JP4103525B2

JP4103525B2 - Exhaust gas purification device for internal combustion engine

Info

Publication number: JP4103525B2
Application number: JP2002289454A
Authority: JP
Inventors: 健治加藤
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2002-10-02
Filing date: 2002-10-02
Publication date: 2008-06-18
Anticipated expiration: 2022-10-02
Also published as: JP2004124799A

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の排気ガスを三元触媒やＮＯｘ吸蔵還元触媒を利用して浄化する排気浄化装置に関する。
【０００２】
【従来の技術】
内燃機関から排出されるＨＣ、ＣＯ、ＮＯｘ（窒素酸化物）の浄化には従来から三元触媒が多用されているが、空燃比を意図的に希薄域（リーン域）に制御する、いわゆるリーンバーンエンジンの普及によりＮＯｘ吸蔵還元触媒も多用されている。ＮＯｘ吸蔵還元触媒は、空燃比がリーン域に制御されている間はＮＯｘを吸蔵し、空燃比が一時的にリッチに制御されたとき、それまで吸蔵していたＮＯｘを還元し、その還元によって得られた酸素でＨＣやＣＯを酸化するものである。そして、内燃機関の始動時に触媒が活性化されてその浄化性能を発揮するまでの対策として、内燃機関の排気通路の上流側に始動時触媒として熱容量が小さい三元触媒を設置し、その下流側にＮＯｘ吸蔵還元触媒を設置した排気浄化装置が提案されている（例えば特許文献１参照）。
【０００３】
また、酸化チタン触媒の上流側に過酸化水素水を噴霧することにより、ＯＨラジカルを生じさせてＮＯｘを除去する技術も提案されている（特開平１０−２６６８３１号公報参照）。さらに、水に対して２００ｋＨｚ付近の超音波を照射して過酸化水素を生成する技術も提案されている（非特許文献１参照）。その他に、本願に関連する従来技術として特許文献２〜４がある。
【０００４】
【特許文献１】
特開平１１−６２５６３号公報
【特許文献２】
特開平９−２８００３５
【特許文献３】
特開平１０−２６６８３１号公報
【特許文献４】
特開平９−２９０１３６号公報
【非特許文献１】
２００１年９月７日付日刊工業新聞
【０００５】
【発明が解決しようとする課題】
ところで、内燃機関において空燃比がリーン域に制御されている場合、始動時触媒ではＨＣやＣＯを十分に浄化できないことがある。そして、ＮＯｘ吸蔵還元触媒の表面近傍に過剰なＨＣが残留するいわゆるＨＣ被毒が生じ、それにより、ＮＯｘ吸蔵還元触媒におけるＮＯ（一酸化窒素）からＮＯ_２（二酸化窒素）への酸化反応が妨害されてＮＯｘの吸蔵能力が低下することがある。
【０００６】
そこで、本発明は、三元触媒及びＮＯｘ吸蔵還元触媒における浄化性能を向上させることが可能な内燃機関の排気浄化装置を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の第１の排気浄化装置は、排気通路に設けられた三元触媒と、前記三元触媒の上流に過酸化水素を存在させる手段とを備え、前記過酸化水素を存在させる手段は、前記排気通路内に超音波を照射して過酸化水素を生成する超音波照射手段を備えることにより、上述した課題を解決する（請求項１）。また、第２の排気浄化装置は、排気通路に設けられたＮＯｘ吸蔵還元触媒と、前記ＮＯｘ吸蔵還元触媒の上流に過酸化水素を存在させる手段とを備え、前記過酸化水素を存在させる手段は、前記排気通路内に超音波を照射して過酸化水素を生成する超音波照射手段を備えることにより、上述した課題を解決する（請求項２）。さらに、第２の排気浄化装置においては、前記ＮＯｘ吸蔵還元触媒の上流に三元触媒が配置され、前記過酸化水素を存在させる手段は、前記三元触媒のさらに上流に過酸化水素を存在させてもよい（請求項３）。また、第３の排気浄化装置は、空燃比を一時的にリッチ側に設定するリッチスパイクが実行されているときは前記ＮＯｘ吸蔵還元触媒の上流側に過酸化水素を存在させないように前記過酸化水素の存在状態を制御する制御手段とを備えることにより、上述した課題を解決する（請求項５）また、第４の排気浄化装置は、排気通路に設けられたＮＯｘ吸蔵還元触媒と、前記ＮＯｘ吸蔵還元触媒の上流に過酸化水素を存在させる手段と、前記ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力の現状を特定し、その特定結果に基づいて前記過酸化水素の存在状態を制御する制御手段とを備えることにより、上述した課題を解決する（請求項６）。また、第５の排気浄化装置は、排気通路に設けられたＮＯｘ吸蔵還元触媒と、前記ＮＯｘ吸蔵還元触媒の上流に過酸化水素を存在させる手段と、前記ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力の将来の低下を予測し、その予測結果に基づいて前記過酸化水素の存在状態を制御する制御手段とを備えることにより、上述した課題を解決する（請求項７）。さらに、第３〜第５の排気浄化装置においては、前記ＮＯｘ吸蔵還元触媒の上流に三元触媒が配置され、前記過酸化水素を存在させる手段は、前記三元触媒のさらに上流に過酸化水素を存在させてもよい（請求項８）。
【０００８】
これらの排気浄化装置によれば、触媒の上流に存在する過酸化水素の酸化作用により、三元触媒やＮＯｘ吸蔵還元触媒におけるＨＣやＣＯの酸化反応が促進されてこれらの浄化性能が向上する。また、特にＮＯｘ吸蔵還元触媒が設けられている場合には、過酸化水素の酸化作用によってＨＣ被毒が解消され、ＮＯからＮＯ_２への酸化反応が促進されてＮＯｘの吸蔵能力が向上する。特に高温域ではＮＯからＮＯ_２への酸化反応がＮＯｘの吸蔵速度を支配する律速工程となるため、その酸化反応を過酸化水素によって促進すればＮＯｘ吸蔵還元触媒における単位時間当たりのＮＯｘ吸蔵量が増加し、その結果、ＮＯｘ吸蔵還元触媒にて吸蔵されることなく下流側に排出されるＮＯｘ量が減少してＮＯｘの浄化性能が向上する。
【０００９】
第１又は第２の排気浄化装置においては、過酸化水素を存在させる手段が排気通路内に超音波を照射して過酸化水素を生成する超音波照射手段を備えているので、排気に含まれる水分を過酸化水素に変えて上述した酸化作用によるＨＣ、ＣＯの浄化と、ＮＯｘ吸蔵還元触媒におけるＨＣ被毒の解消とを図ることができる。排気中の水分を利用して過酸化水素を得るようにしたので、過酸化水素用のタンクを設けてそこに過酸化水素を蓄えておく必要をなくすことができる。また、仮に過酸化水素のタンクを設けるにしても、そのタンクに必要な容量を減少させることができ、かつ過酸化水素を補充する頻度も減らすことができる。
