JP4203730B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

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JP4203730B2
JP4203730B2 JP2003117030A JP2003117030A JP4203730B2 JP 4203730 B2 JP4203730 B2 JP 4203730B2 JP 2003117030 A JP2003117030 A JP 2003117030A JP 2003117030 A JP2003117030 A JP 2003117030A JP 4203730 B2 JP4203730 B2 JP 4203730B2
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exhaust
dpf
temperature
rich
fuel ratio
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JP2004324455A (en
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恵 信ヶ原
道博 畠
和郎 倉田
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Mitsubishi Motors Corp
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Mitsubishi Motors Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9431—Processes characterised by a specific device
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9495—Controlling the catalytic process
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0821—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with particulate filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/029—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a particulate filter
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/1441—Plural sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
    • F02D41/1474—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method by detecting the commutation time of the sensor
    • 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
    • F02M26/45—Sensors specially adapted for EGR systems
    • F02M26/46—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition
    • 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
    • F02M26/45—Sensors specially adapted for EGR systems
    • F02M26/46—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition
    • F02M26/47—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition the characteristics being temperatures, pressures or flow rates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F01N2430/06—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by varying fuel-air ratio, e.g. by enriching fuel-air mixture
    • 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
    • F02B3/00—Engines characterised by air compression and subsequent fuel addition
    • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition
    • 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
    • F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/08—Exhaust gas treatment apparatus parameters
    • F02D2200/0802—Temperature of the exhaust gas treatment apparatus
    • 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
    • F02M26/05—High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream 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
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/09—Constructional details, e.g. structural combinations of EGR systems and supercharger systems; Arrangement of the EGR and supercharger systems with respect to the engine
    • F02M26/10—Constructional details, e.g. structural combinations of EGR systems and supercharger systems; Arrangement of the EGR and supercharger systems with respect to the engine having means to increase the pressure difference between the exhaust and intake system, e.g. venturis, variable geometry turbines, check valves using pressure pulsations or throttles in the air intake or exhaust system
    • 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
