JP2004300981A - Device for judging catalyst degradation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To judge whether a three-way catalyst is degraded or not without impairing drivability. <P>SOLUTION: In the device for judging catalyst degradation, the rate CgoutO2(N) of effluent oxygen from a 1st catalyst is estimated on the basis of a catalyst model constructed on the assumption that the 1st catalyst is a fresh one. An air-fuel ratio feedback control is conducted on the basis of an air-fuel-ratio-sensor output Voxs on a downstream side. In the above control, in points in time (times t1-t4, t10-t60) where the output Voxs takes a 1st state (the output is in a state passing while a rich-side specific value Vrich being increased, or while a lean-side specified value Vlean being decreased), if the probability where the rate CgoutO2(N) takes a 2nd state (a state where the value is smaller than a negative threshold Crefmns, or the value is greater than a positive threshold Crefpls) is smaller than a specified value, the catalyst is determined to be degraded. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００８３】
さらに、上記数１における「ｉ」を「３」に書き換え、これに上記数７及び上記数９の関係を適用すると、下記数１０が導かれる。
【００８４】
【数１０】

【００８５】
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１１が導かれる。
【００８６】
【数１１】
ＣｇｏｕｔＯ２（ｉ）＝ＣｇｉｎＯ２（１）−δＯＳＡ（１）−δＯＳＡ（２）− ・・・ −δＯＳＡ（ｉ−１）−δＯＳＡ（ｉ）
（ｉ＝１，２，・・・，Ｎ）
【００８７】
また、上記数１及び上記数２（又は上記数４）より下記数１２が導かれるから、下記数１２に上記数７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１３も容易に導くことができる。
【００８８】
【数１２】
ＣｇｏｕｔＯ２（ｉ）＝ＣｇｉｎＯ２（ｉ）・（１−Ｈ（ｉ））
【００８９】
【数１３】

【００９０】
次に、上記数３及び数５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）について説明する。この触媒モデルは第１触媒５３が新品の触媒であると想定して構築されているから、各ブロック（ｉ）の最大酸素吸蔵量Ｃｍａｘ（ｉ） （ｉ＝１，・・・，Ｎ）の総和は、第１触媒５３が新品の触媒であるときの同第１触媒５３全体の最大酸素吸蔵量Ｃｍａｘａｌｌの値（一定値）となるように設定されている。また、各ブロック（ｉ）の最大酸素吸蔵量Ｃｍａｘ（ｉ） （ｉ＝１，・・・，Ｎ）は、例えば、前記最大酸素吸蔵量Ｃｍａｘａｌｌの値をブロックの個数Ｎで除した値にそれぞれ設定されている。このように設定された各ブロック（ｉ）の最大酸素吸蔵量Ｃｍａｘ（ｉ） （ｉ＝１，・・・，Ｎ）は、第１触媒５３の劣化の進行に拘わらず変化しない。
【００９１】
（触媒モデルの適用）
次に、以上説明した触媒モデルを、図８に示したように、第１触媒５３に適用し、各種値を求める例について説明する。
【００９２】
以下、第１触媒５３のｉ番目のブロックであるブロック（ｉ）における流入酸素量を流入酸素量ＣｇｉｎＯ２（ｉ），流出酸素量を流出酸素量ＣｇｏｕｔＯ２（ｉ），酸素吸蔵量をＯＳＡ（ｉ），最大酸素吸蔵量をＣｍａｘ（ｉ）とそれぞれ称呼する。また、各ブロックの酸素吸蔵量ＯＳＡ（ｉ） （ｉ＝１，２，・・・，Ｎ） 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ＯＳＡａｌｌと称呼し、各ブロックの最大酸素吸蔵量Ｃｍａｘ（ｉ） （ｉ＝１，２，・・・，Ｎ） 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Ｃｍａｘａｌｌと称呼する。
【００９３】
この触媒モデルにおいては、図８に示したように、第１触媒５３の各ブロックにおける酸素吸蔵量ＯＳＡ（ｉ） （ｉ＝１，２，・・・，Ｎ）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）における流入酸素量ＣｇｉｎＯ２（１）を境界条件として付与すれば、第１触媒５３の各ブロック（ｉ） （ｉ＝１，２，・・・，Ｎ） における酸素吸蔵量ＯＳＡ（ｉ），流入酸素量ＣｇｉｎＯ２（ｉ），及び流出酸素量ＣｇｏｕｔＯ２（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ＯＳＡａｌｌも取得・算出することができる。
【００９４】
そこで、先ず、第１触媒５３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、下流側空燃比センサ６７の出力Ｖｏｘｓ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ＯＳＡ（ｉ） （ｉ＝１，２，・・・，Ｎ） 及び第１触媒５３全体の酸素吸蔵量ＯＳＡａｌｌを全て「０」に設定する。このようにして、第１触媒５３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。
【００９５】
次に、第１触媒５３の最上流のブロック（１）における流入酸素量ＣｇｉｎＯ２（１）を付与する手法について説明すると、本装置は、下記数１４に基づいてＣＰＵ７１の演算周期毎の流入酸素量ＣｇｉｎＯ２（１）を算出する。
【００９６】
【数１４】
ＣｇｉｎＯ２（１）＝０．２３・ｍｆｒ・（ａｂｙｆｓａｖｅ − ｓｔｏｉｃｈ）
【００９７】
上記数１４において、値「０．２３」は大気中に含まれる酸素の重量割合である。ｍｆｒは一演算周期Δｔ内における燃料噴射量Ｆｉの合計量であり、ｓｔｏｉｃｈは理論空燃比（例えば、１４．７）である。また、ａｂｙｆｓａｖｅは一演算周期Δｔ内において上流側空燃比センサ６６により検出された空燃比Ａ／Ｆの平均値である。
【００９８】
この数１４に示したように、一演算周期Δｔ内における噴射量の合計量ｍｆｒに、検出された空燃比Ａ／Ｆの平均値の理論空燃比からの偏移（ａｂｙｆｓａｖｅ − ｓｔｏｉｃｈ）を乗じることでこの一演算周期Δｔ内における空気の過剰量が求められ、この一演算周期Δｔ内における空気の過剰量に酸素の重量割合を乗じることで一演算周期Δｔにおける酸素の過剰量、即ち現時点での流入酸素量ＣｇｉｎＯ２（１）が求められる。
【００９９】
このようにして算出される流入酸素量ＣｇｉｎＯ２（１）は、上記数１４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ａｂｙｆｓａｖｅ＞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ａｂｙｆｓａｖｅ＜ｓｔｏｉｃｈのとき）に負の値となるように計算される。このようにして、ＣＰＵ７１の演算周期毎に第１触媒５３の最上流のブロック（１）における流入酸素量ＣｇｉｎＯ２（１）が境界条件として付与される。
【０１００】
（実際の作動）
次に、上記のように構成された空燃比制御装置の実際の作動について、電気制御装置７０のＣＰＵ７１が実行するルーチンをフローチャートにより示した図９〜図１６を参照しながら説明する。
【０１０１】
ＣＰＵ７１は、図９に示した最終燃料噴射量Ｆｉの計算、及び燃料噴射の指示を行うルーチンを、各気筒のクランク角が各吸気上死点前の所定クランク角度（例えば、ＢＴＤＣ９０°ＣＡ）となる毎に、繰り返し実行するようになっている。従って、任意の気筒のクランク角度が前記所定クランク角度になると、ＣＰＵ７１はステップ９００から処理を開始してステップ９０５に進み、エアフローメータ６１により計測された吸入空気流量Ｇａと、エンジン回転速度ＮＥとに基づいて、機関の空燃比を理論空燃比とするための基本燃料噴射量Ｆｂａｓｅをマップｆから求める。
【０１０２】
次いで、ＣＰＵ７１はステップ９１０に進み、基本燃料噴射量Ｆｂａｓｅに係数Ｋを乗じた値に後述する空燃比フィードバック補正量ＤＦｉを加えた値を最終燃料噴射量Ｆｉに設定する。この係数Ｋの値は、通常は「１．００」であり、後述するように被毒回復処理が実行されるとき、「１．００」以外の所定値に設定される。
【０１０３】
次いで、ＣＰＵ７１はステップ９１５に進んで、前記設定された最終燃料噴射量Ｆｉの燃料を噴射するための指示を吸気行程直前にある気筒のインジェクタ３９に対して行う。その後、ＣＰＵ７１はステップ９２０に進み、その時点の燃料噴射量合計量ｍｆｒに最終燃料噴射量Ｆｉを加えた値を新たな燃料噴射量合計量ｍｆｒに設定する。この燃料噴射量合計量ｍｆｒは、後述する流入酸素量ＣｇｉｎＯ２（１）を算出する際に用いられる。その後、ＣＰＵ７１はステップ９９５に進み、本ルーチンを一旦終了する。以上により、フィードバック補正された最終燃料噴射量Ｆｉの燃料が吸気行程を迎える気筒に対して噴射される。
【０１０４】
次に、上記空燃比フィードバック補正量ＤＦｉの算出について説明すると、ＣＰＵ７１は図１０に示したルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ１０００から処理を開始し、ステップ１００５に進んで空燃比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。空燃比フィードバック制御条件は、例えば、機関の冷却水温ＴＨＷが第１所定温度以上であり、機関の一回転当りの吸入空気量（負荷、筒内吸入空気量Ｍｃ）が所定値以下であり、上流側空燃比センサ６６が正常（活性状態であることを含む。）であり、且つ、後述する被毒回復処理実行中フラグＰＷＭの値が「０」のときに成立する。なお、被毒回復処理実行中フラグＰＷＭは、その値が「１」のとき後述する被毒回復処理を実行していることを示し、その値が「０」のとき同被毒回復処理を実行していないことを示す。
【０１０５】
いま、空燃比フィードバック制御条件が成立しているものとして説明を続けると、ＣＰＵ７１はステップ１００５にて「Ｙｅｓ」と判定してステップ１０１０に進み、現時点の上流側空燃比センサ６６の出力ｖａｂｙｆｓと後述するサブフィードバック制御量ｖａｆｓｆｂとの和（ｖａｂｙｆｓ＋ｖａｆｓｆｂ）を図３に示したマップに基づいて変換することにより、現時点における第１触媒５３の上流側制御用空燃比ａｂｙｆｓを求める。
【０１０６】
次に、ＣＰＵ７１はステップ１０１５に進み、現時点からＮストローク（Ｎ回の吸気行程）前に吸気行程を迎えた気筒の吸入空気量である筒内吸入空気量Ｍｃ（ｋ−Ｎ）を前記求めた上流側制御用空燃比ａｂｙｆｓで除することにより、現時点からＮストローク前の筒内燃料供給量Ｆｃ（ｋ−Ｎ）を求める。値Ｎは、内燃機関の排気量、燃焼室２５から上流側空燃比センサ６６までの距離等により異なる値である。
【０１０７】
このように、現時点からＮストローク前の筒内燃料供給量Ｆｃ（ｋ−Ｎ）を求めるために、現時点からＮストローク前の筒内吸入空気量Ｍｃ（ｋ−Ｎ）を上流側制御用空燃比ａｂｙｆｓで除するのは、燃焼室２５内で燃焼された混合気が上流側空燃比センサ６６に到達するまでには、Ｎストロークに相当する時間を要しているからである。なお、筒内吸入空気量Ｍｃは、各気筒の吸気行程毎に、その時点のエアフローメータ６１により計測された吸入空気流量Ｇａと、エンジン回転速度ＮＥとに基づいて求められ（例えば、エアフローメータ６１により計測された吸入空気流量Ｇａに一次遅れ処理を施した値をエンジン回転速度ＮＥで除することにより求められ）、各吸気行程に対応してＲＡＭ７３内に記憶されている。
【０１０８】
次いで、ＣＰＵ７１はステップ１０２０に進み、現時点からＮストローク前の筒内吸入空気量Ｍｃ（ｋ−Ｎ）を現時点からＮストローク前の時点における目標空燃比ａｂｙｆｒ（ｋ−Ｎ）（この例では、理論空燃比）で除することにより、現時点からＮストローク前の目標筒内燃料供給量Ｆｃｒ（ｋ−Ｎ）を求める。そして、ＣＰＵ７１はステップ１０２５に進んで目標筒内燃料供給量Ｆｃｒ（ｋ−Ｎ）から筒内燃料供給量Ｆｃ（ｋ−Ｎ）を減じた値を筒内燃料供給量偏差ＤＦｃとして設定する。つまり、筒内燃料供給量偏差ＤＦｃは、Ｎストローク前の時点で筒内に供給された燃料の過不足分を表す量となる。次に、ＣＰＵ７１はステップ１０３０に進み、下記数１５に基づいてフィードバック補正量ＤＦｉを求める。
【０１０９】
【数１５】
ＤＦｉ＝（Ｇｐ・ＤＦｃ＋Ｇｉ・ＳＤＦｃ）・ＫＦＢ
【０１１０】
上記数１５において、Ｇｐは予め設定された比例ゲイン、Ｇｉは予め設定された積分ゲインである。なお、数１５の係数ＫＦＢはエンジン回転速度ＮＥ、及び筒内吸入空気量Ｍｃにより可変とすることが好適であるが、ここでは「１」としている。また、値ＳＤＦｃは筒内燃料供給量偏差ＤＦｃの積分値であり、次のステップ１０３５にて更新される。即ち、ＣＰＵ７１は、ステップ１０３５にてその時点における筒内燃料供給量偏差ＤＦｃの積分値ＳＤＦｃに上記ステップ１０２５にて求めた筒内燃料供給量偏差ＤＦｃを加えて、新たな筒内燃料供給量偏差の積分値ＳＤＦｃを求め、ステップ１０９５にて本ルーチンを一旦終了する。以上により、フィードバック補正量ＤＦｉが求められ、このフィードバック補正量ＤＦｉが前述した図９のステップ９１０，９１５により燃料噴射量に反映されるので、Ｎストローク前の燃料供給量の過不足が補償され、機関に供給される混合気の空燃比の平均値が目標空燃比ａｂｙｆｒと略一致せしめられるようにフィードバック制御される。
【０１１１】
一方、ステップ１００５の判定時において、空燃比フィードバック制御条件が不成立であると、ＣＰＵ７１は同ステップ１００５にて「Ｎｏ」と判定してステップ１０４０に進み、空燃比フィードバック補正量ＤＦｉの値を「０」に設定し、ステップ１０９５に進んで本ルーチンを一旦終了する。このように、空燃比フィードバック制御条件が不成立であるときは、空燃比フィードバック補正量ＤＦｉを「０」として空燃比（基本燃料噴射量Ｆｂａｓｅ）の補正を行わない。
【０１１２】
次に、下流側空燃比センサ６７の出力に基づく先に説明した空燃比フィードバック制御について説明する。なお、かかる制御はサブフィードバック制御とも呼ばれる。このサブフィードバック制御により、サブフィードバック制御量ｖａｆｓｆｂが算出される。
【０１１３】
ＣＰＵ７１は、サブフィードバック制御量ｖａｆｓｆｂを求めるために、図１１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１１００から処理を開始し、ステップ１１０５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、例えば、前述したステップ１００５での空燃比フィードバック制御条件に加え、機関の冷却水温ＴＨＷが前記第１所定温度よりも高い第２所定温度以上であり、下流側空燃比センサ６７が正常（活性状態であることを含む。）のときに成立する。
【０１１４】
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１１０５にて「Ｙｅｓ」と判定してステップ１１１０に進み、前記目標値Ｖｏｘｓｒｅｆから現時点の下流側空燃比センサ６７の出力Ｖｏｘｓを減じることにより、出力偏差量ＤＶｏｘｓを求める。次に、ＣＰＵ７１はステップ１１１５に進み、下記数１６に基づいてサブフィードバック制御量ｖａｆｓｆｂを求める。
【０１１５】
【数１６】
ｖａｆｓｆｂ＝Ｋｐ・ＤＶｏｘｓ＋Ｋｉ・ＳＤＶｏｘｓ
【０１１６】
上記数１６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、ＳＤＶｏｘｓは、出力偏差量ＤＶｏｘｓの積分値であって、次のステップ１１２０にて更新される値である。即ち、ＣＰＵ７１は、ステップ１１２０に進むと、その時点における出力偏差量の積分値ＳＤＶｏｘｓに上記ステップ１１１０にて求めた出力偏差量ＤＶｏｘｓを加えて、新たな出力偏差量の積分値ＳＤＶｏｘｓを求め、その後、ステップ１１９５に進んで本ルーチンを一旦終了する。
【０１１７】
このようにして、サブフィードバック制御量ｖａｆｓｆｂが求められ、この値は前述した図１０のステップ１０１０にて上流側空燃比センサ６６の実際の出力ｖａｂｙｆｓに加えられ、その和（ｖａｂｙｆｓ ＋ ｖａｆｓｆｂ）が図３に示したマップに基づいて前記上流側制御用空燃比ａｂｙｆｓに変換される。換言すると、下流側空燃比センサ６７の出力Ｖｏｘｓに基づいて求められる（修正される）上流側制御用空燃比ａｂｙｆｓは、上流側空燃比センサ６６が実際に検出している空燃比に対して、サブフィードバック制御量ｖａｆｓｆｂに相当する分だけ異なる空燃比として求められる。この結果、前述した図１０のステップ１０１５にて計算される筒内燃料供給量Ｆｃ（ｋ−Ｎ）が下流側空燃比センサ６７の出力Ｖｏｘｓに応じて変化し、ステップ１０２５，１０３０にてフィードバック補正量ＤＦｉが同下流側空燃比センサ６７の出力Ｖｏｘｓに応じて変更せしめられる。これにより、第１触媒５３の下流側の空燃比が目標値Ｖｏｘｓｒｅｆに一致するように、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）が制御せしめられる。
【０１１８】
例えば、機関に供給される混合気の平均的な空燃比がリーンであるために下流側空燃比センサ６７の出力Ｖｏｘｓが理論空燃比よりもリーンである空燃比に対応した値を示すと、ステップ１１１０にて求められる出力偏差量ＤＶｏｘｓが正の値となるので、ステップ１１１５にて求められるサブフィードバック制御量ｖａｆｓｆｂは正の値となる（図５（Ａ）においては、例えば、時刻ｔ２’〜ｔ３’）。従って、ステップ１０１０にて求められるａｂｙｆｓは上流側空燃比センサ６６が実際に検出している空燃比よりもリーンな値（より大きな値）として求められる。このため、ステップ１０１５にて求められる筒内燃料供給量Ｆｃ（ｋ−Ｎ）は小さい値となり、ステップ１０２５にて求められる筒内燃料供給量偏差ＤＦｃは大きい正の値として求められるので、ステップ１０３０にて求められる空燃比フィードバック補正量ＤＦｉが大きい正の値となる。これにより、図９のステップ９１０にて求められる最終燃料噴射量Ｆｉは、基本燃料噴射量Ｆｂａｓｅよりも大きくなって、機関に供給される混合気の空燃比がリッチとなるように制御される。
【０１１９】
反対に、機関に供給される混合気の平均的な空燃比がリッチであるために下流側空燃比センサ６７の出力Ｖｏｘｓが理論空燃比よりもリッチ空燃比に対応した値を示すと、ステップ１１１０にて求められる出力偏差量ＤＶｏｘｓが負の値となるので、ステップ１１１５にて求められるサブフィードバック制御量ｖａｆｓｆｂは負の値となる（図５（Ａ）においては、例えば、時刻ｔ１’〜ｔ２’，時刻ｔ３’〜ｔ４’）。従って、ステップ１０１０にて求められるａｂｙｆｓは上流側空燃比センサ６６が実際に検出している空燃比よりもリッチな値（より小さな値）として求められる。このため、ステップ１０１５にて求められる筒内燃料供給量Ｆｃ（ｋ−Ｎ）は大きい値となり、筒内燃料供給量偏差ＤＦｃは負の値として求められるので、フィードバック補正量ＤＦｉが負の値となる。これにより、図９のステップ９１０にて求められる最終燃料噴射量Ｆｉは、基本燃料噴射量Ｆｂａｓｅよりも小さくなって、機関に供給される混合気の空燃比がリーンとなるように制御される。
【０１２０】
一方、サブフィードバック制御条件が不成立であるとき、ＣＰＵ７１はステップ１１０５にて「Ｎｏ」と判定してステップ１１２５に進み、サブフィードバック制御量ｖａｆｓｆｂの値を「０」に設定する。これにより、下流側空燃比センサ６７の出力Ｖｏｘｓに基づくサブフィードバック制御が停止される。
【０１２１】
次に、第１触媒５３の各ブロック毎の流出酸素量，酸素吸蔵量等の算出における作動について説明する。ＣＰＵ７１は図１２及び図１３のフローチャートにより示された各ルーチンを所定時間の経過毎に実行するようになっている。
【０１２２】
