JP2004011428A

JP2004011428A - NOx PURIFYING DEVICE OF INTERNAL COMBUSTION ENGINE

Info

Publication number: JP2004011428A
Application number: JP2002161731A
Authority: JP
Inventors: Shinichi Saito; 斎藤　真一; Yoshihisa Takeda; 武田　好央; Sei Kawatani; 川谷　聖; Satoshi Hiranuma; 平沼　智; Kenji Kawai; 河合　健二; Takeshi Hashizume; 橋詰　剛; ▲高▼橋　嘉則; Yoshinori Takahashi; Ritsuko Shinozaki; 篠▲崎▼　律子; Reiko Domeki; 百目木　礼子
Original assignee: Mitsubishi Fuso Truck and Bus Corp
Current assignee: Mitsubishi Fuso Truck and Bus Corp
Priority date: 2002-06-03
Filing date: 2002-06-03
Publication date: 2004-01-15
Anticipated expiration: 2022-06-03
Also published as: JP4114405B2

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction of durability of an air compressor and prevent fuel economy from being low due to driving of the air compressor. <P>SOLUTION: This NOx purifying device comprises: a SCR catalyst 23 provided to an exhaust system 2 of an engine 1; a urea water supply device 22 which supplies a urea water via a supply passage r1 communicating with the exhaust system in an upstream of the SCR catalyst 23; a boost pressure air pipe 31 driven by the engine 1 or an electric motor and supplying a pressurized air to the supply passage r1 in the upstream of a region of supply of the urea water supplied from the urea water supply device 22; a turbocharger 6 arranged in the upstream of the SCR catalyst 23 of the exhaust system; and an assist air switching control means B1 which supply the supply passage r1 with any one of boost pressure air from a suction passage I in the downstream of the turbocharger 6 and the pressurized air from a compression air pump in accordance with a supply amount of the urea water corresponding to an operating condition. <P>COPYRIGHT: (C)2004,JPO

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中のＮＯｘを浄化するＮＯｘ浄化装置、特に、排気系に設けた還元触媒の上流側にエアアシストにより排気ガス還元剤を添加する装置を配した内燃機関のＮＯｘ浄化装置に関する。
【０００２】
【従来の技術】
内燃機関が排出する排気ガス中のＮＯｘはＮＯｘ浄化装置により浄化されている。例えば、ディーゼルエンジンで用いられるＮＯｘ浄化装置は排気系に選択還元型のＳＣＲ触媒（ＮＯｘ触媒〉を有した触媒コンバータと、その上流側の尿素水供給装置とを順次配備して形成される。
このＳＣＲ触媒は尿素水を還元剤として供給し、酸素過剰雰囲気下においてＮＯｘを浄化できるようにしている。
ここで、ユリア水（尿素水）は式（１）のように加水分解及び熱分解して、ＮＨ３を放出する。
【０００３】
（ＮＨ２）２ＣＯ＋Ｈ_２Ｏ→２ＮＨ_３＋ＣＯ_２・・・・（１）
また、ＳＣＲ触媒上でのＮＨ_３と窒素酸化物との間の脱硝反応は次の（２）、（３）式の反応がそれぞれ行われることが知られている。
４ＮＨ_３＋４ＮＯ＋Ｏ_２→４Ｎ_２＋６Ｈ_２０・・・・（２）
２ＮＨ_３＋ＮＯ＋ＮＯ_２→２Ｎ_２＋３Ｈ_２０・・・・（３）
ところで、アンモニア（又は尿素水）添加式のＮＯｘ浄化装置では内燃機関の運転域に応じて尿素水の添加を断続制御している。即ち、通常運転域では内燃機関の運転条件に応じてエアアシストで尿素水を供給する。
【０００４】
尿素水搬送用の圧縮エアは内燃機関その他の動力源により駆動されるエアコンプレッサより供給される。
一方、燃料無噴射となる無負荷運転時など、尿素水の供給が不要な場合は尿素水の供給を停止する。
この際、尿素水搬送用の圧縮エアを流し続けると無駄にエアコンプレッサを作動させることになり、エアコンプレッサの劣化やエアコンプレッサ負荷による燃費悪化を招く恐れがある。
【０００５】
一方、尿素水搬送用の圧縮エア供給を停止するとエアコンプレッサの耐久性確保や燃費悪化の抑制の上では有効であるが、エアに混入する混入物、例えば尿素が固化し易くなり、供給通路を狭め、閉鎖する恐れがある。
特に、供給通路の下流端に配備され、排気路に対設される添加ノズルは高温の排気ガスに触れて高温化し易い傾向にあり、同部が過度に昇温すると、同部に残留する尿素はもとより、新たに尿素水が流動してきた場合も固化が進み易い。
【０００６】
このようにして供給通路及び添加ノズルが狭まると、尿素水の供給時の流動抵抗が高まり、尿素水供給応答性が低下し、更に、閉鎖すると尿素水の供給不能に陥る。
【０００７】
【発明が解決しようとする課題】
このように尿素供給停止時もエアコンプレッサを作動させるとエアコンプレッサの劣化やエアコンプレッサ負荷による燃費悪化を招く恐れがある一方、尿素水搬送用の圧縮エア供給を停止すると尿素水の供給通路の閉塞を招く恐れがあった。
本発明は、以上のような課題に基づき、エアコンプレッサの耐久性低下やエアコンプレッサ駆動による燃費の悪化を防止できる内燃機関のＮＯｘ浄化装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
請求項１の発明は、内燃機関の排気系に設けられ排気ガス中のＮＯｘを選択還元するＮＯｘ触媒、前記ＮＯｘ触媒上流の前記排気系に連通する供給通路を介して還元剤を供給する還元剤供給手段、前記内燃機関又は電動機により駆動され、前記還元剤供給手段から供給される還元剤の供給部位より上流の前記供給通路に加圧空気を供給する加圧空気供給手段、前記排気系の前記ＮＯｘ触媒の上流に設けられ前記内燃機関に導入される給気を過給する過給機、前記内燃機関の運転状態に応じて、前記供給通路に前記過給機下流の前記吸気系からの過給空気及び前記加圧空気供給手段からの加圧空気の何れか一方を供給する制御手段、を備えたことを特徴とする内燃機関のＮＯｘ浄化装置。
このように、還元剤供給停止時に加圧空気供給手段からの不要な加圧空気の供給を停止して、過給機下流の吸気系から過給空気を供給することにより、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止できる。なお、還元剤が尿素水の場合には、供給通路内への尿素水の還元剤の水分蒸発による尿素の固化を未然に防止できる。
【０００９】
請求項２の発明は、請求項１に記載の内燃機関のＮＯｘ浄化装置において、前記内燃機関が前記過給機下流の前記吸気系の過給圧を検出する圧力センサを備え、前記制御手段は、前記内燃機関の運転状態が還元剤を供給すべき運転状態或いは還元剤の供給中に前記圧力センサにより検出された過給圧が所定値以上のとき、前記供給通路に過給機下流の前記吸気系からの過給空気を供給することを特徴とする。
このように、排気中に還元剤添加が行われ且つ過給圧が所定値以上のときには、供給通路に過給機下流の吸気系からの過給空気を供給することによって、加圧空気供給手段の負荷を必要最小限に抑制でき、その耐久性を確保でき、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止できる。
【００１０】
