JP4032650B2 - Combustion control device for internal combustion engine - Google Patents
Combustion control device for internal combustion engine Download PDFInfo
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- JP4032650B2 JP4032650B2 JP2001010668A JP2001010668A JP4032650B2 JP 4032650 B2 JP4032650 B2 JP 4032650B2 JP 2001010668 A JP2001010668 A JP 2001010668A JP 2001010668 A JP2001010668 A JP 2001010668A JP 4032650 B2 JP4032650 B2 JP 4032650B2
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B1/00—Engines characterised by fuel-air mixture compression
- F02B1/12—Engines characterised by fuel-air mixture compression with compression ignition
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/30—Controlling fuel injection
- F02D41/3011—Controlling fuel injection according to or using specific or several modes of combustion
- F02D41/3017—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used
- F02D41/3035—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the premixed charge compression-ignition mode
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/30—Controlling fuel injection
- F02D41/38—Controlling fuel injection of the high pressure type
- F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
- F02D41/402—Multiple injections
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/30—Controlling fuel injection
- F02D41/3011—Controlling fuel injection according to or using specific or several modes of combustion
- F02D41/3017—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used
- F02D41/3035—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the premixed charge compression-ignition mode
- F02D41/3041—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the premixed charge compression-ignition mode with means for triggering compression ignition, e.g. spark plug
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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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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Ignition Installations For Internal Combustion Engines (AREA)
- Combustion Methods Of Internal-Combustion Engines (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Combined Controls Of Internal Combustion Engines (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、内燃機関の燃焼制御装置に関し、詳しくは、圧縮自己着火燃焼運転における混合気の形成技術に関する。
【０００２】
【従来の技術】
従来から、圧縮自己着火燃焼を行わせる機関が知られている。
上記圧縮自己着火燃焼は、燃焼室の多点で燃焼が同時に開始されるために、燃焼速度が速く、通常の火花点火燃焼に比べて空燃比がリーンな状態でも安定した燃焼を実現することができ、燃料消費率を向上させることができると共に、リーン混合気を燃焼させることで燃焼温度が低下し、排気ガス中のＮＯｘを大幅に低減することができ、燃料と空気を十分に予混合しておけば、空燃比がより均一になって更にＮＯｘを低減することができる。
【０００３】
また、高回転・高負荷領域では通常の火花点火燃焼を行わせ、低回転・低中負荷領域では火花点火燃焼から圧縮自己着火燃焼に燃焼形態を切り替えることよって、高回転・高負荷時に高出力を確保しつつ、低回転・低中負荷時に燃料消費率の向上及びＮＯｘの低減化を図ることができる。
２サイクル型の火花点火式内燃機関では、部分負荷時における燃焼が不安定になることを回避すると共に、ＨＣ（未燃炭化水素）排出量の低減を図るために、燃焼室内における自己着火燃焼を積極的に利用した技術が提案されている。
【０００４】
例えば、特開平７−０７１２７９号公報には、低負荷時に排気通路の一部を遮断することによってシリンダ内の残留ガス濃度を高めることによって、圧縮行程開始時のシリンダ内圧や温度を高め、自己着火の燃焼時期を制御する技術が開示されている。
【０００５】
【発明が解決しようとする課題】
ところで、ガソリンのような自己着火性の低い燃料を用いて圧縮自己着火燃焼を行わせる場合、前記特開平７−０７１２７９号公報に開示されるように、残留ガスの持つ熱エネルギーを有効利用することが有効である。
そこで、４サイクル機関で圧縮自己着火燃焼を実現する方法として、特開平１０−２６６８７８号公報に開示されるように、排気行程から吸気行程に移行する際に、排気バルブと吸気バルブが共に閉となる密閉期間を設けることで残留ガスを積極的に生じさせ、圧縮行程開始時のシリンダ内圧や温度を高める方法があった。
【０００６】
しかしながら、残留ガス量を増加させると充填効率が低下するので、高負荷領域で圧縮自己着火燃焼を行わせることができず、圧縮自己着火燃焼を行える領域が低負荷側の狭い領域に限定され、燃費・エミッションの改善効果が小さくなってしまうという問題があった。
また、特開平１０−１９６４２４号公報には、予混合された混合気を圧縮する際に、上死点付近で追加となる燃料（着火油）の噴射を行い、着火油の燃焼による温度の上昇を利用して、予混合気を自己着火燃焼に至らしめる構成が開示されている。
【０００７】
上記のように追加の噴射を行わせる構成の場合、予混合気の空燃比がリーンとなった場合に着火性が悪化し、係る着火性の悪化を回避するためには、着火油の噴射量を増量する必要があり、着火油の燃焼によってＮＯｘが生成されてしまうという問題がある。
従来、火花点火燃焼において、局所的にリッチ混合気を生成する混合気の成層化を行い、着火性を改善する方法が考えられているが、成層化を行った場合には、リッチな領域からＮＯｘが多量に生成され、エミッションが悪化するという問題があった。
【０００８】
また、混合気中に規則的に燃料部と空気部を設けることで燃料の塊を無くし、エミッションを低減する技術が、特開平１０−２５２５７０号公報に開示されているが、混合気の濃度分布が規則的であるため、同じ濃度の混合気が一度に着火し、ノッキングを引き起こすという問題があった。
本発明は上記問題点に鑑みなされたものであり、圧縮自己着火式内燃機関において、ＮＯｘの排出量を増加させることなく、自己着火燃焼の着火安定性を確保できるようにすることを目的とする。
【０００９】
