JP4048959B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

【００５５】
いま、時刻ｔ〜ｔ＋Δｔ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８に示したように、特定領域の排ガス相（単に、「ガス相」とも称呼する。）における化学種の変化量ΔMは、下記の(1)式に示したとおり、同特定領域に流入した同化学種の量Minから、同特定領域から流出した同化学種の量Moutと同特定領域のコート層に奪われた同化学種の量Mcoatとを減算した量と等しい。このように、触媒モデルは各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。
【００５６】
【数１】

【００５７】
以下、(1)式の各項について個別に検討する。先ず、(1)式の左辺にある化学種の変化量ΔMは、下記(2)式により求めることができる。(2)式は、上記所与の期間における化学種の濃度変化量（化学種の濃度Cgの時間変化量を所与の期間に渡り積分した量）に微小体積σ・dA・dxを乗じた値を着目しているブロック（特定領域）の全体に渡って軸方向に積分したものである。
【００５８】
【数２】

【００５９】
(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ガスの体積に相当する値である「特定領域に流入する排ガスの流速vginと同特定領域の断面積dAの積vgin・dA（実際には、断面積dAで開口率σの触媒内に流速vginの排ガスが流れ込むので、触媒内部での排ガスの流速はvgin／σとなり、この実際の流速vgin／σと触媒の実質的な断面積σ・dAの積）」に同流入する排ガス中の化学種の濃度Cginを乗じた値Cgin・vgin・dAを所与の期間に渡り積分した値である。また、(1)式の右辺第２項のMoutは、特定領域から流出する排ガスの流速vgoutと同特定領域の断面積dAの積vgout・dA（実際には、排ガスの流速vgout／σと実質的な断面積σ・dAの積）に同流出する排ガス中の前記化学種の濃度Cgoutを乗じた値Cgout・vgout・dAを所与の期間に渡り積分した値である。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。
【００６０】
【数３】

【００６１】
ところで、特定領域に流入する排ガスの流速vginと同特定領域から流出する排ガスの流速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。
【００６２】
【数４】

【００６３】
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反応に寄与する表面積であるから、特定領域において化学種の反応に寄与する表面積はSgeo・dA・dxであり、同特定領域の単位長あたりに同反応に寄与する面積は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、上記の表１に示したように、物質伝達率と称呼される値である。
【００６４】
【数５】

【００６５】
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。
【００６６】
【数６】

【００６７】
この(6)式に準定常（quasi state)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。
【００６８】
【数７】

【００６９】
ここで、見かけの拡散速度（実質的な拡散速度）R_Dを(8)式のようにおけば、(7)式は(9)式に書き直される。
【００７０】
【数８】

【００７１】
【数９】

【００７２】
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)式に示したように、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）ΔMcは、単位時間あたりに排ガス相からコート層へ伝達される同化学種の量Mdから、同単位時間あたりにコート層にて反応により消費される同化学種の量Mrを減じた量である。
【００７３】
【数１０】

【００７４】
(10)式の左辺（コート層内における化学種の時間的変化量）ΔMc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。
【００７５】
【数１１】

【００７６】
【数１２】

【００７７】
また、(10)式の右辺第２項（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）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。
【００７８】
【数１３】

【００７９】
従って、(10)〜(13)式から、下記の(14)式が得られる。
【００８０】
【数１４】

【００８１】
この(14)式に準定常（quasi state)近似を適用すると（∂Cw／∂t＝０）、下記の(15)式が得られる。
【００８２】
【数１５】

【００８３】
ここで、(15)式に(8)式を適用すれば、下記の(16)式が得られる。
【００８４】
【数１６】

【００８５】
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、同化学種の「排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。
【００８６】
次に、かかる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。先ず、(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。
【００８７】
【数１７】

【００８８】
ここで、図９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は同特定領域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。かかる考え方は「風上法」と称呼される。換言すると、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。
【００８９】
【数１８】

【００９０】
【数１９】

【００９１】
ところで、反応速度論に基けば、ある化学種のコート層での消費速度Rは、その化学種のコート層の平均濃度Cwの関数fcw（例えば、Cwのｎ乗に比例する関数）となるので、この関数fcwを最も簡便となるようにCwに比例すると設定すれば、消費速度Rは(20)式にて示したように置くことができる。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。
【００９２】
【数２０】

【００９３】
この(20)式を上記(16)式（R=R_D・(Cg-Cw)…(16)）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。
【００９４】
【数２１】

【００９５】
【数２２】

【００９６】
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。
【００９７】
【数２３】

【００９８】
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。
【００９９】
【数２４】

【０１００】
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*)の何れにより律速されているかを示す値となっており、従って、「反応律速因子」と呼ぶこともできる。
【０１０１】
【数２５】

【０１０２】
【数２６】

【０１０３】
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。また、これにより、次の特定領域に流入する化学種濃度Cginが定まるので、同次の特定領域の化学種の濃度Cgoutを算出することが可能となる。以上が、化学種の濃度Cgoutを算出する触媒モデルの基本的考え方である。
【０１０４】
次に、上記消費速度定数R*と見かけの拡散速度R_Dを決定するとともに、特定領域から流出する化学種濃度Cgoutを求める際のより具体的な方法の一例について説明する。この例（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く酸素の吸蔵・放出反応に着目することとする。なお、この仮定（触媒モデル）は、現実的であり且つ精度の良いものである。
【０１０５】
この場合、着目する化学種ｉは、例えば、酸素Ｏ_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）から選ばれた化学種である。
【０１０６】
また、以下において、ストレージ・エージェントの化学種ｉ（この場合、化学種ｉはＯ_２又はＮＯ等）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。
【０１０７】
同様に、リダクション・エージェントの化学種ｉ（この場合、化学種ｉはＣＯ又はＨＣ等）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と表す。このように各値を表すと、上記(20),(23),(25),(26)式から以下の(27)〜(34)式が得られる。
【０１０８】
【数２７】

【０１０９】
【数２８】

【０１１０】
【数２９】

【０１１１】
【数３０】

【０１１２】
【数３１】

【０１１３】
【数３２】

【０１１４】
【数３３】

【０１１５】
【数３４】

【０１１６】
これらの式に基づいて、Cgout,sotr,i（具体的には、特定領域から流出する酸素の濃度Cgout,O2、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）を求めるため、先ず、消費速度定数R*stor,i及び消費速度定数R*reduc,iを求める。
【０１１７】
ところで、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）であるストレージ・エージェントの消費速度Rstor,iは、同コート層のストレージ・エージェント（Ｏ_２、ＮＯｘ等）の濃度Cw,stor,i（例えば、Cw,O2、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と実際の酸素吸蔵密度との差(Ostmax-Ost)の関数ｆ2(Ostmax-Ost)の値とに比例すると考えられる。この最大酸素吸蔵密度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。
【０１１８】
そこで、簡単のために関数f1(x)＝f2(x)＝xとすると、下記の(35)式が得られる。下記(35)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、別途検出又は推定される触媒温度Tempと所定の関数（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でも良い。）とに基づいて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、同触媒劣化程度に応じて求めてもよい。
【０１１９】
【数３５】

【０１２０】
従って、(27)式と(35)式とから、消費速度定数R*stor,iは下記(36)式により求めることができる。
【０１２１】
【数３６】

【０１２２】
また、酸素の吸蔵（吸着）と放出のみに着目しているこの触媒モデルにおいては、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のみに使用されるから、同リダクション・エージェントの消費速度Rreduc,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。
【０１２３】
そこで、酸素の放出速度Rrel,iについて検討すると、同放出速度Rrel,iは、酸素の吸蔵速度Rstor,iと同様に反応速度論に基き、同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)の値とに比例すると考えられる。
【０１２４】
そこで、簡単のために関数g1(x)＝g2(x)＝xとすると、下記の(37)式が得られる。下記(37)式のkrel,iは酸素放出速度係数（吸脱側反応速度係数）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、別途検出又は推定される触媒温度Tempに基づいて所定の関数（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でも良い。）に基づいて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、同触媒劣化程度に応じて求めてもよい。
【０１２５】
【数３７】

【０１２６】
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Rredcu,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(31)式と(37)式とを比較することにより得られる下記(38)式に基づいて求めることができる。
【０１２７】
【数３８】

【０１２８】
以上のことから、酸素吸蔵密度Ostが求められれば(酸素吸蔵密度Ostの求め方については、後述する。）、(36)式から消費速度定数R*stor,i（例えば、R*O2）を求めることができる。一方、見かけの拡散速度R_D,i（例えば、R_D,O2）は(8)式のようにSgeo・h_D,iであるから、温度と流量の関数（触媒の温度と同触媒を通過する排ガスの流量の関数）として実験的に求めておくことができる。この結果、(29)式からSPstor,i（例えば、SPstor,O2）が決定されるので、境界条件としてCgin,stor,i（例えば、Cgin,O2）が与えられるとき、(30)式からCgout,stor,i（例えば、Cout,O2）が求められる。そして、新たなCw,stor,i（例えば、Cw,O2）が(28)式により求められる。
【０１２９】
同様に、酸素吸蔵密度Ostが求められれば、(38)式から消費速度定数R*reduc,i（例えば、R*reduc,CO）を求めることができる。一方、見かけの拡散速度R_D,i（例えば、R_D,CO）は(8)式のようにSgeo・h_D,iであるから、温度と流量の関数（触媒の温度と同触媒を通過する排ガスの流量の関数）として実験的に求めておくことができる。この結果、(33)式からSPreduc,i（例えば、SPreduc,CO）が決定されるので、境界条件としてCgin,reduc,i（例えば、Cgin,CO）が与えられるとき、(34)式からCgout,reduc,i（例えば、Cgout,CO）が求められる。そして、新たなCw,reduc,i（例えば、Cw,CO）が(32)式により求められる。
【０１３０】
次に、Cgout,stor,i、Cgout,reduc,iを求めるために必要となる酸素吸蔵密度Ostの求め方について説明する。
【０１３１】
先ず、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、同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(39)式により記述される。(39)式でdA・Lは特定領域の体積dVである。
【０１３２】
【数３９】

【０１３３】
この(39)式を変形すると、下記(40)式が得られる。
【０１３４】
【数４０】

【０１３５】
この(40)式を、(35)式と(37)式とを用いながら離散化すると、下記の(41)式が得られる。
【０１３６】
【数４１】

【０１３７】
この(41)式を変形すると、下記(42)式〜(44)式が得られ、これらから酸素吸蔵密度Ostを求めること（更新して行くこと）ができる。
【０１３８】
【数４２】

【０１３９】
【数４３】

【０１４０】
【数４４】

【０１４１】
このように、式(42)〜(44)式から酸素吸蔵密度Ostが求められるので、上述したようにCgout,stor,i、Cgout,reduc,iを求めることができる。以上のようにして、各ブロックから流出する排ガス中の酸素濃度を求める手段がガス空燃比関連値取得手段に相当する。また、酸素吸蔵密度Ostが求められるから、下記(45)式に基づいて特定領域の酸素吸蔵量OSAを求めることができる。
【数４５】