請求項３の発明は、請求項２に記載の内燃機関のＮＯｘ浄化装置において、前記内燃機関の運転状態を検出する運転状態判定手段を備え、さらに、前記過給機は、前記吸気系の前記過給機下流の過給圧を調整する過給圧調整部を含み、前記制御手段は、前記内燃機関の運転状態に応じた還元剤供給量がゼロを越え、且つ前記圧力センサにより検出された圧力が所定値未満で且つ前記運転状態判定手段より前記内燃機関が無負荷運転領域にあると判定されたとき、過給圧が増大するよう前記過給圧調整部を制御すると共に前記供給通路に前記過給機下流の吸気系からの過給空気を供給するように制御することを特徴とする。
このように、排気中に還元剤添加が行われ且つ過給圧が所定値未満で、内燃機関が無負荷運転領域にあるきには、過給圧調整部を過給圧増大側に制御すると共に供給通路に過給機下流の吸気系からの過給空気を供給することによって、内燃機関又は電動機で駆動される加圧空気供給手段を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
【００１１】
請求項４の発明は、請求項３に記載の内燃機関のＮＯｘ浄化装置において、少なくとも前記過給圧調整部の調整有無に応じた内燃機関の燃料消費量を求める燃費算出手段を備え、前記制御手段は、前記内燃機関の運転状態に応じた還元剤供給量がゼロを越え、且つ前記圧力センサにより検出された圧力が所定値未満で且つ前記運転状態判定手段により前記内燃機関が無負荷運転領域以外にあると判定されたとき、更に、前記燃費算出手段によって前記加圧空気供給手段の作動による燃費よりも前記加圧空気供給手段の作動停止且つ前記過給圧調整手段を過給圧増大側への制御による燃費が向上する際に、過給圧が増大するよう前記過給圧調整部を制御すると共に前記供給通路に前記過給機下流の前記吸気系からの過給空気を供給するよう制御することを特徴とする。
このように、排気中に還元剤添加が行われ且つ過給圧が所定値未満で、内燃機関が無負荷運転領域以外にあるときに、更に、燃費算出手段によって加圧空気供給手段の作動による燃費よりも加圧空気供給手段の作動停止且つ過給圧調整手段を過給圧増大側への制御による燃費が向上する際に、過給圧調整部を過給圧増大側に制御すると共に供給通路に過給機のコンプレッサ下流の吸気系からの過給空気を供給することによって、内燃機関又は電動機で駆動される加圧空気供給手段を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
【００１２】
請求項５の発明は、内燃機関の排気系に設けられ排気ガス中のＮＯｘを選択還元するＮＯｘ触媒、前記ＮＯｘ触媒上流の前記排気系に連通する供給通路を介して還元剤を供給する還元剤供給手段、前記内燃機関又は電動機により駆動され、前記還元剤供給手段から供給される還元剤の供給部位より上流の前記供給通路に加圧空気を供給する加圧空気供給手段、前記排気系の前記ＮＯｘ触媒の上流に設けられ前記内燃機関に導入される給気を過給する過給機、還元剤の供給有無を検出する還元剤供給検出手段、前記還元剤供給検出手段により検出された還元剤の供給量に応じて、前記供給通路に前記過給機下流の前記吸気系からの過給空気及び前記加圧空気供給手段からの加圧空気の何れか一方を供給する制御手段、を備えたことを特徴とする。
このように、還元剤供給停止時に加圧空気供給手段からの不要な加圧空気の供給を停止して、過給機下流の吸気系から過給空気を供給することにより、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止する。なお、還元剤が尿素水の場合には、供給通路内への尿素水の還元剤の水分蒸発による尿素の固化を未然に防止できる。
【００１３】
【発明の実施の形態】
以下、本発明の一実施形態としての内燃機関のＮＯｘ浄化装置（以後単にＮＯｘ浄化装置）を図１を参照して説明する。ここでのＮＯｘ浄化装置Ｍ１は、図示しない車両に搭載された多気筒ディーゼルエンジン（以後単にエンジンと記す）１の排気系２に装着される。
エンジン１はエンジン制御装置（以後、単にエンジンＥＣＵと記す）３により制御され、ＮＯｘ浄化装置Ｍ１は排気ガス制御装置（以後単に排気系ＥＣＵと記す）４に制御され、エンジンＥＣＵ３と排気系ＥＣＵ４は制御系通信回線５によって相互通信可能に連結される。
【００１４】
図１において、ＮＯｘ浄化装置Ｍ１を装備したエンジン１は図示しない燃焼室に吸気を導く吸気系と、燃料噴射量、噴射圧、噴射時期などを調整する燃料制御系とを備える。
吸気路Ｉには過給機であるＶＧ（Ｖａｒｉａｂｌｅ　Ｇｅｏｍｅｔｒｙ：可変静翼）ターボチャージャー６（以後単にターボチャージャー６と記す）のコンプレッサ１３が介装され、その回転軸１０は排気路Ｅに介装されるターボチャージャー６のタービン７に連結されている。
【００１５】
ここでＶＧターボチャージャー６は過給機下流の過給圧を調整する過給圧調整部を有する。過給圧調整部はタービン７の外周部に複数配備される整流片（図示せず）と、同整流片の傾きを切換えてタービン７に流入する排気の流速を可変することでタービン７の過給仕事を可変させる整流片アクチュエータである過給圧調整手段（以下、過給圧調整部８と記す）とを備え、この過給圧調整部８は駆動回路９を介してエンジンＥＣＵ３に接続されている。
吸気路Ｉのコンプレッサ１３の下流にはインタクーラ１１が設けられ、吸気冷却を行うことで、エンジン１の吸気の体積効率を向上させ、出力アップを図っている。なお、コンプレッサ１３とインタクーラ１１の間の吸気路Ｉにはブースト圧Ｐｂを排気系ＥＣＵ４に出力する圧力センサとしてのブースト圧センサ１２が配備される。
【００１６】
エンジンＥＣＵ３は要求出力が得られるような燃料量及び噴射時期を設定する燃料噴射量設定部Ａａ、燃料噴射時期設定部Ａｂ及びターボ制御手段Ａｃを有する。
エンジンＥＣＵ３の入力側には、アクセルペダル踏込量（アクセル踏込量）θａを検出するアクセル踏込量センサ１４、エンジン回転数Ｎｅを演算するためのクランク角センサ１５等の各種センサ類が接続され、出力側には図示しない高圧燃料ポンプにより供給される高圧燃料を貯留するコモンレール１６と各気筒毎に設けられた燃料噴射ノズル１７との間を接続する燃料通路を開閉する開閉弁１８を駆動する燃料噴射用ドライバ１９、図示しない高圧ポンプの燃料供給量を制御する調量部等の各種デバイス類が接続されている。
【００１７】
これにより、例えば、クランク角センサ１５により検出されたクランク信号θｃに基き演算されたエンジン回転数Ｎｅとアクセル踏込量センサ１４により検出されたアクセルペダル踏込量（アクセル踏込量）θａとに応じて演算された要求燃料噴射Ｑに基き、開閉弁の開弁時期、開弁期間が燃料噴射用ドライバによって可変調整され、さらに、高圧燃料ポンプの調量部がコモンレール１６内の燃料圧力に応じてフィードバック制御される。
更に、エンジンＥＣＵ３のターボ制御手段Ａｃは、過給圧調整部８を用いてブースト圧（過給圧）Ｐｂを調整する機能を有する。このターボ制御手段Ａｃはアクセル踏込量θａ及びエンジン回転数Ｎｅに応じてターボ切換え信号ＶＧαを図示しないマップを用いて設定する。ここでのマップは整流片の傾きを順次切換えるべく、アクセル踏込量θａ及びエンジン回転数Ｎｅに応じて各段相当のターボ切換え信号ＶＧαを設定する。
【００１８】
なお、エンジンＥＣＵ３に後述のブースト圧増大指令Ｓ１が排気系ＥＣＵ４より入力されると、エンジンＥＣＵ３のターボ制御手段Ａｃはターボ切換え信号ＶＧαを駆動回路に出力し、ブースト圧増大処理を実行できる。
図１のＮＯｘ浄化装置Ｍ１は排気管２１の途中に装着されたＮＯｘ触媒であるＳＣＲ触媒２３とその上流の排気路Ｅにエアアシストで尿素水を供給する還元剤供給手段としての尿素水供給装置２２と、制御手段を成す排気系ＥＣＵ４とを備える。
【００１９】
ＳＣＲ触媒２３は排気路Ｅを成す排気管２１の途中のＮＯｘ触媒コンバータ２４に収容される。ＮＯｘ触媒コンバータ２４はケーシング２４１を備え、ケーシング内にハニカム構造のセラミック製の触媒担体（ＳＣＲ触媒２３のブロック表示と重なる）を備え、同触媒担体をシール材２４２を介してずれなく支持しており、同担体にＳＣＲ触媒２３として機能するための触媒金属として、例えば酸化バナジウム（Ｖ_２Ｏ_５）が担持される。
ＳＣＲ触媒２３はアンモニア（ＮＨ_３）を還元剤として排気ガス中のＮＯｘを選択還元可能である。即ち、上述の式（１）のように尿素水は加水分解してアンモニアを生成し、これがＳＣＲ触媒２３において、窒素酸化物との間で脱硝反応を起こす。なお、ＳＣＲ触媒２３には同触媒の温度Ｔｃａを排気系ＥＣＵ４に出力する触媒温度センサ２５が取付けられている。
【００２０】
排気管２１の途中に装着された尿素水供給装置２２はＮＯｘ触媒コンバータ２４の上流開口側に向けて尿素水を噴霧する添加ノズル２６と、添加ノズル２６に接続され供給通路ｒ１を形成する噴射管２７と、噴射管２７の上流端の圧縮エアタンク２８と、噴射管２７の途中の三方切換弁２９と、三方切換弁２９とコンプレッサ１３下流の吸気路Ｉを介し供給通路ｒ１に連通可能なブースト圧エア管３１と、三方切換弁２９より下流側の供給通路ｒ１で開口する尿素水パイプ３２と、尿素水パイプ３２に尿素水を供給する尿素水タンク３３と、尿素水パイプ３２の尿素水の流量を調整する流量調整弁３４と、これらの制御手段を成す排気系ＥＣＵ４とを備える。
【００２１】
