JP2004176637A - Controller for spark ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for a spark ignition engine which can obtain the maximum fuel consumption improving effect by a lean combustion, especially by a compression self-ignition while securing the combustion stability, and the fuel consumption improving effect by stopping the fuel supply in a decelerating region. <P>SOLUTION: Burned gas discharged from preceding cylinders 2A, 2D on the side of exhaust stroke among a pair of cylinders overlapping the exhaust stroke and the intake stroke, is introduced into subsequent cylinders 2B, 2C on the side of intake stroke through a gas passage 22 between cylinders, and only the gas discharged from the subsequent cylinders 2B, 2C is led to an exhaust passage 20. In the preceding cylinders 2A, 2D, combustion is performed in such a state that lean air-fuel ratio is larger than theoretical air-fuel ratio by a predetermined amount. In the subsequent cylinders 2B, 2C, fuel is supplied into the burned gas introduced from the preceding cylinders 2A, 2D and combustion is performed by compression self-ignition. Further, when returning to the fuel supplying state from the fuel supply stopping state, combustion is performed by compulsive ignition in such a state that air-fuel ratio is substantially equal to the theoretical air-fuel ratio in the preceding cylinders 2A, 2D. <P>COPYRIGHT: (C)2004,JPO

Description

【００７１】
吸入空気量制御手段４３は、アクチュエータ１８を制御することによりスロットル弁１７の開度（スロットル開度）を制御するものであり、運転状態に応じてマップ等から目標吸入空気量を求め、その目標吸入空気量に応じてスロットル開度を制御する。ここで、２気筒接続状態として先行気筒２Ａ，２Ｄおよび後続気筒２Ｂ，２Ｃで燃焼を行わせる時は、先行気筒２Ａ，２Ｄに供給された空気で、先行気筒２Ａ，２Ｄおよび後続気筒２Ｂ，２Ｃに供給された燃料を燃焼し得るようにスロットル開度が調節される。
【００７２】
燃焼制御手段４４は、燃料噴射制御手段４５と点火制御手段４６とからなっており、燃料噴射制御手段４５により、各気筒２Ａ〜２Ｄに設けられた燃料噴射弁９からの燃料噴射量や噴射タイミング、或いは燃料供給の停止や復帰をエンジンの運転状態に応じて制御するとともに、点火制御手段４６により運転状態に応じた点火時期の制御及び点火停止等の制御を行う。従って、各気筒における空燃比も燃焼制御手段４４によって設定される。
【００７３】
ガス通路冷却制御手段４９は、２気筒接続状態にあるとき、気筒間ガス通路２２内を流れる既燃ガス温度の制御を行う。ガス通路冷却制御手段４９は、筒内温度状態推測手段５３による後続気筒の混合気温度の推定値（詳細は後述する）に基き、その混合気温度が所定値以上であるとき、冷却用ポンプ駆動モータ５１を作動させる。その冷却用ポンプ駆動モータ５１に駆動される冷却用ポンプ５０によって冷却水が冷却水通路５２内を循環し、ウォータージャケット２６内の気筒間ガス通路２２を冷却する。このため、先行気筒２Ａ，２Ｄから気筒間ガス通路２２を経由して後続気筒２Ｂ，２Ｃに導かれる既燃ガスの温度が降下するので、後続気筒２Ｂ，２Ｃの筒内温度が圧縮自己着火に適した温度に維持される。
【００７４】
筒内温度状態推測手段５３は、特殊運転モード中の後続気筒の筒内温度状態を推測し、燃焼直前の混合気温度を推定する。その推定値に基いて、弁停止機構制御手段４２ではガス流通経路の切換えを行い、燃焼制御手段４４では先行気筒の空燃比の補正を行い、ガス通路冷却制御手段４９では冷却用ポンプ駆動モータ５１のＯＮ／ＯＦＦを切換える。
【００７５】
図５は、筒内温度状態推測手段５３による２気筒接続状態の際の後続気筒２Ｂ，２Ｃの筒内温度推測手順の主要ブロック図である。図５は、縦３列の構成になっているが、左列のＰ１０〜Ｐ２６は、ＥＣＵ４０に入力される各種センサからの信号やＥＣＵ４０内部のパラメータにより、直接あるいは簡単な演算で得られる入力パラメータである。中央列の既燃ガス流量Ｐ３０は、演算過程で得られる中間パラメータである。右列の先行気筒既燃ガス温度Ｐ４０、気筒間ガス通路内の既燃ガス温度Ｐ５０は主要な演算結果であり、後続気筒の燃焼直前の混合気温度Ｐ６０は、最終的な演算結果である。このように筒内温度状態推測手段５３は、各入力パラメータから先行気筒既燃ガス温度Ｐ４０、気筒間ガス通路内の既燃ガス温度Ｐ５０を順に求めて行き、最終的に後続気筒の燃焼直前の混合気温度Ｐ６０を求めるようになっている。
【００７６】
先行気筒既燃ガス温度Ｐ４０を求める過程を先行気筒演算部、気筒間ガス通路内の既燃ガス温度Ｐ５０を求める過程を気筒間ガス通路演算部、そして後続気筒の燃焼直前の混合気温度Ｐ６０を求める過程を後続気筒演算部として、次にこれらについて説明する。
【００７７】
最初の先行気筒演算部では、先行気筒空燃比Ｐ１０、点火時期Ｐ１２、エンジン冷却水温Ｐ１４、吸気温度Ｐ１６、エンジン回転数Ｐ１８および空気充填量Ｐ２０によって先行気筒既燃ガス温度Ｐ４０が求められる。先行気筒空燃比Ｐ１０は、エアフローセンサ１９による吸入空気量と、燃料噴射制御手段４５による燃料噴射量から求められるパラメータであり、リニアＯ_２センサ２５でフィードバック制御される。点火時期Ｐ１２は、燃料噴射制御手段４５により決定されるパラメータである。エンジン冷却水温Ｐ１４、吸気温度Ｐ１６、エンジン回転数Ｐ１８および空気充填量Ｐ２０は、それぞれエンジン冷却水温センサ５６、吸気温センサ２７、回転数センサ４７およびエアフローセンサ１９により得られるパラメータである。
【００７８】
次の気筒間ガス通路演算部では、先行気筒演算部で得られた先行気筒既燃ガス温度Ｐ４０と、吸気温度Ｐ１６、車速Ｐ２２、ガス通路冷却水温Ｐ２４および既燃ガス流量Ｐ３０とから、気筒間ガス通路内の既燃ガス温度Ｐ５０が求められる。車速Ｐ２２およびガス通路冷却水温Ｐ２４は、車速センサ５５およびガス通路冷却水温センサ５７から得られるパラメータである。既燃ガス流量Ｐ３０は、エンジン回転数Ｐ１８と空気充填量Ｐ２０とにより算出される中間パラメータである。
【００７９】
最後の後続気筒演算部では、気筒間ガス通路内の既燃ガス温度Ｐ５０と、エンジン回転数Ｐ１８、空気充填量Ｐ２０、既燃ガス流量Ｐ３０および後続気筒空燃比Ｐ２６とから、後続気筒の燃焼直前の混合気温度Ｐ６０が求められる。後続気筒空燃比Ｐ２６は、先行気筒空燃比Ｐ１０と燃料噴射制御手段４５による燃料噴射量から求められるパラメータであり、Ｏ_２センサ２３でフィードバック制御される。
【００８０】
次に、当実施形態での運転領域と運転運転モードについて説明する。図４（ａ）は、エンジン本体１の運転領域を示す説明図であり、横軸にエンジン回転数、縦軸にエンジン負荷を示す。
【００８１】
低負荷低回転域の運転領域Ａでは、エンジンが未暖気である場合等を除き、原則として特殊運転モードが選択される。特殊運転モードでは、ガス流通経路を２気筒接続状態（気筒間ガス通路２２を開通させて、先行気筒２Ａ，２Ｄから排出される既燃ガスをそのまま後続気筒２Ｂ，２Ｃに導入し、この後続気筒２Ｂ，２Ｃから排出される排ガスが排気通路に導かれる状態）とするとともに、先行気筒２Ａ，２Ｄに対しては理論空燃比よりも所定量大きいリーン空燃比とした状態で燃焼を行わせ、後続気筒２Ｂ，２Ｃに対しては先行気筒２Ａ，２Ｄから導入されたリーン空燃比の既燃ガスに燃料を供給して所定の空燃比とした状態で燃焼を行わせる。当実施形態では、特殊運転モードにおける後続気筒２Ｂ，２Ｃの空燃比を、実質的な理論空燃比としている。ここで実質的な理論空燃比とは、先行気筒２Ａ，２Ｄから導入された既燃ガス中に含まれる酸素量と、後続気筒２Ｂ，２Ｃでの燃焼のために追加供給される燃料の量とが理論空燃比（空気過剰率λ＝１）に相当する関係にあることをいう。このようにすると、排気通路２０に三元触媒２４のみを設けるだけで充分に排気浄化がなされるので、別途排気浄化手段を設ける必要が無く、コストを低減することができる。
【００８２】
更に特殊運転モードは、第１特殊運転モードと第２特殊運転モードとに細別される。第１特殊運転モードは、運転領域Ａの全域において優先的に選択されるモードで、後続気筒２Ｂ，２Ｃで圧縮自己着火による燃焼を行わせる。圧縮自己着火を行うためには、圧縮行程後期に筒内温度が高温になっている必要があるが、後続気筒２Ｂ，２Ｃには先行気筒２Ａ，２Ｄから高温の既燃ガスが導入されるので、外気を導入する従来のエンジンに対し圧縮行程後期の筒内温度を格段に上昇させる事が出来、圧縮自己着火を可能にしている。
【００８３】
第２特殊運転モードは、運転領域Ａの全域において予備的に選択されるモードで、後続気筒２Ｂ，２Ｃで強制点火による燃焼を行わせる。エンジン本体１の運転状態や外気温等の影響で、常に運転領域Ａにおいて後続気筒２Ｂ，２Ｃでの圧縮自己着火による燃焼が安定して行い得るとは限らない。そのようなときは第２特殊運転モードを選択し、強制点火により確実に着火させ、安定した燃焼を行わせるようにしている。
【００８４】
当実施形態では、原則として運転領域Ａの全域で第１特殊運転モードとなるように設定しているが、運転領域Ａを更に分割し、比較的低負荷低回転の領域を第２特殊運転モード、比較的高負荷高回転の領域を第１特殊運転モードとなるように設定しても良い。
【００８５】
また、当実施形態では特殊運転モード中の先行気筒２Ａ，２Ｄでは、強制点火による燃焼を行わせるようにしているが、先行気筒２Ａ，２Ｄの筒内温度を上昇させる手段（たとえば内部ＲＧＲを増大させる等）を用いて、先行気筒２Ａ，２Ｄでも圧縮自己着火を行わせるようにしても良い。
【００８６】
運転領域Ａよりも高負荷ないし高回転の運転領域Ｂでは、通常運転モードが選択される。通常運転モードでは、従来の一般的なエンジンと同様に、ガス流通経路を各気筒独立状態とするとともに各気筒２Ａ〜２Ｄで、それぞれ独立して略理論空燃比もしくはそれよりも小さな空燃比で燃焼を行わせる。
【００８７】
運転者がアクセル開度を全閉、または略全閉とするような減速域では、燃料停止モードが選択される。燃料停止モードでは、各気筒２Ａ〜２Ｄへの燃料供給が停止される。従って、エンジン本体１はタイヤ側から逆駆動されることになり、その負荷は逆駆動負荷特性で示される負値となる。その際、車両としてはエンジンブレーキの効いた状態となる。図４（ａ）に示す運転領域Ｃは、そのような逆駆動負荷特性を示す線上の領域である。即ち、当実施形態では運転領域Ｃにおいて燃料停止モードが選択される。なお、逆駆動負荷特性は、ガス流通経路その他の条件により変化するが、ここでは代表的に１本の特性で示している。
【００８８】
また、燃料停止モード中、エンジン回転数が燃料復帰回転数ｒ６より低下すると、エンジン停止を防止するために燃料供給を再開（燃料復帰）し、特殊運転モードに移行するように設定されている。
【００８９】
以上のような当実施形態の装置の作用を、図４〜図１２を参照しつつ説明する。特殊運転モードでは前述のように第１排気弁３２ａ及び第１吸気弁３１ａが停止状態、第２排気弁３２ｂ及び第２吸気弁３１ｂが作動状態とされることにより、実質的な新気及びガスの流通経路は図７に示すようになり、先行気筒（１番，４番気筒）２Ａ，２Ｄから排出される既燃ガスがそのまま気筒間ガス通路２２を介して後続気筒（２番，３番気筒）２Ｂ，２Ｃに導入されるとともに、この後続気筒２Ｂ，２Ｃから排出されるガスのみが排気通路２０に導かれるような２気筒接続状態とされる。
【００９０】
この状態において、先行気筒２Ａ，２Ｄにそれぞれ吸気行程で吸気通路１５から新気が導入され（図７中の矢印ａ）、先行気筒２Ａ，２ＤではリニアＯ_２センサ２５により検出される空燃比が理論空燃比の略２倍ないしそれ以上の超リーン空燃比となるように燃料噴射量がフィードバック制御されつつ圧縮行程で燃料が噴射され、かつ、所定点火時期に点火が行われて、超リーン空燃比での成層燃焼が行われる（図６参照）。
【００９１】
その後、先行気筒２Ａ，２Ｄの吸気行程と後続気筒２Ｂ，２Ｃの排気行程が重なる期間に、先行気筒２Ａ，２Ｄから排出された既燃ガスがガス通路２２を通って後続気筒２Ｂ，２Ｃに導入される（図６中の白抜き矢印及び図７中の矢印ｂ）。そして、後続気筒２Ｂ，２Ｃでは、先行気筒２Ａ，２Ｄから導入されたリーン空燃比の既燃ガスに燃料が供給されて、実質的に理論空燃比となるように燃料噴射量が制御されつつ、吸気行程で燃料が噴射される。このとき、第１特殊運転モードでは後続気筒２Ｂ，２Ｃにおいて点火プラグ７での強制点火が停止され、圧縮行程の上死点付近で燃焼室内の圧力、温度の上昇により圧縮自己着火が行われ、第２特殊運転モードでは、後続気筒２Ｂ，２Ｃにおいて点火プラグ７での強制点火による燃焼が行われる。
【００９２】
こうして第１特殊運転モードでは、後続気筒２Ｂ，２Ｃで、多量のＥＧＲガス相当の既燃ガス成分を含み、かつ、空燃比がリーンであるという条件下でも、圧縮自己着火により燃焼が急速に行われ、これにより熱効率が大幅に向上されることとなる。
【００９３】
また、筒内温度状態推測手段５３によって後続気筒の燃焼直前の混合気温度Ｔの推定がなされ、その温度が所定値Ｔ１より低くなったときには第２特殊運転モードに切換える（図９のステップＳ１７参照）。即ち、後続気筒２Ｂ，２Ｃの筒内温度が安定して圧縮自己着火を行い得るほど上昇していないときは、強制点火による燃焼を行う。逆に、後続気筒２Ｂ，２Ｃの筒内温度が上昇しすぎ、ノッキング等の懸念が生じた場合には、冷却用ポンプ駆動モータ５１によって冷却用ポンプ５０を作動させ、ウォータージャケット２６内の気筒間ガス通路２２を冷却する。これによって先行気筒２Ａ，２Ｄから後続気筒２Ｂ，２Ｃに導かれる既燃ガスが冷却され、後続気筒２Ｂ，２Ｃの筒内温度上昇が抑制されるので、第１特殊運転モードを継続することができる。
【００９４】
つまり、先行気筒２Ａ，２Ｄでは超リーンでの成層燃焼により熱効率が高められるとともにポンピングロスが低減され、一方、後続気筒２Ｂ，２Ｃでは、先行気筒２Ａ，２Ｄと同様にポンピングロス低減効果が得られるとともに、圧縮自己着火による燃焼を行う場合には、均一な混合気分布状態で圧縮自己着火が行われることにより熱効率が高められるとともに、これらの作用により、燃費が大幅に改善されることとなる。
【００９５】
また、先行気筒２Ａ，２Ｄでは理論空燃比の略２倍もしくはそれ以上のリーン空燃比とされることでＮＯｘ発生量が比較的少なく抑えられ、後続気筒２Ｂ，２Ｃでは、先行気筒２Ａ，２Ｄから既燃ガスが導入されることで多量のＥＧＲが行われているのと同等の状態となることからＮＯｘの発生が充分に抑制される。このような点からもエミッションの向上に有利となる。
【００９６】
一方、通常運転モードでは前述のように第１排気弁３２ａ及び第１吸気弁３１ａが作動状態、第２排気弁３２ｂ及び第２吸気弁３１ｂが停止状態とされることにより、実質的な新気及びガスの流通経路は図８に示すようになり、実質的に各気筒２Ａ〜２Ｄの吸気ポート３１，３１ａ及び排気ポート１２ａ，１２が独立し、吸気通路１５から各気筒２Ａ〜２Ｄの吸気ポート３１，３１ａに新気が導入されるとともに各気筒２Ａ〜２Ｄの排気ポート３１，３１ａから排気通路２０に既燃ガスが排出される。そしてこの場合は、理論空燃比もしくはそれよりリッチとなるように吸入空気量及び燃料噴射量が制御されることにより、出力性能が確保される。
【００９７】
また、燃料停止モードでは、各気筒２Ａ〜２Ｄへの燃料供給が停止される。従って、エンジン出力を必要としない惰行運転時や下り坂における燃料消費が削減され、燃費を向上させることができる。更に、エンジン本体１が逆駆動されることによって得られるエンジンブレーキの効果を高めることができる。なお、燃料停止モード中のガス流通経路は、原則として燃料停止モードに切換わる直前のモードに従う。但し、条件によっては燃料停止モード中に切換える場合もある（図１０のステップＳ５１，Ｓ５５参照）。
【００９８】
