JP3979286B2 - Premixed compression ignition internal combustion engine - Google Patents

Premixed compression ignition internal combustion engine Download PDF

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Publication number
JP3979286B2
JP3979286B2 JP2002365083A JP2002365083A JP3979286B2 JP 3979286 B2 JP3979286 B2 JP 3979286B2 JP 2002365083 A JP2002365083 A JP 2002365083A JP 2002365083 A JP2002365083 A JP 2002365083A JP 3979286 B2 JP3979286 B2 JP 3979286B2
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Prior art keywords
fuel
air
injection valve
fuel injection
fuel ratio
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JP2004197597A (en
Inventor
亮 長谷川
清 藤原
崇志 松本
崇 小山
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Toyota Motor Corp
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Toyota Motor Corp
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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
    • F02D41/3094—Controlling fuel injection the fuel injection being effected by at least two different injectors, e.g. one in the intake manifold and one in the cylinder
    • 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
    • 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
    • F02D41/3047—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 said means being a secondary injection of fuel

Description

【０００１】
【発明の属する技術分野】
本発明は、予混合圧縮着火内燃機関に関する。
【０００２】
【従来の技術】
複数の燃料噴射弁を有する圧縮着火内燃機関において、一の燃料噴射弁より圧縮行程上死点近傍において燃料を燃焼室に噴射するよりも早い時期に、その他の燃料噴射弁より燃料を噴射し、十分な混合時間を与えて希薄予混合気を形成することで、燃料の濃度分布がより均一となり、以てスモークの発生およびＮＯｘの発生を抑制する予混合燃焼が行われている。しかし、予混合燃焼においては、内燃機関の負荷が高くなると、燃焼室内に噴射される燃料の量が増大するため、燃焼室内における燃料分布が不均一となりやすいため、スモークおよびＮＯｘが発生する。
【０００３】
そこで、希薄予混合気を形成する燃料を噴射する燃料噴射弁と、圧縮行程上死点近傍において燃料を噴射する燃料噴射弁とにおける各々の燃料の噴射量および噴射時期を、内燃機関の負荷に応じて、変更する技術が明示されている（例えば、特許文献１参照）
【０００４】
【特許文献１】
特開平９−３２４６３１号公報
【特許文献２】
特開平８−２１０１６９号公報
【０００５】
【発明が解決しようとする課題】
ここで、圧縮着火内燃機関において、排出されるＮＯｘの抑制と排気スモークの発生の抑制を目的として、予混合燃焼が行われる場合、燃焼サイクルにおいて早い時期に燃料を噴射することにより、燃料が圧縮行程上死点近傍よりも早い時期に、予混合気が着火燃焼するいわゆる過早着火が発生する。過早着火が生じることにより、燃焼室内の圧力が急激に上昇し、内燃機関に大きな衝撃や騒音が生じる結果となる。
【０００６】
ここで予混合気の過早着火は、予混合気の燃料濃度分布、即ち空燃比分布が、特に理論空燃比近傍の値となる場合、その発生する可能性が高くなる。ここで、内燃機関の燃焼室に形成される予混合気において、その空燃比分布に偏りが生じた場合、例えば、燃焼室において空燃比分布が連続的に変化している分布となっている場合、その空燃比分布において理論空燃比近傍の空燃比を有する部位が存在しやすくなる。特に、内燃機関の機関負荷が増大し、燃焼室内へ比較的多量の燃料が噴射される場合は、その傾向が強くなる。従って予混合気の空燃比分布において過早着火の生じる可能性が高くなる。
【０００７】
そこで、前記課題に鑑み、本発明では、複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、燃焼室内に形成される予混合気の空燃比分布を、該予混合気の過早着火が生じる空燃比を回避する空燃比分布とすることで、該予混合気の過早着火を回避し、安定した燃焼を可能とする予混合圧縮着火内燃機関を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、上記した課題を解決するために以下のような手段を採用した。即ち、内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、前記主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、内燃機関の機関負荷が中負荷より低いときは、吸気行程中期から圧縮行程中期において前記副燃料噴射弁から燃料を噴射することで予混合気を形成し、内燃機関の機関負荷が中負荷以上のときは、吸気行程初期および圧縮行程後期の少なくとも何れかに前記副燃料噴射弁から燃料を噴射することで予混合気を前記主燃料噴射弁の近傍に形成する予混合気形成手段と、を備え、前記予混合気形成手段は、内燃機関の機関負荷が中負荷以上のときに前記副燃料噴射弁から燃料を噴射するときは、内燃機関の機関負荷が中負荷より低いときに前記副燃料噴射弁から燃料を噴射するときよりも前記副燃料噴射弁の噴射圧を低下することを特徴とする。
【０００９】
内燃機関のシリンダブロックおよびシリンダヘッドの外周部には、冷却水の循環手段が設けられており、燃料の燃焼によって発生した熱の放熱が行われている。しかし、燃焼室の略中心部に設けられた主燃料噴射弁の近傍は、該冷却水の循環手段より離れた部位であるため、該冷却水による放熱の効果が少ない。そのため、燃焼室における主燃料噴射弁の近傍の空間の温度は、該燃焼室のシリンダ壁面に近い周囲の空間の温度と比べて、比較的高くなる。このような内燃機関において、副燃料噴射弁より予混合気を形成すべく燃料を噴射すると、該燃料の量が一定以上である場合、即ち、内燃機関における機関負荷が中負荷以上である場合は、燃焼室の内部にほぼ均一に形成される予混合気の空燃比が理論空燃比側へ移行する。その結果、主燃料噴射弁近傍の空間において、空燃比が理論空燃比程度となった場合、該空間の温度が比較的高いことにも起因して、予混合気の過早着火の発生する虞が非常に高くなる。
【００１０】
そこで、本手段においては、内燃機関の機関負荷が中負荷以上である場合、即ち、内燃機関の機関負荷が低負荷である場合と同様に予混合気を形成したときに、燃焼室内に形成される予混合気において、過早着火の発生する虞のある空燃比となる部位が存在する場合、予混合気を主燃料噴射弁の近傍に集約して形成する。これにより、主燃料噴射弁の近傍の空燃比が予混合気の過早着火が発生する虞の高い空燃比となるのを回避することが可能となり、以て内燃機関の運転負荷にかかわらず安定した燃焼が可能となる。
【００１１】
ここで、主燃料噴射弁の近傍に予混合気を形成する手段として、副燃料噴射弁からの燃料の噴射を吸気行程初期および圧縮行程後期の少なくとも何れかに行うことが考えられる。即ち、吸気行程初期および圧縮行程後期においては、内燃機関のシリンダ内で往復運動をするピストンの位置が比較的高い位置にあるため、その時点で副燃料噴射弁によって燃料を噴射すると、ピストンによって予混合気を形成する燃料がシリンダの内部に広く拡散するのを妨げる結果となり、以て主燃料噴射弁の近傍に予混合気の形成が可能となる。
【００１２】
また、前述までの予混合圧縮着火内燃機関において、内燃機関の機関負荷が中負荷より低いときは、副燃料噴射弁からの燃料の噴射を吸気行程中期から圧縮行程中期において行う。これにより、予混合気の過早着火が発生する虞のない場合、即ち内燃機関の機関負荷が中負荷より低いときは、吸気行程中期から圧縮行程中期、即ちシリンダにおけるピストンの位置が比較的低い位置において、副燃料噴射弁からの燃料の噴射を行うことで、燃焼室内に均一の予混合気を形成し、予混合燃焼によるＮＯｘの抑制と排気スモークの抑制を図ることができる。
【００１３】
さらに、前述までの予混合圧縮着火内燃機関において、前記予混合気形成手段によって内燃機関の機関負荷が中負荷以上のときに副燃料噴射弁より燃料を噴射するときは、内燃機関の機関負荷が中負荷より低いときに副燃料噴射弁から燃料を噴射するときよりも副燃料噴射弁の噴射圧を低下する。噴射圧を低下することによって、副燃料噴射弁から噴射される燃料の粒径が大きくなる。そのため、主燃料噴射弁の近傍に形成される予混合気の燃料の粒径が大きくなることにより、該予混合気が過早着火する虞がより低下する。
【００１４】
ここで、圧縮行程上死点近傍において、主燃料噴射弁より燃料を噴射し燃焼室内において燃料の燃焼が行われるときは、燃焼室内における燃料と空気との混合の程度が促進される方が好ましい。そこで、圧縮上死点近傍において主燃料噴射弁から燃料を噴射する前に、主燃料噴射弁から微量の燃料を噴射する手段が考えられる。即ち、燃焼室内で燃料の燃焼が行われる前に噴射される微量の燃料により、その時点で形成されている混合気に対して空気もしくは混合気の流れを発生させることで、燃焼室における燃料と空気との混合の度合いを促進させるものである。特に、内燃機関の機関負荷が中負荷以上であって、前記予混合気形成手段によって吸気行程初期および圧縮行程後期の少なくとも何れかに副燃料噴射弁から燃料を噴射することで燃料噴射弁近傍に予混合気を形成させている場合は、該予混合気が燃焼室内の空気と混合したうえで広く拡散している状態ではないため、本手段によって主燃料噴射弁近傍に形成されている予混合気と、その周辺に存在する空気とを、程度よく混合させることが可能となる。
【００１５】
複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、該予混合気の過早着火を回避し、安定した燃焼を可能とするその他の手段として、以下の手段を採用した。即ち、内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、燃焼室内に形成される混合気の空燃比分布を検出する空燃比分布検出手段と、空燃比分布検出手段によって検出される前記燃焼室内の空燃比分布に応じて副燃料噴射弁から噴射される燃料の噴射距離を調整することで、前記燃焼室内の空燃比分布を概均一とする噴射距離調整手段と、を有することを特徴とする。
【００１６】
燃焼室内に形成される混合気の空燃比分布が概ね均一とならず、その分布に偏りが生じた場合、該燃焼室の何れかの部位において、該部位の空燃比が過早着火が発生する虞の高い空燃比、即ち理論空燃比近傍の空燃比となり、その結果、該部位を起点として、過早着火が発生する。そこで、上述の手段においては、前記空燃比分布検出手段によって燃焼室内の空燃比分布を検出し、該空燃比分布において偏りが生じている場合は、副燃料噴射弁から噴射される燃料の噴射距離を調整することで、燃焼室内の空燃比を概ね均一なものとする。例えば、副燃料噴射弁から離れた部位において、該部位の空燃比が他の部位と比べて大きい場合は、副燃料噴射弁から噴射される燃料の噴射距離を長くすることで、該部位近傍に燃料が到達させて該部位の空燃比を低下させ、燃焼室内の空燃比分布の偏りを低減させるものである。
【００１７】
本手段によって、複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、燃焼室内に形成される予混合気の空燃比分布を、該予混合気の過早着火が生じる空燃比を回避する空燃比分布とすることで、該予混合気の過早着火を回避し、安定した燃焼が可能となる。
【００１８】
ここで、前記噴射距離調整手段には次に示す手段が考えられる。まず、副燃料噴射弁の噴射圧を調整する手段である。副燃料噴射弁の噴射圧を高くするに従い、該副燃料噴射弁からより離れた部位へ燃料を到達させることが可能となる。従って、前記空燃比分布検出手段によって検出された燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に大きくなっている場合は、該副燃料噴射弁の噴射圧を高くすることで、一方で燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に小さくなっている場合は、該副燃料噴射弁の噴射圧を低くすることで、燃焼室内の空燃比分布を概ね均一なものすることが可能となる。
【００１９】
更に、前記噴射距離調整手段として、副燃料噴射弁の噴射回数を調整する手段が考えられる。副燃料噴射弁によって噴射される燃料の量が同一であっても、噴射回数を増やすことによって、一回の噴射で噴射される燃料の量が減少し、副燃料噴射弁の開弁時間が短くなる。その結果、副燃料噴射弁からの燃料の噴射距離が短縮することになる。従って、前記空燃比分布検出手段によって検出された燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に大きくなっている場合は、該副燃料噴射弁の噴射回数を少なくすることで、一方で燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に小さくなっている場合は、該副燃料噴射弁の噴射回数を多くすることで、燃焼室内の空燃比分布を概ね均一なものすることが可能となる。
【００２０】
更に、前記噴射距離調整手段として、副燃料噴射弁から噴射される燃料の粒径を調整する手段が考えられる。副燃料噴射弁によって噴射される燃料の粒径を小さくなることで燃料の噴射距離が延びる。ここで、燃料の粒径を小さくする手段として、該副燃料噴射弁を温めるヒータが考えられる。ヒータにより該副燃料噴射弁を温めることで、燃料が温められ、その結果燃料の粘性が低下することで、該副燃料噴射弁から噴射される燃料の粒径が小さくなる。従って、前記空燃比分布検出手段によって検出された燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に大きくなっている場合は、該副燃料噴射弁から噴射される燃料の粒径を小さくすることで、例えば前記ヒータの温度を高くすることで、一方で燃焼室内の空燃比分布が、該副燃料噴射弁から距離に従い次第に小さくなっている場合は、該副燃料噴射弁から噴射される燃料の粒径を大きくすることで、例えば前記ヒータの温度を低くすることで、燃焼室内の空燃比分布を概ね均一なものすることが可能となる。
