JP2004116417A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of effectively purifying noxious component by controlling air fuel ratio of gas flowing in a catalyst without fail of feed back control (hunting of air fuel ratio of gas which is controlled by feed back control). <P>SOLUTION: This exhaust emission control device is provided with a first catalyst 53, a second catalyst 54 and a third catalyst 55, a first catalyst down stream air fuel ratio sensor 67, a second catalyst down stream air fuel ratio sensor 68 and a third catalyst down stream air fuel ratio sensor 69, and an electric control device 70. The electric control device controls air fuel ratio of gas flowing into the first catalyst to turn output of the first catalyst down stream air fuel ratio sensor when the maximum oxygen occlusion amount of the first catalyst is higher than a threshold, output of the second catalyst down stream air fuel ratio sensor when sum of the maximum oxygen occlusion amount of the first catalyst and the second catalyst is higher than the threshold, or output of the third catalyst down stream air fuel ratio sensor when sum of the maximum oxygen occlusion amount of the first, the second and the third catalyst is higher than the threshold, into a predetermined target output. <P>COPYRIGHT: (C)2004,JPO

Description

【０１５９】
さらに、上記数４における「ｉ」を「３」に書き換え、これに上記数１０及び上記数１２の関係を適用すると、下記数１３が導かれる。
【０１６０】
【数１３】

【０１６１】
このような手続きを繰り返すことにより、任意のｉ番目のブロック（ｉ）の流出酸素量ＣｇｏｕｔＯ２（ｉ）を求めるための一般式である下記数１４が導かれる。
【０１６２】
【数１４】
ＣｇｏｕｔＯ２（ｉ）＝ＣｇｉｎＯ２（１）−δＯＳＡ（１）−δＯＳＡ（２）−　・・・　−δＯＳＡ（ｉ−１）−δＯＳＡ（ｉ）
（ｉ＝１，２，・・・，Ｎ）
【０１６３】
また、上記数４及び上記数５（又は上記数７）より下記数１５が導かれるから、下記数１５に上記数１０の関係を適用し、その関係を一般的に記述すると、任意のｉ番目のブロック（ｉ）の流出酸素量ＣｇｏｕｔＯ２（ｉ）を求めるための他の一般式である下記数１６も容易に導くことができる。
【０１６４】
【数１５】
ＣｇｏｕｔＯ２（ｉ）＝ＣｇｉｎＯ２（ｉ）・（１−Ｈ（ｉ））
【０１６５】
【数１６】

【０１６６】
次に、上記数６及び数８において反応率Ｈ（ｉ）を求める際に必要となるブロック（ｉ）における最大酸素吸蔵量Ｃｍａｘ（ｉ）の求め方について説明する。図１８は、本触媒モデルにおいて、最大酸素吸蔵量Ｃｍａｘ（ｉ）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触媒全体の最大酸素吸蔵量Ｃｍａｘａｌｌの値に対応している。
【０１６７】
このように、触媒の各ブロック毎の各最大酸素吸蔵量Ｃｍａｘ（ｎ）　（ｎ＝１，・・・，Ｎ）は、同各最大酸素吸蔵量Ｃｍａｘ（ｎ）の総和が同触媒全体の最大酸素吸蔵量Ｃｍａｘａｌｌの値となるように設定されるとともに、上流側のブロックから下流側のブロックに推移するに従い、所定の勾配をもって線形的に増加するとして取り扱われる。これは、触媒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、同上流部分の最大酸素吸蔵量が同下流部分に比して低下し易くなるからである。
【０１６８】
具体的には、本装置は、触媒モデルが対象とする第１触媒５３、第２触媒５４、及び第３触媒５５を、排ガスの流れ方向に沿ってＮ１個、Ｎ２個、及びＮ３個のブロックにそれぞれ仮想的に分割し、第１触媒５３の各ブロック１（ｉ）毎の各最大酸素吸蔵量Ｃｍａｘ１（ｉ）　（ｉ＝１，・・・，Ｎ１）、第２触媒５４の各ブロック２（ｉ）毎の各最大酸素吸蔵量Ｃｍａｘ２（ｉ）　（ｉ＝１，・・・，Ｎ２）、及び第３触媒５５の各ブロック３（ｉ）毎の各最大酸素吸蔵量Ｃｍａｘ３（ｉ）　（ｉ＝１，・・・，Ｎ３）を、図１８に示した最大酸素吸蔵量分布マップに基いた下記数１７〜下記数１９に基いてそれぞれ算出する。
【０１６９】
【数１７】
Ｃｍａｘ１（ｉ）＝Ａ１・（ｉ−（Ｎ１／２））＋（Ｃｍａｘ１ａｌｌ／Ｎ１）　（ｉ＝１，２，・・・，Ｎ１）
【０１７０】
【数１８】
Ｃｍａｘ２（ｉ）＝Ａ２・（ｉ−（Ｎ２／２））＋（Ｃｍａｘ２ａｌｌ／Ｎ２）　（ｉ＝１，２，・・・，Ｎ２）
【０１７１】
【数１９】
Ｃｍａｘ３（ｉ）＝Ａ３・（ｉ−（Ｎ３／２））＋（Ｃｍａｘ３ａｌｌ／Ｎ３）　（ｉ＝１，２，・・・，Ｎ３）
【０１７２】
上記数１７〜上記数１９において、Ａ１，Ａ２，Ａ３はそれぞれ正の定数であって、各ブロック毎の最大酸素吸蔵量の分布の上記勾配を決定する値である。Ａ１，Ａ２，Ａ３は同一の値であってもよいし、それぞれ異なる値であってもよい。また、各触媒の最大酸素吸蔵量Ｃｍａｘ１ａｌｌ，Ｃｍａｘａｌｌ２，Ｃｍａｘａｌｌ３は、上記第１実施形態において求めたＣｍａｘ１，Ｃｍａｘ２，Ｃｍａｘ３とそれぞれ等しいので、ここではその求め方の説明を省略する。なお、触媒の各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。このようにして、第１触媒５３〜第３触媒５５の各ブロック毎の最大酸素吸蔵量が算出される。
【０１７３】
（触媒モデルの適用）
次に、以上説明した触媒モデルを、図１９に示したように、第１〜第３触媒５３〜５５にそれぞれ適用し、各種値を求める例について説明する。
【０１７４】
以下、第１触媒５３のｉ番目のブロックをブロック１（ｉ）と称呼し、同ブロック１（ｉ）における流入酸素量を流入酸素量Ｃｇｉｎ１Ｏ２（ｉ），流出酸素量を流出酸素量Ｃｇｏｕｔ１Ｏ２（ｉ），酸素吸蔵量をＯＳＡ１（ｉ），最大酸素吸蔵量をＣｍａｘ１（ｉ）とそれぞれ称呼する。各ブロックの酸素吸蔵量ＯＳＡ１（ｉ）　（ｉ＝１，２，・・・，Ｎ１）　を積算することにより得られる第１触媒５３全体の酸素吸蔵量を酸素吸蔵量ＯＳＡ１ａｌｌと称呼し、各ブロックの最大酸素吸蔵量Ｃｍａｘ１（ｉ）　（ｉ＝１，２，・・・，Ｎ１）　を積算した値である第１触媒５３全体の最大酸素吸蔵量を最大酸素吸蔵量Ｃｍａｘ１ａｌｌと称呼する。
【０１７５】
同様に、第２触媒５４のｉ番目のブロックをブロック２（ｉ）と称呼し、同ブロック２（ｉ）における流入酸素量を流入酸素量Ｃｇｉｎ２Ｏ２（ｉ），流出酸素量を流出酸素量Ｃｇｏｕｔ２Ｏ２（ｉ），酸素吸蔵量をＯＳＡ２（ｉ），最大酸素吸蔵量をＣｍａｘ２（ｉ）とそれぞれ称呼する。各ブロックの酸素吸蔵量ＯＳＡ２（ｉ）　（ｉ＝１，２，・・・，Ｎ２）　を積算することにより得られる第２触媒５４全体の酸素吸蔵量を酸素吸蔵量ＯＳＡ２ａｌｌと称呼し、各ブロックの最大酸素吸蔵量Ｃｍａｘ２（ｉ）　（ｉ＝１，２，・・・，Ｎ２）　を積算した値である第２触媒５４全体の最大酸素吸蔵量を最大酸素吸蔵量Ｃｍａｘ２ａｌｌと称呼する。
【０１７６】
同様に、第３触媒５５のｉ番目のブロックをブロック３（ｉ）と称呼し、同ブロック３（ｉ）における流入酸素量を流入酸素量Ｃｇｉｎ３Ｏ２（ｉ），流出酸素量を流出酸素量Ｃｇｏｕｔ３Ｏ２（ｉ），酸素吸蔵量をＯＳＡ３（ｉ），最大酸素吸蔵量をＣｍａｘ３（ｉ）とそれぞれ称呼する。各ブロックの酸素吸蔵量ＯＳＡ３（ｉ）　（ｉ＝１，２，・・・，Ｎ３）　を積算することにより得られる第３触媒５５全体の酸素吸蔵量を酸素吸蔵量ＯＳＡ３ａｌｌと称呼し、各ブロックの最大酸素吸蔵量Ｃｍａｘ３（ｉ）　（ｉ＝１，２，・・・，Ｎ３）　を積算した値である第３触媒５５全体の最大酸素吸蔵量を最大酸素吸蔵量Ｃｍａｘ３ａｌｌと称呼する。
【０１７７】
この触媒モデルにおいては、図１９に示したように、第１、第２、第３触媒５３，５４，５５の各々の各ブロックにおける酸素吸蔵量ＯＳＡ１（ｉ）　（ｉ＝１，２，・・・，Ｎ１）、酸素吸蔵量ＯＳＡ２（ｉ）　（ｉ＝１，２，・・・，Ｎ２）、及び酸素吸蔵量ＯＳＡ３（ｉ）　（ｉ＝１，２，・・・，Ｎ３）の初期値を初期条件として付与するとともに、ＣＰＵ７１の演算周期が経過する毎に、第１触媒５３の最上流のブロック１（１）における流入酸素量Ｃｇｉｎ１Ｏ２（１）、第２触媒５４の最上流のブロック２（１）における流入酸素量Ｃｇｉｎ２Ｏ２（１）、及び第３触媒５５の最上流のブロック３（１）における流入酸素量Ｃｇｉｎ３Ｏ２（１）をそれぞれ境界条件として付与すれば、第１触媒５３の各ブロック１（ｉ）　（ｉ＝１，２，・・・，Ｎ１）　における酸素吸蔵量ＯＳＡ１（ｉ），流入酸素量Ｃｇｉｎ１Ｏ２（ｉ），及び流出酸素量Ｃｇｏｕｔ１Ｏ２（ｉ）、第２触媒５４の各ブロック２（ｉ）　（ｉ＝１，２，・・・，Ｎ２）　における酸素吸蔵量ＯＳＡ２（ｉ），流入酸素量Ｃｇｉｎ２Ｏ２（ｉ），及び流出酸素量Ｃｇｏｕｔ２Ｏ２（ｉ）、並びに第３触媒５５の各ブロック３（ｉ）　（ｉ＝１，２，・・・，Ｎ３）　における酸素吸蔵量ＯＳＡ３（ｉ），流入酸素量Ｃｇｉｎ３Ｏ２（ｉ），及び流出酸素量Ｃｇｏｕｔ３Ｏ２（ｉ）を全て算出することができる。これにより、第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌ、第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌ、及び第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌをそれぞれ取得・算出することができる。
【０１７８】
そこで、先ず、第１〜第３触媒５３〜５５の各々の各ブロックにおける酸素吸蔵量の初期値を付与する手法について説明すると、本装置は、第１触媒下流空燃比センサ６７の出力ｖｏｘｓ１が０．７（Ｖ）より大きい値を示したとき、即ち、第１触媒５３の下流側であって第２触媒５４の上流側のガスの空燃比が明白なリッチ空燃比となったときは、同第１触媒５３内に酸素が全く存在せず未燃ＨＣ，ＣＯが浄化されない状態となったことを意味するから、第１触媒５３の各ブロックにおける酸素吸蔵量ＯＳＡ１（ｉ）　（ｉ＝１，２，・・・，Ｎ１）　及び第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌを全て「０」に設定する。
【０１７９】
同様に、本装置は、第２触媒下流空燃比センサ６８の出力ｖｏｘｓ２が０．７（Ｖ）より大きい値を示したとき、即ち、第２触媒５４の下流側の空燃比が明白なリッチ空燃比となったときは、第２触媒５４の各ブロックにおける酸素吸蔵量ＯＳＡ２（ｉ）　（ｉ＝１，２，・・・，Ｎ２）　及び第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌを全て「０」に設定する。
【０１８０】
同様に、本装置は、第３触媒下流空燃比センサ６９の出力ｖｏｘｓ３が０．７（Ｖ）より大きい値を示したとき、即ち、第３触媒５５の下流側の空燃比が明白なリッチ空燃比となったときは、第３触媒５５の各ブロックにおける酸素吸蔵量ＯＳＡ３（ｉ）　（ｉ＝１，２，・・・，Ｎ３）　及び第３触媒５５全体の酸素吸蔵量ＯＳＡ３ａｌｌを全て「０」に設定する。このようにして、第１〜第３触媒５３〜５５の各々の各ブロックにおける酸素吸蔵量の初期値「０」が初期条件として付与される。
【０１８１】
次に、第１触媒５３の最上流のブロック１（１）における流入酸素量Ｃｇｉｎ１Ｏ２（１）を付与する方法について説明すると、本装置は、下記数２０に基いてＣＰＵ７１の演算周期毎の流入酸素量Ｃｇｉｎ１Ｏ２（１）を算出する。上記数２０は、上記数３と同様の式である。但し、ｍｆｒ１は所定時間（演算周期ｔｓａｍｐｌｅ）内の燃料噴射量Ｆｉの合計量である。
【０１８２】
【数２０】
Ｃｇｉｎ１Ｏ２（１）＝０．２３・ｍｆｒ１・（ａｂｙｆｓ　−　ｓｔｏｉｃｈ）
【０１８３】
この流入酸素量Ｃｇｉｎ１Ｏ２（１）は、上記数２０から明らかなように、酸素が過剰であるとき（即ち、空燃比がリーンであってａｂｙｆｓ＞ｓｔｏｉｃｈのとき）に正の値となり、酸素が不足しているとき（即ち、空燃比がリッチであってａｂｙｆｓ＜ｓｔｏｉｃｈのとき）に負の値となるように計算される。
【０１８４】
次に、第２触媒５４の最上流のブロック２（１）における流入酸素量Ｃｇｉｎ２Ｏ２（１）を算出する手法について説明すると、第１触媒５３の最下流のブロック１（Ｎ１）から流出する排ガスは、エキゾーストパイプ５２を通過して外部とのガスの授受がないまま第２触媒５４の最上流のブロック２（１）に流入する。従って、第１触媒５３の最下流のブロック１（Ｎ１）から流出する流出酸素量Ｃｇｏｕｔ１Ｏ２（Ｎ１）と第２触媒５４の最上流のブロック２（１）における流入酸素量Ｃｇｉｎ２Ｏ２（１）とは同一の値となる。よって、本装置は、ＣＰＵ７１の演算周期毎に算出する流出酸素量Ｃｇｏｕｔ１Ｏ２（Ｎ１）の値を流入酸素量Ｃｇｉｎ２Ｏ２（１）として使用する。このようにして、ＣＰＵ７１の演算周期毎に第２触媒５４の最上流のブロック２（１）における流入酸素量Ｃｇｉｎ２Ｏ２（１）が境界条件として付与される。
【０１８５】
第３触媒５５の最上流のブロック３（１）における流入酸素量Ｃｇｉｎ２Ｏ３（１）についても同様であり、本装置は、第２触媒５４の最下流のブロック２（Ｎ２）から流出する流出酸素量Ｃｇｏｕｔ２Ｏ２（Ｎ２）の値を流入酸素量Ｃｇｉｎ３Ｏ２（１）として使用する。このようにして、ＣＰＵ７１の演算周期毎に第３触媒５５の最上流のブロック３（１）における流入酸素量Ｃｇｉｎ３Ｏ２（１）が境界条件として付与される。
【０１８６】
（第２実施形態の実際の作動）
次に、第２実施形態に係る排気浄化装置の実際の作動について説明する。この装置のＣＰＵ７１は、第１実施形態のＣＰＵ７１が実行する図６、図７、及び図１４に示したルーチンに代えて、図２０〜図２２にフローチャートにより示したルーチンを実行するとともに、図２３〜図２６にフローチャートにより示したルーチンを追加的に実行する。以下、第２実施形態に特有のルーチンについて、順に説明する。
【０１８７】
ＣＰＵ７１は、サブフィードバック制御量ｖａｆｓｆｂを求めるために使用される制御用酸素吸蔵量ＯＳＡａｌｌ及び目標酸素吸蔵量ＯＳＡａｌｌｒｅｆを決定・選択する図２０に示したルーチンを所定時間の経過毎に実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ２０００から処理を開始し、ステップ２００５にて第１触媒５３の酸素吸蔵能力を示す同第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１ａｌｌが所定の閾値Ｃｔｈ１より大きいか否かを判定し、同ステップ２００５にて「Ｙｅｓ」と判定したときはステップ２０１０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第１触媒５３の酸素吸蔵量ＯＳＡ１ａｌｌを設定するとともに、ステップ２０１５にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに第１の値ＯＳＡ１ａｌｌｒｅｆを設定し、ステップ２０９５に進んで本ルーチンを一旦終了する。第１の値ＯＳＡ１ａｌｌｒｅｆは、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１ａｌｌの１／２に設定されている。
【０１８８】
一方、ＣＰＵ７１は、ステップ２００５にて「Ｎｏ」と判定したとき、ステップ２０２０に進み、第２触媒５４の酸素吸蔵能力を示す同第２触媒５４の最大酸素吸蔵量Ｃｍａｘ２ａｌｌが所定の閾値Ｃｔｈ２より大きいか否かを判定し、同ステップ２０２０にて「Ｙｅｓ」と判定したときはステップ２０２５に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第２触媒５４の酸素吸蔵量ＯＳＡ２ａｌｌを設定するとともに、ステップ２０３０にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに第２の値ＯＳＡ２ａｌｌｒｅｆを設定し、ステップ２０９５に進んで本ルーチンを一旦終了する。第２の値ＯＳＡ２ａｌｌｒｅｆは、第２触媒５４の最大酸素吸蔵量Ｃｍａｘ２ａｌｌの１／２に設定されている。
【０１８９】
また、ＣＰＵ７１は、ステップ２０２０にて「Ｎｏ」と判定したとき、ステップ２０３５に進み、第３触媒５５の酸素吸蔵能力を示す同第３触媒５５の最大酸素吸蔵量Ｃｍａｘ３ａｌｌが所定の閾値Ｃｔｈ３より大きいか否かを判定し、同ステップ２０３５にて「Ｙｅｓ」と判定したときはステップ２０４０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第３触媒５５の酸素吸蔵量ＯＳＡ３ａｌｌを設定するとともに、ステップ２０４５にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに第３の値ＯＳＡ３ａｌｌｒｅｆを設定し、ステップ２０９５に進んで本ルーチンを一旦終了する。第３の値ＯＳＡ３ａｌｌｒｅｆは、第３触媒５５の最大酸素吸蔵量Ｃｍａｘ３ａｌｌの１／２に設定されている。
【０１９０】
更に、ＣＰＵ７１は、ステップ２０３５にて「Ｎｏ」と判定したとき、ステップ２０５０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに一定値ＯＳＡｉｎｔを設定するとともに、ステップ２０５５にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに同一定値ＯＳＡｉｎｔを設定し、ステップ２０９５に進んで本ルーチンを一旦終了する。このステップ２０５０及びステップ２０５５の処理により、制御用酸素吸蔵量ＯＳＡａｌｌと目標酸素吸蔵量ＯＳＡａｌｌｒｅｆとは等しくなるので、酸素吸蔵量に基づくサブフィードバック制御は事実上停止された状態となる。
【０１９１】
また、ＣＰＵ７１は、サブフィードバック制御量ｖａｆｓｆｂを求めるために、図２１に示したルーチンを図２０に示したルーチンの実行時間間隔と同じ所定時間の経過毎に実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ２１００から処理を開始し、ステップ２１０５に進んでサブフィードバック制御条件が成立しているか否かを判定する。サブフィードバック制御条件は、第１実施形態のサブフィードバック制御条件と同一である。このとき、サブフィードバック制御条件が成立していなければ、ＣＰＵ７１はステップ２１２５に進んでサブフィードバック制御量ｖａｆｓｆｂを「０」に設定し、その後ステップ２１９５に進んで本ルーチンを一旦終了する。
【０１９２】
いま、サブ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２１０５にて「Ｙｅｓ」と判定してステップ２１１０に進み、上記選択された酸素吸蔵量ＯＳＡａｌｌから上記設定された目標酸素吸蔵量（目標値）ＯＳＡａｌｌｒｅｆを減じることにより偏差量ＤＯＳＡａｌｌを求める。次に、ＣＰＵ７１はステップ２１１５に進み、下記数２１に基いてサブフィードバック制御量（酸素吸蔵量補正量）ｖａｆｓｆｂを求める。
【０１９３】
【数２１】
ｖａｆｓｆｂ＝Ｋｐ・ＤＯＳＡａｌｌ＋Ｋｉ・ＳＤＯＳＡａｌｌ
【０１９４】
上記数２１において、Ｋｐは予め設定された比例ゲイン、Ｋｉは予め設定された積分ゲインである。また、ＳＤＯＳＡａｌｌは酸素吸蔵量偏差量ＤＯＳＡａｌｌの積分値であって、次のステップ２１２０にて更新される値である。即ち、ＣＰＵ７１は、ステップ２１２０に進んで、その時点における酸素吸蔵量偏差量の積分値ＳＤＯＳＡａｌｌに上記ステップ２１１０にて求めた酸素吸蔵量偏差量ＤＯＳＡａｌｌを加えて、新たな酸素吸蔵量偏差量の積分値ＳＤＯＳＡ１ａｌｌを求め、その後、ステップ２１９５に進んで本ルーチンを一旦終了する。
【０１９５】
このようにして、酸素吸蔵量補正量ｖａｆｓｆｂが求められ、この値は前述した図５のステップ５１０にて最上流空燃比センサ６６の実際の出力ｖａｂｙｆｓに加えられ、その和（ｖａｂｙｆｓ　＋　ｖａｆｓｆｂ）が図２に示したマップに基いてメインフィードバック制御用空燃比ａｂｙｆｓに変換される。この結果、前述した図５のステップ５１５にて計算される筒内燃料供給量Ｆｃ（ｋ−Ｎ）が酸素吸蔵量ＯＳＡａｌｌに応じて変化し、従って、ステップ５２５，５３０にてフィードバック補正量ＤＦｉが同酸素吸蔵量ＯＳＡａｌｌに応じて変更せしめられる。この結果、前述した図４のステップ４１０にて酸素吸蔵量ＯＳＡａｌｌと目標酸素吸蔵量ＯＳＡａｌｌｒｅｆとの偏差が小さくなるように、最終燃料噴射量Ｆｉが決定される。
【０１９６】
次に、各触媒の最大酸素吸蔵量Ｃｍａｘ１ａｌｌ，Ｃｍａｘ２ａｌｌ，Ｃｍａｘ３ａｌｌ、及び各触媒の各ブロックの最大酸素吸蔵量Ｃｍａｘ１（ｉ），Ｃｍａｘ２（ｉ），Ｃｍａｘ３（ｉ）を算出する際の作動について説明する。ＣＰＵ７１は図２２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。
【０１９７】
従って、所定のタイミングになると、ＣＰＵ７１は図２２のステップ２２００から処理を開始し、ステップ２２０５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２２０５からステップ２２９５に直接進んで本ルーチンを一旦終了する。
【０１９８】
一方、前述した第４モードが終了した直後であるとすると、図１２のステップ１２２０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２２０５にて「Ｙｅｓ」と判定してステップ２２１０に進み、その時点の酸素吸蔵量ＯＳＡ１，ＯＳＡ２，ＯＳＡ３を、それぞれ第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌ、第２触媒５４全体の最大酸素吸蔵量Ｃｍａｘ２ａｌｌ、及び第３触媒５５全体の最大酸素吸蔵量Ｃｍａｘ３ａｌｌとして格納する。
【０１９９】
次いでＣＰＵ７１はステップ２２１５に進み、カウンタ値ｎの値を「０」に設定した後、ステップ２２２０に進んで第１触媒５３の各ブロック１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２２２０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２２２５に進んで上記ステップ２２１０にて取得した第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌの値と、カウンタ値ｎの値と、上記数１７に基くステップ２２２５内に記載した式とに基いて第１触媒５３のブロック１（ｎ）における最大酸素吸蔵量Ｃｍａｘ１（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、ブロック１（１）における最大酸素吸蔵量Ｃｍａｘ１（１）が算出される。
【０２００】
そして、ＣＰＵ７１はステップ２２３０に進んでカウンタ値ｎの値が第１触媒５３のブロック数Ｎ１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２２３０にて「Ｎｏ」と判定し、再びステップ２２２０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２２２５及びステップ２２３０の処理を実行する。即ち、ステップ２２２０及びステップ２２２５の処理は、カウンタ値ｎの値が第１触媒５３のブロック数Ｎ１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（１）から最下流のブロック１（Ｎ１）までの各ブロック１（ｎ）の最大酸素吸蔵量Ｃｍａｘ１（ｎ）の値が順次算出されていく。
【０２０１】
前述のステップ２２２０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Ｎ１と等しくなると、ＣＰＵ７１はステップ２２３０にて「Ｙｅｓ」と判定してステップ２２３５に進み、カウンタ値ｎの値を「０」に設定した後、ステップ２２４０に進んで第２触媒５４の各ブロック２毎の最大酸素吸蔵量を算出する処理を開始する。
【０２０２】
この第２触媒５４の各ブロック２毎の最大酸素吸蔵量を算出する処理は、上述したステップ２２２０〜ステップ２２３０の処理と同様であるステップ２２４０〜ステップ２２５０までの処理を第２触媒５４のブロック数Ｎ２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２２４５における最大酸素吸蔵量Ｃｍａｘ２（ｎ）の算出は、上記ステップ２２１０にて取得した第２触媒５４全体の最大酸素吸蔵量Ｃｍａｘ２ａｌｌの値と、カウンタ値ｎの値と、上記数１８に基くステップ２２４５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２（１）から最下流のブロック２（Ｎ２）までの各ブロック２（ｎ）の最大酸素吸蔵量Ｃｍａｘ２（ｎ）の値が順次算出されていく。
【０２０３】
ステップ２２４０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Ｎ２と等しくなると、ＣＰＵ７１はステップ２２５０にて「Ｙｅｓ」と判定してステップ２２５５に進み、カウンタ値ｎの値を「０」に設定した後、ステップ２２６０〜ステップ２２７０を実行し、第３触媒５５の各ブロック３毎の最大酸素吸蔵量を算出する処理を開始する。
【０２０４】
このステップ２２６０〜ステップ２２７０の処理は、上述したステップ２２２０〜ステップ２２３０の処理と同様であり。最大酸素吸蔵量Ｃｍａｘ３（ｎ）の算出は、上記ステップ２２１０にて取得した第３触媒５５全体の最大酸素吸蔵量Ｃｍａｘ３ａｌｌの値と、カウンタ値ｎの値と、上記数１９に基くステップ２２６５内に記載した式とに基いて行われる。これにより、第３触媒５５の最上流のブロック３（１）から最下流のブロック３（Ｎ３）までの各ブロック３（ｎ）の最大酸素吸蔵量Ｃｍａｘ３（ｎ）の値が順次算出されていく。
【０２０５】
そして、カウンタ値ｎの値が第３触媒５５のブロック数Ｎ３と等しくなると、ＣＰＵ７１はステップ２２７０にて「Ｙｅｓ」と判定してステップ２２７５に進み、酸素吸蔵量ＯＳＡ１〜ＯＳＡ３の各々の値を「０」に設定した後、ステップ２２９５に進んで本ルーチンを一旦終了する。
【０２０６】
次に、第１〜第３触媒５３〜５５の各々の各ブロック毎の流出酸素量及び酸素吸蔵量等の算出についての作動について説明する。ＣＰＵ７１は図２３〜図２５の一連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図２３のルーチンから順に実行するようになっている。
【０２０７】
従って、所定のタイミングになると、ＣＰＵ７１は、第１触媒５３の各ブロック１毎の流出酸素量，酸素吸蔵量等を算出するため、図２３に示されたルーチンのステップ２３００から処理を開始してステップ２３０５に進み、図４のステップ４２５にて逐次更新されている燃料噴射量積算値ｍｆｒ１と、最上流空燃比センサ６６により検出された空燃比ａｂｙｆｓと、上記数２０に基くステップ２３０５内に記載した式とに基いて、第１触媒５３のブロック１（１）の流入酸素量Ｃｇｉｎ１Ｏ２（１）を算出する。
【０２０８】
次いで、ＣＰＵ７１はステップ２３１０に進んでカウンタ値ｎの値、及び第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌの値をそれぞれ「０」に設定した後、ステップ２３１５に進んでカウンタ値ｎの値を「１」だけ増大する。カウンタ値ｎは第１触媒５３のブロック１の番号を示している。この時点ではカウンタ値ｎの値は「１」であり、続くステップ２３２０〜ステップ２３７５までの処理においてカウンタ値ｎの値は「１」に維持されるので、今回の同ステップ２３２０〜ステップ２３７５までの処理においては最上流のブロック１（１）に関する計算が実行される。
【０２０９】
まず、ＣＰＵ７１はステップ２３２０に進んで、流入酸素量Ｃｇｉｎ１Ｏ２（１）の値が「０」以上であるか否かを判定し、流入酸素量Ｃｇｉｎ１Ｏ２（１）の値が「０」以上であれば同ステップ２３２０において「Ｙｅｓ」と判定してステップ２３２５に進み、ブロック１（１）の最大酸素吸蔵量Ｃｍａｘ１（１）の値と、前回本ルーチンが実行されたときに計算（更新）されたブロック１（１）の酸素吸蔵量ＯＳＡ１（１）の値と、上記数６に基くステップ２３２５内に記載した式とに基いてブロック１（１）における反応率Ｈを算出する。
【０２１０】
また、流入酸素量Ｃｇｉｎ１Ｏ２（１）の値が「０」以上でなければＣＰＵ７１は同ステップ２３２０において「Ｎｏ」と判定してステップ２３３０に進み、上記最大酸素吸蔵量Ｃｍａｘ１（１）の値と、上記前回本ルーチンが実行されたときに計算されたブロック１（１）の酸素吸蔵量ＯＳＡ１（１）の値と、上記数８に基くステップ２３３０内に記載した式とに基いてブロック１（１）における反応率Ｈを算出する。
【０２１１】
次いで、ＣＰＵ７１はステップ２３３５に進み、ステップ２３２５又はステップ２３３０にて算出した反応率Ｈの値と、ステップ２３０５にて算出した第１触媒５３のブロック１（１）における流入酸素量Ｃｇｉｎ１Ｏ２（１）の値と、上記数５又は上記数７に基くステップ２３３５内に記載した式とに基いてブロック１（１）における酸素吸蔵量変化量δＯＳＡ１（１）を算出する。
【０２１２】
次に、ＣＰＵ７１はステップ２３４０に進んで、その時点の（即ち、前回本ルーチンが実行されたときに計算された）ブロック１（１）の酸素吸蔵量ＯＳＡ１（１）の値にステップ２３３５にて今回算出したブロック１（１）の酸素吸蔵量変化量δＯＳＡ１（１）の値を加えた値（ＯＳＡ１（１）＋δＯＳＡ１（１））がブロック１（１）の最大酸素吸蔵量Ｃｍａｘ１（１）の値以下であるか否かを判定する。
【０２１３】
ここで、ブロック１（１）の酸素吸蔵量ＯＳＡ１（１）と酸素吸蔵量変化量δＯＳＡ１（１）の和（ＯＳＡ１（１）＋δＯＳＡ１（１））が最大酸素吸蔵量Ｃｍａｘ１（１）以下であれば、ＣＰＵ７１はステップ２３４０にて「Ｙｅｓ」と判定してステップ２３４５に進み、酸素吸蔵量ＯＳＡ１（１）と酸素吸蔵量変化量δＯＳＡ１（１）の和（ＯＳＡ１（１）＋δＯＳＡ１（１））が「０」以上であるか否かを判定する。そして、酸素吸蔵量ＯＳＡ１（１）と酸素吸蔵量変化量δＯＳＡ１（１）の和（ＯＳＡ１（１）＋δＯＳＡ１（１））が「０」以上であれば、ＣＰＵ７１はステップ２３４５にて「Ｙｅｓ」と判定してステップ２３６０に進む。
【０２１４】
一方、ステップ２３４０の判定において、酸素吸蔵量ＯＳＡ１（１）と酸素吸蔵量変化量δＯＳＡ１（１）の和（ＯＳＡ１（１）＋δＯＳＡ１（１））が最大酸素吸蔵量Ｃｍａｘ１（１）より大きければ、ＣＰＵ７１は同ステップ２３４０にて「Ｎｏ」と判定してステップ２３５０に進み、最大酸素吸蔵量Ｃｍａｘ１（１）から酸素吸蔵量変化量δＯＳＡ１（１）を減じた値を酸素吸蔵量変化量δＯＳＡ１（１）として設定し直し、ステップ２３６０に進む。他方、ステップ２３４５の判定において、酸素吸蔵量ＯＳＡ１（１）と酸素吸蔵量変化量δＯＳＡ１（１）の和（ＯＳＡ１（１）＋δＯＳＡ１（１））が「０」より小さければ、ＣＰＵ７１は同ステップ２３４５にて「Ｎｏ」と判定してステップ２３５５に進み、酸素吸蔵量ＯＳＡ１（１）の符号を反転した値（−ＯＳＡ１（１））を酸素吸蔵量変化量δＯＳＡ１（１）に設定し直してステップ２３６０に進む。以上のステップ２３４０〜ステップ２３５５の処理は、次のステップ２３６０にて求められる今回のブロック１（１）の酸素吸蔵量ＯＳＡ１（１）が「０」以上であって最大酸素吸蔵量Ｃｍａｘ１（１）以下の値となるような酸素吸蔵量変化量δＯＳＡ１（１）を求めるための処理である。
【０２１５】
ステップ２３６０に進んだＣＰＵ７１は、その時点（即ち、前回本ルーチンを実行したときに求められた）ブロック１（１）の酸素吸蔵量ＯＳＡ１（１）に上記のようにして求められた酸素吸蔵量変化量δＯＳＡ１（１）を加えた値を今回のブロック１（１）の酸素吸蔵量ＯＳＡ１（１）として設定し、続くステップ２３６５にてブロック１（１）における流入酸素量Ｃｇｉｎ１Ｏ２（１）の値と、今回の酸素吸蔵量変化量δＯＳＡ１（１）の値と、上記数４に基く同ステップ２３６５内に記載した式とに基いてブロック１（１）における流出酸素量Ｃｇｏｕｔ１Ｏ２（１）を算出する。
【０２１６】
次いで、ＣＰＵ７１はステップ２３７０に進んで、現時点における第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌの値に、上記算出されたブロック１（１）の酸素吸蔵量ＯＳＡ１（１）の値を加えた値を新たな第１触媒５３全体の酸素吸蔵量ＯＳＡ１（１）として格納し、ステップ２３７５に進んで同ブロック１（１）の流出酸素量Ｃｇｏｕｔ１Ｏ２（１）の値をブロック１（１）に隣接する下流側のブロック１（２）における流入酸素量Ｃｇｉｎ１Ｏ２（２）に設定する（上記数１０を参照。）。
【０２１７】
そして、ＣＰＵ７１はステップ２３８０に進んでカウンタ値ｎの値が第１触媒５３のブロック数Ｎ１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２３８０にて「Ｎｏ」と判定し、再びステップ２３１５に戻ってカウンタ値ｎの値を「１」だけ増大して「２」に設定した後、続くステップ２３２０〜ステップ２３７５までの処理を実行することで次のブロックであるブロック１（２）についての各種値の計算を実行する。
【０２１８】
このようにして、ステップ２３２０〜ステップ２３７５までの処理は、カウンタ値ｎの値が第１触媒５３のブロック数Ｎ１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（１）から最下流のブロック１（Ｎ１）までの各ブロック１（ｎ）の流入酸素量Ｃｇｉｎ１Ｏ２（ｎ）、流出酸素量Ｃｇｏｕｔ１Ｏ２（ｎ）、酸素吸蔵量変化量δＯＳＡ１（ｎ）、及び酸素吸蔵量ＯＳＡ１（ｎ）の値が順次算出されていく。また、ステップ２３７０の処理が繰り返し実行されることにより、第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌも算出される。
【０２１９】
ステップ２３１５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Ｎ１と等しくなると、ＣＰＵ７１はステップ２３８０にて「Ｙｅｓ」と判定してステップ２３８５に進み、燃料噴射量積算値ｍｆｒ１の値を「０」に設定した後、ステップ２３９５を経由して図２４に示されたルーチンのステップ２４００に進む。
【０２２０】
図２４のルーチンは、第２触媒５４の各ブロック２毎の流出酸素量及び酸素吸蔵量等を算出するためのルーチンであって、ステップ２４０５にて、境界条件である第２触媒５４のブロック２（１）における流入酸素量Ｃｇｉｎ２Ｏ２（１）として図２３のステップ２３６５にて算出済みの第１触媒５３の最下流のブロック１（Ｎ１）からの流出酸素量Ｃｇｏｕｔ１Ｏ２（Ｎ１）を使用する点、及び図２３のステップ２３８５に対応するステップが存在しない点を除き同図２３のルーチンと同様であるので、ここではその詳細な説明を省略する。
【０２２１】
ＣＰＵ７１は、このようにして第２触媒５４の各ブロック２（ｎ）の流入酸素量Ｃｇｉｎ２Ｏ２（ｎ）、流出酸素量Ｃｇｏｕｔ２Ｏ２（ｎ）、酸素吸蔵量変化量δＯＳＡ２（ｎ）、酸素吸蔵量ＯＳＡ２（ｎ）、及び第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌを算出し、ステップ２４９５を経由して図２５に示されたルーチンのステップ２５００に進む。
【０２２２】
図２５のルーチンは、第３触媒５５の各ブロック３毎の流出酸素量及び酸素吸蔵量等を算出するためのルーチンであって、ステップ２５０５にて、境界条件である第３触媒５５のブロック３（１）における流入酸素量Ｃｇｉｎ３Ｏ２（１）として図２４のステップ２４６５にて算出済みの第２触媒５４の最下流のブロック２（Ｎ２）からの流出酸素量Ｃｇｏｕｔ２Ｏ２（Ｎ２）を使用する点を除き同図２４のルーチンと同様であるので、ここではその詳細な説明を省略する。
【０２２３】
これにより、ＣＰＵ７１は、第３触媒５５の各ブロック３（ｎ）の流入酸素量Ｃｇｉｎ３Ｏ２（ｎ）、流出酸素量Ｃｇｏｕｔ３Ｏ２（ｎ）、酸素吸蔵量変化量δＯＳＡ３（ｎ）、酸素吸蔵量ＯＳＡ３（ｎ）、及び第３触媒５５全体の酸素吸蔵量ＯＳＡ３ａｌｌを算出し、ステップ２５９５にて本ルーチンを一旦終了する。
【０２２４】
次に、第１〜第３触媒５３〜５５の各々の各ブロック毎の酸素吸蔵量の値、及び第１〜第３触媒５３〜５５の各々の全体の酸素吸蔵量の値を初期化（クリア）する際の作動について説明する。ＣＰＵ７１は図２６に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。
【０２２５】
従って、ＣＰＵ７１は所定のタイミングになると、ステップ２６００から処理を開始してステップ２６０５に進み、第１触媒下流空燃比センサ６７の出力ｖｏｘｓ１の値が０．７（Ｖ）より大きいか否かをモニタする。このとき、第１触媒下流空燃比センサ６７の出力ｖｏｘｓ１の値が０．７（Ｖ）より大きければ、即ち、第１触媒５３の下流空燃比が明白なリッチ空燃比であれば、同第１触媒５３内全体に吸蔵されている酸素量が「０」であることを意味するので、ＣＰＵ７１はステップ２６１０に進んで第１触媒５３の各ブロック１（ｎ）（ｎ＝１，２，・・・，Ｎ１）の酸素吸蔵量ＯＳＡ１（ｎ）を総べて「０」に設定するとともに、続くステップ２６１５にて第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌの値を「０」に設定する。
【０２２６】
全く同様に、ＣＰＵ７１は、第２触媒下流空燃比センサ６８の出力ｖｏｘｓ２の値が０．７（Ｖ）より大きいとき、これをステップ２６２０で判定してステップ２６２５及びステップ２６３０に進み、第２触媒５４の各ブロック２（ｎ）（ｎ＝１，２，・・・，Ｎ２）の酸素吸蔵量ＯＳＡ２（ｎ）を総べて「０」に設定するとともに、第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌの値を「０」に設定する。
【０２２７】
また、全く同様に、ＣＰＵ７１は、第３触媒下流空燃比センサ６９の出力ｖｏｘｓ３の値が０．７（Ｖ）より大きいとき、これをステップ２６３５で判定してステップ２６４０及びステップ２６４５に進み、第３触媒５５の各ブロック３（ｎ）（ｎ＝１，２，・・・，Ｎ３）の酸素吸蔵量ＯＳＡ３（ｎ）を総べて「０」に設定するとともに、第３触媒５５全体の酸素吸蔵量ＯＳＡ３ａｌｌの値を「０」に設定し、ステップ２６９５にて本ルーチンを一旦終了する。このようにして、第１〜第３触媒５３〜５５の各々の各ブロック毎の酸素吸蔵量の値、及び第１〜第３触媒５３〜５５の各々の全体の酸素吸蔵量の値が初期化される。
【０２２８】
以上、説明したように、本発明による第２実施形態に係る排気浄化装置は、内燃機関の排気通路に直列に介装された複数の触媒（第１触媒５３、第２触媒５４、第３触媒５５）と、前記複数の触媒の各酸素吸蔵能力を表す値（最大酸素吸蔵量Ｃｍａｘ１ａｌｌ，Ｃｍａｘ２ａｌｌ，Ｃｍａｘ３ａｌｌ）を取得する酸素吸蔵能力取得手段（図２２のステップ２２１０等）と、前記取得された酸素吸蔵能力を表す値に基づいて所定の酸素吸蔵能力よりも大きい酸素吸蔵能力を有すると判定される触媒のうち前記排気通路の最も上流に介装された触媒の排気浄化の状態を表す値（その触媒の酸素吸蔵量ＯＳＡ１ａｌｌ，ＯＳＡ２ａｌｌ，ＯＳＡ３ａｌｌの何れか）を取得する排気浄化状態取得手段（図２０、図２２、及び図２３〜図２６に示したルーチン等）と、前記取得された排気浄化の状態を表す値が所定の値となるように前記最も上流に配設された触媒に流入するガスの空燃比を制御する空燃比制御手段（図４、図５、及び図２１に示したルーチンにより達成される空燃比のフィードバック制御ルーチン）と、を備える。
【０２２９】