【０１４２】
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、同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。以上が、本排気浄化装置が使用する触媒モデルである。そして、本排気浄化装置は、先に説明したように、別途後述するように求めた各ブロック毎の最大酸素吸蔵量に基づいて、第１触媒５３の各ブロック及び第２触媒５４の各ブロックの中から上述した制御用ブロックｉ（中間ブロックｉ、１＜ｉ＜（ｒ＋ｍ））を決定（選択）し、触媒モデルにより推定されている同決定された制御用ブロックｉから流出する排ガス中の制御用酸素濃度CgoutO2cを用いて図４に示した空燃比のパータベーション制御を行う。
【０１４３】
（実際の作動）
次に、上記排気浄化装置の第１実施形態の実際の作動について、ＣＰＵ７１が実行するルーチンを示したフローチャートを参照しながら説明する。なお、本排気浄化装置の触媒モデルは、酸素及び一酸化窒素をストレージエージェントとして考慮し、一酸化炭素及び炭化水素をリダクションエージェントとして考慮している。これに対し、酸素のみでストレージエージェントを代表させてもよいし、一酸化炭素のみでリダクションエージェントを代表させてもよい。
【０１４４】
ＣＰＵ７１は、各気筒のクランク角が各吸気上死点前の所定クランク角度（例えば、ＢＴＤＣ９０°ＣＡ）となる毎に、図１０に示したルーチンを繰り返し実行するようになっている。従って、任意の気筒のクランク角度が前記所定クランク角度になると、ＣＰＵ７１はステップ１０００から処理を開始してステップ１００５に進み、エアフローメータ６１により計測された吸入空気流量Ｇａと、エンジン回転速度ＮＥと、後述するルーチンにより求められている目標空燃比abyfr（ｋ）とに基いて、機関に供給される混合気の空燃比を同目標空燃比abyfr（ｋ）とするための基本燃料噴射量Ｆbaseをマップから求める。
【０１４５】
次いで、ＣＰＵ７１はステップ１０１０に進み、基本燃料噴射量Ｆbaseに係数Ｋを乗じた値に後述する空燃比フィードバック補正量（メインフィードバック制御量）ＤＦｉを加えた値を最終燃料噴射量Ｆｉとして設定する。この係数Ｋの値は、通常は「１．００」であり、後述するように、各触媒５３，５４の各最大酸素吸蔵量CmaxSCall，CmaxUFallを求めるために強制的に空燃比を変更するとき、「１．００」以外の所定値に設定される。
【０１４６】
ついで、ＣＰＵ７１はステップ１０１５に進み、最終燃料噴射量Ｆｉの燃料を噴射するための指示をインジェクタ３９に対して行う。その後、ＣＰＵ７１はステップ１０２０に進み、その時点の燃料噴射量合計量mfrに最終燃料噴射量Ｆｉを加えた値を新たな燃料噴射量積算値mfrに設定する。この燃料噴射量積算値mfrは、後述する酸素吸蔵量を算出する際に用いられる。その後、ＣＰＵ７１はステップ１０９５に進み、本ルーチンを一旦終了する。以上により、フィードバック補正された最終燃料噴射量Ｆｉの燃料が吸気行程を迎える気筒に対して噴射される。
【０１４７】
次に、制御用ブロック及び制御用酸素濃度CgoutO2cの決定方法について説明すると、ＣＰＵ７１は図１１に示したルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ１１００から処理を開始し、ステップ１１０５に進んで判定用最大酸素吸蔵量CmaxSChに「０」を設定し、続くステップ１１１０にてカウンタ値ｎの値を「０」に設定する。次いで、ＣＰＵ７１はステップ１１１５に進み、カウンタ値ｎの値を「１」だけ増大してステップ１１２０に進み、現時点の判定用最大酸素吸蔵量CmaxSChに、その時点で求められている第１触媒５３のブロックｎにおける最大酸素吸蔵量CmaxSC<n>（この時点ではカウンタ値ｎの値は「１」であるから、第１触媒５３のブロック１における最大酸素吸蔵量CmaxSC<1>）を加えて新たな判定用最大酸素吸蔵量CmaxSChを求める。
【０１４８】
次に、ＣＰＵ７１はステップ１１２５に進み、判定用最大酸素吸蔵量CmaxSChが所定の閾値Cthより大きいか否かを判定する。このとき、判定用最大酸素吸蔵量CmaxSChが所定の閾値Cthより小さければ、ＣＰＵ７１はステップ１１２５にて「Ｎｏ」と判定してステップ１１３０に進みカウンタ値ｎの値が第１触媒５３の総ブロック数ｒと等しいか否かを判定する。
【０１４９】
現時点ではカウンタ値ｎの値は「１」である。従って、ＣＰＵ７１はステップ１１３０にて「Ｎｏ」と判定し、再びステップ１１１５に戻ってカウンタ値ｎの値を「１」だけ増大し、ステップ１１２０及びステップ１１２５の処理を実行する。この結果、判定用最大酸素吸蔵量CmaxSChは、第１触媒５３の最上流のブロックである第１番目のブロックと第２番目のブロックの最大酸素吸蔵量の積算値CmaxSC<1>+CmaxSC<2>となる。そして、この積算値CmaxSC<1>+CmaxSC<2>が閾値Cthを超えなければＣＰＵ７１はステップ１１２５から再びステップ１１３０に進み、更に、カウンタ値ｎの値が前記ブロック数ｒと等しくなければ再びステップ１１１５にてカウント値ｎの値を「１」だけ増大し、ステップ１１２０の処理を実行する。この結果、その時点の判定用最大酸素吸蔵量CmaxSCh（この時点ではCmaxSC<1>+CmaxSC<2>）に第１触媒５３のブロックｎの最大酸素吸蔵量CmaxSC<n>（この時点ではｎ＝３であるあるからCmaxSC<3>）が加算され、新たな判定用最大酸素吸蔵量CmaxSCh（＝CmaxSC<1>+CmaxSC<2>+CmaxSC<3>）が求められる。
【０１５０】
このような処理は、判定用最大酸素吸蔵量CmaxSChが閾値Cthを超えない限り繰り返し行われる。従って、判定用最大酸素吸蔵量CmaxSChは、第１触媒５３の最上流のブロックである第１番目のブロックから第ｎ番目のブロックまでの各ブロックｎの最大酸素吸蔵量CmaxSC<n>の積算値（合計値）として求められる。
【０１５１】
このような処理の実行中、判定用最大酸素吸蔵量CmaxSChが所定の閾値Cthより大きくなった場合、ＣＰＵ７１はステップ１１２５にて「Ｙｅｓ」と判定してステップ１１３５に進み、制御用酸素濃度CgoutO2cに第１触媒５３の第ｎ番目のブロックｎから流出する後述する排ガス中の酸素濃度CgoutSC,O2<n>を設定し、ステップ１１９５に進んで本ルーチンを一旦終了する。この場合、制御用ブロック（中間ブロック）ｉは、第１触媒５３の第ｎ番目のブロックｎとなる（ｉ＝ｎ）。
【０１５２】
また、第１触媒５３の第１番目のブロックから第ｒ番目のブロックの総べてのブロックの各最大酸素吸蔵量CmaxSC<n>の積算値（即ち、第１触媒５３全体の最大酸素吸蔵量CmaxSCall）が所定の閾値Cthより小さいとき、ＣＰＵ７１はステップ１１２５にて「Ｙｅｓ」と判定することはなく、カウンタ値ｎの値がｒとなったときにステップ１１３０にて「Ｙｅｓ」と判定し、ステップ１１４０に進んで判定用最大酸素吸蔵量CmaxUFhに第１触媒５３全体の最大酸素吸蔵量CmaxSCallを設定する。次いで、ＣＰＵ７１は、ステップ１１４５にてカウンタ値ｎの値を「０」に設定し、ステップ１１５０以降に進む。
【０１５３】
ステップ１１５０〜ステップ１１６５までの処理は、ステップ１１１５〜ステップ１１３０までの処理と同様である。簡単に説明すると、ＣＰＵ７１は、ステップ１１５０及びステップ１１５５にて第１触媒５３全体の最大酸素吸蔵量CmaxSCallに第２触媒５４の最上流のブロック（第１番目のブロック）から同第２触媒５４の第ｎ番目のブロックまでの各ブロックｎの最大酸素吸蔵量CmaxUF<n>の積算値を加えた値を、判定用最大酸素吸蔵量CmaxUFhとして求める。第２触媒５４の第ｎ番目となるブロックｎは第１触媒５３の最上流のブロックから数えて（ｒ+ｎ）番目のブロックということになる。従って、（ｒ+ｎ）をｐとするとき、判定用最大酸素吸蔵量CmaxUFhは、第１触媒５３及び第２触媒５４を一つの触媒装置とみなしたときの最上流のブロックである第１番目のブロックから第ｐ番目のブロックまでのブロックにより構成される触媒装置上流部の各ブロックの最大酸素吸蔵量の積算値ということになる。
【０１５４】
そして、ＣＰＵ７１は、判定用最大酸素吸蔵量CmaxUFhが所定の閾値Cthより大きくなった場合、ステップ１１６０にて「Ｙｅｓ」と判定してステップ１１７０に進み、制御用酸素濃度CgoutO2cに第２触媒５４の第ｎ番目のブロックから流出する後述する排ガス中の酸素濃度CgoutUF,O2<n>を設定し、ステップ１９９５に進んで本ルーチンを一旦終了する。この場合、制御用ブロック（中間ブロック）ｉは、第２触媒５４の第ｎ番目のブロックｎとなる（ｉ＝ｒ＋ｎ）。
【０１５５】
また、第１触媒５３〜第２触媒５４の各最大酸素吸蔵量の和（CmaxSCall+CmaxUFall）が所定の閾値Cthより小さいとき、ＣＰＵ７１はステップ１１６０にて「Ｙｅｓ」と判定することはなく、カウンタ値ｎの値が第２触媒５４のブロック数ｍとなったときステップ１１６５にて「Ｙｅｓ」と判定し、この場合は上記ステップ１１７０を経由してステップ１１９５に進み、本ルーチンを一旦終了する。
【０１５６】
このように、ｎを自然数とし、第１触媒５３〜第２触媒５４を一つの触媒装置とみなしたとき、その触媒装置の第１番目のブロックから第ｎ番目のブロックまでのブロックにより構成される触媒装置上流部の各ブロックの最大酸素吸蔵量の積算値（判定用最大酸素吸蔵量）が所定の閾値Cthを超える触媒装置上流部のうち、前記値ｎが最も小さい触媒装置上流部の最下流のブロック（第１触媒５３の第１番目のブロックから数えて第ｎ番目のブロック）である制御用ブロックｉから流出する排ガス中の酸素濃度が制御用酸素濃度CgoutO2cとして設定される。従って、制御用ブロックｉは、触媒装置が劣化してその最大酸素吸蔵量が低下するにつれて徐々に下流側に移動することになる。
【０１５７】
次に、上記目標空燃比abyfr（ｋ）の算出について説明すると、ＣＰＵ７１は図１２に示したルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ１２００から処理を開始し、ステップ１２０５に進んで、後述する空燃比強制設定制御実行中フラグＸＨＡＮの値が「０」であるか否かを判定する。なお、空燃比強制設定制御実行中フラグＸＨＡＮは、その値が「１」のとき最大酸素吸蔵量CmaxSCall，CmaxUFallの算出のために強制的に空燃比を変更する空燃比制御（アクティブ制御）を実行していることを示し、その値が「０」のとき同最大酸素吸蔵量CmaxSCall，CmaxUFallの算出のための空燃比制御を実行していないことを示す。
【０１５８】
いま、最大酸素吸蔵量算出のための空燃比制御を実行しておらず、且つ、上述した図１１のルーチンにて求められている制御用ブロックｉから流出する排ガス中の酸素濃度である制御用酸素濃度CgoutO2cが正の閾値Crefpls以下の状態から同正の閾値Crefplsより大きい状態へと変化したとして説明を続ける。この場合、ＣＰＵ７１はステップ１２０５にて「Ｙｅｓ」と判定してステップ１２１０に進み、CgoutO2cが正の閾値Crefplsより大きいか否かを判定する。前述の仮定に従えば、CgoutO2cは正の閾値Crefplsより大きいので、ＣＰＵ７１はステップ１２１０にて「Ｙｅｓ」と判定してステップ１２１５に進み、同ステップ１２１５にて本ルーチンを前回実行したときの（前回の）CgoutO2cが閾値Crefpls以下であるか否かを判定する。前述の仮定に従えば、前回のCgoutO2cは正の閾値Crefpls以下であるので、ＣＰＵ７１はステップ１２１５にて「Ｙｅｓ」と判定してステップ１２２０に進み、同ステップ１２２０にて目標空燃比abyfr（ｋ）に理論空燃比stoichよりも所定値α２だけリッチの空燃比を設定し、ステップ１２９５に進んで本ルーチンを一旦終了する。
【０１５９】
このように、本排気浄化装置は、制御用酸素濃度CgoutO2cが正の閾値Crefpls以下の状態から同正の閾値Crefplsより大きい状態へと変化したとき、目標空燃比abyfr（ｋ）を理論空燃比stoichよりも所定値α２だけリッチの空燃比に変更し、これ以降、ＣＰＵ７１は図１０のステップ１００５に進んだとき基本燃料噴射量Ｆbaseを、機関に供給される混合気の空燃比（従って、第１触媒５３に流入する空燃比）を同目標空燃比abyfr（ｋ）（理論空燃比stoich−α２）とするための値に変更する。この結果、第１，第２触媒５３，５４にリッチな空燃比の排ガスが流入するようになり、図４の時刻ｔ２〜ｔ３に示したように、制御ブロックｉから流出する酸素濃度CgoutO2cが略「０」に維持されるようになる。
【０１６０】
なお、今回及び前回の制御用酸素濃度CgoutO2cが正の閾値Crefplsより大きいとき、ＣＰＵ７１はステップ１２１０にて「Ｙｅｓ」、ステップ１２１５にて「Ｎｏ」と判定し、そのままステップ１２９５に進んで本ルーチンを一旦終了する。この結果、目標空燃比abyfr（ｋ）は理論空燃比stoich−α２に維持され、機関に供給される混合気の空燃比も理論空燃比−α２に近づくように調整される。
【０１６１】
一方、最大酸素吸蔵量算出のための空燃比制御を実行しておらず、且つ、制御用ブロックｉから流出する酸素濃度CgoutO2cが負の閾値Crefmns以上の状態から同負の閾値Crefmnsより小さい状態へと変化したとして説明を続ける。この場合、ＣＰＵ７１はステップ１２０５にて「Ｙｅｓ」、ステップ１２１０にて「Ｎｏ」と判定してステップ１２２５に進み、CgoutO2cが負の閾値Crefmnsより小さいか否かを判定する。前述の仮定に従えば、CgoutO2cは負の閾値Crefmnsより小さいので、ＣＰＵ７１はステップ１２２５にて「Ｙｅｓ」と判定してステップ１２３０に進み、同ステップ１２３０にて本ルーチンを前回実行したときの（前回の）CgoutO2cが閾値Crefmns以上であるか否かを判定する。前述の仮定に従えば、前回のCgoutO2cは閾値Crefmns以上であるので、ＣＰＵ７１はステップ１２３０にて「Ｙｅｓ」と判定してステップ１２３５に進み、同ステップ１２３５にて目標空燃比abyfr（ｋ）に理論空燃比stoichよりも所定値α１だけリーンの空燃比を設定し、ステップ１２９５に進んで本ルーチンを一旦終了する。
【０１６２】
このように、本排気浄化装置は、制御用酸素濃度CgoutO2cが負の閾値Crefmns以上の状態から同負の閾値Crefmnsより小さい状態へと変化したとき、目標空燃比abyfr（ｋ）を理論空燃比stoichよりも所定値α１だけリーンの空燃比に変更し、これ以降、ＣＰＵ７１は図１０のステップ１００５に進んだとき基本燃料噴射量Ｆbaseを、機関に供給される混合気の空燃比を同目標空燃比abyfr（ｋ）（理論空燃比stoich＋α１）とするための値に変更する。この結果、第１，第２触媒５３，５４にリーンな空燃比の排ガスが流入するようになり、図４の時刻ｔ１〜ｔ２及び時刻ｔ３〜ｔ４に示したように、制御ブロックｉから流出する酸素濃度CgoutO2cが略「０」に維持されるようになる。
【０１６３】
なお、今回及び前回の酸素濃度CgoutO2cが負の閾値Crefmnsより小さいとき、ＣＰＵ７１はステップ１２１０にて「Ｎｏ」、ステップ１２２５にて「Ｙｅｓ」、ステップ１２３０にて「Ｎｏ」と判定し、そのままステップ１２９５に進んで本ルーチンを一旦終了する。この結果、目標空燃比abyfr（ｋ）は理論空燃比stoich＋α１に維持され、機関に供給される混合気の空燃比も理論空燃比＋α１に近づくように調整される。
【０１６４】
また、最大酸素吸蔵量算出のための空燃比制御を実行中であれば空燃比強制設定制御実行中フラグＸＨＡＮの値が「１」になっているので、ＣＰＵ７１はステップ１２０５にて「Ｎｏ」と判定してステップ１２４０に進み、同ステップ１２４０に目標空燃比abyfr（ｋ）の値を理論空燃比stoichに設定し（上述したように最大酸素吸蔵量算出のための空燃比制御は図１０のステップ１０１０の係数Ｋの値を変更することで行う。）、次いでステップ１２９５に進んで本ルーチンを一旦終了する。以上のように、目標空燃比abyfr（ｋ）は、制御用ブロックｉから流出する排ガス中の酸素濃度である制御用酸素濃度CgoutO2cが正の閾値Crefplsと負の閾値Crefmnsとの間の所定値になるように決定される。
【０１６５】
次に、上記メインフィードバック制御量ＤＦｉの算出について説明すると、ＣＰＵ７１は図１３にフローチャートにより示したルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ１３００から処理を開始し、ステップ１３０５に進んで空燃比フィードバック制御条件（メインフィードバック条件）が成立しているか否かを判定する。この空燃比フィードバック制御条件は、例えば、機関の冷却水温THWが第１所定温度以上であり、機関の一回転当りの吸入空気量（負荷、筒内吸入空気量Ｍｃ）が所定値以下であり、最上流空燃比センサ６６が正常（活性状態であることを含む。）であり、且つ、後述する空燃比強制設定制御実行中フラグＸＨＡＮの値が「０」のときに成立する。
【０１６６】
いま、空燃比フィードバック制御条件が成立しているものとして説明を続けると、ＣＰＵ７１はステップ１３０５にて「Ｙｅｓ」と判定してステップ１３１０に進み、現時点の最上流空燃比センサ６６の出力vabyfsを図２に示したマップに基いて変換することにより、現時点における第１触媒５３上流の実空燃比abyfsを求める。
【０１６７】
次に、ＣＰＵ７１はステップ１３１５に進み、現時点からＮストローク（Ｎ回の吸気行程）前に吸気行程を迎えた気筒の吸入空気量である筒内吸入空気量Ｍｃ（ｋ−Ｎ）を前記求めた実空燃比abyfsで除することにより、現時点からＮストローク前の筒内燃料供給量Ｆｃ（ｋ−Ｎ）を求める。値Ｎは、内燃機関の排気量、燃焼室２５から最上流空燃比センサ６６までの距離等により異なる値である。
【０１６８】
このように、現時点からＮストローク前の筒内燃料供給量Ｆｃ（ｋ−Ｎ）を求めるために、現時点からＮストローク前の筒内吸入空気量Ｍｃ（ｋ−Ｎ）を現時点における実空燃比abyfsで除するのは、燃焼室２５内で燃焼された混合気が最上流空燃比センサ６６に到達するまでには、Ｎストロークに相当する時間を要しているからである。なお、筒内吸入空気量Ｍｃは、各気筒の吸気行程に対応されながらＲＡＭ７３内に記憶されるようになっている。
【０１６９】
次いで、ＣＰＵ７１はステップ１３２０に進み、現時点からＮストローク前の筒内吸入空気量Ｍｃ（ｋ−Ｎ）を現時点からＮストローク前の時点において図１２のルーチンにて既に求められている目標空燃比abyfr（ｋ−Ｎ）で除することにより、現時点からＮストローク前の目標筒内燃料供給量Ｆｃｒ（ｋ−Ｎ）を求める。そして、ＣＰＵ７１はステップ１３２５に進んで目標筒内燃料供給量Ｆｃｒ（ｋ−Ｎ）から筒内燃料供給量Ｆｃ（ｋ−Ｎ）を減じた値を筒内燃料供給量偏差ＤＦｃとして設定する。つまり、筒内燃料供給量偏差ＤＦｃは、Ｎストローク前の時点で筒内に供給された燃料の過不足分を表す量となる。次に、ＣＰＵ７１はステップ１３３０に進み、下記数４６に基いてメインフィードバック制御量ＤＦｉを求める。
【０１７０】
【数４６】
ＤＦｉ＝（Ｇｐ・ＤＦｃ＋Ｇｉ・ＳＤＦｃ）・ＫＦＢ
【０１７１】
上記数４６において、Ｇｐは予め設定された比例ゲイン（比例定数）、Ｇｉは予め設定された積分ゲイン（積分定数）である。なお、数４６の係数ＫＦＢはエンジン回転速度NE、及び筒内吸入空気量Ｍｃ等により可変とすることが好適であるが、ここでは「１」としている。また、値ＳＤＦｃは筒内燃料供給量偏差ＤＦｃの積分値であり、次のステップ１３３５にて更新される。即ち、ＣＰＵ７１は、ステップ１３３５にてその時点における筒内燃料供給量偏差ＤＦｃの積分値ＳＤＦｃに上記ステップ１３２５にて求めた筒内燃料供給量偏差ＤＦｃを加えて、新たな筒内燃料供給量偏差の積分値ＳＤＦｃを求め、ステップ１３９５にて本ルーチンを一旦終了する。
【０１７２】
以上により、メインフィードバック制御量ＤＦｉが比例積分制御により求められ、このメインフィードバック制御量ＤＦｉが前述した図１０のステップ１０１０により燃料噴射量に反映されるので、Ｎストローク前の燃料供給量の過不足が補償され、内燃機関に供給される混合気の空燃比の平均値が目標空燃比abyfrと略一致せしめられるようにフィードバック制御される。
【０１７３】
一方、ステップ１３０５の判定時において、空燃比フィードバック制御条件が不成立であると、ＣＰＵ７１は同ステップ１３０５にて「Ｎｏ」と判定してステップ１３４０に進み、メインフィードバック制御量ＤＦｉの値を「０」に設定し、その後ステップ１３９５に進んで本ルーチンを一旦終了する。このように、空燃比フィードバック制御条件が不成立であるとき（空燃比強制設定制御実行中を含む）は、メインフィードバック制御量ＤＦｉを「０」として空燃比（基本燃料噴射量Ｆbase）の補正を行わない。
【０１７４】
次に、最大酸素吸蔵量算出のために強制的に空燃比を変更する最大酸素吸蔵量取得制御について説明する。ＣＰＵ７１は図１４〜図１８のフローチャートにより示された各ルーチンを所定時間の経過毎に実行するようになっている。
【０１７５】
従って、所定のタイミングになると、ＣＰＵ７１は図１４のステップ１４００から処理を開始し、ステップ１４０５に進んで最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値が「０」であるか否かを判定する。いま、最大酸素吸蔵量算出のための最大酸素吸蔵量取得制御を行っておらず、且つ、最大酸素吸蔵量取得制御開始条件が成立していないとして説明を続けると、最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値は「０」となっている。従って、ＣＰＵ７１はステップ１４０５にて「Ｙｅｓ」と判定してステップ１４１０に進み、先に説明した図１０のステップ１０１０にて使用される係数Ｋの値を１．００に設定する。
【０１７６】
次いで、ＣＰＵ７１はステップ１４１５にて最大酸素吸蔵量取得制御の開始条件が成立しているか否かを判定する。この最大酸素吸蔵量取得制御の開始条件は、冷却水温THWが所定温度以上であり、図示しない車速センサにより得られた車速が所定の高車速以上であり、スロットル弁開度TAの単位時間あたりの変化量が所定量以下である等の機関が定常運転されている条件が成立し、第１，第２触媒下流空燃比センサ出力voxs1,voxs2が共に理論空燃比よりもリッチな空燃比に相当する出力を発生し、且つ、前回の最大酸素吸蔵量取得制御実行時点から所定時間が経過している場合等に成立する。現段階では、上述したように、最大酸素吸蔵量取得制御の開始条件は成立していないから、ＣＰＵ７１はステップ１４１５にて「Ｎｏ」と判定してステップ１４９５に進み、本ルーチンを一旦終了する。
【０１７７】
次に、現時点では最大酸素吸蔵量取得制御を行っていないが、最大酸素吸蔵量取得制御の開始条件が成立したものとして説明を続けると、この場合、ＣＰＵ７１はステップ１４０５にて「Ｙｅｓ」と判定してステップ１４１０に進み、同ステップ１４１０にて係数Ｋの値を１．００に設定する。次いで、ＣＰＵ７１は、開始条件が成立しているので、ステップ１４１５にて「Ｙｅｓ」と判定してステップ１４２０に進み、同ステップ１４２０にて最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値を「１」に設定する。