従って、所定のタイミングになると、ＣＰＵ７１は、第１触媒５３の各ブロック毎の流出酸素量，酸素吸蔵量等を算出するための図１２に示したルーチンのステップ１２００から処理を開始し、ステップ１２０５に進んで、先に説明した上流側空燃比センサ６６により検出された空燃比Ａ／Ｆの平均値ａｂｙｆｓａｖｅと、図９のステップ９２０にて逐次更新されている燃料噴射量合計量ｍｆｒの最新値と、上記数１４に基づくステップ１２０５内に記載した式とに基づいて、先に説明したように境界条件である第１触媒５３のブロック（１）における流入酸素量ＣｇｉｎＯ２（１）を算出する。
【０１２３】
次いで、ＣＰＵ７１はステップ１２１０に進んでカウンタ値ｎの値、及び第１触媒５３の酸素吸蔵量ＯＳＡａｌｌの値をそれぞれ「０」に設定した後、ステップ１２１５に進んで第１触媒５３の各ブロック毎の流出酸素量，酸素吸蔵量等を算出する処理を開始する。まず、ＣＰＵ７１はステップ１２１５においてカウンタ値ｎの値を「１」だけ増大して「１」に設定する。カウンタ値ｎは第１触媒５３のブロック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１２２０からステップ１２７５までの今回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１２２０〜ステップ１２７５までの処理においては最上流のブロック（１）における計算が実行される。
【０１２４】
まず、ＣＰＵ７１はステップ１２２０に進んで、流入酸素量ＣｇｉｎＯ２（１）の値が「０」以上であるか否かを判定し、流入酸素量ＣｇｉｎＯ２（１）の値が「０」以上であれば同ステップ１２２０において「Ｙｅｓ」と判定するとともにステップ１２２５に進んで、先に説明したように予め所定の一定値に設定されているブロック（１）の最大酸素吸蔵量Ｃｍａｘ（１）の値と、後述するステップ１２６０にて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）の酸素吸蔵量ＯＳＡ（１）の値と、上記数３（の右辺）に基づくステップ１２２５内に記載した式とに基づいてブロック（１）における反応率Ｈを算出する。
【０１２５】
また、ステップ１２２０における判定において、流入酸素量ＣｇｉｎＯ２（１）の値が「０」以上でなければＣＰＵ７１は同ステップ１２２０において「Ｎｏ」と判定するとともにステップ１２３０に進んで、上記最大酸素吸蔵量Ｃｍａｘ（１）の値と、上記酸素吸蔵量ＯＳＡ（１）の値と、上記数５（の右辺）に基づくステップ１２３０内に記載した式とに基づいてブロック（１）における反応率Ｈを算出する。
【０１２６】
次いで、ＣＰＵ７１はステップ１２３５に進み、ステップ１２２５又はステップ１２３０にて算出した反応率Ｈの値と、ステップ１２０５にて算出したブロック（１）における流入酸素量ＣｇｉｎＯ２（１）の値と、上記数２（の右辺）又は上記数４（の右辺）に基づくステップ１２３５内に記載した式とに基づいてブロック（１）における酸素吸蔵量変化量δＯＳＡ（１）を算出する。
【０１２７】
次に、ＣＰＵ７１はステップ１２４０に進んで、後述するステップ１２６０にて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）の酸素吸蔵量ＯＳＡ（１）の値とステップ１２３５にて今回算出したブロック（１）の酸素吸蔵量変化量δＯＳＡ（１）の値とを積算した値がブロック（１）における最大酸素吸蔵量Ｃｍａｘ（１）の値以下であるか否かを判定する。
【０１２８】
ここで、前記積算した値が最大酸素吸蔵量Ｃｍａｘ（１）の値以下であればＣＰＵ７１はステップ１２４０にて「Ｙｅｓ」と判定してステップ１２４５に進んで同積算した値が「０」以上であるか否かを判定するとともに、同積算した値が「０」以上であれば同ステップ１２４５にて「Ｙｅｓ」と判定してステップ１２６０に進んで、同積算した値を新たな酸素吸蔵量ＯＳＡ（１）として設定する。このように、前記積算した値が「０」以上最大酸素吸蔵量Ｃｍａｘ（１）以下であればステップ１２３５にて算出された酸素吸蔵量変化量δＯＳＡ（１）の値がそのままブロック（１）における酸素吸蔵量変化量として使用される。
【０１２９】
一方、ステップ１２４０の判定において、前記積算した値が最大酸素吸蔵量Ｃｍａｘ（１）の値を超えていればＣＰＵ７１は同ステップ１２４０にて「Ｎｏ」と判定してステップ１２５０に進み、最大酸素吸蔵量Ｃｍａｘ（１）の値から前回算出した酸素吸蔵量ＯＳＡ（１）の値を減算した値を酸素吸蔵量変化量δＯＳＡ（１）に格納した後、ステップ１２６０に進む。このように、前記積算した値がブロック（１）における最大酸素吸蔵量Ｃｍａｘ（１）を超えていれば今回ステップ１２６０にて算出されるブロック（１）における酸素吸蔵量ＯＳＡ（１）の値が最大酸素吸蔵量Ｃｍａｘ（１）を超えてしまうことを意味するので、今回ステップ１２６０にて算出される酸素吸蔵量ＯＳＡ（１）の値が最大酸素吸蔵量Ｃｍａｘ（１）の値と等しくなるように酸素吸蔵量変化量δＯＳＡ（１）が調整される。
【０１３０】
同様に、ステップ１２４５の判定において、前記積算した値が「０」未満（負の値）となっていればＣＰＵ７１は同ステップ１２４５にて「Ｎｏ」と判定してステップ１２５５に進み、前回算出した酸素吸蔵量ＯＳＡ（１）の値に対して符号を反転させた値を酸素吸蔵量変化量δＯＳＡ（１）に格納した後、ステップ１２６０に進む。このように、前記積算した値が「０」未満であれば今回ステップ１２６０にて算出されるブロック（１）における酸素吸蔵量ＯＳＡ（１）の値が「０」未満（負の値）になってしまうことを意味するので、今回ステップ１２６０にて算出される酸素吸蔵量ＯＳＡ（１）の値が「０」になるように酸素吸蔵量変化量δＯＳＡ（１）が調整される。
【０１３１】
ステップ１２６０にてブロック（１）における今回の酸素吸蔵量ＯＳＡ（１）を算出した後、ＣＰＵ７１はステップ１２６５に進んでステップ１２０５にて算出したブロック（１）における流入酸素量ＣｇｉｎＯ２（１）の値と、上記調整後のブロック（１）における酸素吸蔵量変化量δＯＳＡ（１）の値と、上記数１（の右辺）に基づくステップ１２６５内に記載した式とに基づいてブロック（１）における流出酸素量ＣｇｏｕｔＯ２（１）を算出する。
【０１３２】
次いで、ＣＰＵ７１はステップ１２７０に進んで、（現時点ではステップ１２１０の実行により「０」となっている）現時点における第１触媒５３の酸素吸蔵量ＯＳＡａｌｌの値にステップ１２６０にて算出されたブロック（１）における今回の酸素吸蔵量ＯＳＡ（１）の値を加えた値を新たな酸素吸蔵量ＯＳＡａｌｌとして格納した後、ステップ１２７５に進んで、ステップ１２６５にて算出されたブロック（１）における流出酸素量ＣｇｏｕｔＯ２（１）の値と、上記数７に基づいてブロック（１）に隣接する下流側のブロック（２）における流入酸素量ＣｇｉｎＯ２（２）を算出する。
【０１３３】
そして、ＣＰＵ７１はステップ１２８０に進んでカウンタ値ｎの値が第１触媒５３のブロック数Ｎ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１２８０にて「Ｎｏ」と判定し、再びステッ１２１５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１２２０〜ステップ１２７５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（２）における計算を実行する。このとき、ステップ１２６５における流入酸素量ＣｇｉｎＯ２（２）の値としては前回ステップ１２７５にて算出した流入酸素量ＣｇｉｎＯ２（２）の値が使用される。
【０１３４】
このようにして、ステップ１２２０〜ステップ１２７５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Ｎと等しくなるまで繰り返し実行される。これにより、第１触媒５３の最上流のブロック（１）から最下流のブロック（Ｎ）までの各ブロック（ｎ）の流入酸素量ＣｇｉｎＯ２（ｎ）、流出酸素量ＣｇｏｕｔＯ２（ｎ）、酸素吸蔵量変化量δＯＳＡ（ｎ）、及び酸素吸蔵量ＯＳＡ（ｎ）の値が順次算出されていく。また、ステップ１２７０の処理が繰り返し実行されることにより、第１触媒５３の酸素吸蔵量ＯＳＡａｌｌも算出される。このようにして、カウンタ値ｎの値がブロック数Ｎであるときにステップ１２６５にて算出される値が第１触媒５３から流出するガス中の酸素の過不足量（流出酸素量）ＣｇｏｕｔＯ２（Ｎ）となる。
【０１３５】
ステップ１２１５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Ｎと等しくなると、ＣＰＵ７１はステップ１２８０にて「Ｙｅｓ」と判定し、続くステップ１２８５にて燃料噴射量合計量ｍｆｒの値を「０」に設定した後、ステップ１２９５に進んで本ルーチンを一旦終了する。
【０１３６】
また、ＣＰＵ７１は、所定のタイミングになると、第１触媒５３の各ブロック毎の酸素吸蔵量の値、並びに第１触媒５３の酸素吸蔵量の値を初期化（クリア）するための図１３にフローチャートにより示したルーチンのステップ１３００から処理を開始し、ステップ１３０５に進んで、下流側空燃比センサ６７の出力Ｖｏｘｓの値が０．７（Ｖ）より大きいか否かをモニタする。このとき、下流側空燃比センサ６７の出力Ｖｏｘｓ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１３１０に進んで第１触媒５３の各ブロック毎の酸素吸蔵量の値及び第１触媒５３の酸素吸蔵量の値を総て「０」に設定する処理を開始する。一方、ステップ１３０５の判定において、下流側空燃比センサ６７の出力Ｖｏｘｓの値が０．７（Ｖ）以下であれば、ＣＰＵ７１はステップ１３０５からステップ１３９５に直接進んで本ルーチンを一旦終了する。
【０１３７】
いま、ステップ１３０５の判定において下流側空燃比センサ６７の出力Ｖｏｘｓの値が０．７（Ｖ）より大きくなっているとすると、ＣＰＵ７１はステップ１３１０に進み、カウンタ値ｎの値を「０」に設定した後、ステップ１３１５に進んでカウンタ値ｎの値を「１」だけ増大して「１」に設定する。次いで、ＣＰＵ７１はステップ１３２０に進んで、第１触媒５３のブロック（ｎ）における酸素吸蔵量ＯＳＡ（ｎ）の値を「０」に設定する。この時点ではカウンタ値ｎの値は「１」であるから、最上流のブロック（１）における酸素吸蔵量ＯＳＡ（１）の値が「０」に設定される。
【０１３８】
そして、ＣＰＵ７１はステップ１３２５に進んでカウンタ値ｎの値が第１触媒５３のブロック数Ｎ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１３２５にて「Ｎｏ」と判定し、再びステップ１３１５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１３２０及びステップ１３２５の処理を実行する。即ち、ステップ１３２０及びステップ１３２５の処理は、カウンタ値ｎの値が第１触媒５３のブロック数Ｎと等しくなるまで繰り返し実行される。これにより、第１触媒５３の最上流のブロック（１）から最下流のブロック（Ｎ）までの各ブロック（ｎ）における酸素吸蔵量ＯＳＡ（ｎ）の値が総て「０」にクリアされる。
【０１３９】
前述のステップ１３１５の処理が繰り返されることによりカウンタ値ｎの値が触媒５３のブロック数Ｎと等しくなると、ＣＰＵ７１はステップ１３２５にて「Ｙｅｓ」と判定してステップ１３３０に進み、第１触媒５３の酸素吸蔵量ＯＳＡａｌｌの値を「０」に設定した後、ステップ１３９５に進んで本ルーチンを一旦終了する。
【０１４０】
次に、下流側空燃比センサ６７の出力Ｖｏｘｓが前記第１の状態となる頻度ＳＭＬが前記基準値ＳＭＬ０に達する毎（一サンプリング期間が経過する毎）にこの一サンプリング期間中にて下流側空燃比センサ６７の出力Ｖｏｘｓが同第１の状態となった時点において流出酸素量ＣｇｏｕｔＯ２（Ｎ）が前記第２の状態になっている頻度ＦＲＥを求める際の作動について説明する。ＣＰＵ７１は図１４のフローチャートにより示された各ルーチンを所定時間の経過毎に実行するようになっている。
【０１４１】
従って、所定のタイミングになると、ＣＰＵ７１はステップ１４００から処理を開始し、ステップ１４０５に進んで、前述の図１１のステップ１１０５におけるものと同様のサブフィードバック制御条件が成立していて、且つ、被毒回復処理実行中フラグＰＷＭの値が「０」になっているか否かを判定し、ステップ１４０５にて「Ｎｏ」と判定するときはステップ１４５０に直ちに進んで、現時点での下流側空燃比センサ出力Ｖｏｘｓの値を前回の下流側空燃比センサ出力Ｖｏｘｓｐとして設定した後、本ルーチンを一旦終了する。これは、下流側空燃比センサ６７が正常であって、且つ後述する被毒回復処理が実行されていない場合における前記頻度ＦＲＥを算出するためである。
【０１４２】
いま、サブフィードバック制御条件が成立し、被毒回復処理実行中フラグＰＷＭの値が「０」になっていて、且つ、下流側空燃比センサ６７の出力Ｖｏｘｓがリッチ側所定値Ｖｒｉｃｈを増加しながら、或いはリーン側所定値Ｖｌｅａｎを減少しながら通過する前記第１の状態となっていないものとして説明を続けると、ＣＰＵ７１はステップ１４０５にて「Ｙｅｓ」と判定してステップ１４１０に進み、今回の（現時点での）下流側空燃比センサ出力Ｖｏｘｓの値がリッチ側所定値Ｖｒｉｃｈよりも大きく、且つ、前回本ルーチン実行時にステップ１４５０にて更新されている前回の下流側空燃比センサ出力Ｖｏｘｓｐの値が同リッチ側所定値Ｖｒｉｃｈ以下であるか否か（従って、下流側空燃比センサ出力Ｖｏｘｓがリッチ側所定値Ｖｒｉｃｈを増加しながら通過しているか否か）を判定する。
【０１４３】
現時点では、上記の仮定に従い、ＣＰＵ７１はステップ１４１０にて「Ｎｏ」と判定してステップ１４１５に進み、今回の下流側空燃比センサ出力Ｖｏｘｓの値がリーン側所定値Ｖｌｅａｎよりも小さく、且つ、前回の下流側空燃比センサ出力Ｖｏｘｓｐの値が同リーン側所定値Ｖｌｅａｎ以上であるか否か（従って、下流側空燃比センサ出力Ｖｏｘｓがリーン側所定値Ｖｌｅａｎを減少しながら通過しているか否か）を判定する。
【０１４４】
現時点では、上記の仮定に従い、ＣＰＵ７１はステップ１４１５でも「Ｎｏ」と判定してステップ１４５０に直ちに進む。以降、ＣＰＵ７１は、下流側空燃比センサ６７の出力Ｖｏｘｓが前記第１の状態とならない限りにおいてステップ１４００〜１４１５，１４５０の処理を繰り返し実行する。
【０１４５】
次に、この状態から、下流側空燃比センサ出力Ｖｏｘｓがリッチ側所定値Ｖｒｉｃｈを増加しながら通過した場合（図５（Ａ）においては時刻ｔ１，ｔ３）について説明すると、この場合、ＣＰＵ７１はステップ１４１０に進んだとき「Ｙｅｓ」と判定してステップ１４２０に進み、現時点での頻度ＳＭＬの値を「１」だけ増大した値を新たな頻度ＳＭＬとして設定する。
【０１４６】
次いで、ＣＰＵ７１はステップ１４２５に進んで、前述した図１２のステップ１２６５にて算出されている流出酸素量ＣｇｏｕｔＯ２（Ｎ）の最新値が負の閾値Ｃｒｅｆｍｎｓよりも小さい値になっているか（即ち、流出酸素量ＣｇｏｕｔＯ２（Ｎ）が第２の状態になっているか）否かを判定し、「Ｙｅｓ」と判定するときにはステップ１４３０にて現時点での頻度ＦＲＥの値を「１」だけ増大した値を新たな頻度ＦＲＥとして設定した後にステップ１４５０に進む。一方、ステップ１４２５の判定にて「Ｎｏ」と判定するときにはＣＰＵ７１は頻度ＦＲＥの値を現時点での値に維持したままステップ１４５０に直ちに進む。以降、ＣＰＵ７１は、再び、下流側空燃比センサ６７の出力Ｖｏｘｓが前記第１の状態とならない限りにおいてステップ１４００〜１４１５，１４５０の処理を繰り返し実行するようになる。
【０１４７】
次に、この状態から、下流側空燃比センサ出力Ｖｏｘｓがリーン側所定値Ｖｌｅａｎを減少しながら通過した場合（図５（Ａ）においては時刻ｔ２，ｔ４）について説明すると、この場合、ＣＰＵ７１はステップ１４１５に進んだとき「Ｙｅｓ」と判定してステップ１４３５に進み、現時点での頻度ＳＭＬの値を「１」だけ増大した値を新たな頻度ＳＭＬとして設定する。
【０１４８】
次いで、ＣＰＵ７１はステップ１４４０に進んで、前述した図１２のステップ１２６５にて算出されている流出酸素量ＣｇｏｕｔＯ２（Ｎ）の最新値が正の閾値Ｃｒｅｆｐｌｓよりも大きい値になっているか（即ち、流出酸素量ＣｇｏｕｔＯ２（Ｎ）が第２の状態になっているか）否かを判定し、「Ｙｅｓ」と判定するときにはステップ１４４５にて現時点での頻度ＦＲＥの値を「１」だけ増大した値を新たな頻度ＦＲＥとして設定した後にステップ１４５０に進む。一方、ステップ１４４０の判定にて「Ｎｏ」と判定するときにはＣＰＵ７１は頻度ＦＲＥの値を現時点での値に維持したままステップ１４５０に直ちに進む。以降、ＣＰＵ７１は、再び、下流側空燃比センサ６７の出力Ｖｏｘｓが前記第１の状態とならない限りにおいてステップ１４００〜１４１５、１４５０の処理を繰り返し実行するようになる。
【０１４９】
このように、本ルーチンが繰り返し実行されることにより、下流側空燃比センサ６７の出力Ｖｏｘｓが前記第１の状態となる毎に頻度ＳＭＬの値が「１」だけ増大されるとともに、下流側空燃比センサ６７の出力Ｖｏｘｓが同第１の状態となった時点において流出酸素量ＣｇｏｕｔＯ２（Ｎ）が第２の状態になっている毎に頻度ＦＲＥの値が「１」だけ増大されていく。
【０１５０】
また、ＣＰＵ７１は、図１５にフローチャートにより示した第１触媒５３の劣化判定を行うための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。従って、所定のタイミングになると、ＣＰＵ７１はステップ１５００から処理を開始し、ステップ１５０５に進んで、頻度ＳＭＬの値が前記基準値ＳＭＬ０以上となったか否かを判定する。このとき、頻度ＳＭＬの値が基準値ＳＭＬ０よりも小さければ、ＣＰＵ７１は触媒の劣化判定を行うことなくステップ１５９５に直ちに進んで本ルーチンを一旦終了する。
【０１５１】
一方、頻度ＳＭＬが基準値ＳＭＬ０に達していると（即ち、前記一サンプリング期間が経過すると）、ＣＰＵ７１はステップ１５０５にて「Ｙｅｓ」と判定してステップ１５１０に進み、頻度ＦＲＥの値が劣化判定基準値ＦＲＥｒｅｆ以上であるか否かを判定する。
【０１５２】
いま、第１触媒５３の劣化の程度が少ないものとして説明を続けると、この場合、頻度ＦＲＥの値が劣化判定基準値ＦＲＥｒｅｆ以上となっている。従って、ＣＰＵ７１はステップ１５１０にて「Ｙｅｓ」と判定してステップ１５１５に進んで、劣化判定フラグＸＲの値を「０」に設定し、続くステップ１５２０にてカウンタＣＮＴの値を「０」に設定する。ここで、劣化判定フラグＸＲは、その値が「１」であるとき第１触媒５３が前記劣化触媒であることを示し、その値が「０」であるとき第１触媒５３が前記正常触媒であることを示す。また、カウンタＣＮＴの値は、前記一サンプリング期間の経過毎に連続して劣化判定フラグＸＲが「１」となる（従って、連続して第１触媒５３が劣化触媒であると判定される）回数を示す値である。
【０１５３】
そして、ＣＰＵ７１はステップ１５２５に進み、警報ランプ８２に同警報ランプ８２を消灯させるための指示信号を送出するとともに、続くステップ１５３０にて頻度ＳＭＬの値、及び頻度ＦＲＥの値を共に「０」に設定した後、ステップ１５９５に進んで本ルーチンを一旦終了する。これにより、図１４のルーチンが繰り返し実行されることで、再度、頻度ＳＭＬの値が基準値ＳＭＬ０に達するまで（即ち、次の一サンプリング期間が経過するまで）頻度ＦＲＥの値が「０」から更新されていき、次の一サンプリング期間が経過するとその時点における更新された頻度ＦＲＥの値に基づいて再び第１触媒５３の劣化判定が実行される。そして、かかる頻度ＦＲＥの値が劣化判定基準値ＦＲＥｒｅｆ以上となっている限りにおいて、第１触媒５３は正常触媒であると判定され続ける。
【０１５４】
次に、この状態から、第１触媒５３の劣化が進行して頻度ＦＲＥの値が劣化判定基準値ＦＲＥｒｅｆより小さくなった場合について説明すると、この場合、ＣＰＵ７１はステップ１５１０にて「Ｎｏ」と判定してステップ１５３５に進むようになり、同ステップ１５３５にて劣化判定フラグＸＲの値を「１」に設定し、続くステップ１５４０にて被毒回復処理実行中フラグＰＷＭの値を「１」に設定するとともに、続くステップ１５４５にて現時点でのカウンタＣＮＴの値（現時点では「０」である。）を「１」だけ増大した値（＝１）を新たなカウンタＣＮＴとして設定する。
【０１５５】
次いで、ＣＰＵ７１はステップ１５５０に進み、カウンタＣＮＴの値が「１」以下であるか、即ち、連続して第１触媒５３が劣化触媒であると判定された回数が１回以下であるか否かを判定する。現時点では、カウンタＣＮＴの値は「１」であるから、ＣＰＵ７１はステップ１５５０にて「Ｙｅｓ」と判定してステップ１５３０に直ちに進んで頻度ＳＭＬの値、及び頻度ＦＲＥの値を共に「０」に設定した後、ステップ１５９５に進んで本ルーチンを一旦終了する。
【０１５６】
これにより、被毒回復処理実行中フラグＰＷＭの値が「１」となって前述の空燃比フィードバック制御条件が成立しなくなるから、ＣＰＵ７１は図１０のステップ１００５にて「Ｎｏ」と判定してステップ１０４０に進むようになり、空燃比フィードバック補正量ＤＦｉの値が「０」に設定されて前述の空燃比フィードバック制御が中断されるようになる。また、ＣＰＵ７１は図１４のステップ１４０５にて「Ｎｏ」と判定してステップ１４５０に直ちに進むようになり、頻度ＦＲＥの算出も中断されるようになる。従って、頻度ＳＭＬの値が「０」に維持されるから、ＣＰＵ７１が図１５のステップ１５０５にて「Ｎｏ」と判定し続けることで、第１触媒５３の劣化判定が実行されなくなる。これにより、カウンタＣＮＴの値は「１」に維持される。