次に、各運転モードの変遷と燃料復帰過渡モードについて説明する。図４（ｂ）は、燃料停止モードを挟んで、その前後のモードの組み合わせパターンを示す表である。このパターンに応じて、燃料復帰時の制御が設定されている。図４（ｂ）中に示されるＡ４，Ａ５，Ａ６，Ｂ１，Ｂ２，Ｃ１，Ｃ２，Ｃ４，Ｃ５及びＣ６の各記号は、図４（ａ）に示された各ポイントに相当する運転状態である。従って、運転状態Ａ４，Ａ５及びＡ６は、第１特殊運転モードを代表するポイントであり、運転状態Ｂ１及びＢ２は通常運転モードを代表するポイントであり、運転状態Ｃ１，Ｃ２，Ｃ４，Ｃ５及びＣ６は燃料停止モードを代表するポイントである。運転状態Ｂ１と運転状態Ｃ１のエンジン回転数は略等しく、ｒ１である。以下同様に、運転状態Ｂ２と運転状態Ｃ２のエンジン回転数は略等しく、ｒ２であり、運転状態Ａ４と運転状態Ｃ４のエンジン回転数は略等しく、ｒ４であり、運転状態Ａ５と運転状態Ｃ５のエンジン回転数は略等しく、ｒ５であり、運転状態Ａ６と運転状態Ｃ６のエンジン回転数は略等しく、ｒ６である。なお、エンジン回転数ｒ６は燃料復帰回転数である。
【００９９】
図４（ｂ）の横軸（列）には、燃料停止モード前の運転状態を代表するポイントとして、運転状態Ａ４，Ｂ１を、縦軸（行）には燃料停止モード後の運転状態を代表するポイントとして、運転状態Ａ５，Ａ６，Ｂ２を示す。各欄には、これらの組み合わせからなるパターン番号と、経由する燃料停止モード中の運転状態を示す。例えばパターン１は、運転状態Ａ４（第１特殊運転モード）から、運転状態Ｃ４，Ｃ５（燃料停止モード）を経由して運転状態Ａ５（第１特殊運転モード）に至るパターンを示す。他のパターン２乃至５も同様の表記に従う。なお、パターン１，２，３及び５は減速方向であるが、パターン４は増速方向である。これは、例えば下り坂において、アクセルを全閉としていても増速する場合などに起こる。
【０１００】
パターン１乃至５のうち、パターン１，２および３には、燃料停止モードから第１特殊運転モードに切換える際、燃料復帰過渡モードを経由するように設定されている。
【０１０１】
パターン１における燃料停止モードおよび燃料復帰過渡モードは次のようになっている。パターン１では、運転状態が運転状態Ａ４→Ｃ４→Ｃ５→Ａ５と変遷する。運転状態Ａ４から運転状態Ｃ４となると、第１特殊運転モードから燃料停止モードへ切換わり、燃料の供給が停止される。そして、運転状態Ｃ５までの間、ガス流通経路は運転状態Ａ４と同じ２気筒接続状態に維持される。その後運転状態Ａ５となると、最終的には第１特殊運転モードに切換わるが、それまでの所定期間、燃料復帰過渡モードとなる。パターン１における燃料復帰過渡モードは、第１の段階（燃料復帰時からＳ１サイクル経過まで。なお１サイクルは吸気、圧縮、膨張および排気の４行程からなる。）と、それ以降の第２の段階（Ｓ２サイクル経過（Ｓ２＞Ｓ１）まで）に分かれている。第１の段階では、ガス流通経路を２気筒接続状態に維持したまま、先行気筒２Ａ，２Ｄで理論空燃比（空気過剰率λ＝１）での燃焼を行わせる（図１１のステップＳ１３３参照）。こうすることにより、燃料停止モード中に先行気筒２Ａ，２Ｄ内を通過する空気によって筒内温度が低下した場合でも、確実に失火を防止して安定した燃焼状態で燃料復帰させることができる。また、この第１の段階では後続気筒２Ｂ，２Ｃでの燃焼が行われないが、先行気筒２Ａ，２Ｄから導入された理論空燃比での燃焼による高温の既燃ガスが通過することにより、筒内温度を上昇させている。こうして、先行気筒、後続気筒の双方を加熱している。
【０１０２】
パターン１における燃料復帰過渡モードの第２の段階では、ガス流通経路を２気筒接続状態に維持したまま、先行気筒２Ａ，２Ｄに対しては空気過剰率λ＞１となるようなリーン空燃比での燃焼を行わせ、後続気筒２Ｂ，２Ｃに対しては先行気筒２Ａ，２Ｄから導入されたリーン空燃比の既燃ガスに燃料を供給して実質的な理論空燃比とした状態で強制点火による燃焼を行わせる。即ち、第２特殊運転モードと同等の制御を行う（図１１のステップＳ１４３参照）。この場合の先行気筒２Ａ，２Ｄの空燃比は、一般的な第２特殊運転モードに準じて空気過剰率λ≒２としても良いが、１＜λ≦２として、ややリッチ気味にしておき、均質燃焼させると燃焼がより安定するので望ましい。この第２の段階は、第１の段階に比べ、より第１特殊運転モードに近く、後続気筒２Ｂ，２Ｃの筒内温度が上昇し易いので、第１特殊運転モードへの移行を早期化させることができる。
【０１０３】
ところで、第１の段階のサイクル数Ｓ１および第２の段階のサイクル数Ｓ２は、運転状態によって変動し、燃料停止モードの期間が長いほど、またはエンジン温度が低いほど長くなるように設定されている。従って、燃料停止モードの期間が長く、筒内温度の低下の程度が大きい場合には燃料復帰過渡モードの期間（Ｓ１およびＳ２）を長くして、筒内温度が充分上昇してから第１特殊運転モードに移行させることができる一方、燃料停止モードの期間が短く、筒内温度の低下の程度が小さい場合には燃料復帰過渡モードの期間を短くして、速やかに第１特殊運転モードに移行させることができる。このように燃料復帰過渡モードの期間が必要最小限となるように設定することにより、燃費改善効果を一層高めている。
【０１０４】
こうして燃料復帰からＳ２サイクル後に燃料復帰過渡モードから第１特殊運転モードに切換わるが、その際、筒内温度状態推測手段５３による後続気筒２Ｂ，２Ｃの筒内温度予測値Ｔが、所定のＴ１に達しない時は、第２特殊運転モードと同等の制御のまま燃料復帰過渡モードを終了する（図１１のステップＳ１１７参照）。
【０１０５】
次に、パターン２における燃料停止モードおよび燃料復帰過渡モードは次のようになっている。パターン２では、運転状態が運転状態Ｂ１→Ｃ１→Ｃ５→Ａ５と変遷する。運転状態Ｂ１から運転状態Ｃ１となると、通常運転モードから燃料停止モードへ切換わり、燃料の供給が停止される。そして、運転状態Ｃ５までの間、ガス流通経路は運転状態Ｂ１と同じ各気筒独立状態に維持される。その後運転状態Ａ５となると、最終的には第１特殊運転モードに切換わるが、それまでの所定期間、燃料復帰過渡モードとなる。パターン２における燃料復帰過渡モードは、第１の段階（燃料復帰時からＳ１サイクル経過まで）と、それ以降の第２の段階（Ｓ２サイクル経過（Ｓ２＞Ｓ１）まで）に分かれている。第１の段階では、ガス流通経路を各気筒独立状態に維持したまま、各気筒２Ａ〜２Ｄで理論空燃比（空気過剰率λ＝１）での燃焼を行わせる。即ち通常運転モードと同等の制御を行う（図１１のステップＳ１３５参照）。こうすることにより、先行気筒２Ａ，２Ｄのみならず後続気筒２Ｂ，２Ｃにおいても安定度の高い燃焼で燃料復帰させ、一層確実な安定燃焼を得るとともに、先行気筒、後続気筒ともに筒内を早期に加熱している。
【０１０６】
パターン２における燃料復帰過渡モードの第２の段階では、パターン１における燃料復帰過渡モードの第２の段階と同様の制御、即ち第２特殊運転モードと同等の制御を行う（図１１のステップＳ１４３参照）。この第２の段階は、第１の段階に比べ、より第１特殊運転モードに近く、安定性の高い燃焼を行いながら、円滑なモードの移行を図っている。
【０１０７】
但し、第２の段階であっても、筒内温度状態推測手段５３による後続気筒２Ｂ，２Ｃの筒内温度予測値Ｔが、所定のＴ１に達しない時は、引き続き通常運転モードと同様の制御を行い（図１１のステップＳ１４７参照）、後続気筒２Ｂ，２Ｃの筒内温度上昇の促進を図る。
【０１０８】
そして、パターン１と同様、燃料復帰からＳ２サイクル後に燃料復帰過渡モードから第１特殊運転モードに切換わる。その際もパターン１と同様、筒内温度状態推測手段５３による後続気筒２Ｂ，２Ｃの筒内温度予測値Ｔが、所定のＴ１に達しない時は、第２特殊運転モードと同等の制御としつつ燃料復帰過渡モードを終了する（図１１のステップＳ１１７参照）。また、第１の段階のサイクル数Ｓ１および第２の段階のサイクル数Ｓ２を、燃料停止モードの期間が長いほど、またはエンジン温度が低いほど長くなるように設定することもパターン１と同様である。
【０１０９】
次に、パターン３における燃料停止モードおよび燃料復帰過渡モードは次のようになっている。パターン３では、運転状態が運転状態Ａ４（又はＢ１）→Ｃ４（又はＣ１）→Ｃ６→Ａ６と変遷する。運転状態Ａ４（又は運転状態Ｂ１）から運転状態Ｃ４（又は運転状態Ｃ１）となると、特殊運転モード（又は通常運転モード）から燃料停止モードへ切換わり、燃料の供給が停止される。そして、運転状態Ｃ６付近までの間、ガス流通経路は燃料停止モードへ切換わる前のモードの状態に維持される。そして、筒内温度状態推測手段５３による後続気筒２Ｂ，２Ｃの筒内温度予測値Ｔが、所定の温度Ｔ２以上であるときは、そのまま運転状態Ｃ６まで維持し続け、エンジン回転数が燃料復帰回転数ｒ６となったときに燃料停止モードを終了し、運転状態Ａ６とする。その際、燃料停止モードの前が運転状態Ａ４であった場合にはパターン１の制御に、運転状態Ｂ１であった場合にはパターン２の制御にそれぞれ従う。
【０１１０】
一方、筒内温度予測値Ｔが、所定の温度Ｔ２に達しない場合は、運転状態Ｃ６に達する前（例えばエンジン回転数がｒ６＋２００ｒｐｍより小さくなったとき）に、前のモードによらず、ガス流通経路を各気筒独立状態に切換える（図１０のステップＳ５１参照）。そして、運転状態Ｃ６に達して運転状態Ａ６に切換わる際、パターン２の制御に従う。このようにして、後続気筒２Ｂ，２Ｃが低温の場合には、燃料停止モードの前が特殊運転モードであったとしても、燃料復帰前に予めガス流通経路を各気筒独立状態に切換えておき、燃料復帰後は速やかに（あらためてガス流通経路と切換えることなく）各気筒２Ａ〜２Ｄで理論空燃比での燃焼を行うようにして燃料復帰させ、安定した燃焼状態を得ている。なお、所定の温度Ｔ２は、上記所定の温度Ｔ１と同じであっても良い。
【０１１１】
ところで、図４（ａ）には燃料復帰回転数を所定値ｒ６として示しているが、これを、燃料復帰時のガス流通経路によって変動する燃料復帰回転数Ｎ１としても良い。即ち燃料復帰回転数Ｎ１は、燃料復帰時のガス流通経路が、２気筒接続状態である場合には比較的高い値、各気筒独立状態である場合には比較的低い値に設定される。こうすることで、燃料復帰時のガス流通経路が２気筒接続状態となる場合にはエンジン停止に対する余裕度を充分確保するとともに、各気筒独立状態となる場合には燃料停止の期間を増大させ、燃費改善効果を高めることができる。
【０１１２】
次に、パターン４における燃料停止モードおよび燃料復帰は次のようになっている。パターン４では、運転状態が運転状態Ａ４→Ｃ４→Ｃ２→Ｂ２と変遷する。運転状態Ａ４から運転状態Ｃ４となると、特殊運転モードから燃料停止モードへ切換わり、燃料の供給が停止される。そして、運転状態Ｃ２までの間、ガス流通経路は運転状態Ａ４と同じ２気筒接続状態に維持される。その後運転状態Ｂ２となると、燃料復帰過渡モードを経由することなく、速やかに通常運転モードに移行し、ガス流通経路を各気筒独立状態に切換えるとともに各気筒２Ａ〜２Ｄで理論空燃比（空気過剰率λ＝１）での燃焼を行わせる（図９のステップＳ３１）。なお、燃料停止モード中にエンジン回転数が運転領域Ａの最大回転数ｒ３を超えた場合、予めガス流通経路を各気筒独立状態に切換えておくようにしても良い。
【０１１３】
次に、パターン５における燃料停止モードおよび燃料復帰は次のようになっている。パターン５では、運転状態が運転状態Ｂ１→Ｃ１→Ｃ２→Ｂ２と変遷する。運転状態Ｂ１から運転状態Ｃ１となると、通常運転モードから燃料停止モードへ切換わり、燃料の供給が停止される。そして、運転状態Ｃ２までの間、ガス流通経路は運転状態Ｂ１と同じ各気筒独立状態に維持される。その後運転状態Ｂ２となると、燃料復帰過渡モードを経由することなく通常運転モードに移行する。このとき、ガス流通経路は各気筒独立状態が維持されているので、あらためて切換える必要がなく、速やかに通常運転モードに移行することができる。
【０１１４】
図９は、燃料停止モードから、その後のモードに切換える場合の制御のフローチャートである。制御スタート後、ステップＳ１で各センサ情報（アクセル開度、エンジン回転数、吸入空気量、エンジン水温、ガス流通経路状態、吸気温度、Ｏ_２センサ出力、燃料噴射時期、点火時期、車速等）を読み込む。次のステップＳ３で、運転状態が運転領域Ｂにあるか否かの判定がなされ、ＮＯであればステップＳ５に移行し、筒内温度状態推測手段５３による後続気筒の筒内温度Ｔの推定を行う（図５参照）。次のステップＳ７で運転状態が運転領域Ａにあるか否かの判定がなされ、ＹＥＳであればステップＳ９でモードＭ＝０であるか否かの判定がなされる。モードＭは、現状の運転モードを示すパラメータであり、Ｍ＝０であれば燃料停止モードか燃料復帰過渡モードかの何れかであることを示す。ステップＳ９でＮＯであれば現状のモードは特殊運転モードか通常運転モードであり、更に次のステップＳ１１に移行してエンジン水温によってエンジンが温間（暖気が完了している）にあるか否かの判定がなされる。ステップＳ１１でＹＥＳであれば、特殊運転モードとする事が決定され、次のステップＳ１３に移行して、後続気筒２Ｂ，２Ｃの筒内温度Ｔが所定値Ｔ１以上であるか否かの判定がなされる。ＹＥＳであれば、後続気筒２Ｂ，２Ｃの筒内温度は安定して圧縮自己着火を行い得る高温に達しているので、ステップＳ１５に移行して第１特殊運転モードの制御を行う。次のステップＳ１９でモードＭ＝１（現状モードが特殊運転モードであることを示す）を入力し、リターンする。
【０１１５】
遡って、ステップＳ１３でＮＯと判定されたときには、後続気筒２Ｂ，２Ｃの筒内温度は安定して圧縮自己着火を行い得る高温に達していないので、ステップＳ１７に移行して第２特殊運転モードの制御を行う。
【０１１６】
更に遡って、ステップＳ９でＹＥＳと判定されると、運転領域ＡにありながらモードＭ＝０であることを示す。これは、燃料停止モードから特殊運転モードに切換わる過渡状態であることを示しており、ステップＳ２１に移行して燃料復帰過渡モードの制御（詳細を図１１に示す）を行う。
【０１１７】
また、ステップＳ３でＹＥＳ、つまり運転領域Ｂにあると判定された場合およびステップＳ１１でＮＯ、つまり運転領域Ａにあるが未暖気状態であると判定された場合にはステップＳ３１に移行し、通常運転モードの制御を行い、ステップＳ３３でモードＭ＝２（現状モードが通常運転モードであることを示す）とする。
【０１１８】
また、ステップＳ７でＮＯ、つまり運転領域ＡでもＢでもないと判定されたときには運転領域Ｃにあることを示しており、分岐フロー▲１▼（図１０に示す）に移行する。
【０１１９】
図１０は、図９の分岐フロー▲１▼を示すフローチャートである。ステップＳ３５に移行したとき、運転状態は運転領域Ｃにある。ここでモードＭ＝０であるか否かの判定がなされ、ＹＥＳであれば、運転状態Ｃに移行してから、少なくとも１回以上このステップＳ３５を経過していることを示し、次のステップＳ３９に移行する。ステップＳ３５でＮＯであれば、運転状態Ｃに移行してから、初めてステップＳ３５を経過することを示している。その場合、ステップＳ３７に移行して前モードＭ１にモードＭの値を入力する。前モードＭ１は、燃料停止モードの前の運転モードを示すパラメータである。この時点ではモードＭは運転状態Ｃに移行する前の値であり、１（特殊運転モード）または２（通常運転モード）である。これらの値を前モードＭ１に入力することにより、燃料停止モードに切換わる前のモードが記憶される。その後ステップＳ３９に移行する。
【０１２０】
ステップＳ３９で燃料供給の停止を行い、次のステップＳ４１でモードＭ＝０を入力する。次のステップＳ４３で燃料復帰回転数Ｎ１の設定、更新がなされる。燃料復帰回転数Ｎ１は、ＡＴ車では１，０００ｒｐｍ程度の値であるが、ガス流通経路が２気筒接続状態である場合には、各気筒独立状態である場合よりも高い値に設定される。また、燃料停止モード前が特殊運転モードであったか通常運転モードであったかによって、特殊運転モードであった場合には通常運転モードであった場合に比べて高い値に設定するようにしても良い。その他、燃料復帰回転数Ｎ１は、エンジン水温が低いときには高めに設定する等の補正がなされる。
【０１２１】
次のステップＳ４５では、前モードＭ１＝１であるか否かの判定がなされ、ＹＥＳ（特殊運転モード）であればステップＳ４７に移行し、エンジン回転数Ｎが、Ｎ＜Ｎ１＋２００ｒｐｍであるか否かの判定がなされる。ＹＥＳであればエンジン回転数Ｎが燃料復帰回転数Ｎ１付近まで低下していることを示す。そして、ステップＳ４９に移行し、後続気筒の筒内温度Ｔが所定値Ｔ２以上であるか否かの判定がなされる。ＹＥＳであれば、図４（ｂ）のパターン１と同様の制御で燃料復帰させるため、ステップＳ５５に移行して予めガス流通経路を２気筒接続状態としておく。そしてステップＳ５７でガス流通経路モードＭ２＝１（２気筒接続状態を示す）を入力し、リターンする。
【０１２２】
遡って、ステップＳ４７でＮＯ、つまりＮ≧Ｎ１＋２００ｒｐｍであると判定されると、エンジン回転数Ｎが未だ燃料復帰回転数Ｎ１付近まで低下していないことを示すので、ステップＳ５５に移行してガス流通経路を２気筒接続状態とする。
【０１２３】
更に遡って、ステップＳ４５でＮＯ、つまり前モードＭ１＝２（通常運転モード）と判定された場合、およびステップＳ４９でＮＯ、つまり前モードＭ１＝１（特殊運転モード）であってもエンジン回転数Ｎが燃料復帰回転数Ｎ１付近まで低下しており、かつ後続気筒２Ｂ，２Ｃの筒内温度Ｔが所定値Ｔ２よりも低いと判定された場合には、図４（ｂ）のパターン２と同様の制御で燃料復帰させるため、ステップＳ５１に移行し、予めガス流通経路を各気筒独立態としておく。そしてステップＳ５３でガス流通経路モードＭ２＝２（各気筒独立状態を示す）を入力し、リターンする。
【０１２４】
図１１は、図９のステップＳ２１（燃料復帰過渡モードの制御）の詳細を示すサブルーチンである。燃料復帰過渡モードに入ると、ステップＳ１０１で、燃料復帰時点からのサイクル数Ｓをカウントする。初回はＳ＝０であり、以後７２０°ＣＡ（１サイクルに相当）毎にサイクル数Ｓを増分させる。
【０１２５】