【００２１】
複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、該予混合気の過早着火を回避し、安定した燃焼を可能とするその他の手段として、以下の手段を採用した。即ち、内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、前記主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、前記燃焼室内に形成される混合気の空燃比分布を検出する空燃比分布検出手段と、前記燃焼室における吸気弁または排気弁の少なくとも一方の開閉特性を可変とする可変動弁機構と、を備え、前記空燃比分布検出手段によって検出される前記燃焼室内の空燃比分布に応じて、前記可変動弁機構によって前記吸気弁または排気弁の少なくとも一方を開弁することで、前記燃焼室内の空燃比分布を概均一とすることを特徴とする。
【００２２】
燃焼室内に形成される混合気の空燃比分布が概ね均一とならず、その分布に偏りが生じた場合、該燃焼室の何れかの部位において、該部位の空燃比が過早着火が発生する虞の高い空燃比、即ち理論空燃比近傍の空燃比となり、その結果、該部位を起点として、過早着火が発生する。そこで、上述の手段においては、前記空燃比分布検出手段によって燃焼室内の空燃比分布を検出し、該空燃比分布において偏りが生じている場合は、前記可変動弁機構を介して吸気弁または排気弁の少なくとも一方を開弁することで、燃焼室内の空燃比を概ね均一なものとする。例えば、前記空燃比分布検出手段によって、吸気弁近傍の空燃比がその他の部位の空燃比と比較して小さいと検出された場合は、前記可変動弁機構を介して吸気弁を開弁することで、燃焼室内部の混合気の一部を燃焼室外部に逃がし、吸気弁近傍の空燃比を大きくすることにより、燃焼室内の空燃比分布の偏りを低減させる。一方で排気弁近傍の空燃比がその他の部位の空燃比と比較して小さいと検出された場合は、前記可変動弁機構を介して排気弁を開弁することで、燃焼室内部の混合気の一部を燃焼室外部に逃がし、排気弁近傍の空燃比を大きくすることにより、燃焼室内の空燃比分布の偏りを低減させるものである。
【００２３】
本手段によって、複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、燃焼室内に形成される予混合気の空燃比分布を、該予混合気の過早着火が生じる空燃比を回避する空燃比分布とすることで、該予混合気の過早着火を回避し、安定した燃焼が可能となる。
【００２４】
【発明の実施の形態】
＜第１の実施例＞
ここで、本発明に係る予混合圧縮着火内燃機関の実施の形態について図面に基づいて説明する。図１は、本発明が適用される圧縮着火内燃機関の燃焼室近傍の概略構成およびその制御系統の概略構成を示す図である。
【００２５】
図１の圧縮着火内燃機関は、気筒１の内部において往復運動を行うピストン２を有している。さらに、気筒１とピストン２との間に設けられる燃焼室３に直接燃料を噴射する主燃料噴射弁４を備えている。主燃料噴射弁４は、燃料供給管５２を介して蓄圧室５０および燃料ポンプ５１と連通している。燃料ポンプ５１は内燃機関の出力軸（以後、「クランクシャフト」という）の回転を駆動源とし、図示されない燃料タンクより燃料を吸い上げ、蓄圧室５０へと供給する。蓄圧室５０では一定圧力に燃料が蓄圧されており、主燃料噴射弁４に駆動電流が印加され主燃料噴射弁が開弁することによって、燃焼室３内へ燃料が噴射される。また、主燃料噴射弁４内において噴射されずに残った燃料は燃料送管５３を経て図示されない燃料タンクへと戻る。図１中、実線の矢印は、燃料の流れを表すものである。尚、蓄圧室５０の蓄圧を変更することによって、主燃料噴射弁４の噴射圧を変更することが可能である。
【００２６】
ここで主燃料噴射弁４から噴射される燃料を、以降主燃料というものとする。主燃料は、本実施例において、主に気筒１における燃焼サイクルが圧縮行程上死点近傍において噴射される燃料である。
【００２７】
また、図１の圧縮着火内燃機関は、前記主燃料噴射弁４に加えて副燃料噴射弁５をも備えている。副燃料噴射弁５は、燃料供給管５６を介して蓄圧室５４および燃料ポンプ５５と連通している。燃料ポンプ５５はクランクシャフトを駆動源とし、図示されない燃料タンクより燃料を吸い上げ、蓄圧室５４へと供給する。蓄圧室５４では一定圧力に燃料が蓄圧されており、副燃料噴射弁５に駆動電流が印加され副燃料噴射弁が開弁することによって、燃焼室３内へ燃料が噴射される。また、副燃料噴射弁５内において噴射されずに残った燃料は燃料送管５７を経て図示されない燃料タンクへと戻る。図１中、実線の矢印は、燃料の流れを表すものである。尚、蓄圧室５４の蓄圧を変更することによって、副燃料噴射弁５の噴射圧を変更することが可能である。
【００２８】
ここで副燃料噴射弁５から噴射される燃料を、以降副燃料というものとする。副燃料は、本実施例において、主に予混合気を燃焼室３内部に形成するための燃料である。従って、副燃料の噴射時期は前記主燃料の場合と一般に異なる。また、安定した予混合気を形成するために主燃料とは性状の異なる燃料を使用することも可能である。
【００２９】
次に、図１の圧縮着火内燃機関には、吸気枝管８が気筒１の燃焼室３と連通しており、吸気支管８と燃焼室３の間における吸気の移動は、吸気弁６の開閉動作を介して行われる。同様に、排気枝管９が気筒１の燃焼室３と連通しており、排気枝管９と燃焼室３の間における排気の移動は、排気弁７の開閉動作を介して行われる。
【００３０】
ここで、主燃料噴射弁４および副燃料噴射弁５は、電子制御ユニット（以下、ＥＣＵ：Electronic Control Unitと呼ぶ）１１からの制御信号によって開閉動作を行う。ここで、アクセル開度に応じた信号を発するアクセル開度センサ１３は、電気的にＥＣＵ１１と接続されており、ＥＣＵ１１はアクセル開度センサ１３から得たアクセル開度信号に応じて、主燃料の噴射時期および噴射量と、副燃料の噴射時期および噴射量を決定する。また、ピストン２が連結されているクランクシャフトの回転角を検出するクランクポジションセンサ１２は、電気的にＥＣＵ１１と接続されており、クランクポジションセンサ１２によって検出された回転角がＥＣＵ１１へ読み込まれ、圧縮着火内燃機関の機関回転数の算出や、気筒１の燃焼サイクルにおける行程の判断等が行われる。
【００３１】
このように構成される気筒１においては、ＥＣＵ１１から副燃料噴射弁５に対して副燃料の噴射指令が出され、副燃料が燃焼室３の内部に噴射されることで、予混合気が形成される。その後、圧縮行程上死点近傍において、主燃料噴射弁４から主燃料が噴射され、燃焼室３における燃料の着火、燃焼が行われる。
【００３２】
ここで、圧縮着火内燃機関の機関負荷が大きくなるに従い、予混合気が過早着火する虞が大きくなる。そこで、該予混合気の過早着火を回避する副燃料の噴射について図２、図３および図４に基づいて、以降、説明する。
【００３３】
図２は、圧縮着火内燃機関における機関回転数と機関負荷との関係を示す図である。横軸は圧縮着火内燃機関の機関回転数を、縦軸は圧縮着火内燃機関の機関負荷を示す。ここで、線Ｌ１は本実施例の圧縮着火内燃機関における、各機関回転数に対する最大機関負荷を表している。線１で表される最大機関負荷は、機関回転数がほぼ０のときに機関負荷ＴＱ１を、機関回転数がＮｅ１のときに最大負荷であるＴＱ２を発揮し、且つ機関回転数の最高値がＮｅ２である機関負荷を意味する。従って、本実施例の圧縮着火内燃機関においては、線Ｌ１と、縦軸および横軸とで囲まれる領域（図中、Ｒ１、Ｒ２およびＲ３）に属する機関負荷が発揮されることになる。
【００３４】
ここで、領域Ｒ１は、線Ｌ２と、縦軸および横軸とで囲まれる領域であって、圧縮着火内燃機関の機関負荷における低負荷域を意味し、機関回転数が０からＮｅ３且つ機関負荷が０からＴＱ３で構成される矩形状の領域である。また、領域Ｒ２は、線Ｌ２および線Ｌ３と、縦軸および横軸とで囲まれる領域であって、圧縮着火内燃機関の機関負荷における中負荷域を意味し、機関回転数が０からＮｅ４且つ機関負荷が０からＴＱ４で構成される矩形状の領域から先述の領域Ｒ１を除いた領域である。また、領域Ｒ３は、線Ｌ３および線Ｌ１と、縦軸および横軸とで囲まれる領域であって、圧縮着火内燃機関の機関負荷における高負荷域を意味し、先述の最大機関負荷から領域Ｒ１およびＲ２で表される領域を除いた領域である。本実施例においては、図２のように、圧縮着火内燃機関の機関負荷を低負荷域、中負荷域および高負荷域と分類したが、この機関負荷の分類については図２に示す分類態様には限られず、圧縮着火内燃機関に応じた機関負荷の分類を行うことが可能である。
【００３５】
ここで、Ｒ１、Ｒ２およびＲ３で表される各負荷域に対応する燃料の噴射態様について図３に基づいて詳細に説明する。図３は、圧縮着火内燃機関の機関負荷に応じた燃料の噴射態様を概略的に示した図であって、図３（ａ）は、圧縮着火内燃機関の機関負荷が上記した領域Ｒ１に属している場合、即ち機関負荷が低負荷である場合の副燃料噴射弁５と主燃料噴射弁４における燃料噴射を表している。図３（ｂ）は、圧縮着火内燃機関の機関負荷が上記した領域Ｒ２に属している場合、即ち機関負荷が中負荷である場合の副燃料噴射弁５と主燃料噴射弁４における燃料噴射を表している。図３（ｃ）は、圧縮着火内燃機関の機関負荷が上記した領域Ｒ３に属している場合、即ち機関負荷が高負荷である場合の副燃料噴射弁５と主燃料噴射弁４における燃料噴射を表している。ここで、図３（ａ）から（ｃ）において、横軸は気筒１の燃焼サイクルにおけるクランク角を表している。従って、−３６０ｄｅｇで表される時間は燃焼サイクルにおける吸気行程上死点を、０ｄｅｇで表される時間は圧縮行程上死点を意味する。また、図３（ａ）から（ｃ）において表される矩形Ｊ１からＪ４は、各燃料噴射弁における燃料の噴射を表し、該矩形の横軸方向の長さはクランク角量に換算された燃料噴射時間、即ち燃料噴射量に概ね比例する。
【００３６】
まず、図３（ａ）においては、圧縮着火内燃機関の機関負荷が低負荷であるため、予混合気の過早着火の虞がない。従って、副燃料によって形成される予混合気を燃焼室３内部に均一に拡散させることで、ＮＯｘの低減およびスモークの低減を効果的に発揮することが可能となる。そこで、図３（ａ）に示すように、機関負荷が低負荷域に属している場合は、気筒１の燃焼サイクルにおいて、吸気行程中期から圧縮行程中期までの期間に副燃料噴射弁５より副燃料を噴射する（図３（ａ）中のＪ１で示される）。この際に燃焼室３において形成される予混合気について、図４（ａ）に従い説明する。
【００３７】
図４（ａ）は、ピストン２が気筒１内において下降した位置にある場合に副燃料噴射弁５から副燃料を噴射したときの予混合気の形成の様子を概略的に示している。ピストン２が気筒１内において下降した位置にある場合、即ち吸気行程中期から圧縮行程中期において副燃料噴射弁５から副燃料が噴射されると、ピストン２の下降によって燃焼室３の容積が広く確保されているため、副燃料が広く燃焼室に拡散する。従って、副燃料噴射弁５から噴射された副燃料は、燃焼室３内に均一な予混合気を形成することになる。
【００３８】
また、主燃料の噴射（図３中のＪ２で示される）については、圧縮行程上死点近傍において主燃料が噴射され、該主燃料を基点として、燃焼室３内で燃料の着火燃焼が行われる。その結果、圧縮着火内燃機関の機関負荷が低負荷である場合は、予混合気の形成によるＮＯｘの抑制とスモークの抑制を為し得る。
【００３９】
次に、圧縮着火内燃機関の機関負荷が中負荷以上である場合、図３（ａ）と同様の時期に副燃料の噴射を行うと副燃料の噴射量が増大するため、予混合気が過早着火する虞がある。従って、図３（ｂ）、（ｃ）に示す時期に燃料の噴射を行う。まず、機関負荷が中負荷である場合、図３（ｂ）に示す燃料の噴射が行われる。図３（ｂ）においては、気筒１の燃焼サイクルにおける吸気行程初期に副燃料が燃焼室３の内部に噴射される。この際に燃焼室３において形成される予混合気について、図４（ｂ）に従い説明する。
【００４０】
図４（ｂ）は、ピストン２が気筒１内において上昇した位置にある場合に副燃料噴射弁５から副燃料を噴射したときの予混合気の形成の様子を概略的に示している。ピストン２が気筒１内において上昇した位置にある場合、即ち吸気行程初期もしくは圧縮行程後期において副燃料噴射弁５から副燃料が噴射されると（図３（ｂ）のＪ１で示される）、ピストン２の上昇によって燃焼室３の容積は狭く確保されているため、副燃料が広く燃焼室に拡散しない。従って、副燃料噴射弁５の噴射方向を調整することで、副燃料による予混合気を主燃料噴射弁４の近傍に形成させることが可能となる。従って、燃焼室３における空燃比分布は、主燃料噴射弁４の近傍においては、予混合気の過早着火が発生しにくい程度にリッチな状態となっており、またその周囲部については副燃料がほぼ存在しないため、非常にリーンな状態となっている。即ち、予混合気の過早着火が生じ得る理論空燃比近傍の空燃比を回避した空燃比分布となっている。
【００４１】
また、主燃料の噴射（図３（ｂ）のＪ２で示される）については、圧縮行程上死点近傍において主燃料が噴射されるが、該主燃料の噴射の直前において、主燃料噴射弁４より主燃料を微量に噴射する（図３（ｂ）のＪ３で示される）。これにより燃焼室３の内部に気体の流れを生じさせ、図３（ｂ）のＪ１で示される副燃料の噴射によって主燃料噴射弁４の近傍の一定の範囲に形成されている予混合気の撹拌を行う。主燃料の噴射の直前であるため、予混合気の過早着火による圧縮着火内燃機関への影響はない。この微量の主燃料の噴射によって、主燃料の噴射（図３（ｂ）のＪ２で示される）直前に燃焼室３の内部の空燃比分布を、より均一なものとすることが可能となる。
【００４２】
そして、主燃料の噴射（図３（ｂ）のＪ２で示される）を基点として、燃焼室３内で燃料の着火燃焼が行われる。その結果、圧縮着火内燃機関の機関負荷が中負荷である場合は、圧縮着火内燃機関の機関負荷が中負荷であっても、予混合気を燃焼室３の内部の一定の範囲において形成し該予混合気の過早着火を回避することが可能となり、予混合気の形成によるＮＯｘの抑制とスモークの抑制を為し得る。
【００４３】
次に、機関負荷が高負荷である場合、図３（ｃ）に示す燃料の噴射が行われる。図３（ｃ）においては、気筒１の燃焼サイクルにおける吸気行程初期および圧縮行程後期に副燃料が燃焼室３の内部に噴射される。この際に燃焼室３において形成される予混合気については、先述の図４（ｂ）についての説明の通りである。
【００４４】
機関負荷が高負荷である場合は、中負荷である場合と比較して相対的に燃料の噴射量が増加し、その結果、噴射時間が長期化する。しかし、先述のように機関負荷が高い場合は、副燃料による予混合気を主燃料噴射弁４の近傍に形成するためには、ピストン２がある程度上昇した位置、即ち吸気行程初期もしくは圧縮行程後期に副燃料を噴射しなければならない。そこで、副燃料の噴射量が、吸気行程初期までに噴射することができない程に多い場合は、吸気行程初期における副燃料の噴射（図３（ｃ）のＪ１で表される）の後、副燃料の噴射を一度停止し、その後吸気行程後期に副燃料の噴射を開始するものとする（図３（ｃ）のＪ４で表される）。このようにすることで、副燃料による予混合気を主燃料噴射弁４の近傍に形成することが可能となる。従って、燃焼室３における空燃比分布は、主燃料噴射弁４の近傍においては、予混合気の過早着火が発生しにくい程度にリッチな状態となっており、またその周囲部については燃料がほぼ存在しないため、非常にリーンな状態となっている。即ち、予混合気の過早着火が生じ得る理論空燃比近傍の空燃比を回避した空燃比分布となっている。
