JP2004245172A - Ignition timing control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize ignition timing compensation appropriate to disturbance factors: changes in an operational environment of a spark ignition gas engine or changes in knocking characteristics or combustion stability due to variations or deterioration of apparatuses, if any, with a smaller calculation load and a smaller man-hour for matching. <P>SOLUTION: An MBT ignition timing, a knock limit ignition timing, and a combustion limit ignition timing are determined corresponding to respective operating states to perform ignition timing control on the basis of the latest timing of them. Thus, even if any of the above three timings is changed by disturbance, more preferable ignition timing can be set from the viewpoint of fuel consumption and exhaust gas performance as a result of each of them being corrected separately. <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を計算することができる。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。
【００３８】
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］を計算する。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。
【００３９】
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［％］を計算する。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。
【００４０】
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。
【００４１】
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。
【００４２】
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。
【００４３】
ステップ１５では、基準クランク角θＰＭＡＸ［ｄｅｇＡＴＤＣ］を計算する。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。
【００４４】
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。計算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。
【００４５】
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］を計算する。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。
【００４６】
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を計算するためのものである。
【００４７】
図１０は初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を計算するためのもの、また図１２は主燃焼期間ＢＵＲＮ２［ｄｅｇ］を計算するためのもので、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。
【００４８】
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で計算されている燃焼室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で計算されている燃焼室５の吸気弁閉時期における温度ＴＩＴＩ［Ｋ］、エンジン回転速度ＮＲＰＭ［ｒｐｍ］、図５のステップ１４で計算されている反応確率ＲＰＲＯＢＡ［％］を読み込む。
【００４９】
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、その計算については後述する。
【００５０】
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］を計算する。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を計算する。
【００５１】
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を計算する。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。
【００５２】
ステップ２３では燃焼開始時期における有効圧縮比Ｅｃを計算する。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。
【００５３】
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に基づいて計算する。
【００５４】
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（以下、同様）。
【００５５】
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、一層の計算精度の向上が可能である。
【００５６】
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。
【００５７】
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）
の式により計算する。
【００５８】
ステップ２６では、次式（公知）により層流燃焼速度ＳＬ１［ｍ／ｓｅｃ］を計算する。
【００５９】
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。
【００６０】
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。
【００６１】
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。
【００６２】

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を計算する。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。
【００６３】
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。
【００６４】
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。
【００６５】
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。
【００６６】
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］を次式により計算する。
【００６７】
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。
【００６８】
ステップ２９では、次式により初期燃焼期間ＢＵＲＮ１［ｄｅｇ］を計算する。
【００６９】
ＢＵＲＮ１＝｛（ＮＲＰＭ×６）×（ＢＲ１×Ｖ０）｝／（ＰＲＲＯＢＡ×ＡＦ１×ＦＬＡＭＥ１） … （１９）
