JP2004239143A - Ignition control system of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide stable combustion by avoiding partial combustion. <P>SOLUTION: This control system has a means 31 for calculating a combustion period until a combustion mass rate becomes a prescribed value from a combustion start in a combustion chamber, a means 31 for calculating the total gas quantity in the combustion chamber, a means 44 for calculating compression starting time pressure of the combustion chamber, a means 31 for calculating the compression starting time volume of the combustion chamber, a means 31 for calculating the combustion starting time volume of the combustion chamber and a means 31 for calculating reference crank angle time pressure of the combustion chamber. This control system also has a means 31 for calculating a flame core growth speed at a reference crank angle on the basis of a calculation value of these combustion periods, the total gas quantity, compression starting time pressure, the compression starting time volume, the combustion starting time volume and reference crank angle time pressure, a means 31 for calculating an ignition frequency command value of plural times on the basis of this flame core growth speed and means 31 and 11 for performing multiple ignition on the basis of this calculated ignition frequency command value. <P>COPYRIGHT: (C)2004,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］、
Ｈ ：ピストンピン７６のＴＤＣからの距離［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。
【００５０】
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の吸気弁閉時期ＩＶＣにおける温度ＴＩＮＩ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、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内部不活性ガス率ＭＲＥＳＦＲから次式により求めることができる。
【００５１】
ＴＩＮＩ＝ＴＥＸＨ×ＭＲＥＳＦＲ＋ＴＣＯＬ×（１−ＭＲＥＳＦＲ）…（７）
ステップ１４では、燃焼室５内の混合気の燃えやすさを表す反応確率ＲＰＲＯＢＡ［％］を算出する。反応確率ＲＰＲＯＢＡは無次元の値であり、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。
【００５２】
ＲＰＲＯＢＡ＝ｆ３（ＭＲＥＳＦＲ、ＴＷＫ、ＴＦＢＹＡ）…（８）
具体的に説明すると、ＭＲＥＳＦＲ、ＴＷＫ、ＴＦＢＹＡの３つのパラメータの組み合わせによって得られる反応確率の最大値を１００％とし、これらのパラメータと反応確率ＲＰＲＯＢＡの関係を実験的に求め、求めた反応確率ＲＰＲＯＢＡをパラメータに応じたテーブルとしてエンジンコントローラ３１のメモリに予め格納しておく。ステップ１４ではパラメータに応じてこのテーブルを検索することにより反応確率ＲＰＲＯＢＡを求める。
【００５３】
具体的には、冷却水温ＴＷＫに応じて図７に示すような特性を有する水温補正係数のテーブルと、同様に設定された内部不活性ガス率補正係数のテーブル（図示しない）と、目標当量比Ｔｆｂｙａに応じて図８に示すような特性を有する当量比補正係数のテーブルを予めメモリに格納しておく。各補正係数の最大値はそれぞれ１．０であり、３種類の補正係数の積に反応確率の最大値１００％を掛け合わせることで、反応確率ＲＰＲＯＢＡを算出する。
【００５４】
各テーブルを説明すると、図７に示す水温補正係数は冷却水温ＴＷＫが高いほど大きく、冷却水温ＴＷＫが８０℃以上では１．０になる。図８に示す当量比補正係数は目標当量比ＴＦＢＹＡが１．０のとき、つまり理論空燃比のときに最大値の１．０となり、目標当量比が１．０より大きくても小さくても当量比補正係数は減少する。内部不活性ガス率補正係数は図示しないが、内部不活性ガス率ＭＲＥＳＦＲがゼロの場合に１．０となる。
【００５５】
ステップ１５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。
【００５６】
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９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。
【００５７】
最後にステップ１６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。
【００５８】
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。
【００５９】
図１０は初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を算出するためのもの、また図１２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１０、図１２は図５に続けて実行する。
図１０、図１２はどちらを先に実行してもかまわない。
【００６０】
まず図１０から説明すると、ステップ２１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］、エンジン回転速度ＮＲＰＭ［ｒｐｍ］、図５のステップ１４で算出されている反応確率ＲＰＲＯＢＡ［％］を読み込む。
【００６１】
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後述する。
【００６２】
ステップ２２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。
【００６３】
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。
【００６４】
ステップ２３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。
【００６５】
Ｅｃ＝ｆ７（Ｖ０、ＶＩＶＣ）＝Ｖ０／ＶＩＶＣ…（１２）
ステップ２４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。
【００６６】
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。
【００６７】
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。
【００６８】
図１１は（１３）式を図示したものである。従って、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。
【００６９】
ステップ２５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。
【００７０】
ステップ２６では、次式（公知）により層流燃焼速度ＳＬ１［ｍ／ｓｅｃ］を算出する。
【００７１】
ＳＬ１＝ＳＬｓｔｄ×（Ｔ０×Ｔｓｔｄ）^２．１８×（Ｐ０／Ｐｓｔｄ）^{−０．１６}…（１５）
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］、
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。
【００７２】
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。従って、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。
【００７３】
従って、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。
【００７４】

ステップ２７では、初期燃焼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。
【００７５】
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。
【００７６】
最終的に、初期燃焼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。
【００７７】
ＳＴ１＝ｆ１０（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。
【００７８】
ステップ２８では層流燃焼速度Ｓ１と乱れ強さＳＴ１から、初期燃焼におけるガスの燃焼速度ＦＬＡＭＥ１［ｍ／ｓｅｃ］を次式により算出する。
【００７９】
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。
【００８０】
ステップ２９では、次式により初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を算出する。
【００８１】

ただし、ＡＦ１：火炎核の反応面積（固定値）［ｍ^２］、
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量であり、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）に変換するための措置である。火炎核の反応面積ＡＦ１は実験的に設定される。
【００８２】
次に図１２のフローに移ると、ステップ３１では回転速度ＮＲＰＭ、図５のステップ１４で算出されている反応確率ＲＰＲＯＢＡを読み込む。
【００８３】
ステップ３２では主燃焼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。
【００８４】
ＳＴ２＝ｆ１１（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。
【００８５】
ステップ３３では、層流燃焼速度ＳＬ２［ｍ／ｓｅｃ］と主燃焼におけるガス流動の乱れ強さＳＴ２とから、主燃焼における燃焼速度ＦＬＡＭＥ２［ｍ／ｓｅｃ］を次式により算出する。
【００８６】
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。
【００８７】
前述のように主燃焼期間ＢＵＲＮ２の長さは燃焼室５内の温度や圧力の変化の影響を受けにくい。従って、層流燃焼速度ＳＬ２には予め実験的に求めた固定値を適用する。
【００８８】
ステップ３４では、主燃焼期間ＢＵＲＮ２［ｄｅｇ］を（１９）式に類似した次式で算出する。
【００８９】

ただし、Ｖ２：燃焼室５の主燃焼期間開始時容積［ｍ^３］、
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量である。初期燃焼期間の終了時期に燃焼質量割合が２％になり、その後、主燃焼期間が開始し、燃焼質量割合が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。燃焼室５の主燃焼期間開始時における容積Ｖ２も固定値である。
【００９０】
図１３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１０、図１２のうち遅く実行されるフローに続けて実行する。
【００９１】
ステップ４１では、図１０のステップ２９で算出されている初期燃焼期間ＢＵＲＮ１、図１２のステップ３４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１５で算出されている基準クランク角θＰＭＡＸを読み込む。
【００９２】
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。
【００９３】
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。
【００９４】
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。
【００９５】
このようにして算出した基本点火時期ＭＢＴＣＡＬは、後述するように、部分燃焼発生限界点火時期ＣＣＬＣＡＬ［ｄｅｇＢＴＤＣ］と比較され、より遅角側の値が点火時期指令値ＱＡＤＶ［ｄｅｇＢＴＤＣ］として選択される。この点火時期指令値ＱＡＤＶは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ＱＡＤＶ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。
【００９６】
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１０のステップ２２において用いられる。
【００９７】
以上のように、本実施形態においては、燃焼室５内の未燃ガス量などの質量計算を行わずにＭＢＴの得られる点火時期である基本点火時期ＭＢＴＣＡＬを算出するので、計算負荷を小さく抑えることができる。
【００９８】
また、上記（１９）式に示したように初期燃焼期間ＢＵＲＮ１を、燃焼開始時期における燃焼室容積Ｖ０と、混合気の燃焼のしやすさを表す反応確率ＲＰＲＯＢＡと、燃焼速度ＦＬＡＭＥ１の関数で表している。ここで、燃焼開始時期における燃焼室容積Ｖ０が大きいほど、反応確率ＲＰＲＯＢＡが小さいほど、燃焼速度ＦＬＡＭＥ１が遅いほど、それぞれ初期燃焼期間ＢＵＲＮ１が長くなり、結果として基本点火時期ＭＢＴＣＡＬが進角する。
【００９９】
同様に、上記（２２）式に示したように主燃焼期間ＢＵＲＮ２を、主燃焼期間の開始時期における燃焼室容積Ｖ２と、混合気のしやすさを表す反応確率ＲＰＲＯＢＡと、燃焼速度ＦＬＡＭＥ２の関数で表している。ここで、主燃焼期間開始時期における燃焼室容積Ｖ２が大きいほど、反応確率ＲＰＲＯＢＡが小さいほど、燃焼速度ＦＬＡＭＥ２が遅いほど、それぞれ主燃焼期間ＢＵＲＮ２が長くなり、結果として点火時期ＭＢＴＣＡＬが進角する。
【０１００】
このように、燃焼期間ＢＵＲＮ１とＢＵＲＮ２を、燃焼期間に影響を与える様々なパラメータの関数として算出することで、燃焼期間ＢＵＲＮ１とＢＵＲＮ２を正確に算出することができる。結果として、燃焼期間ＢＵＲＮ１とＢＵＲＮ２に基づき算出される基本点火時期ＭＢＴＣＡＬも高精度に算出することができる。また、燃焼期間ＢＵＲＮを温度や圧力が大きく影響を受けやすい火炎核成長期間に相当する初期燃焼期間ＢＵＲＮ１と、温度や圧力の影響の少ない主燃焼期間とに分けて算出しているので、燃焼期間ＢＵＲＮの算出精度が向上する。燃焼期間ＢＵＲＮを３以上にさらに分割することで、算出精度のさらなる向上も可能である。
【０１０１】
実施形態では、初期燃焼期間ＢＵＲＮ１の算出に用いる燃焼速度ＦＬＡＭＥ１を層流燃焼速度ＳＬ１と乱れ強さＳＴ１の積として、また主燃焼期間ＢＵＲＮ２の算出に用いる燃焼速度ＦＬＡＭＥ２を層流燃焼速度ＳＬ２と乱れ強さＳＴ２の積としてそれぞれ算出しているが、特開平１０−３０５３５号公報に記載されているように足し算による算出方法で求めても良い。
【０１０２】
実施形態では、初期燃焼期間を燃焼質量割合でゼロから２％まで（つまりＢＲ１＝２％）、主燃焼期間を燃焼質量割合で２〜６０％まで（つまりＢＲ２＝５８％）と規定したが、本発明は必ずしもこの数値に限定されるものでない。
【０１０３】
次に、図１４は燃焼室５内の内部不活性ガス率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。
【０１０４】
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）。
【０１０５】
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１５のフローにより説明する。
【０１０６】
図１５（図１４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１６のフローにより説明する。
【０１０７】
図１６（図１５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。
【０１０８】
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。
【０１０９】
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２３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。
【０１１０】
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。
【０１１１】
ステップ７３では、目標当量比ＴＦＢＹＡから図２４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２４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。
【０１１２】
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。
【０１１３】
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。
【０１１４】
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。
【０１１５】
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１５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。
【０１１６】
この不活性ガス量ＭＲＥＳＯＬの算出については図１７のフローにより説明する。
【０１１７】
図１７（図１５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１６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。
【０１１８】
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。
【０１１９】
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。
【０１２０】
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。
【０１２１】
ステップ８３では、吸排気弁のオーバーラップ量ＶＴＣＯＬから、図２５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２５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。
【０１２２】
ここで、図２６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。
【０１２３】
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。
【０１２４】
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２７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２７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。
【０１２５】
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１８のフローにより説明する。
【０１２６】
図１８（図１７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１６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。
【０１２７】
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。
【０１２８】
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。
【０１２９】
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。
【０１３０】
ステップ１０６では、図１４のステップ５１で読み込まれている目標当量比ＴＦＢＹＡから図２８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２８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。
【０１３１】
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。
【０１３２】
ステップ１０８では、図１７のステップ８４または図１８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。
【０１３３】