【００４５】
また、主燃料の噴射（図３（ｃ）のＪ２で示される）、および該主燃料の噴射の直前の噴射（図３（ｃ）のＪ３で示される）については、機関負荷が中負荷である場合と同様である。
【００４６】
主燃料の噴射（図３（ｃ）のＪ２で示される）を基点として、燃焼室３内で燃料の着火燃焼が行われる。その結果、圧縮着火内燃機関の機関負荷が中負荷である場合は、圧縮着火内燃機関の機関負荷が中負荷であっても、予混合気を燃焼室３の内部の一定の範囲において形成し該予混合気の過早着火を回避することが可能となり、予混合気の形成によるＮＯｘの抑制とスモークの抑制を為し得る。
【００４７】
図３（ｂ）および（ｃ）に示した本実施例においては、圧縮着火内燃機関の機関負荷に従い、まず副燃料の噴射を吸気行程初期で行い、該吸気行程初期の期間で副燃料の噴射を完了できない場合は、圧縮行程後期で副燃料の噴射を行っている。しかし、本実施例とは逆に、圧縮着火内燃機関の機関負荷に従い、まず副燃料の噴射を圧縮行程後期で行い、該圧縮行程後期の期間で副燃料の噴射を完了できない場合は、吸気行程初期で副燃料の噴射を行ってもよい。
【００４８】
本実施例の図３（ｂ）および（ｃ）において示したように、圧縮着火内燃機関の機関負荷が中負荷以上である場合に、主燃料噴射弁４の近傍に副燃料による予混合気を形成する際、副燃料噴射弁５の噴射圧を低下させることも有用である。副燃料噴射弁５の噴射圧を低下させることで、副燃料の粒径が大きくなるため、予混合気の過早着火を抑制することができる。尚、図３（ａ）に示すように、圧縮着火内燃機関の機関負荷が低負荷である場合は、予混合気の過早着火の虞はないため副燃料噴射弁５の噴射圧を上昇させ、副燃料の粒径を小さくすることで、燃料の燃焼を促進させることができる。
【００４９】
＜第２の実施例＞
次に、本発明に係る第２の実施例を図５、図６、図７および図８に基づいて説明する。図５は、本発明が適用される圧縮着火内燃機関の燃焼室近傍の概略構成およびその制御系統の概略構成を表す図であり、図１に示される概略構成における構成要素について同一の要素については、同一の参照番号を付することによってその説明を省略する。以下、相違する構成要素について説明する。
【００５０】
図５に示す圧縮着火内燃機関の燃焼室３における予混合気の空燃比を測定する空燃比センサ１４ａおよび１４ｂが、気筒１の上部に設けられている。ここで、図６は、燃焼室３側から気筒２の上部を視した場合の概略構成図である。本実施例では、吸気弁６は吸気弁６ａと６ｂの２弁で構成され、排気弁７は排気弁７ａと７ｂの２弁で構成される。空燃比センサ１４ａは副燃料噴射弁５の近傍であって、吸気弁６ａと吸気弁６ｂの間に位置し、一方の空燃比センサ１４ｂは気筒２の中心部に対して反対側であって排気弁７ａと排気弁７ｂの間に位置する。また、吸気弁６ａおよび吸気弁６ｂの開閉特性を可変とする可変動弁機構１６ａが、排気弁７ａおよび排気弁７ｂの開閉特性を可変とする可変動弁機構１６ｂが備えられている。ここで、可変動弁機構１６ａおよび１６ｂによって可変とされる吸排気弁の開閉特性には、吸排気弁の開弁時期、開弁時間、リフト量、作用角等があげられる。また、副燃料噴射弁５において、副燃料の加熱を行うヒータ１５が備えられている。
【００５１】
ここで、空燃比センサ１４ａおよび１４ｂによって検出された燃焼室３内の空燃比はＥＣＵ１１へと送られ、ＥＣＵ１１によって燃焼室３内に形成される予混合気の空燃比分布が検出される。このＥＣＵ１１による空燃比分布の検出が、本発明に係る空燃比分布検出手段に相当する。図７は、空燃比センサ１４ａおよび１４ｂによって検出された空燃比を基に、ＥＣＵ１１によって検出された燃焼室３内の空燃比分布を示す図である。横軸は、図６に示す直線Ｘに対応しており、縦軸は、直線Ｘ上の部位における空燃比を表す。また、図７における点Ｐ１および点Ｐ２は、それぞれ空燃比センサ１４ａおよび１４ｂによって検出された空燃比であり、この２点を基にＥＣＵ１１によって、燃焼室３内の空燃比分布は直線Ｌ４で表されている。本実施例では、２つの空燃比センサから検出される空燃比の値を基に、直線的に燃焼室３内の空燃比分布を検出しているが、３つ以上の空燃比センサからの空燃比を基に、一定の関数に基づいて燃焼室３内の空燃比分布を検出してもよい。
【００５２】
ここで、図７において、領域Ｒ４で表される空燃比は、燃焼室３内に形成された予混合気が過早着火をする虞のある領域に属する空燃比であり、具体的には理論空燃比近傍の空燃比となる。従って、燃焼室３内の空燃比分布が、図７に示すような直線Ｌ４で表される場合、領域Ｒ４に属する空燃比を有する予混合気が過早着火を起こす虞がある。
【００５３】
そこで、図８に燃焼室３内に形成される予混合気の空燃比分布が領域Ｒ４に属さないように、副燃料噴射弁５の噴射距離を調整することで、予混合気の空燃比を調整する噴射距離制御のフローチャートを示す。噴射距離制御は、ＥＣＵ１１によって繰り返し実行される制御であり、ＥＣＵ１１によって本制御が実行されることは本発明における噴射距離調整手段に相当する。
【００５４】
まず、Ｓ１０１において、燃焼室３内に形成される予混合気の空燃比分布が過早着火領域、即ち図７に示される領域Ｒ４を含むか否かが判定される。先述のように、本実施例においては、２つの空燃比センサ１４ａおよび１４ｂによって検出された空燃比を基に、燃焼室３内の空燃比分布をＥＣＵ１１が検出し、該空燃比分布が領域Ｒ４を含むか否かを判断する。ここで、該空燃比分布が領域Ｒ４を含まないと判断される場合、即ち燃焼室３内において、予混合気の過早着火が発生しないと判断される場合は、Ｓ１０１からＳ１０５へ進み、本制御を終了する。一方で、該空燃比分布が領域Ｒ４を含むと判断される場合、即ち燃焼室３内において、予混合気の過早着火が発生すると判断される場合は、Ｓ１０２へ進む。
【００５５】
Ｓ１０２では、空燃比センサ１４ａによって検出される空燃比と空燃比センサ１４ｂによって検出される空燃比が比較される。本実施例においては、空燃比センサ１４ａの近傍に、副燃料噴射弁５が設けられている。従って、副燃料噴射弁５から噴射される副燃料の噴射距離を短くすることによって、空燃比センサ１４ａ近傍における予混合気の空燃比を小さくする、即ち燃料濃度を高くすることが可能となり、また副燃料噴射弁５から噴射される副燃料の噴射距離を長くすることによって、空燃比センサ１４ａの反対側に位置する空燃比センサ１４ｂ近傍における予混合気の空燃比を小さくする、即ち燃料濃度を高くすることが可能となる。燃焼室３内において空燃比が高い場所、即ち燃料濃度の低い場所が存在する場合は、その場所を中心に副燃料を噴射することによって燃焼室３内における空燃比分布の偏りを緩和し、概ね均一とすることが可能となる。そこで、Ｓ１０２においては、空燃比センサ１４ａによって検出される空燃比と空燃比センサ１４ｂによって検出される空燃比とを比較することで、どの場所を中心として副燃料を噴射すべきかを判断する。Ｓ１０２において、空燃比センサ１４ｂによって検出される空燃比が、空燃比センサ１４ａによって検出される空燃比より大きいと判断されるとＳ１０３へ進み、空燃比センサ１４ｂによって検出される空燃比が、空燃比センサ１４ａによって検出される空燃比以下と判断されるとＳ１０４へ進む。
【００５６】
Ｓ１０３では、副燃料噴射弁５の噴射圧が増加される。これによって、副燃料の噴射距離が遠方にまで達することになる。そして、空燃比センサ１４ｂに、より近い場所を中心として副燃料が燃焼室３内に拡散することになるため、燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となる。その結果、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
【００５７】
Ｓ１０４では、副燃料噴射弁５の噴射圧が減少される。これによって、副燃料の噴射距離が遠方にまで達するのが困難となる。そして、空燃比センサ１４ａに、より近い場所を中心として副燃料が燃焼室３内に拡散することになるため、燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となる。その結果、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
Ｓ１０３およびＳ１０４の処理が終了すると、Ｓ１０５へ進み、本制御を終了する。
【００５８】
また、副燃料噴射弁５から噴射される副燃料の噴射距離を調整するに際して、先の実施例では、副燃料噴射弁５の噴射圧を増減することによって副燃料の噴射距離を調整したが、その他にも副燃料の噴射回数を調整することで、副燃料の噴射距離を調整することが可能である。即ち、副燃料の噴射回数を少なくすることで、一回あたりの副燃料噴射弁５の開弁時間が長くなるため、副燃料の噴射距離が長くなる。一方で、副燃料の噴射回数を多くすることで、一回あたりの副燃料噴射弁５の開弁時間が短くなるため、副燃料の噴射距離が短くなる。従って、図８に示すフローチャートにおいて、Ｓ１０３およびＳ１０４で行う処理に代わり、それぞれ「副燃料の噴射回数低減」、「副燃料の噴射回数増加」という処理を行うことも可能となる。この結果、燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となり、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
【００５９】
また、副燃料の噴射距離を調整するその他の手段として、ヒータ１５の温度を調整することで、副燃料の噴射距離を調整する手段が考えられる。即ち、ヒータ１５の温度を高くすることによって副燃料の温度が上昇し、副燃料の燃料粒径が細かくなり、副燃料の噴射距離が長くなる。一方で、ヒータ１５の温度を低くすることによって副燃料の温度が下降し、副燃料の燃料粒径が大きくなり、副燃料の噴射距離が短くなる。従って、図８に示すフローチャートにおいて、Ｓ１０３およびＳ１０４で行う処理に代わり、それぞれ「ヒータ温度の上昇」、「ヒータ温度の下降」という処理を行うことも可能となる。この結果、燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となり、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
【００６０】
＜第３の実施例＞
図９に燃焼室３内に形成される予混合気の空燃比分布が領域Ｒ４に属さないようにするその他の実施例として、可変動弁機構（図５の吸気側可変動弁機構１６ａ、排気側可変動弁機構１６ｂ）によって、予混合気の空燃比を調整する吸排気弁開閉制御のフローチャートを示す。吸排気弁開閉制御は、ＥＣＵ１１によって繰り返し実行される制御である。ここで、図９に示すフローチャートにおいて、図８に示すフローチャートの処理と同一の処理については、同一の参照番号を付することによって、その説明を省略する。
【００６１】
まず、Ｓ１０１において、燃焼室３内の空燃比分布が領域Ｒ４を含まないと判断される場合、即ち燃焼室３内において、予混合気の過早着火が発生しないと判断される場合は、Ｓ１０１からＳ１０９へ進み、本制御を終了する。一方で、該空燃比分布が領域Ｒ４を含むと判断される場合、即ち燃焼室３内において、予混合気の過早着火が発生すると判断される場合は、Ｓ１０６へ進む。
【００６２】
Ｓ１０６では、空燃比センサ１４ａによって検出される空燃比と空燃比センサ１４ｂによって検出される空燃比が比較される。本実施例においては、空燃比センサ１４ａの近傍に、吸気弁６が設けられている。従って、吸気弁６を開弁することによって燃焼室３内の予混合気の一部を燃焼室３の外へ排出し、吸気弁６近傍の空燃比を上昇させることが可能となり、また排気弁７を開弁することによって燃焼室３内の予混合気の一部を燃焼室３の外へ排出し、排気弁７近傍の空燃比を上昇させることが可能となる。その結果、燃焼室３内における空燃比分布の偏りを緩和し、概ね均一とすることが可能となる。そこで、Ｓ１０６においては、空燃比センサ１４ａによって検出される空燃比と空燃比センサ１４ｂによって検出される空燃比とを比較することで、吸気弁６と排気弁７のどちらの弁を開弁するかを判断する。Ｓ１０６において、空燃比センサ１４ｂによって検出される空燃比が、空燃比センサ１４ａによって検出される空燃比より大きいと判断されるとＳ１０７へ進み、空燃比センサ１４ｂによって検出される空燃比が、空燃比センサ１４ａによって検出される空燃比以下と判断されるとＳ１０８へ進む。
【００６３】
Ｓ１０７では、吸気側可変動弁機構１６ａによって吸気弁６（吸気弁６ａおよび６ｂ）が開弁される。吸気弁６が開弁される時期は、圧縮着火内燃機関の圧縮行程初期が好ましいが、この時期に限られるものではなく燃焼室３内に形成されている予混合気の一部が燃焼室３の外部に放出される時期であればよい。これによって、吸気弁６近傍における燃焼室３内の空燃比が上昇し、以て燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となる。その結果、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
【００６４】
吸気側可変動弁機構１６ａによって吸気弁６を開弁すると、燃焼室３内の予混合気の一部は吸気支管８へ移動することになるが、該予混合気は次の燃焼サイクルにおいて利用が可能であり、また圧縮着火内燃機関が複数の気筒を有する場合は、他の気筒における燃焼に該予混合気が供せられ得る。
【００６５】
Ｓ１０８では、排気側可変動弁機構１７ａによって排気弁７（排気弁７ａおよび７ｂ）が開弁される。排気弁７が開弁される時期は、圧縮着火内燃機関の圧縮行程初期が好ましいが、この時期に限られるものではなく燃焼室３内に形成されている予混合気の一部が燃焼室３の外部に放出される時期であればよい。これによって、排気弁７近傍における燃焼室３内の空燃比が上昇し、以て燃焼室３内における予混合気の空燃比分布における偏りが軽減され、空燃比分布が概ね均一となる。その結果、該空燃比分布が過早着火領域、即ち領域Ｒ４を含まなくなるため、予混合気の過早着火を回避することが可能となる。
Ｓ１０７およびＳ１０８の処理が終了すると、Ｓ１０９へ進み、本制御を終了する。
【００６６】
【発明の効果】
本発明に係る予混合圧縮着火内燃機関は、複数の燃料噴射弁を有する圧縮着火内燃機関において予混合燃焼する場合に、燃焼室内に形成される予混合気の空燃比分布を、該予混合気の過早着火が生じる空燃比を回避する空燃比分布とする。これにより、該予混合気の過早着火を回避し、安定した燃焼が可能となる。
【図面の簡単な説明】
【図１】本実施の形態に係る予混合圧縮着火内燃機関およびその制御系統の概略構成を示す図である。
【図２】本実施の形態に係る予混合圧縮着火内燃機関における機関回転数と機関負荷との関係を示す図である。
【図３】本実施の形態に係る予混合圧縮着火内燃機関における機関負荷と燃料の噴射時期との関係を示す図である。
【図４】本実施の形態に係る予混合圧縮着火内燃機関の燃焼室におけるピストンの位置と燃焼室内に形成される予混合気との関係を示した図である。
【図５】本実施の形態に係る予混合圧縮着火内燃機関およびその制御系統の概略構成を示す第２の図である。
【図６】本実施の形態に係る予混合圧縮着火内燃機関において、燃焼室側から気筒の上部を視した場合の概略構成を示すフロー図である。
