JP3988035B2 - EGR rate estimation device for internal combustion engine - Google Patents

Description

尚、吸気負圧Ｐbとしては１行程間の平均値が適用される。
【００３０】
《筒内ＥＧＲ率Ｒ_C(n)の推定》
一方、算出されたタンク内ＥＧＲ率Ｒ_S(n)は、４行程前のブランチ上流ＥＧＲ率Ｒ_U(n-4)、４行程前のブランチ下流ＥＧＲ率Ｒ_L(n-4)、今回の吸気負圧Ｐｂ(n)、４行程前の吸気負圧Ｐb(n-4)と共に、ブランチ上流ＥＧＲ率演算部３６、ブランチ下流ＥＧＲ率演算部３７、筒内ＥＧＲ率演算部３８の処理に利用され、各ＥＧＲ率演算部３６〜３８によりブランチ上流ＥＧＲ率Ｒ_U(n)、ブランチ下流ＥＧＲ率Ｒ_L(n)、筒内ＥＧＲ率Ｒ_C(n)が算出される（第２のＥＧＲ率演算手段）。
【００３１】
ここで、本実施形態では、ブランチ２a内での混合ガスの圧縮・膨張を加味した上で上記各ＥＧＲ率Ｒ_U(n),Ｒ_L(n),Ｒ_C(n)を算出している。混合ガスの圧縮・膨張は、スロットル弁６の開閉に伴うサージタンク３内の圧力変化により発生するため、吸気負圧Ｐbの変化量（例えば、Ｐb(n)−Ｐb(n-4)の偏差）に基づいて定常、加速、減速を判定し、対応する算出処理を各ＥＧＲ率演算部３６〜３８で実施しており、以下に順次説明する。
【００３２】
〈定常時〉
定常時の混合ガスは、ブランチ２ａ内で圧縮・膨張することなく移送される。従って、このときの推定処理としては、例えば特開２０００−２５４６５９号公報の従来技術と同様に、８行程前のタンク内ＥＧＲ率Ｒ_S(n-8)を筒内ＥＧＲ率Ｒ_C(n)と推定できる。但し、本実施形態では、加減速時の推定処理において４行程前のブランチ上流ＥＧＲ率Ｒ_U(n-4)及びブランチ上流ＥＧＲ率Ｒ_L(n-4)を必要とすることから、次式に従って各値が算出された上で、ブランチ上流ＥＧＲ率Ｒ_U(n)及びブランチ上流ＥＧＲ率Ｒ_L(n)が前回値としてＥＣＵ２１に記憶されると共に（ＥＧＲ率記憶手段）、その記憶値は算出の度に更新される（ＥＧＲ率更新手段）。
Ｒ_C(n)＝Ｒ_L(n-4)………(4)
Ｒ_L(n)＝Ｒ_U(n-4)………(5)
Ｒ_U(n)＝Ｒ_S(n) ………(6)
〈加速時〉
図４は加速時におけるサージタンク３内、ブランチ上流、ブランチ下流、筒内１ａでの混合ガスの挙動を示す模式図である。スロットル弁６が開操作された瞬間の加速初期には、混合ガスは慣性により未だ圧縮されておらず、サージタンク３内には今回のタンク内ＥＧＲ率Ｒ_S(n)の混合ガスが存在し、ブランチ上流には４行程前のブランチ上流ＥＧＲ率Ｒ_U(n-4)の混合ガスが存在し、ブランチ下流には４行程前のブランチ上流ＥＧＲ率Ｒ_L(n-4)の混合ガスが存在している。
【００３３】
その直後、新気及びＥＧＲガスの導入量の増加に伴ってサージタンク３内の圧力が増加し、吸気弁により閉鎖された筒内１ａとの間で、ブランチ内の混合ガスが圧縮される。このときの混合ガスは、今回と各気筒が１巡する４行程前との吸気負圧の比Ｐb(n-4)／Ｐb(n)（体積変化相関値）に従って下流側に向けて圧縮され、結果として、サージタンク３内の混合ガスの一部がブランチ上流に侵入し、ブランチ上流の混合ガスの一部がブランチ下流に侵入することになる。そして、対応する気筒の吸気弁が開放されると、混合ガスはブランチ長の半分のストロークだけ移送される。
【００３４】
このときの筒内１ａには、加速初期においてブランチ下流に存在していた混合ガスの全て、及び加速初期においてブランチ上流に存在していた混合ガスの一部が、上記した比Ｐb(n-4)／Ｐb(n)に従って圧縮された状態で導入され、筒内ＥＧＲ率Ｒ_C(n)は次式(7)で表すことができる。
Ｒ_C(n)＝Ｒ_L(n-4)×Ｐb(n-4)／Ｐb(n)＋Ｒ_U(n-4)×｛１−Ｐb(n-4)／Ｐb(n)｝………(7)
つまり、筒内１ａに導入される混合ガスは、移送前（圧縮後）にはブランチ下流に存在していたものであり、移送前のブランチ下流において、ブランチ下流ＥＧＲ率Ｒ_L(n-4)の混合ガスの占有率（換言すれば、筒内ＥＧＲ率Ｒ_C(n)に対する影響度）は式(4)の前半で表される一方、ブランチ上流ＥＧＲ率Ｒ_U(n-4)の混合ガスの占有率（筒内ＥＧＲ率Ｒ_C(n)に対する影響度）は式(4)の後半で表されるため、これらに基づいて筒内ＥＧＲ率Ｒ_C(n)が算出される。
【００３５】
又、このときのブランチ下流には、加速初期においてブランチ上流に存在していた混合ガスの一部（上記筒内に導入された残存分）、及び加速初期においてサージタンク３内に存在していた混合ガスが、比Ｐb(n-4)／Ｐb(n)に従って圧縮された状態で移送され、ブランチ下流ＥＧＲ率Ｒ_L(n)は次式(8)で表すことができる。
Ｒ_L(n)＝Ｒ_U(n-4)×｛２×Ｐb(n-4)／Ｐb(n)−１｝＋Ｒ_S(n)×｛２−２×Ｐb(n-4)／Ｐb(n)｝………(8)
つまり、ブランチ下流に移送される混合ガスは、移送前（圧縮後）にはブランチ上流に存在していたものであり、移送前のブランチ上流において、ブランチ上流ＥＧＲ率Ｒ_U(n-4)の混合ガスの占有率は式(8)の前半で表される一方、タンク内ＥＧＲ率Ｒ_S(n)の混合ガスの占有率は式(8)の後半で表されるため、これらに基づいてブランチ下流ＥＧＲ率Ｒ_L(n)が算出される。
【００３６】
更に、このときのブランチ上流には、加速初期においてサージタンク３内に存在していた混合ガスのみが移送されるため、圧縮状態に関係なく、ブランチ上流ＥＧＲ率Ｒ_U(n)は次式(9)で表すことができる。
Ｒ_U(n)＝Ｒ_S(n) ………(9)
〈減速時〉
図５は減速時におけるサージタンク内、ブランチ上流、ブランチ下流、筒内１ａでの混合ガスの挙動を示す模式図である。スロットル弁６が閉操作された瞬間の減速初期には、混合ガスは慣性により未だ膨張していないため、各部位での混合ガスのＥＧＲ率は上記した加速初期と同様となる。
【００３７】
その直後、新気及びＥＧＲガスの導入量の減少に伴ってサージタンク３内の圧力が低下し、吸気弁により閉鎖された筒内１ａとの間で、ブランチ内の混合ガスが膨張する。このときの混合ガスは、今回と各気筒が１巡する４行程前との吸気負圧の比Ｐb(n-4)／Ｐb(n)に従って上流側に向けて膨張し、結果として、ブランチ下流の混合ガスの一部がブランチ上流に進入し、ブランチ上流の混合ガスの一部がサージタンク３内に侵入することになる。そして、対応する気筒の吸気弁が開放されると、混合ガスはブランチ長の半分のストロークだけ移送される。