【００１０】
第１又は第２の排気浄化装置においては、超音波照射手段による超音波照射位置又はその上流側にて排気通路に水分を供給する水分供給手段を備えてもよい（請求項４）。この場合には、排気に含まれている水分では十分な過酸化水素を生成することができないときに、水分を追加して必要な量の過酸化水素を生成することができる。
【００１１】
なお、第３〜第５の排気浄化装置において、過酸化水素の存在は、排気通路内において過酸化水素を生成する場合と、排気通路外から排気通路内に過酸化水素を供給する場合のいずれの態様も含むものである。
【００１４】
リッチスパイク時に過酸化水素が存在すると、その過酸化水素の酸化作用によってＮＯからＮＯ２への酸化反応が促進され、ＮＯｘ吸蔵還元触媒におけるＮＯ２の還元が邪魔されてリッチスパイクによるＮＯｘ吸蔵能力の回復が妨げられるおそれがある。第３の排気浄化装置は、空燃比を一時的にリッチ側に設定するリッチスパイクが実行されているときはＮＯｘ吸蔵還元触媒の上流側に過酸化水素を存在させないように過酸化水素の存在状態を制御する制御手段を備えているので、リッチスパイクによるＮＯｘ吸蔵能力の回復効果を確実に発揮させることができる。
【００１５】
第４の排気浄化装置は、ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力の現状を特定し、その特定結果に基づいて過酸化水素の存在状態を制御する制御手段を備えており、第５の排気浄化装置は、ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力の将来の低下を予測し、その予測結果に基づいて過酸化水素の存在状態を制御する制御手段を備えている。そのため、ＨＣ被毒等によってＮＯｘ吸蔵能力が現実に低下し、あるいは将来の低下が予測されるときに過酸化水素によってＨＣを削減し、ＮＯｘ吸蔵能力の回復やその低下の予防を図ることができる。
【００１６】
なお、本発明において、「吸蔵」の語はＮＯｘを最終的にどのような形態で保持するかに拘わりなく、広くＮＯｘ又はこれに基づく生成物を保持するすべての態様を含む意味に解されるべきであり、例えば吸着や吸収の概念もその範疇に含まれる。例えば、ＮＯをＮＯ_２→ＮＯ_３ ⁻の順に変化させて触媒の表面又は内部に保持する場合も、ＮＯをＮＯ_２に変化させた状態で触媒の表面又は内部に保持する場合も本発明の吸蔵の概念に含まれる。
【００１７】
【発明の実施の形態】
図１は本発明の排気浄化装置及びこれが適用される内燃機関の概要を示している。内燃機関１は車両に搭載される４サイクル火花点火式のガソリンエンジンとして構成されている。周知のように、内燃機関１には、燃焼室２に空気を取り込むための吸気通路３と、吸入空気量を制御するためのスロットルバルブ４と、燃焼室２からの排気を所定の排気位置まで導くための排気通路５と、これらの通路３，５を開閉するための吸気バルブ６及び排気バルブ７と、燃料タンク８に蓄えられたガソリン燃料を燃焼室２に直接噴射する燃料噴射弁９と、燃料混合気に着火する点火プラグ１０とが設けられている。
【００１８】
内燃機関１が搭載された車両には、エンジンコントロールユニット（ＥＣＵ）１１が設けられる。ＥＣＵ１１は、マイクロプロセッサ及びその動作に必要なＲＡＭ、ＲＯＭ等の周辺装置を含んだ周知のコンピュータである。ＥＣＵ１１は、そのＲＯＭに記録された各種のプログラム及びデータに基づいて内燃機関１の各種の制御を実行する。例えば、ＥＣＵ１１は、吸気量を検出するエアフロメータ、冷却水温を検出する水温センサ、スロットルバルブ４の開度を検出するスロットルセンサ、空燃比に対応した信号を出力する空燃比センサ等（いずれも図示を省略した。）の出力に基づいて内燃機関１の運転状態や車両の走行状態を検出し、その検出結果に基づいて燃料噴射弁９の燃料噴射時期及び噴射量を制御する。この燃料噴射弁９からの燃料噴射量の制御により、燃焼室２における空燃比が、理論空燃比と、理論空燃比よりも燃料が少ないリーン域と、理論空燃比よりも燃料が多いリッチ域との間で適宜に切替制御される。一般に、燃料噴射弁９から燃焼室２内に燃料を直接噴射する内燃機関１においては、低負荷低回転時に燃料を圧縮行程で噴射して成層燃焼を実現し、高負荷高回転時には吸気行程で燃料を噴射して均質燃焼を実現している。成層燃焼では燃焼室全体からみて空燃比がリーン域に制御される。このようなＥＣＵ１１による空燃比制御は周知の内燃機関と同様でよく、ここでは詳細を省略する。
【００１９】
内燃機関１には排気浄化装置２０が取り付けられている。排気浄化装置２０は、排気通路５に設けられた第１触媒２１と、その下流側に設けられた第２触媒２２とを備えている。第１触媒２１は、内燃機関１の冷間始動時に第２触媒２２が活性化されるまでの有害物質の排出量を低減することを主たる目的として設けられた、いわゆるスタート触媒である。第１触媒２１は早期活性化のために内燃機関１の排気ポートになるべく近付けて配置され、かつその熱容量は第２触媒２２のそれよりも十分に小さく設定される。第１触媒２１には三元触媒が使用される。三元触媒は、排気ガスに含まれるＮＯｘを還元させる一方で、ＨＣ、ＣＯを酸化させてこれらを浄化する周知の排気ガス浄化用の触媒である。
【００２０】
一方、第２触媒２２にはＮＯｘ吸蔵還元触媒が使用される。ＮＯｘ吸蔵還元触媒は、空燃比がリーン域に制御されているときは図２（ａ）に示すようにＮＯｘと白金Ｐｔの表面のＯ^２−又はＯ_２ ⁻とを反応させてＮＯ_２を生成し、これをさらに酸化しつつ吸蔵材の内部にＮＯ_３ ⁻の形で吸蔵して拡散させ、その一方、空燃比がリッチに制御された場合には、図２（ｂ）に示すように吸蔵材からＮＯ_２を放出し、そのＮＯ_２を排気中のＨＣ、ＣＯにて還元してＮ_２へと変化させるとともに、ＨＣ、ＣＯを酸化させる。
【００２１】
図３に示すように、内燃機関１の空燃比（Ａ／Ｆ）が連続的にリーン域に制御されると、ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵量が増加してそのＮＯｘ浄化性能が徐々に低下し、やがては浄化性能が限界に達する。そこで、ＥＣＵ１１は排気通路５から放出される排気ガスの状態を例えば排気通路５の第２触媒２２よりも下流側に設けたＮＯｘセンサ１３やＨＣセンサ１４等の出力に基づいて監視し、ＮＯｘの浄化性能が一定の限界を超えて劣化した場合には、空燃比を意図的にリッチ域に制御してＮＯｘの放出を促し、これによりＮＯｘ浄化性能の回復を図っている。このような処理は、いわゆるリッチスパイクとして知られている。
【００２２】
