JP3680639B2 - Engine control device - Google Patents

Description

【０１４０】
図２８は可変ノズル２ｄの有効面積相当値Ａvntの演算フローである。ステップ１では指令開度の前回値であるVNTstep_n-1、総排気重量Ｑtotal（＝Ｑas0＋Ｑf）、排気温度Ｔexhを読み込む。
【０１４１】
このうち総排気重量Ｑtotalと排気温度Ｔexhからステップ２で
【０１４２】
【数１１】
Ｗexh＝Ｑtotal×Ｔexh／Ｔstd ［m³/sec］
ただし、Ｔstd：標準大気温度、
の式により排気流速相当値Ｗexhを算出する。
【０１４３】
ステップ３では、この排気流速相当値Ｗexhの平方根をとった値から図２９を内容とするテーブルを検索して摩擦損失ξfricを演算する。ステップ４では指令開度の前回値であるVNTstep_n-1と総ガス重量Ｑtotalから図３０を内容とするマップを検索してノズル損失ξconvを演算する。そして、これら２つの損失ξfric、ξconvをステップ５において指令開度の前回値であるVNTstep_n-1に乗算して、つまり
【０１４４】
【数１２】
Ａvnt＝ VNTstep_n-1×ξfric×ξconv
の式により可変ノズルの有効面積相当値Ａvntを演算する。
【０１４５】
図３１は排気圧（タービン入口圧）Ｐexhの演算のフローである。
【０１４６】
ステップ１では吸気量の加重平均値Ｑas0、燃料噴射量Ｑf、有効面積相当値Ａvnt、排気温度Ｔexh、大気圧（コンプレッサ入口圧）Ｐaを読み込み、これらのパラメータを用い、ステップ２において
【０１４７】
【数１３】
Ｐexh0＝Ｋpexh×｛(Ｑas0＋Ｑfuel)／Ａvnt｝²×Ｔexh＋Ｐa
ただし、Ｋpexh：定数、
の式により排気圧Ｐexh0を演算し、この排気圧に対してステップ３で加重平均処理を行い、その加重平均値を排気圧Ｐexhとして求める。
【０１４８】
ここで、上記の有効面積相当値Ａvntと排気圧Ｐexh0の各演算方法は、次のようにして得たものである。
【０１４９】
〈１〉流路面積が縮小する場合の流れの基礎式
図５２のように緩やかに断面積が縮小する管内を流れる理想流体を考える。
【０１５０】
流体の圧力、流速、面積、比重をそれぞれＰ、ｗ、Ａ、ρとし、入口を添字１、出口を添字２とし、入口と出口の断面についてベルヌイ（Bernoulli）の定理を適用すると、
ｗ₁ ²／２＋Ｐ₁／ρ＝ｗ₂ ²／２＋Ｐ₂／ρ ・・・（1a）
また、連続の式より
Ａ₁×ｗ₁＝Ａ₂×ｗ₂ ・・・（1b）
したがって、両式からｗ₁を消去すると、

単位時間に流れる流量Ｑは、連続の式より一定であるから、
Ｑ＝ρ×Ａ₂×ｗ₂

の式より表すことができる。
【０１５１】
（３）式の右辺の１／｛１−(Ａ₂／Ａ₁)²｝^1/2を効率ηnとおくと、次の流れの基礎式を得る。
【０１５２】
Ｑ＝ηn×Ａ₂×｛２ρ×(Ｐ₁−Ｐ₂)｝^1/2 ・・・（４）
〈２〉ターボチャージャの状態方程式
次に、ターボチャージャ２でのコンプレッサ２ｂと仕事の釣合いの関係を調べる。なお、以下で使用する記号は図５３の通りである。
【０１５３】
コンプレッサ２ｂの実効仕事率Ｌcは、
Ｌｃ＝Ｑas0×Ｗc／ηc ［Ｗ］ ・・・（５）
ただし、Ｑas0：吸入新気重量流量［kg/sec］、
Ｗc：コンプレッサ理論仕事［Ｊ／kg］、
ηc：コンプレッサ効率相当値。
【０１５４】
また、タービン２ａの実効仕事率Ｌtは、
Ｌt＝ηt×Ｑtotal×Ｗt ［Ｗ］ ・・・（６）
ただし、Ｑtotal：総排気重量流量［kg/sec］、
Ｗt：タービン理論仕事［Ｊ／kg］、
ηt：タービン効率相当値。
【０１５５】
タービン２ａとコンプレッサ２ｂは軸を介して直結されているので、コンプレッサ２ｂとタービン２ａの実仕事率Ｌc、Ｌtが等しいとおけば（軸受けのフリクションは効率に含まれる）、ターボチャージャ２の状態方程式として次式を得る。
【０１５６】

〈３〉流路面積が縮小する場合の排気圧予測式の検討
（７）式の左辺に上記の（４）式を適用して、

ただし、Ａvnt：可変ノズルの有効面積相当値、
Ｐexh：排気圧、
Ｐa：大気圧相当値、
ρe：排気の密度、
VNTstep：指令開度、
ηn：効率（損失分）、
の式を得る。
【０１５７】
（8a）式を排気圧Ｐexhについて整理すると、

ここで、排気密度ρeは理論式によれば
ρe＝ρstd×(Ｔa／Ｔexh)×(Ｐexh／Ｐa) ・・・（10）
ただし、ρstd：標準大気の密度（≒1.1679g/cm³）、
Ｔa:コンプレッサ入口温度、
Ｔexh：排気温度、
Ｐexh：排気圧、
Ｐa：大気圧、
であるが、この理論式では排気密度ρeを求めるのに排気圧Ｐexhを用いることになって具合が悪いので、
ρe≒ρstd×(Ｔa／Ｔexh)＝Ｔstd／Ｔexh ・・・（11）
ただし、Ｔstd：標準大気の温度（≒298.15Ｋ）、
の近似式を用いる。近似できる理由は、排気圧Ｐexhが高くなれば、排気温度Ｔexhも高くなるので、排気圧Ｐexhの変化分を排気温度Ｔexhに含めて考えることができるからである。
【０１５８】
したがって、（11）式を（９）式に代入することにより、次の式を得る。
【０１５９】

ただし、Ｋpexh：定数。
【０１６０】
ここで、（12a）式右辺のコンプレッサ理論仕事Ｗcとタービン理論仕事Ｗtは次式で与えられる。
【０１６１】
【数１４】

【０１６２】
さて、（12a）式より、排気圧Ｐexhの演算式が求められたが、（12a）式中のηc、ηt、Ｗc、Ｗtの演算は複雑であり（ＥＣＵの能力が要る）、また、（14）式ではこれから求めようとする排気圧Ｐexhを知る必要があるので、さらに考える。
【０１６３】
いま、総排気重量Ｑtotalと吸入新気量Ｑas0および燃料噴射量Ｑf（単位はすべて［kg/sec］とする）の間には次の関係がある。
【０１６４】
Ｑtotal＝Ｑas0＋Ｑf ・・・（15）
（15）式の左辺に上記の（４）式を適用して、
Ａvnt×｛２×ρe×(Ｐexh−Ｐa)｝^1/2＝Ｑas0＋Ｑf ・・・（16a）
Ａvnt＝ηn×VNTstep ・・・（16b）
（16a）式の両辺を２乗して排気圧Ｐexhについて整理すると、次式が得られる。
【０１６５】
Ｐexh＝｛(Ｑas0＋Ｑf)／Ａvnt｝²×(１／ρe)＋Ｐa ・・・（17）
ここでも、上記の排気密度ρeの近似式である（11）式を（17）式に代入することにより、次の最終式を得る。
【０１６６】

ただし、Ｋpexh：定数。
【０１６７】
（18a）式は上記の（12a）式と等価であり、（18a）式による排気圧Ｐexhの演算式には、コンプレッサ２ｂ、タービン２ａの理論仕事の比（Ｗc／Ｗt）と各々の効率の積(ηc×ηt)が含まれており、（18a）式を用いれば、ターボチャージャ２の理論仕事Ｗc、Ｗtと効率ηc、ηtが未知であっても考慮したことになる。ゆえにあとは、可変ノズル２ｃを流れるガスの効率ηnを求めればよい。
【０１６８】
〈４〉ノズルを流れるガスの効率ηn
効率ηnを含んだ可変ノズル２ｄの有効面積相当値Ａvntは上記の(8b)式、(16b)式で与えられるが、さらに効率ηnは次式で表すことができる。
【０１６９】

ただし、ξconv：ノズル損失、
ξfric：摩擦損失。
【０１７０】
（19）式においてノズル損失ξconvは、ノズル開度毎に決まる損失であり、縮まり管の場合、（３）式からわかるように１／｛１−(Ａ₂／Ａ₁)²｝^1/2が効率になる。
【０１７１】
しかしながら、流速の変化が大きい場合、１／｛１−(Ａ₂／Ａ₁)²｝^1/2の値をそのままノズル損失ξconvとみなすと、実際のノズル損失と合わないことが多いので、ノズル開度に対する効率のテーブルを持たせることで記述している（図３０参照）。
【０１７２】
また、（19）式の摩擦損失ξfricは、ノズル内部の流れを層流とみなすとハーゲンポアズイユ（Hagen-Poiseuille）の式が成り立ち、流速の平方根に摩擦損失ξfricが比例する。そこで、
Ｗexh＝Ｑtotal／ρe ・・・（20）
の式により体積流量相当値Ｗexhを算出し、これの平方根を排気流速として、これにより摩擦損失ξfricを検索する（図２９参照）。
【０１７３】
ここでも、排気密度ρeの近似式である（11）式を（20）式に代入して、

このようにして、（19）式によりノズル有効面積相当値Ａvntを演算し、このＡvntのほか、Ｑas0、Ｑf、Ｔexh、Ｐa を用いて、（18a）、（18b）式により排気圧Ｐexhを予測するようにしたわけである。排気圧の実測値と予測値の相関を調べた実験結果を図３２に示す。同図より、予測値でも十分な精度があることがわかる。
【０１７４】
次に、図３３はＥＧＲ(流)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。
【０１７５】
ステップ２では、このＥＧＲ弁実リフト量Ｌiftsから図３４を内容とするテーブルを検索して、ＥＧＲ弁５７の開口面積相当値Ａveを求める。
【０１７６】
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５７の開口面積相当値Ａveとから、
【０１７７】
【数１５】
Ｑe＝Ａve×｛(Ｐexh−Ｐm)×ＫＲ＃｝^1/2
ただし、ＫＲ＃：補正係数（定数）、
の式により計算する。
【０１７８】
図３５は目標過剰率Ｍlamb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、燃料噴射量Ｑf、大気圧（コンプレッサ入口圧）Ｐaを読み込み、このうちＮeとＱfからステップ２において図３６を内容とするマップを検索して目標空気過剰率基本値Ｍlamb0を求める。ステップ３では大気圧Ｐaから図３７を内容とするテーブルを検索して目標空気過剰率補正値Ｈlambを求め、この補正値Ｈlambを目標空気過剰率基本値Ｍlamb0に乗ずることによって目標空気過剰率Ｍlambを計算する。
【０１７９】
図３８は目標シリンダ吸入新気量Ｔqac1を演算するフローである。エンジン回転数Ｎe、目標空気過剰率Ｍlamb、燃料噴射量のサイクル処理値Ｑf0を読み込み、このうち燃料噴射量のサイクル処理値Ｑf0からステップ２において
【０１８０】
【数１６】
Ｍqac＝Ｍlamb×Ｂlamb×Ｑf0
ただしＢlamb：理論空燃比（≒１４．７）、
の式により目標吸入新気量Ｍqacを求める。
【０１８１】
ステップ３ではこの目標吸入新気量Ｍqacに対して、Ｋin×Ｋvolを加重平均係数として
【０１８２】
【数１７】
Ｒqac＝Ｒqac_n-1×（１−Ｋin×Ｋvol）＋Ｍqac×Ｋin×Ｋvol
ただし、Ｒqac_n-1：Ｒqecの前回値、
の式により中間処理値（加重平均値）Ｒqacを演算し、この中間処理値Ｒqacと上記の目標吸入新気量Ｍqacを用いてステップ４で
【０１８３】
【数１８】
Ｔqac1＝Ｍqac×ＧＫＱＥＣ＋Ｒqac_n-1×（１−ＧＫＱＥＣ）
ただし、Ｒqac_n-1：Ｒqacの前回値、
ＧＫＱＥＣ：進み補償ゲイン、
の式により進み処理を行って目標シリンダ吸入新気量Ｔqac1を求める。要求値に対して吸気系の遅れ（すなわちＥＧＲ弁５７→コレクタ５２ａ→吸気マニホールド→吸気弁の容量分の遅れ）があるので、ステップ３、４ではこの遅れ分の進み処理を行うものである。
【０１８４】
図３９は要求新気量Ｔqa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（実測値に相当）、目標シリンダ吸入新気量Ｔqac1を読み込み、これらの差dＱa（＝Ｔqac1−Ｑac）をステップ２において計算する。ステップ３ではこれらの差dＱaから積分制御より積分補正値Ｋqacを演算し、この補正値Ｋqacをステップ４において目標シリンダ吸入新気量Ｔqac1に乗じた値を、改めて目標シリンダ吸入新気量Ｔqacとして求める。
【０１８５】
ステップ５ではこの目標シリンダ吸入新気量Ｔqacから、
【０１８６】
【数１９】
Ｔqa＝（Ｔqac／Ｎe）×ＫＣＯＮ＃
ただし、ＫＣＯＮ＃：定数、
の式により単位変換（１シリンダ当たり→単位時間当たり）を行って、要求新気量Ｔqaを計算する。
【０１８７】
図４０は可変ノズルの指令開度VNTstepを演算するフローである。ステップ１では大気圧Ｐa、排気圧Ｐexh、要求新気量Ｔqa、摩擦損失ξfric、ノズル損失ξconvを読み込む。なお、摩擦損失ξfric、ノズル損失ξconvは、図２８のフローにおいて得た値をＲＡＭに移して保存しておき、このＲＡＭから読み込めばよい。
【０１８８】
ステップ２では可変ノズル２ｄの要求開口面積Ａvnt＿sol0を、
【０１８９】
【数２０】
Ａvnt sol0＝Ｔqa／｛（Ｐexh−Ｐ a）×Ｋv＃｝^1/2
ただし、Ｋv＃：補正係数（定数）、
の式（流体力学の法則）で計算し、この要求開口面積Ａvnt sol0からステップ３において
【０１９０】
【数２１】
Ａvnt＿sol＝Ａvnt＿sol0×ξfric×ξconv
の式により要求有効面積Ａvnt＿solを演算する。
【０１９１】
ステップ４ではこの要求有効面積Ａvnt＿solより図４１を内容とするテーブルを検索して可変ノズルの指令開度VNTstepを求める。
【０１９２】
このようにして得られる可変ノズルの指令開度VNTstepは、図示しない所定のテーブルを検索することにより、ステップ数（可変ノズルアクチュエータとしてのステップモータ２ｃに与える制御量）に変換され、このステップ数により指令開度VNTstepとなるように、ステップモータ２ｃが駆動される。
【０１９３】
図４２は目標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、燃料噴射量Ｑf、シリンダ吸入ガス温度Ｔnを読み込み、このうちＮeとＱfとから図４３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。ステップ３ではシリンダ吸入ガス温度Ｔnから図４４を内容とするテーブルを検索して目標ＥＧＲ率補正値Ｈegrを求め、この目標ＥＧＲ率補正値Ｈegr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。
【０１９４】
図４５は要求ＥＧＲ(流)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、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、このうちシリンダ吸入新気量Ｑacに目標ＥＧＲ率Ｍegrをステップ２において乗ずることで目標吸入ＥＧＲ量Ｍqecを計算する。
【０１９５】
ステップ３（図３８のステップ３と同様）ではこの目標吸入ＥＧＲ量Ｍqecに対して、Ｋin×Ｋvolを加重平均係数として
【０１９６】
【数２２】
Ｒqec＝Ｒqec_n-1×（１−Ｋin×Ｋvol）＋Ｍqec×Ｋin×Ｋvol
ただし、Ｒqec_n-1：Ｒqecの前回値、
の式により中間処理値（加重平均値）Ｒqecを演算し、この中間処理値Ｒqecと上記の目標吸入ＥＧＲ量Ｍqecを用いてステップ４（図３８のステップ４と同様）で
【０１９７】
【数２３】
Ｔqec＝Ｍqec×ＧＫＱＥＣ＋Ｒqec_n-1×（１−ＧＫＱＥＣ）
ただし、Ｒqec_n-1：Ｒqecの前回値、
ＧＫＱＥＣ：進み補償ゲイン、
の式により進み処理を行って目標シリンダ吸入ＥＧＲ量Ｔqecを求める。要求値に対して吸気系の遅れ（すなわちＥＧＲ弁５７→コレクタ５２ａ→吸気マニホールド→吸気弁の容量分の遅れ）があるので、ステップ３、４では、目標シリンダ吸入新気量Ｔqac1と同様に、この遅れ分の進み処理を行うものである。
【０１９８】
ステップ５（図３９のステップ５と同様）ではこの目標シリンダ吸入ＥＧＲ量Ｔqecから、
【０１９９】
【数２４】
Ｔqe＝（Ｔqec／Ｎe）×ＫＣＯＮ＃
ただし、ＫＣＯＮ＃：定数、
の式により単位変換（１シリンダ当たり→単位時間当たり）を行って、要求ＥＧＲ量Ｔqeを計算する。
【０２００】
図４６は指令ＥＧＲ弁開度としての指令ＥＧＲ弁リフト量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を読み込む。ステップ２ではＥＧＲ弁５７の要求開口面積Ｔavを、
【０２０１】
【数２５】
Ｔav＝Ｔqe／｛（Ｐexh−Ｐm）×ＫＲ＃｝^1/2
ただし、ＫＲ＃：補正係数（定数）、
の式（流体力学の法則）で計算する。
【０２０２】
ステップ３ではこのＥＧＲ弁５７の要求開口面積Ｔavより図４７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５７の作動遅れ分の進み処理を行い、その進み処理後の値を指令ＥＧＲ弁リフト量Ｌifttとして求める。
【０２０３】
このようにして求められた指令ＥＧＲ弁リフト量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。
【０２０４】
このように、本発明の実施形態では、吸気量(の加重平均値)Ｑas0、燃料噴射量Ｑf、可変ノズルの有効面積相当値Ａvnt、排気温度Ｔexhの４つの要素からダイレクトにかつ簡単な上記の数１３式を用いて排気圧Ｐexhを演算できることになったので、可変容量ターボチャージャを備える場合においても、過渡時に応答遅れなく排気圧を推定できる。
【０２０５】
また、エンジンの回転数と負荷に応じて目標空気過剰率Ｍlambを演算し、この目標空気過剰率Ｍlambに基づいて要求新気量Ｔqaを演算し、前記推定した排気圧Ｐexhと大気圧Ｐaとの差圧（Ｐexh−Ｐa）およびこの要求新気量Ｔqaから可変ノズル２ｄの要求開口面積Ａvntsol0を上記の数２０式を用いて演算し、この要求開口面積Ａvntsol0となるように可変ノズル２ｄのノズル開度を制御するとともに、エンジンの回転数と負荷に応じて目標ＥＧＲ率Ｍegrを演算し、この目標ＥＧＲ率Ｍegrに基づいて要求ＥＧＲ量Ｔqeを演算し、前記推定した排気圧Ｐexhと吸気圧Ｐmとの差圧（Ｐexh−Ｐm）およびこの要求ＥＧＲ量ＴqeからＥＧＲ弁５７の要求開口面積Ｔavを上記の数２５式を用いて演算し、この要求開口面積ＴavとなるようにＥＧＲ弁開度を制御する。つまり、ＮＯｘとＰＭを同時低減できる酸素濃度を達成するため制御目標値をＥＧＲ弁と可変ノズルに配分するようにしたので、従来装置（特開平６−１７３７５２号公報）のように、過渡時にも制御応答性が悪くなることがなく、これによって過渡時にも最適な過給圧とＥＧＲ量でエンジンを運転することができ、ＮＯｘとＰＭの同時低減を図ることができる。
【０２０６】
また、可変ノズル２ｄの要求開口面積Ａvntsol0に可変ノズル２ｄを流れるガスの効率ηnを乗算した値を可変ノズル２ｄの要求有効面積Ａvntsolとして求めるようにしたので、可変ノズル２ｄを流れるガスの効率ηnを考慮できる。
【０２０７】
同様にして、有効面積相当値Ａvntを、可変ノズル２ｄを流れるガスの効率ηnと可変ノズル２ｄを駆動するステップモータ２ｃに与える指令開度の前回値であるVNTstep_n-1との積で与えるようにしたので、このときも可変ノズル２ｄを流れるガスの効率ηnを考慮できる。
【０２０８】
また、可変ノズル２ｄを流れるガスの効率ηnは摩擦損失ξfricとノズル損失ξconvの積としたので、摩擦損失とノズル損失を別個に考慮できる。
【０２０９】
また、摩擦損失ξfricを、排気流速相当値Ｗexhの平方根に比例する値で与えるようにしたので、排気流速が相違しても、摩擦損失ξfricを精度よく与えることができる。
【０２１０】
また、流速の変化が大きい場合、縮まり管に対する損失（上記（３）式の１／｛１−(Ａ₂／Ａ₁)²｝^1/2の値）をそのままノズル損失とみなすと、実際のノズル損失と合わないことが多いのであるが、本実施形態ではノズル損失ξconvを、指令開度の前回値であるVNTstep_n-1と総排気重量Ｑtotalに応じた値としたので、流速の変化が大きい場合にも実際のノズル損失とよく合致させることができる。
【０２１１】
また、指令開度の前回値であるVNTstep_n-1と排気量Ｑexhに応じて排気温度のノズル開度補正係数Ｋtexh4を演算し、この補正係数Ｋtexh4で排気温度基本値Ｔexhbを補正するようにしたので、排気温度Ｔexhの演算精度が向上し、この向上分だけ排気圧Ｐexhの演算精度が向上する。同様にして、吸気ポートにスワール弁を備える場合には、このスワール弁の開度位置とエンジン回転数Ｎeに応じて排気温度のスワール補正係数Ｋtexh3を演算し、この補正係数Ｋtexh3で排気温度基本値Ｔexhbを補正するようにしたので、吸気ポートにスワール弁を備える場合にも排気温度Ｔexhの演算精度が向上し、この向上分だけ排気圧Ｐexhの演算精度が向上する。
【０２１２】
次に、図４８、図４９は第２実施形態の演算フローで、それぞれ第１実施形態の図３３、図４６に置き換わるものである。なお、第１実施形態と同一部分には同一のステップ番号をつけている。
【０２１３】
第１実施形態では、上記の数１５式に示したように、排気圧Ｐexhと吸気圧Ｐmの差圧からＥＧＲ流量Ｑeを演算していたが、第２実施形態では、さらにＥＧＲ通路５４内でのガスの圧力損失を考慮するようにしたもので、これによってより精度の高いＥＧＲ流量の演算が可能となる。
【０２１４】
第１実施形態と相違する部分を主に説明すると、図４８のステップ１１で吸気圧Ｐm、排気圧Ｐexh、ＥＧＲ弁実リフト量Ｌiftsのほか、排気温度Ｔexhを読み込む。ステップ１２では、
【０２１５】
【数２６】

