JP3943044B2

JP3943044B2 - Engine exhaust purification system

Info

Publication number: JP3943044B2
Application number: JP2003089579A
Authority: JP
Inventors: 公信平田
Original assignee: UD Trucks Corp
Current assignee: UD Trucks Corp
Priority date: 2003-03-28
Filing date: 2003-03-28
Publication date: 2007-07-11
Anticipated expiration: 2023-03-28
Also published as: JP2004293489A

Description

【０００１】
【発明の属する技術分野】
本発明は、排気中に還元剤を添加して、窒素酸化物還元触媒にて窒素酸化物を還元除去するエンジンの排気浄化装置において、特に、還元剤の添加量を最適に制御する技術に関する。
【０００２】
【従来の技術】
ディーゼルエンジンやリーンバーンガソリンエンジン等の機関から排出される排気中に含まれる窒素酸化物（ＮＯ_x）を還元除去する排気浄化装置として、特開２００２−２５０２２０号公報(特許文献１)に開示されるような排気浄化装置が提案されている。かかる排気浄化装置は、酸素過剰雰囲気で窒素酸化物を無害な窒素（Ｎ₂）、酸素（Ｏ₂）に還元除去すべく、エンジンの排気通路に窒素酸化物還元触媒が介装されている。また、窒素酸化物還元触媒における窒素酸化物の浄化効率を高めるべく、尿素（（ＮＨ₂）₂ＣＯ）等の還元剤を搭載し、窒素酸化物還元触媒の上流側の排気通路に還元剤を添加する構成が採用されている。そして、排気中の窒素酸化物が充分に還元除去されるように、窒素酸化物の排出量に見合った量の還元剤を添加するようにしている。
【０００３】
【特許文献１】
特開２００２−２５０２２０号公報
【０００４】
【発明が解決しようとする課題】
しかしながら、添加された還元剤は、その全てが窒素酸化物と反応するのではなく、反応しきれなかった還元剤の一部は窒素酸化物還元触媒に吸着されてしまう。そして、窒素酸化物還元触媒に吸着された還元剤の量が所定量を超えると、過渡運転状況下において、応答遅れによる還元剤の過剰な添加や、触媒温度の変化による還元剤の吸着能力の変化により、窒素酸化物還元触媒に吸着しきれなくなった還元剤の一部が窒素酸化物還元触媒の下流に排出されてしまう。
【０００５】
なお、この還元剤は、アンモニア（ＮＨ₃）や、炭化水素（ＨＣ）であるので、大気中に排出されることは好ましくない。
そこで、本発明は以上のような従来の問題点に鑑み、窒素酸化物還元触媒に吸着されている還元剤の吸着量を演算により推定し、これに応じて還元剤の添加量を制御することによって、窒素酸化物還元触媒に吸着しきれなくなった還元剤が窒素酸化物還元触媒の下流に排出されないようにするエンジンの排気浄化装置を提供することを目的とする。
【０００６】
【課題を解決するための手段】
このため、請求項１記載の発明は、エンジンの排気通路に介装され、還元剤を使用して排気中の窒素酸化物を還元除去する窒素酸化物還元触媒と、前記還元剤を貯蔵する還元剤貯蔵手段と、前記還元剤貯蔵手段に貯蔵された還元剤を前記窒素酸化物還元触媒の上流側に添加する還元剤添加手段と、前記エンジンの運転状況に応じた還元剤の目標添加量を演算する目標添加量演算手段と、前記窒素酸化物還元触媒の上流側に実際に添加された還元剤の実添加量から前記目標添加量演算手段により演算された還元剤の目標添加量を減算した差を順次積算して、前記窒素酸化物還元触媒に吸着されている還元剤の推定吸着量を演算する推定吸着量演算手段と、前記推定吸着量演算手段により演算された還元剤の推定吸着量が上限閾値未満かつ下限閾値以上となるように、前記還元剤添加手段による還元剤の添加量を制御する制御手段と、車両の走行距離を積算した積算走行距離が第１の所定値に達する毎、又は、エンジンの運転時間を積算した積算運転時間が第２の所定値に達する毎に、前記還元剤の推定吸着量を前記窒素酸化物還元触媒に吸着可能な限界吸着量に設定するリセット手段と、を含んでエンジンの排気浄化装置が構成されることを特徴とする。
【０００７】
かかる構成によれば、還元剤の実添加量からエンジンの運転状況に応じた還元剤の目標添加量を減算した差を順次積算して、窒素酸化物還元触媒に吸着されている還元剤の推定吸着量が求められる。そして、この推定吸着量が上限閾値未満かつ下限閾値以上となるように、還元剤の添加量が制御されるので、還元剤の吸着量に見合った適正な量の還元剤が窒素酸化物還元触媒の上流側に添加される。
このとき、車両の走行距離を積算した積算走行距離が第１の所定値に達する毎、又は、エンジンの運転時間を積算した積算運転時間が第２の所定値に達する毎に、還元剤の推定吸着量が限界吸着量に設定されるので、還元剤の添加が停止或いは減量され、窒素酸化物還元触媒に吸着された還元剤が強制的に消費される。そして、還元剤の推定吸着量が下限閾値に達したときには、窒素酸化物還元触媒に吸着されている還元剤の吸着量は下限閾値以下になる。これにより、窒素酸化物還元触媒に吸着されている還元剤の吸着量と還元剤の推定吸着量とが相違しても、所定の積算走行距離又は積算運転時間毎に、両者の差が下限閾値以下になる。
【０００８】
請求項２記載の発明は、吸気流量とエンジン回転速度と燃料供給量とに基づいて、窒素酸化物の排出量を演算する排出量演算手段と、前記窒素酸化物還元触媒の温度に基づいて、窒素酸化物還元触媒における窒素酸化物の浄化率を演算する浄化率演算手段と、を備え、前記目標添加量演算手段は、前記窒素酸化物の排出量及び浄化率に基づいて、前記還元剤の目標添加量を演算することを特徴とする。
【０００９】
かかる構成によれば、吸気流量とエンジン回転速度と燃料供給量とに基づいて演算された窒素酸化物の排出量と、窒素酸化物還元触媒の温度に基づいて演算された窒素酸化物の浄化率と、により、還元剤の目標添加量が演算されるので、エンジンの運転状況に応じた還元剤の目標添加量が求められる。
【００１０】
請求項３記載の発明は、前記窒素酸化物還元触媒の触媒温度に基づいて、前記上限閾値及び下限閾値を夫々設定する閾値設定手段を備えたことを特徴とする。
【００１１】
