JP2004076615A

JP2004076615A - Control device of spark ignition engine

Info

Publication number: JP2004076615A
Application number: JP2002235204A
Authority: JP
Inventors: Yoshiyuki Shinya; 進矢　義之; Mitsuo Hitomi; 人見　光夫; Koji Sumita; 住田　孝司; Yoshinori Hayashi; 林　好徳
Original assignee: Mazda Motor Corp
Current assignee: Mazda Motor Corp
Priority date: 2002-08-12
Filing date: 2002-08-12
Publication date: 2004-03-11
Anticipated expiration: 2022-08-12
Also published as: JP3826858B2

Abstract

<P>PROBLEM TO BE SOLVED: To relieve a torque shock caused by a change in an operation state while obtaining the fuel consumption improving effect and the exhaust emission control effect by controlling combustion according to the operation state of an engine. <P>SOLUTION: This engine is constituted switchable to an ordinary operation mode for burning gas by making respective cylinders 2A to 2D respectively independent and a special operation mode for introducing and burning burnt gas exhausted from the preceding cylinders in an exhaust stroke to and in the succeeding cylinders in an intake stroke as it is, and is switched to the special operation mode when becoming lower load-lower rotation than a prescribed threshold value when switching to the special operation mode from the ordinary operation mode, and is constituted to set the threshold value to the low load side at gentle deceleration time when deceleration of the engine is not more than a prescribed value. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、火花点火式エンジンの制御装置に関し、より詳しくは、多気筒エンジンにおいて燃費改善及びエミッション向上のために各気筒の燃焼状態を制御する装置に関するものである。
【０００２】
【従来の技術】
従来から、火花点火式エンジンにおいて、各気筒内の混合気の空燃比を理論空燃比よりも大きいリーン空燃比とした状態で燃焼を行わせることにより燃費改善を図る技術が知られており、例えば特開平１０−２７４０８５号公報に示されるように、燃焼室内に直接燃料を噴射する燃料噴射弁を備え、低回転低負荷域等では前記燃料噴射弁から圧縮行程で燃料を噴射することにより成層燃焼を行わせ、これによって超リーン燃焼を実現するようにしたものが知られている。
【０００３】
このようなエンジンにおいては、排気ガス浄化用の触媒として通常の三元触媒（ＨＣ，ＣＯ及びＮＯｘに対して理論空燃比付近で浄化性能の高い触媒）だけではリーン運転時にＮＯｘに対して充分な浄化性能が得られないため、前記公報にも示されるように、酸素過剰雰囲気でＮＯｘを吸着して酸素濃度低下雰囲気でＮＯｘの離脱、還元を行うリーンＮＯｘ触媒を設けている。そして、このようなリーンＮＯｘ触媒を用いる場合、リーン運転中にリーンＮＯｘ触媒のＮＯｘ吸着量が増大したときは、例えば前記公報に示されるように主燃焼以外に膨張行程中に追加燃料を噴射することで排気ガスの空燃比をリッチ化するとともにＣＯを生成し、これによってＮＯｘの離脱、還元を促進するようにしている。
【０００４】
【発明が解決しようとする課題】
前記のような従来のリーン運転を行うエンジンでは、リーン運転中のＮＯｘ浄化性能の確保のために前記リーンＮＯｘ触媒を必要とする。そして、高負荷域等の理論空燃比で運転される領域での排気浄化のために三元触媒も必要であって、この三元触媒に加えて前記リーンＮＯｘ触媒が設けられ、かつ、このリーンＮＯｘ触媒はＮＯｘ吸着量をある程度確保するために比較的大容量が必要となり、また、三元触媒と比べて高価であるため、コスト的に不利である。
【０００５】
しかも、前記リーンＮＯｘ触媒の浄化性能を維持するためには、前述のようにＮＯｘ吸着量が増大するような所定の期間毎に、ＮＯｘの離脱、還元のため追加燃料の供給等による一時的な空燃比のリッチ化を行う必要があり、これにより、リーン燃焼による燃費改善効果が目減りしてしまうことになる。
【０００６】
そこで、本願出願人は、かかる課題に鑑み、吸気、圧縮、膨張、排気の各行程からなるサイクルを行う多気筒エンジンにおいて、低負荷低回転域では、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をそのまま吸気行程側の気筒である後続気筒に導入し、この後続気筒から排出されるガスを三元触媒を備えた排気通路に導くようにするとともに、この２気筒接続状態にあるときに、前記先行気筒において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、後続気筒では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理論空燃比とした状態で燃焼を行わせるように燃焼状態等を制御（特殊運転モードという）する一方、高負荷高回転域では、通常通り、各気筒毎を理論空燃比で燃焼を行わせるように燃焼状態等を制御（通常運転モードという）することを考えた（特願２００２−０２４５４８号）。
【０００７】
これによると、低負荷低回転域において特殊運転モードとされることにより、先行気筒ではリーン空燃比での燃焼が行われ、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ることにより大幅な燃費改善効果が得られ、また、前記後続気筒では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が供給されて理論空燃比とされた状態で燃焼が行われて、ポンピングロス低減による燃費効果が得られる。しかも、後続気筒から排出される理論空燃比の既燃ガスのみが三元触媒を備えた排気通路に導かれるため、三元触媒だけで充分に排気浄化性能が確保され、リーンＮＯｘ触媒も不要となる。
【０００８】
ところで、前記のように各気筒の燃焼状態等を制御する場合には、高負荷回転域から低負荷回転域への移行時（通常運転モードから特殊運転モードへの切換え時）に吸気量の応答遅れが生じることが考えられ、そのため単純に特殊運転モードに切換えるだけでは、この応答遅れに起因してトルクショック（一時的にトルクが低下する状態）が生じ搭乗者に違和感を与えることが考えられる。すなわち、通常運転モードから特殊運転モードへ移行する際、後続気筒分の吸気量を含む大量の吸気を先行気筒に導入すべくスロットル弁の開度（スロットル開度）が大きくなるように制御される。しかし、その開度調整に応答遅れが生じて一時的に目標吸気量に満たない量の吸気が行われることとが考えられ、この吸気量に基づいて理論空燃比とした状態で燃焼が行われることにより、一時的にトルクが低下する状態が生じることが考えられる。
【０００９】
本発明は以上のような課題を考慮してなされたものであり、リーン燃焼による燃費改善効果をもたせつつ、リーンＮＯｘ触媒を必要とせず三元触媒を用いるだけで、排気浄化性能を向上することすることができ、しかもトルクショックにより搭乗者に違和感を与えることを防止することができる火花点火式エンジンの制御装置を提供するものである。
【００１０】
【課題を解決するための手段】
請求項１に係る発明は、各気筒にそれぞれ新気を導入する各気筒独立状態と、排気行程と吸気行程が重なる一対の気筒間において先行気筒の排気ガスを気筒間ガス通路を介して後続気筒に導入する２気筒接続状態とに吸気および排気の流通経路が切換え可能に構成され、かつ、この流通経路を前記各気筒独立状態として各気筒においてそれぞれ独立して燃焼を行わせる通常運転モードと、前記２気筒接続状態として先行気筒から排出される既燃ガスをそのまま吸気行程にある後続気筒に導入して燃焼を行わせる特殊運転モードとに運転モードを切換え可能に構成される多気筒の火花点火式エンジンの制御装置であって、エンジンの運転状態に応じて運転モードを前記通常運転モード又は特殊運転モードに切換えるモード切換手段と、前記特殊運転モードにあるときに、先行気筒では理論空燃比よりも所定量だけ大きいリーン空燃比とした状態で燃焼を行わせ、かつ後続気筒では、先行気筒から導出されたリーン空燃比の既燃ガスに燃料を供給して理論空燃比とした状態で燃焼を行わせる一方、前記通常運転モードにあるときには、各気筒での空燃比を理論空燃比とした状態で燃焼を行わせるように各気筒での空燃比を制御する空燃比制御手段とを備え、前記モード切換手段は、前記通常運転モード中のエンジンの運転状態が、所定の閾値よりも低負荷低回転となったときに前記特殊運転モードに切換えるものであるとともに、エンジンの減速度が所定値以下の緩減速時には前記閾値を更に低負荷側に設定することを特徴とする。
【００１１】
この発明によれば、エンジンの低負荷低回転域において、２気筒接続状態で特殊運転モードの燃焼制御が実行されることにより、前記先行気筒ではリーン空燃比での燃焼が行われて、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ることにより大幅な燃費改善効果が得られ、かつ前記後続気筒では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が供給されて理論空燃比とされた状態で燃焼が行われることにより、少なくともポンピングロス低減による燃費効果が得られる。また、後続気筒から排出される理論空燃比の既燃ガスのみが排気通路に導かれるため、三元触媒だけで充分に排気浄化性能が確保される。一方、高負荷・高回転の運転領域では、通常運転モードに設定されることにより出力性能が確保される。
【００１２】
また、特殊運転モードと通常運転モードとを切換えるために、所定の閾値が設けられており、たとえば通常運転モード中のエンジンの運転状態が、所定の閾値よりも低負荷低回転となったときにモード切換手段が通常運転モードから特殊運転モードに切換えられる。この際、前述のトルクショックが発生するが、このトルクショックは、緩減速（エンジンの減速度が小さい）時かつ比較的高負荷時に体感し易く、急減速（エンジンの減速度が大きい）時や、緩減速時であっても比較的低負荷時には体感し難いという特徴がある。
【００１３】
本発明によれば、緩減速時には通常運転モードから特殊運転モードに切換える閾値を更に低負荷側に設定するので、このモードの切換えは急減速時、または緩減速時であっても比較的低負荷時、すなわちトルクショックが体感し難い運転状態でなされる。このように、燃料供給を増加させてトルクを上昇させ、トルクショックを緩和するといった対策をとらなくても、事実上トルクショックを体感し難いようにできるので、燃料消費の増加を抑制しつつ、トルクショックにより搭乗者に違和感を与えることを効果的に防止することができる。
【００１４】
請求項２に係る発明は、請求項１記載の火花点火式エンジンの制御装置において、前記空燃比制御手段は、少なくともエンジンの運転状態が所定の減速域にあるとき、燃料の供給を停止する燃料供給停止モードを有し、前記燃料供給停止モードで、エンジンの運転状態が前記所定の閾値よりも低負荷低回転であるとき、前記空燃比制御手段は燃料の供給を停止し、前記モード切換手段は前記流通経路を前記２気筒接続状態とすることを特徴とする。
【００１５】
このようにすると、燃料供給停止モードで、エンジンの運転状態が所定の閾値よりも低負荷低回転であるとき、燃料の供給が停止されてはいるが、ガスの流通経路は特殊運転モードと同じ２気筒接続状態となる。従って、この状態からエンジン負荷が増加し、燃料供給停止モードが解除された場合、流通経路を切換えることなく、燃料供給を再開するだけで速やかに特殊運転モードに切換えることができる。
【００１６】
請求項３に係る発明は、各気筒にそれぞれ新気を導入する各気筒独立状態と、排気行程と吸気行程が重なる一対の気筒間において先行気筒の排気ガスを気筒間ガス通路を介して後続気筒に導入する２気筒接続状態とに吸気および排気の流通経路が切換え可能に構成され、かつ、この流通経路を前記各気筒独立状態として各気筒においてそれぞれ独立して燃焼を行わせる通常運転モードと、前記２気筒接続状態として先行気筒から排出される既燃ガスをそのまま吸気行程にある後続気筒に導入して燃焼を行わせる特殊運転モードとに運転モードを切換え可能に構成される多気筒の火花点火式エンジンの制御装置であって、エンジンの運転状態に応じて運転モードを前記通常運転モード又は特殊運転モードに切換えるモード切換手段と、前記特殊運転モードにあるときに、先行気筒では理論空燃比よりも所定量だけ大きいリーン空燃比とした状態で燃焼を行わせ、かつ後続気筒では、先行気筒から導出されたリーン空燃比の既燃ガスに燃料を供給して理論空燃比とした状態で燃焼を行わせる一方、前記通常運転モードにあるときには、各気筒での空燃比を理論空燃比とした状態で燃焼を行わせるように各気筒での空燃比を制御する空燃比制御手段とを備え、この空燃比制御手段は、前記通常運転モードから特殊運転モードへの切換後、最初に燃焼行程を迎える先行気筒による生成トルクが、その先行気筒に対する後続気筒による生成トルクより大きくなるように、その先行気筒の空燃比を理論空燃比の２倍よりも小さくするとともに、その先行気筒に対する後続気筒の空燃比が理論空燃比となるような空燃比補正制御を行うことを特徴とする。
【００１７】
この発明によれば、請求項１の場合と同様に、低負荷低回転域において特殊運転モードの燃焼制御が実行されることにより燃費改善効果が得られ、また三元触媒だけで充分に排気浄化性能が確保される。一方、高負荷・高回転の運転領域では、通常運転モードに設定されることにより出力性能が確保される。
【００１８】
そして、通常運転モードから特殊運転モードへの移行時（切換時）には、空燃比補正制御によって、モード切換後、最初に燃焼行程を迎える先行気筒での生成トルクが後続気筒での生成トルクよりも大きくなるように空燃比の補正がなされる。これは、単に空燃比をリッチ化する場合と異なり、後続気筒からの排気が理論空燃比による燃焼に相当するようにしつつ、モード切換え直後の燃焼で発生するトルクを増大させている。即ち、発生トルクの配分を調節することにより、急激なトルク変動を抑制している。このように、全体としては燃料の消費量は増加しないので、燃料消費の増加を招くことなく、トルクショックを緩和することができる。また、後続気筒からの排気は理論空燃比のガスとなるので、排気浄化性能も確保される。
【００１９】
請求項４に係る発明は、請求項３記載の火花点火式エンジンの制御装置において、前記空燃比制御手段は、エンジンの減速度が所定値以下の緩減速時に前記空燃比補正制御を行うことを特徴とする。
【００２０】
このようにすれば、緩減速時のトルクショックを緩和することができるので、トルクショックを体感し易い緩減速時かつ比較的高負荷時に通常運転モードから特殊運転モードに切換えても、トルクショックによる違和感を搭乗者に与えることを効果的に防止することができる。
【００２１】
