JP3979212B2 - Engine air-fuel ratio control device - Google Patents

Description

ただし、Ｔｐ：基本噴射パルス幅［ｍｓｅｃ］、
Ｔｆｂｙａ：目標当量比［無名数］、
Ｋａｔｈｏｓ：過渡補正量［ｍｓｅｃ］、
ＦＨＯＳ：パージ分補正係数（遅れなまし処理後の値）、
α：空燃比フィードバック補正係数、
αｍ：空燃比学習値、
Ｔｓ：無効パルス幅［ｍｓｅｃ］、
の式により燃料噴射弁４に与える燃料噴射パルス幅Ｔｉ［ｍｓｅｃ］を演算する。この演算は図２中の基本噴射パルス幅演算部Ｂ７、空燃比フィードバック補正係数演算部８、燃料噴射パルス幅演算部Ｂ９、空燃比学習制御部Ｂ１６における処理に対応する。
【００９１】
ここで、パージ分補正係数ＦＨＯＳで過渡補正量Ｋａｔｈｏｓを除いた部分（Ｔｐ×Ｔｆｂｙａ）を補正することにしているのは、パージにより供給される燃料は気体燃料であるため壁流補正を行う必要がないためである。
【００９２】
基本噴射パルス幅Ｔｐはほぼ理論空燃比の得られる噴射パルス幅で、吸入空気流量Ｑとエンジン回転速度Ｎから求めている。
【００９３】
目標当量比Ｔｆｂｙａは１．０を中心とする値で、冷却水温が低いときやエンジン始動直後には１．０より大きな値となる。エンジンの暖機完了後はＴｆｂｙａ＝１．０である。
【００９４】
空燃比フィードバック補正係数αは排気空燃比が理論空燃比を中心とするいわゆるウィンドウに収まるように空燃比センサ１５の出力に基づいて演算される値である。具体的には１００％を中心とする値で、定常偏差（ベース空燃比エラー）がないとした場合、検出された空燃比が理論空燃比よりもリッチ側にあるとき１００％よりも小さな値に、検出された空燃比が理論空燃比よりもリーン側にあるときに１００％よりも大きな値になる。
【００９５】
空燃比学習値αｍは空燃比フィードバック補正係数αに基づいて演算される値で、主に定常偏差を補償するために導入されている。
【００９６】
燃料噴射弁４から噴射された燃料の一部は吸気ポート壁や吸気弁傘裏部に壁流燃料を形成し、この壁流燃料は加速や減速といった過渡時に大きな応答遅れを有してシリンダに流入する。過渡補正量Ｋａｔｈｏｓはこの過渡時の壁流燃料の応答遅れ分を補償するための値である。
【００９７】
無効パルス幅Ｔｓは、燃料噴射弁４が所定のタイミングで噴射信号を受けてから実際に開弁するまでの作動遅れを補償するための値である。
【００９８】
また、（７）式はシーケンシャル噴射（４気筒ではエンジン２回転毎に１回、各気筒の点火順序に合わせて噴射）の場合の式であるため、数字の２が入っている。
【００９９】
図１２、図１３は目標パージ率ＭＰＲを設定するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。この演算は図２中の目標パージ率設定部Ｂ１における処理に対応する。
【０１００】
ステップ６１では初回の較正処理後であるか否かを判定する。これは初回の較正処理の前後で目標パージ率の設定方法が異なるためである。初回の較正処理前であるときにはそのまま今回の処理を終了する。なお、初回の較正処理前の目標パージ率の設定については、後述するブートアップ制御のところで説明する。
【０１０１】
初回の較正処理後であるときにはステップ６２に進み、キャニスタモデルに基づき演算された脱離量Ｄｇ（図４ステップ６により演算されている）とパージ流量ＰＱとに基づきパージガスの空燃比（パージ空燃比）を演算する。ここで、パージ流量ＰＱは目標パージ率と吸入空気流量Ｑとの積であり、この場合の目標パージ率には前回値を用いる。
【０１０２】
このパージ空燃比に対しては次のような補正を施してもかまわない。すなわち、運転状態、例えばエンジン回転速度、エンジン負荷、吸入空気流量などのパラメータから、パージ空燃比の誤差を推定する。例えば、図１４を内容とするテーブルを検索することにより求める。図示のように吸入空気流量が少なくなるほど、またパージ率が小さくなるほどパージ空燃比誤差は大きくなる値である。あるいは、パージ空燃比誤差を、図１５に示すようにパージ空燃比とパージ空燃比誤差の関係を規定したテーブルを検索することにより求めるようにしてもよい。パージ空燃比誤差が求まったら、ステップ６２で求めたパージ空燃比をこの誤差に基づいて補正する。
【０１０３】
なお、パージ空燃比はＨＣセンサによって検出するようにしてもよいが、キャニスタモデルに基づき演算される脱離量等に基づき演算によって求めればパージ空燃比を安価かつ正確に演算することができる。
【０１０４】
ステップ６３ではこのようにして求めた（あるいは誤差補正後の）パージ空燃比に基づきパージ率変化量制限値を演算する。パージ率が変化すると排気空燃比が変化するが、このときの理論空燃比からの空燃比偏差が許容幅以内に収まるようにパージ率変化量制限値を演算する。理論空燃比からの空燃比偏差の許容幅は空燃比フィードバック制御により吸収可能な、排気エミッションを悪化させない幅に設定する。
【０１０５】
ステップ６４では、パージバルブ２７のサイズから規定されるパージ率上限値ＰＶＭＸを演算する。このようなパージ率上限値ＰＶＭＸを求めるのは、目標パージ率がパージバルブ２７を最大開度として得られるパージ率よりも大きな値に設定されてしまうと、パージ率と目標パージ率との不一致が生じ、ＦＨＯＳの演算の誤差が大きくなるため、理論空燃比からの空燃比偏差が増加する。これにより、排気エミッション悪化等の問題が生じるからである。具体的には、パージバルブ２７のサイズが一定の場合、パージバルブ２７の前後差圧が大きいほど流せるパージガスの流量も多くなることから、パージバルブ２７の前後差圧が大きいときにパージ率上限値ＰＶＭＸとして大きな値を演算する。
【０１０６】
ステップ６５では、燃料噴射弁４の性能に応じて決まる最小噴射パルス幅、目標パージ率の前回値、パージ分補正係数との関係から燃料噴射弁４の性能に基づくパージ率上限値ＴＩＭＮＭＸを演算する。パージ率が高くなるとパージによってエンジンに供給される燃料量が増加するので、燃料噴射弁４からの燃料噴射量がその分だけ減らされるように燃料噴射パルス幅を補正するが、燃料噴射弁４の噴射精度を確保するためには噴射パルス幅は所定の最小パルス幅よりも大きくなくてはならない。言い換えれば、燃料噴射パルス幅を最小パルス幅より大きくするためにはパージ率はある値よりも小さくしなくてはならない。このような理由から、燃料噴射弁４の噴射性能によってもパージ率の上限を規定する。
【０１０７】
また、ステップ６６では、現在の運転領域から想定しうる全ての運転領域を想定し、その中での最小パージ率を予測し、この最小パージ率とパージ率変化量制限値とからパージ率上限値ＰＲＭＮＭＸを演算する。例えば、アクセルペダルをあるだけ踏み込んで加速した場合に目標パージ率はごく小さな値に設定するが、このアクセルペダルをあるだけ踏み込む直前に目標パージ率が大きな値に設定していると、パージ率の変化量が変化量制限値以下に制限されていることからパージ率を目標パージ率に追従させることができなくなる。この追従遅れは排気エミッション増大の原因等となることから、こうした追従遅れを生じないように想定しうる最小パージ率からもパージ率の上限を規定する必要がある。
【０１０８】
また、ステップ６７では、空燃比フィードバック補正係数αをモニターし、所定値以下であれば空燃比フィードバック補正係数αを所定値以上とするパージ率のうち最も大きな値をパージ率上限値ＡＬＰＭＸとして演算する。このような上限値ＡＬＰＭＸを設けるのは、空燃比フィードバック制御では空燃比フィードバック補正係数αは１００±２５％に収まるように制御されているが、空燃比フィードバック補正係数αが前記制限値近傍（例えば８０％）で制御されているような場合は、大量のパージを行っているとパージ以外の外乱を受けて前記制御範囲から外れやすくなるからである。
【０１０９】
ステップ６８では上記４つの上限値ＰＶＭＸ、ＴＩＭＮＭＸ、ＰＲＭＮＭＸ、ＡＬＰＭＸから最も小さい値を選択し、その値を最大パージ率ＰＲＭＡＸとして設定する。
【０１１０】
ステップ６９、７０では目標パージ率の前回値と最大パージ率ＰＲＭＡＸとを比較し、目標パージ率の前回値と最大パージ率ＰＲＭＡＸとが等しいときにはステップ６９よりステップ７３に進んで目標パージ率を前回値のままとし、目標パージ率の前回値が最大パージ率ＰＲＭＡＸよりも大きいときにはステップ６９、７０よりステップ７２に進んで目標パージ率をその前回値からパージ率変化量制限値を引いた値とし、目標パージ率の前回値が最大パージ率ＰＲＭＡＸよりも小さいときにはステップ６９、７０よりステップ７１に進んで目標パージ率をその前回値にパージ率変化量制限値を加えた値とする。
【０１１１】
図１３のステップ７４〜８１の処理については本願発明により追加した部分であり、後述する。
【０１１２】
このようにして、目標パージ率は、最大パージ率ＰＲＭＡＸを目標としてパージ率変化量制限値の範囲内でこれに追従するように設定され、排気エミッションを悪化させずに大量のパージを行う上で最良のパージ率が設定される。また、最大パージ率ＰＲＭＡＸを設定する際に、物理的な制限、現在の運転領域等で決まる上限値ＰＶＭＸ、ＴＩＭＮＭＸ、ＡＬＰＭＸだけでなく、運転領域が変化した場合でも遅れなくその領域での最大パージ率に移行できるように決定される上限値ＰＲＭＮＭＸをも考慮しているので、運転条件が変化しても排気エミッションを悪化させずに大量パージを行う上で最良のパージ率を設定することができる。
【０１１３】
このようにして設定された目標パージ率はパージバルブへのデューティ比に変換され、パージバルブ２７に出力される。
【０１１４】
ところで、キャニスタモデルに基づくパージ処理（モデル規範パージ処理）は、エンジン始動後に較正処理が一度も行われておらずキャニスタモデルで用いる初期値（初期吸着量）が存在しない間は、実行することができない。しかし、エンジン始動後より大量パージを実現するためには、たとえ較正処理前であってもパージ処理を実行する必要がある。そこで初回の較正処理が実行されるまでは、キャニスタモデルに基づくパージ処理に代えて次に示す制御（図１６に示すブートアップ制御）により目標パージ率を設定し、設定された目標パージ率でパージ処理を実行する。なお、このブートアップ制御では、パージによる排気空燃比への影響は空燃比フィードバック補正係数αによって吸収し、燃料噴射パルス幅の補正は行わない（ＦＨＯＳ＝１．０）。
【０１１５】
図１６はブートアップ制御を行うためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。このブートアップ制御は図２中のブートアップ制御部Ｂ１４、切換スイッチＢ１５における処理に対応する。
【０１１６】
ステップ９１で吸入空気流量Ｑを読み込み、ステップ９２で初回の較正処理前であるか否かを判定する。初回の較正処理前である場合には、ステップ９３で積算パージ流量（パージを開始してからの総パージ流量）ＳＱＰとパージ配管容積（キャニスタ２４からパージバルブ２７までの配管の容積）を比較する。積算パージ流量ＳＱＰがパージ配管容積を超えているときにはステップ９４に進み、これに対して超えていないときにはステップ９７に進む。
【０１１７】
ステップ９７では目標パージ率ＭＰＲとして初期パージ率（１％以下の小さな値）を設定する。このような小さな値に設定するのは、積算パージ流量ＳＱＰがパージ配管容積に達してない場合はパージ開始前にパージ配管内のガスがエンジンに供給されることになるが、このパージ配管内のガスの空燃比が不明であり、このままステップ９４〜９６に示す目標パージ率設定処理を行うとエンジンの燃焼安定性悪化等の問題を生じるからである。
【０１１８】
つまり、パージ開始時にパージ配管中に存在する低濃度のパージガスが供給され、これによる理論空燃比からの空燃比偏差が小さいと、さらに大量のパージが可能であると判断されて大きな目標パージ率ＭＰＲが設定されるが、このようにして大きな目標パージ率ＭＰＲが設定されてしまうと、配管内の低濃度のガスが全て供給されて本来の高濃度のパージガスが供給されるときに大量の脱離燃料が突然供給されることになり、エンジンの燃焼安定性等を悪化させる原因となるからである。
【０１１９】
積算パージ流量ＳＱＰが配管容積を超えたらステップ９４に進み実空燃比フィードバック偏差と目標空燃比フィードバック偏差との差を演算する。
【０１２０】
ここで、目標空燃比フィードバック偏差とは、空燃比フィードバック補正係数の目標値ｔαと空燃比フィードバック補正係数の中心値（１００％）との偏差（＝｜ｔα−１００｜％）をいい、実空燃比フィードバック偏差とは実際の空燃比フィードバック補正係数αと空燃比フィードバック補正係数の中心値との偏差（＝｜α−１００｜％）をいう。例えば、パージによる理論空燃比からの空燃比偏差を空燃比フィードバック制御で十分吸収できる範囲内で大量のパージ流量を確保することを目的として空燃比フィードバック補正係数αの目標値ｔαが８０％に設定されると、目標空燃比フィードバック偏差は｜８０−１００｜＝２０％に設定される。
【０１２１】
ステップ９５では図１７を内容とするテーブルを検索することにより上記目標空燃比フィードバック偏差と実空燃比フィードバック偏差との差に応じたパージ率変化量を算出する。パージ率変化量は、目標空燃比フィードバック偏差と実空燃比フィードバック偏差の差の絶対値が大きくなるほど大きな値を設定して、目標値への収束性を高めるのであるが、目標空燃比フィードバック偏差と実空燃比フィードバック偏差の差の正負によって、偏差の絶対値が同じであっても異なる値を設定し、空燃比フィードバック偏差の差が負側にずれた場合の方が大きな値（絶対値）をパージ率変化量に設定する。
【０１２２】
このようにパージ率変化量を空燃比フィードバック偏差の正負で異なる特性とするのは、空燃比フィードバック偏差の差が負側にずれている場合には空燃比フィードバック補正係数αが目標とする８０％よりも小さな値になっており、逆の正側にずれている場合と比べてパージ以外の外乱によってエンジン安定性、排気エミッションの悪化を招きやすく、不利な状態あるといえるからである。つまり、パージ率変化量を空燃比フィードバック偏差の差の正負に応じて特性を変えるのは、エンジンの燃焼安定性及び排気エミッション悪化防止の観点から、制御点を速やかに安全側に復帰させるためである。
【０１２３】
以上のようにしてパージ率変化量を演算したらステップ９６に進み、本ルーチン前回実行時に求めた目標パージ率に対して、ステップ９５で演算したパージ率変化量を付加し、新たな目標パージ率ＭＰＲを演算する。
【０１２４】
ステップ９８ではこのようにして得た目標パージ率ＭＰＲと吸入空気流量Ｑからパージ流量ＰＱを求め、これをステップ９９において積算パージ流量の前回値であるＳＱＰｚに加算することにより積算パージ流量ＳＱＰを更新する。
【０１２５】
したがって、ステップ９４〜９６の処理によると、キャニスタ２４の吸着状態によらず、最適な目標パージ率ＭＰＲを設定することができ、また、想定以上の濃度のパージガスが供給された場合でも、それによる排気空燃比の変化を受けて目標パージ率ＭＰＲが適宜変更され、常に最適な目標パージ率ＭＰＲを設定することができる。
【０１２６】
一方、初回の較正処理後にはステップ９２よりステップ１００以降に進み、積算パージ流量ＳＱＰに基づいてパージ処理が終了したか否かを判定する。すなわち、ステップ１００でパージ終了判定フラグ（ゼロに初期設定）をみる。エンジン始動直後にはパージ終了判定フラグ＝０であるので、ステップ１０１に進み脱離量Ｄｇ（図４のステップ６で演算されている）と目標パージ率ＭＰＲ（図１２、図１３により演算されている）を読み込む。ステップ１０２では、この読み込んだ目標パージ率ＭＰＲと吸入空気流量Ｑとからパージ流量ＱＰを算出し、これをステップ１０３において積算パージ流量の前回値であるＳＱＰｚに加算することにより積算パージ流量ＳＱＰを更新する。
【０１２７】
ステップ１０４では初回の較正処理タイミングであるか否かを判定する。ここで、初回の較正処理タイミングはステップ９２で初回の較正処理前でなくなった初めてのタイミングであるので、このときだけステップ１０５に進み、ステップ１０２で演算されているパージ流量ＰＱとステップ１０１で読み込んでいる脱離量Ｄｇとに基づいてパージ空燃比を演算し、このパージ空燃比からステップ１０６において図１８を内容とするテーブルを検索することにより、パージ終了判定値ＳＬＳＱＰを演算する。
【０１２８】
ここで、パージ終了判定値ＳＬＳＱＰはキャニスタ２４からのパージガス中にほぼ脱離燃料がなくなったと思われる積算パージ流量である。図１８のように、この判定値ＳＬＳＱＰはパージ空燃比が大きくなるほど小さくなる。
【０１２９】
ステップ１０７ではこのパージ終了判定値ＳＬＳＱＰと積算パージ流量ＳＱＰとを比較する。積算パージ流量ＳＱＰがパージ終了判定値ＳＬＳＱＰ未満であればそのまま今回の処理を終了する。やがて積算パージ流量ＳＱＰがパージ終了判定値ＳＬＳＱＰ以上になればキャニスタ２４からのパージガス中にほぼ脱離燃料がなくなったと判断し、パージが終了したことを表すためステップ１０８に進んでパージ終了判定フラグ＝１とする。
【０１３０】
パージ終了判定フラグ＝１になると次回からはステップ９１、９２、１００と流れてもステップ１０１以降に進むことができないので、そのまま処理を終了する。
【０１３１】
次に、パージ処理を行うことによる本実施形態の全体的な作用について先に説明する。
【０１３２】
パージ処理時、目標パージ率ＭＰＲはエンジン燃焼安定性低下、排気エミッション増大を起こさない範囲でできる限り大きな値が設定され、この目標パージ率ＭＰＲが実現されるようにパージバルブ２７が開かれる（図１２ステップ６１〜７３）。
【０１３３】
パージ処理中はキャニスタ２４から脱離した燃料を含んだパージガスがエンジンに供給されることになるので、エンジンコントローラ１１ではキャニスタ２４から脱離してくる燃料量Ｄｇを推定し、この脱離量Ｄｇ、目標パージ率、吸入吸気質量Ｑｇに基づいて、パージ燃料によって生じる空燃比フィードバック補正係数αの変化を予測する値であるパージ分補正係数ＦＨＯＳを演算し（図４ステップ１、３、４、６、７、８またはステップ１、３、５、６、７、８）、このパージ分補正係数ＦＨＯＳにより基本噴射パルス幅Ｔｐを補正することで、パージによる理論空燃比からの空燃比偏差が小さなものに抑えられる。
【０１３４】
このときキャニスタ２４からの脱離量Ｄｇは、（１）式から（４）式で表されるキャニスタモデルを用いて推定され、脱離量Ｄｇは短時間でかつ正確に推定される。ここで、キャニスタモデルに基づき演算される脱離量Ｄｇ等は誤差を含んでおり、キャニスタモデルの動作時間が長くなるにつれこの誤差が積算され大きくなるので、エンジンコントローラ１１は空燃比フィードバック補正係数αの変化よりキャニスタ２４から脱離された燃料量を推定し、この推定した脱離量から逆演した吸着量Ｙｒでキャニスタモデルの内部変数である吸着量の値を較正する。この較正処理は、パージ以外の外乱が小さく空燃比フィードバック係数αの変化をほぼ全てパージによるものとみなすことができ、かつ、パージによる排気空燃比への影響が比較的大きいときに実行される。
【０１３５】
また、パージバルブ２７が開かれてから脱離燃料がエンジンのシリンダに到達するまでに遅れがあり、また到達するまでに燃料の拡散もあるので、この遅れとなまし作用を考慮して上記のパージ分補正係数ＦＨＯＳに対して遅れ補正が施されている。
【０１３６】
また、上記キャニスタモデルを用いたパージ処理（モデル規範パージ処理）は、較正処理によって吸着量の初期値が求まるまではその効果を発揮することができないが、キャニスタモデルの初期値が演算されるまでは目標空燃比フィードバック偏差と実空燃比フィードバック偏差との差に応じて目標パージ率が設定され、この目標パージ率が実現されるようにパージバルブ２７が開かれる。これにより、較正処理によって初期値が演算される前であってもパージ処理を行うことができ、全領域で効果的なパージを行うことができる。
【０１３７】
これで先願装置（特願２００１−７１５６２号参照）におけるパージ処理と同様の部分の説明を終了し、次には本願発明で追加した図６のステップ１１１〜１１９、図１３のステップ７４〜８１、図１９、図２０、図２１、図２３、図２４、図２６、図２７に示すフローチャートを説明する。
【０１３８】
まず目標パージ率を設定するためのフローチャートの後半部である図１３から説明する。この部分の処理は図３１中のＡＮＤ回路Ｂ３８、パージ率低下処理部Ｂ３９、切換スイッチＢ４０における処理に対応する。
【０１３９】
ステップ７４では目標パージ率を変数ＭＰＲ０に移す。
【０１４０】
ステップ７５では較正実行可能判定フラグ（ゼロに初期設定）をみる。前述の図５では「定常条件」、「パージバルブ精度条件」、「パージ影響度条件」全てが成立した場合に較正処理実行可能タイミングであると判断したが、較正実行可能判定フラグはこのタイミングで１となるフラグである。較正実行可能判定フラグ＝０であるときにはステップ７８に進みＭＰＲ０の値をそのまま目標パージ率ＭＰＲとして設定する。
