JP4328463B2 - In-cylinder injection internal combustion engine control device - Google Patents

In-cylinder injection internal combustion engine control device Download PDF

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JP4328463B2
JP4328463B2 JP2000397592A JP2000397592A JP4328463B2 JP 4328463 B2 JP4328463 B2 JP 4328463B2 JP 2000397592 A JP2000397592 A JP 2000397592A JP 2000397592 A JP2000397592 A JP 2000397592A JP 4328463 B2 JP4328463 B2 JP 4328463B2
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air
stroke injection
fuel ratio
injection mode
fuel
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JP2002195072A (en
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克則 上田
雅之 高垣
淳 青木
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Mitsubishi Motors Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Electrical Control Of Ignition Timing (AREA)
  • Exhaust-Gas Circulating Devices (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、気筒内に直接燃料を噴射する筒内噴射型内燃機関に関し、特に、圧縮行程噴射モードから吸気行程噴射モードへの切換時に空燃比を制御する、筒内噴射型内燃機関の制御装置に関する。
【０００２】
【従来の技術】
近年、気筒内に直接燃料を噴射する筒内噴射型内燃機関にかかる技術が開発されている。このような筒内噴射型内燃機関では、ストイキよりも希薄な空燃比によるリーン燃焼でアイドル運転している状態で外乱により回転速度が低下した場合、空燃比がリッチ化するように噴射量を増大することで燃焼トルクを増大させ、回転速度を回復する技術が知られている。圧縮行程噴射で超リーン燃焼の場合、特にこの効果は大きい。
【０００３】
また、圧縮行程噴射のリーン運転から吸気行程噴射のストイキ運転に切り換える場合、圧縮行程噴射のまま吸気量を減らしながら空燃比がリッチ化するように噴射量を変化させてその後に吸気行程噴射ストイキ運転に切り換えることで、トルクが急変しないようにする技法が知られている。
【０００４】
【発明が解決しようとする課題】
しかしながら、上記のように、筒内噴射型内燃機関において圧縮行程噴射のまま空燃比をリッチにしていくと、プラグ近傍の混合気濃度がオーバーリッチになり、くすぶり失火が発生してしまう。このため、圧縮行程噴射で空燃比をリッチにするにも限界がある。
【０００５】
したがって、アイドル時のトルク増大も制限されることになり、アイドル運転時における外乱等に対する回転速度の低下を十分に抑制することができないという課題や、圧縮行程噴射のリーン運転から吸気行程噴射のストイキ運転に切り換える場合に、トルクの急変防止対策を十分に行なえないという課題がある。
また、上記のような圧縮行程噴射のリーン運転から吸気行程噴射のストイキ運転への空燃比切換時には、ストイキよりもかなりリーンな空燃比で圧縮行程噴射を終了し、吸気行程噴射に切り換える必要があるため、吸気行程噴射切換時にリーン失火が起きやすいという課題がある。
【０００６】
ところで、特開平１０-６８３７５号公報には、圧縮行程噴射モードから吸気行程噴射モードへの切換時に、圧縮行程噴射モードのまま空燃比を徐々にリッチ化して所定の第１リーン空燃比にした後、吸気行程噴射モードに切り換えると同時に第１リーン空燃比よりリッチな所定の第２リーン空燃比に一気に切り換え、その後再び空燃比をリッチ化して吸気行程噴射モードに適した空燃比とすることで、トルクショックを抑制しながら燃料噴射モードの切り換えを行う技術が開示されている（特に、該公報の図３参照）。
【０００７】
ところが、この技術では、吸気行程噴射モードヘの切り換え直後は該モードに適した空燃比とはなっておらず、失火を生じやすいという問題がある。そこで、第２リーン空燃比をリッチ化することも考えられるが、そうすると十分なトルクショック抑制効果が得られなくなる。また、トルクショック抑制効果を高めるために第１リーン空燃比をリッチ化すれば第１リーン空燃比近傍で失火が生じやすくなる別の問題が発生する。このため、従来の手法では失火の防止とトルクショックの抑制を高次元で両立させることが困難であった。
【０００８】
本発明は、上述の課題に鑑み創案されたもので、圧縮行程噴射モードから吸気行程噴射モードへの切換時に、失火を招くことなくトルクショックを抑制することができるようにした、筒内噴射型内燃機関の制御装置を提供することを目的とする。
【０００９】
【課題を解決するための手段】
このため、本発明の筒内噴射型内燃機関の制御装置（請求項１）では、点火プラグと排ガスを還流するＥＧＲ装置とをそなえた内燃機関において、圧縮行程で燃料が噴射されリーン空燃比で運転されこれと共に上記ＥＧＲ装置を作動させる圧縮行程噴射モードと、吸気行程で燃料が噴射され上記圧縮行程噴射モードよりもリッチ側の空燃比で運転される吸気行程噴射モードとを、内燃機関の運転状態に応じて切換可能な筒内噴射型内燃機関において、上記内燃機関が、上記内燃機関のＥＧＲ率と空燃比とによって規定され失火率が０．１パーセント以下の安定燃焼領域を有する失火特性であって、上記圧縮行程噴射モードでの運転中における上記ＥＧＲ装置の作動によって定まる各々のＥＧＲ率では、燃料噴射時期を進角させると、上記安定燃焼領域が空燃比の低い側にシフトする失火特性を有している。そして、上記圧縮行程噴射モードから、吸気行程で燃料が噴射され上記圧縮行程噴射モードよりもリッチ側の空燃比で運転される吸気行程噴射モードに切り換える際に、制御手段が、上記圧縮行程噴射モードのまま燃料噴射時期を進角させると共に空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比とした後、吸気行程噴射モードに切り換えると同時に空燃比をストイキ近傍に切り換え、上記の空燃比を徐々にリッチ化していく過程でこれと並行して上記ＥＧＲ装置を制御しＥＧＲ率を徐々に減少させる。
そして、上記圧縮行程噴射モードから上記吸気行程噴射モードに切り換える際の上記燃料噴射時期の進角は、上記の徐々にリッチ化していく空燃比及び上記の徐々に減少されるＥＧＲ率の各値が上記失火特性における上記安定燃焼領域の中に保持されるように、空燃比のリッチ化に応じて徐々に行なわれる。
【００１０】
このように、圧縮行程噴射モードから吸気行程噴射モードに切り換える際に、吸気行程噴射モードに切り換えると同時にストイキ近傍の空燃比に切り換え、空燃比を徐々にリッチ化していく過程でこれと並行してＥＧＲ装置を制御しＥＧＲ率を徐々に減少させるので、ＥＧＲ率と空燃比とによって規定され失火率が０．１パーセント以下の安定燃焼領域を有する失火特性であって、圧縮行程噴射モードでの運転中におけるＥＧＲ装置の作動によって定まる各々のＥＧＲ率では、燃料噴射時期を進角させると、安定燃焼領域が空燃比の低い側にシフトする失火特性を有する内燃機関にあっては、吸気行程噴射モード切換時の失火を確実に防止できる。この場合、吸気行程噴射モードヘの切換前に圧縮行程噴射モードのまま燃料噴射時期を進角させると共に空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比とし、上記燃料噴射時期の進角は、上記の徐々にリッチ化していく空燃比及び上記の徐々に減少されるＥＧＲ率の各値が上記失火特性における上記安定燃焼領域の中に保持されるように、空燃比のリッチ化に応じて徐々に行なわれることにより、進角により圧縮行程噴射モードにおける安定燃焼領域をリッチ側に拡大することができ所定空燃比をよりリッチ側に設定できるので、失火を防止しながら吸気行程噴射モードとのトルク段差を効率良く低減することができる。このため、失火の防止とトルク段差の低減とを高次元で両立できる。
