JP4378940B2 - An internal combustion engine that controls the compression ratio by focusing on fluctuations in operating conditions - Google Patents

Description

【００３２】
Ａ．装置構成：
図１は、圧縮比可変機構を備えた本実施例のエンジン１０の構成を概念的に示した説明図である。以下では、エンジン１０は、いわゆる火花点火式のエンジンであるものとして説明するが、もちろん、ディーゼルエンジンなどの圧縮着火式のエンジンに適用することもできる。図示されているように、エンジン１０は、大きくはシリンダヘッド２０と、シリンダブロックＡＳＳＹ３０と、メインムービングＡＳＳＹ４０と、吸気通路５０と、排気通路５８と、エンジン制御用ユニット（以下、ＥＣＵ）６０などから構成されている。
【００３３】
シリンダブロックＡＳＳＹ３０は、シリンダヘッド２０が取り付けられるアッパーブロック３１と、メインムービングＡＳＳＹ４０が収納されているロアブロック３２とから構成されている。また、アッパーブロック３１とロアブロック３２との間にはアクチュエータ３３が設けられており、アクチュエータ３３を駆動することで、アッパーブロック３１をロアブロック３２に対して上下方向に移動させることが可能となっている。また、アッパーブロック３１の内部には円筒形のシリンダ３４が形成されている。
【００３４】
メインムービングＡＳＳＹ４０は、シリンダ３４の内部に設けられたピストン４１と、ロアブロック３２の内部で回転するクランクシャフト４３と、ピストン４１をクランクシャフト４３に接続するコネクティングロッド４２などから構成されている。これらピストン４１、コネクティングロッド４２、クランクシャフト４３はいわゆるクランク機構を構成しており、クランクシャフト４３が回転するとそれにつれてピストン４１がシリンダ３４内で上下方向に摺動し、逆に、ピストン４１が上下に摺動すればクランクシャフト４３がロアブロック３２内で回転するようになっている。シリンダブロックＡＳＳＹ３０にシリンダヘッド２０を取り付けると、シリンダヘッド２０の下面側（アッパーブロック３１に接する側）とシリンダ３４とピストン４１とで囲まれた部分に燃焼室が形成される。従って、アクチュエータ３３を用いてアッパーブロック３１を上方に移動させれば、これに伴ってシリンダヘッド２０も上方に移動して燃焼室内の容積が増加するので、圧縮比を小さくすることができる。逆に、アッパーブロック３１とともにシリンダヘッド２０を下方に動かせば、燃焼室内の容積が減少して圧縮比を大きくすることができる。
【００３５】
シリンダヘッド２０には、燃焼室内に空気を取り入れるための吸気ポート２３と、燃焼室内から排気ガスを排出するための排気ポート２４とが形成されており、吸気ポート２３が燃焼室に開口する部分には吸気バルブ２１が、また、排気ポート２４が燃焼室に開口する部分には排気バルブ２２が設けられている。吸気バルブ２１および排気バルブ２２は、ピストン４１の上下動に合わせて、それぞれカム機構によって駆動される。こうしてピストンの動きに同期させて吸気バルブ２１および排気バルブ２２を、それぞれ適切なタイミングで開閉すれば、燃焼室内に空気を吸入したり、あるいは燃焼室内から排気ガスを排出することができる。また、シリンダヘッド２０には、燃焼室内に形成された混合気に火花を飛ばして点火するための点火プラグ２７も設けられている。
【００３６】
シリンダヘッド２０の吸気ポート２３には、外気をシリンダヘッド２０まで導くための吸気通路５０が接続されており、吸気通路５０の上流側端部にはエアクリーナ５１が設けられている。燃焼室内に吸入される空気は、エアクリーナ５１でゴミなどの異物を取り除かれた後、吸気通路５０、吸気ポート２３を経由して燃焼室に流入する。吸気通路５０には、スロットルバルブ５２や燃料噴射弁５５などが設けられており、電動アクチュエータ５３でスロットルバルブ５２の開度を制御すれば、燃焼室内に流入する空気量を制御することができる。燃料は、燃料噴射弁５５から吸気ポート２３に向かって噴射される。噴射された燃料噴霧は、一部が吸気ポート２３内で気化した状態で、残りは燃料噴霧あるいは燃料液膜の状態で燃焼室内に流入した後、燃焼室内で気化しつつ空気と混合して混合気を形成する。また、吸気通路５０には吸気圧センサ５６が設けられており、吸気通路内の圧力を検出することが可能となっている。
【００３７】
シリンダヘッド２０の排気ポート２４には排気通路５８が接続されており、燃焼室から排出された排気ガスは、排気通路５８によって外部に導かれて放出される。
【００３８】
ＥＣＵ６０は、中央処理装置（以下、ＣＰＵ）を中心として、ＲＯＭ、ＲＡＭ、入出力回路などが、バスで相互に接続されたマイクロコンピュータである。詳細には後述するが、ＥＣＵ６０は、クランクシャフト４３に設けられたクランク角センサ６１や、アクセルペダルに内蔵されたアクセル開度センサ６２、更には必要に応じて、吸気圧センサ５６などから必要な情報を取り込んで、点火プラグ２７、燃料噴射弁５５、電動アクチュエータ５３などを駆動することにより、エンジン１０全体の動作を制御する。
【００３９】
Ｂ．エンジン制御の概要：
次に、上述した構成を有するエンジン１０の動作について説明する。図２は、ＥＣＵ６０がエンジン１０の動作を制御する流れを示したフローチャートである。以下、フローチャートに従って説明する。
【００４０】
ＥＣＵ６０は、エンジン制御ルーチンを開始すると先ず初めに、エンジンの回転速度Ｎe およびアクセル開度θacを検出する（ステップＳ１００）。エンジン回転速度Ｎe は、クランク角センサ６１の出力から算出し、また、アクセル開度θacは、アクセル開度センサ６２を用いて検出することができる。
【００４１】
尚、ステップＳ１００では、アクセル開度θacに替えて、吸気圧センサ５６で検出した吸気通路内圧力や、スロットル開度などを用いることも可能である。スロットル開度は、電動アクチュエータ５３に内蔵された図示しないスロットル開度センサによって検出することができる。もちろん、ＥＣＵ６０はスロットル開度を制御しているから、ＥＣＵ６０内部で制御のために使用している開度を利用することも可能である。
【００４２】
こうしてエンジン回転速度Ｎe およびアクセル開度θacを検出したら、エンジン１０の定常運転度合いを判定する処理を開始する（ステップＳ１０２）。詳細には後述するが、「定常運転度合い」とは、エンジン１０が定常状態で運転されているのか、あるいは運転条件が頻繁に変わっているのか、更には変わり方は大きいのか小さいのかといった運転状態を表す指標である。定常運転度合いを判定する処理の詳細については後述する。
【００４３】
エンジン１０の定常運転度合いを判定したら、圧縮比を設定する処理を開始する（ステップＳ１０４）。図１を用いて説明したように本実施例のエンジン１０は、アクチュエータ３３を用いてエンジンの圧縮比を変更することが可能である。そこで、ステップＳ１０４では、先に判定した定常運転度合いを考慮しながら、エンジンの運転条件に応じた適切な圧縮比を求めた後、アクチュエータ３３を駆動して、エンジン１０の圧縮比を適切な圧縮比に設定する処理を行う。圧縮比設定処理の詳細については後述する。
【００４４】
ＥＣＵ６０は、圧縮比設定処理に続いて燃料噴射制御を開始する（ステップＳ１０６）。かかる制御では、燃焼室内に吸入される空気量を検出し、所定空燃比となる分量の燃料を、燃料噴射弁５５から適切なタイミングで噴射する制御を行う。本実施例では、燃焼室内に吸入される空気量は、吸気圧センサ５６により検出した吸気通路内の圧力に基づいて算出している。もちろん、吸気通路５０内にエアフローセンサを設けてエンジン１０が吸い込んだ空気量を計測してもよく、更には簡便に、エンジン回転速度およびアクセル開度（スロットルバルブ５２の開度）をパラメータとして吸入空気量を予め計測してマップとして記憶しておき、このマップを参照して空気量を求めることも可能である。
【００４５】
こうして求めた空気量に対して所定の空燃比となるように燃料を噴射する。空燃比とは、燃料と空気との混合割合を表す指標であり、燃焼室内に供給された空気重量を燃料重量で除算した値として定義される。ＥＣＵ６０に内蔵されたＲＯＭには、エンジン回転速度とアクセル開度（あるいはスロットルバルブ開度）とをパラメータとするマップの形式で、圧縮比毎に、目標の空燃比が記憶されている。
【００４６】
図３は、エンジンの圧縮比毎に目標の空燃比を記憶しているマップを例示した説明図であり、エンジンの圧縮比１３（ε＝１３）、圧縮比１０．５（ε＝１０．５）、圧縮比９（ε＝９）の三枚のマップが記憶されている様子を概念的に表している。例えば、圧縮比設定処理（図２のステップＳ１０４）においてエンジン１０の圧縮比が１３に設定された場合は、図３中で一番手前に表示したマップを参照しながら補間演算を行うことで、エンジン回転速度およびアクセル開度に対する目標の空燃比を算出することができる。もちろん、設定した圧縮比に対応するマップが記憶されていない場合は、異なる圧縮比の間で補間演算を行うことによって、設定した圧縮比についての目標空燃比を算出することができる。
【００４７】
次いで、先に検出した空気量に対して空燃比が目標空燃比となるような燃料噴射量と、燃料噴射量に対応した燃料噴射開始タイミングとを算出する。前述した空燃比の定義から、空気量と目標の空燃比とが決まれば、噴射すべき燃料量は自ずから決定される。また、燃料噴射量が決まれば、燃料の噴射開示タイミングも自ずから決定される。すなわち、本実施例のエンジン１０では燃料の噴射終了タイミングが固定されているので、燃料噴射量と燃料噴射開始タイミングとは一対一の関係にあり、燃料噴射量が決まれば自ずから燃料噴射開始タイミングも決定されるのである。燃料噴射制御（図２のステップＳ１０６）では、以上に説明したようにして燃料噴射開始タイミングを決定した後、クランク角センサ６１の出力に基づいて、適切なタイミングで燃料噴射弁５５を駆動する制御を行う。
【００４８】
ＥＣＵ６０は、燃料噴射制御を終了すると点火制御を開始する（ステップＳ１０８）。点火制御では、適切なタイミングで点火プラグ２７から火花を飛ばすことにより、燃焼室内に形成された混合気に点火する処理を行う。点火のタイミングは、ＥＣＵ６０のＲＯＭに記憶されたマップに基づいて設定される。
【００４９】
図４は、エンジン回転速度とアクセル開度（あるいはスロットルバルブ開度）とをパラメータとするマップの形式で、圧縮比毎に、点火時期が記憶されている様子を概念的に表している。上述した燃料噴射制御の中で目標空燃比を算出する場合と同様にして、点火制御においても、図４に示したマップから補間演算を行って点火タイミングを算出する。点火制御では、こうしてエンジンの運転条件に応じた点火タイミングを算出した後、クランク角センサ６１の出力に基づいて、適切なタイミングで点火プラグ２７を駆動することにより、燃焼室内の混合気に点火する制御を行う。その結果、混合気が燃焼して燃焼室内の圧力が急激に上昇し、ピストン４１が押し下げられる。この力が、コネクティングロッド４２を介してクランクシャフト４３に伝えられ、クランク機構で回転力に変換されて動力として出力されることになる。
【００５０】
次いで、ＥＣＵ６０は、エンジンを停止する旨が設定されたか否かを確認し（ステップＳ１１０）、停止する旨が設定されていなければステップＳ１００に戻って続く一連の処理を繰り返す。エンジンを停止する旨が設定された場合は、そのままエンジン制御ルーチンを終了する。こうして、エンジン１０は、ＥＣＵ６０の制御の下で、図２の制御ルーチンに従って運転され、操作者の設定に応じた動力を発生させる。
【００５１】
Ｃ．圧縮比変更制御：
上述したように、本実施例のエンジン１０は、圧縮比を変更することが可能であり、エンジンの定常運転度合いを考慮して適切な圧縮比に設定することによって、燃料消費効率を大きく改善することが可能となっている。以下では、先ず、定常運転度合いを判定する処理（図２のステップＳ１０２）について説明した後、定常運転度合いを考慮して圧縮比を設定する処理（図２のステップＳ１０４）について説明する。
【００５２】
Ｃ−１．定常運転度合い判定処理：
図５は、エンジン１０の定常運転度合いを判定する処理の流れを示すフローチャートである。かかる処理は、前述したエンジン制御ルーチンの中でＥＣＵ６０によって実行される。尚、以下に説明する定常運転度合い判定処理は、後述するように、定常運転度合いの判定のために、エンジン制御ルーチン中で検出したアクセル開度を利用しているが、エンジン制御ルーチン中でアクセル開度に替えてスロットル開度あるいは吸気通路内圧力を検出する場合には、これらを用いて判定することも可能である。以下、フローチャートに従って説明する。
【００５３】
定常運転度合い判定処理を開始すると、先ず初めに、変数Ｉを１だけインクリメントする処理を行う（ステップＳ２００）。定常運転度合い判定処理はエンジン制御ルーチンが一周、回るたびに一回ずつ行われ（図２参照）、また、エンジン制御ルーチンが一周するために要する時間はほぼ一定であることから、変数Ｉは、エンジン制御ルーチンが回った回数を表すとともに、おおまかではあるが経過時間を表す変数と考えることもできる。