【０１４１】
一方、較正実行可能判定フラグ＝１であるときにはステップ７６、７７に進みデータサンプリング終了フラグ、アクティブ較正要求フラグ（いずれもゼロに初期設定）をみる。後述するように、ベース空燃比エラーがあると判定されたときにアクティブ較正要求フラグ＝１となり、このアクティブ較正要求フラグの０から１への切換タイミングで、パージカット前のデータをサンプリングした後にパージ率低下処理を開始する。このパージ率低下処理はアクティブ較正要求フラグが０から１へと切換わる直前の目標パージ率を初期値として、目標パージ率をゼロになるまで所定時間当たり所定値ずつ低下させる処理であり、このパージ率低下処理により目標パージ率がゼロとなった状態（パージカット状態）で安定化時間を経過したとき、パージカット時のデータをサンプリングし、これでパージカット前後のデータのサンプリングを終了するので、データサンプリング終了フラグ＝１としている。
【０１４２】
このため、アクティブ較正要求フラグ＝１となる前にはデータサンプリング終了フラグ＝０であり、このときにはステップ７６、７７よりステップ７８に進み、またデータサンプリング終了フラグ＝１となったときにはステップ７６よりステップ７８に進みステップ７８の操作を実行する。
【０１４３】
これに対して、アクティブ較正要求フラグ＝１となってからデータサンプリング終了フラグ＝１となる直前までの間はステップ７９に進んでパージ率低下処理を行う。
【０１４４】
ここで、ステップ７７のアクティブ較正要求フラグの設定について図１９のフローより説明する。
【０１４５】
図１９はアクティブ較正要求フラグを設定するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。
【０１４６】
ステップ１２１ではモデルパージ実行中であるかどうかみる。モデルパージ実行中とはキャニスタモデルの初回の較正処理が終了しておりかつパージを禁止していない状態のことである。モデルパージ実行中であればステップ１２２に進み、パージ用リミッタ判定フラグをみる。このパージ用リミッタ判定フラグにはパージ用下限リミッタ判定フラグとパージ用上限リミッタ判定フラグの２つがあり、これら２つのフラグの設定については図２０、図２１のフローより説明する。
【０１４７】
図２０はパージ用下限リミッタ判定フラグを、また図２１はパージ用上限リミッタ判定フラグを設定するためのもので、いずれも一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。これら図２０、図２１の設定処理と図１９の設定処理とが、図３１中のベース空燃比エラー判定部Ｂ３６、アクティブ較正要求部Ｂ３７における処理に対応する。
【０１４８】
空燃比フィードバック補正係数αには、従来よりαによる制御範囲を限定するため図２８に示したように、αの中心値（１００％）を中心として上下に第１リミッタ±ＬＭＴ１（例えば±２５％）を設けている。すなわち、αの第１上限リミッタは１２５％（＝１００＋ＬＭＴ１）、αの第１下限リミッタは７５％（＝１００−ＬＭＴ１）であり、演算されたαが、αの第１上限リミッタである１２５％を超えるときには、このαを１２５％に制限し、この逆に演算されたαが、αの第１下限リミッタである７５％を下回るときには、このαを７５％に制限している。
【０１４９】
本実施形態では、この第１リミッタ±ＬＭＴ１とは別に、パージ用にこれより小さい第２リミッタ±ＬＭＴ２を新たに導入している。すなわち、第２下限リミッタは１００−ＬＭＴ２、第２上限リミッタは１００＋ＬＭＴ２であり、図２８において、αの中心値である１００％と第１下限リミッタである１００−ＬＭＴ１との間に、１００−ＬＭＴ１からある程度の余裕代を持たせた位置に第２下限リミッタである１００−ＬＭＴ２がくるようにしている。すなわち、１００−ＬＭＴ２（第２下限リミッタ）と１００−ＬＭＴ１（第１下限リミッタ）の間をαの補正代として残し、パージ以外の外乱があった場合に、この残したαの補正代により理論空燃比からの空燃比偏差を小さなものとする。
【０１５０】
そして、αが第２下限リミッタ以下の領域にあるか否かあるいは第２上限リミッタ（図２８には示していない）以上の領域にあるか否かを示すため、フラグを設定する。すなわち、演算されたαが第２下限リミッタである１００−ＬＭＴ２以下になるとパージ用下限リミッタ設定フラグ＝１とし、この逆に演算されたαが第２上限リミッタである１００＋ＬＭＴ２以上となるとパージ用上限リミッタ設定フラグ＝１とする。
【０１５１】
ただし、第２下限リミッタ、第２上限リミッタにはそれぞれヒステリシスＨＹＳを設けている。これは、αが各リミッタ付近にいることにより各フラグがゼロとなったり１となったりを頻繁に繰り返すことを防止するためである。
【０１５２】
具体的に図２０から説明すると、ステップ１３１では空燃比フィードバック制御中であるか否かを判定する。空燃比フィードバック制御中でなければそのまま今回の処理を終了する。
【０１５３】
空燃比フィードバック制御中であるときには、ステップ１３２に進んで空燃比フィードバック補正係数αを読み込む。
【０１５４】
このαは図示しないフローにおいて空燃比センサ１５に基づいて演算している。ここでは、簡単のため比例動作の場合で説明すると、空燃比センサ１５により検出される実際の排気空燃比と理論空燃比との偏差を求め、この偏差に比例ゲインを乗算することにより求めればよい。このときαの波形は、実際の排気空燃比が理論空燃比よりリッチ側にあるあいだは、実際の排気空燃比を理論空燃比へと戻すため制御周期毎にαが階段状に小さくなってゆき、この逆に実際の排気空燃比が理論空燃比よりリーン側にあるあいだは、実際の空燃比を理論空燃比へと戻すため制御周期毎にαが階段状に大きくなってゆく。
【０１５５】
ステップ１３３ではパージ用下限リミッタ判定フラグ（エンジン始動時にゼロに初期設定）をみる。始動直後であればパージ用下限リミッタ判定フラグ＝０であることよりステップ１３４に進みαとパージ用下限リミッタである１００−ＬＭ２とを比較する。αが１００−ＬＭＴ２を超えているときにはそのまま今回の処理を終了し、αが１００−ＬＭＴ２以下になると、ステップ１３５に進んでパージ用下限リミッタ判定フラグ＝１として今回の処理を終了する。
【０１５６】
このパージ用下限リミッタ判定フラグ＝１により次回にはステップ１３３よりステップ１３６に進みαと１００−ＬＭＴ２＋ＨＹＳ（ＨＹＳは正の一定値）を比較する。αが１００−ＬＭＴ２＋ＨＹＳ以下であればステップ１３５に進んでパージ用下限リミッタ判定フラグ＝１のままとし、αが１００−ＬＭＴ２＋ＨＹＳを超えるとステップ１３７に進んでパージ用下限リミッタ判定フラグ＝０とする。
【０１５７】
図２１に移ると、ステップ１４１、１４２は図２０のステップ１３１、１３２と同様である。
【０１５８】
ステップ１４３ではαのパージ用上限リミッタ判定フラグ（エンジン始動時にゼロに初期設定）をみる。始動直後であればパージ用上限リミッタ判定フラグ＝０であることよりステップ１４４に進みαとパージ用上限リミッタである１００＋ＬＭＴ２とを比較する。αが１００＋ＬＭＴ２未満であるときにはそのまま今回の処理を終了し、αが１００＋ＬＭＴ２以上になると、ステップ１４５に進んでパージ用上限リミッタ判定フラグ＝１として今回の処理を終了する。
【０１５９】
このパージ用上限リミッタ判定フラグ＝１により次回にはステップ１４３よりステップ１４６に進みαと１００＋ＬＭＴ２−ＨＹＳ（ＨＹＳは正の一定値）を比較する。αが１００＋ＬＭＴ２−ＨＹＳ以上であれステップ１４５に進んでパージ用上限リミッタ判定フラグ＝１のままとし、αが１００＋ＬＭＴ２−ＨＹＳ未満になるとステップ１４７に進んでパージ用上限リミッタ判定フラグ＝０とする。
【０１６０】
図１９のステップ１２２に戻り、パージ用リミッタ判定フラグ（パージ用下限リミッタ判定フラグまたはパージ用上限リミッタ判定フラグ）＝１であるときにはステップ１２３に進みタイマ１（ゼロに初期設定）をインクリメントする。タイマ１は、継続してパージ用リミッタ判定フラグ＝１でいる時間を計測するためのものである。このため、インクリメントの途中でもパージ用リミッタ判定フラグ＝０となればステップ１２６に進んでタイマ１をゼロにクリアし、再びパージ用リミッタ判定フラグ＝１となればステップ１２３に進んでタイマ１をインクリメントする。
【０１６１】
ステップ１２４でタイマ１値と所定値を比較する。所定値はベース空燃比エラーがあるかどうかを判定するための値である。タイマ１値が所定値以上になるとベース空燃比エラーがあると判断し、ステップ１２５に進んでアクティブ較正処理（第２較正処理）を行うため、アクティブ較正要求フラグ（ゼロに初期設定）＝１とする。
【０１６２】
ただし、運転条件が過渡的に変化するときには、ベース空燃比エラーが存在していなくても一時的にパージ用リミッタ判定フラグ＝１となることがあるので、この場合にもベース空燃比エラーがあると誤判定されることがないように所定値を設定する。すなわち、過渡的にパージ用リミッタ判定フラグ＝１となる時間よりも長めの時間（例えば数秒）を所定値として定めておくことで、運転条件の過渡的変化による場合をベース空燃比エラーと誤判定することを回避する。
【０１６３】
これで、図１９の説明を終了するので、図１３に戻り、アクティブ較正要求フラグ＝１となった直後であればデータサンプリング終了フラグ＝０であるため、ステップ７６、７７よりステップ７９に進んでパージ率低下処理を行う。
【０１６４】
このパージ率低下処理は図２２に示したように、アクティブ較正要求フラグ＝１かつ較正実行可能判定フラグが０から１へと切換わったタイミングでの目標パージ率（図１２のステップ６１〜７３で演算されている）を初期値として所定時間Δｔ当たり所定値Δずつ減らし最終的にゼロにする制御である。これは、パージカットを行うための一方法であり、初期値からステップ的にゼロにするのではない。
【０１６５】
図２３、図２４（図１３ステップ７９のサブルーチン）はこのパージ率低下処理を行うためのものである。この処理は図３１中のパージ率低下処理部Ｂ３９、パージカット前データサンプリング部Ｂ４２、パージカット時データサンプリング部Ｂ４３における処理に対応する。
【０１６６】
図２３において、ステップ１５１、１５２では今回と前回の較正実行可能判定フラグをみる。今回に較正実行可能判定フラグ＝１かつ前回に較正実行可能判定フラグ＝０（つまり較正実行可能判定フラグが０より１へと切換わった直後）のときステップ１５３に進み、パージ率低下処理開始時の空燃比フィードバック補正係数α（図示しないαの演算フローにおいて演算されている）、パージ分補正係数ＦＨＯＳ（図４により演算されている）、目標パージ率ＭＰＲ０（図１３ステップ７４で得ている）、吸入空気質量Ｑｇ（吸入空気流量Ｑと吸気温度等から得ている）、空燃比学習値αｍ（図示しない空燃比学習値のマップからそのときの運転条件の属する小領域に入っている空燃比学習値を読み出してくる）を読み込んで、対応するメモリα１、ＦＨＯＳ１、ＭＰＲ１、Ｑｇ１、αｍ１に入れる（パージカット前データのサンプリング）。
【０１６７】
ステップ１５４では同じくパージ率低下処理開始時のＭＰＲ０の値を変数ＭＰＲＧに移す。これは、較正実行可能判定フラグが０より１へと切換わったタイミングでの目標パージ率を初期値としてサンプリングするためである。
【０１６８】
ステップ１５５ではタイマ２を一旦ゼロにクリアした後、ステップ１５６でインクリメントを開始する。
【０１６９】
今回、前回とも較正実行可能判定フラグ＝１であるときにはステップ１５３、１５４、１５５を飛ばしてステップ１５６の操作を実行する。
【０１７０】
ステップ１５７ではタイマ２値と所定時間Δｔを比較する。タイマ２値が所定時間Δｔ以上になると、ステップ１５８、１５９に進み、タイマ２値をゼロにクリアすると共に、
ＭＰＲＧ＝ＭＰＲＧｚ−Δ…（８）
ただし、ＭＰＲＧｚ：ＭＰＲＧの前回値、
の式により変数ＭＰＲＧを所定値Δ（正の値）だけ小さくする。タイマ２値が所定時間Δｔ未満のときにはステップ１６０に進み現在のＭＰＲＧを維持する。
【０１７１】
ステップ１５７〜１６０の操作により、ＭＰＲＧは所定時間Δｔが経過する毎に所定値Δずつ小さくなってゆく（図２２最下段参照）。
【０１７２】
ここで、パージ率を急激に低下させてのパージカットを行うと排気空燃比が変化し運転性や排気エミッションに影響するので、そうならないように所定時間Δｔと所定値Δの値は目標パージ率を設定する際のパージ率変化量制限値を用いて、またはこれに基づいて定めればよい。
【０１７３】
図２４に進み、ステップ１６１ではＭＰＲＧとゼロを比較する。ＭＰＲＧがゼロ以上であればステップ１６２に進みＭＰＲＧを目標パージ率ＭＰＲとして、これに対してＭＰＲＧが負の値になったときにはステップ１６３に進みゼロを目標パージ率ＭＰＲとして設定する。
【０１７４】
ステップ１６４では目標パージ率ＭＰＲとゼロを比較する。ＭＰＲ＝０であるときにはステップ１６５に進んでタイマ３（ゼロに初期設定）をインクリメントする。タイマ３はパージカット状態（目標パージ率ＭＰＲがゼロ）の連続経過時間を計測するためのものである。
【０１７５】
ステップ１６６ではタイマ３値と安定化時間を比較する。安定化時間はパージカット状態が安定するのを待つ時間である。
【０１７６】
タイマ３値が安定化時間以上になるとステップ１６７に進み、そのときの空燃比フィードバック補正係数α、空燃比学習値αｍを対応するメモリα２、αｍ２に入れる。これはパージカット時のデータをサンプリングするものである。これで、パージカット前後でのデータのサンプリングを終了するので、ステップ１６８ではデータサンプリング終了フラグ（ゼロに初期設定）＝１とすると共に、ステップ１６９でタイマ２、３をゼロにクリアする。
【０１７７】
このようにしてパージ率低下処理を終了したら図１３のステップ８０に戻る。ステップ８０ではパージ終了判定フラグ（図１６により設定されている）をみる。パージ終了判定フラグ＝１のときには、空燃比学習を開始するためステップ８１に進み空燃比学習用のパージ率を目標パージ率ＭＰＲに入れる。これによって空燃比学習を開始するときには図２５に示したように目標パージ率ＭＰＲが小さくなる。
【０１７８】
図２６は空燃比学習開始フラグを設定するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。
【０１７９】
ステップ１７１では空燃比学習開始フラグ（ゼロに初期設定）をみる。エンジン始動直後であれば空燃比学習開始フラグ＝０であることよりステップ１７２に進み、パージ終了判定フラグ（図１６により設定されている）をみる。
【０１８０】
パージ終了判定フラグ＝１であるときだけ空燃比学習を開始させるためステップ１７３に進み空燃比学習開始フラグ＝１とする。
【０１８１】
図２７は空燃比学習値の更新を行うためのもので、所定のタイミング毎（例えば所定のエンジン回転速度の間隔毎）に実行する。この空燃比学習値の更新と図２６の空燃比学習開始フラグ設定の各処理は図２中の空燃比学習制御部Ｂ１６における処理に対応する。
【０１８２】
ステップ１８１では空燃比学習開始フラグをみる。空燃比学習開始フラグ＝１であるときにはステップ１８２に進み空燃比学習許可条件が成立しているか否かを判定する。空燃比学習許可条件は従来と同様である。例えば空燃比フィードバック制御中であることや空燃比フィードバック制御に関わる空燃比センサ１５等に故障がないことなどを総て満足するときに空燃比学習許可条件が成立していると判断し、ステップ１８３に進んで空燃比学習値を更新する。この空燃比学習値の更新方法には次式によって更新する方法がある。
【０１８３】
αｍ＝αｍｚ＋（α−１００）×Ｍ…（９）
ただし、αｍ ：更新後の空燃比学習値、
αｍｚ：更新前の空燃比学習値、
Ｍ ：学習割合（一定値）、
この場合、エンジンの回転速度と基本噴射パルス幅Ｔｐ（エンジン負荷相当）をパラメータとする全運転領域が複数の小さな領域に区分けされ、その各小領域毎に独立の空燃比学習値を有している。このため、（９）式右辺の更新前の空燃比学習値は更新タイミングでの運転条件が属する小領域に格納されている空燃比学習値であり、その同じ小領域に（９）式左辺の更新後の空燃比学習値が格納される。
【０１８４】
なお、実施形態は空燃比センサ１５に基づく空燃比フィードバック制御であるが、これに代えてＯ₂センサに基づく空燃比フィードバック制御であってもよく、この場合には、Ｏ₂センサの反転タイミングを空燃比学習値の更新タイミングとすればよい。
【０１８５】
次に、図６に戻ってステップ１１１〜１１９の処理を説明する。この部分の処理は図３１中のアクティブ較正処理部Ｂ４１、切換スイッチＢ４７における処理に対応する。
【０１８６】
ステップ１１１、１１２でアクティブ較正要求フラグ、データサンプリング終了フラグをみる。アクティブ較正要求フラグ＝０であるとき、アクティブ較正要求フラグ＝１であってもデータサンプリング終了フラグ＝０であるときにはステップ３２〜３６に進み先願装置と同様のパッシブ較正処理（第２較正処理）を実行する。
【０１８７】
アクティブ較正要求フラグ＝１かつデータサンプリング終了フラグ＝１であるときにはステップ１１３〜１１７でのアクティブ較正処理（第１較正処理）を行う。すなわち、ステップ１１３ではメモリに格納されているα１、α２、ＦＨＯＳ１、Ｑｇ１、αｍ１、αｍ２を読み込む。ここで、「１」が付いている値がパージカット前の、これに対して「２」が付いている値がパージカット時のデータである。
【０１８８】
ステップ１１４ではこれらパージカット前後のデータを用いて、
ＤＬＴ＝（α１＋αｍ１＋α２＋αｍ２−３）×ＦＨＯＳ１…（１０）
の式により全空燃比補正係数ＤＬＴを算出し、この全空燃比補正係数ＤＬＴとＭＰＲ１、Ｑｇ１とを用いて、
Ｄｇ＝Ｋ１×（１−ＤＬＴ＋Ｋ２×ＭＰＲ１）×Ｑｇ１…（１１）
の式により脱離量Ｄｇを算出する。
【０１８９】
ここで、（１０）式をどのようにして導いたかを説明する。
【０１９０】
（ア）空燃比学習制御を行わない場合：
実施形態は空燃比学習制御部Ｂ１６を備えるものであるが、空燃比学習制御を行わないものが考えの基本となるので、こちらから説明すると、このときには、
ＤＬＴ＝｛α１−（１−α２）｝×ＦＨＯＳ１…（ａ）
の式により全空燃比補正係数ＤＬＴを算出すればよい。ここで、（ａ）式右辺の（１−α２）がパージカット時における、αの中心値からのαの偏差、つまりベース空燃比エラーを表し、これがパージ実行中の値である（ａ）式右辺のα１に含まれてしまうことにより較正エラーとなるので、α１よりベース空燃比エラーを表す（１−α２）を差し引くことにより、ベース空燃比エラー分の誤差をα１から取り去っている。
【０１９１】
（イ）空燃比学習制御を行う場合：
このときには、空燃比学習値についても空燃比フィードバック補正係数αと同様に考える必要があるので、

の式により全空燃比補正係数ＤＬＴを算出する。ここで、（ｂ）式右辺の（１−αｍ２）はパージカット時における、αｍの中心値からのαｍの偏差、つまりこれもベース空燃比エラーを表し、これがパージ実行中の値である（ｂ）式右辺のαｍ１に含まれてしまうことにより較正エラーとなるので、αｍ１よりベース空燃比エラーを表す（１−αｍ２）を差し引くことにより、ベース空燃比エラー分の誤差をαｍ１から取り去っている。ただし、１．０を中心とする｛α１−（１−α２）｝と｛αｍ１−（１−αｍ２）｝の２つの値を足し合わせた合計は２となるので、２つの値の合計から１を差し引くことによって計算上のつじつま合わせをしている。（ｂ）式を整理すると上記（１０）式が得られる。
【０１９２】
このようにして全空燃比補正係数ＤＬＴが得られると、脱離量の演算式は前述の（５ｂ）式と同じである。ただし、この場合の目標パージ率ＭＰＲ、吸入空気質量Ｑｇはパージカット前の値なければならないので、上記（１１）のようにＭＰＲ、Ｑｇに代えてＭＰＲ１、Ｑｇ１を用いている。
【０１９３】
ステップ１１６、１１７はパッシブ較正処理と同様である。すなわち、ステップ１１６では、ステップ１１５で演算した脱離量Ｄｇから上記（６）式により、キャニスタ２４の吸着量Ｙｒ（質量）を演算する。ステップ１１７では、キャニスタモデルに基づき脱離量Ｄｇを演算する際に使用する吸着量Ｙを、ステップ１１６で演算した吸着量Ｙｒに置き換える。
【０１９４】
これでアクティブ較正処理を終了するので、ステップ１１８、１１９ではデータサンプリング終了フラグ＝０、アクティブ較正要求フラグ＝０とする。アクティブ較正要求フラグ＝０より、次回に較正実行可能と判定されたときには図６においてステップ１１１よりステップ３２〜３６へと進みパッシブ較正処理を実行する。
【０１９５】
ここで、本実施形態のパージ実行中の作用を図２８、図２９の波形図を参照しながら説明する。
【０１９６】
