の下流に設ける場合に比べて制御応答がよく、かつ低濃度型のセンサでなくともよいので、検出精度の確保や生産バラツキの抑制が可能である。
【０１６２】
実施形態では、実際のＨＣ／ＮＯｘ比Ｉ ＨＮrと目標ＨＣ／ＮＯｘ比Ｔ ＨＮrの差に応じて要求ＨＣ量ＨＣ０を演算する場合で説明したが、実際のＨＣ／ＮＯｘ比Ｉ ＨＮrと目標ＨＣ／ＮＯｘ比Ｔ ＨＮrに応じて要求ＨＣ量ＨＣ０を演算してもかまわない。Ｔ ＨＮrは簡単には一定値でもよい。
【０１６３】
実施形態では、排気中の酸素濃度ＥＸo2に応じて基本後噴射量Ｑfaf0を補正する場合で説明したが、排気中の酸素濃度ＥＸo2に応じてＭＮＯｘ、ＭＨＣを補正することもできる。ＳＶ比はＥＧＲ制御を行わない場合にも用いることができる。
【０１６４】
実施形態では、コモンレール式燃料噴射装置を用いた場合で説明したが、これに限定されるものでない。たとえばユニットインジェクタを用いる場合にも適用可能である。
【図面の簡単な説明】
【図１】第１実施形態の制御システム図。
【図２】コモンレール式燃料噴射装置のシステム図。
【図３】ＥＧＲ制御システム図。
【図４】ＥＧＲ制御システムのブロック図。
【図５】吸気圧の演算を説明するためのフローチャート。
【図６】排気圧の演算を説明するためのフローチャート。
【図７】シリンダ吸入新気量の演算を説明するためのフローチャート。
【図８】シリンダ吸入ＥＧＲ量の演算を説明するためのフローチャート。
【図９】吸気温度の演算を説明するためのフローチャート。
【図１０】ＥＧＲ温度の演算を説明するためのフローチャート。
【図１１】体積効率相当値の演算を説明するためのフローチャート。
【図１２】体積効率基本値の特性図。
【図１３】体積効率負荷補正値の特性図。
【図１４】排気温度の演算を説明するためのフローチャート。
【図１５】排気温度基本値の特性図。
【図１６】ＥＧＲ流量の演算を説明するためのフローチャート。
【図１７】ＥＧＲ弁流路面積の特性図。
【図１８】サイクル処理を説明するためのフローチャート。
【図１９】燃料噴射量の演算を説明するためのフローチャート。
【図２０】主噴射の基本燃料噴射量の特性図。
【図２１】主噴射の最大噴射量の演算を説明するためのフローチャート。
【図２２】ＥＧＲ弁指令リフト量の演算を説明するためのフローチャート。
【図２３】ＥＧＲ弁目標リフト量の特性図。
【図２４】要求ＥＧＲ量の演算を説明するためのフローチャート。
【図２５】目標ＥＧＲ率の演算を説明するためのフローチャート。
【図２６】目標ＥＧＲ率基本値の特性図。
【図２７】目標ＥＧＲ率補正値の特性図。
【図２８】シリンダ吸気温度の演算を説明するためのフローチャート。
【図２９】後噴射の量と時期の制御システムのブロック図。
【図３０】タービン出口排気温度の演算を説明するためのフローチャート。
【図３１】基準タービン回転数の特性図。
【図３２】タービン出口排気圧の特性図。
【図３３】効率の特性図。
【図３４】触媒入口排気温度の演算を説明するためのフローチャート。
【図３５】車速温度降下係数の特性図。
【図３６】排気流量効果係数の特性図。
【図３７】後噴射時期の演算を説明するためのフローチャート。
【図３８】目標後噴射時期の特性図。
【図３９】触媒ベッド温度の演算を説明するためのフローチャート。
【図４０】ＳＶ比の演算を説明するためのフローチャート。
【図４１】排気中の酸素濃度の演算を説明するためのフローチャート。
【図４２】ＨＣ／ＮＯｘ比の演算を説明するためのフローチャート。
【図４３】基準ＮＯｘ排出量特性図。
【図４４】基準ＨＣ排出量の特性図。
【図４５】噴射時期補正値の特性図。
【図４６】空燃比補正値の特性図。
【図４７】ＥＧＲ補正値の特性図。
【図４８】水温補正値の特性図。
【図４９】要求ＨＣ量の演算を説明するためのフローチャート。
【図５０】目標ＨＣ／ＮＯｘ比の特性図。
【図５１】ＨＣ吸着・脱離量の演算を説明するためのフローチャート。
【図５２】吸着・脱離ゲインの特性図。
【図５３】後噴射量の演算を説明するためのフローチャート。
【図５４】ＨＣ量補正係数の特性図。
【図５５】基本後噴射量の特性図。
【図５６】主噴射時期の排気温度補正を説明するためのフローチャート。
【図５７】主噴射時期の排気温度補正値の特性図。
【図５８】主噴射時期の触媒表面温度補正値の特性図。
【図５９】加速時の触媒入口温度と触媒ベッド温度の変化を示す波形図。
【図６０】第１実施形態の効果を説明するための波形図。
【図６１】第２実施形態の制御システム図。
【図６２】第２実施形態のＥＧＲ制御システムのブロック図。
【図６３】第２実施形態の目標ＥＧＲ率の演算を説明するためのフローチャート。
【図６４】第２実施形態の目標ＮＯｘ排出量の演算を説明するためのフローチャート。
【図６５】第２実施形態の目標ＮＯｘ排出量の特性図。
【図６６】第２実施形態の実測ＮＯｘ排出量の演算を説明するためのフローチャート。
【図６７】第２実施形態の目標ＥＧＲ率のフィードバック補正量の演算を説明するためのフローチャート。
【図６８】第２実施形態の基本ＥＧＲ率補正量の特性図。
【図６９】第２実施形態の補正ゲインの特性図。
【図７０】第２実施形態の後噴射の量と時期の制御システムのブロック図。
【図７１】第２実施形態の実測ＨＣ／ＮＯｘ比の演算を説明するためのフローチャート。
【図７２】第２実施形態の実測ＨＣ排出量の演算を説明するためのフローチャート。
【図７３】第２実施形態の基準ＨＣ排出量の特性図。
【図７４】第２実施形態の噴射時期補正値の特性図。
【図７５】第２実施形態の空燃比補正値の特性図。
【図７６】第２実施形態のＥＧＲ補正値の特性図。
【図７７】第２実施形態の水温補正値の特性図。
【図７８】第２実施形態の要求ＨＣ量の演算を説明するためのフローチャート。
【図７９】第２実施形態の目標ＨＣ／ＮＯｘ比の特性図。
【図８０】第２実施形態の空燃比補正値の特性図。
【図８１】第２実施形態のＥＧＲ補正値の特性図。
【図８２】第１実施形態との違いを説明するための排気特性図。
【図８３】ＳＶ比を変化させたときのＮＯｘ転換率の特性図。
【図８４】排気酸素濃度に対するＮＯｘ転換率、ＨＣ転換率の特性図。
【図８５】第１４の発明のクレーム対応図。
【図８６】第１５の発明のクレーム対応図。
【符号の説明】
１ エンジン本体
１０ コモンレール式燃料噴射装置
１６ コモンレール
１７ 燃料噴射弁
４１ 電子制御ユニット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for a diesel engine, and more particularly to an apparatus for supplying unburned HC in exhaust gas as a reducing agent to a NOx reduction catalyst (hereinafter simply referred to as a NOx catalyst) provided in an exhaust passage.
[0002]
[Prior art]
When a NOx catalyst is installed in the exhaust passage and NOx is reduced and purified by this NOx catalyst, HC as a reducing agent is required. Since the amount is relatively small (generally, the ratio of HC / NOx is 1 or less), a small amount of fuel is used in the expansion stroke or exhaust stroke of each cylinder separately from the main injection using a common rail fuel injection device. Various types have been proposed in which a small amount of fuel is guided to the NOx catalyst in the HC state (see Japanese Patent Laid-Open Nos. Hei 3-253713 and Hei 6-212961).
[0003]
[Problems to be solved by the invention]
By the way, the main injection timing during operation is the reference main injection timing, the air-fuel ratio during operation is the reference air-fuel ratio, and the water temperature during operation is relative to the reference water temperature. When performing EGR control, the EGR rate during operation may be different from the reference EGR rate. In this case, the required HC amount changes from the reference value.
[0004]
However, as in the conventional apparatus, the main injection timing, the air-fuel ratio, the water temperature, and the EGR control during the operation are performed only by obtaining the post-injection amount by map search from the operating conditions such as the engine speed and the load. It is not possible to deal with each deviation in rate, and the amount of HC supplied by post-injection becomes excessive or insufficient. When the HC amount is excessive, the fuel consumption is deteriorated and the HC amount is increased. When the HC amount is insufficient, the NOx reduction efficiency of the catalyst cannot be maximized.
[0005]
In particular, when performing EGR, the exhaust gas flow rate changes according to the EGR amount, and the SV ratio, which is the ratio between the mass flow rate of the exhaust gas passing through the catalyst and the catalyst surface area, greatly changes. As shown in FIG. 83, the reduction performance of the catalyst and the catalyst activation temperature change due to the change in the SV ratio. Therefore, if the post-injection is performed even in the region where the SV ratio increases, the desired NOx reduction is performed. There is a risk that white smoke may be generated and fuel consumption may deteriorate due to excessive supply of HC by post-injection.
[0006]
Accordingly, the present invention provides a main injection timing, a reference air-fuel ratio, a reference, which are the main injection timing, the air-fuel ratio, the water temperature during operation, and the EGR rate during operation when the EGR control is performed. Even if there is a difference between the water temperature and the standard EGR rate, the primary purpose is to provide the required amount of HC without excess or deficiency, and by stopping the post-injection in the region where the SV ratio is large The second object is to prevent deterioration of exhaust gas and fuel consumption due to excessive supply of post-injected fuel.
[0007]
[Means for Solving the Problems]
The first invention includes a device for injecting and supplying fuel, the fuel supply device performs post-injection in the expansion or exhaust stroke after the main injection of fuel, and unburned HC by this post-injection is provided in the exhaust passage. In a diesel engine exhaust gas purification apparatus supplied as a reducing agent to the NOx catalyst, means for calculating a reference HC emission amount MHC and a reference NOx emission amount MNOx based on the engine speed Ne and the engine load, and these Means for calculating at least one of EGR correction values KEGRHC and KEGRNOx when performing the injection timing correction values KITHC, KITNOx, air-fuel ratio correction values KAFHC, KAFNOX, water temperature correction values KTWHC, KTWNOx, and EGR control with respect to the reference emission amount; Calculate with the same engine speed and engine load as this correction value. (In this correction, in addition to correcting each of the reference HC emission amount and the reference NOx emission amount with a correction value, only one of the reference HC emission amount and the reference NOx emission amount is corrected. And calculating the basic HC emission amount HCB and the basic NOx emission amount NOxB, and the actual HC / NOx ratio I which is the ratio of the basic emission amount. Means for calculating HNr and this actual HC / NOx ratio I HNr and target HC / NOx ratio T Means for calculating the required HC amount HC0 according to the difference or ratio of HNr and means for calculating the post injection amount Qfaf0 based on the required HC amount HC0 are provided.