    • 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

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Environmental & Geological Engineering (AREA)
  • Biomedical Technology (AREA)
  • Health & Medical Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Processes For Solid Components From Exhaust (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Filtering Of Dispersed Particles In Gases (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の排気浄化装置に係り、詳しくは、ディーゼル・パティキュレート・フィルタ（ＤＰＦ）の再生に適用される内燃機関の排気浄化装置に関する。
【０００２】
【従来の技術】
一般に、ＤＰＦは、排気中のパティキュレート・マター（ＰＭ）を捕集して処理する排ガス後処理装置である。具体的には、ディーゼルエンジン等の排気中には、ＨＣ、ＣＯ、ＮＯx等の他に、ＰＭが多く含まれていることから、このＰＭをフィルタに捕集した後に約６００℃程度の高温の排ガスを利用し、焼却除去させてＤＰＦの再生を図る。
【０００３】
ここで、ＤＰＦでは、運転条件によってはその自己再生が実現できるものの、あらゆる運転条件を想定した場合には、ＤＰＦの温度を強制的に昇温させる強制再生システムが不可欠である。しかし、この強制再生においては、例えば、ＤＰＦの温度が低すぎると再生速度が遅く、高すぎると急激な再生によってＤＰＦの破損を招く等、その温度制御が困難である。そこで、ＤＰＦでは、内燃機関の空燃比制御により、ＤＰＦでの再生速度を制御する内燃機関の排気浄化装置の技術が提案されている（例えば、特許文献１参照）。
【０００４】
当該装置では、排気系にＤＰＦを備えており、ＤＰＦの強制再生時には、ＤＰＦが所定温度に達するまではリッチ空燃比に設定し、ＤＰＦが所定温度に昇温してからリーン空燃比に切換えてＰＭを燃焼除去している。これにより、ＤＰＦの強制再生を図る。
また、当該装置では、前記ＤＰＦの他、排気系にＮＯｘ吸蔵触媒をも備えており、Ｓ成分の放出（Ｓパージ）時には、上記ＤＰＦが所定温度に達してから、さらにＳＯｘの脱離温度から所定時間に達するまでリッチ空燃比を継続してＳ被毒を解除している。
【０００５】
このＮＯｘ吸蔵触媒は、リーン空燃比のときに排気中のＮＯｘを吸蔵し、リッチ空燃比のときに吸蔵したＮＯｘを放出還元する排ガス後処理装置である。
具体的には、酸素過剰状態（酸化雰囲気）において排気中のＮＯｘを硝酸塩として吸蔵し、この吸蔵したＮＯｘを一酸化炭素過剰状態（還元雰囲気）で窒素に還元させる特性を有している。そして、内燃機関は、ＮＯｘ吸蔵量が飽和する前に排気空燃比を理論空燃比又はその近傍値に制御する如くの空気過剰率が低い（低λ）状態のリッチ運転へ定期的に切換えるリッチスパイクを行い、ＮＯｘ吸蔵触媒の再生を図る。また、ＮＯｘ吸蔵触媒には、燃料中のＳ成分の酸化によるＳＯｘも硫酸塩として堆積されるため、当該堆積した前記Ｓ成分の放出（Ｓパージ）を行うべく、上記と同様にリッチ運転を定期的に実施してＮＯｘ吸蔵触媒の再生を図る。
【０００６】
ここで、このＳパージには、約６５０℃程度の高温であってリッチ乃至ストイキオの排ガスが必要になる。
そこで、上述した当該装置では、ＤＰＦの強制再生時には、ＤＰＦが所定温度に達するまではリッチ空燃比にしてＰＭの燃焼を抑え、Ｓパージ時には、さらにＳＯｘの脱離温度から所定時間に達するまでリッチ空燃比にしている。これによってＳ被毒を解除する。
【０００７】
【特許文献１】
特開２００２−２１３２２９号公報（段落番号００１５〜００２０、図１等）
【０００８】
【発明が解決しようとする課題】
ところで、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとは、上述の如く、ともに約６５０℃程度に達した高温の排ガスを用いれば可能である点で共通するものである。
よって、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとを同時に実施させることが考えられるが、前者はsoot酸化のためにリーン雰囲気の排気が要求されるの対し、後者はストイキオ乃至リッチ雰囲気の排気が要求されることから、基本的にはこれらを同時に実施させることは一般には困難とも考えられる。
【０００９】
しかし、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとを同時に近付けるように実施させることが可能であれば、その再生に要する総再生時間が短縮化され、燃費の悪化をより一層の防止を図ることが可能になる。
また、ＤＰＦの強制再生に要する再生時間が短縮化されるだけでも、燃費の悪化をさらに防止を図ることが可能になる。
【００１０】
ここで、前記従来の技術に記載の内燃機関の排気浄化装置では、Ｓパージを行う場合には、ＤＰＦが所定温度を超えてから、さらに所定時間が経過するまではリッチ空燃比を維持し、その後リーン空燃比に切換えてこのリーン空燃比を維持している。つまり、まずＤＰＦの強制再生を行わずにＳパージを実施し、次にＳパージを行わずにＤＰＦの強制再生を実施していることから、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとを明らかに別個に実施しており、しかも、ＤＰＦの強制再生に要する時間は、Ｓパージが実施される分だけ長期化される。
【００１１】
換言すれば、この場合の総再生時間は、ＤＰＦが所定温度を超えた時点から始まり、Ｓパージの許可によってＳ被毒が解除され、その後、リーン雰囲気の排気に切換えられてＤＰＦの強制再生が実施されて終了するまでに要する時間となって長期化し、その間に消費される燃料量が二重に必要なるという問題がある。すなわち、前記従来の技術では、燃費の悪化の防止を図る点については依然として課題が残されている。
【００１２】
本発明は、このような課題に鑑みてなされたもので、ＤＰＦ等に対する総強制再生時間の短縮化を図ることができる内燃機関の排気浄化装置を提供することを目的とする。
【００１３】
【課題を解決するための手段】
上記の目的を達成するべく、請求項１記載の内燃機関の排気浄化装置は、内燃機関の気筒に連通する排気通路と、排気通路に設けられ、リーン運転時に排気中のＮＯｘを吸蔵するとともにリッチ運転を行うことで吸蔵したＮＯｘを放出還元するＮＯｘ吸蔵触媒と、排気通路に設けられ、排気中のパティキュレート・マターを捕集するフィルタと、フィルタの温度を検出するフィルタ昇温検出手段と、フィルタ昇温検出手段によってフィルタが所定温度に達したと検出されたとき、内燃機関の排気空燃比をリッチ側とリーン側とに短い周期で変化させる排気浄化制御手段とを備え、前記排気浄化制御手段は、前記ＮＯｘ吸蔵触媒の触媒温度及び触媒特性に基づいて前記排気空燃比のリッチ側の期間を設定するとともに、該設定されたリッチ側の期間、前記ＮＯｘ吸蔵触媒と前記フィルタとの再生制御開始時におけるＰＭの堆積量に基づいて、前記排気空燃比のリーン側の期間を設定し、前記フィルタの下流側の排気温度によってパティキュレート・マターの燃焼温度が過大と判定された場合には該設定されたリッチ側の期間を長く、或いは該設定されたリーン側の期間を短く補正することを特徴としている。
【００１４】
したがって、請求項１記載の内燃機関の排気浄化装置によれば、約６００℃以上の如くのＤＰＦの再生に必要な所定温度が実現されたときには、排気浄化制御手段が、排気空燃比をリッチ側とリーン側と短期間で切換えるので、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとが可能な限り同時に近付けて実施されることになり、総再生時間の短縮化を図って消費される燃料量が削減され、燃費の悪化がより一層防止される。
