JP2004293338A - Method for presuming amount of nox occlusion - Google Patents
Method for presuming amount of nox occlusion Download PDFInfo
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- JP2004293338A JP2004293338A JP2003083650A JP2003083650A JP2004293338A JP 2004293338 A JP2004293338 A JP 2004293338A JP 2003083650 A JP2003083650 A JP 2003083650A JP 2003083650 A JP2003083650 A JP 2003083650A JP 2004293338 A JP2004293338 A JP 2004293338A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
- F24F13/08—Air-flow control members, e.g. louvres, grilles, flaps or guide plates
- F24F13/082—Grilles, registers or guards
- F24F13/084—Grilles, registers or guards with mounting arrangements, e.g. snap fasteners for mounting to the wall or duct
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
- F01N3/0842—Nitrogen oxides
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
- F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2200/00—Input parameters for engine control
- F02D2200/02—Input parameters for engine control the parameters being related to the engine
- F02D2200/08—Exhaust gas treatment apparatus parameters
- F02D2200/0806—NOx storage amount, i.e. amount of NOx stored on NOx trap
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
- F24F13/02—Ducting arrangements
- F24F13/06—Outlets for directing or distributing air into rooms or spaces, e.g. ceiling air diffuser
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Combined Controls Of Internal Combustion Engines (AREA)
Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、排気通路に設けられたNOx吸蔵型還元触媒に吸蔵されたNOxの吸蔵量推定方法に関する。
【0002】
【従来の技術】
一般に、ディーゼルエンジンでは、その構造上の特性から排ガス中の酸素が多く酸化雰囲気となる(つまり、排気空燃比がリーンとなる)。また、ガソリンエンジンであっても希薄燃焼可能なものであれば、希薄燃焼時にはやはり排気空燃比がリーンとなる。そこで、このような酸化雰囲気でもNOxを浄化できるよう、従来よりリーンNOx触媒が開発されている。
【0003】
このようなリーンNOx触媒としては、NOx吸蔵型還元触媒(以下、NOx吸蔵触媒、又は単に触媒という)がある。NOx吸蔵触媒では、酸化雰囲気では排気中のNOxが吸蔵され、低酸素濃度下においてCOが存在すると吸蔵されたNOxが放出されるようになっており、NOx吸蔵触媒から放出されたNOxの殆どが、エンジンから排出された未燃HC,CO等の還元剤により無害なN2 へと還元されてから大気へと排出される。
【0004】
そして、NOx吸蔵触媒が装備された車両では一般的にいわゆるリッチスパイク制御が行なわれる。つまり、リーンな空燃比での運転が続くとNOx吸蔵触媒はこれ以上NOxを吸蔵できない飽和状態となるため、タイミングを見計らって空燃比を一時的に強制的にリッチにする(リッチスパイク制御を行なう)ことで排気中の酸素濃度を低下させるとともに、還元剤を供給することでNOx吸蔵触媒からNOxを放出させ、これにより、NOxを吸蔵しうる状態にNOx吸蔵触媒を再生するのである。
【0005】
ところで、上述のようなリッチスパイク制御を行なうには、NOx吸蔵触媒におけるNOx吸蔵量を正確に推定(又は検出)する必要があり、このようなNOx吸蔵量の推定手法としては、例えば下記のような技術が知られている。
▲1▼第1の従来技術:NOxセンサを用いたNOx吸蔵量推定手法
この第1の従来技術では、図6に示すように、触媒101の上流と下流とにそれぞれNOxの濃度を検出するNOxセンサ102,103を設けるとともに、排気通路中に排ガス流量を検出するエアフローセンサ(図示省略)を設ける。
【0006】
そして、ECU104では、NOxセンサ102,103からの情報及びエアフローセンサからの情報に基づいて、下式により、NOx吸蔵量を推定する。
NOx吸蔵量=∫排ガス流量×(触媒上流NOx濃度−触媒下流NOx濃度)
▲2▼第2の従来技術:数学的モデルによる推定手法(例えば、特許文献1)
この第2の従来技術では、吸蔵反応,酸化還元反応及び離脱反応等の触媒の化学現象及び物理現象に基づく数学的な触媒モデルを設け、この触媒モデル式によりNOx吸蔵量を推定する。
【0007】
【特許文献1】
特開平9−72235号公報
【0008】
【発明が解決しようとする課題】
しかしながら、上記第1の従来技術においては、リーン運転中はNOx吸蔵量を算出することは可能だが、リッチ運転中のNOx放出量(吸蔵量の減少量)はNOxセンサでは検出することができない。このためリッチ運転時間が不十分だった場合には、触媒に残留したNOxが累積してNOx吸蔵量の演算誤差が生じるという課題がある。また、触媒の上流と下流とにそれぞれNOxセンサが必要であり、コスト増を招くという課題がある。
【0009】