リッチスパイクが適切に行われた場合にはＮＯｘ吸蔵量がほぼ０まで低減し、ＮＯｘ吸蔵還元触媒のＮＯｘ浄化性能はほぼ初期状態まで回復する。しかしながら、ＮＯｘ吸蔵還元触媒の表面近傍に過剰なＨＣが残留する、いわゆるＨＣ被毒が進行すると、ＮＯｘ吸蔵還元触媒の表面におけるＮＯｘからＮＯ_２への酸化反応が阻止され、その結果、図３に破線で示すようにリッチスパイクを行ってもＮＯｘ浄化性能が初期状態まで戻らず、その後の浄化性能も劣化することがある。図１の第１触媒２１の容量を増加させて、第２触媒（ＮＯｘ吸蔵還元触媒）２２に導かれるＨＣの量を削減すればＨＣ被毒は軽減されるが、第１触媒２１は早期に活性化させる必要があってその容量には制限がある。
【００２３】
以上のような事情を考慮して、図１の排気浄化装置２０は、第１触媒２１よりも上流側にて排気通路５内に水分を供給する水分供給機構２３と、第１触媒２１よりも上流側にて排気通路５内に超音波を照射する超音波照射機構３０とをさらに備えている。水分供給機構２３は、水タンク２４からポンプ２５で汲み上げた水を切替弁２６の開放によってノズル２７に供給し、そのノズル２７から排気通路５内に水分を噴射する。なお、切替弁２６の閉鎖によりノズル２７への水の供給は停止される。
【００２４】
超音波照射機構３０は、排気通路５に向かって超音波を照射する照射器３１と、ＥＣＵ１１からの指示に従って超音波発信用の所定周波数の駆動電流を照射器３１に供給する駆動回路３２とを備えている。照射器３１から照射される超音波の周波数は、排気中の水分を過酸化水素に変換するのに適した周波数域である２００ｋＨｚ前後に設定される。照射器３１は水分供給機構２３のノズル２７よりも排気通路５の下流側に設置される。換言すれば、水分供給機構２３のノズル２７は、超音波照射機構３０による超音波の照射位置又はその上流側の位置にて排気に水分を供給するように設けられている。
【００２５】
以上の構成によれば、水分供給機構２３から排気通路５に水分を供給しつつ超音波照射機構３０の照射器３１から排気通路５に超音波を照射することにより、排気に含まれている水分を過酸化水素に変換することができる。変換された過酸化水素は強い酸化作用を持っているため、第１触媒（三元触媒）２１及び第２触媒（ＮＯｘ吸蔵還元触媒）２２におけるＨＣ、ＣＯの酸化反応が促進されてそれらの浄化性能が向上する。また、第２触媒２２においては、過酸化水素の存在によりＮＯからＮＯ_２への酸化反応が促進されてＮＯｘの浄化能力が高まる。さらに、第１触媒２１及び第２触媒２２におけるＨＣの浄化性能が向上すること、及び第２触媒２２におけるＨＣの酸化が促進されることの相乗効果により、ＮＯｘ吸蔵還元触媒のＨＣ被毒も軽減される。
【００２６】
水分供給機構２３及び超音波照射機構３０を利用した過酸化水素の生成は、その必要性に応じて適宜に行ってよいが、その好適な制御例を図４により説明する。
【００２７】
図４はＥＣＵ１１が一定周期で繰り返し実行する過酸化水素供給制御ルーチンを示している。この図４のルーチンを実行することにより、ＥＣＵ１１は排気浄化装置２０の制御手段として機能する。
【００２８】
図４の過酸化水素供給制御ルーチンにおいて、ＥＣＵ１１はステップＳ１で空燃比制御条件を読み込む。空燃比制御条件は、内燃機関１の空燃比をその運転状態等に応じて適宜に制御するためにＥＣＵ１１が設定するものである。続くステップＳ２では、読み込んだ空燃比制御条件からリッチスパイク処理の実行中か否かを判断する。リッチスパイク中であればステップＳ１２へ進み、水分及び超音波の供給をそれぞれ中止して今回のルーチンを終える。リッチスパイク中に過酸化水素が存在すると、ＮＯｘ吸蔵還元触媒にてＮＯからＮＯ_２の酸化反応が生じてＮＯｘの放出作用が損なわれるおそれがあるためである。
【００２９】
ステップＳ２でリッチスパイク処理の実行中でないときはステップＳ３に進み、ＥＣＵ１１は第２触媒（ＮＯｘ吸蔵還元触媒）２２の近傍に設置された触媒温度センサ１６（図１参照）から触媒温度を読み込み、続くステップＳ４で触媒２２の温度が所定の活性化温度以上か否か（つまり、触媒２２が所定レベルまで暖機されているか否か）を判断する。そして、触媒温度が活性化温度未満のときはステップＳ１２へ進んで過酸化水素の供給を中止する。触媒２２の活性前に過酸化水素によってＨＣ、ＣＯが酸化されると、これらの未燃物の二次燃焼による触媒の暖機の促進効果が損なわれるからである。
【００３０】
ステップＳ４で触媒２２の温度が活性化温度以上であるときはステップＳ５へ進み、排気通路５に設置された排気温センサ１５（図１参照）から排気温度を読み込む。続くステップＳ６では、排気温度が所定の分解温度以上か否かを判断する。分解温度以上であればステップＳ１２へ進んで過酸化水素の供給を中止する。分解温度は過酸化水素が熱によって分解される温度として設定されている。排気温度が分解以上のときに過酸化水素を形成しないのは、排気温度が分解温度以上の状態で過酸化水素を供給しても直ぐに分解され、所定の浄化性能向上効果が得られないためである。
【００３１】
排気温度が分解温度以上でないときはステップＳ７へ進み、ＮＯｘセンサ１３の出力を読み込む。続くステップＳ８では、ＮＯｘセンサ１３の出力を参照して、第２触媒２２を通過するＮＯｘ量が所定量以上か否かを判断する。所定量はＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力が所定レベル未満に低下したときにその下流で検出されるＮＯｘ量に定められる。そして、ＮＯｘ排出量が所定量以上のときはステップＳ１１へ進み、水分供給機構２３による水分の供給と、超音波照射機構３０による超音波の照射とを実行させて過酸化水素を生成させる。これにより、ＨＣ被毒によりＮＯｘ吸蔵還元触媒の吸蔵能力が衰えてＮＯｘ排出量が所定の限度を超えて増加したときに過酸化水素を供給してＨＣ被毒を解消し、ＮＯｘの浄化性能を回復させることができる。つまり、ステップＳ８の判断を設けることにより、ＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力に応じて過酸化水素の供給状態を制御することができる。なお、ＮＯｘの吸蔵は空燃比がリーン域に制御されているときに行われるので、ステップＳ８が肯定される条件として、空燃比がリーン域に制御されていることを追加してもよい。
【００３２】
さらに、ステップＳ８で第２触媒２２を通過するＮＯｘ量が所定量未満であったときにはステップＳ９に進み、ＨＣセンサ１４の出力を読み込む。続くステップＳ１０では、ＨＣセンサ１４の出力を参照して、第２触媒２２を通過するＨＣの量が所定量以上か否かを判断する。所定量は、ＮＯｘ吸蔵還元触媒のＨＣ被毒が懸念されるときのＨＣ排出量に設定される。そして、ＨＣ排出量が所定量未満のときはステップＳ１２へ進み、ＨＣ排出量が所定量以上のときはステップＳ１１へ進む。これにより、ＨＣ被毒によるＮＯｘ吸蔵還元触媒のＮＯｘ吸蔵能力の低下が予想される程にＨＣが排出されているときに過酸化水素を供給し、その酸化作用によって触媒２１，２２のＨＣの浄化能力を向上させ、かつＮＯｘ吸蔵還元触媒におけるＨＣ被毒の進行を阻止することができる。以上のようにしてステップＳ１１又はステップＳ１２で過酸化水素の供給を制御して一回のルーチンを終える。
