JP4265275B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

ここで、ｋは定数である。
【００１７】
ステップ４で、燃料温度センサ５からの燃料温度ＴＦＮを読み込む。
【００１８】
ステップ５では、前ステップで読み込んだ燃料温度ＴＦＮに基づいて燃料温度に対応する燃料供給量の制御補正値、すなわち燃温補正値ＬＴＥＭＰを算出する。燃温補正値ＬＴＥＭＰの算出には、図３に示すマップを用いて算出する。このマップは、学習した基準燃料温度（ＴＦＮ１、ＴＦＮ２）とその推定タイミングでの燃温補正学習値（ＬＴＥＭＰ１、ＬＴＥＭＰ２）との関係を後述する図４のフローチャートからプロットしたものに基づくものであり、この燃料温度と燃温補正値との関係と現在の燃料温度ＴＦＮとから現燃料温度に応じた燃温補正値ＬＴＥＭＰを算出する。なお、燃温補正学習値ＬＴＥＭＰ１、ＬＴＥＭＰ２の算出については図４を用いて詳しく説明する。
【００１９】
ステップ６では、その他の空燃比補正係数である目標当量比ＴＦＢＹＡ、空燃比フィードバック補正係数ＡＬＰＨＡを算出する。ここで、目標当量比ＴＦＢＹＡは、エンジン回転速度とエンジン負荷としての基本燃料噴射量ＴＰとをパラメータとするマップ値であり、低中負荷域などの成層燃焼を行う運転条件では１．０未満の値が、またこれより高負荷側で均質燃焼を行う運転条件では１．０以上の値が設定されている。
【００２０】
空燃比フィードバック補正係数ＡＬＰＨＡは、均質燃焼時等空燃比フィードバックを行う際に排気の実際の空燃比が目標範囲に収まるように空燃比センサ１４の出力に基づいて算出され、目標空燃比が理論空燃比であれば１．０を中心とする値である。
【００２１】
続くステップ７では、これら燃温補正値ＬＴＥＭＰ、目標当量比ＴＦＢＹＡ、空燃比フィードバック補正係数ＡＬＰＨＡにより基本燃料噴射量ＴＰを補正して、つまり次式によりインジェクタ４に与える燃料噴射量ＴＩを算出する。
【００２２】
【数２】

ただし、ＭＫＩＮＪ：インジェクタ倍率補正値、ＴＳ：無効噴射量である。
【００２３】
図４に示すフローチャートは、図３に示す燃料温度ＴＦＮと燃温補正値ＬＴＥＭＰとの関係を示すマップを学習によって作成するためのフローチャートである。コントローラ１３で実施され、燃料温度が所定温度だけ上昇したときに学習が繰り返されるものである。以下、フローチャートについて説明する。
【００２４】
まず、ステップ１１でエンジンの冷却水温、吸気温度、車速（∽エンジン回転速度）を前述の各センサを用いて読み込む。続くステップ１２では、燃料温度ＴＦＮを読み込む。
【００２５】
ステップ１３では、エンジンを始動してから最初の空燃比学習かどうかを判断する。最初の空燃比学習であればステップ１４に進み、２回目であればステップ１５に進む。
【００２６】
ステップ１４では、検出した燃料温度ＴＦＮが所定温度ＴＦＮＡ以下であるかどうかを判定する。温度条件が成立すればステップ１６に進み、不成立であれば、ステップ１７に進む。ここで所定温度ＴＦＮＡは、エンジンが冷間時始動時（燃料温度ＴＦＮが低い学習）か、ホットリスタート（燃料温度ＴＦＮが高い学習）かの区別をするために設けられるしきい値で、例えば、所定温度ＴＦＮＡは５０〜６０℃の値とする。
【００２７】
次に本来の運転条件からすればフィードバック制御によらず空燃比を制御する燃焼状態であっても、燃料温度に対応する燃料供給量の制御補正値の基準学習値を求めるため、ステップ１６では、エンジンの燃焼状態をフィードバック制御によらず空燃比を制御する成層燃焼禁止状態とし、空燃比をフィードバック制御する均質燃焼のみを許可し、ステップ１８に進み、今回検出した燃料温度ＴＦＮを第１の基準燃料温度ＴＦＮ１として記憶する。
【００２８】
続くステップ１９では、空燃比学習を許可し、続くステップ２０で基準燃料温度ＴＦＮ１での燃温補正値の基準学習値ＬＴＥＭＰＡを更新する。燃温補正値の基準学習値ＬＴＥＭＰＡの学習は従来公知の方法を用いて実施することができ、例えば空燃比フィードバック制御中の式（２）における空燃比フィードバック補正係数ＡＬＰＨＡの平均値を算出し、目標空燃比が理論空燃比とされる場合であれば１．０との差を吸収するように、すなわち経年変化などによって生じた目標噴射量に対する実際の噴射量のずれ（誤差）を打ち消すようにＬＴＥＭＰＡを算出することで学習を行う。ステップ２１では、空燃比センサ１４の反転回数等から燃温補正値の基準学習値が収束したかどうかの判定を実施し、収束した場合にはステップ２２に進み、収束していないと判定された場合にはステップ２０に戻り、基準燃料温度ＴＦＮ１での燃温補正値の基準学習値ＬＴＥＭＰＡの更新を繰り返す。
【００２９】
ステップ２２では、基準燃料温度ＴＦＮ１で収束したときの燃温補正値の基準学習値ＬＴＥＭＰＡを燃温補正学習値ＬＴＥＭＰ１に記憶する。そしてステップ２３で成層燃焼の許可を出力して制御を終える。
【００３０】
次にステップ１３で初回の学習が済んだと判断された後、ステップ１５では、基準燃料温度ＴＦＮ１と今回の燃料温度ＴＦＮとの温度差が所定の温度差ΔＴＦＮ以上あるかを判定し、温度差が所定温度差以上であればステップ１７に進み、所定温度差が小さければステップ１２に戻り、温度差ΔＴＦＮの検出を繰り返す。なお、ΔＴＦＮは、燃料温度が２０℃上昇すると燃料密度が２％以上変動することが知られており、このことからΔＴＦＮは２０℃程度に設定する。但し、ΔＴＦＮを小さく設定すれば、空燃比学習の精度が向上する反面、燃費の良い成層燃焼を禁止して、均質燃焼を行うことにより燃費が低下するため、それぞれが両立するように設定することが望ましい。
【００３１】
一方、ステップ１７で成層燃焼を禁止して、空燃比フィードバック制御を行わせ、ステップ２４に進み、今回検出した燃料温度ＴＦＮを第２の基準燃料温度ＴＦＮ２として記憶する。続くステップ２５で空燃比学習の許可を出力し、ステップ２６で基準燃料温度ＴＦＮ２での燃温補正値の基準学習値ＬＴＥＭＰＡを更新する。ステップ２７では、ステップ２１と同様にして学習値が収束したかどうかの判定を実施し、収束した場合にはステップ２８に進み、収束していないと判定された場合にはステップ２６に戻り、基準燃料温度ＴＦＮ２での燃温補正値の基準学習値ＬＴＥＭＰＡの更新を繰り返す。
【００３２】
ステップ２８では、基準燃料温度ＴＦＮ２で収束したときの燃温補正値の基準学習値ＬＴＥＭＰＡを燃温補正学習値ＬＴＥＭＰ２に記憶する。そしてステップ２９で成層燃焼の許可を出力して制御を終える。
【００３３】
図５は図４のフローチャートを時系列的に説明するためのタイミングチャートである。
【００３４】
エンジンが始動し、均質燃焼が行われて、時刻ｔ１で成層燃焼の許可が指令されるまでの制御は、ステップ１１からステップ１４、ステップ１６、ステップ１８からステップ２３までの制御であり、この制御でエンジン始動直後の燃料温度が低い状態での第１の燃温補正学習値を求めている。そして、時刻ｔ１で成層燃焼の許可が指令されるとエンジン燃焼は成層燃焼となり、空燃比はリーン側に変化する。
【００３５】
時刻ｔ２で燃料温度が所定温度だけ上昇したときに（ステップ１５）、第２の燃温補正学習値を求めるために成層燃焼を禁止し、均質燃焼に切り換える（ステップ１６）。空燃比がストイキに達した後に（時刻ｔ３）、ステップ２４以降の制御を実施して第２の燃温補正学習値を求め、制御を終える。
【００３６】