また、第2の従来技術では、少なくとも触媒下流に1つのNOxセンサを設けるだけでNOx吸蔵量を推定可能であるが、この技術は三元触媒の空燃比制御に適用することを主眼としているため、モデル構造がNOx吸蔵触媒とは異なり、NOx吸蔵触媒への応用が困難であるという課題がある。また、その他の触媒モデルによりNOx吸蔵量を推定する場合においても触媒種毎に特性値が異なるためモデル式を変更する必要があり、加えて触媒の劣化などに対応するためには、より詳細なモデル化を必要とするという課題がある。
【0010】
本発明は、このような課題に鑑み創案されたもので、触媒のモデルに常に最新の状態を反映させて高い精度でNOx吸蔵触媒のNOx吸蔵量を推定できるようにした、NOx吸蔵量の推定方法を提供することを目的とする。
【0011】
【課題を解決するための手段】
このため、請求項1記載の本発明のNOx吸蔵量の推定方法は、エンジンの排気通路に介装されたNOx吸蔵触媒のNOx吸蔵量を推定する方法であって、該NOx吸蔵量を、該NOx吸蔵触媒のNOx吸蔵特性を反映させた多項式を用いて推定するとともに、該各多項式の係数を、実測されたNOx浄化率に基づいて逐次補正することを特徴としている。
【0012】
また、該NOx吸蔵触媒におけるNOx放出量を下式により算出してもよい。NOx放出量=∫(触媒入口還元剤濃度×還元剤利用率
−0.5×触媒入口酸素濃度)×排ガス流量
なお、好ましくは、該還元剤利用率をNOx吸蔵触媒のNOx放出特性を反映させた多項式を用いて推定するとともに、該多項式の係数を還元剤の濃度に基づいて逐次補正する。
【0013】
また、好ましくは、該エンジンが、排気空燃比がリーンとなるリーン運転と、該排気空燃比がリッチとなるリッチ運転とを切り替え可能に構成され、該リッチ運転中は該多項式の係数を保持するとともに、リーン運転開始時に該保持された係数を用いて得られるNOx浄化率と該実測されたNOx浄化率との差がしきい値以上であると該NOx吸蔵量を補正する。
【0014】
さらには、該各係数の平均値がいずれか一つでもそれぞれ設定された所定の範囲を逸脱すると、該触媒が異常であると判定するようにしてもよい。
【0015】
【発明の実施の形態】
以下、図面により、本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明すると、図1は本発明が適用される車両の排気系の全体構成を示す模式図である。
図示するように、排気通路2にはNOx吸蔵触媒1が介装されており、このNOx吸蔵触媒1の下流側には触媒出口のNOx濃度を検出するNOxセンサ3が設けられている。
【0016】
また、図示はしないが、排気通路2には、O2 センサ,温度センサ及びエアフローセンサ(AFS)等が接続されており、これらのセンサにより排気通路2内の酸素濃度,排ガス温度及び排ガス流量がそれぞれ検出されるようになっている。
また、各センサ3は制御手段としてのECU4に接続されている。ここで、ECU4は入出力装置,記憶装置(ROM,RAM,不揮発性RAM等),演算装置(CPU),タイマカウンタ等を備えて構成されており、このECU4により、NOx吸蔵触媒1におけるNOx吸蔵量の推定が行なわれるようになっている。
【0017】
また、ECU4には、種々のマップが設けられており、例えばアクセル開度やエンジン回転数をパラメータとして触媒入口のNOx,CO,HCの各濃度(以下、それぞれ触媒入口[NOx],触媒入口[CO],触媒入口[HC]で表す)がマップから読み出されるようになっている。なお、本実施形態では、これらの値をマップから求めているが、排気通路2に種々のセンサを設け、これらの値をセンサから直接検出してもよい。
【0018】
ところで、上述した従来技術2ではNOx吸蔵触媒の特性そのものを数式モデルで記述してNOx吸蔵量を求めていたのに対して、本発明では、NOx吸蔵量を4次元の線形多項式を用いて算出するようになっている。
すなわち、ECU4には下式(1)に示すような多項式が記憶されており、この多項式に基づいてNOx浄化率及びNOx吸蔵触媒1におけNOx吸蔵割合が算出されるようになっている。
なお、式(1)において、rはNOx浄化率、xはNOx吸蔵割合、yは排ガス温度、zはSV値(又は排ガス流速)、k0 ,k1 ,k2 ,・・・は係数である。
【0019】
ここで、NOx吸蔵触媒1のNOx吸蔵特性は、実験等により予め知ることができ、多項式で近似することができる。例えば、パラメータが3つ(3次元)であれば、触媒の特性は図2に示すような曲面で表すことができ、これを多項式で表すことができるのである。もちろん、式(1)は4次元であるので図2に示すような曲面とはならないが、考え方は3次元の場合と同様である。
【0020】
また、各係数ki (i=1,2,・・・)は、予め実験等で求めた特性から適当な値が初期値として入力されている。
そして、エンジン運転中に、触媒下流のNOxセンサ3の検出値に基づいて逐次各係数ki を補正することにより常に、式(1)により、最新の触媒状態を表すことができるのである。
【0021】
以下、NOx推定の手法についてさらに詳しく説明する。まず、式(1)におけるNOx浄化率rは下式(2)でも求めることができる。
r=触媒出口NOx濃度/触媒入口NOx濃度・・・・・・・・・・・・(2)
ここで、触媒出口NOx濃度はNOxセンサ3で検出された値であり、触媒入口NOx濃度はマップから得られる値である。したがって、式(2)で得られるNOx浄化率rはセンサ値(実測値)ということができ、式(1)で得られるNOx浄化率rは推定値(計算値)ということができる。
【0022】
また、式(1)の排ガス温度[y]及びSV値[z]は実測データ又はマップ値が適用される。これにより、式(1)における未知数はNOx吸蔵割合[x]のみとなり、これ以外の値は既知となる。したがって、式(1)を変形した下式(3)により、NOx吸蔵割合[x]を求めることができる。
x=〔r−(k0+k2y+k3z・・)〕/(k1+k4y+・・) ・・(3)
そして、この式(3)で求めたNOx吸蔵割合[x]を再び式(1)に戻して次回の計算周期での計算に用いるようになっている。つまり、式(1)では前回求めたNOx吸蔵割合[x]と、今回の計算周期で新たに検出された[y]及び[z]とを用いて、浄化率rを計算するようになっているのである。
【0023】
ここで、式(1)で算出される浄化率rは推定値であるが、各係数ki が正確な値であれば、この浄化率rの推定値と式(2)で得られる実測値とが一致するはずである。
そこで、本発明では、浄化率rの推定値と実測値とを比較して、推定値と実測値との間に差があれば、推定値が実測値となるように各係数ki を最小二乗法を用いて逐次補正するようになっている。そして、このような計算を繰り返し行ない各係数ki を逐次補正することで、式(1)の多項式を、NOx吸蔵触媒1の状態を正確に反映した式に随時変更することができるのである。
【0024】