ただし、Ａve：ＥＧＲ弁の開口面積相当値、
Ｐexh：排気圧、
Ｐm：吸気圧、
Ｔstd：標準大気温度、
Ｔexh：排気温度、
Ａvps：ＥＧＲ弁５７の全開面積相当値、
λ：ＥＧＲ通路５４の直管損失係数、
ｄ：ＥＧＲ通路５４の直径、
ｌ：ＥＧＲ通路５４の長さ、
ζ：ＥＧＲ通路５４の曲り管損失係数、
ｇ：重力の加速度、
Ｃv：定数、
の式によりＥＧＲ流量Ｑeを演算する。
【０２１６】
ただし、ＥＧＲ通路の直管損失係数λと曲がり管損失係数ζは次の式により計算すればよい。なお、数２６式において、λは直管損失モデル（ブラジウスの式）より、またζは曲がり管損失モデル（ワイズバッハの式）により得られるものである。
【０２１７】
【数２７】

ただし、Ｃs、Ｃb1、Ｃb2：定数、
Ｔstd：標準大気温度、
ν：排気の動粘度、
ｄ：ＥＧＲ通路５４の直径、
Ｒ：ＥＧＲ通路５４の曲率半径、
ｎ：ＥＧＲ通路５４の曲がり部の数。
【０２１８】
上記の数２６式は、公知の式をＥＧＲガスの流れに当てはめて得られる式である。たとえば、次のようにして数２６式を導くことができる。上記の数１式の第３式に上記の（４）式を適用して
Ｑegr＝Ａegr×｛２×ρe×(Ｐexh−Ｐm)｝^1/2 ・・・（22a）Ａegr＝Ａve×ηn2×Ｃv ・・・（22b）ただし、Ａegr：ＥＧＲ弁５７の有効面積相当値、
Ａve：ＥＧＲ弁５７の開口面積相当値、
ηn2：ＥＧＲ弁５７を流れるガスの効率、
Ｃv：定数。
【０２１９】
これは、ＥＧＲ弁５７の開口面積相当値Ａveに対して新たにηn2×Ｃvを導入したものである。
【０２２０】
ここでも、排気密度ρeの近似式である（11）式を（22a）式に代入して、
Ｑe＝Ａegr×｛２×(Ｔstd／Ｔexh)×(Ｐexh−Ｐm)｝^1/2 ・・・（23）
ただし、Ｔstd：標準大気温度
また、（22b）式の効率ηn2を第１実施形態にならって
ηn2＝ξconv-egr×ξfric-egr ・・・（24）
ξconv-egr：ＥＧＲ弁５７での損失、
ξfric-egr：ＥＧＲ通路５４の摩擦損失、
とする。
【０２２１】
ここで、ＥＧＲ弁５７での損失ξconv-egrを縮まり管の原則通りに、
ξconv-egr＝１／｛１−(Ａve／Ａvps)²｝^1/2 ・・・（25）
とおく。
【０２２２】
一方、ＥＧＲ通路５４の摩擦損失ξfric-egrはダルシーワイズバッハ（Darcy-Weisbach）の式より、

ただし、ε：管摩擦係数、
λ：直管損失係数、
ζ：曲がり管損失係数、
ｌ：ＥＧＲ通路長、
ｄ：ＥＧＲ通路の直径、
ｇ：重力の加速度、
と表すことができる。
【０２２３】
（25）式、（26）式を（24）式に代入して、

となり、（27）式を（22b）式に代入することで、次の式を得る。
【０２２４】

この（28）式を（22a）式に代入することで数２６式が得られる。
【０２２５】
さて、上記の数２６式のもととなった式（22a）式、（22b）式は、一般的には定常流の式であるため、非定常流では使えないというのが定説である。しかしながら、このたび、数２６式を用いて実験してみたところ、脈動のある排気のように規則性のある流れの場合には、定常、過渡とも、精度よくＥＧＲ流量Ｑeを演算できていることを初めて見いだした。したがって、数２６式によれば、排気のように非定常流であってもＥＧＲ通路５４内でのガスの圧力損失を考慮することが可能となり、これによってより精度の高いＥＧＲ流量の演算が可能となった。
【０２２６】
また、図４９のステップ１１、１２では、図４８のステップ１１、２と同様にして、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を読み込み、このＥＧＲ弁実リフト量Ｌiftsから図３４を内容とするテーブルを検索して、ＥＧＲ弁５７の開口面積相当値Ａveを求め、このＡveを用いて、ステップ１３で
【０２２７】
【数２８】

の式によりＥＧＲ弁５７の要求開口面積Ｔavを演算する。
【０２２８】
数２８式は次のようにして得たものである。上記の（22a）式、（22b）式で開口面積相当値Ａveに対して定数Ｃvと効率ηn2を導入したので、これに合わせて、ＥＧＲ弁５７の要求開口面積Ｔavを考えるときも
Ｔav＝Ａve×ηn2×Ｃv ・・・（29）
のように開口面積相当値Ａveに対して同じ値の定数Ｃvと効率ηn2を導入する。ここで、効率ηn2は（27）式により与えられているから、（27）式を（29）式に代入することで、数２８式が得られる。
【０２２９】
このように、第２実施形態では、ＥＧＲ通路５４内でのガスの圧力損失を考慮したので、より精度の高いＥＧＲ量Ｑeの演算が可能となる。
【０２３０】
さらに述べると、通路の開口面積相当値を、通路を流れるガスの効率で補正できるのは、一般的には定常流に限られるというのが定説である。しかしながら、このたび、ＥＧＲ弁５７の開口面積相当値Ａveを上記の効率ηn2で補正する場合で実験してみたところ、脈動のある排気のように規則性のある流れの場合には、定常、過渡とも、精度よくＥＧＲ流量Ｑeを演算できていることを初めて見いだした。したがって、第２実施形態によれば、排気のように非定常流であってもＥＧＲ通路内でのガスの圧力損失を容易に考慮することが可能となり、これによってより精度の高いＥＧＲ流量の演算が可能となったのである。
【０２３１】
ここで、図６をみると、ＥＧＲ量Ｑeからシリンダ吸入ＥＧＲ量Ｑecが、シリンダ吸入ＥＧＲ量Ｑecからシリンダ吸入ガス温度Ｔnが、シリンダ吸入ガス温度Ｔnからサイクル処理値Ｔn0が、サイクル処理値Ｔn0から排気温度Ｔexhが、排気温度Ｔexhから排気圧Ｐexhが演算されるので、ＥＧＲ量Ｑeの演算精度を高めることは、排気圧Ｐexhの演算精度を高めることに結びつく。したがって、演算精度の向上した排気圧Ｐexhに基づくことで、過給圧（吸入新気量）とＥＧＲ量を、さらに精度よく制御することが可能となる。
【０２３２】
また、ＥＧＲ弁５７を流れるガスの効率ηn2を、ＥＧＲ弁での圧力損失ξconv-egrとＥＧＲ通路の摩擦損失ξfric-egrとの積としたので、ＥＧＲ弁５７での圧力損失とＥＧＲ通路５４の摩擦損失を別個に考慮できる。
【０２３３】
また、直管損失係数λを、上記の数２７式により演算するようにしたので、排気圧Ｐexhが急激に変化する過渡時にも直管損失係数λを応答よく求めることができる。
【０２３４】
図５０は第３実施形態の可変ノズルの有効面積相当値Ａvntの演算フローで、第１実施形態の図２８に置き換わるものである。
【０２３５】
第３実施形態は、第１実施形態の効率ηnの演算を簡略化したものである。具体的には、ステップ１で指令開度の前回値であるVNTstep_n-1と排気流量Ｑexhを読み込み、これらからステップ２において図５１を内容とするマップを検索することにより有効面積の補正値Ｋvntを求め、これをステップ３において指令開度の前回値であるVNTstep_n-1に乗算して有効面積相当値Ａvntを演算する。
【０２３６】
ここで、補正値Ｋvntは、第１実施形態の効率ηn（＝ξfric×ξconv）に相当する値である。
【０２３７】
このように、第３実施形態では、可変ノズルを流れるガスの効率ηnの演算を簡略化することで、ＣＰＵの演算負荷を軽くできる。
【０２３８】
図５４は第４実施形態の排気圧（タービン入口圧）の演算フローで、第１実施形態の図３１に置き換わるものである。
【０２３９】
第１実施形態では、ノズル２ｄを通過するガスの流れを、流路面積が縮小する場合の流れである（図５２参照）と仮定して排気圧を演算したのに対して、第４実施形態は、ノズルを通過するガスの流れを、理想気体が断熱変化して流動する場合の流れ（図５６参照）と仮定して求めるものである。図５４において具体的には、ステップ１１で
【０２４０】
【数２９】
Ｐexhr＝Ｋpexhn×｛(Ｑas0＋Ｑfuel)／Ａvnt｝²×Ｔexh
ただし、Ｋpexhn：定数、
の式によりタービン入口排気圧相当値Ｐexhrを演算し、このＰexhrと大気圧Ｐaからステップ１２において図５５を内容とするマップを検索することにより排気圧Ｐexh0を求める。後は、図３１と同じであり、このＰexh0に対してステップ３で加重平均処理を行い、その加重平均値を排気圧Ｐexhとして求める。
【０２４１】
ここで、どのようにして数２９式の排気圧の演算方法を得たかを次に説明する。
【０２４２】
〈５〉先細ノズルの場合の流れの基礎式
タービンノズルを通過する通過する流れを考察すると、外部との熱の出入りや仕事がほとんどないため、流体の持つエネルギは、内部エネルギの減少分が運動エネルギと押し出し仕事に変化すると考えられる。また、エンジンの排気は、低圧・高温なので理想気体とみなせる。したがって、タービンノズルを通過する排気の流れは、「理想気体が断熱変化をして流動する」と考えることができる。
【０２４３】
さて、タービンノズルのような先細ノズルにおいて、図５６に示したように、圧力、比容積、流速、面積、温度、比熱比、気体定数をそれぞれ、Ｐ、ｖ、ｗ、Ａ、Ｔ、κ、Ｒとし、入口を添字１、出口を添字２とすると、
【０２４４】
【数３０】

【０２４５】
である。また、定常流動のエネルギ基本式から、次式が成り立つ。
【０２４６】
【数３１】

【０２４７】
数３１式に（31）式を代入して、
【０２４８】
【数３２】

【０２４９】
あるいはＰ₁Ｖ₁＝ＲＴ₁から、
【０２５０】
【数３３】

【０２５１】
先細ノズルでは、入口流速ｗ₁は出口流速ｗ₂に比べてきわめて小さいので省略すると、ノズル出口端の速度ｗ₂は次式で与えられる。
【０２５２】
【数３４】

【０２５３】
ノズルの各断面を単位時間に流れる流量Ｑは、連続の式より一定であるから、Ｑ＝Ａ₂×ｗ₂／ｖ₂＝ρe×Ａ₂×ｗ₂［kg/sec］ ・・・（33）である。また、ノズル内を流れる流体は理想気体で断熱変化するものとみなしているから、上記の（31）式より、
【０２５４】
【数３５】

【０２５５】
である。
【０２５６】
（33）式に（32）式と（34）式を代入すると、
【０２５７】
【数３６】

【０２５８】
（35）式が先細ノズルの場合の流れの基礎式である。
【０２５９】
〈６〉先細ノズルの場合の排気圧予測式の検討
図５３を参照する。（15）式から
Ｑas0＋Ｑf＝Ｑtotal［kg/sec］ ・・・（36）である。この（36）式の右辺に、面積が縮小するノズルの流れの式である上記の（35）式を適用して、
【０２６０】
【数３７】