請求項５に係る発明は、燃焼室内に燃料を直接噴射して吸気行程と排気行程との間に１回の燃焼行程を有する通常運転モードと、吸気行程と排気行程との間に２回の燃焼行程を有する特殊運転モードとに燃焼サイクルを切換え可能に構成される火花点火式エンジンの制御装置であって、エンジンの運転状態に応じて運転モードを前記通常運転モード又は特殊運転モードに切換えるモード切換手段と、前記特殊運転モードにあるときに、先の燃焼では理論空燃比よりも所定量だけ大きいリーン空燃比とした状態で燃焼を行わせ、かつ後の燃焼では、先の燃焼によるリーン空燃比の既燃ガスに燃料を供給して理論空燃比とした状態で燃焼を行わせる一方、前記通常運転モードにあるときには、各気筒での空燃比を理論空燃比とした状態で燃焼を行わせるように各気筒での空燃比を制御する空燃比制御手段とを備え、前記モード切換手段は、前記通常運転モード中のエンジンの運転状態が、所定の閾値よりも低負荷低回転となったときに前記特殊運転モードに切換えるものであるとともに、エンジンの減速度が所定値以下の緩減速時には前記閾値を更に低負荷側に設定することを特徴とする。
【００２２】
この発明によれば、例えばエンジンの低負荷低回転域において、前記特殊運転モードの燃焼制御が実行されることにより、すなわち２回の燃焼に必要な空気が供給されてからリーン空燃比での先の燃焼と理論空燃比での後の燃焼とが行われることにより、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、その結果、大幅な燃費改善効果が得られる。また、既燃ガスの酸素濃度が略理論空燃比の燃焼状態に対応した値となるように各気筒での燃焼行程における空燃比が制御されるため、三元触媒だけで充分に排気浄化性能が確保される。一方、高負荷・高回転の運転領域では、通常運転モードに設定されることにより出力性能が確保される。
【００２３】
そして、請求項１の場合と同様に、特殊運転モードと通常運転モードとを切換えるために、所定の閾値が設けられており、緩減速時には通常運転モードから特殊運転モードに切換える閾値を急減速よりも低負荷側に設定するので、このモードの切換えはトルクショックが体感し難い運転状態でなされる。このように、燃料消費の増加を抑制しつつ、トルクショックにより搭乗者に違和感を与えることを効果的に防止することができる。
【００２４】
請求項６に係る発明は、請求項５記載の火花点火式エンジンの制御装置において、前記空燃比制御手段は、少なくともエンジンの運転状態が所定の減速域にあるとき、燃料の供給を停止する燃料供給停止モードを有し、前記燃料供給停止モードで、エンジンの運転状態が前期所定の閾値よりも低負荷低回転であるとき、前記空燃比制御手段は燃料の供給を停止し、前記モード切換手段は前記特殊運転モードと同等の給排気行程をなすことを特徴とする。
【００２５】
このようにすると、燃料供給停止モードで、エンジンの運転状態が所定の閾値よりも低負荷低回転であるとき、燃料の供給が停止されてはいるが、給排気行程は特殊運転モードと同じ状態となる。従って、この状態からエンジン負荷が増加し、燃料供給停止モードが解除された場合、給排気行程の切換えを行うことなく、燃料供給を再開するだけで速やかに特殊運転モードに切換えることができる。
【００２６】
【発明の実施の形態】
以下、図面に基づいて本発明の第１の実施形態について説明する。
【００２７】
図１は本発明の一実施形態によるエンジンの概略構成を示し、図２はエンジン本体の一つの気筒とそれに対して設けられた吸・排気弁等の構造を概略的に示している。これらの図において、エンジン本体１は複数の気筒を有し、図示の実施形態では４つの気筒２Ａ〜２Ｄを有している。各気筒２Ａ〜２Ｄにはピストン３が嵌挿され、ピストン３の上方に燃焼室４が形成されている。
【００２８】
各気筒気筒２Ａ〜２Ｄの燃焼室４の頂部には点火プラグ７が装備され、そのプラグ先端が燃焼室４内に臨んでいる。この点火プラグ７には、電子制御による点火時期のコントロールが可能な点火回路８が接続されている。
【００２９】
燃焼室４の側方部には、燃焼室４内に燃料を直接噴射する燃料噴射弁９が設けられている。この燃料噴射弁９は、図略のニードル弁及びソレノイドを内蔵し、後述のパルス信号が入力されることにより、そのパルス入力時期にパルス幅に対応する時間だけ駆動されて開弁し、その開弁時間に応じた量の燃料を噴射するように構成されている。なお、この燃料噴射弁９には、図外の燃料ポンプにより燃料供給通路等を介して燃料が供給され、かつ、圧縮行程での燃焼室内の圧力よりも高い燃料圧力を与え得るように燃料供給系統が構成されている。
【００３０】
また、各気筒２Ａ〜２Ｄの燃焼室４に対して吸気ポート１１、１１ａ，１１ｂ及び排気ポート１２、１２ａ，１２ｂが開口し、これらのポートに吸気通路１５、排気通路２０等が接続されるとともに、各ポートが吸気弁３１、３１ａ，３１ｂ及び排気弁３２、３２ａ，３２ｂにより開閉されるようになっている。
【００３１】
そして、各気筒２Ａ〜２Ｄ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燃焼サイクルを行うようになっており、４気筒エンジンの場合、気筒列方向一端側から１番気筒２Ａ、２番気筒２Ｂ、３番気筒２Ｃ、４番気筒２Ｄと呼ぶと、図５に示すように前記サイクルが１番気筒２Ａ、３番気筒２Ｃ、４番気筒２Ｄ、２番気筒２Ｂの順にクランク角で１８０°ずつの位相差をもって燃焼サイクルが行われるようになっている。なお、図５において、ＥＸは排気行程、ＩＮは吸気行程、Ｆは燃料噴射、Ｓは点火をそれぞれ表している。
【００３２】
排気行程と吸気行程が重なる一対の気筒間には、排気行程と吸気行程が重なるときの排気行程側の気筒（当明細書ではこれを先行気筒と呼ぶ）から吸気行程側の気筒（当明細書ではこれを後続気筒と呼ぶ）へ既燃ガスをそのまま導くことができるように、気筒間ガス通路２２が設けられている。当実施形態では、図５に示すように１番気筒２Ａの排気行程（ＥＸ）と２番気筒２Ｂの吸気行程（ＩＮ）とが重なり、また４番気筒２Ｄの排気行程（ＥＸ）と３番気筒２Ｃの吸気行程（ＩＮ）が重なるので、１番気筒２Ａと２番気筒２Ｂ、及び４番気筒２Ｄと３番気筒２Ｃがそれぞれ一対をなし、１番気筒２Ａ及び４番気筒２Ｄが先行気筒、２番気筒２Ｂ及び３番気筒２Ｃが後続気筒となる。
【００３３】
各気筒の吸・排気ポートとこれに接続される吸気通路、排気通路及び気筒間ガス通路は、具体的には次のように構成されている。
【００３４】
先行気筒である１番気筒２Ａ及び４番気筒２Ｄには、それぞれ、新気を導入するための吸気ポート１１と、既燃ガス（排気ガス）を排気通路に送り出すための第１排気ポート１２ａと、既燃ガスを後続気筒に導出するための第２排気ポート１２ｂとが配設されている。また、後続気筒である２番気筒２Ｂ及び３番気筒２Ｃには、それぞれ、新気を導入するための第１吸気ポート１１ａと、先行気筒からの既燃ガスを導入するための第２吸気ポート１１ｂと、既燃ガスを排気通路に送り出すための排気ポート３２とが配設されている。
【００３５】
図１に示す例では、１番，４番気筒２Ａ，２Ｄにおける吸気ポート１１および２番，３番気筒２Ｂ，２Ｃにおける第１吸気ポート１１ａが、１気筒当り２個ずつ、燃焼室の左半部側に並列的に設けられる一方、１番，４番気筒２Ａ，２Ｄにおける第１排気ポート１２ａ及び第２排気ポート１２ｂならびに２番，３番気筒２Ｂ，２Ｃにおける第２吸気ポート１１ｂ及び排気ポート１２が、燃焼室の右半部側に並列的に設けられている。
【００３６】
１番，４番気筒２Ａ，２Ｄにおける吸気ポート１１および２番，３番気筒２Ｂ，２Ｃにおける第１吸気ポート１１ａには、吸気通路１５における気筒別の分岐吸気通路１６の下流端が接続されている。各分岐吸気通路１６の下流端近傍には、共通の軸を介して互いに連動する多連スロットル弁１７が設けられており、この多連スロットル弁１７は制御信号に応じてアクチュエータ１８により駆動され、吸入空気量を調節するようになっている。なお、吸気通路１５における集合部より上流の共通吸気通路には吸気流量を検出するエアフローセンサ１９が設けられている。
【００３７】
１番，４番気筒２Ａ，２Ｄにおける第１排気ポート１２ａおよび２番，３番気筒２Ｂ，２Ｃにおける排気ポート１２には、排気通路２０における気筒別の分岐排気通路２１の上流端が接続されている。また、１番気筒２Ａと２番気筒２Ｂとの間及び３番気筒２Ｃと４番気筒２Ｄとの間には、それぞれ気筒間ガス通路２２が設けられ、先行気筒である１番，４番気筒２Ａ，２Ｄの第２排気ポート１２ｂに気筒間ガス通路２２の上流端が接続されるとともに、後続気筒である２番，３番気筒２Ｂ，２Ｃの第２吸気ポート１１ｂに気筒間ガス通路２２の下流端が接続されている。
【００３８】
排気通路２０における分岐排気通路２１の下流の集合部には理論空燃比検出用の排気ガス濃度検出手段であるＯ_２センサ２３が設けられ、さらにその下流の排気通路２０には、排気浄化用の三元触媒２４が設けられている。この三元触媒２４は、一般に知られているように、排気ガスの空燃比が理論空燃比（つまり空気過剰率λがλ＝１）付近にあるときにＨＣ，ＣＯ及びＮＯｘに対して高い浄化性能を示す触媒である。また、Ｏ_２センサ２３は、排気ガス中の酸素濃度を検出することにより空燃比を検出するもので、特に理論空燃比付近で出力が急変するλＯ_２センサにより構成されている。
【００３９】
前記気筒間ガス通路２２には、排気ガス中の酸素濃度の変化（空燃比の変化）に対して出力がリニアに変化するリニアＯ_２センサ２５（リーン空燃比検出用の排気ガス濃度検出手段）が設けられている。
【００４０】
各気筒の吸・排気ポートを開閉する吸・排気弁とこれらに対する動弁機構は、次のようになっている。すなわち、１番，４番気筒２Ａ，２Ｄにおける吸気ポート１１、第１排気ポート１２ａ及び第２排気ポート１２ｂにはそれぞれ吸気弁３１、第１排気弁３２ａ及び第２排気弁３２ｂが設けられ、また、２番，３番気筒２Ｂ，２Ｃにおける第１吸気ポート１１ａ、第２吸気ポート１１ｂ及び排気ポート１２にはそれぞれ第１吸気弁３１ａ、第２吸気弁３１ｂ及び排気弁３２が設けられている。そして、各気筒の吸気行程や排気行程が前述のような所定の位相差をもって行われるように、これら吸・排気弁がそれぞれカムシャフト３３，３４等からなる動弁機構により所定のタイミングで開閉するように駆動される。
【００４１】
さらに、これらの吸・排気弁のうちで第１排気弁３２ａ、第２排気弁３２ｂ、第１吸気弁３１ａ及び第２吸気弁３１ｂに対しては、各弁を作動状態と停止状態とに切換える弁停止機構３５が設けられている。この弁停止機構３５は、従来から知られているため詳しい図示は省略するが、例えば、カムシャフト３３，３４のカムと弁軸との間に介装されたタペットに作動油の給排が可能な油圧室が設けられ、この油圧室に作動油が供給されている状態ではカムの作動が弁に伝えられて弁が開閉作動され、油圧室から作動油が排出されたときにはカムの作動が弁に伝えられなくなることで弁が停止されるようになっている。
【００４２】
前記第１排気弁３２ａの弁停止機構３５と第１吸気弁３１ａの弁停止機構３５とに対する作動油給排用の通路３６には第１コントロール弁３７が、また第２排気弁３２ｂの弁停止機構３５と第２吸気弁３１ｂの弁停止機構３５とに対する作動油給排用の通路３８には第２コントロール弁３９がそれぞれ設けられている（図３参照）。
【００４３】
図３はエンジンの駆動、制御系統の構成を示している。この図において、マイクロコンピュータ等からなるエンジン制御用のＥＣＵ（コントロールユニット）４０には、エアフローセンサ１９、Ｏ_２センサ２３及びリニアＯ_２センサ２５からの信号が入力され、さらに運転状態を判別するためにエンジン回転数を検出する回転数センサ４５及びアクセル開度（アクセルペダル踏込み量）を検出するアクセル開度センサ４６等からの信号も入力されている。また、このＥＣＵ４０から、各燃料噴射弁９と、多連スロットル弁１７のアクチュエータ１８と、前記第１，第２のコントロール弁３７，３９とに対して制御信号が出力されている。
【００４４】
前記ＥＣＵ４０は、その機能構成として運転状態判別手段４１、弁停止機構３５弁停止機構制御手段４２、吸入空気量制御手段４３、燃料噴射制御手段４４および経路判別手段５１等を備えている。
【００４５】
運転状態判別手段４１は、前記回転数センサ４５およびアクセル開度センサ４６等からの信号によりエンジンの運転状態（エンジン回転数及びエンジン負荷）の変化を調べ、運転状態が図４に示すような低負荷低回転側の運転領域Ａ（更に低負荷の運転領域Ａ’を含む）と高負荷側ないし高回転側の運転領域Ｂのいずれの領域にあるか、を判別したり、エンジン回転数の変化が、所定の減速度以下であるかどうかの判別をしたりする。更には、エンジン負荷がアクセル全閉に相当するような低負荷であるか、またはエンジン回転数が所定の回転数を超えた運転状態である（エンジン停止の虞のある極低回転領域を除く）運転領域Ｃにあるかの判別を行う。そして、その判別結果により、エンジンの運転モードとして特殊運転モード、通常運転モードあるいは燃料供給停止モードのいずれかが選択される（各モードの詳細は後述する）。
【００４６】
具体的には、エンジンの運転状態が図４の運転領域Ａ’（回転数がｒ１以下、エンジン負荷がＴ２以下）にあり、かつ後述の運転領域Ｃにない状態（たとえば運転状態Ｄ３）では特殊運転モードが選択される。運転領域Ｂ（回転数がｒ１を超え、エンジン負荷がＴ１を超える）にあり、かつ後述の運転領域Ｃにない状態（たとえば運転状態Ｄ１）では通常運転モードが選択される。運転領域Ａ（回転数がｒ１以下、エンジン負荷がＴ１以下）であり、運転領域Ａ’ではない領域（たとえば運転状態Ｄ２）では、原則として特殊運転モードが選択されるが、運転領域Ｂ（通常運転モード）から運転領域Ａに移行してきた場合且つエンジンの減速度が所定値よりも小さい場合には通常運転モードを継続する。但しそのような場合でも、運転領域Ａ’に移行すると特殊運転モードに切換える。
【００４７】
運転領域Ｃ（エンジン回転数がｒ３以上ｒ４未満で、エンジン負荷がＴ３以下の領域およびエンジン回転数がｒ４以上の領域）は、運転領域Ａか運転領域Ｂかのいずれかの領域と重複している。いずれの場合も、エンジンの運転状態が運転領域Ｃにあるときは、燃料供給停止モード（以下燃料カットモードという）が優先的に選択される。
【００４８】
弁停止機構制御手段４２は、選択された運転モードに応じて、前記各コントロール弁３７，３９を制御することにより、各弁停止機構３５を次のように制御する。
特殊運転モード：第１排気弁３２ａ及び第１吸気弁３１ａを停止状態
第２排気弁３２ｂ及び第２吸気弁３１ｂを作動状態
通常運転モード：第１排気弁３２ａ及び第１吸気弁３１ａを作動状態
第２排気弁３２ｂ及び第２吸気弁３１ｂを停止状態
燃料カットモード：運転領域Ａでは特殊運転モードと同様
運転領域Ｂでは通常運転モードと同様
【００４９】
つまり、通常運転モードでは、各気筒を独立状態としてそれぞれ気筒毎に燃焼を行わせ、特殊運転モードでは、先行気筒（１番、４番気筒２Ａ，２Ｄ）と後続気筒（２番、３番気筒２Ｂ，２Ｃ）とを気筒間ガス通路２２を介して接続した２気筒接続状態とし、かつ先行気筒から排出される既燃ガスをそのまま吸気行程にある後続気筒に導入して燃焼を行わせるようになっている。また、燃料カットモードでは、運転領域Ａと重複する領域では特殊運転モードと同様に２気筒接続状態とし、運転領域Ｂと重複する領域では通常運転モードと同様に各気筒を独立状態とする（但し燃料カットモードでは燃料の供給を停止するので、いずれの場合も燃焼は行われない）。このように、運転状態判別手段４１及び弁停止機構制御手段４２等はモード切換手段として機能する。
【００５０】
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。特に、特殊運転モードでは、後続気筒（２番、３番気筒２Ｂ，２Ｃ）に対する分岐吸気通路１６からの吸気導入が遮断された状態で、先行気筒から導入されるガス中の過剰空気が燃焼に供せられるように、先行気筒と後続気筒との２気筒分に相当する燃料を燃焼させるのに必要な量の空気が前記先行気筒（１番、４番気筒２Ａ，２Ｄ）に供給されるようにスロットル開度を調節する。
【００５１】
前記燃料噴射制御手段４４は、各気筒２Ａ〜２Ｄに設けられた燃料噴射弁９からの燃料噴射量及び噴射タイミングをエンジンの運転状態に応じて制御するもので、特殊運転モード、通常運転モード或いは燃料カットモードのいずれが選択されているかによって料噴射の制御状態を変更する。この燃料噴射制御手段４４と前記運転状態判別手段４１とにより本発明の空燃比制御手段が構成されている。
【００５２】
すなわち、特殊運転モードが選択されている場合、先行気筒（１番、４番気筒２Ａ，２Ｄ）に対しては、空燃比を理論空燃比よりも大きいリーン空燃比、好ましくは理論空燃比の略２倍もしくはそれ以上とするように燃料噴射量を制御するとともに、圧縮行程で燃料を噴射して成層燃焼を行わせるように噴射タイミングを設定する。一方、後続気筒（２番、３番気筒２Ｂ，２Ｃ）に対しては、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理論空燃比とするように燃料噴射量を制御するとともに、既燃ガスが多い状況下で着火、燃焼が可能なように噴射タイミングが設定され、例えば着火性確保のため圧縮行程で燃料が噴射される。
