JP4211401B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

Info

Publication number
JP4211401B2
JP4211401B2 JP2003006666A JP2003006666A JP4211401B2 JP 4211401 B2 JP4211401 B2 JP 4211401B2 JP 2003006666 A JP2003006666 A JP 2003006666A JP 2003006666 A JP2003006666 A JP 2003006666A JP 4211401 B2 JP4211401 B2 JP 4211401B2
Authority
JP
Japan
Prior art keywords
reducing agent
fuel ratio
air
exhaust gas
amount
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
JP2003006666A
Other languages
Japanese (ja)
Other versions
JP2004218520A (en
Inventor
孝太郎 林
久 大木
正晃 山口
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyota Motor Corp
Original Assignee
Toyota Motor Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyota Motor Corp filed Critical Toyota Motor Corp
Priority to JP2003006666A priority Critical patent/JP4211401B2/en
Publication of JP2004218520A publication Critical patent/JP2004218520A/en
Application granted granted Critical
Publication of JP4211401B2 publication Critical patent/JP4211401B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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

Landscapes

  • Exhaust Gas Treatment By Means Of Catalyst (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】
【発明の属する技術分野】
本発明は、内燃機関の排気浄化装置に関するものであり、特に排気中の硫黄酸化物を保持し、定期的に、保持した硫黄酸化物の除去処理を行う内燃機関の排気浄化装置に関するものである。
【０００２】
【従来の技術】
内燃機関の排気浄化技術として、内燃機関（特に希薄燃焼エンジン、ディーゼルエンジン）の排気系に吸蔵還元型ＮＯｘ触媒（以下単に「ＮＯｘ触媒」という。）を配置して、リーンな空燃比での運転時に排気中の窒素酸化物（以下単に「ＮＯｘ」という場合もある。）を大気中に放出する前に該ＮＯｘ触媒上に一時的に保持する技術が知られているが、このようなＮＯｘ触媒は、排気中のＮＯｘとともに硫黄酸化物（以下単に「ＳＯｘ」という場合もある。）も保持してしまうため、ＳＯｘの保持量が増加した場合には排気中のＮＯｘを保持しきれなくなる、いわゆるＳＯｘ被毒を生じる。
【０００３】
これに対して、ＳＯｘを保持したＳＯｘ保持材としてのＮＯｘ触媒を例えば約６００℃の高温とし、ＮＯｘ触媒へ還元剤たる燃料を供給することによりＮＯｘ触媒に流入する排気の空燃比をリッチな空燃比にして、ＮＯｘ触媒を高温かつ還元雰囲気とすることによりＮＯｘ触媒に保持されたＳＯｘを還元除去し、以ってＮＯｘ触媒のＳＯｘ被毒を解消させている（例えば、特許文献１参照）。
【０００４】
【特許文献１】
特開２００１−８２１３７号公報
【０００５】
【発明が解決しようとする課題】
ところが、ＳＯｘ被毒を解消するために排気の空燃比をリッチな空燃比にする際に、目標のリッチ空燃比よりもリッチ側にずれた場合、すなわち排気中に還元剤が多目に存在する場合、多目に存在する還元剤と排気中の酸素がＮＯｘ触媒上で反応しＮＯｘ触媒の温度が過剰に上昇するおそれがある。一方、目標のリッチ空燃比よりもリーン側にずれた場合、すなわち排気中に還元剤が少な目に存在する場合、ＮＯｘ触媒に保持されたＳＯｘを還元すべき還元剤が不足するため、特にＳＯｘ被毒解消するための処理を所定期間内で実施する場合は、十分にＳＯｘ被毒を解消できなくなるおそれがある。
【０００６】
そのため、通常運転時のリーン空燃比からＳＯｘ被毒解消処理のために一度リッチ空燃比とした後は、リッチ期間中に還元剤添加後の空燃比を目標リッチ空燃比となるようにフィードバック制御している。これは、例えば、ＮＯｘ触媒の上流またはおよび下流に備えられた空燃比センサで排気の空燃比を検出し、この検出値と目標の空燃比との間に差がある場合は、これを補正するように内燃機関内に噴射する燃料あるいは還元剤添加量とを決定するものである。
【０００７】
しかし、リーン空燃比から還元剤を供給して目標のリッチ空燃比にする際に、内燃機関の空燃比がずれていると、たとえ還元剤添加量が適正であっても還元剤添加後の空燃比が目標のリッチな空燃比とずれてしまう。特に、通常運転時のリーンな空燃比からＳＯｘ被毒解消処理のためにリッチ空燃比にする際の最初の還元剤添加時のズレ量が大きいと、その後、リッチ空燃比にしてＳＯｘ被毒解消処理を実施する期間中にＮＯｘ触媒に流入する排気の空燃比をフィードバック制御したとしても、最初に還元剤を添加した時点のＮＯｘ触媒に流入する排気の空燃比が目標空燃比とずれてしまうことから、上述のようにＮＯｘ触媒の温度が過剰に昇温したり、十分にＳＯｘ被毒を解消できなかったりしてしまう。また、ＮＯｘ触媒が過剰に昇温した場合はＮＯｘ触媒の熱劣化を生じさせてしまうおそれがある。
【０００８】
本発明は、上記した問題点に鑑みてなされたものであり、その目的とするところは、ＮＯｘ触媒等のＳＯｘ保持材の熱劣化を防止しつつＳＯｘ保持材からＳＯｘを精度よく除去できる内燃機関の排気浄化装置を提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するために本発明に係る内燃機関の排気浄化装置にあっては、還元剤を添加してＳＯｘ保持材に流入する排気の空燃比を理論空燃比あるいはリッチな空燃比とすることによりＳＯｘ保持材に保持されたＳＯｘを除去する際に、内燃機関内の実際の空燃比と目標空燃比との差分を考慮して還元剤添加量を決定することを特徴とする。
【００１０】
そして、具体的な手段としては、内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するとともに高温且つ還元雰囲気で保持した硫黄酸化物が除去されるＳＯｘ保持材と、前記ＳＯｘ保持材の上流で排気に還元剤を添加する還元剤添加手段と、前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、前記空燃比検出手段の検出値に基づいて内燃機関燃焼室内の実際の空燃比と目標空燃比との差分を算出する算出手段と、前記ＳＯｘ保持材から硫黄酸化物を除去させるべく、前記算出手段にて算出した差分を考慮して決定した還元剤添加量を前記還元剤添加手段から添加させる還元剤添加制御手段と、を備えることを特徴とする。
【００１１】
ここで、ＳＯｘ保持材としては、吸蔵還元型ＮＯｘ触媒のように該触媒に流入する排気の空燃比がリーン（理論空燃比以上）であるときには、排気中のＮＯｘを保持して大気中に放出しないようにし、該触媒に流入する排気の空燃比が理論空燃比あるいはリッチ（理論空燃比以下）となったときには、保持していたＮＯｘを放出及び還元して除去するもの、又は、パティキュレートフィルタに該吸蔵還元型ＮＯｘ触媒を担持したもの等を例示することができる。
【００１２】
また、空燃比検出手段としては、排気通路であって、ＳＯｘ保持材より上流およびまたはＳＯｘ保持材より下流に配置される空燃比センサや酸素濃度センサ等を例示することができる。
【００１３】
そして、ＳＯｘ保持材に保持された硫黄酸化物を除去する場合には、ＳＯｘ保持材に流入する排気の温度を高めた上でＳＯｘ保持材に流入する排気の空燃比を理論空燃比以下にする必要があるが、排気の空燃比を理論空燃比以下にするためにＳＯｘ保持材の上流で還元剤添加手段にて還元剤を添加する。その還元剤添加量は、基本的には、リーンな空燃比で運転している内燃機関燃焼室から排出された直後の排気の空燃比を目標のリッチな空燃比とするのに相当する添加量であるが、リーンな空燃比で運転している内燃機関燃焼室から排出された直後の排気の空燃比は内燃機関内の空燃比が目標の空燃比であることを前提として定められるものである。
【００１４】
しかし、例えば、燃焼室内に燃料を噴射する燃料噴射弁に目詰まり等が生じている場合は、燃焼室内の空燃比が目標の空燃比とずれるおそれがあり、かかる場合は、ＳＯｘ保持材に流入する排気の空燃比も目標のリッチな空燃比からずれるおそれがある。そこで、本発明に係る内燃機関の排気浄化装置は、空燃比検出手段の検出値に基づいて燃焼室内の実際の空燃比と目標空燃比との差分を算出する算出手段と、ＳＯｘ保持材から硫黄酸化物を除去させるべく、算出手段にて算出した差分を考慮して決定した還元剤添加量を還元剤添加手段から添加させる還元剤添加制御手段とを備え、ＳＯｘ保持材から硫黄酸化物を除去するために、ＳＯｘ保持材の上流で排気に還元剤添加手段から還元剤を添加する際、還元剤添加制御手段は内燃機関燃焼室内の空燃比のずれを考慮して還元剤添加量を決定して還元剤添加手段から添加させることとしている。
【００１５】
このようにすることで、ＳＯｘ保持材から硫黄酸化物を除去させるべく、最初に還元剤を添加してＳＯｘ保持材に流入する排気の空燃比を所望の空燃比する際に、精度よく目標の空燃比にすることができるので、還元剤が目標より多めに存在することに起因するＳＯｘ保持材の過剰な昇温を招いたり、還元剤が目標より少なめに存在することに起因して所望量の硫黄酸化物を還元・除去することができなかったりすることを防止することができる。
【００１６】
また、算出手段は、前記還元剤添加手段から還元剤を添加していない時の空燃比検出手段の検出値に基づいて内燃機関燃焼室内の実際の空燃比と目標空燃比との差分を算出するものであることが好適である。
【００１７】
還元剤添加手段から還元剤を添加している時の空燃比検出手段の検出値と内燃機関燃焼室内の目標空燃比との差分を算出する場合、特に空燃比検出手段が還元剤添加手段の下流に備えられているときは、還元剤添加量を考慮して実際の内燃機関内の空燃比と目標空燃比との差分を算出すること必要となる。そのため、例えば還元剤添加手段に不具合が生じており還元剤添加量が適正量でないこと等に起因して差が生じている場合も、内燃機関燃焼室内の空燃比のずれと認識して内燃機関内の実際の空燃比と目標空燃比との差分を算出してしまうおそれがある。そして、かかる場合は、還元剤を適正量添加することができなくなり、ＳＯｘ保持材に流入する排気の空燃比が目標の空燃比からずれるおそれがあるので、還元剤添加手段から還元剤を添加していないときの空燃比検出手段の検出値に基づいて内燃機関燃焼室内の実際の空燃比と目標空燃比との差分を算出することが好適である。
【００１８】
また、前記還元剤添加制御手段は、前記還元剤添加手段から間欠的に還元剤を添加して前記ＳＯｘ保持材に流入する排気の空燃比を理論空燃比あるいはリッチな空燃比とする間欠リッチ制御を実行するものであり、前記算出手段は、前記間欠リッチ制御実行中であって、前記還元剤添加手段から還元剤を添加していない時の前記差分を算出するものであるが好適である。
【００１９】
排気内に添加された還元剤は、高温条件下においてＳＯｘ保持材に保持されたＳＯｘを還元する機能を有する一方、ＳＯｘと反応することによりＳＯｘ保持材の温度をさらに上昇させる特性を有する。そのため、還元剤が添加され続けると、ＳＯｘ保持材の温度が上昇し続け、ＳＯｘ保持材の温度が過剰に高くなるおそれがある。そのため、還元剤添加手段から間欠的に還元剤を添加してＳＯｘ保持材に流入する排気の空燃比を理論空燃比あるいはリッチな空燃比とする間欠リッチ制御を実行することにより、還元剤が添加され続けることに起因するＳＯｘ保持材の過剰昇温を防止することができる。
【００２０】
そして、この間欠リッチ制御実行中においても、算出手段は、還元剤添加手段から還元剤を添加していない時の空燃比検出手段の検出値に基づいて内燃機関燃焼室内の実際の空燃比と目標空燃比との差分を算出するものであることが好適であるのは前述と同様である。
【００２１】
そして、還元剤添加量を算出する手段としては、リーンな空燃比で運転している内燃機関燃焼室からの排気の空燃比を前記還元剤添加手段から還元剤を添加して目標のリッチな空燃比とするのに相当するベース還元剤量と前記差分をゼロにするのに相当する差分還元剤量とに基づいて算出することを例示することができる。
【００２２】
また、前記還元剤添加量は、前記ベース還元剤量に前記差分還元剤量を加算して得た還元剤量と所定の還元剤量とを比較して定められることが好適である。上記のように還元剤添加量を決定する場合、例えば、内燃機関燃焼室内に燃料を噴射する燃料噴射弁に目詰まり等が生じていることに起因して、燃焼室内の空燃比がリーン側に大幅にずれる場合、還元剤添加量を増量させてＳＯｘ保持材に流入する排気の空燃比を所望のリッチにするため、その増量した還元剤がＳＯｘ保持材に保持されたＳＯｘと反応してＳＯｘ保持材の温度を過剰に上昇させるおそれがある。
【００２３】
そこで、例えば、ＳＯｘ保持材の容量等に応じて添加する還元剤量の上限となる所定の還元剤量を予め定めておき、前記ベース還元剤量に前記差分還元剤量を加算して得た還元剤量がこの所定の還元剤量以下である場合は、ベース還元剤量に差分還元剤量を加算して得た還元剤量を還元剤添加量として決定し、ベース還元剤量に差分還元剤量を加算して得た還元剤量が所定の還元剤量より多い場合は、所定の還元剤量を還元剤添加量として決定し、還元剤添加手段から添加するようにする。このようにすることで、ＳＯｘ保持材の温度が過剰に昇温することを防止することができる。
【００２４】
【発明の実施の形態】
以下に図面を参照して、この発明の好適な実施の形態を例示的に詳しく説明する。ただし、この実施の形態に記載されている構成部品の寸法、材質、形状、その相対配置などは、特に特定的な記載がない限りは、この発明の範囲をそれらのみに限定する趣旨のものではない。
【００２５】
＜第１の実施の形態＞
図１は、本発明に係る排気環流装置を備えた内燃機関の概略構成を示す図である。図１に示す内燃機関１は、４つの気筒２を有する水冷式の４気筒ディーゼルエンジンである。
【００２６】
内燃機関１は、各気筒２の燃焼室に直接燃料を噴射する燃料噴射弁３を備えている。各燃料噴射弁３は、蓄圧室（コモンレール）４と接続され、このコモンレール４は、燃料供給管５を介して燃料ポンプ６と連通している。
【００２７】
内燃機関１には、吸気通路７が接続されており、この吸気通路７は、エアクリーナボックス８に接続されている。そして、エアクリーナボックス８より下流の吸気通路７には、該吸気通路７内を流通する吸気の質量に対応した電気信号を出力するエアフローメータ９が取り付けられている。
【００２８】
また、吸気通路７の途中には、過給機（ターボチャージャー）１０のコンプレッサハウジング１０ａが設けられている。コンプレッサハウジング１０ａより下流の吸気通路７にはインタークーラ１１が取り付けられている。更にインタークーラ１１より下流の吸気通路７には、該吸気通路７内を流通する吸気の流量を調節する吸気絞り弁１２が設けられている。この吸気絞り弁１２には、該吸気絞り弁１２を開閉駆動する吸気絞り用アクチュエータ１３が取り付けられている。
【００２９】
そして、コンプレッサハウジング１０ａに流入し、該コンプレッサハウジング１０ａ内で圧縮されて高温となった吸気は、インタークーラ１１にて冷却された後、必要に応じて吸気絞り弁１２によって流量を調節されて吸気通路７を介して各気筒２の燃焼室へ分配され、各気筒２の燃料噴射弁３から噴射された燃料を着火源として燃焼される。
【００３０】
また、内燃機関１には排気通路１４が接続され、この排気通路１４は下流にて図示しないマフラーと接続されている。
【００３１】
また、排気通路１４の途中には、前記過給機１０のタービンハウジング１０ｂが配置されており、排気通路１４のタービンハウジング１０ｂより下流の部位には、吸蔵還元型ＮＯｘ触媒（以下、特に断らない限り「ＮＯｘ触媒」という。）１５が備えられている。そして、ＮＯｘ触媒１５の上流の排気通路１４には排気通路１４内を流通する排気の空燃比に対応した電気信号を出力する空燃比センサ１６が取り付けられている。
【００３２】
そして、タービンハウジング１０ｂから排出された排気は、排気通路１４を介してＮＯｘ触媒１５へ流入し、排気中の物質が浄化される。
【００３３】
また、前記吸気通路７における吸気絞り弁１２より下流の部位と、前記排気通路１４におけるタービンハウジング１０ｂより上流の部位とは、排気の一部を吸気通路７へ再循環させるＥＧＲ通路１８を介して連通されている。このＥＧＲ通路１８の途中には、電磁弁などで構成され、印加電力の大きさに応じて前記ＥＧＲ通路１８内を流通する排気（以下、「ＥＧＲガス」という。）の流量を変更するＥＧＲ弁１９が設けられている。
【００３４】
そして、ＥＧＲ通路１８を介して排気通路１４から吸気通路７へ再循環されたＥＧＲガスは、吸気通路７の上流から流れてきた新気と混ざり合いつつ各気筒２の燃焼室へ導かれ、燃料噴射弁３から噴射される燃料を着火源として燃焼される。
【００３５】
ここで、ＥＧＲガスには、水（Ｈ2Ｏ）や二酸化炭素（ＣＯ2）などのように、自らが燃焼することがなく、且つ、吸熱性を有する不活性ガス成分が含まれているため、ＥＧＲガスが混合気中に含有されると、混合気の燃焼温度が低められ、以てＮＯｘの発生量が抑制される。
【００３６】
また、ＮＯｘ触媒１５より上流の排気通路１４を流通する排気中に還元剤たる燃料（軽油）を添加する還元剤供給手段を備えている。この還元剤供給手段は、図１に示されるようにその噴孔が排気通路１４内に臨むよう内燃機関１のシリンダヘッドに取り付けられ、所定の開弁圧以上の燃料が印加されたときに開弁して燃料を噴射する還元剤添加弁２１と、前述した燃料ポンプ６から吐出された燃料を前記還元剤添加弁２１へ導く還元剤供給路２２とを備えている。
【００３７】
尚、還元剤添加弁２１は、該還元剤添加弁２１の噴孔が排気通路１４におけるＥＧＲ通路１８との接続部位より下流であって、排気通路１４における４つの通路の集合部に最も近い気筒２の排気ポートに突出するとともに、排気通路１４の集合部へ向くようシリンダヘッドに取り付けられることが好ましい。
【００３８】
これは、還元剤添加弁２１から噴射された還元剤（未燃の燃料成分）がＥＧＲ通路１８へ流入するのを防止するとともに、還元剤が排気通路１４内に滞ることなく過給機１０のタービンハウジング１０ｂへ到達するようにするためである。
【００３９】
尚、図１に示す例では、内燃機関１の４つの気筒２のうち１番（＃１）気筒２が排気通路１４の集合部と最も近い位置にあるため、１番（＃１）気筒２の排気ポートに還元剤添加弁２１が取り付けられているが、１番（＃１）気筒２以外の気筒２が排気通路１４の集合部と最も近い位置にあるときは、その気筒２の排気ポートに還元剤添加弁２１が取り付けられるようにする。
【００４０】
このように構成された還元剤供給手段において、還元剤添加弁２１から排気通路１４内へ噴射された還元剤は、排気通路１４の上流から流れてきた排気とともにタービンハウジング１０ｂへ流入する。タービンハウジング１０ｂ内に流入した排気と還元剤とは、タービンホイールの回転によって撹拌されて均質に混合された排気を形成する。
【００４１】
以上述べたように構成された内燃機関１には、該内燃機関１を制御するための電子制御ユニット（ＥＣＵ：Ｅｌｅｃｔｒｏｎｉｃ Ｃｏｎｔｒｏｌ Ｕｎｉｔ）２５が併設されている。このＥＣＵ２５は、ＣＰＵ、ＲＯＭ、ＲＡＭ、バックアップＲＡＭ等からなる算術論理演算回路である。
【００４２】
ＥＣＵ２５には、前述したエアフローメータ９、空燃比センサ１６、排気温度センサ１７に加え、内燃機関１に取り付けられたクランクポジションセンサ２３及び水温センサ２４等の各種センサが電気配線を介して接続され、上記した各種センサの出力信号がＥＣＵ２５に入力されるようになっている。
【００４３】
一方、ＥＣＵ２５には、燃料噴射弁３、吸気絞り用アクチュエータ１３、ＥＧＲ弁１９、還元剤添加弁２１等が電気配線を介して接続され、ＥＣＵ２５が、燃料噴射弁３、吸気絞り用アクチュエータ１３、ＥＧＲ弁１９及び還元剤添加弁２１等を制御することが可能になっている。
【００４４】
例えば、ＥＣＵ２５は、一定時間毎に実行すべき基本ルーチンにおいて、各種センサの出力信号の入力、機関回転数の演算、燃料噴射量の演算、燃料噴射時期の演算等を実行する。基本ルーチンにおいてＥＣＵ２５が入力した各種信号やＥＣＵ２５が演算して得られた各種制御値は、該ＥＣＵ２５のＲＡＭに一時的に記憶される。
【００４５】
例えば、ＥＧＲ制御では、先ず機関回転数、水温センサ２４の出力信号（冷却水温度）、アクセル開度等を読み出し、ＥＧＲ制御の実行条件が成立しているか否かを判別する。このＥＧＲ制御実行条件としては、冷却水温度が所定温度以上にある、内燃機関１が始動時から所定時間以上連続して運転されている、アクセル開度の変化量が正値である等の条件を例示することができる。
【００４６】
そして、上記したようなＥＧＲ制御実行条件が成立していると判定した場合は、ＥＣＵ２５は、機関回転数とアクセル開度とをパラメータとしてＥＧＲ弁開度制御マップへアクセスし、前記機関回転数及び前記アクセル開度に対応した目標ＥＧＲ弁開度を算出し、該目標ＥＧＲ弁開度に対応した駆動電力をＥＧＲ弁１９に印加する。一方、上記したようなＥＧＲ制御実行条件が成立していないと判定した場合は、ＥＣＵ２５は、ＥＧＲ弁１９を全閉状態に保持すべく制御する。
【００４７】
次に、本実施の形態に係る吸蔵還元型ＮＯｘ触媒１５について説明する。
ＮＯｘ触媒１５は、該触媒に流入する排気の空燃比がリーン空燃比（理論空燃比以上）であるときには、排気中のＮＯｘを保持して大気中に放出しないようにし、該触媒に流入する排気の空燃比が理論空燃比あるいはリッチ空燃比（理論空燃比以下）となったときには、保持していたＮＯｘを放出及び還元して除去するものである。
【００４８】
このため、内燃機関１が希薄燃焼運転されている場合は、内燃機関１から排出される排気の空燃比がリーン雰囲気となり排気の酸素濃度が高くなるため、排気中に含まれるＮＯｘがＮＯｘ触媒１５に保持されることになるが、内燃機関１の希薄燃焼運転が長期間継続されると、ＮＯｘ触媒１５のＮＯｘ保持能力が飽和し、排気中のＮＯｘがＮＯｘ触媒１５にて浄化されずに大気中へ放出されてしまう。
【００４９】
特に、内燃機関１のようなディーゼル機関では、大部分の運転領域においてリーン空燃比の混合気が燃焼され、それに応じて大部分の運転領域において排気の空燃比がリーン空燃比となるため、ＮＯｘ触媒１５のＮＯｘ保持能力が飽和し易い。
【００５０】
従って、内燃機関１が希薄燃焼運転されている場合は、ＮＯｘ触媒１５のＮＯｘ保持能力が飽和する前にＮＯｘ触媒１５に流入する排気中の酸素濃度を低下させるとともに還元剤の濃度を高め、ＮＯｘ触媒１５に吸収されたＮＯｘを放出及び還元させる必要がある。そこで、本実施の形態においては、ＥＣＵ２５が、ＮＯｘ触媒１５に流入する排気の空燃比を比較的に短い周期でスパイク的（短時間）にリッチ空燃比とする、リッチスパイク制御を実行する。
【００５１】
このリッチスパイク制御では、ＥＣＵ２５は、所定の周期毎にリッチスパイク制御実行条件が成立しているか否かを判別する。このリッチスパイク制御実行条件としては、例えば、ＮＯｘ触媒１５が活性状態にあるか、排気温度センサ１７の出力信号値（排気温度）が所定の上限値以下であるか、後述するＳＯｘ被毒解消制御が実行されていないか等の条件を例示することができる。
【００５２】
上記したようなリッチスパイク制御実行条件が成立していると判定された場合は、ＥＣＵ２５は、還元剤添加弁２１からスパイク的に還元剤たる燃料を添加させることにより、ＮＯｘ触媒１５に流入する排気の空燃比を一時的に所定の目標リッチ空燃比とする。そして、このようにして形成されたリッチ空燃比の排気は、その後ＮＯｘ触媒１５に流入し、該触媒に保持されていたＮＯｘを放出及び還元することになる。
【００５３】
このようにして、ＮＯｘ触媒１５に流入する排気の空燃比は、比較的に短い周期で「リーン」と「スパイク的な目標リッチ空燃比」とを交互に繰り返すことにより、ＮＯｘ触媒がＮＯｘの保持と放出・還元とを交互に短周期的に繰り返すことができることになる。
【００５４】
また、ＮＯｘ触媒１５は、ＮＯｘと同様のメカニズムによって排気中のＳＯｘを保持するため、ＳＯｘの保持量が増加すると、それに応じてＮＯｘ触媒１５のＮＯｘ保持能力が低減する、いわゆるＳＯｘ被毒が発生する。
【００５５】
そして、このようにＮＯｘ触媒１５にＳＯｘ被毒が生じると、ＮＯｘ保持能力が飽和し、排気中のＮＯｘがＮＯｘ触媒１５にて浄化されずに大気中へ放出されてしまう。したがって、本実施の形態においては、ＮＯｘ触媒１５に吸収されたＳＯｘを放出及び還元させる、ＳＯｘ被毒解消制御を実行することとしている。
【００５６】
このＳＯｘ被毒解消制御では、ＥＣＵ２５は、先ずＮＯｘ触媒１５の床温を約６００℃に高める触媒昇温処理を実行した上で、ＮＯｘ触媒１５に流入する排気の空燃比をリッチ空燃比とするようにする。
【００５７】
具体的に、本実施の形態の触媒昇温処理では、ＮＯｘ触媒１５の温度を早期に上昇させる手段として、内燃機関１の圧縮行程での通常の主燃料噴射に加えて、排気行程中又は膨張行程中に気筒内に燃料を副次的に噴射するポスト噴射又は吸気行程もしくは排気行程の上死点近傍で気筒内に燃料を噴射するビゴム噴射等の副噴射を行うことが有効である。ポスト噴射においては、排気行程中又は膨張行程中に噴射された燃料が未燃燃料としてＮＯｘ触媒に流入し、該触媒との反応熱により該触媒の温度が上昇する。一方、ビゴム噴射においては、吸気行程又は排気行程の上死点近傍で噴射された燃料がその後の行程で蒸発して着火し易いものとなり燃焼を安定させるので、主燃料噴射時期を遅延させることによりピストン運動に消費されるエネルギ量が減少し、それに伴い温度上昇した排気がＮＯｘ触媒１５に到達することにより該触媒の温度が上昇する。更に噴射された燃料の未燃分がＮＯｘ触媒１５に供給され、それが該触媒上で酸化反応を起こし、以って該触媒の温度が上昇する。なお、ポスト噴射及びビゴム噴射等の副噴射は、主燃料噴射との間に必ずしもインターバルを設ける必要はない。
【００５８】
副噴射の量及び噴射時期は、アクセル開度と機関回転数と副噴射量又は副噴射時期との関係を予め経験則に基づいてマップ化しておきＲＯＭに記憶させておけば、そのマップとアクセル開度と機関回転数とから算出することができる。
【００５９】
また、上述の副噴射の代わりにあるいは副噴射とともに、還元剤添加弁２１から排気中へ還元剤たる燃料を添加させることにより、それらの未燃燃料成分をＮＯｘ触媒１５において酸化させ、酸化の際に発生する熱によってＮＯｘ触媒の床温を高めるようにしてもよい。
【００６０】
但し、ＮＯｘ触媒１５が過剰に昇温すると、ＮＯｘ触媒１５の熱劣化を生じさせるおそれがあるため、排気温度センサ１７の出力信号値に基づいて副噴射量及び還元剤添加量をフィードバック制御するようにし、約６００℃に維持することが好ましい。
【００６１】
そして、上記したような触媒昇温処理によりＮＯｘ触媒１５の床温が約６００℃まで上昇したら、ＥＣＵ２５は、ＮＯｘ触媒に流入する排気の空燃比をリッチ空燃比とすべく還元剤添加弁２１から還元剤たる燃料を添加させる還元剤添加制御を実行する。
【００６２】
ただし、排気内に添加された還元剤は、高温条件下においてＮＯｘ触媒１５に保持され蓄積したＳＯｘを還元する機能を有する一方、ＮＯｘ触媒１５の温度をさらに上昇させる特性を有する。そのため、ＮＯｘ触媒１５の温度が約６００℃になった状態から還元剤が添加され続けると、ＮＯｘ触媒１５の温度が上昇し続け、ＮＯｘ触媒１５の温度が過剰に高くなることに起因する熱劣化を生じさせてしまう。そのため、還元剤添加制御中の還元剤添加量を適正な量とする必要がある。
【００６３】
そのため、本実施の形態の還元剤添加制御実行中においては、ＮＯｘ触媒に流入する排気の空燃比をリッチ空燃比とすべく還元剤添加弁２１を通じて還元剤を間欠的に添加し、所定のタイミングで還元剤の添加を停止し、これを繰り返すことにより、ＮＯｘ触媒に保持され蓄積したＳＯｘを放出・還元させつつＮＯｘ触媒の過熱を防止するようする、間欠リッチ制御を実行する。
