JP2004324455A - Exhaust emission control device of internal combustion engine - Google Patents

Exhaust emission control device of internal combustion engine Download PDF

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Publication number
JP2004324455A
JP2004324455A JP2003117030A JP2003117030A JP2004324455A JP 2004324455 A JP2004324455 A JP 2004324455A JP 2003117030 A JP2003117030 A JP 2003117030A JP 2003117030 A JP2003117030 A JP 2003117030A JP 2004324455 A JP2004324455 A JP 2004324455A
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exhaust
filter
dpf
internal combustion
combustion engine
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JP2003117030A
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JP4203730B2 (en
Inventor
Megumi Shigahara
恵 信ヶ原
Michihiro Hatake
道博 畠
Kazuo Kurata
和郎 倉田
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Mitsubishi Motors Corp
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Mitsubishi Motors Corp
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Priority to DE102004019660A priority patent/DE102004019660B4/en
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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)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (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)

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine, in which total forced regeneration time for DPF, etc, can be shortened. <P>SOLUTION: The device is provided with an exhaust passage 20 communicating with a cylinder of the internal combustion engine, an NOx occluded catalyst 22 prepared in the exhaust passage, occluding NOx in the exhaust emission at the time of lean operation, discharging and reducing the occluded NOx by rich operation, a filter 23 for collecting particulate matter in the exhaust emission, a filter temperature rise detecting means 40 for detecting the temperature of the filter, and an exhaust emission control means 46 for changing an exhaust emission air-fuel ratio of the internal combustion engine for a rich side and a lean side with a short period when the filter reaches a predetermined temperature by the filter temperature rise detecting means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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た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。
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。
また、請求項２記載の発明では、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、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たことを特徴としている。
【００１６】
このように、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ことから、ＤＰＦの再生速度が過大にならず、ＤＰＦの強制再生を適切に制御可能になるとともに、従来技術に比してＤＰＦ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。
さらに、請求項３記載の発明では、排気浄化制御手段は、ＮＯｘ吸蔵触媒の触媒温度及び触媒特性に基づいて排気空燃比のリッチ側の期間を設定するとともに、設定されたリッチ側の期間、ＮＯｘ吸蔵触媒とフィルタとの再生制御時におけるＰＭの堆積量に基づいて、排気空燃比のリーン側の期間を設定していることを特徴としている。
【００１７】
このように、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、排ガス性能が良好になる。
なお、リッチ側の期間は、ＮＯｘ吸蔵触媒がＳ成分をＳＯ２として適切に放出できるように、触媒温度及び触媒特性に基づいて決定することが好ましい。また、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。
また、請求項２記載の発明によれば、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ことから、ＤＰＦの再生速度が過大にならず、ＤＰＦの強制再生を適切に制御することができるとともに、従来技術に比してＤＰＦ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を図ることができる。
【００４４】
さらに、請求項３記載の発明によれば、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]
TECHNICAL FIELD 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]
Generally, a DPF is an exhaust gas after-treatment 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., after collecting the PM in a filter, the exhaust gas of about 600 ° C. Recycle DPF by incineration and removal using exhaust gas.
[0003]
Here, in the DPF, the self-regeneration can be realized depending on the operating conditions, but a forced regeneration system for forcibly increasing the temperature of the DPF is indispensable when all the 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 DPF is damaged due to rapid regeneration, which makes it difficult to control the temperature. Therefore, in the DPF, there has been proposed a technology of an exhaust gas purification device for an internal combustion engine that controls the regeneration speed of the DPF by controlling the air-fuel ratio of the internal combustion engine (for example, see Patent Document 1).
[0004]
In this device, a DPF is provided in the exhaust system. During forced regeneration of the DPF, the DPF is set to a rich air-fuel ratio until the DPF reaches a predetermined temperature, and the DPF is heated to a predetermined temperature and then switched to a lean air-fuel ratio. Burns and removes PM. Thereby, forced regeneration of the DPF is achieved.