【００１１】
また、上記制御手段はアイドル運転時(実施例では吸気量小の時)に作動することが好ましい（請求項２）。これにより、機関のアイドル安定性を向上させる効果が大きくなる。
【００１２】
さらに、上記圧縮行程噴射モード時よりも上記吸気行程噴射モード時の方がＥＧＲ量を少なくするＥＧＲ制御手段と、上記の圧縮行程噴射モードから吸気行程噴射モードヘの切換時に上記点火プラグの点火時期を定常状態における吸気行程噴射モード時の点火時期よりも進角させる点火時期制御手段とを更に備えることが好ましい（請求項３）。
【００１３】
これにより、圧縮行程噴射モード時より吸気行程噴射モード時の方がＥＧＲ量が少ない場合、圧縮行程噴射モードから吸気行程噴射モードヘの切り換え直後は残留ＥＧＲの影響によって定常の吸気行程噴射モード時よりもＥＧＲ量が多い状況が過渡的に発生し失火が生じやすくなるのに対して、点火時期を定常状態における吸気行程噴射モードでの点火時期より進角させるので残留ＥＧＲの影響に起因した失火を効果的に抑制できるようになる。
【００１４】
上記点火時期制御手段は、上記進角後、定常状態の点火時期に向けて点火時期を徐々に遅角させることが好ましい。これにより、円滑に定常状態の吸気行程噴射モード運転状態に移行させることができ安定性をより向上できるようになる。
【００１５】
【発明の実施の形態】
以下、図面により、本発明の実施の形態について説明すると、図１〜図６は本発明の一実施形態としての筒内噴射型内燃機関の制御装置を示すものである。
図１は本実施形態の制御装置の構成を示すブロック図、図２は本実施形態にかかる筒内噴射型内燃機関の模式的な構成図、図３，図４は本実施形態にかかる失火特性を示す図、図５，図６は本実施形態にかかる制御内容を説明する図である。
【００１６】
本実施形態にかかる筒内噴射型内燃機関（筒内噴射エンジン，直噴ガソリンエンジン又は単にエンジンともいう）は、自動車に搭載され、図２に示すように構成されており、エンジン１のシリンダヘッド２には、各シリンダ３毎に点火プラグ４と燃焼室５内に直接開口する燃料噴射弁６とが設けられ、点火プラグ４は点火コイル４Ａにより燃料噴射弁６はドライバ６Ａによりそれぞれ駆動される。シリンダ３内には、クランクシャフト７に連結されたピストン８が装備され、このピストン８の頂面には半球状に窪んだキャビティ９が形成されている。
【００１７】
シリンダヘッド２には、吸気弁１０を介して燃焼室５と連通しうる吸気ポート１１と排気弁１２を介して燃焼室５と連通しうる排気ポート１３とが形成されている。吸気ポート１１は燃焼室５上方に略鉛直に配設され、ピストン８の頂面のキャビティ９と協働して燃焼室５内で吸気による逆タンブル流を形成させる。
また、シリンダ３外周のウォータジャケット１５には冷却水温を検出する水温センサ１６が設けられ、クランクシャフト７には所定のクランク角位置で信号を出力するクランク角センサ１７が、吸気弁１０，排気弁１２を駆動するカムシャフト１８，１９にはカムシャフト位置に応じた気筒識別信号を出力する気筒識別センサ（カム角センサ）２０が、それぞれ付設されている。クランク角信号に基づいてエンジン回転速度を算出できるので、クランク角センサ１７はエンジン回転速度検出手段としても機能する。
【００１８】
吸気系は、上流側からエアクリーナ２１，吸気管２２，スロットルボディ２３，サージタンク２４，吸気マニホールド２５の順に構成され、吸気マニホールド２５の下流端部に吸気ポート１１が設けられている。スロットルボディ２３には、燃焼室５内へ流入する空気量を調整する空気量調整手段としての電子制御式スロットル弁（ＥＴＶ）３０がそなえられ、このＥＴＶ３０の開度制御は、アクセル開度に応じた制御のみならず、アイドルスピード制御や、後述するリーン運転時の大量吸気導入の制御も行なえるようになっている。
【００１９】
さらに、エアクリーナ２１の直ぐ下流部分には吸入空気流量を検出するエアフローセンサ３７が、スロットルボディ２３にはＥＴＶ３０のスロットル開度を検出するスロットルポジションセンサ３８とＥＴＶ３０の全閉を検出してアイドル信号を出力するアイドルスイッチ３９とがそれぞれ設けられている。
排気系は、上流側から排気ポート１３を有する排気マニホールド２６，排気管２７の順に構成され、排気管２７には排ガス浄化用の三元触媒２９が介装され、排気マニホールド２６には、Ｏ2センサ４０が設けられている。
【００２０】
なお、燃料供給系については図示しないが、圧力が所定の高圧力〔数十気圧（例えば２〜７ＭＰａ）程度〕に調整された燃料が燃料噴射弁６に導かれ、燃料噴射弁６から高圧燃料が噴射されるようになっている。
また、アクセルペダルの踏込量（アクセル開度）θapを検出するアクセル開度センサ４２が設けられている。
【００２１】
そして、このエンジンには、排気系（ここでは排気ポート１３）から吸気系（ここではサージタンク２４の直上流部）に亘って排ガス還流通路（ＥＧＲ通路）５２と、ＥＧＲ通路５２に介装された排ガス還流弁（ＥＧＲバルブ）５３とからなる排ガス還流装置（ＥＧＲ装置）５１が設けられている。
点火プラグ４，燃料噴射弁６，ＥＴＶ３０，ＥＧＲバルブ５３といった各エンジン制御要素の作動を制御するために、内燃機関の制御手段としての機能を有する電子制御ユニット（ＥＣＵ）６０がそなえられている。このＥＣＵ６０には、入出力装置，制御プログラムや制御マップ等の記憶を行なう記憶装置，中央処理装置，タイマやカウンタ等がそなえられており、前述の種々のセンサ類からの検出情報やキースイッチの位置情報等に基づいて、このＥＣＵ６０が、上述の各エンジン制御要素の制御を行なうようになっている。
【００２２】
特に、本エンジンは、筒内噴射エンジンであり、燃料噴射を自由なタイミングで実施でき、吸気行程を中心とした燃料噴射によって均一混合させ均一燃焼を行なうほか、圧縮行程を中心とした燃料噴射によって前述の逆タンブル流を利用して層状燃焼を行なうことができる。本エンジンの運転モードとしては、Ｏ2センサ４０の検出情報に基づいたフィードバック制御により空燃比を理論空燃比近傍に保持するストイキ運転モードと、空燃比を理論空燃比よりもリッチにするエンリッチ運転モードと、空燃比を理論空燃比よりもリーンにして希薄燃焼させるリーン運転モードとが設けられている。
【００２３】
ＥＣＵ６０では、図示しないマップに基づいて、エンジン回転速度（以下、エンジン回転数という）Ｎｅ及びエンジン負荷状態を示す平均有効圧Ｐｅの目標値（目標Ｐｅ）に応じていずれかの運転モードを選択するようになっており、エンジン回転数Ｎｅが小さく目標Ｐｅも小さい状態では層状燃焼による超リーン運転モード（圧縮リーン運転モード）を選択し、エンジン回転数Ｎｅや目標Ｐｅが増加していくにつれて、均一燃焼によるリーン運転モード（吸気リーン運転モード），ストイキ，エンリッチの順に運転モードを選択していく。
【００２４】
なお、エンジン回転数Ｎｅはクランク角センサ１７の出力信号から算出され、目標Ｐｅはこのエンジン回転数Ｎｅとアクセル開度センサ４２で検出されたアクセル開度とから算出される。
また、ＥＣＵ６０では、ＥＧＲバルブ５３については電磁コイル５３ａを通じて開閉を制御するが、ＥＧＲバルブ５３は燃焼時にＮＯｘが生成され易い圧縮リーン運転モード時やストイキ運転モード時等の運転モード時に開放され、ＮＯｘが特に生成され易い圧縮リーン運転モード時には比較的大開度に、次いでＮＯｘが生成され易いストイキ運転モード時等の運転モード時に小開度に比較的開放され、その開度は、エンジン回転数Ｎｅや目標Ｐｅに応じて設定される。
【００２５】
ここで、このようなエンジン制御を行なう本実施形態のエンジンの制御装置について、図１を参照して説明する。
