JP3791105B2 - Engine air-fuel ratio control device - Google Patents

Description

ただし、Ｔｐ：基本噴射パルス幅
Ｋａｔｈｏｓ：過渡補正量
Ｔｆｂｙａ：目標燃空比相当量
αｍ：空燃比学習値
Ｔｓ：無効パルス幅
の式で計算する。この計算したＴｉの値は、これも図示しないが噴射タイミングで出力レジスタに転送し、エンジン２回転毎に１回、Ｔｉに応じた燃料量を各気筒毎に噴射する。
【００４６】
ここで、（４）式のＴｐはエンジン回転数と吸入空気量から計算される値で、このＴｐによりほぼ理論空燃比の混合気が得られる。Ｔｆｂｙａは水温増量補正係数Ｋｔｗや始動後増量補正係数Ｋａｓなどの和であり、冷間始動直後より空燃比フィードバック制御が開始されるまでのあいだでＴｆｂｙａが１．０より大きい値になって燃料増量が行われ、理論空燃比よりもリッチ側の空燃比で運転される。なお、減速リーンクランプ時などにはＴｆｂｙａが１．０より小さい値になる。また、空燃比フィードバック制御条件の成立時にはＴｆｂｙａ＝１．０となる。
【００４７】
ところで、始動後できるだけ早く空燃比フィードバック制御に入ったほうが排気浄化性能がよくなるので、上流側Ｏ₂センサ３をヒーター加熱などで活性化させ、触媒１０は活性化途中であっても上流側Ｏ₂センサ３が活性化したタイミングで空燃比フィードバック制御に入るようにしている。
【００４８】
この場合に、下流側Ｏ₂センサ出力を用いた比例分修正制御を行うことは触媒１０の活性化途中にも有効であることから、空燃比フィードバック制御定数の修正制御についても空燃比フィードバック制御の開始後できるだけ早く開始することが望ましい。
【００４９】
一方、始動増量（始動時の増量と始動後増量の両方）や水温増量等の影響を受けて、空燃比フィードバック制御を開始してからしばらくのあいだは、図１３上段に示したように触媒内空燃比がリッチ気味になるので、これに対応して空燃比フィードバック制御の開始当初から触媒内空燃比を理論空燃比に制御してやるには、ＰＨＯＳ要求値を図１３下段のように与える必要があり、したがって比例分修正制御開始当初のＰＨＯＳ（ＰＨＯＳ初期値）をリーン化する値に設定することが考えられる。
【００５０】
この場合に、触媒の劣化度合の相違によりＰＨＯＳ初期値に対する要求値が異なり、あるいは燃料壁流特性のバラツキや燃料性状の違いによりＰＨＯＳ初期値に対する要求値が異なるので、ＰＨＯＳ初期値が一定値であるのでは、触媒の劣化度合の相違あるいは燃料壁流特性のバラツキや燃料性状の違いに対応できず、排気浄化性能が悪くなるため、触媒の劣化度合に応じてＰＨＯＳ初期値（ＰＨＯＳＬ）を与えたり、ＰＨＯＳ初期値を学習値で構成することにより、触媒の劣化度合に相違があってもあるいは燃料壁流特性のバラツキや燃料性状の違いがあっても比例分修正制御の開始当初より触媒内空燃比を理論空燃比へと制御するようにしたものを前述の先願装置により提案している。
【００５１】
この先願装置を簡単に説明しておくと、これは図３においてステップ４１、４２、４３を設けたものである。ステップ４１では初回フラグ（電源投入時のイニシャライズで“０”に初期設定される）をみる。始動後に空燃比フィードバック制御が開始され、初めて上流側Ｏ₂センサ出力が反転したときに図３のサブルーチンが起動され、初めてステップ４１に進んできたときには初回フラグ＝０であることよりステップ４２に進み、バックアップＲＡＭに格納されているＰＨＯＳ初期値をＰＨＯＳに入れたあと、ステップ４３において初回フラグに“１”を入れ、図３のルーチンを終了する。この初回フラグの“１”へのセットにより次回制御時以降はエンジンが停止されるまでステップ４１よりステップ２５へと流れる。
【００５２】
ステップ４２が実行されるのは空燃比フィードバック制御の開始後に上流側Ｏ₂センサ出力が反転したタイミングにおいて、かつ後述するように比例分修正制御の成立時においてだけとなる。このタイミングでは図２のステップ１１またはステップ１２を実行することになり、ＰＨＯＳ初期値により比例分ＰＬまたは比例分ＰＲが修正される。ＰＨＯＳ初期値は、触媒の劣化度合に応じた値や、下流側Ｏ₂センサ平滑化電圧ＭＶＲＯ２とスライスレベルＳＬＲの差に基づいて更新される学習値である。なお、ＰＨＯＳ初期値の求め方については省略する（詳しくは特願平８−１３１５５８号、特願平８−２９２７６２号参照）。これで先願装置の説明を終える。
【００５３】
しかしながら、上流側Ｏ₂センサの活性化完了タイミングに対して下流側Ｏ₂センサの活性化完了タイミングが大きく遅れる場合には、先願装置においても下流側Ｏ₂センサ活性化遅れ期間で比例分修正制御を行うことができないため、下流側Ｏ₂センサ活性化遅れ期間での理論空燃比への制御精度が不十分となる。
【００５４】
これに対処するため本発明の第１実施形態では、比例分修正制御の開始後に初めてＰＨＯＳがＰＨＯＳ要求値と交わる点を第一点、その点より所定時間ΔＴが経過したときのＰＨＯＳの点を第二点とし、第一点のＰＨＯＳをＰＨＯＳ１、第一点の始動後時間をＴ１、第二点のＰＨＯＳをＰＨＯＳ２としてこれらＰＨＯＳ１、Ｔ１、ＰＨＯＳ２を記憶しておき、これらを記憶した次の始動後の下流側Ｏ₂センサ活性化遅れ期間でこれらの記憶値に基づいてＰＨＯＳ要求値を推定し、この推定値を用いて比例分修正制御を行う。
【００５５】
ここで、上記ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２の記憶方法およびこの３つの記憶値に基づいての下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定方法とを図６、図７を用いて説明する。
【００５６】
図６に示すように、横軸を始動後時間、縦軸をＰＨＯＳにとったとき、冷間始動時においては下流側Ｏ₂センサの活性化完了タイミング（比例分修正制御の開始タイミング）よりＰＨＯＳ要求値（実線参照）が徐々にプラス側に大きくなってゆくのに対して、演算値としてのＰＨＯＳ（破線参照）のほうはＰＨＯＳ初期値であるＢの値よりＰＨＯＳ要求値に近づいてゆき、ＰＨＯＳ要求値を横切りながら漸増と漸減を繰り返すことになる。。なお、図６にはＰＨＯＳ初期値であるＢの値がＰＨＯＳ要求値よりもプラス側にある（したがって比例分修正制御の開始後にＰＨＯＳがＰＨＯＳ要求値をまず上から下に横切る）場合を示している。ただし、これに限定されるものでなく、ＰＨＯＳ初期値がＰＨＯＳ要求値よりもマイナス側にある（比例分修正制御の開始後にＰＨＯＳがＰＨＯＳの要求値をまず下から上に横切る）場合があり得る。また、説明の便宜上、図６においてＰＨＯＳの波形を、図５と相違して漸増と漸減を繰り返すだけの簡単な波形で示している（図６で示したＰＨＯＳの波形とするには、図３のステップ２６、２７、２８、２９を削除すればよい）。
【００５７】
この場合に、比例分修正制御の開始後に初めてＰＨＯＳがＰＨＯＳ要求値と交わる点が第一点（図で点▲１▼）、その点から所定時間ΔＴが経過したときのＰＨＯＳの点が第二点（図で点▲２▼）である。点▲１▼の座標を（Ｔ１、ＰＨＯＳ１）、点▲２▼の座標を（Ｔ１＋ΔＴ、ＰＨＯＳ２）とし、これら２つの点を図７に示したように改めて採り直し、２つの点を結んだ直線を下流側Ｏ₂センサ活性化遅れ期間（図では期間Ａで示す）にまで延長したとき、その下流側Ｏ₂センサ活性化遅れ期間における直線上の座標を（Ｔ、ＰＨＯＳＳ）としてＰＨＯＳＳ（下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳの推定値を表す）を求めることを考えると、

の式によりＰＨＯＳＳを計算することができる。（５）式右辺の第２項は図７に示したＣの長さであり、ＰＨＯＳ１からこのＣの長さを差し引いた値がＰＨＯＳＳになるわけである。
【００５８】
ここで、（５）式は、比例分修正制御の開始後のＰＨＯＳ要求値の特性を開始前である下流側Ｏ₂センサ活性化遅れ期間にまで延長するものであり、しかも比例分修正制御の開始前後ともＰＨＯＳ要求値の特性を直線で近似したものである。したがって、今回の始動時と次回の始動時とで始動時のエンジンの温度状態、触媒の劣化状態、始動からの触媒温度の上昇過程、使用燃料の燃料性状（特に揮発性）などがそれほど変わらなければ、今回の始動時にＰＨＯＳ１およびＴ１ならびにＰＨＯＳ２の３つを計測して次回の始動時までバックアップＲＡＭに保存しておけば、この３つの値を用いて（５）式により（ΔＴは予め与える値）、次回の始動後の下流側Ｏ₂センサ活性化遅れ期間内におけるＰＨＯＳ要求値を推定することができるのである。
【００５９】
詳細には、図３においてステップ４４、４５、４６、４７を追加するとともに、図８のフローチャートを新たに設けている。
【００６０】
まず、図３のほうから説明すると、ステップ４４では次の条件、
▲４▼フラグＦＬＧＣＬＲ＝１であること（つまり下流側Ｏ₂センサ出力が所定回数（たとえば１回）反転していること）、
をチェックし、この条件を満たしたときは比例分修正制御条件の成立時と判断して、前述したステップ２１以降に進み、▲４▼の条件を満たさないときは比例分修正制御条件の非成立時と判断して、ステップ４５以降に進む。上記▲１▼〜▲３▼の条件に加えて▲４▼の条件を加えたものが比例分修正制御条件となるわけである。先願装置では、下流側Ｏ₂センサ活性化遅れ期間を問題としていなかったので、ステップ４４は考えなくともよかったのであるが、本発明では下流側Ｏ₂センサ活性化遅れ期間を問題とするので、下流側Ｏ₂センサが活性化したかどうかを判定する必要があるのである。したがって、ステップ４５以降へと進むのは、空燃比フィードバック制御の成立時から比例分修正制御条件の成立直前までの期間（下流側Ｏ₂センサ活性化遅れ期間）にあるときだけである。
