JP3750195B2 - Nitrogen oxide purification device for internal combustion engine - Google Patents

Nitrogen oxide purification device for internal combustion engine Download PDF

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JP3750195B2
JP3750195B2 JP16083396A JP16083396A JP3750195B2 JP 3750195 B2 JP3750195 B2 JP 3750195B2 JP 16083396 A JP16083396 A JP 16083396A JP 16083396 A JP16083396 A JP 16083396A JP 3750195 B2 JP3750195 B2 JP 3750195B2
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fuel injection
temperature
catalyst
cylinder
catalyst device
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JPH09317524A (en
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兼仁 中村
司 窪島
耕一 大畑
肇 勝呂
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Denso Corp
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Denso Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/008—Controlling each cylinder individually
    • F02D41/0082—Controlling each cylinder individually per groups or banks
    • 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
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/9454—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] 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
    • 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
    • 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
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • 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
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2053—By-passing catalytic reactors, e.g. to prevent overheating
    • 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
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • F02D41/405—Multiple injections with post injections
    • 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
    • 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
    • Y02T10/12—Improving ICE efficiencies
    • 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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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Biomedical Technology (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Description

【０００１】
【技術分野】
本発明は，内燃機関の排気ガスに含まれる窒素酸化物を浄化する排気浄化装置に関するものである。
【０００２】
【従来技術】
ディーゼルエンジン等の内燃機関から排出される窒素酸化物（ＮＯｘ）は金属担持ゼオライト等を用いた触媒装置を用いて浄化されている。そして，上記触媒装置の浄化率は，図２の符号５１の曲線に示すように，特定の温度範囲（同図のＴ１〜Ｔ３，例えば２００〜３００℃）でだけ高い浄化率を示している。また，この窒素酸化物の触媒装置は，例えば燃料等のＨＣ（炭化水素）成分を添加することにより反応が促進されることが知られている。そのため，触媒装置の上流から軽油等の還元剤を供給して排気ガスと混合し，窒素酸化物の浄化を促進する方法が提案されている。
【０００３】
そして，上記観点だけから言えば，窒素酸化物の浄化率を高めるためには，還元剤であるＨＣを多く供給すれば良いことになる。しかしながら，ＨＣの供給を増やすとＨＣの反応熱により触媒装置の温度が上昇し，上記図２に示したＴ２近傍の浄化率の良好な温度範囲を越えてしまうこととなる。そのため，その状態に応じて適当な量のＨＣを添加し，浄化率の高い状態に触媒装置を維持する必要がある。
【０００４】
そこで，特開平４−２１４９１９号公報では，触媒とＨＣ供給装置とを備えたユニットを複数設け，所定の温度範囲にあるユニットに対してのみＨＣ供給装置を作動させて触媒の過熱を防止し，窒素酸化物の浄化率を向上させる浄化装置が提案されている。
【０００５】
【解決しようとする課題】
しかしながら，上記特開平４−２１４９１９号公報に示された窒素酸化物浄化装置は，触媒装置の数だけＨＣ供給装置が必要となり，装置の構成が複雑となり，大形でコストの高いものとなるという不具合がある。
本発明は，かかる従来の問題点に鑑みてなされたものであり，より簡素な構成により，窒素酸化物の浄化率を高めることのできる優れた窒素酸化物浄化装置を提供しようとするものである。
【０００６】
【課題の解決手段】
請求項１の発明は，気筒毎に設けられた燃料噴射手段と，上記燃料噴射手段を制御する燃料噴射制御手段と，排気通路に配置され窒素酸化物を還元浄化する複数の触媒装置と，上記触媒装置の温度を測定または推定する触媒温度判定手段と，少なくとも気筒の行程位置を検知することの出来る運転状態検知手段とを有する内燃機関の窒素酸化物浄化装置であって，
上記触媒装置は，排気通路の上流側に配置された第１触媒装置と，この第１触媒装置の下流側に直列に配置された第２触媒装置とからなると共に，上記気筒は上記第１触媒装置の上流に接続された第１の気筒群と上記第１触媒装置と第２触媒装置との間の排気通路に接続された第２の気筒群とからなり，
上記燃料噴射制御手段は，上記触媒温度判定手段及び運転状況検知手段の出力信号を受け，圧縮上死点近傍における機関出力発生のための主燃料噴射指令と，膨張行程または排気行程における炭化水素供給のための後燃料噴射指令とを上記燃料噴射手段に対して各気筒毎に発し，上記第１触媒装置又は上記第２触媒装置の温度に対応して各気筒または上記気筒群に対する上記後燃料噴射の量を，上記各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図れるだけの炭化水素供給量が上記第１触媒装置および上記第２触媒装置の両触媒装置に供給されるように調整することを特徴とする内燃機関の窒素酸化物浄化装置にある。
【０００７】
上記，燃料噴射制御手段は，機関出力発生のための主燃料噴射指令と，炭化水素供給のための後燃料噴射指令とを各気筒毎または各気筒群毎に発する。そして，燃料噴射制御手段は，触媒温度判定手段により判定した第１触媒装置及び第２触媒装置の温度に対応して後燃料噴射の量を，各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図れるだけの炭化水素供給量が上記第１触媒装置および上記第２触媒装置の両触媒装置に供給されるように調整する。
【０００８】
上記のように構成されているため，第１の気筒群から排出された排気ガスは，第１の触媒装置に流入し，一方第２の触媒装置には，第２の気筒群から排出された排気ガスと第１触媒装置で浄化された排気ガスとが流入する。そして，後燃料噴射量は気筒毎または気筒群毎に設定できるから，第１触媒装置に供給されるＨＣ還元剤の量，即ち後燃料噴射の量と，第２触媒装置に供給されるＨＣ還元剤の量，即ち後燃料噴射の量とを別個に設定することができる。
【０００９】
それ故，触媒温度判定手段によって判定した第１，第２触媒装置の温度状態に合わせて適切なＨＣ還元剤を各触媒装置に供給することができる。即ち，無駄なＨＣ（後燃料）は触媒装置に供給せず，適切な量のＨＣ（後燃料）を供給し，触媒装置を出来るだけ浄化率の高い状態に制御することが可能となる。
なお，上記後燃料噴射は，膨張行程または排気行程において噴射されるから，気筒内の熱により窒素酸化物の還元に適したＨＣに変化させうるという効果も有している。
【００１０】
次に，請求項２記載のように，請求項１において，上記燃料噴射制御手段は，上記第１の触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記第１の触媒装置の温度が低温の第１の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が上記第１の触媒装置の温度の上昇と共に上昇する第２の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が上記第１の触媒装置の温度の上昇と共に下降する第３の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記第１の触媒装置の温度が高温の第４の温度ゾーンとに温度ゾーンを区分し，
各温度ゾーン毎に各気筒または各気筒群に対する上記後燃料噴射量の大きさ及び配分比率を変化させることを特徴とする内燃機関の窒素酸化物浄化装置とすることが好ましい。
即ち，触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する低温の第１の温度ゾーン（図２のＴ１以下）と，窒素酸化物の浄化率が温度と共に上昇する第２の温度ゾーン（図２のＴ１〜Ｔ２）と，窒素酸化物の浄化率が温度と共に下降する第３の温度ゾーン（図２のＴ２〜Ｔ３）と，窒素酸化物の浄化率が極めて低いレベルで推移する高温の第４の温度ゾーン（図２のＴ３以上）とに温度ゾーンを区分し，各温度ゾーン毎に各気筒または各気筒群に対する後燃料噴射量の大きさ及び配分比率を変化させることにより，効果的な窒素酸化物の浄化を達成することができる（後述する実施形態例参照）。
【００１１】
何故ならば，上記各温度ゾーンによって温度に対する浄化率の増減傾向が全く異なってくるから，その特性に適合した後燃料噴射の制御を行わないと浄化率の最大化を図ることが出来ないからである。
例えば，第２の温度ゾーンと第３の温度ゾーンの間の関係では，請求項３記載のように，第３の温度ゾーンにおいては，第１の気筒群に属する気筒に対して第２の温度ゾーンにおける後燃料噴射量よりも小さい後燃料噴射量を設定し，第２の気筒群に属する気筒に対しては第２の温度ゾーンにおける後燃料噴射量よりも大きい後燃料噴射量を設定することが好ましい。
【００１２】
即ち，第３の温度ゾーンでは，浄化率の最大温度を過ぎた温度の高い上流の第１触媒装置の過昇温を抑制する必要があり，一方，相対的に温度が低い第２の触媒装置を高い浄化率の温度にするためには，通常ＨＣを供給して浄化率を向上させることが適切な制御となるからである。
【００１３】
なお，上記請求項１から請求項３の技術思想に基づく構成は，触媒装置が２個の場合にのみ有効なものではなく，２個を越える３個以上の触媒装置を設ける場合にも適用可能である。
即ち，請求項４に記載のように，気筒毎に設けられた燃料噴射手段と，上記燃料噴射手段を制御する燃料噴射制御手段と，排気通路に配置され窒素酸化物を還元浄化する複数の触媒装置と，上記触媒装置の温度を測定または推定する触媒温度判定手段と，少なくとも気筒の行程位置を検知することの出来る運転状態検知手段とを有する内燃機関の窒素酸化物浄化装置であって，
上記触媒装置は，上流側から第１触媒装置，第２触媒装置，・・・，第Ｎ触媒装置の順序で排気通路に直列に配置されたＮ個の触媒装置からなり，
一方，全体の気筒は，単一または複数の気筒によって構成されるＮ個の気筒群からなると共に，第１の気筒群は上記第１触媒装置の上流に接続され，１を越える自然数Ｉにおける第Ｉ番目の気筒群は上記第（Ｉ−１）触媒装置と第Ｉ触媒装置との間の排気通路に接続されており，
上記燃料噴射制御手段は，上記触媒温度判定手段及び運転状況検知手段の出力信号を受け，圧縮上死点近傍における機関出力発生のための主燃料噴射指令と，膨張行程または排気行程における炭化水素供給のための後燃料噴射指令とを上記燃料噴射手段に対して各気筒毎に発し，上記Ｎ個の触媒装置の温度に対応して各気筒または上記気筒群に対する上記後燃料噴射の量を，各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図れるだけの炭化水素供給量が上記第１触媒装置および上記第２触媒装置の両触媒装置に供給されるように調整することを特徴とする内燃機関の窒素酸化物浄化装置がある。
本発明においては，触媒装置の数をＮ個とすると共に気筒をＮ個の気筒群に分割し，各触媒装置の温度に対応して後燃料噴射の量を調整し，各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図る。
【００１４】
そして，上記のように構成することにより，第Ｉの気筒群から排出された排気ガスは，第Ｉの触媒装置に流入し，一方第（Ｉ＋１）番目の触媒装置には，第（Ｉ＋１）番目の気筒群から排出された排気ガスと第Ｉ触媒装置で浄化された排気ガスとが流入する。そして，後燃料噴射量は気筒毎または気筒群毎に設定できるから，第Ｉ触媒装置に供給されるＨＣ還元剤の量，即ち後燃料噴射の量と，第（Ｉ＋１）触媒装置に供給されるＨＣ還元剤の量，即ち後燃料噴射の量とを別個に設定することができる。
【００１５】
それ故，触媒温度判定手段によって判定した第Ｉ，第（Ｉ＋１）触媒装置の温度状態に合わせて適切なＨＣ還元剤を各触媒装置に供給することができる。即ち，無駄なＨＣ（後燃料）は触媒装置に供給せず，適切な量のＨＣ（後燃料）を供給し，触媒装置を出来るだけ浄化率の高い状態に制御することが可能となる。
そして，触媒装置が３個以上の場合にも請求項５，請求項６記載の発明により，前記請求項２または請求項３と同様の作用効果を奏することが可能となる。
【００１６】
また，上記請求項１から請求項６の各構成において，更に請求項７記載のように，上流側に配置される触媒装置の窒素酸化物浄化可能温度範囲を，下流側に配置される触媒装置の窒素酸化物浄化可能温度範囲よりも低温とすることが好ましい。このように構成することにより，始動時等において昇温の容易な上流側の触媒装置を迅速に昇温し，より低い温度で素早く活性化することが可能となるからである。
【００１７】
また，請求項８記載のように，気筒群におけるトータルの後燃料噴射量を設定し，その気筒群における全後燃料噴射をその気筒群内の一部の気筒に集中させて噴射させるようにすることが好ましい。何故ならば，各気筒に均一に後燃料噴射量を設定した場合より，一部の気筒に後燃料噴射を集中させることにより，噴射させる気筒における後燃料噴射の噴射量を相対的に大きくすることができ，燃料噴射手段は相対的に動作性能（例えば弁の応答速度や操作可能な最小操作量）の低いものを用いることが可能となるからである。
