JP3578049B2 - Internal combustion engine - Google Patents

Internal combustion engine Download PDF

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Publication number
JP3578049B2
JP3578049B2 JP2000149834A JP2000149834A JP3578049B2 JP 3578049 B2 JP3578049 B2 JP 3578049B2 JP 2000149834 A JP2000149834 A JP 2000149834A JP 2000149834 A JP2000149834 A JP 2000149834A JP 3578049 B2 JP3578049 B2 JP 3578049B2
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amount
combustion
soot
injection
inert gas
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JP2000149834A
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JP2001329900A (en
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雅人 後藤
静夫 佐々木
康二 吉崎
丈和 伊藤
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Toyota Motor Corp
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Toyota Motor Corp
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Priority to JP2000149834A priority Critical patent/JP3578049B2/en
Priority to EP01111843A priority patent/EP1156202B1/en
Priority to DE60116546T priority patent/DE60116546T2/en
Publication of JP2001329900A publication Critical patent/JP2001329900A/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/14—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories in relation to the exhaust system
    • F02M26/15—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories in relation to the exhaust system in relation to engine exhaust purifying apparatus
    • 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
    • F02B29/00—Engines characterised by provision for charging or scavenging not provided for in groups F02B25/00, F02B27/00 or F02B33/00 - F02B39/00; Details thereof
    • F02B29/04—Cooling of air intake supply
    • F02B29/0406—Layout of the intake air cooling or coolant circuit
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/06—Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
    • F02M26/23—Layout, e.g. schematics
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/35—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with means for cleaning or treating the recirculated gases, e.g. catalysts, condensate traps, particle filters or heaters

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Exhaust-Gas Circulating Devices (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は内燃機関に関する。
【０００２】
【従来の技術】
従来、燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、燃焼室内に供給される不活性ガスの量を更に増大していくと燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関が知られている。この種の内燃機関の例としては、例えば特開平１１−９３７４８号公報に記載されたものがある。
【０００３】
【発明が解決しようとする課題】
ところで、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼が行われるときの空燃比は、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が少ない第２の燃焼が行われるときの空燃比よりも濃くなっている。つまり、第１の燃焼時には、第２の燃焼時に比べて酸素濃度が不足している。そのため、第１の燃焼時には、第２の燃焼時に比べて燃焼が不安定になっている。ところが、特開平１１−１０７８６１号公報には、第１の燃焼時に第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制する方法について開示されていない。従って、特開平１１−１０７８６１号公報に記載された内燃機関では、第１の燃焼時に第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制することができない。
【０００４】
前記問題点に鑑み、本発明は第１の燃焼時に第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制することができる内燃機関を提供することを目的とする。
【０００５】
【課題を解決するための手段】
請求項１に記載の発明によれば、燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときには常に、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関が提供される。
【０００６】
請求項１に記載の内燃機関では、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼が行われるときには常に、圧縮上死点付近における主噴射に加え、主噴射と異なるタイミングで更なる噴射が行われる。第１の燃焼時には、煤の発生量がピークとなる不活性ガスの量よりも燃焼室内に供給される不活性ガスの量が少ない第２の燃焼時に比べて酸素濃度が不足しているものの、主噴射と異なるタイミングで更なる噴射が行われることにより、過酸化物が生成される。そのため、その過酸化物により酸素濃度不足が補われる。それゆえ、第１の燃焼時に、酸素濃度不足に伴って第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制することができる。
【０００７】
請求項２に記載の発明によれば、前記更なる噴射を行うことにより排気空燃比を筒内空燃比よりも濃くするようにした請求項１に記載の内燃機関が提供される。
【０００８】
請求項２に記載の内燃機関では、更なる噴射を行うことにより排気空燃比が筒内空燃比よりも濃くされる。そのため、筒内空燃比を比較的薄くすることにより燃焼を安定させると共に、排気空燃比を比較的濃くすることにより、排気通路内に配置されている触媒の昇温を促進することができる。
【０００９】
請求項３に記載の発明によれば、触媒を備えた排気ガス再循環通路を有する内燃機関において前記第１の燃焼時に前記更なる噴射を行うようにした請求項１に記載の内燃機関が提供される。
【００１０】
請求項３に記載の内燃機関では、触媒を備えた排気ガス再循環通路を有する内燃機関において第１の燃焼時に更なる噴射が行われる。第１の燃焼時には、第２の燃焼時に比べて排気ガス再循環通路内に流入する燃料量が多くなる。排気ガス再循環通路内に流入した燃料は排気ガス再循環通路内の触媒により浄化されるが、その触媒が活性していない場合には、排気ガス再循環通路内に流入した燃料がそのまま燃焼室内に供給されてしまう。そこで、上述したように第１の燃焼時に更なる噴射が行われることにより、主噴射前に燃焼室内に供給される燃料のうち、再循環された燃料が占める割合を低下せしめることができる。その結果、排気ガス再循環通路内の触媒が活性しているか否かに応じて主噴射前に燃焼室内に供給される燃料量が大きく変動してしまうのを抑制することができる。
【００１１】
請求項４に記載の発明によれば、燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、前記第１の燃焼が行われるときに、空燃比が濃くなるほど主噴射量を減少させると共に前記更なる噴射の噴射量を増加させるようにした内燃機関が提供される。
【００１２】
請求項４に記載の内燃機関では、第１の燃焼時に、空燃比が濃くなるほど主噴射量が減少されると共に更なる噴射の噴射量が増加される。そのため、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量を一定に維持することにより出力の変動を抑制することができる。
【００１３】
請求項５に記載の発明によれば、燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、負荷が低いほど前記更なる噴射の噴射量を増加させるようにした内燃機関が提供される。
【００１４】
請求項５に記載の内燃機関では、負荷が低いほど更なる噴射の噴射量が増加される。つまり、負荷が低いほど主噴射量が少なくされると共に更なる噴射の噴射量が多くされる。そのため、燃焼が不安定になり易い低負荷時に、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量を一定に維持することにより出力の変動を抑制することができる。
【００１５】
請求項６に記載の発明によれば、燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、前記第１の燃焼時に前記更なる噴射を前記主噴射直前の圧縮行程末期に行うと共に、前記第２の燃焼時にも前記主噴射直前の圧縮行程末期に更なる噴射を行い、前記第１の燃焼時の更なる噴射を前記第２の燃焼時の更なる噴射よりも進角させるようにした内燃機関が提供される。
【００１６】
