JP4269666B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

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JP4269666B2
JP4269666B2 JP2002344113A JP2002344113A JP4269666B2 JP 4269666 B2 JP4269666 B2 JP 4269666B2 JP 2002344113 A JP2002344113 A JP 2002344113A JP 2002344113 A JP2002344113 A JP 2002344113A JP 4269666 B2 JP4269666 B2 JP 4269666B2
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air
fuel ratio
internal combustion
combustion engine
reducing agent
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JP2004176632A (en
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耕平 吉田
伸一 竹島
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Toyota Motor Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B29/00—Engines characterised by provision for charging or scavenging not provided for in groups F02B25/00, F02B27/00 or F02B33/00 - F02B39/00; Details thereof
    • F02B29/04—Cooling of air intake supply
    • F02B29/0406—Layout of the intake air cooling or coolant circuit
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/05—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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Exhaust Gas After Treatment (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Exhaust-Gas Circulating Devices (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の排気浄化技術に関し、特に、内燃機関の排気系に設けられたＳＯｘ保持材を再生させる技術に関するものである。
【０００２】
【従来の技術】
近年、自動車等に搭載される内燃機関の排気浄化技術として、内燃機関の排気系にＮＯｘ吸収材を配置して、排気中の窒素酸化物（ＮＯｘ）を除去する技術が知られている。
【０００３】
このようなＮＯｘ吸収材は、排気中の窒素酸化物（ＮＯｘ）とともに硫黄酸化物（ＳＯｘ）も吸収してしまうため、硫黄酸化物（ＳＯｘ）の吸収量が増加した場合には排気中の窒素酸化物（ＮＯｘ）を吸収しきれなくなる、所謂ＳＯｘ被毒を生じる。
【０００４】
これに対して、内燃機関の排気あるいはＮＯｘ吸収材が高温である時に、ＮＯｘ吸収材へ還元剤を供給してＮＯｘ吸収材を高温且つリッチな雰囲気とすることによりＮＯｘ吸収材から硫黄酸化物（ＳＯｘ）を除去し、以ってＮＯｘ吸収材のＳＯｘ被毒を解消させる技術が提案されている（例えば、特許文献１参照）。
【０００５】
【特許文献１】
特許２６０５５８６号公報
【０００６】
【発明が解決しようとする課題】
ところで、自動車などに搭載される内燃機関では、排気系に設けられた酸素濃度センサや空燃比センサの出力信号と目標空燃比との誤差に基づいて内燃機関の空燃比を補正するとともに、その際の補正量を学習する制御が行われている。
【０００７】
しかしながら、圧縮着火式内燃機関（ディーゼル機関）や希薄燃焼可能な火花点火式内燃機関（リーン・バーン・ガソリン機関）のように排気温度や排気系部品の温度が低くなり易い内燃機関では、排気中の炭化水素（ＨＣ）や一酸化炭素（ＣＯ）が酸素濃度センサや空燃比センサに付着してしまい、それらセンサの出力信号値が実際の酸素濃度や空燃比より低い値を示す場合がある。
【０００８】
このような場合に、酸素濃度センサや空燃比センサの出力信号値に基づいて学習制御が行われると、その学習制御により得られた補正量（学習値）が内燃機関の空燃比に反映された時に、内燃機関の実際の空燃比が目標空燃比よりも高くなることが想定される。
【０００９】
内燃機関の空燃比が目標空燃比より高くなった状態で、前述したようなＳＯｘ被毒解消処理がなされると、ＮＯｘ吸収材に流入する排気の空燃比を所望のリッチ空燃比とすべく、還元剤の供給量が過剰に増加される虞がある。
【００１０】
ＮＯｘ吸収材へ供給される還元剤の量が過剰に多くなると、ＮＯｘ吸収材において還元剤が酸化される際に発生する熱量が多くなることからＮＯｘ吸収材の温度が過剰に上昇してしまい、その結果、ＮＯｘ吸収材が劣化し易くなる。
【００１１】
本発明は、上記した問題に鑑みてなされたものであり、その目的とするところは、ＮＯｘ吸収材等のように排気中の硫黄酸化物（ＳＯｘ）を保持するＳＯｘ保持材を備えた内燃機関の排気浄化装置において、ＳＯｘ保持材の劣化の促進を防止しつつＳＯｘ保持材からＳＯｘを除去可能な技術を提供することにある。
【００１２】
【課題を解決するための手段】
上記目的を達成するために本発明に係る内燃機関の排気浄化装置にあっては、内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するＳＯｘ保持材と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて学習される空燃比学習値に従って、内燃機関の空燃比を制御する空燃比制御手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去する際に、前記空燃比検出手段の検出値を理論空燃比以下とすべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する還元剤添加手段と、
前記還元剤添加手段が還元剤の添加を開始する前に、前記空燃比学習値を初期値にリセットする学習値リセット手段と、
を備えることを特徴とする。
【００１３】
この発明は、空燃比検出手段の検出値に基づいて学習された空燃比学習値に従って内燃機関の空燃比を制御する空燃比制御手段と、ＳＯx保持材から硫黄酸化物を除去するときにＳＯx保持材に流入する排気の空燃比が理論空燃比以下となるように排気中へ還元剤を供給する還元剤添加手段とを備えた内燃機関の排気浄化装置において、ＳＯx保持剤から硫黄酸化物を除去すべく還元剤添加手段が作動を開始する前に、空燃比学習値をリセットすることを最大の特徴としている。
【００１４】
空燃比制御手段は、内燃機関の空燃比が所望の機関空燃比（以下、「目標機関空燃比」と称する。）と一致するように内燃機関の空燃比を制御する。
【００１５】
例えば、空燃比制御手段は、先ず、目標機関空燃比に従って内燃機関の目標燃料噴射量を決定する。続いて、空燃比制御手段は、空燃比検出手段の検出値を読み込み、その検出値と目標空燃比との偏差に基づいて目標燃料噴射量を補正するとともに、その際の補正量を空燃比学習値として記憶する。そして、空燃比制御手段は、次回の目標燃料噴射量を決定する際に、前記した空燃比学習値を考慮して目標燃料噴射量を決定する。
【００１６】
このように内燃機関の空燃比が制御されているときに、空燃比検出手段が未燃燃料成分によって被毒していると、空燃比検出手段の検出値が実際の空燃比より低い値（リッチな値）を示すため、内燃機関の空燃比がリーン側へ補正されるとともに、空燃比学習値が内燃機関の空燃比をリーン側へ補正する値となる。
【００１７】
また、ＳＯx保持材に保持された硫黄酸化物を除去する場合には、ＳＯx保持材に流入する排気の温度を高めた上でＳＯx保持材に流入する排気の空燃比を理論空燃比以下にする再生処理を行う必要がある。
【００１８】
空燃比検出手段が被毒した状態でＳＯx保持材の再生処理が行われた場合には、空燃比検出手段に付着していた未燃燃料成分が高温の排気に曝されて燃焼するため、空燃比検出手段の被毒が解消されることになる。
【００１９】
この場合、空燃比検出手段の検出値が実際の空燃比に対応した値を示すようになるが、前記した空燃比学習値に従って内燃機関の空燃比が制御されるため、内燃機関から排出される排気の空燃比（以下、「実機関空燃比」と称する。）が目標機関空燃比よりリーンな空燃比になる。
【００２０】
ところで、ＳＯx保持材の再生処理では、空燃比検出手段の検出値が理論空燃比以下の目標リッチ空燃比と一致するように還元剤の供給量が決定されるため、上記したように空燃比検出手段の検出値が目標機関空燃比よりリーンな空燃比を示している場合には、還元剤の供給量が過剰に多くなることが想定される。
【００２１】
排気中の還元剤はＳＯx保持材に保持されている硫黄酸化物と反応して酸化するため、排気中に多量の還元剤が存在する場合にはＳＯx保持材において多量の還元剤が酸化することとなり、その際に発生する反応熱によってＳＯx保持材が過剰に昇温し、ＳＯx保持材の熱劣化を誘発することが想定される。
【００２２】
これに対し、本発明にかかる内燃機関の排気浄化装置では、ＳＯx保持材の再生処理において還元剤添加手段が作動する前に、学習値リセット手段が空燃比学習値を初期値にリセットする。
【００２３】
この場合、空燃比制御手段が内燃機関の空燃比をリーン側へ補正しなくなるため、実機関空燃比が目標機関空燃比に比して過剰にリーンとなることがなくなる。
【００２４】
この結果、還元剤添加手段が作動を開始した時点で空燃比検出手段の検出値が目標機関空燃比に比して過剰にリーンな値を示すことがなくなり、以て還元剤の供給量を過剰に多くする必要もなくなる。
【００２５】
尚、本発明における空燃比検出手段としては、ＳＯx保持材より上流の排気通路およびまたはＳＯx保持材より下流の排気通路に配置される空燃比センサや酸素濃度センサを例示することができる。
【００２６】
また、排気中の未燃燃料成分は、空燃比検出手段又は排気の温度が低いときに空燃比検出手段に付着し易いため、学習値リセット手段は、空燃比検出手段の温度又は排気温度が所定温度未満であるときに学習された空燃比学習値のみを初期値にリセットするようにしてもよい。
【００２７】
この場合、空燃比検出手段が未燃燃料成分によって被毒されていないときに学習された空燃比学習値を活かしつつ内燃機関の空燃比を制御することが可能となるため、空燃比検出手段の被毒が解消された時点、言い換えれば、還元剤添加手段が作動を開始するときの実機関空燃比を目標機関空燃比に近似させ易くなる。
【００２８】
また、本発明は、前述した課題を解決するために以下のような手段を採用してもよい。すなわち、本発明にかかる内燃機関の排気浄化装置は、内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するＳＯｘ保持材と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて学習される空燃比学習値に従って、内燃機関の空燃比を制御する空燃比制御手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去する際に、前記空燃比検出手段の検出値を理論空燃比以下とすべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第１の還元剤添加手段と、
前記第１の還元剤添加手段が還元剤の添加を開始する前に、前記空燃比検出手段の未燃燃料成分による被毒を解消させる被毒解消手段と、
前記空燃比検出手段の被毒解消後であって前記第１の還元剤添加手段が還元剤の添加を開始する前に、内燃機関の空燃比が所望の目標機関空燃比となるように前記内燃機関の空燃比を補正する空燃比補正手段と、
を備えるようにしてもよい。
【００２９】
この発明は、空燃比検出手段の検出値に基づいて学習された空燃比学習値に従って内燃機関の空燃比を制御する空燃比制御手段と、ＳＯx保持材から硫黄酸化物を除去するときにＳＯx保持材に流入する排気の空燃比が理論空燃比以下となるように排気中へ還元剤を添加する第１の還元剤添加手段とを備えた内燃機関の排気浄化装置において、第１の還元剤添加手段が作動する前に、空燃比検出手段の被毒を解消させるとともに、被毒解消後の内燃機関の空燃比が目標機関空燃比と一致するように内燃機関の空燃比を補正することを最大の特徴としている。
【００３０】
前述したように、空燃比検出手段が被毒した状態でＳＯx保持材の再生処理が開始されると、空燃比検出手段の被毒が解消されるものの、空燃比検出手段の被毒時に学習された空燃比学習値に基づいて内燃機関の空燃比が制御されるため、実機関空燃比が目標機関空燃比よりリーンとなった状態でＳＯx保持材の再生処理が行われることになり、還元剤の供給量が過剰に多くなることが想定される。
【００３１】
これに対し、本発明にかかる内燃機関の排気浄化装置は、ＳＯx保持材の再生処理が行われる前に空燃比検出手段の被毒を解消させるとともに、被毒解消後の内燃機関の空燃比が目標機関空燃比と一致するように内燃機関の空燃比を補正する。
【００３２】
この場合、ＳＯx保持材の再生処理が行われる際の実機関空燃比が目標機関空燃比と一致するようになるため、還元剤の添加量が過剰に多くなることがない。
【００３３】
そして、ＳＯx保持材の再生処理が行われる際の実機関空燃比を目標機関空燃比と一致させる手法として以下の２つを例示することができる。
【００３４】
（１）排気温度を上昇させるべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第２の還元剤添加手段を更に備え、
前記被毒解消手段は、前記第２の還元剤添加手段を作動させることにより前記空燃比検出手段の被毒を解消させ、
