JP4056776B2 - Control device for internal combustion engine - Google Patents

Description

【００３１】
ここで、ｎは１モル燃料中の炭素含有量［ｍｏｌ］、ＣＯ₂は、二酸化炭素分子量［ｇ／ｍｏｌ］、ｃ_CO2は二酸化炭素比熱［Ｊ／(ｋｇ・Ｋ)］、ｍは１モル燃料中の水素含有量［ｍｏｌ］、Ｈ₂Ｏは水分子量［ｇ／ｍｏｌ］、ｃ_H2Oは水（水蒸気）比熱［Ｊ／(ｋｇ・Ｋ)］、χは空気中の酸素に対する窒素容量割合、Ｎ₂は窒素分子量［ｇ／ｍｏｌ］、ｃ_N2は窒素比熱［Ｊ／(ｋｇ・Ｋ)］である。
【００３２】
このように，エンジンシステム内を流れるガスを空気と燃焼ガスの２つの成分のみとして取り扱うことで、常に変化する比熱の演算量を低減することができる。空気と燃焼ガスの混合ガスの比熱ｃ_mixは、下記式（４）により算出される。
ｃ_mix＝ｃ_air・（１−λ）＋ｃ_cmb・λ （４）
【００３３】
ここで、ｃ_airは空気の比熱［Ｊ／(ｋｇ・Ｋ)］、ｃ_cmbは燃焼ガスの比熱［Ｊ／(ｋｇ・Ｋ)］、λはガス成分質量比（全ガス量に対する燃焼ガス量の比率）である。
【００３４】
次にターボチャージャモデル３１を構成するコンプレッサモデル３２について説明する。
コンプレッサモデル３２では、コンプレッサ上流圧力Ｐ_{C_in}、コンプレッサ下流圧力Ｐ_{C_out}、コンプレッサ上流ガス温度Ｔ_{C_in}、タービン回転数Ｎ_tbからコンプレッサ上下流の各ガス流量，成分比，下流ガス温度および圧縮に必要な軸トルクを算出する。コンプレッサ上流ガス体積流量Ｑcは，上下流の圧縮比ＰＲ（＝Ｐ_{C_out}／Ｐ_{C_in}）とタービン回転数Ｎ_tbに応じて、図３（ａ）に示すＱcテーブルを検索して算出する（下記式（５））。
【００３５】
次に下記式（６）により、体積流量Ｑc［ｍ³／ｓ］を質量流量Ｇ_{C_in}［ｋｇ／ｓ］に変換する。また、コンプレッサは機能的に物質交換が無く、上下流の各ガス流量および成分比は同じであるため、式（６）及び（７）が成立する。
【００３６】
【数２】

ここで、Ｒ_Cはガス定数である。
【００３７】
コンプレッサ下流ガス温度Ｔ_{C_out}は、空気が圧縮されることで上昇するが、理想的な断熱圧縮に比べて、実際は温度が高くなる傾向を示す。これを表すための無次元量として、コンプレッサの断熱効率η_Cを用いる。コンプレッサ断熱効率η_Cは、圧縮比ＰＲ及び体積流量Ｑ_Cに応じて図３（ｂ）に示すη_Cテーブルを検索することにより算出される。この断熱効率η_Cを下記式（８）に適用して、コンプレッサ下流温度Ｔ_{C_out}が算出される。
【数３】

ここで、Ｔ_{C_in}は、コンプレッサ上流温度、すなわち大気温度ＴＡであり、ｋ_Cは、コンプレッサ通過ガス、すなわち空気の比熱比である。
【００３８】
ガスを圧縮するために用いた機械エネルギーはエネルギーの保存則にもとづき、コンプレッサ上下流のガスエネルギー差に等しいと考えられる。そこで、下記式（９）により、圧縮に必要とする軸トルクＭ_C［Ｎｍ］が算出される。
【数４】

【００３９】
ここで、Ｇ_Cは式（６）により算出されるコンプレッサ通過ガス質量流量［ｋｇ／ｓ］、ｃ_{P_C}は、コンプレッサ通過ガス、すなわち空気の定圧比熱［Ｊ／(ｋｇ・Ｋ)］である。
【００４０】
次にタービンモデル３４について説明する。
タービンモデル３４は、可変ノズルを装備したものを想定し、タービン上流圧力Ｐ_{tb_in}、タービン下流圧力Ｐ_{tb_out}、タービン上流ガス温度Ｔ_{tb_in}、タービン回転数Ｎ_tb及びノズル開度（ノズル有効開口面積）Ａ_tbから、タービン通過ガス流量Ｇ_tb（＝Ｇ_{tb_in}＝Ｇ_{tb_out}）、タービン下流ガス温度Ｔ_{tb_out}及び膨張によって得た軸トルクＭ_tbを算出する。ノズル有効開口面積Ａ_tbは、ＥＣＵ２０から出力されるデューティ制御信号のデューティ比に応じて予め設定されたテーブル（図示せず）を参照して求められる。
【００４１】
タービン通過ガス流量Ｇ_tbは、コンプレッサと同様に特性テーブルより算出する方法もあるが，データ量削減を考えてベルヌーイの原理にもとづく物理式により算出することとした。また、コンプレッサと同様に上下流ガスの流量および成分比は同じであるとした。
【００４２】
タービン通過ガス質量流量［ｋｇ／ｓ］は、下記式（１０−１）または（１０−２）により算出される。
【数５】

【００４３】
ここで、Ｐ_{tb_in}はタービン上流圧、Ｐ_{tb_out}はタービン下流圧、ｋ_tbはタービン通過ガス比熱比、Ｒ_tbはタービン通過ガス定数、Ｔ_{tb_in}はタービン上流ガス温度である。
【００４４】
タービン通過ガス比熱比ｋ_tbは、タービン通過ガスの定圧比熱と定容比熱の比であり、タービン通過ガス、すなわち空気と燃焼ガスの混合ガスの比熱は、前記式（４）により算出される。
【００４５】
下流ガス温度Ｔ_{tb_out}は、コンプレッサと同様にタービンの断熱効率η_tbを用いて下記式（１２）により算出される。
【数６】

【００４６】
タービンを回転させるための機械エネルギーは、タービン上下流のガスエネルギーの差と等しいと考えられる。そこで、下記式（１３）により、タービン回転に必要とする軸トルクＭ_tbを算出する。
【００４７】
【数７】

ここで、ｃ_{p_tb}はタービン通過ガス定圧比熱であり、前記式（４）により算出される。
【００４８】
次にタービン回転数演算モデル３３について説明する。
タービン回転数Ｎ_tbは、コンプレッサの軸トルクＭ_cとタービンの軸トルクＭ_tbの差、及び回転軸での摩擦トルクＭ_fを下記式（１４）に適用して算出される。
【数８】