このようにして温度の異なる２つの基準燃料温度に対応する２つの燃温補正学習値ＬＴＥＭＰ１、ＬＴＥＭＰ２をプロットしたのが図３である。すなわち、図３は横軸を燃料温度、縦軸を燃温補正値とするグラフであり、（ＴＦＮ１、ＬＴＥＭＰ１）と（ＴＦＮ２、ＬＴＥＭＰ２）の各点を白丸で示している。そして、２つの点を結ぶ直線を作成し、２つの基準燃料温度にないときの燃料温度ＴＦＮに対しては、最小二乗法を用いて作成した線より燃料温度ＴＦＮに対応する燃温補正値を推定する。これにより、図３を用いて、基準燃料温度以外の燃料温度以外のときでも、そのときの燃料温度ＴＦＮに対応する燃温補正値ＬＴＥＭＰを算出することができる。
【００３７】
通常、成層燃焼状態では、特に空燃比センサがＯ２センサの場合フィードバック制御を行うことができず、燃温補正学習値を更新することができない。しかしながら本発明においては、燃焼状態にかかわらず、燃料温度が変化する場合に、燃料温度の変化に応じて一時的に均質燃焼に切り換えて第２の燃温補正学習値を求め、燃料温度が低い状態で得ている第１の燃温補正学習値と合わせて図３に示すようなマップを作成し、その後はそのときの燃料温度に対応する燃温補正学習値を図３に示すマップを用いて算出し、この燃温補正学習値を用いて成層燃焼時の燃料噴射量を設定するため、燃料の性状や燃料の経時劣化等の影響をも含めて、燃料温度に関係なく成層燃焼時に最適な空燃比が得られる。
【００３８】
ステップ１３、ステップ１４で実施するように、始動後すぐの冷間時に燃温補正学習値の学習を行うようにすれば燃料温度が低いエンジンの冷間始動時には燃焼の安定性の確保またはエンジンの暖機を目的として均質燃焼を実施するため、成層燃焼切り換え前に燃温補正学習値の学習を終わらせることができるので、始動後成層燃焼状態から均質燃焼に切り換えてまで第１の燃温補正学習値を求める必要がない。
【００３９】
なお、図４のフローチャートにおけるステップ１６あるいはステップ１７では、成層燃焼を禁止することとしたが、空燃比フィードバックを行わないようなリッチ燃焼を禁止して、空燃比フィードバック制御を行う燃焼に切り換えることもできる。
【００４０】
図６と図７に示す第２の実施形態は、図３と図４に示す第１の実施形態に対して、燃温補正学習値の取得回数を２回から３回にした点で異なり、このため、より精度良く空燃比を算出することができる。
【００４１】
図６に示すように、算出した燃温補正学習値を３点プロットして、最小二乗法にて近似線を設定する。そして燃温補正学習値を求める燃料温度をこの図にプロットすることで燃温補正学習値を算出することが精度良く可能である。
【００４２】
図７はこの実施形態のフローチャートを示し、図４のフローチャートを同じ制御内容のステップには同じステップ数を付与し、この実施形態特有のステップはステップ３１からステップ４０である。特有のステップ３１からステップ４０についても第１の実施形態と技術的な思想は同じであるので、詳細の説明は省略するが、ステップ３３の所定温度ＴＦＮＢは、前述の所定温度ＴＦＮＡより２０℃程度高い温度に設定する。
【００４３】
図８に示す第３の実施形態は、前回および前々回のトリップ時の燃温補正学習値と今回のトリップでの燃温補正学習値とに基づき燃温補正学習値を算出するものである。このように過去の燃温補正学習値を用いることで、プロット数を増やし、より精度良く燃温補正値を算出することができる。
【００４４】
各トリップでの燃料温度と燃温補正学習値との関係を図にプロットし、最小二乗法により近似線を求め、この近似線を用いて燃料温度から燃温補正値を算出することができる。なお、ここでいうトリップとは、１回のエンジン始動から停止までの走行のことを意味する。
【００４５】
図９から図１１は、第４の実施形態を説明するための図であり、これは、第１から第３の実施形態が、燃料温度センサの検出燃料温度に応じて燃温補正学習値を求めるものであったのに対して、インジェクタの駆動回路に流れる電流と目標電流との差を算出し、算出した差に基づいて燃温補正学習値を学習するようにした実施形態である。
【００４６】
図９は、従来行われているインジェクタの駆動回路の通電量と目標電流との差に基づく燃料噴射時間の補正関係を示している。インジェクタの通電量が目標電流より少ない場合には、燃料噴射量が少なくなるため、噴射時間を増加補正して目標噴射量となるようにしている。
【００４７】
燃料温度が上昇するとインジェクタの駆動部の温度が上昇し、駆動部の抵抗が増加する。この結果、駆動回路の通電量が低下することになる。この関係を示すのが図１０である。したがって、目標電流と駆動回路の通電量との差ΔＡｎｏｗを検出し、この差の変化に基づいて燃温補正学習値を学習する。
【００４８】
図１１は、目標電流と駆動回路の通電量との差分ΔＡｎｏｗに応じて学習値を算出する図である。なお、本実施形態においてはインジェクタの駆動回路の通電量を用いて学習を実施するように設定したが、例えば点火プラグ４の抵抗値を用いてもよい。
【００４９】
図１２と図１３は、第５の実施形態を説明するための図であり、本実施形態は、１回目の学習時に設定した第１の燃温補正学習値ＬＴＥＭＰＡを燃料温度ＴＦＮが所定温度ΔＴＦＮ上昇時に実施する次回の学習時まで一定値として保持することを特徴とする。第１の実施形態のように複数の燃温補正学習値から燃温補正値を算出する必要がなく、演算処理の負担を軽減することができる。
【００５０】
図１２のフローチャートは、第１の実施形態のフローチャート（図４参照）に類似するが、ステップ２２とステップ４３で、燃温補正学習値ををそのまま燃温補正値ＬＴＥＭＰに設定する点が第１の実施形態と異なる。
【００５１】
図１４と図１５は、第６の実施形態を説明するための図であり、本実施形態は、１回目の学習時に設定した第１の燃温補正学習値ＬＴＥＭＰＡを１回目の学習時からの経過時間Ｔが所定時間ΔＴ経過時に実施する次回の学習時まで一定値として保持することを特徴とする。第１の実施形態のように複数の燃温補正学習値から燃温補正値を算出する必要がなく、演算処理の負担を軽減することができる。また前回の学習時からの経過時間で次回の学習のタイミングを制御できるので、制御を簡単にできる効果がある。
【００５２】
図１４のフローチャートは、第５の実施形態のフローチャート（図１２参照）に類似するが、ステップ５１の第１の学習からの経過時間Ｔ−Ｔ１が所定経過時間ΔＴ以上の時に次回の燃温補正学習値を学習する点が第５の実施形態と異なる。
【００５３】
したがって、本発明は、内燃機関から排出された排気の空燃比を検出する空燃比検出手段と、内燃機関の運転条件に応じて前記空燃比検出手段の出力に基づくフィードバックによる空燃比制御とフィードバック制御によらない空燃比制御とを行う空燃比制御手段と、燃料温度を検知する燃料温度検知手段と、前記フィードバックによる空燃比制御時に燃料温度に対応した燃料供給量補正値を求めて、該補正値を学習値として学習する学習手段と、前記学習値に基づいて求めた燃料温度に対応した燃料供給量補正値を使って燃料供給量を補正する燃料供給量補正手段とを備えた内燃機関の制御装置において、内燃機関の運転条件がフィードバックによらない空燃比制御を行う条件であっても、燃料温度に応じてフィードバックによる空燃比制御に切り換えて、補正値の学習を行うため、車両加速時におけるリッチ空燃比制御の間や、筒内直噴式エンジンで行われる成層燃焼のようなリーン空燃比制御の間等、空燃比フィードバック制御を行わない運転条件においても燃料温度に応じて空燃比フィードバック制御に切り換えるようにしたので、燃料温度補正値を運転条件に限定されることなく更新して、経年変化などによる補正値のずれ（誤差）を解消させることができる。