【００６４】
図２は、本実施の形態におけるＳ被毒解消制御の実施中であって、特に「ＮＯｘ触媒の床温が６００℃以上に保持されている」といった条件が成立した後に実行される還元剤添加制御時のＮＯｘ触媒１５に流入する排気の空燃比の推移を示す図である。
【００６５】
図２に示すように、本実施の形態の還元剤添加制御は、ＮＯｘ触媒に保持され蓄積したＳＯｘを放出すべきとの要求があり、且つ、ＮＯｘ触媒の床温が６００℃以上に保持されているといった条件が満たされた場合に、ＥＣＵ２５は還元剤添加弁２１を開弁させるための指令信号（以下、「開弁指令信号」という。）を、所定期間（以下、「供給期間」という。）Δｔ１の間中、出力することで、還元剤添加弁２１から霧状の還元剤たる燃料を添加し、ＮＯｘ触媒１５に流入する排気の空燃比を所定のリッチ空燃比になるようにする（図２参照）。その後ＥＣＵ２５は、ＮＯｘ触媒１５の過熱を抑制すべく開弁指令信号の出力を、所定時間（以下、「休止期間」という。）Δｔ２の間休止し、所定のリーン空燃比になるようにする（図２参照）。その後Δｔ２を経た後、還元剤の添加を再開して、再度所定のリッチ空燃比になるようにする（図２参照）。そして、再度Δｔ１間還元剤を添加した後、Δｔ２間還元剤添加を休止し、再度所定のリーン空燃比になるようにする（図２参照）。このように、還元剤添加制御が開始されると、基本的にはＮＯｘ触媒１５に保持され蓄積したＳＯｘが放出されて当該触媒１５の機能が十分に回復するまで、間欠的にＮＯｘ触媒１５に流入する排気の空燃比をリッチ空燃比とするように還元剤の添加及び休止が繰り返される。そして、このように還元剤添加制御として、間欠的に還元剤を添加して間欠的にＮＯｘ触媒１５に流入する排気の空燃比をリッチにすることを間欠リッチ制御という。
【００６６】
そして、このように、還元剤添加弁２１を通じた還元剤添加の開始に伴ってＮＯｘ触媒１５に流入する排気の空燃比を低くし、所定のリッチ空燃比にするのに伴って、ＮＯｘ触媒から放出されるＳＯｘの量が増大する。また同様に、還元剤添加弁２１による還元剤たる燃料の供給の休止に伴ってＮＯｘ触媒１５に流入する排気の空燃比を所定のリーン空燃比とするに伴って、ＮＯｘ触媒１５から放出されるＳＯｘの量は低下する。このように、ＮＯｘ触媒１５に流入する排気の空燃比やＮＯｘ触媒からのＳＯｘ放出量は、還元剤添加弁２１の開閉弁動作に概ね同期して変動する。そして、ＮＯｘ触媒１５の床温は、還元剤添加弁２１を通じた還元剤の供給が開始されることに起因して上昇し、同弁２１による還元剤の供給が休止されることに起因して下降する。
【００６７】
しかし、還元剤添加弁２１から還元剤を添加して、目標のリッチ空燃比とする際、還元剤添加弁２１の開弁指令信号が適正であったとしても還元剤添加弁２１に目詰まり等が生じている場合には、適正量の還元剤を添加することができずにＮＯｘ触媒１５に流入する排気の空燃比が目標のリッチ空燃比からずれてしまう。また、還元剤の添加量が適正な量であったとしても、燃料噴射弁３に目詰まり等が生じていて燃焼室内の空燃比がずれている場合は、その分、ＮＯｘ触媒１５に流入する排気の空燃比が目標のリッチ空燃比からずれることとなる。
【００６８】
これに対して、燃焼室内の空燃比は目標の空燃比である場合であって還元剤添加弁２１に目詰まり等が生じていることのみに起因してＮＯｘ触媒１５に流入する排気の空燃比が目標のリッチ空燃比からずれてしまう場合は、上述のΔｔ１期間内に、ＮＯｘ触媒１５に流入する排気の空燃比の目標のリッチ空燃比と空燃比センサ１６の検出値のずれを開弁指令信号による目標の添加量と実際の添加量のずれであるとして学習し、還元剤を添加するようにフィードバック制御をすればＮＯｘ触媒１５に流入する排気の空燃比を目標のリッチ空燃比となるようにすることができる。
【００６９】
また、還元剤添加弁２１からの還元剤添加量は適正である場合であって燃料噴射弁３に目詰まり等が生じていることに起因して燃焼室内の空燃比がずれてＮＯｘ触媒１５に流入する排気の空燃比が目標のリッチ空燃比からずれてしまう場合は、上述のΔｔ１期間内に、ＮＯｘ触媒１５に流入する排気の空燃比の目標のリッチ空燃比と空燃比センサ１６の検出値のずれを燃料噴射弁３に対する噴射量の指令信号による目標の噴射量と実際の噴射量のずれであるとして学習し、還元剤添加量で補正するようにフィードバック制御すればＮＯｘ触媒１５に流入する排気の空燃比を目標のリッチ空燃比となるようにすることができる。
【００７０】
また、還元剤添加弁２１に目詰まり等が生じ、かつ、燃料噴射弁３に目詰まり等が生じていることに起因してＮＯｘ触媒１５に流入する排気の空燃比が目標のリッチ空燃比からずれている場合も同様に、上述のΔｔ１期間内に、ＮＯｘ触媒１５に流入する排気の空燃比の目標のリッチ空燃比と空燃比センサ１６の検出値のずれを学習し、還元剤添加量で補正するようにフィードバック制御すればＮＯｘ触媒１５に流入する排気の空燃比を目標のリッチ空燃比となるようにすることができる。
【００７１】
しかし、上述のようにΔｔ１期間内にフィードバック制御してＮＯｘ触媒１５に流入する排気の空燃比を目標リッチ空燃比となるようにすることができるとしても、各Δｔ１の開始時、つまり還元剤添加弁２１から還元剤を添加して最初に目標のリッチ空燃比とする時のずれ量が多い場合は、ＮＯｘ触媒の過剰な昇温を招いたり、所望量のＳＯｘを放出・還元することができなかったりするおそれがある。
【００７２】
つまり、通常のリーン運転時から最初に還元剤添加弁２１から還元剤を添加して目標のリッチ空燃比にする際に、目標のリッチ空燃比よりもリッチ側にずれた場合、すなわち排気中に還元剤が多目に存在する場合、多目に存在する還元剤と排気中の酸素がＮＯｘ触媒１５上で反応しＮＯｘ触媒１５の温度が過剰に上昇するおそれがある。一方、目標のリッチ空燃比よりもリーン側にずれた場合、すなわち排気中に還元剤が少な目に存在する場合、ＮＯｘ触媒１５に蓄積されたＳＯｘを還元すべき還元剤が不足するため、その後Δｔ１期間内でフィードバック制御によりＮＯｘ触媒１５に流入する排気の空燃比を目標リッチ空燃比に合わせることができるとしても所定期間内で所望量のＳＯｘを放出・還元させることができないおそれがある。特にΔｔ１が短時間である場合は十分にＳＯｘ被毒を解消できないおそれがある。
【００７３】
そこで、本実施の形態においては、還元剤添加制御を実行する場合、リーン運転時から還元剤添加弁２１から還元剤を添加して最初に目標のリッチ空燃比とする際には、還元剤を添加してリッチ空燃比とする直前のリーン運転時、つまり還元剤を添加していない時の燃焼室内の空燃比のずれを学習して還元剤の添加量を決定するようにした。つまり、燃料噴射弁３に目詰まり等が生じていることに起因して燃焼室内の空燃比が目標リーン空燃比からリーン側にずれている場合は、還元剤添加弁２１から添加する還元剤量を通常より多目にするようにし、コモンレール圧が下がること等に起因して燃料噴射弁３が司令値の開弁期間より長めに開弁して燃焼室内の空燃比が目標リーン空燃比からリッチ側にずれている場合は、還元剤添加弁２１から添加する還元剤量を通常より少な目にするようにする。このように、還元剤添加弁２１から還元剤を添加して最初に目標のリッチ空燃比とする際に、還元剤を添加せずにリーンの空燃比で運転している時点の燃焼室内の空燃比のずれを学習して、目標のリッチ空燃比になるように還元剤を添加するようにすれば、最初から精度よく目標のリッチ空燃比にすることができるので、ＮＯｘ触媒の過剰な昇温を招いたり、所望量のＳＯｘを放出・還元することができなかったりすることを防止することができる。
【００７４】
なお、還元剤添加制御を実行する際、還元剤を添加してリッチ空燃比とする直前のリーン運転時とは、還元剤添加制御実行期間中に最初（１度目）に還元剤を添加して目標のリッチ空燃比にする場合は、還元剤添加制御を開始する直前の通常のリーン運転時であり、その後Δｔ１の期間が終了したら還元剤添加をΔｔ２の期間休止し、その後再度（２度目）還元剤を添加して目標のリッチ空燃比にする場合は、その直前、つまり１度目のΔｔ２の期間のリーン運転時のことをいう。その後、還元剤添加制御期間中にリッチ空燃比とリーン空燃比が繰り返される場合は、そのリッチ空燃比の期間（Δｔ１）の直前のΔｔ２間のリーン運転時のことをいう。
【００７５】
次に、具体的に、図３、図４に示すフローチャートを用いてＳＯｘ被毒解消制御について説明する。
【００７６】
図３は、定期的に実行されるルーチンであり、まず、ステップ１００にて通常のリーン運転領域であるか否かが判定される。ここで、通常のリーン運転領域とは、上述のリッチスパイク制御、ＳＯｘ被毒解消制御あるいはＰＭ再生処理等が実行されていない状態で、内燃機関の燃焼室内の空燃比がリーンで運転される領域のことをいう。そして、ステップ１００にて通常のリーン運転領域であると判定されるとステップ１０１に進み、空燃比センサ１６の検出値と目標リーン空燃比との差をＸ値としてＥＣＵ２５のＲＡＭに記憶して終了する。一方、通常のリーン運転領域ではないと判定するとステップ１０１をスキップして終了する。
【００７７】
次に、図４に示すフローチャートを用いてＳＯｘ被毒解消制御のルーチンについて説明する。
【００７８】
本制御は定期的に実行されるものであり、まず、ステップ２００にてＳＯｘ被毒解消制御実行条件が成立しているか否かが判定される。この条件としては、ＳＯｘ被毒が解消されていない期間が所定期間に達しているか、あるいはＳＯｘ被毒が解消されていない間に車輌が走行した距離が所定距離に達しているか、あるいは排気温度センサ１７の出力信号値（排気温度）が所定の上限値以下であるか等の条件を例示することができる。そして、ＳＯｘ被毒解消制御実行条件が成立していると判定される場合はステップ２０１に進み、上述の触媒昇温処理が実行される。一方、ＳＯｘ被毒解消制御実行条件が成立していない場合は本制御を終了する。
【００７９】
ステップ２０１では、触媒昇温処理が実行されるが、これは上述したようにＮＯｘ触媒１５の温度を約６００℃に上昇させるために、排気行程中又は膨張行程中に気筒内に燃料を副次的に噴射するポスト噴射若しくは吸気行程もしくは排気行程の上死点近傍で気筒内に燃料を噴射するビゴム噴射等の副噴射を行うか又は還元剤添加弁２１から排気中へ還元剤たる燃料を添加するものである。
【００８０】
次に、ステップ２０２では、還元剤添加制御実行条件が成立しているか否かが判定され、成立している場合はステップ２０３に進み、成立していない場合は本制御を終了する。ここで、還元剤添加制御実行条件としては、例えば、ＮＯｘ触媒１５が所定温度（例えば６００℃）に達しているかを例示することができる。そして、ステップ２０３では、上述した図３のステップ１０１にて記憶したＸ値を読込み、ステップ２０４に進む。
【００８１】
次に、ステップ２０４では、還元剤添加休止期間中（Δｔ２期間中）か否かが判定される。そして、休止期間中でないと判定された場合は、ステップ２０６に進み、内燃機関内の目標リーン空燃比とＮＯｘ触媒１５に流入する排気の空燃比の目標リッチ空燃比とから定められるベース還元剤添加量に、ステップ２０３にて読込んだＸ値をゼロにするのに必要な還元剤量を加算して、実際に排気に添加する還元剤添加量を算出する。そして、ステップ２０７に進み、ステップ２０６で算出した還元剤添加量の還元剤を添加し、ステップ２０８に進む。一方、ステップ２０４で、還元剤添加休止期間中（Δｔ２期間中）であると判定された場合は、ステップ２０５に進み、空燃比センサ１６の検出値と目標リーン空燃比との差をＸ値として、すでにステップ２０３で読込む等して記憶してあるＸ値を新たに更新する。そして、再度ステップ２０３へ進む。
【００８２】
ステップ２０８においては、ＳＯｘ被毒解消制御終了条件が成立しているか否かが判定される。このＳＯｘ被毒解消制御終了条件としては、例えば還元剤添加制御実行開始から所定時間経過したことを例示することができる。そして、ＳＯｘ被毒解消制御終了条件が成立している場合はステップ２０９にてＳＯｘ被毒解消制御を終了し本制御を終了する。一方、ＳＯｘ被毒解消制御終了条件が成立していない場合は、再度ステップ２０３へ戻り、その後上述したのと同様な処理が繰り返されることとなる。
【００８３】
このようにしてＳＯｘ被毒解消制御が実行されると、ＮＯｘ触媒１５の床温が高い状況下で、ＮＯｘ触媒１５に流入する排気の空燃比がリッチ空燃比となるため、ＮＯｘ触媒１５に保持され蓄積された硫黄酸化物（ＳＯｘ）が還元されてＮＯｘ触媒１５のＳＯｘ被毒が解消されることになる。
【００８４】
なお、吸蔵還元型ＮＯｘ触媒１５はディーゼルパティキュレートフィルタに担持されたものでもよい。かかる場合は、フィルタの各排気流入通路および各排気流出通路の周壁面、即ち各隔壁の両側表面上および隔壁内の細孔内壁面上に、例えばアルミナからなる担体の層を形成し、この担体上に吸蔵還元型ＮＯｘ触媒が坦持されることとなる。
【００８５】
また、還元剤添加弁２１から還元剤を添加して触媒昇温処理を実行する場合は、還元剤添加制御実行時の還元剤添加と触媒昇温処理実行時の還元剤添加との間に必ずしもインターバルを設ける必要はない。
【００８６】
＜第２の実施の形態＞
本実施の形態は、第１の実施の形態に対してＳＯｘ被毒解消制御の一部のみ異なるものであり、その他は第１の実施の形態と同一なので、異なる部分のみ説明するものとし、その他の説明は省略する。
【００８７】
第１の実施の形態においては、還元剤添加制御実行中において、リーン運転時から還元剤添加弁２１から還元剤を添加して最初に目標のリッチ空燃比とする際には、還元剤を添加してリッチ空燃比とする直前のリーン運転時、つまり還元剤を添加していない時の燃焼室内の空燃比のずれを学習して還元剤の添加量を算出し、その算出した添加量如何にかかわらず還元剤添加量として決定し、添加するものであるが、本実施の形態では、燃焼室内の空燃比のずれを学習して還元剤の添加量（例えばα）を算出した後、該算出した添加量（α）に応じて最終的な還元剤添加量を決定するものである。具体的には、算出した添加量（α）が所定の還元剤添加量（α１）よりも多い場合は、α１を最終的な還元剤添加量として決定する。一方、算出した添加量（α）が所定の還元剤添加量（α１）以下である場合は、αを最終的な還元剤添加量として決定する。
【００８８】
排気内に添加された還元剤は、高温条件下においてＮＯｘ触媒１５に保持され蓄積したＳＯｘを還元する機能を有する一方、ＮＯｘ触媒１５の温度をさらに上昇させる特性を有するため、添加される還元剤の量が多いとＮＯｘ触媒１５が過剰に上昇し、ＮＯｘ触媒１５の熱劣化を生じさせてしまう。そのため、予め、ＮＯｘ触媒１５の容量等の特性から一度に添加してもＮＯｘ触媒を過剰昇温させない最大限の添加量α１を設定しておき、燃焼室内の空燃比のずれを学習して算出した還元剤の添加量αが、α１よりも多い場合は、算出した添加量αをそのまま添加するのではなく、α１を添加量として決定し、ＮＯｘ触媒１５が過剰に昇温するのを未然に防止するようにする。
【００８９】
次に、図５のフローチャートを用いて本実施の形態に係るＳＯｘ被毒解消制御について説明する。
【００９０】
ステップ３００からステップ３０６は図４に示す第１の実施の形態に係るフローチャートと同一であるのでその説明は省略する。ステップ３０７では、ステップ３０６で算出した還元剤添加量αが所定の値α１以下である場合は、還元剤添加量をαと決定しαを添加する。一方、ステップ３０８では、ステップ３０６で算出した還元剤添加量αが所定の値α１より多い場合は、還元剤添加量をα１と決定しα１だけ添加する。それ以降のステップも第１の実施の形態に係るフローチャートと同一であるのでその説明は省略する。
【００９１】
【発明の効果】
以上説明したように、本発明に係る内燃機関の排気浄化装置は、内燃機関内の実際の空燃比と目標空燃比との差分を算出する算出手段と、該算出手段にて算出した差分に基づいて決定した還元剤添加量を、ＳＯｘ保持材から硫黄酸化物を除去させるべく、還元剤添加手段から添加させる還元剤添加制御手段とを備えるので、ＳＯｘ保持材の熱劣化を防止しつつＳＯｘ保持材からＳＯｘを精度よく除去できる。
【図面の簡単な説明】
【図１】第１の実施の形態に係る内燃機関の排気浄化装置を適用する内燃機関とその吸排気系の概略構成を示す図である。
【図２】第１の実施の形態に係る還元剤添加制御時のＮＯｘ触媒１５に流入する排気の空燃比の変化を示す図である。
【図３】第１の実施の形態に係るＳＯｘ解消処理に用いる空燃比センサの検出値と目標のリーン空燃比との差分を記憶するためのフローチャートである。
【図４】第１の実施の形態に係るＳＯｘ被毒解消処理制御のフローチャート図である。
【図５】第２の実施の形態に係るＳＯｘ被毒解消処理制御のフローチャート図である。
【符号の説明】
１ 内燃機関
２ 気筒
３ 燃料噴射弁
４ コモンレール
５ 燃料供給管
６ 燃料ポンプ
７ 吸気通路
８ エアクリーナボックス
９ エアフローメータ
１０ 過給機
１１ インタークーラ
１２ 吸気絞り弁
１３ 吸気絞り用アクチュエータ
１４ 排気通路
１５ 排気浄化装置
１６ 空燃比センサ
１７ 排気温度センサ
１８ ＥＧＲ通路
１９ ＥＧＲ弁
２０ 排気ポート
２１ 還元剤添加弁
２２ 還元剤供給路
２３ クランクポジションセンサ
２４ 水温センサ
２５ ＥＣＵ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine that retains sulfur oxide in exhaust gas and periodically removes the retained sulfur oxide. .
[0002]
[Prior art]
As an exhaust gas purification technique for an internal combustion engine, an NOx storage reduction catalyst (hereinafter simply referred to as “NOx catalyst”) is disposed in the exhaust system of an internal combustion engine (particularly a lean combustion engine or a diesel engine) to operate at a lean air-fuel ratio. A technique for temporarily holding nitrogen oxide (hereinafter sometimes simply referred to as “NOx”) in exhaust gas temporarily on the NOx catalyst before releasing it into the atmosphere is known. Retains sulfur oxide (hereinafter also referred to simply as “SOx”) together with NOx in the exhaust gas, so when the amount of SOx retained increases, the NOx in the exhaust gas cannot be retained. Causes SOx poisoning.
[0003]
On the other hand, the NOx catalyst as the SOx holding material holding SOx is set at a high temperature of about 600 ° C., for example, and the fuel as the reducing agent is supplied to the NOx catalyst, so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is reduced to a rich air. The SOx is reduced and removed by setting the fuel ratio to a high temperature and reducing atmosphere of the NOx catalyst, thereby eliminating SOx poisoning of the NOx catalyst (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP 2001-82137 A
[0005]
[Problems to be solved by the invention]
However, when the air-fuel ratio of the exhaust gas is changed to a rich air-fuel ratio in order to eliminate SOx poisoning, if there is a shift to the rich side from the target rich air-fuel ratio, that is, there are many reducing agents in the exhaust gas. In this case, there is a possibility that the reducing agent present in large numbers and the oxygen in the exhaust gas react on the NOx catalyst and the temperature of the NOx catalyst rises excessively. On the other hand, when there is a deviation from the target rich air-fuel ratio to the lean side, that is, when there is a small amount of reducing agent in the exhaust gas, there is a shortage of reducing agent to reduce the SOx held in the NOx catalyst, so that the SOx coverage is particularly low. When the process for eliminating the poison is performed within a predetermined period, there is a possibility that the SOx poisoning cannot be sufficiently eliminated.
[0006]
Therefore, after the lean air-fuel ratio during normal operation is once made rich for SOx poisoning elimination processing, feedback control is performed so that the air-fuel ratio after addition of the reducing agent becomes the target rich air-fuel ratio during the rich period. ing. For example, the air-fuel ratio of the exhaust gas is detected by an air-fuel ratio sensor provided upstream or downstream of the NOx catalyst, and if there is a difference between the detected value and the target air-fuel ratio, this is corrected. Thus, the amount of fuel or reducing agent added to be injected into the internal combustion engine is determined.
[0007]
However, when the reducing agent is supplied from the lean air-fuel ratio to reach the target rich air-fuel ratio, if the air-fuel ratio of the internal combustion engine is deviated, even if the reducing agent addition amount is appropriate, the air after the reducing agent is added The fuel ratio deviates from the target rich air-fuel ratio. In particular, if the amount of misalignment at the time of the first reducing agent addition when the lean air-fuel ratio is changed from the lean air-fuel ratio during normal operation to the rich air-fuel ratio for the SOx poisoning elimination processing is increased, then the rich air-fuel ratio is changed to the SOx poisoning elimination. Even if feedback control is performed on the air-fuel ratio of the exhaust gas flowing into the NOx catalyst during the processing period, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst at the time when the reducing agent is first added deviates from the target air-fuel ratio. Therefore, as described above, the temperature of the NOx catalyst excessively increases, or the SOx poisoning cannot be sufficiently eliminated. Further, when the temperature of the NOx catalyst is excessively increased, there is a risk of causing thermal degradation of the NOx catalyst.
[0008]
The present invention has been made in view of the above-described problems, and an object thereof is an internal combustion engine capable of accurately removing SOx from a SOx holding material while preventing thermal deterioration of the SOx holding material such as a NOx catalyst. An object of the present invention is to provide an exhaust purification device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the air-fuel ratio of the exhaust gas flowing into the SOx holding material by adding a reducing agent is the stoichiometric air-fuel ratio or rich air-fuel ratio. When the SOx held by the SOx holding material is removed by the above, the reducing agent addition amount is determined in consideration of the difference between the actual air-fuel ratio in the internal combustion engine and the target air-fuel ratio.