ここで、Ｉ_tbはタービンの慣性モーメント［ｋｇ・ｍ²］である。
【００４９】
次にインタークーラモデル３５について説明する。
インタークーラモデル３５では、冷却効率η_IC、インタークーラ上流ガス温度Ｔ_{IC_in}、及び検出される大気温度ＴＡを下記式（１５）に適用して、インタークーラ下流ガス温度Ｔ_{IC_out}が算出される。冷却効率η_ICは、インタークーラ通過ガス流量Ｇ_ICに応じて図４に示すテーブルを用いて算出される。
Ｔ_{IC_out}＝（１−η_IC）・Ｔ_{IC_in}＋η_IC・ＴＡ （１５）
【００５０】
インタークーラでは物質交換が無いことから，下流ガス流量および成分比は上流と等しい。また圧力損失は無視できる程度に小さいので、上下流の各圧力には変化が無いとする。
【００５１】
次にＥＧＲモデル３９について説明する。
ＥＧＲモデル３９では、タービンモデルの可変ノズルと同様に，ベルヌーイの原理を用いてＥＧＲ通過ガス流量Ｇ_EGR（＝Ｇ_{EGR_in}＝Ｇ_{EGR_out}）が下記式（１６−１）または（１６−２）を用いて算出される。
【００５２】
【数９】

ここで、Ｐ_{EGR_in}はＥＧＲ上流圧、Ｐ_{EGR_out}はＥＧＲ下流圧、Ａ_EGRはＥＧＲ弁有効開口面積、ｋ_EGRはＥＧＲ通過ガス比熱比、Ｒ_EGRはＥＧＲ通過ガス定数、Ｔ_{EGR_in}はＥＧＲタービン上流ガス温度である。ＥＧＲ通過ガス比熱比ｋ_EGR及びＥＧＲ通過ガス定数Ｒ_EGRは、それぞれタービン通過ガス比熱比ｋ_tb及びタービン通過ガス定数Ｒ_tbと等しい。また、ＥＧＲ弁有効開口面積Ａ_EGRは、検出されるＥＧＲ弁のリフト量ＬＡＣＴに応じて予め設定されたテーブル（図示せず）を用いて算出される。
【００５３】
次に吸気管モデル３６及び排気管モデル３８について説明する。
吸気管２及び排気管４は、ともにガスが流出入する定容室として考える。管内の圧力Ｐ_chと温度Ｔ_chは、流出入するガスエネルギーと質量バランスを考慮して、下記式（１８−１）〜（１８−４）により算出される。
【００５４】
【数１０】

ここで、Ｇ_{ch_in}は管内流入ガス質量流量、Ｇ_{ch_out}は管内流出ガス質量流量、Ｒ_chは管内ガス定数、ｍ_chは管内滞留ガス質量、Ｔ_{ch_in}は管内流入ガス温度、ｃ_{v_ch}は管内滞留ガス定容比熱、ｃ_{p_ch_in}は管内流入ガス定圧比熱、ｃ_{p_ch}は管内滞留ガス定圧比熱、Ｖ_chは管内容積、Ｐ_ch(0)は管内圧力初期値である。
【００５５】
また吸気管流出ガス成分比λ_{ch_out}は、吸気管内の空気と燃焼ガスが完全に混合したものと仮定して、下記式（１９）により算出される。吸気管流出ガス成分比λ_{ch_out}は、シリンダ吸入ガス成分比λ_{cyl_in}と等しい。
【数１１】

【００５６】
ここで、ｍ_{ch_cmb}は吸気管内滞留燃焼ガス質量、ｍ_{ch_air}は吸気管内滞留空気質量、ｍ_{ch_cmb}(0)は吸気管内滞留燃焼ガス質量の初期値、ｍ_{ch_air}(0)は吸気管内滞留空気質量の初期値、Ｇ_{ch_in}は吸気管流入新気質量流量、Ｇ_{cyl_in_air}はシリンダ流入空気質量流量、Ｇ_{cyl_in_cmb}はシリンダ流入燃焼ガス質量流量、Ｇ_{EGR_air}はＥＧＲ通過空気質量流量、Ｇ_{EGR_cmb}はＥＧＲ通過燃焼ガス質量流量である。
【００５７】
また排気管流入ガス成分比（排気成分比）λ_exは、下記式（２０）により算出される。ＥＧＲ通過ガス成分比λ_EGR及びタービン通過ガス成分比λ_tbは、排気成分比λ_exと等しい。
【数１２】

【００５８】
ここで、ｍ_{ex_cmb}は排気管内滞留燃焼ガス質量、ｍ_{ex_air}は排気管内滞留空気質量、ｍ_{ex_cmb}(0)は排気管内滞留燃焼ガス質量の初期値、ｍ_{ex_air}(0)は排気管内滞留空気質量の初期値、Ｇ_{ex_air}は排気管流入空気質量流量、Ｇ_{ex_cmb}は排気管流入燃焼ガス質量流量、Ｇ_{EGR_air}はＥＧＲ通過空気質量流量、Ｇ_{EGR_cmb}はＥＧＲ通過燃焼ガス質量流量、Ｇ_{tb_air}はタービン通過空気質量流量、Ｇ_{tb_cmb}はタービン通過燃焼ガス質量流量である。
【００５９】
次にシリンダモデル３７について説明する。
シリンンダモデル３７では、シリンダ流入ガスの圧力Ｐ_{cyl_in}、温度Ｔ_{cyl_in}及び成分比、燃料流量Ｇ_fuel、並びにエンジン回転数Ｎｅから、シリンダ流入ガス質量流量Ｇ_{cyl_in}、排気ガス質量流量Ｇ_{cyl_out}、排気温度Ｔ_{cyl_out}及び成分比λ_{cyl_out}を算出する。
【００６０】
シリンダモデル３７では、気筒数やピストンの往復運動による間欠的なガス流動は考慮せず、時間ベースの定常流として表す。シリンダ流入ガス流量Ｇ_{cyl_in}は、シリンダ吸入体積効率η_{v_cyl}、シリンダ吸入ガス圧力Ｐ_{cyl_in}、シリンダ吸入ガス温度Ｔ_{cyl_in}、及びシリンダ排気量Ｖ_{cyl_in}［ｍ³］を、下記式（２１）に適用して算出される。シリンダ吸入体積効率η_{v_cyl}は、エンジン回転数Ｎｅに応じて図５に示すη_{v_cyl}テーブルを検索することにより算出される。シリンダ排気量Ｖ_{cyl_in}は、シリンダ形状により決まる定数である。
【００６１】
また、シリンダ流入空気流量Ｇ_{cyl_in_air}は、ガス成分比λ_{cyl_in}を用いて、下記式（２２）により算出される。シリンダ流入空気流量Ｇ_{cyl_in_air}が、推定吸入空気量ＱＥに相当する。
【００６２】
【数１３】

ここで、Ｒ_{cyl_in}はシリンダ吸入ガス定数である。
【００６３】
排気流量Ｇ_{cyl_out}は、下記式（２３）により、シリンダ流入ガス流量Ｇ_{cyl_in}と燃料流量（燃料噴射量）Ｇ_fuelの和として算出される。
Ｇ_{cyl_out}＝Ｇ_{cyl_in}＋Ｇ_fuel （２３）
【００６４】
排気ガスエネルギーは、吸入ガスエネルギーと燃焼エネルギーの一部との合計と考えられる。燃焼による熱エネルギーは発生した水が蒸気のままであると仮定し、単位重量あたりに燃料が発生するエネルギーとして低発熱量Ｈｕ［Ｊ／ｋｇ］を用いる．排気損失率η_{ex_cyl}と定義した流入エネルギーと排気ガスエネルギーの割合から、下記式（２４）により、排気温度Ｔ_{cyl_out}が算出される。排気損失率η_{ex_cyl}は、エンジン回転数Ｎｅに応じて図６に示すη_{ex_cyl}テーブルを検索することにより算出される。
【００６５】
【数１４】