これによれば、排気浄化の状態を表す値（空燃比フィードバック制御に使用される酸素吸蔵量ＯＳＡ１ａｌｌ，ＯＳＡ２ａｌｌ，ＯＳＡ３ａｌｌのうちの何れか）は、取得された酸素吸蔵能力を表す値（最大酸素吸蔵量Ｃｍａｘ１ａｌｌ，Ｃｍａｘ２ａｌｌ，Ｃｍａｘ３ａｌｌ）に基づいて所定の酸素吸蔵能力（それぞれの最大酸素吸蔵量に対応する閾値Ｃｔｈ１，Ｃｔｈ２，Ｃｔｈ３）よりも大きい酸素吸蔵能力を有すると判定される触媒のうち前記排気通路の最も上流に介装された触媒の排気浄化の状態を表す値となるから、同最も上流の触媒に流入するガスの空燃比の変動が同排気浄化の状態を表す値に直ちに現れることはない。従って、上述した空燃比のハンチングが回避され、その結果、未燃成分や窒素酸化物等の有害成分の排出量の増大を回避することができる。また、前記最も上流に介装された触媒の排気浄化の状態を空燃比フィードバック制御に用いるから、同フィードバック制御の無駄時間が大きくなりすぎることも回避され、好適な空燃比制御が達成される。
【０２３０】
＜第２実施形態の第１変形例＞
次に、上記第２実施形態の第１変形例に係る排気浄化装置について説明する。この変形例は、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１（＝Ｃｍａｘ１ａｌｌ）が所定の閾値Ｃｔｈを超えるとき第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌを、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１は同所定の閾値Ｃｔｈより小さいが第１触媒５３と第２触媒５４の各最大酸素吸蔵量の合計値（Ｃｍａｘ１＋Ｃｍａｘ２＝Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ）が同所定の閾値Ｃｔｈを超えるとき第１触媒５３全体と第２触媒５４全体の各酸素吸蔵量の合計値（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ）を、また、第１触媒５３と第２触媒５４の各最大酸素吸蔵量の合計値（Ｃｍａｘ１＋Ｃｍａｘ２）は同所定の閾値Ｃｔｈより小さいが第１触媒５３全体と第２触媒５４全体と第３触媒５５全体の各最大酸素吸蔵量の合計値（Ｃｍａｘ１＋Ｃｍａｘ２＋Ｃｍａｘ３＝Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ＋Ｃｍａｘ３ａｌｌ）が所定の閾値を超えるとき、これら三つの触媒の酸素吸蔵量の合計値（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ＋ＯＳＡ３ａｌｌ）を、空燃比制御用酸素吸蔵量ＯＳＡａｌｌとして選択し、同選択した制御用酸素吸蔵量ＯＳＡａｌｌが所定の目標酸素吸蔵量となるように制御するものである。
【０２３１】
具体的に述べると、この排気浄化装置のＣＰＵ７１は、上記第２実施形態のＣＰＵ７１が実行する図２０に示したルーチンに代えて図２７に示したルーチンを所定時間の経過毎に実行する点においてのみ、同第２実施形態と異なっている。従って、以下、係る相違点を中心として簡単に説明する。なお、図２７において、図６及び図２０に示したステップと同一のステップには同一の符号を付している。
【０２３２】
ＣＰＵ７１は、所定のタイミングになると、ステップ２７００から処理を開始してステップ６０５に進み、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１が所定の閾値Ｃｔｈより大きいか否かを判定し、同ステップ６０５にて「Ｙｅｓ」と判定したときはステップ２０１０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌを設定する。次いで、ＣＰＵ７１はステップ２７０５に進んで目標酸素吸蔵量（所定の値）ＯＳＡａｌｌｒｅｆに第１の値ＯＳＡｒｅｆ１を設定し、ステップ２７９５に進んで本ルーチンを一旦終了する。なお、第１の値ＯＳＡｒｅｆ１は、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１の１／２としておく。
【０２３３】
一方、ＣＰＵ７１は、ステップ６０５にて「Ｎｏ」と判定したとき、ステップ６１５に進んで第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１と第２触媒５４の最大酸素吸蔵量Ｃｍａｘ２の合計値（Ｃｍａｘ１＋Ｃｍａｘ２）が所定の閾値Ｃｔｈより大きいか否かを判定し、同ステップ６１５にて「Ｙｅｓ」と判定したときはステップ２７１０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌと第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌの和（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ）を設定する。次いで、ＣＰＵ７１はステップ２７１５に進んで目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに第２の値ＯＳＡｒｅｆ２を設定し、ステップ２７９５に進んで本ルーチンを一旦終了する。なお、第２の値ＯＳＡｒｅｆ２は、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１と第２触媒５４の最大酸素吸蔵量Ｃｍａｘ２の和（Ｃｍａｘ１＋Ｃｍａｘ２）の１／２としておく。
【０２３４】
また、ＣＰＵ７１は、ステップ６１５にて「Ｎｏ」と判定したとき、ステップ６２５に進んで第１触媒〜第３触媒の各最大酸素吸蔵量の合計値（Ｃｍａｘ１＋Ｃｍａｘ２＋Ｃｍａｘ３）が同所定の閾値Ｃｔｈより大きいか否かを判定し、同ステップ６２５にて「Ｙｅｓ」と判定したときはステップ２７２０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌと第２触媒５４全体の酸素吸蔵量ＯＳＡ２ａｌｌと第３触媒５５全体の酸素吸蔵量ＯＳＡ３ａｌｌの和（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ＋ＯＳＡ３ａｌｌ）を設定する。次いで、ＣＰＵ７１はステップ２７２５に進んで目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに第３の値ＯＳＡｒｅｆ３を設定し、ステップ２７９５に進んで本ルーチンを一旦終了する。なお、第３の値ＯＳＡｒｅｆ３は、第１触媒５３〜第３触媒５５の各最大酸素吸蔵量の和（Ｃｍａｘ１＋Ｃｍａｘ２＋Ｃｍａｘ３）の１／２としておく。
【０２３５】
更に、ＣＰＵ７１は、ステップ６２５にて「Ｎｏ」と判定したとき、ステップ２０５０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに一定値ＯＳＡｉｎｔを設定するとともに、ステップ２０５５にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに同一定値ＯＳＡｉｎｔを設定し、ステップ２７９５に進んで本ルーチンを一旦終了する。このステップ２０５０及びステップ２０５５の処理により、制御用酸素吸蔵量ＯＳＡａｌｌと目標酸素吸蔵量ＯＳＡａｌｌｒｅｆとは等しくなるので、酸素吸蔵量に基づくサブフィードバック制御は事実上停止された状態となる。
【０２３６】
以上、説明したように、第２実施形態の第１変形例に係る排気浄化装置は、値ｎを自然数とするとき複数の触媒（第１触媒５３、第２触媒５４、第３触媒５５）のうちの最上流の触媒である第１番目の触媒（第１触媒５３）から第ｎ番目の触媒までで構成される触媒装置（即ち、第１触媒５３のみからなる触媒装置、第１触媒５３と第２触媒５４とからなる触媒装置、及び第１触媒〜第３触媒５３〜５５の３個の触媒からなる触媒装置）の酸素吸蔵能力を表す値（即ち、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１、第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１と第２触媒５４の最大酸素吸蔵量Ｃｍａｘ２の和Ｃｍａｘ１＋Ｃｍａｘ２、第１触媒５３，第２触媒５４，及び第３触媒５５の各最大酸素吸蔵量の和Ｃｍａｘ１＋Ｃｍａｘ２＋Ｃｍａｘ３）を取得する酸素吸蔵能力取得手段を備えている。
【０２３７】
更に、この排気浄化装置は、前記取得された酸素吸蔵能力を表す値に基づいて所定の酸素吸蔵能力よりも大きい酸素吸蔵能力を有すると判定される前記触媒装置のうち前記値ｎが最も小さい触媒装置の排気浄化の状態を表す値（ＯＳＡ１ａｌｌ，ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ，又はＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ＋ＯＳＡ３ａｌｌ）を取得する排気浄化状態取得手段と、前記取得された排気浄化の状態を表す値が所定の値（ＯＳＡａｌｌｒｅｆ）となるように前記第１番目の触媒（第１触媒５３）に流入するガスの空燃比を制御する空燃比制御手段とを備えている。
【０２３８】
即ち、空燃比制御に使用されることになる触媒装置の排気浄化の状態を表す値（ＯＳＡ１ａｌｌ，ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ，又はＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ＋ＯＳＡ３ａｌｌ）は、十分な酸素吸蔵能力を有している触媒装置の排気浄化の状態を表すから、第１触媒５３に流入するガスの空燃比の変動が同排気浄化の状態を表す値に直ちに現れることはない。従って、上述した空燃比のハンチングが回避され、その結果、未燃成分や窒素酸化物等の有害成分の排出量の増大を回避することができる。
【０２３９】
また、酸素吸蔵能力が大きい触媒装置の酸素吸蔵量を各触媒装置の最大酸素吸蔵量の略半分程度の量に維持できるので、酸素吸蔵能力を有効に利用でき、排ガスの浄化を効果的に行うことが可能となる。
【０２４０】
＜第２実施形態の第２変形例＞
次に、上記第２実施形態の第２変形例に係る排気浄化装置について説明する。この変形例は、主として、第３触媒５５及び第３触媒下流空燃比センサ６９を備えていない点、及びＣＰＵ７１が図２０に示したルーチンに代えて制御用酸素吸蔵量ＯＳＡａｌｌを選択するための図２８にフローチャートにより示したルーチンを実行する点等において、上記第２実施形態と異なっている。従って、以下、係る相違点を中心として説明する。
【０２４１】
ＣＰＵ７１は、制御用酸素吸蔵量ＯＳＡａｌｌを選択するにあたり、図２８に示したルーチンを所定時間の経過毎に実行する。従って、所定のタイミングになると、ＣＰＵ７１はステップ２８００から処理を開始し、ステップ２８０５に進んで第１触媒５３の最大酸素吸蔵量Ｃｍａｘ１が所定の閾値Ｃｔｈ１より大きいか否かを判定する。このとき、最大酸素吸蔵量Ｃｍａｘ１が所定の閾値Ｃｔｈ１より大きいと、ＣＰＵ７１はステップ２８０５からステップ２８１０に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第１触媒５３全体の酸素吸蔵量ＯＳＡ１ａｌｌを設定し、続くステップ２８１５にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに目標酸素吸蔵量ＯＳＡ１ａｌｌｒｅｆ（第１の値）を設定し、ステップ２８９５に進んで本ルーチンを一旦終了する。前記目標酸素吸蔵量ＯＳＡ１ａｌｌｒｅｆは、最大酸素吸蔵量Ｃｍａｘ１の１／２に設定しておく。
【０２４２】
一方、最大酸素吸蔵量Ｃｍａｘ１が所定の閾値Ｃｔｈ１より小さい（以下である）と、ＣＰＵ７１はステップ２８０５からステップ２８２５に進んで制御用酸素吸蔵量ＯＳＡａｌｌに第２触媒５３全体の酸素吸蔵量ＯＳＡ２ａｌｌを設定し、続くステップ２８３０にて目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに目標酸素吸蔵量ＯＳＡ２ａｌｌｒｅｆ（第２の値）を設定し、ステップ２８９５に進んで本ルーチンを一旦終了する。前記目標酸素吸蔵量ＯＳＡ２ａｌｌｒｅｆは、最大酸素吸蔵量Ｃｍａｘ２の１／２に設定しておく。
【０２４３】
これにより、この第２変形例に係る排気浄化装置は、図２１に示したルーチンを実行することにより上記のように選択された酸素吸蔵量ＯＳＡａｌｌが上記のように設定された目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに一致するようにサブフィードバック制御量ｖａｆｓｆｂを求め、このサブフィードバック制御量ｖａｆｓｆｂを図５に示したルーチンを実行することによりメインフィードバック制御量に反映させ、図４に示したルーチンを実行することにより最終燃料噴射量Ｆｉに反映させる。
【０２４４】
このように、第２実施形態の第２変形例に係る排気浄化装置は、第１触媒５３が十分な酸素吸蔵能力を有している場合には同第１触媒５３の酸素吸蔵量ＯＳＡ１ａｌｌが目標酸素吸蔵量ＯＳＡａｌｌｒｅｆ（＝ＯＳＡ１ａｌｌｒｅｆ）に一致するように機関に供給される混合気の空燃比のフィードバック制御を実行し、第１触媒５３が十分な酸素吸蔵能力を有していない場合には、同第１触媒５３よりも劣化の進行程度が遅いために十分な酸素吸蔵能力を有していると考えられる第２触媒５４の酸素吸蔵量ＯＳＡ１ａｌｌが目標酸素吸蔵量ＯＳＡａｌｌｒｅｆ（＝ＯＳＡ２ａｌｌｒｅｆ）に一致するように同空燃比のフィードバック制御を実行する。
【０２４５】
従って、空燃比のフィードバック制御用として使用される制御用酸素吸蔵量ＯＳＡａｌｌには、第１触媒５３の上流の空燃比の変動が直ちに現れることがないので、空燃比のフィードバック制御の破綻を招くことなく同制御用酸素吸蔵量ＯＳＡａｌｌを目標酸素吸蔵量ＯＳＡａｌｌｒｅｆに一致させることができる。
【０２４６】
＜第３実施形態＞
次に、本発明による第３実施形態に係る排気浄化装置について説明する。この排気浄化装置は、上述した触媒モデルにおける所定のブロックから流出する特定成分の量に関する値（ここでは、流出酸素量ＣｇｏｕｔＯ２）を所定値（ここでは、「０」であるが、「０」を含む所定の幅−β１〜＋β２であってもよい。）に維持する制御（空燃比フィードバック制御）を行う点において、主として第２実施形態に係る排気浄化装置と異なっている。
【０２４７】
具体的に述べると、この第３実施形態に係るＣＰＵ７１は、第２実施形態のＣＰＵ７１が実行する図２０及び図２１に示したルーチンを除く総べてのルーチンを実行するとともに、図２０及び図２１に代わる図２９及び図３０に示したルーチンをそれぞれ所定時間の経過毎に実行するようになっている。従って、以下、図２９及び図３０に示したルーチンを参照しながら、本排気浄化装置の作動を説明する。
【０２４８】
ＣＰＵ７１は、所定のタイミングになると、図２９のステップ２９００から処理を開始し、ステップ２９０２に進んで判定用最大酸素吸蔵量Ｃｍａｘ１ｈに「０」を設定し、続くステップ２９０４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２９０６に進み、カウンタ値ｎの値を「１」だけ増大してステップ２９０８に進み、現時点の判定用最大酸素吸蔵量Ｃｍａｘ１ｈに、その時点で求められている第１触媒５３のブロック１（ｎ）における最大酸素吸蔵量Ｃｍａｘ１（ｎ）（この時点ではカウンタ値ｎの値は「１」であるから、ブロック１（１）における最大酸素吸蔵量Ｃｍａｘ１（１））を加えて新たな判定用最大酸素吸蔵量Ｃｍａｘ１ｈを求める。
【０２４９】
次に、ＣＰＵ７１はステップ２９１０に進み、判定用最大酸素吸蔵量Ｃｍａｘ１ｈ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Ｃｍａｘ１ｈが所定の閾値Ｃｔｈより小さければ、ＣＰＵ７１はステップ２９１０にて「Ｎｏ」と判定してステップ２９１２に進みカウンタ値ｎの値が第１触媒５３のブロック数Ｎ１と等しいか否かを判定する。
【０２５０】
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２９１２にて「Ｎｏ」と判定し、再びステップ２９０６に戻ってカウンタ値ｎの値を「１」だけ増大し、ステップ２９０８及びステップ２９１０の処理を実行する。この結果、判定用最大酸素吸蔵量Ｃｍａｘ１ｈ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Ｃｍａｘ１（１）＋Ｃｍａｘ１（２）となる。そして、この積算値Ｃｍａｘ１（１）＋Ｃｍａｘ１（２）が閾値Ｃｔｈを超えなければＣＰＵ７１はステップ２９１０から再びステップ２９１２に進み、更に、カウンタ値ｎの値がブロック数Ｎ１と等しくなければ再びステップ２９０６にてカウント値ｎの値を「１」だけ増大し、ステップ２９０８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Ｃｍａｘ１ｈ（この時点ではＣｍａｘ１（１）＋Ｃｍａｘ１（２））にブロック１（ｎ）の最大酸素吸蔵量Ｃｍａｘ１（ｎ）（この時点ではｎ＝３であるあるからＣｍａｘ１（３））が加算され、新たな判定用最大酸素吸蔵量Ｃｍａｘ１ｈ（＝Ｃｍａｘ１（１）＋Ｃｍａｘ１（２）＋Ｃｍａｘ１（３））が求められる。
【０２５１】
このような処理は、判定用最大酸素吸蔵量Ｃｍａｘ１ｈ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Ｃｍａｘ１ｈ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１（ｎ）の最大酸素吸蔵量Ｃｍａｘ１（ｎ）の積算値（合計値）として求められる。
【０２５２】
このような処理の実行中、判定用最大酸素吸蔵量Ｃｍａｘ１ｈが所定の閾値Ｃｔｈより大きくなった場合、ＣＰＵ７１はステップ２９１０にて「Ｙｅｓ」と判定してステップ２９１４に進み、制御用流出酸素量ＣｇｏｕｔＯ２ｃに第１触媒５３の第ｎ番目のブロックの流出酸素量Ｃｇｏｕｔ１Ｏ２（ｎ）を設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。
【０２５３】
また、第１触媒５３の第１番目のブロックから第Ｎ１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Ｃｍａｘ１（ｎ）の積算値（即ち、第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌ（＝Ｃｍａｘ１））が所定の閾値Ｃｔｈより小さいとき、ＣＰＵ７１はステップ２９１０にて「Ｙｅｓ」と判定することはなく、カウンタ値ｎの値がＮ１となったときにステップ２９１２にて「Ｙｅｓ」と判定し、ステップ２９１６に進んで判定用最大酸素吸蔵量Ｃｍａｘ２ｈに第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌを設定する。次いで、ＣＰＵ７１は、ステップ２９１８にてカウンタ値ｎの値を「０」に設定し、ステップ２９２０以降に進む。
【０２５４】
ステップ２９２０〜ステップ２９２６までの処理は、ステップ２９０６〜ステップ２９１２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２９２０及びステップ２９２２にて第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌ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２（ｎ）の最大酸素吸蔵量Ｃｍａｘ２（ｎ）の積算値を加えた値を、判定用最大酸素吸蔵量Ｃｍａｘ２ｈとして求める。第２触媒５４の第ｎ番目となるブロック２（ｎ）は第１触媒５３の最上流のブロックから数えて（Ｎ１＋ｎ）番目のブロックということになる。従って、（Ｎ１＋ｎ）をｍとするとき、判定用最大酸素吸蔵量Ｃｍａｘ２ｈ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ｍ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。
【０２５５】
そして、ＣＰＵ７１は、判定用最大酸素吸蔵量Ｃｍａｘ２ｈが所定の閾値Ｃｔｈより大きくなった場合、ステップ２９２４にて「Ｙｅｓ」と判定してステップ２９２８に進み、制御用流出酸素量ＣｇｏｕｔＯ２ｃに第２触媒５４の第ｎ番目のブロックの流出流出酸素量Ｃｇｏｕｔ２Ｏ２（ｎ）を設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。
【０２５６】
同様に、第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌと第２触媒５４全体の最大酸素吸蔵量Ｃｍａｘ２ａｌｌの和（Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ）が所定の閾値Ｃｔｈより小さいとき、ＣＰＵ７１はステップ２９２４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Ｎ２となったときにステップ２９２６にて「Ｙｅｓ」と判定し、ステップ２９３０に進んで判定用最大酸素吸蔵量Ｃｍａｘ３ｈに第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌと第２触媒５４全体の最大酸素吸蔵量Ｃｍａｘ２ａｌｌの和（Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ）を設定する。次いで、ＣＰＵ７１は、ステップ２９３２にてカウンタ値ｎの値を「０」に設定し、ステップ２９３４以降に進む。
【０２５７】
ステップ２９３４〜ステップ２９４０までの処理は、ステップ２９０６〜ステップ２９１２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２９３４及びステップ２９３６にて第１触媒５３全体と第２触媒５４全体の各最大酸素吸蔵量の和（Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ）に第３触媒５５の最上流のブロック（第１番目のブロック）から同第３触媒５５の第ｎ番目のブロックまでの各ブロック３（ｎ）の最大酸素吸蔵量Ｃｍａｘ３（ｎ）の積算値を加えた値を、判定用最大酸素吸蔵量Ｃｍａｘ３ｈとして求める。第３触媒５５の第ｎ番目となるブロック３（ｎ）は、第１触媒５３の最上流のブロックから数えて（Ｎ１＋Ｎ２＋ｎ）番目のブロックということになる。従って、（Ｎ１＋Ｎ２＋ｎ）をｐとするとき、判定用最大酸素吸蔵量Ｃｍａｘ３ｈは、第１触媒５３、第２触媒５４、及び第３触媒５５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。
【０２５８】
そして、ＣＰＵ７１は、判定用最大酸素吸蔵量Ｃｍａｘ３ｈが所定の閾値Ｃｔｈより大きくなった場合、ステップ２９３８にて「Ｙｅｓ」と判定してステップ２９４２に進み、制御用流出酸素量ＣｇｏｕｔＯ２ｃに第３触媒５５の第ｎ番目のブロックの流出酸素濃度Ｃｇｏｕｔ３Ｏ２（ｎ）を設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。
【０２５９】
また、第１触媒５３〜第３触媒５５の各最大酸素吸蔵量の和（Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ＋Ｃｍａｘ３ａｌｌ）が所定の閾値Ｃｔｈより小さいとき、ＣＰＵ７１はステップ２９３８にて「Ｙｅｓ」と判定することはなく、カウンタ値ｎの値が第３触媒５５のブロック数Ｎ３となったときステップ２９４０にて「Ｙｅｓ」と判定し、この場合は上記ステップ２９４２を経由してステップ２９９５に進み、本ルーチンを一旦終了する。
【０２６０】
このように、ｎを自然数とし、第１触媒５３〜第３触媒５５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）の流出酸素量が制御用流出酸素量ＣｇｏｕｔＯ２ｃとして設定される。
【０２６１】
次に、サブフィードバック制御量ｖａｆｓｆｂを求める際の作動について説明する。ＣＰＵ７１は、図３０に示したルーチンを所定時間の経過毎に実行している。図３０において、図７に示したルーチンのステップと同一のステップには同一の符号を付し、その詳細な説明を省略する。
【０２６２】
ＣＰＵ７１は、このルーチンの実行により、前記決定・選択した制御用流出酸素量ＣｇｏｕｔＯ２ｃと所定の値である目標酸素量Ｃｇｏｕｔｒｅｆ（この例では、目標酸素量Ｃｇｏｕｔｒｅｆ＝０）の偏差を求め（ステップ３００５）、この偏差をＰＩ処理してサブフィードバック制御量ｖａｆｓｆｂを求める（ステップ７１５，７２０）。この結果、ＣＰＵ７１が図４及び図５に示したルーチンを実行することにより、制御用流出酸素量ＣｇｏｕｔＯ２ｃと所定の値である目標酸素量Ｃｇｏｕｔｒｅｆとが一致せしめられるように第１触媒５３に流入するガスの空燃比が制御される。
【０２６３】
以上、説明したように、第３実施形態によれば、値ｎを自然数とするとき単数又は複数の触媒（第１〜第３触媒５３〜５５）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２９０８、２９２２、２９３６等）と、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番目のブロックの排気浄化の状態を表す値（各触媒内における反応を考慮して構築された前記触媒モデルに基づいて計算される第ｎ番目のブロックの流出酸素濃度Ｃｇｏｕｔ１Ｏ２（ｎ），Ｃｇｏｕｔ２Ｏ２（ｎ），及びＣｇｏｕｔ３Ｏ２（ｎ）の何れか）を制御用流出酸素量ＣｇｏｕｔＯ２ｃとして取得・選択する排気浄化状態取得手段（図２３〜図２５、及び図２９に示したルーチン等）とを備える。
【０２６４】
また、この排気浄化装置は、前記取得された排気浄化の状態を表す値（制御用流出酸素量ＣｇｏｕｔＯ２ｃ）が所定の値（Ｃｇｏｕｔｒｅｆ）となるように前記触媒装置に流入するガスの空燃比（実際には機関に供給される混合気の空燃比）を制御する空燃比制御手段（図４、図５、及び図３０に示したルーチン等）とを備えている。
【０２６５】
この結果、常に所定の酸素吸蔵能力（所定の閾値Ｃｔｈ以上の最大酸素吸蔵量）を有している触媒装置上流部を介して取得される排気浄化の状態（上記第ｎ番目のブロックの流出酸素濃度である制御用流出酸素量ＣｇｏｕｔＯ２ｃ）に基づいて空燃比のフィードバック制御が行われることとなるので、同排気浄化の状態を、第１触媒５３に流入するガスの空燃比のハンチングを回避しながら所望の値に安定して制御することが可能となり、その結果、排ガスを効果的に浄化することができる。
【０２６６】
＜第３実施形態の変形例＞
次に、上記第３実施形態の変形例に係る排気浄化装置について説明する。この変形例は、第３実施形態の排気浄化装置が上述した触媒装置の所定のブロックの流出酸素濃度ＣｇｏｕｔＯ２を所定値に維持する制御を行っていたのに対し、最大酸素吸蔵量が閾値Ｃｔｈを超える第１番目のブロックから第ｎ番目のブロックまでで構成される触媒装置上流部の各ブロックの酸素吸蔵量の積算値（総和）が所定の目標酸素吸蔵量（目標値）となるように制御を行う点のみにおいて、同第３実施形態に係る排気浄化装置と異なっている。
【０２６７】
具体的に述べると、この変形例に係るＣＰＵ７１は、第３実施形態のＣＰＵ７１が実行する図２９及び図３０に示したルーチンに代えて、図３１及び図３２に示したルーチンをそれぞれ所定時間の経過毎に実行するようになっている。なお、図３１及び図３２のルーチンのステップにおいて、先に説明したステップと同一のステップには同先に示したステップと同一の符号を付し、その詳細な説明を省略する。
【０２６８】
ＣＰＵ７１は、図３１に示した制御用酸素吸蔵量ＯＳＡｃを決定するルーチンを所定時間の経過毎に繰り返し実行し、上述した判定用最大酸素吸蔵量Ｃｍａｘ１ｈが所定の閾値Ｃｔｈより大きくなった場合、ステップ２９１０にて「Ｙｅｓ」と判定してステップ３１０２に進み、制御用酸素吸蔵量ＯＳＡｃに第１触媒５３の第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ｊの酸素吸蔵量ＯＳＡ１（ｊ）の積算値ΣＯＳＡ１（ｊ）を設定する。次いで、ＣＰＵ７１はステップ３１０４に進み、目標酸素吸蔵量ＯＳＡｒｅｆに第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ｊの最大酸素吸蔵量Ｃｍａｘ１（ｊ）の積算値ΣＣｍａｘ１（ｊ）の１／２を設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。
【０２６９】
同様に、ＣＰＵ７１は、上述した判定用最大酸素吸蔵量Ｃｍａｘ２ｈが所定の閾値Ｃｔｈより大きくなった場合、ステップ２９２４にて「Ｙｅｓ」と判定してステップ３１０６に進み、第１触媒５３の全体の酸素吸蔵量ＯＳＡ１ａｌｌに第２触媒５４の第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ｊの酸素吸蔵量ＯＳＡ２（ｊ）の積算値ΣＯＳＡ２（ｊ）を加えた値を制御用酸素吸蔵量ＯＳＡｃとして設定する。次いで、ＣＰＵ７１はステップ３１０８に進み、第１触媒５３の全体の最大酸素吸蔵量Ｃｍａｘ１ａｌｌに第２触媒５４の第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ｊの最大酸素吸蔵量Ｃｍａｘ２（ｊ）の積算値ΣＣｍａｘ２（ｊ）を加えた値の半分の値を目標酸素吸蔵量ＯＳＡｒｅｆとして設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。
【０２７０】
同様に、ＣＰＵ７１は、上述した判定用最大酸素吸蔵量Ｃｍａｘ３ｈが所定の閾値Ｃｔｈより大きくなった場合、ステップ２９３８にて「Ｙｅｓ」と判定してステップ３１１０に進み、第１触媒５３と第２触媒５４の各酸素吸蔵量の和（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ）に第３触媒５５の第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ｊの酸素吸蔵量ＯＳＡ３（ｊ）の積算値ΣＯＳＡ３（ｊ）を加えた値を制御用酸素吸蔵量ＯＳＡｃとして設定する。次いで、ＣＰＵ７１はステップ３１１２に進み、第１触媒５３及び第２触媒５４の各最大酸素吸蔵量の和（Ｃｍａｘ１ａｌｌ＋Ｃｍａｘ２ａｌｌ）に第３触媒５５の第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ｊの最大酸素吸蔵量Ｃｍａｘ３（ｊ）の積算値ΣＣｍａｘ３（ｊ）を加えた値の半分の値を目標酸素吸蔵量ＯＳＡｒｅｆとして設定し、ステップ２９９５に進んで本ルーチンを一旦終了する。以上により、制御用酸素吸蔵量ＯＳＡｃ及び目標酸素吸蔵量ＯＳＡｒｅｆが決定される。
【０２７１】
また、ＣＰＵ７１は、図３１に示したルーチンを所定時間の経過毎に実行し、制御用酸素吸蔵量ＯＳＡｃを目標酸素吸蔵量ＯＳＡｒｅｆと等しくさせるためのサブフィードバック制御量ｖａｆｓｆｂを、制御用酸素吸蔵量ＯＳＡｃ及び目標酸素吸蔵量ＯＳＡｒｅｆの偏差をＰＩ処理することにより求める。このサブフィードバック制御量ｖａｆｓｆｂの求め方は他の実施形態におけるサブフィードバック制御量ｖａｆｓｆｂの求め方と同様であるので、詳細な説明を省略する。
【０２７２】
以上、説明したように、第３実施形態の変形例によれば、値ｎを自然数とするとき単数又は複数の触媒（第１〜第３触媒５３〜５５）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２９０８、２９２２、２９３６等）と、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排気浄化の状態を表す値（酸素吸蔵量ΣＯＳＡ１（ｊ），　ＯＳＡ１ａｌｌ＋ΣＯＳＡ２（ｊ），　及びＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ＋ΣＯＳＡ３（ｊ））を制御用酸素吸蔵量ＯＳＡｃとして取得・選択する排気浄化状態取得手段（図２３〜図２５、及び図３１に示したルーチン等）とを備える。
【０２７３】
また、この排気浄化装置は、前記取得された排気浄化の状態を表す値（制御用酸素吸蔵量ＯＳＡｃ）が所定の値（ＯＳＡｒｅｆ）となるように前記触媒装置に流入するガスの空燃比を制御する空燃比制御手段（図４、図５、及び図３２に示したルーチン等）とを備えている。
【０２７４】
この結果、常に所定の酸素吸蔵能力（所定の閾値Ｃｔｈ以上の最大酸素吸蔵量）を有している触媒装置上流部を介して取得される排気浄化の状態（制御用酸素吸蔵量ＯＳＡｃ）に基づいて第１触媒５３に流入するガスの空燃比のフィードバック制御が行われることとなるので、前記排気浄化の状態を同空燃比のハンチングを回避しながら所望の値に安定して制御することが可能となり、その結果、排ガスを効果的に浄化することができる。
【０２７５】
以上、説明したように、本発明による各実施形態及びその変形例によれば、制御の破綻を来さない酸素吸蔵能力を有する触媒（触媒装置）の全部又は上流部を介して得られる空燃比センサ出力、或いは、同触媒（触媒装置）の全部又は上流部の排気浄化の状態を表す値が所定の目標値となるように第１触媒５３に流入するガスの空燃比が制御されるので、排気浄化性能を良好に維持することができる。また、空燃比の制御に使用する空燃比センサよりも下流、又は排気浄化の状態を取得した位置よりも下流に位置する触媒（の部分）を予備的な触媒として使用することもできるので、流出する有害排気成分をより低減することができる。
【０２７６】
なお、本発明は上記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、上記第２実施形態の第２変形例の図２８に示したルーチンのステップ２８２５において、第１触媒５３の酸素吸蔵量ＯＳＡ１ａｌｌと第２触媒５４の酸素吸蔵量ＯＳＡ１ａｌｌの和（ＯＳＡ１ａｌｌ＋ＯＳＡ２ａｌｌ）を制御用酸素吸蔵量ＯＳＡａｌｌとして設定してもよい。この場合、ステップ２８３０の目標酸素吸蔵量ＯＳＡ２ａｌｌｒｅｆ（第２の値）は、第１触媒の最大酸素吸蔵量Ｃｍａｘ１と第２触媒の最大酸素吸蔵量Ｃｍａｘ２の和の１／２（＝（Ｃｍａｘ１＋Ｃｍａｘ２）／２）とすることが好適である。
【０２７７】
また、同じく図２８に示したルーチンのステップ２８１０において、第１触媒５３から流出する酸素量（第１触媒５３内における反応を考慮して構築された前記触媒モデルに基づいて計算される同第１触媒５３の最下流のブロックの流出酸素量、即ち第１触媒５３の排気浄化の状態を表す値）Ｃｇｏｕｔ１Ｏ２（Ｎ１）を制御用流出酸素量ＣｇｏｕｔＯ２ｃとして設定し、ステップ２８２５において第２触媒５４から流出する酸素量（第２触媒５４内における反応を考慮して構築された前記触媒モデルに基づいて計算される同第２触媒５４の最下流のブロックの流出酸素量、即ち第２触媒５４の排気浄化の状態を表す値）Ｃｇｏｕｔ２Ｏ２（Ｎ２）を制御用流出酸素量ＣｇｏｕｔＯ２ｃとして設定するとともに、ステップ２８１５及びステップ２８３０を省略してもよい。この場合、サブフィードバック制御は、図３０に示したルーチンを採用する。
【０２７８】
これにより、第１触媒５３の酸素吸蔵能力が所定の能力より大きいとき同第１触媒５３から流出する特定成分（この場合、酸素）の量に応じた値を所定の値とする空燃比フィードバック制御が、また、第１触媒５３の酸素吸蔵能力が所定の能力より小さいとき同第２触媒５４から流出する特定成分（この場合、酸素）の量に応じた値を同所定の値とする空燃比フィードバック制御が達成される。
【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内燃機関に適用したシステムの概略図である。
【図２】図１に示した最上流空燃比センサの出力電圧と空燃比との関係を示したマップである。
【図３】図１に示した第１触媒下流空燃比センサ、第２触媒下流空燃比センサ、及び第３触媒下流空燃比センサの出力電圧と空燃比との関係を示したマップである。
【図４】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５】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６】図１に示したＣＰＵが実行するサブフィードバック制御量を求めるために使用される制御用空燃比センサ出力を選択（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７】図１に示したＣＰＵが実行するサブフィードバック制御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８】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９】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１０】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１１】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１２】図１に示したＣＰＵが実行する第４モード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１４】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１５】本発明の第１実施形態の変形例に係る排気浄化装置のＣＰＵが実行する制御用空燃比センサ出力を選択（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１６】本発明の排気浄化装置が採用する触媒モデルを模式的に示した図である。
【図１７】本発明の排気浄化装置が採用する触媒モデルの特定領域に注目したときの同特定領域における酸素吸蔵・放出反応に関係する特定成分の収支を示した図である。
【図１８】本発明の排気浄化装置が採用する触媒モデルが対象とする触媒全体の最大酸素吸蔵量から同触媒の各ブロック毎の最大酸素吸蔵量の分布を求めるためのマップである。
【図１９】本発明の排気浄化装置が採用する触媒モデルを第１，第２，第３触媒にそれぞれ適用した場合の模式図である。
【図２０】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する、サブフィードバック制御量を求めるために使用される制御用酸素吸蔵量及び目標酸素吸蔵量を決定・選択するためのルーチンを示したフローチャートである。
【図２１】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御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２２】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する各触媒の最大酸素吸蔵量及び各ブロックの最大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２３】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する第１触媒の各ブロック毎の流出酸素量、及び酸素吸蔵量等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２４】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する第２触媒の各ブロック毎の流出酸素量、及び酸素吸蔵量等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２５】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する第３触媒の各ブロック毎の流出酸素量、及び酸素吸蔵量等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２６】本発明の第２実施形態に係る排気浄化装置のＣＰＵが実行する第１，第２，第３触媒の各々酸素吸蔵量及びこれらの触媒の各ブロック毎の酸素吸蔵量をクリアするためのルーチンを示したフローチャートである。
【図２７】本発明の第２実施形態の第１変形例に係る排気浄化装置のＣＰＵが実行する、サブフィードバック制御量を求めるために使用される制御用酸素吸蔵量及び目標酸素吸蔵量を決定・選択するためのルーチンを示したフローチャートである。
【図２８】第２実施形態の第２変形例に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御量を求めるために使用される制御用酸素吸蔵量及び目標酸素吸蔵量を決定・選択するためのルーチンを示したフローチャートである。
【図２９】本発明による第３実施形態に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御量を求めるために使用される制御用流出酸素量を決定・選択するためのルーチンを示したフローチャートである。
【図３０】本発明による第３実施形態に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御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３１】第３実施形態の変形例に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御量を求めるために使用される制御用酸素吸蔵量及び目標酸素吸蔵量を決定・選択するためのルーチンを示したフローチャートである。