【００５３】
前記燃料噴射量の制御は、エアフローセンサ１９及びＯ_２センサ２３等からの出力に基づくフィードバック制御により行われる。具体的には、先行気筒で所定のリーン空燃比、後続気筒で理論空燃比となるように、エアフローセンサ１９により検出される吸入空気量に応じてそれぞれの気筒に対する基本噴射量が演算されるとともに、気筒間ガス通路２２に設けられたリニアＯ_２センサ２５からの出力に基づいて先行気筒に対する燃料噴射量がフィードバック補正され、さらに排気通路２０に設けられたＯ_２センサ２３からの出力に基づいて後続気筒に対する燃料噴射量がフィードバック補正されるようになっている。
【００５４】
また、通常運転モードが選択されている場合には、各気筒２Ａ〜２Ｄの空燃比を理論空燃比もしくはそれ以下とするように燃料噴射量を制御し、例えば運転領域の大部分の領域において理論空燃比とし、全開負荷及びその付近の運転領域で理論空燃比よりリッチとする。そして、この場合に、各気筒２Ａ〜２Ｄに対して吸気行程で燃料を噴射することにより均一燃焼を行わせるように噴射タイミングを設定する。
【００５５】
燃料カットモードが選択されている場合には燃料を噴射せず、その供給を停止するので、燃焼は行われない。
【００５６】
前記経路判別手段５１は、エアフローセンサ１９により検出された吸気流量の変化状態と、回転数センサ４５により検出されたエンジン回転数とに応じ、エンジンのクランク軸が一定角度だけ回転する間に発生する吸気脈動の回数を検出するとともに、この検出回数に基づいて吸気および排気の流通経路が前記各気筒独立状態にあるか２気筒接続状態にあるかを判別するように構成されている。すなわち、各気筒２Ａ〜２Ｄにそれぞれ新気が導入される各気筒独立状態では、エンジンのクランク軸が１回転する間に、４回の吸気脈動が発生するのに対し、先行気筒２Ａ，２Ｄのみに新気が導入される２気筒接続状態では、エンジンのクランク軸が１回転する間に、２回の吸気脈動が発生するだけであるため、この吸気脈動の検出回数を予め設定された基準回数と比較する等により、吸気および排気の流通経路が各気筒独立状態にあるか２気筒接続状態にあるかが判別されるようになっている。
【００５７】
以上のような第１実施形態の装置の作用を、図５〜図９を参照しつつ説明する。
【００５８】
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６に示すように、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から排出される既燃ガスのみが三元触媒２４を備えた排気通路２０に導かれるような２気筒接続状態とされる。
【００５９】
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６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所定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、リーン空燃比での成層燃焼が行われる（図５参照）。
【００６０】
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５中の白抜き矢印及び図６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理論空燃比となるように、Ｏ_２センサ２３の出力に基いて燃料噴射量が制御されつつ、適当なタイミング（例えば圧縮行程）で燃料が噴射され、かつ、所定点火時期に点火が行われて燃焼が行われる（図５参照）。後続気筒２Ｂ，２Ｃでの燃焼後の既燃ガスは、三元触媒２４を備えた排気通路２０に排出される（図６中の矢印ｃ）。
【００６１】
このように、先行気筒２Ａ，２Ｄではリーン空燃比での成層燃焼が行われることにより、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、これらの相乗効果で大幅に燃費が改善される。また、後続気筒２Ｂ，２Ｃでは空気過剰状態の既燃ガスに対し燃料が供給されて理論空燃比に制御されつつ燃焼が行われることにより、先行気筒２Ａ，２Ｄのようにリーン空燃比で成層燃焼が行われるものと比べると熱効率では多少劣るものの、ポンピングロス低減による燃費改善効果が充分に得られる。
【００６２】
しかも、後続気筒２Ｂ，２Ｃから排気通路２０に排出される既燃ガスは理論空燃比に対応した値となるため、従来のリーンバーンエンジンのようにリーンＮＯｘ触媒を設ける必要がなく、三元触媒２４だけで充分に排気浄化性能が確保されることとなる。そして、このようにリーンＮＯｘ触媒を設ける必要がないことから、リーンＮＯｘ触媒のＮＯｘ吸蔵量増大時におけるＮＯｘの放出、還元のための一時的な空燃比のリッチ化を行う必要がなく、燃費改善の目減りが避けられる。さらに、リーンＮＯｘ触媒の硫黄被毒の問題が生じることもない。
【００６３】
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。
【００６４】
また、後続気筒２Ｂ，２Ｃには先行気筒２Ａ，２Ｄからの既燃ガスが気筒間ガス通路２２を介して導入されるが、この気筒間ガス通路２２で通路長に応じて放熱量が変化するため、この通路長を適正値に設定することにより、後続気筒２Ｂ，２Ｃに導入される既燃ガスの温度を調整することができる。そして、このように既燃ガスの温度を調整するとともに、後続気筒２Ｂ，２Ｃに対する燃料噴射タイミングを適宜調整することにより、多量の既燃ガスが導入される後続気筒２Ｂ，２Ｃにおいても、着火、燃焼性を良好に保つことができる。
【００６５】
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７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（λ≦１）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。
【００６６】
特殊運転モードと通常運転モードとの切換えは、前述のように運転領域Ａ（運転領域Ｃを除く）では原則として特殊運転モードが選択され、運転領域Ｂ（運転領域Ｃを除く）では通常運転モードが選択される。但し、通常運転モードから運転領域Ａに移行してきた場合且つエンジンの減速度が所定値よりも小さい場合には特殊運転モードに切換えず通常運転モードを継続する。そのような場合でも、運転領域Ａ’に移行すると特殊運転モードに切換える。具体的には図８に示すフローチャートによってモード選択がなされる。
【００６７】
図８に示すように、モード選択のフローがスタートすると、ステップＳ２で運転状態判別手段４１によってエンジンの運転領域が運転領域Ｃにあるか否かの判定がなされる。ステップＳ２でＹＥＳと判定されると、ステップＳ４へ移行し、燃料カットモードの制御に移行する（図９参照。詳細は後述する）。ステップＳ２でＮＯと判定されると、ステップＳ１０に移行し、更にエンジンの運転領域の判別がなされる。ステップＳ１０で運転領域Ａにあると判別されると、ステップＳ１２に移行し、更にエンジンが運転領域Ａ’にあるか否かが判定される。ステップＳ１２でＮＯと判定されると、エンジンの運転状態は、図４に示すように回転数がｒ１以下であり、エンジン負荷がＴ２を越え、Ｔ１以下である（たとえば運転状態Ｄ２）であることを意味する。その場合、更に図８のステップＳ１４に移行し、現状の運転モードの判定を行う。ステップＳ１４で通常運転モードであると判定されると、運転領域Ａでありながら通常運転モードであることを意味する。これは、図４の運転領域Ｂの運転状態（たとえば運転状態Ｄ１）から移行してきた場合で、且つ未だ特殊運転モードに切換わっていない状態を示す。その場合、更に図８のステップＳ１６に移行し、エンジンの減速度が所定値αを超えているか否かの判定を行う。ステップＳ１６でＹＥＳと判定されると、ステップＳ１８に移行し、特殊運転モードの制御を行い、リターンする。ステップＳ１６でＮＯと判定されると、エンジンの減速度が所定値α以下の緩減速状態であることを示す。このようなときは、たとえ運転領域Ａであっても特殊運転モードとはせず、ステップＳ２０に移行して通常運転モードの制御を継続し、リターンする。遡って、ステップＳ１２でＹＥＳと判定された場合、およびステップＳ１４で現状が特殊運転モードであると判定された場合には、ステップＳ１８に移行して特殊運転モードの制御を行い、リターンする。また、ステップＳ１０でエンジンの運転領域が、運転領域Ｂであると判別された場合にはステップＳ２０に移行して通常運転モードの制御を行い、リターンする。
【００６８】
ところで、図４に示すように、運転領域Ａ、Ａ’、ＢおよびＣは、エンジン回転数＝ｒ１、ｒ３またはｒ４の各直線、エンジン負荷＝Ｔ１、Ｔ２またはＴ３の各直線によって仕切られた領域である。すなわち、エンジン回転数ｒ１、ｒ３およびｒ４やエンジン負荷Ｔ１、Ｔ２およびＴ３は、運転モードを切換えるための閾値となっている。本実施形態において、通常運転モードから特殊運転モードに切換えるためのエンジン負荷に関する閾値は、緩減速時にはＴ２であり、緩減速時以外ではＴ２よりも高負荷のＴ１となっている（但し特殊運転モードから通常運転モードに切換えるためのエンジン負荷に関する閾値は、Ｔ１で一定である）。
【００６９】
通常運転モードから特殊運転モードに移行する際、トルクショックが発生する（図１１参照。詳細は後述する）が、このトルクショックは、緩減速（エンジンの減速度が小さい）時かつ比較的高負荷時に体感し易く、急減速（エンジンの減速度が大きい）時や、緩減速時であっても比較的低負荷時には体感し難いという特徴がある。従って、前記のように緩減速時に通常運転モードから特殊運転モードに切換える閾値を急減速時よりも低負荷側に設定すると、モードの切換えはトルクショックが体感し難い運転状態でなされる。従って、燃料供給を増加させてトルクを上昇させ、トルクショックを緩和するといった対策をとらなくても、事実上トルクショックを体感し難いようにでき、燃料消費の増加を抑制しつつ、トルクショックにより搭乗者に違和感を与えることを効果的に防止することができる。
【００７０】
図９は、燃料カットモードの制御のフローチャートである。スタート後、ステップＳ３０で運転状態判別手段４１により運転領域の判別が行われ、運転領域Ａであると判別されると、ステップＳ３２に移行して、流通経路を特殊運転モードと同様の２気筒接続状態とする。その後、ステップＳ３６に移行して燃料の供給を停止してリターンする。また、ステップＳ３０で運転領域Ｂであると判別されると、ステップＳ３４に移行して、流通経路を通常運転モードと同様の各気筒独立状態とする。その後、ステップＳ３６に移行して燃料の供給を停止してリターンする。
【００７１】
このようにすると、燃料カットモードであり、かつエンジンの運転領域が運転領域Ａと重複するような運転状態（たとえば図４の運転状態Ｄ４）では、燃料の供給が停止されてはいるが、流通経路は特殊運転モードと同じ２気筒接続状態となる。従って、この状態からエンジン負荷が増加し、燃料カットモードが解除された場合（たとえば運転状態Ｄ３となったとき）、弁停止機構制御手段４２による流通経路の切換えを行うことなく、燃料供給を再開するだけで速やかに特殊運転モードに切換えることができる。
【００７２】
また、本実施形態で、通常運転モードから特殊運転モードに移行する際に、燃料噴射制御手段４４による空燃比補正制御を追加しても良い。
空燃比補正制御は、通常運転モードから特殊運転モードへ移行する際、移行後（モード切換後）、最初に燃焼行程を迎える先行気筒による生成トルクが、その先行気筒に対する後続気筒による生成トルクより大きくなるように、その先行気筒の空燃比を理論空燃比の２倍よりも小さくするとともに、その先行気筒に対する後続気筒の空燃比が理論空燃比となるように各気筒２Ａ〜２Ｄに対する燃料噴射量を制御するものである。
【００７３】
具体的には、例えば、図１０に示すように４番気筒２Ｄの圧縮行程終了時点（図中▲１▼）でモード切換信号が出力されると、その後、一対の気筒の吸排気弁が共に閉弁状態となる時期に弁停止機構制御手段４２が切換えられる。同図に示す例によると、１番気筒２Ａと２番気筒２Ｂがそれぞれ最初に圧縮行程、膨張行程を迎える時点（図中▲２▼）で当該各気筒２Ａ，２Ｂに対応する第１排気弁３２ａ及び第１吸気弁３１ａが停止状態に切換えられ、また第２排気弁３２ｂ及び第２吸気弁３１ｂが作動状態に切換えられ、さらにその後、３番気筒２Ｃと４番気筒２Ｄがそれぞれ圧縮行程、膨張行程を迎える時点（図中▲３▼）で当該各気筒２Ｃ，２Ｄに対応する第１排気弁３２ａ及び第１吸気弁３１ａが停止状態に切換えられ、また第２排気弁３２ｂ及び第２吸気弁３１ｂが作動状態に切換えられる。そして、通常運転モードから特殊運転モードへの切換えの完了が経路判別手段５１により判別されると（図中▲３▼の時点）、その後、最初に燃焼行程を迎える気筒（当例では４番気筒２Ｄ）の空燃比が、λ＜２（λは空気過剰率。以下同じ）となるように燃料噴射量（図中Ｆ_１で示す）が制御さる。さらにその先行気筒に対する後続気筒（当例では３番気筒２Ｃ）の該燃焼が理論空燃比で行われるように燃料噴射量（図中Ｆ_２で示す）が制御される。この空燃比補正制御を行わない特殊運転モードでは、Ｆ_１の空気過剰率はλ＝２となるように制御されるので、この空燃比補正制御により、Ｆ_１の空燃比はリッチ側に補正される。そしてその分、Ｆ_２の燃料噴射量が通常の特殊運転モードよりも削減されるので、結果的に４番気筒２ＤのＦ_１の燃焼による生成トルクが、３番気筒２ＣのＦ_２の燃焼による生成トルクよりも大きくなる。
【００７４】
このようにモード切換時の各気筒２Ａ〜２Ｄの空燃比が制御されることにより、モード切換えに伴うトルクショック（一時的にトルクが低くなる現象）が有効に緩和され、また、排気浄化性能も確保されることとなる。
【００７５】
すなわち、特殊運転モードでは、先行気筒と後続気筒との２気筒分の燃焼に必要な空気を前記先行気筒（１番、４番気筒２Ａ，２Ｄ）に供給すべくスロットル開度が制御されており、従って通常運転モードから移行時にはスロットル開度が開かれることとなるが、このときスロットル弁１７の作動の応答遅れおよび吸気流動の変化の遅れにより先行気筒の吸入空気量（吸気量という）の変化に図１１の最上段に示すような応答遅れが生じ得る。一方、特殊運転モードへの切換え後の空燃比（図１１の２段目に示す）は、先行気筒での空気過剰率λが、λ＝２となるように制御される。従って、何ら対処がなければ、前記のような応答遅れが生じた吸気量に対応した燃料供給量に制御されることとなり、モード切換え直後の先行気筒での燃料噴射量が図１１の３段目に示す破線のように急減する。それに伴い、全気筒平均トルクが図１１の最下段に示す破線のように急減する。（トルクショックが発生する）。これに対して、モード切換え直後、前記のように最初に燃焼行程を迎える先行気筒について空燃比をリッチ側に補正した状態（図１１の２段目の実線で示す）で燃焼が行われると、先行気筒での燃料噴射量の減少が図１１の３段目に示す実線のように抑制される。一方、先行気筒で燃料噴射量を増やしてリッチ側に補正した分、後続気筒では燃料噴射量を削減して、結果的に理論空燃比での燃焼になるようにしている（図１１の４段目の実線で示す）。このため、先行気筒での生成トルクが、後続気筒での生成トルクよりも大きくなり、全気筒平均トルクの減少が図１１の最下段に示す実線のように抑制される。その結果、トルクショックが効果的に緩和されることとなる。なお、後続気筒での空燃比が理論空燃比となるように燃焼噴射量が制御されることにより、排気浄化性能も三元触媒２４だけで良好に確保されることとなる。
【００７６】
なお、空燃比補正制御によって充分にトルクショックが緩和される場合には、運転領域Ａ’は、運転領域Ａと等しくしても良い。すなわち、エンジンの減速度にかかわらず、運転領域Ｃ以外の運転領域Ａでは常に特殊運転モードが選択されるようにしつつ、エンジンの緩減速時に運転領域Ｂから運転領域Ａに移行するときは空燃比補正制御を行うようにしても良い。
【００７７】
次に本発明の第２の実施形態について図を参照して説明する。なお、第１の実施形態と同じ構成要素については同一符号を付してその説明を省略する。
【００７８】