【００１８】
また，請求項９記載のように，上記後燃料噴射量に加えて，更に気筒群毎に主燃料噴射の量を調整することにより，より適切に各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図ることが可能となる。
即ち，気筒群におけるトータルの主燃料噴射量を調整することにより，その気筒群の接続された触媒装置に流入する排気ガスの量が変化し，これによって触媒装置の昇温速度や降温速度を制御することが可能となるからである。
【００１９】
例えば，請求項１１記載のように，触媒装置が２つである場合には，前記第１の温度ゾーンにおいては主燃料噴射を第１の気筒群に集中させて第１触媒装置の昇温を促進し，請求項２記載の前記第４の温度ゾーンにおいては主燃料噴射を第１の気筒群に集中させて第２触媒装置の冷却を促進すると好適である。
【００２０】
即ち，前記第１の温度ゾーンにおいては主燃料噴射を第１の気筒群に集中させることにより排気ガスの流入を第１触媒装置に集中して第１触媒装置の昇温を促進し，第１触媒装置の浄化率を迅速に高めることが可能となる。また，前記第４の温度ゾーンにおいては主燃料噴射を第１の気筒群に集中させて排気ガスの流入を第１触媒装置に集中して第２触媒装置を冷却し第２触媒装置を浄化率の高いより低温の領域の移行させることが可能となるからである。そして，後者の場合には，高い浄化率を保持する第２触媒装置において全ての排気ガスの窒素酸化物の浄化を行わせる。
【００２１】
そして，触媒装置の数をＮ個とし，より一般化した場合にも，請求項１０に記載のように，上流側に位置する第Ｉ番目の触媒装置の温度が第１の温度ゾーンにある場合おいては主燃料噴射を第Ｉ番目の気筒群に集中させて第Ｉ触媒装置の昇温を促進し，第４の温度ゾーンにある場合においては主燃料噴射を第Ｉ番目の気筒群に集中させて第（Ｉ＋１）番目以降の下流の触媒装置の冷却を促進することにより，同様の効果を得ることができる。
【００２２】
【発明の実施の形態】
実施形態例１
本例は，図１に示すように，気筒８１〜８４毎に設けられた燃料噴射手段としての電磁弁式インジェクタ１１〜１４と，燃料噴射手段（電磁弁式インジェクタ１１〜１４）を制御する燃料噴射制御手段としての電子制御装置（ＥＣＵ）４０と，排気通路３５，３４に配置され窒素酸化物を還元浄化する複数の触媒装置２１，２２と，各触媒装置２１，２２の温度を測定する触媒温度判定手段としての排気温度センサー２４〜２６と，少なくとも気筒８１〜８４の行程位置を検知することの出来る運転状態検知手段としてのエンジンの回転センサー２８及びアクセルセンサー２９とを有する内燃機関の窒素酸化物浄化装置１である。
【００２３】
触媒装置２１，２２は，排気通路３４〜３７の上流側に配置された第１触媒装置２１と，この第１触媒装置２１の下流側に直列に配置された第２の触媒装置２２とからなると共に，気筒８１〜８４は，第１触媒装置２１の上流に接続された第１の気筒８１〜８３群と，第１触媒装置２１と第２触媒装置２２との間の排気通路３６に接続された第２の気筒８４群とからなる（即ち，請求項４記載のＮ＝２に相当する）。
【００２４】
そして，燃料噴射制御手段としての電子制御装置（ＥＣＵ）４０は，上記触媒温度判定手段及び上記運転状況検知手段の出力信号を受け，圧縮上死点近傍における機関出力発生のための主燃料噴射指令と，膨張行程または排気行程における炭化水素供給のための後燃料噴射指令とを上記燃料噴射手段に対して各気筒８１〜８４毎に発し，第１触媒装置２１または第２触媒装置２２の温度に対応して各気筒８１〜８４または気筒８１〜８３群，気筒８４群に対する上記後燃料噴射の量（波形ｂ１〜ｂ４，図３〜図６）を調整し，各触媒装置２１，２２の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図る。
【００２５】
即ち，燃料噴射制御手段（ＥＣＵ４０）は，第１の触媒装置２１の窒素酸化物の浄化率が極めて低いレベルで推移する低温の第１の温度ゾーン（図２のＴ＜Ｔ１）と，第１の触媒装置２１の窒素酸化物の浄化率が温度Ｔと共に上昇する第２の温度ゾーン（図２のＴ１＜Ｔ＜Ｔ２）と，第１の触媒装置２１の窒素酸化物の浄化率が温度Ｔと共に下降する第３の温度ゾーン（図２のＴ２＜Ｔ＜Ｔ３）と，第１の触媒装置２１の窒素酸化物の浄化率が極めて低いレベルで推移する高温の第４の温度ゾーン（図２のＴ＞Ｔ３）とに温度ゾーンを区分し，図３〜図６に示すように各温度ゾーン毎に各気筒８１〜８３群，気筒８４群に対する前記後燃料噴射量（波形ｂ１〜ｂ４）の大きさ及び配分比率を変化させる。
【００２６】
例えば，図５に示すように，第３の温度ゾーンにおいては，第１の気筒群に属する気筒８１〜８３に対して図４に示す第２の温度ゾーンにおける後燃料噴射量（波形ｂ１〜ｂ３）よりも小さい後燃料噴射量（波形ｂ１〜ｂ３）を設定し，第２の気筒群に属する気筒８４に対しては図４に示す第２の温度ゾーンにおける後燃料噴射量（波形ｂ４）よりも大きい後燃料噴射量（波形ｂ４）を設定する。
【００２７】
以下，それぞれについて説明を補足する。
図１に示すように，本例の内燃機関は，ディーゼルエンジン８であり，燃料ポンプ８９から各電磁弁式インジェクタ１１〜１４に対して燃料が供給される。同図において，符号８８は，常時高圧状態で燃料が蓄積されている燃料配管である。そして，第１気筒群の気筒８１〜８３の排気管３１〜３３は一つの排気管３５に集約されて，第１触媒装置２１に接続されている。また，第２気筒群に属する気筒８４の排気管３４は，第１触媒装置２１と第２触媒装置２２とを結ぶ排気管３６に連結されている。
【００２８】
一方，図２は，触媒装置２１，２２の浄化特性を示しており，符号５１で示す曲線は，窒素酸化物の浄化特性を示し，符号５２で示す曲線は，炭化水素の浄化特性を示している。
即ち，触媒の温度ＴがＴ１未満では，窒素酸化物もＨＣも浄化されず，触媒温度ＴがＴ１以上となって始めて窒素酸化物とＨＣの浄化が実質的に開始される。そして，窒素酸化物の浄化率が増加し，やがて窒素酸化物の浄化率が最大となる温度Ｔ２を越えると，窒素酸化物の浄化率は減少し，触媒温度ＴがＴ３以上では，窒素酸化物の浄化率はほぼ零となる。
【００２９】
上記のように，触媒の温度が所定の温度範囲Ｔ１〜Ｔ３にある場合しか，実質的な窒素酸化物の浄化は行われない。例えば，ゼオライトにＰｔを担持した触媒においては，上記Ｔ１は約２００℃，Ｔ２は約２５０℃，Ｔ３は約３００℃である。また，例えば，ゼオライトにＣｕを担持またはイオン交換した触媒においては，上記Ｔ１は約３００℃，Ｔ２は約４００℃，Ｔ３は約５００℃である。
そして，前記のように，燃料等のＨＣ（炭化水素）成分を添加することにより窒素酸化物の浄化反応を促進することが出来るわけであるが，一方このＨＣ添加により触媒装置の上流側での反応が増大し触媒装置２１，２２の昇温により浄化率が低下するという問題がある。
【００３０】
次に，本例の窒素酸化物浄化装置１の動作の態様につき，図３〜図７を用いて説明する。同図において，横軸はクランク角を示し縦軸は燃料の単位時間当たりの噴射率を示す。
図３は，第１触媒装置２１の温度が，Ｔ１未満即ち第１の温度ゾーンにある場合において，ＥＣＵ４０の燃料噴射指令に基づく電磁弁式インジェクタ１１〜１４の燃料噴射の波形を示すものである。即ち，ａ１〜ａ４はそれぞれ気筒８１〜８４の主燃料噴射量の波形を示し，ｂ１〜ｂ４はそれぞれ気筒８１〜８４の後燃料噴射量の波形を示している。また，同図において，ＵＤは気筒の上死点をＬＤは下死点のタイミングを示し，気筒の添え字１〜４は気筒８１〜８４に対応する。
【００３１】
そして，図４は，同様に第１触媒装置２１の温度が，Ｔ１以上Ｔ２未満即ち第２の温度ゾーンにある場合にける電磁弁式インジェクタ１１〜１４の燃料噴射の波形を示すものである。また，図５は，第１触媒装置２１の温度が，Ｔ２以上Ｔ３未満即ち第３の温度ゾーンにある場合の電磁弁式インジェクタ１１〜１４の燃料噴射の波形を，図６は，第１触媒装置２１の温度が，Ｔ３以上即ち第４の温度ゾーンにある場合の電磁弁式インジェクタ１１〜１４の燃料噴射の波形を示す。
【００３２】
そして，図７は，本装置１の動作のフローチャートを示す。
即ち，始めにステップ６０１において，ＥＣＵ４０はアクセルセンサー２９及び回転センサー２８並びに排気温度センサー２４〜２６の出力信号を読み込む。そして，ステップ６０２において，アクセルセンサー２９及び回転センサー２８の信号から，機関出力を得るための主燃料噴射量を算出する。次いで，ステップ６０３において，排気温度センサー２４〜２６の出力信号を基に第１触媒装置２１及び第２触媒装置２２の触媒温度を推定する。
【００３３】
第１触媒装置２１の触媒温度の推定方法としては，例えば，簡便な方法としてその下流の排気温度センサー２５の排気温度を用いるという方法があり，また，上流と下流の排気温度センサー２４，２５のうち高い方を採用するという方法等がある。また，上流と下流の排気温度センサー２４，２５の出力を加重平均した値を用いる方法もある。
【００３４】
同様に，第２触媒装置２２の触媒温度の判定方法としては，例えば，簡便な方法としてその下流の排気温度センサー２６の排気温度を用いるという方法，上流と下流の排気温度センサー２５，２６のうち高い方を採用するという方法等がある。また，上流と下流の排気温度センサー２５，２６の出力を加重平均した値を用いる方法もある。
【００３５】
そして，ステップ６０４で図２に示した第１の境界温度即ち第１設定温度Ｔ１，第２の境界温度即ち第１設定温度Ｔ２，第３の境界温度即ち第１設定温度Ｔ３を読み込む。そして，ステップ６０５において，第１触媒装置２１の触媒温度Ｔが第１設定温度Ｔ１未満であるが否かを判定し，是ならばステップ６０６に進み，否ならばステップ６０７に進む。
【００３６】
そして，ステップ６０６に進んだ場合，即ち第１触媒装置２１の触媒温度が触媒活性開始温度Ｔ１に達していない場合には，第１気筒群に属する気筒８１〜８３の後燃料噴射量を零とする。また，第２気筒群（気筒８４）に対する後燃料噴射量は，第２触媒装置２２の触媒温度Ｔｓに対応した値に設定する。
【００３７】
即ち，下流の第２触媒装置２２の触媒温度は，通常は，第１触媒装置２１の温度よりも低い。その理由は，下流の第２触媒装置２２に達する迄の間に放熱により排気ガスの温度が低下するからである。従って，通常の場合は，図３に示すように，第２触媒装置２２の後燃料噴射ｂ４の量は零に設定される。
【００３８】
しかしながら，触媒装置２２の熱容量即ち熱的な慣性により，第２触媒装置２２の温度の方が第１触媒装置２１よりも高い場合があり，この場合には，その温度Ｔｓに応じて図２のカーブ５１を勘案して窒素酸化物の浄化率を高めに保持する後燃料噴射量に第２気筒群（気筒８４）の値を設定する。そして，ステップ６２０に進み，ＥＣＵ４０は上記設定量と図３に示すタイミングにおいて電磁弁式インジェクタ１１〜１４に主燃料噴射及び後燃料噴射を指令する。
【００３９】
図３における具体的な設定量の例は，例えばａ１〜ａ４の量（積分値，以下同じ）は５０ｍｍ３／ストロークであり，ｂ１〜ｂ４の量は零である。即ち，気筒８１〜８４の後噴射の総量は０ｍｍ３／エンジン２回転であり，従って主燃料噴射量に対する後燃料噴射による燃費の悪化率は０％である。これにより，触媒装置２１，２２の未活性時には，無駄な後噴射を行わず燃費の悪化を回避する。
【００４０】
一方，ステップ６０５の結果が否の場合には，ステップ６０７に進み，ステップ６０７において，第１触媒装置２１の触媒温度Ｔが第２設定温度Ｔ２未満であるが否かを判定し，是ならばステップ６０８に進み，否ならばステップ６０９に進む。
そして，ステップ６０８に進んだ場合，即ち第１触媒装置２１の触媒温度が触媒活性開始温度Ｔ１に達しているが最大温度Ｔ２未満である場合（第２の温度ゾーンの時）には，図４に示すように，第１気筒群に属する気筒８１〜８３の後燃料噴射ｂ１〜ｂ３の量は比較的少なめの量Ａ１とする。
【００４１】
その理由は，第１触媒装置２１に流入する排気ガスのＨＣ濃度を高くすることにより直接的な効果として窒素酸化物の浄化率を高めると共に，ＨＣの反応熱で第１触媒装置２１を昇温し間接的な効果として浄化率を高める為である。そして，この時，通常は供給されたＨＣの全てが上流の触媒装置２１で反応するわけではなく，未反応ＨＣは下流の第２触媒装置２２に流入する。そのため，第２触媒装置２２においても残留ＨＣの反応による触媒装置２２の昇温が生ずることとなる。
【００４２】
そして，第２触媒装置２２の後燃料噴射量は，第２触媒装置２２の触媒温度Ｔｓに対応した値Ａ２に設定する。即ち，下流の第２触媒装置２２の触媒温度が過昇温しないような量に，第２気筒群（気筒８４）の後燃料噴射量を設定する。
そして，ステップ６２０に進み，ＥＣＵ４０は上記設定量と図４に示すタイミングにおいて電磁弁式インジェクタ１１〜１４に主燃料噴射及び後燃料噴射を指令する。
【００４３】
図４における具体的な設定量の例は，例えば主燃料噴射ａ１〜ａ４の量は５０ｍｍ３／ストロークであり，第１気筒群の後燃料噴射ｂ１〜ｂ３の量Ａ１は，主燃料噴射量の２％に相当する１ｍｍ３／ストローク，第２気筒群の後燃料噴射ｂ４の量Ａ２は，主燃料噴射量の２％に相当する１ｍｍ３／ストロークである。即ち，気筒８１〜８４の後噴射の総量は４ｍｍ３／エンジン２回転であり，従って主燃料噴射量に対する後燃料噴射による燃費の悪化率は２％である。
【００４４】
この場合，第２触媒装置２２に流入する排気ガスは，排気管３４から流入する排気ガス（気筒８４の排気ガス）と第１触媒装置２１で排出された排気ガスの混合排気ガスであり，気筒８４の排気ガスのＨＣ濃度は第１触媒装置２１で排出されたＨＣ濃度の低い排気ガスにより希釈化されるから，第２触媒装置２２の排気ガスのＨＣ濃度は第１触媒装置２１の排気ガスＨＣ濃度よりも低くなる。
【００４５】
一方，ステップ６０７の結果が否の場合には，ステップ６０９に進み，ステップ６０９において，第１触媒装置２１の触媒温度Ｔが第３設定温度Ｔ３未満であるが否かを判定し，是ならばステップ６１０に進み，否ならばステップ６１１に進む。
そして，ステップ６１０に進んだ場合，即ち第１触媒装置２１の触媒温度が浄化率最大温度Ｔ２以上で浄化停止温度Ｔ３未満である場合（第３の温度ゾーンの時）には，第１気筒群に属する気筒８１〜８３の後燃料噴射量は前記Ａ１よりも小さい量Ａ３とする。
【００４６】
その理由は，第１触媒装置２１の過昇温を防止するためである。即ち，上流にある第１触媒装置２１ではＨＣがほぼ全量反応するが，後噴射量Ａ３が少ないため過昇温を抑制することが出来る。そして，第１触媒装置２１から流出し第２触媒装置２２に流入する排気ガスの温度は，放熱により低下する。そのため，第２触媒装置２２は，窒素酸化物の浄化率がより高い状態に調整することが可能となる。即ち，通常は第２気筒群（気筒８４）に対する後燃料噴射量を前記Ａ２よりも大きな量Ａ４とすることにより，第２触媒装置２２の浄化率を高めに保持することが出来る。
【００４７】
そして，ステップ６２０に進み，ＥＣＵ４０は上記設定量と図５に示すタイミングにおいて電磁弁式インジェクタ１１〜１４に主燃料噴射及び後燃料噴射を指令する。
図５における具体的な設定量の例は，例えば主燃料噴射ａ１〜ａ４の量は５０ｍｍ３／ストロークであり，第１気筒群の後燃料噴射ｂ１〜ｂ３の量Ａ３は，主燃料噴射量の１％に相当する０．５ｍｍ３／ストローク，第２気筒群の後燃料噴射ｂ４の量Ａ４は，主燃料噴射量の５％に相当する２．５ｍｍ３／ストロークである。即ち，気筒８１〜８４の後噴射の総量は４ｍｍ３／エンジン２回転であり，従って主燃料噴射量に対する後燃料噴射による燃費の悪化率は２％である。
【００４８】
一方，ステップ６１１に進んだ場合，即ち第１触媒装置２１の触媒温度が浄化停止温度Ｔ３以上である場合（第４の温度ゾーンの時）には，第１気筒群（気筒８１〜８３）に対する後燃料噴射量は零にする。一方，第２触媒装置２２に流入する排気ガスの温度は，放熱により第１触媒装置２１の流出排気ガスよりも低くなる。それ故，第２触媒装置２２を窒素酸化物浄化可能な状態，即ち第３の温度ゾーンとすることが可能な場合があり，第２気筒群（気筒８４）に対する後燃料噴射の量は，第２触媒装置２２の触媒温度Ｔｓに対応した値に設定する。
【００４９】
そして，ステップ６２０に進み，ＥＣＵ４０は上記設定量と図６に示すタイミングにおいて電磁弁式インジェクタ１１〜１４に主燃料噴射及び後燃料噴射を指令する。