かかる構成によれば、窒素酸化物還元触媒の触媒温度に応じて上限閾値及び下限閾値が夫々設定されるため、触媒温度の変化による還元剤の吸着能力の変化に対応可能となる。
【００１２】
請求項４記載の発明は、前記窒素酸化物還元触媒の触媒温度に基づいて、前記限界吸着量を設定する限界吸着量設定手段を備えたことを特徴とする。
【００１３】
かかる構成によれば、窒素酸化物還元触媒の触媒温度に応じて限界吸着量が設定されるため、触媒温度の変化による還元剤の吸着能力の変化に対応可能となる。
【００１４】
請求項５記載の発明は、前記推定吸着量演算手段は、前記推定吸着量を０〜限界吸着量の範囲内で演算することを特徴とする。
【００１５】
かかる構成によれば、推定吸着量は、０〜限界吸着量の範囲内で演算される。
【００１６】
【発明の実施の形態】
以下、添付された図面を参照して本発明を詳述する。
図１は、本発明に係るエンジンの排気浄化装置の構成を示すブロック図である。
【００１７】
ディーゼルエンジンやリーンバーンエンジン等のように、酸素が過剰な条件で運転されるエンジン１の排気通路２には、窒素酸化物を還元除去する窒素酸化物還元触媒３が介装されている。
【００１８】
窒素酸化物還元触媒３は、セラミックのコーディライトやＦｅ−Ｃｒ−Ａｌ系の耐熱鋼からなるハニカム形状の横断面を有するモノリスタイプの触媒担体に、例えば、ゼオライト系の活性成分が担持された構成をなす。そして、触媒担体に担持された活性成分は、アンモニア、炭化水素等の還元剤の供給を受けて活性化し、窒素酸化物を効果的に無害物質に転化させる。
【００１９】
更に、還元剤を貯蔵する還元剤タンク４(還元剤貯蔵手段)が設けられている。そして、還元剤タンク４内に貯蔵された還元剤は、還元剤添加装置５(還元剤添加手段)にて、ポンプ６により圧縮された空気と混合し、窒素酸化物還元触媒３の上流側の排気通路２内に添加される。
【００２０】
ところで、エンジン１には、マイクロコンピュータを内蔵し、運転制御を行うエンジンコントローラ７が設けられている。このエンジンコントローラ７からは、吸気流量及びエンジン回転速度、燃料供給量及び走行距離の信号が出力可能になっている。更に、窒素酸化物還元触媒３の触媒温度を直接的又は間接的に検出する触媒温度センサ８が設けられている。また、還元剤添加装置５には、実際に排気通路２に添加された還元剤の実添加量を検出する添加流量センサ９が設けられている。なお、この還元剤の実添加量は還元剤添加装置５及びポンプ６の制御値より演算から求めてもよい。
【００２１】
排気浄化装置には、マイクロコンピュータを内蔵し、ソフトウエア的に目標添加量演算手段、推定吸着量演算手段、制御手段、リセット手段、排出量演算手段、浄化率演算手段、閾値設定手段及び限界吸着量設定手段を実現する還元剤添加コントローラ１０が設けられている。
【００２２】
還元剤添加コントローラ１０は、エンジンコントローラ７から入力した吸気流量、エンジン回転速度、燃料供給量及び走行距離と、触媒温度センサ８により検出された触媒温度と、添加流量センサ９により検出された実添加量と、に基づいて、ポンプ６及び還元剤添加装置５を制御する。
【００２３】
ここで、図２を用いて、還元剤添加コントローラ１０における制御方法を詳述する。まず、還元剤添加コントローラ１０は、キースイッチ等の電源スイッチＯＮにて電源が供給され、制御を開始する。始めにステップ１（図ではＳ１と表記する、以下同様）では、エンジンコントローラ７から出力された吸気流量と、エンジン回転速度と、燃料供給量と、に基づいて窒素酸化物の排出量を演算する。この演算は、あらかじめ還元剤添加コントローラ１０に、吸気流量、エンジン回転速度及び燃料供給量に対応した窒素酸化物の排出量を表したマップを記憶させておき、このマップから、吸気流量、エンジン回転速度及び燃料供給量に対応した窒素酸化物の排出量を読み出すことによって行われる。なお、ステップ１の処理は排出量演算手段に該当する。
【００２４】
ステップ２では、触媒温度センサ８により検出された触媒温度から、窒素酸化物還元触媒３における窒素酸化物の浄化率を演算する。この演算は、あらかじめ還元剤添加コントローラ１０に、窒素酸化物還元触媒３の触媒温度に対応した窒素酸化物の浄化率を表したマップを記憶させておき、このマップから触媒温度に対応した窒素酸化物の浄化率を読み出すことによって行われる。なお、ステップ２の処理は浄化率演算手段に該当する。
【００２５】
ステップ３では、窒素酸化物の排出量と窒素酸化物の浄化率とを乗算することにより、窒素酸化物還元触媒３にて還元除去可能な窒素酸化物の量を求める。
ステップ４では、還元除去可能な窒素酸化物の量より、還元剤の目標添加量を演算する。この演算は、あらかじめ還元剤添加コントローラ１０に、還元除去可能な窒素酸化物の量に対応した還元剤の目標添加量を表したマップを記憶させておき、このマップから還元可能な窒素酸化物の量に対応した還元剤の目標添加量を読み出すことによって行ってもよいし、還元除去可能な窒素酸化物の量から直接算出してもよい。なお、ステップ１〜４の一連の処理は目標添加量演算手段に該当する。
【００２６】
ステップ５では、還元剤の目標添加量を窒素酸化物還元触媒３の上流側の排気通路２に添加するように、還元剤添加装置５及びポンプ６を作動制御する。
ステップ６では、添加流量センサ９により検出された還元剤の実添加量から還元剤の目標添加量を減算した差を求め、この差を順次積算して、還元剤の推定吸着量を求める。但し、窒素酸化物還元触媒３に吸着されている還元剤の吸着量はマイナス或いは窒素酸化物還元触媒３に吸着可能な還元剤の限界吸着量を超えることはないので、この還元剤の推定吸着量がマイナスとなってしまった場合は０にし、限界吸着量を超えた場合には限界吸着量に設定する。なお、ステップ５の処理は推定吸着量演算手段に該当する。
【００２７】
ステップ７では、エンジンコントローラ７から出力された走行距離を順次積算し、積算走行距離を求める。
ステップ８では、積算走行距離が距離設定値（第１の所定値）以上か否かを判定する。積算走行距離が、距離設定値以上である場合は、ステップ９へ進む（ＹＥＳ）。積算走行距離が距離設定値未満である場合は、ステップ１１へ進む（ＮＯ）。なお、この距離設定値は、任意に設定可能とする。
【００２８】
ステップ９では、還元剤の推定吸着量を、窒素酸化物還元触媒３に吸着可能な還元剤の限界吸着量にする。
ステップ１０では、積算走行距離を０にする。そして、ステップ１２へ進む。
【００２９】