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。
【０１３４】
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。
【０１３５】
テップ１０９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１１０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。
【０１３６】
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１１１に進んでチョーク判定フラグＣＨＯＫＥ＝１とする。
【０１３７】
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１７に戻り、ステップ８６〜８８で次の４つの場合分けを行う。
【０１３８】
〈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。
【０１３９】
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１９のフローにより説明する
図１９（図１７ステップ８９のサブルーチン）においてステップ１２１では、図１６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。
【０１４０】
ステップ１２２では、不活性ガスのガス定数ＲＥＸと、図１７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。
【０１４１】
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。
【０１４２】
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。
【０１４３】
ステップ１２３では、図１７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１８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。
【０１４４】

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。
【０１４５】
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２０のフローにより説明する
図２０（図１７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１９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。
【０１４６】
ステップ１３３では、図１７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。
【０１４７】

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。
【０１４８】
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。
【０１４９】
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２１のフローにより説明する
図２１（図１７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。
【０１５０】
ステップ１４２では、図１８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１８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。
【０１５１】

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。
【０１５２】
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。
【０１５３】
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。
【０１５４】
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２２のフローにより説明する
図２２（図１７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２１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２０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。
【０１５５】
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。
【０１５６】
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。
【０１５７】
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１７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。
【０１５８】

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１５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。
【０１５９】
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。
【０１６０】
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１４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、次式により内部不活性ガス率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。
【０１６１】

これで内部不活性ガス率ＭＲＥＳＦＲの算出を総て終了する。
【０１６２】
このように本実施形態によれば、内部不活性ガス量ＭＲＥＳを、燃焼室５の排気弁閉時期における不活性ガス量ＭＲＥＳＣＹＬと、吸排気弁のオーバーラップ中の吹き返しガス量ＭＲＥＳＯＬとで構成し（図１５のステップ６３参照）、この場合に、燃焼室５の排気弁閉時期における温度ＴＥＶ及び圧力ＰＥＶＣを算出し（図１６のステップ７４、７５）、これら温度ＴＥＶＣ、圧力ＰＥＶＣと不活性ガスのガス定数ＲＥＸとに基づいて状態方程式（上記（２４）式）により燃焼室５の排気弁閉時期における不活性ガス量ＭＲＥＳＣＹＬを算出する（図１６のステップ７６参照）ようにしたので、特に、燃焼室５内部の状態量（ＰＥＶＣ、ＶＥＶＣ、ＴＥＶＣ）が刻々と変化する過渡運転時においても、運転条件に関わらず精度良く燃焼室５の排気弁閉時期における不活性ガス量ＭＲＥＳＣＹＬを算出（推定）できる。
【０１６３】
また、燃焼室５の排気弁閉時期における温度ＴＥＶＣ及び圧力ＰＥＶＣ、不活性ガスのガス定数ＲＥＸ及び比熱比ＳＨＥＡＴＲ、吸気圧力ＰＩＮに基づいてオーバーラップ中の吹き返し不活性ガス流量（ＭＲＥＳＯＬｔｍｐ１、ＭＲＥＳＯＬｔｍｐ２）を算出し（図１９、図２０参照）、このガス流量にオーバーラップ中の積算有効面積ＡＳＵＭＯＬを乗算して、オーバーラップ中の吹き返しガス量ＭＲＥＳＯＬを算出する（図１７のステップ９３参照）ようにしたので、精度良くオーバーラップ中吹き返しガス量ＭＲＥＳＯＬを算出（推定）できる。
【０１６４】
このように、燃焼室５の排気弁閉時期における不活性ガス量ＭＲＥＳＣＹＬ、オーバーラップ中吹き返しガス量ＭＲＥＳＯＬとも精度良く算出（推定）できると、これらの和である内部不活性ガス量ＭＲＥＳも精度良く算出（推定）できることになり、この精度良く推定することが可能となった内部不活性ガス量ＭＲＥＳに基づいて算出される内部不活性ガス率ＭＲＥＳＦＲを、点火時期の算出に用いる燃焼室５内の吸気弁閉時期ＩＶＣにおける温度ＴＩＮＩに活かすことで（図５のステップ１３参照）、燃焼室５内の吸気弁閉時期ＩＶＣにおける温度ＴＩＮＩを精度良く算出できる。また、精度良く推定することが可能となった内部不活性ガス量ＭＲＥＳを、燃料噴射量、バルブ開閉タイミング（オーバーラップ量）などにも活かすことで、エンジンを適切に制御することが可能である。
【０１６５】
また、不活性ガスのガス定数ＲＥＸや不活性ガスの比熱比ＳＨＥＡＴＲは、目標当量比ＴＦＢＹＡに応じた値としているので（図２４、図２７参照）、理論空燃比を外れた空燃比での運転時（例えば理論空燃比よりもリーンな空燃比で運転を行うリーン運転時、冷間始動時のようにエンジンが元々不安定な状態を安定させるために理論空燃比の空燃比よりもリッチ側の空燃比で運転するエンジン動直後、同じく大きな出力が要求されるために理論空燃比の空燃比よりもリッチ側の空燃比で運転する全負荷運転時）にも、燃焼室５の排気弁閉時期における不活性ガス量ＭＲＥＳＣＹＬ、オーバーラップ中吹き返しガス量ＭＲＥＳＯＬ、これらの合計である内部不活性ガス量ＭＲＥＳ、これに基づく内部不活性ガス率ＭＲＥＳＦＲを精度良く算出できる。
【０１６６】
また、オーバーラップ期間の積算有効面積ＡＳＵＭＯＬを仮想オリフィスの面積とし、この仮想オリフィスを排気が燃焼室５から吸気系へと吹き抜けると仮定しているので、オーバーラップ中の吹き返し不活性ガス量ＭＲＥＳＯＬの算出が簡略化されている。
【０１６７】
次に、図２９は点火回数指令値ｎ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１３のフローに続けて実行する。
【０１６８】
ステップ１６１では、図１４のステップ５２、５３で算出されているシリンダ新気量ＭＡＣＹＬ及び内部不活性ガス量ＭＲＥＳ、吸気圧力センサ４４（圧縮開始時圧力検出手段）により検出される吸気圧力ＰＩＮ、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、図１０のステップ２３、２５、２７で算出されている燃焼開始時有効圧縮比Ｅｃ、乱れ強さＳＴ１、図１３のステップ４２、４３で算出されている燃焼期間ＢＵＲＮ、基本点火時期ＭＢＴＣＡＬ、エンジン回転速度ＮＲＰＭを読み込む。
【０１６９】
ステップ１６２では、燃焼室５の総ガス量ＭＡＳＳＣを次式により算出する。
【０１７０】
ＭＡＳＳＣ＝ＭＡＣＹＬ＋ＭＲＥＳ…（３９）
ステップ１６３、１６４では、燃焼室５の基準クランク角時における平均温度Ｔｃ及び基準クランク角時における圧力Ｐｃを次式により算出する。
【０１７１】

ただし、ｎ：ポリトロープ指数、
Ｔｕｐ＃：定数、
Ｑ：６０％燃焼発熱量、
Ｖｕｐ＃：定数、
ここで、不可逆断熱変化の場合、ポリトーロープ指数ｎはガスの比熱比κに等しいので、（３９ｂ）式を書き換えると次式が得られる。
【０１７２】

（３９ｃ）式の定数Ｖｕｐ＃は燃焼質量が６０％まで燃焼し燃焼途中のガスになったときの分子量変化に伴うガス容積変化率である。１より若干大きな値（１．０３程度）を用いればよい。
【０１７３】
ステップ１６５では、基準クランク角時の基本火炎核成長速度Ｓｆｍｂｔ０［ｍ／ｓｅｃ］を次式により算出する。
【０１７４】

ただし、Ｖ２ ：燃焼室５の主燃焼期間開始時容積［ｍ^３］、
ＡＦ２：火炎核の反応面積［ｍ^２］、
ρｂ ：既燃ガス密度、
ここで、Ｖ２、ＡＦ２は上記（２２）式で既に用いられている。ρｂは燃焼質量が６０％まで燃焼したときのガス質量／既燃ガス体積であり、一定値である。
【０１７５】
次に、ＳＡＥペーパー２００１−０１−０９６０論文（火花点火エンジンにおける燃焼室内の火炎核の成長と伝播についてのモデリングと実験研究についてのもの）の記載に基づいて、上記（４０）式を導いた処を説明する。
【０１７６】
上記論文における連続の式及び火炎核へのアプローチによれば、質量燃焼モデルで、燃焼質量ｍｂの時間的変化が次式により定義されている。
【０１７７】
ｄｍｂ／ｄｔ＝ρｕ×Ａｂ×（Ｓｄｉｆｆ＋Ｓｃｏｍｂ）＋Ｃ×ρｕ×μｉｎ…（補１）
ただし、ｍｂ ：燃焼質量、
ρｕ ：未燃ガス密度、
Ａｂ ：既燃ガスの表面積、
Ｓｄｉｆｆ ：熱拡散速度、
Ｓｃｏｍｂ ：燃焼速度、
Ｃ ：液体の比熱、
この場合、（補１）式の右辺第２項は小さいので無視すると次式を得る。
【０１７８】
ｄｍｂ／ｄｔ＝ρｕ×Ａｂ×（Ｓｄｉｆｆ＋Ｓｃｏｍｂ）…（補２）
一方、燃焼質量ｍｂは、実験結果によれば、図３０において一点鎖線で示したように曲線で変化するのであるが、ここではその曲線の変化を、実線で示した直線で近似する。このとき、直線の傾きつまりｄｍｂ／ｄｔは幾何学的に次式のように表すことができる。
【０１７９】
ｄｍｂ／ｄｔ≒（ＭＡＳＳＣ×０．６）／ＢＵＲＮ…（補３）
この（補３）式と上記の（補２）式よりｄｍｂ／ｄｔを消去する。
【０１８０】

一方、上記論文において火炎核成長速度ｄｒ／ｄｔは次式により表されている。
【０１８１】

ただし、ｒ ：火炎核の半径、
ρｕ ：未燃ガス密度、
ρｂ ：既燃ガス密度、
Ｓｄｉｆｆ：熱拡散速度、
Ｓｃｏｍｂ：燃焼速度、
Ｖｂ ：既燃ガスの体積、
Ａｂ ：既燃ガスの表面積、
Ｔｂ ：既燃ガス温度、
Ｐ ：ガスの圧力、
（補５）式の火炎核成長速度ｄｒ／ｄｔを改めて本発明の基本火炎核成長速度Ｓｆｍｂｔ０とし、（補４）を代入して、Ｓｄｉｆｆ＋Ｓｃｏｍｂを消去すると、次式が得られる。
【０１８２】