【図７】本実施の形態に係る予混合圧縮着火内燃機関において、空燃比センサによって検出された空燃比を基に、検出された燃焼室内の空燃比分布を示す図である。
【図８】本実施の形態に係る予混合気形成時の該予混合気の過早着火を回避するための副燃料の噴射距離制御を示すフロー図である。
【図９】本実施の形態に係る予混合気形成時の該予混合気の過早着火を回避するための吸排気弁の開閉制御を示すフロー図である。
【符号の説明】
１・・・・気筒
２・・・・ピストン
３・・・・燃焼室
４・・・・主燃料噴射弁
５・・・・副燃料噴射弁
６・・・・吸気弁
６ａ・・・・吸気弁
６ｂ・・・・吸気弁
７・・・・排気弁
７ａ・・・・排気弁
７ｂ・・・・排気弁
１１・・・・ＥＣＵ
１４ａ・・・・空燃比センサ
１４ｂ・・・・空燃比センサ
１５・・・・ヒータ
１６ａ・・・・吸気側可変動弁機構
１６ｂ・・・・排気側可変動弁機構[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a premixed compression ignition internal combustion engine.
[0002]
[Prior art]
In a compression ignition internal combustion engine having a plurality of fuel injection valves, fuel is injected from the other fuel injection valves at a time earlier than the injection of fuel into the combustion chamber near the top dead center of the compression stroke from one fuel injection valve, By giving a sufficient mixing time to form a lean premixed gas, the fuel concentration distribution becomes more uniform, and premixed combustion that suppresses the generation of smoke and NOx is performed. However, in the premixed combustion, when the load on the internal combustion engine increases, the amount of fuel injected into the combustion chamber increases, and the fuel distribution in the combustion chamber tends to become non-uniform, so that smoke and NOx are generated.
[0003]
Therefore, the fuel injection amount and the injection timing of the fuel injection valve that injects the fuel that forms the lean premixed gas and the fuel injection valve that injects the fuel near the top dead center of the compression stroke are determined as the load of the internal combustion engine. Accordingly, the technology to be changed is specified (for example, see Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-324631
[Patent Document 2]
JP-A-8-210169
[0005]
[Problems to be solved by the invention]
Here, in a compression ignition internal combustion engine, when premixed combustion is performed for the purpose of suppressing exhausted NOx and exhaust smoke, the fuel is compressed by injecting the fuel at an early stage in the combustion cycle. So-called pre-ignition occurs where the premixed gas ignites and burns earlier than the vicinity of the stroke top dead center. Due to premature ignition, the pressure in the combustion chamber rises rapidly, resulting in a large impact and noise in the internal combustion engine.
[0006]
Here, the possibility of occurrence of pre-ignition of premixed gas becomes high when the fuel concentration distribution of the premixed gas, that is, the air-fuel ratio distribution becomes a value close to the stoichiometric air-fuel ratio. Here, in the premixed gas formed in the combustion chamber of the internal combustion engine, when the air-fuel ratio distribution is biased, for example, when the air-fuel ratio distribution is continuously changing in the combustion chamber In the air-fuel ratio distribution, a portion having an air-fuel ratio close to the theoretical air-fuel ratio tends to exist. In particular, when the engine load of the internal combustion engine increases and a relatively large amount of fuel is injected into the combustion chamber, the tendency becomes stronger. Therefore, the possibility of premature ignition in the air-fuel ratio distribution of the premixed gas increases.
[0007]
Therefore, in view of the above problems, in the present invention, when premixed combustion is performed in a compression ignition internal combustion engine having a plurality of fuel injection valves, the air-fuel ratio distribution of the premixed gas formed in the combustion chamber is expressed as It is an object of the present invention to provide a premixed compression ignition internal combustion engine that avoids premature ignition of the premixed gas and enables stable combustion by setting an air / fuel ratio distribution that avoids an air / fuel ratio at which premature ignition occurs. To do.
[0008]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above-described problems. That is, the main fuel injection valve that is provided in the substantially central portion of the combustion chamber of the internal combustion engine and injects fuel in the vicinity of the top dead center of the compression stroke, and is provided at a position deviated from the main fuel injection valve. An auxiliary fuel injection valve for injecting fuel forming an air-fuel mixture; When the engine load of the internal combustion engine is lower than the medium load, a premixed gas is formed by injecting fuel from the auxiliary fuel injection valve from the middle of the intake stroke to the middle of the compression stroke, and the engine load of the internal combustion engine exceeds the medium load. A premixed gas forming means for forming a premixed gas in the vicinity of the main fuel injection valve by injecting fuel from the auxiliary fuel injection valve at least in the early stage of the intake stroke or the late stage of the compression stroke. The premixed gas forming means is configured to inject the sub fuel injection when the engine load of the internal combustion engine is lower than the medium load when the fuel is injected from the sub fuel injection valve when the engine load of the internal combustion engine is equal to or higher than the medium load. Lower the injection pressure of the auxiliary fuel injection valve than when fuel is injected from the valve It is characterized by that.
[0009]
Cooling water circulation means is provided on the outer periphery of the cylinder block and cylinder head of the internal combustion engine, and heat generated by the combustion of fuel is radiated. However, since the vicinity of the main fuel injection valve provided at the substantially central portion of the combustion chamber is a part away from the circulating means of the cooling water, the effect of heat radiation by the cooling water is small. Therefore, the temperature of the space near the main fuel injection valve in the combustion chamber is relatively higher than the temperature of the surrounding space near the cylinder wall surface of the combustion chamber. In such an internal combustion engine, when fuel is injected to form a premixed gas from the auxiliary fuel injection valve, when the amount of the fuel is above a certain level, that is, when the engine load in the internal combustion engine is above a medium load Then, the air-fuel ratio of the premixed gas formed substantially uniformly inside the combustion chamber shifts to the stoichiometric air-fuel ratio side. As a result, when the air-fuel ratio is about the stoichiometric air-fuel ratio in the space near the main fuel injection valve, the premixed gas may be prematurely ignited due to the relatively high temperature of the space. Becomes very high.