ここで、ｃ_{p_cyl_in}はシリンダ吸入ガス定圧比熱、Ｇ_{fuel_c}は燃焼燃料質量流量、Ｇ_{cyl_in_air}はシリンダ吸入空気質量流量、ＡＦは理論空燃比である。
【００６６】
また燃料流量Ｇ_fuelと理論空燃比ＡＦの積、すなわち完全燃焼に必要な空気の最低必要量（Ｇ_fuel・ＡＦ）が、シリンダ吸入空気質量流量Ｇ_{cyl_in_air}より大きいときは、燃焼燃料質量流量Ｇ_{fuel_c}は、（Ｇ_{cyl_in_air}／ＡＦ）とし、燃料の一部（Ｇ_fuel−Ｇ_{cyl_in_air}／ＡＦ）はそのまま排出される。一方、完全燃焼に必要な空気の最低必要量（Ｇ_fuel・ＡＦ））が、シリンダ吸入空気質量流量Ｇ_{cyl_in_air}以下であるときは、噴射された燃料が全部燃焼するので、燃焼燃料質量流量Ｇ_{fuel_c}は燃料流量Ｇ_fuelと等しくなる。
【００６７】
なお、上記式（２４）では、シリンダ壁から流出入する熱エネルギーが考慮されていないため、実際には温度補正値ＴＣを加算する必要がある。この温度補正値ＴＣは、対象とするエンジン毎に実験により決定される。
【００６８】
図７及び図８は、上述したエンジンシステムモデルを用いて算出されるパラメータ値と、実測値とを比較して示す図である。
図７（ａ）には、実測時のエンジン回転数Ｎｅ、ＥＧＲ弁のリフト量ＬＡＣＴ及びタービンのノズル開度Ａtbの推移が示されている。同図（ｂ）には、コンプレッサ通過ガス質量流量Ｇ_Cの演算データ（実線）と、実測データ（破線）とが示されている。また図８（ａ）には、吸気管内圧力（吸気管モデルに対応するＰ_ch）と排気管内圧力（排気管モデルに対応するＰ_ch）に対応するの演算データ（実線）と、実測データ（破線）とが示されている。同図（ｂ）には、排気温度Ｔ_{cyl_out}及び吸気温度Ｔ_{cyl_in}の演算データ（実線）と、実測データ（破線）とが示されている。
これらの図から明らかなように、簡易化されたモデルでありながら、実測データを精度よく近似する演算データが得られることがわかる。
【００６９】
以上のように本実施形態では、エンジンシステムを構成する各構成要素のモデルの組み合わせとしてシステム全体のモデルを構成し、かつ排気に含まれるガス組成を、二酸化炭素、窒素、酸素、水蒸気などの個々の成分の比率（複数パラメータ）として扱わずに、空気と燃焼ガスの比率（１つのパラメータ）として把握するようにしたので、排気還流機構を介して接続された排気管及び吸気管内における空気量を比較的少ない演算量で正確に推定することができる。したがって、エンジン１の燃焼室（シリンダ）に流入する空気量（酸素量）を正確に推定することが可能となる。その結果、上述したモデルに基づいて推定されるシリンダ流入空気量を、エンジンのリアルタイム制御に適用し、例えば燃料供給量の不足を防止することができる。
【００７０】
また上述したモデルは、各構成要素に対応するモデル間で受け渡すパラメータとして、ガスエネルギーの算出にかかるパラメータ、すなわち質量流量、温度、ガス成分比、及び圧力を用いるようにしたので、排気還流機構のようなガス交換を発生させる構成要素だけでなく、ターボチャージャやインタークーラのようなガス交換を伴わない構成要素を含むエンジンシステム内のガス挙動を正確に把握することができる。その結果、燃焼室に供給される空気量の推定精度を向上させることができる。
またシステムモデルを各構成要素に対応する複数のモデルの組み合わせとして構成し、かつガスエネルギー算出にかかるパラメータを各モデル間で受け渡すようにしたので、モデルの汎用性（再利用性）を高める効果も得られる。
【００７１】
本実施形態では、ＥＣＵ２０が吸入空気量推定手段を構成する。
【００７２】
なお本発明は上述した実施形態に限るものではなく、種々の変形が可能である。例えば、上述した実施形態では、スロットル弁が設けられていないエンジンシステムについてのモデルを示したが、スロットル弁が設けられているエンジンについては、スロットル弁モデルを追加することにより、容易にモデル化することが可能である。スロットル弁モデルでは、ＥＧＲモデルやタービンモデルと同様の数式に、スロットル弁の有効開口面積を適用することにより、通過ガス質量流量を算出することができる。
【００７３】
また吸入空気量を検出するエアフローセンサを用いる場合には、上記システムモデルを用いてエアフローセンサ出力に対応するパラメータを算出し、そのパラメータとエアフローセンサ出力とを比較することにより、エアフローセンサの劣化または異常を判定するようにしてもよい。
【００７４】
【発明の効果】
以上詳述したように請求項１に記載の発明によれば、吸気系モデル、燃焼室モデル、排気系モデル、及び排気還流系モデルを含む機関システムモデルを用いて、機関燃焼室に供給される空気量の推定が行われ、前記機関システムモデルでは、各モデルにおけるガス組成を表すパラメータとして、空気と、機関燃焼室における完全燃焼によって生成される、空気以外の燃焼ガスとの質量比が用いられる。すなわち、従来のように排気中に含まれる各成分毎のモル数（複数パラメータ）を用いずに、空気とそれ以外の燃焼ガスとの比率（単一パラメータ）が用いられるので、排気還流機構を介して接続された排気管及び吸気管内における空気量を、少ない演算量で正確に推定することができ、機関燃焼室に流入する空気量（酸素量）を正確に推定することが可能となる。その結果、上記機関システムモデルに基づいて推定される燃焼室流入空気量を、内燃機関のリアルタイム制御に適用し、例えば燃料供給量の不足を防止することができる。また各モデル間で受け渡すパラメータとして、ガス質量流量、ガス成分質量比、ガス温度、及びガス圧力を用いることにより、機関システム内のガス挙動を正確に把握することができ、燃焼室に供給される空気量の推定精度を向上させることができるとともに、モデルを再利用する際の利便性を高めることができる。さらに燃焼ガスは二酸化炭素、窒素及び水蒸気を成分とし、各成分の比率は一定として取り扱うことにより、燃焼ガスの比熱を定数として取り扱うことが可能となり、演算量を低減することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態にかかる内燃機関及びその制御装置の構成を示す図である。
【図２】図１に示す内燃機関をモデル化した機関システムモデルの構成を示すブロック図である。
【図３】図２に示すコンプレッサモデルでの演算に使用されるテーブルを示す図である。
【図４】図２に示すインタークーラモデルでの演算に使用されるテーブルを示す図である。
【図５】図２に示すシリンダモデルでの演算に使用されるテーブルを示す図である。
【図６】図２に示すシリンダモデルでの演算に使用されるテーブルを示す図である。
【図７】モデルを用いた演算データと実測データとを比較して示すタイムチャートである。
【図８】モデルを用いた演算データと実測データとを比較して示すタイムチャートである。
【符号の説明】
１ 内燃機関
２ 吸気管
４ 排気管
５ 排気還流通路
６ 排気還流弁
７ リフトセンサ
１１ 燃料噴射弁
２０ 電子制御ユニット（吸入空気量推定手段）
２１ アクセルセンサ
２２ 大気圧センサ
２３ 大気温度センサ
２４ エンジン回転数センサ
３６ 吸気管モデル（吸気系モデル）
３７ シリンダモデル（燃焼室モデル）
３６ 排気管モデル（排気系モデル）
３９ ＥＧＲモデル（排気環流系モデル）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device including an exhaust gas recirculation mechanism.
[0002]
[Prior art]
In Japanese Patent Laid-Open No. 6-26383, in order to obtain the intake air amount of a diesel engine equipped with a turbocharger and an exhaust gas recirculation mechanism as accurately as possible, the engine speed, the fuel amount, the exhaust gas recirculation rate, and the compressor of the turbocharger are disclosed. A control system for estimating the intake air amount is proposed based on a comparison between the power of the engine and the power of the turbine.
[0003]
The paper entitled “Exhaust gas recirculation model for engine control system design and evaluation” published in the Society of Instrument and Control Engineers Vol.35, No.2,230 / 237 (1999) CO2 produced by combustion using a combustion system model that assumes that combustion proceeds according to the chemical reaction formula of₂, O₂, H₂It is shown that the number of moles of each exhaust component such as O is calculated and applied to an exhaust system model, an exhaust recirculation system model, and an intake system model.
[0004]
[Problems to be solved by the invention]
In an internal combustion engine that performs lean combustion with the ratio of air to fuel greater than the stoichiometric air-fuel ratio, a relatively large amount of oxygen is also contained in the exhaust discharged from the combustion chamber. Since the exhaust gas is circulated to the combustion chamber via the exhaust gas recirculation mechanism, the amount of oxygen actually flowing into the combustion chamber is larger than the amount sucked as fresh air. In the system described in JP-A-6-26383, the exhaust gas recirculation rate is considered, but the gas component contained in the reflux gas is not considered. That is, since the calculation considering the amount of oxygen contained in the reflux gas is not performed, if the maximum fuel injection amount is set according to the estimated intake air amount, the fuel injection amount is less than the amount that can be actually injected. The amount of injection is limited. As a result, a sufficient output of the internal combustion engine cannot be obtained, and there is a possibility that the driving performance is impaired.
[0005]
Even when the intake air amount is actually detected by the air flow sensor provided upstream of the exhaust gas recirculation mechanism, the amount of air circulated from the exhaust system is not detected. Is limited.
Furthermore, the method shown in the papers published in the above paper collection requires calculation of the movement of the number of moles for each component contained in the exhaust gas. Therefore, this technique can be used as a technique for engine control system design evaluation, but is not suitable for real-time control of an internal combustion engine.
[0006]
The present invention has been made to solve such problems, and accurately estimates the amount of air (oxygen) in the gas supplied to the combustion chamber of the internal combustion engine equipped with the exhaust gas recirculation mechanism with a small amount of calculation, It is an object of the present invention to provide a control device for an internal combustion engine that can control the internal combustion engine more appropriately.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, the invention described in claim 1 includes intake air amount estimating means for estimating the amount of air supplied to an internal combustion engine having an exhaust gas recirculation mechanism, and the engine is controlled based on the estimated air amount. In the control device for an internal combustion engine to be controlled, the intake air amount estimation means includes an intake system model (36) that models the intake system of the engine, and a combustion chamber model (37) that models the combustion chamber of the engine. The engine system model including an exhaust system model (38) that models the exhaust system of the engine and an exhaust system model (39) that models the exhaust gas recirculation mechanism is supplied to the combustion chamber. Air volume(G cyl_in_air )In the engine system model,As parameters passed between the models, gas mass flow rate (G), gas component mass ratio (λ), gas temperature (T), and gas pressure (P) are used, and the gas component mass ratio (λ) is: It is the mass ratio of air and combustion gas other than air produced by complete combustion in the combustion chamber, and the combustion gas is treated with carbon dioxide, nitrogen and water vapor as components, and the ratio of each component is assumed to be constant. , The amount of air supplied to the combustion chamber (G cyl_in_air ) Is the pressure of the gas flowing into the combustion chamber (P cyl_in ) And temperature (T cyl_in ), The rotational speed (Ne) of the engine, and the gas component mass ratio (λ) corresponding to the gas flowing into the combustion chamber cyl_in ) And calculated according toIt is characterized by that.
[0008]
  According to this configuration, the amount of air supplied to the engine combustion chamber is estimated using an engine system model including an intake system model, a combustion chamber model, an exhaust system model, and an exhaust gas recirculation system model. In the model, parameters representing the gas composition in each model include air and combustion gases other than air generated by complete combustion in the engine combustion chamber.Mass ratioIs used. That is, the ratio of air and other combustion gases (single parameter) is used without using the number of moles (multiple parameters) for each component contained in the exhaust as in the prior art. Thus, the amount of air in the exhaust pipe and the intake pipe connected via the engine can be accurately estimated with a small amount of calculation, and the amount of air (oxygen amount) flowing into the engine combustion chamber can be accurately estimated. As a result, the combustion chamber inflow air amount estimated based on the engine system model can be applied to the real-time control of the internal combustion engine, and for example, a shortage of the fuel supply amount can be prevented.In addition, by using the gas mass flow rate, gas component mass ratio, gas temperature, and gas pressure as parameters passed between models, the gas behavior in the engine system can be accurately grasped and supplied to the combustion chamber. As a result, it is possible to improve the accuracy of estimating the amount of air to be used and to improve the convenience in reusing the model. Further, by treating the combustion gas with carbon dioxide, nitrogen, and water vapor as components, and by treating the ratio of each component as constant, the specific heat of the combustion gas can be handled as a constant, and the amount of calculation can be reduced.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention. An internal combustion engine (hereinafter referred to as “engine”) 1 is a direct injection engine that directly injects fuel into a cylinder, and a fuel injection valve 11 is provided in each cylinder. The fuel injection valve 11 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 20, and the valve opening time of the fuel injection valve 11 is controlled by the ECU 20.