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。
【００７０】
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で計算されている反応確率ＲＰＲＯＢＡを読み込む。
【００７１】
ステップ３２では主燃焼におけるガス流動の乱れ強さＳＴ２を計算する。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。
【００７２】
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。
【００７３】
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］を次式により計算する。
【００７４】
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。
【００７５】
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。
【００７６】
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計算する。
【００７７】
ＢＵＲＮ２＝｛（ＮＲＰＭ×６）×（ＢＲ２×Ｖ２）｝／（ＰＲＲＯＢＡ×ＡＦ２×ＦＬＡＭＥ２） … （２２）
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。
【００７８】
図１３は基本点火時期ＭＢＴＣＡＬ［ｄｅｇＢＴＤＣ］を計算するためのもので、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。
【００７９】
ステップ４１では、図１０のステップ２９で計算されている初期燃焼期間ＢＵＲＮ１、図１２のステップ３４で計算されている主燃焼期間ＢＵＲＮ２、図５のステップ１６で計算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で計算されている基準クランク角θＰＭＡＸを読み込む。
【００８０】
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］として計算する。
【００８１】
ステップ４３では次式により基本点火時期ＭＢＴＣＡＬ［ｄｅｇＢＴＤＣ］を計算する。
【００８２】
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］として計算する。
【００８３】
このようにして計算した基本点火時期ＭＢＴＣＡＬは、後述するノック限界もしくは燃焼限界の点火時期と比較され、これらのうちの最小値（最も近く側の値）が点火時期最小値ＰＡＤＶ［ｄｅｇＢＴＤＣ］として選択される。この点火時期最小値ＰＡＤＶに対して、早期排温上昇のための遅角化、変速時トルクダウンのための遅角化等、各種の補正を加えて、点火時期指令値ＱＡＤＶ［ｄｅｇＢＴＤＣ］を算出する。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。
【００８４】
また、今サイクルの点火時期指令値としてステップ４３で計算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で計算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。
【００８５】
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を計算するので、計算負荷を小さく抑えることができる。
【００８６】
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。
【００８７】
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。
【００８８】
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計算することで、燃焼期間ＢＵＲＮ１とＢＵＲＮ２を正確に計算することができる。結果として、燃焼期間ＢＵＲＮ１とＢＵＲＮ２に基づき計算される基本点火時期ＭＢＴＣＡＬも高精度に計算することができる。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計算しているので、燃焼期間ＢＵＲＮの計算精度が向上する。燃焼期間ＢＵＲＮを３以上にさらに分割することで、計算精度のさらなる向上も可能である。
【００８９】
なお、ここでは初期燃焼期間ＢＵＲＮ１の計算に用いる燃焼速度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の計算に用いる燃焼速度ＦＬＡＭＥ２を層流燃焼速度ＳＬ２と乱れ強さＳＴ２の積としてそれぞれ計算しているが、特開平１０−３０５３５号公報に記載されているように加算による計算方法で求めても良い。また、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。
【００９０】
次に、ノック限界の点火時期ＫＮＫＣＡＬの算出につき図１５〜図１８を用いて説明する。
【００９１】
図１５は算出手法を示すフローチャートである。図において、まずステップ６１にて燃料がハイオクタンガソリンかレギュラーガソリンかを判定する。この判定手法は種々公知であり、例えばノックセンサを用いた点火時期フィードバック制御により行う。次いで、この判定結果に応じて、ハイオクガソリンであった場合にはステップ６２にて、レギュラーガソリンであった場合にはステップ６３にて、それぞれのマップからノック限界に対応する点火時期補正量の基本値ＫＮＭ［ｄｅｇ］を求める。図１６に前記マップの一例を示す。図示したようにこのマップはエンジン回転速度Ｎｅと負荷（燃料噴射量）ＴｐをパラメータとしてＫＮＭの値が割り付けられている。一般に低回転高負荷ほどノッキングが発生しやすいため小さい値つまり遅角側の値が設定されるが、同一回転速度・負荷であっても、燃料オクタン価が高いほど値は大きくなる。
【００９２】
次いで、ステップ６４にて次式により吸入混合気の温度Ｔ０ａ［Ｋ］を求める。
【００９３】
Ｔ０ａ＝Ｔａ×ＷＴＴＡ＃＋Ｔｗ（１−ＷＴＴＡ＃） … （２４）
ただし、Ｔａ：吸気温度［Ｋ］、
Ｔｗ：冷却水温度［Ｋ］
ＷＴＴＡ＃：エンジンに応じて定めた常数
このＴ０ａはエンジンの冷却水温度Ｔｗと吸気温度Ｔａの間を内分するある値となる。すなわち、シリンダに吸入された吸気の温度は、外気の温度（≒Ｔａ）に対し、吸気系でのエンジン温度の影響で温度上昇することから、これを冷却水温度Ｔｗで補正している。
【００９４】
次のステップ６５では、前記吸入混合気温度Ｔ０ａから図１７に示したようなテーブルを参照して温度による補正量ＫＮＴ［ｄｅｇ］を求める。さらに、ステップ６６にて、既知の手法により求めた湿度（水蒸気分圧）から図１８に示したようなテーブルを参照して湿度による補正量ＫＮＷ［ｄｅｇ］を求める。前記各補正量ＫＮＴ、ＫＮＷは図示したように単純な線形特性で変化するので、対応する一次関数を設定して計算により求めるようにしてもよい。なお、吸入混合気温度Ｔ０ａの代わりに、式（１４）で求めた燃焼室温度Ｔ０を用いて温度補正量ＫＮＴを設定するようにしてもよい。
【００９５】
最後に、ステップ６７にて前述のＫＮＭ、ＫＮＴ、ＫＮＷを加算したものをノック限界点火時期ＫＮＫＣＡＬとして設定する。
【００９６】
次に、燃焼限界の点火時期ＣＣＬＣＡＬの算出につき図１９〜図２２を用いて説明する。
【００９７】
図１９は算出手法を示すフローチャートである。図において、まずステップ７１にて、図２０に示したマップを参照して基本値ＣＣＬ［ｄｅｇ］を求める。パラメータはエンジン回転速度Ｎｅと負荷Ｔｐである。一般に、低回転低負荷時ほど混合気の流速が低く、シリンダ内残留ガスと新気との混合が悪いため燃焼火炎が伝搬しにくいことから、安定燃焼する限界点火時期はマップに示されるように遅角側に移動する。
【００９８】
次いで、ステップ７２にて、前出の式（２４）にて求めた吸入混合気温度Ｔ０ａ（または燃焼室温度Ｔ０）から図２１に示したテーブルを参照して温度による補正量ＣＣＬＴ［ｄｅｇ］を求める。高温時ほど燃焼安定性が高くなることから、テーブルの特性も図示したように高温時ほどＣＣＬＴの値が大きくなるように設定されている。
【００９９】
