JP2004100659A

JP2004100659A - Exhaust emission control device and exhaust emission purifying method for diesel engine

Info

Publication number: JP2004100659A
Application number: JP2002267534A
Authority: JP
Inventors: Hidehiro Iizuka; 飯塚　秀宏; Masayuki Kamikawa; 上川　将行; Masahito Kanae; 金枝　雅人; Kojiro Okude; 奥出　幸二郎; Kazuhisa Higashiyama; 東山　和寿; Yuichi Kitahara; 北原　雄一; Osamu Kuroda; 黒田　　修
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2002-09-13
Filing date: 2002-09-13
Publication date: 2004-04-02
Anticipated expiration: 2022-09-13
Also published as: JP4168712B2

Abstract

<P>PROBLEM TO BE SOLVED: To purify NOx included in diesel engine exhaust gas without providing a DPF to the upstream side of an exhaust gas purifying catalyst. <P>SOLUTION: In this exhaust emission control device provided with the exhaust gas purifying catalyst in the exhaust channel of the diesel engine, an exhaust gas rectifying construction for branching exhaust gas into two or more in relation to the horizontal axial line of the exhaust channel is arranged on an exhaust upstream side rather than the exhaust gas purifying catalyst. An exhaust gas flow led to flow into the exhaust gas purifying catalyst is previously rectified in a laminar flow state by the exhaust gas rectifying construction, thereby collision frequency of fine particulates with the catalyst wall of the exhaust gas purifying catalyst is reduced, and adhesion of the particulates to the exhaust gas purifying catalyst is suppressed. Thereby, the performance deterioration of the exhaust gas purifying catalyst is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ディーゼルエンジンで運転する自動車等の内燃機関の排ガス浄化装置及び排ガス浄化方法に関する。
【０００２】
【従来の技術】
ディーゼルエンジンにおいて、排ガスに含まれるパティキュレートが問題になっている。パティキュレートが排ガス浄化触媒に付着すると排ガス浄化触媒の性能が低下する。特許第３２４８１８７号には、排気中の微粒子を捕捉するフィルター（いわゆるＤＰＦ）の排気流出面のみにＮＯｘ蓄積材を配置する排ガス浄化装置が開示されている。
【０００３】
【発明が解決しようとする課題】
本発明の目的は、排ガス浄化触媒の上流にディーゼルパティキュレートフィルターを設置せずとも排ガス浄化触媒にパティキュレートが付着するのを抑制できるようにした排ガス浄化装置及び排ガス浄化方法を提供することにある。
【０００４】
【課題を解決するための手段】
本発明は、排気流路の排ガス浄化触媒よりも排気上流側に、排ガスを排気流路の水平軸線に対して複数に分流する排ガス整流構造体を設けたものである。
【０００５】
パティキュレートは、煤，未燃炭化水素及び硫酸塩が凝集してできた直径１０〜３００ｎｍ程度の微粒子（固体）である。このパティキュレートは、排ガス浄化触媒に流入する排ガスの流れを層流状態に整流すると排ガス浄化触媒の触媒壁に衝突する頻度が低下し、排ガス浄化触媒への付着が抑制される。本発明は、このようなパティキュレートの性質をふまえて、排気流路の排ガス浄化触媒よりも排気上流側に排ガスを排気流路の水平軸線に対して複数に分流する排ガス整流構造体を設けたものである。
【０００６】
排ガス整流構造体は、エンジンから流入する排ガスの流れをほぼ層流に整流できる構造体にすることが好ましい。
【０００７】
排ガス浄化触媒と排ガス整流構造体は、何れもハニカム構造にすることが望ましい。
【０００８】
排ガス整流構造体のハニカム構造体における垂直線方向の単位面積あたりのセル数は、排ガス浄化触媒のセル数に対して１倍以上，５倍以下とするのがよい。１倍以上であれば、整流装置で整流された排ガスが排ガス浄化触媒のセル壁に衝突しても乱流となることなく通過できる。１倍未満の場合には、整流装置で整流された排ガスが排ガス浄化触媒のセル壁に衝突することで乱流が生じるため好ましくない。５倍よりも高くなると、排ガス整流構造体前後での圧力損失が増加するため好ましくない。
【０００９】
排ガス整流構造体と排ガス浄化触媒は、両者の間の距離ができるだけ少なくなるように設置することが望ましい。このために、排ガス整流構造体をハニカム構造体とし、そのハニカム構造体の後流部分に触媒層を形成して、そこを排ガス浄化触媒とすることが望ましい。ハニカム構造体にはコージェライト，アルミナなどの導電性の低い耐熱性無機酸化物やステンレスなどの伝熱性および導電性に優れるメタルを用いることができる。また、ハニカム構造体のセル開口部の形状は四角形，六角形，菱形など何れも適用可能である。
【００１０】
ところで、ディーゼルエンジンから排出される排ガスの温度領域は大略１５０〜３５０℃程度であり、一般的な排ガス浄化触媒の好適な排ガス浄化温度２００〜５００℃にくらべて低い。
【００１１】
このため、排ガス浄化触媒よりも排気上流側で排ガスを加熱することが望まれる。この具体的手段として、排ガス整流構造体に排気ガス加熱機構を設けることが好ましい。
【００１２】
排ガス整流構造体による排ガス加熱方法としては、例えば排ガス整流構造体のセル内壁面に酸化触媒層を形成しておき、排ガス中のＣＯ，ＨＣなどを共存するＯ_２　により酸化することで得られる燃焼熱を利用して排ガスを直接加熱する方法が適用できる。また、排ガス整流構造体を直接加熱し、加熱された排ガス整流構造体の輻射熱を利用して排ガスを加熱する間接加熱方法が適用できる。なお、排ガス整流構造体の表面にコートする酸化触媒はＳＯｘの発生源であるパティキュレートを燃焼しないものが好ましい。
【００１３】
酸化触媒をコートした排ガス整流構造体を用いる場合には、次のようにして酸化触媒を働かせることが望ましい。まず、排ガス浄化触媒に流入する排ガスの温度を温度計にて計測する。排ガス温度が予め決められた所定温度よりも低いならば、排ガス整流構造体に流入する排ガスの還元剤濃度を高めて、還元剤の燃焼により排ガスを加熱する。一方、排ガス温度が予め決められた所定温度よりも高いならば、排ガス整流構造体に流入する排ガスに還元剤が含まれないようにするかあるいは還元剤量を低めて酸化触媒が機能しないようにする。
【００１４】
排ガスへの還元剤の供給方法としては、排ガスに燃料やＨＣ，ＣＯなどの還元剤を注入する方法，エンジンシリンダ内の燃焼タイミングを調整する方法、或いは通常の燃料噴射に加えて膨張行程または排気行程でエンジンシリンダ内に２回目の燃料を噴射する燃料２次噴射方法等が適用可能である。
【００１５】
酸化触媒としては、Ｒｈ，Ｐｔ，Ｐｄなどの貴金属やＮｉ，Ｃｕ，Ｃｏなどの遷移金属をアルミナ，シリカ，チタニアなどの耐火性多孔質無機酸化物担体に担持したものが適用可能である。
【００１６】
間接加熱による加熱機構を備えた排ガス整流構造体の例としては、導電性を有するハニカム構造体（例えば、メタルハニカム）にすることが考えられる。導電性を有するハニカム構造体にした場合、ハニカム構造体に通電して加熱できる。加熱時のハニカムからの輻射熱を利用して、排ガス整流構造体を流通する排ガスを加熱する。この場合の加熱制御は、排ガス浄化触媒に流入する排ガス温度に応じて、例えば次のようにして実施する。排ガス浄化触媒に流入する排ガス温度が所定温度より低い（例えば、１８０℃）場合には加熱装置を作動させて排ガスを加熱する。加熱装置への通電量を多くすると加熱後の排ガス温度も高くなる。通電量は所定温度と排ガス温度の差分から必要量を推定し決定する。排ガス浄化触媒に流入する排ガス温度が所定温度より高い場合には、排ガス整流構造体への通電を停止する。
【００１７】
排ガス整流構造体を導電性ハニカム構造体にして、そのセル内壁に酸化触媒が塗布しておくようにすれば、直接加熱と間接加熱を同時または任意に行うことができ、通電量の抑制効果も期待できる。
【００１８】
なお、排気流路の排ガス浄化触媒よりも下流にＤＰＦを設けておき、パティキュレートをＤＰＦにて捕捉することは、本発明の一実施態様として好適である。この場合、ＤＰＦに蓄積されたパティキュレートの量が一定値を超えると排気流路の内圧が上昇するため、ＤＰＦに捕捉されたパティキュレートの燃焼除去することが望ましい。
【００１９】
パティキュレートの燃焼除去方法の例を以下に示す。
【００２０】
ここでは、排ガス浄化装置に排ガス温度計測装置，排ガス温度判定手段及び
ＤＰＦへのパティキュレート捕捉量推定手段が付加されている。
【００２１】
排ガス温度計測装置はＤＰＦへ流入する排ガス温度を計測する。排ガス温度計測装置はたとえば排ガス温度センサである。パティキュレート捕捉量推定手段はＤＰＦにて捕捉されるパティキュレート量を推定する。パティキュレート量の推定値が予め決められた所定の捕捉量を越えたとき、ＤＰＦの再生制御が行われる。パティキュレート捕捉量は運転時間や走行距離から推定することができる。
【００２２】
しかしながら、流入する排ガス温度がパティキュレート燃焼温度より低いと、パティキュレートの燃焼除去は行われない。そこで、排ガス温度計測装置にて計測される温度が、予め決められた所定温度より低いと判断すると、排ガス整流構造体にて排気ガスを加熱してＤＰＦに捕捉されたパティキュレートを酸化除去する。なお、予め決められた所定温度は、パティキュレート燃焼温度以下の温度に設定する。
【００２３】
捕捉パティキュレートの燃焼除去が行われると、パティキュレート中の硫酸塩はＳＯｘ（気体成分）として排出される。このＳＯｘが排ガス浄化触媒に捕捉されると、排ガス浄化性能の低下が起こる。従って、ＳＯｘ被毒の観点から排ガス流路において排ガス浄化触媒はＤＰＦの上流に配置されることが好ましい。
【００２４】
排ガス浄化触媒は、リーンバーン状態において排ガス中のＮＯｘ，ＨＣ，ＣＯを浄化する能力を有する触媒が望ましい。特に、リーンにおいてＮＯｘを捕捉し、排ガスの空燃比がストイキ（空燃比：１４．７）またはリッチ（空燃比：１４．７未満）において捕捉ＮＯｘをＮ_２　に還元浄化する排ガス浄化触媒は、広い温度範囲にて高いＮＯｘ浄化性能が得られるので好適である。この排ガス浄化触媒は、貴金属とＮＯｘ捕捉材を有する。
【００２５】
ＮＯｘ捕捉方法は、貴金属上でＮＯがＮＯ_２　に酸化（式（１））された後、
ＮＯｘを硝酸化合物としてＮＯｘ捕捉材に捕捉する吸収（吸蔵；式（２））と、ＮＯｘをＮＯ_２　としてＮＯｘ捕捉材に化学吸着する吸着（式（３））とに分類される。なお、以下で単にＮＯｘ捕捉と記述した場合には、吸収と吸着を包含する。
【００２６】
吸収となるＮＯｘ捕捉材は、ＮＯｘ吸収材（例えばＢａＯ）と記載する。ＮＯｘ吸収材としては、アルカリ金属とアルカリ土類金属がある。吸収によるＮＯｘ捕捉機構は、ＮＯ_２　とＢａＯが反応してＢａ（ＮＯ_３）_２の生成する式（２）となる。
【００２７】
吸着となるＮＯｘ捕捉材は、ＮＯｘ吸着材と記載する。ＮＯｘ吸着材としては、（イ）アルカリ金属とチタンから構成される特開平１０−１１８４５８号公報に記載のもの、（ロ）アルカリ土類金属とチタンの複合酸化物よりなる特開平
１０−１０９３２号公報に記載のもの及び（ハ）Ｋ，Ｎａ，Ｍｇ，Ｓｒ及びＣａから選ばれる一種以上の元素を成分の一部として含む特開平１０−２１２９３３号公報に記載のＮＯｘ吸着材などがある。
【００２８】
吸着によるＮＯｘ捕捉機構は、貴金属上で生成したＮＯ_２　（式（１））を、
ＮＯｘ吸着材表面にＮＯ_２　として化学吸着する式（３）となる。
【００２９】
捕捉ＮＯｘはＮ_２　に還元される。例えば、ＮＯｘ吸着の場合、吸着ＮＯ_２　は、ストイキまたはリッチにおいて、排ガス中のＨＣ，ＣＯ，Ｈ_２　等の還元剤によりＮ_２　として還元浄化される（式（４））。ストイキまたはリッチに保持する時間は、数秒ないし数分間で十分である。
【００３０】
なお、ＮＯｘ捕捉材の表面に吸着している化学吸着は、ＮＯｘ捕捉材内部に捕捉する吸収に比べて、捕捉ＮＯｘの還元速度が速いため、ストイキまたはリッチにする時間を短くすることが可能である。
【００３１】
ＮＯ＋０．５Ｏ_２　→　ＮＯ_２　　　　　　　　　　　　　　　　　　　　（１）
２ＮＯ_２＋０．５Ｏ_２＋ＢａＯ　→　Ｂａ（ＮＯ_３）_２　　　　　　　　　　　（２）
ＮＯ_２＋ＮＯｘ吸着材　→　ＮＯ_２−ＮＯｘ吸着材　　　　　　　　　　（３）
ＮＯ_２−ＮＯｘ吸着材＋ＨＣ，ＣＯ，Ｈ_２→Ｎ_２＋ＣＯ_２＋Ｈ_２Ｏ＋ＮＯｘ吸着（４）
上記排ガス浄化触媒を用いてリーン，ストイキまたはリッチにする制御を行うことでディーゼルエンジンにおいて高いＮＯｘ浄化性能が得られる。ディーゼルエンジンは基本的にリーン運転であるため、排ガス浄化触媒に流入する排ガスの空燃比を一時的にストイキまたはリッチにする制御及び方法が必要となる。