【００３８】
このときの筒内１ａには、減速初期においてブランチ下流に存在していた混合ガスの一部のみが移送されるため、圧縮状態に関係なく、筒内ＥＧＲ率Ｒ_C(n)は次式(10)で表すことができる。
Ｒ_C(n)＝Ｒ_L(n-4) ………(10)
又、このときのブランチ下流には、減速初期においてブランチ下流に存在していた混合ガスの一部（上記筒内１ａに導入された残存分）、及び減速初期においてブランチ上流に存在していた混合ガスの一部が、比Ｐb(n-4)／Ｐb(n)に従って膨張した状態で移送され、ブランチ下流ＥＧＲ率Ｒ_L(n)は次式(11)で表すことができる。
Ｒ_L(n)＝Ｒ_L(n-4)×｛Ｐb(n-4)／Ｐb(n)−１｝＋Ｒ_U(n)×｛２−Ｐb(n-4)／Ｐb(n)｝………(11)
つまり、ブランチ下流に移送される混合ガスは、移送前（膨張後）にはブランチ上流に存在していたものであり、移送前のブランチ上流において、ブランチ下流ＥＧＲ率Ｒ_L(n-4)の混合ガスの占有率は式(11)の前半で表される一方、ブランチ上流ＥＧＲ率Ｒ_U(n)の混合ガスの占有率は式(11)の後半で表されるため、これらに基づいてブランチ下流ＥＧＲ率Ｒ_L(n)が算出される。
【００３９】
更に、このときのブランチ上流には、減速初期においてブランチ上流に存在していた混合ガスの一部（上記ブランチ下流に移送された残存分）、及びサージタンク３内に存在していた混合ガスが、比Ｐb(n-4)／Ｐb(n)に従って膨張した状態で移送され、ブランチ上流ＥＧＲ率Ｒ_U(n)は次式(12)で表すことができる。
Ｒ_U(n)＝Ｒ_U(n-4)×｛２×Ｐb(n-4)／Ｐb(n)−２｝＋Ｒ_S(n)×｛３−２×Ｐb(n-4)／Ｐb(n)｝………(12)
つまり、ブランチ上流に移送される混合ガスは、移送前（膨張後）にはサージタンク３内に存在していたものであり、移送前のサージタンク３内において、ブランチ上流ＥＧＲ率Ｒ_L(n-4)の混合ガスの占有率は式(12)の前半で表される一方、タンク内ＥＧＲ率Ｒ_S(n)の混合ガスの占有率は式(12)の後半で表されるため、これらに基づいてブランチ上流ＥＧＲ率Ｒ_U(n-4)が算出される。
【００４０】
以上の手順に従って、図３の各ＥＧＲ率演算部３５〜３８では１行程毎に各ＥＧＲ率Ｒ_S(n),Ｒ_U(n),Ｒ_L(n),Ｒ_C(n)が順次算出されると共に、ＥＧＲ率Ｒ_U(n),Ｒ_L(n)が前回値として記憶・更新され、当該気筒の次回の推定処理では４行程前のＥＧＲ率Ｒ_U(n-4),Ｒ_L(n-4)として用いられる。そして、得られた筒内ＥＧＲ率Ｒ_C(n)が点火時期ＳＡや体積効率係数の設定に適用される。
【００４１】
図６は点火時期ＳＡを設定する処理手順を示す制御フローであり、まず、エンジン回転速度Ｎe及び吸気負圧Ｐbに基づき、ＥＧＲ時点火時期演算部４１でマップからＥＧＲ時の点火時期ＳＡwが算出される一方、非ＥＧＲ時点火時期演算部４２ではマップから非ＥＧＲ時の点火時期ＳＡw/oが算出される。又、エンジン回転速度Ｎe及び吸気負圧Ｐbに基づき、目標ＥＧＲ演算部４３でマップから目標ＥＧＲ率Ｒ_STDが算出される一方、クリップ値演算部４４ではマップから後述するリタード量ＯＦＳの上限を制限するクリップ値ＣＰが算出される。
【００４２】
得られた点火時期ＳＡw，ＳＡw/o、目標ＥＧＲ率Ｒ_STD、及び上記した筒内ＥＧＲ率Ｒ_C(n)は補間処理部４５に入力され、次式(13)に従って現在の筒内ＥＧＲ率Ｒ_C(n)に対応する点火時期ＳＡが直線補完により算出される。
ＳＡ＝ＳＡw/o＋（ＳＡw−ＳＡw/o）×Ｒ_C(n)／Ｒ_STD ………(13)
又、筒内ＥＧＲ率Ｒ_C(n)及び目標ＥＧＲ率Ｒ_STDはリタード量演算部４６に入力され、その比Ｒ_C(n)／Ｒ_STDに基づきマップからリタード量ＯＦＳが算出されると共に、リタード量ＯＦＳの上限が上記クリップ値ＣＰ以下に制限される。そして、減算部４７では上記点火時期ＳＡからリタード量ＯＦＳが減算され、減算後の点火時期ＳＡが点火時期制御において目標値として用いられる。
【００４３】
一方、体積効率係数も上記点火時期ＳＡと同様の手順で算出され、詳細は説明しないが、ＥＧＲ時のマップ及び非ＥＧＲ時のマップから求めた体積効率係数を補間処理し、得られた現在の体積効率係数に基づき新気量を求めて燃料噴射制御に適用しており、この補間処理では、上記した比Ｒ_C(n)／Ｒ_STD、つまり、推定した筒内ＥＧＲ率Ｒ_C(n)が利用される。
【００４４】
以上のように本実施形態のエンジン１のＥＧＲ率推定装置では、従来技術で考慮しなかったブランチ２ａ内での混合ガスの圧縮・膨張を、式(7)〜(12)に基づいて筒内ＥＧＲ率Ｒ_C(n)の算出処理に反映させている。その結果、ブランチ２ａ内での混合ガスの移送過程をより実状に則して模擬でき、もって、エンジン１の運転状態に関わらず、筒内に導入されるＥＧＲ率Ｒ_C(n)を常に正確に推定することができる。
【００４５】
しかも、式(7)〜(12)では、吸気負圧の比Ｐb(n-4)／Ｐb(n)、つまり混合ガスが圧縮・膨張する直接的な要因であるサージタンク３内の圧力変化を適用しているため、一層実状に則した推定処理を実現できる。
一方、本実施形態のエンジン１のＥＧＲ率推定装置では、ＥＧＲ開度Ｓを開口面積相当にリニアライズしたＥＧＲ開度Ｓ’とＥＧＲ流速Ｑとに基づき、式(1)に従ってサージタンク３内に導入されるＥＧＲ量ΔＰr(n)を求め、そのＥＧＲ量ΔＰr(n)に基づき式(2)に従って、サージタンク３内のＥＧＲガスの残存分と新たな流入分とからＥＧＲ分圧Ｐr(n)を算出している。このように具体的な値に基づいて各算出処理を実施しているため、サージタンク３内で生起される混合過程をより実状に則して模擬することができる。
【００４６】
しかも、式(2)で用いられる比Ｖcyl／Ｖstは、特開２０００−２５４６５９号公報の従来技術でサージタンク３内のＥＧＲ率をなまし処理する１次フィルタのフィルタ定数に相当するが、事前のマッチングに基づくフィルタ定数に対して、比Ｖcyl／Ｖstはより現実的なエンジン１の仕様（気筒容積Ｖcyl、サージタンク容積Ｖst）に基づいて設定される。これらの要因により、サージタンク３内のＥＧＲ分圧Ｐr(n)、ひいてはタンク内ＥＧＲ率Ｒ_S(n)を正確に推定でき、結果として、このタンク内ＥＧＲ率Ｒ_S(n)に基づく上記ＥＧＲ率Ｒ_C(n)の推定処理をより的確に実施することができる。
【００４７】