ここで、（補６）式右辺第２項に対してさらに近似を行う。すなわち、ＴｂやＰは基準クランク角時期における温度Ｔｃや圧力Ｐｃであり、ｄＴｂやｄＰはそれぞれ圧縮開始時期から基準クランク角時期までの間の温度（Ｔｂ）や圧力（Ｐ）の変化量であるから、ｄＴｂはＴｃ−ＴＩＮＩ、またｄＰはＰｃ−ＰＩＮである。このとき、ｄｔに相当するのは圧縮開始時期より基準クランク角時期までのクランク角区間となるが、ここではこのクランク角区間に代えて微小クランク角である燃焼期間ＢＵＲＮ［ｄｅｇ］を適用する。
【０１８３】
従って、（補６）式において、ｄｔ→ＢＵＲＮ、Ｔｂ→Ｔｃ、ｄＴｂ→Ｔｃ−ＴＩＮＩ、Ｐ→Ｐｃ、ｄＰ→Ｐｃ−ＰＩＮの置き換えを行うと、次式が得られる。
【０１８４】

次に、（補７）式のＶｂは、主燃焼期間における燃焼室容積の変化が小さいので一定値とみなし、燃焼室５の主燃焼期間開始時期における容積を用いる。これは上記（２２）式のＶ２に等しい。また、（補７）式のＡｂは火炎核の成長過程における平均の火炎表面積、つまり上記（２２）式のＡＦ２に等しい。従って、Ｖｂ→Ｖ２、Ａｂ→ＡＦ２の置き換えを行うと、次式が得られる。
【０１８５】