【００３２】
なお、ディーゼルエンジンの排ガスを整流することについて記載された従来技術としては特表２００１−５１６６３５号公報がある。
【００３３】
【発明の実施の形態】
「実施例１」
図３は、本発明の排ガス浄化触媒を有する内燃機関の一例を示す。自動車１００は、エンジン９９，エキゾーストパイプ１０１，排ガス整流構造体１および排ガス浄化触媒２を有する。ディーゼルエンジン９９は、空燃比１８以上のリーン燃焼と空燃比１４．７　以下のストイキまたはリッチ燃焼を意図的に繰り返す。
【００３４】
ディーゼルエンジン９９からの排ガスは、エキゾーストパイプ１０１を通じて図１の模式図のように排ガス整流構造体１へ流入して整流された後、排ガス浄化触媒２に流入する。排ガス浄化触媒２にて、排ガス中のＮＯｘ，ＨＣ，ＣＯが浄化される。なお、図１において、符号３は排ガスの流れを示している。排ガス整流構造体１は既に述べたように排ガス浄化触媒のセル数に対して１倍以上，５倍以下にすることが好ましく、この範囲を外れると図２の模式図のようになり、排ガス整流構造体１で整流された排ガスが排ガス浄化触媒２のセル壁に衝突して乱流が生じるようになる。
【００３５】
なお、図４に示すように、排ガス浄化触媒２の排気後流側にＤＰＦ４を設けても良い。ＤＰＦ４にはパティキュレートを酸化する機能を持たせることが望ましい。このようにすると、例えば排ガス温度が２５０℃程度以上になるとパティキュレートを排ガス中のＯ_２　を用いて酸化除去してＤＰＦ４を再生することができる。酸化機能は、ＤＰＦ４に貴金属などの触媒活性成分を含有させることで容易に付与できる
「実施例２」
図４は、エキゾーストパイプ１０１内に排気の上流側から順に酸化触媒を備えた排ガス整流構造体１Ａと排ガス浄化触媒２とＤＰＦ４を備えた排ガス浄化装置を示す。
【００３６】
図５は、ＮＯ酸化材としてＲｈ，Ｐｔ，Ｐｄ，ＮＯ_２　吸着材としてＮａ，Ｋ，Ｍｎ及びＴｉを用いた排ガス浄化触媒２の流入排ガス温度に対するＮＯｘ浄化率の一例を示す。
【００３７】
ＮＯｘ浄化率はリーンにおいて排ガス浄化触媒に流入したＮＯｘ量に対する排ガス浄化触媒にて浄化されたＮＯｘ量の比として求めた。ＮＯｘ浄化率は１５０℃にて３５％程度，１８０℃で６５％程度，２００℃で８５％程度となった。
【００３８】
図６は、酸化触媒を備えた排ガス整流構造体１Ａの加熱性能を示す。酸化触媒を備えた排ガス整流構造体１Ａに流入した排ガスは、温度Ｔ１からＴ２に昇温されたのち排ガス整流構造体より流出される。Ｔ１に対してＴ２を３０℃程度高めることで、排ガス浄化触媒に流入する温度範囲は１７０℃以上となり、ＮＯｘ浄化性能は６５％以上と向上する。
【００３９】
「実施例３」
図７は、酸化触媒を有する排ガス整流構造体１Ａと排ガス浄化触媒２とＤＰＦ４を備え、排ガス整流構造体の排気上流側に還元剤供給装置９を備え、更に排ガス温度計測装置５，６を備えた排ガス浄化装置を示している。
【００４０】
ＮＯｘ捕捉量は、排ガス流量，排ガス中のＮＯｘ濃度及び排ガス温度に依存している。そこで、エンジンコントロールユニット（ＥＣＵ）１０２に内蔵されたＮＯｘ捕捉量推定手段は、エンジン回転数，リーン運転時間，吸入排気量，排ガス浄化触媒に流入する排ガス温度から捕捉ＮＯｘ量の積算値推算する。
【００４１】
ＮＯｘ量の積算値が予め決められた一定量を超えたと判断すると、ＥＣＵ内蔵の排ガス空燃比制御手段が捕捉ＮＯｘの還元浄化に必要な還元剤量と還元時間を決定する。続いて、還元剤供給装置９が排ガス空燃比制御手段からの指令に基づいて還元剤量の供給と還元時間の保持を実行する。
【００４２】
ＥＣＵに内蔵された捕捉ＮＯｘの還元量推定手段が所定量の還元剤供給時間が終了したと判断すると、還元剤の供給を停止し、排ガスの空燃比をリーンに戻す。
【００４３】
本実施例においても、リーンにおけるＮＯｘ浄化率を高めるため、排ガス浄化触媒２に流入する排ガス温度を予め決められた所定温度（例えば１８０℃）以上にすることが好ましい。
【００４４】
酸化触媒を有する排ガス整流構造体１Ａにおける制御フローを図８に記す。
【００４５】
排ガス浄化触媒２に流入する排ガス温度（Ｔ）を排ガス温度計測装置５にて計測し（４００１）、ＥＣＵ１０２内の排ガス温度判定手段にて予め決められた所定温度（例えば、１８０℃）に対する温度差（ΔＴ＝１８０−Ｔ）を算出する
（４００２）。
【００４６】
排ガス浄化触媒に流入する排ガス温度（Ｔ）が予め決められた所定の温度範囲（例えば最下値１５０℃より高く、最大値１８０℃より低い）と判断すると酸化触媒を有する排ガス整流構造体１Ａにて排ガスの加熱を実行する。酸化触媒を有する排ガス整流構造体１Ａを実行するΔＴは、０より大きく所定の値ｂ（ｂ：最下値が１５０℃の場合は３０℃）より低い範囲となる（４００３）。なお、ディーゼルエンジンにおいて浄化すべき排ガス温度範囲を設定することで省エネルギーが可能となり燃費の向上につながる。
【００４７】
排ガスの空燃比制御手段は、前記温度差（ΔＴ）をほぼゼロにするのに必要な排ガス整流構造体に流入する排ガスの空燃比のマップ（図１３）を予め備えている。排ガスの空燃比のマップから決定された空燃比となるように還元剤供給装置９は還元剤を供給する（４００４）。
【００４８】
例えば、図９において、ΔＴがΔＴ１と算出されると、排ガス整流構造体１Ａに流入する排ガスの空燃比はａ１と決まる。還元剤供給装置９は前記空燃比（ａ１）となるように還元剤を供給する。
【００４９】
排ガスの空燃比制御手段は、前記温度差（ΔＴ）が制御範囲外と判断すると
（４００３）、還元剤供給装置９は還元剤を停止する（４００５）。
【００５０】
なお、排ガス流路の還元剤供給装置９と排ガス整流構造体１Ａの間に空燃比センサを設けると、決定空燃比と実行空燃比とのずれを計測してフィードバック制御できるので好適である。
【００５１】
上記排ガス整流構造体１Ａの制御フロー（図８）は、ＤＰＦ４が捕捉したパティキュレートの燃焼除去の制御にも適応可能である。
【００５２】
即ち、ＤＰＦ４へのパティキュレート捕捉量推定手段がＤＰＦ４に流入する排ガス温度がパティキュレート燃焼温度より低い状態（例えば、２５０℃以下）が長時間継続してパティキュレートの捕捉量が所定量を超えると判断すると、ＤＰＦ４へ流入する排ガス温度を予め決められた温度（例えば、２５０℃）以上となるように排ガス整流構造体１Ａにて排ガスを加熱し、パティキュレートを燃焼除去する。
【００５３】
「実施例４」
排ガスへの還元剤供給を燃焼タイミングの調整や、通常の燃料噴射に加えて膨張行程または排気行程でエンジンシリンダ内に２回目の燃料を噴射する燃料２次噴射により行う実施例について以下説明する。
【００５４】
本実施例は、図４に示す排ガス浄化装置を基本構成とし、酸化触媒を有する排ガス整流構造体１Ａと排ガス浄化触媒２との間に排ガス温度計測装置５が備えられている。
【００５５】
図１０に制御フロー例を示す。
【００５６】
エンジンコントロールユニット（ＥＣＵ）１０２にて、排ガス浄化触媒に流入する排ガス温度（Ｔ）が予め決められた所定の温度（例えば、１８０℃）より低いと判断すると（２００２）、燃料２次噴射を開始し、排ガス中の還元剤濃度を高める（２００３）。還元剤は排ガス整流構造体１Ａの酸化触媒にて酸化され、排ガス温度が上昇する。また、排ガス温度（Ｔ）が予め決められた所定の温度
（１８０℃）以上と判断すると（２００２）、燃料２次噴射を停止する（２００５）。
【００５７】
「実施例５」
図１１は、伝熱性および導電性を有するハニカム構造体よりなりかつ加熱装置を有する排ガス整流構造体１Ｂを備えた場合の排ガス浄化装置の一例である。排ガス流路には、排気の流れの上流から排ガス整流構造体１Ｂ，排ガス温度計測装置５，排ガス浄化触媒２，ＤＰＦ４の順に設置されている。排ガス浄化触媒２に流入する排ガス温度（Ｔ）は排ガス温度計測装置５で計測され、ＥＣＵ１０２へ伝達される。ＥＣＵ１０２は、計測温度（Ｔ）に応じて排ガス整流構造体１Ｂの加熱装置の制御を実施する。
【００５８】
図１２はフローの一例である。ＥＣＵ１０２にて、排ガス浄化触媒に流入する排ガス温度（Ｔ）が予め決められた所定の温度（例えば、１８０℃）より低いと判断すると（３００２）、排ガス整流構造体１Ｂの加熱装置に通電を開始することで、排ガスの加熱が開始される（３００３）。また、排ガス温度（Ｔ）が予め決められた所定の温度（１８０℃）以上と判断すると（３００２）、排ガス整流構造体への通電を停止することで排ガスの加熱を停止する（３００４）。
【００５９】
図１３は、図１２のフローにおいて排ガス温度の判断基準を変えた例である。排ガス浄化触媒に流入する排ガス温度（Ｔ）が予め決められた所定の温度範囲
（例えば１５０℃より高く、１８０℃より低い）と判断すると（３００６）、排ガス整流構造体１Ｂの加熱装置に通電を開始することで、排ガスの加熱が開始される（３００３）。また、排ガス温度（Ｔ）が予め決められた所定の温度範囲外（１５０℃以下または１８０℃以上）と判断すると（３００２）、排ガス整流構造体への通電を停止することで排ガスの加熱を停止する（３００４）。ディーゼルエンジンにおいて浄化すべき排ガス温度範囲を設定することで省エネルギーが可能となり燃費の向上につながる。
【００６０】
「実施例６」
図１１に示す排ガス浄化装置の構成において、排ガス浄化触媒２とＤＰＦ４との間に、図７に示すように排ガス温度計測装置６を設けて、ＤＰＦ４のパティキュレート捕捉と再生制御を行う実施例について説明する。
【００６１】
ＥＣＵ１０２は、排ガス浄化触媒２に必要な排ガスの加熱とＤＰＦ４の再生に必要な排ガスの加熱の何れかを排ガス整流構造体１Ｂにて実施するかを制御するロジックを備えている。また、排ガス温度が所定温度より高いときには、排ガス整流構造体１Ｂの加熱を停止するロジックを備えている。
【００６２】
ＥＵＣ１０２へは、排ガス浄化触媒２に流入する排ガス温度、及びＤＰＦ４に流入する排ガス温度，エンジンの吸入空気量，エンジン回転数，空燃比などの情報が伝達される。それらの情報に基づき、ＥＣＵ１０２内の各制御手段からの判定を総合的に判断して、排ガス整流装置の加熱装置を作動或いは停止する決定，空燃比をリーン，ストイキまたはリッチにする決定を各装置に命令する。
【００６３】
ＤＰＦ４へのパティキュレート捕捉量推定手段がＤＰＦ４に流入する排ガス温度がパティキュレート燃焼温度より低い状態（例えば、２５０℃以下）が長時間継続してパティキュレートの捕捉量が所定量を超えると判断すると、排ガス整流装置１Ｂの加熱装置を作動させる。ＤＰＦへ流入する排ガス温度を強制的に予め決められた所定温度（例えば、２５０℃）以上に一定時間保持することで、ＤＰＦ４に捕捉されたパティキュレートを燃焼除去する。結果、ＤＰＦ４は再生する。ＤＰＦ４へのパティキュレート捕捉量推定手段がＤＰＦの再生が完了したと判断すると排ガス整流構造体１Ｂの加熱装置を停止させる。
【００６４】
排ガス浄化触媒２に関しては、ＮＯｘ捕捉量推定手段でＮＯｘ捕捉量が所定量を超えたと判断すると、排ガスの空燃比制御手段が、排ガス浄化触媒に流入する空燃比をストイキまたはリッチとし、車速及び排ガス温度に応じて予め決められたストイキまたはリッチの時間を保持する。捕捉ＮＯｘの還元量推定手段にて、捕捉ＮＯｘの還元量推定手段が捕捉ＮＯｘの還元浄化が終了したと判断すると、排ガスの空燃比制御手段は再び通常のリーン空燃比に戻す。
【００６５】
また、リーン，ストイキまたはリッチにおけるＮＯｘ浄化率を高めるため、本実施例においても排ガス浄化触媒２に流入する排ガス温度を予め決められた所定温度（例えば、１８０℃）以上にすることが好ましい。この場合、排ガス浄化触媒２に流入する排ガス温度（Ｔ）を排ガス温度計測装置５にて計測し、ＥＣＵ
１０２内の排ガス温度判定手段にて予め決められた所定温度（例えば、１８０℃）に不足している温度差（ΔＴ＝１８０−Ｔ）を算出する。この温度差（ΔＴ）がほぼゼロとなるように排ガス整流構造体１Ｂの加熱装置を作動させる。
【００６６】
排ガス整流装置１Ｂの加熱装置を作動条件（加熱温度及び時間）に関しては、ＤＰＦ４と排ガス浄化触媒２において、加熱温度は加熱温度の高い方、そして加熱時間は長い方が優先される。
【００６７】
【発明の効果】
本発明の排ガス浄化装置及び排ガス浄化方法により、排ガス浄化触媒よりも排気上流側にＤＰＦを設けずとも排ガス浄化触媒にパティキュレートが付着するのを抑制できる。
【図面の簡単な説明】
【図１】本発明による排ガス浄化装置による排ガスの流れを示す模式図。
【図２】不適当な排ガス整流構造体を用いた場合の排ガスの流れを示す模式図。
【図３】本発明の排ガス浄化装置を備える内燃機関の概略図。
【図４】本発明の排ガス浄化装置を備えた内燃機関の他の実施例を示す概略図。
【図５】
排ガス浄化触媒へ流入する排ガス温度とＮＯｘ浄化率との関係図。
【図６】酸化触媒を有する排ガス整流装置への流入排ガス温度と流出排ガス温度との関係図。
【図７】本発明の排ガス浄化装置を備えた内燃機関の他の実施例を示す概略図。
【図８】図７に示す内燃機関の制御フロー図。
【図９】排ガス整流構造体に流入する排ガスの空燃比の図。
【図１０】燃料２次噴射を行うときの制御フロー図。
【図１１】本発明の排ガス浄化装置を備えた内燃機関の他の実施例を示す概略図。
【図１２】排ガス浄化装置の制御フロー図。
【図１３】排ガス浄化装置の他の制御フロー図。
【符号の説明】
１…排ガス整流構造体、２…排ガス浄化触媒、３…排ガス流れ、４…ＤＰＦ、５，６…排ガス温度計測装置、８…酸化触媒、９…還元剤供給装置、９９…エンジン、１００…自動車、１０１…エキゾーストパイプ、１０２…エンジンコントロールユニット（ＥＣＵ）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus and an exhaust gas purifying method for an internal combustion engine such as an automobile driven by a diesel engine.
[0002]
[Prior art]
