JP2004076642A - Flow control device and EGR control device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to avoid deterioration of control followability due to an excessive increase in a target EGR valve opening while an actual EGR valve opening is limited to a full opening.
An actual EGR amount is estimated and calculated, and an EGR valve opening is closed-loop controlled by PI control based on a deviation from a target EGR amount according to an operation state. If the target EGR amount cannot be achieved even if the EGR valve opening is fully opened, the target EGR valve opening becomes excessively larger than the full opening due to the steady-state error. become worse. In the present invention, when the target EGR valve opening is equivalent to full opening and the deviation is positive, the input of P control is made a constant and the output of I control is reset, so that the target EGR valve opening is equivalent to full opening. Hold. Thus, when the target EGR amount decreases at time t1, the EGR valve opening immediately decreases.
[Selection diagram] FIG.

Description

【００２１】
なお、サンプリング時間Δｔは固定値として与える。また時定数τは固定値として与えてもよく、運転状態によって変化させても良い。
【００２２】
上記実ＥＧＲ量検出手段２では、例えば以下のような方法で実際にシリンダに吸入されるＥＧＲ量（実ＥＧＲ量）を検出する。
【００２３】
第１に、下記の（３）式を演算することによって、コレクタ吸入ＥＧＲ量Ｑｅを演算する。（３）式のＥＧＲ弁開口面積Ａｅｇｒは、例えばそのときの目標ＥＧＲ弁開度からＥＧＲ弁開口面積を推定する。具体的には、ＥＧＲ弁開度とＥＧＲ弁開口面積との関係を予めテーブルとして用意しておき、これから求める。このＥＧＲ弁開口面積を推定するためのテーブルの特性例を図７に示す。尚、ここでは、目標ＥＧＲ弁開度と実ＥＧＲ弁開度とがほぼ一致するものとみなすことになるが、動的な遅れによって違いが無視できない場合は、その動特性を考慮して目標ＥＧＲ弁開度から実ＥＧＲ弁開度を推定した上で、図７のテーブルからＥＧＲ弁開口面積を求めても良い。
【００２４】
またＥＧＲ弁前後差圧ΔＰｅｇｒは、排気還流通路のＥＧＲ弁の前後位置にそれぞれ臨設された圧力センサで直接検出するようにしてもよく、または、従来から公知の手法により推定演算して求めてもよい。
【００２５】
第２に、コレクタに吸入されるＥＧＲ量Ｑｅから（４）式を演算することによって、シリンダに吸入されるＥＧＲ量Ｑｅｃを演算する。（４）式は（２）式と同様に、コレクタに吸入されるガスが吸気弁を通過するまでの動的な特性として、時定数τの一次遅れで近似的に表わされるものとしている。
【００２６】
【数２】

【００２７】
上記目標ＥＧＲ弁開度演算手段３では、例えば以下のようなＰＩ制御方式によるフィードバック演算を行なう。
【００２８】
第１に、（５）式を演算し、目標ＥＧＲ量に対する実ＥＧＲ量の偏差ΔＱｅｃを求める。この偏差ΔＱｅｃは、（５）式から明らかなように、目標ＥＧＲ量が実ＥＧＲ量を上回る場合に、正の値となる。
【００２９】
第２に、Ｐ制御の演算として（６）式の演算を行なう。ここで、ＵｐはＰ制御の入力であるが、上記ＥＧＲ弁制御切替手段５から入力される切替信号に従って、その値が切り替えられる。ここでは、切替信号をＹｅｓとＮｏの２つで表わされるものとする。切替信号がＹｅｓの場合は、入力Ｕｐとして、偏差ΔＱｅｃを与える。切替信号がＮｏの場合は、入力Ｕｐとして、（７）式で求められる定数Ｐｃｏｎｓｔを与える。（７）式では、切替信号がＮｏの場合に、目標ＥＧＲ弁開度が全開相当のＥＶＯｍａｘとなるように、Ｐ制御の比例ゲインｋｐから定数Ｐｃｏｎｓｔを設定する。
【００３０】
第３に、Ｉ制御の演算として（８）式の演算を行なう。ここで、Ｕｉは積分出力リセット用の係数であり、上記の（６）式の場合と同様に、ＥＧＲ弁制御切替手段５から入力される切替信号に従って値が切り替えられる。この係数Ｕｉとしては、切替信号がＹｅｓの場合は、１を与え、Ｎｏの場合は、０を与える。すなわち切替信号がＹｅｓの場合は、入力である偏差ΔＱｅｃを所定の積分ゲインｋｉでもって積分するのに対し、Ｎｏの場合は、Ｉ制御の演算結果が常に０となるようにリセットを行なう。
【００３１】
第４に、（９）式を演算して目標ＥＧＲ弁開度ｔＥＶＯを求める。つまり、Ｐ分ｔＥＶＯｐとＩ分ｔＥＶＯｉとの和となる。
【００３２】
【数３】