図１に示すように、ＥＣＵ６０には、上述のように、エンジン運転状態（Ｎｅ，Ｐｅ等）から燃焼モード（運転モード）を設定する燃焼モード設定手段６１と、燃焼モード設定手段６１の設定及びエンジン運転状態（Ｎｅ，Ｐｅ等）に基づいて空燃比Ａ／Ｆを設定する空燃比設定手段６２と、燃焼モード設定手段６１，空燃比設定手段６２の各設定及びエンジン運転状態（Ｎｅ，Ｐｅ等）に基づいて燃料噴射弁６，点火プラグ４，ＥＧＲ５３の作動を制御する燃料噴射弁制御手段６３，点火プラグ制御手段６４，ＥＧＲ制御手段６５といった各機能要素が備えられている。
【００２６】
また、エンジン回転数Ｎｅとアクセル開度センサ４２で検出されたアクセル開度θaccと目標Ｐｅを設定する目標Ｐｅ設定手段６７が備えられている。もちろん、これ以外に、ＥＴＶ３０を始めとした他の種々のエンジン制御要素を制御する機能も備えている。
特に、空燃比設定手段６２では、燃焼モード設定手段６１の設定に基づいて空燃比Ａ／Ｆを設定するが、ストイキ運転モード（Ｏ2フィードバックモード）では理論空燃比をＯ2センサ４０の出力に応じて補正して目標空燃比を設定するが、圧縮リーン運転モード，吸気リーン運転モード，エンリッチ運転モードのオープンループモードでは、エンジン回転数Ｎｅや目標Ｐｅに応じて目標空燃比を設定する。
【００２７】
そして、ＥＣＵ６０では、圧縮行程噴射モード（ここでは、圧縮リーン運転モード）から吸気行程噴射モード（ここでは、ストイキ運転モード）への運転モード切換時に、燃焼モード設定手段６１，空燃比設定手段６２，燃料噴射弁制御手段６３，点火プラグ制御手段６４，ＥＧＲ制御手段６５を通じて、次のような制御を行なうようになっている。
【００２８】
つまり、図５に示すように、まず、圧縮行程噴射モード（圧縮リーン運転モード）のままを保持して、燃料噴射時期を徐々に進角（或いは、所定の角度だけ進角）させるとともに、空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比として、この後、吸気行程噴射モードに切り換えると同時に空燃比をストイキ近傍に切り換える。また、このように空燃比を徐々にリッチ化していく過程で、これと並行して、ＥＧＲ弁６３を通じてＥＧＲ率（ＥＧＲ量）を徐々に減少させていく。
【００２９】
また、吸気行程噴射モード（ストイキ運転モード）に切り換えた直後は、点火時期を定常状態における吸気行程噴射モード時の点火時期よりも進角させるようにする。この場合、定常状態の点火時期に向けて点火時期を徐々に遅角させることで、円滑に定常状態の吸気行程噴射モード運転状態に移行させ、エンジン燃焼の安定性をより向上できるようにしている。
【００３０】
かかる切換に際して、圧縮行程噴射モードのままを保持して燃料噴射時期を徐々に進角（或いは、所定の角度だけ進角）させるのは、空燃比を徐々にリッチ化していく際に失火の発生を防止するためである。
つまり、通常、圧縮リーン運転モード（空燃比が２０程度以上）における燃料噴射時期（基準噴射時期）は最良燃費点近傍に設定されており、この基準噴射時期では、図３（ａ）に模様を付す範囲内に示すような領域内では略失火が起こらない（失火率０．１％以下）が、この領域を外れると失火率が許容限度以上（失火率０．１％より大）に高まる。したがって、ＥＧＲ率が極端に低下しない限り空燃比が２０程度よりもリッチになると失火率が許容限度以上に高まってしまう。前述のように、通常は圧縮リーン運転モードでは、ＥＧＲを大量導入するので、本来ＥＧＲ率は大きく、また、ＥＧＲ率については制御応答性が低いので、ＥＧＲ率を速やかに低下させることもできない。このため、圧縮行程噴射モードの状態で空燃比を徐々にリッチ化していくと失火を招きやすくなる。
【００３１】
一方、圧縮リーン運転モードにおける燃料噴射時期を基準噴射時期よりも適当に進角させると（この例では５°ＣＡ）、図３（ｂ）に模様を付す範囲で示すように、失火にくい安定燃焼領域が空燃比の低い側にシフトする。したがって、燃料噴射時期を適当に進角させることにより、圧縮行程噴射モードの状態で空燃比を徐々にリッチ化していっても失火を招きにくくなる。
【００３２】
このため、圧縮行程噴射モード（圧縮リーン運転モード）を保持して燃料噴射時期を所定の角度だけ進角させて、この状態で空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比としても、失火を招きにくく、空燃比をよりリッチ化した上で、吸気行程噴射モードに切り換えると同時に空燃比をストイキ近傍に切り換えることにより、エンジンの出力トルクの変動をより低減することが可能になるのである。
【００３３】
また、吸気行程噴射モード（ストイキ運転モード）に切り換えた直後に、点火時期を定常状態における吸気行程噴射モード時の点火時期よりも進角させるようにするのも、失火の発生を防止するためである。
つまり、吸気行程噴射モードでは、空燃比とＥＧＲ率とに対する失火率特性は、図４に示すようになり、吸気行程噴射モードにおける通常のタイミング（圧縮上死点直前のタイミング）で点火を行なった場合、失火し難い安定燃焼領域（失火率０．１％以下）は、図４（ａ）に示すように極めて狭い領域になり、吸気行程噴射モードでは通常ＥＧＲ率が低くされるため失火は招かないが、圧縮行程噴射モード（圧縮リーン運転モード）から吸気行程噴射モード（ストイキ運転モード）に切り換わった直後は、ＥＧＲ率がすぐには低下しないので、失火を招きやすくなる。
【００３４】
これに対して、点火時期を適当に進角させる［ここでは、通常のタイミングよりも大きいＭＢＴ（minimum advance for best toruque）に設定］と、失火し難い安定燃焼領域（失火率０．１％以下）は、図４（ｂ）に示すように拡大し、ＥＧＲ率が比較的高くても失火は招き難くなる。もちろん、吸気行程噴射モード切り換わって時間がたてばＥＧＲ率は低下するので、点火時期は本来のもの［４（ａ）に示す場合のもの］に徐々に復帰させる。
【００３５】
さらに、圧縮行程噴射モードを保持して空燃比を徐々にリッチ化していく際に、これと並行して、ＥＧＲ弁６３を通じてＥＧＲ率を徐々に減少させていくのも、失火を回避しようとするものである。つまり、圧縮行程噴射モードの場合も吸気行程噴射モードの場合も、失火を回避するという観点からは、ＥＧＲ率は低いほうが良いが、排ガス浄化の観点からは、圧縮行程噴射モードではできるだけＥＧＲ率を確保したい。また、ＥＧＲ率は応答遅れから速やか大きく変更することはできない。これらを鑑み、圧縮行程噴射モード時を保持し空燃比を徐々にリッチ化していく際にＥＧＲ率を徐々に減少させるようにしているのである。
【００３６】
本発明の一実施形態としての筒内噴射型内燃機関は、上述のように構成されているので、圧縮行程噴射モードから吸気行程噴射モードに切り換える際の一例を図６に基づいて説明すると、まず、圧縮行程噴射モードを保持して、燃料噴射時期を基準噴射時期よりも所定量（例えば５°ＣＡ）だけ進角させるとともに（ステップＳ１）。空燃比Ａ／Ｆを徐々にリッチ化させていく（ステップＳ２）。この基準噴射時期の進角により、図７に示すように、失火にくい安定燃焼領域が破線で示す内部領域から実線で示す内部領域へと空燃比の低い側にシフトする。
【００３７】
また、空燃比Ａ／Ｆを徐々にリッチ化のとともに、ＥＧＲ率を徐々に低下させていく。これによって、運転状態は、図７に太実線で示すような経過を経る。途中、基準噴射時期の進角による安定燃焼領域の空燃比低側へのシフトによって、失火が回避される。
そして、空燃比Ａ／Ｆが適当に低下した段階（ここでは１９程度）で、吸気行程噴射モード（ストイキ運転モード）に一気に切り換える（図６，ステップＳ３）。これによって、運転状態は、図７に太破線で示すような経過を経る。この、吸気行程噴射モード（ストイキ運転モード）に切り換えた直後には、点火時期を定常状態における吸気行程噴射モード時の点火時期よりも進角（ここでは、ＭＢＴとする）させる（図６，ステップＳ４）。また、ＥＧＲ率は本来の値（微小値または０）に切り換える。その後は、点火時期は本来のものに徐々に復帰させる。
【００３８】
このようにすることで、圧縮行程噴射モードから吸気行程噴射モードに切り換える際に、進角により圧縮行程噴射モードにおける安定燃焼領域をリッチ側に拡大することができ所定空燃比をよりリッチ側に設定でき、失火を確実に防止しながら、吸気行程噴射モードとのトルク段差を小さくすることができて、失火の防止とトルク段差の低減を高次元で両立できるようになる。