ステップ１１では、触媒温度センサ８により検出された触媒温度から、上限閾値を演算する。この演算は、あらかじめ還元剤添加コントローラ１０に図３の実線で示すような触媒温度に対応した上限閾値を表したマップを記憶させておき、このマップから触媒温度に対応した上限閾値を読み出すことによって行われる。上限閾値は、触媒温度に対応した窒素酸化物還元触媒３での還元剤の限界吸着量の略７０％に相当する値である。そして、還元剤の推定吸着量が上限閾値以上か否かを判定する。還元剤の推定吸着量が上限閾値以上である場合は、ステップ１２へ進む（ＹＥＳ）。還元剤の推定吸着量が上限閾値未満である場合は、ステップ１へ戻る（ＮＯ）。
【００３０】
ステップ１２では、還元剤の添加量が０になるように還元剤添加装置５及びポンプ６を作動制御する。または、還元剤の添加量が目標添加量より少なくなるように還元剤添加装置５及びポンプ６を作動制御する。
【００３１】
ステップ１３では、添加流量センサ９により検出された還元剤の実添加量を入力し、ステップ１〜４の一連の制御と同様にして求めた還元剤の目標添加量から還元剤の実添加量を減算して差を求める。そして、この差を窒素酸化物還元触媒３に吸着した還元剤のうち消費された分の還元剤量として、還元剤の推定吸着量から減算する。
【００３２】
ステップ１４では、触媒温度センサ８により検出された触媒温度から、下限閾値を演算する。この演算は、あらかじめ還元剤添加コントローラ１０に図３の破線で示すような触媒温度に対応した下限閾値を表わしたマップを記憶させておき、このマップから触媒温度に対応した下限閾値を読み出すことによって行われる。下限閾値は、触媒温度に対応した窒素酸化物還元触媒３での還元剤の限界吸着量の略３０％に相当する値である。そして、ステップ１３にて減算された還元剤の推定吸着量が下限閾値未満であるか否かを判定する。還元剤の推定吸着量が下限閾値未満である場合は、ステップ１へ戻る（ＹＥＳ）。還元剤の推定吸着量が下限閾値以上の場合は、ステップ１２へ戻る（ＮＯ）。なお、ステップ７〜１４の一連の制御は制御手段に該当する。
【００３３】
以上のようにして、窒素酸化物の排出量と窒素酸化物還元触媒３における窒素酸化物の浄化率とにより、窒素酸化物を還元除去するために必要な還元剤の目標添加量を演算し、この還元剤の目標添加量を窒素酸化物還元触媒３の上流側の排気通路２に添加して、窒素酸化物還元触媒３にて排気中の窒素酸化物を還元除去する。
【００３４】
そして、還元剤の実添加量から還元剤の目標添加量を減算した差を順次積算して、窒素酸化物還元触媒３に吸着された還元剤の推定吸着量を演算する。還元剤の推定吸着量が上限閾値以上である場合は、還元剤の添加を停止或いは減量させるとともに、還元剤の推定吸着量が下限閾値未満である場合は、還元剤の添加の停止或いは減量を中止し、窒素酸化物の排出量に基づく還元剤の添加を再開させるので、窒素酸化物還元触媒３に吸着された還元剤の吸着量は上限閾値及び下限閾値の間に保持される。
【００３５】
これにより、排気中の窒素酸化物と反応しきれなかった還元剤があったとしても、窒素酸化物還元触媒３に吸着して、下流に還元剤が排出されることが防止される。更に、窒素酸化物還元触媒３において還元剤が不足してしまった場合でも、窒素酸化物還元触媒３に吸着されている還元剤が用いられて窒素酸化物の還元除去が効率よく行なわれる。
【００３６】
また、還元剤添加コントローラ１０は、所定の積算走行距離毎に、還元剤の推定吸着量を還元剤の限界吸着量に設定するので、還元剤の添加が停止或いは減量され、窒素酸化物還元触媒３に吸着された還元剤が強制的に消費される。そして、還元剤の推定吸着量が下限閾値に達して還元剤の添加の停止或いは減量が中止されたときには、窒素酸化物還元触媒３に吸着されている還元剤の吸着量は下限閾値以下になる。これにより、窒素酸化物還元触媒３に吸着されている還元剤の吸着量と還元剤の推定吸着量とが相違しても、所定の積算走行距離毎に、窒素酸化物還元触媒３に吸着されている還元剤の吸着量と還元剤の推定吸着量との差は下限閾値以下になる。
【００３７】
なお、本実施例では、還元剤添加コントローラ１０における制御方法のステップ８において、積算走行距離が距離設定値以上か否かを判定したが、積算走行距離ではなく、エンジンの運転時間を順次積算した積算運転時間で判定してもよい。この場合、エンジンの積算運転時間が時間設定値（第２の所定値）以上である場合は、ステップ９に進み、エンジンの積算運転時間が時間設定値未満である場合はステップ１１へ進むように制御する。
【００３８】
また、本実施例では、還元剤添加コントローラ１０における制御方法のステップ１４において、下限閾値を触媒温度に対応した窒素酸化物還元触媒３での還元剤の限界吸着量の略３０％に相当する値に設定したが、下限閾値を０に設定してもよい。この場合、還元剤の吸着量が０である場合はステップ１に戻り、還元剤の吸着量が０でない場合はステップ１２に戻るように制御する。これにより、所定の積算走行距離毎に窒素酸化物還元触媒３に吸着されている還元剤の吸着量と還元剤の推定吸着量との差が０になる。
【００３９】
【発明の効果】
以上説明したように、請求項１の発明によれば、窒素酸化物還元触媒に吸着されている還元剤の推定吸着量が上限閾値未満かつ下限閾値以上となるように、還元剤の添加量が制御されるので、最適な量の還元剤が窒素酸化物還元触媒の上流側に添加される。これにより、窒素酸化物還元触媒において窒素酸化物を還元除去する際に還元剤が余剰となることがなく、還元剤が窒素酸化物還元触媒の下流に排出されることがない。また、窒素酸化物還元触媒において窒素酸化物が還元除去される際に還元剤が不足することもなく、窒素酸化物の還元除去を効率よく行える。
このとき、車両の走行距離を積算した積算走行距離が第１の所定値に達する毎、又は、エンジンの運転時間を積算した積算運転時間が第２の所定値に達する毎に、窒素酸化物還元触媒に吸着された還元剤が強制的に消費される。そして、還元剤の推定吸着量が下限閾値に達したときには、窒素酸化物還元触媒に吸着されている還元剤の吸着量は下限閾値以下になるので、還元剤の推定吸着量と窒素酸化物還元触媒に吸着されている還元剤の吸着量との差が下限閾値以下になる。例えば、下限閾値を０にすると、還元剤の推定吸着量と窒素酸化物還元触媒に吸着されている還元剤の吸着量との差がなくなる。また、還元剤の推定吸着量が上限閾値未満かつ下限閾値以上となるように還元剤の添加量が制御されるので、排気中の窒素酸化物と反応しきれなかった還元剤があったとしても窒素酸化物還元触媒に吸着されるとともに、窒素酸化物還元触媒に吸着されている還元剤により還元剤の一時的な不足があった場合にも還元剤を補うことができる。