【００１５】
しかも、リッチ側とリーン側との複数回の切換えが周期的に行われることから、ＤＰＦの再生速度が過大にならずに適切に制御可能になる。特に、パティキュレート・マターの燃焼温度が過大と判定された場合においても、ＤＰＦの再生速度が適切に制御される。
なお、リッチ側の排気空燃比は、ストイキオを含み、該ストイキオよりも若干リッチ側であることが好ましい。
そして、排気浄化制御手段が、触媒温度、触媒特性及びＰＭの堆積量に応じて、排気空燃比のリッチ側の期間とリーン側の期間とを設定しているので、これらの期間の割合を最適に設定することが可能になり、排ガス性能が良好になる。
この場合、フィルタの昇温状態に応じて、排気空燃比のリッチ側の期間及びリーン側の期間を補正することが好ましく、ＤＰＦの再生速度がより一層適切に制御可能になる。
【００１８】
【発明の実施の形態】
以下、図面により本発明の実施形態について説明する。
図１は、本発明の第一実施形態に係る内燃機関の排気浄化装置が適用される多気筒のディーゼル機関（以下、単にエンジンという）１を備えたエンジンシステム構成図を示しており、以下図１に基づき本発明に係る内燃機関の排気浄化装置の構成を説明する。
【００１９】
エンジン１の各気筒２には、コモンレール型等の燃料噴射装置を有した燃料供給系と、吸気弁６の開弁により燃焼室４に吸入空気を導入させる吸気通路８と、排気弁１８の開弁により燃焼室４からの排気を導出させる排気通路２０とが接続されている。
この吸気通路８の最上流部にはエアクリーナ１６が接続され、その下流側には過給機１４が介装されている。また、過給機１４の下流側には、スロットル弁１０及びサージタンク１２の順に配設されている。なお、このスロットル弁１０は、いわゆるドライブバイワイヤ式のスロットル弁（ＥＴＶ）であり、エンジン運転状態に応じてその開度が変更される。
【００２０】
一方、排気通路２０の下流側にはＮＯｘ吸蔵触媒２２が接続されている。ＮＯｘ吸蔵触媒２２は、排気空燃比がリーンのときに排気中のＮＯｘを吸蔵し、排気空燃比がリッチ等で排気中に還元剤（ＨＣやＣＯ）が存在するときに、吸蔵したＮＯｘの放出還元を行うものであり、このＮＯｘ吸蔵触媒は公知の構成ものである。なお、本実施形態では、ポスト噴射にてＮＯｘの放出還元を行う。
【００２１】
また、ＮＯｘ吸蔵触媒２２の下流側にはＤＰＦ（フィルタ）２３が接続されている。ＤＰＦ２３は、排気中のＰＭを捕集するとともに、高温の排気でＰＭを焼却除去し、その再生を行うものであり、このＤＰＦも公知の構成ものである。
排気通路２０からは排気循環通路（ＥＧＲ通路）２４が分岐して延びており、排気の一部（ＥＧＲガス）を吸気通路８内に再循環させてＮＯｘの排出を抑制させる。このＥＧＲ通路２４の先端は、吸気通路８に接続されている。このＥＧＲ通路２４には、ＥＧＲガスの冷却を図るＥＧＲクーラ２６と、電子コントロールユニット（ＥＣＵ）４４に電気的に接続されたＥＧＲバルブ２８とが設けられ、ＥＧＲバルブ２８の開閉によってＥＧＲ通路２４の流路面積が調節される。
【００２２】
ＥＴＶ１０もまたＥＣＵ４４に電気的に接続されており、吸気通路８の流路面積が調節されることにより、通常の制御時にはＥＧＲガス量を調整する。そして、エアクリーナ１６からの新気は、過給機１４を介して吸気通路８に入ってＥＴＶ１０で調整された後、ＥＧＲガスと合流して各気筒２の燃焼室４内に導かれる。そして、燃料の燃焼が終了すると、排ガスは排気通路２０に排出され、ＮＯｘ吸蔵触媒２２及びＤＰＦ２３に送られる。
【００２３】
ここで、吸気通路８において、エアクリーナ１６の下流側の適宜位置には、エアフローセンサ３４が配設される。また、排気通路２０において、ＮＯｘ吸蔵触媒２２の上流側の適宜位置には、温度センサ３６とＡ／Ｆセンサ３８とが配設され、エンジン１からの排気温度（ＮＯｘ吸蔵触媒２２の触媒温度）Ｔ１とその排気空燃比λとをそれぞれ検出している。また、排気通路２０において、ＤＰＦ２３の下流側の適宜位置には、温度センサ（フィルタ昇温検出手段）４０が配設され、ＮＯｘ吸蔵触媒２２を通過した排気の温度Ｔ２を検出している。
【００２４】
ＥＣＵ４４の入力側には、上述の温度センサ３６、Ａ／Ｆセンサ３８及び温度センサ４０の他、エアフローセンサ３４等のエンジン１の運転状態を検出する各種センサが電気的に接続されている。これに対してＥＣＵ４４の出力側には、上述のＥＴＶ１０及びＥＧＲバルブ２８の各種アクチュエータが電気的に接続されている。
【００２５】
そして、ＥＣＵ４４は、排気浄化制御部４６（排気浄化制御手段）を備えている。当該排気浄化制御部４６では、エンジン１の通常制御時には、酸化雰囲気にて排ガス中のＮＯｘをＮＯｘ吸蔵触媒２２に吸蔵する一方、ＮＯｘ吸蔵触媒２２のＳパージとＤＰＦ２３の強制再生との再生制御時には、圧縮上死点後に追加燃料を噴射し、エンジン１からの高温かつストイキオ乃至リッチ雰囲気の排気をＮＯｘ吸蔵触媒２２に導入させるリッチスパイクを行い、まずＮＯｘ吸蔵触媒２２及びＤＰＦ２３を昇温させ、そして、このＤＰＦ２３の再生に必要な所定温度（約６００℃以上）が実現されたとき、排気空燃比をリッチ側とリーン側とに複数回に亘って短い周期で切換えるよう構成される。
【００２６】
排気空燃比がリッチの場合にはＮＯｘ吸蔵触媒２２のＳパージが実施され、吸蔵したＮＯｘを還元雰囲気で放出還元させ及び付着したＳ成分を還元雰囲気で放出させてＮＯｘ吸蔵触媒２２の再生を図るとともに、排気空燃比がリーンの場合にはＤＰＦ２３の強制再生を図る。
次に、上記排気浄化装置の作用について説明する。
【００２７】
図２は、排気浄化制御部４６における再生制御のタイミングチャートである。まず、排気浄化制御部４６では、１回の昇温でＮＯｘ吸蔵触媒２２のＳパージとＤＰＦ２３の強制再生とを完了させることを目標としている。図示のように、温度センサ３６によるＮＯｘ吸蔵触媒２２の触媒温度Ｔ１が３００℃から昇温して６００℃以上になり、その後３００℃に戻るまでの間に、ＮＯｘ吸蔵触媒２２のＳパージとＤＰＦ２３の強制再生との略同時に近付けた再生が実施される。
【００２８】
そして、ＮＯｘ吸蔵触媒２２の上流側の排気空燃比が弱リッチに設定されると、Ａ／Ｆセンサ３８の検出値は、通常の制御における排気空燃比（λ＝約２．０）から低λ側に移行され、昇温中のＮＯｘは、ＮＯｘ吸蔵触媒２２の還元機能によってほぼ零に抑制される。排気浄化制御部４６では、温度センサ３６によるＮＯｘ吸蔵触媒２２の触媒温度Ｔ１を読み込んで現在のＮＯｘ吸蔵触媒２２の温度を認知し、この触媒温度Ｔ１と触媒特性とに基づき、ＮＯｘ吸蔵触媒２２からＨ2Ｓを放出されずに、Ｓ成分を適切にＳＯ2として放出できるようにリッチ保持期間の設定がなされる。
【００２９】
また、排気浄化制御部４６では、Ａ／Ｆセンサ３８によるＮＯｘ吸蔵触媒２２の排気上流側の排気空燃比λを読み込んで現在のエンジン１の排気空燃比を認知している。これにより、エンジン１の排気空燃比をストイキオ乃至リッチ雰囲気に設定することができ、リッチ側の空燃比として、ストイキオよりも若干リッチ側の弱リッチ雰囲気に設定すれば、前記ＳＯ2の放出がより可能になる。また、ストイキオ雰囲気に設定することは、排ガス性能において有利となる。なぜならば、ＮＯｘ吸蔵触媒２２が備える三元機能を利用してＮＯｘを確実に浄化することができるし、ＤＰＦ２３においても、昇温中のＰＭ燃焼を抑制できるため、温度不足によってＤＰＦ２３内部が局所的で不均一になされるsoot再生をも防止できるからである。
【００３０】
次いで、温度センサ４０によるＤＰＦ２３の下流側の温度Ｔ２が６００℃以上になったとき、排気空燃比をリーン（λ＝１より若干リーン）に切換えて所定のリーン保持時間だけ保持される。このときには、ＤＰＦ２３の強制再生が実施される。