In diesel engines, particulate matter contained in exhaust gas has become a problem. If the particulates adhere to the exhaust gas purifying catalyst, the performance of the exhaust gas purifying catalyst deteriorates. Japanese Patent No. 3248187 discloses an exhaust gas purifying apparatus in which a NOx accumulating material is arranged only on an exhaust outflow surface of a filter (so-called DPF) for trapping fine particles in exhaust gas.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide an exhaust gas purifying apparatus and an exhaust gas purifying method that can suppress the attachment of particulates to an exhaust gas purifying catalyst without installing a diesel particulate filter upstream of the exhaust gas purifying catalyst. .
[0004]
[Means for Solving the Problems]
According to the present invention, an exhaust gas rectification structure for diverting exhaust gas into a plurality of parts with respect to a horizontal axis of the exhaust flow path is provided upstream of the exhaust gas purification catalyst in the exhaust flow path.
[0005]
Particulates are fine particles (solids) having a diameter of about 10 to 300 nm formed by agglomeration of soot, unburned hydrocarbons and sulfates. When the particulates rectify the flow of the exhaust gas flowing into the exhaust gas purifying catalyst into a laminar flow state, the frequency of collision with the catalyst wall of the exhaust gas purifying catalyst decreases, and the adhesion to the exhaust gas purifying catalyst is suppressed. The present invention provides an exhaust gas rectification structure that divides the exhaust gas into a plurality of components with respect to the horizontal axis of the exhaust flow path on the exhaust gas upstream side of the exhaust gas purification catalyst in the exhaust flow path in consideration of such particulate properties. Things.
[0006]
The exhaust gas rectification structure is preferably a structure that can rectify the flow of exhaust gas flowing from the engine into a substantially laminar flow.
[0007]
It is desirable that both the exhaust gas purifying catalyst and the exhaust gas rectification structure have a honeycomb structure.
[0008]
The number of cells per unit area in the vertical direction in the honeycomb structure of the exhaust gas rectification structure is preferably 1 to 5 times the cell number of the exhaust gas purification catalyst. If it is at least one time, even if the exhaust gas rectified by the rectifier collides with the cell wall of the exhaust gas purifying catalyst, the exhaust gas can pass without turbulence. If the ratio is less than 1, the exhaust gas rectified by the rectifying device collides with the cell wall of the exhaust gas purifying catalyst, and turbulence is generated. If it is higher than 5 times, the pressure loss before and after the exhaust gas rectification structure increases, which is not preferable.
[0009]
It is desirable that the exhaust gas rectification structure and the exhaust gas purifying catalyst be installed so that the distance between them is as small as possible. For this purpose, it is desirable that the exhaust gas rectification structure be a honeycomb structure, and that a catalyst layer be formed downstream of the honeycomb structure to be used as an exhaust gas purification catalyst. For the honeycomb structure, a heat-resistant inorganic oxide having low conductivity such as cordierite or alumina, or a metal having excellent heat conductivity and conductivity such as stainless steel can be used. Further, the shape of the cell opening of the honeycomb structure can be any of a square, a hexagon, and a rhombus.
[0010]
The temperature range of exhaust gas discharged from a diesel engine is approximately 150 to 350 ° C., which is lower than the preferable exhaust gas purification temperature of a general exhaust gas purifying catalyst of 200 to 500 ° C.
[0011]
For this reason, it is desired that the exhaust gas be heated on the exhaust gas upstream side of the exhaust gas purifying catalyst. As a specific means, it is preferable to provide an exhaust gas heating mechanism in the exhaust gas rectification structure.
[0012]
As an exhaust gas heating method using an exhaust gas rectification structure, for example, a combustion obtained by forming an oxidation catalyst layer on the inner wall surface of a cell of the exhaust gas rectification structure and oxidizing CO, HC, and the like in the exhaust gas with O ₂ that coexists. A method of directly heating exhaust gas using heat can be applied. Further, an indirect heating method in which the exhaust gas rectification structure is directly heated and the exhaust gas is heated by using the radiant heat of the heated exhaust gas rectification structure can be applied. The oxidation catalyst coated on the surface of the exhaust gas rectification structure preferably does not burn particulates, which is a source of SOx.
[0013]
When an exhaust gas rectification structure coated with an oxidation catalyst is used, it is desirable to operate the oxidation catalyst as follows. First, the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is measured by a thermometer. If the temperature of the exhaust gas is lower than a predetermined temperature, the concentration of the reducing agent in the exhaust gas flowing into the exhaust gas rectification structure is increased, and the exhaust gas is heated by burning the reducing agent. On the other hand, if the exhaust gas temperature is higher than the predetermined temperature, the exhaust gas flowing into the exhaust gas rectification structure is made to contain no reducing agent or the amount of the reducing agent is reduced so that the oxidation catalyst does not function. I do.
[0014]
As a method of supplying the reducing agent to the exhaust gas, a method of injecting a reducing agent such as fuel or HC or CO into the exhaust gas, a method of adjusting a combustion timing in an engine cylinder, or an expansion stroke or an exhaust gas in addition to a normal fuel injection A secondary fuel injection method or the like in which fuel is injected a second time into the engine cylinder during the stroke is applicable.
[0015]
As the oxidation catalyst, a catalyst in which a noble metal such as Rh, Pt, or Pd or a transition metal such as Ni, Cu, or Co is supported on a refractory porous inorganic oxide carrier such as alumina, silica, or titania can be used.
[0016]