圧縮エアタンク２８は図示しない電動機で駆動するエアポンプ３５より適時に圧縮エアの供給を受け、常時一定圧のエアを保持している。ここで圧縮エアタンク２８及びエアポンプ３５が供給通路ｒ１に加圧空気を供給する加圧空気供給手段を成している。加圧空気供給手段であるエアポンプ３５は駆動回路３６に接続され、駆動回路３６は排気系ＥＣＵ４からの駆動指令Ｐｄを受けた際に駆動出力Ｄｐでエアポンプ３５を駆動する。
ブースト圧エア管３１は金属パイプで形成され、その一端がコンプレッサ１３の下流側の吸気路Ｉに、他端が三方切換弁２９の流入ポートｐ１に連結されている。
【００２２】
ここで三方切換弁２９は供給通路ｒ１における還元剤の供給部位より上流で且つ圧縮エアタンク２８（加圧空気供給手段）の下流に設けられる。しかも、三方切換弁２９はコンプレッサ下流の吸気路Ｉ（吸気系）及び圧縮エアタンク２８の何れか一方と供給通路ｒ１とを連通可能な切り替え手段を成している。
この三方切換弁２９は電磁弁であり、排気系ＥＣＵ４に接続される。この三方切換弁２９の一方の流入ポートｐ２は圧縮エアタンク２８側に供給通路ｒ１を介して連通され、他方の流入ポートｐ１はコンプレッサ下流の吸気路Ｉにブースト圧エア管３１を介し連通され、流出ポートｐ３は添加ノズル２６に連通する。
【００２３】
三方切換弁２９は切換え出力Ｄｖがオフ時に供給通路ｒ１を介して圧縮エアタンク２８と添加ノズル２６を連通し、オン時に供給通路ｒ１及びブースト圧エア管３１を介してコンプレッサ下流の吸気路Ｉと添加ノズル２６を連通するよう切換え作動できる。
【００２４】
添加ノズル２６にはそのノズル自体の温度Ｔｎ信号を出力するノズル温度センサ３７が装着され、その検出信号Ｔｎは排気系ＥＣＵ４に出力される。なお、添加ノズル２６に対しては、その過熱時に後述のように冷却用のエアを流動させる処理が排気系ＥＣＵ４により成される。
尿素水タンク３３は尿素を水に溶解し、一定濃度の水溶液としたものが貯蔵されており、適時に補給されるようになっている。
【００２５】
排気系ＥＣＵ４はその入出力回路に多数のポートを有し、ノズル温度センサ３７より添加ノズル２６の温度Ｔｎ信号を、ブースト圧センサ１２よりブースト圧Ｐｂ信号を、触媒温度センサ２５より触媒温度Ｔｃａを入力でき、しかも、添加制御手段Ｂ０、アシストエア切換え制御手段Ｂ１、燃費算出手段Ｂ２、尿素水供給検出手段Ｂ３として機能し、エアポンプ３５、三方切換弁２９、流量調整弁３４、エンジンＥＣＵ３に制御信号を出力する。
【００２６】
添加制御手段（制御手段）Ｂ０は触媒温度Ｔｃａ、或いは触媒温度に相関するパラメータ（例えば排気温度）に基いて尿素水の供給量を図示しないマップを用いて設定し、設定された尿素水供給量ｑｕとなるように流量調整弁３４の開度を制御する。
アシストエア切換え制御手段（制御手段）Ｂ１は尿素水供給量ｑｕに応じて、供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エア（過給空気）及びエアポンプ３５からの加圧空気の何れか一方を添加アシスト用のエアとして供給するように三方切換弁２９を制御する。
【００２７】
なお、三方切換弁２９に代えて、これを排除し、圧縮エアタンク２８の直下に開閉弁ｂ１（図１に２点鎖線で示す）をブースト圧エア管３１の途中に逆止弁ｂ２（図１に２点鎖線で示す）を設けてブースト圧エア（過給空気）及びエアポンプ３５からの加圧空気の何れか一方を添加アシスト用エアとして供給するように構成しても良く、更に、逆止弁ｂ２を図示しない開閉弁に代えても良く、これらの場合も三方切換弁２９と同様の機能を得られる。
燃費算出手段Ｂ２は、少なくとも過給圧調整部８の調整有無に応じたエンジン１の燃料消費量δを求める。即ち、燃費算出手段Ｂ２は、エアポンプ３５の作動時のエンジン回転数Ｎｅ相当の燃料消費量δと、エアポンプ３５の作動停止且つ過給圧調整部８をブースト圧増大のためターボ切換え信号ＶＧαの出力時（過給圧増大側）のエンジン回転数Ｎｅ相当の燃料消費量δを導出する図示しないマップを備える。
【００２８】
尿素水供給検出手段Ｂ３は尿素水の供給有無を検出する、即ち、流量制御弁３４の開度（尿素水供給量ｑｕ相当）信号に応じて供給有無を判定する。
次に、図１のエンジンＥＣＵ３及び排気系ＥＣＵ４の各制御処理を、図２、図３の制御ルーチンに沿って説明する。
【００２９】
ここで、ＮＯｘ浄化装置を搭載したエンジン１のエンジンキーがオンすると、これと同時にエンジンＥＣＵ３は駆動し、エンジン制御ルーチンのステップａ１に達する。ここでは複数の制御系、例えば、燃料制御系で適宜実行されている関連機器、センサ類が正常か否かの自己チェック結果が正常であったか否かを確認し、正常（ＯＫ）ではアクセル踏込量θａ、エンジン回転数Ｎｅ等の関連センサのデータ採り込みを行う。次いで、ステップａ２では上述の燃料噴射量設定部Ａａ及び燃料噴射時期設定部Ａｂが関連センサの各入力値に応じて運転情報（アクセル踏込量θａ、エンジン回転数Ｎｅ、空燃比Ａ／Ｆ、水温Ｔｗ）相当の燃料噴射量、燃料噴射時期を導出し、それら相当の出力Ｄ（Ｇｆ）が燃料噴射用ドライバ１９、調量部等に出力される。これにより、燃料噴射量、燃料噴射時期相当の出力が各開閉弁１８に送出され、各燃料噴射ノズル１７が噴射作動を実行する。
【００３０】
ステップａ３ではブースト圧増大指令Ｓ１の入力を判定し、非入力時にはステップａ４に、入力時にはステップａ５に進む。
排気系ＥＣＵ４よりブースト圧増大指令Ｓ１が入力されステップａ５に達すると、ここでは相当するターボ切換え信号ＶＧαを過給圧調整部８側の駆動手段９に出力し、ステップａ４に進む。これにより過給圧調整部８がブースト圧増大処理を行うことができ、供給通路ｒ１及び添加ノズル２６にコンプレッサ１３の下流の吸気路Ｉからのブースト圧エアを供給する。
ステップａ４ではその他のエンジン制御を実行し、ステップａ２にリターンする。
【００３１】
一方、排気系ＥＣＵ４は図示しない排気系メインルーチンのＮＯｘ浄化処理制御を所定制御サイクル毎に繰り返し、尿素水をエンジン運転条件や触媒温度Ｔｃａに応じた尿素水供給量ｑｕだけ添加すべく流量制御弁３４を駆動し、その途中で図３のアシストエアの切換え制御ルーチンを実行する。
アシストエアの切換え制御ルーチンのステップｓ１に達すると、ここで、ブースト圧Ｐｂ、添加ノズル２６温度Ｔｎ等の関連センサ出力を採り込む。ステップｓ２では流量制御弁３４が全閉か否か判断し、無添加時にはステップｓ３に添加時にはステップｓ４に進む。
【００３２】
無添加時、例えばエンジンブレーキ時でありステップｓ３に達すると、ここでは添加ノズル２６温度Ｔｎが過熱判定値Ｔｎ１以上か否か判定し、過熱時にはステップｓ６に、そうでないとステップｓ５に進む。ステップｓ５では負荷の圧縮エアの供給が必要か否か、即ち、ステップｓ５では流量制御弁３４が全閉してからの経過時間ｔｎが所定の時間ｔｐに達していないか否か判断し、達していない時点ではステップｓ６に進み、経過しているとステップｓ７に進む。
【００３３】
ステップｓ７では、無添加で、添加ノズル２６温度Ｔｎが低く、尿素水供給停止後の時間ｔｐを経過している場合であり、三方切換弁２９をオンし、コンプレッサ１３下流の吸気路Ｉと添加ノズル２６を連通するよう切換え、圧縮エアタンク２８の加圧空気に代えてブースト圧エアを供給通路ｒ１や添加ノズル２６に流し、この回の制御を終了する。
ステップｓ６では添加ノズル２６温度Ｔｎが高く、もしくは時間ｔｐ経過前の場合であり、三方切換弁２９をオフし、圧縮エアタンク２８と添加ノズル２６を連通するよう切換え、圧縮エアタンク２８の加圧空気を供給通路ｒ１や添加ノズル２６に流し、尿素水供給通路内の残留尿素のパージを継続し、この回の制御を終了する。
【００３４】
ステップｓ２で添加時と判断されステップｓ４に進むと、ここでは、ブースト圧Ｐｂが判定値圧Ｐｂβ以上か否か判定し、ブースト圧Ｐｂが判定値圧Ｐｂβ以上ではブースト圧エアを尿素水供給アシストに使用して、圧縮エアタンク２８側の加圧空気の使用を抑え、燃費向上を図るべくステップｓ３側に進む。ブースト圧Ｐｂが判定値圧Ｐｂβに達しないとステップｓ８に進む。
ステップｓ８では、無負荷運転域か否か判定し、無負荷でステップｓ９に負荷時にステップｓ１０に進む。
【００３５】
ステップｓ９ではブースト圧Ｐｂが低い運転域であることより、ブースト圧増大指令をエンジンＥＣＵ３のターボ制御手段Ａｃが受けると、相当するターボ切換え信号ＶＧαを過給圧調整部８に出力し、ステップｓ３以下の制御に進む。
【００３６】
これにより、ターボ制御手段Ａｃがターボ切換え信号ＶＧαを過給圧調整部８に出力し、ブースト圧増大処理を行うことができ、供給通路ｒ１及び添加ノズル２６にコンプレッサ１３下流の吸気路Ｉからのブースト圧エアを供給することができる。
【００３７】
ステップｓ８で負荷時としてステップｓ１０に達すると、ここでは燃費算出手段Ｂ２として、圧縮エアタンク２８に加圧空気を充填するエアポンプ３５の作動に基く燃費と、エアポンプ３５の作動停止且つ過給圧調整部８を過給圧増大側へ制御、即ち、相当するターボ切換え信号ＶＧαを出力し、ブースト圧増大処理をした場合の燃費をエンジン回転数Ｎｅ、アクセル踏込量θａより予め設定されている図示しないマップにより演算する。
【００３８】
その上で、エアポンプ３５の作動に基く燃費よりも、エアポンプ３５の作動停止且つターボ切換え信号ＶＧαの出力によりブースト圧増大処理をした場合の燃費が向上すると判定されるとステップｓ９のブースト圧増大処理に、そうでないとステップｓ６に進み、圧縮エアタンク２８の加圧空気を供給通路や添加ノズル２６に流し、この回の制御を終了する。