[0008]
  In the second invention, in the first invention, the SV ratio is higher than the threshold value TSV #.largeWhen after injection is stopped.
[0009]
In a third aspect, in the second aspect, the SV ratio is predicted by model reference control.
[0010]
In the fourth invention, when the EGR control is performed in any one of the first to third inventions, the post-injection amount Qfaf0 is corrected according to the oxygen concentration EXo2 in the exhaust gas.
[0011]
In a fifth aspect, the oxygen concentration in the exhaust gas is predicted by model reference control in the fourth aspect.
[0012]
In a sixth aspect of the invention, in any one of the first to fifth aspects, an HC adsorbent is provided in front of or in the catalyst, and the amount of HC adsorbed on the adsorbent from the temperature Texhc of the exhaust gas passing through the catalyst. Alternatively, the HC desorption amount HCAB from the adsorbent is calculated, and the required HC amount HC0 is corrected according to the HC adsorption amount or the HC desorption amount HCAB.
[0013]
In the seventh invention, the temperature Texhc of the exhaust gas flowing through the catalyst in the sixth invention is predicted by model reference control.
[0014]
In an eighth invention, in any one of the fourth to seventh inventions, the EGR control is performed by model reference control.
[0015]
In the ninth invention, means for calculating the catalyst surface temperature Texhbd with a first order lag from the temperature Texhc of the exhaust gas flowing through the catalyst in the seventh or eighth invention, and the catalyst surface temperature Texhbd is a predetermined threshold value TEXHBD. # A means for stopping the post-injection was provided at the following times.
[0016]
In the tenth aspect of the invention, when the catalyst surface temperature Texhbd is slightly lower than the activation temperature threshold value T2 # of the catalyst surface, the main injection timing is retarded.
[0017]
In an eleventh aspect of the invention, the post-injection is stopped when the temperature Texhc of the exhaust gas flowing through the catalyst is equal to or lower than a predetermined threshold value TEXHC # in the seventh or eighth aspect.
[0018]
In the twelfth invention, when the temperature Texcd of the exhaust gas flowing through the catalyst is slightly lower than the activation temperature threshold value T1 # of the catalyst in the eleventh invention, the main injection timing is retarded.
[0019]
  A thirteenth aspect of the present invention includes a device for supplying and supplying fuel, and performs post-injection by the fuel supply device in the expansion or exhaust stroke after the main injection of fuel, and provides unburned HC by post-injection in the exhaust passage. Supply as a reducing agent to NOx catalystAnd a turbocharger having a turbine between the engine outlet and the catalyst.In the exhaust gas purification system for diesel engines,Exhaust temperature T at the engine outlet exh And an exhaust temperature T of the engine outlet exh The turbine efficiency equivalent value η t And a decrease in exhaust temperature from the turbine outlet to the catalyst inletMeans for predicting the temperature Texhc of the exhaust gas passing through the catalyst and means for calculating the post-injection timing ITafter according to the temperature Texhc of the exhaust gas passing through the catalyst are provided.
[0020]
As shown in FIG. 85, the fourteenth aspect of the invention comprises a device 81 for injecting and supplying fuel, and performing post-injection by the fuel supply device 81 in the expansion or exhaust stroke after the main injection of fuel. In an exhaust purification device for a diesel engine in which fuel HC is supplied as a reducing agent to a NOx catalyst provided in an exhaust passage, an EGR valve 82 for controlling an EGR amount, an engine speed Ne, and an engine load Means 83 for calculating the target EGR rate, means 84 for controlling the opening of the EGR valve 82 based on the target EGR rate, a sensor 85 for detecting the NOx concentration upstream of the catalyst, and the sensor detection value Based on the measured NOx emission amount RNOx, a sensor 87 for detecting the HC concentration upstream of the catalyst, and the measured HC emission based on the sensor detection value. Means 88 for calculating the amount RHC, and a measured HC / NOx ratio I which is a ratio of the measured HC emission amount RHC and the measured NOx emission amount RNOx. Means 89 for calculating HNr, and this measured HC / NOx ratio I HNr and target HC / NOx ratio T A means 90 for calculating the required HC amount HC0 according to the difference or ratio of HNr, a means 91 for calculating the post-injection fuel amount Qfaf0 based on the required HC amount HC0, and the measured NOx emission amount RNOx being the target NOx. Means 92 for feedback controlling the target EGR rate is provided so as to coincide with the discharge amount TNOx.
[0021]
As shown in FIG. 86, the fifteenth aspect of the present invention includes a device 81 for injecting and supplying fuel, and performs post-injection by the fuel supply device 81 in the expansion or exhaust stroke after the main injection of fuel. In an exhaust purification device for a diesel engine in which fuel HC is supplied as a reducing agent to a NOx catalyst provided in an exhaust passage, an EGR valve 82 for controlling an EGR amount, an engine speed Ne, and an engine load Means 83 for calculating the target EGR rate, means 84 for controlling the opening of the EGR valve 82 based on the target EGR rate, a sensor 85 for detecting the NOx concentration upstream of the catalyst, and the sensor detection value The means 86 for calculating the measured NOx emission amount RNOx based on the engine speed and the means 101 for calculating the reference HC emission amount MHC based on the engine speed Ne and the engine load. , For these, at least one of the injection timing correction value KITHC, the air-fuel ratio correction value KAFHC, the water temperature correction value KTWHC, the EGR correction value KEGRHC, and the basic value by correcting the reference value with these correction values Means 103 for calculating the HC emission amount HCB, and a measured HC / NOx ratio I which is a ratio of the basic HC emission amount HCB and the measured NOx emission amount RNOx. Means 104 for calculating HNr, and this measured HC / NOx ratio I HNr and target HC / NOx ratio T A means 90 for calculating the required HC amount HC0 according to the difference or ratio of HNr, a means 91 for calculating the post-injection fuel amount Qfaf0 based on the required HC amount HC0, and the measured NOx emission amount RNOx being the target NOx. Means 92 for feedback controlling the target EGR rate is provided so as to coincide with the discharge amount TNOx.
[0022]
According to a sixteenth aspect, in the fourteenth or fifteenth aspect, the detection delay of the NOx concentration sensor 85 is regarded as a first-order lag, and advance processing is performed for the detected value of the NOx concentration sensor by a time constant equivalent value.
[0023]
【The invention's effect】
In the first invention, since the required HC amount is calculated according to the difference or ratio between the actual HC / NOx ratio and the target HC / NOx ratio, the main injection timing, air-fuel ratio, water temperature, and EGR control during operation are performed. The EGR rate is the reference main injection timing, the reference air-fuel ratio, the reference water temperature, and when performing EGR control, the required HC amount should not be excessive or insufficient even if the EGR control may deviate from the reference EGR rate. As a result, it is possible to supply only the necessary HC amount with higher accuracy than in the case where the map is searched from the engine speed and the engine load to obtain the post-injection amount.
[0024]
In the second aspect of the invention, the post-injection is stopped in the region where the SV ratio is large where the NOx conversion rate is reduced. Therefore, the deterioration of fuel consumption and the increase in HC due to the execution of the post-injection can also be prevented in this region.
[0025]
Since the NOx catalyst has an action of oxidizing HC according to the oxygen concentration (or excess air ratio) in the exhaust (see FIG. 62), in order to reduce NOx, HC according to the oxygen concentration in the exhaust. However, in the fourth aspect of the invention, the post-injection amount is corrected according to the oxygen concentration in the exhaust gas. Therefore, the catalyst adjusts the HC according to the oxygen concentration in the exhaust gas. Even in the case of oxidizing, the post-injection amount can be calculated accurately.
[0026]
In the sixth invention, the required HC can be given accurately even in a state where HC is adsorbed on the adsorbent or HC is desorbed from the adsorbent.
[0027]
In the eighth invention, it is possible to accurately predict and control the EGR amount.
[0028]
In the ninth aspect of the invention, the post-injection is stopped when the catalyst surface temperature is lower than the threshold value, so that deterioration of fuel consumption and increase in HC are prevented by performing the post-injection even when the catalyst surface temperature is lower than the threshold value. it can.
[0029]
In the tenth invention, when the catalyst surface temperature is slightly lower than the activation temperature threshold of the catalyst surface, and in the twelfth invention, the main injection is performed when the temperature of the exhaust gas flowing through the catalyst is slightly lower than the activation temperature threshold of the catalyst. Since the exhaust gas temperature is raised by correcting the timing delay, the active area of the catalyst is expanded.
[0030]
  In the thirteenth aspect of the invention, the temperature of the exhaust gas passing through the catalyst can be predicted without a response delay by the model reference control, so that the post-injection timing is determined by an exhaust temperature sensor having a large response delay.InIn comparison, the post-injection timing at the time of transition can be appropriately given.
[0031]
In each of the fourteenth and fifteenth inventions, an actual NOx emission amount is calculated based on the detected value of the NOx concentration sensor provided on the upstream side of the catalyst, and the actual HC / NOx ratio I is calculated based on this actual NOx emission amount. While calculating HNr and feedback control of the target EGR rate so that the measured NOx emission amount matches the target NOx emission amount, the control accuracy of the NOx emission amount is increased, and even in a region where the model does not match the actual value, Excessive or insufficient HC amount due to post-injection can be suppressed, and each emission amount of HC and NOx can be further reduced. In addition, the control response is better than when the NOx concentration sensor is provided downstream of the catalyst, and the sensor does not have to be a low concentration sensor, so that it is possible to ensure detection accuracy and suppress production variations.
[0032]
In the sixteenth invention, even if the NOx concentration sensor has a delay at the time of transition, the actually measured NOx emission amount can be obtained with high accuracy.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the NOx catalyst 1 is provided in the exhaust passage 53. This is, for example, a copper-based zeolite catalyst (CU / ZSM-5).
[0034]
The engine includes a known common rail fuel injection device 10.
[0035]
When this is outlined with reference to FIG. 2 (refer to Japanese Patent Application Laid-Open No. 9-112251 for details), the fuel injection device 10 mainly includes a fuel tank 11, a fuel supply passage 12, a supply pump 14, a common rail (accumulation chamber) 16, A fuel injection valve 17 is provided for each cylinder, and the fuel pressurized by the supply pump 14 is temporarily stored in the common rail 16 through the fuel supply passage 15, and then the high-pressure fuel in the common rail 16 is injected by the number of cylinders. Distributed to the valve 17.