As an example of the exhaust gas rectification structure provided with a heating mechanism by indirect heating, a honeycomb structure having conductivity (for example, a metal honeycomb) can be considered. In the case of a honeycomb structure having conductivity, the honeycomb structure can be heated by being energized. The exhaust gas flowing through the exhaust gas rectification structure is heated by using radiant heat from the honeycomb during heating. The heating control in this case is performed, for example, as follows according to the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst. When the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is lower than a predetermined temperature (for example, 180 ° C.), the heating device is operated to heat the exhaust gas. When the amount of electricity supplied to the heating device is increased, the temperature of the exhaust gas after heating also increases. The amount of electricity is determined by estimating the required amount from the difference between the predetermined temperature and the exhaust gas temperature. When the temperature of the exhaust gas flowing into the exhaust gas purification catalyst is higher than a predetermined temperature, the power supply to the exhaust gas rectification structure is stopped.
[0017]
If the exhaust gas rectification structure is a conductive honeycomb structure and the oxidation catalyst is applied to the inner wall of the cell, direct heating and indirect heating can be performed simultaneously or arbitrarily, and the effect of suppressing the amount of electricity can be reduced. Can be expected.
[0018]
It is preferable as one embodiment of the present invention that a DPF is provided downstream of the exhaust gas purifying catalyst in the exhaust passage and the particulates are captured by the DPF. In this case, if the amount of the particulates accumulated in the DPF exceeds a certain value, the internal pressure of the exhaust passage increases, so it is desirable to burn and remove the particulates trapped in the DPF.
[0019]
An example of a method for removing and burning particulates will be described below.
[0020]
Here, the exhaust gas purifying apparatus is provided with an exhaust gas temperature measuring device, an exhaust gas temperature determining unit, and a unit for estimating the amount of particulate trapped in the DPF.
[0021]
The exhaust gas temperature measuring device measures the temperature of the exhaust gas flowing into the DPF. The exhaust gas temperature measuring device is, for example, an exhaust gas temperature sensor. The particulate capture amount estimating means estimates a particulate amount captured by the DPF. When the estimated value of the particulate amount exceeds a predetermined capture amount, DPF regeneration control is performed. The amount of trapped particulates can be estimated from the driving time and the traveling distance.
[0022]
However, if the temperature of the inflowing exhaust gas is lower than the particulate combustion temperature, the particulates are not removed by combustion. Therefore, when it is determined that the temperature measured by the exhaust gas temperature measuring device is lower than a predetermined temperature, the exhaust gas rectifying structure heats the exhaust gas to oxidize and remove the particulates captured by the DPF. The predetermined temperature is set to a temperature equal to or lower than the particulate combustion temperature.
[0023]
When the trapped particulates are burned off, the sulfates in the particulates are discharged as SOx (gas component). When this SOx is captured by the exhaust gas purifying catalyst, the exhaust gas purifying performance decreases. Therefore, from the viewpoint of SOx poisoning, it is preferable that the exhaust gas purifying catalyst be disposed upstream of the DPF in the exhaust gas channel.
[0024]
The exhaust gas purifying catalyst is preferably a catalyst having a capability of purifying NOx, HC, and CO in exhaust gas in a lean burn state. In particular, the NOx captured in the lean air-fuel ratio of the exhaust gas is stoichiometric (air-fuel ratio: 14.7) or rich: exhaust gas purifying catalyst reduces and purifies the trapped NOx to _{N 2} in the (air-fuel ratio lower than 14.7) is wider This is preferable because high NOx purification performance can be obtained in the temperature range. This exhaust gas purifying catalyst has a noble metal and a NOx trapping material.
[0025]
In the NOx trapping method, after NO is oxidized to NO ₂ on a noble metal (formula (1)),
Absorption of trapping the NOx trapping agent to NOx as nitrate compound; and (occluding formula (2)), are classified into the NOx to be chemically adsorbed to the NOx trapping agent as NO ₂ adsorption (Equation (3)). In the following, a simple description of NOx trapping includes absorption and adsorption.
[0026]
The NOx trapping material to be absorbed is described as a NOx absorbing material (for example, BaO). NOx absorbents include alkali metals and alkaline earth metals. NOx trapping mechanism by absorption becomes Equation (2) NO ₂ and BaO is produced in the reaction to Ba _(NO _{3) 2.}
[0027]
The NOx trapping material to be adsorbed is described as a NOx adsorbing material. Examples of the NOx adsorbent include (a) those described in JP-A-10-118458 composed of an alkali metal and titanium, and (b) JP-A-10-10932 composed of a composite oxide of an alkaline earth metal and titanium. There is a NOx adsorbent described in Japanese Unexamined Patent Application Publication No. 10-212933 which includes one or more elements selected from K, Na, Mg, Sr and Ca as a part of the components.
[0028]
The NOx trapping mechanism by adsorption converts NO ₂ (formula (1)) generated on a noble metal into
Equation (3) is obtained in which NO ₂ is chemically adsorbed on the NOx adsorbent surface.
[0029]
The trapped NOx is reduced to _{N 2.} For example, in the case of NOx adsorption, the adsorbed NO ₂ is reduced and purified as N ₂ by a reducing agent such as HC, CO, H ₂ in exhaust gas in stoichiometric or rich conditions (Equation (4)). A few seconds to a few minutes is sufficient for maintaining the stoichiometric or rich condition.
[0030]
In addition, since the chemical adsorption adsorbed on the surface of the NOx trapping material has a higher reduction rate of trapped NOx as compared with the absorption trapped inside the NOx trapping material, it is possible to shorten the stoichiometric or rich time. is there.
[0031]