このリーンを保持する時間もまた、排気浄化制御部４６で設定されている。つまり、まず、再生制御の開始時におけるＮＯｘ吸蔵触媒２２に付着されたＳ成分の堆積量とＤＰＦ２３に捕集されたＰＭの堆積量とのそれぞれを触媒温度Ｔ１、排気温度Ｔ２及び排気空燃比λの読み込みによって推定し、Ｓパージに必要な総リッチ期間とＰＭ燃焼に必要な総リーン期間とを導出する。
【００３１】
そして、この総リッチ期間と総リーン期間とのデューティ比に対して上記設定されたリッチ保持期間を用い、リーン保持期間を設定している。このように、これらの堆積量に応じて排気空燃比のリッチ保持期間とリーン保持期間とを設定しており、これらの期間の割合を最適に設定し、排ガス性能の良好化を図っている。
【００３２】
なお、排気浄化制御部４６で設定されたリッチ保持期間及びとリーン保持期間は、温度センサ４０によるＤＰＦ２３の排気下流側の排気温度Ｔ２によってＰＭの燃焼速度が過大と判定された場合には、例えば、上記リッチ保持期間を長く、或いは上記リーン保持期間を短く補正する。このように、リッチ保持期間とリーン保持期間とが設定されると、ＤＰＦ２３の再生速度が適切に制御され、ＰＭの燃焼による発熱量が急激に大きくなってＤＰＦ２３が破損してしまうこと等を確実に防止できる。
【００３３】
さらに、排気浄化制御部４６では、総リッチ期間と総リーン期間とのデューティ比に対して上述のリッチ側の空燃比を用いることにより、又は上記デューティ比に対して時間平均の目標空燃比及びエンジン１の空気量情報に基づく排ガス流量を用いることにより、リーン空燃比も設定している。これは、ＰＭの燃焼速度が上記目標空燃比（ＤＰＦ２３の上流側の酸素濃度）、又はＤＰＦ２３への酸素供給量に依存すると考えられるからである。
【００３４】
そして、所定のリーン保持時間の経過後には、排気空燃比を弱リッチ（λ＝１より若干リッチ）に切換えて保持する。このときには、ＮＯｘ吸蔵触媒２２のＳパージが実施される。
また、所定のリッチ保持時間の経過後には、上述したリーン側の排気空燃比に再度切換えられて所定時間保持され、その後上述したリッチ側の排気空燃比にさらに切換えられて所定時間保持される如く、複数回のリッチ側と複数回のリーン側との排気空燃比の切換えが短期間に周期的に実施される。これにより、ＤＰＦ２３の再生速度を適切に制御し、再生速度が過大となることによるＤＰＦ２３の破損・溶損を防止する。
【００３５】
なお、ＤＰＦ２３の強制再生やＮＯｘ吸蔵触媒２２のＳパージが要求された時間分行われた後は、通常のディーゼルエンジン制御に戻される。
以上のように、本発明では、ＤＰＦ２３が所定温度に達したとき、排気空燃比をリッチ側とリーン側とに周期的に切換え、かつ、切換えを複数回行う排気浄化制御手段４６を備えているので、昇温中のリッチ乃至ストイキオ状態、及びＤＰＦ２３再生中の周期的なリッチ状態を利用して、ＤＰＦ２３の強制再生とＮＯｘ吸蔵触媒２２のＳパージとを可能な限り同時に近付けて実施することができる。
【００３６】
また、ＤＰＦ２３の強制再生は、充分な温度条件を与えつつ、排気空燃比の周期的な変化でＰＭの燃焼速度を制御しているため、ＤＰＦ２３の異常昇温による破損等を回避できる。
しかも、ＮＯｘ吸蔵触媒２２とＤＰＦ２３とを同時に昇温させていることから、昇温に要する時間及び燃料量が削減され、燃費の悪化をより一層低減できる。
【００３７】
なお、ストイキオでの昇温を行えば、ＤＰＦ２３の急激な再生を抑制させつつ、ＮＯｘ吸蔵触媒２２とＤＰＦ２３との全体に亘って充分に昇温させることができる。
図３は、本発明の第二実施形態を示すものである。当該第二の実施形態では、触媒の構成等の点を除き、前記第一実施形態と同一の構成からなるものであることから、この触媒の構成等について詳細に説明する。
【００３８】
本実施形態における排気通路２０の下流側にはＤＰＦ（フィルタ）２３Ａのみが接続されている。そして、ＥＣＵ４４は、排気浄化制御部４６Ａ（排気浄化制御手段）を備えている。
当該排気浄化制御部４６Ａでは、エンジン１の通常制御時には、ＤＰＦ２３ＡにＰＭを捕集させる一方、ＤＰＦ２３Ａの強制再生との再生制御時には、まず、エンジン１からの高温かつストイキオ乃至リッチ雰囲気の排気をＤＰＦ２３Ａに導入させて昇温させる。そして、このＤＰＦ２３Ａの再生に必要な所定温度（約６００℃以上）が実現されたとき、排気空燃比がリッチ側とリーン側とを短期間に切換えてＤＰＦ２３Ａの強制再生を図っている。
【００３９】
そして、図４の再生制御のタイミングチャートに示すように、本実施形態ではＮＯｘ吸蔵触媒が備えられていないことから、そのＳパージを考慮する必要がなく、Ａ／Ｆセンサ３８による排気空燃比λの値が上記第一実施形態の場合に比してややストイキオ近傍に設定されている。
このように、本実施形態の排気浄化制御手段４６Ａによれば、短期間にてリッチ側とリーン側とに切換えられるので、リーン側の場合にはＤＰＦ２３Ａの再生速度が過大にならずにＤＰＦ２３Ａの強制再生を実施でき、従来に比してＤＰＦ２３Ａの強制再生に要する時間の短縮化が図られ、燃費の悪化のさらなる防止が図られる。
【００４０】
以上で本発明の一実施形態についての説明を終えるが、本発明は上記実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々の変更ができるものである。
例えば、上記第一実施形態では、ＮＯｘ吸蔵触媒２２がＤＰＦ２３の排気上流側に配置されている。これは、ＤＰＦ２３の強制再生によって、このＤＰＦ２３の排気下流側の温度がより上昇することを考慮したものである。しかし、本発明は、必ずしもこの実施形態に限定されるものではなく、ＮＯｘ吸蔵触媒２２がＤＰＦ２３の排気下流側に配置される、又は両者を一体化させても良い。
【００４１】
また、エンジンとしてはディーゼル機関が好ましいが、これに限定されるものではなく、本発明の内燃機関の排気浄化装置は、排気通路にＮＯｘ吸蔵触媒を備え、リッチ運転可能な全てのエンジンシステムに適用させることができる。
【００４２】
【発明の効果】
以上の説明から理解できるように、請求項１記載の本発明の内燃機関の排気浄化装置によれば、約６００℃以上の如くのＤＰＦの再生に必要な所定温度が実現されたときには、排気浄化制御手段が、排気空燃比をリッチ側とリーン側と短期間で切換えるので、ＤＰＦの強制再生とＮＯｘ吸蔵触媒のＳパージとが可能な限り同時に近付けて実施されることになり、総再生時間の短縮化を図って消費される燃料量が削減され、燃費の悪化をより一層防止することができる。
【００４３】
しかも、リッチ側とリーン側との複数回の切換えが周期的に行われることから、ＤＰＦの再生速度が過大にならずに適切に制御することができる。特に、パティキュレート・マターの燃焼温度が過大と判定された場合においてもＤＰＦの再生速度を適切に制御でき、パティキュレート・マターの燃焼による発熱量が急激に大きくなってＤＰＦが破損してしまうこと等を確実に防止できる。
さらに、排気浄化制御手段が、触媒温度、触媒特性及びＰＭの堆積量に応じて、排気空燃比のリッチ側の期間とリーン側の期間とを設定しているので、これらの期間の割合を最適に設定することが可能になり、排ガス性能を良好にすることができる。
【図面の簡単な説明】
【図１】本発明の第一実施形態に係る内燃機関の排気浄化装置が適用されるエンジンの構成図である。
【図２】図１の排気浄化装置における再生制御のタイミングチャートである。
【図３】本発明の第二実施形態に係る内燃機関の排気浄化装置が適用されるエンジンの構成図である。
【図４】図３の排気浄化装置における再生制御のタイミングチャートである。
【符号の説明】
１ 内燃機関
２ 気筒
２０ 排気通路
２２ ＮＯｘ吸蔵触媒
２３ ＤＰＦ（フィルタ）
２３Ａ ＤＰＦ（フィルタ）
４０ 温度センサ（フィルタ昇温検出手段）
４４ ＥＣＵ（電子コントロールユニット）
４６ 排気浄化制御部（排気浄化制御手段）
４６Ａ 排気浄化制御部（排気浄化制御手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine applied to regeneration of a diesel particulate filter (DPF).