図２８の右側は、ベース空燃比エラーはなく、空燃比学習機能は考えないものとした状態で、パージ分補正係数ＦＨＯＳが正しく演算されているときの空燃比フィードバック補正係数α、パージ分補正係数ＦＨＯＳの各波形を、これに対して図２８の左側は同じくベース空燃比エラーはなく、空燃比学習機能は考えないものとした状態で、較正エラーに伴ってＦＨＯＳが正しく演算されていないときの空燃比フィードバック補正係数α、パージ分補正係数ＦＨＯＳの各波形をモデル的に示す。ただし、運転条件は理想的な定常でなく、目標パージ率が緩やかに変化しているように緩やかに変化している場合で示している。
【０１９７】
図２８右側に示したように、設定された目標パージ率のもとでパージ処理を行っているとき、パージ分補正係数ＦＨＯＳが正しく演算されていれば、このＦＨＯＳにより理論空燃比からの空燃比偏差が小さくなるため、空燃比フィードバック制御が働くまでもないことから、空燃比フィードバック補正係数αは補正代がフル（最大）となる位置（つまりαの中心値である１００％）の付近にとどまっている。
【０１９８】
これに対して、較正エラーに伴ってＦＨＯＳが正しく演算されていないときには空燃比フィードバック制御中における理論空燃比からの空燃比偏差が大きくなり、この大きくなった空燃比偏差を小さなものにしようと、空燃比フィードバック制御が働く。すなわち、図２８左側に示したようにαが第１下限リミッタである７５％からは少し余裕を残した位置で緩やかに振れており、このことは、この状態で理論空燃比からの空燃比偏差が小さくなっていることを現している。言い換えると、ＦＨＯＳが誤って１００％に近い値に演算されたために排気空燃比が理論空燃比よりリッチ側に傾き、このリッチ側に傾いた排気空燃比を理論空燃比に戻そうとαが１００％より小さくなっている。
【０１９９】
この場合に、本実施形態では、αの第１下限リミッタである７５％よりもαの中心値（１００％）までの幅が狭い第２下限リミッタである１００−ＬＭＴ２を設定しており、図２８左側のようにこの第２下限リミッタを横切りながらαが推移するとき、パージ用下限リミッタ判定フラグが０から１になったり、再び０に戻ったりを繰り返す（図２８左側、最下段参照）。これは、αとヒステリシス付きの判定値との比較による。すなわち、αが判定値である１００−ＬＭＴ２を横切って小さくなったタイミングでパージ用下限リミッタ判定フラグが０から１に切換わる（図２０ステップ１３３、１３４、１３５）。その後にαが今度は１００−ＬＭＴ２を横切って大きくなる側に変化すると、１００−ＬＭＴ２＋ＨＹＳ以下にある間はパージ用下限リミッタ判定フラグ＝１のままであるが（図２０ステップ１３３、１３６、１３５）、αが１００−ＬＭＴ２＋ＨＹＳより大きくなったタイミングでパージ用下限リミッタ判定フラグが１から０に切換わる（図２０ステップ１３３、１３６、１３７）。αが再び１００−ＬＭＴ２を横切って小さくなると、パージ用下限リミッタ判定フラグが０から１に切換わる（図２０ステップ１３３、１３４、１３５）。このような繰り返しによりパージ用下限リミッタ判定フラグが図２８左側の最下段に示すようになる。
【０２００】
そして、パージ用下限リミッタ判定フラグ＝１となっている連続時間（タイマ２値）が所定値以上になるとアクティブ較正要求フラグが０から１に切換わる（図１９ステップ１２４、１２５）。
【０２０１】
図２９は空燃比学習制御を行っているものの、何らの原因でエンジン始動後にベース空燃比エラーが露わになっており、しかも空燃比学習が開始される前にあるとした状態で、なおかつ較正エラーに伴ってパージ分補正係数ＦＨＯＳが正しく演算されていないときの空燃比フィードバック補正係数α、パージ分補正係数ＦＨＯＳ、空燃比学習値αｍの各波形をモデル的に示す。すなわちｔ１以前ではベース空燃比エラーに起因して排気空燃比が理論空燃比よりリーン側に傾き、このリーン側に傾いた排気空燃比を理論空燃比に戻そうと空燃比フィードバック補正係数αが１００％より大きくなっている。ただし、運転条件は緩やかな加速時のものである。
【０２０２】
なお、空燃比学習値αｍはエンジンの回転速度と負荷とで表される全運転領域をいくつかの小領域に分割し、その各小領域毎に別々の空燃比学習値を格納している場合を想定しており、このため、最下段に示したようにｔ１とｔ２の間で空燃比学習値αｍが変化している。これは、運転条件が別の小領域に移ったために読み出される空燃比学習値が異なったことを示している。
【０２０３】
また、目標パージ率ＭＰＲ、パージ分補正係数ＦＨＯＳ、空燃比フィードバック補正係数αとも、図２８に示したように実際には演算周期毎に階段状に動く値であるが、簡単のため図２８と相違して図２９では直線で示している。また、ｔ１、ｔ３のタイミングは縦の２つの破線のうち左側の破線位置のタイミングであり、右側の破線位置のタイミングは次の演算タイミング（従って２つの破線の幅が演算周期）を表している。
【０２０４】
さて、ｔ１のタイミング以前でアクティブ較正要求フラグ＝１となっており、較正実行可能判定フラグが０より１に切換わるｔ１のタイミングでパージ率低下処理が開始される（図１３ステップ７５、７６、７７、７９）。このパージ率低下処理では、パージ率低下処理開始時の目標パージ率を初期値として所定時間当Δｔたり所定値Δずつ小さくされてゆき（図２２参照）、ｔ２で目標パージ率がゼロに達する（図２９第４段目参照）。この場合、パージ分補正係数ＦＨＯＳは目標パージ率に比例する値であるので、このように目標パージ率を低下させると、ＦＨＯＳもＦＨＯＳの中心値である１００％に向かって小さくなる（図２９第５段目参照）。
【０２０５】
ここで、パージ率低下処理はパージカットを行うための一方法であり、パージカット前であるパージ率低下処理開始時には、そのときのα、ＦＨＯＳ、ＭＰＲ、αｍ、Ｑｇが、対応するメモリα１、ＦＨＯＳ１、ＭＰＲ１、αｍ１、Ｑｇ１にパージカット前のデータとしてサンプリングされる（図２３ステップ１５１、１５２、１５３）。
【０２０６】
また、目標パージ率がゼロになるとパージカット状態となり、この状態ですぐにパージカット時のデータをサンプリングするのではなく、安定化時間が経過したｔ３のタイミングでのα、αｍが、対応するメモリα２、αｍ２にパージカット時のデータとしてサンプリングされる（図２４ステップ１６４、１６５、１６６、１６７）。
【０２０７】
これでパージカット前後のデータサンプリングが終了するので、データサンプリング終了フラグが０から１へと切換わり（図２４ステップ１６６、１６８）、このパージカット前後のデータを用いｔ４のタイミングでアクティブ較正処理が行われる。
【０２０８】
このアクティブ較正処理では、上記（５ａ）、（５ｂ）式に代えて、上記（１０）、（１１）式により全空燃比補正係数ＤＬＴと脱離量Ｄｇが算出され、このようにして得た脱離量Ｄｇより逆演算によって吸着量Ｙｒを演算し、キャニスタモデル中の吸着量のデータをこの吸着量Ｙｒに置き換える（図６ステップ１１１、１１２、１１３、１１４、１１５、１１６、１１７）。この結果、アクティブ較正処理後はパージ分補正係数ＦＨＯＳが正しく演算される。
【０２０９】
アクティブ較正処理が終了したあとは、アクティブ較正要求フラグ＝０、データサンプリングフラグ＝０となり（図６ステップ１１８、１１９）、これによって目標パージ率がパージカット前の値へと戻される（図１３ステップ７５、７６、７７、７８）。すなわち目標パージ率は、パージ率変化量制限値に従ってパージカット前の値へと徐々に戻され、この目標パージ率の増大を受けてパージ分補正係数ＦＨＯＳも中心値である１００％から離れて小さくなってゆく。このときのＦＨＯＳはアクティブ較正処理の実行によって正しく演算されるため、αがその中心値である１００％へと収束しており、パージ以外の外乱に備えることになる。
【０２１０】
また、アクティブ較正処理が終了したあとに較正実行可能となったときには先願装置と同様の較正処理であるパッシブ較正処理が行われる（図３０参照）。
【０２１１】
このようにして、本実施形態（請求項１に記載の発明）によれば、空燃比学習制御を行っているものの、何からの原因でエンジン始動直後にベース空燃比エラーが露わになっている場合には、パッシブ較正処理を継続している限りキャニスタモデルの較正にベース空燃比エラー分の誤差が生じ、これによってパージ分補正係数ＦＨＯＳが不正確にしか演算されず、これに起因して理論空燃比からの空燃比偏差が大きくなり、この空燃比偏差を小さくするために空燃比フィードバック制御が働いて空燃比フィードバック補正係数αの補正代が小さくなるのであるが、本実施形態によれば、第１リミッタよりも空燃比フィードバック補正係数αの中心値までの幅が狭い第２リミッタ±ＬＭＴ２を設定し、演算される空燃比フィードバック補正係数αと第２リミッタとの比較によりベース空燃比エラーがあるか否かを判定し、ベース空燃比エラーがあると判定した場合に較正タイミングとなったとき、パージカットを行い、キャニスタモデルに対してこのパージカット前後のデータに基づいてアクティブ較正処理（第１較正処理）を行うので、エンジン始動後にベース空燃比エラーが露わになっている場合において較正タイミングとなっても、キャニスタモデルの較正を、ベース空燃比エラーの影響を受けることなく精度良く行うことができ、これによってパージ分補正係数ＦＨＯＳの演算精度が向上すると共に、空燃比フィードバック補正係数αの補正代を無駄に使うことがない。
【０２１２】
また、運転条件が過渡的に変化するときには、ベース空燃比エラーがなくても、演算される空燃比フィードバック補正係数αが第２リミッタを含んで中心値の側に収まらないことがあり、このとき即座にベース空燃比エラーがあると判定したのでは誤判定になってしまうが、本実施形態（請求項７に記載の発明）によれば、所定値（遅れ時間）の経過後にベース空燃比エラーがあるか否かの判定を行うので（図１９ステップ１２１、１２２、１２３、１２４、１２５）、ベース空燃比エラーと通常の空燃比エラー（ベース空燃比エラーはないのに過渡などでの理論空燃比からの空燃比偏差をもつこと）との分離を行うことが可能になり、ベース空燃比エラーの判定精度が向上する。
【０２１３】
また、本実施形態（請求項８に記載の発明）によれば、ベース空燃比エラーがある場合に較正タイミングとなったときの目標パージ率を初期値として所定時間間隔で所定値ずつゼロまで低下させる処理（パージ率低下処理）を行うので、ベース空燃比エラーによる較正エラーが生じ、これに伴ってパージ分補正係数ＦＨＯＳが正しく演算されていない場合においても急激に目標パージ率を低下させることがなく、かつ空燃比フィードバック制御が可能な範囲で目標パージ率を変化させることができる。
【０２１４】
また、アクティブ較正処理によれば、キャニスタモデルの状態の推定をベース空燃比の影響を受けずに精度良く行うことが可能であるため、アクティブ較正処理の結果をパージ処理が終了していることを確認するために用いることができる。すなわち、エンジン始動後初めての較正タイミングでアクティブ較正処理が行われた後は、キャニスタモデルにより演算される脱離量Ｄｇが精度の良いものとなり、これによって積算パージ流量ＳＱＰと比較するための判定値ＳＬＳＱＰが正確に演算されるため、パージ処理が終了したか否かの判定精度が向上する（図１６ステップ９２、１００〜１０８）。
【０２１５】
空燃比学習制御の精度を向上させるためには、パージなどの外乱要因を取り除いた状態で行うことが望ましい。一方、燃料タンク２１から発生する蒸発燃料の処理を行うためにパージ処理は必要であり、始動直後より可能な限り大量のパージ処理を行うことが車両から大気へのパージ燃料の放出防止につながる。このように空燃比学習制御とパージ処理の２つの制御は相反する要求を持つが、パージ燃料を十分に処理できた時点においてはパージ率（パージ流量）を必要最低限の値に保持し（図１３ステップ８０、８１、図２５）、空燃比学習値の更新を行うことで（図２６ステップ１７１〜１７３、図２７ステップ１８１〜１８３）、空燃比学習制御の精度の保証を行うことができている。
【０２１６】
このように、本実施形態（請求項９に記載の発明）によれば、アクティブ較正処理の結果をパージ処理の終了判定に活かすことで、パージ処理終了判定の精度を高め、このようにして高い精度でパージ終了判定を行った後で、パージ率を小さくして空燃比学習値の更新を行うので、空燃比学習制御の精度向上と始動直後よりの大量のパージ処理とを両立させることができる。
【０２１７】
さらに、キャニスタ２４からの燃料の脱離特性は、キャニスタ内の燃料吸着剤（活性炭等）の温度の影響を受けるので、脱離量演算式は吸着剤温度と脱離量の関係を考慮した式とする（請求項１５に記載の発明）。脱離量が多い領域では脱離量の演算誤差が排気空燃比に及ぼす影響が大きく特に高い演算精度が要求され、しかも、キャニスタ２４からの燃料の脱離現象が吸熱反応であるため、大量の脱離が行われるときはキャニスタ内の吸着剤温度が低下し脱離特性も変化する。そのため、吸着剤温度と脱離量の関係を考慮しないと脱離量が多い領域では脱離量の演算精度が低下するが、吸着剤温度も考慮に入れて脱離量を演算するようにキャニスタモデルを構成すれば、脱離量の演算精度の悪化を抑え、演算精度の悪化に起因する排気エミッション悪化等を防止できる。
【０２１８】
なお、吸着燃料量とパージ率と吸着剤温度とに基づき脱離燃料量を演算する脱離量演算式としては、フロイントリッヒ（Freundlich）の式をベースにキャニスタ２４の脱離現象に応用した式を用いることができる。また、吸着剤温度はキャニスタ２４からの燃料の脱離量に基づき吸着剤温度の降下量を求めることによって求めることができる（請求項１６に記載の発明）。
【０２１９】
また、本実施形態（請求項１１に記載の発明）によれば、ベース空燃比エラーがない場合に較正タイミングとなったとき、キャニスタモデルに対してパージ実行中のデータに基づくパッシブ較正処理（第２較正処理）も行われる。キャニスタモデルは近似モデルであり、それによって演算される値は幾らかの誤差を含んだものとなり、また、キャニスタモデルは前回値を用いて新たな値を演算するため、その動作時間が長くなるにつれ誤差が積分され大きくなるが、このようなパッシブ較正処理を行うことで誤差を適宜修正し、高い演算精度を保つことができる。なお、このパッシブ較正処理は、理論空燃比からの空燃比偏差から推定される脱離量から吸着量を逆算し、内部変数の吸着量をこの逆算された吸着量で較正するというものであり、特殊なシーケンスを踏む必要が無く、パージ率を落とす必要もない。なお、吸着量はキャニスタモデルにおける脱離量演算式の逆演算によって求めることができる（請求項１７に記載の発明）。
【０２２０】
上記較正処理はパージ以外の外乱による理論空燃比からの空燃比偏差が生じないときに行われ、理論空燃比からの空燃比偏差を全てパージによるものとみなしてキャニスタからの燃料の脱離量を推定し、この推定脱離量から逆算したキャニスタ２４の実吸着量に基づき較正が行われるので、較正処理の精度が確保できる（請求項１８に記載の発明）。
【０２２１】
また、本実施形態（請求項１９、２０に記載の発明）によれば、脱離量の演算精度を高めるべく、較正処理はパージによる理論空燃比からの空燃比偏差が比較的大きなとき（パージ率が高く、パージ空燃比が濃いとき）に行われる。運転領域によっては十分な較正処理の演算精度が得られない場合があるが、このように十分な精度が得られる領域のみで較正処理を実行することにより、較正処理の精度を向上させ、キャニスタモデルの精度をさらに向上させることができる。
【０２２２】
以上、本発明の実施の形態について説明したが、上記実施形態の構成は本発明が適用される構成の一例を示したものであり、本発明の範囲を上記構成に限定するものではない。上述した通り、上記実施形態においては、キャニスタモデルによるパージ処理が可能となるまでは、図１６に示したパージ処理が補助的に実行されるが、図１６に示したパージ処理を継続して用いるようにしてもよい。
【図面の簡単な説明】
【図１】本発明に係る蒸発燃料処理装置の全体構成図。
【図２】エンジンコントローラにおけるパージ処理の概要を示したブロック図。
【図３】キャニスタモデルの構成を示したブロック図。
【図４】パージ分補正係数の演算を説明するためのフローチャート。
【図５】較正処理可能条件を示したフローチャート。
【図６】較正処理を説明するためのフローチャート。
【図７】キャニスタモデルに基づく脱離量の演算を説明するためのフローチャート。
【図８】遅れ補正を説明するためのフローチャート。
【図９】吸入空気流量と無駄時間の関係を示す特性図。
【図１０】吸入空気流量となまし係数の関係を示す特性図。
【図１１】遅れ補正における無駄時間処理の概要を示した図。
【図１２】目標パージ率の設定を説明するためのフローチャート。
【図１３】目標パージ率の設定を説明するためのフローチャート。
【図１４】吸入空気流量及びパージ率に対するパージ空燃比誤差の関係を示す特性図。
【図１５】パージ空燃比に対するパージ空燃比誤差の関係を示す特性図。
【図１６】ブートアップ制御を説明するためのフローチャート。
【図１７】空燃比フィードバック偏差の差（＝目標空燃比フィードバック偏差−実空燃比フィードバック偏差）とパージ率変化量の関係を示す特性図。
【図１８】パージ空燃比に対するパージ終了判定値の関係を示す特性図。
【図１９】アクティブ較正要求フラグの設定を説明するためのフローチャート。
【図２０】パージ用下限リミッタ判定フラグの設定を説明するためのフローチャート。
【図２１】パージ用上限リミッタ判定フラグの設定を説明するためのフローチャート。
【図２２】パージ率低下処理を説明するための波形図。
【図２３】パージ率低下処理を説明するためのフローチャート。
【図２４】パージ率低下処理を説明するためのフローチャート。
【図２５】パージ終了が判定されたときの目標パージ率の変化を示す波形図。
【図２６】空燃比学習開始フラグの設定を説明するためのフローチャート。
【図２７】空燃比学習値の更新を説明するためのフローチャート。
【図２８】正常に較正が行われたときと較正エラーがあるときとを比較して説明するための波形図。
【図２９】アクティブ較正処理の内容を示す波形図。
【図３０】パッシブ較正処理の内容を示す波形図。
【図３１】較正処理の概要を示したブロック図。
【符号の説明】
４ 燃料噴射弁
５ 排気通路
８ 吸気通路
１１ エンジンコントローラ
１３ エアフローメータ
１５ 空燃比センサ（空燃比検出手段）
２１ 燃料タンク
２２ 配管
２４ キャニスタ
２６ 配管
２７ パージバルブ[0001]
[Industrial application fields]
The present invention relates to an air-fuel ratio control device for an engine, and more particularly to a device provided with an evaporated fuel processing device.
[0002]
[Prior art]
The engine once adsorbs the evaporated fuel generated in the fuel tank while the engine is stopped to the activated carbon in the canister, and uses the intake pipe pressure (pressure lower than atmospheric pressure) under the predetermined operating conditions after engine startup. The fuel adsorbed by the activated carbon is desorbed and introduced into the intake passage downstream of the intake throttle valve, and an evaporative fuel treatment device is provided for combustion treatment (see Japanese Patent Laid-Open No. 7-166978).
[0003]
In the following, “purge” or “purge process” refers to desorbing the fuel adsorbed by the canister and supplying it to the engine, “purge fuel” as the fuel desorbed from the canister, and not only the purge fuel but also the purge fuel. The fresh air supplied to the engine is sometimes referred to as “purge gas”.