NO + 0.5O ₂ → NO ₂ (1)
2NO ₂ + 0.5O ₂ + BaO → Ba (NO ₃ ) ₂ (2)
NO ₂ + NOx adsorbent → NO ₂ -NOx adsorbent (3)
NO ₂ -NOx adsorbent _{+ HC, CO, H 2 →} N 2 + CO 2 + H 2 O + NOx adsorption (4)
By performing lean, stoichiometric or rich control using the exhaust gas purifying catalyst, high NOx purifying performance can be obtained in a diesel engine. Since a diesel engine is basically operated in a lean operation, control and a method for temporarily making the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst stoichiometric or rich are required.
[0032]
In addition, Japanese Patent Application Laid-Open No. 2001-516635 is an example of a conventional technology that describes rectifying exhaust gas from a diesel engine.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
"Example 1"
FIG. 3 shows an example of an internal combustion engine having the exhaust gas purifying catalyst of the present invention. The automobile 100 has an engine 99, an exhaust pipe 101, an exhaust gas rectification structure 1, and an exhaust gas purification catalyst 2. The diesel engine 99 intentionally repeats lean combustion with an air-fuel ratio of 18 or more and stoichiometric or rich combustion with an air-fuel ratio of 14.7 or less.
[0034]
Exhaust gas from the diesel engine 99 flows through the exhaust pipe 101 into the exhaust gas rectification structure 1 as shown in the schematic diagram of FIG. 1 and is rectified, and then flows into the exhaust gas purification catalyst 2. The exhaust gas purification catalyst 2 purifies NOx, HC, and CO in the exhaust gas. In addition, in FIG. 1, the code | symbol 3 has shown the flow of the exhaust gas. As described above, the exhaust gas rectification structure 1 is preferably at least one time and no more than five times the number of cells of the exhaust gas purifying catalyst. The exhaust gas rectified by the structure 1 collides with the cell wall of the exhaust gas purifying catalyst 2 to generate turbulence.
[0035]
As shown in FIG. 4, a DPF 4 may be provided on the exhaust gas downstream side of the exhaust gas purifying catalyst 2. It is desirable that the DPF 4 has a function of oxidizing particulates. In this way, for example, when the temperature of the exhaust gas becomes about 250 ° C. or higher, the particulates are oxidized and removed using O ₂ in the exhaust gas, and the DPF 4 can be regenerated. The oxidizing function can be easily provided by including a catalytically active component such as a noble metal in DPF4 [Example 2]
FIG. 4 shows an exhaust gas purification apparatus provided with an exhaust gas rectification structure 1A provided with an oxidation catalyst, an exhaust gas purification catalyst 2, and a DPF 4 in the exhaust pipe 101 in order from the upstream side of exhaust gas.
[0036]
FIG. 5 shows an example of the NOx purification rate with respect to the inflow exhaust gas temperature of the exhaust gas purification catalyst 2 using Rh, Pt, Pd as the NO oxidant and Na, K, Mn and Ti as the NO ₂ adsorbent.
[0037]
The NOx purification rate was obtained as a ratio of the amount of NOx purified by the exhaust gas purification catalyst to the amount of NOx flowing into the exhaust gas purification catalyst in a lean state. The NOx purification rate was about 35% at 150 ° C, about 65% at 180 ° C, and about 85% at 200 ° C.
[0038]
FIG. 6 shows the heating performance of the exhaust gas rectification structure 1A provided with the oxidation catalyst. The exhaust gas that has flowed into the exhaust gas rectification structure 1A provided with the oxidation catalyst is heated from the temperature T1 to T2 and then flows out of the exhaust gas rectification structure. By increasing T2 by about 30 ° C. with respect to T1, the temperature range flowing into the exhaust gas purification catalyst becomes 170 ° C. or more, and the NOx purification performance is improved to 65% or more.
[0039]
"Example 3"
FIG. 7 includes an exhaust gas rectification structure 1A having an oxidation catalyst, an exhaust gas purification catalyst 2 and a DPF 4, a reducing agent supply device 9 upstream of the exhaust gas rectification structure, and exhaust gas temperature measurement devices 5 and 6. 1 shows an exhaust gas purifying apparatus.
[0040]
The amount of trapped NOx depends on the flow rate of the exhaust gas, the NOx concentration in the exhaust gas, and the exhaust gas temperature. Therefore, the NOx trapping amount estimating means built in the engine control unit (ECU) 102 estimates the integrated value of the trapped NOx amount from the engine speed, the lean operation time, the intake exhaust amount, and the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst.
[0041]
When it is determined that the integrated value of the NOx amount exceeds a predetermined amount, the exhaust gas air-fuel ratio control means built in the ECU determines the amount of the reducing agent and the reduction time necessary for the reduction and purification of the trapped NOx. Subsequently, the reducing agent supply device 9 executes the supply of the reducing agent amount and the maintenance of the reducing time based on a command from the exhaust gas air-fuel ratio control means.
[0042]
When the reduction amount estimating means of the trapped NOx incorporated in the ECU determines that the predetermined amount of the reducing agent supply time has ended, the supply of the reducing agent is stopped and the air-fuel ratio of the exhaust gas is returned to lean.
[0043]
Also in this embodiment, in order to increase the lean NOx purification rate, it is preferable that the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 2 be equal to or higher than a predetermined temperature (for example, 180 ° C.).
[0044]
FIG. 8 shows a control flow in the exhaust gas rectification structure 1A having the oxidation catalyst.
[0045]
The temperature (T) of the exhaust gas flowing into the exhaust gas purification catalyst 2 is measured by the exhaust gas temperature measuring device 5 (4001), and the temperature difference from a predetermined temperature (for example, 180 ° C.) predetermined by the exhaust gas temperature determination means in the ECU 102 is determined. (ΔT = 180−T) is calculated (4002).
[0046]