【００５４】
前記燃料温度は、温度センサにより検出されるため、内燃機関の構成に応じて燃料温度の変化を算出することができる。また、前記燃料温度は、内燃機関の冷却水温度またはインジェクタ回路の電流または前回の空燃比学習からの経過時間に基づく推定から求められるため、内燃機関の構成に応じて燃料温度の変化を算出することができる。
【００５５】
本発明は、上記した実施形態に限定されるものではなく、本発明の技術的思想の範囲内でさまざまな変更がなしうることは明白である。
【図面の簡単な説明】
【図１】本発明のエンジンのシステムの構成図である。
【図２】燃料噴射時間を算出するフローチャートである。
【図３】燃料温度と空燃比学習値の関係を示す図である。
【図４】空燃比学習値を算出するフローチャートである。
【図５】図４のフローチャートを時系列で示すタイミングチャートである。
【図６】第２の実施形態としての燃料温度と空燃比学習値の関係を示す図である。
【図７】第２の実施形態としての空燃比学習値を算出するフローチャートである。
【図８】第３の実施形態としての燃料温度と空燃比学習値の関係を示す図である。
【図９】電流偏差と無効パルス幅の関係を示す図である。
【図１０】電流偏差と燃料温度の関係を示す図である。
【図１１】第４の実施形態としての燃料温度と空燃比学習値の関係を示す図である。
【図１２】第５の実施形態としての空燃比学習値を算出するフローチャートである。
【図１３】第５の実施形態としての燃料温度と空燃比学習値の関係を示す図である。
【図１４】第６の実施形態としての空燃比学習値を算出するフローチャートである。
【図１５】第６の実施形態としての燃料温度と空燃比学習値の関係を示す図である。
【符号の説明】
１ エンジン本体
２ 吸気通路
３ 排気通路
４ インジェクタ
５ 燃料温度センサ
６ 冷却水温度センサ
７ クランク角速度センサ
８ エアフローメータ
９ 吸気温度センサ
１０ スロットル弁開度センサ
１１ ポンプ
１２ 燃料タンク
１３ コントローラ
１４ 空燃比センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.
[0002]
[Prior art]
When a change occurs in the temperature of the fuel used for combustion of the internal combustion engine, even if the fuel is injected with the same pulse width due to a change in the density of the fuel, the weight of the injected fuel changes and the air-fuel ratio deviates from the target value. In order to avoid this, there is a technique for estimating the fuel temperature and correcting the pulse width of the fuel injection from the estimated fuel temperature (see, for example, Patent Document 1). By this correction, even if the fuel density changes due to temperature change, the total amount (numerator number) of injected fuel is prevented from changing and the air-fuel ratio does not deviate from the target value.
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-200908
[Problems to be solved by the invention]
By the way, considering that there is a deviation (error) in the actual injection amount with respect to the target injection amount of fuel due to secular change, the fuel temperature correction value is stored as a learning value, and the fuel temperature correction value is obtained by repeating learning. The learning value can be updated. However, since the learning value is updated while air-fuel ratio feedback control is performed, it is performed during rich air-fuel ratio control during vehicle acceleration, or during lean air-fuel ratio control such as stratified combustion performed in a direct injection engine. For example, there is a problem that learning for eliminating the deviation of the correction value cannot be performed under an operating condition in which the air-fuel ratio feedback control is not performed.
[0005]
Therefore, in view of the above problems, an object of the present invention is to eliminate deviations in correction values during air-fuel ratio control.
[0006]
[Means for Solving the Problems]