【００３９】
このように、図１のＮＯｘ浄化装置Ｍ１は、尿素水供給装置２２の停止時にエアポンプ３５からの不要な加圧空気の供給を停止して、コンプレッサ下流の吸気路Ｉからのブースト圧エアを供給することにより、エンジン１の駆動力損失、或いはエアポンプ３５の電動機の電力消費を低減して燃費悪化を防止できる。しかも、供給通路ｒ１、添加ノズル２６内の尿素水の水分蒸発による尿素の固化を未然に防止できる。
【００４０】
更に、図１のＮＯｘ浄化装置Ｍ１はエンジン１の運転状態相当の尿素水を供給中で且つブースト圧センサ１２より検出されたブースト圧Ｐｂが所定値Ｐｂβ以上のとき（ステップｓ４のＹｅｓ側参照）、供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エアを供給する（ステップｓ７参照）。
この場合、エアポンプ３５の負荷を必要最小限に抑制でき、その耐久性を確保でき、エンジン１の駆動力損失或いはエアポンプ３５の電動機の電力消費を低減して燃費悪化を防止できる。
【００４１】
更に、図１のＮＯｘ浄化装置Ｍ１は、運転状態判定手段で無負荷判定時と判定した時（ステップｓ８参照）、エンジン１の運転状態相当の還元剤供給量がゼロを越え、且つブースト圧Ｐｂが所定値Ｐｂβ未満（ステップｓ４参照）で且つアクセルペダル踏込み量θａがゼロであると判定されたとき、ブースト圧が増大するよう（ステップｓ９参照）、即ち、相当するターボ切換え信号ＶＧαで過給圧調整部８を駆動すると共に供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エア（過給空気）を供給するように三方切換弁２９を制御する。なお、この場合、図示しないアイドルスイッチがオンで無負荷判定時と判定してもよい。
この場合、エンジン１又は電動機で駆動される圧縮エアポンプ３５を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
【００４２】
更に、図１のＮＯｘ浄化装置Ｍ１は、尿素水供給量がゼロを越え、且つブースト圧センサ１２より検出されたブースト圧Ｐｂが所定値Ｐｂβ未満で、アクセルペダル踏込み量θａがゼロ以外の時更に、燃費算出手段Ｂ２によってブースト圧増大のための制御後の燃費がエアコンプレッサ作動を継続する場合の燃費より向上すると判定された際に（ステップｓ２、ｓ４、ｓ９参照）、ターボ切換え信号ＶＧαを過給圧調整部８に出力すると共に供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エアを供給するように三方切換弁２９を制御する。
【００４３】
この場合、過給圧調整部８を過給圧増大側に制御すると共に供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エアを供給することによって、エンジン１又は電動機で駆動されるエアポンプ３５を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
更に、図１のＮＯｘ浄化装置Ｍ１は、還元剤供給検出手段Ｂ３により検出された尿素水の供給量（流量制御弁３４の開度）に応じて、供給通路ｒ１にコンプレッサ下流の吸気路Ｉからのブースト圧エア及び加圧空気の何れか一方を供給する。
【００４４】
このように、尿素水供給停止時にエアポンプ３５側からの不要な加圧空気の供給を停止して、コンプレッサ下流の吸気路Ｉからのブースト圧エアを供給することにより、エンジン１又はエアポンプ３５を作動させる電動機の電力消費を低減して燃費悪化を防止する。なお、供給通路ｒ１内の尿素水の水分蒸発による尿素の固化を未然に防止できる。
【００４５】
【発明の効果】
以上のように、本発明は、還元剤供給停止時に加圧空気供給手段からの不要な加圧空気の供給を停止して、過給機下流の吸気系から過給空気を供給することにより、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止できる。なお、還元剤が尿素水の場合には、供給通路内への尿素水の還元剤の水分蒸発による尿素の固化を未然に防止できる。
【００４６】
請求項２の発明は、排気中に還元剤添加が行われ且つ過給圧が所定値以上のときには、供給通路に過給機下流の吸気系からの過給空気を供給することによって、加圧空気供給手段の負荷を必要最小限に抑制でき、その耐久性を確保でき、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止できる。
【００４７】
請求項３の発明は、排気中に還元剤添加が行われ且つ過給圧が所定値未満で、内燃機関が無負荷運転領域にあるきには、過給圧調整部を過給圧増大側に制御すると共に供給通路に過給機下流の吸気系からの過給空気を供給することによって、内燃機関又は電動機で駆動される加圧空気供給手段を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
【００４８】
請求項４の発明は、排気中に還元剤添加が行われ且つ過給圧が所定値未満で、内燃機関が無負荷運転領域以外にあるときに、更に、燃費算出手段によって加圧空気供給手段の作動による燃費よりも加圧空気供給手段の作動停止且つ過給圧調整手段を過給圧増大側への制御による燃費が向上する際に、過給圧調整部を過給圧増大側に制御すると共に供給通路に過給機のコンプレッサ下流の吸気系からの過給空気を供給することによって、内燃機関又は電動機で駆動される加圧空気供給手段を作動させる運転域を狭くし駆動力損失を低減して燃費悪化を防止できる。
【００４９】
請求項５の発明は、還元剤供給停止時に加圧空気供給手段からの不要な加圧空気の供給を停止して、過給機下流の吸気系から過給空気を供給することにより、内燃機関の駆動力損失或いは電動機の電力消費を低減して燃費悪化を防止する。なお、還元剤が尿素水の場合には、供給通路内への尿素水の還元剤の水分蒸発による尿素の固化を未然に防止できる。
【図面の簡単な説明】
【図１】本発明の一実施形態としての内燃機関のＮＯｘ浄化装置とこれを装着するエンジンの概略構成図である。
【図２】図１のＮＯｘ浄化装置のエンジン制御ルーチンのフローチャートである。
【図３】図１のＮＯｘ浄化装置のアシストエアの切換え制御ルーチンのフローチャートである。
【符号の説明】
１　　エンジン
２　　排気系
３　　エンジンＥＣＵ
４　　排気系ＥＣＵ
６　　ターボチャージャー
２３　　ＳＣＲ触媒
２２　　尿素水供給装置
２９　　三方切換弁
３１　　ブースト圧エア管
３４　　流量調整弁
３５　　エアコンプレッサ
ｒ１　　供給通路
ｑｕ　　運転状態相当の尿素水供給量
Ａｃ　　ターボ制御手段
Ｂ０　　添加制御手段
Ｂ１　　アシストエア切換え制御手段
Ｂ２　　燃費算出手段
Ｂ３　　尿素水供給検出手段
Ｉ　　吸気路
Ｔｃａ　　触媒温度
ＶＧα　　ターボ切換え信号[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a NOx purifying device for purifying NOx in exhaust gas of an internal combustion engine, and more particularly, to an NOx of an internal combustion engine provided with a device for adding an exhaust gas reducing agent by air assist upstream of a reducing catalyst provided in an exhaust system. It relates to a purification device.
[0002]
[Prior art]
NOx in exhaust gas discharged from the internal combustion engine is purified by a NOx purification device. For example, a NOx purification device used in a diesel engine is formed by sequentially disposing a catalytic converter having a selective reduction type SCR catalyst (NOx catalyst) in an exhaust system and a urea water supply device on the upstream side thereof.
This SCR catalyst supplies urea water as a reducing agent so that NOx can be purified under an oxygen-excess atmosphere.
Here, the urea water (urea water) is hydrolyzed and thermally decomposed as in the formula (1) to release NH3.