更に、圧縮自己着火燃焼運転を行える運転領域を拡大して、圧縮自己着火式内燃機関の燃費・排気を改善することを目的とする。
【００１０】
【課題を解決するための手段】
そのため、請求項１記載の発明では、圧縮自己着火燃焼運転時に、燃料を２回以上に分けて周期的に噴射する多重噴射によって、燃焼室内の混合気に不規則な濃度分布を与え、この不規則な濃度分布が与えられた混合気のうちのリッチ部分から圧縮自己着火燃焼を開始させると共に、機関回転速度が高く機関負荷が小さいときほど、前記多重噴射を行わせる期間を長くすることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくする構成とした。また、請求項２記載の発明では、機関回転速度が高く機関負荷が小さいときほど、前記多重噴射の噴射回数を多くすることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくする構成とし、請求項３記載の発明では、機関回転速度が高く機関負荷が小さいときほど、前記多重噴射の噴射開始時期を遅角させることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくする構成とした。
【００１２】
係る構成によると、燃焼室内の混合気が、均一な空燃比ではなく、かつ、成層化させた場合のようにリッチ領域とリーン領域とに規則的に区分される構成でもなく、不規則な濃度分布が与えられるように多重噴射によって混合気形成が行われ、形成された混合気の中のリッチな部分から圧縮自己着火燃焼を開始させる。そして、機関回転速度が高く機関負荷が小さいときほど、多重噴射を行わせる期間を長くし、噴射回数を多くし、また、噴射開始時期を遅角させることで、機関回転速度が高く機関負荷が小さいときほど、多重噴射で形成される混合気における最大空燃比と最小空燃比との差を大きくする。請求項４記載の発明では、前記多重噴射の開始時期を吸気行程中とする構成とした。
【００１４】
請求項５記載の発明では、前記多重噴射の後の上死点付近で追加の燃料噴射を行わせ、これにより燃料噴射弁直下の局所領域にリッチ混合気を形成し、前記局所的なリッチ混合気の火花点火燃焼又は圧縮自己着火燃焼により、前記不規則な濃度分布が与えられた混合気を圧縮自己着火燃焼に至らしめる構成とした。係る構成のよると、多重噴射の後の追加の燃料噴射により、燃料噴射弁直下の局所領域にリッチ混合気場を形成する混合気の成層化を行い、前記リッチ混合気を点火プラグによって火花点火燃焼させるか、圧縮自己着火燃焼させることで、周囲の不規則な濃度分布が与えられた混合気をそのリッチ部分から圧縮自己着火燃焼に至らしめる。
【００１５】
請求項６記載の発明では、機関の燃焼安定度及びノッキング強度を検出し、機関の燃焼安定度及びノッキング強度がそれぞれ許容範囲内になるように、前記多重噴射期間，噴射回数，噴射開始時期のいずれかを変更する構成とした。係る構成によると、機関の燃焼安定度（トルク変動）が許容範囲内で、かつ、ノッキング強度が許容範囲内となるように、前記多重噴射期間，噴射回数，噴射開始時期が変更される。
【００２０】
【発明の効果】
請求項１〜４記載の発明によると、不規則な濃度分布を有する混合気のリッチな部分から自己着火燃焼が開始するため、均一な空燃比の混合気が形成される場合に比べて混合気の自己着火性が良くなり、また、成層混合気を形成させる場合よりも最大空燃比と最小空燃比との差は小さいので、リッチ部の燃焼で発生するＮＯｘ及び煤が少なく、エミッションを悪化させることなく、圧縮自己着火燃焼の安定性を改善することができ、また、エミッションの悪化を抑制しつつ、負荷・回転の変化に対して圧縮自己着火燃焼の安定性を維持することができるという効果がある。
【００２１】
請求項５記載の発明によると、圧縮自己着火燃焼の時期を制御しつつ、エミッションの悪化がなく、高い安定性の圧縮自己着火燃焼を行わせることができるという効果がある。
【００２２】
請求項６記載の発明によると、運転条件の変化や機関ばらつきがあっても、ノッキング強度及び燃焼安定度を許容範囲内とした圧縮自己着火燃焼を行わせることができるという効果がある。
【００２４】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
図１は、本発明に係る内燃機関の燃焼制御装置を、ガソリン機関に適用した実施の形態の構成を示すシステム構成図である。
図１に示すガソリン機関１は、筒内直接噴射式ガソリン機関であって、運転条件に応じて圧縮自己着火燃焼と火花点火燃焼とが切り換えられる構成である。
【００２５】
この機関１において、シリンダ２内に連通する吸気ポート３には吸気バルブ４が介装され、同じくシリンダ２内に連通する排気ポート５には排気バルブ６が介装される。
前記シリンダヘッド７はペントルーフ型に形成され、前記吸気バルブ４及び排気バルブ６はＶ型に配置され、このペントルーフ型のシリンダヘッド７の略中央には、燃料噴射弁８及び点火プラグ９が配置される。
【００２６】
前記燃料噴射弁８による噴射量・噴射時期及び点火プラグ９による点火時期を制御するエンジンコントロールユニット（以下、ＥＣＵという）２０には、クランク角センサ１０からのクランク角センサ信号や、図示省略したアクセル開度センサからのアクセル開度信号などが入力される。
前記ＥＣＵ２０は、圧縮自己着火燃焼と火花点火燃焼とのいずれの燃焼方式で運転を行うかを運転条件に応じて判定する燃焼パターン判定部２１、火花点火燃焼時に前記燃料噴射弁８及び点火プラグ９を制御する火花点火燃焼制御部２２、圧縮自己着火燃焼時に前記燃料噴射弁８を制御する自己着火燃焼制御部２３によって構成される。
【００２７】
前記燃焼パターン判定部２１は、図２に示すように、機関負荷Ｔと機関回転速度Ｎに基づいて燃焼方式を判別する構成であり、低中負荷・低中回転領域を圧縮自己着火燃焼領域として判定し、それ以外の高負荷・高回転領域を火花点火燃焼領域と判定する。
また、圧縮自己着火燃焼時には、１サイクル中に燃料を２回以上に分けて周期的に噴射する多重噴射を行わせることで、燃焼室内の混合気に不規則な空燃比ばらつきを設ける構成となっており、前記自己着火燃焼制御部２３は、噴射回数制御部２４，噴射期間制御部２５及び噴射時期制御部２６を介して、前記多重噴射における噴射回数，噴射期間，噴射時期を制御する。
【００２８】
図３のフローチャートは、上記ハードウェア構成を用いた燃料噴射制御の第１実施形態を示すものである。
ステップＳ１１では、機関回転速度Ｎ及び機関負荷Ｔを検出する。
尚、本実施の形態では、クランク角センサ信号に基づいて機関回転速度Ｎが算出される一方、機関負荷Ｔをアクセル開度で代表させるものとする。
【００２９】
ステップＳ１２では、前記検出した機関回転速度Ｎ及び機関負荷Ｔに基づいて、現在の運転条件が圧縮自己着火燃焼領域であるか火花点火燃焼領域であるかを判別する（図２参照）。
ステップＳ１２で火花点火燃焼領域であると判別されたときには、ステップＳ１３へ進み、要求される量の燃料を吸気行程中に１回の噴射で供給して、予混合された均質混合気を形成し、次のステップＳ１４では、前記均質混合気を点火プラグ９による火花点火によって燃焼させる。
【００３０】
尚、火花点火燃焼領域においても、燃料を複数回に分けて噴射させても良いし、また、吸気行程中に限らず、成層混合気を形成するため、圧縮行程中に噴射しても良い。
一方、ステップＳ１２で圧縮自己着火燃焼領域であると判別されると、ステップＳ１５へ進み、１サイクル中に燃料を２回以上に分けて周期的に噴射する多重噴射におけるトータル噴射期間を設定する。
【００３１】
前記多重噴射とは、図４に示すように、休止期間を挟んで複数回の噴射を繰り返す噴射であり、前記トータル噴射期間とは、１回目の噴射開始から最後の噴射の終了までの期間である。
尚、上記多重噴射における各噴射の噴射時間（噴射パルス幅）を、図４では均一にしたが、それぞれに異なる噴射時間（噴射パルス幅）で噴射させる構成としても良いし、休止期間をそれぞれに異ならせても良い。
【００３２】
前記ステップＳ１５では、図５に示すように、予め機関回転速度Ｎ及び機関負荷Ｔに応じてトータル噴射期間を記憶したマップから、そのときの機関回転速度Ｎ及び機関負荷Ｔに対応するトータル噴射期間を検索して求める。
ここで、トータル噴射期間は、機関回転速度Ｎが高いほど、機関負荷Ｔが小さいときほど、より長く設定されるようになっており、図６に示すように、トータル噴射期間が長くなるほど、多重噴射で形成される混合気の空燃比（当量比）ばらつき（最大空燃比と最小空燃比との差）が大きくなる。
【００３３】
ステップＳ１６では、前記多重噴射において燃料を何回に分けて噴射するかを示す噴射回数を設定する。
上記噴射回数も、前記トータル噴射期間と同様に、予め機関回転速度Ｎ及び機関負荷Ｔに応じて噴射回数を記憶したマップ（図７参照）から、そのときの機関回転速度Ｎ及び機関負荷Ｔに対応する噴射回数を検索して求めるようになっており、噴射回数は、機関回転速度Ｎが高いほど、機関負荷Ｔが小さいときほど、より多く設定されるようになっている。
【００３４】