The present invention relates to an O2 sensor installed in an exhaust passage, air-fuel ratio control based on feedback based on the output of the O2 sensor according to the operating conditions of the internal combustion engine, and the air-fuel ratio at the time of control is a lean air-fuel ratio and feedback control Air-fuel ratio control means for performing air-fuel ratio control not depending on the fuel , fuel temperature detection means for detecting the fuel temperature, and a fuel supply amount correction value corresponding to the fuel temperature based on the fuel temperature detected by the fuel temperature detection means And calculating the fuel supply amount correction value corresponding to the fuel temperature and using the fuel supply amount correction value corresponding to the calculated fuel temperature during the air-fuel ratio control by the feedback and the feedback air-fuel ratio and the fuel supply amount correcting means for correcting the fuel supply amount at the time of control, operation conditions of the internal combustion engine at least two different fuel temperature does not depend on Fuel supply but also a condition for the air-fuel ratio control that is not based on feedback, in which the switching Ru switching means to the air-fuel ratio control by the feedback corresponding to each fuel temperature of the control during the time the air-fuel ratio control by the feedback after the switching A learning unit that obtains an amount correction value and learns the correction value as a learning value, and creates a map of the fuel supply amount correction value corresponding to the fuel temperature based on at least two learning values obtained by the learning Map creating means .
[0007]
【The invention's effect】
According to the present invention, even during operating conditions in which air-fuel ratio feedback control is not performed, such as during rich air-fuel ratio control during vehicle acceleration, or during lean air-fuel ratio control such as stratified combustion performed in an in-cylinder direct injection engine. Since the air-fuel ratio feedback control is switched according to the fuel temperature, the fuel temperature correction value can be updated without being limited to the operating conditions, and the deviation (error) of the correction value due to secular change can be eliminated. .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram showing an example of an engine system to which the air-fuel ratio control of the present invention is applied.
[0009]
An intake passage 2 and an exhaust passage 3 are connected to the engine body 1. Air is supplied into the cylinder, mixed with fuel and burned, and exhaust is discharged through the exhaust passage 3.
[0010]
The engine body 1 includes an injector 4 for injecting fuel into the cylinder, a fuel temperature sensor 5 for detecting the temperature of the fuel injected from the injector 4, and a cooling water temperature sensor for detecting the cooling water temperature of the engine. 6 and a crank angular velocity sensor 7 for detecting the rotational speed of the engine. The intake passage 2 has an air flow meter 8 for detecting the amount of air sucked into the cylinder, an intake air temperature sensor 9 for detecting the temperature of air sucked into the cylinder, and a throttle valve for controlling the air amount. And a throttle valve opening sensor 10 for detecting the opening of the. On the other hand, an air-fuel ratio sensor 14 such as an O2 sensor or a linear sensor is installed in the exhaust passage 3 to detect the air-fuel ratio of the exhaust.