[0036]
The injection nozzle 17 includes a needle valve 18, a nozzle chamber 19, a fuel supply passage 20 to the nozzle chamber 19, a retainer 21, a hydraulic piston 22, a return spring 23 that urges the needle valve 18 in the valve closing direction (downward in the drawing), A fuel supply passage 24 to the hydraulic piston 22, a three-way valve (solenoid valve) 25 interposed in the passage 24, etc., and the passages 20 and 24 in the valve body communicate with each other between the upper portion of the hydraulic piston 22 and the nozzle chamber 19. Since the pressure receiving area of the hydraulic piston 22 is larger than the pressure receiving area of the needle valve 18 when the three-way valve 25 to which high pressure fuel is guided is turned off (ports A and B are connected and ports B and C are shut off), the needle valve 18 is in the seating state, but when the three-way valve 25 is in the ON state (ports A and B are shut off and ports B and C are in communication), the fuel above the hydraulic piston 22 passes through the return passage 28 to the fuel tank 11. Is, the fuel pressure acting on the hydraulic piston 22 is lowered. As a result, the needle valve 18 rises and fuel is injected from the injection hole at the tip of the injection valve. When the three-way valve 25 is returned to the OFF state again, the high pressure fuel in the pressure accumulating chamber 16 is guided to the hydraulic piston 22 and the fuel injection is completed. That is, if the fuel injection amount is adjusted by the ON time of the three-way valve 25 and the pressure in the pressure accumulating chamber 16 is the same, the fuel injection amount increases as the ON time increases. 26 is a check valve and 27 is an orifice.
[0037]
The fuel injection device 10 further includes a pressure control valve 31 in the passage 13 for returning the fuel discharged from the supply pump 14 in order to control the common rail pressure. The pressure control valve 31 is for changing the flow passage area of the passage 13 in accordance with the duty signal from the control unit 41, and controls the common rail pressure by adjusting the fuel discharge amount to the common rail 16. The fuel injection amount also varies depending on the fuel pressure of the common rail 16. If the ON time of the three-way valve 25 is the same, the fuel injection amount increases as the fuel pressure of the common rail 16 increases.
[0038]
A signal from a sensor 32 that detects the common rail pressure PCR1 includes an accelerator opening sensor 33 (generates an output L proportional to the amount of depression of the accelerator pedal), a crank angle sensor 34 (detects the engine speed and crank angle), a crank angle A control unit 41 that is input together with the sensor 35 (cylinder discrimination) and the water temperature sensor 36 calculates the target fuel injection amount Qf of the main injection and the target pressure of the common rail 16 according to the engine speed and the accelerator opening, The fuel pressure of the common rail 16 is feedback-controlled through the pressure control valve 31 so that the common rail pressure detected by the sensor 32 matches this target pressure. In addition to controlling the ON time of the three-way valve 25 corresponding to the calculated target fuel injection amount Qf of the main injection, the post-injection is performed in the expansion stroke or the exhaust stroke of each cylinder separately from the main injection, and unburned HC is removed. The NOx catalyst 1 is supplied.
[0039]
The engine is also provided with an exhaust gas recirculation device (EGR device). Referring to FIG. 3, 51 is a diesel engine body, 52 is an intake passage, 53 is an exhaust passage, and 54 is a passage (EGR passage) for returning a part of the exhaust in the exhaust passage 53 to the intake passage. .
[0040]
The intake passage 52 is provided with an air flow meter 55 for measuring the intake air amount, and an intake throttle valve 56 for restricting the intake air in two stages is provided downstream thereof. The aforementioned EGR passage 54 is connected to the downstream side of the intake throttle valve 56, and a valve (EGR valve) 57 for controlling the exhaust gas recirculation amount is interposed in the middle of the EGR passage 54.
[0041]
Therefore, the recirculation amount of the exhaust gas flowing from the exhaust passage 53 to the intake passage 52 depends on the differential pressure between the suction negative pressure generated according to the opening of the intake throttle valve 56 and the exhaust pressure of the exhaust passage 53, and Is determined in accordance with the opening degree of the EGR valve 57 at the time.
[0042]
The opening of the intake throttle valve 56 is controlled in two stages by a negative pressure actuator 56a, and a first negative pressure passage for guiding negative pressure from a vacuum pump (not shown) to the negative pressure actuator 56a via a first electromagnetic valve 61. 62 and a second negative pressure passage 64 that also guides a negative pressure through the second electromagnetic valve 63 is connected, and the opening of the intake throttle valve 56 is controlled by the negative pressure regulated by the electromagnetic valves 61 and 62. Is controlled in two stages, and the suction negative pressure generated downstream thereof is controlled.
[0043]
For example, when the first electromagnetic valve 61 stops introducing negative pressure, introduces atmospheric pressure, and the second electromagnetic valve 63 introduces negative pressure, the negative pressure of the negative pressure actuator 56a is weak and the intake throttle is reduced. On the other hand, the opening degree of the valve 56 becomes relatively large. On the other hand, when the first electromagnetic valve 61 also introduces a negative pressure, the negative pressure is strong and the opening degree of the intake throttle valve 56 becomes small. When both the first and second electromagnetic valves 61 and 63 are introducing atmospheric pressure, the intake throttle valve 56 is held in the fully open position by the return spring.
[0044]
The lift amount of the EGR valve 57 is changed by the rotation of the step motor 57a, the opening degree thereof is adjusted, and the exhaust gas recirculation amount flowing into the intake air through the EGR passage 54 is increased or decreased according to the opening degree. Reference numeral 57b denotes a means for detecting the opening degree of the EGR valve 57.
[0045]
The control unit 41 controls the operation of the first and second electromagnetic valves 61 and 63 and the step motor 57a to control the exhaust gas recirculation amount.
[0046]
Returning to FIG. 1, 2 is a turbocharger in which the exhaust turbine 2a and the intake compressor 2b are coaxially arranged, 3 is an intercooler provided in the intake passage downstream of the intake compressor 2b and upstream of the collector 52a, and 4 is a swirl control valve. is there.
[0047]
The main injection timing during operation is the reference main injection timing, the air-fuel ratio during operation is the reference air-fuel ratio, and the water temperature during operation is relative to the reference water temperature. When performing EGR control, the EGR rate during operation may be different from the reference EGR rate. In this case, the required HC amount changes from the reference value.
[0048]
However, as in the conventional apparatus, the main injection timing, the air-fuel ratio, the water temperature, and the EGR control during the operation are performed only by obtaining the post-injection amount by map search from the operating conditions such as the engine speed and the load. It is not possible to deal with each deviation in rate, and the amount of HC supplied by post-injection becomes excessive or insufficient.
[0049]
In order to cope with this, in the first embodiment of the present invention, the reference HC emission amount MHC and the reference NOx emission amount MNOx are calculated based on the engine speed Ne and the engine load, and the injection timing correction value is calculated for these. When performing KITHC, KITNOx, air-fuel ratio correction values KAFHC, KAFNOX, water temperature correction values KTWHC, KTWNOx, and EGR control, EGR correction values KEGRHC, KEGRNOx are calculated, and these correction values are used to correct the corresponding reference values. The basic HC emission amount HCB and the basic NOx emission amount NOxB are calculated, and the actual HC / NOx ratio I, which is the ratio of these, HNr is calculated and this actual HC / NOx ratio I HNr and target HC / NOx ratio T The required HC amount HC0 is calculated according to the difference in HNr, and the post injection amount Qfaf0 is calculated based on the required HC amount HC0.
[0050]
This control performed by the control unit 41 will be described in detail below.
[0051]
As for EGR control, a rough block diagram of the control is shown in FIG. 4, a detailed flowchart and maps and tables used for the flow are shown in FIGS. 5 to 28 (FIGS. 5 to 21 are described in Japanese Patent Application No. 9-125892). In addition, for each control of the injection timing and the post-injection amount of the post-injection, which has already been proposed), a rough block diagram of the control is shown in FIG. 29, and a detailed flowchart and maps and tables used for the flow are shown in FIGS. 58, respectively.
[0052]
Here, the control method performed by the control unit 41 is model reference control (one of the controls using a model of a multivariable input control system).
[0053]
For this reason, the sensors other than the accelerator opening sensor 33, the crank angle sensors 34 and 35, and the water temperature sensor 36 are required for control only by the air flow meter 55 and the intake air temperature sensor 71 provided in the vicinity of the air flow meter 55. Various parameters (for example, intake pressure and exhaust pressure described later) are all predicted and calculated in the control unit 41. The image of the model reference control is, for example, that each block in FIGS. 4 and 29 performs the operation given to each block instantaneously while exchanging parameters with the surrounding blocks. . In recent years, the theoretical analysis of model reference control has progressed rapidly, so that it can be applied to engine control, and it has been confirmed by experiments that it is at a level that is practically acceptable.
[0054]
Hereinafter, the same parts as those of the prior application apparatus will be described first for EGR control, and then the description of the present invention part will be started.
[0055]
First, FIG. 5 shows a calculation flow of the intake pressure (inside the intake manifold), which is executed in synchronization with the Ref signal (crank angle reference position signal).
[0056]
In step 1, the cylinder intake fresh air amount Qac, the cylinder intake EGR amount Qec, the intake fresh air temperature Ta, the EGR temperature Te, and the volumetric efficiency equivalent value Kin are read. The calculation of these five parameters is performed in a separate flow. Therefore, it will be described in detail later.
[0057]
Step 2 is based on these parameters

Where R: gas constant
Kvol: 1 cylinder volume / intake system volume
Kpm, Opm: Constant
The intake pressure Pm is calculated by the following formula (theoretical formula). The initial value of Pm is stored in the ROM.
[0058]
FIG. 6 is a calculation flow of the exhaust pressure (EGR outlet).
[0059]
In step 1, the exhaust amount Qexh discharged from the cylinder, the exhaust temperature Texh, and the engine speed Ne are read. However, the calculation of each parameter of the exhaust amount Qexh and the exhaust temperature Texh will be described in detail later by another flow.
[0060]
In step 2, exhaust pressure Pexh
Pexh = (Qexh × Ne / Kcon)²× Texh × Kpexh + Opexh (2)
Kcon, Kpexh, Opexh: constants
This is calculated by the following formula (empirical formula obtained from dimensional analysis). The initial value of Pexh is stored in the ROM.
[0061]
Next, a method for calculating each parameter described above will be described.
[0062]
First, FIG. 7 is a flow for calculating the cylinder intake fresh air amount Qac. In step 1, the output voltage of the air flow meter AMF is read, and in step 2, the intake air amount is calculated from the output voltage by table conversion. In Step 3, a weighted average process is performed on the calculated intake air amount in order to smooth out the influence of the intake pulsation.
[0063]
In Step 4, the engine speed Ne is read. In Step 5, the intake air amount Qac0 per cylinder is calculated from the rotational speed Ne and the weighted average value Qas0 of the intake air amount.
Qac0 = (Qas0 / Ne) × KCON #
Where KCON #: constant
Calculate with the following formula.