【０１７８】
そして、ＣＰＵ７１はステップ１４２５に進み、第１モードに移行するためにModeの値を「１」に設定するとともに、続くステップ１４３０にて係数Ｋの値を０．９８に設定し、ステップ１４９５に進んで本ルーチンを一旦終了する。これにより、前述の空燃比フィードバック制御条件が成立しなくなるから、ＣＰＵ７１は図１３のステップ１３０５にて「Ｎｏ」と判定してステップ１３４０に進むようになり、空燃比フィードバック補正量ＤＦｉの値は「０」に設定される。この結果、図１０のステップ１０１０の実行により、基本燃料噴射量Ｆbaseが０.９８倍された値が最終燃料噴射量Ｆｉとして算出され、この最終燃料噴射量Ｆｉの燃料が噴射されるので、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）は理論空燃比よりもリーンな所定のリーン空燃比に制御される。
【０１７９】
以降、ＣＰＵ７１は図１４のルーチンの処理をステップ１４００から繰り返し実行するが、最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値が「１」となっていることから、ステップ１４０５にて「Ｎｏ」と判定して直ちにステップ１４９５に進み、本ルーチンを一旦終了するようになる。
【０１８０】
一方、ＣＰＵ７１は図１５に示した第１モード制御ルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングとなると、ＣＰＵ７１はステップ１５００から処理を開始してステップ１５０５に進み、同ステップ１５０５にてModeの値が「１」であるか否かを判定する。このとき、Modeの値が「１」でなければ、ＣＰＵ７１は直ちにステップ１５９５に進んで本ルーチンを一旦終了する。以下、先の図１４のステップ１４２５の処理によりModeの値が「１」に変更された直後であるとして説明を続けると、この場合、ＣＰＵ７１はステップ１５０５にて「Ｙｅｓ」と判定してステップ１５１０に進み、第１触媒下流空燃比センサ出力voxs1、及び第２触媒下流空燃比センサ出力voxs2が共に理論空燃比よりもリーンな空燃比に相当する出力（酸素が過剰に存在する場合の出力）となったか否かを判定する。
【０１８１】
現時点では、機関に供給される混合気の空燃比を所定のリーン空燃比に変更した直後であるから、第１触媒下流空燃比センサ出力voxs1、及び第２触媒下流空燃比センサ出力voxs2が共に理論空燃比よりもリーンな空燃比に相当する出力とはなっていないので、ＣＰＵ７１はステップ１５１０にて「Ｎｏ」と判定し、ステップ１５９５にて本ルーチンを一旦終了する。
【０１８２】
以降、ＣＰＵ７１は図１５のステップ１５００〜１５１０を繰り返し実行する。また、空燃比は所定のリーン空燃比に維持されているから、時間経過に伴って第１触媒５３から第２触媒５４の順に各酸素吸蔵量が各触媒の最大酸素吸蔵量に到達する。従って、これに応じて第１触媒下流空燃比センサ出力voxs1、及び第２触媒下流空燃比センサ出力voxs2は、順に理論空燃比よりもリーンな空燃比に相当する出力に変化する。これにより、ＣＰＵ７１はステップ１５１０に進んだとき、同ステップ１５１０にて「Ｙｅｓ」と判定してステップ１５１５に進み、同ステップ１５１５にてModeの値を「２」に設定するとともに、続くステップ１５２０にて係数Ｋの値を１．０２に設定し、その後ステップ１５９５にて本ルーチンを一旦終了する。この結果、機関に供給される混合気の空燃比が理論空燃比よりリッチな所定のリッチ空燃比に制御される。
【０１８３】
また、ＣＰＵ７１は図１６にフローチャートにより示した第２モード制御ルーチンを所定時間の経過毎に繰り返し実行している。従って、ＣＰＵ７１は、所定のタイミングになると、ステップ１６００から処理を開始し、ステップ１６０５にてModeの値が「２」であるか否かを判定し、Modeの値が「２」でなければステップ１６０５からステップ１６９５に進んで本ルーチンを一旦終了するように作動している。
【０１８４】
一方、先のステップ１５１５の処理によりModeの値が「２」に変更されると、ＣＰＵ７１はステップ１６０５に進んだとき「Ｙｅｓ」と判定してステップ１６１０に進み、同ステップ１６１０にて第１触媒下流空燃比センサ６７の出力voxs1が理論空燃比よりリーンな空燃比を示す値から同理論空燃比よりリッチな空燃比を示す値に変化したか否かを判定する。この時点では、空燃比が前記所定のリッチ空燃比に変更された直後であるから、ＣＰＵ７１はステップ１６１０にて「Ｎｏ」と判定し、ステップ１６９５に進んで本ルーチンを一旦終了する。
【０１８５】
これ以降、機関に供給される混合気の空燃比は前記所定のリッチ空燃比に維持されるから、第１触媒５３に貯蔵されている酸素が消費されて行き、所定の時間が経過すると同第１触媒５３の酸素吸蔵量が「０」に至る。この結果、第１触媒５３から未燃ＨＣ，ＣＯが流出し始めるので、第１触媒下流空燃比センサ６７の出力voxs1が理論空燃比よりリーンな空燃比を示す値から同理論空燃比よりリッチな空燃比を示す値に変化する。これにより、ＣＰＵ７１は、ステップ１６１０に進んだとき同ステップ１６１０にて「Ｙｅｓ」と判定してステップ１６１５に進み、同ステップ１６１５にてModeの値を「３」に変更し、ステップ１６９５にて本ルーチンを一旦終了する。
【０１８６】
同様に、ＣＰＵ７１は、所定時間の経過毎に繰り返し実行する図１７にフローチャートにより示した第３モード制御ルーチンにおいて、ステップ１７０５にてModeの値が「３」であるか否かを判定し、Modeの値が「３」でなければステップ１７０５からステップ１７９５に進んで本ルーチンを一旦終了している。
【０１８７】
一方、先のステップ１６１５の処理によりModeの値が「３」に変更されると、ＣＰＵ７１はステップ１７０５に進んだとき「Ｙｅｓ」と判定してステップ１７１０に進み、同ステップ１７１０にて第２触媒下流空燃比センサ６８の出力voxs2が理論空燃比よりリーンな空燃比を示す値から同理論空燃比よりリッチな空燃比を示す値に変化したか否かを判定する。この時点では、第１触媒５３から未燃ＨＣ，ＣＯが流出し始めた直後であり、第２触媒５４から未燃ＨＣ，ＣＯは流出してこないので、ＣＰＵ７１はステップ１７１０にて「Ｎｏ」と判定し、ステップ１７９５に進んで本ルーチンを一旦終了する。
【０１８８】
その後、機関に供給される混合気の空燃比は、引き続いて前記所定のリッチ空燃比に維持されるから、第２触媒５４に貯蔵されている酸素が消費されて行き、所定の時間が経過すると同第２触媒５４の酸素吸蔵量が「０」に至る。この結果、第２触媒５４から未燃ＨＣ，ＣＯが流出し始めるので、第２触媒下流空燃比センサ６８の出力voxs2が理論空燃比よりリーンな空燃比を示す値から同理論空燃比よりリッチな空燃比を示す値に変化する。これにより、ＣＰＵ７１はステップ１７１０からステップ１７１５に進み、Modeの値を「０」に再設定し、続くステップ１７２０にて最大酸素吸蔵量取得制御から前述したパータベーション制御に移行するため目標空燃比abyfr（ｋ）を理論空燃比stoichから前記所定値α１だけリーンな空燃比に設定した後、続くステップ１７２５にて最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値を「０」に設定し、ステップ１７９５に進んで本ルーチンを一旦終了する。
【０１８９】
この状態となると、ＣＰＵ７１は図１４のルーチンを実行する際、ステップ１４０５にて「Ｙｅｓ」と判定してステップ１４１０に進むので、係数Ｋの値が１．００に戻される。また、図１０のステップ１００５にて機関に供給される混合気の空燃比をリーン空燃比（stoich＋α１）に設定されている目標空燃比abyfr（ｋ）とするための基本燃料噴射量Ｆbaseが算出され、また、空燃比フィードバック制御条件が成立していれば、ＣＰＵ７１は図１３のルーチンのステップ１３０５にて「Ｙｅｓ」と判定するから、空燃比フィードバック制御（メインフィードバック制御）が再開される。
【０１９０】
以上、説明したように、最大酸素吸蔵量取得制御の開始条件が成立すると、機関に供給される混合気の空燃比が所定のリーン空燃比、所定のリッチ空燃比の順に１回づつ強制的に制御される。
【０１９１】
次に、最大酸素吸蔵量取得のための酸素吸蔵量の算出における作動について説明する。ＣＰＵ７１は図１８のフローチャートにより示されたルーチンを所定時間（演算周期tsample）の経過毎に実行するようになっている。従って、所定のタイミングになると、ＣＰＵ７１はステップ１８００から処理を開始し、ステップ１８０５に進んで下記数４７により酸素吸蔵量変化量ΔO2を求める。
【０１９２】
【数４７】
ΔO2＝０．２３・mfr・（stoich − abyfsave）
【０１９３】
上記数４７において、値「０．２３」は大気中に含まれる酸素の重量割合である。mfrは所定時間tsample内の燃料噴射量Ｆｉの合計量であり、stoichは理論空燃比（例えば、１４．７）である。abyfsaveは所定時間tsampleにおいて最上流空燃比センサ６６により検出された空燃比Ａ／Ｆの平均値である。この数４７に示したように、所定時間tsample内の噴射量の合計量mfrに、検出された空燃比Ａ／Ｆの平均値の理論空燃比からの偏移（stoich − abyfsave）を乗じることで、同所定時間tsampleにおける空気の消費量（不足量）が求められる。この空気の消費量に酸素の重量割合を乗じることで同所定時間tsampleにおける酸素の消費量（酸素吸蔵量変化量ΔO2）が求められる。
【０１９４】
次いで、ＣＰＵ７１はステップ１８１０に進んでModeの値が「２」であるか否か（第２モードであるか否か）を判定し、Modeの値が「２」であれば同ステップ１８１０にて「Ｙｅｓ」と判定してステップ１８１５に進み、その時点の酸素吸蔵量ＯＳＡ１に上記酸素吸蔵量変化量ΔO2を加えた値を新たな酸素吸蔵量ＯＳＡ１として設定し、その後ステップ１８３０に進む。
【０１９５】
このような処置（ステップ１８００〜１８１５）は、Modeの値が「２」である限り繰り返し実行される。この結果、第１触媒５３の上流の空燃比が所定のリッチ空燃比とされる第２モード（Mode=2）において、第１触媒５３の酸素吸蔵量ＯＳＡ１が算出されて行く。第２モードにおいては、第１触媒５３に貯蔵されている酸素が消費されて行くからである。なお、ステップ１８１０での判定において「Ｎｏ」と判定される場合、ＣＰＵ７１は同ステップ１８１０からステップ１８２０に直接進む。
【０１９６】
ＣＰＵ７１は、ステップ１８２０に進んだ場合、Modeの値が「３」であるか否か（第３モードであるか否か）を判定し、Modeの値が「３」であれば同ステップ１８２０にて「Ｙｅｓ」と判定してステップ１８２５に進み、その時点の酸素吸蔵量ＯＳＡ２に上記酸素吸蔵量変化量ΔO2を加えた値を新たな酸素吸蔵量ＯＳＡ２として設定し、その後ステップ１８３０に進む。
【０１９７】
このような処置（ステップ１８００，１８０５，１８１０，１８２０，１８２５）は、Modeの値が「３」である限り繰り返し実行される。この結果、第１触媒５３の上流の空燃比が所定のリッチ空燃比とされる第３モード（Mode=3）において、第２触媒５４の酸素吸蔵量ＯＳＡ２が算出されて行く。第３モードにおいては、第２触媒５４に貯蔵されている酸素が消費されて行くからである。なお、ステップ１８２０での判定において「Ｎｏ」と判定される場合、ＣＰＵ７１は同ステップ１８２０からステップ１８３０に直接進む。そして、ＣＰＵ７１は、ステップ１８３０に進むと、燃料噴射量Ｆｉの合計量mfrを「０」に設定し、その後ステップ１８９５に進んで本ルーチンを一旦終了する。
【０１９８】
次に、第１，第２触媒５３，５４の各最大酸素吸蔵量CmaxSCall,CmaxUFall、及び各触媒の各ブロックの最大酸素吸蔵量CmaxSC<n>,CmaxUF<n>を算出する際の作動について説明する。ＣＰＵ７１は図１９のフローチャートにより示されたルーチンを所定時間の経過毎に実行するようになっている。
【０１９９】
従って、所定のタイミングになると、ＣＰＵ７１は図１９のステップ１９００から処理を開始し、ステップ１９０５に進んで最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値が「１」から「０」に変化したか否かをモニタする。このとき、最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値が変化していなければ、ＣＰＵ７１はステップ１９０５からステップ１９９５に直接進んで本ルーチンを一旦終了する。
【０２００】
一方、前述した第３モードが終了した直後であるとすると、図１７のステップ１７２５にて最大酸素吸蔵量取得制御実行中フラグＸＨＡＮの値が「１」から「０」に変更されるから、ＣＰＵ７１はステップ１９０５にて「Ｙｅｓ」と判定してステップ１９１０に進み、その時点の酸素吸蔵量ＯＳＡ１，ＯＳＡ２を、それぞれ第１触媒５３全体の最大酸素吸蔵量CmaxSCall、第２触媒５４全体の最大酸素吸蔵量CmaxUFallとして格納する。
【０２０１】
次いでＣＰＵ７１はステップ１９１５に進み、カウンタ値ｎの値を「０」に設定した後、ステップ１９２０に進んで第１触媒５３のブロック毎の最大酸素吸蔵量を算出する処理を開始する。まず、ＣＰＵ７１はステップ１９２０においてカウンタ値ｎの値を「１」だけ増大して「１」に設定した後、ステップ１９２５に進んで上記ステップ１９１０にて取得した第１触媒５３全体の最大酸素吸蔵量CmaxSCallの値と、カウンタ値ｎの値と、ステップ１９２５内に記載した式とに基いて第１触媒５３のブロックｎにおける最大酸素吸蔵量CmaxSC<n>を算出する。この時点ではカウンタ値ｎの値は「１」であるから、第１触媒５３のブロック１における最大酸素吸蔵量CmaxSC(1)が算出される。
【０２０２】
ここで、ステップ１９２５内に記載した式について図２０を用いて簡単に説明する。図２０は、第１触媒５３のブロック毎の最大酸素吸蔵量CmaxSC<n> (n=1,・・・,ｒ)を求める考え方を示した最大酸素吸蔵量分布マップであり、斜線で示された部分の面積は第１触媒５３全体の最大酸素吸蔵量CmaxSCallの値に対応している。
【０２０３】
このように、第１触媒５３のブロック毎の各最大酸素吸蔵量CmaxSC<n>は、同各最大酸素吸蔵量CmaxSC<n>の総和が第１触媒５３全体の最大酸素吸蔵量CmaxSCallの値となるように設定されるとともに、上流側のブロック１から下流側のブロックｒに推移するに従い、所定の勾配をもって線形的に増加するように設定される。これは、第１触媒５３の上流側部分の方が下流側部分に比して、内部に流入する排ガス中の鉛や硫黄等により被毒し易いので、同上流側部分の最大酸素吸蔵量が同下流側部分のものに比して低下し易くなるからである。
【０２０４】
かかる図２０に示した最大酸素吸蔵量分布マップに基いて第１触媒５３のブロック毎の各最大酸素吸蔵量CmaxSC<n>を求める式がステップ１９２５内に記載の式である。前記ステップ１９２５内に記載の式において、値A1は正の定数であって、上記所定の勾配に相当する値である。なお、第１触媒５３のブロック毎の各最大酸素吸蔵量は、上流側のブロックから下流側のブロックに推移するに従い増加するように設定されていればよく、例えば、非線形的に増加するように設定されていてもよい。
【０２０５】
再び、図１９を参照すると、ＣＰＵ７１はステップ１９２５からステップ１９３０に進んでカウンタ値ｎの値が第１触媒５３のブロック数ｒと等しいか否かを判定する。現時点ではカウンタ値ｎの値は「１」であるから、ＣＰＵ７１はステップ１９３０にて「Ｎｏ」と判定し、再びステップ１９２０に戻ってカウンタ値ｎの値を「１」だけ増大した後ステップ１９２５及びステップ１９３０の処理を実行する。即ち、ステップ１９２０及びステップ１９２５の処理は、カウンタ値ｎの値が第１触媒５３のブロック数ｒと等しくなるまで繰り返し実行される。これにより、第１触媒５３の最上流のブロック１から最下流のブロックｒまでの各ブロックｎの最大酸素吸蔵量CmaxSC<n>の値が順次算出されていく。
【０２０６】
前述のステップ１９２０の処理が繰り返されることによりカウンタ値ｎの値が第１触媒５３のブロック数ｒと等しくなると、ＣＰＵ７１はステップ１９３０にて「Ｙｅｓ」と判定してステップ１９３５に進み、カウンタ値ｎの値を「０」に設定した後、ステップ１９４０に進んで第２触媒５４のブロック毎の各最大酸素吸蔵量CmaxUF<n> (n=1,・・・,ｍ)を算出する処理を開始する。
【０２０７】
この第２触媒５４のブロック毎の各最大酸素吸蔵量CmaxUF<n>を算出する処理は、上述したステップ１９２０〜ステップ１９３０の処理と同様であるステップ１９４０〜ステップ１９５０までの処理を第２触媒５４のブロック数ｍ回だけ繰り返し実行することにより達成される。ステップ１９４５における最大酸素吸蔵量CmaxUF<n>の算出は、上記ステップ１９１０にて取得した第２触媒５４全体の最大酸素吸蔵量CmaxUFallの値と、カウンタ値ｎの値と、前記ステップ１９２５内に記載の式と同様のステップ１９４５内に記載した式とに基いて行われる。これにより、第２触媒５４の最上流のブロック１から最下流のブロックｍまでの各ブロックｎの最大酸素吸蔵量CmaxUF<n>の値が順次算出されていく。ステップ１９４５内に記載の式において、値A2は前記値A1と同様に正の定数であって、上記所定の勾配に相当する値である。なお、値A2は値A1と同一の値であっても異なる値であってもよい。
【０２０８】
ステップ１９４０の処理が繰り返されることによりカウンタ値ｎの値が第２触媒５４のブロック数ｍと等しくなると、ＣＰＵ７１はステップ１９５０にて「Ｙｅｓ」と判定してステップ１９５５に進み、酸素吸蔵量ＯＳＡ１,ＯＳＡ２の各々の値を「０」に設定した後、ステップ１９９５に進んで本ルーチンを一旦終了する。
【０２０９】
次に、触媒モデルにより第１触媒５３の各特定成分のCgoutSCを算出するためのルーチンについて説明する。このルーチンは図２１〜図２５の一連のフローチャートにより示されていて、ＣＰＵ７１はこれらのルーチンを所定時間の経過毎に繰り返し実行することで第１触媒５３の各ブロックｊ（j＝1,・・・,r）から流出する酸素濃度CgoutSC,O2<j>、一酸化窒素濃度CgoutSC,NO<j>、一酸化炭素濃度CgoutSC,CO<j>、及び炭化水素濃度CgoutSC,HC<j>を逐次算出する。
【０２１０】
従って、所定のタイミングになると、ＣＰＵ７１はステップ２１００から処理を開始し、ステップ２１０５に進んで第１触媒５３用の酸素吸蔵速度係数kstorSC,O2(k)<j>及びkstorSC,NO(k)<j>と、酸素放出速度係数krelSC,CO(k)<j>及びkrelSC,HC(k)<j>とを、第１触媒５３の温度TempSCと同第１触媒５３の劣化程度を表す劣化指標値REKKASCと図２６に示したようなマップ（ルックアップテーブル）とから決定する。なお、例えば、kstorSC,O2(k)<j>のように、SCが付与されている値は第１触媒用の値であることを意味し、<j>が付与されている値はブロックｊ（ｊ番目のブロック）に対する値であることを意味する（以下、同じ。）。
【０２１１】
上記触媒温度TempSC及び後述する第２触媒５４の触媒温度TempUFは、機関１０の運転状態（例えば、吸入空気流量Ｇａとエンジン回転速度NE）に応じて推定される。上記第１触媒５３の劣化指標値REKKASC及び後述する第２触媒５４の劣化指標値REKKAUFは、前述の第１触媒５３の最大酸素吸蔵量CmaxSCall及び第２触媒５４の最大酸素吸蔵量CmaxUFallに応じてそれぞれ求められる。例えば、劣化指標値REKKASCは最大酸素吸蔵量CmaxSCallが減少するほど増大する値として、劣化指標値REKKAUFは最大酸素吸蔵量CmaxUFallが減少するほど増大する値として求められる。
【０２１２】
次に、ＣＰＵ７１はステップ２１１０に進んで変数ｊの値を「０」に設定する。この変数ｊは、以下において何番目のブロックについての演算を行うのかを決定する変数である。次いで、ＣＰＵ７１は、ステップ２１１５にて変数ｊの値を「１」だけ増大するとともに、ステップ２１２０にて変数ｊの値がｒ＋１と等しくなったか否か、即ち、第１触媒５３の総べてのブロックについて各特定成分の算出が終了したか否かを判定する。
【０２１３】
現段階での変数ｊの値は「１」であるから、ＣＰＵ７１はステップ２１２０にて「Ｎｏ」と判定してステップ２１２５に進み、前回の本ルーチンの演算時において後述するステップ２１６０にて算出された第１触媒５３のｊ番目のブロック（ブロックｊ）のコート層の酸素濃度CwSC,O2(k+1)<j>を今回のコート層の酸素濃度CwSC,O2(k)<j>に設定し、続くステップ２１３０にて前回の本ルーチンの演算時において後述する図２５のステップ２５１５にて算出された酸素吸蔵密度OstSC(k+1)<j>を今回の酸素吸蔵密度Ostの値OstSC(k)<j>に設定する。なお、今回の演算が機関１０の始動後初めてである場合、上記各値には適当な初期値が与えられる。
【０２１４】
次いで、ＣＰＵ７１は、ステップ２１３５にて同ステップ２１３５内に記載した式（上記(36)式を参照。）に従って酸素の消費速度定数R*storSC,O2(k)<j>を求める。ステップ２１３５にて用いる最大酸素吸蔵密度OstSCmax<j>は、一定値としてもよいが、前記劣化指標値REKKASC（又は、最大酸素吸蔵量CmaxSCall）に応じて決定されることが望ましい（以下、同じ。）。その後、ＣＰＵ７１はステップ２１４０にて見かけの拡散速度R_DSC,O2(k)<j>を触媒温度TempSCとマップMapR_DSCO2とから決定する。
【０２１５】
続いて、ＣＰＵ７１はステップ２１４５にて酸素の反応律速因子SPstorSC,O2<j>を同ステップ２１４５内に記載した式（上記(29)式を参照。）により求め、ステップ２１５０にて第１触媒５３のブロックｊよりも前の（即ち、上流の）ブロックｊ−１から流出する酸素濃度CgoutSC,O2(k)<j-1>を同ブロックｊに流入する酸素濃度CginSC,O2(k)<j>として取り込む。
【０２１６】
この段階でｊの値は「１」であるから、ブロックｊは第１触媒５３の最も上流のブロックであって、それより前の（上流の）ブロックｊ−１は存在しない。従って、ステップ２１５０における前のブロックのCgoutSC,O2(k)<j-1>は、同第１触媒５３に流入する排ガスの酸素濃度CginSC,O2である。この第１触媒５３に流入する排ガスの酸素濃度CginSC,O2(=Cgin,O2)は、同第１触媒５３に流入する排ガスの空燃比と同排ガスの流量とに基く関数fO2により求められる。下記の(48)式の右辺は、この関数fO2の具体例である。(48)式で用いられる排ガスの空燃比AFは、エアフローメータ６１が計測する単位時間あたりの吸入空気質量Ｇａを最終燃料噴射量Ｆｉとエンジン回転速度NEとに基づいて求められる単位時間あたりの供給燃料質量Ｇｆで除することにより求められる。なお、この排ガスの空燃比AFは、最上流空燃比センサ６６の出力vabyfsと図２に示したマップとから求めても良い。
【０２１７】
【数４８】