[0010]
Therefore, in this means, when the engine load of the internal combustion engine is equal to or higher than the medium load, that is, when the premixed gas is formed in the same manner as when the engine load of the internal combustion engine is low, it is formed in the combustion chamber. In the premixed gas, when there is a portion having an air-fuel ratio in which premature ignition may occur, the premixed gas is formed in the vicinity of the main fuel injection valve. This makes it possible to avoid that the air-fuel ratio in the vicinity of the main fuel injection valve becomes an air-fuel ratio that is likely to cause premature ignition of the premixed gas, and is stable regardless of the operating load of the internal combustion engine. Combustion becomes possible.
[0011]
Here, as a means for forming a premixed gas in the vicinity of the main fuel injection valve, fuel injection from the sub fuel injection valve is performed at the initial stage of the intake stroke. and It is conceivable to carry out at least one of the later stages of the compression stroke. That is, In the early intake stroke and late compression stroke Since the position of the piston that reciprocates in the cylinder of the internal combustion engine is relatively high, if fuel is injected by the auxiliary fuel injection valve at that time, the fuel that forms the premixed gas by the piston is introduced into the cylinder. As a result, the premixed gas can be formed in the vicinity of the main fuel injection valve.
[0012]
Further, in the premixed compression ignition internal combustion engine up to the above, when the engine load of the internal combustion engine is lower than the medium load, the fuel injection from the auxiliary fuel injection valve is performed as an intake line. In the middle From the beginning to the middle of the compression stroke. As a result, when there is no possibility of pre-ignition of the premixed gas, that is, when the engine load of the internal combustion engine is lower than the medium load, In the middle In the middle of the compression stroke, that is, in a position where the piston position in the cylinder is relatively low, by injecting fuel from the auxiliary fuel injection valve, a uniform premixed gas is formed in the combustion chamber, and NOx due to premixed combustion is formed. And exhaust smoke can be suppressed.
[0013]
Further, in the premixed compression ignition internal combustion engine described above, the premixed gas forming means When the engine load of the internal combustion engine is more than medium load From auxiliary fuel injection valve Fuel When injecting, the injection pressure of the auxiliary fuel injection valve is lower than when the fuel is injected from the auxiliary fuel injection valve when the engine load of the internal combustion engine is lower than the medium load. By reducing the injection pressure, the particle size of the fuel injected from the auxiliary fuel injection valve increases. Therefore, since the particle diameter of the fuel of the premixed gas formed in the vicinity of the main fuel injection valve is increased, the possibility that the premixed gas is prematurely ignited is further reduced.
[0014]
Here, in the vicinity of the top dead center of the compression stroke, when fuel is injected from the main fuel injection valve and combustion of the fuel is performed in the combustion chamber, it is preferable that the degree of mixing of fuel and air in the combustion chamber is promoted. . Therefore, means for injecting a small amount of fuel from the main fuel injection valve before injecting fuel from the main fuel injection valve in the vicinity of the compression top dead center can be considered. That is, by generating a flow of air or a mixture to the air-fuel mixture formed at that time with a small amount of fuel injected before fuel is combusted in the combustion chamber, the fuel in the combustion chamber It promotes the degree of mixing with air. In particular, the engine load of the internal combustion engine is greater than or equal to the medium load, By injecting fuel from the auxiliary fuel injection valve at least one of the initial stage of the intake stroke and the late stage of the compression stroke When the premixed gas is formed in the vicinity of the fuel injection valve, the premixed gas is not in a state of being widely diffused after being mixed with the air in the combustion chamber. It is possible to mix the premixed gas that has been mixed with the air present in the vicinity thereof to a good degree.
[0015]
In the case of premixed combustion in a compression ignition internal combustion engine having a plurality of fuel injection valves, the following means are employed as other means for avoiding pre-ignition of the premixed gas and enabling stable combustion. That is, the main fuel injection valve that is provided in the substantially central portion of the combustion chamber of the internal combustion engine and injects fuel in the vicinity of the top dead center of the compression stroke, and is provided at a position displaced from the main fuel injection valve, and is premixed. An auxiliary fuel injection valve that injects fuel that forms gas, an air-fuel ratio distribution detecting means that detects an air-fuel ratio distribution of an air-fuel mixture formed in the combustion chamber, and an air-fuel ratio distribution detecting means that detects air in the combustion chamber detected by the air-fuel ratio distribution detecting means. And an injection distance adjusting means for making the air-fuel ratio distribution in the combustion chamber substantially uniform by adjusting the injection distance of the fuel injected from the sub fuel injection valve in accordance with the fuel ratio distribution.
[0016]
When the air-fuel ratio distribution of the air-fuel mixture formed in the combustion chamber is not substantially uniform and the distribution is biased, the air-fuel ratio of the portion is prematurely ignited in any portion of the combustion chamber. The air / fuel ratio is high, that is, the air / fuel ratio is close to the stoichiometric air / fuel ratio, and as a result, pre-ignition occurs starting from the site. Therefore, in the above-described means, the air-fuel ratio distribution detecting means detects the air-fuel ratio distribution in the combustion chamber, and if there is a deviation in the air-fuel ratio distribution, the injection distance of the fuel injected from the sub fuel injection valve By adjusting this, the air-fuel ratio in the combustion chamber is made substantially uniform. For example, if the air-fuel ratio of the part is large compared to other parts at a part away from the auxiliary fuel injection valve, the injection distance of the fuel injected from the auxiliary fuel injection valve is lengthened to bring it close to the part. The fuel reaches to lower the air-fuel ratio of the part, and the bias of the air-fuel ratio distribution in the combustion chamber is reduced.
[0017]
By this means, when premixed combustion is performed in a compression ignition internal combustion engine having a plurality of fuel injection valves, the air-fuel ratio distribution of the premixed gas formed in the combustion chamber is determined as the air-fuel ratio at which premature ignition of the premixed gas occurs. By setting the air-fuel ratio distribution to avoid the pre-mixed gas, pre-ignition is prevented from pre-ignition and stable combustion is possible.
[0018]
Here, the following means can be considered as the injection distance adjusting means. First, it is means for adjusting the injection pressure of the auxiliary fuel injection valve. As the injection pressure of the auxiliary fuel injection valve is increased, the fuel can reach a part further away from the auxiliary fuel injection valve. Therefore, when the air-fuel ratio distribution in the combustion chamber detected by the air-fuel ratio distribution detecting means gradually increases according to the distance from the sub fuel injection valve, by increasing the injection pressure of the sub fuel injection valve, On the other hand, when the air-fuel ratio distribution in the combustion chamber becomes gradually smaller according to the distance from the sub fuel injection valve, the air fuel ratio distribution in the combustion chamber is made substantially uniform by lowering the injection pressure of the sub fuel injection valve. It becomes possible to do things.
[0019]
Further, as the injection distance adjusting means, means for adjusting the number of injections of the auxiliary fuel injection valve can be considered. Even if the amount of fuel injected by the auxiliary fuel injection valve is the same, increasing the number of injections reduces the amount of fuel injected by one injection and shortens the opening time of the auxiliary fuel injection valve. Become. As a result, the fuel injection distance from the auxiliary fuel injection valve is shortened. Therefore, when the air-fuel ratio distribution in the combustion chamber detected by the air-fuel ratio distribution detecting means gradually increases according to the distance from the auxiliary fuel injection valve, by reducing the number of injections of the auxiliary fuel injection valve, On the other hand, when the air-fuel ratio distribution in the combustion chamber becomes gradually smaller according to the distance from the sub fuel injection valve, the air fuel ratio distribution in the combustion chamber is made substantially uniform by increasing the number of injections of the sub fuel injection valve. It becomes possible to do things.
[0020]
Further, as the injection distance adjusting means, means for adjusting the particle size of the fuel injected from the auxiliary fuel injection valve can be considered. The fuel injection distance is extended by reducing the particle size of the fuel injected by the auxiliary fuel injection valve. Here, as a means for reducing the particle size of the fuel, a heater for warming the auxiliary fuel injection valve can be considered. By heating the auxiliary fuel injection valve by the heater, the fuel is heated, and as a result, the viscosity of the fuel is reduced, so that the particle size of the fuel injected from the auxiliary fuel injection valve is reduced. Therefore, when the air-fuel ratio distribution in the combustion chamber detected by the air-fuel ratio distribution detecting means gradually increases according to the distance from the sub fuel injection valve, the particle size of the fuel injected from the sub fuel injection valve is set. By reducing the temperature, for example, by increasing the temperature of the heater, on the other hand, if the air-fuel ratio distribution in the combustion chamber gradually decreases with distance from the auxiliary fuel injection valve, the heater is injected from the auxiliary fuel injection valve. By increasing the particle size of the fuel, for example, by lowering the temperature of the heater, the air-fuel ratio distribution in the combustion chamber can be made substantially uniform.
[0021]
In the case of premixed combustion in a compression ignition internal combustion engine having a plurality of fuel injection valves, the following means are employed as other means for avoiding pre-ignition of the premixed gas and enabling stable combustion. That is, the main fuel injection valve that is provided in the substantially central portion of the combustion chamber of the internal combustion engine and injects fuel in the vicinity of the top dead center of the compression stroke, and is provided at a position deviated from the main fuel injection valve. At least one of an auxiliary fuel injection valve that injects fuel that forms an air-fuel mixture, an air-fuel ratio distribution detecting unit that detects an air-fuel ratio distribution of the air-fuel mixture formed in the combustion chamber, and an intake valve or an exhaust valve in the combustion chamber A variable valve mechanism that varies the opening / closing characteristics of the intake valve or the exhaust valve according to the air / fuel ratio distribution in the combustion chamber detected by the air / fuel ratio distribution detecting means. The air-fuel ratio distribution in the combustion chamber is made substantially uniform by opening at least one of the valves.
[0022]
When the air-fuel ratio distribution of the air-fuel mixture formed in the combustion chamber is not substantially uniform and the distribution is biased, the air-fuel ratio of the portion is prematurely ignited in any portion of the combustion chamber. The air / fuel ratio is high, that is, the air / fuel ratio is close to the stoichiometric air / fuel ratio, and as a result, pre-ignition occurs starting from the site. Therefore, in the above-described means, the air-fuel ratio distribution in the combustion chamber is detected by the air-fuel ratio distribution detecting means, and when there is a deviation in the air-fuel ratio distribution, the intake valve or exhaust gas is passed through the variable valve mechanism. By opening at least one of the valves, the air-fuel ratio in the combustion chamber is made substantially uniform. For example, when the air-fuel ratio distribution detecting means detects that the air-fuel ratio in the vicinity of the intake valve is smaller than the air-fuel ratio in other parts, the intake valve is opened via the variable valve mechanism. Thus, a part of the air-fuel mixture in the combustion chamber is released to the outside of the combustion chamber, and the air-fuel ratio in the vicinity of the intake valve is increased, thereby reducing the deviation of the air-fuel ratio distribution in the combustion chamber. On the other hand, when it is detected that the air-fuel ratio in the vicinity of the exhaust valve is smaller than the air-fuel ratio in other parts, the air-fuel ratio in the combustion chamber is opened by opening the exhaust valve via the variable valve mechanism. A part of the air is released to the outside of the combustion chamber, and the air-fuel ratio in the vicinity of the exhaust valve is increased, thereby reducing the deviation of the air-fuel ratio distribution in the combustion chamber.
[0023]
By this means, when premixed combustion is performed in a compression ignition internal combustion engine having a plurality of fuel injection valves, the air-fuel ratio distribution of the premixed gas formed in the combustion chamber is determined as the air-fuel ratio at which premature ignition of the premixed gas occurs. By setting the air-fuel ratio distribution to avoid the pre-mixed gas, pre-ignition is prevented from pre-ignition and stable combustion is possible.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
<First embodiment>
Here, an embodiment of a premixed compression ignition internal combustion engine according to the present invention will be described based on the drawings. FIG. 1 is a diagram showing a schematic configuration in the vicinity of a combustion chamber of a compression ignition internal combustion engine to which the present invention is applied and a schematic configuration of its control system.