[0013]
The engine 1 includes an intake pipe 2, an exhaust pipe 4, and a turbocharger 8. The turbocharger 8 includes a turbine 10 driven by exhaust kinetic energy, and a compressor 9 that is rotationally driven by the turbine 10 and compresses intake air. An intercooler 3 for cooling the compressed air is provided on the downstream side of the compressor 9.
[0014]
The turbine 10 is configured to change the turbine rotational speed (rotational speed) by changing the nozzle opening. The nozzle opening degree of the turbine 10 is electromagnetically controlled by the ECU 20. More specifically, the ECU 20 supplies a control signal having a variable duty ratio to the turbine 10 to thereby control the nozzle opening.
[0015]
Between the exhaust pipe 4 and the intake pipe 2, an exhaust gas recirculation passage 5 that circulates exhaust gas to the intake pipe 2 is provided. The exhaust gas recirculation passage 5 is provided with an exhaust gas recirculation valve (hereinafter referred to as “EGR valve”) 6 for controlling the exhaust gas recirculation amount. The EGR valve 6 is an electromagnetic valve having a solenoid, and the valve opening degree is controlled by the ECU 20. The EGR valve 6 is provided with a lift sensor 7 for detecting the valve opening degree (valve lift amount) LACT, and the detection signal is supplied to the ECU 20. An exhaust gas recirculation mechanism is configured by the exhaust gas recirculation passage 5 and the EGR valve 6.
[0016]
An accelerator sensor 21 for detecting a depression amount AP of an accelerator pedal (not shown) of a vehicle driven by the engine 1, an atmospheric pressure sensor 22 for detecting an atmospheric pressure PA, an atmospheric temperature difference sensor 23 for detecting an atmospheric temperature TA, and An engine speed sensor 24 for detecting the engine speed (rotation speed) Ne is provided. Detection signals from these sensors are supplied to the ECU 20.
[0017]
The ECU 20 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, a central processing unit (hereinafter referred to as “CPU”). A storage circuit that stores various calculation programs executed by the CPU and calculation results, an output circuit that supplies a drive signal to the fuel injection valve 11, the EGR valve 6, and the like.
[0018]
The ECU 20 calculates the valve opening time TOUT of the fuel injection valve 11 according to the accelerator depression amount AP detected by the accelerator sensor 21 and supplies a drive signal corresponding to the valve opening time TOUT to the fuel injection valve 11. Since the amount of fuel injected from the fuel injection valve 11 is proportional to the fuel injection time TOUT, it is hereinafter referred to as “fuel injection amount TOUT”.
[0019]
The ECU 20 further calculates an estimated value QE of the intake air amount of the engine 1 based on an engine model described in detail below, and calculates a maximum value TOUTMAX of the fuel injection amount according to the intake air amount estimated value QE. The fuel injection amount TOUT is controlled so as not to exceed the maximum value TOUTMAX corresponding to the intake air amount.
[0020]
The ECU 20 further determines the exhaust gas recirculation amount and the boost pressure based on the intake air amount estimated value QE, and controls the lift amount (valve opening amount) of the EGR valve 6 and the nozzle opening degree of the turbine 10.
[0021]
In the present embodiment, an engine system model including the engine 1, the intake pipe 2, the intercooler 3, the exhaust pipe 3, the exhaust gas recirculation mechanism, and the turbocharger 8 is defined by a combination of models for each component, and the model Based on the above, the behavior of the gas in the engine system is estimated. FIG. 2 is a block diagram showing the configuration of the engine system model. As shown in this figure, the engine system model includes a turbocharger model 31 that models the turbocharger 8, an intercooler model 35 that models the intercooler 3, and an intake pipe model 36 that models the intake pipe 2. The cylinder model 37 that models the engine 1, the exhaust pipe model 38 that models the exhaust pipe 4, and the EGR model 39 that models the exhaust gas recirculation mechanism. The turbocharger model 31 includes a compressor model 32 that models the compressor 9, a turbine model 34 that models the turbine 10, and a turbine rotation speed calculation model 33 for calculating the turbine rotation speed.
[0022]
The model of each component shown in FIG. 2 is not a strict model of a distributed parameter system but an approximate model of a lumped parameter system. It has been confirmed that sufficient estimation accuracy can be obtained also by the approximate model, and the required amount of calculation can be greatly reduced by using the approximate model.
[0023]
Further, the model shown in FIG. 2 employs a parameter for calculating the energy of the gas flowing between each component as an input / output parameter between the models corresponding to each component. That is, the gas mass flow rate, the gas component ratio, and the temperature directly related to the calculation of the gas energy and the pressure necessary for the calculation of the mass flow rate are used. G, λ, T, and P shown in FIG. 2 indicate mass flow rate, gas component ratio, temperature, and pressure, respectively. In the turbocharger model 31, the turbine speed NT and the torque M are used as parameters. In the turbine model 34, the effective opening area SN corresponding to the nozzle opening is used as an input parameter, and in the EGR model 39, the effective opening area SE corresponding to the valve opening amount of the EGR valve 6 is used as an input parameter. Further, the cylinder model 37 uses the engine speed Ne and the fuel supply flow rate GF as input parameters.
[0024]
In this way, the entire system model is constructed by combining the models for each component, and the parameters (G, λ, T, P) for energy calculation are used as input / output parameters between the models. Convenience (reusability) when reusing can be improved. That is, the model once constructed can be easily applied to other systems.
[0025]
Hereinafter, the engine system model shown in FIG. 2 will be described in more detail.
The gas flowing through the engine system varies in pressure, temperature, and gas components by compression and expansion by the turbocharger 8, cooling by the intercooler 3, combustion in the cylinder (engine 1), and gas mixing by the exhaust gas recirculation mechanism. The change is formed by a subordinate relationship of a plurality of parameters expressed by the gas state equation (formula (1)).
pv = mRT (1)
Here, p is pressure [Pa], and v is volume [m.^Three], M is mass [kg], R is gas constant [J / (kg · K)], and T is temperature [K].
[0026]
The state of the gas, which varies depending on the functions of the elements that make up the engine system, can be applied by applying the concept of the law of conservation of energy and the law of conservation of mass. It can be captured as a decrease, and gas mixing by exhaust gas recirculation is mass exchange, so it can be considered as the addition of energy and mass of air and reflux gas, respectively. By representing various phenomena surrounding gas in this way by simple calculation of energy and mass, it becomes easy to convert them into measurable physical quantities such as temperature and pressure.
[0027]
The energy of the gas is grasped as an energy flow rate H [J / s] calculated by the following formula (2).
H = G · c_P・ T (2)
Where G is the mass flow rate [kg / s], c_PIs the constant pressure specific heat [J / (kg · K)], and T is the temperature [K].
[0028]
The specific heat that varies depending on the gas component is determined by the gas component and its mass ratio. In particular, since the EGR valve 6 constantly adjusts the recirculation amount of the exhaust gas, the specific heat always changes with the mixing ratio of air and exhaust gas. Therefore, it is necessary to always calculate the specific heat of the gas in the intake pipe 2 in the model calculation.
[0029]
The gas generated by combustion in the exhaust is carbon dioxide CO₂And water H₂Only O was handled, and NOx (nitrogen oxide), CO (carbon monoxide), and HC (hydrocarbon) were excluded because they were trace amounts in normal combustion. Air (N₂, O₂) And fuel (C_nH_m) Reacts at the ideal air-fuel ratio (fuel is completely burned)₂, N₂(Nitrogen) and H₂O is collectively defined as “combustion gas”, and only two types of gas are used in the model: combustion gas and air. The composition of the combustion gas is always constant and its specific heat C_cmbIs treated as a constant. Combustion gas specific heat C_cmbIs calculated by the following equation (3).
[0030]
[Expression 1]