前記噴射回数を多くすると、図８に示すように、多重噴射で形成される混合気の空燃比（当量比）ばらつきが大きくなる。
尚、第１実施形態では、多重噴射の噴射時期（噴射開始時期）は、吸気行程中の所定時期に固定されるものとする。
ステップＳ１７では、要求噴射量（噴射時間）の噴射を、前記噴射回数に分けてトータル噴射期間で噴射させる多重噴射を、前記固定の噴射時期（噴射開始時期）に開始させ、該噴射で形成される混合気を上死点付近で圧縮自己着火燃焼させる。
【００３５】
前記多重噴射を行わせると、図９に示すように、燃焼室内の混合気に不規則な空燃比ばらつきが生じ、この不規則な空燃比ばらつきが与えられた混合気のうちのリッチ部分から圧縮自己着火燃焼が開始されることになる。
圧縮自己着火燃焼させる場合には、図１０に示すように、空燃比をリーン化させると燃焼安定性が悪化し、逆にリッチ化するとノッキング強度が増大し、燃焼安定性を許容範囲内にできるリーン限界空燃比ＡＦＬと、ノッキング強度を許容範囲内に抑制できるリッチ限界空燃比ＡＦＲとの間の狭い範囲に空燃比を制御する必要があり、特にリーン限界が狭いため圧縮自己着火燃焼領域の低負荷化を進めることが困難である。
【００３６】
尚、図１０では、ガスと燃料との割合を示す指標として空燃比を用いたが、残留ガス或いは還流排気ガスが含まれる場合についても同様の傾向を示し、この場合、横軸は、新気と既燃ガスを合わせたトータルガス量と燃料との割合となる。そこで、リーン化を進めつつ燃焼安定性を確保する方法として、燃焼室の一部にリッチな混合気を形成する混合気の成層化が考えられるが、リッチ混合気の燃焼によってＮＯｘ排出量が多くなってしまう。
【００３７】
これに対し、上記のように多重噴射によって不規則な空燃比のばらつきを生じさせる構成であれば、ＮＯｘ排出量の増大を抑制しつつ、空燃比のリーン化を進めて、圧縮自己着火燃焼領域を低負荷側に拡大することができる。
前記多重噴射を行わせると、前述のように、燃焼室内の混合気に不規則な空燃比ばらつきが生じるが（図９参照）、吸気行程で要求燃料量を１回で噴射させる場合（本実施形態における火花点火燃焼時の場合）には、図１１に示すように、燃焼室内に略均一な空燃比が形成され、また、圧縮行程で燃料を１回で噴射させることで点火プラグ９近傍の局所領域にリッチ混合気を形成させる混合気の成層化を行う場合には、図１２に示すように、燃焼室中心付近のリッチ混合気の周辺は、局所領域からの拡散によって極めてリーンな混合気が形成されることになる。
【００３８】
従って、吸気行程１回噴射（均質），多重噴射，圧縮行程噴射（成層）それぞれで形成される混合気における空燃比（当量比）の頻度分布は、図１３に示すようになり、多重噴射における空燃比（当量比）のばらつきは、吸気行程１回噴射よりも大きく、圧縮行程噴射よりも小さくなる。
一方、空燃比（当量比）のばらつきが大きくなるほど、図１４に示すように、リーン限界空燃比ＡＦＬ（平均空燃比のリーン限界）は燃焼安定性が改善されることからよりリーン化するが、ばらつきがある限界を超えると、リッチ限界空燃比ＡＦＲ（平均空燃比のリッチ限界）はリーン化してしまう。
【００３９】
図１５は、空燃比（当量比）のばらつきと自己着火燃焼の成立範囲との相関を示すものであり、空燃比のばらつきが大きくなると、自己着火燃焼の成立範囲はより低負荷側に拡大するが、空燃比のばらつきがあまり大きくなると、リッチ限界が低負荷化するため、成立範囲としては狭くなってしまう。
ここで、リッチ限界が急激に低負荷化する領域は、圧縮行程噴射により成層化した場合の空燃比ばらつき領域であり、成層化させる場合よりも小さい多重噴射による空燃比のばらつき領域では、リッチ限界を低負荷化させることなく、自己着火燃焼の成立範囲を低負荷側に拡大できる。
【００４０】
また、図１６は、空燃比（当量比）のばらつきとＨＣ・ＮＯｘ排出量との相関を示すものであり、空燃比ばらつきがあまり大きくなると、ＮＯｘ排出量が増加するが、ＮＯｘ排出量が増加傾向を示す空燃比ばらつき領域よりも小さい領域では、ＨＣ排出量・ＮＯｘ排出量は共に変化しない。
上記の図１５，１６に示すように、成層化すると圧縮自己着火燃焼の成立範囲を低負荷化できるもののＮＯｘ排出量が増大する。
【００４１】
これに対し、不規則な空燃比ばらつきを設定した場合には、ＮＯｘ排出量を増大させることなく、圧縮自己着火燃焼の成立範囲を低負荷化でき、本実施形態では、多重噴射によって混合気に不規則な空燃比のばらつきを設定して圧縮自己着火燃焼を行わせることで、均質混合気による自己着火燃焼では成立範囲とならない低負荷側を圧縮自己着火燃焼領域に含め、かつ、ＮＯｘ排出量の増大を回避できるようにしている。
【００４２】
更に、上記の実施形態では、多重噴射によって混合気に与える空燃比のばらつきの大きさを、噴射回数及びトータル噴射期間によって制御している。
圧縮自己着火燃焼における着火性は、機関回転速度が高いほど、機関負荷が低いほど悪化する傾向を示す一方、空燃比ばらつきが大きくなるほど、燃焼安定性が良くなる。
【００４３】
また、多重噴射における噴射回数が多いほど、多重噴射におけるトータル噴射期間が長くなるほど、空燃比ばらつきは大きくなる（図６，８参照）。
そこで、本実施形態では、前述のように、機関回転速度が高いほど、機関負荷が低いほど、噴射回数を多くし、また、トータル噴射期間を長くするようにしてある。
【００４４】
尚、噴射回数とトータル噴射期間とのいずれか一方を固定とし、他方を機関回転速度及び機関負荷に応じて変化させる構成としても良い。
ところで、上記第１実施形態では、多重噴射の噴射開始時期を固定として、噴射回数及びトータル噴射期間で空燃比ばらつきを制御する構成としたが、多重噴射の噴射開始時期を制御することで、空燃比ばらつきを制御する構成としても良く、係る構成とした第２の実施形態を、図１７のフローチャートに従って説明する。
【００４５】
図１７のフローチャートは、ステップＳ２６における噴射回数の設定に続けて、ステップＳ２７で噴射時期（噴射開始時期）の設定を行い、ステップＳ２８では、設定されたトータル噴射期間及び噴射回数の多重噴射を、ステップＳ２７で設定された開始時期において開始させる。
尚、上記に示した以外の各ステップは、図３のフローチャートと同様な処理を行うので説明を省略する。
【００４６】
前記ステップＳ２７では、図１８に示すように、機関回転速度が高いほど、機関負荷が低いほど、多重噴射の噴射開始時期をより遅角させる設定を行う。これは、機関回転速度が高いほど、また、機関負荷が低いほど着火性が悪化する一方、図１９に示すように、多重噴射の噴射開始時期を遅角するほど空燃比（当量比）のばらつきが大きくなって着火安定性が改善されるためである。
【００４７】
尚、噴射開始時期のみを変更して空燃比ばらつきを制御する構成としても良いし、トータル噴射期間と噴射回数とのいずれか一方と、噴射開始時期とを可変に設定して空燃比ばらつきを制御する構成としても良い。
ところで、上記実施の形態では、多重噴射によって形成した不規則な空燃比ばらつきを有する混合気をそれ自身で圧縮自己着火燃焼させる構成としたが、それ自身では自己着火に至らない不規則な空燃比ばらつきを有する混合気場（以下、主混合気場という）を多重噴射によって形成し、該主混合気場に付加的な温度上昇を与えることで、自己着火燃焼に至らしめる燃焼形態を実行する第３の実施形態を以下に説明する。
【００４８】
図２０は、第３の実施形態における噴射制御を示すものであり、ステップＳ３２で圧縮自己着火燃焼領域であると判別されると、ステップＳ３５〜３７で多重噴射におけるトータル噴射期間，噴射回数，噴射開始時期を第２実施形態と同様に設定する。
ステップＳ３８では、図２１に示すように、圧縮自己着火燃焼領域のうちの高負荷・高回転側に設定される２段燃焼領域であるか、それ以外の１段燃焼領域であるかを判別する。
【００４９】
前記１段燃焼領域とは、多重噴射によって形成させた不規則な空燃比ばらつきを有する混合気をそれ自身で自己着火燃焼させる燃焼であり、前記２段燃焼とは、１段燃焼時と同様に多重噴射で形成させた混合気（主混合気場）を、多重噴射の後に追加噴射させた燃料の燃焼による発熱で、自己着火燃焼に至らしめる燃焼形態であり、主混合気場を自己着火燃焼に至らしめるトリガーとなる燃焼と、その後の主混合気場の燃焼との２回の燃焼が行われるので、ここでは２段燃焼と称するものとする（図２２参照）。
【００５０】
ステップＳ３８で１段噴射領域であると判別されると、ステップＳ３９へ進んで、圧縮上死点付近で自己着火燃焼に至る量の燃料を、トータル噴射期間，噴射回数及び噴射開始時期の設定に従った多重噴射で噴射させる。
一方、ステップＳ３８で２段燃焼領域であると判別されると、ステップＳ４０へ進み、トータル噴射期間，噴射回数及び噴射開始時期の設定に従って多重噴射を行わせるが、ここでは、目標とする燃焼時期以前に自己着火燃焼を開始しない燃料量を多重噴射で噴射させ、トリガー燃焼時までに予混合される主混合気場を形成させる。
【００５１】