次のステップＳ１０３でサイクル数Ｓが所定値Ｓ１よりも小か否かの判定がなされる。ＹＥＳであれば燃料復帰過渡モードの第１の段階であることを示し、ステップＳ１３１，Ｓ１３２に移行する。ステップＳ１３１およびステップＳ１３２では、前モードＭ１とガス流通経路モードＭ２の判定がなされ、前モードＭ１＝１かつガス流通経路モードＭ２＝１の場合のみステップＳ１３３に移行して、ガス流通経路を２気筒接続状態としつつ先行気筒２Ａ，２Ｄで理論空燃比（空気過剰率λ＝１）での燃焼を行わせる。その後、モードＭ＝０のままリターンする。ステップＳ１３１およびステップＳ１３２で、前モードＭ１とガス流通経路モードＭ２の少なくとも一方が２である場合は、ステップＳ１３５に移行し、通常運転モードと同等の制御、即ちガス流通経路を各気筒独立状態としつつ、各気筒２Ａ〜２Ｄで理論空燃比（空気過剰率λ＝１）での燃焼を行わせる。その後、モードＭ＝０のままリターンする。
【０１２６】
遡ってステップＳ１０３でＮＯ、即ち燃料復帰過渡モードの第１の段階が終了したと判定されるとステップＳ１０５に移行し、サイクル数Ｓが所定値Ｓ２（Ｓ２＞Ｓ１）よりも小か否かの判定がなされる。所定値Ｓ１、Ｓ２は、燃料停止モードの期間（サイクル数）が長いほど、またはエンジン温度が低いほど長くなるように設定されており、数〜数十サイクル程度の期間である。ステップＳ１０５でＹＥＳと判定されると、燃料復帰過渡モードの第２の段階であることを示し、ステップＳ１４１に移行する。ステップＳ１４１で前モードＭ１の判定がなされ、前モードＭ１＝１（特殊運転モード）であればステップＳ１４３に移行し、第２特殊運転モードと同等の制御、即ちガス流通経路を２気筒接続状態としつつ、先行気筒２Ａ，２Ｄではリーン空燃比で強制点火による燃焼を行わせ、後続気筒２Ｂ，２Ｃでは先行気筒２Ａ，２Ｄから導入された既燃ガスに燃料を供給して実質的な理論空燃比（空気過剰率λ＝１）とし、強制点火による燃焼を行わせる。その後、モードＭ＝０のままリターンする。ステップＳ１４１で前モードＭ１＝２（通常運転モード）と判定されればステップＳ１４５に移行し、後続気筒２Ｂ，２Ｃの筒内温度Ｔが所定値Ｔ１以上であるか否かの判定がなされる。ＹＥＳであればステップＳ１４３に移行するが、ＮＯであればステップＳ１４７に移行し、ステップＳ１３５と同様の、通常運転モードと同等の制御を行い、その後、モードＭ＝０のままリターンする。
【０１２７】
遡ってステップＳ１０５でＮＯ、即ち燃料復帰過渡モードの第２の段階が終了したと判定されるとステップＳ１０７に移行し、サイクル数Ｓのリセットを行う。そしてステップＳ１０９に移行してエンジン水温によってエンジンが温間にあるか否かの判定がなされる。ステップＳ１０９でＹＥＳであれば、ステップＳ１１１に移行して、後続気筒の筒内温度Ｔが所定値Ｔ１以上であるか否かの判定がなされる。ＹＥＳであれば、後続気筒２Ｂ，２Ｃの筒内温度は安定して圧縮自己着火を行い得る高温に達しているので、ステップＳ１１３に移行して第１特殊運転モードと同等の制御、即ちガス流通経路を２気筒接続状態としつつ、先行気筒２Ａ，２Ｄではリーン空燃比で強制点火による燃焼を行わせ、後続気筒２Ｂ，２Ｃでは先行気筒２Ａ，２Ｄから導入された既燃ガスに燃料を供給して実質的な理論空燃比（空気過剰率λ＝１）とし、圧縮自己着火による燃焼を行わせる。その後、ステップＳ１１９に移行し、モードＭ＝１を入力してリターンする。このモードＭ＝１を入力することにより、燃料復帰過渡モードの終了となり、次のルーチンでは図９のステップＳ９でＮＯと判定され、ステップＳ１１へ移行することとなる。
【０１２８】
遡って、ステップＳ１１１でＮＯと判定されたときには、後続気筒２Ｂ，２Ｃの筒内温度は安定して圧縮自己着火を行い得る高温に達していないので、ステップＳ１１７に移行してステップＳ１４３と同様の、第２特殊運転モードと同等の制御を行い、ステップＳ１１９に移行する。
【０１２９】
また、ステップＳ１０９でＮＯ、つまり未暖気状態であると判定された場合にはステップＳ１１５に移行し、ステップＳ１３５と同様の、通常運転モードと同等の制御を行い、ステップＳ１１９に移行する。
【０１３０】
次に、当実施形態の変形例について図４（ｂ）および図１２を参照しつつ説明する。この変形例は、図４（ｂ）のパターン１の第１の段階、および第２の段階に関する部分の制御である。変形例のパターン１における燃料復帰過渡モードは次のようになっている。第１の段階では、第２特殊運転モードと同等の制御、即ちガス流通経路を２気筒接続状態としつつ、先行気筒２Ａ，２Ｄではリーン空燃比で強制点火による燃焼を行わせ、後続気筒２Ｂ，２Ｃでは先行気筒２Ａ，２Ｄから導入された既燃ガスに燃料を供給して実質的な理論空燃比（空気過剰率λ＝１）とし、強制点火による燃焼を行わせる（図１２のステップＳ２０３参照）。但し、未暖気の場合は暖気を促進させるため、通常運転モードと同等の制御を行う（図１２のステップＳ２０１，Ｓ１３５参照）。
【０１３１】
変形例のパターン１における燃料復帰過渡モードの第２の段階は、図１１のステップＳ１４３に替えて図１２のステップＳ２０５を適用する。即ち、第２特殊運転モードをベースに、後続気筒２Ｂ，２Ｃの燃料を先行気筒２Ａ，２Ｄにおいて先行気筒２Ａ，２Ｄの膨張行程後半に噴射する。このようにすると、先行気筒２Ａ，２Ｄで噴射された燃料は先行気筒２Ａ，２Ｄから排出される高温の既燃ガスと混合して後続気筒２Ｂ，２Ｃに導かれるため、活性化が促進される。そして、その噴射時期が後続気筒２Ｂ，２Ｃの吸気行程に先立つ、前サイクルの排気行程後半に相当するので、後続気筒２Ｂ，２Ｃでの点火時期までの間に、燃料活性化の時間が充分確保される。
【０１３２】
また、後続気筒２Ｂ，２Ｃの燃料を２以上に分割し、少なくとも１の燃料噴射を先行気筒２Ａ，２Ｄで行うとともに、その燃料噴射時期を先行気筒２Ａ，２Ｄの膨張行程後半に設定し、少なくとも１の燃料噴射を後続気筒２Ｂ，２Ｃで行うようにしても良い。このようにすると、後続気筒２Ｂ，２Ｃでの点火時に、点火プラグ７の周辺に２種類の燃料状態を形成することができる。１つは先行気筒２Ａ，２Ｄ内で噴射され、均一に混合され、活性化された混合気であり、もう１つは、後続気筒２Ｂ，２Ｃ内で噴射され、点火プラグ７を中心に偏在する燃料である。点火プラグ７周辺に偏在する比較的高濃度の燃料によって後続気筒２Ｂ，２Ｃでの着火性をより高めることができるとともに、均一に活性化された混合気によって燃焼の安定化をもはかることができる。
【０１３３】
本発明の実施形態は、上記実施形態、あるいはその変形例に限定するものではなく、特許請求の範囲内で適宜変形して良い。例えば、ウォータージャケット２６による冷却機構を設けず、第２特殊運転モード中に後続気筒２Ｂ，２Ｃの筒内温度が上昇しすぎた場合には、通常運転モードに切換えるようにしても良い。
【０１３４】
【発明の効果】
以上のように本発明の火花点火式エンジンの制御装置は、各気筒が所定の位相差をもって吸気、圧縮、膨張、排気の各行程からなるサイクルを行うようになっている多気筒の火花点火式エンジンにおいて、排気行程と吸気行程が重なる一対の気筒間において排気行程側の気筒である先行気筒から排出される既燃ガスがそのまま吸気行程側の気筒である後続気筒に気筒間ガス通路を介して導入され、この後続気筒から排出される排ガスが排気通路に導かれるような２気筒接続状態にガス流通経路が構成されるとともに、運転状態に応じ、少なくとも所定の低負荷低回転域では特殊運転モードが選択され、所定の減速域では燃料停止モードが選択されるように構成され、上記特殊運転モードでは、上記ガス流通経路を上記２気筒接続状態とするとともに、上記先行気筒に対しては理論空燃比よりも所定量大きいリーン空燃比とした状態で燃焼を行わせ、上記後続気筒に対しては上記先行気筒から導入されたリーン空燃比の既燃ガスに燃料を供給して所定の空燃比とした状態で燃焼を行わせ、上記特殊運転モードとされる場合の一部又は全部において、上記後続気筒で圧縮自己着火による燃焼を行わせ、上記燃料停止モードでは、各気筒への燃料供給を停止するものとし、上記燃料停止モードから、上記後続気筒で圧縮自己着火による燃焼を行わせる特殊運転モードに切換える際、その切換えを円滑にするように、少なくとも各気筒に対する燃焼状態を過渡的に制御する燃料復帰過渡モードを所定期間経由させるように構成し、上記燃料復帰過渡モードの少なくとも燃料復帰時を含む初期において、少なくとも上記先行気筒に対して略理論空燃比とした状態で強制点火による燃焼を行わせることを特徴とするので、２気筒接続状態としつつ後続気筒で圧縮自己着火による燃焼をさせる技術と、減速域で燃料供給を停止する技術とを併用して、より高い燃費改善効果を得つつ、燃料復帰後の燃焼の安定性を高めることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態による装置を備えたエンジン全体の概略平面図である。
【図２】エンジン本体等の概略断面図である。
【図３】制御系統のブロック図である。
【図４】（ａ）は運転領域を示す説明図であり、（ｂ）は燃料停止モード前後のモードの組み合わせパターンを示す表である。
【図５】後続気筒の燃焼前の筒内温度状態を推測する手順を示す主要ブロック図である。
【図６】各気筒の排気行程、吸気行程、燃料噴射時期および点火時期等を示す図である。
【図７】低負荷低回転時の実質的な新気およびガスの流通経路を示す説明図である。
【図８】高負荷、高低回転側の運転領域にある時の実質的な新気およびガスの流通経路を示す説明図である。
【図９】燃料停止モードから、その後のモードに切換える場合の制御のフローチャートである。
【図１０】図９からの分岐フローチャートである。
【図１１】燃料復帰過渡モードの制御を示すサブルーチンのフローチャートである。
【図１２】燃料復帰過渡モードの制御の変形例を示すサブルーチンのフローチャートである。
【符号の説明】
１ エンジン本体
２Ａ，２Ｄ 気筒（先行気筒）
２Ｂ，２Ｃ 気筒（後続気筒）
９ 燃料噴射弁
１１ 吸気ポート
１１ａ，１１ｂ 吸気ポート
１２，１２ａ，１２ｂ 排気ポート
１５ 吸気通路
２０ 排気通路
２２ 気筒間ガス通路
２５ リニアＯ_２センサ
３１，３１ａ，３１ｂ 吸気弁
３２，３２ａ，３２ｂ 排気弁
３５ 弁停止機構
４０ ＥＣＵ
４１ 運転状態判別手段
４２ 弁停止機構制御手段
４３ 吸入空気量制御手段
４４ 燃焼制御手段
５３ 筒内温度状態推測手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for a spark ignition type engine, and more particularly, to a device for controlling a combustion state of each cylinder in a multi-cylinder engine for improving fuel efficiency and emission.
[0002]
[Prior art]
Conventionally, in a spark ignition engine, a technology for improving fuel efficiency by performing combustion in a state in which an air-fuel ratio of an air-fuel mixture in each cylinder is set to a lean air-fuel ratio larger than a stoichiometric air-fuel ratio has been studied. A fuel injection valve that injects fuel directly into the room is provided.In low-speed, low-load regions, etc., stratified combustion is performed by injecting fuel in the compression stroke from the fuel injection valve, thereby realizing super-lean combustion. The following is known (for example, refer to Patent Document 1).
[0003]
When the super-lean combustion is performed by the stratified combustion as described above, the thermal efficiency is improved, and the intake air amount is increased to reduce the intake negative pressure, thereby significantly improving the fuel efficiency. Further, in such a super-lean stratified combustion state, since a part of excess air can be sufficiently combusted even if it is replaced by EGR, a relatively large amount of EGR can be performed, thereby reducing NOx. It is advantageous. And even if such a large amount of EGR is introduced, the pumping loss reduction effect can be obtained without change, and the thermal efficiency can be increased as compared with normal combustion in which the amount of intake air and the amount of EGR are limited without stratification. The fuel efficiency improvement effect is obtained.
[0004]
By the way, when the stratified combustion is performed, the fuel efficiency improvement effect is increased as the air-fuel ratio becomes lean to some extent, but when the air-fuel ratio becomes lean to a certain extent, the combustion speed becomes too slow and the combustion near the end does not contribute to the work As a result, the fuel efficiency tends to deteriorate. As described above, there is a limit to the improvement of fuel efficiency by lean operation in stratified combustion.
[0005]
On the other hand, compression self-ignition has been studied as another method for improving fuel efficiency. In the compression self-ignition, similar to the diesel engine, at the end of the compression stroke, the combustion chamber is heated to a high temperature and a high pressure so that the fuel self-ignites, and the air-fuel ratio is super lean and a large amount of EGR is introduced. Even in such a state, if such compression self-ignition is performed, the entire combustion chamber burns at a stretch, so that slow combustion that does not contribute to work is avoided, which is advantageous for improving fuel efficiency.
[0006]
However, in a normal spark ignition engine (gasoline engine), forced ignition is required for combustion, and the temperature and pressure in the combustion chamber near the compression top dead center are increased to the extent that compression self-ignition occurs. In order to perform the compression self-ignition, a special device for greatly increasing the temperature or pressure in the combustion chamber is required.