【００３３】
ここで、比例ゲインｋｐおよび積分ゲインｋｉは定数として与えても良いし、運転状態によって変化させても良い。またサンプリング時間Δｔ、および全開相当の上限開度ＥＶＯｍａｘは定数として与える。
【００３４】
図８は、上記の目標ＥＧＲ弁開度演算手段３の演算内容を示すブロック図であり、Ｐ分を求めるＰ制御要素８１とＩ分を求めるＩ制御要素８２とを含み、加算点８３で求められた両者の和が目標ＥＧＲ弁開度として出力される。目標ＥＧＲ量と実ＥＧＲ量との偏差は、加算点８４で求められ、Ｐ制御要素８１の入力が、上述した切替信号に応じて、切替部８５により、偏差もしくは定数Ｐｃｏｎｓｔに切り替えられる。同様に、Ｉ制御要素８２内の切替部８６から出力される係数Ｕｉにより、Ｉ分のリセットが行われる。
【００３５】
ＥＧＲ弁制御切替手段５は、上述したように、目標ＥＧＲ弁開度演算手段３に対し、ＹｅｓとＮｏの信号（切替信号）を出力するものである。これは、下記の条件を満たす場合に、Ｎｏを出力し、目標ＥＧＲ弁開度を全開相当に制限する。下記の条件以外の場合は、Ｙｅｓを出力し、通常のクローズドループ制御つまりＥＧＲ量の制御偏差に従って目標ＥＧＲ弁開度を演算する。下記のＮｏと判定する運転状態は、実際のＥＧＲ弁開度が全開相当の開度で制限されていて、目標ＥＧＲ量を実現できていない場合に相当する。
【００３６】
【数４】
Ｎｏ判定条件：　Ｑｅｃ＜ｔＱｅｃ　かつ　ｔＥＶＯ≧ＥＶＯｍａｘ
但し、
Ｑｅｃ：シリンダ吸入ＥＧＲ量［ｍｇ／ｓｔ］
ｔＱｅｃ：目標ＥＧＲ量［ｍｇ／ｓｔ］
ｔＥＶＯ：目標ＥＧＲ弁開度［％］
ＥＶＯｍａｘ：全開相当ＥＧＲ弁開度［％］
以上のような第１実施例によれば、実際のＥＧＲ弁開度が全開相当の開度で制限されることによって目標ＥＧＲ量を実現できていない状態において、目標ＥＧＲ弁開度が全開相当の開度に保持される。図３は、前述した図２と同様に、実際のＥＧＲ弁開度が全開相当の開度で制限されることによって目標ＥＧＲ量を実現できていない状態から、時刻ｔ１で運転状態が変化して目標ＥＧＲ量がステップ的に減少した場合のＥＧＲ弁開度およびＥＧＲ流量の変化を示しており、いずれも太実線が目標値、細実線が実値である。
【００３７】
この場合、時刻ｔ１以前においては、目標ＥＧＲ量と実ＥＧＲ量との定常偏差が大であるが、Ｐ制御の入力が、全開相当の開度に対応した定数Ｐｃｏｎｓｔに切り替えられるとともに、Ｉ分が０にリセットされ続けるので、目標ＥＧＲ弁開度は、全開相当の開度となる。そのため、時刻ｔ１において目標ＥＧＲ量がステップ的に減少して実ＥＧＲ量よりも小さくなると、目標ＥＧＲ弁開度は直ちに減少する。そのため、目標ＥＧＲ量に対する追従性能が向上する。
【００３８】
次に、第２実施例を図９のブロック図に基づいて説明する。このＥＧＲ制御装置は、内燃機関の排気系から吸気系に至る排気還流通路に介装されたＥＧＲ弁４と、内燃機関の運転状態に従って、シリンダに吸入させたい目標ＥＧＲ量を設定する目標ＥＧＲ量設定手段１と、実際にシリンダに吸入される実ＥＧＲ量を後述する推定演算により検出する実ＥＧＲ量検出手段２と、上記目標ＥＧＲ量と上記実ＥＧＲ量との偏差に基づいて、ＰＩ制御により、上記ＥＧＲ弁４の目標ＥＧＲ弁開度を演算する目標ＥＧＲ弁開度演算手段１３と、を備えており、さらに、上記ＥＧＲ弁４の前後の差圧を検出するＥＧＲ弁前後差圧検出手段１６と、目標ＥＧＲ弁開度演算手段１３の制御の方式を切り替えるＥＧＲ弁制御切替手段１５と、を有している。ここで、上記ＥＧＲ弁４、目標ＥＧＲ量設定手段１および実ＥＧＲ量検出手段２は、前述した第１実施例と特に変わりはない。
【００３９】
上記目標ＥＧＲ弁開度演算手段１３は、第１実施例のものとは僅かに異なるものであり、例えば以下のような演算を行なう。
【００４０】
第１に、ＥＧＲ弁前後差圧検出手段１６が検出したＥＧＲ弁前後の差圧から、ＥＧＲ弁開度を制限する上限開度ＥＶＯｌｉｍを設定する。ＥＧＲ弁前後差圧とＥＧＲ弁開度上限値ＥＶＯｌｉｍとの関係は予めテーブルとして用意しておく。このテーブルの特性例を図１０に示す。図１０に示すように、前後差圧が大きいほど全開近くに上限開度ＥＶＯｌｉｍを設定し、前後差圧が小さいときには、上限開度ＥＶＯｌｉｍをより小さく与える。
【００４１】
第２に、（１０）式を演算して目標ＥＧＲ量に対する実ＥＧＲ量の偏差ΔＱｅｃを求める。この偏差ΔＱｅｃは、（１０）式から明らかなように、目標ＥＧＲ量が実ＥＧＲ量を上回る場合に、正の値となる。
【００４２】
第３に、Ｐ制御の演算として（１１）式の演算を行なう。ここで、ＵｐはＰ制御の入力であるが、ＥＧＲ弁制御切替手段１５から入力される切替信号に従って、その値が切り替えられる。ここでは、切替信号をＹｅｓとＮｏの２つで表わされるものとする。切替信号がＹｅｓの場合は、入力Ｕｐとして、ΔＱｅｃを与える。切替信号がＮｏの場合は、入力Ｕｐとして（１２）式で求められる定数Ｐｃｏｎｓｔを与える。（１２）式では、切替信号がＮｏの場合に、目標ＥＧＲ弁開度が、図１０のテーブルから求められる上限開度ＥＶＯｌｉｍとなるように、Ｐ制御の比例ゲインｋｐを用いて定数Ｐｃｏｎｓｔを設定する。
【００４３】
第４に、Ｉ制御の演算として（１３）式の演算を行なう。第１実施例と同様に、Ｕｉは積分出力リセット用の係数であり、上記の（１１）式の場合と同じく、ＥＧＲ弁制御切替手段１５から入力される切替信号に従って値が切り替えられる。切替信号がＹｅｓの場合は、１を与え、Ｎｏの場合は、０を与える。すなわち切替信号がＹｅｓの場合は、入力である偏差ΔＱｅｃを積分するのに対し、Ｎｏの場合は、Ｉ制御の演算結果が常に０となるようにリセットを行なう。
【００４４】
第５に、（１４）式を演算して目標ＥＧＲ弁開度ｔＥＶＯを求める。
【００４５】
【数５】

【００４６】
ここで、比例ゲインｋｐおよび積分ゲインｋｉは定数として与えても良いし、運転状態によって変化させても良い。またサンプリング時間Δｔは定数として与える。
【００４７】
ＥＧＲ弁前後差圧検出手段１６は、上述したようにＥＧＲ弁４の前後差圧を検出するものであるが、これは、直接にセンサで検出してもよく、または、従来から公知の手法により推定演算して求めてもよい。
【００４８】
ＥＧＲ弁制御切替手段１５は、上述したように、目標ＥＧＲ弁開度演算手段１３に対し、ＹｅｓとＮｏの信号（切替信号）を出力するものである。これは、下記の条件を満たす場合に、Ｎｏを出力し、目標ＥＧＲ弁開度を、図１０のテーブルから求めた上限開度ＥＶＯｌｉｍに制限する。下記の条件以外の場合は、Ｙｅｓを出力し、通常のクローズドループ制御つまりＥＧＲ量の制御偏差に従って目標ＥＧＲ弁開度を演算する。下記のＮｏと判定する運転状態は、目標ＥＧＲ弁開度が上限開度ＥＶＯｌｉｍに達しており、かつ目標ＥＧＲ量を実現できていない場合に相当する。
【００４９】
【数６】
Ｎｏ判定条件：　Ｑｅｃ＜ｔＱｅｃ　かつ　ｔＥＶＯ≧ＥＶＯｌｉｍ
但し、
Ｑｅｃ：シリンダ吸入ＥＧＲ量［ｍｇ／ｓｔ］
ｔＱｅｃ：目標ＥＧＲ量［ｍｇ／ｓｔ］
ｔＥＶＯ：目標ＥＧＲ弁開度［％］
ＥＶＯｌｉｍ：ＥＧＲ弁開度上限［％］
この第２実施例は、図４に示すようなＥＧＲ流量とＥＧＲ弁開度とＥＧＲ弁前後差圧との関係を考慮している。図４に示すように、ＥＧＲ弁開度の差が同じであっても、ＥＧＲ弁前後差圧が低いときは、ＥＧＲ流量の変化は少ない。
【００５０】
前述した図３のように目標ＥＧＲ量が変化する場合に、第１実施例では、時刻ｔ１以前の目標ＥＧＲ弁開度を全開相当に制限しているが、この第２実施例では、ＥＧＲ弁前後差圧が小さいときは、全開よりも小さい開度、つまり前後差圧に応じて設定された上限開度ＥＶＯｌｉｍに保持される。これによって、時刻ｔ１以降のＥＧＲ弁の開度変化幅が、全開位置から動かす場合に比べて小さくなる。そのため、ＥＧＲ弁開度を、目標ＥＧＲ量を実現し得る開度により早く収束させることができ、目標ＥＧＲ量への追従性をさらに向上させることができる。なお、これによって、時刻ｔ１以前のＥＧＲ量の定常偏差は増加するが、定常偏差への影響が大きい、ＥＧＲ弁前後差圧が大きい運転状態では、ＥＧＲ弁開度をより全開に近い開度で制限することになる。
【００５１】
上記第２実施例においては、切替信号に応じて、（１２）式から求めた定数Ｐｃｏｎｓｔを、Ｐ制御の入力として与えるようになっているが、この定数Ｐｃｏｎｓｔの値を、切替の直後から時間経過に伴って、目標ＥＧＲ弁開度が全開開度相当になるまで徐々に増加させるようにしても良い。このようにすれば、全開開度以下で長時間制限することにより派生する問題を回避することができる。
【００５２】
例えば、（１５）式を演算することによって、定数Ｐｃｏｎｓｔを所定の増加割合Δｐｃｏｎｓｔに従って徐々に増加させていく。ただし、定数Ｐｃｏｎｓｔは、ＥＧＲ弁制御切替手段１５の出力信号がＹｅｓからＮｏに切り変わった時点で、（１２）式で求めた初期値にリセットする。また、（１６）式で求めた上限値でもって定数Ｐｃｏｎｓｔの上限を制限する。
【００５３】
【数７】