次のステップＳ４１では、前記ステップＳ４０における多重噴射の後の上死点付近で追加の燃料噴射を１回行わせ、これにより燃料噴射弁８直下の局所領域にリッチ混合気を形成して混合気を成層化する（図２３参照）。
前記上死点付近において噴射される燃料は、圧縮自己着火燃焼を開始するだけの最低限の量であり、該上死点付近において噴射される燃料が圧縮自己着火燃焼すると、該燃焼による発熱で主混合気場を圧縮自己着火燃焼に至らしめる。
【００５２】
上記構成によると、２段燃焼を行わせる場合においても、主混合気場が不規則な空燃比ばらつきを有することで着火性が良いから、局所的なリッチ混合気を形成するときの燃料量を少なくでき、リッチ混合気の燃焼によるＮＯｘの排出を抑制できる。
更に、２段燃焼を行わせる構成とすることで、筒内圧の上昇速度を抑制してノッキングの発生を回避できるので、１段燃焼を行わせる場合よりも高負荷側で圧縮自己着火燃焼を成立させることができる。
【００５３】
尚、上記では、局所的なリッチ混合気を圧縮自己着火燃焼させる構成としたが、点火プラグ９による火花点火で局所的なリッチ混合気を燃焼させ、該燃焼による発熱で、主混合気場を圧縮自己着火燃焼に至らしめる構成としても良い。
ところで、上記各実施形態では、機関回転速度及び機関負荷から要求される空燃比ばらつきを予めマップ化し、該マップに従って空燃比ばらつきに相関するトータル噴射期間，噴射回数，噴射開始時期をフィードホワード制御する構成としたが、ノッキング強度及び燃焼安定度を検出し、これらが許容値になるように、空燃比ばらつき（トータル噴射期間，噴射回数，噴射開始時期）をフィードバック制御する構成としても良く、係る構成とした第４の実施形態を、図２４のフローチャートに従って説明する。
【００５４】
圧縮自己着火燃焼領域において、機関回転速度及び機関負荷からトータル噴射期間，噴射回数，噴射開始時期を設定し、該設定に基づいて多重噴射を行わせ、不規則な空燃比ばらつきを有する混合気を形成させるのは（ステップＳ４５〜ステップＳ４８）、第２の実施形態と同様である。
ステップＳ４９では、ノッキング強度及び燃焼安定度を検出させる。
【００５５】
前記ノッキング強度は、図１に示すように、シリンダブロックに設けられるノックセンサ（振動センサ）１１からの検出信号に基づいて検出する。
また、燃焼安定度は、クランク角センサ１０の検出信号に基づき機関回転変動を求め、この回転変動から判別させるものとする。
ステップＳ５０では、前記検出されたノッキング強度及び燃焼安定度が共に許容値内である状態、共に許容値内でない状態、一方が許容値内で他方が許容値内でない状態のいずれかを判別する。
【００５６】
ノッキング強度及び燃焼安定度が共に許容値内でない場合には、圧縮自己着火燃焼の成立範囲が存在しない状態であり、このときには、圧縮自己着火燃焼から火花点火燃焼に切り換えるようにする。
また、ノッキング強度及び燃焼安定度が共に許容値内であるときには、ステップＳ５１へ進み、多重噴射で形成させる混合気の空燃比ばらつきを減少させることで、必要最小限のばらつきで圧縮自己着火燃焼を成立させるようにする。
【００５７】
空燃比ばらつきの減少補正は、多重噴射の噴射開始時期を進角補正して行わせる。但し、トータル噴射期間の短縮補正或いは噴射回数の減少補正によって、空燃比ばらつきを減少させる構成としても良いし、噴射開始時期の進角補正，トータル噴射期間の短縮補正，噴射回数の減少補正のうちの２つ以上を組み合わせる構成としても良い。
【００５８】
更に、一方が許容値内（ＯＫ）で他方が許容値内でない（ＮＧ）状態であるときには、ステップＳ５２へ進み、ノッキング強度が許容値内（ＯＫ）であるか否かを判別する。
そして、ノッキング強度が許容値内でない（ＮＧ）状態であるとき、即ち、燃焼安定度が許容値内（ＯＫ）であるが、ノッキング強度が許容値を超えて大きいときには、ステップＳ５１へ進み、多重噴射で形成させる混合気の空燃比ばらつきを減少させる。
【００５９】
一方、ノッキング強度が許容値内（ＯＫ）であるとき、即ち、燃焼安定度が許容値内でない（ＮＧ）状態であるときには、ステップＳ５３へ進み、多重噴射で形成させる混合気の空燃比ばらつきを増大補正する。
空燃比ばらつきの増大補正は、多重噴射の噴射開始時期を遅角補正して行わせる。但し、トータル噴射期間の増大補正或いは噴射回数の増大補正によって、空燃比ばらつきを増大させる構成としても良いし、噴射開始時期の増大補正，トータル噴射期間の増大補正，噴射回数の増大補正のうちの２つ以上を組み合わせる構成としても良い。
【図面の簡単な説明】
【図１】実施形態における内燃機関のシステム構成図。
【図２】実施形態における自己着火燃焼領域と火花点火燃焼領域とを示す図。
【図３】第１の実施形態における燃料噴射制御を示すフローチャート。
【図４】多重噴射制御時の噴射信号のパターンを示す図。
【図５】多重噴射におけるトータル噴射期間と機関負荷・回転との相関を示す線図。
【図６】多重噴射におけるトータル噴射期間と空燃比ばらつきとの相関を示す線図。
【図７】多重噴射における噴射回数と機関負荷・回転との相関を示す線図。
【図８】多重噴射における噴射回数と空燃比ばらつきとの相関を示す線図。
【図９】多重噴射で形成される混合気の空燃比ばらつきを示す図。
【図１０】空燃比とノッキング強度・燃焼安定度・燃焼時期との相関を示す線図。
【図１１】吸気行程１回噴射で形成される混合気の空燃比ばらつきを示す図。
【図１２】圧縮行程噴射によって成層化した場合の空燃比ばらつきを示す図。
【図１３】多重噴射・吸気行程１回噴射・圧縮行程噴射でそれぞれ形成される混合気における空燃比の頻度分布を示す線図。
【図１４】空燃比とリッチ・リーン限界空燃比との相関を示す線図。
【図１５】空燃比ばらつきと圧縮自己着火燃焼の成立範囲との相関を示す線図。
【図１６】空燃比ばらつきとＮＯｘ・ＨＣ排出量との相関を示す線図。
【図１７】第２の実施形態における燃料噴射制御を示すフローチャート。
【図１８】多重噴射における噴射開始時期と機関負荷・回転との相関を示す線図。
【図１９】多重噴射における噴射開始期間と空燃比ばらつきとの相関を示す線図。
【図２０】第３の実施形態における燃料噴射制御を示すフローチャート。
【図２１】第３の実施形態における火花点火燃焼領域及び１段燃料領域と２段燃焼領域とからなる圧縮自己着火燃焼領域を示す線図。
【図２２】第３の実施形態における２段燃焼時の筒内圧力の変化を示す線図。
【図２３】２段燃焼領域で形成される混合気の空燃比ばらつきを示す図。
【図２４】第４の実施形態における燃料噴射制御を示すフローチャート。
【符号の説明】
１…内燃機関
２…シリンダ
３…吸気ポート
４…吸気バルブ
５…排気ポート
６…排気バルブ
７…シリンダヘッド
８…燃料噴射弁
９…点火プラグ
１０…クランク角センサ
１１…ノックセンサ
２０…エンジンコントロールユニット（ＥＣＵ）
２１…燃焼パターン判定部
２２…火花点火燃焼制御部
２３…自己着火燃焼制御部
２４…噴射回数制御部
２５…噴射期間制御部
２６…噴射時期制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion control device for an internal combustion engine, and more particularly to a technique for forming an air-fuel mixture in a compression self-ignition combustion operation.
[0002]
[Prior art]
Conventionally, engines that perform compression self-ignition combustion are known.
In the compression self-ignition combustion, since combustion is started simultaneously at multiple points in the combustion chamber, the combustion speed is high, and stable combustion can be realized even when the air-fuel ratio is lean compared to normal spark ignition combustion. It is possible to improve the fuel consumption rate, and by burning the lean air-fuel mixture, the combustion temperature can be lowered and the NOx in the exhaust gas can be greatly reduced, and the fuel and air are sufficiently premixed. If so, the air-fuel ratio becomes more uniform, and NOx can be further reduced.