【００５４】
次いで、アクセル開度の変化量、すなわち、今回のルーチンで検出されたアクセル開度が、前回のルーチンで検出したアクセル開度からどの程度変化したかを算出する（ステップＳ２０２）。アクセルペダルが踏み増されていれば、アクセル開度の変化量は正の値となり、逆にアクセルペダルが戻されていれば、変化量は負の値となる。
【００５５】
そして、アクセル開度の変化量が反転したか否かを判断する（ステップＳ２０４）。変化量の符号が変わっていなければ変化量は反転していないと判断し、逆に符号が変わっていれば変化量が反転していると判断することができる。そして、変化量が反転している場合は（ステップＳ２０４：ｙｅｓ）、反転回数Ｎを１つだけインクリメントする（ステップＳ２０６）。変化量が反転していない場合は（ステップＳ２０４：ｎｏ）、反転回数Ｎをインクリメントする処理（ステップＳ２０６）はスキップする。
【００５６】
次いで、変化量の絶対値を累積して、アクセル操作量として記憶する（ステップＳ２０８）。こうして反転回数を計数しながら、変化量の絶対値を累積していく結果、例えば、アクセルペダルを小刻みに変更しながら頻繁に操作した場合は、反転回数Ｎは大きな値を取り、アクセル操作量は反転回数の割には小さな値を取ることになる。また、アクセルペダルをゆっくりと大きく操作した場合は、反転回数Ｎは小さく、アクセル操作量は大きな値となる。アクセルペダルを大きく且つ頻繁に操作した場合は、反転回数Ｎもアクセル操作量も大きな値を取ることになる。
【００５７】
尚、アクセル開度の変化量が小さい場合（例えば、変化量の絶対値が所定値以下の場合）は、反転回数Ｎのインクリメントを行わず、あるいは変化量の絶対値を累積しないこととしても良い。こうすれば、閾値を適切な値に調整することで、定常運転度合いをより適切に判定することも可能となる。
【００５８】
こうして変化量の累積値をアクセル操作量として記憶したら、エンジン制御ルーチンが回った回数を示す変数Ｉが、所定回数に達したか否かを判断し（ステップＳ２１０）、所定回数に達していない場合は（ステップＳ２１０：ｎｏ）、定常運転度合い判定処理を終了して、図２に示したエンジン制御ルーチンに復帰する。こうしてエンジン制御ルーチンが一回実行される度に、定常運転度合い判定処理が実行され、反転回数Ｎやアクセル操作量が更新される。そして、変数Ｉが所定回数に達すると（ステップＳ２１０：ｙｅｓ）、反転回数Ｎとアクセル操作量とに基づいて、後述する方法で定常安定度合いを判定した後（ステップＳ２１２）、反転回数Ｎやアクセル操作量、変数Ｉをリセットして（ステップＳ２１４）、定常運転度合い判定処理を終了する。すなわち、ステップＳ２１０では、エンジン制御ルーチンが所定回数だけ回る間に、アクセルペダルが操作された回数とアクセルペダルの操作量とに基づいて定常運転度合いを判定していることになる。この様子を、図６を参照しながら補足して説明する。
【００５９】
図６は、時間の経過とともにアクセルペダルが操作される様子を概念的に表した説明図である。図６は、経過時間を横軸にとって、アクセル開度が変化する様子を示したものである。アクセル開度の変化を示す曲線上に、一定間隔で設けられた小さな白丸は、エンジン制御ルーチン中でアクセル開度が検出されたことを表している。ここでは、エンジン制御ルーチンが一周するのに要する時間は、ほぼｄｔ時間であり、従って、アクセル開度は時間ｄｔ毎に計測されているものとしている。また、図中に示したｄθは、時間ｄｔ毎に計測されたアクセル開度の変化量である。
【００６０】
図６に示した例では、初めの間は、アクセル開度は検出する度に増加しており、変化量ｄθは正の値を取り続けるが、時刻ｔａに達すると、それまで正の値を取っていた変化量ｄθが負の値に転じる。従って、このとき反転回数Ｎが１だけインクリメントされて、Ｎ＝１となる。次いで、時刻ｔｂに達すると、アクセル開度の変化量ｄθが再び正の値に転じ、反転回数ＮがインクリメントされてＮ＝２となる。以下、同様に、時刻ｔｃ、時刻ｔｄにおいて、反転回数Ｎが、それぞれＮ＝３、Ｎ＝４とインクリメントされる。こうした操作を行うことで、エンジン制御ルーチンが所定回数だけ回る間に、アクセル開度の変化量ｄθが反転した回数を検出することができる。また、変化量ｄθの絶対値を累積していけば、アクセルの操作量を求めることが可能となる。
【００６１】
以上のようにして、エンジン制御ルーチンが所定回数だけ実行される間の、反転回数Ｎとアクセル操作量とを検出したら、図７に示すようなマップを参照することによって、定常運転度合いの判定を行う。ＥＣＵ６０のＲＯＭには、反転回数とアクセル操作量との組合せに応じて、定常運転度合いが設定されたマップが記憶されている。図７に示すように、本実施例では、定常運転度合いとして、「定常運転」、「準定常運転」、「非定常運転」の三つの段階が設定されている。「定常運転」は、反転回数もアクセル操作量もいずれも小さい場合が該当する。また、アクセル操作量は大きいものの反転回数が小さい場合（例えば、一回だけアクセルペダルを大きく動かした場合など）や、逆に反転回数は多いもののアクセル操作量が小さい場合（例えば、アクセルペダルを微調整するものの、全体としては一定条件で運転している場合など）も「定常運転」に設定されている。反転回数もアクセル操作量もいずれも大きな値を取る場合は「非定常運転」に設定されている。反転回数あるいはアクセル操作量が非定常運転より小さく、定常運転と非定常運転との中間的な状態は「準定常運転」に設定されている。
【００６２】
図５に示した定常運転度合い判定処理中のステップＳ２１２では、検出された反転回数Ｎと、アクセル操作量とに基づいて、図７に示したマップを参照することにより、定常運転度合いを反転するのである。
【００６３】
尚、以上の説明においては、エンジン制御ルーチンが回った回数をカウントして、ルーチンが所定回数だけ実行される間の反転回数Ｎおよびアクセル操作量を検出し、これらの値に基づいて定常運転度合いを判定した。もちろん、ルーチンが回った回数をカウントするのではなく、タイマーをセットすることによって、所定時間が経過する間の反転回数Ｎおよびアクセル操作量を検出して、定常運転度合いを判定することとしても良い。
【００６４】
また、以上の説明では、定常運転度合いは、「定常運転」、「準定常運転」、「非定常運転」の三つの段階が設定されているものとしたが、より多くの段階を設定することも可能である。更には、定常運転度合いを数値によって表現し、反転回数とアクセル操作量とに基づいて数値を決定することとしてもよい。
【００６５】
あるいは、以上の説明では、エンジン制御ルーチンが所定回数だけ回る間のｄθ（アクセル開度の変化量）の絶対値を累積し、この累積値をアクセル操作量とした。これに対して、変化量ｄθが反転してから再び反転するまでの間で変化量ｄθの絶対値を累積して、反転するたび毎にアクセル操作量を求めても良い。こうして、エンジン制御ルーチンが所定回数だけ回る間の、反転回数と、反転するたび毎のアクセル操作量とを求め、平均のアクセル操作量を算出して、定常運転度合いを判定しても良い。あるいは、それぞれのアクセル操作量を、例えば変化量ｄθの符号やエンジンの運転条件などに応じて適宜、重みを付けながら平均し、得られたアクセル操作量と反転回数とに基づいて定常運転度合いを判定することとしても良い。
【００６６】
Ｃ−２．圧縮比設定処理：
以上のようにして、定常運転度合いを判定したら、判定結果を考慮しながら圧縮比を設定する。図８は、本実施例のエンジン１０が圧縮比を設定する処理の流れを示したフローチャートである。この処理は、エンジン制御ルーチンが一回、回る度にＥＣＵ６０によって実行される。以下、図８に従って説明する。
【００６７】
圧縮比設定処理を開始すると、先ず初めに、エンジン回転速度およびアクセル開度に基づいて圧縮比を決定する（ステップＳ３００）。エンジン回転速度およびアクセル開度は、エンジン制御ルーチン中のステップＳ１００において既に検出されている。また、圧縮比の決定に際して定常運転度合いを考慮してないことからも明らかなように、このときに決定される圧縮比は、エンジン１０が定常運転している状態で最適となるように設定された圧縮比である。こうした圧縮比は、ＥＣＵ６０のＲＯＭ内にマップの形式で記憶されている。
【００６８】
図９は、ＥＣＵ６０のＲＯＭ内に記憶されているマップ、すなわち、エンジン１０の定常運転時に、燃料消費効率が最も高くなるような圧縮比が設定されたマップを概念的に示した説明図である。図示されているように、本実施例では、アクセル開度が大きくなるほど、すなわちエンジン負荷が高くなるほど、圧縮比が低くなるように設定されている。また、エンジン回転速度が比較的低い領域内には、回転速度が低くなるほど圧縮比も低くなるように設定された領域が存在している。
【００６９】
一般に、エンジン負荷が高くなるほどノッキングが発生し易くなり、ノッキングが発生すると点火時期を遅角させてノッキングを回避しなければならず、結果として燃料消費効率が悪化してしまう。従って、エンジン負荷が高くなるほど圧縮比を低く設定しておけば、ノッキングの発生を回避し、延いては燃料消費効率の悪化を避けることができる。また、エンジン回転速度が低い運転条件ではノッキングが発生し易いので、エンジン回転速度が比較的低い領域内に、回転速度が低くなるほど圧縮比も低くなるように設定された領域を設けておくことで、ノッキングの発生を回避して、燃料消費効率の悪化を避けることが可能である。図８に示した圧縮比設定処理中のステップＳ３００では、図９に示すマップを参照することによって、定常運転時の圧縮比を決定するのである。
【００７０】
こうして定常運転時の圧縮比を決定したら、定常運転度合いを考慮して補正する処理を行う（ステップＳ３０２）。圧縮比の補正量は、ＥＣＵ６０内のＲＯＭに予め記憶されている。図１０は、ＲＯＭに記憶された圧縮比の補正量を例示した説明図である。例えば、現在の定常運転度合いが「定常運転」であると判定されているとする。この場合は、ステップＳ３００で決定した圧縮比をそのまま採用すればよいので、補正量は「０」が記憶されている。定常運転度合いが「準定常運転」と判定されている場合は、ステップＳ３００で決定した圧縮比を「１．５」だけ低い圧縮比に補正する。また、定常運転度合いが「非定常運転」と判定されている場合は、圧縮比を「２．５」だけ低い圧縮比に補正する。図８に示した圧縮比設定処理中のステップＳ３０２では、こうして、定常運転度合いに応じて圧縮比を補正する処理を行う。
【００７１】
次いで、圧縮比が上限値を超えていないことを確認する（ステップＳ３０４）。すなわち、仮に、何らかの理由で異常に高い圧縮比が算出された場合を考慮して、圧縮比には、定常運転度合いに応じた上限値が予め定められている。図１０は、ＥＣＵ６０のＲＯＭ内に、定常運転度合いに応じて圧縮比の上限値が記憶されている様子を概念的に例示した説明図である。ステップＳ３０４では、補正された圧縮比が、このように定常運転度合いに応じて定められた圧縮比の上限値を超えていないことを確認し、仮に上限値を超えている場合は（ステップＳ３０４：ｎｏ）、圧縮比を上限値に変更する（ステップＳ３０６）。この結果、エンジン１０の圧縮比は、定常運転度合いに応じた圧縮比にクリップされ、決して上限値を超えることはない。
【００７２】
ＥＣＵ６０は、こうして補正した圧縮比に応じてアクチュエータ３３を駆動することにより、エンジン１０の圧縮比を変更する（ステップＳ３０８）。アクチュエータ３３は電力を動力源として動作するリニアアクチュエータであり、ＥＣＵ６０との間で、位置サーボを行うサーボ制御系を構成している。もちろん、アクチュエータ３３の替わりに、油圧などの他の動力源によって動作するアクチュエータを用いることも可能である。ＥＣＵ６０は、アクチュエータ３３を制御してエンジン１０の圧縮比を補正された圧縮比に変更したら、図８に示す圧縮比設定処理を終了して図２のエンジン制御ルーチンに復帰する。
【００７３】
以上に説明したように、本実施例のエンジン１０では、定常運転度合いを考慮して圧縮比を設定している。このため、以下に説明する理由から、圧縮比を変更可能な効果を十分に引き出して燃料消費効率を大きく向上させることが可能となる。
【００７４】
エンジンが、ほぼ一定の運転状態で運転されている場合には、運転条件（代表的には、エンジン回転速度およびエンジン負荷）に応じて適切な圧縮比に設定してやることで、エンジンの燃料消費効率を大きく改善することが可能である。ところが、エンジンは運転条件（特にエンジン負荷）の変動の変化が、大きく、あるいは頻繁に変更されながら運転されることが多いので、運転条件の変動に応じて圧縮比も変更する必要が生じる。しかし圧縮比を変更するためには、アクチュエータ３３を駆動してアッパーブロック３１およびシリンダヘッド２０を移動させるための大きなエネルギが必要となり、従って、頻繁にあるいは大きく圧縮比を変更したのでは、圧縮比変更によって本来ならば得られるであろう燃料消費効率の改善効果を減殺することになる。こうした点を鑑みて、上述したように定常運転度合いを考慮して圧縮比を設定することとすれば、運転条件の変更を見越して適切な圧縮比に設定することができ、延いては燃料消費効率を大きく向上させることが可能となるのである。
【００７５】
更には、圧縮比を高圧縮比から低圧縮比に変更する場合、運転条件の変化に対して圧縮比の変更が遅れると、強いノッキングが発生することがある。ノッキングの発生を回避するために点火時期を遅角させたのでは、燃料消費効率の低下を招いてしまう。もちろん、運転条件の変動に対して圧縮比の変更が遅れることの無いように、大型のアクチュエータ３３を用いてアッパーブロック３１およびシリンダヘッド２０を素早く動かしてやれば、ノッキングの発生を回避することができるが、これでは、アクチュエータ３３を駆動するために大きなエネルギが必要となってしまい、結局は、燃料消費効率の低下を招いてしまう。これに対して、上述したように定常運転度合いを考慮することによって、運転条件の変更を見越して適切な圧縮比に設定してやれば、こうした事態の発生を回避することができるので、燃料消費効率を大きく向上させることが可能となる。
【００７６】
Ｄ．変形例：
以上に説明した実施例では、定常運転時の最適な圧縮比を記憶しておき（図９参照）、この圧縮比を、定常運転度合いに応じて補正するものとして説明した。もっとも、定常運転度合いの判定結果を考慮しながら適切な圧縮比を設定する方法は、こうした方法に限られるものではなく、種々の方法を適用することが可能である。例えば、図１１に示すように、定常運転度合い毎に適切な圧縮比を予め記憶しておき、定常運転度合いの判定結果に応じて、対応するマップを参照しながら圧縮比を設定することとしても良い。
【００７７】
また、以上の説明では、エンジン１０の圧縮比は連続的に変更可能として説明したが、もちろん、圧縮比を何段階かに切り換え可能としても構わない。こうすれば、制御内容を簡素なものとすることが可能となる。
【００７８】
以上に説明した実施例では、アクチュエータ３３を用いてアッパーブロック３１およびシリンダヘッド２０を動かすことによって、圧縮比を変更するものとした。しかし、圧縮比を変更する方法は、こうした方法に限られるものではなく、種々の方法に適用することも可能である。いずれの切り換え方法を用いた場合でも、上述した実施例と同様に、運転条件の変動に対して圧縮比の切り換えが遅れた場合には、ノッキングの発生を回避するために点火時期を遅角させる必要が生じる。また、圧縮比の切り換えには大きなエネルギが必要であるため、頻繁に切り換えたり、あるいは速やかに切り換えるためには大きなエネルギが消費される点でも同様である。従って、本発明は、こうした場合にも好適に適用可能なことは言うまでもない。
【００７９】
更に、上述した本実施例のエンジン１０は、車両の動力源として好適に搭載することができる。車両は走行状況が変化するので、これに伴って内燃機関の運転条件が大きくあるいは頻繁に変更されることが多い。従って、上述したエンジン１０を動力源として用いれば、燃料消費効率を大きく改善することが可能となる。
【００８０】
以上、各種の実施例について説明してきたが、本発明は上記すべての実施例に限られるものではなく、その要旨を逸脱しない範囲において種々の態様で実施することができる。
【図面の簡単な説明】
【図１】 本実施例のエンジンの構成を概念的に示した説明図である。
【図２】 エンジン運転制御ルーチンの流れを示すフローチャートである。
【図３】 圧縮比に応じて空燃比の制御目標値が設定されているマップを概念的に示した説明図である。
【図４】 圧縮比に応じて点火時期の制御目標値が設定されているマップを概念的に示した説明図である。
【図５】 エンジン制御ルーチンの中で実行される本実施例の定常運転度合い判定処理の流れを示したフローチャートである。
【図６】 定常運転度合いを判定するために、アクセル開度の変化量が反転した回数とアクセル操作量とを検出している様子を概念的に示した説明図である。
【図７】 反転回数とアクセル操作量とに応じて定常運転度合いが決定される様子を例示した説明図である。
【図８】 エンジン制御ルーチンの中で実行される本実施例の圧縮比設定処理の流れを示したフローチャートである。
【図９】 エンジンの運転条件に応じて、定常運転状態での圧縮比が設定されているマップを概念的に例示した説明図である。
【図１０】 圧縮比の補正量と圧縮比の上限値とが定常運転度合いに応じて設定されている様子を例示した説明図である。
【図１１】 定常運転度合いに応じて適切な圧縮比がマップの形式で記憶されている様子を概念的に示した説明図である。
【符号の説明】
１０…エンジン
２０…シリンダヘッド
２１…吸気バルブ
２２…排気バルブ
２３…吸気ポート
２４…排気ポート
２７…点火プラグ
３０…シリンダブロックＡＳＳＹ
３１…アッパーブロック
３２…ロアブロック
３３…アクチュエータ
３４…シリンダ
４０…メインムービングＡＳＳＹ
４１…ピストン
４２…コネクティングロッド
４３…クランクシャフト
５０…吸気通路
５１…エアクリーナ
５２…スロットルバルブ
５３…電動アクチュエータ
５５…燃料噴射弁
５６…吸気圧センサ
５８…排気通路
６０…ＥＣＵ
６１…クランク角センサ
６２…アクセル開度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for changing the compression ratio of an internal combustion engine, and more particularly to a technique for reducing the fuel consumption of the internal combustion engine by appropriately changing the compression ratio.
[0002]
[Prior art]
Since an internal combustion engine has an excellent characteristic that it can output relatively large power even though it is small, it is used as a power source for various transport machines such as automobiles, ships, and airplanes, or as a power source for various stationary machines. As widely used. These internal combustion engines have an operating principle of combusting an air-fuel mixture compressed in a combustion chamber, converting the combustion pressure generated at this time into mechanical work, and taking it out as power.
[0003]
In general, an internal combustion engine can extract power efficiently as the compression ratio, which is an index representing the compression ratio of the air-fuel mixture, becomes higher. However, if the compression ratio becomes too high, the friction loss increases and the efficiency decreases. There is a tendency. Therefore, it is theoretically known that there exists an optimum compression ratio at which the thermal efficiency is highest in the compression ratio. However, in an actual internal combustion engine, if the compression ratio is increased, abnormal combustion called knocking may occur depending on the operating conditions. To avoid this, the value must be set lower than the optimal compression ratio. There are many.
[0004]
In view of these points, attempts have been made to switch the compression ratio in accordance with operating conditions in order to improve the thermal efficiency of the internal combustion engine (for example, Patent Document 1, Patent Document 2, etc.). That is, it is possible to improve the thermal efficiency of the internal combustion engine by increasing the compression ratio under operating conditions in which knocking does not occur and decreasing the compression ratio in operating conditions in which knocking occurs. In the above-mentioned patent document, knocking is likely to occur when the intake air amount of the internal combustion engine is large (that is, when the accelerator opening is large). Therefore, the compression ratio is set to a low value to avoid the occurrence of knocking. Since it is difficult for knocking to occur under a condition where the amount is small (that is, a condition where the accelerator opening is small), a technique for improving the thermal efficiency by setting the compression ratio to a high value is disclosed.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 62-258153
[Patent Document 2]
JP-A 63-159642
[0006]
[Problems to be solved by the invention]
However, if the compression ratio is switched according to the operating conditions such as the accelerator opening, no matter how the compression ratio setting for the operating conditions is changed, the fuel consumption can be improved as much as originally expected. There was a problem that it was often not possible to obtain.
[0007]
The present invention has been made to solve the above-described problems in the prior art, and provides a technique capable of further reducing fuel consumption by appropriately changing the compression ratio of the internal combustion engine. With the goal.
[0008]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of the problems described above, the internal combustion engine of the present invention employs the following configuration. That is,
An internal combustion engine having a compression ratio control mechanism capable of controlling a compression ratio,
An operating condition detecting means for detecting an operating condition of the internal combustion engine;
Steady operation degree determination means for determining a steady operation degree representing the degree of operation of the internal combustion engine based on the detected operation condition;
A target compression ratio setting means for setting a control target value of the compression ratio in consideration of the detected operating condition and the determined steady operation degree;
It is a summary to provide.
[0009]
Further, the control method of the internal combustion engine of the present invention corresponding to the internal combustion engine described above,
A control method for an internal combustion engine having a compression ratio control mechanism capable of controlling a compression ratio,
A first step of detecting an operating condition of the internal combustion engine;
A second step of determining, based on the detected operating condition, a steady operation degree indicating a degree of operation of the internal combustion engine in a steady state;
A third step of setting a control target value of the compression ratio in consideration of the detected operating condition and the determined steady operation degree;
A fourth step of controlling the compression ratio of the internal combustion engine to the set control target value;
It is a summary to provide.
[0010]
In the internal combustion engine and the control method of the internal combustion engine of the present invention, the operating condition of the internal combustion engine is detected, and the steady operation degree indicating the degree of operation of the internal combustion engine in the steady state is determined. That is, it is determined whether the internal combustion engine is operated under a constant operating condition or whether the operating condition is large or frequently changed. Next, after setting the control target value of the compression ratio in consideration of the detected operating condition and the steady operation degree, the compression ratio of the internal combustion engine is set to this target value using the compression ratio control mechanism.
[0011]
Normally, an internal combustion engine is often operated while the operating condition is changed. Therefore, in an internal combustion engine that can change the compression ratio, if the compression ratio is set according to the operating condition, the operating condition is changed each time. It is necessary to change the compression ratio. In view of these points, in the internal combustion engine and the control method for the internal combustion engine of the present invention, the compression ratio is set in consideration of the steady operation degree in addition to the operation conditions. For this reason, when the operating conditions are frequently changed, the situation in which the compression ratio is frequently changed can be avoided by setting the compression ratio in anticipation of the change. Since changing the compression ratio requires energy, a large amount of energy is consumed if the compression ratio is changed frequently, and the effect of reducing the fuel consumption that would be obtained by changing the compression ratio may be reduced. . On the other hand, if the compression ratio is set in consideration of the degree of steady operation, such a situation can be avoided, so that it is possible to reliably obtain the effect of reducing the fuel consumption by changing the compression ratio. Become.
[0012]
In addition, when the compression ratio is changed from a high compression ratio to a low compression ratio in accordance with a change in operating conditions, strong knocking may occur if the change in the compression ratio is delayed with respect to the change in operating conditions. When strong knocking occurs in this way, in order to avoid this, it is necessary to retard the ignition timing until the compression ratio change is completed. However, retarding the ignition timing reduces the thermal efficiency of the internal combustion engine, resulting in an increase in fuel consumption and a reduction in the fuel consumption reduction effect that would be obtained by changing the compression ratio. It becomes. Of course, if the compression ratio is changed more quickly so as not to be delayed by changes in the operating conditions, it is not necessary to retard the ignition timing, and a reduction in the thermal efficiency of the internal combustion engine can be avoided. However, in order to change the compression ratio quickly, such a large amount of energy is required, so the fuel consumption is also increased and the effect of changing the compression ratio is diminished. According to the internal combustion engine and the control method for an internal combustion engine of the present invention described above, the compression ratio is set in anticipation of changes in the operating conditions by considering the steady operation degree in addition to the operating conditions when setting the compression ratio, As a result, it is possible to avoid an increase in fuel consumption due to these reasons, and to reliably obtain an effect of improving the fuel consumption by changing the compression ratio.