【００６１】
ここで、フラグＦＬＧＣＬＲの設定については、フラグＦＬＧＣＬ（図２のスライスレベル１のところで前述した）の設定と同じでよく、始動後に下流側Ｏ₂センサ出力ＯＳＲ２が所定値ＶＣＬＳＲ以上になったとき（あるいは所定値ＶＣＬＳＬ以下となったとき）、図示しないルーチンにおいてＦＬＧＣＬＲ＝１とする。ＦＬＧＣＬＲ＝１となるタイミングが下流側Ｏ₂センサが活性化したタイミングである。
【００６２】
ステップ４５では今回運転時の始動後時間ＴとバックアップＲＡＭに格納されているＰＨＯＳ１、Ｔ１およびＰＨＯＳ２の３つの値を読み込む。
【００６３】
ここで、今回運転時の始動後時間ｔを計測するにはＣＰＵ内部のタイマを用いればよい。残りのＰＨＯＳ１、Ｔ１およびＰＨＯＳ２の記憶については図８のフローチャートにより説明する。
【００６４】
図８のフローチャートは図２、図３とは独立にかつ図２、図３に続けて一定時間毎（たとえば１０ｍｓ毎）に実行する。
【００６５】
ステップ６１、６２、６３、６４では、次の条件、
▲１▼Ｔｗ＞ＴＷＣＬＭＰであること、
▲２▼Ｔfbya＝１であること、
▲３▼フラグＦＬＧＣＬ＝１であること、
▲４▼フラグＦＬＧＣＬＲ＝１であること、
を一つずつチェックする。これらの条件は図２のステップ１、図３のステップ４４において述べたところとそっくり同じであり、▲１▼〜▲４▼のすべてを満足するとき（比例分修正制御条件の成立時）だけステップ６５以降に進む。
【００６６】
ステップ６５では今回運転時の始動後時間ＴとＰＨＯＳ（図３のステップ２８、２９、３１、３２ですでに得ている）を読み込み、ステップ６６ではフラグＴＯＮＥをみる。今回運転時の比例分修正制御の開始当初はＴＯＮＥ＝０であるので、ステップ６７に進み、２つのフラグＡＦＲ０、ＡＦＲ１（図３のステップ２３、２４、３３ですでに得ている）を比較する。比較の結果、両者の値が等しくないときは今回運転時の比例分修正制御の開始後初めての下流側Ｏ₂センサ出力のリッチからリーンへの反転時（あるいはその反対に比例分修正制御の開始後初めての下流側Ｏ₂センサ出力のリーンからリッチへの反転時）であり、この反転時を図６に示した点▲１▼（比例分修正制御の開始後初めてＰＨＯＳがＰＨＯＳ要求値と交わる点）であるとみなしてステップ６８〜７１に進む。
【００６７】
ステップ６８、６９では、そのときの始動後時間Ｔと比例分修正値ＰＨＯＳを用いて
Ｔ１（new）＝Ｔ×ｋ＋Ｔ１（old）×（１−ｋ） …（６）
ＰＨＯＳ１（new）＝ＰＨＯＳ×ｋ＋ＰＨＯＳ１（old）×（１−ｋ）…（７）
ただし、ｋ：平滑化定数（ｋ＜１）
Ｔ１（new）：更新後のＴ１
Ｔ１（old）：更新前のＴ１
ＰＨＯＳ１（new）：更新後のＰＨＯＳ１
ＰＨＯＳ１（old）：更新前のＰＨＯＳ１
の式によりＴ１（点▲１▼の始動後時間）とＰＨＯＳ１（点▲１▼のＰＨＯＳ）を更新し、更新後のＴ１とＰＨＯＳ１の値をステップ７０においてバッテリバックアップＲＡＭに格納する。つまり、Ｔ１、ＰＨＯＳ１は、後述するＰＨＯＳ２とともに学習値であり、出荷時にいずれも初期値の０（もしくは仕向地に合わせてマッチングした値）になっている。
【００６８】
これで図６に示す点▲１▼での値（Ｔ１とＰＨＯＳ１）の更新を経験したので、その経験したことを表すためステップ７１においてフラグＴＯＮＥを“１”にセットして図８のフローを終了する。
【００６９】
このＴＯＮＥ＝１より次回からはステップ６６よりステップ７２に流れ、ここでフラグＴＴＷＯをみる。このフラグＴＴＷＯも今回運転時の比例分修正制御の開始当初はＴＴＷＯ＝０であるので、ステップ７３に進み、始動後時間Ｔと更新後のＴ１（ステップ６８、７０ですでに得ている）に所定時間ΔＴを加算した値とを比較する。Ｔ≦Ｔ１（new）＋ΔＴであるあいだはそのまま図８のフローを終了し、Ｔ＞Ｔ１（new）＋ΔＴとなったタイミングで図６に示す点▲２▼になったとみなしてステップ７４、７５、７６に進む。
【００７０】
ステップ７４、７５ではステップ６９、７０と同様にして
ＰＨＯＳ２（new）＝ＰＨＯＳ×ｋ＋ＰＨＯＳ２（old）×（１−ｋ）…（８）
ただし、ｋ：平滑化定数（ｋ＜１）
ＰＨＯＳ２（new）：更新後のＰＨＯＳ２
ＰＨＯＳ２（old）：更新前のＰＨＯＳ２
の式によりＰＨＯＳ２（点▲２▼のＰＨＯＳ）を更新し、更新後のＰＨＯＳ２をバッテリバックアップＲＡＭに格納する。ステップ７６では点▲２▼での値の更新を経験したことを表すためフラグＴＴＷＯを“１”にセットして図８のフローを終了する。このＴＴＷＯ＝１より次回からはステップ７２よりステップ７３以降に進むことができない。
【００７１】
このようにしてＰＨＯＳ１、Ｔ１、ＰＨＯＳ２の値は、図８によれば今回運転時の比例分修正制御の開始後に一度更新された後はエンジンが停止されるまで更新されることがなく、かつ次回の始動時まで保存される。
【００７２】
ここで、ＰＨＯＳの履歴として保存する値（ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２）を、（６）、（７）、（８）式のように前回運転時までの加重平均で求めるようにしたのは、ＰＨＯＳの履歴として保存する値を安定させるため、あるいは触媒の劣化度合の進行や燃料性状（特に揮発性）の異なる燃料が使用される場合にも対処するためである。したがって、同一の燃料、同一の触媒の劣化状態において、比例分修正制御の開始直後の運転状態（たとえばエンジン温度の状態や触媒温度の上昇の仕方）が同じであれば、１運転当たり１回の更新を繰り返すことによってＰＨＯＳ１、Ｔ１、ＰＨＯＳ２の値が最適値に収束していく。また、ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２が最適値に収束した状態より触媒の劣化度合が進み、あるいはそれまでと燃料性状の異なる燃料が使用されたときには、その後に何度か更新が繰り返されれば、劣化度合の進んだ触媒や燃料性状の異なる燃料に対する最適値へと収束していく。
【００７３】
図３に戻り、ステップ４５において読み込まれるＰＨＯＳ１、Ｔ１、ＰＨＯＳ２の３つの記憶値は、前回運転時の比例分修正制御の開始直後に上記の（６）、（７）、（８）式により更新された値である。ステップ４６ではこれら３つの記憶値とそのときの始動後時間Ｔを用いて上記の（５）式により下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定値であるＰＨＯＳＳを算出し、これをステップ４７においてＰＨＯＳに移す。つまり、下流側Ｏ₂センサ活性化遅れ期間では図２のステップ１１またはステップ１２でのＰＨＯＳがＰＨＯＳＳとなり、このＰＨＯＳＳにより比例分ＰＬまたはＰＲが修正される（ＰＨＯＳＳを用いての比例分修正制御が行われる）のである。
【００７４】
ここで、本実施形態の作用を説明する。
【００７５】
本実施形態では、比例分修正制御の開始後に下流側Ｏ₂センサ平滑化電圧ＭＶＲＯ２（下流側Ｏ₂センサ出力）が初めてスライスレベルＳＬＲを横切って反転した点のＰＨＯＳであるＰＨＯＳ１および同じ点の始動後時間であるＴ１ならびにこの点から所定時間が経過した点のＰＨＯＳであるＰＨＯＳ２が記憶され、これら２つの点を結んで下流側Ｏ₂センサ活性化遅れ期間にまで延長したときの下流側Ｏ₂センサ活性化遅れ期間における直線上の値が、下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定値ＰＨＯＳＳ（図６の一点鎖線参照）として計算される。
【００７６】
この場合に、同一の燃料、同一の触媒を用いて今回運転時も前回運転時とほぼ同じ運転条件（エンジンの温度状態や触媒温度の上昇の仕方が同じ）で始動を行うのであれば、ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２を用いて計算されるＰＨＯＳＳが今回運転時の下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値を精度良く与えるため、今回運転時の下流側Ｏ₂センサ活性化遅れ期間における触媒内空燃比を理論空燃比へと近づけることができる。
【００７７】
一方、その後に触媒の劣化度合が進んだ場合には始動時における触媒内空燃比のリッチ化の程度が弱くなり（ＰＨＯＳ初期値に対する要求値がよりリーン側の値となり）、また、重質燃料のほうが軽質燃料よりもＰＨＯＳ初期値に対する要求値がよりリーン側の値となる。したがって、触媒の劣化が前回運転時より大きく進んでいたときや前回運転時まで使用していた軽質燃料に代えて今回運転時に重質燃料を使用したときにまで、前回運転時に記憶しておいたＰＨＯＳ１、Ｔ１、ＰＨＯＳ２を用いたのでは、そのときのＰＨＯＳＳが、今回運転時の下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値から外れてしまう（したがって、今回運転時の下流側Ｏ₂センサ活性化遅れ期間における触媒内空燃比の理論空燃比への制御性が不十分となる）。
【００７８】
しかしながら、本実施形態では、ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２を前回運転時までの加重平均値（つまり学習値）で構成しているので、今回運転時を含めてその後に何度か運転を繰り返せば、ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２が劣化度合の進んだ触媒や重質燃料に対する最適値へと収束するので、その後は下流側Ｏ₂センサ活性化遅れ期間での触媒内空燃比が理論空燃比へとふたたび制御されることになる。