【００４０】
請求項２記載の発明によれば、吸気流量とエンジン回転速度と燃料供給量とに基づいて演算された窒素酸化物の排出量と、窒素酸化物還元触媒の温度に基づいて演算された窒素酸化物の浄化率と、により、還元剤の目標添加量が演算されるので、エンジンの運転状況に応じた還元剤の目標添加量が求められる。
【００４１】
請求項３記載の発明によれば、窒素酸化物還元触媒の触媒温度に応じて上限閾値及び下限閾値が夫々設定されるため、触媒温度の変化による還元剤の吸着能力の変化に対応することができる。
【００４２】
請求項４記載の発明によれば、窒素酸化物還元触媒の触媒温度に応じて限界吸着量が設定されるため、触媒温度の変化による還元剤の吸着能力の変化に対応することができる。
【００４３】
請求項５記載の発明によれば、推定吸着量を０〜限界吸着量の範囲内で演算することができる。
【図面の簡単な説明】
【図１】本発明のエンジンの排気浄化装置の構成を示すブロック図
【図２】還元剤添加コントローラにおける制御内容を示すフローチャート
【図３】触媒温度に対応する上限及び下限閾値を示すマップの説明図
【符号の説明】
１エンジン
３窒素酸化物還元触媒
４還元剤タンク
５還元剤添加装置
７エンジンコントローラ
８触媒温度センサ
９添加流量センサ
１０還元剤添加コントローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine exhaust gas purification apparatus in which a reducing agent is added to exhaust gas and nitrogen oxides are reduced and removed by a nitrogen oxide reduction catalyst, and more particularly to a technique for optimally controlling the amount of reducing agent added.
[0002]
[Prior art]
Japanese Patent Laid-Open No. 2002-250220 (Patent Document 1) discloses an exhaust gas purification device that reduces and removes nitrogen oxides (NO _x ) contained in exhaust gas discharged from engines such as diesel engines and lean burn gasoline engines. Such exhaust purification devices have been proposed. In such an exhaust purification apparatus, a nitrogen oxide reduction catalyst is interposed in the exhaust passage of the engine in order to reduce and remove nitrogen oxides to harmless nitrogen (N ₂ ) and oxygen (O ₂ ) in an oxygen-excess atmosphere. In order to improve the nitrogen oxide purification efficiency in the nitrogen oxide reduction catalyst, a reducing agent such as urea ((NH ₂ ) ₂ CO) is mounted, and the reducing agent is placed in the exhaust passage upstream of the nitrogen oxide reduction catalyst. The composition to add is adopted. An amount of reducing agent commensurate with the amount of nitrogen oxide discharged is added so that the nitrogen oxide in the exhaust gas is sufficiently reduced and removed.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-250220
[Problems to be solved by the invention]
However, all of the added reducing agent does not react with the nitrogen oxide, and a part of the reducing agent that cannot be reacted is adsorbed by the nitrogen oxide reduction catalyst. When the amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst exceeds a predetermined amount, excessive addition of the reducing agent due to a response delay or the reducing agent adsorption capacity due to a change in the catalyst temperature under transient operation conditions. Due to the change, a part of the reducing agent that can no longer be adsorbed on the nitrogen oxide reduction catalyst is discharged downstream of the nitrogen oxide reduction catalyst.