【０１５７】
また、ＣＰＵ７１は、図１６にフローチャートにより示した被毒回復処理を実行するためのルーチンを実行するようになっている。一般に、第１触媒５３のような三元触媒の劣化には、大別すると、熱による劣化と被毒による劣化が存在する。ここで、三元触媒が熱により劣化した場合、その劣化状態を解消することは困難である。一方、三元触媒が被毒により劣化した場合、所定の被毒回復処理を実行することでその劣化状態を解消できる可能性があることが知られている。以下、かかる被毒による劣化、及び、被毒回復処理について簡単に説明する。
【０１５８】
触媒は、排気ガス中の還元剤（例えば、ＨＣ，ＣＯ等の未燃成分）が所定量だけ連続的に流入すると、同還元剤が同触媒内の貴金属やセリア（ＣｅＯ_２）（以下、「貴金属等」と称呼する。）の表面に付着して貴金属等の表面積が小さくなることにより被毒（所謂、一次被毒）し、かかる被毒により劣化する（例えば、触媒の最大酸素吸蔵量が低下する）ことが知られている。また、一方では、還元剤による触媒の一次被毒状態は、同触媒に所定量の酸素（従って、リーン空燃比のガス）を供給することにより解消することも知られている。
【０１５９】
他方、触媒は、排気ガス中の硫黄成分が所定量だけ連続的に流入すると、同硫黄成分が同触媒内の貴金属等の表面に付着して貴金属等の表面積が小さくなることにより被毒（所謂、一次被毒）し、かかる被毒によっても劣化することが知られている。また、一方では、硫黄成分による触媒の一次被毒状態は、同触媒に所定量の還元剤（例えば、ＨＣ，ＣＯ等の未燃成分。従って、リッチ空燃比のガス）を供給することにより解消することも知られている。
【０１６０】
以上のことから、本触媒劣化判定装置は、第１触媒５３が劣化触媒であると判定される毎に（即ち、図１５のステップ１５４０が実行されて被毒回復処理実行中フラグＰＷＭの値が「０」から「１」に変更される毎に）、前述の空燃比フィードバック制御を中止して機関に供給される混合気の空燃比を、所定の期間の経過毎に所定のリッチ空燃比、所定のリーン空燃比、同所定のリッチ空燃比、同所定のリーン空燃比の順に強制的に制御する被毒回復処理を実行する。
【０１６１】
このような被毒回復処理を実行するため、ＣＰＵ７１は、図１６のルーチンを所定時間の経過毎に繰り返し実行している。従って、所定のタイミングになると、ＣＰＵ７１はステップ１６００から処理を開始し、ステップ１６０５に進んで、被毒回復処理実行中フラグＰＷＭの値が「１」であるか否かを判定し、「Ｎｏ」と判定する場合、被毒回復処理を実行することなくステップ１６９５に直ちに進んで本ルーチンを一旦終了する。
【０１６２】
いま、前述の図１５のステップ１５４０が実行された直後であるものとして説明を続けると、ＣＰＵ７１はステップ１６０５にて「Ｙｅｓ」と判定してステップ１６１０に進み、被毒回復処理実行中フラグＰＷＭの値が「０」から「１」に変更されたか否かを判定する。現時点は、図１５のステップ１５４０が実行された直後であって被毒回復処理実行中フラグＰＷＭの値が「０」から「１」に変更された直後であるから、ＣＰＵ７１はステップ１６１０にて「Ｙｅｓ」と判定してステップ１６１５に進み、カウンタ値Ｔを「０」に設定するとともに、続くステップ１６２０にて図９のステップ９１０にて使用される係数Ｋの値を「１．０２」に設定する。ここで、カウンタ値Ｔは被毒回復処理が開始された時点からの経過時間を表す値である。
【０１６３】
次いで、ＣＰＵ７１はステップ１６２５に進み、カウンタ値を「１」だけ増大し、続くステップ１６３０にてカウンタ値Ｔが「４・Ｔ１」よりも小さいか否かを判定する。ここで、Ｔ１は前記所定の期間に相当する値である。従って、このステップ１６３０では、被毒回復処理が開始された後に前記所定の期間が４回繰り返されていないか否か、即ち、被毒回復処理を終了すべき時期が到来していないか否かが判定される。
【０１６４】
現時点は被毒回復処理が開始された直後であるから、ＣＰＵ７１はステップ１６３０にて「Ｙｅｓ」と判定してステップ１６３５に進み、カウンタ値Ｔが値「Ｔ１」又は値「３・Ｔ１」の何れかになっているか否かを判定する。現時点は被毒回復処理が開始された直後であるから、ＣＰＵ７１はステップ１６３０にて「Ｎｏ」と判定してステップ１６４０に進み、カウンタ値Ｔが値「２・Ｔ１」になっているか否かを判定する。現時点は被毒回復処理が開始された直後であるから、ＣＰＵ７１はステップ１６４０でも「Ｎｏ」と判定してステップ１６９５に直ちに進んで本ルーチンを一旦終了する。
【０１６５】
以降、ステップ１６２５が繰り返し実行されてカウンタ値Ｔが値Ｔ１になるまで（従って、被毒回復処理開始後に前記所定の期間が経過するまで）ＣＰＵ７１は、ステップ１６００〜１６１０，１６２５〜１６４０，１６９５の処理を繰り返し実行する。従って、被毒回復処理開始後に前記所定の期間が経過するまでの間、図９のステップ９１０の実行により、基本燃料噴射量Ｆｂａｓｅが１．０２倍された値が最終燃料噴射量Ｆｉとして算出され（空燃比フィードバック補正量ＤＦｉの値は「０」に設定されている。）、この最終燃料噴射量Ｆｉの燃料が噴射されるので、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）は理論空燃比よりもリッチな前記所定のリッチ空燃比に制御され続ける。これにより、硫黄成分による第１触媒５３の一次被毒状態が解消される可能性がある。
【０１６６】
次に、この状態から、カウンタ値Ｔが値Ｔ１になった場合について説明する。この場合、ＣＰＵ７１はステップ１６３５に進んだとき「Ｙｅｓ」と判定してステップ１６４５に進んで係数Ｋの値を「１．０２」から「０．９８」に変更した後、ステップ１６９５に進んで本ルーチンを一旦終了する。以降、ステップ１６２５が繰り返し実行されてカウンタ値Ｔが値Ｔ２になるまで（従って、１回目の所定の期間の経過後、２回目の所定の期間が経過するまで）ＣＰＵ７１は、ステップ１６００〜１６１０，１６２５〜１６４０，１６９５の処理を再び繰り返し実行するようになる。従って、１回目の所定の期間の経過後、２回目の所定の期間が経過するまでの間、基本燃料噴射量Ｆｂａｓｅが０．９８倍された値が最終燃料噴射量Ｆｉとして算出されるから、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）は理論空燃比よりもリーンな前記所定のリーン空燃比に制御され続ける。これにより、還元剤による第１触媒５３の一次被毒状態が解消される可能性がある。
【０１６７】
同様に、カウンタ値Ｔが値Ｔ１から増大していき値Ｔ２になると、ＣＰＵ７１はステップ１６４０に進んだとき「Ｙｅｓ」と判定してステップ１６５０に進み、係数Ｋの値を「０．９８」から再び「１．０２」に変更する。これにより、２回目の所定の期間の経過後、３回目の所定の期間が経過するまでの間、再び、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）は理論空燃比よりも前記所定のリッチ空燃比に制御され続ける。また、同様に、カウンタ値Ｔが値Ｔ２から増大していき値Ｔ３になると、ＣＰＵ７１はステップ１６３５に進んだとき「Ｙｅｓ」と判定してステップ１６４５に進み、係数Ｋの値を「１．０２」から再度「０．９８」に変更する。これにより、３回目の所定の期間の経過後、４回目の所定の期間が経過するまでの間、再び、機関に供給される混合気の空燃比（従って、第１触媒５３に流入するガスの空燃比）は理論空燃比よりも前記所定のリーン空燃比に制御され続ける。
【０１６８】
そして、カウンタ値Ｔが値Ｔ３から増大していき値Ｔ４になると、ＣＰＵ７１はステップ１６３０に進んだとき「Ｎｏ」と判定してステップ１６５５に進み、係数Ｋの値を「１．００」に再設定するとともに、続くステップ１６６０にて被毒回復処理実行中フラグＰＷＭの値を「１」から「０」に変更した後、ステップ１６９５に進んで本ルーチンを一旦終了する。
【０１６９】
以降、被毒回復処理実行中フラグＰＷＭの値が「０」になっているから、図１５のステップ１５４０にて被毒回復処理実行中フラグＰＷＭの値が再び「１」に設定されるまでの間、ＣＰＵ７１はステップ１６０５からステップ１６９５に直ちに進んで本ルーチンを一旦終了するようになる。また、空燃比フィードバック制御条件、及びサブフィードバック制御条件が成立していれば、ＣＰＵ７１は図１０のステップ１００５及び図１１のステップ１１０５にて「Ｙｅｓ」と判定するようになるから、空燃比フィードバック制御が再開されるともに、図１４のステップ１４０５にて「Ｙｅｓ」と判定するようになるから、頻度ＦＲＥの算出が再開される。
【０１７０】
従って、被毒回復処理が終了した時点以降、再び、頻度ＳＭＬが基準値ＳＭＬ０に達すると（即ち、一サンプリング期間が経過すると）、ＣＰＵ７１は図１５のステップ１５０５にて「Ｙｅｓ」と判定してステップ１５１０以降に進み、第１触媒５３の劣化判定を行う。そして、被毒回復処理により第１触媒５３の劣化状態が解消している場合、ＣＰＵ７１はステップ１５１０にて「Ｙｅｓ」と判定し、ステップ１５２０にてカウンタＣＮＴの値を現時点での値「１」から「０」にクリアする。
【０１７１】
一方、被毒回復処理によっても第１触媒５３の劣化状態が解消していない場合、ＣＰＵ７１はステップ１５１０にて再び「Ｎｏ」と判定し、ステップ１５４５にてカウンタＣＮＴの値を現時点での値「１」から「１」だけ増大して「２」に設定する。従って、ＣＰＵ７１は続くステップ１５５０にて「Ｎｏ」と判定するようになり、ステップ１５５５に進んで警報ランプ８２に同警報ランプ８２を点灯させるための指示信号を送出する。これにより、警報ランプ８２が点灯する。
【０１７２】
即ち、警報ランプ８２は、一旦、第１触媒５３が劣化触媒であると判定された後に被毒回復処理が１回実行されてもなお、第１触媒５３の劣化状態が解消しなかった場合に点灯されることになる。また、この場合、ステップ１５４０の処理によりその後に被毒回復処理が再び実行されることになる。そして、仮に、被毒回復処理が繰り返し実行されることでその後において第１触媒５３の劣化状態が解消されるようなことがあった場合、ＣＰＵ７１がステップ１５１０にて「Ｙｅｓ」と判定することで、ステップ１５２０にてカウンタＣＮＴの値が「０」にクリアされるとともに、ステップ１５２５にて現時点まで点灯し続けていた警報ランプ８２が消灯される。一方、第１触媒５３の劣化状態が引き続き解消されない場合は、ステップ１５２５の処理が実行されないことから警報ランプ８２は継続して点灯し続ける。
【０１７３】
以上、説明したように、本発明の実施形態によれば、第１触媒５３が新品の触媒であると想定して構築された同第１触媒５３を対象とする触媒モデルに基づき、第１触媒５３から流出するガス中の特定成分の量（流出酸素量ＣｇｏｕｔＯ２（Ｎ））を推定（算出）する。そして、本発明の実施形態は、第１触媒５３下流の下流側空燃比センサ６７の出力Ｖｏｘｓに基づく空燃比フィードバック制御中において、下流側空燃比センサ出力Ｖｏｘｓが第１の状態（リッチ側所定値Ｖｒｉｃｈを増加しながら、又はリーン側所定値Ｖｌｅａｎを減少しながら通過する状態）となる毎に触媒モデルが推定している流出酸素量ＣｇｏｕｔＯ２（Ｎ）が第２の状態（負の閾値Ｃｒｅｆｍｎｓよりも小さい値、又は正の閾値Ｃｒｅｆｐｌｓよりも大きい値になっている状態）になっているか否かを判定するとともに、下流側空燃比センサ出力Ｖｏｘｓが第１の状態となる頻度ＳＭＬが所定の基準値ＳＭＬ０に達する毎（一サンプリング期間が経過する毎）に、この一サンプリング期間中にて下流側空燃比センサ出力Ｖｏｘｓが第１の状態となった時点において流出酸素量ＣｇｏｕｔＯ２（Ｎ）が第２の状態になっている頻度ＦＲＥを求め、この頻度ＦＲＥが劣化判定基準値ＦＲＥｒｅｆ以上か否か（従って、頻度ＳＭＬ０に対する頻度ＦＲＥの割合が所定値以上か否か）に基づいて第１触媒５３が正常触媒であるか劣化触媒であるかを判定する。
【０１７４】
このような触媒劣化判定方法は、通常の空燃比フィードバック（サブフィードバック）における空燃比変動を伴うのみであって、従来技術のように機関が定常状態にあるときに空燃比を強制的に変化させないので、触媒劣化判定をドライバビリティの悪化を招くことなく行うことができた。また、通常の空燃比フィードバック制御（サブフィードバック制御）中に触媒劣化判定がなされるので、触媒劣化判定の機会を多く確保でき、この結果、第１触媒５３が正常触媒であるか劣化触媒であるかを遅滞なく判定することができた。
【０１７５】
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、上記実施形態においては、下流側空燃比センサ出力Ｖｏｘｓが第１の状態となる頻度ＳＭＬが基準値ＳＭＬ０に達する毎に頻度ＦＲＥと劣化判定基準値ＦＲＥｒｅｆとの比較結果に基づいて触媒の劣化判定を実行しているが、所定の（一定の）サンプリング時間の経過毎に同サンプリング時間内における頻度ＳＭＬに対する頻度ＦＲＥの割合と所定値との比較結果に基づいて触媒の劣化判定を実行するように構成してもよい。
【０１７６】
また、上記実施形態においては、下流側空燃比センサ出力Ｖｏｘｓが第１の状態（リッチ側所定値Ｖｒｉｃｈを増加しながら、又はリーン側所定値Ｖｌｅａｎを減少しながら通過する状態）となる頻度ＳＭＬ（ＳＭＬ０）に対する、同下流側空燃比センサ出力Ｖｏｘｓが第１の状態となる時点において第１触媒５３から流出する特定成分の量（流出酸素量ＣｇｏｕｔＯ２（Ｎ））が第２の状態（負の閾値Ｃｒｅｆｍｎｓよりも小さい値、又は正の閾値Ｃｒｅｆｐｌｓよりも大きい値になっている状態）になっている頻度ＦＲＥの割合に応じて第１触媒５３の劣化判定が実行されているが、前記第２の状態を、「減少している、又は増加している状態」としてもよい。また、第１触媒５３から流出する特定成分の量（流出酸素量ＣｇｏｕｔＯ２（Ｎ））が第１の状態（負の閾値Ｃｒｅｆｍｎｓを減少しながら、又は正の閾値Ｃｒｅｆｐｌｓを増加しながら通過する状態）となる頻度ＳＭＬ（ＳＭＬ０）に対する、同特定成分の量が第１の状態となる時点において下流側空燃比センサ出力Ｖｏｘｓが第２の状態（リッチ側所定値Ｖｒｉｃｈよりも大きい値、又はリーン側所定値Ｖｌｅａｎよりも小さい値になっている状態）になっている頻度ＦＲＥの割合に応じて第１触媒５３の劣化判定が実行されるように構成されてもよい。この場合、前記第２の状態を、「増加している、又は減少している状態」としてもよい。また、上述のリッチ側所定値Ｖｒｉｃｈ、及びリーン側所定値Ｖｌｅａｎは共に、目標値Ｖｏｘｓｒｅｆと等しい値に設定してもよい。
【０１７７】
また、上記実施形態においては、空燃比フィードバック制御（サブフィードバック制御）は下流側空燃比センサ６７の出力Ｖｏｘｓに基づいて実行されているが、触媒モデルにより推定されている流出酸素量ＣｇｏｕｔＯ２（Ｎ）に基づいて実行されるように構成してもよい。この場合、図１１のステップ１１１０を「ＤＶｏｘｓ ← ＣｇｏｕｔＯ２（Ｎ） − ＣｇｏｕｔＯ２ｒｅｆ」に書き換えればよい。ここで、ＣｇｏｕｔＯ２ｒｅｆは流出酸素量ＣｇｏｕｔＯ２（Ｎ）の目標値であって、例えば「０」である。
【０１７８】
また、サブフィードバック制御は、上記ＰＩ制御でなく、ＰＩＤ制御であってもよい。更に、下流側空燃比センサ６７は、上流側空燃比センサ６６と同様な空燃比センサであってもよい。また、下流側空燃比センサ６７の出力Ｖｏｘｓのみに基づいて機関に供給される混合気の空燃比をフィードバック制御するように構成してもよい。
【図面の簡単な説明】
【図１】本発明による触媒劣化判定装置を適用した内燃機関の概略図である。
【図２】図１に示したエアフローメータの出力電圧と計測された吸入空気流量との関係を示したマップである。
【図３】図１に示した上流側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に示した下流側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５】（Ａ）は第１触媒が新品の触媒である場合の空燃比フィードバック制御（サブフィードバック制御）における下流側空燃比センサの出力、及び本発明の触媒劣化判定装置が採用する触媒モデルにより推定される第１触媒から流出する流出酸素量の変化を示したタイムチャートであり、（Ｂ）は第１触媒が劣化触媒である場合の空燃比フィードバック制御における同下流側空燃比センサの出力、及び同流出酸素量の変化を示したタイムチャートである。
【図６】本発明の触媒劣化判定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７】本発明の触媒劣化判定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８】本発明の触媒劣化判定装置が採用する触媒モデルを第１触媒に適用した場合の模式図である。
【図９】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１０】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の計算のためのルーチンを示したフローチャートである。
【図１１】図１に示したＣＰＵが実行するサブフィードバック制御量の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１２】図１に示したＣＰＵが実行する第１触媒の各ブロック毎の流出酸素量、酸素吸蔵量等の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１３】図１に示したＣＰＵが実行する第１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１４】図１に示したＣＰＵが実行する触媒劣化判定に使用する頻度ＦＲＥ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１５】図１に示したＣＰＵが実行する第１触媒が正常触媒であるか劣化触媒であるかを判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】図１に示したＣＰＵが実行する第１触媒の被毒回復処理を行う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、６６…上流側空燃比センサ、６７…下流側空燃比センサ、７０…電気制御装置、７１…ＣＰＵ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst deterioration determination device that determines whether a three-way catalyst disposed in an exhaust passage of an internal combustion engine has deteriorated.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a three-way catalyst for purifying exhaust gas of an internal combustion engine (also referred to simply as a “catalyst” in the present specification) is disposed in an exhaust passage of the engine. This three-way catalyst is an oxygen storage O ₂ When it has a storage function (oxygen storage function) and the air-fuel ratio of the inflowing gas is rich, unburned components such as HC and CO are oxidized by the stored oxygen, When the fuel ratio is lean, nitrogen oxides (NOx) are reduced and the oxygen taken from the NOx is stored (occluded) inside. This allows the three-way catalyst to purify unburned components and nitrogen oxides even when the air-fuel ratio of the gas flowing into the catalyst deviates from the stoichiometric air-fuel ratio. Therefore, the larger the maximum value of the amount of oxygen (hereinafter, referred to as “oxygen storage amount”) that the three-way catalyst can store (hereinafter, referred to as “maximum oxygen storage amount”), the more the three-way catalyst is purified. Ability is high.