[0010]
As specific means, an SOx holding material that is provided in an exhaust passage of the internal combustion engine and holds sulfur oxide in the exhaust gas and removes sulfur oxide held in a high temperature and reducing atmosphere, and the SOx holding Reducing agent addition means for adding a reducing agent to exhaust gas upstream of the material, air-fuel ratio detection means for detecting an air-fuel ratio of at least one of exhaust gas flowing into the SOx holding material or exhaust gas flowing out from the SOx holding material, Calculation means for calculating the difference between the actual air-fuel ratio in the combustion chamber of the internal combustion engine and the target air-fuel ratio based on the detection value of the air-fuel ratio detection means; and the calculation means for removing sulfur oxide from the SOx holding material. And a reducing agent addition control means for adding the reducing agent addition amount determined in consideration of the difference calculated in this manner from the reducing agent addition means.
[0011]
Here, as the SOx holding material, when the air-fuel ratio of the exhaust gas flowing into the catalyst is lean (greater than the theoretical air-fuel ratio) like the NOx storage reduction catalyst, the NOx in the exhaust gas is held and released into the atmosphere. When the air-fuel ratio of the exhaust gas flowing into the catalyst becomes the stoichiometric air-fuel ratio or rich (below the stoichiometric air-fuel ratio), the retained NOx is released and reduced, or the particulate filter Examples of the catalyst that support the NOx storage reduction catalyst are shown below.
[0012]
Further, examples of the air-fuel ratio detection means include an air-fuel ratio sensor and an oxygen concentration sensor that are disposed in the exhaust passage upstream of the SOx holding material and / or downstream of the SOx holding material.
[0013]
When removing the sulfur oxide held in the SOx holding material, the temperature of the exhaust gas flowing into the SOx holding material is raised and the air-fuel ratio of the exhaust gas flowing into the SOx holding material is made lower than the stoichiometric air-fuel ratio. Although necessary, a reducing agent is added by a reducing agent addition means upstream of the SOx holding material in order to make the air-fuel ratio of the exhaust gas equal to or lower than the stoichiometric air-fuel ratio. The reducing agent addition amount is basically an addition amount corresponding to setting the air-fuel ratio of the exhaust immediately after being discharged from the combustion chamber of the internal combustion engine operating at a lean air-fuel ratio to the target rich air-fuel ratio. However, the air / fuel ratio of the exhaust gas immediately after being discharged from the combustion chamber of the internal combustion engine operating at a lean air / fuel ratio is determined on the assumption that the air / fuel ratio in the internal combustion engine is the target air / fuel ratio. .
[0014]
However, for example, if the fuel injection valve that injects fuel into the combustion chamber is clogged, the air-fuel ratio in the combustion chamber may shift from the target air-fuel ratio. In such a case, the fuel flows into the SOx holding material. The air-fuel ratio of the exhaust gas that is exhausted may also deviate from the target rich air-fuel ratio. Therefore, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a calculating means for calculating a difference between an actual air-fuel ratio in the combustion chamber and a target air-fuel ratio based on a detection value of the air-fuel ratio detecting means, and a sulfur from the SOx holding material. In order to remove the oxide, the reducing agent addition control means for adding the reducing agent addition amount determined in consideration of the difference calculated by the calculating means from the reducing agent addition means is provided, and the sulfur oxide is removed from the SOx holding material. Therefore, when the reducing agent is added from the reducing agent addition means to the exhaust gas upstream of the SOx holding material, the reducing agent addition control means determines the reducing agent addition amount in consideration of the deviation of the air-fuel ratio in the combustion chamber of the internal combustion engine. Therefore, it is added from the reducing agent addition means.
[0015]
In this way, in order to remove the sulfur oxide from the SOx holding material, when the air-fuel ratio of the exhaust gas flowing into the SOx holding material is first added by adding a reducing agent, the target air-fuel ratio is accurately adjusted. Since the air-fuel ratio can be set, the SOx holding material is excessively heated due to the presence of the reducing agent in a larger amount than the target, or the desired amount due to the presence of the reducing agent in a smaller amount than the target. It is possible to prevent the sulfur oxides from being reduced or removed.
[0016]
The calculating means calculates the difference between the actual air-fuel ratio in the combustion chamber of the internal combustion engine and the target air-fuel ratio based on the detected value of the air-fuel ratio detecting means when no reducing agent is added from the reducing agent adding means. It is suitable.
[0017]
When calculating the difference between the detected value of the air-fuel ratio detection means when the reducing agent is added from the reducing agent addition means and the target air-fuel ratio in the combustion chamber of the internal combustion engine, the air-fuel ratio detection means is particularly downstream of the reducing agent addition means. If it is provided, the difference between the actual air-fuel ratio in the internal combustion engine and the target air-fuel ratio needs to be calculated in consideration of the reducing agent addition amount. For this reason, for example, even when there is a difference in the reducing agent addition means and the difference in the amount of addition of the reducing agent is not an appropriate amount, the internal combustion engine is recognized as a deviation of the air-fuel ratio in the combustion chamber of the internal combustion engine. The difference between the actual air-fuel ratio and the target air-fuel ratio may be calculated. In such a case, an appropriate amount of reducing agent cannot be added, and the air-fuel ratio of the exhaust gas flowing into the SOx holding material may shift from the target air-fuel ratio. It is preferable to calculate the difference between the actual air-fuel ratio in the combustion chamber of the internal combustion engine and the target air-fuel ratio based on the detected value of the air-fuel ratio detecting means when not.
[0018]
Further, the reducing agent addition control means is an intermittent rich control in which the reducing agent is intermittently added from the reducing agent addition means so that the air-fuel ratio of the exhaust gas flowing into the SOx holding material is the stoichiometric air-fuel ratio or a rich air-fuel ratio. Preferably, the calculation means calculates the difference when the intermittent rich control is being executed and no reducing agent is added from the reducing agent addition means.
[0019]
The reducing agent added in the exhaust has a function of reducing SOx held in the SOx holding material under a high temperature condition, and has a characteristic of further increasing the temperature of the SOx holding material by reacting with SOx. Therefore, if the reducing agent is continuously added, the temperature of the SOx holding material continues to rise, and the temperature of the SOx holding material may become excessively high. Therefore, the reducing agent is added by executing intermittent rich control in which the reducing agent is intermittently added from the reducing agent addition means and the air-fuel ratio of the exhaust gas flowing into the SOx holding material is made the stoichiometric air-fuel ratio or rich air-fuel ratio. It is possible to prevent an excessive increase in temperature of the SOx holding material due to continuing to be performed.
[0020]
Even during the execution of the intermittent rich control, the calculation means calculates the actual air-fuel ratio in the combustion chamber of the internal combustion engine and the target based on the detection value of the air-fuel ratio detection means when no reducing agent is added from the reducing agent addition means. It is preferable to calculate the difference from the air / fuel ratio as described above.
[0021]
As a means for calculating the reducing agent addition amount, the air-fuel ratio of the exhaust gas from the combustion chamber operating at a lean air-fuel ratio is added to the target rich air by adding the reducing agent from the reducing agent addition means. The calculation can be exemplified based on the base reducing agent amount corresponding to the fuel ratio and the differential reducing agent amount corresponding to setting the difference to zero.
[0022]
The reducing agent addition amount is preferably determined by comparing a reducing agent amount obtained by adding the differential reducing agent amount to the base reducing agent amount with a predetermined reducing agent amount. When the reducing agent addition amount is determined as described above, for example, the fuel injection valve that injects fuel into the combustion chamber of the internal combustion engine is clogged or the like, so that the air-fuel ratio in the combustion chamber becomes leaner. In the case of a significant deviation, in order to increase the reducing agent addition amount and to make the air-fuel ratio of the exhaust gas flowing into the SOx holding material rich as desired, the increased reducing agent reacts with the SOx held in the SOx holding material and SOx There is a risk of excessively raising the temperature of the holding material.
[0023]
Therefore, for example, a predetermined reducing agent amount that is the upper limit of the amount of reducing agent added according to the capacity of the SOx holding material, etc. is determined in advance, and obtained by adding the differential reducing agent amount to the base reducing agent amount. If the amount of reducing agent is less than or equal to this predetermined amount of reducing agent, the amount of reducing agent obtained by adding the amount of differential reducing agent to the amount of base reducing agent is determined as the amount of reducing agent added, and the amount of reducing agent is reduced to the amount of base reducing agent. When the amount of reducing agent obtained by adding the amount of the agent is larger than the predetermined amount of reducing agent, the predetermined amount of reducing agent is determined as the amount of reducing agent added and added from the reducing agent addition means. By doing so, it is possible to prevent the temperature of the SOx holding material from rising excessively.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0025]
<First Embodiment>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine provided with an exhaust gas recirculation device according to the present invention. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cylinder diesel engine having four cylinders 2.
[0026]
The internal combustion engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulating chamber (common rail) 4, and the common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5.
[0027]
An intake passage 7 is connected to the internal combustion engine 1, and the intake passage 7 is connected to an air cleaner box 8. An air flow meter 9 that outputs an electric signal corresponding to the mass of the intake air flowing through the intake passage 7 is attached to the intake passage 7 downstream of the air cleaner box 8.
[0028]
A compressor housing 10 a of a supercharger (turbocharger) 10 is provided in the middle of the intake passage 7. An intercooler 11 is attached to the intake passage 7 downstream of the compressor housing 10a. Further, an intake throttle valve 12 for adjusting the flow rate of intake air flowing through the intake passage 7 is provided in the intake passage 7 downstream of the intercooler 11. An intake throttle actuator 13 that opens and closes the intake throttle valve 12 is attached to the intake throttle valve 12.