In addition, the apparatus further includes a NOx storage catalyst in the exhaust system in addition to the DPF, and when releasing the S component (S purge), after the DPF reaches a predetermined temperature, the temperature is further reduced from the SOx desorption temperature. Until the predetermined time is reached, the S-poisoning is released by maintaining the rich air-fuel ratio.
[0005]
This NOx storage catalyst is an exhaust gas aftertreatment device that stores NOx in exhaust gas at a lean air-fuel ratio and releases and reduces the stored NOx at a rich air-fuel ratio.
Specifically, it has a characteristic of storing NOx in exhaust gas as a nitrate in an excess oxygen state (oxidizing atmosphere) and reducing the stored NOx to nitrogen in a excess carbon monoxide state (reducing atmosphere). The internal combustion engine periodically switches to a rich operation in which the excess air ratio is low (low λ) such that the exhaust air-fuel ratio is controlled to a stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio before the NOx storage amount is saturated. To regenerate the NOx storage catalyst. In addition, SOx resulting from the oxidation of the S component in the fuel is also deposited as sulfate on the NOx storage catalyst. Therefore, in order to release the deposited S component (S purge), the rich operation is periodically performed in the same manner as described above. To regenerate the NOx storage catalyst.
[0006]
Here, the S purge requires a high temperature of about 650 ° C. and a rich or stoichiometric exhaust gas.
Therefore, in the above-described apparatus, during forced regeneration of the DPF, the combustion of PM is suppressed by setting the rich air-fuel ratio until the DPF reaches a predetermined temperature, and during the S purge, the rich air-fuel ratio is further maintained until the predetermined time from the desorption temperature of SOx is reached. The air-fuel ratio is set. This releases the S poisoning.
[0007]
[Patent Document 1]
JP-A-2002-213229 (paragraph numbers 0015 to 0020, FIG. 1 and the like)
[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, as described above, both can be performed using high-temperature exhaust gas that has reached about 650 ° C.
Therefore, it is conceivable that the forced regeneration of the DPF and the S-purge of the NOx storage catalyst are simultaneously performed. The former requires exhaustion in a lean atmosphere for soot oxidation, whereas the latter requires exhaustion in a stoichiometric or rich atmosphere. Therefore, it is generally considered that it is generally difficult to carry out these steps 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 can be shortened, and the deterioration of fuel efficiency can be further prevented. It becomes possible.
Further, even if the regeneration time required for the forced regeneration of the DPF is shortened only, it is possible to further prevent deterioration of fuel efficiency.
[0010]
Here, in the exhaust gas purifying apparatus for an internal combustion engine according to the related art, when performing the S purge, after the DPF exceeds a predetermined temperature, the rich air-fuel ratio is maintained until a predetermined time elapses, Thereafter, the air-fuel ratio is switched to the lean air-fuel ratio to maintain the lean air-fuel ratio. That is, first, the S purge is performed without performing the forced regeneration of the DPF, and then the forced regeneration of the DPF is performed without performing the S purge. Therefore, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed. Obviously, they are separately performed, and the time required for forced regeneration of the DPF is prolonged by the amount of the S purge.
[0011]
In other words, the total regeneration time in this case starts from the point in time when the DPF exceeds a predetermined temperature, the S poisoning is released by permitting the S purge, and then the exhaust gas is switched to a lean atmosphere to perform the forced regeneration of the DPF. There is a problem that the time required for the operation to be completed is prolonged, and the amount of fuel consumed during that time is required twice. That is, in the above-described conventional technology, there is still a problem in preventing deterioration of fuel efficiency.
[0012]
The present invention has been made in view of such a problem, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can reduce 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 gas purifying apparatus 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. A NOx storage catalyst that releases and reduces the NOx stored by performing the operation, a filter that is provided in the exhaust passage and collects particulate matter in the exhaust gas, and a filter temperature rise detection unit that detects the temperature of the filter; 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 detecting means detects that the filter has reached a predetermined temperature. I have.
[0014]
Therefore, according to the first aspect of the present invention, when the predetermined temperature required for the regeneration of the DPF, such as about 600 ° C. or higher, is achieved, the exhaust purification control means increases the exhaust air-fuel ratio to the rich side. And the lean side are switched in a short period of time, so that the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed as close as possible to each other, and the amount of fuel consumed by shortening the total regeneration time , And deterioration of fuel efficiency is further prevented.