【００３９】
また、圧縮行程噴射モードから吸気行程噴射モードヘの切り換え直後は残留ＥＧＲの影響によって定常の吸気行程噴射モード時よりもＥＧＲ量が多い状況が過渡的に発生し失火が生じやすくなるが、点火時期を定常状態における吸気行程噴射モードでの点火時期より進角させるので残留ＥＧＲの影響に起因した失火を効果的に抑制できるようになる効果もある。
【００４０】
なお、上述の実施形態は何れも一例であって、本発明はかかる実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で、上述の実施形態を種々変形して実施することができる。
【００４１】
【発明の効果】
以上詳述したように、請求項１記載の本発明の筒内噴射型内燃機関の制御装置によれば、圧縮行程で燃料が噴射されリーン空燃比で運転されこれと共に上記ＥＧＲ装置を作動させる圧縮行程噴射モードから吸気行程で燃料が噴射され圧縮行程噴射モードよりもリッチ側の空燃比で運転される吸気行程噴射モードに切り換える際に、吸気行程噴射モードに切り換えると同時にストイキ近傍の空燃比に切り換えるので、吸気行程噴射モード切換時の失火を確実に防止できる効果がある。つまり、吸気行程噴射モードヘの切換前に圧縮行程噴射モードのまま燃料噴射時期を進角させると共に空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比とし、上記燃料噴射時期の進角は、上記の徐々にリッチ化していく空燃比及び上記の徐々に減少されるＥＧＲ率の各値が上記失火特性における上記安定燃焼領域の中に保持されるように、空燃比のリッチ化に応じて徐々に行なわれることにより、進角により安定燃焼領域が空燃比の低い側（リッチ側）にシフトさせることができ所定空燃比をより低い側（リッチ側）に設定しても、失火を防止しながら吸気行程噴射モードとのトルク段差を効率良く低減することができる。このため、失火の防止とトルク段差の低減とを高次元で両立できる利点がある。
【００４２】
また、請求項３記載の本発明の筒内噴射型内燃機関の制御装置によれば、圧縮行程噴射モード時より吸気行程噴射モード時の方がＥＧＲ量が少ない場合、圧縮行程噴射モードから吸気行程噴射モードヘの切り換え直後は残留ＥＧＲの影響によって定常の吸気行程噴射モード時よりもＥＧＲ量が多い状況が過渡的に発生し失火が生じやすくなるのに対して、点火時期を定常状態における吸気行程噴射モードでの点火時期より進角させるので残留ＥＧＲの影響に起因した失火を効果的に抑制できるようになる効果がある。
【図面の簡単な説明】
【図１】本発明の一実施形態としての筒内噴射型内燃機関の制御装置の構成を示すブロック図である。
【図２】本発明の一実施形態にかかる筒内噴射型内燃機関の模式的な断面図である。
【図３】本発明の一実施形態にかかる筒内噴射型内燃機関の失火特性を示す図であり、（ａ）は制御装置による燃料噴射時期の進角を行なわない場合を示す図、（ａ）は制御装置による燃料噴射時期の進角を行なった場合を示す図である。
【図４】本発明の一実施形態にかかる筒内噴射型内燃機関の失火特性を示す図であり、（ａ）は制御装置による点火時期の進角を行なわない場合を示す図、（ａ）は制御装置による点火時期の進角を行なった場合を示す図である。
【図５】本発明の一実施形態にかかる制御装置の制御内容を説明するタイムチャートである。
【図６】本発明の一実施形態にかかる制御装置の制御内容を説明するフローチャートである。
【図７】本発明の一実施形態にかかる制御装置の制御内容を説明する図である。
【符号の説明】
４ 点火プラグ
６ 燃料噴射弁
５１ ＥＧＲ装置
６０ ＥＣＵ（制御手段）
６１ 燃焼モード設定手段
６２ 空燃比設定手段
６３ 燃料噴射弁制御手段
６４ 点火プラグ制御手段
６５ ＥＧＲ制御手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection internal combustion engine that injects fuel directly into a cylinder, and more particularly to a control device for a direct injection internal combustion engine that controls an air-fuel ratio when switching from a compression stroke injection mode to an intake stroke injection mode. About.
[0002]
[Prior art]
2. Description of the Related Art In recent years, techniques related to a direct injection internal combustion engine that injects fuel directly into a cylinder have been developed. In such an in-cylinder injection type internal combustion engine, when the rotational speed decreases due to disturbance while idling with lean combustion with an air-fuel ratio that is leaner than stoichiometric, the injection amount is increased so that the air-fuel ratio becomes richer. Thus, a technique for increasing the combustion torque and restoring the rotational speed is known. This effect is particularly significant in the case of super lean combustion with compression stroke injection.
[0003]
In addition, when switching from the lean operation of the compression stroke injection to the stoichiometric operation of the intake stroke injection, the injection amount is changed so that the air-fuel ratio becomes rich while reducing the intake amount while maintaining the compression stroke injection, and then the intake stroke injection stoichiometric operation. There is known a technique for preventing torque from changing suddenly by switching to.
[0004]
[Problems to be solved by the invention]
However, as described above, when the air-fuel ratio is made rich while the compression stroke injection is performed in the direct injection internal combustion engine, the mixture concentration near the plug becomes overrich, and smoldering misfire occurs. For this reason, there is a limit in making the air-fuel ratio rich by compression stroke injection.