【００７９】
このように本実施形態では、比例分修正制御の開始後のＰＨＯＳの履歴を記憶しておき、その記憶した運転時の次の下流側Ｏ₂センサ活性化遅れ期間でその記憶値に基づいてＰＨＯＳ要求値を推定し、その推定値を用いて比例分修正制御を行うので、下流側Ｏ₂センサ活性化遅れ期間での比例分修正制御が可能となり、これによって、下流側Ｏ₂センサ活性化遅れ期間においても触媒内空燃比を理論空燃比へと精度良く制御することができ、排気性能が一段と向上する。
【００８０】
図９、図１０のフローチャートは第２実施形態で、それぞれ第１実施形態の図３、図８に対応する。図９において図３と同一の部分には同一のステップ番号を、また図１０において図８と同一の部分には同一のステップ番号をそれぞれつけている。
【００８１】
第２実施形態は、第１実施形態と第二点の求め方が異なり、点▲１▼よりＰＨＯＳが所定値ΔＰＨＯＳだけ変化した点を第二点（図１１に示す点▲２▼）とする。したがって、図１１において点▲２▼の座標を（Ｔ２、ＰＨＯＳ１＋ΔＰＨＯＳ）とすれば、第２実施形態では上記の（５）式に代えて

の式により下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値を推定する。つまり、第２実施形態では（９）式のＰＨＯＳＳ２が下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定値を表す。したがって、第２実施形態では比例分修正制御の開始後のＰＨＯＳの履歴として記憶する値がＰＨＯＳ１、Ｔ１、Ｔ２となる。
【００８２】
フローチャートに移り、第１実施形態と異なる部分を主に説明すると、図１０のステップ９１ではＰＨＯＳとＰＨＯＳ１（図１０のステップ６９ですでに得ている）の差の絶対値と所定値ΔＰＨＯＳを比較し、｜ＰＨＯＳ−ＰＨＯＳ１｜≦ΔＰＨＯＳであるあいだはそのまま図１０のフローを終了し、｜ＰＨＯＳ−ＰＨＯＳ１｜＞ΔＰＨＯＳとなったタイミングで図１１に示す点▲２▼になったとみなしてステップ９２、９３に進み、図１０のステップ６８、７０と同様にして、
Ｔ２（new）＝Ｔ×ｋ＋Ｔ２（old）×（１−ｋ） …（１０）
ただし、ｋ：平滑化定数（ｋ＜１）
Ｔ２（new）：更新後のＴ２
Ｔ２（old）：更新前のＴ２
の式によりＴ２（点▲２▼の始動後時間）を更新し、更新後のＴ２をバックアップＲＡＭに格納する。
【００８３】
一方、図９のステップ８１、８２、８３では、始動後時間ＴとバックアップＲＡＭに格納されているＰＨＯＳ１、Ｔ１、Ｔ２を読み込み、これらを用いて上記の（９）式により下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定値ＰＨＯＳＳ２を計算し、これをＰＨＯＳに移す。
【００８４】
次に、第３実施形態は、第１実施形態のうち図８のフローチャートを図１２のフローチャートに置き換えたものである。なお、図１２においても図８と同一の部分には同一のステップ番号をつけている。
【００８５】
第３実施形態は、第１実施形態に対して第一点の求め方を異ならせたものである。第１実施形態と異なる部分を主に説明すると、ステップ１０１では２つのフラグＡＦＲ０、ＡＦＲ１を比較する。比較の結果、両者の値が等しいときだけ（つまりＰＨＯＳのリッチ継続時かリーン継続時）ステップ１０２に進み、フラグＡＦＲ１をみて、ＡＦＲ１＝１のとき（ＰＨＯＳのリッチ継続時）はステップ１０３でＰＨＯＳとＰＨＯＳ（old）（ＰＨＯＳ（old）はＰＨＯＳの前回値）の差と０を比較する。ＰＨＯＳ−ＰＨＯＳ（old）＜０のときはＰＨＯＳの減少傾向が続いていると判断して図１２のフローを終了し、ＰＨＯＳ−ＰＨＯＳ（old）≧０となったタイミング（ＰＨＯＳが減少から増加へと転じたタイミング）で図６に示す点▲１▼になったとみなしてステップ６８以降に進む。
【００８６】
同様にして、ＰＨＯＳのリーン継続時にはステップ１０２よりステップ１０４に進み、ここでＰＨＯＳとＰＨＯＳ（old）の差と０を比較する。ＰＨＯＳ−ＰＨＯＳ（old）＞０のときはＰＨＯＳの増加傾向が続いていると判断して図１２のフローを終了し、ＰＨＯＳ−ＰＨＯＳ（old）≦０となったタイミング（ＰＨＯＳが増加から減少へと転じたタイミング）で図６に示す点▲１▼になったとみなしてステップ６８以降に進む。
【００８７】
第２と第３の各実施形態でも第１実施形態と同様の作用効果を奏する。
【００８８】
第３実施形態は、第１実施形態に対して図６に示す点▲１▼の求め方を異ならせたものであったが、第２実施形態に対して図１１に示す点▲１▼の求め方を異ならせるようにしてもかまわない。
【００８９】
実施形態では、ＰＨＯＳ１、Ｔ１、ＰＨＯＳ２、Ｔ２を加重平均式により求めているが、これに限られるわけでなく、前回運転時の第一点でのＰＨＯＳ、第一点での始動後時間、第二点でのＰＨＯＳ、第二点での始動後時間をそのままＰＨＯＳ１、Ｔ１、ＰＨＯＳ２、Ｔ２としてバックアップＲＡＭに記憶しておくものでも、また、加重平均式に代えて単純平均式によりＰＨＯＳ１、Ｔ１、ＰＨＯＳ２、Ｔ２を求めてバックアップＲＡＭに記憶しておくものでもかまわない。
【００９０】
実施形態では、第一点と第二点の２つの点より下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値を推定しているが、２点以上から下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値を推定してもかまわない。また、実施形態では、下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値を直線で近似しているが、これに限られるものでなく滑らかに変化する曲線で近似することもできる。
【００９１】
３つの実施形態では、空燃比フィードバック制御定数が比例分である場合で説明したが、これに限られることはなく、積分分ＩＬ、ＩＲ、上流側Ｏ₂センサ出力の遅延時間、上流側Ｏ₂センサ出力と比較するスライスレベルＳＬＦ等であっても同様に構成することができる。
【００９２】
実施形態では比例分修正値ＰＨＯＳをマップ値である比例分ＰＬ、ＰＲとは別に構成した場合（つまり変数が２つの場合）で説明したが、これらを１つの変数で扱うようにしたものに対しても本発明を適用することができる。また、上流側Ｏ₂センサ出力に基づいて第１の空燃比フィードバック補正係数を、下流側Ｏ₂センサ出力に基づいて第２の空燃比フィードバック補正係数をそれぞれ独立に求め、これら２つの補正係数で空燃比フィードバック制御を行うものに対しても本発明を適用することができる。
【図面の簡単な説明】
【図１】第１実施形態の制御システム図である。
【図２】空燃比フィードバック補正係数αの演算を説明するためのフローチャートである。
【図３】サブルーチン説明するためのフローチャートである。
【図４】下流側Ｏ₂ センサ平滑化電圧ＭＶＲＯ２の演算を説明するためのフローチャートである。
【図５】比例分修正値ＰＨＯＳの波形図である。
【図６】下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定を説明するための波形図である。
【図７】下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定を説明するための波形図である。
【図８】Ｔ１、ＰＨＯＳ１、ＰＨＯＳ２の記憶を説明するためのフローチャートである。
【図９】第２実施形態のサブルーチン説明するためのフローチャートである。
【図１０】第２実施形態のＴ１、ＰＨＯＳ１、Ｔ２の記憶を説明するためのフローチャートである。
【図１１】第２実施形態の下流側Ｏ₂センサ活性化遅れ期間におけるＰＨＯＳ要求値の推定を説明するための波形図である。
【図１２】第３実施形態のＴ１、ＰＨＯＳ１、ＰＨＯＳ２の記憶を説明するためのフローチャートである。
【図１３】先願装置の作用を説明するための波形図である。
【図１４】第１の発明のクレーム対応図である。
【符号の説明】
２ コントロールユニット
３ 上流側Ｏ₂センサ
４ クランク角センサ
６ エアフローメータ
９ 排気通路
１０ 三元触媒
１３ 下流側Ｏ₂センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an engine.
[0002]
[Prior art]
O upstream and downstream of the three-way catalyst for exhaust purification ₂ Provide a sensor, upstream O ₂ Based on the sensor output, air-fuel ratio feedback control is performed, and a control constant (for example, a proportional component) used for the air-fuel ratio feedback control is set to the downstream side O ₂ Correction based on sensor output, so-called double O ₂ Various sensor system devices have been proposed (see Japanese Patent Laid-Open No. 4-34249).