【００５４】
すなわち、第２実施例は、将来的に目標ＥＧＲ量が下がることを想定して、ＥＧＲ弁を閉じるまでの時間が短くなるように、予めＥＧＲ弁開度を全開よりも小さい開度に制限するものである。しかしながら、ＥＧＲ弁前後差圧に基づいて目標ＥＧＲ弁開度を制限することで影響は少なくしているものの、ＥＧＲ弁開度を全開相当よりも小さく制限している間は、第１実施例よりも定常偏差は増加する。そのため、制限されている期間が長いほど、相対的に定常偏差増加による悪影響が大きくなる。上記のように定数Ｐｃｏｎｓｔを徐々に増加させるようにすれば、ＥＧＲ弁開度が制限されている期間が長くなるほど、定数Ｐｃｏｎｓｔが増加することから、ＥＧＲ弁開度の制限が緩和されることになり、定常偏差増加による問題が抑制される。
【００５５】
次に、第３実施例を図１１のブロック図に基づいて説明する。このＥＧＲ制御装置は、内燃機関の排気系から吸気系に至る排気還流通路に介装されたＥＧＲ弁４と、内燃機関の運転状態に従って、シリンダに吸入させたい目標ＥＧＲ量を設定する目標ＥＧＲ量設定手段１と、実際にシリンダに吸入される実ＥＧＲ量を後述する推定演算により検出する実ＥＧＲ量検出手段２と、上記目標ＥＧＲ量と上記実ＥＧＲ量との偏差に基づいて、ＰＩ制御により、上記ＥＧＲ弁４の目標ＥＧＲ弁開度を演算する目標ＥＧＲ弁開度演算手段２３と、を備えており、さらに、上記ＥＧＲ弁４の前後の差圧を検出するＥＧＲ弁前後差圧検出手段１６と、この差圧を所定の閾値と比較して、その大小関係を判定するＥＧＲ弁前後差圧大小関係判定手段２７と、目標ＥＧＲ弁開度演算手段２３の制御の方式を切り替えるＥＧＲ弁制御切替手段２５を有している。ここで、上記ＥＧＲ弁４、目標ＥＧＲ量設定手段１および実ＥＧＲ量検出手段２は、前述した第１，第２実施例と特に変わりはなく、またＥＧＲ弁前後差圧検出手段１６は、第２実施例のものと特に変わりはない。
【００５６】
上記目標ＥＧＲ弁開度演算手段２３は、第１，第２実施例のものとは僅かに異なるものであり、例えば以下のような演算を行なう。
【００５７】
第１に、ＥＧＲ弁前後差圧大小関係判定手段２７の判定結果に基づいて、（１７−１）式および（１７−２）式に示すように、ＥＧＲ弁開度を制限する上限開度ＥＶＯｌｉｍを設定する。
【００５８】
【数８】
差圧が閾値より大きいとき
ＥＶＯｌｉｍ＝ＥＶＯｈｉ　……（１７−１）
差圧が所定値より小さいとき
ＥＶＯｌｉｍ＝ＥＶＯｌｏｗ　……（１７−２）
但し
ＥＶＯｌｉｍ：ＥＧＲ弁開度上限［％］
ＥＶＯｈｉ：差圧が閾値より大きい場合のＥＧＲ弁開度上限［％］
ＥＶＯｌｏｗ：差圧が閾値より小さい場合のＥＧＲ弁開度上限［％］
ここで、ＥＶＯｈｉとＥＶＯｌｏｗは定数として与える。また、ＥＶＯｈｉはＥＶＯｌｏｗよりも大きい値とする。つまり差圧が大きいほうが上限開度ＥＶＯｌｉｍは、相対的に大きくなる。
【００５９】
第２に、（１８）式を演算して目標ＥＧＲ量に対する実ＥＧＲ量の偏差ΔＱｅｃを求める。この偏差ΔＱｅｃは、（１８）式から明らかなように、目標ＥＧＲ量が実ＥＧＲ量を上回る場合に、正の値となる。
【００６０】
第３に、Ｐ制御の演算として（１９）式の演算を行なう。ここで、ＵｐはＰ制御の入力であるが、ＥＧＲ弁制御切替手段２５から入力される切替信号に従って、その値が切り替えられる。ここでは、切替信号をＹｅｓとＮｏの２つで表わされるものとする。切替信号がＹｅｓの場合は、入力Ｕｐとして、ΔＱｅｃを与える。切替信号がＮｏの場合は、入力Ｕｐとして（２０）式で求められる定数Ｐｃｏｎｓｔを与える。（２０）式では、切替信号がＮｏの場合に、目標ＥＧＲ弁開度が、（１７）式で求めた上限開度ＥＶＯｌｉｍ（ＥＶＯｈｉもしくはＥＶＯｌｏｗ）となるように、Ｐ制御の比例ゲインｋｐを用いて定数Ｐｃｏｎｓｔを設定する。
【００６１】
第４に、Ｉ制御の演算として（２１）式の演算を行なう。第１，第２実施例と同様に、Ｕｉは積分出力リセット用の係数であり、上記の（１９）式の場合と同じく、ＥＧＲ弁制御切替手段２５から入力される切替信号に従って値が切り替えられる。切替信号がＹｅｓの場合は、１を与え、Ｎｏの場合は、０を与える。すなわち切替信号がＹｅｓの場合は、入力である偏差ΔＱｅｃを積分するのに対し、Ｎｏの場合は、Ｉ制御の演算結果が常に０となるようにリセットを行なう。
【００６２】
第５に、（２２）式を演算して目標ＥＧＲ弁開度ｔＥＶＯを求める。
【００６３】
【数９】

【００６４】
ここで、比例ゲインｋｐおよび積分ゲインｋｉは定数として与えても良いし、運転状態によって変化させても良い。またサンプリング時間Δｔは定数として与える。
【００６５】
ＥＶＯｈｉ＞ＥＶＯｌｏｗであるので、（２０）式から求める定数Ｐｃｏｎｓｔは、ＥＧＲ弁前後差圧が閾値よりも小さい場合は、閾値より大きい場合に比べて、より小さい値となる。すなわちより小さい開度でＥＧＲ弁開度上限を制限することになる。第２実施例について説明したように、小さい開度で過度に長期間制限することは好ましくないので、このように小さい開度で制限される状態が所定時間経過したときに、差圧が閾値より大きい場合に設定される定数Ｐｃｏｎｓｔの値にＰ制御の入力を切り替えるようにしても良い。この差圧が大きい場合に設定されるＰ制御の入力は（２３）式から求められる。
【００６６】
【数１０】

【００６７】
ＥＧＲ弁制御切替手段２５は、上述したように、目標ＥＧＲ弁開度演算手段１３に対し、ＹｅｓとＮｏの信号（切替信号）を出力するものである。これは、下記の条件を満たす場合に、Ｎｏを出力し、目標ＥＧＲ弁開度を、（１７）式のいずれかの開度ＥＶＯｈｉ，ＥＶＯｌｏｗに制限する。下記の条件以外の場合は、Ｙｅｓを出力し、通常のクローズドループ制御つまりＥＧＲ量の制御偏差に従って目標ＥＧＲ弁開度を演算する。下記のＮｏと判定する運転状態は、目標ＥＧＲ弁開度が上限開度ＥＶＯｌｉｍ（ＥＶＯｈｉ，ＥＶＯｌｏｗ）に達しており、かつ目標ＥＧＲ量を実現できていない場合に相当する。
【００６８】
【数１１】
Ｎｏ判定条件：　Ｑｅｃ＜ｔＱｅｃ　かつ　ｔＥＶＯ≧ＥＶＯｌｉｍ
但し、
Ｑｅｃ：シリンダ吸入ＥＧＲ量［ｍｇ／ｓｔ］
ｔＱｅｃ：目標ＥＧＲ量［ｍｇ／ｓｔ］
ｔＥＶＯ：目標ＥＧＲ弁開度［％］
ＥＶＯｌｉｍ：ＥＧＲ弁開度上限［％］
上記の第３実施例では、前述した第２実施例と同様に、ＥＧＲ弁前後差圧が小さいときは、全開よりも小さい開度（ＥＶＯｌｏｗ）に保持される。これによって、時刻ｔ１以降のＥＧＲ弁の開度変化幅が、全開位置から動かす場合に比べて小さくなる。そのため、ＥＧＲ弁開度を、目標ＥＧＲ量を実現し得る開度により早く収束させることができ、目標ＥＧＲ量への追従性をさらに向上させることができる。特に、この第３実施例では、上限開度を単純に２段階に切り替えるので、第２実施例のように前後差圧とＥＧＲ弁開度との関係を規定するテーブルが不要であり、プログラムサイズを減らすことができる。
【図面の簡単な説明】
【図１】従来例を示すブロック図。
【図２】この従来例によるＥＧＲ弁開度とＥＧＲ流量との変化の一例を示すタイムチャート。
【図３】本発明によるＥＧＲ弁開度とＥＧＲ流量との変化の一例を示すタイムチャート。
【図４】ＥＧＲ弁開度と前後差圧とＥＧＲ流量との関係を示す特性図。
【図５】本発明の第１実施例を示すブロック図。
【図６】目標ＥＧＲ率設定マップの例を示す特性図。
【図７】ＥＧＲ弁開口面積推定テーブルを示す特性図。
【図８】目標ＥＧＲ弁開度演算手段の詳細を示す機能ブロック図。
【図９】本発明の第２実施例を示すブロック図。
【図１０】前後差圧に対するＥＧＲ弁の上限開度の設定テーブルの例を示す特性図。
【図１１】本発明の第３実施例を示すブロック図。
【符号の説明】
１…目標ＥＧＲ量設定手段
２…実ＥＧＲ量検出手段
３…目標ＥＧＲ弁開度演算手段
４…ＥＧＲ弁
５…ＥＧＲ弁制御切替手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flow rate control device in which the opening degree of a flow rate control valve is controlled in a closed loop by PI control (proportional integration control), and more particularly to an EGR control device for an internal combustion engine that controls an EGR amount of the internal combustion engine.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. Hei 9-177616 discloses a PI control so that an EGR amount (actual EGR amount) actually sucked into a cylinder follows an EGR amount (a target EGR amount) to be sucked into a cylinder of an internal combustion engine. Discloses an apparatus for controlling the EGR valve opening.
[0003]
FIG. 1 is a block diagram showing the configuration of this conventional example. A target EGR amount setting means 101 sets a target EGR amount in accordance with an operating state, and an actual EGR amount detecting means 102 calculates an actual EGR amount by an estimation calculation. To detect. The target EGR valve opening calculating means 103 calculates the target EGR valve opening by PI control from the difference between the target EGR amount and the actual EGR amount. In the P control, a proportional component (P component) is calculated by multiplying the deviation by a proportional gain. As for the I control, the integral is multiplied by multiplying the deviation by an integral gain to calculate an integral (I). Then, the target EGR valve opening is calculated as the sum of the P component and the I component. The target EGR valve opening determined in this way is output to the EGR valve 104 located in the exhaust gas recirculation passage.
[0004]
[Problems to be solved by the invention]
However, in the conventional PI control as described above, since the calculated target EGR valve opening may be larger than the opening corresponding to full opening, the response to a change in the operating state may deteriorate.
[0005]
FIG. 2 shows that the operating state changes at time t1 and the target EGR amount decreases stepwise from a state where the target EGR amount cannot be realized because the actual EGR valve opening is limited by the opening corresponding to the full opening. The change of the EGR valve opening degree and the EGR flow rate in the case of having performed is shown, and the thick solid line is a target value and the thin solid line is a real value.
[0006]
Before time t1, the I component increases with time due to a steady-state deviation between the target EGR amount and the actual EGR amount, so that the target EGR valve opening increases as shown in the figure. However, the actual EGR valve opening is limited by the full opening, so that the steady-state deviation of the EGR amount does not decrease. Next, at time t1, when the target EGR amount decreases stepwise and becomes smaller than the actual EGR amount, the target EGR valve opening is reduced by the P control at time t1, as shown in the drawing. Then, after time t1, the target EGR valve opening gradually decreases as the I component decreases with time.
[0007]
In this way, after time t1, the target EGR valve opening decreases, but until a certain time t2, the target EGR valve opening is larger than the full opening, and the actual EGR valve opening is fully open until time t2. And then gradually decreases. As described above, ideally, the EGR valve should be started to be closed from time t1, but the state before time t1 has an influence, and the EGR valve opening degree stops at time t2 corresponding to the fully open state. As a result, the performance of following the target EGR amount deteriorates.
[0008]
Such a problem similarly occurs not only in the EGR control but also in the flow rate control by the PI control.
[0009]
[Means for Solving the Problems]
A flow control device according to the present invention includes a flow control valve that controls a flow rate of a fluid, a target flow rate setting unit that sets a target flow rate, an actual flow rate detection unit that detects an actual flowing flow rate, A target valve opening calculating means for calculating a target valve opening of the flow control valve by PI control based on a deviation from an actual flow rate, so as to follow the target flow rate by the PI control. Closed loop control is realized.
[0010]
In particular, there is provided a valve control switching means for switching valve control in the target valve opening calculating means. By this valve control switching means, when the target valve opening reaches a predetermined upper limit opening corresponding to full opening and the deviation is positive, the input of P control in the target valve opening calculating means is changed from the deviation. While switching to a predetermined value, the integral output in the I control is kept reset to zero.
[0011]
The predetermined value that is input to the P control is set, for example, to a value at which the target valve opening is held at the upper limit opening. Since the integrated output is 0, the calculated target valve opening is equivalent to full opening, and does not become excessively large.
[0012]
The EGR control device for an internal combustion engine according to the present invention sets an EGR valve for controlling an exhaust gas flow rate recirculated from an exhaust system of the internal combustion engine to an intake system, and a target EGR amount to be taken into a cylinder according to an operation state of the internal combustion engine. A target EGR amount setting means, an actual EGR amount detecting means for detecting an actual EGR amount actually sucked into a cylinder, and the EGR valve based on a deviation between the target EGR amount and the actual EGR amount by PI control. And a target EGR valve opening calculating means for calculating the target EGR valve opening. Closed loop control is realized by the PI control so as to follow the target EGR amount.
[0013]
When the target EGR valve opening reaches a predetermined upper limit opening corresponding to full opening and the deviation is positive, the input of the P control in the target EGR valve opening calculating means is changed from the deviation to a predetermined value. EGR valve control switching means is provided for switching and continuously resetting the integrated output in I control to zero. Thus, the target EGR valve opening does not become excessively large.
[0014]
【The invention's effect】
According to the present invention, after the target valve opening reaches the predetermined upper limit opening during the PI control, it is limited that the target valve opening becomes excessively large. Can be followed more quickly.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an EGR control device for an internal combustion engine will be described in detail.
[0016]
FIG. 5 is a block diagram showing the first embodiment. This EGR control device includes an EGR valve 4 provided in an exhaust gas recirculation passage from an exhaust system to an intake system of the internal combustion engine, and a target EGR amount for setting a target EGR amount to be taken into a cylinder according to an operation state of the internal combustion engine. Setting means 1, actual EGR amount detecting means 2 for detecting the actual EGR amount actually sucked into the cylinder by an estimation calculation described later, and PI control based on a deviation between the target EGR amount and the actual EGR amount. A target EGR valve opening calculating means 3 for calculating a target EGR valve opening of the EGR valve 4, and further, an EGR valve control switching for switching a control method of the target EGR valve opening calculating means 3. Means 5 is provided.
[0017]
The target EGR amount setting means 1 sets the target EGR amount by, for example, the following method.
[0018]
First, a target EGR rate is set from the accelerator opening and the engine speed. The relationship between the accelerator opening, the engine speed, and the target EGR rate is prepared in advance as a map. FIG. 6 shows an example of the target EGR rate setting map.
[0019]
Second, the target EGR amount tQe is calculated by performing the calculation of Expression (1). The cylinder intake new air amount Qac is obtained, for example, by measuring the collector intake new air amount Qa with an air flow meter and calculating equation (2). Equation (2) is a dynamic characteristic until the gas sucked into the collector passes through the intake valve, and is approximately expressed by a first-order delay of the time constant τ. Hereinafter, Z ^-1 Is an operator representing one operation delay.
[0020]
(Equation 1)

[0021]
Note that the sampling time Δt is given as a fixed value. Further, the time constant τ may be given as a fixed value or may be changed depending on the operation state.
[0022]
The actual EGR amount detecting means 2 detects an EGR amount (actual EGR amount) actually sucked into the cylinder by the following method, for example.
[0023]
First, a collector intake EGR amount Qe is calculated by calculating the following equation (3). The EGR valve opening area Aegr of the formula (3) estimates the EGR valve opening area from the target EGR valve opening at that time, for example. Specifically, the relationship between the EGR valve opening and the EGR valve opening area is prepared in advance as a table, and is determined from this. FIG. 7 shows a characteristic example of a table for estimating the opening area of the EGR valve. Here, it is assumed that the target EGR valve opening and the actual EGR valve opening substantially coincide with each other. However, if the difference cannot be ignored due to dynamic delay, the target EGR valve is considered in consideration of its dynamic characteristics. After estimating the actual EGR valve opening from the valve opening, the EGR valve opening area may be obtained from the table in FIG.
[0024]
The pressure difference ΔPegr before and after the EGR valve may be directly detected by pressure sensors provided respectively at the front and rear positions of the EGR valve in the exhaust gas recirculation passage, or may be calculated and estimated by a conventionally known method. Good.
[0025]
Second, the EGR amount Qec sucked into the cylinder is calculated by calculating equation (4) from the EGR amount Qe sucked into the collector. Equation (4) is, like equation (2), approximately expressed by a first-order delay of a time constant τ as a dynamic characteristic until the gas sucked into the collector passes through the intake valve.
[0026]
(Equation 2)

[0027]
The target EGR valve opening calculating means 3 performs a feedback calculation by the following PI control method, for example.
[0028]
First, the equation (5) is calculated, and a deviation ΔQec of the actual EGR amount from the target EGR amount is obtained. This deviation ΔQec becomes a positive value when the target EGR amount exceeds the actual EGR amount, as is apparent from the equation (5).
[0029]
Second, the calculation of equation (6) is performed as the calculation of the P control. Here, Up is an input of the P control, and its value is switched according to a switching signal input from the EGR valve control switching means 5. Here, it is assumed that the switching signal is represented by two of Yes and No. When the switching signal is Yes, a deviation ΔQec is given as the input Up. When the switching signal is No, a constant Pconst obtained by Expression (7) is given as the input Up. In the equation (7), when the switching signal is No, the constant Pconst is set from the proportional gain kp of the P control so that the target EGR valve opening becomes EVOmax corresponding to the full opening.
[0030]
Third, the calculation of equation (8) is performed as the calculation of the I control. Here, Ui is a coefficient for resetting the integral output, and the value is switched in accordance with the switching signal input from the EGR valve control switching means 5, as in the case of the above equation (6). As the coefficient Ui, 1 is given when the switching signal is Yes, and 0 when it is No. That is, when the switching signal is Yes, the input deviation ΔQec is integrated with a predetermined integration gain ki, whereas when No, the reset is performed so that the calculation result of the I control is always 0.
[0031]
Fourth, the target EGR valve opening tEVO is obtained by calculating equation (9). In other words, it is the sum of the P component tEVOp and the I component tEVOi.
[0032]
[Equation 3]

[0033]
Here, the proportional gain kp and the integral gain ki may be given as constants, or may be changed depending on the operation state. Further, the sampling time Δt and the upper limit opening EVOmax corresponding to the full opening are given as constants.
[0034]
FIG. 8 is a block diagram showing the calculation contents of the target EGR valve opening degree calculation means 3 and includes a P control element 81 for obtaining the P component and an I control element 82 for obtaining the I component. The sum of the two is output as the target EGR valve opening. The deviation between the target EGR amount and the actual EGR amount is obtained at an addition point 84, and the input of the P control element 81 is switched to the deviation or the constant Pconst by the switching unit 85 according to the above-described switching signal. Similarly, the I component is reset by the coefficient Ui output from the switching unit 86 in the I control element 82.
[0035]
As described above, the EGR valve control switching means 5 outputs Yes and No signals (switching signals) to the target EGR valve opening calculating means 3. In this case, when the following condition is satisfied, No is output and the target EGR valve opening is limited to a value corresponding to full opening. If the following conditions are not satisfied, Yes is output, and the target EGR valve opening is calculated in accordance with the normal closed loop control, that is, the control deviation of the EGR amount. The operation state determined as No in the following corresponds to a case where the actual EGR valve opening is limited by the opening corresponding to the full opening and the target EGR amount cannot be achieved.
[0036]
(Equation 4)
No determination condition: Qec <tQec and tEVO ≧ EVOmax
However,
Qec: cylinder intake EGR amount [mg / st]
tQec: target EGR amount [mg / st]
tEVO: target EGR valve opening [%]
EVOmax: full open equivalent EGR valve opening [%]
According to the first embodiment described above, in a state where the actual EGR valve opening is limited by the opening equivalent to the full opening and the target EGR amount cannot be realized, the target EGR valve opening corresponds to the full opening. It is held at the opening. FIG. 3 shows that the operating state changes at time t1 from a state in which the target EGR amount cannot be realized due to the fact that the actual EGR valve opening is limited by the opening corresponding to the full opening similarly to FIG. 2 described above. Changes in the EGR valve opening and the EGR flow rate when the target EGR amount decreases in a stepwise manner are shown. In each case, the thick solid line is the target value and the thin solid line is the actual value.
[0037]
In this case, before the time t1, the steady-state deviation between the target EGR amount and the actual EGR amount is large, but the input of the P control is switched to the constant Pconst corresponding to the opening corresponding to the full opening, and the I component is reduced. Since the target EGR valve opening is continuously reset to 0, the target EGR valve opening becomes an opening equivalent to full opening. Therefore, when the target EGR amount decreases stepwise at time t1 and becomes smaller than the actual EGR amount, the target EGR valve opening immediately decreases. Therefore, the performance of following the target EGR amount is improved.
[0038]
Next, a second embodiment will be described with reference to the block diagram of FIG. This EGR control device includes an EGR valve 4 provided in an exhaust gas recirculation passage from an exhaust system to an intake system of the internal combustion engine, and a target EGR amount for setting a target EGR amount to be taken into a cylinder according to an operation state of the internal combustion engine. Setting means 1, actual EGR amount detecting means 2 for detecting the actual EGR amount actually sucked into the cylinder by an estimation calculation described later, and PI control based on a deviation between the target EGR amount and the actual EGR amount. A target EGR valve opening calculating means 13 for calculating a target EGR valve opening of the EGR valve 4, and a EGR valve front / rear differential pressure detecting means for detecting a differential pressure across the EGR valve 4. 16 and an EGR valve control switching means 15 for switching the control method of the target EGR valve opening calculating means 13. Here, the EGR valve 4, the target EGR amount setting means 1 and the actual EGR amount detecting means 2 are not particularly different from the first embodiment.
[0039]
The target EGR valve opening calculating means 13 is slightly different from that of the first embodiment, and performs, for example, the following calculation.
[0040]
First, the upper limit opening EVOlim for limiting the EGR valve opening is set based on the differential pressure across the EGR valve detected by the EGR valve differential pressure detecting means 16. The relationship between the EGR valve differential pressure and the EGR valve opening upper limit EVOlim is prepared in advance as a table. FIG. 10 shows a characteristic example of this table. As shown in FIG. 10, the upper limit opening EVOlim is set closer to full opening as the front-rear pressure difference is larger, and the upper limit opening EVOlim is set smaller when the front-rear pressure difference is small.
[0041]
Second, a deviation ΔQec of the actual EGR amount from the target EGR amount is calculated by calculating the equation (10). This deviation ΔQec becomes a positive value when the target EGR amount exceeds the actual EGR amount, as is apparent from the equation (10).
[0042]
Third, the calculation of equation (11) is performed as the calculation of the P control. Here, Up is an input of the P control, and its value is switched according to a switching signal input from the EGR valve control switching unit 15. Here, it is assumed that the switching signal is represented by two of Yes and No. When the switching signal is Yes, ΔQec is given as the input Up. When the switching signal is No, a constant Pconst obtained by Expression (12) is given as the input Up. In the equation (12), when the switching signal is No, the constant Pconst is set using the proportional gain kp of the P control so that the target EGR valve opening becomes the upper limit opening EVOlim obtained from the table of FIG. I do.
[0043]
Fourth, the calculation of Expression (13) is performed as the calculation of the I control. As in the first embodiment, Ui is a coefficient for resetting the integral output, and the value is switched in accordance with the switching signal input from the EGR valve control switching means 15, as in the case of the above-mentioned equation (11). When the switching signal is Yes, 1 is given, and when No, 0 is given. That is, when the switching signal is Yes, the input deviation ΔQec is integrated, while when No, the reset is performed so that the calculation result of the I control is always 0.
[0044]
Fifth, the target EGR valve opening tEVO is obtained by calculating equation (14).
[0045]
(Equation 5)

[0046]
Here, the proportional gain kp and the integral gain ki may be given as constants, or may be changed depending on the operation state. The sampling time Δt is given as a constant.
[0047]
The EGR valve front-back differential pressure detecting means 16 detects the front-back differential pressure of the EGR valve 4 as described above. This may be detected directly by a sensor, or by a conventionally known method. It may be obtained by an estimation calculation.
[0048]
As described above, the EGR valve control switching means 15 outputs Yes and No signals (switching signals) to the target EGR valve opening calculating means 13. When the following condition is satisfied, No is output and the target EGR valve opening is limited to the upper limit opening EVOlim obtained from the table of FIG. If the following conditions are not satisfied, Yes is output, and the target EGR valve opening is calculated in accordance with the normal closed loop control, that is, the control deviation of the EGR amount. The operation state determined as No in the following corresponds to a case where the target EGR valve opening has reached the upper limit opening EVOlim and the target EGR amount has not been realized.
[0049]
(Equation 6)
No determination condition: Qec <tQec and tEVO ≧ EVOlim
However,
Qec: cylinder intake EGR amount [mg / st]
tQec: target EGR amount [mg / st]
tEVO: target EGR valve opening [%]
EVOlim: EGR valve opening upper limit [%]
In the second embodiment, the relationship between the EGR flow rate, the EGR valve opening, and the differential pressure across the EGR valve as shown in FIG. 4 is considered. As shown in FIG. 4, even when the difference in the EGR valve opening is the same, when the differential pressure across the EGR valve is low, the change in the EGR flow rate is small.
[0050]
When the target EGR amount changes as shown in FIG. 3 described above, in the first embodiment, the target EGR valve opening before time t1 is limited to a value equivalent to full opening, but in the second embodiment, the EGR valve is opened. When the front-back differential pressure is small, the opening is smaller than the full opening, that is, the upper limit opening EVOlim set according to the front-back differential pressure. As a result, the width of change in the opening degree of the EGR valve after the time t1 becomes smaller than when the EGR valve is moved from the fully open position. Therefore, the EGR valve opening can be made to converge more quickly to an opening that can achieve the target EGR amount, and the ability to follow the target EGR amount can be further improved. In this case, the steady-state deviation of the EGR amount before time t1 increases, but in an operating state where the influence on the steady-state deviation is large and the differential pressure across the EGR valve is large, the EGR valve opening is set to an opening closer to full opening. Will be limited.
[0051]
In the second embodiment, the constant Pconst obtained from Expression (12) is given as an input of the P control according to the switching signal. As the time elapses, the target EGR valve opening may be gradually increased until it becomes equivalent to the full opening. In this way, it is possible to avoid a problem that is caused by limiting for a long time below the full opening degree.
[0052]
For example, by calculating the equation (15), the constant Pconst is gradually increased according to a predetermined increase rate Δpconst. However, the constant Pconst is reset to the initial value obtained by the equation (12) when the output signal of the EGR valve control switching means 15 changes from Yes to No. Further, the upper limit of the constant Pconst is limited by the upper limit obtained by the equation (16).
[0053]
(Equation 7)

[0054]
That is, in the second embodiment, assuming that the target EGR amount will decrease in the future, the EGR valve opening is limited to an opening smaller than the full opening in advance so that the time until the EGR valve is closed is shortened. Things. However, although the effect is reduced by limiting the target EGR valve opening based on the differential pressure between the EGR valve front and rear, while the EGR valve opening is limited to a value smaller than the full opening, the first embodiment is different from the first embodiment. The steady-state deviation also increases. Therefore, the longer the restricted period is, the greater the adverse effect due to the increase in the steady-state deviation is. If the constant Pconst is gradually increased as described above, the constant Pconst increases as the period during which the EGR valve opening is restricted becomes longer, so that the restriction on the EGR valve opening is eased. That is, the problem due to the increase in the steady-state deviation is suppressed.
[0055]
Next, a third embodiment will be described with reference to the block diagram of FIG. This EGR control device includes an EGR valve 4 provided in an exhaust gas recirculation passage from an exhaust system to an intake system of the internal combustion engine, and a target EGR amount for setting a target EGR amount to be taken into a cylinder according to an operation state of the internal combustion engine. Setting means 1, actual EGR amount detecting means 2 for detecting the actual EGR amount actually sucked into the cylinder by an estimation calculation described later, and PI control based on a deviation between the target EGR amount and the actual EGR amount. A target EGR valve opening calculating means 23 for calculating a target EGR valve opening of the EGR valve 4, and a differential pressure detecting means for detecting a differential pressure across the EGR valve 4. EGR valve 16 for comparing the control method of the EGR valve front-rear differential pressure magnitude relation determining means 27 for comparing the differential pressure with a predetermined threshold value to determine the magnitude relation thereof, and the target EGR valve opening degree computing means 23. And a control switching unit 25. Here, the EGR valve 4, the target EGR amount setting means 1 and the actual EGR amount detecting means 2 are not particularly different from those of the first and second embodiments. There is no particular difference from the two embodiments.
[0056]
The target EGR valve opening calculating means 23 is slightly different from the first and second embodiments, and performs, for example, the following calculation.
[0057]
First, based on the determination result of the EGR valve front / rear differential pressure magnitude relationship determining means 27, the upper limit opening EVOlim for limiting the EGR valve opening as shown in the equations (17-1) and (17-2). Set.
[0058]
(Equation 8)
When the differential pressure is greater than the threshold
EVOlim = EVOhi (17-1)
When the differential pressure is smaller than the specified value
EVOlim = EVOlow (17-2)
However
EVOlim: EGR valve opening upper limit [%]
EVOhi: EGR valve opening upper limit [%] when differential pressure is larger than threshold
EVOlow: EGR valve opening upper limit [%] when differential pressure is smaller than threshold
Here, EVOhi and EVOlow are given as constants. EVOhi is a value larger than EVOlow. That is, the larger the differential pressure, the larger the upper limit opening EVOlim becomes.
[0059]
Second, a deviation ΔQec of the actual EGR amount from the target EGR amount is obtained by calculating equation (18). This deviation ΔQec becomes a positive value when the target EGR amount exceeds the actual EGR amount, as is apparent from the equation (18).
[0060]
Third, the calculation of equation (19) is performed as the calculation of the P control. Here, Up is an input of the P control, and its value is switched according to a switching signal input from the EGR valve control switching means 25. Here, it is assumed that the switching signal is represented by two of Yes and No. When the switching signal is Yes, ΔQec is given as the input Up. When the switching signal is No, a constant Pconst obtained by Expression (20) is given as the input Up. In the equation (20), when the switching signal is No, the proportional gain kp of the P control is used so that the target EGR valve opening becomes the upper limit opening EVOlim (EVOhi or EVOlow) obtained by the equation (17). To set a constant Pconst.
[0061]
Fourth, the calculation of equation (21) is performed as the calculation of I control. As in the first and second embodiments, Ui is a coefficient for resetting the integral output, and the value is switched according to the switching signal input from the EGR valve control switching means 25, as in the case of the above equation (19). . When the switching signal is Yes, 1 is given, and when No, 0 is given. That is, when the switching signal is Yes, the input deviation ΔQec is integrated, while when No, the reset is performed so that the calculation result of the I control is always 0.
[0062]
Fifth, the target EGR valve opening tEVO is obtained by calculating equation (22).
[0063]
(Equation 9)

[0064]
Here, the proportional gain kp and the integral gain ki may be given as constants, or may be changed depending on the operation state. The sampling time Δt is given as a constant.
[0065]
Since EVOhi> EVOlow, the constant Pconst obtained from Expression (20) has a smaller value when the differential pressure across the EGR valve is smaller than the threshold value, as compared with a case where the differential pressure across the EGR valve is larger than the threshold value. That is, the upper limit of the EGR valve opening is limited by a smaller opening. As described in the second embodiment, it is not preferable to restrict the opening at a small opening for an excessively long period of time. The input of the P control may be switched to the value of the constant Pconst set when the value is large. The input of the P control that is set when the differential pressure is large is obtained from Expression (23).
[0066]
(Equation 10)

[0067]
The EGR valve control switching means 25 outputs Yes and No signals (switching signals) to the target EGR valve opening calculating means 13 as described above. In this case, when the following condition is satisfied, No is output, and the target EGR valve opening is limited to one of the openings EVOhi and EVOlow in the equation (17). If the following conditions are not satisfied, Yes is output, and the target EGR valve opening is calculated in accordance with the normal closed loop control, that is, the control deviation of the EGR amount. The operation state determined as No in the following corresponds to a case where the target EGR valve opening has reached the upper limit opening EVOlim (EVOhi, EVOlow) and the target EGR amount has not been realized.
[0068]
[Equation 11]
No determination condition: Qec <tQec and tEVO ≧ EVOlim
However,
Qec: cylinder intake EGR amount [mg / st]
tQec: target EGR amount [mg / st]
tEVO: target EGR valve opening [%]
EVOlim: EGR valve opening upper limit [%]
In the third embodiment, similarly to the above-described second embodiment, when the differential pressure across the EGR valve is small, the opening degree (EVOlow) is kept smaller than the fully opened state. As a result, the width of change in the opening degree of the EGR valve after the time t1 becomes smaller than when the EGR valve is moved from the fully open position. Therefore, the EGR valve opening can be made to converge more quickly to an opening that can achieve the target EGR amount, and the ability to follow the target EGR amount can be further improved. In particular, in the third embodiment, since the upper limit opening is simply switched in two stages, a table for defining the relationship between the front-rear differential pressure and the EGR valve opening as in the second embodiment is unnecessary, and the program size is reduced. Can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a conventional example.
FIG. 2 is a time chart showing an example of a change in an EGR valve opening and an EGR flow rate according to the conventional example.
FIG. 3 is a time chart showing an example of a change in an EGR valve opening and an EGR flow rate according to the present invention.
FIG. 4 is a characteristic diagram showing a relationship among an EGR valve opening degree, a differential pressure between front and rear, and an EGR flow rate.
FIG. 5 is a block diagram showing a first embodiment of the present invention.
FIG. 6 is a characteristic diagram showing an example of a target EGR rate setting map.
FIG. 7 is a characteristic diagram showing an EGR valve opening area estimation table.
FIG. 8 is a functional block diagram showing details of a target EGR valve opening calculating means.
FIG. 9 is a block diagram showing a second embodiment of the present invention.
FIG. 10 is a characteristic diagram showing an example of a setting table of an upper limit opening of an EGR valve with respect to a differential pressure between front and rear.
FIG. 11 is a block diagram showing a third embodiment of the present invention.
[Explanation of symbols]
1. Target EGR amount setting means
2. Actual EGR amount detecting means
3. Target EGR valve opening calculating means
4: EGR valve
5 EGR valve control switching means

Claims (8)

A flow control valve for controlling the flow rate of the fluid,
Target flow rate setting means for setting a target flow rate;
Actual flow detecting means for detecting an actual flowing flow;
A target valve opening calculating means for calculating a target valve opening of the flow control valve by PI control based on a deviation between the target flow and the actual flow;
When the target valve opening reaches a predetermined upper limit opening corresponding to full opening and the deviation is positive, the input of P control in the target valve opening calculating means is switched from the deviation to a predetermined value, and Valve control switching means for continuously resetting the integrated output in the control to 0;
A flow control device characterized by comprising: A flow control valve for controlling the flow rate of the fluid,
Target flow rate setting means for setting a target flow rate;
Actual flow detecting means for detecting an actual flowing flow;
A target valve opening calculating means for calculating a target valve opening of the flow control valve by PI control based on a deviation between the target flow and the actual flow;
Differential pressure detecting means for detecting a differential pressure before and after the flow control valve,
When the target valve opening reaches the upper limit opening set based on the differential pressure and the deviation is positive, the input of the P control in the target valve opening calculating means is set to a predetermined value from the deviation. And a valve control switching means for outputting a command signal to the target valve opening calculating means so as to continuously reset the integrated output in the I control to 0,
A flow control device characterized by comprising: A flow control valve for controlling the flow rate of the fluid,
Target flow rate setting means for setting a target flow rate;
Actual flow detecting means for detecting an actual flowing flow;
A target valve opening calculating means for calculating a target valve opening of the flow control valve by PI control based on a deviation between the target flow and the actual flow;
Differential pressure detecting means for detecting a differential pressure before and after the flow control valve,
A differential pressure magnitude relationship determining means for comparing the differential pressure with a predetermined threshold value to determine the magnitude relationship;
When the target valve opening reaches the upper limit opening set respectively corresponding to the magnitude relationship and the deviation is positive, the input of the P control in the target valve opening calculating means is set to the deviation And a predetermined value, and a valve control switching means for outputting a command signal to the target valve opening calculating means so as to continuously reset the integrated output in the I control to 0;
A flow control device characterized by comprising: An EGR valve for controlling the flow rate of exhaust gas recirculated from the exhaust system of the internal combustion engine to the intake system;
Target EGR amount setting means for setting a target EGR amount desired to be taken into the cylinder according to an operation state of the internal combustion engine;
An actual EGR amount detecting means for detecting an actual EGR amount actually sucked into the cylinder;
A target EGR valve opening calculating means for calculating a target EGR valve opening of the EGR valve by PI control based on a deviation between the target EGR amount and the actual EGR amount;
When the target EGR valve opening reaches a predetermined upper limit opening corresponding to full opening and the deviation is positive, the input of P control in the target EGR valve opening calculating means is switched from the deviation to a predetermined value, EGR valve control switching means for continuously resetting the integrated output in I control to 0,
An EGR control device for an internal combustion engine, comprising: An EGR valve for controlling the flow rate of exhaust gas recirculated from the exhaust system of the internal combustion engine to the intake system;
Target EGR amount setting means for setting a target EGR amount desired to be taken into the cylinder according to an operation state of the internal combustion engine;
An actual EGR amount detecting means for detecting an actual EGR amount actually sucked into the cylinder;
A target EGR valve opening calculating means for calculating a target EGR valve opening of the EGR valve by PI control based on a deviation between the target EGR amount and the actual EGR amount;
A differential pressure detecting means for detecting a differential pressure before and after the EGR valve;
When the target EGR valve opening reaches the upper limit opening set based on the differential pressure and the deviation is positive, the input of the P control in the target EGR valve opening calculation means is changed from the deviation. EGR valve control switching means for outputting a command signal to the target EGR valve opening calculating means so as to switch to a predetermined value and continue to reset the integrated output in I control to 0;
An EGR control device for an internal combustion engine, comprising: 6. The method according to claim 5, wherein the predetermined value, which is an input of the P control by the EGR valve control switching means, is gradually increased from the start of the switching until the target EGR valve opening becomes an opening corresponding to full opening. An EGR control device for an internal combustion engine according to claim 1. An EGR valve for controlling the flow rate of exhaust gas recirculated from the exhaust system of the internal combustion engine to the intake system;
Target EGR amount setting means for setting a target EGR amount desired to be taken into the cylinder according to an operation state of the internal combustion engine;
An actual EGR amount detecting means for detecting an actual EGR amount actually sucked into the cylinder;
A target EGR valve opening calculating means for calculating a target EGR valve opening of the EGR valve by PI control based on a deviation between the target EGR amount and the actual EGR amount;
A differential pressure detecting means for detecting a differential pressure before and after the EGR valve;
A differential pressure magnitude relationship determining means for comparing the differential pressure with a predetermined threshold value to determine the magnitude relationship;
When the target EGR valve opening reaches the upper limit opening set respectively corresponding to the magnitude relationship and the deviation is positive, the input of the P control in the target EGR valve opening calculating means is performed. EGR valve control switching means for outputting a command signal to the target EGR valve opening calculating means so as to switch from the deviation to a predetermined value and continue to reset the integrated output in the I control to 0;
An EGR control device for an internal combustion engine, comprising: The predetermined value that is input to the P control by the EGR valve control switching means is set to a first predetermined value and a second predetermined value in accordance with the magnitude relationship with the threshold value, and is smaller than the threshold value. 8. The EGR control device for an internal combustion engine according to claim 7, wherein the switching to the second predetermined value is performed after a predetermined time has elapsed after the switching to the first predetermined value.

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