[0029]
The intake air that flows into the compressor housing 10a and is compressed in the compressor housing 10a to a high temperature is cooled by the intercooler 11, and then the flow rate is adjusted by the intake throttle valve 12 as necessary. The fuel is distributed to the combustion chambers of the respective cylinders 2 through the passages 7 and burned by using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0030]
Further, an exhaust passage 14 is connected to the internal combustion engine 1, and this exhaust passage 14 is connected downstream with a muffler (not shown).
[0031]
Further, a turbine housing 10b of the supercharger 10 is disposed in the middle of the exhaust passage 14, and a NOx storage reduction catalyst (hereinafter, not particularly specified) is disposed in a portion of the exhaust passage 14 downstream from the turbine housing 10b. As long as it is referred to as “NOx catalyst”) 15. An air-fuel ratio sensor 16 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust passage 14 is attached to the exhaust passage 14 upstream of the NOx catalyst 15.
[0032]
The exhaust discharged from the turbine housing 10b flows into the NOx catalyst 15 through the exhaust passage 14, and the substance in the exhaust is purified.
[0033]
A portion of the intake passage 7 downstream of the intake throttle valve 12 and a portion of the exhaust passage 14 upstream of the turbine housing 10 b are connected via an EGR passage 18 that recirculates part of the exhaust to the intake passage 7. It is communicated. In the middle of the EGR passage 18, an EGR valve configured by an electromagnetic valve or the like that changes the flow rate of exhaust gas (hereinafter referred to as “EGR gas”) that flows through the EGR passage 18 according to the magnitude of applied power. 19 is provided.
[0034]
Then, the EGR gas recirculated from the exhaust passage 14 to the intake passage 7 via the EGR passage 18 is guided to the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream of the intake passage 7. The fuel injected from the injection valve 3 is burned using an ignition source.
[0035]
Here, the EGR gas contains water (H 2 O) and carbon dioxide (CO 2 ) And the like, and an inert gas component having endothermic properties is contained in the mixture, so if EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. Therefore, the amount of NOx generated is suppressed.
[0036]
Further, there is provided a reducing agent supply means for adding fuel (light oil) as a reducing agent into the exhaust gas flowing through the exhaust passage 14 upstream from the NOx catalyst 15. As shown in FIG. 1, this reducing agent supply means is attached to the cylinder head of the internal combustion engine 1 so that its nozzle hole faces the exhaust passage 14, and opens when fuel of a predetermined valve opening pressure or higher is applied. There are provided a reducing agent addition valve 21 that injects the fuel and a reducing agent supply path 22 that guides the fuel discharged from the fuel pump 6 to the reducing agent addition valve 21.
[0037]
Note that the reducing agent addition valve 21 is a cylinder in which the nozzle hole of the reducing agent addition valve 21 is downstream of the connection portion of the exhaust passage 14 with the EGR passage 18 and is closest to the four passages in the exhaust passage 14. It is preferable to attach to the cylinder head so that it protrudes to the exhaust port of 2 and faces toward the collecting portion of the exhaust passage 14.
[0038]
This prevents the reducing agent (unburned fuel component) injected from the reducing agent addition valve 21 from flowing into the EGR passage 18, and the reducing agent does not stagnate in the exhaust passage 14. This is to reach the turbine housing 10b.
[0039]
In the example shown in FIG. 1, the first (# 1) cylinder 2 of the four cylinders 2 of the internal combustion engine 1 is located closest to the collecting portion of the exhaust passage 14. Although the reducing agent addition valve 21 is attached to the exhaust port of the cylinder 2, when the cylinders 2 other than the first (# 1) cylinder 2 are located closest to the collecting portion of the exhaust passage 14, the exhaust port of the cylinder 2 The reducing agent addition valve 21 is attached to the above.
[0040]
In the reducing agent supply means configured as described above, the reducing agent injected from the reducing agent addition valve 21 into the exhaust passage 14 flows into the turbine housing 10 b together with the exhaust flowing from the upstream of the exhaust passage 14. The exhaust gas flowing into the turbine housing 10b and the reducing agent are agitated by the rotation of the turbine wheel to form a homogeneously mixed exhaust gas.
[0041]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 25 for controlling the internal combustion engine 1. The ECU 25 is an arithmetic logic circuit including a CPU, ROM, RAM, backup RAM, and the like.
[0042]
Various sensors such as a crank position sensor 23 and a water temperature sensor 24 attached to the internal combustion engine 1 are connected to the ECU 25 through electric wiring in addition to the air flow meter 9, the air-fuel ratio sensor 16, and the exhaust gas temperature sensor 17 described above. The output signals of the various sensors described above are input to the ECU 25.
[0043]
On the other hand, the fuel injection valve 3, the intake throttle actuator 13, the EGR valve 19, the reducing agent addition valve 21 and the like are connected to the ECU 25 via electrical wiring. The ECU 25 is connected to the fuel injection valve 3, the intake throttle actuator 13, The EGR valve 19 and the reducing agent addition valve 21 can be controlled.
[0044]
For example, the ECU 25 executes input of output signals from various sensors, calculation of engine speed, calculation of fuel injection amount, calculation of fuel injection timing, and the like in a basic routine to be executed at regular intervals. Various signals input by the ECU 25 and various control values obtained by the ECU 25 in the basic routine are temporarily stored in the RAM of the ECU 25.
[0045]
For example, in the EGR control, first, the engine speed, the output signal (cooling water temperature) of the water temperature sensor 24, the accelerator opening, and the like are read to determine whether or not an execution condition for the EGR control is satisfied. The EGR control execution condition includes a condition that the cooling water temperature is equal to or higher than a predetermined temperature, the internal combustion engine 1 is continuously operated for a predetermined time or more from the start, and the amount of change in the accelerator opening is a positive value. Can be illustrated.
[0046]
If it is determined that the EGR control execution condition as described above is satisfied, the ECU 25 accesses the EGR valve opening degree control map using the engine speed and the accelerator opening as parameters, and the engine speed and A target EGR valve opening corresponding to the accelerator opening is calculated, and driving power corresponding to the target EGR valve opening is applied to the EGR valve 19. On the other hand, when it is determined that the EGR control execution condition as described above is not satisfied, the ECU 25 performs control so as to keep the EGR valve 19 in the fully closed state.
[0047]
Next, the NOx storage reduction catalyst 15 according to the present embodiment will be described.
When the air-fuel ratio of the exhaust gas flowing into the catalyst is a lean air-fuel ratio (greater than the stoichiometric air-fuel ratio), the NOx catalyst 15 holds NOx in the exhaust gas so as not to be released into the atmosphere, and the exhaust gas flowing into the catalyst When the air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio (below the stoichiometric air-fuel ratio), the retained NOx is released and reduced.
[0048]
For this reason, when the internal combustion engine 1 is operated in lean combustion, the air-fuel ratio of the exhaust exhausted from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high, so that NOx contained in the exhaust becomes NOx catalyst 15. However, if the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx retention capacity of the NOx catalyst 15 is saturated, and the NOx in the exhaust gas is not purified by the NOx catalyst 15 and is not purified. It will be released inside.
[0049]
In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel ratio mixture is combusted in the most operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in the most operating region accordingly. The NOx retention capacity of the catalyst 15 is easily saturated.
[0050]
Therefore, when the internal combustion engine 1 is operating in lean burn, before the NOx retention capacity of the NOx catalyst 15 is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst 15 is reduced and the concentration of the reducing agent is increased. It is necessary to release and reduce the NOx absorbed by the catalyst 15. Therefore, in the present embodiment, the ECU 25 executes rich spike control in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 is changed to a rich air-fuel ratio in a spike (short time) with a relatively short cycle.
[0051]
In this rich spike control, the ECU 25 determines whether or not a rich spike control execution condition is satisfied every predetermined cycle. As the rich spike control execution condition, for example, whether the NOx catalyst 15 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 17 is equal to or lower than a predetermined upper limit value, or SOx poisoning elimination control described later. The condition such as whether or not is executed can be exemplified.
[0052]
When it is determined that the rich spike control execution condition as described above is satisfied, the ECU 25 adds the fuel that is the reducing agent in a spike manner from the reducing agent addition valve 21, thereby causing the exhaust gas flowing into the NOx catalyst 15. Is temporarily set to a predetermined target rich air-fuel ratio. The rich air-fuel ratio exhaust gas thus formed then flows into the NOx catalyst 15 and releases and reduces the NOx held in the catalyst.
[0053]
In this way, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 alternately repeats “lean” and “spike target rich air-fuel ratio” in a relatively short cycle, so that the NOx catalyst holds NOx. And release / reduction can be alternately repeated in a short cycle.
[0054]
Further, since the NOx catalyst 15 holds SOx in the exhaust gas by a mechanism similar to NOx, when the amount of SOx held increases, the NOx holding capacity of the NOx catalyst 15 decreases accordingly, so-called SOx poisoning occurs. To do.
[0055]
When SOx poisoning occurs in the NOx catalyst 15 in this way, the NOx retention capacity is saturated, and NOx in the exhaust gas is released into the atmosphere without being purified by the NOx catalyst 15. Therefore, in the present embodiment, SOx poisoning elimination control for releasing and reducing SOx absorbed by the NOx catalyst 15 is executed.
[0056]
In this SOx poisoning elimination control, the ECU 25 first executes a catalyst temperature raising process for raising the bed temperature of the NOx catalyst 15 to about 600 ° C., and then makes the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 a rich air-fuel ratio. Like that.
[0057]
Specifically, in the catalyst temperature increasing process of the present embodiment, as means for increasing the temperature of the NOx catalyst 15 at an early stage, in addition to normal main fuel injection in the compression stroke of the internal combustion engine 1, during the exhaust stroke or expansion It is effective to perform sub-injection such as post-injection in which fuel is sub-injected into the cylinder during the stroke or big rubber injection in which fuel is injected into the cylinder in the vicinity of the top dead center of the intake or exhaust stroke. In the post-injection, the fuel injected during the exhaust stroke or the expansion stroke flows into the NOx catalyst as unburned fuel, and the temperature of the catalyst rises due to the heat of reaction with the catalyst. On the other hand, in the rubber injection, the fuel injected near the top dead center of the intake stroke or the exhaust stroke evaporates in the subsequent stroke and easily ignites and stabilizes the combustion. The amount of energy consumed for the piston motion decreases, and the exhaust gas whose temperature has increased accordingly reaches the NOx catalyst 15, whereby the temperature of the catalyst increases. Further, the unburned portion of the injected fuel is supplied to the NOx catalyst 15, which causes an oxidation reaction on the catalyst, thereby increasing the temperature of the catalyst. In addition, it is not always necessary to provide an interval between the main fuel injection and the secondary injection such as post injection and big rubber injection.