図１２および図１３は、複数の気筒２を有し、各気筒２内に燃料を直接噴射して吸気行程と排気行程との間に１回の燃焼を行う通常運転モードと、吸気行程と排気行程との間に２回の燃焼を行う特殊運転モードとにエンジンの運転状態に応じて燃焼サイクルを切換えるとともに、排気通路２０に排出される排気ガスの酸素濃度が略理論空燃比の燃焼状態に対応した値となるように前記吸気行程で各気筒２Ａ〜２Ｄ内に導入される吸入空気量および前記２回の燃焼を行うための燃料噴射量を制御するように構成され、かつ排気通路２０に三元触媒２４が配設された火花点火式エンジンの制御装置を示している。
【００７９】
前記各気筒２の燃焼室４に対してそれぞれ一対の吸気ポート１１，１１および排気ポート１２，１２が開口し、これらのポート１１，１１，１２，１２が吸気弁３１，３１および排気弁３２，３２により開閉されるようになっている。そして、各気筒２が所定の位相差、つまりクランク角で１８０°ずつの位相差をもって所定の順番で燃焼が行われるようになっている。
【００８０】
前記吸・排気弁３１，３２は、それぞれ動弁機構５３により駆動されるように構成されている。この動弁機構５３は、図１３に示すように、非磁性材料からなるハウジング５４と、このハウジング５４内に摺動自在に配設されるとともに、前記吸・排気弁３１，３２と一体に連結されたアーマチュア・コア５５と、ハウジング３４内の上下両端部に配設された一対の電磁石５６，５７および戻しばね５８，５９とを備えている。そして、上方の電磁石５６に通電してアーマチュア・コア５５を上方に吸引することにより、吸気弁３１および排気弁３２をそれぞれ所定のタイミングで開放状態とし、下方の電磁石５７に通電してアーマチュア・コア５５を下方に吸引することにより、吸気弁３１および排気弁３２をそれぞれ所定のタイミングで閉止状態とするようになっている。
【００８１】
前記動弁機構５３等を制御するマイクロコンピュータ等からなるエンジン制御用のＥＣＵ（コントロールユニット）４０にはエアフローセンサ１９およびＯ_２センサ２３からの信号が入力され、さらに運転状態を判別するためにエンジン回転数を検出する回転数センサ４５およびアクセル開度（アクセルペダル踏込み量）を検出するアクセル開度センサ４６等からの信号も入力されている。
【００８２】
前記ＥＣＵ４０は、エンジンの運転状態を判別する運転状態判別手段４１、前記吸気弁３１および排気弁３２の開閉タイミングを制御する弁開閉制御手段６０と、エンジンの燃焼室４への吸入空気量を制御する吸入空気量制御手段４３と、燃料の噴射状態を制御する燃料噴射制御手段４４とを備えている。
【００８３】
前記弁開閉制御手段６０は、運転状態判別手段４１等とともにモード切換手段として機能し、通常運転モードが選択された場合と特殊運転モードが選択された場合とで、動弁機構５３に出力される制御信号の出力タイミングを変化させて吸気弁３１および排気弁３２の開閉タイミングを次のように制御するように構成されている。
【００８４】
通常運転モードでは、図１４（ａ）に示すように、燃料噴射を伴う吸気行程ＩＮと、後期に点火Ｓを伴う圧縮行程と、燃焼を伴う膨張行程と、排気行程ＥＸとからなる通常運転モード、つまり吸気行程ＩＮと排気行程ＥＸとの間に一回の均一燃焼を行う一般的な４サイクルの燃焼制御を実行するように前記吸気弁３１および排気弁３２の開閉タイミングが設定される。なお、図１４において、Ｔはピストン行程の上死点、Ｂは下死点である。
【００８５】
特殊運転モードでは、図１４（ｂ）に示すように、吸気行程ＩＮ（第１行程）と、後期に燃料噴射Ｆおよび点火Ｓを伴う第１圧縮行程（第２行程）と、燃焼を伴い、かつ後期に燃料噴射Ｆを行う第１膨張行程（第３行程）と、後期に点火Ｓを伴う第２圧縮行程（第４行程）と、燃焼を伴う第２膨張行程（第５行程）と、排気行程ＥＸ（第６行程）とからなる特殊運転モード、つまり吸気行程ＩＮと排気行程ＥＸとの間に二回の燃焼を行う６サイクルの燃焼制御を実行するように前記吸気弁３１および排気弁３２の開閉タイミングが設定される。
【００８６】
前記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ように構成されている。特に、主として低負荷・低回転側の運転領域Ａにおいて実行される特殊運転モードでは、前記二回の燃焼後における排気行程ＥＸで排気通路２０に排出される排気ガスの既燃ガス濃度が、略理論空燃比の燃焼状態に対応した値となるようにスロットル開度が調節される。また、主として高負荷・高回転側の運転領域Ｂにおいて実行される通常運転モードでは、気筒２内の空燃比がλ≦１となるようにスロットル開度が調節される。
【００８７】
前記燃料噴射制御手段４４は、各気筒２に設けられた燃料噴射弁９からの燃料噴射量および噴射タイミングをエンジンの運転状態に応じて制御するもので、特に特殊運転モードと通常運転モードとに、燃料噴射の制御状態を変更するものであり、この燃料噴射制御手段４４と前記運転状態判別手段４１とにより本発明の空燃比制御手段が構成されている。
【００８８】
すなわち、特殊運転モードでは、図１４（ｂ）に示すように、第１膨張行程（第３行程）で行われる最初の燃焼が成層燃焼状態となるように、空燃比が理論空燃比よりも大きいリーン空燃比、好ましくは理論空燃比の略２倍もしくはそれ以上となるように第１圧縮行程（第２行程）の燃料噴射量を設定するとともに、燃料噴射Ｆのタイミングを設定する。また、前記最初の燃焼により生じたリーン空燃比の既燃ガス中に燃料を供給する（第３行程）ことにより、理論空燃比の条件下において第２膨張行程（第５行程）で２回目の燃焼が行われるように、燃料噴射量を制御するとともに、既燃ガスが多い状況下で着火、燃焼が可能なように燃料噴射Ｆのタイミングが設定され、例えば第１膨張行程（第３行程）の後期に燃料噴射Ｆが行われる。なお、前記燃料噴射量の制御は、エアフローセンサ１９およびＯ_２センサ２３等からの出力に基づくフィードバック制御により行われる。
【００８９】
また、通常運転モードでは、各気筒２の空燃比を理論空燃比もしくはそれ以下とするように燃料噴射量を制御し、例えば運転領域の大部分において理論空燃比とし、全開負荷およびその付近の運転領域で理論空燃比よりリッチとなるように燃料噴射量を制御する。
【００９０】
なお、エンジンの運転状態と運転モードの切換えに関しては、第１の実施形態と同様の制御がなされる。すなわち、エンジンの運転状態が図４の運転領域Ａ’かつ運転領域Ｃにない状態では特殊運転モードが選択される。運転領域Ｂかつ運転領域Ｃにない状態では通常運転モードが選択される。運転領域Ａであり、運転領域Ａ’ではない領域では、原則として特殊運転モードが選択されるが、運転領域Ｂから運転領域Ａに移行してきた場合且つエンジンの減速度が所定値よりも小さい場合には特殊運転モードに切換えず通常運転モードを継続する。但しそのような場合でも、運転領域Ａ’に移行すると特殊運転モードに切換える。運転領域Ｃは、運転領域Ａか運転領域Ｂかのいずれかの領域と重複している。いずれの場合も、エンジンの運転状態が運転領域Ｃにあるときは、燃料カットモードが優先的に選択される。
【００９１】
前記経路判別手段５１および始動時判別手段５２は、図３に示す実施形態の経路判別手段５１および始動時制御手段５２と同様に構成されたものであり、吸気通路１５に配設されて吸気の脈動を検出する吸気脈動検出手段（エアフローセンサ１９）から出力された検出信号に応じ、エンジンの始動時に、通常運転モードの制御状態にあるか、特殊運転モードの制御状態にあるかを前記経路判別手段５１において判別し、かつこの経路判別手段５１の判別結果に応じて特殊運転モードの制御状態にあることが確認された場合には、エンジン始動時における最初の燃焼制御時において、第１回目に噴射された燃料の点火を禁止する等の制御を前記始動時制御手段５２において実行するように構成されている。
【００９２】
以上のような第２実施形態の装置によると、特殊運転モードでは吸気行程と排気行程との間に二回の燃焼が行われ、第１膨張行程で行われる最初の燃焼がリーン空燃比での成層燃焼状態とされることにより、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、これらの相乗効果で大幅に燃費が改善される。また、前記最初の燃焼により生成された空気過剰状態の既燃ガス中に燃料を供給して理論空燃比に制御しつつ、第２膨張行程において２回目の燃焼を行わせることにより、通常のエンジンのようにリーン空燃比で成層燃焼させるものと比べると熱効率では劣るものの、ポンピングロス低減による燃費効果が得られることになる。
【００９３】
しかも、前記２回目の燃焼が行われた後に、排出行程で排気通路２０に排出される既燃ガスの濃度が理論空燃比に対応した値となるため、従来のリーンバーンエンジンのようにリーンＮＯｘ触媒を設ける必要がなくなり、三元触媒２４だけで充分に排気浄化性能が確保されることとなる。そして、このようにリーンＮＯｘ触媒を設ける必要がないことから、リーンＮＯｘ触媒のＮＯｘ吸蔵量の増大時におけるＮＯｘの放出、還元のための一時的な空燃比のリッチ化を行う必要がなく、燃費改善の目減りが避けられる。さらに、リーンＮＯｘ触媒の硫黄被毒の問題が生じることもない。
【００９４】
一方、通常運転モードでは、前述のように吸気行程ＩＮと排気行程ＥＸとの間に一回の均一燃焼を行う一般的な４サイクルの燃焼制御が実行され、かつ各気筒２Ａ〜２Ｄ内の空燃比がλ≦１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。
【００９５】
エンジンの運転状態が運転領域Ｃにないとき、特殊運転モードと通常運転モードとの切換えは、第１の実施形態と同様に、運転領域Ａでは原則として特殊運転モードが選択され、運転領域Ｂでは通常運転モードが選択される。但し、運転領域Ｂ（通常運転モード）から運転領域Ａに移行してきた場合且つエンジンの減速度が所定値よりも小さい場合には特殊運転モードに切換えず通常運転モードを継続する。そのような場合でも、運転領域Ａ’に移行すると特殊運転モードに切換える。具体的には前述の図８に示すフローチャートによってモード選択がなされる。
【００９６】
また、第１の実施形態と同様、図４に示すエンジン回転数ｒ１、ｒ３およびｒ４やエンジン負荷Ｔ１、Ｔ２およびＴ３は、運転モードを切換えるための閾値となっている。本実施形態においても、通常運転モードから特殊運転モードに切換えるためのエンジン負荷に関する閾値は、緩減速時にはＴ２であり、緩減速時以外ではＴ２よりも高負荷のＴ１となっている。このように制御することにより、第１の実施形態と同様、トルクショックが体感し難い運転状態で通常運転モードから特殊運転モードに切換えることができる。従って、燃料消費の増加を抑制しつつ、トルクショックにより搭乗者に違和感を与えることを効果的に防止することができる。
【００９７】
燃料カットモードでの制御は、第１の実施形態と同様、運転領域Ａにあるとき（たとえば運転状態Ｄ４）は、燃料の供給が停止されてはいるが、給排気行程は特殊運転モードと同じ状態となる。従って、この状態からエンジン負荷が増加し、燃料供給停止モードが解除された場合（たとえば運転状態Ｄ３となったとき）、弁開閉制御手段６０による吸気弁３１や排気弁３２の開閉タイミングの切換えを行うことなく、燃料供給を再開するだけで速やかに特殊運転モードに切換えることができる。同様に運転領域Ｂにあるときは、燃料の供給を停止するとともに、給排気行程を通常運転モードと同じ状態とする。
【００９８】
なお、第２の実施形態では、特殊運転モードにおいて、吸気行程ＩＮと、第１圧縮行程と、燃焼を伴う第１膨張行程と、第２圧縮行程と、燃焼を伴う第２膨張行程と、排気行程ＥＸとからなる６サイクルの燃焼制御を実行することにより、吸気行程ＩＮと排気行程ＥＸとの間で２回の燃焼を行うように構成（図１４（ｂ）参照）しているが、その変形例として図１４（ｃ）に示すように、吸気行程ＩＮと、第１圧縮行程と、燃焼を伴う第１膨張行程と、第２圧縮行程と、燃焼を伴わない第２膨張行程と、第３圧縮行程と、燃焼を伴う第３膨張行程と、排気行程ＥＸとからなる８サイクルの燃焼制御を実行することにより、吸気行程と排気行程との間で２回の燃焼を行うように構成してもよい。
【００９９】
【発明の効果】
以上のように本発明の制御装置は、各気筒においてそれぞれ独立して燃焼を行わせる通常運転モードと、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にある先行気筒から排出される既燃ガスをそのまま吸気行程にある後続気筒に導入して燃焼を行わせる特殊運転モードとに切換え可能に構成され、例えば低負荷低回転の運転領域では特殊運転モードに設定されることにより、先行気筒ではリーン空燃比での燃焼が行われて、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ることにより大幅な燃費改善効果が得られ、かつ前記後続気筒では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が供給されて理論空燃比とされた状態で燃焼が行われることにより、少なくともポンピングロス低減による燃費効果が得られる。また、後続気筒から排出される理論空燃比の既燃ガスのみが排気通路に導かれるため、三元触媒だけで充分に排気浄化性能が確保される。一方、高負荷・高回転の運転領域では、通常運転モードに設定されることにより出力性能が確保される。そして、通常運転モードから特殊運転モードへの移行に際し、エンジンの運転状態が、所定の閾値よりも低負荷低回転となったときに特殊運転モードに切換えるものであるとともに、エンジンの減速度が所定値以下の緩減速時にはその閾値を更に低負荷側に設定するようにしているので、燃料消費の増加を抑制しつつ、トルクショックにより搭乗者に違和感を与えることを効果的に防止することができる。
【図面の簡単な説明】
【図１】本発明に係る制御装置を備えたエンジン全体の概略平面図（第１の実施形態）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】運転領域を示す説明図である。
【図５】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６】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７】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８】特殊運転モード、通常運転モードおよび燃料カットモードの選択のためのフローチャートである。
【図９】燃料カットモードにおける制御のフローチャートである。
【図１０】通常運転モードから特殊運転モードへ移行される際の各気筒の排気行程、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１１】通常運転モードから特殊運転モードへ移行される際の吸入空気量、空燃比、燃料噴射量および発生トルクの変化を示す図である。
【図１２】本発明に係る制御装置を備えたエンジン全体の概略平面図（第２の実施形態）である。
【図１３】第２の実施形態における動弁機構の構成と制御系統のブロック構成を示す図である。
【図１４】第２の実施形態における気筒の燃焼サイクル、燃料噴射時期および点火時期等を示す説明図である。
【符号の説明】
１　エンジン本体
２Ａ〜２Ｄ　気筒
９　燃料噴射弁
１１　吸気ポート
１１ａ　第１吸気ポート
１１ｂ　第２吸気ポート
１２　排気ポート
１２ａ　第１排気ポート
１２ｂ　第２排気ポート
１５　吸気通路
２０　排気通路
２２　気筒間ガス通路
２４　三元触媒
３１　吸気弁
３１ａ　第１吸気弁
３１ｂ　第２吸気弁
３２　排気弁
３２ａ　第１排気弁
３２ｂ　第２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　燃料噴射制御手段
５１　経路判別手段[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 type engine, there is known 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. As disclosed in JP-A-10-274085, a fuel injection valve for directly injecting fuel into a combustion chamber is provided, and in a low-speed low-load region or the like, stratified combustion is performed by injecting fuel from the fuel injection valve in a compression stroke. And thereby realizing super-lean combustion.