[0003]
(NH2) 2CO + H ₂ O → 2NH ₃ + CO ₂ ... (1)
Also, NH on the SCR catalyst ₃ It is known that the denitration reaction between nitrogen and nitrogen oxides is carried out by the following equations (2) and (3).
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ 0 ... (2)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ 0 ... (3)
By the way, in the NOx purification device of the ammonia (or urea water) addition type, the addition of urea water is intermittently controlled according to the operating range of the internal combustion engine. That is, in the normal operation range, the urea water is supplied by air assist according to the operation conditions of the internal combustion engine.
[0004]
The compressed air for transporting the urea water is supplied from an air compressor driven by an internal combustion engine or another power source.
On the other hand, when the supply of urea water is unnecessary, such as during a no-load operation in which fuel is not injected, the supply of urea water is stopped.
At this time, if the compressed air for transporting the urea water continues to flow, the air compressor is operated uselessly, which may cause deterioration of the air compressor and deterioration of fuel efficiency due to the load of the air compressor.
[0005]
On the other hand, stopping the supply of the compressed air for transporting the urea water is effective in securing the durability of the air compressor and suppressing the deterioration of fuel efficiency, but the contaminants, for example, urea mixed into the air are likely to solidify, and the supply passage becomes difficult. May narrow and close.
In particular, the addition nozzle provided at the downstream end of the supply passage and opposed to the exhaust passage tends to come in contact with the high-temperature exhaust gas and easily become high in temperature. Of course, when urea water newly flows, solidification is likely to proceed.
[0006]
When the supply passage and the addition nozzle are narrowed in this way, the flow resistance during the supply of the urea water increases, the responsiveness of the urea water supply decreases, and when the urea water is closed, the supply of the urea water becomes impossible.
[0007]
[Problems to be solved by the invention]
As described above, even when the supply of urea water is stopped, operating the air compressor may cause deterioration of the air compressor or deterioration of fuel efficiency due to the load of the air compressor. Was feared.
An object of the present invention is to provide a NOx purifying device for an internal combustion engine that can prevent deterioration in durability of an air compressor and deterioration in fuel efficiency due to driving of the air compressor, based on the above-described problems.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas, and a reducing agent for supplying a reducing agent via a supply passage upstream of the NOx catalyst and communicating with the exhaust system. Supply means, pressurized air supply means driven by the internal combustion engine or an electric motor, for supplying pressurized air to the supply passage upstream of a supply portion of the reducing agent supplied from the reducing agent supply means, A supercharger that is provided upstream of the NOx catalyst and supercharges supply air introduced into the internal combustion engine; and a supercharger that flows from the intake system downstream of the supercharger to the supply passage according to an operation state of the internal combustion engine. A NOx purifying device for an internal combustion engine, comprising: control means for supplying one of supply air and pressurized air from the pressurized air supply means.
In this way, when the supply of the unnecessary pressurized air from the pressurized air supply unit is stopped when the supply of the reducing agent is stopped, and the supercharged air is supplied from the intake system downstream of the supercharger, the driving force of the internal combustion engine is reduced. Loss or power consumption of the motor can be reduced to prevent deterioration of fuel efficiency. When the reducing agent is urea water, it is possible to prevent urea from solidifying due to water evaporation of the reducing agent in the supply passage.
[0009]
According to a second aspect of the present invention, in the NOx purifying apparatus for an internal combustion engine according to the first aspect, the internal combustion engine includes a pressure sensor that detects a supercharging pressure of the intake system downstream of the supercharger, and the control unit includes: When the operating state of the internal combustion engine is an operating state in which a reducing agent is to be supplied or the supercharging pressure detected by the pressure sensor during the supply of the reducing agent is equal to or higher than a predetermined value, the supercharger downstream of the supercharger is supplied to the supply passage. It is characterized by supplying supercharged air from an intake system.
As described above, when the reducing agent is added to the exhaust gas and the supercharging pressure is equal to or higher than the predetermined value, the pressurized air supply means is supplied to the supply passage by supplying the supercharged air from the intake system downstream of the supercharger. Can be suppressed to a necessary minimum, the durability thereof can be secured, and the driving force loss of the internal combustion engine or the electric power consumption of the electric motor can be reduced to prevent deterioration of fuel efficiency.
[0010]
According to a third aspect of the present invention, in the NOx purifying apparatus for an internal combustion engine according to the second aspect, there is provided an operating state determining means for detecting an operating state of the internal combustion engine. A control unit that controls a supercharging pressure downstream of the supercharger, wherein the control unit detects that a reducing agent supply amount according to an operation state of the internal combustion engine exceeds zero and is detected by the pressure sensor. When the pressure is less than a predetermined value and the operating state determination means determines that the internal combustion engine is in the no-load operation range, the control unit controls the supercharging pressure adjusting unit so as to increase the supercharging pressure, and controls the supply passage. The supercharger is controlled so as to supply supercharged air from an intake system downstream of the supercharger.
As described above, when the reducing agent is added to the exhaust gas and the supercharging pressure is less than the predetermined value, and the internal combustion engine is in the no-load operation range, the supercharging pressure adjustment unit is controlled to the supercharging pressure increasing side, and By supplying supercharged air from the intake system downstream of the supercharger to the supply passage, the operating range for operating the pressurized air supply means driven by the internal combustion engine or the electric motor is narrowed, and the driving force loss is reduced to reduce fuel consumption. Deterioration can be prevented.
[0011]
According to a fourth aspect of the present invention, there is provided the NOx purifying apparatus for an internal combustion engine according to the third aspect, further comprising a fuel efficiency calculating means for calculating a fuel consumption of the internal combustion engine at least according to whether or not the supercharging pressure adjusting unit is adjusted. Means for reducing the supply amount of the reducing agent according to the operating state of the internal combustion engine to be greater than zero, the pressure detected by the pressure sensor to be less than a predetermined value, and the operating state determining means for determining that the internal combustion engine is in a no-load operating region. When it is determined that the pressure is other than the above, the fuel consumption calculating means further stops the operation of the pressurized air supply means and sets the supercharging pressure adjusting means on the side of increasing the supercharging pressure with respect to the fuel efficiency caused by the operation of the pressurized air supply means. When the fuel efficiency is improved by controlling the supercharger, the supercharging pressure adjusting section is controlled so that the supercharging pressure increases, and supercharging air from the intake system downstream of the supercharger is supplied to the supply passage. control And wherein the Rukoto.
As described above, when the reducing agent is added to the exhaust gas and the supercharging pressure is less than the predetermined value, and the internal combustion engine is in a region other than the no-load operation region, the fuel efficiency calculation unit further operates the pressurized air supply unit. When the operation of the pressurized air supply means is stopped more than the fuel efficiency and the fuel pressure is improved by controlling the supercharging pressure adjusting means to the supercharging pressure increasing side, the supercharging pressure adjusting unit is controlled to the supercharging pressure increasing side and supplied. By supplying supercharged air from the intake system downstream of the compressor of the supercharger to the passage, the operating range for operating the pressurized air supply means driven by the internal combustion engine or the electric motor is narrowed, and the driving force loss is reduced. Fuel economy deterioration can be prevented.
[0012]
According to a fifth aspect of the present invention, there is provided a NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas, and a reducing agent for supplying a reducing agent via a supply passage upstream of the NOx catalyst and communicating with the exhaust system. Supply means, pressurized air supply means driven by the internal combustion engine or an electric motor, for supplying pressurized air to the supply passage upstream of a supply portion of the reducing agent supplied from the reducing agent supply means, A supercharger provided upstream of the NOx catalyst for supercharging air supplied to the internal combustion engine, a reducing agent supply detecting unit for detecting whether or not a reducing agent is supplied, and a reducing agent detected by the reducing agent supply detecting unit Control means for supplying one of supercharged air from the intake system downstream of the supercharger and pressurized air from the pressurized air supply means to the supply passage in accordance with the supply amount of Characterized by
In this way, when the supply of the unnecessary pressurized air from the pressurized air supply unit is stopped when the supply of the reducing agent is stopped, and the supercharged air is supplied from the intake system downstream of the supercharger, the driving force of the internal combustion engine is reduced. Loss or power consumption of the motor is reduced to prevent deterioration of fuel efficiency. When the reducing agent is urea water, it is possible to prevent urea from solidifying due to water evaporation of the reducing agent in the supply passage.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a NOx purification device for an internal combustion engine (hereinafter simply referred to as a NOx purification device) as one embodiment of the present invention will be described with reference to FIG. The NOx purifying device M1 is mounted on an exhaust system 2 of a multi-cylinder diesel engine (hereinafter simply referred to as an engine) 1 mounted on a vehicle (not shown).
The engine 1 is controlled by an engine control device (hereinafter simply referred to as an engine ECU) 3, the NOx purifying device M1 is controlled by an exhaust gas control device (hereinafter simply referred to as an exhaust system ECU) 4, and the engine ECU 3 and the exhaust system ECU 4 The control system communication line 5 is connected to enable mutual communication.
[0014]
In FIG. 1, an engine 1 equipped with a NOx purifying device M1 includes an intake system that guides intake air to a combustion chamber (not shown), and a fuel control system that adjusts a fuel injection amount, an injection pressure, an injection timing, and the like.