[0031]
Here, n is the carbon content [mol] in 1 mol fuel, CO₂Is carbon dioxide molecular weight [g / mol], c_CO2Is the specific heat of carbon dioxide [J / (kg · K)], m is the hydrogen content in 1 mol fuel [mol], H₂O is water molecular weight [g / mol], c_H2OIs the specific heat of water (steam) [J / (kg · K)], χ is the nitrogen capacity ratio to oxygen in the air, N₂Is nitrogen molecular weight [g / mol], c_N2Is the specific heat of nitrogen [J / (kg · K)].
[0032]
In this way, by handling the gas flowing in the engine system as only two components, air and combustion gas, it is possible to reduce the amount of calculation of specific heat that constantly changes. Specific heat c of mixed gas of air and combustion gas_mixIs calculated by the following equation (4).
c_mix= C_air(1-λ) + c_cmb・ Λ (4)
[0033]
Where c_airIs the specific heat of air [J / (kg · K)], c_cmbIs the specific heat [J / (kg · K)] of the combustion gas, and λ is the gas component mass ratio (ratio of the combustion gas amount to the total gas amount).
[0034]
Next, the compressor model 32 constituting the turbocharger model 31 will be described.
In the compressor model 32, the compressor upstream pressure P_{C_in}, Compressor downstream pressure P_{C_out}, Compressor upstream gas temperature T_{C_in}, Turbine speed N_tbTo calculate each gas flow rate, component ratio, downstream gas temperature, and shaft torque required for compression. The compressor upstream gas volume flow Qc is determined by the upstream / downstream compression ratio PR (= P_{C_out}/ P_{C_in}) And turbine speed N_tbAccordingly, the Qc table shown in FIG. 3A is searched and calculated (the following formula (5)).
[0035]
Next, according to the following formula (6), the volume flow rate Qc [m^Three/ S] is the mass flow rate G_{C_in}Convert to [kg / s]. Further, since the compressor has no functional material exchange and the upstream and downstream gas flow rates and component ratios are the same, the equations (6) and (7) are established.
[0036]
[Expression 2]