[0003]
In such an engine, an ordinary three-way catalyst (a catalyst having a high purification performance near the stoichiometric air-fuel ratio with respect to HC, CO and NOx) alone as an exhaust gas purification catalyst is sufficient for NOx during lean operation. Since the purification performance cannot be obtained, a lean NOx catalyst for adsorbing NOx in an oxygen-excess atmosphere and desorbing and reducing NOx in an oxygen-low concentration atmosphere is provided as shown in the above-mentioned publication. When such a lean NOx catalyst is used, if the amount of NOx adsorbed by the lean NOx catalyst increases during the lean operation, additional fuel is injected during the expansion stroke other than the main combustion, for example, as described in the above-mentioned publication. As a result, the air-fuel ratio of the exhaust gas is enriched and CO is generated, thereby promoting the separation and reduction of NOx.
[0004]
[Problems to be solved by the invention]
In the engine performing the conventional lean operation as described above, the lean NOx catalyst is required to secure NOx purification performance during the lean operation. In addition, a three-way catalyst is required for purifying exhaust gas in a region operated at a stoichiometric air-fuel ratio such as a high load region, and the lean NOx catalyst is provided in addition to the three-way catalyst. The NOx catalyst requires a relatively large capacity in order to secure a certain amount of NOx adsorption, and is expensive as compared with the three-way catalyst, which is disadvantageous in cost.
[0005]
Moreover, in order to maintain the purification performance of the lean NOx catalyst, as described above, it is necessary to temporarily supply additional fuel to separate and reduce NOx every predetermined period in which the NOx adsorption amount increases. It is necessary to enrich the air-fuel ratio, and as a result, the fuel efficiency improvement effect due to lean combustion is reduced.
[0006]
In view of 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. In a low-load, low-speed range, the exhaust stroke and the intake stroke overlap between a pair of cylinders. 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 discharged into the exhaust passage provided with the three-way catalyst. When the two-cylinder connection state is established, combustion is performed in the preceding cylinder at a lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio by a predetermined amount, and in the succeeding cylinder, the lean air introduced from the preceding cylinder is used. While controlling the combustion state and the like so that fuel is supplied to the burned gas of the air-fuel ratio to achieve the stoichiometric air-fuel ratio (called a special operation mode), in the high-load high-speed range, Normally, it is considered to control the combustion conditions or the like so as to perform the combusting respective cylinders at the stoichiometric air-fuel ratio (referred to the normal operation mode) (Japanese Patent Application No. 2002-024548).
[0007]
According to this, by setting the special operation mode in the low-load low-speed range, combustion at the lean air-fuel ratio is performed in the leading cylinder, which increases the thermal efficiency and reduces pumping loss, thereby significantly improving the fuel efficiency. Further, in the subsequent cylinder, fuel is supplied to burned gas having a lean air-fuel ratio introduced from the preceding cylinder, and combustion is performed in a state where the stoichiometric air-fuel ratio is obtained. can get. Moreover, since only burned gas having a stoichiometric air-fuel ratio discharged from the succeeding cylinder is guided to the exhaust passage provided with the three-way catalyst, sufficient exhaust purification performance can be secured only with the three-way catalyst, and a lean NOx catalyst is not required. Become.
[0008]
Incidentally, when controlling the combustion state of each cylinder as described above, the response of the intake air amount at the time of transition from the high load rotation range to the low load rotation range (at the time of switching from the normal operation mode to the special operation mode). It is conceivable that a delay occurs. Therefore, simply switching to the special operation mode may cause a torque shock (a state in which the torque is temporarily reduced) due to the response delay, giving the passenger an uncomfortable feeling. . That is, when shifting from the normal operation mode to the special operation mode, the opening degree of the throttle valve (throttle opening degree) is controlled so as to increase a large amount of intake air including the intake air amount of the succeeding cylinder into the preceding cylinder. . However, it is considered that a response delay occurs in the opening degree adjustment, and intake of an amount less than the target intake amount is temporarily performed, and combustion is performed in a state where the stoichiometric air-fuel ratio is set based on the intake amount. As a result, a state in which the torque temporarily decreases may occur.
[0009]
The present invention has been made in consideration of the above-described problems, and has an effect of improving fuel efficiency by lean combustion and improving exhaust gas purification performance only by using a three-way catalyst without using a lean NOx catalyst. It is intended to provide a control device for a spark ignition type engine which can prevent a passenger from feeling uncomfortable due to torque shock.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the exhaust gas of the preceding cylinder is passed through the inter-cylinder gas passage between the pair of cylinders in which the exhaust stroke and the intake stroke overlap each other, and each cylinder is in an independent state in which fresh air is introduced into each cylinder. A normal operation mode in which the intake and exhaust flow paths are configured to be switchable between a two-cylinder connection state to be introduced into the first and second cylinders, and the combustion paths are independently performed in the respective cylinders by setting the flow paths to the respective cylinder independent states; Multi-cylinder spark ignition configured to be capable of switching the operation mode between a special operation mode in which burned gas discharged from a preceding cylinder is directly introduced into a succeeding cylinder in an intake stroke to perform combustion in the two-cylinder connection state. A mode switching means for switching an operation mode to the normal operation mode or the special operation mode according to an operation state of the engine; In the reverse mode, combustion is performed in a state in which the preceding cylinder has a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and in the succeeding cylinder, the burned gas having the lean air-fuel ratio derived from the preceding cylinder is converted to the burned gas. While fuel is supplied and combustion is performed at a stoichiometric air-fuel ratio, when in the normal operation mode, combustion is performed at each cylinder so that combustion is performed at an air-fuel ratio at each cylinder at a stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling an air-fuel ratio, wherein the mode switching means switches to the special operation mode when the operating state of the engine in the normal operation mode becomes lower in load and lower than a predetermined threshold. The threshold value is further set to a lower load side when the deceleration of the engine is slower than a predetermined value.
[0011]
According to the present invention, in the low-load low-speed range of the engine, by performing the combustion control in the special operation mode in the two-cylinder connection state, the preceding cylinder performs combustion at a lean air-fuel ratio, and the thermal efficiency is reduced. By increasing the pumping loss and reducing the pumping loss, a significant fuel efficiency improvement effect was obtained, and in the succeeding cylinder, fuel was supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder to obtain the stoichiometric air-fuel ratio. By performing combustion in this state, at least a fuel efficiency effect by reducing pumping loss can be obtained. Further, only the burned gas having the stoichiometric air-fuel ratio discharged from the subsequent cylinder is guided to the exhaust passage, so that the exhaust gas purifying performance is sufficiently ensured only by the three-way catalyst. On the other hand, in the high load / high speed operation region, the output performance is ensured by setting the normal operation mode.
[0012]
Further, a predetermined threshold value is provided to switch between the special operation mode and the normal operation mode. For example, when the operating state of the engine during the normal operation mode becomes lower in load and lower than the predetermined threshold value, The mode switching means switches from the normal operation mode to the special operation mode. At this time, the above-mentioned torque shock is generated. This torque shock is easily felt when the vehicle is slowly decelerated (the engine deceleration is small) and at a relatively high load, and is suddenly decelerated (the engine deceleration is large). In addition, there is a characteristic that even when slow deceleration is performed, it is difficult to sense the feeling when the load is relatively low.
[0013]
According to the present invention, at the time of slow deceleration, the threshold for switching from the normal operation mode to the special operation mode is set to a further low load side. At that time, that is, in a driving state in which the torque shock is hardly felt. In this way, without taking measures such as increasing the fuel supply to increase the torque and mitigating the torque shock, the torque shock can be made substantially less sensible, so while suppressing the increase in fuel consumption, It is possible to effectively prevent the passenger from feeling uncomfortable due to the torque shock.
[0014]
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 air-fuel ratio control means stops the supply of fuel when at least the operating state of the engine is in a predetermined deceleration range. A supply stop mode, wherein, in the fuel supply stop mode, when the operating state of the engine is lower than the predetermined threshold and the load is low, the air-fuel ratio control means stops the supply of fuel, and the mode switching means Is characterized in that the circulation path is in the two-cylinder connection state.
[0015]
In this manner, in the fuel supply stop mode, when the engine operating state is at a low load and low speed lower than the predetermined threshold, the fuel supply is stopped, but the gas flow path is the same as in the special operation mode. It becomes a two-cylinder connection state. Therefore, when the engine load increases from this state and the fuel supply stop mode is released, it is possible to quickly switch to the special operation mode simply by restarting the fuel supply without switching the distribution route.
[0016]
According to a third aspect of the present invention, an exhaust gas of a preceding cylinder is passed through an inter-cylinder gas passage between a pair of cylinders in which an exhaust stroke and an intake stroke overlap each other, and each cylinder is in an independent state in which fresh air is introduced into each cylinder. A normal operation mode in which the intake and exhaust flow paths are configured to be switchable between a two-cylinder connection state to be introduced into the first and second cylinders, and the combustion paths are independently performed in the respective cylinders by setting the flow paths to the respective cylinder independent states; Multi-cylinder spark ignition configured to be capable of switching the operation mode between a special operation mode in which burned gas discharged from a preceding cylinder is directly introduced into a succeeding cylinder in an intake stroke to perform combustion in the two-cylinder connection state. A mode switching means for switching an operation mode to the normal operation mode or the special operation mode according to an operation state of the engine; In the reverse mode, combustion is performed in a state in which the preceding cylinder has a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and in the succeeding cylinder, the burned gas having the lean air-fuel ratio derived from the preceding cylinder is converted to the burned gas. While fuel is supplied and combustion is performed at a stoichiometric air-fuel ratio, when in the normal operation mode, combustion is performed at each cylinder so that combustion is performed at an air-fuel ratio at each cylinder at a stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio, the air-fuel ratio control means, after switching from the normal operation mode to the special operation mode, the torque generated by the preceding cylinder that first enters the combustion stroke, the torque generated by the preceding cylinder The air-fuel ratio of the preceding cylinder is made smaller than twice the stoichiometric air-fuel ratio so that the torque generated by the succeeding cylinder becomes larger than the stoichiometric air-fuel ratio. And performing air-fuel ratio correction control such that.
[0017]
According to the present invention, as in the case of the first aspect, the combustion control in the special operation mode is executed in the low load and low speed range, so that the fuel efficiency can be improved, and the exhaust gas can be sufficiently purified only by the three-way catalyst. Performance is ensured. On the other hand, in the high load / high speed operation region, the output performance is ensured by setting the normal operation mode.
[0018]
Then, at the time of transition from the normal operation mode to the special operation mode (at the time of switching), the air-fuel ratio correction control causes the generated torque in the preceding cylinder that first enters the combustion stroke after the mode switching to be smaller than the generated torque in the subsequent cylinder. The correction of the air-fuel ratio is made so that This is different from the case of simply enriching the air-fuel ratio, while increasing the torque generated in the combustion immediately after the mode switching while making the exhaust from the subsequent cylinder correspond to the combustion based on the stoichiometric air-fuel ratio. That is, by adjusting the distribution of the generated torque, rapid torque fluctuation is suppressed. As described above, since the fuel consumption does not increase as a whole, the torque shock can be reduced without increasing the fuel consumption. In addition, since the exhaust gas from the subsequent cylinder becomes gas having the stoichiometric air-fuel ratio, the exhaust gas purification performance is also ensured.
[0019]
According to a fourth aspect of the present invention, in the control apparatus for a spark ignition engine according to the third aspect, the air-fuel ratio control means performs the air-fuel ratio correction control when the deceleration of the engine is slower than a predetermined value. Features.
[0020]
In this way, the torque shock at the time of slow deceleration can be mitigated. It is possible to effectively prevent the passenger from feeling uncomfortable.
[0021]
According to a fifth aspect of the present invention, there is provided a normal operation mode in which fuel is directly injected into a combustion chamber and one combustion stroke is performed between an intake stroke and an exhaust stroke, and two normal operation modes are performed between an intake stroke and an exhaust stroke. A control device for a spark ignition engine configured to be capable of switching a combustion cycle between a special operation mode having a combustion stroke and a special operation mode, wherein the operation mode is switched to the normal operation mode or the special operation mode according to an operation state of the engine. Switching means, when in the special operation mode, causes combustion to be performed in a state where a lean air-fuel ratio is larger by a predetermined amount than a stoichiometric air-fuel ratio in the previous combustion, and lean air generated by the previous combustion in the subsequent combustion. While the fuel is supplied to the burned gas having the fuel ratio to cause combustion at the stoichiometric air-fuel ratio, while in the normal operation mode, combustion is performed with the air-fuel ratio of each cylinder at the stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio in each cylinder so that the engine operating state during the normal operation mode has a low-load low-speed lower than a predetermined threshold value. When the engine decelerates slowly below a predetermined value, the threshold value is set to a lower load side.
[0022]
According to the present invention, for example, in the low-load low-speed range of the engine, the combustion control in the special operation mode is performed, that is, after the air necessary for the two combustions is supplied, the air-fuel ratio in the lean air-fuel ratio is increased. Is performed and the subsequent combustion at the stoichiometric air-fuel ratio is performed, so that the thermal efficiency is increased and the pumping loss is reduced, and as a result, a significant fuel efficiency improvement effect is obtained. In addition, since the air-fuel ratio in the combustion stroke of each cylinder is controlled so that the oxygen concentration of the burned gas becomes a value corresponding to the combustion state of approximately the stoichiometric air-fuel ratio, exhaust purification performance can be sufficiently achieved only with the three-way catalyst. Secured. On the other hand, in the high load / high speed operation region, the output performance is ensured by setting the normal operation mode.
[0023]
As in the case of the first aspect, a predetermined threshold is provided for switching between the special operation mode and the normal operation mode. Is also set to the low load side, this mode switching is performed in an operating state where it is difficult to feel a torque shock. As described above, it is possible to effectively prevent the passenger from feeling uncomfortable due to the torque shock while suppressing an increase in fuel consumption.