請求項６に記載の内燃機関では、第１の燃焼時の主噴射直前の圧縮行程末期に行われる更なる噴射が、第２の燃焼時の主噴射直前の圧縮行程末期に行われる更なる噴射よりも進角せしめられる。主噴射の他に更なる噴射が行われることにより、更なる噴射時に生成される過酸化物によって燃焼が安定化される。一方、主噴射直前の圧縮行程末期に更なる噴射が行われると、その際に酸素が消費されるため、主噴射が行われるときに酸素が不足する傾向がある。従って、上述したように第１の燃焼時の主噴射直前の圧縮行程末期に行われる更なる噴射が、第２の燃焼時の主噴射直前の圧縮行程末期に行われる更なる噴射よりも進角せしめられることにより、つまり、第１の燃焼時に第２の燃焼時に比べて更なる噴射の噴射時期を進角させることにより、第１の燃焼時に主噴射が行われるときの酸素不足を抑制すると共に、第１の燃焼時に、更なる噴射を行うことにより、更なる噴射により生成される過酸化物によって燃焼を安定化させることができる。
【００１７】
【発明の実施の形態】
以下、添付図面を用いて本発明の実施形態について説明する。
【００１８】
図１は本発明を４ストローク圧縮着火式内燃機関に適用した第一の実施形態を示している。図１を参照すると、１は機関本体、２はシリンダブロック、３はシリンダヘッド、４はピストン、５は燃焼室、６は電気制御式燃料噴射弁、７は吸気弁、８は吸気ポート、９は排気弁、１０は排気ポートを夫々示す。吸気ポート８は対応する吸気枝管１１を介してサージタンク１２に連結され、サージタンク１２は吸気ダクト１３及びインタークーラ１４を介して過給機、例えば排気ターボチャージャ１５のコンプレッサ１６の出口部に連結される。コンプレッサ１６の入口部は空気吸込管１７を介してエアクリーナ１８に連結され、空気吸込管１７内にはステップモータ１９により駆動されるスロットル弁２０が配置される。また、スロットル弁２０上流の空気吸込管１７内には、吸入空気の質量流量を検出するための質量流量検出器２１が配置される。
【００１９】
一方、排気ポート１０は排気マニホルド２２を介して排気ターボチャージャ１５の排気タービン２３の入口部に連結され、排気タービン２３の出口部は排気管２４を介して酸化機能を有する触媒２５を内蔵した触媒コンバータ２６に連結される。排気マニホルド２２内には空燃比センサ２７が配置される。触媒コンバータ２６の出口部に連結された排気管２８とスロットル弁２０下流の空気吸込管１７とは排気ガス再循環（以下、ＥＧＲと称す）通路２９を介して互いに連結され、ＥＧＲ通路２９内にはステップモータ３０により駆動されるＥＧＲ制御弁３１が配置される。また、ＥＧＲ通路２９内にはＥＧＲ通路２９内を流れるＥＧＲガスを冷却するためのＥＧＲクーラ３２が配置される。図１に示される実施形態では機関冷却水がＥＧＲクーラ３２内に導びかれ、機関冷却水によってＥＧＲガスが冷却される。更に、ＥＧＲ通路２９内にはＥＧＲ通路２９内を流れるＥＧＲガスを浄化するための触媒５３が配置される。
【００２０】
一方、燃料噴射弁６は燃料供給管３３を介して燃料リザーバ、いわゆるコモンレール３４に連結される。このコモンレール３４内へは電気制御式の吐出量可変な燃料ポンプ３５から燃料が供給され、コモンレール３４内に供給された燃料は各燃料供給管３３を介して燃料噴射弁６に供給される。コモンレール３４にはコモンレール３４内の燃料圧を検出するための燃料圧センサ３６が取付けられ、燃料圧センサ３６の出力信号に基づいてコモンレール３４内の燃料圧が目標燃料圧となるように燃料ポンプ３５の吐出量が制御される。
【００２１】
電子制御ユニット４０はデジタルコンピュータからなり、双方向性バス４１によって互いに接続されたＲＯＭ（リードオンリメモリ）４２、ＲＡＭ（ランダムアクセスメモリ）４３、ＣＰＵ（マイクロプロセッサ）４４、入力ポート４５及び出力ポート４６を具備する。質量流量検出器２１の出力信号は対応するＡＤ変換器４７を介して入力ポート４５に入力され、空燃比センサ２７の出力信号は対応するＡＤ変換器４７を介して入力ポート４５に入力され、燃料圧センサ３６の出力信号は対応するＡＤ変換器（図示せず）を介して入力ポート４５に入力される。アクセルペダル５０にはアクセルペダル５０の踏込み量Ｌに比例した出力電圧を発生する負荷センサ５１が接続され、負荷センサ５１の出力電圧は対応するＡＤ変換器４７を介して入力ポート４５に入力される。また、入力ポート４５にはクランクシャフトが例えば３０°回転する毎に出力パルスを発生するクランク角センサ５２が接続される。機関回転数は入力されたクランク角センサ５２からの出力信号に基づいて算出される。一方、出力ポート４６は対応する駆動回路４８を介して燃料噴射弁６、スロットル弁制御用ステップモータ１９、ＥＧＲ制御弁制御用ステップモータ３０、及び燃料ポンプ３５に接続される。
【００２２】
図２は機関低負荷運転時にスロットル弁２０の開度及びＥＧＲ率を変化させることにより空燃比Ａ／Ｆ（図２の横軸）を変化させたときの出力トルクの変化、及びスモーク、ＨＣ，ＣＯ，ＮＯｘの排出量の変化を示す実験例を表している。図２からわかるようにこの実験例では空燃比Ａ／Ｆが小さくなるほどＥＧＲ率が大きくなり、理論空燃比（≒１４．６）以下のときにはＥＧＲ率は６５パーセント以上となっている。図２に示されるようにＥＧＲ率を増大することにより空燃比Ａ／Ｆを小さくしていくとＥＧＲ率が４０パーセント付近となり空燃比Ａ／Ｆが３０程度になったときにスモークの発生量が増大を開始する。次いで、更にＥＧＲ率を高め、空燃比Ａ／Ｆを小さくするとスモークの発生量が急激に増大してピークに達する。次いで更にＥＧＲ率を高め、空燃比Ａ／Ｆを小さくすると今度はスモークが急激に低下し、ＥＧＲ率を６５パーセント以上とし、空燃比Ａ／Ｆが１５．０付近になるとスモークがほぼ零となる。即ち、煤がほとんど発生しなくなる。このとき機関の出力トルクは若干低下し、またＮＯｘの発生量がかなり低くなる。一方、このときＨＣ，ＣＯの発生量は増大し始める。
【００２３】
図３（Ａ）は空燃比Ａ／Ｆが２１付近でスモークの発生量が最も多いときの燃焼室５内の燃焼圧変化を示しており、図３（Ｂ）は空燃比Ａ／Ｆが１８付近でスモークの発生量がほぼ零のときの燃焼室５内の燃焼圧の変化を示している。図３（Ａ）と図３（Ｂ）とを比較すればわかるようにスモークの発生量がほぼ零である図３（Ｂ）に示す場合はスモークの発生量が多い図３（Ａ）に示す場合に比べて燃焼圧が低いことがわかる。尚、図示しないが図３と同様の実験結果から、煤の発生量がピークとなるＥＧＲガスの量よりも燃焼室５内に供給されるＥＧＲガスの量が多く煤がほとんど発生しない第１の燃焼（低温燃焼）時の燃焼圧の極大値（ピーク）は、煤の発生量がピークとなるＥＧＲガスの量よりも燃焼室５内に供給されるＥＧＲガスの量が少ない第２の燃焼（従来の燃焼方法による燃焼）時の燃焼圧の極大値（ピーク）よりも低いことが判っている。そのことから、第１の燃焼時の爆発に伴う機関回転むらは第２の燃焼時の爆発に伴う機関回転むらよりも小さいと言える。
【００２４】
図２及び図３に示される実験結果から次のことが言える。即ち、まず第１に空燃比Ａ／Ｆが１５．０以下でスモークの発生量がほぼ零のときには図２に示されるようにＮＯｘの発生量がかなり低下する。ＮＯｘの発生量が低下したということは燃焼室５内の燃焼温度が低下していることを意味しており、従って煤がほとんど発生しないときには燃焼室５内の燃焼温度が低くなっていると言える。同じことが図３からも言える。即ち、煤がほとんど発生していない図３（Ｂ）に示す状態では燃焼圧が低くなっており、従ってこのとき燃焼室５内の燃焼温度は低くなっていることになる。
【００２５】
第２にスモークの発生量、即ち煤の発生量がほぼ零になると図２に示されるようにＨＣ及びＣＯの排出量が増大する。このことは炭化水素が煤まで成長せずに排出されることを意味している。即ち、燃料中に含まれる図４に示されるような直鎖状炭化水素や芳香族炭化水素は酸素不足の状態で温度上昇せしめられると熱分解して煤の前駆体が形成され、次いで主に炭素原子が集合した固体からなる煤が生成される。この場合、実際の煤の生成過程は複雑であり、煤の前駆体がどのような形態をとるかは明確ではないがいずれにしても図４に示されるような炭化水素は煤の前駆体を経て煤まで成長することになる。従って、上述したように煤の発生量がほぼ零になると図２に示される如くＨＣ及びＣＯの排出量が増大するがこのときのＨＣは煤の前駆体又はその前の状態の炭化水素である。
【００２６】
図２及び図３に示される実験結果に基づくこれらの考察をまとめると燃焼室５内の燃焼温度が低いときには煤の発生量がほぼ零になり、このとき煤の前駆体又はその前の状態の炭化水素が燃焼室５から排出されることになる。このことについて更に詳細に実験研究を重ねた結果、燃焼室５内における燃料及びその周囲のガス温度が或る温度以下である場合には煤の成長過程が途中で停止してしまい、即ち煤が全く発生せず、燃焼室５内における燃料及びその周囲の温度が或る温度以上になると煤が生成されることが判明したのである。
【００２７】
ところで煤の前駆体の状態で炭化水素の生成過程が停止するときの燃料及びその周囲の温度、即ち上述の或る温度は燃料の種類や空燃比の圧縮比等の種々の要因によって変化するので何度であるかということは言えないがこの或る温度はＮＯｘの発生量と深い関係を有しており、従ってこの或る温度はＮＯｘの発生量から或る程度規定することができる。即ち、ＥＧＲ率が増大するほど燃焼時の燃料及びその周囲のガス温度は低下し、ＮＯｘの発生量が低下する。このときＮＯｘの発生量が１０ｐ．ｐ．ｍ 前後又はそれ以下になったときに煤がほとんど発生しなくなる。従って上述の或る温度はＮＯｘの発生量が１０ｐ．ｐ．ｍ 前後又はそれ以下になったときの温度にほぼ一致する。一旦、煤が生成されるとこの煤は酸化機能を有する触媒を用いた後処理でもって浄化することはできない。これに対して煤の前駆体又はその前の状態の炭化水素は酸化機能を有する触媒を用いた後処理でもって容易に浄化することができる。このように酸化機能を有する触媒による後処理を考えると炭化水素を煤の前駆体又はその前の状態で燃焼室５から排出させるか、或いは煤の形で燃焼室５から排出させるかについては極めて大きな差がある。本発明において採用されている新たな燃焼システムは燃焼室５内において煤を生成させることなく炭化水素を煤の前駆体又はその前の状態の形でもって燃焼室５から排出させ、この炭化水素を酸化機能を有する触媒により酸化せしめることを核としている。
【００２８】
さて、煤が生成される前の状態で炭化水素の成長を停止させるには燃焼室５内における燃焼時の燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に抑制する必要がある。この場合、燃料及びその周囲のガス温度を抑制するには燃料が燃焼した際の燃料周りのガスの吸熱作用が極めて大きく影響することが判明している。即ち、燃料周りに空気しか存在しないと蒸発した燃料はただちに空気中の酸素と反応して燃焼する。この場合、燃料から離れている空気の温度はさほど上昇せず、燃料周りの温度のみが局所的に極めて高くなる。即ち、このときには燃料から離れている空気は燃料の燃焼熱の吸熱作用をほとんど行わない。この場合には燃焼温度が局所的に極めて高くなるために、この燃焼熱を受けた未燃炭化水素は煤を生成することになる。
【００２９】
一方、多量の不活性ガスと少量の空気の混合ガス中に燃料が存在する場合には若干状況が異なる。この場合には蒸発燃料は周囲に拡散して不活性ガス中に混在する酸素と反応し、燃焼することになる。この場合には燃焼熱は周りの不活性ガスに吸収されるために燃焼温度はさほど上昇しなくなる。即ち、燃焼温度を低く抑えることができることになる。即ち、燃焼温度を抑制するには不活性ガスの存在が重要な役割を果しており、不活性ガスの吸熱作用によって燃焼温度を低く抑えることができることになる。この場合、燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に抑制するにはそうするのに十分な熱量を吸収しうるだけの不活性ガス量が必要となる。従って燃料量が増大すれば必要となる不活性ガス量はそれに伴なって増大することになる。なお、この場合、不活性ガスの比熱が大きいほど吸熱作用が強力となり、従って不活性ガスは比熱の大きなガスが好ましいことになる。この点、ＣＯ２ やＥＧＲガスは比較的比熱が大きいので不活性ガスとしてＥＧＲガスを用いることは好ましいと言える。