[0005]
Since the reducing agent is ammonia (NH ₃ ) or hydrocarbon (HC), it is not preferable to be discharged into the atmosphere.
Therefore, in view of the conventional problems as described above, the present invention estimates the amount of reducing agent adsorbed on the nitrogen oxide reduction catalyst by calculation, and controls the amount of reducing agent added accordingly. Thus, an object of the present invention is to provide an engine exhaust purification device that prevents the reducing agent that cannot be adsorbed by the nitrogen oxide reduction catalyst from being discharged downstream of the nitrogen oxide reduction catalyst.
[0006]
[Means for Solving the Problems]
For this reason, the invention according to claim 1 is provided in the exhaust passage of the engine and uses a reducing agent to reduce and remove nitrogen oxides in the exhaust gas, and a reducing agent that stores the reducing agent. A reductant storage means, a reductant addition means for adding the reductant stored in the reductant storage means to the upstream side of the nitrogen oxide reduction catalyst, and a target addition amount of the reductant according to the operating condition of the engine. The target addition amount calculating means for calculating, and the target addition amount of the reducing agent calculated by the target addition amount calculating means is subtracted from the actual addition amount of the reducing agent actually added upstream of the nitrogen oxide reduction catalyst. sequentially accumulating the difference, the estimated adsorbed amount of the nitrogen oxides and the estimated adsorbed amount calculating means for calculating an estimated amount of adsorption of the reducing agent adsorbed on the reduction catalyst, the estimated adsorbed amount calculating means by the calculated reducing agent Is less than upper threshold and lower threshold As the above, the control means for controlling the addition amount of the reducing agent by the reducing agent adding means, each accumulated running distance obtained by accumulating the running distance of the vehicle reaches a first predetermined value, or the engine operating time of the Resetting means for setting the estimated adsorption amount of the reducing agent to a limit adsorption amount that can be adsorbed to the nitrogen oxide reduction catalyst every time the accumulated operation time obtained by integrating the above reaches a second predetermined value . An exhaust emission control device is configured.
[0007]
According to such a configuration, the difference obtained by subtracting the target addition amount of the reducing agent according to the operating condition of the engine from the actual addition amount of the reducing agent is sequentially integrated to estimate the reducing agent adsorbed on the nitrogen oxide reduction catalyst. The amount of adsorption is required. And since the addition amount of a reducing agent is controlled so that this estimated adsorption amount is less than the upper threshold value and more than the lower threshold value , an appropriate amount of the reducing agent corresponding to the adsorption amount of the reducing agent is a nitrogen oxide reduction catalyst. To the upstream side.
At this time, every time the cumulative travel distance obtained by integrating the travel distance of the vehicle reaches the first predetermined value or every time the cumulative operation time obtained by integrating the engine operation time reaches the second predetermined value, the reducing agent is estimated. Since the adsorption amount is set to the limit adsorption amount, the addition of the reducing agent is stopped or reduced, and the reducing agent adsorbed on the nitrogen oxide reduction catalyst is forcibly consumed. Then, when the estimated adsorption amount of the reducing agent reaches the lower threshold value, the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst becomes equal to or lower than the lower threshold value. As a result, even if the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst is different from the estimated adsorption amount of the reducing agent, the difference between the two becomes the lower threshold value for each predetermined cumulative travel distance or cumulative operation time. It becomes the following.
[0008]
The invention according to claim 2 is based on the discharge amount calculating means for calculating the discharge amount of nitrogen oxides based on the intake flow rate, the engine rotation speed, and the fuel supply amount, and on the basis of the temperature of the nitrogen oxide reduction catalyst, Purification rate calculating means for calculating the purification rate of nitrogen oxides in the nitrogen oxide reduction catalyst, the target addition amount calculating means is based on the discharge amount and the purification rate of the nitrogen oxides of the reducing agent The target addition amount is calculated.
[0009]
According to this configuration, the nitrogen oxide emission amount calculated based on the intake air flow rate, the engine rotation speed, and the fuel supply amount, and the nitrogen oxide purification rate calculated based on the temperature of the nitrogen oxide reduction catalyst Thus, since the target addition amount of the reducing agent is calculated, the target addition amount of the reducing agent corresponding to the operating condition of the engine is obtained.
[0010]
The invention described in claim 3 is characterized by comprising threshold setting means for setting the upper limit threshold and the lower limit threshold based on the catalyst temperature of the nitrogen oxide reduction catalyst .
[0011]
According to such a configuration, since the upper limit threshold and the lower limit threshold are respectively set according to the catalyst temperature of the nitrogen oxide reduction catalyst, it is possible to cope with a change in the reducing agent adsorption capacity due to a change in the catalyst temperature.
[0012]
According to a fourth aspect of the present invention, there is provided a limit adsorption amount setting means for setting the limit adsorption amount based on a catalyst temperature of the nitrogen oxide reduction catalyst .
[0013]
According to this configuration, since the limit adsorption amount is set according to the catalyst temperature of the nitrogen oxide reduction catalyst, it is possible to cope with a change in the reducing agent adsorption capacity due to a change in the catalyst temperature.
[0014]
The invention according to claim 5 is characterized in that the estimated adsorption amount calculating means calculates the estimated adsorption amount within a range of 0 to a limit adsorption amount.
[0015]
According to this configuration, the estimated adsorption amount is calculated within the range of 0 to the limit adsorption amount .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing the configuration of an exhaust emission control device for an engine according to the present invention.