[0058]
The amount and timing of the sub-injection can be determined by mapping the relationship between the accelerator opening, the engine speed, the sub-injection amount or the sub-injection timing in advance based on an empirical rule and storing it in the ROM. It can be calculated from the opening degree and the engine speed.
[0059]
Further, by adding fuel as a reducing agent into the exhaust gas from the reducing agent addition valve 21 in place of or in addition to the above-described auxiliary injection, these unburned fuel components are oxidized in the NOx catalyst 15, and at the time of oxidation. The bed temperature of the NOx catalyst may be increased by the heat generated in the catalyst.
[0060]
However, if the temperature of the NOx catalyst 15 is excessively increased, the NOx catalyst 15 may be thermally deteriorated. Therefore, the sub-injection amount and the reducing agent addition amount are feedback-controlled based on the output signal value of the exhaust temperature sensor 17. And maintained at about 600 ° C.
[0061]
When the bed temperature of the NOx catalyst 15 rises to about 600 ° C. by the catalyst temperature raising process as described above, the ECU 25 starts from the reducing agent addition valve 21 so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a rich air-fuel ratio. Reducing agent addition control for adding fuel as a reducing agent is executed.
[0062]
However, the reducing agent added in the exhaust has a function of reducing the accumulated SOx held in the NOx catalyst 15 under a high temperature condition, and has a characteristic of further increasing the temperature of the NOx catalyst 15. For this reason, if the reducing agent is continuously added from the state where the temperature of the NOx catalyst 15 is about 600 ° C., the temperature of the NOx catalyst 15 continues to rise, and the thermal deterioration due to the temperature of the NOx catalyst 15 becoming excessively high. Will be caused. Therefore, it is necessary to make the amount of reducing agent added during the reducing agent addition control appropriate.
[0063]
Therefore, during the execution of the reducing agent addition control of the present embodiment, the reducing agent is intermittently added through the reducing agent addition valve 21 so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a rich air-fuel ratio, and the predetermined timing is reached. Then, the addition of the reducing agent is stopped, and by repeating this, intermittent rich control is performed to prevent the NOx catalyst from being overheated while releasing and reducing the SOx retained and accumulated in the NOx catalyst.
[0064]
FIG. 2 shows that the S-poisoning elimination control according to the present embodiment is being implemented, and in particular, the reducing agent addition that is executed after the condition that “the bed temperature of the NOx catalyst is maintained at 600 ° C. or higher” is satisfied. It is a figure which shows transition of the air fuel ratio of the exhaust_gas | exhaustion which flows in into the NOx catalyst 15 at the time of control.
[0065]
As shown in FIG. 2, the reducing agent addition control of the present embodiment requires that the SOx retained and accumulated in the NOx catalyst should be released, and the bed temperature of the NOx catalyst is maintained at 600 ° C. or higher. When the condition is satisfied, the ECU 25 sends a command signal for opening the reducing agent addition valve 21 (hereinafter referred to as “valve opening command signal”) for a predetermined period (hereinafter referred to as “supply period”). .) By outputting during Δt1, fuel as a mist reducing agent is added from the reducing agent addition valve 21 so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 becomes a predetermined rich air-fuel ratio. (See FIG. 2). Thereafter, the ECU 25 pauses the output of the valve opening command signal for a predetermined time (hereinafter referred to as “pause period”) Δt2 so as to suppress overheating of the NOx catalyst 15 so as to reach a predetermined lean air-fuel ratio ( (See FIG. 2). Thereafter, after Δt2, the addition of the reducing agent is restarted so as to reach a predetermined rich air-fuel ratio again (see FIG. 2). Then, after adding the reducing agent during Δt1 again, the addition of the reducing agent during Δt2 is paused so that the predetermined lean air-fuel ratio is obtained again (see FIG. 2). As described above, when the reducing agent addition control is started, basically, the NOx catalyst 15 is intermittently supplied to the NOx catalyst 15 until the SOx retained and accumulated in the NOx catalyst 15 is released and the function of the catalyst 15 is sufficiently restored. The addition and pause of the reducing agent are repeated so that the air-fuel ratio of the inflowing exhaust gas becomes the rich air-fuel ratio. In this way, as the reducing agent addition control, intermittently adding the reducing agent to intermittently enrich the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 is referred to as intermittent rich control.
[0066]
As described above, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 is lowered with the start of the addition of the reducing agent through the reducing agent addition valve 21, and the NOx catalyst starts with the predetermined rich air-fuel ratio. The amount of SOx released increases. Similarly, when the supply of fuel as a reducing agent by the reducing agent addition valve 21 is stopped, the air / fuel ratio of the exhaust gas flowing into the NOx catalyst 15 is released from the NOx catalyst 15 as a predetermined lean air / fuel ratio. The amount of SOx decreases. As described above, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 and the SOx release amount from the NOx catalyst fluctuate substantially in synchronization with the opening / closing valve operation of the reducing agent addition valve 21. The bed temperature of the NOx catalyst 15 rises due to the start of the supply of the reducing agent through the reducing agent addition valve 21 and the supply of the reducing agent by the valve 21 is stopped. Descend.
[0067]
However, when the reducing agent is added from the reducing agent addition valve 21 to achieve the target rich air-fuel ratio, the reducing agent addition valve 21 is clogged even if the opening command signal of the reducing agent addition valve 21 is appropriate. If this occurs, an appropriate amount of reducing agent cannot be added, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 deviates from the target rich air-fuel ratio. Even when the reducing agent is added in an appropriate amount, if the fuel injection valve 3 is clogged or the like and the air-fuel ratio in the combustion chamber is deviated, it flows into the NOx catalyst 15 correspondingly. The air-fuel ratio of the exhaust gas deviates from the target rich air-fuel ratio.
[0068]
On the other hand, the air-fuel ratio in the combustion chamber is the target air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 only due to clogging or the like occurring in the reducing agent addition valve 21. Is deviated from the target rich air-fuel ratio, the difference between the target rich air-fuel ratio of the air-fuel ratio of the exhaust flowing into the NOx catalyst 15 and the detected value of the air-fuel ratio sensor 16 is opened within the above-described Δt1 period. If it is learned that there is a difference between the target addition amount and the actual addition amount based on the signal and feedback control is performed so that the reducing agent is added, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 becomes the target rich air-fuel ratio. Can be.
[0069]
Further, when the amount of reducing agent added from the reducing agent addition valve 21 is appropriate and the fuel injection valve 3 is clogged or the like, the air-fuel ratio in the combustion chamber is shifted and the NOx catalyst 15 is shifted. When the air-fuel ratio of the inflowing exhaust gas deviates from the target rich air-fuel ratio, the target rich air-fuel ratio of the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 and the detected value of the air-fuel ratio sensor 16 within the above-described Δt1 period. Is detected as a difference between the target injection amount and the actual injection amount based on the injection amount command signal for the fuel injection valve 3, and the feedback control is performed so as to correct it with the reducing agent addition amount, the flow into the NOx catalyst 15 occurs. The air / fuel ratio of the exhaust gas can be set to the target rich air / fuel ratio.
[0070]
Further, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 due to the clogging of the reducing agent addition valve 21 and the clogging of the fuel injection valve 3 from the target rich air-fuel ratio. Similarly, when there is a deviation, the deviation between the target rich air-fuel ratio of the exhaust air flowing into the NOx catalyst 15 and the detected value of the air-fuel ratio sensor 16 is learned within the above-described Δt1 period, and the amount of reducing agent added is calculated. If feedback control is performed so as to correct, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 can be made the target rich air-fuel ratio.
[0071]
However, even if the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 can be set to the target rich air-fuel ratio by performing feedback control within the Δt1 period as described above, at the start of each Δt1, that is, adding the reducing agent If there is a large amount of deviation when the reducing agent is added from the valve 21 to obtain the target rich air-fuel ratio for the first time, the NOx catalyst can be excessively heated, or a desired amount of SOx can be released / reduced. There is a risk of not.
[0072]
That is, when the reducing agent is first added from the reducing agent addition valve 21 to the target rich air-fuel ratio from the normal lean operation, when the target rich air-fuel ratio is shifted to the rich side, that is, during exhaust. If there are many reducing agents, there is a risk that the reducing agents present in the multiples and the oxygen in the exhaust will react on the NOx catalyst 15 and the temperature of the NOx catalyst 15 will rise excessively. On the other hand, when there is a shift to the lean side from the target rich air-fuel ratio, that is, when there is a small amount of reducing agent in the exhaust gas, there is a shortage of reducing agent to reduce the SOx accumulated in the NOx catalyst 15, and thereafter Δt1 Even if the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 can be adjusted to the target rich air-fuel ratio by feedback control within the period, there is a possibility that a desired amount of SOx cannot be released / reduced within the predetermined period. In particular, when Δt1 is short, SOx poisoning may not be sufficiently eliminated.
[0073]
Therefore, in the present embodiment, when the reducing agent addition control is executed, when the reducing agent is added from the reducing agent addition valve 21 from the lean operation to obtain the target rich air-fuel ratio for the first time, the reducing agent is used. The amount of reducing agent added is determined by learning the deviation of the air-fuel ratio in the combustion chamber at the time of lean operation immediately before the rich air-fuel ratio is added, that is, when no reducing agent is added. That is, when the air-fuel ratio in the combustion chamber deviates from the target lean air-fuel ratio to the lean side due to clogging or the like in the fuel injection valve 3, the amount of reducing agent added from the reducing agent addition valve 21 Therefore, the fuel injection valve 3 is opened longer than the opening period of the command value due to a decrease in the common rail pressure, and the air-fuel ratio in the combustion chamber is rich from the target lean air-fuel ratio. When it is shifted to the side, the amount of the reducing agent added from the reducing agent addition valve 21 is made smaller than usual. As described above, when the reducing agent is added from the reducing agent addition valve 21 to obtain the target rich air-fuel ratio for the first time, the air in the combustion chamber at the time of operating at the lean air-fuel ratio without adding the reducing agent is used. If the reducing agent is added so as to achieve the target rich air-fuel ratio by learning the deviation of the fuel ratio, the target rich air-fuel ratio can be accurately obtained from the beginning. Can be prevented, and a desired amount of SOx cannot be released / reduced.