【０２１８】
上記(48)式の導出過程を簡単に述べると、第１触媒５３に流入する排ガスの空燃比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、理論空燃比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(49)式が得られ、この(49)式から上記(48)式が得られる。
【０２１９】
【数４９】

【０２２０】
次に、ＣＰＵ７１はステップ２１５５に進み、同ステップ２１５５に記述した式（上記(30)式を参照。）に従ってCgoutSC,O2(k+1)<j>を求める。vgの値はエアフローメータ６１が検出した吸入空気流量ＡＦＭ（＝Ｇａ）とする。このように、ステップ２１５５では、対象としているブロックｊから流出する酸素濃度CgoutSC,O2を新たに算出する。次いで、ＣＰＵ７１はステップ２１６０に進み、同ステップ２１６０に記述した式（上記(28)式を参照。）に従ってCwSC,O2(k+1)<j>を求める。即ち、ＣＰＵ７１は、ステップ２１６０にて対象としている第１触媒５３のブロックｊのコート層の酸素濃度CwSC,O2を新たに算出し、ステップ２１６５を経由して図２２に示したステップ２２００に進む。このように、図２１により示したルーチンは、第１触媒５３のブロックｊ（特定領域ｊ）における排ガス相の酸素濃度推定手段、及びコート層の酸素濃度推定手段を構成している。
【０２２１】
図２２に示したルーチンは、一酸化窒素NOについての演算を行うルーチンであり、酸素O2についての演算を行うための先に説明した図２１のルーチンと同様なルーチンである。簡単に説明すると、ＣＰＵ７１はステップ２２００からステップ２２０５に進んで、前回の本ルーチンの演算時において後述するステップ２２３５にて算出された第１触媒５３のｊ番目のブロック（ブロックｊ）のコート層の一酸化窒素濃度CwSC,NO(k+1)<j>を今回のコート層の一酸化窒素濃度CwSC,NO(k)<j>に設定する。なお、今回の演算が機関１０の始動後初めてである場合、上記CwSC,NO(k)<j>には適当な初期値が与えられる。
【０２２２】
次いで、ＣＰＵ７１は、ステップ２２１０にて同ステップ２２１０内に記載した式（上記(36)式を参照。）に従って消費速度定数R*storSC,NO(k)<j>を求める。ここで、酸素吸蔵密度OstSC(k)<j>，及び最大酸素吸蔵密度OstSCmax<j>は、前述のステップ２１３５にて使用した値をそれぞれ用いる。その後、ＣＰＵ７１はステップ２２１５にて見かけの拡散速度R_DSC,NO(k)<j>を触媒温度TempSCとマップMapR_DSCNOとから決定する。
【０２２３】
続いて、ＣＰＵ７１はステップ２２２０にて一酸化窒素の反応律速因子SPstorSC,NO<j>を同ステップ２２２０内に記載した式（上記(29)式を参照。）により求め、ステップ２２２５にて第１触媒５３のブロックｊよりも前の（即ち、上流の）ブロックｊ−１から流出する一酸化窒素濃度CgoutSC,NO(k)<j-1>を同ブロックｊに流入する一酸化窒素濃度CginSC,NO(k)<j>として取り込む。
【０２２４】
この段階でｊの値は「１」であるから、対象としているブロックｊは第１触媒５３の最も上流のブロックであって、それより上流のブロックｊ−１は存在しない。従って、ステップ２２２５における前のブロックのCgoutSC,NO(k)<j-1>は、同第１触媒５３に流入する排ガスの一酸化窒素濃度CginSC,NOである。この場合、第１触媒５３に流入する排ガスの空燃比A/F（「Ｇａ／Ｇｆ」として計算により求められる。）と一酸化窒素濃度CginSC,NOとの関係は図２７のグラフに示したようであるから、この関係を予め実験により求めてマップとして記憶しておき、計算により求められる実際の排ガスの空燃比A/Fと同マップとから一酸化窒素濃度CginSC,NOを求める。
【０２２５】
次に、ＣＰＵ７１はステップ２２３０に進み、同ステップ２２３０に記述した式（上記(30)式を参照。）に従ってCgoutSC,NO(k+1)<j>を求める。即ち、対象としているブロックｊから流出する一酸化窒素濃度CgoutSC,NOを新たに算出する。次いで、ＣＰＵ７１はステップ２２３５に進み、同ステップ２２３５に記述した式（上記(28)式を参照。）に従ってCwSC,NO(k+1)<j>を求める。即ち、ＣＰＵ７１は、ステップ２２３５にて対象としている第１触媒５３のブロックｊのコート層の一酸化窒素濃度CwSC,NOを新たに算出し、ステップ２２９５を経由して図２３に示したステップ２３００に進む。このように、図２２により示したルーチンは、第１触媒５３のブロックｊ（特定領域ｊ）における排ガス相の一酸化窒素濃度推定手段、及びコート層の一酸化窒素濃度推定手段を構成している。
【０２２６】
図２３に示したルーチンは、一酸化炭素COについての演算を行うルーチンである。ＣＰＵ７１はステップ２２００からステップ２２０５に進んで、前回の本ルーチンの演算時において後述するステップ２３３５にて算出されたコート層の一酸化炭素濃度CwSC,CO(k+1)<j>を今回のコート層の一酸化炭素濃度CwSC,CO<j>(k)に設定する。なお、今回の演算が機関１０の始動後初めてである場合、上記CwSC,CO<j>(k)には適当な初期値が与えられる。
【０２２７】
次に、ＣＰＵ７１は、ステップ２３１０にて同ステップ２３１０内に記載した式（上記(38)式を参照。）に従って消費速度定数R*reducSC,CO(k)<j>を求め、その後、ステップ２３１５にて見かけの拡散速度R_DSC,CO(k)<j>を触媒温度TempSCとマップMapR_DSCCOとから決定する。
【０２２８】
続いて、ＣＰＵ７１はステップ２３２０にて一酸化炭素の反応律速因子SPreducSC,CO<j>を同ステップ２３２０内に記載した式（上記(33)式を参照。）により求め、ステップ２３２５にて、第１触媒５３のブロックｊよりも前の（即ち、上流の）ブロックｊ−１から流出する一酸化炭素濃度CgoutSC,CO(k)<j-1>を、ブロックｊに流入する一酸化炭素濃度CginSC,CO(k)<j>として取り込む。
【０２２９】
この段階でｊの値は「１」であるから、対象としているブロックｊは第１触媒５３の最も上流のブロックであって、それより上流のブロックｊ−１は存在しない。従って、ステップ２３２５における前のブロックのCgoutSC,CO(k)<j-1>は、同第１触媒５３に流入する排ガスの一酸化炭素濃度CginSC,COである。この場合、第１触媒５３に流入する排ガスの空燃比A/F（「Ｇａ／Ｇｆ」として計算により求められる。）と一酸化炭素濃度CginSC,COとの関係は図２８のグラフに示したようであるから、この関係を予め実験により求めてマップとして記憶しておき、計算により求められる実際の排ガスの空燃比A/Fと同マップとから一酸化炭素濃度CginSC,COを求める。
【０２３０】
次に、ＣＰＵ７１はステップ２３３０に進み、同ステップ２３３０に記述した式（上記(34)式を参照。）に従ってCgoutSC,CO(k+1)<j>を求める。即ち、第１触媒５３のブロックｊから流出する一酸化炭素濃度CgoutSC,COを新たに算出する。次いで、ＣＰＵ７１はステップ２３３５に進み、同ステップ２３３５に記述した式（上記(32)式を参照。）に従ってCwSC,CO(k+1)<j>を求める。即ち、ＣＰＵ７１は、ステップ２３３５にて対象としている第１触媒５３のブロックｊのコート層の一酸化炭素濃度CwSC,COを新たに算出し、ステップ２３９５を経由して図２４に示したステップ２４００に進む。このように、図２３により示したルーチンは、第１触媒５３のブロックｊにおける排ガス相の一酸化炭素濃度推定手段、及びコート層の一酸化炭素濃度推定手段を構成している。
【０２３１】
図２４に示したルーチンは、炭化水素HCについての演算を行うルーチンであり、一酸化炭素COについての演算を行うための先に説明した図２３のルーチンと同様なルーチンである。簡単に説明すると、ＣＰＵ７１はステップ２４００からステップ２４０５に進んで、前回の本ルーチンの演算時において後述するステップ２４３５にて算出されたコート層の炭化水素濃度CwSC,HC(k+1)<j>を今回のコート層の炭化水素濃度Cw,HCの値であるCwSC,HC(k)<j>に設定する。なお、今回の演算が機関１０の始動後初めてである場合、上記各値には適当な初期値が与えられる。
【０２３２】
次に、ＣＰＵ７１は、ステップ２４１０にて同ステップ２４１０内に記載した式（上記(38)式を参照。）に従って消費速度定数R*reducSC,HC(k)<j>を求め、その後、ステップ２４１５にて見かけの拡散速度R_DSC,HC(k)<j>を触媒温度TempSCとマップMapR_DSCHCとから決定する。
【０２３３】
続いて、ＣＰＵ７１はステップ２４２０にて炭化水素の反応律速因子SPreducSC,HC<j>を同ステップ２４２０内に記載した式（上記(33)式を参照。）により求め、ステップ２４２５にて、第１触媒５３のブロックｊよりも前の（即ち、上流の）ブロックｊ−１から流出する炭化水素濃度CgoutSC,HC(k)<j-1>をブロックｊに流入する炭化水素濃度CginSC,HC(k)<j>として取り込む。
【０２３４】
この段階でｊの値は「１」であるから、ブロックｊは第１触媒５３の最も上流のブロックであって、それより上流のブロックｊ−１は存在しない。従って、ステップ２４２５におけるCgout,HC(k)<j-1>は、同第１触媒５３に流入する排ガスの炭化水素濃度Cgin,HCである。この場合、第１触媒５３に流入する排ガスの空燃比A/F（「Ｇａ／Ｇｆ」として計算により求められる。）と炭化水素濃度Cgin,HCとの関係は図２９のグラフに示したようであるから、この関係を予め実験により求めてマップとして記憶しておき、計算により求められる実際の排ガスの空燃比A/Fと同マップとから炭化水素濃度Cgin,HCを求める。
【０２３５】
次に、ＣＰＵ７１はステップ２４３０に進み、同ステップ２４３０に記述した式（上記(34)式を参照。）に従ってCgoutSC,HC(k+1)<j>を求める。即ち、第１触媒５３のブロックｊから流出する炭化水素濃度CgoutSC,HCを新たに算出する。次いで、ＣＰＵ７１はステップ２４３５に進み、同ステップ２４３５に記述した式（上記(32)式を参照。）に従ってCwSC,HC(k+1)<j>を求める。即ち、ＣＰＵ７１は、ステップ２４３５にて第１触媒５３のブロックｊのコート層の炭化水素濃度Cw,HCを新たに算出し、ステップ２４９５を経由して図２５に示したステップ２５００に進む。このように、図２４により示したルーチンは、第１触媒５３のブロックｊ（特定領域ｊ）における排ガス相の炭化水素濃度推定手段、及びコート層の炭化水素濃度推定手段を構成している。
【０２３６】
図２５に示したルーチンは、酸素吸蔵密度Ostについての演算を行うルーチンである。ＣＰＵ７１は、ステップ２５００からステップ２５０５に進むと、上記(43)式に基く同ステップ２５０５内に記述した式により係数Ｐ<j>を求めるとともに、続くステップ２５１０にて上記(44)式に基く同ステップ２５１０に記述した式により係数Ｑ<j>を求める。次いで、ＣＰＵ７１はステップ２５１５にて上記(42)式に基く同ステップ２５１５に記述した式により酸素吸蔵密度OstSC(k+1)<j>を求め、次のステップ２５２０にて上記(45)式に基づく同ステップ２５２０に記述した式によりこのブロックｊの酸素吸蔵量OstSC(k+1)<j>・dA・Lをブロック１〜ブロックｊ−１までの酸素吸蔵量OSASC(j-1)に加えることにより、ブロック１〜ブロックｊまでの酸素吸蔵量OSASC(j)を求め、ステップ２５９５を経由して図２１のステップ２１１５に戻る。なお、酸素吸蔵量OSASC(0)の値は「０」に設定してある。このように、図２５に示したルーチンは、第１触媒５３のブロックｊの酸素吸蔵密度算出手段、及び第１触媒５３のブロック１〜ブロックｊまでの酸素吸蔵量算出手段を構成している。
【０２３７】
図２１のステップ２１１５に戻ったＣＰＵ７１は、変数ｊの値を「１」だけ増大するから、上述と同様にして第１触媒５３内の次に下流にあるブロックの各種値が順次演算されて行く。そして、ブロックｒまでの各種値が演算されると、変数ｊの値はステップ２１１５にてｒ＋１と等しくされるので、ＣＰＵ７１はステップ２１２０にて「Ｙｅｓ」と判定し、ステップ２１９５に進んで、第１触媒５３の各特定成分のCgoutSCを算出するための図２１〜図２５に示した一連のルーチンを一旦終了する。
【０２３８】
次に、触媒モデルにより第２触媒５４の各特定成分のCgoutUFを算出するためのルーチンについて説明する。このルーチンは前述の図２１〜図２５の一連のフローチャートに示されたルーチンとそれぞれ同様の図３０〜図３４の一連のフローチャートにより示されていて、ＣＰＵ７１はこれらのルーチンを実行することで第２触媒５４の各ブロックｊ（j＝1,・・・,m）から流出する酸素濃度CgoutUF,O2<j>、一酸化窒素濃度CgoutUF,NO<j>、一酸化炭素濃度CgoutUF,CO<j>、及び炭化水素濃度CgoutUF,HC<j>を算出する。かかる図３０〜図３４の一連のルーチンは前述の図２１〜図２５の一連のルーチンと同様であるので、これらの詳細な説明を省略する。
【０２３９】
なお、変数ｊの値が「１」である場合、ＣＰＵ７１は、図３０のステップ３０５０、図３１のステップ３１２５、図３２のステップ３２２５、及び図３３のステップ３３２５にてそれぞれ必要となる値である第２触媒５４に流入する排ガスの酸素濃度CginUF,O2（＝CginUF,O2(k)<1>）、同排ガスの一酸化窒素濃度CginUF,NO（＝CginUF,NO(k)<1>）、同排ガスの一酸化炭素濃度CginUF,CO（＝CginUF,CO(k)<1>）、及び同排ガスの炭素水素濃度CginUF,HC（＝CginUF,HC(k)<1>）として、第１触媒５３から流出する排ガス中の酸素濃度CgoutSC,O2<r>の値、同排ガス中の一酸化窒素濃度CgoutSC,NO<r>の値、同排ガス中の一酸化炭素濃度CgoutSC,CO<r>の値、及び同排ガス中の炭素水素濃度CgoutSC,HC<r>の値をそれぞれ使用する。第１触媒５３から流出した排ガスは外部との授受がないまま第２触媒５４に流入するので、第２触媒５４に流入する排ガス中の各特定成分の濃度は第１触媒５３から流出した排ガス中の各特定成分の濃度と等しいと考えられるからである。
【０２４０】
以上、図３０により示したルーチンは、第２触媒５４のブロックｊ（特定領域ｊ）における排ガス相の酸素濃度推定手段、及びコート層の酸素濃度推定手段を構成している。図３１により示したルーチンは、第２触媒５４のブロックｊ（特定領域ｊ）における排ガス相の一酸化窒素濃度推定手段、及びコート層の一酸化窒素濃度推定手段を構成している。図３２により示したルーチンは、第２触媒５４のブロックｊにおける排ガス相の一酸化炭素濃度推定手段、及びコート層の一酸化炭素濃度推定手段を構成している。図３３により示したルーチンは、第２触媒５４のブロックｊ（特定領域ｊ）における排ガス相の炭化水素濃度推定手段、及びコート層の炭化水素濃度推定手段を構成している。図３４に示したルーチンは、第２触媒５４のブロックｊの酸素吸蔵密度算出手段、及び第２触媒５４のブロック１〜ブロックｊまでの酸素吸蔵量算出手段を構成している。
【０２４１】
このように、ＣＰＵ７１は触媒モデルを使用し、第１，第２触媒５３，５４からなる触媒装置の劣化の進行（最大酸素吸蔵量の減少）に応じて下流側に移動する制御用ブロック（中間ブロック）ｉから流出するガスの空燃比に関連する値、即ち、制御用ブロックｉから流出する特定成分の量に関する値としての酸素の過不足量に関する値である制御用酸素濃度CgoutO2cを取得し、同制御用酸素濃度CgoutO2cが所定の程度を超えるリッチな空燃比であることを示す値となったとき（負の閾値Crefmnsよりも小さい値となったとき）同触媒装置に流入するガスの空燃比を所定のリーン空燃比（理論空燃比よりも所定値α１だけリーンな空燃比）に制御するとともに、同制御用酸素濃度CgoutO2cが所定の程度を超えるリーンな空燃比であることを示す値となったとき（正の閾値Crefplsよりも大きい値となったとき）同触媒装置に流入するガスの空燃比を所定のリッチ空燃比（理論空燃比よりも所定値α２だけリッチな空燃比）に制御することで同触媒装置に流入するガスの空燃比を強制的に振動させる（従って、パータベーション制御する）。
【０２４２】
従って、本排気浄化装置は、制御用ブロックｉの下流に設けられた空燃比センサの出力変化よりも早い時点で同制御用ブロックｉから流出するガスの空燃比の変化の情報（この場合、制御用酸素濃度CgoutO2c）を取得し、この取得した制御用ブロックｉから流出するガスの空燃比の変化の情報に直接着目して、触媒装置に流入するガスの空燃比を強制的に切り替えるタイミングを決定するパータベーション制御を行うので、同制御用ブロックｉから流出するガスの空燃比を安定的、且つ確実に理論空燃比近傍に維持することができ、その結果、制御用ブロックｉの下流側の有害成分の排出量を安定的、且つ確実に低減することができた。
【０２４３】
また、本排気浄化装置は、値ｎを自然数とするとき単数又は複数の触媒（第１，第２触媒５３，５４）からなる触媒装置の最上流のブロックである第１番目のブロックから第ｎ番目のブロックまでのブロックにより構成される触媒装置上流部の各ブロックの最大酸素吸蔵量を積算して同触媒装置上流部の最大酸素吸蔵量積算値（判定用酸素吸蔵量）を求める積算値算出手段（ステップ１１２０、１１５５）を備え、前記最大酸素吸蔵量積算値が所定の閾値Cthより大きい値をとる前記触媒装置上流部のうち前記値ｎが最も小さい第ｎ番目のブロックまでからなる前記触媒装置上流部の第ｎ番目のブロックを制御用ブロック（中間ブロック）ｉとして設定する。換言すれば、触媒装置の劣化の進行（最大酸素吸蔵量の減少）に応じて制御用ブロックｉは下流側に移動する。
【０２４４】
この結果、触媒装置の最上流に位置するブロックから中間ブロックｉまでの各ブロックで構成される触媒装置上流部の酸素吸蔵能力をパータベーション制御の破綻を来さない程度に設定された前記所定の閾値Cthに相当する所定の酸素吸蔵能力よりも大きい値に維持できるとともに、予備的な触媒（バッファ的な触媒）として機能し得る同中間ブロックｉよりも下流側のブロック数を最大とすることができる。従って、触媒装置に流入するガスの空燃比のハンチングを回避しつつ、触媒装置の最下流位置から流出する有害成分の排出量を極力低減できた。
【０２４５】
＜第２実施形態＞
次に、本発明による排気浄化装置の第２実施形態について説明すると、この排気浄化装置は、前記制御用ブロックｉから流出する排ガス中の酸素濃度である制御用酸素濃度CgoutO2cに代えて、同制御用ブロックｉから流出する排ガス中の酸化剤の量に関する値である一酸化窒素濃度（制御用一酸化窒素濃度CgoutNOc）、及び同制御用ブロックｉから流出する排ガス中の還元剤の量に関する値である一酸化炭素濃度（制御用一酸化炭素濃度CgoutCOc）を利用して、触媒装置に流入するガスの空燃比を強制的に切り替えるタイミングを決定するパータベーション制御を行う点においてのみ、上記第１実施形態の排気浄化装置と異なっている。従って、以下、かかる相違点についてのみ説明する。
【０２４６】
（第２実施形態の空燃比制御（パータベーション制御））
先ず、第２実施形態に係る排気浄化装置の空燃比制御について説明する。図３５は、第２実施形態によるパータベーション制御におけるタイムチャートであり、（Ａ）は機関１０に供給される混合気の空燃比（従って、第１触媒上流の排ガスの空燃比）を示し、（Ｂ）は前述した触媒モデルにより算出される前述の制御用ブロックｉから流出する制御用一酸化炭素濃度CgoutCOcを示し、（Ｃ）は同制御用ブロックｉから流出する制御用一酸化窒素濃度CgoutNOcを示している。図３５に示すように、本排気浄化装置は、前記制御用ブロックｉから流出する（正の値のみを採る）制御用一酸化窒素濃度CgoutNOc、及び制御用一酸化炭素濃度CgoutCOcを触媒モデルにより求め、同制御用一酸化窒素濃度CgoutNOc、及び制御用一酸化炭素濃度CgoutCOcを「０」付近に維持するように機関１０に供給される混合気の空燃比をパータベーション制御する。
【０２４７】
より具体的に述べると、本排気浄化装置は、CgoutCOcが正の閾値Crefpls1より大きくなったとき（即ち、還元剤の量（濃度）が所定の程度を超えた量になっていることを示す値となったとき、或いは、ガスの空燃比が所定の程度を超えるリッチな空燃比であることを示す値となったとき）、制御用ブロックｉから未燃成分が多く流出し始めたことを意味するので、機関１０に供給される混合気の目標空燃比を理論空燃比よりも所定値α１だけリーンに設定するとともに機関１０に供給される混合気の実際の空燃比が同目標空燃比になるように制御する（時刻ｔ11，ｔ13を参照。）。
【０２４８】
これに対し、CgoutNOcが正の閾値Crefpls2より大きくなったとき（即ち、酸化剤の量（濃度）が所定の程度を超えた量になっていることを示す値となったとき、或いは、ガスの空燃比が所定の程度を超えるリーンな空燃比であることを示す値となったとき）、制御用ブロックｉから窒素酸化物ＮＯｘが多く流出し始めたことを意味するので、機関１０に供給される混合気の目標空燃比を理論空燃比よりも所定値α２だけリッチに設定するとともに前記実際の空燃比が同目標空燃比になるように制御する（時刻ｔ12を参照。）。なお、所定値α１と所定値α２とは異なる値でもよく、等しい値であってもよい。また、正の閾値Crefpls1と正の閾値Crefpls2とは異なる値でもよく、等しい値であってもよい。
【０２４９】
（実際の作動）
次に、上記排気浄化装置の実際の作動について、ＣＰＵ７１が実行するルーチンを示したフローチャートを参照しながら説明する。本排気浄化装置のＣＰＵ７１は、図１１、図１２に代わる図３６、図３７にフローチャートにより示したルーチンを実行する点を除き、第１実施形態に係る排気浄化装置のＣＰＵ７１と同一のルーチンを実行する。図３６、図３７おいて図１１、図１２と同一のステップには同一の符号を付している。
【０２５０】
図３６のルーチンは、制御用ブロックｉから流出する排ガス中の酸素濃度である制御用酸素濃度CgoutO2cに代えて、同制御用ブロックｉから流出する排ガス中の一酸化窒素濃度、及び一酸化炭素濃度である制御用一酸化窒素濃度CgoutNOc、及び制御用一酸化炭素濃度CgoutCOcを求めるため、ステップ１１３５、１１７０に代えてステップ３６３５、３６７０を採用している点においてのみ図１１のルーチンと相違する。従って、図３６のルーチンの詳細な説明は省略する。
【０２５１】
また、図３７のルーチンは、正負の値を採りえる制御用酸素濃度CgoutO2cに代えて、常に正の値のみを採る制御用一酸化窒素濃度CgoutNOc、及び制御用一酸化炭素濃度CgoutCOcの各値を利用して触媒装置に流入するガスの空燃比を切り替えるため、ステップ１２１０、１２１５、１２２５、及び１２３０に代えてステップ３７１０、３７１５、３７２５、３７３０を採用している点においてのみ図１２のルーチンと相違する。従って、図３７のルーチンの詳細な説明は省略する。
【０２５２】
このように、第２実施形態に係る排気浄化装置は、触媒モデルにより触媒装置内での酸素吸蔵反応速度及び酸素放出反応速度をそれぞれ決定する酸素吸蔵速度係数（kstorSC,O2(k)<j>及びkstorSC,NO(k)<j>）及び酸素放出速度係数（krelSC,CO(k)<j>及びkrelSC,HC(k)<j>）を個別に設定し、これらの反応速度差を考慮してそれぞれ個別に且つ正確に算出され得る制御用一酸化窒素濃度CgoutNOc、及び制御用一酸化炭素濃度CgoutCOcの各値に基づいて、触媒装置に流入するガスの空燃比の切り替え時期を決定する。この結果、制御用ブロックｉから流出するガスの空燃比をさらに確実に理論空燃比近傍に維持することができ、触媒装置の最下流位置から流出する有害成分の排出量をさらに一層低減できた。
【０２５３】
なお、上記第２実施形態は、制御用ブロックｉから流出する制御用一酸化炭素濃度CgoutCOcが正の閾値Crefpls1より大きくなったとき、及び制御用ブロックｉから流出する制御用一酸化窒素濃度CgoutNOcが正の閾値Crefpls2より大きくなったときに触媒装置に流入するガスの空燃比を切り替えるように構成されているが、制御用ブロックｉから流出する炭化水素濃度である制御用炭化水素濃度CgoutHCc及び同制御用一酸化炭素濃度CgoutCOcが共に正の閾値Crefpls1より大きくなったとき、並びに制御用ブロックｉから流出する酸素濃度である制御用酸素濃度CgoutO2c及び同制御用一酸化窒素濃度CgoutNOcが共に正の閾値Crefpls2より大きくなったときに触媒装置に流入するガスの空燃比を切り替えるように構成してもよい。
【０２５４】
本発明は上記各実施形態に限定されることはなく、本発明の範囲内において種々の変形例を採用することができる。例えば、上記各実施形態においては、上述の触媒モデルを使用することなく、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）が所定の酸素吸蔵能力よりも大きい（所定の閾値Cthよりも大きい）ときは同第１触媒５３の下流であって第２触媒５４の上流の排気通路に配置された第１触媒下流空燃比センサ６７の出力を、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）が所定の酸素吸蔵能力以下（所定の閾値Cth以下）のときは同第２触媒５４の下流の排気通路に配置された第２触媒下流空燃比センサ６８の出力を制御用空燃比センサ出力として選択し、選択された制御用空燃比センサ出力が理論空燃比よりも所定の程度を超えるリッチな空燃比であることを示す値（例えば、０．７Ｖ以上）となったとき触媒装置に流入するガスの空燃比を所定のリーン空燃比に制御するとともに、同選択された制御用空燃比センサ出力が理論空燃比よりも所定の程度を超えるリーンな空燃比であることを示す値（例えば、０．３Ｖ以下）となったとき同触媒装置に流入するガスの空燃比を所定のリッチ空燃比に制御することで同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。
【０２５５】
また、上記各実施形態においては、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）が所定の酸素吸蔵能力よりも大きい（所定の閾値Cthよりも大きい）ときは同第１触媒５３から流出する排ガス中の特定成分の量に関する値（例えば、CgoutSC,X<r>。Xは酸素の場合O2、一酸化炭素の場合CO、炭化水素の場合HC、窒素酸化物の場合NO）を、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）が所定の酸素吸蔵能力以下（所定の閾値Cth以下）のときは同第２触媒５４から流出する排ガス中の特定成分の量に関する値（例えば、CgoutUF,X<m>）を制御用特定成分量（例えば、制御用特定成分濃度CgoutXc）として選択し、選択された制御用特定成分量が理論空燃比よりも所定の程度を超えるリッチな空燃比であることを示す値となったとき（例えば、制御用酸素濃度CgoutO2cが負の閾値Crefmnsよりも小さいとき）触媒装置に流入するガスの空燃比を所定のリーン空燃比に制御するとともに、同選択された制御用特定成分量が理論空燃比よりも所定の程度を超えるリーンな空燃比であることを示す値となったとき（例えば、制御用酸素濃度CgoutO2cが正の閾値Crefplsよりも大きいとき）同触媒装置に流入するガスの空燃比を所定のリッチ空燃比に制御することで同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。
【０２５６】
また、上記各実施形態においては、制御用ブロックｉは第１，第２触媒５３，５４からなる触媒装置の最上流に位置するブロック（第１触媒５３のブロック１）から最下流に位置するブロック（第２触媒５４のブロックｍ）までのブロックの中から選択されるように構成されているが、制御用ブロックｉは第１触媒５３のみからなる触媒装置の最上流に位置するブロック（第１触媒５３のブロック１）から最下流に位置するブロック（第１触媒５３のブロックｒ）までのブロックの中から選択されるように構成し、第２触媒５４は予備的な触媒（バッファ的な触媒）として機能させるように構成してもよい。
【０２５７】
この場合、第２触媒５４を省略してもよい。また、第２触媒５４を省略した場合、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）の大きさに係わらず、常に第１触媒下流空燃比センサ６７の出力を制御用空燃比センサ出力として使用し、同制御用空燃比センサ出力が理論空燃比よりも所定の程度を超えるリッチな空燃比であることを示す値（例えば、０．７Ｖ以上）となったとき触媒装置に流入するガスの空燃比を所定のリーン空燃比に制御するとともに、同選択された制御用空燃比センサ出力が理論空燃比よりも所定の程度を超えるリーンな空燃比であることを示す値（例えば、０．３Ｖ以下）となったとき同触媒装置に流入するガスの空燃比を所定のリッチ空燃比に制御することで同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。
【０２５８】
また、第２触媒５４を省略した場合、第１触媒５３の酸素吸蔵能力（最大酸素吸蔵量CmaxSCall）の大きさに係わらず、常に第１触媒５３から流出する排ガス中の特定成分の量に関する値（例えば、CgoutSC,X<r>。Xは酸素の場合O2、一酸化炭素の場合CO、炭化水素の場合HC、窒素酸化物の場合NO）を制御用特定成分量（例えば、制御用特定成分濃度CgoutXc）として使用し、同制御用特定成分量が理論空燃比よりも所定の程度を超えるリッチな空燃比であることを示す値となったとき（例えば、制御用酸素濃度CgoutO2cが負の閾値Crefmnsよりも小さいとき）触媒装置に流入するガスの空燃比を所定のリーン空燃比に制御するとともに、同選択された制御用特定成分量が理論空燃比よりも所定の程度を超えるリーンな空燃比であることを示す値となったとき（例えば、制御用酸素濃度CgoutO2cが正の閾値Crefplsよりも大きいとき）同触媒装置に流入するガスの空燃比を所定のリッチ空燃比に制御することで同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。
【０２５９】
また、上記各実施形態においては、第１，第２触媒５３，５４からなる触媒装置の下流の排気通路に配設された第２触媒下流空燃比センサ６８の出力を常に制御用空燃比センサ出力として使用し、同制御用空燃比センサ出力に基づいて上記と同様に同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。また、第１，第２触媒５３，５４からなる触媒装置から流出する排ガス中の特定成分の量に関する値（例えば、CgoutUF,X<m>。Xは酸素の場合O2、一酸化炭素の場合CO、炭化水素の場合HC、窒素酸化物の場合NO）を常に制御用特定成分量（例えば、制御用特定成分濃度CgoutXc）として使用し、同制御用特定成分量の値に基づいて上記と同様に同触媒装置に流入するガスの空燃比を強制的に振動させるように構成してもよい。
【０２６０】
また、上記各実施形態においては、酸素吸蔵能力を示す値である前述の触媒装置上流部の最大酸素吸蔵量に基づいて制御用ブロックｉを選択していたが、触媒装置の酸素吸蔵能力を間接的に示す車両の走行距離、触媒装置の温度、吸入空気流量Ｇａに基づいて制御用ブロックｉを選択してもよい。
【０２６１】
この場合、走行距離の増加に応じて、触媒温度の低下に応じて、吸入空気流量Ｇａの増加に応じて、制御ブロックｉの位置を下流側に移動するように構成することが好適である。走行距離の増加に伴って触媒装置が劣化してその最大酸素吸蔵量が低下するからであり、触媒装置の温度の低下に伴って同触媒装置の酸素吸蔵能力が低下するからであり、また、吸入空気量Ｇａの増大に伴って触媒装置が吸蔵し得る酸素量（即ち、酸素吸蔵能力である実質的な最大酸素吸蔵量）が低下するからである。
【０２６２】
また、上記各実施形態においては、上記パータベーション制御における理論空燃比からの振幅α（α１，α２により表される。）は、図３８に示したように、第１触媒５３の温度TempSC（第２触媒５４の温度TempUF）、吸入空気量Ｇａ、及び第１触媒５３の劣化指標値REKKASC（第２触媒５４の劣化指標値REKKAUF）等の少なくとも一つに応じて可変としてもよい。これによれば、触媒装置の酸素による一次被毒を適切に解消して、同触媒装置の状態をより良好に維持することが可能となる。
【図面の簡単な説明】
【図１】 本発明の第１実施形態に係る排気浄化装置を搭載した内燃機関の概略図である。
【図２】 図１に示した最上流空燃比センサの出力と空燃比との関係を示したグラフである。
【図３】 図１に示した第１触媒下流空燃比センサ及び第２触媒下流空燃比センサの各出力と空燃比との関係を示したグラフである。
【図４】 図１に示した排気浄化装置によるパータベーション制御を説明するためのタイムチャートである。
【図５】 触媒モデルを説明するための触媒の模式図である。
【図６】 図１に示した触媒の外観図である。
【図７】 図６に示した触媒の部分断面図である。
【図８】 触媒モデルを説明するための模式図である。
【図９】 触媒モデルで使用する風上法を説明するための模式図である。
【図１０】 図１に示したＣＰＵが実行する燃料噴射量計算のためのルーチンを示したフローチャートである。
【図１１】 図１に示したＣＰＵが実行する制御用酸素濃度を決定するためのルーチンを示したフローチャートである。
【図１２】 図１に示したＣＰＵが実行する目標空燃比を設定するためのルーチンを示したフローチャートである。
【図１３】 図１に示したＣＰＵが実行する空燃比フィードバック補正量を計算するためのルーチンを示したフローチャートである。
【図１４】 図１に示したＣＰＵが実行する最大酸素吸蔵量取得制御を開始するか否かを決定するためのルーチンを示したフローチャートである。
【図１５】 図１に示したＣＰＵが実行する第１モードのルーチンを示したフローチャートである。
【図１６】 図１に示したＣＰＵが実行する第２モードのルーチンを示したフローチャートである。
【図１７】 図１に示したＣＰＵが実行する第３モードのルーチンを示したフローチャートである。
【図１８】 図１に示したＣＰＵが実行する酸素吸蔵量を算出するためのルーチンを示したフローチャートである。
【図１９】 図１に示したＣＰＵが実行する最大酸素吸蔵量を算出するためのルーチンを示したフローチャートである。
【図２０】 第１触媒全体の最大酸素吸蔵量から同第１触媒のブロック毎の最大酸素吸蔵量を求めるためのマップである。
【図２１】 触媒モデルにしたがって第１触媒内部における酸素濃度を求めるためのルーチンを示したフローチャートである。
【図２２】 触媒モデルにしたがって第１触媒内部における一酸化窒素濃度を求めるためのルーチンを示したフローチャートである。
【図２３】 触媒モデルにしたがって第１触媒内部における一酸化炭素濃度を求めるためのルーチンを示したフローチャートである。
【図２４】 触媒モデルにしたがって第１触媒内部における炭化水素濃度を求めるためのルーチンを示したフローチャートである。
【図２５】 触媒モデルにしたがって第１触媒の酸素吸蔵密度と酸素吸蔵量を求めるためのルーチンを示したフローチャートである。
【図２６】 触媒劣化度と触媒温度とから触媒モデルにて使用する各係数（各乗数）を求めるためのマップである。
【図２７】 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ガスの空燃比と同一酸化窒素濃度との関係を規定したマップである。
【図２８】 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ガスの空燃比と同一酸化炭素濃度との関係を規定したマップである。
【図２９】 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ガスの空燃比と同炭化水素濃度との関係を規定したマップである。
【図３０】 触媒モデルにしたがって第２触媒内部における酸素濃度を求めるためのルーチンを示したフローチャートである。
【図３１】 触媒モデルにしたがって第２触媒内部における一酸化窒素濃度を求めるためのルーチンを示したフローチャートである。
【図３２】 触媒モデルにしたがって第２触媒内部における一酸化炭素濃度を求めるためのルーチンを示したフローチャートである。
【図３３】 触媒モデルにしたがって第２触媒内部における炭化水素濃度を求めるためのルーチンを示したフローチャートである。
【図３４】 触媒モデルにしたがって第２触媒の酸素吸蔵密度と酸素吸蔵量を求めるためのルーチンを示したフローチャートである。
【図３５】 本発明の第２実施形態に係る排気浄化装置によるパータベーション制御を説明するためのタイムチャートである。
【図３６】 第２実施形態に係る排気浄化装置のＣＰＵが実行する制御用一酸化窒素濃度、及び制御用一酸化炭素濃度を決定するためのルーチンを示したフローチャートである。
【図３７】 第２実施形態に係る排気浄化装置のＣＰＵが実行する目標空燃比を設定するためのルーチンを示したフローチャートである。
【図３８】 各実施形態のパータベーション制御における空燃比の制御幅を示したグラフである。
【符号の説明】
１０…内燃機関、５３…第１触媒、５４…第２触媒、６６…最上流空燃比センサ、６７…第１触媒下流空燃比センサ、６８…第２触媒下流空燃比センサ、７０…電気制御装置、７１…ＣＰＵ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine in which a catalyst is disposed in an exhaust passage.
[0002]
[Prior art]
Conventionally, in this type of exhaust purification device, control for forcibly oscillating the air-fuel ratio of the gas flowing into the catalyst around the theoretical air-fuel ratio (hereinafter sometimes referred to as “perturbation control”). It is known that when this is done, the catalyst is activated and the purification rate of the catalyst is improved. And patent document 1 is disclosing the exhaust gas purification apparatus (air-fuel-ratio control apparatus) which can always ensure the maximum purification rate of a catalyst, when performing this perturbation control.
[0003]
More specifically, this exhaust gas purification apparatus is configured such that the amount of oxygen stored in the catalyst (hereinafter referred to as “oxygen storage amount”) and the maximum amount of oxygen that can be stored in the catalyst (hereinafter referred to as “ And the oxygen utilization rate is calculated based on the calculated oxygen utilization rate, and the mixture gas supplied to the internal combustion engine is maximized based on the calculated oxygen utilization rate. Force the air-fuel ratio to oscillate. At the same time, this exhaust purification device updates the frequency of forced vibration and the change speed of the amplitude linearly or hyperbola in accordance with the space velocity corresponding to the amount of exhaust gas and the catalyst temperature. Patent Document 1 describes that with such a configuration, it is possible to always ensure the maximum purification rate of the catalyst according to the operating state of the internal combustion engine and the state of the catalyst and to improve the emission characteristics of the exhaust gas. .
[0004]
[Patent Document 1]
JP 7-259600 A
[0005]
[Problems to be solved by the invention]
In the perturbation control performed by the conventional exhaust purification apparatus, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is forced to vibrate by paying attention to the calculated oxygen utilization rate (catalyst purification rate). It is not forcedly vibrated by directly paying attention to the state of the exhaust gas flowing out from the catalyst, for example, the air-fuel ratio of the exhaust gas, the discharge amount of the specific component in the exhaust gas, and the like. Therefore, if there is a situation in which the air-fuel ratio of the exhaust gas flowing out from the catalyst temporarily deviates greatly from the stoichiometric air-fuel ratio due to the operating state of the internal combustion engine, even if the purification rate of the catalyst is good, There was a problem that a large amount of emissions were discharged.
[0006]
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to reduce the emission emission amount stably and reliably by directly controlling the air-fuel ratio of the gas flowing into the catalyst by paying attention directly to the state of the exhaust gas flowing out from the catalyst. An object is to provide an exhaust emission control device.
[0007]
  In order to achieve this object, an exhaust emission control device for an internal combustion engine according to the present invention comprises a single catalyst provided in an exhaust passage of the internal combustion engine or a catalyst device comprising a plurality of catalysts provided in series in the exhaust passage. ,in frontTouchWhen the medium device is divided into multiple blocks along the flow direction of the gas flowing into the catalyst deviceControl block that is one block located upstream from the most downstream blockGas air-fuel ratio related value acquisition means for acquiring a value related to the air-fuel ratio of the gas flowing out from the gas, and the value related to the air-fuel ratio of the acquired gas is such that the air-fuel ratio of the gas is a predetermined degree than the stoichiometric air-fuel ratio The air-fuel ratio of the gas flowing into the catalyst device when the value indicates that the air-fuel ratio is rich.Leaner than theoretical air-fuel ratioWhen controlling to a predetermined lean air-fuel ratio, and the value related to the air-fuel ratio of the same gas becomes a value indicating that the air-fuel ratio of the same gas is a lean air-fuel ratio that exceeds the theoretical air-fuel ratio by a predetermined degree The air-fuel ratio of the gas flowing into the catalyst deviceRicher than the theoretical air-fuel ratioBy controlling to a predetermined rich air-fuel ratio, the air-fuel ratio of the gas flowing into the catalyst device is reduced.By alternately switching from the predetermined lean air-fuel ratio to the predetermined rich air-fuel ratio or from the predetermined rich air-fuel ratio to the predetermined lean air-fuel ratioAir-fuel ratio forced oscillation means for forcibly oscillating.
[0008]
  Here, the “block” isWhen the catalyst device is composed of a single (one) catalyst, the oneEach of the plurality of blocks when the catalyst is virtually divided into a plurality of blocks along the exhaust gas flow directionIs. Moreover, when a catalyst apparatus consists of a some catalyst, the block caught by the catalyst unit and the some block when one catalyst is divided | segmented virtually may be mixed.
[0009]
  The gas air / fuel ratio related value acquisition means for acquiring a value related to the air / fuel ratio of the gas flowing out from the control block is, for example, an exhaust passage downstream of the control block (single on the downstream side of the control block). Or there are multiple blocksFrom, specifically,The air-fuel ratio of the gas flowing out from the control block is reduced by an air-fuel ratio sensor disposed in the exhaust passage upstream of the block located downstream of the control block and downstream of the control block. Even if it is means for physically detecting the value related to the air-fuel ratio of the same gas, the value related to the amount of the specific component in the gas flowing out from the control block (for example, the concentration of the specific component or the absolute value of the specific component) (Amount etc.) may be estimated (acquired) as a value related to the air-fuel ratio of the gas by calculation taking into account the reaction in the control block. Examples of the specific component include components to be purified with a catalyst such as carbon monoxide CO, hydrocarbon HC, nitrogen oxide NOx, and oxygen O₂(Excess and deficiency). When the gas air-fuel ratio related value acquisition means is composed of the air-fuel ratio sensor, the control block is limited to the block located in the most downstream in the nearest catalyst located upstream of the air-fuel ratio sensor.
[0010]
The air-fuel ratio forced oscillation means for forcibly oscillating the air-fuel ratio of the gas flowing into the catalyst device may be means for forcibly oscillating the air-fuel ratio of the air-fuel mixture supplied to the engine, or The air-fuel ratio of the gas flowing into the catalyst device by controlling the air-fuel ratio of the air-fuel mixture sucked into the engine and supplying air or fuel from a nozzle or the like provided in the exhaust passage upstream of the catalyst device It may be a means for forcibly vibrating. If the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled, the air-fuel ratio of the gas flowing into the catalyst device can be controlled.
[0011]
  According to this, one of the catalyst devicesPartDirectly paying attention to the value related to the air-fuel ratio of the gas flowing out from the control block, the air-fuel ratio of the gas flowing into the catalyst device is changed from the predetermined rich air-fuel ratio to the predetermined lean air-fuel ratio, or the predetermined predetermined air-fuel ratio. Since the perturbation control for switching from the lean air-fuel ratio to the predetermined rich air-fuel ratio is performed, the air-fuel ratio of the gas flowing out from the control block can be stably and reliably maintained in the vicinity of the theoretical air-fuel ratio, As a result, it is possible to stably and reliably reduce the discharge amount of harmful components at least downstream of the control block.
[0012]
In this case, the gas air-fuel ratio related value acquisition means is configured to acquire a value related to the amount of the specific component in the gas flowing out from the control block as a value related to the air-fuel ratio of the gas. Is preferred.
[0013]
When the air-fuel ratio of the gas flowing out from the control block is detected as a value related to the air-fuel ratio of the gas by an air-fuel ratio sensor (for example, an O2 sensor) disposed in the exhaust passage downstream of the control block, The exhaust gas flowing out from the block reaches the air-fuel ratio sensor after a predetermined time from the time when it flows out, and then the air-fuel ratio is detected when the response delay time of the air-fuel ratio sensor elapses. Therefore, a predetermined time is required until the change in the air-fuel ratio of the gas flowing out from the control block appears as the change in the output of the air-fuel ratio sensor.
[0014]
On the other hand, as described above, if the value related to the amount of the specific component in the gas flowing out from the control block is obtained by calculation as a value related to the air-fuel ratio of the gas, more appropriate timing can be obtained. Thus, the air-fuel ratio of the gas flowing into the catalyst device can be switched from the predetermined rich air-fuel ratio to the predetermined lean air-fuel ratio, or from the predetermined lean air-fuel ratio to the predetermined rich air-fuel ratio. As a result, the air-fuel ratio of the gas flowing out from the control block can be more reliably maintained near the stoichiometric air-fuel ratio.
[0015]
Further, in the exhaust purification apparatus, the gas air-fuel ratio related value acquisition means acquires a value related to an excess / deficiency amount of oxygen in the gas flowing out from the control block as a value related to the amount of the specific component in the gas. The air-fuel ratio forced oscillation means is configured such that the value relating to the excess / deficiency of oxygen in the gas becomes a value indicating that the degree of oxygen deficiency in the gas exceeds a predetermined level. The air-fuel ratio of the gas flowing into the catalyst device is controlled to the predetermined lean air-fuel ratio, and the value relating to the excess / deficiency of oxygen in the gas exceeds the predetermined extent of the oxygen excess in the gas The air-fuel ratio of the gas flowing into the catalyst device is controlled to the predetermined rich air-fuel ratio by forcing the air-fuel ratio of the gas flowing into the catalyst device to oscillate. To be done It is suitable.
[0016]
The air-fuel ratio of the gas flowing out from the control block becomes a lean air-fuel ratio when oxygen in the gas is excessive, and becomes a rich air-fuel ratio when oxygen in the gas is insufficient. Therefore, the excess or deficiency of oxygen in the gas can be a value (related to the air / fuel ratio) indicating the air / fuel ratio of the gas. Therefore, if configured as described above, the air-fuel ratio of the gas flowing into the catalyst device is determined based on one value obtained by calculation, which is “a value relating to the excess or deficiency of oxygen in the gas flowing out from the control block”. Therefore, the calculation required for air-fuel ratio control can be simplified.
[0017]