[0011]
By the action of the pump 11, fuel is supplied to the injector 4 from the fuel tank 12 that stores the fuel. In the present system, a pipe for returning fuel that has been supplied to the engine 1 but not used for combustion or the like to the fuel tank 12, so-called return pipe, is not installed. According to this configuration, the cost can be reduced and the generation of fuel vapor in the fuel tank 12 can be suppressed.
[0012]
A controller (indicated by ECM in the figure) 13 for integrated control of engine operation is installed. The controller 13 includes a fuel temperature of the fuel temperature sensor 5, a cooling water temperature of the cooling water temperature sensor 6, and a crank angular velocity. The engine speed is input from the detection value of the sensor 7. The vehicle speed is input from a vehicle speed signal from a vehicle speed sensor (not shown). Based on these input values, the controller 13 controls the injector 4 and the pump 11 to inject fuel with an appropriate fuel injection amount. The calculation of the fuel injection amount will be described in detail with reference to the flowchart of FIG.
[0013]
Furthermore, the controller 13 inputs the detection value of the fuel temperature sensor 5 and calculates a fuel supply amount control correction value corresponding to the fuel temperature, that is, a fuel temperature correction value, according to the fuel temperature.
[0014]
FIG. 2 is a flowchart for calculating the fuel injection amount of the present invention.
[0015]
First, in step 1, the engine rotational speed Ne is read from the output of the crank angular velocity sensor 8 and the intake air amount Qa is read from the output of the air flow meter 8. In step 2, the engine coolant temperature and the intake air amount from the output of the coolant temperature sensor 6 are read. The intake air temperature and the vehicle speed are read from the output of the temperature sensor 9. In step 3, the basic fuel injection amount TP is calculated by the following equation.
[0016]
[Expression 1]

Here, k is a constant.
[0017]
In step 4, the fuel temperature TFN from the fuel temperature sensor 5 is read.
[0018]
In step 5, the control correction value of the fuel supply amount corresponding to the fuel temperature, that is, the fuel temperature correction value LTEMP is calculated based on the fuel temperature TFN read in the previous step. The fuel temperature correction value LTEMP is calculated using the map shown in FIG. This map is based on the relationship between the learned reference fuel temperature (TFN1, TFN2) and the fuel temperature correction learned value (LTEMP1, LTEMP2) at the estimated timing plotted from the flowchart of FIG. 4 to be described later. A fuel temperature correction value LTEMP corresponding to the current fuel temperature is calculated from the relationship between the fuel temperature and the fuel temperature correction value and the current fuel temperature TFN. The calculation of the fuel temperature correction learned values LTEMP1 and LTEMP2 will be described in detail with reference to FIG.
[0019]
In step 6, a target equivalent ratio TFBYA and an air-fuel ratio feedback correction coefficient ALPHA, which are other air-fuel ratio correction coefficients, are calculated. Here, the target equivalent ratio TFBYA is a map value that uses the engine speed and the basic fuel injection amount TP as the engine load as parameters, and is less than 1.0 under the operating conditions for performing stratified combustion in a low and medium load range or the like. The value is set to 1.0 or more under the operating conditions in which homogeneous combustion is performed on the higher load side than this value.
[0020]
The air-fuel ratio feedback correction coefficient ALPHA is calculated on the basis of the output of the air-fuel ratio sensor 14 so that the actual air-fuel ratio of the exhaust gas falls within the target range when performing the equal air-fuel ratio feedback at the time of homogeneous combustion. If the fuel ratio, the value is centered on 1.0.
[0021]
In the subsequent step 7, the basic fuel injection amount TP is corrected by the fuel temperature correction value LTEMP, the target equivalent ratio TFBYA, and the air-fuel ratio feedback correction coefficient ALPHA, that is, the fuel injection amount TI given to the injector 4 is calculated by the following equation.
[0022]
[Expression 2]

However, MKINJ: injector magnification correction value, TS: invalid injection amount.
[0023]
The flowchart shown in FIG. 4 is a flowchart for creating a map showing the relationship between the fuel temperature TFN and the fuel temperature correction value LTEMP shown in FIG. 3 by learning. The learning is repeated by the controller 13 when the fuel temperature rises by a predetermined temperature. The flowchart will be described below.
[0024]
First, in step 11, the engine coolant temperature, the intake air temperature, and the vehicle speed (the engine speed) are read using the aforementioned sensors. In the following step 12, the fuel temperature TFN is read.
[0025]
In step 13, it is determined whether or not it is the first air-fuel ratio learning after the engine is started. If it is the first air-fuel ratio learning, the process proceeds to step 14, and if it is the second time, the process proceeds to step 15.
[0026]
In step 14, it is determined whether or not the detected fuel temperature TFN is equal to or lower than a predetermined temperature TFNA. If the temperature condition is satisfied, the process proceeds to step 16, and if not, the process proceeds to step 17. Here, the predetermined temperature TFNA is a threshold value provided to distinguish whether the engine is cold start (learning when the fuel temperature TFN is low) or hot restart (learning when the fuel temperature TFN is high). The predetermined temperature TFNA is set to a value of 50 to 60 ° C.