[0003]
In addition, normal spark ignition combustion is performed in the high rotation / high load range, and high output at high rotation / high load is achieved by switching the combustion mode from spark ignition combustion to compression self-ignition combustion in the low rotation / low / medium load range. The fuel consumption rate can be improved and NOx can be reduced at the time of low rotation and low / medium load.
In a two-cycle spark ignition type internal combustion engine, in order to avoid unstable combustion at partial load and to reduce HC (unburned hydrocarbon) emissions, self-ignition combustion is not performed in the combustion chamber. Proactive technology has been proposed.
[0004]
For example, Japanese Patent Application Laid-Open No. 7-071279 discloses that self-ignition is achieved by increasing the pressure and temperature in the cylinder at the start of the compression stroke by increasing the residual gas concentration in the cylinder by blocking a part of the exhaust passage at low load. A technique for controlling the combustion timing of the gas is disclosed.
[0005]
[Problems to be solved by the invention]
By the way, when compression self-ignition combustion is performed using a low self-ignition fuel such as gasoline, the thermal energy of the residual gas must be effectively used as disclosed in the above-mentioned JP-A-7-071279. Is effective.
Therefore, as a method for realizing compression self-ignition combustion in a 4-cycle engine, as disclosed in Japanese Patent Laid-Open No. 10-266878, when shifting from the exhaust stroke to the intake stroke, both the exhaust valve and the intake valve are closed. There has been a method in which residual gas is generated positively by providing such a sealing period to increase the cylinder internal pressure and temperature at the start of the compression stroke.
[0006]
However, if the residual gas amount is increased, the charging efficiency is reduced, so compression self-ignition combustion cannot be performed in a high load region, and the region where compression self-ignition combustion can be performed is limited to a narrow region on the low load side, There was a problem that the improvement effect of fuel consumption and emission would be reduced.
Japanese Patent Laid-Open No. 10-196424 discloses that when premixed air-fuel mixture is compressed, additional fuel (ignition oil) is injected near top dead center, and the temperature rises due to combustion of the ignition oil. A configuration is disclosed in which the premixed gas is brought to self-ignition combustion using the above.
[0007]
In the case of the configuration in which additional injection is performed as described above, the ignition amount deteriorates when the air-fuel ratio of the premixed gas becomes lean, and in order to avoid such deterioration of the ignition property, the injection amount of ignition oil There is a problem that NOx is generated by combustion of ignition oil.
Conventionally, in spark ignition combustion, a method of stratifying an air-fuel mixture that locally generates a rich air-fuel mixture and improving ignitability has been considered, but when stratification is performed, from a rich region There was a problem that NOx was produced in a large amount and the emission deteriorated.
[0008]
Japanese Patent Laid-Open No. 10-252570 discloses a technique for eliminating the lump of fuel by regularly providing a fuel portion and an air portion in the air-fuel mixture to reduce emissions. However, there is a problem that the air-fuel mixture with the same concentration ignites at once and causes knocking.
The present invention has been made in view of the above problems, and an object of the present invention is to ensure ignition stability of self-ignition combustion without increasing NOx emission in a compression self-ignition internal combustion engine. .
[0009]
Another object of the present invention is to improve the fuel efficiency and exhaust of a compression self-ignition internal combustion engine by expanding the operating range in which the compression self-ignition combustion operation can be performed.
[0010]
[Means for Solving the Problems]
Therefore, in the invention according to claim 1, during the compression self-ignition combustion operation, by the multiple injection that periodically injects the fuel into two or more times,Irregular concentration distribution is given to the air-fuel mixture in the combustion chamber, and compression self-ignition combustion is started from the rich portion of the air-fuel mixture given this irregular concentration distribution, and the engine speed is high and the engine load is small. As the time has passed, the period for performing the multiple injection is lengthened to increase the difference between the maximum air-fuel ratio and the minimum air-fuel ratio in the concentration distribution. In the invention according to claim 2, the difference between the maximum air fuel ratio and the minimum air fuel ratio in the concentration distribution is increased by increasing the number of times of the multiple injection as the engine rotational speed is higher and the engine load is smaller. In the invention according to claim 3, the maximum air-fuel ratio and the minimum air-fuel ratio in the concentration distribution are retarded by retarding the injection start timing of the multiple injection as the engine rotational speed is high and the engine load is small. The difference is made large.
[0012]
According to such a configuration, the air-fuel ratio in the combustion chamber is not a uniform air-fuel ratio, and is not configured to be regularly divided into a rich region and a lean region as in the case of stratification, but an irregular concentration Mixture formation is performed by multiple injection so that the distribution is given, and compression self-ignition combustion is started from a rich portion in the formed mixture. As the engine rotational speed is higher and the engine load is smaller, the period for performing multiple injections is lengthened, the number of injections is increased, and the injection start timing is retarded so that the engine rotational speed is higher and the engine load is reduced. The smaller the value, the larger the difference between the maximum air-fuel ratio and the minimum air-fuel ratio in the air-fuel mixture formed by multiple injection.Claim4In the described invention, the start timing of the multiple injection is set to be during the intake stroke.
[0014]
In invention of Claim 5,Additional fuel injection is performed near the top dead center after the multiple injection, thereby forming a rich mixture in a local region directly below the fuel injection valve, and spark ignition combustion or compression self of the local rich mixture A configuration in which the air-fuel mixture having the irregular concentration distribution is brought to compression self-ignition combustion by ignition combustion. According to such a configuration, the additional fuel injection after the multiple injection stratifies the air-fuel mixture that forms a rich air-fuel mixture field in the local region directly under the fuel injection valve, and the rich air-fuel mixture is spark-ignited by the spark plug. Combustion or compression self-ignition combustion causes the surrounding air-fuel mixture with an irregular concentration distribution to reach compression self-ignition combustion from its rich portion.
[0015]
In the invention of claim 6, the combustion stability and knocking strength of the engine are detected, and the combustion stability and knocking strength of the engine are within allowable ranges, respectively.Change any of the multiple injection period, number of injections, and injection start timeThe configuration. According to such a configuration, the combustion stability (torque fluctuation) of the engine is within the allowable range, and the knocking strength is within the allowable range.The multiple injection period, the number of injections, and the injection start time are changed.
[0020]
【The invention's effect】
Claim1-4According to the described invention, irregularConcentration distributionWhen self-ignition combustion starts from a rich portion of the air-fuel mixture, the self-ignitability of the air-fuel mixture becomes better than when a uniform air-fuel ratio air-fuel mixture is formed, and a stratified air-fuel mixture is formed thanDifference between maximum and minimum air / fuel ratioIs small, NOx generated by combustion of the rich part andsootAnd can improve the stability of compression self-ignition combustion without deteriorating emissionsIn addition, the stability of compression auto-ignition combustion can be maintained against changes in load and rotation while suppressing deterioration of emissions.There is an effect that.
[0021]
Claim5According to the described invention, while controlling the timing of compression self-ignition combustion, it is possible to perform compression self-ignition combustion with high stability without deterioration of emissions.effective.
[0022]
According to the sixth aspect of the present invention, even if there are changes in operating conditions and engine variations, compression self-ignition combustion can be performed with knocking strength and combustion stability within allowable ranges.There is an effect.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 is a system configuration diagram showing the configuration of an embodiment in which a combustion control device for an internal combustion engine according to the present invention is applied to a gasoline engine.
A gasoline engine 1 shown in FIG. 1 is an in-cylinder direct injection gasoline engine, and is configured to switch between compression self-ignition combustion and spark ignition combustion according to operating conditions.
[0025]
In the engine 1, an intake valve 4 is interposed in the intake port 3 that communicates with the cylinder 2, and an exhaust valve 6 is interposed in the exhaust port 5 that also communicates with the cylinder 2.
The
[0026]
An engine control unit (hereinafter referred to as ECU) 20 that controls the injection amount / injection timing by the fuel injection valve 8 and the ignition timing by the spark plug 9 includes a crank angle sensor signal from the
The
[0027]
As shown in FIG. 2, the combustion pattern determination unit 21 is configured to determine the combustion method based on the engine load T and the engine rotation speed N, and the low-medium load / low-medium rotation region is a compression self-ignition combustion region. The other high load / high rotation region is determined as the spark ignition combustion region.