[0017]
A nitrogen oxide reduction catalyst 3 for reducing and removing nitrogen oxides is interposed in an exhaust passage 2 of an engine 1 that is operated under an excessive oxygen condition, such as a diesel engine or a lean burn engine.
[0018]
The nitrogen oxide reduction catalyst 3 has a configuration in which, for example, a zeolite-based active component is supported on a monolith type catalyst carrier having a honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel. Make. Then, the active component supported on the catalyst carrier is activated by receiving a reducing agent such as ammonia or hydrocarbon, and effectively converts nitrogen oxides into harmless substances.
[0019]
Furthermore, a reducing agent tank 4 (reducing agent storage means) for storing the reducing agent is provided. Then, the reducing agent stored in the reducing agent tank 4 is mixed with the air compressed by the pump 6 in the reducing agent addition device 5 (reducing agent addition means), and the upstream side of the nitrogen oxide reduction catalyst 3 is mixed. It is added into the exhaust passage 2.
[0020]
By the way, the engine 1 is provided with an engine controller 7 that incorporates a microcomputer and performs operation control. The engine controller 7 can output signals of intake air flow rate, engine rotation speed, fuel supply amount, and travel distance. Furthermore, a catalyst temperature sensor 8 that directly or indirectly detects the catalyst temperature of the nitrogen oxide reduction catalyst 3 is provided. In addition, the reducing agent addition device 5 is provided with an addition flow sensor 9 for detecting the actual addition amount of the reducing agent actually added to the exhaust passage 2. The actual addition amount of the reducing agent may be obtained by calculation from the control values of the reducing agent addition device 5 and the pump 6.
[0021]
The exhaust purification device has a built-in microcomputer, and the target addition amount calculation means, estimated adsorption amount calculation means, control means, reset means, emission amount calculation means, purification rate calculation means, threshold setting means, and limit adsorption in software A reducing agent addition controller 10 that realizes the amount setting means is provided.
[0022]
The reducing agent addition controller 10 includes an intake air flow rate, an engine rotation speed, a fuel supply amount and a travel distance input from the engine controller 7, a catalyst temperature detected by the catalyst temperature sensor 8, and an actual addition detected by the addition flow rate sensor 9. Based on the amount, the pump 6 and the reducing agent addition device 5 are controlled.
[0023]
Here, the control method in the reducing agent addition controller 10 will be described in detail with reference to FIG. First, the reducing agent addition controller 10 is supplied with power by turning on a power switch such as a key switch and starts control. First, in step 1 (denoted as S1 in the figure, the same applies hereinafter), a nitrogen oxide emission amount is calculated based on the intake air flow rate output from the engine controller 7, the engine rotation speed, and the fuel supply amount. . In this calculation, the reducing agent addition controller 10 stores in advance a map representing the nitrogen oxide emission amount corresponding to the intake air flow rate, the engine rotational speed, and the fuel supply amount. This is done by reading out the nitrogen oxide emissions corresponding to the speed and fuel supply. Note that the processing in step 1 corresponds to an emission amount calculating means.
[0024]
In step 2, the nitrogen oxide purification rate in the nitrogen oxide reduction catalyst 3 is calculated from the catalyst temperature detected by the catalyst temperature sensor 8. In this calculation, a map representing the purification rate of nitrogen oxides corresponding to the catalyst temperature of the nitrogen oxide reduction catalyst 3 is stored in advance in the reducing agent addition controller 10, and the nitrogen oxidation corresponding to the catalyst temperature is stored from this map. This is done by reading the purification rate of the object. In addition, the process of step 2 corresponds to a purification rate calculating means.
[0025]
In step 3, the amount of nitrogen oxides that can be reduced and removed by the nitrogen oxide reduction catalyst 3 is determined by multiplying the nitrogen oxide emission amount by the nitrogen oxide purification rate.
In step 4, the target addition amount of the reducing agent is calculated from the amount of nitrogen oxide that can be reduced and removed. In this calculation, the reducing agent addition controller 10 stores in advance a map representing the target addition amount of the reducing agent corresponding to the amount of nitrogen oxide that can be reduced and removed. It may be performed by reading the target addition amount of the reducing agent corresponding to the amount, or may be directly calculated from the amount of nitrogen oxide that can be reduced and removed. The series of processes in steps 1 to 4 corresponds to the target addition amount calculation means.
[0026]
In step 5, the reducing agent addition device 5 and the pump 6 are controlled so that the target addition amount of the reducing agent is added to the exhaust passage 2 upstream of the nitrogen oxide reduction catalyst 3.
In step 6, a difference obtained by subtracting the target addition amount of the reducing agent from the actual addition amount of the reducing agent detected by the addition flow sensor 9 is obtained, and the difference is sequentially integrated to obtain an estimated adsorption amount of the reducing agent. However, since the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 is not negative or exceeds the limit adsorption amount of the reducing agent that can be adsorbed on the nitrogen oxide reduction catalyst 3, the estimated adsorption of the reducing agent When the amount becomes negative, it is set to 0, and when the amount exceeds the limit adsorption amount, the limit adsorption amount is set. In addition, the process of step 5 corresponds to an estimated adsorption amount calculation means.
[0027]
In step 7, the travel distances output from the engine controller 7 are sequentially integrated to obtain the integrated travel distance.
In step 8, it is determined whether or not the accumulated travel distance is equal to or greater than a distance setting value ( first predetermined value ). If the accumulated travel distance is equal to or greater than the distance setting value, the process proceeds to step 9 (YES). If the integrated travel distance is less than the distance setting value, the process proceeds to step 11 (NO). This distance setting value can be arbitrarily set.
[0028]
In step 9, the estimated adsorption amount of the reducing agent is set to a limit adsorption amount of the reducing agent that can be adsorbed to the nitrogen oxide reduction catalyst 3.
In step 10, the accumulated travel distance is set to zero. Then, the process proceeds to Step 12.