【図３２】第３実施形態の変形例に係る排気浄化装置のＣＰＵが実行するサブフィードバック制御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。
【符号の説明】
１０…内燃機関、２５…燃焼室、３９…インジェクタ、５２…エキゾーストパイプ（排気管）、５３…第１触媒、５４…第２触媒、５５…第３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、６９…第３触媒下流空燃比センサ、７０…電気制御装置、７１…ＣＰＵ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine having a three-way catalyst interposed in an exhaust passage.
[0002]
[Prior art]
Conventionally, a three-way catalyst (hereinafter referred to as a “start converter”) (hereinafter referred to as a “start converter”) is provided in an exhaust passage of an engine in order to ensure exhaust purification performance immediately after the start of an internal combustion engine and further improve exhaust purification performance after a complete warm-up. A three-way catalyst (hereinafter, referred to as a "second catalyst") called an under-floor converter is provided in an exhaust passage downstream of the first catalyst. A configuration of disposing may be adopted. In this case, the first catalyst is disposed at a position closer to the exhaust port of the engine than the second catalyst, and the exhaust gas having a high temperature flows therein. Demonstrate. On the other hand, the second catalyst takes a longer time to warm up than the first catalyst, but after warming up once, exhibits an excellent exhaust purification function in cooperation with the first catalyst.
[0003]
As described above, the conventional exhaust gas purifying apparatus in which the first catalyst and the second catalyst are arranged in series in the exhaust passage of the internal combustion engine is provided between the engine and the first catalyst, between the first catalyst and the second catalyst, and between the first catalyst and the second catalyst. An air-fuel ratio sensor (oxygen concentration sensor) is disposed downstream of each of the two catalysts, and when the air-fuel ratio sensor downstream of the second catalyst is in an inactive state, the air-fuel ratio sensor and the first catalyst between the engine and the first catalyst are provided. Controlling the air-fuel ratio of the air-fuel mixture supplied to the engine based on the output of the air-fuel ratio sensor between the first and second catalysts, and when the air-fuel ratio sensor downstream of the second catalyst is active, the engine and the first catalyst The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled based on the outputs of the air-fuel ratio sensor and the air-fuel ratio sensor downstream of the second catalyst during the period (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-6-294342 (pages 5 to 6, FIGS. 4 to 6)
[0005]
[Problems to be solved by the invention]
By the way, when the air-fuel ratio of the exhaust gas of the internal combustion engine flowing into the three-way catalyst (hereinafter simply referred to as “catalyst”) is approximately the stoichiometric air-fuel ratio, the unburned components (HC, CO) in the exhaust gas The exhaust gas is purified by a function of oxidizing NOx and simultaneously reducing nitrogen oxides (NOx) (hereinafter, referred to as a "catalytic function" or a "redox function"). The catalyst has an oxygen storage function (O 2) for storing (storing) oxygen. ₂ If the air-fuel ratio of the inflowing exhaust gas is rich, the stored oxygen oxidizes unburned components such as unburned HC and CO (releases oxygen), If the air-fuel ratio of the exhaust gas to be exhausted is lean, oxygen obtained by reducing oxygen and NOx in the exhaust gas is stored inside. Accordingly, the catalyst can effectively purify unburned HC, CO, and NOx even when the air-fuel ratio of the air-fuel mixture supplied to the engine deviates from the stoichiometric air-fuel ratio to some extent.
[0006]
As described above, since the catalyst has an oxygen storage function, even if the air-fuel ratio of the exhaust gas upstream of the catalyst changes richly, the downstream of the catalyst continues until all the oxygen stored in the catalyst is consumed. Since almost no oxygen flows out, the output of the air-fuel ratio sensor provided downstream of the catalyst continues to generate an output substantially equivalent to the stoichiometric air-fuel ratio or the lean air-fuel ratio. Similarly, even if the air-fuel ratio of the exhaust gas upstream of the catalyst changes lean, the amount of oxygen stored in the catalyst (hereinafter referred to as “oxygen storage amount”) is the maximum amount of oxygen that can be stored in the catalyst. (Hereinafter referred to as "maximum oxygen storage amount.") Unburned HC and CO hardly flow out to the downstream of the catalyst until the catalyst reaches the maximum oxygen storage amount. Therefore, the output of the air-fuel ratio sensor provided downstream of the catalyst is substantially reduced. The output corresponding to the stoichiometric air-fuel ratio or the rich air-fuel ratio is continuously generated.
[0007]
That is, the change in the air-fuel ratio of the exhaust gas upstream of the catalyst does not immediately appear in the output of the air-fuel ratio sensor provided downstream of the catalyst, and the output of the air-fuel ratio sensor downstream of the catalyst is the output of the air-fuel ratio of the exhaust gas flowing into the catalyst. The value corresponds to an average value (hereinafter, referred to as “center air-fuel ratio”). Therefore, by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so that the output of the air-fuel ratio sensor downstream of the catalyst matches a predetermined target output (for example, an output corresponding to the stoichiometric air-fuel ratio), the exhaust gas flowing into the catalyst is controlled. Can be controlled to a desired value (for example, a stoichiometric air-fuel ratio).
[0008]
However, for example, when the maximum oxygen storage amount of the catalyst is reduced to a certain degree due to, for example, deterioration of the catalyst, the oxygen storage amount reaches “0” or the maximum oxygen storage amount within a relatively short time. Fluctuations in the air-fuel ratio of the exhaust gas upstream will immediately appear in the output of the air-fuel ratio sensor downstream of the catalyst. Therefore, if the above-described air-fuel ratio feedback control is performed in such a case, the air-fuel ratio of the exhaust gas upstream of the catalyst will fluctuate greatly (hunting), and as a result, the center air-fuel ratio of the exhaust gas flowing into the catalyst will be reduced. And the exhaust gas purification performance is reduced.
[0009]
As is clear from this, the above-described conventional apparatus selects an air-fuel ratio sensor to be used by focusing only on the activation state of the air-fuel ratio sensor, and focuses on the maximum oxygen storage amount (that is, oxygen storage capacity) of the catalyst. Since the air-fuel ratio sensor is not selected, the center air-fuel ratio of the exhaust gas flowing upstream of the first catalyst deviates from the stoichiometric air-fuel ratio when the first catalyst is deteriorated, and as a result, the purification performance is reduced. there is a possibility. Accordingly, an object of the present invention is to perform control in consideration of the oxygen storage capacity of the catalyst to avoid failure of feedback control in which the air-fuel ratio of exhaust gas upstream of the catalyst fluctuates greatly, and to prevent unburned components and nitrogen oxidation. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can more effectively purify harmful components such as substances.
[0010]
Summary of the Invention
An exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a plurality of catalysts interposed in series in an exhaust passage of the internal combustion engine, and a plurality of idlers disposed downstream of the plurality of catalysts and disposed in the exhaust passage. The fuel cell system includes a fuel ratio sensor, an oxygen storage capacity obtaining unit, and an air-fuel ratio control unit.
[0011]
The oxygen storage capacity obtaining means is a value representing the oxygen storage capacity of the catalyst device including the first to n-th catalysts, which is the most upstream catalyst among the plurality of catalysts (for example, the maximum oxygen Occlusion amount). As a specific example, in a device in which the first catalyst, the second catalyst, and the third catalyst are interposed in the exhaust passage in order from the most upstream, the maximum oxygen storage amount of the catalyst device including only the first catalyst, The maximum oxygen storage amount of the catalyst device including the first catalyst and the second catalyst (that is, the total value of the maximum oxygen storage amounts of the first catalyst and the second catalyst), and the maximum oxygen amount of the catalyst device including the first to third catalysts The storage amount (that is, the total value of the maximum oxygen storage amounts of the first to third catalysts) is obtained.
[0012]
The air-fuel ratio control means is a catalyst device having the smallest value n among the catalyst devices determined to have an oxygen storage capability greater than a predetermined oxygen storage capability based on the acquired value representing the oxygen storage capability. Disposed in the exhaust passage downstream of the n-th catalyst (the exhaust passage downstream of the n-th catalyst and upstream of the (n + 1) -th catalyst when the (n + 1) -th catalyst is present). The air-fuel ratio of the gas flowing into the first catalyst (the most upstream catalyst) is controlled such that the output of one of the plurality of air-fuel ratio sensors becomes a predetermined target output.
[0013]
That is, in the above specific example, when the maximum oxygen storage amount of the catalyst device including only the first catalyst exceeds a predetermined threshold value (when the first catalyst has an oxygen storage capability larger than the predetermined oxygen storage capability). In this case, since both the maximum oxygen storage amount of the catalyst device including the first catalyst and the second catalyst and the maximum oxygen storage amount of the catalyst device including the first to third catalysts exceed a predetermined threshold value, , Downstream of the first (n-th) catalyst (downstream of the first catalyst and upstream of the second catalyst) constituting the catalyst device consisting of only the first catalyst having the smallest value n. ) Is selected as the air-fuel ratio sensor used for the feedback control of the air-fuel ratio, and flows into the first catalyst so that the output of the selected air-fuel ratio sensor becomes the target output. The air-fuel ratio of the gas is controlled
[0014]
Further, for example, the maximum oxygen storage amount of the catalyst device including only the first catalyst is smaller than a predetermined threshold, but the maximum oxygen storage amount of the catalyst device including the first catalyst and the second catalyst exceeds the predetermined threshold value. In some cases, the maximum oxygen storage amount of the catalyst device including the first to third catalysts also exceeds the predetermined threshold. In this case, the smallest value n is 2, so that it is downstream of the second (n-th) catalyst (downstream of the second catalyst and upstream of the third catalyst) constituting the catalyst device including the first catalyst and the second catalyst. The air-fuel ratio sensor disposed in the exhaust passage) is selected as the air-fuel ratio sensor used for feedback control, and the gas flowing into the first catalyst so that the output of the selected air-fuel ratio sensor becomes the target output. Is controlled.
[0015]
Therefore, in such an exhaust gas purification device, the catalyst device located upstream of the air-fuel ratio sensor used for feedback control has a large oxygen storage capacity to such an extent that the feedback control does not fail. The above-described hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided.
[0016]
The air-fuel ratio of the gas flowing into the first catalyst (the most upstream catalyst) may be controlled by controlling only the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine. In addition to or independent of the control of the air-fuel ratio of the air-fuel mixture, the reducing agent (unburned HC, etc.) or the oxidizing agent (air, etc.) supplied between the engine and the first catalyst is It may be controlled by controlling the amount. This point is similarly applied to other exhaust gas purifying devices described below.
[0017]
Another exhaust purification device according to the present invention includes a first catalyst disposed in an exhaust passage of an internal combustion engine, a first catalyst downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the first catalyst, A second catalyst disposed in the exhaust passage downstream of the first catalyst downstream air-fuel ratio sensor, a second catalyst downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the second catalyst, First catalyst oxygen storage capacity obtaining means for obtaining a value representing the oxygen storage capacity of the first catalyst; and an oxygen storage capacity of the first catalyst based on the obtained value indicating the oxygen storage capacity of the first catalyst. When it is determined that the output is greater than the predetermined oxygen storage capacity (threshold), the air-fuel ratio of the gas flowing into the first catalyst is controlled so that the output of the first catalyst downstream air-fuel ratio sensor becomes a predetermined first target output. At the same time, the oxygen storage capacity of the first catalyst is the same as the predetermined oxygen. Air-fuel ratio control means for controlling the air-fuel ratio of gas flowing into the first catalyst so that the output of the second catalyst downstream air-fuel ratio sensor becomes a predetermined second target output when it is determined that the storage capacity is smaller than the storage capacity. It has.
[0018]
According to this, when the oxygen storage capacity of the first catalyst represented by the maximum oxygen storage capacity of the first catalyst or the like is larger than the predetermined oxygen storage capacity, the first catalyst is disposed between the first catalyst and the second catalyst. The air-fuel ratio of the gas flowing into the first catalyst is controlled such that the output of the first catalyst downstream air-fuel ratio sensor becomes a predetermined first target output. Further, when the oxygen storage capacity of the first catalyst is smaller than the predetermined oxygen storage capacity, the first catalyst is provided such that the output of the second catalyst downstream air-fuel ratio sensor provided downstream of the second catalyst becomes the predetermined second target output. The air-fuel ratio of the gas flowing into the catalyst is controlled.
[0019]
As a result, the first catalyst (catalyst device composed of the first catalyst) having a predetermined oxygen storage capacity (capability equal to or higher than the predetermined oxygen storage capability), or the catalyst device composed of the first catalyst and the second catalyst is used. Since the air-fuel ratio of the gas flowing into the first catalyst is controlled based on the output of the air-fuel ratio sensor disposed downstream, the center air-fuel ratio of the exhaust gas flowing into the catalyst device is stabilized at a desired value ( That is, control can be performed without causing control failure such as generation of hunting, and exhaust gas can be effectively purified. The first target output and the second target output may be the same or different.
[0020]
By the way, in order to make the catalyst function effectively, feedback control of the air-fuel ratio is performed so that the output of the air-fuel ratio sensor matches the target output, and a value representing the state of exhaust purification of the catalyst (for example, It is effective to obtain the amount of the specific component flowing out of the catalyst) and perform feedback control of the air-fuel ratio so that the value representing the state of exhaust gas purification matches a predetermined value. Further, even when performing feedback control based on a value indicating the state of exhaust gas purification of the catalyst, in order to avoid hunting of the air-fuel ratio, a catalyst or a catalyst that acquires a value indicating the state of exhaust gas purification is used. It is necessary that a catalyst device including a catalyst interposed upstream of the catalyst has an oxygen storage capacity equal to or higher than a predetermined threshold.
[0021]
Based on such a viewpoint, another exhaust gas purification apparatus according to the present invention includes a plurality of catalysts interposed in series in an exhaust passage of an internal combustion engine, and an oxygen acquisition device that obtains a value representing each oxygen storage capacity of the plurality of catalysts. A storage capacity obtaining means, and a catalyst which is determined to have an oxygen storage capacity larger than a predetermined oxygen storage capacity based on the obtained value indicating the oxygen storage capacity, is disposed at the most upstream of the exhaust passage. Exhaust purification state acquisition means for acquiring a value representing the state of exhaust gas purification of the catalyst, and flowing into the catalyst disposed at the most upstream so that the acquired value representing the state of exhaust purification becomes a predetermined value. Air-fuel ratio control means for controlling the air-fuel ratio of the gas. Here, "controlling the air-fuel ratio of the gas flowing into the most upstream catalyst" means that the catalyst (the most upstream catalyst), the upstream catalyst, or the exhaust gas. And controlling the air-fuel ratio of the gas flowing into the catalyst located upstream of the passage.