次に、ステップ７３にて、吸気系にスワールコントロールバルブを備える場合に、その開度に応じた補正量ＣＣＬＳ［ｄｅｇ］を求める。スワールコントロールバルブは、エンジン吸入ポート部の開口面積を制約することによりシリンダ内に流入する吸入混合気の流速を高める装置である。その開度を減じるほど吸気流速が速くなり、新気と残留ガスとの混合が促されることなどから燃焼限界も進角側に移動する。そこで、図２２に示したように、スワールコントロールバルブの開度が小さくなるほど進角側の値を与えるように設定されたテーブルを参照することでＣＣＬＳを設定する。
【０１００】
図２１および図２２の特性も線形であるので、テーブル検索ではなく関数式を演算する手法によりＣＣＬＴ、ＣＣＬＳを求めるようにしてもコントローラの演算負荷を過大にするおそれはない。
【０１０１】
最後のステップ７４にて前述のＣＣＬ、ＣＣＬＴ、ＣＣＬＳを加算したものをノック限界点火時期ＣＣＬＣＡＬとして設定する。
【０１０２】
前述のようにして求められた基本点火時期ＭＢＴＣＡＬ、ノック限界点火時期ＫＮＫＣＡＬ、燃焼限界点火時期ＣＣＬＣＡＬのうち、図１４により説明したように最小のもの、すなわち最も遅角側の点火時期を与えるものが外乱に対応した点火時期最小値ＰＡＤＶとして選択され、この点火時期最小値ＰＡＤＶに対して各種の補正を施して算出された点火時期指令値ＱＡＤＶが図２の点火時期制御部６１に付与される。
【０１０３】
この実施形態ではＭＢＴを与える基本点火時期ＭＢＴＣＡＬ、ノック限界点火時期ＫＮＫＣＡＬ、燃焼限界点火時期ＣＬＣＣＡＬの三者を比較して最小のものを選択するようにしているが、基本点火時期ＭＢＴＣＡＬと、ノック限界点火時期ＫＮＫＣＡＬまたは燃焼限界点火時期ＣＬＣＣＡＬの何れか一方とを比較して、より小さいほうを最適点火時期最小値ＰＡＤＶとして選択するようにしてもよい。
【０１０４】
このようにして、基本点火時期ＭＢＴＣＡＬを基本としてこれをノック限界点火時期ＫＮＫＣＡＬまたは燃焼限界点火時期ＣＬＣＣＡＬと比較し、最遅角となる点火時期を選択する構成とすることにより、外乱によって変動する点火時期の特性からより適切なものを比較的簡単な演算処理により求めて適切に点火時期を制御することが可能となる。
【０１０５】
図２３〜図２５は本発明の点火時期算出手法に関する第２の実施形態を示している。この実施形態は、前提となるエンジンシステムおよび点火時期システムの構成は図１または図２に示したものと同じであるが、既出の基本点火時期ＭＢＴＣＡＬの演算に用いた主燃焼期間（ＢＵＲＮ２）をノック限界点火時期ＫＮＫＣＡＬの算出にも適用することにより、より物理モデルに近い形で高精度に最適点火時期値ＰＡＤＶを求められるようにした点で第１の実施形態と相違する。
【０１０６】
図２３に沿って説明すると、まずステップ８１にてシリンダ内で排気されずに残る残留ガスの量ＭＡＳＳＺと温度Ｔｅを算出する。残留ガス量ＭＡＳＳＺは燃焼室容積分の残ガス量と吸排気弁オーバーラップ中に排気系から吸気系へ逆流した排気ガスの量を加算して求めることができる。温度Ｔｅは吸入空気量等から近似的にテーブルで求めることができる。何れも算出手法そのものは例えば特開２００１−２２１１０５号公報等により公知である。
【０１０７】
続いて、ステップ８２にて、エアフローメータ３２、吸気温度センサ４３（図１参照）の出力結果からそれぞれ新気の量ＭＡＳＳＡとその温度Ｔａを読み込む。
【０１０８】
次に、ステップ８３では、前記ＭＡＳＳＺ、Ｔｅ、ＭＡＳＳＡ、Ｔａを用いて、次の（２５）式、（２６）式により、それぞれ圧縮開始時（吸気弁閉時）の混合気の量ＭＡＳＳＣ、混合気温度Ｔｃ０を求める。
ＭＡＳＳＣ＝ＭＡＳＳＡ＋ＭＡＳＳＺ … （２５）
Ｔｃ０＝（ＭＡＳＳＡ×Ｔａ＋ＭＡＳＳＺ×Ｔｅ）／（ＭＡＳＳＡ＋ＭＡＳＳＺ） ［Ｋ］ … （２６）
また、圧縮開始時の圧力Ｐｃ０を、吸気圧力センサ４４（図１参照）の出力結果から求める。圧力Ｐｃ０は、吸入空気量と回転速度から予測した値を用いてもよい。
【０１０９】
次のステップ８４では、既述した手法によりＭＢＴとなる基本点火時期ＭＢＴＣＡＬを求める。なお、この実施形態では前記ＭＢＴＣＡＬの演算過程（図１２）で求めた主燃焼期間ＢＵＲＮ２を燃焼速度の代表値として後の演算に用いている。
【０１１０】
ステップ８５以降は、ノック限界点火時期ＫＮＫＣＡＬの計算をするためのフローである。まずステップ８５にてノック指標値ＭＢＴＫＮを求める。ノック指標値ＭＢＴＫＮはＭＢＴ時の燃焼圧最大値クランク角から温度最高値クランク角近傍での瞬間的な自己着火時間（ｍｓ）であり、ここでは圧力最大値を示すクランクアングルを１３ｄｅｇＡＴＤＣ（以下、θＰＭＡＸ＝１３度と表す。）に設定した場合の例を、図２６のタイムチャートを参照しながら説明する。最初にθＰＭＡＸ＝１３度での平均温度Ｔｃと圧力Ｐｃとをそれぞれ次の（２７）式、（２８）式から求める。
Ｔｃ＝Ｔｃ０×ε^ｐｔ−１＋ＴＵＰ＃×Ｑ／ＭＡＳＳＣ ［Ｋ］ … （２７）
Ｐｃ＝Ｐｃ０×ε^ｐｔ（Ｔｃ＋ＴＵＰ＃×Ｑ／ＭＡＳＳＣ）／Ｔｃ×ＶＵＰ＃［ａｔａ］ … （２８）
ただし、ε ：圧縮比率、
Ｑ ：燃焼発熱量、
ＴＵＰ＃：温度上昇係数、
ｐｔ ：ポリトロープ指数＝１．３５
ＶＵＰ＃：ガス容積変化率
圧縮比率εは、吸気弁閉時（ＩＶＣ）の容積の、θＰＭＡＸ＝１３度時の容積に対する比率である。吸気弁の開閉時期を制御可能な可変吸気弁機構を備えたエンジンではその制御値から求めればよいし、開閉時期固定であれば既知の定数として設定すればよい。さらに精度を上げるには実質吸気量が確定するＩＶＣ＝実効ＩＶＣを用いればよいが、それは回転速度によってクランク角で進角方向に移動するため、回転速度からεを求める手法としてもよい。
【０１１１】
燃焼発熱量Ｑは、θＰＭＡＸ＝１３度での燃焼割合を６０％としたときの混合気の燃焼による発熱量である。
【０１１２】
温度上昇係数ＴＵＰ＃は、前記燃焼発熱量ＱがＭＡＳＳＣの量の混合気を加熱するときの計算に適用する係数である。ＴＵＰ＃にはもちろん比熱分も含まれる。
【０１１３】
ガス容積変化率ＶＵＰ＃は、ガソリンと空気の混合気が６０％燃焼して燃焼途中のガスになったときの分子量変化によるガス容積変化率である。具体的には、１より若干大きな値（例えば１．０３程度）を適用すればよい。
【０１１４】
また、ピストンの上昇と燃焼ガスの昇温膨張で圧縮された未燃混合気の温度Ｔを、次式から求める。
Ｔ＝Ｔｃ０×ε^ｐｔ−１（Ｔｃ／Ｔｃ０×ε^ｐｔ−１）^ｐｔ−１ ［Ｋ］… （２９）
最後に、前述のようにして求めたθＰＭＡＸ＝１３度での圧力Ｐｃと未燃混合気温度Ｔを用いて、次式からノック指標値ＭＢＴＫＮを求める。
ＭＢＴＫＮ＝ＯＣＴ×Ｐｃ^−１．７×ｅｘｐ（３８００／Ｔ）［ｍｓ］… （３０）
式中のＯＣＴは燃料のオクタン価によって決まる係数であり、例えばハイオクタンガソリンで１５程度、レギュラーガソリンで１０程度の値を用いる。この式は素反応の自己着火時間を求める式であり、基本的に従来から知られているものに基づいている。
【０１１５】
次のステップ８６では、ノック指標値ＭＢＴＫＮに対する燃焼速度補正係数ＫＮＦＬＶを求める。エンジンのノッキングの発生においては温度・圧力が時々刻々と変化するため、実際の自己着火時間は温度・圧力が高く保持される時間の影響を強く受けるので、燃焼が早いとノックが起きにくく、遅いとノッキングが起きやすい。そこでこの実施形態では、ＭＢＴ計算で求めた主燃焼期間ＢＵＲＮ２を用いて前記補正係数ＫＮＦＬＶを求める。その特性例を図２４に示すが、主燃焼期間ＢＵＲＮ２が長い、つまり燃焼が遅いと小さな値となり、ノッキングが起きやすい方向に補正される特性となっている。
【０１１６】
次に、ステップ８７にて、前記ＭＢＴＫＮとＫＮＦＬＶを用いたマップ検索により、トレースノックを得るためのＭＢＴからの遅角量ＫＮＲＴを求める。図２５にその特性例を示すが、縦軸ＭＢＴＫＮ×ＫＮＦＬＶで割り付けられ、横軸回転速度Ｎｅで割り付けられたマップから遅角量ＫＮＲＴを求める。これは縦軸の数値が増大するほど、回転速度が低下するほど、遅角量が増大する特性となっている。
【０１１７】
次のステップ８８で、次式からノック限界点火時期ＫＮＫＣＡＬを求める。
ＫＮＫＣＡＬ＝ＭＢＴＣＡＬ−ＫＮＲＴ … （３１）
ステップ８９，９０では、ＭＢＴＣＡＬとＫＮＫＣＡＬのうちから小さい方つまり遅角側のものを点火時期最小値ＰＡＤＶとして選択し、これに各種の補正を加えたものを図２の点火時期制御部６１に引き渡す点火時期指令値ＱＡＤＶとして設定して今回の処理を終了する。
【図面の簡単な説明】
【図１】本発明の実施形態に係る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】物理量の計算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】初期燃焼期間の計算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】主燃焼期間の計算を説明するためのフローチャート。