[0015]
In addition, since the switching between the rich side and the lean side is performed a plurality of times, the DPF regeneration speed can be appropriately controlled without becoming excessively high.
Note that the rich side exhaust air-fuel ratio includes stoichiometry and is preferably slightly richer than the stoichiometry.
According to the second aspect of the present invention, an exhaust passage communicating with a cylinder of the internal combustion engine, a filter provided in the exhaust passage for collecting particulate matter in the exhaust gas, and a filter temperature rise detecting a temperature of the filter are provided. Detection means, and exhaust purification control means for changing the exhaust air-fuel ratio of the internal combustion engine between the rich side and the lean side in a short cycle when the filter temperature detection section detects that the filter has reached a predetermined temperature. It is characterized by:
[0016]
As described above, since the exhaust gas purification control means switches the exhaust air-fuel ratio between the rich side and the lean side in a short period of time, the regeneration speed of the DPF does not become excessive, and the forced regeneration of the DPF can be appropriately controlled. The time required for the forced regeneration of the DPF is shortened as compared with the related art, and the deterioration of fuel efficiency is further prevented.
Further, according to the third aspect of the present invention, the exhaust gas 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 sets the set rich side period, NOx It is characterized in that the period on the lean side of the exhaust air-fuel ratio is set based on the amount of PM accumulated during the regeneration control of the storage catalyst and the filter.
[0017]
As described above, since the exhaust gas purification control means sets the period on the rich side and the period on the lean side of the exhaust air-fuel ratio in accordance with the catalyst temperature, the catalyst characteristics, and the amount of accumulated PM, the ratio of these periods Can be set optimally, and the exhaust gas performance can be improved.
The rich side period is preferably determined based on the catalyst temperature and the catalyst characteristics so that the NOx storage catalyst can appropriately release the S component as SO 2 . In addition, it is preferable to correct the rich side and the lean side of the exhaust air-fuel ratio in accordance with the temperature rise state of the filter, so that the DPF regeneration speed can be controlled more appropriately.
[0018]
BEST MODE FOR CARRYING OUT 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 device for an internal combustion engine according to a first embodiment of the present invention is applied. The configuration of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described based on FIG.
[0019]
Each cylinder 2 of the engine 1 has a fuel supply system having a common rail type fuel injection device, an intake passage 8 through which intake air is introduced into the combustion chamber 4 by opening an intake valve 6, and an opening of an exhaust valve 18. The valve is connected to an exhaust passage 20 through which exhaust gas 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. A throttle valve 10 and a surge tank 12 are arranged downstream of the supercharger 14 in this order. The throttle valve 10 is a so-called drive-by-wire type throttle valve (ETV), and its opening is changed according to the engine operating state.
[0020]
On the other hand, a NOx storage catalyst 22 is connected downstream of the exhaust passage 20. The NOx storage catalyst 22 stores NOx in exhaust when the exhaust air-fuel ratio is lean, and releases the stored NOx when the exhaust air-fuel ratio is rich and a reducing agent (HC or CO) exists in the exhaust. This NOx storage catalyst has a known structure. In this embodiment, NOx is released and reduced by post injection.
[0021]
A DPF (filter) 23 is connected downstream of the NOx storage catalyst 22. The DPF 23 captures PM in the exhaust gas, incinerates and removes the PM with high-temperature exhaust gas, and regenerates the PM. This DPF also has 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 the emission of NOx. The tip of the EGR passage 24 is connected to the intake passage 8. An EGR cooler 26 for cooling EGR gas and an EGR valve 28 electrically connected to an electronic control unit (ECU) 44 are provided in the EGR passage 24. The channel 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 to the exhaust passage 20 and sent to the NOx storage catalyst 22 and the DPF 23.
[0023]
Here, an airflow sensor 34 is provided at an appropriate position downstream of the air cleaner 16 in the intake passage 8. In the exhaust passage 20, a temperature sensor 36 and an A / F sensor 38 are disposed at appropriate positions on the upstream side of the NOx storage catalyst 22, and an exhaust temperature from the engine 1 (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 rise detecting means) 40 is disposed at an appropriate position on the downstream side of the DPF 23, and detects the temperature T2 of the exhaust gas passing through the NOx storage catalyst 22.