[0003]
Incidentally, the catalyst is deteriorated by poisoning by lead, sulfur, or the like contained in the fuel, or by heat applied to the catalyst. As a result, the oxygen storage function of the catalyst gradually decreases. That is, as the deterioration of the catalyst progresses, the maximum oxygen storage amount of the catalyst decreases. From this, if the maximum oxygen storage amount of the catalyst can be estimated, it can be determined whether or not the catalyst has deteriorated based on the estimated maximum oxygen storage amount.
[0004]
The catalyst deterioration determination device disclosed in Patent Document 1 is based on such knowledge, and forcibly changes the air-fuel ratio of the engine from a predetermined rich air-fuel ratio to a lean air-fuel ratio (or vice versa). At that time, the maximum oxygen storage amount of the catalyst is estimated based on the output of an air-fuel ratio sensor (hereinafter, referred to as “downstream air-fuel ratio sensor”) disposed downstream of the catalyst, and the estimated maximum oxygen storage amount is determined. It is configured to determine whether or not the catalyst has deteriorated based on the amount.
[0005]
More specifically, the disclosed device controls the air-fuel ratio upstream of the catalyst to a predetermined rich air-fuel ratio to set the oxygen storage amount to “0”, and then sets the air-fuel ratio of the catalyst to a predetermined value. The air-fuel ratio was controlled to a lean air-fuel ratio, and the unit flowed into the same catalyst per unit time as the time until the oxygen storage amount of the catalyst exceeded the maximum oxygen storage amount and the output of the air-fuel ratio sensor downstream of the catalyst changed to lean. The maximum oxygen storage amount is estimated by multiplying by the oxygen amount. Alternatively, the air-fuel ratio upstream of the catalyst is controlled to a predetermined lean air-fuel ratio, and the oxygen storage amount is set to the maximum oxygen storage amount. Thereafter, the air-fuel ratio of the catalyst is controlled to a predetermined rich air-fuel ratio, and the oxygen By multiplying the time until the occlusion amount becomes “0” and the output of the air-fuel ratio sensor downstream of the catalyst changes to rich, and the amount of oxygen released (consumed) per unit time in the same catalyst, the same is obtained. Estimate the maximum oxygen storage capacity.
[0006]
As described above, according to the apparatus disclosed above, it is necessary to measure the amount of oxygen flowing into the catalyst or the amount of oxygen consumed by the catalyst in order to estimate the maximum oxygen storage amount. This oxygen amount is measured based on the intake air amount of the engine. Therefore, in order to accurately determine the maximum oxygen storage amount, the intake air amount of the engine must be measured with high accuracy. For this reason, the determination of the degree of catalyst deterioration needs to be performed in an operating state in which the intake air amount can be accurately measured, that is, when the engine is operating in a steady state.
[0007]
[Patent Document 1]
JP-A-5-133264
[0008]
[Problems to be solved by the invention]
However, since there is no guarantee that the steady state of the engine will continue for a long time, it is necessary to terminate the measurement of the maximum oxygen storage amount in a short period of time. Therefore, the difference between the predetermined rich air-fuel ratio and the predetermined lean air-fuel ratio described above is required. Must be set relatively large. As a result, there is a problem that the output of the engine fluctuates with such a large change in the air-fuel ratio and drivability deteriorates. In addition, since the forced change of the air-fuel ratio is started when the engine is in a steady operation in which the output of the engine is stable, the problem that the output fluctuation of the engine is easily perceived by the driver and deterioration of the drivability is easily detected. There is.
[0009]
Therefore, an object of the present invention is to provide a catalyst deterioration determination device capable of accurately determining whether or not a catalyst has deteriorated without sacrificing drivability.
[0010]
[Overview of the present invention]
The feature of the present invention is applied to an exhaust gas purification device for an internal combustion engine including a catalyst disposed in an exhaust passage of an internal combustion engine, and an air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst. A catalyst deterioration determining means for determining whether the catalyst is a normal catalyst that has not deteriorated to a degree that should be determined to be a deteriorated catalyst or a deteriorated catalyst that has deteriorated to a degree that should be determined to be a deteriorated catalyst. The catalyst degradation determination device provided with, based on the catalyst model constructed in consideration of the reaction in the catalyst when the catalyst is assumed to be the normal catalyst, the specific component of the gas flowing out of the catalyst based on the catalyst model Specific catalyst amount estimating means for estimating a value related to the amount, wherein the catalyst deterioration determining means determines that the relationship between the output value of the air-fuel ratio sensor and the estimated value related to the amount of the specific component is the output value of the air-fuel ratio sensor And the features When the degree of departure from the predetermined correlation to be obtained between the actual value of the component amount and the actual value is equal to or less than a predetermined degree, the catalyst is determined to be the normal catalyst, and the relation is determined to be the same as the predetermined catalyst. When the degree of deviation from the correlation exceeds the predetermined degree, the catalyst is determined to be the deteriorated catalyst.
[0011]
Here, the value relating to the amount of the specific component in the gas flowing out of the catalyst is, for example, the absolute amount of the specific component, the concentration of the specific component, or the like. The specific component is, for example, a component to be purified by a catalyst such as carbon monoxide CO, hydrocarbon HC, nitrogen oxide NOx, or oxygen O 2. ₂ (Amount of excess or deficiency).
[0012]
In this case, the catalyst deterioration determination device according to the feature of the present invention may be configured such that any one of the output value of the air-fuel ratio sensor or the value related to the estimated amount of the specific component becomes a predetermined target value. Air-fuel ratio control means for feedback-controlling the air-fuel ratio of the gas flowing into the catalyst based on the value, wherein the catalyst deterioration determination means determines whether the catalyst is the normal catalyst or the deteriorated catalyst during the feedback control. It is preferable to be configured to determine Here, the air-fuel ratio control unit that performs feedback control of the air-fuel ratio of the gas flowing into the catalyst may be, for example, a unit that controls the air-fuel ratio of the air-fuel mixture supplied to the engine. Means for controlling the air-fuel ratio of the air-fuel mixture to be supplied and controlling the air-fuel ratio of the gas flowing into the catalyst by supplying air or fuel from a nozzle or the like provided in the exhaust passage upstream of the catalyst. You may. If the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled, the air-fuel ratio of the gas flowing into the catalyst can be controlled.
[0013]
The air-fuel ratio of the gas flowing out of the catalyst depends on the oxidizing agent (for example, nitrogen oxide NOx, oxygen O ₂ ) Is large (at this time, the amount of the reducing agent (for example, carbon monoxide CO, hydrocarbon HC) in the gas is very small). When the amount of the oxidizing agent is large (at this time, the amount of the oxidizing agent in the gas is very small), the air-fuel ratio becomes rich. Therefore, the amount of the oxidizing agent and the amount of the reducing agent in the gas (therefore, the amount (the value relating to) of the specific component) changes according to the air-fuel ratio of the gas. Therefore, a predetermined correlation is established between the output value of the air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst and the actual value of a value related to the amount of the specific component in the gas flowing out of the catalyst (for example, the excess or deficiency of oxygen). They can be said to be in a relationship.
[0014]
By the way, as will be described in detail later, the inventor has identified a gas contained in a gas flowing out of the catalyst based on a catalyst model constructed in consideration of a reaction in the catalyst (oxygen storage / release reaction based on an oxygen storage function). A method for estimating (the value of) the amount of components was developed. The relationship between the value relating to the amount of the specific component estimated based on the catalyst model and the output value of the air-fuel ratio sensor disposed in the exhaust passage downstream of the actual catalyst targeted by the catalyst model is the predetermined correlation. When in relationship, it means that the catalyst model faithfully represents the actual reaction in the catalyst. On the other hand, when the relationship between the value related to the estimated amount of the specific component and the output value of the air-fuel ratio sensor deviates from the predetermined correlation, the catalyst model does not faithfully represent the actual reaction in the catalyst. It means that.
[0015]
Further, as described above, as the deterioration of the catalyst progresses, the maximum oxygen storage amount that affects the reaction in the catalyst decreases, and the reaction rate in the catalyst changes. Therefore, the degree of the reaction in the catalyst changes as the deterioration of the catalyst progresses.
[0016]
From the above, it is a normal catalyst (for example, a new catalyst) that has not deteriorated to the extent that the actual catalyst targeted by the catalyst model should be determined to be a deteriorated catalyst (for example, the maximum oxygen storage amount is always constant). It is assumed that the catalyst model is constructed in consideration of the actual reaction in the catalyst when it is assumed that the catalyst model is new. Then, when the actual catalyst is the normal catalyst, the catalyst model can faithfully represent the reaction in the actual catalyst. Therefore, the value related to the amount of the specific component estimated by the catalyst model and the output value of the air-fuel ratio sensor Does not deviate from the predetermined correlation. On the other hand, as the actual deterioration of the catalyst progresses from the degree of deterioration of the normal catalyst, the degree of reaction represented by the catalyst model becomes different from the degree of reaction in the actual catalyst, and the same catalyst model Since the reaction in the catalyst cannot be faithfully represented, the degree of the relationship between the estimated value of the specific component and the output value of the air-fuel ratio sensor deviating from the predetermined correlation gradually increases.
[0017]
Therefore, depending on whether the degree of the relationship between the value related to the estimated amount of the specific component and the output value of the air-fuel ratio sensor deviates from the predetermined correlation exceeds a predetermined degree, the actual It can be determined whether or not the catalyst is a deteriorated catalyst that has been deteriorated to the extent that it should be determined that the catalyst is a deteriorated catalyst. The catalyst deterioration determination device according to the above-described feature of the present invention determines whether the catalyst is a normal catalyst or a deteriorated catalyst by using such a phenomenon.
[0018]
According to this, it is not necessary to forcibly change the air-fuel ratio when the engine is operating in a steady state in order to determine the deterioration of the catalyst. During the control, a catalyst deterioration determination may be performed. As a result, it is possible to determine whether the catalyst is a normal catalyst or a deteriorated catalyst without sacrificing drivability.
[0019]
In any one of the above catalyst deterioration determining devices, the catalyst deterioration determining means may determine whether one of the output value of the air-fuel ratio sensor or the estimated value of the specific component is a rich air-fuel ratio or a lean air-fuel ratio from the catalyst. Each time the state becomes the first state indicating that the gas of the fuel ratio flows out, the other value changes to the second state indicating that the gas of the same rich air-fuel ratio or lean air-fuel ratio flows out from the same catalyst. It is determined whether or not the other value is in the second state when the same value is in the first state with respect to the frequency of the one value being in the first state. When the ratio of the frequency of occurrence is equal to or greater than a predetermined value, the degree of the relationship between the output value of the air-fuel ratio sensor and the value related to the estimated amount of the specific component deviating from the predetermined correlation is equal to or less than the predetermined degree. Is determined to be When the ratio of the frequency is less than the predetermined value, it is preferable that the degree to which the relationship deviates from the predetermined correlation is configured to determine that exceeds the same extent predetermined.
[0020]
In this case, when the ratio of the frequency at which the one value is in the first state to the frequency at which the other value is in the second state is equal to or greater than a predetermined value, it is determined that the catalyst is a normal catalyst. When the ratio of the same frequency is less than the predetermined value, the catalyst is determined to be a deteriorated catalyst. According to this, the frequency at which one value of the output value of the air-fuel ratio sensor or the value related to the estimated amount of the specific component is in the first state and the frequency at which the other value is in the second state are It is possible to determine the deterioration of the catalyst with a simple configuration of counting.
[0021]
In any one of the above catalyst deterioration determination devices, the specific component amount estimating means estimates a value relating to the excess or deficiency of oxygen in the gas flowing out of the catalyst as a value relating to the amount of the specific component in the gas. It is preferable to be configured as follows. Excessive oxygen in the gas flowing out of the catalyst means that the amount of the oxidizing agent in the gas is large (at this time, the amount of the reducing agent in the gas is small). In other words, the lack of oxygen in the gas means that the amount of the reducing agent in the gas is large (at this time, the amount of the oxidizing agent in the gas is small). Means In other words, the state of the gas flowing out of the catalyst can be represented based on only one value, which is a value relating to the excess or deficiency of oxygen in the gas. Therefore, if configured as described above, it is not necessary to calculate a value other than the value relating to the excess or deficiency of oxygen as a value relating to the amount of the specific component in the gas flowing out of the catalyst, and the calculation necessary for determining the deterioration of the catalyst is not required. It can be simple.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an air-fuel ratio control device (exhaust gas purification device) including a catalyst deterioration determination device according to the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a system in which such a catalyst deterioration determination device is applied to a spark ignition type multi-cylinder (four cylinder) internal combustion engine 10.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
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. A throttle valve 43 for varying the opening cross-sectional area of the intake passage, a throttle valve actuator 43a comprising a DC motor constituting a throttle valve driving means, a swirl control valve (hereinafter referred to as "SCV") 44, and a DC motor. SCV actuator 44a.
[0027]
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 (start catalyst) disposed (interposed) in the exhaust pipe 52. Converter) 53 and a second catalyst (disposed below the floor of the vehicle, which is disposed (interposed) in the exhaust pipe 52 downstream of the first catalyst 53, so that an underfloor catalytic Converter 54). The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Note that the present catalyst deterioration determination apparatus determines whether the first catalyst 53 has deteriorated.
[0028]
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, referred to as an “upstream air-fuel ratio sensor 66”), an air-fuel ratio sensor 67 (hereinafter “downstream air-fuel ratio sensor”) disposed in the exhaust passage downstream of the first catalyst 53 and upstream of the second catalyst 54. A fuel ratio sensor 67 ”) and an accelerator opening sensor 68.
[0029]
The hot wire air flow meter 61 outputs a voltage Vg according to the mass flow rate of the intake air flowing through the intake pipe 41. The relationship between the output Vg of the air flow meter 61 and the measured intake air flow rate Ga is as shown in FIG. 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.
[0030]
As shown in FIG. 3, the upstream side air-fuel ratio sensor 66 outputs a current corresponding to the air-fuel ratio A / F, and outputs a voltage vabyfs corresponding to the current. 3, the upstream air-fuel ratio sensor 66 can accurately detect the air-fuel ratio A / F over a wide range. As shown in FIG. 4, the downstream air-fuel ratio sensor 67 outputs a voltage Voxs that changes abruptly at the stoichiometric air-fuel ratio. More specifically, the downstream air-fuel ratio sensor 67 outputs approximately 0.1 (V) when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio and approximately 0.1 V when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. When the air-fuel ratio is 9 (V) and the stoichiometric air-fuel ratio, a voltage of approximately 0.5 (V) is output. The accelerator opening sensor 68 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.
[0031]
The electric control device 70 includes a CPU 71 connected to the bus 71, a routine (program) to be executed by the CPU 71, a table (lookup table, map), a ROM 72 in which constants and the like are stored in advance, and the CPU 71 temporarily stores data as needed. The microcomputer includes a RAM 73 for storing data in a power supply, a backup RAM 74 for storing data while the power is on and the stored data while the power is off, an interface 75 including an AD converter, and the like. The interface 75 is connected to the sensors 61 to 68, supplies signals from the sensors 61 to 68 to the CPU 71, and controls the actuator 33a of the variable intake timing device 33, the igniter 38, the injector 39, A drive signal is transmitted to the valve actuator 43a and the SCV actuator 44a. Further, the interface 75 sends an instruction signal for turning on / off the alarm lamp 82 to an alarm lamp 82 for notifying the user of the deterioration of the first catalyst 53 in accordance with an instruction from the CPU 71. .
[0032]
(Overview of air-fuel ratio feedback control)
The first catalyst 53 (the same applies to the second catalyst 54), which is a three-way catalyst, oxidizes unburned components (HC, CO) when the air-fuel ratio is substantially at the stoichiometric air-fuel ratio, and simultaneously oxidizes nitrogen oxides (NOx). ) Is reduced. Further, the first catalyst 53 has a function of storing oxygen (oxygen storage function, O ₂ Storage function), and this oxygen storage function can purify HC, CO, and NOx even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio to some extent. That is, when the air-fuel ratio of the air-fuel mixture supplied to the engine becomes lean and the gas flowing into the first catalyst 53 contains a large amount of NOx, the first catalyst 53 deprives NOx of oxygen molecules and reduces NOx. This purifies NOx. When the air-fuel ratio of the air-fuel mixture supplied to the engine becomes rich and the gas flowing into the first catalyst 53 contains a large amount of HC and CO, the first catalyst 53 gives them oxygen molecules to oxidize them. This purifies HC and CO.