つまり、NOx吸蔵触媒1は使用状況や経年劣化等によりその特性が変化するものであるが、何度も係数ki を繰り返し補正することにより、式(1)が正確に触媒1の状態を表す式となり、高い精度でNOx吸蔵量を推定することができるようになるのである。なお、式(3)で求めたNOx吸蔵割合[x]は、初期はその計算周期における瞬間的なNOx吸蔵量であるが、この計算結果を繰り返し式(1)に戻して浄化率rを算出することで、触媒1に吸蔵されたNOxの積算値を算出することができる。
【0025】
このように、NOxを吸蔵するリーン運転時においては、触媒下流に設けられたNOxセンサ3から触媒出口[NOx]を取り込むとともに、式(2)による推定値とを比較し、その都度、最小二乗法により係数ki を補正することで正確なNOx吸蔵量を得ることができる。
ところで、リッチ運転中はNOxが放出されるため、正確なNOx放出量を検出又は推定できないと、次回のリーン運転時におけるNOx吸蔵量の初期値を正確に算出できなくなる。
【0026】
そこで、リッチ運転中はki を保持するとともに、下式(4),(5)によりNOx放出量を算出し、リッチ運転時開始直前のNOx吸蔵量から式(4),(5)により算出されたNOx放出量を差し引いてリッチ運転中のNOx吸蔵量を演算するようになっている。
NOx放出量=∫(触媒入口還元剤濃度×還元剤利用率[r′]−0.5×触媒入口[O2])×排ガス流量・・・・・(4)
還元剤利用率[r′]=f(y,z) ・・・・・・・(5)
ここで、ECU1には、図3に示すような還元剤利用率設定マップが設けられている。このマップには、排ガス温度[y]及びSV値[z]に基づく還元剤利用率の特性が記憶されており、これらのパラメータ[y],[z]に基づいて還元剤利用率が設定されるようになっている。
【0027】
また、触媒入口還元剤濃度(触媒入口[CO],触媒入口[HC])は、上述したようにアクセル開度やエンジン回転数をパラメータとしてマップから求めることができ、他のパラメータも同様にマップ値又は検出値として得ることができる。
したがって、リーン運転からリッチ運転に切り替えられると、ECU4ではリーン運転終了時の各係数ki を保持するとともにNOx吸蔵量を記憶しておき、再びリッチ運転からリーン運転に切り替えられると、上記NOx吸蔵量からリッチ運転終了時のNOx放出量を引き算することによりNOxの残存量が算出される。
【0028】
また、ECU4では、リーン運転開始時のNOx浄化率rの実測値と推定値との差がしきい値以上であると、NOx吸蔵量を補正するようになっている。つまり、リッチ運転からリーン運転への切り替え直後において、式(1)で推定されるNOx浄化率と式(2)で得られるNOx浄化率との差が所定値以上であると、リーン運転開始時に算出されたNOx残存量(=前回のリーン運転終了時のNOx吸蔵量−リッチ運転終了時のNOx放出量)が正確ではないと判断して、このNOx残存量[x](つまり、リーン運転開始時のNOx吸蔵量)を、式(3)に基づいて補正するようになっている。
【0029】
さらに、ECU4は突発的な触媒1の異常等により係数ki が正常ではない値になると、これを検出してドライバに知らせる機能も有している。具体的には、各係数ki について、所定の連続した計算周期における移動平均を常時算出し、この移動平均の値が各係数毎に設定された所定の範囲から逸脱すると、触媒1が劣化又は破損した等の異常が生じたと判定するようになっている。なお、所定の範囲は、例えば各係数ki の初期値に±α(αは一定値)を加算して設定されるようになっている。
【0030】
また、ECU4により触媒1の異常が判定されると、例えばインストルメントパネルの警告灯を点灯させるとともにリッチ運転が禁止されるようなっている。そして、このように触媒1の異常時にリッチ運転を禁止することにより、COを排出するような事態を未然に回避することができる。
本発明の一実施形態にかかるNOx吸蔵量の推定方法は、上述のように構成されているので、以下のようにしてNOx吸蔵量が推定される。
【0031】
まず、リーン運転時において、式(2)から実NOx浄化率rを算出するとともに、実測データ又はマップ値から排ガス温度[y]及びSV値[z]を求める。また、式(1)の多項式において、各係数ki に実験等により求めた適当な値を初期値として入力する。そして、式(1)を変形した式(3)に各値を代入し、NOx吸蔵割合[x]を算出する。
【0032】
次に、式(3)で得られたNOx吸蔵割合[x]と、新たに求めた排ガス温度[y]及びSV値[z]とを式(1)に代入してNOx浄化率r(推定値)を求める。そして、この推定NOx浄化率rと、式(2)で新たに算出した実NOx浄化率rとを比較し、推定NOx浄化率が、実NOx浄化率と一致するように各係数ki を最小二乗法により補正する。
【0033】
そして、このような計算を繰り返し実行し、各係数ki を随時更新することで式(1)が正確に触媒1の状態を表す式となり、高い精度でNOx吸蔵量を推定することができるようになる。また、式(3)を用いて繰り返しNOx吸蔵割合[x]を算出することにより、触媒1に吸蔵されたNOxの積算値を算出することができる。
【0034】
また、リッチ運転中はNOxが放出されるので、このときには式(1)によるNOx吸蔵量の算出を中断して各係数ki を記憶しておくとともに、上述した式(4),(5)によりNOx放出量を算出する。
そして、再びリッチ運転からリーン運転に切り替えられると、リーン運転終了時のNOx吸蔵量からリッチ運転終了時のNOx放出量を減じることにより、リーン運転開始時のNOx残存量が算出される。
【0035】
また、リーン運転開始時のNOx浄化率rの実測値と推定値との差がしきい値以上であると、NOx吸蔵量が補正される。ここで、NOx吸蔵量の補正手法について図4のフローチャートに基づいて説明すると、まず、リーン運転時に多項式(1)の各係数ki を逐次補正して各係数ki を同定する(ステップS1)。
そして、リッチ運転が開始したと判定されると(ステップS2)、各係数ki を保持しておき(ステップS3)、その後、リッチ運転が終了すると(ステップS4)、NOx浄化率の実測値と推定値とを比較し、これらの差がしきい値以上であるかが判定される(ステップS5)。
【0036】
NOx浄化率の実測値と推定値との差がしきい値未満であれば、再びステップ1に戻ってリーン運転時の各係数ki の更新を続行し、しきい値以上であればNOx吸蔵量を式(3)で算出される値に補正して(ステップS6)リターンする。
そして、このようにしてNOx吸蔵量を補正することにより、NOx吸蔵量の推定精度をさらに高めることができる。
【0037】
一方、触媒1の劣化や異常が判定されると、インストルメントパネルの警告灯を点灯させて、ドライバに知らせるとともに、リッチ運転が禁止される。これを図5のフローチャートに基づいて説明すると、まず、多項式(1)の各係数ki を逐次補正して各係数ki を同定し(ステップS11)、次に各係数ki の一定期間の移動平均を算出する(ステップS12)。