[0024]
On the input side of the ECU 44, in addition to the temperature sensor 36, the A / F sensor 38, and the temperature sensor 40, various sensors for detecting the operating state of the engine 1, such as the air flow sensor 34, are electrically connected. On the other hand, on the output side of the ECU 44, various actuators of the ETV 10 and the EGR valve 28 described above are electrically connected.
[0025]
The ECU 44 includes an exhaust gas purification control unit 46 (exhaust gas purification control means). In the exhaust gas purification control unit 46, during normal control of the engine 1, NOx in exhaust gas is stored in the NOx storage catalyst 22 in an oxidizing atmosphere, while during regeneration control of S purge of the NOx storage catalyst 22 and forced regeneration of the DPF 23. After the compression top dead center, additional fuel is injected, and a rich spike is performed to introduce high temperature and stoichiometric or rich exhaust gas from the engine 1 to the NOx storage catalyst 22, and first, the NOx storage catalyst 22 and the DPF 23 are heated, and When a predetermined temperature (about 600 ° C. or higher) required for regeneration of the DPF 23 is realized, the exhaust air-fuel ratio is switched between the rich side and the lean side several times in a short cycle.
[0026]
When the exhaust air-fuel ratio is rich, the S purge of the NOx storage catalyst 22 is performed, and the stored NOx is released and reduced in a reducing atmosphere, and the attached 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 forcibly regenerated.
Next, the operation of the exhaust gas purification device will be described.
[0027]
FIG. 2 is a timing chart of the regeneration control in the exhaust gas purification control unit 46.
First, the exhaust gas purification control unit 46 aims to complete the S purge of the NOx storage catalyst 22 and the forced regeneration of the DPF 23 by one temperature increase. As shown, the catalyst temperature T1 of the NOx storage catalyst 22 measured by the temperature sensor 36 rises from 300 ° C. to 600 ° C. or more, and thereafter returns to 300 ° C. before the S purge of the NOx storage catalyst 22 and the DPF 23 And near-simultaneous regeneration with the forced regeneration is performed.
[0028]
When the exhaust air-fuel ratio on the upstream side of the NOx storage catalyst 22 is set to be slightly rich, the detection value of the A / F sensor 38 becomes lower than the exhaust air-fuel ratio (λ = about 2.0) in the normal control. The NOx during temperature rise is suppressed to almost zero by the reducing function of the NOx storage catalyst 22. The exhaust gas purification control unit 46 reads the catalyst temperature T1 of the NOx storage catalyst 22 by the temperature sensor 36 to recognize the current temperature of the NOx storage catalyst 22. Based on the catalyst temperature T1 and the catalyst characteristics, 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 gas purification control unit 46 reads the exhaust air-fuel ratio λ on the exhaust gas 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. Thus, the exhaust air-fuel ratio of the engine 1 can be set to a stoichiometric or rich atmosphere. If the rich-side air-fuel ratio is set to a slightly rich side slightly richer than the stoichiometric, the release of the SO 2 can be further improved. Will be possible. Further, setting the stoichiometric atmosphere is advantageous in exhaust gas performance. This is because the three-way function of the NOx storage catalyst 22 can be used to reliably purify NOx, and the DPF 23 can also suppress PM combustion during temperature rise. This is because it is possible to prevent the soot reproduction which is not performed uniformly.
[0030]
Next, when the temperature T2 on the downstream side of the DPF 23 by the temperature sensor 40 becomes equal to or higher than 600 ° C., the exhaust air-fuel ratio is switched to lean (slightly lean from λ = 1) and is maintained for a predetermined lean holding time. At this time, forced regeneration of the DPF 23 is performed.