[0033]
Therefore, in order for the first catalyst 53 to efficiently purify a large amount of HC and CO that flow continuously, the first catalyst 53 must store a large amount of oxygen, and conversely, continuously store a large amount of oxygen. In order to efficiently purify a large amount of inflowing NOx, the first catalyst 53 must be able to sufficiently store oxygen. 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.
[0034]
On the other hand, the first catalyst 53 is deteriorated by poisoning by lead or sulfur contained in the fuel or by heat applied to the catalyst, so that the maximum oxygen storage amount gradually decreases. Even in the case where the maximum oxygen storage amount is reduced as described above, in order to maintain a state in which the emission amount is small, the air-fuel ratio of the gas discharged from the first catalyst 53 must be very close to the stoichiometric air-fuel ratio. It is necessary to control so that
[0035]
Thus, in the air-fuel ratio control device of the present embodiment, the target value at which the output Voxs of the downstream air-fuel ratio sensor 67 substantially corresponds to the stoichiometric air-fuel ratio (that is, the target value for improving the purification efficiency of the first catalyst 53). The engine is based on the sub-feedback control amount vafsfb obtained by subtracting the output DVoxs of the downstream air-fuel ratio sensor 67 from the target value Voxsref so as to be Voxsref (= 0.5 (V)) and performing a proportional / integral process on the deviation DVoxs. (In this embodiment, the air-fuel ratio is feedback-controlled in accordance with the upstream air-fuel ratio sensor output vabyfs.)
[0036]
That is, when the output of the downstream air-fuel ratio sensor 67 becomes a value representing an air-fuel ratio leaner than the stoichiometric air-fuel ratio (actually, when the sub-feedback control amount vafsfb becomes a positive value), the air-fuel mixture supplied to the engine becomes empty. The fuel ratio is controlled to the rich side, and when the output of the downstream air-fuel ratio sensor 67 becomes a value representing an air-fuel ratio richer than the stoichiometric air-fuel ratio (actually, when the sub-feedback control amount vafsfb becomes a negative value), the fuel is supplied to the engine. The air-fuel ratio of the air-fuel mixture is controlled to the lean side. As described above, the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled based on the downstream air-fuel ratio sensor output Voxs (accordingly, the sub-feedback control amount vafsfb). The means for controlling the air-fuel ratio supplied to the engine (therefore, the air-fuel ratio of the gas flowing into the first catalyst 53) corresponds to the air-fuel ratio control means.
[0037]
(Principle of catalyst deterioration judgment)
During the above-described air-fuel ratio feedback control, if the amount of unburned CO and HC in the gas flowing out of the first catalyst 53 becomes insufficient due to the lack of oxygen in the gas (at this time, the amount of nitrogen oxide NOx The amount is very small.) The output Voxs of the downstream air-fuel ratio sensor 67 approaches a value indicating rich while increasing. On the other hand, when the oxygen in the gas flowing out of the first catalyst 53 becomes excessive and the amount of nitrogen oxide NOx in the gas increases, the amount of unburned CO and HC in the gas becomes very small. The output Voxs of the downstream air-fuel ratio sensor 67 approaches a value indicating lean while decreasing.
[0038]
In other words, when the output Voxs of the downstream air-fuel ratio sensor 67 passes while increasing the rich predetermined value Vrich larger than the target value Voxsref corresponding to the stoichiometric air-fuel ratio, at least the gas flowing out of the first catalyst 53 The amount of oxygen shortage exceeds a certain threshold. On the other hand, when the output Voxs of the downstream air-fuel ratio sensor 67 passes while decreasing the lean-side predetermined value Vlean that is smaller than the target value Voxsref, at least the excess amount of oxygen in the gas flowing out of the first catalyst 53 is a certain amount. The amount exceeds the threshold. The output Voxs of the downstream air-fuel ratio sensor 67 and the amount (actual amount) of specific components (excess or deficiency of oxygen, nitrogen oxides NOx, unburned CO, HC, etc.) in the gas flowing out of the first catalyst 53 are as follows. There is at least such a predetermined correlation.
[0039]
On the other hand, the amount of the specific component in the gas flowing out of the first catalyst 53 (in this example, the excess or deficiency of oxygen (outflow oxygen amount) CgoutO2 (N)) is, as described later in detail, the inside of the first catalyst 53. Can be estimated based on a catalyst model constructed in consideration of the reaction (oxygen storage / release reaction based on the oxygen storage function). Here, when the outflow oxygen amount CgoutO2 (N) is a positive value, it means that oxygen is excessive and NOx is flowing out of the first catalyst 53, and the value is negative. Means that oxygen is insufficient and unburned CO and HC are flowing out of the first catalyst 53.
[0040]
When the relationship between the outflow oxygen amount CgoutO2 (N) estimated based on this catalyst model and the output Voxs of the downstream air-fuel ratio sensor 67 is in the above-described predetermined correlation, the catalyst model uses the reaction in the first catalyst 53. Means faithfully. On the other hand, when the relationship between the estimated outflow oxygen amount CgoutO2 (N) and the output Voxs of the downstream air-fuel ratio sensor 67 deviates from the predetermined correlation, the catalyst model faithfully performs the reaction in the first catalyst 53. It does not mean that it is not expressed.
[0041]
Further, as described above, generally, as the deterioration of the catalyst progresses, the maximum oxygen storage amount that affects the reaction in the catalyst decreases, and the reaction rate in the catalyst changes. Therefore, the degree of the reaction in the catalyst changes as the deterioration of the catalyst progresses.
[0042]
From the above, the catalyst in the first catalyst 53 is considered in consideration of the reaction in the first catalyst 53 when it is assumed that the first catalyst 53 is a new catalyst (for example, the maximum oxygen storage amount is always the value at the time of the new catalyst). Consider the case where a model has been built. Then, when the first catalyst 53 is a new catalyst, the catalyst model can faithfully represent the reaction in the first catalyst 53. Therefore, the outflow oxygen amount CgoutO2 (N) estimated by the catalyst model and the downstream air-fuel ratio sensor The relationship with the output value Voxs of 67 does not deviate from the predetermined correlation. On the other hand, as the deterioration of the first catalyst 53 progresses (from the time of new product), the degree of the reaction represented by the catalyst model becomes different from the degree of the reaction in the first catalyst 53, and the catalyst model becomes the first catalyst. Since the reaction in 53 cannot be faithfully represented, the degree of the relationship between the outflow oxygen amount CgoutO2 (N) and the output value Voxs of the downstream air-fuel ratio sensor 67 deviating from the predetermined correlation gradually increases.
[0043]
Hereinafter, this point will be described more specifically with reference to FIG. (A) shows an example of a change in the output Voxs of the downstream air-fuel ratio sensor 67 when the first catalyst 53 is a new catalyst, and a change in the outflow oxygen amount CgoutO2 (N) calculated by a catalyst model described later. It is a time chart. As described above, since the catalyst model is constructed on the assumption that the first catalyst 53 is a new catalyst, the catalyst model faithfully represents the reaction in the first catalyst 53 which is a new catalyst. Therefore, the change in the outflow oxygen amount CgoutO2 (N) calculated by the catalyst model shown in (A) coincides with the change in the actual amount of oxygen in the gas flowing out of the first catalyst 53. .
[0044]
That is, before the time t1, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the rich side (that is, the above-described sub-feedback control amount vafsfb is a positive value), so that the first catalyst 53 When the oxygen storage amount in the chamber approaches “0”, the first catalyst 53 cannot completely oxidize a large amount of unburned CO and HC in the inflowing gas, and unburned CO and HC flow out of the first catalyst 53. (The oxygen in the gas flowing out of the first catalyst 53 starts to run short). In response, the outflow oxygen amount CgoutO2 (N) starts decreasing from substantially “0” and the output Voxs of the downstream air-fuel ratio sensor 67 starts increasing. At time t1, the output Voxs becomes the rich predetermined value Vrich. Pass while increasing. Further, the outflow oxygen amount CgoutO2 (N), which is a negative value, is smaller than the negative threshold value Crefmns at time t1 and continues to decrease thereafter.
[0045]
At time t1 ′ immediately after time t1, the sub-feedback control amount vafsfb changes from a positive value to a negative value, whereby the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the lean side. Accordingly, after time t1 ′, the outflow oxygen amount CgoutO2 (N) is maintained at approximately “0” again because unburned CO and HC do not flow out of the first catalyst 53. Here, the time when the sub-feedback control amount vafsfb changes from a positive value to a negative value (time t1 ′) is later than the time when the output Voxs passes while increasing the target value Voxsref (immediately before time t1). Is based on the fact that the value of the integral term in the proportional / integral processing for obtaining the sub-feedback control amount vafsfb is a large positive value immediately before the time t1.
[0046]
After the time t1 (t1 ′), the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the lean side (that is, the sub-feedback control amount vafsfb becomes a negative value), so that the first catalyst 53 When the oxygen storage amount of the gas approaches the maximum oxygen storage amount, the first catalyst 53 cannot completely reduce a large amount of nitrogen oxide NOx in the inflowing gas, and the nitrogen oxide NOx starts flowing out of the first catalyst 53 ( Therefore, the oxygen in the gas flowing out of the first catalyst 53 starts to become excessive.) In response, the outflow oxygen amount CgoutO2 (N) starts to increase from substantially “0” and the output Voxs of the downstream air-fuel ratio sensor 67 starts to decrease. At time t2, the output Voxs becomes the lean predetermined value Vlean. Pass while decreasing. Further, the outflow oxygen amount CgoutO2 (N), which is a positive value, is larger than the positive threshold value Crefpls at time t2, and continues to increase thereafter.
[0047]
At time t2 'immediately after time t2, the sub-feedback control amount vafsfb changes from a negative value to a positive value again so that the air-fuel ratio of the mixture supplied to the engine is controlled to the rich side. become. Accordingly, after time t2 ', the outflow oxygen amount CgoutO2 (N) is maintained at substantially "0" again because the nitrogen oxide NOx does not flow out of the first catalyst 53. Here, the time when the sub-feedback control amount vafsfb changes from a negative value to a positive value (time t2 ′) is later than the time when the output Voxs passes while decreasing the target value Voxsref (immediately before time t2). Is based on the fact that the value of the integral term for obtaining the sub-feedback control amount vafsfb is a large negative value immediately before the time t2.
[0048]
Similarly, after time t2 (t2 ′), at time t3, the output Voxs passes while increasing the rich-side predetermined value Vrich, and the outflowing oxygen amount CgoutO2 (N) becomes the negative threshold value as in the case of the time t1 described above. The value is smaller than Crefmns. Also, at time t4, the output Voxs passes while decreasing the lean-side predetermined value Vlean, and the outflow oxygen amount CgoutO2 (N) has a value larger than the positive threshold value Crefpls, as at time t2. .
[0049]
As described above, when the first catalyst 53 is a new catalyst, each time the output Voxs passes while increasing the rich-side predetermined value Vrich (at (A), times t1 and t3), the outflow oxygen calculated by the catalyst model is calculated. The amount CgoutO2 (N) is always smaller than the negative threshold value Crefmns, and every time the output Voxs passes while decreasing the lean-side predetermined value Vlean (at (A), times t2 and t4). The quantity CgoutO2 (N) is always a value larger than the positive threshold value Crefpls. In other words, the relationship between the outflow oxygen amount CgoutO2 (N) and the output value Voxs of the downstream air-fuel ratio sensor 67 does not deviate from the predetermined correlation.
[0050]
On the other hand, FIG. 5B shows the output Voxs of the downstream air-fuel ratio sensor 67 and the outflow oxygen amount CgoutO2 (N 4 is a time chart showing an example of a change in the example. As described above, the catalyst model is constructed on the assumption that the first catalyst 53 is a new catalyst. In this case, the reaction in the first catalyst 53 that is the deteriorated catalyst cannot be faithfully represented.
[0051]
More specifically, in this case, since the first catalyst 53 is the deteriorated catalyst, the maximum oxygen storage amount in the first catalyst 53 is considerably reduced. Therefore, the actual oxygen storage amount in the first catalyst 53 comes to approach “0” or the maximum oxygen storage amount in a short time, and accordingly, the air-fuel ratio of the air-fuel mixture supplied to the engine changes from the rich side. It frequently changes to the lean side or from the lean side to the rich side. On the other hand, in the catalyst model, a large value at the time of a new product is always assumed as the maximum oxygen storage amount of the first catalyst 53, so the oxygen storage amount (estimated value, calculated value) in the first catalyst 53 is the empty amount. Although it frequently increases and decreases in response to frequent changes in the fuel ratio, it hardly reaches “0” or the maximum oxygen storage amount. In other words, when the actual oxygen storage amount in the first catalyst 53 approaches “0” or the maximum oxygen storage amount and the oxygen storage amount (estimated value) in the first catalyst 53 calculated in the catalyst model is “ It is different from the point of time approaching "0" or the maximum oxygen storage amount. Therefore, the change in the outflow oxygen amount CgoutO2 (N) calculated by the catalyst model does not coincide with the change in (the actual amount of) oxygen in the gas flowing out of the first catalyst 53.
[0052]
Accordingly, in (B), each time the output Voxs passes while increasing the rich-side predetermined value Vrich (time t10, t30, t50), the excess or deficiency of oxygen in the gas flowing out of the first catalyst 53 (actually, Is always smaller than the negative threshold Crefmns, while the outflow oxygen amount CgoutO2 (N) calculated by the catalyst model is smaller than the negative threshold Crefmns only at time t50. Every time the output Voxs passes while decreasing the lean-side predetermined value Vlean (time t20, t40, t60), the excess or deficiency (actual amount) of oxygen in the gas flowing out of the first catalyst 53 is always a positive threshold. On the other hand, the outflow oxygen amount CgoutO2 (N) has a value larger than the positive threshold value Crefpls only at time t20, while the value is larger than Crefpls.
[0053]
In other words, when the first catalyst 53 becomes the deteriorated catalyst, the extent of the relationship between the outflow oxygen amount CgoutO2 (N) and the output value Voxs of the downstream air-fuel ratio sensor 67 deviating from the predetermined correlation is considerably large. Become. The extent to which the relationship between the outflow oxygen amount CgoutO2 (N) and the output value Voxs of the downstream air-fuel ratio sensor 67 deviates from the predetermined correlation is assumed by the maximum oxygen storage amount of the first catalyst 53 in the catalyst model. As the value of the first catalyst 53 decreases from a large value at the time of the new product, that is, as the deterioration of the first catalyst 53 progresses (from the time of the new product), it gradually increases.
[0054]
To the extent that the relationship between the outflow oxygen amount CgoutO2 (N) and the output value Voxs of the downstream air-fuel ratio sensor 67 deviates from the predetermined correlation, the output Voxs (one value) increases the rich-side predetermined value Vrich. At the time when the output Voxs of the downstream-side air-fuel ratio sensor 67 is in the first state (i.e., when the output Voxs of the downstream air-fuel ratio sensor 67 is in the first state), or when the output Voxs of the downstream air-fuel ratio sensor 67 is in the first state, It can be represented by the probability that the value is smaller than the negative threshold value Crefmns or larger than the positive threshold value Crefpls (that is, the outflow oxygen amount CgoutO2 (N) is in the second state). As the probability decreases, it grows larger. For example, in the example shown in FIG. 5A, the probability is 100% (4 times / 4 times), whereas in the example shown in FIG. 5B, the probability is about 33% (2 times / 6 times). ) And deviates from the above-mentioned predetermined correlation.
[0055]
From the above, the present catalyst deterioration determination apparatus constructs a catalyst model for the first catalyst 53 on the assumption that the first catalyst 53 is a new catalyst. In addition, during the above-described air-fuel ratio feedback control, the present catalyst deterioration determination device performs the outflow oxygen amount CgoutO2 (N) calculated by the catalyst model every time the output Voxs of the downstream air-fuel ratio sensor 67 becomes the first state. ) Is in the second state, and the output (Voxs) of the downstream air-fuel ratio sensor 67 indicates that the frequency (number of times) SML in which the output state becomes the first state has been sufficiently sampled. Each time the output value Voxs of the downstream air-fuel ratio sensor 67 reaches the first state during this one sampling period every time the reference value SML0 is reached (each time one sampling period elapses), the outflowing oxygen amount CgoutO2 (N ) Is in the second state.
[0056]
If the frequency FRE is equal to or more than the deterioration determination reference value FREF (therefore, the ratio of the frequency FRE to the frequency SML0 is equal to or more than a predetermined value), the present catalyst deterioration determination apparatus determines that the first catalyst 53 is a deteriorated catalyst. While it is determined that the normal catalyst has not deteriorated to the extent that it should be deteriorated, if the frequency FRE is less than the deterioration determination reference value FRE (therefore, the ratio of the frequency FRE to the frequency SML0 is less than a predetermined value), the first catalyst 53 It is determined that the catalyst has deteriorated to the extent that it should be determined that the catalyst has deteriorated. The means for determining the deterioration of the first catalyst 53 in this way corresponds to the catalyst deterioration determining means.
[0057]
(Catalyst model)
Next, a description will be given of a catalyst model for determining the amount of a specific component in the gas flowing out of the first catalyst 53 (in this example, the excess / deficiency amount of oxygen (outflow oxygen amount) CgoutO2 (N)). 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.
[0058]
Further, the oxygen storage amount of the catalyst changes according to the degree of the oxygen storage / release reaction generated 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. If the oxygen storage amount of the catalyst can be accurately obtained, the amount of the specific component in the gas flowing out of the catalyst can be accurately calculated. Therefore, the present apparatus applies the catalyst model described below to the first catalyst 53 to thereby determine the oxygen storage amount OSAall in the first catalyst 53 and the amount of the specific component flowing out of the first catalyst 53 (in this example, , Outflow oxygen amount CgoutO2 (N)) is calculated.
[0059]
In this catalyst model, as schematically shown in FIG. 6, a columnar catalyst having a constant cross-sectional shape perpendicular to the axis is divided into N (plural) regions ("blocks") by a surface 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, symbols, and the like related to an arbitrary i-th block have (i) at the end thereof.
[0060]
In this catalyst model, as shown in FIG. 7, 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. . This assumption (catalyst model) is realistic and has high calculation accuracy. The exhaust gas phase shown in FIG. 7 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
[0061]
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, Og in the exhaust gas). ₂ And when NOx is present), and becomes a negative value when the oxygen is insufficient (ie, when unburned HC and CO are present in the exhaust gas).
[0062]
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.
[0063]
Now, considering the balance of the oxygen amount CgO2 in the block (i) shown in FIG. 7 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 not occluded in the coat layer of the inflow oxygen amount CginO2 (i) becomes the outflow oxygen amount CgoutO2 (i). (1) The relationship shown in the following equation 1 is established between the outflow oxygen amount CgoutO2 (i) and the oxygen storage amount change amount δOSA (i). The relationship shown in Equation 1 below is the basic equation of the present catalyst model.
[0064]
(Equation 1)
CgoutO2 (i) = CginO2 (i) -δOSA (i)
[0065]
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 the oxygen in the exhaust gas flowing into the exhaust gas phase of the block (i) is excessive, and a part of the oxygen in the exhaust gas is in the block (i). Therefore, the oxygen storage amount change amount δOSA (i) becomes a positive value because it is occluded by the coat layer. 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. Therefore, 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 2 and 3.
[0066]
(Equation 2)
δOSA (i) = H (i) · CginO2 (i)
[0067]
[Equation 3]
H (i) = h · ((Cmax (i) −OSA (i)) / Cmax (i)) (0 ≦ H (i) <1)
[0068]
In the above equations 2 and 3, H (i) is a reaction rate indicating the ratio of the amount of stored oxygen (δOSA (i)) to the inflowing oxygen amount CginO2 (i) in the block (i). h is a reaction rate constant when it is assumed that the first catalyst 53 is a new catalyst, and is a constant positive value in this model, but a positive value that changes according to the temperature of the catalyst (for example, the temperature of the catalyst). (A positive value that monotonically increases in accordance with the increase). 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 (3) 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.