【００３０】
図５は不活性ガスとしてＥＧＲガスを用い、ＥＧＲガスの冷却度合を変えたときのＥＧＲ率とスモークとの関係を示している。即ち、図５において曲線ＡはＥＧＲガスを強力に冷却してＥＧＲガス温をほぼ９０℃に維持した場合を示しており、曲線Ｂは小型の冷却装置でＥＧＲガスを冷却した場合を示しており、曲線ＣはＥＧＲガスを強制的に冷却していない場合を示している。図５の曲線Ａで示されるようにＥＧＲガスを強力に冷却した場合にはＥＧＲ率が５０パーセントよりも少し低いところで煤の発生量がピークとなり、この場合にはＥＧＲ率をほぼ５５パーセント以上にすれば煤がほとんど発生しなくなる。
【００３１】
一方、図５の曲線Ｂで示されるようにＥＧＲガスを少し冷却した場合にはＥＧＲ率が５０パーセントよりも少し高いところで煤の発生量がピークとなり、この場合にはＥＧＲ率をほぼ６５パーセント以上にすれば煤がほとんど発生しなくなる。また、図５の曲線Ｃで示されるようにＥＧＲガスを強制的に冷却していない場合にはＥＧＲ率が５５パーセントの付近で煤の発生量がピークとなり、この場合にはＥＧＲ率をほぼ７０パーセント以上にすれば煤がほとんど発生しなくなる。なお、図５は機関負荷が比較的高いときのスモークの発生量を示しており、機関負荷が小さくなると煤の発生量がピークとなるＥＧＲ率は若干低下し、煤がほとんど発生しなくなるＥＧＲ率の下限も若干低下する。このように煤がほとんど発生しなくなるＥＧＲ率の下限はＥＧＲガスの冷却度合や機関負荷に応じて変化する。
【００３２】
図６は不活性ガスとしてＥＧＲガスを用いた場合において燃焼時の燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度にするために必要なＥＧＲガスと空気の混合ガス量、及びこの混合ガス量中の空気の割合、及びこの混合ガス中のＥＧＲガスの割合を示している。なお、図６において縦軸は燃焼室５内に吸入される全吸入ガス量を示しており、鎖線Ｙは過給が行われないときに燃焼室５内に吸入しうる全吸入ガス量を示している。また、横軸は要求負荷を示している。
【００３３】
図６を参照すると空気の割合、即ち混合ガス中の空気量は噴射された燃料を完全に燃焼せしめるのに必要な空気量を示している。即ち、図６に示される場合では空気量と噴射燃料量との比は理論空燃比となっている。一方、図６においてＥＧＲガスの割合、即ち混合ガス中のＥＧＲガス量は噴射燃料が燃焼せしめられたときに燃料及びその周囲のガス温度を煤が形成される温度よりも低い温度にするのに必要最低限のＥＧＲガス量を示している。このＥＧＲガス量はＥＧＲ率で表すとほぼ５５パーセント以上であり、図６に示す実施形態では７０パーセント以上である。即ち、燃焼室５内に吸入された全吸入ガス量を図６において実線Ｘとし、この全吸入ガス量Ｘのうちの空気量とＥＧＲガス量との割合を図６に示すような割合にすると燃料及びその周囲のガス温度は煤が生成される温度よりも低い温度となり、斯くして煤が全く発生しなくなる。また、このときのＮＯｘ発生量は１０ｐ．ｐ．ｍ 前後、又はそれ以下であり、従ってＮＯｘの発生量は極めて少量となる。
【００３４】
燃料噴射量が増大すれば燃料が燃焼した際の発熱量が増大するので燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に維持するためにはＥＧＲガスによる熱の吸収量を増大しなければならない。従って図６に示されるようにＥＧＲガス量は噴射燃料量が増大するにつれて増大せしめなければならない。即ち、ＥＧＲガス量は要求負荷が高くなるにつれて増大する必要がある。
【００３５】
ところで過給が行われていない場合には燃焼室５内に吸入される全吸入ガス量Ｘの上限はＹであり、従って図６において要求負荷がＬｏ よりも大きい領域では要求負荷が大きくなるにつれてＥＧＲガス割合を低下させない限り空燃比を理論空燃比に維持することができない。云い換えると過給が行われていない場合に要求負荷がＬｏ よりも大きい領域において空燃比を理論空燃比に維持しようとした場合には要求負荷が高くなるにつれてＥＧＲ率が低下し、斯くして要求負荷がＬｏ よりも大きい領域では燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に維持しえなくなる。
【００３６】
ところが図１に示されるようにＥＧＲ通路２９を介して過給機の入口側即ち排気ターボチャージャ１５の空気吸込管１７内にＥＧＲガスを再循環させると要求負荷がＬo よりも大きい領域においてＥＧＲ率を５５パーセント以上、例えば７０パーセントに維持することができ、斯くして燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に維持することができる。即ち、空気吸込管１７内におけるＥＧＲ率が例えば７０パーセントになるようにＥＧＲガスを再循環させれば排気ターボチャージャ１５のコンプレッサ１６により昇圧された吸入ガスのＥＧＲ率も７０パーセントとなり、斯くしてコンプレッサ１６により昇圧しうる限度まで燃料及びその周囲のガス温度を煤が生成される温度よりも低い温度に維持することができる。従って、低温燃焼を生じさせることのできる機関の運転領域を拡大することができることになる。要求負荷がＬo よりも大きい領域でＥＧＲ率を５５パーセント以上にする際にはＥＧＲ制御弁３１が全開せしめられ、スロットル弁２０が若干閉弁せしめられる。
【００３７】
前述したように図６は燃料を理論空燃比のもとで燃焼させる場合を示しているが空気量を図６に示される空気量よりも少くしても、即ち空燃比をリッチにしても煤の発生を阻止しつつＮＯｘの発生量を１０ｐ．ｐ．ｍ 前後又はそれ以下にすることができ、また空気量を図６に示される空気量よりも多くしても、即ち空燃比の平均値を１７から１８のリーンにしても煤の発生を阻止しつつＮＯｘの発生量を１０ｐ．ｐ．ｍ 前後又はそれ以下にすることができる。
【００３８】
即ち、空燃比がリッチにされると燃料が過剰となるが燃焼温度が低い温度に抑制されているために過剰な燃料は煤まで成長せず、斯くして煤が生成されることがない。また、このときＮＯｘも極めて少量しか発生しない。一方、平均空燃比がリーンのとき、或いは空燃比が理論空燃比のときでも燃焼温度が高くなれば少量の煤が生成されるが本発明では燃焼温度が低い温度に抑制されているので煤は全く生成されない。更に、ＮＯｘも極めて少量しか発生しない。
【００３９】
このように、低温燃焼が行われているときには空燃比にかかわらずに、即ち空燃比がリッチであろうと、理論空燃比であろうと、或いは平均空燃比がリーンであろうと煤が発生されず、ＮＯｘの発生量が極めて少量となる。従って燃料消費率の向上を考えるとこのとき平均空燃比をリーンにすることが好ましいと言える。
【００４０】
ところで燃焼室内における燃焼時の燃料及びその周囲のガス温度を炭化水素の成長が途中で停止する温度以下に抑制しうるのは燃焼による発熱量が比較的少ない機関中低負荷運転時に限られる。従って本発明による実施形態では機関中低負荷運転時には燃焼時の燃料及びその周囲のガス温度を炭化水素の成長が途中で停止する温度以下に抑制して第１の燃焼、即ち低温燃焼を行い得るようにし、機関高負荷運転時には第２の燃焼、即ち従来より普通に行われている燃焼を行うようにしている。但し、機関中低負荷運転時であっても、機関運転状態によっては第２の燃焼が行われる。なお、ここで第１の燃焼、即ち低温燃焼とはこれまでの説明から明らかなように煤の発生量がピークとなる不活性ガス量よりも燃焼室内の不活性ガス量が多く煤がほとんど発生しない燃焼のことを言い、第２の燃焼、即ち従来より普通に行われている燃焼とは煤の発生量がピークとなる不活性ガス量よりも燃焼室内の不活性ガス量が少い燃焼のことを言う。
【００４１】
図７は第１の燃焼、即ち低温燃焼が行われ得る第１の運転領域Ｉと、第２の燃焼、即ち従来の燃焼方法による燃焼が行われる第２の運転領域ＩＩとを示している。なお、図７において縦軸Ｌはアクセルペダル５０の踏込み量、即ち要求負荷を示しており、横軸Ｎは機関回転数を示している。また、図７においてＸ（Ｎ）は第１の運転領域Ｉと第２の運転領域ＩＩとの第１の境界を示しており、Ｙ（Ｎ）は第１の運転領域Ｉと第２の運転領域ＩＩとの第２の境界を示している。第１の運転領域Ｉから第２の運転領域ＩＩへの運転領域の変化判断は第１の境界Ｘ（Ｎ）に基づいて行われ、第２の運転領域ＩＩから第１の運転領域Ｉへの運転領域の変化判断は第２の境界Ｙ（Ｎ）に基づいて行われる。
【００４２】
即ち、機関の運転状態が第１の運転領域Ｉにあって低温燃焼が行われているときに要求負荷Ｌが機関回転数Ｎの関数である第１の境界Ｘ（Ｎ）を越えると運転領域が第２の運転領域ＩＩに移ったと判断され、従来の燃焼方法による燃焼が行われる。次いで要求負荷Ｌが機関回転数Ｎの関数である第２の境界Ｙ（Ｎ）よりも低くなると運転領域が第１の運転領域Ｉに移ったと判断され、再び低温燃焼が行われ得る。
【００４３】
このように第１の境界Ｘ（Ｎ）と第１の境界Ｘ（Ｎ）よりも低負荷側の第２の境界Ｙ（Ｎ）との二つの境界を設けたのは次の二つの理由による。第１の理由は、第２の運転領域ＩＩの高負荷側では比較的燃焼温度が高く、このとき要求負荷Ｌが第１の境界Ｘ（Ｎ）より低くなったとしてもただちに低温燃焼を行えないからである。即ち、要求負荷Ｌがかなり低くなったとき、即ち第２の境界Ｙ（Ｎ）よりも低くなったときでなければただちに低温燃焼が開始されないからである。第２の理由は第１の運転領域Ｉと第２の運転領域ＩＩ間の運転領域の変化に対してヒステリシスを設けるためである。
【００４４】
ところで機関の運転領域が第１の運転領域Ｉにあって低温燃焼が行われているときには煤はほとんど発生せず、その代り未燃炭化水素が煤の前駆体又はその前の状態の形でもって燃焼室５から排出される。このとき燃焼室５から排出された未燃炭化水素は酸化機能を有する触媒２５により良好に酸化せしめられる。触媒２５としては酸化触媒を用いることができる。
【００４５】
図８は空燃比センサ２７の出力を示している。図８に示されるように空燃比センサ２７の出力電流Ｉは空燃比Ａ／Ｆに応じて変化する。従って空燃比センサ２７の出力電流Ｉから空燃比を知ることができる。
【００４６】
図９（Ａ）は第１の運転領域Ｉにおける目標空燃比Ａ／Ｆを示している。図９（Ａ）において、Ａ／Ｆ＝１５．５，Ａ／Ｆ＝１６，Ａ／Ｆ＝１７，Ａ／Ｆ＝１８で示される各曲線は夫々目標空燃比が１５．５，１６，１７，１８であるときを示しており、各曲線間の空燃比は比例配分により定められる。図９（Ａ）に示されるように第１の運転領域Ｉでは空燃比がリーンとなっており、更に第１の運転領域Ｉでは要求負荷Ｌが低くなるほど目標空燃比Ａ／Ｆがリーンとされる。即ち、要求負荷Ｌが低くなるほど燃焼による発熱量が少くなる。従って要求負荷Ｌが低くなるほどＥＧＲ率を低下させても低温燃焼を行うことができる。ＥＧＲ率を低下させると空燃比は大きくなり、従って図９（Ａ）に示されるように要求負荷Ｌが低くなるにつれて目標空燃比Ａ／Ｆが大きくされる。目標空燃比Ａ／Ｆが大きくなるほど燃料消費率は向上し、従ってできる限り空燃比をリーンにするために本発明による実施形態では要求負荷Ｌが低くなるにつれて目標空燃比Ａ／Ｆが大きくされる。
【００４７】