[0029]
In step 11, an upper limit threshold value is calculated from the catalyst temperature detected by the catalyst temperature sensor 8. In this calculation, a map representing the upper limit threshold value corresponding to the catalyst temperature as shown by the solid line in FIG. 3 is stored in advance in the reducing agent addition controller 10, and the upper limit threshold value corresponding to the catalyst temperature is read from this map. Done. The upper threshold is a value corresponding to approximately 70% of the limit adsorption amount of the reducing agent in the nitrogen oxide reduction catalyst 3 corresponding to the catalyst temperature. And it is determined whether the presumed adsorption amount of a reducing agent is more than an upper limit threshold value. When the estimated adsorption amount of the reducing agent is equal to or greater than the upper limit threshold value, the process proceeds to step 12 (YES). When the estimated adsorption amount of the reducing agent is less than the upper threshold, the process returns to step 1 (NO).
[0030]
In step 12, the operation of the reducing agent adding device 5 and the pump 6 is controlled so that the amount of reducing agent added becomes zero. Alternatively, the reducing agent addition device 5 and the pump 6 are controlled to operate so that the addition amount of the reducing agent is smaller than the target addition amount.
[0031]
In step 13, the actual addition amount of the reducing agent detected by the addition flow sensor 9 is input, and the actual addition amount of the reducing agent is calculated from the target addition amount of the reducing agent obtained in the same manner as the series of controls in steps 1 to 4. Subtract to find the difference. Then, this difference is subtracted from the estimated adsorption amount of the reducing agent as the amount of reducing agent consumed for the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3.
[0032]
In step 14, a lower limit threshold value is calculated from the catalyst temperature detected by the catalyst temperature sensor 8. In this calculation, a map representing the lower limit threshold value corresponding to the catalyst temperature as shown by the broken line in FIG. 3 is stored in the reducing agent addition controller 10 in advance, and the lower limit threshold value corresponding to the catalyst temperature is read from this map. Done. The lower limit threshold is a value corresponding to approximately 30% of the limit adsorption amount of the reducing agent in the nitrogen oxide reduction catalyst 3 corresponding to the catalyst temperature. Then, it is determined whether or not the estimated adsorption amount of the reducing agent subtracted in step 13 is less than a lower limit threshold value. When the estimated adsorption amount of the reducing agent is less than the lower limit threshold, the process returns to Step 1 (YES). If the estimated adsorption amount of the reducing agent is equal to or greater than the lower limit threshold, the process returns to step 12 (NO). Note that a series of control in steps 7 to 14 corresponds to control means.
[0033]
As described above, the target addition amount of the reducing agent necessary for reducing and removing nitrogen oxides is calculated based on the nitrogen oxide emission amount and the nitrogen oxide purification rate in the nitrogen oxide reduction catalyst 3, The target addition amount of this reducing agent is added to the exhaust passage 2 upstream of the nitrogen oxide reduction catalyst 3, and the nitrogen oxides in the exhaust gas are reduced and removed by the nitrogen oxide reduction catalyst 3.
[0034]
Then, the difference obtained by subtracting the target addition amount of the reducing agent from the actual addition amount of the reducing agent is sequentially integrated to calculate the estimated adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3. When the estimated adsorption amount of the reducing agent is equal to or higher than the upper threshold, the addition of the reducing agent is stopped or reduced, and when the estimated adsorption amount of the reducing agent is less than the lower threshold, the addition or reduction of the reducing agent is stopped. Since it is stopped and the addition of the reducing agent based on the nitrogen oxide emission amount is resumed, the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 is maintained between the upper threshold value and the lower threshold value.
[0035]
As a result, even if there is a reducing agent that could not react with the nitrogen oxide in the exhaust, it is prevented from being adsorbed to the nitrogen oxide reducing catalyst 3 and being discharged downstream. Further, even when the nitrogen oxide reduction catalyst 3 runs short of the reducing agent, the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 is used to efficiently reduce and remove the nitrogen oxide.
[0036]
Moreover, since the reducing agent addition controller 10 sets the reducing agent's estimated adsorption amount to the limiting adsorption amount of the reducing agent for each predetermined total travel distance, the addition of the reducing agent is stopped or reduced, and the nitrogen oxide reduction catalyst. The reducing agent adsorbed on 3 is forcibly consumed. When the estimated adsorption amount of the reducing agent reaches the lower limit threshold and the addition or reduction of the reducing agent is stopped, the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 becomes equal to or lower than the lower limit threshold. . Thereby, even if the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 is different from the estimated adsorption amount of the reducing agent, the adsorption agent is adsorbed on the nitrogen oxide reduction catalyst 3 for each predetermined integrated travel distance. The difference between the adsorbed amount of the reducing agent and the estimated adsorbed amount of the reducing agent is not more than the lower limit threshold.
[0037]
In this embodiment, in step 8 of the control method in the reducing agent addition controller 10, it is determined whether or not the accumulated travel distance is equal to or greater than the distance setting value. However, not the accumulated travel distance but the engine operation time is sequentially accumulated. The determination may be made based on the accumulated operation time. In this case, when the accumulated operation time of the engine is equal to or longer than the time set value ( second predetermined value ), the process proceeds to step 9, and when the accumulated operation time of the engine is less than the time set value, the process proceeds to step 11. Control.
[0038]
Further, in this embodiment, in step 14 of the control method in the reducing agent addition controller 10, a value corresponding to about 30% of the limit adsorption amount of the reducing agent on the nitrogen oxide reduction catalyst 3 corresponding to the catalyst temperature as the lower limit threshold value. However, the lower threshold may be set to 0. In this case, when the reducing agent adsorption amount is 0, the process returns to step 1, and when the reducing agent adsorption amount is not 0, the process returns to step 12. As a result, the difference between the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst 3 and the estimated adsorption amount of the reducing agent becomes zero for each predetermined cumulative travel distance.