When it is determined that the temperature (T) of the exhaust gas flowing into the exhaust gas purifying catalyst is within a predetermined temperature range (for example, higher than the lowest value of 150 ° C. and lower than the maximum value of 180 ° C.), the exhaust gas rectifying structure 1A having the oxidation catalyst has Execute the heating of the exhaust gas. ΔT at which the exhaust gas rectification structure 1A having the oxidation catalyst is executed is in a range larger than 0 and lower than a predetermined value b (b: 30 ° C. when the lowest value is 150 ° C.) (4003). By setting the temperature range of exhaust gas to be purified in the diesel engine, energy can be saved and fuel efficiency can be improved.
[0047]
The exhaust gas air-fuel ratio control means is provided in advance with a map (FIG. 13) of the air-fuel ratio of the exhaust gas flowing into the exhaust gas rectification structure required to make the temperature difference (ΔT) substantially zero. The reducing agent supply device 9 supplies the reducing agent so as to have the air-fuel ratio determined from the map of the air-fuel ratio of the exhaust gas (4004).
[0048]
For example, in FIG. 9, when ΔT is calculated as ΔT1, the air-fuel ratio of the exhaust gas flowing into the exhaust gas rectification structure 1A is determined as a1. The reducing agent supply device 9 supplies the reducing agent so as to have the air-fuel ratio (a1).
[0049]
When the air-fuel ratio control means for the exhaust gas determines that the temperature difference (ΔT) is out of the control range (4003), the reducing agent supply device 9 stops the reducing agent (4005).
[0050]
It is preferable to provide an air-fuel ratio sensor between the reducing agent supply device 9 in the exhaust gas flow path and the exhaust gas rectification structure 1A, since the difference between the determined air-fuel ratio and the effective air-fuel ratio can be measured and feedback controlled.
[0051]
The control flow (FIG. 8) of the exhaust gas rectification structure 1A is also applicable to the control of the combustion removal of the particulates captured by the DPF 4.
[0052]
That is, the state in which the temperature of the exhaust gas flowing into the DPF 4 is lower than the particulate combustion temperature (for example, 250 ° C. or less) continues for a long time, and the amount of trapped particulate exceeds the predetermined amount. When it is determined, the exhaust gas is heated by the exhaust gas rectification structure 1A so that the temperature of the exhaust gas flowing into the DPF 4 becomes equal to or higher than a predetermined temperature (for example, 250 ° C.), and the particulates are burned and removed.
[0053]
"Example 4"
An embodiment in which the supply of the reducing agent to the exhaust gas is performed by adjusting the combustion timing or by performing the second fuel injection in which the fuel is injected into the engine cylinder for the second time in the expansion stroke or the exhaust stroke in addition to the normal fuel injection will be described.
[0054]
In this embodiment, the exhaust gas purifying apparatus shown in FIG. 4 has a basic configuration, and an exhaust gas temperature measuring device 5 is provided between an exhaust gas rectifying structure 1A having an oxidation catalyst and an exhaust gas purifying catalyst 2.
[0055]
FIG. 10 shows a control flow example.
[0056]
When the engine control unit (ECU) 102 determines that the exhaust gas temperature (T) flowing into the exhaust gas purifying catalyst is lower than a predetermined temperature (for example, 180 ° C.) (2002), the secondary fuel injection is started. Then, the concentration of the reducing agent in the exhaust gas is increased (2003). The reducing agent is oxidized by the oxidation catalyst of the exhaust gas rectification structure 1A, and the exhaust gas temperature rises. When it is determined that the exhaust gas temperature (T) is equal to or higher than a predetermined temperature (180 ° C.) (2002), the secondary fuel injection is stopped (2005).
[0057]
"Example 5"
FIG. 11 shows an example of an exhaust gas purifying apparatus including an exhaust gas rectifying structure 1B including a honeycomb structure having heat conductivity and conductivity and having a heating device. In the exhaust gas flow path, an exhaust gas rectification structure 1B, an exhaust gas temperature measurement device 5, an exhaust gas purification catalyst 2, and a DPF 4 are installed in this order from the upstream of the flow of exhaust gas. The temperature (T) of the exhaust gas flowing into the exhaust gas purifying catalyst 2 is measured by the exhaust gas temperature measuring device 5 and transmitted to the ECU 102. The ECU 102 controls the heating device of the exhaust gas rectification structure 1B according to the measured temperature (T).
[0058]
FIG. 12 is an example of a flow. When the ECU 102 determines that the temperature (T) of the exhaust gas flowing into the exhaust gas purifying catalyst is lower than a predetermined temperature (for example, 180 ° C.) (3002), the heating of the heating device of the exhaust gas rectification structure 1B is started. Then, the heating of the exhaust gas is started (3003). When it is determined that the exhaust gas temperature (T) is equal to or higher than the predetermined temperature (180 ° C.) (3002), the heating of the exhaust gas is stopped by stopping the power supply to the exhaust gas rectification structure (3004).
[0059]
FIG. 13 is an example in which the judgment standard of the exhaust gas temperature is changed in the flow of FIG. When it is determined that the temperature (T) of the exhaust gas flowing into the exhaust gas purification catalyst is within a predetermined temperature range (for example, higher than 150 ° C. and lower than 180 ° C.) (3006), the heating device of the exhaust gas rectification structure 1B is energized. By starting, the heating of the exhaust gas is started (3003). When it is determined that the exhaust gas temperature (T) is out of the predetermined temperature range (150 ° C. or lower or 180 ° C. or higher) (3002), the heating of the exhaust gas is stopped by stopping the power supply to the exhaust gas rectification structure. (3004). By setting the temperature range of exhaust gas to be purified in a diesel engine, energy can be saved and fuel efficiency can be improved.
[0060]
"Example 6"
