JPH05263633A - Exhaust emission control device for internal combustion engine - Google Patents
Exhaust emission control device for internal combustion engineInfo
- Publication number
- JPH05263633A JPH05263633A JP4092346A JP9234692A JPH05263633A JP H05263633 A JPH05263633 A JP H05263633A JP 4092346 A JP4092346 A JP 4092346A JP 9234692 A JP9234692 A JP 9234692A JP H05263633 A JPH05263633 A JP H05263633A
- Authority
- JP
- Japan
- Prior art keywords
- temperature
- catalyst
- lean nox
- nox
- lean
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
Landscapes
- Exhaust Gas After Treatment (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、加速時等、エンジンか
らのＮＯｘの排出量が多い時でも、ＮＯｘを十分に浄化
できる内燃機関の排気浄化装置に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification system for an internal combustion engine, which is capable of sufficiently purifying NOx even when a large amount of NOx is discharged from the engine, such as during acceleration.
【０００２】[0002]
【従来の技術】遷移金属をイオン交換してゼオライトに
担持した触媒は、空燃比リーンで燃焼の排気中でも、Ｈ
Ｃの存在下でＮＯｘを浄化できることが知られている
（たとえば、特開平１−１３０７３５号公報。以下、こ
のような触媒をリーンＮＯｘ触媒という）。2. Description of the Related Art A catalyst in which a transition metal is ion-exchanged and supported on zeolite has a high air-fuel ratio and is
It is known that NOx can be purified in the presence of C (for example, JP-A-1-130735. Hereinafter, such a catalyst is referred to as a lean NOx catalyst).
【０００３】リーンＮＯｘ触媒が高いＮＯｘ浄化率を示
すのは、定常状態においてある温度ウインドウ（たとえ
ば、３５０−５５０℃）に限られている。また、本出願
人は、リーンＮＯｘ触媒が、定常状態や温度下降状態に
おいてよりも、昇温状態において高いＮＯｘ浄化率を示
すことを見い出し、特願平２−３１７６６４号（ただ
し、公開前）において、内燃機関の排気系に同種のリー
ンＮＯｘ触媒を並列に配置し、排気流を交互に切替えて
触媒の昇温過程を強制的に作り出し、ＮＯｘ浄化率を向
上せしめる発明を提案した。The high NOx purification rate of the lean NOx catalyst is limited to a certain temperature window (for example, 350 to 550 ° C.) in the steady state. Further, the present applicant has found that the lean NOx catalyst exhibits a higher NOx purification rate in a temperature rising state than in a steady state or a temperature lowering state, and in Japanese Patent Application No. 2-317664 (but before publication). The present invention has proposed an invention in which lean NOx catalysts of the same kind are arranged in parallel in the exhaust system of an internal combustion engine, and the exhaust flow is alternately switched to forcibly create a temperature rising process of the catalyst to improve the NOx purification rate.
【０００４】[0004]
【発明が解決しようとする課題】しかし、上記先願にお
いては、リーンＮＯｘ触媒の温度を、定常状態において
高ＮＯｘ浄化率を示す温度ウインドウ（たとえば、３５
０−５５０℃）内で振らせるため、加速時のように急激
に排気ガス温度が上昇してエンジンのＮＯｘ排出量も多
くなる時には、排気ガス中のＨＣの大部分が、高温とな
っているリーンＮＯｘ触媒で直接酸化されて二酸化炭素
と水となり、ＮＯｘの還元に必要な、ＨＣの部分酸化に
よって生じる活性種が不足し、増加したＮＯｘを十分に
浄化できなくなる場合が生じるおそれがあるという問題
があった。However, in the above-mentioned prior application, the temperature of the lean NOx catalyst is set to a temperature window (for example, 35) which shows a high NOx purification rate in a steady state.
(0-550 ° C.), so when the exhaust gas temperature rises rapidly and the NOx emission amount of the engine also increases, such as during acceleration, most of the HC in the exhaust gas is at a high temperature. There is a possibility that the lean NOx catalyst may directly oxidize to carbon dioxide and water, and the active species necessary for the reduction of NOx, which are generated by partial oxidation of HC, may be insufficient and the increased NOx may not be sufficiently purified. was there.
【０００５】本発明の目的は、排気ガス温が高くなりエ
ンジンからのＮＯｘ排出量も増える加速時においても、
良好なＮＯｘ浄化性能を示す、内燃機関の排気浄化装置
（システム）を提供することにある。An object of the present invention is to increase the exhaust gas temperature and increase the NOx emission amount from the engine even during acceleration.