[0022]
According to this, the value representing the state of the exhaust gas purification is based on the acquired value representing the oxygen storage capacity, and the catalyst determined to have the oxygen storage capacity larger than the predetermined oxygen storage capacity among the catalysts in the exhaust passage. Since the value indicates the state of purification of exhaust gas of the catalyst disposed at the most upstream side, the fluctuation of the air-fuel ratio of the gas flowing into the most upstream catalyst does not immediately appear in the value indicating the state of purification of exhaust gas. Therefore, the above-described hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided.
[0023]
Further, another exhaust gas purifying apparatus according to the present invention based on the above viewpoint includes a plurality of catalysts disposed in series in an exhaust passage of an internal combustion engine, and a most upstream catalyst among the plurality of catalysts when a value n is a natural number. Oxygen storage capacity obtaining means for obtaining a value indicating the oxygen storage capacity of the catalyst device composed of the first to n-th catalysts, based on the obtained value indicating the oxygen storage capacity Out of the catalyst devices determined to have an oxygen storage capability greater than the predetermined oxygen storage capability by the catalyst device having the smallest value n, or the nth catalyst device constituting the catalyst device having the smallest value n. Exhaust purification state acquisition means for acquiring a value representing the state of exhaust gas purification of the catalyst, and a method of obtaining the value representing the state of exhaust gas purification so that the acquired value representing the state of exhaust gas purification becomes a predetermined value. Control the air-fuel ratio It includes a ratio control means.
[0024]
According to this, the value indicating the state of the exhaust gas purification is determined to be the first (most upstream) that is determined to have the oxygen storage capacity larger than the predetermined oxygen storage capacity based on the value indicating the obtained oxygen storage capacity. Of the catalyst devices having the smallest value n among the catalyst devices constituted by the catalysts from the first catalyst to the nth catalyst (n is a natural number) or the nth catalyst constituting the catalyst device having the smallest value n Is a value representing the state of exhaust gas purification, the fluctuation of the air-fuel ratio of the gas flowing into the first catalyst does not immediately appear in the value representing the state of exhaust gas purification. Therefore, the above-described hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided.
[0025]
Further, as described above, depending on the operation state of the internal combustion engine, even if the air-fuel ratio of the gas flowing into the catalyst (catalyst device) shifts to the rich side or the lean side, the oxygen storage amount in the catalyst is “0” or Unless the maximum oxygen storage amount is reached, almost no unburned HC, CO or nitrogen oxide NOx is emitted from the catalyst. Therefore, maintaining the oxygen storage amount of the catalyst at a desired amount, for example, about half of the maximum oxygen storage amount of the catalyst, requires that the oxygen storage amount of the catalyst be “0” and the maximum oxygen storage amount. Since it is difficult to reach, it is suitable for exhaust gas purification.
[0026]
Therefore, the exhaust purification state acquisition means determines the oxygen storage amount of the entire catalyst device having the smallest value n or the oxygen storage amount of the n-th catalyst constituting the catalyst device having the smallest value n in the exhaust purification. If it is configured to acquire the value indicating the state, it is possible to perform control for maintaining the oxygen storage amount at a desired amount, and it is possible to reduce the emission amount of unburned HC, CO, and NOx. it can.
[0027]
Further, the air-fuel ratio sensor detects the exhaust gas purification state of the catalyst with a time delay until the gas flowing out of the catalyst reaches the gas and the time until the output corresponding to the gas that has reached the gas is generated. Will be. On the other hand, the exhaust gas purification state acquisition means flows out from the n-th catalyst constituting the catalyst device having the smallest value n calculated based on the catalyst model constructed in consideration of the reaction in the catalyst. If the configuration is such that the amount of the specific component is acquired as a value indicating the state of exhaust gas purification, the state of exhaust gas purification of the catalyst can be quickly controlled to a desired state.
[0028]
Another exhaust purification device according to the present invention includes a first catalyst provided in an exhaust passage of an internal combustion engine, a second catalyst provided in the exhaust passage downstream of the first catalyst, and a first catalyst provided in the exhaust passage. First catalyst oxygen storage capacity obtaining means for obtaining a value indicating the oxygen storage capacity of the first catalyst, first catalyst exhaust purification state obtaining means for obtaining a value indicating the exhaust purification state of the first catalyst, and Second catalyst exhaust purification state acquisition means for acquiring a value relating to the state of exhaust gas purification; and, based on the acquired value representing the oxygen storage capacity of the first catalyst, the first catalyst has a predetermined oxygen storage capacity. When it is determined that the value is larger than the predetermined value, the air-fuel ratio of the gas flowing into the first catalyst is controlled so that the acquired value indicating the state of exhaust gas purification of the first catalyst becomes a predetermined first value. The oxygen storage capacity of the first catalyst is equal to the predetermined oxygen storage capacity. When it is determined to be small, the air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the first catalyst so that the acquired value relating to the exhaust purification state of the second catalyst becomes a predetermined second value; , Is provided.
[0029]
According to this, when the oxygen storage capacity represented by the maximum oxygen storage amount or the like of the first catalyst is larger than the predetermined threshold value, the value representing the state of exhaust purification of the first catalyst becomes the predetermined first value. As described above, the air-fuel ratio of the gas flowing into the first catalyst is controlled, and when the oxygen storage capacity of the first catalyst is smaller than the predetermined threshold, the value relating to the exhaust purification state of the second catalyst is changed to a predetermined value. The air-fuel ratio of the gas flowing into the first catalyst is controlled so as to have a value of 2.
[0030]
Therefore, the exhaust gas purification state used for controlling the air-fuel ratio of the gas flowing into the first catalyst indicates the exhaust gas purification state of the catalyst (catalyst device) whose oxygen storage capacity is larger than the predetermined threshold. Since the value does not immediately reflect the air-fuel ratio of the gas upstream of the first catalyst, the hunting of the air-fuel ratio described above is avoided, and as a result, an increase in the emission of harmful components such as unburned HC, CO, and NOx is avoided. can do.
[0031]
In this case, the first catalyst exhaust gas purification state acquisition means may calculate the oxygen storage amount of the first catalyst or the first catalyst calculated based on a catalyst model constructed in consideration of a reaction in the first catalyst. A value corresponding to the amount of the specific component flowing out of the first catalyst is obtained as a value representing the state of exhaust gas purification of the first catalyst, and the second catalyst exhaust gas purification state acquisition means is configured to store oxygen in the second catalyst. Amount, the total oxygen storage amount of the first catalyst oxygen storage amount and the second catalyst oxygen storage amount, and a catalyst model calculated based on a reaction model in the second catalyst. It is preferable that one of the values according to the amount of the specific component flowing out of the second catalyst is obtained as a value relating to the exhaust gas purification state of the second catalyst.
[0032]
According to this, since the respective oxygen storage amounts and the amounts of the specific components flowing out can be controlled to desired values, the exhaust gas can be effectively purified.
[0033]
In any one of the above-described exhaust gas purification devices, the value representing the oxygen storage capacity is a value indicating the maximum oxygen storage amount of the target catalyst or the catalyst device, or a value having a certain correlation with the maximum oxygen storage amount. It is preferred that Here, the value having a certain correlation with the maximum oxygen storage amount is a value that indirectly represents the maximum oxygen storage amount, and includes, for example, the temperature of the catalyst, the usage time of the catalyst (the running time of the vehicle, Travel distance) or the intake air flow rate of the internal combustion engine.
[0034]
Another exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a catalyst device including one or more catalysts interposed in an exhaust passage of the internal combustion engine, and the catalyst device is disposed along a flow direction of a gas flowing into the catalyst device. Acquisition means for acquiring the maximum oxygen storage amount of each block when virtually divided into a plurality of blocks, and from the first block, which is the most upstream block of the catalyst device, when the value n is a natural number. integrated value calculating means for integrating the maximum oxygen storage amount of each block in the upstream portion of the catalyst device constituted by the blocks up to the n-th block to obtain an integrated value of the maximum oxygen storage amount in the upstream portion of the catalyst device; The table shows the state of exhaust gas purification in the upstream portion of the catalytic device, which includes the nth block having the smallest value n among the upstream portions of the catalytic device in which the integrated value of the oxygen storage amount is larger than a predetermined threshold value. Exhaust purification state acquisition means for acquiring a value or a value representing an exhaust purification state of the n-th block; and flowing into the catalyst device such that the acquired value representing the exhaust purification state becomes a predetermined value. Air-fuel ratio control means for controlling the air-fuel ratio of the generated gas.
[0035]
This exhaust gas purification device obtains the maximum oxygen storage amount of each block when a catalyst device comprising one or a plurality of catalysts is virtually divided into a plurality of blocks along the flow direction of gas (exhaust gas). The maximum oxygen storage amount of each block from the block (that is, the first block) to the n-th block (n is a natural number) is integrated. Then, the smallest one of the upstream portions of the catalyst device composed of n blocks whose integrated value of the maximum oxygen storage amount is larger than the predetermined threshold (that is, a block group capable of securing the maximum oxygen storage amount equal to or higher than the predetermined threshold). A value representing the state of exhaust gas purification (for example, oxygen storage amount) in the upstream portion of the catalyst device having the value n and the value of the state of exhaust gas purification for the n-th block (for example, a specific component flowing out of the n-th block) (A value according to the amount) is set as a control target, and the air-fuel ratio of the gas flowing into the catalyst device is controlled so that the control target has a predetermined value.
[0036]
As a result, the feedback control of the air-fuel ratio is performed via the upstream portion of the catalyst device which always has a predetermined oxygen storage capacity (a maximum oxygen storage amount equal to or higher than a predetermined threshold). Can be stably controlled to a desired value while avoiding hunting, and as a result, exhaust gas can be effectively purified. Note that the predetermined value is a value that changes according to the value n (for example, when the acquired exhaust gas purification state is the oxygen storage amount, the catalyst device including the first to n-th blocks It may be a value approximately equal to about half of the maximum oxygen storage amount in the upstream portion, and may be a constant value (for example, a value corresponding to the amount of the specific component flowing out of the n-th block when the acquired exhaust gas purification state is obtained). , It may be “0” or substantially “0”).
[0037]
In this case, the exhaust gas purification state acquiring means for acquiring a value representing the state of exhaust gas purification is configured such that the value n is the smallest in the upstream portion of the catalyst device where the maximum oxygen storage amount integrated value takes a value larger than a predetermined threshold value ( (Consisting of the first to n-th blocks) depending on the amount of oxygen stored upstream of the catalytic device or the amount of the specific component flowing out of the n-th block upstream of the catalytic device having the smallest equivalent value n. Preferably, a value is obtained as a value representing the state of the exhaust gas purification.
[0038]
According to this, the oxygen storage amount in the upstream portion of the catalyst device and the amount of the specific component flowing out from the n-th block, which is the most downstream block in the upstream portion of the catalyst device, are stabilized without causing hunting of the air-fuel ratio. Thus, the exhaust gas can be effectively purified.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
Hereinafter, embodiments of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a system in which an exhaust gas purification device for an internal combustion engine according to a first embodiment of the present invention is applied to a spark ignition type multi-cylinder (four cylinder) internal combustion engine 10. Although FIG. 1 shows a cross section of one cylinder, other cylinders have the same configuration.
[0040]
The internal combustion engine 10 includes a cylinder block 20 including a cylinder block, a cylinder block lower case, and an oil pan, a cylinder head 30 fixed on the cylinder block 20, and a gasoline mixture in the cylinder block 20. And an exhaust system 50 for discharging exhaust gas from the cylinder block 20 to the outside.
[0041]
The cylinder block section 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 via the connecting rod 23, whereby the crankshaft 24 rotates. The heads of the cylinder 21 and the piston 22 together with the cylinder head 30 form a combustion chamber 25.
[0042]
The cylinder head section 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 for opening and closing the intake port 31, and an intake camshaft for driving the intake valve 32, and continuously changes the phase angle of the intake camshaft. Variable intake timing device 33, an actuator 33a of the variable intake timing device 33, an exhaust port 34 communicating with the combustion chamber 25, an exhaust valve 35 for opening and closing the exhaust port 34, an exhaust camshaft 36 for driving the exhaust valve 35, and a spark plug 37 And an igniter 38 including an ignition coil for generating a high voltage applied to the ignition plug 37, and an injector (fuel injection means) 39 for injecting fuel into the intake port 31.
[0043]
The intake system 40 includes an intake pipe 41 including an intake manifold communicating with the intake port 31 and forming an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and an intake pipe 41. The throttle valve 43 includes a throttle valve 43 that changes the opening cross-sectional area of the intake passage, and a throttle valve actuator 43a that includes a DC motor that constitutes a throttle valve driving unit.
[0044]
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 a first catalyst (most upstream three-way) disposed (interposed) in the exhaust pipe 52. 53, a second catalyst (intermediate three-way catalyst, or a lower part of the vehicle floor) provided (interposed) in an exhaust pipe 52 downstream of the first catalyst 53. Therefore, it is also referred to as a first under-floor converter.) 54 and a third catalyst (most downstream three-way catalyst or second catalyst) provided (interposed) in an exhaust pipe 52 downstream of the second catalyst 54. 55, which is also referred to as an underfloor converter. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.
[0045]
On the other hand, this system includes a hot-wire type 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 an exhaust passage upstream of the first catalyst 53). Hereinafter, this will be referred to as an “upstream air-fuel ratio sensor 66”), and an air-fuel ratio sensor 67 (hereinafter, “first catalyst”) disposed in the exhaust passage downstream of the first catalyst 53 and upstream of the second catalyst 54. An air-fuel ratio sensor 68 (hereinafter referred to as a “second catalyst downstream air-fuel ratio sensor 68”) disposed in the exhaust passage downstream of the second catalyst 54 and upstream of the third catalyst 54. ), An air-fuel ratio sensor 69 (hereinafter, referred to as a “third catalyst downstream air-fuel ratio sensor 69”) disposed in an exhaust passage downstream of the third catalyst 55, and an accelerator opening sensor. It is equipped with a 2.
[0046]
The hot wire air flow meter 61 detects the mass flow rate of the intake air flowing through the intake pipe 41 and outputs a signal indicating the same mass flow rate Ga. The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal indicating the throttle valve opening TA. The cam position sensor 63 generates a signal (G2 signal) having one pulse each time the intake camshaft rotates 90 ° (that is, each time the crankshaft 24 rotates 180 °). The crank position sensor 64 outputs a signal having a narrow pulse each time the crankshaft 24 rotates 10 ° and a wide pulse each time the crankshaft 24 rotates 360 °. This signal indicates 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 indicating the cooling water temperature THW.
[0047]
The most upstream air-fuel ratio sensor 66 is a limiting current type oxygen concentration sensor, and outputs a voltage vabyfs according to the air-fuel ratio A / F as shown in FIG. As is clear from FIG. 2, the uppermost-stream air-fuel ratio sensor 66 can accurately detect the air-fuel ratio A / F over a wide range. The first to third catalyst downstream air-fuel ratio sensors 67 to 69 are concentration cell type oxygen concentration sensors, and output voltages voxs1, voxs2, voxs3, which rapidly change in the stoichiometric air-fuel ratio, as shown in FIG. It has become. More specifically, each of the first to third catalyst downstream air-fuel ratio sensors 67 to 69 has an air-fuel ratio of approximately 0.1 (V) when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. A voltage of approximately 0.9 (V) is output when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and approximately 0.5 (V) when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio. The accelerator opening sensor 82 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal indicating the operation amount Accp of the accelerator pedal 81.
[0048]
Further, the system includes an electric control device 70. The electric control device 70 includes a CPU 71 connected to the CPU 71 via 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. A microcomputer including a RAM 73 for temporarily storing data, a backup RAM 74 for storing data while the power is turned on and holding the stored data even when the power is turned off, an interface 75 including an AD converter, and the like. . The interface 75 is connected to the sensors 61 to 69 and 82, supplies signals from the sensors 61 to 69 and 82 to the CPU 71, and in accordance with instructions from the CPU 71, the actuator 33a of the variable intake timing device 33, the igniter 38, A drive signal is sent to the injector 39 and the throttle valve actuator 43a.
[0049]
(Overview of air-fuel ratio feedback control)
Next, the outline of the air-fuel ratio feedback control performed by the exhaust gas purification device for an internal combustion engine configured as described above will be described.
[0050]
The first catalyst 53 (the same applies to the second catalyst 54 and the third catalyst 55), which is a three-way catalyst, has the above-described oxygen storage function, so that the first catalyst 53 flows in continuously. In order to efficiently purify a large amount of HC and CO, the first catalyst 53 must store a large amount of oxygen. Conversely, in order to efficiently purify a large amount of NOx that flows continuously. This means that the first catalyst 53 must be able to store oxygen sufficiently. As is clear from the above, the purification ability of the first catalyst 53 depends on the maximum oxygen amount (maximum oxygen storage amount) that the first catalyst 53 can store, that is, the oxygen storage ability.
[0051]
On the other hand, a three-way catalyst such as the first catalyst 53 is deteriorated by poisoning by lead or sulfur contained in the fuel or by heat applied to the catalyst, and accordingly, the maximum oxygen storage amount gradually decreases. Even if the maximum oxygen storage amount decreases in this way, in order to prevent the emission amount of the harmful gas component from increasing, the average value of the air-fuel ratio of the gas discharged from the first catalyst 53 (the first catalyst It is considered that it is preferable to control so that the central air-fuel ratio of the gas flowing into the fuel tank 53 is very close to the stoichiometric air-fuel ratio.
[0052]
Therefore, the exhaust gas purification apparatus according to the first embodiment provides the first to third catalyst downstream air-fuel ratio sensors 67 to 69 such that the center air-fuel ratio of the exhaust gas flowing into the first catalyst 53 becomes a value near the stoichiometric air-fuel ratio. One of the outputs voxs1, vosx2, voxs3 of the above is selected as the control air-fuel ratio sensor output voxs as described later, and the selected air-fuel ratio sensor output voxs is substantially equal to the stoichiometric air-fuel ratio. ) The air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled so that voxref is obtained.
[0053]
More specifically, when the selected air-fuel ratio sensor output voxs becomes a value representing an air-fuel ratio leaner than the stoichiometric air-fuel ratio, the selected air-fuel ratio sensor output voxs and a target output voxref substantially corresponding to the stoichiometric air-fuel ratio are obtained. Is obtained by performing a proportional / integral process (PI process) to obtain the sub feedback control amount vafsfb, and corrects the output vabyfs of the uppermost stream air-fuel ratio sensor 66 by the sub feedback control amount vafsfb, thereby supplying the output to the engine. The air-fuel ratio of the air-fuel mixture is set to be apparently leaner than the air-fuel ratio detected by the uppermost-stream air-fuel ratio sensor 66, and the corrected apparent air-fuel ratio is set to the target air-fuel ratio (the target air-fuel ratio of the engine, The air-fuel ratio of the air-fuel mixture is feedback-controlled so as to achieve the stoichiometric air-fuel ratio.
[0054]
Similarly, when the selected air-fuel ratio sensor output voxs becomes a value representing an air-fuel ratio richer than the stoichiometric air-fuel ratio, the deviation between the selected air-fuel ratio sensor output voxs and the target output voxref substantially corresponding to the stoichiometric air-fuel ratio is proportionally calculated. An integration process (PI process) is performed to obtain a sub-feedback control amount vafsfb, and the output vabyfs of the uppermost-stream air-fuel ratio sensor 66 is corrected by the same sub-feedback control amount vafsfb. The fuel ratio is set to be apparently richer than the air-fuel ratio detected by the uppermost stream air-fuel ratio sensor 66, and the corrected apparent air-fuel ratio is the target air-fuel ratio (the target air-fuel ratio of the engine, here, the stoichiometric air-fuel ratio). The air-fuel ratio of the air-fuel mixture is feedback-controlled so that As described above, the center air-fuel ratio of the exhaust gas flowing into the first catalyst 53 is matched with the target air-fuel ratio (substantially the stoichiometric air-fuel ratio).
[0055]
By the way, since the first catalyst 53 has the above-described oxygen storage function, a change in the air-fuel ratio of the exhaust gas upstream of the first catalyst 53 does not immediately appear in the first catalyst downstream air-fuel ratio sensor output voxs1. In other words, the first catalyst downstream air-fuel ratio sensor output voxs1 has a value corresponding to the temporal average value of the air-fuel ratio of the exhaust gas flowing into the first catalyst 53. Therefore, the first catalyst is controlled by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so that the first catalyst downstream air-fuel ratio sensor output voxs1 matches a predetermined target output (for example, an output corresponding to the stoichiometric air-fuel ratio). It is possible to control the central air-fuel ratio of the gas flowing into 53 to a desired value.
[0056]
However, if the maximum oxygen storage amount of the first catalyst 53 is smaller than a predetermined threshold value because the first catalyst 53 has deteriorated or the temperature of the first catalyst 53 is low immediately after the engine is started, The change in the air-fuel ratio of the exhaust gas upstream of the first catalyst 53 immediately appears in the output voxs1 of the first catalyst downstream air-fuel ratio sensor. Even in such a case, if the above-described air-fuel ratio feedback control is performed, the first The air-fuel ratio of the exhaust gas upstream of the catalyst 53 hunts, and as a result, the center air-fuel ratio of the exhaust gas flowing into the first catalyst 53 may deviate from the stoichiometric air-fuel ratio. In other words, in the sub-feedback control using the sub-feedback control amount vafsfb determined based on the first catalyst downstream air-fuel ratio sensor output voxs1, the maximum oxygen storage amount indicating the oxygen storage capacity of the first catalyst 53 is smaller than a predetermined threshold. This control is established only when it is larger.
[0057]
Therefore, when the maximum oxygen storage amount Cmax1 of the first catalyst 53 is larger than the predetermined threshold value Cth, the present exhaust gas purification apparatus uses the output voxs1 of the first catalyst downstream air-fuel ratio sensor 67 as the maximum oxygen storage amount Cmax1 of the first catalyst 53. Is smaller than the predetermined threshold value Cth and the sum (Cmax1 + Cmax2) of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54 is larger than the predetermined threshold value Cth, The output voxs2 of the fuel ratio sensor 68 and the total value (Cmax1 + Cmax2) of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54 are obtained. The total value of the respective maximum oxygen storage amounts of the first catalyst to the third catalyst is smaller than the predetermined threshold value Cth ( When (max1 + Cmax2 + Cmax3) is larger than the predetermined threshold value Cth, the output voxs3 of the third catalyst downstream air-fuel ratio sensor 69 is selected as the air-fuel ratio sensor output voxs, and the sub feedback control is performed based on the selected control air-fuel ratio sensor output voxs. The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled by obtaining the amount vafsfb.
[0058]
As a result, the catalyst device including one or more catalysts upstream of the air-fuel ratio sensor selected as the control air-fuel ratio sensor has a maximum oxygen storage amount (oxygen storage capacity) larger than a predetermined threshold value Cth. In addition, a change in the air-fuel ratio of the gas upstream of the catalyst device does not immediately appear in the output voxs of the control air-fuel ratio sensor. In other words, the output voxs of the control air-fuel ratio sensor indicates a value corresponding to the center air-fuel ratio of the gas flowing into the catalyst device. Therefore, by the air-fuel ratio feedback control based on the output voxs of the control air-fuel ratio sensor, the air-fuel ratio of the gas flowing into the catalyst device is stably controlled to a predetermined target air-fuel ratio without hunting. The emission amount of harmful components such as CO and NOx can be reduced.
[0059]
(Actual operation of the first embodiment)
Next, the actual operation of the exhaust gas purification device according to the first embodiment will be described.
<Air-fuel ratio feedback control>
The CPU 71 executes a routine for calculating the final fuel injection amount Fi and instructing the fuel injection shown in the flowchart in FIG. 4 by setting the crank angle of each cylinder to a predetermined crank angle before each intake top dead center (for example, BTDC 90 ° CA). Is executed repeatedly every time. Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts the process from step 400 and proceeds to step 405, where the CPU 71 determines the value based on the intake air flow rate Ga measured by the air flow meter 61 and the engine speed NE. Then, a basic fuel injection amount Fbase for obtaining the stoichiometric air-fuel ratio of the air-fuel mixture of the mixture supplied to the engine is obtained. Specifically, the in-cylinder intake air amount Mc is calculated by dividing the value obtained by performing the first-order lag processing on the intake air flow rate Ga measured by the air flow meter 61 by the engine rotation speed NE, and calculating the target air-fuel ratio. The basic fuel injection amount Fbase is obtained by a function f divided by the theoretical air-fuel ratio.
[0060]
Next, the CPU 71 proceeds to step 410, and sets a value obtained by adding an air-fuel ratio feedback correction amount (main feedback control amount) DFi described later to a value obtained by multiplying the basic fuel injection amount Fbase by the coefficient K as the final fuel injection amount Fi. The value of the coefficient K is usually “1.00”, and as will be described later, when the air-fuel ratio is forcibly changed in order to obtain the maximum oxygen storage amounts Cmax1 to Cmax3, a value other than “1.00” is used. Is set to a predetermined value.
[0061]
Next, the CPU 71 proceeds to step 415, and instructs the injector 39 to inject fuel of the same final fuel injection amount Fi in step 415. Thereafter, the CPU 71 proceeds to step 420, and sets a value obtained by adding the final fuel injection amount Fi to the total fuel injection amount mfr at that time as a new fuel injection amount integrated value mfr. The fuel injection amount integrated value mfr is used when calculating an oxygen storage amount described later. Thereafter, the CPU 71 proceeds to step 495, and ends this routine once. As described above, the fuel of the final fuel injection amount Fi subjected to the feedback correction is injected into the cylinders that are in the intake stroke. Step 425 of setting a value obtained by adding the final fuel injection amount Fi to the total fuel injection amount mfr1 at that time to a new fuel injection amount integrated value mfr1 is performed in another embodiment such as a second embodiment described later. This is a necessary step and is not used in the first embodiment.
[0062]
Next, the calculation of the main feedback control amount DFi will be described. The CPU 71 repeatedly executes the routine shown by the flowchart in FIG. 5 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 500 and proceeds to step 505 to determine whether the air-fuel ratio feedback control condition (main feedback condition) is satisfied. The air-fuel ratio feedback control condition is, for example, that the cooling water temperature THW of the engine is equal to or higher than a first predetermined temperature, and the amount of intake air per one rotation of the engine (load, cylinder intake air amount Mc) is equal to or less than a predetermined value. The condition is satisfied when the upstream-most air-fuel ratio sensor 66 is normal (including the active state) and the value of the air-fuel ratio compulsory setting control execution flag XHAN described later is “0”. When the value of the air-fuel ratio compulsory setting control execution flag XHAN is “1”, air-fuel ratio control (active control) for forcibly changing the air-fuel ratio for calculating the maximum oxygen storage amounts Cmax1 to Cmax3 is executed. When the value is "0", it indicates that the air-fuel ratio control for calculating the maximum oxygen storage amounts Cmax1 to Cmax3 has not been executed.
[0063]
Now, assuming that the air-fuel ratio feedback control condition is satisfied, the CPU 71 determines “Yes” in step 505 and proceeds to step 510, where the output Vabyfs of the most upstream air-fuel ratio sensor 66 at the present time and the output The air-fuel ratio abyfs for main feedback control of the first catalyst 53 at the present time is obtained by converting the sum (vabyfs + vafsfb) with the sub-feedback control amount vafsfb based on the map shown in FIG. The main feedback control air-fuel ratio abyfs is the above-mentioned “apparent air-fuel ratio” upstream of the first catalyst 53 obtained by correcting the output of the most upstream air-fuel ratio sensor 66 with the sub-feedback control amount vafsfb.
[0064]
Next, the CPU 71 proceeds to step 515, and calculates the in-cylinder intake air amount Mc (k−N) that is the intake air amount of the cylinder that has reached the intake stroke N strokes (N intake strokes) before the current time. By dividing by the main feedback control air-fuel ratio abyfs, the in-cylinder fuel supply amount Fc (k−N) N strokes before the current 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.
[0065]
As described above, in order to obtain the in-cylinder fuel supply amount Fc (k−N) N strokes before the current time, the in-cylinder intake air amount Mc (k−N) N strokes before the current time is determined by the main feedback control air-fuel ratio. The reason for dividing by abyfs is that it takes a time corresponding to N strokes for the air-fuel mixture burned in the combustion chamber 25 to reach the most upstream air-fuel ratio sensor 66. The in-cylinder intake air amount Mc is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.
[0066]
Next, the CPU 71 proceeds to step 520 to increase the in-cylinder intake air amount Mc (k−N) N strokes before the current time by the target air-fuel ratio abyfr (k−N) at the time N strokes before the current time (in this example, theoretically By dividing by the air-fuel ratio, the target in-cylinder fuel supply amount Fcr (k−N) N strokes before the current time is obtained. Then, the CPU 71 proceeds to step 525 and sets 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 before the N stroke. Next, the CPU 71 proceeds to step 530 to obtain the main feedback control amount DFi based on the following equation (1).
[0067]
(Equation 1)
DFi = (Gp · DFc + Gi · SDFc) · KFB
[0068]
In the above formula 1, Gp is a preset proportional gain (proportional constant), and Gi is a preset integral gain (integral constant). It is preferable that the coefficient KFB in Equation 1 is 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 535. That is, the CPU 71 adds, in step 535, the in-cylinder fuel supply amount deviation DFc obtained in step 525 to the integrated value SDFc of the in-cylinder fuel supply amount deviation DFc at that point, and obtains a new in-cylinder fuel supply amount deviation. Is obtained, and the routine is terminated once in step 595.
[0069]
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 in step 410 of FIG. 4 described above. Is feedback-controlled 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.
[0070]
On the other hand, if the air-fuel ratio feedback control condition is not satisfied at the time of determination in step 505, the CPU 71 determines “No” in step 505 and proceeds to step 540, and sets the value of the main feedback control amount DFi to “0”. , And then the process proceeds to step 595 to end this routine once. As described above, when the air-fuel ratio feedback control condition is not satisfied (including the execution of the air-fuel ratio compulsory setting control), the air-fuel ratio (basic fuel injection amount Fbase) is corrected by setting the main feedback control amount DFi to “0”. Absent.
[0071]
Next, the air-fuel ratio feedback control (sub-feedback control) based on the air-fuel ratio sensor output voxs of any one of the first to third catalyst downstream air-fuel ratio sensors 67 to 69 will be described. By this sub-feedback control, the sub-feedback control amount vafsfb is calculated.
[0072]
The CPU 71 executes a routine shown in FIG. 6 for selecting the control air-fuel ratio sensor output voxs used for obtaining the sub feedback control amount vafsfb every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 600, and in step 605, the maximum oxygen storage amount Cmax1 of the first catalyst 53, which indicates the oxygen storage capacity of the first catalyst 53, is larger than the predetermined threshold Cth. If it is determined “Yes” in step 605, the process proceeds to step 610 to set the first catalyst downstream air-fuel ratio sensor output voxs1 as the control air-fuel ratio sensor output voxs (control air-fuel ratio). The first catalyst downstream air-fuel ratio sensor 67 is selected as a sensor), and the routine proceeds to step 695, where the present routine is temporarily ended. Note that the maximum oxygen storage amounts Cmax1, Cmax2, and Cmax3 are separately obtained by a routine described later.
[0073]
On the other hand, when the CPU 71 determines “No” in step 605, the process proceeds to step 615, where the total value (Cmax1 + Cmax2) of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54 is determined. It is determined whether or not the value is greater than a predetermined threshold value Cth. If “Yes” is determined in step 615, the process proceeds to step 620 to set the second catalyst downstream air-fuel ratio sensor output voxs2 as the control air-fuel ratio sensor output voxs. (The second catalyst downstream air-fuel ratio sensor 68 is selected as the control air-fuel ratio sensor), and the routine proceeds to step 695, where the present routine is temporarily terminated.