【0038】
次に、算出された各係数ki の移動平均がそれぞれ所定の範囲内か否かを判定し(ステップS13)、各係数ki の移動平均がいずれも所定の範囲内であれば、再びステップS2に戻り、各係数ki の移動平均のうちいずれか一つでも所定の範囲外であると、触媒1に異常が生じたと判定して警報を行なう(ステップS14)とともに、リッチ運転を禁止するのである(ステップS15)。
以上詳述したように、本願発明の一実施形態にかかるNOx吸蔵量の推定方法によれば、NOx吸蔵量を、NOx吸蔵触媒1のNOx吸蔵特性を反映させた多項式を用いて推定するとともに、多項式の係数ki を、実測されたNOx浄化率に基づいて逐次補正するので、常に最新の触媒状態をモデル化した多項式とすることができ、高い精度でNOx吸蔵量を推定することができるという利点がある。また、NOx吸蔵量を正確に推定することでNOx吸蔵量に基づいた最適なリッチ運転制御を実行することができ、燃費を向上させることができる。
【0039】
また、NOx吸蔵触媒1を変更した場合でも、変更後の触媒1の特性に応じた各係数ki に更新されるので、モデル式を変更する必要がないという利点がある。これに対して、従来のように数学的なモデル式を適用した場合には、各触媒の特性に応じて係数を特定する作業(合わせ込み)が必要となり多大な労力を要するという課題があるが、本願発明ではこのような合わせ込みを行なうことなく、正確にNOx吸蔵量を推定することができる。
【0040】
NOx放出量を還元剤利用率に基づいて算出するので、比較的高い精度でNOx放出量を推定することができる。
また、リッチ運転中は多項式の係数ki を保持するとともに、リーン運転開始時に保持された係数を用いて推定されるNOx浄化率と、実測されたNOx浄化率との差がしきい値以上であるとNOx吸蔵量を補正するので、やはりNOx吸蔵量の推定精度を高めることができる。
【0041】
各係数ki の所定期間における平均値が所定の範囲を逸脱すると、触媒1が異常であると判定するので、高い精度で触媒1の異常を判定できる。また、このような異常判定時にはドライバに警報を発するので、速やかにドライバは触媒1の異常を認識でき、早期にドライバに触媒1の交換を促すことができる。また、このような触媒1の異常時にはリッチ運転が禁止されるのでCOがそのまま排出されるような事態を回避することができる。
【0042】
なお、本発明のNOx吸蔵量の推定方法は、上述の実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々の変形が可能である。例えば、NOxの放出量については、NOx吸蔵量の推定手法と同様の手法により求めてもよい。
つまり、上述ではNOx放出量を計算する際に用いる還元剤利用率[r′]を図3に示す還元剤利用率設定マップから求めているが、下式(6)に示すように、触媒入口還元剤濃度[x′],排ガス温度[y],SV値[z]の多項式から求めてもよい。
なお、mi (i=1,2,・・・)は係数である。また、式(6)はNOx吸蔵触媒1のNOx放出特性を反映させた多項式であって、各係数mi には、式(1)と同様に実験等から得られた適当な値が初期値として入力されている。
【0043】
また、この場合には少なくとも排気通路2上に還元剤(具体的にはCO)濃度を検出するセンサ(COセンサ)を設け、このCOセンサから得られる還元剤濃度[x′]の実測値と、式(6)から得られる還元剤濃度[x′]の推定値とから各係数miを逐次更新して還元剤利用率r′を求め、この値を上述した式(4)に代入することでNOx放出量を求めることができる。
【0044】
そして、このようにしてNOx放出量を求めることでNOx放出量の推定精度を高めることができる。
【0045】
【発明の効果】
以上詳述したように、本発明のNOx吸蔵量の推定方法によれば、NOx吸蔵量を、NOx吸蔵触媒のNOx吸蔵特性を反映させた多項式を用いて推定するとともに、多項式の係数を、実測されたNOx浄化率に基づいて逐次補正するので、高い精度でNOx吸蔵量を推定することができるという利点がある。また、NOx吸蔵量を正確に推定することでNOx吸蔵量に基づいた最適なリッチ運転制御を実行することができ、燃費を向上させることができる。また、NOx吸蔵触媒を変更した場合でも、変更後の触媒の特性に応じた各係数に更新されるので、モデル式を変更する必要がないという利点がある(請求項1)。
また、NOx放出量を還元剤利用率に基づいて算出するので、比較的高い精度でNOx放出量を推定することができる(請求項2)。
また、還元剤利用率を触媒のNOx放出特性を反映させた多項式を用いて推定するとともに、多項式の係数を還元剤の濃度に基づいて逐次補正するので、NOx放出量の推定精度をさらに高めることができるという利点がある(請求項3)。
また、リッチ運転中は多項式の係数を保持するとともに、リーン運転開始時に推定NOx浄化率と、実NOx浄化率との差がしきい値以上であるとNOx吸蔵量を補正することにより、NOx吸蔵量の推定精度をさらに高めることができる(請求項4)。
また、多項式における各係数の所定期間の平均値が所定の範囲を逸脱すると、触媒が異常である判定するので、触媒の異常判定を高い精度で実行することができる利点がある(請求項5)。
【図面の簡単な説明】
【図1】本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明するための模式的なブロック図である。
【図2】本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明するためのマップであって、NOx触媒のNOx吸蔵時の特性を示すマップである。
【図3】本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明するためマップであって、NOx触媒のNOx放出時の特性を示すマップである。
【図4】本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明するためのフローチャートである。
【図5】本発明の一実施形態にかかるNOx吸蔵量の推定方法について説明するためのフローチャートである。
【図6】従来の技術について説明する図である。
【符号の説明】
1 NOx吸蔵触媒(触媒)
2 排気通路
3 NOxセンサ(NOx濃度検出手段)
4 ECU[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for estimating the amount of NOx stored in a NOx storage-type reduction catalyst provided in an exhaust passage.