An object of the present invention is to provide an exhaust gas purification device (system) for an internal combustion engine, which exhibits good NOx purification performance.
【０００６】[0006]
【課題を解決するための手段】上記目的は、本発明によ
れば、次の内燃機関の排気浄化装置によって達成され
る。すなわち、内燃機関の排気系に並列に配置された複
数のリーンＮＯｘ触媒と、前記リーンＮＯｘ触媒の触媒
床温を代表する温度を検出する温度検出手段と、前記内
燃機関の運転状態を検出する運転状態検出手段と、前記
温度検出手段によって検出された前記触媒床温を代表す
る温度が所定温度より低いと判定したときに前記複数の
リーンＮＯｘ触媒のうち一部のリーンＮＯｘ触媒の触媒
床温を降温させ、かつ前記運転状態検出手段によって検
出された機関運転状態が加速状態にあると判定したとき
に前記一部のリーンＮＯｘ触媒の触媒床温の降温を解除
する触媒床温制御手段と、を備えた内燃機関の排気浄化
装置。According to the present invention, the above object is achieved by the following exhaust gas purification apparatus for an internal combustion engine. That is, a plurality of lean NOx catalysts arranged in parallel with the exhaust system of the internal combustion engine, temperature detecting means for detecting a temperature representing the catalyst bed temperature of the lean NOx catalyst, and operation for detecting the operating state of the internal combustion engine. When it is determined that the temperature representative of the catalyst bed temperature detected by the state detection means and the temperature detection means is lower than a predetermined temperature, the catalyst bed temperatures of some of the lean NOx catalysts among the plurality of lean NOx catalysts are set. And a catalyst bed temperature control means for releasing the temperature drop of the catalyst bed temperature of the part of the lean NOx catalyst when it is determined that the engine operation state detected by the operation state detection means is in an accelerating state. Exhaust gas purification device for internal combustion engine equipped.
【０００７】[0007]
【作用】本発明の内燃機関の排気浄化装置では、リーン
ＮＯｘ触媒床温を代表する温度（たとえば排気ガス温）
が、所定温（たとえば、リーンＮＯｘ触媒が定常状態で
高ＮＯｘ浄化率を示す温度ウインドウの下限側の温度３
５０℃）よりも低いと判定されたときは、触媒床温制御
手段による制御によってそのリーンＮＯｘ触媒はますま
す低温（たとえば、約１００℃）になる。この状態で運
転状態が加速状態になると、触媒床温制御手段による触
媒床温降温が解除されて、低温になっていたリーンＮＯ
ｘ触媒に急激に温度が上昇しつつある排気ガスが流れ
る。排気ガス中には加速時であるから多量のＮＯｘとＨ
Ｃが含まれているが、今迄低温とされていたリーンＮＯ
ｘ触媒に流れても、リーンＮＯｘ触媒自体は相当大きな
熱容量をもつためすぐには高温にならず、ＨＣの大部分
は直接酸化が抑えられて部分酸化が促進され、その結
果、多量の活性種が生成され、ＮＯｘを高ＮＯｘ浄化率
で浄化する。In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, a temperature representative of the lean NOx catalyst bed temperature (for example, exhaust gas temperature).
At a predetermined temperature (for example, the temperature 3 on the lower limit side of the temperature window where the lean NOx catalyst shows a high NOx purification rate in a steady state).
If it is determined that the temperature is lower than 50 ° C.), the lean NOx catalyst becomes even lower temperature (for example, about 100 ° C.) by the control by the catalyst bed temperature control means. When the operating state is accelerated in this state, the catalyst bed temperature decrease by the catalyst bed temperature control means is released, and the lean NO that has become low temperature is reached.
x Exhaust gas whose temperature is rapidly rising flows through the catalyst. Exhaust gas is accelerating, so a large amount of NOx and H
Lean NO, which contains C, but has been kept at a low temperature until now
Even if it flows to the x catalyst, the lean NOx catalyst itself does not reach a high temperature immediately because it has a considerably large heat capacity, and most of HC is suppressed from being directly oxidized and promotes partial oxidation. As a result, a large amount of active species is generated. Are generated, and NOx is purified at a high NOx purification rate.