[0002]
[Prior art]
In general, the DPF is an exhaust gas aftertreatment device that collects and processes particulate matter (PM) in exhaust gas. Specifically, since exhaust gas from a diesel engine or the like contains a large amount of PM in addition to HC, CO, NOx, etc., the temperature of about 600 ° C. is high after the PM is collected in a filter. Recycle DPF by incineration and removal using exhaust gas.
[0003]
Here, in the DPF, self-regeneration can be realized depending on operating conditions, but a forced regeneration system that forcibly raises the temperature of the DPF is indispensable when all operating conditions are assumed. However, in this forced regeneration, for example, if the temperature of the DPF is too low, the regeneration speed is slow, and if it is too high, the temperature of the DPF is difficult to control due to rapid regeneration. Therefore, in the DPF, a technique of an exhaust gas purification apparatus for an internal combustion engine that controls the regeneration speed in the DPF by air-fuel ratio control of the internal combustion engine has been proposed (see, for example, Patent Document 1).
[0004]
In this apparatus, the exhaust system is provided with a DPF, and when the DPF is forcibly regenerated, the rich air-fuel ratio is set until the DPF reaches a predetermined temperature, and after the DPF is raised to the predetermined temperature, the lean air-fuel ratio is switched. PM is burned and removed. Thereby, forced regeneration of DPF is aimed at.
In addition to the DPF, the apparatus also includes a NOx occlusion catalyst in the exhaust system. When the S component is released (S purge), the DPF reaches a predetermined temperature, and further from the desorption temperature of SOx. The rich poisoning is continued until the predetermined time is reached, and S poisoning is released.
[0005]
This NOx occlusion catalyst is an exhaust gas aftertreatment device that occludes NOx in exhaust gas at a lean air-fuel ratio and releases and reduces the NOx occluded at a rich air-fuel ratio.
Specifically, NOx in the exhaust gas is occluded as nitrate in an oxygen excess state (oxidation atmosphere), and the occluded NOx is reduced to nitrogen in a carbon monoxide excess state (reduction atmosphere). The internal combustion engine then periodically switches to a rich operation in which the excess air ratio is low (low λ) so that the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close thereto before the NOx occlusion amount is saturated. To regenerate the NOx storage catalyst. In addition, since SOx resulting from oxidation of the S component in the fuel is also deposited as a sulfate on the NOx storage catalyst, the rich operation is periodically performed in the same manner as described above in order to release the accumulated S component (S purge). To regenerate the NOx storage catalyst.
[0006]
Here, the S purge requires a high temperature of about 650 ° C. and rich or stoichiometric exhaust gas.
Therefore, in the above-described apparatus, when the DPF is forcibly regenerated, the rich air-fuel ratio is suppressed until the DPF reaches a predetermined temperature, and PM combustion is suppressed, and during the S purge, the rich is continued until the predetermined time is reached from the SOx desorption temperature. The air-fuel ratio is set. This releases S poisoning.
[0007]
[Patent Document 1]
JP 2002-213229 A (paragraph numbers 0015 to 0020, FIG. 1, etc.)
[0008]
[Problems to be solved by the invention]
By the way, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are common in that both can be performed using high-temperature exhaust gas that has reached about 650 ° C. as described above.
Therefore, it is conceivable to simultaneously perform forced regeneration of the DPF and S purge of the NOx storage catalyst. The former requires exhaust in a lean atmosphere for soot oxidation, whereas the latter in exhaust in a stoichiometric or rich atmosphere. In general, it is generally considered difficult to implement these simultaneously.
[0009]
However, if the forced regeneration of the DPF and the S purge of the NOx storage catalyst can be performed at the same time, the total regeneration time required for the regeneration is shortened, and the deterioration of fuel consumption is further prevented. It becomes possible.
Further, it is possible to further prevent the deterioration of fuel consumption only by shortening the regeneration time required for the forced regeneration of the DPF.
[0010]
Here, in the exhaust gas purification apparatus for an internal combustion engine described in the conventional technique, when performing the S purge, the rich air-fuel ratio is maintained until a predetermined time elapses after the DPF exceeds a predetermined temperature, Thereafter, the lean air-fuel ratio is switched to maintain the lean air-fuel ratio. In other words, since the S purge is performed first without performing the forced regeneration of the DPF, and then the forced regeneration of the DPF is performed without performing the S purge, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed. Obviously, it is performed separately, and the time required for forced regeneration of the DPF is prolonged by the amount of S purge.
[0011]
In other words, the total regeneration time in this case starts from the time when the DPF exceeds the predetermined temperature, the S poisoning is released by permitting the S purge, and then the exhaust gas is switched to a lean atmosphere to forcibly regenerate the DPF. There is a problem that the time required to complete the process is prolonged, and the amount of fuel consumed during that time is doubled. In other words, the conventional technique still has a problem in terms of preventing the deterioration of fuel consumption.