Alternatively, in the exhaust emission control device, the gas air-fuel ratio related value acquisition means specifies a value relating to the amount of oxidant in the gas flowing out from the control block and a value relating to the amount of reducing agent respectively in the gas. The air-fuel ratio forced oscillation means is configured to obtain a value relating to the amount of a component, and the value relating to the amount of reducing agent in the gas is an amount in which the amount of reducing agent in the gas exceeds a predetermined level. When the air-fuel ratio of the gas flowing into the catalyst device is controlled to the predetermined lean air-fuel ratio, the value related to the amount of oxidant in the gas is the value of the oxidant in the gas. Gas flowing into the catalyst device by controlling the air-fuel ratio of the gas flowing into the catalyst device to the predetermined rich air-fuel ratio when the amount becomes a value indicating that the amount exceeds a predetermined level Force the air-fuel ratio of It is preferably configured so as to dynamic. Here, the “oxidant” in the gas is, for example, nitrogen oxide NOx, oxygen O₂The “reducing agent” in the gas is, for example, carbon monoxide CO or hydrocarbon HC.
[0018]
The air-fuel ratio of the gas flowing out from the control block becomes a lean air-fuel ratio when the amount of oxidizing agent in the gas is large (the amount of reducing agent in the gas is very small at this time), and the same When the amount of reducing agent in the gas is large (the amount of oxidizing agent in the gas is very small at this time), the air-fuel ratio becomes rich. Therefore, the amount of the oxidizing agent and the amount of the reducing agent in the gas can be a value indicating the air / fuel ratio of the gas (related to the air / fuel ratio). Further, the amount of oxidant in the gas flowing out from the control block is the amount of oxygen stored in the catalyst (in the control block).₂While depending on the oxygen storage speed related to the storage function (hereinafter referred to as “oxygen storage function”), the amount of reducing agent in the outflowing gas depends on the oxygen release (storage) related to the oxygen storage function. De) depends on speed. Therefore, if configured as described above, for example, the oxygen storage rate and the oxygen release rate in the catalyst (in the control block) are individually set and the difference between these reaction rates is considered individually and accurately. The switching timing of the air-fuel ratio of the gas flowing into the catalyst device can be determined on the basis of the amount of oxidant flowing out from the control block and the amount of reducing agent that can be calculated in the control block. It is possible to maintain the air-fuel ratio of the gas to be in the vicinity of the theoretical air-fuel ratio more reliably.
[0019]
  Furthermore, in the exhaust emission control device according to the present invention, the control block in which the value related to the air / fuel ratio of the gas acquired by the gas / air / fuel ratio related value acquisition means is located upstream of the block located in the most downstream position. Related to gas flowing out of
[0020]
According to this, the air-fuel ratio of the exhaust gas can be maintained in the vicinity of the theoretical air-fuel ratio at the position of the outlet of the intermediate block of the catalyst device (or the amount of the specific component in the exhaust gas is made substantially “0”). Can do). Therefore, even if harmful components flow out of the intermediate block due to an unavoidable control delay of perturbation control (air-fuel ratio feedback control), the amount of outflow is very small and the block located downstream from the intermediate block Therefore, it is possible to further reduce the discharge amount of harmful components in the exhaust gas flowing out from the most downstream position of the catalyst device. In other words, the block downstream of the intermediate block can function as a preliminary catalyst.
[0021]
  Furthermore, in the exhaust emission control device according to the present invention,The gas air-fuel ratio related value acquisition means is the catalyst device.Maximum amount of oxygen that can be stored (maximum oxygen storage amount)According to the decline ofFor controlConfigured to move the block position downstreamThe
[0022]
  In the perturbation control described above, when the air-fuel ratio of the gas flowing into the catalyst device is controlled to a predetermined rich air-fuel ratio, the block located at the uppermost stream isFor controlAfter all the oxygen stored in each block up to the block is consumed and the oxygen storage amount in each block reaches substantially “0”,For controlWhen the air-fuel ratio of the gas flowing out from the block turns rich, the air-fuel ratio of the gas flowing into the catalyst device is switched to a predetermined lean air-fuel ratio. Similarly, when the air-fuel ratio of the gas flowing into the catalyst device is controlled to the predetermined lean air-fuel ratio, all the oxygen storage amounts in the respective blocks substantially reach the maximum oxygen storage amount, sameFor controlWhen the air-fuel ratio of the gas flowing out from the block changes to lean, the air-fuel ratio of the gas flowing into the catalyst device is switched to the predetermined rich air-fuel ratio. In other words, the air-fuel ratio switching period in the perturbation control is changed from the block located at the uppermost stream to the above-mentioned.For controlOf the upstream part (or the entire catalytic device) of the catalytic device composed of each block up to the blockMaximum oxygen storage capacityThe smaller the value, the shorter.
[0023]
  Therefore, due to the deterioration of the catalytic device, the catalytic device (upstream part)Maximum oxygen storage capacityWhen the air-fuel ratio becomes small to some extent, the air-fuel ratio switching period in the perturbation control becomes extremely short, so that the air-fuel ratio largely fluctuates (hunts), and as a result, the perturbation control fails. In contrast, as described above, the catalytic deviceMaximum oxygen storage capacityAccording to the decline ofFor controlIf the block position is configured to move downstream, the upstream portion of the catalytic deviceMaximum oxygen storage capacitySameFor controlThe block position is increased by the amount moved downstream. Therefore, even if the catalyst device is deteriorated, the upstream portion of the catalyst deviceMaximum oxygen storage capacityCan be maintained at a value large enough not to cause perturbation control failure. As a result, the air-fuel ratio hunting described above can be avoided, and an increase in the emission amount of harmful components in the exhaust gas can be avoided.
[0024]
  More specifically, the exhaust emission control device is configured by blocks from a first block to an nth block which are the most upstream blocks among the plurality of blocks when the value n is a natural number. The upstream of the catalytic deviceMaximum oxygen storage capacityOxygen storage capacity acquisition means for acquiring the gas air-fuel ratio related value acquisition means,Maximum oxygen storage capacityBased on the prescribedvalueBigger thanMaximum oxygen storage capacityThe nth block constituting the upstream portion of the catalytic device having the smallest value n among the upstream portion of the catalytic device determined to haveFor controlSuitably configured to be set as a block.
[0025]
  According to this, from the block located in the most upstream, the saidFor controlOf the upstream part of the catalytic device composed of each block up toMaximum oxygen storage capacityCan be set to a level that does not cause the perturbation control to failvalueCan be maintained at a higher value, and can function as a preliminary catalyst as described above.For controlThe number of blocks downstream from the blocks can be maximized. Therefore, the amount of harmful components discharged from the most downstream position of the catalyst device can be reduced as much as possible while avoiding the air-fuel ratio hunting described above.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Embodiments of an exhaust emission control device according to the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a system in which an exhaust emission control device (air-fuel ratio control device) according to a first embodiment of the present invention is applied to a spark ignition type multi-cylinder (four-cylinder) internal combustion engine 10. In addition, in FIG. 1, although the cross section of one cylinder is shown, the other cylinder is also equipped with the same structure.
[0028]
The internal combustion engine 10 includes a cylinder block unit 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head unit 30 fixed on the cylinder block unit 20, and a gasoline mixture in the cylinder block unit 20. An intake system 40 for supplying the exhaust gas, and an exhaust system 50 for releasing the exhaust gas from the cylinder block 20 to the outside.
[0029]
The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The heads of the cylinder 21 and the piston 22 form a combustion chamber 25 together with the cylinder head portion 30.
[0030]
The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and continuously changes the phase angle of the intake camshaft. The variable intake timing device 33, the actuator 33 a of the variable intake timing device 33, the exhaust port 34 communicating with the combustion chamber 25, the exhaust valve 35 that opens and closes the exhaust port 34, the exhaust camshaft 36 that drives the exhaust valve 35, and the spark plug 37 And an igniter 38 including an ignition coil that generates a high voltage to be applied to the spark plug 37, and an injector (fuel injection means) 39 for injecting fuel into the intake port 31.
[0031]
The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. A throttle valve 43 that makes the opening cross-sectional area of the intake passage variable, and a throttle valve actuator 43a composed of a DC motor that constitutes the throttle valve driving means are provided.
[0032]
The exhaust system 50 includes an exhaust manifold 51 communicating with the exhaust port 34, an exhaust pipe (exhaust pipe) 52 connected to the exhaust manifold 51, and an upstream first catalyst (upstream) disposed (intervened) in the exhaust pipe 52. And a second catalyst (downstream three-way catalyst or vehicle floor) disposed (intervened) in the exhaust pipe 52 downstream of the first catalyst 53. (It is also called an under-floor converter because it is disposed below.) 54. Here, the exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Further, the first catalyst 53 and the second catalyst 54 arranged in series constitute a catalyst device.
[0033]
On the other hand, this system includes a hot-wire air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, and an air-fuel ratio sensor 66 (disposed in the exhaust passage upstream of the first catalyst 53). Hereinafter, it is referred to as “the most upstream air-fuel ratio sensor 66”), and an air-fuel ratio sensor 67 (hereinafter referred to as “first catalyst”) disposed in the exhaust passage downstream of the first catalyst 53 and upstream of the second catalyst 54. A downstream air-fuel ratio sensor 67 "), an air-fuel ratio sensor 68 (hereinafter referred to as" second catalyst downstream air-fuel ratio sensor 68 ") disposed in the exhaust passage downstream of the second catalyst 54, and An accelerator opening sensor 69 is provided.
[0034]
The hot-wire air flow meter 61 outputs a voltage corresponding to the mass flow rate AFM (= Ga) of the intake air flowing through the intake pipe 41. The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal representing the throttle valve opening TA. The cam position sensor 63 generates a signal (G2 signal) having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). The crank position sensor 64 outputs a signal having a narrow pulse every time the crankshaft 24 rotates 10 °, and a wide pulse every time the crankshaft 24 rotates 360 °. This signal represents the engine speed NE. The water temperature sensor 65 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.
[0035]
As shown in FIG. 2, the most upstream air-fuel ratio sensor 66 outputs a current corresponding to the air-fuel ratio A / F and outputs a voltage vabyfs corresponding to this current. As is apparent from FIG. 2, the most upstream air-fuel ratio sensor 66 can detect the air-fuel ratio A / F over a wide range with high accuracy. As shown in FIG. 3, the first catalyst downstream air-fuel ratio sensor 67 and the second catalyst downstream air-fuel ratio sensor 68 output voltages Voxs1 and Voxs2 that suddenly change at the stoichiometric air-fuel ratio. More specifically, the first and second catalyst downstream air-fuel ratio sensors 67 and 68 are approximately 0.1 (V) when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas is When the air-fuel ratio is richer than the stoichiometric air-fuel ratio, a voltage of approximately 0.9 (V) is output, and when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, a voltage of approximately 0.5 (V) is output. The accelerator opening sensor 69 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81.
[0036]
In addition, the system includes an electrical control device 70. The electric control device 70 includes a CPU 71 connected by a bus, a routine (program) executed by the CPU 71, a table (look-up table, map), a ROM 72 in which constants and the like are stored in advance, and the CPU 71 temporarily stores data as necessary. This is a microcomputer comprising a RAM 73 for storing data, a backup RAM 74 for storing data while the power is turned on and holding the stored data while the power is shut off, an interface 75 including an AD converter, and the like. . The interface 75 is connected to the sensors 61 to 69, supplies signals from the sensors 61 to 69 to the CPU 71, and in response to instructions from the CPU 71, the actuator 33a, the igniter 38, the injector 39, and the variable intake timing device 33 A drive signal is sent to the throttle valve actuator 43a.
[0037]
(Perturbation control of the first embodiment)
Next, the perturbation control of the exhaust purification device will be described. FIG. 4 is a time chart in the perturbation control. FIG. 4A shows the air-fuel ratio of the air-fuel mixture supplied to the engine 10 (accordingly, the air-fuel ratio of the exhaust gas upstream of the first catalyst), and FIG. Out of a later-described control block (i.e., an i-th block as a catalyst device comprising an intermediate block, a first catalyst 53 and a second catalyst 54, hereinafter also referred to as "block i") calculated by the catalyst model. The control oxygen concentration CgoutO2c is shown.
[0038]
Here, the control oxygen concentration CgoutO2c flowing out from the control block (block i) constituting a part of the catalyst device will be briefly described. In the catalyst model to be described later, as shown in FIG. 5, a cylindrical catalyst is virtually divided at equal intervals from the upstream side of the catalyst on a plane orthogonal to the axis of the cylinder. Form a block. The catalyst model performs a predetermined calculation for each block of each catalyst, and obtains a concentration Cgout of a specific component (for example, oxygen, carbon monoxide, hydrocarbon, nitrogen oxide, etc.) flowing out from each block. . Each block is defined as a first block, a second block,..., An nth block in order from the most upstream (the side into which exhaust gas flows) of each catalyst.
[0039]
In the catalyst model of the present embodiment, the first catalyst 53 is divided into r blocks (r is an integer of 2 or more) and the second catalyst 54 is divided into m blocks (m is an integer of 2 or more). I do. In this specification, when the specific component is X and the target block is the k-th block (block k) of each catalyst, the specific component X in the exhaust gas flowing out from the block k of the first catalyst 53 is used. The concentration of (X is O2 for oxygen, CO for carbon monoxide, HC for hydrocarbons, NO for nitrogen oxides) is CgoutSC, X <k>, and flows out from the kth block of the second catalyst 54. The concentration of the specific component X in the exhaust gas is expressed as CgoutUF, X <k>.
[0040]
As is apparent from the above, the control oxygen concentration CgoutO2c is set when the control block (block i) is set to one of r blocks of the first catalyst 53 (1 <i ≦ r ) Is the oxygen concentration CgoutSC, O2 <i> in the exhaust gas flowing out from the block i of the first catalyst 53, and the control block is set to one of the m blocks of the second catalyst 54. (R <i <(r + m)) is the oxygen concentration CgoutUF, O2 <ir> in the exhaust gas flowing out from the block (ir) of the second catalyst 54. That is, the value “i” is determined to be an integer greater than “1” and smaller than “r + m” (1 <i <(r + m)). Here, the control oxygen concentration CgoutO2c is expressed as “a plurality of ((r + m)) blocks along the flow direction of the exhaust gas flowing into the catalyst device including the first catalyst 53 and the second catalyst 54”. An intermediate block (control block, block i) located upstream from the block located downstream (block m of the second catalyst 54) when virtually divided (when divided into a plurality of blocks). It is a value related to the air-fuel ratio of the gas flowing out from. Further, when the control oxygen concentration CgoutO2c is a positive value, it means that oxygen is excessive and NOx is flowing out from the block i, and when it is a negative value, oxygen is insufficient. This means that unburned CO and HC are flowing out from the block i. Therefore, the control oxygen concentration CgoutO2c can be said to be a value related to the excess or deficiency of oxygen in the exhaust gas flowing out from the control block.
[0041]
Referring to FIG. 4 again, the present exhaust purification apparatus obtains the control oxygen concentration CgoutO2c flowing out from the control block i set as described later from the catalyst model, and calculates the control oxygen concentration CgoutO2c near “0”. The air-fuel ratio of the air-fuel mixture supplied to the engine 10 is perturbed so as to be maintained at the above. More specifically, the present exhaust purification apparatus is configured such that when CgoutO2c becomes smaller than the negative threshold value Crefmns (that is, when the value of oxygen deficiency exceeds a predetermined level, or When the gas air-fuel ratio becomes a value indicating that the air-fuel ratio is a rich air-fuel ratio exceeding a predetermined level), it means that a large amount of unburned components have started to flow out from the control block i. The target air-fuel ratio of the supplied air-fuel mixture is set to be lean by a predetermined value α1 from the stoichiometric air-fuel ratio, and control is performed so that the actual air-fuel ratio of the air-fuel mixture supplied to the engine 10 becomes the target air-fuel ratio (time). (See t1, t3.)
[0042]
On the other hand, when CgoutO2c becomes larger than the positive threshold Crefpls (that is, when the oxygen excess level exceeds a predetermined level, or when the gas air-fuel ratio is a predetermined level) This means that a large amount of oxygen (and therefore NOx) has started to flow out of the control block i, so that the air-fuel ratio supplied to the engine 10 The target air-fuel ratio is set to be richer by a predetermined value α2 than the theoretical air-fuel ratio, and control is performed so that the actual air-fuel ratio becomes the target air-fuel ratio (see time t2). The predetermined value α1 and the predetermined value α2 may be different values or may be equal values. The means for forcibly oscillating (switching) the air-fuel ratio of the gas flowing into the catalyst device in this way corresponds to the air-fuel ratio forced oscillation means.
[0043]
(Catalyst model)
Next, a catalyst model (estimated model) employed by the exhaust purification apparatus will be described. In constructing the catalyst model, since the first catalyst 53 and the second catalyst 54 have the same configuration and function, the following description will be given mainly using the first catalyst 53 as an example.
[0044]
As shown in FIG. 6, the first catalyst 53 is a three-way catalyst called a columnar monolith catalytic converter having an elliptical cross section (having a constant cross section of dA), and is the same in a plane perpendicular to the axis. As shown in FIG. 7 which is an enlarged cross-sectional view of the first catalyst 53, the inside thereof is subdivided into an axial space extending in the axial direction by a carrier 53a 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 referred to as a cell. The carrier 53a is coated with an alumina coating layer 53b. The coating layer 53b includes an active component (catalyst component) made of a noble metal such as platinum (Pt) and ceria (CeO).₂) And other components.
[0045]
Since the first catalyst 53 carries a noble metal such as platinum, when the air-fuel ratio of the exhaust gas flowing into the first catalyst 53 is the stoichiometric air-fuel ratio, the unburned components (HC, CO) are oxidized and simultaneously It has a catalytic function to reduce nitrogen oxides (NOx). Further, the first catalyst 53 has the above-described oxygen storage function of storing (adsorbing) and releasing oxygen molecules in the exhaust gas flowing into the first catalyst 53 by supporting the components such as ceria. Therefore, even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio to a certain extent by this oxygen storage function, HC, CO, and NOx can be purified.
[0046]
Therefore, in the perturbation control as shown in FIG. 4, the air-fuel ratio of the gas flowing into the first catalyst 53 is controlled to a predetermined rich air-fuel ratio (the air-fuel ratio richer by the predetermined value α2 than the theoretical air-fuel ratio). At this time, the oxygen stored in the catalyst device composed of the first catalyst 53 and the second catalyst 54 changes from that in the block located at the uppermost stream of the first catalyst 53 to the most of the second catalyst 54. From the time when the oxygen stored in all the ((r + m)) blocks in the catalyst device is consumed substantially until the one in the block located downstream is consumed. A large amount of unburned components HC and CO start to flow out from the most downstream block m of the second catalyst 54, and the oxygen concentration CgoutUF, O2 <m> in the exhaust gas flowing out from the most downstream block m becomes smaller than the negative threshold value Crefmns.
[0047]
On the other hand, when the air-fuel ratio of the gas flowing into the first catalyst 53 is controlled to a predetermined lean air-fuel ratio (an air-fuel ratio leaner than the theoretical air-fuel ratio by the predetermined value α1), oxygen flowing into the catalyst device Are sequentially stored from the block located at the uppermost stream of the first catalyst 53, and the oxygen storage amount of all ((r + m)) blocks in the catalyst device is substantially all the maximum oxygen storage amount. From the time when the gas reaches NO, a large amount of nitrogen oxide NOx starts to flow out from the most downstream block m of the second catalyst 54, and the oxygen concentration CgoutUF, O2 <m> in the exhaust gas flowing out from the most downstream block m of the second catalyst 54 becomes It becomes larger than the positive threshold value Crefpls.
[0048]
Therefore, if the oxygen concentration CgoutUF, O2 <m> in the exhaust gas flowing out from the second catalyst 54 can be estimated without time delay, perturbation control focusing on the oxygen concentration can be performed, so that unburned components (HC, CO), Exhaust of harmful components such as nitrogen oxides NOx can be suppressed with high accuracy. Further, in the catalyst device, the oxygen concentration in the exhaust gas flowing out from the intermediate block i (control block) upstream of the most downstream block m of the second catalyst 54 is estimated, and the estimated oxygen concentration is set to a predetermined value. If perturbation control is performed so as to maintain the negative threshold value Crefmns (for example, a value between the negative threshold value Crefmns and the positive threshold value Crefpls), even if there is an unavoidable control delay in the control, The amount of harmful components flowing out from the downstream position can be reliably reduced. In other words, a block downstream of the intermediate block i can be used as a preliminary catalyst (buffer).
[0049]
When the oxygen concentration in the exhaust gas flowing out from the intermediate block i is used in this way, the air-fuel ratio switching period in the perturbation control is from the block located at the most upstream of the first catalyst 53 to the intermediate block. The smaller the maximum oxygen storage amount in the upstream portion of the catalyst device constituted by each block, the shorter the oxygen storage amount. Accordingly, when the maximum oxygen storage amount in the upstream portion of the catalyst device is reduced to some extent due to deterioration of the catalyst device, the air-fuel ratio fluctuates greatly due to the extremely short air-fuel ratio switching period in perturbation control. As a result, the perturbation control may fail. Therefore, according to the deterioration of the catalyst device, the maximum oxygen storage amount in the upstream portion of the catalyst device is always larger than the threshold value Cth, which is a value that is large enough not to cause the perturbation control to fail. If the intermediate block i is configured so that the position of the intermediate block i is sequentially moved to the downstream side, the air-fuel ratio hunting described above can be avoided.
[0050]
From the above requirements, the exhaust gas purification apparatus uses the catalyst model, so that the concentration of each specific exhaust gas component, including the oxygen concentration in the exhaust gas flowing out from each block, for each catalyst 53, 54 and for each block, And the maximum oxygen storage amount is estimated. Then, the exhaust purification apparatus accumulates the maximum oxygen storage amount of each block at the current stage sequentially from the first block located at the most upstream of the first catalyst 53, and from the first block to the nth The integrated value of the maximum oxygen storage amount of each block in the upstream portion of the catalyst device constituted by blocks up to the block (value n is a natural number, 1 <n <(r + m)) is larger than the threshold value Cth. The nth block constituting the catalyst device upstream portion having the smallest value n is set as the intermediate block i (control block) at the present stage, and from the set intermediate block i The perturbation control shown in FIG. 4 described above is executed based on the control oxygen concentration CgoutO2c in the exhaust gas flowing out. Therefore, the intermediate block i gradually moves to the downstream side as the catalytic device deteriorates and the maximum oxygen storage amount decreases.
[0051]
Hereinafter, the specific configuration and contents of the catalyst model will be described. This catalyst model is applied to both the first catalyst 53 and the second catalyst 54. For convenience of explanation, a catalyst model for the first catalyst 53 will be described below.
[0052]
First, in the catalyst model, as described above, the first catalyst 53 is divided into a plurality of planes orthogonal to the axis extending from the exhaust gas inlet (inflow side, most upstream side) Fr to the outlet (outflow side, most downstream side) Rr. The block is divided into blocks (see FIG. 5). That is, the first catalyst 53 is virtually divided into a plurality of blocks along the flow direction of the exhaust gas. The length of each divided block in the axial direction is L (it is a minute length and is also written as dx). Note that an area of a cross section cut along a plane orthogonal to the axial direction of the first catalyst 53 is dA.
[0053]
Next, paying attention to an arbitrary block (hereinafter referred to as “specific region”), the balance of a substance of a specific chemical species (specific component) passing through the specific region is considered. A chemical species is a component contained in exhaust gas, for example, oxygen O₂Carbon monoxide CO, hydrocarbon HC, and nitrogen oxides NOx. The chemical species is a combination of the components contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is rich (rich component), or when the air-fuel ratio of the exhaust gas flowing into the catalyst is lean It can also be a combination of components contained in the exhaust gas (lean component). In the catalyst model, various values are defined as shown in Table 1 below.
[0054]
[Table 1]