[0027]
Next, in order to obtain the reference learning value of the control correction value of the fuel supply amount corresponding to the fuel temperature even in the combustion state in which the air-fuel ratio is controlled without using the feedback control based on the original operating condition, The engine combustion state is set to the stratified combustion prohibition state in which the air-fuel ratio is controlled without feedback control, only the homogeneous combustion in which the air-fuel ratio is feedback-controlled is permitted, and the routine proceeds to step 18 where the detected fuel temperature TFN is the first reference. Stored as fuel temperature TFN1.
[0028]
In the subsequent step 19, air-fuel ratio learning is permitted, and in the subsequent step 20, the reference learning value LTEMPA of the fuel temperature correction value at the reference fuel temperature TFN1 is updated. The learning of the reference learning value LTEMPA of the fuel temperature correction value can be performed using a conventionally known method. For example, the average value of the air-fuel ratio feedback correction coefficient ALPHA in equation (2) during the air-fuel ratio feedback control is calculated, If the target air-fuel ratio is the stoichiometric air-fuel ratio, the difference from 1.0 is absorbed, that is, the deviation (error) of the actual injection amount with respect to the target injection amount caused by secular change or the like is cancelled. Learning is performed by calculating LTEMPA. In step 21, it is determined whether or not the reference learning value of the fuel temperature correction value has converged from the number of inversions of the air-fuel ratio sensor 14. If so, the process proceeds to step 22, where it is determined that it has not converged. In this case, the process returns to step 20, and the update of the reference learning value LTEMPA of the fuel temperature correction value at the reference fuel temperature TFN1 is repeated.
[0029]
In step 22, the reference learning value LTEMPA of the fuel temperature correction value when it converges at the reference fuel temperature TFN1 is stored in the fuel temperature correction learning value LTEMP1. In step 23, the permission of stratified combustion is output and the control is finished.
[0030]
Next, after it is determined in step 13 that the initial learning has been completed, in step 15, it is determined whether the temperature difference between the reference fuel temperature TFN1 and the current fuel temperature TFN is equal to or greater than a predetermined temperature difference ΔTFN. If the predetermined temperature difference is equal to or greater than the predetermined temperature difference, the process proceeds to step 17, and if the predetermined temperature difference is small, the process returns to step 12 to repeat the detection of the temperature difference ΔTFN. Note that ΔTFN is known to change the fuel density by 2% or more when the fuel temperature rises by 20 ° C. Therefore, ΔTFN is set to about 20 ° C. However, if ΔTFN is set to a small value, the accuracy of air-fuel ratio learning will be improved, but stratified combustion with good fuel efficiency will be prohibited and the fuel efficiency will be reduced by performing homogeneous combustion. Is desirable.
[0031]
On the other hand, in step 17, stratified combustion is prohibited, air-fuel ratio feedback control is performed, the process proceeds to step 24, and the fuel temperature TFN detected this time is stored as the second reference fuel temperature TFN2. Subsequently, in step 25, permission of air-fuel ratio learning is output, and in step 26, the reference learning value LTEMPA of the fuel temperature correction value at the reference fuel temperature TFN2 is updated. In step 27, it is determined whether or not the learning value has converged in the same manner as in step 21. If the learning value has converged, the process proceeds to step 28. If it is determined that the learning value has not converged, the process returns to step 26 to The update of the reference learning value LTEMPA of the fuel temperature correction value at the fuel temperature TFN2 is repeated.
[0032]
In step 28, the reference learning value LTEMPA of the fuel temperature correction value when converged at the reference fuel temperature TFN2 is stored in the fuel temperature correction learning value LTEMP2. In step 29, the permission of stratified combustion is output and the control is finished.
[0033]
FIG. 5 is a timing chart for explaining the flowchart of FIG. 4 in time series.
[0034]
Control from when the engine is started and homogeneous combustion is performed until permission for stratified combustion is commanded at time t1 is control from step 11 to step 14, step 16, and step 18 to step 23. Thus, the first fuel temperature correction learning value is obtained in a state where the fuel temperature is low immediately after the engine is started. When permission for stratified combustion is commanded at time t1, engine combustion becomes stratified combustion, and the air-fuel ratio changes to the lean side.
[0035]
When the fuel temperature rises by a predetermined temperature at time t2 (step 15), stratified combustion is prohibited to obtain the second fuel temperature correction learning value, and the combustion is switched to homogeneous combustion (step 16). After the air-fuel ratio reaches stoichiometric (time t3), the control after step 24 is performed to obtain the second fuel temperature correction learning value, and the control is finished.
[0036]
FIG. 3 plots two fuel temperature correction learning values LTEMP1 and LTEMP2 corresponding to two reference fuel temperatures having different temperatures in this way. That is, FIG. 3 is a graph in which the horizontal axis represents the fuel temperature and the vertical axis represents the fuel temperature correction value, and each point of (TFN1, LTEMP1) and (TFN2, LTEMP2) is indicated by a white circle. Then, a straight line connecting the two points is created, and for the fuel temperature TFN when the two reference fuel temperatures are not present, the fuel temperature correction value corresponding to the fuel temperature TFN is obtained from the line created using the least square method. presume. Thus, the fuel temperature correction value LTEMP corresponding to the fuel temperature TFN at that time can be calculated using FIG. 3 even when the fuel temperature is other than the reference fuel temperature.
[0037]
Normally, in the stratified combustion state, particularly when the air-fuel ratio sensor is an O2 sensor, feedback control cannot be performed, and the fuel temperature correction learned value cannot be updated. However, in the present invention, when the fuel temperature changes regardless of the combustion state, the second fuel temperature correction learning value is obtained by temporarily switching to homogeneous combustion according to the change in the fuel temperature, and the fuel temperature is low. A map as shown in FIG. 3 is created together with the first fuel temperature correction learning value obtained in the state, and thereafter, the fuel temperature correction learning value corresponding to the fuel temperature at that time is used as a map shown in FIG. The fuel injection amount at the time of stratified combustion is set using this fuel temperature correction learning value, so it is optimal at the time of stratified combustion regardless of the fuel temperature, including the effects of fuel properties and fuel deterioration over time. An air-fuel ratio can be obtained.