【０００８】すなわち、特願平２−３１７６６４号は、
温度ウインドウ内で触媒昇温を上下に振らして昇温過程
の高ＮＯｘ浄化率を繰返し利用するものであったが、本
発明では温度ウインドウ下限よりさらにリーンＮＯｘ触
媒を低温にしておき、加速時に急激に排気温が上昇して
もリーンＮＯｘ触媒が高温になる迄は触媒の低温を利用
してＨＣの部分酸化を促進し、加速時に増えるＮＯｘを
効果的に浄化するものである。かくして、特願平２−３
１７６６４号では十分に浄化しきれなかった、加速時の
多量のＮＯｘも、リーンＮＯｘ触媒が高温となってＨＣ
の大部分が直接酸化されるようになる迄は、十分に浄化
される。That is, Japanese Patent Application No. 2-317664
In the present invention, the temperature rise of the catalyst is oscillated up and down to repeatedly use the high NOx purification rate in the temperature raising process. However, in the present invention, the lean NOx catalyst is kept at a temperature lower than the lower limit of the temperature window to accelerate the acceleration. Even if the exhaust gas temperature rises rapidly, the low temperature of the lean NOx catalyst is used to accelerate the partial oxidation of HC by effectively using the low temperature of the catalyst to effectively purify NOx that increases during acceleration. Thus, Japanese Patent Application 2-3
Even with a large amount of NOx during acceleration, which could not be sufficiently purified by No. 17664, the lean NOx catalyst becomes hot and HC
It is fully purified until most of it is directly oxidized.
【０００９】[0009]
【実施例】以下に、本発明に係る内燃機関の排気浄化装
置の望ましい実施例を、図１、図２を参照して説明す
る。図１において、空燃比リーンでの燃焼が可能な内燃
機関（たとえば、ディーゼルエンジン）２の排気系４に
は、複数の通路４ａ、４ｂが並列された通路部が設けら
れ、各通路４ａ、４ｂに、リーンＮＯｘ触媒６ａ、６ｂ
が、設けられている。すなわち、通路４ａには触媒６ａ
が、通路４ｂには触媒６ｂが設けられるといった具合で
ある。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIGS. In FIG. 1, an exhaust system 4 of an internal combustion engine (for example, a diesel engine) 2 capable of performing combustion with a lean air-fuel ratio is provided with a passage portion in which a plurality of passages 4a and 4b are arranged in parallel, and the passages 4a and 4b are provided. In addition, the lean NOx catalysts 6a and 6b
Is provided. That is, the catalyst 6a is provided in the passage 4a.
However, the catalyst 6b is provided in the passage 4b.
【００１０】リーンＮＯｘ触媒は、遷移金属をイオン交
換してゼオライトまたはアルミナ、または貴金属をゼオ
ライトまたはアルミナに担持したものから成り、ＨＣの
存在下で、空燃比リーンの燃焼の排気中で、ＮＯｘを還
元する触媒である。The lean NOx catalyst consists of zeolite or alumina on which a transition metal is ion-exchanged, or a noble metal supported on zeolite or alumina. NOx is converted into NOx in the exhaust gas of lean-fuel combustion in the presence of HC. It is a reducing catalyst.
【００１１】リーンＮＯｘ触媒６ａ、６ｂの触媒床温を
代表する温度、たとえば排気温、を検出するための温度
検出手段としての温度センサ１０が設けられている。こ
の温度センサ１０は、図１の例では複数の通路４ａ、４
ｂの分岐部に設けられている。温度センサ１０の出力は
電子制御装置（ＥＣＵ）１２に入力される。A temperature sensor 10 is provided as a temperature detecting means for detecting a temperature representative of the catalyst bed temperature of the lean NOx catalysts 6a, 6b, for example, an exhaust temperature. The temperature sensor 10 includes a plurality of passages 4a and 4a in the example of FIG.
It is provided at the branch portion of b. The output of the temperature sensor 10 is input to the electronic control unit (ECU) 12.
【００１２】また、内燃機関の運転状態を検出する運転
状態検出手段として、エンジンが加速時にあるか否かを
判定するための信号、たとえばアクセル開度、を検出す
るセンサ１４が設けられており、その出力信号ＡＣＣＰ
がＥＣＵ１２に入力される。たとえばアクセル開度から
アクセル開度の開き速度を演算し、それが一定値を超え
れば加速時と判定する。Further, as an operating state detecting means for detecting the operating state of the internal combustion engine, a sensor 14 for detecting a signal for determining whether or not the engine is accelerating, for example, an accelerator opening, is provided. Its output signal ACCP
Is input to the ECU 12. For example, the opening speed of the accelerator opening is calculated from the accelerator opening, and if it exceeds a certain value, it is determined to be during acceleration.