【０２６１】
の式を得る。
【０２６２】
ここで、タービン入口排気圧相当値Ｐexhrを、
【０２６３】
【数３８】

【０２６４】
とおくと、（37a）式は

となるので、（39）式をタービン入口排気圧相当値Ｐexhrについて整理すると、次式が得られる。
【０２６５】

ここでも、排気密度ρeの近似式である（11）式を（40）式に代入することにより、次の最終式を得る。
【０２６６】
Ｐexhr＝Ｋpexhn×｛(Ｑas0＋Ｑf)／Ａvnt｝²×Ｔexh［Ｐａ］・・・（41a）
Ｋpexhn＝(１／(２×ρe))×(κe／(κe−１)) ・・・（41b）
ただし、Ｋpexhn：定数。
【０２６７】
さて、上記の数１３式のように、ノズルを通過するガスの流れを、流路面積が縮小する場合の流れであると仮定して排気圧を演算するものでは、標準状態（298Ｋ、0.1ＭＰａ）において排気圧の高い演算精度が得られるのであるが、実験によると、標準状態と異なる場合（たとえば高地、標準温度より温度が高い場合、湿度が標準状態と異なる場合など）に、排気圧の演算精度が低下することがわかっている。これは、数１３式が比重の変化を考慮してはいるが、まだ正確でないためと思われる。
【０２６８】
これに対して、ノズルを通過するガスの流れを、理想気体が断熱変化して流動する場合の流れであると仮定して求めた第４実施形態によれば、演算式により単位時間当たりの流量と圧力（つまり比重の変化）が正確に記述できているので、標準状態と異なる気圧や温度の状態においても、排気圧の高い演算精度が得られることになった。
【０２６９】
しかも第４実施形態でマッチングしなければならない図５１の特性は、図示のように単純なものであるため、ほとんど計算だけで足り（マッチングの必要なし）、机上のみの計算でも排気圧の演算精度は高いのである（実験により確認している）。
【０２７０】
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。
【０２７１】
実施形態ではディーゼルエンジンの場合で説明したが、ガソリンエンジンに対しても適用できることはいうまでもない。
【０２７２】
実施形態ではコンプレッサ入口圧Ｐaを検出するセンサ７３を設けた場合で説明したが、上記ＥＧＲ装置と可変容量ターボチャージャとを備えるエンジンを搭載する車両が標準大気（やこれに近い大気）のもとで運転される限りにおいては、コンプレッサ入口圧センサは不要である。このときは、標準大気に対するＰaの値を設定してやれば済むからである。
【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】ＮＯｘ、ＰＭの各排出量に対するＥＧＲ率、新気量（過給圧）の各感度の関係を示す特性図。
【図５】ＥＧＲ制御と過給圧制御の基本的な考え方を示すブロック図。
【図６】制御システムのブロック図。
【図７】モデル規範制御におけるパラメータの演算順を示すフローチャート。
【図８】サイクル処理を説明するためのフローチャート。
【図９】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１０】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】空気密度の特性図。
【図１３】吸気圧の演算を説明するためのフローチャート。
【図１４】センサ出力電圧に対する圧力の特性図。
【図１５】吸気温度の演算を説明するためのフローチャート。
【図１６】吸気温度の車速補正値の特性図。
【図１７】吸気温度の吸気量補正値の特性図。
【図１８】シリンダ吸入ガス温度の演算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】基本燃料噴射量の特性図。
【図２１】最大噴射量の特性図。
【図２２】排気温度の演算を説明するためのフローチャート。
【図２３】排気温度基本値の特性図。
【図２４】吸気温度補正係数の特性図。
【図２５】排気圧補正係数の特性図。
【図２６】スワール補正係数の特性図。
【図２７】ノズル開度補正係数の特性図。
【図２８】ノズル有効面積相当値の演算を説明するためのフローチャート。
【図２９】摩擦損失の特性図。
【図３０】ノズル損失の特性図。
【図３１】排気圧の演算を説明するためのフローチャート。
【図３２】排気圧の実測値と予測値の相関を調べた特性図。
【図３３】ＥＧＲ流量の演算を説明するためのフローチャート。
【図３４】ＥＧＲ弁開口面積相当値の特性図。
【図３５】目標空気過剰率の演算を説明するためのフローチャート。
【図３６】目標空気過剰率基本値の特性図。
【図３７】目標空気過剰率補正値の特性図。
【図３８】目標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３９】要求新気量の演算を説明するためのフローチャート。
【図４０】可変ノズルアクチュエータに与える指令開度の演算を説明するためのフローチャート。
【図４１】指令開度の特性図。
【図４２】目標ＥＧＲ率の演算を説明するためのフローチャート。
【図４３】目標ＥＧＲ率基本値の特性図。
【図４４】目標ＥＧＲ率補正値の特性図。
【図４５】要求ＥＧＲ量の演算を説明するためのフローチャート。
【図４６】指令ＥＧＲ弁リフト量の演算を説明するためのフローチャート。
【図４７】ＥＧＲ弁目標リフト量の特性図。
【図４８】第２実施形態のＥＧＲ量の演算を説明するためのフローチャート。
【図４９】第２実施形態の指令ＥＧＲ弁リフト量の演算を説明するためのフローチャート。
【図５０】第３実施形態のノズル有効面積相当値の演算を説明するためのフローチャート。
【図５１】第３実施形態の有効面積補正値の特性図。
【図５２】流路面積が縮小する流れのモデル図。
【図５３】吸排気系の力学的釣合いの検討に使用したモデル図。
【図５４】第４実施形態の排気圧の演算を説明するためのフローチャート。
【図５５】第４実施形態の排気圧Ｐexh0の特性図。
【図５６】先細ノズルのモデル図。
【図５７】第１の発明のクレーム対応図。
【図５８】第１１、第２８の発明のクレーム対応図。
【図５９】第１８の発明のクレーム対応図。
【符号の説明】
１ エンジン本体
２ 可変容量ターボチャージャ
２ｄ 可変ノズル
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
５４ ＥＧＲ通路
５７ ＥＧＲ弁
７２ 吸気圧センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine control device, in particular, an EGR device and a variable displacement turbocharger.
[0002]
[Prior art]
In order to efficiently use the turbocharger according to the operating conditions (that is, to obtain high supercharging in the low speed range and to operate with high efficiency in the high speed range), as shown in JP-A-8-270454, A variable capacity turbocharger with a variable nozzle has been put into practical use.
[0003]
[Problems to be solved by the invention]
By the way, although a large amount of EGR can reduce nitrogen oxides, a large amount of EGR lowers the air-fuel ratio. Therefore, in order to avoid this, it is necessary to increase the supercharging in a practical operation range (low speed or low load). It is conceivable to improve both the exhaust composition and operability of the engine by combining an EGR device capable of mass EGR and the above-described variable capacity turbocharger.
[0004]
In this case, the relationship between the exhaust amount Qexh passing through the turbine and the EGR amount Qegr passing through the EGR valve and the gas weight Qcyl sucked into one cylinder is expressed by the following equation (1). It is difficult to control the supercharging pressure) and the EGR amount independently of each other, and it is necessary to correct the other amount in response to the result of controlling one amount.
[0005]
[Expression 1]
Qcyl = Qac + Qec [mg / st.cyl]
Qexh = Avnt × (2 × ρe × (Pexh−Pa))^1/2[Kg / sec]
Qegr = Aegr × (2 × ρe × (Pexh−Pm))^1/2[Kg / sec]
Qac: Cylinder intake fresh air volume
Qec: Cylinder suction EGR amount
Avnt: Effective area equivalent value of variable nozzle
Aegr: EGR valve effective area equivalent value
Pexh: Exhaust pressure (turbine inlet pressure)
Pm: Intake pressure (compressor outlet pressure)
Pa: Atmospheric pressure (compressor inlet pressure)
ρe: exhaust density
For example, consider a case where the amount of fresh inhaled air is increased. By changing the nozzle opening degree of the variable nozzle to change the effective area equivalent value (including turbine efficiency) Avnt of the variable nozzle, the rate at which the exhaust pressure Pexh increases and the effective area equivalent value Avnt of the variable nozzle change. The turbine rotation speed increases according to the ratio, and the exhaust amount Qexh (≈ intake fresh air amount) increases (If the nozzle opening is reduced (nozzle is throttled), the actual area of the variable nozzle through which the exhaust passes) However, since the efficiency of the turbine also changes, the effective area equivalent value Avnt of the variable nozzle is not necessarily reduced). That is, since the exhaust pressure Pexh is changed by changing the nozzle opening, the EGR amount Qegr is also changed from the third formula of Formula 1. In the transient operation state, the intake pressure Pm increases after the exhaust pressure Pexh is raised, and thereby the EGR amount Qegr increases. As is well known, since NOx and particulate matter (PM) / HC / CO are in a trade-off relationship, if the EGR amount Qegr increases excessively in this way, NOx decreases, but particulates There is a possibility that substances, HC, and CO are greatly deteriorated and fuel consumption is deteriorated.
[0006]
Next, consider a case where the EGR amount Qegr is increased. When the effective area equivalent value Aegr of the EGR valve is changed by changing the EGR valve opening, the EGR amount Qegr increases in accordance with the ratio of the effective area equivalent value Aegr changing. That is, since the exhaust pressure Pexh changes by changing the EGR valve opening, the exhaust amount Qexh also changes from the second equation of the equation (1). In other words, when the EGR amount Qegr is increased, the exhaust pressure Pexh is decreased, so that the intake fresh air amount is decreased. For this reason, the desired amount of fresh air cannot be obtained, and there is a risk that the smoke will be deteriorated or the output will be reduced due to the insufficient amount of air.
[0007]
Thus, it is difficult to control the intake fresh air amount (supercharging pressure) and the EGR amount independently of each other, and it is necessary to correct the other in response to the result of controlling one.
[0008]
Therefore, for such a problem, the intake pressure sensor selectively detects the supercharging pressure and the control negative pressure supplied to the EGR valve by time sharing, and based on the control negative pressure and the supercharging pressure. JP-A-6-173752 discloses a technique for controlling the EGR amount and the supercharging pressure.
[0009]
However, with this technique, the control responsiveness at the time of transition becomes worse. Theoretically, the control response should be improved as the time-sharing cycle is shortened, but in reality, there is a delay in response to the intake pressure sensor, and while the intake pressure sensor does not respond, the control target state is detected. Can not. In other words, the time sharing period cannot be made shorter than the response delay period of the intake pressure sensor, and the control value may diverge if the time sharing period is made shorter than the response delay period of the intake pressure sensor. For this reason, the engine cannot be operated with the optimum supercharging pressure and EGR amount at the time of transition, and there is a concern that the desired exhaust gas reduction may not be performed or the fuel consumption and output performance may deteriorate in the actual operation state.
[0010]
Here, the relationship between the sensitivity of the EGR rate and the amount of fresh air (supercharging pressure) for each emission amount of NOx and PM is shown again in FIG. From the figure, the amount of fresh air (supercharging pressure) does not significantly affect the NOx emission amount, but greatly affects the PM emission amount. On the other hand, as the EGR rate increases, the NOx emission amount gradually decreases. On the other hand, there is almost no effect on the PM emission amount up to a predetermined EGR rate, but when the EGR rate is exceeded, the PM emission amount suddenly increases. To increase. From these characteristics, it can be seen that the NOx emission amount is determined by the oxygen concentration (≈EGR rate), and the PM emission amount does not increase if it exceeds a predetermined oxygen concentration (≈air excess ratio). Therefore, in order to obtain an oxygen concentration that can simultaneously reduce NOx and PM, the target excess air ratio and the target EGR ratio are determined in advance, and as shown in FIG. 5, the target excess air ratio and the target EGR ratio are obtained. Thus, it is necessary to control the opening degree of the variable nozzle 2d and the opening degree of the EGR valve 57 in a coordinated manner.
[0011]
Referring to FIG. 5, since the excess air ratio = (fresh air amount / fuel amount) / theoretical air-fuel ratio, the target fresh air amount Qa is calculated using the target excess air rate Mlamb and the fuel injection amount Qf.
Qa = Mlamb × Qf × theoretical air-fuel ratio (a)
The opening area Avntsol0 of the variable nozzle 2d when the target fresh air amount Qa flows is calculated from the formula of fluid dynamics.
Avntsol0 = Qa / {2 × ρe × (Pexh−Pa)}^1/2        ... (b)
Where Pexh: Exhaust pressure
Pa: Atmospheric pressure (compressor inlet pressure)
ρe: exhaust density
It can obtain | require by the type | formula.
[0012]
On the other hand, since the EGR rate = EGR amount / fresh air amount, the target EGR amount Qegr is calculated using the target fresh air amount Qa and the target EGR rate Megr.
Qegr = Qa × Megr (c)
The opening area Ae of the EGR valve 57 when the target EGR amount Qegr flows is calculated from the formula of fluid dynamics.
Ae = Qegr / {2 × ρe × (Pexh−Pm)}^1/2              ... (d)
Where Pexh: Exhaust pressure
Pm is the intake pressure (compressor outlet pressure)
ρe: exhaust density
It can obtain | require by the type | formula.
[0013]
Therefore, if the three variables of the intake pressure Pm, the exhaust pressure Pexh, and the atmospheric pressure Pa can be obtained from the equations (b) and (d), the nozzle opening (supercharging pressure) and the EGR valve opening (EGR amount) can be determined. The control target value can be distributed to the EGR valve and the variable nozzle in order to achieve coordinated control and achieve an oxygen concentration that can simultaneously reduce NOx and PM.
[0014]
Here, among the above three variables, variables other than the exhaust pressure Pexh are relatively easy to detect, but it is generally difficult to obtain a sensor having durability at high exhaust temperature and oxidizing atmosphere. And it is expensive as a vehicle-mounted sensor. In addition, it is difficult to obtain sufficient responsiveness to provide durability under the use conditions as described above. Therefore, in order to control the nozzle opening and the EGR valve opening with high accuracy and without impairing responsiveness and stability, means for estimating the exhaust pressure Pexh is required.
[0015]
Now, as a method for estimating the exhaust pressure without using a pressure sensor, as described in JP-A-9-14023, a steady exhaust pressure Pw is calculated based on the total intake air amount (Qa), and this steady exhaust pressure is calculated. Turbine acceleration energy F from Pw and exhaust gas flow ratio Kg, and previous turbine speed V_(i-1)From the difference between the turbine acceleration energy F and the load resistance FL, the current turbine speed V is calculated._(i)This turbine speed V_(i)There are some which calculate the exhaust pressure Pex according to the above. This method simply estimates the exhaust pressure by correcting the steady exhaust pressure according to the total intake air amount according to the change in the turbine speed.
[0016]
However, if the exhaust pressure is estimated from the steady exhaust pressure as in this method, if there is a delay in the calculation of the steady exhaust pressure, the exhaust pressure at the time of transition cannot be accurately estimated.
[0017]
It is difficult to apply this method to a variable capacity turbocharger. This is because when the nozzle opening is changed, the intake air amount increases and decreases with a non-linear characteristic, so that it is difficult to obtain the steady exhaust pressure Pw. In addition, it is difficult to estimate the turbine speed with high accuracy by the disclosed technology, and it is necessary to estimate the turbine speed according to the nozzle opening degree in order to obtain a high-precision turbine speed.
[0018]
For this reason, when an EGR device and a variable capacity turbocharger are provided, the exhaust pressure is directly and simply calculated using the four elements of the intake air amount, the fuel injection amount, the variable nozzle effective area equivalent value, and the exhaust temperature. By calculating (estimating), an apparatus that accurately estimates the exhaust pressure even during a transition is proposed almost simultaneously with the present invention.
[0019]
Therefore, according to the present invention, EGR control and supercharging pressure control are performed using the estimated exhaust pressure. In this case, in order to achieve an oxygen concentration that can simultaneously reduce NOx and PM, the control target value is set to the EGR valve. The object is to reduce NOx and PM at the same time while ensuring control response at the time of transition by allocating to variable nozzles.
[0020]
[Means for Solving the Problems]
The first invention comprises a variable displacement turbocharger having a variable nozzle in the turbine and an EGR valve capable of controlling the EGR amount, and as shown in FIG. 57, means 81 for detecting the intake air amount Qas0, A means 82 for detecting the load, a means 83 for detecting the effective area equivalent value Avnt of the variable nozzle, a means 84 for detecting the exhaust gas temperature Texh, and a means 85 for estimating the exhaust pressure Pexh using these four elements Based on the target excess air ratio, the means 86 for calculating the differential pressure between the estimated exhaust pressure Pexh and the atmospheric pressure Pa, the means 87 for calculating the target excess air rate Mlamb according to the engine speed and the load, and the like. Means 88 for calculating the required fresh air amount Tqa, means 89 for calculating the required opening area Avntsol0 of the variable nozzle from the required fresh air amount Tqa and the differential pressure (Pexh−Pa) between the atmospheric pressure, and this requirement Opening Means 90 for controlling the opening of the variable nozzle so as to have a product Avntsol0; a sensor 91 for detecting the intake pressure Pm; a means 92 for calculating a differential pressure between the estimated exhaust pressure Pexh and the intake pressure Pm; Means 93 for calculating the target EGR rate Megr according to the engine speed and load, means 94 for calculating the required EGR amount Tqe based on the target EGR rate, and the difference between the required EGR amount Tqe and the intake pressure Means 95 for calculating the required opening area Tav of the EGR valve from the pressure (Pexh-Pm) and means 96 for controlling the opening degree of the EGR valve so as to be the required opening area Tav are provided.
[0021]
In a second invention, the fuel injection amount Qf is used as the engine load in the first invention, and the exhaust pressure Pexh is
Pexh = Kpexh × {(Qas0 + Qf) / Avnt)}²× Texh + Pa
Where Pexh: exhaust pressure,
Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value,
Texh: Turbine inlet exhaust temperature,
Pa: compressor inlet pressure,
Kpexh: constant,
It calculates by the formula of
[0022]
  In the third invention, the fuel injection amount Qf is used as the engine load in the first invention, and the turbine inlet exhaust pressure equivalent value Pexhr is calculated as follows:
    P exhr= Kpexhn × {(Qas0 + Qf) / Avnt)}²× Texh
      However,Qas0: intake air volume,
              Qf: fuel injection amount,
              Avnt: Effective area equivalent value of variable nozzle,
              Texh: Turbine inlet exhaust temperature,
              Kpexhn: constant,
The exhaust pressure Pexh is calculated from the turbine inlet exhaust pressure equivalent value Pexhr and the compressor inlet pressure Pa.
[0023]
According to a fourth invention, there is provided a sensor for detecting the compressor inlet pressure Pa in the second or third invention.
[0024]
In a fifth aspect of the invention, in any one of the first to fourth aspects of the invention, the effective area equivalent value Avnt is an efficiency ηn of the gas flowing through the variable nozzle and a nozzle opening command given to an actuator that drives the variable nozzle. It is the product of the value VNTstep.
[0025]
In a sixth aspect of the invention, in any one of the first to fifth aspects, the required opening area Avntsol0 of the variable nozzle is corrected by the efficiency ηn of the gas flowing through the variable nozzle.
[0026]
In the seventh invention, the efficiency ηn of the gas flowing through the variable nozzle in the fifth or sixth invention is a product of the friction loss ξfric and the nozzle loss ξconv.
[0027]
In the eighth invention, the friction loss ξfric in the seventh invention is a value proportional to the square root of the exhaust flow velocity equivalent value Wexh.
[0028]
In a ninth invention, in the seventh invention, the nozzle loss ξconv is a value corresponding to the nozzle opening command value VNTstep and the total exhaust weight Qtotal.
[0029]
In the tenth invention, the efficiency ηn of the gas flowing through the variable nozzle in the fifth or sixth invention is a value corresponding to the nozzle opening command value VNTstep and the exhaust amount Qexh.
[0030]
In an eleventh aspect of the invention, the means 84 for detecting the exhaust gas temperature Texh in any one of the first to tenth aspects of the present invention, as shown in FIG. 58, from the actual opening Lifts of the EGR valve, Means 101 for calculating the opening area equivalent value Ave, means 102 for calculating the EGR amount Qe based on the differential pressure (Pexh−Pm) between the opening area equivalent value Ave and the intake pressure, and the EGR amount Qe Means 103 for calculating the cylinder intake EGR amount Qec based on the engine speed Ne, the cylinder intake EGR amount Qec, the compressor inlet temperature Ta, the cylinder intake fresh air amount Qac, and the previous exhaust temperature Texh_n-1Based on the above, the means 104 for calculating the cylinder intake gas temperature Tn, the means 105 for calculating the cycle processing value Tn0 of the cylinder intake gas temperature Tn, the means 106 for calculating the fuel injection amount Qf, and the fuel injection amount Qf Means 107 for calculating the cycle processing value Qf0, means 108 for calculating the exhaust gas temperature basic value Texhb based on the cycle processing value Qf0, and calculating the intake air temperature correction coefficient Ktexh1 from the cycle processing value Tn0 of the cylinder intake gas temperature Tn. Means 109 for correcting the exhaust gas temperature basic value Texhb with the correction coefficient Ktexh1 and calculating the exhaust gas temperature Texh this time, the opening area equivalent value Ave of the EGR valve is set to the EGR valve. Correct with the efficiency ηn2 of the flowing gas.
[0031]
In the twelfth invention, in the eleventh invention, the efficiency ηn2 of the gas flowing through the EGR valve is determined by the pressure loss ξconv-egr at the EGR valve and the friction loss ξfric-egr in the EGR passage communicating the exhaust pipe and the intake pipe. Is the product of
[0032]
In a thirteenth invention, the pressure loss ξconv-egr at the EGR valve in the twelfth invention is
ξconv-egr = 1 / {1- (Ave / Avps)²}^1/2
However, Ave: EGR valve opening area equivalent value,
Avps: EGR valve fully open area equivalent value,
It calculates by the formula of
[0033]
In a fourteenth invention, the friction loss ξfric-egr of the EGR passage in the twelfth invention is
ξfric-egr = {λ × ζ × (l / d) × (1 / (2g))}^1/2
  Where λ: straight pipe loss coefficient,
ζ: bending pipe loss coefficient,
l: EGR passage length,
d: Diameter of EGR passage,
g: acceleration of gravity,
It calculates by the formula of
[0034]
In a fifteenth aspect, in the twelfth aspect, the straight pipe loss coefficient λ is
λ = Cs × [{2 × (Tstd / Texh) × (Pexh−Pm)}^1/2/ (Ν × d)]^-1/4
Where Tstd: standard atmospheric temperature,
Texh: exhaust temperature,
Pexh: Exhaust pressure,
Pm: Intake pressure
ν: Kinematic viscosity of exhaust,
d: Diameter of EGR passage,
Cs: constant,
It calculates by the formula of
[0035]
According to a sixteenth invention, in any one of the eleventh to fifteenth inventions, a nozzle opening correction coefficient Ktexh4 of exhaust temperature is calculated according to the nozzle opening command value VNTstep and the exhaust amount Qexh, and this correction coefficient Ktexh4 To correct the exhaust gas temperature basic value Texhb.
[0036]
In the seventeenth invention, when the intake port is provided with a swirl valve in any one of the eleventh to sixteenth inventions, the swirl correction coefficient for the exhaust gas temperature according to the opening position of the swirl valve and the engine speed Ne. Ktexh3 is calculated, and the exhaust gas basic value Texhb is corrected with the correction coefficient Ktexh3.
[0037]
The eighteenth invention comprises a variable displacement turbocharger having a variable nozzle in the turbine and an EGR valve capable of controlling the EGR amount, and as shown in FIG. 59, means 81 for detecting the intake air amount Qas0, A means 82 for detecting the load, a means 83 for detecting the effective area equivalent value Avnt of the variable nozzle, a means 84 for detecting the exhaust gas temperature Texh, and a means 85 for estimating the exhaust pressure Pexh using these four elements Based on the target excess air ratio, the means 86 for calculating the differential pressure between the estimated exhaust pressure Pexh and the atmospheric pressure Pa, the means 87 for calculating the target excess air rate Mlamb according to the engine speed and the load, and the like. Means 88 for calculating the required fresh air amount Tqa, means 89 for calculating the required opening area Avntsol0 of the variable nozzle from the required fresh air amount Tqa and the differential pressure (Pexh−Pa) between the atmospheric pressure, and this requirement Open A means 90 for controlling the opening of the variable nozzle so as to have an area Avntsol0; a sensor 91 for detecting the intake pressure Pm; a means 92 for calculating a differential pressure between the estimated exhaust pressure Pexh and the intake pressure Pm; A means 121 for calculating the straight pipe loss λ of the EGR passage communicating the exhaust pipe and the intake pipe based on the differential pressure (Pexh−Pm) with the intake pressure, and the straight pipe loss λ and the bent pipe loss of the EGR passage. means 122 for calculating the friction loss ξfric-egr of the EGR passage based on ζ, means 123 for calculating the opening area equivalent value Ave of the EGR valve based on the actual opening of the EGR valve, and the opening area The means 124 for calculating the loss ξconv-egr at the EGR valve based on the equivalent value Ave, and the product of the loss ξconv-egr at the EGR valve and the friction loss ξfric-egr at the EGR passage, the gas flowing through the EGR valve To calculate the efficiency of ηn2 125, means 126 for calculating a value obtained by correcting the opening area equivalent value Ave of the EGR valve with the efficiency ηn2 as a required opening area Tav of the EGR valve, and opening of the EGR valve so as to be the required opening area Tav And a means 127 for controlling the degree.
[0038]
In a nineteenth aspect, the fuel injection amount Qf is used as the engine load in the eighteenth aspect, and the exhaust pressure Pexh is
Pexh = Kpexh × {(Qas0 + Qf) / Avnt)}²× Texh + Pa
Where Pexh: exhaust pressure,
Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value,
Texh: Turbine inlet exhaust temperature,
Pa: compressor inlet pressure,
Kpexh: constant,
It calculates by the formula of
[0039]
  In a twentieth invention, a fuel injection amount Qf is used as the engine load in the eighteenth invention, and the turbine inlet exhaust pressure equivalent value Pexhr is
    P exhr= Kpexhn × {(Qas0 + Qf) / Avnt)}²× Texh
      However,Qas0: intake air volume,
              Qf: fuel injection amount,
              Avnt: Effective area equivalent value of variable nozzle,
              Texh: Turbine inlet exhaust temperature,
              Kpexhn: constant,
The exhaust pressure Pexh is calculated from the turbine inlet exhaust pressure equivalent value Pexhr and the compressor inlet pressure Pa.
[0040]
According to a twenty-first aspect, the sensor for detecting the compressor inlet pressure Pa in the nineteenth or twentieth aspect is provided.
[0041]
According to a twenty-second aspect, in any one of the eighteenth to twenty-first aspects, the effective area equivalent value Avnt is an efficiency ηn of the gas flowing through the variable nozzle and a nozzle opening command given to an actuator that drives the variable nozzle. It is the product of the value VNTstep.
[0042]
In a twenty-third aspect, in any one of the eighteenth to twenty-second aspects, the required opening area Avntsol0 of the variable nozzle is corrected by the efficiency ηn of the gas flowing through the variable nozzle.
[0043]
In the twenty-fourth invention, the efficiency ηn of the gas flowing through the variable nozzle in the twenty-second or twenty-third invention is the product of the friction loss ξfric and the nozzle loss ξconv.
[0044]
In a twenty-fifth aspect, in the twenty-fourth aspect, the friction loss ξfric is a value proportional to the square root of the exhaust flow velocity equivalent value Wexh.
[0045]
In a twenty-sixth aspect, in the twenty-fourth aspect, the nozzle loss ξconv is a value corresponding to the nozzle opening command value VNTstep and the total exhaust weight Qtotal.
[0046]
In a twenty-seventh aspect, in the twenty-second or twenty-third aspect, the efficiency ηn of the gas flowing through the variable nozzle is a value corresponding to the nozzle opening command value VNTstep and the exhaust amount Qexh.
[0047]
In a twenty-eighth aspect of the invention, the means 84 for detecting the exhaust gas temperature Texh in any one of the eighteenth to the twenty-seventh aspects of the present invention, as shown in FIG. 58, from the actual opening Lifts of the EGR valve, Means 101 for calculating the opening area equivalent value Ave, means 102 for calculating the EGR amount Qe based on the differential pressure (Pexh−Pm) between the opening area equivalent value Ave and the intake pressure, and the EGR amount Qe Means 103 for calculating the cylinder intake EGR amount Qec based on the engine speed Ne, the cylinder intake EGR amount Qec, the compressor inlet temperature Ta, the cylinder intake fresh air amount Qac, and the previous exhaust temperature Texh_n-1Based on the above, the means 104 for calculating the cylinder intake gas temperature Tn, the means 105 for calculating the cycle processing value Tn0 of the cylinder intake gas temperature Tn, the means 106 for calculating the fuel injection amount Qf, and the fuel injection amount Qf Means 107 for calculating the cycle processing value Qf0, means 108 for calculating the exhaust gas temperature basic value Texhb based on the cycle processing value Qf0, and calculating the intake air temperature correction coefficient Ktexh1 from the cycle processing value Tn0 of the cylinder intake gas temperature Tn. Means 109 for correcting the exhaust gas temperature basic value Texhb with the correction coefficient Ktexh1 and calculating the exhaust gas temperature Texh this time, the opening area equivalent value Ave of the EGR valve is set to the EGR valve. Correct with the efficiency ηn2 of the flowing gas.
[0048]
According to a twenty-ninth aspect, in the twenty-eighth aspect, the efficiency ηn2 of the gas flowing through the EGR valve is determined by the pressure loss ξconv-egr at the EGR valve and the friction loss ξfric-egr of the EGR passage communicating the exhaust pipe and the intake pipe Is the product of
[0049]
In a thirtieth aspect, in the twenty-ninth aspect, the pressure loss ξconv-egr at the EGR valve is
ξconv-egr = 1 / {1- (Ave / Avps)²}^1/2
However, Ave: EGR valve opening area equivalent value,
Avps: EGR valve fully open area equivalent value,
It calculates by the formula of
[0050]
In a thirty-first aspect, the friction loss ξfric-egr of the EGR passage in the twenty-ninth aspect is
ξfric-egr = {λ × ζ × (l / d) × (1 / (2g))}^1/2
  Where λ: straight pipe loss coefficient,
ζ: bending pipe loss coefficient,
l: EGR passage length,
d: Diameter of EGR passage,