なお、図９（Ａ）に示される目標空燃比Ａ／Ｆは図９（Ｂ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。また、空燃比を図９（Ａ）に示す目標空燃比Ａ／Ｆとするのに必要なスロットル弁２０の目標開度ＳＴが図１０（Ａ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されており、空燃比を図９（Ａ）に示す目標空燃比Ａ／Ｆとするのに必要なＥＧＲ制御弁３１の目標開度ＳＥが図１０（Ｂ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。
【００４８】
更に、第１の燃焼が行われているとき、主噴射の燃料噴射量Ｑｍは要求負荷Ｌ及び機関回転数Ｎに基づいて算出される。この主噴射の燃料噴射量Ｑｍは図１１（Ａ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。また、主噴射の燃料噴射開始時期θＳは、圧縮上死点ＴＤＣ付近に設定されており、要求負荷Ｌが高くなるにつれて遅くなるように図１１（Ｂ）に示す要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。
【００４９】
図１２（Ａ）は第２の燃焼、即ち従来の燃焼方法による普通の燃焼が行われるときの目標空燃比Ａ／Ｆを示している。なお、図１２（Ａ）においてＡ／Ｆ＝２４，Ａ／Ｆ＝３５，Ａ／Ｆ＝４５，Ａ／Ｆ＝６０で示される各曲線は夫々目標空燃比２４，３５，４５，６０を示している。図１２（Ａ）に示される目標空燃比Ａ／Ｆは図１２（Ｂ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。また、空燃比を図１２（Ａ）に示す目標空燃比Ａ／Ｆとするのに必要なスロットル弁２０の目標開度ＳＴが図１３（Ａ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されており、空燃比を図１２（Ａ）に示す目標空燃比Ａ／Ｆとするのに必要なＥＧＲ制御弁３１の目標開度ＳＥが図１３（Ｂ）に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。また、第２の燃焼が行われているとき、燃料噴射量Ｑは要求負荷Ｌ及び機関回転数Ｎに基づいて算出される。この燃料噴射量Ｑは図１４に示されるように要求負荷Ｌ及び機関回転数Ｎの関数としてマップの形で予めＲＯＭ４２内に記憶されている。
【００５０】
次に図１５及び図１６を参照しつつ本実施形態の運転制御について説明する。図１５及び図１６を参照すると、まず初めにステップ１００において機関の運転状態が第１の運転領域Ｉであることを示すフラグＩがセットされているか否かが判別される。フラグＩがセットされているとき、即ち機関の運転状態が第１の運転領域Ｉであるときにはステップ１０１に進んで要求負荷Ｌが第１の境界Ｘ（Ｎ）よりも大きくなったか否かが判別される。Ｌ≦Ｘ（Ｎ）のときにはステップ１０３に進み、第１の燃焼（低温燃焼）が行われる。一方、ステップ１０１においてＬ＞Ｘ（Ｎ）になったと判別されたときにはステップ１０２に進んでフラグＩがリセットされ、次いでステップ１１８に進み、第２の燃焼（通常燃焼、つまり、従来の燃焼方法による燃焼）が行われる。
【００５１】
ステップ１００において、フラグＩがセットされていないとき、即ち機関の運転状態が第２の運転領域ＩＩにあるときにはステップ１１６に進んで要求負荷Ｌが第２の境界Ｙ（Ｎ）よりも低くなったか否かが判別される。Ｌ≧Ｙ（Ｎ）のときにはステップ１１８に進み、第２の燃焼が行われる。一方、ステップ１１６においてＬ＜Ｙ（Ｎ）になったと判別されたときにはステップ１１７に進んでフラグＩがセットされ、次いでステップ１０３に進み、第１の燃焼が行われる。
【００５２】
ステップ１０３では図１０（Ａ）に示すマップからスロットル弁２０の目標開度ＳＴが算出され、スロットル弁２０の開度がこの目標開度ＳＴとされる。次いでステップ１０４では図１０（Ｂ）に示すマップからＥＧＲ制御弁３１の目標開度ＳＥが算出され、ＥＧＲ制御弁３１の開度がこの目標開度ＳＥとされる。次いでステップ１０５では図１１（Ａ）に示されるマップから主噴射の目標燃料噴射量Ｑｍが算出され、主噴射の燃料噴射量がこの目標燃料噴射量Ｑｍとされる。次いでステップ１０６では図１１（Ｂ）に示されるマップから主噴射の目標燃料噴射開始時期θＳが算出され、主噴射の燃料噴射開始時期がこの目標燃料噴射開始時期θＳとされる。
【００５３】
次いでステップ１０７では、排気ガスのリッチ化要求があるか否かが判断される。ＮＯのときにはステップ１０８に進み、圧縮上死点ＴＤＣ付近における主噴射の直前の圧縮行程末期の補助燃料噴射、いわゆる、パイロット噴射が行われる。一方、ＹＥＳのときにはステップ１１３に進み、圧縮上死点ＴＤＣ付近における主噴射よりも後の膨張行程中の補助燃料噴射が行われる。
【００５４】
ステップ１０８では、パイロット噴射の基本噴射量Ｑｐｂａｓｅが、要求負荷Ｌ及び機関回転数Ｎの関数として予めＲＯＭ４２内に記憶されている図１７（Ａ）に示すマップに基づいて算出される。詳細には、パイロット噴射の基本噴射量Ｑｐｂａｓｅは、要求負荷Ｌが低くなるほど多くなり、機関回転数Ｎが高くなるほど多くなるように設定されている。次いでステップ１０９では、空燃比センサ２７の出力値に基づいてＡ／Ｆが算出される。次いでステップ１１０では、ステップ１０９において算出されたＡ／Ｆと、Ａ／Ｆと基本噴射量の補正量Ｑｐａｄｊとの関係を示した図１７（Ｂ）に示すマップとに基づき、基本噴射量の補正量Ｑｐａｄｊが算出される。詳細には、補正量Ｑｐａｄｊは空燃比が濃くなるほど多くなるように設定されている。次いでステップ１１１では、基本噴射量Ｑｐｂａｓｅとその補正量Ｑｐａｄｊとに基づいてパイロット噴射の最終噴射量Ｑｐｆｉｎが算出される（Ｑｐｆｉｎ←Ｑｐｂａｓｅ＋Ｑｐａｄｊ）。つまり、空燃比が濃くなるほどパイロット噴射の最終噴射量Ｑｐｆｉｎは多くなる。次いでステップ１１２では、図１７（Ｃ）に示されるマップからパイロット噴射の目標燃料噴射開始時期θＳｐが算出され、パイロット噴射の燃料噴射開始時期がこの目標燃料噴射開始時期θＳｐとされる。詳細には、パイロット噴射の燃料噴射開始時期θＳｐは、要求負荷Ｌが低くなるほど早くなり、機関回転数Ｎが高くなるほど早くなるように設定されている。
【００５５】
ステップ１１３では、パイロット噴射の最終噴射量Ｑｐｆｉｎが零とされる。次いでステップ１１４では、質量流量検出器２１により検出された吸入空気量Ｇａが取込まれる。次いでステップ１１５では、膨張行程噴射の噴射量Ｑａが算出される（Ｑａ←Ｇａ／１２−Ｑｍ）。
【００５６】
上述したように本実施形態では、第１の燃焼が行われるときに、圧縮上死点ＴＤＣ付近における主噴射に加え、主噴射と異なるタイミングでパイロット噴射又は膨張行程噴射が行われる。詳細には、第１の燃焼が行われるときであって排気ガスのリッチ化要求がないときには、図１８（Ａ）に示すように、まず圧縮行程末期のパイロット噴射（Ｑｐ）が行われ、次いで圧縮上死点ＴＤＣ付近の主噴射（Ｑｍ）が行われる。一方、第１の燃焼が行われるときであって排気ガスのリッチ化要求があるときには、図１８（Ｂ）に示すように、まず圧縮上死点ＴＤＣ付近の主噴射（Ｑｍ）が行われ、次いで膨張行程中の膨張行程噴射（Ｑａ）が行われる。
【００５７】
一方、ステップ１１８では図１４に示されるマップから目標燃料噴射量Ｑが算出され、燃料噴射量がこの目標燃料噴射量Ｑとされる。次いでステップ１１９では図１３（Ａ）に示すマップからスロットル弁２０の目標開度ＳＴが算出される。次いでステップ１２０では図１３（Ｂ）に示すマップからＥＧＲ制御弁３１の目標開度ＳＥが算出され、ＥＧＲ制御弁３１の開度がこの目標開度ＳＥとされる。次いでステップ１２１では質量流量検出器２１により検出された吸入空気量Ｇａが取込まれる。
【００５８】
次いでステップ１２２では燃料噴射量Ｑと吸入空気量Ｇａから実際の空燃比（Ａ／Ｆ）Ｒ が算出される。次いでステップ１２３では図１２（Ｂ）に示すマップから目標空燃比Ａ／Ｆが算出される。次いでステップ１２４では実際の空燃比（Ａ／Ｆ）Ｒ が目標空燃比Ａ／Ｆよりも大きいか否かが判別される。（Ａ／Ｆ）Ｒ ＞Ａ／Ｆのときにはステップ１２５に進んでスロットル開度の補正値ΔＳＴが一定値αだけ減少せしめられ、次いでステップ１２７へ進む。これに対して（Ａ／Ｆ）Ｒ ≦Ａ／Ｆのときにはステップ１２６に進んで補正値ΔＳＴが一定値αだけ増大せしめられ、次いでステップ１２７に進む。ステップ１２７ではスロットル弁２０の目標開度ＳＴに補正値ΔＳＴを加算することにより最終的な目標開度ＳＴが算出され、スロットル弁２０の開度がこの最終的な目標開度ＳＴとされる。即ち、実際の空燃比（Ａ／Ｆ）Ｒ が目標空燃比Ａ／Ｆとなるようにスロットル弁２０の開度が制御される。
【００５９】
このように第２の燃焼が行われているときには要求負荷Ｌ又は機関回転数Ｎが変化すると燃料噴射量がただちに要求負荷Ｌおよび機関回転数Ｎに応じた目標燃料噴射量Ｑに一致せしめられる。例えば要求負荷Ｌが増大せしめられるとただちに燃料噴射量が増大せしめられ、斯くして機関の発生トルクがただちに増大せしめられる。一方、燃料噴射量Ｑが増大せしめられて空燃比が目標空燃比Ａ／Ｆからずれると空燃比が目標空燃比Ａ／Ｆとなるようにスロットル弁２０の開度が制御される。即ち、燃料噴射量Ｑが変化した後に空燃比が変化せしめられることになる。
【００６０】
本実施形態によれば、図１８（Ａ）又は図１８（Ｂ）に示すように、第１の燃焼が行われるとき、ステップ１０５で算出された噴射量Ｑｍの燃料が圧縮上死点付近において主噴射として噴射されるのに加え、ステップ１１１で算出された噴射量Ｑｐｆｉｎ又はステップ１１５で算出された噴射量Ｑａの燃料が主噴射と異なるタイミングでパイロット噴射又は膨張行程噴射として噴射される。そのため、第１の燃焼時には、第２の燃焼時に比べて酸素濃度が不足しているものの、パイロット噴射又は膨張行程噴射が行われることによって過酸化物が生成され、その過酸化物により酸素濃度不足が補われる。それゆえ、第１の燃焼時に、酸素濃度不足に伴って第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制することができる。
【００６１】
更に本実施形態によれば、排気ガスのリッチ化要求があるとき、ステップ１１５において膨張行程噴射を行うことにより排気空燃比が筒内空燃比よりも濃くされる。そのため、筒内空燃比を比較的薄くすることにより燃焼を安定させると共に、排気空燃比を比較的濃くすることにより、排気通路内に配置されている触媒２５の昇温を促進することができる。
【００６２】
また本実施形態によれば、第１の燃焼時に、空燃比が濃くなるほど、主噴射の噴射量Ｑｍが減少されると共に、ステップ１１０及びステップ１１１においてパイロット噴射の噴射量Ｑｐｆｉｎが増加される。そのため、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量（Ｑｍ＋Ｑｐｆｉｎ）を一定に維持することにより出力の変動を抑制することができる。
【００６３】
また本実施形態によれば、図１７（Ａ）について説明したように、要求負荷Ｌが低いほどパイロット噴射の基本噴射量Ｑｐｂａｓｅが増加される。つまり、要求負荷が低いほど主噴射の噴射量Ｑｍが少なくされると共にパイロット噴射の噴射量Ｑｐｆｉｎが多くされる。そのため、燃焼が不安定になり易い低負荷時に、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量（Ｑｍ＋Ｑｐｆｉｎ）を一定に維持することにより出力の変動を抑制することができる。
【００６４】