[0064]
In step 6, a delay process for n times of Qac0 is performed, and a value Qac0 · Z after the delay process is performed.^-nIs calculated as the fresh air amount Qacn at the inlet of the collector 52a. This takes into account the delay of the intake air from the air flow meter 55 to the collector 52a inlet.
[0065]
In step 7, the volume ratio Kvol and the volume efficiency equivalent value Kin are used to calculate the fresh air amount Qacn at the collector 52a inlet.
Qac = Qac_n-1× (1-Kvol × Kin) + Qacn × Kvol × Kin (3)
However, Qac_n-1: Previous value of Qac
The cylinder intake fresh air amount (new air amount sucked into the cylinder) Qac is obtained by performing a delay process according to the following equation. This takes into account the delay in the intake air from the collector 52a inlet to the cylinder.
[0066]
FIG. 8 is a flow for calculating the cylinder intake EGR amount Qec.
[0067]
The content of this calculation is the same as the calculation method of the cylinder intake fresh air amount Qac shown in FIG. In step 1, the EGR amount Qe obtained as described later (see FIG. 16) is read, and in step 2, the engine speed Ne is read. In step 3, a weighted average process is performed on Qe, and in step 4, a suction EGR amount Qecn per inlet of the collector 52a and per cylinder is calculated from Qes0, Ne, which is a weighted average value of Qe, and a constant KCON #. Further, in step 5, using the inlet 52 of the collector 52a and the suction EGR amount Qecn per cylinder, the volume ratio Kvol, and the volume efficiency equivalent value Kin,
Qec = Qec_n-1× (1-Kvol × Kin) + Qecn × Kvol × Kin (4)
However, Qec_n-1: Previous value of Qec
The cylinder intake EGR amount Qec is calculated by performing a delay process according to the following equation. This takes into account the delay of EGR gas from the collector 52a inlet to the cylinder.
[0068]
FIG. 9 is a flow for calculating the intake fresh air temperature Ta. In step 1, the previous value Pm of intake pressure_n-1And the intake air temperature detection value Ta0 are read and the previous value Pm of the intake pressure is read._n-1In step 2, the pressure correction coefficient Ktmpi is set to Ktmpi = Pm_n-1X Calculated from the equation of PA #. However, PA # is a constant.
[0069]
In step 3, the intake fresh air temperature Ta at the inlet of the collector 52a is calculated based on the pressure correction coefficient Ktmpi by an equation (approximate equation) of Ta = Ta0 × Ktmpi + TOFF #. However, TOFF # is a constant. TOFF # may be corrected by the water temperature, the vehicle speed, or the like.
[0070]
FIG. 10 is a flow for calculating the EGR gas temperature Te at the collector 52a inlet. In step 1, the exhaust gas temperature Texh and the exhaust gas temperature drop coefficient KTLOS # in the EGR passage are read, and the EGR gas temperature Te at the collector inlet 52a is calculated by the equation Te = Texh × KTLOS #. This takes into account the temperature drop from the EGR outlet to the collector inlet. The calculation of the exhaust temperature Texh will be described later.
[0071]
FIG. 11 is a flow for calculating the above-described volumetric efficiency equivalent value Kin. In step 1, the cylinder intake fresh air amount Qac, the target fuel injection amount of main injection (hereinafter simply referred to as fuel injection amount) Qf, and the engine speed Ne are read (however, the fuel injection amount Qf will be described later with reference to FIG. 19). In steps 2 and 3, a map having the contents shown in FIG. 12 is retrieved from the cylinder intake fresh air amount Qac and the rotational speed Ne to obtain the volumetric efficiency basic value KinH1, and the fuel injection quantity Qf and the rotational speed Ne to obtain FIG. The volume efficiency load correction value KinH2 is obtained by searching the map to be obtained, and in step 4, these KinH1 and KinH2 are multiplied to obtain the volume efficiency equivalent value Kin.
[0072]
FIG. 14 is a flow for calculating the exhaust temperature Texh. In steps 1 and 2, the fuel injection amount cycle processing value Qf0 and the cylinder intake temperature cycle processing value Tn0 are read (both will be described later with reference to FIG. 18). Further, in step 3, the previous value Pexh of the exhaust pressure_n-1Is read.
[0073]
In step 4, the exhaust temperature basic value Texhb is obtained by searching a table having the contents shown in FIG. 15 from the cycle processing value Qf0 of the fuel injection amount.
[0074]
In step 5, the intake air temperature correction coefficient Ktexh1 is calculated from the intake air temperature cycle processing value Tn0, and Ktexh1 = (Tn0 / TA #).^KN Calculate using the formula #. However, TA # and KN # are constants.
[0075]
Next, in step 6, the exhaust pressure correction coefficient Ktexh2 of the exhaust temperature is set to the previous value Pexh of the exhaust pressure._n-1From Ktexh2 = (Pexh_n-1/ PA #)⁽ #^{Ke-1) /} #^KeCalculate with the following formula. However, PA # and # Ke are constants.
[0076]
In step 7, the exhaust gas temperature Texh is calculated by multiplying the exhaust gas temperature basic value Texhb by the correction coefficients Ktexh1 and Ktexh2.
[0077]
FIG. 16 is a flow for calculating the EGR amount Qe. In step 1, the intake pressure Pm, the exhaust pressure Pexh, and the EGR valve actual lift amount Lifts as the EGR valve actual opening are read. Alternatively, the target EGR valve lift amount may be used if the actual EGR valve lift amount is uniquely determined by giving the target value as in the step motor.
[0078]
In step 2, a table having the contents shown in FIG. 17 is retrieved from the EGR valve actual lift amount Lifts to obtain the EGR valve flow passage area Ave.
[0079]
In step 3, the EGR flow rate Qe is calculated from the intake pressure Pm, the exhaust pressure Pexh, and the EGR valve passage area Ave by Qe = Ave × (Pexh−Pm).^1/2* Calculated by the equation of KR #. However, KR # is a constant and is approximately equal to 2 × ρ (ρ is exhaust density).
[0080]
FIG. 18 shows a flow of cycle processing of the cylinder intake fresh air amount, the fuel injection amount, and the cylinder intake temperature. In step 1, the cylinder intake fresh air amount Qac, the fuel injection amount Qf, and the cylinder intake temperature Tn are read. The cylinder intake temperature Tn is calculated by the average temperature of the mixed gas of fresh air and EGR gas sucked into the cylinder, that is, Tn = (Qac × Ta + Qec × Te) / (Qac + Qec) (FIG. 28). Will be described later).
[0081]
In step 2, using these Qac, Qf, and Tn, Qexh = Qac · Z^-(CYLN#^-1), Qf0 = Qf · Z^-(CYLN#^-2), Tn0 = Tn · Z^-(CYLN#^-1)Cycle processing is performed according to the following equation, which performs correction based on the phase difference with respect to the read timing of the air flow meter. However, CYLN # is the number of cylinders. For example, in a 4-cylinder engine, fuel injection is 180 CA × (cylinder number−2) with respect to the air flow meter reading timing, and therefore, delay processing is performed by subtracting 2 from the number of cylinders.
[0082]
FIG. 19 is a flow for calculating the fuel injection amount Qf. In step 1, the engine speed Ne and the control lever opening CL (determined by the accelerator pedal opening) CL are read, and in step 2, a map containing FIG. 20 is retrieved from these Ne and CL to obtain the basic fuel injection amount Mqdrv. .
[0083]
In step 3, various corrections are made on the basic fuel injection amount based on the engine coolant temperature, etc., and the fuel injection is further performed on the corrected value Qf1 on the basis of the map containing FIG. 21 in step 4. The amount is limited by the maximum value Qf1MAX, and the value after the limitation is calculated as the fuel injection amount Qf.
[0084]
This completes the description of the same parts as the prior application apparatus.
[0085]
Next, FIG. 22 is a flow for calculating the EGR valve command lift amount Liftt as the EGR valve command opening. In step 1, the intake pressure Pm, the exhaust pressure Pexh, and the required EGR amount Tqe (described later with reference to FIG. 24) are read. In step 2, the EGR valve required flow path area Tav is set to Tav = {(Pexh−Pm) × KR #}.^1/2The following formula (the law of fluid mechanics) is used. However, KR # is a correction coefficient. In step 3, a table having the contents shown in FIG. 23 is searched from the EGR valve required flow path area Tav to obtain an EGR valve target lift amount Mlift as the target EGR valve opening, and step 4 is performed on the target lift amount Mlift. , The advance processing for the operation delay of the EGR valve is performed, and the value after the advance processing is obtained as the EGR valve command lift amount Liftt.
[0086]
The EGR valve command lift amount Liftt determined in this way is output to the step motor 57a by a flow (not shown), and the EGR valve 57 is driven.
[0087]
FIG. 24 is a calculation flow of the required EGR amount Tqe. In step 1, the engine speed Ne, the target EGR rate Megr (described later with reference to FIG. 25), the cylinder intake fresh air amount Qac, and the cycle processing value Qf0 of the fuel injection amount are read. The target inhalation EGR amount Tqec0 is calculated by multiplying the rate Megr.
[0088]
In Step 3, for this target inhalation EGR amount Tqec0
Tqec = Tqec_n-1・ (1-Kin ・ Kvol) + Tqec0 ・ Kin ・ Kvol (5)
However, Tqec_n-1: Previous value of Tqecn
The target cylinder intake EGR amount Tqec (per cylinder) is obtained by performing the advance processing for the intake system capacity by the following equation.
[0089]
In step 4, the required EGR flow rate Tqe (for all cylinders) is calculated from the target cylinder suction EGR amount Tqec, the rotational speed Ne, and the constant KCON # by the following equation: Tqe = (Tqec / Ne) × KCON #.
[0090]
FIG. 25 is a flow for calculating the target EGR rate Megr. In step 1, the engine speed Ne, the fuel injection amount Qf, and the cylinder intake air temperature Tn (described later with reference to FIG. 28) are read, and a map containing FIG. 26 is retrieved from Ne and Qf, and the target EGR rate basic The value Megr0 is obtained.
[0091]
In step 3, a table having the contents shown in FIG. 27 is searched from the cylinder intake gas temperature Tint to obtain a target EGR rate correction value Hegr1. Calculate Megr.
[0092]
FIG. 28 is a flow for calculating the cylinder intake temperature Tn. In step 1, the cylinder intake fresh air amount Qac, the intake fresh air temperature Ta, the cylinder intake EGR amount Qec, and the EGR gas temperature Te are read. The average temperature of the gas and the cylinder intake EGR gas is obtained and this is set as the cylinder intake temperature Tn.
[0093]
Next, the control of the timing and amount of post-injection for supplying HC to the NOx catalyst 1 will be described.