[0005]
Accordingly, an increase in torque during idling is also limited, and a problem that the reduction in rotational speed due to disturbances during idling cannot be sufficiently suppressed, or a stoichiometry of the intake stroke injection from the lean operation of the compression stroke injection. When switching to operation, there is a problem that it is not possible to take sufficient measures to prevent sudden torque changes.
Further, when the air-fuel ratio is switched from the lean operation of the compression stroke injection to the stoichiometric operation of the intake stroke injection as described above, it is necessary to end the compression stroke injection at an air-fuel ratio that is considerably leaner than the stoichiometry and switch to the intake stroke injection. Therefore, there is a problem that lean misfire tends to occur at the time of intake stroke injection switching.
[0006]
By the way, in Japanese Patent Laid-Open No. 10-68375, after switching from the compression stroke injection mode to the intake stroke injection mode, the air-fuel ratio is gradually enriched to the predetermined first lean air-fuel ratio in the compression stroke injection mode. By switching to the intake stroke injection mode at the same time as switching to a predetermined second lean air / fuel ratio that is richer than the first lean air / fuel ratio, the air / fuel ratio is made rich again to obtain an air / fuel ratio suitable for the intake stroke injection mode. A technique for switching the fuel injection mode while suppressing torque shock is disclosed (particularly, see FIG. 3 of the publication).
[0007]
However, this technique has a problem that immediately after switching to the intake stroke injection mode, the air-fuel ratio is not suitable for the mode, and misfire is likely to occur. Therefore, it is conceivable to enrich the second lean air-fuel ratio, but in that case, a sufficient torque shock suppression effect cannot be obtained. In addition, if the first lean air-fuel ratio is enriched in order to enhance the torque shock suppression effect, another problem that misfire tends to occur near the first lean air-fuel ratio occurs. For this reason, it has been difficult to achieve both high-dimensional prevention of misfire and suppression of torque shock by the conventional method.
[0008]
The present invention has been devised in view of the above-described problems, and is capable of suppressing a torque shock without causing misfire when switching from the compression stroke injection mode to the intake stroke injection mode. An object of the present invention is to provide a control device for an internal combustion engine.
[0009]
[Means for Solving the Problems]
For this reason, in the control apparatus for a cylinder injection internal combustion engine of the present invention (Claim 1), in an internal combustion engine having an ignition plug and an EGR device that recirculates exhaust gas, fuel is injected in a compression stroke and a lean air-fuel ratio is achieved. The operation of the internal combustion engine includes a compression stroke injection mode in which the EGR device is operated together with this, and an intake stroke injection mode in which fuel is injected in the intake stroke and is operated at an air-fuel ratio richer than the compression stroke injection mode. In a direct injection internal combustion engine that can be switched according to a state, the internal combustion engine has a misfire characteristic having a stable combustion region that is defined by an EGR rate and an air-fuel ratio of the internal combustion engine and has a misfire rate of 0.1% or less. At each EGR rate determined by the operation of the EGR device during the operation in the compression stroke injection mode, if the fuel injection timing is advanced, the stable Baked region has a misfire characteristics to shift to a low air-fuel ratio side. Then, from the compression stroke injection mode, when switching to the intake stroke injection mode in which the fuel in the intake stroke is operated at an air-fuel ratio richer than injected the compression stroke injection mode, the control means, the compression stroke injection mode The fuel injection timing is advanced and the air-fuel ratio is gradually enriched to a predetermined air-fuel ratio that is leaner than the stoichiometric ratio, and at the same time, the air-fuel ratio is switched to the stoichiometric vicinity at the same time as switching to the intake stroke injection mode. In the process of gradually enriching, in parallel with this, the EGR device is controlled to gradually decrease the EGR rate.
The advance angle of the fuel injection timing when switching from the compression stroke injection mode to the intake stroke injection mode is determined by the values of the air-fuel ratio that gradually increases and the gradually decreased EGR rate. It is gradually performed according to the enrichment of the air-fuel ratio so as to be maintained in the stable combustion region in the misfire characteristic.
[0010]
In this way, when switching from the compression stroke injection mode to the intake stroke injection mode, simultaneously with the process of switching to the intake stroke injection mode and simultaneously switching to the air-fuel ratio near the stoichiometric and gradually enriching the air-fuel ratio. gradually reducing the EGR rate by controlling the EGR device Runode, EGR rate and air-fuel ratio and the prescribed misfire rate a misfire characteristic with 0.1 percent or less stable combustion region, in the compression stroke injection mode At each EGR rate determined by the operation of the EGR device during operation, if the internal combustion engine has a misfire characteristic in which the stable combustion region shifts to a lower air-fuel ratio when the fuel injection timing is advanced, the intake stroke injection Misfires can be reliably prevented when switching modes. In this case, the fuel injection timing is advanced in the compression stroke injection mode before switching to the intake stroke injection mode, the air-fuel ratio is gradually enriched to a predetermined air-fuel ratio that is leaner than the stoichiometry, and the advance of the fuel injection timing is In accordance with the enrichment of the air-fuel ratio, the values of the gradually enriched air-fuel ratio and the gradually decreased EGR rate are maintained in the stable combustion region in the misfire characteristics. By performing gradually, the stable combustion region in the compression stroke injection mode can be expanded to the rich side by the advance angle, and the predetermined air-fuel ratio can be set to the rich side, so that the intake stroke injection mode and the intake stroke injection mode can be prevented while preventing misfire. The torque step can be reduced efficiently. For this reason, the prevention of misfire and the reduction of the torque step can be achieved at a high level.
[0011]
Also, it is preferable that the control means idling operation (in the embodiment when the intake air amount is small) operates (claim 2). As a result, the effect of improving the idle stability of the engine is increased.
[0012]
Further, the upper SL and EGR control means towards the compression stroke injection mode the intake stroke injection mode than when to decrease the EGR amount, the ignition timing of the spark plug upon switching of the intake stroke injection Modohe from the compression stroke injection mode It is preferable to further include ignition timing control means for advancing the ignition timing with respect to the ignition timing in the intake stroke injection mode in the steady state.
[0013]
As a result, when the EGR amount is smaller in the intake stroke injection mode than in the compression stroke injection mode, immediately after switching from the compression stroke injection mode to the intake stroke injection mode, the effect of the residual EGR is higher than in the steady intake stroke injection mode. While a situation with a large amount of EGR occurs transiently and misfire is likely to occur, the ignition timing is advanced from the ignition timing in the intake stroke injection mode in the steady state, so misfire due to the effect of residual EGR is effective Can be suppressed.
[0014]
Preferably, the ignition timing control means gradually retards the ignition timing toward the steady ignition timing after the advance. Thereby, it is possible to smoothly shift to the steady-state intake stroke injection mode operation state, and it is possible to further improve the stability.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1 to 6 show a control apparatus for a direct injection internal combustion engine as one embodiment of the present invention.
FIG. 1 is a block diagram showing the configuration of the control device of the present embodiment, FIG. 2 is a schematic configuration diagram of a direct injection internal combustion engine according to the present embodiment, and FIGS. 3 and 4 are misfire characteristics according to the present embodiment. FIG. 5 and FIG. 6 are diagrams for explaining the control contents according to the present embodiment.
