JPH1162559A - Exhaust emission control device of internal combustion engine - Google Patents
Exhaust emission control device of internal combustion engineInfo
- Publication number
- JPH1162559A JPH1162559A JP21481897A JP21481897A JPH1162559A JP H1162559 A JPH1162559 A JP H1162559A JP 21481897 A JP21481897 A JP 21481897A JP 21481897 A JP21481897 A JP 21481897A JP H1162559 A JPH1162559 A JP H1162559A
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- Prior art keywords
- catalyst
- amount
- hydrocarbon
- supply
- limit value
- Prior art date
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- Exhaust Gas After Treatment (AREA)
Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、内燃機関の排気中
に含まれる窒素酸化物を浄化する内燃機関の排気浄化装
置に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine for purifying nitrogen oxides contained in exhaust gas of an internal combustion engine.
【0002】[0002]
【従来の技術】ディーゼルエンジン等の酸素過剰下で燃
料の燃焼が行われる内燃機関から排出される排気中の窒
素酸化物(NOx)を浄化するために、排気管内にNO
x触媒を設置し、燃料等の炭化水素(HC)を還元剤と
してNOx触媒に供給してNOxを還元浄化するNOx
触媒システムが開発されている。このNOx触媒システ
ムでは、近年、特開平9一4437号公報に示すよう
に、触媒への過剰な燃料の供給による燃費悪化を少なく
するために、触媒のHC吸着割合と触媒からのHC脱離
速度等に応じて触媒へのHC供給量を制御することが提
案されている。2. Description of the Related Art In order to purify nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine in which fuel is burned under an excessive amount of oxygen such as a diesel engine, a NO.
NOx for reducing and purifying NOx by installing a x-catalyst and supplying hydrocarbon (HC) such as fuel as a reducing agent to the NOx catalyst
Catalyst systems have been developed. In this NOx catalyst system, as disclosed in Japanese Patent Application Laid-Open No. Hei 9-14437, in order to reduce fuel consumption deterioration due to excessive supply of fuel to the catalyst, the HC adsorption ratio of the catalyst and the HC desorption rate from the catalyst have recently been reduced. It has been proposed to control the amount of HC supplied to the catalyst according to the conditions.
【0003】[0003]
【発明が解決しようとする課題】本発明者らは、最近、
NOx触媒システムにおけるNOx触媒の被毒現象を調
査したところ、供給したHCが触媒に多量に吸着される
と、そのHCによって触媒が被毒を受けて元の状態まで
回復しにくい状態となり、NOx浄化性能が著しく低下
する現象を発見した。このような触媒の被毒は、触媒の
HC吸着量が一定値を越えたときに発生し始め(以下、
この時のHC吸着量を「被毒限界値」と呼ぶ)、一旦、
触媒が被毒されると、ガソリンエンジンと比較して排気
温度が低い通常のディーゼルエンジンの運転条件では、
触媒からHCが脱離しにくい状態になって、触媒の回復
が因難になることが分かってきた。SUMMARY OF THE INVENTION The present inventors have recently
When the poisoning phenomenon of the NOx catalyst in the NOx catalyst system was investigated, when a large amount of the supplied HC was adsorbed on the catalyst, the catalyst was poisoned by the HC and became difficult to recover to the original state. A phenomenon that the performance is significantly reduced was discovered. Such poisoning of the catalyst starts to occur when the amount of HC adsorbed by the catalyst exceeds a certain value (hereinafter, referred to as “HC poisoning”).
The amount of HC adsorption at this time is called "poisoning limit value").
When the catalyst is poisoned, under normal diesel engine operating conditions with lower exhaust temperatures compared to gasoline engines,
It has been found that it becomes difficult for HC to be desorbed from the catalyst, and that recovery of the catalyst becomes difficult.
【0004】しかるに、上記公報のHC供給量制御方法
では、触媒のHC吸着割合を検出するものの、専ら燃費
改善とNOx浄化率向上とを優先した制御であるため、
時として触媒のHC吸着量が被毒限界値を越えてしま
い、元の状態まで回復し得ない被毒が発生し、NOx浄
化性能が低下するという問題がある。[0004] However, in the method of controlling the amount of HC supplied in the above-mentioned publication, although the HC adsorption ratio of the catalyst is detected, the control is performed mainly with priority given to the improvement of the fuel consumption and the improvement of the NOx purification rate.
In some cases, the amount of HC adsorbed by the catalyst exceeds the poisoning limit value, and poisoning that cannot be recovered to the original state occurs, and the NOx purification performance is reduced.
【0005】本発明はこのような事情を考慮してなされ
たものであり、従ってその目的は、触媒が過剰なHCの
吸着による被毒を起こさないように、触媒へのHC供給
量を適正化することができて、長期間に亘って高いNO
x浄化性能を維持できる内燃機関の排気浄化装置を提供
することにある。The present invention has been made in view of such circumstances, and accordingly, an object of the present invention is to optimize the amount of HC supplied to a catalyst so that the catalyst is not poisoned by excessive adsorption of HC. Can have high NO over a long period of time
An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can maintain x purification performance.
【0006】[0006]
【課題を解決するための手段】上記目的を達成するため
に、本発明の請求項1の内燃機関の排気浄化装置によれ
ば、内燃機関の運転状態に基づいて触媒に供給すべき炭
化水素量(以下「基本炭化水素供給量」という)を基本
炭化水素供給量演算手段により演算すると共に、触媒に
吸着された炭化水素吸着量を炭化水素吸着量検出手段に
より検出し、その炭化水素吸着量が設定値を越えないよ
うに前記基本炭化水素供給量を補正手段により補正して
目標炭化水素供給量を決定し、この目標炭化水素供給量
に応じて炭化水素供給手段を制御手段により制御して、
触媒に対して目標炭化水素供給量に相当する量の炭化水
素を供給する。このようにすれば、触媒の炭化水素吸着
量が過剰とならないように触媒への炭化水素供給量を適
正に制限することができ、過剰な炭化水素の吸着による
触媒の被毒が従来より発生しにくくなり、長期間に亘っ
て高いNOx浄化性能を維持することができる。According to the first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, the amount of hydrocarbons to be supplied to a catalyst based on an operating state of the internal combustion engine. (Hereinafter, referred to as "basic hydrocarbon supply amount") is calculated by the basic hydrocarbon supply amount calculating means, and the amount of hydrocarbon adsorbed on the catalyst is detected by the hydrocarbon adsorption amount detecting means. The target hydrocarbon supply amount is determined by correcting the basic hydrocarbon supply amount by the correction unit so as not to exceed the set value, and the hydrocarbon supply unit is controlled by the control unit in accordance with the target hydrocarbon supply amount,
An amount of hydrocarbon corresponding to the target hydrocarbon supply amount is supplied to the catalyst. In this manner, the amount of hydrocarbon supplied to the catalyst can be appropriately limited so that the amount of hydrocarbon adsorbed by the catalyst does not become excessive, and poisoning of the catalyst due to excessive adsorption of hydrocarbons occurs more than before. Therefore, high NOx purification performance can be maintained for a long period of time.
【0007】この場合、請求項2のように、触媒の炭化
水素吸着量を制限するための設定値を、触媒の被毒限界
値又はそれ以下の値に設定することが好ましい。このよ
うにすれば、触媒の炭化水素吸着量が被毒限界値を越え
ないように、触媒への炭化水素供給量を適正化すること
ができ、過剰な炭化水素の吸着による触媒の被毒を確実
に防止することができる。In this case, it is preferable that the set value for limiting the amount of hydrocarbon adsorbed by the catalyst is set to a poisoning limit value of the catalyst or a value lower than the limit value. In this way, the amount of hydrocarbon supplied to the catalyst can be optimized so that the amount of hydrocarbon adsorbed by the catalyst does not exceed the poisoning limit value, and poisoning of the catalyst due to excessive adsorption of hydrocarbons can be prevented. It can be reliably prevented.
【0008】また、請求項3のように、触媒の炭化水素
吸着量に応じて補正係数を設定し、この補正係数を基本
炭化水素供給量に乗算して目標炭化水素供給量を求める
ようにしても良い。このようにすれば、比較的簡単な演
算処理で、炭化水素供給量の補正量を触媒の炭化水素吸
着量に応じて適正に設定することができ、NOx浄化性
能の低下を最小限に抑えながら触媒の被毒を有効に防止
することができる。According to a third aspect of the present invention, a correction coefficient is set according to the amount of hydrocarbon adsorbed by the catalyst, and the correction coefficient is multiplied by the basic hydrocarbon supply amount to obtain a target hydrocarbon supply amount. Is also good. By doing so, the correction amount of the hydrocarbon supply amount can be appropriately set in accordance with the hydrocarbon adsorption amount of the catalyst by relatively simple arithmetic processing, and the decrease in NOx purification performance can be minimized. Poisoning of the catalyst can be effectively prevented.
【0009】また、請求項3のように、触媒の炭化水素
吸着量が触媒の被毒限界値を越えた時に、炭化水素供給
手段による炭化水素の供給を、該炭化水素吸着量が被毒
限界値以下となるまで停止させるようにしても良い。こ
のようにすれば、触媒の炭化水素吸着量が被毒限界値を
越えて増加することを確実に防止でき、触媒の被毒をよ
り確実に防止することができる。Further, when the amount of adsorbed hydrocarbons of the catalyst exceeds the poisoning limit value of the catalyst, the supply of hydrocarbons by the hydrocarbon supply means is reduced by the amount of adsorbed hydrocarbons. Stopping may be performed until the value becomes equal to or less than the value. By doing so, it is possible to reliably prevent the amount of hydrocarbon adsorbed by the catalyst from exceeding the poisoning limit value, and it is possible to more reliably prevent poisoning of the catalyst.
【0010】[0010]
【発明の実施の形態】以下、本発明の一実施形態を図面
に基づいて説明する。まず、図1に基づいてシステム全
体の構成を説明する。内燃機関であるディーゼルエンジ
ン11の排気管12(排気通路)の途中には、排気中の
NOxを還元浄化するNOx触媒13が設けられてい
る。このNOx触媒13は、活性金属である白金を多孔
質ゼオライトの一種に担持させたものであり、このNO
x触媒13の内部で排気中のNOxが炭化水素(HC)
と反応して浄化される。このNOx触媒13の入口部に
は、触媒温度を評価するために、NOx触媒13に流入
する排気の温度を検出する排気温度センサ14が設置さ
れている。DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, the configuration of the entire system will be described with reference to FIG. A NOx catalyst 13 that reduces and purifies NOx in exhaust gas is provided in the exhaust pipe 12 (exhaust passage) of a diesel engine 11 that is an internal combustion engine. The NOx catalyst 13 is obtained by supporting platinum as an active metal on a kind of porous zeolite.
NOx in the exhaust gas inside the x catalyst 13 is converted into hydrocarbon (HC)
And purified. An exhaust temperature sensor 14 for detecting the temperature of exhaust gas flowing into the NOx catalyst 13 is installed at the inlet of the NOx catalyst 13 to evaluate the catalyst temperature.
【0011】また、排気管12のうちのNOx触媒13
の上流側には、還元剤用のHCとして軽油等の燃料をN
Ox触媒13に供給するHC供給ノズル15(炭化水素
供給手段)が設けられている。このHC供給ノズル15
には、燃料タンク(図示せず)から噴射ポンプ16で汲
み上げた燃料が供給される。この噴射ポンプ16を駆動
する駆動回路17は、エンジン制御回路18(制御手
段)からの目標HC供給量信号によって制御される。The NOx catalyst 13 in the exhaust pipe 12
Upstream of the fuel, such as light oil as HC for the reducing agent
An HC supply nozzle 15 (hydrocarbon supply means) for supplying to the Ox catalyst 13 is provided. This HC supply nozzle 15
Is supplied with fuel pumped by an injection pump 16 from a fuel tank (not shown). A drive circuit 17 for driving the injection pump 16 is controlled by a target HC supply amount signal from an engine control circuit 18 (control means).
【0012】NOx触媒13の過剰なHC吸着による被
毒を回避するために、NOx触媒13のHC吸着量を検
出するHC吸着量検出装置19(炭化水素吸着量検出手
段)が設けられている。HC吸着量の検出原理は、過
去のエンジン運転条件の履歴から推定、NOx触媒1
3の重量の変化量を測定、外部からNOx触媒13に
エネルギーを与えてその応答性から推定、などが考えら
れるが、いずれの方法でも良い。In order to avoid poisoning of the NOx catalyst 13 due to excessive HC adsorption, an HC adsorption amount detecting device 19 (hydrocarbon adsorption amount detecting means) for detecting the HC adsorption amount of the NOx catalyst 13 is provided. The detection principle of the HC adsorption amount is estimated from the history of the past engine operating conditions.
For example, the amount of change in the weight of No. 3 may be measured, the energy may be externally applied to the NOx catalyst 13, and the NOx catalyst 13 may be estimated from its response.
【0013】ここで、過去のエンジン運転条件の履歴か
らNOx触媒13のHC吸着量を推定する場合には次の
ようにして推定する。Here, when estimating the HC adsorption amount of the NOx catalyst 13 from the history of past engine operating conditions, the estimation is performed as follows.
【0014】(1)所定時間Δt内にNOx触媒13に
流入するHC流入量ΔHCinを次式により算出する。 ΔHCin=ΔHCex+ΔHCfd ここで、ΔHCexは、所定時間Δt内にディーゼルエン
ジン11から排出されるHC量、ΔHCfdは、所定時間
Δt内にHC供給ノズル15から添加されるHC量であ
る。(1) The HC inflow amount ΔHCin flowing into the NOx catalyst 13 within a predetermined time Δt is calculated by the following equation. ΔHCin = ΔHCex + ΔHCfd Here, ΔHCex is the amount of HC discharged from the diesel engine 11 within the predetermined time Δt, and ΔHCfd is the amount of HC added from the HC supply nozzle 15 within the predetermined time Δt.
【0015】(2)所定時間Δt内にNOx触媒13内
で反応して消費されるHC消費量ΔHCrec を次式によ
り算出する。 ΔHCrec =ΔHCin×Krep ここで、Krep はNOx触媒13のHC浄化率であり、
触媒温度(NOx触媒13に流入する排気の温度)やエ
ンジン運転条件等をパラメータとするマップから算出さ
れる。(2) The HC consumption amount ΔHCrec consumed by reacting in the NOx catalyst 13 within a predetermined time Δt is calculated by the following equation. ΔHCrec = ΔHCin × Krep where Krep is the HC purification rate of the NOx catalyst 13,
It is calculated from a map in which the catalyst temperature (temperature of exhaust gas flowing into the NOx catalyst 13), engine operating conditions, and the like are used as parameters.
【0016】(3)所定時間Δt内にNOx触媒13に
吸着されるHC吸着量ΔHCcad をHC流入量ΔHCin
からHC消費量ΔHCrec を差し引いた値に吸着係数f
1 を乗算して求める。 ΔHCcad =(ΔHCin−ΔHCrec )×f1 (3) The HC adsorbed amount ΔHCcad adsorbed by the NOx catalyst 13 within a predetermined time Δt is converted into the HC inflow amount ΔHCin
To the value obtained by subtracting the HC consumption ΔHCrec from the
Multiply by 1 and find. ΔHCcad = (ΔHCin−ΔHCrec) × f 1
【0017】ここで、吸着係数f1 は、次式により算出
される。 f1 =f11×f12×f13×f14 f11:最新のHC吸着量HCadsoから求めた係数 f12:NOx触媒13に流入するHC濃度から求めた係
数 f13:触媒温度から求めた係数 f14:排気流量から求めた係数 これらの係数f11〜f14は、いずれも0〜1の範囲内の
値をとり、マップ等により求められる。Here, the adsorption coefficient f 1 is calculated by the following equation. f 1 = f 11 × f 12 × f 13 × f 14 f 11 : coefficient obtained from the latest HC adsorption amount HCadso f 12 : coefficient obtained from the concentration of HC flowing into the NOx catalyst 13 f 13 : obtained from the catalyst temperature factor f 14: the coefficients of these coefficient f 11 ~f 14 obtained from the exhaust flow, either takes a value in the range of 0 to 1, is determined by a map or the like.
【0018】(4)所定時間Δt内にNOx触媒13か
ら脱離するHC脱離量ΔHCdisoを次式により算出す
る。 ΔHCdiso=ΔHCcad ×f2 (4) The HC desorption amount ΔHCdiso desorbed from the NOx catalyst 13 within a predetermined time Δt is calculated by the following equation. ΔHCdiso = ΔHCcad × f 2
【0019】ここで、f2 は脱離係数であり、次式によ
り算出される。 f2 =f21×f22×f23×f24 f21:最新のHC吸着量HCadsoから求めた係数 f22:NOx触媒13に流入するHC濃度から求めた係
数 f23:触媒温度から求めた係数 f24:排気流量から求めた係数 これらの係数f21〜f24は、いずれも0〜1の範囲内の
値をとり、マップ等により求められる。Here, f 2 is a desorption coefficient, which is calculated by the following equation. f 2 = f 21 × f 22 × f 23 × f 24 f 21 : coefficient obtained from the latest HC adsorption amount HCadso f 22 : coefficient obtained from the concentration of HC flowing into the NOx catalyst 13 f 23 : obtained from the catalyst temperature Coefficient f 24 : Coefficient obtained from exhaust gas flow rate These coefficients f 21 to f 24 each take a value in the range of 0 to 1 and are obtained by a map or the like.
【0020】(5)現時点t0 におけるNOx触媒13
のHC吸着量HCadso(t0 )を次式により算出する。(5) NOx catalyst 13 at time t 0
Of HC adsorption amount HCadso a (t 0) is calculated by the following equation.
【0021】[0021]
【数1】 (Equation 1)
【0022】ところで、NOx触媒13に流入する軽油
には、化学構造(カーボンナンバー)の異なる多くの種
類のHCが含まれ、それらのHCの沸点も異なる。低沸
点のHCは、NOx触媒13に吸着されても、排気熱に
より比較的短時間でNOx触媒13から揮発して脱離す
るため、低沸点のHCは、NOx触媒13の被毒には影
響しない。従って、上述したHC流入量ΔHCin、HC
消費量ΔHCrec 、HC吸着量ΔHCcad 、HC脱離量
ΔHCdiso、現時点t0 のHC吸着量HCadsoについて
は、いずれも、被毒に影響しない低沸点のHCを除外し
て考え、被毒を生じさせる可能性のある沸点の比較的高
いHCのみについて算出することが好ましい。By the way, light oil flowing into the NOx catalyst 13 contains many kinds of HCs having different chemical structures (carbon numbers), and the boiling points of the HCs are also different. Even if the low-boiling HC is adsorbed on the NOx catalyst 13, it is volatilized and desorbed from the NOx catalyst 13 in a relatively short time by the exhaust heat, so that the low-boiling HC affects the poisoning of the NOx catalyst 13. do not do. Therefore, the above-mentioned HC inflow amount ΔHCin, HC
Regarding the consumption amount ΔHCrec, the HC adsorption amount ΔHCcad, the HC desorption amount ΔHCdiso, and the HC adsorption amount HCadso at the present time t 0 , it is possible to consider poisoning by excluding low-boiling-point HC which does not affect poisoning, thereby causing poisoning. It is preferable to calculate only for HC having a relatively high boiling point.
【0023】但し、このようなHCの沸点による区別を
せずに、低沸点のHCも含めた全てのHCの吸着量で評
価するようにしても良く、この場合でも、後述する被毒
限界値を低沸点のHCの存在を考慮して設定すること
で、本発明の所期の目的を十分に達成できる。However, instead of such a distinction based on the boiling point of HC, the evaluation may be made based on the adsorbed amounts of all HCs including HCs having a low boiling point. Is set in consideration of the existence of HC having a low boiling point, the intended object of the present invention can be sufficiently achieved.
【0024】以上のようにしてHC吸着量検出装置19
で検出した現時点t0 のHC吸着量HCadsoの情報は、
エンジン制御回路18へ送られる。このエンジン制御回
路18は、マイクロコンピュータを主体として構成さ
れ、排気温度センサ14、エンジン回転数センサ(図示
せず)等、エンジン運転状態を検出する各種センサの出
力に基づいてディーゼルエンジン11の各気筒への燃料
噴射量を制御する。As described above, the HC adsorption amount detecting device 19
The information of the HC adsorption amount HCadso at the present time t 0 detected in
It is sent to the engine control circuit 18. The engine control circuit 18 is mainly configured by a microcomputer, and each cylinder of the diesel engine 11 is based on outputs of various sensors for detecting an engine operating state, such as an exhaust temperature sensor 14 and an engine speed sensor (not shown). Control the amount of fuel injected to the engine.
【0025】更に、エンジン制御回路18は、ROM
(記憶媒体)に記憶された図2の目標HC供給量演算プ
ログラムを所定時間毎又は所定クランク角毎に実行する
ことで、目標HC供給量を次のようにして算出する。ま
ず、ステップ101で、排気温度センサ14、エンジン
回転数センサ(図示せず)等、エンジン運転状態を検出
する各種センサの出力を読み込んだ後、ステップ102
で、排気温度(触媒温度)とエンジン回転数とをパラメ
ータとする図3の基本HC供給量マップを検索し、その
時点の排気温度(触媒温度)とエンジン回転数とに応じ
た基本HC供給量HCbaseを求める。図3の基本HC供
給量マップは、NOx触媒13のNOx浄化率が触媒活
性温度範囲(例えば200〜350℃)においてのみ高
いというNOx触媒13のNOx浄化特性を考慮して設
定されている。このステップ102の処理が、特許請求
の範囲でいう基本炭化水素供給量演算手段としての役割
を果たす。Further, the engine control circuit 18 has a ROM
The target HC supply amount is calculated as follows by executing the target HC supply amount calculation program of FIG. 2 stored in the (storage medium) at predetermined time intervals or at predetermined crank angle intervals. First, in step 101, the outputs of various sensors for detecting the operating state of the engine, such as the exhaust gas temperature sensor 14 and the engine speed sensor (not shown), are read.
Then, the basic HC supply amount map of FIG. 3 is searched using the exhaust temperature (catalyst temperature) and the engine speed as parameters, and the basic HC supply amount according to the exhaust temperature (catalyst temperature) and the engine speed at that time. Ask for HCbase. The basic HC supply amount map of FIG. 3 is set in consideration of the NOx purification characteristics of the NOx catalyst 13 that the NOx purification rate of the NOx catalyst 13 is high only in the catalyst activation temperature range (for example, 200 to 350 ° C.). The processing in step 102 serves as a basic hydrocarbon supply amount calculation means referred to in the claims.
【0026】基本HC供給量HCbaseの算出後、ステッ
プ103に進み、HC吸着量検出装置19で検出した現
時点t0 のHC吸着量HCadsoの情報を読み込む。尚、
図1のシステム構成例では、HC吸着量検出装置19と
エンジン制御回路18とを別々に設けているが、HC吸
着量検出装置19の機能をエンジン制御回路18に組み
込み、ステップ103で、現時点t0 のHC吸着量HC
adsoを前述した算出方法で算出するようにしても良い。[0026] After calculating the basic HC supply amount HCbase, the process proceeds to step 103, reads the information of the HC adsorption amount HCadso of current t 0 detected by the HC adsorption amount detection device 19. still,
In the system configuration example of FIG. 1, the HC adsorption amount detection device 19 and the engine control circuit 18 are separately provided. However, the function of the HC adsorption amount detection device 19 is incorporated in the engine control circuit 18, and the current time t HC adsorption amount HC of 0
adso may be calculated by the calculation method described above.
【0027】この後、ステップ104で、HC吸着量H
Cadsoが予め設定された被毒限界値を越えているか否か
を判定する。ここで、被毒限界値とは、これ以上のHC
がNOx触媒13に吸着されると、NOx触媒13が元
の状態まで回復しにくい状態となる限界のHC吸着量で
あり、本発明者らの実験結果によれば、触媒1g当たり
4mgのHCが吸着されると、触媒が元の状態まで回復
しにくい状態になることを確認している。この場合は、
触媒1g当たり4mgのHCが被毒限界値となる。Thereafter, at step 104, the HC adsorption amount H
It is determined whether Cadso exceeds a preset poisoning limit value. Here, the poisoning limit value is the HC value
Is the limit HC adsorption amount at which the NOx catalyst 13 becomes difficult to recover to the original state when adsorbed on the NOx catalyst 13. According to the experimental results of the present inventors, 4 mg of HC per 1 g of the catalyst is It has been confirmed that the catalyst becomes difficult to recover to its original state when adsorbed. in this case,
4 mg of HC per gram of catalyst is the poisoning limit.
【0028】もし、HC吸着量HCadsoが被毒限界値を
越えていれば、ステップ107に進み、目標HC供給量
HCtをゼロにして、HC供給ノズル15からNOx触
媒13へのHCの供給を停止する。この場合は、HC吸
着量HCadsoが被毒限界値以下になるまで、NOx触媒
13へのHCの供給が停止される。これにより、HC吸
着量HCadsoが被毒限界値を越えて増加し続けることが
防止され、NOx触媒13のNOx浄化能力が保たれ
る。If the HC adsorption amount HCadso exceeds the poisoning limit value, the routine proceeds to step 107, where the target HC supply amount HCt is set to zero, and the supply of HC from the HC supply nozzle 15 to the NOx catalyst 13 is stopped. I do. In this case, the supply of HC to the NOx catalyst 13 is stopped until the HC adsorption amount HCadso becomes equal to or less than the poisoning limit value. As a result, the HC adsorption amount HCadso is prevented from continuing to increase beyond the poisoning limit value, and the NOx purification ability of the NOx catalyst 13 is maintained.
【0029】一方、HC吸着量HCadsoが被毒限界値以
下の場合には、ステップ105に進み、HC吸着量HC
adsoをパラメータとする図4の補正係数マップを検索
し、その時点のHC吸着量HCadsoに応じた補正係数K
hcを求める。この補正係数Khcは、HC吸着量HCadso
に応じて基本HC供給量HCbaseを補正するための補正
係数であり、HC吸着量HCadso≦0の時には補正係数
Khc=1、HC吸着量HCadso≧被毒限界値の時には補
正係数Khc=0であり、HC吸着量HCadsoが0から被
毒限界値の範囲では、HC吸着量HCadsoが増加するに
従って、補正係数Khcが1からリニアに減少する。On the other hand, if the HC adsorption amount HCadso is equal to or less than the poisoning limit value, the routine proceeds to step 105, where the HC adsorption amount HCadso
The correction coefficient map shown in FIG. 4 using adso as a parameter is searched, and a correction coefficient K corresponding to the HC adsorption amount HCadso at that time is searched.
Find hc. This correction coefficient Khc is based on the HC adsorption amount HCadso
Correction coefficient Khc = 1 when the HC adsorption amount HCadso ≦ 0, and the correction coefficient Khc = 0 when the HC adsorption amount HCadso ≧ poisoning limit value. When the HC adsorption amount HCadso is in the range of 0 to the poisoning limit value, the correction coefficient Khc decreases linearly from 1 as the HC adsorption amount HCadso increases.
【0030】尚、HC吸着量HCadsoに応じた補正係数
Khcの変化は、リニア(直線)に限定されず、2次曲線
等の曲線であっても良く、また、階段状(ステップ状)
に変化するものであっても良い。The change of the correction coefficient Khc according to the HC adsorption amount HCadso is not limited to a linear (linear) curve, but may be a curve such as a quadratic curve, or a step-like (step-like) curve.
May be changed.
【0031】補正係数Khcの設定後、ステップ106に
進み、基本HC供給量HCbaseに補正係数Khcを乗算し
て基本HC供給量HCbaseを補正し、目標HC供給量H
Ctを求める。エンジン制御回路18は、この目標HC
供給量HCtの信号を駆動回路17に出力して噴射ポン
プ16を制御し、HC供給ノズル15から目標HC供給
量HCtに相当する量の燃料を排ガスに添加する。上述
したステップ104〜107の処理が特許請求の範囲で
いう補正手段としての役割を果たす。After setting the correction coefficient Khc, the routine proceeds to step 106, where the basic HC supply amount HCbase is multiplied by the correction coefficient Khc to correct the basic HC supply amount HCbase, and the target HC supply amount Hbase is set.
Find Ct. The engine control circuit 18 calculates the target HC
A signal of the supply amount HCt is output to the drive circuit 17 to control the injection pump 16, and the amount of fuel corresponding to the target HC supply amount HCt from the HC supply nozzle 15 is added to the exhaust gas. The processing of steps 104 to 107 described above plays a role as correction means in the claims.
【0032】本発明者は、以上説明した図2の目標HC
供給量演算プログラムによりHC供給量をHC吸着量H
Cadsoに応じて補正した場合の効果を評価する試験を行
ったので、その試験結果について図5及び図6に基づい
て説明する。この評価試験では、4.2リットルの直噴
ディーゼルエンジンを用いて、排気温度が図5に示すパ
ターンで変化するようにベンチ上で負荷を制御し、白金
ゼオライト触媒に空間速度42000(リットル/H
r)で流通させる試験を20サイクル行った。この試験
により、触媒のHC吸着量に応じてHC供給量を補正し
た場合(本実施形態に相当)と、HC供給量を補正しな
い場合(従来に相当)について、235℃(NOx浄化
率がピークを示す温度)におけるNOx浄化率を測定し
たところ、図6に示すような結果が得られた。The inventor of the present invention described the target HC of FIG.
The HC supply amount is converted to the HC adsorption amount H by the supply amount calculation program.
Since a test for evaluating the effect of the correction in accordance with Cadso was performed, the test result will be described with reference to FIGS. In this evaluation test, the load was controlled on a bench using a 4.2-liter direct-injection diesel engine so that the exhaust gas temperature changed in the pattern shown in FIG. 5, and the space velocity of 42,000 (liter / H) was applied to the platinum zeolite catalyst.
The test for circulation in r) was performed for 20 cycles. According to this test, when the HC supply amount is corrected according to the HC adsorption amount of the catalyst (corresponding to the present embodiment) and when the HC supply amount is not corrected (corresponding to the related art), 235 ° C. (NOx purification rate peaks) When the NOx purification rate was measured at the temperature shown in FIG. 6, the result as shown in FIG. 6 was obtained.
【0033】この試験結果から明らかなように、触媒の
HC吸着量に応じてHC供給量を補正した場合は、初期
時のNOx浄化特性と同等の性能を維持でき、NOx浄
化率の低下は見られなかったが、補正なしの場合は、初
期時と比較してNOx浄化率が大幅に低下した。As is apparent from the test results, when the HC supply amount is corrected in accordance with the HC adsorption amount of the catalyst, the performance equivalent to the initial NOx purification characteristic can be maintained, and the decrease in the NOx purification rate is not observed. However, when no correction was made, the NOx purification rate was significantly reduced as compared with the initial stage.
【0034】つまり、本実施形態では、HC吸着量に応
じてNOx触媒13へのHC供給量を補正するようにし
たので、NOx触媒13のHC吸着量が被毒限界値を越
えないように、NOx触媒13へのHC供給量を適正化
することができ、過剰なHCの吸着によるNOx触媒1
3の被毒を確実に防止することができて、長期間に亘っ
て高いNOx浄化性能を維持できる。That is, in the present embodiment, the amount of HC supplied to the NOx catalyst 13 is corrected according to the amount of HC adsorption, so that the amount of HC adsorption of the NOx catalyst 13 does not exceed the poisoning limit value. The amount of HC supplied to the NOx catalyst 13 can be optimized, and the NOx catalyst 1
No. 3 poisoning can be reliably prevented, and high NOx purification performance can be maintained over a long period of time.
【0035】尚、本実施形態では、HC吸着量HCadso
が被毒限界値を越えた時に、目標HC供給量HCtをゼ
ロにしてNOx触媒13へのHCの供給を停止するよう
にしたが、HCの供給を停止する領域を被毒限界値より
低い値に設定して、HC吸着量HCadsoが被毒限界値に
近付いた時にHC供給を停止するようにしても良い。こ
のようにしても、補正係数Khcのマップを適宜変更する
ことで、本実施形態とほぼ同様の効果を得ることができ
る。In this embodiment, the HC adsorption amount HCadso
When the value exceeds the poisoning limit value, the target HC supply amount HCt is set to zero and the supply of HC to the NOx catalyst 13 is stopped, but the range in which the supply of HC is stopped is set to a value lower than the poisoning limit value. The supply of HC may be stopped when the HC adsorption amount HCadso approaches the poisoning limit value. Even in this case, substantially the same effect as that of the present embodiment can be obtained by appropriately changing the map of the correction coefficient Khc.
【0036】また、本実施形態では、NOx触媒13に
HCを供給する手段として、排気管12にHC供給ノズ
ル15を設けたが、これに代え、燃料噴射ノズルからエ
ンジンに燃料を噴射した後の膨脹行程で、燃料噴射ノズ
ルから後噴射により少量の燃料を噴射し、これをNOx
触媒13に供給するようにしても良い。In this embodiment, the HC supply nozzle 15 is provided in the exhaust pipe 12 as a means for supplying HC to the NOx catalyst 13. However, instead of this, the HC injection nozzle 15 is provided after the fuel is injected from the fuel injection nozzle to the engine. During the expansion stroke, a small amount of fuel is injected from the fuel injection nozzle by post-injection,
You may make it supply to the catalyst 13.
【0037】また、本実施形態では、NOx触媒13に
供給するHCとして燃料(軽油)を用いたが、灯油等の
液状のHCや、プロパン等のガス状のHCを用いるよう
にしても良い。In this embodiment, fuel (light oil) is used as HC supplied to the NOx catalyst 13. However, liquid HC such as kerosene or gaseous HC such as propane may be used.
【図1】本発明の一実施形態を示す排気浄化システム全
体の構成図FIG. 1 is a configuration diagram of an entire exhaust gas purification system according to an embodiment of the present invention.
【図2】目標HC供給量演算プログラムの処理の流れを
示すフローチャートFIG. 2 is a flowchart showing a processing flow of a target HC supply amount calculation program;
【図3】基本HC供給量マップを概念的に示す図FIG. 3 is a diagram conceptually showing a basic HC supply amount map;
【図4】補正係数マップを概念的に示す図FIG. 4 is a diagram conceptually showing a correction coefficient map;
【図5】評価試験の排気温度変化パターンを示す図FIG. 5 is a diagram showing an exhaust temperature change pattern of an evaluation test.
【図6】触媒のHC吸着量に応じてHC供給量を補正し
た場合(本実施形態に相当)とHC供給量を補正しない
場合(従来に相当)について、235℃におけるNOx
浄化率を測定した結果を示す図FIG. 6 shows NOx at 235 ° C. when the HC supply amount is corrected according to the HC adsorption amount of the catalyst (corresponding to the present embodiment) and when the HC supply amount is not corrected (corresponding to the related art).
Diagram showing the results of measuring the purification rate
11…ディーゼルエンジン(内燃機関)、12…排気管
(排気通路)、13…NOx触媒、15…HC供給ノズ
ル(炭化水素供給手段)、18…エンジン制御回路(制
御手段,基本炭化水素供給量演算手段,補正手段)、1
9…HC吸着量検出装置(炭化水素吸着量検出手段)。11: Diesel engine (internal combustion engine), 12: Exhaust pipe (exhaust passage), 13: NOx catalyst, 15: HC supply nozzle (hydrocarbon supply means), 18: Engine control circuit (control means, calculation of basic hydrocarbon supply amount) Means, correction means), 1
9 ... HC adsorption amount detection device (hydrocarbon adsorption amount detection means).
───────────────────────────────────────────────────── フロントページの続き (72)発明者 大山 尚久 愛知県西尾市下羽角町岩谷14番地 株式会 社日本自動車部品総合研究所内 (72)発明者 広田 信也 愛知県豊田市トヨタ町1番地 トヨタ自動 車株式会社内 (72)発明者 岩▲崎▼ 英二 愛知県豊田市トヨタ町1番地 トヨタ自動 車株式会社内 (72)発明者 田中 俊明 愛知県豊田市トヨタ町1番地 トヨタ自動 車株式会社内 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naohisa Oyama 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Japan Inside the Japan Automotive Parts Research Institute (72) Inventor Shinya Hirota 1-Toyota-cho, Toyota-shi, Toyota-shi, Aichi Inside (72) Inventor Iwa ▲ saki ▼ Eiji 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation
Claims (4)
化物を還元浄化する触媒と、 前記触媒に対して窒素酸化物の還元剤として炭化水素を
供給する炭化水素供給手段と、 内燃機関の運転状態に基づいて前記触媒に供給すべき炭
化水素量(以下「基本炭化水素供給量」という)を演算
する基本炭化水素供給量演算手段と、 前記触媒に吸着された炭化水素吸着量を検出する炭化水
素吸着量検出手段と、 前記炭化水素吸着量が設定値を越えないように前記基本
炭化水素供給量を補正して目標炭化水素供給量を求める
補正手段と、 前記目標炭化水素供給量に応じて前記炭化水素供給手段
を制御する制御手段とを備えていることを特徴とする内
燃機関の排気浄化装置。1. A catalyst installed in an exhaust passage of an internal combustion engine for reducing and purifying nitrogen oxides; a hydrocarbon supply unit for supplying hydrocarbons as a nitrogen oxide reducing agent to the catalyst; Basic hydrocarbon supply amount calculating means for calculating the amount of hydrocarbons to be supplied to the catalyst (hereinafter referred to as "basic hydrocarbon supply amount") based on the operating state; and detecting the amount of hydrocarbon adsorbed on the catalyst. Hydrocarbon adsorption amount detection means, correction means for correcting the basic hydrocarbon supply amount so that the hydrocarbon adsorption amount does not exceed a set value to obtain a target hydrocarbon supply amount, And control means for controlling the hydrocarbon supply means.
はそれ以下の値に設定されていることを特徴とする請求
項1に記載の内燃機関の排気浄化装置。2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the set value is set to a poisoning limit value of the catalyst or a value less than the poisoning limit value.
応じて補正係数を設定し、この補正係数を前記基本炭化
水素供給量に乗算して目標炭化水素供給量を求めること
を特徴とする請求項1又は2に記載の内燃機関の排気浄
化装置。3. The correction means sets a correction coefficient according to the hydrocarbon adsorption amount, and calculates a target hydrocarbon supply amount by multiplying the correction coefficient by the basic hydrocarbon supply amount. An exhaust purification device for an internal combustion engine according to claim 1 or 2.
前記触媒の被毒限界値を越えた時に、前記炭化水素供給
手段による炭化水素の供給を、該炭化水素吸着量が被毒
限界値以下となるまで停止させることを特徴とする請求
項1乃至3のいずれかに記載の内燃機関の排気浄化装
置。4. The correction means, when the hydrocarbon adsorption amount exceeds the poisoning limit value of the catalyst, adjusts the supply of hydrocarbons by the hydrocarbon supply means to the catalyst poisoning limit value. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the apparatus is stopped until the following conditions are satisfied.
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JP21481897A JP3750766B2 (en) | 1997-08-08 | 1997-08-08 | Exhaust gas purification device for internal combustion engine |
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Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2010057788A1 (en) * | 2008-11-19 | 2010-05-27 | Continental Automotive Gmbh | Method and device for operating an internal combustion engine |
US7845163B2 (en) | 2005-12-02 | 2010-12-07 | Toyota Jidosha Kabushiki Kaisha | Device for purifying exhaust gas of an internal combustion engine |
JP2017025862A (en) * | 2015-07-27 | 2017-02-02 | 本田技研工業株式会社 | Exhaust emission control device for internal combustion engine |
US9623375B2 (en) | 2010-03-15 | 2017-04-18 | Toyota Jidosha Kabushiki Kaisha | Exhaust purification system of internal combustion engine |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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KR102095045B1 (en) * | 2019-01-07 | 2020-03-30 | 주식회사 현대케피코 | Method and apparatus for controlling heating catalyst temperature based on prediction model of unburned hydrocarbon in heating catalyst |
-
1997
- 1997-08-08 JP JP21481897A patent/JP3750766B2/en not_active Expired - Fee Related
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7845163B2 (en) | 2005-12-02 | 2010-12-07 | Toyota Jidosha Kabushiki Kaisha | Device for purifying exhaust gas of an internal combustion engine |
WO2010057788A1 (en) * | 2008-11-19 | 2010-05-27 | Continental Automotive Gmbh | Method and device for operating an internal combustion engine |
US9623375B2 (en) | 2010-03-15 | 2017-04-18 | Toyota Jidosha Kabushiki Kaisha | Exhaust purification system of internal combustion engine |
JP2017025862A (en) * | 2015-07-27 | 2017-02-02 | 本田技研工業株式会社 | Exhaust emission control device for internal combustion engine |
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