[0003]
[Problems to be solved by the invention]
By the way, since the exhaust purification performance is improved when the air-fuel ratio feedback control is started as soon as possible after starting, the upstream side O ₂ The sensor is activated by heating the heater and the catalyst is upstream O ₂ The air-fuel ratio feedback control is entered at the timing when the sensor is activated.
[0004]
In this case, downstream O ₂ Performing correction control of the air-fuel ratio feedback control constant using the sensor output is effective even during the activation of the catalyst (this correction control is performed on the downstream side O ₂ Since the sensor output is always observed while monitoring the catalyst state, the correction control is performed even during the activation of the catalyst rather than the correction control after the activation of the catalyst. The exhaust gas purification performance can be improved by optimizing the air-fuel ratio from the start of activation to the end of catalyst activation). Therefore, the correction control of the air-fuel ratio feedback control constant can be performed as much as possible after the start of the air-fuel ratio feedback control. It is desirable to start early.
[0005]
For example, FIG. 13 shows the characteristics of the in-catalyst air-fuel ratio from the start and the required value for PHOS when the proportional components PR and PL (one of the air-fuel ratio feedback control constants) are corrected by the proportional component correction value PHOS. . The required air-fuel ratio of the catalyst is the catalyst O ₂ It is determined by the balance between storage capacity and HC and CO in the exhaust. The stoichiometric air-fuel ratio is a state in which these are balanced, and PHOS at this time is zero. More specifically, since the catalyst is not activated immediately after starting, the catalyst O ₂ The amount of storage is not sufficient, and more HC and CO are present in the exhaust gas due to the effects of increased starting and increased water temperature, and the catalyst becomes richer, so the PHOS required value becomes a negative value. Thereafter, as the catalyst is activated, the balance gradually recovers and the equilibrium state continues for a while. At this time, the PHOS request value becomes 0 (that is, the stoichiometric air-fuel ratio). Furthermore, after that, the catalyst temperature becomes equal to or higher than a predetermined value. ₂ As the storage amount increases, the air-fuel ratio in the catalyst becomes leaner and the PHOS request value becomes positive.
[0006]
Now, for a while after the start of the air-fuel ratio feedback control due to the influence of the increase in starting, the increase in water temperature, etc., the air-fuel ratio in the catalyst becomes rich as shown in the upper part of FIG. Corresponding to this, in order to control the air-fuel ratio in the catalyst to the stoichiometric air-fuel ratio from the beginning of the proportional correction control, the PHOS required value is as shown in the lower part of FIG. Therefore, the PHOS (PHOS initial value) at the beginning of starting the proportional correction control (in the figure, the start of the air-fuel ratio feedback control and the start of the proportional correction control are substantially equal) is set as a lean value. It is possible.
[0007]
In this case, the required value for the PHOS initial value differs depending on the degree of deterioration of the catalyst (the required value for the PHOS initial value is a leaner value when the catalyst is not deteriorated than when the catalyst is deteriorated. ) Or, the required value for the PHOS initial value differs depending on the variation in fuel wall flow characteristics and the difference in fuel properties (the required value for the PHOS initial value is higher on the lean side than that for light fuel) If the PHOS initial value is a constant value, it cannot cope with a difference in the degree of deterioration of the catalyst, a variation in fuel wall flow characteristics or a difference in fuel properties, and the exhaust purification performance deteriorates.
[0008]
Therefore, by giving a PHOS initial value (PHOSL) according to the degree of deterioration of the catalyst, or by configuring the PHOS initial value with a learning value, even if there is a difference in the degree of deterioration of the catalyst, the variation in the fuel wall flow characteristics, A device (prior application) has been proposed in which the air-fuel ratio in the catalyst is controlled to the stoichiometric air-fuel ratio from the beginning of the proportional correction control even if there is a difference in fuel properties (Japanese Patent Application No. 8-131558, No. 8-292762).
[0009]
However, upstream O ₂ Downstream of the sensor activation completion timing ₂ When the activation completion timing of the sensor is greatly delayed, the delay period (hereinafter referred to as the downstream O) is also applied to the above-mentioned prior application device. ₂ The proportional correction control cannot be performed during the sensor activation delay period. This is downstream O ₂ Since the proportional correction control cannot be started until the sensor completes the activation, the downstream side O ₂ This is because if the activation of the sensor is delayed, the start of the proportional correction control is also delayed accordingly. In other words, even if it is desired to start the proportional correction control early, it is not possible to do this. ₂ This is because the control accuracy to the stoichiometric air-fuel ratio in the sensor activation delay period becomes insufficient.
[0010]
Therefore, the present invention stores a history of correction values after the start of the correction control of the air-fuel ratio feedback control constant, and the downstream air-fuel ratio sensor activation delay period after the next start at the time of the stored operation. By estimating the required value of the correction value based on the stored value and performing correction control using the estimated value, it is possible to improve the control accuracy to the theoretical air-fuel ratio in the downstream air-fuel ratio sensor activation delay period. Objective.
[0011]
[Means for Solving the Problems]
In the first invention, as shown in FIG. 14, the basic control constants of the air-fuel ratio feedback control based on the air-fuel ratio sensors 31 and 32 on the upstream and downstream sides of the catalyst and the output of the upstream air-fuel ratio sensor 31. Means 33 for calculating (for example, proportional parts PL, PR, integral parts IL, IR, delay time of upstream air-fuel ratio sensor output, slice level SLF to be compared with upstream air-fuel ratio sensor output, etc.) and air-fuel ratio feedback control conditions Means 34 for determining whether or not the condition is satisfied, means 35 for determining whether or not the correction control condition for the control constant used for the air-fuel ratio feedback control is satisfied, and the air-fuel ratio feedback control condition based on these determination results. When the correction control condition is satisfied and when the correction control condition is satisfied, a correction value (for example, proportional correction) for the basic control constant based on the output of the downstream air-fuel ratio sensor 32 Value PHOS), and the correction value and the basic control constant are used to perform air-fuel ratio feedback control when the air-fuel ratio feedback control condition is satisfied, and when the air-fuel ratio feedback control condition is satisfied and the correction control is performed. An engine air-fuel ratio control device comprising means 37 for starting correction control when a condition is met, the first point is the timing at which the downstream air-fuel ratio sensor output reverses across the slice level for the first time after the start of the correction control. The correction value of the first point and the post-start time and the correction value of the second point after the start of the correction control are set with the point at which the correction value has passed a predetermined time from the first point as the second point. Means 38 for storing the history of the engine and the period from when the air-fuel ratio feedback control condition is satisfied to when the correction control condition is satisfied And determining means 39 out if the store request value of the correction value in this period time from the determination result is this period The corrected value of the first point and the post-start time and the corrected value of the second point And means 41 for performing feedback control and correction control of the air-fuel ratio in the period using the estimated value and the basic control constant.
[0013]
First 2 In the invention of the 1 In the invention, the correction value PHOS1 and the post-start time T1 of the first point and the correction value PHOS2 of the second point are weighted average values until the previous operation.
[0014]
First 3 In this invention, the air-fuel ratio sensors on the upstream and downstream sides of the catalyst, the means for calculating the basic control constant of the air-fuel ratio feedback control based on the output of the upstream air-fuel ratio sensor, and the establishment of the air-fuel ratio feedback control condition Means for determining whether or not the time is satisfied, means for determining whether or not the correction control condition for the control constant used for the air-fuel ratio feedback control is satisfied, and the determination result indicates that the air-fuel ratio feedback control condition is satisfied and Means for calculating a correction value for the basic control constant based on the output of the downstream air-fuel ratio sensor when the correction control condition is satisfied, and when the air-fuel ratio feedback control condition is satisfied using the correction value and the basic control constant Air-fuel ratio feedback control is performed. When the air-fuel ratio feedback control condition is satisfied and when the correction control condition is satisfied, the correction control is performed. In the engine air-fuel ratio control device comprising the means for starting the correction, the first point is the timing at which the corrected value is inverted across the slice level for the first time after the correction control is started. The correction value PHOS1 and the post-start time T1 of the first point and the post-start time T2 of the second point are the correction points after the start of the correction control, with the second point being the point where the correction value PHOS has increased by the predetermined value ΔPHOS from the point. Means for storing value history, means for determining whether or not the period from when the air-fuel ratio feedback control condition is satisfied to when the correction control condition is satisfied, and when this period is based on this determination result The required value of the correction value in the memory The corrected value of the first point and the time after starting and the time after starting the second point And a means for performing air-fuel ratio feedback control and correction control in the period using the estimated value and the basic control constant.
[0015]
First 4 In the invention of the 3 In the invention, the correction value PHOS1 and the post-start time T1 of the first point and the post-start time T2 of the second point are weighted average values up to the previous operation.
[0017]
First 5 In the invention of the 1 or 3 In the invention of Instead of the timing at which the downstream air-fuel ratio sensor output is reversed across the slice level for the first time after the start of the correction control, The first point is the timing at which the downstream air-fuel ratio sensor output reverses from decrease to increase or from increase to decrease for the first time after the start of the correction control.
[0018]
First 6 In the invention of the 1 To the second 5 In any one of the above inventions, the required value of the correction value in the period is estimated from a straight line connecting the first point and the second point and extending to the period.
[0019]
First 7 In the invention of the first to first 6 In any one of the inventions, the timing at which the downstream air-fuel ratio sensor is activated is the timing at which the correction control condition is satisfied.
[0020]
【The invention's effect】
In contrast to the conventional device in which the correction control cannot be performed in the activation delay period of the downstream air-fuel ratio sensor, the first invention stores a history of correction values after the start of the correction control, The required value of the correction value is estimated based on this stored value in the activation delay period of the downstream side air-fuel ratio sensor after the next start during operation storing the history, and correction control is performed using the estimated value (that is, Since correction control is also possible during the activation delay period of the downstream air-fuel ratio sensor), the controllability of the in-catalyst air-fuel ratio to the stoichiometric air-fuel ratio is enhanced, thereby further improving the exhaust performance.