[0038]
If the learning of the fuel temperature correction learning value is performed when the engine is cold immediately after the start as in step 13 and step 14, the stability of the combustion is ensured during the cold start of the engine having a low fuel temperature or the engine Since homogeneous combustion is performed for the purpose of warming up, learning of the fuel temperature correction learning value can be ended before switching to stratified combustion, so the first fuel temperature correction is made until switching from stratified combustion state after startup to homogeneous combustion. There is no need to obtain a learning value.
[0039]
In step 16 or step 17 in the flowchart of FIG. 4, stratified combustion is prohibited. However, rich combustion that does not perform air-fuel ratio feedback is prohibited, and switching to combustion that performs air-fuel ratio feedback control may be performed. it can.
[0040]
The second embodiment shown in FIGS. 6 and 7 differs from the first embodiment shown in FIGS. 3 and 4 in that the number of acquisitions of the fuel temperature correction learning value is changed from two to three. For this reason, the air-fuel ratio can be calculated with higher accuracy.
[0041]
As shown in FIG. 6, the calculated fuel temperature correction learning value is plotted at three points, and an approximate line is set by the least square method. The fuel temperature correction learning value can be calculated with high accuracy by plotting the fuel temperature for obtaining the fuel temperature correction learning value in this figure.
[0042]
FIG. 7 shows a flowchart of this embodiment. In the flowchart of FIG. 4, steps having the same control contents are given the same number of steps, and steps unique to this embodiment are step 31 to step 40. The specific steps 31 to 40 have the same technical idea as that of the first embodiment, and detailed description thereof will be omitted. However, the predetermined temperature TFNB in step 33 is about 20 ° C. than the predetermined temperature TFNA. Set to a higher temperature.
[0043]
In the third embodiment shown in FIG. 8, the fuel temperature correction learned value is calculated based on the fuel temperature correction learned value at the previous trip and the previous trip and the fuel temperature correction learned value at the current trip. Thus, by using the past fuel temperature correction learned value, the number of plots can be increased, and the fuel temperature correction value can be calculated more accurately.
[0044]
The relationship between the fuel temperature and the fuel temperature correction learning value in each trip is plotted in the figure, an approximate line is obtained by the least square method, and the fuel temperature correction value can be calculated from the fuel temperature using this approximate line. In addition, the trip here means the driving | running | working from one engine starting to a stop.
[0045]
FIGS. 9 to 11 are diagrams for explaining the fourth embodiment. This is because the first to third embodiments set the fuel temperature correction learning value according to the detected fuel temperature of the fuel temperature sensor. In contrast to what has been obtained, the difference between the current flowing through the injector drive circuit and the target current is calculated, and the fuel temperature correction learning value is learned based on the calculated difference.
[0046]
FIG. 9 shows a correction relationship of the fuel injection time based on the difference between the energization amount of the injector drive circuit and the target current, which has been conventionally performed. When the energization amount of the injector is smaller than the target current, the fuel injection amount is reduced, so that the injection time is corrected to increase to the target injection amount.
[0047]
When the fuel temperature rises, the temperature of the drive unit of the injector rises and the resistance of the drive unit increases. As a result, the energization amount of the drive circuit is reduced. This relationship is shown in FIG. Therefore, the difference ΔAnow between the target current and the energization amount of the drive circuit is detected, and the fuel temperature correction learning value is learned based on the change in the difference.
[0048]
FIG. 11 is a diagram for calculating the learning value according to the difference ΔAnow between the target current and the energization amount of the drive circuit. In the present embodiment, learning is performed using the energization amount of the injector drive circuit, but the resistance value of the spark plug 4 may be used, for example.
[0049]
FIG. 12 and FIG. 13 are diagrams for explaining the fifth embodiment. In the present embodiment, the fuel temperature TFN is equal to the predetermined temperature ΔTFN as the first fuel temperature correction learning value LTEMPA set at the first learning. It is characterized in that it is held as a constant value until the next learning that is performed at the time of ascent. There is no need to calculate a fuel temperature correction value from a plurality of fuel temperature correction learning values as in the first embodiment, and the burden of calculation processing can be reduced.
[0050]
The flowchart of FIG. 12 is similar to the flowchart of the first embodiment (see FIG. 4), but the first point is that the fuel temperature correction learned value is set to the fuel temperature correction value LTEMP as it is in step 22 and step 43. Different from the embodiment.
[0051]
FIG. 14 and FIG. 15 are diagrams for explaining the sixth embodiment. In this embodiment, the first fuel temperature correction learning value LTEMPA set at the first learning is obtained from the first learning. The elapsed time T is held as a constant value until the next learning that is performed when the predetermined time ΔT has elapsed. There is no need to calculate a fuel temperature correction value from a plurality of fuel temperature correction learning values as in the first embodiment, and the burden of calculation processing can be reduced. In addition, since the next learning timing can be controlled by the elapsed time from the previous learning, there is an effect that the control can be simplified.
[0052]
The flowchart in FIG. 14 is similar to the flowchart in the fifth embodiment (see FIG. 12), but the next fuel temperature correction is performed when the elapsed time T-T1 from the first learning in step 51 is equal to or longer than the predetermined elapsed time ΔT. The point which learns a learning value differs from 5th Embodiment.