また、第１の燃焼時には、第２の燃焼時に比べてＥＧＲ通路２９内に流入する燃料量が多くなる。一方、ＥＧＲ通路２９内に流入した燃料はＥＧＲ通路２９内に配置された触媒５３により浄化されるが、その触媒５３が活性していない場合には、ＥＧＲ通路２９内に流入した燃料がそのまま燃焼室５内に供給されてしまう。そこで本実施形態では、第１の燃焼時にパイロット噴射が行われることにより、主噴射前に燃焼室５内に供給されるすべての燃料のうち、再循環された燃料が占める割合を低下せしめることができる。その結果、ＥＧＲ通路２９内の触媒５３が活性しているか否かに応じて主噴射前に燃焼室５内に供給される総燃料量が大きく変動してしまうのを抑制することができる。
【００６５】
以下、本発明の内燃機関の第二の実施形態について説明する。本実施形態の構成は図１に示した第一の実施形態の構成とほぼ同様である。従って、本実施形態によれば第一の実施形態とほぼ同様の効果を奏することができる。更に本実施形態では、図示しないが、第１の燃焼時のみならず第２の燃焼時にも主噴射直前の圧縮行程末期にパイロット噴射が行われる。その上、第１の燃焼時の主噴射直前の圧縮行程末期に行われるパイロット噴射の燃料噴射開始時期が、第２の燃焼時の主噴射直前の圧縮行程末期に行われるパイロット噴射の燃料噴射開始時期よりも進角せしめられる。本実施形態によれば、第一の実施形態と同様に、主噴射の他にパイロット噴射が行われることにより、パイロット噴射時に生成される過酸化物によって燃焼を安定化させることができる。一方、主噴射直前の圧縮行程末期にパイロット噴射が行われると、その際に酸素が消費されるため、主噴射が行われるときに酸素が不足する傾向がある。従って、上述したように第１の燃焼時の主噴射直前の圧縮行程末期に行われるパイロット噴射の燃料噴射開始時期が、第２の燃焼時の主噴射直前の圧縮行程末期に行われるパイロット噴射の燃料噴射開始時期よりも進角せしめられることにより、つまり、第１の燃焼時に第２の燃焼時に比べてパイロット噴射の燃料噴射開始時期を進角させることにより、第１の燃焼時に主噴射が行われるときの酸素不足を抑制すると共に、第１の燃焼時に、パイロット噴射を行うことにより、パイロット噴射により生成される過酸化物によって燃焼を安定化させることができる。
【００６６】
以下、本発明の内燃機関の第三の実施形態について説明する。本実施形態の構成は図１に示した第一の実施形態の構成とほぼ同様である。図１９は本実施形態の燃料噴射タイミングを示した図１８と同様の図である。図１９に示すように本実施形態では、第１の燃焼が行われるときに、圧縮上死点ＴＤＣ付近における主噴射に加え、主噴射と異なるタイミングでＶＩＧＯＭ噴射又は膨張行程噴射が行われる。詳細には、第１の燃焼が行われるときであって排気ガスのリッチ化要求がないときには、図１９（Ａ）に示すように、まず排気行程と吸気行程との間でＶＩＧＯＭ噴射（Ｑｖ）が行われ、次いで圧縮上死点ＴＤＣ付近の主噴射（Ｑｍ）が行われる。一方、第１の燃焼が行われるときであって排気ガスのリッチ化要求があるときには、図１９（Ｂ）に示すように、まず圧縮上死点ＴＤＣ付近の主噴射（Ｑｍ）が行われ、次いで膨張行程中の膨張行程噴射（Ｑａ）が行われる。本実施形態によっても第一の実施形態とほぼ同様の効果を奏することができる。
【００６７】
上述した実施形態において、主噴射と異なるタイミングで行われる更なる噴射の噴射時期が特定の噴射時期に限定されているが、本発明の内燃機関の更なる噴射の噴射時期は、上述した特定の噴射時期に限定されるものではなく、主噴射のタイミングと異なるものであればどのタイミングでもよい。
【００６８】
【発明の効果】
請求項１に記載の発明によれば、主噴射と異なるタイミングで更なる噴射が行われることによって生成される過酸化物により、酸素濃度不足を補い、それゆえ、第１の燃焼時に、酸素濃度不足に伴って第２の燃焼時に比べて燃焼が不安定になってしまうのを抑制することができる。
【００６９】
請求項２に記載の発明によれば、筒内空燃比を比較的薄くすることにより燃焼を安定させると共に、排気空燃比を比較的濃くすることにより、排気通路内に配置されている触媒の昇温を促進することができる。
【００７０】
請求項３に記載の発明によれば、主噴射前に燃焼室内に供給される燃料のうち、再循環された燃料が占める割合を低下せしめることができる。その結果、排気ガス再循環通路内の触媒が活性しているか否かに応じて主噴射前に燃焼室内に供給される燃料量が大きく変動してしまうのを抑制することができる。
【００７１】
請求項４に記載の発明によれば、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量を一定に維持することにより出力の変動を抑制することができる。
【００７２】
請求項５に記載の発明によれば、燃焼が不安定になり易い低負荷時に、筒内空燃比が濃くなるのに伴って燃焼が不安定になってしまうのを抑制しつつ、総噴射量を一定に維持することにより出力の変動を抑制することができる。
【００７３】
請求項６に記載の発明によれば、第１の燃焼時に第２の燃焼時に比べて更なる噴射の噴射時期を進角させることにより、第１の燃焼時に主噴射が行われるときの酸素不足を抑制すると共に、第１の燃焼時に、更なる噴射を行うことにより、更なる噴射により生成される過酸化物によって燃焼を安定化させることができる。
【図面の簡単な説明】
【図１】第一の実施形態の圧縮着火式内燃機関の全体図である。
【図２】スモークおよびＮＯｘの発生量等を示す図である。
【図３】燃焼圧を示す図である。
【図４】燃料分子を示す図である。
【図５】スモークの発生量とＥＧＲ率との関係を示す図である。
【図６】噴射燃料量と混合ガス量との関係を示す図である。
【図７】第１の運転領域Ｉおよび第２の運転領域ＩＩを示す図である。
【図８】空燃比センサの出力を示す図である。
【図９】第１の運転領域Ｉにおける空燃比等を示す図である。
【図１０】スロットル弁等の目標開度のマップを示す図である。
【図１１】燃料噴射量等のマップを示す図である。
【図１２】第２の燃焼における空燃比等を示す図である。
【図１３】スロットル弁等の目標開度のマップを示す図である。
【図１４】燃料噴射量のマップを示す図である。
【図１５】機関の運転を制御するためのフローチャートである。
【図１６】機関の運転を制御するためのフローチャートである。
【図１７】パイロット噴射の基本噴射量等のマップを示す図である。
【図１８】第一の実施形態の燃料噴射タイミングを示した図である。
【図１９】第三の実施形態の燃料噴射タイミングを示した図である。
【符号の説明】
５…燃焼室
６…燃料噴射弁
２０…スロットル弁
２４…排気管
２５，５３…触媒
２９…ＥＧＲ通路
３１…ＥＧＲ制御弁[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine.
[0002]
[Prior art]
Conventionally, when the amount of inert gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied to the combustion chamber is further increased, The temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than the soot generation temperature, so that almost no soot is generated, and the amount of generated soot is supplied into the combustion chamber more than the amount of the inert gas that peaks. And the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. 2. Description of the Related Art There is known an internal combustion engine that can selectively switch between combustion and combustion. An example of this type of internal combustion engine is described in, for example, Japanese Patent Application Laid-Open No. 11-93748.
[0003]
[Problems to be solved by the invention]
By the way, the air-fuel ratio at the time of performing the first combustion in which the amount of the inert gas supplied into the combustion chamber is large and the soot is hardly generated is larger than the amount of the inert gas at which the amount of generated soot becomes a peak, The amount of the inert gas supplied into the combustion chamber is smaller than the amount of the inert gas at which the generation amount reaches a peak, and is higher than the air-fuel ratio when the second combustion is performed. That is, during the first combustion, the oxygen concentration is lower than during the second combustion. Therefore, during the first combustion, the combustion is more unstable than during the second combustion. However, Japanese Patent Application Laid-Open No. H11-107861 does not disclose a method for suppressing the combustion from becoming unstable during the first combustion as compared with the second combustion. Therefore, in the internal combustion engine described in Japanese Patent Application Laid-Open No. H11-107861, it is not possible to suppress the combustion from becoming unstable during the first combustion as compared to during the second combustion.
[0004]
In view of the above problems, an object of the present invention is to provide an internal combustion engine that can suppress the combustion from becoming unstable during the first combustion as compared to the second combustion.