[0074]
When performing the reducing agent addition control, the lean operation immediately before adding the reducing agent to the rich air-fuel ratio means that the reducing agent is added first (first time) during the reducing agent addition control execution period. The target rich air-fuel ratio is a normal lean operation immediately before starting the reducing agent addition control. After the period of Δt1, the reducing agent addition is stopped for the period of Δt2, and then again (second time). When the reducing agent is added to achieve the target rich air-fuel ratio, it means the lean operation immediately before that, that is, during the first Δt2. Thereafter, when the rich air-fuel ratio and the lean air-fuel ratio are repeated during the reducing agent addition control period, it means the lean operation during Δt2 immediately before the rich air-fuel ratio period (Δt1).
[0075]
Next, the SOx poisoning elimination control will be specifically described with reference to the flowcharts shown in FIGS.
[0076]
FIG. 3 is a routine that is periodically executed. First, at step 100, it is determined whether or not the vehicle is in a normal lean operation region. Here, the normal lean operation region is a region in which the air-fuel ratio in the combustion chamber of the internal combustion engine is operated lean while the above-described rich spike control, SOx poisoning elimination control, PM regeneration processing, or the like is not executed. I mean. If it is determined in step 100 that the vehicle is in the normal lean operation region, the process proceeds to step 101, where the difference between the detected value of the air-fuel ratio sensor 16 and the target lean air-fuel ratio is stored in the RAM of the ECU 25 as an X value, and the process ends. To do. On the other hand, if it is determined that it is not the normal lean operation region, step 101 is skipped and the process ends.
[0077]
Next, a routine for SOx poisoning elimination control will be described using the flowchart shown in FIG.
[0078]
This control is executed periodically. First, at step 200, it is determined whether or not the SOx poisoning elimination control execution condition is satisfied. This condition may be that the period during which SOx poisoning has not been eliminated has reached a predetermined period, or that the distance traveled by the vehicle while SOx poisoning has not been eliminated has reached a prescribed distance, or an exhaust temperature sensor A condition such as whether the output signal value (exhaust temperature) of 17 is equal to or lower than a predetermined upper limit value can be exemplified. And when it determines with SOx poisoning elimination control execution conditions being satisfied, it progresses to step 201 and the above-mentioned catalyst temperature rising process is performed. On the other hand, when the SOx poisoning elimination control execution condition is not satisfied, this control is terminated.
[0079]
In step 201, the catalyst temperature raising process is executed. As described above, in order to raise the temperature of the NOx catalyst 15 to about 600 ° C., the fuel is subsidized in the cylinder during the exhaust stroke or the expansion stroke. Secondary injection, such as post-injection, or intake stroke or exhaust stroke in which fuel is injected into the cylinder in the vicinity of the top dead center, or fuel as a reducing agent is added from the reducing agent addition valve 21 into the exhaust. To do.
[0080]
Next, in step 202, it is determined whether or not the reducing agent addition control execution condition is satisfied. If satisfied, the process proceeds to step 203. If not satisfied, the present control is terminated. Here, as the reducing agent addition control execution condition, for example, it can be exemplified whether the NOx catalyst 15 has reached a predetermined temperature (for example, 600 ° C.). In step 203, the X value stored in step 101 of FIG.
[0081]
Next, in step 204, it is determined whether or not it is during the reducing agent addition suspension period (during the period Δt2). If it is determined that the engine is not in the stop period, the routine proceeds to step 206 where the base reducing agent addition determined from the target lean air-fuel ratio in the internal combustion engine and the target rich air-fuel ratio of the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 is performed. The amount of reducing agent added to make the X value read in step 203 zero is added to the amount to calculate the amount of reducing agent added to be actually added to the exhaust. Then, the process proceeds to step 207, the reducing agent addition amount calculated in step 206 is added, and the process proceeds to step 208. On the other hand, if it is determined in step 204 that the reducing agent addition suspension period (during Δt2), the routine proceeds to step 205, where the difference between the detected value of the air-fuel ratio sensor 16 and the target lean air-fuel ratio is set as the X value. The X value already read and stored in step 203 is newly updated. And it progresses to step 203 again.
[0082]
In step 208, it is determined whether or not the SOx poisoning elimination control end condition is satisfied. As the SOx poisoning elimination control end condition, for example, it can be exemplified that a predetermined time has elapsed from the start of execution of the reducing agent addition control. If the SOx poisoning elimination control termination condition is satisfied, the SOx poisoning elimination control is terminated at step 209 and the present control is terminated. On the other hand, when the SOx poisoning elimination control termination condition is not satisfied, the process returns to step 203 again, and then the same processing as described above is repeated.
[0083]
When the SOx poisoning elimination control is executed in this way, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 becomes a rich air-fuel ratio under a situation where the bed temperature of the NOx catalyst 15 is high, so that the NOx catalyst 15 holds it. The accumulated sulfur oxide (SOx) is reduced and SOx poisoning of the NOx catalyst 15 is eliminated.
[0084]
The NOx storage reduction catalyst 15 may be carried on a diesel particulate filter. In such a case, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of each exhaust inflow passage and each exhaust outflow passage of the filter, that is, on both side surfaces of each partition wall and on the pore inner wall surface in the partition wall. The NOx storage reduction catalyst is carried on the top.
[0085]
Further, when the catalyst temperature raising process is executed by adding the reducing agent from the reducing agent addition valve 21, it is not always between the reducing agent addition at the time of executing the reducing agent addition control and the reducing agent addition at the time of executing the catalyst temperature raising process. There is no need to provide an interval.
[0086]
<Second Embodiment>
This embodiment is different from the first embodiment only in part of the SOx poisoning elimination control, and the others are the same as the first embodiment, so only the different parts will be described. Description of is omitted.
[0087]
In the first embodiment, during the execution of the reducing agent addition control, the reducing agent is added when the reducing agent is added from the reducing agent addition valve 21 to the target rich air-fuel ratio for the first time during the lean operation. Learn the air / fuel ratio deviation in the combustion chamber during lean operation just before the rich air / fuel ratio, that is, when no reducing agent is added, and calculate the amount of reducing agent added. Regardless of this, it is determined and added as the reducing agent addition amount. In this embodiment, after calculating the reducing agent addition amount (for example, α) by learning the deviation of the air-fuel ratio in the combustion chamber, the calculation is performed. The final reducing agent addition amount is determined according to the added amount (α). Specifically, when the calculated addition amount (α) is larger than the predetermined reducing agent addition amount (α1), α1 is determined as the final reducing agent addition amount. On the other hand, when the calculated addition amount (α) is equal to or less than the predetermined reducing agent addition amount (α1), α is determined as the final reducing agent addition amount.
[0088]
The reducing agent added to the exhaust has a function of reducing the SOx retained and accumulated in the NOx catalyst 15 under a high temperature condition, and has a characteristic of further increasing the temperature of the NOx catalyst 15. If the amount of NOx is large, the NOx catalyst 15 rises excessively and causes thermal degradation of the NOx catalyst 15. Therefore, a maximum addition amount α1 that does not cause excessive temperature rise of the NOx catalyst even if added at once from the characteristics such as the capacity of the NOx catalyst 15 is set in advance, and learning and calculation of the deviation of the air-fuel ratio in the combustion chamber is performed. When the added amount α of the reducing agent is larger than α1, the calculated addition amount α is not added as it is, but α1 is determined as the added amount, and the NOx catalyst 15 is not heated excessively. Try to prevent.
[0089]
Next, SOx poisoning elimination control according to the present embodiment will be described using the flowchart of FIG.
[0090]
Steps 300 to 306 are the same as those in the flowchart according to the first embodiment shown in FIG. In step 307, when the reducing agent addition amount α calculated in step 306 is equal to or less than the predetermined value α1, the reducing agent addition amount is determined as α and α is added. On the other hand, in step 308, when the reducing agent addition amount α calculated in step 306 is larger than the predetermined value α1, the reducing agent addition amount is determined as α1, and only α1 is added. Since the subsequent steps are the same as those in the flowchart according to the first embodiment, the description thereof is omitted.
[0091]
【The invention's effect】
As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is based on the calculation means for calculating the difference between the actual air-fuel ratio in the internal combustion engine and the target air-fuel ratio, and the difference calculated by the calculation means. In order to remove the sulfur oxide from the SOx holding material, the reducing agent addition control means is added from the reducing agent addition means, so that the SOx holding material can be held while preventing thermal deterioration of the SOx holding material. SOx can be accurately removed from the material.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment is applied and an intake / exhaust system thereof.
FIG. 2 is a view showing a change in the air-fuel ratio of exhaust gas flowing into the NOx catalyst 15 at the time of reducing agent addition control according to the first embodiment.
FIG. 3 is a flowchart for storing a difference between a detected value of an air-fuel ratio sensor used for SOx elimination processing according to the first embodiment and a target lean air-fuel ratio.
FIG. 4 is a flowchart of SOx poisoning elimination process control according to the first embodiment.
FIG. 5 is a flowchart of SOx poisoning elimination process control according to the second embodiment.
[Explanation of symbols]
1 Internal combustion engine
2-cylinder
3 Fuel injection valve
4 Common rail
5 Fuel supply pipe
6 Fuel pump
7 Intake passage
8 Air cleaner box
9 Air flow meter
10 Turbocharger
11 Intercooler
12 Inlet throttle valve
13 Inlet throttle actuator
14 Exhaust passage
15 Exhaust purification device
16 Air-fuel ratio sensor
17 Exhaust temperature sensor
18 EGR passage
19 EGR valve
20 Exhaust port
21 Reducing agent addition valve
22 Reducing agent supply path
23 Crank position sensor
24 Water temperature sensor
25 ECU