In addition, during compression self-ignition combustion, multiple air injections are performed in which fuel is periodically injected in two or more cycles, thereby providing irregular air-fuel ratio variations in the air-fuel mixture in the combustion chamber. The self-ignition
[0028]
The flowchart of FIG. 3 shows a first embodiment of fuel injection control using the above hardware configuration.
In step S11, the engine speed N and the engine load T are detected.
In the present embodiment, the engine speed N is calculated based on the crank angle sensor signal, while the engine load T is represented by the accelerator opening.
[0029]
In step S12, based on the detected engine speed N and engine load T, it is determined whether the current operating condition is a compression self-ignition combustion region or a spark ignition combustion region (see FIG. 2).
When it is determined in step S12 that the region is a spark ignition combustion region, the process proceeds to step S13, and a required amount of fuel is supplied in one injection during the intake stroke to form a premixed homogeneous mixture. In the next step S14, the homogeneous mixture is burned by spark ignition by the spark plug 9.
[0030]
Even in the spark ignition combustion region, the fuel may be injected in a plurality of times, or not only during the intake stroke, but also during the compression stroke in order to form a stratified mixture.
On the other hand, if it is determined in step S12 that the region is the compression self-ignition combustion region, the process proceeds to step S15, and the total injection period in the multiple injection in which fuel is periodically injected in two cycles or more is set.
[0031]
As shown in FIG. 4, the multiple injection is an injection in which a plurality of injections are repeated with a pause period in between, and the total injection period is a period from the start of the first injection to the end of the last injection. is there.
In addition, although the injection time (injection pulse width) of each injection in the above-mentioned multiple injection is made uniform in FIG. 4, it may be configured to inject with different injection times (injection pulse widths), and the rest period may be set for each. It may be different.
[0032]
In step S15, as shown in FIG. 5, a total injection period corresponding to the engine speed N and the engine load T at that time is obtained from a map in which the total injection period is stored in advance according to the engine speed N and the engine load T. Search for and ask.
Here, the total injection period is set longer as the engine rotational speed N is higher and the engine load T is smaller. As shown in FIG. The air-fuel ratio (equivalent ratio) variation (difference between the maximum air-fuel ratio and the minimum air-fuel ratio) of the air-fuel mixture formed by injection increases.
[0033]
In step S16, the number of injections indicating how many times the fuel is to be injected in the multiple injection is set.
Similarly to the total injection period, the number of injections is determined from the map (see FIG. 7) in which the number of injections is stored in advance according to the engine speed N and the engine load T. The corresponding number of injections is obtained by searching, and the number of injections is set to be larger as the engine rotational speed N is higher and the engine load T is smaller.
[0034]
Increasing the number of injections increases the air-fuel ratio (equivalent ratio) variation of the air-fuel mixture formed by multiple injection, as shown in FIG.
In the first embodiment, the injection timing (injection start timing) of multiple injection is fixed at a predetermined timing during the intake stroke.
In step S17, multiple injections in which the injection of the required injection amount (injection time) is injected in the total injection period by dividing the number of injections are started at the fixed injection timing (injection start timing) and formed by the injection. Compressed self-ignition combustion near the top dead center.
[0035]
When the multiple injection is performed, as shown in FIG. 9, irregular air-fuel ratio variation occurs in the air-fuel mixture in the combustion chamber, and compression is performed from a rich portion of the air-fuel mixture to which this irregular air-fuel ratio variation is given. Self-igniting combustion will be started.
In the case of compression self-ignition combustion, as shown in FIG. 10, when the air-fuel ratio is made lean, the combustion stability is deteriorated, and conversely, when it is enriched, the knocking strength is increased and the combustion stability can be within an allowable range. It is necessary to control the air-fuel ratio to a narrow range between the lean limit air-fuel ratio AFL and the rich limit air-fuel ratio AFR that can suppress the knocking intensity within an allowable range. In particular, since the lean limit is narrow, the compression self-ignition combustion region is low. It is difficult to advance the load.
[0036]
In FIG. 10, the air-fuel ratio is used as an index indicating the ratio of gas and fuel. However, the same tendency is shown when residual gas or recirculated exhaust gas is included. In this case, the horizontal axis indicates fresh air. It is the ratio of the total gas amount and fuel combined with the burned gas. Therefore, stratification of the air-fuel mixture that forms a rich air-fuel mixture in a part of the combustion chamber can be considered as a method of ensuring the combustion stability while promoting leaning, but the NOx emissions are increased due to the combustion of the rich air-fuel mixture. turn into.
[0037]
On the other hand, with the configuration that causes irregular air-fuel ratio variations due to multiple injection as described above, the air-fuel ratio is made leaner while suppressing the increase in NOx emission, and the compression self-ignition combustion region Can be expanded to the low load side.
When the multiple injection is performed, as described above, irregular air-fuel ratio variation occurs in the air-fuel mixture in the combustion chamber (see FIG. 9), but when the required fuel amount is injected once in the intake stroke (this embodiment) In the case of spark ignition combustion in the embodiment), as shown in FIG. 11, a substantially uniform air-fuel ratio is formed in the combustion chamber, and fuel is injected at a time in the compression stroke so that the vicinity of the spark plug 9 is formed. In the case of stratification of the air-fuel mixture that forms a rich air-fuel mixture in the local region, as shown in FIG. 12, the periphery of the rich air-fuel mixture near the center of the combustion chamber is an extremely lean air-fuel mixture due to diffusion from the local region. Will be formed.
[0038]
Therefore, the frequency distribution of the air-fuel ratio (equivalent ratio) in the air-fuel mixture formed by the intake stroke single injection (homogeneous), multiple injection, and compression stroke injection (stratification) is as shown in FIG. The variation in the air-fuel ratio (equivalent ratio) is larger than the single intake stroke injection and smaller than the compression stroke injection.
On the other hand, as the variation in the air-fuel ratio (equivalent ratio) increases, the lean limit air-fuel ratio AFL (lean limit of the average air-fuel ratio) becomes leaner as the combustion stability improves as shown in FIG. If the variation exceeds a certain limit, the rich limit air-fuel ratio AFR (the rich limit of the average air-fuel ratio) becomes lean.
[0039]
FIG. 15 shows the correlation between the variation in the air-fuel ratio (equivalent ratio) and the range in which self-ignition combustion is established. When the variation in the air-fuel ratio increases, the range in which self-ignition combustion is established expands to the lower load side. However, if the variation of the air-fuel ratio becomes too large, the rich limit is reduced, and the establishment range becomes narrow.
Here, the region where the rich limit is suddenly reduced is the air-fuel ratio variation region when stratified by compression stroke injection, and the rich limit is the region where the air-fuel ratio variation due to multiple injection is smaller than when stratified. The range of establishment of self-ignition combustion can be expanded to the low load side without reducing the load.
[0040]
FIG. 16 shows the correlation between the variation in the air-fuel ratio (equivalent ratio) and the HC / NOx emission amount. When the variation in the air-fuel ratio becomes too large, the NOx emission amount increases, but the NOx emission amount increases. In the region smaller than the air-fuel ratio variation region showing the tendency, both the HC emission amount and the NOx emission amount do not change.
As shown in FIGS. 15 and 16 above, stratification increases the amount of NOx emissions although the range of formation of compression self-ignition combustion can be reduced.
[0041]
On the other hand, when the irregular air-fuel ratio variation is set, it is possible to reduce the formation range of the compression self-ignition combustion without increasing the NOx emission amount. By setting the irregular air-fuel ratio variation to perform compression self-ignition combustion, the low-load side that does not hold in the self-ignition combustion with a homogeneous mixture is included in the compression self-ignition combustion region, and NOx emissions It is possible to avoid the increase of
[0042]
Furthermore, in the above embodiment, the magnitude of the variation in the air-fuel ratio given to the air-fuel mixture by multiple injection is controlled by the number of injections and the total injection period.
The ignitability in the compression self-ignition combustion tends to deteriorate as the engine speed increases and the engine load decreases. On the other hand, as the air-fuel ratio variation increases, the combustion stability improves.
[0043]
In addition, the variation in the air-fuel ratio increases as the number of injections in the multiple injection increases and the total injection period in the multiple injection increases (see FIGS. 6 and 8).
Therefore, in the present embodiment, as described above, the higher the engine speed and the lower the engine load, the greater the number of injections and the longer the total injection period.