[0012]
The present invention has been made in view of such problems, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can shorten the total forced regeneration time for a DPF or the like.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to claim 1 is provided in an exhaust passage communicating with a cylinder of the internal combustion engine and an exhaust passage, and stores NOx in the exhaust during a lean operation and is rich. NOx occlusion catalyst that releases and reduces NOx occluded by operation, a filter that is provided in the exhaust passage and collects particulate matter in the exhaust, filter temperature rise detection means that detects the temperature of the filter, An exhaust purification control means for changing the exhaust air-fuel ratio of the internal combustion engine between a rich side and a lean side in a short cycle when the filter temperature rise detection means detects that the filter has reached a predetermined temperature, and the exhaust purification control The means sets the rich side period of the exhaust air-fuel ratio based on the catalyst temperature and the catalyst characteristics of the NOx storage catalyst, and sets the rich side of the set rich side. During the said that the NOx storage catalyst on the basis of the deposition amount of PM during regeneration control start of the filter, to set the duration of the lean side of the exhaust air-fuel ratio, particulate matter by the exhaust temperature on the downstream side of the filter When the combustion temperature is determined to be excessive, the set rich side period is corrected to be long, or the set lean side period is corrected to be short .
[0014]
Therefore, according to the exhaust gas purification apparatus for an internal combustion engine according to claim 1, when a predetermined temperature necessary for regeneration of the DPF such as about 600 ° C. or higher is realized, the exhaust gas purification control means sets the exhaust air / fuel ratio to the rich side. Therefore, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed at the same time as close as possible, and the amount of fuel consumed by shortening the total regeneration time Is reduced and fuel consumption is further prevented from deteriorating.
[0015]
In addition, since the multiple switching between the rich side and the lean side is performed periodically, the DPF regeneration speed can be appropriately controlled without becoming excessive. In particular, even when the combustion temperature of the particulate matter is determined to be excessive, the regeneration rate of the DPF is appropriately controlled.
Note that the exhaust air-fuel ratio on the rich side includes stoichiometric and is preferably slightly richer than the stoichiometric.
The exhaust purification control means sets the rich side period and the lean side period of the exhaust air-fuel ratio in accordance with the catalyst temperature, catalyst characteristics, and PM accumulation amount, so the ratio of these periods is optimal. Therefore, the exhaust gas performance is improved.
In this case, it is preferable to correct the rich side period and the lean side period of the exhaust air-fuel ratio in accordance with the temperature rise state of the filter, so that the regeneration rate of the DPF can be controlled more appropriately .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an engine system configuration diagram including a multi-cylinder diesel engine (hereinafter simply referred to as an engine) 1 to which an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment of the present invention is applied. 1, the configuration of the exhaust emission control device for an internal combustion engine according to the present invention will be described.
[0019]
In each cylinder 2 of the engine 1, a fuel supply system having a common rail type fuel injection device, an intake passage 8 for introducing intake air into the combustion chamber 4 by opening the intake valve 6, and an exhaust valve 18 being opened. The valve is connected to an exhaust passage 20 through which exhaust from the combustion chamber 4 is led out.
An air cleaner 16 is connected to the most upstream portion of the intake passage 8, and a supercharger 14 is interposed downstream thereof. Further, the throttle valve 10 and the surge tank 12 are arranged in this order on the downstream side of the supercharger 14. The throttle valve 10 is a so-called drive-by-wire throttle valve (ETV), and its opening degree is changed according to the engine operating state.
[0020]
On the other hand, a NOx storage catalyst 22 is connected to the downstream side of the exhaust passage 20. The NOx occlusion catalyst 22 occludes NOx in the exhaust when the exhaust air-fuel ratio is lean, and releases the occluded NOx when the exhaust air-fuel ratio is rich or the like and a reducing agent (HC or CO) is present in the exhaust. This NOx occlusion catalyst has a known configuration. In the present embodiment, NOx is released and reduced by post injection.
[0021]
A DPF (filter) 23 is connected to the downstream side of the NOx storage catalyst 22. The DPF 23 collects PM in the exhaust gas, incinerates and removes the PM with high-temperature exhaust gas, and regenerates the DPF 23. This DPF is also a known configuration.
An exhaust circulation passage (EGR passage) 24 branches and extends from the exhaust passage 20, and a part of the exhaust gas (EGR gas) is recirculated into the intake passage 8 to suppress NOx emission. The tip of the EGR passage 24 is connected to the intake passage 8. The EGR passage 24 is provided with an EGR cooler 26 that cools the EGR gas and an EGR valve 28 that is electrically connected to an electronic control unit (ECU) 44. The EGR passage 24 opens and closes to open the EGR passage 24. The flow path area is adjusted.
[0022]
The ETV 10 is also electrically connected to the ECU 44 and adjusts the EGR gas amount during normal control by adjusting the flow passage area of the intake passage 8. Then, fresh air from the air cleaner 16 enters the intake passage 8 via the supercharger 14, is adjusted by the ETV 10, merges with the EGR gas, and is guided into the combustion chamber 4 of each cylinder 2. When the combustion of the fuel is completed, the exhaust gas is discharged into the exhaust passage 20 and sent to the NOx storage catalyst 22 and the DPF 23.
[0023]
Here, in the intake passage 8, an air flow sensor 34 is disposed at an appropriate position on the downstream side of the air cleaner 16. In the exhaust passage 20, a temperature sensor 36 and an A / F sensor 38 are disposed at appropriate positions upstream of the NOx storage catalyst 22, and the exhaust temperature from the engine 1 (the catalyst temperature of the NOx storage catalyst 22). T1 and its exhaust air-fuel ratio λ are detected. In the exhaust passage 20, a temperature sensor (filter temperature increase detection means) 40 is disposed at an appropriate position downstream of the DPF 23 to detect the temperature T 2 of the exhaust gas that has passed through the NOx storage catalyst 22.
[0024]
In addition to the temperature sensor 36, the A / F sensor 38, and the temperature sensor 40 described above, various sensors that detect the operating state of the engine 1 such as the air flow sensor 34 are electrically connected to the input side of the ECU 44. On the other hand, the actuators of the ETV 10 and the EGR valve 28 described above are electrically connected to the output side of the ECU 44.
[0025]
The ECU 44 includes an exhaust purification control unit 46 (exhaust purification control means). The exhaust purification control unit 46 stores NOx in the exhaust gas in the NOx occlusion catalyst 22 in the oxidizing atmosphere during normal control of the engine 1, while during regeneration control of the S purge of the NOx occlusion catalyst 22 and forced regeneration of the DPF 23. Then, after the compression top dead center, the additional fuel is injected, a rich spike is performed to introduce exhaust gas of high temperature and stoichiometric or rich atmosphere from the engine 1 into the NOx storage catalyst 22, firstly, the NOx storage catalyst 22 and the DPF 23 are heated, and When the predetermined temperature (about 600 ° C. or higher) necessary for regeneration of the DPF 23 is realized, the exhaust air-fuel ratio is switched between the rich side and the lean side at short intervals over a plurality of times.