このようにして（補８）式つまり上記（４０）式を導くことができた。
【０１８６】
ステップ１６６では、乱れ強さＳＴ１から図３１を内容とするテーブルを検索することにより、乱れ強さ補正係数Ｓｍｂを算出する。この補正係数Ｓｍｂは無名数であり、図３１に示したように乱れ強さＳＴ１が強くなるほど大きくなる値である。これは、ガス流動の乱れ強さＳＴ１は火炎核成長速度に寄与するので、ガス流動の乱れ強さＳＴ１を火炎核成長速度に反映させるためのものである。ガス流動の乱れ強さＳＴ１が火炎核成長速度にどのように寄与するかは、エンジン仕様により異なってくるので、補正係数Ｓｍｂの特性は実験により適合することになる。
【０１８７】
ステップ１６７ではこの乱れ強さ補正係数Ｓｍｂを基本火炎核成長速度Ｓｆｍｂｔ０に乗算して、つまり次式により基準クランク角時の火炎核成長速度Ｓｆｍｂｔ［ｍ／ｓｅｃ］を算出する。
【０１８８】
Ｓｆｍｂｔ＝Ｓｆｍｂｔ０×Ｓｍｂ …（４１）
ステップ１６８ではこの基準クランク角時の火炎核成長速度Ｓｆｍｂｔと燃焼期間ＢＵＲＮとから図３２を内容とするマップを検索することにより、点火回数ｎ１を、またステップ１６９では同じく燃焼開始時の火炎核成長速度Ｓｆｍｂｔとエンジン回転速度ＮＲＰＭとから図３３を内容とするマップを検索することにより、点火回数ｎ２をそれぞれ算出し、ステップ１７０でこれら点火回数ｎ１とｎ２のうちより大きい側の値を点火回数指令値ｎとして選択する。
【０１８９】
点火回数ｎ１は、図３２に示したように燃焼期間ＢＵＲＮが同じであれば基準クランク角時の火炎核成長速度Ｓｆｍｂｔが遅いほど、また基準クランク角時の火炎核成長速度Ｓｆｍｂｔが同じであれば燃焼期間ＢＵＲＮが長くなるほど２回、３回と大きくなる値である。燃焼期間が同じでありながら基準クランク角時の火炎核成長速度Ｓｆｍｂｔが遅いということは、あるいは基準クランク角時の火炎核成長速度Ｓｆｍｂｔが同じでありながら燃焼期間ＢＵＲＮが長くなっているということは、燃焼状態が悪く部分燃焼に至る可能性があることを表すので、この場合には、基本点火時期ＭＢＴＣＡＬによる１回目の点火に続く２回目の点火、いわゆる「つぎ火」を行い、この「つぎ火」により再び点火プラグ１４の周りの混合気温度を上昇させて火炎核の成長を促進させ、部分燃焼に至ることを回避するためである。
【０１９０】
点火回数ｎ２は図３３に示したように基準クランク角時の火炎核成長速度Ｓｆｍｂｔが遅くかつ低回転速度域で２回と大きくなる値である。これは基準クランク角時の火炎核成長速度Ｓｆｍｂｔが遅くかつ低回転速度域では部分燃焼に至る可能性があるので、このときにも基本点火時期ＭＢＴＣＡＬによる１回目の点火に続く２回目の点火、いわゆる「つぎ火」を行い、この「つぎ火」により再び点火プラグ１４の周りの混合気温度を上昇させて火炎核の成長を促進させ、部分燃焼に至ることを回避するためである。
【０１９１】
ここでは、点火回数指令値ｎを求めるためのパラメータが３つ（火炎核成長速度Ｓｆｍｂｔ、燃焼期間ＢＵＲＮ、回転速度ＮＲＰＭ）であるので、これらをパラメータとする３次元のマップより直接に点火時期指令値ｎを求めるようにしてもかまわない。
【０１９２】
図３４は基本点火時期ＭＢＴＣＡＬに続く２回目の点火時期θＩＧＮ２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２９のフローに続けて実行する。
【０１９３】
なお、点火回数指令値ｎが３回であることもあるが、３回目の点火時期の算出については、基本的に２回目の点火時期θＩＧＮ２の算出と同様であるため、その説明は省略する。
【０１９４】
ステップ１７１では図１３のステップ４３で算出されている基本点火時期ＭＢＴＣＡＬ、エンジン回転速度ＮＲＰＭを読み込む。
【０１９５】
ステップ１７２ではエンジン回転速度ＮＲＰＭから図３５を内容とするテーブルを検索することにより、１回目の通電角ＤＷＥＬＬ１［ｄｅｇ］を算出する。１回目の通電角ＤＷＥＬＬ１はバッテリ電圧の影響も受けるので、バッテリ電圧とエンジン回転速度から所定のマップを検索することにより、１回目の通電角ＤＷＥＬＬ１を算出するようにしてもよい。
【０１９６】
ステップ１７３ではこの１回目の通電角ＤＷＥＬＬ１から所定のテーブルを検索することにより、２回目の通電角ＤＷＥＬＬ２［ｄｅｇ］を算出する。２回目の通電角ＤＷＥＬＬ２も、図３５に示したようにエンジン回転速度に対する特性は、１回目の通電角ＤＷＥＬＬ１と同様である（絶対値は異なる）。
【０１９７】
ステップ１７４では次式により２回目の点火時期θＩＧＮ２［ｄｅｇＢＴＤＣ］を算出する。
【０１９８】
θＩＧＮ２＝ＭＢＴＣＡＬ−ＤＷＥＬＬ２−所定角…（４２）
図３６に示したように１つの点火コイル１３で１サイクル当たり２回の点火を行うには、一回目の点火を行った後に２回目の点火に備えて点火コイル１３の一次側を閉じる必要がある。（４２）式の所定角は、１回目の点火時期である基本点火時期ＭＢＴＣＡＬから点火コイル１３の一次側を閉じるまでのクランク角区間（一定値）である。
【０１９９】
ステップ１７５、１７６では次式により１回目の通電開始時期θＤＷＬ１［ｄｅｇＢＴＤＣ］、２回目の通電開始時期θＤＷＬ２［ｄｅｇＢＴＤＣ］を算出する。
【０２００】
θＤＷＬ１＝ＭＢＴ＋ＤＷＥＬＬ１…（４３）
θＤＷＬ２＝ＭＢＴ−所定角…（４４）
このようにして、算出された２点火分の通電開始時期θＤＷＬ１、θＤＷＬ２と点火時期ＭＢＴＣＡＬ、θＩＧＮ２とから図示しない点火時期制御のフローでは、図３６上段に示す２点点火信号（多重点火信号）が作られ、この２点点火信号が点火コイル１３の１次側回路を連通、遮断するパワートランジスタに送られる。
【０２０１】
ここで、本実施形態の作用を図３６を参照しながら説明すると、
燃焼室５内に残留する不活性ガス量が多い場合、圧縮比が低い場合、燃焼室５の吸気弁閉時期における温度が低い場合など、燃焼室５内の圧力と温度が上昇しない場合には、通常の１回点火では火炎核が成長しにくくなり（図３６下段の破線参照）、部分燃焼が生じることが燃焼解析実験等により知られている。
【０２０２】
このように火炎核成長速度と部分燃焼とは強い相関を持つのであり、本実施形態（請求項１に記載の発明）によれば、部分燃焼そのものに相関する基準クランク角時の基本火炎核成長速度Ｓｆｍｂｔ０を算出し、その算出した基本火炎核成長速度Ｓｆｍｂｔ０に基づいて複数回の点火回数指令値ｎを算出する（図２９のステップ１６１〜１６９）。このため、基本火炎核成長速度Ｓｆｍｂｔ０が遅くて部分燃焼が発生していることを示していれば、２回以上の点火回数指令値ｎが算出されるのであり、この点火回数指令値ｎにより、基本点火時期ＭＢＴＣＡＬによる１回目の点火に続けて、２回目の点火時期θＩＧＮ２による２回目の点火が行われる（図３６上段の多重点火信号参照）。この２回目の点火は、いわゆる「つぎ火」となるのであり、これによって再び点火プラグ１４周りの混合気温度を上昇させて火炎核の成長を促進することが可能となり、部分燃焼に至らず燃焼させることができる。
【０２０３】
このように部分燃焼そのものに相関する基準クランク角時の基本火炎核成長速度Ｓｆｍｂｔ０に基づいて多重点火を行うことで、新気、燃焼室５内に残留する不活性ガスの各量、混合気の温度、燃焼室５内のガス流動などのばらつきがあっても、部分燃焼が生じないようにすることができる。
【０２０４】
また、本実施形態（請求項４に記載の発明）によれば、点火回数指令値ｎを算出するのに燃焼期間ＢＵＲＮをも加味するので（図３２参照）、それだけ点火回数指令値ｎの算出精度がよくなる。
【０２０５】
また、エンジンの低回転速度域では部分燃焼が発生し易いのであるが、本実施形態（請求項６に記載の発明）によれば、点火回数指令値ｎを算出するのにエンジンの回転速度ＮＲＰＭをも加味するので（図３３参照）、低回転速度域での部分燃焼を確実に回避できる。
【０２０６】
また、点火プラグ１４周りのガス流動の乱れ強さが強すぎると火炎核が点火プラグ１４から流れて、火炎の成長が妨げられ部分燃焼に至る可能性が高いのであるが、本実施形態（請求項１０に記載の発明）によれば、基本火炎核成長速度Ｓｆｍｂｔ０を燃焼室内のガス流動の乱れ強さＳＴ１により補正して基準クランク角時の火炎核成長速度Ｓｆｍｂｔを算出するので（図２９のステップ１６５、１６６参照）、点火プラグ１４周りのガス流動の乱れ強さが強すぎる場合に多重点火が行われ、これによって部分燃焼を回避できる。
【０２０７】
請求項１に記載の発明において、燃焼期間算出手段の機能は図１３のステップ４２により、総ガス量算出手段の機能は図２９のステップ１６２により、圧縮開始時容積算出手段の機能は図５のステップ１２により、燃焼開始時容積算出手段の機能は図１０のステップ２２により、基準クランク角時圧力算出手段の機能は図２９のステップ１６３、１６４により、基準クランク角時火炎核成長速度算出手段の機能は図２９のステップ１６５により、点火回数指令値算出手段の機能は図２９のステップ１６８〜１７０により、多重点火手段の機能は図３４、図２の点火時期制御部６１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】水温補正係数の特性図。
【図８】当量比補正係数の特性図。
【図９】基準クランク角の特性図。
【図１０】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１１】温度上昇率の特性図。
【図１２】主燃焼期間の算出を説明するためのフローチャート。
【図１３】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１４】内部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１５】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１６】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１７】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１８】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１９】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２０】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２１】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２２】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２３】排気弁閉時期における燃焼室容積の特性図。
【図２４】不活性ガスのガス定数の特性図。
【図２５】オーバーラップ中の積算有効面積の特性図。
【図２６】オーバーラップ中の積算有効面積の説明図。
【図２７】不活性ガスの比熱比の特性図。
【図２８】混合気の比熱比の特性図。
【図２９】点火回数指令値の算出を説明するためのフローチャート。
【図３０】燃焼質量の変化を示す波形図。
【図３１】乱れ強さ補正係数の特性図。
【図３２】点火回数ｎ１の特性図。
【図３３】点火回数ｎ２の特性図。
【図３４】２回目点火時期の算出を説明するためのフローチャート。
【図３５】通電角の特性図。
【図３６】本実施形態の作用を説明するための波形図。
【図３７】多重点火時期指令値算出部のブロック図。
【図３８】部分燃焼と火炎核成長速度の関係を示す波形図。
【符号の説明】
１ エンジン
５ 燃焼室
１３ 点火コイル
１４ 点火プラグ
１５ 吸気弁
１６ 排気弁
２１ 燃料インジェクタ
２７ 吸気ＶＴＣ機構
２８ 排気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（圧縮開始時圧力算出手段）
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 control device for an engine (internal combustion engine), and more particularly to control for avoiding partial combustion.
[0002]
[Prior art]
There is one that performs double ignition control (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-2002-130028
[0004]
[Problems to be solved by the invention]
By the way, burning with a mixture leaner (thiner) than the mixture with a stoichiometric air-fuel ratio or burning with a large amount of inert gas remaining in the combustion chamber reduces pumping loss and improves fuel efficiency. However, in recent years, from the viewpoint of energy resource problems and environmental conservation, there is an increasing demand to make the air-fuel mixture leaner and more inert gas to remain in the combustion chamber. .
[0005]
However, as the mixture becomes leaner and the amount of the inert gas remaining in the combustion chamber or the amount of the inert gas recirculated to the exhaust gas increases, the combustion state becomes unstable, and partial misfire occurs. When a partial misfire occurs, drivability deteriorates and exhaust emissions also deteriorate.
[0006]
For this reason, the set ratio of the equivalent ratio that determines whether the mixture is rich or thin, the ratio of the inert gas remaining in the combustion chamber, and the ratio of the inert gas that recirculates the exhaust gas are adjusted while checking the occurrence level of misfire for each operation region. Needed. In the actual engine, despite adapting while checking the level of misfire occurrence in this way, parts such as fuel injectors and ignition devices, sensors such as air flow meters and crank angle sensors, assembly, cylinder distribution, fresh air, combustion Factors such as residual gas in the chamber, the amount of inert gas returning to the exhaust gas, the temperature of the air-fuel mixture, the distribution of the air-fuel mixture in the combustion chamber, and the gas flow in the combustion chamber are combined to affect the combustion state in the combustion chamber. Therefore, combustion may not be stable and a partial misfire may occur.
[0007]
In this case, the mechanism of partial misfire occurrence for various factors has not been elucidated, and there is a time constraint, so it is necessary to confirm experimentally what the partial misfire mechanism for each factor is for each variation factor. At present, the set values are adjusted with a margin in the safe direction (the side where the equivalent ratio decreases, the rate of inert gas remaining in the combustion chamber, and the rate of inert gas returning to the exhaust gas). It is. For this reason, the effect of improving fuel efficiency and reducing exhaust emissions cannot be avoided.
[0008]
On the other hand, recently, studies on combustion analysis in a combustion chamber of a spark ignition engine have been advanced, for example, modeling and experimental results on the growth and propagation of a flame kernel have been published in a paper.
[0009]
In this case, the inventor of the present invention came up with an idea that it should be considered that there is a strong correlation between the partial misfire, that is, the partial combustion and the flame nucleus growth rate. This will be described with reference to FIG. 38. The combustion in which partial combustion does not occur is referred to as “normal combustion”. At this time, the flame nucleus growth rate should increase steadily. It is known from combustion analysis experiments that the flame nucleus growth rate becomes slower as the fuel gas becomes leaner than the stoichiometric air-fuel ratio and as the amount of inert gas in the combustion chamber increases, and eventually partial combustion occurs. Have been. From this, it can be considered that the increase in the flame nucleus growth rate is slower in the partial combustion than in the normal combustion.
[0010]
Then, how to calculate the flame kernel growth rate,
(1) The calculation formula of the change rate of the combustion mass (mb) by the mass combustion model and the calculation formula of the flame nucleus growth rate (dr / dt) are described in the paper of SAE Paper 2000-01-0960. Both equations are linked via the rate of thermal diffusion (Sdiff) and the rate of combustion (Scomb) (detailed in embodiments of the present invention).
(2) It has been clarified by an experiment how the combustion mass ratio changes from the start of combustion.
[0011]
As a result of considering these (1) and (2), the inventor can basically calculate the flame nucleus growth rate based on the combustion period from the start of combustion until the combustion mass ratio reaches a predetermined value. Was found.
[0012]
The present invention has been created based on such an idea of the inventor, and calculates a combustion period from a combustion start time until a combustion mass ratio reaches a predetermined value, and calculates a flame kernel growth rate based on the combustion period. Then, the energy required for ignition is calculated based on the flame kernel growth speed, and a plurality of ignition frequency command values are calculated based on the ignition energy or based on the flame kernel growth speed. An object of the present invention is to obtain stable combustion by avoiding partial combustion by performing multiple ignition based on the above.
[0013]
On the other hand, since the above patent documents are not based on the results of combustion analysis, the technical idea is different from the present invention based on the results of combustion analysis.
[0014]
[Means for Solving the Problems]
The present invention provides a combustion period calculating means for calculating a combustion period (BURN) from the start of combustion in a combustion chamber until a combustion mass ratio reaches a predetermined value, and a total gas amount calculation for calculating a total gas amount (MASSC) in the combustion chamber. Means, compression start pressure calculation means for calculating a compression start pressure (PIN) of the combustion chamber, compression start volume calculation means for calculating a compression start volume (VIVC) of the combustion chamber, and combustion start of the combustion chamber Combustion start volume calculation means for calculating the hourly volume (V2), reference crank angle pressure calculation means for calculating the reference crank angle pressure (Pc) of the combustion chamber, and the combustion period, total gas amount, and compression start time A combustion start flame nucleus growth speed calculating means for calculating the flame nucleus growth speed at the reference crank angle based on the calculated values of the pressure, the compression start volume, the combustion start volume, and the reference crank angle pressure; and a flame nucleus growth speed. And a plurality of times of ignition count command value calculating means for calculating the number of times of ignition command value, and a multiple ignition means for performing multiple ignition based on the ignition count command value thus calculated on the basis of.
[0015]
【The invention's effect】
When the pressure and temperature in the combustion chamber do not rise, such as when the amount of inert gas remaining in the combustion chamber is large, when the compression ratio is low, or when the temperature at the time of closing the intake valve of the combustion chamber is low, ordinary one-time ignition It is known from combustion analysis experiments that flame nuclei hardly grow at the start of combustion and partial combustion occurs.
[0016]
As described above, the flame nucleus growth rate and the partial combustion have a strong correlation, and according to the present invention, the energy required for ignition based on the flame nucleus growth rate at the reference crank angle correlated with the partial combustion itself, specifically, Specifically, a plurality of ignition number command values are calculated. For this reason, if the flame nucleus growth rate at the reference crank angle is low, indicating that partial combustion is occurring, an ignition number command value of two or more times is calculated. When the second ignition is performed after the first ignition, the second ignition is a so-called “next ignition”, whereby the temperature of the air-fuel mixture around the ignition plug is increased again, and the flame nucleus is increased. Can be promoted, and can be burned without reaching partial combustion.
[0017]
By performing multiple ignition based on the flame nucleus growth rate at the reference crank angle which correlates to the partial combustion itself, fresh air, residual gas in the combustion chamber, each amount of inert gas returning to the exhaust gas, and the mixture Even if there are variations in the temperature, gas flow in the combustion chamber, etc., partial combustion can be prevented from occurring.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 is a schematic diagram for explaining the system of the present invention.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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 the ratio of the amount of intake air to 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) and the amount of The engine controller 31 controls the fuel from the fuel injector 21 based on the intake air flow rate signal from the air flow meter 32 and the signal from the crank angle sensors (33, 34) so that the ratio with the fuel injection amount becomes the stoichiometric air-fuel ratio. The injection amount is determined, and the O is provided upstream of the three-way catalyst 9. ₂ The air-fuel ratio is feedback-controlled based on a signal from the sensor 35.
[0024]
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.
[0025]
A cam sprocket and a crank sprocket are attached to the front portions of the intake valve camshaft 25, the exhaust valve camshaft 26, and the crankshaft 7, respectively, and a timing chain (not shown) is wrapped 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 "I referred to.) 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. Therefore, 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 exhaust gas. The 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. 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.
[0026]
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 air 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 cooling water temperature signal, controls the ignition timing, which is the cutoff timing of the primary current of the ignition plug 14, via the power transistor 13.
[0027]
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, a previous combustion start timing calculator 56, and a multiple ignition timing command value calculator. It consists of 57.
[0028]
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 ignition to the maximum combustion pressure Pmax. The basic ignition timing calculation operation unit 55 calculates an ignition timing (this ignition timing is referred to as “basic ignition timing”) MBTCAL at which MBT is obtained based on the combustion period BURN.
[0029]
As shown in FIG. 37, the multiple ignition timing command value calculation unit 57 includes a reference flame angle-based basic flame kernel growth speed calculation unit 81, a reference crank angle-based flame kernel growth speed calculation unit 82, and an ignition number command value calculation unit 83. And a multiple ignition timing calculation section 87. The ignition number command value calculation unit 83 includes ignition number calculation units 84 and 85 and a large side selection unit 86.
[0030]
The reference flame angle basic flame nucleus growth speed calculation unit 81 calculates the basic flame kernel growth speed Sfmbt0 at the reference crank angle when the turbulence intensity of the gas flow in the combustion chamber 5 is a predetermined value. The reference crank angle flame nucleus growth speed calculation unit 82 corrects the basic flame nucleus growth speed Sfmbt0 in accordance with the actual turbulence intensity ST1 of the gas flow in the combustion chamber 5 to correct the turbulence intensity at that time. The flame kernel growth speed Sfmbt at the reference crank angle is calculated. The number-of-ignitions calculation unit 84 determines the number of ignitions n1 based on the flame kernel growth speed Sfmbt and the combustion period BURN, and the number-of-ignitions calculation unit 85 determines the number of ignitions n2 based on the flame kernel growth speed Sfmbt and the engine rotation speed NRPM. Is calculated respectively. The larger side selector 86 selects the larger one of these n1 and n2 as the ignition number command value n. The multiple ignition timing calculation section 87 calculates n ignition timing command values per cycle based on the ignition number command value n calculated by the ignition number command value calculation section 83 in this way.
[0031]
Returning to FIG. 2, the ignition timing control unit 61 causes the ignition plug 14 to ignite the air-fuel mixture in the combustion chamber 5 with the multiple ignition timing command values calculated in this manner n times per cycle. The energization angle and the non-energization angle to the ignition coil 13 are controlled.
[0032]
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 based on the result obtained from the combustion analysis. Things. Hereinafter, this ignition timing control based on combustion analysis will be further described.
[0033]
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.
[0034]
FIG. 4 shows a change in the combustion mass ratio R obtained by the combustion analysis in the combustion chamber in the spark ignition engine. The combustion mass ratio R representing the ratio of the combustion mass to the fuel supplied to the combustion chamber is 0% at the time of ignition, and reaches 100% by complete combustion. The combustion mass ratio Rmax at the reference crank angle θPMAX is constant and about 60%.
[0035]
The combustion period from when the combustion mass ratio R reaches 0% to approximately 60% corresponding to the reference crank angle θPMAX includes an initial combustion period in which there is almost no change in the combustion mass ratio or the combustion pressure immediately after ignition, and a combustion period. It is divided into a main combustion period in which the 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 at a timing of 2% to 10% in terms of a combustion mass ratio. During this 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.
[0036]
On the other hand, during the main combustion period, the flame propagates from the flame core to the outside, and the combustion speed rises sharply. 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.
[0037]
The engine controller 31 sets an initial combustion period BURN1 [deg] until the combustion mass ratio reaches 2%, and a section from the end of the initial combustion period BURN1 to the reference crank angle θPMAX (in terms of the combustion chamber amount ratio, 2). % Until it reaches about 60%) as the main combustion period BURN2 [deg]. Then, a combustion period BURN [deg], which is a sum of the initial combustion period BURN1 and the main combustion period BURN2, is calculated, the 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.
[0038]
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.
[0039]
Next, the calculation of the ignition timing command value QADV executed by the engine controller 31 will be described in detail with reference to the following flowchart.
[0040]
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).
[0041]
First, in step 11, the intake valve closing timing IVC [degBTDC], the collector internal temperature TCOL [K] detected by the temperature sensor 43, the exhaust temperature TEXH [K] detected by the temperature sensor 45, and the internal inert gas rate MRESFR [ %], The coolant temperature TWK [K] detected by the temperature sensor 37, the target equivalent ratio TFBYA, the engine speed NRPM [rpm] detected by the crank angle sensor, and the ignition dead time DEADTIME [μsec].
[0042]
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.
[0043]
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.
[0044]
The internal 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.
[0045]
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.
[0046]
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.
[0047]
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 [m ³ ] 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.
[0048]
Referring to FIG. 6, consider a case where the rotation center 72 of the crankshaft 71 of the engine is offset from the 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).
[0049]

Here, Vc: clearance volume [m ³ ],
ε: compression ratio,
D: Cylinder bore diameter [m]
ST: Full stroke of piston [m],
H: distance [m] of the 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: angle [deg] that a line connecting the piston pin 76 and the crankshaft rotation center 72 forms with 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 at the intake valve closing timing used is that set in a table using the intake valve closing timing IVC as a parameter. When the intake VTC mechanism 27 is not provided, it can be given as a constant.
[0050]
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 TINI of the combustion chamber 5 at the intake valve closing timing IVC is a temperature of a gas in which fresh air flowing into the combustion chamber 5 and inert gas remaining in the combustion chamber 5 are mixed. Is equal to the fresh air temperature TCOL in the intake collector 2, and the temperature of the inert gas remaining in the combustion chamber 5 can be approximated by the exhaust temperature TEXH near the exhaust port. It can be obtained from TCOL, the exhaust gas temperature TEXH, and the internal inert gas ratio MRESFR, which is the ratio of the inert gas remaining in the combustion chamber 5, by the following equation.
[0051]
TINI = TEXH × MRESFR + TCOL × (1-MRESFR) (7)
In step 14, a reaction probability RPROBA [%] representing the flammability of the air-fuel mixture in the combustion chamber 5 is calculated. The reaction probability RPROBA is a dimensionless value and depends on three parameters of the residual inert gas ratio MRESFR, the cooling water temperature TWK [K], and the target equivalent ratio TFBYA, and can be expressed by the following equation.
[0052]
RPROBA = f3 (MRESFR, TWK, TFBYA) (8)
More specifically, the maximum value of the reaction probability obtained by a combination of the three parameters MRESFR, TWK, and TFBYA is defined as 100%, and the relationship between these parameters and the reaction probability RPROBA is experimentally obtained. Is stored in the memory of the engine controller 31 in advance as a table corresponding to the parameters. In step 14, the reaction probability RPROBA is obtained by searching this table according to the parameters.
[0053]
Specifically, a table of a water temperature correction coefficient having a characteristic as shown in FIG. 7 according to the cooling water temperature TWK, a table of a similarly set internal inert gas rate correction coefficient (not shown), and a target equivalent ratio A table of equivalence ratio correction coefficients having characteristics as shown in FIG. 8 is stored in the memory in advance in accordance with Tfbya. The maximum value of each correction coefficient is 1.0, and the reaction probability RPROBA is calculated by multiplying the product of the three types of correction coefficients by the maximum value 100% of the reaction probability.
[0054]
Explaining each table, the water temperature correction coefficient shown in FIG. 7 increases as the cooling water temperature TWK increases, and becomes 1.0 when the cooling water temperature TWK is 80 ° C. or higher. When the target equivalence ratio TFBYA is 1.0, that is, at the stoichiometric air-fuel ratio, the equivalence ratio correction coefficient shown in FIG. The ratio correction coefficient decreases. The internal inert gas ratio correction coefficient is not shown, but becomes 1.0 when the internal inert gas ratio MRESFR is zero.
[0055]
In step 15, 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.
[0056]
θPMAX = f4 (NRPM) (9)
Specifically, a reference crank angle θPMAX is obtained by searching a table of characteristics shown in FIG. 9 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.
[0057]
Finally, in step 16, 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. .
[0058]
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.
[0059]
FIG. 10 is for calculating the initial combustion period BURN1 [deg], and FIG. 12 is for calculating the main combustion period BURN2 [deg], and is executed at regular intervals (for example, every 10 msec). 10 and 12 are executed after FIG.
10 and 12 do not matter which one is executed first.
[0060]
First, referring to FIG. 10, in step 21, the last combustion start timing MBTCCYCL [degBTDC] and 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 at step 13 in FIG. 5, the engine rotation speed NRPM [rpm], and the reaction probability RPROBA [% calculated at step 14 in FIG. ] Is read.
[0061]
Here, the previous combustion start timing MBTCYCL is a value one cycle before [degBTDC] of the basic ignition timing MBTCAL, and the calculation thereof will be described later.
[0062]
In step 22, the volume V0 [m ³ ] 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.
[0063]
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. Here, MBTCYCL is set 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.
[0064]
In step 23, 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.
[0065]
Ec = f7 (V0, VIVC) = V0 / VIVC (12)
In step 24, the temperature rise 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.
[0066]
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.
[0067]
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.
[0068]
FIG. 11 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.
[0069]
In step 25, 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.
[0070]
In step 26, the laminar combustion speed SL1 [m / sec] is calculated by the following equation (known).
[0071]
SL1 = SLstd × (T0 × Tstd) ^2.18 × (P0 / Pstd) ^-0.16 … (15)
Here, Tstd: reference temperature [K],
Pstd: Reference pressure [Pa],
SLstd: reference laminar combustion speed [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 reference temperature Tstd, the reference pressure Pstd, and the reference laminar combustion speed SLstd are values determined in advance by experiments.
[0072]
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) ^-0.16 Is a small value. Therefore, the pressure term (P0 / Pstd) ^-0.16 May be defined as a constant value, and the reference laminar flow combustion speed SLstd may be defined only by the reference temperature Tstd.
[0073]
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 timing are obtained. The relationship with SL1 can be approximately defined by the following equation.
[0074]

In step 27, the turbulence strength ST1 of the gas flow in the initial combustion 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.
[0075]
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.
[0076]
Finally, the turbulence strength ST1 of the gas flow in the initial combustion can be expressed by the following equation as a function of the engine speed NRPM.
[0077]
ST1 = f10 (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.
[0078]
In step 28, the gas burning speed FLAME1 [m / sec] in the initial combustion is calculated from the following equation based on the laminar burning speed S1 and the turbulence intensity ST1.
[0079]
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.
[0080]
In step 29, the initial combustion period BURN1 [deg] is calculated by the following equation.
[0081]

However, AF1: reaction area of the flame nucleus (fixed value) [m ² ],
Here, BR1 on the right side of the equation (19) is a change amount of the combustion mass ratio from the combustion start timing to the end timing of the initial combustion period BURN1. Here, BR1 is set to 2%. (19) (NRPM × 6) on the right side of the equation is a measure for converting the unit from rpm to crank angle (deg). The reaction area AF1 of the flame kernel is set experimentally.
[0082]
Next, in the flow of FIG. 12, at step 31, the rotational speed NRPM and the reaction probability RPROBA calculated at step 14 of FIG. 5 are read.
[0083]
In step 32, the turbulence strength ST2 of the gas flow in the main combustion is calculated. Like the turbulence strength ST1 of the gas flow in the initial combustion, the turbulence strength ST2 of the gas flow can be expressed by the following equation as a function of the engine rotation speed NRPM.
[0084]
ST2 = f11 (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.
[0085]
In step 33, the combustion speed FLAME2 [m / sec] in the main combustion is calculated from the following equation from the laminar combustion speed SL2 [m / sec] and the turbulence strength ST2 of the gas flow in the main combustion.
[0086]
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).
[0087]
As described above, the length of the main combustion period BURN2 is not easily affected by changes in the temperature and pressure in the combustion chamber 5. Therefore, a fixed value experimentally obtained in advance is applied to the laminar combustion speed SL2.
[0088]
In step 34, the main combustion period BURN2 [deg] is calculated by the following equation similar to the equation (19).
[0089]