[0025]
The compression ignition internal combustion engine of FIG. 1 has a piston 2 that reciprocates inside a cylinder 1. Furthermore, a main fuel injection valve 4 that directly injects fuel into a combustion chamber 3 provided between the cylinder 1 and the piston 2 is provided. The main fuel injection valve 4 communicates with the pressure accumulation chamber 50 and the fuel pump 51 via the fuel supply pipe 52. The fuel pump 51 uses the rotation of the output shaft (hereinafter referred to as “crankshaft”) of the internal combustion engine as a drive source, sucks up fuel from a fuel tank (not shown), and supplies it to the pressure accumulating chamber 50. Fuel is accumulated at a constant pressure in the pressure accumulating chamber 50, and fuel is injected into the combustion chamber 3 by applying a driving current to the main fuel injector 4 and opening the main fuel injector. Further, the fuel remaining without being injected in the main fuel injection valve 4 returns to a fuel tank (not shown) through the fuel feed pipe 53. In FIG. 1, solid arrows indicate the flow of fuel. Note that the injection pressure of the main fuel injection valve 4 can be changed by changing the pressure accumulation in the pressure accumulation chamber 50.
[0026]
Here, the fuel injected from the main fuel injection valve 4 is hereinafter referred to as main fuel. In this embodiment, the main fuel is a fuel that is injected mainly in the vicinity of the compression stroke top dead center in the combustion cycle in the cylinder 1.
[0027]
The compression ignition internal combustion engine of FIG. 1 also includes a sub fuel injection valve 5 in addition to the main fuel injection valve 4. The auxiliary fuel injection valve 5 communicates with the pressure accumulation chamber 54 and the fuel pump 55 via the fuel supply pipe 56. The fuel pump 55 uses a crankshaft as a drive source, sucks up fuel from a fuel tank (not shown), and supplies the fuel to the pressure accumulation chamber 54. In the pressure accumulating chamber 54, fuel is accumulated at a constant pressure, and when a driving current is applied to the sub fuel injection valve 5 and the sub fuel injection valve is opened, fuel is injected into the combustion chamber 3. Further, the fuel remaining without being injected in the auxiliary fuel injection valve 5 returns to the fuel tank (not shown) through the fuel feed pipe 57. In FIG. 1, solid arrows indicate the flow of fuel. The injection pressure of the auxiliary fuel injection valve 5 can be changed by changing the pressure accumulation in the pressure accumulation chamber 54.
[0028]
Here, the fuel injected from the auxiliary fuel injection valve 5 is hereinafter referred to as auxiliary fuel. In the present embodiment, the auxiliary fuel is mainly a fuel for forming a premixed gas in the combustion chamber 3. Therefore, the injection timing of the auxiliary fuel is generally different from that of the main fuel. It is also possible to use a fuel having a different property from the main fuel in order to form a stable premixed gas.
[0029]
Next, in the compression ignition internal combustion engine of FIG. 1, an intake branch pipe 8 communicates with the combustion chamber 3 of the cylinder 1, and the movement of intake air between the intake branch pipe 8 and the combustion chamber 3 opens and closes the intake valve 6. Done through the action. Similarly, the exhaust branch pipe 9 communicates with the combustion chamber 3 of the cylinder 1, and the movement of exhaust gas between the exhaust branch pipe 9 and the combustion chamber 3 is performed through the opening / closing operation of the exhaust valve 7.
[0030]
Here, the main fuel injection valve 4 and the auxiliary fuel injection valve 5 are opened and closed by a control signal from an electronic control unit (hereinafter referred to as ECU: Electronic Control Unit) 11. Here, the accelerator opening sensor 13 that emits a signal corresponding to the accelerator opening is electrically connected to the ECU 11, and the ECU 11 detects the main fuel according to the accelerator opening signal obtained from the accelerator opening sensor 13. The injection timing and injection amount, and the injection timing and injection amount of the auxiliary fuel are determined. The crank position sensor 12 that detects the rotation angle of the crankshaft to which the piston 2 is coupled is electrically connected to the ECU 11, and the rotation angle detected by the crank position sensor 12 is read into the ECU 11 and compressed. Calculation of the engine speed of the ignition internal combustion engine, determination of the stroke in the combustion cycle of the cylinder 1 and the like are performed.
[0031]
In the cylinder 1 configured as described above, a sub fuel injection command is issued from the ECU 11 to the sub fuel injection valve 5 and the sub fuel is injected into the combustion chamber 3 to form a premixed gas. Is done. Thereafter, near the top dead center of the compression stroke, the main fuel is injected from the main fuel injection valve 4, and the fuel is ignited and burned in the combustion chamber 3.
[0032]
Here, as the engine load of the compression ignition internal combustion engine increases, the risk that the premixed gas will ignite prematurely increases. Accordingly, sub fuel injection for avoiding pre-ignition of the premixed gas will be described hereinafter with reference to FIGS. 2, 3, and 4.
[0033]
FIG. 2 is a diagram showing the relationship between engine speed and engine load in a compression ignition internal combustion engine. The horizontal axis represents the engine speed of the compression ignition internal combustion engine, and the vertical axis represents the engine load of the compression ignition internal combustion engine. Here, the line L1 represents the maximum engine load for each engine speed in the compression ignition internal combustion engine of the present embodiment. The maximum engine load represented by the line 1 exhibits the engine load TQ1 when the engine speed is substantially zero, the maximum load TQ2 when the engine speed is Ne1, and the maximum engine speed is It means the engine load which is Ne2. Therefore, in the compression ignition internal combustion engine of the present embodiment, an engine load belonging to a region (R1, R2, and R3 in the drawing) surrounded by the line L1, the vertical axis, and the horizontal axis is exhibited.
[0034]
Here, the region R1 is a region surrounded by the line L2, the vertical axis, and the horizontal axis, which means a low load region in the engine load of the compression ignition internal combustion engine, and the engine speed is 0 to Ne3 and the engine load. Is a rectangular region composed of 0 to TQ3. The region R2 is a region surrounded by the lines L2 and L3, the vertical axis, and the horizontal axis, which means a medium load region in the engine load of the compression ignition internal combustion engine, and the engine speed ranges from 0 to Ne4 and This is a region obtained by removing the above-described region R1 from a rectangular region where the engine load is 0 to TQ4. The region R3 is a region surrounded by the line L3 and the line L1, the vertical axis and the horizontal axis, which means a high load region in the engine load of the compression ignition internal combustion engine, and the region R1 from the maximum engine load described above. And a region excluding the region represented by R2. In this embodiment, as shown in FIG. 2, the engine load of the compression ignition internal combustion engine is classified into a low load region, a medium load region, and a high load region. The classification of the engine load is classified into the classification modes shown in FIG. The engine load can be classified according to the compression ignition internal combustion engine.
[0035]
Here, the fuel injection mode corresponding to each load region represented by R1, R2, and R3 will be described in detail with reference to FIG. FIG. 3 is a diagram schematically showing the fuel injection mode according to the engine load of the compression ignition internal combustion engine. FIG. 3A shows the engine load of the compression ignition internal combustion engine belonging to the region R1 described above. In other words, the fuel injection in the auxiliary fuel injection valve 5 and the main fuel injection valve 4 when the engine load is low is shown. FIG. 3B shows the fuel injection in the sub fuel injection valve 5 and the main fuel injection valve 4 when the engine load of the compression ignition internal combustion engine belongs to the region R2 described above, that is, when the engine load is a medium load. Represents. FIG. 3C shows the fuel injection in the auxiliary fuel injection valve 5 and the main fuel injection valve 4 when the engine load of the compression ignition internal combustion engine belongs to the above-described region R3, that is, when the engine load is high. Represents. Here, in FIGS. 3A to 3C, the horizontal axis represents the crank angle in the combustion cycle of the cylinder 1. Therefore, the time represented by -360 deg means the top dead center of the intake stroke in the combustion cycle, and the time represented by 0 deg means the top dead center of the compression stroke. In addition, rectangles J1 to J4 represented in FIGS. 3A to 3C represent fuel injection in each fuel injection valve, and the length of the rectangle in the horizontal axis direction is the fuel converted into the crank angle amount. It is roughly proportional to the injection time, that is, the fuel injection amount.
[0036]
First, in FIG. 3A, since the engine load of the compression ignition internal combustion engine is low, there is no risk of pre-ignition premature ignition. Therefore, by uniformly diffusing the premixed gas formed by the auxiliary fuel into the combustion chamber 3, it is possible to effectively reduce NOx and smoke. Therefore, as shown in FIG. 3 (a), when the engine load belongs to the low load region, the auxiliary fuel injection valve 5 uses the auxiliary fuel injection valve 5 during the period from the middle of the intake stroke to the middle of the compression stroke in the combustion cycle of the cylinder 1. Fuel is injected (indicated by J1 in FIG. 3A). The premixed gas formed in the combustion chamber 3 at this time will be described with reference to FIG.
[0037]
FIG. 4A schematically shows how the premixed gas is formed when the sub fuel is injected from the sub fuel injection valve 5 when the piston 2 is in the lowered position in the cylinder 1. When the piston 2 is in the lowered position in the cylinder 1, that is, when the auxiliary fuel is injected from the auxiliary fuel injection valve 5 from the middle of the intake stroke to the middle of the compression stroke, the piston 2 descends to secure a large volume of the combustion chamber 3. As a result, the secondary fuel diffuses widely into the combustion chamber. Therefore, the auxiliary fuel injected from the auxiliary fuel injection valve 5 forms a uniform premixed gas in the combustion chamber 3.
[0038]
As for the main fuel injection (indicated by J2 in FIG. 3), the main fuel is injected in the vicinity of the top dead center of the compression stroke, and the ignition combustion of the fuel is performed in the combustion chamber 3 with the main fuel as a base point. Is called. As a result, when the engine load of the compression ignition internal combustion engine is low, it is possible to suppress NOx and smoke by forming a premixed gas.
[0039]
Next, when the engine load of the compression ignition internal combustion engine is equal to or higher than the medium load, if the auxiliary fuel is injected at the same timing as in FIG. There is a risk of early ignition. Therefore, fuel is injected at the timing shown in FIGS. First, when the engine load is a medium load, the fuel injection shown in FIG. 3B is performed. In FIG. 3 (b), the auxiliary fuel is injected into the combustion chamber 3 at the beginning of the intake stroke in the combustion cycle of the cylinder 1. The premixed gas formed in the combustion chamber 3 at this time will be described with reference to FIG.
[0040]
FIG. 4B schematically shows how the premixed gas is formed when the auxiliary fuel is injected from the auxiliary fuel injection valve 5 when the piston 2 is in the raised position in the cylinder 1. When the piston 2 is in the raised position in the cylinder 1, that is, when the auxiliary fuel is injected from the auxiliary fuel injection valve 5 at the initial stage of the intake stroke or the late stage of the compression stroke (indicated by J1 in FIG. 3B), the piston Since the volume of the combustion chamber 3 is ensured by the rise of 2, the auxiliary fuel is not diffused widely into the combustion chamber. Therefore, by adjusting the injection direction of the auxiliary fuel injection valve 5, it becomes possible to form a premixed gas by the auxiliary fuel in the vicinity of the main fuel injection valve 4. Accordingly, the air-fuel ratio distribution in the combustion chamber 3 is rich in the vicinity of the main fuel injection valve 4 to such an extent that the premixed gas is not prematurely ignited, and the surrounding portion is sub fuel. Because there is almost no, it is in a very lean state. That is, the air-fuel ratio distribution avoids an air-fuel ratio in the vicinity of the theoretical air-fuel ratio that can cause pre-ignition of the premixed gas.
[0041]
As for the main fuel injection (indicated by J2 in FIG. 3B), the main fuel is injected near the top dead center of the compression stroke, but immediately before the main fuel injection, the main fuel injection valve 4 A smaller amount of main fuel is injected (indicated by J3 in FIG. 3B). As a result, a gas flow is generated inside the combustion chamber 3, and the premixed gas formed in a certain range in the vicinity of the main fuel injection valve 4 by the injection of auxiliary fuel indicated by J1 in FIG. Stir. Since it is immediately before the main fuel injection, there is no effect on the compression ignition internal combustion engine due to the pre-ignition of the premixed gas. This minute amount of main fuel injection makes it possible to make the air-fuel ratio distribution inside the combustion chamber 3 more uniform immediately before the main fuel injection (indicated by J2 in FIG. 3B).
[0042]
The fuel is ignited and burned in the combustion chamber 3 with the main fuel injection (indicated by J2 in FIG. 3B) as a base point. As a result, when the engine load of the compression ignition internal combustion engine is a medium load, a premixed gas is formed in a certain range inside the combustion chamber 3 even if the engine load of the compression ignition internal combustion engine is a medium load. It becomes possible to avoid pre-ignition of the premixed gas, and it is possible to suppress NOx and smoke by forming the premixed gas.
[0043]
Next, when the engine load is high, fuel injection shown in FIG. 3C is performed. In FIG. 3 (c), the auxiliary fuel is injected into the combustion chamber 3 at the early stage of the intake stroke and the latter stage of the compression stroke in the combustion cycle of the cylinder 1. The premixed gas formed in the combustion chamber 3 at this time is as described above with reference to FIG.