g: acceleration of gravity,
It calculates by the formula of
[0051]
In a thirty-second invention, in the twenty-ninth invention, the straight pipe loss coefficient λ is
λ = Cs × [{2 × (Tstd / Texh) × (Pexh−Pm)}^1/2/ (Ν × d)]^-1/4
Where Tstd: standard atmospheric temperature,
Texh: exhaust temperature,
Pexh: Exhaust pressure,
Pm: Intake pressure
ν: Kinematic viscosity of exhaust,
d: Diameter of EGR passage,
Cs: constant,
It calculates by the formula of
[0052]
In a thirty-third invention, in any one of the twenty-eighth to thirty-second inventions, a nozzle opening correction coefficient Ktexh4 of the exhaust temperature is calculated according to the nozzle opening command value VNTstep and the exhaust amount Qexh, and this correction coefficient Ktexh4 To correct the exhaust gas temperature basic value Texhb.
[0053]
In a thirty-fourth aspect of the invention, when the intake port is provided with a swirl valve in any one of the twenty-eighth to thirty-third aspects of the invention, the swirl correction coefficient for the exhaust gas temperature is determined according to the opening position of the swirl valve and the engine speed Ne. Ktexh3 is calculated, and the exhaust gas basic value Texhb is corrected with the correction coefficient Ktexh3.
[0054]
【The invention's effect】
In the first, thirteenth, fourteenth, thirty-first, and thirty-first inventions, a target excess air ratio is calculated according to the engine speed and load, and a required fresh air amount is calculated based on the target excess air ratio. Calculating the required opening area of the variable nozzle from the differential pressure between the estimated exhaust pressure and the intake pressure and the required fresh air amount, and controlling the nozzle opening of the variable nozzle so that the required opening area is obtained; The target EGR rate is calculated according to the engine speed and the load, the required EGR amount is calculated based on the target EGR rate, and the differential pressure between the estimated exhaust pressure and the intake pressure and the required EGR amount are used to calculate the EGR valve. The required opening area is calculated, and the EGR valve opening is controlled so as to be the required opening area. In other words, since the control target value is distributed to the EGR valve and the variable nozzle in order to achieve an oxygen concentration that can simultaneously reduce NOx and PM, as in the conventional device (Japanese Patent Laid-Open No. 6-173752), even in a transient state. The control responsiveness is not deteriorated, so that the engine can be operated with the optimum supercharging pressure and the optimum EGR amount even during the transition, and NOx and PM can be simultaneously reduced.
[0055]
In the first and eighteenth inventions, the exhaust pressure can be directly calculated from the four elements of the intake air amount, the engine load, the variable nozzle effective area equivalent value, and the exhaust temperature. Even when a charger is provided, the exhaust pressure can be estimated without a delay in response during a transition.
In the second and nineteenth inventions, the exhaust pressure is calculated on the assumption that the gas flow passing through the turbine nozzle is a flow when the flow path area is reduced. According to this invention, high calculation accuracy of exhaust pressure can be obtained in the standard state.
[0056]
If the exhaust pressure is calculated on the assumption that the flow of gas passing through the turbine nozzle is a flow when the flow path area is reduced, if the exhaust pressure is different from the standard state (for example, if the temperature is higher than the high altitude, standard temperature, the humidity will be According to the third and twentieth inventions, the flow of gas passing through the turbine nozzle is adiabatically changed to flow when the ideal gas is adiabatically changed. Since the flow rate and pressure per unit time (that is, the change in specific gravity) can be accurately described by the calculation formula that assumes the flow in the case of High calculation accuracy can be obtained. In addition, since the characteristic that must be matched in this case is simple, only calculation is sufficient (no need for matching), and the calculation accuracy of the exhaust pressure can be increased by calculation only on the desk.
[0057]
According to the fourth and twenty-first aspects, even if the compressor inlet pressure changes due to a change in altitude, the accuracy of the exhaust pressure does not decrease.
[0058]
According to the fifth and sixth aspects, the efficiency of the gas flowing through the variable nozzle can be considered.
[0059]
According to the seventh and twenty-fourth inventions, friction loss and nozzle loss can be considered separately.
[0060]
According to the eighth and twenty-fifth aspects, even if the exhaust flow velocity is different, the friction loss can be given with high accuracy.
[0061]
When the change in the flow velocity is large, the loss to the contraction tube (1 / {1- (A₂/ A₁)²}^1/2If the nozzle loss is considered as it is, the actual nozzle loss often does not match. However, according to the ninth and twenty-sixth inventions, the actual nozzle loss is good even when the flow rate changes greatly. Can be matched.
[0062]
According to the tenth and twenty-seventh aspects, the calculation load of the CPU can be reduced by simplifying the calculation of the efficiency of the gas flowing through the variable nozzle.
[0063]
The theory is that the value corresponding to the opening area can be corrected by the efficiency of the gas flowing through the valve, generally only in the steady flow. However, this time, when an experiment was performed in a case where the value corresponding to the opening area of the EGR valve was corrected by the efficiency of the gas flowing through the EGR valve, in the case of a regular flow such as pulsating exhaust, We found for the first time that the EGR flow rate could be calculated accurately with both transients. Therefore, according to the eleventh and twenty-eighth aspects, it is possible to take into account the pressure loss of the gas in the EGR passage even in the case of an unsteady flow such as exhaust gas. Arithmetic became possible.
[0064]
According to the twelfth and twenty-ninth inventions, the pressure loss in the EGR valve and the friction loss in the EGR passage can be considered separately.
[0065]
According to the fifteenth and thirty-second inventions, the straight pipe loss coefficient can be obtained with good response even during a transient in which the exhaust pressure changes rapidly.
[0066]
According to the sixteenth, seventeenth, thirty-third, and thirty-fourth inventions, the calculation accuracy of the exhaust temperature is improved, and the calculation accuracy of the exhaust pressure is improved by this improvement.
[0067]
According to the eighteenth aspect of the invention, the calculation accuracy of the required opening area during the transient state of the EGR valve is improved by the improvement of the calculation accuracy of the exhaust pressure, and even in an unsteady flow like exhaust, Gas pressure loss can be taken into account, which makes it possible to calculate the required opening area of the EGR valve with higher accuracy.
[0068]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the engine includes a known common rail fuel injection device 10.
[0069]
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.
[0070]
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.
[0071]
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.
[0072]
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 via the pressure control valve 31 so that the common rail pressure detected by the sensor 32 matches this target pressure. Further, the ON time of the three-way valve 25 is controlled in accordance with the calculated target fuel injection amount Qf of the main injection.
[0073]
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. .
[0074]
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.
[0075]
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.
[0076]
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.
[0077]
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.
[0078]
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.
[0079]
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.
[0080]
Returning to FIG. 1, the variable capacity turbocharger 2 is provided in the exhaust passage 53 downstream of the opening of the EGR passage 54. This is provided with a variable nozzle 2d driven by a step motor 2c at the scroll inlet of an exhaust turbine 2a arranged coaxially with the intake compressor 2b. In order to obtain the supercharging pressure, the nozzle opening (inclined state) increases the flow rate of the exhaust gas introduced into the exhaust turbine 2a on the low rotation side, and the exhaust gas is introduced into the exhaust turbine 2a without resistance on the high rotation side. Degree (fully open state). Moreover, when it is in a predetermined condition, the variable nozzle 2d is controlled by the nozzle opening degree which reduces a supercharging pressure.
[0081]
In this embodiment, the nozzle opening degree of the variable nozzle 2d is explained by a method of driving by the step motor 2c. However, it is driven by a diaphragm actuator and an electromagnetic solenoid for adjusting the control negative pressure to the actuator or by a DC motor. A method may be used. Further, the nozzle opening may be feedback controlled based on a signal from the nozzle position sensor.
[0082]
1 is a NOx catalyst (for example, a copper-based zeolite catalyst), 3 is an intercooler provided in the intake passage 52 downstream of the intake compressor 2b and upstream of the collector 52a, and 4 is a swirl control valve.
[0083]
From the viewpoint of supercharging pressure control, EGR control also physically plays the role of supercharging pressure control. That is, the supercharging pressure also changes by changing the EGR amount. On the other hand, when the supercharging pressure is changed, the exhaust pressure changes, so the EGR amount also changes, and the supercharging pressure and the EGR amount cannot be controlled independently. In addition, there is a disturbance in control of each other.
[0084]
Therefore, the supercharging pressure and the control negative pressure supplied to the EGR valve are selectively detected by the intake pressure sensor by time sharing, and the EGR amount is controlled and supercharged based on the control negative pressure and the supercharging pressure. A technique for controlling the pressure is disclosed, but this technique deteriorates the control responsiveness particularly during the transition as described above.
[0085]
Here, the relationship between the sensitivity of the EGR rate and the amount of fresh air (supercharging pressure) for each emission amount of NOx and PM is as shown in FIG. 4, so that the oxygen concentration can be reduced simultaneously with NOx and PM. Sets the target excess air ratio and the target EGR ratio in advance, and controls the opening of the variable nozzle 2d and the opening of the EGR valve 57 in a coordinated manner so as to obtain the target excess air ratio and the target EGR ratio. There is a need. For this purpose, as described above with reference to FIG. 5, the target fresh air amount Qa is calculated by the above-described equation (a) using the target excess air rate Mlamb and the fuel injection amount Qf, and this target fresh air amount Qa flows. The opening area Avntsol0 of the variable nozzle 2d at the time is obtained by the above equation (b), and the target EGR amount Qegr is calculated by the above equation (c) using the target fresh air amount Qa and the target EGR rate Megr. What is necessary is just to obtain | require the opening area Ae of the EGR valve 57 when this target EGR amount Qegr flows by said (d) Formula. If the three variables of the intake pressure Pm, the exhaust pressure Pexh, and the atmospheric pressure Pa can be known from the equations (b) and (d), the nozzle opening (supercharging pressure) and the EGR valve opening (EGR amount) can be determined. In order to achieve coordinated control and to achieve an oxygen concentration that can simultaneously reduce NOx and PM, the control target value can be distributed to the EGR valve and the variable nozzle.
[0086]
Of the above three variables, variables other than the exhaust pressure Pexh are relatively easy to detect, but it is generally difficult to obtain a sensor having durability at high exhaust temperature and oxidizing atmosphere. In addition, it is expensive as a vehicle-mounted sensor. In addition, it is difficult to obtain sufficient responsiveness to provide durability under the use conditions as described above. Therefore, a means for estimating the exhaust pressure Pexh is required to control the supercharging pressure and the EGR amount with high accuracy and without impairing responsiveness and stability. As a method of estimating the exhaust pressure without using a pressure sensor, the steady exhaust pressure is calculated based on the total intake air amount, the turbine acceleration energy is calculated from the steady exhaust pressure and the exhaust gas flow ratio, and the load resistance is calculated from the previous turbine speed. There is a method that calculates the current turbine speed from the difference between the turbine acceleration energy and the load resistance, and calculates the exhaust pressure according to the current turbine speed. Since the exhaust pressure is estimated by correcting the steady exhaust pressure according to the amount according to the change in the turbine speed, it is difficult to apply this method to the variable capacity turbocharger. This is because when the nozzle opening is changed, the intake air amount increases or decreases with a non-linear characteristic, and it becomes difficult to obtain the steady exhaust pressure. In addition, it is difficult to estimate the turbine speed with high accuracy by the disclosed technology, and it is necessary to estimate the turbine speed according to the nozzle opening degree in order to obtain a high-precision turbine speed.
[0087]
For this reason, in the control unit 41, the exhaust pressure Pexh is directly used by using four elements of the intake air amount Qas0, the engine load (for example, the fuel injection amount Qf), the effective area equivalent value Avnt of the variable nozzle, and the exhaust temperature Texh. It is calculated (estimated) with a simple calculation formula.
[0088]
Further, EGR control and supercharging pressure control are performed according to FIG. 5 using the estimated exhaust pressure Pexh. However, FIG. 5 shows a basic concept. In actuality, with respect to the supercharging pressure control, the target excess air rate Mlamb is calculated in accordance with the engine speed and the load (see FIG. 35). The required fresh air amount Tqa is calculated based on the excess rate Mlamb (see FIGS. 38 and 39), and the required opening of the variable nozzle 2d is calculated from the difference between the estimated exhaust pressure Pexh and the intake pressure Pm and the required fresh air amount Tqa. The area Avntsol0 is calculated (see FIG. 40), and the nozzle opening degree of the variable nozzle 2d is controlled so as to be the required opening area Avntsol0. For EGR control, the target EGR rate Megr is calculated according to the engine speed and load (see FIG. 42), and the required EGR amount Tqe is calculated based on the target EGR rate Megr (see FIG. 45). The required opening area Tav of the EGR valve 57 is calculated from the difference between the estimated exhaust pressure Pexh and the intake pressure Pm and the required EGR amount Tqe (see FIG. 46), and the EGR valve opening degree is set so as to be the required opening area Tav. To control.
[0089]
This control performed by the control unit 41 will be described in detail below.
[0090]
First, a rough block diagram of the control is shown in FIG. 6, a detailed flowchart of EGR control and maps and tables used for the flow are shown in FIGS. 8 to 31, 33, 34, and 42 to 47. A detailed flowchart of the supply pressure control and maps and tables used for the flow are shown in FIGS.
[0091]
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). For this reason, as for sensors other than the accelerator opening sensor 33, the crank angle sensors 34 and 35, and the water temperature sensor 36, an air flow meter 55, an intake air temperature sensor 71 provided in the vicinity of the air flow meter 55, and a new one in the present embodiment are provided. With the intake pressure sensor 72 alone, various parameters required for control (for example, exhaust pressure described later) are all predicted and calculated in the control unit 41. The image of model reference control is that each block in FIG. 6 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.
[0092]
More specifically, (1) sampling of sensor detection values such as the air flow meter 55 is performed at regular intervals (see steps 1 to 3, FIG. 13, and FIG. 9), and (2) parameter calculation in model reference control. Basically, every time a Ref signal (crank angle reference position signal) is input (steps 4 to 7, FIG. 10, FIG. 11, FIG. 18, FIG. 19, FIG. 22, FIG. 22, FIG. 28, FIG. 31, FIG. 33, FIG. 35, FIG. 38, FIG. 39, FIG. 40, FIG. 42, FIG. 45, FIG. 46), (3) The output to the final actuator is executed at regular intervals. In the following description, a job for each input of the Ref signal is described as a job for every fixed time (see FIG. 8).
[0093]
The calculation of each parameter in the above (2) is performed in the order shown in FIG. In FIG. 7, it does not take a long time to perform all the processes, and all the processes are completed in an instant by inputting the Ref signal. In the figure, “n−1” after the symbol means the previous value (that is, the value calculated before 1 Ref signal).
[0094]
Hereinafter, the calculation of each parameter will be described in the order shown in FIG.
[0095]
The EGR control itself has already been disclosed in Japanese Patent Application No. 10-31460 (hereinafter referred to as “prior application device”).
[0096]
FIG. 8 is a flow of cycle processing of the cylinder intake fresh air amount, the fuel injection amount, and the cylinder intake gas temperature. In step 1, the cylinder intake fresh air amount Qac, the fuel injection amount Qf, and the cylinder intake gas temperature Tn are read. The calculation of the cylinder intake fresh air amount Qac, the fuel injection amount Qf, and the cylinder intake gas temperature Tn will be described later with reference to FIGS. 9, 19, and 18, respectively.
[0097]
In step 2, using these Qac, Qf, and Tn, Qexh = Qac · Z^{-(CYLN # -1)}, Qf0 = Qf · Z^{-(CYLN # -2)}, Tn0 = Tn · Z^{-(CYLN # -1)}The 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 55. 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.
[0098]
FIG. 9 is a flow for calculating the cylinder intake fresh air amount Qac.
[0099]
In step 1, the output voltage of the air flow meter (AMF) 55 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.
[0100]
In Step 4, the engine speed Ne is read. In Step 5, the cylinder intake air amount (per intake stroke) Qac0 is calculated from the speed Ne and the weighted average value Qas0 of the intake air amount.
[0101]
[Expression 2]
Qac0 = (Qas0 / Ne) × KCON #
Where KCON # is a constant,
Calculate with the following formula.
[0102]
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 a cylinder fresh air amount (per intake stroke) 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.
[0103]
In step 7, the volume ratio Kvol and the previous value Kin of the volume efficiency equivalent value_n-1From the above-described cylinder fresh air amount Qacn at the collector 52a inlet
[0104]
[Equation 3]
Qac = Qac_n-1× (1-Kvol × Kin_n-1) + Qacn x Kvol x Kin_n-1
However, Qac_n-1: The previous value of Qac,
Kin_n-1: The previous value of Kin,
The cylinder intake fresh air amount (per intake stroke) 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.
[0105]
FIG. 10 is a flow for calculating the cylinder intake EGR amount Qec.
[0106]
The content of this calculation is the same as the calculation method of the cylinder intake fresh air amount Qac shown in FIG. Qe which is the previous value of the EGR (flow) amount Qe obtained in step 1 as described later (see FIG. 33)._n-1In step 2, the engine speed Ne is read.
[0107]
In step 4, Qe_n-1, Ne, and constant KCON #, the cylinder intake EGR amount (per intake stroke) Qecn at the collector 52a inlet
[0108]
[Expression 4]
Qecn = (Qe_n-1/ Ne) x KCON #
Where KCON # is a constant,
Calculate with the following formula. Further, in step 5, the value Qecn at the collector inlet 52a, the volume ratio Kvol, and the previous value Kin corresponding to the volumetric efficiency equivalent value._n-1Using,
[0109]
[Equation 5]
Qec = Qec_n-1× (1-Kvol × Kin_n-1) + Qecn × Kvol × Kin_n-1
However, Qec_n-1: The previous value of Qec,
Kin_n-1: The previous value of Kin,
The cylinder intake EGR amount (per intake stroke) 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.
[0110]
In the prior application device, the weighted average processing is performed to smooth the influence of exhaust pulsation on the EGR amount Qe. However, in this embodiment, the weighted average processing is not performed on Qe. This is due to the following reason. Even if the weighted average processing value of Qe is used, the cylinder intake EGR amount Qec is calculated including an error associated with the weighted average even though the effect of exhaust pulsation is smoothed. Therefore, in this embodiment, the calculation accuracy of Qec is increased as much as possible by calculating Qec with Qe having pulsation.
[0111]
FIG. 11 is a flow for calculating the volumetric efficiency equivalent value Kin.
[0112]
In step 1, the cylinder intake fresh air amount Qac, the cylinder intake EGR amount Qec, the intake pressure Pm, and the previous value of the intake gas temperature, Tn_n-1Of which Pm and Tn_n-1From step 2, the map having the contents shown in FIG. 12 is searched to obtain the gas density ROUqcyl. In step 3, the gas density ROUqcyl and the cylinder gas weight Qcyl (= Qac + Qec) are used.
[0113]
[Formula 6]
Kin = Qcyl / (Vc / ROUqcyl)
Vc: 1 cylinder volume,
The volume efficiency equivalent value Kin is calculated by the following formula (volume efficiency definition formula).
[0114]
Here, the calculation method of the volume efficiency equivalent value Kin is different from that of the prior application device (simpler than the prior application device). This is because the intake air pressure sensor 72 is added in the present embodiment, and the volumetric efficiency can be calculated from the definition formula using this sensor detection value. Thereby, in this embodiment, the adaptation man-hour can be reduced about the calculation of volumetric efficiency.
[0115]
FIG. 13 is a flow of calculation (detection) of the intake pressure (in the collector).
[0116]
In step 1, the output voltage Pm_v of the intake pressure sensor 72 is read. In step 2, the output voltage Pm_v is converted into a pressure Pm_0 by searching a table having the contents shown in FIG. 14, and the pressure value is weighted in step 3. An average process is performed, and the weighted average value Pm1 is calculated as the intake pressure Pm.
[0117]
Unlike the prior application apparatus in which the intake pressure sensor is not provided, in the present embodiment, since the intake pressure sensor is provided, the calculation of the intake pressure Pm is simplified.
[0118]
Here, the reason why the intake pressure sensor is newly added is as follows. While the turbocharger was not a variable displacement type in the prior application device, the turbocharger of this embodiment is a variable displacement type, so the nozzle opening is newly added as an unknown number (degree of freedom). The unknown has increased by one. Therefore, in order to make the unknown the same as the prior application device, an intake pressure sensor 72 is provided (in the prior application device, the intake pressure is also an unknown, but in this embodiment, the intake pressure is not an unknown).
[0119]
FIG. 15 is a flow for calculating the intake fresh air temperature Ta.
[0120]
In step 1, the output voltage Ta_v of the intake air temperature sensor 71 is read. In step 2, the output voltage Ta_v is converted into the temperature Ta0 by searching a table having the same characteristics as in FIG. 14 in step 2.
[0121]
In step 3, it is determined whether the intake air temperature sensor 71 is mounted on the upstream side or the downstream side of the intercooler 3.
[0122]
As shown in FIG. 1, when the intake air temperature sensor 71 is on the upstream side of the intercooler 3, the routine proceeds to step 4 where Pm, which is the previous value of the intake air pressure._n-1Pressure correction coefficient Ktmpi based on the following equation: Ktmpi = Pm_n-1X Calculated from the equation of PA #. However, PA # is a constant.
[0123]
In step 5, the intake fresh air temperature Ta at the collector 52a inlet is determined based on the pressure correction coefficient Ktmpi.
[0124]
[Expression 7]
Ta = Ta0 × Ktmpi + TOFF #
Where TOFF # is a constant
Calculated by the formula (approximate formula) This calculation is a temperature change prediction calculation based on the laws of thermodynamics.
[0125]
The intake air temperature may be corrected by the vehicle speed, the intake air amount, or the like. At this time, a table containing the characteristics shown in FIGS. 16 and 17 is created in advance, and each table is searched from the vehicle speed and the intake air amount (Qas0), whereby the intake air temperature correction value Kvsp, An intake air amount correction value Kqa for temperature is obtained, and instead of the above equation 7,
[0126]
[Equation 8]
Ta = Kvsp × Kqa × Ta0 × Ktmpi + TOFF #
The intake fresh air temperature Ta may be obtained by the following equation.
[0127]
On the other hand, if the intake air temperature sensor is mounted downstream of the intercooler 3, both the temperature rise due to supercharging and the temperature drop due to the intercooler have already been factored in. After the intake fresh air temperature Ta is set as it is, the processing is terminated.
[0128]
FIG. 18 is a flow for calculating the cylinder intake gas temperature Tn. In step 1, the previous value of the cylinder intake fresh air amount Qac, the intake fresh air temperature Ta, the cylinder intake EGR amount Qec, and the exhaust temperature is Texh._n-1Of which, in step 2, the previous value Texh of the exhaust temperature_n-1Is multiplied by the exhaust gas temperature drop coefficient Ktlos in the EGR passage 54 to calculate the cylinder intake EGR gas temperature Te.
[0129]
[Equation 9]
Tn = (Qac × Ta + Qec × Te) / (Qac + Qec)
The average temperature of the cylinder intake fresh air and the cylinder intake EGR gas is obtained by the following equation, and this is set as the cylinder intake temperature Tn.
[0130]
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. .
[0131]
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.
[0132]
FIG. 22 is a flow for calculating the exhaust temperature Texh. In steps 1 and 2, the cycle processing value Qf0 of the fuel injection amount and the cycle processing value Tn0 of the cylinder intake gas temperature are read. Furthermore, in step 3, Pexh which is the previous value of the exhaust pressure_n-1Is read.
[0133]
In step 4, the exhaust temperature basic value Texhb is obtained by searching a table having the contents shown in FIG. 23 from the cycle processing value Qf0 of the fuel injection amount.
[0134]
In step 5, the intake air temperature correction coefficient Ktexh1 of the exhaust temperature is calculated from the cycle processing value Tn0 of the intake gas temperature described above, and Ktexh1 = (Tn0 / TA #).^{KN #}(Where TA # and KN # are constants), and 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-1To Ktexh2 = (Pexh_n-1/ PA #)^{(# Ke-1) / # Ke}(Where PA # and #Ke are constants) are calculated respectively. These two correction coefficients Ktexh1 and Ktexh2 may be obtained by table search (see FIGS. 24 and 25).
[0135]
Next, in step 7, the exhaust temperature swirl correction coefficient Ktexh3 is determined by searching a table having the contents shown in FIG. 26 from the swirl valve opening position (two positions of fully open and fully closed) and the engine speed Ne. 8 is the previous value of command opening VNTstep_n-1The exhaust opening quantity nozzle opening correction coefficient Ktexh4 is obtained by searching a map having the contents shown in FIG. 27 from the exhaust amount Qexh.
[0136]
In step 9, the exhaust gas temperature Texh is calculated by multiplying the exhaust gas basic value Texhb by the four correction coefficients Ktexh1, Ktexh2, Ktexh3, and Ktexh4.
[0137]
Here, in this embodiment, since two correction coefficients Ktexh3 and Ktexh4 that are not present in the prior application apparatus are newly introduced, the calculation accuracy of the exhaust temperature Texh is improved in this embodiment. The reason for improving the calculation accuracy of the exhaust temperature Texh is as follows. As described later in FIG. 31, the exhaust temperature Texh is used for calculating the exhaust pressure Pexh. Therefore, improvement in the calculation accuracy of the exhaust temperature Texh leads to improvement in the calculation accuracy of the exhaust pressure Pexh. Therefore, in order to improve the calculation accuracy of the exhaust pressure Pexh, two correction coefficients Ktexh3 and Ktexh4 are newly introduced. .
[0138]
Note that the process of FIG. 22 approximates the following expression derived from the thermodynamic expression.
[0139]
[Expression 10]