前記空燃比補正手段は、前記空燃比検出手段の検出値と前記第２の還元剤添加手段による還元剤添加量とに基づいて前記内燃機関の実際の空燃比を演算し、その空燃比が前記目標機関空燃比となるように前記内燃機関の空燃比を制御する。
【００３５】
（２）排気温度を上昇させるべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第２の還元剤添加手段を更に備え、
前記被毒解消手段は、前記第２の還元剤添加手段を作動させることにより前記空燃比検出手段の被毒を解消させ、
前記空燃比補正手段は、前記第２の還元剤添加手段による還元剤添加終了後の前記空燃比検出手段の検出値が前記目標機関空燃比となるように前記内燃機関の空燃比を制御する。
【００３６】
尚、本発明にかかる内燃機関の排気浄化装置は、内燃機関の排気の一部を該内燃機関に再循環させるＥＧＲ機構を更に備え、空燃比補正手段は、前記ＥＧＲ機構により再循環される排気（以下、「ＥＧＲガス」と称する。）の量を調節することにより前記内燃機関の空燃比を補正するようにしてもよい。
【００３７】
例えば、空燃比補正手段は、内燃機関の空燃比を低くする場合にはＥＧＲガス量を増加させ、内燃機関の空燃比を高くする場合にはＥＧＲガス量を減少させるようにすればよい。
【００３８】
かかる構成とすることにより、空燃比補正手段は、内燃機関の燃料噴射量を変更することなく、内燃機関の空燃比を補正することが可能となる。特に、内燃機関の空燃比を低下させる場合には、空燃比補正手段は、内燃機関の燃料噴射量を増加させる代わりに、ＥＧＲガス量を増加させることにより内燃機関の空燃比を低下させることが可能となるため、燃料噴射量の低減、内燃機関から排出される未燃燃料成分の減少、及び内燃機関から排出される窒素酸化物（ＮＯｘ）の減少等を図ることができる。
【００３９】
次に、本発明は、前述した課題を解決するために以下のような手段を採用してもよい。すなわち、本発明にかかる内燃機関の排気浄化装置は、
内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するＳＯｘ保持材と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて学習される空燃比学習値に従って、内燃機関の空燃比を制御する空燃比制御手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去する際に、前記空燃比検出手段の検出値を理論空燃比以下とすべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する還元剤添加手段と、
前記還元剤添加手段が還元剤の添加を開始する前に、前記空燃比検出手段の未燃燃料成分による被毒を解消させる被毒解消手段と、
前記還元剤添加手段の作動開始後に、前記内燃機関の実際の空燃比が所望の目標機関空燃比となるように前記内燃機関の空燃比を補正する空燃比補正手段と、を備えるようにしてもよい。
【００４０】
この発明は、空燃比検出手段の検出値に基づいて学習された空燃比学習値に従って内燃機関の空燃比を制御する空燃比制御手段と、ＳＯx保持材から硫黄酸化物を除去するときにＳＯx保持材に流入する排気の空燃比が理論空燃比以下となるように排気中へ還元剤を添加する還元剤添加手段とを備えた内燃機関の排気浄化装置において、還元剤添加手段の作動開始後に、実機関空燃比が所望の目標機関空燃比となるように前記内燃機関の空燃比を補正することを最大の特徴としている。
【００４１】
前述したように、空燃比検出手段が被毒した状態でＳＯx保持材の再生処理が開始されると、空燃比検出手段の被毒が解消されるものの、空燃比検出手段の被毒時に学習された空燃比学習値に基づいて内燃機関の空燃比が制御されるため、実機関空燃比が目標機関空燃比よりリーンな状態となってしまう。
【００４２】
これに対し、本発明にかかる内燃機関の排気浄化装置は、ＳＯx保持材の再生処理中に実機関空燃比を目標機関空燃比に一致させるべく内燃機関の空燃比を補正する。
【００４３】
このようにＳＯx保持材の再生処理中に実機関空燃比が目標機関空燃比と一致するようになると、それ以降の再生処理において還元剤添加手段から排気中へ添加される還元剤の量が減少するため、ＳＯx保持材において過剰な量の還元剤が酸化するようなことがなくなる。
【００４４】
ＳＯx保持材の再生処理中に実機関空燃比を目標機関空燃比と一致させる方法としては、（１）空燃比検出手段の検出値と還元剤添加手段の還元剤添加量とに基づいて実機関空燃比を演算し、その実機関空燃比と目標機関空燃比との偏差に従って内燃機関の空燃比を補正する方法、（２）還元剤添加手段の作動を一時的に停止させ、その際の空燃比検出手段の検出値が目標機関空燃比と一致するように内燃機関の空燃比を補正する方法などを例示することができる。
【００４５】
尚、本発明にかかる内燃機関の排気浄化装置は、内燃機関の排気の一部を該内燃機関に再循環させるＥＧＲ機構を更に備え、空燃比補正手段は、ＥＧＲガスの量を調節することにより前記内燃機関の空燃比を補正するようにしてもよいのは上述と同様である。
【００４６】
また、本発明において、ＳＯx保持剤としては、ＮＯx吸蔵還元型触媒のように酸化能を有するＮＯx吸収剤を例示することができる。
【００４７】
【発明の実施の形態】
以下に図面を参照して、この発明の好適な実施の形態を例示的に詳しく説明する。ただし、この実施の形態に記載されている構成部品の寸法、材質、形状、その相対配置などは、特に特定的な記載がない限りは、この発明の範囲をそれらのみに限定する趣旨のものではない。
【００４８】
また、ここでは、本発明に係る排気浄化装置を車輌駆動用の圧縮着火式内燃機関（ディーゼル機関）に適用した場合を例に挙げて説明する。
【００４９】
＜第１の実施の形態＞
本発明の第１の実施の形態に係る排気浄化装置を適用する内燃機関とその吸排気系の概略構成を示したのが図１である。
【００５０】
図１に示す内燃機関１は、４つの気筒２を有する水冷式の４サイクル・ディーゼル機関である。
【００５１】
内燃機関１は、各気筒２の燃焼室に直接燃料を噴射する燃料噴射弁３を備えている。各燃料噴射弁３は、蓄圧室（コモンレール）４と接続され、このコモンレール４は燃料供給管５を介して燃料ポンプ６と連通している。
【００５２】
内燃機関１には吸気通路７が接続されており、この吸気通路７はエアクリーナボックス８に接続されている。そして、このエアクリーナボックス８より下流の吸気通路７には、該吸気通路７内を流通する吸気の質量に対応した電気信号を出力するエアフローメータ９が取り付けられている。
【００５３】
また、吸気通路７の途中には、遠心過給器（ターボチャージャー）１０のコンプレッサハウジング１０ａが設けられている。コンプレッサハウジング１０ａより下流の吸気通路７にはインタークーラ１１が取り付けられている。更にインタークーラ１１より下流の吸気通路７には、該吸気通路７内を流通する吸気の流量を調節する吸気絞り弁１２が設けられている。この吸気絞り弁１２には吸気絞り用アクチュエータ１３が取り付けられている。
【００５４】
また、内燃機関１には排気通路１４が接続され、この排気通路１４は、下流にてマフラーと接続されている。そして、排気通路１４の途中には、前記遠心過給機１０のタービンハウジング１０ｂが配置されている。
【００５５】
排気通路１４におけるタービンハウジング１０ｂより下流の部位には、排気中の有害ガス成分を浄化するための排気浄化触媒１５が配置されている。この排気浄化触媒１５は、該排気浄化触媒１５に流入する排気の空燃比がリーン空燃比（理論空燃比以上）であるときには、排気中の窒素酸化物（ＮＯx）を吸蔵し、該排気浄化触媒１５に流入する排気の空燃比がリッチ空燃比（理論空燃比以下）となったときには、吸蔵していた窒素酸化物（ＮＯx）を還元する吸蔵還元型ＮＯｘ触媒である。
【００５６】
排気浄化触媒２０より下流の排気通路１４には、該排気通路１４内を流通する排気の空燃比に対応した電気信号を出力する空燃比検出手段である空燃比センサ１６と、該排気通路１４内を流通する排気の温度に対応した電気信号を出力する排気温度センサ１７とが取り付けられている。なお、本実施の形態では、排気浄化触媒２０より下流の排気通路１４に空燃比センサ１６を設けて排気浄化触媒２０から流出する排気の空燃比を検出しているが、排気浄化触媒２０より上流の排気通路１４に更に空燃比センサを設けて排気浄化触媒２０に流入する排気の空燃比を検出して、排気通路１４内を流通する排気の空燃比を検出してもよいし、排気浄化触媒２０より上流の排気通路１４のみに空燃比センサを設けて、排気通路１４内を流通する排気の空燃比を検出してもよい。
【００５７】
前記吸気通路７における吸気絞り弁１２より下流の部位と、前記排気通路１４におけるタービンハウジング１０ｂより上流の部位とは、排気再循環通路（以下「ＥＧＲ通路」と称する。）１８を介して連通されている。このＥＧＲ通路１８の途中には、流量調整弁（ＥＧＲ弁）１９が設けられている。
【００５８】
また、内燃機関１の１番気筒２の排気ポート２０には、該排気ポート２０内を流通する排気中に還元剤たる燃料を添加する還元剤添加弁２１が取り付けられ、この還元剤添加弁２１は燃料通路２２を介して前記燃料ポンプ６と接続されている。
【００５９】
以上述べたように構成された内燃機関１には、該内燃機関１を制御するための電子制御ユニット（ＥＣＵ：ElectronicControl Unit）２５が併設されている。このＥＣＵ２５は、ＣＰＵ、ＲＯＭ、ＲＡＭ、バックアップＲＡＭなどからなる算術論理演算回路である。
【００６０】
ＥＣＵ２５には、前述したエアフローメータ９、空燃比センサ１６、排気温度センサ１７に加え、内燃機関１に取り付けられたクランクポジションセンサ２３及び水温センサ２４等の各種センサが電気配線を介して接続され、上記した各種センサの出力信号がＥＣＵ２５に入力されるようになっている。
【００６１】
一方、ＥＣＵ２５には、燃料噴射弁３、吸気絞り用アクチュエータ１３、ＥＧＲ弁１９、還元剤添加弁２１等が電気配線を介して接続され、ＥＣＵ２５が燃料噴射弁３、吸気絞り用アクチュエータ１３、ＥＧＲ弁１９、及び還元剤添加弁２１を制御することが可能になっている。
【００６２】
例えば、ＥＣＵ２５は、一定時間毎に実行すべき基本ルーチンにおいて、各種センサの出力信号の入力、機関回転数の演算、燃料噴射量の演算、燃料噴射時期の演算等を実行する。基本ルーチンにおいてＥＣＵ２５が入力した各種信号やＥＣＵ２５が演算して得られた各種制御値は、該ＥＣＵ２５のＲＡＭに一時的に記憶される。
【００６３】
燃料噴射量を演算する場合には、ＥＣＵ２５は、下記の式（１）に基づき最終燃料噴射量Ｑｆｉｎを算出する。
【００６４】
Ｑｆｉｎ＝Ｑｂｓｅ＊ＦＡＦ＊ＫＧ（ｉ）＊Ａ……（１）
Ｑｂｓｅ：基本燃料噴射量
ＦＡＦ：フィードバック補正係数
ＫＧ（ｉ）：空燃比学習値
Ａ：増量係数
【００６５】
更に、ＥＣＵ２５は、各種のセンサやスイッチからの信号の入力、一定時間の経過、或いはクランクポジションセンサ２３からのパルス信号の入力などをトリガーとした割り込み処理において、ＲＡＭから各種制御値を読み出し、それら制御値に従って燃料噴射弁３を制御する。
【００６６】
また、ＥＣＵ２５は、クランクポジションセンサ２３に基づく割り込み処理、或は一定時間毎の割り込み処理として、以下に述べるような排気浄化制御を実行する。
【００６７】
排気浄化制御では、ＥＣＵ２５は、内燃機関１が一定時間以上連続してリーン空燃比で運転されているか否かを判別する。内燃機関１が一定時間以上連続してリーン空燃比で運転されている場合には、ＥＣＵ２５は、排気浄化触媒１５のＮＯx吸蔵能力を再生させるべく還元剤添加弁２１を開弁させる。
【００６８】
還元剤添加弁２１が開弁させられると、燃料ポンプ６から吐出された燃料が燃料通路７及び還元剤添加弁２１を介して１番気筒２の排気ポートへ噴射され、次いで排気ポートから排気通路１４へ導かれることになる。排気通路１４へ導かれた燃料は、該排気通路１４の上流から流れてきた排気ととともにタービンハウジング１０ｂへ流入する。タービンハウジング１０ｂ内に流入した排気と還元剤とは、タービンホイールの回転によって撹拌されて均質に混合され、リッチ空燃比の排気を形成する。
【００６９】
このようにして形成されたリッチ空燃比の排気は、タービンハウジング１０ｂから排気通路１４を介して排気浄化触媒１５に流入し、排気浄化触媒１５に吸収されていた窒素酸化物（ＮＯｘ）を還元することになる。この結果、排気浄化触媒１５に吸蔵されていた窒素酸化物（ＮＯx）が該排気浄化触媒１５から除去されることとなり、排気浄化触媒１５のＮＯx吸蔵能力が再生される。
【００７０】
ところで、排気浄化触媒１５は、窒素酸化物（ＮＯx）と同様のメカニズムによって排気中の硫黄酸化物（ＳＯx）を吸蔵するため、硫黄酸化物（ＳＯx）の吸蔵量が増加すると、それに応じて吸蔵還元型ＮＯｘ触媒のＮＯx吸蔵能力が低減する、いわゆるＳＯx被毒が発生する。
【００７１】
これに対し、ＥＣＵ２５は、以下に示すような方法に従って排気浄化触媒１５のＳＯx被毒解消処理を実行する。
【００７２】
排気浄化触媒１５のＳＯｘ被毒を解消する方法としては、排気浄化触媒１５の雰囲気温度をおよそ５００℃〜７００℃の高温域まで昇温させるとともに、排気浄化触媒１５に流入する排気の空燃比をリッチ空燃比とすることにより、排気浄化触媒１５から硫黄酸化物（ＳＯx）を放出させつつ気体状のＳＯ２ −に還元する方法を例示することができる。
【００７３】
そこで、ＥＣＵ２５は、先ず排気浄化触媒１５の雰囲気温度を高めるべく触媒昇温処理を実行する。
【００７４】
排気浄化触媒１５の雰囲気温度を高める方法としては、（１）排気温度を上昇させて排気の熱を排気浄化触媒１５へ伝達させる方法と、（２）排気浄化触媒１５において未燃燃料を酸化させることによりその際に発生する反応熱により排気浄化触媒１５自体を昇温させる方法とを例示することができる。
【００７５】
上記した（１）の具体的な方法としては、内燃機関１における混合気の燃焼時期を遅角させる方法、内燃機関１において膨張行程時の気筒２の燃料噴射弁３から副次的に燃料を噴射させる方法、図示しない排気絞り弁の開度を小さくすることにより内燃機関１の負荷を高める方法、ＥＧＲガスの量を増加させることにより内燃機関１において低温燃焼を行わせる方法などを例示することができる。
【００７６】