[0004]
In such a conventional apparatus, the influence of the purge on the exhaust air / fuel ratio is treated as a disturbance, and even if the exhaust air / fuel ratio deviates from the theoretical air / fuel ratio due to the disturbance, the oxygen concentration sensor provided in the exhaust passage is used. Air-fuel ratio feedback control is performed to return the exhaust air-fuel ratio to the stoichiometric air-fuel ratio, so that the conversion efficiency of the three-way catalyst provided in the exhaust passage is not lowered.
[0005]
[Problems to be solved by the invention]
By the way, since the change of the air-fuel ratio feedback correction coefficient α (air-fuel ratio feedback correction amount) due to the supply of purge fuel to the engine can be predicted, the predictable air-fuel ratio feedback correction coefficient α is set to the purge correction coefficient FHOS (purge And a basic value of the amount of fuel supplied to the engine with this purge correction coefficient FHOS so that the air-fuel ratio deviation from the theoretical air-fuel ratio due to the purge becomes small,
(1) an expression for calculating the amount of fuel adsorbed by the canister;
(2) an equation for calculating the amount of fuel desorbed from the canister based on the amount of adsorbed fuel and the target purge rate;
An apparatus that estimates the amount of fuel desorbed from the canister using a canister model configured as follows, and calculates the purge correction coefficient FHOS based on the desorbed fuel amount, the target purge rate, and the intake air mass Has been previously proposed by the same applicant as the present application (see Japanese Patent Application No. 2001-71562).
[0006]
According to the purge process (model reference purge process) by this prior application apparatus, the disturbance due to the purge is exclusively handled by the purge correction coefficient FHOS, and there is no base air-fuel ratio error and the FHOS is accurately calculated. For example, even if the purge process is performed before the air-fuel ratio feedback control is started, the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio. That is, when the air-fuel ratio feedback control condition is satisfied during the purge process and the air-fuel ratio feedback control is started, the air-fuel ratio feedback correction coefficient α moves as if there is no purge.
[0007]
For the air-fuel ratio feedback correction coefficient α, a first limiter that determines the limit of the correction allowance is provided in advance, for example, ± 25%, and α is increased from 100%, which is the central value of α, to 125% (upper limiter). Side full correction allowance, and 75% (lower limiter) from 100% is the full correction allowance for reducing α. According to the conventional apparatus, the influence of the purge on the exhaust air / fuel ratio is controlled by air / fuel ratio feedback. Since the correction coefficient α compensated, the correction amount of α with respect to the disturbance was reduced accordingly, but according to the prior application device, the air-fuel ratio feedback correction coefficient α becomes free for purging, and α Can be fully used for disturbances other than purge.
[0008]
In addition, by setting the maximum purge rate within a certain limit range depending on the flow rate of the purge valve as the target purge rate, a large amount of purge can be performed earlier than immediately after the engine is started.
[0009]
However, since the canister model is an approximate model to the last, values (desorption amount, adsorption amount, etc.) calculated using this can be somewhat deviated from actual values. Since the canister model is a recurrence formula as will be described later, the error is integrated as the operation time of the canister model becomes longer, and the deviation between the calculated value and the actual value increases. Therefore, in order to eliminate this shift and maintain high calculation accuracy of the canister model, at the calibration timing, the value of the adsorption amount of the canister, which is one of the internal variables of the canister model, is calibrated based on the data being purged. is doing.
[0010]
On the other hand, the deviation of the base air-fuel ratio from the stoichiometric air-fuel ratio due to aging deterioration and variation of components such as the air flow meter and fuel injection valve, and the non-linearity of the injection pulse width-flow characteristic of the fuel injection valve is referred to as the base air-fuel ratio error. In order to eliminate this base air-fuel ratio error, air-fuel ratio learning control is performed during the stoichiometric operation (when the stoichiometric air-fuel ratio is the target air-fuel ratio).
[0011]
When such air-fuel ratio learning control is combined with the purge processing of the prior application device that performs a large amount of purge immediately after the engine is started, the following problem occurs. That is, even if there is a base air-fuel ratio error, if the air-fuel ratio learning control is operating normally, the base air-fuel ratio error is absorbed by the air-fuel ratio learning value, so that the base air-fuel ratio error does not exist, If there is a significant base air-fuel ratio error immediately after the engine is started for some reason, there may be a case where the correction allowance is not sufficient by the correction allowance by the air-fuel ratio feedback correction coefficient α and cannot be corrected. If it cannot be corrected, exhaust emissions will deteriorate.
[0012]
On the other hand, since purging is required to flow in a large amount after starting for the purpose of reducing deterioration of exhaust emission due to purging, it is desirable to start the purging process early as in the prior application apparatus.
[0013]
Accordingly, when the calibration timing comes after starting a large amount of purge immediately after starting in a state where the base air-fuel ratio error has occurred, the calibration process is performed assuming that the base air-fuel ratio error is also due to the purge. Therefore, a large calibration error is generated by the base air-fuel ratio error, and the purge correction coefficient FHOS is not accurately calculated. That is, an error also occurs in the purge correction factor FHOS due to the influence of the calibration error accompanying the base air-fuel ratio error. Even if the error occurs in the purge correction factor FHOS in this way, the air-fuel ratio feedback control is performed. If medium, the air-fuel ratio deviation from the stoichiometric air-fuel ratio due to purge is eliminated by the air-fuel ratio feedback correction coefficient α.
[0014]
This is based on the fact that according to the prior application device, the correction amount of the air-fuel ratio feedback correction coefficient α should be fully usable by compensating the influence of the purge on the exhaust air-fuel ratio by the purge correction coefficient FHOS. If an error occurs in the purge correction coefficient FHOS due to the calibration error in the state where the air-fuel ratio error is exposed, it means that the correction margin for the air-fuel ratio feedback correction coefficient α becomes narrow again.
[0015]
Therefore, the present invention is based on the premise that the second limiter is used as a purge limiter between the central value of the air-fuel ratio feedback correction coefficient α and the limiter (first limiter) for the original air-fuel ratio feedback correction coefficient α. And determining whether or not there is a base air-fuel ratio error by comparing the calculated air-fuel ratio feedback correction coefficient α and the second limiter, and when it is determined that there is a base air-fuel ratio error, the calibration timing is reached When the base air-fuel ratio error is exposed immediately after starting by performing a purge cut and performing a calibration process (first calibration process) on the canister model based on the data before and after the purge cut. Even when timing comes, the accuracy of canister model calibration is improved by eliminating the effect of base air-fuel ratio error. Keeping (calculation accuracy FHOS also kept high) that is an object.
[0016]
[Means for solving problems]
According to the first aspect of the present invention, the air-fuel ratio detection means for detecting the air-fuel ratio in the exhaust gas and the air-fuel ratio feedback correction amount are set so that the exhaust air-fuel ratio detected by the air-fuel ratio detection means matches the stoichiometric air-fuel ratio. Air-fuel ratio feedback correction amount calculating means for calculating; first limiter setting means for setting a first limiter having a predetermined width from the center value of the air-fuel ratio feedback correction amount; From the center value 1st limiter This first upper limit limiter is exceeded when the first upper limit limiter is exceeded, and when the air-fuel ratio feedback correction amount is less than the first lower limiter that is smaller than the center value by the first limiter, the first lower limiter is exceeded. In An air-fuel ratio feedback correction amount limiting means for limiting the calculated air-fuel ratio feedback correction amount, and an air-fuel ratio feedback correction means for correcting the amount of fuel supplied to the engine with the limited air-fuel ratio feedback correction amount. In the air-fuel ratio control device, a canister that adsorbs the evaporated fuel generated in the fuel tank, a purge valve that opens and closes a pipe that connects the canister and the intake passage of the engine, and a purge valve control that controls the purge valve so as to obtain a target purge rate Means,
at least,
(A) an adsorbed fuel amount calculation formula for calculating the amount of fuel adsorbed to the canister based on the previous value of the fuel amount adsorbed on the canister and the previous value of the amount of fuel desorbed from the canister;
(B) a desorbed fuel amount calculation formula for calculating a fuel amount desorbed from the canister based on the adsorbed fuel amount calculation formula and the target purge rate;
A canister model consisting of
Purge amount correction that calculates the purge amount correction amount based on the desorbed fuel amount calculated using the canister model so that the air-fuel ratio deviation from the theoretical air-fuel ratio becomes smaller by performing the purge process at the target purge rate An amount calculation means, a purge amount correction means for correcting the amount of fuel supplied to the engine by the purge amount correction amount, a calibration timing determination means for determining whether or not it is a calibration timing, and an air-fuel ratio feedback from the first limiter A base air-fuel ratio for determining whether or not there is a base air-fuel ratio error by comparing the second limiter with a means for setting the second limiter having a narrow range to the center value of the correction amount, and the calculated air-fuel ratio feedback correction amount An error determination means, and a purge cut means for performing a purge cut when the calibration timing comes when there is a base air-fuel ratio error from the determination result; And a first calibration processing means for performing first calibration processing based on the purge cut before and after the data to Yanisutamoderu.
[0017]
[Action and effect]
If the base air-fuel ratio error is exposed immediately after starting the engine, it rarely occurs, but in that rare case it was outside the scope of consideration in the prior application device, so in that rare case calibration As long as the calibration process (second calibration process) of the prior application device continues, the calibration error associated with the base air-fuel ratio error cannot be eliminated from the calibration process. Since the purge correction amount cannot be calculated correctly due to the calibration error, the air-fuel ratio deviation from the stoichiometric air-fuel ratio becomes large, and the correction amount of the air-fuel ratio feedback correction amount becomes narrow to reduce this air-fuel ratio deviation. On the other hand, according to the first aspect of the present invention, when the base air-fuel ratio error is exposed immediately after the engine is started, the purge cut is performed when the calibration timing comes, and the canister model is Since the first calibration process is performed based on the data before and after the purge cut, the canister model can be calibrated at the calibration timing when the base air-fuel ratio error is exposed after the engine is started. This can be performed with high accuracy without being affected by an error, thereby improving the calculation accuracy of the purge correction amount and not wastefully using the correction allowance for the air-fuel ratio feedback correction amount.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0019]
FIG. 1 shows the overall configuration of an engine equipped with an evaporative fuel processing device.
[0020]
Reference numeral 1 denotes an engine body. A fuel injection valve 4 is provided for each cylinder in the intake passage 2 downstream of the intake throttle valve 3, and a predetermined air-fuel ratio is set according to an operating condition by an injection signal from the engine controller 11. Thus, fuel is injected and supplied during intake. More specifically, a signal from the crank angle sensor 12, a signal of the intake air flow rate from the air flow meter 13, a signal of the engine cooling water temperature from the water temperature sensor 14, etc. are input to the engine controller 11 mainly composed of a microcomputer, and the engine Based on these signals, the controller 11 calculates a basic injection pulse width Tp that provides a basic air-fuel ratio (theoretical air-fuel ratio), and performs various corrections such as an increase in water temperature to obtain the fuel injection pulse width Ti. The fuel injection valve 4 is opened for a period corresponding to this Ti at a predetermined timing.
[0021]
The exhaust passage 5 is provided with a three-way catalyst (not shown). The three-way catalyst reduces NOx in the exhaust gas and oxidizes HC and CO with maximum conversion efficiency when the air-fuel ratio in the exhaust gas is in a narrow range centered on the stoichiometric air-fuel ratio. Therefore, the engine controller 11 calculates the air-fuel ratio feedback correction coefficient α so that the air-fuel ratio in the exhaust detected by the air-fuel ratio sensor 15 matches the stoichiometric air-fuel ratio, and this air-fuel ratio feedback correction coefficient α (air-fuel ratio feedback) The air-fuel ratio feedback control is performed by correcting the basic injection pulse width Tp (basic value of the amount of fuel supplied to the engine) with the correction amount).
[0022]
In this case, with respect to the air-fuel ratio feedback correction coefficient α, a first limiter ± LMT1 (± 25%) having a predetermined width around the center value (100%) of α as a range in which α can move is provided in advance. When the calculated α becomes larger than the center value and exceeds the upper limit limit 100 + LMT1, the upper limit limiter is used. Limited.
[0023]
In addition, in order to eliminate the base air-fuel ratio error caused by the aging deterioration and variation of components such as the air flow meter 13 and the fuel injection valve 4 and the non-linearity of the injection pulse width-flow rate characteristic of the fuel injection valve 4, the engine controller 11 The air-fuel ratio learning control is performed during stoichiometric operation (when the stoichiometric air-fuel ratio is the target air-fuel ratio).
[0024]
On the other hand, the evaporative fuel processing device is for processing evaporative fuel generated in the fuel tank 21. The evaporative fuel generated in the fuel tank 21 is a canister 24, a pipe 22 communicating the canister 24 and the fuel tank 21, and the canister 24 and the intake throttle valve 3 of the engine. A pipe 26 that communicates with the downstream intake passage 2 and a purge valve 27 that opens and closes the pipe 26 are provided.
[0025]
The evaporated fuel generated in the fuel tank 21 is guided to the canister 24 via the pipe 22, and only the fuel component is adsorbed by the fuel adsorbent (activated carbon) 24 a in the canister 24, and the remaining air is supplied from the atmosphere release port 25. Released to the outside. In order to combust the fuel adsorbed on the activated carbon 24a, the purge valve 27 is opened, and fresh air is introduced into the canister 24 from the atmosphere opening 25 using the intake pipe pressure (pressure lower than the atmosphere) developed downstream of the intake throttle valve 3. Is introduced. As a result, the fuel adsorbed on the activated carbon 24a by the fresh air is desorbed and introduced into the intake passage 2 of the engine 1 through the pipe 26 together with the fresh air.
[0026]
When performing processing (purge processing) in which the fuel adsorbed on the canister 24 is desorbed and supplied to the engine (purge processing), the engine controller 21 uses the target purge rate as high as possible without deteriorating the combustion stability and exhaust emissions of the engine. The ratio of the purge flow rate to the intake air flow rate is set, and the opening degree of the purge valve 27 is controlled so that the target purge rate is realized after the engine is started.
[0027]
Further, after the purge process is started, the purge becomes a disturbance and an air-fuel ratio deviation from the stoichiometric air-fuel ratio occurs. Since the exhaust air-fuel ratio deviates to the rich side from the stoichiometric air-fuel ratio at the beginning of the purge, the air-fuel ratio feedback correction coefficient α moves to a side smaller than the center value until the deviated air-fuel ratio returns to the stoichiometric air-fuel ratio. The target purge rate is set as high as possible after the start, and when a large amount of purging is performed, α moves close to 75%, which is the lower limiter of α.
[0028]
In this case, if a disturbance other than purge occurs and the exhaust air / fuel ratio deviates from the stoichiometric air / fuel ratio and becomes richer, α moves to a smaller side, but immediately reaches the lower limiter and decreases further. Don't be. In other words, since the α correction amount for reducing α to the disturbance caused by the purge is almost used up, there is little correction fee remaining for the disturbance other than the purge. Even if it is used, if the exhaust air-fuel ratio cannot be returned to the stoichiometric air-fuel ratio, the exhaust emission deteriorates.
[0029]
For this reason, the engine controller 11 estimates the amount of fuel desorbed from the canister using a canister model, which will be described later, and a purge correction coefficient based on the estimated amount of desorbed fuel Dg, target purge rate, and intake air mass By calculating FHOS and correcting the basic injection pulse width Tp with this purge correction coefficient FHOS, even if a large amount of purge is performed with a target purge rate set as high as possible after engine startup, the theoretical air-fuel ratio The air-fuel ratio deviation from That is, since the purge correction coefficient FHOS compensates for the influence of the purge on the exhaust air / fuel ratio, the air / fuel ratio feedback correction coefficient α behaves in the same manner as when there is no purge, and thus α is caused by the purge. It is not necessary to use a correction allowance for the disturbance, and the correction allowance remains full, and has strong robustness against disturbances other than purge.
[0030]
As will be described later, a change in the air-fuel ratio feedback correction coefficient α can be predicted by supplying the desorption amount Dg calculated by the canister model to the engine. This predicted α is a purge correction coefficient FHOS. is there. Therefore, the predicted α increases as the target purge rate increases, increases as the desorption amount Dg increases, and decreases as the intake air mass Qg increases. Therefore, the purge correction coefficient FHOS increases as the target purge rate increases, increases as the desorption amount Dg increases, and decreases as the intake air mass Qg increases.
[0031]
In addition, it is necessary to perform a calibration process on the canister model, which causes a calibration error. The biggest factor causing calibration errors is due to base air-fuel ratio errors. This is because when the canister model calibration process is performed, it is assumed that the air-fuel ratio deviation from the stoichiometric air-fuel ratio is caused by the purge, even if the air-fuel ratio learning control is performed. If, for some reason, the base air-fuel ratio error is exposed immediately after the engine is started and the calibration timing is reached, the calibration process is performed and the amount of change in the air-fuel ratio feedback correction coefficient α due to the base air-fuel ratio error This is because the calibration process is performed as if it were a purge.
[0032]
Therefore, the engine controller 11 sets the second limiter ± LMT2 whose width to the center value of the air-fuel ratio feedback correction coefficient α is narrower than the first limiter ± LMT1, and calculates the calculated air-fuel ratio feedback correction coefficient α and the second limiter. It is determined whether or not there is a base air-fuel ratio error by comparing the above, and when it is determined that there is a base air-fuel ratio error, when the calibration timing comes, it is not the same calibration process as the prior application device, but the base air-fuel ratio error Perform a new calibration process in an unaffected way.
[0033]
A bypass valve 29 that bypasses the vacuum cut valve 23 that opens when the passage on the fuel tank 21 side becomes lower than atmospheric pressure is provided in the pipe 22, and a pressure sensor 30 that measures the pressure in the pipe is provided in the pipe 26. Further, a drain cut valve 28 is provided at the air release port 25 of the canister 24, but these are necessary for the diagnosis of the evaporation processing apparatus and are not directly related to the purge processing.
[0034]
Such control performed by the engine controller 11 will be first outlined with reference to the block diagrams shown in FIGS.
[0035]
FIG. 2 is a block diagram showing an outline of a portion related to purge processing and air-fuel ratio control. In FIG. 2, the target purge rate setting unit B1 calculates the maximum purge rate that can be set in the current operation region based on the performance limit of parts related to the purge process, and sets the target purge rate to follow this maximum purge rate. Set. However, sudden changes in the purge rate cause large fluctuations in the exhaust air / fuel ratio (increase in the air / fuel ratio deviation from the theoretical air / fuel ratio) and cause deterioration of exhaust emissions, etc., so the purge rate is not changed rapidly. Thus, the change amount of the purge rate is limited to a predetermined amount (purge rate change amount limit value) or less.
[0036]
Further, the duty ratio calculation unit B2 calculates the duty ratio of the purge valve 27 necessary for realizing the target purge rate, and the purge valve drive unit B3 drives the purge valve 27 with the duty ratio calculated by the duty ratio calculation unit B2.
[0037]
On the other hand, in the desorption amount calculation unit B4, the amount of fuel desorbed from the canister 24 when purging at the target purge rate using a physical model of the canister 24 (hereinafter referred to as “canister model”) which will be described later. Is calculated.
[0038]
In the purge correction coefficient calculation unit B5, the purge correction coefficient is calculated so that the deviation of the air-fuel ratio from the theoretical air-fuel ratio caused by the purge is reduced based on the estimated desorption amount (desorbed fuel amount), the target purge rate, and the intake air flow rate. Calculate FHOS. The delay correction unit B6 applies a delay correction including a dead time correction and a smoothing process in consideration of the intake air flow rate to the purge correction coefficient FHOS, and the correction coefficient after the delay correction is changed to a purge correction coefficient FHOS. .
[0039]
The basic injection pulse width calculation unit B7 calculates the basic injection pulse width Tp from the intake air flow rate and the engine speed, and the air-fuel ratio feedback correction coefficient calculation unit B8 calculates the air-fuel ratio feedback correction coefficient α based on the actual exhaust air-fuel ratio. In the fuel injection pulse width calculation unit B9, various corrections and corrections using the air-fuel ratio feedback correction coefficient α are performed on the basic injection pulse width Tp as described above, and the purge correction coefficient FHOS after delay correction is used. Correction is performed to calculate the final fuel injection pulse width Ti. The fuel injection valve drive unit B10 drives the fuel injection valve 4 with the fuel injection pulse width Ti calculated in this way.
[0040]
As shown in FIG. 3, the canister model includes an adsorption amount calculation unit B21, a reference desorption amount calculation unit B22, a purge flow rate equivalent desorption amount calculation unit B23, and an activated carbon temperature calculation unit B24. Each calculation is performed every time.
[0041]
The adsorption amount calculation unit B21 calculates the current value Y of the fuel amount adsorbed by the canister 24 by the following formula.
[0042]
[Adsorption amount calculation formula]
Y = Yz−Dgz (1)
Where Y: current value of adsorption amount,
Yz: previous value of adsorption amount,
Dgz: previous value of desorption amount,
This adsorption amount calculation formula calculates the current (current) adsorption amount Y [g] by subtracting Dgz which is the fuel amount desorbed last time from the previous value Yz of the adsorption amount (adsorbed fuel amount).
[0043]
The reference desorption amount calculation unit B22 calculates the desorption amount Dgk [g] at the reference purge flow rate by the following equation.