そして、以上のように筒内ＥＧＲ率Ｒ_C(n)が正確に推定されることから、この筒内ＥＧＲ率Ｒ_C(n)を利用した処理、例えば上記点火時期ＳＡや体積効率係数の設定処理を適切に実施して、これらの設定値に基づく点火時期制御や燃料噴射制御の精度を大幅に向上することができる。よって、例えば点火時期制御では、エンジン１の過渡運転時でもＭＢＴ相当の適切な点火時期ＳＡを実現でき、失火やノックの防止により燃費及びドライバビリティを大幅に向上させることができる。
【００４８】
以上で実施形態の説明を終えるが、本発明の態様はこの実施形態に限定されるものではない。例えば、上記実施形態では、吸気管噴射型の直列４気筒ガソリンエンジン１用のＥＧＲ率推定装置に具体化したが、エンジンの形式等はこれに限ることはなく、例えば筒内に燃料を直接噴射する筒内噴射型ガソリンエンジンやディーゼルエンジンに適用したり、気筒配列や気筒数の異なるエンジンに適用したりしてもよい。
【００４９】
又、上記実施形態では、ブランチ２ａを上流と下流に分割して個別にＥＧＲ率Ｒ_U(n),Ｒ_L(n)を算出したが、上記説明から明らかなようにブランチ２ａの分割数は、ブランチ２ａの容積と気筒容積との比に基づいて決定され、例えばブランチ２ａの容積が気筒容積の３倍のときには、ブランチ２ａを上流、中流、下流の３領域に分割して個別にＥＧＲ率を算出することになる。
【００５０】
【発明の効果】
以上説明したように請求項１，２の発明の内燃機関のＥＧＲ率推定装置によれば、混合ガスの圧縮・膨張を加味した上でブランチ内での混合ガスの移送過程を実状に則して模擬でき、もって、内燃機関の運転状態に関わらず、筒内に導入される混合ガスのＥＧＲ率を常に正確に推定することができる。
【００５１】
請求項３の発明の内燃機関のＥＧＲ率推定装置によれば、請求項１，２の発明に加えて、サージタンク内での混合ガスの混合過程を実状に則して模擬でき、サージタンク内のＥＧＲ率を正確に推定でき、ひいては筒内に導入される混合ガスのＥＧＲ率を一層正確に推定することができる。
【図面の簡単な説明】
【図１】実施形態のエンジンのＥＧＲ率推定装置を示す全体構成図である。
【図２】エンジンの吸気系を模式的に示した説明図である。
【図３】筒内ＥＧＲ率Ｒ_C(n)を推定するときの制御フローを示す説明図である。
【図４】加速時における混合ガスの挙動を示す模式図である。
【図５】減速時における混合ガスの挙動を示す模式図である。
【図６】点火時期ＳＡを設定するときの制御フローを示す説明図である。
【符号の説明】
１ エンジン（内燃機関）
１ａ 筒内
２ インテークマニホールド
２ａ ブランチ
３ サージタンク
１１ ＥＧＲ弁
２１ ＥＣＵ（第１のＥＧＲ率演算手段、第２のＥＧＲ率演算手段、ＥＧＲ率記憶手段、ＥＧＲ率更新手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EGR rate estimation device that estimates an EGR rate in an EGR device that recirculates exhaust gas of an internal combustion engine (hereinafter referred to as an engine) to the intake side.
[0002]
[Related background]
In order to reduce the NOx emission amount by lowering the combustion temperature in the cylinder, EGR devices that recirculate engine exhaust gas as EGR gas to the intake side are widely implemented. In this type of EGR device, as a countermeasure for slowing down combustion due to EGR recirculation, a process of advancing the ignition timing according to the EGR rate (EGR gas / fresh air) is performed. On the other hand, the recirculation of EGR also has the effect of reducing the throttle loss because the pressure in the intake pipe increases even with the same torque, and at an appropriate ignition timing equivalent to MBT (Minimum advance for the Best Torque), compared with non-EGR On the contrary, another advantage that fuel efficiency can be improved has been confirmed.
[0003]
However, in order to achieve the above-described improvement in fuel consumption by MBT, it is necessary to appropriately control the ignition timing in accordance with the EGR rate introduced into the cylinder. In a transient state in which the EGR rate changes, it is very difficult to appropriately control the ignition timing following the change in the EGR rate. As a result, not only the advantage of fuel efficiency improvement by MBT can be obtained, but also misfire due to over-retarding, knocking due to over-advanced angle, etc. may occur, and the fuel efficiency and drivability may be deteriorated.