【００１３】また、触媒床温の降温、降温解除を制御す
る触媒床温制御手段が設けられる。この触媒床温制御手
段は、たとえば弁手段、弁手段の切替を制御する弁制御
手段、触媒冷却装置を含む。具体的には、各通路４ａ、
４ｂに、リーンＮＯｘ触媒６ａ、６ｂの上流側に、弁
（弁手段）８ａ、８ｂが設けられ、各弁８ａ、８ｂはリ
ーンＮＯｘ触媒６ａ、６ｂへの排気ガスの流れを減量で
きる弁から成る。この場合、減量の概念の中には、完全
な遮断も含む。Further, there is provided catalyst bed temperature control means for controlling the lowering and lowering of the catalyst bed temperature. The catalyst bed temperature control means includes, for example, valve means, valve control means for controlling switching of the valve means, and catalyst cooling device. Specifically, each passage 4a,
4b is provided with valves (valve means) 8a and 8b on the upstream side of the lean NOx catalysts 6a and 6b, and each valve 8a and 8b is a valve capable of reducing the flow of exhaust gas to the lean NOx catalysts 6a and 6b. .. In this case, the concept of weight loss includes complete cutoff.
【００１４】並設された複数のリーンＮＯｘ触媒６ａ、
６ｂのうち一部のリーンＮＯｘ触媒６ｂには、該リーン
ＮＯｘ触媒６ｂを冷却することができる触媒冷却装置１
６が設けられる。A plurality of lean NOx catalysts 6a arranged in parallel,
A catalyst cooling device 1 capable of cooling the lean NOx catalyst 6b is provided in part of the lean NOx catalyst 6b.
6 is provided.
【００１５】触媒冷却装置１６は、たとえばエンジン冷
却水の配管１６ａをリーンＮＯｘ触媒６ｂにとりまわ
し、該配管の途中に制御弁１６ｂを設け、ＥＣＵ１２か
らの指令によって制御弁１６ｂの開閉を制御して、リー
ンＮＯｘ触媒６ｂの冷却を制御するようにしたものから
成る。In the catalyst cooling device 16, for example, a pipe 16a for engine cooling water is routed around the lean NOx catalyst 6b, a control valve 16b is provided in the middle of the pipe, and opening / closing of the control valve 16b is controlled by a command from the ECU 12, The lean NOx catalyst 6b is configured to control cooling.
【００１６】触媒冷却装置１６は、また、リーンＮＯｘ
触媒６ｂとその上流の弁８ｂとの間に二次空気の供給ポ
ートを設け、該ポートと二次空気供給源を結ぶエア配管
上に制御弁を設け、該制御弁をＥＣＵ１２からの指令に
よって開閉して、リーンＮＯｘ触媒６ｂの冷却を制御す
るようにしたものから成ってもよい。The catalyst cooling device 16 also uses lean NOx.
A secondary air supply port is provided between the catalyst 6b and the valve 8b upstream thereof, a control valve is provided on the air pipe connecting the port and the secondary air supply source, and the control valve is opened / closed by a command from the ECU 12. The lean NOx catalyst 6b may be controlled to be cooled.
【００１７】ＥＣＵ１２はマイクロコンピュータから成
り、インプットインタフェース、アウトプットインタフ
ェース、一時記憶用のランダムアクセスメモリ（ＲＡ
Ｍ）、読出し専用の記憶素子であるリードオンリメモリ
（ＲＯＭ）、演算を実行する部分であるセントラルプロ
セッサユニット（ＣＰＵ）を有する。センサからの出力
がアナログ信号である場合はアナログ／ディジタル変換
器でディジタル信号に変換してインプットインタフェー
スに入力する。The ECU 12 comprises a microcomputer, and has an input interface, an output interface, and a random access memory (RA) for temporary storage.
M), a read-only memory (ROM) that is a read-only storage element, and a central processor unit (CPU) that is a part that executes operations. When the output from the sensor is an analog signal, it is converted into a digital signal by an analog / digital converter and input to the input interface.