[0016]
An in-cylinder injection internal combustion engine (also referred to as an in-cylinder injection engine, a direct injection gasoline engine, or simply an engine) according to the present embodiment is mounted on an automobile and configured as shown in FIG. 2, each cylinder 3 is provided with an ignition plug 4 and a fuel injection valve 6 that opens directly into the combustion chamber 5. The ignition plug 4 is driven by an ignition coil 4A and the fuel injection valve 6 is driven by a driver 6A. . A piston 8 connected to the crankshaft 7 is provided in the cylinder 3, and a cavity 9 recessed in a hemispherical shape is formed on the top surface of the piston 8.
[0017]
An intake port 11 that can communicate with the combustion chamber 5 via the intake valve 10 and an exhaust port 13 that can communicate with the combustion chamber 5 via the exhaust valve 12 are formed in the cylinder head 2. The intake port 11 is disposed substantially vertically above the combustion chamber 5 and forms a reverse tumble flow by intake air in the combustion chamber 5 in cooperation with the cavity 9 on the top surface of the piston 8.
A water temperature sensor 16 for detecting the cooling water temperature is provided on the water jacket 15 on the outer periphery of the cylinder 3, and a crank angle sensor 17 for outputting a signal at a predetermined crank angle position is provided on the crankshaft 7 with the intake valve 10 and the exhaust valve. A cylinder identification sensor (cam angle sensor) 20 that outputs a cylinder identification signal corresponding to the camshaft position is attached to each of the camshafts 18 and 19 that drive the cylinder 12. Since the engine speed can be calculated based on the crank angle signal, the crank angle sensor 17 also functions as an engine speed detecting means.
[0018]
The intake system is configured from the upstream side in the order of an air cleaner 21, an intake pipe 22, a throttle body 23, a surge tank 24, and an intake manifold 25, and an intake port 11 is provided at the downstream end of the intake manifold 25. The throttle body 23 is provided with an electronically controlled throttle valve (ETV) 30 as an air amount adjusting means for adjusting the air amount flowing into the combustion chamber 5, and the opening degree control of the ETV 30 is performed according to the accelerator opening degree. In addition to the above control, idle speed control and control of introducing a large amount of intake air during lean operation, which will be described later, can be performed.
[0019]
Further, an air flow sensor 37 for detecting the intake air flow rate is provided immediately downstream of the air cleaner 21, and a throttle position sensor 38 for detecting the throttle opening of the ETV 30 and a fully closed state of the ETV 30 are detected on the throttle body 23 to generate an idle signal. An idle switch 39 for outputting is provided.
The exhaust system includes an exhaust manifold 26 having an exhaust port 13 and an exhaust pipe 27 in this order from the upstream side. A three-way catalyst 29 for exhaust gas purification is interposed in the exhaust pipe 27, and an O 2 is connected to the exhaust manifold 26. A sensor 40 is provided.
[0020]
Although the fuel supply system is not shown, the fuel whose pressure is adjusted to a predetermined high pressure (several tens of atmospheres (for example, about 2 to 7 MPa)) is guided to the fuel injection valve 6, and the high pressure fuel is supplied from the fuel injection valve 6. Is to be injected.
Further, an accelerator opening sensor 42 for detecting an accelerator pedal depression amount (accelerator opening) θap is provided.
[0021]
The engine is interposed in an exhaust gas recirculation passage (EGR passage) 52 and an EGR passage 52 from the exhaust system (here, the exhaust port 13) to the intake system (here, immediately upstream of the surge tank 24). An exhaust gas recirculation device (EGR device) 51 including an exhaust gas recirculation valve (EGR valve) 53 is provided.
In order to control the operation of each engine control element such as the spark plug 4, the fuel injection valve 6, the ETV 30, and the EGR valve 53, an electronic control unit (ECU) 60 having a function as a control means of the internal combustion engine is provided. The ECU 60 includes an input / output device, a storage device for storing a control program, a control map, etc., a central processing unit, a timer, a counter, and the like. Based on the position information and the like, the ECU 60 controls the engine control elements described above.
[0022]
In particular, this engine is an in-cylinder injection engine. Fuel injection can be performed at any timing, and uniform mixing is performed by fuel injection centered on the intake stroke to perform uniform combustion, and fuel injection centered on the compression stroke. Stratified combustion can be performed using the above-described reverse tumble flow. As an operation mode of this engine, a stoichiometric operation mode in which the air-fuel ratio is maintained near the theoretical air-fuel ratio by feedback control based on detection information of the O 2 sensor 40, and an enrichment operation mode in which the air-fuel ratio is richer than the theoretical air-fuel ratio. And a lean operation mode in which lean combustion is performed with the air-fuel ratio leaner than the stoichiometric air-fuel ratio.
[0023]
The ECU 60 selects one of the operation modes according to an engine rotation speed (hereinafter referred to as engine rotation speed) Ne and a target value (target Pe) of the average effective pressure Pe indicating the engine load state based on a map (not shown). In the state where the engine speed Ne is small and the target Pe is small, the super lean operation mode (compressed lean operation mode) by the stratified combustion is selected, and as the engine speed Ne and the target Pe increase, they become uniform. The operation mode is selected in the order of lean operation mode by combustion (intake lean operation mode), stoichiometric, and enrichment.
[0024]
The engine speed Ne is calculated from the output signal of the crank angle sensor 17, and the target Pe is calculated from the engine speed Ne and the accelerator opening detected by the accelerator opening sensor 42.
The ECU 60 controls the opening and closing of the EGR valve 53 through the electromagnetic coil 53a. However, the EGR valve 53 is opened in an operation mode such as a compression lean operation mode or a stoichiometric operation mode in which NOx is easily generated during combustion. Is opened to a relatively large opening in the compression lean operation mode, which is particularly easy to generate, and then to a small opening in an operation mode such as a stoichiometric operation mode in which NOx is easily generated. It is set according to the target Pe.
[0025]
Here, the engine control apparatus of the present embodiment that performs such engine control will be described with reference to FIG.
As shown in FIG. 1, in the ECU 60, as described above, the combustion mode setting means 61 for setting the combustion mode (operation mode) from the engine operating state (Ne, Pe, etc.), the setting of the combustion mode setting means 61, and Air-fuel ratio setting means 62 for setting the air-fuel ratio A / F based on the engine operating state (Ne, Pe, etc.), each setting of the combustion mode setting means 61, the air-fuel ratio setting means 62, and the engine operating state (Ne, Pe, etc.) ), The fuel injection valve control means 63 for controlling the operation of the fuel injection valve 6, the spark plug 4, and the EGR 53, the spark plug control means 64, and the EGR control means 65 are provided.
[0026]
Further, target Pe setting means 67 for setting the engine speed Ne, the accelerator opening θ acc detected by the accelerator opening sensor 42 and the target Pe is provided. Of course, in addition to this, a function of controlling various other engine control elements such as the ETV 30 is also provided.
In particular, the air-fuel ratio setting means 62 sets the air-fuel ratio A / F based on the setting of the combustion mode setting means 61. In the stoichiometric operation mode (O 2 feedback mode), the stoichiometric air-fuel ratio is set to the output of the O 2 sensor 40. The target air-fuel ratio is corrected and set in accordance with the target air-fuel ratio. However, in the open loop mode of the compression lean operation mode, the intake lean operation mode, and the enrichment operation mode, the target air-fuel ratio is set according to the engine speed Ne and the target Pe.
[0027]
In the ECU 60, when the operation mode is switched from the compression stroke injection mode (here, the compression lean operation mode) to the intake stroke injection mode (here, the stoichiometric operation mode), the combustion mode setting means 61, the air-fuel ratio setting means 62, The following control is performed through the fuel injection valve control means 63, the spark plug control means 64, and the EGR control means 65.