[0055]
Considering the balance of chemical species in a specific region in a given period from time t to t + Δt, as shown in FIG. 8, in the exhaust gas phase (simply referred to as “gas phase”) in the specific region. As shown in the following formula (1), the change amount ΔM of the chemical species is calculated from the amount Min of the same species flowing into the specific region, and the amount Mout of the same species flowing out of the specific region. It is equal to the amount obtained by subtracting the amount Mcoat of the same chemical species taken away by the coat layer. Thus, the catalyst model is constructed based on the mass balance of specific components in each specific region.
[0056]
[Expression 1]

[0057]
In the following, each term in equation (1) will be examined individually. First, the change amount ΔM of the chemical species on the left side of the equation (1) can be obtained by the following equation (2). Equation (2) is obtained by multiplying the concentration change of the chemical species in the given period (the amount obtained by integrating the time change of the concentration Cg of the chemical species over the given period) by the microvolume σ · dA · dx. The value is integrated in the axial direction over the entire block (specific area) in which the value is focused.
[0058]
[Expression 2]

[0059]
Min in the first term on the right side of equation (1) is a value corresponding to the volume of exhaust gas flowing into the specific area per unit time “the flow velocity vgin of the exhaust gas flowing into the specific area and the cross-sectional area dA of the specific area. Product vgin · dA (Actually, exhaust gas at a flow rate of vgin flows into the catalyst having a cross-sectional area dA and an aperture ratio σ, so the flow rate of exhaust gas inside the catalyst is vgin / σ, and this actual flow rate vgin / σ and the catalyst Is a value obtained by integrating the value Cgin · vgin · dA over a given period by multiplying the concentration Cgin of the chemical species in the inflowing exhaust gas by the product (substantial cross-sectional area σ · dA). Also, Mout in the second term on the right side of equation (1) is the product vgout · dA of the flow velocity vgout of the exhaust gas flowing out from the specific region and the cross-sectional area dA of the specific region (actually, the actual flow rate vgout / σ of the exhaust gas) Value obtained by multiplying a value Cgout · vgout · dA over a given period by multiplying the concentration Cgout of the chemical species in the exhaust gas flowing out to the product (a product of a typical sectional area σ · dA). That is, the first term and the second term on the right side of the above equation (1) can be described as the following equation (3).
[0060]
[Equation 3]

[0061]
By the way, since there is no significant difference between the flow velocity vgin of the exhaust gas flowing into the specific region and the flow velocity vgout of the exhaust gas flowing out from the specific region, when vg = vgin = vgout, the equation (3) is expressed as (4 It is transformed like
[0062]
[Expression 4]

[0063]
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 the surface area that contributes to the reaction of chemical species per unit volume of the catalyst, the surface area that contributes to the reaction of chemical species in a specific region is Sgeo · dA · dx, and the unit length of the specific region The area contributing to this reaction is Sgeo · dA. The amount of chemical species transmitted to the coating 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 coating layer from Fick's law. From these, the following equation (5) is obtained. H_DIs a proportionality constant, but as shown in Table 1 above, it is a value called mass transfer rate.
[0064]
[Equation 5]

[0065]
Accordingly, the following expression (6) is obtained from the expressions (1), (2), (4), and (5).
[0066]
[Formula 6]

[0067]
If the quasi state approximation is applied to this equation (6), the left side of equation (6) can be considered to be “0” (∂Cg / ∂t = 0) (that is, the concentration Cg is The following equation (7) is obtained because it is considered that the steady value is reached instantaneously.
[0068]
[Expression 7]

[0069]
Where apparent diffusion rate (substantial diffusion rate) R_D(7) can be rewritten as (9).
[0070]
[Equation 8]

[0071]
[Equation 9]

[0072]
Next, considering the balance of chemical species (material balance of specific components) in the coating layer in a specific area as described above, the amount of change in chemical species in the coating layer over time as shown in the following equation (10) (Change amount per unit time) ΔMc is the amount of the same chemical species that is transmitted from the exhaust gas phase to the coat layer per unit time from the amount Md of the same chemical species consumed by the reaction in the coat layer per unit time. The amount obtained by subtracting the amount Mr.
[0073]
[Expression 10]

[0074]
The left side of equation (10) (temporal change of chemical species in the coat layer) ΔMc is expressed in the concentration change (∂Cw / ∂t) of the species ((1 -Σ) · dA · dx), the first term on the right side (the amount of chemical species Md transferred from the exhaust gas phase to the coating layer per unit time) is the same as the reason explained in Equation (5) For the reason, that is, from Fick's law, it can be described as the following equation (12).
[0075]
## EQU11 ##

[0076]
[Expression 12]

[0077]
The second term on the right side of the equation (10) (the amount of chemical species consumed by the reaction in the coat layer per unit time Mr) is the following (13) using the consumption rate R of the chemical species in the coat layer. It is calculated by the formula.
[0078]
[Formula 13]

[0079]
Therefore, the following expression (14) is obtained from the expressions (10) to (13).
[0080]
[Expression 14]

[0081]
When a quasi-state approximation is applied to this equation (14) (∂Cw / ∂t = 0), the following equation (15) is obtained.
[0082]
[Expression 15]

[0083]
Here, if the equation (8) is applied to the equation (15), the following equation (16) is obtained.
[0084]
[Expression 16]

[0085]
In summary, Equations (9) and (16) are basic equations of the catalyst model. Equation (9) shows that the “inflow amount into a specific region” of a certain chemical species is balanced with “the diffusion amount from the exhaust gas phase to the coating layer + the outflow amount from the specific region”. Indicates that the “amount of diffusion from the exhaust gas phase to the coat layer” and the “consumption amount in the coat layer” are balanced.
[0086]
Next, a method for actually calculating the concentration Cgout of a specific chemical species i flowing out from a specific region using such a 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.
[0087]
[Expression 17]

[0088]
Here, as conceptually shown in FIG. 9, it is considered that the concentration Cgout of the chemical species flowing out from the specific region I is strongly influenced by the concentration Cg (I) of the chemical species in the specific region I. (18) can be placed. This concept is called “windward method”. In other words, the upwind method is an idea that “a chemical species having a concentration Cg (I-1) in the upstream region (I-1) adjacent to the specific region I flows into the specific region I”. The following equation (19) can also be used.
[0089]
[Formula 18]

[0090]
[Equation 19]

[0091]
By the way, based on the reaction kinetics, the consumption rate R in a coat layer of a certain chemical species is a function fcw of the average concentration Cw of the coat layer of the chemical species (for example, a function proportional to the nth power of Cw). Therefore, if this function fcw is set to be proportional to Cw so as to be the simplest, the consumption speed R can be set as shown in the equation (20). In the following, R * in equation (20) is referred to as “consumption rate constant” for convenience.
[0092]
[Expression 20]

[0093]
This equation (20) is replaced with the above equation (16) (R = R_DWhen applied to (Cg-Cw) (16)), the following formula (21) is obtained, and the following formula (22) is obtained by modifying the formula (21).
[0094]
[Expression 21]

[0095]
[Expression 22]

[0096]
Further, according to the above-mentioned upwind method, since Cg = Cgout, equation (22) can be rewritten as the following equation (23).
[0097]
[Expression 23]

[0098]
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.
[0099]
[Expression 24]

[0100]
Therefore, if the value SP is set as the following formula (25), the formula (24) can be rewritten as the formula (26). The value SP is the apparent diffusion rate R_DAnd the consumption rate constant R * is a value that is strongly influenced by the smaller value._D) Or a chemical reaction (R *), it is a value indicating that the rate is limited, and can therefore be called a “reaction rate-limiting factor”.
[0101]
[Expression 25]

[0102]
[Equation 26]

[0103]
From the above, consumption rate constant R * and apparent diffusion rate R_DCan be determined, the concentration Cgout of the chemical species flowing out from the specific region can be obtained based on the equations (25) and (26) by giving the chemical species concentration Cgin flowing into the specific region. Further, since the chemical species concentration Cgin flowing into the next specific region is determined in this way, it is possible to calculate the chemical species concentration Cgout of the same specific region. The above is the basic concept of the catalyst model for calculating the concentration Cgout of the chemical species.
[0104]
Next, the consumption rate constant R * and the apparent diffusion rate R_DAn example of a more specific method for determining the chemical species concentration Cgout flowing out from the specific region will be described. In this example (catalyst model), it is assumed that the three-way reaction, which is an oxidation / reduction reaction at the catalyst, ends instantaneously and completely, and the resulting oxygen storage / release reaction is based on the excess or deficiency of oxygen. Pay attention. This assumption (catalyst model) is realistic and accurate.
[0105]
In this case, the chemical species i of interest is, for example, oxygen O₂And oxygen species such as nitrogen monoxide NO, which is one of the nitrogen oxides (contains oxygen), and oxygen is consumed like carbon monoxide CO and hydrocarbon HC It is a chemical species selected from chemical species (reduction agents).
[0106]
In the following, the chemical species i of the storage agent (in this case, the chemical species i is O₂Or NO, etc.) Cgout is Cgout, stor, i, Cw of the same species i is Cw, stor, i, Cgin of the same species i is Cgin, stor, i, and apparent diffusion rate R of the same species i_DR_D, i, the consumption rate of the chemical species i is represented as Rstor, i, the consumption rate constant of the chemical species i is represented as R * stor, i, and the reaction rate limiting factor of the chemical species i is represented as SPstor, i.
[0107]
Similarly, Cgout of reduction agent chemical species i (in this case, chemical species i is CO or HC, etc.) is Cgout, reduced, i, Cw of chemical species i is Cw, reduced, i, chemical species i Cgin, Cgin, reduced, i, apparent diffusion rate R of the same species i_DR_D, i, the consumption rate of the chemical species i is represented by Rreduc, i, the consumption rate constant of the chemical species i is represented by R * reduc, i, and the reaction rate limiting factor SPreduc, i of the chemical species i. When each value is represented in this way, the following equations (27) to (34) are obtained from the above equations (20), (23), (25), and (26).
[0108]
[Expression 27]

[0109]
[Expression 28]

[0110]
[Expression 29]

[0111]
[30]

[0112]
[31]

[0113]
[Expression 32]

[0114]
[Expression 33]

[0115]
[Expression 34]

[0116]
Based on these equations, Cgout, sotr, i (specifically, the concentration Cgout, O2 of oxygen flowing out from the specific region, the concentration Cgout, NO of nitrogen monoxide flowing out from the specific region) and Cgout, reduc, i (Specifically, in order to obtain the concentration Cgout, CO of carbon monoxide flowing out from the specific region and the concentration Cgout, HC of hydrocarbon flowing out from the specific region), first, the consumption rate constant R * stor, i and the consumption rate Find the constant R * reduc, i.
[0117]
By the way, according to the reaction kinetics, the consumption rate Rstor, i of the storage agent, which is the rate at which oxygen is occluded in the coat layer in a specific region (oxygen occlusion rate), is the storage agent (O₂, NOx, etc.) is proportional to the value of the function f1 (Cw, stor, i) of the concentration Cw, stor, i (for example, Cw, O2, Cw, NO), and the maximum oxygen storage density of the coat layer in a specific region It is considered that it is proportional to the value of the function f2 (Ostmax-Ost) of the difference (Ostmax-Ost) from the actual oxygen storage density. The difference (Ostmax−Ost) between the maximum oxygen storage density and the oxygen storage density represents the oxygen storage margin in the specific region of interest.
[0118]
Therefore, for the sake of simplicity, assuming that the function f1 (x) = f2 (x) = x, the following equation (35) is obtained. In the following equation (35), kstor, i is the oxygen storage rate coefficient (storage side reaction rate coefficient, storage agent consumption rate coefficient), which varies depending on the temperature expressed by the well-known Arrhenius equation And is obtained based on a separately detected or estimated catalyst temperature Temp and a predetermined function (may be a map defining the relationship between the oxygen storage rate coefficient kstor, i and the catalyst temperature Temp). it can. The oxygen storage rate coefficient kstor, i varies depending on the degree of catalyst deterioration, and may be obtained according to the degree of catalyst deterioration.
[0119]
[Expression 35]

[0120]
Therefore, the consumption rate constant R * stor, i can be obtained from the following equation (36) from the equations (27) and (35).
[0121]
[Expression 36]

[0122]
In addition, in this catalyst model that focuses only on oxygen storage (adsorption) and release, the reduction agent, which is a reducing agent, is used only to release oxygen stored in the coat layer. The agent consumption rate Rreduc, i is equal to the rate at which oxygen stored in the coat layer is released (oxygen release rate) Rrel, i.
[0123]
Therefore, when the oxygen release rate Rrel, i is examined, the release rate Rrel, i is based on the reaction kinetics in the same manner as the oxygen storage rate Rstor, i, and is a chemical species that consumes oxygen in the coat layer (for example, (CO, HC) concentration Cw, reduc, i (for example, Cw, CO, Cw, HC) is proportional to the value of function g1 (Cw, reduc, i), and oxygen storage density Ost of function g2 (Ost) It is considered to be proportional to the value.
[0124]
Therefore, for the sake of simplicity, assuming that the function g1 (x) = g2 (x) = x, the following equation (37) is obtained. In the following equation (37), krel, i is an oxygen release rate coefficient (adsorption-desorption side reaction rate coefficient), and changes depending on the temperature expressed by the Arrhenius equation, as does the oxygen storage rate coefficient kstor, i. It is a coefficient, and is obtained based on a predetermined function (may be a map defining the relationship between the oxygen release rate coefficient krel, i and the catalyst temperature Temp) based on the catalyst temperature Temp separately detected or estimated. it can. Note that the oxygen release rate coefficient krel, i changes depending on the degree of catalyst deterioration, and may be obtained according to the degree of catalyst deterioration.
[0125]
[Expression 37]

[0126]
As a result, since the consumption rate Rredcu, i of the reduction agent is equal to the oxygen release rate Rrel, i of the coating layer as described above, the consumption rate constant R * reduc, i is expressed by the equations (31) and (37). Can be obtained based on the following equation (38) obtained by comparing.
[0127]
[Formula 38]

[0128]
From the above, if the oxygen storage density Ost is obtained (the method for obtaining the oxygen storage density Ost will be described later), the consumption rate constant R * stor, i (for example, R * O2) is calculated from the equation (36). Can be sought. On the other hand, apparent diffusion rate R_D, i (for example, R_D, O2) is Sgeo · h as shown in equation (8)._D, i can be experimentally obtained as a function of temperature and flow rate (a function of the catalyst temperature and the flow rate of exhaust gas passing through the catalyst). As a result, SPstor, i (for example, SPstor, O2) is determined from the expression (29). Therefore, when Cgin, stor, i (for example, Cgin, O2) is given as the boundary condition, Cgout from the expression (30) , stor, i (eg, Cout, O2). Then, new Cw, stor, i (for example, Cw, O2) is obtained by the equation (28).
[0129]
Similarly, if the oxygen storage density Ost is obtained, the consumption rate constant R * reduc, i (for example, R * reduc, CO) can be obtained from the equation (38). On the other hand, apparent diffusion rate R_D, i (for example, R_D, CO) is Sgeo · h as shown in equation (8)._D, i can be experimentally obtained as a function of temperature and flow rate (a function of the catalyst temperature and the flow rate of exhaust gas passing through the catalyst). As a result, SPreduc, i (for example, SPreduc, CO) is determined from the expression (33). Therefore, when Cgin, reduc, i (for example, Cgin, CO) is given as the boundary condition, Cgout from the expression (34) , reduce, i (eg, Cgout, CO). Then, new Cw, reduc, i (for example, Cw, CO) is obtained by the equation (32).
[0130]
Next, how to obtain the oxygen storage density Ost required for obtaining Cgout, stor, i and Cgout, reduc, i will be described.
[0131]
First, paying attention to the balance of oxygen as a chemical species in the coat layer, the balance is the difference between the amount of occluded oxygen and the amount of released oxygen in the coat layer, and is described by the following equation (39). In equation (39), dA · L is the volume dV of the specific region.
[0132]
[39]