[0013]
In such an internal combustion engine and a control method for the internal combustion engine, at least a value related to the load of the internal combustion engine may be detected as the operating condition. As a value related to the load, various values can be detected. For example, a value for instructing output to the internal combustion engine, an opening of a throttle valve provided in the internal combustion engine, Various values that can indirectly detect the pressure in the intake passage, the amount of intake air, and the like can be used.
[0014]
Among the operating conditions of the internal combustion engine, the load-related conditions are often changed frequently or greatly. Therefore, if at least a value related to the load is detected as the operating condition, the degree of steady operation is appropriately set. It becomes possible to judge.
[0015]
Further, in the internal combustion engine and the control method, a value related to the load is detected, a change amount and a change frequency of the load are extracted from the detection result, and the steady operation degree is determined based on these values. Also good.
[0016]
Regardless of whether the operating conditions have been changed significantly or frequently, it cannot be said that they are operating in a steady state. When determining the degree of steady operation, the amount of change in operating conditions and the frequency of change It can be said that it is desirable to consider. Therefore, it is preferable to extract the load change amount and the change frequency from the detection result of the value related to the load of the internal combustion engine, and to determine the degree of steady operation based on these, because it is possible to make an appropriate determination. .
[0017]
In the internal combustion engine and the control method for the internal combustion engine described above, when the determined steady operation degree does not satisfy the predetermined standard, the control target value of the compression ratio is set to a lower value than when the standard is satisfied. Also good.
[0018]
By doing so, the compression ratio of the internal combustion engine is set to be lower as the operation condition of the internal combustion engine is deviated from the steady operation state, in other words, as the operation condition is increased or changed frequently. Normally, knocking is more likely to occur as the compression ratio becomes higher. Therefore, if the compression ratio is set to a lower compression ratio in this manner, occurrence of knocking due to fluctuations in operating conditions can be avoided. As a result, it is possible to reliably avoid an increase in fuel consumption by retarding the ignition timing to avoid knocking or consuming a large amount of energy to switch the compression ratio quickly. It becomes.
[0019]
Alternatively, in the above-described internal combustion engine and internal combustion engine control method, when the determined steady operation degree does not satisfy a predetermined reference, the control target value of the compression ratio is set to be limited to a value equal to or less than the predetermined value. Also good.
[0020]
By limiting the compression ratio to a value equal to or less than a predetermined value in this way, it is possible to avoid the occurrence of knocking due to fluctuations in operating conditions and to reliably avoid an increase in fuel consumption. It becomes.
[0021]
Furthermore, in the above-described internal combustion engine and control method, the upper limit value of the compression ratio is stored in advance according to the degree of steady operation, and the control target value of the set compression ratio exceeds the upper limit value. Alternatively, the control target value may be changed to the upper limit value.
[0022]
As the operating condition of the internal combustion engine moves away from the steady operating state, knocking is more likely to occur with the fluctuation of the operating condition. Therefore, if the upper limit value of the compression ratio is stored in accordance with the steady operation degree and the control target value of the compression ratio is clipped to this upper limit value, it is possible to appropriately avoid the occurrence of knocking due to fluctuations in operating conditions. However, it becomes possible to reduce the fuel consumption.
[0023]
In the internal combustion engine and the control method described above, in which the operation condition detects at least a value related to the load, the control target value of the compression ratio is set as follows. Also good. That is, the allowable value of the compression ratio is stored in advance for each of a plurality of areas determined according to the load change amount and the load change frequency. And when the control target value of the compression ratio set based on the operating condition exceeds the allowable value stored for each region, the control target value of the compression ratio may be changed to the allowable value. good.
[0024]
Thus, if the allowable value of the compression ratio is determined for each of a plurality of regions determined according to the load change amount and the load change frequency, an appropriate allowable value is determined according to the steady operation degree. Therefore, it is possible to reduce the fuel consumption while appropriately avoiding the occurrence of knocking due to fluctuations in the operating conditions.
[0025]
In addition, as the allowable value of the compression ratio, a larger value may be stored at least in a region where the load change amount and the load change frequency are smaller.
[0026]
If it carries out like this, it will be set to a high compression ratio, so that the driving | running condition of an internal combustion engine approaches a steady operation state, and conversely, it will be set to a low compression ratio, so that it leaves | separates from a steady operation state. Therefore, it is preferable because the internal combustion engine can be operated at an appropriate compression ratio.
[0027]
In the internal combustion engine and the control method described above, at least a value related to the load of the internal combustion engine and the rotational speed of the internal combustion engine are detected as the operating condition, and the control target value of the compression ratio is as follows. It is good also as setting. That is, for each operating condition including at least the rotational speed, a reference compression ratio corresponding to the operating condition is stored. At this time, as the standard compression ratio, the standard compression ratio is stored such that at least the region below the predetermined rotational speed includes a region where the stored compression ratio decreases as the rotational speed decreases. Keep it. Then, after reading the stored standard compression ratio according to the detected operating condition, a value corrected based on the steady operation degree may be set as the control target value.
[0028]
Usually, an internal combustion engine may have a region where knocking is likely to occur in a region where the rotational speed is low. Therefore, if the reference compression ratio is stored so as to include a region where the stored value becomes smaller as the rotational speed becomes lower, occurrence of knocking in such a region can be avoided. Further, in such a region, there is a tendency for the deviation between the operation state assumed at the time of control of the internal combustion engine and the actual operation state, so that knocking tends to occur also in this respect. Accordingly, in the region where the rotational speed of the internal combustion engine is equal to or lower than the predetermined rotational speed, if the reference compression ratio is stored in the above state, that is, in a state including a region that becomes smaller as the rotational speed is lower, Even when the operating conditions are changed, knocking is less likely to occur. For this reason, it is possible to avoid an increase in fuel consumption due to the retard of the ignition timing or the like, which is preferable.
[0029]
The present invention can also be effectively applied to a vehicle using an internal combustion engine as a power source. That is, the vehicle of the present invention is
A vehicle equipped with an internal combustion engine having a compression ratio control mechanism capable of controlling the compression ratio as a power source,
An accelerator pedal for setting an output required for the internal combustion engine;
Steady operation degree determination means for determining a steady operation degree representing the degree of operation of the internal combustion engine in a steady state based on an operation amount of the accelerator pedal;
A target compression ratio setting means for setting a control target value of the compression ratio in consideration of the detected operating condition and the determined steady operation degree;
It is a summary to provide.
[0030]
In the vehicle according to the present invention, the steady operation degree is determined based on the operation amount of the accelerator pedal, and the compression ratio of the internal combustion engine is set while considering the determination result. In this way, it is possible to reliably obtain an improvement effect of the fuel consumption by changing the compression ratio.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
In order to more clearly describe the operation and effect of the present invention, examples of the present invention will be described in the following order.

[0032]
A. Device configuration:
FIG. 1 is an explanatory diagram conceptually showing the configuration of the engine 10 of this embodiment provided with a variable compression ratio mechanism. In the following description, the engine 10 is described as a so-called spark ignition type engine, but of course, it can also be applied to a compression ignition type engine such as a diesel engine. As shown in the figure, the engine 10 is roughly composed of a cylinder head 20, a cylinder block ASSY 30, a main moving ASSY 40, an intake passage 50, an exhaust passage 58, an engine control unit (hereinafter referred to as ECU) 60, and the like. It is configured.
[0033]
The cylinder block ASSY 30 includes an upper block 31 to which the cylinder head 20 is attached and a lower block 32 in which the main moving ASSY 40 is accommodated. Further, an actuator 33 is provided between the upper block 31 and the lower block 32, and by driving the actuator 33, the upper block 31 can be moved in the vertical direction with respect to the lower block 32. ing. A cylindrical cylinder 34 is formed inside the upper block 31.
[0034]
The main moving assembly 40 includes a piston 41 provided inside the cylinder 34, a crankshaft 43 that rotates inside the lower block 32, a connecting rod 42 that connects the piston 41 to the crankshaft 43, and the like. The piston 41, the connecting rod 42, and the crankshaft 43 constitute a so-called crank mechanism. As the crankshaft 43 rotates, the piston 41 slides up and down in the cylinder 34 as the crankshaft 43 rotates. As a result, the crankshaft 43 rotates in the lower block 32. When the cylinder head 20 is attached to the cylinder block ASSY 30, a combustion chamber is formed in a portion surrounded by the lower surface side (side contacting the upper block 31) of the cylinder head 20, the cylinder 34 and the piston 41. Therefore, if the upper block 31 is moved upward using the actuator 33, the cylinder head 20 is also moved upward along with this, and the volume in the combustion chamber increases, so that the compression ratio can be reduced. Conversely, if the cylinder head 20 is moved downward together with the upper block 31, the volume in the combustion chamber can be reduced and the compression ratio can be increased.
[0035]
The cylinder head 20 is formed with an intake port 23 for taking air into the combustion chamber and an exhaust port 24 for discharging exhaust gas from the combustion chamber. The intake valve 21 is provided, and the exhaust valve 22 is provided at a portion where the exhaust port 24 opens into the combustion chamber. The intake valve 21 and the exhaust valve 22 are each driven by a cam mechanism in accordance with the vertical movement of the piston 41. Thus, if the intake valve 21 and the exhaust valve 22 are opened and closed in synchronization with the movement of the piston, the air can be sucked into the combustion chamber or the exhaust gas can be discharged from the combustion chamber. The cylinder head 20 is also provided with a spark plug 27 for sparking and igniting the air-fuel mixture formed in the combustion chamber.