[0140]
FIG. 28 is a calculation flow of the effective area equivalent value Avnt of the variable nozzle 2d. In step 1, VNTstep is the previous value of the command opening._n-1The total exhaust weight Qtotal (= Qas0 + Qf) and the exhaust temperature Texh are read.
[0141]
Of these, step 2 from total exhaust weight Qtotal and exhaust temperature Texh
[0142]
## EQU11 ##
Wexh = Qtotal × Texh / Tstd [m^Three/ sec]
Where Tstd: standard atmospheric temperature,
The exhaust gas flow rate equivalent value Wexh is calculated by the following formula.
[0143]
In Step 3, a table having the contents shown in FIG. 29 is searched from the value obtained by taking the square root of the exhaust flow velocity equivalent value Wexh to calculate the friction loss ξfric. In step 4, VNTstep is the previous value of the command opening._n-1Then, a map having the contents shown in FIG. 30 is retrieved from the total gas weight Qtotal to calculate the nozzle loss ξconv. Then, these two losses ξfric and ξconv are converted to VNTstep which is the previous value of the command opening in step 5._n-1Multiply by
[0144]
[Expression 12]
Avnt = VNTstep_n-1× ξfric × ξconv
The effective area equivalent value Avnt of the variable nozzle is calculated by the following equation.
[0145]
FIG. 31 is a flowchart for calculating the exhaust pressure (turbine inlet pressure) Pexh.
[0146]
In step 1, the weighted average value Qas0 of the intake air amount, the fuel injection amount Qf, the effective area equivalent value Avnt, the exhaust gas temperature Texh, and the atmospheric pressure (compressor inlet pressure) Pa are read. Using these parameters, in step 2,
[0147]
[Formula 13]
Pexh0 = Kpexh × {(Qas0 + Qfuel) / Avnt}²× Texh + Pa
Where Kpexh: constant,
The exhaust pressure Pexh0 is calculated by the following equation, and a weighted average process is performed on the exhaust pressure in step 3, and the weighted average value is obtained as the exhaust pressure Pexh.
[0148]
Here, each calculation method of the effective area equivalent value Avnt and the exhaust pressure Pexh0 is obtained as follows.
[0149]
<1> Basic equation of flow when the channel area is reduced
Consider an ideal fluid flowing in a pipe whose sectional area gradually decreases as shown in FIG.
[0150]
When the fluid pressure, flow velocity, area, and specific gravity are P, w, A, and ρ, respectively, the inlet is subscript 1, the outlet is subscript 2, and Bernoulli's theorem is applied to the inlet and outlet cross sections.
w₁ ²/ 2 + P₁/ Ρ = w₂ ²/ 2 + P₂/ Ρ (1a)
From the continuous formula
A₁× w₁= A₂× w₂                                    ... (1b)
Therefore, from both equations, w₁If you delete