[0044]
When the engine load is high, the fuel injection amount is relatively increased as compared to when the engine load is medium, and as a result, the injection time is prolonged. However, when the engine load is high as described above, in order to form the premixed gas by the auxiliary fuel in the vicinity of the main fuel injection valve 4, the position where the piston 2 is raised to some extent, that is, the initial stage of the intake stroke or the late stage of the compression stroke It is necessary to inject auxiliary fuel. Therefore, when the injection amount of the auxiliary fuel is so large that it cannot be injected by the beginning of the intake stroke, the auxiliary fuel is injected after the injection of the auxiliary fuel at the early stage of the intake stroke (represented by J1 in FIG. 3C). It is assumed that the fuel injection is stopped once and then the auxiliary fuel injection is started in the latter half of the intake stroke (represented by J4 in FIG. 3C). By doing in this way, it becomes possible to form the premixed gas by auxiliary fuel in the vicinity of the main fuel injection valve 4. Therefore, the air-fuel ratio distribution in the combustion chamber 3 is rich in the vicinity of the main fuel injection valve 4 to such an extent that the premixed gas is unlikely to be prematurely ignited. Because it is almost nonexistent, it is in a very lean state. That is, the air-fuel ratio distribution avoids an air-fuel ratio in the vicinity of the theoretical air-fuel ratio that can cause pre-ignition of the premixed gas.
[0045]
Further, regarding the main fuel injection (indicated by J2 in FIG. 3 (c)) and the injection just before the main fuel injection (indicated by J3 in FIG. 3 (c)), the engine load is a medium load. It is the same as in some cases.
[0046]
From the main fuel injection (indicated by J2 in FIG. 3C), ignition combustion of the fuel is performed in the combustion chamber 3. As a result, when the engine load of the compression ignition internal combustion engine is a medium load, a premixed gas is formed in a certain range inside the combustion chamber 3 even if the engine load of the compression ignition internal combustion engine is a medium load. It becomes possible to avoid pre-ignition of the premixed gas, and it is possible to suppress NOx and smoke by forming the premixed gas.
[0047]
In the present embodiment shown in FIGS. 3B and 3C, according to the engine load of the compression ignition internal combustion engine, first, the auxiliary fuel is injected at the beginning of the intake stroke, and the auxiliary fuel is injected during the initial period of the intake stroke. Is not completed, the secondary fuel is injected later in the compression stroke. However, contrary to the present embodiment, according to the engine load of the compression ignition internal combustion engine, first, the injection of the auxiliary fuel is performed in the latter half of the compression stroke, and if the injection of the auxiliary fuel cannot be completed in the latter period of the compression stroke, the intake stroke The auxiliary fuel may be injected in the initial stage.
[0048]
As shown in FIGS. 3 (b) and 3 (c) of this embodiment, when the engine load of the compression ignition internal combustion engine is equal to or higher than the medium load, the premixed gas by the auxiliary fuel is introduced in the vicinity of the main fuel injection valve 4. When forming, it is also useful to reduce the injection pressure of the auxiliary fuel injection valve 5. By reducing the injection pressure of the auxiliary fuel injection valve 5, the particle size of the auxiliary fuel is increased, so that pre-ignition of the premixed gas can be suppressed. As shown in FIG. 3 (a), when the engine load of the compression ignition internal combustion engine is low, the injection pressure of the auxiliary fuel injection valve 5 is increased because there is no risk of pre-ignition premature ignition. The combustion of the fuel can be promoted by reducing the particle size of the auxiliary fuel.
[0049]
<Second embodiment>
Next, a second embodiment according to the present invention will be described with reference to FIG. 5, FIG. 6, FIG. 7, and FIG. FIG. 5 is a diagram showing a schematic configuration in the vicinity of a combustion chamber of a compression ignition internal combustion engine to which the present invention is applied and a schematic configuration of a control system thereof. The same components as those in the schematic configuration shown in FIG. The description will be omitted by giving the same reference numerals. Hereinafter, different components will be described.
[0050]
Air-fuel ratio sensors 14 a and 14 b for measuring the air-fuel ratio of the premixed gas in the combustion chamber 3 of the compression ignition internal combustion engine shown in FIG. Here, FIG. 6 is a schematic configuration diagram when the upper part of the cylinder 2 is viewed from the combustion chamber 3 side. In this embodiment, the intake valve 6 is composed of two valves, intake valves 6a and 6b, and the exhaust valve 7 is composed of two valves, exhaust valves 7a and 7b. The air-fuel ratio sensor 14a is located in the vicinity of the auxiliary fuel injection valve 5 and between the intake valve 6a and the intake valve 6b. One air-fuel ratio sensor 14b is on the opposite side to the center of the cylinder 2 and is exhausted. Located between the valve 7a and the exhaust valve 7b. Further, a variable valve mechanism 16a that varies the opening / closing characteristics of the intake valve 6a and the intake valve 6b is provided, and a variable valve mechanism 16b that varies the opening / closing characteristics of the exhaust valve 7a and the exhaust valve 7b. Here, the opening / closing characteristics of the intake / exhaust valves that are variable by the variable valve mechanisms 16a and 16b include the valve opening timing, valve opening time, lift amount, working angle, and the like of the intake / exhaust valves. Further, the auxiliary fuel injection valve 5 is provided with a heater 15 for heating the auxiliary fuel.
[0051]
Here, the air-fuel ratio in the combustion chamber 3 detected by the air-fuel ratio sensors 14 a and 14 b is sent to the ECU 11, and the air-fuel ratio distribution of the premixed gas formed in the combustion chamber 3 is detected by the ECU 11. The detection of the air-fuel ratio distribution by the ECU 11 corresponds to the air-fuel ratio distribution detecting means according to the present invention. FIG. 7 is a diagram showing the air-fuel ratio distribution in the combustion chamber 3 detected by the ECU 11 based on the air-fuel ratio detected by the air-fuel ratio sensors 14a and 14b. The horizontal axis corresponds to the straight line X shown in FIG. 6, and the vertical axis represents the air-fuel ratio at a site on the straight line X. Further, points P1 and P2 in FIG. 7 are air-fuel ratios detected by the air-fuel ratio sensors 14a and 14b, respectively, and the air-fuel ratio distribution in the combustion chamber 3 is represented by a straight line L4 by the ECU 11 based on these two points. Has been. In the present embodiment, the air-fuel ratio distribution in the combustion chamber 3 is detected linearly based on the air-fuel ratio values detected from the two air-fuel ratio sensors, but the air-fuel ratio distribution from three or more air-fuel ratio sensors is detected. The air-fuel ratio distribution in the combustion chamber 3 may be detected based on a certain function based on the fuel ratio.
[0052]
Here, in FIG. 7, the air-fuel ratio represented by the region R4 is an air-fuel ratio belonging to a region where the premixed gas formed in the combustion chamber 3 may be prematurely ignited. The air-fuel ratio is in the vicinity of the air-fuel ratio. Therefore, when the air-fuel ratio distribution in the combustion chamber 3 is represented by a straight line L4 as shown in FIG. 7, the premixed gas having the air-fuel ratio belonging to the region R4 may be prematurely ignited.
[0053]
Therefore, by adjusting the injection distance of the auxiliary fuel injection valve 5 so that the air-fuel ratio distribution of the pre-mixed gas formed in the combustion chamber 3 does not belong to the region R4 in FIG. The flowchart of the injection distance control to adjust is shown. The injection distance control is a control that is repeatedly executed by the ECU 11. The execution of this control by the ECU 11 corresponds to the injection distance adjusting means in the present invention.
[0054]
First, in S101, it is determined whether or not the air-fuel ratio distribution of the premixed gas formed in the combustion chamber 3 includes the pre-ignition region, that is, the region R4 shown in FIG. As described above, in this embodiment, the ECU 11 detects the air-fuel ratio distribution in the combustion chamber 3 based on the air-fuel ratio detected by the two air-fuel ratio sensors 14a and 14b, and the air-fuel ratio distribution is in the region R4. Whether or not is included. Here, when it is determined that the air-fuel ratio distribution does not include the region R4, that is, when it is determined that pre-ignition does not occur in the combustion chamber 3, the process proceeds from S101 to S105. End control. On the other hand, when it is determined that the air-fuel ratio distribution includes the region R4, that is, when it is determined that pre-ignition of the premixed gas occurs in the combustion chamber 3, the process proceeds to S102.
[0055]
In S102, the air-fuel ratio detected by the air-fuel ratio sensor 14a is compared with the air-fuel ratio detected by the air-fuel ratio sensor 14b. In the present embodiment, the auxiliary fuel injection valve 5 is provided in the vicinity of the air-fuel ratio sensor 14a. Therefore, by shortening the injection distance of the auxiliary fuel injected from the auxiliary fuel injection valve 5, the air-fuel ratio of the premixed gas in the vicinity of the air-fuel ratio sensor 14a can be reduced, that is, the fuel concentration can be increased. By increasing the injection distance of the auxiliary fuel injected from the auxiliary fuel injection valve 5, the air-fuel ratio of the premixed gas in the vicinity of the air-fuel ratio sensor 14b located on the opposite side of the air-fuel ratio sensor 14a is reduced, that is, the fuel concentration is reduced. It becomes possible to make it higher. When there is a place where the air-fuel ratio is high in the combustion chamber 3, that is, a place where the fuel concentration is low, the sub-fuel is injected around the place to alleviate the bias of the air-fuel ratio distribution in the combustion chamber 3. It becomes possible to make it uniform. Therefore, in S102, the air-fuel ratio detected by the air-fuel ratio sensor 14a and the air-fuel ratio detected by the air-fuel ratio sensor 14b are compared to determine at which location the auxiliary fuel should be injected. If it is determined in S102 that the air-fuel ratio detected by the air-fuel ratio sensor 14b is greater than the air-fuel ratio detected by the air-fuel ratio sensor 14a, the process proceeds to S103, where the air-fuel ratio detected by the air-fuel ratio sensor 14b is If it is determined that the air-fuel ratio is equal to or lower than the air-fuel ratio detected by the sensor 14a, the process proceeds to S104.
[0056]
In S103, the injection pressure of the auxiliary fuel injection valve 5 is increased. As a result, the injection distance of the auxiliary fuel reaches far. Then, since the auxiliary fuel diffuses into the combustion chamber 3 around a place closer to the air-fuel ratio sensor 14b, the bias in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3 is reduced, and the air-fuel ratio distribution is reduced. Is almost uniform. As a result, since the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4, it is possible to avoid pre-ignition pre-ignition.
[0057]
In S104, the injection pressure of the auxiliary fuel injection valve 5 is decreased. This makes it difficult for the injection distance of the auxiliary fuel to reach far. Then, since the auxiliary fuel diffuses into the combustion chamber 3 around a place closer to the air-fuel ratio sensor 14a, the bias in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3 is reduced, and the air-fuel ratio distribution is reduced. Is almost uniform. As a result, since the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4, it is possible to avoid pre-ignition pre-ignition.
When the processes of S103 and S104 are completed, the process proceeds to S105 and this control is terminated.
[0058]
Further, in adjusting the injection distance of the auxiliary fuel injected from the auxiliary fuel injection valve 5, in the previous embodiment, the injection distance of the auxiliary fuel was adjusted by increasing or decreasing the injection pressure of the auxiliary fuel injection valve 5. In addition, it is possible to adjust the injection distance of the auxiliary fuel by adjusting the number of injections of the auxiliary fuel. That is, by reducing the number of injections of the auxiliary fuel, the opening time of the auxiliary fuel injection valve 5 per time becomes longer, so that the injection distance of the auxiliary fuel becomes longer. On the other hand, by increasing the number of injections of the auxiliary fuel, the opening time of the auxiliary fuel injection valve 5 per time is shortened, so that the injection distance of the auxiliary fuel is shortened. Accordingly, in the flowchart shown in FIG. 8, instead of the processes performed in S103 and S104, processes of “reducing the number of injections of sub fuel” and “increasing the number of injections of sub fuel” can be performed. As a result, the deviation in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3 is reduced, the air-fuel ratio distribution becomes substantially uniform, and the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4. This makes it possible to avoid premature ignition.
[0059]
Further, as another means for adjusting the injection distance of the auxiliary fuel, a means for adjusting the injection distance of the auxiliary fuel by adjusting the temperature of the heater 15 can be considered. That is, by raising the temperature of the heater 15, the temperature of the auxiliary fuel rises, the fuel particle size of the auxiliary fuel becomes finer, and the injection distance of the auxiliary fuel becomes longer. On the other hand, lowering the temperature of the heater 15 lowers the temperature of the auxiliary fuel, increases the fuel particle size of the auxiliary fuel, and shortens the injection distance of the auxiliary fuel. Therefore, in the flowchart shown in FIG. 8, instead of the processes performed in S103 and S104, processes of “rising the heater temperature” and “decreasing the heater temperature” can be performed. As a result, the bias in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3 is reduced, the air-fuel ratio distribution becomes substantially uniform, and the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4. This makes it possible to avoid premature ignition.