A compressor 13 of a VG (Variable Geometry: Variable Stator Blade) turbocharger 6 (hereinafter simply referred to as a turbocharger 6), which is a supercharger, is interposed in the intake path I, and a rotary shaft 10 is interposed in the exhaust path E. The turbocharger 6 is connected to a turbine 7.
[0015]
Here, the VG turbocharger 6 has a supercharging pressure adjusting unit for adjusting the supercharging pressure downstream of the supercharger. The supercharging pressure adjusting unit is provided with a plurality of rectifying pieces (not shown) arranged on the outer peripheral portion of the turbine 7 and changes the flow rate of the exhaust gas flowing into the turbine 7 by switching the inclination of the rectifying pieces to change the supercharging pressure of the turbine 7. A boost pressure adjusting means (hereinafter, referred to as a boost pressure adjusting section 8) which is a rectifying piece actuator for varying the supply work is provided. The boost pressure adjusting section 8 is connected to the engine ECU 3 via a drive circuit 9. ing.
An intercooler 11 is provided downstream of the compressor 13 in the intake passage I, and performs intake cooling to improve the volumetric efficiency of intake air of the engine 1 and increase output. In addition, a boost pressure sensor 12 as a pressure sensor that outputs a boost pressure Pb to the exhaust system ECU 4 is provided in an intake path I between the compressor 13 and the intercooler 11.
[0016]
The engine ECU 3 includes a fuel injection amount setting unit Aa, a fuel injection timing setting unit Ab, and a turbo control unit Ac for setting a fuel amount and an injection timing so as to obtain a required output.
The input side of the engine ECU 3 is connected to various sensors such as an accelerator pedal depression amount sensor 14 for detecting an accelerator pedal depression amount (accelerator depression amount) θa, a crank angle sensor 15 for calculating an engine speed Ne, and the like. On the side, fuel injection for driving an on-off valve 18 for opening and closing a fuel passage connecting between a common rail 16 for storing high-pressure fuel supplied by a high-pressure fuel pump (not shown) and a fuel injection nozzle 17 provided for each cylinder. A driver 19 and various devices such as a metering unit for controlling a fuel supply amount of a high-pressure pump (not shown) are connected.
[0017]
Thereby, for example, the calculation is performed according to the engine speed Ne calculated based on the crank signal θc detected by the crank angle sensor 15 and the accelerator pedal depression amount (accelerator depression amount) θa detected by the accelerator depression amount sensor 14. Based on the requested fuel injection Q, the valve opening timing and the valve opening period of the on-off valve are variably adjusted by the fuel injection driver. Further, the metering section of the high-pressure fuel pump performs feedback control according to the fuel pressure in the common rail 16. Is done.
Further, the turbo control means Ac of the engine ECU 3 has a function of adjusting the boost pressure (supercharging pressure) Pb using the supercharging pressure adjusting unit 8. The turbo control unit Ac sets the turbo switching signal VGα using a map (not shown) according to the accelerator pedal depression amount θa and the engine speed Ne. In this map, a turbo switching signal VGα corresponding to each stage is set according to the accelerator pedal depression amount θa and the engine speed Ne so as to sequentially switch the inclination of the rectifying pieces.
[0018]
When a boost pressure increase command S1 described later is input from the exhaust system ECU 4 to the engine ECU 3, the turbo control means Ac of the engine ECU 3 outputs a turbo switching signal VGα to the drive circuit, and can execute boost pressure increase processing.
The NOx purifying device M1 shown in FIG. 1 is a urea water supply device as a reducing agent supply means for supplying urea water to the SCR catalyst 23, which is a NOx catalyst, mounted in the middle of the exhaust pipe 21 and an exhaust passage E upstream thereof by air assist. 22 and an exhaust system ECU 4 serving as control means.
[0019]
The SCR catalyst 23 is housed in a NOx catalytic converter 24 in the exhaust pipe 21 forming the exhaust path E. The NOx catalytic converter 24 includes a casing 241, and includes a ceramic catalyst carrier having a honeycomb structure (overlapping the block display of the SCR catalyst 23) in the casing, and supports the catalyst carrier via a sealing material 242 without displacement. As the catalytic metal for the carrier to function as the SCR catalyst 23, for example, vanadium oxide (V ₂ O ₅ ) Is carried.
The SCR catalyst 23 uses ammonia (NH ₃ ) Can be used as a reducing agent to selectively reduce NOx in exhaust gas. That is, as shown in the above formula (1), the urea water is hydrolyzed to produce ammonia, which causes a denitration reaction with nitrogen oxides in the SCR catalyst 23. The SCR catalyst 23 is provided with a catalyst temperature sensor 25 that outputs the temperature Tca of the catalyst to the exhaust system ECU 4.
[0020]
A urea water supply device 22 mounted in the middle of the exhaust pipe 21 has an addition nozzle 26 for spraying urea water toward the upstream opening side of the NOx catalytic converter 24, and an injection pipe connected to the addition nozzle 26 to form a supply passage r1. 27, a compressed air tank 28 at the upstream end of the injection pipe 27, a three-way switching valve 29 in the middle of the injection pipe 27, and a boost pressure that can communicate with the supply passage r1 via the three-way switching valve 29 and the intake path I downstream of the compressor 13. Air pipe 31, urea water pipe 32 opening in supply passage r1 downstream of three-way switching valve 29, urea water tank 33 for supplying urea water to urea water pipe 32, and flow rate of urea water in urea water pipe 32 And a flow control valve 34 for adjusting the pressure, and an exhaust system ECU 4 serving as a control means for controlling the flow rate.
[0021]
The compressed air tank 28 is supplied with compressed air at an appropriate time from an air pump 35 driven by an electric motor (not shown), and constantly holds air at a constant pressure. Here, the compressed air tank 28 and the air pump 35 constitute pressurized air supply means for supplying pressurized air to the supply passage r1. The air pump 35, which is a pressurized air supply unit, is connected to a drive circuit 36. The drive circuit 36 drives the air pump 35 with a drive output Dp when receiving a drive command Pd from the exhaust system ECU 4.
The boost pressure air pipe 31 is formed of a metal pipe, and one end thereof is connected to the intake path I on the downstream side of the compressor 13 and the other end is connected to the inflow port p1 of the three-way switching valve 29.
[0022]
Here, the three-way switching valve 29 is provided upstream of the supply portion of the reducing agent in the supply passage r1 and downstream of the compressed air tank 28 (pressurized air supply means). In addition, the three-way switching valve 29 constitutes switching means capable of communicating either the intake passage I (intake system) downstream of the compressor or the compressed air tank 28 with the supply passage r1.
The three-way switching valve 29 is an electromagnetic valve and is connected to the exhaust system ECU 4. One inflow port p2 of the three-way switching valve 29 is connected to the compressed air tank 28 via a supply passage r1, and the other inflow port p1 is connected to an intake passage I downstream of the compressor via a boost pressure air pipe 31 to be discharged. The port p3 communicates with the addition nozzle 26.
[0023]
When the switching output Dv is off, the three-way switching valve 29 communicates the compressed air tank 28 with the addition nozzle 26 via the supply passage r1. When the switching output Dv is on, the three-way switching valve 29 communicates with the intake passage I downstream of the compressor via the supply passage r1 and the boost pressure air pipe 31. A switching operation can be performed to communicate the nozzle 26.
[0024]
A nozzle temperature sensor 37 that outputs a temperature Tn signal of the nozzle itself is attached to the addition nozzle 26, and a detection signal Tn is output to the exhaust system ECU 4. The exhaust system ECU 4 performs a process of flowing cooling air to the addition nozzle 26 when the addition nozzle 26 is overheated, as described later.
The urea water tank 33 stores a solution in which urea is dissolved in water to form an aqueous solution of a certain concentration, and is replenished in a timely manner.
[0025]
The exhaust system ECU 4 has a number of ports in its input / output circuit. The exhaust temperature ECU 4 receives the temperature Tn signal of the addition nozzle 26 from the nozzle temperature sensor 37, the boost pressure Pb signal from the boost pressure sensor 12, and the catalyst temperature Tca from the catalyst temperature sensor 25. It can be input and functions as addition control means B0, assist air switching control means B1, fuel efficiency calculation means B2, and urea water supply detection means B3, and provides control signals to the air pump 35, the three-way switching valve 29, the flow control valve 34, and the engine ECU 3. Is output.
[0026]
The addition control means (control means) B0 sets the supply amount of urea water using a map (not shown) based on the catalyst temperature Tca or a parameter (for example, exhaust temperature) correlated with the catalyst temperature, and sets the set urea water supply amount. The opening degree of the flow control valve 34 is controlled so as to be qu.
The assist air switching control means (control means) B1 supplies boost air (supercharged air) from the intake passage I downstream of the compressor or pressurized air from the air pump 35 to the supply passage r1 in accordance with the urea water supply amount qu. The three-way switching valve 29 is controlled so that one of them is supplied as air for assisting addition.