[0021]
First 2 And second 4 In each of the inventions, the memory value of the correction value history can be stabilized, and even if the degree of deterioration of the catalyst progresses, the fuel wall flow characteristics vary, or there is a difference in fuel properties (especially volatility). can do. For example, if the same fuel and the same catalyst are in a deteriorated state and the operation state immediately after the start of the correction control (for example, the engine temperature state or the way of increasing the catalyst temperature) is the same, the weighted average is repeated at each start. As a result, the stored value of the correction value history converges to the optimum value. Even when the stored value of the correction value history has converged to the optimum value, when the degree of deterioration of the catalyst has progressed or fuel with a different fuel property has been used, what is the weighted average at each start after that? If it is repeated several times, it converges to an optimum value for a catalyst with a deteriorated degree and a fuel with different fuel properties.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, reference numeral 1 denotes an engine body. A fuel injection valve 7 is provided in the intake passage 8 downstream of the intake throttle valve 5, and an injection signal from a control unit (abbreviated as C / U in the figure) 2. Thus, fuel is injected and supplied during intake so that a predetermined air-fuel ratio is obtained according to operating conditions.
[0023]
The control unit 2 receives a Ref signal (reference position signal) and a Pos signal (1 ° signal) from the crank angle sensor 4, an intake air amount signal from the air flow meter 6, an engine cooling water temperature signal from the water temperature sensor 11, and the like. Based on these, the basic injection pulse width Tp is calculated, and the upstream side of the three-way catalyst 10 in the exhaust passage 9 is installed. ₂ Based on the air-fuel ratio (oxygen concentration) signal from the sensor 3, air-fuel ratio feedback control is performed, and a proportional component used for the air-fuel ratio feedback control is installed downstream of the three-way catalyst 10. ₂ Correction is performed by an air-fuel ratio (oxygen concentration) signal from the sensor 13.
[0024]
Here, the air-fuel ratio feedback control is a control in which the exhaust air-fuel ratio is periodically swung around the theoretical air-fuel ratio. At this time, the three-way catalyst 10 provided in the exhaust passage 9 has the maximum conversion efficiency, NOx reduction in exhaust gas and oxidation of HC and CO are performed.
[0025]
The contents of this control executed by the control unit 2 will be described according to the following flowchart.
[0026]
The flowchart of FIG. ₂ This is for calculating the air-fuel ratio feedback correction coefficient α based on the sensor output OSR1, and is executed in synchronization with the Ref signal. The reason for synchronizing with the Ref signal is that the fuel injection is synchronized with the Ref signal, and the disturbance of the system is also synchronized with the Ref signal.
[0027]
In step 1, upstream O ₂ Check whether the air-fuel ratio feedback control condition based on the sensor output is satisfied. For example, the following condition:
(1) The cooling water temperature Tw exceeds the start water temperature TWCLMP of the air-fuel ratio feedback control,
(2) Target fuel-air ratio equivalent amount Tfbya (described later) = 1
(3) The flag FLGCL = 1 (that is, upstream O ₂ The sensor output is reversed a predetermined number of times (for example, once)),
2 is checked one by one, and if neither of them is satisfied, it is determined that the air-fuel ratio feedback control condition is not satisfied, and the process proceeds to step 2, α is set to 1.0 (α is clamped), and End the flow.
[0028]
Here, (3) above is upstream O ₂ This is a part to check whether the sensor is activated. ₂ When the sensor output OSR1 becomes equal to or higher than the predetermined value VCLSR (or when it becomes equal to or lower than the predetermined value VCLSL), FLGCL = 1 is set in a routine (not shown). The timing when FLGCL = 1 becomes upstream O ₂ This is the timing when the sensor is activated.
[0029]
When all of the above (1) to (3) are satisfied, it is determined that the air-fuel ratio feedback control condition is satisfied, and the routine proceeds to step 3.
[0030]
In step 3, upstream O ₂ The sensor output OSR1 is captured by A / D conversion, and in step 4, OSR1 is compared with the slice level (for example, around 500 mV) SLF. If OSR1> SLF, upstream O ₂ It is determined that the sensor output is on the rich side. In step 5, “1” is set in the flag AFF1, and when OSR1 ≦ SLF, the upstream side O ₂ It is determined that the sensor output is on the lean side, and in step 6, “0” is set in the flag AFF1. As a result, AFF1 = 0 becomes upstream O ₂ AFF1 = 1 indicates that the sensor output is on the lean side, and AFF1 = 1 indicates that the sensor output is on the rich side.
[0031]
Note that the flag AFF1 is “0” at the time of power-on initialization together with the flag AFF0 that comes out immediately afterwards and other flags to be described later (flags AFR0 and AFR1 in FIG. 3, flags FLGCL, FLGCLR, TONE, and TTWO in FIG. 8). The memory α (old), which will be described later, and other memories (the memory PHOS (old) in FIG. 3 and the memory MVRO2 (old) in FIG. 4), which will be described later, are also initialized to 0 at power-on initialization. In the following flowchart, the initial setting of the flag and the memory is omitted.
[0032]
In step 7, the value of the flag AFF0 is read. This flag AFF0 is a flag indicating whether the air-fuel ratio was on the rich side or lean side last time. AFF0 = 0 represents the previous lean side, and AFF0 = 1 represents the previous rich side. .
[0033]
In step 8, the two flags AFF0 and AFF1 are compared. If the two values are not equal, it is determined that the OSR1 is inverted from rich to lean or vice versa, Execute the subroutine. The execution of this subroutine (executed every inversion of OSR1) will be described with reference to the flowchart of FIG. In FIG. 3, steps 41, 42 and 43 are added by the prior application apparatus, and steps 44, 45, 46 and 47 are added by the present invention, which will be described later.
[0034]
Steps 21 to 33 in FIG. 3 are the same as the remaining steps except for steps 1, 2 and 9 in FIG. Specifically, in step 21, the downstream O ₂ The sensor smoothing voltage MVRO2 is read, and this MVRO2 is compared with a slice level (for example, around 500 mV) SLR in step 22.
[0035]
Where downstream O ₂ As shown in FIG. 4, the sensor smoothing voltage MVRO <b> 2 is equal to the downstream side O for every engine rotation. ₂ The sensor output OSR2 is A / D converted and captured,
MVRO2 = MVRO2 (old) × (1-A) + OSR2 × A (1)
Where A: smoothing constant (A <1)
MVRO2 (old): Previous value of MVRO2
This value is updated by the expression However, when the power is turned on for the first time, OSR2 is put in MVRO2 as it is.
[0036]
If MVRO2> SLR, the flag AFR1 is set to “1” in step 23, and if MVRO2 ≦ SLR, the flag AFR1 is set to “0” in step 24. As a result, AFR1 = 0 becomes downstream O ₂ The sensor output is on the lean side, and AFR1 = 1 indicates that it is on the rich side.
[0037]
In step 25, the value of the flag AFR0 is read. AFR0 = 0 is downstream O ₂ The sensor output was on the lean side last time, and AFR0 = 1 is downstream O ₂ Since the sensor output indicates that it was on the rich side last time, the two flags AFR0 and AFR1 are compared in step 26, and when both values are not equal (that is, when reversing from rich to lean or vice versa) At the time of inversion to rich), the flag AFR1 is checked in step 27. When AFR1 = 0 (when reversing from rich to lean), the value obtained by adding a proportional amount PHPL to PHOS (old) (previous value of PHOS) in step 28 is set to PHOS, and AFR1 = 1 (from lean) In the case of rich inversion), in step 29, the value obtained by subtracting the proportional amount PHPR from PHOS (old) is set as PHOS, thereby updating each PHOS.
[0038]
When AFR0 and AFR1 are equal in step 26, the process proceeds to step 30, and when the value of the flag AFR1 is checked, if AFR1 = 0 (least last time and this time), the integral DPHOSL is added to PHOS (old) in step 31 When the value is PHOS, and when AFR1 = 1 (rich both in the previous time and this time), the value obtained by subtracting the integral DPHOSR from PHOS (old) in step 32 is set as PHOS, thereby updating the PHOS.
[0039]
The proportional components PHPL, PHPR, integral components DPHOSL, DPHOSR may be constant values, or may be map values using the rotation speed and load (Tp) as parameters.
[0040]
In step 33, after the value of the flag AFR1 is moved to the flag AFR0 for the next control, the flow of FIG.
[0041]
In this way, when the proportional correction value PHOS is updated, the PHOS is obtained as shown in FIG. ₂ The sensor smoothing voltage MVRO2 changes stepwise at the time of reversal from rich to lean and from reversal to lean, and has a waveform that repeats gradual increase and decrease while continuing lean and rich.
[0042]
When the execution of the subroutine is completed, the process returns to step 10 in FIG. 2 to see the value of the flag AFF1. If AFF1 = 0 (when reversing from rich to lean), in step 11
α = α (old) + (PL + PHOS) (2)
Where α (old): previous value of α
When AFF1 = 1 (at the time of reversal from lean to rich), in step 12,
α = α (old) − (PR−PHOS) (3)
Where α (old): previous value of α
Each α is updated by the following formula.
[0043]
On the other hand, if the values of the two flags AFF0 and AFF1 are equal in step 8, it is determined that the time is not reversed, and the process proceeds to S13 to check the value of the flag AFF1. If AFF1 = 0 (lean for the previous time and this time), the integral IL is added to α (old) in step 14, and if AFF1 = 1 (rich for both the previous time and this time), α in step 15 Each α is updated by subtracting the integral IR from (old).
[0044]
In step 16, the value of the flag AFF1 is moved to the flag AFF0 for the next control, and the flow of FIG.
[0045]
Using the air-fuel ratio feedback correction coefficient α calculated in this way, the fuel injection pulse width Ti given to the fuel injection valve 7 is determined by a routine (not shown).