[0024]
According to a sixth aspect of the present invention, in the control apparatus for a spark ignition type engine according to the fifth aspect, the air-fuel ratio control means stops the supply of fuel at least when the operating state of the engine is in a predetermined deceleration range. A supply stop mode, wherein in the fuel supply stop mode, when the operating state of the engine is lower than the predetermined threshold value and the engine speed is lower than the predetermined threshold, the air-fuel ratio control means stops the supply of fuel, and the mode switching means Performs a supply / exhaust stroke equivalent to that of the special operation mode.
[0025]
In this manner, in the fuel supply stop mode, when the operation state of the engine is lower than the predetermined threshold and the load is low, the fuel supply is stopped, but the supply / exhaust stroke is the same as in the special operation mode. It becomes. Therefore, when the engine load increases from this state and the fuel supply stop mode is canceled, the special operation mode can be promptly switched to the special operation mode simply by restarting the fuel supply without switching the supply / exhaust stroke.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
[0027]
FIG. 1 shows a schematic configuration of an engine according to an embodiment of the present invention, and FIG. 2 schematically shows a structure of one cylinder of an engine main body and intake and 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.
[0028]
A spark plug 7 is provided at the top of the combustion chamber 4 of each of the cylinders 2A to 2D, and the tip of the plug faces the combustion chamber 4. The ignition plug 7 is connected to an ignition circuit 8 capable of controlling the ignition timing by electronic control.
[0029]
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 has a built-in needle valve and a solenoid (not shown). When a pulse signal described later is input, the fuel injection valve 9 is driven for a time corresponding to the pulse width at the pulse input time, and opens. It is configured to inject an amount of fuel according to the valve time. 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.
[0030]
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.
[0031]
Each of the cylinders 2A to 2D performs a combustion cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of a four-cylinder engine, the first cylinder from one end in the cylinder row direction 2A, the second cylinder 2B, the third cylinder 2C, and the fourth cylinder 2D, as shown in FIG. 5, the cycle is performed in the order of the first cylinder 2A, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B. The combustion cycle is performed with a phase difference of 180 ° at each crank angle. In FIG. 5, EX represents an exhaust stroke, IN represents an intake stroke, F represents fuel injection, and S represents ignition.
[0032]
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) and the cylinder on the intake stroke side (this specification) when the exhaust stroke and the intake stroke overlap. 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 this embodiment, as shown in FIG. 5, 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 third Since the intake strokes (IN) of the cylinders 2C overlap, the first cylinder 2A and the second cylinder 2B, and the fourth cylinder 2D and the third cylinder 2C each form a pair, and the first cylinder 2A and the fourth cylinder 2D are the leading cylinders. The second cylinder 2B and the third cylinder 2C are subsequent cylinders.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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. Note that an airflow sensor 19 for detecting an intake air flow rate is provided in a common intake passage upstream of the collecting portion in the intake passage 15.
[0037]
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. In addition, an inter-cylinder gas passage 22 is 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 which are the preceding cylinders are provided. The upstream end of the inter-cylinder gas passage 22 is connected to the second exhaust ports 12b of the 2A and 2D, and the inter-cylinder gas passage 22 is connected to the second intake ports 11b of the second and third cylinders 2B and 2C, which are subsequent cylinders. The downstream end is connected.
[0038]
An exhaust gas concentration detecting means for detecting a stoichiometric air-fuel ratio is provided at a collecting portion of the exhaust passage 20 downstream of the branch exhaust passage 21. ₂ A sensor 23 is provided, and a three-way catalyst 24 for purifying exhaust gas is provided in the exhaust passage 20 downstream of the sensor 23. 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. Also, O ₂ The sensor 23 detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas. ₂ It is composed of a sensor.
[0039]
In the inter-cylinder gas passage 22, there is provided a linear O, whose output varies linearly with a change in the oxygen concentration in the exhaust gas (a change in the air-fuel ratio). ₂ A sensor 25 (exhaust gas concentration detecting means for detecting a lean air-fuel ratio) is provided.
[0040]
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. That is, 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. The first intake port 11a, the second intake port 11b, and the exhaust port 12 of the second and third cylinders 2B, 2C are provided with a first intake valve 31a, a second intake valve 31b, and an exhaust valve 32, respectively. These intake and exhaust valves are opened and closed at a predetermined timing 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.
[0041]
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.
[0042]
A first control valve 37 is provided in a passage 36 for supplying and discharging hydraulic oil to a valve stop mechanism 35 of the first exhaust valve 32a and a 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).
[0043]
FIG. 3 shows the configuration of the drive and control system of the engine. 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 and linear O ₂ Signals from the sensor 25 are input, and signals from a rotation speed sensor 45 for detecting an engine rotation speed and an accelerator opening sensor 46 for detecting an accelerator opening (accelerator pedal depression amount) for determining an operation state are also provided. Has been entered. Control signals are output from the ECU 40 to each of the fuel injection valves 9, the actuator 18 of the multiple throttle valve 17, and the first and second control valves 37 and 39.
[0044]
The ECU 40 includes an operating state determination unit 41, a valve stop mechanism 35, a valve stop mechanism control unit 42, an intake air amount control unit 43, a fuel injection control unit 44, a route determination unit 51, and the like as its functional components.
[0045]
The operating state determining means 41 checks changes in the operating state of the engine (engine speed and engine load) based on signals from the rotation speed sensor 45 and the accelerator opening sensor 46 and the like. A determination is made as to which of the operating range A (including the low load operating range A ′) on the low load side and the high load side or the high speed side operating range B is included, and a change in the engine speed. Is determined to be less than or equal to a predetermined deceleration. Further, the engine load is low such that the accelerator load is fully closed, or the engine is in an operating state in which the engine speed exceeds a predetermined speed (excluding an extremely low speed region where the engine may be stopped). It is determined whether the vehicle is in the operation region C. Then, according to the determination result, any one of the special operation mode, the normal operation mode, and the fuel supply stop mode is selected as the operation mode of the engine (the details of each mode will be described later).
[0046]
Specifically, when the operation state of the engine is in the operation region A ′ (the rotation speed is r1 or less and the engine load is T2 or less) in FIG. 4 and is not in the operation region C described later (for example, the operation state D3), the special The operation mode is selected. The normal operation mode is selected in the operation region B (the rotation speed exceeds r1 and the engine load exceeds T1) and is not in the operation region C described later (for example, the operation state D1). In the operation region A (the rotation speed is r1 or less and the engine load is T1 or less) and the operation region is not the operation region A ′ (for example, the operation state D2), the special operation mode is selected in principle. When the operation mode has shifted from the operation mode to the operation region A and the deceleration of the engine is smaller than a predetermined value, the normal operation mode is continued. However, even in such a case, the mode is switched to the special operation mode when shifting to the operation region A '.
[0047]
The operation region C (the region where the engine speed is r3 or more and less than r4 and the engine load is T3 or less and the region where the engine speed is r4 or more) overlaps with either the operation region A or the operation region B. I have. In any case, when the operation state of the engine is in the operation region C, the fuel supply stop mode (hereinafter, referred to as the fuel cut mode) is preferentially selected.
[0048]
The valve stop mechanism control means 42 controls each valve stop mechanism 35 as follows by controlling the control valves 37 and 39 according to the selected operation mode.
Special operation mode: the first exhaust valve 32a and the first intake valve 31a are stopped.
Operate the second exhaust valve 32b and the second intake valve 31b
Normal operation mode: operating the first exhaust valve 32a and the first intake valve 31a
The second exhaust valve 32b and the second intake valve 31b are stopped.
Fuel cut mode: Same as special operation mode in operation area A
In operation area B, same as normal operation mode
[0049]
That is, in the normal operation mode, each cylinder is made to be in an independent state and combustion is performed for each cylinder. In the special operation mode, the preceding cylinder (the first and fourth cylinders 2A and 2D) and the subsequent cylinder (the second and third cylinders) are used. 2B, 2C) via the inter-cylinder gas passage 22 so that the burned gas discharged from the preceding cylinder is directly introduced into the succeeding cylinder in the intake stroke for combustion. Has become. Further, in the fuel cut mode, the two cylinders are connected in a region overlapping with the operation region A as in the special operation mode, and in the region overlapping with the operation region B, each cylinder is set in the independent state as in the normal operation mode (however, In the fuel cut mode, the supply of fuel is stopped, so that combustion is not performed in any case). As described above, the operation state determination unit 41 and the valve stop mechanism control unit 42 function as mode switching units.
[0050]
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. In particular, in the special operation mode, in a state in which the intake of the succeeding cylinders (the second and third cylinders 2B and 2C) from the branch intake passage 16 is blocked, excess air in the gas introduced from the preceding cylinder is burned. As a result, the amount of air necessary to burn fuel corresponding to two cylinders, the leading cylinder and the trailing cylinder, is supplied to the leading cylinders (the first and fourth cylinders 2A and 2D). Adjust the throttle opening.
[0051]
The fuel injection control means 44 controls the fuel injection amount and the injection timing from the fuel injection valve 9 provided in each of the cylinders 2A to 2D according to the operation state of the engine. The control state of the fuel injection is changed depending on which of the fuel cut modes is selected. The fuel injection control means 44 and the operating state determination means 41 constitute an air-fuel ratio control means of the present invention.
[0052]
That is, when the special operation mode is selected, for the preceding cylinders (the first and fourth cylinders 2A and 2D), the air-fuel ratio is set to a lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio, and preferably approximately the stoichiometric air-fuel ratio. The fuel injection amount is controlled so as to be twice or more, and the injection timing is set so that the fuel is injected in the compression stroke to perform stratified combustion. On the other hand, for the succeeding cylinders (the second and third cylinders 2B and 2C), fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the preceding cylinder and the fuel injection amount is adjusted so as to obtain the stoichiometric air-fuel ratio. In addition to the control, the injection timing is set so that ignition and combustion can be performed in a situation where there is a large amount of burned gas. For example, fuel is injected in a compression stroke to ensure ignitability.
[0053]
The fuel injection amount is controlled by the air flow sensor 19 and the O ₂ This is performed by feedback control based on the output from the sensor 23 and the like. Specifically, the basic injection amount for each cylinder is calculated in accordance with the intake air amount detected by the airflow sensor 19 so that the preceding cylinder has a predetermined lean air-fuel ratio and the subsequent cylinder has a stoichiometric air-fuel ratio. , A linear O provided in the inter-cylinder gas passage 22 ₂ The fuel injection amount for the preceding cylinder is feedback-corrected based on the output from the sensor 25, ₂ The fuel injection amount for the subsequent cylinder is feedback-corrected based on the output from the sensor 23.
[0054]
When the normal operation mode is selected, the fuel injection amount is controlled so that the air-fuel ratio of each of the cylinders 2A to 2D is equal to or lower than the stoichiometric air-fuel ratio. The air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio in the full-open load and the operating region in the vicinity thereof. In this case, the injection timing is set so that uniform combustion is performed by injecting fuel into each of the cylinders 2A to 2D in the intake stroke.
[0055]
When the fuel cut mode is selected, the fuel is not injected and its supply is stopped, so that no combustion is performed.
[0056]
The path determination means 51 is generated during the rotation of the crankshaft of the engine by a certain angle according to the change state of the intake air flow rate detected by the air flow sensor 19 and the engine speed detected by the speed sensor 45. The number of intake pulsations is detected, and based on the detected number of times, it is determined whether the intake and exhaust passages are in the above-described cylinder-independent state or in the two-cylinder connection state. In other words, in each cylinder independent state in which fresh air is introduced into each of the cylinders 2A to 2D, four intake pulsations occur during one rotation of the crankshaft of the engine, whereas only the preceding cylinders 2A and 2D In the two-cylinder connection state in which fresh air is introduced, only two intake pulsations are generated during one revolution of the engine crankshaft. Therefore, the number of times of detection of the intake pulsation is set to a predetermined reference number. By comparing with the above, it is determined whether the intake and exhaust passages are in the cylinder independent state or the two-cylinder connected state.
[0057]
The operation of the apparatus of the first embodiment as described above will be described with reference to FIGS.
[0058]
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 As shown in FIG. 6, the gas circulation route is such 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 to the subsequent cylinders (No. 2 and No. 3). The two-cylinder connection state is such that only the burned gas discharged from the following cylinders 2B and 2C is introduced into the exhaust passage 20 provided with the three-way catalyst 24 while being introduced into the cylinders 2B and 2C.
[0059]
In this state, fresh air is introduced into the preceding cylinders 2A and 2D from the intake passage 15 in the intake stroke, respectively (arrow a in FIG. 6), and the leading cylinders 2A and 2D have linear O. ₂ 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 predetermined lean air-fuel ratio, and ignition is performed at a predetermined ignition timing. Stratified combustion is performed (see FIG. 5).
[0060]
Thereafter, during a period in which the intake strokes of the preceding cylinders 2A, 2D and the exhaust strokes of the following cylinders 2B, 2C overlap, the burned gas discharged from the preceding cylinders 2A, 2D is introduced into the following cylinders 2B, 2C through the gas passage 22. (Open arrow in FIG. 5 and arrow b in FIG. 6). Then, in the succeeding cylinders 2B and 2C, the fuel is supplied to the burned gas having the lean air-fuel ratio introduced from the preceding cylinders 2A and 2D so that the burned gas reaches the stoichiometric air-fuel ratio. ₂ While the fuel injection amount is controlled based on the output of the sensor 23, fuel is injected at an appropriate timing (for example, a compression stroke), and ignition is performed at a predetermined ignition timing to perform combustion (see FIG. 5). The burned gas after combustion in the subsequent cylinders 2B and 2C is discharged to the exhaust passage 20 provided with the three-way catalyst 24 (arrow c in FIG. 6).
[0061]
Thus, in the preceding cylinders 2A and 2D, the stratified combustion at the lean air-fuel ratio is performed, so that the thermal efficiency is increased and the pumping loss is reduced, and the fuel efficiency is greatly improved by the synergistic effect of these. Further, in the subsequent cylinders 2B and 2C, fuel is supplied to the burned gas in an excess air state, and combustion is performed while being controlled to a stoichiometric air-fuel ratio, so that stratified combustion is performed at a lean air-fuel ratio as in the preceding cylinders 2A and 2D. Although the thermal efficiency is somewhat inferior to that performed, the effect of improving fuel efficiency by reducing the pumping loss can be sufficiently obtained.
[0062]
Moreover, since the burned gas discharged from the subsequent cylinders 2B and 2C to the exhaust passage 20 has a value corresponding to the stoichiometric air-fuel ratio, there is no need to provide a lean NOx catalyst unlike a conventional lean burn engine, and the three-way catalyst is not required. With only 24, exhaust purification performance is sufficiently ensured. Since there is no need to provide a lean NOx catalyst in this manner, there is no need to temporarily enrich the air-fuel ratio for NOx emission and reduction when the NOx storage amount of the lean NOx catalyst increases, thereby improving fuel efficiency. Can be avoided. Further, the problem of sulfur poisoning of the lean NOx catalyst does not occur.
[0063]
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. 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.
[0064]
The burned gas from the preceding cylinders 2A, 2D is introduced into the succeeding cylinders 2B, 2C via the inter-cylinder gas passage 22, and the amount of heat released in the inter-cylinder gas passage 22 varies according to the passage length. Therefore, by setting this passage length to an appropriate value, the temperature of the burned gas introduced into the subsequent cylinders 2B and 2C can be adjusted. By adjusting the temperature of the burned gas and the fuel injection timing to the subsequent cylinders 2B and 2C as described above, the ignition and the ignition can be performed in the subsequent cylinders 2B and 2C into which a large amount of burned gas is introduced. Good flammability can be maintained.
[0065]
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. The gas and gas circulation paths are as shown in FIG. 7. The intake ports 31, 31 a and the exhaust ports 12 a, 12 of each of the cylinders 2 A to 2 D are substantially independent, and the intake air of each of the cylinders 2 A to 2 D from the intake passage 15. Fresh air is introduced into the ports 31 and 31a, and burned gas is discharged from the exhaust ports 31 and 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 that the stoichiometric air-fuel ratio or the rich air-fuel ratio (λ ≦ 1) is obtained.