[0060]
<Third embodiment>
As another embodiment for preventing the air-fuel ratio distribution of the premixed gas formed in the combustion chamber 3 from belonging to the region R4 in FIG. 9, a variable valve mechanism (the intake side variable valve mechanism 16a in FIG. 6 is a flowchart of intake / exhaust valve opening / closing control for adjusting the air-fuel ratio of the premixed gas by the side variable valve mechanism 16b). The intake / exhaust valve opening / closing control is a control repeatedly executed by the ECU 11. In the flowchart shown in FIG. 9, the same processes as those in the flowchart shown in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted.
[0061]
First, in S101, when it is determined that the air-fuel ratio distribution in the combustion chamber 3 does not include the region R4, that is, when it is determined that pre-ignition does not occur in the combustion chamber 3, S101. The process proceeds from S109 to S109 to end the present control. On the other hand, when it is determined that the air-fuel ratio distribution includes the region R4, that is, when it is determined that the premixed gas is prematurely ignited in the combustion chamber 3, the process proceeds to S106.
[0062]
In S106, the air-fuel ratio detected by the air-fuel ratio sensor 14a is compared with the air-fuel ratio detected by the air-fuel ratio sensor 14b. In the present embodiment, the intake valve 6 is provided in the vicinity of the air-fuel ratio sensor 14a. Therefore, by opening the intake valve 6, it is possible to discharge a part of the premixed gas in the combustion chamber 3 to the outside of the combustion chamber 3, thereby increasing the air-fuel ratio in the vicinity of the intake valve 6, and the exhaust valve. By opening 7, part of the premixed gas in the combustion chamber 3 can be discharged out of the combustion chamber 3, and the air-fuel ratio in the vicinity of the exhaust valve 7 can be increased. As a result, it is possible to alleviate the deviation of the air-fuel ratio distribution in the combustion chamber 3 and make it substantially uniform. Therefore, in S106, which of the intake valve 6 and the exhaust valve 7 is opened is compared by comparing the air-fuel ratio detected by the air-fuel ratio sensor 14a with the air-fuel ratio detected by the air-fuel ratio sensor 14b. Judging. If it is determined in S106 that the air-fuel ratio detected by the air-fuel ratio sensor 14b is greater than the air-fuel ratio detected by the air-fuel ratio sensor 14a, the process proceeds to S107, and the air-fuel ratio detected by the air-fuel ratio sensor 14b is If it is determined that the air-fuel ratio is equal to or lower than the air-fuel ratio detected by the sensor 14a, the process proceeds to S108.
[0063]
In S107, the intake valve 6 (intake valves 6a and 6b) is opened by the intake side variable valve mechanism 16a. The timing when the intake valve 6 is opened is preferably the initial stage of the compression stroke of the compression ignition internal combustion engine, but is not limited to this timing, and part of the premixed gas formed in the combustion chamber 3 is the combustion chamber 3. It may be time when it is released to the outside. As a result, the air-fuel ratio in the combustion chamber 3 in the vicinity of the intake valve 6 rises, thereby reducing the bias in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3, and the air-fuel ratio distribution becomes substantially uniform. As a result, since the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4, it is possible to avoid pre-ignition pre-ignition.
[0064]
When the intake valve 6 is opened by the intake side variable valve mechanism 16a, a part of the premixed gas in the combustion chamber 3 moves to the intake branch pipe 8, but this premixed gas is used in the next combustion cycle. When the compression ignition internal combustion engine has a plurality of cylinders, the premixed gas can be provided for combustion in other cylinders.
[0065]
In S108, the exhaust valve 7 (exhaust valves 7a and 7b) is opened by the exhaust side variable valve mechanism 17a. The timing when the exhaust valve 7 is opened is preferably in the initial stage of the compression stroke of the compression ignition internal combustion engine. However, the timing is not limited to this timing, and a part of the premixed gas formed in the combustion chamber 3 is part of the combustion chamber 3. It may be time when it is released to the outside. As a result, the air-fuel ratio in the combustion chamber 3 in the vicinity of the exhaust valve 7 rises, thereby reducing the bias in the air-fuel ratio distribution of the premixed gas in the combustion chamber 3, and the air-fuel ratio distribution becomes substantially uniform. As a result, since the air-fuel ratio distribution does not include the pre-ignition region, that is, the region R4, it is possible to avoid pre-ignition pre-ignition.
When the processes of S107 and S108 are completed, the process proceeds to S109 and this control is terminated.
[0066]
【The invention's effect】
The premixed compression ignition internal combustion engine according to the present invention shows the air-fuel ratio distribution of the premixed gas formed in the combustion chamber when premixed combustion is performed in the compression ignition internal combustion engine having a plurality of fuel injection valves. An air-fuel ratio distribution that avoids an air-fuel ratio at which excessive pre-ignition occurs is used. This avoids pre-ignition of the premixed gas and enables stable combustion.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a premixed compression ignition internal combustion engine and its control system according to the present embodiment.
FIG. 2 is a diagram showing a relationship between an engine speed and an engine load in the premixed compression ignition internal combustion engine according to the present embodiment.
FIG. 3 is a diagram showing a relationship between engine load and fuel injection timing in the premixed compression ignition internal combustion engine according to the present embodiment.
FIG. 4 is a view showing a relationship between a position of a piston in a combustion chamber of the premixed compression ignition internal combustion engine according to the present embodiment and a premixed gas formed in the combustion chamber.
FIG. 5 is a second diagram showing a schematic configuration of the premixed compression ignition internal combustion engine and its control system according to the present embodiment.
FIG. 6 is a flowchart showing a schematic configuration when the upper part of a cylinder is viewed from the combustion chamber side in the premixed compression ignition internal combustion engine according to the present embodiment.
FIG. 7 is a diagram showing the detected air-fuel ratio distribution in the combustion chamber based on the air-fuel ratio detected by the air-fuel ratio sensor in the premixed compression ignition internal combustion engine according to the present embodiment.
FIG. 8 is a flowchart showing sub fuel injection distance control for avoiding pre-ignition pre-ignition during pre-mixture formation according to the present embodiment;
FIG. 9 is a flowchart showing opening / closing control of intake / exhaust valves for avoiding pre-ignition of the premixed gas when premixed gas is formed according to the present embodiment.
[Explanation of symbols]
1 ... Cylinder
2. Piston
3. Combustion chamber
4 .... Main fuel injection valve
5 .... Sub fuel injection valve
6. Intake valve
6a ... Intake valve
6b ... Intake valve
7. Exhaust valve
7a ... Exhaust valve
7b ... Exhaust valve
11 .... ECU
14a ... Air-fuel ratio sensor
14b ... Air-fuel ratio sensor
15 .... Heater
16a... Intake side variable valve mechanism
16b... Exhaust side variable valve mechanism

Claims (7)

内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、
前記主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、
内燃機関の機関負荷が中負荷より低いときは、吸気行程中期から圧縮行程中期において前記副燃料噴射弁から燃料を噴射することで予混合気を形成し、内燃機関の機関負荷が中負荷以上のときは、吸気行程初期および圧縮行程後期の少なくとも何れかに前記副燃料噴射弁から燃料を噴射することで予混合気を前記主燃料噴射弁の近傍に形成する予混合気形成手段と、を備え、
前記予混合気形成手段は、内燃機関の機関負荷が中負荷以上のときに前記副燃料噴射弁から燃料を噴射するときは、内燃機関の機関負荷が中負荷より低いときに前記副燃料噴射弁から燃料を噴射するときよりも前記副燃料噴射弁の噴射圧を低下することを特徴とする予混合圧縮着火内燃機関。A main fuel injection valve that is provided at substantially the center of the combustion chamber of the internal combustion engine and injects fuel near the top dead center of the compression stroke;
An auxiliary fuel injection valve that is provided at a position displaced with respect to the main fuel injection valve and injects fuel that forms a premixed gas;
When the engine load of the internal combustion engine is lower than the medium load, a premixed gas is formed by injecting fuel from the auxiliary fuel injection valve from the middle of the intake stroke to the middle of the compression stroke, and the engine load of the internal combustion engine exceeds the medium load. A premixed gas forming means for forming a premixed gas in the vicinity of the main fuel injection valve by injecting fuel from the auxiliary fuel injection valve at least in the early stage of the intake stroke or the late stage of the compression stroke. ,
When the engine load of the internal combustion engine is lower than the medium load when the engine load of the internal combustion engine is lower than the sub fuel injection valve, A premixed compression ignition internal combustion engine characterized by lowering the injection pressure of the auxiliary fuel injection valve than when injecting fuel from. 圧縮上死点近傍において前記主燃料噴射弁から燃料を噴射する前に、前記主燃料噴射弁から微量の燃料を噴射することを特徴とする請求項１に記載の予混合圧縮着火内燃機関。Before injecting the fuel from the main fuel injection valve in the compression top dead center near the premixed compression ignition internal combustion engine according to claim 1, characterized in that injects fuel traces from the main fuel injection valve. 内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、
前記主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、
前記燃焼室内に形成される混合気の空燃比分布を検出する空燃比分布検出手段と、
前記空燃比分布検出手段によって検出される前記燃焼室内の空燃比分布に応じて前記副燃料噴射弁から噴射される燃料の噴射距離を調整することで、前記燃焼室内の空燃比分布を概均一とする噴射距離調整手段と、を有することを特徴とする予混合圧縮着火内燃機関。A main fuel injection valve that is provided at substantially the center of the combustion chamber of the internal combustion engine and injects fuel near the top dead center of the compression stroke;
An auxiliary fuel injection valve that is provided at a position displaced with respect to the main fuel injection valve and injects fuel that forms a premixed gas;
Air-fuel ratio distribution detecting means for detecting the air-fuel ratio distribution of the air-fuel mixture formed in the combustion chamber;
By adjusting the injection distance of the fuel injected from the sub fuel injection valve in accordance with the air-fuel ratio distribution in the combustion chamber detected by the air-fuel ratio distribution detecting means, the air-fuel ratio distribution in the combustion chamber is made substantially uniform. A premixed compression ignition internal combustion engine characterized by comprising: 前記噴射距離調整手段は、前記副燃料噴射弁の噴射圧を調整する手段であることを特徴とする請求項３に記載の予混合圧縮着火内燃機関。The premixed compression ignition internal combustion engine according to claim 3 , wherein the injection distance adjusting means is means for adjusting an injection pressure of the auxiliary fuel injection valve. 前記噴射距離調整手段は、前記副燃料噴射弁の噴射回数を調整する手段であることを特徴
とする請求項３に記載の予混合圧縮着火内燃機関。4. The premixed compression ignition internal combustion engine according to claim 3 , wherein the injection distance adjusting means is means for adjusting the number of injections of the auxiliary fuel injection valve. 前記噴射距離調整手段は、前記副燃料噴射弁から噴射される燃料の粒径を調整する手段であることを特徴とする請求項３に記載の予混合圧縮着火内燃機関。4. The premixed compression ignition internal combustion engine according to claim 3 , wherein the injection distance adjusting means is means for adjusting a particle size of fuel injected from the auxiliary fuel injection valve. 内燃機関の燃焼室の略中心部に設けられ、圧縮行程上死点近傍において燃料の噴射を行う主燃料噴射弁と、
前記主燃料噴射弁に対して偏位した位置に設けられ、予混合気を形成する燃料を噴射する副燃料噴射弁と、
前記燃焼室内に形成される混合気の空燃比分布を検出する空燃比分布検出手段と、
前記燃焼室における吸気弁または排気弁の少なくとも一方の開閉特性を可変とする可変動弁機構と、を備え、
前記空燃比分布検出手段によって検出される前記燃焼室内の空燃比分布に応じて、前記可変動弁機構によって前記吸気弁または排気弁の少なくとも一方を開弁することで、前記燃焼室内の空燃比分布を概均一とすることを特徴とする予混合圧縮着火内燃機関。A main fuel injection valve that is provided at substantially the center of the combustion chamber of the internal combustion engine and injects fuel near the top dead center of the compression stroke;
An auxiliary fuel injection valve that is provided at a position displaced with respect to the main fuel injection valve and injects fuel that forms a premixed gas;
Air-fuel ratio distribution detecting means for detecting the air-fuel ratio distribution of the air-fuel mixture formed in the combustion chamber;
A variable valve mechanism that varies an opening / closing characteristic of at least one of an intake valve and an exhaust valve in the combustion chamber,
In accordance with the air-fuel ratio distribution in the combustion chamber detected by the air-fuel ratio distribution detecting means, at least one of the intake valve or the exhaust valve is opened by the variable valve mechanism, so that the air-fuel ratio distribution in the combustion chamber is opened. A premixed compression ignition internal combustion engine characterized in that
JP2002365083A 2002-12-17 2002-12-17 Premixed compression ignition internal combustion engine Expired - Lifetime JP3979286B2 (en)

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