[0094]
FIG. 30 is a flow for calculating the turbine 2b outlet temperature equivalent value Texhcb of the turbocharger 2. In step 1, exhaust pressure (also turbine inlet pressure) Pexh, exhaust temperature (also turbine inlet temperature) Texh, and exhaust flow rate Qexh are read. In step 2, a map containing FIG. 31 from exhaust flow rate Qexh and exhaust temperature Texh is shown. A search is made for the reference turbine speed Nt, and a table having the contents shown in FIG. 32 is searched from the exhaust flow rate Qexh to obtain the turbine outlet exhaust pressure (= catalyst inlet exhaust pressure) Pexhc.
[0095]
In step 3, a map (set based on the pressure ratio of the turbine alone and the efficiency performance diagram) is searched from Pexh / Pexhc, which is the pressure ratio between the exhaust pressure Pexh and the turbine outlet exhaust pressure Pexhc, and the turbine speed Nt. Then, an efficiency equivalent value ηt is obtained.
[0096]
In step 4, a value obtained by multiplying the exhaust temperature Texh by the efficiency equivalent value ηt thus determined is obtained as a turbine outlet temperature equivalent value Texhcb.
[0097]
  FIG. 34 is a flow for calculating the catalyst inlet temperature equivalent value Texhc. In step 1, the turbine outlet temperature equivalent value Texhcb, the displacement Qexh, and the vehicle speed VSP are read. In step 2, a table having the contents shown in FIG. 35 is retrieved from the vehicle speed VSP, and the vehicle speed temperature from the exhaust pipe surface by the vehicle speed is retrieved. The descent coefficient KTELOS1 is againDisplacement Q exh36 is searched to obtain an exhaust flow rate drop coefficient KTELOS2 indicating the heat transfer rate to the exhaust pipe surface by the exhaust flow velocity.
[0098]
In step 3, a value obtained by multiplying these coefficients KTELOS1 and KTELOS2 by the turbine outlet temperature equivalent value Texhcb is calculated as the catalyst inlet exhaust temperature equivalent value Texhc. This takes into account the decrease in the exhaust temperature from the turbine 2b outlet to the catalyst 1 inlet.
[0099]
FIG. 37 is a calculation flow of the target post-injection timing (target post-injection start timing) ITafter. In step 1, the catalyst inlet temperature equivalent value Texhc is read. In step 2, the target inlet injection timing ITafter is obtained by searching a table having the contents shown in FIG. 38 from the catalyst inlet temperature equivalent value Texhc. In FIG. 38, the temperature range where the catalyst inlet temperature equivalent value Texhc is small (that is, the low load range) is the region used mainly, and the angle is retarded in the region where the catalyst inlet temperature equivalent value Texhc is large (ie, the high load range). This is to avoid HC burning when Texhc is large.
[0100]
FIG. 39 is a calculation flow of the catalyst bed temperature equivalent value Texhbd. In step 1, the above catalyst inlet temperature equivalent value Texhc is read. In step 2,
Texhbd = Texhbd_n-1* TDBED # + Texhc * (1-TDBED #) (6)
However, Texhbd_n-1: Previous value of Texhbd
TDBED #: constant (equivalent value of temperature rise time constant)
The catalyst bed temperature equivalent value Texhbd is calculated from the above equation (first-order lag equation). This is because the catalyst bed temperature changes with a response delay with respect to the catalyst inlet temperature. Note that the initial value of Texhbd may be a constant value.
[0101]
FIG. 40 is a calculation flow of the SV ratio, which is the ratio between the surface area of the catalyst 1 and the mass flow rate of the gas passing through the catalyst 1. In step 1, the exhaust amount Qexh is read, and in step 2, the SV ratio is calculated from the formula SV ratio = Qexh × ρ / SCAT #. Where ρ is the exhaust specific gravity, and SCAT # is the total catalyst surface area.
[0102]
FIG. 41 is a calculation flow of the oxygen concentration EXo2 in the exhaust gas passing through the catalyst 1. In step 1, the exhaust amount Qexh, the cylinder intake EGR amount Qec, the cylinder intake fresh air amount Qac, the engine rotational speed Ne, and the fuel injection amount Qf are read. In step 2, the exhaust amount Qexh and the rotational speed Ne are used.
Qdry = Qexh / {MOLAIR # × (Ne / 2) × NCYL # × 60 × 1000} (7)
Where MOLAIR #: apparent molecular weight of air
NCYL #: Number of cylinders
The dry air flow rate Qdry is obtained from the above equation, and the fuel injection amount Qf is used in step 3

However, HF #: H mass ratio
CF #: C mass ratio
AC #: C atomic weight
AH #: H atomic weight
The required oxygen amount Qo is calculated from the following equation, and the dry air flow rate Qdry and the required oxygen amount Qo are used.

Where O2AIR #: oxygen concentration in the atmosphere
The oxygen concentration Ceo2 is calculated by the following formula.
[0103]
In step 5, using the cylinder intake EGR amount Qec and the cylinder intake fresh air amount Qac, an actual EGR rate equivalent value Regr is calculated by an equation of Regr = (Qec / Qac) × 100, and this actual EGR rate equivalent value Regr and In step 6, using the above oxygen concentration Ceo2.

The oxygen concentration EXo2 in the exhaust gas is calculated by the following formula.
[0104]
FIG. 42 is a calculation flow of the HC / NOx ratio in the exhaust. In step 1, the cylinder intake fresh air amount Qac, the engine speed Ne, the fuel injection amount Qf, the target main injection timing (target main injection start timing) ITs, and the actual EGR rate equivalent value Regr are read. The air-fuel ratio Lambda is calculated from the formula Lambda = Qac / (THAF # × Qf) using the fresh air amount Qac and the fuel injection amount Qf. However, THAF # is a constant.
[0105]
In step 3, a reference NOx emission amount MNOx and a reference HC emission amount MHC are obtained by searching a map having the contents shown in FIGS. 43 and 44 from Qf and Ne.
[0106]
Steps 4 to 7 are parts for calculating various correction values for these. That is, in order to correct MNOx and MHC by the amount by which the injection timing during operation deviates from the reference injection timing by searching a table having the contents shown in FIG. 45 from the target main injection timing ITs in step 4. 46, the MNOx and MHC are corrected by the amount of deviation of the operating air-fuel ratio with respect to the reference air-fuel ratio by searching the table containing the contents of FIG. 46 from the air-fuel ratio Lambda in step 5. 47. From the actual EGR rate equivalent value Regr in the step 6, the table containing the values shown in FIG. 47 is used to search for the values KAFNOX and KAFHC, so that the EGR rate during operation deviates from the reference EGR rate. The values KEGRNOX and KEGRHC for correcting MNOx and MHC are retrieved in step 7 from the cooling water temperature Tw in the table having the contents shown in FIG. Thus, values KTWNOX and KTWHC for correcting MNOx and MHC are obtained by the amount of deviation of the cooling water temperature during operation from the reference cooling water temperature.
[0107]
Here, the reference injection timing, the reference air-fuel ratio, the reference EGR rate, and the reference cooling water temperature are the engine speed and load (fuel) in the standard state (intake air temperature, cooling water temperature, atmospheric pressure). It is the value of the control target during steady operation set by (injection amount).
[0108]
In step 8, using these correction values

The basic NOx emission amount NOxB and the basic HC emission amount HCB are calculated by the following equation, and the actual HC / NOx ratio I in step 9 is calculated from these two values NOxB and HCB. HNr, I Calculation is performed using the formula HNr = HCB / NOxB.
[0109]
FIG. 49 is a calculation flow of the required HC amount HC0. In step 1, the fuel injection amount Qf and the engine speed Ne are read. In step 2, a map having the contents shown in FIG. 50 is searched from Qf and Ne, and the target HC / NOx ratio T Find HNr, and in step 3,
HC0 = (T HNr-I HNr) × HCB (13)
The required HC amount HC0 is calculated from the following equation.
[0110]
Usually, the target HC / NOx ratio is T I which is the actual HC / NOx ratio than HNr Since HNr is smaller, the required HC amount HC0 is obtained according to the difference, and the post-injection amount is calculated based on this value (to be described later with reference to FIG. 53). Compared with the conventional apparatus that only determines the injection amount, only the necessary HC amount can be supplied with high accuracy.
[0111]
FIG. 51 is a calculation flow of the amount of adsorption / desorption of HC in the HC adsorbent when the HC adsorbent is attached in front of or inside the NOx catalyst 1. In step 1, the catalyst inlet temperature equivalent value Texhc is read. In step 2, a table having the contents shown in FIG. 52 is searched from Texhc to obtain the HC adsorption / desorption gain GKCAT.
HCAB = HCAB_n-1+ GKCAT (14)
However, HCAB_n-1: Previous value of HCAB
The total HC adsorption index HCAB is calculated by the following formula.
[0112]
Here, when HC is adsorbed by the adsorbent, since the adsorption / desorption gain GKCAT becomes positive, the total HC adsorption amount index HCAB increases to the plus side, and conversely, HC is desorbed from the adsorbent. At this time, since the adsorption / desorption gain GKCAT becomes negative, the total HC adsorption amount index HCAB decreases to the negative side. That is, HCAB corresponds to the total amount of HC adsorbed on the adsorbent (however, the lower limit is 0).
[0113]
In step 4, it is determined whether GKCAT <0 (that is, HC desorption mode) and the total HC adsorption amount index HAB is 0 (that is, no HC is adsorbed). In step 5, GKCAT> HC (that is, HC). Whether the total HC adsorption amount index HCAB is FULL (that is, the HC adsorption amount to the adsorbent is full).
[0114]
When in the HC desorption mode and HC is not adsorbed at all, and when in the adsorption mode and the amount of HC adsorbed on the adsorbent is full, the routine proceeds to step 7, and the required HC amount HC0 is directly used as the target HC. T which is quantity HC.
[0115]
On the other hand, in cases other than the above two cases (when the amount of adsorption to the adsorbent is not full and HC is adsorbed or HC is present in the adsorbent and the HC is desorbed) ) Goes from Steps 4 and 5 to Step 6,
T HC = HC0 + GKCAT × KAB # (15)
However, KAB #: Conversion factor to HC amount
The target HC amount T HC is calculated.
[0116]
According to the equation (15), when HC is adsorbed on the adsorbent, the adsorption / desorption gain GKCAT becomes positive and the target HC amount T When the amount of HC is corrected and the HC is desorbed from the adsorbent, the adsorption / desorption gain GKCAT becomes negative and the target HC amount T HC is corrected to decrease. This means that when HC is adsorbed by the adsorbent, the corresponding amount of HC is not supplied to the catalyst 1 (that is, the post-injection amount is insufficient), and when HC is desorbed from the adsorbent, The amount of HC is excessively supplied to the catalyst 1 (that is, the post-injection amount is too large), so this is corrected.
[0117]
FIG. 53 is a calculation flow of the post injection amount. In step 1, the catalyst inlet temperature equivalent value Texhc, the catalyst bed temperature equivalent value Texhbd, the SV ratio, the fuel injection amount Qf, and the engine speed Ne are read.
[0118]
Steps 2 to 13 are parts for determining whether or not the conditions for performing the post-injection amount are as follows.