[0044]
[Desorption amount calculation formula at the reference purge flow rate]
Dgk = (Y / A) ^ n (T) (2)
Where Y: adsorption amount,
A: Desorption constant,
n (T): Desorption index,
T: Activated carbon temperature,
This formula applies the concept of adsorption / desorption phenomenon (Freundlich's formula) to the fuel desorption phenomenon from the canister 24, and thereby expresses the fuel desorption characteristics from the canister 24 almost accurately. The Freundlich formula is described in “Theory on the Surface II” (Maruzen, Tsukada), p.25-p.27, p.108-p.115.
[0045]
The purge flow equivalent desorption amount calculation unit B23 calculates the desorption amount Dg [g] from the following equation.
[0046]
[Desorption calculation formula according to purge flow rate]
Dg = K × PQ × Dgk (3)
Where K is a constant,
PQ: purge flow rate (= target purge rate × intake air flow rate),
Dgk: Desorption amount at the reference flow rate,
The desorption amount calculation formula corresponding to the purge flow rate PQ is to calculate the desorption amount by linear approximation since the purge flow rate PQ and the desorption amount are substantially proportional. Here, the desorption amount Dgk at the reference flow rate is obtained from the equation (2), and the desorption amount Dg is calculated by multiplying this by the purge flow rate PQ in the equation (3), but the equation (2) , (3) may be combined into one expression.
[0047]
The activated carbon temperature calculation unit B24 calculates the activated carbon temperature T [K] by the following equation.
[0048]
[Activated carbon temperature calculation formula]
T = Tz−Kt1 × (Yz2−Yz) + Kt2 × (Tz−Ta) (4)
Where T: current value of activated carbon temperature,
Tz: previous value of activated carbon temperature,
Kt1: endothermic coefficient,
Yz2: value before and after adsorption amount,
Yz: previous value of adsorption amount,
Kt2: heat transfer coefficient,
Ta: Canister ambient temperature,
This activated carbon temperature calculation formula includes the past temperature (first term on the right side), a temperature drop proportional to the desorption amount (Yz2-Yz) (second term on the right side), and a temperature rise due to heat transfer (third on the right side). Item). The activated carbon temperature T is calculated in this way because the desorption index n (T) in the equation (2) is affected by the activated carbon temperature T, and particularly when the desorption amount is large, the decrease in the activated carbon temperature T is large. This is because the influence on the fuel desorption characteristics in the canister 24 cannot be ignored.
[0049]
Therefore, the canister model is composed of the above four expressions (1) to (4), and when the expressions (2) and (3) are combined, the canister model is composed of three expressions.
[0050]
Returning to FIG. 2, the canister model expresses the desorption characteristics of the canister with high accuracy as described above. However, since the canister model is an approximate model, values calculated using the canister model (desorption amount, adsorption amount, etc.) ) Is slightly different from the actual value. Further, since the canister model is a recurrence formula using the previous calculation result as shown in the above equation (1), the error is integrated as the model operation time becomes longer, and the deviation between the calculated value and the actual value increases. To do.
[0051]
Therefore, in order to calibrate this deviation and maintain high calculation accuracy of the canister model, when the calibration timing determination unit B11 determines that the calibration processing is possible, the calibration processing unit B12 is one of the internal variables of the canister model. The adsorption amount value of the canister 4 is calibrated. Specifically, as shown in FIG. 31, in the calibration timing determination unit B11, almost all deviations from the center value (100%) of the air-fuel ratio feedback correction coefficient α during the air-fuel ratio feedback control are considered to be due to the purge. When the condition that can be performed is satisfied, it is determined that the calibration process can be executed, and the switch B13 is turned on. The data sampling unit B32 corrects the air-fuel ratio feedback correction coefficient α and the purge amount at that timing (during the purge process). The coefficient FHOS, the target purge rate MPR, and the intake air mass Qg are read, the desorption amount calculation unit B33 estimates the amount of fuel desorption from the canister 24 based on these purge execution data, and the adsorption amount calculation unit B34 The adsorption amount is calculated backward from the estimated desorption amount. And the calibration part B35 calibrates the value of the adsorption amount that the canister model has with this value.
[0052]
On the other hand, when the base air-fuel ratio error is exposed immediately after the engine is started for some reason even though the air-fuel ratio learning control unit B16 (see FIG. 2) is provided, the calibration timing has been reached. Similar to the prior application device, when the calibration process based on the data being purged is performed (this calibration process is hereinafter referred to as “passive calibration process”), the amount of change in the air-fuel ratio feedback correction coefficient α due to the base air-fuel ratio error is also increased. In this embodiment, the calibration process based on the data before and after the purge cut (hereinafter referred to as “active calibration”) is performed separately from the passive calibration processing unit B31 including the blocks B32 to B35. An active calibration processing unit B41 that performs “calibration processing”) is additionally provided.
[0053]
Here, the active calibration processing unit B41 includes a pre-purge-cut data sampling unit B42, a purge-cut data sampling unit B43, a desorption amount calculation unit B44, an adsorption amount calculation unit B45, and a calibration unit B46, and the active calibration processing unit B41. Are provided with a base air-fuel ratio error determination unit B36, an active calibration request unit B37, an AND circuit B38, a purge rate reduction processing unit B39, and changeover switches B40 and B47.
[0054]
That is, the base air / fuel ratio error determination unit 36 determines whether or not there is a base air / fuel ratio error based on the air / fuel ratio feedback correction coefficient α and the second limiter ± LMT2, and when it determines that there is a base air / fuel ratio error, it is active. The calibration request unit B37 outputs a high level signal to the AND circuit B38. In the AND circuit B38, only when the signal from the active calibration request unit B37 is at a high level and the signal from the calibration timing determination unit is at a high level, the two changeover switches B40 and B47 are moved from the illustrated state to the opposite side. Switch.
[0055]
The purge rate reduction processing unit 39 performs a process of setting the target purge rate MPR immediately before switching of the changeover switch B40 to an initial value and decreasing it by a predetermined value per predetermined time to finally make the target purge rate zero. The target purge rate that decreases in this way is output to the changeover switch 15 via the changeover switch B40 after the changeover of the changeover switch B40.
[0056]
In the purge rate reduction process by the purge rate reduction processing unit 39, when the purge rate reduction process is started, the pre-purge cut data sampling unit B42 at that time has the air / fuel ratio feedback correction coefficient α, the air / fuel ratio learning value αm, and the purge correction coefficient FHOS. The target purge rate MPR and the intake air mass Qg are sampled as data before purge cut. When the target purge rate MPR becomes zero by the purge rate reduction process, the purge cut time data sampling unit B43 samples α and αm at that time as purge cut data.
[0057]
Detachment amount The calculation unit B44 estimates the amount of fuel desorption from the canister 24 using the data before and after the purge cut, and the adsorption amount calculation unit B45 calculates the adsorption amount from the estimated desorption amount. After the changeover switch B47 is switched, the calibration unit B46 calibrates the suction amount value of the canister model with this back-calculated value via the changeover switch B47.
[0058]
Hereinafter, specific contents of the purge process and air-fuel ratio control performed by the engine controller 11 will be described with reference to the flowcharts.
[0059]
FIG. 4 is for calculating the purge correction coefficient, and is executed at regular intervals (for example, every 10 msec).
[0060]
In step 1, it is determined whether or not a purge permission condition is satisfied. If the purge permission condition is not satisfied, the process proceeds to step 2 where the purge correction coefficient FHOS = 1.0 and the current process is terminated. Note that step 1 may be omitted, and the determination in step 3 may be executed immediately after starting.
[0061]
When the purge permission condition is satisfied, the process proceeds to step 3 to determine whether or not it is a timing at which the calibration process of the adsorption amount, which is an internal variable of the canister model, can be executed. When the disturbance due to factors other than purge is small and the influence of the purge on the air-fuel ratio feedback correction coefficient α is relatively large, that is, almost all deviations from the center value of the air-fuel ratio feedback correction coefficient α can be regarded as the influence of the purge. If it is possible, it is determined that the calibration processing can be executed.
[0062]
Specifically, if all of the “steady condition”, “purge valve accuracy condition”, and “purge influence condition” shown in FIG. If any one of them is not established, it is determined that the calibration process cannot be executed. This determination process corresponds to the process in the calibration timing determination unit B11 in FIG.
[0063]
As shown in FIG. 5, “steady-state conditions” include misfire conditions (the engine has not misfired), fuel cut conditions (no fuel cut), blow-by conditions (no blow-by gas), EGR condition (exhaust gas recirculation rate is constant), intake throttle valve opening area and engine rotation speed condition (intake throttle valve opening area, engine rotation speed are constant), purge rate condition (purge rate is constant) )) Is set. When all of these conditions are satisfied and it is determined that the disturbance other than the purge is small, it is determined that the steady condition is satisfied.
[0064]
Further, as the “purge valve accuracy condition”, a purge flow rate condition (the purge flow rate is a predetermined amount or more) is set. When the purge flow rate is small, the control accuracy of the purge flow rate is lowered, and the calculation accuracy in the calibration process described later is lowered. Therefore, when the purge flow rate is smaller than the predetermined amount, it is determined that the purge valve accuracy condition is not satisfied.
[0065]
The “purging influence condition” includes a purge establishment condition (purging is performed), a purge concentration condition (purge gas concentration is higher than a predetermined concentration, for example, an α change amount per purge rate of 1% is 1%. The purge rate condition (the purge rate is a predetermined value or more, for example, the purge rate is 30% or more) is set. When all of these conditions are satisfied and it is determined that the influence of the purge on the air-fuel ratio is relatively large, it is determined that the purge influence degree condition is satisfied.
[0066]
Thus, if it is determined in step 1 that the calibration process can be performed, the process proceeds to step 4 to execute the calibration process. This calibration process will be described with reference to the flow of FIG. 6. The calibration process estimates the amount of fuel desorbed from the canister 24 based on the change in the air-fuel ratio feedback correction coefficient α, and further returns the estimated desorption amount to the canister 24 by inverse calculation. The amount of fuel that has been adsorbed is calculated, and the value of the amount of adsorption, which is an internal variable of the canister model, is calibrated to the value of the amount of adsorption obtained by this inverse operation. This calibration process is a passive calibration process in FIG. This corresponds to the processing in part B31.
[0067]
In addition, since the process of steps 111-119 is a part added by this invention, it mentions later.
[0068]
In step 31, it is determined whether purge is being executed. The determination of whether or not the purge is being executed is based on the premise that the arithmetic processing in the subsequent steps 32 to 35 is the purge execution. Therefore, if these processes are performed when the purge is not executed, correct calibration is performed. It is because it becomes impossible. Therefore, when the purge is not being executed, this routine is ended and the calibration process is not performed.
[0069]
When it is determined that the purge is being performed, the routine proceeds to step 32 where the intake air mass Qg [g] obtained from the intake air flow rate Q and the intake air temperature, the target purge rate MPR, the purge correction factor FHOS, the air-fuel ratio feedback correction factor α Is read.
[0070]
In step 33, the air-fuel ratio feedback correction coefficient α and the purge correction coefficient FHOS (data during purge execution) are used.
DLT = α × FHOS (5a)
The total air-fuel ratio correction coefficient DLT is calculated by the following formula. From this total air-fuel ratio correction coefficient DLT, the target purge rate MPR, and the intake air mass Qg, in step 34,
Dg = K1 × (1−DLT + K2 × MPR) × Qg (5b)
Where Dg: Desorption amount,
DLT: Total air-fuel ratio correction coefficient,
MPR: target purge rate,
K1: coefficient (a constant determined by the nature of the desorbed fuel),
K2: coefficient (a constant determined by the nature of the air),
Qg: weight of intake air,
The desorption amount Dg [g] is calculated by the following formula.
[0071]
This equation (5b) is the deviation of the total air-fuel ratio correction coefficient from 1.0 (center value) (first term and second term on the right side), the target purge rate MPR (third term on the right side) and the intake air at that time This is an equation for calculating the amount of fuel Dg desorbed from the canister 4 from the mass Qg. That is, both the air-fuel ratio feedback correction coefficient α and the purge component correction coefficient FHOS are values having a center value of 1.0, and the center value of the total air-fuel ratio correction coefficient DLT, which is a value obtained by multiplying these α and FHOS. The amount of desorption is estimated by assuming that all deviations from (1.0) are caused by purging.
[0072]
In step 35, from the desorption amount Dg calculated in step 34,
Yr = KD × Dg ^ (1 / n (T)) (6)
Where n (T): desorption index,
KD: Desorption coefficient,
T: Activated carbon temperature,
The amount of adsorption Yr (mass) of the canister 24 is calculated by the following equation. Equation (6) is an inverse operation of Equation (2), which is one of the equations constituting the above-mentioned canister model.
[0073]
In step 36, the adsorption amount Y used when calculating the desorption amount Dg based on the canister model is replaced with the adsorption amount Yr calculated in step 35. Thereby, the value of the adsorption amount used in the canister model can be calibrated to a correct value, and the calculation accuracy of the subsequent desorption amount Dg can be improved.
[0074]
When the calibration process (second calibration process) is completed in this way, the process returns to FIG. 4, and in step 6, the desorption amount Dg from the canister 4 is calculated using the canister model. The calculation of the desorption amount Dg will be described with reference to the flowchart of FIG. This process corresponds to the process in the desorption amount calculation unit B4 in FIG.
[0075]
In step 41, the current value Y of the amount of fuel adsorbed by the canister is calculated by the above equation (1). However, when the calibration process shown in FIG. 6 is executed, the calculation of the expression (1) is not performed, or the value calculated by the expression (1) is ignored, and in the subsequent calculations, the adsorption amount calculated by the calibration process is ignored. Yr is used as the adsorption amount Y.
[0076]
In step 42, the desorption amount Dgk at the reference purge flow rate is calculated from the adsorption amount Y by the above equation (2). In step 43, the desorption amount is calculated from the reference desorption amount Dgk and the purge flow rate PQ by the above equation (3). Dg is calculated. In step 44, the activated carbon temperature T is calculated from the desorption amount Dg by the above equation (4).
[0077]
When the calculation of the desorption amount Dg and the activated carbon temperature T is completed in this way, the process returns to FIG. 4. In Step 7, the purge correction coefficient FHOS is calculated based on the target purge rate in addition to the desorption amount Dg and the intake air mass Qg. . The calculated purge correction coefficient FHOS is sequentially stored in a predetermined data storage location (see FIG. 11) in the engine controller 11.
[0078]
A change in the air-fuel ratio feedback correction coefficient α can be predicted by supplying the desorption amount Dg calculated by the canister model to the engine. The predicted α is the purge correction coefficient FHOS. Therefore, FHOS is the same unit as α, and the center value of FHOS is 1.0 (= 100%), which is the same as α. For example, when the desorption amount Dg from the canister 24 increases or the target purge rate increases and the amount of fuel supplied to the engine increases, the exhaust air-fuel ratio shifts to a richer side than the stoichiometric air-fuel ratio. Since the air-fuel ratio feedback correction coefficient α is expected to change to be smaller than 100% in order to return to the value, the purge correction coefficient FHOS changes correspondingly to a value smaller than 100%. Further, even if the desorption amount Dg and the target purge rate are the same, if the intake air mass Qg increases, the air-fuel ratio of the exhaust gas shifts to the lean side from the stoichiometric air-fuel ratio, and the air-fuel ratio feedback correction coefficient α is Since it is expected to change to the larger side, the purge correction coefficient FHOS changes to the larger side accordingly.
[0079]
In step 8, the purge correction coefficient FHOS is subjected to delay correction composed of dead time correction and smoothing processing. The dead time correction is performed because there is a delay corresponding to the purge gas transition speed and the distance between the purge valve 27 and the engine cylinder until the purge gas reaches the engine cylinder after the purge valve 27 is opened. The reason why the annealing process is performed is that there is fuel diffusion until the fuel desorbed from the canister 24 reaches the cylinder of the engine.
[0080]
This delay correction will be described with reference to the flow of FIG. 8. The delay correction corresponds to the processing in the delay correction unit B6 in FIG.
[0081]
In step 51, the intake air flow rate is calculated from the output of the air flow meter 13, and in steps 52 and 53, the dead time and the smoothing coefficient are obtained by searching tables having the contents shown in FIGS. As the intake air flow rate increases, the intake air flow rate increases, so the value decreases as the intake air flow rate increases during the dead time.When the intake air flow rate increases and the intake air flow rate increases, the speed at which the detached fuel diffuses also increases. Since the speed increases, the value that increases as the intake air flow rate increases is set for the smoothing coefficient.
[0082]
In step 54, the purge gas moving speed equivalent value is calculated from the dead time. This purge gas movement speed equivalent value is calculated as the reciprocal of the dead time obtained in step 22.
[0083]
In step 55, the purge correction coefficient FHOS stored in the data storage location (see FIG. 11) in the engine controller 11 corresponding to the distance between the purge valve 27 and the cylinder of the engine is read. In step 56, the purge gas is moved. Data is shifted to the cylinder side by the speed equivalent value. In step 57, the average value of the data overflowed from the data storage location due to the data shift is obtained.
[0084]
In step 58, the average value of the overflow data obtained in step 57 is subjected to a smoothing process using the smoothing coefficient obtained in step 52, and the value after the smoothing process is again set as a purge correction coefficient FHOS. . Note that the annealing process is a general annealing process using a first-order lag system, and the degree of annealing increases as the annealing coefficient decreases.
[0085]
FIG. 11 is a diagram showing an outline of dead time correction in delay correction. In the drawing, black circles and white circles indicate data before the data shift and data after the data shift, respectively.
[0086]
As shown in this figure, the memory of the engine controller 11 is provided with a data storage location corresponding to the distance between the purge valve 27 and the cylinder of the engine, and the purge amount calculated according to the amount of fuel desorbed from the canister 24. Correction coefficients FHOS are sequentially stored in the storage location. In the dead time correction, these data are shifted to the cylinder side by the amount corresponding to the purge gas transition speed (reciprocal of the dead time), and the overflow gas from the data storage location by this data shift reaches the cylinder and is supplied to the purge gas. Is a correction coefficient corresponding to. A value obtained by subjecting the average value of the overflowed data to a smoothing process is used for correcting the fuel injection pulse width Ti described later. Thus, the arrival delay of the purge gas can be accurately corrected by combining the dead time correction and the annealing process.
[0087]
When the delay correction is completed in this way, the process returns to FIG. 4 to complete the process at the calibration executable timing.
[0088]
On the other hand, if it is determined in step 3 that the calibration process cannot be performed, the process proceeds to step 5 to determine whether the calibration process has been executed in the past. Such a determination is made because the initial value (initial adsorption amount) necessary for operating the canister model does not yet exist when the calibration process has never been performed. In such a case, the canister This is because the purge process based on the model is not performed. As a result of the determination, if the calibration process has been performed once in the past, the operations of steps 6 to 8 are executed. If the calibration process has not been performed for this, the routine is performed after the operation of step 2 is performed. Exit.
[0089]
The purge process is not performed when the calibration process has never been performed, and the purge process is executed by a purge process (FIG. 16, boot-up control) that does not use a canister model, which will be described later.
[0090]
In the calculation routine of the fuel injection pulse width Ti (not shown) using the purge correction coefficient FHOS calculated in this way,

Where Tp: basic injection pulse width [msec],
Tfbya: target equivalent ratio [anonymous number],
Kathos: transient correction amount [msec],
FHOS: purge correction coefficient (value after delay smoothing),
α: Air-fuel ratio feedback correction coefficient,
αm: air-fuel ratio learning value,
Ts: Invalid pulse width [msec],
The fuel injection pulse width Ti [msec] given to the fuel injection valve 4 is calculated by the following equation. This calculation corresponds to the processing in the basic injection pulse width calculation unit B7, air-fuel ratio feedback correction coefficient calculation unit 8, fuel injection pulse width calculation unit B9, and air-fuel ratio learning control unit B16 in FIG.
[0091]
Here, the part (Tp × Tfbya) excluding the transient correction amount Kathos is corrected by the purge correction coefficient FHOS because the fuel supplied by the purge is a gaseous fuel, and it is necessary to correct the wall flow. Because there is no.
[0092]
The basic injection pulse width Tp is an injection pulse width at which a theoretical air-fuel ratio can be obtained, and is obtained from the intake air flow rate Q and the engine speed N.
[0093]
The target equivalent ratio Tfbya is a value centering on 1.0, and becomes a value larger than 1.0 when the cooling water temperature is low or immediately after the engine is started. After the engine is warmed up, Tfbya = 1.0.
[0094]
The air-fuel ratio feedback correction coefficient α is a value calculated based on the output of the air-fuel ratio sensor 15 so that the exhaust air-fuel ratio falls within a so-called window centered on the stoichiometric air-fuel ratio. Specifically, when the value is centered on 100% and there is no steady deviation (base air-fuel ratio error), when the detected air-fuel ratio is on the rich side with respect to the theoretical air-fuel ratio, the value is smaller than 100%. When the detected air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the value becomes larger than 100%.
[0095]
The air-fuel ratio learning value αm is a value calculated based on the air-fuel ratio feedback correction coefficient α, and is introduced mainly to compensate for a steady deviation.
[0096]
Part of the fuel injected from the fuel injection valve 4 forms wall flow fuel on the intake port wall and the back of the intake valve umbrella, and this wall flow fuel has a large response delay in the transient state such as acceleration and deceleration, and enters the cylinder. Inflow. The transient correction amount Kathos is a value for compensating for the response delay of the wall flow fuel during the transient.