【図１３】基本点火時期の計算を説明するためのフローチャート。
【図１４】本発明による点火時期制御に係る第一の実施形態の処理手順を表したフローチャート。
【図１５】ノック限界点火時期の計算を説明するためのフローチャート。
【図１６】ノック限界点火時期の基本値を与えるマップの説明図。
【図１７】ノック限界点火時期に対する温度補正量を与えるテーブルの説明図。
【図１８】ノック限界点火時期に対する湿度補正量を与えるテーブルの説明図。
【図１９】燃焼限界点火時期の計算を説明するためのフローチャート。
【図２０】燃焼限界点火時期の基本値を与えるマップの説明図。
【図２１】燃焼限界点火時期に対する温度補正量を与えるテーブルの説明図。
【図２２】燃焼限界点火時期に対してスワールコントロールバルブ開度に応じた補正量を与えるテーブルの説明図。
【図２３】本発明による点火時期制御に係る第二の実施形態の処理手順を表したフローチャート。
【図２４】ノック指標値の特性図。
【図２５】トレースノックを与えるＭＢＴからの遅角量の特性図。
【図２６】第二の実施形態の制御に係るタイムチャート。
【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
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 improvement in an ignition timing control device for a spark ignition engine.
[0002]
[Prior art]
2. Description of the Related Art As a conventional ignition timing control device, there has been known an ignition timing control device as shown in Patent Document 1. In this type of conventional ignition timing control device, a basic correction timing determined based on an operation state signal such as an engine speed or a load is subjected to a predetermined correction in consideration of a coolant temperature, a combustion speed, and the like. Basically, the ignition timing is controlled near the maximum torque point MBT. However, the control target is not always the MBT. For example, in a region where knocking occurs, it is necessary to correct the ignition timing to be delayed from the MBT so as to cause a trace knock. In the region, in the MBT, the combustion stability is reduced and partial combustion or misfire occurs due to blowout, and the amount of HC emission is large. Therefore, the ignition timing retard is also required. For such ignition timing correction, for example, a method of referring to a trimming map in which a correction amount is assigned by rotation and load is used.
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 10-30535
[0004]
[Problems to be solved by the invention]
However, if the knocking characteristics or combustion stability changes due to changes in the operating environment or operating conditions of the engine, or variations or deterioration of the equipment, it is necessary to correct the ignition timing to cope with such changes. Since the region where the disturbance factor acts cannot be specified accurately, there is a possibility that the fuel consumption and the exhaust performance may be impaired by correcting the unnecessary region. If an attempt is made to correct the ignition timing accurately for such a disturbance factor, the number of determination conditions increases, the control logic becomes complicated, or an extremely large number of man-hours are required for preliminary matching.
[0005]
Summary of the Invention
According to the present invention, an MBT ignition timing and a knock limit ignition timing are respectively obtained as basic ignition timing elements of a spark ignition type engine in accordance with an operation state, and the ignition timing control is performed based on the later one of these. As a result, even if either the MBT or the knock limit ignition timing changes due to disturbance, it is possible to set a more preferable ignition timing in terms of fuel consumption and exhaust performance as a result of separately correcting each of them. Further, in this case, since the correction for the disturbance is performed by the calculation, the optimum ignition timing control can be realized with relatively simple logic and man-hour.
[0006]
The MBT ignition timing or the knock limit ignition timing can be calculated using the combustion speed of the air-fuel mixture in the cylinder, thereby obtaining a highly accurate calculation result while reducing a calculation load such as a memory capacity and a calculation time. be able to.