<1> The flag FTEXHC = 1 (that is, the catalyst inlet temperature equivalent value Texhc is equal to or greater than the threshold value).
<2> The flag FTEXBD = 1 (that is, the catalyst bed temperature equivalent value Texhbd is equal to or greater than the threshold value).
<3> The SV ratio is equal to or less than the threshold value TSV # (step 12).
<4> The rotational speed Ne is not less than the threshold value TNE # and the fuel injection amount Qf is not less than the threshold value TQf # (step 13).
When all of the above conditions are satisfied (when the post-injection condition is satisfied), the process proceeds to step 14 and thereafter, and the post-injection amount is calculated. When any of the above conditions is not satisfied (when the post-injection condition is not satisfied), step 18 is performed. And the post-injection amount is not calculated (post-injection amount Qfaf = 0).
[0119]
<1> and <2> above are for confirming whether or not the catalyst 1 is activated. If post-injection is performed when the catalyst 1 is not activated, the fuel consumption is deteriorated and the HC is increased. In order to prevent this, <1> and <2> are used as conditions.
[0120]
Here, the flag FTEXHC and the flag FTEXBD are necessary because hysteresis is provided in the threshold values for the catalyst inlet temperature equivalent value Texhc and the catalyst bed temperature equivalent value Texhbd. Since the setting methods of the two flags FTEXHC and FTEXBD are the same, the flag FTEXHC is representatively described. In the state where the flag FTEXHC = 1, the catalyst inlet temperature equivalent value Texhc is high, and the temperature has dropped from this state. When the temperature falls below the first temperature threshold value Ttexhc1 #, the flag FTEXHC is not switched to "0". When the temperature drops further and falls below the second temperature threshold value Ttexhc2 # (Ttexhc2 # <Ttexhc1 #), the flag FTEXHC is finally reached. Is switched to “0” (steps 2, 3, 4). On the contrary, when the flag FTEXHC = 0, the catalyst inlet temperature equivalent value Texhc is low, and even if the temperature rises from this state, the flag FTEXHC is not switched to “1” when the temperature exceeds the second temperature threshold value Ttexhc2 #. When the temperature further rises and exceeds the first temperature threshold value Ttexhc1 #, the flag FTEXHC is switched to "1" (steps 2, 5, 6).
[0121]
Now, when the post-injection condition is satisfied, in step 14, the target HC amount T HC and the oxygen concentration EXo2 in the exhaust gas are read, and a table having the contents shown in FIG. 54 is retrieved from the oxygen concentration EXo2 in step 15 to obtain the HC amount correction coefficient Kqf. In FIG. T which is target HC amount using table HC is converted into a basic post-injection amount Qfaf0. In step 17, the target post-injection amount Qfaf1 is calculated by multiplying the basic injection amount Qfaf0 by the HC amount correction coefficient Kqf.
[0122]
Since the catalyst 1 has an action of oxidizing HC according to the oxygen concentration (or excess air ratio) in the exhaust (see FIG. 84), in order to reduce NOx, the HC depends on the oxygen concentration in the exhaust. Although it is necessary to supply more HC than is oxidized, the catalyst 1 is adjusted to the oxygen concentration EXo2 in the exhaust by correcting the basic post-injection amount Qfaf0 in accordance with the oxygen concentration EXo2 in the exhaust. Accordingly, even when HC is oxidized, the post-injection amount can be accurately calculated.
[0123]
Next, FIG. 56 is an exhaust temperature correction flow at the main injection timing. In step 1, the target main injection timing ITsb, the catalyst inlet temperature equivalent value Texhc, and the catalyst bed temperature equivalent value Texhbd are read. The target main injection timing ITsb is basically determined from the engine speed and load, and this basic value is obtained by correcting the NOx emission amount, the water temperature, and the like.
[0124]
In step 2, the difference dT1 between the catalyst active exhaust temperature threshold value T1 # and the catalyst inlet temperature equivalent value Texhc and the difference dT2 between the catalyst bed activation temperature threshold value T2 # and the catalyst bed temperature equivalent value Texhbd are calculated. Then, a table having the contents shown in FIGS. 57 and 58 is retrieved from these temperature differences dT1 and dT2 to obtain the exhaust temperature correction value ITh1 for the main injection timing and the catalyst surface temperature correction value ITh2 for the main injection timing. In step 4, the main injection timing is retarded by setting the value obtained by subtracting these two correction values ITh1 and ITh2 from the target main injection timing ITsb as the command main injection timing ITs.
[0125]
The symbol ITs is confusing because it is described as the target main injection timing up to FIG. 55, but the target main injection timing ITs described up to FIG. 55 may be either ITsb or ITs in FIG. .
[0126]
Here, the main injection timing is corrected for delay when the catalyst inlet temperature equivalent value Texhc is slightly lower than the catalyst active exhaust temperature threshold value T1 # or with respect to the catalyst bed active temperature threshold value T2 #. The catalyst bed temperature equivalent value Texhbd is slightly below.
[0127]
Specifically, referring to FIG. 59, the catalyst inlet temperature equivalent value Texhc changes more responsively with respect to the change in the vehicle speed VSP, but the catalyst bed temperature equivalent value Texhbd changes with a delay. ing. As a result, both of them exceed the temperature threshold value in the A section shown in the figure, and according to FIG. 53, the post-injection is performed only in this A section (the supply of HC to the NOx catalyst by this post-injection) Reduction purification is performed with high accuracy).
[0128]
In this case, in the B section and the C section adjacent to the A section, the catalyst bed temperature equivalent value Texhbd and the catalyst inlet temperature equivalent value Texhc are only slightly below the corresponding temperature threshold value, so the exhaust temperature is slightly reduced. As long as it is increased, both the catalyst bed temperature equivalent value Texhbd and the catalyst inlet temperature equivalent value Texhc exceed the temperature threshold (that is, the post-injection condition is satisfied), and the post-injection is performed and the NOx reduction efficiency Is increased.
[0129]
Therefore, when the catalyst inlet temperature equivalent value Texhc or the catalyst bed temperature equivalent value Texhbd is slightly below the corresponding temperature threshold value, the exhaust gas temperature is raised by correcting the main injection timing to retard the catalyst 1. In this way, the NOx reduction purification is further advanced.
[0130]
Thus, in the embodiment of the present invention, the reference HC emission amount MHC and the reference NOx emission amount MNOx are calculated based on the engine speed Ne and the engine load, and the injection timing correction values KITHC, KITNOx, When performing air-fuel ratio correction values KAFHC, KAFNOX, water temperature correction values KTWHC, KTWNOx, and EGR control, EGR correction values KEGRHC, KEGRNOx are calculated, and these correction values are used to correct the reference values corresponding thereto, thereby generating basic HC emission amounts. The HCB and basic NOx emission amount NOxB are calculated, and the actual HC / NOx ratio I, which is the ratio of these, is calculated. HNr is calculated and this actual HC / NOx ratio I HNr and target HC / NOx ratio T The required HC amount HC0 is calculated according to the difference in HNr, and the post-injection amount Qfaf0 is calculated based on the required HC amount HC0. Therefore, when performing main injection timing, air-fuel ratio, water temperature, and EGR control during operation, EGR The required HC amount is obtained without excess or deficiency even if the rate is different from the reference EGR rate when the rate is different from the reference main injection timing, reference air-fuel ratio, reference water temperature, and EGR control. This makes it possible to supply only the necessary HC amount with higher accuracy than searching the map from the engine speed and the engine load to obtain the post-injection amount.
[0131]
As a result, as shown in FIG. 60, wasteful supply of HC by post-injection can be suppressed and NOx reduction performance during transient operation can be dramatically improved as compared with the conventional device (shown by map control in the figure). It was.
[0132]
Also, particularly when EGR control is performed, the post-injection is stopped in a region where the SV ratio is large where the NOx conversion rate is reduced, so that generation of white smoke due to excessive supply of HC accompanying the execution of post-injection in this region Deterioration of fuel consumption can be suppressed.
[0133]
  61 to 82 show the second embodiment, which is the first embodiment.WhenThe relationship is as follows.
[0134]
(1) FIG. 61 is shown in FIG. 1, FIG. 62 is shown in FIG. 4, FIG. 63 is shown in FIG. 25, FIG. 70 is shown in FIG. Each corresponds.
[0135]
(2) FIGS. 2, 3, 5 to 24, 26 to 28, 30 to 41, and 51 to 59 are used as they are in the second embodiment. 43 to 48 are not used in the second embodiment.
[0136]
(3) Additional FIGS. 64 to 69 and 72 to 77 are provided.
[0137]
In the first embodiment, the NOx emission amount is predicted by model reference control. For this reason, the system is described using physical laws, but the description (model) does not match the actual situation (for example, shifting when increasing vehicle speed when mode driving is performed by a vehicle with an automatic transmission) It is known that there is an excess or deficiency in the amount of HC due to post-injection in that region, and the HC emission amount and NOx emission amount slightly increase.
[0138]
On the other hand, since there has been no NOx concentration sensor that can be applied to vehicles in a small size, high reliability, and low cost, there have been few examples of applying the NOx sensor to an actual vehicle. As a result of development, sensors applicable to actual vehicles are being developed (for example, a solid electrolyte type NOx concentration sensor shown by SAE960344 or a substance having a single crystal-like structure shown in Japanese Patent Laid-Open No. 7-325059 is a NOx sensitive body. For detecting NOx concentration).
[0139]
Therefore, it is conceivable to perform feedback control of the NOx emission amount using such a NOx concentration sensor.
[0140]
In this case, since the amount to be controlled is the NOx emission amount at the catalyst outlet, even if a NOx concentration sensor is provided downstream of the NOx catalyst 1 and feedback control is performed based on this sensor detection value, the catalyst itself becomes a large delay factor. Therefore, the control gain of feedback control cannot be increased. For this reason, the control response is deteriorated and the control accuracy is not good. Moreover, since the gas purified by the catalyst must be detected, a low concentration type sensor is required, and it is difficult to ensure detection accuracy, suppress production variations, and reduce costs.
[0141]
Therefore, in the second embodiment, a NOx concentration sensor is provided upstream of the NOx catalyst 1, the measured NOx emission amount is calculated based on the sensor detection value, and this measured NOx emission amount is predicted as the NOx emission amount in the first embodiment. In addition to using this value, feedback control of the target EGR rate so that the measured NOx emission amount matches the target NOx emission amount, so that the excess or deficiency of the HC amount due to the post-injection can be reduced even in a region where the model does not match the actual value. In addition to further reducing each emission amount of HC and NOx, even if a NOx concentration sensor is used, the control response is enhanced and an expensive low concentration type sensor need not be used. .
[0142]
Specifically, first, feedback control of the NOx emission amount using the sensor detection value from the NOx concentration sensor 72 (see FIG. 1) provided on the upstream side of the catalyst 1 will be described.