[0007]
In order to solve such a problem, the applicant of the present application has proposed a multi-cylinder engine that performs a cycle including intake, compression, expansion, and exhaust strokes, and at least in a low-load low-speed range, a pair of cylinders in which an exhaust stroke and an intake stroke overlap. In between, the burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, is directly introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, and the gas discharged from this subsequent cylinder is guided to the exhaust passage. In this two-cylinder connection state, combustion is performed by forced ignition in a state in which the lean air-fuel ratio is larger than the stoichiometric air-fuel ratio by a predetermined amount in the preceding cylinder, and in the succeeding cylinder, the lean air-fuel ratio introduced from the preceding cylinder is calculated. It has been considered that fuel is supplied to burned gas and combustion is performed by compression self-ignition (Japanese Patent Application No. 2002-029836).
[0008]
According to this, at least in the low-load low-speed range, combustion is performed by forced ignition at a lean air-fuel ratio in the leading cylinder, thereby improving thermal efficiency and reducing pumping loss, thereby achieving a significant fuel efficiency improvement effect. In the succeeding cylinder, fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion. At this time, the temperature of the gas guided from the preceding cylinder through the cylinder pipe gas passage is high, so that the temperature in the combustion chamber rises to the extent that compression self-ignition is possible at the end of the compression stroke, and compression self-ignition is performed. Since the combustion is rapidly performed by the compression self-ignition, the combustion efficiently contributes to the work, and the fuel consumption is greatly improved by reducing the pumping loss.
[0009]
On the other hand, as a conventionally known fuel efficiency improvement technique, there is one in which fuel supply is stopped in a deceleration region where the engine load is extremely small. With this configuration, fuel can be prevented from being consumed when the engine output is unnecessary, so that fuel efficiency can be improved particularly in an operation state in which a low load region is frequently used.
[0010]
[Patent Document 1]
JP-A-10-274085
[0011]
[Problems to be solved by the invention]
However, when the technique of performing combustion by compression self-ignition in the subsequent cylinder while maintaining the two-cylinder connection state as described above and the technique of stopping the fuel supply in the deceleration region are used together, the two-cylinder connection state is changed from the fuel stopped state. When transitioning to a state in which combustion by compression self-ignition is performed in the subsequent cylinder, there has been a problem that combustion after fuel return (restarting fuel supply) tends to be unstable. This is because, although the in-cylinder temperature must be maintained sufficiently high to perform combustion by compression self-ignition in the succeeding cylinder, the state where only air passes through the cylinder due to fuel stoppage continues The main cause is that the subsequent cylinder is cooled and the temperature is lowered.
[0012]
The present invention has been made in view of such a problem, and uses a technique of performing combustion by compression self-ignition in a subsequent cylinder while maintaining a two-cylinder connection state, and a technique of stopping fuel supply in a deceleration region. Accordingly, it is an object of the present invention to provide a control device for a spark ignition type engine capable of improving the stability of combustion after returning fuel while obtaining a higher fuel efficiency improvement effect.
[0013]
[Means for Solving the Problems]
According to a first aspect of the present invention, in a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference, an exhaust stroke and an intake stroke are different. The burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of overlapping cylinders is directly introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, via the inter-cylinder gas passage, and is discharged from this succeeding cylinder. The gas flow path is configured in a two-cylinder connection state in which exhaust gas is guided to an exhaust passage, and a special operation mode is selected at least in a predetermined low-load low-speed range according to an operation state, and in a predetermined deceleration range. The fuel stop mode is configured to be selected. In the special operation mode, the gas flow path is set to the two-cylinder connection state, and the gas flow path is theoretically set to the preceding cylinder. The combustion is performed in a state where the lean air-fuel ratio is a predetermined amount larger than the fuel ratio, and for the subsequent cylinder, fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the preceding cylinder, and the predetermined air-fuel ratio is determined. In the above-mentioned special operation mode, combustion is performed by compression self-ignition in the following cylinders, and fuel supply to each cylinder is stopped in the fuel stop mode. When switching from the fuel stop mode to a special operation mode in which combustion is performed by compression self-ignition in the subsequent cylinder, at least the combustion state of at least each cylinder is transiently controlled so as to facilitate the switching. The fuel return transient mode is configured to pass through for a predetermined period, and at least in the initial stage of the fuel return transient mode including at least fuel return, at least in the preceding cylinder. A control device for a spark ignition engine, characterized in that to perform combustion by forced ignition in a state of being substantially stoichiometric air-fuel ratio by.
[0014]
According to this configuration, at least in the low-load low-speed range, combustion is performed at a lean air-fuel ratio in which excess air exists in the leading cylinder, and this lean combustion increases thermal efficiency, reduces pumping loss, and significantly improves fuel efficiency. The effect is obtained. Further, in the succeeding cylinder, additional fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion. Since the gas introduced from the preceding cylinder through the inter-cylinder gas passage has a high temperature, the vaporization of the additional fuel is promoted, and good combustion in the succeeding cylinder can be obtained. Further, in the preceding cylinder, the combustion is performed at a lean air-fuel ratio, so that the amount of NOx generated is suppressed to a relatively small amount. In the succeeding cylinder, a large amount of EGR (exhaust gas recirculation) is introduced by introducing burned gas from the preceding cylinder. Since the state is the same as that performed, the generation of NOx is sufficiently suppressed, and the purification of exhaust gas is promoted. Further, when the compression self-ignition is performed in the succeeding cylinder, since the combustion is performed at once in the entire combustion chamber, the slow combustion which does not contribute to the work is avoided, and a high fuel consumption improvement effect is obtained. Further, since the supply of fuel is stopped in the predetermined deceleration range, fuel is not consumed when engine output is unnecessary, so that fuel efficiency can be further improved. The above operation and effect are common to claims 5, 10 and 11.
[0015]
Further, when switching from the fuel stop mode to a special operation mode in which combustion by compression self-ignition is performed in a subsequent cylinder (hereinafter referred to as a first special operation mode), at least a stoichiometric air-fuel ratio is set in at least a preceding cylinder in a fuel return transient mode. Causes combustion by forced ignition. In such combustion, stable combustion can be easily obtained as compared with combustion at a lean air-fuel ratio or combustion by compression self-ignition, and the combustion gas temperature can be increased by combustion near a stoichiometric air-fuel ratio. Therefore, even if the temperature inside the cylinder is reduced by the air passing through each cylinder during the fuel stop mode, misfire can be reliably prevented and fuel can be returned in a stable combustion state, and the leading cylinder and the following cylinder can be returned. Since both can be heated, it is possible to smoothly shift to the next first special operation mode.
[0016]
According to a second aspect of the present invention, in the control apparatus for a spark ignition type engine according to the first aspect, the gas flow path is configured to be switchable to a cylinder independent state in which fresh air is introduced into each cylinder. Accordingly, in a predetermined high-load or high-speed region, the gas flow paths are set to the respective cylinder independent states, and the respective cylinders are independently burned at a substantially stoichiometric air-fuel ratio or an air-fuel ratio smaller than the stoichiometric air-fuel ratio. When the normal operation mode is selected immediately before the fuel stop mode and the normal operation mode is selected, the gas flow paths are initially connected to the respective cylinders at an initial time including the fuel return in the fuel return transient mode. In addition to the independent state, combustion is performed by forced ignition in a state where each cylinder has a substantially stoichiometric air-fuel ratio. In both cases, combustion is performed by forced ignition with the lean air-fuel ratio set for the preceding cylinder, and fuel is supplied to the succeeding cylinder to burnt gas having a lean air-fuel ratio introduced from the leading cylinder. Combustion by forced ignition in a state where the stoichiometric air-fuel ratio is substantially maintained.
[0017]
With this configuration, when the fuel returns from the normal operation mode to the fuel stop mode and then to the first special operation mode, at least two stages of the fuel return transition mode are performed.
[0018]
The first stage including the time of fuel return is to make the gas flow path independent of each cylinder and to perform combustion by forced ignition in a state where each cylinder has a substantially stoichiometric air-fuel ratio. With this configuration, the fuel can be returned by the highly stable combustion not only in the preceding cylinder but also in the succeeding cylinder, so that more reliable stable combustion can be obtained, and both the leading cylinder and the succeeding cylinder have the inside of the cylinder. The heating can be performed early, and the mode shifts to the first special operation mode, and the compression self-ignition in the subsequent cylinder becomes possible.
[0019]
It should be noted that the gas flow path in the first stage is in the same cylinder independent state as in the normal operation mode. Therefore, even if the number of revolutions corresponding to the normal operation mode decreases to the number of revolutions corresponding to the special operation mode during the fuel stop mode, it is not necessary to immediately switch the gas circulation path to the two-cylinder connection state. Just leave it there. By doing so, for example, during the fuel stop mode, the load is rapidly increased (the accelerator is greatly depressed) from the operating state in which the engine speed is reduced to the low speed corresponding to the special operation mode, and the fuel is operated in the normal operation mode region. In the case of returning the fuel, the fuel can be returned without switching the gas flow path in each cylinder independent state, and the normal operation mode can be promptly shifted.
[0020]
In the second stage of the fuel return mode, the gas circulation path is switched to the two-cylinder connection state, the preceding cylinder is caused to perform combustion by forced ignition with a lean air-fuel ratio, and the succeeding cylinder is caused to proceed with the preceding cylinder. The fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the fuel cell and the combustion by the forced ignition is performed in a state where the stoichiometric air-fuel ratio is substantially set. Here, the substantial stoichiometric air-fuel ratio is defined as the stoichiometric air-fuel ratio between the amount of oxygen contained in the burned gas introduced from the preceding cylinder and the amount of fuel additionally supplied for combustion in the following cylinder. It means that they have a corresponding relationship.
[0021]
Such a combustion mode is obtained by a control equivalent to a special operation mode in which combustion by forced ignition is performed in a subsequent cylinder (hereinafter, referred to as a second special operation mode). 1 Different from the special operation mode. Therefore, rather than directly shifting from the first stage to the first special operation mode, the subsequent cylinder performs combustion by highly stable forced ignition through the second stage and then shifts to the first special operation mode. By doing so, it is possible to achieve higher stability and smooth mode transition.
[0022]
Further, during the first and second stages in the fuel return mode, the in-cylinder temperature of the subsequent cylinder increases due to combustion. Therefore, stable combustion by compression self-ignition can be obtained when shifting to the first special operation mode.
[0023]
According to a third aspect of the present invention, in the control apparatus for a spark ignition engine according to the first or second aspect, when the special operation mode is performed immediately before the fuel stop mode, the gas flow path is provided during the fuel return transient mode. In the two-cylinder connection state, and at the initial stage including at least fuel return in the fuel return transient mode, the preceding cylinder is caused to perform combustion by forced ignition at a substantially stoichiometric air-fuel ratio. I do.
[0024]
With this configuration, at least at the initial stage of the fuel return transient mode including the time of fuel return, the preceding cylinder is caused to perform combustion by forced ignition with a substantially stoichiometric air-fuel ratio, so that fuel can be returned with stable combustion. At the same time, both the preceding cylinder and the succeeding cylinder can be heated.
[0025]
Further, during the transition from the special operation mode to the first special operation mode via the fuel stop mode and the fuel return transient mode, the gas circulation path is always in the two-cylinder connection state, so that there is a response delay accompanying the switching of the gas circulation path. The transition between the modes can be performed promptly without any change.
[0026]
In addition, although combustion is not performed in the succeeding cylinder, combustion is performed in the preceding cylinder at substantially the stoichiometric air-fuel ratio, so that the combustion temperature is high, and high-temperature burned gas introduced from the preceding cylinder passes therethrough. The temperature in the cylinder is increased.
[0027]
According to a fourth aspect of the present invention, in the control apparatus for a spark ignition engine according to the third aspect, when the special operation mode is performed immediately before the fuel stop mode, the control unit controls the preceding cylinder in a later stage of the fuel return transient mode. On the other hand, homogeneous combustion by forced ignition is performed in a state where the air-fuel ratio is set so that the excess air ratio is greater than 1 and equal to or less than 2, and the lean air-fuel ratio introduced from the preceding cylinder is applied to the following cylinder. The fuel is supplied to the burned gas to cause combustion by forced ignition in a state of a substantial stoichiometric air-fuel ratio, and then the operation mode is switched to the special operation mode in which combustion by compression self-ignition is performed in the subsequent cylinder, and It is characterized in that stratified combustion by forced ignition is performed by setting the air-fuel ratio of the cylinder larger.
[0028]
By doing so, in the initial stage of the fuel return transient mode, combustion by forced ignition is performed in a state in which the preceding cylinder has a substantially stoichiometric air-fuel ratio to achieve stable fuel return, and in the latter period, the second special operation mode By performing the same control as described above, the in-cylinder temperature of the subsequent cylinder can be quickly increased, and the combustion by compression self-ignition can be easily performed early.
[0029]
According to a fifth aspect of the present invention, there is provided a multi-cylinder spark ignition type engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. The burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of overlapping cylinders is directly introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, via the inter-cylinder gas passage, and is discharged from this succeeding cylinder. The gas flow path is configured in a two-cylinder connection state in which exhaust gas is guided to an exhaust passage, and a special operation mode is selected at least in a predetermined low-load low-speed range according to an operation state, and in a predetermined deceleration range. The fuel stop mode is configured to be selected. In the special operation mode, the gas flow path is set to the two-cylinder connection state, and the gas flow path is theoretically set to the preceding cylinder. The combustion is performed in a state where the lean air-fuel ratio is a predetermined amount larger than the fuel ratio, and for the subsequent cylinder, fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the preceding cylinder, and the predetermined air-fuel ratio is determined. In the above-mentioned special operation mode, combustion is performed by compression self-ignition in the following cylinders, and fuel supply to each cylinder is stopped in the fuel stop mode. When switching from the fuel stop mode to a special operation mode in which combustion is performed by compression self-ignition in the subsequent cylinder, at least the combustion state of at least each cylinder is transiently controlled so as to facilitate the switching. The fuel return transient mode is configured to pass through for a predetermined period. In the fuel return transient mode, the gas circulation path is set to the two-cylinder connection state, For the cylinders, combustion is performed by forced ignition in a state of a lean air-fuel ratio, and for the succeeding cylinders, fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinder to substantially reduce combustion. In addition to performing combustion by forced ignition with the stoichiometric air-fuel ratio, the fuel injection timing for performing combustion in the following cylinders after fuel return is advanced-adjusted so that fuel activation is promoted. A control device for a spark ignition engine.
[0030]
According to a sixth aspect of the present invention, in the control apparatus for a spark ignition engine according to the fifth aspect, the advance correction is performed by performing fuel injection for performing combustion in the succeeding cylinder in the preceding cylinder, and controlling the fuel injection. The injection timing is set between the expansion stroke and the exhaust stroke of the preceding cylinder.
[0031]
By doing so, the same functions and effects as those of the first, fifth, tenth, and eleventh aspects are obtained, and the two-cylinder connection state is set in the transient fuel return mode, and combustion is also performed in the subsequent cylinder from the time of fuel return. Therefore, the in-cylinder temperature of the succeeding cylinder can be raised more quickly, and combustion by compression self-ignition can be easily performed at an early stage. After the fuel is restored, the fuel injection timing for performing combustion in the following cylinder is advanced (corrected earlier than in the normal special operation mode) to promote the activation of the fuel, thereby further stabilizing the fuel. Combustion in the following cylinder can be obtained.
[0032]
In particular, when fuel injection for performing combustion in the succeeding cylinder is performed in the preceding cylinder, the fuel is mixed with high-temperature burned gas discharged from the preceding cylinder and guided to the succeeding cylinder, so that activation is promoted. Is done. If the injection timing is between the expansion stroke and the exhaust stroke of the preceding cylinder (corresponding to the interval between the exhaust stroke of the previous cycle and the intake stroke of the cycle in the subsequent cylinder), the injection timing is between the ignition timing of the following cylinder and the subsequent cylinder. In addition, sufficient time for fuel activation can be secured.
[0033]
According to a seventh aspect of the present invention, in the control apparatus for a spark ignition type engine according to the fifth aspect, the advance correction is performed by injecting fuel for performing combustion in the subsequent cylinder in at least two parts. The fuel injection is performed in the preceding cylinder, the fuel injection timing is set during an expansion stroke or an exhaust stroke of the preceding cylinder, and at least one fuel injection is performed in the subsequent cylinder. It is characterized by.
[0034]
In this way, two types of fuel states can be formed around the ignition plug at the time of ignition in the subsequent cylinder. One is an air-fuel mixture which is injected in the preceding cylinder, is uniformly mixed and activated, and the other is a fuel which is injected in the following cylinder and is unevenly distributed around the periphery of the spark plug. The ignitability in the subsequent cylinder can be further improved by the relatively high concentration of fuel unevenly distributed around the spark plug, and the combustion can be stabilized by the uniformly activated air-fuel mixture.
[0035]
According to an eighth aspect of the present invention, in the control apparatus for a spark ignition engine according to any one of the first to seventh aspects, the period of the fuel return transient mode is such that the longer the period of the fuel stop mode or the engine The temperature is set to be longer as the temperature is lower.
[0036]
In this case, when the period of the fuel stop mode is long and the degree of decrease in the in-cylinder temperature is large, the period of the fuel return transient mode is extended so that the first special operation mode On the other hand, if the period of the fuel stop mode is short and the degree of decrease in the in-cylinder temperature is small, the period of the fuel return transient mode should be shortened and the system immediately shifts to the first special operation mode. Can be. That is, the period of the fuel return transient mode can be set to a necessary minimum, and the effect of improving fuel efficiency can be further enhanced.
[0037]
The term “period” here may be time, but may also be a time-substituting characteristic, such as the elapsed amount of a cycle (one cycle consists of four strokes of intake, compression, expansion, and exhaust) or The amount of decrease in the number of rotations may be used.