[0026]
When the exhaust air-fuel ratio is rich, S purge of the NOx storage catalyst 22 is performed, and the stored NOx is released and reduced in a reducing atmosphere, and the adhering S component is released in a reducing atmosphere to regenerate the NOx storage catalyst 22. At the same time, when the exhaust air-fuel ratio is lean, the DPF 23 is forcedly regenerated.
Next, the operation of the exhaust purification device will be described.
[0027]
FIG. 2 is a timing chart of regeneration control in the exhaust purification control unit 46. First, the exhaust purification control unit 46 aims to complete the S purge of the NOx storage catalyst 22 and the forced regeneration of the DPF 23 with one temperature increase. As shown in the figure, the S purge of the NOx storage catalyst 22 and the DPF 23 until the catalyst temperature T1 of the NOx storage catalyst 22 is increased from 300 ° C. to 600 ° C. or higher and then returned to 300 ° C. by the temperature sensor 36. At the same time as the forced regeneration, the regeneration approaching is performed.
[0028]
When the exhaust air-fuel ratio upstream of the NOx storage catalyst 22 is set to be slightly rich, the detected value of the A / F sensor 38 is lower than the exhaust air-fuel ratio (λ = about 2.0) in normal control. The NOx during the temperature increase is suppressed to substantially zero by the reduction function of the NOx storage catalyst 22. The exhaust purification control unit 46 reads the catalyst temperature T1 of the NOx storage catalyst 22 by the temperature sensor 36, recognizes the current temperature of the NOx storage catalyst 22, and based on this catalyst temperature T1 and catalyst characteristics, from the NOx storage catalyst 22 The rich retention period is set so that the S component can be appropriately released as SO 2 without releasing H 2 S.
[0029]
Further, the exhaust purification control unit 46 reads the exhaust air-fuel ratio λ on the exhaust upstream side of the NOx storage catalyst 22 by the A / F sensor 38 and recognizes the current exhaust air-fuel ratio of the engine 1. As a result, the exhaust air-fuel ratio of the engine 1 can be set to a stoichiometric or rich atmosphere, and if the rich-side air-fuel ratio is set to a slightly rich atmosphere slightly richer than stoichio, the SO 2 emission is further reduced. It becomes possible. Moreover, setting to a stoichiometric atmosphere is advantageous in exhaust gas performance. This is because NOx can be reliably purified using the three-way function of the NOx storage catalyst 22, and PM combustion during temperature rise can be suppressed even in the DPF 23. This is because it is possible to prevent soot regeneration that is made uneven.
[0030]
Next, when the temperature T2 downstream of the DPF 23 by the temperature sensor 40 becomes 600 ° C. or higher, the exhaust air-fuel ratio is switched to lean (slightly lean from λ = 1) and held for a predetermined lean holding time. At this time, forced regeneration of the DPF 23 is performed.
The time during which the lean is maintained is also set by the exhaust purification control unit 46. That is, first, the accumulation amount of the S component adhering to the NOx storage catalyst 22 at the start of the regeneration control and the accumulation amount of PM collected in the DPF 23 are respectively determined as the catalyst temperature T1, the exhaust temperature T2, and the exhaust air-fuel ratio λ. The total rich period required for S purge and the total lean period required for PM combustion are derived.
[0031]
The lean retention period is set using the rich retention period set as described above for the duty ratio between the total rich period and the total lean period. In this way, the rich retention period and the lean retention period of the exhaust air-fuel ratio are set according to these accumulation amounts, and the ratio of these periods is set optimally to improve the exhaust gas performance.
[0032]
Note that the rich retention period and the lean retention period set by the exhaust purification control unit 46 are, for example, when the PM combustion speed is determined to be excessive by the exhaust gas temperature T2 on the exhaust downstream side of the DPF 23 by the temperature sensor 40, for example, The rich retention period is lengthened or the lean retention period is shortened. As described above, when the rich holding period and the lean holding period are set, the regeneration speed of the DPF 23 is appropriately controlled, and it is ensured that the amount of heat generated by the combustion of PM suddenly increases and the DPF 23 is damaged. Can be prevented.
[0033]
Further, the exhaust purification control unit 46 uses the above-mentioned rich-side air-fuel ratio with respect to the duty ratio between the total rich period and the total lean period, or the time-average target air-fuel ratio and engine with respect to the duty ratio. By using the exhaust gas flow rate based on the air quantity information of 1, the lean air-fuel ratio is also set. This is because the PM combustion speed is considered to depend on the target air-fuel ratio (the oxygen concentration upstream of the DPF 23) or the oxygen supply amount to the DPF 23.
[0034]
Then, after the elapse of a predetermined lean holding time, the exhaust air-fuel ratio is switched to slightly rich (slightly richer than λ = 1) and held. At this time, the S purge of the NOx storage catalyst 22 is performed.
In addition, after the predetermined rich holding time has elapsed, the above-described lean-side exhaust air-fuel ratio is switched again to be held for a predetermined time, and then further switched to the above-described rich-side exhaust air-fuel ratio to be held for a predetermined time. The exhaust air-fuel ratio switching between the rich side and the lean side is performed periodically in a short period of time. As a result, the regeneration speed of the DPF 23 is appropriately controlled, and damage or melting of the DPF 23 due to an excessive regeneration speed is prevented.
[0035]
After the forced regeneration of the DPF 23 and the S purge of the NOx storage catalyst 22 are performed for the required time, the control is returned to the normal diesel engine control.
As described above, the present invention includes the exhaust purification control means 46 that periodically switches the exhaust air-fuel ratio between the rich side and the lean side when the DPF 23 reaches a predetermined temperature and performs the switching a plurality of times. Therefore, the forced regeneration of the DPF 23 and the S purge of the NOx storage catalyst 22 may be performed as close as possible using the rich or stoichiometric state during the temperature rise and the periodic rich state during the regeneration of the DPF 23. it can.
[0036]
Further, the forced regeneration of the DPF 23 controls the PM combustion speed by periodically changing the exhaust air-fuel ratio while giving sufficient temperature conditions, so that damage due to abnormal temperature rise of the DPF 23 can be avoided.
In addition, since the NOx storage catalyst 22 and the DPF 23 are heated at the same time, the time and amount of fuel required for the temperature increase are reduced, and the deterioration of fuel consumption can be further reduced.
[0037]
If the temperature is increased by stoichiometry, the temperature of the NOx storage catalyst 22 and the DPF 23 can be sufficiently increased while suppressing the rapid regeneration of the DPF 23.