Since the flow rate Q flowing per unit time is constant from the continuous equation,
Q = ρ × A₂× w₂

It can be expressed by the following formula.
[0151]
(3) 1 / {1- (A₂/ A₁)²}^1/2Is the efficiency ηn, the following basic equation is obtained.
[0152]
Q = ηn × A₂× {2ρ × (P₁-P₂)}^1/2              ... (4)
<2> State equation of turbocharger
Next, the relationship between the compressor 2b and the work balance in the turbocharger 2 is examined. The symbols used below are as shown in FIG.
[0153]
The effective power Lc of the compressor 2b is
Lc = Qas0 × Wc / ηc [W] (5)
However, Qas0: intake fresh air weight flow [kg / sec],
Wc: Compressor theory work [J / kg]
ηc: Compressor efficiency equivalent value.
[0154]
The effective power Lt of the turbine 2a is
Lt = ηt × Qtotal × Wt [W] (6)
Where Qtotal: total exhaust weight flow rate [kg / sec]
Wt: Turbine theory work [J / kg],
ηt: Value equivalent to turbine efficiency.
[0155]
Since the turbine 2a and the compressor 2b are directly connected via a shaft, if the actual work rates Lc and Lt of the compressor 2b and the turbine 2a are equal (bearing friction is included in the efficiency), the state equation of the turbocharger 2 As follows.
[0156]

<3> Exhaust pressure prediction formula when the flow path area is reduced
Applying the above equation (4) to the left side of the equation (7),

Where Avnt: effective area equivalent value of variable nozzle,
Pexh: Exhaust pressure,
Pa: Atmospheric pressure equivalent value,
ρe: exhaust density,
VNTstep: Command opening,
ηn: Efficiency (loss),
To get the formula
[0157]
When formula (8a) is arranged for exhaust pressure Pexh,

Here, the exhaust density ρe is
ρe = ρstd × (Ta / Texh) × (Pexh / Pa) (10)
Where ρstd: density of standard atmosphere (≒ 1.1679g / cm^Three),
Ta: compressor inlet temperature,
Texh: exhaust temperature,
Pexh: Exhaust pressure,
Pa: atmospheric pressure,
However, in this theoretical formula, the exhaust pressure Pexh is used to determine the exhaust density ρe, so it is not good.
ρe≈ρstd × (Ta / Texh) = Tstd / Texh (11)
Where Tstd: standard atmospheric temperature (≒ 298.15K),
The approximate expression is used. The reason why it can be approximated is that if the exhaust pressure Pexh increases, the exhaust temperature Texh also increases, so that the change in the exhaust pressure Pexh can be considered to be included in the exhaust temperature Texh.
[0158]
Therefore, the following equation is obtained by substituting equation (11) into equation (9).
[0159]

However, Kpexh: constant.
[0160]
Here, the compressor theoretical work Wc and the turbine theoretical work Wt on the right side of the equation (12a) are given by the following equations.
[0161]
[Expression 14]

[0162]
Now, the calculation formula of the exhaust pressure Pexh was obtained from the formula (12a). However, the calculation of ηc, ηt, Wc, Wt in the formula (12a) is complicated (the capability of the ECU is required). Since it is necessary to know the exhaust pressure Pexh to be obtained from the equation (14), further consideration will be given.
[0163]
Now, there is the following relationship between the total exhaust weight Qtotal, the intake fresh air amount Qas0, and the fuel injection amount Qf (the unit is all [kg / sec]).
[0164]
Qtotal = Qas0 + Qf (15)
Applying the above equation (4) to the left side of equation (15),
Avnt × {2 × ρe × (Pexh−Pa)}^1/2= Qas0 + Qf (16a)
Avnt = ηn × VNTstep (16b)
When the exhaust pressure Pexh is arranged by squaring both sides of the equation (16a), the following equation is obtained.
[0165]
Pexh = {(Qas0 + Qf) / Avnt}²× (1 / ρe) + Pa (17)
Again, the following final expression is obtained by substituting Expression (11), which is an approximate expression of the exhaust density ρe, into Expression (17).
[0166]

However, Kpexh: constant.
[0167]
The expression (18a) is equivalent to the above expression (12a). The calculation formula of the exhaust pressure Pexh by the expression (18a) includes the ratio of theoretical work (Wc / Wt) of the compressor 2b and the turbine 2a and the efficiency of each. The product (ηc × ηt) is included, and if the equation (18a) is used, the theoretical work Wc, Wt and the efficiency ηc, ηt of the turbocharger 2 are considered even if they are unknown. Therefore, what is necessary is just to obtain | require the efficiency (eta) n of the gas which flows through the variable nozzle 2c afterward.
[0168]
<4> Efficiency of gas flowing through nozzle ηn
The effective area equivalent value Avnt of the variable nozzle 2d including the efficiency ηn is given by the above equations (8b) and (16b), and the efficiency ηn can be expressed by the following equation.
[0169]

Where ξconv: nozzle loss,
ξfric: friction loss.
[0170]
In equation (19), the nozzle loss ξconv is a loss determined for each nozzle opening, and in the case of a contraction pipe, as can be seen from equation (3), 1 / {1- (A₂/ A₁)²}^1/2Becomes efficient.
[0171]
However, if the change in flow velocity is large, 1 / {1- (A₂/ A₁)²}^1/2If this value is regarded as the nozzle loss ξconv as it is, it often does not match the actual nozzle loss, so it is described by providing a table of efficiency with respect to the nozzle opening (see FIG. 30).
[0172]
Further, the friction loss ξfric in the equation (19) is the Hagen-Poiseuille equation when the flow inside the nozzle is regarded as a laminar flow, and the friction loss ξfric is proportional to the square root of the flow velocity. there,
Wexh = Qtotal / ρe (20)
The volume flow rate equivalent value Wexh is calculated by the following formula, and the square root of the volume flow rate is set as the exhaust flow velocity, thereby searching for the friction loss ξfric (see FIG. 29).
[0173]
Again, substituting equation (11), which is an approximate expression of exhaust density ρe, into equation (20),

In this way, the nozzle effective area equivalent value Avnt is calculated by the equation (19), and the exhaust pressure Pexh is predicted by the equations (18a) and (18b) using Qas0, Qf, Texh and Pa in addition to this Avnt. That is why. FIG. 32 shows the experimental results of examining the correlation between the actual measured value and the predicted value of the exhaust pressure. From the figure, it can be seen that the predicted value is sufficiently accurate.
[0174]
Next, FIG. 33 is a flow for calculating the EGR (flow) 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.
[0175]
In step 2, a table having the contents shown in FIG. 34 is retrieved from the EGR valve actual lift amount Lifts to obtain an opening area equivalent value Ave of the EGR valve 57.
[0176]
In step 3, the EGR flow rate Qe is calculated from the intake pressure Pm, the exhaust pressure Pexh, and the opening area equivalent value Ave of the EGR valve 57.
[0177]
[Expression 15]
Qe = Ave * {(Pexh-Pm) * KR #}^1/2
However, KR #: correction coefficient (constant),
Calculate with the following formula.
[0178]
FIG. 35 is a flow for calculating the target excess rate Mlamb. In step 1, the engine speed Ne, the fuel injection amount Qf, and the atmospheric pressure (compressor inlet pressure) Pa are read. Of these, the map containing the contents shown in FIG. Find Mlamb0. In step 3, a table containing the contents shown in FIG. 37 is retrieved from the atmospheric pressure Pa to obtain a target excess air ratio correction value Hlamb, and the target excess air ratio Mlamb is obtained by multiplying the correction value Hlamb by the target excess air ratio basic value Mlamb0. calculate.
[0179]
FIG. 38 is a flow for calculating the target cylinder intake fresh air amount Tqac1. The engine speed Ne, the target excess air ratio Mlamb, and the fuel injection amount cycle processing value Qf0 are read. Of these, the fuel injection amount cycle processing value Qf0 is read in step 2.
[0180]
[Expression 16]
Mqac = Mlamb × Blamb × Qf0
Blamb: Theoretical air-fuel ratio (≈14.7)
The target intake fresh air amount Mqac is obtained by the following formula.
[0181]
In step 3, Kin × Kvol is used as a weighted average coefficient for the target intake fresh air amount Mqac.
[0182]
[Expression 17]
Rqac = Rqac_n-1× (1-Kin × Kvol) + Mqac × Kin × Kvol
However, Rqac_n-1: The previous value of Rqec,
The intermediate processing value (weighted average value) Rqac is calculated by the following formula, and the intermediate processing value Rqac and the above-described target intake fresh air amount Mqac are used in step 4.
[0183]
[Expression 18]
Tqac1 = Mqac × GKQEC + Rqac_n-1× (1-GKQEC)
However, Rqac_n-1: The previous value of Rqac,
GKQEC: Lead compensation gain,
The target cylinder intake fresh air amount Tqac1 is obtained by performing the advance processing according to the following equation. Since there is a delay in the intake system with respect to the required value (that is, a delay corresponding to the capacity of the EGR valve 57 → the collector 52a → the intake manifold → the intake valve), in steps 3 and 4, advance processing for this delay is performed.
[0184]
FIG. 39 is a flow for calculating the required fresh air amount Tqa. In step 1, the cylinder intake fresh air amount Qac (corresponding to the actual measurement value) and the target cylinder intake fresh air amount Tqac1 are read, and the difference dQa (= Tqac1-Qac) is calculated in step 2. In step 3, an integral correction value Kqac is calculated from these differences dQa by integral control, and a value obtained by multiplying the correction value Kqac by the target cylinder intake fresh air amount Tqac1 in step 4 is obtained again as a target cylinder intake fresh air amount Tqac. .
[0185]
In step 5, from this target cylinder intake fresh air amount Tqac,
[0186]
[Equation 19]
Tqa = (Tqac / Ne) × KCON #
Where KCON # is a constant,
The required fresh air amount Tqa is calculated by performing unit conversion (per cylinder → per unit time) by the following formula.
[0187]
FIG. 40 is a flow for calculating the command opening VNTstep of the variable nozzle. In step 1, the atmospheric pressure Pa, the exhaust pressure Pexh, the required fresh air amount Tqa, the friction loss ξfric, and the nozzle loss ξconv are read. Note that the friction loss ξfric and nozzle loss ξconv may be stored by transferring the values obtained in the flow of FIG. 28 to the RAM and storing them.
[0188]
In step 2, the required opening area Avnt_sol0 of the variable nozzle 2d is
[0189]
[Expression 20]
    Avnt sol0 = Tqa / {(Pexh-P a) × Kv #}^1/2
      Where Kv #: correction coefficient (constant),
This required opening area Avnt is calculated using the following formula (the law of fluid dynamics) In step 3 from sol0
[0190]
[Expression 21]
Avnt_sol = Avnt_sol0 × ξfric × ξconv
The required effective area Avnt_sol is calculated by the following formula.
[0191]
In step 4, a table having the contents shown in FIG. 41 is retrieved from the required effective area Avnt_sol to obtain the command opening VNTstep of the variable nozzle.
[0192]
The variable nozzle command opening VNTstep obtained in this way is converted into a step number (a control amount given to the step motor 2c as a variable nozzle actuator) by searching a predetermined table (not shown). The step motor 2c is driven so that the command opening degree VNTstep is obtained.
[0193]
FIG. 42 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 gas temperature Tn are read, and a map having the contents shown in FIG. 43 is retrieved from Ne and Qf to obtain the target EGR rate basic value Megr0. In step 3, a table containing the contents of FIG. 44 is retrieved from the cylinder intake gas temperature Tn to obtain a target EGR rate correction value Hegr, and this target EGR rate correction value Hegr is multiplied by the target EGR rate basic value Megr0 to obtain the target EGR rate. Calculate Megr.
[0194]
FIG. 45 is a calculation flow of the required EGR (flow) amount Tqe. In step 1, the engine speed Ne, the target EGR rate Megr, the cylinder intake fresh air amount Qac, and the cycle processing value Qf0 of the fuel injection amount are read. Of these, the cylinder intake fresh air amount Qac is multiplied by the target EGR rate Megr in step 2. To calculate the target inhalation EGR amount Mqec.
[0195]
In step 3 (same as step 3 in FIG. 38), Kin × Kvol is used as a weighted average coefficient for the target inhalation EGR amount Mqec.
[0196]
[Expression 22]
Rqec = Rqec_n-1× (1-Kin × Kvol) + Mqec × Kin × Kvol
However, Rqec_n-1: The previous value of Rqec,
The intermediate processing value (weighted average value) Rqec is calculated by the following equation, and the intermediate processing value Rqec and the target intake EGR amount Mqec are used in step 4 (similar to step 4 in FIG. 38).
[0197]
[Expression 23]
Tqec = Mqec x GKQEC + Rqec_n-1× (1-GKQEC)
However, Rqec_n-1: The previous value of Rqec,
GKQEC: Lead compensation gain,
The target cylinder intake EGR amount Tqec is obtained by performing the advance processing according to the following equation. Since there is a delay in the intake system with respect to the required value (that is, a delay corresponding to the capacity of the EGR valve 57 → the collector 52a → the intake manifold → the intake valve), in steps 3 and 4, as with the target cylinder intake fresh air amount Tqac1, Advance processing for this delay is performed.
[0198]
In step 5 (similar to step 5 in FIG. 39), from this target cylinder intake EGR amount Tqec,
[0199]
[Expression 24]
Tqe = (Tqec / Ne) × KCON #
Where KCON # is a constant,
The required EGR amount Tqe is calculated by performing unit conversion (per cylinder → per unit time) by the following formula.
[0200]
FIG. 46 is a flow for calculating the command EGR valve lift amount Liftt as the command EGR valve opening degree. In step 1, the intake pressure Pm, the exhaust pressure Pexh, and the required EGR amount Tqe are read. In step 2, the required opening area Tav of the EGR valve 57 is
[0201]
[Expression 25]
Tav = Tqe / {(Pexh−Pm) × KR #}^1/2
However, KR #: correction coefficient (constant),
The following formula (the law of fluid mechanics) is used.
[0202]
In step 3, a table having the contents shown in FIG. 47 is retrieved from the required opening area Tav of the EGR valve 57 to obtain the EGR valve target lift amount Mlift as the target EGR valve opening, and the step is performed on the target lift amount Mlift. 4, the advance process for the operation delay of the EGR valve 57 is performed, and the value after the advance process is obtained as the command EGR valve lift amount Liftt.
[0203]
The command EGR valve 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.
[0204]
As described above, according to the embodiment of the present invention, the above-described direct and simple above-mentioned four elements, that is, the intake air amount (weighted average value) Qas0, the fuel injection amount Qf, the effective area equivalent value Avnt of the variable nozzle, and the exhaust gas temperature Texh. Since the exhaust pressure Pexh can be calculated using the equation (13), the exhaust pressure can be estimated without delay in response even when a variable capacity turbocharger is provided.
[0205]
Further, the target excess air ratio Mlamb is calculated according to the engine speed and the load, the required fresh air amount Tqa is calculated based on the target excess air ratio Mlamb, and the estimated exhaust pressure Pexh and the atmospheric pressure Pa are calculated. The required opening area Avntsol0 of the variable nozzle 2d is calculated from the differential pressure (Pexh-Pa) and the required fresh air amount Tqa using the above equation (20), and the nozzle opening of the variable nozzle 2d is set so as to be the required opening area Avntsol0. The target EGR rate Megr is calculated according to the engine speed and the load, the required EGR amount Tqe is calculated based on the target EGR rate Megr, and the estimated exhaust pressure Pexh and intake pressure Pm are calculated. The required opening area Tav of the EGR valve 57 is calculated from the differential pressure (Pexh−Pm) and the required EGR amount Tqe using the above equation 25, and the EGR valve opening is controlled so as to be the required opening area Tav. To do. In other words, since the control target value is distributed to the EGR valve and the variable nozzle in order to achieve an oxygen concentration capable of simultaneously reducing NOx and PM, as in the conventional device (Japanese Patent Laid-Open No. 6-173752), even during a transient state Control responsiveness does not deteriorate, and this makes it possible to operate the engine with the optimum supercharging pressure and EGR amount even during a transition, and to simultaneously reduce NOx and PM.
[0206]
Further, since the value obtained by multiplying the required opening area Avntsol0 of the variable nozzle 2d by the efficiency ηn of the gas flowing through the variable nozzle 2d is obtained as the required effective area Avntsol of the variable nozzle 2d, the efficiency ηn of the gas flowing through the variable nozzle 2d is obtained. Can be considered.
[0207]
Similarly, the effective area equivalent value Avnt is the previous value of the command opening degree given to the efficiency ηn of the gas flowing through the variable nozzle 2d and the stepping motor 2c that drives the variable nozzle 2d._n-1In this case, the efficiency ηn of the gas flowing through the variable nozzle 2d can be taken into consideration.
[0208]
Further, since the efficiency ηn of the gas flowing through the variable nozzle 2d is the product of the friction loss ξfric and the nozzle loss ξconv, the friction loss and the nozzle loss can be considered separately.
[0209]
Further, since the friction loss ξfric is given as a value proportional to the square root of the exhaust flow velocity equivalent value Wexh, the friction loss ξfric can be given accurately even if the exhaust flow velocity is different.
[0210]
Further, when the change in the flow velocity is large, the loss to the constricted pipe (1 / {1- (A₂/ A₁)²}^1/2In this embodiment, the nozzle loss ξconv is changed to the previous value of the command opening VNTstep._n-1Therefore, even if the change in the flow velocity is large, the value can be matched well with the actual nozzle loss.
[0211]
Also, VNTstep is the previous value of command opening_n-1The exhaust temperature nozzle opening correction coefficient Ktexh4 is calculated according to the exhaust amount Qexh, and the exhaust temperature basic value Texhb is corrected with this correction coefficient Ktexh4. The calculation accuracy of the exhaust pressure Pexh is improved by that amount. Similarly, when the intake port is provided with a swirl valve, the exhaust temperature swirl correction coefficient Ktexh3 is calculated in accordance with the position of the swirl valve and the engine speed Ne, and the exhaust gas basic value is calculated using the correction coefficient Ktexh3. Since Texhb is corrected, even when the intake port is provided with a swirl valve, the calculation accuracy of the exhaust temperature Texh is improved, and the calculation accuracy of the exhaust pressure Pexh is improved by this improvement.
[0212]
Next, FIG. 48 and FIG. 49 are the calculation flows of the second embodiment, respectively replacing FIG. 33 and FIG. 46 of the first embodiment. In addition, the same step number is attached | subjected to the same part as 1st Embodiment.
[0213]
In the first embodiment, the EGR flow rate Qe is calculated from the differential pressure between the exhaust pressure Pexh and the intake pressure Pm as shown in the equation (15). However, in the second embodiment, the EGR passage 54 is further operated in the EGR passage 54. This makes it possible to calculate the EGR flow rate with higher accuracy.
[0214]
The difference from the first embodiment will be mainly described. In step 11 of FIG. 48, in addition to the intake pressure Pm, the exhaust pressure Pexh, the EGR valve actual lift amount Lifts, the exhaust temperature Texh is read. In step 12,
[0215]
[Equation 26]