[0027]
In place of the three-way switching valve 29, this is eliminated and an on-off valve b1 (shown by a two-dot chain line in FIG. 1) is provided immediately below the compressed air tank 28 in the middle of the boost pressure air pipe 31 in a check valve b2 (FIG. 1). May be configured to supply either one of boost pressure air (supercharged air) and pressurized air from the air pump 35 as addition assist air. The valve b2 may be replaced with an open / close valve (not shown). In these cases, the same function as the three-way switching valve 29 can be obtained.
The fuel efficiency calculation means B2 obtains the fuel consumption δ of the engine 1 at least according to the presence or absence of the adjustment of the supercharging pressure adjusting unit 8. That is, the fuel efficiency calculating means B2 outputs the fuel consumption amount δ corresponding to the engine speed Ne when the air pump 35 is operated, the output of the turbo switching signal VGα for stopping the operation of the air pump 35 and increasing the boost pressure in the boost pressure adjusting unit 8. A map (not shown) is provided for deriving a fuel consumption δ corresponding to the engine speed Ne at the time (the boost pressure increasing side).
[0028]
The urea water supply detecting means B3 detects the presence or absence of supply of urea water, that is, determines the presence or absence of supply in accordance with the opening degree (equivalent to the urea water supply amount qu) signal of the flow rate control valve 34.
Next, each control process of the engine ECU 3 and the exhaust system ECU 4 of FIG. 1 will be described with reference to the control routines of FIGS.
[0029]
Here, when the engine key of the engine 1 equipped with the NOx purification device is turned on, the engine ECU 3 is driven at the same time, and reaches step a1 of the engine control routine. Here, it is confirmed whether or not a self-check result of a plurality of control systems, for example, related devices and sensors appropriately executed in the fuel control system is normal, and if the result is normal (OK), the accelerator depression amount is determined. Data of related sensors such as θa and engine speed Ne are taken in. Next, in step a2, the fuel injection amount setting unit Aa and the fuel injection timing setting unit Ab described above operate information (accelerator depression amount θa, engine speed Ne, air-fuel ratio A / F, water temperature) according to each input value of the related sensor. Tw) corresponding fuel injection amount and fuel injection timing are derived, and the corresponding output D (Gf) is output to the fuel injection driver 19, the metering unit, and the like. As a result, an output corresponding to the fuel injection amount and the fuel injection timing is sent to each on-off valve 18, and each fuel injection nozzle 17 executes an injection operation.
[0030]
At step a3, it is determined whether the boost pressure increase command S1 has been input. If no, the process proceeds to step a4.
When the boost pressure increase command S1 is input from the exhaust system ECU 4 and the process reaches step a5, the corresponding turbo switching signal VGα is output to the drive means 9 of the supercharging pressure adjusting unit 8 and the process proceeds to step a4. As a result, the boost pressure adjusting unit 8 can perform boost pressure increasing processing, and supplies boost pressure air from the intake passage I downstream of the compressor 13 to the supply passage r1 and the addition nozzle 26.
At step a4, other engine control is executed, and the process returns to step a2.
[0031]
On the other hand, the exhaust system ECU 4 repeats the NOx purification process control of the exhaust system main routine (not shown) at every predetermined control cycle, and adds a urea water supply amount qu according to the engine operating conditions and the catalyst temperature Tca. 34, and the assist air switching control routine shown in FIG.
When the process reaches step s1 of the assist air switching control routine, the relevant sensor outputs such as the boost pressure Pb and the addition nozzle 26 temperature Tn are taken in here. In step s2, it is determined whether or not the flow control valve 34 is fully closed. If the flow rate is not added, the flow proceeds to step s3. If the flow rate is added, the flow proceeds to step s4.
[0032]
At the time of non-addition, for example, at the time of engine braking, and reaches step s3, it is determined here whether or not the addition nozzle 26 temperature Tn is equal to or higher than the overheat determination value Tn1. In step s5, it is determined whether or not the supply of the compressed air of the load is necessary. That is, in step s5, it is determined whether or not the elapsed time tn after the flow control valve 34 is fully closed has not reached the predetermined time tp. If not, the process proceeds to step s6, and if it has elapsed, the process proceeds to step s7.
[0033]
In step s7, the case where no addition is performed, the addition nozzle 26 temperature Tn is low, and the time tp after the urea water supply is stopped has elapsed, the three-way switching valve 29 is turned on, and the addition to the intake path I downstream of the compressor 13 and the addition is performed. The nozzle 26 is switched to communicate, and boost pressure air is supplied to the supply passage r1 and the addition nozzle 26 in place of the pressurized air in the compressed air tank 28, and this control is terminated.
In step s6, the case where the addition nozzle 26 temperature Tn is high or before the time tp has elapsed, the three-way switching valve 29 is turned off, and the compressed air tank 28 is switched to communicate with the addition nozzle 26, and the compressed air in the compressed air tank 28 is discharged. The urea is supplied to the supply passage r1 and the addition nozzle 26, and the purging of the residual urea in the urea water supply passage is continued, and this control is terminated.
[0034]
When it is determined in step s2 that addition is being performed and the process proceeds to step s4, it is determined here whether the boost pressure Pb is equal to or higher than the determination value pressure Pbβ. Then, the use of pressurized air on the compressed air tank 28 side is suppressed, and the process proceeds to step s3 in order to improve fuel efficiency. If the boost pressure Pb has not reached the determination value pressure Pbβ, the process proceeds to step s8.
In step s8, it is determined whether or not the vehicle is in the no-load operation range, and the process proceeds to step s9 with no load and proceeds to step s10 with the load.
[0035]
In step s9, since the boost pressure Pb is in the low operating range, when the boost control command Ac of the engine ECU 3 receives the boost pressure increase command, the corresponding turbo switching signal VGα is output to the supercharging pressure adjusting unit 8, and the process proceeds to step s3. Proceed to the following control.
[0036]
As a result, the turbo control means Ac outputs the turbo switching signal VGα to the supercharging pressure adjusting section 8 so that the boost pressure increasing process can be performed, and the supply passage r1 and the addition nozzle 26 are supplied from the intake passage I downstream of the compressor 13 to the supply passage r1 and the addition nozzle 26. Boost pressure air can be supplied.
[0037]
In step s8, when the load reaches step s10, the fuel consumption calculating means B2 determines the fuel consumption based on the operation of the air pump 35 for filling the compressed air tank 28 with the pressurized air, the operation stop of the air pump 35, and the supercharging pressure adjusting unit. 8 is increased to the supercharging pressure side, that is, a corresponding turbo switching signal VGα is output, and the fuel efficiency in the case of performing the boost pressure increasing process is a map (not shown) in which the fuel efficiency is preset from the engine speed Ne and the accelerator pedal depression amount θa. Is calculated by
[0038]
Then, if it is determined that the fuel efficiency in the case where the boost operation is performed by stopping the operation of the air pump 35 and the output of the turbo switching signal VGα is higher than the fuel efficiency based on the operation of the air pump 35, the boost pressure increase process in step s9. Otherwise, the process proceeds to step s6, in which the pressurized air in the compressed air tank 28 is caused to flow through the supply passage and the addition nozzle 26, and this control is terminated.
[0039]
As described above, the NOx purification device M1 of FIG. 1 stops the supply of unnecessary pressurized air from the air pump 35 when the urea water supply device 22 stops, and supplies the boost pressure air from the intake passage I downstream of the compressor. By doing so, it is possible to reduce the driving force loss of the engine 1 or the power consumption of the electric motor of the air pump 35 to prevent deterioration of fuel efficiency. Moreover, solidification of urea due to evaporation of urea water in the supply passage r1 and the addition nozzle 26 can be prevented.
[0040]
Further, when the NOx purifying device M1 in FIG. 1 is supplying urea water corresponding to the operating state of the engine 1 and the boost pressure Pb detected by the boost pressure sensor 12 is equal to or higher than a predetermined value Pbβ (see Yes in step s4). Then, boost pressure air is supplied to the supply passage r1 from the intake passage I downstream of the compressor (see step s7).
In this case, the load on the air pump 35 can be suppressed to a necessary minimum, the durability thereof can be ensured, and the driving force loss of the engine 1 or the power consumption of the electric motor of the air pump 35 can be reduced to prevent the fuel efficiency from deteriorating.
[0041]
Further, in the NOx purifying device M1 of FIG. 1, when the operating state determining means determines that there is no load determination (see step s8), the supply amount of the reducing agent corresponding to the operating state of the engine 1 exceeds zero and the boost pressure Pb Is smaller than the predetermined value Pbβ (see step s4) and the accelerator pedal depression amount θa is determined to be zero, the boost pressure is increased (see step s9), that is, the supercharging is performed by the corresponding turbo switching signal VGα. The three-way switching valve 29 is controlled so as to drive the pressure adjusting unit 8 and to supply boost pressure air (supercharged air) from the intake passage I downstream of the compressor to the supply passage r1. In this case, it may be determined that the idle switch (not shown) is turned on and no load is determined.
In this case, the operating range in which the compressed air pump 35 driven by the engine 1 or the electric motor is operated is narrowed, the driving force loss is reduced, and deterioration in fuel efficiency can be prevented.