Here, V2: the volume at the start of the main combustion period of the combustion chamber 5 [m ³ ],
AF2: reaction area of flame kernel [m ² ]
Here, BR2 on the right side of the equation (22) is a change amount of the combustion mass ratio from the start time to the end time of the main combustion period. At the end of the initial combustion period, the combustion mass ratio becomes 2%, and thereafter, the main combustion period starts, and it is considered that the combustion mass ratio reaches 60% and the main combustion period ends, so 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). The volume V2 of the combustion chamber 5 at the start of the main combustion period is also a fixed value.
[0090]
FIG. 13 is for calculating the basic ignition timing MBTCAL [degBTDC], and is executed at regular intervals (for example, every 10 msec). It is executed following the later executed flow of FIGS.
[0091]
In step 41, the initial combustion period BURN1 calculated in step 29 of FIG. 10, the main combustion period BURN2 calculated in step 34 of FIG. 12, and the ignition timing dead time equivalent crank calculated in step 16 of FIG. The angle IGNDEAD and the reference crank angle θPMAX calculated in step 15 of FIG. 5 are read.
[0092]
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].
[0093]
In step 43, the basic ignition timing MBTCAL [degBTDC] is calculated by the following equation.
[0094]
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].
[0095]
The basic ignition timing MBTCAL calculated in this way is compared with the partial combustion occurrence limit ignition timing CCLCAL [degBTDC] as described later, and the value on the more retarded side is selected as the ignition timing command value QADV [degBTDC]. . The ignition timing command value QADV is transferred to the ignition register, and an ignition signal for cutting off the primary current is output from the engine controller 31 to the ignition coil 13 at a timing when the actual crank angle matches the ignition timing command value QADV.
[0096]
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. Used in ten steps 22.
[0097]
As described above, in the present embodiment, since the basic ignition timing MBTCAL, which is the ignition timing at which MBT can be obtained, is calculated without performing the mass calculation of the unburned gas amount in the combustion chamber 5, the calculation load is reduced. be able to.
[0098]
Further, as shown in the above equation (19), the initial combustion period BURN1 is represented by a function of the combustion chamber volume V0 at the start of combustion, the reaction probability RPROBA indicating the ease of combustion of the air-fuel mixture, and the combustion speed FLAME1. ing. Here, as the combustion chamber volume V0 at the start of combustion is larger, the reaction probability RPROBA is smaller, and the combustion speed FLAME1 is slower, the initial combustion period BURN1 is longer, and as a result, the basic ignition timing MBTCAL is advanced.
[0099]
Similarly, as shown in the above equation (22), the main combustion period BURN2 is a function of the combustion chamber volume V2 at the start time of the main combustion period, the reaction probability RPROBA indicating the ease of mixture, and the combustion speed FLAME2. It is represented by Here, the larger the combustion chamber volume V2 at the start of the main combustion period, the smaller the reaction probability RPROBA, and the lower the combustion speed FLAME2, the longer the main combustion period BURN2, and as a result, the ignition timing MBTCAL is advanced.
[0100]
Thus, by calculating the combustion periods BURN1 and BURN2 as functions of various parameters that affect the combustion period, the combustion periods BURN1 and BURN2 can be accurately calculated. As a result, the basic ignition timing MBTCAL calculated based on the combustion periods BURN1 and BURN2 can also be calculated with high accuracy. Further, the combustion period BURN is calculated by dividing the combustion period BURN1 into an initial combustion period BURN1 corresponding to a flame kernel growth period in which the temperature and pressure are greatly affected, and a main combustion period in which the temperature and pressure are less affected. BURN calculation accuracy is improved. By further dividing the combustion period BURN into three or more, the calculation accuracy can be further improved.
[0101]
In the embodiment, the combustion speed FLAME1 used for calculating the initial combustion period BURN1 is the product of the laminar combustion speed SL1 and the turbulence intensity ST1, and the combustion speed FLAME2 used for calculating the main combustion period BURN2 is turbulent with the laminar combustion speed SL2. Although each is calculated as the product of the strengths ST2, it may be obtained by a calculation method by addition as described in JP-A-10-30535.
[0102]
In the embodiment, the initial combustion period is defined as a combustion mass ratio from zero to 2% (that is, BR1 = 2%), and the main combustion period is defined as a combustion mass ratio from 2 to 60% (that is, BR2 = 58%). The present invention is not necessarily limited to this numerical value.
[0103]
Next, FIG. 14 is for calculating the internal 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.
[0104]
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).
[0105]
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 flow of FIG.
[0106]
In FIG. 15 (subroutine of step 53 in FIG. 14), 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.
[0107]
In FIG. 16 (subroutine of step 61 in FIG. 15), 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.
[0108]
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.
[0109]
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. 23 from the exhaust valve closing timing EVC. When the exhaust VTC mechanism 28 is not provided, it can be given as a constant.
[0110]
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.
[0111]
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. 24 from the target equivalent ratio TFBYA. As shown in FIG. 24, the gas constant REX of the inert gas is the smallest when the target equivalent ratio TFBYA is 1.0, that is, at the stoichiometric air-fuel ratio, and becomes larger when the target equivalent ratio TFBYA is larger or smaller.
[0112]
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.
[0113]
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.
[0114]
In step 76, the exhaust valve of the combustion chamber 5 is obtained from the volume VEVC at the exhaust valve closing timing EVC of the combustion chamber 5, 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.
[0115]
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. 15, and at step 62, the overlap of the intake and exhaust valves 15 and 16 (“O / L” in the figure). 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.
[0116]
The calculation of the inert gas amount MRESOL will be described with reference to the flowchart of FIG.
[0117]
In FIG. 17 (subroutine of step 62 in FIG. 15), 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 in FIG. The temperature TEVC at the closing timing EVC is read.
[0118]
Here, the intake valve opening timing IVO is a timing that is earlier than the intake valve closing timing IVC by the opening angle of the intake valve 15, so that the opening angle of the intake valve 15 (which is known in advance) before the intake valve closing timing IVC. You can ask.
[0119]
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.
[0120]
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. The exhaust valve closing timing EVC is at the exhaust top dead center when the actuator for the exhaust VTC mechanism 28 is not energized, and the exhaust valve closing timing EVC is set at the exhaust top dead center when the actuator for the exhaust valve VTC mechanism 28 is energized. 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.
[0121]
In step 83, the integrated effective area ASUMOL during the overlap is calculated by searching the table shown in FIG. 25 from the overlap amount VTCOL of the intake and exhaust valves. As shown in FIG. 25, 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.
[0122]
Here, FIG. 26 is an explanatory diagram of the integrated effective area ASAMOL during the overlap of the intake and exhaust valves. The horizontal axis indicates the crank angle, and the vertical axis indicates 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 integral value (the shaded portion in the figure) during the period when the intake valve 15 and the exhaust valve 16 are open.
[0123]
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.
[0124]
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. 27 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. 27, 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.
[0125]
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.
[0126]
In FIG. 18 (subroutine of step 85 in FIG. 17), 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.
[0127]
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.
[0128]
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.
[0129]
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.
[0130]
In step 106, the specific heat ratio MIXAIRSHR of the air-fuel mixture is obtained by searching the table shown in FIG. 28 from the target equivalent ratio TFBYA read in step 51 in FIG. 14, and this is calculated in step 107. Replace with SHEATR. As shown in FIG. 28, the specific heat ratio MIXAIRSHR of the air-fuel mixture is a value that increases as the target equivalent ratio TFBYA decreases.
[0131]
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.
[0132]
In step 108, the minimum and maximum choke determination thresholds SLCHOKEEL 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. 17 or steps 106 and 107 of FIG. I do.
[0133]

These choke determination thresholds SLCHOKEL and SLCHOKEH are calculated as choke limit values.
[0134]
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.
[0135]
At step 109, it is determined whether or not the intake / exhaust pressure ratio PINBYEX is within 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. 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 110, where the choke determination flag CHOKE (initial setting to zero) = 0.
[0136]
If the intake / exhaust pressure ratio P1NBYEX is not within the range, it is determined that there is a choke, and the routine proceeds to step 111, where the choke determination flag CHOKE = 1.
[0137]
When the setting of the supercharging determination flag and the setting of the choke determination flag are completed, the process returns to FIG. 17, and the following four cases are performed in steps 86 to 88.
[0138]
<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
Then, in the case of the above <1>, the routine proceeds to step 89, in which the average blowback inert gas flow rate MRESOLtmp1 during the overlap when there is no supercharging and there is no choke, and in the above <2>, the routine proceeds to step 90, where there is no supercharging and The flow rate MRESOLtmp2 of the blown-back inert gas during the overlap with the choke is set, and in the case of the above <3>, the routine proceeds to step 91, and the average flow rate MRESOLtmp3 of the blown-back inert gas during the overlap with the supercharge and without the choke is set at the above-mentioned < In the case of <4>, the routine proceeds to step 92, in which the flow rate MRESOLtmp4 of the blowback inert gas when the supercharge is present and the choke is present is calculated, and the calculation result is transferred to the flow rate MRESOLtmp of the blowback inert gas during the overlap.
[0139]
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. 19 (subroutine of step 89 in FIG. 17), in step 121, the gas constant REX of the inert gas calculated in steps 73 and 75 of FIG.
[0140]
In step 122, the density term MRSOLD used in the 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.
[0141]
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.
[0142]
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.
[0143]
In step 123, based on the specific heat ratio SHEATR of the inert gas calculated in step 84 of FIG. 17 and the intake / exhaust pressure ratio PINBYEX calculated in step 102 of FIG. The pressure difference term MRSOLP to be used is calculated by the following equation.
[0144]

In step 124, from the density term MRSOLD, the pressure difference term MRSOLP, and the pressure PEVC at the time 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 represented by the following equation. (Calculation formula for gas flow rate), and the calculated value is transferred to the inert gas flow rate MRESOLtmp during the backflow in step 125.
[0145]
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. 20 (subroutine of step 90 in FIG. 17), the gas constant REX of the inert gas and the pressure PEVC at the exhaust valve closing timing 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).
[0146]
In step 133, the choke-time pressure difference term MRSOLPC is calculated by the following equation based on the specific heat ratio SHEATR of the inert gas calculated in step 84 of FIG.
[0147]

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.
[0148]
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.
[0149]
MRESOLtmp2 = PEVC × MRSOLD × MRSOLPC (32)
Next, the calculation of the blowback gas flow rate when there is a supercharge and there is no choke will be described with reference to the flow of FIG.
In step 141 of FIG. 21 (subroutine of step 91 in FIG. 17), the intake pressure PIN detected by the intake pressure sensor 44 is read.
[0150]
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. 18 and the intake / exhaust pressure ratio PINBYEX calculated in step 102 in FIG. Is calculated by the following equation.
[0151]

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.
[0152]
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.
[0153]
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.
[0154]
Next, the calculation of the flow rate of the inert gas that is blown back during the overlap when there is supercharging and choke will be described with reference to the flow of FIG.
In FIG. 22 (subroutine of step 92 in FIG. 17), in steps 151 and 152, the intake pressure PIN detected by the intake pressure sensor 44 is read in the same manner as in step 141 of FIG. The term MRSOLPC is calculated by the aforementioned equation (31).
[0155]
In step 153, based on the choke-time pressure difference term MRSOLPC and the intake pressure PIN, an overlapped blow-back 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.
[0156]
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.
[0157]
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 supercharging and the presence or absence of the choke, the flow 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.
[0158]

When the calculation of the inert gas amount MRESOL returned during the overlap in this way is completed, the process returns to FIG. 15, and in step 63, the inert gas amount MRESCYL at the exhaust valve closing timing EVC in the combustion chamber 5 and the return gas 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.
[0159]
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.
[0160]
When the calculation of the internal inert gas amount MRES is completed in this manner, the process returns to FIG. 14, and in step 54, using the internal inert gas amount MRES and the target equivalent ratio TFBYA, the internal 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.
[0161]