In the configuration of the exhaust gas purifying device shown in FIG. 11, an exhaust gas temperature measuring device 6 is provided between the exhaust gas purifying catalyst 2 and the DPF 4 as shown in FIG. 7 to perform particulate capture and regeneration control of the DPF 4. explain.
[0061]
The ECU 102 has a logic for controlling which of the heating of the exhaust gas required for the exhaust gas purifying catalyst 2 and the heating of the exhaust gas required for regeneration of the DPF 4 is performed by the exhaust gas rectification structure 1B. Further, a logic is provided for stopping the heating of the exhaust gas rectification structure 1B when the exhaust gas temperature is higher than a predetermined temperature.
[0062]
Information such as the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst 2, the temperature of the exhaust gas flowing into the DPF 4, the intake air amount of the engine, the engine speed, and the air-fuel ratio is transmitted to the EUC 102. Based on the information, the determinations from the respective control means in the ECU 102 are comprehensively determined, and each device determines whether to operate or stop the heating device of the exhaust gas rectification device, and to determine whether the air-fuel ratio is lean, stoichiometric or rich. To order.
[0063]
If the means for estimating the amount of trapped particulates in the DPF 4 determines that the temperature of the exhaust gas flowing into the DPF 4 is lower than the particulate combustion temperature (for example, 250 ° C. or less) for a long time, and the amount of trapped particulates exceeds a predetermined amount. Then, the heating device of the exhaust gas rectification device 1B is operated. The temperature of the exhaust gas flowing into the DPF is forcibly maintained at a predetermined temperature (for example, 250 ° C.) or higher for a certain period of time, so that the particulates captured by the DPF 4 are burned and removed. As a result, the DPF 4 is regenerated. When the means for estimating the amount of particulates trapped in the DPF 4 determines that the regeneration of the DPF has been completed, the heating device of the exhaust gas rectification structure 1B is stopped.
[0064]
As for the exhaust gas purifying catalyst 2, when the NOx trapping amount estimating means judges that the NOx trapping amount exceeds a predetermined amount, the air-fuel ratio control means of the exhaust gas sets the air-fuel ratio flowing into the exhaust gas purifying catalyst to stoichiometric or rich, A predetermined stoichiometric or rich time is maintained according to the temperature. In the trapped NOx reduction amount estimating means, when the trapped NOx reduction amount estimating means determines that the reduction and purification of the trapped NOx has been completed, the exhaust gas air-fuel ratio control means returns to the normal lean air-fuel ratio again.
[0065]
Also, in order to increase the NOx purification rate in lean, stoichiometric, or rich conditions, it is preferable in this embodiment that the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 2 is set to a predetermined temperature (for example, 180 ° C.) or higher. In this case, the temperature (T) of the exhaust gas flowing into the exhaust gas purifying catalyst 2 is measured by the exhaust gas temperature measuring device 5, and the
A temperature difference (ΔT = 180−T) that is insufficient at a predetermined temperature (for example, 180 ° C.) predetermined by an exhaust gas temperature determination unit in 102 is calculated. The heating device of the exhaust gas rectification structure 1B is operated so that the temperature difference (ΔT) becomes substantially zero.
[0066]
Regarding the operating conditions (heating temperature and time) of the heating device of the exhaust gas rectification device 1B, in the DPF 4 and the exhaust gas purifying catalyst 2, the higher the heating temperature and the longer the heating time are prioritized.
[0067]
【The invention's effect】
According to the exhaust gas purifying apparatus and the exhaust gas purifying method of the present invention, it is possible to suppress the attachment of particulates to the exhaust gas purifying catalyst without providing a DPF upstream of the exhaust gas purifying catalyst.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a flow of exhaust gas by an exhaust gas purifying apparatus according to the present invention.
FIG. 2 is a schematic diagram showing the flow of exhaust gas when an inappropriate exhaust gas rectification structure is used.
FIG. 3 is a schematic diagram of an internal combustion engine including the exhaust gas purifying apparatus of the present invention.
FIG. 4 is a schematic diagram showing another embodiment of the internal combustion engine provided with the exhaust gas purifying apparatus of the present invention.
FIG. 5
FIG. 4 is a relationship diagram between the temperature of exhaust gas flowing into the exhaust gas purification catalyst and the NOx purification rate.
FIG. 6 is a graph showing the relationship between the temperature of an exhaust gas flowing into an exhaust gas rectifier having an oxidation catalyst and the temperature of an exhaust gas flowing out of the device.
FIG. 7 is a schematic diagram showing another embodiment of the internal combustion engine provided with the exhaust gas purifying apparatus of the present invention.
FIG. 8 is a control flowchart of the internal combustion engine shown in FIG. 7;
FIG. 9 is a diagram showing an air-fuel ratio of exhaust gas flowing into an exhaust gas rectification structure.
FIG. 10 is a control flow chart when performing secondary fuel injection.
FIG. 11 is a schematic view showing another embodiment of the internal combustion engine provided with the exhaust gas purifying apparatus of the present invention.
FIG. 12 is a control flowchart of the exhaust gas purifying apparatus.
FIG. 13 is another control flow chart of the exhaust gas purifying apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Exhaust gas rectification structure, 2 ... Exhaust gas purification catalyst, 3 ... Exhaust gas flow, 4 ... DPF, 5, 6 ... Exhaust gas temperature measurement device, 8 ... Oxidation catalyst, 9 ... Reducing agent supply device, 99 ... Engine, 100 ... Automobile Reference numeral 101 denotes an exhaust pipe, 102 denotes an engine control unit (ECU).