[0002]
[Prior art]
In general, in a diesel engine, due to its structural characteristics, exhaust gas contains a large amount of oxygen and the atmosphere becomes an oxidizing atmosphere (that is, the exhaust air-fuel ratio becomes lean). Also, if a gasoline engine is capable of lean burn, the exhaust air-fuel ratio will also be lean during lean burn. Therefore, a lean NOx catalyst has been conventionally developed so that NOx can be purified even in such an oxidizing atmosphere.
[0003]
As such a lean NOx catalyst, there is a NOx storage type reduction catalyst (hereinafter, referred to as a NOx storage catalyst or simply a catalyst). In the NOx storage catalyst, NOx in the exhaust gas is stored in an oxidizing atmosphere, and the stored NOx is released when CO is present under a low oxygen concentration. Most of the NOx released from the NOx storage catalyst is released. The gas is reduced to harmless N 2 by a reducing agent such as unburned HC and CO discharged from the engine and then discharged to the atmosphere.
[0004]
In a vehicle equipped with a NOx storage catalyst, generally, so-called rich spike control is performed. In other words, if the operation is continued at a lean air-fuel ratio, the NOx storage catalyst is in a saturated state in which NOx can no longer be stored, so that the air-fuel ratio is temporarily forcibly made rich at an appropriate timing (rich spike control is performed. This reduces the concentration of oxygen in the exhaust gas, and releases NOx from the NOx storage catalyst by supplying a reducing agent, thereby regenerating the NOx storage catalyst to a state where NOx can be stored.
[0005]
By the way, in order to perform the rich spike control as described above, it is necessary to accurately estimate (or detect) the NOx storage amount in the NOx storage catalyst. As a method for estimating the NOx storage amount, for example, the following method is used. Techniques are known.
(1) First prior art: NOx occlusion amount estimation method using NOx sensor In this first prior art, as shown in FIG. 6, NOx concentration is detected upstream and downstream of the catalyst 101, respectively. In addition to providing the sensors 102 and 103, an air flow sensor (not shown) for detecting the exhaust gas flow rate is provided in the exhaust passage.
[0006]
Then, the
NOx storage amount = exhaust gas flow rate x (catalyst upstream NOx concentration-catalyst downstream NOx concentration)
{Circle around (2)} Second prior art: estimation method using a mathematical model (for example, Patent Document 1)
In the second prior art, a mathematical catalyst model based on the chemical phenomena and physical phenomena of a catalyst such as an occlusion reaction, an oxidation-reduction reaction, and a desorption reaction is provided, and the NOx occlusion amount is estimated using the catalyst model formula.
[0007]
[Patent Document 1]
JP-A-9-72235
[Problems to be solved by the invention]
However, in the first prior art, the NOx storage amount can be calculated during the lean operation, but the NOx release amount (decrease in the storage amount) during the rich operation cannot be detected by the NOx sensor. For this reason, when the rich operation time is insufficient, there is a problem that the NOx remaining in the catalyst is accumulated and a calculation error of the NOx storage amount occurs. In addition, there is a problem that NOx sensors are required upstream and downstream of the catalyst, respectively, which causes an increase in cost.
[0009]
Further, in the second conventional technique, the NOx storage amount can be estimated only by providing at least one NOx sensor downstream of the catalyst. However, since this technique is mainly applied to the air-fuel ratio control of the three-way catalyst. However, there is a problem that the model structure is different from the NOx storage catalyst, and it is difficult to apply the NOx storage catalyst to the NOx storage catalyst. Also, when estimating the NOx occlusion amount using other catalyst models, it is necessary to change the model formula because the characteristic values are different for each catalyst type. There is a problem that requires modeling.
[0010]
The present invention has been made in view of such a problem, and has been proposed in order to estimate the NOx storage amount of the NOx storage catalyst with high accuracy by always reflecting the latest state in the catalyst model. The aim is to provide a method.
[0011]
[Means for Solving the Problems]
For this reason, the method for estimating the NOx storage amount according to the first aspect of the present invention is a method for estimating the NOx storage amount of the NOx storage catalyst provided in the exhaust passage of the engine. The estimation is performed using a polynomial that reflects the NOx storage characteristics of the NOx storage catalyst, and the coefficient of each polynomial is sequentially corrected based on the actually measured NOx purification rate.
[0012]
Further, the NOx release amount of the NOx storage catalyst may be calculated by the following equation. NOx emission amount = ∫ (catalyst inlet reducing agent concentration × reducing agent utilization rate−0.5 × catalyst inlet oxygen concentration) × exhaust gas flow rate Preferably, the reducing agent utilization rate reflects the NOx emission characteristics of the NOx storage catalyst. And the coefficients of the polynomial are sequentially corrected based on the concentration of the reducing agent.
[0013]
Preferably, the engine is configured to be capable of switching between a lean operation in which the exhaust air-fuel ratio is lean and a rich operation in which the exhaust air-fuel ratio is rich, and holds the coefficient of the polynomial during the rich operation. At the same time, when the difference between the NOx purification rate obtained by using the held coefficient at the start of the lean operation and the actually measured NOx purification rate is equal to or larger than a threshold value, the NOx storage amount is corrected.
[0014]
Furthermore, when any one of the average values of the coefficients deviates from the set predetermined range, the catalyst may be determined to be abnormal.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for estimating the NOx occlusion amount according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the entire configuration of an exhaust system of a vehicle to which the present invention is applied.
As shown in the drawing, a NOx storage catalyst 1 is interposed in the exhaust passage 2, and a NOx sensor 3 for detecting the NOx concentration at the catalyst outlet is provided downstream of the NOx storage catalyst 1.
[0016]
Although not shown, an O 2 sensor, a temperature sensor, an air flow sensor (AFS), and the like are connected to the exhaust passage 2, and the oxygen concentration, the exhaust gas temperature, and the exhaust gas flow rate in the exhaust passage 2 are detected by these sensors. Each is detected.