However, Ave: EGR valve opening area equivalent value,
Pexh: Exhaust pressure,
Pm: Intake pressure
Tstd: Standard atmospheric temperature,
Texh: exhaust temperature,
Avps: EGR valve 57 full open area equivalent value,
λ: Straight pipe loss coefficient of the EGR passage 54,
d: diameter of the EGR passage 54,
l: length of EGR passage 54,
ζ: bending pipe loss coefficient of EGR passage 54,
g: acceleration of gravity,
Cv: constant,
The EGR flow rate Qe is calculated by the following formula.
[0216]
However, the straight pipe loss coefficient λ and the bent pipe loss coefficient ζ of the EGR passage may be calculated by the following equations. In Equation 26, λ is obtained from a straight tube loss model (Brazius equation), and ζ is obtained from a bent tube loss model (Wisebach equation).
[0217]
[Expression 27]

Where Cs, Cb1, Cb2 are constants,
Tstd: Standard atmospheric temperature,
ν: Kinematic viscosity of exhaust,
d: diameter of the EGR passage 54,
R: radius of curvature of EGR passage 54,
n: The number of bent portions of the EGR passage 54.
[0218]
The above equation (26) is an equation obtained by applying a known equation to the flow of EGR gas. For example, Equation 26 can be derived as follows. Applying the above equation (4) to the third equation of the above equation 1
Qegr = Aegr × {2 × ρe × (Pexh−Pm)}^1/2... (22a) Aegr = Ave x ηn2 x Cv (22b) However, Aegr: EGR valve 57 effective area equivalent value,
Ave: EGR valve 57 opening area equivalent value,
ηn2: efficiency of gas flowing through the EGR valve 57,
Cv: constant.
[0219]
This is a new introduction of ηn2 × Cv for the opening area equivalent value Ave of the EGR valve 57.
[0220]
Again, substituting equation (11), which is an approximation of exhaust density ρe, into equation (22a)
Qe = Aegr × {2 × (Tstd / Texh) × (Pexh−Pm)}^1/2···(twenty three)
Where Tstd: Standard atmospheric temperature
Further, the efficiency ηn2 of the equation (22b) is set according to the first embodiment.
ηn2 ＝ ξconv-egr × ξfric-egr (24)
ξconv-egr: loss at the EGR valve 57,
ξfric-egr: friction loss of EGR passage 54,
And
[0221]
Here, the loss ξconv-egr at the EGR valve 57 is reduced in accordance with the principle of the pipe,
ξconv-egr = 1 / {1- (Ave / Avps)²}^1/2···(twenty five)
far.
[0222]
On the other hand, the friction loss ξfric-egr of the EGR passage 54 is obtained from the Darcy-Weisbach equation.

Where ε: pipe friction coefficient,
λ: Straight pipe loss coefficient,
ζ: bending pipe loss coefficient,
l: EGR passage length,
d: Diameter of EGR passage,
g: acceleration of gravity,
It can be expressed as.
[0223]
Substituting Equations (25) and (26) into Equation (24),

By substituting equation (27) into equation (22b), the following equation is obtained.
[0224]

By substituting this equation (28) into equation (22a), equation 26 is obtained.
[0225]
The formulas (22a) and (22b), which are the basis of the above formula 26, are generally steady flow formulas, and therefore are not used in unsteady flow. However, this time, an experiment using the equation (26) shows that the EGR flow rate Qe can be accurately calculated for both steady and transient in the case of a regular flow such as pulsating exhaust. For the first time. Therefore, according to the equation (26), it is possible to consider the pressure loss of the gas in the EGR passage 54 even in the case of an unsteady flow such as exhaust gas, and this makes it possible to calculate the EGR flow rate with higher accuracy. It became.
[0226]
In steps 11 and 12 of FIG. 49, as in steps 11 and 2 of FIG. 48, the intake pressure Pm, the exhaust pressure Pexh, and the EGR valve actual lift amount Lifts as the actual EGR valve opening are read. A table having the contents shown in FIG. 34 is retrieved from the actual lift amount Lifts, and an opening area equivalent value Ave of the EGR valve 57 is obtained.
[0227]
[Expression 28]

The required opening area Tav of the EGR valve 57 is calculated by the following equation.
[0228]
Equation 28 is obtained as follows. Since the constant Cv and the efficiency ηn2 are introduced to the opening area equivalent value Ave in the above equations (22a) and (22b), when considering the required opening area Tav of the EGR valve 57 in accordance with this,
Tav = Ave × ηn2 × Cv (29)
Thus, the constant Cv and the efficiency ηn2 having the same value are introduced for the opening area equivalent value Ave. Here, since the efficiency ηn2 is given by the equation (27), the equation (28) is obtained by substituting the equation (27) into the equation (29).
[0229]
Thus, in the second embodiment, since the gas pressure loss in the EGR passage 54 is taken into consideration, the EGR amount Qe can be calculated with higher accuracy.
[0230]
Further, it is theorized that the value corresponding to the opening area of the passage can be corrected by the efficiency of the gas flowing through the passage, generally only in a steady flow. However, this time, when an experiment was performed in a case where the opening area equivalent value Ave of the EGR valve 57 was corrected by the above-mentioned efficiency ηn2, in the case of a regular flow such as pulsating exhaust, steady, transient In both cases, it was found for the first time that the EGR flow rate Qe was accurately calculated. Therefore, according to the second embodiment, it is possible to easily consider the pressure loss of the gas in the EGR passage even in the case of an unsteady flow such as exhaust gas, thereby calculating the EGR flow rate with higher accuracy. Is now possible.
[0231]
Here, referring to FIG. 6, the cylinder intake EGR amount Qec from the EGR amount Qe, the cylinder intake gas temperature Tn from the cylinder intake EGR amount Qec, the cycle process value Tn0 from the cylinder intake gas temperature Tn, and the cycle process value Tn0. Since the exhaust gas temperature Pexh is calculated from the exhaust gas temperature Texh, increasing the calculation accuracy of the EGR amount Qe leads to increasing the calculation accuracy of the exhaust gas pressure Pexh. Therefore, based on the exhaust pressure Pexh with improved calculation accuracy, the supercharging pressure (intake fresh air amount) and the EGR amount can be controlled with higher accuracy.
[0232]
Further, since the efficiency ηn2 of the gas flowing through the EGR valve 57 is the product of the pressure loss ξconv-egr at the EGR valve and the friction loss ξfric-egr at the EGR passage, the pressure loss at the EGR valve 57 and the EGR passage 54 Friction loss can be considered separately.
[0233]
Further, since the straight pipe loss coefficient λ is calculated by the above equation 27, the straight pipe loss coefficient λ can be obtained with good response even during a transient in which the exhaust pressure Pexh changes rapidly.
[0234]
FIG. 50 is a calculation flow of the effective area equivalent value Avnt of the variable nozzle of the third embodiment, which replaces FIG. 28 of the first embodiment.
[0235]
In the third embodiment, the calculation of the efficiency ηn of the first embodiment is simplified. Specifically, in step 1, VNTstep is the previous value of the command opening._n-1And the exhaust flow rate Qexh are read, and a map containing the contents shown in FIG. 51 is retrieved from these in step 2 to obtain an effective area correction value Kvnt, which is obtained in step 3 as the previous value of the command opening VNTstep._n-1Is multiplied by to calculate an effective area equivalent value Avnt.
[0236]
Here, the correction value Kvnt is a value corresponding to the efficiency ηn (= ξfric × ξconv) of the first embodiment.
[0237]
Thus, in the third embodiment, the calculation load of the CPU can be reduced by simplifying the calculation of the efficiency ηn of the gas flowing through the variable nozzle.
[0238]
FIG. 54 is a calculation flow of the exhaust pressure (turbine inlet pressure) of the fourth embodiment, which replaces FIG. 31 of the first embodiment.
[0239]
In the first embodiment, the exhaust pressure is calculated on the assumption that the flow of the gas passing through the nozzle 2d is a flow when the flow path area is reduced (see FIG. 52), whereas in the fourth embodiment Is obtained on the assumption that the flow of gas passing through the nozzle is a flow (see FIG. 56) when the ideal gas flows with adiabatic change. Specifically, in FIG.
[0240]
[Expression 29]
Pexhr = Kpexhn × {(Qas0 + Qfuel) / Avnt}²× Texh
Where Kpexhn: constant,
The turbine inlet exhaust pressure equivalent value Pexhr is calculated by the following formula, and the exhaust pressure Pexh0 is obtained by searching a map having the contents shown in FIG. 55 in step 12 from this Pexhr and the atmospheric pressure Pa. The rest is the same as in FIG. 31, and a weighted average process is performed on this Pexh0 in step 3, and the weighted average value is obtained as the exhaust pressure Pexh.
[0241]
Here, how the calculation method of the exhaust pressure of Expression 29 is obtained will be described next.
[0242]
<5> Basic formula of flow in case of tapered nozzle
Considering the flow passing through the turbine nozzle, there is almost no heat input / output or work from outside, and therefore, the energy of the fluid is considered to change from the decrease in internal energy to kinetic energy and extrusion work. The engine exhaust can be regarded as an ideal gas because of its low pressure and high temperature. Therefore, the flow of exhaust gas passing through the turbine nozzle can be considered as “the ideal gas flows with adiabatic change”.
[0243]
Now, in a tapered nozzle such as a turbine nozzle, as shown in FIG. 56, the pressure, specific volume, flow velocity, area, temperature, specific heat ratio, and gas constant are P, v, w, A, T, κ, Let R be the subscript 1 for the entrance and subscript 2 for the exit.
[0244]
[30]

[0245]
It is. Further, the following equation is established from the basic equation of steady flow energy.
[0246]
[31]

[0247]
Substituting equation (31) into equation 31,
[0248]
[Expression 32]

[0249]
Or P₁V₁= RT₁From
[0250]
[Expression 33]

[0251]
For tapered nozzles, inlet flow velocity w₁Is the exit velocity w₂If it is omitted, the speed w at the nozzle outlet end₂Is given by:
[0252]
[Expression 34]

[0253]
Since the flow rate Q flowing through each section of the nozzle per unit time is constant from the continuous equation, Q = A₂× w₂/ V₂= Ρe × A₂× w₂[Kg / sec] (33). Also, since the fluid flowing in the nozzle is considered to be an adiabatic change with an ideal gas, from the above equation (31),
[0254]
[Expression 35]

[0255]
It is.
[0256]
Substituting (32) and (34) into (33),
[0257]
[Expression 36]

[0258]
Equation (35) is a basic equation for the flow in the case of a tapered nozzle.
[0259]
<6> Exhaust pressure prediction formula for tapered nozzles
Refer to FIG. From equation (15)
Qas0 + Qf = Qtotal [kg / sec] (36) Applying the above equation (35), which is a nozzle flow equation whose area is reduced, to the right side of this equation (36),
[0260]
[Expression 37]

[0261]
To get the formula
[0262]
Here, the turbine inlet exhaust pressure equivalent value Pexhr is
[0263]
[Formula 38]

[0264]
Then, the equation (37a) is

Therefore, when the equation (39) is arranged for the turbine inlet exhaust pressure equivalent value Pexhr, the following equation is obtained.
[0265]