The time during which this lean is maintained is also set by the exhaust gas purification control unit 46. That is, first, the amount of the S component deposited on the NOx storage catalyst 22 and the amount of the PM trapped by the DPF 23 at the start of the regeneration control are respectively represented by 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]
Then, the lean holding period is set using the set rich holding period for the duty ratio between the total rich period and the total lean period. As described above, the rich air-fuel ratio and the lean air-fuel ratio are set in accordance with the accumulation amount, and the ratio of these periods is optimally set to improve the exhaust gas performance.
[0032]
In the rich holding period and the lean holding period set by the exhaust gas purification control unit 46, when the PM combustion speed is determined to be excessive based on the exhaust gas temperature T2 on the exhaust gas downstream side of the DPF 23 by the temperature sensor 40, for example, , The rich holding period is lengthened, or the lean holding 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 the PM sharply increases and the DPF 23 is damaged. Can be prevented.
[0033]
Further, the exhaust gas purification control unit 46 uses the above-described rich-side air-fuel ratio for the duty ratio between the total rich period and the total lean period, or the time-average target air-fuel ratio and the engine for the duty ratio. The lean air-fuel ratio is also set by using the exhaust gas flow rate based on the air amount information of No. 1. This is because the PM combustion speed is considered to depend on the target air-fuel ratio (oxygen concentration on the upstream side of the DPF 23) or the amount of oxygen supplied to the DPF 23.
[0034]
Then, after the elapse of a predetermined lean holding time, the exhaust air-fuel ratio is switched to a weak rich (slightly rich from λ = 1) and held. At this time, the S purge of the NOx storage catalyst 22 is performed.
Further, after a predetermined rich holding time has elapsed, the exhaust air-fuel ratio is switched again to the above-described lean side exhaust air-fuel ratio and held for a predetermined time, and then further switched to the above-described rich side exhaust air-fuel ratio and held for a predetermined time. The switching of the exhaust air-fuel ratio between the rich side and the lean side a plurality of times is periodically performed in a short period. Thereby, the regeneration speed of the DPF 23 is appropriately controlled, and damage or melting damage 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 have been performed for the requested time, the control is returned to the normal diesel engine control.
As described above, in the present invention, when the DPF 23 reaches a predetermined temperature, the exhaust gas purification control means 46 is provided which periodically switches the exhaust air-fuel ratio between the rich side and the lean side and performs the switching a plurality of times. Therefore, by utilizing the rich or stoichiometric state during the temperature rise and the periodic rich state during the regeneration of the DPF 23, it is possible to perform the forced regeneration of the DPF 23 and the S purge of the NOx storage catalyst 22 as simultaneously as possible. it can.
[0036]
In the forced regeneration of the DPF 23, the PM combustion speed is controlled by a periodic change in the exhaust air-fuel ratio while giving sufficient temperature conditions, so that damage or the like due to abnormal temperature rise of the DPF 23 can be avoided.
In addition, since the temperature of the NOx storage catalyst 22 and the temperature of the DPF 23 are raised at the same time, the time required for raising the temperature and the amount of fuel are reduced, and the deterioration of fuel efficiency can be further reduced.
[0037]
If the temperature is raised in stoichiometry, the temperature of the entire 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. The second embodiment has the same configuration as that of the first embodiment except for the configuration of the catalyst and the like. Therefore, the configuration and the like of the catalyst will be described in detail.
[0038]
Only the DPF (filter) 23A is connected downstream of the exhaust passage 20 in the present embodiment. The ECU 44 includes an exhaust gas purification control unit 46A (exhaust gas purification control means).
In the exhaust gas purification control unit 46A, during normal control of the engine 1, PM is collected by the DPF 23A, and during regeneration control with forced regeneration of the DPF 23A, first, high-temperature and stoichiometric or rich exhaust gas from the engine 1 is discharged to the DPF 23A. And the temperature is raised. When a predetermined temperature (about 600 ° C. or higher) required for the 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 to perform the forced regeneration of the DPF 23A.
[0039]
Further, as shown in the timing chart of the regeneration control in FIG. 4, since the present embodiment is not provided with the NOx storage catalyst, it is not necessary to consider the S purge, and the exhaust air-fuel ratio λ by the A / F sensor 38 is used. Is set slightly closer to stoichio than in the first embodiment.