Where Tp: basic injection pulse width
Kathos: Transient correction amount
Tfbya: target fuel-air ratio equivalent
αm: Air-fuel ratio learning value
Ts: Invalid pulse width
Calculate with the following formula. The calculated Ti value is transferred to the output register at an injection timing (not shown), and a fuel amount corresponding to Ti is injected for each cylinder once every two engine revolutions.
[0046]
Here, Tp in the equation (4) is a value calculated from the engine speed and the intake air amount, and an almost stoichiometric air-fuel mixture is obtained by this Tp. Tfbya is the sum of the water temperature increase correction coefficient Ktw, the post-startup increase correction coefficient Kas, etc., and Tfbya becomes a value greater than 1.0 immediately after the cold start until the air-fuel ratio feedback control is started. And is operated at an air-fuel ratio richer than the stoichiometric air-fuel ratio. It should be noted that Tfbya becomes a value smaller than 1.0 at the time of deceleration lean clamping or the like. Further, Tfbya = 1.0 when the air-fuel ratio feedback control condition is satisfied.
[0047]
By the way, since the exhaust purification performance is improved when the air-fuel ratio feedback control is started as soon as possible after starting, the upstream side O ₂ The sensor 3 is activated by heating the heater, and the catalyst 10 is upstream O even during activation. ₂ The air-fuel ratio feedback control is entered at the timing when the sensor 3 is activated.
[0048]
In this case, downstream O ₂ Since it is effective during the activation of the catalyst 10 to perform the proportional correction control using the sensor output, the correction control of the air-fuel ratio feedback control constant can be started as soon as possible after the start of the air-fuel ratio feedback control. desirable.
[0049]
On the other hand, for a while after the start of the air-fuel ratio feedback control due to the influence of the start increase (both increase at start-up and increase after start-up) and the water temperature increase, as shown in the upper part of FIG. Since the air-fuel ratio becomes rich, in order to control the air-fuel ratio in the catalyst to the stoichiometric air-fuel ratio from the beginning of the air-fuel ratio feedback control correspondingly, it is necessary to give the PHOS request value as shown in the lower part of FIG. Therefore, it is conceivable to set the PHOS (PHOS initial value) at the beginning of the proportional correction control to a value for leaning.
[0050]
In this case, the required value for the PHOS initial value varies depending on the degree of deterioration of the catalyst, or the required value for the PHOS initial value varies depending on variations in fuel wall flow characteristics and fuel properties. In this case, the catalyst cannot cope with the difference in the degree of deterioration of the catalyst, the variation in the fuel wall flow characteristics or the difference in the fuel properties, and the exhaust purification performance deteriorates. Therefore, the PHOS initial value (PHOSL) is given according to the degree of deterioration of the catalyst By configuring the PHOS initial value as a learned value, even if there is a difference in the degree of deterioration of the catalyst, a variation in fuel wall flow characteristics or a difference in fuel properties, the proportional amount correction control is started from the beginning. A device in which the air-fuel ratio is controlled to the stoichiometric air-fuel ratio has been proposed by the aforementioned prior application device.
[0051]
Briefly explaining this prior application device, this is the one in which steps 41, 42 and 43 are provided in FIG. In step 41, an initial flag (initialized to "0" at initialization at power-on) is observed. After starting, air-fuel ratio feedback control is started, and for the first time upstream O ₂ When the sensor output is reversed, the subroutine shown in FIG. 3 is started. When the process proceeds to step 41 for the first time, the initial flag = 0, so that the process proceeds to step 42 and the PHOS initial value stored in the backup RAM is entered into PHOS. After that, in step 43, “1” is set in the initial flag, and the routine of FIG. By setting the initial flag to “1”, the flow proceeds from step 41 to step 25 until the engine is stopped after the next control.
[0052]
Step 42 is executed after the start of air-fuel ratio feedback control. ₂ Only when the sensor output is reversed and when proportional correction control is established, as will be described later. At this timing, Step 11 or Step 12 in FIG. 2 is executed, and the proportionality PL or proportionality PR is corrected by the PHOS initial value. The PHOS initial value is a value corresponding to the degree of deterioration of the catalyst or a downstream O ₂ This learning value is updated based on the difference between the sensor smoothing voltage MVRO2 and the slice level SLR. The method of obtaining the PHOS initial value is omitted (refer to Japanese Patent Application Nos. 8-131558 and 8-292762 for details). This completes the description of the prior application device.
[0053]
However, upstream O ₂ Downstream of the sensor activation completion timing ₂ If the sensor activation completion timing is greatly delayed, the downstream side ₂ Since the proportional correction control cannot be performed in the sensor activation delay period, the downstream O ₂ The control accuracy to the stoichiometric air-fuel ratio in the sensor activation delay period becomes insufficient.
[0054]
In order to cope with this, in the first embodiment of the present invention, the first point at which PHOS intersects the PHOS request value for the first time after the start of proportional correction control is the first point, and the PHOS point when a predetermined time ΔT has elapsed from that point. The second point, PHOS1 of the first point is PHOS1, the time after start of the first point is T1, PHOS of the second point is PHOS2, and these PHOS1, T1, and PHOS2 are stored, and the next start after storing these Rear downstream O ₂ The PHOS request value is estimated based on these stored values during the sensor activation delay period, and proportionality correction control is performed using this estimated value.
[0055]
Here, the storage method of PHOS1, T1, and PHOS2 and the downstream O based on the three stored values ₂ A method for estimating the PHOS request value during the sensor activation delay period will be described with reference to FIGS.
[0056]
As shown in FIG. 6, when the horizontal axis represents the time after startup and the vertical axis represents PHOS, the downstream side O ₂ The PHOS request value (see solid line) gradually increases to the plus side from the sensor activation completion timing (proportional correction control start timing), whereas the calculated value PHOS (see broken line) is The PHOS required value approaches the PHOS initial value B, and gradually increases and decreases while crossing the PHOS required value. . FIG. 6 shows a case where the value of B, which is the PHOS initial value, is on the plus side of the PHOS request value (therefore, the PHOS first crosses the PHOS request value from the top after the start of proportional correction control). Yes. However, the present invention is not limited to this, and there may be a case where the PHOS initial value is on the minus side of the PHOS request value (PHOS crosses the PHOS request value first from the bottom up after the start of proportional correction control). . For convenience of explanation, the waveform of PHOS in FIG. 6 is shown as a simple waveform that only repeats gradual increase and decrease unlike FIG. 5 (in order to obtain the PHOS waveform shown in FIG. Steps 26, 27, 28, and 29 may be deleted).
[0057]
In this case, the first point (the point (1) in the figure) where PHOS intersects the PHOS required value for the first time after the start of the proportional correction control, and the point of PHOS when the predetermined time ΔT has elapsed from that point is the second point. It is a point (point (2) in the figure). The coordinates of the point (1) are (T1, PHOS1), the coordinates of the point (2) are (T1 + ΔT, PHOS2), and these two points are taken again as shown in FIG. 7, and a straight line connecting the two points Downstream O ₂ When it is extended to the sensor activation delay period (indicated by period A in the figure), its downstream side O ₂ The coordinates on the straight line in the sensor activation delay period are defined as (T, PHOSS) and PHOSS (downstream O ₂ (Representing an estimated value of PHOS in the sensor activation delay period)

PHOSS can be calculated by the following equation. The second term on the right side of equation (5) is the length of C shown in FIG. 7, and the value obtained by subtracting the length of C from PHOS1 is PHOSS.
[0058]
Here, the equation (5) indicates the characteristic of the PHOS request value after the start of the proportional correction control before the downstream O ₂ This is extended to the sensor activation delay period, and the characteristics of the PHOS required value are approximated by a straight line both before and after the start of the proportional correction control. Therefore, the engine temperature state at the start, the deterioration state of the catalyst, the process of increasing the catalyst temperature from the start, the fuel properties (especially volatility) of the fuel used, etc. should not change so much between this start and the next start. For example, if three of PHOS1, T1, and PHOS2 are measured at the time of the current start and stored in the backup RAM until the next start, using these three values, (ΔT is a value given in advance. ) Downstream O after the next start ₂ The PHOS requirement value within the sensor activation delay period can be estimated.
[0059]
Specifically, steps 44, 45, 46, and 47 are added in FIG. 3, and a flowchart of FIG. 8 is newly provided.
[0060]
First, referring to FIG. 3, in step 44, the following conditions are satisfied:
(4) The flag FLGCLR = 1 (that is, downstream O ₂ The sensor output is reversed a predetermined number of times (for example, once)),
If this condition is satisfied, it is determined that the proportional correction control condition is satisfied, and the process proceeds to step 21 and subsequent steps. If the condition (4) is not satisfied, the proportional correction control condition is not satisfied. It is determined that it is time, and the process proceeds to step 45 and thereafter. The proportional correction control condition is obtained by adding the condition (4) in addition to the conditions (1) to (3). In the prior application device, downstream O ₂ Since the sensor activation delay period was not considered as a problem, step 44 may not be considered. ₂ Since the sensor activation delay period is a problem, downstream O ₂ It is necessary to determine whether the sensor is activated. Therefore, the process proceeds to step 45 and subsequent steps from the time when the air-fuel ratio feedback control is established to the time immediately before the proportionality correction control condition is established (downstream O ₂ It is only when it is in the sensor activation delay period.
[0061]
Here, the setting of the flag FLGCLR may be the same as the setting of the flag FLGCL (described above at the slice level 1 in FIG. 2). ₂ When the sensor output OSR2 becomes equal to or higher than the predetermined value VCLSR (or when it becomes equal to or lower than the predetermined value VCLSL), FLGCLR = 1 is set in a routine not shown. The timing when FLGCLR = 1 becomes downstream O ₂ This is the timing when the sensor is activated.