[0004]
In order to solve the above problem, it is important to accurately estimate the EGR rate introduced into the cylinder even in a transient state. JP 2001-254659 A The technique described in the publication is proposed. In this publication, the EGR gas is applied to a four-cylinder engine that recirculates to the surge tank, and the internal volume of the branch from the surge tank to each cylinder is set to be twice the cylinder volume.
[0005]
The estimation process of the EGR rate is roughly composed of two processes. First, the EGR rate of the mixed gas (new air + EGR gas) newly introduced into the surge tank is determined from the opening degree of the EGR valve and the operating state of the engine. The EGR rate is smoothed by a primary filter. The annealing process is for simulating a process in which a new gas mixture is mixed with the gas mixture in the surge tank. The obtained EGR rate is regarded as the current EGR rate in the surge tank, and is stored in sequence. deep.
[0006]
On the other hand, the mixed gas in the surge tank is introduced into the cylinder after two strokes of each cylinder, that is, after eight strokes. The EGR rate is sequentially read out and regarded as the EGR rate introduced into the cylinder, and applied to the ignition timing control and the like.
[0007]
[Problems to be solved by the invention]
However, the technique described in the above publication has the following two problems.
First, the mixing speed of the mixed gas in the surge tank is greatly influenced by the operating state of the engine, and the amount of fresh air or EGR gas introduced into the surge tank changes greatly accordingly. In the technique of the above publication, the filter constant of the primary filter is changed according to the engine speed and the load. However, if the filter constant is changed based on the prior matching, the mixing process can be performed in accordance with the actual situation. It was difficult to simulate the above, and to estimate the EGR rate accurately.
[0008]
On the other hand, in order for the EGR rate in the surge tank to be reflected in the EGR rate in the cylinder after 8 strokes, it is premised that the mixed gas flows without changing the volume in the branch. However, the actual mixed gas is compressed in the branch as the pressure in the surge tank increases, for example, when the vehicle is accelerated, and expands in the branch as the pressure in the surge tank decreases when the vehicle is decelerated. Since the EGR rate introduced into the cylinder changes according to the compression / expansion of the mixed gas, this factor also leads to an estimation error of the EGR rate.
[0009]
As a result, the EGR rate in the transient state cannot be accurately estimated. As a result, processing using the estimated EGR rate, for example, setting processing such as ignition timing and volumetric efficiency coefficient becomes inappropriate, and ignition based on these set values is performed. There was a problem that timing control and fuel injection control could not be implemented properly.
Therefore, the object of the inventions of claims 1 and 2 is to simulate the process of transporting the mixed gas in the branch in consideration of the compression / expansion of the mixed gas, so that the operation state of the internal combustion engine can be obtained. Regardless, it is an object to provide an EGR rate estimation device for an internal combustion engine that can always accurately estimate the EGR rate of a mixed gas introduced into a cylinder.
[0010]
In addition to the inventions of claims 1 and 2, the object of the invention of claim 3 is to simulate the mixing process of the mixed gas in the surge tank in accordance with the actual situation, and to accurately calculate the EGR rate in the surge tank. An object of the present invention is to provide an EGR rate estimation device for an internal combustion engine that can be estimated.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, fresh air is introduced from the intake system of the engine, while EGR gas is recirculated from the exhaust system of the engine according to the opening degree of the EGR valve. A surge tank that mixes gas internally, a branch of the intake manifold that connects the surge tank and each cylinder of the engine, and every time mixed gas from the surge tank is transferred through the branch with intake of the engine The first EGR rate calculating means for calculating the EGR rate in the surge tank, and the EGR rate of the internal mixed gas as the previous value for each region of the branch divided in advance by the mixed gas transfer stroke accompanying the intake air EGR rate storage means for storing, and EGR rate in the surge tank calculated by the first EGR rate calculating means for each transfer of the mixed gas accompanying the intake air, EGR rate The previous value of the EGR rate of each area stored in the storage means, and Due to pressure change in surge tank A second EGR that calculates the EGR rate of the mixed gas in each region after the transfer and the EGR rate of the mixed gas introduced into the cylinder based on the volume change correlation value that correlates with the volume change of the mixed gas in the branch. And a rate calculating means and an EGR rate updating means for updating the EGR rate of the storage means by the calculated EGR rate of the mixed gas in each region for each calculation of the second EGR rate calculating means.
[0012]
Accordingly, the fresh air introduced from the intake system and the EGR gas recirculated from the exhaust system are mixed in the surge tank, and the mixed gas after mixing is introduced into the cylinder of each cylinder of the engine via each branch. The EGR rate of the mixed gas in the surge tank is calculated by the first EGR rate calculating means every time the mixed gas is transferred with the intake of the engine.
On the other hand, for each transfer of the mixed gas accompanying the intake air, the EGR rate in the surge tank, the previous value of the EGR rate in each region of the branch stored in the EGR rate storage means, and Due to pressure change in surge tank Based on the volume change correlation value that correlates with the volume change of the mixed gas in the branch, the second EGR rate calculation means calculates the EGR rate of each region after transfer and the EGR rate of the mixed gas introduced into the cylinder. At the same time, the EGR rate of the EGR rate storage means is updated by the calculated EGR rate of each region and used for the next calculation process.
[0013]
The calculation of the EGR rate by the second EGR rate calculating means is performed as follows, for example. Since the mixed gas in the branch is transferred by an amount corresponding to each region for each intake of the engine, when the mixed gas does not change in volume, the EGR rate from the surge tank to the cylinder through each region is sequentially decreased downstream. Just move to.
In contrast, when the volume of the mixed gas changes in the branch, that is, the pressure in the surge tank increases as the vehicle accelerates and the mixed gas is compressed, or the pressure in the surge tank decreases as the vehicle decelerates. When the mixed gas expands, the position of the mixed gas is shifted in each region before transfer. Since this positional shift corresponds to the volume change of the mixed gas, the volume change of the mixed gas can be reflected in the EGR rate calculation process by taking into account the volume change correlation value correlated with the volume change. Therefore, the process of transferring the mixed gas in the branch is more realistically simulated, and the EGR rate of the mixed gas introduced into the cylinder can be accurately estimated regardless of the operating state of the engine.
[0014]
In the invention of claim 2, the second EGR rate calculating means sets the volume change correlation value based on the previous value and the current value of the pressure in the surge tank.
Since the volume change of the mixed gas in the branch is caused by the pressure change in the surge tank, the volume change correlation value as a ratio or deviation, for example, based on the previous value and the current value of the pressure in the surge tank. If is set, it is possible to realize estimation processing that is more realistic.