[0069]
On the other hand, when the inflowing oxygen amount CginO2 (i) is a negative value, it means that the exhaust gas flowing into the exhaust gas phase of the block (i) is short of oxygen, and the exhaust gas in the exhaust gas phase of the block (i) has a coating layer of the block (i). , The amount of change in the oxygen storage amount δOSA (i) becomes 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 4 and 5 showing the same relationship as Expression 2 above. it can.
[0070]
(Equation 4)
δOSA (i) = H (i) · CginO2 (i)
[0071]
(Equation 5)
H (i) = h · (OSA (i) / Cmax (i)) (0 ≦ H (i) <1)
[0072]
In the above Expressions 4 and 5, H (i) represents the ratio of the released oxygen amount (δOSA (i), negative value) to the inflowing oxygen amount CginO2 (i) (negative value) in the block (i). It is a reaction rate shown. h is a reaction rate constant assuming that the first catalyst 53 is a new catalyst, and is the same as that used in the above equation (3). Further, the value of the oxygen storage amount OSA (i) at the present time in the above equation (5) indicates the oxygen release allowance at the present time 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.
[0073]
The maximum oxygen storage amount Cmax (i) in the block (i) used in Equations 3 and 5 will be described later. Further, the oxygen storage amount OSA (i) at the present time in the block (i) used in Expressions 3 and 5 is the oxygen storage amount change amount δOSA (i) from the time when the initial value is given to the present time. Can be calculated based on the following equation (6).
[0074]
(Equation 6)
OSA (i) = ΣδOSA (i) (0 ≦ OSA (i) ≦ Cmax (i))
[0075]
Next, considering the boundary conditions between the blocks, as shown in FIG. 6, 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, as shown in FIG. Since the inflow surfaces are continuous with each other, as shown in FIG. 7, 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 equation 7 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.
[0076]
(Equation 7)
CginO2 (i + 1) = CgoutO2 (i)
[0077]
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 (2) or (4). ) Is obtained. As a result, the oxygen storage amount OSA (1) in the block (1) can be updated by the above equation (6), and the outflow oxygen amount CgoutO2 (1) in the block (1) can be obtained by the above equation (1). 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 (7). As a result, the block (2) is obtained from the above equation (2) or (4). ) Is obtained. Thereby, the oxygen storage amount OSA (2) in the block (2) can be updated by the above equation (6), and the outflow oxygen amount CgoutO2 (2) in the block (2) can be obtained by the above equation (1).
[0078]
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 1 to 7. ), 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 obtained. Can be calculated. 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. . Further, the outflow oxygen amount CgoutO2 (i) (i = 1, 2,..., N) flowing out from each block can be calculated, whereby the block (N) (therefore, the first catalyst 53) can be calculated. Outflow oxygen amount CgoutO2 (N) flowing out of the fuel cell can be calculated. In this way, based on the catalyst model constructed on the assumption that the first catalyst 53 is a new catalyst, the amount of oxygen in the gas flowing out of the first catalyst 53 (outflow oxygen amount) CgoutO2 ( The means for estimating N) corresponds to the specific component amount estimating means.
[0079]
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 1 is rewritten to “1”, the following equation 8 is derived.
[0080]
(Equation 8)
CgoutO2 (1) = CginO2 (1) -δOSA (1)
[0081]
Also, when “i” in the above equation 1 is rewritten to “2” and the relationship of the above equations 7 and 8 is applied to this, the following equation 9 is derived.
[0082]
(Equation 9)

[0083]
Further, when “i” in the above equation 1 is rewritten to “3”, and the relationship of the above equations 7 and 9 is applied thereto, the following equation 10 is derived.
[0084]
(Equation 10)

[0085]
By repeating such a procedure, the following equation 11, which is a general formula for obtaining the outflow oxygen amount CgoutO2 (i) of an arbitrary i-th block (i), is derived.
[0086]
[Equation 11]
CgoutO2 (i) = CginO2 (1) −δOSA (1) −δOSA (2) −... −δOSA (i−1) −δOSA (i)
(I = 1, 2,..., N)
[0087]
In addition, since the following equation 12 is derived from the above equations 1 and 2 (or the above equation 4), the relationship of the above equation 7 is applied to the following equation 12, and the relationship is generally described. Equation 13 below, which is another general formula for obtaining the outflow oxygen amount CgoutO2 (i) of the block (i), can be easily derived.
[0088]
(Equation 12)
CgoutO2 (i) = CginO2 (i) · (1-H (i))
[0089]
(Equation 13)

[0090]
Next, the maximum oxygen storage amount Cmax (i) in the block (i) necessary for obtaining the reaction rate H (i) in Equations 3 and 5 will be described. Since this catalyst model is constructed on the assumption that the first catalyst 53 is a new catalyst, the maximum oxygen storage amount Cmax (i) (i = 1,..., N) of each block (i) is obtained. The sum is set to be the value (constant value) of the maximum oxygen storage amount Cmaxall of the first catalyst 53 as a whole when the first catalyst 53 is a new catalyst. The maximum oxygen storage amount Cmax (i) (i = 1,..., N) of each block (i) is, for example, a value obtained by dividing the value of the maximum oxygen storage amount Cmaxall by the number N of blocks. Is set. The maximum oxygen storage amount Cmax (i) (i = 1,..., N) of each block (i) set as described above does not change regardless of the progress of the deterioration of the first catalyst 53.
[0091]
(Application of catalyst model)
Next, an example in which the above-described catalyst model is applied to the first catalyst 53 as shown in FIG. 8 to obtain various values will be described.
[0092]
Hereinafter, in the block (i) that is the i-th block of the first catalyst 53, the inflow oxygen amount is the inflow oxygen amount CginO2 (i), the outflow oxygen amount is the outflow oxygen amount CgoutO2 (i), and the oxygen storage amount is OSA (i). , The maximum oxygen storage amount is referred to as Cmax (i). Further, the oxygen storage amount of the entire first catalyst 53 obtained by integrating the oxygen storage amounts OSA (i) (i = 1, 2,..., N) of each block is referred to as an oxygen storage amount OSAall, The maximum oxygen storage amount of the entire first catalyst 53, which is a value obtained by integrating the maximum oxygen storage amount Cmax (i) (i = 1, 2,..., N) of each block, is referred to as a maximum oxygen storage amount Cmaxall.
[0093]
In this catalyst model, as shown in FIG. 8, an initial value of the oxygen storage amount OSA (i) (i = 1, 2,..., N) in each block of the first catalyst 53 is given as an initial condition. In addition, every time the calculation cycle of the CPU 71 elapses, if the inflowing oxygen amount CginO2 (1) in the most upstream block (1) of the first catalyst 53 is given as a boundary condition, each block (i The oxygen storage amount OSA (i), the inflowing oxygen amount CginO2 (i), and the outflowing oxygen amount CgoutO2 (i) at (i = 1, 2,..., N) can all be calculated. Thus, the oxygen storage amount OSAall of the entire first catalyst 53 can also be obtained and calculated.
[0094]
Therefore, first, a method of giving an initial value of the oxygen storage amount in each block of the first catalyst 53 will be described. The present apparatus determines that the output Voxs of the downstream air-fuel ratio sensor 67 is larger than 0.7 (V). In other words, when the air-fuel ratio on the downstream side of the first catalyst 53 becomes a clear rich air-fuel ratio, no oxygen exists in the first catalyst 53 and unburned HC and CO are not purified. Therefore, the oxygen storage amount OSA (i) (i = 1, 2,..., N) in each block of the first catalyst 53 and the oxygen storage amount OSAall of the entire first catalyst 53 are all calculated. Set to “0”. Thus, the initial value “0” of the oxygen storage amount in each block of the first catalyst 53 is given as the initial condition.
[0095]
Next, a method of giving the inflowing oxygen amount CginO2 (1) in the most upstream block (1) of the first catalyst 53 will be described. The present apparatus uses the following formula 14 to calculate the inflowing oxygen amount for each calculation cycle of the CPU 71. Calculate CginO2 (1).
[0096]
[Equation 14]
CginO2 (1) = 0.23 · mfr · (abyfsave-stoich)
[0097]
In the above Expression 14, 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 one calculation cycle Δt, and stoich is the stoichiometric air-fuel ratio (for example, 14.7). Abyfsave is an average value of the air-fuel ratio A / F detected by the upstream air-fuel ratio sensor 66 within one calculation cycle Δt.
[0098]
As shown in Equation 14, the total amount mfr of the injection amount in one calculation cycle Δt is multiplied by a deviation (abysfave-stoich) of the detected average value of the air-fuel ratio A / F from the stoichiometric air-fuel ratio. The excess amount of air in this one operation cycle Δt is obtained, and the excess amount of air in this one operation cycle Δt is multiplied by the weight ratio of oxygen, so that the excess amount of oxygen in one operation cycle Δt, The inflowing oxygen amount CginO2 (1) is obtained.
[0099]
The inflowing oxygen amount CginO2 (1) calculated as described above is positive when the oxygen is excessive (that is, when the air-fuel ratio is lean and abyfsave> stoich), as is apparent from the above equation (14). It is calculated to be a negative value when oxygen is insufficient (that is, when the air-fuel ratio is rich and abyfsave <stoich). In this way, the inflowing oxygen amount CginO2 (1) in the most upstream block (1) of the first catalyst 53 is given as a boundary condition for each calculation cycle of the CPU 71.
[0100]
(Actual operation)
Next, the actual operation of the air-fuel ratio control device configured as described above will be described with reference to FIGS. 9 to 16 which show a flowchart of a routine executed by the CPU 71 of the electric control device 70.
[0101]
The CPU 71 calculates the final fuel injection amount Fi shown in FIG. 9 and performs a routine for instructing fuel injection based on a predetermined crank angle (for example, BTDC 90 ° CA) before the intake top dead center of each cylinder. Each time, it is repeatedly executed. Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts processing from step 900 and proceeds to step 905, where the CPU 71 determines the intake air flow rate Ga measured by the air flow meter 61 and the engine rotation speed NE. Based on the map f, a basic fuel injection amount Fbase for setting the air-fuel ratio of the engine to the stoichiometric air-fuel ratio is determined based on the map.
[0102]
Next, the CPU 71 proceeds to step 910, and sets a value obtained by adding an air-fuel ratio feedback correction 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 normally “1.00”, and is set to a predetermined value other than “1.00” when the poisoning recovery process is executed as described later.
[0103]
Next, the CPU 71 proceeds to step 915, and issues an instruction to inject fuel of the set final fuel injection amount Fi to the injector 39 of the cylinder immediately before the intake stroke. Thereafter, the CPU 71 proceeds to step 920, 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 total fuel injection amount mfr. This total fuel injection amount mfr is used when calculating an inflow oxygen amount CginO2 (1) described later. Thereafter, the CPU 71 proceeds to step 995, and once ends this routine. 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.
[0104]
Next, the calculation of the air-fuel ratio feedback correction amount DFi will be described. The CPU 71 repeatedly executes the routine shown in FIG. 10 every predetermined time. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1000 and proceeds to step 1005 to determine whether the air-fuel ratio feedback control 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, the intake air amount per one revolution of the engine (load, cylinder intake air amount Mc) is equal to or lower than a predetermined value, and The condition is satisfied when the side air-fuel ratio sensor 66 is normal (including an active state) and the value of a poisoning recovery process execution flag PWM described later is “0”. When the poisoning recovery processing in progress flag PWM is “1”, it indicates that the poisoning recovery processing to be described later is being executed, and when the value is “0”, the poisoning recovery processing is being executed. Indicates that they have not.
[0105]
Now, assuming that the air-fuel ratio feedback control condition is satisfied, the CPU 71 determines “Yes” in step 1005, and proceeds to step 1010, where the output vabyfs of the current upstream air-fuel ratio sensor 66 and a later-described value are described. By converting the sum (vabyfs + vafsfb) with the sub-feedback control amount vafsfb based on the map shown in FIG. 3, the air-fuel ratio abyfs for control on the upstream side of the first catalyst 53 at the present time is obtained.
[0106]
Next, the CPU 71 proceeds to step 1015 and calculates the in-cylinder intake air amount Mc (k−N), which 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 upstream 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 upstream air-fuel ratio sensor 66, and the like.
[0107]
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 air-fuel ratio for upstream control. The reason why the air-fuel ratio is divided by abyfs is that a time corresponding to N strokes is required until the air-fuel mixture burned in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 66. The in-cylinder intake air amount Mc is obtained for each intake stroke of each cylinder based on the intake air flow rate Ga measured by the air flow meter 61 at that time and the engine speed NE (for example, the air flow meter 61). Is obtained by dividing the value obtained by performing the first-order lag process on the intake air flow rate Ga measured by the engine rotation speed NE), and is stored in the RAM 73 corresponding to each intake stroke.
[0108]
Next, the CPU 71 proceeds to step 1020 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 1025 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 1030 to obtain the feedback correction amount DFi based on the following equation (15).
[0109]
(Equation 15)
DFi = (Gp · DFc + Gi · SDFc) · KFB
[0110]
In the above Expression 15, Gp is a preset proportional gain, and Gi is a preset integral gain. It is preferable that the coefficient KFB in Equation 15 be variable depending on the engine rotation speed NE and the in-cylinder intake air amount Mc, 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 1035. That is, in step 1035, the CPU 71 adds the in-cylinder fuel supply amount deviation DFc obtained in step 1025 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at that time, and obtains a new in-cylinder fuel supply amount deviation. Is obtained, and this routine is ended once in step 1095. As described above, the feedback correction amount DFi is obtained, and the feedback correction amount DFi is reflected on the fuel injection amount in steps 910 and 915 in FIG. 9 described above. Feedback control is performed so that the average value of the air-fuel ratio of the air-fuel mixture supplied to the engine substantially matches the target air-fuel ratio abyfr.
[0111]
On the other hand, if the air-fuel ratio feedback control condition is not satisfied at the time of the determination at step 1005, the CPU 71 determines “No” at step 1005, and proceeds to step 1040 to change the value of the air-fuel ratio feedback correction amount DFi to “0”. ”, The routine proceeds to step 1095, and this routine is temporarily ended. As described above, when the air-fuel ratio feedback control condition is not satisfied, the air-fuel ratio feedback correction amount DFi is set to “0” and the air-fuel ratio (basic fuel injection amount Fbase) is not corrected.
[0112]
Next, the above-described air-fuel ratio feedback control based on the output of the downstream air-fuel ratio sensor 67 will be described. This control is also called sub feedback control. By this sub-feedback control, the sub-feedback control amount vafsfb is calculated.
[0113]
The CPU 71 executes the routine shown in FIG. 11 every time a predetermined time elapses in order to obtain the sub feedback control amount vafsfb. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1100 and proceeds to step 1105 to determine whether the sub feedback control condition is satisfied. The sub-feedback control condition is, for example, in addition to the air-fuel ratio feedback control condition in step 1005 described above, the engine coolant temperature THW is equal to or higher than a second predetermined temperature higher than the first predetermined temperature, and the downstream air-fuel ratio sensor 67 Is normal (including an active state).
[0114]
Now, assuming that the sub-feedback control condition is satisfied, the CPU 71 determines “Yes” in step 1105 and proceeds to step 1110, where the CPU 71 determines the current value of the downstream air-fuel ratio sensor 67 from the target value Voxsref. The output deviation amount DVoxs is obtained by subtracting the output Voxs. Next, the CPU 71 proceeds to step 1115 to obtain the sub feedback control amount vafsfb based on the following equation (16).
[0115]
(Equation 16)
vafsfb = Kp · DVoxs + Ki · SDVoxs
[0116]
In Equation 16, Kp is a preset proportional gain, and Ki is a preset integral gain. SDVoxs is an integrated value of the output deviation DVoxs, and is a value updated in the next step 1120. That is, when the CPU 71 proceeds to step 1120, the CPU 71 adds the output deviation DVoxs obtained in step 1110 to the integrated value SDVoxs of the output deviation at that time to obtain a new integrated value SDVoxs of the output deviation. Then, the routine proceeds to step 1195, and this routine is temporarily ended.
[0117]
In this way, the sub-feedback control amount vafsfb is obtained, and this value is added to the actual output vabyfs of the upstream air-fuel ratio sensor 66 in step 1010 of FIG. 10 described above, and the sum (vabyfs + vafsfb) is calculated. 3 is converted into the upstream control air-fuel ratio abyfs based on the map shown in FIG. In other words, the upstream control air-fuel ratio abyfs obtained (corrected) based on the output Voxs of the downstream air-fuel ratio sensor 67 is calculated based on the air-fuel ratio actually detected by the upstream air-fuel ratio sensor 66. The air-fuel ratio is obtained as a different air-fuel ratio by an amount corresponding to the sub-feedback control amount vafsfb. As a result, the in-cylinder fuel supply amount Fc (k−N) calculated in step 1015 in FIG. 10 changes according to the output Voxs of the downstream air-fuel ratio sensor 67, and feedback correction is performed in steps 1025 and 1030. The amount DFi is changed according to the output Voxs of the downstream air-fuel ratio sensor 67. Accordingly, the air-fuel ratio of the air-fuel mixture supplied to the engine (therefore, the air-fuel ratio of the gas flowing into the first catalyst 53) is controlled such that the air-fuel ratio downstream of the first catalyst 53 matches the target value Voxsref. I'm sullen.
[0118]
For example, if the output Voxs of the downstream air-fuel ratio sensor 67 indicates a value corresponding to the air-fuel ratio leaner than the stoichiometric air-fuel ratio because the average air-fuel ratio of the air-fuel mixture supplied to the engine is lean, Since the output deviation amount DVoxs obtained in 1110 has a positive value, the sub-feedback control amount vafsfb obtained in step 1115 has a positive value (in FIG. 5A, for example, from time t2 ′ to t3). '). Therefore, abyfs obtained in step 1010 is obtained as a value leaner (larger value) than the air-fuel ratio actually detected by the upstream air-fuel ratio sensor 66. Therefore, the in-cylinder fuel supply amount Fc (k−N) obtained in step 1015 becomes a small value, and the in-cylinder fuel supply amount deviation DFc obtained in step 1025 is obtained as a large positive value. Is a large positive value. As a result, the final fuel injection amount Fi obtained in step 910 in FIG. 9 is controlled to be larger than the basic fuel injection amount Fbase, so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes rich.
[0119]
Conversely, if the output Voxs of the downstream air-fuel ratio sensor 67 indicates a value corresponding to the rich air-fuel ratio from the stoichiometric air-fuel ratio because the average air-fuel ratio of the air-fuel mixture supplied to the engine is rich, step 1110 Since the output deviation amount DVoxs obtained in step (1) takes a negative value, the sub-feedback control amount vafsfb obtained in step 1115 takes a negative value (in FIG. 5A, for example, times t1 'to t2'). , Times t3 'to t4'). Therefore, abyfs obtained in step 1010 is obtained as a value (smaller value) richer than the air-fuel ratio actually detected by the upstream air-fuel ratio sensor 66. Therefore, the in-cylinder fuel supply amount Fc (k−N) obtained in step 1015 becomes a large value, and the in-cylinder fuel supply amount deviation DFc is obtained as a negative value. Become. As a result, the final fuel injection amount Fi obtained in step 910 in FIG. 9 is controlled to be smaller than the basic fuel injection amount Fbase so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes lean.
[0120]
On the other hand, when the sub-feedback control condition is not satisfied, the CPU 71 determines “No” in step 1105, proceeds to step 1125, and sets the value of the sub-feedback control amount vafsfb to “0”. Thus, the sub-feedback control based on the output Voxs of the downstream air-fuel ratio sensor 67 is stopped.
[0121]
Next, the operation of the first catalyst 53 in calculating the outflow oxygen amount, oxygen storage amount, and the like for each block will be described. The CPU 71 executes each routine shown by the flowcharts of FIGS. 12 and 13 every time a predetermined time elapses.
[0122]
Therefore, at a predetermined timing, the CPU 71 starts processing from step 1200 of the routine shown in FIG. 12 for calculating the outflow oxygen amount, the oxygen storage amount, and the like for each block of the first catalyst 53, and proceeds to step 1205. The average value abyfsave of the air-fuel ratio A / F detected by the upstream air-fuel ratio sensor 66 described above and the latest value of the total fuel injection amount mfr sequentially updated in step 920 in FIG. As described above, the inflowing oxygen amount CginO2 (1) in the block (1) of the first catalyst 53, which is the boundary condition, is calculated based on the equation described in step 1205 based on the above equation (14).