[0062]
In step 45, three values of the time T after starting at the time of the current operation and PHOS1, T1, and PHOS2 stored in the backup RAM are read.
[0063]
Here, a timer in the CPU may be used to measure the time t after start-up during the current operation. The storage of the remaining PHOS1, T1, and PHOS2 will be described with reference to the flowchart of FIG.
[0064]
The flowchart in FIG. 8 is executed independently of FIGS. 2 and 3 and at regular intervals (for example, every 10 ms) following FIGS.
[0065]
In steps 61, 62, 63 and 64, the following conditions are satisfied:
(1) Tw> TWCLMP
(2) Tfbya = 1
(3) The flag FLGCL = 1.
(4) The flag FLGCLR = 1.
Check one by one. These conditions are exactly the same as those described in step 1 of FIG. 2 and step 44 of FIG. 3, and are only performed when all of (1) to (4) are satisfied (when the proportionality correction control condition is satisfied). Proceed to 65 and later.
[0066]
In step 65, the start time T and PHOS (which has already been obtained in steps 28, 29, 31, and 32 in FIG. 3) are read, and in step 66, the flag TONE is viewed. Since TONE = 0 at the start of the proportional correction control during the current operation, the process proceeds to step 67 and the two flags AFR0 and AFR1 (already obtained in steps 23, 24, and 33 in FIG. 3) are compared. . As a result of the comparison, if the two values are not equal, the first downstream O after the start of the proportional correction control during the current operation ₂ When the sensor output is reversed from rich to lean (or vice versa) ₂ The sensor output is assumed to be the point {circle around (1)} at which the PHOS intersects the PHOS required value for the first time after the start of the proportional correction control. Proceed to steps 68-71.
[0067]
In steps 68 and 69, the time T after the start and the proportional correction value PHOS are used.
T1 (new) = T * k + T1 (old) * (1-k) (6)
PHOS1 (new) = PHOS × k + PHOS1 (old) × (1-k) (7)
Where k: smoothing constant (k <1)
T1 (new): T1 after update
T1 (old): T1 before update
PHOS1 (new): PHOS1 after update
PHOS1 (old): PHOS1 before update
T1 (time after start of point {circle around (1)}) and PHOS1 (PHOS at point {circle around (1)}) are updated, and the updated values of T1 and PHOS1 are stored in the battery backup RAM in step 70. That is, T1 and PHOS1 are learning values together with PHOS2, which will be described later, and both have initial values of 0 (or values that match the destination) at the time of shipment.
[0068]
As a result of updating the values (T1 and PHOS1) at the point {circle around (1)} shown in FIG. 6, the flag TONE is set to “1” in step 71 in order to express the experience, and the flow of FIG. finish.
[0069]
From this time TONE = 1, the flow from the next step to the step 72 from the step 66, where the flag TTWO is seen. Since this flag TTWO is also TTWO = 0 at the beginning of the proportional correction control at the time of the current operation, the process proceeds to step 73, and after the start time T and updated T1 (already obtained in steps 68 and 70). A value obtained by adding the predetermined time ΔT is compared. While T ≦ T1 (new) + ΔT, the flow of FIG. 8 is terminated as it is, and it is assumed that the point {circle around (2)} shown in FIG. 6 has been reached at the timing when T> T1 (new) + ΔT. Proceed to 76.
[0070]
Steps 74 and 75 are the same as steps 69 and 70.
PHOS2 (new) = PHOS × k + PHOS2 (old) × (1-k) (8)
Where k: smoothing constant (k <1)
PHOS2 (new): PHOS2 after update
PHOS2 (old): PHOS2 before update
PHOS2 (PHOS at point {circle around (2)}) is updated by the following formula, and the updated PHOS2 is stored in the battery backup RAM. In step 76, the flag TTWO is set to "1" to indicate that the value has been updated at point (2), and the flow of FIG. From TTWO = 1, it is not possible to proceed from step 72 to step 73 onward from the next time.
[0071]
Thus, according to FIG. 8, the values of PHOS1, T1, and PHOS2 are not updated until the engine is stopped after being updated once after the start of the proportional correction control during the current operation, and next time. Stored until the start of.
[0072]
Here, the values (PHOS1, T1, PHOS2) to be stored as the history of PHOS are obtained by the weighted average until the previous operation as shown in equations (6), (7), (8). This is to stabilize the value stored as the history of the catalyst, or to cope with the case where the deterioration degree of the catalyst and the fuel having different fuel properties (particularly volatile) are used. Therefore, in the same fuel and the same catalyst deterioration state, if the operation state immediately after the start of the proportional correction control (for example, the state of the engine temperature or the way of increasing the catalyst temperature) is the same, once per operation By repeating the update, the values of PHOS1, T1, and PHOS2 converge to the optimum values. Further, when the degree of deterioration of the catalyst proceeds from the state where PHOS1, T1, and PHOS2 have converged to the optimum values, or when a fuel having a different fuel property from that used is used, if the degree of deterioration is repeated several times thereafter, the degree of deterioration is reduced. Convergence to optimum values for advanced catalysts and fuels with different fuel properties.
[0073]
Returning to FIG. 3, the three stored values PHOS1, T1, and PHOS2 read in step 45 are updated by the above equations (6), (7), and (8) immediately after the start of the proportional correction control during the previous operation. Value. In step 46, using these three stored values and the post-start time T at that time, the downstream O ₂ PHOSS, which is an estimated value of the PHOS request value during the sensor activation delay period, is calculated, and this is transferred to PHOS in step 47. That is, downstream O ₂ In the sensor activation delay period, PHOS in step 11 or step 12 in FIG. 2 becomes PHOSS, and the proportionality PL or PR is corrected by this PHOSS (proportionality correction control using PHOSS is performed).
[0074]
Here, the operation of the present embodiment will be described.
[0075]
In the present embodiment, the downstream O after the start of the proportional correction control. ₂ Sensor smoothing voltage MVRO2 (downstream O ₂ PHOS1 which is the PHOS at the point where the sensor output) is reversed across the slice level SLR for the first time, T1 which is the post-start time of the same point, and PHOS2 which is the PHOS when the predetermined time has elapsed from this point are stored. Connecting two points downstream O ₂ Downstream O when extended to sensor activation delay period ₂ The value on the straight line in the sensor activation delay period is the downstream O ₂ It is calculated as an estimated value PHOSS of the PHOS request value during the sensor activation delay period (see the dashed line in FIG. 6).
[0076]
In this case, if the same fuel and the same catalyst are used and the engine is started under the same operating conditions (the engine temperature state and the catalyst temperature increase method are the same) during the current operation as in the previous operation, PHOS1 , T1, PHOS calculated using PHOS2 is the downstream O ₂ In order to accurately provide the PHOS requirement value during the sensor activation delay period, the downstream side O ₂ The air-fuel ratio in the catalyst during the sensor activation delay period can be brought close to the theoretical air-fuel ratio.
[0077]
On the other hand, when the degree of deterioration of the catalyst progresses thereafter, the degree of enrichment of the air-fuel ratio in the catalyst at the start becomes weak (the required value for the PHOS initial value becomes a leaner value), and heavy fuel In this case, the required value for the PHOS initial value becomes a leaner value than the light fuel. Therefore, it was memorized at the time of the previous operation until the deterioration of the catalyst progressed significantly from the previous operation or when heavy fuel was used at the current operation instead of the light fuel used until the previous operation. When PHOS1, T1, and PHOS2 are used, the PHOSS at that time is the downstream side O ₂ It will deviate from the PHOS requirement value in the sensor activation delay period (thus, the downstream side O ₂ The controllability of the air-fuel ratio in the catalyst to the stoichiometric air-fuel ratio in the sensor activation delay period becomes insufficient).
[0078]
However, in this embodiment, PHOS1, T1, and PHOS2 are configured with weighted average values (that is, learned values) up to the previous operation, so if the operation is repeated several times after that including the current operation, PHOS1 , T1 and PHOS2 converge to the optimum values for the catalyst and heavy fuel with a high degree of deterioration. ₂ The air-fuel ratio in the catalyst during the sensor activation delay period is again controlled to the stoichiometric air-fuel ratio.
[0079]
As described above, in this embodiment, the history of PHOS after the start of the proportional correction control is stored, and the next downstream O during the stored operation is stored. ₂ Since the PHOS request value is estimated based on the stored value in the sensor activation delay period, and the proportional correction control is performed using the estimated value, the downstream O ₂ Proportional correction control is possible during the sensor activation delay period, which enables downstream O ₂ Even in the sensor activation delay period, the air-fuel ratio in the catalyst can be accurately controlled to the stoichiometric air-fuel ratio, and the exhaust performance is further improved.
[0080]
The flowcharts of FIGS. 9 and 10 are the second embodiment and correspond to FIGS. 3 and 8 of the first embodiment, respectively. 9, the same step number is assigned to the same part as FIG. 3, and the same step number is assigned to the same part in FIG.
[0081]
The second embodiment differs from the first embodiment in obtaining the second point, and the point where the PHOS has changed by a predetermined value ΔPHOS from the point (1) is the second point (point (2) shown in FIG. 11). . Therefore, if the coordinates of the point (2) in FIG. 11 are (T2, PHOS1 + ΔPHOS), in the second embodiment, instead of the above equation (5),

The downstream O ₂ The PHOS request value in the sensor activation delay period is estimated. That is, in the second embodiment, PHOSS2 in the formula (9) is ₂ The estimated value of the PHOS request value in the sensor activation delay period is represented. Therefore, in the second embodiment, the values stored as the PHOS history after the start of the proportional correction control are PHOS1, T1, and T2.
[0082]
Moving on to the flowchart, the difference from the first embodiment will be mainly described. In step 91 of FIG. 10, the absolute value of the difference between PHOS and PHOS1 (already obtained in step 69 of FIG. 10) is compared with a predetermined value ΔPHOS. Then, while | PHOS-PHOS1 | ≦ ΔPHOS, the flow of FIG. 10 is terminated as it is, and it is considered that the point {circle around (2)} shown in FIG. 11 is reached at the timing when | PHOS−PHOS1 |> ΔPHOS. 93 and proceed to steps 68 and 70 in FIG.