上記した（２）の具体的な方法としては、還元剤添加弁２１から排気中へ燃料を添加させる方法、内燃機関１において排気行程時の気筒２の燃料噴射弁３から副次的に燃料を噴射させる方法などを例示することができる。
【００７７】
上記したような触媒昇温処理により排気浄化触媒１５の床温が５００℃〜７００℃程度の高温域まで上昇すると、ＥＣＵ２５は、排気浄化触媒１５に流入する排気の空燃比をリッチ空燃比とすべく還元剤添加弁２１から排気中へ還元剤たる燃料を添加させる。
【００７８】
その際、ＥＣＵ２５は、排気浄化触媒１５へ流入する排気の空燃比が所望の目標リッチ空燃比となるように還元剤添加量をフィードバック制御する。具体的には、ＥＣＵ２５は、空燃比センサ１６の出力信号値が前記目標リッチ空燃比と一致するように還元剤添加弁２１の開度をフィードバック制御する。
【００７９】
これは、排気中に添加された還元剤は排気浄化触媒１５において酸化することになるため、過剰に多量の還元剤が排気中に添加されると、排気浄化触媒１５において多量の還元剤が酸化されることとなり、還元剤が酸化する際に発生する熱量によって排気浄化触媒１５が過熱してしまう虞があるからである。
【００８０】
一方、内燃機関１のような圧縮着火式内燃機関では、排気温度が低くなり易いため、排気中に含まれる未燃燃料成分であるＨＣが空燃比センサ１６に付着し、空燃比センサ１６の出力値が実際の空燃比よりリッチ側にずれてしまう、いわゆるセンサ被毒が発生する。
【００８１】
このように空燃比センサ１６が被毒している状況下で、空燃比センサの出力値に基づいて前述した空燃比学習係数：ＫＧ（ｉ）が学習され、その空燃比学習値：ＫＧ（ｉ）に従って内燃機関の空燃比が制御されると、内燃機関１の実際の空燃比（実機関空燃比）が目標機関空燃比よりも高くなる、すなわち、実機関空燃比が目標機関空燃比よりリーンになる（高くなる）ことが想定される。
【００８２】
そして、実機関空燃比が目標機関空燃比より高くなった状態で、前述したＳＯｘ被毒解消処理が実行されると、ＥＣＵ２５は、排気浄化触媒１５に流入する排気の空燃比を目標リッチ空燃比とすべく、還元剤添加弁２１から添加される還元剤の添加量を過剰に増加させる虞がある（図２参照）。
【００８３】
そこで、本実施の形態では、ＥＣＵ２５は、ＳＯｘ被毒解消処理を実行する際に、センサ被毒解消制御を実行するとともに空燃比学習値を初期値にリセットするようにする。
【００８４】
具体的に図５のフローチャートを用いて本実施の形態に係るＳＯｘ被毒解消処理について説明する。
【００８５】
先ず、ステップ１００にてセンサ被毒解消制御を実行する。このセンサ被毒解消制御としては、ＥＣＵ２５は、例えば、内燃機関１の空燃比を高くして排気の酸素濃度を高くした状態で、還元剤添加弁２１から排気中へ還元剤たる燃料を添加させることにより、それらの未燃燃料成分を排気浄化触媒１５において酸化させ、酸化の際に発生する熱によって、空燃比センサ１６近傍の排気温を高温（３００〜５００℃、好ましくは５００℃以上）にするものである。
【００８６】
そして、空燃比センサ１６に付着した未燃燃料成分である炭化水素（ＨＣ）は、３００℃〜５００℃の高温になると酸素濃度が高いために十分に酸化され、空燃比センサ１６の被毒が解消されることになる。
【００８７】
次にステップ１０１にて、空燃比学習値を初期値にリセットする。なお、空燃比学習値をリセットするにあたっては、空燃比センサの温度を検出する温度検出手段である空燃比センサ温度センサを設け、該空燃比センサ温度センサにより検出された温度が、センサ被毒を生じたまま空燃比を検出してしまう温度である、例えば４００℃未満である時に学習された空燃比学習値を初期値にリセットするようにしてもよい。かかる場合、空燃比センサが被毒していない状態で学習された学習値は有効に活かすことができる。
【００８８】
次にステップ１０２にて、排気温度が所定温度Ｔ以上であるか否かが判定される。上述したように、ＳＯｘ被毒を解消するにあたっては、排気浄化触媒１５の雰囲気温度をおよそ５００℃〜７００℃の高温域にすることから、本ステップにて排気温度センサ１７で検出した排気温度が所定温度の例えば５００℃以上であるか否かを判定する。なお、該所定温度は、排気浄化用触媒１５の種類等に応じて決定されるものである。
【００８９】
そして、排気温度が所定温度Ｔ以上である場合は、ステップ１０３へ進み、Ｔ未満である場合は、ステップ１０４にて、上述の触媒昇温処理を実行した上で、ステップ１０３へ進む。
【００９０】
ステップ１０３においては、排気の空燃比がＳＯｘ被毒を解消するための目標空燃比であるリッチ空燃比であるか否かが判定される。そして排気の空燃比が目標のリッチ空燃比でない場合は、ステップ１０５にて目標のリッチ空燃比とすべく還元剤添加弁２１から還元剤を添加して行なう還元剤添加制御を実行する。
【００９１】
このようにして、内燃機関１の始動直後のように排気温度が低い状態からＳＯｘ被毒解消処理へと移行する場合にも、センサが被毒したまま学習された空燃比学習値に従って燃料噴射量が決定されることがないので、ＳＯｘ被毒解消処理の際に適正な量の還元剤が添加されることとなり（図３参照）、排気浄化触媒１５に過剰な還元剤が添加されて過昇温となることに起因する排気浄化触媒１５の熱劣化の促進を防止することができる。
【００９２】
＜第２の実施の形態＞
本実施の形態は、第１の実施の形態に対して、ＳＯｘ被毒解消処理を実行する際の排気浄化触媒１５の過昇温に起因する熱劣化の促進を防止する手段のみを変更したものであり、その他の構成および作用については第１の実施の形態と同一なので、同一の構成部分については同一の符号を付して、その説明は省略する。
【００９３】
ＳＯｘ被毒解消処理を実行する際に、還元剤添加弁２１から過剰な還元剤が添加されると、それらの還元剤が排気浄化触媒１５で急激に燃焼して排気浄化触媒１５が過熱するおそれがあるため、ＥＣＵ２５は、空燃比センサ１６の出力信号に基づいて還元剤添加弁２１からの還元剤添加量を制御するようにする。
【００９４】
しかし、第１の実施の形態で述べたように内燃機関１の始動直後のように排気温度が低い状態からＳＯｘ被毒解消処理へと移行する場合には、空燃比センサ１６がセンサ被毒を生じているおそれがあることから、空燃比センサ１６の出力信号に基づいて還元剤添加弁２１からの還元剤添加量を制御するには、まずは空燃比センサ１６のセンサ被毒を解消しておく必要がある。そこで、まずは空燃比センサ被毒を解消すべく、上述のセンサ被毒解消制御を実施する。
【００９５】
また、空燃比センサ被毒が解消されたとしても、実機関空燃比が目標機関空燃比より高くなった状態で、前述したＳＯｘ被毒解消処理が実行されると、ＥＣＵ２５は、排気浄化触媒１５に流入する排気の空燃比を目標リッチ空燃比とすべく、還元剤添加弁２１から添加される還元剤の添加量を過剰に増加させる虞がある（図２参照）。
【００９６】
そこで、空燃比センサ被毒を解消させた後、センサ被毒が解消した空燃比センサ１６の検出値と目標空燃比との差分に基づいて内燃機関１の空燃比をフィードバック制御する、機関空燃比制御を実行し、内燃機関１の空燃比を目標空燃比とした上で、還元剤添加弁２１から添加される還元剤の量を決定するようにする（図４参照）。
【００９７】
センサ被毒が解消した空燃比センサ１６の検出値と目標空燃比との差分に基づいて内燃機関１の空燃比をフィードバック制御する、機関空燃比制御を実行する手法としては以下の２つを例示することができる。
【００９８】
（１）センサ被毒解消制御を実行するにあたっては、排気の空燃比を高く（リーンに）した状態で温度を３００℃〜５００℃にすべく還元剤が添加され、ＳＯｘ被毒解消処理は温度を５００℃〜７００℃にするとともに空燃比をリッチにすべく還元剤を添加することから、センサ被毒解消制御中に添加していた還元剤をＳＯｘ被毒解消処理の際にもそのまま添加し続けて、センサ被毒が解消した空燃比センサ１６の検出値と目標空燃比との差分から添加した還元剤の分を差し引いてフィードバック制御するようにする。
【００９９】
（２）上述のようにセンサ被毒解消制御は還元剤たる燃料を添加して行なうことから、センサ被毒が解消したら、還元剤の添加を中止し、センサ被毒が解消した空燃比センサ１６の検出値と目標空燃比との差分に基づいてフィードバック制御するようにする。
【０１００】
なお、具体的に本実施の形態に係るＳＯｘ被毒解消処理をフローチャート図で示したものが図６であるが、第１の実施の形態に係るＳＯｘ被毒解消処理のフローチャートと比較すると、図５のステップ１０１で空燃比学習値をリセットする代わりに、図６ではステップ２０１として上述した機関空燃比制御を実行する点のみ異なる。その他については図５と同一なので、その説明は省略する。
【０１０１】
このようにして、ＳＯｘ被毒解消処理を実行する際に、まず、センサ被毒解消制御を実行した後、目標空燃比と空燃比センサ１６の検出値のずれをフィードバックし、内燃機関１の空燃比を制御することにより、排気浄化触媒１５に流入する排気の空燃比を目標のリッチな空燃比とする際、リーンずれした内燃機関の空燃比を基に還元剤が添加されることがないので、還元剤が過剰に添加されて排気浄化触媒１５が過昇温となることに起因する排気浄化触媒１５の熱劣化の促進を防ぐことができる。
【０１０２】
また、上述のように排気浄化触媒１５に流入する排気の空燃比を、センサ被毒解消制御実行中のリーンからリッチにしてＳＯｘ被毒解消処理を実行するが、排気の空燃比をリーンからリッチにするのに内燃機関１の空燃比をある程度リッチにする際、燃料噴射弁３からの燃料噴射量を増加してリッチにするのではなく、ＥＧＲ機構により機関内に再循環させる排気量を増加してリッチにするようにしてもよい。
【０１０３】
これは、燃料噴射弁３から燃料噴射量を増加して空燃比をリッチとする方法だと、未燃の燃料は触媒の発熱に寄与する分が多いため触媒が過熱されてしまうおそれがある。それに対してＥＧＲ機構により内燃機関内に再循環される排気量を増加する方法では、ＥＧＲガスは燃焼済みの排気であるため触媒の発熱に寄与することが少なく、触媒の過熱が抑制されるためである。
【０１０４】
また、ＥＧＲガスには、水（Ｈ２Ｏ）や二酸化炭素（ＣＯ２）などのように、自らが燃焼することがなく、且つ、吸熱性を有する不活性ガス成分が含まれているため、ＥＧＲガスが混合気中に含有されると、混合気の燃焼温度が低められ、以て窒素酸化物（ＮＯｘ）の発生量が抑制されるからである。
【０１０５】
なお、センサ被毒解消制御を実行する際に還元剤を添加する場合、センサ被毒解消用に還元剤を添加する還元剤添加手段と、ＳＯｘ被毒解消処理用に還元剤を添加する還元剤添加手段とは、上述の実施の形態では同一のものである還元剤添加弁２１を使用しているが、特にスペース等に制限がない限り異なる物を使用してもよい。
【０１０６】
＜第３の実施の形態＞
本実施の形態は、第１の実施の形態に対して、ＳＯｘ被毒解消処理を実行する際の排気浄化触媒１５の過昇温に起因する熱劣化の促進を防止する手段のみを変更したものであり、その他の構成および作用については第１の実施の形態と同一なので、同一の構成部分については同一の符号を付して、その説明は省略する。
【０１０７】
ＳＯｘ被毒解消処理を実行する際に、還元剤添加弁２１から過剰な還元剤が添加されると、それらの還元剤が排気浄化触媒１５で急激に燃焼して排気浄化触媒１５が過熱するおそれがあるため、ＥＣＵ２５は、空燃比センサ１６の出力信号に基づいて還元剤添加弁２１からの還元剤添加量を制御するようにする。
【０１０８】
しかし、第１の実施の形態で述べたように内燃機関１の始動直後のように排気温度が低い状態からＳＯｘ被毒解消処理へと移行する場合には、空燃比センサ１６がセンサ被毒を生じているおそれがあることから、空燃比センサ１６の出力信号に基づいて還元剤添加弁２１からの還元剤添加量を制御するには、まずは空燃比センサ１６のセンサ被毒を解消しておく必要がある。そこで、まずは空燃比センサ被毒を解消すべく、上述のセンサ被毒解消制御を実行する。
【０１０９】
また、空燃比センサ被毒が解消されたとしても、実機関空燃比が目標機関空燃比より高くなった状態で、前述したＳＯｘ被毒解消処理が実行されると、ＥＣＵ２５は、排気浄化触媒１５に流入する排気の空燃比を目標リッチ空燃比とすべく、還元剤添加弁２１から添加される還元剤の添加量を過剰に増加させる虞がある（図２参照）。
【０１１０】
そこで、空燃比センサ被毒を解消させた後、還元剤添加弁２１から還元剤を添加して行なう還元剤添加制御を実行する際に、センサ被毒が解消した空燃比センサ１６の検出値と目標空燃比との差分に基づいて内燃機関１の空燃比をフィードバック制御する、機関空燃比制御を実行する。なお、第２の実施の形態においては、機関空燃比制御を実行し、内燃機関１の空燃比を目標空燃比と一致させた後、還元剤添加制御を実行するが、本実施の形態においては、還元剤添加制御を実行しつつ機関空燃比制御を実行するものである。
【０１１１】
そして、還元剤添加制御を実行しつつ機関空燃比制御を実行する手法としては、（１）センサ被毒が解消した空燃比センサ１６の検出値と還元剤添加弁２１の還元剤添加量とに基づいて内燃機関１の空燃比を演算し、その内燃機関１の空燃比と目標機関空燃比との偏差に従って内燃機関１の空燃比を補正する手法、（２）還元剤添加弁２１の還元剤添加を一時的に停止させ、その際の空燃比センサ１６の検出値が目標機関空燃比と一致するように内燃機関１の空燃比を補正し、その後再度還元剤添加を開始する手法などを例示することができる。
【０１１２】
具体的に図７のフローチャートを用いて本実施の形態に係るＳＯｘ被毒解消処理について説明する。
【０１１３】
先ず、ステップ３００にて上述したセンサ被毒解消制御を実行する。
【０１１４】
次にステップ３０１にて、排気温度が所定温度Ｔ以上であるか否かが判定される。上述したように、ＳＯｘ被毒を解消するにあたっては、排気浄化触媒１５の雰囲気温度をおよそ５００℃〜７００℃の高温域にすることから、本ステップにて排気温度センサ１７で検出した排気温度が所定温度の例えば５００℃以上であるか否かを判定する。なお、該所定温度は、排気浄化用触媒１５の種類等に応じて決定されるものである。
【０１１５】
そして、排気温度が所定温度Ｔ以上である場合は、ステップ３０２へ進み、Ｔ未満である場合は、ステップ３０３にて、上述の触媒昇温処理を実行した上で、ステップ３０２へ進む。
【０１１６】
ステップ３０２においては、排気の空燃比がＳＯｘ被毒を解消するための目標空燃比であるリッチ空燃比であるか否かが判定される。そして排気の空燃比が目標のリッチ空燃比でない場合は、ステップ３０４にて目標のリッチ空燃比とすべく還元剤添加弁２１から還元剤を添加して行なう還元剤添加制御を実行する。そしてこの際に上述の機関空燃比制御を実行する。