[0036]
An intake passage 50 for guiding outside air to the cylinder head 20 is connected to the intake port 23 of the cylinder head 20, and an air cleaner 51 is provided at the upstream end of the intake passage 50. The air sucked into the combustion chamber flows into the combustion chamber via the intake passage 50 and the intake port 23 after foreign matter such as dust is removed by the air cleaner 51. The intake passage 50 is provided with a throttle valve 52, a fuel injection valve 55, and the like. If the opening degree of the throttle valve 52 is controlled by the electric actuator 53, the amount of air flowing into the combustion chamber can be controlled. The fuel is injected from the fuel injection valve 55 toward the intake port 23. A part of the injected fuel spray is vaporized in the intake port 23 and the rest flows into the combustion chamber in the form of fuel spray or fuel liquid film, and then mixed with air while being vaporized in the combustion chamber. Form a mind. In addition, an intake pressure sensor 56 is provided in the intake passage 50 so that the pressure in the intake passage can be detected.
[0037]
An exhaust passage 58 is connected to the exhaust port 24 of the cylinder head 20, and exhaust gas discharged from the combustion chamber is guided to the outside by the exhaust passage 58 and released.
[0038]
The ECU 60 is a microcomputer in which a ROM, a RAM, an input / output circuit, and the like are connected to each other via a bus with a central processing unit (hereinafter referred to as a CPU) as a center. As will be described in detail later, the ECU 60 is necessary from a crank angle sensor 61 provided on the crankshaft 43, an accelerator opening sensor 62 built in the accelerator pedal, and an intake pressure sensor 56 as necessary. By taking in the information and driving the spark plug 27, the fuel injection valve 55, the electric actuator 53, etc., the operation of the entire engine 10 is controlled.
[0039]
B. Overview of engine control:
Next, the operation of the engine 10 having the above-described configuration will be described. FIG. 2 is a flowchart showing a flow in which the ECU 60 controls the operation of the engine 10. Hereinafter, it demonstrates according to a flowchart.
[0040]
When the engine control routine is started, the ECU 60 first detects the engine speed Ne and the accelerator opening θac (step S100). The engine rotation speed Ne is calculated from the output of the crank angle sensor 61, and the accelerator opening degree θac can be detected using the accelerator opening degree sensor 62.
[0041]
In step S100, the pressure in the intake passage detected by the intake pressure sensor 56, the throttle opening degree, or the like can be used instead of the accelerator opening degree θac. The throttle opening can be detected by a throttle opening sensor (not shown) built in the electric actuator 53. Of course, since the ECU 60 controls the throttle opening, it is also possible to use the opening used for control inside the ECU 60.
[0042]
When the engine rotational speed Ne and the accelerator opening degree θac are detected in this way, a process for determining the degree of steady operation of the engine 10 is started (step S102). As will be described later in detail, the “steady operation degree” is an operation state such as whether the engine 10 is operated in a steady state, whether the operation conditions are frequently changed, and whether the change is large or small. It is an index representing Details of the process for determining the degree of steady operation will be described later.
[0043]
When the steady operation degree of the engine 10 is determined, a process for setting the compression ratio is started (step S104). As described with reference to FIG. 1, the engine 10 of this embodiment can change the compression ratio of the engine using the actuator 33. Therefore, in step S104, an appropriate compression ratio corresponding to the engine operating conditions is obtained while taking into account the previously determined steady operation degree, and then the actuator 33 is driven to reduce the compression ratio of the engine 10 to an appropriate compression. Processing to set the ratio. Details of the compression ratio setting process will be described later.
[0044]
The ECU 60 starts fuel injection control following the compression ratio setting process (step S106). In this control, the amount of air taken into the combustion chamber is detected, and control is performed to inject an amount of fuel corresponding to a predetermined air-fuel ratio from the fuel injection valve 55 at an appropriate timing. In this embodiment, the amount of air taken into the combustion chamber is calculated based on the pressure in the intake passage detected by the intake pressure sensor 56. Of course, an air flow sensor may be provided in the intake passage 50 to measure the amount of air sucked in by the engine 10, and more simply, the engine speed and the accelerator opening (the opening of the throttle valve 52) are used as parameters. It is also possible to measure the air amount in advance and store it as a map, and obtain the air amount with reference to this map.
[0045]
The fuel is injected so as to achieve a predetermined air-fuel ratio with respect to the air amount thus obtained. The air-fuel ratio is an index representing the mixing ratio of fuel and air, and is defined as a value obtained by dividing the weight of air supplied into the combustion chamber by the weight of fuel. The ROM built in the ECU 60 stores a target air-fuel ratio for each compression ratio in the form of a map with the engine speed and the accelerator opening (or throttle valve opening) as parameters.
[0046]
FIG. 3 is an explanatory diagram exemplifying a map storing a target air-fuel ratio for each engine compression ratio. The engine compression ratio 13 (ε = 13) and the compression ratio 10.5 (ε = 10.5). ) Conceptually shows a state in which three maps having a compression ratio of 9 (ε = 9) are stored. For example, when the compression ratio of the engine 10 is set to 13 in the compression ratio setting process (step S104 in FIG. 2), an interpolation calculation is performed by referring to the map displayed at the forefront in FIG. The target air-fuel ratio with respect to the engine speed and the accelerator opening can be calculated. Of course, when the map corresponding to the set compression ratio is not stored, the target air-fuel ratio for the set compression ratio can be calculated by performing an interpolation operation between the different compression ratios.
[0047]
Next, a fuel injection amount so that the air-fuel ratio becomes the target air-fuel ratio with respect to the previously detected air amount, and a fuel injection start timing corresponding to the fuel injection amount are calculated. If the air amount and the target air-fuel ratio are determined from the above-described definition of the air-fuel ratio, the amount of fuel to be injected is naturally determined. Further, if the fuel injection amount is determined, the fuel injection disclosure timing is also determined automatically. That is, since the fuel injection end timing is fixed in the engine 10 of the present embodiment, there is a one-to-one relationship between the fuel injection amount and the fuel injection start timing. If the fuel injection amount is determined, the fuel injection start timing is also automatically determined. It is decided. In the fuel injection control (step S106 in FIG. 2), after the fuel injection start timing is determined as described above, the fuel injection valve 55 is driven at an appropriate timing based on the output of the crank angle sensor 61. I do.
[0048]
The ECU 60 starts the ignition control when the fuel injection control ends (step S108). In the ignition control, a process of igniting the air-fuel mixture formed in the combustion chamber is performed by blowing a spark from the spark plug 27 at an appropriate timing. The timing of ignition is set based on a map stored in the ROM of the ECU 60.
[0049]
FIG. 4 conceptually shows how ignition timing is stored for each compression ratio in the form of a map using the engine speed and the accelerator opening (or throttle valve opening) as parameters. Similarly to the case where the target air-fuel ratio is calculated in the fuel injection control described above, also in the ignition control, the interpolation timing is calculated from the map shown in FIG. 4 to calculate the ignition timing. In the ignition control, after calculating the ignition timing according to the operating condition of the engine in this way, the ignition plug 27 is driven at an appropriate timing based on the output of the crank angle sensor 61 to ignite the air-fuel mixture in the combustion chamber. Take control. As a result, the air-fuel mixture burns, the pressure in the combustion chamber rises rapidly, and the piston 41 is pushed down. This force is transmitted to the crankshaft 43 via the connecting rod 42, converted into a rotational force by the crank mechanism, and output as power.
[0050]
Next, the ECU 60 confirms whether or not to stop the engine has been set (step S110). If not set to stop, the ECU 60 returns to step S100 and repeats a series of subsequent processes. If it is set to stop the engine, the engine control routine is terminated as it is. Thus, the engine 10 is operated according to the control routine of FIG. 2 under the control of the ECU 60, and generates power according to the setting of the operator.
[0051]
C. Compression ratio change control:
As described above, the engine 10 of the present embodiment can change the compression ratio, and greatly improves fuel consumption efficiency by setting an appropriate compression ratio in consideration of the steady operation degree of the engine. It is possible. In the following, the process for determining the degree of steady operation (step S102 in FIG. 2) will be described first, and then the process for setting the compression ratio in consideration of the degree of steady operation (step S104 in FIG. 2) will be described.
[0052]
C-1. Steady driving degree determination process:
FIG. 5 is a flowchart showing a flow of processing for determining the steady operation degree of the engine 10. Such processing is executed by the ECU 60 in the engine control routine described above. Note that the steady operation degree determination process described below uses the accelerator opening detected in the engine control routine to determine the steady operation degree as described later. When the throttle opening or the intake passage pressure is detected instead of the opening, it is possible to make a determination using these. Hereinafter, it demonstrates according to a flowchart.
[0053]
When the steady operation degree determination process is started, first, a process of incrementing the variable I by 1 is performed (step S200). The steady operation degree determination process is performed once for each rotation of the engine control routine (see FIG. 2), and since the time required for the engine control routine to complete the rotation is substantially constant, the variable I is In addition to representing the number of times the engine control routine has been turned, it can also be considered as a variable that represents the elapsed time roughly.
[0054]
Next, the amount of change in the accelerator opening, that is, how much the accelerator opening detected in the current routine has changed from the accelerator opening detected in the previous routine is calculated (step S202). If the accelerator pedal is stepped on, the amount of change in the accelerator opening is a positive value. Conversely, if the accelerator pedal is returned, the amount of change is a negative value.
[0055]
Then, it is determined whether or not the change amount of the accelerator opening is reversed (step S204). If the sign of the amount of change has not changed, it can be determined that the amount of change has not been reversed. Conversely, if the sign has changed, it can be determined that the amount of change has been reversed. If the change amount is reversed (step S204: yes), the inversion number N is incremented by one (step S206). If the amount of change is not reversed (step S204: no), the process of incrementing the number N of inversions (step S206) is skipped.