[0143]
FIG. 64 is a flow for calculating the target NOx emission amount TNOx. In step 1, the fuel injection amount Qf and the engine speed Ne are read, and from these, a map having the contents shown in FIG. 65 is retrieved to obtain the target NOx emission amount TNOx.
[0144]
FIG. 66 is a flow for calculating the measured NOx emission amount RNOx. In step 1, the cylinder intake fresh air amount Qac and the fuel injection amount cycle processing value Qf0 are read and used, and in step 2, the intake dry molar flow rate M is read. Qac

Where MOLAIR #: apparent molecular weight of air
HF #: Mass ratio of H
CF #: C mass ratio
AH #: H atomic weight
Calculate with the following formula.
[0145]
In step 3, the engine speed Ne is read. In step 4, the output voltage NOx of the NOx concentration sensor 72 io is read and this sensor output voltage NOx In step 5, a table giving the relationship between the sensor output voltage and the NOx concentration is retrieved from io, and the NOx concentration C NOx is obtained, and in step 7, this NOx concentration C NOx, intake air dry molar flow rate M above Using Qac and engine speed Ne, the NOx emission amount (mass flow rate) RNOx0 in the steady state is calculated.

However, AN: N molecular weight
AO: Molecular weight of O
NCYL #: Number of cylinders
Calculate with the following formula.
[0146]
In step 8, the detection delay of the NOx concentration sensor 72 is regarded as a primary delay,

However, RNOx_n-1: Previous value of RNOx
K NOxi #: Time constant equivalent value
The value obtained by performing the advance processing by the time constant equivalent value is obtained as the measured NOx emission amount RNOx. Note that the initial value of RNOx is a fixed value (≈1).
[0147]
FIG. 67 is a flow for calculating the feedback correction amount Hegr2 of the target EGR rate. In step 1, the target NOx emission amount TNOx, the measured NOx emission amount RNOx, and the target EGR rate basic value Megr0 are read. Based on this difference dNOx, a table having the contents shown in FIG. 68 is searched in step 3 to obtain the basic EGR rate feedback correction amount KEGRH. In step 4, a table having the contents shown in FIG. 69 is searched to obtain a feedback correction gain GEGRH, and in step 5, the correction gain GEGRH is multiplied by the basic EGR rate feedback correction amount KEGRH to obtain a feedback correction amount Hegr2 of the target EGR rate. Calculate
[0148]
Then, as shown in step 3 of FIG. 63, the target EGR rate is feedback controlled by further multiplying Hegr1 × Megr0 by the feedback correction amount Hegr2 of the target EGR rate.
[0149]
Here, as shown in FIG. 68, when RNOx is smaller than TNOx (that is, dNOx is positive), the basic EGR rate feedback correction amount KEGRH is given a value exceeding 1.0 to increase the target EGR rate Megr (NOx). If the RNOx is larger than TNOx (that is, dNOx is negative), the basic EGR rate feedback correction amount KEGRH is given a value less than 1.0 to reduce the target EGR rate Megr. (Correction is made so that the amount of NOx emission decreases). The dead zone shown in FIG. 68 is provided in the NOx concentration detection range guaranteed by the NOx concentration sensor 72 to prevent erroneous feedback control above the detection accuracy of the NOx concentration sensor 72, and the feedback of the target EGR rate described above. Interference with control is avoided.
[0150]
In addition, as shown in FIG. 69, the feedback correction gain GEGRH is made smaller as the target EGR rate basic value Megr0 becomes smaller. In general, the operating sensitivity of the EGR amount is smaller for the change sensitivity of the NOx emission amount due to the increase / decrease in the EGR rate. This is because the NOx emission amount does not change significantly by making the control sensitivity of the feedback control dull under operating conditions with a small EGR amount.
[0151]
FIG. 71 is a flow for calculating the actually measured HC / NOx ratio in the exhaust. In step 1, the measured NOx emission amount RNOx (calculated based on the NOx concentration sensor 72) and the measured HC emission amount RHC (calculated based on the HC concentration sensor 73 (see FIG. 1)) are read. Is the measured HC / NOx ratio I HNr to I Calculation is performed using the formula HNr = RHC / RNOx.
[0152]
Depending on the engine specifications, the engine-out HC emission amount can be predicted according to the flow shown in FIG. 72 and the characteristics shown in FIGS. 73 to 77 without using the HC concentration sensor 73. 72 to 77 are obtained by deleting and recalculating the calculation part for the basic NOx emission amount NOxB from FIGS. 42 to 48, and thus the description thereof is omitted.
[0153]
FIG. 78 is a calculation flow of the required HC amount HC0. In Step 1, the engine speed Ne, the fuel injection amount Qf, the air-fuel ratio Lambda, the actual EGR rate equivalent value Regr, the measured HC / NOx ratio I HNr is read, and a map having the contents shown in FIG. 79 is retrieved from Ne and Qf in step 2, and the target HC / NOx ratio T Obtain HNr.
[0154]
  Step3Then, a table having the contents shown in FIGS. 80 and 81 is retrieved from the air-fuel ratio Lambda and the actual EGR rate equivalent value Regr, and the air-fuel ratio correction value KAFHN and the EGR correction value KEGRHN of the target HC / NOx ratio are obtained. The above target HC / NOx ratio T The value multiplied by HNr is the step4The target HC / NOx ratio T HNr.
[0155]
Here, the air-fuel ratio correction value KAFHN is a value that becomes smaller on the rich side of the air-fuel ratio as shown in FIG. This is the target HC / NOx ratio T in FIG. When the air-fuel ratio is richer than the air-fuel ratio (reference air-fuel ratio) when HNr is matched, HC increases> NOx increases as compared with the reference air-fuel ratio. Therefore, T is determined by the air-fuel ratio correction value KAFHN. This is because HNr is corrected to the HC reduction side.
[0156]
The EGR correction value KEGRHN is a value that increases as the actual EGR rate equivalent value Regr decreases, as shown in FIG. This is the target HC / NOx ratio T in FIG. When the EGR rate is smaller than the EGR rate (reference EGR rate) when HNr is matched, HC increase <NOx increase compared to the case of the reference EGR rate. Therefore, T is determined by the EGR correction value KEGRHN. This is to correct HNr to the HC increasing side.
[0157]
  Step5Then
    HC0 = (T HNr-I HNr) × RHC (19)
The required HC amount HC0 is calculated from the following equation.
[0158]
When the engine-out HC emission amount is predicted by the flow shown in FIG. 72 without providing the HC concentration sensor 73, instead of (19).
HC0 = (T HNr-I HNr) × HCB (20)
Is used.
[0159]
As described above, in the second embodiment, the NOx concentration sensor 72 is provided upstream of the catalyst 1, and the actual NOx emission amount RNOx is calculated based on the sensor detection value. Since the target EGR rate is feedback-controlled so that the measured NOx emission amount RNOx matches the target NOx emission amount TNOx, it is used instead of the predicted value of the emission amount. Excessive or insufficient HC amount due to injection can be suppressed, and each emission amount of HC and NOx can be further reduced.
[0160]
FIG. 82 shows the exhaust characteristics when tested in the same running mode. As shown in the figure, according to the second embodiment, when compared in the same travel mode, each emission amount of HC and NOx is further reduced than in the first embodiment.
[0161]
In addition, the control response is better than when the NOx concentration sensor is provided downstream of the catalyst, and the sensor does not have to be a low concentration sensor, so that it is possible to ensure detection accuracy and suppress production variations.
[0162]
In the embodiment, the actual HC / NOx ratio I HNr and target HC / NOx ratio T Although the case where the required HC amount HC0 is calculated according to the difference in HNr has been described, the actual HC / NOx ratio I HNr and target HC / NOx ratio T The required HC amount HC0 may be calculated according to HNr. T HNr may simply be a constant value.
[0163]
In the embodiment, the basic post-injection amount Qfaf0 is corrected according to the oxygen concentration EXo2 in the exhaust gas. However, MNOx and MHC can be corrected according to the oxygen concentration EXo2 in the exhaust gas. The SV ratio can also be used when EGR control is not performed.
[0164]
In the embodiment, the case where the common rail fuel injection device is used has been described. However, the present invention is not limited to this. For example, the present invention can also be applied when a unit injector is used.
[Brief description of the drawings]
FIG. 1 is a control system diagram of a first embodiment.
FIG. 2 is a system diagram of a common rail fuel injection device.
FIG. 3 is an EGR control system diagram.
FIG. 4 is a block diagram of an EGR control system.
FIG. 5 is a flowchart for explaining calculation of intake pressure.
FIG. 6 is a flowchart for explaining calculation of exhaust pressure.
FIG. 7 is a flowchart for explaining calculation of a cylinder intake fresh air amount.
FIG. 8 is a flowchart for explaining calculation of a cylinder suction EGR amount.
FIG. 9 is a flowchart for explaining calculation of intake air temperature.
FIG. 10 is a flowchart for explaining calculation of EGR temperature.
FIG. 11 is a flowchart for explaining calculation of a volumetric efficiency equivalent value.
FIG. 12 is a characteristic diagram of volumetric efficiency basic values.
FIG. 13 is a characteristic diagram of a volumetric efficiency load correction value.
FIG. 14 is a flowchart for explaining calculation of exhaust gas temperature.
FIG. 15 is a characteristic diagram of an exhaust gas temperature basic value.
FIG. 16 is a flowchart for explaining calculation of an EGR flow rate.
FIG. 17 is a characteristic diagram of an EGR valve channel area.
FIG. 18 is a flowchart for explaining cycle processing;
FIG. 19 is a flowchart for explaining calculation of a fuel injection amount.
FIG. 20 is a characteristic diagram of a basic fuel injection amount of main injection.
FIG. 21 is a flowchart for explaining calculation of a maximum injection amount of main injection.
FIG. 22 is a flowchart for explaining calculation of an EGR valve command lift amount;
FIG. 23 is a characteristic diagram of an EGR valve target lift amount.
FIG. 24 is a flowchart for explaining calculation of a required EGR amount.
FIG. 25 is a flowchart for explaining calculation of a target EGR rate.
FIG. 26 is a characteristic diagram of a target EGR rate basic value.
FIG. 27 is a characteristic diagram of a target EGR rate correction value.
FIG. 28 is a flowchart for explaining calculation of cylinder intake air temperature.
FIG. 29 is a block diagram of a control system for the amount and timing of post-injection.
FIG. 30 is a flowchart for explaining calculation of a turbine outlet exhaust temperature.
FIG. 31 is a characteristic diagram of a reference turbine speed.
FIG. 32 is a characteristic diagram of turbine outlet exhaust pressure.
FIG. 33 is a characteristic diagram of efficiency.
FIG. 34 is a flowchart for explaining calculation of catalyst inlet exhaust temperature;
FIG. 35 is a characteristic diagram of a vehicle speed temperature drop coefficient.
FIG. 36 is a characteristic diagram of an exhaust flow rate effect coefficient.