Where R_CIs the gas constant.
[0037]
Compressor downstream gas temperature T_{C_out}Increases as the air is compressed, but the temperature actually tends to be higher than the ideal adiabatic compression. As a dimensionless quantity to express this, the adiabatic efficiency η of the compressor_CIs used. Compressor insulation efficiency η_CIs compression ratio PR and volumetric flow rate Q_CΗ shown in FIG._CCalculated by searching the table. This thermal insulation efficiency η_CIs applied to the following equation (8), and the compressor downstream temperature T_{C_out}Is calculated.
[Equation 3]

Where T_{C_in}Is the compressor upstream temperature, that is, the atmospheric temperature TA, and k_CIs the specific heat ratio of the gas passing through the compressor, that is, air.
[0038]
The mechanical energy used to compress the gas is considered to be equal to the gas energy difference between the upstream and downstream of the compressor based on the energy conservation law. Therefore, the shaft torque M required for compression is calculated by the following equation (9)._C[Nm] is calculated.
[Expression 4]

[0039]
Where G_CIs the compressor passing gas mass flow rate [kg / s] calculated by the equation (6), c_{P_C}Is the constant-pressure specific heat [J / (kg · K)] of the compressor passing gas, that is, air.
[0040]
Next, the turbine model 34 will be described.
The turbine model 34 is assumed to be equipped with a variable nozzle, and the turbine upstream pressure P_{tb_in}, Turbine downstream pressure P_{tb_out}, Turbine upstream gas temperature T_{tb_in}, Turbine speed N_tbAnd nozzle opening (nozzle effective opening area) A_tbFrom the turbine passing gas flow rate G_tb(= G_{tb_in}= G_{tb_out}), Turbine downstream gas temperature T_{tb_out}And shaft torque M obtained by expansion_tbIs calculated. Nozzle effective opening area A_tbIs obtained with reference to a table (not shown) set in advance according to the duty ratio of the duty control signal output from the ECU 20.
[0041]
Turbine passing gas flow rate G_tbAs with the compressor, there is a method of calculating from the characteristic table, but considering the reduction of the data amount, it was determined by a physical formula based on Bernoulli's principle. In addition, the flow rate and the component ratio of the upstream and downstream gases are the same as in the compressor.
[0042]
The turbine passing gas mass flow rate [kg / s] is calculated by the following equation (10-1) or (10-2).
[Equation 5]

[0043]
Where P_{tb_in}Is the turbine upstream pressure, P_{tb_out}Is the turbine downstream pressure, k_tbIs the specific heat ratio of the gas passing through the turbine, R_tbIs the turbine passing gas constant, T_{tb_in}Is the turbine upstream gas temperature.
[0044]
Turbine passing gas specific heat ratio k_tbIs the ratio of the constant pressure specific heat and the constant volume specific heat of the turbine passing gas, and the specific heat of the turbine passing gas, that is, the mixed gas of air and combustion gas, is calculated by the equation (4).
[0045]
Downstream gas temperature T_{tb_out}Is the thermal insulation efficiency of the turbine_tbIs calculated by the following equation (12).
[Formula 6]

[0046]
The mechanical energy for rotating the turbine is considered to be equal to the difference in gas energy upstream and downstream of the turbine. Therefore, the shaft torque M required for turbine rotation is expressed by the following equation (13)._tbIs calculated.
[0047]
[Expression 7]

Where c_{p_tb}Is the specific heat of the turbine passing gas constant pressure, and is calculated by the equation (4).
[0048]
Next, the turbine speed calculation model 33 will be described.
Turbine speed N_tbIs the compressor shaft torque M_cAnd turbine shaft torque M_tbAnd frictional torque M at the rotating shaft_fIs applied to the following equation (14).
[Equation 8]

Where I_tbIs the moment of inertia of the turbine [kg · m²].
[0049]
Next, the intercooler model 35 will be described.
In the intercooler model 35, the cooling efficiency η_{I c}, Intercooler upstream gas temperature T_{IC_in}, And the detected atmospheric temperature TA to the following equation (15), the intercooler downstream gas temperature T_{IC_out}Is calculated. Cooling efficiency η_{I c}Is the intercooler passage gas flow rate G_{I c}Is calculated using the table shown in FIG.
T_{IC_out}= (1-η_{I c}) ・ T_{IC_in}+ Η_{I c}・ TA (15)
[0050]
Since there is no material exchange in the intercooler, the downstream gas flow rate and the component ratio are equal to the upstream. Further, since the pressure loss is negligibly small, it is assumed that there is no change in the upstream and downstream pressures.
[0051]
Next, the EGR model 39 will be described.
In the EGR model 39, the EGR passage gas flow rate G is calculated using Bernoulli's principle, like the variable nozzle of the turbine model._EGR(= G_{EGR_in}= G_{EGR_out}) Is calculated using the following formula (16-1) or (16-2).
[0052]
[Equation 9]