Again, the following final expression is obtained by substituting Expression (11), which is an approximate expression of the exhaust density ρe, into Expression (40).
[0266]
Pexhr = Kpexhn × {(Qas0 + Qf) / Avnt}²× Texh [Pa] (41a)
Kpexhn = (1 / (2 × ρe)) × (κe / (κe−1)) (41b)
However, Kpexhn: constant.
[0267]
Now, as shown in the above equation 13, if the exhaust pressure is calculated assuming that the flow of gas passing through the nozzle is a flow when the flow path area is reduced, the standard state (298K, 0.1 MPa ), The calculation accuracy of the exhaust pressure is high. However, according to experiments, when the exhaust pressure is different from the standard state (for example, when the temperature is higher than the high altitude, the standard temperature, or the humidity is different from the standard state) It is known that the calculation accuracy decreases. This seems to be because Equation 13 considers the change in specific gravity but is not yet accurate.
[0268]
On the other hand, according to the fourth embodiment obtained by assuming that the flow of gas passing through the nozzle is a flow when the ideal gas is adiabatically changed and flows, the flow rate per unit time is calculated by an arithmetic expression. Since the pressure and pressure (that is, the change in specific gravity) can be accurately described, high calculation accuracy of the exhaust pressure can be obtained even in a state of atmospheric pressure or temperature different from the standard state.
[0269]
In addition, since the characteristics of FIG. 51 that must be matched in the fourth embodiment are simple as shown in the figure, only calculation is sufficient (no matching is necessary), and exhaust pressure calculation accuracy is also possible only on the desk. Is expensive (confirmed by experiment).
[0270]
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.
[0271]
Although the embodiment has been described in the case of a diesel engine, it is needless to say that the present invention can also be applied to a gasoline engine.
[0272]
In the embodiment, the case where the sensor 73 for detecting the compressor inlet pressure Pa is provided has been described. However, the vehicle equipped with the engine including the EGR device and the variable capacity turbocharger is in a standard atmosphere (or an atmosphere close thereto). The compressor inlet pressure sensor is not required as long as it is operated at This is because it is sufficient to set the value of Pa for the standard atmosphere.
[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 characteristic diagram showing the relationship between the sensitivity of the EGR rate and the amount of fresh air (supercharging pressure) with respect to the discharge amounts of NOx and PM.
FIG. 5 is a block diagram showing the basic concept of EGR control and supercharging pressure control.
FIG. 6 is a block diagram of a control system.
FIG. 7 is a flowchart showing the calculation order of parameters in model reference control.
FIG. 8 is a flowchart for explaining cycle processing;
FIG. 9 is a flowchart for explaining calculation of a cylinder intake fresh air amount.
FIG. 10 is a flowchart for explaining calculation of a cylinder suction EGR amount.
FIG. 11 is a flowchart for explaining calculation of a volumetric efficiency equivalent value.
FIG. 12 is a characteristic diagram of air density.
FIG. 13 is a flowchart for explaining calculation of intake pressure.
FIG. 14 is a characteristic diagram of pressure with respect to sensor output voltage.
FIG. 15 is a flowchart for explaining calculation of intake air temperature;
FIG. 16 is a characteristic diagram of a vehicle speed correction value of intake air temperature.
FIG. 17 is a characteristic diagram of an intake air amount correction value of intake air temperature.
FIG. 18 is a flowchart for explaining calculation of cylinder intake gas temperature.
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.
FIG. 21 is a characteristic diagram of a maximum injection amount.
FIG. 22 is a flowchart for explaining calculation of exhaust gas temperature.
FIG. 23 is a characteristic diagram of an exhaust gas temperature basic value.
FIG. 24 is a characteristic diagram of an intake air temperature correction coefficient.
FIG. 25 is a characteristic diagram of an exhaust pressure correction coefficient.
FIG. 26 is a characteristic diagram of a swirl correction coefficient.
FIG. 27 is a characteristic diagram of a nozzle opening correction coefficient.
FIG. 28 is a flowchart for explaining calculation of a nozzle effective area equivalent value;
FIG. 29 is a characteristic diagram of friction loss.
FIG. 30 is a characteristic diagram of nozzle loss.
FIG. 31 is a flowchart for explaining exhaust pressure calculation;
FIG. 32 is a characteristic diagram in which the correlation between the measured value and the predicted value of the exhaust pressure is examined.
FIG. 33 is a flowchart for explaining calculation of an EGR flow rate.
FIG. 34 is a characteristic diagram of an EGR valve opening area equivalent value.
FIG. 35 is a flowchart for explaining calculation of a target excess air ratio.
FIG. 36 is a characteristic diagram of a target excess air ratio basic value.
FIG. 37 is a characteristic diagram of a target excess air ratio correction value.
FIG. 38 is a flowchart for explaining calculation of a target cylinder intake fresh air amount;
FIG. 39 is a flowchart for explaining calculation of a required fresh air amount.
FIG. 40 is a flowchart for explaining calculation of a command opening given to the variable nozzle actuator.
FIG. 41 is a characteristic diagram of command opening.
FIG. 42 is a flowchart for explaining calculation of a target EGR rate.
FIG. 43 is a characteristic diagram of a target EGR rate basic value.
FIG. 44 is a characteristic diagram of a target EGR rate correction value.
FIG. 45 is a flowchart for explaining calculation of a required EGR amount.
FIG. 46 is a flowchart for explaining calculation of a command EGR valve lift amount;
FIG. 47 is a characteristic diagram of an EGR valve target lift amount.
FIG. 48 is a flowchart for explaining calculation of an EGR amount according to the second embodiment;
FIG. 49 is a flowchart for explaining calculation of a command EGR valve lift amount according to the second embodiment;
FIG. 50 is a flowchart for explaining calculation of a nozzle effective area equivalent value according to the third embodiment;
FIG. 51 is a characteristic diagram of an effective area correction value according to the third embodiment.
FIG. 52 is a model diagram of a flow in which the flow path area is reduced.
FIG. 53 is a model diagram used for examining the mechanical balance of the intake and exhaust systems.
FIG. 54 is a flowchart for explaining calculation of exhaust pressure in the fourth embodiment.
FIG. 55 is a characteristic diagram of the exhaust pressure Pexh0 of the fourth embodiment.
FIG. 56 is a model diagram of a tapered nozzle.
FIG. 57 is a view corresponding to claims of the first invention.
FIG. 58 is a view corresponding to claims of the eleventh and twenty-eighth aspects of the invention.
FIG. 59 is a diagram corresponding to a claim of the eighteenth invention.
[Explanation of symbols]
1 Engine body
2 Variable capacity turbocharger
2d variable nozzle
10 Common rail fuel injection system
16 Common rail
17 Fuel injection valve
41 Electronic control unit
54 EGR passage
57 EGR valve
72 Intake pressure sensor

Claims (34)

A variable capacity turbocharger having a variable nozzle in the turbine and an EGR valve capable of controlling the EGR amount;
Means for detecting the amount of intake air;
Means for detecting engine load;
Means for detecting an effective area equivalent value of the variable nozzle;
Means for detecting the exhaust temperature;
Means for estimating the exhaust pressure using these four elements;
Means for calculating a pressure difference between the estimated exhaust pressure and atmospheric pressure;
Means for calculating a target excess air ratio according to the engine speed and load;
Means for calculating a required fresh air amount based on the target excess air ratio;
Means for calculating a required opening area of the variable nozzle from a differential pressure between the required fresh air amount and the atmospheric pressure;
Means for controlling the opening of the variable nozzle so as to be the required opening area;
A sensor for detecting the intake pressure;
Means for calculating a differential pressure between the estimated exhaust pressure and the intake pressure;
Means for calculating a target EGR rate according to the engine speed and load;
Means for calculating a required EGR amount based on the target EGR rate;
Means for calculating a required opening area of the EGR valve from a differential pressure between the required EGR amount and the intake pressure;
An engine control apparatus comprising: means for controlling the opening degree of the EGR valve so as to satisfy the required opening area. Using the fuel injection amount Qf as the engine load, the exhaust pressure Pexh is
Pexh = Kpexh × {(Qas0 + Qf) / Avnt)} ² × Texh + Pa
Where Pexh: exhaust pressure,
Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value,
Texh: Turbine inlet exhaust temperature,
Pa: compressor inlet pressure,
Kpexh: constant,
The engine control device according to claim 1, wherein the calculation is performed according to the equation: Using the fuel injection amount Qf as the engine load, the turbine inlet exhaust pressure equivalent value Pexhr is
P exhr = Kpexhn × {(Qas0 + Qf) / Avnt)} ² × Texh
Where Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value of variable nozzle,
Texh: Turbine inlet exhaust temperature,
Kpexhn: constant,
The engine control apparatus according to claim 1, wherein the exhaust pressure Pexh is calculated from the turbine inlet exhaust pressure equivalent value Pexhr and the compressor inlet pressure Pa. The engine control device according to claim 2, further comprising a sensor that detects the compressor inlet pressure. 5. The effective area equivalent value is a product of an efficiency of gas flowing through the variable nozzle and a nozzle opening command value given to an actuator that drives the variable nozzle. The engine control device according to one. 6. The engine control device according to claim 1, wherein a required opening area of the variable nozzle is corrected by an efficiency of a gas flowing through the variable nozzle. 7. The engine control device according to claim 5 or 6, wherein the efficiency of the gas flowing through the variable nozzle is a product of friction loss and nozzle loss. The engine control apparatus according to claim 7, wherein the friction loss is a value proportional to a square root of an exhaust flow velocity equivalent value. The engine control apparatus according to claim 7, wherein the nozzle loss is a value corresponding to the nozzle opening command value and a total exhaust weight. 7. The engine control device according to claim 5, wherein the efficiency of the gas flowing through the variable nozzle is a value corresponding to the nozzle opening command value and an exhaust amount. Means for detecting the exhaust temperature;
Means for calculating an opening area equivalent value of the EGR valve from the actual opening of the EGR valve, means for calculating an EGR amount based on a differential pressure between the opening area equivalent value and the intake pressure;
Means for calculating the cylinder intake EGR amount based on the EGR amount and the engine speed;
Means for calculating the cylinder intake gas temperature based on the cylinder intake EGR amount, the compressor inlet temperature, the cylinder intake fresh air amount, and the previous exhaust temperature;
Means for calculating a cycle processing value of the cylinder intake gas temperature;
Means for calculating the fuel injection amount;
Means for calculating a cycle processing value of the fuel injection amount;
Means for calculating an exhaust gas temperature basic value based on the cycle processing value;
Means for calculating an intake air temperature correction coefficient from a cycle processing value of the cylinder intake gas temperature;
When the exhaust gas basic value is corrected by this correction coefficient to calculate the current exhaust temperature, the opening area equivalent value of the EGR valve is corrected by the efficiency of the gas flowing through the EGR valve. The engine control device according to any one of claims 1 to 10. The engine control according to claim 11, wherein the efficiency of the gas flowing through the EGR valve is a product of a pressure loss in the EGR valve and a friction loss in an EGR passage communicating the exhaust pipe and the intake pipe. apparatus. The pressure loss ξconv-egr at the EGR valve is
ξconv-egr = 1 / {1- (Ave / Avps) ² } ^1/2
However, Ave: EGR valve opening area equivalent value,
Avps: EGR valve fully open area equivalent value,
The engine control apparatus according to claim 12, wherein the calculation is performed according to the equation: The friction loss ξfric-egr of the EGR passage is
ξfric-egr = {λ × ζ × (l / d) × (1 / (2g))} ^1/2
Where λ: straight pipe loss coefficient,
ζ: bending pipe loss coefficient,
l: EGR passage length,
d: Diameter of EGR passage,
g: acceleration of gravity,
The engine control apparatus according to claim 12, wherein the calculation is performed according to the equation: The straight pipe loss coefficient λ is
λ = Cs × [{2 × (Tstd / Texh) × (Pexh−Pm)} ^1/2 / (ν × d)] ^−1/4
Where Tstd: standard atmospheric temperature,
Texh: exhaust temperature,
Pexh: Exhaust pressure,
Pm: Intake pressure
ν: Kinematic viscosity of exhaust,
d: Diameter of EGR passage,
Cs: constant,
The engine control apparatus according to claim 12, wherein the calculation is performed according to the equation: 16. An exhaust temperature nozzle opening correction coefficient is calculated according to the nozzle opening command value and the exhaust amount, and the exhaust temperature basic value is corrected by the correction coefficient. The engine control device according to claim 1. When the intake port is provided with a swirl valve, the exhaust temperature swirl correction coefficient is calculated according to the position of the swirl valve and the engine speed, and the exhaust temperature basic value is corrected with the correction coefficient. The engine control device according to any one of claims 11 to 16. A variable capacity turbocharger having a variable nozzle in the turbine and an EGR valve capable of controlling the EGR amount;
Means for detecting the amount of intake air;
Means for detecting engine load;
Means for detecting an effective area equivalent value of the variable nozzle;
Means for detecting the exhaust temperature;
Means for estimating the exhaust pressure using these four elements;
Means for calculating a pressure difference between the estimated exhaust pressure and atmospheric pressure;
Means for calculating a target excess air ratio according to the engine speed and load;
Means for calculating a required fresh air amount based on the target excess air ratio;
Means for calculating a required opening area of the variable nozzle from a differential pressure between the required fresh air amount and the atmospheric pressure;
Means for controlling the opening of the variable nozzle so as to be the required opening area;
A sensor for detecting the intake pressure;
Means for calculating a differential pressure between the estimated exhaust pressure and the intake pressure;
Means for calculating a straight pipe loss of the EGR passage communicating the exhaust pipe and the intake pipe based on the differential pressure with the intake pressure;
Means for calculating a friction loss of the EGR passage based on the straight pipe loss and the bent pipe loss of the EGR passage;
Means for calculating an opening area equivalent value of the EGR valve based on an actual opening of the EGR valve;
Means for calculating a loss in the EGR valve based on the opening area equivalent value;
Means for calculating the product of the loss in the EGR valve and the friction loss in the EGR passage as the efficiency of the gas flowing through the EGR valve;
Means for calculating a value obtained by correcting the value corresponding to the opening area of the EGR valve with this efficiency as a required opening area of the EGR valve;
An engine control apparatus comprising: means for controlling the opening degree of the EGR valve so as to satisfy the required opening area. Using the fuel injection amount Qf as the engine load, the exhaust pressure Pexh is
Pexh = Kpexh × {(Qas0 + Qf) / Avnt)} ² × Texh + Pa
Where Pexh: exhaust pressure,
Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value,
Texh: Turbine inlet exhaust temperature,
Pa: compressor inlet pressure,
Kpexh: constant,
The engine control apparatus according to claim 18, wherein the calculation is performed according to the equation: Using the fuel injection amount Qf as the engine load, the turbine inlet exhaust pressure equivalent value Pexhr is
P exhr = Kpexhn × {(Qas0 + Qf) / Avnt)} ² × Texh
Where Qas0: intake air volume,
Qf: fuel injection amount,
Avnt: Effective area equivalent value of variable nozzle,
Texh: Turbine inlet exhaust temperature,
Kpexhn: constant,
The engine control device according to claim 18, wherein the exhaust pressure Pexh is calculated from the turbine inlet exhaust pressure equivalent value Pexhr and the compressor inlet pressure Pa. 21. The engine control device according to claim 19, further comprising a sensor that detects the compressor inlet pressure. The effective area equivalent value is a product of an efficiency of gas flowing through the variable nozzle and a nozzle opening command value to be given to an actuator that drives the variable nozzle. The engine control device according to one. The engine control device according to any one of claims 18 to 22, wherein the required opening area of the variable nozzle is corrected by the efficiency of gas flowing through the variable nozzle. The engine control device according to claim 22 or 23, wherein the efficiency of the gas flowing through the variable nozzle is a product of friction loss and nozzle loss. The engine control device according to claim 24, wherein the friction loss is a value proportional to a square root of an exhaust flow velocity equivalent value. The engine control device according to claim 24, wherein the nozzle loss is a value corresponding to the nozzle opening command value and a total exhaust weight. The engine control apparatus according to claim 22 or 23, wherein the efficiency of the gas flowing through the variable nozzle is a value corresponding to the nozzle opening command value and an exhaust amount. Means for detecting the exhaust temperature Texh;
Means for calculating an opening area equivalent value of the EGR valve from the actual opening of the EGR valve, means for calculating an EGR amount based on a differential pressure between the opening area equivalent value and the intake pressure;
Means for calculating the cylinder intake EGR amount based on the EGR amount and the engine speed;
Means for calculating the cylinder intake gas temperature based on the cylinder intake EGR amount, the compressor inlet temperature, the cylinder intake fresh air amount, and the previous exhaust temperature;
Means for calculating a cycle processing value of the cylinder intake gas temperature;
Means for calculating the fuel injection amount;
Means for calculating a cycle processing value of the fuel injection amount;
Means for calculating an exhaust gas temperature basic value based on the cycle processing value;
Means for calculating an intake air temperature correction coefficient from a cycle processing value of the cylinder intake gas temperature;
When the exhaust gas basic value is corrected by this correction coefficient to calculate the current exhaust temperature, the opening area equivalent value of the EGR valve is corrected by the efficiency of the gas flowing through the EGR valve. The engine control device according to any one of claims 18 to 27. The engine control according to claim 28, wherein the efficiency of the gas flowing through the EGR valve is a product of a pressure loss at the EGR valve and a friction loss in an EGR passage communicating the exhaust pipe and the intake pipe. apparatus. The pressure loss ξconv-egr at the EGR valve is
ξconv-egr = 1 / {1- (Ave / Avps) ² } ^1/2
However, Ave: EGR valve opening area equivalent value,
Avps: EGR valve fully open area equivalent value,
30. The engine control apparatus according to claim 29, wherein the calculation is performed according to the following formula. The friction loss ξfric-egr of the EGR passage is
ξfric-egr = {λ × ζ × (l / d) × (1 / (2g))} ^1/2
Where λ: straight pipe loss coefficient,
ζ: bending pipe loss coefficient,
l: EGR passage length,
d: Diameter of EGR passage,
g: acceleration of gravity,
30. The engine control apparatus according to claim 29, wherein the calculation is performed according to the following formula. The straight pipe loss coefficient λ is
λ = Cs × [{2 × (Tstd / Texh) × (Pexh−Pm)} ^1/2 / (ν × d)] ^−1/4
Where Tstd: standard atmospheric temperature,
Texh: exhaust temperature,
Pexh: Exhaust pressure,
Pm: Intake pressure
ν: Kinematic viscosity of exhaust,
d: Diameter of EGR passage,
Cs: constant,
30. The engine control apparatus according to claim 29, wherein the calculation is performed according to the following formula. The exhaust gas temperature basic value is corrected with the correction coefficient by calculating a nozzle opening correction coefficient of the exhaust gas temperature in accordance with the nozzle opening command value and the exhaust amount. The engine control device according to claim 1. When the intake port is provided with a swirl valve, the exhaust temperature swirl correction coefficient is calculated according to the position of the swirl valve and the engine speed, and the exhaust temperature basic value is corrected with the correction coefficient. The engine control device according to any one of claims 28 to 33.

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