【０１１７】
このようにして、ＳＯｘ被毒解消処理を実行する際に、まず、センサ被毒解消制御を実行した後、還元剤を添加して空燃比センサ１６の検出値を目標のリッチ空燃比とする際、内燃機関１の空燃比が目標機関空燃比と一致するようになると、それ以降の還元剤添加量が適正な量となるので、排気浄化触媒１５において過剰な量の還元剤が酸化するようなことがなくなる。そして、還元剤が過剰に添加されて排気浄化触媒１５が過昇温となることに起因する排気浄化触媒１５の熱劣化の促進を防ぐことができる。
【０１１８】
また、上述のように排気浄化触媒１５に流入する排気の空燃比を、センサ被毒解消制御実行中のリーンからリッチにしてＳＯｘ被毒解消処理を実行するが、排気の空燃比をリーンからリッチにするのに内燃機関１の空燃比をある程度リッチにする際、燃料噴射弁３からの燃料噴射量を増加してリッチにするのではなく、ＥＧＲ機構により機関内に再循環させる排気量を増加してリッチにするようにしてもよい。
【０１１９】
これは、燃料噴射弁３から燃料噴射量を増加して空燃比をリッチとする方法だと、未燃の燃料は触媒の発熱に寄与する分が多いため触媒が過熱されてしまうおそれがある。それに対してＥＧＲ機構により内燃機関内に再循環される排気量を増加する方法では、ＥＧＲガスは燃焼済みの排気であるため触媒の発熱に寄与することが少なく、触媒の過熱が抑制されるためである。
【０１２０】
また、ＥＧＲガスには、水（Ｈ２Ｏ）や二酸化炭素（ＣＯ２）などのように、自らが燃焼することがなく、且つ、吸熱性を有する不活性ガス成分が含まれているため、ＥＧＲガスが混合気中に含有されると、混合気の燃焼温度が低められ、以て窒素酸化物（ＮＯｘ）の発生量が抑制されるからである。
【０１２１】
【発明の効果】
以上説明したように、本発明に係る内燃機関の排気浄化装置は、ＮＯｘ吸収材等のように排気中の硫黄酸化物（ＳＯｘ）を保持するＳＯｘ保持材の劣化の促進を防止しつつＳＯｘ保持材からＳＯｘを除去することができる。
【０１２２】
また、ＳＯｘ保持材に流入する排気の空燃比を低くしてＳＯｘを除去する際、ＥＧＲ機構により機関内に再循環させる排気量を増加して機関内の空燃比を低くすることにより、混合気の燃焼温度が低められ窒素酸化物（ＮＯｘ）の発生量を抑制することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態に係る内燃機関の排気浄化装置を適用する内燃機関とその吸排気系の概略構成を示す図である。
【図２】本発明を適用しない場合の内燃機関の空燃比と吸蔵還元型ＮＯｘ触媒の温度の変化を示す図である。
【図３】本発明の第１の実施の形態に係る排気浄化装置を用いた場合の内燃機関の空燃比と吸蔵還元型ＮＯｘ触媒の温度の変化を示す図である。
【図４】本発明の第２の実施の形態に係る排気浄化装置を用いた場合の内燃機関の空燃比の変化を示す図である。
【図５】本発明の第１の実施の形態に係るＳＯｘ被毒解消処理のフローチャート図である。
【図６】本発明の第２の実施の形態に係るＳＯｘ被毒解消処理のフローチャート図である。
【図７】本発明の第３の実施の形態に係るＳＯｘ被毒解消処理のフローチャート図である。
【符号の説明】
１ 内燃機関
２ 気筒
３ 燃料噴射弁
４ コモンレール
５ 燃料供給管
６ 燃料ポンプ
７ 吸気通路
８ エアクリーナボックス
９ エアフローメータ
１０ 遠心過給器
１１ インタークーラ
１２ 吸気絞り弁
１３ 吸気絞り用アクチュエータ
１４ 排気通路
１５ 排気浄化触媒
１６ 空燃比センサ
１７ 排気温度センサ
１８ ＥＧＲ通路
１９ ＥＧＲ弁
２０ 排気ポート
２１ 還元剤添加弁
２２ 還元剤供給路
２３ クランクポジションセンサ
２４ 水温センサ
２５ ＥＣＵ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification technology for an internal combustion engine, and more particularly to a technology for regenerating an SOx holding material provided in an exhaust system of an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as an exhaust purification technique for an internal combustion engine mounted on an automobile or the like, a technique for removing nitrogen oxide (NOx) in exhaust gas by arranging a NOx absorbent in an exhaust system of the internal combustion engine is known.
[0003]
Such a NOx absorbent absorbs sulfur oxide (SOx) as well as nitrogen oxide (NOx) in the exhaust gas. Therefore, when the amount of sulfur oxide (SOx) absorbed increases, nitrogen in the exhaust gas This results in so-called SOx poisoning in which oxide (NOx) cannot be absorbed.
[0004]
On the other hand, when the exhaust gas of the internal combustion engine or the NOx absorbent is at a high temperature, a reducing agent is supplied to the NOx absorbent to make the NOx absorbent at a high temperature and rich atmosphere, so that the sulfur oxide ( A technique for removing SOx) and thereby eliminating SOx poisoning of the NOx absorbent material has been proposed (for example, see Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent No. 2605586
[0006]
[Problems to be solved by the invention]
Incidentally, in an internal combustion engine mounted on an automobile or the like, the air-fuel ratio of the internal combustion engine is corrected based on an error between an output signal of an oxygen concentration sensor or an air-fuel ratio sensor provided in an exhaust system and a target air-fuel ratio. Control for learning the correction amount is performed.
[0007]
However, in an internal combustion engine such as a compression ignition type internal combustion engine (diesel engine) or a spark ignition type internal combustion engine (lean burn gasoline engine) capable of lean combustion, the exhaust temperature or the temperature of exhaust system components tends to be low. Hydrocarbon (HC) and carbon monoxide (CO) may adhere to the oxygen concentration sensor or the air-fuel ratio sensor, and the output signal values of these sensors may be lower than the actual oxygen concentration or air-fuel ratio.
[0008]
In such a case, when the learning control is performed based on the output signal value of the oxygen concentration sensor or the air-fuel ratio sensor, the correction amount (learning value) obtained by the learning control is reflected in the air-fuel ratio of the internal combustion engine. Sometimes it is assumed that the actual air-fuel ratio of the internal combustion engine will be higher than the target air-fuel ratio.
[0009]
When the SOx poisoning elimination process as described above is performed in a state where the air-fuel ratio of the internal combustion engine is higher than the target air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is set to a desired rich air-fuel ratio. There is a possibility that the supply amount of the reducing agent is excessively increased.
[0010]
If the amount of reducing agent supplied to the NOx absorbent excessively increases, the amount of heat generated when the reducing agent is oxidized in the NOx absorbent increases, so the temperature of the NOx absorbent excessively increases. As a result, the NOx absorbent tends to deteriorate.
[0011]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an internal combustion engine including a SOx holding material that holds sulfur oxide (SOx) in exhaust gas such as a NOx absorbent. It is an object of the present invention to provide a technique capable of removing SOx from the SOx holding material while preventing the deterioration of the SOx holding material from being promoted.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, an SOx holding material that is provided in an exhaust passage of the internal combustion engine and holds sulfur oxides in the exhaust,
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the air-fuel ratio learning value learned based on the detection value of the air-fuel ratio detection means;
Reducing agent addition means for adding a reducing agent into the exhaust gas upstream of the SOx holding material so that the detected value of the air / fuel ratio detecting means is equal to or lower than the stoichiometric air / fuel ratio when removing sulfur oxide from the SOx holding material; ,
A learning value resetting means for resetting the air-fuel ratio learning value to an initial value before the reducing agent adding means starts adding a reducing agent;
It is characterized by providing.