[0074]
When the CPU 71 determines “No” in step 615, the process proceeds to step 625 and determines whether the total value (Cmax1 + Cmax2 + Cmax3) of the maximum oxygen storage amounts of the first to third catalysts is greater than the predetermined threshold Cth. If it is determined as “Yes” in step 625, the process proceeds to step 630 to set the third catalyst downstream air-fuel ratio sensor output voxs3 as the control air-fuel ratio sensor output voxs (control air-fuel ratio sensor). Is selected as the third catalyst downstream air-fuel ratio sensor 69), the routine proceeds to step 695, and this routine is temporarily ended.
[0075]
Further, when determining “No” in step 625, the CPU 71 proceeds to step 635 and sets the sub feedback control target output voxref as the control air-fuel ratio sensor output voxs. As described above, the sub-feedback control is a control in which the deviation between the air-fuel ratio sensor output voxs and the target output voxref is reduced by the PI control. Therefore, the sub-feedback control is substantially stopped by the processing in step 635. It becomes.
[0076]
Further, the CPU 71 executes the routine shown in FIG. 7 every time a predetermined time equal to the execution time interval of the routine shown in FIG. 6 elapses in order to obtain the sub-feedback control amount vafsfb. Therefore, at a predetermined timing, the CPU 71 starts the process from step 700 and proceeds to step 705 to determine whether the sub feedback control condition is satisfied. The sub-feedback control conditions include, for example, the air-fuel ratio feedback control condition in step 505 described above, and when the cooling water temperature THW of the engine is equal to or higher than a second predetermined temperature higher than the first predetermined temperature, and This is established when the catalyst downstream air-fuel ratio sensors 67 to 69 are normal (including an active state).
[0077]
Now, assuming that the sub-feedback control condition is satisfied, the CPU 71 determines “Yes” in step 705 and proceeds to step 710, where the CPU 71 determines the selected control signal from the target output voxref of the air-fuel ratio sensor. By subtracting the air-fuel ratio sensor output voxs, an output deviation amount Dvoxs is obtained. The target output voxref is determined so that the purification efficiency of the first catalyst 53 is good (best), and is set here to a constant value corresponding to the stoichiometric air-fuel ratio. Note that the target output voxref may be variable according to the selected control sensor.
[0078]
Next, the CPU 71 proceeds to step 715, and obtains the sub feedback control amount vafsfb based on the following equation (2). The proportional gain Kp and the integral gain Ki in Equation 2 may be fixed values, and are variable according to the selected control sensor (for example, values that increase as the downstream air-fuel ratio sensor is selected). Is also good. This is because, for example, the exhaust passage length from the upstream position of the first catalyst 53 to the selected air-fuel ratio sensor is different, the fluctuation of the air-fuel ratio upstream of the first catalyst 53 is selected by the selected air-fuel ratio sensor. This is because the dead time of control until it appears in the output voxs differs.
[0079]
(Equation 2)
vafsfb = Kp · Dboxs + Ki · SDboxes
[0080]
In the above equation 2, SDvoxs is an integrated value of the output deviation amount Dvoxs, and is a value updated in the next step 720. That is, when the CPU 71 proceeds to step 720, the CPU 71 adds the output deviation amount Dvoxs obtained in step 710 to the integrated value SDvoxs of the output deviation amount at that time to obtain a new integrated value SDvoxs of the output deviation amount. Then, the routine proceeds to step 795, and this routine is temporarily ended. As described above, the sub feedback control amount vafsfb is obtained.
[0081]
On the other hand, when the sub-feedback control condition is not satisfied, the CPU 71 determines “No” in step 705 and proceeds to step 725, and in step 725, sets the sub-feedback control amount vafsfb to “0”. Thus, the sub-feedback control based on the selected control air-fuel ratio sensor output voxs is stopped.
[0082]
(Maximum oxygen storage amount acquisition control for calculating maximum oxygen storage amounts Cmax1 to Cmax3)
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 by the flowcharts of FIGS. 8 to 13 every time a predetermined time elapses.
[0083]
Accordingly, at a predetermined timing, the CPU 71 starts the process from step 800 in FIG. 8 and proceeds to step 805 to determine whether or not the value of the maximum oxygen storage amount acquisition control execution flag XHAN is “0”. . Now, if the description is continued assuming that the maximum oxygen storage amount acquisition control for calculating the maximum oxygen storage amount is not performed and the start condition of the maximum oxygen storage amount acquisition control start condition is not satisfied, the maximum oxygen storage amount acquisition control is executed. The value of the middle flag XHAN is “0”. Therefore, the CPU 71 determines “Yes” in step 805 and proceeds to step 810, and sets the value of the coefficient K used in step 410 of FIG. 4 described above to 1.00.
[0084]
Next, in step 815, the CPU 71 determines whether or not a condition for starting the maximum oxygen storage amount acquisition control is satisfied. The start condition of the maximum oxygen storage amount acquisition control is that the cooling water 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 degree TA per unit time. The condition that the engine is in steady operation, such as the amount of change being equal to or less than the predetermined amount, is satisfied, and all of the first to third catalyst downstream air-fuel ratio sensor outputs voxs1, voxs2, voxs3 are richer than the stoichiometric air-fuel ratio. This is established when an output corresponding to an appropriate air-fuel ratio 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 of the maximum oxygen storage amount acquisition control is not satisfied, the CPU 71 determines “No” in step 815, proceeds to step 895, and ends this routine once.
[0085]
Next, although the maximum oxygen storage amount acquisition control is not performed at this time, the description is continued assuming that the start condition of the maximum oxygen storage amount acquisition control is satisfied. In this case, the CPU 71 determines “Yes” in step 805. Then, the process proceeds to step 810, where the value of the coefficient K is set to 1.00. Next, since the start condition is satisfied, the CPU 71 determines “Yes” in step 815 and proceeds to step 820, and in step 820, sets the value of the maximum oxygen storage amount acquisition control execution flag XHAN to “1”. To "."
[0086]
Then, the CPU 71 proceeds to step 825, sets the value of Mode to “1” in order to shift to the first mode, sets the value of the coefficient K to 0.98 in the following step 830, and proceeds to step 895. To end this routine once. As a result, the above-described air-fuel ratio feedback control condition is not satisfied, so the CPU 71 determines “No” in step 505 of FIG. 5 and proceeds to step 540, and the value of the air-fuel ratio feedback correction amount DFi is “ 0 "is set. As a result, by executing step 410 in FIG. 4, a value obtained by multiplying the basic fuel injection amount Fbase by 0.98 is calculated as the final fuel injection amount Fi, and the fuel having the final fuel injection amount Fi is injected. The air-fuel ratio of the air-fuel mixture supplied to the first catalyst 53 (therefore, the air-fuel ratio of the gas flowing into the first catalyst 53) is controlled to a predetermined lean air-fuel ratio leaner than the stoichiometric air-fuel ratio.
[0087]
Thereafter, the CPU 71 repeatedly executes the processing of the routine in FIG. 8 from step 800. However, since the value of the maximum oxygen storage amount acquisition control execution flag XHAN is “1”, “No” is determined in step 805. After the determination, the process immediately proceeds to step 895, and this routine is temporarily ended.
[0088]
On the other hand, the CPU 71 repeatedly executes the first mode control routine shown in FIG. 9 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 900 and proceeds to step 905, where the CPU 71 determines whether or not the value of the Mode is “1”. At this time, if the value of Mode is not “1”, the CPU 71 immediately proceeds to step 995 to end this routine once. Hereinafter, the description will be continued on the assumption that the value of Mode has been changed to “1” by the process of step 825 in FIG. 8 above. In this case, the CPU 71 determines “Yes” in step 905 and proceeds to step 910. The first catalyst downstream air-fuel ratio sensor output voxs1, the second catalyst downstream air-fuel ratio sensor output voxs2, and the third catalyst downstream air-fuel ratio sensor output voxs3 all correspond to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. It is determined whether or not the output (output when oxygen is excessively present) is obtained.
[0089]
At this time, since the air-fuel ratio of the air-fuel mixture supplied to the engine has just been changed to the predetermined lean air-fuel ratio, the first catalyst downstream air-fuel ratio sensor output voxs1, the second catalyst downstream air-fuel ratio sensor output voxs2, and the third Since not all of the catalyst downstream air-fuel ratio sensor outputs voxs3 are outputs corresponding to air-fuel ratios leaner than the stoichiometric air-fuel ratio, the CPU 71 determines “No” in step 910, and determines “No” in step 995. The routine ends once.
[0090]
Thereafter, the CPU 71 repeatedly executes steps 900 to 910 in FIG. Further, since the air-fuel ratio is maintained at a predetermined lean air-fuel ratio, the respective oxygen storage amounts of the first catalyst 53, the second catalyst 54, and the third catalyst 55 are sequentially increased over time with the passage of time. Reach the quantity. Accordingly, the first catalyst downstream air-fuel ratio sensor output voxs1, the second catalyst downstream air-fuel ratio sensor output voxs2, and the third catalyst downstream air-fuel ratio sensor output voxs3 correspond to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. Output. Accordingly, when the CPU 71 proceeds to step 910, the CPU 71 determines “Yes” in step 910, proceeds to step 915, sets the mode value to “2” in step 915, and proceeds to step 920. Then, the value of the coefficient K is set to 1.02, and thereafter, the routine is temporarily ended in step 995. 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 richer than the stoichiometric air-fuel ratio.
[0091]
Further, the CPU 71 repeatedly executes the second mode control routine shown by the flowchart in FIG. 10 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1000, and determines in step 1005 whether or not the value of Mode is “2”. The routine proceeds from step 1005 to step 1095 to terminate the present routine once.
[0092]
On the other hand, when the value of the Mode is changed to “2” by the processing of the previous step 915, the CPU 71 determines “Yes” when the processing proceeds to step 1005, proceeds to step 1010, and proceeds to step 1010 where 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 has just been changed to the predetermined rich air-fuel ratio, the CPU 71 determines “No” in step 1010, proceeds to step 1095, and ends this routine once.
[0093]
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 after a predetermined period of time, the air-fuel ratio becomes higher. The oxygen storage amount of one catalyst 53 reaches “0”. As a result, unburned HC and CO begin to flow out of 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. Thus, when the CPU 71 proceeds to step 1010, the CPU 71 determines “Yes” in step 1010, proceeds to step 1015, changes the value of Mode to “3” in step 1015, and The routine ends once.
[0094]
Similarly, in the third mode control routine shown in the flowchart of FIG. 11 that is repeatedly executed every predetermined time, the CPU 71 determines whether or not the value of Mode is “3” in step 1105. If the value of is not "3", the process proceeds from step 1105 to step 1195 to end this routine once.
[0095]
On the other hand, when the value of the Mode is changed to “3” by the processing of the previous step 1015, the CPU 71 determines “Yes” when proceeding to step 1105, proceeds to step 1110, and proceeds to step 1110, where 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, the unburned HC and CO have just started flowing out of the first catalyst 53, and since the unburned HC and CO have not flowed out of the second catalyst 54, the CPU 71 determines “No” in step 1110. , And the process proceeds to step 1195 to end this routine once.
[0096]
Thereafter, since the air-fuel ratio of the air-fuel mixture supplied to the engine is continuously maintained at the predetermined rich air-fuel ratio, the oxygen stored in the second catalyst 54 is consumed, and when a predetermined time elapses, The oxygen storage amount of the second catalyst 54 reaches “0”. As a result, unburned HC and CO begin to flow out of the second catalyst 54, so that the output voxs2 of the second catalyst downstream air-fuel ratio sensor 68 becomes 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. Accordingly, the CPU 71 determines “Yes” in step 1110 and proceeds to step 1115, sets the value of Mode to “4” to shift to the fourth mode, and proceeds to step 1195.
[0097]
Similarly, in the fourth mode control routine shown in the flowchart of FIG. 12 which is repeatedly executed every predetermined time, the CPU 71 determines in step 1205 whether or not the value of Mode is “4”. If the value of is not "4", the process proceeds from step 1205 to step 1295 to end this routine once.
[0098]
On the other hand, when the value of the Mode is changed to “4” by the processing of the previous step 1115, the CPU 71 determines “Yes” when proceeding to step 1205, proceeds to step 1210, and proceeds to step 1210, where It is determined whether or not the output voxs3 of the downstream air-fuel ratio sensor 69 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 unburned HC and CO have just started flowing out of the second catalyst 54 and the unburned HC and CO have not flowed out of the third catalyst 55, the CPU 71 returns “No” in step 1210. Then, the process proceeds to step 1295 to end this routine once.
[0099]
Thereafter, since the air-fuel ratio of the air-fuel mixture supplied to the engine is continuously maintained at the predetermined rich air-fuel ratio, the oxygen stored in the third catalyst 55 is consumed, and when a predetermined time elapses, The oxygen storage amount of the third catalyst 55 reaches “0”. As a result, unburned HC and CO begin to flow out of the third catalyst 55, so that the output voxs3 of the third catalyst downstream air-fuel ratio sensor 69 becomes 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. Accordingly, the CPU 71 proceeds from step 1210 to step 1215, resets the value of Mode to “0”, and sets the value of the flag XHAN during execution of the maximum oxygen storage amount acquisition control to “0” in subsequent step 1220. Then, the routine proceeds to step 1295, and this routine is temporarily ended.
[0100]
In such a state, when executing the routine in FIG. 8, the CPU 71 determines “Yes” in step 805 and proceeds to step 810, so that the value of the coefficient K is returned to 1.00. If the air-fuel ratio feedback control condition is satisfied, the CPU 71 determines “Yes” in step 505 of the routine of FIG. 5 and step 705 of the routine of FIG. 7, so that the air-fuel ratio feedback control (main feedback control and Sub-feedback control) is resumed.
[0101]
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 one by one in the order of a predetermined lean air-fuel ratio and a predetermined rich air-fuel ratio. Controlled.
[0102]
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 by the flowchart in FIG. 13 every time a predetermined time (calculation period tsample) elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1300, proceeds to step 1305, and obtains the oxygen storage amount change amount ΔO2 by the following equation (3).
[0103]
[Equation 3]
ΔO2 = 0.23 · mfr · (stoich-abyfsave)
[0104]
In the above Equation 3, 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 the average value of the air-fuel ratio A / F detected by the most upstream air-fuel ratio sensor 66 during the predetermined time tsample. As shown in Expression 3, by multiplying the total amount mfr of the injection amount within the predetermined time tsample by the deviation (stoichi-abysave) of the average value of the detected air-fuel ratio A / F from the stoichiometric air-fuel ratio. , The amount of air consumption (deficient amount) at the same predetermined time tsample is obtained. By multiplying the consumption of air by the weight ratio of oxygen, the consumption of oxygen (the amount of change in oxygen storage amount ΔO2) at the same predetermined time tsample is obtained.
[0105]
Next, the CPU 71 proceeds to step 1310 to determine whether or not the value of Mode is “2” (whether or not the mode is the second mode). If the value of Mode is “2”, the process proceeds to step 1310. The determination is "Yes" and the routine proceeds to step 1315, where a value obtained by adding the oxygen storage amount change amount .DELTA.O2 to the oxygen storage amount OSA1 at that time is set as a new oxygen storage amount OSA1, and then the routine proceeds to step 1340.
[0106]
Such a process (steps 1300 to 1315) is repeatedly executed as long as the value of Mode is “2”. As a result, in the second mode (Mode = 2) in which the air-fuel ratio upstream of the first catalyst 53 is set to a predetermined rich air-fuel ratio, the oxygen storage amount OSA1 of the first catalyst 53 is calculated. This is because in the second mode, the oxygen stored in the first catalyst 53 is consumed. If the determination in step 1310 is “No”, the CPU 71 proceeds directly from step 1310 to step 1320.
[0107]
When the CPU 71 proceeds to step 1320, the CPU 71 determines whether or not the value of Mode is “3” (whether or not the mode is the third mode). If the value of Mode is “3”, the process proceeds to step 1320. Then, the process proceeds to step 1325, and a value obtained by adding the oxygen storage amount change amount ΔO2 to the oxygen storage amount OSA2 at that time is set as a new oxygen storage amount OSA2, and thereafter, the process proceeds to step 1340.
[0108]
Such measures (steps 1300, 1305, 1310, 1320, 1325) are repeatedly executed as long as the value of Mode is “3”. As a result, in the third mode (Mode = 3) in which the air-fuel ratio upstream of the first catalyst 53 is set to a predetermined rich air-fuel ratio, the oxygen storage amount OSA2 of the second catalyst 54 is calculated. This is because in the third mode, the oxygen stored in the second catalyst 54 is consumed.
[0109]
If the determination in step 1320 is “No”, the CPU 71 proceeds from step 1320 to step 1330 to determine whether the value of Mode is “4” (whether the mode is the fourth mode). If the value of Mode is “4”, the process proceeds to step 1335 to set a value obtained by adding the oxygen storage amount change amount ΔO2 to the oxygen storage amount OSA3 at that time as a new oxygen storage amount OSA3, and thereafter Proceed to step 1340.
[0110]
Such measures (steps 1300, 1305, 1310, 1320, 1330, 1335) are repeatedly executed as long as the value of Mode is “4”. As a result, in the fourth mode (Mode = 4) in which the air-fuel ratio upstream of the first catalyst 53 is a predetermined rich air-fuel ratio, the oxygen storage amount OSA3 of the third catalyst 55 is calculated. This is because in the fourth mode, the oxygen stored in the third catalyst 55 is consumed. If the determination in step 1330 is “No”, the CPU 71 proceeds directly from step 1330 to step 1340.
[0111]
Then, when proceeding to step 1340, the CPU 71 sets the total amount mfr of the fuel injection amount Fi to “0”, and then proceeds to step 1395 to end this routine once.
[0112]
Next, the operation in calculating the maximum oxygen storage amount will be described. The CPU 71 executes the routine shown by the flowchart of FIG. 14 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1400 in FIG. 14 and proceeds to step 1405 to determine whether the value of the maximum oxygen storage amount acquisition control execution flag XHAN has changed from “1” to “0”. Determine whether or not. At this time, if the value of the maximum oxygen storage amount acquisition control execution flag XHAN has not changed from “1” to “0”, the CPU 71 proceeds directly from step 1405 to step 1495 and ends this routine once.
[0113]
On the other hand, if the value of the maximum oxygen storage amount acquisition control execution flag XHAN is changed to “0” in step 1220 of FIG. 12 described above (that is, immediately after the fourth mode ends), the CPU 71 When the process proceeds to step 1405, "Yes" is determined in step 1405, and the process proceeds to step 1410, in which the oxygen storage amounts OSA1 to OSA3 at that time are determined by the maximum oxygen storage amounts of the first to third catalysts 53 to 55. They are stored as Cmax1 to Cmax3, respectively. Next, the CPU 71 proceeds to step 1415 to clear all the oxygen storage amounts OSA1 to OSA3 to “0”, proceeds to step 1495, and ends this routine once. Thus, the maximum oxygen storage amounts Cmax1 to Cmax3 are obtained.
[0114]
As described above, the exhaust gas purification apparatus according to the first embodiment includes a plurality of catalysts (the first catalyst 53, the second catalyst 54, and the third catalyst 55) disposed in series in the exhaust passage of the internal combustion engine. A plurality of air-fuel ratio sensors (a first catalyst downstream air-fuel ratio sensor 67, a second catalyst downstream air-fuel ratio sensor 68, a third catalyst downstream air-fuel ratio) disposed downstream of each of the plurality of catalysts and disposed in the exhaust passage. Sensor 69).
[0115]
Further, this exhaust gas purification device is configured from the first catalyst (first catalyst 53) to the n-th catalyst which is the most upstream catalyst among the plurality of catalysts when the value n is a natural number. A catalyst device (that is, a catalyst device including only the first catalyst 53, a catalyst device including the first catalyst 53 and the second catalyst 54, and a catalyst device including three catalysts of the first catalyst to the third catalyst 53 to 55) ) (The maximum oxygen storage amount Cmax1 of the first catalyst 53, the sum Cmax1 + Cmax2 of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54, the first catalyst 53, The oxygen storage capacity acquisition means (the routine shown in FIGS. 8 to 14 and the step 60 in FIG. 6) for acquiring the sum Cmax1 + Cmax2 + Cmax3 of the respective maximum oxygen storage amounts of the second catalyst 54 and the third catalyst 55. Comprises 615, and 625).
[0116]
Further, the exhaust purification device is determined to have an oxygen storage capacity that is greater than the predetermined oxygen storage capacity based on the acquired value indicating the oxygen storage capacity (any one of the maximum oxygen storage amounts Cmax1, Cmax1 + Cmax2, Cmax1 + Cmax2 + Cmax3). The n-th catalyst constituting the catalyst device having the smallest value n among the catalyst devices (the value of which is larger than the threshold value Cth) (when the catalyst interposed at the most upstream in the exhaust passage is the first catalyst, Downstream (from the first catalyst to the n-th catalyst counted from the first catalyst) (downstream, and when the (n + 1) -th catalyst is present, the exhaust passage upstream of the (n + 1) -th catalyst) The gas flowing into the first catalyst 53 is controlled so that the output of one of the plurality of air-fuel ratio sensors 67 to 69 is a predetermined target output. Air-fuel ratio control means for controlling the fuel ratio (actually the air-fuel ratio of the air-fuel mixture supplied to the engine; the same applies hereinafter) (the control air-fuel ratio sensor (output) determination / selection routine shown in FIG. 6; An air-fuel ratio feedback control routine (main feedback control and sub-feedback control) achieved by the routines shown in FIG. 4, FIG. 5, and FIG.
[0117]
Therefore, in such an exhaust purification device, the catalyst device located upstream of the air-fuel ratio sensor used for the air-fuel ratio feedback control has a large oxygen storage capacity (maximum oxygen storage amount) that does not cause the feedback control to fail. ), Hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided.
[0118]
In the routine shown in FIG. 6, the maximum oxygen storage amount Cmax1 of the first catalyst 53, which is a value indicating the oxygen storage capacity, the total value of the maximum oxygen storage amounts of the first catalyst 53 and the second catalyst 54 (Cmax1 + Cmax2), Although the control air-fuel ratio sensor output voxs is selected based on the total value (Cmax1 + Cmax2 + Cmax3) of the maximum oxygen storage amounts of the first to third catalysts 53 to 55, the value indirectly indicates the oxygen storage capacity. (A value having a certain correlation with the maximum oxygen storage amount of the target catalyst or the catalyst device), the control air-fuel ratio sensor output voxs based on the travel distance of the vehicle, the temperature of each catalyst, the intake air flow rate Ga, and the like. May be selected.
[0119]
In this case, when the traveling distance is shorter than the first traveling distance, the first catalyst downstream air-fuel ratio sensor output voxs1 is set to be shorter than the second traveling distance whose traveling distance is longer than the first traveling distance and longer than the first traveling distance. In this case, the second catalyst downstream air-fuel ratio sensor output voxs2 is selected as the control catalyst air-fuel ratio sensor output voxs2 when the travel distance is longer than the second travel distance. It is preferred to configure. This is because each catalyst deteriorates as the traveling distance increases, and the maximum oxygen storage amount decreases.
[0120]
When the control air-fuel ratio sensor output voxs is selected based on the catalyst temperature, when the temperature of the first catalyst 53 (first catalyst temperature) is higher than the first threshold temperature, the first catalyst downstream air-fuel ratio sensor output voxs1 is set. When the first catalyst temperature is lower than the first threshold temperature and higher than a second threshold temperature lower than the first threshold temperature, the second catalyst downstream air-fuel ratio sensor output voxs2 is output. When the temperature is lower than the threshold temperature of 2, it is preferable to select the third catalyst downstream air-fuel ratio sensor output voxs3 as the control air-fuel ratio sensor output voxs. This is because the maximum oxygen storage capacity of each catalyst decreases as the temperature of the first catalyst 53 decreases (therefore, the temperatures of the second catalyst 54 and the third catalyst 55 decrease).
[0121]
When the control air-fuel ratio sensor output voxs is selected based on the intake air flow rate Ga, if the intake air flow rate Ga is smaller than the first threshold flow rate, the first catalyst downstream air-fuel ratio sensor output voxs1 is converted to the intake air flow rate Gax. Is larger than the first threshold flow rate and smaller than the second threshold flow rate that is larger than the first threshold flow rate, the second catalyst downstream air-fuel ratio sensor output voxs2 is set to the same value as the intake air flow rate Ga is larger than the second threshold flow rate. In this case, it is preferable to select the third catalyst downstream air-fuel ratio sensor output voxs3 as the control air-fuel ratio sensor output voxs. This is because, as the intake air flow rate Ga increases, the amount of oxygen that can be stored by each catalyst (that is, the substantial maximum oxygen storage amount that is the maximum oxygen storage capacity) decreases.
[0122]
<Modification of First Embodiment>
Next, an exhaust emission control device according to a modification of the first embodiment will be described. This modification mainly has a point that the third catalyst 55 and the third catalyst downstream air-fuel ratio sensor 69 are not provided, and that the CPU 71 selects the control air-fuel ratio sensor output voxs instead of the routine shown in FIG. This embodiment differs from the first embodiment in that the routine shown by the flowchart in FIG. 15 is executed. Therefore, the following description will focus on such differences.
[0123]
In selecting the control air-fuel ratio sensor output voxs, the CPU 71 executes the routine shown in FIG. 15 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1500 and proceeds to step 1505 to determine whether the maximum oxygen storage amount Cmax1 of the first catalyst 53 is larger than a predetermined threshold Cth. At this time, if the maximum oxygen storage amount Cmax1 is larger than the predetermined threshold value Cth, the CPU 71 proceeds from step 1505 to step 1510 to set the first catalyst downstream air-fuel ratio sensor output voxs1 as the control air-fuel ratio sensor output voxs, and proceeds to step 1595. To end this routine once.
[0124]
On the other hand, if the maximum oxygen storage amount Cmax1 is smaller than (or less than) the predetermined threshold value Cth, the CPU 71 proceeds from step 1505 to step 1515 to set the second catalyst downstream air-fuel ratio sensor output voxs2 as the control air-fuel ratio sensor output voxs. Then, the routine proceeds to step 1595, and this routine is temporarily ended.
[0125]
Thus, the reason why the second catalyst downstream air-fuel ratio sensor output voxs2 is selected as the control air-fuel ratio sensor output voxs is that the oxygen storage capacity (maximum oxygen storage amount Cmax1) of the first catalyst 53 is a predetermined capacity (threshold Cth). If it is smaller, the catalyst device composed of the first catalyst 53 and the second catalyst 54 naturally has a larger oxygen storage capacity than the first catalyst 53. Since the thermal degradation and the poisoning of the first catalyst 53 progress more rapidly as they are disposed upstream, even if the oxygen storage capacity (maximum oxygen storage amount Cmax1) of the first catalyst 53 decreases due to the deterioration, the second catalyst This is because the oxygen storage capacity of 54 (maximum oxygen storage amount Cmax2) is considered to be maintained at a relatively large value.
[0126]
In this modified example, step 1015 in FIG. 10 is changed to a step of setting the value of the flag XHAN during execution of the maximum oxygen storage amount acquisition control to “0” (the same step as step 1220), and FIG. 12 is omitted, steps 1320 to 1335 in FIG. 13 are omitted, and the routine proceeds to step 1340 when “No” is determined in step 1310. Is desirable. Further, step 910 in FIG. 9 proceeds to step 915 when the first catalyst downstream air-fuel ratio sensor output voxs1 indicates an output corresponding to the lean air-fuel ratio, and to step 915 when the output voxs1 does not indicate an output corresponding to the lean air-fuel ratio. It is corrected so as to proceed to 995. In addition, in steps 1410 and 1415 of FIG. 14, the processing regarding OSA2, OSA3, Cmax2, and Cmax3 is omitted.
[0127]
As described above, the exhaust purification device according to the modified example of the first embodiment includes the first catalyst 53 and the second catalyst 54 that are provided in series in the exhaust passage, and the oxygen storage capacity of the first catalyst 53. The first catalyst oxygen storage capacity obtaining means (routine shown in FIGS. 8, 9, 10, 13, and 14) for obtaining the maximum oxygen storage amount Cmax1, which is a value representing When it is determined that the oxygen storage capacity of the first catalyst 54 is larger than the predetermined oxygen storage capacity (maximum oxygen storage amount Cmax1> threshold value Cth) based on the value representing the oxygen storage capacity of the catalyst 54, the first catalyst downstream air-fuel ratio The air-fuel ratio of the gas flowing into the first catalyst 53 is controlled so that the output voxs1 of the sensor 67 becomes a predetermined first target output voxref, and the oxygen storage capacity of the first catalyst 53 is smaller than the predetermined oxygen storage capacity. And judgment In this case, the gas flowing into the first catalyst 53 is set so that the output voxs2 of the second catalyst downstream air-fuel ratio sensor 54 becomes a predetermined second target output voxref (in this case, the same as the first target output). Air-fuel ratio control means for controlling the air-fuel ratio (the control air-fuel ratio sensor (output) determination / selection routine shown in FIG. 15 and the air-fuel ratio feedback achieved by the routines shown in FIGS. 4, 5 and 7) Control routine).
[0128]
Therefore, according to the present exhaust gas purification apparatus, when the first catalyst 53 has a predetermined oxygen storage capacity, the first catalyst 53 provided downstream of the first catalyst (catalyst device including the first catalyst) 53 is provided. Based on the catalyst downstream air-fuel ratio sensor output voxs1, otherwise, the first catalyst 53 based on the second catalyst downstream air-fuel ratio sensor output voxs2 disposed downstream of the catalyst device including the first catalyst 53 and the second catalyst 54. Since the air-fuel ratio of the gas flowing into the catalyst device is controlled, the center air-fuel ratio of the exhaust gas flowing into the catalyst device is controlled to a desired value stably (that is, without causing control failure such as generation of hunting). Exhaust gas can be effectively purified.
[0129]
In addition, in FIG. 15 of the modified example, a step of setting the first target output voxref1 to the target output voxref is added between step 1510 and step 1595, and the target output voxref is set between step 1515 and step 1595. A step of setting a second target output voxref2 having a value different from the first target output voxref1 to voxref may be added.
[0130]
In the routine shown in FIG. 15, the control air-fuel ratio sensor output voxs is selected based on the maximum oxygen storage amount Cmax1 of the first catalyst 53 which is a value indicating the oxygen storage capacity. The control air-fuel ratio sensor output voxs may be selected based on the indirectly indicated traveling distance of the vehicle, the temperature of the first catalyst 53, and the intake air flow rate Ga.
[0131]
In this case, when the traveling distance is shorter than the first traveling distance, the first catalyst downstream air-fuel ratio sensor output voxs1 is controlled, and when the traveling distance is longer than the first traveling distance, the second catalyst downstream air-fuel ratio sensor output voxs2 is controlled. It is preferable to select the air-fuel ratio sensor output voxs. When the temperature of the first catalyst 53 is higher than the first threshold temperature, the output voxs1 of the first catalyst downstream air-fuel ratio sensor is determined. When the temperature of the first catalyst 53 is lower than the first threshold temperature, the output voxs1 is determined. It is preferable to select the catalyst downstream air-fuel ratio sensor output voxs2 as the control air-fuel ratio sensor output voxs. Further, when the intake air flow rate Ga is smaller than the first threshold flow rate, the first catalyst downstream air-fuel ratio sensor output voxs1 is determined. When the intake air flow rate Ga is greater than the first threshold flow rate, the second catalyst downstream air-fuel ratio is determined. It is preferable that the sensor output voxs2 be selected as the control air-fuel ratio sensor output voxs.
[0132]
<Second embodiment>
Next, an exhaust emission control device according to a second embodiment of the present invention will be described. This exhaust gas purification apparatus performs control to maintain the oxygen storage amount, which is a value indicating the state of exhaust gas purification of the catalyst, at a predetermined value, and determines which catalyst has the controlled oxygen storage amount as the oxygen storage amount. It differs from the exhaust gas purification device according to the first embodiment mainly in that it is selected and that the oxygen storage amount is obtained using a catalyst model. Therefore, the following description will focus on such differences.