[0123]
Next, the CPU 71 proceeds to step 1210 to set the value of the counter value n and the value of the oxygen storage amount OSAall of the first catalyst 53 to “0”, respectively, and then proceeds to step 1215 for each block of the first catalyst 53. The processing for calculating the outflow oxygen amount, the oxygen storage amount, and the like of the engine is started. First, in step 1215, the CPU 71 increases the value of the counter value n by “1” and sets it to “1”. The counter value n indicates the block number of the first catalyst 53. At this point, the value of the counter value n is “1”, and the value of the counter value n is maintained at “1” in the current process from step 1220 to step 1275. In the processing up to, the calculation in the most upstream block (1) is executed.
[0124]
First, the CPU 71 proceeds to step 1220 to determine whether or not the value of the inflowing oxygen amount CginO2 (1) is equal to or greater than “0”. In step 1220, “Yes” is determined, and the process proceeds to step 1225. As described above, the value of the maximum oxygen storage amount Cmax (1) of the block (1) set to a predetermined constant value as described above, In step 1225 based on the value of the oxygen storage amount OSA (1) of the block (1) calculated (updated) when the present routine was executed last time in step 1260 described later and the right side of the above equation (3). The reaction rate H in the block (1) is calculated based on the equation described above.
[0125]
If it is determined in step 1220 that the value of the inflowing oxygen amount CginO2 (1) is not equal to or greater than “0”, the CPU 71 determines “No” in step 1220 and proceeds to step 1230, where the maximum oxygen storage amount Cmax is determined. The reaction rate H in the block (1) is calculated based on the value of (1), the value of the oxygen storage amount OSA (1), and the expression described in step 1230 based on (the right side of) the above equation (5). .
[0126]
Next, the CPU 71 proceeds to step 1235, where the value of the reaction rate H calculated in step 1225 or step 1230, the value of the inflowing oxygen amount CginO2 (1) in block (1) calculated in step 1205, and Then, the oxygen storage amount change amount δOSA (1) in the block (1) is calculated based on (the right side of) or the equation described in step 1235 based on (4).
[0127]
Next, the CPU 71 proceeds to step 1240, in which the value of the oxygen storage amount OSA (1) of the block (1) calculated when the routine was last executed in step 1260 described later and the current calculation in step 1235. It is determined whether or not the value obtained by integrating the value of the oxygen storage amount change amount δOSA (1) of the block (1) is equal to or less than the value of the maximum oxygen storage amount Cmax (1) in the block (1).
[0128]
Here, if the integrated value is equal to or less than the value of the maximum oxygen storage amount Cmax (1), the CPU 71 determines “Yes” in step 1240 and proceeds to step 1245 to determine whether the integrated value is “0” or more. In addition, it is determined whether or not there is a value. If the integrated value is equal to or greater than "0", "Yes" is determined in step 1245, and the process proceeds to step 1260, where the integrated value is stored as a new oxygen storage amount OSA. Set as (1). As described above, if the integrated value is equal to or more than “0” and equal to or less than the maximum oxygen storage amount Cmax (1), the value of the oxygen storage amount change amount δOSA (1) calculated in step 1235 is directly used in the block (1). It is used as the oxygen storage amount change amount.
[0129]
On the other hand, if it is determined in step 1240 that the integrated value exceeds the value of the maximum oxygen storage amount Cmax (1), the CPU 71 determines “No” in step 1240 and proceeds to step 1250, where After the value obtained by subtracting the value of the previously stored oxygen storage amount OSA (1) from the value of the amount Cmax (1) is stored in the oxygen storage amount change amount δOSA (1), the process proceeds to step 1260. As described above, if the integrated value exceeds the maximum oxygen storage amount Cmax (1) in the block (1), the value of the oxygen storage amount OSA (1) in the block (1) calculated in step 1260 is calculated. This means that the value exceeds the maximum oxygen storage amount Cmax (1), so that the value of the oxygen storage amount OSA (1) calculated in step 1260 this time becomes equal to the value of the maximum oxygen storage amount Cmax (1). The oxygen storage amount change amount δOSA (1) is adjusted.
[0130]
Similarly, in the determination of step 1245, if the integrated value is less than “0” (negative value), the CPU 71 determines “No” in step 1245, proceeds to step 1255, and calculates the value calculated last time. After a value obtained by inverting the sign of the value of the oxygen storage amount OSA (1) is stored in the oxygen storage amount change amount δOSA (1), the process proceeds to step 1260. As described above, if the integrated value is less than “0”, the value of the oxygen storage amount OSA (1) in block (1) calculated in step 1260 this time becomes less than “0” (negative value). Therefore, the oxygen storage amount change amount δOSA (1) is adjusted so that the value of the oxygen storage amount OSA (1) calculated in step 1260 this time becomes “0”.
[0131]
After calculating the current oxygen storage amount OSA (1) in block (1) in step 1260, the CPU 71 proceeds to step 1265 and calculates the value of the inflowing oxygen amount CginO2 (1) in block (1) calculated in step 1205. And the value of the oxygen storage amount change amount δOSA (1) in the block (1) after the above adjustment and the outflow in the block (1) based on the equation described in step 1265 based on the above equation (1). The oxygen amount CgoutO2 (1) is calculated.
[0132]
Next, the CPU 71 proceeds to step 1270, where the value of the oxygen storage amount OSAall of the first catalyst 53 at this time (which is “0” by execution of step 1210) is calculated at the block (1 ), The value obtained by adding the value of the current oxygen storage amount OSA (1) is stored as a new oxygen storage amount OSAall, and the routine proceeds to step 1275, where the outflowing oxygen amount in the block (1) calculated in step 1265 Based on the value of CgoutO2 (1) and Equation 7, the inflowing oxygen amount CginO2 (2) in the downstream block (2) adjacent to the block (1) is calculated.
[0133]
Then, the CPU 71 proceeds to step 1280 to determine whether or not the value of the counter value n is equal to the number N 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 1280, returns to step 1215 again, and increases the value of the counter value n by “1” to “2”. Then, by executing the processing of the following steps 1220 to 1275, the calculation in the next block (2) is executed. At this time, the value of the inflowing oxygen amount CginO2 (2) calculated in the previous step 1275 is used as the value of the inflowing oxygen amount CginO2 (2) in step 1265.
[0134]
In this manner, the processing from step 1220 to step 1275 is repeatedly executed until the value of the counter value n becomes equal to the number N of blocks of the first catalyst 53. Thereby, the inflow oxygen amount CginO2 (n), the outflow oxygen amount CgoutO2 (n), the oxygen storage amount of each block (n) from the most upstream block (1) to the most downstream block (N) of the first catalyst 53. The values of the change amount δOSA (n) and the oxygen storage amount OSA (n) are sequentially calculated. Further, by repeatedly executing the process of step 1270, the oxygen storage amount OSAall of the first catalyst 53 is also calculated. In this way, when the value of the counter value n is the number of blocks N, the value calculated in step 1265 is an excess / deficiency amount (outflow oxygen amount) of oxygen in the gas flowing out of the first catalyst 53 CgoutO2 (N ).
[0135]
When the value of the counter value n becomes equal to the number N of blocks of the first catalyst 53 by repeating the processing of step 1215, the CPU 71 determines “Yes” in step 1280, and in the subsequent step 1285, the total fuel injection amount After setting the value of mfr to "0", the routine proceeds to step 1295, where the present routine is temporarily terminated.
[0136]
At a predetermined timing, the CPU 71 initializes (clears) the value of the oxygen storage amount of each block of the first catalyst 53 and the value of the oxygen storage amount of the first catalyst 53, as shown in the flowchart of FIG. The process starts from step 1300 of the routine indicated by, and proceeds to step 1305 to monitor whether or not the value of the output Voxs of the downstream air-fuel ratio sensor 67 is larger than 0.7 (V). At this time, if the value of the output Voxs of the downstream air-fuel ratio sensor 67 is larger than 0.7 (V), that is, if the downstream air-fuel ratio of the first catalyst 53 is a rich air-fuel ratio, the entire first catalyst 53 Means that the amount of oxygen stored in the first catalyst 53 is “0”, so the CPU 71 proceeds to step 1310 and determines the value of the amount of oxygen stored in each block of the first catalyst 53 and the value of the amount of oxygen stored in the first catalyst 53. The process of setting all the values to “0” starts. On the other hand, if it is determined in step 1305 that the value of the output Voxs of the downstream air-fuel ratio sensor 67 is 0.7 (V) or less, the CPU 71 proceeds directly from step 1305 to step 1395 and ends this routine once.
[0137]
Now, assuming that the value of the output Voxs of the downstream air-fuel ratio sensor 67 is larger than 0.7 (V) in the determination of step 1305, the CPU 71 proceeds to step 1310 and sets the value of the counter value n to “0”. After the setting, the process proceeds to step 1315, where the value of the counter value n is increased by “1” and set to “1”. Next, the CPU 71 proceeds to step 1320 to set the value of the oxygen storage amount OSA (n) in the block (n) of the first catalyst 53 to “0”. At this point, the value of the counter value n is “1”, so that the value of the oxygen storage amount OSA (1) in the most upstream block (1) is set to “0”.
[0138]
Then, the CPU 71 proceeds to step 1325 to determine whether or not the value of the counter value n is equal to the number N 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 1325, returns to step 1315 again, increases the value of the counter value n by “1”, and returns to step 1320 The processing of step 1325 is executed. That is, the processing of steps 1320 and 1325 is repeatedly executed until the value of the counter value n becomes equal to the number N of blocks of the first catalyst 53. Thereby, the value of the oxygen storage amount OSA (n) in each block (n) from the most upstream block (1) to the most downstream block (N) of the first catalyst 53 is all cleared to “0”. .
[0139]
When the value of the counter value n becomes equal to the number N of blocks of the catalyst 53 by repeating the processing of the above-described step 1315, the CPU 71 determines “Yes” in step 1325, proceeds to step 1330, and proceeds to step 1330. After setting the value of the oxygen storage amount OSAall to “0”, the routine proceeds to step 1395, and this routine is temporarily ended.
[0140]
Next, each time the frequency SML at which the output Voxs of the downstream air-fuel ratio sensor 67 enters the first state reaches the reference value SML0 (every one sampling period elapses), the downstream air-fuel ratio is reduced during this one sampling period. The operation for obtaining the frequency FRE at which the outflow oxygen amount CgoutO2 (N) is in the second state when the output Voxs of the fuel ratio sensor 67 is in the first state will be described. The CPU 71 executes each routine shown by the flowchart of FIG. 14 every time a predetermined time elapses.
[0141]
Therefore, at a predetermined timing, the CPU 71 starts the process from step 1400 and proceeds to step 1405, where the same sub-feedback control condition as that in step 1105 in FIG. It is determined whether or not the value of the recovery process execution flag PWM is “0”. If “No” is determined in step 1405, the process immediately proceeds to step 1450, and the output of the downstream air-fuel ratio sensor at the present time is determined. After setting the value of Voxs as the previous downstream air-fuel ratio sensor output Voxsp, the present routine is ended once. This is to calculate the frequency FRE when the downstream air-fuel ratio sensor 67 is normal and the poisoning recovery process described below has not been executed.
[0142]
Now, the sub-feedback control condition is satisfied, the value of the poisoning recovery process execution flag PWM is “0”, and the output Voxs of the downstream air-fuel ratio sensor 67 increases the rich-side predetermined value Vrich. Alternatively, if the description is continued assuming that the first state of passing while decreasing the lean-side predetermined value Vlean is not reached, the CPU 71 determines “Yes” in step 1405 and proceeds to step 1410, The value of the downstream air-fuel ratio sensor output Voxs (at this time) is larger than the rich predetermined value Vrich, and the value of the previous downstream air-fuel ratio sensor output Voxsp updated in step 1450 at the last execution of this routine is Whether or not the value is equal to or lower than the rich-side predetermined value Vrich (accordingly, the downstream-side air-fuel ratio sensor output Voxs becomes the rich-side predetermined value Vr It determines an increase whether passed with) the ch.
[0143]
At this time, according to the above assumption, the CPU 71 determines “No” in step 1410 and proceeds to step 1415, in which the current value of the downstream air-fuel ratio sensor output Voxs is smaller than the lean side predetermined value Vlean and Of the downstream air-fuel ratio sensor output Voxsp is equal to or more than the lean predetermined value Vlean (accordingly, whether the downstream air-fuel ratio sensor output Voxs passes while decreasing the lean predetermined value Vlean). Is determined.
[0144]
At this time, according to the above assumption, the CPU 71 also determines “No” in step 1415 and proceeds to step 1450 immediately. Thereafter, the CPU 71 repeatedly executes the processing of steps 1400 to 1415 and 1450 as long as the output Voxs of the downstream air-fuel ratio sensor 67 does not enter the first state.
[0145]
Next, the case where the downstream air-fuel ratio sensor output Voxs passes while increasing the rich-side predetermined value Vrich from this state (time t1 and t3 in FIG. 5A) will be described. When the process proceeds to 1410, it is determined as “Yes” and the process proceeds to step 1420, and a value obtained by increasing the value of the current frequency SML by “1” is set as a new frequency SML.
[0146]
Next, the CPU 71 proceeds to step 1425, and determines whether the latest value of the outflow oxygen amount CgoutO2 (N) calculated in step 1265 of FIG. 12 is smaller than the negative threshold value Crefmns (that is, the outflow oxygen amount CgoutO2 (N)). It is determined whether or not the oxygen amount CgoutO2 (N) is in the second state), and when it is determined to be “Yes”, a value obtained by increasing the value of the current frequency FRE by “1” in step 1430 is newly set. After setting the frequency FRE, the process proceeds to step 1450. On the other hand, if the determination in step 1425 is “No”, the CPU 71 immediately proceeds to step 1450 while maintaining the value of the frequency FRE at the current value. Thereafter, the CPU 71 repeatedly executes the processing of steps 1400 to 1415 and 1450 as long as the output Voxs of the downstream air-fuel ratio sensor 67 does not become the first state.
[0147]
Next, a case where the downstream air-fuel ratio sensor output Voxs passes while decreasing the lean-side predetermined value Vlean from this state (time t2 and t4 in FIG. 5A) will be described. When proceeding to 1415, it is determined as “Yes” and the process proceeds to step 1435, and a value obtained by increasing the value of the current frequency SML by “1” is set as a new frequency SML.
[0148]
Next, the CPU 71 proceeds to step 1440, and determines whether the latest value of the outflow oxygen amount CgoutO2 (N) calculated in step 1265 in FIG. 12 is greater than the positive threshold value Crefpls (that is, the outflow oxygen amount CgoutO2 (N)). It is determined whether or not the oxygen amount CgoutO2 (N) is in the second state), and when it is determined to be “Yes”, a value obtained by increasing the value of the current frequency FRE by “1” in step 1445 is newly set. After setting the frequency FRE, the process proceeds to step 1450. On the other hand, if the determination in step 1440 is “No”, the CPU 71 immediately proceeds to step 1450 while maintaining the value of the frequency FRE at the current value. Thereafter, the CPU 71 repeatedly executes the processing of steps 1400 to 1415 and 1450 as long as the output Voxs of the downstream air-fuel ratio sensor 67 does not become the first state.
[0149]
In this way, by repeatedly executing this routine, the value of the frequency SML is increased by “1” each time the output Voxs of the downstream air-fuel ratio sensor 67 enters the first state, and the downstream air-fuel ratio is increased. When the output Voxs of the fuel ratio sensor 67 becomes the first state, the value of the frequency FRE is increased by "1" every time the outflow oxygen amount CgoutO2 (N) is in the second state.
[0150]
Further, the CPU 71 executes a routine for determining the deterioration of the first catalyst 53 shown by the flowchart 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 or not the value of the frequency SML is equal to or more than the reference value SML0. At this time, if the value of the frequency SML is smaller than the reference value SML0, the CPU 71 immediately proceeds to step 1595 without performing the catalyst deterioration determination, and ends this routine once.
[0151]
On the other hand, when the frequency SML has reached the reference value SML0 (that is, when the one sampling period has elapsed), the CPU 71 determines “Yes” in step 1505 and proceeds to step 1510, where the value of the frequency FRE is determined to be deteriorated. It is determined whether or not the value is equal to or more than the reference value FREF.
[0152]
Now, the description will be continued assuming that the degree of deterioration of the first catalyst 53 is small. In this case, the value of the frequency FRE is equal to or larger than the deterioration determination reference value FREF. Accordingly, the CPU 71 determines “Yes” in step 1510, proceeds to step 1515, sets the value of the deterioration determination flag XR to “0”, and sets the value of the counter CNT to “0” in the following step 1520. I do. Here, when the deterioration determination flag XR is “1”, it indicates that the first catalyst 53 is the deteriorated catalyst, and when the value is “0”, the first catalyst 53 is the normal catalyst. Indicates that there is. Further, the value of the counter CNT is the number of times that the deterioration determination flag XR continuously becomes “1” every time the one sampling period elapses (therefore, the first catalyst 53 is continuously determined to be the deteriorated catalyst). Is a value that indicates
[0153]
Then, the CPU 71 proceeds to step 1525, sends an instruction signal for turning off the alarm lamp 82 to the alarm lamp 82, and sets the value of the frequency SML and the value of the frequency FRE to “0” in the following step 1530. After the setting, the process proceeds to step 1595, and this routine is temporarily ended. As a result, by repeatedly executing the routine of FIG. 14, the value of the frequency FRE is changed from “0” until the value of the frequency SML reaches the reference value SML0 again (that is, until the next one sampling period elapses). It is updated, and when the next one sampling period has elapsed, the deterioration determination of the first catalyst 53 is executed again based on the updated value of the frequency FRE at that time. Then, as long as the value of the frequency FRE is equal to or greater than the deterioration determination reference value FREF, it is determined that the first catalyst 53 is a normal catalyst.
[0154]
Next, a description will be given of a case where the deterioration of the first catalyst 53 progresses from this state and the value of the frequency FRE becomes smaller than the deterioration determination reference value FREF. In this case, the CPU 71 determines “No” in step 1510. In step 1535, the value of the deterioration determination flag XR is set to “1”, and in the next step 1540, the value of the poisoning recovery processing execution flag PWM is set to “1”. At the same time, in the following step 1545, a value (= 1) obtained by increasing the value of the counter CNT at the present time (currently “0”) by “1” is set as a new counter CNT.
[0155]
Next, the CPU 71 proceeds to step 1550, and determines whether or not the value of the counter CNT is equal to or less than “1”, that is, whether or not the number of times that the first catalyst 53 is continuously determined to be the deteriorated catalyst is equal to or less than one. Is determined. At this time, since the value of the counter CNT is “1”, the CPU 71 determines “Yes” in step 1550 and immediately proceeds to step 1530 to set both the value of the frequency SML and the value of the frequency FRE to “0”. After the setting, the process proceeds to step 1595, and this routine is temporarily ended.
[0156]
As a result, the value of the poisoning recovery processing in-execution flag PWM becomes “1” and the above-described air-fuel ratio feedback control condition is not satisfied, so the CPU 71 determines “No” in step 1005 of FIG. The process proceeds to 1040, the value of the air-fuel ratio feedback correction amount DFi is set to “0”, and the above-described air-fuel ratio feedback control is interrupted. Further, the CPU 71 determines “No” in step 1405 in FIG. 14 and immediately proceeds to step 1450, and the calculation of the frequency FRE is also interrupted. Therefore, since the value of the frequency SML is maintained at “0”, if the CPU 71 continues to determine “No” in step 1505 of FIG. 15, the deterioration determination of the first catalyst 53 is not executed. As a result, the value of the counter CNT is maintained at “1”.
[0157]
Further, the CPU 71 executes a routine for executing the poisoning recovery process shown by the flowchart in FIG. Generally, deterioration of a three-way catalyst such as the first catalyst 53 is roughly classified into deterioration due to heat and deterioration due to poisoning. Here, when the three-way catalyst is deteriorated by heat, it is difficult to eliminate the deteriorated state. On the other hand, when the three-way catalyst is deteriorated due to poisoning, it is known that the deterioration state can be eliminated by executing a predetermined poisoning recovery process. Hereinafter, the deterioration due to poisoning and the poisoning recovery processing will be briefly described.