Claims (5)

内燃機関の排気通路に設けられ、排気中の硫黄酸化物を保持するとともに高温且つ還元雰囲気で保持した硫黄酸化物が除去されるＳＯｘ保持材と、
前記ＳＯｘ保持材の上流で排気に還元剤を添加する還元剤添加手段と、
前記ＳＯｘ保持材へ流入する排気または前記ＳＯｘ保持材から流出する排気の少なくとも一方の空燃比を検出する空燃比検出手段と、
前記空燃比検出手段の検出値に基づいて内燃機関燃焼室内の実際の空燃比と目標空燃比との差分を算出する算出手段と、
前記ＳＯｘ保持材から硫黄酸化物を除去させるべく、前記算出手段にて算出した差分を考慮して決定した還元剤添加量を前記還元剤添加手段から添加させる還元剤添加制御手段と、を備えることを特徴とする内燃機関の排気浄化装置。An SOx holding material that is provided in an exhaust passage of the internal combustion engine, holds sulfur oxide in the exhaust, and removes sulfur oxide held in a reducing atmosphere at a high temperature;
Reducing agent addition means for adding a reducing agent to the exhaust gas upstream of the SOx holding material;
Air-fuel ratio detecting means for detecting an air-fuel ratio of at least one of exhaust flowing into the SOx holding material or exhaust flowing out from the SOx holding material;
Calculation means for calculating a difference between an actual air-fuel ratio in the combustion chamber of the internal combustion engine and a target air-fuel ratio based on a detection value of the air-fuel ratio detection means;
Reducing agent addition control means for adding a reducing agent addition amount determined in consideration of the difference calculated by the calculating means from the reducing agent addition means to remove sulfur oxide from the SOx holding material. An exhaust gas purification apparatus for an internal combustion engine characterized by the above. 前記算出手段は、前記還元剤添加手段から還元剤を添加していない時の前記差分を算出するものであることを特徴とする請求項１に記載の内燃機関の排気浄化装置。The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the calculating means calculates the difference when no reducing agent is added from the reducing agent adding means. 前記還元剤添加制御手段は、前記還元剤添加手段から間欠的に還元剤を添加して前記ＳＯｘ保持材に流入する排気の空燃比を理論空燃比あるいはリッチな空燃比とする間欠リッチ制御を実行するものであり、
前記算出手段は、前記間欠リッチ制御実行中であって、前記還元剤添加手段から還元剤を添加していない時の前記差分を算出するものであることを特徴とする請求項１または２に記載の内燃機関の排気浄化装置。The reducing agent addition control means executes intermittent rich control in which the reducing agent is intermittently added from the reducing agent addition means so that the air-fuel ratio of the exhaust gas flowing into the SOx holding material is the stoichiometric or rich air-fuel ratio. Is what
3. The calculation unit according to claim 1, wherein the calculation unit calculates the difference when the intermittent rich control is being executed and no reducing agent is added from the reducing agent addition unit. Exhaust gas purification device for internal combustion engine. 前記還元剤添加量は、リーンな空燃比で運転している内燃機関燃焼室からの排気の空燃比を前記還元剤添加手段から還元剤を添加して目標のリッチな空燃比とするのに相当するベース還元剤量と前記差分をゼロにするのに相当する差分還元剤量とに基づいて定められることを特徴とする請求項１、２または３に記載の内燃機関の排気浄化装置。The amount of addition of the reducing agent is equivalent to making the air-fuel ratio of the exhaust from the combustion chamber of the internal combustion engine operating at a lean air-fuel ratio a target rich air-fuel ratio by adding the reducing agent from the reducing agent addition means. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, 2 or 3, characterized in that it is determined based on a base reducing agent amount to be performed and a differential reducing agent amount corresponding to making the difference zero. 前記還元剤添加量は、前記ベース還元剤量に前記差分還元剤量を加算して得た還元剤量と所定の還元剤量とを比較して定められることを特徴とする請求項４に記載の内燃機関の排気浄化装置。5. The reducing agent addition amount is determined by comparing a reducing agent amount obtained by adding the differential reducing agent amount to the base reducing agent amount and a predetermined reducing agent amount. Exhaust gas purification device for internal combustion engine.
JP2003006666A 2003-01-15 2003-01-15 Exhaust gas purification device for internal combustion engine Expired - Lifetime JP4211401B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2003006666A JP4211401B2 (en) 2003-01-15 2003-01-15 Exhaust gas purification device for internal combustion engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2003006666A JP4211401B2 (en) 2003-01-15 2003-01-15 Exhaust gas purification device for internal combustion engine