As described above, according to the exhaust gas purification control means 46A of the present embodiment, the switching between the rich side and the lean side is performed in a short period of time, so that in the case of the lean side, the regeneration speed of the DPF 23A does not become excessive and the DPF 23A Forced regeneration can be performed, and the time required for forced regeneration of the DPF 23A can be reduced as compared with the related art, thereby further preventing deterioration of fuel efficiency.
[0040]
The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.
For example, in the first embodiment, the NOx storage catalyst 22 is disposed on the exhaust gas upstream side of the DPF 23. This takes into account that the temperature of the DPF 23 on the exhaust gas downstream side is further increased by 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 downstream of the DPF 23 on the exhaust side, or both may be integrated.
[0041]
The engine is preferably a diesel engine, but is not limited to this. The exhaust gas purifying apparatus for an internal combustion engine of the present invention is applicable to all engine systems that have a NOx storage catalyst in an exhaust passage and can perform a rich operation. Can be done.
[0042]
【The invention's effect】
As can be understood from the above description, according to the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect of the present invention, when the predetermined temperature required for the regeneration of the DPF, such as about 600 ° C. or more, is realized, the exhaust gas purifying method is performed. Since the control means switches the exhaust air-fuel ratio between the rich side and the lean side in a short period of time, the forced regeneration of the DPF and the S purge of the NOx storage catalyst are performed as close as possible to each other, and the total regeneration time is reduced. The amount of fuel consumed by shortening is reduced, and deterioration of fuel efficiency can be further prevented.
[0043]
In addition, since the switching between the rich side and the lean side is performed a plurality of times, the regeneration speed of the DPF can be appropriately controlled without becoming excessive.
According to the second aspect of the present invention, since the exhaust gas purification control means switches the exhaust air-fuel ratio between the rich side and the lean side in a short period of time, the regeneration speed of the DPF does not become excessive, and the forced regeneration of the DPF is performed. The control can be appropriately performed, and the time required for forcibly regenerating the DPF can be reduced as compared with the related art, so that it is possible to further prevent deterioration of fuel efficiency.
[0044]
Further, according to the third aspect of the present invention, the exhaust gas purification control means sets a rich period and a lean period of the exhaust air-fuel ratio in accordance with the catalyst temperature, the catalyst characteristics, and the amount of accumulated PM. Therefore, the ratio of these periods can be set optimally, and 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 device 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 device of FIG.
FIG. 3 is a configuration diagram of an engine to which an exhaust gas purification device for an internal combustion engine according to a second embodiment of the present invention is applied.
FIG. 4 is a timing chart of regeneration control in the exhaust gas purification device of FIG. 3;
[Explanation of symbols]
Reference Signs List 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 gas purification control unit (Exhaust gas purification control means)
46A Exhaust gas purification control unit (Exhaust gas purification control means)

Claims (3)

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、を備えたことを特徴とする内燃機関の排気浄化装置。An exhaust passage communicating with a cylinder of the internal combustion engine;
A NOx storage catalyst that is provided in the exhaust passage and stores NOx in exhaust gas during a lean operation and performs a rich operation to release and reduce the stored NOx;
A filter provided in the exhaust passage, for collecting particulate matter in the exhaust;
Filter temperature rise detection means for detecting the temperature of the filter,
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. An exhaust gas purifying apparatus for an internal combustion engine, comprising: 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、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、を備えたことを特徴とする内燃機関の排気浄化装置。An exhaust passage communicating with a cylinder of the internal combustion engine;
A filter provided in the exhaust passage, for collecting particulate matter in the exhaust;
Filter temperature rise detection means for detecting the temperature of the filter,
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. An exhaust gas purifying apparatus for an internal combustion engine, comprising: 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ていることを特徴とする請求項１記載の内燃機関の排気浄化装置。The exhaust purification control means sets a rich-side period of the exhaust air-fuel ratio based on a catalyst temperature and a catalyst characteristic of the NOx storage catalyst, and sets the NOx storage catalyst and the filter in the set rich-side period. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a period on the lean side of the exhaust air-fuel ratio is set based on the amount of accumulated PM during the regeneration control.
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