JP2004332658A - Ignition timing control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel ignition timing control device for an internal combustion engine, in which recent combustion analysis results are incorporated by making the volume of combustion gas approximate to the current capacity of a combustion chamber, introducing the mass of combustion gas instead and calculating a combustion period in accordance with the capacity of the combustion chamber and the mass of the combustion gas. <P>SOLUTION: A mol fraction of a combustion component accounting for a total mol fraction in the combustion chamber is detected in accordance with the operated condition of the internal combustion engine, and reaction probability showing how easy the combustion gas is burnt is calculated in accordance with the detected mol fraction. The combustion period from starting the combustion to reaching a preset crank angle is calculated in accordance with the reaction probability, the combustion speed of the combustion gas, the capacity equivalent to the volume of the combustion gas in the combustion chamber, and the mass of the combustion gas to be burnt in the combustion chamber in a period from starting the combustion to reaching the reference crank angle at which combustion pressure is maximized, and spark ignition is performed at a basic ignition timing from which MBT is obtained, in accordance with the combustion period. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ただし、Ｖｃ：隙間容積［ｍ^３］、
ε ：圧縮比、
Ｄ ：シリンダボア径［ｍ］、
ＳＴ ：ピストンの全ストローク［ｍ］、
Ｈｉｖｃ ：吸気弁閉時期におけるピストンピン７６のＴＤＣからの距離［ｍ］、
Ｈｘ ：ピストンピン７６のＴＤＣからの距離の最大値と最小値との差［ｍ］、
ＣＮＤ ：コネクティングロッド７４の長さ［ｍ］、
ＣＲｏｆｆ ：結節点７５のシリンダ中心軸７３からのオフセット距離［ｍ］、
ＰＩＳｏｆｆ：クランクシャフト回転中心７２のシリンダ中心 軸７３からのオフセット距離［ｍ］、
θｉｖｃ ：吸気弁閉時期のクランク角［ｄｅｇＡＴＤＣ］、
θｏｆｆ ：ピストンピン７６とクランクシャフト回転中心
７２とを結ぶ線がＴＤＣにおいて垂直線となす角度［ｄｅｇ］、
Ｘ ：結節点７５とピストンピン７６との水平距離［ｍ］、
吸気弁閉時期のクランク角θｉｖｃは前述のように、エンジンコントローラ３１から吸気ＶＴＣ機構２７への指令信号によって決まるので、既知である。式（２）〜（６）にこのときのクランク角θｉｖｃ（＝ＩＶＣ）を代入すれば、燃焼室５の吸気弁閉時期における容積ＶＩＶＣを算出することができる。したがって、実用上は燃焼室５の吸気弁閉時期における容積ＶＩＶＣは吸気弁閉時期ＩＶＣをパラメータとするテーブルで設定したものを用いる。吸気ＶＴＣ機構２７を備えないときには定数で与えることができる。
【００４２】
ステップ１３では、燃焼室５の吸気弁閉時期ＩＶＣにおける温度（つまり圧縮開始時期温度）ＴＩＮＩ［Ｋ］を算出する。燃焼室５に流入するガスの温度は、燃焼室５に流入する新気と燃焼室５に残留する不活性ガスとが混じったガスの温度であり、燃焼室５に流入する新気の温度は吸気コレクタ２内の新気温度ＴＣＯＬに等しく、また燃焼室５内に残留する不活性ガスの温度は排気ポート部近傍の排気温度ＴＥＸＨで近似できるので、燃焼室５の吸気弁閉時期ＩＶＣにおける温度ＴＩＮＩは吸気弁閉時期ＩＶＣになったタイミングでの、吸気コレクタ２内の新気温度ＴＣＯＬ、排気温度ＴＥＸＨ、燃焼室５内に残留する不活性ガスの割合である残留不活性ガス率ＭＲＥＳＦＲから次式により求めることができる。
【００４３】
ＴＩＮＩ＝ＴＥＸＨ×ＭＲＥＳＦＲ＋ＴＣＯＬ×（１−ＭＲＥＳＦＲ）…（７）
ステップ１４では燃焼室５の吸気弁閉時期ＩＶＣにおける圧力（つまり圧縮開始時期圧力）ＰＩＮＩ［Ｐａ］を算出する。すなわち、吸気弁閉時期ＩＶＣになったタイミングでのコレクタ内圧力ＰＣＯＬを吸気弁閉時期ＩＶＣにおける圧力ＰＩＮＩとして取り込む。
【００４４】
ステップ１５では、反応確率ＲＰＲＯＢＡ［％］を算出する。この反応確率ＲＰＲＯＢＡは燃焼室５内の混合気の燃えやすさを表す無次元の値であり、残留不活性ガス率ＭＲＥＳＦＲ、冷却水温ＴＷＫ［Ｋ］、目標当量比ＴＦＢＹＡの３つのパラメータに依存するので、次式により表すことができる。
【００４５】
ＲＰＲＯＢＡ＝ｆ３（ＭＲＥＳＦＲ、ＴＷＫ、ＴＦＢＹＡ）…（８）
以下、反応確率ＲＰＲＯＢＡについて説明する。燃焼室内の燃焼を定容燃焼で近似したとき、燃焼室内の混合気が燃焼する際の総括化学反応における反応速度（燃焼速度）は以下で表すことができる。
【００４６】
【数１】

さらに［Ｆ］，［Ｏ_２］は以下で表される。
【００４７】
【数２】

また、層流燃焼速度Ｓ_Ｌは一般に以下で表される。
【００４８】
【数３】

したがって以下になる。
【００４９】
【数４】

この式のうち、「Ａ_１」が定数項、「Ｆ_１（Ｐ）」が圧力依存項、「Ｇ_１（Ｔ）」が温度依存項であるので、「ｘ_Ｆ ^ｍ／２・ｘ_Ｏ２ ^ｎ／２」が反応確率に相当することになる。すなわち、この反応確率が大きければ燃焼速度が速くなり、小さければ燃焼速度が遅くなる。反応確率は燃焼室内の混合気の燃えやすさを表す補正項である。
【００５０】
ここで、燃料モル分率ｘ_Ｆと酸素モル分率ｘ_Ｏ２との関係を求める。まず、ｍ_ＡＩＲ；吸入空気質量、ｍ_Ｆ；吸入燃料質量、ｍ_Ｏ２；吸入酸素質量とすると以下の関係がある。
【００５１】
ｍ_ＡＩＲ：ｍ_Ｆ ＝１４．７：１
ｍ_ＡＩＲ：ｍ_Ｏ２ ＝１：０．２３
また以下の関係がある。
【００５２】
ｘ_Ｆ＝ｍ_Ｆ／Ｍ_Ｆ
ｘ_Ｏ２＝ｍ_Ｏ２／Ｍ_Ｏ２
なお燃料の平均分子量ＭＦは冷却水温ＴＷＫによって変化する。すなわち、ガソリンにはいろいろな成分が含まれているので、温度が変わると気化する成分が変わる。したがって温度によって燃料平均分子量ＭＦは変わる。低温であるほど「軽質成分」が多いので、燃料平均分子量ＭＦも小さいが高温になるほど燃料平均分子量ＭＦも大きくなる。燃料平均分子量ＭＦはその点を補正して決定する。一般的なガソリン燃料の温度変化に対する蒸発特性は分かっているので、この特性から雰囲気温度に対する燃料平均分子量ＭＦの値をマップ化しておくことができる。またエンジン冷却水温に対する吸気行程中の吸気ポート及び燃焼室内の雰囲気温度は予め実験等により求めておくことができる。したがって、これらよりエンジン冷却水温に対する燃料平均分子量の値を求めることができる。
【００５３】
また（１）式の通り、「ＴＦＢＹＡ＝１４．７（理論空燃比）／目標空燃比」である。
【００５４】
以上より燃料モル分率ｘ_Ｆと酸素モル分率ｘ_Ｏ２とのあいだには以下の関係がある。
【００５５】
【数５】

したがって反応確率ＲＰＲＯＢＡは以下になる。
【００５６】
【数６】

この（６７）式及び（６６）式から明らかなように、燃料又は酸素のどちらか一方のモル分率がわかれば反応確率を求めることができる。
【００５７】
また、例えば、酸素のモル分率ｘ_Ｏ２は、残留不活性ガス率ＭＲＥＳＦＲ（＝ＭＲＥＳ／｛ＭＲＥＳ＋ＭＡＣＹＬ×（１＋ＴＦＢＹＡ／１４．７）｝）により以下のように表される。
【００５８】
【数７】

したがって反応確率は以下になる。
【００５９】
【数８】

この式から明らかなように、残留不活性ガス率ＭＲＥＳＦＲがわかれば反応確率を求めることができ、また残留不活性ガス率ＭＲＥＳＦＲ＝ｍ_ＥＧＲ／｛ｍ_ＥＧＲ＋ｍ_ＡＩＲ×（１＋ＴＦＢＹＡ／１４．７）｝であるので、残留不活性ガス質量ｍ_ＥＧＲと、吸入空気質量ｍ_ＡＩＲと、空燃比又は当量比とを検出すれば、反応確率を求めることができる。具体的な算出法については後述する。なお、この残留不活性ガス質量ｍ_ＥＧＲを、以下ではラベル「ＭＲＥＳ」として記述する。
【００６０】
なお、冷却水温が一定の状態であれば燃料平均分子量ＭＦを一定にすればよい。また理論空燃比付近で制御する場合であればＴＦＢＹＡ＝１．０（一定値）として制御すればよい。このようにすることで、計算を単純化することができ、より高速に反応確率ＲＰＲＯＢＡを算出することができる。
【００６１】
ステップ１６では、基準クランク角θＰＭＡＸ［ｄｅｇＡＴＤＣ］を算出する。前述のように基準クランク角θＰＭＡＸはあまり変動しないが、それでもエンジン回転速度ＮＲＰＭの上昇に応じて進角する傾向があるため、基準クランク角θＰＭＡＸはエンジン回転速度ＮＲＰＭの関数として次式で表すことができる。
【００６２】
θＰＭＡＸ＝ｆ４（ＮＲＰＭ）…（９）
具体的にはエンジン回転速度ＮＲＰＭから、エンジンコントローラ３１のメモリに予め格納された図７に示す特性のテーブルを検索することにより基準クランク角θＰＭＡＸを求める。算出を容易にするために、基準クランク角θＰＭＡＸを一定とみなすことも可能である。
【００６３】
最後にステップ１７では、点火無駄時間相当クランク角ＩＧＮＤＥＡＤ［ｄｅｇ］を算出する。点火無駄時間相当クランク角ＩＧＮＤＥＡＤは、エンジンコントローラ３１から点火コイル１３の一次電流を遮断する信号を出力したタイミングから点火プラグ１４が実際に点火するまでのクランク角区間で、次式により表すことができる。
【００６４】
ＩＧＮＤＥＡＤ＝ｆ５（ＤＥＡＤＴＩＭＥ、ＮＲＰＭ）…（１０）
ここでは、点火無駄時間ＤＥＡＤＴＩＭＥを２００μｓｅｃとする。（１０）式は、エンジン回転速度ＮＲＰＭから点火無駄時間ＤＥＡＤＴＩＭＥに相当するクランク角である点火無駄時間相当クランク角ＩＧＮＤＥＡＤを算出するためのものである。
【００６５】
図８は初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を算出するためのもの、また図１０は主燃焼期間ＢＵＲＮ２［ｄｅｇ］を算出するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。図８、図１０は図５に続けて実行する。図８、図１０はどちらを先に実行してもよい。
【００６６】
まず図８から説明すると、ステップ１６１では、前回燃焼開始時期ＭＢＴＣＹＣＬ［ｄｅｇＢＴＤＣ］、図５のステップ１２で算出されている燃焼室５の吸気弁閉時期における容積ＶＩＶＣ［ｍ^３］、図５のステップ１３で算出されている燃焼室５の吸気弁閉時期における温度ＴＩＮＩ［Ｋ］、図５のステップ１４で算出されている燃焼室５の吸気弁閉時期における圧力ＰＩＮＩ［Ｐａ］、エンジン回転速度ＮＲＰＭ［ｒｐｍ］、図５のステップ１５で算出されている反応確率ＲＰＲＯＢＡ［％］を読み込む。
【００６７】
ここで、前回燃焼開始時期ＭＢＴＣＹＣＬは、基本点火時期ＭＢＴＣＡＬの［ｄｅｇＢＴＤＣ］の１サイクル前の値であり、その算出については図１１により後述する。
【００６８】
ステップ１６２では燃焼室５の燃焼開始時期における容積Ｖ０［ｍ^３］を算出する。前述したように、ここでの点火時期（燃焼開始時期）は今回のサイクルで演算する基本点火時期ＭＢＴＣＡＬではなく基本点火時期の１サイクル前の値である。すなわち、基本点火時期の１サイクル前の値であるＭＢＴＣＹＣＬから次式により燃焼室５の燃焼開始時期における容積Ｖ０を算出する。
【００６９】
Ｖ０＝ｆ６（ＭＢＴＣＹＣＬ）…（１１）
具体的には前回燃焼開始時期ＭＢＴＣＹＣＬにおけるピストン６のストローク位置と、燃焼室５のボア径から、燃焼室５のＭＢＴＣＹＣＬにおける容積Ｖ０を算出する。図５のステップ１２では、燃焼室５の吸気弁閉時期ＩＶＣにおける容積ＶＩＶＣを、吸気弁閉時期をパラメータとする吸気弁閉時期容積のテーブルを検索することにより求めたが、ここではＭＢＴＣＹＣＬをパラメータとする前回燃焼開始時期容積のテーブルを検索することにより、燃焼室５の前回燃焼開始時期ＭＢＴＣＹＣＬにおける容積Ｖ０を求めればよい。
【００７０】
ステップ１６３では燃焼開始時期における有効圧縮比Ｅｃを算出する。有効圧縮比Ｅｃは無次元の値であり、次式に示すように燃焼室５の燃焼開始時期における容積Ｖ０を燃焼室５の吸気弁閉時期における容積ＶＩＶＣで除した値である。
【００７１】
Ｅｃ＝ｆ７（Ｖ０、ＶＩＶＣ）＝Ｖ０／ＶＩＶＣ…（１２）
ステップ１６４では吸気弁閉時期ＩＶＣから燃焼開始時期に至る間の燃焼室５内の温度上昇率ＴＣＯＭＰを次式に示すように有効圧縮比Ｅｃに基づいて算出する。
【００７２】
ＴＣＯＭＰ＝ｆ８（Ｅｃ）＝Ｅｃ＾（κ−１）…（１３）
ただし、κ：比熱比、
（１３）式は断熱圧縮されるガスの温度上昇率の式である。なお、（１３）式右辺の「＾」は累乗計算を表している。この記号は後述する式でも使用する。
【００７３】
κは断熱圧縮されるガスの定圧比熱を定容比熱で除した値で、断熱圧縮されるガスが空気であればκ＝１．４であり、簡単にはこの値を用いればよい。ただし、混合気に対してκの値を実験的に求めることで、一層の算出精度の向上が可能である。
【００７４】
図９は（１３）式を図示したものである。したがって、このような特性のテーブルを予めエンジンコントローラ３１のメモリに格納しておき、有効圧縮比Ｅｃに基づき当該テーブルを検索することにより温度上昇率ＴＣＯＭＰを求めることも可能である。
【００７５】
ステップ１６５では、燃焼室５の燃焼開始時期における温度Ｔ０［Ｋ］を、燃焼室５の吸気弁閉時期における温度ＴＩＮＩに温度上昇率ＴＣＯＭＰを乗じることで、つまり
Ｔ０＝ＴＩＮＩ×ＴＣＯＭＰ…（１４）
の式により算出する。
【００７６】
ステップ１６６、１６７はステップ１６４、１６５と同様である。すなわち、ステップ１６６では吸気弁閉時期ＩＶＣから燃焼開始時期に至る間の燃焼室５内の圧力上昇率ＰＣＯＭＰを次式に示すように有効圧縮比Ｅｃに基づいて算出する。
【００７７】
ＰＣＯＭＰ＝ｆ９（Ｅｃ）＝Ｅｃ＾κ…（４１）
ただし、κ：比熱比、
（４１）式も（１３）式と同じに断熱圧縮されるガスの圧力上昇率の式である。（４１）式右辺の「＾」も（１３）式と同じに累乗計算を表している。
【００７８】
κは上記（１３）式で用いている値と同じで、断熱圧縮されるガスが空気であればκ＝１．４であり、簡単にはこの値を用いればよい。ただし、混合気に対してその組成、温度からκの値を求めることで、一層の算出精度の向上が可能である。
【００７９】
図９と同様の特性のテーブルを予めエンジンコントローラ３１のメモリに格納しておき、有効圧縮比Ｅｃに基づき当該テーブルを検索することにより圧力上昇率ＰＣＯＭＰを求めることも可能である。
【００８０】
ステップ１６７では、燃焼室５の燃焼開始時期における圧力Ｐ０［Ｐａ］を、燃焼室５の吸気弁閉時期における圧力ＰＩＮＩに圧力上昇率ＰＣＯＭＰを乗じることで、つまり
Ｐ０＝ＰＩＮＩ×ＰＣＯＭＰ…（４２）
の式により算出する。
【００８１】
ステップ１６８では、初期燃焼期間における層流燃焼速度ＳＬ１［ｍ／ｓｅｃ］を次式（公知）により算出する。
【００８２】