図６における具体的な設定量の例は，例えば主燃料噴射ａ１〜ａ４の量は５０ｍｍ３／ストロークであり，第１気筒群の後燃料噴射ｂ１〜ｂ３の量は零，第２気筒群の後燃料噴射ｂ４の量Ａ５は，主燃料噴射量の２％に相当する１ｍｍ３／ストロークである。即ち，気筒８１〜８４の後噴射の総量は１ｍｍ３／エンジン２回転であり，従って主燃料噴射量に対する後燃料噴射による燃費の悪化率は０．５％である。
【００５０】
図８は，本例の窒素酸化物浄化装置１の効果を，本例のような制御を行わず後燃料噴射を一律に一定量にした場合と比較して図示したものであり，横軸に触媒装置に流入する排気ガスの温度を取り縦軸に窒素酸化物の浄化率を％で示したものである。
同図の符号５４で示す曲線は，第１触媒装置２１及び第２触媒装置２２の触媒温度Ｔ，Ｔｓによらず気筒８１〜８４に対する後燃料噴射量を小さめの値，例えば０．５ｍｍ３／ストロークにした場合の浄化特性である。そして，符号５５で示す曲線は，第１触媒装置２１及び第２触媒装置２２の触媒温度Ｔ，Ｔｓによらず気筒８１〜８４に対する後燃料噴射量を大きめの値，例えば１ｍｍ３／ストロークにした場合の浄化特性である。
【００５１】
後者の特性（符号５５）は，前者の特性（符号５４）に比較すると，ＨＣの量を多くしたため流入排気ガスの低温側ではＨＣの反応熱で触媒が昇温して浄化率が向上し，最大浄化率が得られる排気ガス温度が低下すると共にＨＣの増加により最大の浄化率の値も大きくなる。しかしながら，高温排気ガスの側では，ＨＣの反応熱により触媒装置が過昇温し浄化率が低下する。
【００５２】
一方，本例の窒素酸化物浄化装置１の場合，即ち，第１触媒装置２１の温度が低温（第２温度ゾーン）の場合には全ての気筒８１〜８４の後噴射量を比較的大きな値（例えば１ｍｍ３／ストローク）にし，第１触媒装置２１の温度がより高い（第３温度ゾーン）の場合には第１気筒群（気筒８１〜８３）の後噴射量を小さな値（例えば０．５ｍｍ３／ストロークとし第２気筒群（気筒８４）の後噴射量を大きな値（例えば２．５ｍｍ３／ストローク）とした場合の特性を，符号５６で示す。同図から分かるように，本例の窒素酸化物浄化装置１は，広い範囲の排気ガス温度領域で高い窒素酸化物の浄化率を示す。
【００５３】
上記のように，本例によれば触媒の温度が低い場合は昇温を促進し，触媒の温度が高い場合には，過昇温を抑制し，広い範囲で高い窒素酸化物の浄化率を達成することが出来る。
そして，本例によれば装置が大形化したり大幅に複雑化したりするようなこともない。
【００５４】
なお，上記例では，触媒装置２１，２２が合計２個の場合について説明したが，４気筒の場合には最大４個の触媒装置を用いることが可能である。この場合，触媒装置の数を多くすれば，それだけ構成が複雑となるが，窒素酸化物の浄化率は向上する。
【００５５】
また，第１触媒装置２１と第２触媒装置２２とは，同一の特性のものを用いても良いが，異なった特性の触媒装置２１，２２とすることもできる。後者の場合には，特に，上流に配置する第１触媒装置２１により低温の領域で窒素酸化物の浄化が可能である触媒（例えばＰｔ／ゼオライト触媒）を用い，下流側の第２触媒装置２２により高温の領域で活性化する触媒（例えばＣｕ／ゼオライト触媒）を用いることにより，窒素酸化物を浄化することの出来る温度範囲をより広くすることができると共に，上流側の触媒装置２１は排気ガスの熱により早く昇温するから一段と迅速に触媒装置２１を活性化出来るという利点がある。
【００５６】
なお，従来は，より低温で活性化する触媒装置と高温で活性化する触媒装置とを直列に配置する場合には，以下に述べる理由から，上流側により高温で活性化する触媒装置を配置する方法が採用されていた。即ち，その理由は，触媒装置の上流側からＨＣを供給する場合に，上流側に低温で活性化する触媒を配置すると，上流側の触媒装置でＨＣが全て反応してしまい，下流側の触媒にＨＣが供給できなくなる恐れがあるとの理由によるものである。
【００５７】
そして，このような方式を採用すると，アイドリングから加速を行う場合には，上流側にある昇温の容易な触媒装置を速やかに活性化し窒素酸化物を浄化したいのにも係わらず，上流側の触媒は高温にならないと活性化しないため，モード走行では浄化率が低くなるという結果をもたらしていた。
しかしながら，本例では，上流の触媒装置２１と下流の触媒装置２２のそれぞれにＨＣを供給できるから，上記の理由による不具合は発生せず，従って上流側に低温で活性化する触媒装置２１を配置することにより何ら問題なく迅速に触媒装置を立ち上げることが可能となる。
【００５８】
実施形態例２
本例は，図９に示すように，実施形態例１において，第１気筒群（気筒８１〜８３）の後燃料噴射を１つの気筒８１（または８２，８３）において纏めて噴射させ，他の気筒８２，８３は後噴射を実施しないようにしたもう一つの実施形態例である。図９は実施形態例１の図４に対応する状態（第２温度ゾーン）の燃料噴射波形を示すものである。
また，本例では第２気筒群の気筒数が１個の場合であるが，仮に第２気筒群が複数の気筒からなる場合には，第２気筒群に属する１つの気筒のみが後噴射を実施する。
【００５９】
例えば主燃料噴射ａ１〜ａ４の量は５０ｍｍ３／ストローク）であり，第１気筒群の後燃料噴射の量は，気筒８１の後噴射ｂ１の量を主燃料噴射量の６％に相当する３ｍｍ３／ストロークとし気筒８２，８３の後噴射ｂ２，ｂ３の量を零とする。そして，第２気筒群の後燃料噴射ｂ４の量は，主燃料噴射量の２％に相当する１ｍｍ３／ストロークとする。即ち，気筒８１〜８４の後噴射の総量は４ｍｍ３／エンジン２回転であり，従って主燃料噴射量に対する後燃料噴射による燃費の悪化率は２％である。
【００６０】
本例によれば，電磁弁式インジェクタ１１〜１４のうち，高感度，高速応答の電磁弁式インジェクタは第１，第４の電磁弁式インジェクタ１１，１４だけでよい。それ故，インジェクタの小型化と低コスト化が可能となり，また第２，第３の電磁弁式インジェクタ１２，１３の動作回数が半減化し耐久性も向上する。その他については実施形態例１と同様である。
【００６１】
実施形態例３
本例は，図１０，図１１に示すように，実施形態例１において，主燃料噴射量を第１気筒群と第２気筒群とで異なった値としたもう一つの実施形態例である。
即ち，エンジンの運転状況，触媒装置２１，２２の温度に対応して主燃料噴射量を異なった量とする。
【００６２】
図１０は，第１触媒装置２１の触媒温度が前記Ｔ１未満（第１温度ゾーン）の場合の電磁弁式インジェクタ１１〜１４の燃料噴射の波形を示すものであり，実施形態例１の図３に対応する。
第１気筒群（気筒８１〜８３）の各気筒の主燃料噴射量は，同一量（例えば６７ｍｍ３／ストローク）であり，第２気筒群の気筒８４の主燃料噴射量は零である。即ち，トータルの主燃料の量は実施形態例１の図３と同じにし，その配分だけを変化させる。そして，第２気筒群の主燃料噴射が零であるため，気筒８４はエアーポンプの作用をすることとなる。
【００６３】
上記のように，第１気筒群の対してだけ主燃料を分担させるから，第１触媒装置２１に流入する排気ガスの温度が高くなり，昇温が促進され，窒素酸化物の浄化率が迅速に立ち上がることとなる。
そして，後噴射の量は，第１気筒群の気筒８１〜８３は少なめの値（例えば１ｍｍ３／ストローク）とし，第２気筒の気筒８４は零である。第１気筒群に対して後燃料噴射を実施する理由は，主燃料噴射により第１触媒装置２１が急速昇温し，急速に第１触媒装置２１での窒素酸化物の浄化が可能となるからである。
【００６４】
その結果，上記数値の場合の後噴射の総量は３ｍｍ３／エンジン２回転であり，主燃料噴射量に対する後噴射による燃費の悪化は平均して１．５％である。
また，第２気筒群の後噴射を零としたのは，第１気筒群の気筒８４がエアーポンプとなり第２触媒装置２２の温度が低下し，窒素酸化物の浄化作用を期待出来ないからである。
【００６５】
一方，図１１は，第１触媒装置２１の触媒温度が前記Ｔ３以上（第４温度ゾーン）の場合の電磁弁式インジェクタ１１〜１４の燃料噴射の波形を示すものであり，実施形態例１の図６に対応する。
第１気筒群（気筒８１〜８３）の各気筒の主燃料噴射量は，同一量（例えば６７ｍｍ３／ストローク）であり，第２気筒群の気筒８４の主燃料噴射量は零である。即ち，トータルの主燃料の量は実施形態例１の図６と同じにし，その配分だけを変化させる。そして，第２気筒群の主燃料噴射が零であるため，第２気筒群の気筒８４はエアーポンプの作用をすることとなる。
【００６６】
また，後噴射の量は，第１気筒群の気筒８１〜８３は零であり，第２気筒の気筒８４は多めの値（例えば４ｍｍ３／ストローク）である。それ故，後噴射の総量は４ｍｍ３／エンジン２回転であり，主燃料噴射量に対する後噴射による燃費の悪化は平均して２．０％である。
上記のように，第２気筒群の気筒８４をエアーポンプとして作動させるから，下流の第２触媒装置２２の温度が低下し，窒素酸化物の浄化可能な温度に保持することができる。
【００６７】
そして，第１気筒群の後噴射を零としたのは，第１触媒装置２１が高温で浄化作用をすることが出来ないからである。また，第２気筒群の気筒８４の後噴射量を大きめにしたのは，全ての気筒８１〜８４の排気ガスが窒素酸化物を浄化することなく第２触媒装置２２に流入するため，ＨＣを多めに投入し窒素酸化物の浄化率を高めんとするためである。
上記のように本例によれば，第１触媒装置２１が第１，第４の温度ゾーンにある場合にも，触媒装置の浄化を促進する制御が実施可能となる。その他については実施形態例１と同様である。
【００６８】
実施形態例４
本例は，図１２に示すように，実施形態例３において，第１気筒群に属する気筒の数を２つとし，第２気筒群に属する気筒の数を２つとしたもう一つの実施形態例である。
このようにすることにより，第１触媒装置２１が第１，第４温度ゾーンにある場合に，より広い温度範囲において，触媒装置２１または触媒装置２２による窒素酸化物の浄化作用を発揮することが可能となる。
【００６９】
即ち，第１温度ゾーンにある場合には，主燃料を第１気筒群の２つの気筒８１，８３に集中し，３つの気筒８１〜８３に集中した実施形態例３よりも第１触媒装置２１の昇温をより早めることができる。また，第４温度ゾーンにある場合にも，第２気筒群に属する２つの気筒８２，８４がエアーポンプの作用をすることになるから１つの気筒がエアーポンプの作用をした実施形態例３の場合よりも第２触媒装置２２の冷却が強められ，第１触媒装置２１のより広い温度範囲において第２触媒装置２２の浄化作用を維持することができる。その他については実施形態例３と同様である。
【００７０】
実施形態例５
本例は，図１３に示すように，実施形態例１においてエンジンの気筒８１〜８６及び電磁弁式インジェクタ１１〜１６の数を６とし，第１気筒群に属する気筒８１〜８５を５つとし，第２気筒群に属する気筒８６を１つとした例である。その他については実施形態例１と同様である。
【００７１】
なお，上記において，触媒装置２１，２２の数は２個に限定されるものではなく，３個以上としてもよい。
また，第１気筒群の気筒数を４つの気筒として第２気筒群の気筒の数を２気筒とすることもできる。
そして，３気筒エンジン，８気筒エンジンにおいても同様に各実施形態例の考え方を適用することができる。
【図面の簡単な説明】
【図１】実施形態例１の窒素酸化物浄化装置のシステム構成図。
【図２】実施形態例１の窒素酸化物浄化装置の触媒温度と浄化率の関係を示す図。
【図３】実施形態例１の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第１の温度ゾーン）。
【図４】実施形態例１の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第２の温度ゾーン）。
【図５】実施形態例１の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第３の温度ゾーン）。
【図６】実施形態例１の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第４の温度ゾーン）。
【図７】実施形態例１の窒素酸化物浄化装置の浄化特性（符号５６）を単純な制御を行った場合（符号５４，５５）と共に表示した図。
【図８】実施形態例１の窒素酸化物浄化装置の制御手順を示すフローチャート。
【図９】実施形態例２の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第２の温度ゾーン）。
【図１０】実施形態例３の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第１の温度ゾーン）。
【図１１】実施形態例３の窒素酸化物浄化装置における気筒毎の燃料噴射の波形を示す図（第４の温度ゾーン）。
【図１２】実施形態例４の窒素酸化物浄化装置のシステム構成図。
【図１３】実施形態例５の窒素酸化物浄化装置のシステム構成図。
【符号の説明】
１．．．窒素酸化物浄化装置，
１１〜１４．．．電磁弁式インジェクション（燃料噴射手段），
２１，２２．．．触媒装置，
２４〜２６．．．排気温度センサー，
４０．．．ＥＣＵ（燃料噴射制御手段），[0001]
【Technical field】
The present invention relates to an exhaust purification device that purifies nitrogen oxides contained in exhaust gas of an internal combustion engine.
[0002]
[Prior art]
Nitrogen oxide (NOx) discharged from an internal combustion engine such as a diesel engine is purified using a catalyst device using a metal-supported zeolite or the like. And the purification rate of the said catalyst apparatus has shown the high purification rate only in the specific temperature range (T1-T3 of the same figure, for example, 200-300 degreeC), as shown to the curve of the code | symbol 51 of FIG. In addition, it is known that the reaction of this nitrogen oxide catalyst device is promoted by adding an HC (hydrocarbon) component such as fuel. Therefore, a method has been proposed in which a reducing agent such as light oil is supplied from the upstream side of the catalyst device and mixed with exhaust gas to promote the purification of nitrogen oxides.
[0003]
From the above viewpoint alone, in order to increase the purification rate of nitrogen oxides, it is sufficient to supply a large amount of HC as a reducing agent. However, if the supply of HC is increased, the temperature of the catalyst device rises due to the reaction heat of HC, and the temperature range in which the purification rate near T2 shown in FIG. 2 is good is exceeded. Therefore, it is necessary to add an appropriate amount of HC according to the state and maintain the catalyst device in a high purification rate.
[0004]
Therefore, in JP-A-4-214919, a plurality of units each including a catalyst and an HC supply device are provided, and the HC supply device is operated only for a unit within a predetermined temperature range to prevent overheating of the catalyst. A purification device that improves the purification rate of nitrogen oxides has been proposed.
[0005]
[Problems to be solved]
However, the nitrogen oxide purification apparatus disclosed in the above Japanese Patent Laid-Open No. 4-214919 requires HC supply devices as many as the number of catalyst devices, and the configuration of the device becomes complicated, resulting in a large size and high cost. There is a bug.
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an excellent nitrogen oxide purification device capable of increasing the purification rate of nitrogen oxides with a simpler configuration. .
[0006]
[Means for solving problems]
  According to a first aspect of the present invention, there is provided a fuel injection means provided for each cylinder, a fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices disposed in an exhaust passage for reducing and purifying nitrogen oxides, A nitrogen oxide purifying device for an internal combustion engine having a catalyst temperature determining means for measuring or estimating the temperature of the catalyst device, and an operating state detecting means capable of detecting at least the stroke position of the cylinder,
  The catalyst device includes a first catalyst device disposed upstream of the exhaust passage and a second catalyst device disposed in series downstream of the first catalyst device, and the cylinder includes the first catalyst device. A first cylinder group connected upstream of the apparatus and a second cylinder group connected to the exhaust passage between the first catalyst apparatus and the second catalyst apparatus,
  The fuel injection control means receives the output signals of the catalyst temperature determination means and the operating condition detection means, and receives a main fuel injection command for generating engine output near the compression top dead center and a hydrocarbon supply in the expansion stroke or exhaust stroke. And a post fuel injection command for each cylinder to the fuel injection means,the aboveThe first catalytic device orthe aboveEach cylinder or the temperature corresponding to the temperature of the second catalytic devicethe aboveAmount of post fuel injection for cylinder groupThe aboveMaximizing the purification rate of nitrogen oxides while suppressing overheating of each catalyst deviceSo as to supply a sufficient amount of hydrocarbon to be supplied to both the first catalyst device and the second catalyst device.The present invention provides a nitrogen oxide purifying device for an internal combustion engine.
[0007]
  the aboveThe fuel injection control means issues a main fuel injection command for generating engine output and a post fuel injection command for supplying hydrocarbons for each cylinder or each cylinder group. The fuel injection control means then determines the amount of post-fuel injection corresponding to the temperatures of the first catalyst device and the second catalyst device determined by the catalyst temperature determination means.,Maximizing the purification rate of nitrogen oxides while suppressing overheating of each catalyst deviceSo as to supply a sufficient amount of hydrocarbon to be supplied to both the first catalyst device and the second catalyst device..
[0008]
Since it is configured as described above, the exhaust gas discharged from the first cylinder group flows into the first catalyst device, while the second catalyst device is discharged from the second cylinder group. Exhaust gas and exhaust gas purified by the first catalyst device flow in. Since the post fuel injection amount can be set for each cylinder or cylinder group, the amount of HC reducing agent supplied to the first catalytic device, that is, the amount of post fuel injection, and the HC reduction supplied to the second catalytic device. The amount of agent, i.e. the amount of post fuel injection, can be set separately.
[0009]
Therefore, an appropriate HC reducing agent can be supplied to each catalyst device in accordance with the temperature state of the first and second catalyst devices determined by the catalyst temperature determining means. That is, wasteful HC (post-fuel) is not supplied to the catalyst device, but an appropriate amount of HC (post-fuel) is supplied to control the catalyst device as high as possible in the purification rate.
Since the post fuel injection is performed in the expansion stroke or the exhaust stroke, it has an effect that it can be changed to HC suitable for reduction of nitrogen oxides by heat in the cylinder.
[0010]
  nextAs in claim 2,The fuel injection control means according to claim 1, wherein the temperature of the first catalyst device in which the nitrogen oxide purification rate of the first catalyst device changes at a very low level is a low temperature first temperature zone,
A second temperature zone in which the nitrogen oxide purification rate of the first catalytic device rises with increasing temperature of the first catalytic device;
A third temperature zone in which the nitrogen oxide purification rate of the first catalyst device decreases as the temperature of the first catalyst device rises;
Dividing the temperature zone into a fourth temperature zone in which the temperature of the first catalyst device in which the purification rate of nitrogen oxides of the first catalyst device changes at an extremely low level is high;
It is preferable to provide a nitrogen oxide purifying apparatus for an internal combustion engine characterized by changing the magnitude and distribution ratio of the post fuel injection amount for each cylinder or each cylinder group for each temperature zone.
That is,A low temperature first temperature zone (below T1 in FIG. 2) in which the nitrogen oxide purification rate of the catalyst device transitions at a very low level, and a second temperature zone in which the nitrogen oxide purification rate increases with temperature (FIG. 2). 2 (T1 to T2), a third temperature zone (T2 to T3 in FIG. 2) in which the nitrogen oxide purification rate decreases with temperature, and a high temperature first in which the nitrogen oxide purification rate changes at a very low level. By dividing the temperature zone into four temperature zones (T3 or more in FIG. 2) and changing the size and distribution ratio of the post fuel injection amount for each cylinder or each cylinder group for each temperature zone, it is effective. Nitrogen oxide purification can be achieved (see example embodiments described below).
[0011]
This is because the tendency of increase / decrease of the purification rate with respect to the temperature is completely different depending on each temperature zone, and the purification rate cannot be maximized unless the fuel injection is controlled after conforming to the characteristics. is there.
For example, in the relationship between the second temperature zone and the third temperature zone, as described in claim 3, in the third temperature zone, the second temperature with respect to the cylinders belonging to the first cylinder group. A post fuel injection amount that is smaller than the post fuel injection amount in the zone is set, and a post fuel injection amount that is larger than the post fuel injection amount in the second temperature zone is set for the cylinders belonging to the second cylinder group. Is preferred.
[0012]
That is, in the third temperature zone, it is necessary to suppress the excessive temperature rise of the upstream first catalytic device having a high temperature that exceeds the maximum temperature of the purification rate, while the second catalytic device having a relatively low temperature. This is because, in order to obtain a high purification rate, it is appropriate to supply HC normally to improve the purification rate.
[0013]
  The configuration based on the technical ideas of claims 1 to 3 is not only effective when there are two catalyst devices, but can also be applied when three or more catalyst devices exceeding two are provided. It is.
  That is, as described in claim 4, Fuel injection means provided for each cylinder, fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices disposed in the exhaust passage for reducing and purifying nitrogen oxides, and measuring the temperature of the catalyst devices Or a nitrogen oxide purifying device for an internal combustion engine having a catalyst temperature determining means for estimating and an operating state detecting means capable of detecting at least a stroke position of a cylinder,
The catalyst device comprises N catalyst devices arranged in series in the exhaust passage in the order of the first catalyst device, the second catalyst device,..., The Nth catalyst device from the upstream side,
On the other hand, the entire cylinder is composed of N cylinder groups each composed of a single cylinder or a plurality of cylinders, and the first cylinder group is connected upstream of the first catalyst device, and the first cylinder group having a natural number I exceeding 1 is connected. The I-th cylinder group is connected to the exhaust passage between the (I-1) th catalyst device and the I-th catalyst device,
The fuel injection control means receives the output signals of the catalyst temperature determination means and the operating condition detection means, and receives a main fuel injection command for generating engine output near the compression top dead center and a hydrocarbon supply in the expansion stroke or exhaust stroke. A post fuel injection command for each cylinder to each of the cylinders or the group of cylinders corresponding to the temperatures of the N catalyst devices. Adjustment is made so that a hydrocarbon supply amount sufficient to maximize the purification rate of nitrogen oxides is supplied to both the first catalyst device and the second catalyst device while suppressing overheating of the catalyst device. There is a nitrogen oxide purification device for an internal combustion engine.
In the present invention,The number of catalyst devices is N, and the cylinders are divided into N cylinder groups. The amount of post-fuel injection is adjusted according to the temperature of each catalyst device, and nitrogen oxidation is performed while suppressing overheating of each catalyst device. Maximize the purification rate of waste.
[0014]
With the configuration described above, the exhaust gas discharged from the I-th cylinder group flows into the I-th catalyst device, while the (I + 1) -th catalyst device has the (I + 1) -th catalyst device. The exhaust gas discharged from the cylinder group and the exhaust gas purified by the first catalyst device flow in. Since the post fuel injection amount can be set for each cylinder or each cylinder group, the amount of the HC reducing agent supplied to the first catalyst device, that is, the post fuel injection amount, and the (I + 1) th catalyst device is supplied. The amount of HC reducing agent, that is, the amount of post fuel injection can be set separately.
[0015]
Therefore, an appropriate HC reducing agent can be supplied to each catalyst device in accordance with the temperature state of the Ith and (I + 1) th catalyst devices determined by the catalyst temperature determining means. That is, wasteful HC (post-fuel) is not supplied to the catalyst device, but an appropriate amount of HC (post-fuel) is supplied to control the catalyst device as high as possible in the purification rate.
Even when the number of catalyst devices is three or more, the same effects as in the second or third aspect can be achieved by the inventions according to the fifth and sixth aspects.
[0016]
Further, in each of the above-described configurations of claims 1 to 6, the nitrogen oxide purifying temperature range of the catalyst device disposed on the upstream side is further defined as the catalyst device disposed on the downstream side as in claim 7. The temperature is preferably lower than the temperature range in which nitrogen oxides can be purified. With this configuration, it is possible to quickly raise the temperature of the upstream catalyst device, which can be easily raised, at the time of start-up or the like, and to activate quickly at a lower temperature.
[0017]
According to another aspect of the present invention, the total after-fuel injection amount in the cylinder group is set, and all the after-fuel injections in the cylinder group are concentrated on some cylinders in the cylinder group for injection. It is preferable. This is because the post-fuel injection amount in the cylinder to be injected is relatively increased by concentrating the post-fuel injection in a part of the cylinders, compared to the case where the post-fuel injection amount is uniformly set in each cylinder. This is because it is possible to use a fuel injection means having a relatively low operation performance (for example, a valve response speed or a minimum operable amount).
[0018]
Further, as described in claim 9, in addition to the post fuel injection amount, the amount of main fuel injection is further adjusted for each cylinder group, so that the nitrogen oxides can be more appropriately suppressed while suppressing overheating of each catalyst device. It is possible to maximize the purification rate.
That is, by adjusting the total main fuel injection amount in the cylinder group, the amount of exhaust gas flowing into the catalyst device connected to the cylinder group changes, thereby controlling the temperature rise rate and temperature drop rate of the catalyst device. Because it becomes possible to do.
[0019]
For example, when there are two catalyst devices as described in claim 11, in the first temperature zone, the main fuel injection is concentrated on the first cylinder group to raise the temperature of the first catalyst device. In the fourth temperature zone according to claim 2, it is preferable to concentrate the main fuel injection on the first cylinder group to promote the cooling of the second catalytic device.
[0020]
That is, in the first temperature zone, the main fuel injection is concentrated in the first cylinder group, so that the inflow of exhaust gas is concentrated in the first catalyst device to promote the temperature rise of the first catalyst device. It is possible to quickly increase the purification rate of the catalyst device. Further, in the fourth temperature zone, the main fuel injection is concentrated in the first cylinder group, the exhaust gas inflow is concentrated in the first catalyst device, the second catalyst device is cooled, and the purification rate of the second catalyst device is increased. This is because it is possible to shift to a higher and lower temperature region. In the latter case, nitrogen oxides of all exhaust gases are purified in the second catalyst device that maintains a high purification rate.
[0021]
Even when the number of catalyst devices is N, and the generalization is more general, the temperature of the I-th catalyst device located on the upstream side is in the first temperature zone as described in claim 10. In this case, the main fuel injection is concentrated on the I-th cylinder group to promote the temperature rise of the I-th catalyst device, and when it is in the fourth temperature zone, the main fuel injection is concentrated on the I-th cylinder group. The same effect can be obtained by promoting cooling of the (I + 1) th and subsequent downstream catalytic devices.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
In this example, as shown in FIG. 1, the solenoid valve injectors 11 to 14 as fuel injection means provided for each of the cylinders 81 to 84 and the fuel for controlling the fuel injection means (solenoid valve injectors 11 to 14). Electronic control unit (ECU) 40 as injection control means, a plurality of catalyst devices 21 and 22 disposed in the exhaust passages 35 and 34 for reducing and purifying nitrogen oxides, and a catalyst for measuring the temperature of each of the catalyst devices 21 and 22 Nitrogen oxidation of an internal combustion engine having exhaust temperature sensors 24-26 as temperature determination means and an engine rotation sensor 28 and an accelerator sensor 29 as operating state detection means capable of detecting at least the stroke positions of the cylinders 81-84 This is an object purification device 1.
[0023]
The catalyst devices 21 and 22 include a first catalyst device 21 disposed upstream of the exhaust passages 34 to 37 and a second catalyst device 22 disposed in series downstream of the first catalyst device 21. At the same time, the cylinders 81 to 84 are connected to an exhaust passage 36 between the first catalyst device 21 and the second catalyst device 22, and the first cylinder 81 to 83 group connected upstream of the first catalyst device 21. And a second group of cylinders 84 (ie, corresponding to N = 2 in claim 4).
[0024]
An electronic control unit (ECU) 40 as fuel injection control means receives the output signals of the catalyst temperature determination means and the operating condition detection means, and receives a main fuel injection command for generating engine output near the compression top dead center. And a post-fuel injection command for supplying hydrocarbons in the expansion stroke or the exhaust stroke are issued to the fuel injection means for each of the cylinders 81 to 84 and the temperature of the first catalyst device 21 or the second catalyst device 22 is set. Correspondingly, the amount of the post fuel injection (waveforms b1 to b4, FIGS. 3 to 6) for each of the cylinders 81 to 84 or the cylinders 81 to 83 and the cylinder 84 group is adjusted, and the overheating of the catalyst devices 21 and 22 is controlled. Maximize the purification rate of nitrogen oxides while controlling.
[0025]
That is, the fuel injection control means (ECU 40) includes a first temperature zone (T <T1 in FIG. 2) in which the nitrogen oxide purification rate of the first catalyst device 21 changes at an extremely low level, The second temperature zone (T1 <T <T2 in FIG. 2) in which the nitrogen oxide purification rate of the catalyst device 21 increases with the temperature T, and the nitrogen oxide purification rate of the first catalyst device 21 is the temperature T. And a third temperature zone (T2 <T <T3 in FIG. 2) descending together with a high temperature fourth temperature zone (FIG. 2) in which the purification rate of nitrogen oxides of the first catalyst device 21 changes at an extremely low level. T> T3) and the temperature zones are divided into the following fuel injection amounts (waveforms b1 to b4) for the cylinders 81 to 83 and the cylinders 84 for each temperature zone as shown in FIGS. Change the size and distribution ratio.
[0026]
For example, as shown in FIG. 5, in the third temperature zone, the post-fuel injection amounts (waveforms b1 to b3) in the second temperature zone shown in FIG. 4 with respect to the cylinders 81 to 83 belonging to the first cylinder group. ) Is set to be smaller than (), and for the cylinders 84 belonging to the second cylinder group, the post-fuel injection amount (waveform b4) in the second temperature zone shown in FIG. 4 is set. Is set to a larger post-fuel injection amount (waveform b4).
[0027]
The following is a supplementary explanation for each.
As shown in FIG. 1, the internal combustion engine of this example is a diesel engine 8, and fuel is supplied from a fuel pump 89 to the solenoid valve injectors 11 to 14. In the figure, reference numeral 88 denotes a fuel pipe in which fuel is always accumulated in a high pressure state. The exhaust pipes 31 to 33 of the cylinders 81 to 83 in the first cylinder group are integrated into one exhaust pipe 35 and connected to the first catalyst device 21. Further, the exhaust pipe 34 of the cylinder 84 belonging to the second cylinder group is connected to an exhaust pipe 36 connecting the first catalytic device 21 and the second catalytic device 22.
[0028]
On the other hand, FIG. 2 shows the purification characteristics of the catalyst devices 21 and 22. The curve indicated by reference numeral 51 indicates the purification characteristics of nitrogen oxides, and the curve indicated by reference numeral 52 indicates the purification characteristics of hydrocarbons. Yes.
That is, when the catalyst temperature T is lower than T1, neither nitrogen oxides nor HC is purified, and purification of nitrogen oxides and HC starts substantially only when the catalyst temperature T becomes T1 or higher. The nitrogen oxide purification rate increases, and eventually, when the temperature exceeds the temperature T2 at which the nitrogen oxide purification rate reaches the maximum, the nitrogen oxide purification rate decreases. When the catalyst temperature T is T3 or higher, the nitrogen oxide purification rate decreases. The purification rate is almost zero.
[0029]
As described above, substantial purification of nitrogen oxides is performed only when the temperature of the catalyst is in the predetermined temperature range T1 to T3. For example, in a catalyst in which Pt is supported on zeolite, T1 is about 200 ° C., T2 is about 250 ° C., and T3 is about 300 ° C. For example, in a catalyst in which Cu is supported or ion exchanged on zeolite, the T1 is about 300 ° C., T2 is about 400 ° C., and T3 is about 500 ° C.
As described above, by adding an HC (hydrocarbon) component such as fuel, the purification reaction of nitrogen oxides can be promoted. There is a problem that the reaction rate increases and the purification rate decreases due to the temperature rise of the catalyst devices 21 and 22.
[0030]
Next, the mode of operation of the nitrogen oxide purification apparatus 1 of this example will be described with reference to FIGS. In the figure, the horizontal axis represents the crank angle, and the vertical axis represents the fuel injection rate per unit time.
FIG. 3 shows the fuel injection waveforms of the solenoid valve injectors 11 to 14 based on the fuel injection command of the ECU 40 when the temperature of the first catalyst device 21 is less than T1, that is, in the first temperature zone. . That is, a1 to a4 show the waveforms of the main fuel injection amounts of the cylinders 81 to 84, respectively, and b1 to b4 show the waveforms of the post fuel injection amounts of the cylinders 81 to 84, respectively. In the figure, UD indicates the top dead center of the cylinder, LD indicates the timing of the bottom dead center, and cylinder subscripts 1-4 correspond to the cylinders 81-84.
[0031]
FIG. 4 shows the waveform of fuel injection of the solenoid valve injectors 11 to 14 when the temperature of the first catalyst device 21 is equal to or higher than T1 and lower than T2, that is, in the second temperature zone. 5 shows the fuel injection waveform of the electromagnetic valve injectors 11 to 14 when the temperature of the first catalyst device 21 is T2 or more and less than T3, that is, in the third temperature zone, and FIG. 6 shows the first catalyst device. The waveform of the fuel injection of the solenoid valve injectors 11 to 14 when the temperature of the device 21 is equal to or higher than T3, that is, in the fourth temperature zone is shown.
[0032]
FIG. 7 shows a flowchart of the operation of the apparatus 1.
That is, first in step 601, the ECU 40 reads output signals from the accelerator sensor 29, the rotation sensor 28, and the exhaust temperature sensors 24-26. In step 602, the main fuel injection amount for obtaining the engine output is calculated from the signals of the accelerator sensor 29 and the rotation sensor 28. Next, in step 603, the catalyst temperatures of the first catalyst device 21 and the second catalyst device 22 are estimated based on the output signals of the exhaust temperature sensors 24-26.
[0033]
As a method for estimating the catalyst temperature of the first catalyst device 21, for example, there is a method of using the exhaust temperature of the downstream exhaust temperature sensor 25 as a simple method, and the upstream and downstream exhaust temperature sensors 24, 25 are used. There is a method of adopting the higher one. There is also a method using a weighted average value of the outputs of the upstream and downstream exhaust temperature sensors 24, 25.
[0034]
Similarly, as a method for determining the catalyst temperature of the second catalyst device 22, for example, as a simple method, the exhaust temperature of the exhaust temperature sensor 26 downstream thereof is used, and among the exhaust temperature sensors 25, 26 upstream and downstream, There is a method of adopting the higher one. There is also a method using a value obtained by weighted averaging the outputs of the upstream and downstream exhaust temperature sensors 25 and 26.
[0035]
In step 604, the first boundary temperature, that is, the first set temperature T1, the second boundary temperature, that is, the first set temperature T2, and the third boundary temperature, that is, the first set temperature T3 shown in FIG. In step 605, it is determined whether or not the catalyst temperature T of the first catalyst device 21 is lower than the first set temperature T1. If YES, the process proceeds to step 606. If NO, the process proceeds to step 607.
[0036]
When the routine proceeds to step 606, that is, when the catalyst temperature of the first catalyst device 21 has not reached the catalyst activation start temperature T1, the post fuel injection amount of the cylinders 81 to 83 belonging to the first cylinder group is set to zero. To do. The post fuel injection amount for the second cylinder group (cylinder 84) is set to a value corresponding to the catalyst temperature Ts of the second catalytic device 22.
[0037]
That is, the catalyst temperature of the downstream second catalyst device 22 is usually lower than the temperature of the first catalyst device 21. The reason is that the temperature of the exhaust gas decreases due to heat radiation before reaching the downstream second catalyst device 22. Therefore, in the normal case, as shown in FIG. 3, the amount of the rear fuel injection b4 of the second catalytic device 22 is set to zero.
[0038]
However, the temperature of the second catalyst device 22 may be higher than that of the first catalyst device 21 due to the heat capacity of the catalyst device 22, that is, thermal inertia. In this case, the temperature shown in FIG. Considering the curve 51, the value of the second cylinder group (cylinder 84) is set to the post-fuel injection amount that keeps the nitrogen oxide purification rate high. Then, the process proceeds to step 620, where the ECU 40 commands the solenoid valve injectors 11-14 to perform main fuel injection and post fuel injection at the set amount and the timing shown in FIG.
[0039]
In the example of specific set amounts in FIG. 3, for example, the amounts of a1 to a4 (integrated values, the same applies hereinafter) are 50 mm3 / stroke, and the amounts of b1 to b4 are zero. That is, the total amount of post-injection of the cylinders 81 to 84 is 0 mm 3 / two revolutions of the engine. Therefore, the deterioration rate of the fuel consumption due to the post-fuel injection with respect to the main fuel injection amount is 0%. Thereby, when the catalyst devices 21 and 22 are inactive, wasteful post-injection is not performed and deterioration of fuel consumption is avoided.
[0040]
On the other hand, if the result of step 605 is NO, the process proceeds to step 607, where it is determined whether or not the catalyst temperature T of the first catalyst device 21 is lower than the second set temperature T2, and if YES, The process proceeds to step 608, and if not, the process proceeds to step 609.
When the process proceeds to step 608, that is, when the catalyst temperature of the first catalyst device 21 reaches the catalyst activation start temperature T1 but is lower than the maximum temperature T2 (in the second temperature zone), FIG. As shown, the amounts of the post fuel injections b1 to b3 of the cylinders 81 to 83 belonging to the first cylinder group are set to a relatively small amount A1.
[0041]
The reason is that by increasing the HC concentration of the exhaust gas flowing into the first catalyst device 21, the purification rate of nitrogen oxides is increased as a direct effect, and the temperature of the first catalyst device 21 is raised by the reaction heat of HC. However, this is to increase the purification rate as an indirect effect. At this time, not all of the supplied HC usually reacts in the upstream catalytic device 21, and unreacted HC flows into the downstream second catalytic device 22. Therefore, also in the second catalyst device 22, the temperature of the catalyst device 22 rises due to the reaction of residual HC.
[0042]
Then, the post fuel injection amount of the second catalyst device 22 is set to a value A2 corresponding to the catalyst temperature Ts of the second catalyst device 22. That is, the post-fuel injection amount of the second cylinder group (cylinder 84) is set to such an amount that the catalyst temperature of the downstream second catalyst device 22 does not overheat.
Then, the process proceeds to step 620, where the ECU 40 instructs the solenoid valve injectors 11-14 to perform main fuel injection and post fuel injection at the set amount and the timing shown in FIG.
[0043]
As an example of specific set amounts in FIG. 4, for example, the amount of the main fuel injections a1 to a4 is 50 mm 3 / stroke, and the amount A1 of the rear fuel injections b1 to b3 of the first cylinder group is 2 of the main fuel injection amount. The amount A2 of 1 mm 3 / stroke corresponding to% and the post-fuel injection b4 of the second cylinder group is 1 mm 3 / stroke corresponding to 2% of the main fuel injection amount. That is, the total amount of post-injection of the cylinders 81 to 84 is 4 mm 3 / two revolutions of the engine. Therefore, the deterioration rate of fuel consumption due to the post-fuel injection with respect to the main fuel injection amount is 2%.
[0044]
In this case, the exhaust gas flowing into the second catalyst device 22 is a mixed exhaust gas of the exhaust gas flowing from the exhaust pipe 34 (the exhaust gas of the cylinder 84) and the exhaust gas discharged from the first catalyst device 21, and the cylinder Since the HC concentration of the exhaust gas 84 is diluted by the exhaust gas having a low HC concentration discharged from the first catalyst device 21, the HC concentration of the exhaust gas of the second catalyst device 22 is the exhaust gas of the first catalyst device 21. It becomes lower than the HC concentration.
[0045]
On the other hand, if the result of step 607 is negative, the process proceeds to step 609, where it is determined whether or not the catalyst temperature T of the first catalyst device 21 is lower than the third set temperature T3. Proceed to step 610. If not, proceed to step 611.
When the process proceeds to step 610, that is, when the catalyst temperature of the first catalyst device 21 is equal to or higher than the maximum purification rate temperature T2 and lower than the purification stop temperature T3 (in the third temperature zone), the first cylinder group Is set to an amount A3 smaller than A1.
[0046]
The reason is to prevent excessive temperature rise of the first catalyst device 21. That is, almost all the HC reacts in the upstream first catalyst device 21, but the excessive injection temperature can be suppressed because the post-injection amount A3 is small. Then, the temperature of the exhaust gas flowing out from the first catalyst device 21 and flowing into the second catalyst device 22 decreases due to heat dissipation. Therefore, the second catalyst device 22 can be adjusted to a state in which the nitrogen oxide purification rate is higher. That is, normally, by setting the post fuel injection amount for the second cylinder group (cylinder 84) to an amount A4 larger than A2, the purification rate of the second catalyst device 22 can be kept high.
[0047]
Then, the process proceeds to step 620, where the ECU 40 instructs the solenoid valve injectors 11-14 to perform main fuel injection and post fuel injection at the set amount and the timing shown in FIG.
As an example of specific set amounts in FIG. 5, for example, the amount of main fuel injections a1 to a4 is 50 mm 3 / stroke, and the amount A3 of rear fuel injections b1 to b3 of the first cylinder group is 1 of the main fuel injection amount. The amount A4 of 0.5 mm3 / stroke corresponding to% and the post-fuel injection b4 of the second cylinder group is 2.5 mm3 / stroke corresponding to 5% of the main fuel injection amount. That is, the total amount of post-injection of the cylinders 81 to 84 is 4 mm 3 / two revolutions of the engine. Therefore, the deterioration rate of fuel consumption due to the post-fuel injection with respect to the main fuel injection amount is 2%.
[0048]
On the other hand, when the process proceeds to step 611, that is, when the catalyst temperature of the first catalyst device 21 is equal to or higher than the purification stop temperature T3 (in the fourth temperature zone), the first cylinder group (cylinders 81 to 83) The post fuel injection amount is made zero. On the other hand, the temperature of the exhaust gas flowing into the second catalyst device 22 becomes lower than the exhaust gas flowing out of the first catalyst device 21 due to heat dissipation. Therefore, there is a case where the second catalyst device 22 can be in a state capable of purifying nitrogen oxides, that is, the third temperature zone, and the amount of post-fuel injection for the second cylinder group (cylinder 84) is A value corresponding to the catalyst temperature Ts of the two-catalyst device 22 is set.
[0049]
In step 620, the ECU 40 commands the main fuel injection and the post fuel injection to the solenoid valve injectors 11 to 14 at the set amount and the timing shown in FIG.
In the example of specific set amounts in FIG. 6, for example, the amount of main fuel injections a1 to a4 is 50 mm3 / stroke, the amount of rear fuel injections b1 to b3 of the first cylinder group is zero, and the amount of rear fuel injection of the second cylinder group is The amount A5 of the fuel injection b4 is 1 mm 3 / stroke corresponding to 2% of the main fuel injection amount. That is, the total amount of post-injection of the cylinders 81 to 84 is 1 mm 3 / two revolutions of the engine. Therefore, the deterioration rate of fuel consumption due to post-fuel injection with respect to the main fuel injection amount is 0.5%.
[0050]
FIG. 8 illustrates the effect of the nitrogen oxide purifying apparatus 1 of this example in comparison with the case where the post fuel injection is uniformly made constant without performing the control as in this example. The temperature of the exhaust gas flowing into the catalyst device is taken, and the purification rate of nitrogen oxide is shown in% on the vertical axis.
The curve indicated by reference numeral 54 in the figure shows a small value for the post fuel injection amount for the cylinders 81 to 84, for example, 0.5 mm 3 / stroke, regardless of the catalyst temperatures T and Ts of the first catalyst device 21 and the second catalyst device 22. It is a purification characteristic in the case of. A curve indicated by reference numeral 55 indicates a case where the post fuel injection amount for the cylinders 81 to 84 is set to a large value, for example, 1 mm 3 / stroke, regardless of the catalyst temperatures T and Ts of the first catalyst device 21 and the second catalyst device 22. It is a purification characteristic.
[0051]
Compared with the former characteristic (reference numeral 54), the latter characteristic (reference numeral 55) increases the amount of HC, so that the catalyst is heated by the reaction heat of HC on the low temperature side of the inflowing exhaust gas, and the purification rate is improved. The exhaust gas temperature at which the maximum purification rate can be obtained decreases, and the maximum purification rate increases as HC increases. However, on the high-temperature exhaust gas side, the catalytic device overheats due to the reaction heat of HC and the purification rate decreases.
[0052]
On the other hand, in the case of the nitrogen oxide purification device 1 of this example, that is, when the temperature of the first catalyst device 21 is low (second temperature zone), the post-injection amounts of all the cylinders 81 to 84 are relatively large values. (For example, 1 mm3 / stroke), and when the temperature of the first catalyst device 21 is higher (third temperature zone), the post-injection amount of the first cylinder group (cylinders 81 to 83) is set to a small value (for example, 0.5 mm3). The characteristic when the post-injection amount of the second cylinder group (cylinder 84) is set to a large value (for example, 2.5 mm3 / stroke) is indicated by reference numeral 56. As can be seen from FIG. The object purification device 1 exhibits a high nitrogen oxide purification rate in a wide range of exhaust gas temperatures.
[0053]
As described above, according to this example, when the temperature of the catalyst is low, the temperature increase is promoted. When the temperature of the catalyst is high, the excessive temperature increase is suppressed, and a high nitrogen oxide purification rate is achieved over a wide range. Can be achieved.
According to this example, the apparatus is not increased in size or greatly complicated.
[0054]
In the above example, a case where the total number of catalyst devices 21 and 22 is two has been described. However, in the case of four cylinders, a maximum of four catalyst devices can be used. In this case, if the number of catalyst devices is increased, the configuration becomes more complicated, but the purification rate of nitrogen oxides is improved.
[0055]
In addition, the first catalyst device 21 and the second catalyst device 22 may have the same characteristics, but may also be the catalyst apparatuses 21 and 22 having different characteristics. In the latter case, in particular, a catalyst (for example, Pt / zeolite catalyst) capable of purifying nitrogen oxides in a low temperature region by the first catalyst device 21 arranged upstream is used, and the second catalyst device 22 on the downstream side. By using a catalyst (for example, a Cu / zeolite catalyst) that is activated in a higher temperature region, the temperature range in which nitrogen oxides can be purified can be broadened, and the upstream side catalytic device 21 can be an exhaust gas. Since the temperature is quickly raised by the heat of the catalyst, there is an advantage that the catalyst device 21 can be activated more rapidly.
[0056]
Conventionally, when a catalyst device that is activated at a lower temperature and a catalyst device that is activated at a higher temperature are arranged in series, a catalyst device that is activated at a higher temperature on the upstream side is arranged for the reason described below. The method was adopted. That is, when supplying HC from the upstream side of the catalyst device, if a catalyst that is activated at a low temperature is arranged on the upstream side, all the HC reacts in the upstream catalyst device, and the downstream catalyst This is because HC may not be supplied.
[0057]
And when such a method is adopted, when accelerating from idling, the upstream upstream catalyst device, which is easy to raise the temperature, is quickly activated to purify nitrogen oxides. Since the catalyst does not activate unless the temperature rises, the mode running results in a low purification rate.
However, in this example, since HC can be supplied to each of the upstream catalyst device 21 and the downstream catalyst device 22, there is no problem due to the above reason, and therefore the catalyst device 21 that is activated at a low temperature is arranged upstream. By doing so, it is possible to quickly start up the catalyst device without any problem.
[0058]
Embodiment 2
In this example, as shown in FIG. 9, in the first embodiment, the post fuel injection of the first cylinder group (cylinders 81 to 83) is collectively injected into one cylinder 81 (or 82, 83), and the other The cylinders 82 and 83 are another embodiment in which post-injection is not performed. FIG. 9 shows a fuel injection waveform in a state (second temperature zone) corresponding to FIG. 4 of the first embodiment.
In this example, the number of cylinders in the second cylinder group is one. However, if the second cylinder group is composed of a plurality of cylinders, only one cylinder belonging to the second cylinder group performs post-injection. carry out.
[0059]
For example, the amount of main fuel injection a1 to a4 is 50 mm3 / stroke), and the amount of post-fuel injection of the first cylinder group is 3 mm3 / equivalent to the amount of post-injection b1 of cylinder 81 corresponding to 6% of the main fuel injection amount. Stroke is set so that the amount of post-injection b2 and b3 of the cylinders 82 and 83 is zero. The amount of the post-fuel injection b4 of the second cylinder group is 1 mm 3 / stroke corresponding to 2% of the main fuel injection amount. That is, the total amount of post-injection of the cylinders 81 to 84 is 4 mm 3 / two revolutions of the engine. Therefore, the deterioration rate of fuel consumption due to the post-fuel injection with respect to the main fuel injection amount is 2%.
[0060]
According to this example, among the solenoid valve injectors 11 to 14, only the first and fourth solenoid valve injectors 11 and 14 need to be the high sensitivity and fast response solenoid valve injectors. Therefore, the injector can be reduced in size and cost, and the number of operations of the second and third solenoid valve injectors 12 and 13 can be halved and the durability can be improved. Others are the same as in the first embodiment.
[0061]
Embodiment 3
As shown in FIGS. 10 and 11, this example is another embodiment in which the main fuel injection amount is different between the first cylinder group and the second cylinder group in the first embodiment.
That is, the main fuel injection amount is set to a different amount corresponding to the operating state of the engine and the temperature of the catalyst devices 21 and 22.
[0062]
FIG. 10 shows the fuel injection waveforms of the solenoid valve injectors 11 to 14 when the catalyst temperature of the first catalyst device 21 is lower than the T1 (first temperature zone). Corresponding to
The main fuel injection amount of each cylinder of the first cylinder group (cylinders 81 to 83) is the same amount (for example, 67 mm3 / stroke), and the main fuel injection amount of the cylinder 84 of the second cylinder group is zero. That is, the total amount of main fuel is the same as that in FIG. 3 of the first embodiment, and only its distribution is changed. Since the main fuel injection of the second cylinder group is zero, the cylinder 84 functions as an air pump.
[0063]
As described above, since the main fuel is shared only for the first cylinder group, the temperature of the exhaust gas flowing into the first catalyst device 21 is increased, the temperature rise is promoted, and the nitrogen oxide purification rate is rapidly increased. Will stand up.
The amount of post-injection is set to a small value (for example, 1 mm 3 / stroke) in the cylinders 81 to 83 in the first cylinder group, and the cylinder 84 in the second cylinder is zero. The reason why the post fuel injection is performed on the first cylinder group is that the temperature of the first catalyst device 21 is rapidly raised by the main fuel injection, and the nitrogen oxide can be purified in the first catalyst device 21 rapidly. It is.
[0064]
As a result, in the case of the above numerical values, the total amount of post-injection is 3 mm 3 / two revolutions of the engine, and the deterioration of fuel consumption due to post-injection with respect to the main fuel injection amount is 1.5% on average.
The reason why the second injection of the second cylinder group is set to zero is that the cylinder 84 of the first cylinder group becomes an air pump, the temperature of the second catalytic device 22 is lowered, and the purifying action of nitrogen oxides cannot be expected. is there.
[0065]
On the other hand, FIG. 11 shows the waveform of fuel injection of the solenoid valve injectors 11 to 14 when the catalyst temperature of the first catalyst device 21 is equal to or higher than T3 (fourth temperature zone). This corresponds to FIG.
The main fuel injection amount of each cylinder of the first cylinder group (cylinders 81 to 83) is the same amount (for example, 67 mm3 / stroke), and the main fuel injection amount of the cylinder 84 of the second cylinder group is zero. That is, the total amount of main fuel is the same as that in FIG. 6 of the first embodiment, and only the distribution is changed. Since the main fuel injection of the second cylinder group is zero, the cylinder 84 of the second cylinder group acts as an air pump.
[0066]
Further, the amount of post-injection is zero for the cylinders 81 to 83 of the first cylinder group, and the cylinder 84 of the second cylinder has a larger value (for example, 4 mm3 / stroke). Therefore, the total amount of post-injection is 4 mm <3> / two revolutions of the engine, and the deterioration of fuel consumption due to post-injection with respect to the main fuel injection amount is 2.0% on average.
As described above, since the cylinder 84 of the second cylinder group is operated as an air pump, the temperature of the downstream second catalytic device 22 can be lowered and maintained at a temperature at which nitrogen oxides can be purified.
[0067]
The reason why the post-injection of the first cylinder group is set to zero is that the first catalyst device 21 cannot perform a purification action at a high temperature. The reason why the post-injection amount of the cylinder 84 of the second cylinder group is increased is that the exhaust gas of all the cylinders 81 to 84 flows into the second catalyst device 22 without purifying the nitrogen oxides, This is because a large amount is added to increase the purification rate of nitrogen oxides.
As described above, according to this example, even when the first catalyst device 21 is in the first and fourth temperature zones, it is possible to perform control for promoting purification of the catalyst device. Others are the same as in the first embodiment.
[0068]
Embodiment 4
As shown in FIG. 12, this example is another embodiment in which the number of cylinders belonging to the first cylinder group is two and the number of cylinders belonging to the second cylinder group is two in the third embodiment. It is.
Thus, when the first catalyst device 21 is in the first and fourth temperature zones, the purifying action of nitrogen oxides by the catalyst device 21 or the catalyst device 22 can be exhibited in a wider temperature range. It becomes possible.
[0069]
In other words, when in the first temperature zone, the main fuel is concentrated in the two cylinders 81 and 83 of the first cylinder group, and the first catalyst device 21 than in the third embodiment where the main fuel is concentrated in the three cylinders 81 to 83. The temperature can be increased more quickly. Further, even in the fourth temperature zone, the two cylinders 82 and 84 belonging to the second cylinder group act as an air pump, so that one cylinder acts as an air pump. The cooling of the second catalyst device 22 is strengthened more than the case, and the purification action of the second catalyst device 22 can be maintained in a wider temperature range of the first catalyst device 21. Others are the same as in the third embodiment.
[0070]
Embodiment 5
In this example, as shown in FIG. 13, the number of engine cylinders 81 to 86 and the number of solenoid valve injectors 11 to 16 in the first embodiment is six, and the number of cylinders 81 to 85 belonging to the first cylinder group is five. This is an example in which one cylinder 86 belonging to the second cylinder group is provided. Others are the same as in the first embodiment.
[0071]
In the above, the number of the catalyst devices 21 and 22 is not limited to two, but may be three or more.
Further, the number of cylinders in the first cylinder group may be four, and the number of cylinders in the second cylinder group may be two.
The concept of each embodiment can be similarly applied to a 3-cylinder engine and an 8-cylinder engine.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a nitrogen oxide purification apparatus according to Embodiment 1;
FIG. 2 is a graph showing the relationship between the catalyst temperature and the purification rate of the nitrogen oxide purification apparatus according to Embodiment 1;
3 is a diagram (first temperature zone) showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of Embodiment 1; FIG.
FIG. 4 is a view showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of Embodiment 1 (second temperature zone).
FIG. 5 is a view showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus according to Embodiment 1 (third temperature zone).
6 is a view showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus according to Embodiment 1 (fourth temperature zone). FIG.
7 is a diagram showing the purification characteristics (reference numeral 56) of the nitrogen oxide purification apparatus of Embodiment 1 together with a case where simple control is performed (reference numerals 54 and 55). FIG.
FIG. 8 is a flowchart showing a control procedure of the nitrogen oxide purification apparatus according to Embodiment 1;
9 is a diagram (second temperature zone) showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of Embodiment 2. FIG.
FIG. 10 is a diagram (first temperature zone) showing a waveform of fuel injection for each cylinder in the nitrogen oxide purification apparatus of Embodiment 3;
FIG. 11 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of Embodiment 3 (fourth temperature zone).
FIG. 12 is a system configuration diagram of a nitrogen oxide purification apparatus according to Embodiment 4;
13 is a system configuration diagram of a nitrogen oxide purifying apparatus according to Embodiment 5. FIG.
[Explanation of symbols]
1. . . Nitrogen oxide purification equipment,
11-14. . . Solenoid valve injection (fuel injection means),
21,22. . . Catalytic equipment,
24-26. . . Exhaust temperature sensor,
40. . . ECU (fuel injection control means),

Claims (11)

気筒毎に設けられた燃料噴射手段と，上記燃料噴射手段を制御する燃料噴射制御手段と，排気通路に配置され窒素酸化物を還元浄化する複数の触媒装置と，上記触媒装置の温度を測定または推定する触媒温度判定手段と，少なくとも気筒の行程位置を検知することの出来る運転状態検知手段とを有する内燃機関の窒素酸化物浄化装置であって，
上記触媒装置は，排気通路の上流側に配置された第１触媒装置と，この第１触媒装置の下流側に直列に配置された第２触媒装置とからなると共に，上記気筒は上記第１触媒装置の上流に接続された第１の気筒群と上記第１触媒装置と第２触媒装置との間の排気通路に接続された第２の気筒群とからなり，
上記燃料噴射制御手段は，上記触媒温度判定手段及び運転状況検知手段の出力信号を受け，圧縮上死点近傍における機関出力発生のための主燃料噴射指令と，膨張行程または排気行程における炭化水素供給のための後燃料噴射指令とを上記燃料噴射手段に対して各気筒毎に発し，上記第１触媒装置又は上記第２触媒装置の温度に対応して各気筒または上記気筒群に対する上記後燃料噴射の量を，上記各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図れるだけの炭化水素供給量が，上記第１触媒装置および上記第２触媒装置の両触媒装置に供給されるように調整することを特徴とする内燃機関の窒素酸化物浄化装置。Fuel injection means provided for each cylinder, fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices disposed in the exhaust passage for reducing and purifying nitrogen oxides, and measuring the temperature of the catalyst devices A nitrogen oxide purifying device for an internal combustion engine having an estimated catalyst temperature determining means and an operating state detecting means capable of detecting at least a stroke position of a cylinder,
The catalyst device includes a first catalyst device disposed upstream of the exhaust passage and a second catalyst device disposed in series downstream of the first catalyst device, and the cylinder includes the first catalyst device. A first cylinder group connected upstream of the apparatus and a second cylinder group connected to the exhaust passage between the first catalyst apparatus and the second catalyst apparatus,
The fuel injection control means receives the output signals of the catalyst temperature determination means and the operating condition detection means, and receives a main fuel injection command for generating engine output near the compression top dead center and a hydrocarbon supply in the expansion stroke or exhaust stroke. a fuel injection command issued to each cylinder with respect to the fuel injection means, said first catalytic device or the post fuel injection for each cylinder or the cylinder group in response to the temperature of the second catalytic converter after for the amount of the hydrocarbon feed rate of only Figure is to maximize the purification rate of the nitrogen oxides while suppressing overheating of the respective catalytic device, both the catalytic device of the first catalytic device and the second catalytic device An apparatus for purifying nitrogen oxides of an internal combustion engine, characterized by being adjusted so as to be supplied . 請求項１において，上記燃料噴射制御手段は，上記第１の触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記第１の触媒装置の温度が低温の第１の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が上記第１の触媒装置の温度の上昇と共に上昇する第２の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が上記第１の触媒装置の温度の上昇と共に下降する第３の温度ゾーンと，
上記第１の触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記第１の触媒装置の温度が高温の第４の温度ゾーンとに温度ゾーンを区分し，
各温度ゾーン毎に各気筒または各気筒群に対する上記後燃料噴射量の大きさ及び配分比率を変化させることを特徴とする内燃機関の窒素酸化物浄化装置。According to claim 1, said fuel injection control means includes a first temperature zone temperature is low in the first catalyst device purifying rate of the nitrogen oxide in the first catalyst device to remain at very low levels,
A second temperature zone in which the nitrogen oxide purification rate of the first catalytic device rises with increasing temperature of the first catalytic device ;
A third temperature zone in which the nitrogen oxide purification rate of the first catalyst device decreases as the temperature of the first catalyst device rises ;
Dividing the temperature zone into a fourth temperature zone in which the temperature of the first catalyst device in which the purification rate of nitrogen oxides of the first catalyst device changes at an extremely low level is high;
Nitrogen oxide purification system of an internal combustion engine, characterized in that changing the size and distribution ratio of the rear fuel injection amount for each cylinder or each cylinder group for each temperature zone. 請求項２において，上記燃料噴射制御手段は，上記第３の温度ゾーンにおいては，第１の気筒群に属する気筒に対して第２の温度ゾーンにおいて設定した後燃料噴射量よりも小さい後燃料噴射量を設定し，第２の気筒群に属する気筒に対しては第２の温度ゾーンにおいて設定した後燃料噴射量よりも大きい後燃料噴射量を設定することを特徴とする内燃機関の窒素酸化物浄化装置。In claim 2, the fuel injection control means, in the above-described third temperature zone, the fuel injection after less than the fuel injection amount after setting the second temperature zones for the cylinders belonging to the first cylinder group And a post-fuel injection amount larger than the post-fuel injection amount set in the second temperature zone is set for the cylinders belonging to the second cylinder group. Purification equipment. 気筒毎に設けられた燃料噴射手段と，上記燃料噴射手段を制御する燃料噴射制御手段と，排気通路に配置され窒素酸化物を還元浄化する複数の触媒装置と，上記触媒装置の温度を測定または推定する触媒温度判定手段と，少なくとも気筒の行程位置を検知することの出来る運転状態検知手段とを有する内燃機関の窒素酸化物浄化装置であって，
上記触媒装置は，上流側から第１触媒装置，第２触媒装置，・・・，第Ｎ触媒装置の順序で排気通路に直列に配置されたＮ個の触媒装置からなり，
一方，全体の気筒は，単一または複数の気筒によって構成されるＮ個の気筒群からなると共に，第１の気筒群は上記第１触媒装置の上流に接続され，１を越える自然数Ｉにおける第Ｉ番目の気筒群は上記第（Ｉ−１）触媒装置と第Ｉ触媒装置との間の排気通路に接続されており，
上記燃料噴射制御手段は，上記触媒温度判定手段及び運転状況検知手段の出力信号を受け，圧縮上死点近傍における機関出力発生のための主燃料噴射指令と，膨張行程または排気行程における炭化水素供給のための後燃料噴射指令とを上記燃料噴射手段に対して各気筒毎に発し，上記Ｎ個の触媒装置の温度に対応して各気筒または上記気筒群に対する上記後燃料噴射の量を，上記各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図れるだけの炭化水素供給量が，上記第１触媒装置および上記第２触媒装置の両触媒装置に供給されるように調整することを特徴とする内燃機関の窒素酸化物浄化装置。Fuel injection means provided for each cylinder, fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices disposed in the exhaust passage for reducing and purifying nitrogen oxides, and measuring the temperature of the catalyst devices A nitrogen oxide purifying device for an internal combustion engine having an estimated catalyst temperature determining means and an operating state detecting means capable of detecting at least a stroke position of a cylinder,
The catalyst device comprises N catalyst devices arranged in series in the exhaust passage in the order of the first catalyst device, the second catalyst device,..., The Nth catalyst device from the upstream side,
On the other hand, the entire cylinder is composed of N cylinder groups each composed of a single cylinder or a plurality of cylinders, and the first cylinder group is connected upstream of the first catalyst device, and the first cylinder group having a natural number I exceeding 1 is connected. The I-th cylinder group is connected to the exhaust passage between the (I-1) th catalyst device and the I-th catalyst device,
The fuel injection control means receives the output signals of the catalyst temperature determination means and the operating condition detection means, and receives a main fuel injection command for generating engine output near the compression top dead center and a hydrocarbon supply in the expansion stroke or exhaust stroke. the amount after the fuel injection command issued to each cylinder with respect to the fuel injection means, the rear fuel injection in response to the temperature of the N catalyzer for each cylinder or the cylinder group for, the as the hydrocarbon feed rate of only Figure it is to maximize the purification rate of the nitrogen oxides while suppressing overheating of the catalyst device is supplied to both the catalytic device of the first catalytic device and the second catalytic device A nitrogen oxide purifying device for an internal combustion engine, characterized by adjusting . 請求項４において，上記燃料噴射制御手段は，上記各触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記触媒装置の温度が低温の第１の温度ゾーンと，
上記各触媒装置の窒素酸化物の浄化率が上記触媒装置の温度の上昇と共に上昇する第２の温度ゾーンと，
上記各触媒装置の窒素酸化物の浄化率が上記触媒装置の温度の上昇と共に下降する第３の温度ゾーンと，
上記各触媒装置の窒素酸化物の浄化率が極めて低いレベルで推移する上記触媒装置の温度が高温の第４の温度ゾーンとに温度ゾーンを区分し，
各温度ゾーン毎に各気筒または各気筒群に対する上記後燃料噴射量の大きさ及び配分比率を変化させることを特徴とする内燃機関の窒素酸化物浄化装置。In claim 4, the fuel injection control means includes a first temperature zone temperature is low in the catalytic device purification rate of the nitrogen oxides of the respective catalytic device to remain at very low levels,
A second temperature zone in which the purification rate of nitrogen oxides of each of the catalyst devices rises as the temperature of the catalyst device rises;
A third temperature zone in which the purification rate of nitrogen oxides of each of the catalyst devices decreases as the temperature of the catalyst device increases ;
A temperature zone is divided into a fourth temperature zone in which the temperature of the catalyst device in which the purification rate of nitrogen oxides of each catalyst device changes at an extremely low level is high,
Nitrogen oxide purification system of an internal combustion engine, characterized in that changing the size and distribution ratio of the rear fuel injection amount for each cylinder or each cylinder group for each temperature zone. 請求項５において，上記燃料噴射制御手段は，上記第Ｉ番目の触媒装置の温度が上記第３の温度ゾーンにある場合においては，第Ｉ番目の気筒群に属する気筒に対して第２の温度ゾーンにおいて設定した後燃料噴射量よりも小さい後燃料噴射量を設定し，第（Ｉ＋１）番目以降の気筒群に属する気筒に対しては第２の温度ゾーンにおいて設定した後燃料噴射量よりも大きい後燃料噴射量を設定することを特徴とする内燃機関の窒素酸化物浄化装置。In claim 5, said fuel injection control means, in the above-described case where the temperature of the I-th catalytic device is in the third temperature zone, the second temperature into the cylinder belonging to the I-th cylinder group A post-fuel injection amount smaller than the post-fuel injection amount set in the zone is set, and is larger than the post-fuel injection amount set in the second temperature zone for cylinders belonging to the (I + 1) th and subsequent cylinder groups. An apparatus for purifying nitrogen oxides for an internal combustion engine, wherein an after-fuel injection amount is set. 請求項１から請求項６のいずれか１項において，上記触媒装置の特性は，上流側に配置される触媒装置の窒素酸化物浄化可能温度範囲が，下流側に配置される触媒装置の窒素酸化物浄化可能温度範囲よりも低温であることを特徴とする内燃機関の窒素酸化物浄化装置。In any one of claims 1 to 6, the characteristics of the catalytic converter, the nitrogen oxide purification possible temperature range of the catalytic converter arranged upstream side, the NOx catalyst device disposed downstream An apparatus for purifying nitrogen oxides of an internal combustion engine, characterized in that the temperature is lower than a temperature range capable of purifying an object. 請求項１から請求項７のいずれか１項において，上記燃料噴射制御手段は，気筒群におけるトータルの後燃料噴射量を設定し，その気筒群における後燃料噴射をその気筒群内の一部の気筒に集中させて噴射させることを特徴とする内燃機関の窒素酸化物浄化装置。8. The fuel injection control means according to claim 1, wherein the fuel injection control means sets a total post fuel injection amount in the cylinder group, and the post fuel injection in the cylinder group is set to a part of the cylinder group. An apparatus for purifying nitrogen oxides for an internal combustion engine, wherein the fuel is concentrated and injected in a cylinder. 請求項１から請求項８のいずれか１項において，上記燃料噴射制御手段は，上記後燃料噴射量に加えて，更に気筒群毎に主燃料噴射の量を調整し，各触媒装置の過熱を抑制しつつ窒素酸化物の浄化率の最大化を図ることを特徴とする内燃機関の窒素酸化物浄化装置。In any one of claims 1 to 8, the fuel injection control means, in addition to the fuel injection amount after the, and adjusting the amount of main fuel injection further in each cylinder group, the overheating of the catalytic converter An apparatus for purifying nitrogen oxides for an internal combustion engine, wherein the purification rate of nitrogen oxides is maximized while being suppressed. 請求項９において，上流側に位置する第Ｉ番目の触媒装置の温度が，請求項２または請求項５記載の上記第１の温度ゾーンにある場合においては，主燃料噴射を第Ｉ番目の気筒群に集中させて第Ｉ触媒装置の昇温を促進し，
請求項２または請求項５記載の上記第４の温度ゾーンにある場合においては，主燃料噴射を第Ｉ番目の気筒群に集中させて第（Ｉ＋１）番目以降の下流の触媒装置の冷却を促進することを特徴とする内燃機関の窒素酸化物浄化装置。In claim 9, the temperature of the I-th catalyzer located upstream is In no event in claim 2 or claim 5 said first temperature zone described, the I-th main fuel injection To increase the temperature of the first catalyst device by concentrating on the cylinder group of
In cases in claim 2 or claim 5 in the fourth temperature zone of the described, facilitate cooling of the by concentrating the main fuel injection in the I-th cylinder group (I + 1) th and subsequent downstream of the catalytic converter A nitrogen oxide purifying device for an internal combustion engine. 請求項９において，上記触媒装置は第１，第２触媒装置からなり，上記燃料噴射制御手段は，請求項２記載の上記第１の温度ゾーンにおいては，主燃料噴射を第１の気筒群に集中させて第１触媒装置の昇温を促進し，
請求項２記載の上記第４の温度ゾーンにおいては，主燃料噴射を第１の気筒群に集中させて第２触媒装置の冷却を促進することを特徴とする内燃機関の窒素酸化物浄化装置。In Claim 9, the said catalyst apparatus consists of a 1st, 2nd catalyst apparatus, and the said fuel-injection control means makes the main fuel injection to a 1st cylinder group in the said 1st temperature zone of Claim 2. Concentrate to promote the temperature rise of the first catalytic device,
In the fourth temperature zone of the second aspect, the nitrogen oxide purification device for an internal combustion engine, characterized in that to promote the cooling of the second catalytic device to concentrate the main fuel injection to the first cylinder group.
JP16083396A 1996-05-30 1996-05-30 Nitrogen oxide purification device for internal combustion engine Expired - Fee Related JP3750195B2 (en)

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DE19722147A DE19722147B4 (en) 1996-05-30 1997-05-27 Exhaust emission cleaning device for purifying nitrogen oxides
FR9706604A FR2749351B1 (en) 1996-05-30 1997-05-29 APPARATUS FOR CONVERTING NITROGEN OXIDES FOR AN INTERNAL COMBUSTION ENGINE

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