[0007]
As an element of the ignition timing affected by the disturbance, an ignition timing of a combustion stable limit (hereinafter simply referred to as a combustion limit) can be further added. By comparing and selecting the latest ignition timing, more accurate ignition timing control can be performed.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining the system of the present invention.
[0009]
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.
[0010]
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.
[0011]
When a spark is blown by the spark plug 14 and ignites the compressed air-fuel mixture slightly before the compression top dead center, the flame spreads and burns rapidly, 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.
[0012]
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.
[0013]
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.
[0014]
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. Depending on the operating conditions, as the amount of the inert gas in the combustion chamber 5 increases, the pumping loss decreases and the fuel efficiency improves, so the target intake valve closing is determined as to how much inert gas should remain in the combustion chamber 5 depending on the operating conditions. The timing and the target exhaust valve closing timing are determined in advance. 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. As described above, 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.
[0015]
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.
[0016]
FIG. 2 is a block diagram of the ignition timing control performed in the engine controller 31 and mainly shows details of a part for obtaining an ignition timing MBTCAL which becomes MBT. This system mainly 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 an ignition timing command value calculator 57. Become.
[0017]
The initial combustion period calculation unit 52 calculates a period from the time when the air-fuel mixture is ignited to the time when the flame kernel is formed as an initial combustion period BURN1. The main combustion period calculation unit 53 calculates a period from the formation of the flame kernel to the combustion pressure reaching 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 a 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 can be obtained based on the combustion period BURN.
[0018]
The ignition timing command value calculator 57 compares the MBTCAL with a knock limit ignition timing KNKCAL and a combustion limit ignition timing CCLCAL calculated by a method described later, based on the MBTCAL, as shown in the flow chart of FIG. Is selected as the ignition timing minimum value PADV, the ignition timing command value QADV is calculated by adding various corrections to the ignition timing minimum value PADV, and is output to the ignition timing control unit 61. . In addition, the flowchart used in the following description including FIG. 14 shows the procedure of the arithmetic processing repeatedly executed by the controller 31 at a fixed time, for example, at a cycle of about 10 ms.
[0019]
The ignition timing control unit 61 determines the energization angle and the non-energization angle to the ignition coil 13 so that the ignition plug 14 ignites the air-fuel mixture in the combustion chamber 5 with the ignition timing command value QADV obtained in this manner. Control.
[0020]
Hereinafter, an example of a calculation method of the above-described basic ignition timing MBTCAL, knock limit ignition timing KNKCAL, and combustion limit ignition timing CCLCAL will be described in further detail.
[0021]
As shown in FIG. 3, the crank angle at which the combustion pressure of the air-fuel mixture becomes 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 within a range of 12 to 15 degrees, and a maximum of 10 to 20 degrees.
[0022]
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%.
[0023]
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.
[0024]
On the other hand, during the main combustion period, the flame propagates from the flame nucleus to the outer region, 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.
[0025]
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 the 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 the ignition timing dead time, which will be described later, is further obtained. The crank angle position to which the crank angle IGNDEAD [deg] is added is set as the basic ignition timing MBTCAL [degBTDC], which is the ignition timing at which MBT can be obtained.
[0026]
The pressure and temperature in the combustion chamber 5 during the initial combustion period in which the flame nucleus is formed are almost 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 time MBTCCYCL [degBTDC] by the previous combustion start time 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.
[0027]
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.
[0028]
FIG. 5 is for calculating various physical quantities required for calculating the ignition timing, and is executed at regular intervals (for example, every 10 msec).
[0029]
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].
[0030]
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] has been calculated.
[0031]
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.
[0032]
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 a calculation method thereof is known, for example, from Japanese Patent Application Laid-Open No. 2001-221105. The dead ignition time DEADTIME is a constant value.
[0033]
The target equivalent 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.
[0034]
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.
[0035]
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.
[0036]
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).
[0037]

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 node 75 and 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), the volume VIVC of the combustion chamber 5 at the intake valve closing timing can be calculated. 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.
[0038]
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.
[0039]
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.
[0040]
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.
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
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 can be considered to be constant.
[0045]
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. .
[0046]
IGNDEAD = f5 (DEADTIME, NRPM) (10)
Here, the dead ignition time DEADTIME is set to 200 μsec. The equation (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.
[0047]
FIG. 10 is for calculating the initial combustion period BURN1 [deg], and FIG. 12 is for calculating the main combustion period BURN2 [deg], which 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.
[0048]
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 TITI [K] at the intake valve closing timing of the combustion chamber 5 calculated in step 13 of FIG. 5, the engine speed NRPM [rpm], and the reaction probability RPROBA [% calculated in step 14 of FIG. ] Is read.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
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.
[0053]
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.
[0054]
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 a power calculation (the same applies hereinafter).
[0055]
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, the calculation accuracy can be further improved by experimentally obtaining the value of κ for the air-fuel mixture.
[0056]
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.
[0057]
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.
[0058]
In step 26, the laminar combustion speed SL1 [m / sec] is calculated by the following equation (known).
[0059]
SL1 = SLstd × (T0 × Tstd) ^2.18 × (P0 / Pstd) ^-0.16 … (15)
Here, Tstd: reference temperature [K],
Pstd: Reference pressure [Pa],
SLstd: reference laminar combustion velocity [m / sec] at reference temperature Tstd and reference pressure Pstd,
T0: temperature [K] at the combustion start timing of the combustion chamber 5,
P0: pressure [Pa] at the combustion start timing of the combustion chamber 5
The reference temperature Tstd, the reference pressure Pstd, and the reference laminar combustion speed SLstd are values determined in advance by experiments.
[0060]
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.
[0061]
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.
[0062]

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.
[0063]
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.
[0064]
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.
[0065]
ST1 = f10 (NRPM) = C1 × NRPM (17)
Where C1: constant
The turbulence strength ST1 can also be obtained from a table using the rotation speed NRPM as a parameter.