Where P_{EGR_in}Is EGR upstream pressure, P_{EGR_out}Is EGR downstream pressure, A_EGRIs the effective opening area of the EGR valve, k_EGRIs the EGR passing gas specific heat ratio, R_EGRIs the EGR passage gas constant, T_{EGR_in}Is the EGR turbine upstream gas temperature. EGR passage gas specific heat ratio k_EGRAnd EGR passage gas constant R_EGRIs the specific heat ratio k of the gas passing through the turbine._tbAnd turbine gas constant R_tbIs equal to EGR valve effective opening area A_EGRIs calculated using a table (not shown) set in advance according to the detected lift amount LACT of the EGR valve.
[0053]
Next, the intake pipe model 36 and the exhaust pipe model 38 will be described.
Both the intake pipe 2 and the exhaust pipe 4 are considered as constant volume chambers through which gas flows in and out. Pressure P in the pipe_chAnd temperature T_chIs calculated by the following formulas (18-1) to (18-4) in consideration of gas energy flowing in and out and mass balance.
[0054]
[Expression 10]

Where G_{ch_in}Is the mass flow rate of the incoming gas in the pipe, G_{ch_out}Is the mass flow rate of outflow gas in the pipe, R_chIs the gas constant in the pipe, m_chIs the mass of gas in the pipe, T_{ch_in}Is the pipe inflow gas temperature, c_{v_ch}Is constant heat capacity of the gas staying in the tube, c_{p_ch_in}Is the constant pressure specific heat of the inflow gas in the pipe, c_{p_ch}Is the specific heat of the gas staying in the tube, V_chIs the pipe volume, P_{ch (0)}Is the initial pressure in the pipe.
[0055]
Also, the intake pipe outflow gas component ratio λ_{ch_out}Is calculated by the following equation (19) on the assumption that the air in the intake pipe and the combustion gas are completely mixed. Intake pipe outflow gas component ratio λ_{ch_out}Is the cylinder intake gas component ratio λ_{cyl_in}Is equal to
## EQU11 ##

[0056]
Where m_{ch_cmb}Is the mass of accumulated combustion gas in the intake pipe, m_{ch_air}Is the mass of air in the intake pipe, m_{ch_cmb}(0) is the initial value of the mass of combustion gas staying in the intake pipe, m_{ch_air}(0) is the initial value of the mass of air staying in the intake pipe,_{ch_in}Is the intake air inlet fresh air mass flow, G_{cyl_in_air}Is the mass flow rate of air flowing into the cylinder, G_{cyl_in_cmb}Is the cylinder inflow combustion gas mass flow, G_{EGR_air}Is the EGR passing air mass flow rate, G_{EGR_cmb}Is the EGR passing combustion gas mass flow rate.
[0057]
Also, exhaust pipe inflow gas component ratio (exhaust component ratio) λ_exIs calculated by the following equation (20). EGR passage gas component ratio λ_EGRAnd turbine passing gas component ratio λ_tbIs the exhaust component ratio λ_exIs equal to
[Expression 12]

[0058]
Where m_{ex_cmb}Is the mass of the accumulated combustion gas in the exhaust pipe, m_{ex_air}Is the mass of accumulated air in the exhaust pipe, m_{ex_cmb}(0) is the initial value of the mass of the combustion gas staying in the exhaust pipe, m_{ex_air}(0) is the initial value of the mass of accumulated air in the exhaust pipe, G_{ex_air}Is the exhaust pipe inflow air mass flow rate, G_{ex_cmb}Is the mass flow rate of the exhaust gas entering the exhaust pipe, G_{EGR_air}Is the EGR passing air mass flow rate, G_{EGR_cmb}Is EGR passage combustion gas mass flow rate, G_{tb_air}Is the air mass flow rate through the turbine, G_{tb_cmb}Is the mass flow rate of the combustion gas passing through the turbine.
[0059]
Next, the cylinder model 37 will be described.
In the cylinder model 37, the cylinder inlet gas pressure P_{cyl_in}, Temperature T_{cyl_in}And component ratio, fuel flow rate G_fuelAs well as the engine speed Ne, the cylinder inflow gas mass flow rate G_{cyl_in}, Exhaust gas mass flow rate G_{cyl_out}, Exhaust temperature T_{cyl_out}And component ratio λ_{cyl_out}Is calculated.
[0060]
In the cylinder model 37, the intermittent flow of gas due to the number of cylinders and the reciprocating motion of the piston is not considered, and is expressed as a time-based steady flow. Cylinder inflow gas flow rate G_{cyl_in}Is the cylinder suction volume efficiency η_{v_cyl}, Cylinder suction gas pressure P_{cyl_in}, Cylinder suction gas temperature T_{cyl_in}, And cylinder displacement V_{cyl_in}[M^Three] Is applied to the following equation (21). Cylinder suction volume efficiency η_{v_cyl}Is shown in FIG. 5 according to the engine speed Ne._{v_cyl}Calculated by searching the table. Cylinder displacement V_{cyl_in}Is a constant determined by the cylinder shape.
[0061]
Also, the cylinder inflow air flow rate G_{cyl_in_air}Is the gas component ratio λ_{cyl_in}Is calculated by the following equation (22). Cylinder inflow air flow rate G_{cyl_in_air}Corresponds to the estimated intake air amount QE.
[0062]
[Formula 13]

Where R_{cyl_in}Is the cylinder suction gas constant.
[0063]
Exhaust flow rate G_{cyl_out}Is the cylinder inflow gas flow rate G according to the following equation (23)._{cyl_in}And fuel flow rate (fuel injection amount) G_fuelIs calculated as the sum of
G_{cyl_out}= G_{cyl_in}+ G_fuel          (23)
[0064]
The exhaust gas energy is considered as the sum of the intake gas energy and a part of the combustion energy. Assuming that the heat energy generated by combustion is still steam, the low heating value Hu [J / kg] is used as the energy generated by the fuel per unit weight. Exhaust loss rate η_{ex_cyl}From the ratio of the inflow energy and exhaust gas energy defined as follows, the exhaust temperature T_{cyl_out}Is calculated. Exhaust loss rate η_{ex_cyl}Is shown in FIG. 6 according to the engine speed Ne._{ex_cyl}Calculated by searching the table.
[0065]
[Expression 14]