[0038]
According to a ninth aspect of the present invention, in the control apparatus for a spark ignition type engine according to any one of the first to eighth aspects, when the engine speed becomes equal to or lower than a predetermined fuel return speed during the fuel stop mode. The fuel supply is restarted to exit the fuel stop mode, and the fuel return rotational speed is in the special operation mode more than in the normal operation mode immediately before the fuel stop mode. In such a case, the value is set to be higher in the case where it is set.
[0039]
By doing so, the fuel return rotational speed can be set to the minimum necessary according to the mode before the fuel stop mode. The fuel return rotation speed is set as a rotation speed at which fuel supply should be restarted in order to prevent the engine from stopping when the rotation speed becomes lower than or equal to the rotation speed during the fuel stop mode. Therefore, the lower the fuel return rotation speed, the longer the fuel suspension period tends to be, and the effect of improving the fuel economy increases, while the margin for stopping the engine decreases. That is, it is desirable that the fuel return rotational speed be a minimum rotational speed capable of securing a margin for stopping the engine. When the mode before the fuel stop mode is the special operation mode, the in-cylinder temperature is relatively lower than in the case of the normal operation mode, so that the margin for stopping the engine at low rotation is smaller. Therefore, in such a case, by setting the fuel return rotation speed to a high value, a sufficient margin for stopping the engine is secured, and when the mode before the fuel stop mode is the normal operation mode, the fuel return rotation speed is increased. By setting it lower, the fuel efficiency improvement effect by stopping the fuel can be enhanced.
[0040]
According to a tenth aspect of the present invention, in a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference, the exhaust stroke and the intake stroke are different. The burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of overlapping cylinders is directly introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, via the inter-cylinder gas passage, and is discharged from this succeeding cylinder. The gas circulation path is switched between a two-cylinder connection state in which exhaust gas is led to an exhaust passage and an independent state in which each cylinder introduces fresh air into each cylinder. The special operation mode is selected in the low load rotation range, the normal operation mode is selected in the predetermined high load or high rotation range, and the fuel stop mode is selected in the predetermined deceleration range. In the special operation mode, the gas flow path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state in which a lean air-fuel ratio is larger than a stoichiometric air-fuel ratio by a predetermined amount. For the succeeding cylinder, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to cause combustion at a predetermined air-fuel ratio, and in the normal operation mode, the gas flow path is While making each cylinder independent state, in each cylinder independently perform combustion at a stoichiometric air-fuel ratio or an air-fuel ratio smaller than the stoichiometric air-fuel ratio, and in the fuel stop mode, stop supplying fuel to each cylinder, During the fuel stop mode, when the engine speed becomes equal to or lower than the predetermined fuel return speed, the fuel supply is restarted to exit the fuel stop mode. The fuel return rotation speed is set to be higher when the gas circulation path at the time of fuel return is in the two-cylinder connection state than in the individual cylinder independent state. This is a control device for a spark ignition type engine.
[0041]
With this configuration, the same functions and effects as those of the first, fifth, tenth, and eleventh aspects can be obtained, and when the gas circulation path at the time of fuel return is in the two-cylinder connection state, the engine speed can be relatively high. By returning the fuel, sufficient margin for stopping the engine is secured, and when each cylinder becomes independent, the fuel is returned at a relatively low engine speed to extend the period of stopping the fuel, thereby improving the fuel efficiency improvement effect. be able to.
[0042]
The invention according to claim 11 is a multi-cylinder spark ignition type engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. The burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of overlapping cylinders is directly introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, via the inter-cylinder gas passage, and is discharged from this succeeding cylinder. The gas circulation path is switched between a two-cylinder connection state in which exhaust gas is led to an exhaust passage and an independent state in which each cylinder introduces fresh air into each cylinder. The special operation mode is selected in the low load rotation range, the normal operation mode is selected in the predetermined high load or high rotation range, and the fuel stop mode is selected in the predetermined deceleration range. In the special operation mode, the gas flow path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state in which a lean air-fuel ratio is larger than a stoichiometric air-fuel ratio by a predetermined amount. For the succeeding cylinder, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to cause combustion at a predetermined air-fuel ratio, and in the normal operation mode, the gas flow path is In addition to the above-described cylinder independent state, each cylinder is caused to independently perform combustion at a stoichiometric air-fuel ratio or an air-fuel ratio smaller than the stoichiometric air-fuel ratio, and in the fuel stop mode, fuel supply to each cylinder is stopped. A cylinder temperature predicting means for the subsequent cylinder, wherein when the fuel supply mode is shifted from the special operation mode to the fuel stop mode, the cylinder temperature of the subsequent cylinder is set during the fuel stop mode. When the predicted value by the degree predicting means is lower than a predetermined temperature, the gas distribution channels is a control apparatus for a spark ignition engine, characterized in that switching to the respective cylinders independently state.
[0043]
With this configuration, the same operation and effect as those of the first, fifth, tenth, and eleventh aspects can be obtained, and when the in-cylinder temperature of the subsequent cylinder in the fuel stop mode is low, after the fuel return, the fuel return transient In the mode, control equivalent to that in the normal operation mode can be quickly performed, and stable fuel return can be performed. That is, even if the special operation mode is performed before the fuel stop mode, the in-cylinder temperature of the subsequent cylinder is predicted during the fuel stop mode, and if the predicted value is equal to or lower than the predetermined temperature, the gas flow path is set in advance. Switch to each cylinder independent state, and after returning to fuel, return to fuel immediately (without switching the gas flow path again) under the same control as in the normal operation mode (combustion at the stoichiometric air-fuel ratio in each cylinder). And a stable combustion state can be obtained.
[0044]
The operation modes of the special operation mode, the normal operation mode, the fuel stop mode, and the fuel return transient mode described in the above claims are only those which can be externally distinguished from the control of the mode (for example, in the form of a subroutine). However, the present invention also includes those in which the substantial control in which the gas flow path, fuel injection control (amount and timing), ignition timing control, and the like are integrated is equivalent to the control in each of the above modes.
[0045]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0046]
FIG. 1 shows a schematic structure of an engine according to an embodiment of the present invention, and FIG. 2 schematically shows a structure of one cylinder of an engine body 1 and intake / exhaust valves provided for the cylinder. In these drawings, the engine body 1 has a plurality of cylinders, and in the illustrated embodiment, has four cylinders 2A to 2D. A piston 3 is fitted into each of the cylinders 2A to 2D, and a combustion chamber 4 is formed above the piston 3.
[0047]
A spark plug 7 is provided at the top of the combustion chamber 4 of each of the cylinders 2A to 2D, and the plug tip faces the inside of the combustion chamber 4. The ignition plug 7 is connected to an ignition circuit 8 capable of controlling the ignition timing by electronic control.
[0048]
A fuel injection valve 9 for directly injecting fuel into the combustion chamber 4 is provided on a side portion of the combustion chamber 4. The fuel injection valve 9 incorporates a needle valve and a solenoid (not shown). When a pulse signal is input, the fuel injection valve 9 is driven and opened for a time corresponding to the pulse width at the pulse input time. Is configured to inject an amount of fuel according to the following. It should be noted that fuel is supplied to the fuel injection valve 9 through a fuel supply passage or the like by a fuel pump (not shown), and the fuel is supplied so that a fuel pressure higher than the pressure in the combustion chamber during the compression stroke can be given. The system is configured.
[0049]
In addition, intake ports 11, 11a, 11b and exhaust ports 12, 12a, 12b are opened to the combustion chambers 4 of the cylinders 2A to 2D, and these ports are connected to an intake passage 15, an exhaust passage 20, and the like. Each port is opened and closed by intake valves 31, 31a, 31b and exhaust valves 32, 32a, 32b.
[0050]
Each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of a four-cylinder engine, the first cylinder 2A and the second cylinder 2A are arranged from one end in the cylinder row direction. When the cylinders are referred to as cylinders 2B, 3C, and 2D, as shown in FIG. 6, the above cycle is performed in the order of the first cylinder 2A, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B at a crank angle of 180. It is performed with a phase difference of every °. In FIG. 6, EX indicates an exhaust stroke, IN indicates an intake stroke, F indicates fuel injection, S indicates forced ignition, and the star mark in the figure indicates compression self-ignition (forced ignition depending on conditions). It is expressed that
[0051]
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, between the cylinder on the exhaust stroke side (hereinafter referred to as a preceding cylinder in this specification) when the exhaust stroke and the intake stroke overlap, the cylinder on the intake stroke side (this specification). In this case, an inter-cylinder gas passage 22 is provided so that the burned gas can be directly guided to the subsequent cylinder. In the four-cylinder engine of this embodiment, as shown in FIG. 6, the exhaust stroke (EX) of the first cylinder 2A and the intake stroke (IN) of the second cylinder 2B overlap, and the exhaust stroke (EX) of the fourth cylinder 2D. ) And the intake stroke (IN) of the third cylinder 2C overlap, so that the first cylinder 2A and the second cylinder 2B and the fourth cylinder 2D and the third cylinder 2C form a pair, respectively, and the first cylinder 2A and the fourth cylinder 2C. The cylinder 2D is a preceding cylinder, the second cylinder 2B, and the third cylinder 2C are subsequent cylinders.
[0052]
The intake / exhaust ports of each cylinder and the intake passage, exhaust passage and inter-cylinder gas passage connected thereto are specifically configured as follows.
[0053]
The first cylinder 2A and the fourth cylinder 2D, which are the preceding cylinders, have an intake port 11 for introducing fresh air and a first exhaust port 12a for sending burned gas (exhaust gas) to an exhaust passage, respectively. , And a second exhaust port 12b for leading burned gas to a subsequent cylinder. A second intake port 11a for introducing fresh air and a second intake port for introducing burned gas from the preceding cylinder are respectively provided to the second cylinder 2B and the third cylinder 2C, which are subsequent cylinders. 11b and an exhaust port 32 for sending burned gas to an exhaust passage are provided.
[0054]
In the example shown in FIG. 1, the number of intake ports 11 in the first and fourth cylinders 2A and 2D and the number of first intake ports 11a in the second and third cylinders 2B and 2C are two for each cylinder and the left half of the combustion chamber. The first exhaust port 12a and the second exhaust port 12b in the first and fourth cylinders 2A and 2D, and the second intake port 11b and the exhaust port in the second and third cylinders 2B and 2C. 12 are provided in parallel on the right half side of the combustion chamber.
[0055]
The downstream end of the cylinder-specific branch intake passage 16 in the intake passage 15 is connected to the intake port 11 in the first and fourth cylinders 2A and 2D and the first intake port 11a in the second and third cylinders 2B and 2C. I have. In the vicinity of the downstream end of each branch intake passage 16, a multiple throttle valve 17 interlocking with each other via a common shaft is provided, and the multiple throttle valve 17 is driven by an actuator 18 according to a control signal, The intake air volume is adjusted.
[0056]
An airflow sensor 19 for detecting an intake air flow rate and an intake air temperature sensor 27 for measuring an intake air temperature are provided in a common intake passage upstream of the gathering portion in the intake passage 15. The air flow sensor 19 can detect the state of the gas flow path by detecting the pulsation of the intake air as well as detecting the intake air flow rate. That is, in the cylinder independent state, intake pulsation occurs at a cycle of 180 ° CA (crank angle), whereas when the two cylinders are connected, intake pulsation occurs at a cycle of 360 ° CA. To detect. The reason why the intake pulsation has a 360 ° CA cycle in the two-cylinder connection state is that the intake air to the subsequent cylinders 2B and 2C is made not from the intake passage 15 but from the inter-cylinder gas passage 22.
[0057]
The upstream end of a branch exhaust passage 21 for each cylinder in the exhaust passage 20 is connected to the first exhaust port 12a in the first and fourth cylinders 2A and 2D and the exhaust port 12 in the second and third cylinders 2B and 2C. I have. Further, inter-cylinder gas passages 22 are provided between the first cylinder 2A and the second cylinder 2B and between the third cylinder 2C and the fourth cylinder 2D, respectively, and the first and fourth cylinders 2A and 2A, which are the preceding cylinders, are provided. The upstream end of the inter-cylinder gas passage 22 is connected to the 2D second exhaust port 12b, and the downstream end of the inter-cylinder gas passage 22 is connected to the second intake ports 11b of the second and third cylinders 2B and 2C that are subsequent cylinders. Is connected.
[0058]
The inter-cylinder gas passage 22 is a relatively short passage connecting between adjacent cylinders, and is covered by a water jacket 26. The water jacket 26 includes a cooling water passage 52 (see FIG. 3) surrounding the inter-cylinder gas passage 22 therein. When the burned gas discharged from the preceding cylinder passes through the inter-cylinder gas passage 22, the cooling water is stopped to suppress the heat radiation, and the cooling water is circulated to promote the heat radiation. The cooling water passage 52 is provided with a cooling pump 50 for circulating the cooling water and a cooling pump driving motor 51 for driving the cooling water, and a gas passage cooling water temperature sensor for measuring the temperature of the cooling water. 57 are provided (see FIG. 3).
[0059]
In the inter-cylinder gas passage 22, there is provided a linear O, whose output varies linearly in accordance with the oxygen concentration. ₂ A sensor 25 is provided, and a fuel injection amount for the preceding cylinders 2A and 2D having a predetermined lean air-fuel ratio is feedback-controlled in accordance with the output of the sensor 25.
[0060]
An O-fuel ratio is detected by detecting the oxygen concentration in the exhaust gas at a collecting portion of the exhaust passage 20 downstream of the branch exhaust passage 21. ₂ A sensor 23 is provided. O ₂ The sensor 23 detects the λO at which the output suddenly changes near the stoichiometric air-fuel ratio. ₂ Sensor, and this O ₂ Based on the output of the sensor 23, the fuel injection amount for the following cylinders 2B and 2C (including the cylinders 2A and 2D when the respective cylinders are in the independent state) is feedback-controlled. Further O ₂ An exhaust passage 20 downstream of the sensor 23 is provided with a three-way catalyst 24 for purifying exhaust gas. As is generally known, the three-way catalyst 24 purifies HC, CO, and NOx when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (that is, when the excess air ratio λ is λ = 1). It is a catalyst that shows performance.
[0061]
The intake / exhaust valves for opening and closing the intake / exhaust ports of each cylinder and the valve operating mechanism for these valves are as follows.
[0062]
The intake port 11, the first exhaust port 12a, and the second exhaust port 12b of the first and fourth cylinders 2A, 2D are provided with an intake valve 31, a first exhaust valve 32a, and a second exhaust valve 32b, respectively. A first intake valve 31a, a second intake valve 31b, and an exhaust valve 32 are provided at the first intake port 11a, the second intake port 11b, and the exhaust port 12, respectively, of the third and third cylinders 2B, 2C. Then, these intake and exhaust valves are opened and closed at predetermined timings by a valve mechanism including the camshafts 33 and 34 so that the intake stroke and the exhaust stroke of each cylinder are performed with the above-described predetermined phase difference. Driven as follows.
[0063]
Further, among these intake / exhaust valves, for the first exhaust valve 32a, the second exhaust valve 32b, the first intake valve 31a, and the second intake valve 31b, each valve is switched between an operating state and a stopped state. A valve stop mechanism 35 is provided. The valve stop mechanism 35 is conventionally known, so a detailed illustration thereof is omitted. For example, hydraulic oil can be supplied and discharged to and from a tappet interposed between the cams of the camshafts 33 and 34 and the valve shaft. When the hydraulic oil is supplied to the hydraulic chamber, the operation of the cam is transmitted to the valve to open and close the valve, and when the hydraulic oil is discharged from the hydraulic chamber, the operation of the cam is controlled by the valve. The valve is stopped because it cannot be communicated to.
[0064]
A first control valve 37 is provided in a passage 36 for supplying and discharging hydraulic oil to the valve stop mechanism 35 of the first exhaust valve 32a and the valve stop mechanism 35 of the first intake valve 31a, and a valve stop of the second exhaust valve 32b. A second control valve 39 is provided in a passage 38 for supplying and discharging hydraulic oil to the mechanism 35 and the valve stop mechanism 35 of the second intake valve 31b (see FIG. 3).
[0065]
FIG. 3 shows the configuration of the drive and control system. In this figure, an engine control ECU (control unit) 40 including a microcomputer and the like includes an air flow sensor 19, an O ₂ Sensor 23, linear O ₂ Signals from the sensor 25 and the intake air temperature sensor 27 are input, and a rotation speed sensor 47 for detecting an engine rotation speed for determining an operation state, an accelerator opening sensor 48 for detecting an accelerator opening (accelerator pedal depression amount), and Signals from a vehicle speed sensor 55 and the like are input, and further, signals from an engine cooling water temperature sensor 56 and a gas passage cooling water temperature sensor 57 are input to detect the temperature of each cooling water. The ECU 40 outputs control signals to each of the fuel injection valves 9, the actuator 18 of the multiple throttle valve 17, the first and second control valves 37 and 39, and the cooling pump drive motor 51. ing.
[0066]
The ECU 40 constitutes control means for controlling a special operation mode in which combustion is performed at least in a low-load low-speed range while the gas circulation path is in a two-cylinder connection state (see FIG. 7). A means 41, a valve stop mechanism control means 42, an intake air amount control means 43, a combustion control means 44, a gas passage cooling control means 49 and an in-cylinder temperature state estimating means 53 are provided.
[0067]
The operating state discriminating means 41 checks the operating state (engine speed and engine load) of the engine based on signals from the rotation speed sensor 45 and the accelerator opening sensor 46 and the like, and the operation state is as shown in FIG. It is determined which of a low-load low-rotation-side operation area A, a high-load-side or high-rotation-side operation area B, and a deceleration-range operation area C.