Each sensor 3 is connected to an
[0017]
The
[0018]
By the way, in the prior art 2 described above, the characteristic itself of the NOx storage catalyst is described by a mathematical model to determine the NOx storage amount, whereas in the present invention, the NOx storage amount is calculated using a four-dimensional linear polynomial. It is supposed to.
That is, the
In the equation (1), r is the NOx purification rate, x is the NOx storage ratio, y is the exhaust gas temperature, z is the SV value (or the exhaust gas flow rate), and k 0 , k 1 , k 2 ,. is there.
[0019]
Here, the NOx storage characteristics of the NOx storage catalyst 1 can be known in advance by experiments or the like, and can be approximated by a polynomial. For example, if the number of parameters is three (three-dimensional), the characteristics of the catalyst can be represented by a curved surface as shown in FIG. 2, and this can be represented by a polynomial. Of course, since equation (1) is four-dimensional, it does not have a curved surface as shown in FIG. 2, but the concept is the same as in the case of three-dimensional.
[0020]
For each coefficient k i (i = 1, 2,...), An appropriate value is input as an initial value from characteristics previously obtained through experiments or the like.
Then, during engine operation, always by sequentially correcting the coefficients k i based on the value detected by the catalyst downstream of the NOx sensor 3 by the equation (1), it is possible to represent the latest catalytic state.
[0021]
Hereinafter, the method of NOx estimation will be described in more detail. First, the NOx purification rate r in the equation (1) can also be obtained by the following equation (2).
r = NOx concentration at catalyst outlet / NOx concentration at catalyst inlet ... (2)
Here, the catalyst outlet NOx concentration is a value detected by the NOx sensor 3, and the catalyst inlet NOx concentration is a value obtained from a map. Therefore, the NOx purification rate r obtained by the equation (2) can be called a sensor value (actually measured value), and the NOx purification rate r obtained by the equation (1) can be called an estimated value (calculated value).
[0022]
As the exhaust gas temperature [y] and the SV value [z] in the equation (1), measured data or map values are applied. Thus, the only unknown value in the equation (1) is the NOx storage ratio [x], and the other values are known. Therefore, the NOx occlusion ratio [x] can be obtained by the following equation (3) obtained by modifying the equation (1).
x = [r- (k 0 + k 2 y + k 3 z ··) ] / (k 1 + k 4 y + ··) ·· (3)
Then, the NOx storage ratio [x] obtained by the equation (3) is returned to the equation (1) and used for the calculation in the next calculation cycle. That is, in equation (1), the purification rate r is calculated using the NOx storage ratio [x] obtained last time and [y] and [z] newly detected in the current calculation cycle. It is.
[0023]
Here, a purification rate r is the estimated value calculated by Equation (1), if the coefficient k i is the exact value, the estimated value and the measured value obtained by the equation (2) of the purification rate r Should match.
Therefore, in the present invention, the estimated value and the measured value of the purification rate r are compared, and if there is a difference between the estimated value and the measured value, each coefficient k i is minimized so that the estimated value becomes the measured value. The correction is performed sequentially using the square method. Then, by repeatedly performing such calculation and sequentially correcting each coefficient k i , the polynomial of Expression (1) can be changed to an expression that accurately reflects the state of the NOx storage catalyst 1 as needed.
[0024]
That, NOx occlusion catalyst 1 is one in which its properties by usage and aging and the like are changed by correcting repeatedly even coefficients k i times represents formula (1) is exactly of the catalyst 1 state Thus, the NOx storage amount can be estimated with high accuracy. The NOx occlusion ratio [x] obtained by the equation (3) is an instantaneous NOx occlusion amount in the calculation cycle at the beginning, but this calculation result is repeatedly returned to the equation (1) to calculate the purification rate r. By doing so, the integrated value of NOx stored in the catalyst 1 can be calculated.
[0025]
As described above, during the lean operation for storing NOx, the catalyst outlet [NOx] is taken in from the NOx sensor 3 provided downstream of the catalyst, and is compared with the estimated value obtained by the equation (2). Correcting the coefficient k i by the multiplicative method makes it possible to obtain an accurate NOx storage amount.
By the way, since NOx is released during the rich operation, if the accurate NOx release amount cannot be detected or estimated, the initial value of the NOx occlusion amount in the next lean operation cannot be accurately calculated.
[0026]
Therefore, along with being rich operation keeps the k i, the following equation (4), (5) to calculate the NOx emission amount, equation (4) from the NOx occlusion amount at the time immediately before the start rich operation, calculated by (5) The calculated NOx release amount is subtracted to calculate the NOx storage amount during the rich operation.
NOx emission amount = ∫ (catalyst inlet reducing agent concentration × reducing agent utilization rate [r ′] − 0.5 × catalyst inlet [O 2 ]) × exhaust gas flow rate (4)
Reducing agent utilization rate [r '] = f (y, z) (5)
Here, the ECU 1 is provided with a reducing agent utilization rate setting map as shown in FIG. This map stores characteristics of the reducing agent utilization based on the exhaust gas temperature [y] and the SV value [z], and sets the reducing agent utilization based on these parameters [y] and [z]. It has become so.
[0027]
Further, the catalyst inlet reducing agent concentration (catalyst inlet [CO], catalyst inlet [HC]) can be obtained from the map using the accelerator opening and the engine speed as parameters as described above. Value or detected value.
Accordingly, when switched to rich operation from the lean operation, stores the NOx occlusion amount holds each coefficient k i during the lean operation end in
[0028]
The
[0029]
Further,
[0030]
Further, when the
Since the method for estimating the NOx storage amount according to one embodiment of the present invention is configured as described above, the NOx storage amount is estimated as follows.
[0031]
First, during the lean operation, the actual NOx purification rate r is calculated from the equation (2), and the exhaust gas temperature [y] and the SV value [z] are obtained from the measured data or the map value. In the polynomial of the equation (1), an appropriate value obtained by an experiment or the like is input as an initial value for each coefficient k i . Then, the respective values are substituted into Expression (3) obtained by modifying Expression (1), and the NOx storage ratio [x] is calculated.