[0028]
That is, as shown in FIG. 5, first, while maintaining the compression stroke injection mode (compression lean operation mode), the fuel injection timing is gradually advanced (or advanced by a predetermined angle), and the fuel injection timing is advanced. The fuel ratio is gradually enriched to obtain a predetermined air-fuel ratio that is leaner than the stoichiometric ratio. Thereafter, the air-fuel ratio is switched to the vicinity of the stoichiometric ratio at the same time as switching to the intake stroke injection mode. In the process of gradually enriching the air-fuel ratio, the EGR rate (EGR amount) is gradually decreased through the EGR valve 63 in parallel with this process.
[0029]
Immediately after switching to the intake stroke injection mode (stoichiometric operation mode), the ignition timing is advanced from the ignition timing in the intake stroke injection mode in the steady state. In this case, by gradually retarding the ignition timing toward the steady-state ignition timing, it is possible to smoothly shift to the steady-state intake stroke injection mode operation state and further improve the stability of engine combustion. .
[0030]
In such switching, the fuel injection timing is gradually advanced (or advanced by a predetermined angle) while maintaining the compression stroke injection mode, so that misfire occurs when the air-fuel ratio is gradually enriched. It is for preventing.
That is, normally, the fuel injection timing (reference injection timing) in the compression lean operation mode (the air-fuel ratio is about 20 or more) is set in the vicinity of the best fuel consumption point. At this reference injection timing, a pattern is shown in FIG. In the region shown in the attached range, almost no misfire occurs (misfire rate of 0.1% or less), but if it is outside this region, the misfire rate increases to an allowable limit or more (greater than misfire rate of 0.1%). Accordingly, if the air-fuel ratio becomes richer than about 20 unless the EGR rate is extremely lowered, the misfire rate increases beyond the allowable limit. As described above, normally, in the compression lean operation mode, since a large amount of EGR is introduced, the EGR rate is originally large, and the control response is low with respect to the EGR rate, so that the EGR rate cannot be quickly reduced. For this reason, if the air-fuel ratio is gradually enriched in the compression stroke injection mode, misfire is likely to occur.
[0031]
On the other hand, when the fuel injection timing in the compression lean operation mode is appropriately advanced from the reference injection timing (5 ° CA in this example), as shown in the range shown in FIG. The region shifts to the low air-fuel ratio side. Accordingly, by appropriately advancing the fuel injection timing, misfire is less likely to occur even if the air-fuel ratio is gradually enriched in the compression stroke injection mode.
[0032]
For this reason, the compression stroke injection mode (compression lean operation mode) is maintained, the fuel injection timing is advanced by a predetermined angle, and in this state, the air-fuel ratio is gradually enriched to obtain a predetermined air-fuel ratio that is leaner than the stoichiometry. The engine output torque fluctuations can be further reduced by switching to the intake stroke injection mode and simultaneously switching the air-fuel ratio to near the stoichiometric condition after making the air-fuel ratio richer and less likely to cause misfire. is there.
[0033]
In addition, immediately after switching to the intake stroke injection mode (stoichiometric operation mode), the ignition timing is advanced from the ignition timing in the intake stroke injection mode in the steady state in order to prevent the occurrence of misfire. is there.
That is, in the intake stroke injection mode, the misfire rate characteristic with respect to the air-fuel ratio and the EGR rate is as shown in FIG. 4, and ignition was performed at the normal timing (timing immediately before the compression top dead center) in the intake stroke injection mode. In this case, the stable combustion region (misfire rate of 0.1% or less) that is difficult to misfire becomes an extremely narrow region as shown in FIG. 4A, and the EGR rate is usually lowered in the intake stroke injection mode, so misfire does not occur. However, immediately after switching from the compression stroke injection mode (compression lean operation mode) to the intake stroke injection mode (stoichiometric operation mode), the EGR rate does not decrease immediately, and misfire is likely to occur.
[0034]
On the other hand, the ignition timing is appropriately advanced [here, set to a minimum advance for best toruque (MBT) larger than the normal timing], and a stable combustion region (misfire rate of 0.1% or less) that is difficult to misfire. ) Is enlarged as shown in FIG. 4B, and misfire is less likely to occur even if the EGR rate is relatively high. Of course, the EGR rate decreases with time after switching to the intake stroke injection mode, so that the ignition timing is gradually restored to the original timing (as shown in 4 (a)).
[0035]
Further, when the air-fuel ratio is gradually enriched while maintaining the compression stroke injection mode, the EGR rate is gradually decreased through the EGR valve 63 in parallel with this, in order to avoid misfire. Is. That is, in both the compression stroke injection mode and the intake stroke injection mode, the EGR rate should be low from the viewpoint of avoiding misfire, but from the viewpoint of exhaust gas purification, the EGR rate should be as low as possible in the compression stroke injection mode. I want to secure it. Also, the EGR rate cannot be changed quickly and greatly from the response delay. In view of these, the EGR rate is gradually decreased when the compression stroke injection mode is maintained and the air-fuel ratio is gradually enriched.
[0036]
Since the direct injection internal combustion engine as one embodiment of the present invention is configured as described above, an example of switching from the compression stroke injection mode to the intake stroke injection mode will be described with reference to FIG. Then, while maintaining the compression stroke injection mode, the fuel injection timing is advanced by a predetermined amount (for example, 5 ° CA) from the reference injection timing (step S1). The air-fuel ratio A / F is gradually enriched (step S2). Due to the advance of the reference injection timing, as shown in FIG. 7, the stable combustion region in which misfire is difficult is shifted from the internal region indicated by the broken line to the internal region indicated by the solid line to the low air-fuel ratio side.
[0037]
Further, the air-fuel ratio A / F is gradually enriched and the EGR rate is gradually decreased. As a result, the operating state goes through a process as shown by a thick solid line in FIG. In the middle, misfire is avoided by shifting the stable combustion region to the low side of the air-fuel ratio due to the advance of the reference injection timing.
Then, when the air-fuel ratio A / F is appropriately reduced (about 19 in this case), the air-fuel ratio A / F is switched to the intake stroke injection mode (stoichiometric operation mode) at once (FIG. 6, step S3). As a result, the operating state goes through a process as shown by a thick broken line in FIG. Immediately after switching to the intake stroke injection mode (stoichiometric operation mode), the ignition timing is advanced (here, MBT) from the ignition timing in the intake stroke injection mode in the steady state (FIG. 6, step). S4). The EGR rate is switched to the original value (small value or 0). Thereafter, the ignition timing is gradually returned to the original one.
[0038]
By doing this, when switching from the compression stroke injection mode to the intake stroke injection mode, the stable combustion region in the compression stroke injection mode can be expanded to the rich side by the advance angle, and the predetermined air-fuel ratio is set to the rich side Thus, it is possible to reduce the torque level difference from the intake stroke injection mode while reliably preventing misfire, and to achieve both high-dimensional prevention of misfire and reduction of the torque level.
[0039]
In addition, immediately after switching from the compression stroke injection mode to the intake stroke injection mode, a situation in which the EGR amount is larger than that in the steady intake stroke injection mode occurs transiently due to the influence of the residual EGR, and misfire is likely to occur. Since the ignition timing is advanced from the ignition timing in the intake stroke injection mode in the steady state, there is also an effect that misfire caused by the influence of the residual EGR can be effectively suppressed.
[0040]
In addition, all the above-mentioned embodiment is an example, Comprising: This invention is not limited to this embodiment, In the range which does not deviate from the meaning of this invention, it carries out various deformation | transformation of the above-mentioned embodiment. Can do.