Claims

In an exhaust gas purifying apparatus provided with an exhaust gas purifying catalyst in an exhaust flow path of a diesel engine, an exhaust gas rectifying structure is provided on an exhaust gas upstream side of the exhaust gas purifying catalyst to divide the exhaust gas into a plurality of parts with respect to a horizontal axis of the exhaust flow path. An exhaust gas purifying apparatus for a diesel engine, comprising:

In an exhaust gas purifying apparatus provided with an exhaust gas purifying catalyst in an exhaust flow path of a diesel engine, an exhaust gas rectifying structure and an exhaust gas rectifying structure that diverge exhaust gas into a plurality of parts with respect to a horizontal axis of the exhaust flow path upstream of the exhaust gas purifying catalyst. An exhaust gas purifying apparatus for a diesel engine, comprising a superheating means for heating exhaust gas flowing into a purification catalyst.

In claim 1, both the exhaust gas purifying catalyst and the exhaust gas rectifying structure are honeycomb structures, and the number of cells per unit area in the vertical direction in the exhaust gas rectifying structure is relative to the number of cells of the exhaust gas purifying catalyst. Exhaust gas purifying device for a diesel engine, wherein the exhaust gas purifying device is at least 1 to 5 times.

2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the exhaust gas rectifying structure is a honeycomb structure, and a downstream part of the honeycomb structure is coated with a catalyst to form an exhaust gas purifying catalyst.

2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein an oxidation catalyst layer for oxidizing carbon monoxide and hydrocarbons in the exhaust gas is provided on a cell inner wall of the exhaust gas rectification structure.

The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the exhaust gas rectification structure is a honeycomb structure having heat conductivity and conductivity, and heating means for heating the honeycomb structure is provided.

2. The exhaust gas purifying catalyst according to claim 1, wherein the temperature of the exhaust gas flowing into the exhaust gas purification catalyst is measured, and when the temperature is lower than a predetermined temperature, the concentration of the reducing agent in the exhaust gas flowing into the exhaust gas rectification structure is increased. An exhaust gas purifying apparatus for a diesel engine, comprising a control means for heating the exhaust gas.

2. The exhaust gas purifying catalyst according to claim 1, wherein the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst is measured, and when the temperature is higher than a predetermined temperature, the concentration of the reducing agent in the exhaust gas flowing into the exhaust gas rectification structure is reduced. An exhaust gas purifying apparatus for a diesel engine, comprising: a control unit for stopping heating of exhaust gas by the engine.

In claim 1, a reducing agent supply device is provided upstream of the exhaust gas rectification structure, and the temperature of the exhaust gas flowing into the exhaust gas purification catalyst is measured. When the exhaust gas temperature is lower than a predetermined temperature, the exhaust gas is brought to a predetermined temperature. An exhaust gas purifying apparatus for a diesel engine, comprising: control means for estimating an amount of a reducing agent necessary for increasing the amount, and supplying the estimated amount to the exhaust gas from the reducing agent supply device.

10. The exhaust gas purification system for a diesel engine according to claim 9, further comprising a control unit for measuring a temperature of the exhaust gas flowing into the exhaust gas purification catalyst and stopping the supply of the reducing agent when the exhaust gas temperature is higher than a predetermined temperature. apparatus.

In claim 1, the temperature of the exhaust gas flowing into the exhaust gas purification catalyst is measured, and when the temperature of the exhaust gas is lower than a predetermined temperature, the combustion timing is adjusted or the fuel is injected into the engine cylinder in the expansion stroke or the exhaust stroke in addition to the normal fuel injection. By the second fuel injection for injecting the second fuel, a reducing agent necessary for increasing the temperature of the exhaust gas is supplied into the exhaust gas. When the exhaust gas temperature is higher than a predetermined temperature, the combustion timing is adjusted or the normal operation is performed. An exhaust gas purifying apparatus for a diesel engine, comprising: control means for stopping a secondary fuel injection for injecting a second fuel into an engine cylinder in an expansion stroke or an exhaust stroke in addition to fuel injection.

2. A method according to claim 1, further comprising the step of: providing a reducing agent supply device upstream of the exhaust gas rectifying structure, measuring the temperature of the exhaust gas flowing into the exhaust gas purifying catalyst, determining an amount necessary for raising the exhaust gas temperature to a predetermined temperature, An exhaust gas purifying apparatus for a diesel engine, comprising: control means for supplying a reduced amount of a reducing agent.

7. The diesel engine according to claim 6, wherein the exhaust gas rectifying structure is a conductive honeycomb, and further has a structure capable of heating the honeycomb by applying a current to the honeycomb, wherein the exhaust gas is heated using radiant heat at the time of heating. Exhaust gas purification equipment for engines.

14. The exhaust gas purifying apparatus for a diesel engine according to claim 13, wherein a temperature flowing into the exhaust gas purifying catalyst is measured, and when the temperature is lower than a predetermined temperature, heating of the exhaust gas rectifying structure is started.

15. The exhaust gas purifying apparatus for a diesel engine according to claim 14, wherein a temperature flowing into the exhaust gas purifying catalyst is measured, and when the temperature is higher than a predetermined temperature, heating of the exhaust gas rectifying structure is stopped.

2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, further comprising a particulate filter capable of capturing diesel particulates downstream of the exhaust gas purifying catalyst.

2. The exhaust gas purifying catalyst according to claim 1, further comprising a reducing agent supply device for supplying a reducing agent such as CO or HC upstream of the exhaust gas purifying catalyst, wherein the exhaust gas flowing into the exhaust gas purifying catalyst emits NOx in the exhaust gas in an oxidizing atmosphere. An exhaust gas purifying catalyst that captures the exhaust gas in a reducing atmosphere and reduces the trapped NOx to N ₂ in a reducing atmosphere. The exhaust gas purifying catalyst has a control of switching between an oxidizing atmosphere and a reducing atmosphere according to a vehicle speed, a time or a traveling distance of the oxidizing atmosphere. An exhaust gas purifying apparatus for a diesel engine, comprising:

In a method of purifying exhaust gas by an exhaust gas purifying catalyst installed in an exhaust flow path of a diesel engine, exhaust gas flowing into the exhaust gas purifying catalyst is divided into a plurality of flow streams in advance with respect to a horizontal axis of the exhaust flow path and rectified. Purification method for diesel engine exhaust.

19. The method for purifying exhaust gas of a diesel engine according to claim 18, wherein the exhaust gas flowing out of the exhaust gas purifying catalyst flows into a diesel particulate filter to remove particulates in the exhaust gas.

19. The method according to claim 18, wherein the temperature of the exhaust gas flowing into the diesel particulate filter is measured, and the amount of the particulate captured by the diesel particulate filter is estimated. If it is determined that the exhaust gas measurement temperature when exceeding the trapped amount of the exhaust gas is lower than a predetermined temperature, the exhaust gas is cooled to a temperature at which particulates are oxidized before flowing into the diesel particulate filter. A method for purifying exhaust gas of a diesel engine, comprising heating to oxidize and remove the particulates captured by the diesel particulate filter.