[0066]
In step 28, the gas burning speed FLAME1 [m / sec] in the initial combustion is calculated from the following equation from the laminar burning speed S1 and the turbulence intensity ST1.
[0067]
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.
[0068]
In step 29, the initial combustion period BURN1 [deg] is calculated by the following equation.
[0069]
BURN1 = {(NRPM × 6) × (BR1 × V0)} / (PROROBA × AF1 × FLAME1) (19)
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.
[0070]
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.
[0071]
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.
[0072]
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.
[0073]
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.
[0074]
FLAME2 = SL2 × ST2 (21)
Here, SL2: laminar combustion velocity [m / sec]
Equation (21) takes into account the contribution to the combustion speed due to gas turbulence, as in equation (18).
[0075]
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.
[0076]
In step 34, the main combustion period BURN2 [deg] is calculated by the following equation similar to the equation (19).
[0077]
BURN2 = {(NRPM × 6) × (BR2 × V2)} / (PROROBA × AF2 × FLAME2) (22)
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 ]
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.
[0078]
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.
[0079]
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 crank equivalent to the ignition timing dead time calculated in step 16 of FIG. The angle IGNDEAD and the reference crank angle θPMAX calculated in step 15 of FIG. 5 are read.
[0080]
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].
[0081]
In step 43, the basic ignition timing MBTCAL [degBTDC] is calculated by the following equation.
[0082]
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].
[0083]
The basic ignition timing MBTCAL calculated in this way is compared with a knock limit or a combustion limit ignition timing to be described later, and the minimum value (the closest value) of these is selected as the ignition timing minimum value PADV [degBTDC]. Is done. The ignition timing command value QADV [degBTDC] is calculated by adding various corrections to the ignition timing minimum value PADV, such as retarding for early exhaust temperature rise and retarding for shifting down torque. I do. 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.
[0084]
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.
[0085]
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.
[0086]
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.
[0087]
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.
[0088]
Thus, by calculating the combustion periods BURN1 and BURN2 as a function of various parameters affecting 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, since the combustion period BURN is calculated separately for the initial combustion period BURN1 corresponding to the flame kernel growth period in which the temperature and pressure are greatly affected, and the main combustion period in which the temperature and pressure are less affected, the combustion period BURN is calculated. BURN calculation accuracy is improved. By further dividing the combustion period BURN into three or more, the calculation accuracy can be further improved.
[0089]
Here, the combustion speed FLAME1 used in the calculation of 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 in the calculation of the main combustion period BURN2 is the turbulence with the laminar combustion speed SL2. Although each is calculated as a product of the strengths ST2, it may be obtained by a calculation method by addition as described in JP-A-10-30535. In addition, 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%). Is not necessarily limited to this numerical value.
[0090]
Next, calculation of knock limit ignition timing KNKCAL will be described with reference to FIGS.
[0091]
FIG. 15 is a flowchart showing the calculation method. In the figure, first, at step 61, it is determined whether the fuel is high-octane gasoline or regular gasoline. This determination method is variously known, and is performed by, for example, ignition timing feedback control using a knock sensor. Next, according to the determination result, if it is high-octane gasoline, in step 62, if it is regular gasoline, in step 63, the basics of the ignition timing correction amount corresponding to the knock limit are obtained from the respective maps. The value KNM [deg] is obtained. FIG. 16 shows an example of the map. As shown in the drawing, the value of KNM is assigned to this map using the engine speed Ne and the load (fuel injection amount) Tp as parameters. In general, a smaller value, that is, a value on the retard side is set because knocking is more likely to occur at a lower rotation and a higher load, but the value increases as the fuel octane number increases, even at the same rotation speed and load.
[0092]
Next, at step 64, the temperature T0a [K] of the intake air-fuel mixture is obtained by the following equation.
[0093]
T0a = Ta × WTTA # + Tw (1-WTTA #) (24)
Here, Ta: intake air temperature [K],
Tw: Cooling water temperature [K]
WTTA #: Constant determined according to the engine
This T0a is a value that internally divides between the engine coolant temperature Tw and the intake air temperature Ta. That is, since the temperature of the intake air taken into the cylinder rises with respect to the temperature of the outside air (≒ Ta) due to the effect of the engine temperature in the intake system, the temperature is corrected by the cooling water temperature Tw.
[0094]
In the next step 65, a temperature-dependent correction amount KNT [deg] is obtained from the intake air-fuel mixture temperature T0a with reference to a table as shown in FIG. Further, in step 66, a correction amount KNW [deg] based on the humidity is obtained from the humidity (water vapor partial pressure) obtained by a known method with reference to a table as shown in FIG. Since each of the correction amounts KNT and KNW changes with a simple linear characteristic as shown, a corresponding linear function may be set and calculated. It should be noted that the temperature correction amount KNT may be set using the combustion chamber temperature T0 obtained by the equation (14) instead of the intake air-fuel mixture temperature T0a.
[0095]
Finally, in step 67, the sum of the aforementioned KNM, KNT, and KNW is set as knock limit ignition timing KNKCAL.
[0096]
Next, the calculation of the ignition timing CCLCAL at the combustion limit will be described with reference to FIGS.
[0097]
FIG. 19 is a flowchart showing the calculation method. In the figure, first, at step 71, a basic value CCL [deg] is obtained with reference to the map shown in FIG. The parameters are the engine speed Ne and the load Tp. Generally, the lower the rotational speed and the lower the load, the lower the flow velocity of the air-fuel mixture, and the poorer the mixture of the residual gas in the cylinder and the fresh air, so that the combustion flame is difficult to propagate. Move to the retard side.
[0098]
Next, in step 72, a correction amount CCLT [deg] based on the temperature is calculated from the intake air-fuel mixture temperature T0a (or the combustion chamber temperature T0) obtained by the above equation (24) with reference to the table shown in FIG. Ask. Since the combustion stability increases as the temperature increases, the characteristics of the table are also set so that the CCLT value increases as the temperature increases, as shown in the drawing.