[0032]
Next, the NOx storage ratio [x] obtained by the equation (3) and the newly obtained exhaust gas temperature [y] and SV value [z] are substituted into the equation (1) to obtain the NOx purification rate r (estimated). Value). The minimum and the estimated NOx purification ratio r, is compared with the actual NOx purification rate r newly calculated by the equation (2), the estimated NOx purification rate, each coefficient k i to match the actual NOx purification rate Correct by the square method.
[0033]
Then, such calculations the repeatedly executed, so that each coefficient k i Equation (1) by updated at any time becomes equation accurately represent the state of the catalyst 1, it is possible to estimate the NOx adsorption amount with high accuracy become. Further, by repeatedly calculating the NOx storage ratio [x] using the equation (3), the integrated value of the NOx stored in the catalyst 1 can be calculated.
[0034]
Furthermore, since during rich operation NOx is released, along with storing the respective coefficients k i to interrupt the calculation of the NOx occlusion amount by the formula (1) in this case, the above-mentioned formula (4), (5) To calculate the NOx release amount.
When the operation is switched from the rich operation to the lean operation again, the NOx remaining amount at the start of the lean operation is calculated by subtracting the NOx release amount at the end of the rich operation from the NOx storage amount at the end of the lean operation.
[0035]
If the difference between the measured value and the estimated value of the NOx purification rate r at the start of the lean operation is equal to or larger than the threshold value, the NOx storage amount is corrected. Here, it will be described with reference to the flowchart of FIG method for correcting the NOx occlusion amount, firstly, sequentially corrected and identifying each coefficient k i of each coefficient k i of the polynomial (1) during lean operation (step S1) .
When it is determined that the rich operation is started (step S2), and holds the respective coefficient k i (step S3), and thereafter, when the rich operation is completed (step S4), and the measured value of the NOx purification rate The estimated values are compared with each other, and it is determined whether these differences are equal to or larger than a threshold value (step S5).
[0036]
If the difference is less than the threshold value between the actual measurement value and the estimated value of the NOx purification rate, and continue to update the coefficients k i during lean operation returns to Step 1 again, NOx occlusion if equal to or greater than the threshold value The amount is corrected to the value calculated by equation (3) (step S6), and the routine returns.
By correcting the NOx storage amount in this way, the estimation accuracy of the NOx storage amount can be further improved.
[0037]
On the other hand, when it is determined that the catalyst 1 has deteriorated or is abnormal, the warning light on the instrument panel is turned on to inform the driver and rich operation is prohibited. This will be described with reference to the flowchart of FIG. 5, first, the polynomial (1) sequentially corrects each coefficient k i of identifying the coefficients k i (step S11), and then a period of time of each coefficient k i A moving average is calculated (step S12).
[0038]
Next, it is determined whether or not the calculated moving average of each coefficient k i is within a predetermined range (step S13). If the moving average of each coefficient k i is within the predetermined range, step S13 is performed again. returning to S2, if there in a predetermined range in one of the moving average of the coefficients k i, it is determined that the abnormality in the catalyst 1 resulted perform an alarm (step S14), and prohibits the rich operation (Step S15).
As described in detail above, according to the method for estimating the NOx storage amount according to one embodiment of the present invention, the NOx storage amount is estimated using a polynomial that reflects the NOx storage characteristics of the NOx storage catalyst 1, and Since the coefficient k i of the polynomial is successively corrected based on the actually measured NOx purification rate, it is possible to always use a polynomial that models the latest catalyst state, and to estimate the NOx storage amount with high accuracy. There are advantages. Further, by accurately estimating the NOx storage amount, it is possible to execute optimal rich operation control based on the NOx storage amount, and to improve fuel efficiency.
[0039]
Also, when you change the NOx storage catalyst 1, therefore it is updated each coefficient k i corresponding to the characteristics of the catalyst 1 after the change, there is an advantage that there is no need to change the model equation. On the other hand, when a mathematical model formula is applied as in the related art, there is a problem that an operation (adjustment) of specifying a coefficient according to the characteristics of each catalyst is required, and a great deal of labor is required. According to the present invention, the NOx storage amount can be accurately estimated without performing such adjustment.
[0040]
Since the NOx emission amount is calculated based on the reducing agent utilization rate, the NOx emission amount can be estimated with relatively high accuracy.
In addition, holds the coefficients k i during rich operation polynomials, the NOx purification rate is estimated using a coefficient which is held at the lean operation start, the difference between the actually measured NOx purification rate than the threshold value If there is, the NOx storage amount is corrected, so that the estimation accuracy of the NOx storage amount can also be improved.
[0041]
If the average value in a predetermined period of each coefficient k i deviates from the predetermined range, determines that the catalyst 1 is abnormal, it can determine an abnormality of the catalyst 1 with high accuracy. Further, when such an abnormality is determined, an alarm is issued to the driver, so that the driver can quickly recognize the abnormality of the catalyst 1 and prompt the driver to replace the catalyst 1 at an early stage. In addition, when the catalyst 1 is abnormal, the rich operation is prohibited, so that a situation in which CO is directly discharged can be avoided.
[0042]
Note that the method of estimating the NOx storage amount of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the amount of released NOx may be obtained by a method similar to the method of estimating the amount of stored NOx.
That is, in the above description, the reductant utilization rate [r '] used in calculating the NOx release amount is obtained from the reductant utilization rate setting map shown in FIG. 3, but as shown in the following equation (6), It may be obtained from a polynomial of the reducing agent concentration [x '], the exhaust gas temperature [y], and the SV value [z].
Note that mi (i = 1, 2,...) Is a coefficient. Further, equation (6) is a polynomial which reflects the NOx emission characteristics of NOx storage catalyst 1, each coefficient m i, equation (1) and the appropriate value is an initial value obtained from the same experiment, etc. Is entered as
[0043]
In this case, a sensor (CO sensor) for detecting the concentration of the reducing agent (specifically, CO) is provided at least on the exhaust passage 2, and the measured value of the reducing agent concentration [x '] obtained from this CO sensor is From the estimated value of the reducing agent concentration [x '] obtained from the equation (6), each coefficient mi is successively updated to obtain the reducing agent utilization rate r', and this value is substituted into the above-described equation (4). Thus, the NOx release amount can be obtained.