[0005]
[Means for Solving the Problems]
According to the first aspect of the invention, when the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the inert gas supplied into the combustion chamber is increased. When the amount of gas is further increased, the temperature of fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, so that almost no soot is generated, and the amount of soot generated peaks. First combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of active gas and soot is hardly generated, When the first combustion is performed in an internal combustion engine in which the amount of the inert gas supplied is selectively switched to the second combustion,AlwaysIn addition, there is provided an internal combustion engine in which, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection.
[0006]
In the internal combustion engine according to the first aspect, the first combustion is performed in which the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the generation amount of soot reaches a peak, and soot is hardly generated. sometimesAlwaysIn addition to the main injection near the compression top dead center, further injection is performed at a different timing from the main injection. At the time of the first combustion, although the amount of the inert gas supplied into the combustion chamber is smaller than the amount of the inert gas at which the amount of generated soot becomes a peak, the oxygen concentration is lower than at the time of the second combustion, By performing the further injection at a timing different from the main injection, peroxide is generated. Therefore, the lack of oxygen concentration is compensated by the peroxide. Therefore, it is possible to prevent the combustion from becoming unstable during the first combustion as compared with the second combustion due to the insufficient oxygen concentration.
[0007]
According to the second aspect of the present invention, there is provided the internal combustion engine according to the first aspect, wherein the further injection is performed to make the exhaust air-fuel ratio higher than the in-cylinder air-fuel ratio.
[0008]
In the internal combustion engine according to the second aspect, the exhaust air-fuel ratio is made higher than the in-cylinder air-fuel ratio by performing further injection. Therefore, the combustion can be stabilized by making the in-cylinder air-fuel ratio relatively thin, and the temperature of the catalyst disposed in the exhaust passage can be promoted by making the exhaust air-fuel ratio relatively rich.
[0009]
According to the invention described in claim 3,In the internal combustion engine having an exhaust gas recirculation passage provided with a catalyst, the further injection is performed during the first combustion.An internal combustion engine according to claim 1 is provided.
[0010]
In the internal combustion engine according to claim 3,Further injections take place during the first combustion in an internal combustion engine having an exhaust gas recirculation passage with a catalyst. At the time of the first combustion, the amount of fuel flowing into the exhaust gas recirculation passage is larger than at the time of the second combustion. The fuel flowing into the exhaust gas recirculation passage is purified by the catalyst in the exhaust gas recirculation passage. If the catalyst is not activated, the fuel flowing into the exhaust gas recirculation passage is used as it is in the combustion chamber. Will be supplied to Therefore, by performing the further injection during the first combustion as described above, the proportion of the recirculated fuel in the fuel supplied to the combustion chamber before the main injection can be reduced. As a result, it is possible to suppress a large change in the amount of fuel supplied to the combustion chamber before the main injection depending on whether the catalyst in the exhaust gas recirculation passage is activated.
[0011]
According to the invention described in claim 4,As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine , When the first combustion is performed, and to increase the injection amount of the further injection while decreasing the main injection amount as the air fuel ratio becomes richAn internal combustion engine is provided.
[0012]
In the internal combustion engine according to claim 4,During the first combustion, as the air-fuel ratio becomes richer, the main injection amount is reduced and the injection amount of the further injection is increased. for that reason,By suppressing the combustion from becoming unstable as the in-cylinder air-fuel ratio increases, the output variation can be suppressed by keeping the total injection amount constant.
[0013]
According to the invention described in claim 5,As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine Was to increase the injection amount of the further injection load as lowAn internal combustion engine is provided.
[0014]
In the internal combustion engine according to claim 5,As the load is lower, the injection amount of the further injection is increased. That is, the lower the load, the smaller the main injection amount and the larger the injection amount of the further injection. Therefore, at a low load where combustion is likely to be unstable, the output is maintained by keeping the total injection amount constant while suppressing the combustion from becoming unstable as the in-cylinder air-fuel ratio increases. Fluctuations can be suppressed.
[0015]
According to the invention described in claim 6,As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine Performing the further injection at the end of the compression stroke immediately before the main injection at the time of the first combustion, and performing the further injection at the end of the compression stroke immediately before the main injection also at the time of the second combustion, The further injection at the time of combustion is advanced more than the further injection at the time of the second combustion.An internal combustion engine is provided.
[0016]
In the internal combustion engine according to claim 6,The further injection performed at the end of the compression stroke immediately before the main injection during the first combustion is advanced more than the further injection performed at the end of the compression stroke immediately before the main injection during the second combustion. By performing the further injection in addition to the main injection, the combustion is stabilized by the peroxide generated at the time of the further injection. On the other hand, if further injection is performed at the end of the compression stroke immediately before the main injection, oxygen is consumed at that time, so that there is a tendency that oxygen is insufficient when the main injection is performed. Therefore, as described above, the further injection performed at the end of the compression stroke immediately before the main injection during the first combustion is more advanced than the further injection performed at the end of the compression stroke immediately before the main injection during the second combustion. By being restricted, that is, by advancing the injection timing of the further injection in the first combustion as compared with the second combustion, it is possible to suppress the oxygen deficiency when the main injection is performed in the first combustion and By performing the further injection during the first combustion, the combustion can be stabilized by the peroxide generated by the further injection.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0018]
FIG. 1 shows a first embodiment in which the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. A mass flow detector 21 for detecting the mass flow of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20.
[0019]
On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 23 of an exhaust turbocharger 15 via an exhaust manifold 22, and an outlet of the exhaust turbine 23 is provided with a catalyst 25 having an oxidizing function via an exhaust pipe 24. Connected to converter 26. An air-fuel ratio sensor 27 is disposed in the exhaust manifold 22. The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 29. An EGR control valve 31 driven by a step motor 30 is disposed. An EGR cooler 32 for cooling the EGR gas flowing in the EGR passage 29 is disposed in the EGR passage 29. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooler 32, and the engine cooling water cools the EGR gas. Further, a catalyst 53 for purifying EGR gas flowing in the EGR passage 29 is disposed in the EGR passage 29.
[0020]
On the other hand, the fuel injection valve 6 is connected via a fuel supply pipe 33 to a fuel reservoir, a so-called common rail 34. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.
[0021]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41 such as a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an output port 46. Is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and the fuel The output signal of the pressure sensor 36 is input to the input port 45 via a corresponding AD converter (not shown). A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. The engine speed is calculated based on the output signal from the input crank angle sensor 52. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle motor control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via the corresponding drive circuit 48.
[0022]
FIG. 2 shows a change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening of the throttle valve 20 and the EGR rate during low-load operation of the engine, and smoke, HC, An experimental example showing a change in CO and NOx emissions is shown. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (．14.6), the EGR rate is 65% or more. As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the amount of smoke generated when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30 is reduced. Start growing. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more, and the air-fuel ratio A / F becomes about 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine is slightly reduced, and the amount of generated NOx is considerably reduced. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0023]
FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. The graph shows changes in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is almost zero in the vicinity. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), FIG. 3 (B) in which the amount of smoke generation is almost zero is shown in FIG. 3 (A) where the amount of smoke generation is large. It can be seen that the combustion pressure is lower than in the case. Although not shown, from the same experimental results as in FIG. 3, the first amount of EGR gas supplied into the combustion chamber 5 is larger than the amount of EGR gas at which the generation amount of soot reaches a peak, and soot is hardly generated. The maximum value (peak) of the combustion pressure at the time of combustion (low-temperature combustion) is the second combustion (where the amount of the EGR gas supplied into the combustion chamber 5 is smaller than the amount of the EGR gas at which the generation amount of soot becomes a peak). It is known that the combustion pressure during combustion by the conventional combustion method) is lower than the maximum value (peak). Accordingly, it can be said that the engine rotation unevenness caused by the explosion during the first combustion is smaller than the engine rotation unevenness caused by the explosion during the second combustion.
[0024]
The following can be said from the experimental results shown in FIGS. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of generated smoke is almost zero, the amount of generated NOx is considerably reduced as shown in FIG. The decrease in the amount of generated NOx means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 has decreased when little soot is generated. . The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low, and the combustion temperature in the combustion chamber 5 is low at this time.
[0025]
Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, the amount of HC and CO emissions increases as shown in FIG. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbon and the aromatic hydrocarbon contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, so that a precursor of soot is formed. A soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot generation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the generation amount of soot becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a soot precursor or a hydrocarbon in a state before it. .
[0026]
Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber 5 is low, the amount of generated soot becomes almost zero. The hydrocarbon will be discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.
[0027]
By the way, the temperature of the fuel and its surrounding when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature varies depending on various factors such as the type of the fuel and the compression ratio of the air-fuel ratio. Although it cannot be said how many times, this certain temperature is closely related to the amount of NOx generated, so that this certain temperature can be defined to some extent from the amount of NOx generated. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas temperature around it decrease, and the amount of generated NOx decreases. At this time, the amount of generated NOx is 10 p. p. When it is less or equal to or less than m, almost no soot is generated. Therefore, at the above-mentioned certain temperature, the amount of generated NOx is 10 p. p. m The temperature almost coincides with the temperature when the temperature becomes lower or higher. Once soot is produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with the catalyst having the oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of the precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a precursor or previous soot without producing soot in the combustion chamber 5 and removing the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.
[0028]
Now, in order to stop the growth of hydrocarbons before the soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 to a temperature lower than the temperature at which the soot is generated. There is. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel. That is, if there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.
[0029]
On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different. In this case, the evaporated fuel diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, since the combustion heat is absorbed by the surrounding inert gas, the combustion temperature does not rise so much. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be kept low by the endothermic effect of the inert gas. In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas is required to be able to absorb enough heat to do so. Therefore, if the amount of fuel increases, the required amount of inert gas increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action, and therefore, the inert gas is preferably a gas having a large specific heat. In this regard, CO2Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.
[0030]
FIG. 5 shows the relationship between the EGR rate and smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, the curve A shows a case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows a case where the EGR gas is cooled by a small cooling device. , Curve C shows the case where the EGR gas is not forcibly cooled. As shown by the curve A in FIG. 5, when the EGR gas is cooled strongly, the amount of soot generation peaks at a point where the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to approximately 55% or more. Then, almost no soot is generated.
[0031]
On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. So that almost no soot is generated. As shown by the curve C in FIG. 5, when the EGR gas is not forcibly cooled, the amount of soot generation reaches a peak when the EGR rate is around 55%. Above a percentage, soot is hardly generated. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which almost no soot is generated Also lowers slightly. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.
[0032]
FIG. 6 shows a mixed gas amount of the EGR gas and the air necessary for setting the fuel temperature during combustion and the surrounding gas temperature to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas; And the ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount drawn into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis shows the required load.