[0056]
Next, the absolute value of the change amount is accumulated and stored as an accelerator operation amount (step S208). As a result of accumulating the absolute value of the change amount while counting the number of inversions in this way, for example, if the accelerator pedal is changed frequently in small increments, the inversion number N takes a large value and the accelerator operation amount is A small value is taken for the number of inversions. Further, when the accelerator pedal is operated slowly and greatly, the number of inversions N is small and the accelerator operation amount becomes a large value. When the accelerator pedal is large and frequently operated, both the number of inversions N and the accelerator operation amount take large values.
[0057]
When the change amount of the accelerator opening is small (for example, when the absolute value of the change amount is not more than a predetermined value), the inversion number N is not incremented or the absolute value of the change amount may not be accumulated. . If it carries out like this, it will also become possible to determine a steady driving | running degree more appropriately by adjusting a threshold value to an appropriate value.
[0058]
When the accumulated value of the change amount is stored as the accelerator operation amount in this way, it is determined whether or not the variable I indicating the number of times the engine control routine has been turned has reached a predetermined number (step S210), and the predetermined number has not been reached. (Step S210: no), the steady operation degree determination process is terminated, and the process returns to the engine control routine shown in FIG. Thus, each time the engine control routine is executed once, the steady operation degree determination process is executed, and the number N of inversions and the accelerator operation amount are updated. When the variable I reaches the predetermined number of times (step S210: yes), the degree of steady state stability is determined by a method described later (step S212) based on the number of inversions N and the accelerator operation amount (step S212). The manipulated variable and variable I are reset (step S214), and the steady operation degree determination process is terminated. That is, in step S210, the steady driving degree is determined based on the number of times the accelerator pedal is operated and the amount of operation of the accelerator pedal while the engine control routine is rotated a predetermined number of times. This situation will be supplementarily described with reference to FIG.
[0059]
FIG. 6 is an explanatory diagram conceptually showing how the accelerator pedal is operated over time. FIG. 6 shows how the accelerator opening changes with the elapsed time on the horizontal axis. Small white circles provided at regular intervals on the curve indicating the change in accelerator opening indicate that the accelerator opening is detected in the engine control routine. Here, the time required for the engine control routine to make a round is approximately dt time, and accordingly, the accelerator opening is measured every time dt. Further, dθ shown in the figure is a change amount of the accelerator opening measured every time dt.
[0060]
In the example shown in FIG. 6, during the beginning, the accelerator opening increases every time it is detected, and the change amount dθ continues to take a positive value, but when the time ta is reached, it takes a positive value until then. The amount of change dθ that has been changed to a negative value. Therefore, at this time, the inversion number N is incremented by 1, and N = 1. Next, when the time tb is reached, the change amount dθ of the accelerator opening is again changed to a positive value, the inversion number N is incremented, and N = 2. Similarly, at times tc and td, the number of inversions N is incremented to N = 3 and N = 4, respectively. By performing such an operation, it is possible to detect the number of times the change amount dθ of the accelerator opening is reversed while the engine control routine rotates a predetermined number of times. Further, if the absolute value of the change amount dθ is accumulated, the operation amount of the accelerator can be obtained.
[0061]
As described above, when the inversion number N and the accelerator operation amount are detected while the engine control routine is executed a predetermined number of times, the steady operation degree is determined by referring to a map as shown in FIG. Do. In the ROM of the ECU 60, a map in which the steady operation degree is set according to the combination of the number of inversions and the accelerator operation amount is stored. As shown in FIG. 7, in this embodiment, three stages of “steady operation”, “quasi-steady operation”, and “unsteady operation” are set as the degree of steady operation. The “steady operation” corresponds to a case where both the number of inversions and the accelerator operation amount are small. In addition, when the accelerator operation amount is large but the number of inversions is small (for example, when the accelerator pedal is moved a large amount only once), or conversely, although the number of inversions is large, the accelerator operation amount is small (for example, slightly depressing the accelerator pedal). Although it is adjusted, as a whole, it is also set to “steady operation” when it is operated under a constant condition. When both the number of inversions and the amount of accelerator operation have large values, “unsteady operation” is set. The number of inversions or the amount of accelerator operation is smaller than in the unsteady operation, and the intermediate state between the steady operation and the unsteady operation is set to “quasi-steady operation”.
[0062]
In step S212 during the steady operation degree determination process shown in FIG. 5, the steady operation degree is reversed by referring to the map shown in FIG. 7 based on the detected number of inversions N and the accelerator operation amount. It is.
[0063]
In the above description, the number of times the engine control routine has been turned is counted, the number N of inversions and the accelerator operation amount are detected while the routine is executed a predetermined number of times, and the degree of steady operation based on these values. Was judged. Of course, instead of counting the number of times the routine has been turned, the number of inversions N and the amount of accelerator operation during a predetermined time may be detected by setting a timer to determine the degree of steady operation. .
[0064]
In the above description, the steady operation degree is assumed to have three stages of “steady operation”, “quasi-steady operation”, and “unsteady operation”, but more stages should be set. Is also possible. Furthermore, the steady operation degree may be expressed by a numerical value, and the numerical value may be determined based on the number of inversions and the accelerator operation amount.
[0065]
Alternatively, in the above description, the absolute value of dθ (amount of change in accelerator opening) is accumulated while the engine control routine rotates a predetermined number of times, and this accumulated value is used as the accelerator operation amount. On the other hand, the absolute value of the change amount dθ may be accumulated from when the change amount dθ is inverted to when it is inverted again, and the accelerator operation amount may be obtained each time the change amount dθ is inverted. Thus, the number of inversions during the engine control routine rotating a predetermined number of times and the accelerator operation amount for each inversion may be obtained, and the average accelerator operation amount may be calculated to determine the steady operation degree. Alternatively, each accelerator operation amount is averaged with appropriate weighting depending on, for example, the sign of the change amount dθ or the engine operating condition, and the steady operation degree is determined based on the obtained accelerator operation amount and the number of inversions. It may be determined.
[0066]
C-2. Compression ratio setting process:
When the degree of steady operation is determined as described above, the compression ratio is set in consideration of the determination result. FIG. 8 is a flowchart showing the flow of processing in which the engine 10 of this embodiment sets the compression ratio. This process is executed by the ECU 60 every time the engine control routine rotates once. Hereinafter, a description will be given with reference to FIG.
[0067]
When the compression ratio setting process is started, first, the compression ratio is determined based on the engine speed and the accelerator opening (step S300). The engine speed and the accelerator opening are already detected in step S100 during the engine control routine. As is clear from the fact that the degree of steady operation is not taken into account when determining the compression ratio, the compression ratio determined at this time is set to be optimal when the engine 10 is in steady operation. Compression ratio. Such a compression ratio is stored in the form of a map in the ROM of the ECU 60.
[0068]
FIG. 9 is an explanatory diagram conceptually showing a map stored in the ROM of the ECU 60, that is, a map in which a compression ratio is set such that the fuel consumption efficiency is highest during steady operation of the engine 10. . As shown in the figure, in this embodiment, the compression ratio is set to be lower as the accelerator opening is larger, that is, as the engine load is higher. Further, in the region where the engine rotational speed is relatively low, there is a region where the compression ratio is set to be lower as the rotational speed is lower.
[0069]
In general, as the engine load increases, knocking is more likely to occur. When knocking occurs, the ignition timing must be retarded to avoid knocking, resulting in a deterioration in fuel consumption efficiency. Therefore, if the compression ratio is set lower as the engine load becomes higher, the occurrence of knocking can be avoided, and further deterioration of fuel consumption efficiency can be avoided. In addition, knocking is likely to occur under operating conditions where the engine speed is low. Therefore, by setting a region in the region where the engine speed is relatively low so that the compression ratio decreases as the rotational speed decreases. It is possible to avoid the occurrence of knocking and avoid the deterioration of the fuel consumption efficiency. In step S300 during the compression ratio setting process shown in FIG. 8, the compression ratio during steady operation is determined by referring to the map shown in FIG.
[0070]
When the compression ratio at the time of steady operation is thus determined, a correction process is performed in consideration of the degree of steady operation (step S302). The correction amount of the compression ratio is stored in advance in the ROM in the ECU 60. FIG. 10 is an explanatory diagram illustrating the correction amount of the compression ratio stored in the ROM. For example, it is assumed that the current steady operation degree is determined to be “steady operation”. In this case, since the compression ratio determined in step S300 may be adopted as it is, “0” is stored as the correction amount. When the steady operation degree is determined to be “quasi-steady operation”, the compression ratio determined in step S300 is corrected to a compression ratio that is lower by “1.5”. When the steady operation degree is determined to be “unsteady operation”, the compression ratio is corrected to a compression ratio that is lower by “2.5”. In step S302 during the compression ratio setting process shown in FIG. 8, the process of correcting the compression ratio according to the steady operation degree is thus performed.
[0071]
Next, it is confirmed that the compression ratio does not exceed the upper limit value (step S304). That is, if an abnormally high compression ratio is calculated for some reason, an upper limit value corresponding to the degree of steady operation is determined in advance for the compression ratio. FIG. 10 is an explanatory diagram conceptually illustrating the state in which the upper limit value of the compression ratio is stored in the ROM of the ECU 60 in accordance with the steady operation degree. In step S304, it is confirmed that the corrected compression ratio does not exceed the upper limit value of the compression ratio thus determined according to the steady operation degree. If the upper limit value is exceeded (step S304: no), the compression ratio is changed to the upper limit (step S306). As a result, the compression ratio of the engine 10 is clipped to the compression ratio corresponding to the steady operation degree, and never exceeds the upper limit value.
[0072]
The ECU 60 changes the compression ratio of the engine 10 by driving the actuator 33 in accordance with the compression ratio thus corrected (step S308). The actuator 33 is a linear actuator that operates using electric power as a power source, and constitutes a servo control system that performs position servo with the ECU 60. Of course, instead of the actuator 33, it is also possible to use an actuator that is operated by another power source such as hydraulic pressure. When the ECU 60 controls the actuator 33 to change the compression ratio of the engine 10 to the corrected compression ratio, the ECU 60 ends the compression ratio setting process shown in FIG. 8 and returns to the engine control routine of FIG.