ただし、Ｔｓｔｄ ：基準温度［Ｋ］、
Ｐｓｔｄ ：基準圧力［Ｐａ］、
ＳＬｓｔｄ：基準温度Ｔｓｔｄと基準圧力Ｐｓｔｄにおける基準層流燃焼速度［ｍ／ｓｅｃ］、
Ｔ０ ：燃焼室５の燃焼開始時期における温度［Ｋ］、
Ｐ０ ：燃焼室５の燃焼開始時期における圧力［Ｐａ］、
層流燃焼速度（層流火炎速度）は気体の流れがない状態での火炎の伝播速度のことであり、燃焼室５内の圧縮速度、燃焼室５内の吸気流速に因らず、燃焼室５の温度及び圧力の関数となることが知られていることから、初期燃焼期間における層流燃焼速度を燃焼開始時温度Ｔ０と燃焼開始時圧力Ｐ０の関数として、また後述するように主燃焼期における層流燃焼速度を圧縮上死点時温度ＴＴＤＣと圧縮上死点圧力ＰＴＤＣの関数としている。これは、層流燃焼速度は一般的に、エンジン負荷、燃焼室５内の残留不活性ガス率、吸気弁閉時期、比熱比、吸気温度により変化するのであるが、これらは燃焼室５内の温度Ｔと圧力Ｐに影響する因子であるので、層流燃焼速度は最終的に燃焼室５内の温度Ｔと圧力Ｐにより規定できるとするものである。
【００８３】
上記の（１５）式において基準温度Ｔｓｔｄと基準圧力Ｐｓｔｄと基準層流燃焼速度ＳＬｓｔｄは実験により予め定められる値である。
【００８４】
燃焼室５の通常の圧力である２ｂａｒ以上の圧力下では、（１５）式の圧力項（Ｐ０／Ｐｓｔｄ）^{−０．１６}は小さな値となる。したがって、圧力項（Ｐ０／Ｐｓｔｄ）^{−０．１６}を一定値として、基準層流燃焼速度ＳＬｓｔｄを基準温度Ｔｓｔｄのみで規定することも可能である。
【００８５】
したがって、基準温度Ｔｓｔｄが５５０［Ｋ］で、基準層流燃焼速度ＳＬｓｔｄが１．０［ｍ／ｓｅｃ］で、圧力項が０．７である場合の燃焼開始時期における温度Ｔ０と層流燃焼速度ＳＬ１との関係は近似的に次式で定義することができる。
【００８６】

ステップ１６９では、初期燃焼期間におけるガス流動の乱れ強さＳＴ１を算出する。このガス流動の乱れ強さＳＴ１は無次元の値であり、燃焼室５に流入する新気の流速と燃料インジェクタ２１の噴射燃料のペネトレーションとに依存する。
【００８７】
燃焼室５に流入する新気の流速は、吸気通路の形状と、吸気弁１５の作動状態と、吸気弁１５を設ける吸気ポート４の形状に依存する。噴射燃料のペネトレーションは燃料インジェクタ２１の噴射圧力と、燃料噴射期間と、燃焼噴射タイミングに依存する。
【００８８】
最終的に、初期燃焼期間におけるガス流動の乱れ強さＳＴ１は、エンジン回転速度ＮＲＰＭの関数として次式で表すことができる。
【００８９】
ＳＴ１＝ｆ１２（ＮＲＰＭ）＝Ｃ１×ＮＲＰＭ…（１７）
ただし、Ｃ１：定数、
乱れ強さＳＴ１を回転速度ＮＲＰＭをパラメータとするテーブルから求めることも可能である。
【００９０】
ステップ１７０では層流燃焼速度Ｓ１と乱れ強さＳＴ１から、初期燃焼期間におけるガスの燃焼速度ＦＬＡＭＥ１［ｍ／ｓｅｃ］を次式により算出する。
【００９１】
ＦＬＡＭＥ１＝ＳＬ１×ＳＴ１…（１８）
燃焼室５内にガス乱れがあるとガスの燃焼速度が変化する。（１８）式はこのガス乱れに伴う燃焼速度への寄与（影響）を考慮したものである。
【００９２】
ステップ１７１では、次式により初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を算出する。
【００９３】

ただし、ＡＦ１：火炎核の反応面積（固定値）［ｍ^２］、
この（１９）式および後述する（２２）式は、燃焼ガス質量を燃焼速度で割ると燃焼期間が得られるとする次の基本式より導いたものであるが、（１９）、（２２）式右辺の分子、分母ががただちに燃焼ガス質量、燃焼速度を表すものではない。
【００９４】

（補１）式右辺分母の未燃ガス密度は、未燃ガス質量［ｇ］を未燃ガス体積［ｍ^３］で割った値であるので、従来装置のように質量に相当する充填効率ＩＴＡＣのみの関数では未燃ガス密度を正確に計算できているとはいえない。そこで、（補１）式に対して実験結果とを照らし合わせつつ所定の近似を導入して初めて得られたのが上記（１９）式及び後述する（２２）式に示す実験式である。
【００９５】
ここで、（１９）式右辺のＢＲ１は燃焼開始時期より初期燃焼期間ＢＵＲＮ１の終了時期までの燃焼質量割合の変化代であり、ここではＢＲ１＝２％に設定している。（１９）式右辺の（ＮＲＰＭ×６）は単位をｒｐｍからクランク角（ｄｅｇ）に変換するための処理である。火炎核の反応面積ＡＦ１は実験的に設定される。
【００９６】
また、初期燃焼期間中はほぼ燃焼室容積は変わらないとみなすことができる。したがって、初期燃焼期間ＢＵＲＮ１を算出するに際して最初の燃焼室容積である燃焼開始時の燃焼室容積Ｖ０を採用している。
【００９７】
次に図１０のフローに移ると、ステップ１８１では図８のステップ１６１と同様に、図５のステップ１２で算出されている燃焼室５の吸気弁閉時期における容積ＶＩＶＣ［ｍ^３］、図５のステップ１３で算出されている燃焼室５の吸気弁閉時期における温度ＴＩＮＩ［Ｋ］、図５のステップ１４で算出されている燃焼室５の吸気弁閉時期における圧力ＰＩＮＩ［Ｐａ］、エンジン回転速度ＮＲＰＭ［ｒｐｍ］、図５のステップ１５で算出されている反応確率ＲＰＲＯＢＡ［％］を読み込み、さらにシリンダ新気量ＭＡＣＹＬ［ｇ］、目標当量比ＴＦＢＹＡ、内部不活性ガス量ＭＲＥＳ［ｇ］、外部不活性ガス量ＭＥＧＲ［ｇ］を読み込む。
【００９８】
ここで、図１には外部ＥＧＲ装置は示していないが、図１０に関する限り外部ＥＧＲ装置を備えているエンジンを前提として説明する。この場合に、外部不活性ガス量ＭＥＧＲは例えば公知の手法（特開平１０−１４１１５０号公報参照）を用いて算出すればよい。なお、図１に示す本実施形態のように外部ＥＧＲ装置を備えていないエンジンを対象とするときには外部不活性ガス量ＭＥＧＲ＝０で扱えば足りる。シリンダ新気量ＭＡＣＹＬ、内部不活性ガス量ＭＲＥＳの算出については図１２以降で後述する。
【００９９】
ステップ１８２、１８３は図８のステップ１６３、１６４と同様である。すなわち、ステップ１８２で圧縮上死点時期における有効圧縮比Ｅｃ ２を算出する。有効圧縮比Ｅｃ ２も上記（１２）式の有効圧縮比Ｅｃと同様に無次元の値であり、次式に示すように燃焼室５の圧縮上死点時における容積ＶＴＤＣを燃焼室５の吸気弁閉時期における容積ＶＩＶＣで除した値である。
【０１００】
Ｅｃ ２＝ｆ１３（ＶＴＤＣ、ＶＩＶＣ）＝ＶＴＤＣ／ＶＩＶＣ…（４３）（４３）式において燃焼室５の圧縮上死点時における容積ＶＴＤＣは運転条件によらず一定であり、予めエンジンコントローラ３１のメモリに格納しておけばよい。
【０１０１】
ステップ１８３では吸気弁閉時期ＩＶＣから圧縮上死点に至る間の燃焼室５内の断熱圧縮による温度上昇率ＴＣＯＭＰ ２を次式に示すように有効圧縮比Ｅｃ ２に基づいて算出する。
【０１０２】

ただし、κ：比熱比、
図９と同様の特性のテーブルを予めエンジンコントローラ３１のメモリに格納しておき、有効圧縮比Ｅｃ ２から当該テーブルを検索することにより温度上昇率ＴＣＯＭＰ ２を求めることも可能である。
【０１０３】
ステップ１８４ではシリンダ新気量ＭＡＣＹＬ、目標当量比ＴＦＢＹＡ、内部不活性ガス量ＭＲＥＳ、外部不活性ガス量ＭＥＧＲから次式により燃焼室５の総ガス質量ＭＧＡＳ［ｇ］を算出する。
【０１０４】

（４５）式右辺の括弧内の「１」は新気分、「ＴＦＢＹＡ／１４．７」は燃料分である。
【０１０５】
ステップ１８５ではこの燃焼室５の総ガス質量ＭＧＡＳと、シリンダ新気量ＭＡＣＹＬ、目標当量比ＴＦＢＹＡを用い、次式により混合気の燃焼による温度上昇量（燃焼上昇温度）ＴＢＵＲＮ［Ｋ］を算出する。
【０１０６】

ただし、Ｑ：燃料の定発熱量、
ＢＲｋ：シリンダ内燃料の燃焼質量割合、
Ｃｖ：定積比熱、
（４６）式右辺の分子はシリンダ内燃料による発生総熱量［Ｊ］、分母は単位発生熱量当たりの温度上昇率［Ｊ／Ｋ］を意味している。すなわち、（４６）式は熱力学の公式に当てはめた近似式である。
【０１０７】
ここで、シリンダ内燃料の燃焼質量割合ＢＲｋとしては予め実験等で適合しておく。簡易的には例えば６０％／２＝３０％を設定する。これは、本実施形態では燃焼質量割合ＢＲが約６０％に達するまでを燃焼期間として扱うので、そのちょうど中間の３０％をＢＲｋとして設定するものである。
【０１０８】
燃料の定発熱量Ｑは燃料の種類により異なる値であるので、燃料の種類に応じ予め実験等で求めておく。定積比熱Ｃｖは２〜３の値であり予め実験等で代表値を適合しておく。ただし、混合気に対してその組成、温度から定積比熱Ｃｖの値を求めることで、一層の算出精度の向上が可能である。
【０１０９】
ステップ１８６では、燃焼室５の圧縮上死点における温度ＴＴＤＣ［Ｋ］を、燃焼室５の吸気弁閉時期における温度ＴＩＮＩに圧縮上死点までの温度上昇率ＴＣＯＭＰ ２を乗じその乗算値に上記の燃焼上昇温度ＴＢＵＲＮを加算することで、つまり次式により算出する。
【０１１０】
ＴＴＤＣ＝ＴＩＮＩ×ＴＣＯＭＰ ２＋ＴＢＵＲＮ…（４７）
ステップ１８７では、この燃焼室５の圧縮上死点における温度ＴＴＤＣと容積ＶＴＤＣ及び燃焼室５の吸気弁閉時期における圧力ＰＩＮＩ、容積ＶＩＶＣ及び温度ＴＩＮＩから次式により燃焼室５の圧縮上死点における圧力ＰＴＤＣ［Ｋ］を算出する。
【０１１１】
ＰＴＤＣ＝ＰＩＮＩ×ＶＩＶＣ×ＴＴＤＣ／（ＶＴＤＣ×ＴＩＮＩ）…（４８）
（４８）式は状態方程式を用いて得たものである。すなわち、吸気弁閉時期における圧力、容積及び温度（ＰＩＮＩ、ＶＩＶＣ、ＴＩＮＩ）を用いて次の状態方程式が成立する。
【０１１２】
ＰＩＮＩ×ＶＩＶＣ＝ｎ・Ｒ・ＴＩＮＩ…（補２）

圧縮上死点近傍では容積はほぼ等しいので、圧縮上死点での圧力、容積及び温度（ＰＴＤＣ、ＶＴＤＣ、ＴＴＤＣ）を用いて次の状態方程式が成立する。
【０１１３】
ＰＴＤＣ×ＶＴＤＣ＝ｎ・Ｒ・ＴＴＤＣ…（補３）
この（補３）式と上記（補２）との両式からｎ・Ｒを消去しＰＴＤＣについて解くと、上記（４８）式が得られる。
【０１１４】
ステップ１８８では図８のステップ１６８と同様にして、次式（公知）により、主燃焼期間における層流燃焼速度ＳＬ２［ｍ／ｓｅｃ］を算出する。
【０１１５】

ただし、Ｔｓｔｄ ：基準温度［Ｋ］、
Ｐｓｔｄ ：基準圧力［Ｐａ］、
ＳＬｓｔｄ：基準温度Ｔｓｔｄと基準圧力Ｐｓｔｄにおける基準層流燃焼速度［ｍ／ｓｅｃ］、
ＴＴＤＣ：燃焼室５の圧縮上死点における温度［Ｋ］、
ＰＴＤＣ：燃焼室５の圧縮上死点における圧力［Ｐａ］、
（４９）式の解説は上記（１６）式と同様ある。すなわち、（４９）式の基準温度Ｔｓｔｄと基準圧力Ｐｓｔｄと基準層流燃焼速度ＳＬｓｔｄは実験により予め定められる値である。燃焼室５の通常の圧力である２ｂａｒ以上の圧力下では、（４９）式の圧力項（ＰＴＤＣ／Ｐｓｔｄ）^{−０．１６}は小さな値となる。したがって、圧力項（ＰＴＤＣ／Ｐｓｔｄ）^{−０．１６}を一定値として、基準層流燃焼速度ＳＬｓｔｄを基準温度Ｔｓｔｄのみで規定することも可能である。よって、基準温度Ｔｓｔｄが５５０［Ｋ］で、基準層流燃焼速度ＳＬｓｔｄが１．０［ｍ／ｓｅｃ］で、圧力項が０．７である場合の圧縮上死点における温度ＴＴＤＣと層流燃焼速度ＳＬ２との関係は近似的に次式で定義することができる。
【０１１６】

ステップ１８９期間では主燃焼期間におけるガス流動の乱れ強さＳＴ２を算出する。このガス流動の乱れ強さＳＴ２も初期燃焼期間におけるガス流動の乱れ強さＳＴ１と同様に、エンジン回転速度ＮＲＰＭの関数として次式で表すことができる。
【０１１７】
ＳＴ２＝ｆ１７（ＮＲＰＭ）＝Ｃ２×ＮＲＰＭ…（２０）
ただし、Ｃ２：定数、
乱れ強さＳＴ２を回転速度をパラメータとするテーブルから求めることも可能である。
【０１１８】
ステップ１９０では、層流燃焼速度ＳＬ２［ｍ／ｓｅｃ］と主燃焼期間におけるガス流動の乱れ強さＳＴ２とから、主燃焼期間における燃焼速度ＦＬＡＭＥ２［ｍ／ｓｅｃ］を次式により算出する。
【０１１９】
ＦＬＡＭＥ２＝ＳＬ２×ＳＴ２…（２１）
ただし、ＳＬ２：層流燃焼速度［ｍ／ｓｅｃ］、
（２１）式は（１８）式と同様、ガス乱れに伴う燃焼速度への寄与を考慮したものである。
【０１２０】
ステップ１９１では、主燃焼期間ＢＵＲＮ２［ｄｅｇ］を（１９）式に類似した次式で算出する。
【０１２１】

ただし、ＡＦ２：火炎核の反応面積［ｍ^２］
ここで、（２２）式右辺のＢＲ２は主燃焼期間の開始時期より終了時期までの燃焼質量割合の変化代である。初期燃焼期間の終了時期に燃焼質量割合ＢＲが２％になり、その後、主燃焼期間が開始し、燃焼質量割合ＢＲが６０％に達して主燃焼期間が終了すると考えているので、ＢＲ２＝６０％−２％＝５８％を設定している。ＡＦ２は火炎核の成長行程における平均の反応面積であり、（１９）式のＡＦ１と同様に、予め実験的に定めた固定値とする。
【０１２２】
主燃焼期間では圧縮上死点を挟んで燃焼室容積が変化する。つまり、主燃焼期間の開始時期と、主燃焼期間の終了時期のほぼ中央に圧縮上死点位置が存在するとみなすことができる。また、圧縮上死点付近ではクランク角が変化しても燃焼室容積があまり変化しない。そこで主燃焼期間での燃焼室容積としてはこの圧縮上死点での燃焼室容積ＶＴＤＣで代表させることとしている。
【０１２３】
図１１は基本点火時期ＭＢＴＣＡＬ［ｄｅｇＢＴＤＣ］を算出するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。図８、図１０のうち遅く実行されるフローに続けて実行する。
【０１２４】
ステップ４１では、図８のステップ１７１で算出されている初期燃焼期間ＢＵＲＮ１、図１０のステップ１９１で算出されている主燃焼期間ＢＵＲＮ２、図５のステップ１６で算出されている点火時期無駄時間相当クランク角ＩＧＮＤＥＡＤ、図５のステップ１７で算出されている基準クランク角θＰＭＡＸを読み込む。
【０１２５】
ステップ４２では、初期燃焼期間ＢＵＲＮ１と主燃焼期間ＢＵＲＮ２の合計を燃焼期間ＢＵＲＮ［ｄｅｇ］として算出する。
【０１２６】
ステップ４３では次式により基本点火時期ＭＢＴＣＡＬ［ｄｅｇＢＴＤＣ］を算出する。
【０１２７】
ＭＢＴＣＡＬ＝ＢＵＲＮ−θＰＭＡＸ＋ＩＧＮＤＥＡＤ…（２３）
ステップ４４では、この基本点火時期ＭＢＴＣＡＬから点火無駄時間相当クランク角ＩＧＮＤＥＡＤを差し引いた値を前回燃焼開始時期ＭＢＴＣＹＣＬ［ｄｅｇＢＴＤＣ］として算出する。
【０１２８】
このようにして算出した基本点火時期ＭＢＴＣＡＬは、点火時期指令値として点火レジスタに移され、実際のクランク角がこの点火時期指令値と一致したタイミングでエンジンコントローラ３１より一次電流を遮断する点火信号が点火コイル１３に出力される。
【０１２９】
また、今サイクルの点火時期指令値としてステップ４３で算出された基本点火時期ＭＢＴＣＡＬが用いられたとすると、次サイクルの点火時期になるまでの間、ステップ４４で算出された前回燃焼開始時期ＭＢＴＣＹＣＬが図８のステップ１６２において用いられる。
【０１３０】
次に、図１２は燃焼室５内の残留不活性ガス率ＭＲＥＳＦＲを算出するためのもので、一定時間毎（例えば１０ｍｓｅｃ毎）に実行する。このフローは上記図５のフローに先立って実行する。
【０１３１】
ステップ５１ではエアフローメータ３２の出力と目標当量比ＴＦＢＹＡを読み込む。ステップ５２ではエアフロメータ３２の出力に基づいて、燃焼室５に流入する新気量（シリンダ新気量）ＭＡＣＹＬを算出する。このシリンダ新気量ＭＡＣＹＬの算出方法については公知の方法を用いればよい（特開２００１−５００９１号公報参照）。
【０１３２】
ステップ５３では、燃焼室５内の内部不活性ガス量ＭＲＥＳを算出する。この内部不活性ガス量ＭＲＥＳの算出については、図１３のフローにより説明する。
【０１３３】
図１３（図１２ステップ５３のサブルーチン）においてステップ６１では、燃焼室５内の排気弁閉時期ＥＶＣにおける不活性ガス量ＭＲＥＳＣＹＬを算出する。この不活性ガス量ＭＲＥＳＣＹＬの算出についてはさらに図１４のフローにより説明する。
【０１３４】
図１４（図１３ステップ６１のサブルーチン）においてステップ７１では、排気弁閉時期ＥＶＣ［ｄｅｇＢＴＤＣ］、温度センサ４５により検出される排気温度ＴＥＸＨ［Ｋ］、圧力センサ４６により検出される排気圧力ＰＥＸＨ［ｋＰａ］を読み込む。
【０１３５】
ここで、吸気弁閉時期ＩＶＣが吸気ＶＴＣ機構２７に与える指令値から既知であったように、排気弁閉時期ＥＶＣも排気ＶＴＣ機構２８に与える指令値から既知である。
【０１３６】
ステップ７２では燃焼室５の排気弁閉時期ＥＶＣにおける容積ＶＥＶＣを算出する。これは吸気弁閉時期ＩＶＣにおける容積ＶＩＶＣと同様に、排気弁閉時期をパラメータとするテーブルを検索することにより求めればよい。すなわち、排気弁ＶＴＣ機構２８を備える場合には、排気弁閉時期ＥＶＣから図２１に示すテーブルを検索することにより、燃焼室５の排気弁閉時期ＥＶＣにおける容積ＶＥＶＣを求めればよい。排気ＶＴＣ機構２８を備えないときには定数で与えることができる。
【０１３７】
また、図示しないが圧縮比を変化させる機構を有する場合には、圧縮比の変化量に応じた排気弁閉時期における燃焼室容積ＶＥＶＣをテーブルから求める。排気ＶＴＣ機構２８に加えて圧縮比を変化させる機構をも有する場合には、排気弁閉時期と圧縮比変化量とに応じたマップを検索することにより排気弁閉時期における燃焼室容積を求める。
【０１３８】
ステップ７３では、目標当量比ＴＦＢＹＡから図２２に示すテーブルを検索することにより、燃焼室５内の不活性ガスのガス定数ＲＥＸを求める。図２２に示すように、不活性ガスのガス定数ＲＥＸは目標当量比ＴＦＢＹＡが１．０のとき、つまり理論空燃比のとき最も小さく、これより大きくても小さくても大きくなる。
【０１３９】
ステップ７４では、排気温度ＴＥＸＨに基づいて燃焼室５の排気弁閉時期ＥＶＣにおける温度ＴＥＶＣを推定する。簡単には排気温度ＴＥＸＨをそのままＴＥＶＣとおけばよい。なお、燃焼室５の排気弁閉時期における温度ＴＥＶＣは、インジェクタ２１の燃料噴射量に応じた熱量により変化するため、このような特性をも加味すれば、ＴＥＶＣの算出精度が向上する。
【０１４０】
ステップ７５では、排気圧力ＰＥＸＨに基づいて燃焼室５の排気弁閉時期ＥＶＣにおける圧力ＰＥＶＣを算出する。簡単には排気圧力ＰＥＸＨをＰＥＶＣと置けばよい。
【０１４１】
ステップ７６では、燃焼室５の排気弁閉時期ＥＶＣにおける容積ＶＥＶＣ、排気弁閉時期ＥＶＣにおける温度ＴＥＶＣ、排気弁閉時期ＥＶＣにおける圧力ＰＥＶＣ及び不活性ガスのガス定数ＲＥＸから、燃焼室５の排気弁閉時期ＥＶＣにおける不活性ガス量ＭＲＥＳＣＹＬを次式により算出する。
【０１４２】
ＭＲＥＳＣＹＬ＝（ＰＥＶＣ×ＶＥＶＣ）／（ＲＥＸ×ＴＥＶＣ）…（２４）
このようにして燃焼室５の排気弁閉時期ＥＶＣにおける不活性ガス量ＭＲＥＳＣＹＬの算出を終了したら図１３に戻り、ステップ６２で吸排気弁１５、１６のオーバーラップ（図では「Ｏ／Ｌ」と略記する）中に排気側から吸気側へ吹き返す不活性ガス量であるオーバーラップ中吹き返し不活性ガス量ＭＲＥＳＯＬを算出する。
【０１４３】
この不活性ガス量ＭＲＥＳＯＬの算出については図１５のフローにより説明する。
【０１４４】
図１５（図１３ステップ６２のサブルーチン）においてステップ８１では、吸気弁開時期ＩＶＯ［ｄｅｇＢＴＤＣ］と、排気弁閉時期ＥＶＣ［ｄｅｇＢＴＤＣ］、図１４のステップ７４で算出されている燃焼室５の排気弁閉時期ＥＶＣにおける温度ＴＥＶＣを読み込む。
【０１４５】
ここで、吸気弁開時期ＩＶＯは、吸気弁閉時期ＩＶＣより吸気弁１５の開き角だけ前の時期となるので、吸気弁閉時期ＩＶＣより吸気弁１５の開き角（予め分かっている）とから求めることができる。
【０１４６】
ステップ８２では吸気弁開時期ＩＶＯと排気弁閉時期ＥＶＣとから、吸排気弁のオーバーラップ量ＶＴＣＯＬ［ｄｅｇ］を次式により算出する。
【０１４７】
ＶＴＣＯＬ＝ＩＶＯ＋ＥＶＣ…（２５）
例えば、吸気ＶＴＣ機構２７用アクチュエータへの非通電時に吸気弁開時期ＩＶＯが吸気上死点位置にあり、吸気ＶＴＣ機構２７用アクチュエータへの通電時に吸気弁開時期が吸気上死点より進角する特性であり、かつ排気ＶＴＣ機構２８用アクチュエータへの非通電時に排気弁閉時期ＥＶＣが排気上死点にあり、排気弁ＶＴＣ機構２８用アクチュエータへの通電時に排気弁閉時期ＥＶＣが排気上死点より進角する特性である場合には、ＩＶＯとＥＶＣの合計が吸排気弁のオーバーラップ量ＶＴＣＯＬとなる。
【０１４８】
ステップ８３では、吸排気弁のオーバーラップ量ＶＴＣＯＬから、図２３に示すテーブルを検索することによりオーバーラップ中の積算有効面積ＡＳＵＭＯＬを算出する。図２３に示すようにオーバーラップ中の積算有効面積ＡＳＵＭＯＬは吸排気弁のオーバーラップ量ＶＴＣＯＬが大きくなるほど大きくなる値である。
【０１４９】
ここで、図２４は、吸排気弁のオーバーラップ中の積算有効面積ＡＳＵＭＯＬの説明図であり、横軸はクランク角、縦軸は吸気弁１２と排気弁１５とのそれぞれの開口面積を示している。オーバーラップ中の任意の時点における有効開口面積は、排気弁開口面積と吸気弁開口面積とのうち小さい方とする。オーバーラップ中の全期間における積算有効面積ＡＳＵＭＯＬは、吸気弁１５及び排気弁１６が開いている期間の積分値（図中の斜線部）である。
【０１５０】
このようにオーバーラップ中積算有効面積ＡＳＵＭＯＬを算出することで、吸気弁１５と排気弁１６とのオーバーラップ量を１つのオリフィス（流出孔）であると近似することができ、排気系の状態と吸気系の状態とからこの仮想オリフィスを通過するガス流量を簡略的に算出し得る。
【０１５１】
ステップ８４では、目標当量比ＴＦＢＹＡと、燃焼室５の排気弁閉時期ＥＶＣにおける温度ＴＥＶＣとから、図２５に示すマップを検索することにより、燃焼室５に残留する不活性ガスの比熱比ＳＨＥＡＴＲを算出する。図２５に示したように、燃焼室に残留する不活性ガスの比熱比ＳＨＥＡＴＲは目標当量比ＴＦＢＹＡが１．０の近傍にあるときが最も小さくなり、それより大きくても小さくても大きくなる。また、目標当量比ＴＦＢＹＡが一定の条件では、燃焼室５の排気弁閉時期ＥＶＣにおける温度ＴＥＶＣが高くなるほど小さくなる。
【０１５２】
ステップ８５では過給判定フラグＴＢＣＲＧ及びチョーク判定フラグＣＨＯＫＥを設定する。この過給判定フラグＴＢＣＲＧ及びチョーク判定フラグＣＨＯＫＥの設定については図１６のフローにより説明する。
【０１５３】
図１６（図１５ステップ８５のサブルーチン）においてステップ１０１では、吸気圧力センサ４４により検出される吸気圧力ＰＩＮと、図１４のステップ７５で算出されている燃焼室５の排気弁閉時期ＥＶＣにおける圧力ＰＥＶＣを読み込む。
【０１５４】
ステップ１０２では、吸気圧力ＰＩＮと、燃焼室５の排気弁閉時期ＥＶＣにおける圧力ＰＥＶＣとから、次式により吸気排気圧力比ＰＩＮＢＹＥＸを算出する。
【０１５５】
ＰＩＮＢＹＥＸ＝ＰＩＮ／ＰＥＶＣ…（２６）
この吸気排気圧力比ＰＩＮＢＹＥＸは無名数であり、これと１をステップ１０３で比較する。吸気排気圧力比ＰＩＮＢＹＥＸが１以下の場合には過給無しと判断し、ステップ１０４に進んで過給判定フラグＴＢＣＲＧ（ゼロに初期設定）＝０とする。
【０１５６】
吸気排気圧力比ＰＩＮＢＹＥＸが１より大きい場合には過給有りと判断し、ステップ１０５へ進んで過給判定フラグＴＢＣＲＧ＝１とする。
【０１５７】
ステップ１０６では、図１２のステップ５１で読み込まれている目標当量比ＴＦＢＹＡから図２６に示すテーブルを検索することにより、混合気の比熱比ＭＩＸＡＩＲＳＨＲを求め、これをステップ１０７で不活性ガスの比熱比ＳＨＥＡＴＲと入れ換える。図２６に示したように、混合気の比熱比ＭＩＸＡＩＲＳＨＲは、目標当量比ＴＦＢＹＡが小さくなるほど大きくなる値である。
【０１５８】
ステップ１０６、１０７において、不活性ガスの比熱比ＳＨＥＡＴＲを混合気の比熱比ＭＩＸＡＩＲＳＨＲに置き換えるのは、ターボ過給や慣性過給等の過給時を考慮したものである。すなわち、過給時には吸排気弁のオーバーラップ中のガス流れが吸気系から排気系へ向かう（吹き抜ける）ので、この場合においては、上記の仮想オリフィスを通過するガスの比熱比を不活性ガスの比熱比から混合気の比熱比に変更することで、吹き抜けるガス量を精度良く推定し、内部不活性ガス量を精度良く算出するためである。
【０１５９】
ステップ１０８では、図１５のステップ８４または図１６のステップ１０６、１０７で算出している不活性ガスの比熱比ＳＨＥＡＴＲに基づき、最小と最大とのチョーク判定しきい値ＳＬＣＨＯＫＥＬ、ＳＬＣＨＯＫＥＨを次式により算出する。
【０１６０】

これらのチョーク判定しきい値ＳＬＣＨＯＫＥＬ、ＳＬＣＨＯＫＥＨは、チョークする限界値を算出している。
【０１６１】
ステップ１０８において、（２７ａ）右辺、（２７ｂ）右辺の各累乗計算が困難な場合には、（２７ａ）、（２７ｂ）式の算出結果を、最小チョーク判定しきい値ＳＬＣＨＯＫＥＬのテーブルと最大チョーク判定しきい値ＳＬＣＨＯＫＥＨのテーブルとしてそれぞれエンジンコントローラ３１のメモリに予め記憶しておき、不活性ガスの比熱比ＳＨＥＡＴＲから当該テーブルを検索することにより求めてもよい。
【０１６２】
ステップ１０９、ステップ１１０では、吸気排気圧力比ＰＩＮＢＹＥＸが、最小チョーク判定しきい値ＳＬＣＨＯＫＥＬ以上でかつ最大チョーク判定しきい値ＳＬＣＨＯＫＥＨ以下の範囲内にあるか否か、すなわちチョーク状態にないか否かを判定する。吸気排気圧力比ＰＩＮＢＹＥＸが範囲内にある場合にはチョーク無しと判断し、ステップ１１１に進んでチョーク判定フラグＣＨＯＫＥ（ゼロに初期設定）＝０とする。
【０１６３】
吸気排気圧力比Ｐ１ＮＢＹＥＸが範囲内にない場合にはチョーク有りと判断し、ステップ１１２に進んでチョーク判定フラグＣＨＯＫＥ＝１とする。
【０１６４】
このようにして過給判定フラグとチョーク判定フラグの設定を終了したら図１５に戻り、ステップ８６〜８８で次の４つの場合分けを行う。
【０１６５】
〈１〉過給判定フラグＴＢＣＲＧ＝０かつチョーク判定フラグＣＨＯＫＥ＝０のとき
〈２〉過給判定フラグＴＢＣＲＧ＝０かつチョーク判定フラグＣＨＯＫＥ＝０のとき
〈３〉過給判定フラグＴＢＣＲＧ＝０かつチョーク判定フラグＣＨＯＫＥ＝１のとき
〈４〉過給判定フラグＴＢＣＲＧ＝１かつチョーク判定フラグＣＨＯＫＥ＝０のとき
そして、上記〈１〉のときにはステップ８９に進んで、過給無しかつチョーク無し時のオーバーラップ中の平均吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ１を、上記〈２〉のときにはステップ９０に進んで過給無しかつチョーク有り時のオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ２を、上記〈３〉のときにはステップ９１に進んで過給有りかつチョーク無し時のオーバーラップ中の平均吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ３を、上記〈４〉のときにはステップ９２に進んで過給有りかつチョーク有り時の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ４をそれぞれ算出し、算出結果をオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐに移す。
【０１６６】
ここで、過給無しかつチョーク無し時のオーバーラップ中吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ１の算出について図１７のフローにより説明する
図１７（図１５ステップ８９のサブルーチン）においてステップ１２１では、図１４のステップ７３、７５で算出されている不活性ガスのガス定数ＲＥＸ、燃焼室５の排気弁閉時期における圧力ＰＥＶＣを読み込む。
【０１６７】
ステップ１２２では、不活性ガスのガス定数ＲＥＸと、図１５のステップ８１で読み込まれている燃焼室５の排気弁閉時期における温度ＴＥＶＣとに基づき、後述するガス流量の算出式に用いる密度項ＭＲＳＯＬＤを次式により算出する。
【０１６８】
ＭＲＳＯＬＤ＝ＳＱＲＴ｛１／（ＲＥＸ×ＴＥＶＣ）｝…（２８）
ここで、（２８）式右辺の「ＳＱＲＴ」はすぐ右のカッコ内の値の平方根を計算させる関数である。
【０１６９】
なお、密度項ＭＲＳＯＬＤの平方根計算が困難な場合は、（２８）式の算出結果をマップとしてエンジンコントローラ３１のメモリに予め記憶しておき、ガス定数ＲＥＸと燃焼室５の排気弁閉時期における温度ＴＥＶＣとからそのマップを検索することにより求めてもよい。
【０１７０】
ステップ１２３では、図１５のステップ８４で算出されている不活性ガスの比熱比ＳＨＥＡＴＲと、図１６のステップ１０２で算出されている吸気排気圧力比ＰＩＮＢＹＥＸとに基づき、後述するガス流量の算出式に用いる圧力差項ＭＲＳＯＬＰを次式により算出する。
【０１７１】

ステップ１２４では、これら密度項ＭＲＳＯＬＤ、圧力差項ＭＲＳＯＬＰと、燃焼室５の排気弁閉時期における圧力ＰＥＶＣとから、過給無しかつチョーク無し時のオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ１を次式（ガス流量の算出式）により算出し、その算出値をステップ１２５でオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐに移す。
【０１７２】
ＭＲＥＳＯＬｔｍｐ１＝１．４×ＰＥＶＣ×ＭＲＳＯＬＤ×ＭＲＳＯＬＰ…（３０）
次に、過給無しかつチョーク有り時の吹き返し不活性ガス流量の算出について図１８のフローにより説明する
図１８（図１５ステップ９０のサブルーチン）においてステップ１３１、１３２では、図１７のステップ１２１、１２２と同様にして、不活性ガスのガス定数ＲＥＸ、燃焼室５の排気弁閉時期における圧力ＰＥＶＣを読み込み、これらから前述の（２８）式により密度項ＭＲＳＯＬＤを算出する。
【０１７３】
ステップ１３３では、図１５のステップ８４で算出されている不活性ガスの比熱比ＳＨＥＡＴＲに基づき、チョーク時圧力差項ＭＲＳＯＬＰＣを次式により算出する。
【０１７４】

なお、（３１）式の累乗計算と平方根計算とが困難な場合には、（３１）式の算出結果を、チョーク時圧力差項ＭＲＳＯＬＰＣのテーブルとしてエンジンコントローラ３１のメモリに予めに記憶しておき、不活性ガスの比熱比ＳＨＥＡＴＲからそのテーブルを検索することにより求めてもよい。
【０１７５】
ステップ１３４では、これら密度項ＭＲＳＯＬＤ、チョーク時圧力差項ＭＲＳＯＬＰＣと、燃焼室５の排気弁閉時期における圧力ＰＥＶＣとから、過給無しかつチョーク有り時のオーバーラップ中吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ２を次式により算出し、その算出値をステップ１３５でオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐに移す。
【０１７６】
ＭＲＥＳＯＬｔｍｐ２＝ＰＥＶＣ×ＭＲＳＯＬＤ×ＭＲＳＯＬＰＣ…（３２）
次に、過給有りかつチョーク無し時の吹き返しガス流量の算出について図１９のフローにより説明する
図１９（図１５ステップ９１のサブルーチン）においてステップ１４１では、吸気圧力センサ４４により検出される吸気圧力ＰＩＮを読み込む。
【０１７７】
ステップ１４２では、図１６のステップ１０６、１０７で算出されている不活性ガスの比熱比ＳＨＥＡＴＲと、図１６のステップ１０２で算出されている吸気排気圧力比ＰＩＮＢＹＥＸとから、過給時圧力差項ＭＲＳＯＬＰＴを次式により算出する。
【０１７８】

なお、（３３）式の累乗計算と平方根計算とが困難な場合は、（３３）式の算出結果を、過給時圧力差項ＭＲＳＯＬＰＴのマップとしてエンジンコントローラ３１のメモリに予め記憶しておき、不活性ガスの比熱比ＳＨＥＡＴＲと吸気排気圧力比ＰＩＮＢＹＥＸとからそのマップを検索することにより求めてもよい。
【０１７９】
ステップ１４３では、この過給時圧力差項ＭＲＳＯＬＰＴと吸気圧力ＰＩＮとに基づいて、過給有りかつチョーク無し時のオーバーラップ中吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ３を次式により算出し、その算出値をステップ１４４でオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐに移す。
【０１８０】
ＭＲＥＳＯＬｔｍｐ３＝−０．１５２×ＰＩＮ×ＭＲＳＯＬＰＴ…（３４）
ここで、（３４）式の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ３は負の値とすることで、オーバーラップ中に吸気系から排気系へ吹き抜ける混合気のガス流量を表すことができる。
【０１８１】
次に、過給有りかつチョーク有り時のオーバーラップ中吹き返し不活性ガス流量の算出について図２０のフローにより説明する
図２０（図１５ステップ９２のサブルーチン）においてステップ１５１、１５２では、図１９のステップ１４１と同じく吸気圧力センサ４４により検出される吸気圧力ＰＩＮを読み込むと共に、図１８のステップ１３２と同じくチョーク時圧力差項ＭＲＳＯＬＰＣを前述の（３１）式により算出する。
【０１８２】
ステップ１５３では、このチョーク時圧力差項ＭＲＳＯＬＰＣと吸気圧力ＰＩＮとに基づいて、過給有りかつチョーク有り時のオーバーラップ中吹き返しガス流量ＭＲＥＳＯＬｔｍｐ４を次式により算出し、その算出値をステップ１５４でオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐに移す。
【０１８３】
ＭＲＥＳＯＬｔｍｐ４＝−０．１０８×ＰＩＮ×ＭＲＳＯＬＰＣ…（３５）
ここで、（３５）式の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐ４も、ＭＲＥＳＯＬｔｍｐ３と同様、負の値とすることで、オーバーラップ中に吸気側から排気側へ吹き抜ける混合気のガス流量を表すことができる。
【０１８４】
このようにして、過給の有無とチョークの有無との組み合わせにより場合分けした、オーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐの算出を終了したら図１５に戻り、ステップ９３においてこのオーバーラップ中の吹き返し不活性ガス流量ＭＲＥＳＯＬｔｍｐとオーバーラップ期間中の積算有効面積ＡＳＵＭＯＬとから、次式によりオーバーラップ中の吹き返し不活性ガス量ＭＲＥＳＯＬを算出する。
【０１８５】

このようにしてオーバーラップ中の吹き返し不活性ガス量ＭＲＥＳＯＬの算出を終了したら図１３に戻り、ステップ６３において燃焼室５内の排気弁閉時期ＥＶＣにおける不活性ガス量ＭＲＥＳＣＹＬと、このオーバーラップ中吹き返しガス量ＭＲＥＳＯＬとを加算して、つまり次式により内部不活性ガス量ＭＲＥＳを算出する。
【０１８６】
ＭＲＥＳ＝ＭＲＥＳＣＹＬ＋ＭＲＥＳＯＬ…（３７）
前述のように、過給有り時にはオーバーラップ中吹き返し不活性ガス流量（ＭＲＥＳＯＬｔｍｐ３、ＭＲＥＳＯＬｔｍｐ４）が負となるため、上記（３６）式のオーバーラップ中の吹き返し不活性ガス量ＭＲＥＳＯＬも負となり、このとき（３７）式によれば、オーバーラップ中の吹き返し不活性ガス量ＭＲＥＳＯＬの分だけ内部不活性ガス量が減じられる。
【０１８７】
このようにして内部不活性ガス量ＭＲＥＳの算出を終了したら図１２に戻り、ステップ５４においてこの内部不活性ガス量ＭＲＥＳと、目標当量比ＴＦＢＹＡとを用いて、次式により残留不活性ガス率ＭＲＥＳＦＲ（燃焼室５内の総ガス量に対する内部不活性ガス量の割合）を算出する。
【０１８８】

これで残留不活性ガス率ＭＲＥＳＦＲの算出を総て終了する。
【０１８９】
（本実施形態の効果）
本実施形態では、燃料のモル分率や酸素のモル分率から反応確率ＲＰＲＯＢＡを求めている。これらのモル分率は、（６８）式にあるように目標当量比ＴＦＢＹＡ及び残留不活性ガス率ＭＲＥＳＦＲから算出することができ、また残留不活性ガス率ＭＲＥＳＦＲは、残留不活性ガス質量ＭＲＥＳ、吸入空気質量ＭＡＣＹＬ及び目標当量比ＴＦＢＹＡに基づいて求めることができる。したがって、残留不活性ガス質量ＭＲＥＳ、吸入空気質量ＭＡＣＹＬ及び目標当量比ＴＦＢＹＡを検出することで、反応確率ＲＰＲＯＢＡを求めることができるのである。そして、その反応確率ＲＰＲＯＢＡと、燃焼ガスの層流状態での燃焼速度である層流燃焼速度（ＳＬ１、ＳＬ２）と、燃焼ガス体積に近似させた燃焼ガス体積相当容積（Ｖ０、ＶＴＤＣ）と、基準クランク角θＰＭＡＸ（所定クランク角）までの燃焼質量割合の変化代（ＢＲ１、ＢＲ２）とに基づいて、燃焼開始から基準クランク角θＰＭＡＸまでの燃焼期間ＢＵＲＮ（＝ＢＵＲＮ１＋ＢＵＲＮ２）を算出するようにしたので、従来装置のように未燃ガス密度を用いることなく燃焼期間ＢＵＲＮを算出することが可能となり、これにより正確かつ容易にＭＢＴの得られる基本点火時期ＭＢＴＣＡＬを算出することができる。反応確率ＲＰＲＯＢＡを求める方法としては、例えば、想定される運転状態ごとのマップを作成しておき、そのマップに基づいて求める方法も考えられるが、そのような方法ではマッチングの工数が膨大なものとなる。しかし、本実施形態では、上述の通り反応確率ＲＰＲＯＢＡを、残留不活性ガス質量ｍ_ＥＧＲ、吸入空気質量ｍ_ＡＩＲを検出して、それらより算出するようにしたので、そのようなマッチング工数を必要としない。
【０１９０】
なお、燃料の平均分子量ＭＦは冷却水温ＴＷＫによって変化し、低温であるほど「軽質成分」が多いので、燃料平均分子量ＭＦも小さいが高温になるほど燃料平均分子量ＭＦも大きくなる。そこで、その変化特性をマップ化しておき、このマップによりエンジン冷却水温に対する燃料平均分子量ＭＦを求めれば、より正確な反応確率ＲＰＲＯＢＡを算出することができ、また、冷却水温が一定の状態については燃料平均分子量ＭＦを一定値にすることで、より高速に反応確率ＲＰＲＯＢＡを算出することができる。また、理論空燃比付近で制御する場合であれば、空燃比を検出することなくＴＦＢＹＡ＝１．０（一定値）として制御すればよい。そのようにすれば、より高速な処理が可能になる。
【０１９１】
以上説明した実施形態に限定されることなく、その技術的思想の範囲内において種々の変形や変更が可能であり、それらも本発明と均等であることは明白である。
【０１９２】
例えば、上記実施形態では、例えば、（６８）式において酸素モル分率ｘ_０２を算出し、その酸素モル分率ｘ_０２から反応確率ＲＰＲＯＢＡを算出する場合で詳細に説明したが、（６６）式を利用して酸素モル分率ｘ_０２から燃料モル分率ｘ_Ｆを算出することが可能である。したがって、まず燃料モル分率ｘ_Ｆを算出し、その燃料モル分率ｘ_Ｆから反応確率ＲＰＲＯＢＡを算出しても同様の効果を得ることができる。
【０１９３】
実施形態では、排気の一部を吸気に導入する外部ＥＧＲ装置を備えてない場合で説明したが、外部ＥＧＲ装置を備える場合にも本発明を適用することができる。この場合は外部ＥＧＲ装置による残留不活性ガス率を前述の残留不活性ガス率ＭＲＥＳＦＲに加えてやればよい。なお、外部ＥＧＲ装置による残留不活性ガス率の算出方法は公知である（特開平１０−１４１１５０号公報参照）。
【０１９４】
なお、請求項１に記載の発明において、モル分率検出手段及び反応確率算出手段の機能は図５のステップ１５により、燃焼速度算出手段の機能は図８のステップ１６８、図１０のステップ１８８により、容積算出手段の機能は図８のステップ１６２により、質量算出手段の機能は図８のステップ１７１、図１０のステップ１９１により、燃焼期間算出手段の機能は図８のステップ１７１、図１０のステップ１９１、図１１のステップ４２により、基本点火時期算出手段の機能は図１１のステップ４３によりそれぞれ果たされている。
【図面の簡単な説明】
【図１】一実施形態のエンジンの制御システム図。
【図２】エンジンコントローラで実行される点火時期制御のブロック図。
【図３】燃焼室の圧力変化図。
【図４】燃焼質量割合の変化を説明する特性図。
【図５】物理量の算出を説明するためのフローチャート。
【図６】エンジンのクランクシャフトとコネクティングロッドの位置関係を説明するダイアグラム。
【図７】基準クランク角の特性図。
【図８】初期燃焼期間の算出を説明するためのフローチャート。
【図９】温度上昇率の特性図。
【図１０】主燃焼期間の算出を説明するためのフローチャート。
【図１１】基本点火時期の算出を説明するためのフローチャート。
【図１２】残留不活性ガス率の算出を説明するためのフローチャート。
【図１３】内部不活性ガス量の算出を説明するためのフローチャート。
【図１４】ＥＶＣ時不活性ガス量の算出を説明するためのフローチャート。
【図１５】オーバーラップ中吹き返し不活性ガス量の算出を説明するためのフローチャート。
【図１６】過給判定フラグ、チョーク判定フラグの設定を説明するためのフローチャート。
【図１７】過給無しかつチョーク無し時のオーバーラップ中吹き返し不活性ガス流量の算出を説明するためのフローチャート。
【図１８】過給無しかつチョーク有り時のオーバーラップ中吹き返し不活性ガス流量の算出を説明するためのフローチャート。
【図１９】過給有りかつチョーク無し時のオーバーラップ中吹き返し不活性ガス流量の算出を説明するためのフローチャート。
【図２０】過給有りかつチョーク有り時のオーバーラップ中吹き返し不活性ガス流量の算出を説明するためのフローチャート。
【図２１】排気弁閉時期における燃焼室容積の特性図。
【図２２】不活性ガスのガス定数の特性図。
【図２３】オーバーラップ中の積算有効面積の特性図。
【図２４】オーバーラップ中の積算有効面積の説明図。
【図２５】不活性ガスの比熱比の特性図。
【図２６】混合気の比熱比の特性図。
【符号の説明】
１ エンジン
５ 燃焼室
１１ 点火装置（火花点火手段）
１５ 吸気弁
２１ 燃料インジェクタ
２７ 吸気ＶＴＣ機構
３１ エンジンコントローラ
３３、３４ クランク角センサ
４３ 吸気温度センサ
４４ 吸気圧力センサ
４５ 排気温度センサ
４６ 排気圧力センサ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ignition timing control device for an internal combustion engine, and more particularly to an ignition timing control for setting a minimum ignition advance value (so-called MBT) required to generate a maximum shaft torque.
[0002]
[Prior art]
A predetermined ignition delay time B1 is added to a value obtained by dividing the total gas mass MASSC in the cylinder by the unburned gas density basic value DENS and the laminar flame speed SLV, and a value obtained by converting the added value into a crank angle is obtained as MBT. There is one that calculates the basic ignition timing to be used (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-10-30535
[0004]
[Problems to be solved by the invention]
Incidentally, the knowledge obtained by the combustion analysis will be described with reference to FIG. FIG. 4 shows a change in the combustion mass ratio BR from the intake bottom dead center to the first half of the expansion stroke. The combustion mass ratio BR represents the ratio of the mass of combustion gas to the fuel supplied to the combustion chamber, and is a physical quantity that can be detected by combustion analysis. This combustion gas mass BR is 0% at the start of combustion and reaches 100% by complete combustion. In this case, the inventor has newly found that the combustion mass ratio BR at the reference crank angle θPMAX is constant and about 60%.
[0005]
The reference crank angle θPMAX will be supplemented with reference to FIG. FIG. 3 is a diagram showing a change in the pressure of the combustion chamber from the bottom dead center of the intake air to the first half of the expansion stroke. The crank angle at which the pressure (combustion pressure) in the combustion chamber reaches the maximum value Pmax when the mixture is ignited by MBT is the reference crank angle θPMAX. The reference crank angle θPMAX is substantially constant irrespective of the combustion method, and generally ranges from 12 to 15 degrees after the compression top dead center, and at most 10 to 20 degrees after the compression top dead center.
[0006]
Here, if the period from the start of combustion until the combustion pressure of the air-fuel mixture reaches the maximum value is defined as the combustion period, this combustion period is obtained by dividing the total gas mass in the combustion chamber by the laminar combustion velocity. It is basically possible to ask. Therefore, in the above conventional apparatus, the combustion period is obtained by dividing the total gas mass MASSC by the basic value of unburned gas density DENS and the basic value of turbulent flame velocity FLMT. Since the unburned gas density basic value DENS in the conventional apparatus is a value obtained by dividing the unburned gas mass by the unburned gas volume, theoretically, if the unburned gas mass and the unburned gas volume are detected, the unburned gas becomes unburned. The gas density basic value DENS can be determined accurately. However, since it is actually difficult to estimate the unburned gas volume in the combustion chamber, the conventional apparatus determines the unburned gas density basic value DENS based on the charging efficiency ITAC.
[0007]
However, if the unburned gas density basic value DENS is calculated using only the function of the charging efficiency ITAC corresponding to the mass as in the conventional apparatus, the calculation accuracy is deteriorated only by the unburned gas volume integral that changes depending on the operating conditions. , The calculation accuracy of the combustion period is reduced, the calculation of the basic ignition timing becomes inaccurate, and a situation where MBT cannot be obtained may occur.
[0008]
The present invention has been made in view of such a conventional problem, and the combustion gas volume is approximated by the combustion chamber volume at that time, and instead, the combustion gas mass is introduced, and the combustion chamber volume and the combustion volume are reduced. It is an object of the present invention to provide a new ignition timing control device for an internal combustion engine that incorporates recent combustion analysis results by calculating a combustion period based on gas mass.
[0009]
[Means for Solving the Problems]
The present invention detects a mole fraction of a combustion component in a total number of moles in a combustion chamber based on an operation state of an internal combustion engine, and based on the detected mole fraction, a reaction probability indicating the ease of combustion of a combustion gas. Combustion based on the combustion speed of the combustion gas, the volume corresponding to the volume of the combustion gas in the combustion chamber, and the mass of the combustion gas burning in the combustion chamber from the start of combustion to the reference crank angle at which the combustion pressure becomes maximum. A combustion period from the start to the reference crank angle is calculated, and spark ignition is performed as a basic ignition timing at which MBT is obtained based on the combustion period.
[0010]
[Action / Effect]
According to the present invention, the combustion period is calculated based on the laminar combustion velocity, the combustion gas volume equivalent volume approximated to the combustion gas volume, the newly introduced combustion gas mass, and the reaction probability. The combustion period can be calculated without using the density, whereby the basic ignition timing at which the MBT can be obtained can be calculated accurately and easily.
[0011]
In this case, since the above reaction probability depends on the residual inert gas ratio, the cooling water temperature, and the target equivalent ratio, the maximum value of the reaction probability obtained by a combination of these three parameters is set to 100%. Although it is conceivable to experimentally determine the relationship with, and store the determined reaction probability in a memory in advance as a table corresponding to the parameters, this method may increase the number of matching steps. In contrast, in the present invention, the mole fraction of the combustion component in the total number of moles in the combustion chamber is detected, and the reaction probability is calculated based on the mole fraction of the combustion component. Since the reaction probability can be calculated only by a certain calculation formula (see formula (67) described later), the matching can be made unnecessary.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings and the like.
[0013]
FIG. 1 is a schematic diagram for explaining the system of the present invention.
[0014]
After the air is stored in the intake collector 2, it is introduced into the combustion chamber 5 of each cylinder via the intake manifold 3. The fuel is injected and supplied from a fuel injector 21 arranged in the intake port 4 of each cylinder. The fuel injected into the air is vaporized and mixed with the air to form a gas (air-fuel mixture), which flows into the combustion chamber 5. This air-fuel mixture is confined in the combustion chamber 5 by closing the intake valve 15, and is compressed by the rise of the piston 6.
[0015]
In order to ignite the compressed air-fuel mixture with a high-pressure spark, an ignition device 11 of an electronic power distribution system having an ignition coil with a built-in power transistor in each cylinder is provided. That is, the ignition device 11 includes an ignition coil 13 for storing electric energy from a battery, a power transistor for energizing and interrupting the primary side of the ignition coil 13, and a primary current for the ignition coil 13 provided on the ceiling of the combustion chamber 5. And a spark plug 14 that receives a high voltage generated on the secondary side of the ignition coil 13 by the interruption of the spark plug 13 and performs a spark discharge.
[0016]
When a spark is blown by the spark plug 14 and ignites the compressed air-fuel mixture shortly before the compression top dead center, the flame spreads and burns explosively, and the gas pressure by this combustion performs the work of pushing down the piston 6. This work is taken out as the rotational force of the crankshaft 7. The burned gas (exhaust gas) is discharged to the exhaust passage 8 when the exhaust valve 16 is opened.
[0017]
The exhaust passage 8 includes a three-way catalyst 9. When the air-fuel ratio of the exhaust gas is in a narrow range (window) centered on the stoichiometric air-fuel ratio, the three-way catalyst 9 can simultaneously efficiently remove harmful three components such as HC, CO, and NOx contained in the exhaust gas. Since the air-fuel ratio is a ratio between the amount of intake air and the amount of fuel, the amount of intake air introduced into the combustion chamber 5 per one cycle of the engine (in a 4-cycle engine, 720 ° section in crank angle), The engine controller 31 controls the fuel injector 21 based on the signal of the intake air flow rate from the air flow meter 32 and the signal from the crank angle sensors (33, 34) so that the ratio between the fuel injection amount and the stoichiometric air-fuel ratio becomes the stoichiometric air-fuel ratio. The fuel injection amount is determined, and O provided upstream of the three-way catalyst 9 is determined.₂The air-fuel ratio is feedback-controlled based on a signal from the sensor 35.
[0018]
An upstream of the intake collector 2 is provided with a so-called electronic control throttle 22 in which a throttle valve 23 is driven by a throttle motor 24. Since the torque required by the driver appears in the amount of depression of the accelerator pedal 41 (accelerator opening), the engine controller 31 determines a target torque based on a signal from the accelerator sensor 42 and sets a target air for realizing the target torque. The throttle valve 23 is controlled via the throttle motor 24 so that the target air amount is obtained.
[0019]
A cam sprocket and a crank sprocket are respectively attached to the front portions of the intake valve camshaft 25, the exhaust valve camshaft 26, and the crankshaft 7, and a timing chain (not shown) is wound around these sprockets to form a camshaft. 25 and 26 are driven by the crankshaft 7 of the engine, and are interposed between the cam sprocket and the camshaft 25 for the intake valve to continuously shift the phase of the cam for the intake valve while keeping the operating angle constant. A controllable intake valve timing control mechanism (hereinafter referred to as “intake VTC mechanism”) 27 and a cam sprocket and an exhaust valve camshaft 26 interposed between the camshaft 26 and the exhaust valve cam phase with a constant operating angle. Valve timing control mechanism (hereinafter referred to as “exhaust VTC mechanism”) that can continuously control Say.) And a 28. When the opening / closing timing of the intake valve 15 or the opening / closing timing of the exhaust valve 16 is changed, the amount of the inert gas remaining in the combustion chamber 5 changes. As the amount of the inert gas in the combustion chamber 5 increases, the pumping loss decreases and the fuel efficiency improves, so how much inert gas should remain in the combustion chamber 5 depending on the operating conditions is determined by the target intake valve closing timing and the target. The exhaust valve closing timing is predetermined, and the engine controller 31 determines the target intake valve closing timing and the target exhaust valve closing timing based on the operating conditions (engine load and rotation speed) at that time, and obtains these target values. Thus, the intake valve closing timing and the exhaust valve closing timing are controlled via the actuators of the intake VTC mechanism 27 and the exhaust VTC mechanism 28.
[0020]
An intake air temperature signal from the intake air temperature sensor 43, an intake air pressure signal from the intake air pressure sensor 44, an exhaust air temperature signal from the exhaust air temperature sensor 45, and an exhaust pressure signal from the exhaust air pressure sensor 46 are output from the water temperature sensor 37. The engine controller 31, which is input together with the signal of the cooling water temperature, controls the ignition timing, which is the interruption timing of the primary current of the ignition plug 14, via the power transistor 13.
[0021]
FIG. 2 is a block diagram of the ignition timing control performed in the engine controller 31. The ignition timing control unit 61 includes an ignition timing calculation unit 51 and an ignition timing control unit 61. The ignition timing calculator 51 further includes an initial combustion period calculator 52, a main combustion period calculator 53, a combustion period calculator 54, a basic ignition timing calculator 55, and a previous combustion start timing calculator 56.
[0022]
The initial combustion period calculation unit 52 calculates a period from when the air-fuel mixture is ignited to when a flame kernel is formed as an initial combustion period BURN1. The main combustion period calculation unit 53 calculates a period from when the flame kernel is formed to when the combustion pressure reaches the maximum value Pmax as the main combustion period BURN2. The combustion period calculation unit 54 calculates the sum of the initial combustion period BURN1 and the main combustion period BURN2 as the combustion period BURN from the start of combustion to the maximum combustion pressure Pmax. The basic ignition timing calculation unit 55 calculates an ignition timing at which MBT is obtained (this ignition timing is referred to as “basic ignition timing”) MBTCAL based on the combustion period BURN.
[0023]
The ignition timing control unit 61 uses the basic ignition timing calculated in this manner as an ignition timing command value. The ignition plug 14 ignites the air-fuel mixture in the combustion chamber 5 with this command value. And the non-energizing angle are controlled.
[0024]
As described above, the combustion period BURN is calculated by dividing the initial combustion period BURN1 and the main combustion period BURN2, and the basic ignition timing MBTCAL is determined according to the combustion period BURN. It is based on Hereinafter, this ignition timing control based on combustion analysis will be further described.
[0025]
As shown in FIG. 3, the crank angle at which the combustion pressure of the air-fuel mixture reaches the maximum value Pmax when the air-fuel mixture is ignited at MBT (the minimum advance value at which the maximum torque is obtained) is defined as a reference crank angle θPMAX [degATDC]. The reference crank angle θPMAX is almost constant irrespective of the combustion method, and is generally in the range of 12 to 15 degrees after the compression top dead center and at most 10 to 20 degrees after the compression top dead center.
[0026]
FIG. 4 shows the change of the combustion mass ratio BR (combustion gas mass ratio) obtained by the combustion analysis in the combustion chamber in the spark ignition engine. The combustion mass ratio BR representing the ratio of the combustion mass to the fuel supplied to the combustion chamber is 0% at the start of combustion, and reaches 100% by complete combustion. Experiments have confirmed that the combustion mass ratio at the reference crank angle θPMAX is constant and about 60%.
[0027]
The combustion period corresponding to the change margin from the time when the combustion mass ratio BR reaches 0% to about 60% corresponding to the reference crank angle θPMAX is a period immediately after the start of combustion, in which there is almost no change in the combustion mass ratio or the combustion pressure. It is divided into an initial combustion period and a main combustion period in which the combustion mass ratio and the combustion pressure increase rapidly. The initial combustion period is a stage from the start of combustion to the formation of a flame nucleus. The flame nucleus is formed when the combustion mass ratio changes from 0% to 2% to 10%. During this initial combustion period, the rising speed of the combustion pressure and the combustion temperature is small, and the initial combustion period is long with respect to the change in the combustion mass ratio. The length of the initial combustion period is susceptible to changes in temperature and pressure in the combustion chamber.
[0028]
On the other hand, during the main combustion period, the flame propagates outward from the flame kernel, and the flame speed (that is, the combustion speed) sharply increases. Therefore, the change in the combustion mass ratio during the main combustion period is larger than the change in the combustion mass ratio during the initial combustion period.
[0029]
The engine controller 31 sets an initial combustion period BURN1 [deg] until the combustion mass ratio reaches (changes) 2%, and a section (combustion chamber amount ratio) from the end of the initial combustion period BURN1 to the reference crank angle θPMAX. In other words, from 2% to about 60%) is distinguished as the main combustion period BURN2 [deg]. Then, a combustion period BURN [deg], which is the sum of the initial combustion period BURN1 and the main combustion period BURN2, is calculated, a reference crank angle θPMAX [degATDC] is subtracted from the combustion period BURN, and a crank equivalent to an ignition dead time described later is further calculated. The crank angle position to which the angle IGNDEAD [deg] is added is set as a basic ignition timing MBTCAL [degBTDC] which is an ignition timing at which MBT can be obtained.
[0030]
The pressure and temperature in the combustion chamber 5 during the initial combustion period in which the flame nucleus is formed are substantially equivalent to the pressure and temperature at the time of ignition. The time cannot be set. Therefore, as shown in FIG. 2, the previous value of the basic ignition timing is calculated as the previous combustion start timing MBTCYCL [degBTDC] by the previous combustion start timing calculation unit 56, and this value is given to the initial combustion period calculation unit 52. By repeating the calculation of the initial combustion period cyclically in the initial combustion period calculation section 52, a highly accurate result can be obtained without time delay.
[0031]
Next, the calculation of the basic ignition timing MBTCAL executed by the engine controller 31 will be described in detail with reference to the following flowchart.
[0032]
FIG. 5 is for calculating various physical quantities necessary for calculating the ignition timing, and is executed at regular intervals (for example, every 10 msec).
[0033]
First, in step 11, the intake valve closing timing IVC [degBTDC], the collector internal temperature TCOL [K] detected by the temperature sensor 43, the collector internal pressure PCOL [Pa] detected by the pressure sensor 44, and the temperature sensor 45 detect it. Exhaust gas temperature TEXH [K], residual inert gas ratio MRESFR [%], cooling water temperature TWK [K] detected by temperature sensor 37, target equivalent ratio TFBYA, engine speed NRPM [rpm] detected by crank angle sensor. ] And the ignition dead time DEADTIME [μsec] is read.
[0034]
Here, the crank angle sensor is composed of a position sensor 33 for detecting the position of the crankshaft 7 and a phase sensor 34 for detecting the position of the intake camshaft 25. Based on signals from these two sensors 33 and 34, the engine The rotation speed NRPM [rpm] is calculated.
[0035]
The intake valve closing timing IVC is known from a command value given to the intake VTC mechanism 27. Alternatively, the actual intake valve closing timing may be detected by the phase sensor 34.
[0036]
The residual inert gas ratio MRESFR is a value obtained by dividing the amount of inert gas remaining in the combustion chamber by the total gas amount in the combustion chamber, and its calculation will be described later. The dead ignition time DEADTIME is a constant value.
[0037]
The target equivalence ratio TFBYA is calculated in a fuel injection amount calculation flow (not shown). The target equivalence ratio TFBYA is an anonymous number, and is a value represented by the following equation when the stoichiometric air-fuel ratio is 14.7.
[0038]
TFBYA = 14.7 / target air-fuel ratio ... (1)
For example, from equation (1), when the target air-fuel ratio is the stoichiometric air-fuel ratio, TFBYA = 1.0. When the target air-fuel ratio is a lean value such as 22.0, TFBYA is a positive value less than 1.0. is there.
[0039]
In step 12, the volume of the combustion chamber 5 at the intake valve closing timing IVC (that is, the volume at the compression start timing) VIVC [m³] Is calculated. The volume VIVC of the combustion chamber 5 when the intake valve is closed is determined by the stroke position of the piston 6. The stroke position of the piston 6 is determined by the crank angle position of the engine.
[0040]
Referring to FIG. 6, consider a case where rotation center 72 of crankshaft 71 of the engine is offset from center axis 73 of the cylinder. Assume that a connecting rod 74, a node 75 between the connecting rod 74 and the crankshaft 71, and a piston pin 76 connecting the connecting rod 74 and the piston are in the relationship shown in the figure. At this time, the volume VIVC of the combustion chamber 5 when the intake valve is closed can be expressed by the following equations (2) to (6).
[0041]

Here, Vc: clearance volume [m³],
ε: compression ratio,
D: Cylinder bore diameter [m]
ST: Full stroke of piston [m],
Hivc: distance [m] of piston pin 76 from TDC at intake valve closing timing,
Hx: difference [m] between the maximum value and the minimum value of the distance of piston pin 76 from TDC,
CND: length [m] of connecting rod 74,
CRoff: offset distance [m] of node 75 from cylinder center axis 73,
PISoff: offset distance [m] of the crankshaft rotation center 72 from the cylinder center axis 73,
θivc: crank angle of intake valve closing timing [degATDC],
θoff: piston pin 76 and crankshaft rotation center
The angle [deg] that the line connecting with 72 makes a vertical line in TDC,
X: horizontal distance [m] between the node 75 and the piston pin 76,
The crank angle θivc at the intake valve closing timing is known because it is determined by the command signal from the engine controller 31 to the intake VTC mechanism 27 as described above. By substituting the crank angle θivc (= IVC) at this time into the equations (2) to (6), it is possible to calculate the volume VIVC of the combustion chamber 5 when the intake valve is closed. Therefore, in practice, the volume VIVC of the combustion chamber 5 when the intake valve is closed is set using a table that uses the intake valve closed timing IVC as a parameter. When the intake VTC mechanism 27 is not provided, it can be given as a constant.
[0042]
In step 13, the temperature TINI [K] of the combustion chamber 5 at the intake valve closing timing IVC (that is, the compression start timing temperature) is calculated. The temperature of the gas flowing into the combustion chamber 5 is a temperature of a gas in which fresh air flowing into the combustion chamber 5 and an inert gas remaining in the combustion chamber 5 are mixed, and the temperature of the fresh air flowing into the combustion chamber 5 is Since the temperature of the inert gas remaining in the combustion chamber 5 can be approximated by the exhaust temperature TEXH near the exhaust port, the temperature of the inert gas remaining in the combustion chamber 5 at the intake valve closing time IVC is equal to the fresh air temperature TCOL in the intake collector 2. TINI is calculated based on the fresh air temperature TCOL in the intake collector 2, the exhaust gas temperature TEXH, and the residual inert gas ratio MRESFR which is a ratio of the inert gas remaining in the combustion chamber 5 at the timing when the intake valve closing timing IVC is reached. It can be obtained by an equation.
[0043]
TINI = TEXH × MRESFR + TCOL × (1-MRESFR) (7)
In step 14, the pressure PINI [Pa] of the combustion chamber 5 at the intake valve closing timing IVC (that is, the compression start timing pressure) is calculated. That is, the collector pressure PCOL at the timing when the intake valve closing timing IVC is reached is taken in as the pressure PINI at the intake valve closing timing IVC.
[0044]
In step 15, the reaction probability RPROBA [%] is calculated. The reaction probability RPROBA is a dimensionless value representing the flammability of the air-fuel mixture in the combustion chamber 5, and depends on three parameters: the residual inert gas ratio MRESFR, the cooling water temperature TWK [K], and the target equivalent ratio TFBYA. Therefore, it can be expressed by the following equation.
[0045]
RPROBA = f3 (MRESFR, TWK, TFBYA) (8)
Hereinafter, the reaction probability RPROBA will be described. When the combustion in the combustion chamber is approximated by constant volume combustion, the reaction rate (combustion rate) in the overall chemical reaction when the air-fuel mixture in the combustion chamber burns can be expressed as follows.
[0046]
(Equation 1)

Furthermore, [F], [O₂] Is represented by the following.
[0047]
(Equation 2)

In addition, the laminar combustion velocity S_LIs generally represented by:
[0048]
(Equation 3)

Therefore:
[0049]
(Equation 4)

In this equation, "A₁Is a constant term, "F₁(P) ”is a pressure-dependent term,“ G₁(T) ”is a temperature-dependent term, so“ x_F ^{m / 2}・ X_O2 ^{n / 2}] Corresponds to the reaction probability. That is, if the reaction probability is high, the combustion speed is high, and if the reaction probability is low, the combustion speed is low. The reaction probability is a correction term indicating the flammability of the air-fuel mixture in the combustion chamber.
[0050]
Here, the fuel mole fraction x_FAnd oxygen mole fraction x_O2Ask for a relationship. First, m_AIR; Intake air mass, m_F; Mass of intake fuel, m_O2The following relationship with the inhaled oxygen mass:
[0051]
m_AIR: M_F  = 14.7: 1
m_AIR: M_O2  = 1: 0.23
In addition, there is the following relationship.
[0052]
x_F= M_F/ M_F
x_O2= M_O2/ M_O2
The average molecular weight MF of the fuel changes depending on the cooling water temperature TWK. That is, since various components are contained in gasoline, the components to be vaporized change when the temperature changes. Therefore, the fuel average molecular weight MF changes depending on the temperature. The lower the temperature, the more "light components", the lower the fuel average molecular weight MF, but the higher the temperature, the higher the fuel average molecular weight MF. The fuel average molecular weight MF is determined by correcting that point. Since the evaporation characteristic of a general gasoline fuel with respect to a temperature change is known, the value of the fuel average molecular weight MF with respect to the ambient temperature can be mapped from this characteristic. The ambient temperature in the intake port and the combustion chamber during the intake stroke with respect to the engine cooling water temperature can be obtained in advance by experiments or the like. Therefore, the value of the average molecular weight of the fuel with respect to the temperature of the engine cooling water can be determined from these.
[0053]
Further, as in the equation (1), “TFBYA = 14.7 (theoretical air-fuel ratio) / target air-fuel ratio”.
[0054]
From the above, the fuel mole fraction x_FAnd oxygen mole fraction x_O2Has the following relationship.
[0055]
(Equation 5)

Therefore, the reaction probability RPROBA is as follows.
[0056]
(Equation 6)

As is apparent from the equations (67) and (66), the reaction probability can be obtained if the molar fraction of either fuel or oxygen is known.
[0057]
Also, for example, the molar fraction of oxygen x_O2Is expressed as follows by a residual inert gas ratio MRESFR (= MRES / {MRES + MACYL × (1 + TFBYA / 14.7)}).
[0058]
(Equation 7)

Therefore, the reaction probability is as follows.
[0059]
(Equation 8)

As is clear from this equation, the reaction probability can be obtained if the residual inert gas ratio MRESFR is known, and the residual inert gas ratio MRESFR = m_EGR/ ｛M_EGR+ M_AIR× (1 + TFBYA / 14.7)｝, the residual inert gas mass m_EGRAnd the intake air mass m_AIRAnd the air-fuel ratio or the equivalence ratio, the reaction probability can be obtained. A specific calculation method will be described later. In addition, this residual inert gas mass m_EGRIs hereinafter described as a label “MRES”.
[0060]
If the cooling water temperature is constant, the fuel average molecular weight MF may be kept constant. If the control is performed near the stoichiometric air-fuel ratio, the control may be performed with TFBYA = 1.0 (constant value). By doing so, the calculation can be simplified, and the reaction probability RPROBA can be calculated more quickly.
[0061]
In step 16, the reference crank angle θPMAX [degATDC] is calculated. As described above, although the reference crank angle θPMAX does not change much, it still tends to advance according to the increase in the engine speed NRPM. Therefore, the reference crank angle θPMAX can be expressed by the following equation as a function of the engine speed NRPM. it can.
[0062]
θPMAX = f4 (NRPM) (9)
Specifically, the reference crank angle θPMAX is obtained by searching a table of characteristics shown in FIG. 7 stored in advance in the memory of the engine controller 31 from the engine rotation speed NRPM. In order to facilitate the calculation, the reference crank angle θPMAX may be considered to be constant.
[0063]
Finally, in step 17, the crank angle IGNDEAD [deg] corresponding to the ignition dead time is calculated. The crank angle IGNDEAD equivalent to the ignition dead time is a crank angle section from the timing at which a signal for cutting off the primary current of the ignition coil 13 is output from the engine controller 31 to the time when the spark plug 14 actually ignites, and can be expressed by the following equation. .
[0064]
IGNDEAD = f5 (DEADTIME, NRPM) (10)
Here, the dead ignition time DEADTIME is set to 200 μsec. Expression (10) is used to calculate a crank angle IGNDEAD corresponding to an ignition dead time which is a crank angle corresponding to the ignition dead time DEADTIME from the engine rotation speed NRPM.
[0065]
FIG. 8 is for calculating the initial combustion period BURN1 [deg], and FIG. 10 is for calculating the main combustion period BURN2 [deg], which is executed at regular intervals (for example, every 10 msec). 8 and 10 are executed after FIG. 8 and 10 may be performed first.
[0066]
First, referring to FIG. 8, in step 161, the previous combustion start timing MBTCCYCL [degBTDC], the volume VIVC [m at the intake valve closing timing of the combustion chamber 5 calculated in step 12 in FIG.³], The temperature TINI [K] at the intake valve closing timing of the combustion chamber 5 calculated in step 13 of FIG. 5, and the pressure PINI [Pa] at the intake valve closing timing of the combustion chamber 5 calculated in step 14 of FIG. ], The engine rotation speed NRPM [rpm], and the reaction probability RPROBA [%] calculated in step 15 of FIG.
[0067]
Here, the previous combustion start timing MBTCYCL is a value one cycle before [degBTDC] of the basic ignition timing MBTCAL, and its calculation will be described later with reference to FIG.
[0068]
In step 162, the volume V0 [m³] Is calculated. As described above, the ignition timing (combustion start timing) here is not the basic ignition timing MBTCAL calculated in this cycle but a value one cycle before the basic ignition timing. That is, the volume V0 of the combustion chamber 5 at the combustion start timing is calculated from MBTCCYCL, which is one cycle before the basic ignition timing, by the following equation.
[0069]
V0 = f6 (MBTCYCL) (11)
Specifically, a volume V0 of the combustion chamber 5 in the MBTCYCL is calculated from the stroke position of the piston 6 at the previous combustion start timing MBTCYCL and the bore diameter of the combustion chamber 5. In step 12 of FIG. 5, the volume VIVC of the combustion chamber 5 at the intake valve closing timing IVC was obtained by searching a table of the intake valve closing timing volume using the intake valve closing timing as a parameter. The volume V0 of the combustion chamber 5 at the previous combustion start timing MBTCYCL may be obtained by searching a table of the previous combustion start timing volume.
[0070]
In step 163, the effective compression ratio Ec at the combustion start timing is calculated. The effective compression ratio Ec is a dimensionless value, and is a value obtained by dividing the volume V0 of the combustion chamber 5 at the combustion start timing by the volume VIVC of the combustion chamber 5 at the intake valve closing timing as shown in the following equation.
[0071]
Ec = f7 (V0, VIVC) = V0 / VIVC (12)
In step 164, the temperature increase rate TCOMP in the combustion chamber 5 from the intake valve closing timing IVC to the combustion start timing is calculated based on the effective compression ratio Ec as shown in the following equation.
[0072]
TCOMP = f8 (Ec) = Ec ＾ (κ−1) (13)
Where κ: specific heat ratio,
Equation (13) is an equation for the temperature rise rate of the gas to be adiabatically compressed. Note that “＾” on the right side of Expression (13) represents power calculation. This symbol is also used in the equations described below.
[0073]
κ is a value obtained by dividing the constant pressure specific heat of the gas to be adiabatically compressed by the constant volume specific heat. If the gas to be adiabatically compressed is air, κ is 1.4, and this value may be simply used. However, it is possible to further improve the calculation accuracy by experimentally obtaining the value of κ for the air-fuel mixture.
[0074]
FIG. 9 illustrates equation (13). Therefore, it is also possible to store a table of such characteristics in the memory of the engine controller 31 in advance and search the table based on the effective compression ratio Ec to determine the temperature rise rate TCOMP.
[0075]
In step 165, the temperature T0 [K] at the combustion start timing of the combustion chamber 5 is multiplied by the temperature increase rate TCOMP to the temperature TINI of the combustion chamber 5 at the intake valve closing timing.
T0 = TINI × TCOMP (14)
It is calculated by the following equation.
[0076]
Steps 166 and 167 are the same as steps 164 and 165. That is, in step 166, the pressure increase rate PCOMP in the combustion chamber 5 from the intake valve closing timing IVC to the combustion start timing is calculated based on the effective compression ratio Ec as shown in the following equation.
[0077]
PCOMP = f9 (Ec) = Ec ＾ κ (41)
Where κ: specific heat ratio,
Equation (41) is also an equation of the pressure rise rate of the gas to be adiabatically compressed, similar to equation (13). “＾” on the right side of the equation (41) also represents the exponentiation calculation as in the equation (13).
[0078]
κ is the same as the value used in the above equation (13). If the gas to be adiabatically compressed is air, κ is 1.4, and this value may be simply used. However, by calculating the value of κ from the composition and the temperature of the air-fuel mixture, the calculation accuracy can be further improved.
[0079]
A table having the same characteristics as in FIG. 9 may be stored in the memory of the engine controller 31 in advance, and the pressure increase rate PCOMP may be obtained by searching the table based on the effective compression ratio Ec.
[0080]
In step 167, the pressure P0 [Pa] at the combustion start timing of the combustion chamber 5 is multiplied by the pressure PINI at the intake valve closing timing of the combustion chamber 5 by the pressure increase rate PCOMP.
P0 = PINI × PCOMP (42)
It is calculated by the following equation.
[0081]
In step 168, the laminar combustion speed SL1 [m / sec] during the initial combustion period is calculated by the following equation (known).
[0082]

Here, Tstd: reference temperature [K],
Pstd: Reference pressure [Pa],
SLstd: reference laminar combustion velocity [m / sec] at reference temperature Tstd and reference pressure Pstd,
T0: temperature [K] at the combustion start timing of the combustion chamber 5,
P0: pressure [Pa] at the combustion start timing of the combustion chamber 5;
The laminar combustion velocity (laminar flame velocity) is the speed of propagation of the flame in a state where there is no gas flow, regardless of the compression velocity in the combustion chamber 5 and the intake flow velocity in the combustion chamber 5. It is known that the laminar combustion velocity during the initial combustion period is a function of the temperature T0 at the start of combustion and the pressure P0 at the start of combustion. Is a function of the compression top dead center temperature TTDC and the compression top dead center pressure PTDC. This is because the laminar combustion velocity generally varies depending on the engine load, the residual inert gas ratio in the combustion chamber 5, the intake valve closing timing, the specific heat ratio, and the intake air temperature. Since it is a factor that affects the temperature T and the pressure P, the laminar combustion speed can be finally specified by the temperature T and the pressure P in the combustion chamber 5.
[0083]
In the above equation (15), the reference temperature Tstd, the reference pressure Pstd, and the reference laminar combustion speed SLstd are values determined in advance by experiments.
[0084]
Under the pressure of 2 bar or more, which is the normal pressure of the combustion chamber 5, the pressure term (P0 / Pstd) of the equation (15)^-0.16Is a small value. Therefore, the pressure term (P0 / Pstd)^-0.16May be defined as a constant value, and the reference laminar flow combustion speed SLstd may be defined only by the reference temperature Tstd.
[0085]
Therefore, when the reference temperature Tstd is 550 [K], the reference laminar combustion speed SLstd is 1.0 [m / sec], and the pressure term is 0.7, the temperature T0 and the laminar combustion speed at the combustion start time are obtained. The relationship with SL1 can be approximately defined by the following equation.
[0086]

In step 169, the turbulence strength ST1 of the gas flow during the initial combustion period is calculated. The turbulence strength ST1 of the gas flow is a dimensionless value and depends on the flow velocity of the fresh air flowing into the combustion chamber 5 and the penetration of the fuel injected by the fuel injector 21.
[0087]
The flow velocity of the fresh air flowing into the combustion chamber 5 depends on the shape of the intake passage, the operating state of the intake valve 15, and the shape of the intake port 4 where the intake valve 15 is provided. The penetration of the injected fuel depends on the injection pressure of the fuel injector 21, the fuel injection period, and the combustion injection timing.
[0088]
Finally, the turbulence strength ST1 of the gas flow during the initial combustion period can be expressed by the following equation as a function of the engine speed NRPM.
[0089]
ST1 = f12 (NRPM) = C1 × NRPM (17)
Where C1: a constant,
The turbulence strength ST1 can also be obtained from a table using the rotation speed NRPM as a parameter.
[0090]
In step 170, the gas burning speed FLAME1 [m / sec] during the initial burning period is calculated from the laminar burning speed S1 and the turbulence intensity ST1 by the following equation.
[0091]
FLAME1 = SL1 × ST1 (18)
If there is gas turbulence in the combustion chamber 5, the combustion speed of the gas changes. Equation (18) takes into account the contribution (effect) of the gas turbulence to the combustion speed.
[0092]
In step 171, the initial combustion period BURN1 [deg] is calculated by the following equation.
[0093]

However, AF1: reaction area of the flame nucleus (fixed value) [m²],
This equation (19) and the equation (22) described later are derived from the following basic equation that divides the mass of the combustion gas by the combustion rate to obtain a combustion period. Equations (19) and (22) The numerator and denominator on the right side do not immediately indicate the combustion gas mass and the combustion rate.
[0094]

(Supplement 1) The unburned gas density of the denominator on the right side of the equation is obtained by dividing the unburned gas mass [g] by the unburned gas volume [m].³], It cannot be said that the unburned gas density can be accurately calculated by the function of only the charging efficiency ITAC corresponding to the mass as in the conventional apparatus. Therefore, the experimental equations shown in Equation (19) and Equation (22) described below are obtained only by introducing a predetermined approximation while comparing the experimental results with Equation (Complement 1).
[0095]
Here, BR1 on the right side of the equation (19) is a margin of change of the combustion mass ratio from the combustion start timing to the end timing of the initial combustion period BURN1, and here, BR1 is set to 2%. (19) (NRPM × 6) on the right side of the equation is a process for converting the unit from rpm to crank angle (deg). The reaction area AF1 of the flame kernel is set experimentally.
[0096]
In addition, it can be considered that the combustion chamber volume does not substantially change during the initial combustion period. Therefore, when calculating the initial combustion period BURN1, the combustion chamber volume V0 at the start of combustion, which is the first combustion chamber volume, is employed.
[0097]
Next, in step 181, as in step 161 of FIG. 8, the volume VIVC [m of the combustion chamber 5 at the intake valve closing timing calculated in step 12 of FIG.³], The temperature TINI [K] at the intake valve closing timing of the combustion chamber 5 calculated in step 13 of FIG. 5, and the pressure PINI [Pa] at the intake valve closing timing of the combustion chamber 5 calculated in step 14 of FIG. ], The engine rotational speed NRPM [rpm], the reaction probability RPROBA [%] calculated in step 15 of FIG. 5, and further, a cylinder fresh air amount MACYL [g], a target equivalent ratio TFBYA, and an internal inert gas amount MRES. [G], the external inert gas amount MEGR [g] is read.
[0098]
Here, the external EGR device is not shown in FIG. 1, but as far as FIG. 10 is concerned, the description will be made on the assumption that the engine has the external EGR device. In this case, the external inert gas amount MEGR may be calculated using, for example, a known method (see JP-A-10-141150). When an engine not provided with an external EGR device as in the present embodiment shown in FIG. 1 is targeted, it suffices to handle the external inert gas amount MEGR = 0. The calculation of the cylinder fresh air amount MACYL and the internal inert gas amount MRES will be described later with reference to FIG.
[0099]
Steps 182 and 183 are the same as steps 163 and 164 in FIG. That is, at step 182, the effective compression ratio Ec at the compression top dead center time 2 is calculated. Effective compression ratio Ec 2 is a dimensionless value similarly to the effective compression ratio Ec in the above equation (12), and as shown in the following equation, the volume VTDC at the compression top dead center of the combustion chamber 5 is calculated when the intake valve of the combustion chamber 5 is closed. It is the value divided by the volume VIVC.
[0100]
Ec 2 = f13 (VTDC, VIVC) = VTDC / VIVC (43) In equation (43), the volume VTDC at the compression top dead center of the combustion chamber 5 is constant irrespective of operating conditions, and is stored in the memory of the engine controller 31 in advance. It should be stored.
[0101]
In step 183, the temperature rise rate TCOMP due to adiabatic compression in the combustion chamber 5 from the intake valve closing timing IVC to the compression top dead center. The effective compression ratio Ec is expressed as 2 is calculated.
[0102]

Where κ: specific heat ratio,
A table having the same characteristics as in FIG. 9 is stored in advance in the memory of the engine controller 31, and the effective compression ratio Ec is stored. 2 by searching the table, the temperature rise rate TCOMP It is also possible to find 2.
[0103]
In step 184, the total gas mass MGAS [g] of the combustion chamber 5 is calculated from the following equation using the cylinder fresh air amount MACYL, the target equivalent ratio TFBYA, the internal inert gas amount MRES, and the external inert gas amount MEGR.
[0104]

“1” in the parentheses on the right side of the equation (45) indicates a fresh mood, and “TFBYA / 14.7” indicates a fuel.
[0105]
In step 185, using the total gas mass MGAS of the combustion chamber 5, the cylinder fresh air amount MACYL, and the target equivalence ratio TFBYA, a temperature increase amount (combustion increase temperature) TBURN [K] due to combustion of the air-fuel mixture is calculated by the following equation. .
[0106]

However, Q: constant calorific value of fuel,
BRk: combustion mass ratio of fuel in the cylinder,
Cv: constant volume specific heat,
The numerator on the right side of the equation (46) indicates the total amount of heat generated by the fuel in the cylinder [J], and the denominator indicates the rate of temperature rise per unit generated heat [J / K]. That is, equation (46) is an approximate equation applied to the thermodynamic formula.
[0107]
Here, the combustion mass ratio BRk of the fuel in the cylinder is adapted in advance through experiments and the like. For simplicity, for example, 60% / 2 = 30% is set. In this embodiment, since the combustion period until the combustion mass ratio BR reaches about 60% is treated as the combustion period, just the middle 30% is set as BRk.
[0108]
Since the constant calorific value Q of the fuel varies depending on the type of fuel, it is determined in advance by experiments or the like according to the type of fuel. The constant volume specific heat Cv is a value of 2 to 3, and a representative value is adapted in advance by experiments or the like. However, the calculation accuracy can be further improved by determining the value of the constant volume specific heat Cv from the composition and temperature of the air-fuel mixture.
[0109]
In step 186, the temperature TTDC [K] at the compression top dead center of the combustion chamber 5 is converted to the temperature TINI at the intake valve closing timing of the combustion chamber 5 by the temperature increase rate TCOMP up to the compression top dead center. It is calculated by multiplying 2 and adding the above-mentioned combustion rise temperature TBURN to the multiplied value, that is, by the following equation.
[0110]
TTDC = TINI × TCOMP 2 + TBURN ... (47)
In step 187, the temperature TTDC and volume VTDC at the compression top dead center of the combustion chamber 5 and the pressure PINI, volume VIVC and the temperature TINI at the intake valve closing timing of the combustion chamber 5 at the compression top dead center of the combustion chamber 5 are calculated by the following equation. The pressure PTDC [K] is calculated.
[0111]
PTDC = PINI × VIVC × TTDC / (VTDC × TINI) (48)
Equation (48) is obtained using the state equation. That is, the following equation of state is established using the pressure, volume and temperature (PINI, VIVC, TINI) at the intake valve closing timing.
[0112]
PINI × VIVC = n · R · TINI (supplement 2)

Since the volumes are almost equal near the compression top dead center, the following equation of state is established using the pressure, volume and temperature (PTDC, VTDC, TTDC) at the compression top dead center.
[0113]
PTDC × VTDC = n · R · TTDC (complement 3)
Eliminating n · R from both equations (complement 3) and (complement 2) above and solving for PTDC yields equation (48).
[0114]
In step 188, the laminar combustion speed SL2 [m / sec] during the main combustion period is calculated by the following equation (known) in the same manner as in step 168 of FIG.
[0115]

Here, Tstd: reference temperature [K],
Pstd: Reference pressure [Pa],
SLstd: reference laminar combustion velocity [m / sec] at reference temperature Tstd and reference pressure Pstd,
TTDC: temperature at the compression top dead center of the combustion chamber 5 [K],
PTDC: pressure [Pa] at the compression top dead center of the combustion chamber 5,
The explanation of equation (49) is the same as that of equation (16). That is, the reference temperature Tstd, the reference pressure Pstd, and the reference laminar combustion speed SLstd in the equation (49) are values determined in advance by experiments. Under the pressure of 2 bar or more, which is the normal pressure of the combustion chamber 5, the pressure term (PTDC / Pstd) of equation (49)^-0.16Is a small value. Therefore, the pressure term (PTDC / Pstd)^-0.16May be defined as a constant value, and the reference laminar flow combustion speed SLstd may be defined only by the reference temperature Tstd. Therefore, when the reference temperature Tstd is 550 [K], the reference laminar combustion speed SLstd is 1.0 [m / sec], and the pressure term is 0.7, the temperature TTDC at the compression top dead center and the laminar combustion are obtained. The relationship with the speed SL2 can be approximately defined by the following equation.
[0116]

In step 189, the turbulence strength ST2 of the gas flow during the main combustion period is calculated. Like the turbulence strength ST1 of the gas flow during the initial combustion period, the turbulence strength ST2 of the gas flow can be expressed by the following equation as a function of the engine speed NRPM.
[0117]
ST2 = f17 (NRPM) = C2 × NRPM (20)
Where C2: constant,
It is also possible to obtain the turbulence strength ST2 from a table using the rotation speed as a parameter.
[0118]
In step 190, the combustion speed FLAME2 [m / sec] during the main combustion period is calculated from the following equation based on the laminar combustion speed SL2 [m / sec] and the turbulence strength ST2 of the gas flow during the main combustion period.
[0119]
FLAME2 = SL2 × ST2 (21)
However, SL2: laminar combustion speed [m / sec],
Equation (21) takes into account the contribution to the combustion speed due to gas turbulence, as in equation (18).
[0120]
In step 191, the main combustion period BURN2 [deg] is calculated by the following equation similar to the equation (19).
[0121]

Where AF2: reaction area of flame nucleus [m²]
Here, BR2 on the right side of Expression (22) is a change in the combustion mass ratio from the start time to the end time of the main combustion period. Since it is considered that the combustion mass ratio BR becomes 2% at the end of the initial combustion period, and then the main combustion period starts, the combustion mass ratio BR reaches 60% and the main combustion period ends, BR2 = 60 %-2% = 58% is set. AF2 is an average reaction area in the growth process of the flame nucleus, and is a fixed value experimentally determined in advance, similarly to AF1 in Expression (19).
[0122]
In the main combustion period, the volume of the combustion chamber changes with the top dead center of compression in between. That is, it can be considered that the compression top dead center position exists approximately at the center between the start time of the main combustion period and the end time of the main combustion period. Further, near the compression top dead center, the combustion chamber volume does not change much even if the crank angle changes. Therefore, the combustion chamber volume during the main combustion period is represented by the combustion chamber volume VTDC at the compression top dead center.
[0123]
FIG. 11 is for calculating the basic ignition timing MBTCAL [degBTDC], and is executed every fixed time (for example, every 10 msec). It is executed following the later executed flow of FIGS.
[0124]
In step 41, the initial combustion period BURN1 calculated in step 171 in FIG. 8, the main combustion period BURN2 calculated in step 191 in FIG. 10, and the crank equivalent to the ignition timing dead time calculated in step 16 in FIG. The angle IGNDEAD and the reference crank angle θPMAX calculated in step 17 of FIG. 5 are read.
[0125]
In step 42, the sum of the initial combustion period BURN1 and the main combustion period BURN2 is calculated as the combustion period BURN [deg].
[0126]
In step 43, the basic ignition timing MBTCAL [degBTDC] is calculated by the following equation.
[0127]
MBTCAL = BURN−θPMAX + IGNDEAD (23)
In step 44, a value obtained by subtracting the crank angle IGNDEAD corresponding to the ignition dead time from the basic ignition timing MBTCAL is calculated as the previous combustion start timing MBTCYCL [degBTDC].
[0128]
The basic ignition timing MBTCAL calculated in this way is transferred to the ignition register as an ignition timing command value, and an ignition signal for cutting off the primary current from the engine controller 31 at the timing when the actual crank angle matches this ignition timing command value is output. Output to the ignition coil 13.
[0129]
Further, assuming that the basic ignition timing MBTCAL calculated in step 43 is used as the ignition timing command value for the current cycle, the previous combustion start timing MBTCYCL calculated in step 44 is not changed until the ignition timing for the next cycle. 8 in step 162.
[0130]
Next, FIG. 12 is for calculating the residual inert gas ratio MRESFR in the combustion chamber 5, and is executed at regular intervals (for example, every 10 msec). This flow is executed prior to the flow of FIG.
[0131]
In step 51, the output of the air flow meter 32 and the target equivalent ratio TFBYA are read. In step 52, based on the output of the air flow meter 32, a fresh air amount (cylinder fresh air amount) MACYL flowing into the combustion chamber 5 is calculated. A known method may be used for calculating the cylinder fresh air amount MACYL (see Japanese Patent Application Laid-Open No. 2001-50091).
[0132]
In step 53, the internal inert gas amount MRES in the combustion chamber 5 is calculated. The calculation of the internal inert gas amount MRES will be described with reference to the flowchart of FIG.
[0133]
In FIG. 13 (subroutine of step 53 in FIG. 12), in step 61, the inert gas amount MRESCYL at the exhaust valve closing timing EVC in the combustion chamber 5 is calculated. The calculation of the inert gas amount MRESCYL will be further described with reference to the flowchart of FIG.
[0134]
In FIG. 14 (subroutine of step 61 in FIG. 13), in step 71, the exhaust valve closing timing EVC [degBTDC], the exhaust temperature TEXH [K] detected by the temperature sensor 45, and the exhaust pressure PEXH [kPa] detected by the pressure sensor 46. ] Is read.
[0135]
Here, just like the intake valve closing timing IVC is known from the command value given to the intake VTC mechanism 27, the exhaust valve closing timing EVC is also known from the command value given to the exhaust VTC mechanism 28.
[0136]
In step 72, a volume VEVC of the combustion chamber 5 at the exhaust valve closing timing EVC is calculated. This may be obtained by searching a table using the exhaust valve closing timing as a parameter, similarly to the volume VIVC at the intake valve closing timing IVC. That is, when the exhaust valve VTC mechanism 28 is provided, the volume VEVC of the combustion chamber 5 at the exhaust valve closing timing EVC may be obtained by searching the table shown in FIG. 21 from the exhaust valve closing timing EVC. When the exhaust VTC mechanism 28 is not provided, it can be given as a constant.
[0137]
Further, although not shown, when a mechanism for changing the compression ratio is provided, the combustion chamber volume VEVC at the exhaust valve closing timing according to the change amount of the compression ratio is obtained from the table. When a mechanism for changing the compression ratio is provided in addition to the exhaust VTC mechanism 28, the combustion chamber volume at the exhaust valve closing timing is obtained by searching a map corresponding to the exhaust valve closing timing and the compression ratio change amount.
[0138]
In step 73, the gas constant REX of the inert gas in the combustion chamber 5 is obtained by searching the table shown in FIG. 22 from the target equivalent ratio TFBYA. As shown in FIG. 22, the gas constant REX of the inert gas is smallest when the target equivalent ratio TFBYA is 1.0, that is, when the stoichiometric air-fuel ratio is reached, and becomes larger when it is larger or smaller.
[0139]
In step 74, the temperature TEVC of the combustion chamber 5 at the exhaust valve closing timing EVC is estimated based on the exhaust gas temperature TEXH. Simply, the exhaust temperature TEXH may be used as it is as TEVC. Since the temperature TEVC at the exhaust valve closing timing of the combustion chamber 5 changes depending on the amount of heat corresponding to the fuel injection amount of the injector 21, the calculation accuracy of the TEVC is improved by taking such characteristics into consideration.
[0140]
In step 75, the pressure PEVC at the exhaust valve closing timing EVC of the combustion chamber 5 is calculated based on the exhaust pressure PEXH. In brief, the exhaust pressure PEXH may be set to PEVC.
[0141]
In step 76, the exhaust valve of the combustion chamber 5 is obtained from the volume VEVC of the combustion chamber 5 at the exhaust valve closing timing EVC, the temperature TEVC at the exhaust valve closing timing EVC, the pressure PEVC at the exhaust valve closing timing EVC, and the gas constant REX of the inert gas. The inert gas amount MRESCYL at the closing timing EVC is calculated by the following equation.
[0142]
MRESCYL = (PEVC × VEVC) / (REX × TEVC) (24)
When the calculation of the inert gas amount MRESCYL at the exhaust valve closing timing EVC of the combustion chamber 5 is completed in this way, the process returns to FIG. 13, and in step 62, the overlap of the intake and exhaust valves 15 and 16 (“O / L” in FIG. During the overlap, the inert gas amount MRESOL that is blown back during the overlap, which is the inert gas amount that blows back from the exhaust side to the intake side.
[0143]
The calculation of the inert gas amount MRESOL will be described with reference to the flowchart of FIG.
[0144]
In FIG. 15 (subroutine of step 62 in FIG. 13), in step 81, the intake valve opening timing IVO [degBTDC], the exhaust valve closing timing EVC [degBTDC], and the exhaust valve of the combustion chamber 5 calculated in step 74 of FIG. The temperature TEVC at the closing timing EVC is read.
[0145]
Here, since the intake valve opening timing IVO is a timing preceding the intake valve closing timing IVC by the opening angle of the intake valve 15, the opening angle of the intake valve 15 (which is known in advance) before the intake valve closing timing IVC. You can ask.
[0146]
In step 82, the overlap amount VTCOL [deg] of the intake and exhaust valves is calculated from the following equation based on the intake valve opening timing IVO and the exhaust valve closing timing EVC.
[0147]
VTCOL = IVO + EVC (25)
For example, when the actuator for intake VTC mechanism 27 is not energized, intake valve opening timing IVO is at the intake top dead center position, and when the actuator for intake VTC mechanism 27 is energized, the intake valve opening timing is advanced from intake top dead center. When the actuator for the exhaust VTC mechanism 28 is not energized, the exhaust valve closing timing EVC is at the exhaust top dead center. When the actuator for the exhaust valve VTC mechanism 28 is energized, the exhaust valve closing timing EVC is set at the exhaust top dead center. In the case of a more advanced characteristic, the sum of IVO and EVC is the overlap amount VTCOL of the intake and exhaust valves.
[0148]
In step 83, the integrated effective area ASUMOL during the overlap is calculated by searching the table shown in FIG. 23 from the overlap amount VTCOL of the intake and exhaust valves. As shown in FIG. 23, the integrated effective area ASAMOL during the overlap is a value that increases as the overlap amount VTCOL of the intake and exhaust valves increases.
[0149]
Here, FIG. 24 is an explanatory diagram of the integrated effective area ASUMOL during the overlap of the intake and exhaust valves. The horizontal axis shows the crank angle, and the vertical axis shows the respective opening areas of the intake valve 12 and the exhaust valve 15. I have. The effective opening area at any time during the overlap is the smaller of the exhaust valve opening area and the intake valve opening area. The integrated effective area ASAMOL for the entire period during the overlap is the integrated value (the shaded portion in the figure) during the period when the intake valve 15 and the exhaust valve 16 are open.
[0150]
By calculating the integrated effective area ASAMOL during the overlap in this manner, the amount of overlap between the intake valve 15 and the exhaust valve 16 can be approximated to one orifice (outflow hole), and the state of the exhaust system can be determined. The flow rate of the gas passing through the virtual orifice can be simply calculated from the state of the intake system.
[0151]
In step 84, the specific heat ratio SHEATR of the inert gas remaining in the combustion chamber 5 is determined by searching a map shown in FIG. 25 from the target equivalent ratio TFBYA and the temperature TEVC at the exhaust valve closing timing EVC of the combustion chamber 5. calculate. As shown in FIG. 25, the specific heat ratio SHEATR of the inert gas remaining in the combustion chamber becomes smallest when the target equivalent ratio TFBYA is near 1.0, and becomes larger when it is larger or smaller. Further, under the condition that the target equivalent ratio TFBYA is constant, the temperature TEVC becomes lower as the temperature TEVC at the exhaust valve closing timing EVC of the combustion chamber 5 becomes higher.
[0152]
In step 85, a supercharge determination flag TBCRG and a choke determination flag CHOKE are set. The setting of the supercharge determination flag TBCRG and the choke determination flag CHOKE will be described with reference to the flow of FIG.
[0153]
In FIG. 16 (subroutine of step 85 in FIG. 15), in step 101, the intake pressure PIN detected by the intake pressure sensor 44 and the pressure PEVC at the exhaust valve closing timing EVC of the combustion chamber 5 calculated in step 75 of FIG. Read.
[0154]
In step 102, an intake / exhaust pressure ratio PINBYEX is calculated from the intake pressure PIN and the pressure PEVC at the exhaust valve closing timing EVC of the combustion chamber 5 by the following equation.
[0155]
PINBYEX = PIN / PEVC (26)
The intake / exhaust pressure ratio PINBYEX is an infinite number, and is compared with 1 in step 103. If the intake / exhaust pressure ratio PINBYEX is 1 or less, it is determined that there is no supercharging, and the routine proceeds to step 104, where the supercharging determination flag TBCRG (initial setting to zero) = 0.
[0156]
If the intake / exhaust pressure ratio PINBYEX is greater than 1, it is determined that there is supercharging, and the routine proceeds to step 105, where the supercharging determination flag TBCRG = 1.
[0157]
In step 106, the specific heat ratio MIXAIRSHR of the air-fuel mixture is obtained by searching the table shown in FIG. 26 from the target equivalent ratio TFBYA read in step 51 in FIG. 12, and this is calculated in step 107. Replace with SHEATR. As shown in FIG. 26, the specific heat ratio MIXAIRSHR of the air-fuel mixture is a value that increases as the target equivalent ratio TFBYA decreases.
[0158]
In Steps 106 and 107, the reason why the specific heat ratio SHEATR of the inert gas is replaced with the specific heat ratio MIXAIRSHR of the mixture is in consideration of supercharging such as turbocharging or inertia supercharging. That is, at the time of supercharging, the gas flow during the overlap of the intake and exhaust valves goes from the intake system to the exhaust system (blows through), and in this case, the specific heat ratio of the gas passing through the virtual orifice is determined by the specific heat of the inert gas. By changing the ratio to the specific heat ratio of the air-fuel mixture, the amount of gas flowing through is accurately estimated, and the amount of internal inert gas is accurately calculated.
[0159]
In step 108, the minimum and maximum choke determination thresholds SLCHOKEL and SLCHOKEH are calculated by the following equations based on the specific heat ratio SHEATR of the inert gas calculated in step 84 of FIG. 15 or steps 106 and 107 of FIG. I do.
[0160]