[0066]
Switching between the special operation mode and the normal operation mode is, as described above, in principle, the special operation mode is selected in the operation region A (excluding the operation region C), and the normal operation mode is selected in the operation region B (except the operation region C). Is selected. However, when shifting from the normal operation mode to the operation region A and when the deceleration of the engine is smaller than a predetermined value, the normal operation mode is continued without switching to the special operation mode. Even in such a case, the mode is switched to the special operation mode when shifting to the operation area A '. Specifically, the mode is selected according to the flowchart shown in FIG.
[0067]
As shown in FIG. 8, when the mode selection flow starts, the operation state determination means 41 determines whether or not the operation region of the engine is in the operation region C in step S2. If “YES” is determined in the step S2, the process shifts to a step S4, and shifts to a control of a fuel cut mode (see FIG. 9, details will be described later). If NO is determined in the step S2, the process shifts to a step S10 to further determine an operating region of the engine. If it is determined in step S10 that the engine is in the operating region A, the process proceeds to step S12, and it is determined whether the engine is in the operating region A '. If NO is determined in step S12, the engine operating state is such that the engine speed is r1 or less and the engine load exceeds T2 and T1 or less (for example, operating state D2), as shown in FIG. Means In that case, the process further proceeds to step S14 in FIG. 8 to determine the current operation mode. When it is determined in step S14 that the operation mode is the normal operation mode, it means that the operation mode is the normal operation mode even in the operation region A. This indicates a case where the operation state has shifted from the operation state (for example, the operation state D1) in the operation area B of FIG. 4 and the state has not yet been switched to the special operation mode. In that case, the process further proceeds to step S16 in FIG. 8, and it is determined whether or not the deceleration of the engine exceeds a predetermined value α. If YES is determined in the step S16, the process shifts to a step S18 to control the special operation mode and return. If NO is determined in step S16, it indicates that the deceleration of the engine is in a slow deceleration state equal to or less than the predetermined value α. In such a case, even in the operation region A, the special operation mode is not set, the process proceeds to step S20, the control in the normal operation mode is continued, and the process returns. Backward, when YES is determined in step S12, and when it is determined in step S14 that the current state is the special operation mode, the process proceeds to step S18 to control the special operation mode and returns. If it is determined in step S10 that the operation region of the engine is the operation region B, the process proceeds to step S20 to control the normal operation mode and returns.
[0068]
By the way, as shown in FIG. 4, the operating regions A, A ', B and C are divided by engine speed = r1, r3 or r4 straight lines and engine load = T1, T2 or T3 straight lines. It is. That is, the engine speeds r1, r3 and r4 and the engine loads T1, T2 and T3 are threshold values for switching the operation mode. In the present embodiment, the threshold value for the engine load for switching from the normal operation mode to the special operation mode is T2 at the time of slow deceleration, and is T1 at a higher load than T2 except at the time of slow deceleration (except for the special operation mode). The threshold value for the engine load for switching from the normal operation mode to the normal operation mode is constant at T1).
[0069]
When shifting from the normal operation mode to the special operation mode, a torque shock occurs (see FIG. 11; details will be described later). This torque shock is generated when the vehicle is slowly decelerated (the engine deceleration is small) and the load is relatively high. There is a characteristic that it is easy to feel at times, and it is difficult to feel at the time of rapid deceleration (large deceleration of the engine) or at a relatively low load even during slow deceleration. Therefore, if the threshold for switching from the normal operation mode to the special operation mode at the time of slow deceleration is set to a lower load side than at the time of rapid deceleration as described above, the mode switching is performed in an operating state in which a torque shock is hardly felt. Therefore, even without taking measures such as increasing the fuel supply to increase the torque and mitigating the torque shock, it is possible to make it practically difficult to feel the torque shock, and to suppress the increase in fuel consumption while reducing the torque shock. It is possible to effectively prevent the passenger from feeling uncomfortable.
[0070]
FIG. 9 is a flowchart of the control in the fuel cut mode. After the start, in step S30, the operating state is determined by the operating state determining means 41. If it is determined that the operating area is the operating area A, the process proceeds to step S32, where the circulation route is set to the same two-cylinder connection as in the special operating mode. State. Thereafter, the flow shifts to step S36 to stop the supply of the fuel and returns. If it is determined in step S30 that the operating range is the operating region B, the process proceeds to step S34, and the distribution path is set to the individual cylinder independent state as in the normal operation mode. Thereafter, the flow shifts to step S36 to stop the supply of the fuel and returns.
[0071]
In this manner, in the fuel cut mode and an operation state in which the operation area of the engine overlaps with the operation area A (for example, the operation state D4 in FIG. 4), the fuel supply is stopped, but the fuel supply is stopped. The route is in the same two-cylinder connection state as in the special operation mode. Therefore, when the engine load increases from this state and the fuel cut mode is canceled (for example, when the operating state becomes D3), the fuel supply is restarted without switching the circulation path by the valve stop mechanism control means 42. It is possible to quickly switch to the special operation mode simply by doing.
[0072]
Further, in the present embodiment, when shifting from the normal operation mode to the special operation mode, the air-fuel ratio correction control by the fuel injection control means 44 may be added.
In the air-fuel ratio correction control, when shifting from the normal operation mode to the special operation mode, after the shift (after mode switching), the torque generated by the preceding cylinder that first enters the combustion stroke is larger than the torque generated by the following cylinder with respect to the preceding cylinder. So that the air-fuel ratio of the preceding cylinder is smaller than twice the stoichiometric air-fuel ratio, and the fuel injection amount for each of the cylinders 2A to 2D is adjusted so that the air-fuel ratio of the following cylinder with respect to the preceding cylinder becomes the stoichiometric air-fuel ratio. Control.
[0073]
Specifically, for example, as shown in FIG. 10, when the mode switching signal is output at the end of the compression stroke of the fourth cylinder 2D ((1) in the figure), the intake and exhaust valves of the pair of cylinders are thereafter The valve stop mechanism control means 42 is switched at the time when the valve is closed. According to the example shown in the drawing, when the first cylinder 2A and the second cylinder 2B first enter the compression stroke and the expansion stroke, respectively ((2) in the figure), the first exhaust valves corresponding to the respective cylinders 2A and 2B. 32a and the first intake valve 31a are switched to a stopped state, the second exhaust valve 32b and the second intake valve 31b are switched to an activated state, and thereafter, the third cylinder 2C and the fourth cylinder 2D respectively perform a compression stroke, At the time of the expansion stroke ((3) in the figure), the first exhaust valve 32a and the first intake valve 31a corresponding to each of the cylinders 2C and 2D are switched to the stopped state, and the second exhaust valve 32b and the second intake valve The valve 31b is switched to the operating state. Then, when the completion of the switching from the normal operation mode to the special operation mode is determined by the path determination means 51 (at the point of {circle around (3)} in the figure), the cylinder that first enters the combustion stroke (the fourth cylinder in this example) 2D) so that the air-fuel ratio becomes λ <2 (where λ is the excess air ratio; the same applies hereinafter). ₁ ) Is controlled. Further, the fuel injection amount (F in the figure) is set such that the combustion of the succeeding cylinder (third cylinder 2C in this example) with respect to the preceding cylinder is performed at the stoichiometric air-fuel ratio. ₂ ) Is controlled. In the special operation mode in which the air-fuel ratio correction control is not performed, F ₁ Is controlled such that λ = 2, so that the air-fuel ratio correction control ₁ Is corrected to the rich side. And that much, F ₂ The fuel injection amount of the fourth cylinder 2D is reduced as compared with the normal special operation mode. ₁ Is generated by the combustion of the third cylinder 2C. ₂ Becomes larger than the torque generated by the combustion of.
[0074]
By controlling the air-fuel ratio of each of the cylinders 2A to 2D at the time of mode switching in this manner, torque shock (a phenomenon in which torque temporarily decreases) accompanying mode switching is effectively mitigated, and exhaust purification performance is also improved. Will be secured.
[0075]
That is, in the special operation mode, the throttle opening is controlled so as to supply air necessary for combustion of two cylinders of the preceding cylinder and the succeeding cylinder to the preceding cylinders (the first and fourth cylinders 2A and 2D). Therefore, the throttle opening is opened at the time of transition from the normal operation mode. At this time, a change in the intake air amount (referred to as an intake amount) of the preceding cylinder occurs due to a delay in the response of the operation of the throttle valve 17 and a delay in the change in the intake flow. 11 may have a response delay as shown in the uppermost part of FIG. On the other hand, the air-fuel ratio after switching to the special operation mode (shown at the second stage in FIG. 11) is controlled such that the excess air ratio λ in the preceding cylinder becomes λ = 2. Therefore, if no countermeasures are taken, the fuel supply amount is controlled to correspond to the intake air amount where the response delay has occurred as described above, and the fuel injection amount in the preceding cylinder immediately after the mode switching is changed to the third stage in FIG. As shown by the broken line in FIG. Along with this, the average torque of all cylinders sharply decreases as shown by the broken line at the bottom of FIG. (Torque shock occurs). On the other hand, immediately after the mode switching, if combustion is performed in a state where the air-fuel ratio is corrected to the rich side (shown by the second solid line in FIG. 11) for the preceding cylinder that first enters the combustion stroke as described above, The decrease in the fuel injection amount in the preceding cylinder is suppressed as shown by the solid line in the third row of FIG. On the other hand, the fuel injection amount is reduced in the succeeding cylinder by an amount corresponding to the correction to the rich side by increasing the fuel injection amount in the preceding cylinder, and as a result, combustion is performed at the stoichiometric air-fuel ratio (four stages in FIG. 11). (Shown by solid lines in the eye). Therefore, the generated torque in the preceding cylinder becomes larger than the generated torque in the succeeding cylinder, and the decrease in the average torque of all cylinders is suppressed as shown by the solid line at the bottom of FIG. As a result, the torque shock is effectively reduced. In addition, by controlling the combustion injection amount so that the air-fuel ratio in the subsequent cylinder becomes the stoichiometric air-fuel ratio, the exhaust gas purifying performance can be sufficiently ensured only by the three-way catalyst 24.
[0076]
When the torque shock is sufficiently reduced by the air-fuel ratio correction control, the operation region A ′ may be equal to the operation region A. That is, regardless of the deceleration of the engine, the special operation mode is always selected in the operation region A other than the operation region C. Correction control may be performed.
[0077]
Next, a second embodiment of the present invention will be described with reference to the drawings. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0078]
12 and 13 show a normal operation mode in which a plurality of cylinders 2 are provided and fuel is directly injected into each of the cylinders 2 to perform one combustion between an intake stroke and an exhaust stroke, and an intake stroke and an exhaust stroke. The combustion cycle is switched to a special operation mode in which combustion is performed twice during a stroke according to the operation state of the engine, and the oxygen concentration of the exhaust gas discharged to the exhaust passage 20 is reduced to a combustion state having a substantially stoichiometric air-fuel ratio. It is configured to control the amount of intake air introduced into each of the cylinders 2A to 2D in the intake stroke and the amount of fuel injection for performing the two combustions so as to have a corresponding value. 1 shows a control device of a spark ignition type engine in which a three-way catalyst 24 is provided.
[0079]
A pair of intake ports 11, 11 and exhaust ports 12, 12 are respectively opened to the combustion chamber 4 of each cylinder 2, and these ports 11, 11, 12, 12 are connected to intake valves 31, 31, exhaust valves 32, 32 is opened and closed. Each cylinder 2 performs combustion in a predetermined order with a predetermined phase difference, that is, a phase difference of 180 ° in crank angle.
[0080]
The intake / exhaust valves 31 and 32 are each configured to be driven by a valve operating mechanism 53. As shown in FIG. 13, the valve mechanism 53 is slidably disposed in a housing 54 made of a non-magnetic material and is integrally connected to the intake / exhaust valves 31 and 32. Armature core 55, and a pair of electromagnets 56, 57 and return springs 58, 59 disposed at both upper and lower ends in the housing 34. Then, the upper electromagnet 56 is energized to attract the armature core 55 upward, thereby opening the intake valve 31 and the exhaust valve 32 at a predetermined timing, respectively, and energizing the lower electromagnet 57 to energize the armature core 55. By suctioning 55 downward, the intake valve 31 and the exhaust valve 32 are each closed at a predetermined timing.
[0081]
An engine control ECU (control unit) 40 including a microcomputer or the like for controlling the valve operating mechanism 53 and the like has an airflow sensor 19 and an O ₂ A signal from the sensor 23 is input, and signals from a rotation speed sensor 45 for detecting an engine rotation speed and an accelerator opening sensor 46 for detecting an accelerator opening (accelerator pedal depression amount) for determining an operation state are also provided. Has been entered.
[0082]
The ECU 40 controls an operating state determining unit 41 for determining an operating state of the engine, a valve opening / closing control unit 60 for controlling the opening / closing timing of the intake valve 31 and the exhaust valve 32, and controls the amount of intake air to the combustion chamber 4 of the engine. And a fuel injection control means 44 for controlling a fuel injection state.
[0083]
The valve opening / closing control unit 60 functions as a mode switching unit together with the operation state determination unit 41 and the like, and is output to the valve mechanism 53 when the normal operation mode is selected and when the special operation mode is selected. The output timing of the control signal is changed to control the opening / closing timing of the intake valve 31 and the exhaust valve 32 as follows.
[0084]
In the normal operation mode, as shown in FIG. 14A, a normal operation mode including an intake stroke IN with fuel injection, a compression stroke with ignition S in the latter half, an expansion stroke with combustion, and an exhaust stroke EX. That is, the opening and closing timings of the intake valve 31 and the exhaust valve 32 are set so as to execute a general four-cycle combustion control for performing one-time uniform combustion between the intake stroke IN and the exhaust stroke EX. In FIG. 14, T is the top dead center of the piston stroke, and B is the bottom dead center.
[0085]
In the special operation mode, as shown in FIG. 14 (b), an intake stroke IN (first stroke), a first compression stroke (second stroke) involving fuel injection F and ignition S in a later period, and combustion are involved. And a first expansion stroke (third stroke) in which fuel injection F is performed in a later stage, a second compression stroke (ignition S) in the latter stage with ignition S (fourth stroke), a second expansion stroke with combustion (fifth stroke), The intake valve 31 and the exhaust valve are configured to execute a special operation mode including an exhaust stroke EX (sixth stroke), that is, six cycles of combustion control in which combustion is performed twice between the intake stroke IN and the exhaust stroke EX. 32 are set.
[0086]
The intake air amount control means 43 controls the opening degree of the throttle valve 17 (throttle opening degree) by controlling the actuator 18, and obtains a target intake air amount from a map or the like according to an operation state. The throttle opening is controlled in accordance with the target intake air amount. In particular, in the special operation mode mainly executed in the low-load / low-rotation-side operation region A, the burned gas concentration of the exhaust gas discharged into the exhaust passage 20 in the exhaust stroke EX after the two combustions is substantially reduced. The throttle opening is adjusted to a value corresponding to the combustion state of the stoichiometric air-fuel ratio. Further, in the normal operation mode mainly executed in the operation region B on the high load / high rotation side, the throttle opening is adjusted so that the air-fuel ratio in the cylinder 2 satisfies λ ≦ 1.
[0087]
The fuel injection control means 44 controls the fuel injection amount and the injection timing from the fuel injection valve 9 provided in each cylinder 2 according to the operating state of the engine. In particular, the fuel injection control means 44 switches between the special operation mode and the normal operation mode. The fuel injection control means changes the control state of the fuel injection. The fuel injection control means 44 and the operation state determination means 41 constitute an air-fuel ratio control means of the present invention.