[0133]
<Catalyst model>
First, a description will be given of a catalyst model employed by the exhaust gas purification apparatus of the present embodiment. Generally, when a lean air-fuel ratio gas flows into the catalyst, more oxygen is stored upstream of the catalyst, and when a rich air-fuel ratio gas flows into the catalyst, the oxygen is stored from the upstream side of the catalyst. Oxygen is being consumed. Therefore, the oxygen stored in the catalyst is not uniformly distributed in the flow direction of the exhaust gas of the catalyst. Therefore, in order to accurately determine the oxygen storage amount in the catalyst, it is necessary to perform a calculation in consideration of the distribution of the stored oxygen.
[0134]
Further, the oxygen storage amount of the catalyst changes according to the degree of the oxygen storage / release reaction occurring in the catalyst. The degree of the oxygen storage / release reaction depends on the amount of the specific component related to the oxygen storage / release reaction contained in the exhaust gas flowing into the catalyst. Therefore, in order to accurately determine the oxygen storage amount of the catalyst, it is necessary to perform a calculation in consideration of the amount of the specific component. Therefore, the present apparatus calculates the oxygen storage amounts of the first to third catalysts 53 to 55 by applying the catalyst model described below to the first to third catalysts 53 to 55.
[0135]
In this catalyst model, as schematically shown in FIG. 16, a columnar catalyst having a constant cross section perpendicular to the axis is divided into N (plural) regions ("blocks") by a plane perpendicular to the coaxial line. ). That is, the catalyst targeted by the catalyst model is divided into N blocks along the flow direction of the exhaust gas. The length in the axial direction of each divided block is L. For convenience of explanation, each block is numbered sequentially from the upstream side along the flow direction of the exhaust gas as shown in FIG. In addition, variables and symbols related to an arbitrary i-th block are appended with (i) at the end.
[0136]
In this catalyst model, as shown in FIG. 17, the i-th block (i) (specific region) among the divided blocks is focused on and related to the oxygen storage / release reaction in the block (i). Consider the balance of the specific component per calculation cycle of the CPU 71. At this time, it is assumed that the three-way reaction, which is an oxidation / reduction reaction using a catalyst, is completed instantaneously and completely, and attention is paid only to the resulting oxygen storage / release reaction based on the excess / deficiency of oxygen. . Such an assumption (catalyst model) is realistic and has high calculation accuracy. The exhaust gas phase shown in FIG. 17 is a space through which the exhaust gas passes, and the coat layer is an active component made of a noble metal such as platinum (Pt) that generates a catalytic function and ceria (CeO) that generates an oxygen storage function. ₂ ) Is a layer in which components such as
[0137]
The specific component is, for example, oxygen (molecule) O ₂ May be a component selected from nitrogen oxides NOx, carbon monoxide CO, and hydrocarbon HC. However, in this catalyst model, the exhaust gas in a state where the three-way reaction is assumed to end instantaneously and completely is described. Oxygen (oxygen of oxygen molecules and nitrogen oxides. In this specification, oxygen of oxygen molecules and nitrogen oxides are collectively referred to as “oxygen”) (excess or insufficient) is selected as a specific component. I have. The oxygen amount CgO2, which is the amount of oxygen, is determined when the oxygen is excessive (that is, O ₂ And when NOx is excessively present, and becomes a negative value when the oxygen is insufficient (that is, when unburned HC and CO are excessively present in the exhaust gas). Is done.
[0138]
In the block (i) of interest, the amount of oxygen CgO2 flowing into the exhaust gas phase of the block (i) per calculation cycle of the CPU 71 is calculated as the amount of oxygen CginO2 (i) flowing into the exhaust gas phase of the block (i) per calculation cycle. The amount of oxygen CgO2 flowing out of the block is referred to as the outflowing oxygen amount CgoutO2 (i), and the amount of oxygen CgO2 absorbed or released from the coat layer of the same block (i) per the same operation cycle is the amount of change in the oxygen storage amount. It is referred to as δOSA (i). The oxygen storage amount change amount δOSA (i) is calculated to have a positive value when oxygen is occluded in the coat layer and a negative value when oxygen is released from the coat layer. Further, the oxygen storage amount in the coat layer of the block (i) at the present time is referred to as oxygen storage amount OSA (i), and the maximum oxygen storage amount in the coat layer of the block (i) at the present time is the maximum oxygen storage amount Cmax (i). Called.
[0139]
Now, considering the balance of the oxygen amount CgO2 in the block (i) shown in FIG. 17 per the above calculation cycle, the oxygen storage amount change amount of the inflowing oxygen amount CginO2 (i) flowing into the exhaust gas phase of the block (i) is considered. Only δOSA (i) is occluded in the coat layer, and the remaining oxygen amount CgO2 of the inflow oxygen amount CginO2 (i) not occluded in the coat layer becomes the outflow oxygen amount CgoutO2 (i), so the inflow oxygen amount CginO2 (I), the relationship shown in the following Expression 4 holds between the outflow oxygen amount CgoutO2 (i) and the oxygen storage amount change amount δOSA (i). The relationship shown in Equation 4 below is the basic equation of the present catalyst model.
[0140]
(Equation 4)
CgoutO2 (i) = CginO2 (i) -δOSA (i)
[0141]
Next, the oxygen storage amount change amount δOSA (i) will be considered. When the inflowing oxygen amount CginO2 (i) is a positive value, it means that oxygen is excessively present in the exhaust gas flowing into the exhaust gas phase of the block (i), and a part of the oxygen in the exhaust gas is blocked. Since the oxygen is absorbed in the coat layer (i), the oxygen storage amount change amount δOSA (i) is a positive value. The amount of the oxygen storage reaction at this time, that is, the oxygen storage amount change amount δOSA (i) is proportional to the value of the inflowing oxygen amount CginO2 (i), and the current maximum oxygen storage amount Cmax (i) of the block (i). And the oxygen storage amount OSA (i) at this time. Accordingly, when the inflowing oxygen amount CginO2 (i) is a positive value, the oxygen storage amount change amount δOSA (i) can be calculated based on the following Expressions 5 and 6.
[0142]
(Equation 5)
δOSA (i) = H (i) · CginO2 (i)
[0143]
(Equation 6)
H (i) = h · ((Cmax (i) −OSA (i)) / Cmax (i)) (0 ≦ H (i) <1)
[0144]
In the above Expressions 5 and 6, H (i) is a reaction rate indicating the ratio of the stored oxygen amount (δOSA (i)) to the inflowing oxygen amount CginO2 (i) in the block (i). h is a reaction rate constant, which is a constant positive value in this model, but may be a positive value that changes according to the temperature of the catalyst (for example, a positive value that monotonically increases as the temperature of the catalyst increases). Further, the value (Cmax (i) -OSA (i)) of the difference between the current maximum oxygen storage amount Cmax (i) and the current oxygen storage amount OSA (i) in the above equation (6) is represented by the block (i). Indicates the oxygen storage allowance at this time. As described above, in the present catalyst model, the amount of oxygen stored from the exhaust gas flowing into the inside of the catalyst is calculated based on at least the amount of oxygen stored in the catalyst.
[0145]
On the other hand, when the inflowing oxygen amount CginO2 (i) is a negative value, it means that the oxygen in the exhaust gas flowing into the exhaust gas phase of the block (i) is insufficient. Since the oxygen released from the layer is provided, the oxygen storage amount change amount δOSA (i) has a negative value. The amount of oxygen release reaction at this time, that is, the oxygen storage amount change amount δOSA (i) (absolute value) is proportional to the value of the inflowing oxygen amount CginO2 (i) and the oxygen storage amount at the present time in the block (i). It is considered to be proportional to the value of OSA (i). Therefore, when the inflowing oxygen amount CginO2 (i) is a negative value, the oxygen storage amount change amount δOSA (i) can be calculated based on the following Expressions 7 and 8 showing the same relationship as Expression 5 above.
[0146]
(Equation 7)
δOSA (i) = H (i) · CginO2 (i)
[0147]
(Equation 8)
H (i) = h · (OSA (i) / Cmax (i)) (0 ≦ H (i) <1)
[0148]
In Equations 7 and 8, H (i) represents the ratio of the amount of released oxygen (δOSA (i), negative value) to the inflowing oxygen amount CginO2 (i) (negative value) in block (i). It is a reaction rate shown. h is a reaction rate constant, which is the same as that used in the above equation (6). Further, the value of the current oxygen storage amount OSA (i) in the above equation 8 indicates the current oxygen release allowance in the block (i). As described above, in the present catalyst model, the amount of oxygen released from the oxygen stored inside the catalyst is calculated based on at least the amount of oxygen stored in the catalyst.
[0149]
The maximum oxygen storage amount Cmax (i) in the block (i) used in Equations 6 and 8 is obtained in advance by a method described later. The current oxygen storage amount OSA (i) in the block (i) used in Equations 6 and 8 is the change in the oxygen storage amount δOSA (i) from the time when the initial value is given to the current time. Can be calculated based on the following equation (9).
[0150]
(Equation 9)
OSA (i) = ΣδOSA (i) (0 ≦ OSA (i) ≦ Cmax (i))
[0151]
Next, considering the boundary condition between the blocks, as shown in FIG. 16, the outflow surface of the exhaust gas phase of the upstream block and the exhaust gas phase of the downstream block of the two blocks adjacent to each other are shown in FIG. Since the inflow surfaces are continuous with each other, as shown in FIG. 17, the inflowing oxygen amount CginO2 (i) flowing into the block (i) is equal to the upstream block (i-1) adjacent to the block (i). The amount of oxygen CgoutO2 (i) flowing out of the block (i) is equal to the amount of oxygen CgoutO2 (i-1) flowing out of the block (i), and flows into the downstream block (i + 1) adjacent to the block (i). It is equal to the inflowing oxygen amount CginO2 (i + 1). Therefore, the relationship shown in the following Expression 10 is established. In other words, if the outflow oxygen amount CgoutO2 (i) of an arbitrary i-th block (i) is obtained, the inflow oxygen amount CginO2 (i + 1) of the downstream block (i + 1) adjacent to the block (i) is obtained.
[0152]
(Equation 10)
CginO2 (i + 1) = CgoutO2 (i)
[0153]
From the above, if the inflowing oxygen amount CginO2 (1) in the most upstream block (1) is given as a boundary condition, the oxygen storage amount change amount δOSA (1) in the block (1) is calculated by the above equation (5) or (7). ) Is obtained. As a result, the oxygen storage amount OSA (1) in the block (1) can be updated by the above equation (9), and the outflow oxygen amount CgoutO2 (1) in the block (1) can be obtained by the above equation (4). If the outflow oxygen amount CgoutO2 (1) in the block (1) is obtained, the inflow oxygen amount CginO2 (2) in the block (2) is obtained from the above equation (10), and as a result, the block (2) is obtained from the above equation (5) or (7). ) Is obtained. As a result, the oxygen storage amount OSA (2) in the block (2) can be updated by the equation (9), and the outflow oxygen amount CgoutO2 (2) in the block (2) can be obtained by the equation (4).
[0154]
The CPU 71 repeatedly executes such processing at every predetermined calculation cycle. Therefore, if the inflowing oxygen amount CginO2 (1) in the most upstream block (1) is given as a boundary condition every time the calculation cycle of the CPU 71 elapses, the most upstream block (1) is obtained from the above equations 4 to 10. ), The oxygen storage amount OSA (i), the inflowing oxygen amount CginO2 (i), and the outflowing oxygen amount CgoutO2 (i) in each block (i) (i = 1, 2,..., N) are sequentially calculated. can do. Thereby, the distribution of the oxygen storage amount inside the catalyst is accurately calculated. In addition, if the oxygen storage amount OSA (i) (i = 1, 2,..., N) of each block is integrated for the entire catalyst, the oxygen storage amount OSAall of the entire catalyst can be accurately calculated. .
[0155]
In the following, a general formula for calculating the outflow oxygen amount CgoutO2 (i) of an arbitrary i-th block (i) is obtained. First, when “i” in the above equation 4 is rewritten to “1”, the following equation 11 is derived.
[0156]
[Equation 11]
CgoutO2 (1) = CginO2 (1) -δOSA (1)
[0157]
Also, when “i” in the above equation 4 is rewritten to “2” and the relationship of the above equations 10 and 11 is applied thereto, the following equation 12 is derived.
[0158]
(Equation 12)

[0159]
Further, when “i” in the above equation 4 is rewritten to “3” and the relation of the above equations 10 and 12 is applied thereto, the following equation 13 is derived.
[0160]
(Equation 13)

[0161]
By repeating such a procedure, the following Expression 14, which is a general formula for obtaining the outflow oxygen amount CgoutO2 (i) of an arbitrary i-th block (i), is derived.
[0162]
[Equation 14]
CgoutO2 (i) = CginO2 (1) −δOSA (1) −δOSA (2) −... −δOSA (i−1) −δOSA (i)
(I = 1, 2,..., N)
[0163]
In addition, since the following Expression 15 is derived from the above Expression 4 and the above Expression 5 (or the above Expression 7), the relationship of the above Expression 10 is applied to the following Expression 15, and the relationship is generally described. Equation (16), which is another general formula for obtaining the outflow oxygen amount CgoutO2 (i) of the block (i), can be easily derived.
[0164]
[Equation 15]
CgoutO2 (i) = CginO2 (i) · (1-H (i))
[0165]
(Equation 16)

[0166]
Next, a method of obtaining the maximum oxygen storage amount Cmax (i) in the block (i) necessary for obtaining the reaction rate H (i) in the above equations 6 and 8 will be described. FIG. 18 is a maximum oxygen storage amount distribution map showing the concept of obtaining the maximum oxygen storage amount Cmax (i) in the present catalyst model. The area indicated by hatching indicates the maximum oxygen storage amount Cmaxall of the entire catalyst. Corresponds to the value.
[0167]
As described above, the maximum oxygen storage amount Cmax (n) (n = 1,..., N) for each block of the catalyst is determined by the sum of the maximum oxygen storage amounts Cmax (n) being the maximum of the entire catalyst. The oxygen storage amount Cmaxall is set to be equal to the value, and is treated as increasing linearly with a predetermined gradient as the block moves from the upstream block to the downstream block. This is because the upstream part of the catalyst is more susceptible to poisoning by lead or sulfur in the exhaust gas flowing into the inside than the downstream part, so the maximum oxygen storage amount of the upstream part is lower than that of the downstream part. This is because it tends to lower as compared with the above.
[0168]
Specifically, the present apparatus divides the first catalyst 53, the second catalyst 54, and the third catalyst 55, which are the target of the catalyst model, into N1, N2, and N3 blocks along the flow direction of the exhaust gas. Each of the maximum oxygen storage amounts Cmax1 (i) (i = 1,..., N1) for each block 1 (i) of the first catalyst 53, and each block 2 of the second catalyst 54 Each maximum oxygen storage amount Cmax2 (i) (i = 1,..., N2) for each (i) and each maximum oxygen storage amount Cmax3 (i) for each block 3 (i) of the third catalyst 55 i = 1,..., N3) are calculated based on the following Expressions 17 to 19 based on the maximum oxygen storage amount distribution map shown in FIG.
[0169]
[Equation 17]
Cmax1 (i) = A1 · (i− (N1 / 2)) + (Cmax1all / N1) (i = 1, 2,..., N1)
[0170]
(Equation 18)
Cmax2 (i) = A2 · (i− (N2 / 2)) + (Cmax2all / N2) (i = 1, 2,..., N2)
[0171]
[Equation 19]
Cmax3 (i) = A3 · (i− (N3 / 2)) + (Cmax3all / N3) (i = 1, 2,..., N3)
[0172]
In Expressions 17 to 19, A1, A2, and A3 are positive constants, and are values that determine the gradient of the distribution of the maximum oxygen storage amount for each block. A1, A2, and A3 may have the same value or different values. Further, the maximum oxygen storage amounts Cmax1all, Cmaxall2, and Cmaxall3 of the respective catalysts are respectively equal to Cmax1, Cmax2, and Cmax3 obtained in the first embodiment, and the description of how to obtain them is omitted here. Note that each maximum oxygen storage amount of each block of the catalyst may be set so as to increase as the transition from the upstream block to the downstream block is performed.For example, the maximum oxygen storage amount is set to increase nonlinearly. May be. Thus, the maximum oxygen storage amount of each block of the first catalyst 53 to the third catalyst 55 is calculated.
[0173]
(Application of catalyst model)
Next, an example in which the above-described catalyst model is applied to the first to third catalysts 53 to 55 as shown in FIG. 19 to obtain various values will be described.
[0174]
Hereinafter, the i-th block of the first catalyst 53 is referred to as block 1 (i), and the inflow oxygen amount in the block 1 (i) is the inflow oxygen amount Cgin1O2 (i), and the outflow oxygen amount is the outflow oxygen amount Cgout1O2 (i). ), The oxygen storage amount is referred to as OSA1 (i), and the maximum oxygen storage amount is referred to as Cmax1 (i). The oxygen storage amount of the first catalyst 53 as a whole obtained by integrating the oxygen storage amounts OSA1 (i) (i = 1, 2,..., N1) of each block is referred to as an oxygen storage amount OSA1all. The maximum oxygen storage amount Cmax1 (i) (i = 1, 2,..., N1) is referred to as a maximum oxygen storage amount Cmax1all.
[0175]
Similarly, the i-th block of the second catalyst 54 is referred to as a block 2 (i), and the inflow oxygen amount in the block 2 (i) is the inflow oxygen amount Cgin2O2 (i), and the outflow oxygen amount is the outflow oxygen amount Cgout2O2 ( i), the oxygen storage amount is referred to as OSA2 (i), and the maximum oxygen storage amount is referred to as Cmax2 (i). The oxygen storage amount of the second catalyst 54 as a whole obtained by integrating the oxygen storage amount OSA2 (i) (i = 1, 2,..., N2) of each block is referred to as an oxygen storage amount OSA2all. The maximum oxygen storage amount of the entire second catalyst 54, which is a value obtained by integrating the maximum oxygen storage amount Cmax2 (i) (i = 1, 2,..., N2), is referred to as a maximum oxygen storage amount Cmax2all.
[0176]
Similarly, the i-th block of the third catalyst 55 is referred to as a block 3 (i), and the inflow oxygen amount in the block 3 (i) is the inflow oxygen amount Cgin3O2 (i), and the outflow oxygen amount is the outflow oxygen amount Cgout3O2 ( i), the oxygen storage amount is referred to as OSA3 (i), and the maximum oxygen storage amount is referred to as Cmax3 (i). The oxygen storage amount of the entire third catalyst 55 obtained by integrating the oxygen storage amounts OSA3 (i) (i = 1, 2,..., N3) of each block is referred to as an oxygen storage amount OSA3all. The maximum oxygen storage amount Cmax3 (i) (i = 1, 2,..., N3) of the third catalyst 55 is referred to as a maximum oxygen storage amount Cmax3all.
[0177]
In this catalyst model, as shown in FIG. 19, the oxygen storage amount OSA1 (i) (i = 1, 2,...) In each block of the first, second, and third catalysts 53, 54, 55 , N1), the initial values of the oxygen storage amount OSA2 (i) (i = 1, 2,..., N2) and the oxygen storage amount OSA3 (i) (i = 1, 2,..., N3) Is given as an initial condition, and every time the calculation cycle of the CPU 71 elapses, the inflowing oxygen amount Cgin1O2 (1) in the most upstream block 1 (1) of the first catalyst 53 and the most upstream block 2 of the second catalyst 54 If the inflowing oxygen amount Cgin2O2 (1) in (1) and the inflowing oxygen amount Cgin3O2 (1) in the most upstream block 3 (1) of the third catalyst 55 are given as boundary conditions, respectively, the respective blocks of the first catalyst 53 can be obtained. 1 (i) (i = 1 , 2,..., N1), the oxygen storage amount OSA1 (i), the inflowing oxygen amount Cgin1O2 (i), and the outflowing oxygen amount Cgout1O2 (i), and each block 2 (i) of the second catalyst 54 (i = 1 , 2,..., N2), the oxygen storage amount OSA2 (i), the inflowing oxygen amount Cgin2O2 (i), and the outflowing oxygen amount Cgout2O2 (i), and each block 3 (i) of the third catalyst 55 (i = , N3), the oxygen storage amount OSA3 (i), the inflowing oxygen amount Cgin3O2 (i), and the outflowing oxygen amount Cgout3O2 (i) can all be calculated. Thus, the oxygen storage amount OSA1all of the entire first catalyst 53, the oxygen storage amount OSA2all of the entire second catalyst 54, and the oxygen storage amount OSA2all of the entire second catalyst 54 can be obtained and calculated.
[0178]
Therefore, first, a method of giving an initial value of the oxygen storage amount in each block of the first to third catalysts 53 to 55 will be described. This device is configured such that the output voxs1 of the first catalyst downstream air-fuel ratio sensor 67 is 0. 0.7 (V), that is, when the air-fuel ratio of the gas downstream of the first catalyst 53 and upstream of the second catalyst 54 becomes a definite rich air-fuel ratio, This means that there was no oxygen in the first catalyst 53 and unburned HC and CO were not purified, so the oxygen storage amount OSA1 (i) (i = 1, 2) in each block of the first catalyst 53 2,..., N1) and the oxygen storage amount OSA1all of the entire first catalyst 53 are set to “0”.
[0179]
Similarly, when the output voxs2 of the second catalyst downstream air-fuel ratio sensor 68 indicates a value larger than 0.7 (V), that is, when the air-fuel ratio on the downstream side of the second catalyst 54 is clear, the present device is rich air-fuel ratio. When the fuel ratio is reached, the oxygen storage amount OSA2 (i) (i = 1, 2,..., N2) in each block of the second catalyst 54 and the oxygen storage amount OSA2all of the entire second catalyst 54 are all set to “0”. To "."
[0180]
Similarly, when the output voxs3 of the third catalyst downstream air-fuel ratio sensor 69 indicates a value larger than 0.7 (V), that is, the air-fuel ratio downstream of the third catalyst 55 is rich air, When the fuel ratio is reached, the oxygen storage amount OSA3 (i) (i = 1, 2,..., N3) in each block of the third catalyst 55 and the oxygen storage amount OSA3all of the entire third catalyst 55 are all set to “0”. To "." In this way, the initial value “0” of the oxygen storage amount in each of the first to third catalysts 53 to 55 is given as the initial condition.
[0181]
Next, a method for giving the inflowing oxygen amount Cgin1O2 (1) in the block 1 (1) at the uppermost stream of the first catalyst 53 will be described. The quantity Cgin1O2 (1) is calculated. Equation (20) is an equation similar to Equation (3). Here, mfr1 is the total amount of the fuel injection amount Fi within a predetermined time (calculation period tsample).
[0182]
(Equation 20)
Cgin1O2 (1) = 0.23 · mfr1 · (abysfs-stoich)
[0183]
As is apparent from Equation 20, the inflowing oxygen amount Cgin1O2 (1) becomes a positive value when oxygen is excessive (that is, when the air-fuel ratio is lean and abyfs> stoich), and the oxygen is insufficient. Is calculated (ie, when the air-fuel ratio is rich and abyfs <stoich), the value is calculated to be a negative value.
[0184]
Next, a method of calculating the inflowing oxygen amount Cgin2O2 (1) in the most upstream block 2 (1) of the second catalyst 54 will be described. Exhaust gas flowing out of the most downstream block 1 (N1) of the first catalyst 53 is After passing through the exhaust pipe 52, the gas flows into the uppermost block 2 (1) of the second catalyst 54 without gas being exchanged with the outside. Therefore, the outflow oxygen amount Cgout1O2 (N1) flowing out of the block 1 (N1) at the most downstream side of the first catalyst 53 is the same as the inflowing oxygen amount Cgin2O2 (1) at the most upstream block 2 (1) of the second catalyst 54. Value. Therefore, the present apparatus uses the value of the outflow oxygen amount Cgout1O2 (N1) calculated for each calculation cycle of the CPU 71 as the inflow oxygen amount Cgin2O2 (1). In this way, the inflowing oxygen amount Cgin2O2 (1) in the most upstream block 2 (1) of the second catalyst 54 is given as a boundary condition for each calculation cycle of the CPU 71.
[0185]
The same applies to the inflowing oxygen amount Cgin2O3 (1) in the most upstream block 3 (1) of the third catalyst 55, and the present apparatus uses the outflowing oxygen amount flowing out of the most downstream block 2 (N2) of the second catalyst 54. The value of Cgout2O2 (N2) is used as the inflowing oxygen amount Cgin3O2 (1). In this way, the inflowing oxygen amount Cgin3O2 (1) in the most upstream block 3 (1) of the third catalyst 55 is given as a boundary condition every calculation cycle of the CPU 71.
[0186]
(Actual operation of the second embodiment)
Next, the actual operation of the exhaust gas purification device according to the second embodiment will be described. The CPU 71 of this apparatus executes the routine shown by the flowcharts in FIGS. 20 to 22 instead of the routine shown in FIGS. 6, 7, and 14 executed by the CPU 71 of the first embodiment, and FIG. 26 are additionally executed. Hereinafter, routines specific to the second embodiment will be sequentially described.
[0187]
The CPU 71 executes a routine shown in FIG. 20 for determining and selecting the control oxygen storage amount OSAall and the target oxygen storage amount OSAallref used for obtaining the sub-feedback control amount vafsfb every time a predetermined time elapses. Accordingly, at a predetermined timing, the CPU 71 starts the process from step 2000, and in step 2005, the maximum oxygen storage amount Cmax1all of the first catalyst 53 indicating the oxygen storage capacity of the first catalyst 53 is larger than the predetermined threshold Cth1. If the determination is “Yes” in step 2005, the process proceeds to step 2010, in which the oxygen storage amount OSA1all of the first catalyst 53 is set as the control oxygen storage amount OSAall, and in step 2015, The first value OSA1allref is set as the target oxygen storage amount OSAallref, and the routine proceeds to step 2095, where the present routine is temporarily ended. The first value OSA1allref is set to の of the maximum oxygen storage amount Cmax1all of the first catalyst 53.
[0188]
On the other hand, when determining “No” in step 2005, the CPU 71 proceeds to step 2020, and the maximum oxygen storage amount Cmax2all of the second catalyst 54, which indicates the oxygen storage capacity of the second catalyst 54, is larger than the predetermined threshold Cth2. If it is determined “Yes” in step 2020, the process proceeds to step 2025 to set the oxygen storage amount OSA2all of the second catalyst 54 as the control oxygen storage amount OSAall, and in step 2030 A second value OSA2allref is set as the target oxygen storage amount OSAallref, and the routine proceeds to step 2095, where the present routine is temporarily ended. The second value OSA2allref is set to の of the maximum oxygen storage amount Cmax2all of the second catalyst 54.
[0189]
When the CPU 71 determines “No” in step 2020, the process proceeds to step 2035, where the maximum oxygen storage amount Cmax3all of the third catalyst 55 indicating the oxygen storage capacity of the third catalyst 55 is larger than the predetermined threshold Cth3. If it is determined “Yes” in step 2035, the process proceeds to step 2040 to set the oxygen storage amount OSA3all of the third catalyst 55 as the control oxygen storage amount OSAall, and in step 2045 A third value OSA3allref is set as the target oxygen storage amount OSAallref, and the routine proceeds to step 2095, where the present routine is ended once. The third value OSA3allref is set to の of the maximum oxygen storage amount Cmax3all of the third catalyst 55.
[0190]
Further, when determining "No" in step 2035, the CPU 71 proceeds to step 2050 to set the control oxygen storage amount OSAall to a constant value OSAint, and in step 2055, sets the target oxygen storage amount OSAallref to the same constant value. OSAint is set, and the routine proceeds to step 2095, where the present routine is temporarily ended. By the processing of steps 2050 and 2055, the control oxygen storage amount OSAall and the target oxygen storage amount OSAallref become equal, so that the sub feedback control based on the oxygen storage amount is effectively stopped.
[0191]
In addition, the CPU 71 executes the routine shown in FIG. 21 every time a predetermined time equal to the execution time interval of the routine shown in FIG. 20 elapses in order to obtain the sub-feedback control amount vafsfb. Therefore, at a predetermined timing, the CPU 71 starts the process from step 2100 and proceeds to step 2105 to determine whether the sub-feedback control condition is satisfied. The sub feedback control condition is the same as the sub feedback control condition of the first embodiment. At this time, if the sub-feedback control condition is not satisfied, the CPU 71 proceeds to step 2125 to set the sub-feedback control amount vafsfb to “0”, and then proceeds to step 2195 to end this routine once.
[0192]
Now, assuming that the sub-feedback control condition is satisfied, the CPU 71 determines “Yes” in step 2105 and proceeds to step 2110, where the CPU 71 determines the set target from the selected oxygen storage amount OSAall. The deviation DOSAall is obtained by subtracting the oxygen storage amount (target value) OSAallref. Next, the CPU 71 proceeds to step 2115, and obtains a sub feedback control amount (oxygen storage amount correction amount) vafsfb based on the following equation (21).
[0193]
(Equation 21)
vafsfb = Kp · DOSAall + Ki · SDOSAall
[0194]
In the above equation 21, Kp is a preset proportional gain, and Ki is a preset integral gain. SDOSAall is an integrated value of the oxygen storage amount deviation DOSAall, and is a value updated in the next step 2120. That is, the CPU 71 proceeds to step 2120, adds the oxygen storage amount deviation DOSAall obtained in step 2110 to the integrated value of the oxygen storage amount deviation SDOSAll at that time, and integrates the new oxygen storage amount deviation. The value SDOSA1all is obtained, and thereafter, the process proceeds to step 2195, where the present routine is temporarily ended.
[0195]
In this way, the oxygen storage amount correction amount vafsfb is obtained, and this value is added to the actual output vacyfs of the uppermost-stream air-fuel ratio sensor 66 in step 510 of FIG. 5 described above, and the sum (vabyfs + vafsfb) is obtained. The air-fuel ratio for main feedback control is converted to abyfs based on the map shown in FIG. As a result, the in-cylinder fuel supply amount Fc (k−N) calculated in step 515 of FIG. 5 described above changes according to the oxygen storage amount OSAall, and therefore, in steps 525 and 530, the feedback correction amount DFi is changed. It is changed according to the oxygen storage amount OSAall. As a result, in step 410 of FIG. 4 described above, the final fuel injection amount Fi is determined so that the deviation between the oxygen storage amount OSAall and the target oxygen storage amount OSAallref becomes small.
[0196]
Next, the operation for calculating the maximum oxygen storage amounts Cmax1all, Cmax2all, Cmax3all of each catalyst and the maximum oxygen storage amounts Cmax1 (i), Cmax2 (i), Cmax3 (i) of each block of each catalyst will be described. . The CPU 71 executes the routine shown by the flowchart in FIG. 22 every time a predetermined time elapses.
[0197]
Therefore, at a predetermined timing, the CPU 71 starts the process from step 2200 in FIG. 22 and proceeds to step 2205 to determine whether the value of the maximum oxygen storage amount acquisition control execution flag XHAN has changed from “1” to “0”. Monitors for absence. 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 2205 to step 2295, and ends this routine once.
[0198]
On the other hand, assuming that immediately after the above-described fourth mode is ended, the value of the maximum oxygen storage amount acquisition control execution flag XHAN is changed from “1” to “0” in step 1220 of FIG. Is determined to be "Yes" in step 2205, and the process proceeds to step 2210, in which the oxygen storage amounts OSA1, OSA2, and OSA3 at that time are respectively set to the maximum oxygen storage amount Cmax1all of the entire first catalyst 53 and the maximum oxygen storage amount The oxygen storage amount Cmax2all and the maximum oxygen storage amount Cmax3all of the entire third catalyst 55 are stored.