[0044]
By obtaining the NOx release amount in this way, the estimation accuracy of the NOx release amount can be improved.
[0045]
【The invention's effect】
As described in detail above, according to the NOx storage amount estimation method of the present invention, the NOx storage amount is estimated using a polynomial that reflects the NOx storage characteristics of the NOx storage catalyst, and the coefficient of the polynomial is measured. Since the correction is sequentially performed based on the determined NOx purification rate, there is an advantage that the NOx storage amount can be estimated with high accuracy. Further, by accurately estimating the NOx storage amount, it is possible to execute optimal rich operation control based on the NOx storage amount, and to improve fuel efficiency. Further, even when the NOx storage catalyst is changed, the coefficient is updated to each coefficient according to the changed characteristics of the catalyst, so that there is an advantage that it is not necessary to change the model formula (claim 1).
Further, since the NOx emission amount is calculated based on the reducing agent utilization rate, the NOx emission amount can be estimated with relatively high accuracy (claim 2).
Further, since the reducing agent utilization rate is estimated using a polynomial that reflects the NOx emission characteristics of the catalyst, and the coefficient of the polynomial is sequentially corrected based on the concentration of the reducing agent, the estimation accuracy of the NOx emission amount is further improved. (Claim 3).
In addition, during the rich operation, the polynomial coefficient is held, and when the difference between the estimated NOx purification rate and the actual NOx purification rate at the start of the lean operation is equal to or larger than a threshold value, the NOx storage amount is corrected to thereby store NOx. The accuracy of estimating the amount can be further improved (claim 4).
Further, when the average value of each coefficient in the polynomial in a predetermined period deviates from a predetermined range, it is determined that the catalyst is abnormal. Therefore, there is an advantage that the abnormality determination of the catalyst can be performed with high accuracy. .
[Brief description of the drawings]
FIG. 1 is a schematic block diagram for explaining a method for estimating an NOx storage amount according to an embodiment of the present invention.
FIG. 2 is a map for explaining a method of estimating a NOx storage amount according to one embodiment of the present invention, and is a map showing characteristics of a NOx catalyst during NOx storage.
FIG. 3 is a map for explaining a method of estimating the NOx storage amount according to one embodiment of the present invention, and is a map showing characteristics of the NOx catalyst at the time of releasing NOx.
FIG. 4 is a flowchart illustrating a method for estimating the amount of stored NOx according to an embodiment of the present invention.
FIG. 5 is a flowchart illustrating a method for estimating an NOx storage amount according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating a conventional technique.
[Explanation of symbols]
1 NOx storage catalyst (catalyst)
2 Exhaust passage 3 NOx sensor (NOx concentration detecting means)
4 ECU
Claims (5)
該NOx吸蔵量を、該NOx吸蔵触媒のNOx吸蔵特性を反映させた多項式を用いて推定するとともに、
該多項式の各係数を、実測されたNOx浄化率に基づいて逐次補正する
ことを特徴とする、NOx吸蔵量の推定方法。A method for estimating the NOx storage amount of a NOx storage catalyst provided in an exhaust passage of an engine,
The NOx storage amount is estimated using a polynomial that reflects the NOx storage characteristics of the NOx storage catalyst,
A method for estimating a NOx storage amount, wherein each coefficient of the polynomial is sequentially corrected based on an actually measured NOx purification rate.
ことを特徴とする、請求項1記載のNOx吸蔵量の推定方法。
NOx放出量=∫(触媒入口還元剤濃度×還元剤利用率−0.5×触媒入口酸素濃度)×排ガス流量2. The method according to claim 1, wherein the NOx release amount in the NOx storage catalyst is calculated by the following equation.
NOx emission amount = ∫ (catalyst inlet reducing agent concentration x reducing agent utilization rate-0.5 x catalyst inlet oxygen concentration) x exhaust gas flow rate
該多項式の係数を還元剤の濃度に基づいて逐次補正する
ことを特徴とする、請求項2記載のNOx吸蔵量の推定方法。Estimating the reducing agent utilization rate using a polynomial that reflects the NOx release characteristics of the NOx storage catalyst,
3. The method according to claim 2, wherein the coefficient of the polynomial is corrected sequentially based on the concentration of the reducing agent.
該リッチ運転中は該多項式の係数を保持するとともに、リーン運転開始時に該保持された係数を用いて得られるNOx浄化率と、該実測されたNOx浄化率との差がしきい値以上であると該NOx吸蔵量を補正する
ことを特徴とする、請求項1記載のNOx吸蔵量の推定方法。The engine is configured to be capable of switching between a lean operation in which the exhaust air-fuel ratio is lean and a rich operation in which the exhaust air-fuel ratio is rich,
During the rich operation, the coefficient of the polynomial is retained, and the difference between the NOx purification rate obtained using the retained coefficient at the start of the lean operation and the actually measured NOx purification rate is equal to or greater than a threshold value. 2. The method for estimating a NOx storage amount according to claim 1, wherein the NOx storage amount is corrected.
ことを特徴とする、請求項1〜5のいずれか1項記載のNOx吸蔵量推定方法。6. The NOx storage amount estimating method according to claim 1, wherein the catalyst is determined to be abnormal when the average value of each coefficient in a predetermined period deviates from a predetermined range.
Priority Applications (4)
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JP2003083650A JP2004293338A (en) | 2003-03-25 | 2003-03-25 | Method for presuming amount of nox occlusion |
DE102004013604A DE102004013604B4 (en) | 2003-03-25 | 2004-03-19 | Method of estimating a NOx absorption amount |
KR1020040019311A KR100592414B1 (en) | 2003-03-25 | 2004-03-22 | Method of Estimating NOX Storage |
US10/807,236 US20040244361A1 (en) | 2003-03-25 | 2004-03-24 | Estimating method of NOx occlusion amount |
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JP2003083650A JP2004293338A (en) | 2003-03-25 | 2003-03-25 | Method for presuming amount of nox occlusion |
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WO2011027469A1 (en) | 2009-09-01 | 2011-03-10 | トヨタ自動車株式会社 | Exhaust purification device for internal combustion engine |
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US20040244361A1 (en) | 2004-12-09 |
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