[0088]
That is, in the special operation mode, as shown in FIG. 14B, the air-fuel ratio is larger than the stoichiometric air-fuel ratio so that the first combustion performed in the first expansion stroke (third stroke) is in a stratified combustion state. The fuel injection amount in the first compression stroke (second stroke) is set so that the lean air-fuel ratio is preferably approximately twice or more than the stoichiometric air-fuel ratio, and the timing of the fuel injection F is set. Further, by supplying the fuel into the burned gas having the lean air-fuel ratio generated by the first combustion (third stroke), the second expansion stroke (fifth stroke) is performed for the second time under the condition of the stoichiometric air-fuel ratio. The fuel injection amount is controlled so that combustion is performed, and the timing of fuel injection F is set so that ignition and combustion can be performed in a situation where there is a large amount of burned gas. For example, a first expansion stroke (third stroke) The fuel injection F is performed in the latter period. The fuel injection amount is controlled by the air flow sensor 19 and O ₂ This is performed by feedback control based on the output from the sensor 23 and the like.
[0089]
In the normal operation mode, the fuel injection amount is controlled so that the air-fuel ratio of each cylinder 2 is equal to or less than the stoichiometric air-fuel ratio. The fuel injection amount is controlled so as to be richer than the stoichiometric air-fuel ratio in the region.
[0090]
Note that the same control as in the first embodiment is performed for switching between the operation state and the operation mode of the engine. That is, the special operation mode is selected when the operation state of the engine is not in the operation area A ′ and the operation area C in FIG. The normal operation mode is selected in a state not in the operation region B and the operation region C. In the operation area A and the operation area A ', which is not the operation area A', the special operation mode is selected in principle. However, when the operation area is shifted from the operation area B to the operation area A and the engine deceleration is smaller than a predetermined value. , The normal operation mode is continued without switching to the special operation mode. However, even in such a case, the mode is switched to the special operation mode when shifting to the operation region A '. The operation region C overlaps with either the operation region A or the operation region B. In any case, when the operating state of the engine is in the operating region C, the fuel cut mode is preferentially selected.
[0091]
The path discriminating means 51 and the start-time discriminating means 52 are configured similarly to the path discriminating means 51 and the starting-time control means 52 of the embodiment shown in FIG. According to the detection signal output from the intake pulsation detecting means (air flow sensor 19) for detecting pulsation, the path discrimination is performed when the engine is started to determine whether the engine is in the control state of the normal operation mode or the special operation mode. If the determination is made by the means 51 and it is confirmed that the vehicle is in the control state of the special operation mode according to the determination result of the path determination means 51, the first combustion control at the time of starting the engine is performed for the first time. The starting time control means 52 is configured to execute control such as prohibiting ignition of the injected fuel.
[0092]
According to the above-described device of the second embodiment, in the special operation mode, two combustions are performed between the intake stroke and the exhaust stroke, and the first combustion performed in the first expansion stroke is performed at the lean air-fuel ratio. By being in the stratified combustion state, the thermal efficiency is enhanced and the pumping loss is reduced, and the fuel efficiency is greatly improved by the synergistic effect of these. In addition, by supplying fuel to the burned gas in an excess air state generated by the first combustion and controlling the stoichiometric air-fuel ratio to perform the second combustion in the second expansion stroke, a normal engine is used. Although the thermal efficiency is inferior to that in the case of stratified combustion at a lean air-fuel ratio as described above, the fuel efficiency can be obtained by reducing the pumping loss.
[0093]
Moreover, after the second combustion is performed, the concentration of the burned gas discharged into the exhaust passage 20 in the discharge stroke becomes a value corresponding to the stoichiometric air-fuel ratio. There is no need to provide a catalyst, and the three-way catalyst 24 alone ensures sufficient exhaust gas purification performance. Since there is no need to provide a lean NOx catalyst in this manner, there is no need to temporarily enrich the air-fuel ratio for the release and reduction of NOx when the NOx storage amount of the lean NOx catalyst increases, and the fuel consumption is reduced. Loss of improvement is avoided. Further, the problem of sulfur poisoning of the lean NOx catalyst does not occur.
[0094]
On the other hand, in the normal operation mode, the general four-cycle combustion control for performing one-time uniform combustion between the intake stroke IN and the exhaust stroke EX is executed as described above, and the air in each of the cylinders 2A to 2D is controlled. The output performance is ensured by controlling the intake air amount and the fuel injection amount so that the fuel ratio becomes λ ≦ 1.
[0095]
When the operation state of the engine is not in the operation region C, the switching between the special operation mode and the normal operation mode is performed in the same manner as in the first embodiment. The normal operation mode is selected. However, when the vehicle shifts from the operation region B (normal operation mode) to the operation region A and the deceleration of the engine is smaller than a predetermined value, the normal operation mode is continued without switching to the special operation mode. Even in such a case, the mode is switched to the special operation mode when shifting to the operation area A '. Specifically, the mode is selected according to the flowchart shown in FIG.
[0096]
Further, similarly to the first embodiment, the engine speeds r1, r3 and r4 and the engine loads T1, T2 and T3 shown in FIG. 4 are threshold values for switching the operation mode. Also in the present embodiment, the threshold value regarding the engine load for switching from the normal operation mode to the special operation mode is T2 at the time of slow deceleration, and is T1 which is higher than T2 except at the time of slow deceleration. By controlling in this way, it is possible to switch from the normal operation mode to the special operation mode in an operation state in which the torque shock is hardly felt, as in the first embodiment. Therefore, it is possible to effectively prevent the passenger from feeling uncomfortable due to the torque shock while suppressing an increase in fuel consumption.
[0097]
As in the first embodiment, the control in the fuel cut mode is the same as in the first embodiment. When the fuel supply mode is in the operation range A (for example, the operation state D4), the supply of fuel is stopped, but the supply and exhaust strokes are the same as in the special operation mode. State. Therefore, when the engine load increases from this state and the fuel supply stop mode is released (for example, when the operating state becomes D3), switching of the opening / closing timing of the intake valve 31 and the exhaust valve 32 by the valve opening / closing control means 60 is performed. It is possible to quickly switch to the special operation mode simply by restarting the fuel supply without performing the operation. Similarly, when in the operating region B, the supply of fuel is stopped, and the supply / exhaust stroke is set to the same state as in the normal operation mode.
[0098]
In the second embodiment, in the special operation mode, the intake stroke IN, the first compression stroke, the first expansion stroke with combustion, the second compression stroke, the second expansion stroke with combustion, and the exhaust stroke. By performing six cycles of combustion control consisting of the stroke EX, the combustion is performed twice between the intake stroke IN and the exhaust stroke EX (see FIG. 14B). As a modification, as shown in FIG. 14 (c), an intake stroke IN, a first compression stroke, a first expansion stroke with combustion, a second compression stroke, a second expansion stroke without combustion, By performing eight cycles of combustion control including three compression strokes, a third expansion stroke involving combustion, and an exhaust stroke EX, two combustions are performed between the intake stroke and the exhaust stroke. You may.
[0099]
【The invention's effect】
As described above, the control device according to the present invention includes the normal operation mode in which combustion is performed independently in each cylinder, and the existing operation in which the exhaust gas is discharged from the preceding cylinder in the exhaust stroke between a pair of cylinders in which the exhaust stroke and the intake stroke overlap. It is configured to be able to switch to a special operation mode in which fuel gas is directly introduced into a succeeding cylinder in an intake stroke to perform combustion.For example, in a low-load low-speed operation region, a special operation mode is set so that a preceding cylinder is set. In this case, combustion is performed at a lean air-fuel ratio, thereby improving thermal efficiency and reducing pumping loss, thereby achieving a significant fuel efficiency improvement effect.In the subsequent cylinder, the lean air-fuel ratio introduced from the preceding cylinder is already used. Fuel is supplied to the fuel gas and combustion is performed in a state where the stoichiometric air-fuel ratio is set, so that at least a fuel efficiency effect by reducing pumping loss can be obtained. . Further, only the burned gas having the stoichiometric air-fuel ratio discharged from the subsequent cylinder is guided to the exhaust passage, so that the exhaust gas purifying performance is sufficiently ensured only by the three-way catalyst. On the other hand, in the high load / high speed operation region, the output performance is ensured by setting the normal operation mode. In the transition from the normal operation mode to the special operation mode, the engine is switched to the special operation mode when the operation state of the engine is lower than the predetermined threshold value and the load is low, and the deceleration of the engine is set to the predetermined value. At the time of slow deceleration below the value, the threshold value is set to a lower load side, so that it is possible to effectively prevent the passenger from feeling uncomfortable due to torque shock while suppressing an increase in fuel consumption. .
[Brief description of the drawings]
FIG. 1 is a schematic plan view (first embodiment) of an entire engine including a control device according to 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. 4 is an explanatory diagram showing an operation area.
FIG. 5 is a diagram showing an exhaust stroke, an intake stroke, a fuel injection timing, an ignition timing, and the like of each cylinder.
FIG. 6 is an explanatory diagram showing a substantial fresh air and gas flow path at low load and low rotation.
FIG. 7 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. 8 is a flowchart for selecting a special operation mode, a normal operation mode, and a fuel cut mode.
FIG. 9 is a flowchart of control in a fuel cut mode.
FIG. 10 is a diagram showing an exhaust stroke, an intake stroke, a fuel injection timing, an ignition timing, and the like of each cylinder when shifting from the normal operation mode to the special operation mode.
FIG. 11 is a diagram showing changes in the intake air amount, the air-fuel ratio, the fuel injection amount, and the generated torque when shifting from the normal operation mode to the special operation mode.
FIG. 12 is a schematic plan view (second embodiment) of the entire engine including the control device according to the present invention.
FIG. 13 is a diagram illustrating a configuration of a valve train and a block configuration of a control system according to a second embodiment.
FIG. 14 is an explanatory diagram showing a combustion cycle of a cylinder, a fuel injection timing, an ignition timing, and the like in a second embodiment.
[Explanation of symbols]
1 Engine body
2A-2D cylinder
9 Fuel injection valve
11 Intake port
11a 1st intake port
11b Second intake port
12 Exhaust port
12a First exhaust port
12b Second exhaust port
15 Intake passage
20 Exhaust passage
22 Gas passage between cylinders
24 Three-way catalyst
31 Intake valve
31a First intake valve
31b Second intake valve
32 exhaust valve
32a first exhaust valve
32b second 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 Fuel injection control means
51 Route determination means

Claims

A cylinder independent state in which fresh air is introduced into each cylinder, and a two-cylinder connection state in which exhaust gas of a preceding cylinder is introduced into a succeeding cylinder via a gas passage between cylinders between a pair of cylinders where an exhaust stroke and an intake stroke overlap. A normal operation mode in which the flow paths of intake air and exhaust gas are switchable, and the flow paths are independent of each other and combustion is performed independently in each cylinder, and the preceding cylinder is connected to the two cylinders. A control device for a multi-cylinder spark ignition engine configured to be capable of switching an operation mode between a special operation mode in which burned gas discharged from the cylinder is directly introduced into a subsequent cylinder in an intake stroke to perform combustion, and ,
Mode switching means for switching an operation mode to the normal operation mode or the special operation mode according to an operation state of the engine;
In the special operation mode, combustion is performed in a state in which the preceding cylinder has a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and in the succeeding cylinder, the burned fuel having the lean air-fuel ratio derived from the preceding cylinder has been burned. While the fuel is supplied to the gas to perform combustion in a state where the stoichiometric air-fuel ratio is set, while in the normal operation mode, each cylinder is set to perform combustion in a state where the air-fuel ratio in each cylinder is set to the stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio at
The mode switching means is for switching to the special operation mode when the operating state of the engine in the normal operation mode is lower than the predetermined threshold value and the load is low, and the deceleration of the engine is a predetermined value. A controller for a spark ignition type engine, wherein the threshold value is further set to a lower load side during the following slow deceleration.

The air-fuel ratio control means has a fuel supply stop mode for stopping fuel supply at least when the engine operating state is in a predetermined low load range. 2. The air-fuel ratio control unit stops supplying fuel when the load is low and the rotation is lower than the threshold value, and the mode switching unit sets the circulation path to the two-cylinder connection state. Control system for spark ignition engines.

A cylinder independent state in which fresh air is introduced into each cylinder, and a two-cylinder connection state in which exhaust gas of a preceding cylinder is introduced into a succeeding cylinder via a gas passage between cylinders between a pair of cylinders where an exhaust stroke and an intake stroke overlap. A normal operation mode in which the flow paths of intake air and exhaust gas are switchable, and the flow paths are independent of each other and combustion is performed independently in each cylinder, and the preceding cylinder is connected to the two cylinders. A control device for a multi-cylinder spark ignition engine configured to be capable of switching an operation mode between a special operation mode in which burned gas discharged from the cylinder is directly introduced into a subsequent cylinder in an intake stroke to perform combustion, and ,
Mode switching means for switching an operation mode to the normal operation mode or the special operation mode according to an operation state of the engine;
In the special operation mode, combustion is performed in a state in which the preceding cylinder has a lean air-fuel ratio larger than the stoichiometric air-fuel ratio by a predetermined amount, and in the succeeding cylinder, the burned fuel having the lean air-fuel ratio derived from the preceding cylinder has been burned. While the fuel is supplied to the gas to perform combustion in a state where the stoichiometric air-fuel ratio is set, while in the normal operation mode, each cylinder is set to perform combustion in a state where the air-fuel ratio in each cylinder is set to the stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio at
The air-fuel ratio control means operates so that after the switching from the normal operation mode to the special operation mode, the torque generated by the preceding cylinder which first enters the combustion stroke becomes larger than the torque generated by the succeeding cylinder with respect to the preceding cylinder. A spark-ignition engine for controlling the air-fuel ratio of a cylinder to be smaller than twice the stoichiometric air-fuel ratio and performing air-fuel ratio correction control such that the air-fuel ratio of a subsequent cylinder with respect to the preceding cylinder becomes the stoichiometric air-fuel ratio. Control device.

4. The control apparatus according to claim 3, wherein the air-fuel ratio control means performs the air-fuel ratio correction control when the deceleration of the engine is gradually reduced to a predetermined value or less.

A normal operation mode in which fuel is directly injected into a combustion chamber and one combustion stroke is performed between an intake stroke and an exhaust stroke, and a special operation mode in which two combustion strokes are performed between an intake stroke and an exhaust stroke. A control device for a spark ignition engine configured to be capable of switching a combustion cycle to
Mode switching means for switching an operation mode to the normal operation mode or the special operation mode according to an operation state of the engine;
In the special operation mode, the combustion is performed in a state where the lean air-fuel ratio is larger than the stoichiometric air-fuel ratio by a predetermined amount in the previous combustion, and the burned lean air-fuel ratio due to the previous combustion is performed in the subsequent combustion. While the fuel is supplied to the gas to perform combustion in a state where the stoichiometric air-fuel ratio is set, while in the normal operation mode, each cylinder is set to perform combustion in a state where the air-fuel ratio in each cylinder is set to the stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio at
The mode switching means is for switching to the special operation mode when the operating state of the engine in the normal operation mode is lower than the predetermined threshold value and the load is low, and the deceleration of the engine is a predetermined value. A controller for a spark ignition type engine, wherein the threshold value is further set to a lower load side during the following slow deceleration.

The air-fuel ratio control means has a fuel supply stop mode for stopping supply of fuel when at least the operating state of the engine is in a predetermined deceleration range,
In the fuel supply stop mode, when the operating state of the engine is lower than the predetermined threshold value and the engine speed is lower than the predetermined threshold, the air-fuel ratio control means stops the supply of fuel, and the mode switching means is equivalent to the special operation mode. 6. The control device for a spark ignition type engine according to claim 5, wherein the supply / exhaust process is performed.