[0199]
Next, the CPU 71 proceeds to step 2215, sets the value of the counter value n to “0”, and then proceeds to step 2220 to start processing for calculating the maximum oxygen storage amount of each block 1 of the first catalyst 53. First, the CPU 71 increases the value of the counter value n by “1” in step 2220 and sets it to “1”, and then proceeds to step 2225 to obtain the maximum oxygen storage amount of the entire first catalyst 53 obtained in step 2210 above. The maximum oxygen storage amount Cmax1 (n) in the block 1 (n) of the first catalyst 53 is calculated based on the value of Cmax1all, the value of the counter value n, and the equation described in step 2225 based on the above equation (17). . At this time, since the value of the counter value n is “1”, the maximum oxygen storage amount Cmax1 (1) in the block 1 (1) is calculated.
[0200]
Then, the CPU 71 proceeds to step 2230 to determine whether or not the value of the counter value n is equal to the number N1 of blocks 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 2230, returns to step 2220 again, increases the value of the counter value n by “1”, and then proceeds to steps 2225 and The processing of step 2230 is executed. That is, the processing of steps 2220 and 2225 is repeatedly executed until the value of the counter value n becomes equal to the number N1 of blocks of the first catalyst 53. Thereby, the value of the maximum oxygen storage amount Cmax1 (n) of each block 1 (n) from the most upstream block 1 (1) to the most downstream block 1 (N1) of the first catalyst 53 is sequentially calculated. .
[0201]
When the value of the counter value n becomes equal to the number N1 of blocks of the first catalyst 53 by repeating the processing of the above-described step 2220, the CPU 71 determines “Yes” in step 2230, proceeds to step 2235, and proceeds to step 2235. Is set to "0", the routine proceeds to step 2240, in which the processing for calculating the maximum oxygen storage amount of each block 2 of the second catalyst 54 is started.
[0202]
The processing of calculating the maximum oxygen storage amount for each block 2 of the second catalyst 54 is the same as the processing of steps 2220 to 2230 described above, except that the processing of steps 2240 to 2250 is the number of blocks of the second catalyst 54. This is achieved by executing repeatedly N2 times. The calculation of the maximum oxygen storage amount Cmax2 (n) in step 2245 is performed based on the value of the maximum oxygen storage amount Cmax2all of the entire second catalyst 54 acquired in step 2210, the value of the counter value n, and the above-described equation (18). This is performed based on the formula described in 2245. Thus, the value of the maximum oxygen storage amount Cmax2 (n) of each block 2 (n) from the most upstream block 2 (1) to the most downstream block 2 (N2) of the second catalyst 54 is sequentially calculated. .
[0203]
When the value of the counter value n becomes equal to the number N2 of blocks of the second catalyst 54 by repeating the process of step 2240, the CPU 71 determines “Yes” in step 2250, proceeds to step 2255, and proceeds to step 2255. Is set to “0”, steps 2260 to 2270 are executed, and the process of calculating the maximum oxygen storage amount of each block 3 of the third catalyst 55 is started.
[0204]
Steps 2260 to 2270 are the same as steps 2220 to 2230 described above. The maximum oxygen storage amount Cmax3 (n) is calculated in step 2265 based on the value of the maximum oxygen storage amount Cmax3all of the entire third catalyst 55 obtained in step 2210, the value of the counter value n, and the above equation (19). This is performed based on the described formula. Thus, the value of the maximum oxygen storage amount Cmax3 (n) of each block 3 (n) from the most upstream block 3 (1) to the most downstream block 3 (N3) of the third catalyst 55 is sequentially calculated. .
[0205]
Then, when the value of the counter value n becomes equal to the number of blocks N3 of the third catalyst 55, the CPU 71 determines “Yes” in step 2270, proceeds to step 2275, and sets each of the oxygen storage amounts OSA1 to OSA3 to “ After setting to “0”, the process proceeds to step 2295 to temporarily end the present routine.
[0206]
Next, the operation for calculating the outflow oxygen amount, the oxygen storage amount, and the like for each block of each of the first to third catalysts 53 to 55 will be described. The CPU 71 executes the routine shown by the series of flowcharts of FIGS. 23 to 25 in order from the routine of FIG. 23 every time a predetermined time elapses.
[0207]
Therefore, at a predetermined timing, the CPU 71 starts processing from step 2300 of the routine shown in FIG. 23 to calculate the outflow oxygen amount, oxygen storage amount, and the like for each block 1 of the first catalyst 53. Proceeding to step 2305, the fuel injection amount integrated value mfr1 sequentially updated in step 425 of FIG. 4, the air-fuel ratio abyfs detected by the most upstream air-fuel ratio sensor 66, and the description in step 2305 based on the above equation (20) Based on the above equation, the inflowing oxygen amount Cgin1O2 (1) of the block 1 (1) of the first catalyst 53 is calculated.
[0208]
Next, the CPU 71 proceeds to step 2310, sets the value of the counter value n and the value of the oxygen storage amount OSA1all of the entire first catalyst 53 to “0”, and then proceeds to step 2315 to change the value of the counter value n to “0”. 1 ". The counter value n indicates the number of the block 1 of the first catalyst 53. At this time, the value of the counter value n is “1”, and the value of the counter value n is maintained at “1” in the subsequent processing of steps 2320 to 2375. In the processing, calculation relating to the most upstream block 1 (1) is performed.
[0209]
First, the CPU 71 proceeds to step 2320, and determines whether or not the value of the inflowing oxygen amount Cgin1O2 (1) is equal to or greater than “0”, and if the value of the inflowing oxygen amount Cgin1O2 (1) is equal to or greater than “0”. In step 2320, “Yes” is determined, and the process proceeds to step 2325, where the value of the maximum oxygen storage amount Cmax1 (1) in block 1 (1) and the block calculated (updated) when the previous routine was executed last time are described. The reaction rate H in the block 1 (1) is calculated based on the value of the oxygen storage amount OSA1 (1) of 1 (1) and the expression described in step 2325 based on the above equation (6).
[0210]
If the value of the inflowing oxygen amount Cgin1O2 (1) is not equal to or greater than “0”, the CPU 71 determines “No” in step 2320 and proceeds to step 2330, where the CPU 71 determines the value of the maximum oxygen storage amount Cmax1 (1), Based on the value of the oxygen storage amount OSA1 (1) of the block 1 (1) calculated when the routine was executed last time and the expression described in the step 2330 based on the equation 8, the block 1 (1) ) Is calculated.
[0211]
Next, the CPU 71 proceeds to step 2335, where the value of the reaction rate H calculated in step 2325 or 2330 and the inflowing oxygen amount Cgin1O2 (1) in the block 1 (1) of the first catalyst 53 calculated in step 2305 are determined. The oxygen storage amount change amount δOSA1 (1) in the block 1 (1) is calculated based on the value and the expression described in step 2335 based on the above equation 5 or the above equation 7.
[0212]
Next, the CPU 71 proceeds to step 2340, in which the value of the oxygen storage amount OSA1 (1) of the block 1 (1) at that time (that is, calculated when the present routine was executed last time) is added at step 2335. The value (OSA1 (1) + δOSA1 (1)) obtained by adding the value of the oxygen storage amount change amount δOSA1 (1) of the block 1 (1) calculated this time is the maximum oxygen storage amount Cmax1 (1) of the block 1 (1). It is determined whether the value is equal to or less than the value.
[0213]
Here, the sum (OSA1 (1) + δOSA1 (1)) of the oxygen storage amount OSA1 (1) and the oxygen storage amount change amount δOSA1 (1) of the block 1 (1) is equal to or less than the maximum oxygen storage amount Cmax1 (1). For example, the CPU 71 determines “Yes” in step 2340 and proceeds to step 2345, where the sum (OSA1 (1) + δOSA1 (1)) of the oxygen storage amount OSA1 (1) and the oxygen storage amount change amount δOSA1 (1) is calculated. It is determined whether the value is “0” or more. If the sum of the oxygen storage amount OSA1 (1) and the oxygen storage amount change amount δOSA1 (1) (OSA1 (1) + δOSA1 (1)) is equal to or greater than “0”, the CPU 71 determines “Yes” in step 2345. The determination proceeds to step 2360.
[0214]
On the other hand, if it is determined in step 2340 that the sum of the oxygen storage amount OSA1 (1) and the oxygen storage amount change amount δOSA1 (1) (OSA1 (1) + δOSA1 (1)) is larger than the maximum oxygen storage amount Cmax1 (1), The CPU 71 makes a “No” determination at step 2340 and proceeds to step 2350, at which the value obtained by subtracting the oxygen storage amount change amount δOSA1 (1) from the maximum oxygen storage amount Cmax1 (1) is used as the oxygen storage amount change amount δOSA1 (1). ) And go to step 2360. On the other hand, if it is determined in step 2345 that the sum (OSA1 (1) + δOSA1 (1)) of the oxygen storage amount OSA1 (1) and the oxygen storage amount change amount δOSA1 (1) is smaller than “0”, the CPU 71 proceeds to step 2345. Is determined to be "No," and the process proceeds to step 2355, in which the value obtained by inverting the sign of the oxygen storage amount OSA1 (1) (-OSA1 (1)) is reset to the oxygen storage amount change amount δOSA1 (1), and the process proceeds to step 2355. Proceed to 2360. In the processing of steps 2340 to 2355 described above, the oxygen storage amount OSA1 (1) of the current block 1 (1) obtained in the next step 2360 is “0” or more and the maximum oxygen storage amount Cmax1 (1) This is a process for obtaining the oxygen storage amount change amount δOSA1 (1) having the following value.
[0215]
The CPU 71 that has proceeded to step 2360 adds the oxygen storage amount obtained as described above to the oxygen storage amount OSA1 (1) of block 1 (1) at that time (that is, obtained the last time this routine was executed). The value obtained by adding the change amount δOSA1 (1) is set as the oxygen storage amount OSA1 (1) of the current block 1 (1), and in the next step 2365, the value of the inflowing oxygen amount Cgin1O2 (1) in the block 1 (1) Then, the outflow oxygen amount Cgout1O2 (1) in the block 1 (1) is calculated based on the value of the current oxygen storage amount change amount δOSA1 (1) and the expression described in the step 2365 based on the above equation (4). .
[0216]
Next, the CPU 71 proceeds to step 2370 to add a value obtained by adding the calculated value of the oxygen storage amount OSA1 (1) of the block 1 (1) to the value of the oxygen storage amount OSA1all of the entire first catalyst 53 at the present time. The new oxygen storage amount OSA1 (1) of the entire first catalyst 53 is stored, and the flow advances to step 2375 to set the value of the outflow oxygen amount Cgout1O2 (1) of the block 1 (1) to the downstream adjacent to the block 1 (1). It is set to the inflowing oxygen amount Cgin1O2 (2) in the block 1 (2) on the side (refer to Expression 10 above).
[0217]
Then, the CPU 71 proceeds to step 2380 to determine whether or not the value of the counter value n is equal to the number N1 of blocks 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 2380, returns to step 2315 again, increases the value of the counter value n by “1”, and increases the value by “2”. After that, by executing the processing of the following steps 2320 to 2375, various values are calculated for the next block, block 1 (2).
[0218]
In this way, the processing from step 2320 to step 2375 is repeatedly executed until the value of the counter value n becomes equal to the block number N1 of the first catalyst 53. Thereby, the inflow oxygen amount Cgin1O2 (n), the outflow oxygen amount Cgout1O2 (n), and the outflow oxygen amount of each block 1 (n) from the most upstream block 1 (1) to the most downstream block 1 (N1) of the first catalyst 53, The values of the oxygen storage amount change amount δOSA1 (n) and the oxygen storage amount OSA1 (n) are sequentially calculated. Further, by repeatedly executing the process of step 2370, the oxygen storage amount OSA1all of the entire first catalyst 53 is also calculated.
[0219]
When the value of the counter value n becomes equal to the number N1 of blocks of the first catalyst 53 by repeating the processing of step 2315, the CPU 71 determines “Yes” in step 2380, proceeds to step 2385, and proceeds to step 2385. After setting the value of mfr1 to “0”, the process proceeds to step 2400 of the routine shown in FIG.
[0220]
The routine of FIG. 24 is a routine for calculating the outflow oxygen amount, the oxygen storage amount, and the like for each block 2 of the second catalyst 54. In step 2405, the boundary condition of the block 2 The use of the outflow oxygen amount Cgout1O2 (N1) from the block 1 (N1) at the most downstream of the first catalyst 53 calculated in step 2365 in FIG. 23 as the inflow oxygen amount Cgin2O2 (1) in (1), and 23 is the same as the routine in FIG. 23 except that there is no step corresponding to step 2385 in FIG. 23, and a detailed description thereof is omitted here.
[0221]
The CPU 71 thus determines the inflow oxygen amount Cgin2O2 (n), the outflow oxygen amount Cgout2O2 (n), the oxygen storage amount change amount δOSA2 (n), and the oxygen storage amount OSA2 () of each block 2 (n) of the second catalyst 54 in this manner. n), and the oxygen storage amount OSA2all of the entire second catalyst 54 is calculated, and the routine proceeds to step 2500 of the routine shown in FIG.
[0222]
The routine in FIG. 25 is a routine for calculating the outflow oxygen amount, the oxygen storage amount, and the like for each block 3 of the third catalyst 55, and in step 2505, the block 3 of the third catalyst 55, which is the boundary condition, is set. Except for using the outflow oxygen amount Cgout2O2 (N2) from the most downstream block 2 (N2) of the second catalyst 54 calculated in step 2465 in FIG. 24 as the inflow oxygen amount Cgin3O2 (1) in (1). Since this is the same as the routine of FIG. 24, a detailed description thereof will be omitted here.
[0223]
Accordingly, the CPU 71 determines that the inflow oxygen amount Cgin3O2 (n), the outflow oxygen amount Cgout3O2 (n), the oxygen storage amount change amount δOSA3 (n), and the oxygen storage amount OSA3 (n) of each block 3 (n) of the third catalyst 55. ), And the oxygen storage amount OSA3all of the entire third catalyst 55 is calculated, and the routine is temporarily ended in step 2595.
[0224]
Next, the value of the oxygen storage amount for each block of each of the first to third catalysts 53 to 55 and the value of the total oxygen storage amount of each of the first to third catalysts 53 to 55 are initialized (cleared). ) Will be described. The CPU 71 executes the routine shown by the flowchart in FIG. 26 every time a predetermined time elapses.
[0225]
Therefore, at a predetermined timing, the CPU 71 starts the process from step 2600 and proceeds to step 2605 to monitor whether the value of the output voxs1 of the first catalyst downstream air-fuel ratio sensor 67 is larger than 0.7 (V). I do. At this time, if the value of the output voxs1 of the first catalyst downstream air-fuel ratio sensor 67 is greater than 0.7 (V), that is, if the downstream air-fuel ratio of the first catalyst 53 is a clear rich air-fuel ratio, the first Since it means that the amount of oxygen stored in the entire catalyst 53 is “0”, the CPU 71 proceeds to step 2610 and the respective blocks 1 (n) (n = 1, 2,...) Of the first catalyst 53. , N1), the oxygen storage amounts OSA1 (n) are all set to “0”, and the value of the oxygen storage amount OSA1all of the entire first catalyst 53 is set to “0” in the following step 2615.
[0226]
In exactly the same manner, when the value of the output voxs2 of the second catalyst downstream air-fuel ratio sensor 68 is larger than 0.7 (V), the CPU 71 determines this in step 2620 and proceeds to steps 2625 and 2630, where the second catalyst The oxygen storage amount OSA2 (n) of each of the blocks 2 (n) (n = 1, 2,..., N2) of the block 54 is set to “0”, and the oxygen storage amount of the entire second catalyst 54 is set. The value of OSA2all is set to “0”.
[0227]
Similarly, when the value of the output voxs3 of the third catalyst downstream air-fuel ratio sensor 69 is larger than 0.7 (V), the CPU 71 determines this in step 2635, proceeds to steps 2640 and 2645, and The oxygen storage amounts OSA3 (n) of the respective blocks 3 (n) (n = 1, 2,..., N3) of the third catalyst 55 are all set to “0”, and the oxygen The value of the storage amount OSA3all is set to “0”, and the routine is once ended in step 2695. Thus, the value of the oxygen storage amount of each block of each of the first to third catalysts 53 to 55 and the value of the total oxygen storage amount of each of the first to third catalysts 53 to 55 are initialized. Is done.
[0228]
As described above, the exhaust gas purification apparatus according to the second embodiment of the present invention includes a plurality of catalysts (the first catalyst 53, the second catalyst 54, and the third catalyst) disposed in series in the exhaust passage of the internal combustion engine. 55), oxygen storage capacity obtaining means (step 2210 in FIG. 22, etc.) for obtaining values (maximum oxygen storage amounts Cmax1all, Cmax2all, Cmax3all) representing the respective oxygen storage capacities of the plurality of catalysts, A value representing the state of exhaust purification of a catalyst that is determined to have an oxygen storage capacity greater than a predetermined oxygen storage capacity based on a value representing the storage capacity and that is disposed at the most upstream side of the exhaust passage. Exhaust gas purifying state acquiring means for acquiring the oxygen storage amount OSA1all, OSA2all, or OSA3all of the catalyst (see FIGS. 20, 22, and 23 to 26). 4) and air-fuel ratio control means (FIG. 4) for controlling the air-fuel ratio of the gas flowing into the most upstream catalyst so that the acquired value indicating the state of exhaust gas purification becomes a predetermined value. , An air-fuel ratio feedback control routine achieved by the routines shown in FIGS. 5 and 21).
[0229]
According to this, the value representing the state of the exhaust gas purification (any of the oxygen storage amounts OSA1all, OSA2all, and OSA3all used for the air-fuel ratio feedback control) is a value representing the acquired oxygen storage capacity (maximum oxygen storage capacity). The exhaust passage of the catalyst determined to have an oxygen storage capacity greater than a predetermined oxygen storage capacity (thresholds Cth1, Cth2, Cth3 corresponding to the respective maximum oxygen storage capacities) based on the amounts Cmax1all, Cmax2all, Cmax3all). Is the value representing the state of exhaust gas purification of the catalyst interposed at the most upstream side, so that the fluctuation of the air-fuel ratio of the gas flowing into the most upstream catalyst does not immediately appear in the value representing the state of exhaust gas purification. . Therefore, the above-described hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided. Further, since the exhaust purification state of the catalyst disposed at the most upstream position is used for the air-fuel ratio feedback control, it is possible to avoid that the dead time of the feedback control becomes too long, and to achieve a suitable air-fuel ratio control.
[0230]
<First Modification of Second Embodiment>
Next, an exhaust emission control device according to a first modification of the second embodiment will be described. In this modification, when the maximum oxygen storage amount Cmax1 (= Cmax1all) of the first catalyst 53 exceeds a predetermined threshold value Cth, the oxygen storage amount OSA1all of the first catalyst 53 as a whole and the maximum oxygen storage amount Cmax1 of the first catalyst 53 are When the total value (Cmax1 + Cmax2 = Cmax1all + Cmax2all) of the maximum oxygen storage amounts of the first catalyst 53 and the second catalyst 54 is smaller than the predetermined threshold Cth but exceeds the predetermined threshold Cth, the entire first catalyst 53 and the second catalyst 54 The total value (OSA1all + OSA2all) of the entire oxygen storage amounts and the total value (Cmax1 + Cmax2) of the maximum oxygen storage amounts of the first catalyst 53 and the second catalyst 54 are smaller than the predetermined threshold value Cth, but the first catalyst 53 The total value (Cmax1) of the maximum oxygen storage amounts of the entirety, the entire second catalyst 54, and the entirety of the third catalyst 55. When Cmax2 + Cmax3 = Cmax1all + Cmax2all + Cmax3all) exceeds a predetermined threshold value, the total value (OSA1all + OSA2all + OSA3all) of the oxygen storage amounts of these three catalysts is selected as the oxygen storage amount for air-fuel ratio control OSAall, and the same oxygen storage amount is selected by the selected OS. The control is performed so as to reach a predetermined target oxygen storage amount.
[0231]
More specifically, the CPU 71 of this exhaust gas purification apparatus is different from the CPU 71 of the second embodiment in that the routine shown in FIG. 27 is executed every predetermined time instead of the routine shown in FIG. Only the second embodiment differs from the second embodiment. Therefore, a brief description will be given below focusing on such differences. In FIG. 27, the same steps as those shown in FIGS. 6 and 20 are denoted by the same reference numerals.
[0232]
At a predetermined timing, the CPU 71 starts the process from step 2700 and proceeds to step 605, determines whether the maximum oxygen storage amount Cmax1 of the first catalyst 53 is larger than a predetermined threshold value Cth, and proceeds to step 605. When the determination is “Yes”, the process proceeds to step 2010, and the oxygen storage amount OSA1all of the entire first catalyst 53 is set as the control oxygen storage amount OSAall. Next, the CPU 71 proceeds to step 2705, sets the first value OSAref1 to the target oxygen storage amount (predetermined value) OSAallref, proceeds to step 2795, and ends this routine once. The first value OSAref1 is set to １ ／ of the maximum oxygen storage amount Cmax1 of the first catalyst 53.
[0233]
On the other hand, when the CPU 71 determines “No” in step 605, the process proceeds to step 615, where the total value (Cmax1 + Cmax2) of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54 is determined. It is determined whether or not the value is greater than a predetermined threshold value Cth. If “Yes” is determined in step 615, the process proceeds to step 2710 to set the control oxygen storage amount OSAall as the oxygen storage amount OSA1all of the first catalyst 53 as a whole. The sum (OSA1all + OSA2all) of the oxygen storage amount OSA2all of the entire catalyst 2 is set. Next, the CPU 71 proceeds to step 2715 to set the second value OSAref2 to the target oxygen storage amount OSAallref, and proceeds to step 2795 to end this routine once. Note that the second value OSAref2 is set to １ ／ of the sum of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54 (Cmax1 + Cmax2).
[0234]
When the CPU 71 determines “No” in step 615, the process proceeds to step 625 and determines whether the total value (Cmax1 + Cmax2 + Cmax3) of the maximum oxygen storage amounts of the first to third catalysts is greater than the predetermined threshold Cth. If it is determined “Yes” in step 625, the process proceeds to step 2720 to set the control oxygen storage amount OSAall as the oxygen storage amount OSA1all of the entire first catalyst 53 and the oxygen storage amount of the entire second catalyst 54. The sum (OSA1all + OSA2all + OSA3all) of the amount OSA2all and the oxygen storage amount OSA3all of the entire third catalyst 55 is set. Next, the CPU 71 proceeds to step 2725 to set a third value OSAref3 to the target oxygen storage amount OSAallref, and proceeds to step 2795 to end this routine once. Note that the third value OSAref3 is set to １ ／ of the sum (Cmax1 + Cmax2 + Cmax3) of the maximum oxygen storage amounts of the first catalyst 53 to the third catalyst 55.
[0235]
Further, when determining "No" in step 625, the CPU 71 proceeds to step 2050 to set the control oxygen storage amount OSAall to a constant value OSAint, and in step 2055, sets the target oxygen storage amount OSAallref to the same constant value. OSAint is set, and the routine proceeds to step 2795, where this routine is temporarily ended. By the processing of steps 2050 and 2055, the control oxygen storage amount OSAall and the target oxygen storage amount OSAallref become equal, so that the sub feedback control based on the oxygen storage amount is effectively stopped.
[0236]
As described above, the exhaust gas purification apparatus according to the first modified example of the second embodiment includes a plurality of catalysts (the first catalyst 53, the second catalyst 54, and the third catalyst 55) when the value n is a natural number. A catalyst device composed of a first catalyst (first catalyst 53) to an n-th catalyst which is the most upstream catalyst (that is, a catalyst device including only the first catalyst 53; A value representing the oxygen storage capacity of the catalyst device including the second catalyst 54 and the catalyst device including the three catalysts of the first catalyst to the third catalyst 53 to 55 (that is, the maximum oxygen storage amount of the first catalyst 53) Cmax1, the sum Cmax1 + Cmax2 of the maximum oxygen storage amount Cmax1 of the first catalyst 53 and the maximum oxygen storage amount Cmax2 of the second catalyst 54, and the sum of the maximum oxygen storage amounts of the first catalyst 53, the second catalyst 54, and the third catalyst 55 Cmax1 + Cmax2 + Cmax ) And a oxygen storage capability obtaining means for obtaining.
[0237]
Further, the exhaust purification device is a catalyst device in which the value n is the smallest among the catalyst devices that are determined to have an oxygen storage capability greater than a predetermined oxygen storage capability based on the acquired value representing the oxygen storage capability. Exhaust purification state acquisition means for acquiring a value (OSA1all, OSA1all + OSA2all, or OSA1all + OSA2all + OSA3all) representing an exhaust purification state of the device, and an exhaust purification state acquisition means for acquiring the acquired exhaust purification state to a predetermined value (OSAallref). Air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the first catalyst (first catalyst 53).
[0238]
That is, the value (OSA1all, OSA1all + OSA2all, or OSA1all + OSA2all + OSA3all) representing the exhaust gas purification state of the catalyst device to be used for the air-fuel ratio control indicates the exhaust gas purification state of the catalyst device having a sufficient oxygen storage capacity. Therefore, the fluctuation of the air-fuel ratio of the gas flowing into the first catalyst 53 does not immediately appear in the value indicating the state of the exhaust gas purification. Therefore, the above-described hunting of the air-fuel ratio is avoided, and as a result, an increase in the emission of harmful components such as unburned components and nitrogen oxides can be avoided.
[0239]
In addition, since the oxygen storage capacity of the catalyst device having a large oxygen storage capacity can be maintained at about half of the maximum oxygen storage capacity of each catalyst device, the oxygen storage capacity can be used effectively and the exhaust gas can be purified effectively. It becomes possible.
[0240]
<Second Modification of Second Embodiment>
Next, an exhaust emission control device according to a second modification of the second embodiment will be described. This modification mainly has a point that the third catalyst 55 and the third catalyst downstream air-fuel ratio sensor 69 are not provided, and a diagram in which the CPU 71 selects the control oxygen storage amount OSAall instead of the routine shown in FIG. The second embodiment differs from the second embodiment in that the routine shown by the flowchart in FIG. 28 is executed. Therefore, the following description will focus on such differences.
[0241]
When selecting the control oxygen storage amount OSAall, the CPU 71 executes the routine shown in FIG. 28 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 2800 and proceeds to step 2805 to determine whether the maximum oxygen storage amount Cmax1 of the first catalyst 53 is larger than a predetermined threshold value Cth1. At this time, if the maximum oxygen storage amount Cmax1 is larger than the predetermined threshold value Cth1, the CPU 71 proceeds from step 2805 to step 2810, sets the control oxygen storage amount OSAall to the oxygen storage amount OSA1all of the entire first catalyst 53, and proceeds to the next step. At 2815, the target oxygen storage amount OSAallref is set to the target oxygen storage amount OSA1allref (first value), and the routine proceeds to step 2895, where the present routine is ended once. The target oxygen storage amount OSA1allref is set to 1/2 of the maximum oxygen storage amount Cmax1.
[0242]
On the other hand, if the maximum oxygen storage amount Cmax1 is smaller than the predetermined threshold value Cth1 (is less than or equal to), the CPU 71 proceeds from step 2805 to step 2825, and sets the control oxygen storage amount OSAall to the oxygen storage amount OSA2all of the entire second catalyst 53. Then, in the next step 2830, the target oxygen storage amount OSAallref is set to the target oxygen storage amount OSA2allref (second value), and the routine proceeds to step 2895, where the present routine is ended once. The target oxygen storage amount OSA2allref is set to 1/2 of the maximum oxygen storage amount Cmax2.
[0243]
As a result, the exhaust gas purification apparatus according to the second modified example executes the routine shown in FIG. 21 so that the oxygen storage amount OSAall selected as described above becomes the target oxygen storage amount OSAallref set as described above. The sub-feedback control amount vafsfb is determined so as to match the sub feedback control amount vafsfb, the sub-feedback control amount vafsfb is reflected in the main feedback control amount by executing the routine shown in FIG. 5, and the routine shown in FIG. This is reflected in the final fuel injection amount Fi.
[0244]
As described above, in the exhaust emission control device according to the second modification of the second embodiment, when the first catalyst 53 has a sufficient oxygen storage capacity, the oxygen storage amount OSA1all of the first catalyst 53 is set to the target. The feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine is performed so as to match the oxygen storage amount OSAallref (= OSA1allref). If the first catalyst 53 does not have sufficient oxygen storage capacity, the same control is performed. The oxygen storage amount OSA1all of the second catalyst 54, which is considered to have a sufficient oxygen storage capacity because the degree of progress of deterioration is slower than that of the first catalyst 53, matches the target oxygen storage amount OSAallref (= OSA2allref). Then, the feedback control of the air-fuel ratio is executed.
[0245]
Accordingly, the control oxygen storage amount OSAall used for the feedback control of the air-fuel ratio does not immediately show a change in the air-fuel ratio upstream of the first catalyst 53, which may cause failure of the feedback control of the air-fuel ratio. Instead, the control oxygen storage amount OSAall can be made to match the target oxygen storage amount OSAallref.
[0246]
<Third embodiment>
Next, an exhaust emission control device according to a third embodiment of the present invention will be described. This exhaust gas purification device sets a value (here, the outflow oxygen amount CgoutO2) relating to the amount of the specific component flowing out of the predetermined block in the above-described catalyst model to a predetermined value (here, “0”, but “0”). This is mainly different from the exhaust gas purification apparatus according to the second embodiment in that control (air-fuel ratio feedback control) for maintaining the predetermined width including the predetermined width -β1 to + β2 is performed.
[0247]
Specifically, the CPU 71 according to the third embodiment executes all routines except the routines shown in FIGS. 20 and 21 which are executed by the CPU 71 of the second embodiment, and The routine shown in FIGS. 29 and 30 in place of the routine 21 is executed each time a predetermined time elapses. Therefore, the operation of the present exhaust gas purification apparatus will be described below with reference to the routines shown in FIGS. 29 and 30.
[0248]
At a predetermined timing, the CPU 71 starts the process from step 2900 in FIG. 29, proceeds to step 2902, sets “0” to the maximum oxygen storage amount Cmax1h for determination, and in a subsequent step 2904, sets the value of the counter value n. Is set to “0”. Next, the CPU 71 proceeds to step 2906, increases the value of the counter value n by “1”, proceeds to step 2908, and adds the maximum oxygen storage amount Cmax1h for the current determination to the first catalyst 53 obtained at that time. The maximum oxygen storage amount Cmax1 (n) in the block 1 (n) (at this point, since the counter value n is “1”, the maximum oxygen storage amount Cmax1 (1) in the block 1 (1)) is newly added. The maximum determination oxygen storage amount Cmax1h is determined.
[0249]
Next, the CPU 71 proceeds to step 2910, and determines whether or not the determination maximum oxygen storage amount Cmax1h is larger than a predetermined threshold value Cth. At this time, if the determination maximum oxygen storage amount Cmax1h is smaller than the predetermined threshold value Cth, the CPU 71 determines “No” in step 2910, proceeds to step 2912, and sets the counter value n to the block number N1 of the first catalyst 53. It is determined whether it is equal to or not.
[0250]
At present, the value of the counter value n is “1”. Accordingly, the CPU 71 determines “No” in step 2912, returns to step 2906 again, increases the value of the counter value n by “1”, and executes the processing in steps 2908 and 2910. As a result, the maximum oxygen storage amount for determination Cmax1h is the integrated value Cmax1 (1) + Cmax1 (2) of the maximum oxygen storage amounts of the first block and the second block, which are the most upstream blocks of the first catalyst 53. It becomes. If this integrated value Cmax1 (1) + Cmax1 (2) does not exceed the threshold value Cth, the CPU 71 proceeds from step 2910 to step 2912 again. If the value of the counter value n is not equal to the block number N1, the CPU 71 returns to step 2906 again. Then, the value of the count value n is increased by “1”, and the process of step 2908 is executed. As a result, the maximum oxygen storage amount Cmax1h (at this time, Cmax1 (1) + Cmax1 (2)) for the determination at this time is the maximum oxygen storage amount Cmax1 (n) of block 1 (n) (n = 3 at this time). Therefore, Cmax1 (3)) is added, and a new determination maximum oxygen storage amount Cmax1h (= Cmax1 (1) + Cmax1 (2) + Cmax1 (3)) is obtained.