This completes the calculation of the internal inert gas ratio MRESFR.
[0162]
As described above, according to the present embodiment, the internal inert gas amount MRES is composed of the inert gas amount MRESCYL when the exhaust valve of the combustion chamber 5 is closed, and the blowback gas amount MRESOL during the overlap of the intake and exhaust valves. In this case, the temperature TEV and the pressure PEVC at the exhaust valve closing timing of the combustion chamber 5 are calculated (steps 74 and 75 in FIG. 16), and the temperature TEVC, the pressure PEVC and the inert gas are calculated. Since the inert gas amount MRESCYL at the exhaust valve closing timing of the combustion chamber 5 is calculated from the state equation (Equation (24)) based on the gas constant REX (see step 76 in FIG. 16), Even during the transient operation in which the state quantities (PEVC, VEVC, TEVC) inside the combustion chamber 5 change every moment, the combustion chamber 5 is accurately determined regardless of the operation conditions. The inert gas amount MRESCYL in the exhaust valve closing timing can be calculated (estimated).
[0163]
Further, based on the temperature TEVC and the pressure PEVC at the time of closing the exhaust valve of the combustion chamber 5, the inert gas constant REX and the specific heat ratio SHEATR, and the intake pressure PIN, the blown-back inert gas flow rates (MRESOLtmp1 and MRESOLtmp2) during the overlap are determined. This is calculated (see FIGS. 19 and 20), and the gas flow rate is multiplied by the integrated effective area ASAMOL during the overlap to calculate the blowback gas amount MRESOL during the overlap (see step 93 in FIG. 17). Therefore, it is possible to accurately calculate (estimate) the amount MRESOL of the blown-back gas during the overlap.
[0164]
As described above, if the inert gas amount MRESCYL and the overlapped returning gas amount MRESOL can be accurately calculated (estimated) when the exhaust valve of the combustion chamber 5 is closed, the internal inert gas amount MRES, which is the sum of these, is also accurately determined. The internal inert gas ratio MRESFR calculated based on the internal inert gas amount MRES that can be calculated (estimated) with high accuracy can be calculated (estimated). The temperature TINI at the intake valve closing timing IVC in the combustion chamber 5 can be accurately calculated by utilizing the temperature TINI at the intake valve closing timing IVC (see step 13 in FIG. 5). In addition, the engine can be appropriately controlled by utilizing the internal inert gas amount MRES, which can be accurately estimated, for the fuel injection amount, valve opening / closing timing (overlap amount), and the like. .
[0165]
Further, since the gas constant REX of the inert gas and the specific heat ratio SHEATR of the inert gas are set to values corresponding to the target equivalent ratio TFBYA (see FIGS. 24 and 27), the operation at an air-fuel ratio outside the stoichiometric air-fuel ratio is performed. Time (for example, during lean operation in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, in order to stabilize the originally unstable state of the engine, such as during cold start, the air-fuel ratio of the stoichiometric air-fuel ratio is richer than the stoichiometric air-fuel ratio). Immediately after the operation of the engine operating at the air-fuel ratio, a large output is also required, so that the exhaust valve closing timing of the combustion chamber 5 also at the time of full-load operation operating at an air-fuel ratio richer than the stoichiometric air-fuel ratio). , The internal inert gas amount MRES which is the sum of the inert gas amount MRESCYL, the overlapped blow-back gas amount MRESOL, and the internal inert gas ratio MRESFR based on this is accurately calculated. Kill.
[0166]
In addition, since the integrated effective area ASAMOL of the overlap period is defined as the area of the virtual orifice, and it is assumed that the exhaust gas flows through the virtual orifice from the combustion chamber 5 to the intake system, the return inert gas amount MRESOL during the overlap is calculated. Calculations have been simplified.
[0167]
Next, FIG. 29 is for calculating the number-of-ignitions command value n, which is executed at regular intervals (for example, every 10 msec). It is executed following the flow of FIG.
[0168]
In step 161, the cylinder fresh air amount MACYL and the internal inert gas amount MRES calculated in steps 52 and 53 of FIG. 14, the intake pressure PIN detected by the intake pressure sensor 44 (compression start pressure detecting means), and FIG. 5, the temperature TINI of the combustion chamber 5 at the intake valve closing timing calculated in step 13 of FIG. 5, the effective compression ratio Ec at the start of combustion calculated in steps 23, 25, and 27 of FIG. The combustion period BURN, the basic ignition timing MBTCAL, and the engine speed NRPM calculated in steps 42 and 43 are read.
[0169]
In step 162, the total gas amount MASSC in the combustion chamber 5 is calculated by the following equation.
[0170]
MASSC = MACYL + MRES (39)
In steps 163 and 164, the average temperature Tc of the combustion chamber 5 at the reference crank angle and the pressure Pc at the reference crank angle are calculated by the following equations.
[0171]

Where n: polytropic index,
Tup #: constant,
Q: 60% combustion calorific value,
Vup #: constant,
Here, in the case of irreversible adiabatic change, since the polytrope index n is equal to the specific heat ratio κ of the gas, the following equation can be obtained by rewriting the equation (39b).
[0172]

The constant Vup # in the equation (39c) is a gas volume change rate accompanying a change in molecular weight when the combustion mass is burned up to 60% and becomes a gas in the course of combustion. A value slightly larger than 1 (about 1.03) may be used.
[0173]
In step 165, the basic flame kernel growth speed Sfmbt0 [m / sec] at the reference crank angle is calculated by the following equation.
[0174]

Here, V2: volume at the start of the main combustion period of the combustion chamber 5 [m ³ ],
AF2: reaction area of flame kernel [m ² ],
ρb: burned gas density,
Here, V2 and AF2 are already used in the above equation (22). ρb is the gas mass / burned gas volume when the combustion mass is burned up to 60%, and is a constant value.
[0175]
Next, based on the description in SAE Paper 2001-01-0960 paper (for modeling and experimental research on growth and propagation of a flame nucleus in a combustion chamber in a spark ignition engine), the above-mentioned formula (40) was derived. Will be described.
[0176]
According to the equation of continuity and the approach to the flame kernel in the above-mentioned paper, the temporal change of the combustion mass mb is defined by the following equation in the mass combustion model.
[0177]
dmb / dt = ρu × Ab × (Sdiff + Scomb) + C × ρu × μin (complement 1)
Here, mb: combustion mass,
ρu: unburned gas density,
Ab: surface area of burned gas,
Sdiff: thermal diffusion rate,
Scomb: burning speed,
C: Specific heat of liquid,
In this case, the second term on the right side of the expression (1) is small and is ignored, and the following expression is obtained.
[0178]
dmb / dt = ρu × Ab × (Sdiff + Scomb) (complement 2)
On the other hand, according to the experimental results, the combustion mass mb changes in a curve as shown by a dashed line in FIG. 30. Here, the change in the curve is approximated by a straight line shown by a solid line. At this time, the inclination of the straight line, that is, dmb / dt, can be geometrically expressed as the following equation.
[0179]
dmb / dt ≒ (MASSC × 0.6) / BURN (supplement 3)
Dmb / dt is eliminated from the expression (complement 3) and the expression (supplement 2).
[0180]

On the other hand, in the above-mentioned paper, the flame nucleus growth rate dr / dt is expressed by the following equation.
[0181]

Where r is the radius of the flame kernel,
ρu: unburned gas density,
ρb: burned gas density,
Sdiff: thermal diffusion rate,
Scomb: burning rate,
Vb: volume of burned gas,
Ab: surface area of burned gas,
Tb: burned gas temperature,
P: gas pressure,
When the flame nucleus growth rate dr / dt in the (Equation 5) equation is newly set as the basic flame nucleus growth rate Sfmbt0 of the present invention, and (Supplement 4) is substituted, and Sdiff + Scomb is eliminated, the following equation is obtained.
[0182]

Here, approximation is further performed on the second term on the right side of Expression (6). That is, Tb and P are the temperature Tc and the pressure Pc at the reference crank angle timing, and dTb and dP are the change amounts of the temperature (Tb) and the pressure (P) from the compression start timing to the reference crank angle timing, respectively. Therefore, dTb is Tc-TINI, and dP is Pc-PIN. At this time, dt corresponds to a crank angle section from the compression start timing to the reference crank angle timing. Here, a combustion period BURN [deg], which is a minute crank angle, is applied instead of this crank angle section.
[0183]
Therefore, in the formula (complement 6), when dt → BURN, Tb → Tc, dTb → Tc-TINI, P → Pc, and dP → Pc-PIN are replaced, the following formula is obtained.
[0184]

Next, since the change in the volume of the combustion chamber during the main combustion period is small, Vb in equation (7) is regarded as a constant value, and the volume of the combustion chamber 5 at the start of the main combustion period is used. This is equal to V2 in the above equation (22). Ab in equation (7) is equal to the average flame surface area during the growth process of the flame nuclei, that is, AF2 in equation (22). Therefore, the following equation is obtained by replacing Vb → V2 and Ab → AF2.
[0185]