FIG. 3 shows a second embodiment of the present invention. Since the second embodiment has the same configuration as the first embodiment except for the configuration of the catalyst, the configuration of the catalyst will be described in detail.
[0038]
In the present embodiment, only the DPF (filter) 23A is connected to the downstream side of the exhaust passage 20. The ECU 44 includes an exhaust purification control unit 46A (exhaust purification control means).
In the exhaust purification control unit 46A, during normal control of the engine 1, the DPF 23A collects PM, while during regeneration control with forced regeneration of the DPF 23A, first, exhaust of high-temperature, stoichiometric or rich atmosphere from the engine 1 is DPF 23A. The temperature is increased by introducing it into When a predetermined temperature (about 600 ° C. or higher) necessary for regeneration of the DPF 23A is realized, the exhaust air / fuel ratio is switched between the rich side and the lean side in a short period of time, thereby forcibly regenerating the DPF 23A.
[0039]
As shown in the timing chart of the regeneration control in FIG. 4, since the NOx storage catalyst is not provided in this embodiment, it is not necessary to consider the S purge, and the exhaust air / fuel ratio λ by the A / F sensor 38 is not required. Is set slightly closer to the stoichiometric ratio than in the case of the first embodiment.
As described above, according to the exhaust purification control means 46A of the present embodiment, the rich side and the lean side can be switched in a short period of time, so that the regeneration speed of the DPF 23A does not become excessive in the case of the lean side. Compulsory regeneration can be performed, and the time required for forced regeneration of the DPF 23A can be shortened compared to the conventional case, thereby further preventing deterioration of fuel consumption.
[0040]
The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the first embodiment, the NOx storage catalyst 22 is arranged on the exhaust upstream side of the DPF 23. This is because the temperature on the exhaust downstream side of the DPF 23 rises due to the forced regeneration of the DPF 23. However, the present invention is not necessarily limited to this embodiment, and the NOx storage catalyst 22 may be disposed on the exhaust downstream side of the DPF 23, or both may be integrated.
[0041]
The engine is preferably a diesel engine. However, the present invention is not limited to this, and the exhaust gas purification apparatus for an internal combustion engine of the present invention is applicable to all engine systems that have a NOx occlusion catalyst in the exhaust passage and are capable of rich operation. Can be made.
[0042]
【The invention's effect】
As can be understood from the above description, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, when a predetermined temperature necessary for regeneration of the DPF, such as about 600 ° C. or higher, is realized, the exhaust gas purification is performed. Since the control means switches the exhaust air-fuel ratio between the rich side and the lean side in a short period, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed as close as possible, and the total regeneration time is reduced. The amount of fuel consumed by shortening can be reduced, and the deterioration of fuel consumption can be further prevented.
[0043]
In addition, since the switching between the rich side and the lean side is performed a plurality of times periodically, the DPF regeneration speed can be appropriately controlled without becoming excessive. In particular, even if the combustion temperature of the particulate matter is determined to be excessive, the regeneration rate of the DPF can be appropriately controlled, and the amount of heat generated by the burning of the particulate matter increases rapidly, resulting in damage to the DPF. Etc. can be reliably prevented.
Further, since the exhaust purification control means sets the rich-side period and lean-side period of the exhaust air-fuel ratio according to the catalyst temperature, catalyst characteristics and PM accumulation amount, the ratio of these periods is optimal. Therefore, the exhaust gas performance can be improved .
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment of the present invention is applied.
FIG. 2 is a timing chart of regeneration control in the exhaust gas purification apparatus of FIG.
FIG. 3 is a configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to a second embodiment of the present invention is applied.
4 is a timing chart of regeneration control in the exhaust emission control device of FIG. 3;
[Explanation of symbols]
1 Internal combustion engine 2 Cylinder 20 Exhaust passage 22 NOx storage catalyst 23 DPF (filter)
23A DPF (filter)
40 Temperature sensor (filter temperature rise detection means)
44 ECU (Electronic Control Unit)
46 Exhaust purification control unit (exhaust purification control means)
46A Exhaust gas purification control unit (exhaust gas purification control means)

Claims (1)

内燃機関の気筒に連通する排気通路と、
該排気通路に設けられ、リーン運転時に排気中のＮＯｘを吸蔵するとともにリッチ運転を行うことで該吸蔵したＮＯｘを放出還元するＮＯｘ吸蔵触媒と、
前記排気通路に設けられ、排気中のパティキュレート・マターを捕集するフィルタと、
該フィルタの温度を検出するフィルタ昇温検出手段と、
該フィルタ昇温検出手段によって前記フィルタが所定温度に達したと検出されたとき、前記内燃機関の排気空燃比をリッチ側とリーン側とに短い周期で変化させる排気浄化制御手段と、を備え、
前記排気浄化制御手段は、前記ＮＯｘ吸蔵触媒の触媒温度及び触媒特性に基づいて前記排気空燃比のリッチ側の期間を設定するとともに、該設定されたリッチ側の期間、前記ＮＯｘ吸蔵触媒と前記フィルタとの再生制御開始時におけるＰＭの堆積量に基づいて、前記排気空燃比のリーン側の期間を設定し、前記フィルタの下流側の排気温度によってパティキュレート・マターの燃焼温度が過大と判定された場合には該設定されたリッチ側の期間を長く、或いは該設定されたリーン側の期間を短く補正することを特徴とする内燃機関の排気浄化装置。An exhaust passage communicating with the cylinder of the internal combustion engine;
A NOx storage catalyst that is provided in the exhaust passage and stores NOx in the exhaust during lean operation and releases and stores the stored NOx by performing rich operation;
A filter that is provided in the exhaust passage and collects particulate matter in the exhaust;
Filter temperature rise detection means for detecting the temperature of the filter;
An exhaust purification control means for changing the exhaust air-fuel ratio of the internal combustion engine between a rich side and a lean side in a short cycle when the filter temperature rise detecting means detects that the filter has reached a predetermined temperature;
The exhaust purification control means sets the rich side period of the exhaust air-fuel ratio based on the catalyst temperature and the catalyst characteristics of the NOx storage catalyst, and the NOx storage catalyst and the filter during the set rich side period Based on the amount of PM accumulated at the start of regeneration control, a lean period of the exhaust air-fuel ratio is set , and the combustion temperature of the particulate matter is determined to be excessive due to the exhaust temperature downstream of the filter. In this case, the exhaust purification apparatus for an internal combustion engine is characterized in that the set rich side period is lengthened or the set lean side period is shortened .
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