[0133]
When this equation (39) is modified, the following equation (40) is obtained.
[0134]
[Formula 40]

[0135]
When this equation (40) is discretized using the equations (35) and (37), the following equation (41) is obtained.
[0136]
[Expression 41]

[0137]
When the equation (41) is modified, the following equations (42) to (44) are obtained, and the oxygen storage density Ost can be obtained (updated) from these.
[0138]
[Expression 42]

[0139]
[Expression 43]

[0140]
(44)

[0141]
In this way, since the oxygen storage density Ost is obtained from the equations (42) to (44), Cgout, stor, i, Cgout, reduce, i can be obtained as described above. As described above, the means for obtaining the oxygen concentration in the exhaust gas flowing out from each block corresponds to the gas air-fuel ratio related value obtaining means. Further, since the oxygen storage density Ost is obtained, the oxygen storage amount OSA of the specific region can be obtained based on the following equation (45).
[Equation 45]

[0142]
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 obtained sequentially from the block upstream of the catalyst (specific region) using equation (45). As a result, 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 also be accurately estimated. The above is the catalyst model used by the present exhaust purification apparatus. Then, as described above, the present exhaust purification apparatus, based on the maximum oxygen storage amount for each block obtained as described later separately, for each block of the first catalyst 53 and each block of the second catalyst 54. Control block i (intermediate block i, 1 <i <(r + m)) described above is determined (selected), and control in exhaust gas flowing out from the determined control block i estimated by the catalyst model is performed. The air-fuel ratio perturbation control shown in FIG. 4 is performed using the oxygen concentration CgoutO2c.
[0143]
(Actual operation)
Next, the actual operation of the first embodiment of the exhaust emission control device will be described with reference to a flowchart showing a routine executed by the CPU 71. Note that the catalyst model of the exhaust purification apparatus considers oxygen and nitric oxide as storage agents, and considers carbon monoxide and hydrocarbons as reduction agents. On the other hand, the storage agent may be represented by only oxygen, or the reduction agent may be represented by only carbon monoxide.
[0144]
The CPU 71 repeatedly executes the routine shown in FIG. 10 every time the crank angle of each cylinder reaches a predetermined crank angle before each intake top dead center (for example, BTDC 90 ° CA). Accordingly, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts processing from step 1000 and proceeds to step 1005, and the intake air flow rate Ga measured by the air flow meter 61, the engine speed NE, Based on the target air-fuel ratio abyfr (k) obtained by a routine to be described later, the basic fuel injection amount Fbase for making the air-fuel ratio of the air-fuel mixture supplied to the engine the same target air-fuel ratio abyfr (k) is mapped. Ask from.
[0145]
Next, the CPU 71 proceeds to step 1010 and sets a value obtained by adding a later-described air-fuel ratio feedback correction amount (main feedback control amount) DFi to a value obtained by multiplying the basic fuel injection amount Fbase by a coefficient K as the final fuel injection amount Fi. The value of the coefficient K is normally “1.00”, and as will be described later, when the air-fuel ratio is forcibly changed to obtain the maximum oxygen storage amounts CmaxSCall and CmaxUFall of the catalysts 53 and 54, respectively. A predetermined value other than “1.00” is set.
[0146]
Next, the CPU 71 proceeds to step 1015 to instruct the injector 39 to inject the fuel of the final fuel injection amount Fi. Thereafter, the CPU 71 proceeds to step 1020, and sets a value obtained by adding the final fuel injection amount Fi to the fuel injection amount total amount mfr at that time as a new fuel injection amount integrated value mfr. This fuel injection amount integrated value mfr is used when calculating an oxygen storage amount described later. Thereafter, the CPU 71 proceeds to step 1095 to end the present routine tentatively. As described above, the fuel of the final fuel injection amount Fi that has been feedback-corrected is injected into the cylinder that reaches the intake stroke.
[0147]
Next, the method for determining the control block and the control oxygen concentration CgoutO2c will be described. The CPU 71 repeatedly executes the routine shown in FIG. 11 every elapse of a predetermined time. Accordingly, when the predetermined timing comes, the CPU 71 starts processing from step 1100, proceeds to step 1105, sets “0” to the maximum oxygen storage amount CmaxSCh for determination, and sets the counter value n to “ Set to “0”. Next, the CPU 71 proceeds to step 1115 to increase the value of the counter value n by “1” and proceeds to step 1120, and the current determination maximum oxygen storage amount CmaxSCh is set to the current determination maximum oxygen storage amount CmaxSCh. The maximum oxygen storage amount CmaxSC <n> in block n (the value of the counter value n is “1” at this time, so the maximum oxygen storage amount CmaxSC <1> in block 1 of the first catalyst 53) is added, and a new value is added. The maximum oxygen storage amount CmaxSCh for determination is obtained.
[0148]
Next, the CPU 71 proceeds to step 1125 to determine whether or not the maximum oxygen storage amount CmaxSCh for determination is greater than a predetermined threshold Cth. At this time, if the maximum oxygen storage amount CmaxSCh for determination is smaller than the predetermined threshold Cth, the CPU 71 determines “No” in step 1125, proceeds to step 1130, and the value of the counter value n is the total number of blocks of the first catalyst 53. It is determined whether or not it is equal to r.
[0149]
At present, the value of the counter value n is “1”. Accordingly, the CPU 71 makes a “No” determination at step 1130, returns to step 1115 again, increments the counter value n by “1”, and executes the processing of step 1120 and step 1125. As a result, the determination maximum oxygen storage amount CmaxSCh is an integrated value CmaxSC <1> + CmaxSC <2 of the maximum oxygen storage amount of the first block and the second block which are the most upstream blocks of the first catalyst 53. > If the integrated value CmaxSC <1> + CmaxSC <2> does not exceed the threshold value Cth, the CPU 71 proceeds from step 1125 to step 1130 again. If the value of the counter value n is not equal to the block number r, the step is again performed. In 1115, the value of the count value n is increased by “1”, and the process of step 1120 is executed. As a result, the maximum oxygen storage amount CmaxSCh for determination at that time (CmaxSC <1> + CmaxSC <2> at this time) is added to the maximum oxygen storage amount CmaxSC <n> of the block n of the first catalyst 53 (n = n at this time). Since CmaxSC <3>) is added, a new maximum oxygen storage amount for determination CmaxSCh (= CmaxSC <1> + CmaxSC <2> + CmaxSC <3>) is obtained.
[0150]
Such processing is repeated as long as the maximum oxygen storage amount CmaxSCh for determination does not exceed the threshold value Cth. Therefore, the determination maximum oxygen storage amount CmaxSCh is an integrated value of the maximum oxygen storage amount CmaxSC <n> of each block n from the first block to the nth block, which is the most upstream block of the first catalyst 53. It is calculated as (total value).
[0151]
When the determination maximum oxygen storage amount CmaxSCh becomes larger than the predetermined threshold Cth during execution of such processing, the CPU 71 determines “Yes” in step 1125 and proceeds to step 1135 to set the control oxygen concentration CgoutO2c. An oxygen concentration CgoutSC, O2 <n> in exhaust gas described later flowing out from the nth block n of the first catalyst 53 is set, and the routine proceeds to step 1195 to end the present routine tentatively. In this case, the control block (intermediate block) i is the nth block n of the first catalyst 53 (i = n).
[0152]
Further, the integrated value of the maximum oxygen storage amounts CmaxSC <n> of all the blocks from the first block to the r-th block of the first catalyst 53 (that is, the maximum oxygen storage amount of the entire first catalyst 53). When CmaxSCall) is smaller than the predetermined threshold Cth, the CPU 71 does not determine “Yes” in step 1125, and determines “Yes” in step 1130 when the value of the counter value n becomes r, Proceeding to step 1140, the maximum oxygen storage amount CmaxSCall of the entire first catalyst 53 is set as the determination maximum oxygen storage amount CmaxUFh. Next, the CPU 71 sets the value of the counter value n to “0” in step 1145, and proceeds to step 1150 and subsequent steps.
[0153]
The processing from step 1150 to step 1165 is the same as the processing from step 1115 to step 1130. Briefly, in step 1150 and step 1155, the CPU 71 changes the maximum oxygen storage amount CmaxSCall of the entire first catalyst 53 from the most upstream block (first block) of the second catalyst 54 to the second catalyst 54. A value obtained by adding the integrated value of the maximum oxygen storage amount CmaxUF <n> of each block n up to the nth block is obtained as the determination maximum oxygen storage amount CmaxUFh. The nth block n of the second catalyst 54 is the (r + n) th block counted from the most upstream block of the first catalyst 53. Therefore, when (r + n) is p, the determination maximum oxygen storage amount CmaxUFh is the first block that is the most upstream block when the first catalyst 53 and the second catalyst 54 are regarded as one catalyst device. That is, the integrated value of the maximum oxygen storage amount of each block upstream of the catalyst device constituted by the blocks from the first block to the p-th block.
[0154]
When the determination maximum oxygen storage amount CmaxUFh becomes larger than the predetermined threshold Cth, the CPU 71 determines “Yes” in step 1160 and proceeds to step 1170 to set the control oxygen concentration CgoutO2c to the control oxygen concentration CgoutO2c. An oxygen concentration CgoutUF, O2 <n> in exhaust gas to be described later flowing out from the nth block is set, and the routine proceeds to step 1995 to end this routine once. In this case, the control block (intermediate block) i is the nth block n of the second catalyst 54 (i = r + n).
[0155]
Further, when the sum of the maximum oxygen storage amounts (CmaxSCall + CmaxUFall) of the first catalyst 53 to the second catalyst 54 is smaller than the predetermined threshold Cth, the CPU 71 does not determine “Yes” in step 1160, and the counter When the value n reaches the number m of blocks of the second catalyst 54, “Yes” is determined in step 1165. In this case, the process proceeds to step 1195 via step 1170, and this routine is temporarily terminated.
[0156]
As described above, when n is a natural number and the first catalyst 53 to the second catalyst 54 are regarded as one catalyst device, the catalyst device is constituted by blocks from the first block to the nth block. Of the upstream part of the catalytic device where the integrated value (maximum oxygen storage amount for determination) of each block in the upstream part of the catalytic device exceeds a predetermined threshold value Cth, the downstream side of the upstream part of the catalytic device having the smallest value n The oxygen concentration in the exhaust gas flowing out from the control block i which is the first block (the nth block counted from the first block of the first catalyst 53) is set as the control oxygen concentration CgoutO2c. Therefore, the control block i gradually moves to the downstream side as the catalyst device deteriorates and the maximum oxygen storage amount decreases.
[0157]
Next, the calculation of the target air-fuel ratio abyfr (k) will be described. The CPU 71 repeatedly executes the routine shown in FIG. 12 every predetermined time. Accordingly, when the predetermined timing is reached, the CPU 71 starts the process from step 1200, proceeds to step 1205, and determines whether or not the value of an air-fuel ratio forced setting control execution flag XHAN described later is “0”. When the value of the air-fuel ratio forced setting control execution flag XHAN is “1”, air-fuel ratio control (active control) for forcibly changing the air-fuel ratio is executed to calculate the maximum oxygen storage amounts CmaxSCall and CmaxUFall. When the value is “0”, it indicates that the air-fuel ratio control for calculating the maximum oxygen storage amounts CmaxSCall and CmaxUFall is not being executed.
[0158]
Currently, the air-fuel ratio control for calculating the maximum oxygen storage amount is not executed, and the oxygen concentration in the exhaust gas flowing out from the control block i obtained in the routine of FIG. The description will be continued assuming that the oxygen concentration CgoutO2c has changed from a state below the positive threshold Crefpls to a state greater than the positive threshold Crefpls. In this case, the CPU 71 determines “Yes” in step 1205 and proceeds to step 1210 to determine whether or not CgoutO2c is larger than the positive threshold Crefpls. According to the above assumption, CgoutO2c is larger than the positive threshold value Crefpls, so the CPU 71 determines “Yes” in step 1210 and proceeds to step 1215. Determine whether CgoutO2c is less than or equal to the threshold Crefpls. According to the above assumption, since the previous CgoutO2c is equal to or less than the positive threshold value Crefpls, the CPU 71 determines “Yes” in step 1215 and proceeds to step 1220. In step 1220, the target air-fuel ratio abyfr (k) The air / fuel ratio richer than the stoichiometric air / fuel ratio stoich by a predetermined value α2 is set, and the routine proceeds to step 1295 to end the present routine tentatively.
[0159]
As described above, when the control oxygen concentration CgoutO2c changes from a state below the positive threshold Crefpls to a state above the same positive threshold Crefpls, the exhaust purification apparatus changes the target air-fuel ratio abyfr (k) to the stoichiometric air-fuel ratio stoich. After that, the CPU 71 changes the air-fuel ratio to a rich value by a predetermined value α2, and when the CPU 71 proceeds to step 1005 in FIG. 10, the basic fuel injection amount Fbase is changed to the air-fuel ratio of the air-fuel mixture supplied to the engine (accordingly, the first The air / fuel ratio flowing into the catalyst 53 is changed to a value for setting the target air / fuel ratio abyfr (k) (theoretical air / fuel ratio stoich−α2). As a result, rich air-fuel ratio exhaust gas flows into the first and second catalysts 53 and 54, and the oxygen concentration CgoutO2c flowing out from the control block i is substantially reduced as shown at times t2 to t3 in FIG. It is maintained at “0”.
[0160]
When the current and previous control oxygen concentration CgoutO2c is larger than the positive threshold value Crefpls, the CPU 71 determines “Yes” in step 1210 and “No” in step 1215, and proceeds to step 1295 as it is. Exit once. As a result, the target air-fuel ratio abyfr (k) is maintained at the stoichiometric air-fuel ratio stoich-α2, and the air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted so as to approach the stoichiometric air-fuel ratio -α2.
[0161]
On the other hand, from the state in which the air-fuel ratio control for calculating the maximum oxygen storage amount is not executed and the oxygen concentration CgoutO2c flowing out from the control block i is greater than or equal to the negative threshold Crefmns is smaller than the negative threshold Crefmns. The explanation will continue as if it had changed. In this case, the CPU 71 determines “Yes” in step 1205 and “No” in step 1210, proceeds to step 1225, and determines whether CgoutO 2 c is smaller than the negative threshold value Crefmns. According to the above assumption, CgoutO2c is smaller than the negative threshold value Crefmns. Therefore, the CPU 71 determines “Yes” in step 1225 and proceeds to step 1230. It is determined whether or not CgoutO2c is equal to or greater than a threshold value Crefmns. According to the above assumption, since the previous CgoutO2c is equal to or greater than the threshold value Crefmns, the CPU 71 makes a “Yes” determination at step 1230 to proceed to step 1235, where the theoretical target air-fuel ratio abyfr (k) is obtained. An air-fuel ratio that is leaner than the air-fuel ratio stoich by a predetermined value α1 is set, and the routine proceeds to step 1295 to end the present routine tentatively.
[0162]
Thus, when the control oxygen concentration CgoutO2c changes from a state equal to or higher than the negative threshold value Crefmns to a state smaller than the negative threshold value Crefmns, the present exhaust purification device changes the target air-fuel ratio abyfr (k) to the stoichiometric air-fuel ratio stoich. After that, the CPU 71 changes the air fuel ratio to a lean value by the predetermined value α1, and thereafter, the CPU 71 proceeds to step 1005 in FIG. 10 to set the basic fuel injection amount Fbase and the air fuel ratio of the air-fuel mixture supplied to the engine to the target air fuel ratio. The value is changed to abyfr (k) (theoretical air-fuel ratio stoich + α1). As a result, lean air-fuel ratio exhaust gas flows into the first and second catalysts 53 and 54, and flows out from the control block i as shown at times t1 to t2 and t3 to t4 in FIG. The oxygen concentration CgoutO2c is maintained at substantially “0”.
[0163]
When the current and previous oxygen concentrations CgoutO2c are smaller than the negative threshold value Crefmns, the CPU 71 determines “No” at step 1210, “Yes” at step 1225, “No” at step 1230, and continues to step 1295. Proceed to to end the present routine. As a result, the target air-fuel ratio abyfr (k) is maintained at the stoichiometric air-fuel ratio stoich + α1, and the air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted so as to approach the stoichiometric air-fuel ratio + α1.
[0164]
Further, if the air-fuel ratio control for calculating the maximum oxygen storage amount is being executed, the value of the air-fuel ratio forced setting control execution flag XHAN is “1”, so that the CPU 71 determines “No” in step 1205. Then, the process proceeds to step 1240. In step 1240, the target air-fuel ratio abyfr (k) is set to the stoichiometric air-fuel ratio stoich (the air-fuel ratio control for calculating the maximum oxygen storage amount is performed as shown in FIG. 10). This is done by changing the value of the coefficient K of 1010.) Next, the routine proceeds to step 1295, where the present routine is temporarily terminated. As described above, the target air-fuel ratio abyfr (k) is set so that the control oxygen concentration CgoutO2c, which is the oxygen concentration in the exhaust gas flowing out from the control block i, is a predetermined value between the positive threshold Crefpls and the negative threshold Crefmns. To be determined.
[0165]
Next, the calculation of the main feedback control amount DFi will be described. The CPU 71 repeatedly executes the routine shown in the flowchart of FIG. 13 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 71 starts processing from step 1300 and proceeds to step 1305 to determine whether or not the air-fuel ratio feedback control condition (main feedback condition) is satisfied. The air-fuel ratio feedback control condition is, for example, that the engine coolant temperature THW is equal to or higher than a first predetermined temperature, and the intake air amount (load, in-cylinder intake air amount Mc) per revolution of the engine is a predetermined value or less. This is established when the most upstream air-fuel ratio sensor 66 is normal (including an active state) and the value of an air-fuel ratio forced setting control execution flag XHAN described later is “0”.
[0166]
Now, assuming that the air-fuel ratio feedback control condition is satisfied, the CPU 71 determines “Yes” in step 1305 and proceeds to step 1310 to display the current output vabyfs of the most upstream air-fuel ratio sensor 66. By converting based on the map shown in FIG. 2, the actual air-fuel ratio abyfs upstream of the first catalyst 53 at the present time is obtained.
[0167]
Next, the CPU 71 proceeds to step 1315 to obtain the in-cylinder intake air amount Mc (k−N), which is the intake air amount of the cylinder that has reached the intake stroke before N strokes (N intake strokes) from the present time. By dividing by the actual air-fuel ratio abyfs, the in-cylinder fuel supply amount Fc (k−N) N strokes before the present time is obtained. The value N varies depending on the displacement of the internal combustion engine, the distance from the combustion chamber 25 to the most upstream air-fuel ratio sensor 66, and the like.
[0168]
Thus, in order to obtain the in-cylinder fuel supply amount Fc (k−N) before the N stroke from the current time, the in-cylinder intake air amount Mc (k−N) before the N stroke from the current time is determined as the actual air-fuel ratio abyfs at the current time. This is because it takes a time corresponding to the N stroke until the air-fuel mixture burned in the combustion chamber 25 reaches the most upstream air-fuel ratio sensor 66. The cylinder intake air amount Mc is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.
[0169]
Next, the CPU 71 proceeds to step 1320 to determine the in-cylinder intake air amount Mc (k−N) N strokes before the current time from the current time and the target air-fuel ratio abyfr already obtained by the routine of FIG. By dividing by (k−N), the target in-cylinder fuel supply amount Fcr (k−N) N strokes before the present time is obtained. Then, the CPU 71 proceeds to step 1325 to set a value obtained by subtracting the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) as the in-cylinder fuel supply amount deviation DFc. That is, the in-cylinder fuel supply amount deviation DFc is an amount representing the excess or deficiency of the fuel supplied into the cylinder at the time point before N strokes. Next, the CPU 71 proceeds to step 1330 to obtain the main feedback control amount DFi based on the following equation 46.
[0170]
[Equation 46]
DFi = (Gp · DFc + Gi · SDFc) · KFB
[0171]
In the above equation 46, Gp is a preset proportional gain (proportional constant), and Gi is a preset integral gain (integral constant). Note that the coefficient KFB of Equation 46 is preferably variable depending on the engine speed NE, the in-cylinder intake air amount Mc, and the like, but is set to “1” here. The value SDFc is an integral value of the in-cylinder fuel supply amount deviation DFc, and is updated in the next step 1335. That is, in step 1335, the CPU 71 adds the in-cylinder fuel supply amount deviation DFc obtained in step 1325 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at that time, thereby obtaining a new in-cylinder fuel supply amount deviation. The integrated value SDFc is obtained, and this routine is once terminated in step 1395.
[0172]
As described above, the main feedback control amount DFi is obtained by the proportional integral control, and this main feedback control amount DFi is reflected in the fuel injection amount by the above-described step 1010 of FIG. Is compensated, and feedback control is performed so that the average value of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is made substantially equal to the target air-fuel ratio abyfr.
[0173]
On the other hand, if the air-fuel ratio feedback control condition is not satisfied at the time of determination in step 1305, the CPU 71 determines “No” in step 1305 and proceeds to step 1340 to set the value of the main feedback control amount DFi to “0”. Then, the routine proceeds to step 1395 to end the present routine tentatively. As described above, when the air-fuel ratio feedback control condition is not satisfied (including when the air-fuel ratio forced setting control is being executed), the main feedback control amount DFi is set to “0” and the air-fuel ratio (basic fuel injection amount Fbase) is corrected. Absent.
[0174]
Next, the maximum oxygen storage amount acquisition control for forcibly changing the air-fuel ratio for calculating the maximum oxygen storage amount will be described. The CPU 71 executes each routine shown in the flowcharts of FIGS. 14 to 18 every elapse of a predetermined time.
[0175]
Therefore, when the predetermined timing comes, the CPU 71 starts the processing from step 1400 in FIG. 14 and proceeds to step 1405 to determine whether or not the value of the maximum oxygen storage amount acquisition control execution flag XHAN is “0”. . If we continue with the explanation that the maximum oxygen storage amount acquisition control for calculating the maximum oxygen storage amount is not being performed and the conditions for starting the maximum oxygen storage amount acquisition control are not satisfied, the maximum oxygen storage amount acquisition control is executed. The value of the middle flag XHAN is “0”. Accordingly, the CPU 71 determines “Yes” in step 1405, proceeds to step 1410, and sets the value of the coefficient K used in step 1010 of FIG. 10 described above to 1.00.
[0176]
Next, the CPU 71 determines in step 1415 whether the start condition for the maximum oxygen storage amount acquisition control is satisfied. The starting condition for this maximum oxygen storage amount acquisition control is that the coolant temperature THW is equal to or higher than a predetermined temperature, the vehicle speed obtained by a vehicle speed sensor (not shown) is equal to or higher than a predetermined high vehicle speed, and the throttle valve opening TA per unit time is Conditions such as the amount of change being equal to or less than the predetermined amount are satisfied, and the first and second catalyst downstream air-fuel ratio sensor outputs voxs1, voxs2 both correspond to an air-fuel ratio richer than the stoichiometric air-fuel ratio. This is established, for example, when an output is generated and a predetermined time has elapsed since the previous execution of the maximum oxygen storage amount acquisition control. At this stage, as described above, since the start condition for the maximum oxygen storage amount acquisition control is not satisfied, the CPU 71 makes a “No” determination at step 1415 to proceed to step 1495 to end the present routine tentatively.
[0177]
Next, although the maximum oxygen storage amount acquisition control is not currently performed, if the description is continued assuming that the start condition of the maximum oxygen storage amount acquisition control is satisfied, the CPU 71 determines “Yes” in step 1405 in this case. In step 1410, the coefficient K is set to 1.00. Next, since the start condition is satisfied, the CPU 71 makes a “Yes” determination at step 1415 to proceed to step 1420. At step 1420, the CPU 71 sets the value of the maximum oxygen storage amount acquisition control execution flag XHAN to “1”. To "".
[0178]
Then, the CPU 71 proceeds to step 1425, sets the value of Mode to “1” in order to shift to the first mode, sets the value of coefficient K to 0.98 in subsequent step 1430, and proceeds to step 1495. This routine is finished once. As a result, the above-described air-fuel ratio feedback control condition is not satisfied, so the CPU 71 makes a “No” determination at step 1305 in FIG. 13 to proceed to step 1340, and the value of the air-fuel ratio feedback correction amount DFi is “ 0 "is set. As a result, by executing step 1010 in FIG. 10, a value obtained by multiplying the basic fuel injection amount Fbase by 0.98 is calculated as the final fuel injection amount Fi, and fuel of this final fuel injection amount Fi is injected. The air-fuel ratio of the air-fuel mixture supplied to the air-fuel ratio (and hence the air-fuel ratio of the gas flowing into the first catalyst 53) is controlled to a predetermined lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.
[0179]
Thereafter, the CPU 71 repeatedly executes the processing of the routine of FIG. 14 from step 1400. Since the value of the maximum oxygen storage amount acquisition control execution flag XHAN is “1”, “No” is determined in step 1405. Immediately after the determination, the routine proceeds to step 1495 to end the present routine tentatively.
[0180]
On the other hand, the CPU 71 repeatedly executes the first mode control routine shown in FIG. 15 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 71 starts processing from step 1500 and proceeds to step 1505, where it is determined whether or not the value of Mode is “1”. At this time, if the value of Mode is not “1”, the CPU 71 immediately proceeds to step 1595 to end the present routine tentatively. Hereinafter, the description will be continued assuming that the value of Mode has been changed to “1” by the processing of Step 1425 of FIG. 14. In this case, the CPU 71 determines “Yes” in Step 1505 and determines Step 1510. The first catalyst downstream air-fuel ratio sensor output voxs1 and the second catalyst downstream air-fuel ratio sensor output voxs2 are both outputs corresponding to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio (output when oxygen is excessive). It is determined whether or not.
[0181]
At present, since the air-fuel ratio of the air-fuel mixture supplied to the engine has just been changed to a predetermined lean air-fuel ratio, both the first catalyst downstream air-fuel ratio sensor output voxs1 and the second catalyst downstream air-fuel ratio sensor output voxs2 are theoretically both. Since the output does not correspond to an air-fuel ratio that is leaner than the air-fuel ratio, the CPU 71 makes a “No” determination at step 1510, and once ends this routine at step 1595.
[0182]
Thereafter, the CPU 71 repeatedly executes steps 1500 to 1510 in FIG. Further, since the air-fuel ratio is maintained at a predetermined lean air-fuel ratio, each oxygen storage amount reaches the maximum oxygen storage amount of each catalyst in order from the first catalyst 53 to the second catalyst 54 with the passage of time. Accordingly, in response to this, the first catalyst downstream air-fuel ratio sensor output voxs1 and the second catalyst downstream air-fuel ratio sensor output voxs2 sequentially change to outputs corresponding to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. As a result, when the CPU 71 proceeds to step 1510, it determines “Yes” in step 1510 and proceeds to step 1515. In step 1515, the value of Mode is set to “2”, and to the subsequent step 1520. Then, the value of the coefficient K is set to 1.02, and then this routine is once ended in step 1595. As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to a predetermined rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio.
[0183]
Further, the CPU 71 repeatedly executes the second mode control routine shown by the flowchart in FIG. 16 every elapse of a predetermined time. Therefore, the CPU 71 starts processing from step 1600 at a predetermined timing, and determines whether or not the value of Mode is “2” in step 1605. If the value of Mode is not “2”, the step is performed. The operation proceeds from step 1605 to step 1695 to end this routine once.
[0184]
On the other hand, when the value of Mode is changed to “2” by the processing in the previous step 1515, the CPU 71 determines “Yes” when the process proceeds to step 1605, and proceeds to step 1610. In step 1610, the first catalyst It is determined whether the output voxs1 of the downstream air-fuel ratio sensor 67 has changed from a value indicating an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a value indicating an air-fuel ratio richer than the stoichiometric air-fuel ratio. At this time, since the air-fuel ratio is immediately after the predetermined rich air-fuel ratio is changed, the CPU 71 makes a “No” determination at step 1610 to proceed to step 1695 to end the present routine tentatively.
[0185]
Thereafter, since the air-fuel ratio of the air-fuel mixture supplied to the engine is maintained at the predetermined rich air-fuel ratio, the oxygen stored in the first catalyst 53 is consumed, and when the predetermined time elapses. The oxygen storage amount of one catalyst 53 reaches “0”. As a result, unburned HC and CO start to flow out from the first catalyst 53, so that the output voxs1 of the first catalyst downstream air-fuel ratio sensor 67 is richer than the stoichiometric air-fuel ratio from a value indicating an air-fuel ratio leaner than the stoichiometric air-fuel ratio. It changes to a value indicating the air-fuel ratio. As a result, when the CPU 71 proceeds to step 1610, it determines “Yes” at step 1610 and proceeds to step 1615. At step 1615, the value of Mode is changed to “3”. The routine is temporarily terminated.
[0186]
Similarly, the CPU 71 determines whether or not the value of Mode is “3” in Step 1705 in the third mode control routine shown by the flowchart in FIG. If the value of is not "3", the routine proceeds from step 1705 to step 1795, and this routine is temporarily terminated.
[0187]
On the other hand, when the value of Mode is changed to “3” by the processing of the previous step 1615, the CPU 71 determines “Yes” when proceeding to step 1705, proceeds to step 1710, and in step 1710, the second catalyst It is determined whether or not the output voxs2 of the downstream air-fuel ratio sensor 68 has changed from a value indicating an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a value indicating an air-fuel ratio richer than the stoichiometric air-fuel ratio. At this time point, immediately after the unburned HC and CO starts to flow out from the first catalyst 53, and the unburned HC and CO does not flow out from the second catalyst 54, the CPU 71 determines “No” in step 1710. Determination is made and the routine proceeds to step 1795 to end the present routine tentatively.
[0188]
Thereafter, the air-fuel ratio of the air-fuel mixture supplied to the engine is continuously maintained at the predetermined rich air-fuel ratio, so that oxygen stored in the second catalyst 54 is consumed and a predetermined time elapses. The oxygen storage amount of the second catalyst 54 reaches “0”. As a result, unburned HC and CO start to flow out from the second catalyst 54, so that the output voxs2 of the second catalyst downstream air-fuel ratio sensor 68 is richer than the stoichiometric air-fuel ratio from a value indicating an air-fuel ratio leaner than the stoichiometric air-fuel ratio. It changes to a value indicating the air-fuel ratio. As a result, the CPU 71 proceeds from step 1710 to step 1715, resets the value of Mode to “0”, and in subsequent step 1720, the target air-fuel ratio abyfr is shifted to shift from the maximum oxygen storage amount acquisition control to the above-described perturbation control. After setting (k) from the stoichiometric air-fuel ratio stoich to an air-fuel ratio that is lean by the predetermined value α1, the value of the maximum oxygen storage amount acquisition control execution flag XHAN is set to “0” in the following step 1725, and step 1795 Proceed to to end the present routine.
[0189]
In this state, when the CPU 71 executes the routine of FIG. 14, the CPU 71 makes a “Yes” determination at step 1405 to proceed to step 1410, so that the value of the coefficient K is returned to 1.00. Further, in step 1005 of FIG. 10, a basic fuel injection amount Fbase is calculated for setting the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio abyfr (k) set to the lean air-fuel ratio (stoich + α1). If the air-fuel ratio feedback control condition is satisfied, the CPU 71 makes a “Yes” determination at step 1305 of the routine of FIG. 13, so the air-fuel ratio feedback control (main feedback control) is resumed.
[0190]
As described above, when the start condition of the maximum oxygen storage amount acquisition control is satisfied, the air-fuel ratio of the air-fuel mixture supplied to the engine is forcibly changed once in the order of the predetermined lean air-fuel ratio and the predetermined rich air-fuel ratio. Be controlled.
[0191]
Next, the operation in calculating the oxygen storage amount for obtaining the maximum oxygen storage amount will be described. The CPU 71 executes the routine shown in the flowchart of FIG. 18 every elapse of a predetermined time (calculation cycle tsample). Accordingly, when the predetermined timing is reached, the CPU 71 starts processing from step 1800, proceeds to step 1805, and obtains the oxygen storage amount change ΔO2 by the following equation 47.
[0192]
[Equation 47]
ΔO2 = 0.23 ・ mfr ・ (stoich − abyfsave)
[0193]
In the above formula 47, the value “0.23” is the weight ratio of oxygen contained in the atmosphere. mfr is the total amount of the fuel injection amount Fi within the predetermined time tsample, and stoich is the stoichiometric air fuel ratio (for example, 14.7). abyfsave is an average value of the air-fuel ratio A / F detected by the most upstream air-fuel ratio sensor 66 at a predetermined time tsample. As shown in Equation 47, the total amount mfr of the injection amount within the predetermined time tsample is multiplied by the deviation (stoich-abyfsave) of the average value of the detected air-fuel ratio A / F from the stoichiometric air-fuel ratio. The air consumption (insufficient amount) at the same predetermined time tsample is obtained. By multiplying the air consumption by the weight ratio of oxygen, the oxygen consumption (oxygen storage amount change ΔO2) at the same predetermined time tsample is obtained.
[0194]
Next, the CPU 71 proceeds to step 1810 to determine whether or not the value of Mode is “2” (whether or not it is the second mode). If the value of Mode is “2”, the CPU 71 proceeds to step 1810. The determination is “Yes” and the process proceeds to step 1815. A value obtained by adding the oxygen storage amount change amount ΔO2 to the oxygen storage amount OSA1 at that time is set as a new oxygen storage amount OSA1, and then the process proceeds to step 1830.
[0195]
Such treatment (steps 1800 to 1815) is repeatedly executed as long as the value of Mode is “2”. As a result, the oxygen storage amount OSA1 of the first catalyst 53 is calculated in the second mode (Mode = 2) in which the air-fuel ratio upstream of the first catalyst 53 is a predetermined rich air-fuel ratio. This is because in the second mode, oxygen stored in the first catalyst 53 is consumed. If the determination in step 1810 is “No”, the CPU 71 proceeds directly from step 1810 to step 1820.
[0196]
When the CPU 71 proceeds to step 1820, the CPU 71 determines whether or not the value of Mode is “3” (whether or not it is the third mode). If the value of Mode is “3”, the CPU 71 proceeds to step 1820. Then, the process proceeds to step 1825, where a value obtained by adding the oxygen storage amount change ΔO2 to the oxygen storage amount OSA2 at that time is set as a new oxygen storage amount OSA2, and then the process proceeds to step 1830.
[0197]
Such treatment (steps 1800, 1805, 1810, 1820, 1825) is repeatedly executed as long as the value of Mode is “3”. As a result, the oxygen storage amount OSA2 of the second catalyst 54 is calculated in the third mode (Mode = 3) in which the air-fuel ratio upstream of the first catalyst 53 is a predetermined rich air-fuel ratio. This is because in the third mode, oxygen stored in the second catalyst 54 is consumed. If the determination in step 1820 is “No”, the CPU 71 proceeds directly from step 1820 to step 1830. Then, when the CPU 71 proceeds to step 1830, the CPU 71 sets the total amount mfr of the fuel injection amount Fi to “0”, and thereafter proceeds to step 1895 to end this routine once.
[0198]
Next, the operation when calculating the maximum oxygen storage amounts CmaxSCall, CmaxUFall of the first and second catalysts 53, 54 and the maximum oxygen storage amounts CmaxSC <n>, CmaxUF <n> of the blocks of the respective catalysts will be described. To do. The CPU 71 executes the routine shown by the flowchart of FIG. 19 every elapse of a predetermined time.
[0199]
Accordingly, when the predetermined timing is reached, the CPU 71 starts processing from step 1900 of FIG. 19 and proceeds to step 1905 to determine whether the value of the maximum oxygen storage amount acquisition control execution flag XHAN has changed from “1” to “0”. Monitor whether or not. At this time, if the value of the maximum oxygen storage amount acquisition control execution flag XHAN has not changed, the CPU 71 proceeds directly from step 1905 to step 1995 to end the present routine tentatively.
[0200]
On the other hand, if it is immediately after the end of the third mode, the value of the maximum oxygen storage amount acquisition control execution flag XHAN is changed from “1” to “0” in step 1725 of FIG. Determines “Yes” in step 1905 and proceeds to step 1910, where the oxygen storage amounts OSA 1 and OSA 2 at that time are set to the maximum oxygen storage amount CmaxSCall of the entire first catalyst 53 and the maximum oxygen storage amount of the entire second catalyst 54, respectively. Store as quantity CmaxUFall.
[0201]
Next, the CPU 71 proceeds to step 1915 to set the counter value n to “0”, and then proceeds to step 1920 to start processing for calculating the maximum oxygen storage amount for each block of the first catalyst 53. First, the CPU 71 increases the counter value n by “1” and sets it to “1” in step 1920, and then proceeds to step 1925 to obtain the maximum oxygen storage amount of the entire first catalyst 53 acquired in step 1910. Based on the value of CmaxSCall, the value of the counter value n, and the formula described in Step 1925, the maximum oxygen storage amount CmaxSC <n> in the block n of the first catalyst 53 is calculated. Since the value of the counter value n is “1” at this time, the maximum oxygen storage amount CmaxSC (1) in the block 1 of the first catalyst 53 is calculated.
[0202]
Here, the equations described in step 1925 will be briefly described with reference to FIG. FIG. 20 is a maximum oxygen storage amount distribution map showing the concept of obtaining the maximum oxygen storage amount CmaxSC <n> (n = 1,..., R) for each block of the first catalyst 53, and is indicated by hatching. The area of the portion corresponds to the value of the maximum oxygen storage amount CmaxSCall of the entire first catalyst 53.
[0203]
Thus, each maximum oxygen storage amount CmaxSC <n> for each block of the first catalyst 53 is the sum of the respective maximum oxygen storage amounts CmaxSC <n> and the value of the maximum oxygen storage amount CmaxSCall of the entire first catalyst 53. And set so as to increase linearly with a predetermined gradient as the block 1 moves from the upstream block 1 to the downstream block r. This is because the upstream portion of the first catalyst 53 is more easily poisoned by lead, sulfur, etc. in the exhaust gas flowing into the interior than the downstream portion, so the maximum oxygen storage amount of the upstream portion is higher. It is because it becomes easy to fall compared with the thing of the downstream part.
[0204]
An equation for obtaining the maximum oxygen storage amount CmaxSC <n> for each block of the first catalyst 53 based on the maximum oxygen storage amount distribution map shown in FIG. In the expression described in the step 1925, the value A1 is a positive constant and is a value corresponding to the predetermined gradient. The maximum oxygen storage amount for each block of the first catalyst 53 may be set so as to increase as it transitions from the upstream block to the downstream block. For example, it increases nonlinearly. It may be set.
[0205]
Referring to FIG. 19 again, the CPU 71 proceeds from step 1925 to step 1930 and determines whether or not the value of the counter value n is equal to the block number r of the first catalyst 53. Since the value of the counter value n is “1” at this time, the CPU 71 determines “No” in Step 1930 and returns to Step 1920 again to increase the value of the counter value n by “1”. The process of step 1930 is executed. That is, the processing of step 1920 and step 1925 is repeatedly executed until the value of the counter value n becomes equal to the number of blocks r of the first catalyst 53. Thus, the value of the maximum oxygen storage amount CmaxSC <n> of each block n from the most upstream block 1 to the most downstream block r of the first catalyst 53 is sequentially calculated.
[0206]
When the value of the counter value n becomes equal to the block number r of the first catalyst 53 by repeating the process of step 1920 described above, the CPU 71 makes a “Yes” determination at step 1930 to proceed to step 1935, where the counter value n After setting the value of “0” to “0”, the routine proceeds to step 1940, where the processing for calculating the maximum oxygen storage amount CmaxUF <n> (n = 1,..., M) for each block of the second catalyst 54 is started. To do.
[0207]
The processing for calculating each maximum oxygen storage amount CmaxUF <n> for each block of the second catalyst 54 is the same as the processing of Step 1920 to Step 1930 described above, but the processing from Step 1940 to Step 1950 is performed. This is achieved by repeatedly executing the block m times. The calculation of the maximum oxygen storage amount CmaxUF <n> in Step 1945 is described in Step 1925, the value of the maximum oxygen storage amount CmaxUFall of the entire second catalyst 54 acquired in Step 1910 and the value of the counter value n. This is performed based on the formula described in step 1945 which is the same as the above formula. Accordingly, the value of the maximum oxygen storage amount CmaxUF <n> of each block n from the most upstream block 1 to the most downstream block m of the second catalyst 54 is sequentially calculated. In the equation described in step 1945, the value A2 is a positive constant, similar to the value A1, and is a value corresponding to the predetermined gradient. The value A2 may be the same value as the value A1 or a different value.
[0208]
When the process of step 1940 is repeated and the value of the counter value n becomes equal to the number of blocks m of the second catalyst 54, the CPU 71 makes a “Yes” determination at step 1950 to proceed to step 1955, where the oxygen storage amount OSA1, After each value of OSA2 is set to “0”, the routine proceeds to step 1995, and this routine is once terminated.
[0209]
Next, a routine for calculating CgoutSC of each specific component of the first catalyst 53 using the catalyst model will be described. This routine is shown by a series of flowcharts in FIGS. 21 to 25, and the CPU 71 repeatedly executes these routines every elapse of a predetermined time, whereby each block j (j = 1,.・ Sequentially, oxygen concentration CgoutSC, O2 <j>, nitrogen monoxide concentration CgoutSC, NO <j>, carbon monoxide concentration CgoutSC, CO <j>, and hydrocarbon concentration CgoutSC, HC <j> calculate.
[0210]
Therefore, when the predetermined timing is reached, the CPU 71 starts the process from step 2100, proceeds to step 2105, and stores the oxygen storage rate coefficients kstorSC, O2 (k) <j> and kstorSC, NO (k) <for the first catalyst 53. j>, the oxygen release rate coefficient krelSC, CO (k) <j>, and krelSC, HC (k) <j>, the deterioration index indicating the temperature TempSC of the first catalyst 53 and the degree of deterioration of the first catalyst 53. It is determined from the value REKKASC and a map (lookup table) as shown in FIG. Note that, for example, a value to which SC is assigned, such as kstorSC, O2 (k) <j>, is a value for the first catalyst, and a value to which <j> is assigned is a block j. (Jth block) means a value (hereinafter the same).
[0211]
The catalyst temperature TempSC and the catalyst temperature TempUF of the second catalyst 54 described later are estimated according to the operating state of the engine 10 (for example, the intake air flow rate Ga and the engine rotational speed NE). The deterioration index value REKKASC of the first catalyst 53 and the deterioration index value REKKAUF of the second catalyst 54 described later correspond to the maximum oxygen storage amount CmaxSCall of the first catalyst 53 and the maximum oxygen storage amount CmaxUFall of the second catalyst 54 described above. Each is required. For example, the deterioration index value REKKASC is obtained as a value that increases as the maximum oxygen storage amount CmaxSCall decreases, and the deterioration index value REKKAUF is obtained as a value that increases as the maximum oxygen storage amount CmaxUFall decreases.
[0212]
Next, the CPU 71 proceeds to step 2110 to set the value of the variable j to “0”. This variable j is a variable that determines what number of block the operation is to be performed below. Next, the CPU 71 increases the value of the variable j by “1” in Step 2115 and determines whether or not the value of the variable j becomes equal to r + 1 in Step 2120, that is, all the first catalysts 53 are in total. It is determined whether or not calculation of each specific component has been completed for the block.
[0213]
Since the value of the variable j at the current stage is “1”, the CPU 71 makes a “No” determination at step 2120 to proceed to step 2125 and is calculated at step 2160 described later at the time of the previous calculation of this routine. The oxygen concentration CwSC, O2 (k + 1) <j> of the coating layer of the jth block (block j) of the first catalyst 53 is set to the oxygen concentration CwSC, O2 (k) <j> of the current coating layer. In step 2130, the oxygen storage density OstSC (k + 1) <j> calculated in step 2515 of FIG. k) Set to <j>. When the current calculation is the first time after the engine 10 is started, appropriate initial values are given to the above values.
[0214]
Next, in step 2135, the CPU 71 obtains the oxygen consumption rate constant R * storSC, O2 (k) <j> in accordance with the equation described in step 2135 (see the above equation (36)). The maximum oxygen storage density OstSCmax <j> used in step 2135 may be a constant value, but is preferably determined according to the deterioration index value REKKASC (or the maximum oxygen storage amount CmaxSCall) (hereinafter the same). ). Thereafter, the CPU 71 determines the apparent diffusion rate R in step 2140._DSC, O2 (k) <j> with catalyst temperature TempSC and map MapR_DDetermined from SCO2.
[0215]
Subsequently, the CPU 71 obtains the oxygen reaction rate-determining factor SPstorSC, O2 <j> in step 2145 by the equation described in step 2145 (see the above equation (29)), and in step 2150, the first catalyst 53 The oxygen concentration CgoutSC, O2 (k) <j-1> flowing out from the block j-1 before (ie, upstream) the block j of FIG. Import as>.
[0216]
Since the value of j is “1” at this stage, the block j is the most upstream block of the first catalyst 53, and there is no previous (upstream) block j−1. Therefore, CgoutSC, O2 (k) <j-1> in the previous block in Step 2150 is the oxygen concentration CginSC, O2 of the exhaust gas flowing into the first catalyst 53. The oxygen concentration CginSC, O2 (= Cgin, O2) of the exhaust gas flowing into the first catalyst 53 is obtained by a function fO2 based on the air-fuel ratio of the exhaust gas flowing into the first catalyst 53 and the flow rate of the exhaust gas. The right side of the following equation (48) is a specific example of this function fO2. The air-fuel ratio AF of exhaust gas used in the equation (48) is the supply per unit time obtained from the intake air mass Ga per unit time measured by the air flow meter 61 based on the final fuel injection amount Fi and the engine speed NE. It is obtained by dividing by the fuel mass Gf. Note that the air-fuel ratio AF of the exhaust gas may be obtained from the output vabyfs of the most upstream air-fuel ratio sensor 66 and the map shown in FIG.
[0217]
[Formula 48]