[0044]
In addition, it is good also as a structure which fixes either one of the frequency | count of injection and a total injection period, and changes the other according to an engine speed and an engine load.
In the first embodiment, the injection start timing of multiple injection is fixed and the air-fuel ratio variation is controlled by the number of injections and the total injection period. However, by controlling the injection start timing of multiple injection, A configuration for controlling the variation in the fuel ratio may be employed, and a second embodiment having such a configuration will be described with reference to the flowchart of FIG.
[0045]
In the flowchart of FIG. 17, following the setting of the number of injections in step S26, the injection timing (injection start timing) is set in step S27. In step S28, multiple injections with the set total injection period and number of injections are performed. Start at the start time set in step S27.
The steps other than those described above perform the same processing as in the flowchart of FIG.
[0046]
In step S27, as shown in FIG. 18, the setting is made such that the higher the engine speed and the lower the engine load, the more retarded the injection start timing of the multiple injection. This is because the higher the engine speed and the lower the engine load, the worse the ignitability. On the other hand, as shown in FIG. 19, the variation in the air-fuel ratio (equivalent ratio) is delayed as the injection start timing of multiple injection is retarded. This is because the ignition stability increases and the ignition stability is improved.
[0047]
In addition, it is good also as a structure which changes only an injection start time, and controls air-fuel-ratio dispersion | variation, or controls either air-fuel-ratio dispersion | variation by setting either one of a total injection period or the frequency | count of injection, and an injection start time variably. It is good also as composition to do.
By the way, in the above-described embodiment, the air-fuel mixture having irregular air-fuel ratio variation formed by multiple injection is compressed and self-ignited and combusted by itself. However, the irregular air-fuel ratio that does not lead to self-ignition by itself. A combustion mode that leads to self-ignition combustion is formed by forming an air-fuel mixture field having variation (hereinafter referred to as a main air-fuel mixture field) by multiple injection and giving an additional temperature rise to the main air-fuel mixture field. The third embodiment will be described below.
[0048]
FIG. 20 shows the injection control in the third embodiment. When it is determined in step S32 that the region is the compression self-ignition combustion region, the total injection period, the number of injections, and the injection in the multiple injection are determined in steps S35 to S37. The start time is set as in the second embodiment.
In step S38, as shown in FIG. 21, it is determined whether it is a two-stage combustion area set on the high-load / high-rotation side in the compression self-ignition combustion area or another one-stage combustion area. .
[0049]
The first stage combustion region is combustion in which an air-fuel mixture having irregular air-fuel ratio variations formed by multiple injection is self-ignited and combusted by itself, and the second stage combustion is the same as in the first stage combustion. This is a combustion mode in which an air-fuel mixture formed by multiple injection (main air-fuel mixture field) is brought into self-ignition combustion by the heat generated by combustion of additional fuel injected after multiple injection, and the main air-fuel mixture field is self-ignited and combusted. Since the combustion that serves as a trigger to reach the first combustion and the subsequent combustion in the main air-fuel mixture field are performed twice, they are referred to herein as two-stage combustion (see FIG. 22).
[0050]
If it is determined in step S38 that it is the first-stage injection region, the process proceeds to step S39, and the amount of fuel that reaches self-ignition combustion near the compression top dead center is set to the total injection period, the number of injections, and the injection start timing. It is made to inject by the following multiple injection.
On the other hand, when it is determined in step S38 that the region is the two-stage combustion region, the process proceeds to step S40, and multiple injection is performed according to the settings of the total injection period, the number of injections, and the injection start timing. The amount of fuel that has not previously started self-ignition combustion is injected by multiple injection to form a main mixture field that is premixed by the time of trigger combustion.
[0051]
In the next step S41, an additional fuel injection is performed once near the top dead center after the multiple injection in the step S40, thereby forming a rich air-fuel mixture in a local region immediately below the fuel injection valve 8 and the air-fuel mixture. Is stratified (see FIG. 23).
The fuel injected in the vicinity of the top dead center is the minimum amount that can start the compression self-ignition combustion. When the fuel injected in the vicinity of the top dead center burns in the compression self-ignition combustion, the heat generated by the combustion The main air-fuel mixture is brought to compression self-ignition combustion.
[0052]
According to the above configuration, even when two-stage combustion is performed, since the ignitability is good because the main mixture field has irregular air-fuel ratio variations, the amount of fuel when forming a local rich mixture is reduced. The amount of NOx emission due to the combustion of the rich air-fuel mixture can be suppressed.
Furthermore, by adopting a configuration that performs two-stage combustion, it is possible to suppress the rate of increase of in-cylinder pressure and avoid the occurrence of knocking. Therefore, compression self-ignition combustion is established on the higher load side than when one-stage combustion is performed. Can be made.
[0053]
In the above, the local rich mixture is compressed and self-ignited and combusted. However, the local rich mixture is combusted by spark ignition by the spark plug 9, and the main mixture field is generated by the heat generated by the combustion. It is good also as a structure which leads to compression self-ignition combustion.
By the way, in each of the above embodiments, the air-fuel ratio variation required from the engine speed and the engine load is mapped in advance, and the total injection period, the number of injections, and the injection start timing correlated with the air-fuel ratio variation are fed-forward controlled according to the map. The configuration may be such that the knocking strength and the combustion stability are detected, and the air-fuel ratio variation (total injection period, number of injections, injection start timing) may be feedback controlled so that these are acceptable values. The fourth embodiment will be described with reference to the flowchart of FIG.
[0054]
In the compression self-ignition combustion region, the total injection period, the number of injections, and the injection start timing are set from the engine speed and engine load, and multiple injections are performed based on the settings, and the air-fuel mixture having irregular air-fuel ratio variation is The formation (step S45 to step S48) is the same as in the second embodiment.
In step S49, knocking strength and combustion stability are detected.
[0055]
As shown in FIG. 1, the knocking strength is detected based on a detection signal from a knock sensor (vibration sensor) 11 provided in the cylinder block.
Further, the combustion stability is determined from engine rotation fluctuation based on a detection signal of the
In step S50, it is determined whether the detected knocking strength and combustion stability are both within the allowable value, both are not within the allowable value, and one is within the allowable value and the other is not within the allowable value.
[0056]
When both the knocking strength and the combustion stability are not within the allowable values, there is no formation range of the compression self-ignition combustion. At this time, the compression self-ignition combustion is switched to the spark ignition combustion.
When both the knocking strength and the combustion stability are within the allowable values, the process proceeds to step S51, where the compression self-ignition combustion is performed with the minimum necessary variation by reducing the air-fuel ratio variation of the air-fuel mixture formed by multiple injection. Make it happen.
[0057]
The reduction correction of the air-fuel ratio variation is performed by correcting the advance of the injection start timing of the multiple injection. However, it may be configured to reduce the variation in the air-fuel ratio by correcting the total injection period or correcting the number of injections, and among the advance correction of the injection start timing, the correction of the total injection period, and the correction of the number of injections It is good also as a structure which combines two or more of these.
[0058]
Further, when one is within the permissible value (OK) and the other is not within the permissible value (NG), the process proceeds to step S52 to determine whether or not the knocking strength is within the permissible value (OK).
When the knocking strength is not within the permissible value (NG), that is, when the combustion stability is within the permissible value (OK), but when the knocking strength exceeds the permissible value, the process proceeds to step S51, where The air-fuel ratio variation of the air-fuel mixture formed by injection is reduced.
[0059]
On the other hand, when the knocking strength is within the permissible value (OK), that is, when the combustion stability is not within the permissible value (NG), the routine proceeds to step S53, where the variation in the air-fuel ratio of the air-fuel mixture formed by multiple injection is determined. Increase correction.
The increase correction of the air-fuel ratio variation is performed by correcting the delay of the injection start timing of the multiple injection. However, it may be configured to increase the variation in the air-fuel ratio by increasing the total injection period or increasing the number of injections, and among the increase correction of the injection start timing, the increase correction of the total injection period, and the increase correction of the number of injections. It is good also as a structure which combines two or more.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an internal combustion engine in an embodiment.
FIG. 2 is a diagram showing a self-ignition combustion region and a spark ignition combustion region in the embodiment.
FIG. 3 is a flowchart showing fuel injection control in the first embodiment.
FIG. 4 is a diagram showing a pattern of an injection signal at the time of multiple injection control.