[0015]
According to a third aspect of the present invention, the first EGR rate calculating means calculates the EGR amount introduced into the surge tank based on the opening degree of the EGR valve and the EGR flow velocity linearized corresponding to the opening area. The EGR rate in the surge tank is calculated based on the EGR partial pressure in the surge tank obtained from the amount and the fresh air partial pressure corresponding to the fresh air amount introduced into the surge tank.
[0016]
Therefore, the EGR amount is obtained from the opening degree of the EGR valve corresponding to the opening area and the EGR flow velocity, and the EGR rate in the surge tank is calculated from the EGR partial pressure and the fresh air partial pressure obtained from the EGR amount. Since each calculation process is performed based on specific values in this way, the mixing process occurring in the surge tank is more realistically simulated, and the EGR partial pressure in the surge tank is accurate. A simple EGR rate can be calculated.
[0017]
Preferably, the first EGR rate calculating means calculates the EGR amount remaining in the surge tank after the transfer of the mixed gas to the branch, the EGR amount introduced into the surge tank, and the ratio between the cylinder volume and the surge tank volume. Based on this, it can be configured to calculate the EGR partial pressure in the surge tank.
The ratio between the cylinder volume and the surge tank volume represents the degree of influence of the mixed gas flow in and out of the cylinder on the entire surge tank. Based on this ratio, the remaining amount of EGR gas in the surge tank and new introduction If the minute is corrected, a more accurate EGR partial pressure in the surge tank can be calculated.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an engine EGR rate estimating apparatus embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing an EGR rate estimating apparatus for an engine according to the present embodiment. The engine 1 is configured as an intake pipe injection type in-line four-cylinder gasoline engine. The cylinder 1 a of each cylinder of the engine 1 is connected to a common surge tank 3 via a branch 2 a of the intake manifold 2, and the surge tank 3 is connected to an air cleaner 5 via an intake passage 4. The intake air introduced into the intake passage 4 via the air cleaner 5 is introduced into the surge tank 3 after the flow rate is adjusted in accordance with the opening of the throttle valve 6, and flows through each branch 2 a of the intake manifold 2, After fuel is injected from the fuel injection valve 7 provided in each branch 2a, the fuel is introduced into the cylinder 1a of each cylinder as the intake valve (not shown) is opened.
[0019]
On the other hand, an exhaust passage 9 is connected to the cylinder interior 1 a of each cylinder via an exhaust manifold 8. The exhaust passage 9 and the surge tank 3 are connected by an EGR passage 10, and an EGR valve 11 is provided in the EGR passage 10. The injected fuel introduced into the cylinder 1a together with the intake air is ignited at a predetermined timing by the ignition plug 12 of each cylinder, and the exhaust gas after combustion is discharged from the cylinder when an exhaust valve (not shown) is opened, and the exhaust manifold 8 The exhaust passage 9 is exhausted to the outside through a catalyst (not shown), while a part of the exhaust gas is recirculated as EGR gas from the EGR passage 10 into the surge tank 3 according to the opening degree of the EGR valve 11.
[0020]
Here, as is well known, the EGR gas may be recirculated to each branch 2a in addition to being recirculated to the surge tank 3, but both methods have advantages and disadvantages. The reflux to the surge tank 3 is not advantageous in terms of engine output because it does not attenuate the inertia supercharging by connecting the branches 2a unlike the reflux to each branch 2a, but is introduced into the cylinder 1a. When estimating the EGR rate of the mixed gas (new air + EGR gas), it is necessary to consider gas mixing in the surge tank 3 and gas transfer in each branch 2a, and the estimation of the EGR rate becomes complicated Tend.
[0021]
On the other hand, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storage of a control program, a control map, etc., a central processing unit (CPU), a timer counter, etc. Control unit) 21 is installed. Various sensors such as a rotation speed sensor 22 for detecting the engine rotation speed Ne and an intake pressure sensor 23 for detecting the intake negative pressure Pb in the surge tank 3 are connected to the input side of the ECU 21, and the fuel is connected to the output side. Various devices such as the injection valve 7, the EGR valve 11, and the spark plug 12 are connected.
[0022]
The ECU 21 sets target values such as the fuel injection amount, EGR rate, and ignition timing based on detection information from various sensors, and controls the fuel injection valve 7, the EGR valve 11, and the spark plug 12 based on the target values. To do. Since the ignition timing and the fuel injection amount are set by interpolating a preset map of EGR and non-EGR according to the current EGR rate, the mixture gas introduced into the cylinder 1a of each cylinder is set. EGR rate (hereinafter, in-cylinder EGR rate R _C (referred to as (n)). Therefore, next, in-cylinder EGR rate R _C The estimation process (n) will be described in detail.
[0023]
FIG. 2 is an explanatory view schematically showing the intake system of the engine 1, and fresh air from the intake passage 4 and EGR gas from the EGR passage 10 are introduced into the surge tank 3, and these fresh air and Due to the mixing of EGR gas, the mixed gas in the surge tank 3 becomes an EGR rate (hereinafter referred to as EGR rate R in the tank _S (referred to as (n)), each branch 2a is transferred in accordance with the ignition sequence (# 1- # 3- # 4- # 2) and introduced into the cylinder 1a of the corresponding cylinder.
[0024]
The EGR rate estimation process is performed based on the following assumptions.
1) The volume in each branch 2a is set to be twice the cylinder volume (displacement).
2) It is assumed that newly introduced fresh air and EGR gas are uniformly mixed during one stroke of the engine 1 with respect to the mixed gas in the surge tank 3.
3) The mixed gas in each branch 2a is transferred to the downstream side for each intake stroke of the corresponding cylinder while being compressed / expanded in accordance with a pressure change from the surge tank 3 side (due to acceleration / deceleration described later). Shall be.
[0025]
Accordingly, since the mixed gas in the surge tank 3 is transferred by the cylinder volume, that is, a stroke that is half the branch length, as shown in FIG. EGR rate of mixed gas between upstream and downstream (hereinafter, branch upstream EGR rate R _U (n), Branch downstream EGR rate R _L (referred to as (n)), the mixed gas of the EGR rate is sequentially introduced into the cylinder 1a.
[0026]
On the other hand, in-cylinder EGR rate R _C (n) is roughly estimated through two processes. That is, first, the EGR rate R in the tank is simulated by simulating the mixing process of the mixed gas introduced into the surge tank 3. _S (n) is estimated, and then the in-cylinder EGR rate R is simulated by simulating the transfer process of the mixed gas in the branch 2a. _C (n) is estimated. The above estimation process is executed by the ECU 21 for each stroke of the engine 1 according to the control flow shown in FIG.
[0027]
<< EGR rate R in tank _S Estimation of (n) >>
First, the opening degree S of the EGR valve 11 is input to the EGR opening area calculation unit 31 as a step number (for example, correlates with the valve lift amount), and based on a map in which the EGR opening degree S is linearized corresponding to the opening area. From the EGR opening degree S, the EGR opening degree S ′ correlated with the opening area is obtained. On the other hand, the engine rotation speed Ne and the intake negative pressure Pb are input to the EGR flow velocity calculation unit 32, and the EGR flow velocity Q is calculated from the map based on these pieces of information.