FIG. 37 is a flowchart for explaining the calculation of the post-injection timing.
FIG. 38 is a characteristic diagram of target post-injection timing.
FIG. 39 is a flowchart for explaining the calculation of the catalyst bed temperature.
FIG. 40 is a flowchart for explaining calculation of an SV ratio.
FIG. 41 is a flowchart for explaining calculation of oxygen concentration in exhaust gas.
FIG. 42 is a flowchart for explaining calculation of an HC / NOx ratio.
FIG. 43 is a reference NOx emission characteristic chart.
FIG. 44 is a characteristic diagram of a reference HC emission amount.
FIG. 45 is a characteristic diagram of an injection timing correction value.
FIG. 46 is a characteristic diagram of an air-fuel ratio correction value.
FIG. 47 is a characteristic diagram of an EGR correction value.
FIG. 48 is a characteristic diagram of a water temperature correction value.
FIG. 49 is a flowchart for explaining calculation of a required HC amount.
FIG. 50 is a characteristic diagram of a target HC / NOx ratio.
FIG. 51 is a flowchart for explaining calculation of HC adsorption / desorption amount.
FIG. 52 is a characteristic diagram of adsorption / desorption gain.
FIG. 53 is a flowchart for explaining calculation of a post-injection amount.
FIG. 54 is a characteristic diagram of an HC amount correction coefficient.
FIG. 55 is a characteristic diagram of a basic post-injection amount.
FIG. 56 is a flowchart for explaining exhaust temperature correction at the main injection timing.
FIG. 57 is a characteristic diagram of an exhaust temperature correction value at the main injection timing.
FIG. 58 is a characteristic diagram of the catalyst surface temperature correction value at the main injection timing.
FIG. 59 is a waveform diagram showing changes in catalyst inlet temperature and catalyst bed temperature during acceleration.
FIG. 60 is a waveform diagram for explaining the effect of the first embodiment;
FIG. 61 is a control system diagram of the second embodiment.
FIG. 62 is a block diagram of an EGR control system according to the second embodiment.
FIG. 63 is a flowchart for explaining calculation of a target EGR rate according to the second embodiment;
FIG. 64 is a flowchart for explaining calculation of a target NOx emission amount according to the second embodiment.
FIG. 65 is a characteristic diagram of the target NOx emission amount of the second embodiment.
FIG. 66 is a flowchart for explaining the calculation of the measured NOx emission amount of the second embodiment.
FIG. 67 is a flowchart for explaining calculation of a feedback correction amount for a target EGR rate according to the second embodiment;
FIG. 68 is a characteristic diagram of a basic EGR rate correction amount according to the second embodiment.
FIG. 69 is a characteristic diagram of the correction gain according to the second embodiment.
FIG. 70 is a block diagram of a control system for the amount and timing of post-injection according to the second embodiment.
FIG. 71 is a flowchart for explaining calculation of an actually measured HC / NOx ratio according to the second embodiment.
FIG. 72 is a flowchart for explaining calculation of an actually measured HC emission amount according to the second embodiment.
FIG. 73 is a characteristic diagram of a reference HC emission amount according to the second embodiment.
FIG. 74 is a characteristic diagram of an injection timing correction value according to the second embodiment.
FIG. 75 is a characteristic diagram of an air-fuel ratio correction value according to the second embodiment.
FIG. 76 is a characteristic diagram of an EGR correction value according to the second embodiment.
FIG. 77 is a characteristic diagram of a water temperature correction value according to the second embodiment.
FIG. 78 is a flowchart for explaining calculation of a required HC amount according to the second embodiment;
FIG. 79 is a characteristic diagram of a target HC / NOx ratio according to the second embodiment.
FIG. 80 is a characteristic diagram of an air-fuel ratio correction value according to the second embodiment.
FIG. 81 is a characteristic diagram of an EGR correction value according to the second embodiment.
FIG. 82 is an exhaust characteristic diagram for explaining a difference from the first embodiment.
FIG. 83 is a characteristic diagram of the NOx conversion rate when the SV ratio is changed.
FIG. 84 is a characteristic diagram of NOx conversion rate and HC conversion rate with respect to exhaust oxygen concentration.
FIG. 85 is a claim correspondence diagram of the fourteenth invention.
FIG. 86 is a claim correspondence diagram of the fifteenth aspect of the present invention.
[Explanation of symbols]
1 Engine body
10 Common rail fuel injection system
16 Common rail
17 Fuel injection valve
41 Electronic control unit

Claims (16)

A device for injecting and supplying fuel, performing post-injection by the fuel supply device in the expansion or exhaust stroke after the main injection of fuel, and reducing the unburned HC by the post-injection to the NOx catalyst provided in the exhaust passage In the exhaust purification system of a diesel engine that is supplied as
Means for calculating a reference HC emission amount and a reference NOx emission amount based on the engine speed and the engine load;
Means for calculating at least one of an injection timing correction value, an air-fuel ratio correction value, a water temperature correction value, and an EGR correction value when performing EGR control on these reference discharge amounts;
Means for calculating the basic HC emission amount and the basic NOx emission amount by correcting the reference emission amount calculated by the engine speed and the engine load equal to the correction value by the at least one correction value;
Means for calculating an actual HC / NOx ratio which is a ratio of the basic emission amount;
Means for calculating a required HC amount according to the difference or ratio between the actual HC / NOx ratio and the target HC / NOx ratio;
An exhaust emission control device for a diesel engine, comprising means for calculating a post-injection amount based on the required HC amount. 2. The exhaust emission control device for a diesel engine according to claim 1, wherein the post-injection is stopped when the ratio of the catalyst surface area to the volume flow rate of the gas passing through the catalyst (hereinafter referred to as the SV ratio) is greater than a threshold value. The exhaust purification device for a diesel engine according to claim 2, wherein the SV ratio is predicted by model reference control. The exhaust purification device for a diesel engine according to any one of claims 1 to 3, wherein when performing EGR control, the post-injection amount is corrected according to the oxygen concentration in the exhaust gas. The exhaust gas purification apparatus for a diesel engine according to claim 4, wherein the oxygen concentration in the exhaust gas is predicted by model reference control. An HC adsorbent is provided in front of or inside the catalyst, and the amount of HC adsorbed on the adsorbent or the amount of HC desorbed from the adsorbent is calculated from the temperature of the exhaust gas passing through the catalyst. 6. The diesel engine exhaust gas purification apparatus according to claim 1, wherein the required HC amount is corrected according to a desorption amount. The exhaust gas purification apparatus for a diesel engine according to claim 6, wherein the temperature of the exhaust gas flowing through the catalyst is predicted by model reference control. The diesel engine exhaust gas purification apparatus according to any one of claims 4 to 7, wherein the EGR control is performed by model reference control. Means for calculating the surface temperature of the catalyst with a first order lag from the temperature of the exhaust gas flowing through the catalyst, and means for stopping post-injection when the catalyst surface temperature is below a predetermined threshold value are provided. The exhaust emission control device for a diesel engine according to claim 7 or 8. The exhaust purification device for a diesel engine according to claim 9, wherein when the catalyst surface temperature is slightly lower than an activation temperature threshold value of the catalyst surface, the main injection timing is retarded. The exhaust purification device for a diesel engine according to claim 7 or 8, wherein after-injection is stopped when the temperature of the exhaust gas flowing through the catalyst is equal to or lower than a predetermined threshold value. The exhaust gas purification apparatus for a diesel engine according to claim 11, wherein the main injection timing is retarded when the temperature of the exhaust gas flowing through the catalyst is slightly lower than a catalyst activation temperature threshold value. A device for injecting and supplying fuel, performing post-injection by the fuel supply device in the expansion or exhaust stroke after the main injection of fuel, and reducing the unburned HC by the post-injection to the NOx catalyst provided in the exhaust passage In an exhaust emission control device for a diesel engine including a turbocharger having a turbine between an engine outlet and the catalyst ,
Means for calculating the exhaust temperature of the engine outlet;
Means for predicting the temperature of the exhaust gas passing through the catalyst in consideration of the efficiency equivalent value of the turbine with respect to the exhaust temperature of the engine outlet and the decrease in the exhaust temperature from the turbine outlet to the catalyst inlet ;
And a means for calculating a post-injection timing according to the temperature of the exhaust gas passing through the catalyst. A device for injecting and supplying fuel, performing post-injection by the fuel supply device in the expansion or exhaust stroke after the main injection of fuel, and reducing the unburned HC by the post-injection to the NOx catalyst provided in the exhaust passage In the exhaust purification system of a diesel engine that is supplied as
An EGR valve for controlling the EGR amount;
Means for calculating a target EGR rate based on the engine speed and the engine load;
Means for controlling the opening of the EGR valve based on the target EGR rate;
A sensor for detecting the NOx concentration upstream of the catalyst;
Means for calculating the measured NOx emission based on the sensor detection value;
A sensor for detecting the HC concentration upstream of the catalyst;
Means for calculating the actually measured HC emission amount based on the sensor detection value;
Means for calculating a measured HC / NOx ratio, which is a ratio between the measured HC emission amount and the measured NOx emission amount;
Means for calculating a required HC amount according to a difference or ratio between the measured HC / NOx ratio and the target HC / NOx ratio;
Means for calculating the fuel amount of the post-injection based on the required HC amount;
And a means for feedback-controlling the target EGR rate so that the measured NOx emission amount coincides with the target NOx emission amount. A device for injecting and supplying fuel, performing post-injection by the fuel supply device in the expansion or exhaust stroke after the main injection of fuel, and reducing the unburned HC by the post-injection to the NOx catalyst provided in the exhaust passage In the exhaust purification system of a diesel engine that is supplied as
An EGR valve for controlling the EGR amount;
Means for calculating a target EGR rate based on the engine speed and the engine load;
Means for controlling the opening of the EGR valve based on the target EGR rate;
A sensor for detecting the NOx concentration upstream of the catalyst;
Means for calculating the measured NOx emission based on the sensor detection value;
Means for calculating a reference HC emission amount based on the engine speed and the engine load;
A means for calculating at least one of at least an injection timing correction value, an air-fuel ratio correction value, a water temperature correction value, and an EGR correction value for these;
Means for calculating the basic HC emission amount by correcting the reference value with these correction values;
Means for calculating a measured HC / NOx ratio, which is a ratio between the basic HC emission amount and the measured NOx emission amount;
Means for calculating a required HC amount according to a difference or ratio between the measured HC / NOx ratio and the target HC / NOx ratio;
Means for calculating the fuel amount of the post-injection based on the required HC amount;
An exhaust emission control device for a diesel engine, comprising means for feedback-controlling the target EGR rate so that the measured NOx emission amount coincides with the target NOx emission amount. The exhaust of a diesel engine according to claim 14 or 15, wherein the detection delay of the NOx concentration sensor is regarded as a primary delay, and the advance processing is performed for the detected value of the NOx concentration sensor by a time constant equivalent value. Purification equipment.

Images