[0099]
Next, in step 73, when the intake system is provided with a swirl control valve, a correction amount CCLS [deg] corresponding to the opening degree is obtained. The swirl control valve is a device that increases the flow rate of the intake air-fuel mixture flowing into the cylinder by restricting the opening area of the engine intake port. As the opening is reduced, the intake flow velocity becomes faster, and the mixing of fresh air and residual gas is promoted, so that the combustion limit also moves to the advanced side. Therefore, as shown in FIG. 22, the CCLS is set by referring to a table set to give a value on the advance side as the opening of the swirl control valve decreases.
[0100]
Since the characteristics in FIGS. 21 and 22 are also linear, even if the CCLT and CCLS are obtained by a method of calculating a function expression instead of a table search, there is no possibility that the calculation load of the controller becomes excessive.
[0101]
In the last step 74, the sum of the above-mentioned CCL, CCLT and CCLS is set as knock limit ignition timing CCLCAL.
[0102]
Among the basic ignition timing MBTCAL, the knock limit ignition timing KNKCAL, and the combustion limit ignition timing CCLCAL obtained as described above, the one giving the smallest ignition timing as described with reference to FIG. The ignition timing command value QADV, which is selected as the ignition timing minimum value PADV corresponding to the disturbance and is obtained by performing various corrections on the ignition timing minimum value PADV, is given to the ignition timing control unit 61 in FIG.
[0103]
In this embodiment, the minimum value is selected by comparing the basic ignition timing MBTCAL giving the MBT, the knock limit ignition timing KNKCAL, and the combustion limit ignition timing CLCCAL, but the basic ignition timing MBTCAL and the knock limit The ignition timing may be compared with one of the ignition timing KNKCAL and the combustion limit ignition timing CLCCAL, and the smaller one may be selected as the optimum ignition timing minimum value PADV.
[0104]
In this manner, the basic ignition timing MBTCAL is basically compared with the knock limit ignition timing KNKCAL or the combustion limit ignition timing CLCCAL, and the ignition timing with the most retarded angle is selected, so that the ignition timing fluctuates due to disturbance. From the characteristics of the timing, a more appropriate one can be obtained by relatively simple arithmetic processing, and the ignition timing can be appropriately controlled.
[0105]
23 to 25 show a second embodiment relating to the ignition timing calculation method of the present invention. In this embodiment, the configurations of the engine system and the ignition timing system which are the premise are the same as those shown in FIG. 1 or FIG. 2, but the main combustion period (BURN2) used for the calculation of the basic ignition timing MBTCAL already described is used. The present embodiment is different from the first embodiment in that the present invention is applied to the calculation of the knock limit ignition timing KNKCAL so that the optimum ignition timing value PADV can be obtained with high accuracy in a form closer to a physical model.
[0106]
Referring to FIG. 23, first, in step 81, the amount MASSZ of residual gas remaining without being exhausted in the cylinder and the temperature Te are calculated. The residual gas amount MASSZ can be obtained by adding the residual gas amount corresponding to the volume of the combustion chamber and the amount of the exhaust gas flowing backward from the exhaust system to the intake system during the overlap of the intake and exhaust valves. The temperature Te can be approximately obtained from a table from the intake air amount or the like. In any case, the calculation method itself is known from, for example, JP-A-2001-221105.
[0107]
Subsequently, in step 82, the fresh air amount MASASA and its temperature Ta are read from the output results of the air flow meter 32 and the intake air temperature sensor 43 (see FIG. 1).
[0108]
Next, in step 83, using the MASSZ, Te, MASSA, and Ta, the following formulas (25) and (26) are used to calculate the amount MASSC of the air-fuel mixture at the start of compression (when the intake valve is closed). The air temperature Tc0 is determined.
MASSC = MASSA + MASSZ (25)
Tc0 = (MASSA × Ta + MASSZ × Te) / (MASSA + MASSZ) [K] (26)
Further, the pressure Pc0 at the start of compression is obtained from the output result of the intake pressure sensor 44 (see FIG. 1). As the pressure Pc0, a value predicted from the intake air amount and the rotation speed may be used.
[0109]
In the next step 84, the basic ignition timing MBTCAL that becomes the MBT is obtained by the method described above. In this embodiment, the main combustion period BURN2 obtained in the process of calculating the MBTCAL (FIG. 12) is used as a representative value of the combustion speed in subsequent calculations.
[0110]
Step 85 and subsequent steps are a flow for calculating the knock limit ignition timing KNKCAL. First, at step 85, a knock index value MBTKN is determined. Knock index value MBTKN is an instantaneous self-ignition time (ms) from the maximum combustion pressure crank angle at the time of MBT to the vicinity of the maximum temperature crank angle. Here, the crank angle indicating the maximum pressure is 13 degATDC (hereinafter, θPMAX). = 13 degrees) will be described with reference to the time chart of FIG. First, the average temperature Tc and pressure Pc at θPMAX = 13 degrees are obtained from the following equations (27) and (28), respectively.
Tc = Tc0 × ε ^pt-1 + TUP # × Q / MASSC [K] (27)
Pc = Pc0 × ε ^pt (Tc + TUP # × Q / MASSC) / Tc × VUP # [ata] (28)
Where ε: compression ratio,
Q: calorific value of combustion,
TUP #: temperature rise coefficient,
pt: polytropic index = 1.35
VUP #: Gas volume change rate
The compression ratio ε is a ratio of the volume when the intake valve is closed (IVC) to the volume when θPMAX = 13 degrees. In an engine provided with a variable intake valve mechanism capable of controlling the opening and closing timing of an intake valve, the value may be obtained from the control value. If the opening and closing timing is fixed, it may be set as a known constant. In order to further improve the accuracy, it is sufficient to use IVC = effective IVC at which the actual intake air amount is determined. However, since it moves in the advance direction at the crank angle depending on the rotation speed, a method of obtaining ε from the rotation speed may be used.
[0111]
The combustion calorific value Q is a calorific value due to combustion of the air-fuel mixture when the combustion ratio at θPMAX = 13 degrees is 60%.