[0042]
Further, the NOx purification device M1 of FIG. 1 further operates when the urea water supply amount exceeds zero, the boost pressure Pb detected by the boost pressure sensor 12 is less than the predetermined value Pbβ, and the accelerator pedal depression amount θa is other than zero. When the fuel efficiency calculating means B2 determines that the fuel efficiency after the control for increasing the boost pressure is higher than the fuel efficiency when the air compressor continues to operate (see steps s2, s4, and s9), the turbo switching signal VGα is exceeded. The three-way switching valve 29 is controlled so as to output the boost pressure air from the intake passage I downstream of the compressor to the supply passage r1 while outputting to the supply pressure adjusting unit 8.
[0043]
In this case, by controlling the boost pressure adjusting section 8 to the boost pressure increasing side and supplying boost pressure air from the intake passage I downstream of the compressor to the supply passage r1, the air pump 35 driven by the engine 1 or the electric motor is provided. The operating range in which is operated is narrowed, the driving force loss is reduced, and deterioration of fuel efficiency can be prevented.
Further, the NOx purifying device M1 of FIG. 1 supplies the supply passage r1 from the intake passage I downstream of the compressor to the supply passage r1 in accordance with the supply amount of urea water (the opening degree of the flow control valve 34) detected by the reducing agent supply detection means B3. Of the boost pressure air and the pressurized air.
[0044]
As described above, when the supply of the urea water is stopped, the supply of the unnecessary pressurized air from the air pump 35 is stopped, and the boost pressure air is supplied from the intake passage I downstream of the compressor, thereby operating the engine 1 or the air pump 35. The power consumption of the electric motor to be reduced is reduced to prevent deterioration of fuel efficiency. Note that solidification of urea due to evaporation of urea water in the supply passage r1 can be prevented.
[0045]
【The invention's effect】
As described above, the present invention stops the supply of unnecessary pressurized air from the pressurized air supply unit when the supply of the reducing agent is stopped, and supplies the supercharged air from the intake system downstream of the supercharger, The driving force loss of the internal combustion engine or the power consumption of the electric motor can be reduced to prevent the fuel consumption from deteriorating. When the reducing agent is urea water, it is possible to prevent urea from solidifying due to water evaporation of the reducing agent in the supply passage.
[0046]
According to a second aspect of the present invention, when the reducing agent is added to the exhaust gas and the supercharging pressure is equal to or higher than a predetermined value, the pressurized air is supplied to the supply passage from the intake system downstream of the supercharger to increase the pressure. The load on the air supply means can be suppressed to a necessary minimum, the durability thereof can be ensured, and the driving force loss of the internal combustion engine or the power consumption of the electric motor can be reduced to prevent the deterioration of fuel efficiency.
[0047]
According to a third aspect of the present invention, when the reducing agent is added to the exhaust gas and the supercharging pressure is less than a predetermined value, and the internal combustion engine is in the no-load operation range, the supercharging pressure adjusting unit is moved to the supercharging pressure increasing side. By controlling and supplying supercharged air from the intake system downstream of the supercharger to the supply passage, the operating range for operating the pressurized air supply means driven by the internal combustion engine or the electric motor is narrowed, and the driving force loss is reduced. As a result, deterioration of fuel efficiency can be prevented.
[0048]
According to a fourth aspect of the present invention, when the reducing agent is added to the exhaust gas, the supercharging pressure is less than a predetermined value, and the internal combustion engine is outside the no-load operation range, the fuel efficiency calculating means further includes a pressurized air supply means. When the operation of the pressurized air supply means is stopped and the supercharging pressure adjustment means is controlled to increase the supercharging pressure, the supercharging pressure adjustment unit is controlled to increase the supercharging pressure rather than the fuel economy caused by the operation of In addition, by supplying supercharged air from the intake system downstream of the compressor of the supercharger to the supply passage, the operating range for operating the pressurized air supply means driven by the internal combustion engine or the electric motor is narrowed, and the driving force loss is reduced. The fuel consumption can be reduced to prevent deterioration of fuel efficiency.
[0049]
According to a fifth aspect of the present invention, an internal combustion engine is provided in which the supply of unnecessary pressurized air from the pressurized air supply means is stopped when the supply of the reducing agent is stopped, and the supercharged air is supplied from an intake system downstream of the supercharger. The driving power loss or the electric power consumption of the electric motor is reduced to prevent the fuel efficiency from deteriorating. When the reducing agent is urea water, it is possible to prevent urea from solidifying due to water evaporation of the reducing agent in the supply passage.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a NOx purifying device for an internal combustion engine as an embodiment of the present invention and an engine equipped with the NOx purifying device.
FIG. 2 is a flowchart of an engine control routine of the NOx purification device of FIG.
FIG. 3 is a flowchart of an assist air switching control routine of the NOx purification device of FIG. 1;
[Explanation of symbols]
1 engine
2 Exhaust system
3 Engine ECU
4 Exhaust ECU
6 Turbocharger
23 SCR catalyst
22 Urea water supply device
29 Three-way switching valve
31 boost pressure air pipe
34 Flow control valve
35 air compressor
r1 supply passage
qu Amount of urea water supply equivalent to the operating state
Ac turbo control means
B0 addition control means
B1 Assist air switching control means
B2 Fuel consumption calculation means
B3 Urea water supply detection means
I intake path
Tca catalyst temperature
VGα turbo switching signal

Claims

A NOx catalyst provided in an exhaust system of the internal combustion engine for selectively reducing NOx in exhaust gas;
Reducing agent supply means for supplying a reducing agent via a supply passage communicating with the exhaust system upstream of the NOx catalyst;
Pressurized air supply means driven by the internal combustion engine or the electric motor and supplying pressurized air to the supply passage upstream of a supply portion of the reducing agent supplied from the reducing agent supply means,
A supercharger provided upstream of the NOx catalyst in the exhaust system to supercharge supply air introduced into the internal combustion engine;
Control means for supplying one of supercharged air from the intake system downstream of the supercharger and pressurized air from the pressurized air supply means to the supply passage, depending on an operation state of the internal combustion engine;
A NOx purification device for an internal combustion engine, comprising:

The NOx purification device for an internal combustion engine according to claim 1,
The internal combustion engine includes a pressure sensor that detects a supercharging pressure of the intake system downstream of the supercharger,
The control unit is configured to supercharge the supply passage when the operation state of the internal combustion engine is an operation state in which a reducing agent is to be supplied or a supercharging pressure detected by the pressure sensor during the supply of the reducing agent is equal to or higher than a predetermined value. A NOx purifying device for an internal combustion engine, which supplies supercharged air from the intake system downstream of the engine.

The NOx purification device for an internal combustion engine according to claim 2,
An operating state determination unit that detects an operating state of the internal combustion engine is further provided.The supercharger further includes a supercharging pressure adjustment unit that adjusts a supercharging pressure downstream of the supercharger in the intake system.
The control means may be configured such that the supply amount of the reducing agent according to the operation state of the internal combustion engine exceeds zero, the pressure detected by the pressure sensor is less than a predetermined value, and the operation state determination means determines that the internal combustion engine has no load. When it is determined that the supercharging pressure is in the operating range, the supercharging pressure adjusting unit is controlled so as to increase the supercharging pressure, and the supercharged air is supplied to the supply passage from the intake system downstream of the supercharger. A NOx purifying device for an internal combustion engine.

The NOx purification device for an internal combustion engine according to claim 3,
Fuel consumption calculating means for calculating the fuel consumption of the internal combustion engine according to at least the presence or absence of the adjustment of the supercharging pressure adjusting unit,
The control means is configured such that the supply amount of the reducing agent according to the operation state of the internal combustion engine exceeds zero, the pressure detected by the pressure sensor is less than a predetermined value, and the internal combustion engine is not loaded by the operation state determination means. When it is determined that the fuel pressure is outside the operating range, the fuel efficiency calculating means further stops the operation of the pressurized air supply means and sets the supercharging pressure adjusting means in comparison with the fuel efficiency caused by the operation of the pressurized air supplying means. When the fuel efficiency is improved by the control to the increasing side, the supercharging pressure adjusting unit is controlled so that the supercharging pressure increases, and the supercharging air is supplied to the supply passage from the intake system downstream of the supercharger. A NOx purification device for an internal combustion engine, characterized in that the control is performed.

A NOx catalyst provided in an exhaust system of the internal combustion engine for selectively reducing NOx in exhaust gas;
Reducing agent supply means for supplying a reducing agent via a supply passage communicating with the exhaust system upstream of the NOx catalyst;
Pressurized air supply means driven by the internal combustion engine or the electric motor and supplying pressurized air to the supply passage upstream of a supply portion of the reducing agent supplied from the reducing agent supply means,
A supercharger provided upstream of the NOx catalyst in the exhaust system to supercharge supply air introduced into the internal combustion engine;
Reducing agent supply detecting means for detecting whether or not the reducing agent is supplied,
Depending on the supply amount of the reducing agent detected by the reducing agent supply detecting unit, the supply passage is configured to supply supercharged air from the intake system downstream of the supercharger and pressurized air from the pressurized air supply unit. Control means for supplying one of them,
A NOx purification device for an internal combustion engine, comprising: