JP2004169607A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine with improved estimation precision of a mathematical model when the control device grasps the state of an exhaust emission control catalyst using the mathematical model and controls the internal combustion engine based on the state of the catalyst. <P>SOLUTION: The control device is equipped with an estimation means for estimating an emission amount of specific components inside and downstream of the exhaust emission control catalyst according to the mathematical model based on an exhaust air-fuel ratio (or an emission amount of specific components) on the downstream side of the exhaust emission control catalyst, a specific component detecting sensor positioned on the downstream side of the exhaust emission control catalyst, and a rich/lean setting means for forcedly vibrating the exhaust air-fuel ratio on the downstream side of the exhaust emission control catalyst into a rich side and a lean side. The estimation means calculates a constant of the mathematical model based on the result detected by the specific component detecting sensor while forcedly vibrating the exhaust air-fuel ratio by the rich/lean setting means, and calculates an estimation value by the mathematical model using the calculated constant. <P>COPYRIGHT: (C)2004,JPO

Description

【００２９】
いま、時刻ｔ〜ｔ＋△ｔの所与の期間における特定領域での化学種の収支を考えると、図５に示したように、特定領域の排気ガス相（単に「排気ガス相」とも言う）における化学種の変化量△Ｍは、下記の（１）式に示したように、「特定領域に流入した化学種の量Ｍｉｎ」から「流出した化学種の量Ｍｏｕｔ」及び「コート層に伝達された化学種の量Ｍｃｏａｔ」を減算した量に等しい。このように、触媒モデルは特定領域における特定成分の物質収支に基づいて構築される。
【００３０】
【数１】

【００３１】
以下、（１）式の各項について個別に検討する。まず、（１）式の左辺にある化学種の変化量△Ｍは、下記（２）式により求めることができる。（２）式は、上述した期間Δｔにおける化学種の濃度変化量（化学種の濃度Ｃｇの時間変化量を期間Δｔにわたって積分した量）に微小体積σ・ｄＡ・ｄｘを乗じた値を特定領域にわたって軸方向に積分したものである。
【００３２】
【数２】

【００３３】
（１）式の右辺第１項のＭｉｎは、単位時間あたりに特定領域に流入する排気ガスの体積ｖｇｉｎ・ｄＡに、流入する排気ガス中の化学種の濃度Ｃｇｉｎを乗じた値Ｃｇｉｎ・ｖｇｉｎ・ｄＡを期間ｔ→ｔ＋Δｔにわたって積分した値である。ここで、「単位時間あたりに特定領域に流入する排気ガスの体積ｖｇｉｎ・ｄＡ」は、「特定領域に流入する排気ガスの流速ｖｇｉｎ」と「特定領域の断面積ｄＡ」との積である。なお、実際には、断面積ｄＡで開口率σの触媒内に流速ｖｇｉｎの排気ガスが流れ込むので、触媒内部での排気ガスの流速はｖｇｉｎ／σとなり、この実際の流速ｖｇｉｎ／σと触媒の実質的な排ガス通過断面積σ・ｄＡの積として求められる。
【００３４】
また、（１）式の右辺第２項のＭｏｕｔは、単位時間あたりに特定領域から流出する排気ガスの体積ｖｇｏｕｔ・ｄＡに、流出する排気ガス中の化学種の濃度Ｃｇｏｕｔを乗じた値Ｃｇｏｕｔ・ｖｇｏｕｔ・ｄＡを期間ｔ→ｔ＋Δｔにわたって積分した値である。ここで、「単位時間あたりに特定領域から流出する排気ガスの体積ｖｇｏｕｔ・ｄＡ」は、「特定領域から流出する排気ガスの流速ｖｇｏｕｔ」と「特定領域の断面積ｄＡ」との積である。なお、実際には、排気ガスの流速ｖｇｏｕｔ／σと実質的な排ガス通過断面積σ・ｄＡの積である。即ち、上記（１）式の右辺第１項及び第２項は下記（３）式のように記述することができる。
【００３５】
【数３】

【００３６】
ところで、特定領域に流入する排気ガスの流速ｖｇｉｎと特定領域から流出する排気ガスの流速ｖｇｏｕｔとの間に大きな差異はないので、ｖｇ＝ｖｇｉｎ＝ｖｇｏｕｔとおくと、（３）式は、下記（４）式のように変形される。
【００３７】
【数４】

【００３８】
次に、（１）式の右辺第３項のコート層に伝達される（移動する）化学種の量Ｍｃｏａｔについて検討する。幾何学的表面積Ｓｇｅｏは触媒の単位体積あたりの化学種の物質及び熱の伝達に寄与する表面積であるから、特定領域において排気ガス相からコート層への伝達に寄与する表面積はＳｇｅｏ・ｄＡ・ｄｘであり、特定領域の単位長あたりの物質伝達寄与面積はＳｇｅｏ・ｄＡとなる。また、コート層に伝達される化学種の量は、フィックの法則から、排気ガス相の化学種の濃度Ｃｇとコート層の化学種の濃度Ｃｗとの差に比例すると考えることができる。これらから、下記の（５）式が得られる。なお、ｈ_Ｄは比例定数であるが、［表１］に示したように、物質伝達率と称呼される値である。
【００３９】
【数５】

【００４０】
従って、上記（１），（２），（４）式、及び（５）式から、以下の（６）式が得られる。
【００４１】
【数６】

【００４２】
この（６）式に準定常（ｑｕａｓｉｓｔａｔｅ）近似を適用すると、（６）式の左辺は「０」（∂Ｃｇ／∂ｔ＝０）であると考えることができるから（即ち、濃度Ｃｇは瞬間的に定常値に至ると考えられるから）、下記の（７）式が得られる。
【００４３】
【数７】

【００４４】
ここで、見かけの拡散速度（実質的な拡散速度）Ｒ_Ｄを以下の（８）式のようにおけば、（７）式は（９）式のように書き直される。
【００４５】
【数８】

【数９】

【００４６】
次に、特定領域のコート層における化学種の収支（特定成分の物質収支）を上記と同様に考えると、下記（１０）式に示されるように、コート層内における化学種の時間的変化量（単位時間あたりの変化量）△Ｍｃは、単位時間あたりに排気ガス相からコート層へ伝達される化学種の量Ｍｄから、単位時間あたりにコート層にて反応により消費される化学種の量Ｍｒを減じた量である。
【００４７】
【数１０】

【００４８】
（１０）式の左辺（コート層内における化学種の時間的変化量）△Ｍｃは、下記（１１）式に示したように、化学種の濃度変化（∂Ｃｗ／∂ｔ）に体積（（１―σ）・ｄＡ・ｄｘ）を乗じることにより求められ、右辺第１項（単位時間あたりに排気ガス相からコート層へ伝達される化学種の量Ｍｄ）は（５）式で説明した理由と同じ理由により、即ち、フィックの法則から考えると、下記（１２）式のように記述することができる。
【００４９】
【数１１】

【数１２】

【００５０】
また、（１０）式の右辺第２項（単位時間あたりにコート層において反応によって消費される化学種の量Ｍｒ）は、コート層での化学種の消費速度Ｒを用いた下記（１３）式により求められる。
【００５１】
【数１３】

【００５２】
従って、（１０）〜（１３）式から、下記の（１４）式が得られる。
【００５３】
【数１４】

【００５４】
この（１４）式に準定常（ｑｕａｓｉｓｔａｔｅ）近似を適用すると（∂Ｃｗ／∂ｔ＝０）、下記の（１５）式が得られる。
【００５５】
【数１５】

【００５６】
ここで、（１５）式に（８）式を適用すれば、下記の（１６）式が得られる。
【００５７】
【数１６】

【００５８】
以上を要約すると、（９）式及び（１６）式が触媒モデルの基本式である。（９）式は、ある化学種の「特定領域への流入量」と「排気ガス相からコート層への拡散量＋特定領域からの流出量」とが釣り合っていることを示し、（１６）式は、化学種の「排気ガス相からコート層への拡散量」と「コート層での消費量」とが釣り合っていることを示している。
【００５９】
次に、上述した触媒モデルを使用して特定領域から流出する特定の化学種ｉの濃度Ｃｇｏｕｔを実際に算出するための方法について説明する。まず、（９）式を離散化すると、下記（１７）式が得られる。なお、以下においては上記ｄｘをＬとして表す。
【００６０】
【数１７】

【００６１】
ここで、図６に概念的に示したように、特定領域Ｉから流出する化学種の濃度Ｃｇｏｕｔは特定領域Ｉの化学種の濃度Ｃｇ（Ｉ）の影響を強く受けると考えられるので、下記の（１８）式のように置くことができる。
【００６２】
【数１８】

この考え方は「風上法」と呼ばれる。即ち、風上法とは、「特定領域Ｉに隣接する上流側の領域（Ｉ−１）における濃度Ｃｇ（Ｉ−１）の化学種が、特定領域Ｉに流入する」という考え方であり、下記（１９）式のように記述することもできる。
【００６３】
【数１９】

【００６４】
ところで、反応速度論に基けば、ある化学種の消費速度Ｒは、その化学種のコート層での平均濃度Ｃｗの関数ｆｃｗ（例えば、ＣＷのｎ乗）となるので、この関数ｆｃｗを最も簡便となるようにｆｃｗ（ｘ）＝ｘとおけば、消費速度Ｒは下記の（２０）式のようにあらわすことができる。なお、以下において、（２０）式中のＲ＊を便宜上「消費速度定数」と称呼する。
【００６５】
【数２０】

【００６６】
この（２０）式を上記（１６）式に適用すると下記（２１）式が得られ、同（２１）式を変形することにより下記（２２）式が得られる。
【００６７】
【数２１】

【数２２】

【００６８】
また、上述した風上法によれば、Ｃｇ＝Ｃｇｏｕｔであるから、（２２）式は下記（２３）式に書き換えられる。
【００６９】
【数２３】

【００７０】
そして、Ｃｇ＝Ｃｇｏｕｔなる関係を上記（１７）式に適用してＣｇを消去するとともに、同（１７）式と上記（２３）式とからＣｗを消去すると、下記（２４）式が得られる。
【００７１】
【数２４】

【００７２】
そこで、値ＳＰを下記（２５）式のようにおけば、（２４）式は（２６）式のように書き直すことができる。値ＳＰは、見かけの拡散速度Ｒ_Ｄと消費速度定数Ｒ＊のうちの小さい方の値に強い影響を受ける値であるから、Ｃｇｏｕｔの変化が物質の伝達（Ｒ_Ｄ）又は化学的反応（Ｒ＊）の何れによって律速されているかを示す値であり、「反応律速因子」と呼ぶこともできる。
【００７３】
【数２５】

【数２６】

【００７４】
以上のことから、消費速度定数Ｒ＊と見かけの拡散速度Ｒ_Ｄとを決定できれば、特定領域に流入する化学種濃度Ｃｇｉｎを与えることにより、（２５）式と（２６）式とに基づいて同特定領域から流出する化学種の濃度Ｃｇｏｕｔを求めることができる。以上が、化学種の濃度Ｃｇｏｕｔを算出する基本的考え方である。
【００７５】
本実施形態の空燃比制御では、上述したように触媒モデルを用いて算出される「特定領域から流出する特定成分（化学種）の濃度Ｃｇｏｕｔ」に基づいて内燃機関制御（空燃比制御）を行う。このＣｇｏｕｔに対して目標値を設定し、Ｃｇｏｕｔがこの目標値となるような空燃比となるように燃料を噴射する。このとき、特定領域をまず触媒１９の最上流側に設定すれば、この特定領域に流入する特定成分の濃度Ｃｇｉｎは、触媒１９の上流側に設定された空燃比センサ２５によって検出できる。このＣｇｉｎに基づいてＣｇｏｕｔを算出すれば、このＣｇｏｕｔは一つ下流側の特定領域のＣｇｉｎとなる。このように順次計算することで、触媒１９の状態を詳しく（触媒１９のコート層における特定成分の濃度Ｃｗの流れ方向の分布など）把握することができ、最終的に触媒１９から排出される特定成分の濃度（排出量）もより正確に求められる。
【００７６】
排気ガス中の浄化すべき成分とされているＣＯ，ＮＯ（ＮＯｘ），ＨＣについてのＣｇｏｕｔ（Ｃｇｏｕｔ，ＣＯ・Ｃｇｏｕｔ，ＮＯ・Ｃｇｏｕｔ，ＨＣ）を推定し、これらの排出量（濃度）を触媒１９の下流で少なくなるように制御すれば、排気浄化性能を向上させることができる。また、触媒１９の酸素吸蔵量を利用して浄化性能をより向上させようとした場合は、Ｏ_２についてのＣｇｏｕｔ（Ｃｇｏｕｔ，Ｏ_２）を触媒内部について求めて分布を把握すれば、酸素吸蔵機能をより一層効果的に利用して排気浄化性能を向上させることができる。
【００７７】
触媒モデルを用いてＣｇｉｎからＣｇｏｕｔを算出するには、上述したように、消費速度定数Ｒ＊と見かけの拡散速度Ｒ_Ｄとを決定する必要がある。まず、拡散速度Ｒ_Ｄについてであるが、（８）式から分かるように、Ｒ_Ｄ＝Ｓｇｅｏ・ｈ_Ｄである。［表１］に示されるように、Ｓｇｅｏは触媒１９の固定の数値となるので、Ｒ_Ｄはｈ_Ｄに左右される。ｈ_Ｄ
は、［表１］に示されるように、特定成分（化学種）毎に異なり、触媒１９の温度に依存する。このため、拡散速度Ｒ_Ｄは、予め実験などを行い触媒温度Ｔｅｍｐの関数として決定しておき、これをマップ化してＥＣＵ１８内のＲＯＭに格納しておく。
【００７８】
一方、消費速度定数Ｒ＊は、制御中に制御装置において算出・更新し、この算出・更新した値を用いる。このように、実際の制御系における検出結果に基づいて消費速度定数Ｒ＊を算出・更新することで、制御精度をより一層精度の高いものとすることができる。以下、消費速度定数Ｒ＊の決定方法について説明する。
【００７９】
まず、触媒１９の最も下流側の特定領域Ｉ（あるいは、触媒１９全体と把握することも可能）についてのＣｇｏｕｔを求める。このとき、消費速度定数Ｒ＊がまだ決定されていない（また、一つ上流側のＣｇｏｕｔも算出されていない）のであるから、当然上述した触媒モデルによってＣｇｏｕｔを算出することはできない。このため、まずＯ２濃度について説明するが、下記（２７）式によってＣｇｏｕｔ，Ｏ_２を算出する。このとき、下記（２７）式に示されるように、触媒１９の下流側の排気ガス中のＯ_２濃度を検出する特定成分検出センサ２６の出力を利用する。
【００８０】
【数２７】

【００８１】
（２７）式において、ＡＦ−ＡＦｓｔｏｉｃｈは理論空燃比からどの程度リッチ又はリーン側に寄っているかを示す空燃比差であり、これに供給燃料量Ｇｆをかけることで空気の質量流量が得られる。さらに、この空気質量に対して空気中の酸素の重量割合０．２３をかけることで、過剰又は不足の酸素量が得られる。つまり、これが、触媒モデル（数学的モデル）によらずに実際の検出に基づいて算出された、触媒１９の最下流側の特定領域Ｉから流出する（即ち、触媒１９から流出する）酸素排出量である。
【００８２】
本実施例では、Ｃｇｏｕｔ，Ｏ_２を算出するに際し、ＥＣＵ１８によってインジェクタ５からの燃料噴射量を調節したり、スロットルバルブ９の開度を調節することで、排気空燃比を強制的にリーンにする。即ち、ＥＣＵ１８やインジェクタ５、スロットルバルブ９などが、リッチ・リーン設定手段として機能する。リーン時には排気ガス中にＮＯも含まれるため、（（２７）式相当式を用いて）同様の手法によってＣｇｏｕｔ，ＮＯも算出し得る。このとき、特定成分検出センサ２６はＮＯを検出する。
【００８３】
一方、Ｃｇｏｕｔ，ＣＯやＣｇｏｕｔ，ＨＣを算出するには、特定成分検出センサ２６においてＣＯ濃度やＨＣ濃度が検出されなくてはならない。そこで、この場合は、上述したリッチ・リーン設定手段によって排気空燃比を強制的にリッチにする。その後、やはり、（（２７）式相当式を用いて）同様の手法によってＣｇｏｕｔ，ＣＯやＣｇｏｕｔ，ＨＣを算出する。このとき、特定成分検出センサ２６はＣＯやＨＣを検出する。このようにして、実際の制御系における検出結果に基づいて、触媒１９（の最下流側の特定領域Ｉ）から流出する排気ガスについての各特定成分についてのＣｇｏｕｔが算出された。
【００８４】
次に、Ｃｇｉｎを算出する。まず、Ｃｇｉｎ，Ｏ_２について説明する。このときも、消費速度定数Ｒ＊がまだ決定されていない（また、一つ上流側のＣｇｏｕｔというものも存在しない）のであるから、当然上述した触媒モデルによってＣｇｉｎ，Ｏ_２を算出することはできない。そこで、まず、触媒１９の最も上流側の領域（あるいは、触媒１９全体と把握することも可能）に流入する排気ガスについてのＣｇｉｎ，Ｏ_２を、下記（２８）式によって算出する。このとき、下記（２８）式に示されるように、触媒１９の上流側の排気空燃比を検出する空燃比センサ２５の出力を利用する。
【００８５】
【数２８】

【００８６】
上記（２８）式の導入過程を簡単に述べると、触媒１９に流入する排気ガスの空燃比ＡＦはＧａ／Ｇｆであり、Ｇｆに対して理論空燃比を得るために必要な空気質量をＧａｓｔｏｉｃｈとすると、理論空燃比ＡＦｓｔｏｉｃｈはＧａｓｔｏｉｃｈ／Ｇｆとなる。一方、供給燃料質量がＧｆであるときに空燃比がＡＦとなったとき、理想空燃比ＡＦｓｔｏｉｃｈを得るために必要な空気質量に対する過剰な空気質量はＧａ−Ｇａｓｔｏｉｃｈであるから、酸素の質量をＭａｓｓＯ２とおくと、下記（２９）式が得られ、この（２９）式から上述した（２８）式が導かれている。
【００８７】
【数２９】

【００８８】
Ｃｇｉｎ，ＮＯ・Ｃｇｉｎ，ＣＯ・Ｃｇｉｎ，ＨＣについては、図７〜図９に示されるマップに基づいて推定する。なお、ここでは、最も上流側のＣｇｉｎ，ＮＯ・Ｃｇｉｎ，ＣＯ・Ｃｇｉｎ，ＨＣを触媒１９の上流側の排気空燃比に基づいて決定したが、図７〜図９のパラメータを増やして多次元のマップとしても良いことは言うまでもない。このときのパラメータとしては、排気温度や点火時期、冷却水温、排気ガスの流速、触媒１９に流入する排気ガス流量（エアフロメータ１３によって検出される吸入空気量）等が挙げられる。このようにして、各特定成分毎のＣｇｏｕｔとＣｇｉｎとが、制御系における検出結果に基づいて算出された。
【００８９】
一方、この触媒モデルでは、触媒での酸化・還元反応である三元反応は瞬時に且つ完全に終了するものと仮定し、その結果としての酸素の過不足に基づく酸素の吸蔵・放出反応に着目して上述した特定成分（化学種ｉ）を以下のようにストレージ・エージェントとリダクション・エージェントとして定義する。例えば、酸素０_２や窒素酸化物の一つである一酸化窒素ＮＯのように酸素を生成する（酸素をもたらす）化学種（ストレージ・エージェント）、及び、一酸化炭素ＣＯや炭化水素ＨＣのように酸素を消費する化学種（リダクション・エージェント）である。
【００９０】
ストレージ・エージェントの化学種ｉのＣｇｏｕｔをＣｇｏｕｔ，ｓｔｏｒ，ｉ、同化学種ｉのＣｗをＣｗ，ｓｔｏｒ，ｉ、同化学種ｉのＣｇｉｎをＣｇｉｎ，ｓｔｏｒ，ｉ、同化学種ｉの見かけの拡散速度Ｒ_ＤをＲ_Ｄ，ｉ、同化学種ｉの消費速度をＲｓｔｏｒ，ｉ、同化学種ｉの消費速度定数をＲ＊ｓｔｏｒ，ｉ、及び、同化学種ｉの反応律速因子をＳＰｓｔｏｒ，ｉと表す（この場合、化学種ｉはＯ_２又はＮＯ等）。同様に、リダクション・エージェントの化学種ｉのＣｇｏｕｔをＣｇｏｕｔ，ｒｅｄｕｃ，ｉ、同化学種ｉのＣｗをＣｗ，ｒｅｄｕｃ，ｉ、同化学種ｉのＣｇｉｎをＣｇｉｎ，ｒｅｄｕｃ，ｉ、同化学種ｉの見かけの拡散速度Ｒ_ＤをＲ_Ｄ，ｉ、同化学種ｉの消費速度をＲｒｅｄｕｃ，ｉ、同化学種ｉの消費速度定数をＲ＊ｒｅｄｕｃ，ｉ、及び、同化学種ｉの反応律速因子ＳＰｒｅｄｕｃ，ｉ（この場合、化学種ｉはＣＯ又はＨＣ等）と表す。このように各値を表すと、上記（２０），（２３），（２５），（２６）式から、ストレージ・エージェント及びリダクション・エージェント毎に、以下の（３０）〜（３３）式及び（３４）〜（３７）式が得られる。
【００９１】
【数３０】

【数３１】

【数３２】

【数３３】

【００９２】
【数３４】

【数３５】

【数３６】

【数３７】

【００９３】
ここで、特定成分がＯ_２である場合に関しては、上記（３３）式及び（３２）式において、Ｃｇｏｕｔ，ｓｔｏｒ，ｉに（２７）式を用いて算出した触媒１９から流出するＣｇｏｕｔ，Ｏ_２を適用し、Ｃｇｉｎ，ｓｔｏｒ，ｉに（２８）式を用いて算出した触媒１９に流入するＣｇｉｎ，Ｏ_２を適用し、予め触媒１９の温度の関数として決定される拡散速度Ｒ_ＤＯ_２を適用することで、消費速度定数Ｒ＊Ｏ_２を算出することができる。同様に、特定成分がＮＯである場合に関しては、上記（３３）式及び（３２）式において、Ｃｇｏｕｔ，ｓｔｏｒ，ｉに（２７）式相当式を用いて算出した触媒１９から流出するＣｇｏｕｔ，ＮＯを適用し、Ｃｇｉｎ，ｓｔｏｒ，ｉに図７から求めた触媒１９に流入するＣｇｉｎ，ＮＯを適用し、予め触媒１９の温度の関数として決定される拡散速度Ｒ_ＤＮＯを適用することで、消費速度定数Ｒ＊ＮＯを算出することができる。
【００９４】
さらに、特定成分がＣＯである場合に関しては、上記（３７）式及び（３６）式において、Ｃｇｏｕｔ，ｒｅｄｕｃ，ｉに（２７）式相当式を用いて算出した触媒１９から流出するＣｇｏｕｔ，ＣＯを適用し、Ｃｇｉｎ，ｒｅｄｕｃ，ｉに図８から求めた触媒１９に流入するＣｇｉｎ，ＣＯを適用し、予め触媒１９の温度の関数として決定される拡散速度Ｒ_ＤＣＯを適用することで、消費速度定数Ｒ＊ＣＯを算出することができる。同様に、特定成分がＨＣである場合に関しては、上記（３７）式及び（３６）式において、Ｃｇｏｕｔ，ｒｅｄｕｃ，ｉに（２７）式相当式を用いて算出した触媒１９から流出するＣｇｏｕｔ，ＨＣを適用し、Ｃｇｉｎ，ｒｅｄｕｃ，ｉに図９から求めた触媒１９に流入するＣｇｉｎ，ＨＣを適用し、予め触媒１９の温度の関数として決定される拡散速度Ｒ_ＤＨＣを適用することで、消費速度定数Ｒ＊ＨＣを算出することができる。
【００９５】
これで、各特定成分毎の消費速度定数Ｒ＊が算出されたので、触媒１９の上流側の特定領域Ｉから下流側の向けて順に各特定成分毎のＣｇｏｕｔを算出することができる。このときは、上述した触媒モデルにおける（２４）式又はこれと同値な（２５），（２６）式［＝（３２），（３３）式／（３６），（３７）式］を用いて順次算出する。併せて、（２３）式［＝（３１）式／（３５）式］を用いることで、触媒１９内部のコート層における特定成分の濃度も算出できる。もちろん、最上流側の特定領域ＩについてのＣｇｉｎは（２８）式や図７〜図９のマップによって求めた値を用いる。そして、ある特定領域のＣｇｉｎは、一つ上流側の特定領域におけるＣｇｏｕｔである。
【００９６】
このように、実際の制御系における検出結果に基づいて消費速度定数Ｒ＊を算出し、この消費速度定数Ｒ＊を用いた数学的モデル（触媒モデル）を用いて触媒１９の状態を詳しく把握することで、触媒１９の能力をより一層有効に活用することができる。その結果、本実施形態では、触媒１９から最終的に流出する（即ち、最も下流側の特定領域Ｉから流出する）各特定成分のＣｇｏｕｔに対して目標値を設定し、各Ｃｇｏｕｔがこの目標値となるように燃料噴射量及び吸入空気量を調節する空燃比制御を行っている。
【００９７】
例えば、窒素酸化物ＮＯｘ、一酸化炭素ＣＯ、炭化水素ＨＣの排出量は少ない程良いので、触媒１９から流出するＣｇｏｕｔ，ＮＯやＣｇｏｕｔ，ＣＯやＣｇｏｕｔ，ＨＣをゼロとする目標を設定する。また、触媒の内部の各特定領域ＩについてのＣｇｏｕｔ，ＮＯやＣｇｏｕｔ，ＣＯやＣｇｏｕｔ，ＨＣはゼロでない各成分の浄化が進むような目標を設定することも考えられる。例えば、ある特定領域ＩにおけるＣｗ，ＨＣが高い場合には、これを酸化させるためにその一つ上流側の特定領域（Ｉ−１）のＣｇｏｕｔ，ＮＯを多くするような目標を設定することも考えられる。
【００９８】
さらに、上述したように、触媒１９の浄化性能を向上させるために、触媒１９の酸素吸蔵機能を利用することがある。そして、触媒１９の酸素吸蔵密度Ｏｓｔは、触媒の中で分布をもち得る。この触媒１９内部における酸素吸蔵密度Ｏｓｔの状態をより効率よく把握・制御することで、排気浄化性能をより一向上させることができる。この場合、Ｃｇｏｕｔを制御目標とせずに、酸素吸蔵密度Ｏｓｔを制御目標とすることも考えられる。これについて以下に説明する。
【００９９】
上述したように、触媒１９の酸素の吸蔵／放出に着目して、ストレージ・エージェント及びリダクション・エージェント毎に、（３０）〜（３３）式及び（３４）〜（３７）式を得た。これらの式に基づいて、Ｃｇｏｕｔ，ｓｔｏｒ，ｉ（具体的には、特定領域から流出する酸素の濃度Ｃｇｏｕｔ，０_２、特定領域から流出する一酸化窒素の濃度Ｃｇｏｕｔ，ＮＯ）及びＣｇｏｕｔ，ｒｅｄｕｃ，ｉ（具体的には、特定領域から流出する一酸化炭素の濃度Ｃｇｏｕｔ，ＣＯ、特定領域から流出する炭化水素の濃度Ｃｇｏｕｔ，ＨＣ）を各特定領域毎に上述したように求めることができる。また、各特定成分に関しての消費速度定数Ｒ＊ｓｔｏｒ，ｉ及びＲ＊ｒｅｄｕｃ，ｉも、各特定領域毎のＣｇｏｕｔを算出する上で上述したように決定されるのも上述したとおりである。
【０１００】
反応速度論によれば、特定領域のコート層で酸素が吸蔵される速度（酸素の吸蔵速度）Ｒｓｔｏｒ，ｉは、「コート層のストレージ・エージェント（０_２、ＮＯ等）の濃度Ｃｗ，ｓｔｏｒ，ｉ（例えば、Ｃｗ，０_２、Ｃｗ，ＮＯ）の関数ｆ１（Ｃｗ，ｓｔｏｒ，ｉ）」の値に比例するとともに、「特定領域のコート層の最大酸素吸蔵密度Ｏｓｔｍａｘと実際の酸素吸蔵密度Ｏｓｔとの差（Ｏｓｔｍａｘ−Ｏｓｔ）の関数ｆ２（Ｏｓｔｍａｘ−Ｏｓｔ）」の値に比例すると考えられる。この最大酸素吸蔵密度Ｏｓｔｍａｘと酸素吸蔵密度との差（Ｏｓｔｍａｘ−Ｏｓｔ）は、着目している特定領域における酸素吸蔵余裕量を表す。そこで、簡単のために関数ｆ１（ｘ）＝ｆ２（ｘ）＝ｘとすると、下記の（３８）式が得られる。
【０１０１】
【数３８】

【０１０２】
（３８）式のｋｓｔｏｒ，ｉは酸素吸蔵速度係数（吸蔵側反応速度係数，ストレージ・エージェントの消費速度係数）であって、よく知られたアレニウスの式で表される温度に依存して変化する係数であり、別途検出（推定）される触媒温度Ｔｅｍｐの関数として（あるいは、酸素吸蔵速度係数ｋｓｔｏｒ，ｉと触媒温度Ｔｅｍｐとの間の関係を規定したマップから）求めることができる。なお、酸素吸蔵速度係数ｋｓｔｏｒ，ｉは、触媒劣化程度に応じても変化するので、触媒劣化程度に応じて求めてもよい。従って、（３０）式と（３８）式とから、消費速度定数Ｒ＊ｓｔｏｒ，ｉは、最大酸素吸蔵密度Ｏｓｔｍａｘと酸素吸蔵密度との差（Ｏｓｔｍａｘ−Ｏｓｔ）を用いて、下記（３９）式のようにあらわすこともできる。
【０１０３】
【数３９】

【０１０４】
また、酸素の吸蔵（吸着）と放出とに着目しているこのモデルにおいては、還元剤であるリダクション・エージェントはコート層に吸蔵されている酸素の放出にのみ使用されるから、リダクション・エージェントの消費速度Ｒｒｅｄｃｕ，ｉはコート層に吸蔵されている酸素が放出される速度（酸素の放出速度）Ｒｒｅｌ，ｉと等しい。そこで、酸素の放出速度Ｒｒｅｌ，ｉについて検討すると、この放出速度Ｒｒｅｌ，ｉは、酸素の吸蔵速度Ｒｓｔｏｒ，ｉと同様に反応速度論に基づいて、「コート層において酸素を消費する化学種（例えば、ＣＯ，ＨＣ）の濃度Ｃｗ，ｒｅｄｕｃ，ｉ（例えば、Ｃｗ，ＣＯ、Ｃｗ，ＨＣ）の関数ｇ１（Ｃｗ，ｒｅｄｕｃ，ｉ）」の値に比例するとともに、「酸素吸蔵密度Ｏｓｔの関数ｇ２（Ｏｓｔ）」の値に比例すると考えられる。そこで・簡単のために関数ｇ１（ｘ）＝ｇ２（ｘ）＝ｘとすると、下記の（４０）式が得られる。
【０１０５】
【数４０】

【０１０６】
（４０）式のｋｒｅｌ，ｉは酸素放出速度係数（吸脱側反応速度係数，リダクション・エージェントの消費速度係数）であって、酸素吸蔵速度係数ｋｓｔｏｒ，ｉと同様にアレニウスの式で表される温度に依存して変化する係数であり、別途検出（推定）される触媒温度Ｔｅｍｐの関数として（あるいは、酸素放出速度係数ｋｒｅｌ，ｉと触媒温度Ｔｅｍｐとの間の関係を規定したマップから）求めることができる。なお、酸素放出速度係数ｋｒｅｌ，ｉは、触媒劣化程度に応じても変化するので、触媒劣化程度に応じて求めてもよい。この結果、上述したようにリダクション・エージェントの消費速度Ｒｒｅｄｃ，ｉはコート層の酸素の放出速度Ｒｒｅｌ，ｉと等しいから、消費速度定数Ｒ＊ｒｅｄｕｃ，ｉは（３４）式と（４０）式とから、酸素吸蔵密度Ｏｓｔを用いて、下記（４１）式のようにあらわすこともできる。
【０１０７】
【数４１】

【０１０８】
（３９）式及び（４１）式には、消費速度定数Ｒ＊と酸素吸蔵密度Ｏｓｔとの関係があらわされている。ここで、コート層での化学種としての酸素の収支について着目すると、この酸素の収支はコート層での酸素の吸蔵分と酸素の放出分の差であるから、下記（４２）式により記述される。（４２）式でｄＡ・Ｌは特定領域の体積ｄＶである。また、下記（４２）式を変形すると、下記（４３）式が得られる。
【０１０９】
【数４２】

【数４３】

【０１１０】
この（４３）式を、（３８）式と（４０）式とを用いながら離散化すると、下記の（４４）式が得られる。この（４４）式を変形すると、下記（４５）式〜（４７）式が得られ、これらから酸素吸蔵密度Ｏｓｔを更新して行くことができる。
【０１１１】
【数４４】

【数４５】

【数４６】

【数４７】

【０１１２】
このように、式（４５）〜（４７）式を用いて、触媒モデルに基づいて酸素吸蔵密度Ｏｓｔを算出することができる。また、酸素吸蔵密度Ｏｓｔに基づいて、下記（４８）式を用いて酸素吸蔵量ＯＳＡも算出することができる。
【０１１３】
【数４８】

【０１１４】
従って、触媒に流入する化学種濃度Ｃｇｉｎ，ｉが境界条件として与えられたとき、触媒上流のブロック（特定領域）から、順次、（４５）式を用いて各ブロックの酸素吸蔵量ＯＳＡを求めることができ、これにより、触媒内部の酸素吸蔵量の分布が精度良く推定される。また、各ブロックの酸素吸蔵量ＯＳＡを触媒全体について積算すれば、触媒全体の酸素吸蔵量についても精度良く推定することができる。そして、この特定領域毎の酸素吸蔵量ＯＳＡ（酸素吸蔵密度Ｏｓｔ）を所望の状態とすべく、Ｃｇｉｎ，Ｃｇｏｕｔ，Ｃｗを制御することで排気浄化性能をより一層向上させることができる。
【０１１５】
例えば、リッチな排気ガスが連続して流入した結果、触媒１９の上流側の領域では、リッチな排気ガス中のＣＯやＨＣを酸化するために触媒１９に吸蔵されているＯ_２が消費される。その消費量が多い場合は、さらにリッチな排気ガスが流入したときに十分に浄化できなくなることが懸念される。このような場合は、上流側の特定領域の酸素吸蔵量ＯＳＡ（酸素吸蔵密度Ｏｓｔ）の低下を抑止するような制御を行うことが考えられる。あるいは、既に排気空燃比がリーンに移行しているような場合は、低下してしまった酸素吸蔵量ＯＳＡ（酸素吸蔵密度Ｏｓｔ）を早期に回復させるような制御を行うことも考えられる。
【０１１６】
【発明の効果】
本発明によれば、数学的モデルを用いた推定に基づいて内燃機関を制御する場合に、この数学的モデルの推定精度を向上させることができる。また、本発明によれば、排気浄化触媒の内部の状況もより詳しく推定することが可能となるので、より高度な内燃機関制御を行うことも可能となる。
【図面の簡単な説明】
【図１】
本発明の制御装置の実施形態を有する内燃機関を示す断面図である。
【図２】
図１に示した排気浄化触媒の外観図である。
【図３】
図２の排気浄化触媒の部分断面図である。
【図４】
本発明における触媒モデル（数学的モデル）を説明するための模式図である。
【図５】
本発明における触媒モデル（数学的モデル）を説明するための模式図である。
【図６】
本発明における触媒モデル（数学的モデル）で使用される風上法を説明するための模式図である。
【図７】
排気浄化触媒に流入する一酸化窒素濃度を決定するために使用される排気空燃比と一酸化窒素濃度との関係を規定したマップである。
【図８】
排気浄化触媒に流入する一酸化炭素濃度を決定するために使用される排気空燃比と一酸化炭素濃度との関係を規定したマップである。
【図９】
排気浄化触媒に流入する炭化水素濃度を決定するために使用される排気空燃比と炭化水素濃度との関係を規定したマップである。
【符号の説明】
１…エンジン（内燃機関）、２…点火プラグ、３…シリンダ、４…吸気通路、５…インジェクタ、７…排気通路、９…スロットルバルブ、１８…ＥＣＵ（推定手段、リッチ・リーン設定手段）、１９…排気浄化触媒、２５…空燃比検出センサ、２６…特定成分検出センサ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an internal combustion engine.
[0002]
[Prior art]
In an internal combustion engine, an exhaust purification catalyst (three-way catalyst) is disposed on an exhaust passage to purify exhaust gas, and an air-fuel ratio is detected by an air-fuel ratio sensor provided in the exhaust passage. By performing the feedback control as described above, nitrogen oxide NOx, carbon monoxide CO, and hydrocarbon HC are simultaneously reduced. In order to further improve the purification rate of the exhaust gas discharged from the internal combustion engine, it is effective to perform the above-described feedback control with high accuracy. At present, the state of the exhaust gas is determined by detecting the concentration of oxygen in the exhaust gas flowing out of the exhaust purification catalyst using an air-fuel ratio sensor installed downstream of the exhaust purification catalyst.
[0003]
[Patent Document 1]
JP-A-10-184424
[Patent Document 2]
JP 2001-140686 A
[0004]
[Problems to be solved by the invention]
However, the conventional control as described above detects only whether the exhaust air-fuel ratio flowing out of the exhaust gas purification catalyst is rich or lean, and detects the amount (concentration) of the specific component to be purified in the exhaust gas. ) Was not detected or estimated. By estimating the emission amount (concentration) of the specific component to be purified, more effective exhaust gas purification control and fuel efficiency control can be performed. Therefore, the present inventors have estimated the specific components inside and downstream of the exhaust purification catalyst using a mathematical model using a mathematical model.
[0005]
An object of the present invention is to improve the estimation accuracy of a mathematical model when controlling an internal combustion engine based on the estimation using a mathematical model as described above. Further, inside the exhaust purification catalyst, the situation may be different between the upstream side and the downstream side. For example, it is known that the purification rate is improved by utilizing the oxygen storage function of the exhaust purification catalyst (Patent Documents 1 and 2), but the distribution of oxygen storage inside the exhaust purification catalyst has an upstream side and a downstream side. And may vary. According to the present invention, it is also possible to estimate the state inside the exhaust purification catalyst (such as the distribution described above), so that it is possible to perform more advanced internal combustion engine control.
[0006]
[Means for Solving the Problems]
The present invention provides a method for controlling the amount of specific components contained in exhaust gas downstream of an exhaust purification catalyst based on an exhaust air-fuel ratio of exhaust gas flowing into an exhaust purification catalyst disposed on an exhaust passage of an internal combustion engine. Estimating means based on a mathematical model, a specific component detection sensor that detects a specific component disposed downstream of the exhaust gas purification catalyst, and an exhaust air-fuel ratio downstream of the exhaust gas purification catalyst on the rich side and lean side. And rich / lean setting means for forcibly vibrating. Here, the estimating means calculates a predetermined constant used in the mathematical model based on the detection result detected by the specific component detection sensor while forcibly vibrating the exhaust air-fuel ratio by the rich / lean setting means, It is characterized by estimating the estimated value by a mathematical model using the obtained constant.
[0007]
In the present invention, “the emission amount of at least one specific component contained in the exhaust gas” may include “at least one representative value indicating the state of the exhaust gas”. As an example of “at least one representative value indicating the state of the exhaust gas”, a representative value (lean component value) that generally indicates the amounts of a plurality of specific components contained in the exhaust gas when the exhaust air-fuel ratio is lean or rich And rich component values). Further, it goes without saying that the “discharge amount” in the present invention includes the discharge amount represented as “concentration”.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the configuration of the control device of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an internal combustion engine in which the control device of the present embodiment is incorporated.
[0009]
The control device according to the present embodiment controls an engine 1 that is an internal combustion engine. The engine 1 is a multi-cylinder engine, but here, only one of the cylinders is shown as a sectional view. As shown in FIG. 1, the engine 1 generates a driving force by igniting an air-fuel mixture in each cylinder 3 with a spark plug 2. During combustion of the engine 1, air taken in from the outside passes through the intake passage 4, is mixed with fuel injected from the injector 5, and is taken into the cylinder 3 as a mixture. The interior of the cylinder 3 and the intake passage 4 are opened and closed by an intake valve 6. The air-fuel mixture burned inside the cylinder 3 is exhausted to the exhaust passage 7 as exhaust gas. The interior of the cylinder 3 and the exhaust passage 7 are opened and closed by an exhaust valve 8.
[0010]
On the intake passage 4, a throttle valve 9 for adjusting the amount of intake air taken into the cylinder 3 is provided. The throttle valve 9 is connected to a throttle position sensor 10 for detecting the opening degree. The throttle valve 9 is connected to a throttle motor 11 and is opened and closed by a driving force of the throttle motor 11. An accelerator position sensor 12 for detecting an operation amount of an accelerator pedal (accelerator opening) is also provided near the throttle valve 9. That is, an electronically controlled throttle system for electronically controlling the opening of the throttle valve 9 is employed. Further, an air flow meter 13 for detecting the amount of intake air is mounted on the intake passage 4.
[0011]
In the vicinity of the crankshaft of the engine 1, a crank position sensor 14 for detecting the position of the crankshaft is attached. From the output of the crank position sensor 14, the position of the piston 15 in the cylinder 3 and the engine speed NE can also be obtained. The engine 1 is also provided with a knock sensor 16 for detecting knocking of the engine 1 and a water temperature sensor 17 for detecting the temperature of cooling water.
[0012]
An exhaust purification catalyst 19 is provided on the exhaust passage 7. A plurality of exhaust purification catalysts may be provided on the exhaust passage. In this case, a plurality of exhaust purification catalysts may be provided in series, or a plurality of exhaust purification catalysts may be provided in parallel at the branch portion. For example, for a four-cylinder engine, one exhaust purification catalyst is installed at a location where the exhaust pipes of two cylinders are integrated into one, and a location where the exhaust pipes of the remaining two cylinders are integrated. There is a case where another exhaust gas purification catalyst is installed in the vehicle. In the present embodiment, one exhaust gas purifying catalyst 19 is provided downstream of a location where exhaust pipes for each cylinder 3 are united.
[0013]
The ignition plug 2, the injector 5, the throttle position sensor 10, the throttle motor 11, the accelerator position sensor 12, the air flow meter 13, the crank position sensor 14, the knock sensor 16, the water temperature sensor 17, and other sensors are integrated with the engine 1. The ECU 18 is connected to an electronic control unit (ECU) 18 that performs control, and is controlled based on a signal from the ECU 18 or sends a detection result to the ECU 18. A catalyst temperature sensor 21 for measuring the temperature of the exhaust gas purification catalyst 19 disposed on the exhaust passage 7, a purge control valve 24 for purging the evaporated fuel in the fuel tank collected by the charcoal canister 23 onto the intake passage 4. Are also connected to the ECU 18.
[0014]
Further, the ECU 18 is also connected to an air-fuel ratio sensor 25 mounted on the upstream side of the exhaust purification catalyst 19 and a specific component detection sensor 26 mounted on the downstream side of the exhaust purification catalyst 19. The air-fuel ratio sensor 25 detects the exhaust air-fuel ratio from the oxygen concentration in the exhaust gas at the mounting position. As the air-fuel ratio sensor 25, a linear air-fuel ratio sensor that linearly detects the exhaust air-fuel ratio is used, or an oxygen sensor that detects the exhaust air-fuel ratio on-off. In addition, since the air-fuel ratio sensor 25 cannot perform accurate detection unless the temperature becomes equal to or higher than a predetermined temperature (activation temperature), the power supplied via the ECU 18 is increased so that the temperature is quickly raised to the activation temperature. Temperature.
[0015]
The specific component detection sensor 26 detects the concentration (discharge amount) of the specific component in the exhaust gas at the mounting position. In the present embodiment, O2, NO, CO, and HC are handled as specific components. That is, the specific component detection sensor 26 is a sensor in which the function of detecting these concentrations is integrated. The specific component detection sensor 26 may have an activation temperature similarly to the air-fuel ratio sensor 25. In this case, the temperature is increased by electric power supplied through the ECU 18.
[0016]
The ECU 18 has a CPU for performing calculations therein, a RAM for storing various amounts of information such as calculation results, a backup RAM for storing the stored contents by a battery, a ROM for storing each control program, and the like. The ECU 18 controls the engine 1 based on the air-fuel ratio and calculates the amount of oxygen stored in the exhaust purification catalyst 19. The ECU 18 also calculates the amount of fuel injected by the injector 5, controls the ignition timing of the spark plug 2, and performs model correction and sensor diagnosis, which will be described later. That is, the ECU 18 controls the engine 1 based on the detected exhaust air-fuel ratio, the calculated oxygen storage amount, and the like.
[0017]
As described above, in the present invention, the emission amount (or a representative value representing the state of the exhaust gas) of a specific component contained in the exhaust gas flowing out of the exhaust purification catalyst is estimated using a mathematical model. The exhaust gas purification performance is improved by performing air-fuel ratio control so that the estimated value is set to a predetermined target state. Here, a method of estimating the emission amount of a specific component contained in the exhaust gas (or a representative value representing the state of the exhaust gas) is referred to as a catalyst model. In the catalyst model according to the present embodiment, the above-described emission amount and the representative value are estimated in consideration of the oxygen storage effect of the exhaust purification catalyst.
[0018]
First, the oxygen storage effect of the exhaust purification catalyst (hereinafter, also simply referred to as a catalyst) 19 will be briefly described, and then a catalyst model will be described.
[0019]
As shown in FIG. 2, the catalyst 19 is a three-way catalyst called a columnar monolith catalytic converter having an elliptical cross section (constant cross-sectional area is dA). As shown in FIG. 3 which is a cut-away enlarged sectional view, the inside is subdivided into an axial space extending in the axial direction by a carrier 19a made of cordierite which is a kind of ceramic. Each axial space has a substantially square shape when cut along a plane perpendicular to the axis, and is also called a cell. The carrier 19a is coated with an alumina coat layer 19b. The coat layer 19b is composed of an active component (catalyst component) made of a noble metal such as platinum (Pt) and ceria (CeO).₂) Is carried.
[0020]
This catalyst 19 oxidizes unburned components (HC, CO) and reduces nitrogen oxides (NOx) when the air-fuel ratio of the inflowing exhaust gas is a stoichiometric air-fuel ratio (this is referred to as a "catalytic function" or (Referred to as “redox function”). The catalyst 19 has the property of storing (storing and adsorbing) and releasing oxygen molecules in the inflowing exhaust gas (oxygen storage function) by supporting the above-mentioned components such as ceria. With the function, HC, CO and NOx can be purified even if the air-fuel ratio deviates to some extent from the stoichiometric air-fuel ratio. That is, when the exhaust gas flowing lean and the exhaust air-fuel ratio contains a large amount of excess oxygen and nitrogen oxide NOx, the catalyst 19 stores excess oxygen and deprives the nitrogen oxide NOx of oxygen. Oxygen is stored (by reducing NOx), thereby purifying NOx. Further, when the exhaust gas having a rich exhaust air-fuel ratio and a large amount of unburned components such as hydrocarbon HC and carbon monoxide CO are contained in the exhaust gas that flows in, the catalyst 19 removes oxygen molecules occluded therein. It is given to the unburned components to oxidize the unburned components, thereby purifying HC and CO.
[0021]
Therefore, if the catalyst 19 has stored oxygen to the extent that it can store oxygen, oxygen cannot be stored when the exhaust air-fuel ratio becomes lean, so that it is possible to contribute to NOx purification using the oxygen storage function. Disappears. On the other hand, if the exhaust air-fuel ratio becomes rich, oxygen cannot be released unless the catalyst 19 has completely released oxygen and does not occlude oxygen at all, contributing to HC and CO purification using the oxygen storage function. become unable. For this reason, even if the air-fuel ratio of the exhaust gas flowing into the catalyst 19 becomes transiently lean or rich, the oxygen storage amount is accurately estimated so that the components to be purified can be sufficiently purified. In addition, it is desirable to perform air-fuel ratio control so as to maintain the oxygen storage amount at a predetermined value.
[0022]
When exhaust gas with a lean air-fuel ratio flows into the catalyst 19, more oxygen is stored upstream of the catalyst 19, and when exhaust gas with a rich air-fuel ratio flows into the catalyst 19, the oxygen upstream of the catalyst 19 is increased. The oxygen stored from the side is consumed. Therefore, if the total amount of oxygen storage from the most upstream position of the catalyst 19 to an arbitrary position is estimated and the air-fuel ratio control is performed based on the estimated value, the oxygen storage becomes exhausted or the oxygen storage becomes full. This makes it easier to avoid situations in which the As a result, even if there is an unavoidable control delay in the control of the air-fuel ratio, more effective exhaust gas purification can be performed.
[0023]
Here, if the emission amount (concentration) of the specific component can be estimated by the above-described catalyst model, the emission of the specific component can be suppressed with high accuracy by performing the air-fuel ratio control based on the estimated value. The control device of the present embodiment improves the exhaust purification performance by using a catalyst model described later and the above-described control on the oxygen storage amount. Therefore, the emission amount (concentration) and the oxygen storage amount of the specific component are estimated.
[0024]
Hereinafter, the catalyst model will be described.
[0025]
As shown in FIG. 4, the catalyst 19 is divided into a plurality of regions (also referred to as “blocks”) by a surface orthogonal to the axis from the inflow side Fr to the outflow side Rr of the exhaust gas. That is, the catalyst 19 is divided into a plurality of regions along the flow direction of the exhaust gas. The length in the axial direction of each of the divided regions is L (also referred to as a minute length dx). As described above, the cross-sectional area of the catalyst 19 is constant at dA. Note that this catalyst model is a model constructed by dividing the catalyst into a plurality of regions. However, by considering the entire catalyst as one region described below, the catalyst 19 can be divided without dividing the catalyst 19 into a plurality of regions. You can also build models.
[0026]
Next, attention is paid to an arbitrary specific region among the divided regions, and the balance of a specific component (specific chemical species) passing through the specific region is considered. The chemical species is a component contained in the exhaust gas.₂, Carbon monoxide CO, hydrocarbon HC, and nitrogen oxide NOx. The chemical species is a sum of components contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is rich (rich component), or the air-fuel ratio of the exhaust gas flowing into the catalyst is lean. In this case, the component contained in the exhaust gas may be integrated (lean component).
[0027]
Various values used in the present catalyst model are defined as in the following [Table 1].
[0028]
[Table 1]

[0029]
Now, considering the balance of chemical species in a specific region in a given period from time t to t + Δt, as shown in FIG. 5, an exhaust gas phase in a specific region (also simply referred to as an “exhaust gas phase”). The amount of change ΔM of the chemical species at the time is calculated from the “amount Min of the chemical species flowing into the specific region” to the “amount Mout of the chemical species flowing out” and the “transmission amount to the coat layer” as shown in the following equation (1). The amount of the applied chemical species Mcoat "is subtracted. As described above, the catalyst model is constructed based on the material balance of the specific component in the specific region.
[0030]
(Equation 1)

[0031]
Hereinafter, each term of the equation (1) will be individually examined. First, the variation ΔM of the chemical species on the left side of the equation (1) can be obtained by the following equation (2). The expression (2) is obtained by multiplying the concentration change amount of the chemical species (the amount obtained by integrating the time change amount of the concentration Cg of the chemical species over the period Δt) by the minute volume σ · dA · dx in the above-mentioned period Δt in the specific region. Is integrated in the axial direction.
[0032]
(Equation 2)

[0033]
Min of the first term on the right side of the equation (1) is a value Cgin · vgin · obtained by multiplying the volume vgin · dA of the exhaust gas flowing into the specific region per unit time by the concentration Cgin of the chemical species in the flowing exhaust gas. This is a value obtained by integrating dA over the period t → t + Δt. Here, the “volume vgin · dA of the exhaust gas flowing into the specific region per unit time” is a product of the “flow velocity vgin of the exhaust gas flowing into the specific region” and the “cross-sectional area dA of the specific region”. Actually, since the exhaust gas having the flow rate vgin flows into the catalyst having the cross-sectional area dA and the opening ratio σ, the flow rate of the exhaust gas inside the catalyst becomes vgin / σ. It is obtained as the product of the substantial exhaust gas passage cross section σ · dA.
[0034]
Further, Mout of the second term on the right side of the equation (1) is a value Cgout · obtained by multiplying the volume vgout · dA of the exhaust gas flowing out of the specific area per unit time by the concentration Cgout of the chemical species in the exhaust gas flowing out. This is a value obtained by integrating vgout · dA over the period t → t + Δt. Here, the “volume vgout · dA of the exhaust gas flowing out of the specific area per unit time” is a product of the “flow velocity vgout of the exhaust gas flowing out of the specific area” and the “cross-sectional area dA of the specific area”. Actually, it is the product of the exhaust gas flow rate vgout / σ and the substantial exhaust gas passage sectional area σ · dA. That is, the first and second terms on the right side of the above equation (1) can be described as the following equation (3).
[0035]
(Equation 3)

[0036]
By the way, since there is no significant difference between the flow rate vgin of the exhaust gas flowing into the specific area and the flow rate vgout of the exhaust gas flowing out of the specific area, if vg = vgin = vgout, the equation (3) becomes It is transformed as in equation 4).
[0037]
(Equation 4)

[0038]
Next, the amount Mcoat of the chemical species transmitted (moved) to the coat layer in the third term on the right side of the equation (1) will be examined. Since the geometric surface area Sgeo is a surface area that contributes to the transfer of chemical substances and heat per unit volume of the catalyst, the surface area that contributes to the transfer from the exhaust gas phase to the coat layer in a specific region is Sgeo · dA · dx. And the mass transfer contribution area per unit length of the specific region is Sgeo · dA. Further, the amount of the chemical species transmitted to the coat layer can be considered to be proportional to the difference between the concentration Cg of the chemical species in the exhaust gas phase and the concentration Cw of the chemical species in the coat layer from Fick's law. From these, the following equation (5) is obtained. Note that h_DIs a proportionality constant, and as shown in Table 1, is a value called a mass transfer rate.
[0039]
(Equation 5)

[0040]
Therefore, from the above equations (1), (2), (4) and (5), the following equation (6) is obtained.
[0041]
(Equation 6)

[0042]
When a quasi-state approximation is applied to the equation (6), the left side of the equation (6) can be considered to be “0” (∂Cg / ∂t = 0) (that is, the concentration Cg is instantaneous). (It is considered that the steady state value is reached) in the following manner.
[0043]
(Equation 7)

[0044]
Here, the apparent diffusion rate (substantial diffusion rate) R_DIs written as the following equation (8), the equation (7) is rewritten as the equation (9).
[0045]
(Equation 8)

(Equation 9)

[0046]
Next, considering the balance of the chemical species (the material balance of the specific component) in the coat layer in the specific region in the same manner as described above, the time change amount of the chemical species in the coat layer as shown in the following equation (10) (Change per unit time) ΔMc is the amount of chemical species consumed by the reaction in the coat layer per unit time from the amount Md of chemical species transferred from the exhaust gas phase to the coat layer per unit time. It is an amount obtained by subtracting Mr.
[0047]
(Equation 10)

[0048]
The left side of the equation (10) (the amount of temporal change of the chemical species in the coat layer) △ Mc is, as shown in the following equation (11), the volume change of the chemical species concentration change (∂Cw / ∂t) 1−σ) · dA · dx), and the first term on the right-hand side (the amount Md of chemical species transferred from the exhaust gas phase to the coat layer per unit time) is the reason explained by the equation (5). For the same reason as above, that is, considering Fick's law, it can be described as the following equation (12).
[0049]
(Equation 11)

(Equation 12)

[0050]
The second term on the right side of the equation (10) (the amount Mr of the chemical species consumed by the reaction in the coat layer per unit time) is expressed by the following equation (13) using the consumption rate R of the chemical species in the coat layer. Required by
[0051]
(Equation 13)

[0052]
Therefore, the following expression (14) is obtained from the expressions (10) to (13).
[0053]
[Equation 14]

[0054]
When the quasi-state approximation is applied to the equation (14) (∂Cw / ∂t = 0), the following equation (15) is obtained.
[0055]
[Equation 15]

[0056]
Here, if the equation (8) is applied to the equation (15), the following equation (16) is obtained.
[0057]
(Equation 16)

[0058]
To summarize the above, equations (9) and (16) are the basic equations of the catalyst model. Equation (9) indicates that the “inflow amount into a specific region” of a certain chemical species and the “diffusion amount from the exhaust gas phase into the coat layer + the outflow amount from the specific region” are balanced, and (16) The equation shows that the “diffusion amount of the chemical species from the exhaust gas phase to the coat layer” and the “consumption amount in the coat layer” are balanced.
[0059]
Next, a method for actually calculating the concentration Cgout of the specific chemical species i flowing out of the specific region using the above-described catalyst model will be described. First, when the equation (9) is discretized, the following equation (17) is obtained. In the following, the above dx is represented as L.
[0060]
[Equation 17]

[0061]
Here, as conceptually shown in FIG. 6, the concentration Cgout of the chemical species flowing out of the specific region I is considered to be strongly influenced by the concentration Cg (I) of the chemical species in the specific region I. Equation (18) can be used.
[0062]
(Equation 18)

This concept is called the "windward method." That is, the windward method is based on the idea that "chemical species having a concentration Cg (I-1) in the upstream region (I-1) adjacent to the specific region I flow into the specific region I". Expression (19) can also be described.
[0063]
[Equation 19]

[0064]
By the way, based on the reaction kinetics, the consumption rate R of a certain chemical species is a function fcw of the average concentration Cw of the chemical species in the coat layer (for example, the nth power of CW). If fcw (x) = x is set for simplicity, the consumption speed R can be expressed as the following equation (20). In the following, R * in equation (20) is referred to as “consumption rate constant” for convenience.
[0065]
(Equation 20)

[0066]
When this equation (20) is applied to the above equation (16), the following equation (21) is obtained. By modifying the equation (21), the following equation (22) is obtained.
[0067]
(Equation 21)

(Equation 22)

[0068]
Further, according to the above-mentioned upwind method, since Cg = Cgout, the expression (22) can be rewritten into the following expression (23).
[0069]
(Equation 23)

[0070]
Then, the relationship Cg = Cgout is applied to the above equation (17) to eliminate Cg, and when Cw is eliminated from the equation (17) and the above equation (23), the following equation (24) is obtained.
[0071]
[Equation 24]

[0072]
Therefore, if the value SP is set as in the following equation (25), the equation (24) can be rewritten as the equation (26). The value SP is the apparent diffusion rate R_DAnd the consumption rate constant R * are values that are strongly affected by the smaller value of Cgout._D) Or a chemical reaction (R *), which can be referred to as a “reaction-limiting factor”.
[0073]
(Equation 25)

(Equation 26)

[0074]
From the above, the consumption rate constant R * and the apparent diffusion rate R_DIs determined, the concentration Cgout of the chemical species flowing out of the specific area can be obtained based on the equations (25) and (26) by giving the chemical species concentration Cgin flowing into the specific area. The above is the basic idea of calculating the concentration Cgout of the chemical species.
[0075]
In the air-fuel ratio control of the present embodiment, the internal combustion engine control (air-fuel ratio control) is performed based on the “concentration Cgout of the specific component (chemical species) flowing out of the specific region” calculated using the catalyst model as described above. . A target value is set for this Cgout, and fuel is injected so that the air-fuel ratio becomes such that Cgout becomes this target value. At this time, if the specific region is first set on the most upstream side of the catalyst 19, the concentration Cgin of the specific component flowing into the specific region can be detected by the air-fuel ratio sensor 25 set on the upstream side of the catalyst 19. If Cgout is calculated based on this Cgin, this Cgout becomes a Cgin of a specific region one downstream side. By sequentially calculating in this manner, the state of the catalyst 19 can be grasped in detail (such as the distribution of the concentration Cw of the specific component in the coating layer of the catalyst 19 in the flow direction), and the specific state finally discharged from the catalyst 19 can be determined. The concentrations (emissions) of the components are also determined more accurately.
[0076]
The Cgout (Cgout, CO.Cgout, NO.Cgout, HC) for CO, NO (NOx), and HC, which are components to be purified in the exhaust gas, is estimated, and the amount (concentration) of these emissions is determined by the catalyst 19. , The exhaust gas purification performance can be improved. When the purifying performance is to be further improved by utilizing the oxygen storage amount of the catalyst 19, O₂Cgout (Cgout, O₂If the distribution is obtained by obtaining the above (2) inside the catalyst, the exhaust gas purifying performance can be improved by using the oxygen storage function more effectively.
[0077]
In order to calculate Cgout from Cgin using the catalyst model, as described above, the consumption rate constant R * and the apparent diffusion rate R_DAnd need to decide. First, the diffusion rate R_D, As can be seen from equation (8), R_D= Sgeo · h_DIt is. As shown in [Table 1], Sgeo is a fixed value of the catalyst 19,_DIs h_DDepends on h_D
Is different for each specific component (chemical species) and depends on the temperature of the catalyst 19, as shown in [Table 1]. Therefore, the diffusion speed R_DIs determined in advance as a function of the catalyst temperature Temp by performing an experiment or the like, and is mapped and stored in the ROM in the ECU 18.
[0078]
On the other hand, the consumption rate constant R * is calculated and updated in the control device during control, and the calculated and updated value is used. As described above, by calculating and updating the consumption rate constant R * based on the detection result in the actual control system, the control accuracy can be further improved. Hereinafter, a method of determining the consumption rate constant R * will be described.
[0079]
First, Cgout for the specific region I on the most downstream side of the catalyst 19 (or it can be grasped as the entire catalyst 19) is obtained. At this time, since the consumption rate constant R * has not yet been determined (and the Cgout on one upstream side has not been calculated), it is naturally impossible to calculate Cgout using the above-described catalyst model. For this reason, the O2 concentration will be described first, but Cgout, O₂Is calculated. At this time, as shown in the following equation (27), O 2 in the exhaust gas on the downstream side of the catalyst 19 is₂The output of the specific component detection sensor 26 for detecting the concentration is used.
[0080]
[Equation 27]

[0081]
In the equation (27), AF-AFstoich is an air-fuel ratio difference indicating a degree of leaning or leaning from the stoichiometric air-fuel ratio, and a mass flow rate of air can be obtained by multiplying the difference by the supplied fuel amount Gf. Further, by multiplying the mass of air by the weight ratio of oxygen in the air of 0.23, an excess or insufficient oxygen amount can be obtained. That is, this is the amount of oxygen emission flowing out of the specific region I on the most downstream side of the catalyst 19 (that is, flowing out of the catalyst 19), which is calculated based on actual detection without depending on the catalyst model (mathematical model). It is.
[0082]
In the present embodiment, Cgout, O₂Is calculated by adjusting the fuel injection amount from the injector 5 or the opening of the throttle valve 9 by the ECU 18 to forcibly make the exhaust air-fuel ratio lean. That is, the ECU 18, the injector 5, the throttle valve 9, and the like function as rich / lean setting means. Since NO is also included in the exhaust gas at the time of lean operation, Cgout and NO can be calculated by the same method (using the equation corresponding to the equation (27)). At this time, the specific component detection sensor 26 detects NO.
[0083]
On the other hand, in order to calculate Cgout, CO, Cgout, HC, the specific component detection sensor 26 must detect the CO concentration or the HC concentration. Therefore, in this case, the exhaust air-fuel ratio is forcibly made rich by the above-described rich / lean setting means. Thereafter, Cgout, CO and Cgout, HC are calculated by the same method (using the equation corresponding to the equation (27)). At this time, the specific component detection sensor 26 detects CO and HC. In this manner, Cgout for each specific component of the exhaust gas flowing out from (the specific region I on the most downstream side of) the catalyst 19 was calculated based on the detection result in the actual control system.
[0084]
Next, Cgin is calculated. First, Cgin, O₂Will be described. At this time, the consumption rate constant R * has not yet been determined (and there is no upstream Cgout).₂Cannot be calculated. Therefore, first, Cgin, O with respect to the exhaust gas flowing into the most upstream region of the catalyst 19 (or it can be understood as the whole catalyst 19).₂Is calculated by the following equation (28). At this time, as shown in the following equation (28), the output of the air-fuel ratio sensor 25 that detects the exhaust air-fuel ratio on the upstream side of the catalyst 19 is used.
[0085]
[Equation 28]

[0086]
Briefly describing the introduction process of the above equation (28), the air-fuel ratio AF of the exhaust gas flowing into the catalyst 19 is Ga / Gf, and the air mass required for obtaining the stoichiometric air-fuel ratio with respect to Gf is defined as Gastoich. Then, the stoichiometric air-fuel ratio AFstoich becomes Gastoich / Gf. On the other hand, when the air-fuel ratio becomes AF when the supplied fuel mass is Gf, the excess air mass with respect to the air mass necessary to obtain the ideal air-fuel ratio AFstoich is Ga-Gastoch. In other words, the following equation (29) is obtained, and the above equation (28) is derived from the equation (29).
[0087]
(Equation 29)

[0088]
Cgin, NO · Cgin, CO · Cgin, and HC are estimated based on the maps shown in FIGS. 7 to 9. Here, the most upstream Cgin, NO · Cgin, CO · Cgin, and HC are determined based on the exhaust air-fuel ratio on the upstream side of the catalyst 19, but the parameters of FIGS. Needless to say, it can be used as a map. The parameters at this time include the exhaust gas temperature, the ignition timing, the cooling water temperature, the flow rate of the exhaust gas, the flow rate of the exhaust gas flowing into the catalyst 19 (the amount of intake air detected by the air flow meter 13), and the like. In this manner, Cgout and Cgin for each specific component were calculated based on the detection result in the control system.
[0089]
On the other hand, in this catalyst model, it is assumed that the three-way reaction, which is an oxidation / reduction reaction in the catalyst, is completed instantaneously and completely, and as a result, attention is paid to the oxygen storage / release reaction based on excess / deficiency of oxygen. Then, the above-mentioned specific component (chemical species i) is defined as a storage agent and a reduction agent as follows. For example, oxygen 0₂Species (storage agents) that produce oxygen (produce oxygen), like nitrogen monoxide NO, which is one of nitrogen oxides, and consume oxygen like carbon monoxide CO and hydrocarbon HC It is a chemical species (reduction agent).
[0090]
Apparent diffusion of Cgout of chemical species i of the storage agent, Cgout, sto, i, Cw of chemical species i of Cw, sto, i, and Cgin of chemical species i of Cgin, stor, i, and chemical species i Speed R_DTo R_D, I, the consumption rate of the same species i is represented by Rstor, i, the consumption rate constant of the same species i is represented by R * stor, i, and the reaction-limiting factor of the same species i is represented by SPstor, i (in this case, Species i is O₂Or NO). Similarly, Cgout of the species i of the reduction agent is Cgout, reduc, i, Cw of the species i is Cw, reduc, i, and Cgin of the species i is Cgin, reduc, i, and Apparent diffusion rate R_DTo R_D, I, the consumption rate of the same species i is Rreduc, i, the consumption rate constant of the same species i is R * reduc, i, and the reaction-limiting factor SPreduc, i of the same species i (in this case, the species i Represents CO or HC). Expressing each value in this way, from the above equations (20), (23), (25), and (26), the following equations (30) to (33) and (33) for each storage agent and reduction agent are used. Expressions 34) to (37) are obtained.
[0091]
[Equation 30]

(Equation 31)

(Equation 32)

[Equation 33]

[0092]
[Equation 34]

(Equation 35)

[Equation 36]

(37)

[0093]
Here, the specific component is O₂In the above-mentioned equations (33) and (32), Cgout, stor, i are calculated by using equation (27) as Cgout, stor, i.₂Is applied to Cgin, stor, i, and Cgin, O flowing into the catalyst 19 calculated using the equation (28).₂And the diffusion rate R previously determined as a function of the temperature of the catalyst 19_DO₂Is applied, the consumption rate constant R * O₂Can be calculated. Similarly, regarding the case where the specific component is NO, Cgout, NO flowing out of the catalyst 19 calculated by using the equation (27) corresponding to the equation (27) in the equations (33) and (32). Is applied, Cgin, NO flowing into the catalyst 19 obtained from FIG. 7 is applied to Cgin, sto, i, and the diffusion rate R determined in advance as a function of the temperature of the catalyst 19 is calculated._DBy applying NO, the consumption rate constant R * NO can be calculated.
[0094]
Further, as for the case where the specific component is CO, Cgout, CO flowing out of the catalyst 19 calculated by using the equation (27) corresponding to Cgout, reduc, i in the above equations (37) and (36). Applying Cgin, CO flowing into the catalyst 19 obtained from FIG. 8 to Cgin, reduc, i, the diffusion rate R previously determined as a function of the temperature of the catalyst 19_DBy applying CO, the consumption rate constant R * CO can be calculated. Similarly, in the case where the specific component is HC, Cgout, HC flowing out of the catalyst 19 calculated by using the equation (27) corresponding to the equation (27) in the equations (37) and (36). Is applied, and Cgin, HC flowing into the catalyst 19 obtained from FIG. 9 is applied to Cgin, reduc, i, and the diffusion rate R determined in advance as a function of the temperature of the catalyst 19 is calculated._DBy applying HC, the consumption rate constant R * HC can be calculated.
[0095]
Thus, the consumption rate constant R * for each specific component has been calculated, so that Cgout for each specific component can be calculated in order from the specific region I on the upstream side of the catalyst 19 to the downstream side. At this time, the following equation (24) or equivalent equations (25) and (26) [= (32), (33) / (36), (37)] in the above-described catalyst model are used in this order. calculate. In addition, by using the equation (23) [= (31) / (35)], the concentration of the specific component in the coat layer inside the catalyst 19 can also be calculated. As a matter of course, Cgin for the specific region I on the most upstream side uses the value obtained from the equation (28) and the maps in FIGS. 7 to 9. And Cgin of a certain specific region is Cgout in the specific region one upstream side.
[0096]
As described above, the consumption rate constant R * is calculated based on the detection result in the actual control system, and the state of the catalyst 19 is grasped in detail using a mathematical model (catalyst model) using the consumption rate constant R *. Thus, the ability of the catalyst 19 can be more effectively utilized. As a result, in the present embodiment, a target value is set for Cgout of each specific component that finally flows out of the catalyst 19 (that is, flows out of the specific region I on the most downstream side), and each Cgout is set to the target value. The air-fuel ratio control for adjusting the fuel injection amount and the intake air amount is performed so that
[0097]
For example, the smaller the emissions of nitrogen oxides NOx, carbon monoxide CO, and hydrocarbons HC, the better. Therefore, a target is set for reducing Cgout, NO, Cgout, CO, C, Cgout, and HC flowing out of the catalyst 19 to zero. It is also conceivable to set a target such that the purification of non-zero components of Cgout, NO, Cgout, CO, Cgout, and HC for each specific region I inside the catalyst proceeds. For example, when Cw and HC in a specific region I are high, a target may be set such that Cgout and NO in the specific region (I-1) one upstream side are increased to oxidize the Cw and HC. Conceivable.
[0098]
Furthermore, as described above, in order to improve the purification performance of the catalyst 19, the oxygen storage function of the catalyst 19 may be used. The oxygen storage density Ost of the catalyst 19 may have a distribution in the catalyst. By more efficiently grasping and controlling the state of the oxygen storage density Ost inside the catalyst 19, the exhaust gas purification performance can be further improved. In this case, it is conceivable to set the oxygen storage density Ost as the control target without setting Cgout as the control target. This will be described below.
[0099]
As described above, the expressions (30) to (33) and the expressions (34) to (37) are obtained for each storage agent and reduction agent, focusing on the occlusion / release of oxygen of the catalyst 19. Based on these equations, Cgout, sto, i (specifically, the concentration of oxygen Cgout, 0₂, Concentration of nitric oxide flowing out of the specific region Cgout, NO) and Cgout, reduc, i (specifically, concentration of carbon monoxide flowing out of the specific region Cgout, CO, concentration of hydrocarbon flowing out of the specific region) Cgout, HC) can be obtained for each specific region as described above. Further, as described above, the consumption rate constants R * stor, i and R * reduc, i for each specific component are also determined as described above when calculating Cgout for each specific region.
[0100]
According to the reaction kinetics, the rate at which oxygen is occluded in the coat layer in a specific region (oxygen occlusion rate) Rstor, i is “storage agent (0₂, NO, etc.) concentration Cw, sto, i (eg, Cw, 0)₂, Cw, NO) and the difference between the maximum oxygen storage density Ostmax of the coat layer in the specific region and the actual oxygen storage density Ost (Ostmax−Ost). Function f2 (Ostmax−Ost) ”. The difference between the maximum oxygen storage density Ostmax and the oxygen storage density (Ostmax-Ost) indicates the oxygen storage allowance in the specific region of interest. Therefore, if the function f1 (x) = f2 (x) = x for simplicity, the following equation (38) is obtained.
[0101]
[Equation 38]

[0102]
In Equation (38), kstor, i is an oxygen storage rate coefficient (storage side reaction rate coefficient, storage agent consumption rate coefficient), and varies depending on the temperature expressed by the well-known Arrhenius equation. It is a coefficient and can be obtained as a function of the catalyst temperature Temp that is separately detected (estimated) (or from a map that defines the relationship between the oxygen storage rate coefficient kstor, i and the catalyst temperature Temp). It should be noted that the oxygen storage rate coefficient kstor, i changes depending on the degree of catalyst deterioration, and thus may be obtained according to the degree of catalyst deterioration. Therefore, from the equations (30) and (38), the consumption rate constant R * stor, i is calculated by the following equation (39) using the difference between the maximum oxygen storage density Ostmax and the oxygen storage density (Ostmax−Ost). It can also be expressed as
[0103]
[Equation 39]

[0104]
In this model, which focuses on the occlusion (adsorption) and release of oxygen, the reduction agent, which is a reducing agent, is used only to release the oxygen stored in the coat layer. The consumption speed Rredcu, i is equal to the speed (releasing speed of oxygen) Rrel, i at which the oxygen stored in the coat layer is released. Considering the oxygen release rate Rrel, i, the release rate Rrel, i is calculated based on the reaction kinetics, as in the case of the oxygen storage rate Rstor, i. , CO, HC) in proportion to the value of the function g1 (Cw, reduc, i) of the concentration Cw, reduc, i (for example, Cw, CO, Cw, HC) and the “function g2 (oxygen storage density Ost) g2 ( Ost) ". Then, if the function g1 (x) = g2 (x) = x for simplicity, the following equation (40) is obtained.
[0105]
(Equation 40)

[0106]
Krel, i in the equation (40) is an oxygen release rate coefficient (removal rate coefficient on the desorption side, consumption rate coefficient of the reduction agent), and is represented by an Arrhenius equation like the oxygen storage rate coefficient kstor, i. A coefficient that varies depending on the temperature, and is obtained as a function of the separately detected (estimated) catalyst temperature Temp (or from a map that defines the relationship between the oxygen release rate coefficient krel, i and the catalyst temperature Temp). be able to. Since the oxygen release rate coefficient krel, i changes depending on the degree of catalyst deterioration, it may be determined according to the degree of catalyst deterioration. As a result, as described above, the consumption rate Rredc, i of the reduction agent is equal to the oxygen release rate Rrel, i of the coat layer. Therefore, the consumption rate constant R * reduc, i is given by the equations (34) and (40). Therefore, using the oxygen storage density Ost, the following equation (41) can be used.
[0107]
(Equation 41)

[0108]
Equations (39) and (41) show the relationship between the consumption rate constant R * and the oxygen storage density Ost. Here, paying attention to the balance of oxygen as a chemical species in the coat layer, since this balance of oxygen is the difference between the amount of oxygen absorbed and the amount of released oxygen in the coat layer, it is described by the following equation (42). You. In the equation (42), dA · L is the volume dV of the specific area. Further, when the following equation (42) is modified, the following equation (43) is obtained.
[0109]
(Equation 42)

[Equation 43]

[0110]
When the equation (43) is discretized using the equations (38) and (40), the following equation (44) is obtained. By transforming the equation (44), the following equations (45) to (47) are obtained, from which the oxygen storage density Ost can be updated.
[0111]
[Equation 44]

[Equation 45]

[Equation 46]

[Equation 47]

[0112]
As described above, the oxygen storage density Ost can be calculated based on the catalyst model using the equations (45) to (47). Further, based on the oxygen storage density Ost, the oxygen storage amount OSA can be calculated using the following equation (48).
[0113]
[Equation 48]

[0114]
Therefore, when the chemical species concentration Cgin, i flowing into the catalyst is given as a boundary condition, the oxygen storage amount OSA of each block is sequentially obtained from the block (specific region) upstream of the catalyst using the equation (45). Thereby, the distribution of the oxygen storage amount inside the catalyst is accurately estimated. Further, if the oxygen storage amount OSA of each block is integrated for the entire catalyst, the oxygen storage amount of the entire catalyst can be accurately estimated. By controlling Cgin, Cgout, and Cw in order to set the oxygen storage amount OSA (oxygen storage density Ost) for each specific region to a desired state, it is possible to further improve exhaust gas purification performance.
[0115]
For example, as a result of the continuous flow of the rich exhaust gas, in the region on the upstream side of the catalyst 19, the O stored in the catalyst 19 to oxidize the CO and HC in the rich exhaust gas.₂Is consumed. If the amount of consumption is large, there is a concern that purification may not be sufficiently performed when richer exhaust gas flows. In such a case, it is conceivable to perform control to suppress a decrease in the oxygen storage amount OSA (oxygen storage density Ost) in the specific region on the upstream side. Alternatively, in a case where the exhaust air-fuel ratio has already shifted to a lean state, it is conceivable to perform control to recover the decreased oxygen storage amount OSA (oxygen storage density Ost) at an early stage.
[0116]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, when controlling an internal combustion engine based on the estimation using a mathematical model, the estimation accuracy of this mathematical model can be improved. Further, according to the present invention, it is possible to estimate the situation inside the exhaust gas purification catalyst in more detail, so that it is possible to perform more advanced internal combustion engine control.
[Brief description of the drawings]
FIG.
It is a sectional view showing the internal-combustion engine which has an embodiment of a control device of the present invention.
FIG. 2
FIG. 2 is an external view of the exhaust purification catalyst shown in FIG. 1.
FIG. 3
FIG. 3 is a partial sectional view of the exhaust purification catalyst of FIG. 2.
FIG. 4
It is a schematic diagram for explaining the catalyst model (mathematical model) in the present invention.
FIG. 5
It is a schematic diagram for explaining the catalyst model (mathematical model) in the present invention.
FIG. 6
It is a schematic diagram for explaining the upwind method used in the catalyst model (mathematical model) in the present invention.
FIG. 7
4 is a map that defines the relationship between the exhaust air-fuel ratio and the concentration of nitric oxide used to determine the concentration of nitric oxide flowing into the exhaust purification catalyst.
FIG. 8
4 is a map that defines a relationship between an exhaust air-fuel ratio and a carbon monoxide concentration used to determine the concentration of carbon monoxide flowing into the exhaust purification catalyst.
FIG. 9
4 is a map that defines a relationship between an exhaust air-fuel ratio and a hydrocarbon concentration used for determining a hydrocarbon concentration flowing into an exhaust purification catalyst.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 2 ... Spark plug, 3 ... Cylinder, 4 ... Intake passage, 5 ... Injector, 7 ... Exhaust passage, 9 ... Throttle valve, 18 ... ECU (Estimation means, rich / lean setting means), 19: exhaust purification catalyst, 25: air-fuel ratio detection sensor, 26: specific component detection sensor.

Claims (1)

The exhaust air-fuel ratio on the upstream side of the exhaust purification catalyst provided on the exhaust passage of the internal combustion engine or the amount of at least one specific component contained in the exhaust gas on the upstream side of the exhaust purification catalyst; Estimating means for estimating the emission of at least one specific component contained in the purification catalyst and in the exhaust gas on the downstream side based on a mathematical model,
A specific component detection sensor that detects the specific component disposed downstream of the exhaust purification catalyst;
Rich / lean setting means for forcibly oscillating the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst between the rich side and the lean side,
The estimating means calculates and calculates a constant used in the mathematical model based on the detection result detected by the specific component detection sensor while forcibly oscillating the exhaust air-fuel ratio by the rich / lean setting means. The control device for an internal combustion engine, wherein the specific component emission amount is calculated by a mathematical model using the constant.

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