[0053]
Accordingly, the present invention provides an air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas discharged from an internal combustion engine, and an air-fuel ratio control and feedback control based on feedback based on the output of the air-fuel ratio detection means according to the operating conditions of the internal combustion engine. An air-fuel ratio control means for performing air-fuel ratio control not depending on the fuel; a fuel temperature detection means for detecting the fuel temperature; and a fuel supply amount correction value corresponding to the fuel temperature at the time of air-fuel ratio control by the feedback. And a fuel supply amount correction means for correcting the fuel supply amount using a fuel supply amount correction value corresponding to the fuel temperature obtained based on the learned value. In the system, even if the operating condition of the internal combustion engine is a condition for performing air-fuel ratio control without feedback, the air-fuel ratio control by feedback according to the fuel temperature In order to switch and learn the correction value, air-fuel ratio feedback control is performed during rich air-fuel ratio control during vehicle acceleration, or during lean air-fuel ratio control such as stratified combustion performed in an in-cylinder direct injection engine Even under non-operating conditions, the air-fuel ratio feedback control is switched according to the fuel temperature, so the fuel temperature correction value is updated without being limited to the operating conditions, and the deviation (error) of the correction value due to secular change, etc. It can be eliminated.
[0054]
Since the fuel temperature is detected by a temperature sensor, the change in the fuel temperature can be calculated according to the configuration of the internal combustion engine. Further, since the fuel temperature is obtained from the estimation based on the coolant temperature of the internal combustion engine, the current of the injector circuit or the elapsed time from the previous air-fuel ratio learning, the change in the fuel temperature is calculated according to the configuration of the internal combustion engine. be able to.
[0055]
The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea of the present invention.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an engine system according to the present invention.
FIG. 2 is a flowchart for calculating a fuel injection time.
FIG. 3 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value.
FIG. 4 is a flowchart for calculating an air-fuel ratio learning value.
FIG. 5 is a timing chart showing the flowchart of FIG. 4 in time series.
FIG. 6 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value as a second embodiment.
FIG. 7 is a flowchart for calculating an air-fuel ratio learning value as a second embodiment.
FIG. 8 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value as a third embodiment.
FIG. 9 is a diagram showing the relationship between current deviation and invalid pulse width.
FIG. 10 is a graph showing the relationship between current deviation and fuel temperature.
FIG. 11 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value as a fourth embodiment.
FIG. 12 is a flowchart for calculating an air-fuel ratio learning value as a fifth embodiment.
FIG. 13 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value as a fifth embodiment.
FIG. 14 is a flowchart for calculating an air-fuel ratio learning value as a sixth embodiment.
FIG. 15 is a diagram showing a relationship between a fuel temperature and an air-fuel ratio learning value as a sixth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine body 2 Intake passage 3 Exhaust passage 4 Injector 5 Fuel temperature sensor 6 Coolant temperature sensor 7 Crank angular velocity sensor 8 Air flow meter 9 Intake temperature sensor 10 Throttle valve opening sensor 11 Pump 12 Fuel tank 13 Controller 14 Air-fuel ratio sensor

Claims (7)

An O2 sensor installed in the exhaust passage ;
Air-fuel ratio control means for performing air-fuel ratio control by feedback based on the output of the O2 sensor in accordance with operating conditions of the internal combustion engine, and air-fuel ratio control in which the air-fuel ratio at the time of control is a lean air-fuel ratio and is not based on feedback control; ,
Fuel temperature detection means for detecting the fuel temperature;
Means for calculating a fuel supply amount correction value corresponding to the fuel temperature using a map of the fuel supply amount correction value corresponding to the fuel temperature based on the fuel temperature detected by the fuel temperature detection means;
Fuel supply amount correction means for correcting the fuel supply amount at the time of air-fuel ratio control by the feedback and at the time of air-fuel ratio control not by the feedback using the fuel supply amount correction value corresponding to the calculated fuel temperature;
Even conditions operating conditions of at least two different fuel temperature in an internal combustion engine performs the air-fuel ratio control that is not based on the feedback, the switching Ru switching means to the air-fuel ratio control by feedback,
Learning means for obtaining a fuel supply amount correction value corresponding to each fuel temperature at the time of air-fuel ratio control by feedback after the switching , and learning the correction value as a learning value;
Map creating means for creating a map of a fuel supply amount correction value corresponding to the fuel temperature based on at least two learning values obtained by the learning;
Control apparatus for an internal combustion engine, characterized in that it comprises a. The learning means includes storage means for storing the fuel temperature and the learning value in association with each other,
When the at least two learning values are two learning values, the map creating means plots two learning values on a graph with the horizontal axis representing the fuel temperature and the vertical axis representing the learning value. 2. The control device for an internal combustion engine according to claim 1 , wherein a characteristic of a straight line connecting two points is created as a map of a fuel supply amount correction value corresponding to the fuel temperature . After the last learning, the air-fuel ratio control not based on the feedback is performed, and when the fuel temperature rises by a predetermined value as compared with the previous learning, the air-fuel ratio control not based on the feedback is started. the control apparatus according to claim 1 or claim 2, characterized in that the lines have the learn switch to air-fuel ratio control by the feedback.   The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the learning value of the correction value is performed at least immediately after starting the internal combustion engine. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the at least two different fuel temperatures are two or three different fuel temperatures per trip .   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the fuel temperature is detected by a temperature sensor. The said fuel temperature is calculated | required from the estimation based on the elapsed time from the cooling water temperature of an internal combustion engine, the electric current of an injector circuit, or the last air fuel ratio learning, The Claim 1 characterized by the above-mentioned. air-fuel ratio control system for an internal combustion agencies.

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