【００３３】
本発明は以上の実施形態に限定されず、種々の形態にて実施してよい。例えば、上記の実施形態では第２触媒２２の下流に配置したＮＯｘセンサ１３及びＨＣセンサ１４の出力を参照してＮＯｘ吸蔵能力の現実の低下や将来の低下の可能性を判別したが、空燃比センサ、Ｏ_２（酸素）センサ、ＣＯセンサ等の排気状態を検出するために使用される各種のセンサを利用してＮＯｘ吸蔵能力の現状や将来の低下を判別してもよい。また、これらのセンサは第２触媒２２の下流側に限らず、第２触媒２２の前後に配置してもよい。さらに、ＮＯｘ吸蔵還元触媒におけるＮＯｘ吸蔵能力の低下が、リッチスパイクの実行回数や実行時間、あるいはリーン運転の継続時間等の内燃機関１の運転制御状態に基づいて特定可能な場合には、これらの運転制御の履歴からＮＯｘ吸蔵能力の現状の特定や将来の低下の予測を行ってもよい。
【００３４】
上記の実施形態では、水分供給機構２３と超音波照射機構３０との組み合わせによって過酸化水素を存在させる手段が構成される。但し、水分供給機構２３については、排気に含まれる水分により十分な過酸化水素が得られる場合にはこれを省略してもよい。本発明は、超音波を利用して排気通路内で過酸化水素を生成する例に限らず、予め排気通路外のタンクに備蓄された過酸化水素をポンプで吸い上げて排気通路内に噴霧する等、排気通路外から過酸化水素を供給する構成もその範囲に含むものである。
【００３５】
本発明は三元触媒とＮＯｘ吸蔵還元触媒とを組み合わせた排気浄化装置に限らず、いずれか一方の触媒のみを利用した排気浄化装置にも適用可能である。本発明は燃料を燃焼室内に直接噴射する内燃機関に限らず、吸気ポートに燃料を噴射する形式の内燃機関にも適用可能である。特には空燃比を意図的にリーン域に設定して内燃機関の運転を継続させる、いわゆるリーンバーンエンジンにおいてＮＯｘ吸蔵還元触媒を利用する際に本発明は好適に適用できるが、それ以外の内燃機関においても過酸化水素の優れた酸化作用が有効に利用できる限りは本発明を適用してよい。
【００３６】
【発明の効果】
以上に説明したように、本発明の排気浄化装置によれば、触媒の上流に存在する過酸化水素の酸化作用を利用して、三元触媒やＮＯｘ吸蔵還元触媒におけるＨＣやＣＯの酸化反応を促進してこれらの浄化性能を向上させ、特にＮＯｘ吸蔵還元触媒においては、過酸化水素によってＨＣ被毒を解消し、ＮＯからＮＯ_２への酸化反応を促進してＮＯｘの吸蔵能力、浄化能力を向上させることができる。
【図面の簡単な説明】
【図１】本発明の排気浄化装置及びこれが適用される内燃機関の概要を示す図。
【図２】ＮＯｘ吸蔵還元触媒におけるＮＯｘ吸蔵作用と、ＮＯｘ還元作用とを説明するための図。
【図３】空燃比（Ａ／Ｆ）の変化と、ＮＯｘ吸蔵還元触媒のＮＯｘ浄化性能との関係を示す図。
【図４】図１のＥＣＵが実行する過酸化水素供給制御ルーチンを示すフローチャート。
【符号の説明】
１内燃機関
２燃焼室
３吸気通路
５排気通路
９燃料噴射弁
１０点火プラグ
１１エンジンコントロールユニット（制御手段）
１３ＮＯｘセンサ
１４ＨＣセンサ
１５排気温センサ
１６触媒温度センサ
２０排気浄化装置
２１第１触媒（三元触媒）
２２第２触媒（ＮＯｘ吸蔵還元触媒）
２３水分供給機構（水分供給手段）
２４水タンク
２５ポンプ
２６切替弁
２７ノズル
３０超音波照射機構（超音波照射手段）
３１照射器
３２駆動回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification device that purifies exhaust gas of an internal combustion engine using a three-way catalyst or a NOx storage reduction catalyst.
[0002]
[Prior art]
Conventionally, three-way catalysts have been widely used to purify HC, CO, and NOx (nitrogen oxides) discharged from an internal combustion engine. However, the so-called lean control that intentionally controls the air-fuel ratio to a lean region (lean region). Due to the widespread use of burn engines, NOx storage reduction catalysts are also frequently used. The NOx occlusion reduction catalyst occludes NOx while the air-fuel ratio is controlled in the lean region. When the air-fuel ratio is temporarily controlled to be rich, the NOx occlusion is reduced until the reduction is achieved. HC and CO are oxidized with the obtained oxygen. Then, as a measure until the catalyst is activated at the start of the internal combustion engine and exhibits its purification performance, a three-way catalyst having a small heat capacity is installed on the upstream side of the exhaust passage of the internal combustion engine as a start-up catalyst, and the downstream side thereof An exhaust purification device in which a NOx occlusion reduction catalyst is installed is proposed (for example, see Patent Document 1).