In this way, the formula (complement 8), that is, the above formula (40) could be derived.
[0186]
In step 166, a turbulence intensity correction coefficient Smb is calculated by searching a table having the contents shown in FIG. 31 from the turbulence intensity ST1. This correction coefficient Smb is an anonymous number, and as shown in FIG. 31, is a value that increases as the disturbance strength ST1 increases. This is to reflect the turbulence strength ST1 of the gas flow on the flame nucleus growth rate because the turbulence strength ST1 of the gas flow contributes to the flame nucleus growth rate. How the turbulence strength ST1 of the gas flow contributes to the flame nucleus growth rate differs depending on the engine specifications, so that the characteristics of the correction coefficient Smb are more suitable for experiments.
[0187]
In step 167, the turbulence intensity correction coefficient Smb is multiplied by the basic flame kernel growth speed Sfmbt0, that is, the flame kernel growth speed Sfmbt [m / sec] at the reference crank angle is calculated by the following equation.
[0188]
Sfmbt = Sfmbt0 × Smb (41)
In step 168, a map having the contents shown in FIG. 32 is retrieved from the flame nucleus growth speed Sfmbt at the reference crank angle and the combustion period BURN, and the number of ignitions n1 is determined. The number of ignitions n2 is calculated by searching a map having the contents shown in FIG. 33 from the speed Sfmbt and the engine rotation speed NRPM, and the larger value of the ignition times n1 and n2 is determined in step 170 as the ignition number command. Select as value n.
[0189]
If the number of ignitions n1 is the same during the combustion period BURN as shown in FIG. 32, the lower the flame nucleus growth speed Sfmbt at the reference crank angle is, the more the flame nucleus growth speed Sfmbt at the reference crank angle is the same. This value is increased twice and three times as the combustion period BURN becomes longer. The fact that the flame nucleus growth speed Sfmbt at the reference crank angle is slow while the combustion period is the same, or that the combustion period BURN is long while the flame nucleus growth speed Sfmbt at the reference crank angle is the same, In this case, the second ignition following the first ignition based on the basic ignition timing MBTCAL, that is, the second ignition, that is, the next ignition is performed. This is to raise the temperature of the air-fuel mixture around the spark plug 14 again by "fire" to promote the growth of the flame nucleus and to avoid reaching partial combustion.
[0190]
As shown in FIG. 33, the number of ignitions n2 is a value at which the flame nucleus growth speed Sfmbt at the reference crank angle is slow and increases to twice in the low rotation speed region. This is because the flame nucleus growth rate Sfmbt at the reference crank angle is low and partial combustion may occur in the low rotation speed range. Therefore, at this time, the second ignition following the first ignition by the basic ignition timing MBTCAL, This is because a so-called “next fire” is performed, and the temperature of the air-fuel mixture around the spark plug 14 is increased again by the “next fire” to promote the growth of the flame nucleus and avoid partial combustion.
[0191]
Here, there are three parameters (flame nucleus growth speed Sfmbt, combustion period BURN, rotation speed NRPM) for obtaining the ignition number command value n, so that the ignition timing command is directly obtained from a three-dimensional map using these as parameters. The value n may be determined.
[0192]
FIG. 34 is for calculating the second ignition timing θIGN2 following the basic ignition timing MBTCAL, and is executed at regular intervals (for example, every 10 msec). It is executed following the flow of FIG.
[0193]
Although the number-of-times-of-ignition command value n may be three times, the calculation of the third ignition timing is basically the same as the calculation of the second ignition timing θIGN2, and a description thereof will be omitted.
[0194]
In step 171, the basic ignition timing MBTCAL and the engine speed NRPM calculated in step 43 of FIG. 13 are read.
[0195]
In step 172, a first energization angle DWELL1 [deg] is calculated by searching a table having the contents shown in FIG. 35 from the engine rotation speed NRPM. Since the first energization angle DWELL1 is also affected by the battery voltage, the first energization angle DWELL1 may be calculated by searching a predetermined map from the battery voltage and the engine speed.
[0196]
In step 173, a predetermined table is searched from the first energization angle DWELL1 to calculate a second energization angle DWELL2 [deg]. As shown in FIG. 35, the characteristic of the second energization angle DWELL2 with respect to the engine rotational speed is the same as that of the first energization angle DWELL1 (the absolute value is different).
[0197]
In step 174, the second ignition timing θIGN2 [degBTDC] is calculated by the following equation.
[0198]
θIGN2 = MBTCAL-DWELL2-predetermined angle (42)
In order to perform two ignitions per cycle with one ignition coil 13 as shown in FIG. 36, it is necessary to close the primary side of the ignition coil 13 in preparation for the second ignition after performing the first ignition. is there. The predetermined angle in the equation (42) is a crank angle section (constant value) from the basic ignition timing MBTCAL, which is the first ignition timing, until the primary side of the ignition coil 13 is closed.
[0199]
In steps 175 and 176, the first energization start timing θDWL1 [degBTDC] and the second energization start timing θDWL2 [degBTDC] are calculated by the following equations.
[0200]
θDWL1 = MBT + DWELL1 (43)
θDWL2 = MBT−predetermined angle (44)
In the ignition timing control flow (not shown) based on the calculated energization start timings θDWL1 and θDWL2 and the ignition timings MBTCAL and θIGN2 for the two ignitions thus calculated, a two-point ignition signal (multiple ignition signal) shown in the upper part of FIG. The two-point ignition signal is sent to a power transistor that communicates with and shuts off the primary circuit of the ignition coil 13.
[0201]
Here, the operation of the present embodiment will be described with reference to FIG.
When the pressure and temperature in the combustion chamber 5 do not rise, such as when the amount of the inert gas remaining in the combustion chamber 5 is large, when the compression ratio is low, and when the temperature of the combustion chamber 5 at the time of closing the intake valve is low. It is known from a combustion analysis experiment or the like that the flame nucleus becomes difficult to grow by the normal single ignition (see the broken line in the lower part of FIG. 36), and partial combustion occurs.
[0202]
As described above, the flame nucleus growth rate and the partial combustion have a strong correlation, and according to the present embodiment (the invention described in claim 1), the basic flame nucleus growth at the reference crank angle correlated to the partial combustion itself. The speed Sfmbt0 is calculated, and a plurality of ignition number command values n are calculated based on the calculated basic flame kernel growth speed Sfmbt0 (steps 161 to 169 in FIG. 29). For this reason, if the basic flame nucleus growth rate Sfmbt0 is low and indicates that partial combustion is occurring, the ignition number command value n of two or more times is calculated. Subsequent to the first ignition with the basic ignition timing MBTCAL, the second ignition with the second ignition timing θIGN2 is performed (see the multiple ignition signal in the upper part of FIG. 36). This second ignition is a so-called “next ignition”, which makes it possible to increase the temperature of the air-fuel mixture around the ignition plug 14 again to promote the growth of the flame nucleus. Can be done.
[0203]
By performing multiple ignitions based on the basic flame kernel growth rate Sfmbt0 at the reference crank angle correlated to the partial combustion itself, fresh air, the amount of the inert gas remaining in the combustion chamber 5, and the mixture Even if there is variation in the temperature, gas flow in the combustion chamber 5, etc., partial combustion can be prevented from occurring.
[0204]
In addition, according to the present embodiment (the invention according to claim 4), since the combustion period BURN is also taken into account in calculating the ignition number command value n (see FIG. 32), the calculation of the ignition number command value n is correspondingly performed. Accuracy improves.
[0205]
Further, although partial combustion is likely to occur in the low rotational speed range of the engine, according to the present embodiment (the invention according to claim 6), the engine rotational speed NRPM is used to calculate the ignition number command value n. (See FIG. 33), it is possible to reliably avoid partial combustion in the low rotation speed range.
[0206]
Also, if the turbulence of the gas flow around the spark plug 14 is too strong, the flame nucleus flows from the spark plug 14 and the growth of the flame is likely to be hindered, resulting in a high possibility of partial combustion. According to the invention described in Item 10, the flame nucleus growth speed Sfmbt0 at the reference crank angle is calculated by correcting the basic flame nucleus growth speed Sfmbt0 by the turbulence strength ST1 of the gas flow in the combustion chamber (FIG. 29). In steps 165 and 166), when the turbulence of the gas flow around the spark plug 14 is too strong, multiple ignition is performed, thereby avoiding partial combustion.
[0207]
In the invention according to claim 1, the function of the combustion period calculating means is determined by step 42 in FIG. 13, the function of the total gas amount calculating means is determined by step 162 in FIG. 29, and the function of the compression start volume calculating means is determined by FIG. According to step 12, the function of the combustion start volume calculating means is determined by step 22 in FIG. 10, and the function of the reference crank angle pressure calculating means is determined by the steps 163 and 164 in FIG. The function of the ignition number command value calculating means is performed by steps 168 to 170 of FIG. 29, and the function of the multiple ignition means is performed by the ignition timing control unit 61 of FIGS. ing.
[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 water temperature correction coefficient.
FIG. 8 is a characteristic diagram of an equivalent ratio correction coefficient.
FIG. 9 is a characteristic diagram of a reference crank angle.
FIG. 10 is a flowchart for explaining calculation of an initial combustion period.
FIG. 11 is a characteristic diagram of a temperature rise rate.
FIG. 12 is a flowchart for explaining calculation of a main combustion period.
FIG. 13 is a flowchart for explaining calculation of a basic ignition timing.
FIG. 14 is a flowchart for explaining calculation of an internal inert gas ratio.
FIG. 15 is a flowchart for explaining calculation of an internal inert gas amount.
FIG. 16 is a flowchart for explaining calculation of an inert gas amount at the time of EVC.
FIG. 17 is a flowchart for explaining the calculation of the amount of inert gas blown back during the overlap.
FIG. 18 is a flowchart for explaining setting of a supercharge determination flag and a choke determination flag.
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 no supercharging and there is no choke.
FIG. 20 is a flowchart for explaining calculation of a flow rate of inert gas blown back during overlap when there is no supercharging and there is a choke;
FIG. 21 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 a supercharge and there is no choke;
FIG. 22 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. 23 is a characteristic diagram of a combustion chamber volume at an exhaust valve closing timing.
FIG. 24 is a characteristic diagram of a gas constant of an inert gas.
FIG. 25 is a characteristic diagram of an integrated effective area during an overlap.
FIG. 26 is an explanatory diagram of an integrated effective area during overlap.
FIG. 27 is a characteristic diagram of a specific heat ratio of an inert gas.
FIG. 28 is a characteristic diagram of a specific heat ratio of an air-fuel mixture.
FIG. 29 is a flowchart for explaining calculation of an ignition number command value.
FIG. 30 is a waveform chart showing a change in combustion mass.
FIG. 31 is a characteristic diagram of a turbulence intensity correction coefficient.
FIG. 32 is a characteristic diagram of the number of ignitions n1.
FIG. 33 is a characteristic diagram of the number of ignitions n2.
FIG. 34 is a flowchart for explaining calculation of a second ignition timing.
FIG. 35 is a characteristic diagram of a conduction angle.
FIG. 36 is a waveform chart for explaining the operation of the present embodiment.
FIG. 37 is a block diagram of a multiple ignition timing command value calculation unit.
FIG. 38 is a waveform chart showing a relationship between partial combustion and a flame nucleus growth rate.
[Explanation of symbols]
1 engine
5 Combustion chamber
13 Ignition coil
14 Spark plug
15 Intake valve
16 Exhaust valve
21 Fuel injector
27 Intake VTC mechanism
28 Exhaust VTC mechanism
31 Engine Controller
33, 34 Crank angle sensor
43 Intake air temperature sensor
44 intake pressure sensor (compression start pressure calculation means)
45 Exhaust gas temperature sensor
46 Exhaust pressure sensor

Claims (14)

Combustion period calculation means for calculating a combustion period from the start of combustion in the combustion chamber until the combustion mass ratio reaches a predetermined value,
Total gas amount calculating means for calculating the total gas amount in the combustion chamber,
Compression start pressure calculation means for calculating the compression start pressure of the combustion chamber,
Compression start volume calculation means for calculating the compression start volume of the combustion chamber,
A combustion start volume calculation means for calculating a combustion start volume of the combustion chamber,
Reference crank angle pressure calculation means for calculating a reference crank angle pressure of the combustion chamber,
At the reference crank angle, the flame kernel growth rate at the reference crank angle is calculated based on the calculated values of the combustion period, the total gas amount, the compression start pressure, the compression start volume, the combustion start volume, and the reference crank angle pressure. Flame nucleus growth rate calculating means;
Ignition number command value calculating means for calculating a plurality of ignition number command values based on the flame kernel growth rate,
An ignition control device for an engine, comprising: multiple ignition means for performing multiple ignition based on the calculated number-of-ignitions command value. 2. An ignition timing at which MBT is obtained based on a calculated value of the combustion period is calculated as a basic ignition timing, and multiple ignition is performed based on the basic ignition timing and the ignition number command value. An ignition control device for an engine according to claim 1. 3. The engine ignition control device according to claim 2, wherein the ignition number command value increases as the flame nucleus growth rate at the start of combustion decreases. The ignition control device for an engine according to claim 2, wherein a combustion period is taken into account in calculating the ignition number command value. The ignition control device for an engine according to claim 4, wherein the ignition number command value is a value that increases as a combustion period increases. 3. The engine ignition control device according to claim 2, wherein an engine rotation speed is taken into account in calculating the ignition number command value. 7. The ignition control device for an engine according to claim 6, wherein the ignition number command value is a value that increases in a low rotation speed range. The ignition control device for an engine according to claim 2, wherein a combustion period and an engine rotation speed are taken into account in calculating the ignition number command value. The ignition control device for an engine according to claim 1, wherein the predetermined value is a combustion mass ratio at a reference crank angle. The ignition control device for an engine according to claim 9, wherein the reference crank angle is set in a range of 10 to 20 degrees after the compression top dead center. 2. The engine ignition control device according to claim 1, wherein the flame nucleus growth rate is corrected by a turbulence of gas flow in the combustion chamber. 10. The ignition control device for an engine according to claim 9, wherein a period from the start of ignition to the formation of the flame nucleus is defined as an initial combustion period, and a period thereafter until reaching a reference crank angle is defined as a main combustion period. . The initial combustion period calculating means for calculating the initial combustion period,
Means for calculating the combustion start volume of the combustion chamber;
Means for calculating a reaction probability indicating the ease of combustion of the combustion gas in the combustion chamber;
Means for calculating the combustion rate of the combustion gas in the combustion chamber;
13. The ignition control device for an engine according to claim 12, comprising means for calculating an initial combustion period based on the calculated values at the start of combustion, the reaction probability, and the combustion speed. The main combustion period calculating means for calculating the main combustion period,
Means for calculating the volume at the end of the initial combustion period of the combustion chamber,
Means for calculating a reaction probability indicating the ease of combustion of the combustion gas in the combustion chamber;
Means for calculating the combustion rate of the combustion gas in the combustion chamber;
13. The engine ignition control device according to claim 12, comprising means for calculating a main combustion period based on the calculated values of the initial combustion period end volume, the reaction probability, and the combustion speed.

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