Publications (2)

Publication Number Publication Date
JP2004218520A JP2004218520A (en) 2004-08-05
JP4211401B2 true JP4211401B2 (en) 2009-01-21

Family

ID=32896969

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2003006666A Expired - Lifetime JP4211401B2 (en) 2003-01-15 2003-01-15 Exhaust gas purification device for internal combustion engine

Country Status (1)

Country Link
JP (1) JP4211401B2 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1818522B1 (en) 2004-11-30 2012-06-13 Isuzu Motors Limited Sulfur purge control method for exhaust gas purifying system and exhaust gas purifying system
JP4574610B2 (en) * 2006-12-15 2010-11-04 本田技研工業株式会社 Control device for internal combustion engine
JP5448310B2 (en) * 2007-07-11 2014-03-19 日野自動車株式会社 Exhaust purification device
JP5142048B2 (en) * 2008-04-08 2013-02-13 株式会社デンソー Exhaust gas purification device for internal combustion engine

Also Published As

Publication number Publication date
JP2004218520A (en) 2004-08-05

Similar Documents

Publication Publication Date Title
JP3599012B2 (en) Exhaust gas purification device for internal combustion engine
US7246485B2 (en) Exhaust gas purifying device and method for internal combustion engine
JP3617450B2 (en) Exhaust gas purification device for internal combustion engine
JP2004176663A (en) Exhaust emission control device for internal combustion engine
KR100441481B1 (en) Exhaust gas purification device for internal combustion engine
JP4482848B2 (en) Exhaust gas purification device for turbocharged engine
JP4211401B2 (en) Exhaust gas purification device for internal combustion engine
JP3558019B2 (en) Abnormality detection device for reducing agent supply device
JP3912001B2 (en) Exhaust gas purification device for internal combustion engine
JP3897621B2 (en) Exhaust gas purification device for internal combustion engine
JP2004285947A (en) Exhaust emission control device for internal combustion engine
JP2002155737A (en) Exhaust emission control device of internal combustion engine
EP1887202B1 (en) Sulfur purge control device for an internal combustion engine
JP4357241B2 (en) Exhaust purification equipment
JP4639565B2 (en) Exhaust gas purification device for internal combustion engine
JP4193553B2 (en) Exhaust gas purification device for internal combustion engine
JP3800065B2 (en) Exhaust gas purification device for internal combustion engine
JP3788314B2 (en) Exhaust gas purification device for internal combustion engine
JP4314835B2 (en) Exhaust gas purification system for internal combustion engine
JP3791312B2 (en) Exhaust gas purification device for internal combustion engine
JP3858758B2 (en) Exhaust gas purification device for internal combustion engine
JP3620446B2 (en) Exhaust gas purification device for internal combustion engine
JP2002180816A (en) Exhaust emission control device of internal combustion engine
JP2002364439A (en) Exhaust emission control device for internal combustion engine
JP3851151B2 (en) Internal combustion engine

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20051226

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20080910

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20081007

A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20081020

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20111107

Year of fee payment: 3

R151 Written notification of patent or utility model registration

Ref document number: 4211401

Country of ref document: JP

Free format text: JAPANESE INTERMEDIATE CODE: R151

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20111107

Year of fee payment: 3

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20111107

Year of fee payment: 3

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20121107

Year of fee payment: 4

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20121107

Year of fee payment: 4

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20131107

Year of fee payment: 5

EXPY Cancellation because of completion of term