[0158]
When a predetermined amount of the reducing agent (for example, unburned components such as HC and CO) in the exhaust gas continuously flows into the catalyst, the reducing agent is noble metal or ceria (CeO) in the catalyst. ₂ ) (Hereinafter referred to as “noble metal”), which is poisoned (so-called primary poisoning) by reducing the surface area of the noble metal and the like, and deteriorated by the poisoning (for example, the catalyst). It is known that the maximum oxygen storage amount decreases). On the other hand, it is also known that the primary poisoning state of the catalyst by the reducing agent is eliminated by supplying a predetermined amount of oxygen (accordingly, a gas having a lean air-fuel ratio) to the catalyst.
[0159]
On the other hand, when the sulfur component in the exhaust gas continuously flows by a predetermined amount, the catalyst adheres to the surface of the noble metal or the like in the catalyst, and the surface area of the noble metal or the like becomes small. , Primary poisoning), and is also known to deteriorate by such poisoning. On the other hand, the primary poisoning state of the catalyst due to the sulfur component is eliminated by supplying the catalyst with a predetermined amount of a reducing agent (for example, unburned components such as HC and CO. Therefore, a gas having a rich air-fuel ratio). It is also known to do.
[0160]
From the above, the present catalyst deterioration determination apparatus sets the value of the poisoning recovery process execution flag PWM every time the first catalyst 53 is determined to be a deteriorated catalyst (that is, when step 1540 in FIG. 15 is executed). Each time the air-fuel ratio feedback control is stopped and the air-fuel ratio of the air-fuel mixture supplied to the engine is changed to a predetermined rich air-fuel ratio every time a predetermined period elapses. A poisoning recovery process is performed in which a predetermined lean air-fuel ratio, a predetermined rich air-fuel ratio, and a predetermined lean air-fuel ratio are forcibly controlled in this order.
[0161]
In order to execute such poisoning recovery processing, the CPU 71 repeatedly executes the routine of FIG. 16 every time a predetermined time elapses. Therefore, at a predetermined timing, the CPU 71 starts the process from step 1600 and proceeds to step 1605 to determine whether or not the value of the poisoning recovery process execution flag PWM is “1” and “No”. When the determination is made, the process immediately proceeds to step 1695 without executing the poisoning recovery process, and the present routine is temporarily ended.
[0162]
Now, assuming that it is immediately after the execution of step 1540 in FIG. 15 described above, the CPU 71 determines “Yes” in step 1605, proceeds to step 1610, and sets the flag of the poisoning recovery processing execution flag PWM. It is determined whether the value has been changed from “0” to “1”. At this time, immediately after the execution of step 1540 in FIG. 15 and immediately after the value of the poisoning recovery processing execution flag PWM is changed from “0” to “1”, the CPU 71 determines “ The result of the determination is "Yes" and the operation proceeds to step 1615, where the counter value T is set to "0", and the value of the coefficient K used in step 910 of FIG. I do. Here, the counter value T is a value representing the elapsed time from the time when the poisoning recovery processing is started.
[0163]
Next, the CPU 71 proceeds to step 1625 to increase the counter value by “1”, and determines in a subsequent step 1630 whether or not the counter value T is smaller than “4 · T1”. Here, T1 is a value corresponding to the predetermined period. Therefore, in this step 1630, it is determined whether or not the predetermined period has been repeated four times after the poisoning recovery processing has been started, that is, whether or not the time to end the poisoning recovery processing has come. Is determined.
[0164]
Since the current time is immediately after the poisoning recovery processing has started, the CPU 71 determines “Yes” in step 1630 and proceeds to step 1635, and determines whether the counter value T is the value “T1” or the value “3 · T1”. Is determined. At this time, since the poisoning recovery process has just started, the CPU 71 determines “No” in step 1630 and proceeds to step 1640 to determine whether or not the counter value T has reached the value “2 · T1”. judge. At this time, it is immediately after the poisoning recovery process is started, so that the CPU 71 also determines “No” in step 1640 and immediately proceeds to step 1695 to end this routine once.
[0165]
Thereafter, until step 1625 is repeatedly executed and the counter value T becomes the value T1 (therefore, until the predetermined period elapses after the start of the poisoning recovery process), the CPU 71 proceeds to steps 1600 to 1610, 1625 to 1640, and 1695. Repeat the process. Accordingly, a value obtained by multiplying the basic fuel injection amount Fbase by 1.02 by the execution of step 910 in FIG. 9 is calculated as the final fuel injection amount Fi until the predetermined period elapses after the start of the poisoning recovery process. (The value of the air-fuel ratio feedback correction amount DFi is set to “0”.) Since the fuel of the final fuel injection amount Fi is injected, the air-fuel ratio of the air-fuel mixture supplied to the engine (accordingly, the first The air-fuel ratio of the gas flowing into the catalyst 53) is continuously controlled to the predetermined rich air-fuel ratio richer than the stoichiometric air-fuel ratio. Thereby, the primary poisoning state of the first catalyst 53 by the sulfur component may be eliminated.
[0166]
Next, a case where the counter value T becomes the value T1 from this state will be described. In this case, the CPU 71 determines “Yes” when proceeding to step 1635, proceeds to step 1645 to change the value of the coefficient K from “1.02” to “0.98”, and then proceeds to step 1695 to execute The routine ends once. Thereafter, the CPU 71 repeats Step 1625 until the counter value T reaches the value T2 (therefore, until the second predetermined period elapses after the first predetermined period elapses), the CPU 71 proceeds to Steps 1600 to 1610. The processing of 1625 to 1640 and 1695 is repeatedly executed again. Therefore, a value obtained by multiplying the basic fuel injection amount Fbase by 0.98 is calculated as the final fuel injection amount Fi after the first predetermined period elapses and before the second predetermined period elapses. The air-fuel ratio of the air-fuel mixture supplied to the engine (therefore, the air-fuel ratio of the gas flowing into the first catalyst 53) is continuously controlled to the predetermined lean air-fuel ratio leaner than the stoichiometric air-fuel ratio. Thereby, the primary poisoning state of the first catalyst 53 by the reducing agent may be eliminated.
[0167]
Similarly, when the counter value T increases from the value T1 to reach the value T2, the CPU 71 determines “Yes” when proceeding to step 1640, proceeds to step 1650, and increases the value of the coefficient K from “0.98”. It is changed to "1.02" again. Thus, after the elapse of the second predetermined period, until the elapse of the third predetermined period, the air-fuel ratio of the air-fuel mixture supplied to the engine (therefore, the ratio of the gas flowing into the first catalyst 53) is reduced. The air-fuel ratio is continuously controlled to the predetermined rich air-fuel ratio above the stoichiometric air-fuel ratio. Similarly, when the counter value T increases from the value T2 to reach the value T3, the CPU 71 determines “Yes” when proceeding to step 1635, proceeds to step 1645, and changes the value of the coefficient K to “1.02”. "To" 0.98 "again. Thus, after the third predetermined period elapses, the air-fuel ratio of the air-fuel mixture supplied to the engine (therefore, the ratio of the gas flowing into the first catalyst 53) continues until the fourth predetermined period elapses. The air-fuel ratio is continuously controlled to the predetermined lean air-fuel ratio above the stoichiometric air-fuel ratio.
[0168]
Then, when the counter value T increases from the value T3 to the value T4, the CPU 71 determines “No” when proceeding to step 1630, proceeds to step 1655, and resets the value of the coefficient K to “1.00”. In addition to the setting, the value of the poisoning recovery process execution flag PWM is changed from “1” to “0” in the subsequent step 1660, and then the routine proceeds to step 1695 to end this routine once.
[0169]
Thereafter, the value of the poisoning recovery processing in-execution flag PWM is “0”, so that the value of the poisoning recovery processing in-execution flag PWM in step 1540 in FIG. 15 is set to “1” again. During this time, the CPU 71 immediately proceeds from step 1605 to step 1695 to end this routine once. If the air-fuel ratio feedback control condition and the sub-feedback control condition are satisfied, the CPU 71 determines “Yes” in step 1005 of FIG. 10 and step 1105 of FIG. Is restarted and the determination of “Yes” is made in step 1405 of FIG. 14, so that the calculation of the frequency FRE is restarted.
[0170]
Therefore, after the end of the poisoning recovery process, if the frequency SML again reaches the reference value SML0 (that is, if one sampling period has elapsed), the CPU 71 determines “Yes” in step 1505 of FIG. Proceeding to step 1510 and thereafter, the deterioration of the first catalyst 53 is determined. Then, when the deterioration state of the first catalyst 53 has been resolved by the poisoning recovery process, the CPU 71 determines “Yes” in step 1510, and sets the value of the counter CNT to the current value “1” in step 1520. From "0" to "0".
[0171]
On the other hand, if the deterioration state of the first catalyst 53 has not been resolved by the poisoning recovery process, the CPU 71 again determines “No” in step 1510, and in step 1545 sets the value of the counter CNT to the current value “ "1" is increased by "1" and set to "2". Accordingly, the CPU 71 determines “No” in the subsequent step 1550, and proceeds to step 1555 to send an instruction signal to the alarm lamp 82 to turn on the alarm lamp 82. Thereby, the warning lamp 82 is turned on.
[0172]
That is, the alarm lamp 82 is provided when the poisoning recovery process is performed once after the first catalyst 53 is determined to be the deteriorated catalyst, but the deteriorated state of the first catalyst 53 is not solved. It will be lit. Further, in this case, the poisoning recovery process is executed again by the process of step 1540. If the poisoning recovery process is repeatedly executed and the degradation state of the first catalyst 53 may be subsequently resolved, the CPU 71 determines “Yes” in step 1510. In step 1520, the value of the counter CNT is cleared to "0", and in step 1525, the alarm lamp 82 that has been lit up to the present time is turned off. On the other hand, when the deterioration state of the first catalyst 53 is not continued, the alarm lamp 82 is continuously lit because the processing of step 1525 is not executed.
[0173]
As described above, according to the embodiment of the present invention, based on the catalyst model for the first catalyst 53 constructed on the assumption that the first catalyst 53 is a new catalyst, the first catalyst 53 is used. The amount (outflow oxygen amount CgoutO2 (N)) of the specific component in the gas flowing out of the engine 53 is estimated (calculated). In the embodiment of the present invention, during the air-fuel ratio feedback control based on the output Voxs of the downstream-side air-fuel ratio sensor 67 downstream of the first catalyst 53, the downstream-side air-fuel ratio sensor output Voxs is in the first state (the rich-side predetermined value). Each time Vrich is increased or the lean-side predetermined value Vlean is reduced, the outflow oxygen amount CgoutO2 (N) estimated by the catalyst model becomes higher than the second state (negative threshold Crefmns). And a frequency SML at which the downstream-side air-fuel ratio sensor output Voxs becomes the first state is determined by a predetermined reference value. Each time SML0 is reached (each time one sampling period elapses), the downstream air-fuel ratio sensor output Voxs is changed during this one sampling period. The frequency FRE at which the outflow oxygen amount CgoutO2 (N) is in the second state at the time when the state becomes 1 is obtained. It is determined whether the first catalyst 53 is a normal catalyst or a deteriorated catalyst based on whether the ratio of the first catalyst 53 is equal to or more than a predetermined value.
[0174]
Such a method for determining catalyst deterioration only involves air-fuel ratio fluctuations in normal air-fuel ratio feedback (sub-feedback), and does not forcibly change the air-fuel ratio when the engine is in a steady state as in the prior art. Therefore, the catalyst deterioration determination can be performed without deteriorating drivability. Further, since the catalyst deterioration determination is performed during the normal air-fuel ratio feedback control (sub-feedback control), many opportunities for the catalyst deterioration determination can be secured. As a result, the first catalyst 53 is a normal catalyst or a deteriorated catalyst. Could be determined without delay.
[0175]
The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, in the above embodiment, each time the frequency SML at which the downstream air-fuel ratio sensor output Voxs becomes the first state reaches the reference value SML0, the catalyst deterioration is determined based on the comparison result between the frequency FRE and the deterioration determination reference value FREFref. Although the determination is performed, the deterioration determination of the catalyst is performed every time a predetermined (constant) sampling time elapses, based on the comparison result between the ratio of the frequency FRE to the frequency SML and the predetermined value within the same sampling time. May be configured.
[0176]
Further, in the above-described embodiment, the frequency SML (the state in which the downstream air-fuel ratio sensor output Voxs passes through the first state (the state in which the rich-side predetermined value Vrich is increased or the lean-side predetermined value Vlean is decreased while passing therethrough)). SML0), the amount of the specific component flowing out of the first catalyst 53 (outflow oxygen amount CgoutO2 (N)) at the time when the downstream air-fuel ratio sensor output Voxs is in the first state is equal to the second state (negative threshold value). Deterioration determination of the first catalyst 53 is performed in accordance with the ratio of the frequency FRE that is smaller than Crefmns or greater than the positive threshold value Crefpls). The state may be a “decreasing or increasing state”. In addition, the amount of the specific component flowing out of the first catalyst 53 (outflow oxygen amount CgoutO2 (N)) is in the first state (a state in which the negative threshold value Crefmns is reduced or the positive threshold value Crefpls is increased). At the time when the amount of the specific component becomes the first state with respect to the frequency SML (SML0), the downstream-side air-fuel ratio sensor output Voxs becomes the second state (a value larger than the rich-side predetermined value Vrich, or the lean-side predetermined value). The deterioration of the first catalyst 53 may be determined in accordance with the ratio of the frequency FRE at which the value is smaller than the value Vlean). In this case, the second state may be "an increasing or decreasing state". Further, both the above-described rich-side predetermined value Vrich and lean-side predetermined value Vlean may be set to values equal to the target value Voxsref.
[0177]
Further, in the above embodiment, the air-fuel ratio feedback control (sub-feedback control) is executed based on the output Voxs of the downstream air-fuel ratio sensor 67, but the outflow oxygen amount CgoutO2 (N) estimated by the catalyst model. It may be configured to be executed based on. In this case, step 1110 in FIG. 11 may be rewritten as “DVoxs ← CgoutO2 (N) −CgoutO2ref”. Here, CgoutO2ref is a target value of the outflow oxygen amount CgoutO2 (N), and is, for example, “0”.
[0178]
Further, the sub-feedback control may be PID control instead of the PI control. Further, the downstream air-fuel ratio sensor 67 may be the same air-fuel ratio sensor as the upstream air-fuel ratio sensor 66. Further, the air-fuel ratio of the air-fuel mixture supplied to the engine may be feedback-controlled based only on the output Voxs of the downstream air-fuel ratio sensor 67.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an internal combustion engine to which a catalyst deterioration determination device according to the present invention is applied.
FIG. 2 is a map showing a relationship between an output voltage of the air flow meter shown in FIG. 1 and a measured intake air flow rate.
FIG. 3 is a map showing a relationship between an output voltage of an upstream air-fuel ratio sensor shown in FIG. 1 and an air-fuel ratio.
FIG. 4 is a map showing a relationship between an output voltage of a downstream air-fuel ratio sensor shown in FIG. 1 and an air-fuel ratio.
FIG. 5A shows the output of a downstream air-fuel ratio sensor in air-fuel ratio feedback control (sub-feedback control) when the first catalyst is a new catalyst, and a catalyst model employed by the catalyst deterioration determination device of the present invention. 5B is a time chart showing a change in the amount of oxygen flowing out of the first catalyst estimated by the following equation. FIG. 7B is an output of the downstream-side air-fuel ratio sensor in the air-fuel ratio feedback control when the first catalyst is a deteriorated catalyst. 5 is a time chart showing changes in the outflow oxygen amount.
FIG. 6 is a diagram schematically showing a catalyst model used by the catalyst deterioration determination device of the present invention.
FIG. 7 is a diagram showing a balance of a specific component related to an oxygen storage / release reaction in a specific region of the catalyst model used in the catalyst deterioration determination device of the present invention when focusing on the specific region.
FIG. 8 is a schematic diagram when a catalyst model adopted by the catalyst deterioration determination device of the present invention is applied to a first catalyst.
FIG. 9 is a flowchart showing a routine for calculating a fuel injection amount executed by a CPU shown in FIG. 1;
FIG. 10 is a flowchart showing a routine for calculating an air-fuel ratio feedback correction amount executed by the CPU shown in FIG. 1;
11 is a flowchart illustrating a routine for calculating a sub-feedback control amount executed by a CPU illustrated in FIG. 1;
12 is a flowchart showing a routine executed by the CPU shown in FIG. 1 for calculating an outflow oxygen amount, an oxygen storage amount, and the like for each block of the first catalyst.
13 is a flowchart showing a routine executed by the CPU shown in FIG. 1 for clearing the oxygen storage amount of each block of the first catalyst.
FIG. 14 is a flowchart showing a routine for obtaining a frequency FRE used for catalyst deterioration determination executed by the CPU shown in FIG. 1;
FIG. 15 is a flowchart showing a routine executed by the CPU shown in FIG. 1 to determine whether the first catalyst is a normal catalyst or a deteriorated catalyst.
FIG. 16 is a flowchart showing a routine for performing a first catalyst poisoning recovery process executed by the CPU shown in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39 ... Injector, 52 ... Exhaust pipe (exhaust pipe), 53 ... 1st catalyst, 66 ... Upstream air-fuel ratio sensor, 67 ... Downstream air-fuel ratio sensor, 70 ... Electric control device , 71 ... CPU

Claims (4)

A catalyst disposed in an exhaust passage of the internal combustion engine;
An air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst,
Applied to exhaust gas purification devices for internal combustion engines with
Catalyst deterioration determining means for determining whether the catalyst is a normal catalyst that has not deteriorated to the extent that it should be determined to be a deteriorated catalyst or a deteriorated catalyst that has deteriorated to the extent that it should be determined that the catalyst has deteriorated; A catalyst deterioration determination device comprising:
A specific component amount for estimating a value relating to an amount of a specific component in a gas flowing out from the catalyst based on a catalyst model constructed in consideration of a reaction in the catalyst when the catalyst is assumed to be the normal catalyst. Equipped with estimating means,
The catalyst deterioration determining means may determine that a relationship between an output value of the air-fuel ratio sensor and a value related to the estimated specific component amount is between an output value of the air-fuel ratio sensor and an actual value of a value related to the specific component amount. When the degree of departure from the predetermined correlation to be obtained is less than or equal to a predetermined degree, the catalyst is determined to be the normal catalyst, and the degree of departure from the predetermined correlation is the same as the predetermined degree. A catalyst deterioration determination device configured to determine that the catalyst is the deteriorated catalyst when the value exceeds the above. The catalyst deterioration determination device according to claim 1,
Feedback control of the air-fuel ratio of the gas flowing into the catalyst based on the output value of the air-fuel ratio sensor or the value related to the estimated amount of the specific component based on the value of the specific component so that the value becomes a predetermined target value. Air-fuel ratio control means,
The catalyst deterioration determining device is configured to determine whether the catalyst is the normal catalyst or the deteriorated catalyst during the feedback control. The catalyst deterioration determination device according to claim 1 or 2,
The catalyst deterioration determination means,
Each time one of the output value of the air-fuel ratio sensor or the value related to the estimated amount of the specific component is in the first state indicating that a gas having a rich air-fuel ratio or a lean air-fuel ratio is flowing out of the catalyst. It is determined whether or not the other value is in the second state indicating that the same rich air-fuel ratio or lean air-fuel ratio gas is flowing out of the same catalyst,
A ratio of the frequency at which the one value is in the first state to the frequency at which the other value is in the second state at the time when the same value is in the first state is equal to or more than a predetermined value. When the relationship between the output value of the air-fuel ratio sensor and the value related to the estimated amount of the specific component deviates from the predetermined correlation is determined to be less than or equal to the predetermined degree, Is smaller than the predetermined value, it is determined that the degree of the relationship deviating from the predetermined correlation exceeds the predetermined level. In the catalyst deterioration determination device according to any one of claims 1 to 3,
The catalyst deterioration determination device, wherein the specific component amount estimating means is configured to estimate a value relating to the excess or deficiency of oxygen in the gas flowing out of the catalyst as a value relating to the amount of the specific component in the gas.

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