[0039]
【The invention's effect】
As described above, according to the first aspect of the present invention, the amount of reducing agent added is set so that the estimated adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst is less than the upper threshold and equal to or greater than the lower threshold. As controlled, an optimal amount of reducing agent is added upstream of the nitrogen oxide reduction catalyst. Accordingly, when the nitrogen oxide is reduced and removed in the nitrogen oxide reduction catalyst, the reducing agent is not excessive, and the reducing agent is not discharged downstream of the nitrogen oxide reduction catalyst. Further, when the nitrogen oxide is reduced and removed in the nitrogen oxide reduction catalyst, the reducing agent can be efficiently reduced and removed without a shortage of the reducing agent.
At this time, every time the cumulative travel distance obtained by integrating the travel distance of the vehicle reaches the first predetermined value or every time the cumulative operation time obtained by integrating the operation time of the engine reaches the second predetermined value, nitrogen oxide reduction The reducing agent adsorbed on the catalyst is forcibly consumed. When the estimated amount of adsorption of the reducing agent reaches the lower threshold, the amount of adsorption of the reducing agent adsorbed on the nitrogen oxide reduction catalyst falls below the lower threshold, so the estimated amount of reducing agent adsorption and nitrogen oxide reduction The difference from the adsorption amount of the reducing agent adsorbed on the catalyst is equal to or less than the lower limit threshold. For example, when the lower threshold is set to 0, there is no difference between the estimated adsorption amount of the reducing agent and the adsorption amount of the reducing agent adsorbed on the nitrogen oxide reduction catalyst. In addition, since the amount of reducing agent added is controlled so that the estimated amount of reducing agent adsorption is less than the upper threshold and greater than or equal to the lower threshold, even if there is a reducing agent that could not react with the nitrogen oxides in the exhaust. The reducing agent can be supplemented even when there is a temporary shortage of the reducing agent due to the reducing agent adsorbed on the nitrogen oxide reduction catalyst and also on the nitrogen oxide reduction catalyst.
[0040]
According to the second aspect of the present invention, the nitrogen oxide emission amount calculated based on the intake air flow rate, the engine rotational speed, and the fuel supply amount, and the nitrogen oxidation calculated based on the temperature of the nitrogen oxide reduction catalyst. Since the target addition amount of the reducing agent is calculated based on the purification rate of the object, the target addition amount of the reducing agent corresponding to the operating condition of the engine is obtained.
[0041]
According to the third aspect of the present invention, since the upper limit threshold and the lower limit threshold are respectively set according to the catalyst temperature of the nitrogen oxide reduction catalyst, it is possible to cope with a change in the reducing agent adsorption capacity due to a change in the catalyst temperature. it can.
[0042]
According to the fourth aspect of the present invention, since the limit adsorption amount is set according to the catalyst temperature of the nitrogen oxide reduction catalyst, it is possible to cope with a change in the reducing agent adsorption capacity due to a change in the catalyst temperature.
[0043]
According to the fifth aspect of the present invention, the estimated adsorption amount can be calculated within the range of 0 to the limit adsorption amount .
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of an exhaust emission control device for an engine of the present invention. FIG. 2 is a flowchart showing the contents of control in a reducing agent addition controller. FIG. 3 is an explanation of a map showing upper and lower thresholds corresponding to catalyst temperature. Figure [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 3 Nitrogen oxide reduction catalyst 4 Reductant tank 5 Reductant addition apparatus 7 Engine controller 8 Catalyst temperature sensor 9 Addition flow sensor 10 Reductant addition controller

Claims

A nitrogen oxide reduction catalyst that is interposed in the exhaust passage of the engine and uses a reducing agent to reduce and remove nitrogen oxides in the exhaust;
Reducing agent storage means for storing the reducing agent;
Reducing agent addition means for adding the reducing agent stored in the reducing agent storage means to the upstream side of the nitrogen oxide reduction catalyst;
Target addition amount calculating means for calculating a target addition amount of the reducing agent according to the operating state of the engine;
The difference obtained by subtracting the target addition amount of the reducing agent calculated by the target addition amount calculating means from the actual addition amount of the reducing agent actually added to the upstream side of the nitrogen oxide reduction catalyst is sequentially integrated, and the nitrogen An estimated adsorption amount calculating means for calculating an estimated adsorption amount of the reducing agent adsorbed on the oxide reduction catalyst;
Control means for controlling the addition amount of the reducing agent by the reducing agent addition means so that the estimated adsorption amount of the reducing agent calculated by the estimated adsorption amount calculation means is less than the upper limit threshold and equal to or more than the lower limit threshold ;
Each time the cumulative travel distance obtained by integrating the travel distance of the vehicle reaches a first predetermined value, or every time the cumulative operation time obtained by integrating the operation time of the engine reaches a second predetermined value, the estimated adsorption amount of the reducing agent Reset means for setting a limit adsorption amount that can be adsorbed to the nitrogen oxide reduction catalyst,
An exhaust emission control device for an engine characterized by comprising:

A discharge amount calculating means for calculating a discharge amount of nitrogen oxides based on the intake flow rate, the engine rotation speed, and the fuel supply amount;
Based on the temperature of the nitrogen oxide reduction catalyst, a purification rate calculating means for calculating a nitrogen oxide purification rate in the nitrogen oxide reduction catalyst;
With
2. The engine exhaust gas purification apparatus according to claim 1, wherein the target addition amount calculating means calculates a target addition amount of the reducing agent based on a discharge amount and a purification rate of the nitrogen oxides.

The engine exhaust purification device according to claim 1 or 2 , further comprising threshold setting means for setting the upper threshold and the lower threshold based on a catalyst temperature of the nitrogen oxide reduction catalyst .

The engine according to any one of claims 1 to 3, further comprising a limit adsorption amount setting unit that sets the limit adsorption amount based on a catalyst temperature of the nitrogen oxide reduction catalyst . Exhaust purification device.

The engine exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the estimated adsorption amount calculating means calculates the estimated adsorption amount within a range of 0 to a limit adsorption amount .