[0097]
The invalid pulse width Ts is a value for compensating for an operation delay from when the fuel injection valve 4 receives the injection signal at a predetermined timing until it actually opens.
[0098]
In addition, since the expression (7) is an expression in the case of sequential injection (in the case of four cylinders, injection is performed once every two engine revolutions in accordance with the ignition order of each cylinder), the number 2 is entered.
[0099]
12 and 13 are for setting the target purge rate MPR, and are executed at regular intervals (for example, every 10 msec). This calculation corresponds to the processing in the target purge rate setting unit B1 in FIG.
[0100]
In step 61, it is determined whether or not it is after the first calibration process. This is because the target purge rate setting method differs before and after the initial calibration process. If it is before the first calibration process, the current process is terminated. The setting of the target purge rate before the first calibration process will be described in the bootup control described later.
[0101]
When it is after the first calibration process, the routine proceeds to step 62 where the purge gas air-fuel ratio (purge air-fuel ratio) is calculated based on the desorption amount Dg calculated based on the canister model (calculated in step 6 in FIG. 4) and the purge flow rate PQ. ) Is calculated. Here, the purge flow rate PQ is the product of the target purge rate and the intake air flow rate Q, and the previous value is used as the target purge rate in this case.
[0102]
The purge air-fuel ratio may be corrected as follows. That is, the purge air-fuel ratio error is estimated from parameters such as operating conditions, such as engine speed, engine load, and intake air flow rate. For example, it is obtained by searching a table having the contents shown in FIG. As shown in the figure, the purge air-fuel ratio error increases as the intake air flow rate decreases and the purge rate decreases. Alternatively, the purge air-fuel ratio error may be obtained by searching a table that defines the relationship between the purge air-fuel ratio and the purge air-fuel ratio error as shown in FIG. When the purge air-fuel ratio error is obtained, the purge air-fuel ratio obtained in step 62 is corrected based on this error.
[0103]
Although the purge air-fuel ratio may be detected by an HC sensor, the purge air-fuel ratio can be calculated inexpensively and accurately if it is obtained by calculation based on the desorption amount calculated based on the canister model.
[0104]
In step 63, the purge rate change limit value is calculated based on the purge air-fuel ratio thus obtained (or after error correction). When the purge rate changes, the exhaust air-fuel ratio changes. The purge rate change amount limit value is calculated so that the air-fuel ratio deviation from the theoretical air-fuel ratio at this time is within the allowable range. The allowable width of the air-fuel ratio deviation from the stoichiometric air-fuel ratio is set to a width that can be absorbed by the air-fuel ratio feedback control and does not deteriorate the exhaust emission.
[0105]
In step 64, a purge rate upper limit value PVMX defined by the size of the purge valve 27 is calculated. Such a purge rate upper limit value PVMX is obtained when the target purge rate is set to a value larger than the purge rate obtained by setting the purge valve 27 to the maximum opening degree, and the mismatch between the purge rate and the target purge rate occurs. Since the error in calculating FHOS increases, the air-fuel ratio deviation from the stoichiometric air-fuel ratio increases. This is because problems such as deterioration of exhaust emission occur. Specifically, when the size of the purge valve 27 is constant, the larger the differential pressure across the purge valve 27, the larger the flow rate of purge gas that can flow. Therefore, when the differential pressure across the purge valve 27 is large, the purge rate upper limit PVMX is large. Calculate the value.
[0106]
In step 65, the purge rate upper limit TIMNMX based on the performance of the fuel injection valve 4 is calculated from the relationship between the minimum injection pulse width determined according to the performance of the fuel injection valve 4, the previous value of the target purge rate, and the purge correction coefficient. . As the purge rate increases, the amount of fuel supplied to the engine by the purge increases, so the fuel injection pulse width is corrected so that the fuel injection amount from the fuel injection valve 4 is reduced by that amount. In order to ensure the injection accuracy, the injection pulse width must be larger than the predetermined minimum pulse width. In other words, in order to make the fuel injection pulse width larger than the minimum pulse width, the purge rate must be smaller than a certain value. For this reason, the upper limit of the purge rate is also defined by the injection performance of the fuel injection valve 4.
[0107]
In step 66, all the operation regions that can be assumed from the current operation region are assumed, the minimum purge rate is predicted, and the purge rate upper limit value is calculated from the minimum purge rate and the purge rate change limit value. Calculate PRMNMX. For example, depress the accelerator pedal as much as possible In addition When the speed is high, the target purge rate is set to a very small value.However, if the target purge rate is set to a large value immediately before the accelerator pedal is depressed as much as possible, the amount of change in the purge rate is less than the change amount limit value. Since it is limited, the purge rate cannot follow the target purge rate. Since this follow-up delay causes an increase in exhaust emission, it is necessary to define the upper limit of the purge rate from the minimum purge rate that can be assumed so as not to cause such follow-up delay.
[0108]
In step 67, the air-fuel ratio feedback correction coefficient α is monitored, and if it is equal to or less than a predetermined value, the largest value among the purge rates that make the air-fuel ratio feedback correction coefficient α equal to or greater than the predetermined value is calculated as the purge rate upper limit value ALPMX. . The upper limit value ALPMX is provided so that the air-fuel ratio feedback correction coefficient α is controlled to be within 100 ± 25% in the air-fuel ratio feedback control, but the air-fuel ratio feedback correction coefficient α is close to the limit value (for example, 80%), if a large amount of purging is performed, disturbances other than purging may occur and the control range tends to deviate.
[0109]
In step 68, the smallest value is selected from the above four upper limit values PVMX, TIMNMX, PRMNMX, and ALPMX, and that value is set as the maximum purge rate PRMAX.
[0110]
In steps 69 and 70, the previous value of the target purge rate is compared with the maximum purge rate PRMAX. When the previous value of the target purge rate and the maximum purge rate PRMAX are equal, the routine proceeds from step 69 to step 73, where the target purge rate is set to the previous value. When the previous value of the target purge rate is larger than the maximum purge rate PRMAX, the routine proceeds from step 69 and step 70 to step 72, where the target purge rate is set to a value obtained by subtracting the purge rate change limit value from the previous value. When the previous value of the purge rate is smaller than the maximum purge rate PRMAX, the routine proceeds from step 69, 70 to step 71, where the target purge rate is set to the previous value plus the purge rate change amount limiting value.
[0111]
The processing in steps 74 to 81 in FIG. 13 is a portion added according to the present invention and will be described later.
[0112]
In this way, the target purge rate is set to follow the purge rate change amount limit value with the maximum purge rate PRMAX as a target, and when performing a large amount of purge without deteriorating exhaust emissions. The best purge rate is set. In addition, when setting the maximum purge rate PRMAX, not only the upper limit values PVMX, TIMNMX, and ALPMX determined by physical limitations and the current operation region, but also the maximum purge in that region without delay even if the operation region changes Since the upper limit value PRMNMX determined so as to be able to shift to the rate is also taken into consideration, the best purge rate can be set for performing a large purge without deteriorating the exhaust emission even if the operating condition changes. .
[0113]
The target purge rate set in this way is converted into a duty ratio for the purge valve and is output to the purge valve 27.
[0114]
By the way, the purge process based on the canister model (model reference purge process) can be executed while the calibration process has never been performed after the engine is started and there is no initial value (initial adsorption amount) used in the canister model. Can not. However, in order to realize a large purge after the engine is started, it is necessary to execute the purge process even before the calibration process. Therefore, until the first calibration process is executed, the target purge rate is set by the following control (boot-up control shown in FIG. 16) instead of the purge process based on the canister model, and the purge is performed at the set target purge rate. Execute the process. In this boot-up control, the influence of the purge on the exhaust air / fuel ratio is absorbed by the air / fuel ratio feedback correction coefficient α, and the fuel injection pulse width is not corrected (FHOS = 1.0).
[0115]
FIG. 16 is for performing boot-up control, and is executed at regular intervals (for example, every 10 msec). This boot-up control corresponds to the processing in the boot-up control unit B14 and changeover switch B15 in FIG.
[0116]
In step 91, the intake air flow rate Q is read, and in step 92, it is determined whether or not it is before the first calibration process. If it is before the first calibration process, in step 93, the integrated purge flow rate (total purge flow rate after starting the purge) SQP and the purge pipe volume (the volume of the pipe from the canister 24 to the purge valve 27) are compared. When the integrated purge flow rate SQP exceeds the purge pipe volume, the routine proceeds to step 94, and when it does not exceed this, the routine proceeds to step 97.
[0117]
In step 97, an initial purge rate (a small value of 1% or less) is set as the target purge rate MPR. This small value is set when the accumulated purge flow rate SQP does not reach the purge pipe volume, the gas in the purge pipe is supplied to the engine before the purge starts. This is because the air-fuel ratio of the gas is unknown, and if the target purge rate setting process shown in steps 94 to 96 is performed as it is, problems such as deterioration in engine combustion stability occur.
[0118]
That is, when the low concentration purge gas existing in the purge pipe is supplied at the start of the purge, and the air / fuel ratio deviation from the theoretical air / fuel ratio is small, it is determined that a larger amount of purge is possible and a larger target purge rate MPR. However, if a large target purge rate MPR is set in this way, a large amount of desorption occurs when all of the low concentration gas in the pipe is supplied and the original high concentration purge gas is supplied. This is because the fuel is suddenly supplied, which causes deterioration of combustion stability of the engine.
[0119]
When the integrated purge flow rate SQP exceeds the pipe volume, the routine proceeds to step 94 where the difference between the actual air-fuel ratio feedback deviation and the target air-fuel ratio feedback deviation is calculated.
[0120]
Here, the target air-fuel ratio feedback deviation means a deviation (= | tα-100 |%) between the target value tα of the air-fuel ratio feedback correction coefficient and the center value (100%) of the air-fuel ratio feedback correction coefficient. The fuel ratio feedback deviation is a deviation (= | α−100 |%) between the actual air fuel ratio feedback correction coefficient α and the center value of the air fuel ratio feedback correction coefficient. For example, the target value tα of the air-fuel ratio feedback correction coefficient α is set to 80% for the purpose of securing a large purge flow rate within a range where the air-fuel ratio deviation from the theoretical air-fuel ratio due to purge can be sufficiently absorbed by the air-fuel ratio feedback control. Then, the target air-fuel ratio feedback deviation is set to | 80-100 | = 20%.
[0121]
In step 95, a purge rate change amount corresponding to the difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation is calculated by searching a table having the contents shown in FIG. The purge rate change amount is set to a larger value as the absolute value of the difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation increases to improve the convergence to the target value. Even if the absolute value of the deviation is the same depending on whether the difference in the actual air-fuel ratio feedback deviation is positive or negative, a larger value (absolute value) is set if the difference in the air-fuel ratio feedback deviation is shifted to the negative side. Set the purge rate change amount.
[0122]
In this way, the purge rate change amount has different characteristics depending on whether the air-fuel ratio feedback deviation is positive or negative. When the air-fuel ratio feedback deviation difference is shifted to the negative side, the target air-fuel ratio feedback correction coefficient α is 80%. This is because a disturbance other than purging tends to cause deterioration of engine stability and exhaust emission, as compared to a case where the value is smaller than the opposite positive side. In other words, the reason for changing the characteristics of the purge rate change amount according to the difference in the difference in air-fuel ratio feedback deviation is to quickly return the control point to the safe side from the viewpoint of engine combustion stability and prevention of exhaust emission deterioration. is there.
[0123]
When the purge rate change amount is calculated as described above, the process proceeds to step 96, where the purge rate change amount calculated in step 95 is added to the target purge rate obtained at the previous execution of this routine, and a new target purge rate MPR is obtained. Is calculated.
[0124]
In step 98, the purge flow rate PQ is obtained from the target purge rate MPR thus obtained and the intake air flow rate Q, and is added to SQPz, which is the previous value of the cumulative purge flow rate, in step 99, thereby updating the integrated purge flow rate SQP. To do.
[0125]
Therefore, according to the processing of steps 94 to 96, the optimum target purge rate MPR can be set regardless of the adsorption state of the canister 24, and even when a purge gas having a concentration higher than expected is supplied. The target purge rate MPR is appropriately changed in response to the change in the exhaust air-fuel ratio, and the optimum target purge rate MPR can always be set.
[0126]
On the other hand, after the first calibration process, the process proceeds from step 92 to step 100 and the subsequent steps, and it is determined whether the purge process is completed based on the integrated purge flow rate SQP. That is, in step 100, the purge end determination flag (initially set to zero) is checked. Immediately after the engine is started, the purge end determination flag = 0, so that the process proceeds to step 101 and the desorption amount Dg (calculated in step 6 in FIG. 4) and the target purge rate MPR (calculated in FIGS. 12 and 13). Read). In step 102, the purge flow rate QP is calculated from the read target purge rate MPR and the intake air flow rate Q, and in step 103, this is added to SQPz which is the previous value of the cumulative purge flow rate, thereby updating the cumulative purge flow rate SQP. To do.
[0127]
In step 104, it is determined whether or not it is the first calibration processing timing. Here, since the first calibration process timing is the first timing that disappeared before the first calibration process in step 92, the process proceeds to step 105 only at this time, and the purge flow rate PQ calculated in step 102 is read in step 101. The purge air-fuel ratio is calculated based on the desorption amount Dg, and the purge end determination value SLSQP is calculated by searching the purge air-fuel ratio from the purge air-fuel ratio in step 106 with the table shown in FIG.
[0128]
Here, the purge end determination value SLSQP is an integrated purge flow rate at which almost no desorbed fuel appears in the purge gas from the canister 24. As shown in FIG. 18, the determination value SLSQP decreases as the purge air-fuel ratio increases.
[0129]
In step 107, the purge end determination value SLSQP is compared with the integrated purge flow rate SQP. If the integrated purge flow rate SQP is less than the purge end determination value SLSQP, the current process is terminated. Eventually, if the integrated purge flow rate SQP becomes equal to or higher than the purge end determination value SLSQP, it is determined that almost no desorbed fuel is present in the purge gas from the canister 24, and the process proceeds to step 108 to indicate that the purge has ended. Set to 1.
[0130]
When the purge end determination flag = 1, since it is not possible to proceed to step 101 and subsequent steps even if it flows through steps 91, 92, and 100 from the next time, the processing is ended as it is.
[0131]
Next, the overall operation of the present embodiment by performing the purge process will be described first.
[0132]
During the purge process, the target purge rate MPR is set as large as possible within a range in which the engine combustion stability is not lowered and the exhaust emission is not increased, and the purge valve 27 is opened so as to realize the target purge rate MPR (FIG. 12). Steps 61-73).
[0133]
During the purging process, purge gas containing fuel desorbed from the canister 24 is supplied to the engine. Therefore, the engine controller 11 estimates the amount of fuel Dg desorbed from the canister 24, and this desorption amount Dg, Based on the target purge rate and the intake air mass Qg, a purge correction coefficient FHOS, which is a value for predicting a change in the air-fuel ratio feedback correction coefficient α caused by the purge fuel, is calculated (steps 1, 3, 4, 6, and 6 in FIG. 4). 7, 8 or steps 1, 3, 5, 6, 7, 8), the basic injection pulse width Tp is corrected by the purge correction coefficient FHOS, so that the air-fuel ratio deviation from the theoretical air-fuel ratio due to the purge is small. It can be suppressed.
[0134]
At this time, the desorption amount Dg from the canister 24 is estimated using a canister model expressed by the equations (1) to (4), and the desorption amount Dg is estimated accurately in a short time. Here, the desorption amount Dg calculated based on the canister model includes an error, and this error is integrated and increased as the operation time of the canister model becomes longer. From this change, the amount of fuel desorbed from the canister 24 is estimated, and the value of the amount of adsorption, which is an internal variable of the canister model, is calibrated with the amount of adsorption Yr reversed from this estimated amount of desorption. This calibration process is executed when disturbances other than purge are small and almost all changes in the air-fuel ratio feedback coefficient α can be regarded as being caused by the purge, and when the influence of the purge on the exhaust air-fuel ratio is relatively large.
[0135]
In addition, there is a delay from when the purge valve 27 is opened until the desorbed fuel reaches the cylinder of the engine, and there is also fuel diffusion until it reaches the purge cylinder 27. Delay correction is applied to the minute correction coefficient FHOS.
[0136]
Further, the purge process using the canister model (model reference purge process) cannot exert its effect until the initial value of the adsorption amount is obtained by the calibration process, but until the initial value of the canister model is calculated. The target purge rate is set according to the difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation, and the purge valve 27 is opened so that this target purge rate is realized. Thus, the purge process can be performed even before the initial value is calculated by the calibration process, and the effective purge can be performed in the entire region.
[0137]
This completes the description of the same part as the purging process in the prior application device (see Japanese Patent Application No. 2001-71562), and then steps 111 to 119 in FIG. 6 and steps 74 to 81 in FIG. 19, FIG. 20, FIG. 21, FIG. 23, FIG. 24, FIG. 26, and FIG.
[0138]
First, a description will be given from FIG. 13, which is the latter half of the flowchart for setting the target purge rate. The processing in this portion corresponds to the processing in the AND circuit B38, purge rate lowering processing unit B39, and changeover switch B40 in FIG.
[0139]
In step 74, the target purge rate is shifted to the variable MPR0.
[0140]
In step 75, the calibration feasibility determination flag (initially set to zero) is checked. In FIG. 5 described above, it is determined that the calibration process can be executed when all of the “steady condition”, “purge valve accuracy condition”, and “purge influence degree condition” are satisfied, but the calibration execution determination flag is 1 at this timing. Is a flag. When the calibration executable determination flag = 0, the routine proceeds to step 78, where the value of MPR0 is set as the target purge rate MPR as it is.
[0141]
On the other hand, when the calibration feasibility determination flag = 1, the routine proceeds to steps 76 and 77, where the data sampling end flag and the active calibration request flag (both are initially set to zero) are observed. As will be described later, when it is determined that there is a base air-fuel ratio error, the active calibration request flag becomes 1, and the purge is performed after sampling the data before the purge cut at the timing of switching the active calibration request flag from 0 to 1. Start rate reduction processing. This purge rate lowering process is a process of lowering the target purge rate by a predetermined value per predetermined time until the target purge rate becomes zero with the target purge rate immediately before the active calibration request flag is switched from 0 to 1 as an initial value. When the stabilization time elapses when the target purge rate becomes zero due to the rate reduction process (purge cut state), the data at the time of purge cut is sampled, and this completes the sampling of data before and after the purge cut. The data sampling end flag = 1.
[0142]
Therefore, before the active calibration request flag = 1, the data sampling end flag = 0, and in this case, step 76 is performed. , 77, the process proceeds to step 78. When the data sampling end flag = 1, the process proceeds from step 76 to step 78, where the operation of step 78 is executed.
[0143]
On the other hand, during the period from when the active calibration request flag = 1 to immediately before the data sampling end flag = 1, the routine proceeds to step 79 where purge rate reduction processing is performed.
[0144]
Here, the setting of the active calibration request flag in step 77 will be described with reference to the flowchart of FIG.
[0145]
FIG. 19 is for setting an active calibration request flag, and is executed at regular intervals (for example, every 10 msec).
[0146]
In step 121, it is checked whether the model purge is being executed. The execution of the model purge is a state where the initial calibration process of the canister model has been completed and the purge is not prohibited. If the model purge is being executed, the process proceeds to step 122 and the purge limiter determination flag is checked. There are two purge limiter determination flags, a purge lower limiter determination flag and a purge upper limiter determination flag. The setting of these two flags will be described with reference to the flowcharts of FIGS.
[0147]
20 is for setting a purge lower limiter determination flag, and FIG. 21 is for setting a purge upper limiter determination flag, both of which are executed at regular intervals (for example, every 10 msec). These setting processes in FIGS. 20 and 21 and the setting process in FIG. 19 correspond to the processes in the base air-fuel ratio error determination unit B36 and the active calibration request unit B37 in FIG.
[0148]
As shown in FIG. 28, the air-fuel ratio feedback correction coefficient α has a first limiter ± LMT1 (for example, ± 25%) up and down around the center value of α (100%) as shown in FIG. ). That is, the first upper limiter of α is 125% (= 100 + LMT1), the first lower limiter of α is 75% (= 100−LMT1), and the calculated α is 125%, which is the first upper limiter of α. Is exceeded to 125%, and conversely, when α is less than 75%, which is the first lower limiter of α, this α is limited to 75%.
[0149]
In the present embodiment, apart from the first limiter ± LMT1, a smaller second limiter ± LMT2 is newly introduced for purging. That is, the second lower limiter is 100-LMT2, and the second upper limiter is 100 + LMT2. In FIG. 28, 100-LMT1 is set between 100% which is the center value of α and 100-LMT1 which is the first lower limiter. Therefore, the second lower limiter 100-LMT2 comes to a position having a certain margin. That is, between 100-LMT2 (second lower limiter) and 100-LMT1 (first lower limiter) is left as a correction allowance for α, and when there is a disturbance other than purge, the theory is based on the remaining α correction allowance. Let the air-fuel ratio deviation from the air-fuel ratio be small.
[0150]
Then, a flag is set to indicate whether α is in a region below the second lower limiter or whether it is in a region above the second upper limiter (not shown in FIG. 28). That is, when the calculated α becomes 100−LMT2 or less which is the second lower limiter, the purge lower limit limiter setting flag = 1, and conversely, when the calculated α becomes 100 + LMT2 or more which is the second upper limiter, the purge upper limit Limiter setting flag = 1.