[0068]
Any one of the special operation mode, the normal operation mode, the fuel stop mode, and the fuel return transient mode is selected according to each operation region or the transition state of the operation region. Each operation mode will be described later.
[0069]
The valve stop mechanism control means 42 controls each of the control valves 37 and 39 according to the gas flow path (two-cylinder connection state or each cylinder independent state), thereby causing each valve stop mechanism 35 to operate as follows. Control.
[0070]

[0071]
The intake air amount control means 43 controls the opening degree of the throttle valve 17 (throttle opening degree) by controlling the actuator 18, obtains a target intake air amount from a map or the like according to the operating state, and obtains the target intake air amount. The throttle opening is controlled according to the amount of intake air. Here, when the combustion is performed in the preceding cylinders 2A, 2D and the succeeding cylinders 2B, 2C in the two-cylinder connection state, the air supplied to the preceding cylinders 2A, 2D uses the air supplied to the preceding cylinders 2A, 2D and the succeeding cylinders 2B, 2C. The throttle opening is adjusted so that the fuel supplied to the throttle can be burned.
[0072]
The combustion control unit 44 includes a fuel injection control unit 45 and an ignition control unit 46. The fuel injection control unit 45 controls the fuel injection amount and the injection timing from the fuel injection valve 9 provided in each of the cylinders 2A to 2D. Alternatively, the stop and return of the fuel supply are controlled in accordance with the operating state of the engine, and the ignition control means 46 controls the ignition timing and the ignition stop according to the operating state. Therefore, the air-fuel ratio in each cylinder is also set by the combustion control means 44.
[0073]
The gas passage cooling control unit 49 controls the temperature of the burned gas flowing in the inter-cylinder gas passage 22 when the two cylinders are connected. The gas passage cooling control means 49 drives the cooling pump when the temperature of the air-fuel mixture is equal to or higher than a predetermined value based on the estimated value of the air-fuel mixture of the succeeding cylinder by the in-cylinder temperature state estimating means 53 (to be described in detail later). The motor 51 is operated. The cooling water is circulated in the cooling water passage 52 by the cooling pump 50 driven by the cooling pump drive motor 51, and cools the inter-cylinder gas passage 22 in the water jacket 26. As a result, the temperature of the burned gas guided from the preceding cylinders 2A, 2D to the succeeding cylinders 2B, 2C via the inter-cylinder gas passage 22 drops, so that the in-cylinder temperatures of the following cylinders 2B, 2C cause compression self-ignition. Maintain a suitable temperature.
[0074]
The in-cylinder temperature state estimating means 53 estimates the in-cylinder temperature state of the subsequent cylinder in the special operation mode, and estimates the mixture temperature immediately before combustion. Based on the estimated value, the valve stop mechanism control means 42 switches the gas flow path, the combustion control means 44 corrects the air-fuel ratio of the preceding cylinder, and the gas passage cooling control means 49 controls the cooling pump drive motor 51. Is switched on / off.
[0075]
FIG. 5 is a main block diagram of the procedure for estimating the in-cylinder temperature of the subsequent cylinders 2B and 2C in the two-cylinder connection state by the in-cylinder temperature state estimating means 53. FIG. 5 shows a configuration in which three columns are arranged vertically. P10 to P26 in the left column indicate input parameters obtained directly or by a simple calculation based on signals from various sensors input to the ECU 40 and parameters inside the ECU 40. It is. The burned gas flow rate P30 in the center row is an intermediate parameter obtained in the calculation process. The burned gas temperature P40 of the preceding cylinder in the right column and the burned gas temperature P50 in the inter-cylinder gas passage are the main calculation results, and the mixture temperature P60 immediately before the combustion of the succeeding cylinder is the final calculation result. As described above, the in-cylinder temperature state estimating means 53 sequentially obtains the burned gas temperature P40 of the preceding cylinder and the burned gas temperature P50 in the inter-cylinder gas passage from each input parameter, and finally obtains the temperature immediately before the combustion of the succeeding cylinder. The mixture temperature P60 is determined.
[0076]
The process for obtaining the preceding cylinder burned gas temperature P40 is referred to as the preceding cylinder calculation unit, the process for obtaining the burned gas temperature P50 in the inter-cylinder gas passage is referred to as the inter-cylinder gas passage calculation unit, and the mixture gas temperature P60 immediately before combustion of the subsequent cylinder is referred to. These processes will be described below assuming that the process to be determined is a subsequent cylinder calculation unit.
[0077]
In the first preceding cylinder calculation unit, the preceding cylinder burned gas temperature P40 is obtained from the preceding cylinder air-fuel ratio P10, the ignition timing P12, the engine coolant temperature P14, the intake air temperature P16, the engine speed P18, and the air charge P20. The preceding cylinder air-fuel ratio P10 is a parameter obtained from the intake air amount by the air flow sensor 19 and the fuel injection amount by the fuel injection control means 45, and ₂ Feedback control is performed by the sensor 25. The ignition timing P12 is a parameter determined by the fuel injection control unit 45. The engine coolant temperature P14, the intake temperature P16, the engine speed P18, and the air charge P20 are parameters obtained by the engine coolant temperature sensor 56, the intake temperature sensor 27, the speed sensor 47, and the air flow sensor 19, respectively.
[0078]
The next inter-cylinder gas passage calculation unit calculates the inter-cylinder combustion temperature based on the preceding cylinder burned gas temperature P40 obtained by the preceding cylinder calculation unit, the intake temperature P16, the vehicle speed P22, the gas passage cooling water temperature P24, and the burned gas flow rate P30. The burned gas temperature P50 in the gas passage is determined. The vehicle speed P22 and the gas passage cooling water temperature P24 are parameters obtained from the vehicle speed sensor 55 and the gas passage cooling water temperature sensor 57. The burned gas flow rate P30 is an intermediate parameter calculated from the engine speed P18 and the air charge amount P20.
[0079]
The last succeeding cylinder calculation unit calculates the burned gas temperature P50 in the inter-cylinder gas passage, the engine speed P18, the air charge amount P20, the burned gas flow rate P30, and the succeeding cylinder air-fuel ratio P26 immediately before the combustion of the succeeding cylinder. Is obtained. The succeeding cylinder air-fuel ratio P26 is a parameter obtained from the preceding cylinder air-fuel ratio P10 and the fuel injection amount by the fuel injection control means 45. ₂ Feedback control is performed by the sensor 23.
[0080]
Next, an operation region and an operation operation mode in the present embodiment will be described. FIG. 4A is an explanatory diagram showing an operating region of the engine body 1, in which the horizontal axis indicates the engine speed and the vertical axis indicates the engine load.
[0081]
In the operation region A in the low-load low-speed region, the special operation mode is selected in principle, except when the engine is not warm. In the special operation mode, the gas circulation path is connected to the two cylinders (the inter-cylinder gas passage 22 is opened, and the burned gas discharged from the preceding cylinders 2A and 2D is introduced into the succeeding cylinders 2B and 2C as it is. 2B and 2C are guided to the exhaust passage), and the preceding cylinders 2A and 2D are burned with a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount. For the cylinders 2B and 2C, fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinders 2A and 2D, and combustion is performed at a predetermined air-fuel ratio. In the present embodiment, the air-fuel ratio of the subsequent cylinders 2B and 2C in the special operation mode is set to a substantial stoichiometric air-fuel ratio. Here, the substantial stoichiometric air-fuel ratio refers to the amount of oxygen contained in the burned gas introduced from the preceding cylinders 2A and 2D, and the amount of fuel additionally supplied for combustion in the following cylinders 2B and 2C. Is equivalent to a stoichiometric air-fuel ratio (excess air ratio λ = 1). With this configuration, exhaust gas purification is sufficiently performed only by providing the three-way catalyst 24 in the exhaust passage 20, so that it is not necessary to separately provide an exhaust gas purification unit, and cost can be reduced.
[0082]
Further, the special operation mode is subdivided into a first special operation mode and a second special operation mode. The first special operation mode is a mode that is preferentially selected in the entire operation region A, and causes the subsequent cylinders 2B and 2C to perform combustion by compression self-ignition. In order to perform the compression self-ignition, the in-cylinder temperature must be high in the latter half of the compression stroke. However, since high-temperature burned gas is introduced into the subsequent cylinders 2B and 2C from the preceding cylinders 2A and 2D. As compared with a conventional engine that introduces outside air, the temperature in the cylinder at the latter stage of the compression stroke can be significantly increased, thereby enabling compression self-ignition.
[0083]
The second special operation mode is a mode that is preliminarily selected in the entire operation region A, and causes the subsequent cylinders 2B and 2C to perform combustion by forced ignition. Due to the operating state of the engine body 1 and the influence of the outside air temperature, the combustion by the compression self-ignition in the following cylinders 2B and 2C cannot always be stably performed in the operating region A. In such a case, the second special operation mode is selected, the ignition is reliably performed by the forced ignition, and the stable combustion is performed.
[0084]
In the present embodiment, the first special operation mode is set in principle over the entire operation region A. However, the operation region A is further divided, and the region of relatively low load and low rotation is set to the second special operation mode. Alternatively, the region of relatively high load and high rotation may be set to be the first special operation mode.
[0085]
In this embodiment, combustion is performed by forced ignition in the preceding cylinders 2A, 2D in the special operation mode. However, means for increasing the in-cylinder temperature of the preceding cylinders 2A, 2D (for example, increasing the internal RGR) Compressed self-ignition may also be performed in the preceding cylinders 2A and 2D.
[0086]
In the operation region B having a higher load or higher rotation than the operation region A, the normal operation mode is selected. In the normal operation mode, as in the case of a conventional general engine, the gas circulation path is made independent of each cylinder, and each of the cylinders 2A to 2D is independently burned at a substantially stoichiometric air-fuel ratio or an air-fuel ratio smaller than that. Is performed.
[0087]
The fuel stop mode is selected in a deceleration range in which the driver fully or almost completely closes the accelerator opening. In the fuel stop mode, the supply of fuel to each of the cylinders 2A to 2D is stopped. Therefore, the engine body 1 is reversely driven from the tire side, and the load becomes a negative value indicated by the reverse driving load characteristic. At that time, the vehicle is in a state where the engine brake is applied. The operation region C shown in FIG. 4A is a region on the line showing such reverse drive load characteristics. That is, in this embodiment, the fuel stop mode is selected in the operation region C. Note that the reverse drive load characteristic varies depending on the gas flow path and other conditions, but is typically shown here as a single characteristic.
[0088]
In addition, during the fuel stop mode, when the engine speed drops below the fuel return speed r6, the fuel supply is restarted (fuel return) to prevent the engine from stopping, and the mode is shifted to the special operation mode.
[0089]
The operation of the apparatus of the present embodiment as described above will be described with reference to FIGS. In the special operation mode, as described above, the first exhaust valve 32a and the first intake valve 31a are stopped and the second exhaust valve 32b and the second intake valve 31b are activated, so that substantially fresh air and gas are generated. 7 shows that the burned gas discharged from the preceding cylinders (No. 1 and No. 4 cylinders) 2A and 2D passes through the inter-cylinder gas passage 22 as it is and the subsequent cylinders (No. 2 and No. 3). The two-cylinder connection state is such that only the gas discharged from the following cylinders 2B and 2C is introduced into the exhaust passage 20 while being introduced into the cylinders 2B and 2C.
[0090]
In this state, fresh air is introduced into the preceding cylinders 2A and 2D from the intake passage 15 in the intake stroke (arrows a in FIG. 7), and the leading cylinders 2A and 2D are linear O. ₂ The fuel is injected in the compression stroke while the fuel injection amount is feedback-controlled so that the air-fuel ratio detected by the sensor 25 becomes a super-lean air-fuel ratio approximately twice or more of the stoichiometric air-fuel ratio. Ignition is performed, and stratified combustion is performed at a super lean air-fuel ratio (see FIG. 6).
[0091]
Thereafter, during a period in which the intake strokes of the preceding cylinders 2A and 2D and the exhaust strokes of the succeeding cylinders 2B and 2C overlap, the burned gas discharged from the preceding cylinders 2A and 2D is introduced into the succeeding cylinders 2B and 2C through the gas passage 22. (A white arrow in FIG. 6 and an arrow b in FIG. 7). Then, in the subsequent cylinders 2B and 2C, fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the preceding cylinders 2A and 2D, and the fuel injection amount is controlled so as to be substantially the stoichiometric air-fuel ratio. Fuel is injected during the intake stroke. At this time, in the first special operation mode, the forced ignition by the ignition plug 7 is stopped in the subsequent cylinders 2B and 2C, and the compression self-ignition is performed by increasing the pressure and temperature in the combustion chamber near the top dead center of the compression stroke, In the second special operation mode, combustion is performed by forced ignition at the spark plug 7 in the subsequent cylinders 2B and 2C.
[0092]
Thus, in the first special operation mode, combustion is rapidly performed by the compression self-ignition in the subsequent cylinders 2B and 2C even under the condition that the burned gas component corresponding to a large amount of EGR gas is included and the air-fuel ratio is lean. As a result, the thermal efficiency is greatly improved.
[0093]
Further, the in-cylinder temperature state estimating means 53 estimates the mixture temperature T immediately before combustion of the subsequent cylinder, and switches to the second special operation mode when the temperature becomes lower than the predetermined value T1 (see step S17 in FIG. 9). ). That is, when the in-cylinder temperatures of the subsequent cylinders 2B and 2C have not risen sufficiently to perform the compression self-ignition stably, combustion is performed by forced ignition. Conversely, when the in-cylinder temperatures of the subsequent cylinders 2B and 2C are too high and there is a concern of knocking or the like, the cooling pump 50 is operated by the cooling pump driving motor 51, and the inter-cylinder in the water jacket 26 is operated. The gas passage 22 is cooled. As a result, the burned gas guided from the preceding cylinders 2A, 2D to the succeeding cylinders 2B, 2C is cooled, and the in-cylinder temperature rise of the succeeding cylinders 2B, 2C is suppressed, so that the first special operation mode can be continued. .
[0094]
That is, in the leading cylinders 2A and 2D, the thermal efficiency is increased and the pumping loss is reduced by the super-lean stratified combustion. On the other hand, in the trailing cylinders 2B and 2C, the pumping loss reduction effect is obtained as in the leading cylinders 2A and 2D. In addition, in the case of performing combustion by compression self-ignition, thermal efficiency is enhanced by performing compression self-ignition in a uniform mixture distribution state, and fuel efficiency is greatly improved by these actions.
[0095]
Further, in the preceding cylinders 2A and 2D, the lean air-fuel ratio is set to be approximately twice or more than the stoichiometric air-fuel ratio, so that the NOx generation amount is suppressed to a relatively small amount, and in the succeeding cylinders 2B and 2C, the leading cylinders 2A and 2D By introducing the burned gas, the state becomes equivalent to the state where a large amount of EGR is performed, so that the generation of NOx is sufficiently suppressed. From such a point, it is advantageous for improving the emission.
[0096]
On the other hand, in the normal operation mode, as described above, the first exhaust valve 32a and the first intake valve 31a are in the operating state, and the second exhaust valve 32b and the second intake valve 31b are in the stopped state. 8 and the gas flow paths are as shown in FIG. 8. The intake ports 31, 31a and the exhaust ports 12a, 12 of the cylinders 2A to 2D are substantially independent, and the intake ports of the cylinders 2A to 2D are separated from the intake passage 15. Fresh air is introduced into 31, 31a, and burned gas is discharged from the exhaust ports 31, 31a of the cylinders 2A to 2D to the exhaust passage 20. In this case, the output performance is ensured by controlling the intake air amount and the fuel injection amount so as to be stoichiometric air-fuel ratio or richer.
[0097]
In the fuel stop mode, fuel supply to each of the cylinders 2A to 2D is stopped. Therefore, fuel consumption during coasting operation or downhill where engine output is not required is reduced, and fuel efficiency can be improved. Further, the effect of the engine brake obtained by reversely driving the engine body 1 can be enhanced. The gas flow path in the fuel stop mode follows the mode immediately before switching to the fuel stop mode in principle. However, switching may be performed during the fuel stop mode depending on conditions (see steps S51 and S55 in FIG. 10).
[0098]
Next, the transition of each operation mode and the fuel return transition mode will be described. FIG. 4B is a table showing a combination pattern of modes before and after the fuel stop mode. Control at the time of fuel return is set according to this pattern. Symbols A4, A5, A6, B1, B2, C1, C2, C4, C5, and C6 shown in FIG. 4B are operating states corresponding to the points shown in FIG. is there. Accordingly, the operating states A4, A5 and A6 are points representing the first special operation mode, the operating states B1 and B2 are points representing the normal operation mode, and the operating states C1, C2, C4, C5 and C6 Is a point representing the fuel stop mode. The engine speeds in the operating state B1 and the operating state C1 are substantially equal, and are r1. Similarly, the engine speeds of the operating state B2 and the operating state C2 are substantially equal and r2, the engine speeds of the operating state A4 and the operating state C4 are substantially equal and r4, and the operating state A5 and the operating state C5 are the same. The engine speeds are substantially equal and r5, and the engine speeds in the operating state A6 and the operating state C6 are substantially equal and r6. The engine speed r6 is the fuel return speed.