[0251]
Such processing is repeatedly performed as long as the determination maximum oxygen storage amount Cmax1h does not exceed the threshold value Cth. Therefore, the maximum oxygen storage amount Cmax1h for determination is the maximum oxygen storage amount Cmax1 (n) of each block 1 (n) from the first block to the n-th block which is the most upstream block of the first catalyst 53. Is obtained as an integrated value (total value) of
[0252]
If the maximum oxygen storage amount Cmax1h for determination becomes larger than the predetermined threshold value Cth during execution of such processing, the CPU 71 determines “Yes” in step 2910 and proceeds to step 2914, and proceeds to step 2914 to output the control outflow oxygen amount CgoutO2c. Is set as the outgoing oxygen amount Cgout1O2 (n) of the n-th block of the first catalyst 53, and the routine proceeds to step 2995 to end this routine once.
[0253]
Further, the integrated value of the maximum oxygen storage amounts Cmax1 (n) of all the blocks from the first block to the N1st block of the first catalyst 53 (that is, the maximum oxygen storage amount of the entire first catalyst 53) When Cmax1all (= Cmax1) is smaller than the predetermined threshold value Cth, the CPU 71 does not determine “Yes” in step 2910, and “Yes” in step 2912 when the value of the counter value n becomes N1. Then, the routine proceeds to step 2916, where the maximum oxygen storage amount Cmax1all of the entire first catalyst 53 is set as the maximum oxygen storage amount Cmax2h for determination. Next, the CPU 71 sets the value of the counter value n to “0” in step 2918, and proceeds to step 2920 and subsequent steps.
[0254]
Steps 2920 to 2926 are the same as steps 2906 to 2912. In brief, the CPU 71 determines in steps 2920 and 2922 that the maximum oxygen storage amount Cmax1all of the first catalyst 53 as a whole 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 Cmax2 (n) of each block 2 (n) up to the n-th block is obtained as the determination maximum oxygen storage amount Cmax2h. The n-th block 2 (n) of the second catalyst 54 is the (N1 + n) -th block counted from the most upstream block of the first catalyst 53. Therefore, when (N1 + n) is m, the maximum oxygen storage amount for determination Cmax2h is the first block which is the most upstream block when the first catalyst 53 and the second catalyst 54 are regarded as one catalyst device. It is the integrated value of the maximum oxygen storage amount of each block in the upstream part of the catalyst device constituted by the blocks from the mth block to the mth block.
[0255]
When the determination maximum oxygen storage amount Cmax2h is greater than the predetermined threshold value Cth, the CPU 71 determines “Yes” in step 2924, proceeds to step 2928, and adds the control catalyst outflow oxygen amount CgoutO2c to the second catalyst 54. Of the outflow / outflow oxygen amount Cgout2O2 (n) of the n-th block is set, and the routine proceeds to step 2995, where the present routine is temporarily terminated.
[0256]
Similarly, when the sum of the maximum oxygen storage amount Cmax1all of the entire first catalyst 53 and the maximum oxygen storage amount Cmax2all of the second catalyst 54 (Cmax1all + Cmax2all) is smaller than the predetermined threshold value Cth, the CPU 71 determines “Yes” in step 2924. No determination is made. When the value of the counter value n reaches the number of blocks N2 of the second catalyst 54, “Yes” is determined in step 2926, and the process proceeds to step 2930, where the determination maximum oxygen storage amount Cmax3h is set to The sum (Cmax1all + Cmax2all) of the maximum oxygen storage amount Cmax1all of the entire first catalyst 53 and the maximum oxygen storage amount Cmax2all of the entire second catalyst 54 is set. Next, the CPU 71 sets the value of the counter value n to “0” in step 2932, and proceeds to step 2934 and thereafter.
[0257]
Steps 2934 to 2940 are the same as steps 2906 to 2912. In brief, the CPU 71 calculates the sum of the maximum oxygen storage amounts (Cmax1all + Cmax2all) of the entire first catalyst 53 and the entire second catalyst 54 in steps 2934 and 2936 (the first block of the third catalyst 55 (the first block)). The sum of the maximum oxygen storage amount Cmax3 (n) of each block 3 (n) from the block of the third catalyst 55 to the n-th block of the third catalyst 55 is obtained as the determination maximum oxygen storage amount Cmax3h. . The n-th block 3 (n) of the third catalyst 55 is the (N1 + N2 + n) -th block counted from the most upstream block of the first catalyst 53. Therefore, when (N1 + N2 + n) is p, the maximum oxygen storage amount for determination Cmax3h is the most upstream block when the first catalyst 53, the second catalyst 54, and the third catalyst 55 are regarded as one catalyst device. This is an integrated value of the maximum oxygen storage amount of each block upstream of the catalyst device constituted by a certain first block to a p-th block.
[0258]
When the determination maximum oxygen storage amount Cmax3h is larger than the predetermined threshold value Cth, the CPU 71 determines “Yes” in step 2938, proceeds to step 2942, and adds the third catalyst 55 to the control outflow oxygen amount CgoutO2c. , The outgoing oxygen concentration Cgout3O2 (n) of the n-th block is set, and the routine proceeds to step 2995, where the present routine is temporarily terminated.
[0259]
When the sum (Cmax1all + Cmax2all + Cmax3all) of the respective maximum oxygen storage amounts of the first catalyst 53 to the third catalyst 55 is smaller than the predetermined threshold value Cth, the CPU 71 does not determine “Yes” in step 2938, and does not determine “Yes” in step 2938, but the counter value n Is equal to "Yes" in step 2940, in this case, the process proceeds to step 2995 via step 2942, and the present routine is ended once.
[0260]
As described above, when n is a natural number and the first catalyst 53 to the third catalyst 55 are regarded as one catalyst device, the catalyst device is constituted by blocks from the first block to the n-th block of the catalyst device. Among the catalyst device upstream portions in which the integrated value of the maximum oxygen storage amount (judgment maximum oxygen storage amount) of each block of the catalyst device upstream portion exceeds the predetermined threshold value Cth, the downstream end of the catalyst device upstream portion having the smallest value n (The n-th block counted from the first block of the first catalyst 53) is set as the control outflow oxygen amount CgoutO2c.
[0261]
Next, an operation for obtaining the sub feedback control amount vafsfb will be described. The CPU 71 executes the routine shown in FIG. 30 every time a predetermined time elapses. 30, the same steps as those of the routine shown in FIG. 7 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0262]
By executing this routine, the CPU 71 obtains a difference between the determined and selected control outflow oxygen amount CgoutO2c and a predetermined target oxygen amount Cgoutref (in this example, the target oxygen amount Cgoutref = 0) (step 3005). Then, the difference is subjected to PI processing to obtain the sub feedback control amount vafsfb (steps 715 and 720). As a result, the CPU 71 executes the routine shown in FIGS. 4 and 5, and flows into the first catalyst 53 so that the control outflow oxygen amount CgoutO2c and the target oxygen amount Cgoutref, which is a predetermined value, are matched. The air-fuel ratio of the gas is controlled.
[0263]
As described above, according to the third embodiment, when the value n is a natural number, the first block, which is the most upstream block of the catalyst device including one or a plurality of catalysts (first to third catalysts 53 to 55). The maximum oxygen storage amount of each block in the upstream portion of the catalyst device constituted by the first block to the n-th block is integrated, and the integrated value of the maximum oxygen storage amount in the upstream portion of the catalyst device (oxygen storage for determination) Amount) (steps 2908, 2922, 2936, etc.), and a value of the smallest value n among the upstream portions of the catalytic device in which the maximum oxygen storage amount is larger than a predetermined threshold value Cth. A value representing the state of exhaust gas purification of the n-th block upstream of the catalyst device consisting of the n-th block (calculated based on the catalyst model constructed in consideration of the reaction in each catalyst) Exhaust gas purification state acquisition means for acquiring / selecting the outflow oxygen concentration Cgout1O2 (n), Cgout2O2 (n), or Cgout3O2 (n) of the n-th block as the control outflow oxygen amount CgoutO2c (FIGS. 23 to 23). 25 and 29).
[0264]
Further, the exhaust gas purifying apparatus has an air-fuel ratio (actual value) of the gas flowing into the catalyst device such that the obtained value indicating the state of exhaust gas purification (control outflow oxygen amount CgoutO2c) becomes a predetermined value (Cgoutref). Is provided with air-fuel ratio control means (such as the routines shown in FIGS. 4, 5, and 30) for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine.
[0265]
As a result, the state of the exhaust gas purification obtained through the upstream portion of the catalyst device that always has the predetermined oxygen storage capacity (the maximum oxygen storage amount equal to or higher than the predetermined threshold value Cth) (the oxygen discharged from the n-th block) Since the feedback control of the air-fuel ratio is performed based on the control outflow oxygen amount CgoutO2c), the exhaust gas purification state is changed while avoiding the air-fuel ratio hunting of the gas flowing into the first catalyst 53. Control can be stably performed at a desired value, and as a result, exhaust gas can be effectively purified.
[0266]
<Modification of Third Embodiment>
Next, an exhaust emission control device according to a modification of the third embodiment will be described. In this modification, while the exhaust gas purification apparatus of the third embodiment performs control to maintain the outflow oxygen concentration CgoutO2 of a predetermined block of the above-described catalyst device at a predetermined value, the maximum oxygen storage amount is less than a threshold value Cth. Control is performed such that the integrated value (sum) of the oxygen storage amounts of the respective blocks in the upstream portion of the catalyst device including the first block to the n-th block exceeds a predetermined target oxygen storage amount (target value). Only in that the exhaust gas purification apparatus according to the third embodiment is performed.
[0267]
More specifically, the CPU 71 according to this modified example executes the routine shown in FIGS. 31 and 32 for a predetermined time, instead of the routine shown in FIGS. 29 and 30 which is executed by the CPU 71 of the third embodiment. It is executed every time. Note that, in the steps of the routine in FIGS. 31 and 32, the same steps as those described above are denoted by the same reference numerals as the steps described above, and detailed description thereof will be omitted.
[0268]
The CPU 71 repeatedly executes a routine for determining the control oxygen storage amount OSAc shown in FIG. 31 every time a predetermined time elapses. When the above-described determination maximum oxygen storage amount Cmax1h becomes larger than the predetermined threshold value Cth, At 2910, “Yes” is determined and the routine proceeds to step 3102, where the control oxygen storage amount OSAc is set to the oxygen storage amount OSA1 (j of each block j from the first block to the n-th block of the first catalyst 53. ) Is set. Next, the CPU 71 proceeds to step 3104, where the target oxygen storage amount OSAref is 1 / (1) of the integrated value ΣCmax1 (j) of the maximum oxygen storage amount Cmax1 (j) of each block j from the first block to the n-th block. 2 is set, the routine proceeds to step 2995, and this routine is temporarily ended.
[0269]
Similarly, when the above-described maximum oxygen storage amount Cmax2h for determination is greater than the predetermined threshold value Cth, the CPU 71 determines “Yes” in step 2924, proceeds to step 3106, and proceeds to step 3106 to determine the total oxygen content of the first catalyst 53. The value obtained by adding the integrated value ΣOSA2 (j) of the oxygen storage amount OSA2 (j) of each block j from the first block to the n-th block of the second catalyst 54 to the storage amount OSA1all is the control oxygen storage amount. Set as OSAc. Next, the CPU 71 proceeds to step 3108, where the maximum oxygen storage amount Cmax1all of the first catalyst 53 is set to the maximum oxygen storage amount Cmax2 () of each block j from the first block to the n-th block of the second catalyst 54. A half of the value obtained by adding the integrated value ΣCmax2 (j) of j) is set as the target oxygen storage amount OSAref, and the routine proceeds to step 2995, where the present routine is temporarily terminated.
[0270]
Similarly, when the above-described maximum oxygen storage amount Cmax3h for determination is greater than the predetermined threshold value Cth, the CPU 71 determines “Yes” in step 2938, proceeds to step 3110, and proceeds to the first catalyst 53 and the second catalyst 53. The integrated value ＯＳOSA3 (j) of the oxygen storage amount OSA3 (j) of each block j from the first block to the n-th block of the third catalyst 55 is added to the sum of the respective oxygen storage amounts (OSA1all + OSA2all) of 54. The obtained value is set as the control oxygen storage amount OSAc. Next, the CPU 71 proceeds to step 3112 to calculate the sum of the maximum oxygen storage amounts of the first catalyst 53 and the second catalyst 54 (Cmax1all + Cmax2all) in the respective blocks from the first block to the n-th block of the third catalyst 55. A value half of the value obtained by adding the integrated value ΣCmax3 (j) of the maximum oxygen storage amount Cmax3 (j) of j is set as the target oxygen storage amount OSAref, and the routine proceeds to step 2995 to end this routine once. As described above, the control oxygen storage amount OSAc and the target oxygen storage amount OSAref are determined.
[0271]
The CPU 71 executes the routine shown in FIG. 31 every time a predetermined time elapses, and sets the sub feedback control amount vafsfb for making the control oxygen storage amount OSAc equal to the target oxygen storage amount OSAref, and sets the control oxygen storage amount. The deviation between OSAc and the target oxygen storage amount OSAref is obtained by performing PI processing. The method of obtaining the sub-feedback control amount vafsfb is the same as the method of obtaining the sub-feedback control amount vafsfb in the other embodiments, and thus a detailed description is omitted.
[0272]
As described above, according to the modification of the third embodiment, when the value n is a natural number, the most upstream block of the catalyst device including one or a plurality of catalysts (first to third catalysts 53 to 55) The maximum oxygen storage amount of each block in the upstream portion of the catalyst device constituted by the first block to the n-th block is integrated and the integrated value of the maximum oxygen storage amount in the upstream portion of the catalyst device (determination Integrated value calculating means (steps 2908, 2922, 2936, etc.) for calculating the maximum oxygen storage amount, and the value n of the upstream portion of the catalyst device in which the maximum oxygen storage amount integrated value is larger than a predetermined threshold value Cth. Values representing the state of purification of exhaust gas upstream of the catalyst device including the smallest n-th block (oxygen storage amount ΣOSA1 (j), OSA1all + ΣOSA2 (j), and OSA1all) OSA2all + ΣOSA3 (j)) exhaust gas purification state acquiring means for acquiring and selecting as the controlling oxygen storage amount OSAc the (23-25, and a routine like) shown in FIG. 31.
[0273]
Further, the exhaust gas control apparatus controls the air-fuel ratio of the gas flowing into the catalyst device such that the value (the control oxygen storage amount OSAc) indicating the obtained exhaust gas purification state becomes a predetermined value (OSAref). Air-fuel ratio control means (the routines shown in FIGS. 4, 5, and 32, etc.).
[0274]
As a result, based on the exhaust gas purification state (control oxygen storage amount OSAc) acquired via the upstream portion of the catalyst device that always has the predetermined oxygen storage capacity (the maximum oxygen storage amount equal to or greater than the predetermined threshold value Cth). As a result, the air-fuel ratio of the gas flowing into the first catalyst 53 is feedback-controlled, so that the exhaust gas purification state can be stably controlled to a desired value while avoiding hunting of the air-fuel ratio. As a result, the exhaust gas can be effectively purified.
[0275]
As described above, according to the embodiments and the modifications thereof according to the present invention, the air-fuel ratio obtained through all or the upstream portion of the catalyst (catalyst device) having the oxygen storage ability without causing control failure. Since the air-fuel ratio of the gas flowing into the first catalyst 53 is controlled such that the sensor output or the value representing the state of exhaust gas purification of the entire or upstream portion of the catalyst (catalyst device) becomes a predetermined target value, Exhaust gas purification performance can be favorably maintained. Further, a catalyst (part) located downstream from the air-fuel ratio sensor used for controlling the air-fuel ratio or downstream from the position where the exhaust gas purification state is acquired can be used as a preliminary catalyst, so Harmful exhaust components can be further reduced.
[0276]
Note that the present invention is not limited to the above embodiment, and various modifications can be adopted within the scope of the present invention. For example, in step 2825 of the routine shown in FIG. 28 of the second modification of the second embodiment, the sum (OSA1all + OSA2all) of the oxygen storage amount OSA1all of the first catalyst 53 and the oxygen storage amount OSA1all of the second catalyst 54 is controlled. The oxygen storage amount for use OSAall may be set. In this case, the target oxygen storage amount OSA2allref (second value) in step 2830 is 1/2 (= (Cmax1 + Cmax2) / the sum of the maximum oxygen storage amount Cmax1 of the first catalyst and the maximum oxygen storage amount Cmax2 of the second catalyst. 2) is preferable.
[0277]
In step 2810 of the routine also shown in FIG. 28, the amount of oxygen flowing out of the first catalyst 53 (the first amount calculated based on the catalyst model constructed in consideration of the reaction in the first catalyst 53). The value of Cgout1O2 (N1) is set as a control outflow oxygen amount CgoutO2c, and the flow out of the second catalyst 54 in step 2825. (The amount of oxygen flowing out of the block located at the most downstream side of the second catalyst 54, calculated based on the catalyst model constructed in consideration of the reaction in the second catalyst 54, ie, the exhaust purification of the second catalyst 54) Cgout2O2 (N2) is set as the control outflow oxygen amount CgoutO2c, and the step 2815 and the step 2830 may be omitted. In this case, the sub-feedback control employs the routine shown in FIG.
[0278]
Thus, when the oxygen storage capacity of the first catalyst 53 is larger than the predetermined capacity, the air-fuel ratio feedback control that sets a value corresponding to the amount of the specific component (in this case, oxygen) flowing out of the first catalyst 53 to a predetermined value. However, when the oxygen storage capacity of the first catalyst 53 is smaller than the predetermined capacity, the air-fuel ratio is set to a value corresponding to the amount of the specific component (in this case, oxygen) flowing out of the second catalyst 54 to the predetermined value. Feedback control is achieved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a system in which an exhaust gas purification device according to a first embodiment of the present invention is applied to an internal combustion engine.
FIG. 2 is a map showing a relationship between an output voltage of an uppermost stream air-fuel ratio sensor shown in FIG. 1 and an air-fuel ratio.
FIG. 3 is a map showing a relationship between an output voltage and an air-fuel ratio of a first catalyst downstream air-fuel ratio sensor, a second catalyst downstream air-fuel ratio sensor, and a third catalyst downstream air-fuel ratio sensor shown in FIG.
FIG. 4 is a flowchart showing a routine for calculating a fuel injection amount executed by a CPU shown in FIG. 1;
FIG. 5 is a flowchart illustrating a routine for calculating an air-fuel ratio feedback correction amount executed by a CPU illustrated in FIG. 1;
6 is a flowchart showing a routine for selecting (determining) a control air-fuel ratio sensor output used for obtaining a sub-feedback control amount executed by the CPU shown in FIG. 1;
FIG. 7 is a flowchart showing a routine for obtaining a sub-feedback control amount executed by a CPU shown in FIG. 1;
FIG. 8 is a flowchart showing a routine for determining whether to start a maximum oxygen storage amount acquisition control executed by the CPU shown in FIG. 1;
FIG. 9 is a flowchart showing a first mode routine executed by the CPU shown in FIG. 1;
FIG. 10 is a flowchart showing a second mode routine executed by the CPU shown in FIG. 1;
FIG. 11 is a flowchart showing a third mode routine executed by the CPU shown in FIG. 1;
FIG. 12 is a flowchart showing a routine in a fourth mode executed by the CPU shown in FIG. 1;
FIG. 13 is a flowchart showing a routine for calculating an oxygen storage amount executed by the CPU shown in FIG. 1;
FIG. 14 is a flowchart illustrating a routine for calculating a maximum oxygen storage amount executed by a CPU illustrated in FIG. 1;
FIG. 15 is a flowchart showing a routine for selecting (determining) a control air-fuel ratio sensor output executed by a CPU of an exhaust emission control device according to a modification of the first embodiment of the present invention.
FIG. 16 is a diagram schematically showing a catalyst model used in the exhaust gas purification apparatus of the present invention.
FIG. 17 is a diagram showing the balance of specific components related to the oxygen storage / release reaction in the specific region of the catalyst model employed in the exhaust gas purification apparatus of the present invention when focusing on the specific region.
FIG. 18 is a map for obtaining a distribution of a maximum oxygen storage amount for each block of the catalyst from a maximum oxygen storage amount of the entire catalyst which is a target of a catalyst model used in the exhaust purification device of the present invention.
FIG. 19 is a schematic diagram when a catalyst model used in the exhaust gas purification apparatus of the present invention is applied to first, second, and third catalysts, respectively.
FIG. 20 is a flow chart for determining and selecting a control oxygen storage amount and a target oxygen storage amount used by the CPU of the exhaust gas purification apparatus according to the second embodiment of the present invention to determine the sub-feedback control amount. 9 is a flowchart illustrating a routine.
FIG. 21 is a flowchart showing a routine for obtaining a sub-feedback control amount executed by a CPU of an exhaust gas purification device according to a second embodiment of the present invention.
FIG. 22 is a flowchart showing a routine for obtaining a maximum oxygen storage amount of each catalyst and a maximum oxygen storage amount of each block, which is executed by the CPU of the exhaust gas purification apparatus according to the second embodiment of the present invention.
FIG. 23 is a flowchart illustrating a routine for calculating an outflow oxygen amount, an oxygen storage amount, and the like for each block of a first catalyst, which is executed by a CPU of an exhaust gas purification apparatus according to a second embodiment of the present invention. .
FIG. 24 is a flowchart illustrating a routine for calculating an outflow oxygen amount, an oxygen storage amount, and the like for each block of a second catalyst, which is executed by a CPU of an exhaust emission control device according to a second embodiment of the present invention. .
FIG. 25 is a flowchart illustrating a routine for calculating an outflow oxygen amount, an oxygen storage amount, and the like for each block of a third catalyst, which is executed by the CPU of the exhaust gas purification apparatus according to the second embodiment of the present invention. .
FIG. 26 clears the oxygen storage amount of each of the first, second, and third catalysts and the oxygen storage amount of each block of these catalysts, which is executed by the CPU of the exhaust gas purification apparatus according to the second embodiment of the present invention. Is a flow chart showing a routine for this.
FIG. 27 determines a control oxygen storage amount and a target oxygen storage amount used by the CPU of the exhaust gas purification apparatus according to the first modification of the second embodiment of the present invention, which are used to obtain a sub-feedback control amount. 6 is a flowchart showing a routine for selecting.
FIG. 28 is a diagram for determining and selecting a control oxygen storage amount and a target oxygen storage amount used for obtaining a sub-feedback control amount executed by a CPU of an exhaust gas purification apparatus according to a second modification of the second embodiment. 5 is a flowchart showing a routine of FIG.
FIG. 29 is a flowchart showing a routine for determining and selecting a control outflow oxygen amount used for obtaining a sub-feedback control amount executed by a CPU of an exhaust gas purification apparatus according to a third embodiment of the present invention. is there.
FIG. 30 is a flowchart showing a routine for obtaining a sub-feedback control amount executed by a CPU of an exhaust emission control device according to a third embodiment of the present invention.
FIG. 31 is a routine for determining and selecting a control oxygen storage amount and a target oxygen storage amount used for obtaining a sub-feedback control amount executed by a CPU of an exhaust gas purification apparatus according to a modification of the third embodiment. 5 is a flowchart illustrating the operation of the embodiment.
FIG. 32 is a flowchart illustrating a routine for obtaining a sub-feedback control amount executed by a CPU of an exhaust emission control device according to a modification of the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39 ... Injector, 52 ... Exhaust pipe (exhaust pipe), 53 ... First catalyst, 54 ... Second catalyst, 55 ... Third catalyst, 66 ... Most upstream air-fuel ratio sensor, 67 .. A first catalyst downstream air-fuel ratio sensor, 68 a second catalyst downstream air-fuel ratio sensor, 69 a third catalyst downstream air-fuel ratio sensor, 70 an electric control device, 71 a CPU.

Claims (10)

A plurality of catalysts interposed in series in the exhaust passage of the internal combustion engine,
A plurality of air-fuel ratio sensors downstream of each of the plurality of catalysts and arranged in the exhaust passage;
When the value n is a natural number, the oxygen storage unit obtains a value representing the oxygen storage capacity of the catalyst device including the first to n-th catalysts, which are the most upstream catalysts of the plurality of catalysts. Ability acquisition means,
Based on the obtained value representing the oxygen storage capacity, the n-th catalyst apparatus having the smallest value n among the catalyst apparatuses determined to have the oxygen storage capacity larger than the predetermined oxygen storage capacity. An air for controlling an air-fuel ratio of gas flowing into the first catalyst so that an output of one of the plurality of air-fuel ratio sensors disposed downstream of the catalyst becomes a predetermined target output. Fuel ratio control means,
An exhaust gas purification device for an internal combustion engine, comprising: A first catalyst interposed in an exhaust passage of the internal combustion engine;
A first catalyst downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the first catalyst;
A second catalyst interposed in the exhaust passage downstream of the first catalyst downstream air-fuel ratio sensor;
A second catalyst downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the second catalyst;
First catalyst oxygen storage capacity obtaining means for obtaining a value representing the oxygen storage capacity of the first catalyst;
When it is determined that the oxygen storage capacity of the first catalyst is larger than a predetermined oxygen storage capacity based on the obtained value representing the oxygen storage capacity of the first catalyst, the output of the first catalyst downstream air-fuel ratio sensor is set to a predetermined value. The air-fuel ratio of the gas flowing into the first catalyst is controlled so as to attain the first target output of the first catalyst, and when it is determined that the oxygen storage capacity of the first catalyst is smaller than the predetermined oxygen storage capacity, the second Air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the first catalyst so that the output of the catalyst downstream air-fuel ratio sensor becomes a predetermined second target output;
An exhaust gas purification device for an internal combustion engine, comprising: A plurality of catalysts interposed in series in the exhaust passage of the internal combustion engine,
Oxygen storage capacity obtaining means for obtaining a value representing each oxygen storage capacity of the plurality of catalysts,
The state of exhaust gas purification of the catalyst that is determined to have an oxygen storage capacity greater than a predetermined oxygen storage capacity based on the obtained value representing the oxygen storage capacity and that is disposed at the most upstream position in the exhaust passage. Exhaust purification state acquisition means for acquiring a value representing
Air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the most upstream catalyst so that the value representing the obtained exhaust gas purification state becomes a predetermined value;
An exhaust gas purification device for an internal combustion engine, comprising: A plurality of catalysts interposed in series in the exhaust passage of the internal combustion engine,
When the value n is a natural number, the oxygen storage unit obtains a value representing the oxygen storage capacity of the catalyst device including the first to n-th catalysts, which are the most upstream catalysts of the plurality of catalysts. Ability acquisition means,
The value n represents the state of the exhaust gas purification of the catalyst device having the smallest value n among the catalyst devices determined to have the oxygen storage capability larger than the predetermined oxygen storage capability based on the obtained value representing the oxygen storage capability. Exhaust purification state acquisition means for acquiring a value representing an exhaust purification state of the n-th catalyst constituting the catalyst device having the smallest value or the same value n;
Air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the first catalyst so that the value representing the obtained state of exhaust gas purification becomes a predetermined value;
An exhaust gas purification device for an internal combustion engine, comprising: The exhaust gas purification device for an internal combustion engine according to claim 4,
The exhaust purification state acquisition means includes an oxygen storage amount of the entire catalyst device having the smallest value n, an oxygen storage amount of an n-th catalyst constituting the catalyst device having the smallest value n, and a catalyst device having the smallest value n. One of the values according to the amount of the specific component flowing out of the n-th catalyst calculated based on the catalyst model constructed in consideration of the reaction in the n-th catalyst constituting Is obtained as a value indicating the state of the exhaust gas purification. A first catalyst interposed in an exhaust passage of the internal combustion engine;
A second catalyst interposed in the exhaust passage downstream of the first catalyst;
First catalyst oxygen storage capacity obtaining means for obtaining a value representing the oxygen storage capacity of the first catalyst;
First catalyst exhaust purification state acquisition means for acquiring a value representing an exhaust purification state of the first catalyst;
Second catalyst exhaust purification state acquisition means for acquiring a value relating to an exhaust purification state of the second catalyst;
When it is determined that the oxygen storage capacity of the first catalyst is larger than a predetermined oxygen storage capacity based on the obtained value representing the oxygen storage capacity of the first catalyst, the obtained exhaust purification state of the first catalyst is determined. And the air-fuel ratio of the gas flowing into the first catalyst is controlled so that the value representing the predetermined value becomes a predetermined first value, and it is determined that the oxygen storage capacity of the first catalyst is smaller than the predetermined oxygen storage capacity. Air-fuel ratio control means for controlling the air-fuel ratio of the gas flowing into the first catalyst so that the obtained value related to the state of exhaust gas purification of the second catalyst becomes a predetermined second value.
An exhaust gas purification device for an internal combustion engine, comprising: The exhaust gas purification device for an internal combustion engine according to claim 6,
The first catalyst exhaust gas purification state acquiring means flows out of the first catalyst calculated based on a catalyst model constructed in consideration of the oxygen storage amount of the first catalyst or a reaction in the first catalyst. Configured to acquire a value corresponding to the amount of the specific component as a value representing a state of exhaust gas purification of the first catalyst,
The second catalyst exhaust gas purification state acquisition means includes an oxygen storage amount of the second catalyst, a total oxygen storage amount of the oxygen storage amount of the first catalyst and the oxygen storage amount of the second catalyst, and an amount of oxygen stored in the second catalyst. One of the values according to the amount of the specific component flowing out of the second catalyst calculated based on the catalyst model constructed in consideration of the reaction is obtained as a value relating to the exhaust purification state of the second catalyst. An exhaust gas purification device for an internal combustion engine configured to perform the following. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 7,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the value representing the oxygen storage capacity is a value indicating a maximum oxygen storage amount of a target catalyst or a catalyst device, or a value having a certain correlation with the maximum oxygen storage amount. A catalyst device comprising one or more catalysts interposed in the exhaust passage of the internal combustion engine,
Acquisition means for acquiring the maximum oxygen storage amount of each block when the catalyst device is virtually divided into a plurality of blocks along the flow direction of the gas flowing into the catalyst device,
When the value n is a natural number, the maximum oxygen storage amount of each block in the upstream portion of the catalyst device constituted by the first to n-th blocks which are the most upstream blocks of the catalyst device is integrated. Integrated value calculating means for obtaining the maximum oxygen storage amount integrated value of the upstream portion of the catalyst device,
A value representing the state of exhaust gas purification in the upstream portion of the catalytic device, which includes the nth block having the smallest value n among the upstream portions of the catalytic device in which the integrated value of the maximum oxygen storage amount is larger than a predetermined threshold value. Or, an exhaust gas purification state acquisition unit that acquires a value representing an exhaust gas purification state of the n-th block,
Air-fuel ratio control means for controlling the air-fuel ratio of gas flowing into the catalyst device so that the obtained value indicating the state of exhaust gas purification becomes a predetermined value;
An exhaust gas purification device for an internal combustion engine, comprising: The exhaust gas purification device for an internal combustion engine according to claim 9,
The exhaust gas purification state acquisition unit is configured to: the oxygen storage amount of the upstream portion of the catalyst device in which the value n is smallest among the upstream portions of the catalyst device in which the integrated value of the maximum oxygen storage amount takes a value larger than a predetermined threshold, or An exhaust gas purification device for an internal combustion engine configured to acquire a value corresponding to the amount of a specific component flowing out of an n-th block in the upstream portion of the catalyst device, where n is the smallest, as a value representing the exhaust gas purification state.

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