[0151]
However, a hysteresis HYS is provided for each of the second lower limiter and the second upper limiter. This is to prevent frequent repetition of each flag becoming zero or one due to α being in the vicinity of each limiter.
[0152]
Specifically, referring to FIG. 20, it is determined in step 131 whether air-fuel ratio feedback control is being performed. If the air-fuel ratio feedback control is not in progress, the current process is terminated.
[0153]
When the air-fuel ratio feedback control is being performed, the routine proceeds to step 132, where the air-fuel ratio feedback correction coefficient α is read.
[0154]
This α is calculated based on the air-fuel ratio sensor 15 in a flow (not shown). Here, for the sake of simplicity, the case of proportional operation will be described. The deviation between the actual exhaust air-fuel ratio detected by the air-fuel ratio sensor 15 and the theoretical air-fuel ratio is obtained, and this deviation is multiplied by a proportional gain. . At this time, while the actual exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio, the waveform of α decreases stepwise at each control period in order to return the actual exhaust air-fuel ratio to the stoichiometric air-fuel ratio. On the contrary, while the actual exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, in order to return the actual air-fuel ratio to the stoichiometric air-fuel ratio, α increases stepwise for each control cycle.
[0155]
In step 133, a purge lower limit limiter determination flag (initially set to zero when the engine is started) is checked. If it is immediately after the start, the purge lower limiter determination flag = 0, so that the routine proceeds to step 134, where α is compared with the purge lower limiter 100-LM2. When α exceeds 100−LMT2, the current process is terminated as it is. When α becomes 100−LMT2 or less, the routine proceeds to step 135 where the purge lower limit limiter determination flag = 1 is set and the current process is terminated.
[0156]
Next, the purge lower limit limiter determination flag = 1 proceeds from step 133 to step 136, where α is compared with 100−LMT2 + HYS (HYS is a positive constant value). If α is less than or equal to 100−LMT2 + HYS, the routine proceeds to step 135 where the purge lower limit limiter determination flag = 1 is maintained, and if α exceeds 100−LMT2 + HYS, the routine proceeds to step 137 where the purge lower limit limiter determination flag = 0.
[0157]
Moving to FIG. 21, steps 141 and 142 are the same as steps 131 and 132 of FIG.
[0158]
In step 143, an α purge upper limit limiter determination flag (initially set to zero when the engine is started) is checked. If it is immediately after the start, the purge upper limit limiter determination flag = 0, so that the routine proceeds to step 144, where α is compared with the purge upper limiter 100 + LMT2. When α is less than 100 + LMT2, the current process is terminated as it is. When α is equal to or greater than 100 + LMT2, the process proceeds to step 145, where the purge upper limit limiter determination flag = 1 is set and the current process is terminated.
[0159]
The purge upper limit limiter determination flag = 1 next time, the process proceeds from step 143 to step 146 to compare α with 100 + LMT2-HYS (HYS is a positive constant value). If α is equal to or greater than 100 + LMT2-HYS, the process proceeds to step 145 and the purge upper limit limiter determination flag = 1 is maintained, and if α is less than 100 + LMT2-HYS, the process proceeds to step 147 to set the purge upper limit limiter determination flag = 0.
[0160]
Returning to step 122 in FIG. 19, when the purge limiter determination flag (purge lower limiter determination flag or purge upper limiter determination flag) = 1, the routine proceeds to step 123 and timer 1 (initially set to zero) is incremented. The timer 1 is for continuously measuring the time during which the purge limiter determination flag = 1. For this reason, if the purge limiter determination flag = 0 even during the increment, the routine proceeds to step 126 and the timer 1 is cleared to zero, and if the purge limiter determination flag = 1 again, the routine proceeds to step 123 and the timer 1 is incremented. To do.
[0161]
In step 124, the timer 1 value is compared with a predetermined value. The predetermined value is a value for determining whether or not there is a base air-fuel ratio error. When the timer 1 value exceeds the predetermined value, it is determined that there is a base air-fuel ratio error, and the process proceeds to step 125 to perform the active calibration process (second calibration process). Therefore, the active calibration request flag (initially set to zero) = 1 To do.
[0162]
However, when the operating condition changes transiently, even if the base air-fuel ratio error does not exist, the purge limiter determination flag may be temporarily set to 1, so that there is also a base air-fuel ratio error in this case. The predetermined value is set so as not to be erroneously determined. That is, by setting a predetermined time as a time (for example, several seconds) longer than the time when the purge limiter determination flag = 1 is transiently set, a case of a transient change in operating conditions is erroneously determined as a base air-fuel ratio error. Avoid doing that.
[0163]
Now, the explanation of FIG. 19 is completed. Returning to FIG. 13, if it is immediately after the active calibration request flag = 1, the data sampling end flag = 0, so that the process advances from Steps 76 and 77 to Step 79. A purge rate reduction process is performed.
[0164]
As shown in FIG. 22, this purge rate lowering process is performed at the target purge rate at the timing when the active calibration request flag = 1 and the calibration executable determination flag is switched from 0 to 1 (in steps 61 to 73 in FIG. 12). (Calculated) is set as an initial value, and is decreased by a predetermined value Δ per predetermined time Δt to finally become zero. This is a method for performing the purge cut, and is not made zero stepwise from the initial value.
[0165]
FIGS. 23 and 24 (subroutine of step 79 in FIG. 13) are for performing the purge rate lowering process. This processing corresponds to the processing in the purge rate reduction processing unit B39, the data sampling unit B42 before purge cut, and the data sampling unit B43 during purge cut in FIG.
[0166]
In FIG. 23, in steps 151 and 152, the current and previous calibration executable determination flags are viewed. If the calibration feasibility determination flag = 1 at this time and the calibration feasibility judgment flag = 0 at the previous time (that is, immediately after the calibration feasibility judgment flag is switched from 0 to 1), the process proceeds to step 153 and the purge rate reduction process starts. Air-fuel ratio feedback correction coefficient α (calculated in the calculation flow of α not shown), purge correction coefficient FHOS (calculated according to FIG. 4), target purge rate MPR0 (obtained at step 74 in FIG. 13) , Intake air mass Qg (obtained from intake air flow rate Q and intake air temperature, etc.), air-fuel ratio learning value αm (air-fuel ratio in a small region to which the operating condition at that time belongs from a map of air-fuel ratio learning value not shown) Read the learning value) and read it into the corresponding memory α1, FHOS1, MPR1, Qg1, αm1 (sampling of data before purge cut) ).
[0167]
In step 154, the value of MPR0 at the start of the purge rate lowering process is similarly transferred to the variable MPRG. This is because the target purge rate at the timing when the calibration executable determination flag is switched from 0 to 1 is sampled as an initial value.
[0168]
In step 155, the timer 2 is once cleared to zero, and then, in step 156, the increment is started.
[0169]
At this time, when the calibration execution possibility determination flag = 1 in both the previous time, steps 153, 154, and 155 are skipped and the operation of step 156 is executed.
[0170]
In step 157, the timer 2 value is compared with a predetermined time Δt. When the timer 2 value exceeds the predetermined time Δt, the process proceeds to steps 158 and 159 to clear the timer 2 value to zero,
MPRG = MPRGz−Δ (8)
However, MPRGz: the previous value of MPRG,
The variable MPRG is reduced by a predetermined value Δ (positive value) by the following equation. When the timer 2 value is less than the predetermined time Δt, the routine proceeds to step 160 where the current MPRG is maintained.
[0171]
By the operations in steps 157 to 160, MPRG decreases by a predetermined value Δ every time the predetermined time Δt elapses (see the lowermost stage in FIG. 22).
[0172]
Here, if the purge cut is performed with the purge rate drastically lowered, the exhaust air-fuel ratio changes and affects the operability and exhaust emission. Therefore, the values of the predetermined time Δt and the predetermined value Δ May be determined using or based on the purge rate change amount limit value when setting.
[0173]
Proceeding to FIG. 24, MPRG is compared with zero in step 161. If MPRG is greater than or equal to zero, the routine proceeds to step 162, where MPRG is set as the target purge rate MPR, whereas when MPRG becomes a negative value, the routine proceeds to step 163 where zero is set as the target purge rate MPR.
[0174]
In step 164, the target purge rate MPR is compared with zero. When MPR = 0, the routine proceeds to step 165, where timer 3 (initially set to zero) is incremented. The timer 3 is for measuring the continuous elapsed time in the purge cut state (the target purge rate MPR is zero).
[0175]
In step 166, the timer 3 value is compared with the stabilization time. The stabilization time is a time for waiting for the purge cut state to stabilize.
[0176]
When the timer 3 value becomes equal to or longer than the stabilization time, the routine proceeds to step 167, where the air-fuel ratio feedback correction coefficient α and the air-fuel ratio learning value αm at that time are stored in the corresponding memories α2 and αm2. This is to sample data at the time of purge cut. Since the sampling of data before and after the purge cut is completed, the data sampling end flag (initially set to zero) = 1 is set at step 168, and the timers 2 and 3 are cleared to zero at step 169.
[0177]
When the purge rate reduction process is completed in this manner, FIG. Three Return to step 80. In step 80, the purge end determination flag (set by FIG. 16) is checked. When the purge end determination flag = 1, the routine proceeds to step 81 in order to start air-fuel ratio learning, and the purge rate for air-fuel ratio learning is set to the target purge rate MPR. As a result, when the air-fuel ratio learning is started, the target purge rate MPR becomes small as shown in FIG.
[0178]
FIG. 26 is for setting the air-fuel ratio learning start flag, and is executed at regular intervals (for example, every 10 msec).
[0179]
In step 171, the air-fuel ratio learning start flag (initially set to zero) is checked. If it is immediately after the engine is started, the air-fuel ratio learning start flag = 0, so that the routine proceeds to step 172 and the purge end determination flag (set by FIG. 16) is observed.
[0180]
In order to start air-fuel ratio learning only when the purge end determination flag = 1, the routine proceeds to step 173, where the air-fuel ratio learning start flag = 1 is set.
[0181]
FIG. 27 is for updating the air-fuel ratio learning value, and is executed at predetermined timings (for example, at predetermined engine speed intervals). Each process of updating the air-fuel ratio learning value and setting the air-fuel ratio learning start flag in FIG. 26 corresponds to the process in the air-fuel ratio learning control unit B16 in FIG.
[0182]
In step 181, the air-fuel ratio learning start flag is checked. When the air-fuel ratio learning start flag = 1, the routine proceeds to step 182 where it is determined whether the air-fuel ratio learning permission condition is satisfied. The air-fuel ratio learning permission condition is the same as the conventional one. For example, it is determined that the air-fuel ratio learning permission condition is satisfied when the air-fuel ratio feedback control is being performed and the air-fuel ratio sensor 15 and the like related to the air-fuel ratio feedback control are all satisfied. Proceed to, and the air-fuel ratio learning value is updated. There is a method of updating the air-fuel ratio learning value by the following equation.
[0183]
αm = αmz + (α−100) × M (9)
Where αm is the updated air-fuel ratio learning value,
αmz: Air-fuel ratio learning value before update,
M: learning ratio (constant value),
In this case, the entire operation region using the engine speed and the basic injection pulse width Tp (corresponding to the engine load) as parameters is divided into a plurality of small regions, and each small region has an independent air-fuel ratio learning value. Yes. For this reason, the air-fuel ratio learned value before updating the right side of equation (9) is the air-fuel ratio learned value stored in the small region to which the operating condition at the update timing belongs, and the left side of equation (9) is stored in the same small region. The updated air-fuel ratio learning value is stored.
[0184]
The embodiment is air-fuel ratio feedback control based on the air-fuel ratio sensor 15, but instead of this, O ₂ It may be air-fuel ratio feedback control based on a sensor. In this case, O ₂ The sensor inversion timing may be used as the update timing of the air-fuel ratio learning value.
[0185]
Next, returning to FIG. 6, the processing of steps 111 to 119 will be described. The processing in this portion corresponds to the processing in the active calibration processing unit B41 and the changeover switch B47 in FIG.
[0186]
In steps 111 and 112, the active calibration request flag and the data sampling end flag are checked. When the active calibration request flag = 0, even if the active calibration request flag = 1, the data sampling end flag = 0, the process proceeds to steps 32 to 36, and the same passive calibration process (second calibration process) as that of the prior application apparatus. Execute.
[0187]
When the active calibration request flag = 1 and the data sampling end flag = 1, the active calibration process (first calibration process) in steps 113 to 117 is performed. That is, in step 113, α1, α2, FHOS1, Qg1, αm1, and αm2 stored in the memory are read. Here, the value with “1” is the data before the purge cut, and the value with “2” is the data at the time of the purge cut.
[0188]
In step 114, using the data before and after the purge cut,
DLT = (α1 + αm1 + α2 + αm2−3) × FHOS1 (10)
The total air-fuel ratio correction coefficient DLT is calculated by the following formula, and using this total air-fuel ratio correction coefficient DLT and MPR1, Qg1,
Dg = K1 × (1−DLT + K2 × MPR1) × Qg1 (11)
The desorption amount Dg is calculated by the following formula.
[0189]
Here, how the equation (10) is derived will be described.
[0190]
(A) When air-fuel ratio learning control is not performed:
The embodiment includes the air-fuel ratio learning control unit B16. However, what does not perform the air-fuel ratio learning control is the basis of the idea.
DLT = {α1- (1-α2)} × FHOS1 (a)
The total air / fuel ratio correction coefficient DLT may be calculated by the following equation. Here, (1-α2) on the right side of equation (a) represents a deviation of α from the center value of α at the time of purge cut, that is, a base air-fuel ratio error, and this is a value during purge execution (equation (a)) Since a calibration error occurs due to being included in α1 on the right side, the error corresponding to the base air-fuel ratio error is removed from α1 by subtracting (1-α2) representing the base air-fuel ratio error from α1.
[0191]
(A) When performing air-fuel ratio learning control:
At this time, it is necessary to consider the air-fuel ratio learning value in the same manner as the air-fuel ratio feedback correction coefficient α.

The total air-fuel ratio correction coefficient DLT is calculated by the following formula. Here, (1-αm2) on the right side of the equation (b) represents a deviation of αm from the center value of αm at the time of purge cut, that is, this also represents a base air-fuel ratio error, which is a value during purge execution (b ) Is included in αm1 on the right side of the equation, a calibration error occurs. Therefore, by subtracting (1-αm2) representing the base air-fuel ratio error from αm1, the error corresponding to the base air-fuel ratio error is removed from αm1. However, the sum of the two values {α1- (1-α2)} and {αm1- (1-αm2)} centered at 1.0 is 2, so 1 from the sum of the two values. The balance is calculated by subtracting. When the formula (b) is arranged, the above formula (10) is obtained.
[0192]
When the total air-fuel ratio correction coefficient DLT is obtained in this way, the calculation formula for the desorption amount is the same as the above-described formula (5b). However, since the target purge rate MPR and the intake air mass Qg in this case must be values before the purge cut, MPR1 and Qg1 are used instead of MPR and Qg as in (11) above.
[0193]
Steps 116 and 117 are similar to the passive calibration process. That is, in step 116, the adsorption amount Yr (mass) of the canister 24 is calculated from the desorption amount Dg calculated in step 115 by the above equation (6). In step 117, the adsorption amount Y used when calculating the desorption amount Dg based on the canister model is replaced with the adsorption amount Yr calculated in step 116.
[0194]
This completes the active calibration process. In steps 118 and 119, the data sampling end flag = 0 and the active calibration request flag = 0. When it is determined that the calibration can be executed next time from the active calibration request flag = 0, the process proceeds from step 111 to steps 32-36 in FIG. 6 to execute the passive calibration process.
[0195]
Here, the action during the purge execution of this embodiment will be described with reference to the waveform diagrams of FIGS.
[0196]
The right side of FIG. 28 shows the air-fuel ratio feedback correction coefficient α and the purge correction coefficient when the purge correction coefficient FHOS is correctly calculated in the state where there is no base air-fuel ratio error and the air-fuel ratio learning function is not considered. Each waveform of FHOS This On the other hand, on the left side of FIG. 28, there is no base air-fuel ratio error and the air-fuel ratio learning function is not considered, and the air-fuel ratio feedback correction coefficient α when the FHOS is not correctly calculated along with the calibration error. Each waveform of the purge correction coefficient FHOS is shown as a model. However, the operating conditions are not ideal steady-state, but are shown when the target purge rate is changing slowly as if it is changing slowly.
[0197]
As shown on the right side of FIG. 28, when the purge process is performed under the set target purge rate, if the purge correction coefficient FHOS is correctly calculated, the air-fuel ratio from the stoichiometric air-fuel ratio is calculated by this FHOS. Since the deviation is small and the air-fuel ratio feedback control does not need to be activated, the air-fuel ratio feedback correction coefficient α remains in the vicinity of the position where the correction margin is full (maximum) (that is, the central value of α is 100%). ing.
[0198]
On the other hand, when the FHOS is not correctly calculated due to the calibration error, the air-fuel ratio deviation from the stoichiometric air-fuel ratio during the air-fuel ratio feedback control becomes large, and an attempt is made to make the large air-fuel ratio deviation small. Air-fuel ratio feedback control works. That is, as shown on the left side of FIG. 28, α is gently oscillating at a position leaving a little margin from 75% which is the first lower limiter, and this indicates that the air-fuel ratio deviation from the stoichiometric air-fuel ratio in this state. Is becoming smaller. In other words, since FHOS is erroneously calculated to a value close to 100%, the exhaust air / fuel ratio is inclined to the rich side from the stoichiometric air / fuel ratio, and α is set to 100 to return the exhaust air / fuel ratio inclined to the rich side to the stoichiometric air / fuel ratio. % Is smaller.
[0199]
In this case, in the present embodiment, 100-LMT2, which is a second lower limiter that is narrower to the central value (100%) of α than 75% that is the first lower limiter of α, is set. When α changes across the second lower limiter as shown on the left side of 28, the purge lower limit limiter determination flag changes from 0 to 1 and returns to 0 again (the left side of FIG. 28, Bottom reference). This is based on a comparison between α and a determination value with hysteresis. That is, the purge lower limit limiter determination flag is switched from 0 to 1 at a timing when α becomes smaller than the determination value 100-LMT2 (steps 133, 134, and 135 in FIG. 20). Thereafter, when α changes to become larger across 100-LMT2, the purge lower limit limiter determination flag remains 1 while it is 100-LMT2 + HYS or less (steps 133, 136, and 135 in FIG. 20). , Α is switched from 1 to 0 at the timing when α becomes larger than 100−LMT2 + HYS (steps 133, 136, and 137 in FIG. 20). When α again decreases across 100-LMT2, the purge lower limit limiter determination flag is switched from 0 to 1 (steps 133, 134, and 135 in FIG. 20). As a result of such repetition, the purge lower limiter determination flag is changed to the left side of FIG. Bottom As shown.
[0200]
Then, when the continuous time (timer 2 value) in which the purge lower limit limiter determination flag = 1 is equal to or greater than a predetermined value, the active calibration request flag is switched from 0 to 1 (steps 124 and 125 in FIG. 19).
[0201]
In FIG. 29, although the air-fuel ratio learning control is performed, the base air-fuel ratio error is exposed after the engine is started for some reason, and the air-fuel ratio learning is started before the calibration is started, and the calibration is performed. The waveforms of the air-fuel ratio feedback correction coefficient α, the purge correction coefficient FHOS, and the air-fuel ratio learning value αm when the purge correction coefficient FHOS is not correctly calculated due to an error are shown as models. That is, before t1, the exhaust air-fuel ratio is inclined leaner than the stoichiometric air-fuel ratio due to the base air-fuel ratio error, and the air-fuel ratio feedback correction coefficient α is set to 100 to return the lean air-fuel ratio to the stoichiometric air-fuel ratio. It is larger than%. However, the operating conditions are those during moderate acceleration.
[0202]
Note that the air-fuel ratio learning value αm is obtained by dividing the entire operating region represented by the engine speed and load into several small regions and storing a separate air-fuel ratio learning value for each small region. For this reason, the air-fuel ratio learning value αm changes between t1 and t2 as shown in the lowermost stage. This indicates that the air-fuel ratio learning value read out is different because the operating condition has shifted to another small region.
[0203]
Further, the target purge rate MPR, the purge correction coefficient FHOS, and the air-fuel ratio feedback correction coefficient α are actually values that move stepwise for each calculation cycle as shown in FIG. 28. Unlike FIG. 29, it is indicated by a straight line. The timings t1 and t3 are the timings of the left broken line position among the two vertical broken lines, and the right broken line timing represents the next calculation timing (therefore, the width of the two broken lines is the calculation cycle). .
[0204]
The active calibration request flag is set to 1 before the timing of t1, and the purge rate reduction process is started at the timing of t1 when the calibration execution determination flag is switched from 0 to 1 (steps 75 and 76 in FIG. 13). 77, 79). In this purge rate reduction process, the target purge rate at the start of the purge rate reduction process is reduced by a predetermined time Δt or a predetermined value Δ with an initial value (see FIG. 22), and the target purge rate reaches zero at t2 (see FIG. 22). (See FIG. 29, fourth row). In this case, since the purge correction coefficient FHOS is a value proportional to the target purge rate, when the target purge rate is lowered in this way, FHOS also decreases toward 100%, which is the center value of FHOS (FIG. 29, FIG. 29). (Refer to the fifth row).