[0013]
The present invention provides an air-fuel ratio control means for controlling the air-fuel ratio of an internal combustion engine according to an air-fuel ratio learning value learned based on a detection value of the air-fuel ratio detection means, and SOx retention when removing sulfur oxide from the SOx retention material. In an exhaust gas purification apparatus for an internal combustion engine equipped with a reducing agent adding means for supplying a reducing agent into the exhaust gas so that the air-fuel ratio of the exhaust gas flowing into the material is equal to or lower than the stoichiometric air-fuel ratio, sulfur oxides are removed from the SOx holding agent. Therefore, the most important feature is that the air-fuel ratio learning value is reset before the reducing agent addition means starts operating.
[0014]
The air-fuel ratio control means controls the air-fuel ratio of the internal combustion engine so that the air-fuel ratio of the internal combustion engine coincides with a desired engine air-fuel ratio (hereinafter referred to as “target engine air-fuel ratio”).
[0015]
For example, the air-fuel ratio control means first determines the target fuel injection amount of the internal combustion engine according to the target engine air-fuel ratio. Subsequently, the air-fuel ratio control means reads the detection value of the air-fuel ratio detection means, corrects the target fuel injection amount based on the deviation between the detected value and the target air-fuel ratio, and calculates the correction amount at that time as the air-fuel ratio learning. Store as a value. Then, when determining the next target fuel injection amount, the air-fuel ratio control means determines the target fuel injection amount in consideration of the aforementioned air-fuel ratio learning value.
[0016]
When the air-fuel ratio of the internal combustion engine is controlled in this way, if the air-fuel ratio detection means is poisoned by the unburned fuel component, the detected value of the air-fuel ratio detection means is lower than the actual air-fuel ratio (rich). Therefore, the air-fuel ratio of the internal combustion engine is corrected to the lean side, and the air-fuel ratio learning value is a value that corrects the air-fuel ratio of the internal combustion engine to the lean side.
[0017]
Further, when removing the sulfur oxide held in the SOx holding material, the temperature of the exhaust gas flowing into the SOx holding material is raised, and the air-fuel ratio of the exhaust gas flowing into the SOx holding material is made lower than the stoichiometric air-fuel ratio. It is necessary to perform a reproduction process.
[0018]
When regeneration processing of the SOx holding material is performed while the air-fuel ratio detection means is poisoned, the unburned fuel component adhering to the air-fuel ratio detection means is exposed to high-temperature exhaust gas and combusted. The poisoning of the fuel ratio detection means is eliminated.
[0019]
In this case, the detection value of the air-fuel ratio detection means shows a value corresponding to the actual air-fuel ratio. However, since the air-fuel ratio of the internal combustion engine is controlled according to the above-described air-fuel ratio learning value, it is discharged from the internal combustion engine. The air-fuel ratio of the exhaust (hereinafter referred to as “actual engine air-fuel ratio”) becomes an air-fuel ratio leaner than the target engine air-fuel ratio.
[0020]
By the way, in the regeneration processing of the SOx holding material, the supply amount of the reducing agent is determined so that the detection value of the air-fuel ratio detection means coincides with the target rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio. When the detected value of the means indicates an air-fuel ratio leaner than the target engine air-fuel ratio, it is assumed that the amount of reducing agent supplied becomes excessive.
[0021]
Since the reducing agent in the exhaust gas reacts with the sulfur oxides held in the SOx holding material and oxidizes, if a large amount of reducing agent is present in the exhaust gas, a large amount of reducing agent is oxidized in the SOx holding material. Thus, it is assumed that the SOx holding material is excessively heated by the reaction heat generated at that time, thereby inducing thermal deterioration of the SOx holding material.
[0022]
On the other hand, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the learning value resetting means resets the air-fuel ratio learning value to the initial value before the reducing agent adding means operates in the regeneration processing of the SOx holding material.
[0023]
In this case, since the air-fuel ratio control means does not correct the air-fuel ratio of the internal combustion engine to the lean side, the actual engine air-fuel ratio will not become excessively lean as compared with the target engine air-fuel ratio.
[0024]
As a result, the detection value of the air-fuel ratio detection means does not show an excessively lean value as compared with the target engine air-fuel ratio at the time when the reducing agent addition means starts to operate, so that the amount of reducing agent supplied is excessive. There is no need to increase it.
[0025]
The air-fuel ratio detection means in the present invention can be exemplified by an air-fuel ratio sensor and an oxygen concentration sensor disposed in the exhaust passage upstream of the SOx holding material and / or the exhaust passage downstream of the SOx holding material.
[0026]
Further, since the unburned fuel component in the exhaust gas easily adheres to the air-fuel ratio detecting means or the air-fuel ratio detecting means when the temperature of the exhaust gas is low, the learning value resetting means has a predetermined temperature or exhaust temperature of the air-fuel ratio detecting means. Only the air-fuel ratio learning value learned when the temperature is lower than the temperature may be reset to the initial value.
[0027]
In this case, it becomes possible to control the air-fuel ratio of the internal combustion engine while utilizing the learned air-fuel ratio value when the air-fuel ratio detecting means is not poisoned by the unburned fuel component. It becomes easy to approximate the actual engine air-fuel ratio when the poisoning is eliminated, in other words, the actual engine air-fuel ratio when the reducing agent adding means starts to operate.
[0028]
The present invention may employ the following means in order to solve the above-described problems. That is, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of the internal combustion engine, and an SOx holding material that holds sulfur oxide in the exhaust gas,
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the air-fuel ratio learning value learned based on the detection value of the air-fuel ratio detection means;
A first reducing agent that adds a reducing agent into the exhaust gas upstream of the SOx holding material so that the detected value of the air-fuel ratio detecting means is equal to or lower than the stoichiometric air-fuel ratio when removing sulfur oxide from the SOx holding material. Adding means;
Poisoning elimination means for eliminating the poisoning due to the unburned fuel component of the air-fuel ratio detection means before the first reducing agent addition means starts adding the reducing agent;
The internal combustion engine is configured so that the air-fuel ratio of the internal combustion engine becomes a desired target engine air-fuel ratio after the poisoning of the air-fuel ratio detection means is eliminated and before the first reducing agent addition means starts adding the reducing agent. Air-fuel ratio correcting means for correcting the air-fuel ratio of the engine;
You may make it provide.
[0029]
The present invention provides an air-fuel ratio control means for controlling the air-fuel ratio of an internal combustion engine according to an air-fuel ratio learning value learned based on a detection value of the air-fuel ratio detection means, and SOx retention when removing sulfur oxide from the SOx retention material. In the exhaust gas purification apparatus for an internal combustion engine, comprising: a first reducing agent adding means for adding a reducing agent into the exhaust gas so that an air-fuel ratio of the exhaust gas flowing into the material is equal to or lower than a stoichiometric air-fuel ratio. Before the means is operated, it is necessary to eliminate the poisoning of the air-fuel ratio detection means, and to correct the air-fuel ratio of the internal combustion engine so that the air-fuel ratio of the internal combustion engine after the poisoning elimination matches the target engine air-fuel ratio. It has the characteristics of
[0030]
As described above, when the regeneration processing of the SOx holding material is started in a state where the air-fuel ratio detecting means is poisoned, the poisoning of the air-fuel ratio detecting means is eliminated, but it is learned when the air-fuel ratio detecting means is poisoned. Since the air-fuel ratio of the internal combustion engine is controlled based on the learned value of the air-fuel ratio, the regeneration processing of the SOx holding material is performed in a state where the actual engine air-fuel ratio is leaner than the target engine air-fuel ratio. It is assumed that the supply amount will increase excessively.
[0031]
In contrast, the exhaust gas purification apparatus for an internal combustion engine according to the present invention eliminates the poisoning of the air-fuel ratio detection means before the regeneration processing of the SOx holding material, and the air-fuel ratio of the internal combustion engine after the poisoning elimination is reduced. The air-fuel ratio of the internal combustion engine is corrected so as to coincide with the target engine air-fuel ratio.
[0032]
In this case, since the actual engine air-fuel ratio when the regeneration processing of the SOx holding material is performed matches the target engine air-fuel ratio, the amount of reducing agent added does not become excessive.
[0033]
The following two methods can be exemplified as a method of matching the actual engine air-fuel ratio with the target engine air-fuel ratio when the regeneration processing of the SOx holding material is performed.
[0034]
(1) further comprising a second reducing agent adding means for adding a reducing agent into the exhaust gas upstream of the SOx holding material in order to raise the exhaust gas temperature;
The poisoning elimination means eliminates poisoning of the air-fuel ratio detection means by operating the second reducing agent addition means,
The air-fuel ratio correction means calculates an actual air-fuel ratio of the internal combustion engine based on a detection value of the air-fuel ratio detection means and a reducing agent addition amount by the second reducing agent addition means, and the air-fuel ratio is The air-fuel ratio of the internal combustion engine is controlled so as to be the target engine air-fuel ratio.
[0035]
(2) further comprising a second reducing agent adding means for adding a reducing agent into the exhaust gas upstream of the SOx holding material to raise the exhaust gas temperature;
The poisoning elimination means eliminates poisoning of the air-fuel ratio detection means by operating the second reducing agent addition means,
The air-fuel ratio correcting means controls the air-fuel ratio of the internal combustion engine so that the detected value of the air-fuel ratio detecting means after the addition of the reducing agent by the second reducing agent adding means becomes the target engine air-fuel ratio.
[0036]
The exhaust gas purification apparatus for an internal combustion engine according to the present invention further includes an EGR mechanism for recirculating a part of the exhaust gas of the internal combustion engine to the internal combustion engine, and the air-fuel ratio correcting means is an exhaust gas recirculated by the EGR mechanism. The air-fuel ratio of the internal combustion engine may be corrected by adjusting the amount (hereinafter referred to as “EGR gas”).
[0037]
For example, the air-fuel ratio correction means may increase the EGR gas amount when lowering the air-fuel ratio of the internal combustion engine, and decrease the EGR gas amount when increasing the air-fuel ratio of the internal combustion engine.
[0038]
With this configuration, the air-fuel ratio correcting unit can correct the air-fuel ratio of the internal combustion engine without changing the fuel injection amount of the internal combustion engine. In particular, when the air-fuel ratio of the internal combustion engine is decreased, the air-fuel ratio correction means may decrease the air-fuel ratio of the internal combustion engine by increasing the EGR gas amount instead of increasing the fuel injection amount of the internal combustion engine. Therefore, it is possible to reduce the fuel injection amount, reduce the unburned fuel component discharged from the internal combustion engine, reduce the nitrogen oxide (NOx) discharged from the internal combustion engine, and the like.
[0039]
Next, the present invention may employ the following means in order to solve the above-described problems. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
An SOx holding material that is provided in an exhaust passage of the internal combustion engine and holds sulfur oxide in the exhaust;
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the air-fuel ratio learning value learned based on the detection value of the air-fuel ratio detection means;
Reducing agent addition means for adding a reducing agent into the exhaust gas upstream of the SOx holding material so that the detected value of the air / fuel ratio detecting means is equal to or lower than the stoichiometric air / fuel ratio when removing sulfur oxide from the SOx holding material; ,
Before the reducing agent adding means starts adding the reducing agent, poisoning eliminating means for eliminating poisoning due to unburned fuel components of the air-fuel ratio detecting means,
Air-fuel ratio correction means for correcting the air-fuel ratio of the internal combustion engine so that the actual air-fuel ratio of the internal combustion engine becomes a desired target engine air-fuel ratio after the start of the operation of the reducing agent addition means. Good.
[0040]
The present invention provides an air-fuel ratio control means for controlling the air-fuel ratio of an internal combustion engine according to an air-fuel ratio learning value learned based on a detection value of the air-fuel ratio detection means, and SOx retention when removing sulfur oxide from the SOx retention material. In an exhaust gas purification apparatus for an internal combustion engine comprising a reducing agent adding means for adding a reducing agent into the exhaust gas so that the air-fuel ratio of the exhaust gas flowing into the material is equal to or lower than the stoichiometric air-fuel ratio, after the operation of the reducing agent adding means is started, The greatest feature is that the air-fuel ratio of the internal combustion engine is corrected so that the actual engine air-fuel ratio becomes the desired target engine air-fuel ratio.
[0041]
As described above, when the regeneration processing of the SOx holding material is started in a state where the air-fuel ratio detecting means is poisoned, the poisoning of the air-fuel ratio detecting means is eliminated, but it is learned when the air-fuel ratio detecting means is poisoned. Since the air-fuel ratio of the internal combustion engine is controlled based on the learned air-fuel ratio, the actual engine air-fuel ratio becomes leaner than the target engine air-fuel ratio.
[0042]
In contrast, the exhaust gas purification apparatus for an internal combustion engine according to the present invention corrects the air-fuel ratio of the internal combustion engine so that the actual engine air-fuel ratio matches the target engine air-fuel ratio during the regeneration processing of the SOx holding material.
[0043]
As described above, when the actual engine air-fuel ratio coincides with the target engine air-fuel ratio during the regeneration processing of the SOx holding material, the amount of reducing agent added from the reducing agent addition means to the exhaust gas in the subsequent regeneration processing decreases. Therefore, an excessive amount of the reducing agent is not oxidized in the SOx holding material.
[0044]
As a method of matching the actual engine air-fuel ratio with the target engine air-fuel ratio during the regeneration processing of the SOx holding material, (1) the actual engine air-fuel ratio is based on the detection value of the air-fuel ratio detection means and the reducing agent addition amount of the reducing agent addition means. And (2) the operation of the reducing agent adding means is temporarily stopped, and the air-fuel ratio detecting means at that time is temporarily stopped in accordance with the deviation between the actual engine air-fuel ratio and the target engine air-fuel ratio. For example, a method of correcting the air-fuel ratio of the internal combustion engine so that the detected value coincides with the target engine air-fuel ratio can be exemplified.
[0045]
The exhaust gas purification apparatus for an internal combustion engine according to the present invention further includes an EGR mechanism for recirculating a part of the exhaust gas of the internal combustion engine to the internal combustion engine, and the air-fuel ratio correction means adjusts the amount of EGR gas. The air-fuel ratio of the internal combustion engine may be corrected as described above.
[0046]
In the present invention, examples of the SOx retention agent include NOx absorbents having oxidation ability such as NOx occlusion reduction type catalysts.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0048]
Here, the case where the exhaust emission control device according to the present invention is applied to a compression ignition internal combustion engine (diesel engine) for driving a vehicle will be described as an example.
[0049]
<First Embodiment>
FIG. 1 shows a schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus according to the first embodiment of the present invention is applied and its intake and exhaust system.
[0050]
An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0051]
The internal combustion engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4, and the common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5.
[0052]
An intake passage 7 is connected to the internal combustion engine 1, and the intake passage 7 is connected to an air cleaner box 8. An air flow meter 9 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake passage 7 is attached to the intake passage 7 downstream of the air cleaner box 8.
[0053]
A compressor housing 10 a of a centrifugal supercharger (turbocharger) 10 is provided in the middle of the intake passage 7. An intercooler 11 is attached to the intake passage 7 downstream of the compressor housing 10a. Further, an intake throttle valve 12 for adjusting the flow rate of intake air flowing through the intake passage 7 is provided in the intake passage 7 downstream of the intercooler 11. An intake throttle actuator 13 is attached to the intake throttle valve 12.
[0054]
An exhaust passage 14 is connected to the internal combustion engine 1, and the exhaust passage 14 is connected to a muffler downstream. A turbine housing 10 b of the centrifugal supercharger 10 is disposed in the middle of the exhaust passage 14.
[0055]
An exhaust purification catalyst 15 for purifying harmful gas components in the exhaust is disposed in a portion of the exhaust passage 14 downstream of the turbine housing 10b. The exhaust purification catalyst 15 occludes nitrogen oxide (NOx) in the exhaust when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 15 is a lean air-fuel ratio (greater than the theoretical air-fuel ratio), and the exhaust purification catalyst 15 The NOx storage reduction catalyst reduces the nitrogen oxide (NOx) stored when the air-fuel ratio of the exhaust gas flowing into the exhaust gas 15 becomes a rich air-fuel ratio (below the theoretical air-fuel ratio).
[0056]
In the exhaust passage 14 downstream of the exhaust purification catalyst 20, an air-fuel ratio sensor 16, which is an air-fuel ratio detection means for outputting an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing in the exhaust passage 14, and the exhaust passage 14 And an exhaust gas temperature sensor 17 for outputting an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust gas. In the present embodiment, the air-fuel ratio sensor 16 is provided in the exhaust passage 14 downstream of the exhaust purification catalyst 20 to detect the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst 20, but upstream of the exhaust purification catalyst 20 Further, an air-fuel ratio sensor may be provided in the exhaust passage 14 to detect the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst 20, and the air-fuel ratio of the exhaust flowing through the exhaust passage 14 may be detected. An air-fuel ratio sensor may be provided only in the exhaust passage 14 upstream of 20 to detect the air-fuel ratio of the exhaust gas flowing through the exhaust passage 14.
[0057]
A portion of the intake passage 7 downstream from the intake throttle valve 12 and a portion of the exhaust passage 14 upstream of the turbine housing 10 b are communicated via an exhaust recirculation passage (hereinafter referred to as “EGR passage”) 18. ing. A flow rate adjustment valve (EGR valve) 19 is provided in the middle of the EGR passage 18.
[0058]
Further, a reducing agent addition valve 21 for adding a fuel as a reducing agent to the exhaust gas flowing through the exhaust port 20 is attached to the exhaust port 20 of the first cylinder 2 of the internal combustion engine 1. Is connected to the fuel pump 6 through a fuel passage 22.
[0059]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 25 for controlling the internal combustion engine 1. The ECU 25 is an arithmetic logic operation circuit including a CPU, ROM, RAM, backup RAM, and the like.
[0060]
Various sensors such as a crank position sensor 23 and a water temperature sensor 24 attached to the internal combustion engine 1 are connected to the ECU 25 through electric wiring in addition to the air flow meter 9, the air-fuel ratio sensor 16, and the exhaust gas temperature sensor 17 described above. The output signals of the various sensors described above are input to the ECU 25.
[0061]
On the other hand, the fuel injection valve 3, the intake throttle actuator 13, the EGR valve 19, the reducing agent addition valve 21 and the like are connected to the ECU 25 through electrical wiring, and the ECU 25 is connected to the fuel injection valve 3, the intake throttle actuator 13, and the EGR. The valve 19 and the reducing agent addition valve 21 can be controlled.
[0062]
For example, the ECU 25 executes input of output signals from various sensors, calculation of engine speed, calculation of fuel injection amount, calculation of fuel injection timing, and the like in a basic routine to be executed at regular intervals. Various signals input by the ECU 25 and various control values obtained by the ECU 25 in the basic routine are temporarily stored in the RAM of the ECU 25.
[0063]
When calculating the fuel injection amount, the ECU 25 calculates the final fuel injection amount Qfin based on the following equation (1).
[0064]
Qfin = Qbse * FAF * KG (i) * A (1)
Qbse: Basic fuel injection amount
FAF: Feedback correction coefficient
KG (i): Air-fuel ratio learning value
A: Increase coefficient
[0065]
Further, the ECU 25 reads various control values from the RAM in an interrupt process triggered by input of signals from various sensors and switches, elapse of a predetermined time, or input of a pulse signal from the crank position sensor 23, and the like. The fuel injection valve 3 is controlled according to the control value.
[0066]
Further, the ECU 25 executes exhaust purification control as described below as interrupt processing based on the crank position sensor 23 or interrupt processing at regular intervals.
[0067]
In the exhaust purification control, the ECU 25 determines whether or not the internal combustion engine 1 is operated at a lean air-fuel ratio continuously for a certain time or more. When the internal combustion engine 1 is continuously operated at a lean air-fuel ratio for a predetermined time or longer, the ECU 25 opens the reducing agent addition valve 21 to regenerate the NOx storage capacity of the exhaust purification catalyst 15.
[0068]
When the reducing agent addition valve 21 is opened, the fuel discharged from the fuel pump 6 is injected into the exhaust port of the first cylinder 2 through the fuel passage 7 and the reducing agent addition valve 21, and then from the exhaust port to the exhaust passage. 14 will be led. The fuel guided to the exhaust passage 14 flows into the turbine housing 10b together with the exhaust flowing from the upstream side of the exhaust passage 14. The exhaust gas flowing into the turbine housing 10b and the reducing agent are agitated and uniformly mixed by the rotation of the turbine wheel to form a rich air-fuel ratio exhaust gas.
[0069]
The rich air-fuel ratio exhaust gas thus formed flows into the exhaust purification catalyst 15 from the turbine housing 10b via the exhaust passage 14, and reduces nitrogen oxides (NOx) absorbed by the exhaust purification catalyst 15. It will be. As a result, nitrogen oxides (NOx) stored in the exhaust purification catalyst 15 are removed from the exhaust purification catalyst 15, and the NOx storage capability of the exhaust purification catalyst 15 is regenerated.
[0070]
By the way, the exhaust purification catalyst 15 occludes sulfur oxide (SOx) in the exhaust gas by the same mechanism as nitrogen oxide (NOx). Therefore, when the occlusion amount of the sulfur oxide (SOx) increases, occlusion occurs accordingly. So-called SOx poisoning occurs in which the NOx storage capacity of the reduced NOx catalyst is reduced.
[0071]
On the other hand, the ECU 25 executes the SOx poisoning elimination process of the exhaust purification catalyst 15 according to the following method.
[0072]
As a method for eliminating SOx poisoning of the exhaust purification catalyst 15, the temperature of the exhaust purification catalyst 15 is raised to a high temperature range of about 500 ° C. to 700 ° C., and the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst 15 is increased. By setting the rich air-fuel ratio, gaseous SO2 is released from the exhaust purification catalyst 15 while releasing sulfur oxide (SOx).2 −An example of the method for reduction is shown.
[0073]
Therefore, the ECU 25 first executes a catalyst temperature raising process to increase the ambient temperature of the exhaust purification catalyst 15.
[0074]
As a method for increasing the atmospheric temperature of the exhaust purification catalyst 15, (1) a method of increasing the exhaust temperature to transmit the heat of the exhaust to the exhaust purification catalyst 15, and (2) oxidizing unburned fuel in the exhaust purification catalyst 15. Thus, a method of raising the temperature of the exhaust purification catalyst 15 itself by the reaction heat generated at that time can be exemplified.
[0075]
As a specific method of the above (1), a method of retarding the combustion timing of the air-fuel mixture in the internal combustion engine 1, fuel is subsidiarily supplied from the fuel injection valve 3 of the cylinder 2 during the expansion stroke in the internal combustion engine 1. Exemplifying a method of injecting, a method of increasing the load of the internal combustion engine 1 by reducing the opening of an exhaust throttle valve (not shown), a method of causing low temperature combustion in the internal combustion engine 1 by increasing the amount of EGR gas, etc. Can do.
[0076]
As a specific method of the above (2), a method of adding fuel into the exhaust gas from the reducing agent addition valve 21, a fuel is secondaryly supplied from the fuel injection valve 3 of the cylinder 2 during the exhaust stroke in the internal combustion engine 1. A method of spraying can be exemplified.
[0077]
When the bed temperature of the exhaust purification catalyst 15 rises to a high temperature range of about 500 ° C. to 700 ° C. by the catalyst temperature raising process as described above, the ECU 25 sets the air / fuel ratio of the exhaust flowing into the exhaust purification catalyst 15 to the rich air / fuel ratio. Therefore, the fuel as the reducing agent is added from the reducing agent addition valve 21 into the exhaust gas.
[0078]
At that time, the ECU 25 feedback-controls the reducing agent addition amount so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 15 becomes a desired target rich air-fuel ratio. Specifically, the ECU 25 feedback-controls the opening degree of the reducing agent addition valve 21 so that the output signal value of the air-fuel ratio sensor 16 matches the target rich air-fuel ratio.
[0079]
This is because the reducing agent added to the exhaust gas is oxidized in the exhaust purification catalyst 15, so if an excessive amount of reducing agent is added to the exhaust gas, a large amount of reducing agent is oxidized in the exhaust purification catalyst 15. This is because the exhaust purification catalyst 15 may be overheated by the amount of heat generated when the reducing agent is oxidized.
[0080]
On the other hand, in a compression ignition type internal combustion engine such as the internal combustion engine 1, since the exhaust temperature tends to be low, HC, which is an unburned fuel component contained in the exhaust, adheres to the air-fuel ratio sensor 16 and the output of the air-fuel ratio sensor 16 So-called sensor poisoning occurs in which the value deviates to the rich side from the actual air-fuel ratio.
[0081]
In this way, under the situation where the air-fuel ratio sensor 16 is poisoned, the aforementioned air-fuel ratio learning coefficient: KG (i) is learned based on the output value of the air-fuel ratio sensor, and the air-fuel ratio learned value: KG (i ), The actual air / fuel ratio of the internal combustion engine 1 (actual engine air / fuel ratio) becomes higher than the target engine air / fuel ratio, that is, the actual engine air / fuel ratio becomes leaner than the target engine air / fuel ratio. (Becomes higher).
[0082]
When the SOx poisoning elimination process described above is executed in a state where the actual engine air-fuel ratio is higher than the target engine air-fuel ratio, the ECU 25 sets the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst 15 to the target rich air-fuel ratio. Therefore, there is a possibility that the amount of the reducing agent added from the reducing agent addition valve 21 is excessively increased (see FIG. 2).
[0083]
Therefore, in the present embodiment, when executing the SOx poisoning elimination process, the ECU 25 executes the sensor poisoning elimination control and resets the air-fuel ratio learning value to the initial value.
[0084]
Specifically, the SOx poisoning elimination processing according to the present embodiment will be described using the flowchart of FIG.
[0085]
First, in step 100, sensor poisoning elimination control is executed. As the sensor poisoning elimination control, for example, the ECU 25 adds the fuel as the reducing agent into the exhaust gas from the reducing agent addition valve 21 in a state where the air-fuel ratio of the internal combustion engine 1 is increased and the oxygen concentration of the exhaust gas is increased. As a result, these unburned fuel components are oxidized in the exhaust purification catalyst 15, and the exhaust temperature in the vicinity of the air-fuel ratio sensor 16 is raised to a high temperature (300 to 500 ° C., preferably 500 ° C. or higher) by the heat generated during the oxidation. To do.
[0086]
The hydrocarbon (HC), which is an unburned fuel component adhering to the air-fuel ratio sensor 16, is sufficiently oxidized at a high temperature of 300 ° C. to 500 ° C. due to the high oxygen concentration. Will be resolved.
[0087]
Next, at step 101, the air-fuel ratio learning value is reset to the initial value. In order to reset the air-fuel ratio learning value, an air-fuel ratio sensor temperature sensor, which is a temperature detecting means for detecting the temperature of the air-fuel ratio sensor, is provided, and the temperature detected by the air-fuel ratio sensor temperature sensor detects the sensor poisoning. The air-fuel ratio learned value learned when the air-fuel ratio is detected as it is, for example, less than 400 ° C., may be reset to the initial value. In such a case, the learned value learned while the air-fuel ratio sensor is not poisoned can be effectively utilized.
[0088]
Next, in step 102, it is determined whether or not the exhaust temperature is equal to or higher than a predetermined temperature T. As described above, in order to eliminate SOx poisoning, the atmosphere temperature of the exhaust purification catalyst 15 is set to a high temperature range of about 500 ° C. to 700 ° C. Therefore, the exhaust temperature detected by the exhaust temperature sensor 17 in this step is It is determined whether or not the predetermined temperature is, for example, 500 ° C. or higher. The predetermined temperature is determined according to the type of the exhaust purification catalyst 15 and the like.
[0089]
If the exhaust temperature is equal to or higher than the predetermined temperature T, the process proceeds to step 103. If the exhaust temperature is lower than T, the process proceeds to step 103 after performing the above-described catalyst temperature raising process in step 104.
[0090]
In step 103, it is determined whether or not the air-fuel ratio of the exhaust gas is a rich air-fuel ratio that is a target air-fuel ratio for eliminating SOx poisoning. If the air-fuel ratio of the exhaust gas is not the target rich air-fuel ratio, the reducing agent addition control is performed in step 105 by adding the reducing agent from the reducing agent addition valve 21 so as to obtain the target rich air-fuel ratio.
[0091]
In this way, even when the exhaust gas temperature shifts from a low exhaust temperature state immediately after the start of the internal combustion engine 1 to the SOx poisoning elimination process, the fuel injection amount according to the air-fuel ratio learned value learned while the sensor is poisoned. Therefore, an appropriate amount of reducing agent is added during the SOx poisoning elimination process (see FIG. 3), and an excessive reducing agent is added to the exhaust purification catalyst 15 and excessive heating occurs. It is possible to prevent the heat deterioration of the exhaust purification catalyst 15 due to the temperature becoming higher.
[0092]
<Second Embodiment>
This embodiment is different from the first embodiment in that only the means for preventing the promotion of thermal deterioration due to the excessive temperature rise of the exhaust purification catalyst 15 when performing the SOx poisoning elimination process is changed. Since other configurations and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.
[0093]
When an excessive reducing agent is added from the reducing agent addition valve 21 when performing the SOx poisoning elimination processing, the reducing agent may burn suddenly in the exhaust purification catalyst 15 and the exhaust purification catalyst 15 may overheat. Therefore, the ECU 25 controls the reducing agent addition amount from the reducing agent addition valve 21 based on the output signal of the air-fuel ratio sensor 16.
[0094]
However, as described in the first embodiment, when the exhaust gas temperature is shifted to a SOx poisoning elimination process immediately after the internal combustion engine 1 is started, the air-fuel ratio sensor 16 performs sensor poisoning. In order to control the reducing agent addition amount from the reducing agent addition valve 21 based on the output signal of the air-fuel ratio sensor 16, first, the sensor poisoning of the air-fuel ratio sensor 16 is eliminated. There is a need. Therefore, first, the above-described sensor poisoning elimination control is performed in order to eliminate air-fuel ratio sensor poisoning.
[0095]
Even if the air-fuel ratio sensor poisoning is eliminated, if the SOx poisoning elimination process described above is executed in a state where the actual engine air-fuel ratio is higher than the target engine air-fuel ratio, the ECU 25 causes the exhaust purification catalyst 15 to There is a possibility that the amount of reducing agent added from the reducing agent addition valve 21 is excessively increased so that the air-fuel ratio of the inflowing exhaust gas becomes the target rich air-fuel ratio (see FIG. 2).
[0096]
Therefore, after the air-fuel ratio sensor poisoning is eliminated, the air-fuel ratio of the internal combustion engine 1 is feedback-controlled based on the difference between the detected value of the air-fuel ratio sensor 16 where the sensor poisoning has been eliminated and the target air-fuel ratio. The control is executed, and the amount of reducing agent added from the reducing agent addition valve 21 is determined after the air-fuel ratio of the internal combustion engine 1 is set to the target air-fuel ratio (see FIG. 4).
[0097]
The following two methods are exemplified as the engine air-fuel ratio control method in which the air-fuel ratio of the internal combustion engine 1 is feedback-controlled based on the difference between the detected value of the air-fuel ratio sensor 16 in which sensor poisoning has been eliminated and the target air-fuel ratio. can do.
[0098]
(1) In executing the sensor poisoning elimination control, a reducing agent is added to increase the temperature to 300 ° C. to 500 ° C. with the air-fuel ratio of the exhaust gas being made high (lean), and the SOx poisoning elimination processing is performed at the temperature. Since the reducing agent is added to make the air-fuel ratio rich at 500 ° C. to 700 ° C., the reducing agent added during the sensor poisoning elimination control is added as it is during the SOx poisoning elimination processing. Subsequently, feedback control is performed by subtracting the added reducing agent from the difference between the detected value of the air-fuel ratio sensor 16 in which sensor poisoning has been eliminated and the target air-fuel ratio.
[0099]
(2) Since the sensor poisoning elimination control is performed by adding fuel as a reducing agent as described above, when the sensor poisoning is eliminated, the addition of the reducing agent is stopped, and the air-fuel ratio sensor 16 in which the sensor poisoning is eliminated. The feedback control is performed based on the difference between the detected value and the target air-fuel ratio.
[0100]
FIG. 6 is a flowchart showing the SOx poisoning elimination process according to the present embodiment. Compared to the flowchart of the SOx poisoning elimination process according to the first embodiment, FIG. Instead of resetting the air-fuel ratio learning value at step 101 of FIG. Others are the same as in FIG.
[0101]
In this way, when performing the SOx poisoning elimination process, first, after performing the sensor poisoning elimination control, the deviation between the target air-fuel ratio and the detected value of the air-fuel ratio sensor 16 is fed back, and the air-fuel ratio of the internal combustion engine 1 is fed back. When the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 15 is set to the target rich air-fuel ratio by controlling the fuel ratio, no reducing agent is added based on the lean air-fuel ratio of the internal combustion engine. Further, it is possible to prevent the heat purification of the exhaust purification catalyst 15 from being accelerated due to the excessive addition of the reducing agent and the exhaust purification catalyst 15 being overheated.
[0102]
Further, as described above, the SOx poisoning elimination processing is executed by setting the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 15 from the lean state during the execution of the sensor poisoning elimination control, but the exhaust air-fuel ratio is changed from lean to rich. However, when the air-fuel ratio of the internal combustion engine 1 is made rich to some extent, the amount of fuel injected from the fuel injection valve 3 is not increased and made rich, but the exhaust amount recirculated into the engine by the EGR mechanism is increased. You may make it rich.
[0103]
This is a method in which the fuel injection amount is increased from the fuel injection valve 3 to enrich the air-fuel ratio, and unburnt fuel contributes to the heat generation of the catalyst, and thus the catalyst may be overheated. On the other hand, in the method of increasing the amount of exhaust gas recirculated into the internal combustion engine by the EGR mechanism, the EGR gas is exhausted after combustion, and therefore contributes little to the heat generation of the catalyst, thereby suppressing overheating of the catalyst. It is.
[0104]
EGR gas contains water (H2O) and carbon dioxide (CO2) And the like, and an inert gas component having endothermic properties is contained in the mixture, so if EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. This is because the generation amount of nitrogen oxides (NOx) is suppressed.
[0105]
In addition, when adding a reducing agent when performing sensor poisoning elimination control, a reducing agent addition means for adding a reducing agent for sensor poisoning elimination, and a reducing agent for adding a reducing agent for SOx poisoning elimination processing As the addition means, the reducing agent addition valve 21 which is the same in the above-described embodiment is used, but different ones may be used as long as the space or the like is not particularly limited.
[0106]
<Third Embodiment>
This embodiment is different from the first embodiment in that only the means for preventing the promotion of thermal deterioration due to the excessive temperature rise of the exhaust purification catalyst 15 when performing the SOx poisoning elimination process is changed. Since other configurations and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.
[0107]
When an excessive reducing agent is added from the reducing agent addition valve 21 when performing the SOx poisoning elimination processing, the reducing agent may burn suddenly in the exhaust purification catalyst 15 and the exhaust purification catalyst 15 may overheat. Therefore, the ECU 25 controls the reducing agent addition amount from the reducing agent addition valve 21 based on the output signal of the air-fuel ratio sensor 16.
[0108]
However, as described in the first embodiment, when the exhaust gas temperature is shifted to a SOx poisoning elimination process immediately after the internal combustion engine 1 is started, the air-fuel ratio sensor 16 performs sensor poisoning. In order to control the reducing agent addition amount from the reducing agent addition valve 21 based on the output signal of the air-fuel ratio sensor 16, first, the sensor poisoning of the air-fuel ratio sensor 16 is eliminated. There is a need. Therefore, first, the above-described sensor poisoning elimination control is executed to eliminate the air-fuel ratio sensor poisoning.
[0109]
Even if the air-fuel ratio sensor poisoning is eliminated, if the SOx poisoning elimination process described above is executed in a state where the actual engine air-fuel ratio is higher than the target engine air-fuel ratio, the ECU 25 causes the exhaust purification catalyst 15 to There is a possibility that the amount of reducing agent added from the reducing agent addition valve 21 is excessively increased so that the air-fuel ratio of the inflowing exhaust gas becomes the target rich air-fuel ratio (see FIG. 2).
[0110]
Therefore, when the reducing agent addition control is performed by adding the reducing agent from the reducing agent addition valve 21 after eliminating the air-fuel ratio sensor poisoning, the detected value of the air-fuel ratio sensor 16 in which the sensor poisoning has been eliminated An engine air-fuel ratio control is performed in which the air-fuel ratio of the internal combustion engine 1 is feedback-controlled based on the difference from the target air-fuel ratio. In the second embodiment, the engine air-fuel ratio control is executed, and after the air-fuel ratio of the internal combustion engine 1 is matched with the target air-fuel ratio, the reducing agent addition control is executed. In the present embodiment, The engine air-fuel ratio control is executed while the reducing agent addition control is executed.
[0111]
As a technique for executing the engine air-fuel ratio control while executing the reducing agent addition control, (1) the detected value of the air-fuel ratio sensor 16 in which sensor poisoning has been eliminated and the reducing agent addition amount of the reducing agent addition valve 21 are used. A method for calculating the air-fuel ratio of the internal combustion engine 1 based on the difference between the air-fuel ratio of the internal combustion engine 1 and the target engine air-fuel ratio, and (2) a reducing agent for the reducing agent addition valve 21. An example is a method in which the addition is temporarily stopped, the air-fuel ratio of the internal combustion engine 1 is corrected so that the detected value of the air-fuel ratio sensor 16 coincides with the target engine air-fuel ratio, and then the reducing agent addition is started again. can do.
[0112]
Specifically, the SOx poisoning elimination processing according to the present embodiment will be described using the flowchart of FIG.
[0113]
First, at step 300, the above-described sensor poisoning elimination control is executed.
[0114]
Next, in step 301, it is determined whether or not the exhaust temperature is equal to or higher than a predetermined temperature T. As described above, in order to eliminate SOx poisoning, the atmosphere temperature of the exhaust purification catalyst 15 is set to a high temperature range of about 500 ° C. to 700 ° C. Therefore, the exhaust temperature detected by the exhaust temperature sensor 17 in this step is It is determined whether or not the predetermined temperature is, for example, 500 ° C. or higher. The predetermined temperature is determined according to the type of the exhaust purification catalyst 15 and the like.
[0115]
If the exhaust temperature is equal to or higher than the predetermined temperature T, the process proceeds to step 302. If the exhaust temperature is lower than T, the process proceeds to step 302 after performing the above-described catalyst temperature raising process in step 303.
[0116]
In step 302, it is determined whether or not the air-fuel ratio of the exhaust gas is a rich air-fuel ratio that is a target air-fuel ratio for eliminating SOx poisoning. If the air-fuel ratio of the exhaust gas is not the target rich air-fuel ratio, the reducing agent addition control is performed in step 304 by adding the reducing agent from the reducing agent addition valve 21 so as to obtain the target rich air-fuel ratio. At this time, the engine air-fuel ratio control described above is executed.
[0117]
In this way, when performing the SOx poisoning elimination process, first, after performing the sensor poisoning elimination control, the reducing agent is added and the detection value of the air-fuel ratio sensor 16 is set to the target rich air-fuel ratio. When the air-fuel ratio of the internal combustion engine 1 coincides with the target engine air-fuel ratio, the subsequent reducing agent addition amount becomes an appropriate amount, so that an excessive amount of reducing agent is oxidized in the exhaust purification catalyst 15. Nothing will happen. Further, it is possible to prevent the exhaust purification catalyst 15 from being promoted to be thermally deteriorated due to the excessive addition of the reducing agent and the exhaust purification catalyst 15 being overheated.
[0118]
Further, as described above, the SOx poisoning elimination processing is executed by setting the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 15 from the lean state during the execution of the sensor poisoning elimination control, but the exhaust air-fuel ratio is changed from lean to rich. However, when the air-fuel ratio of the internal combustion engine 1 is made rich to some extent, the amount of fuel injected from the fuel injection valve 3 is not increased and made rich, but the exhaust amount recirculated into the engine by the EGR mechanism is increased. You may make it rich.
[0119]
This is a method in which the fuel injection amount is increased from the fuel injection valve 3 to enrich the air-fuel ratio, and unburnt fuel contributes to the heat generation of the catalyst, and thus the catalyst may be overheated. On the other hand, in the method of increasing the amount of exhaust gas recirculated into the internal combustion engine by the EGR mechanism, the EGR gas is exhausted after combustion, and therefore contributes little to the heat generation of the catalyst, thereby suppressing overheating of the catalyst. It is.
[0120]
EGR gas contains water (H2O) and carbon dioxide (CO2) And the like, and an inert gas component having endothermic properties is contained in the mixture, so if EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. This is because the generation amount of nitrogen oxides (NOx) is suppressed.
[0121]
【The invention's effect】
As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present invention retains SOx while preventing the deterioration of the SOx retaining material that retains sulfur oxide (SOx) in the exhaust gas, such as a NOx absorbent, etc. SOx can be removed from the material.
[0122]
Further, when SOx is removed by lowering the air-fuel ratio of the exhaust flowing into the SOx holding material, the amount of exhaust gas recirculated into the engine by the EGR mechanism is increased to lower the air-fuel ratio in the engine, thereby reducing the air-fuel mixture. The combustion temperature can be lowered and the amount of nitrogen oxide (NOx) generated can be suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2 is a graph showing changes in the air-fuel ratio of the internal combustion engine and the temperature of the NOx storage reduction catalyst when the present invention is not applied.
FIG. 3 is a graph showing changes in the air-fuel ratio of the internal combustion engine and the temperature of the NOx storage reduction catalyst when the exhaust gas purification apparatus according to the first embodiment of the present invention is used.
FIG. 4 is a diagram showing changes in the air-fuel ratio of an internal combustion engine when using an exhaust emission control device according to a second embodiment of the present invention.
FIG. 5 is a flowchart of SOx poisoning elimination processing according to the first embodiment of the present invention.
FIG. 6 is a flowchart of SOx poisoning elimination processing according to the second embodiment of the present invention.
FIG. 7 is a flowchart of SOx poisoning elimination processing according to a third embodiment of the present invention.
[Explanation of symbols]
1 Internal combustion engine
2-cylinder
3 Fuel injection valve
4 Common rail
5 Fuel supply pipe
6 Fuel pump
7 Intake passage
8 Air cleaner box
9 Air flow meter
10 Centrifugal supercharger
11 Intercooler
12 Inlet throttle valve
13 Inlet throttle actuator
14 Exhaust passage
15 Exhaust gas purification catalyst
16 Air-fuel ratio sensor
17 Exhaust temperature sensor
18 EGR passage
19 EGR valve
20 Exhaust port
21 Reducing agent addition valve
22 Reducing agent supply path
23 Crank position sensor
24 Water temperature sensor
25 ECU

Claims (7)

内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するＳＯｘ保持材と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて学習される空燃比学習値に従って、内燃機関の空燃比を制御する空燃比制御手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去する際に、前記空燃比検出手段の検出値を理論空燃比以下とすべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第１の還元剤添加手段と、
前記第１の還元剤添加手段が還元剤の添加を開始する前に、前記空燃比検出手段の未燃燃料成分による被毒を解消させる被毒解消手段と、
前記空燃比検出手段の被毒解消後であって前記第１の還元剤添加手段が還元剤の添加を開始する前に、内燃機関の空燃比が所望の目標機関空燃比となるように前記内燃機関の空燃比を補正する空燃比補正手段と、
を備えることを特徴とする内燃機関の排気浄化装置。An SOx holding material that is provided in an exhaust passage of the internal combustion engine and holds sulfur oxide in the exhaust;
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the air-fuel ratio learning value learned based on the detection value of the air-fuel ratio detection means;
A first reducing agent that adds a reducing agent into the exhaust gas upstream of the SOx holding material so that the detected value of the air-fuel ratio detecting means is equal to or lower than the stoichiometric air-fuel ratio when removing sulfur oxide from the SOx holding material. Addition means;
Poisoning elimination means for eliminating the poisoning due to the unburned fuel component of the air-fuel ratio detection means before the first reducing agent addition means starts adding the reducing agent;
The internal combustion engine is configured so that the air-fuel ratio of the internal combustion engine becomes a desired target engine air-fuel ratio after the poisoning of the air-fuel ratio detection means is eliminated and before the first reducing agent addition means starts adding the reducing agent. Air-fuel ratio correcting means for correcting the air-fuel ratio of the engine;
An exhaust emission control device for an internal combustion engine, comprising: 排気温度を上昇させるべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第２の還元剤添加手段を更に備え、
前記被毒解消手段は、前記第２の還元剤添加手段を作動させることにより前記空燃比検出手段の被毒を解消させ、
前記空燃比補正手段は、前記空燃比検出手段の検出値と前記第２の還元剤添加手段による還元剤添加量とに基づいて前記内燃機関の実際の空燃比を演算し、その空燃比が前記目標機関空燃比となるように前記内燃機関の空燃比を制御することを特徴とする請求項１に記載の内燃機関の排気浄化装置。A second reducing agent adding means for adding a reducing agent into the exhaust gas upstream of the SOx holding material to raise the exhaust gas temperature;
The poisoning elimination means eliminates poisoning of the air-fuel ratio detection means by operating the second reducing agent addition means,
The air-fuel ratio correction means calculates an actual air-fuel ratio of the internal combustion engine based on a detection value of the air-fuel ratio detection means and a reducing agent addition amount by the second reducing agent addition means, and the air-fuel ratio is an exhaust purification system of an internal combustion engine according to claim 1, characterized in that to control the air-fuel ratio of the internal combustion engine so that the target engine air-fuel ratio. 排気温度を上昇させるべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する第２の還元剤添加手段を更に備え、
前記被毒解消手段は、前記第２の還元剤添加手段を作動させることにより前記空燃比検出手段の被毒を解消させ、
前記空燃比補正手段は、前記第２の還元剤添加手段による還元剤添加終了後の前記空燃比検出手段の検出値が前記目標機関空燃比となるように前記内燃機関の空燃比を制御することを特徴とする請求項１に記載の内燃機関の排気浄化装置。A second reducing agent adding means for adding a reducing agent into the exhaust gas upstream of the SOx holding material to raise the exhaust gas temperature;
The poisoning elimination means eliminates poisoning of the air-fuel ratio detection means by operating the second reducing agent addition means,
The air-fuel ratio correcting means controls the air-fuel ratio of the internal combustion engine so that the detection value of the air-fuel ratio detecting means after the addition of the reducing agent by the second reducing agent adding means becomes the target engine air-fuel ratio. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 . 内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するＳＯｘ保持材と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて学習される空燃比学習値に従って、内燃機関の空燃比を制御する空燃比制御手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去する際に、前記空燃比検出手段の検出値を理論空燃比以下とすべく前記ＳＯｘ保持材の上流の排気中へ還元剤を添加する還元剤添加手段と、
前記還元剤添加手段が還元剤の添加を開始する前に、前記空燃比検出手段の未燃燃料成分による被毒を解消させる被毒解消手段と、
前記還元剤添加手段の作動開始後に、前記内燃機関の実際の空燃比が所望の目標機関空燃比となるように前記内燃機関の空燃比を補正する空燃比補正手段と、を備えることを特徴とする内燃機関の排気浄化装置。An SOx holding material that is provided in an exhaust passage of the internal combustion engine and holds sulfur oxide in the exhaust;
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the air-fuel ratio learning value learned based on the detection value of the air-fuel ratio detection means;
Reducing agent addition means for adding a reducing agent into the exhaust gas upstream of the SOx holding material so that the detected value of the air / fuel ratio detecting means is equal to or lower than the stoichiometric air / fuel ratio when removing sulfur oxide from the SOx holding material; ,
Before the reducing agent adding means starts adding the reducing agent, poisoning eliminating means for eliminating poisoning due to unburned fuel components of the air-fuel ratio detecting means,
Air-fuel ratio correcting means for correcting the air-fuel ratio of the internal combustion engine so that the actual air-fuel ratio of the internal combustion engine becomes a desired target engine air-fuel ratio after the start of the operation of the reducing agent adding means. An exhaust purification device for an internal combustion engine. 前記空燃比補正手段は、前記空燃比検出手段の検出値と前記還元剤添加手段による還元剤添加量とに基づいて前記内燃機関の実際の空燃比を演算し、その空燃比が前記目標機関空燃比となるように前記内燃機関の空燃比を制御することを特徴とする請求項４に記載の内燃機関の排気浄化装置。The air-fuel ratio correction means calculates an actual air-fuel ratio of the internal combustion engine based on a detection value of the air-fuel ratio detection means and a reducing agent addition amount by the reducing agent addition means, and the air-fuel ratio is calculated as the target engine air-fuel ratio. 5. The exhaust gas purification apparatus for an internal combustion engine according to claim 4 , wherein the air-fuel ratio of the internal combustion engine is controlled so as to be the fuel ratio. 前記空燃比補正手段は、前記還元剤添加手段の作動を一時的に停止させ、その際の空燃比検出手段の検出値が前記目標機関空燃比となるように前記内燃機関の空燃比を制御することを特徴とする請求項４に記載の内燃機関の排気浄化装置。The air-fuel ratio correcting means temporarily stops the operation of the reducing agent adding means and controls the air-fuel ratio of the internal combustion engine so that the detection value of the air-fuel ratio detecting means at that time becomes the target engine air-fuel ratio. The exhaust emission control device for an internal combustion engine according to claim 4 , wherein the exhaust gas purification device is an internal combustion engine. 内燃機関の排気の一部を該内燃機関に再循環させるＥＧＲ機構を更に備え、
前記空燃比制御手段は、前記ＥＧＲ機構により再循環される排気量を調節することにより前記内燃機関の空燃比を制御することを特徴とする請求項１〜６の何れか１項に記載の内燃機関の排気浄化装置。An EGR mechanism for recirculating a part of the exhaust gas of the internal combustion engine to the internal combustion engine;
The internal combustion engine according to any one of claims 1 to 6 , wherein the air-fuel ratio control means controls an air-fuel ratio of the internal combustion engine by adjusting an exhaust amount recirculated by the EGR mechanism. Engine exhaust purification system.
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