[0003]
In addition, a technique has also been proposed in which OH radicals are generated to remove NOx by spraying hydrogen peroxide water upstream of the titanium oxide catalyst (see Japanese Patent Laid-Open No. 10-266831). Furthermore, a technique for generating hydrogen peroxide by irradiating water with an ultrasonic wave around 200 kHz has been proposed (see Non-Patent Document 1). In addition, there are Patent Documents 2 to 4 as conventional techniques related to the present application.
[0004]
[Patent Document 1]
JP-A-11-62563 [Patent Document 2]
JP-A-9-280035
[Patent Document 3]
JP-A-10-266831 [Patent Document 4]
JP-A-9-290136 [Non-patent Document 1]
Nikkan Kogyo Shimbun dated September 7, 2001 [0005]
[Problems to be solved by the invention]
By the way, when the air-fuel ratio is controlled in the lean region in the internal combustion engine, the start-up catalyst may not be able to sufficiently purify HC and CO. Then, so-called HC poisoning occurs in which excess HC remains in the vicinity of the surface of the NOx storage reduction catalyst, thereby preventing the oxidation reaction from NO (nitrogen monoxide) to NO ₂ (nitrogen dioxide) in the NOx storage reduction catalyst. As a result, the NOx storage capacity may be reduced.
[0006]
Therefore, an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can improve the purification performance of a three-way catalyst and a NOx storage reduction catalyst.
[0007]
[Means for Solving the Problems]
The first exhaust gas purification apparatus of the present invention includes a three-way catalyst provided in an exhaust passage, and means for causing hydrogen peroxide to exist upstream of the three-way catalyst, and means for causing the hydrogen peroxide to exist, the Rukoto with ultrasonic irradiation means for producing hydrogen peroxide by irradiating ultrasonic waves to the exhaust passage, to solve the problems described above (claim 1). The second exhaust purification device includes a NOx occlusion reduction catalyst provided in the exhaust passage, and means for causing hydrogen peroxide to exist upstream of the NOx occlusion reduction catalyst, and means for causing the hydrogen peroxide to exist. The above-described problem is solved by providing ultrasonic irradiation means for generating hydrogen peroxide by irradiating ultrasonic waves into the exhaust passage (claim 2). Further, in the second exhaust gas purification apparatus, a three-way catalyst is disposed upstream of the NOx storage reduction catalyst, and the means for causing the hydrogen peroxide to exist allows hydrogen peroxide to exist further upstream of the three-way catalyst. (Claim 3). In addition, the third exhaust purification device is configured to prevent the hydrogen peroxide from being present on the upstream side of the NOx storage reduction catalyst when a rich spike that temporarily sets the air-fuel ratio to the rich side is executed. By providing a control means for controlling the presence state of hydrogen, the above-described problem is solved. (Claim 5) Further, the fourth exhaust purification device includes a NOx storage reduction catalyst provided in an exhaust passage, and the NOx A means for causing hydrogen peroxide to exist upstream of the storage reduction catalyst; and a control means for specifying the current state of the NOx storage capacity of the NOx storage reduction catalyst and controlling the presence state of the hydrogen peroxide based on the specification result. By providing, the above-described problem is solved (claim 6). The fifth exhaust purification device includes a NOx storage reduction catalyst provided in the exhaust passage, a means for causing hydrogen peroxide to exist upstream of the NOx storage reduction catalyst, and a future of the NOx storage capability of the NOx storage reduction catalyst. The above-described problem is solved by providing a control unit that predicts a decrease in the amount of hydrogen peroxide and controls the presence state of the hydrogen peroxide based on the prediction result. Furthermore, in the third to fifth exhaust gas purification apparatuses, a three-way catalyst is disposed upstream of the NOx storage reduction catalyst, and the means for causing the hydrogen peroxide to exist is a hydrogen peroxide further upstream of the three-way catalyst. (Claim 8).
[0008]
According to these exhaust purification apparatuses, the oxidation action of hydrogen peroxide existing upstream of the catalyst promotes the oxidation reaction of HC and CO in the three-way catalyst and the NOx storage reduction catalyst, thereby improving the purification performance. In particular, when a NOx occlusion reduction catalyst is provided, HC poisoning is eliminated by the oxidizing action of hydrogen peroxide, the oxidation reaction from NO to NO ₂ is promoted, and the NOx occlusion capability is improved. In particular, in the high temperature range, the oxidation reaction from NO to NO ₂ is a rate-determining process that governs the NOx occlusion rate. Therefore, if the oxidation reaction is promoted by hydrogen peroxide, the NOx occlusion amount per unit time in the NOx occlusion reduction catalyst is As a result, the amount of NOx discharged downstream without being stored by the NOx storage reduction catalyst is reduced, and the NOx purification performance is improved.
[0009]
In the first or second exhaust gas purification device, since the means for the presence of hydrogen peroxide is provided with the ultrasonic wave irradiation means for producing hydrogen peroxide by irradiating ultrasonic waves in the exhaust passage, in the exhaust By changing the moisture to hydrogen peroxide, it is possible to purify HC and CO by the above-mentioned oxidation action and to eliminate HC poisoning in the NOx storage reduction catalyst. Since hydrogen peroxide is obtained using the moisture in the exhaust gas, it is possible to eliminate the need to provide a hydrogen peroxide tank and store the hydrogen peroxide there. Even if a hydrogen peroxide tank is provided, the capacity required for the tank can be reduced, and the frequency of hydrogen peroxide replenishment can be reduced.
[0010]
In the first or second exhaust purification device may be provided with a water supply means for supplying water to the exhaust passage at ultrasonic irradiation position or the upstream side by the ultrasonic wave irradiation means (claim 4). In this case, when sufficient hydrogen peroxide cannot be generated with the moisture contained in the exhaust gas, the necessary amount of hydrogen peroxide can be generated by adding moisture.
[0011]
Note that in the third to fifth exhaust purification system of the presence of hydrogen peroxide, a case of generating hydrogen peroxide in the exhaust passage, which supplies field if the hydrogen peroxide into the exhaust passage from the outside of the exhaust passage Any aspect is included.
[0014]
When hydrogen peroxide is present during re Tchisupaiku, its oxidation reaction from NO by the oxidizing action of hydrogen peroxide into NO2 is promoted, recovery of the NOx occlusion capacity by the rich spike reduction of NO2 in the NOx storage reduction catalyst is disturbed May be disturbed. The third exhaust purification device is in a state where hydrogen peroxide is present so that hydrogen peroxide does not exist upstream of the NOx storage reduction catalyst when a rich spike that temporarily sets the air-fuel ratio to the rich side is executed. Since the control means for controlling the NOx is stored, the effect of restoring the NOx occlusion ability by the rich spike can be surely exhibited.
[0015]
Fourth exhaust gas purification device identifies the current state of the NOx storage capacity of N Ox storage reduction catalyst is provided with a control means for controlling the state of presence of hydrogen peroxide based on the specification result, a fifth exhaust gas purification apparatus includes a control unit that predicts a decrease in future NOx occlusion capacity of the NOx storage-reduction catalyst, and controls the state of presence of hydrogen peroxide based on the prediction result. Therefore, when NOx occlusion ability actually decreases due to HC poisoning or the like, or when a future decline is predicted, HC can be reduced by hydrogen peroxide, and recovery of NOx occlusion ability and prevention of the reduction can be achieved. .
[0016]
In the present invention, the term “occlusion” is broadly understood to include all aspects of retaining NOx or a product based thereon, regardless of the form in which NOx is finally retained. For example, the concept of adsorption and absorption is included in the category. For example, in the case where NO is changed in the order of NO ₂ → NO ₃ ⁻ and held on the surface or inside of the catalyst, or when NO is changed to NO ₂ and held on the surface or inside of the catalyst, the occlusion of the present invention is performed. Included in the concept.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an outline of an exhaust emission control device of the present invention and an internal combustion engine to which the exhaust purification device is applied. The internal combustion engine 1 is configured as a 4-cycle spark ignition gasoline engine mounted on a vehicle. As is well known, the internal combustion engine 1 has an intake passage 3 for taking air into the combustion chamber 2, a throttle valve 4 for controlling the intake air amount, and exhaust from the combustion chamber 2 to a predetermined exhaust position. An exhaust passage 5 for guiding, an intake valve 6 and an exhaust valve 7 for opening and closing these passages 3, 5; a fuel injection valve 9 for directly injecting gasoline fuel stored in the fuel tank 8 into the combustion chamber 2; A spark plug 10 for igniting the fuel mixture is provided.
[0018]
An engine control unit (ECU) 11 is provided in a vehicle on which the internal combustion engine 1 is mounted. The ECU 11 is a known computer including a microprocessor and peripheral devices such as RAM and ROM necessary for its operation. The ECU 11 executes various controls of the internal combustion engine 1 based on various programs and data recorded in the ROM. For example, the ECU 11 includes an air flow meter that detects the intake air amount, a water temperature sensor that detects the cooling water temperature, a throttle sensor that detects the opening of the throttle valve 4, an air-fuel ratio sensor that outputs a signal corresponding to the air-fuel ratio, etc. The operation state of the internal combustion engine 1 and the traveling state of the vehicle are detected on the basis of the output of), and the fuel injection timing and the injection amount of the fuel injection valve 9 are controlled based on the detection result. By controlling the fuel injection amount from the fuel injection valve 9, the air-fuel ratio in the combustion chamber 2 is the stoichiometric air-fuel ratio, a lean region where the fuel is less than the stoichiometric air-fuel ratio, and a rich region where the fuel is greater than the stoichiometric air-fuel ratio. Is appropriately switched between the two. In general, in the internal combustion engine 1 that directly injects fuel from the fuel injection valve 9 into the combustion chamber 2, stratified combustion is realized by injecting fuel in a compression stroke at a low load and low rotation, and in an intake stroke at a high load and high rotation. The fuel is injected to achieve homogeneous combustion. In stratified combustion, the air-fuel ratio is controlled to a lean region as seen from the entire combustion chamber. Such air-fuel ratio control by the ECU 11 may be the same as that of a known internal combustion engine, and details thereof are omitted here.
[0019]
An exhaust gas purification device 20 is attached to the internal combustion engine 1. The exhaust purification device 20 includes a first catalyst 21 provided in the exhaust passage 5 and a second catalyst 22 provided on the downstream side thereof. The first catalyst 21 is a so-called start catalyst provided mainly for the purpose of reducing the amount of harmful substances discharged until the second catalyst 22 is activated during the cold start of the internal combustion engine 1. The first catalyst 21 is arranged as close as possible to the exhaust port of the internal combustion engine 1 for early activation, and its heat capacity is set sufficiently smaller than that of the second catalyst 22. A three-way catalyst is used for the first catalyst 21. The three-way catalyst is a well-known exhaust gas purifying catalyst that purifies NOx contained in exhaust gas while oxidizing HC and CO.
[0020]
On the other hand, a NOx storage reduction catalyst is used for the second catalyst 22. When the air-fuel ratio is controlled in the lean region, the NOx storage reduction catalyst generates NO ₂ by reacting NOx with O ²⁻ or O ₂ ^{− on} the surface of platinum Pt as shown in FIG. 2 (a). However, when this is further oxidized, it is stored and diffused in the form of NO ₃ ⁻ inside the storage material. On the other hand, when the air-fuel ratio is controlled to be rich, the storage is performed as shown in FIG. releases NO ₂ from wood, the NO ₂ to HC in the exhaust gas, with varying to _{N 2} by reducing with CO, HC, oxidize CO.
[0021]
As shown in FIG. 3, when the air-fuel ratio (A / F) of the internal combustion engine 1 is continuously controlled to a lean region, the NOx storage amount of the NOx storage reduction catalyst increases and the NOx purification performance gradually decreases. Eventually, the purification performance reaches its limit. Therefore, the ECU 11 monitors the state of the exhaust gas discharged from the exhaust passage 5 based on the output of the NOx sensor 13 and the HC sensor 14 provided on the downstream side of the second catalyst 22 in the exhaust passage 5, for example. When the purification performance deteriorates beyond a certain limit, the air-fuel ratio is intentionally controlled to a rich region to promote NOx release, thereby recovering the NOx purification performance. Such a process is known as a so-called rich spike.
[0022]
When the rich spike is appropriately performed, the NOx occlusion amount is reduced to almost zero, and the NOx purification performance of the NOx occlusion reduction catalyst is restored to the almost initial state. However, when so-called HC poisoning in which excessive HC remains in the vicinity of the surface of the NOx storage reduction catalyst, the oxidation reaction from NOx to NO ₂ on the surface of the NOx storage reduction catalyst is prevented, and as a result, FIG. As shown by the broken line, even if rich spike is performed, the NOx purification performance does not return to the initial state, and the subsequent purification performance may also deteriorate. If the capacity of the first catalyst 21 in FIG. 1 is increased and the amount of HC guided to the second catalyst (NOx storage reduction catalyst) 22 is reduced, HC poisoning can be reduced, but the first catalyst 21 can be used early. It needs to be activated and its capacity is limited.