FIG. 5 is a diagram showing a correlation between a total injection period and engine load / rotation in multiple injection.
FIG. 6 is a diagram showing a correlation between a total injection period and air-fuel ratio variation in multiple injection.
FIG. 7 is a diagram showing a correlation between the number of injections and engine load / rotation in multiple injection.
FIG. 8 is a diagram showing a correlation between the number of injections and air-fuel ratio variation in multiple injection.
FIG. 9 is a view showing variations in the air-fuel ratio of the air-fuel mixture formed by multiple injection.
FIG. 10 is a diagram showing a correlation between an air-fuel ratio and knocking strength, combustion stability, and combustion timing.
FIG. 11 is a diagram showing the air-fuel ratio variation of the air-fuel mixture formed by one intake stroke injection.
FIG. 12 is a diagram showing variation in air-fuel ratio when stratified by compression stroke injection.
FIG. 13 is a diagram showing the frequency distribution of the air-fuel ratio in the air-fuel mixture formed by multiple injection, single intake stroke injection, and compression stroke injection, respectively.
FIG. 14 is a diagram showing a correlation between an air-fuel ratio and a rich / lean limit air-fuel ratio.
FIG. 15 is a diagram showing a correlation between air-fuel ratio variation and a range where compression self-ignition combustion is established;
FIG. 16 is a diagram showing a correlation between air-fuel ratio variation and NOx / HC emissions.
FIG. 17 is a flowchart showing fuel injection control in the second embodiment.
FIG. 18 is a diagram showing a correlation between injection start timing and engine load / rotation in multiple injection.
FIG. 19 is a diagram showing a correlation between an injection start period and air-fuel ratio variation in multiple injection.
FIG. 20 is a flowchart showing fuel injection control in the third embodiment.
FIG. 21 is a diagram showing a spark ignition combustion region and a compression self-ignition combustion region including a first stage fuel region and a second stage combustion region in the third embodiment.
FIG. 22 is a diagram showing a change in in-cylinder pressure during two-stage combustion in the third embodiment.
FIG. 23 is a diagram showing the air-fuel ratio variation of the air-fuel mixture formed in the two-stage combustion region.
FIG. 24 is a flowchart showing fuel injection control in the fourth embodiment.
[Explanation of symbols]
1. Internal combustion engine
2 ... Cylinder
3 ... Intake port
4 ... Intake valve
5 ... Exhaust port
6 ... Exhaust valve
7 ... Cylinder head
8 ... Fuel injection valve
9 ... Spark plug
10 ... Crank angle sensor
11 ... Knock sensor
20 ... Engine control unit (ECU)
21 ... Combustion pattern determination unit
22 ... Spark ignition combustion control unit
23 ... Self-ignition combustion control unit
24 ... Number of injection control section
25 ... Injection period control unit
26 ... Injection timing control unit
Claims (6)
圧縮自己着火燃焼運転時に、燃料を２回以上に分けて周期的に噴射する多重噴射によって、燃焼室内の混合気に不規則な濃度分布を与え、この不規則な濃度分布が与えられた混合気のうちのリッチ部分から圧縮自己着火燃焼を開始させると共に、
機関回転速度が高く機関負荷が小さいときほど、前記多重噴射を行わせる期間を長くすることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくすることを特徴とする内燃機関の燃焼制御装置。A combustion control device for an internal combustion engine that performs compression self-ignition combustion operation,
During the compression self-ignition combustion operation, an irregular concentration distribution is given to the air-fuel mixture in the combustion chamber by the multiple injection in which the fuel is periodically injected in two or more times, and the air-fuel mixture to which the irregular concentration distribution is given. And start compression self-ignition combustion from the rich part of
The difference between the maximum air fuel ratio and the minimum air fuel ratio in the concentration distribution is increased by increasing the period during which the multiple injection is performed as the engine rotational speed is high and the engine load is small . Combustion control device.
圧縮自己着火燃焼運転時に、燃料を２回以上に分けて周期的に噴射する多重噴射によって、燃焼室内の混合気に不規則な濃度分布を与え、この不規則な濃度分布が与えられた混合気のうちのリッチ部分から圧縮自己着火燃焼を開始させると共に、
機関回転速度が高く機関負荷が小さいときほど、前記多重噴射の噴射回数を多くすることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくすることを特徴とする内燃機関の燃焼制御装置。A combustion control device for an internal combustion engine that performs compression self-ignition combustion operation,
During the compression self-ignition combustion operation, an irregular concentration distribution is given to the air-fuel mixture in the combustion chamber by the multiple injection in which the fuel is periodically injected in two or more times, and the air-fuel mixture to which the irregular concentration distribution is given. And start compression self-ignition combustion from the rich part of
Combustion of an internal combustion engine characterized in that the difference between the maximum air fuel ratio and the minimum air fuel ratio in the concentration distribution is increased by increasing the number of injections of the multiple injection as the engine rotational speed is high and the engine load is small. Control device.
圧縮自己着火燃焼運転時に、燃料を２回以上に分けて周期的に噴射する多重噴射によって、燃焼室内の混合気に不規則な濃度分布を与え、この不規則な濃度分布が与えられた混合気のうちのリッチ部分から圧縮自己着火燃焼を開始させると共に、
機関回転速度が高く機関負荷が小さいときほど、前記多重噴射の噴射開始時期を遅角させることで、前記濃度分布における最大空燃比と最小空燃比との差を大きくすることを特徴とする内燃機関の燃焼制御装置。A combustion control device for an internal combustion engine that performs compression self-ignition combustion operation,
During the compression self-ignition combustion operation, an irregular concentration distribution is given to the air-fuel mixture in the combustion chamber by the multiple injection in which the fuel is periodically injected in two or more times, and the air-fuel mixture to which the irregular concentration distribution is given. And start compression self-ignition combustion from the rich part of
The difference between the maximum air-fuel ratio and the minimum air-fuel ratio in the concentration distribution is increased by retarding the injection start timing of the multiple injection as the engine rotational speed is high and the engine load is small. Combustion control device.
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| JP2001010668A JP4032650B2 (en) | 2001-01-18 | 2001-01-18 | Combustion control device for internal combustion engine |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4023239B2 (en) * | 2002-07-10 | 2007-12-19 | トヨタ自動車株式会社 | INTERNAL COMBUSTION ENGINE FOR COMPRESSED IGNITION OF MIXED AIR AND CONTROL METHOD FOR INTERNAL COMBUSTION ENGINE |
| JP4493593B2 (en) * | 2005-12-28 | 2010-06-30 | 本田技研工業株式会社 | Self-igniting engine |
| JP2008196387A (en) * | 2007-02-13 | 2008-08-28 | Toyota Motor Corp | Control device for cylinder injection type internal combustion engine |
| JP5034678B2 (en) * | 2007-05-25 | 2012-09-26 | トヨタ自動車株式会社 | Fuel injection control device |
| JP5594022B2 (en) * | 2010-09-29 | 2014-09-24 | マツダ株式会社 | Gasoline engine combustion control device |
| JP5423717B2 (en) * | 2011-03-31 | 2014-02-19 | マツダ株式会社 | Spark ignition gasoline engine |
| JP5884407B2 (en) * | 2011-10-28 | 2016-03-15 | スズキ株式会社 | Internal combustion engine |
| JP6558406B2 (en) * | 2017-08-25 | 2019-08-14 | マツダ株式会社 | Engine control device |
| JP6597736B2 (en) * | 2017-08-25 | 2019-10-30 | マツダ株式会社 | Engine control device |
| JP6642539B2 (en) * | 2017-08-25 | 2020-02-05 | マツダ株式会社 | Control device for compression ignition engine |
| US10711708B2 (en) | 2017-08-25 | 2020-07-14 | Mazda Motor Corporation | Control device for engine |
| JP2021021340A (en) * | 2019-07-24 | 2021-02-18 | マツダ株式会社 | Fuel injection control device for engine |
| JP2021021337A (en) * | 2019-07-24 | 2021-02-18 | マツダ株式会社 | Fuel injection control device for engine |
| JP2021021339A (en) * | 2019-07-24 | 2021-02-18 | マツダ株式会社 | Fuel injection control device for engine |
| JP2021021338A (en) * | 2019-07-24 | 2021-02-18 | マツダ株式会社 | Fuel injection control device for engine |
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