[0218]
The derivation process of the above equation (48) will be briefly described. The air-fuel ratio AF of the exhaust gas flowing into the first catalyst 53 is Ga / Gf, and the air mass necessary for obtaining the stoichiometric air-fuel ratio with respect to Gf is expressed by Gastoich. Then, the theoretical 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 stoichiometric air-fuel ratio AFstoich is Ga-Gastoich. Then, the following equation (49) is obtained, and the above equation (48) is obtained from this equation (49).
[0219]
[Equation 49]

[0220]
Next, the CPU 71 proceeds to step 2155 to obtain CgoutSC, O2 (k + 1) <j> according to the equation described in step 2155 (see the above equation (30)). The value of vg is the intake air flow rate AFM (= Ga) detected by the air flow meter 61. Thus, in step 2155, the oxygen concentration CgoutSC, O2 flowing out from the target block j is newly calculated. Next, the CPU 71 proceeds to step 2160 and obtains CwSC, O2 (k + 1) <j> according to the equation described in step 2160 (see the above equation (28)). That is, the CPU 71 newly calculates the oxygen concentration CwSC, O2 of the coat layer of the block j of the first catalyst 53 that is the target in step 2160, and proceeds to step 2200 shown in FIG. In this way, the routine shown in FIG. 21 constitutes the oxygen concentration estimating means for the exhaust gas phase and the oxygen concentration estimating means for the coat layer in the block j (specific region j) of the first catalyst 53.
[0221]
The routine shown in FIG. 22 is a routine for performing an operation on nitric oxide NO, and is the same routine as the routine of FIG. 21 described above for performing an operation on oxygen O2. Briefly, the CPU 71 proceeds from step 2200 to step 2205, and the coating layer of the jth block (block j) of the first catalyst 53 calculated in step 2235 described later at the time of the previous calculation of this routine. The nitric oxide concentration CwSC, NO (k + 1) <j> is set to the nitric oxide concentration CwSC, NO (k) <j> of the current coating layer. When the current calculation is the first time after the engine 10 is started, an appropriate initial value is given to the CwSC, NO (k) <j>.
[0222]
Next, the CPU 71 obtains a consumption rate constant R * storSC, NO (k) <j> in step 2210 according to the equation described in step 2210 (see the above equation (36)). Here, as the oxygen storage density OstSC (k) <j> and the maximum oxygen storage density OstSCmax <j>, the values used in Step 2135 described above are used. Thereafter, the CPU 71 determines the apparent diffusion rate R in step 2215._DSC, NO (k) <j> with catalyst temperature TempSC and map MapR_DDetermined from SCNO.
[0223]
Subsequently, the CPU 71 obtains the reaction rate limiting factor SPstorSC, NO <j> of nitric oxide in step 2220 by the formula described in step 2220 (see the above formula (29)), and in step 2225 the first The nitric oxide concentration CgoutSC, NO (k) <j-1> flowing out from the block j-1 before (ie, upstream) the block j of the catalyst 53 is the nitrogen monoxide concentration CginSC, flowing into the block j. Capture as NO (k) <j>.
[0224]
Since the value of j is “1” at this stage, the target block j is the most upstream block of the first catalyst 53, and there is no upstream block j−1. Accordingly, CgoutSC, NO (k) <j-1> in the previous block in Step 2225 is the nitrogen monoxide concentration CginSC, NO of the exhaust gas flowing into the first catalyst 53. In this case, the relationship between the air-fuel ratio A / F of the exhaust gas flowing into the first catalyst 53 (calculated as “Ga / Gf”) and the nitric oxide concentration CginSC, NO is as shown in the graph of FIG. Therefore, this relationship is obtained in advance by experiment and stored as a map, and the nitric oxide concentration CginSC, NO is obtained from the actual air-fuel ratio A / F of exhaust gas obtained by calculation and the map.
[0225]
Next, the CPU 71 proceeds to step 2230 and obtains CgoutSC, NO (k + 1) <j> according to the equation described in step 2230 (see the above equation (30)). That is, the nitric oxide concentration CgoutSC, NO flowing out from the target block j is newly calculated. Next, the CPU 71 proceeds to step 2235 and obtains CwSC, NO (k + 1) <j> according to the equation described in step 2235 (see the above equation (28)). That is, the CPU 71 newly calculates the nitric oxide concentration CwSC, NO of the coat layer of the block j of the first catalyst 53 that is the target in step 2235, and then goes to step 2300 shown in FIG. move on. As described above, the routine shown in FIG. 22 constitutes the nitrogen monoxide concentration estimating means for the exhaust gas phase in the block j (specific region j) of the first catalyst 53 and the nitrogen monoxide concentration estimating means for the coat layer. .
[0226]
The routine shown in FIG. 23 is a routine for performing computation on carbon monoxide CO. The CPU 71 proceeds from step 2200 to step 2205, and uses the coating layer carbon monoxide concentration CwSC, CO (k + 1) <j> calculated in step 2335, which will be described later, in the previous calculation of this routine. The carbon monoxide concentration of the layer is set to CwSC, CO <j> (k). If this calculation is the first time after the engine 10 is started, an appropriate initial value is given to CwSC, CO <j> (k).
[0227]
Next, in step 2310, the CPU 71 obtains a consumption rate constant R * reducSC, CO (k) <j> according to the equation described in step 2310 (see the above equation (38)), and then step 2315. Apparent diffusion rate R at_DSC, CO (k) <j> with catalyst temperature TempSC and map MapR_DDecide from SCCO.
[0228]
Subsequently, the CPU 71 obtains the carbon monoxide reaction rate-determining factor SPreducSC, CO <j> in step 2320 according to the equation described in the step 2320 (see the above equation (33)). The carbon monoxide concentration CgoutSC, CO (k) <j-1> flowing out from the block j-1 before (ie, upstream) the block j of one catalyst 53 is changed to the carbon monoxide concentration CginSC flowing into the block j. , CO (k) <j>.
[0229]
Since the value of j is “1” at this stage, the target block j is the most upstream block of the first catalyst 53, and there is no upstream block j−1. Therefore, CgoutSC, CO (k) <j-1> in the previous block in step 2325 is the carbon monoxide concentration CginSC, CO of the exhaust gas flowing into the first catalyst 53. In this case, the relationship between the air-fuel ratio A / F of the exhaust gas flowing into the first catalyst 53 (calculated as “Ga / Gf”) and the carbon monoxide concentrations CginSC, CO is as shown in the graph of FIG. Therefore, this relationship is obtained in advance by experiment and stored as a map, and the carbon monoxide concentrations CginSC and CO are obtained from the actual air-fuel ratio A / F of exhaust gas obtained by calculation and the map.
[0230]
Next, the CPU 71 proceeds to step 2330 and obtains CgoutSC, CO (k + 1) <j> according to the equation described in step 2330 (see the above equation (34)). That is, the carbon monoxide concentration CgoutSC, CO flowing out from the block j of the first catalyst 53 is newly calculated. Next, the CPU 71 proceeds to step 2335 to obtain CwSC, CO (k + 1) <j> according to the equation described in step 2335 (see the above equation (32)). That is, the CPU 71 newly calculates the carbon monoxide concentration CwSC, CO of the coating layer of the block j of the first catalyst 53 that is the target in step 2335, and goes to step 2400 shown in FIG. move on. In this way, the routine shown in FIG. 23 constitutes the carbon monoxide concentration estimating means for the exhaust gas phase in the block j of the first catalyst 53 and the carbon monoxide concentration estimating means for the coat layer.
[0231]
The routine shown in FIG. 24 is a routine for performing an operation on hydrocarbon HC, and is the same routine as the routine of FIG. 23 described above for performing an operation on carbon monoxide CO. Briefly, the CPU 71 proceeds from step 2400 to step 2405, where the hydrocarbon concentration CwSC, HC (k + 1) <j> of the coating layer calculated in step 2435 described later at the time of the previous calculation of this routine. Is set to CwSC, HC (k) <j> which is the value of the hydrocarbon concentration Cw, HC of the coat layer this time. When the current calculation is the first time after the engine 10 is started, appropriate initial values are given to the above values.
[0232]
Next, in step 2410, the CPU 71 obtains a consumption rate constant R * reducSC, HC (k) <j> in accordance with the equation described in step 2410 (see the equation (38) above), and then step 2415 Apparent diffusion rate R at_DSC, HC (k) <j> to catalyst temperature TempSC and map MapR_DDetermined from SCHC.
[0233]
Subsequently, the CPU 71 obtains the hydrocarbon reaction rate limiting factor SPreducSC, HC <j> in step 2420 by the equation described in the step 2420 (see the above equation (33)). The hydrocarbon concentration CgoutSC, HC (k) <j-1> flowing out from the block j-1 before (that is, upstream) of the block 53 of the catalyst 53 is the hydrocarbon concentration CginSC, HC (k ) Import as <j>.
[0234]
Since the value of j is “1” at this stage, the block j is the most upstream block of the first catalyst 53, and there is no upstream block j−1. Therefore, Cgout, HC (k) <j-1> in step 2425 is the hydrocarbon concentration Cgin, HC of the exhaust gas flowing into the first catalyst 53. In this case, the relationship between the air-fuel ratio A / F of the exhaust gas flowing into the first catalyst 53 (calculated as “Ga / Gf”) and the hydrocarbon concentrations Cgin, HC is as shown in the graph of FIG. Therefore, this relationship is obtained in advance by experiments and stored as a map, and the hydrocarbon concentrations Cgin and HC are obtained from the actual air-fuel ratio A / F of exhaust gas obtained by calculation and the same map.
[0235]
Next, the CPU 71 proceeds to step 2430 to obtain CgoutSC, HC (k + 1) <j> according to the equation described in step 2430 (see the above equation (34)). That is, the hydrocarbon concentration CgoutSC, HC flowing out from the block j of the first catalyst 53 is newly calculated. Next, the CPU 71 proceeds to step 2435 and obtains CwSC, HC (k + 1) <j> according to the equation described in step 2435 (see the above equation (32)). That is, the CPU 71 newly calculates the hydrocarbon concentration Cw, HC of the coat layer of the block j of the first catalyst 53 in step 2435, and proceeds to step 2500 shown in FIG. In this way, the routine shown in FIG. 24 constitutes the hydrocarbon concentration estimating means for the exhaust gas phase and the hydrocarbon concentration estimating means for the coat layer in the block j (specific region j) of the first catalyst 53.
[0236]
The routine shown in FIG. 25 is a routine for calculating the oxygen storage density Ost. When the CPU 71 proceeds from step 2500 to step 2505, the CPU 71 obtains a coefficient P <j> from the formula described in step 2505 based on the above formula (43), and in step 2510, the CPU 71 obtains the same coefficient based on the above formula (44). The coefficient Q <j> is obtained by the formula described in step 2510. Next, in step 2515, the CPU 71 obtains the oxygen storage density OstSC (k + 1) <j> from the equation described in step 2515 based on the above equation (42), and in the next step 2520, the above equation (45) is obtained. The oxygen storage amount OstSC (k + 1) <j> · dA · L of the block j is added to the oxygen storage amount OSASC (j-1) from the block 1 to the block j-1 by the formula described in the same step 2520. Thus, the oxygen storage amount OSASC (j) from block 1 to block j is obtained, and the process returns to step 2115 in FIG. Note that the value of the oxygen storage amount OSASC (0) is set to “0”. In this way, the routine shown in FIG. 25 constitutes the oxygen storage density calculating means for block j of the first catalyst 53 and the oxygen storage amount calculating means for blocks 1 to j of the first catalyst 53.
[0237]
Since the CPU 71 that has returned to step 2115 in FIG. 21 increases the value of the variable j by “1”, the various values of the next downstream block in the first catalyst 53 are sequentially calculated in the same manner as described above. . When various values up to the block r are calculated, the value of the variable j is made equal to r + 1 in step 2115, so the CPU 71 determines “Yes” in step 2120, and proceeds to step 2195. A series of routines shown in FIG. 21 to FIG. 25 for calculating CgoutSC of each specific component of one catalyst 53 are temporarily ended.
[0238]
Next, a routine for calculating CgoutUF of each specific component of the second catalyst 54 using the catalyst model will be described. This routine is shown by a series of flowcharts of FIGS. 30 to 34 similar to the routines shown in the series of flowcharts of FIGS. 21 to 25, respectively, and the CPU 71 executes the second routine by executing these routines. Oxygen concentration CgoutUF, O2 <j>, nitrogen monoxide concentration CgoutUF, NO <j>, carbon monoxide concentration CgoutUF, CO <j> flowing out from each block j (j = 1,..., M) of the catalyst 54. , And hydrocarbon concentration CgoutUF, HC <j> is calculated. Since the series of routines shown in FIGS. 30 to 34 are the same as the series of routines shown in FIGS. 21 to 25, detailed description thereof will be omitted.
[0239]
When the value of the variable j is “1”, the CPU 71 is a value required at step 3050 in FIG. 30, step 3125 in FIG. 31, step 3225 in FIG. 32, and step 3325 in FIG. The oxygen concentration CginUF, O2 (= CginUF, O2 (k) <1>) of the exhaust gas flowing into the second catalyst 54, the nitrogen monoxide concentration CginUF, NO (= CginUF, NO (k) <1>) of the exhaust gas, The first catalyst with carbon monoxide concentration CginUF, CO (= CginUF, CO (k) <1>) and carbon hydrogen concentration CginUF, HC (= CginUF, HC (k) <1>) of the exhaust gas Of the oxygen concentration CgoutSC, O2 <r> in the exhaust gas flowing out from 53, the value of the nitrogen monoxide concentration CgoutSC, NO <r> in the exhaust gas, and the carbon monoxide concentration CgoutSC, CO <r> in the exhaust gas Value and carbon hydrogen concentration CgoutSC, HC <r> in the exhaust gas are used. Since the exhaust gas flowing out from the first catalyst 53 flows into the second catalyst 54 without being exchanged with the outside, the concentration of each specific component in the exhaust gas flowing into the second catalyst 54 is in the exhaust gas flowing out from the first catalyst 53. It is because it is thought that it is equal to the density | concentration of each specific component.
[0240]
As described above, the routine shown in FIG. 30 constitutes the oxygen concentration estimation means for the exhaust gas phase and the oxygen concentration estimation means for the coat layer in the block j (specific region j) of the second catalyst 54. The routine shown in FIG. 31 constitutes a nitrogen monoxide concentration estimating means for the exhaust gas phase in the block j (specific region j) of the second catalyst 54 and a nitrogen monoxide concentration estimating means for the coat layer. The routine shown in FIG. 32 constitutes the carbon monoxide concentration estimating means for the exhaust gas phase in the block j of the second catalyst 54 and the carbon monoxide concentration estimating means for the coat layer. The routine shown in FIG. 33 constitutes an exhaust gas phase hydrocarbon concentration estimation means and a coat layer hydrocarbon concentration estimation means in block j (specific region j) of the second catalyst 54. The routine shown in FIG. 34 constitutes an oxygen storage density calculating means for block j of the second catalyst 54 and an oxygen storage amount calculating means for blocks 1 to j of the second catalyst 54.
[0241]
As described above, the CPU 71 uses the catalyst model, and the control block (intermediate) moves to the downstream side in accordance with the progress of deterioration of the catalyst device including the first and second catalysts 53 and 54 (decrease in the maximum oxygen storage amount). A control oxygen concentration CgoutO2c, which is a value related to the excess / deficiency of oxygen as a value related to the air-fuel ratio of the gas flowing out from the block i, that is, a value related to the amount of the specific component flowing out from the control block i, When the control oxygen concentration CgoutO2c becomes a value indicating that the air-fuel ratio is richer than a predetermined level (when the value is smaller than the negative threshold Crefmns), the air-fuel ratio of the gas flowing into the catalyst device Is controlled to a predetermined lean air-fuel ratio (an air-fuel ratio leaner by a predetermined value α1 than the theoretical air-fuel ratio), and the control oxygen concentration CgoutO2c is a value indicating a lean air-fuel ratio exceeding a predetermined level. The (When the value becomes larger than the positive threshold Crefpls), the air-fuel ratio of the gas flowing into the catalyst device is controlled to a predetermined rich air-fuel ratio (the air-fuel ratio richer by a predetermined value α2 than the theoretical air-fuel ratio). Thus, the air-fuel ratio of the gas flowing into the catalyst device is forcibly oscillated (accordingly, perturbation control).
[0242]
Therefore, the present exhaust gas purification apparatus provides information on the change in the air-fuel ratio of the gas flowing out from the control block i at a time earlier than the output change of the air-fuel ratio sensor provided downstream of the control block i (in this case, the control The oxygen concentration CgoutO2c) is acquired, and the timing for forcibly switching the air-fuel ratio of the gas flowing into the catalyst device is determined by paying attention directly to the information on the change in the air-fuel ratio of the gas flowing out from the acquired control block i. Since the perturbation control is performed, the air-fuel ratio of the gas flowing out from the control block i can be stably and surely maintained in the vicinity of the theoretical air-fuel ratio. As a result, harmful effects on the downstream side of the control block i The discharge amount of the components could be stably and reliably reduced.
[0243]
In addition, the present exhaust purification apparatus has the first to nth blocks that are the most upstream block of the catalyst apparatus including one or a plurality of catalysts (first and second catalysts 53 and 54) when the value n is a natural number. Integration value calculation to obtain the maximum oxygen storage amount integrated value (determination oxygen storage amount) in the upstream part of the catalyst device by integrating the maximum oxygen storage amount of each block upstream of the catalyst device composed of the blocks up to the second block Means (steps 1120 and 1155), the catalyst comprising the nth block having the smallest value n in the upstream portion of the catalyst device in which the maximum accumulated oxygen storage value is larger than a predetermined threshold Cth. The nth block upstream of the apparatus is set as a control block (intermediate block) i. In other words, the control block i moves downstream as the deterioration of the catalyst device progresses (decrease in the maximum oxygen storage amount).
[0244]
As a result, the oxygen storage capacity of the upstream portion of the catalyst device constituted by each block from the block located in the uppermost stream of the catalyst device to the intermediate block i is set to the predetermined value set so as not to cause perturbation of perturbation control. The number of blocks downstream from the intermediate block i which can be maintained as a value larger than a predetermined oxygen storage capacity corresponding to the threshold value Cth and can function as a preliminary catalyst (buffer catalyst) is maximized. it can. Therefore, the amount of harmful components discharged from the most downstream position of the catalyst device can be reduced as much as possible while avoiding hunting of the air-fuel ratio of the gas flowing into the catalyst device.
[0245]
Second Embodiment
Next, a second embodiment of the exhaust gas purification apparatus according to the present invention will be described. This exhaust gas purification apparatus uses the same control in place of the control oxygen concentration CgoutO2c which is the oxygen concentration in the exhaust gas flowing out from the control block i. Nitric oxide concentration (control nitrogen monoxide concentration CgoutNOc), which is a value related to the amount of oxidant in the exhaust gas flowing out from the control block i, and a value related to the amount of reducing agent in the exhaust gas flowing out from the control block i The above first implementation is performed only in that perturbation control is performed using a certain carbon monoxide concentration (control carbon monoxide concentration CgoutCOc) to determine the timing for forcibly switching the air-fuel ratio of the gas flowing into the catalyst device. It differs from the exhaust gas purification device of the form. Accordingly, only such differences will be described below.
[0246]
(Air-fuel ratio control (perturbation control) of the second embodiment)
First, the air-fuel ratio control of the exhaust emission control device according to the second embodiment will be described. FIG. 35 is a time chart in the perturbation control according to the second embodiment. FIG. 35A shows the air-fuel ratio of the air-fuel mixture supplied to the engine 10 (accordingly, the air-fuel ratio of the exhaust gas upstream of the first catalyst). B) shows the control carbon monoxide concentration CgoutCOc flowing out from the control block i calculated by the above-mentioned catalyst model, and (C) shows the control nitric oxide concentration CgoutNOc flowing out from the control block i. Show. As shown in FIG. 35, the present exhaust purification system obtains the control nitrogen monoxide concentration CgoutNOc and the control carbon monoxide concentration CgoutCOc flowing out from the control block i (taking only positive values) by the catalyst model. Then, perturbation control is performed on the air-fuel ratio of the air-fuel mixture supplied to the engine 10 so that the control nitrogen monoxide concentration CgoutNOc and the control carbon monoxide concentration CgoutCOc are maintained near “0”.
[0247]
More specifically, this exhaust gas purification apparatus is a value indicating that the amount (concentration) of the reducing agent exceeds the predetermined level when CgoutCOc becomes larger than the positive threshold value Crefpls1. Or when the air / fuel ratio of the gas reaches a value that indicates a rich air / fuel ratio exceeding a predetermined level), this means that a large amount of unburned components have started to flow out of the control block i. Therefore, the target air-fuel ratio of the air-fuel mixture supplied to the engine 10 is set to be lean by a predetermined value α1 from the stoichiometric air-fuel ratio, and the actual air-fuel ratio of the air-fuel mixture supplied to the engine 10 becomes the target air-fuel ratio. (See times t11 and t13.)
[0248]
On the other hand, when CgoutNOc becomes larger than the positive threshold Crefpls2 (that is, when the amount (concentration) of the oxidizer exceeds the predetermined level), or When the air / fuel ratio reaches a value indicating that the air / fuel ratio is a lean air / fuel ratio exceeding a predetermined level), it means that a large amount of nitrogen oxide NOx starts to flow out from the control block i, and is supplied to the engine 10. The target air-fuel ratio of the air-fuel mixture is set to be richer by a predetermined value α2 than the stoichiometric air-fuel ratio and controlled so that the actual air-fuel ratio becomes the target air-fuel ratio (see time t12). The predetermined value α1 and the predetermined value α2 may be different values or may be equal values. Further, the positive threshold value Crefpls1 and the positive threshold value Crefpls2 may be different values or equal values.
[0249]
(Actual operation)
Next, the actual operation of the exhaust emission control device will be described with reference to a flowchart showing a routine executed by the CPU 71. The CPU 71 of the exhaust purification apparatus executes the same routine as the CPU 71 of the exhaust purification apparatus according to the first embodiment except that the routine shown in the flowcharts of FIGS. 36 and 37 instead of FIGS. 11 and 12 is executed. To do. 36 and 37, the same steps as those in FIGS. 11 and 12 are denoted by the same reference numerals.
[0250]
In the routine of FIG. 36, instead of the control oxygen concentration CgoutO2c which is the oxygen concentration in the exhaust gas flowing out from the control block i, the nitrogen monoxide concentration and the carbon monoxide concentration in the exhaust gas flowing out from the control block i 11 is different from the routine of FIG. 11 only in that steps 3635 and 3670 are employed instead of steps 1135 and 1170 in order to obtain the control nitrogen monoxide concentration CgoutNOc and the control carbon monoxide concentration CgoutCOc. Therefore, detailed description of the routine of FIG. 36 is omitted.
[0251]
In the routine of FIG. 37, instead of the control oxygen concentration CgoutO2c which can take positive and negative values, the control nitric oxide concentration CgoutNOc and the control carbon monoxide concentration CgoutCOc which always take only positive values are obtained. 12 differs from the routine of FIG. 12 only in that steps 3710, 3715, 3725, and 3730 are employed instead of steps 1210, 1215, 1225, and 1230 in order to switch the air-fuel ratio of the gas flowing into the catalyst device. To do. Therefore, detailed description of the routine of FIG. 37 is omitted.
[0252]
As described above, the exhaust gas purification apparatus according to the second embodiment has the oxygen storage rate coefficient (kstorSC, O2 (k) <j>) that determines the oxygen storage reaction rate and the oxygen release reaction rate in the catalyst device by the catalyst model. And kstorSC, NO (k) <j>) and oxygen release rate coefficients (krelSC, CO (k) <j> and krelSC, HC (k) <j>) are set individually, and the reaction rate difference between them is considered. Then, based on the respective values of the control nitric oxide concentration CgoutNOc and the control carbon monoxide concentration CgoutCOc that can be calculated individually and accurately, the switching timing of the air-fuel ratio of the gas flowing into the catalyst device is determined. As a result, the air-fuel ratio of the gas flowing out from the control block i can be more reliably maintained in the vicinity of the theoretical air-fuel ratio, and the amount of harmful components discharged from the most downstream position of the catalyst device can be further reduced.
[0253]
In the second embodiment, when the control carbon monoxide concentration CgoutCOc flowing out from the control block i becomes larger than the positive threshold Crefpls1, and when the control nitric oxide concentration CgoutNOc flowing out from the control block i is Although it is configured to switch the air-fuel ratio of the gas flowing into the catalyst device when the positive threshold value Crefpls2 becomes larger, the control hydrocarbon concentration CgoutHCc, which is the hydrocarbon concentration flowing out from the control block i, and the same control When both the carbon monoxide concentration CgoutCOc for use is larger than the positive threshold value Crefpls1, the control oxygen concentration CgoutO2c that is the oxygen concentration flowing out from the control block i and the control nitric oxide concentration CgoutNOc are both positive threshold values Crefpls2 You may comprise so that the air fuel ratio of the gas which flows into a catalyst apparatus when it becomes larger may be switched.
[0254]
The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, in each of the above embodiments, the oxygen storage capacity (maximum oxygen storage amount CmaxSCall) of the first catalyst 53 is larger than a predetermined oxygen storage capacity (greater than a predetermined threshold Cth) without using the catalyst model described above. Is greater than the second catalyst 54, the output of the first catalyst downstream air-fuel ratio sensor 67 disposed in the exhaust passage downstream of the first catalyst 53 is the oxygen storage capacity (maximum oxygen) of the first catalyst 53. When the storage amount CmaxSCall) is equal to or less than a predetermined oxygen storage capacity (less than a predetermined threshold Cth), the output of the second catalyst downstream air-fuel ratio sensor 68 disposed in the exhaust passage downstream of the second catalyst 54 is used as the control air-fuel ratio. When the sensor output is selected as a sensor output, and the selected control air-fuel ratio sensor output becomes a value (for example, 0.7 V or more) indicating that the air-fuel ratio is richer than a theoretical air-fuel ratio, the catalyst device Gas flowing into The air-fuel ratio is controlled to a predetermined lean air-fuel ratio, and a value indicating that the selected control air-fuel ratio sensor output is a lean air-fuel ratio exceeding a predetermined degree than the theoretical air-fuel ratio (for example, 0.3 V) The air-fuel ratio of the gas flowing into the catalyst device may be forcibly oscillated by controlling the air-fuel ratio of the gas flowing into the catalyst device to a predetermined rich air-fuel ratio. .
[0255]
In the above embodiments, when the oxygen storage capacity (maximum oxygen storage amount CmaxSCall) of the first catalyst 53 is larger than the predetermined oxygen storage capacity (larger than the predetermined threshold Cth), the first catalyst 53 Values related to the amount of specific components in the exhaust gas flowing out (for example, CgoutSC, X <r>, where X is O2 for oxygen, CO for carbon monoxide, HC for hydrocarbons, NO for nitrogen oxides) When the oxygen storage capacity (maximum oxygen storage amount CmaxSCall) of the first catalyst 53 is not more than a predetermined oxygen storage capacity (not more than a predetermined threshold Cth), a value relating to the amount of a specific component in the exhaust gas flowing out from the second catalyst 54 ( For example, CgoutUF, X <m>) is selected as the control specific component amount (for example, control specific component concentration CgoutXc), and the selected control specific component amount is richer than the stoichiometric air-fuel ratio. When the air / fuel ratio is reached (for example, When the control oxygen concentration CgoutO2c is smaller than the negative threshold value Crefmns), the air-fuel ratio of the gas flowing into the catalyst device is controlled to a predetermined lean air-fuel ratio, and the selected control specific component amount is determined to be higher than the stoichiometric air-fuel ratio. When the air-fuel ratio becomes a value that indicates a lean air-fuel ratio that exceeds a certain level (for example, when the control oxygen concentration CgoutO2c is greater than the positive threshold Crefpls), the air-fuel ratio of the gas flowing into the catalyst device is set to a predetermined rich value. The air / fuel ratio of the gas flowing into the catalyst device may be forcibly oscillated by controlling the air / fuel ratio.
[0256]
In each of the above embodiments, the control block i is located on the most downstream side of the block located on the most upstream side of the catalyst device composed of the first and second catalysts 53 and 54 (block 1 on the first catalyst 53). The block up to (the block m of the second catalyst 54) is selected, but the control block i is the block (first block) located in the uppermost stream of the catalyst device including only the first catalyst 53. The second catalyst 54 is selected from the blocks from the block 1) of the catalyst 53 to the block located at the most downstream (block r of the first catalyst 53), and the second catalyst 54 is a preliminary catalyst (buffer catalyst). ) May function.
[0257]
In this case, the second catalyst 54 may be omitted. When the second catalyst 54 is omitted, the output of the first catalyst downstream air-fuel ratio sensor 67 is always controlled regardless of the oxygen storage capacity (maximum oxygen storage amount CmaxSCall) of the first catalyst 53. When used as an output, the control air-fuel ratio sensor output flows into the catalyst device when it becomes a value (for example, 0.7 V or more) indicating that the air-fuel ratio is a rich air-fuel ratio that exceeds a predetermined level than the theoretical air-fuel ratio. A value (for example, 0) indicating that the air / fuel ratio of the gas is controlled to a predetermined lean air / fuel ratio, and that the selected control air / fuel ratio sensor output is a lean air / fuel ratio that exceeds a predetermined degree than the theoretical air / fuel ratio. .3V or less), the air-fuel ratio of the gas flowing into the catalyst device is controlled to a predetermined rich air-fuel ratio to forcibly oscillate the air-fuel ratio of the gas flowing into the catalyst device. Also good.
[0258]
Further, when the second catalyst 54 is omitted, regardless of the oxygen storage capacity (maximum oxygen storage amount CmaxSCall) of the first catalyst 53, a value related to the amount of the specific component in the exhaust gas always flowing out from the first catalyst 53. (For example, CgoutSC, X <r>. X is O2 for oxygen, CO for carbon monoxide, HC for hydrocarbon, NO for nitrogen oxide) specific amount for control (for example, specific component for control (Concentration CgoutXc), and when the control specific component amount is a value indicating that the air / fuel ratio is richer than the stoichiometric air / fuel ratio, the control oxygen concentration CgoutO2c is a negative threshold value. (When smaller than Crefmns) The air-fuel ratio of the gas flowing into the catalyst device is controlled to a predetermined lean air-fuel ratio, and the selected specific component amount for control exceeds the stoichiometric air-fuel ratio by a predetermined degree. When the value indicates that For example, when the control oxygen concentration CgoutO2c is larger than the positive threshold Crefpls), the air-fuel ratio of the gas flowing into the catalyst device is forced by controlling the air-fuel ratio of the gas flowing into the catalyst device to a predetermined rich air-fuel ratio. It may be configured to vibrate automatically.
[0259]
Further, in each of the above embodiments, the output of the second catalyst downstream air-fuel ratio sensor 68 disposed in the exhaust passage downstream of the catalyst device composed of the first and second catalysts 53 and 54 is always output from the control air-fuel ratio sensor output. The air-fuel ratio of the gas flowing into the catalyst device may be forcibly oscillated based on the output of the control air-fuel ratio sensor. Further, a value related to the amount of a specific component in the exhaust gas flowing out from the catalyst device including the first and second catalysts 53 and 54 (for example, CgoutUF, X <m>. X is O2 in the case of oxygen, CO in the case of carbon monoxide. HC for hydrocarbons, NO for nitrogen oxides) is always used as the control specific component amount (for example, control specific component concentration CgoutXc), and based on the value of the control specific component amount as above You may comprise so that the air fuel ratio of the gas which flows into the catalyst apparatus may be forcedly vibrated.
[0260]
In each of the above embodiments, the control block i is selected based on the maximum oxygen storage amount in the upstream portion of the catalyst device, which is a value indicating the oxygen storage capability. However, the oxygen storage capability of the catalyst device is indirectly determined. The control block i may be selected based on the vehicle travel distance, the temperature of the catalyst device, and the intake air flow rate Ga.
[0261]
In this case, it is preferable that the position of the control block i is moved to the downstream side in accordance with the increase in the travel distance, the decrease in the catalyst temperature, and the increase in the intake air flow rate Ga. This is because the maximum oxygen storage amount of the catalyst device deteriorates as the travel distance increases, and the oxygen storage capacity of the catalyst device decreases as the temperature of the catalyst device decreases. This is because as the intake air amount Ga increases, the amount of oxygen that can be stored by the catalyst device (that is, the substantial maximum oxygen storage amount that is the oxygen storage capacity) decreases.
[0262]
Further, in each of the above embodiments, the amplitude α (expressed by α1, α2) from the theoretical air-fuel ratio in the perturbation control is represented by the temperature TempSC (the first temperature of the first catalyst 53) as shown in FIG. The temperature TempUF of the second catalyst 54), the intake air amount Ga, the deterioration index value REKKASC of the first catalyst 53 (the deterioration index value REKKAUF of the second catalyst 54), and the like. According to this, primary poisoning due to oxygen in the catalyst device can be appropriately eliminated, and the state of the catalyst device can be better maintained.
[Brief description of the drawings]
FIG. 1 is a schematic view of an internal combustion engine equipped with an exhaust purification device according to a first embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the output of the most upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio.
FIG. 3 is a graph showing the relationship between each output of the first catalyst downstream air-fuel ratio sensor and the second catalyst downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio.
4 is a time chart for explaining perturbation control by the exhaust emission control device shown in FIG. 1; FIG.
FIG. 5 is a schematic diagram of a catalyst for explaining a catalyst model.
FIG. 6 is an external view of the catalyst shown in FIG.
7 is a partial cross-sectional view of the catalyst shown in FIG.
FIG. 8 is a schematic diagram for explaining a catalyst model.
FIG. 9 is a schematic diagram for explaining an upwind method used in a catalyst model.
FIG. 10 is a flowchart showing a routine for fuel injection amount calculation executed by a CPU shown in FIG. 1;
FIG. 11 is a flowchart showing a routine for determining a control oxygen concentration executed by the CPU shown in FIG. 1;
12 is a flowchart showing a routine for setting a target air-fuel ratio that is executed by the CPU shown in FIG. 1; FIG.
FIG. 13 is a flowchart showing a routine for calculating an air-fuel ratio feedback correction amount executed by the CPU shown in FIG. 1;
FIG. 14 is a flowchart showing a routine for determining whether or not to start maximum oxygen storage amount acquisition control executed by the CPU shown in FIG. 1;
FIG. 15 is a flowchart showing a first mode routine executed by the CPU shown in FIG. 1;
FIG. 16 is a flowchart showing a second mode routine executed by the CPU shown in FIG. 1;
FIG. 17 is a flowchart showing a third mode routine executed by the CPU shown in FIG. 1;
FIG. 18 is a flowchart showing a routine for calculating an oxygen storage amount executed by the CPU shown in FIG. 1;
FIG. 19 is a flowchart showing a routine for calculating a maximum oxygen storage amount executed by the CPU shown in FIG. 1;
FIG. 20 is a map for obtaining the maximum oxygen storage amount for each block of the first catalyst from the maximum oxygen storage amount of the entire first catalyst.
FIG. 21 is a flowchart showing a routine for obtaining the oxygen concentration in the first catalyst according to the catalyst model.
FIG. 22 is a flowchart showing a routine for obtaining the concentration of nitric oxide in the first catalyst according to the catalyst model.
FIG. 23 is a flowchart showing a routine for obtaining the carbon monoxide concentration in the first catalyst according to the catalyst model.
FIG. 24 is a flowchart showing a routine for obtaining a hydrocarbon concentration in the first catalyst according to a catalyst model.
FIG. 25 is a flowchart showing a routine for obtaining an oxygen storage density and an oxygen storage amount of a first catalyst according to a catalyst model.
FIG. 26 is a map for obtaining each coefficient (each multiplier) used in the catalyst model from the degree of catalyst deterioration and the catalyst temperature.
FIG. 27 is a map that defines the relationship between the air-fuel ratio of exhaust gas used to determine the concentration of nitric oxide flowing into the catalyst and the same nitric oxide concentration.
FIG. 28 is a map that defines the relationship between the air-fuel ratio of exhaust gas used to determine the concentration of carbon monoxide flowing into the catalyst and the same carbon oxide concentration.
FIG. 29 is a map that defines the relationship between the air-fuel ratio of exhaust gas used to determine the hydrocarbon concentration flowing into the catalyst and the hydrocarbon concentration.
FIG. 30 is a flowchart showing a routine for obtaining the oxygen concentration in the second catalyst according to the catalyst model.
FIG. 31 is a flowchart showing a routine for obtaining a nitric oxide concentration in the second catalyst according to a catalyst model.
FIG. 32 is a flowchart showing a routine for obtaining a carbon monoxide concentration in the second catalyst according to a catalyst model.
FIG. 33 is a flowchart showing a routine for obtaining a hydrocarbon concentration in the second catalyst according to a catalyst model.
FIG. 34 is a flowchart showing a routine for obtaining an oxygen storage density and an oxygen storage amount of a second catalyst according to a catalyst model.
FIG. 35 is a time chart for explaining perturbation control by the exhaust gas purification apparatus according to the second embodiment of the present invention.
FIG. 36 is a flowchart showing a routine for determining a control nitrogen monoxide concentration and a control carbon monoxide concentration executed by the CPU of the exhaust gas purification apparatus according to the second embodiment.
FIG. 37 is a flowchart showing a routine for setting a target air-fuel ratio that is executed by the CPU of the exhaust emission control system according to the second embodiment.
FIG. 38 is a graph showing the control range of the air-fuel ratio in the perturbation control of each embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 53 ... 1st catalyst, 54 ... 2nd catalyst, 66 ... Most upstream air fuel ratio sensor, 67 ... 1st catalyst downstream air fuel ratio sensor, 68 ... 2nd catalyst downstream air fuel ratio sensor, 70 ... Electric control apparatus 71 CPU

Claims (5)

A catalyst device comprising a single catalyst interposed in an exhaust passage of an internal combustion engine or a plurality of catalysts interposed in series in the exhaust passage;
One block located upstream of the block located most downstream is control block when captured is divided into a plurality of blocks along the flow direction of the gas flowing before the catalyst device Kisawa medium device Gas air-fuel ratio related value acquisition means for acquiring a value related to the air-fuel ratio of the gas flowing out from
The gas that flows into the catalyst device when the value related to the air-fuel ratio of the acquired gas becomes a value indicating that the air-fuel ratio of the gas is a rich air-fuel ratio that exceeds a predetermined degree than the stoichiometric air-fuel ratio. The air-fuel ratio of the gas is controlled to be a predetermined lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, and the value related to the air-fuel ratio of the gas is a lean air-fuel ratio that exceeds the stoichiometric air-fuel ratio. The air-fuel ratio of the gas flowing into the catalyst device is controlled by controlling the air-fuel ratio of the gas flowing into the catalyst device to a predetermined rich air-fuel ratio richer than the stoichiometric air-fuel ratio when a value indicating that the fuel ratio is reached. An air-fuel ratio forced oscillation means for forcibly switching the predetermined lean air-fuel ratio to the predetermined rich air-fuel ratio or from the predetermined rich air-fuel ratio to the predetermined lean air-fuel ratio alternately, and forcibly oscillating;
In an exhaust gas purification apparatus for an internal combustion engine comprising :
The exhaust gas purifying apparatus for an internal combustion engine, wherein the gas air / fuel ratio related value acquiring means is configured to move the position of the control block to the downstream side in accordance with a decrease in the maximum amount of oxygen that can be stored in the catalyst device. An exhaust emission control device for an internal combustion engine according to claim 1 ,
When the value n is a natural number, the maximum amount of oxygen that can be stored in the upstream portion of the catalyst device constituted by the blocks from the first block to the n-th block, which is the most upstream block among the plurality of blocks. Oxygen storage capacity acquisition means for acquiring a large amount of maximum oxygen storage capacity ,
The gas air-fuel ratio related value acquisition means is a catalyst having the smallest value n in the upstream portion of the catalyst device that is determined to have a maximum oxygen storage amount larger than a predetermined value based on the acquired maximum oxygen storage amount. An exhaust emission control device for an internal combustion engine configured to set an nth block constituting an upstream portion of the device as the control block. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The gas air-fuel ratio related value acquisition means is configured to acquire a value related to the amount of a specific component in the gas flowing out from the control block as a value related to the air-fuel ratio of the gas by calculation. Purification equipment. The exhaust emission control device for an internal combustion engine according to claim 3 ,
The gas air-fuel ratio related value acquisition means is configured to acquire a value related to an excess / deficiency amount of oxygen in the gas flowing out of the control block as a value related to the amount of a specific component in the gas,
The air-fuel ratio forced oscillation means flows into the catalyst device when a value relating to the excess or deficiency of oxygen in the gas becomes a value indicating that the deficiency of oxygen in the gas exceeds a predetermined level. A value indicating that the excess or deficiency of oxygen in the gas exceeds a predetermined level, while controlling the air / fuel ratio of the gas to the predetermined lean air / fuel ratio. An internal combustion engine configured to forcibly vibrate the air-fuel ratio of the gas flowing into the catalyst device by controlling the air-fuel ratio of the gas flowing into the catalyst device to the predetermined rich air-fuel ratio. Exhaust purification device. The exhaust emission control device for an internal combustion engine according to claim 3 ,
The gas air-fuel ratio related value acquisition means acquires a value relating to the amount of oxidant in the gas flowing out from the control block and a value relating to the amount of reducing agent as values relating to the amount of the specific component in the gas. Composed of
The catalytic device when the air-fuel ratio forced oscillation means has a value indicating that the amount of the reducing agent in the gas exceeds the predetermined level. The air-fuel ratio of the gas flowing into the gas is controlled to the predetermined lean air-fuel ratio, and the value relating to the amount of oxidant in the gas is an amount in which the amount of oxidant in the gas exceeds a predetermined level. When the air-fuel ratio of the gas flowing into the catalyst device is controlled to the predetermined rich air-fuel ratio, the air-fuel ratio of the gas flowing into the catalyst device is forcibly oscillated. Exhaust gas purification device for internal combustion engine.

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