[0033]
Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is made lower than the temperature at which soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 6, and the ratio between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and the gas around it will be lower than the temperature at which soot is produced, so that no soot is generated. At this time, the NOx generation amount is 10 p. p. m or less, so the amount of NOx generated is extremely small.
[0034]
As the amount of fuel injection increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which soot is generated, the amount of heat absorbed by the EGR gas Must be increased. Accordingly, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases. That is, the EGR gas amount needs to increase as the required load increases.
[0035]
By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y, and therefore, in FIG. 6, in the region where the required load is larger than Lo, as the required load increases, Unless the EGR gas ratio is reduced, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio. In other words, when supercharging is not performed, when the required air-fuel ratio is to be maintained at the stoichiometric air-fuel ratio in an area where the required load is larger than Lo, the EGR rate decreases as the required load increases. In the region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.
[0036]
However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 into the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the EGR rate is increased in a region where the required load is larger than Lo. Can be maintained at or above 55 percent, for example, 70 percent, and thus the temperature of the fuel and its surrounding gas can be maintained below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, the EGR control valve 31Fully opened,The throttle valve 20 is slightly closed.
[0037]
As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. NOx generation is reduced to 10 p. p. m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. While the amount of generated NOx is 10 p. p. m can be around or below.
[0038]
That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow to soot, and thus no soot is generated. At this time, only a very small amount of NOx is generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated when the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Further, only a very small amount of NOx is generated.
[0039]
In this way, when low-temperature combustion is being performed, soot is not generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, The generation amount of NOx becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.
[0040]
By the way, the temperature of the fuel and the surrounding gas at the time of combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, only during the low load operation in the engine where the calorific value due to combustion is relatively small. Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion can be performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In this way, the second combustion, that is, the combustion that has been performed conventionally, is performed during the high load operation of the engine. However, even during the low engine load operation, the second combustion is performed depending on the engine operation state. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the generation amount of soot is a peak, as is apparent from the description so far, and almost all the soot is generated. The second combustion, that is, the combustion that has been performed conventionally, is a combustion in which the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas at which the amount of soot is peaked. Say that.
[0041]
FIG. 7 shows a first operation region I in which first combustion, that is, low-temperature combustion, can be performed, and a second operation region II, in which second combustion, that is, combustion by a conventional combustion method, is performed. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) indicates a first boundary between the first operation region I and the second operation region II, and Y (N) indicates the first operation region I and the second operation region. The second boundary with the area II is shown. The determination of the change of the operation region from the first operation region I to the second operation region II is made based on the first boundary X (N), and the change from the second operation region II to the first operation region I is performed. The determination of the change of the operating region is performed based on the second boundary Y (N).
[0042]
That is, if the required load L exceeds a first boundary X (N), which is a function of the engine speed N, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, the operating region Is shifted to the second operation region II, and combustion is performed by the conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion can be performed again.
[0043]
The two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower load side than the first boundary X (N) are provided for the following two reasons. . The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not start immediately unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.
[0044]
By the way, when the operation region of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbon is in the form of a precursor of soot or a state before it. It is discharged from the combustion chamber 5. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function. As the catalyst 25, an oxidation catalyst can be used.
[0045]
FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.
[0046]
FIG. 9A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 9A, curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have target air-fuel ratios of 15.5, 16, and 17, respectively. , 18 and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 9A, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L decreases. You. That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low-temperature combustion can be performed even if the EGR rate is reduced. When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 9A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, the embodiment according to the present invention increases the target air-fuel ratio A / F as the required load L decreases. .
[0047]
The target air-fuel ratio A / F shown in FIG. 9A is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 9B. . Also, as shown in FIG. 10A, the target opening ST of the throttle valve 20 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 9A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 10 (B), it is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.
[0048]
Further, when the first combustion is being performed, the fuel injection amount Qm of the main injection is calculated based on the required load L and the engine speed N. The fuel injection amount Qm of the main injection is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. The fuel injection start timing θS of the main injection is set near the compression top dead center TDC, and the required load L and the engine speed N shown in FIG. Are stored in the ROM 42 in advance in the form of a map as a function of
[0049]
FIG. 12A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion according to the conventional combustion method is performed. In FIG. 12A, curves A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. ing. The target air-fuel ratio A / F shown in FIG. 12A is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. Further, as shown in FIG. 13A, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 12A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 13B, a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N. Further, when the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance as a function of the required load L and the engine speed N as shown in FIG.
[0050]
Next, the operation control of the present embodiment will be described with reference to FIGS. Referring to FIGS. 15 and 16, first, at step 100, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 101, where it is determined whether the required load L has become larger than the first boundary X (N). Is done. When L ≦ X (N), the routine proceeds to step 103, where the first combustion (low-temperature combustion) is performed. On the other hand, when it is determined in step 101 that L> X (N), the routine proceeds to step 102, where the flag I is reset, and then proceeds to step 118, where the second combustion (normal combustion, that is, the conventional combustion method) is performed. Combustion) is performed.
[0051]
In step 100, when the flag I is not set, that is, when the operating state of the engine is in the second operating region II, the process proceeds to step 116, and the required load L becomes lower than the second boundary Y (N). It is determined whether or not it is. When L ≧ Y (N), the routine proceeds to step 118, where the second combustion is performed. On the other hand, when it is determined in step 116 that L <Y (N), the routine proceeds to step 117, where the flag I is set. Then, the routine proceeds to step 103, where the first combustion is performed.
[0052]
In step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 10A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 104, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 10B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 105, the target fuel injection amount Qm of the main injection is calculated from the map shown in FIG. 11A, and the fuel injection amount of the main injection is set as the target fuel injection amount Qm. Next, at step 106, the target fuel injection start timing θS of the main injection is calculated from the map shown in FIG. 11B, and the fuel injection start timing of the main injection is set to the target fuel injection start timing θS.
[0053]
Next, at step 107, it is determined whether or not there is an exhaust gas enrichment request. If NO, the process proceeds to step 108, where auxiliary fuel injection at the end of the compression stroke immediately before the main injection near the compression top dead center TDC, that is, pilot injection is performed. On the other hand, if YES, the routine proceeds to step 113, where auxiliary fuel injection during the expansion stroke after the main injection near the compression top dead center TDC is performed.
[0054]
In step 108, the basic injection amount Qpbase of the pilot injection is calculated as a function of the required load L and the engine speed N based on the map shown in FIG. Specifically, the basic injection amount Qpbase of the pilot injection is set to increase as the required load L decreases and increase as the engine speed N increases. Next, at step 109, A / F is calculated based on the output value of the air-fuel ratio sensor 27. Next, in step 110, the basic injection amount is corrected based on the A / F calculated in step 109 and the map shown in FIG. 17B showing the relationship between the A / F and the basic injection amount correction amount Qpadj. The quantity Qpadj is calculated. More specifically, the correction amount Qpadj is set to increase as the air-fuel ratio increases. Next, at step 111, the final injection amount Qpfin of the pilot injection is calculated based on the basic injection amount Qpbase and its correction amount Qpadj (Qpfin ← Qpbase + Qpadj). In other words, the final injection amount Qpfin of the pilot injection increases as the air-fuel ratio increases. Next, at step 112, the target fuel injection start timing θSp of the pilot injection is calculated from the map shown in FIG. 17C, and the fuel injection start timing of the pilot injection is set to the target fuel injection start timing θSp. Specifically, the fuel injection start timing θSp of the pilot injection is set to be earlier as the required load L is lower, and to be earlier as the engine speed N is higher.
[0055]
In step 113, the final injection amount Qpfin of the pilot injection is set to zero. Next, at step 114, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 115, the injection amount Qa of the expansion stroke injection is calculated (Qa ← Ga / 12-Qm).
[0056]
As described above, in the present embodiment, when the first combustion is performed, in addition to the main injection near the compression top dead center TDC, the pilot injection or the expansion stroke injection is performed at a timing different from the main injection. More specifically, when the first combustion is performed and there is no request to enrich the exhaust gas, first, as shown in FIG. 18A, pilot injection (Qp) at the end of the compression stroke is performed, and then, The main injection (Qm) near the compression top dead center TDC is performed. On the other hand, when the first combustion is performed and there is an exhaust gas enrichment request, first, as shown in FIG. 18B, the main injection (Qm) near the compression top dead center TDC is performed, Next, expansion stroke injection (Qa) during the expansion stroke is performed.
[0057]
On the other hand, at step 118, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 119, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 120, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 13B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 121, the intake air amount Ga detected by the mass flow detector 21 is taken.
[0058]
Next, at step 122, the actual air-fuel ratio (A / F) is calculated from the fuel injection amount Q and the intake air amount Ga.RIs calculated. Next, at step 123, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 124, the actual air-fuel ratio (A / F)RIs larger than the target air-fuel ratio A / F. (A / F)RIf> A / F, the routine proceeds to step 125, where the correction value ΔST of the throttle opening is decreased by a constant value α, and then the routine proceeds to step 127. (A / F)RIf .ltoreq.A / F, the routine proceeds to step 126, where the correction value .DELTA.ST is increased by a constant value .alpha., And then the routine proceeds to step 127. In step 127, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is set as the final target opening ST. That is, the actual air-fuel ratio (A / F)ROf the throttle valve 20 is controlled so that the target air-fuel ratio A / F is obtained.
[0059]
As described above, when the required load L or the engine speed N changes during the second combustion, the fuel injection amount is immediately matched with the target fuel injection amount Q corresponding to the required load L and the engine speed N. For example, when the required load L is increased, the fuel injection amount is immediately increased, and thus the torque generated by the engine is immediately increased. On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.
[0060]
According to the present embodiment, as shown in FIG. 18 (A) or FIG. 18 (B), when the first combustion is performed, the fuel of the injection amount Qm calculated in step 105 is near the compression top dead center. In addition to being injected as the main injection, the fuel having the injection amount Qpfin calculated in step 111 or the injection amount Qa calculated in step 115 is injected as pilot injection or expansion stroke injection at a timing different from the main injection. Therefore, during the first combustion, although the oxygen concentration is insufficient compared with the second combustion, peroxide is generated by the pilot injection or the expansion stroke injection, and the oxygen concentration is insufficient due to the peroxide. Is supplemented. Therefore, it is possible to prevent the combustion from becoming unstable during the first combustion as compared with the second combustion due to the insufficient oxygen concentration.
[0061]
Further, according to the present embodiment, when there is a request for enrichment of exhaust gas, the exhaust air-fuel ratio is made higher than the in-cylinder air-fuel ratio by performing the expansion stroke injection in step 115. Therefore, the combustion can be stabilized by making the in-cylinder air-fuel ratio relatively thin, and the temperature of the catalyst 25 disposed in the exhaust passage can be promoted by making the exhaust air-fuel ratio relatively rich.