[0112]
The temperature rise coefficient TUP # is a coefficient applied to the calculation when the combustion heat generation amount Q heats the air-fuel mixture of the amount of MASSC. TUP # naturally includes specific heat.
[0113]
The gas volume change rate VUP # is a gas volume change rate due to a change in molecular weight when a mixture of gasoline and air is burned by 60% to become a gas during combustion. Specifically, a value slightly larger than 1 (for example, about 1.03) may be applied.
[0114]
Further, the temperature T of the unburned air-fuel mixture compressed by the rise of the piston and the thermal expansion of the combustion gas is obtained from the following equation.
T = Tc0 × ε ^pt-1 (Tc / Tc0 × ε ^pt-1 ) ^pt-1 [K] ... (29)
Finally, using the pressure Pc at θPMAX = 13 degrees and the unburned mixture temperature T obtained as described above, a knock index value MBTKN is obtained from the following equation.
MBTKN = OCT × Pc ^-1.7 × exp (3800 / T) [ms] (30)
OCT in the equation is a coefficient determined by the octane number of the fuel. For example, a value of about 15 for high-octane gasoline and about 10 for regular gasoline is used. This equation is for calculating the self-ignition time of the elementary reaction, and is basically based on a conventionally known one.
[0115]
In the next step 86, a combustion speed correction coefficient KNFLV for the knock index value MBTKN is determined. In the event of engine knocking, the temperature and pressure change every moment, so the actual self-ignition time is strongly affected by the time during which the temperature and pressure are maintained at a high level. And knocking is easy to occur. Therefore, in this embodiment, the correction coefficient KNFLV is obtained by using the main combustion period BURN2 obtained by MBT calculation. FIG. 24 shows an example of the characteristic. When the main combustion period BURN2 is long, that is, when the combustion is slow, the value becomes small, and the characteristic is corrected in a direction in which knocking is likely to occur.
[0116]
Next, at step 87, a map search is performed using the MBTKN and KNFLV to obtain a retardation amount KNRT from the MBT for obtaining a trace knock. FIG. 25 shows an example of the characteristic. The retardation amount KNRT is obtained from a map which is assigned by the vertical axis MBTKN × KNFLV and assigned by the horizontal axis rotation speed Ne. This is a characteristic that the retard amount increases as the numerical value on the vertical axis increases and the rotational speed decreases.
[0117]
In the next step 88, knock limit ignition timing KNKCAL is determined from the following equation.
KNKCAL = MBTCAL-KNRT (31)
In steps 89 and 90, the smaller one of MBTCAL and KNKCAL, that is, the one on the retard side is selected as the ignition timing minimum value PADV, and a value obtained by adding various corrections to the selected value is delivered to the ignition timing controller 61 in FIG. This is set as the ignition timing command value QADV, and the current process ends.
[Brief description of the drawings]
FIG. 1 is a control system diagram of an engine according to an embodiment of the present invention.
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 illustrating the 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 showing a processing procedure of a first embodiment relating to ignition timing control according to the present invention.
FIG. 15 is a flowchart for explaining calculation of a knock limit ignition timing.
FIG. 16 is an explanatory diagram of a map for giving a basic value of a knock limit ignition timing.
FIG. 17 is an explanatory diagram of a table for giving a temperature correction amount with respect to a knock limit ignition timing.
FIG. 18 is an explanatory diagram of a table for providing a humidity correction amount with respect to a knock limit ignition timing.
FIG. 19 is a flowchart for explaining calculation of a combustion limit ignition timing.
FIG. 20 is an explanatory diagram of a map that gives a basic value of a combustion limit ignition timing.
FIG. 21 is an explanatory diagram of a table for giving a temperature correction amount with respect to a combustion limit ignition timing.
FIG. 22 is an explanatory diagram of a table that gives a correction amount corresponding to a swirl control valve opening to a combustion limit ignition timing.
FIG. 23 is a flowchart showing a processing procedure of a second embodiment relating to ignition timing control according to the present invention.
FIG. 24 is a characteristic diagram of a knock index value.
FIG. 25 is a characteristic diagram of the amount of retard from the MBT that gives a trace knock.
FIG. 26 is a time chart according to the control of the second embodiment.
[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
45 Exhaust gas temperature sensor
46 Exhaust pressure sensor

Claims (4)

Operating state detecting means for detecting an operating state of the spark ignition engine;
MBT calculating means for calculating MBT ignition timing using the operating state;
Knock limit calculation means for calculating a knock limit ignition timing using the operating state,
Ignition timing selecting means for selecting a later one of the MBT ignition timing and the knock limit ignition timing;
An ignition timing control device for outputting an ignition timing based on the selected ignition timing. Operating state detecting means for detecting an operating state of the spark ignition engine;
MBT calculating means for calculating MBT ignition timing using the operating state;
Combustion limit calculation means for calculating the ignition timing of the combustion limit using the operating state,
Ignition timing selecting means for selecting a later one of the MBT ignition timing and the combustion limit ignition timing;
An ignition timing control device for outputting an ignition timing based on the selected ignition timing. Operating state detecting means for detecting an operating state of the spark ignition engine;
MBT calculating means for calculating MBT ignition timing using the operating state;
Knock limit calculation means for calculating a knock limit ignition timing using the operating state,
Combustion limit calculation means for calculating the ignition timing of the combustion limit using the operating state,
Ignition timing selecting means for selecting the latest ignition timing among the MBT ignition timing, knock limit ignition timing, and combustion limit ignition timing;
An ignition timing control device for outputting an ignition timing based on the selected ignition timing. Operating state detecting means for detecting an operating state of the spark ignition engine;
Combustion speed calculation means for calculating the combustion speed of the air-fuel mixture in the cylinder using the operating state;
MBT calculating means for calculating MBT ignition timing using the combustion speed;
Knock limit calculating means for calculating a knock limit ignition timing using the combustion speed,
Ignition timing selecting means for selecting a later one of the MBT ignition timing and the knock limit ignition timing;
An ignition timing control device for outputting an ignition timing based on the selected ignition timing.

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