【００１８】ＲＯＭには図２に示すような制御ルーチン
をもつ弁制御手段が格納されており、該制御ルーチンは
ＣＰＵに呼出されて演算が実行される。図２の制御ルー
チンは、機関運転中に、一定時間毎、たとえば０．５秒
毎に割込まれる。まず、ステップ１０２で、温度センサ
１０の出力から現在の排気温（触媒床温を代表する温
度）Ｔを読込むとともに、加速中か否かを判定するため
の機関運転状態信号、たとえばアクセル開度信号ＡＣＣ
Ｐを読込む。A valve control means having a control routine as shown in FIG. 2 is stored in the ROM, and the control routine is called by the CPU to execute the calculation. The control routine of FIG. 2 is interrupted at regular intervals, for example, every 0.5 seconds, during engine operation. First, in step 102, the current exhaust gas temperature (a temperature representative of the catalyst bed temperature) T is read from the output of the temperature sensor 10, and an engine operating state signal for determining whether or not acceleration is being performed, for example, an accelerator opening signal. ACC
Read P.
【００１９】続いて、ステップ１０４で、後述するフラ
グＣＴＨが１か否かを判定し、ＣＴＨ＝１ならステップ
１１４に進み、ＣＴＨが０ならステップ１０６に進む。
ステップ１０６で、現在の排気温Ｔが所定値Ｔ0 （たと
えば、３５０℃）より低いか否かを判定することによ
り、リーンＮＯｘ触媒６ａ、６ｂの触媒床温が、リーン
ＮＯｘ触媒が高ＮＯｘ浄化率を示す温度ウインドウの下
限値より低か否かを判定する。Subsequently, in step 104, it is determined whether or not a flag CTH, which will be described later, is 1, and if CTH = 1, the process proceeds to step 114, and if CTH is 0, the process proceeds to step 106.
In step 106, it is determined whether or not the current exhaust temperature T is lower than a predetermined value T 0 (for example, 350 ° C.), so that the catalyst bed temperature of the lean NOx catalysts 6a and 6b is high NOx purification by the lean NOx catalyst. It is determined whether it is lower than the lower limit value of the temperature window indicating the rate.
【００２０】ステップ１０６でＴ≧Ｔ0 と判定された場
合は、リーンＮＯｘ触媒６ａ、６ｂは、高ＮＯｘ浄化率
を示せる温度ウインドウにあると判断し、その状態を続
けてＮＯｘを浄化すればよいから、そのままリターンス
テップに進む。この場合は、すべての弁８ａ、８ｂが全
開となっているので、すべてのリーンＮＯｘ触媒６ａ、
６ｂに排気ガスが流れ、低空間速度となって各リーンＮ
Ｏｘ触媒６ａ、６ｂのＮＯｘ浄化率はさらに高くなる。When it is determined in step 106 that T ≧ T 0, it is determined that the lean NOx catalysts 6a and 6b are in a temperature window that can show a high NOx purification rate, and that state is continued to purify NOx. Then, proceed to the return step as it is. In this case, since all the valves 8a and 8b are fully opened, all the lean NOx catalysts 6a,
Exhaust gas flows into 6b and becomes low space velocity, and each lean N
The NOx purification rate of the Ox catalysts 6a and 6b becomes higher.
【００２１】ステップ１０６でＴ＜Ｔ0 と判定された場
合は、リーンＮＯｘ触媒６ａ、６ｂが不活性領域に入り
そのＮＯｘ浄化率は低下してくるが、排気温が低温にな
るようなとき、たとえばアイドル時や低速走行時はエン
ジンからのＮＯｘ排出量自体が少ないので、リーンＮＯ
ｘ触媒６ａ、６ｂのＮＯｘ浄化率が低下していても、Ｎ
Ｏｘ規制上は問題にならなくなる。この低温時を利用し
て、つぎに加速時のようにＮＯｘ排出量が多くなる時の
ＮＯｘ浄化に備えて、ステップ１０８−１２６の操作を
施す。When it is judged at step 106 that T <T 0 , the lean NOx catalysts 6a, 6b enter the inactive region and the NOx purification rate thereof is lowered, but when the exhaust temperature becomes low, For example, the amount of NOx emissions from the engine itself is small during idle or low speed running, so lean NO
Even if the NOx purification rate of the x catalysts 6a and 6b is reduced, N
It will not be a problem for Ox regulation. By utilizing this low temperature, the operations of steps 108 to 126 are performed in preparation for NOx purification when the NOx emission amount increases next time during acceleration.
【００２２】すなわち、ステップ１０８で、複数のリー
ンＮＯｘ触媒６ａ、６ｂのうち一部のリーンＮＯｘ触媒
６ｂの上流に設けた弁８ｂを閉めるかまたは絞って、下
流のリーンＮＯｘ触媒６ｂに流れる排気ガス流量を減少
（０を含む）させる。このような状態では、温度の高い
排気ガスが流れてこないリーンＮＯｘ触媒６ｂは冷却可
能の状態になる。That is, at step 108, the exhaust gas flowing to the downstream lean NOx catalyst 6b is closed or throttled by closing the valve 8b provided upstream of some of the lean NOx catalysts 6a and 6b. Decrease the flow rate (including 0). In such a state, the lean NOx catalyst 6b into which the exhaust gas having a high temperature does not flow becomes a state in which it can be cooled.
【００２３】続いてステップ１１０に進み、触媒冷却装
置１６をＯＮにし、たとえば、エンジン冷却水をリーン
ＮＯｘ触媒６ｂ側に流すようにしたり、二次空気のエア
ポンプを作動させて二次空気をリーンＮＯｘ触媒６ｂの
上流に供給する。この状態が続くと、リーンＮＯｘ触媒
６ｂは冷却されていき、触媒床温が次第に下っていく。
エンジン冷却水や二次空気供給によって積極的に冷却す
る場合は、リーンＮＯｘ触媒６ｂの触媒床温は、ついに
は１００℃程度にまで下げられる。Subsequently, the routine proceeds to step 110, where the catalyst cooling device 16 is turned on, for example, engine cooling water is made to flow to the lean NOx catalyst 6b side, or the secondary air is operated by operating the secondary air air pump. It is supplied upstream of the catalyst 6b. If this state continues, the lean NOx catalyst 6b is cooled and the catalyst bed temperature is gradually lowered.
In the case of actively cooling the engine with cooling water or secondary air supply, the catalyst bed temperature of the lean NOx catalyst 6b is finally lowered to about 100 ° C.
【００２４】また、ステップ１０８で弁８ｂが完全に閉
められない場合や、ステップ１０８で弁８ｂが完全に閉
められてもリーンＮＯｘ触媒６ｂと弁８ｂとの間に二次
空気とともにＨＣが供給される場合は、冷却されつつあ
るリーンＮＯｘ触媒６にＨＣが吸着され、そのＨＣはリ
ーンＮＯｘ触媒６が低温のため全量が完全酸化されるこ
となく一部は吸着されて残る。そしてこの吸着されたＨ
Ｃは、加速時に弁８ｂが開いたときにエンジンから流れ
てくるＨＣとともにＮＯｘ浄化に有効に利用される。When the valve 8b is not completely closed in step 108, or even when the valve 8b is completely closed in step 108, HC is supplied between the lean NOx catalyst 6b and the valve 8b together with the secondary air. In this case, HC is adsorbed by the lean NOx catalyst 6 that is being cooled, and the HC is partially adsorbed and remains without being completely oxidized because the lean NOx catalyst 6 is at a low temperature. And this adsorbed H
C is effectively used for NOx purification together with HC flowing from the engine when the valve 8b is opened during acceleration.
【００２５】ステップ１１０からステップ１１２に進
み、ステップ１１２で現在の機関運転状態が加速時か否
かが判定される。加速時の判定は、たとえばスロットル
開度の開速度（ＡＣＣＰの変化の速度）が所定値を超え
たか否かで判定できる。ステップ１１２で機関運転状態
が加速時でないと判定されたときには、そのままリーン
ＮＯｘ触媒６ｂの冷却を続行させればいいから、弁８
ａ、８ｂを操作することなく、そのままリターンステッ
プに進んでリターンする。The routine proceeds from step 110 to step 112, where it is judged at step 112 whether the current engine operating condition is acceleration. The determination during acceleration can be made, for example, based on whether or not the opening speed of the throttle opening (speed of change of ACCP) exceeds a predetermined value. When it is determined in step 112 that the engine operating state is not during acceleration, the cooling of the lean NOx catalyst 6b may be continued as it is.
The operation directly proceeds to the return step and returns without operating a and 8b.
【００２６】ステップ１１２で現在の機関運転状態が非
加速状態から加速時に変ったと判定されると、ステップ
１１４に進む。ステップ１１４では、今まで開となって
いた弁８ａを閉または絞り、今まで閉または絞られてい
た弁８ｂを全開または開度を大にする。続いて、ステッ
プ１１６では、さらに触媒冷却装置１６をＯＦＦにして
触媒冷却を停止させる。これにより、今まで冷却されて
いたリーンＮＯｘ触媒６ｂに、加速時になって急激に温
度が上昇するとともにＮＯｘ含有量の増えた排気ガスが
流れる。この場合、排気ガスは低温のリーンＮＯｘ触媒
６ｂに触れて触媒中で温度が低下するため、排気ガス中
に含まれているＨＣ（たとえばエンジンでの燃料の未燃
焼分）は、相当量の部分が部分酸化されて多量の活性種
を生じ、この多量の活性種がＮＯｘと反応して、ＮＯｘ
を効果的に浄化する。When it is determined in step 112 that the current engine operating state has changed from the non-accelerated state during acceleration, the routine proceeds to step 114. In step 114, the valve 8a that has been open until now is closed or throttled, and the valve 8b that has been closed or throttled up to now is fully opened or the opening degree is increased. Subsequently, at step 116, the catalyst cooling device 16 is further turned off to stop the catalyst cooling. As a result, the lean NOx catalyst 6b, which has been cooled so far, flows with exhaust gas whose NOx content has increased as the temperature rapidly rises during acceleration. In this case, since the exhaust gas comes into contact with the low temperature lean NOx catalyst 6b and the temperature of the exhaust gas lowers in the catalyst, the HC (for example, unburned fuel of the engine) contained in the exhaust gas has a considerable portion. Is partially oxidized to produce a large amount of active species, which react with NOx to generate NOx.
Effectively purify.
【００２７】もしも、ステップ１０８、１１０によるリ
ーンＮＯｘ触媒６ｂの冷却なしに加速時の排気ガスがリ
ーンＮＯｘ触媒６ｂに流れると、ＨＣは大部分が触媒中
で完全酸化されて、ＮＯｘを十分に浄化できなくなる場
合が生じるおそれがあるが、本発明では、加速時に変化
する前に一部のリーンＮＯｘ触媒６ｂが十分に冷やされ
ているので、加速時に今まで冷やされていたリーンＮＯ
ｘ触媒６ｂに高温になりつつある排気ガスが流れてきて
も、上記のようなおそれは生じず、良好なＮＯｘ浄化が
得られる。If the exhaust gas during acceleration flows into the lean NOx catalyst 6b without cooling the lean NOx catalyst 6b in steps 108 and 110, most of the HC is completely oxidized in the catalyst and the NOx is sufficiently purified. However, in the present invention, since some of the lean NOx catalysts 6b are sufficiently cooled before they change during acceleration, the lean NOx that has been cooled up to now at the time of acceleration.
Even if exhaust gas that is becoming high temperature flows into the x-catalyst 6b, the above-mentioned fear does not occur, and good NOx purification can be obtained.
【００２８】ステップ１１４、１１６による良好なＮＯ
ｘ浄化は、冷却されていたリーンＮＯｘ触媒６ｂが高温
になってＨＣの直接酸化が生じる状態になる迄のみ続
き、高温になってしまうとリーンＮＯｘ触媒６ｂの低温
によるＨＣの部分酸化促進状態は得られなくなるので、
高温になった後ではすべてのリーンＮＯｘ触媒６ａ、６
ｂに排気ガスを流して、低空間速度によるＮＯｘ浄化の
向上をはかった方がよい。この意味で、ステップ１１
４、１１６の弁８ｂの開とリーンＮＯｘ触媒６ｂへの排
気ガスの流しは、一定時間のみ続けることとすることが
望ましい。この操作をするのがステップ１１８−１２６
およびステップ１０４である。Good NO from steps 114 and 116
The x purification continues only until the temperature of the cooled lean NOx catalyst 6b rises to a state where direct oxidation of HC occurs, and when the temperature rises to a high temperature, the partial oxidation promotion state of HC due to the low temperature of the lean NOx catalyst 6b is reached. I will not be able to get it, so
After the temperature becomes high, all the lean NOx catalysts 6a, 6
It is better to let the exhaust gas flow in b to improve the NOx purification by the low space velocity. In this sense, step 11
It is desirable that the opening of the valves 8b of Nos. 4 and 116 and the flow of the exhaust gas to the lean NOx catalyst 6b be continued for a certain period of time. This is done by steps 118-126.
And step 104.