[0062]
Further, according to the present embodiment, during the first combustion, as the air-fuel ratio increases, the injection amount Qm of the main injection decreases and the injection amount Qpfin of the pilot injection increases in steps 110 and 111. Therefore, fluctuations in output can be suppressed by keeping the total injection amount (Qm + Qpfin) constant while suppressing combustion from becoming unstable as the in-cylinder air-fuel ratio increases.
[0063]
According to the present embodiment, as described with reference to FIG. 17A, the lower the required load L, the greater the basic injection amount Qpbase of the pilot injection. In other words, the lower the required load, the smaller the injection amount Qm of the main injection and the larger the injection amount Qpfin of the pilot injection. Therefore, at a low load where combustion is likely to be unstable, the total injection amount (Qm + Qpfin) is kept constant while suppressing combustion from becoming unstable as the in-cylinder air-fuel ratio increases. Thus, fluctuations in output can be suppressed.
[0064]
In addition, the amount of fuel flowing into the EGR passage 29 during the first combustion is larger than that during the second combustion. On the other hand, the fuel flowing into the EGR passage 29 is purified by the catalyst 53 disposed in the EGR passage 29. When the catalyst 53 is not activated, the fuel flowing into the EGR passage 29 is directly burned. It is supplied into the chamber 5. Therefore, in the present embodiment, by performing the pilot injection during the first combustion, it is possible to reduce the proportion of the recirculated fuel among all the fuel supplied into the combustion chamber 5 before the main injection. it can. As a result, whether or not the catalyst 53 in the EGR passage 29 is activeToAccordingly, it is possible to suppress a large change in the total fuel amount supplied into the combustion chamber 5 before the main injection.
[0065]
Hereinafter, a second embodiment of the internal combustion engine of the present invention will be described. The configuration of this embodiment is substantially the same as the configuration of the first embodiment shown in FIG. Therefore, according to the present embodiment, substantially the same effects as in the first embodiment can be obtained. Further, in the present embodiment, although not shown, the pilot injection is performed at the end of the compression stroke immediately before the main injection not only during the first combustion but also during the second combustion. In addition, the fuel injection start timing of the pilot injection performed at the end of the compression stroke immediately before the main injection during the first combustion is changed to the fuel injection start of the pilot injection performed at the end of the compression stroke immediately before the main injection during the second combustion. It is advanced more than time. According to the present embodiment, similarly to the first embodiment, by performing pilot injection in addition to main injection, combustion can be stabilized by peroxide generated during pilot injection. On the other hand, if the pilot injection is performed at the end of the compression stroke immediately before the main injection, oxygen is consumed at that time, and thus the oxygen tends to be insufficient when the main injection is performed. Therefore, as described above, the fuel injection start timing of the pilot injection performed at the end of the compression stroke immediately before the main injection during the first combustion is different from the pilot injection performed at the end of the compression stroke immediately before the main injection during the second combustion. The main injection is performed at the time of the first combustion by being advanced from the fuel injection start timing, that is, by making the fuel injection start timing of the pilot injection advanced at the time of the first combustion as compared with the time of the second combustion. In addition to suppressing the shortage of oxygen when the fuel injection is performed, by performing the pilot injection during the first combustion, the combustion can be stabilized by the peroxide generated by the pilot injection.
[0066]
Hereinafter, a third embodiment of the internal combustion engine of the present invention will be described. The configuration of this embodiment is substantially the same as the configuration of the first embodiment shown in FIG. FIG. 19 is a view similar to FIG. 18 showing the fuel injection timing of the present embodiment. As shown in FIG. 19, in the present embodiment, when the first combustion is performed, in addition to the main injection near the compression top dead center TDC, the VIGOM injection or the expansion stroke injection is performed at a different timing from the main injection. More specifically, when the first combustion is performed and there is no request for enrichment of exhaust gas, first, as shown in FIG. 19A, VIGOM injection (Qv) is performed between the exhaust stroke and the intake stroke. Is performed, and then the main injection (Qm) near the compression top dead center TDC is performed. On the other hand, when the first combustion is performed and there is an exhaust gas enrichment request, first, as shown in FIG. 19B, the main injection (Qm) near the compression top dead center TDC is performed, Next, expansion stroke injection (Qa) during the expansion stroke is performed. According to the present embodiment, substantially the same effects as in the first embodiment can be obtained.
[0067]
In the above-described embodiment, the injection timing of the further injection performed at a timing different from the main injection is limited to the specific injection timing, but the injection timing of the further injection of the internal combustion engine of the present invention is the specific injection timing described above. The timing is not limited to the injection timing, and may be any timing as long as it differs from the timing of the main injection.
[0068]
【The invention's effect】
According to the first aspect of the present invention, the insufficient oxygen concentration is compensated for by the peroxide generated by the further injection being performed at a different timing from the main injection, and therefore, the oxygen concentration is reduced during the first combustion. It is possible to prevent the combustion from becoming unstable as compared with the second combustion due to the shortage.
[0069]
According to the second aspect of the invention, the combustion is stabilized by making the in-cylinder air-fuel ratio relatively thin, and the exhaust air-fuel ratio is made relatively high, so that the catalyst disposed in the exhaust passage can be raised. Can promote warmth.
[0070]
According to the invention described in claim 3,The proportion of the recirculated fuel in the fuel supplied to the combustion chamber before the main injection can be reduced. As a result, it is possible to suppress a large change in the amount of fuel supplied to the combustion chamber before the main injection depending on whether the catalyst in the exhaust gas recirculation passage is activated.
[0071]
According to the invention described in claim 4,By suppressing the combustion from becoming unstable as the in-cylinder air-fuel ratio increases, the output variation can be suppressed by keeping the total injection amount constant.
[0072]
According to the invention described in claim 5,At low load, where combustion is likely to be unstable, fluctuations in output are maintained by keeping the total injection amount constant while suppressing combustion from becoming unstable as the in-cylinder air-fuel ratio increases. Can be suppressed.
[0073]
According to the invention described in claim 6,By advancing the injection timing of the further injection at the time of the first combustion as compared with the time of the second combustion, oxygen shortage at the time of the main injection being performed at the time of the first combustion is suppressed, and at the time of the first combustion, By performing the further injection, the combustion can be stabilized by the peroxide generated by the further injection.
[Brief description of the drawings]
FIG. 1 is an overall view of a compression ignition type internal combustion engine of a first embodiment.
FIG. 2 is a diagram showing the amounts of smoke and NOx generated;
FIG. 3 is a diagram showing a combustion pressure.
FIG. 4 is a diagram showing fuel molecules.
FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.
FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.
FIG. 7 is a diagram showing a first operation region I and a second operation region II.
FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.
FIG. 9 is a diagram showing an air-fuel ratio and the like in a first operation region I.
FIG. 10 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 11 is a diagram showing a map of a fuel injection amount and the like.
FIG. 12 is a diagram showing an air-fuel ratio and the like in a second combustion.
FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 14 is a diagram showing a map of a fuel injection amount.
FIG. 15 is a flowchart for controlling operation of the engine.
FIG. 16 is a flowchart for controlling operation of the engine.
FIG. 17 is a view showing a map of a basic injection amount of pilot injection and the like.
FIG. 18 is a diagram illustrating fuel injection timing according to the first embodiment.
FIG. 19 is a diagram illustrating fuel injection timing according to a third embodiment.
[Explanation of symbols]
5. Combustion chamber
6 ... Fuel injection valve
20 ... Throttle valve
24 ... exhaust pipe
25, 53 ... catalyst
29… EGR passage
31 ... EGR control valve

Claims (6)

燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときには常に、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関。As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. in 2 of the combustion and is selectively switched is an internal combustion engine, whenever the first combustion is performed, in addition to the main injection near the compression top dead center, performs a further injection at a timing different from said main injection Internal combustion engine 前記更なる噴射を行うことにより排気空燃比を筒内空燃比よりも濃くするようにした請求項１に記載の内燃機関。The internal combustion engine according to claim 1, wherein the further injection is performed to make the exhaust air-fuel ratio higher than the in-cylinder air-fuel ratio. 触媒を備えた排気ガス再循環通路を有する内燃機関において前記第１の燃焼時に前記更なる噴射を行うようにした請求項１に記載の内燃機関。The internal combustion engine according to claim 1, wherein the further injection is performed during the first combustion in an internal combustion engine having an exhaust gas recirculation passage including a catalyst. 燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine ,
前記第１の燃焼が行われるときに、空燃比が濃くなるほど主噴射量を減少させると共に前記更なる噴射の噴射量を増加させるようにした内燃機関。  An internal combustion engine wherein, when the first combustion is performed, the main injection amount is decreased and the injection amount of the further injection is increased as the air-fuel ratio becomes rich. 燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine ,
負荷が低いほど前記更なる噴射の噴射量を増加させるようにした内燃機関。  An internal combustion engine configured to increase the injection amount of the further injection as the load decreases. 燃焼室内に供給される不活性ガスの量を増大していくと煤の発生量が次第に増大してピークに達し、前記燃焼室内に供給される不活性ガスの量を更に増大していくと前記燃焼室内における燃焼時の燃料およびその周囲のガス温が煤の生成温度よりも低くなって煤がほとんど発生しなくなり、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が多く煤がほとんど発生しない第１の燃焼と、煤の発生量がピークとなる不活性ガスの量よりも前記燃焼室内に供給される不活性ガスの量が少ない第２の燃焼とが選択的に切り換えられる内燃機関において、前記第１の燃焼が行われるときに、圧縮上死点付近における主噴射に加え、前記主噴射と異なるタイミングで更なる噴射を行うようにした内燃機関であって、As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. The temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature, soot is hardly generated, and the amount of generated soot is supplied to the combustion chamber more than the amount of the inert gas that peaks. The first combustion in which the amount of inert gas to be performed is large and soot is hardly generated, and the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. In the internal combustion engine in which the second combustion is selectively switched, when the first combustion is performed, in addition to the main injection near the compression top dead center, further injection is performed at a timing different from the main injection. Internal combustion engine ,
前記第１の燃焼時に前記更なる噴射を前記主噴射直前の圧縮行程末期に行うと共に、前記第２の燃焼時にも前記主噴射直前の圧縮行程末期に更なる噴射を行い、前記第１の燃焼時の更なる噴射を前記第２の燃焼時の更なる噴射よりも進角させるようにした内燃機関。  The further injection is performed at the end of the compression stroke immediately before the main injection at the time of the first combustion, and the further injection is also performed at the end of the compression stroke immediately before the main injection at the time of the second combustion. An internal combustion engine wherein the further injection at the time is advanced more than the further injection at the time of the second combustion.
JP2000149834A 2000-05-17 2000-05-17 Internal combustion engine Expired - Fee Related JP3578049B2 (en)

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