[0099]
In FIG. 4B, the horizontal axis (column) represents operating states A4 and B1 as points representing the operating state before the fuel stop mode, and the vertical axis (row) represents the operating state after the fuel stop mode. Operation points A5, A6, and B2 are shown as points to be performed. Each column shows a pattern number composed of these combinations and an operating state in the passing fuel stop mode. For example, pattern 1 shows a pattern from operation state A4 (first special operation mode) to operation state A5 (first special operation mode) via operation states C4 and C5 (fuel stop mode). Other patterns 2 to 5 follow the same notation. Note that patterns 1, 2, 3, and 5 are in the deceleration direction, while pattern 4 is in the speed increasing direction. This occurs, for example, on a downhill where the speed increases even when the accelerator is fully closed.
[0100]
Of the patterns 1 to 5, the patterns 1, 2, and 3 are set so as to pass through the fuel return transient mode when switching from the fuel stop mode to the first special operation mode.
[0101]
The fuel stop mode and the fuel return transient mode in Pattern 1 are as follows. In Pattern 1, the operation state changes from operation state A4 to C4 to C5 to A5. When the operation state changes from the operation state A4 to the operation state C4, the mode is switched from the first special operation mode to the fuel stop mode, and the supply of fuel is stopped. Then, until the operation state C5, the gas circulation path is maintained in the same two-cylinder connection state as the operation state A4. After that, when the operation state is changed to A5, the mode is finally switched to the first special operation mode, but the fuel return transient mode is set for a predetermined period until then. The fuel return transient mode in the pattern 1 includes a first stage (from the time of fuel return to the lapse of the S1 cycle. One cycle includes four strokes of intake, compression, expansion, and exhaust), and a second stage thereafter. (Until the S2 cycle has passed (S2> S1)). In the first stage, combustion is performed at the stoichiometric air-fuel ratio (excess air ratio λ = 1) in the preceding cylinders 2A and 2D while maintaining the gas circulation path in the two-cylinder connection state (see step S133 in FIG. 11). . By doing so, even if the temperature inside the cylinder is reduced by air passing through the preceding cylinders 2A and 2D during the fuel stop mode, misfire can be reliably prevented and fuel can be returned in a stable combustion state. In this first stage, combustion is not performed in the subsequent cylinders 2B and 2C, but the high temperature burned gas generated by combustion at the stoichiometric air-fuel ratio introduced from the preceding cylinders 2A and 2D passes through, thereby causing the cylinder The internal temperature is increasing. Thus, both the preceding cylinder and the succeeding cylinder are heated.
[0102]
In the second stage of the fuel return transient mode in Pattern 1, the lean air-fuel ratio is such that the excess air ratio λ> 1 for the leading cylinders 2A and 2D while maintaining the gas circulation path in the two-cylinder connection state. Is supplied to the subsequent cylinders 2B and 2C, and fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinders 2A and 2D to form a substantially stoichiometric air-fuel ratio, thereby performing forced ignition. Cause combustion. That is, control equivalent to the second special operation mode is performed (see step S143 in FIG. 11). In this case, the air-fuel ratio of the preceding cylinders 2A and 2D may be set to an excess air ratio λ ≒ 2 according to the general second special operation mode. Combustion is desirable because combustion becomes more stable. This second stage is closer to the first special operation mode than the first stage, and the in-cylinder temperature of the subsequent cylinders 2B and 2C tends to increase, so that the transition to the first special operation mode is accelerated. be able to.
[0103]
By the way, the cycle number S1 of the first stage and the cycle number S2 of the second stage vary depending on the operation state, and are set to be longer as the period of the fuel stop mode is longer or the engine temperature is lower. . Therefore, when the period of the fuel stop mode is long and the degree of decrease in the in-cylinder temperature is large, the period (S1 and S2) of the fuel return transient mode is lengthened, and the first special While the mode can be shifted to the operation mode, when the period of the fuel stop mode is short and the degree of decrease in the in-cylinder temperature is small, the period of the fuel return transient mode is shortened and the mode immediately shifts to the first special operation mode. Can be done. By setting the period of the fuel return transient mode to be a necessary minimum as described above, the fuel efficiency improvement effect is further enhanced.
[0104]
In this manner, the mode is switched from the fuel return transient mode to the first special operation mode after the S2 cycle from the fuel return. At this time, the in-cylinder temperature predicted value T of the subsequent cylinders 2B and 2C by the in-cylinder temperature state estimating means 53 is changed to a predetermined T1. If not, the fuel return transient mode ends with the same control as in the second special operation mode (see step S117 in FIG. 11).
[0105]
Next, the fuel stop mode and the fuel return transient mode in pattern 2 are as follows. In Pattern 2, the operation state changes from operation state B1 to C1 to C5 to A5. When the operation state changes from the operation state B1 to the operation state C1, the mode is switched from the normal operation mode to the fuel stop mode, and the supply of fuel is stopped. Until the operating state C5, the gas circulation path is maintained in the same cylinder independent state as the operating state B1. After that, when the operation state is changed to A5, the mode is finally switched to the first special operation mode, but the fuel return transient mode is set for a predetermined period until then. The fuel return transient mode in Pattern 2 is divided into a first stage (from the time of fuel return to the lapse of the S1 cycle) and a subsequent second stage (from the lapse of the S2 cycle (S2> S1)). In the first stage, combustion at the stoichiometric air-fuel ratio (excess air ratio [lambda] = 1) is performed in each of the cylinders 2A to 2D while maintaining the gas flow path in an independent state for each cylinder. That is, control equivalent to that in the normal operation mode is performed (see step S135 in FIG. 11). By doing so, not only the preceding cylinders 2A and 2D, but also the following cylinders 2B and 2C, the fuel is restored by high-stability combustion, and more reliable stable combustion is obtained. Heating.
[0106]
In the second stage of the transient fuel return mode in the pattern 2, the same control as that in the second stage of the transient fuel return mode in the pattern 1, that is, control equivalent to the second special operation mode is performed (see step S143 in FIG. 11). ). The second stage is closer to the first special operation mode than the first stage, and achieves a smooth mode transition while performing highly stable combustion.
[0107]
However, even in the second stage, when the in-cylinder temperature estimation value T of the following cylinders 2B and 2C by the in-cylinder temperature state estimating means 53 does not reach the predetermined T1, control similar to the normal operation mode is continued. (See step S147 in FIG. 11) to promote the increase in the in-cylinder temperature of the subsequent cylinders 2B and 2C.
[0108]
Then, as in the case of the pattern 1, after the fuel is returned to the S2 cycle, the mode is switched from the fuel return transient mode to the first special operation mode. In this case, similarly to the pattern 1, when the in-cylinder temperature predicted value T of the subsequent cylinders 2B and 2C by the in-cylinder temperature state estimating means 53 does not reach the predetermined T1, the control is performed in the same manner as in the second special operation mode. The fuel return transient mode ends (see step S117 in FIG. 11). Further, the cycle number S1 in the first stage and the cycle number S2 in the second stage are set to be longer as the period of the fuel stop mode is longer or the engine temperature is lower, similarly to the pattern 1. .
[0109]
Next, the fuel stop mode and the fuel return transient mode in pattern 3 are as follows. In Pattern 3, the operating state changes from operating state A4 (or B1) to C4 (or C1) → C6 → A6. When the operation state changes from the operation state A4 (or the operation state B1) to the operation state C4 (or the operation state C1), the mode is switched from the special operation mode (or the normal operation mode) to the fuel stop mode, and the supply of the fuel is stopped. The gas flow path is maintained in the mode before switching to the fuel stop mode until near the operating state C6. When the in-cylinder temperature estimation value T of the following cylinders 2B and 2C by the in-cylinder temperature state estimating means 53 is equal to or higher than the predetermined temperature T2, the engine continues to be maintained up to the operating state C6, and the engine speed becomes the fuel return rotation When the number reaches r6, the fuel stop mode is ended, and the operation state is set to A6. At this time, when the operation state is A4 before the fuel stop mode, the control of pattern 1 is performed, and when the operation state is B1, the control of pattern 2 is performed.
[0110]
On the other hand, if the in-cylinder temperature predicted value T does not reach the predetermined temperature T2, before the operating state C6 is reached (for example, when the engine speed becomes smaller than r6 + 200 rpm), the gas circulation is performed regardless of the previous mode. The path is switched to each cylinder independent state (see step S51 in FIG. 10). Then, when reaching the operation state C6 and switching to the operation state A6, the control according to the pattern 2 is performed. In this manner, when the subsequent cylinders 2B and 2C are at low temperatures, even if the special operation mode is performed before the fuel stop mode, the gas flow paths are switched to the cylinder independent states before the fuel return, and After the return of fuel, the fuel is returned immediately by performing combustion at the stoichiometric air-fuel ratio in each of the cylinders 2A to 2D (without switching to the gas flow path again) to obtain a stable combustion state. Note that the predetermined temperature T2 may be the same as the predetermined temperature T1.
[0111]
Incidentally, FIG. 4A shows the fuel return rotational speed as the predetermined value r6, but this may be the fuel return rotational speed N1 that varies depending on the gas flow path at the time of fuel return. That is, the fuel return rotation speed N1 is set to a relatively high value when the gas circulation path at the time of fuel return is in the two-cylinder connection state, and is set to a relatively low value when the gas circulation path is in the individual cylinder independent state. By doing so, when the gas circulation path at the time of fuel return is in the two-cylinder connection state, sufficient margin for stopping the engine is ensured, and when each cylinder is in the independent state, the period of fuel stop is increased, The fuel efficiency improvement effect can be enhanced.
[0112]
Next, the fuel stop mode and the fuel return in the pattern 4 are as follows. In pattern 4, the operation state changes from operation state A4 to C4 to C2 to B2. When the operation state changes from the operation state A4 to the operation state C4, the mode is switched from the special operation mode to the fuel stop mode, and the supply of fuel is stopped. Then, until the operation state C2, the gas circulation path is maintained in the same two-cylinder connection state as the operation state A4. Thereafter, when the operation state becomes the operation state B2, the operation mode immediately shifts to the normal operation mode without passing through the fuel return transient mode, switches the gas circulation path to the cylinder independent state, and sets the stoichiometric air-fuel ratio (excess air ratio) in each of the cylinders 2A to 2D. (λ = 1) is performed (step S31 in FIG. 9). When the engine speed exceeds the maximum speed r3 in the operation region A during the fuel stop mode, the gas flow path may be switched to each of the cylinders in advance.
[0113]
Next, the fuel stop mode and the fuel return in the pattern 5 are as follows. In Pattern 5, the operation state changes from operation state B1 to C1 to C2 to B2. When the operation state changes from the operation state B1 to the operation state C1, the mode is switched from the normal operation mode to the fuel stop mode, and the supply of fuel is stopped. Then, until the operation state C2, the gas circulation path is maintained in the same cylinder independent state as the operation state B1. After that, when the operation state becomes B2, the operation mode is shifted to the normal operation mode without passing through the fuel return transient mode. At this time, since the cylinders are kept independent of each other in the gas flow path, there is no need to switch again, and it is possible to quickly shift to the normal operation mode.
[0114]
FIG. 9 is a flowchart of control when switching from the fuel stop mode to a subsequent mode. After the control is started, in step S1, each sensor information (accelerator opening, engine speed, intake air amount, engine water temperature, gas flow path state, intake air temperature, O ₂ Sensor output, fuel injection timing, ignition timing, vehicle speed, etc.). In the next step S3, it is determined whether or not the operating state is in the operating region B. If NO, the process proceeds to step S5, where the in-cylinder temperature state estimating means 53 estimates the in-cylinder temperature T of the subsequent cylinder. (See FIG. 5). At the next step S7, it is determined whether or not the operating state is in the operating region A. If YES, it is determined at step S9 whether or not the mode M = 0. The mode M is a parameter indicating the current operation mode. If M = 0, it indicates either the fuel stop mode or the fuel return transient mode. If “NO” in the step S9, the present mode is the special operation mode or the normal operation mode, and further proceeds to the next step S11 to determine whether or not the engine is warm (warm-up is completed) by the engine water temperature. Is determined. If “YES” in the step S11, it is determined that the special operation mode is set, and the process shifts to a next step S13 to determine whether or not the in-cylinder temperature T of the subsequent cylinders 2B and 2C is equal to or higher than a predetermined value T1. Done. If YES, the in-cylinder temperatures of the subsequent cylinders 2B and 2C have reached a high temperature at which compression self-ignition can be performed stably, so the flow shifts to step S15 to control the first special operation mode. In the next step S19, mode M = 1 (indicating that the current mode is the special operation mode) is input, and the routine returns.
[0115]
Backward, when NO is determined in step S13, since the in-cylinder temperatures of the subsequent cylinders 2B and 2C have not reached a high temperature at which compression self-ignition can be performed stably, the process shifts to step S17 and proceeds to the second special operation mode. Control.
[0116]
Looking further back, if YES is determined in step S9, it indicates that the mode M = 0 while in the operation area A. This indicates a transitional state in which the mode is switched from the fuel stop mode to the special operation mode, and the flow shifts to step S21 to control the transient fuel return mode (details are shown in FIG. 11).
[0117]
If YES in step S3, that is, if it is determined that the vehicle is in the operating region B, and if NO in step S11, that is, if it is determined that the vehicle is in the operating region A but not in the warmed-up state, the process proceeds to step S31. The control of the operation mode is performed, and in step S33, the mode M is set to 2 (indicating that the current mode is the normal operation mode).
[0118]
If NO in step S7, that is, if it is determined that neither the operating region A nor the operating region B, it indicates that the vehicle is in the operating region C, and the flow shifts to the branch flow (1) (shown in FIG. 10).
[0119]
FIG. 10 is a flowchart showing the branch flow (1) of FIG. When the process proceeds to step S35, the operation state is in the operation region C. Here, it is determined whether or not the mode M = 0, and if YES, it is indicated that at least one or more of this step S35 has passed since the shift to the operating state C, and the next step S39 Move to If “NO” in the step S35, it is indicated that the step S35 is passed for the first time after the shift to the operating state C. In that case, the process shifts to step S37 to input the value of the mode M to the previous mode M1. The previous mode M1 is a parameter indicating an operation mode before the fuel stop mode. At this time, the mode M is a value before shifting to the operation state C, and is 1 (special operation mode) or 2 (normal operation mode). By inputting these values to the previous mode M1, the mode before switching to the fuel stop mode is stored. Then, control goes to a step S39.
[0120]
In step S39, the fuel supply is stopped, and in the next step S41, the mode M = 0 is input. In the next step S43, setting and updating of the fuel return rotational speed N1 are performed. The fuel return rotation speed N1 is a value of about 1,000 rpm in an AT vehicle, but is set to a higher value when the gas circulation path is in the two-cylinder connection state than in the case where each cylinder is in the independent state. In addition, depending on whether the previous mode was the special operation mode or the normal operation mode before the fuel stop mode, a higher value may be set in the special operation mode than in the normal operation mode. In addition, correction such as setting the fuel return rotation speed N1 higher when the engine coolant temperature is low is performed.
[0121]
In the next step S45, it is determined whether or not the previous mode M1 = 1, and if YES (special operation mode), the process shifts to step S47 to determine whether or not the engine speed N is N <N1 + 200 rpm. Is determined. If YES, it indicates that the engine speed N has decreased to around the fuel return speed N1. Then, the process shifts to step S49 to determine whether or not the in-cylinder temperature T of the subsequent cylinder is equal to or higher than a predetermined value T2. If YES, the process returns to step S55 to set the gas circulation path to the two-cylinder connection state in advance in order to return the fuel under the same control as the pattern 1 in FIG. 4B. Then, in step S57, the gas flow path mode M2 = 1 (indicating a two-cylinder connection state) is input, and the routine returns.
[0122]
Backward, if it is determined NO in step S47, that is, if N ≧ N1 + 200 rpm, it indicates that the engine speed N has not yet decreased to near the fuel return speed N1, so the flow proceeds to step S55 to perform gas circulation. The path is set to a two-cylinder connection state.
[0123]
Further back, when it is determined in step S45 that it is NO, that is, when the previous mode M1 = 2 (normal operation mode), and when it is NO in step S49, that is, when it is NO in the previous mode M1 = 1 (special operation mode), the engine speed is increased. When it is determined that N has dropped to near the fuel return rotational speed N1 and that the in-cylinder temperature T of the subsequent cylinders 2B and 2C is lower than the predetermined value T2, it is the same as the pattern 2 in FIG. In order to return the fuel by the control of (1), the process proceeds to step S51, and the gas circulation path is set in advance to each cylinder independently. Then, in step S53, the gas flow path mode M2 = 2 (indicating each cylinder independent state) is input, and the routine returns.
[0124]
FIG. 11 is a subroutine showing details of step S21 (control of the fuel return transient mode) in FIG. When entering the fuel return transient mode, in step S101, the number of cycles S from the time of fuel return is counted. At the first time, S = 0, and thereafter the cycle number S is incremented every 720 ° CA (corresponding to one cycle).
[0125]
In the next step S103, it is determined whether or not the cycle number S is smaller than a predetermined value S1. If YES, it indicates that this is the first stage of the fuel return transient mode, and the process proceeds to steps S131 and S132. In step S131 and step S132, the previous mode M1 and the gas flow path mode M2 are determined, and only when the previous mode M1 = 1 and the gas flow path mode M2 = 1, the process proceeds to step S133 to change the gas flow path to the two-cylinder mode. Combustion is performed at the stoichiometric air-fuel ratio (excess air ratio λ = 1) in the preceding cylinders 2A and 2D while being in the connected state. Thereafter, the process returns with the mode M = 0. In step S131 and step S132, if at least one of the previous mode M1 and the gas flow path mode M2 is 2, the process proceeds to step S135, where control equivalent to that in the normal operation mode is performed, that is, the gas flow path is set to an independent state for each cylinder. At the same time, combustion at the stoichiometric air-fuel ratio (excess air ratio λ = 1) is performed in each of the cylinders 2A to 2D. Thereafter, the process returns with the mode M = 0.