These choke determination thresholds SLCHOKEL and SLCHOKEH are calculated as choke limit values.
[0161]
In step 108, when it is difficult to calculate each power of (27a) right side and (27b) right side, the calculation results of equations (27a) and (27b) are converted into a table of minimum choke determination threshold value SLCHOKEL and a maximum choke determination. The threshold SLCHOKEH may be stored in the memory of the engine controller 31 in advance as a table, and may be obtained by searching the table from the specific heat ratio SEATR of the inert gas.
[0162]
In steps 109 and 110, it is determined whether or not the intake / exhaust pressure ratio PINBYEX is in the range of not less than the minimum choke determination threshold value SLCHOKEEL and not more than the maximum choke determination threshold value SLCHOKEH, that is, whether or not there is a choke state. judge. If the intake / exhaust pressure ratio PINBYEX is within the range, it is determined that there is no choke, and the routine proceeds to step 111, where the choke determination flag CHOKE (initial setting to zero) = 0.
[0163]
If the intake / exhaust pressure ratio P1NBYEX is not within the range, it is determined that there is choke, and the routine proceeds to step 112, where the choke determination flag CHOKE = 1.
[0164]
When the setting of the supercharging determination flag and the setting of the choke determination flag are completed in this way, the process returns to FIG. 15, and the following four cases are performed in steps 86 to 88.
[0165]
<1> When the supercharge determination flag TBCRG = 0 and the choke determination flag CHOKE = 0
<2> When the supercharge determination flag TBCRG = 0 and the choke determination flag CHOKE = 0
<3> When the supercharge determination flag TBCRG = 0 and the choke determination flag CHOKE = 1
<4> When the supercharging determination flag TBCRG = 1 and the choke determination flag CHOKE = 0
In the case of <1>, the routine proceeds to step 89, in which the average blowback inert gas flow rate MRESOLtmp1 during the overlap without supercharging and no chalk is determined. In the case of <3>, the flow returns to step 91 when the inert gas flow rate MRESOLtmp2 during the overlap with the choke is present. In the case of <4>, the routine proceeds to step 92, where the blowback inert gas flow rate MRESOLtmp4 when there is supercharging and choke is calculated, and the calculation result is transferred to the blowback inert gas flow rate MRESOLtmp during overlap.
[0166]
Here, the calculation of the inert gas flow rate MRESOLtmp1 to be blown back during the overlap when there is no supercharging and no choke will be described with reference to the flow of FIG.
In FIG. 17 (subroutine of step 89 in FIG. 15), in step 121, the gas constant REX of the inert gas and the pressure PEVC at the exhaust valve closing timing of the combustion chamber 5 calculated in steps 73 and 75 in FIG.
[0167]
In step 122, a density term MRSOLD used in a gas flow rate calculation formula described later is based on the gas constant REX of the inert gas and the temperature TEVC at the exhaust valve closing timing of the combustion chamber 5 read in step 81 of FIG. Is calculated by the following equation.
[0168]
MRSOLD = SQRT {1 / (REX × TEVC)} (28)
Here, “SQRT” on the right side of the equation (28) is a function for calculating the square root of the value in parentheses immediately to the right.
[0169]
If it is difficult to calculate the square root of the density term MRSOLD, the calculation result of equation (28) is stored in advance in the memory of the engine controller 31 as a map, and the gas constant REX and the temperature of the combustion chamber 5 at the time of closing the exhaust valve. It may be obtained by searching the map from TEVC.
[0170]
In step 123, based on the specific heat ratio SHEATR of the inert gas calculated in step 84 in FIG. 15 and the intake / exhaust pressure ratio PINBYEX calculated in step 102 in FIG. The pressure difference term MRSOLP to be used is calculated by the following equation.
[0171]

In step 124, from the density term MRSOLD, the pressure difference term MRSOLP, and the pressure PEVC when the exhaust valve of the combustion chamber 5 is closed, the blowback inert gas flow rate MRESOLtmp1 during the overlap without supercharging and without choke is given by the following equation. (Calculation formula of gas flow rate), and the calculated value is transferred to the inert gas flow rate MRESOLtmp in the overlapped state at step 125.
[0172]
MRESOLtmp1 = 1.4 × PEVC × MRSOLD × MRSOLP (30)
Next, the calculation of the flow rate of the inert gas to be blown back when there is no supercharging and there is a choke will be described with reference to the flow of FIG.
In steps 131 and 132 in FIG. 18 (subroutine of step 90 in FIG. 15), the gas constant REX of the inert gas and the pressure PEVC at the time of closing the exhaust valve of the combustion chamber 5 are read in the same manner as steps 121 and 122 in FIG. From these, the density term MRSOLD is calculated by the aforementioned equation (28).
[0173]
In step 133, based on the specific heat ratio SHEATR of the inert gas calculated in step 84 of FIG. 15, the choke pressure difference term MRSOLPC is calculated by the following equation.
[0174]

If it is difficult to calculate the power and the square root of the equation (31), the calculation result of the equation (31) is stored in the memory of the engine controller 31 in advance as a table of the pressure difference term MRSOLPC during choke. , May be obtained by searching the table from the specific heat ratio SEATR of the inert gas.
[0175]
In step 134, from the density term MRSOLLD, the choke-time pressure difference term MRSOLPC, and the pressure PEVC at the time of closing the exhaust valve of the combustion chamber 5, the inert gas flow rate MRESOLtmp2 that is blown back during the overlap without supercharging and with choke is determined. It is calculated by the formula, and the calculated value is transferred to the flow back inert gas flow rate MRESOLtmp during the overlap in step 135.
[0176]
MRESOLtmp2 = PEVC × MRSOLD × MRSOLPC (32)
Next, the calculation of the blowback gas flow rate when there is supercharging and no choke will be described with reference to the flow of FIG.
In step 141 of FIG. 19 (subroutine of step 91 in FIG. 15), the intake pressure PIN detected by the intake pressure sensor 44 is read.
[0177]
In step 142, the supercharging pressure difference term MRSOLPT is obtained from the specific heat ratio SHEATR of the inert gas calculated in steps 106 and 107 in FIG. 16 and the intake / exhaust pressure ratio PINBYEX calculated in step 102 in FIG. Is calculated by the following equation.
[0178]

If it is difficult to calculate the power and the square root of the equation (33), the calculation result of the equation (33) is stored in advance in the memory of the engine controller 31 as a map of the pressure difference term MRSOLPT at the time of supercharging. It may be determined by searching the map from the specific heat ratio SHEATR of the inert gas and the intake / exhaust pressure ratio PINBYEX.
[0179]
In step 143, based on the pressure difference term MRSOLPT during supercharging and the intake pressure PIN, an inert gas flow rate MRESOLtmp3 during back-up during supercharging with supercharging and without choke is calculated by the following equation. At 144, the flow is returned to the inert gas flow rate MRESOLtmp that is blown back during the overlap.
[0180]
MRESOLtmp3 = −0.152 × PIN × MRSOLPT (34)
Here, by setting the flowback inert gas flow rate MRESOLtmp3 of the expression (34) to a negative value, the gas flow rate of the air-fuel mixture flowing through the intake system to the exhaust system during the overlap can be represented.
[0181]
Next, the calculation of the flow rate of the inert gas blown back during the overlap with the supercharge and the choke will be described with reference to the flow of FIG.
In FIG. 20 (subroutine of step 92 in FIG. 15), in steps 151 and 152, the intake pressure PIN detected by the intake pressure sensor 44 is read as in step 141 in FIG. The term MRSOLPC is calculated by the aforementioned equation (31).
[0182]
In step 153, based on the choke-time pressure difference term MRSOLPC and the intake pressure PIN, an overlapping blowback gas flow rate MRESOLtmp4 with supercharging and choke is calculated by the following equation, and the calculated value is exceeded in step 154. The flow is returned to the inert gas flow rate MRESOLtmp during the lap.
[0183]
MRESOLtmp4 = −0.108 × PIN × MRSOLPC (35)
Here, the flowback inert gas flow rate MRESOLtmp4 of the equation (35) can be set to a negative value, similarly to MRESOLtmp3, to represent the gas flow rate of the air-fuel mixture flowing from the intake side to the exhaust side during the overlap.
[0184]
After the calculation of the inert gas flow rate MRESOLtmp during the overlap, which is divided according to the combination of the presence or absence of the supercharging and the presence or absence of the choke, the process returns to FIG. From the inert gas flow rate MRESOLtmp and the integrated effective area ASUMOL during the overlap period, the blow-back inert gas amount MRESOL during the overlap is calculated by the following equation.
[0185]

When the calculation of the inert gas amount MRESOL returned during the overlap in this way is completed, the process returns to FIG. 13. In step 63, the inert gas amount MRESCYL at the exhaust valve closing timing EVC in the combustion chamber 5 and the blowback during the overlap are returned. The gas amount MRESOL is added, that is, the internal inert gas amount MRES is calculated by the following equation.
[0186]
MRES = MRESCYL + MRESOL ... (37)
As described above, when there is a supercharging, the inert gas flow rate (MRESOLtmp3, MRESOLtmp4) during the overlap becomes negative during the overlap. Therefore, the inert gas amount MRESOL during the overlap in the above formula (36) becomes negative. According to the equation (37), the internal inert gas amount is reduced by the amount MRESOL of the blown-back inert gas during the overlap.
[0187]
When the calculation of the internal inert gas amount MRES is completed in this way, the process returns to FIG. 12, and in step 54, using the internal inert gas amount MRES and the target equivalent ratio TFBYA, the residual inert gas ratio MRESFR is calculated by the following equation. (Ratio of internal inert gas amount to total gas amount in combustion chamber 5) is calculated.
[0188]

This completes the calculation of the residual inert gas ratio MRESFR.
[0189]
(Effect of this embodiment)
In the present embodiment, the reaction probability RPROBA is obtained from the mole fraction of fuel and the mole fraction of oxygen. These molar fractions can be calculated from the target equivalent ratio TFBYA and the residual inert gas ratio MRESFR as shown in the equation (68), and the residual inert gas ratio MRESFR is obtained by calculating the residual inert gas mass MRES, It can be determined based on the air mass MACYL and the target equivalent ratio TFBYA. Therefore, the reaction probability RPROBA can be obtained by detecting the residual inert gas mass MRES, the intake air mass MACYL, and the target equivalent ratio TFBYA. Then, the reaction probability RPROBA, the laminar combustion velocity (SL1, SL2), which is the combustion velocity of the combustion gas in a laminar flow state, and the combustion gas volume equivalent volume (V0, VTDC) approximated to the combustion gas volume, The combustion period BURN (= BURN1 + BURN2) from the start of combustion to the reference crank angle θPMAX is calculated based on the change in the combustion mass ratio (BR1, BR2) up to the reference crank angle θPMAX (predetermined crank angle). Further, it is possible to calculate the combustion period BURN without using the unburned gas density unlike the conventional apparatus, and thereby it is possible to calculate the basic ignition timing MBTCAL from which the MBT can be obtained accurately and easily. As a method of calculating the reaction probability RPROBA, for example, a method is also conceivable in which a map is created for each assumed driving state and the map is calculated based on the map. However, such a method requires a large number of man-hours for matching. Become. However, in the present embodiment, as described above, the reaction probability RPROBA is set to the residual inert gas mass m_EGR, Intake air mass m_AIRAre detected and calculated from them, so that such matching man-hours are not required.
[0190]
The average molecular weight MF of the fuel changes depending on the cooling water temperature TWK. The lower the temperature, the more "light components". Therefore, the average molecular weight MF of the fuel is smaller, but the higher the temperature, the higher the average molecular weight MF of the fuel. Therefore, if the change characteristics are mapped and the fuel average molecular weight MF with respect to the engine cooling water temperature is determined from this map, a more accurate reaction probability RPROBA can be calculated. By setting the average molecular weight MF to a constant value, the reaction probability RPROBA can be calculated more quickly. If the control is performed near the stoichiometric air-fuel ratio, the control may be performed with TFBYA = 1.0 (constant value) without detecting the air-fuel ratio. By doing so, higher-speed processing becomes possible.
[0191]
Without being limited to the embodiments described above, various modifications and changes can be made within the scope of the technical idea, and it is apparent that they are equivalent to the present invention.
[0192]
For example, in the above embodiment, for example, the oxygen mole fraction x₀₂Is calculated, and its oxygen mole fraction x₀₂Is described in detail in the case where the reaction probability RPROBA is calculated from the following equation.₀₂From the fuel mole fraction x_FCan be calculated. Therefore, first, the fuel mole fraction x_FIs calculated, and the fuel mole fraction x_FThe same effect can be obtained by calculating the reaction probability RPROBA from
[0193]
In the embodiment, the case where the external EGR device for introducing a part of the exhaust gas into the intake air is not provided is described. However, the present invention can be applied to the case where the external EGR device is provided. In this case, the residual inert gas ratio by the external EGR device may be added to the residual inert gas ratio MRESFR. A method for calculating the residual inert gas ratio by an external EGR device is known (see Japanese Patent Application Laid-Open No. H10-141150).
[0194]
In the invention described in claim 1, the functions of the mole fraction detecting means and the reaction probability calculating means are determined by step 15 in FIG. 5, and the functions of the combustion rate calculating means are determined by step 168 in FIG. 8 and step 188 in FIG. The function of the volume calculation means is determined by step 162 in FIG. 8, the function of the mass calculation means is determined by step 171 in FIG. 8, and the function of the combustion period calculation means is determined by step 171 in FIG. 191, the function of the basic ignition timing calculating means is fulfilled by step 43 of FIG.
[Brief description of the drawings]
FIG. 1 is a control system diagram of an engine according to an embodiment.
FIG. 2 is a block diagram of ignition timing control executed by an engine controller.
FIG. 3 is a pressure change diagram of a combustion chamber.
FIG. 4 is a characteristic diagram illustrating a change in a combustion mass ratio.
FIG. 5 is a flowchart for explaining calculation of a physical quantity.
FIG. 6 is a diagram illustrating a positional relationship between a crankshaft of an engine and a connecting rod.
FIG. 7 is a characteristic diagram of a reference crank angle.
FIG. 8 is a flowchart for explaining calculation of an initial combustion period.
FIG. 9 is a characteristic diagram of a temperature rise rate.
FIG. 10 is a flowchart for explaining calculation of a main combustion period.
FIG. 11 is a flowchart for explaining calculation of a basic ignition timing.
FIG. 12 is a flowchart for explaining calculation of a residual inert gas ratio.
FIG. 13 is a flowchart for explaining calculation of an internal inert gas amount.
FIG. 14 is a flowchart for explaining calculation of an inert gas amount at the time of EVC.
FIG. 15 is a flowchart for explaining the calculation of the amount of inert gas blown back during the overlap.
FIG. 16 is a flowchart for explaining setting of a supercharge determination flag and a choke determination flag.
FIG. 17 is a flowchart for explaining the calculation of the flow rate of the inert gas to be blown back during the overlap when there is no supercharging and there is no choke.
FIG. 18 is a flowchart for explaining the calculation of the inert gas flow rate that is blown back during the overlap when there is no supercharging and there is a choke;
FIG. 19 is a flowchart for explaining the calculation of the flow rate of the inert gas that is blown back during the overlap when there is a supercharge and there is no choke.
FIG. 20 is a flowchart for explaining the calculation of the flow rate of the inert gas that is blown back during the overlap when there is a supercharge and a choke is present.
FIG. 21 is a characteristic diagram of a combustion chamber volume at an exhaust valve closing time.
FIG. 22 is a characteristic diagram of a gas constant of an inert gas.
FIG. 23 is a characteristic diagram of an integrated effective area during an overlap.
FIG. 24 is an explanatory diagram of an integrated effective area during overlap.
FIG. 25 is a characteristic diagram of a specific heat ratio of an inert gas.
FIG. 26 is a characteristic diagram of a specific heat ratio of an air-fuel mixture.
[Explanation of symbols]
1 engine
5 Combustion chamber
11 Ignition device (spark ignition means)
15 Intake valve
21 Fuel injector
27 Intake VTC mechanism
31 Engine Controller
33, 34 Crank angle sensor
43 Intake air temperature sensor
44 Intake pressure sensor
45 Exhaust gas temperature sensor
46 Exhaust pressure sensor

Claims (9)

Molar fraction detection means for detecting the molar fraction of the combustion component in the total number of moles in the combustion chamber,
Reaction probability calculation means for calculating a reaction probability indicating the ease of combustion of the combustion gas based on the mole fraction of the combustion component,
Combustion speed calculation means for calculating the combustion speed of the combustion gas based on the reaction probability,
Volume calculation means for calculating a volume corresponding to the volume of combustion gas in the combustion chamber,
Mass calculation means for calculating the mass of combustion gas burning in the combustion chamber from the start of combustion to the reference crank angle at which the combustion pressure becomes maximum,
A combustion period calculating unit that calculates a combustion period from the start of combustion to the reference crank angle based on the reaction probability, the combustion speed, the combustion gas volume equivalent volume, and the combustion gas mass;
Basic ignition timing calculation means for calculating a basic ignition timing at which MBT is obtained based on the combustion period;
Spark ignition means for performing spark ignition at the basic ignition timing,
An ignition timing control device for an internal combustion engine, comprising: The mole fraction of the combustion component is the mole fraction of the fuel,
The ignition timing control apparatus for an internal combustion engine according to claim 1, wherein: The mole fraction of the combustion component is a mole fraction of oxygen,
The ignition timing control apparatus for an internal combustion engine according to claim 1, wherein: The ignition timing control device for an internal combustion engine according to claim 1, wherein the mole fraction of the combustion component is a product of a mole fraction of fuel and a mole fraction of oxygen. Having a residual inert gas ratio calculation means for calculating a residual inert gas ratio that is a residual ratio of the inert gas in the total gas in the combustion chamber,
Calculating a mole fraction of the fuel based on the residual inert gas rate,
The ignition timing control device for an internal combustion engine according to claim 2 or 4, wherein: Having a residual inert gas ratio calculation means for calculating a residual inert gas ratio that is a residual ratio of the inert gas in the total gas in the combustion chamber,
Calculating the mole fraction of the oxygen based on the residual inert gas rate,
The ignition timing control device for an internal combustion engine according to claim 3 or 4, wherein: When changing the air-fuel ratio according to the operating conditions,
Means for calculating or detecting the air-fuel ratio,
Calculating the mole fraction of the fuel based on the air-fuel ratio,
The ignition timing control device for an internal combustion engine according to claim 5, wherein: When changing the air-fuel ratio according to the operating conditions,
Means for calculating or detecting the air-fuel ratio,
Calculating the molar fraction of the oxygen based on the air-fuel ratio,
7. The ignition timing control device for an internal combustion engine according to claim 6, wherein: Having engine temperature detecting means for detecting the engine temperature,
Correcting the mole fraction of the fuel according to the engine temperature,
The ignition timing control device for an internal combustion engine according to any one of claims 2, 4, 5, or 7, wherein:

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