[0023]
In consideration of the above circumstances, the exhaust purification device 20 of FIG. 1 has a moisture supply mechanism 23 for supplying moisture into the exhaust passage 5 on the upstream side of the first catalyst 21, and the first catalyst 21. An ultrasonic irradiation mechanism 30 that irradiates ultrasonic waves into the exhaust passage 5 on the upstream side is further provided. The water supply mechanism 23 supplies water pumped up from the water tank 24 by the pump 25 to the nozzle 27 by opening the switching valve 26, and injects water into the exhaust passage 5 from the nozzle 27. Note that the supply of water to the nozzle 27 is stopped by closing the switching valve 26.
[0024]
The ultrasonic irradiation mechanism 30 includes an irradiator 31 that irradiates ultrasonic waves toward the exhaust passage 5, and a drive circuit 32 that supplies a drive current of a predetermined frequency for ultrasonic transmission to the irradiator 31 in accordance with an instruction from the ECU 11. I have. The frequency of the ultrasonic wave irradiated from the irradiator 31 is set to around 200 kHz which is a frequency range suitable for converting moisture in the exhaust gas to hydrogen peroxide. The irradiator 31 is installed on the downstream side of the exhaust passage 5 with respect to the nozzle 27 of the moisture supply mechanism 23. In other words, the nozzle 27 of the moisture supply mechanism 23 is provided so as to supply moisture to the exhaust gas at an ultrasonic irradiation position by the ultrasonic irradiation mechanism 30 or a position upstream thereof.
[0025]
According to the above configuration, moisture contained in the exhaust gas is obtained by irradiating the exhaust passage 5 with ultrasonic waves from the irradiator 31 of the ultrasonic irradiation mechanism 30 while supplying moisture from the moisture supply mechanism 23 to the exhaust passage 5. Can be converted to hydrogen peroxide. Since the converted hydrogen peroxide has a strong oxidizing action, the oxidation reaction of HC and CO in the first catalyst (three-way catalyst) 21 and the second catalyst (NOx storage reduction catalyst) 22 is promoted to purify them. Performance is improved. Further, in the second catalyst 22, the oxidation reaction from NO to NO ₂ is promoted by the presence of hydrogen peroxide, and the NOx purification ability is increased. Furthermore, HC poisoning of the NOx storage reduction catalyst is also reduced by the synergistic effect of improving the HC purification performance of the first catalyst 21 and the second catalyst 22 and promoting the oxidation of HC in the second catalyst 22. Is done.
[0026]
The generation of hydrogen peroxide using the water supply mechanism 23 and the ultrasonic irradiation mechanism 30 may be appropriately performed according to the necessity, but a suitable control example will be described with reference to FIG.
[0027]
FIG. 4 shows a hydrogen peroxide supply control routine that the ECU 11 repeatedly executes at a constant cycle. By executing the routine of FIG. 4, the ECU 11 functions as a control unit of the exhaust purification device 20.
[0028]
In the hydrogen peroxide supply control routine of FIG. 4, the ECU 11 reads the air-fuel ratio control condition in step S1. The air-fuel ratio control condition is set by the ECU 11 in order to appropriately control the air-fuel ratio of the internal combustion engine 1 according to its operating state and the like. In the subsequent step S2, it is determined whether or not the rich spike processing is being executed from the read air-fuel ratio control conditions. If the rich spike is in progress, the process proceeds to step S12, the supply of moisture and ultrasonic waves is stopped, and the current routine is finished. When hydrogen peroxide is present in the rich spike, there is a possibility that oxidation of NO ₂ from NO in the NOx storage reduction catalyst release action of NOx is impaired occurs.
[0029]
When the rich spike process is not being executed in step S2, the process proceeds to step S3, where the ECU 11 reads the catalyst temperature from the catalyst temperature sensor 16 (see FIG. 1) installed in the vicinity of the second catalyst (NOx storage reduction catalyst) 22, In subsequent step S4, it is determined whether or not the temperature of the catalyst 22 is equal to or higher than a predetermined activation temperature (that is, whether or not the catalyst 22 is warmed up to a predetermined level). When the catalyst temperature is lower than the activation temperature, the process proceeds to step S12 and the supply of hydrogen peroxide is stopped. This is because, if HC and CO are oxidized by hydrogen peroxide before the activation of the catalyst 22, the effect of promoting the warm-up of the catalyst due to the secondary combustion of these unburned substances is impaired.
[0030]
When the temperature of the catalyst 22 is equal to or higher than the activation temperature in step S4, the process proceeds to step S5, and the exhaust temperature is read from the exhaust temperature sensor 15 (see FIG. 1) installed in the exhaust passage 5. In subsequent step S6, it is determined whether or not the exhaust gas temperature is equal to or higher than a predetermined decomposition temperature. If it is above the decomposition temperature, the process proceeds to step S12 and the supply of hydrogen peroxide is stopped. The decomposition temperature is set as a temperature at which hydrogen peroxide is decomposed by heat. The reason why hydrogen peroxide is not formed when the exhaust gas temperature is higher than the decomposition temperature is that even if hydrogen peroxide is supplied when the exhaust gas temperature is higher than the decomposition temperature, the hydrogen peroxide is decomposed immediately and the specified purification performance improvement effect cannot be obtained. is there.
[0031]
When the exhaust temperature is not higher than the decomposition temperature, the process proceeds to step S7, and the output of the NOx sensor 13 is read. In subsequent step S8, referring to the output of the NOx sensor 13, it is determined whether or not the amount of NOx passing through the second catalyst 22 is a predetermined amount or more. The predetermined amount is determined to be the NOx amount detected downstream when the NOx storage capacity of the NOx storage reduction catalyst falls below a predetermined level. When the NOx discharge amount is equal to or larger than the predetermined amount, the process proceeds to step S11, where water supply by the water supply mechanism 23 and ultrasonic irradiation by the ultrasonic irradiation mechanism 30 are executed to generate hydrogen peroxide. As a result, when the storage capacity of the NOx storage reduction catalyst declines due to HC poisoning and the amount of NOx emissions exceeds a predetermined limit, hydrogen peroxide is supplied to eliminate HC poisoning and improve NOx purification performance. Can be recovered. That is, by providing the determination in step S8, the supply state of hydrogen peroxide can be controlled according to the NOx storage capacity of the NOx storage reduction catalyst. Since NOx occlusion is performed when the air-fuel ratio is controlled in the lean region, it may be added that the air-fuel ratio is controlled in the lean region as a condition for affirming step S8.
[0032]
Further, when the amount of NOx passing through the second catalyst 22 is less than the predetermined amount in step S8, the process proceeds to step S9, and the output of the HC sensor 14 is read. In the subsequent step S10, the output of the HC sensor 14 is referred to and it is determined whether or not the amount of HC passing through the second catalyst 22 is a predetermined amount or more. The predetermined amount is set to the HC emission amount when there is a concern about HC poisoning of the NOx storage reduction catalyst. When the HC discharge amount is less than the predetermined amount, the process proceeds to step S12, and when the HC discharge amount is not less than the predetermined amount, the process proceeds to step S11. As a result, hydrogen peroxide is supplied when HC is discharged to such an extent that the NOx occlusion capacity of the NOx occlusion reduction catalyst is expected to decrease due to HC poisoning, and HC purification of the catalysts 21 and 22 is performed by the oxidation action. The capacity can be improved and the progress of HC poisoning in the NOx storage reduction catalyst can be prevented. As described above, the supply of hydrogen peroxide is controlled in step S11 or step S12, and one routine is completed.