[0028]
The obtained EGR opening area S and EGR flow velocity Q are input to the EGR amount calculation unit 33, and an EGR amount ΔPr (n) introduced into the surge tank 3 in one stroke is calculated according to the following equation (1). The unit of the EGR amount ΔPr (n) is expressed by the partial pressure of the surge tank 3.
ΔPr (n) = S × Q (1)
The EGR amount ΔPr (n) is input to the EGR partial pressure calculation unit 34, and the EGR partial pressure Pr (n) in the surge tank 3 is calculated according to the following equation (2).
Pr (n) = Pr (n−1) × (1−Vcyl / Vst) + ΔPr (n) × Vcyl / Vst (2)
Here, Vcyl is the cylinder volume, Vst is the surge tank volume, and the ratio Vcyl / Vst represents the degree of influence of the mixed gas inflow / outflow per cylinder on the entire surge tank 3. Therefore, the first half of equation (2) corresponds to the remaining amount after the EGR gas partial pressure Pr (n-1) at the time of the previous processing (before one stroke) flows out by the cylinder volume, and the latter half of equation (2). Corresponds to a new inflow, and the current EGR partial pressure Pr (n) in the surge tank 3 is obtained by adding these partial pressures.
[0029]
The EGR partial pressure Pr (n) is input to the in-tank EGR rate calculator 35, and the in-tank EGR rate R according to the following equation (3): _S (n) is calculated (first EGR rate calculation means).

Note that an average value for one stroke is applied as the intake negative pressure Pb.
[0030]
<< In-cylinder EGR rate R _C Estimation of (n) >>
On the other hand, the calculated EGR rate R in the tank _S (n) is the branch upstream EGR rate R 4 strokes before _U (n-4) Branch downstream EGR rate R 4 strokes before _L (n-4), intake negative pressure Pb (n) of this time, intake negative pressure Pb (n-4) before 4 strokes, branch upstream EGR rate calculation unit 36, branch downstream EGR rate calculation unit 37, in-cylinder EGR It is used for the processing of the rate calculation unit 38, and the branch upstream EGR rate R is obtained by each EGR rate calculation unit 36-38. _U (n) Branch downstream EGR rate R _L (n), In-cylinder EGR rate R _C (n) is calculated (second EGR rate calculating means).
[0031]
Here, in the present embodiment, each EGR rate R is taken into account after taking into account the compression / expansion of the mixed gas in the branch 2a. _U (n), R _L (n), R _C (n) is calculated. Since the compression / expansion of the mixed gas occurs due to the pressure change in the surge tank 3 accompanying the opening / closing of the throttle valve 6, the amount of change in the intake negative pressure Pb (for example, the deviation of Pb (n) -Pb (n-4)) ), Steady, acceleration, and deceleration are determined, and the corresponding calculation processing is performed by the EGR rate calculation units 36 to 38, which will be sequentially described below.
[0032]
<Normal time>
The regular mixed gas is transferred without being compressed or expanded in the branch 2a. Therefore, as an estimation process at this time, the EGR rate R in the tank 8 strokes before, for example, as in the prior art of Japanese Patent Laid-Open No. 2000-254659 _S (n-8) is in-cylinder EGR rate R _C (n) can be estimated. However, in this embodiment, the branch upstream EGR rate R four strokes before in the acceleration / deceleration estimation process _U (n-4) and branch upstream EGR rate R _L Since (n-4) is required, each value is calculated according to the following equation, and then the branch upstream EGR rate R _U (n) and branch upstream EGR rate R _L (n) is stored as the previous value in the ECU 21 (EGR rate storage means), and the stored value is updated every time it is calculated (EGR rate update means).
R _C (n) = R _L (n-4) ……… (4)
R _L (n) = R _U (n-4) ……… (5)
R _U (n) = R _S (n) ……… (6)
<At acceleration>
FIG. 4 is a schematic diagram showing the behavior of the mixed gas in the surge tank 3, the upstream of the branch, the downstream of the branch, and the cylinder 1a during acceleration. At the beginning of acceleration at the moment when the throttle valve 6 is opened, the mixed gas is not yet compressed due to inertia, and the current EGR rate R in the tank is contained in the surge tank 3. _S (n) mixed gas exists, and the branch upstream EGR rate R 4 strokes before the branch upstream _U (n-4) mixed gas exists, and the branch upstream EGR rate R 4 strokes before the branch downstream _L There is a mixed gas of (n-4).
[0033]
Immediately thereafter, the pressure in the surge tank 3 increases as the amount of fresh air and EGR gas introduced increases, and the mixed gas in the branch is compressed between the cylinder 1a closed by the intake valve. The mixed gas at this time is compressed toward the downstream side in accordance with the ratio Pb (n-4) / Pb (n) (volume change correlation value) of the intake negative pressure between this time and the four strokes before each cylinder makes one round. As a result, a part of the mixed gas in the surge tank 3 enters the upstream of the branch, and a part of the mixed gas upstream of the branch enters the downstream of the branch. When the intake valve of the corresponding cylinder is opened, the mixed gas is transferred by a stroke that is half the branch length.
[0034]
In the cylinder 1a at this time, all of the mixed gas existing downstream of the branch at the initial stage of acceleration and a part of mixed gas existing upstream of the branch at the initial stage of acceleration contain the ratio Pb (n-4 ) / Pb (n) is introduced in a compressed state, and the in-cylinder EGR rate R _C (n) can be expressed by the following formula (7).
R _C (n) = R _L (n-4) × Pb (n-4) / Pb (n) + R _U (n-4) × {1-Pb (n-4) / Pb (n)} (7)
That is, the mixed gas introduced into the cylinder 1a was present downstream of the branch before transfer (after compression), and the branch downstream EGR rate R is downstream of the branch before transfer. _L (n-4) mixed gas occupancy (in other words, in-cylinder EGR rate R _C (Influence on (n)) is expressed in the first half of equation (4), while branch upstream EGR rate R _U (n-4) mixed gas occupancy (in-cylinder EGR rate R _C (Influence on (n)) is expressed in the latter half of the equation (4), and therefore the in-cylinder EGR rate R is based on these. _C (n) is calculated.
[0035]
In addition, downstream of the branch at this time, a part of the mixed gas existing in the upstream of the branch in the early stage of acceleration (remaining amount introduced into the cylinder) and in the surge tank 3 in the initial stage of acceleration The mixed gas is transferred in a compressed state according to the ratio Pb (n-4) / Pb (n), and the branch downstream EGR rate R _L (n) can be expressed by the following formula (8).