[0205]
Here, the purge rate reduction process is a method for performing a purge cut, and at the start of the purge rate reduction process before the purge cut, α, FHOS, MPR, αm, and Qg at that time correspond to the corresponding memory α1, FHOS1, MPR1, αm1, and Qg1 are sampled as data before purge cut (steps 151, 152, and 153 in FIG. 23).
[0206]
Further, when the target purge rate becomes zero, the purge cut state is entered. In this state, the data at the time of purge cut is not sampled immediately, but α and αm at the timing of t3 when the stabilization time has elapsed are the corresponding memories. The data is sampled as α2 and αm2 as purge cut data (steps 164, 165, 166, and 167 in FIG. 24).
[0207]
This completes the data sampling before and after the purge cut, so the data sampling end flag is switched from 0 to 1 (steps 166 and 168 in FIG. 24), and the active calibration process is performed at the timing t4 using the data before and after the purge cut. Done.
[0208]
In this active calibration process, instead of the above equations (5a) and (5b), the total air-fuel ratio correction coefficient DLT and the desorption amount Dg are calculated by the above equations (10) and (11), and thus obtained. The adsorption amount Yr is calculated by reverse calculation from the desorption amount Dg, and the adsorption amount data in the canister model is replaced with this adsorption amount Yr (steps 111, 112, 113, 114, 115, 116, 117 in FIG. 6). As a result, the purge correction coefficient FHOS is correctly calculated after the active calibration process.
[0209]
After the active calibration process is completed, the active calibration request flag = 0 and the data sampling flag = 0 (steps 118 and 119 in FIG. 6), thereby returning the target purge rate to the value before the purge cut (step in FIG. 13). 75, 76, 77, 78). In other words, the target purge rate is gradually returned to the value before the purge cut according to the purge rate change amount limit value, and the purge correction coefficient FHOS is decreased away from the central value of 100% as the target purge rate increases. It will become. Since the FHOS at this time is correctly calculated by executing the active calibration process, α converges to its central value of 100%, and prepares for disturbances other than purge.
[0210]
Further, when the calibration can be executed after the active calibration process is completed, a passive calibration process, which is a calibration process similar to that of the prior application apparatus, is performed (see FIG. 30).
[0211]
Thus, according to the present embodiment (the invention described in claim 1), although the air-fuel ratio learning control is performed, the base air-fuel ratio error is exposed immediately after the engine is started for any reason. As long as the passive calibration process is continued, an error corresponding to the base air-fuel ratio error occurs in the calibration of the canister model, which causes the purge correction factor FHOS to be calculated only inaccurately. The air-fuel ratio deviation from the stoichiometric air-fuel ratio increases, and the air-fuel ratio feedback control is performed to reduce the air-fuel ratio deviation, and the correction allowance for the air-fuel ratio feedback correction coefficient α is reduced. The second limiter ± LMT2 having a narrower range up to the center value of the air-fuel ratio feedback correction coefficient α than the first limiter is set, and the calculated air-fuel ratio feedback correction coefficient α It is determined whether or not there is a base air-fuel ratio error by comparison with the second limiter, and when it is determined that there is a base air-fuel ratio error, the purge cut is performed and this purge is performed on the canister model. Since the active calibration process (first calibration process) is performed based on the data before and after the cut, the calibration of the canister model is performed at the calibration timing when the base air-fuel ratio error is exposed after the engine is started. This can be performed accurately without being affected by the air-fuel ratio error, thereby improving the calculation accuracy of the purge correction coefficient FHOS and not wastefully using the correction allowance for the air-fuel ratio feedback correction coefficient α.
[0212]
Further, when the operating condition changes transiently, even if there is no base air-fuel ratio error, the calculated air-fuel ratio feedback correction coefficient α may not be within the center value side including the second limiter. If it is immediately determined that there is a base air-fuel ratio error, an erroneous determination is made. However, according to the present embodiment (the invention according to claim 7), the base air-fuel ratio error occurs after a predetermined value (delay time) has elapsed. (Steps 121, 122, 123, 124, and 125 in FIG. 19), the base air-fuel ratio error and the normal air-fuel ratio error (there is no base air-fuel ratio error but theoretical The air-fuel ratio deviation from the fuel ratio) can be separated, and the determination accuracy of the base air-fuel ratio error is improved.
[0213]
Further, according to the present embodiment (the invention described in claim 8), the target purge rate when the calibration timing is reached when there is a base air-fuel ratio error is decreased to zero by a predetermined value at predetermined time intervals as an initial value. Therefore, a calibration error due to a base air-fuel ratio error occurs, and accordingly, even when the purge correction coefficient FHOS is not correctly calculated, the target purge rate can be rapidly reduced. And the target purge rate can be changed within a range where air-fuel ratio feedback control is possible.
[0214]
Further, according to the active calibration process, it is possible to accurately estimate the state of the canister model without being affected by the base air-fuel ratio. Therefore, it is confirmed that the purge process is completed based on the result of the active calibration process. Can be used to confirm. That is, after the active calibration process is performed at the first calibration timing after the engine is started, the desorption amount Dg calculated by the canister model becomes accurate, and thereby a determination value for comparison with the integrated purge flow rate SQP. Since SLSQP is accurately calculated, the determination accuracy of whether or not the purge process is completed is improved (steps 92 and 100 to 108 in FIG. 16).
[0215]
In order to improve the accuracy of the air-fuel ratio learning control, it is desirable that the disturbance factor such as purge is removed. On the other hand, a purge process is necessary to process the evaporated fuel generated from the fuel tank 21, and performing as much purge process as possible immediately after startup leads to prevention of purge fuel release from the vehicle to the atmosphere. As described above, the two controls, the air-fuel ratio learning control and the purge process, have conflicting demands, but the purge rate (purge flow rate) is maintained at the minimum necessary value when the purge fuel can be sufficiently processed (see FIG. 13 steps 80 and 81, FIG. 25), and by updating the air-fuel ratio learning value (steps 171 to 173 in FIG. 26 and steps 181 to 183 in FIG. 27), the accuracy of the air-fuel ratio learning control can be guaranteed. Yes.
[0216]
Thus, according to the present embodiment (the invention described in claim 9), the accuracy of the purge process end determination is improved by utilizing the result of the active calibration process for the purge process end determination, and thus is high. After performing the purge end determination with high accuracy, the purge rate is reduced and the air-fuel ratio learning value is updated, so that it is possible to improve both the accuracy of air-fuel ratio learning control and a large amount of purge processing immediately after starting. .
[0217]
Further, since the desorption characteristics of the fuel from the canister 24 are affected by the temperature of the fuel adsorbent (activated carbon or the like) in the canister, the desorption amount calculation formula is an equation considering the relationship between the adsorbent temperature and the desorption amount. (Invention of claim 15) In the region where the desorption amount is large, the calculation error of the desorption amount greatly affects the exhaust air / fuel ratio, and particularly high calculation accuracy is required. Moreover, since the desorption phenomenon of the fuel from the canister 24 is an endothermic reaction, When desorption is performed, the temperature of the adsorbent in the canister decreases and the desorption characteristics also change. Therefore, if the relationship between the adsorbent temperature and the desorption amount is not taken into account, the calculation accuracy of the desorption amount is reduced in a region where the desorption amount is large, but the canister is calculated so that the desorption amount is also taken into account. If the model is configured, it is possible to suppress the deterioration in the calculation accuracy of the desorption amount and prevent the exhaust emission deterioration caused by the deterioration in the calculation accuracy.
[0218]
As a desorption amount calculation formula for calculating the desorbed fuel amount based on the adsorbed fuel amount, the purge rate, and the adsorbent temperature, an equation applied to the desorption phenomenon of the canister 24 based on the Freundlich equation. Can be used. Further, the adsorbent temperature can be determined by determining the amount of decrease in adsorbent temperature based on the amount of fuel desorbed from the canister 24 (the invention according to claim 16).
[0219]
In addition, this embodiment (claim 1) 1 According to the described invention, when the calibration timing comes when there is no base air-fuel ratio error, a passive calibration process (second calibration process) based on the data being purged is also performed on the canister model. The canister model is an approximate model, and the values calculated by it are some errors, and the canister model calculates a new value using the previous value, so that its operation time becomes longer. Although the error is integrated and becomes large, by performing such a passive calibration process, the error can be appropriately corrected and high calculation accuracy can be maintained. In this passive calibration process, the adsorption amount is calculated backward from the desorption amount estimated from the air-fuel ratio deviation from the stoichiometric air-fuel ratio, and the adsorption amount of the internal variable is calibrated with the calculated reverse adsorption amount. There is no need to go through a special sequence and there is no need to reduce the purge rate. The adsorption amount can be obtained by inverse calculation of the desorption amount calculation formula in the canister model (the invention according to claim 17).
[0220]
The calibration process is performed when there is no air-fuel ratio deviation from the stoichiometric air-fuel ratio due to disturbances other than purge, and all the air-fuel ratio deviation from the stoichiometric air-fuel ratio is considered to be due to purge, and the amount of fuel desorption from the canister is determined. Since calibration is performed based on the actual adsorption amount of the canister 24 that is estimated and calculated backward from the estimated desorption amount, the accuracy of the calibration process can be ensured (the invention according to claim 18).
[0221]
Further, according to the present embodiment (the invention described in claims 19 and 20), in order to improve the calculation accuracy of the desorption amount, the calibration process is performed when the air-fuel ratio deviation from the theoretical air-fuel ratio due to purge is relatively large (purge When the rate is high and the purge air-fuel ratio is high). Depending on the operation area, sufficient calculation accuracy of the calibration process may not be obtained, but by executing the calibration process only in the area where sufficient accuracy is obtained in this way, the accuracy of the calibration process is improved, and the canister model Accuracy can be further improved.
[0222]
Although the embodiment of the present invention has been described above, the configuration of the above embodiment shows an example of the configuration to which the present invention is applied, and the scope of the present invention is not limited to the above configuration. As described above, in the above-described embodiment, the purge process illustrated in FIG. 16 is performed supplementarily until the purge process using the canister model is enabled, but the purge process illustrated in FIG. 16 is continuously used. You may do it.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a fuel vapor processing apparatus according to the present invention.
FIG. 2 is a block diagram showing an outline of purge processing in an engine controller.
FIG. 3 is a block diagram showing the configuration of a canister model.
FIG. 4 is a flowchart for explaining calculation of a purge correction coefficient.
FIG. 5 is a flowchart showing conditions for enabling calibration processing.
FIG. 6 is a flowchart for explaining calibration processing;
FIG. 7 is a flowchart for explaining calculation of a desorption amount based on a canister model.
FIG. 8 is a flowchart for explaining delay correction;
FIG. 9 is a characteristic diagram showing the relationship between the intake air flow rate and the dead time.
FIG. 10 is a characteristic diagram showing a relationship between an intake air flow rate and a smoothing coefficient.
FIG. 11 is a diagram showing an outline of dead time processing in delay correction.
FIG. 12 is a flowchart for explaining setting of a target purge rate.
FIG. 13 is a flowchart for explaining setting of a target purge rate.
FIG. 14 is a characteristic diagram showing the relationship of the purge air-fuel ratio error with respect to the intake air flow rate and the purge rate.
FIG. 15 is a characteristic diagram showing a relationship between a purge air-fuel ratio error and a purge air-fuel ratio.
FIG. 16 is a flowchart for explaining boot-up control;
FIG. 17 is a characteristic diagram showing the relationship between the difference in air-fuel ratio feedback deviation (= target air-fuel ratio feedback deviation−actual air-fuel ratio feedback deviation) and the purge rate change amount;
FIG. 18 is a characteristic diagram showing the relationship between the purge end determination value and the purge air-fuel ratio.
FIG. 19 is a flowchart for explaining the setting of an active calibration request flag.
FIG. 20 is a flowchart for explaining setting of a purge lower limit limiter determination flag;
FIG. 21 is a flowchart for explaining the setting of a purge upper limit limiter determination flag;
FIG. 22 is a waveform diagram for explaining purge rate reduction processing;
FIG. 23 is a flowchart for explaining purge rate reduction processing;
FIG. 24 is a flowchart for explaining purge rate reduction processing;
FIG. 25 is a waveform diagram showing a change in the target purge rate when it is determined that the purge has been completed.
FIG. 26 is a flowchart for explaining the setting of an air-fuel ratio learning start flag.
FIG. 27 is a flowchart for explaining the update of the air-fuel ratio learning value.
FIG. 28 is a waveform diagram for comparing and explaining when calibration is normally performed and when there is a calibration error.
FIG. 29 is a waveform diagram showing the contents of an active calibration process.
FIG. 30 is a waveform diagram showing the contents of passive calibration processing.
FIG. 31 is a block diagram showing an outline of calibration processing.
[Explanation of symbols]
4 Fuel injection valve
5 Exhaust passage
8 Intake passage
11 Engine controller
13 Air flow meter
15 Air-fuel ratio sensor (air-fuel ratio detection means)
21 Fuel tank
22 Piping
24 Canister
26 Piping
27 Purge valve

Claims (20)

Air-fuel ratio detection means for detecting the air-fuel ratio in the exhaust;
Air-fuel ratio feedback correction amount calculating means for calculating the air-fuel ratio feedback correction amount so that the exhaust air-fuel ratio detected by the air-fuel ratio detection means matches the stoichiometric air-fuel ratio;
First limiter setting means for setting a first limiter having a predetermined width from the center value of the air-fuel ratio feedback correction amount;
When the first upper limiter, which is larger than the center value by the first limiter , is exceeded, the first upper limiter is exceeded, and when the air-fuel ratio feedback correction amount is less than the first lower limiter, which is smaller by the first limiter than the center value. Is an air-fuel ratio feedback correction amount limiting means for limiting the calculated air-fuel ratio feedback correction amount to the first lower limiter ;
In an air-fuel ratio control apparatus for an engine, comprising:
A canister that adsorbs the evaporated fuel generated in the fuel tank;
A purge valve that opens and closes a pipe that communicates the canister and the intake passage of the engine;
Purge valve control means for controlling the purge valve so as to obtain a target purge rate;
at least,
(A) an adsorbed fuel amount calculation formula for calculating the amount of fuel adsorbed to the canister based on the previous value of the fuel amount adsorbed on the canister and the previous value of the amount of fuel desorbed from the canister;
(B) a canister model composed of an adsorbed fuel amount calculated by an adsorbed fuel amount calculating equation and a desorbed fuel amount calculating equation for calculating an amount of fuel desorbed from the canister based on a target purge rate;
Purging correction that calculates the purge correction amount based on the desorbed fuel amount calculated using the canister model so that the air-fuel ratio deviation from the stoichiometric air-fuel ratio is reduced by performing the purge process at the target purge rate. A quantity calculation means;
A purge correction means for correcting the amount of fuel supplied to the engine by the purge correction amount;
Calibration timing determination means for determining whether it is calibration timing;
Means for setting a second limiter having a narrower range to the center value of the air-fuel ratio feedback correction amount than the first limiter;
Base air-fuel ratio error determining means for determining whether or not there is a base air-fuel ratio error by comparing the calculated air-fuel ratio feedback correction amount and the second limiter;
From this determination result, when there is a base air-fuel ratio error, purge cut means for performing a purge cut when the calibration timing comes,
An air-fuel ratio control apparatus for an engine, comprising: a first calibration processing unit that performs a first calibration process on the canister model based on data before and after the purge cut. The first calibration processing means includes
A pre-purge cut data sampling means for sampling the data at that time as pre-purge cut data when the calibration timing comes when there is a base air-fuel ratio error;
A purge-cut data sampling means for sampling the air-fuel ratio feedback correction amount at that time as purge-cut data at the time of purge-cut,
Desorbed fuel amount estimation means for estimating the amount of fuel desorbed from the canister based on the data before and after the purge cut,
An adsorbed fuel amount back calculating means for calculating back the amount of fuel adsorbed to the canister from the estimated desorbed fuel amount;
2. The engine air-fuel ratio control apparatus according to claim 1, further comprising calibration means for calibrating the value of the adsorbed fuel amount, which is an internal variable in the canister model, with the value of the adsorbed fuel amount calculated in reverse.   The air-fuel ratio control apparatus for an engine according to claim 1 or 2, wherein an air-fuel ratio learning value is added as purge cut time data when air-fuel ratio learning control is performed.   The engine air-fuel ratio control apparatus according to claim 2, wherein the data before purge cut is at least an air-fuel ratio feedback correction amount, a purge correction amount, and a target purge rate.   The air-fuel ratio control apparatus for an engine according to claim 2, wherein when the air-fuel ratio learning control is performed, an air-fuel ratio learning value is added to the data before purge cut.   The engine air-fuel ratio control apparatus according to claim 2, wherein the sampling timing of the purge sampling data sampling means is a timing at which a stabilization time has elapsed after the target purge rate becomes zero. The base air-fuel ratio error determination means, when the calculated air-fuel ratio feedback correction amount exceeds the second upper limit limiter, which is larger than the center value by the second limiter, determines the time during which the excess state continues , When the fuel ratio feedback correction amount falls below the second lower limiter, which is a value that is smaller than the center value by the second limiter, a time measuring means for measuring the time during which the lowering state continues and a comparison between this duration time and a predetermined value The engine air-fuel ratio control apparatus according to claim 1 or 2, further comprising comparison means for determining whether or not there is an air-fuel ratio error.   The purge cut means is a purge rate reduction processing means for performing a process of reducing the target purge rate when the calibration timing is reached when there is a base air-fuel ratio error to zero by a predetermined value at predetermined time intervals. The air-fuel ratio control apparatus for an engine according to claim 1 or 2, characterized by the above-mentioned.   When the calibration timing is reached for the first time after the engine is started, the calibration process at the first calibration timing is performed in the first calibration process, and according to the desorption amount calculated using the canister model calibrated by the first calibration process. A determination value is calculated, and based on this determination value, it is determined whether or not the purge process is completed. When it is determined that the purge process is completed, the purge rate or the purge flow rate is decreased and the air-fuel ratio learning value is updated. The engine air-fuel ratio control apparatus according to claim 1, wherein the engine air-fuel ratio control apparatus is performed.   The engine air-fuel ratio according to claim 9, wherein the determination value is a determination value for the integrated purge flow rate, and it is determined that the purge process has ended when the integrated purge flow rate from the start of the engine exceeds a determination value. Control device.   3. The engine air-fuel ratio according to claim 1, wherein when the calibration timing comes when there is no base air-fuel ratio error, a second calibration process based on the data being purged is performed on the canister model. Control device. The second calibration processing means includes
A desorbed fuel amount estimating means for estimating the amount of fuel desorbed from the canister based on the data being purged;
An adsorbed fuel amount back calculating means for calculating back the amount of fuel adsorbed to the canister from the estimated desorbed fuel amount;
The engine air-fuel ratio control apparatus according to claim 11, comprising calibration means for calibrating the value of the amount of adsorbed fuel, which is an internal variable in the canister model, with the value of the amount of adsorbed fuel calculated in reverse.   The engine air-fuel ratio control apparatus according to claim 10 or 11, wherein the data during the execution of the purge is at least an air-fuel ratio feedback correction amount, a purge correction amount, and a target purge rate.   The engine air-fuel ratio control apparatus according to claim 1 or 2, wherein a hysteresis is provided in the second limiter.   The desorbed fuel amount calculation formula of the canister model calculates the amount of fuel desorbed from the canister based on the adsorbed fuel amount calculated by the adsorbed fuel amount calculation formula, the target purge rate, and the temperature of the fuel adsorbent in the canister The air-fuel ratio control apparatus for an engine according to claim 1 or 2, characterized in that:   The canister model further includes an adsorbent temperature calculation formula that calculates the temperature drop of the fuel adsorbent based on the amount of fuel desorbed from the canister and calculates the temperature of the fuel adsorbent based on the temperature drop. The engine air-fuel ratio control apparatus according to claim 15,   The means for calculating back the amount of fuel adsorbed to the canister calculates the amount of fuel adsorbed to the canister from the estimated amount of desorbed fuel by inverse calculation of the desorbed fuel amount calculation formula of the canister model. The engine air-fuel ratio control apparatus according to claim 1 or 2.   The means for estimating the amount of desorbed fuel estimates the amount of desorbed fuel from the canister based on the air-fuel ratio deviation from the stoichiometric air-fuel ratio when there is no air-fuel ratio deviation from the stoichiometric air-fuel ratio due to disturbances other than purge. The air-fuel ratio control apparatus for an engine according to claim 1 or 2, characterized by the above-mentioned.   The means for estimating the amount of desorbed fuel is the desorption from the canister based on the air / fuel ratio deviation from the stoichiometric air / fuel ratio when the purge air / fuel ratio is deeper than a predetermined value and the air / fuel ratio deviation from the stoichiometric air / fuel ratio is sufficiently expressed by the purge. The engine air-fuel ratio control apparatus according to claim 1 or 2, wherein the fuel amount is estimated.   The means for estimating the amount of desorbed fuel is the desorbed fuel from the canister based on the air-fuel ratio deviation from the stoichiometric air-fuel ratio when the purge rate is higher than a predetermined value and the air-fuel ratio deviation from the stoichiometric air-fuel ratio by the purge is sufficiently expressed. The engine air-fuel ratio control apparatus according to claim 1 or 2, wherein the amount is estimated.

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