[0033]
This invention is not limited to the above embodiment, You may implement with a various form. For example, in the above embodiment, the actual decrease in the NOx storage capacity and the possibility of the future decrease are determined by referring to the outputs of the NOx sensor 13 and the HC sensor 14 disposed downstream of the second catalyst 22. Various sensors used for detecting the exhaust state such as a sensor, an O ₂ (oxygen) sensor, a CO sensor, and the like may be used to determine the current state of NOx storage capacity and future decline. These sensors are not limited to the downstream side of the second catalyst 22, and may be disposed before and after the second catalyst 22. Further, when the NOx storage capacity reduction in the NOx storage reduction catalyst can be specified based on the operation control state of the internal combustion engine 1 such as the number of executions of rich spike, the execution time, or the duration of the lean operation, these From the history of operation control, the current state of NOx storage capacity and the prediction of future decline may be performed.
[0034]
In the above embodiment, the combination of the water supply mechanism 23 and the ultrasonic irradiation mechanism 30 constitutes a means for causing hydrogen peroxide to exist. However, the water supply mechanism 23 may be omitted when sufficient hydrogen peroxide is obtained by the water contained in the exhaust. The present invention is not limited to an example in which hydrogen peroxide is generated in the exhaust passage using ultrasonic waves, but hydrogen peroxide stored in a tank outside the exhaust passage is sucked up by a pump and sprayed in the exhaust passage. Further, a configuration in which hydrogen peroxide is supplied from outside the exhaust passage is also included in the range.
[0035]
The present invention is not limited to an exhaust purification device that combines a three-way catalyst and a NOx occlusion reduction catalyst, but can also be applied to an exhaust purification device that uses only one of the catalysts. The present invention is not limited to an internal combustion engine that directly injects fuel into a combustion chamber, but can also be applied to an internal combustion engine that injects fuel into an intake port. In particular, the present invention can be suitably applied when the NOx storage reduction catalyst is used in a so-called lean burn engine in which the air-fuel ratio is intentionally set to a lean region and the operation of the internal combustion engine is continued. However, the present invention may be applied as long as the excellent oxidizing action of hydrogen peroxide can be effectively utilized.
[0036]
【The invention's effect】
As described above, according to the exhaust gas purification apparatus of the present invention, the oxidation reaction of HC and CO in the three-way catalyst and the NOx storage reduction catalyst is performed using the oxidation action of hydrogen peroxide existing upstream of the catalyst. promotion to improve these purification performance, particularly NOx storage reduction catalyst to solve the HC poisoning by hydrogen peroxide, and promote oxidation reaction of NO to NO ₂ NOx occlusion capacity, purification capacity Can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an exhaust emission control device of the present invention and an internal combustion engine to which the exhaust purification device is applied.
FIG. 2 is a diagram for explaining a NOx occlusion action and a NOx reduction action in a NOx occlusion reduction catalyst.
FIG. 3 is a graph showing a relationship between a change in air-fuel ratio (A / F) and NOx purification performance of a NOx storage reduction catalyst.
FIG. 4 is a flowchart showing a hydrogen peroxide supply control routine executed by the ECU of FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 3 Intake passage 5 Exhaust passage 9 Fuel injection valve 10 Spark plug 11 Engine control unit (control means)
13 NOx sensor 14 HC sensor 15 Exhaust temperature sensor 16 Catalyst temperature sensor 20 Exhaust purification device 21 First catalyst (three-way catalyst)
22 Second catalyst (NOx storage reduction catalyst)
23 Moisture supply mechanism (moisture supply means)
24 Water tank 25 Pump 26 Switching valve 27 Nozzle 30 Ultrasonic irradiation mechanism (ultrasonic irradiation means)
31 Irradiator 32 Drive circuit

Claims

Comprising a three-way catalyst provided in an exhaust passage, and means for the presence of hydrogen peroxide upstream of the three-way catalyst, means for the presence of the hydrogen peroxide is irradiated with ultrasonic waves in the exhaust passage An exhaust emission control device for an internal combustion engine, comprising ultrasonic irradiation means for generating hydrogen peroxide.

A NOx occlusion reduction catalyst provided in the exhaust passage; and a means for causing hydrogen peroxide to exist upstream of the NOx occlusion reduction catalyst , wherein the means for causing the hydrogen peroxide to exist irradiates ultrasonic waves in the exhaust passage. An exhaust gas purification device for an internal combustion engine, characterized by comprising ultrasonic irradiation means for generating hydrogen peroxide.

The three-way catalyst is disposed upstream of the NOx occlusion reduction catalyst, and the means for causing the hydrogen peroxide to exist causes hydrogen peroxide to exist further upstream of the three-way catalyst. Exhaust purification device.

The exhaust gas purification device according to any one of claims 1 to 3, further comprising a water supply unit that supplies water to the exhaust passage at an ultrasonic irradiation position by the ultrasonic irradiation unit or upstream thereof. apparatus.

Wherein when the NOx storage reduction catalyst provided in an exhaust passage, means the presence of hydrogen peroxide upstream of the NOx storage reduction catalyst, the rich spike temporarily set to a rich side air-fuel ratio is being performed exhaust purification system of an internal combustion engine, characterized in that a control means for controlling the state of presence of the hydrogen peroxide so as not to present the hydrogen peroxide upstream of the NOx storage reduction catalyst.

A NOx storage reduction catalyst provided in an exhaust passage, means the presence of hydrogen peroxide upstream of the NOx storage-reduction catalyst, to identify the current state of the NOx occlusion capability of the NOx storage-reduction catalyst, based on the identification result exhaust purification system of an internal combustion engine, characterized in that a control means for controlling the state of presence of the hydrogen peroxide.

A NOx storage reduction catalyst provided in an exhaust passage, means the presence of hydrogen peroxide upstream of the NOx storage-reduction catalyst, to predict the reduction in future NOx occlusion capacity of the NOx storage reduction catalyst, the result of the prediction based on the exhaust purification system of an internal combustion engine, characterized in that a control means for controlling the state of presence of the hydrogen peroxide.

The three-way catalyst is disposed upstream of the NOx occlusion reduction catalyst, and the means for causing the hydrogen peroxide to exist causes hydrogen peroxide to exist further upstream of the three-way catalyst . The exhaust emission control device according to any one of claims.