[0126]
If NO in step S103, that is, if it is determined that the first stage of the transient fuel return mode has been completed, the process proceeds to step S105 to determine whether the cycle number S is smaller than a predetermined value S2 (S2> S1). A determination is made. The predetermined values S1 and S2 are set to be longer as the period (the number of cycles) of the fuel stop mode is longer or as the engine temperature is lower, and is a period of about several to several tens of cycles. If “YES” is determined in the step S105, it indicates that it is the second stage of the fuel return transient mode, and the process shifts to the step S141. In step S141, the previous mode M1 is determined. If the previous mode M1 = 1 (special operation mode), the process proceeds to step S143, where control equivalent to the second special operation mode, that is, the gas flow path is set to the two-cylinder connection state. On the other hand, the leading cylinders 2A and 2D perform combustion by forced ignition at a lean air-fuel ratio, and the succeeding cylinders 2B and 2C supply fuel to burned gas introduced from the leading cylinders 2A and 2D to supply a substantial stoichiometric air-fuel ratio. (Excess air ratio λ = 1), and combustion by forced ignition is performed. Thereafter, the process returns with the mode M = 0. If it is determined in step S141 that the previous mode M1 = 2 (normal operation mode), the process proceeds to step S145, and it is determined whether the in-cylinder temperature T of the subsequent cylinders 2B and 2C is equal to or higher than a predetermined value T1. If the determination is YES, the process proceeds to step S143. If the determination is NO, the process proceeds to step S147 to perform the same control as in the normal operation mode as in step S135, and thereafter, the process returns with the mode M = 0.
[0127]
If NO in step S105, that is, if it is determined that the second stage of the fuel return transient mode has been completed, the process proceeds to step S107, and the cycle number S is reset. Then, the process shifts to step S109 to determine whether or not the engine is in a warm state based on the engine water temperature. If “YES” in the step S109, the process shifts to a step S111 to determine whether or not the in-cylinder temperature T of the subsequent cylinder is equal to or higher than a predetermined value T1. If YES, since the in-cylinder temperatures of the subsequent cylinders 2B and 2C have reached a high temperature at which compression self-ignition can be performed stably, the flow shifts to step S113 to perform control equivalent to that in the first special operation mode, that is, gas flow. While the path is connected to the two cylinders, the leading cylinders 2A and 2D perform combustion by forced ignition at a lean air-fuel ratio, and the trailing cylinders 2B and 2C supply fuel to burned gas introduced from the leading cylinders 2A and 2D. To make a substantial stoichiometric air-fuel ratio (excess air ratio λ = 1) to perform combustion by compression self-ignition. Thereafter, the flow shifts to step S119, the mode M = 1 is input, and the flow returns. By inputting the mode M = 1, the fuel return transient mode ends, and in the next routine, the determination in step S9 of FIG. 9 is NO, and the process proceeds to step S11.
[0128]
Backward, when NO is determined in step S111, the in-cylinder temperatures of the subsequent cylinders 2B and 2C have not reached a high temperature at which compression self-ignition can be performed stably, so the process proceeds to step S117 and is similar to step S143. Then, the same control as in the second special operation mode is performed, and the routine goes to Step S119.
[0129]
If NO in step S109, that is, if it is determined that the vehicle is in the non-warmed state, the process proceeds to step S115, performs the same control as in the normal operation mode similar to step S135, and proceeds to step S119.
[0130]
Next, a modified example of the present embodiment will be described with reference to FIGS. This modification is a control of a portion related to the first stage and the second stage of the pattern 1 in FIG. The fuel return transient mode in Pattern 1 of the modified example is as follows. In the first stage, the same control as in the second special operation mode is performed, that is, while the gas circulation path is connected to the two cylinders, the leading cylinders 2A and 2D perform combustion by forced ignition at a lean air-fuel ratio, and the subsequent cylinders 2B and 2B In 2C, fuel is supplied to the burned gas introduced from the preceding cylinders 2A and 2D to obtain a substantial stoichiometric air-fuel ratio (excess air ratio λ = 1), and combustion is performed by forced ignition (see step S203 in FIG. 12). ). However, in the case of unwarmed air, the same control as in the normal operation mode is performed to promote warm air (see steps S201 and S135 in FIG. 12).
[0131]
In the second stage of the transient fuel return mode in Pattern 1 of the modification, Step S205 in FIG. 12 is applied instead of Step S143 in FIG. That is, based on the second special operation mode, the fuel of the following cylinders 2B, 2C is injected into the preceding cylinders 2A, 2D in the latter half of the expansion stroke of the preceding cylinders 2A, 2D. In this way, the fuel injected in the preceding cylinders 2A and 2D is mixed with the high-temperature burned gas discharged from the preceding cylinders 2A and 2D and guided to the succeeding cylinders 2B and 2C, so that activation is promoted. . Since the injection timing corresponds to the latter half of the exhaust stroke of the previous cycle prior to the intake stroke of the subsequent cylinders 2B and 2C, sufficient time for fuel activation is secured before the ignition timing in the subsequent cylinders 2B and 2C. Is done.
[0132]
Further, the fuel of the following cylinders 2B, 2C is divided into two or more, at least one fuel injection is performed in the preceding cylinders 2A, 2D, and the fuel injection timing is set in the latter half of the expansion stroke of the preceding cylinders 2A, 2D. The first fuel injection may be performed in the subsequent cylinders 2B and 2C. In this way, two types of fuel states can be formed around the ignition plug 7 at the time of ignition in the subsequent cylinders 2B and 2C. One is an air-fuel mixture which is injected in the preceding cylinders 2A, 2D, is uniformly mixed and activated, and the other is injected in the following cylinders 2B, 2C and is unevenly distributed around the ignition plug 7. Fuel. The ignitability in the subsequent cylinders 2B and 2C can be further enhanced by the relatively high concentration fuel unevenly distributed around the spark plug 7, and the combustion can be stabilized by the uniformly activated air-fuel mixture. .
[0133]
The embodiment of the present invention is not limited to the above-described embodiment or its modified example, and may be appropriately modified within the scope of the claims. For example, without providing a cooling mechanism by the water jacket 26, when the in-cylinder temperature of the subsequent cylinders 2B and 2C has risen excessively during the second special operation mode, the mode may be switched to the normal operation mode.
[0134]
【The invention's effect】
As described above, the control apparatus for a spark ignition engine according to the present invention provides a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the engine, between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, burned gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, passes through the inter-cylinder gas passage to the subsequent cylinder, which is the cylinder on the intake stroke side. The gas circulation path is configured in a two-cylinder connection state in which the exhaust gas introduced and discharged from the subsequent cylinder is guided to the exhaust passage, and the special operation mode is set at least in a predetermined low-load low-speed range according to the operation state. Is selected, and a fuel stop mode is selected in a predetermined deceleration range. In the special operation mode, the gas circulation path is set to the two-cylinder connection state. In addition, combustion is performed for the preceding cylinder at a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and for the succeeding cylinder, the burned fuel having the lean air-fuel ratio introduced from the preceding cylinder is burned. The fuel is supplied to the gas to perform combustion in a state of a predetermined air-fuel ratio, and in part or all of the special operation mode, the subsequent cylinder performs combustion by compression self-ignition, and In the stop mode, the fuel supply to each cylinder is stopped, and when switching from the fuel stop mode to the special operation mode in which the subsequent cylinder performs combustion by compression self-ignition, the switching is smoothly performed. A fuel return transient mode for transiently controlling the combustion state of at least each cylinder is configured to pass through for a predetermined period, and an initial state including at least a fuel return time of the fuel return transient mode is configured. Here, at least the preceding cylinder is characterized by performing combustion by forced ignition in a state of substantially stoichiometric air-fuel ratio. By using the technique of stopping the fuel supply in the deceleration region together, it is possible to improve the fuel efficiency and to improve the stability of the combustion after returning the fuel.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of an entire engine including a device according to an embodiment of the present invention.
FIG. 2 is a schematic sectional view of an engine body and the like.
FIG. 3 is a block diagram of a control system.
FIG. 4A is an explanatory diagram showing an operation region, and FIG. 4B is a table showing a combination pattern of modes before and after a fuel stop mode.
FIG. 5 is a main block diagram showing a procedure for estimating an in-cylinder temperature state before combustion of a subsequent cylinder.
FIG. 6 is a diagram showing an exhaust stroke, an intake stroke, a fuel injection timing, an ignition timing, and the like of each cylinder.
FIG. 7 is an explanatory diagram showing a substantial flow path of fresh air and gas during low load and low rotation.
FIG. 8 is an explanatory diagram showing a substantial fresh air and gas flow path when the engine is in a high-load, high-low rotation side operation region.
FIG. 9 is a flowchart of control when switching from a fuel stop mode to a subsequent mode.
FIG. 10 is a branch flowchart from FIG. 9;
FIG. 11 is a flowchart of a subroutine showing control in a transient fuel return mode.
FIG. 12 is a flowchart of a subroutine showing a modified example of the control in the fuel return transient mode.
[Explanation of symbols]
1 Engine body
2A, 2D cylinder (preceding cylinder)
2B, 2C cylinder (following cylinder)
9 Fuel injection valve
11 Intake port
11a, 11b Intake port
12, 12a, 12b Exhaust port
15 Intake passage
20 Exhaust passage
22 Gas passage between cylinders
25 Linear O ₂ Sensor
31, 31a, 31b Intake valve
32, 32a, 32b Exhaust valve
35 Valve stop mechanism
40 ECU
41 Operating state determination means
42 Valve stop mechanism control means
43 Intake air amount control means
44 Combustion control means
53 In-cylinder temperature state estimation means

Claims (11)

In a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, burned gas discharged from the preceding cylinder which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, A gas circulation path is configured in a two-cylinder connection state in which exhaust gas discharged from the subsequent cylinder is guided to an exhaust passage,
According to the operating state, at least in a predetermined low-load low-speed range, a special operation mode is selected, and in a predetermined deceleration range, a fuel stop mode is selected,
In the special operation mode, the gas circulation path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state of a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and In response to this, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion in a state of a predetermined air-fuel ratio,
In some or all of the special operation mode, the following cylinders perform combustion by compression self-ignition,
In the fuel stop mode, fuel supply to each cylinder is stopped,
When switching from the fuel stop mode to a special operation mode in which combustion by compression self-ignition is performed in the subsequent cylinder, a fuel return transient mode in which at least the combustion state of each cylinder is transiently controlled so as to facilitate the switching. Through a predetermined period,
A control device for a spark ignition engine, characterized in that at least in the initial stage of the fuel return transient mode including at the time of fuel return, at least the preceding cylinder is caused to perform combustion by forced ignition with a substantially stoichiometric air-fuel ratio. The gas flow path is configured to be switchable to each cylinder independent state for introducing fresh air to each cylinder,
According to the operating state, in a predetermined high load or high rotation region, the gas flow path is set to the cylinder independent state, and each cylinder is independently burned at a substantially stoichiometric air-fuel ratio or an air-fuel ratio smaller than that. Is configured to select the normal operation mode for performing
When the normal operation mode is performed immediately before the fuel stop mode, the gas circulation path is set to the cylinder independent state at an initial stage including the fuel return in the fuel return transient mode, and substantially theoretically idle in each cylinder. Combustion by forced ignition is performed with the fuel ratio set, and in the latter period, the gas circulation path is connected to the two cylinders, and combustion by forced ignition is performed on the preceding cylinder with the lean air-fuel ratio. In addition, for the subsequent cylinder, fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinder, and combustion is performed by forced ignition in a state of a substantially stoichiometric air-fuel ratio. The control device for a spark ignition engine according to claim 1. If the special operation mode is immediately before the fuel stop mode, the gas circulation path is set to the two-cylinder connection state during the fuel return transient mode, and the initial state including at least the fuel return of the fuel return transient mode is performed. 3. The control apparatus for a spark ignition engine according to claim 1, wherein the combustion by forced ignition is performed in the preceding cylinder at a substantially stoichiometric air-fuel ratio. When the special operation mode is performed immediately before the fuel stop mode, the air-fuel ratio is set so that the excess air ratio is greater than 1 and less than or equal to 2 with respect to the preceding cylinder in the latter half of the fuel return transient mode. In this state, homogeneous combustion is performed by forced ignition, and fuel is supplied to the succeeding cylinders to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to forcibly maintain the stoichiometric air-fuel ratio. Let the combustion by ignition,
4. The spark according to claim 3, further comprising: switching to a special operation mode in which combustion by compression self-ignition is performed in the succeeding cylinder, and setting a larger air-fuel ratio of the preceding cylinder to perform stratified combustion by forced ignition. Control device for ignition engine. In a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, burned gas discharged from the preceding cylinder which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, A gas circulation path is configured in a two-cylinder connection state in which exhaust gas discharged from the subsequent cylinder is guided to an exhaust passage,
According to the operating state, at least in a predetermined low-load low-speed range, a special operation mode is selected, and in a predetermined deceleration range, a fuel stop mode is selected,
In the special operation mode, the gas circulation path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state of a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and In response to this, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion in a state of a predetermined air-fuel ratio,
In some or all of the special operation mode, the following cylinders perform combustion by compression self-ignition,
In the fuel stop mode, fuel supply to each cylinder is stopped,
When switching from the fuel stop mode to a special operation mode in which combustion by compression self-ignition is performed in the subsequent cylinder, a fuel return transient mode in which at least the combustion state of each cylinder is transiently controlled so as to facilitate the switching. Through a predetermined period,
In the fuel return transient mode, the gas circulation path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion by forced ignition in a state of a lean air-fuel ratio. Fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion by forced ignition in a state of a substantially stoichiometric air-fuel ratio, and after returning to fuel, combustion in the following cylinder is performed. A control device for a spark ignition engine, wherein an advance timing of a fuel injection timing to be performed is corrected so that fuel activation is promoted. The advance angle correction is performed by performing fuel injection for performing combustion in the subsequent cylinder in the preceding cylinder and setting the fuel injection timing during an expansion stroke or an exhaust stroke of the preceding cylinder. The control device for a spark ignition type engine according to claim 5, characterized in that: The lead angle correction is
Fuel for performing combustion in the subsequent cylinder is divided into at least two fuels and injected.
Performing at least one fuel injection in the preceding cylinder, and setting the fuel injection timing during an expansion stroke or an exhaust stroke of the preceding cylinder;
The control apparatus for a spark ignition engine according to claim 5, wherein the control is performed by performing at least one fuel injection in the subsequent cylinder. The period of the fuel return transient mode is set to be longer as the period of the fuel stop mode is longer or the engine temperature is lower. Control device for spark ignition engine. During the fuel stop mode, when the engine speed becomes equal to or lower than a predetermined fuel return speed, the fuel supply is restarted to exit the fuel stop mode,
The fuel return rotation speed is set to be higher in the special operation mode than in the normal operation mode immediately before the fuel stop mode. Item 9. The control device for a spark ignition engine according to any one of Items 1 to 8. In a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, burned gas discharged from the preceding cylinder which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, The gas flow path is configured to be switched between a two-cylinder connection state in which exhaust gas discharged from the subsequent cylinder is guided to an exhaust passage and a cylinder independent state in which fresh air is introduced into each cylinder,
According to the operation state, a special operation mode is selected in a predetermined low-load low-speed range, a normal operation mode is selected in a predetermined high-load or high-speed range, and a fuel stop mode is selected in a predetermined deceleration range. Is composed of
In the special operation mode, the gas circulation path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state of a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and In response to this, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion in a state of a predetermined air-fuel ratio,
In the normal operation mode, the gas flow path is set to the cylinder independent state, and combustion is performed in each cylinder independently at a stoichiometric air-fuel ratio or an air-fuel ratio smaller than the stoichiometric air-fuel ratio.
In the fuel stop mode, the fuel supply to each cylinder is stopped, and during the fuel stop mode, when the engine speed becomes equal to or lower than the predetermined fuel return speed, the fuel supply is restarted and the fuel stop mode is set. Configured to escape,
The fuel return rotation speed is set to be higher when the gas flow path at the time of fuel return is in the two-cylinder connection state than in the individual cylinder independent state. The control device of the spark ignition type engine. In a multi-cylinder spark ignition engine in which each cylinder performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, burned gas discharged from the preceding cylinder which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, The gas flow path is configured to be switched between a two-cylinder connection state in which exhaust gas discharged from the subsequent cylinder is guided to an exhaust passage and a cylinder independent state in which fresh air is introduced into each cylinder,
According to the operation state, a special operation mode is selected in a predetermined low-load low-speed range, a normal operation mode is selected in a predetermined high-load or high-speed range, and a fuel stop mode is selected in a predetermined deceleration range. Is composed of
In the special operation mode, the gas circulation path is set to the two-cylinder connection state, and the preceding cylinder is caused to perform combustion in a state of a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and In response to this, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to perform combustion in a state of a predetermined air-fuel ratio,
In the normal operation mode, the gas flow path is set to the cylinder independent state, and combustion is performed in each cylinder independently at a stoichiometric air-fuel ratio or an air-fuel ratio smaller than the stoichiometric air-fuel ratio.
In the fuel stop mode, fuel supply to each cylinder is stopped.
In-cylinder temperature prediction means of the subsequent cylinder,
In the case where the fuel supply mode is shifted from the special operation mode to the fuel stop mode, when the predicted value by the in-cylinder temperature prediction means of the subsequent cylinder is lower than a predetermined temperature during the fuel stop mode, the gas flow path is set to the individual cylinder independent state. A control device for a spark-ignition engine, characterized by switching to (1)

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