Where c_{p_cyl_in}Is the cylinder suction gas constant pressure specific heat, G_{fuel_c}Is the combustion fuel mass flow, G_{cyl_in_air}Is the cylinder intake air mass flow rate, and AF is the stoichiometric air-fuel ratio.
[0066]
Fuel flow rate G_fuelAnd the theoretical air-fuel ratio AF, that is, the minimum required amount of air required for complete combustion (G_fuelAF) is the cylinder intake air mass flow rate G_{cyl_in_air}When it is larger, the combustion fuel mass flow rate G_{fuel_c}(G_{cyl_in_air}/ AF) and part of the fuel (G_fuel-G_{cyl_in_air}/ AF) is discharged as it is. On the other hand, the minimum amount of air required for complete combustion (G_fuelAF)) is the cylinder intake air mass flow rate G_{cyl_in_air}When the following is true, all of the injected fuel burns, so the combustion fuel mass flow rate G_{fuel_c}Is the fuel flow rate G_fuelIs equal to
[0067]
In the above equation (24), since the heat energy flowing in and out from the cylinder wall is not taken into consideration, it is actually necessary to add the temperature correction value TC. The temperature correction value TC is determined by experiment for each target engine.
[0068]
7 and 8 are diagrams showing a comparison between the parameter value calculated using the engine system model described above and the actually measured value.
FIG. 7A shows changes in the engine speed Ne at the time of actual measurement, the lift amount LACT of the EGR valve, and the nozzle opening degree Atb of the turbine. In the same figure (b), the compressor passing gas mass flow rate G_CCalculation data (solid line) and actual measurement data (broken line) are shown. FIG. 8A shows the intake pipe pressure (P corresponding to the intake pipe model)._ch) And exhaust pipe pressure (P corresponding to exhaust pipe model)_ch) Corresponding to the calculation data (solid line) and actual measurement data (broken line). In FIG. 5B, the exhaust temperature T_{cyl_out}And intake air temperature T_{cyl_in}Calculation data (solid line) and actual measurement data (broken line) are shown.
As is apparent from these drawings, it is understood that calculation data that approximates the actual measurement data with high accuracy can be obtained with the simplified model.
[0069]
As described above, in the present embodiment, a model of the entire system is configured as a combination of models of each component constituting the engine system, and the gas composition contained in the exhaust is changed to individual carbon dioxide, nitrogen, oxygen, water vapor, and the like. The ratio of air and combustion gas (one parameter) is not grasped as a component ratio (multiple parameters), so the amount of air in the exhaust pipe and the intake pipe connected via the exhaust gas recirculation mechanism is determined. Accurate estimation can be performed with a relatively small amount of calculation. Therefore, it is possible to accurately estimate the amount of air (oxygen amount) flowing into the combustion chamber (cylinder) of the engine 1. As a result, the cylinder inflow air amount estimated based on the above-described model can be applied to engine real-time control, and for example, a shortage of fuel supply can be prevented.
[0070]
In addition, since the above-described model uses parameters relating to calculation of gas energy, that is, mass flow rate, temperature, gas component ratio, and pressure, as parameters passed between models corresponding to each component, the exhaust gas recirculation mechanism It is possible to accurately grasp the gas behavior in the engine system including not only the components that generate gas exchange as described above but also the components that do not involve gas exchange such as a turbocharger and an intercooler. As a result, it is possible to improve the estimation accuracy of the amount of air supplied to the combustion chamber.
In addition, the system model is configured as a combination of multiple models corresponding to each component, and the parameters for calculating gas energy are passed between the models, so that the versatility (reusability) of the model is improved. Can also be obtained.
[0071]
In the present embodiment, the ECU 20 constitutes intake air amount estimation means.
[0072]
The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, a model for an engine system without a throttle valve is shown. However, an engine with a throttle valve can be easily modeled by adding a throttle valve model. It is possible. In the throttle valve model, the passing gas mass flow rate can be calculated by applying the effective opening area of the throttle valve to the same mathematical expression as the EGR model and the turbine model.
[0073]
When an air flow sensor that detects the intake air amount is used, a parameter corresponding to the air flow sensor output is calculated using the above system model, and the parameter is compared with the air flow sensor output, so that the deterioration of the air flow sensor or You may make it determine abnormality.
[0074]
【The invention's effect】
  As described above in detail, according to the first aspect of the present invention, the engine system model including the intake system model, the combustion chamber model, the exhaust system model, and the exhaust gas recirculation system model is used to supply the engine combustion chamber. In the engine system model, air and a combustion gas other than air generated by complete combustion in the engine combustion chamber are used as parameters representing the gas composition in each model.Mass ratioIs used. That is, the ratio of air and other combustion gases (single parameter) is used without using the number of moles (multiple parameters) for each component contained in the exhaust as in the prior art. Thus, the amount of air in the exhaust pipe and the intake pipe connected via the engine can be accurately estimated with a small amount of calculation, and the amount of air (oxygen amount) flowing into the engine combustion chamber can be accurately estimated. As a result, the combustion chamber inflow air amount estimated based on the engine system model can be applied to the real-time control of the internal combustion engine, and for example, a shortage of the fuel supply amount can be prevented.In addition, by using the gas mass flow rate, gas component mass ratio, gas temperature, and gas pressure as parameters passed between models, the gas behavior in the engine system can be accurately grasped and supplied to the combustion chamber. As a result, it is possible to improve the accuracy of estimating the amount of air to be used and to improve the convenience in reusing the model. Further, by treating the combustion gas with carbon dioxide, nitrogen, and water vapor as components, and by treating the ratio of each component as constant, the specific heat of the combustion gas can be handled as a constant, and the amount of calculation can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an engine system model that models the internal combustion engine shown in FIG. 1;
FIG. 3 is a diagram showing a table used for calculation in the compressor model shown in FIG. 2;
4 is a diagram showing a table used for calculation in the intercooler model shown in FIG. 2. FIG.
FIG. 5 is a diagram showing a table used for calculation in the cylinder model shown in FIG. 2;
6 is a diagram showing a table used for calculation in the cylinder model shown in FIG. 2. FIG.
FIG. 7 is a time chart showing comparison between calculated data using a model and measured data.
FIG. 8 is a time chart showing comparison between calculation data using a model and actual measurement data.
[Explanation of symbols]
1 Internal combustion engine
2 Intake pipe
4 Exhaust pipe
5 Exhaust gas recirculation passage
6 Exhaust gas recirculation valve
7 Lift sensor
11 Fuel injection valve
20 Electronic control unit (intake air amount estimation means)
21 Accelerator sensor
22 Atmospheric pressure sensor
23 Atmospheric temperature sensor
24 Engine speed sensor
36 Intake pipe model (Intake system model)
37 Cylinder model (combustion chamber model)
36 Exhaust pipe model (exhaust system model)
39 EGR model (exhaust reflux system model)

Claims (1)

In a control device for an internal combustion engine, comprising an intake air amount estimating means for estimating an air amount supplied to an internal combustion engine having an exhaust gas recirculation mechanism, and controlling the engine based on the estimated air amount,
The intake air amount estimation means includes an intake system model that models the intake system of the engine, a combustion chamber model that models the combustion chamber of the engine, an exhaust system model that models the exhaust system of the engine, Using an engine system model including an exhaust gas recirculation system model that models the exhaust gas recirculation mechanism, the amount of air supplied to the combustion chamber is estimated,
In the engine system model , gas mass flow rate, gas component mass ratio, gas temperature, and gas pressure are used as parameters passed between the models.
The gas component mass ratio is a mass ratio of air and a combustion gas other than air generated by complete combustion in the combustion chamber. The combustion gas includes carbon dioxide, nitrogen, and water vapor as components. The ratio will be treated as constant,
The amount of air supplied to the combustion chamber is calculated according to the pressure and temperature of the gas flowing into the combustion chamber, the rotational speed of the engine, and the gas component mass ratio corresponding to the gas flowing into the combustion chamber. by the control device for an internal combustion engine characterized by Rukoto.

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