T2 (new) = T * k + T2 (old) * (1-k) (10)
Where k: smoothing constant (k <1)
T2 (new): T2 after update
T2 (old): T2 before update
T2 (time after start of point {circle around (2)}) is updated by the following formula, and the updated T2 is stored in the backup RAM.
[0083]
On the other hand, in steps 81, 82, 83 of FIG. 9, the post-start time T and PHOS1, T1, T2 stored in the backup RAM are read, and these are used to calculate the downstream O according to the above equation (9). ₂ An estimated value PHOSS2 of the PHOS request value in the sensor activation delay period is calculated, and this is transferred to PHOS.
[0084]
Next, the third embodiment is obtained by replacing the flowchart of FIG. 8 in the first embodiment with the flowchart of FIG. In FIG. 12, the same step numbers are assigned to the same parts as those in FIG.
[0085]
The third embodiment is different from the first embodiment in how to obtain the first point. The difference from the first embodiment will be mainly described. In step 101, two flags AFR0 and AFR1 are compared. As a result of the comparison, only when both values are equal (that is, when PHOS is rich or continuous), the process proceeds to step 102. When flag AFR1 is checked, when AFR1 = 1 (when PHOS is rich), PHOS at step 103 And PHOS (old) (PHOS (old) is the previous value of PHOS) and 0 are compared. When PHOS-PHOS (old) <0, it is determined that the decreasing trend of PHOS continues, the flow of FIG. 12 is terminated, and the timing when PHOS-PHOS (old) ≧ 0 (PHOS is increased from decreasing to increasing) 6), it is assumed that the point {circle around (1)} shown in FIG.
[0086]
Similarly, when the PHOS lean continues, the process proceeds from step 102 to step 104, where the difference between PHOS and PHOS (old) is compared with 0. When PHOS-PHOS (old)> 0, it is determined that the increasing tendency of PHOS continues, the flow of FIG. 12 is terminated, and the timing when PHOS-PHOS (old) ≦ 0 is reached (PHOS is increased to decreased) 6), it is assumed that the point {circle around (1)} shown in FIG.
[0087]
The second and third embodiments also have the same operational effects as the first embodiment.
[0088]
The third embodiment is different from the first embodiment in obtaining the point {circle around (1)} shown in FIG. 6, but the point {circle around (1)} shown in FIG. 11 is different from the second embodiment. It doesn't matter if you ask differently.
[0089]
In the embodiment, PHOS1, T1, PHOS2, and T2 are obtained by a weighted average formula. However, the present invention is not limited to this, and PHOS at the first point during the previous operation, time after start at the first point, PHOS at two points, time after starting at the second point are stored in the backup RAM as PHOS1, T1, PHOS2, T2 as they are, or PHOS1, T1, It is also possible to obtain PHOS2 and T2 and store them in the backup RAM.
[0090]
In the embodiment, the downstream side O from the two points of the first point and the second point. ₂ Estimating the PHOS requirement value during the sensor activation delay period. ₂ The PHOS request value during the sensor activation delay period may be estimated. In the embodiment, the downstream O ₂ Although the PHOS requirement value in the sensor activation delay period is approximated by a straight line, the PHOS request value is not limited to this, and can be approximated by a smoothly changing curve.
[0091]
In the three embodiments, the case has been described in which the air-fuel ratio feedback control constant is a proportional component, but the present invention is not limited to this, and the integral component IL, IR, upstream O ₂ Sensor output delay time, upstream O ₂ A slice level SLF or the like to be compared with the sensor output can be similarly configured.
[0092]
In the embodiment, the proportional component correction value PHOS has been described when configured separately from the proportional components PL and PR that are map values (that is, when there are two variables), but for those in which these are handled by one variable However, the present invention can be applied. Also upstream O ₂ Based on the sensor output, the first air-fuel ratio feedback correction coefficient is set to the downstream O ₂ The present invention can also be applied to an apparatus in which the second air-fuel ratio feedback correction coefficient is independently obtained based on the sensor output and the air-fuel ratio feedback control is performed using these two correction coefficients.
[Brief description of the drawings]
FIG. 1 is a control system diagram of a first embodiment.
FIG. 2 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α.
FIG. 3 is a flowchart for explaining a subroutine.
FIG. 4 Downstream O ₂ It is a flowchart for demonstrating the calculation of the sensor smoothing voltage MVRO2.
FIG. 5 is a waveform diagram of a proportional correction value PHOS.
FIG. 6 Downstream O ₂ It is a wave form diagram for demonstrating estimation of the PHOS request value in a sensor activation delay period.
FIG. 7: Downstream side O ₂ It is a wave form diagram for demonstrating estimation of the PHOS request value in a sensor activation delay period.
FIG. 8 is a flowchart for explaining storage of T1, PHOS1, and PHOS2.
FIG. 9 is a flowchart for explaining a subroutine of the second embodiment.
FIG. 10 is a flowchart for explaining storage of T1, PHOS1, and T2 of the second embodiment.
FIG. 11 shows a downstream side O of the second embodiment. ₂ It is a wave form diagram for demonstrating estimation of the PHOS request value in a sensor activation delay period.
FIG. 12 is a flowchart for explaining storage of T1, PHOS1, and PHOS2 of the third embodiment.
FIG. 13 is a waveform diagram for explaining the operation of the prior application device.
FIG. 14 is a view corresponding to a claim of the first invention.
[Explanation of symbols]
2 Control unit
3 Upstream O ₂ Sensor
4 Crank angle sensor
6 Air flow meter
9 Exhaust passage
10 Three-way catalyst
13 Downstream side O ₂ Sensor

Claims (7)

Each air-fuel ratio sensor on the upstream side and downstream side of the catalyst,
Means for calculating a basic control constant of air-fuel ratio feedback control based on the output of the upstream air-fuel ratio sensor;
Means for determining whether or not the air-fuel ratio feedback control condition is satisfied;
Means for determining whether or not a correction control condition for a control constant used for air-fuel ratio feedback control is satisfied;
Means for calculating a correction value for the basic control constant based on the output of the downstream air-fuel ratio sensor when the air-fuel ratio feedback control condition is satisfied and when the correction control condition is satisfied from these determination results;
Using this correction value and the basic control constant, air-fuel ratio feedback control is performed when the air-fuel ratio feedback control condition is satisfied, and correction control is started when the air-fuel ratio feedback control condition is satisfied and when the correction control condition is satisfied. An air-fuel ratio control apparatus for an engine comprising:
The first point is the timing at which the downstream air-fuel ratio sensor output reverses across the slice level for the first time after the start of the correction control, and the second point is the point at which the correction value has elapsed from this first point. Means for storing the correction value and the post-start time and the correction value of the second point as a history of the correction value after the start of the correction control;
Means for determining whether or not a period from when the air-fuel ratio feedback control condition is satisfied to when the correction control condition is satisfied;
Means for estimating the required value of the correction value in this period based on the stored correction value of the first point and the post-start time and the correction value of the second point when this period is from this determination result; ,
An engine air-fuel ratio control apparatus comprising: means for performing feedback control and correction control of the air-fuel ratio in the period using the estimated value and the basic control constant. 2. The engine air-fuel ratio control apparatus according to claim 1 , wherein the correction value of the first point, the post-start time, and the correction value of the second point are weighted average values up to the previous operation. Each air-fuel ratio sensor on the upstream side and downstream side of the catalyst,
Means for calculating a basic control constant of air-fuel ratio feedback control based on the output of the upstream air-fuel ratio sensor;
Means for determining whether or not the air-fuel ratio feedback control condition is satisfied;
Means for determining whether or not a correction control condition for a control constant used for air-fuel ratio feedback control is satisfied;
Means for calculating a correction value for the basic control constant based on the output of the downstream air-fuel ratio sensor when the air-fuel ratio feedback control condition is satisfied and when the correction control condition is satisfied from these determination results;
Using this correction value and the basic control constant, air-fuel ratio feedback control is performed when the air-fuel ratio feedback control condition is satisfied, and correction control is started when the air-fuel ratio feedback control condition is satisfied and when the correction control condition is satisfied. An air-fuel ratio control apparatus for an engine comprising:
The first point is the timing at which the downstream air-fuel ratio sensor output reverses across the slice level for the first time after the start of the correction control, and the second point is the point where the correction value has increased by a predetermined value from this first point. Means for storing the correction value and the post-start time and the post-start time of the second point as a history of the correction value after the start of the correction control;
Means for determining whether or not a period from when the air-fuel ratio feedback control condition is satisfied to when the correction control condition is satisfied;
Means for estimating the required value of the correction value during this period based on the stored correction value and the post-start time of the first point and the post-start time of the second point when this period is from this determination result ,
An engine air-fuel ratio control apparatus comprising: means for performing feedback control and correction control of the air-fuel ratio in the period using the estimated value and the basic control constant. 4. The engine air-fuel ratio control apparatus according to claim 3 , wherein the correction value and the post-start time of the first point and the post-start time of the second point are weighted average values until the previous operation. Instead of the timing at which the downstream air-fuel ratio sensor output is reversed across the slice level for the first time after the start of the correction control, the downstream air-fuel ratio sensor output is reversed from decrease to increase for the first time after the correction control is started. air-fuel ratio control system for an engine according to the timing to reverse the from an increase to a decrease in claim 1 or 3, characterized in that said first point. According to any one of claims 1 to 5, characterized in that estimating the required value of the correction value in the period from a line extending to the period by connecting the second point and the first point Engine air-fuel ratio control device. The engine air-fuel ratio control apparatus according to any one of claims 1 to 6, wherein the timing at which the downstream air-fuel ratio sensor is activated is a timing at which the correction control condition is satisfied.

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