[0041]
【The invention's effect】
As described above in detail, according to the control device for a direct injection internal combustion engine of the present invention, the compression is performed in which the fuel is injected in the compression stroke and operated at the lean air-fuel ratio, and the EGR device is operated together with the fuel. When switching from the stroke injection mode to the intake stroke injection mode in which fuel is injected in the intake stroke and operated at a richer air-fuel ratio than the compression stroke injection mode, the mode is switched to the intake stroke injection mode and simultaneously to the air-fuel ratio in the vicinity of the stoichiometry. Therefore, there is an effect that the misfire at the time of switching the intake stroke injection mode can be surely prevented. That is , the fuel injection timing is advanced in the compression stroke injection mode before switching to the intake stroke injection mode, and the air-fuel ratio is gradually enriched to a predetermined air-fuel ratio that is leaner than the stoichiometry. Gradually as the air-fuel ratio is enriched, the gradually enriched air-fuel ratio and the gradually decreased EGR rate are held in the stable combustion region in the misfire characteristics. As a result, the stable combustion region can be shifted to the low air-fuel ratio side (rich side) by advance, and even if the predetermined air-fuel ratio is set to the lower side (rich side ) , misfire is prevented. The torque step with the intake stroke injection mode can be efficiently reduced. For this reason, there is an advantage that both prevention of misfire and reduction of the torque step can be achieved at a high level.
[0042]
According to a third aspect of the present invention, there is provided a control device for a direct injection internal combustion engine according to the present invention, wherein when the EGR amount is smaller in the intake stroke injection mode than in the compression stroke injection mode, the intake stroke is changed from the compression stroke injection mode. Immediately after switching to the injection mode, a situation in which the EGR amount is larger than that in the steady intake stroke injection mode occurs transiently due to the effect of the residual EGR, and misfire is likely to occur. Since the ignition timing is advanced from the ignition timing in the mode, there is an effect that the misfire due to the influence of the residual EGR can be effectively suppressed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of a control device for a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 3 is a diagram showing misfire characteristics of a direct injection internal combustion engine according to an embodiment of the present invention, where (a) is a diagram showing a case where the fuel injection timing is not advanced by the control device; ) Is a diagram showing a case where the fuel injection timing is advanced by the control device.
4A and 4B are diagrams showing misfire characteristics of a direct injection internal combustion engine according to an embodiment of the present invention. FIG. 4A is a diagram showing a case where the ignition timing is not advanced by a control device. These are figures which show the case where the ignition timing is advanced by the control device.
FIG. 5 is a time chart for explaining the control content of the control device according to the embodiment of the present invention.
FIG. 6 is a flowchart illustrating the control content of the control device according to the embodiment of the present invention.
FIG. 7 is a diagram for explaining the control contents of the control device according to the embodiment of the present invention.
[Explanation of symbols]
4 Spark plug 6 Fuel injection valve 51 EGR device 60 ECU (control means)
61 Combustion mode setting means 62 Air-fuel ratio setting means 63 Fuel injection valve control means 64 Spark plug control means 65 EGR control means

Claims (3)

点火プラグと、排ガスを還流するＥＧＲ装置とをそなえ、圧縮行程で燃料が噴射されリーン空燃比で運転されこれと共に上記ＥＧＲ装置を作動させる圧縮行程噴射モードと、吸気行程で燃料が噴射され上記圧縮行程噴射モードよりもリッチ側の空燃比で運転される吸気行程噴射モードとを、内燃機関の運転状態に応じて切換可能な筒内噴射型内燃機関において、
上記内燃機関が、上記内燃機関のＥＧＲ率と空燃比とによって規定され失火率が０．１パーセント以下の安定燃焼領域を有する失火特性であって、上記圧縮行程噴射モードでの運転中における上記ＥＧＲ装置の作動によって定まる各々のＥＧＲ率では、燃料噴射時期を進角させると、上記安定燃焼領域が空燃比の低い側にシフトする失火特性を有し、
上記圧縮行程噴射モードから上記吸気行程噴射モードに切り換える際に、上記圧縮行程噴射モードのまま燃料噴射時期を進角させると共に空燃比を徐々にリッチ化してストイキよりリーンな所定空燃比とした後、吸気行程噴射モードに切り換えると同時に空燃比をストイキ近傍に切り換え、上記の空燃比を徐々にリッチ化していく過程でこれと並行して上記ＥＧＲ装置を制御しＥＧＲ率を徐々に減少させる制御手段を備え、
上記圧縮行程噴射モードから上記吸気行程噴射モードに切り換える際の上記燃料噴射時期の進角は、上記の徐々にリッチ化していく空燃比及び上記の徐々に減少されるＥＧＲ率の各値が上記失火特性における上記安定燃焼領域の中に保持されるように、空燃比のリッチ化に応じて徐々に行なわれる
ことを特徴とする、筒内噴射型内燃機関の制御装置。 A spark plug, and an EGR device for recirculating exhaust gas, which together with a compression stroke injection mode Ru actuates the EGR device is operated at a lean air-fuel ratio is injected fuel in the compression stroke, the fuel in the intake stroke is injected above In the in-cylinder injection internal combustion engine capable of switching between the intake stroke injection mode operated at an air-fuel ratio richer than the compression stroke injection mode according to the operating state of the internal combustion engine,
The internal combustion engine has a misfire characteristic having a stable combustion region defined by an EGR rate and an air-fuel ratio of the internal combustion engine and having a misfire rate of 0.1% or less, and the EGR during operation in the compression stroke injection mode At each EGR rate determined by the operation of the device, when the fuel injection timing is advanced, the stable combustion region has a misfire characteristic that shifts to a low air-fuel ratio side,
When switching from the compression stroke injection mode to the intake stroke injection mode, the fuel injection timing is advanced in the compression stroke injection mode and the air-fuel ratio is gradually enriched to a predetermined air-fuel ratio that is leaner than the stoichiometry. by switching to the intake stroke injection mode for switching the air-fuel ratio to near stoichiometric simultaneously, Ru gradually decrease the EGR rate to control the EGR device in parallel to this in the process of gradually enriching the air-fuel ratio of the With control means,
The advance angle of the fuel injection timing at the time of switching from the compression stroke injection mode to the intake stroke injection mode is such that each of the gradually increasing air-fuel ratio and the gradually decreasing EGR rate is the misfire. A control apparatus for a direct injection internal combustion engine, which is gradually performed in accordance with the enrichment of the air-fuel ratio so as to be maintained in the stable combustion region in the characteristics. 上記制御手段は、上記エンジンのアイドル運転時に作動する
ことを特徴とする、請求項１記載の筒内噴射型内燃機関の制御装置。2. The control apparatus for a direct injection internal combustion engine according to claim 1, wherein the control means operates during idle operation of the engine. 上記圧縮行程噴射モード時よりも上記吸気行程噴射モード時の方が上記ＥＧＲ率を少なくするＥＧＲ制御手段と、上記の圧縮行程噴射モードから吸気行程噴射モードヘの切換時に上記点火プラグの点火時期を定常状態における吸気行程噴射モード時の点火時期よりも進角させる点火時期制御手段とを更に備えた
ことを特徴とする、請求項１又は２記載の筒内噴射型内燃機関の制御装置。The upper Symbol EGR control means it is to reduce the EGR rate of the compression stroke injection mode the intake stroke injection mode than when the ignition timing of the spark plug upon switching of the intake stroke injection Modohe from the compression stroke injection mode 3. The control apparatus for a direct injection internal combustion engine according to claim 1, further comprising ignition timing control means for advancing the ignition timing in the intake stroke injection mode in a steady state.
JP2000397592A 2000-12-27 2000-12-27 In-cylinder injection internal combustion engine control device Expired - Fee Related JP4328463B2 (en)

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