[0073]
As described above, in the engine 10 of this embodiment, the compression ratio is set in consideration of the steady operation degree. For this reason, for the reason explained below, it is possible to sufficiently improve the fuel consumption efficiency by sufficiently extracting the effect of changing the compression ratio.
[0074]
When the engine is operating in an almost constant operating state, the fuel consumption efficiency of the engine is set by setting an appropriate compression ratio according to the operating conditions (typically, engine speed and engine load). Can be greatly improved. However, since the engine is often operated while the change in the operating condition (especially the engine load) is large or frequently changed, it is necessary to change the compression ratio according to the change in the operating condition. However, in order to change the compression ratio, a large amount of energy is required to drive the actuator 33 and move the upper block 31 and the cylinder head 20. Therefore, if the compression ratio is changed frequently or greatly, the compression ratio The change would reduce the fuel consumption efficiency improvement effect that would otherwise be obtained. In view of these points, if the compression ratio is set in consideration of the degree of steady operation as described above, it is possible to set an appropriate compression ratio in anticipation of changes in operating conditions, and thus fuel consumption. The efficiency can be greatly improved.
[0075]
Furthermore, when the compression ratio is changed from a high compression ratio to a low compression ratio, strong knocking may occur if the change in the compression ratio is delayed with respect to the change in operating conditions. If the ignition timing is retarded in order to avoid the occurrence of knocking, the fuel consumption efficiency is reduced. Of course, knocking can be avoided if the upper block 31 and the cylinder head 20 are quickly moved using the large actuator 33 so that the change in the compression ratio is not delayed with respect to fluctuations in the operating conditions. However, in this case, a large amount of energy is required to drive the actuator 33, resulting in a decrease in fuel consumption efficiency. On the other hand, if the appropriate compression ratio is set in anticipation of changes in operating conditions by considering the degree of steady operation as described above, the occurrence of such a situation can be avoided, so the fuel consumption efficiency can be reduced. It is possible to greatly improve.
[0076]
D. Variations:
In the embodiment described above, the optimum compression ratio at the time of steady operation is stored (see FIG. 9), and this compression ratio is corrected according to the degree of steady operation. However, the method of setting an appropriate compression ratio in consideration of the determination result of the steady operation degree is not limited to such a method, and various methods can be applied. For example, as shown in FIG. 11, an appropriate compression ratio may be stored in advance for each steady operation degree, and the compression ratio may be set with reference to the corresponding map according to the determination result of the steady operation degree. good.
[0077]
In the above description, the compression ratio of the engine 10 has been described as being continuously changeable. Of course, the compression ratio may be switched in several steps. This makes it possible to simplify the control content.
[0078]
In the embodiment described above, the compression ratio is changed by moving the upper block 31 and the cylinder head 20 using the actuator 33. However, the method of changing the compression ratio is not limited to such a method, and can be applied to various methods. Whichever switching method is used, the ignition timing is retarded in order to avoid the occurrence of knocking when the switching of the compression ratio is delayed with respect to fluctuations in operating conditions, as in the above-described embodiment. Need arises. Further, since a large amount of energy is required to switch the compression ratio, the same is true in that a large amount of energy is consumed to switch frequently or quickly. Therefore, it goes without saying that the present invention can be suitably applied to such a case.
[0079]
Furthermore, the engine 10 of the present embodiment described above can be suitably mounted as a power source for the vehicle. Since the traveling state of the vehicle changes, the operating conditions of the internal combustion engine are often changed frequently or frequently. Therefore, if the engine 10 described above is used as a power source, fuel consumption efficiency can be greatly improved.
[0080]
Although various embodiments have been described above, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the scope of the invention.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram conceptually showing the configuration of an engine of the present embodiment.
FIG. 2 is a flowchart showing a flow of an engine operation control routine.
FIG. 3 is an explanatory diagram conceptually showing a map in which an air-fuel ratio control target value is set according to a compression ratio.
FIG. 4 is an explanatory diagram conceptually showing a map in which a control target value of ignition timing is set according to a compression ratio.
FIG. 5 is a flowchart showing the flow of steady operation degree determination processing of the present embodiment, which is executed in an engine control routine.
FIG. 6 is an explanatory diagram conceptually showing a state in which the number of times the change amount of the accelerator opening is inverted and the accelerator operation amount are detected in order to determine the steady operation degree.
FIG. 7 is an explanatory view exemplifying a state in which a steady operation degree is determined according to the number of inversions and an accelerator operation amount.
FIG. 8 is a flowchart showing the flow of a compression ratio setting process of the present embodiment that is executed in an engine control routine.
FIG. 9 is an explanatory diagram conceptually illustrating a map in which a compression ratio in a steady operation state is set according to an engine operating condition.
FIG. 10 is an explanatory diagram illustrating a state in which a compression amount correction amount and an upper limit value of the compression ratio are set according to the steady operation degree.
FIG. 11 is an explanatory diagram conceptually showing a state in which an appropriate compression ratio is stored in the form of a map in accordance with the steady operation degree.
[Explanation of symbols]
10 ... Engine
20 ... Cylinder head
21 ... Intake valve
22 ... Exhaust valve
23 ... Intake port
24 ... Exhaust port
27 ... Spark plug
30 ... Cylinder block assembly
31 ... Upper block
32 ... Lower block
33 ... Actuator
34 ... Cylinder
40 ... Main Moving ASSY
41 ... Piston
42 ... Connecting rod
43 ... Crankshaft
50. Intake passage
51 ... Air cleaner
52 ... Throttle valve
53 ... Electric actuator
55 ... Fuel injection valve
56 ... Intake pressure sensor
58 ... Exhaust passage
60 ... ECU
61 ... Crank angle sensor
62 ... Accelerator opening sensor

Claims (7)

An internal combustion engine having a compression ratio control mechanism capable of controlling a compression ratio,
As the operating condition of the internal combustion engine, an operating condition detecting means for detecting a value related to the load of the internal combustion engine,
A steady operation degree determination means for determining a steady operation degree representing a degree of operation of the internal combustion engine based on the detected operation condition, and a predetermined period from a detection result of a value related to the load The amount of change in the load and the number of positive and negative inversions of the amount of change in the load are extracted, and the steady operation degree determination means for determining the degree of steady operation using the amount of change and the number of inversions ;
When the control target value of the compression ratio when the internal combustion engine is operating in steady operation is determined using the detected load change amount, and the determined steady operation degree indicates a degree not corresponding to steady operation Is an internal combustion engine comprising target compression ratio setting means for reducing the determined control target value . The internal combustion engine according to claim 1,
Upper limit compression ratio storage means for storing an upper limit value of the compression ratio according to the steady operation degree;
Target compression ratio changing means for changing the control target value of the compression ratio to the upper limit value when the control target value of the set compression ratio exceeds the upper limit value stored in accordance with the steady operation degree; An internal combustion engine. The internal combustion engine according to claim 1,
A permissible compression ratio storage means for storing a permissible value of the compression ratio for each of a plurality of areas determined according to the load change amount and the load reversal count ;
And a target compression ratio changing means for changing the control target value of the compression ratio to the allowable value when the control target value of the set compression ratio exceeds the allowable value stored for each region. Internal combustion engine. An internal combustion engine according to claim 3,
The allowable compression ratio storage means is an internal combustion engine that stores a larger value of the allowable value in a region where at least the amount of change in the load and the number of inversions of the load are smaller . The internal combustion engine according to claim 1,
The operating condition detecting means is means for detecting at least a value related to the load of the internal combustion engine and the rotational speed of the internal combustion engine as the operating condition,
The target compression ratio setting means includes
Reference compression ratio storage means for storing a reference compression ratio according to the operation condition for each operation condition including at least the rotational speed;
The compression ratio of the reference stored in accordance with the operating conditions, with and a reference compression ratio correcting means for reducing-out based on the steady operation degree,
The internal combustion engine, wherein the reference compression ratio storage means has a region in which the stored reference compression ratio decreases as the rotational speed decreases, at least in a region below a predetermined rotational speed. A vehicle equipped with an internal combustion engine having a compression ratio control mechanism capable of controlling the compression ratio as a power source,
An accelerator pedal for setting an output required for the internal combustion engine;
Determining the degree of steady operation, which represents the degree to which the internal combustion engine is operating in a steady state, based on the amount of operation of the accelerator pedal and the number of changes in the amount of change in the degree of opening of the accelerator pedal within a predetermined period Means for determining a steady operation level,
When the control target value of the compression ratio is determined when the internal combustion engine is operated in steady operation using the operation amount of the accelerator pedal, and the determined steady operation degree indicates a degree not corresponding to steady operation A vehicle comprising target compression ratio setting means for reducing the determined control target value . A control method for an internal combustion engine having a compression ratio control mechanism capable of controlling a compression ratio,
A first step of detecting a value related to a load of the internal combustion engine as an operating condition of the internal combustion engine;
The amount of change in the load and the amount of change in the load within a predetermined period extracted from the detection result of the value related to the load, the degree of steady operation representing the degree of operation of the internal combustion engine in a steady state . A second step of determining using the number of positive and negative inversions ;
When the control target value of the compression ratio when the internal combustion engine is operating in steady operation is determined using the detected load change amount , and the determined steady operation degree indicates a degree not corresponding to steady operation A third step of reducing the determined control target value ;
And a fourth step of controlling the compression ratio of the internal combustion engine to the determined or reduced control target value.

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