R _L (n) = R _U (n-4) * {2 * Pb (n-4) / Pb (n) -1} + R _S (n) × {2-2 × Pb (n-4) / Pb (n)} (8)
That is, the mixed gas transferred downstream of the branch is present upstream of the branch before transfer (after compression), and the branch upstream EGR rate R is upstream of the branch before transfer. _U The occupancy ratio of the mixed gas of (n-4) is expressed by the first half of the equation (8), while the EGR ratio R in the tank _S Since the occupation ratio of the mixed gas of (n) is expressed in the latter half of the equation (8), the branch downstream EGR rate R is based on these. _L (n) is calculated.
[0036]
Further, since only the mixed gas existing in the surge tank 3 in the early stage of acceleration is transferred to the upstream side of the branch at this time, the EGR rate R of the upstream side of the branch regardless of the compression state. _U (n) can be expressed by the following formula (9).
R _U (n) = R _S (n) ……… (9)
<Deceleration>
FIG. 5 is a schematic diagram showing the behavior of the mixed gas in the surge tank, upstream of the branch, downstream of the branch, and in the cylinder 1a during deceleration. Since the mixed gas has not yet expanded due to inertia at the initial stage of deceleration at the moment when the throttle valve 6 is closed, the EGR rate of the mixed gas at each part is the same as in the initial stage of acceleration described above.
[0037]
Immediately thereafter, the pressure in the surge tank 3 decreases as the amount of fresh air and EGR gas introduced decreases, and the mixed gas in the branch expands between the cylinder 1a closed by the intake valve. The mixed gas at this time expands toward the upstream side according to the ratio Pb (n-4) / Pb (n) of the intake negative pressure between this time and the four strokes before each cylinder makes one round, and as a result, downstream of the branch A part of the mixed gas enters the upstream of the branch, and a part of the mixed gas upstream of the branch enters the surge tank 3. When the intake valve of the corresponding cylinder is opened, the mixed gas is transferred by a stroke that is half the branch length.
[0038]
Since only a part of the mixed gas existing downstream of the branch at the initial stage of deceleration is transferred to the cylinder 1a at this time, the cylinder EGR rate R is independent of the compression state. _C (n) can be expressed by the following formula (10).
R _C (n) = R _L (n-4) ……… (10)
At this time, downstream of the branch, a part of the mixed gas existing in the downstream of the branch at the beginning of deceleration (remaining amount introduced into the cylinder 1a) and the mixture existing in the upstream of the branch at the initial stage of deceleration Part of the gas is transferred in an expanded state according to the ratio Pb (n-4) / Pb (n), and the branch downstream EGR rate R _L (n) can be expressed by the following formula (11).
R _L (n) = R _L (n-4) × {Pb (n-4) / Pb (n) -1} + R _U (n) × {2-Pb (n-4) / Pb (n)} (11)
That is, the mixed gas transferred downstream of the branch is present upstream of the branch before transfer (after expansion), and the branch downstream EGR rate R is upstream of the branch before transfer. _L The occupation ratio of the mixed gas of (n-4) is expressed by the first half of the equation (11), while the branch upstream EGR rate R _U Since the occupation ratio of the mixed gas of (n) is expressed in the latter half of the equation (11), the branch downstream EGR rate R is based on these. _L (n) is calculated.
[0039]
Further, at this time, a part of the mixed gas existing in the upstream of the branch in the early stage of deceleration (remaining amount transferred to the downstream of the branch) and the mixed gas existing in the surge tank 3 are present in the upstream of the branch. , Transferred in an expanded state according to the ratio Pb (n-4) / Pb (n), and the branch upstream EGR rate R _U (n) can be expressed by the following formula (12).
R _U (n) = R _U (n-4) × {2 × Pb (n-4) / Pb (n) -2} + R _S (n) * {3-2 * Pb (n-4) / Pb (n)} (12)
That is, the mixed gas transferred to the upstream side of the branch was present in the surge tank 3 before the transfer (after expansion), and the branch upstream EGR rate R in the surge tank 3 before the transfer. _L The occupancy ratio of the mixed gas of (n-4) is expressed by the first half of the equation (12), while the EGR ratio R in the tank _S Since the occupation ratio of the mixed gas of (n) is expressed in the latter half of the equation (12), the branch upstream EGR rate R is based on these. _U (n-4) is calculated.
[0040]
In accordance with the above procedure, each EGR rate calculation unit 35-38 in FIG. _S (n), R _U (n), R _L (n), R _C (n) is calculated sequentially and the EGR rate R _U (n), R _L (n) is stored and updated as the previous value, and in the next estimation process for the cylinder, the EGR rate R 4 stroke before _U (n-4), R _L Used as (n-4). And the obtained in-cylinder EGR rate R _C (n) is applied to the setting of the ignition timing SA and the volumetric efficiency coefficient.
[0041]
FIG. 6 is a control flow showing a processing procedure for setting the ignition timing SA. First, based on the engine rotational speed Ne and the intake negative pressure Pb, the EGR ignition timing calculation unit 41 calculates the ignition timing SAw at EGR from the map. On the other hand, the non-EGR time-of-fire timing calculation unit 42 calculates the ignition timing SAw / o at the time of non-EGR from the map. Further, based on the engine speed Ne and the intake negative pressure Pb, the target EGR calculation unit 43 calculates the target EGR rate R from the map. _STD On the other hand, the clip value calculation unit 44 calculates a clip value CP that limits the upper limit of the retard amount OFS described later from the map.
[0042]
Obtained ignition timings SAw, SAw / o, target EGR rate R _STD In-cylinder EGR rate R described above _C (n) is input to the interpolation processing unit 45, and the current in-cylinder EGR rate R according to the following equation (13): _C The ignition timing SA corresponding to (n) is calculated by linear interpolation.
SA = SAw / o + (SAw−SAw / o) × R _C (n) / R _STD ………(13)
In-cylinder EGR rate R _C (n) and target EGR rate R _STD Is input to the retard amount calculation unit 46 and its ratio R _C (n) / R _STD Based on the map, the retard amount OFS is calculated, and the upper limit of the retard amount OFS is limited to the clip value CP or less. The subtracting unit 47 subtracts the retard amount OFS from the ignition timing SA, and uses the subtracted ignition timing SA as a target value in the ignition timing control.
[0043]
On the other hand, the volumetric efficiency coefficient is calculated in the same procedure as the ignition timing SA, and details will not be described. However, the volumetric efficiency coefficient obtained from the EGR map and the non-EGR map is interpolated to obtain the present current efficiency. The fresh air amount is obtained based on the volumetric efficiency coefficient and applied to the fuel injection control. In this interpolation process, the ratio R described above is used. _C (n) / R _STD That is, the estimated in-cylinder EGR rate R _C (n) is used.
[0044]
As described above, in the EGR rate estimating apparatus for the engine 1 of the present embodiment, the compression / expansion of the mixed gas in the branch 2a, which is not considered in the prior art, EGR rate R _C (n) is reflected in the calculation process. As a result, the process of transporting the mixed gas in the branch 2a can be simulated more realistically, so that the EGR rate R introduced into the cylinder regardless of the operating state of the engine 1 is achieved. _C (n) can always be estimated accurately.
[0045]
Moreover, in the equations (7) to (12), the intake negative pressure ratio Pb (n-4) / Pb (n), that is, the pressure change in the surge tank 3 which is a direct factor of the compression / expansion of the mixed gas. Therefore, it is possible to realize estimation processing that is more realistic.
On the other hand, in the EGR rate estimating apparatus for the engine 1 of the present embodiment, the EGR opening S is linearized in the opening area and the EGR opening S ′ and the EGR flow velocity Q are set in the surge tank 3 according to the equation (1). The EGR amount ΔPr (n) to be introduced is obtained, and the EGR partial pressure Pr (n) is calculated from the remaining amount of EGR gas in the surge tank 3 and the new inflow amount according to the equation (2) based on the EGR amount ΔPr (n). ) Is calculated. Thus, since each calculation process is implemented based on a concrete value, the mixing process produced in the surge tank 3 can be simulated more according to the actual condition.
[0046]
Moreover, the ratio Vcyl / Vst used in equation (2) corresponds to the filter constant of the primary filter that smoothes the EGR rate in the surge tank 3 according to the prior art disclosed in Japanese Patent Laid-Open No. 2000-254659. The ratio Vcyl / Vst is set based on more realistic engine 1 specifications (cylinder volume Vcyl, surge tank volume Vst). Due to these factors, the EGR partial pressure Pr (n) in the surge tank 3 and thus the EGR rate R in the tank _S (n) can be estimated accurately, and as a result, the EGR rate R in the tank _S EGR rate R based on (n) _C The estimation process (n) can be performed more accurately.
[0047]
And, as described above, the in-cylinder EGR rate R _C Since (n) is accurately estimated, this in-cylinder EGR rate R _C By appropriately performing the process using (n), for example, the process for setting the ignition timing SA and the volumetric efficiency coefficient, the accuracy of the ignition timing control and the fuel injection control based on these set values can be greatly improved. . Therefore, for example, in the ignition timing control, an appropriate ignition timing SA equivalent to MBT can be realized even during transient operation of the engine 1, and fuel consumption and drivability can be greatly improved by preventing misfire and knocking.
[0048]
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the EGR rate estimating device for the intake pipe injection type in-line four-cylinder gasoline engine 1 is embodied, but the engine type is not limited to this, and for example, fuel is directly injected into a cylinder. The present invention may be applied to an in-cylinder injection gasoline engine or a diesel engine, or an engine having a different cylinder arrangement or number of cylinders.
[0049]
In the above embodiment, the branch 2a is divided into the upstream and downstream, and the EGR rate R is individually divided. _U (n), R _L (n) is calculated. As is clear from the above description, the number of branches 2a is determined based on the ratio of the volume of the branch 2a to the cylinder volume. For example, the volume of the branch 2a is three times the cylinder volume. Sometimes, the branch 2a is divided into three areas, upstream, middle stream, and downstream, and the EGR rate is calculated individually.
[0050]
【The invention's effect】
As described above, according to the EGR rate estimating apparatus for an internal combustion engine of the first and second aspects of the invention, the process of transporting the mixed gas in the branch is taken into consideration in consideration of the compression / expansion of the mixed gas. Therefore, the EGR rate of the mixed gas introduced into the cylinder can always be accurately estimated regardless of the operating state of the internal combustion engine.
[0051]
According to the EGR rate estimating apparatus for an internal combustion engine of the third aspect of the invention, in addition to the first and second aspects of the invention, the mixing process of the mixed gas in the surge tank can be simulated according to the actual situation, Therefore, the EGR rate of the mixed gas introduced into the cylinder can be estimated more accurately.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an engine EGR rate estimating apparatus according to an embodiment;
FIG. 2 is an explanatory view schematically showing an intake system of an engine.
[Fig. 3] In-cylinder EGR rate R _C It is explanatory drawing which shows the control flow when estimating (n).
FIG. 4 is a schematic diagram showing the behavior of a mixed gas during acceleration.
FIG. 5 is a schematic diagram showing the behavior of the mixed gas during deceleration.
FIG. 6 is an explanatory diagram showing a control flow when setting an ignition timing SA.
[Explanation of symbols]
1 engine (internal combustion engine)
1a In-cylinder
2 Intake manifold
2a branch
3 Surge tank
11 EGR valve
21 ECU (first EGR rate calculation means, second EGR rate calculation means, EGR rate storage means, EGR rate update means)

Claims (3)

A surge tank in which fresh air is introduced from the intake system of the engine, EGR gas is recirculated from the exhaust system of the engine according to the opening of the EGR valve, and the fresh air and EGR gas are mixed inside;
A branch of an intake manifold that connects the surge tank and each cylinder of the engine;
A first EGR rate calculating means for calculating an EGR rate in the surge tank each time a mixed gas from the surge tank is transferred in the branch in accordance with intake of the engine;
EGR rate storage means for storing the EGR rate of the internal mixed gas as the previous value for each region of the branch previously divided by the transfer stroke of the mixed gas accompanying the intake air;
For each transfer of the mixed gas due to the intake, the EGR rate within the first surge tank which is calculated by the EGR rate calculating means, the previous value of the EGR rate for each region stored in the EGR rate storage unit, and the Based on the volume change correlation value correlated with the volume change of the mixed gas in the branch due to the pressure change in the surge tank, the EGR rate of the mixed gas in each region after the transfer, and the EGR rate of the mixed gas introduced into the cylinder Second EGR rate calculating means for calculating
An internal combustion engine comprising: an EGR rate updating unit that updates the EGR rate of the storage unit with the calculated EGR rate of the mixed gas in each region for each calculation of the second EGR rate calculating unit. EGR rate estimation device. 2. The EGR rate estimation for an internal combustion engine according to claim 1, wherein the second EGR rate calculation means sets a volume change correlation value based on a previous value and a current value of the pressure in the surge tank. apparatus. The first EGR rate calculation means calculates an EGR amount introduced into the surge tank based on the opening degree of the EGR valve and the EGR flow velocity linearized corresponding to the opening area, and obtains the EGR amount from the EGR amount. The EGR rate in the surge tank is calculated based on an EGR partial pressure in the surge tank and a fresh air partial pressure corresponding to a fresh air amount introduced into the surge tank. 2. The EGR rate estimation device for an internal combustion engine according to 2.

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