【００２９】ステップ１１６からステップ１１８に進
み、ステップ１１８で、冷却しておいたリーンＮＯｘ触
媒６ｂに排気ガスを流し始めた時点からの時間ＣＴをカ
ウントアップしていく。ＣＴはステップ１１８を通る割
込み毎に１づつ増えていく。たとえば、割込みが０．５
秒づつあり、その割込みにおいてステップ１１８を通過
する毎に１づつＣＴは増えていく。このような割込みが
２０回続くと、１０秒間でＣＴは２０になる。The routine proceeds from step 116 to step 118, and in step 118, the time CT from the time when the exhaust gas starts flowing to the cooled lean NOx catalyst 6b is counted up. CT is incremented by 1 for each interrupt passing through step 118. For example, if the interrupt is 0.5
There are seconds, and CT increases by 1 each time step 118 is passed in the interrupt. If such an interrupt continues 20 times, the CT becomes 20 in 10 seconds.
【００３０】続いて、ステップ１２０に進み、ＣＴが所
定のＣＴ０を超えたか否かを判定する。冷却しておいた
リーンＮＯｘ触媒６ｂによるＮＯｘ浄化向上効果を加速
に変って１０秒間得るときはＣＴ０は２０と設定してお
く。ステップ１２０でＣＴがＣＴ０を超えていないな
ら、ステップ１２４でリーンＮＯｘ触媒６ｂによるＮＯ
ｘ浄化向上がホールドされていることを示すフラグＣＴ
Ｈを１（ホールド）とおいてリターンする。ステップ１
２０でＣＴがＣＴ０を超えたと判定されると、リーンＮ
Ｏｘ触媒６ｂが高温になってもはや低温によるＨＣ部分
酸化促進効果が得られなくなったと判断して、ステップ
１２２に進み、フラグ１２２を０にクリアして、ステッ
プ１２６に進み、すべての弁８ａ、８ｂを全開にする。
その後リターンする。Subsequently, the routine proceeds to step 120, where it is judged whether or not CT exceeds a predetermined CT0. When the NOx purification improving effect by the cooled lean NOx catalyst 6b is changed to acceleration and obtained for 10 seconds, CT0 is set to 20. If CT does not exceed CT0 at step 120, NO at step 124 by the lean NOx catalyst 6b.
Flag CT indicating that x purification improvement is being held
Return H with 1 (hold). Step 1
If it is judged that CT exceeds CT0 in 20, lean N
It is judged that the Ox catalyst 6b has reached a high temperature and no longer has the effect of promoting the partial oxidation of HC due to a low temperature, the process proceeds to step 122, the flag 122 is cleared to 0, the process proceeds to step 126, and all the valves 8a, 8b. Fully open.
Then return.
【００３１】ステップ１０４でフラグＣＴＨが１か否か
を判定しＣＴＨ＝１ならステップ１０６、１１２を飛び
越えてステップ１１４に進むようにしたので、いったん
ＣＴＨがステップ１２４で１にされると一定時間ＣＴ０
だけは、ステップ１１４、１１６で設定された状態が保
持される。In step 104, it is determined whether or not the flag CTH is 1, and if CTH = 1, the steps 106 and 112 are skipped and the process proceeds to step 114. Therefore, once CTH is set to 1 in step 124, CT0 is maintained for a certain period of time.
Only, the state set in steps 114 and 116 is retained.
【００３２】つぎに、作用を説明する。触媒床温が活性
温度域にある時、たとえば排気ガス温ＴがＴ０以上の時
は、弁８ａ、８ｂは全開で、複数のリーンＮＯｘ触媒６
ａ、６ｂのすべてを利用して低空間速度下で高ＮＯｘ浄
化率を得る。リーンＮＯｘ触媒６ａ、６ｂが活性温度以
下になった時（Ｔ＜Ｔ０に対応）、一部のリーンＮＯｘ
触媒６ｂに流れる排気ガスを減量（完全遮断を含む）し
て、そのリーンＮＯｘ触媒６ｂを冷却する（触媒冷却装
置１６による積極的冷却を含む）。これによって、リー
ンＮＯｘ触媒６ｂは活性温度以下の、Ｔ０よりかなり低
い温度にまで冷却される。少量の排気ガスがリーンＮＯ
ｘ触媒６ｂに流れている時は、ＨＣが冷却中のリーンＮ
Ｏｘ触媒６ｂに吸着される。Next, the operation will be described. When the catalyst bed temperature is in the active temperature range, for example, when the exhaust gas temperature T is T0 or higher, the valves 8a and 8b are fully opened and the plurality of lean NOx catalysts 6 are
A high NOx purification rate is obtained under a low space velocity by utilizing all of a and 6b. When the lean NOx catalysts 6a and 6b are below the activation temperature (corresponding to T <T0), some lean NOx
The lean NOx catalyst 6b is cooled by reducing the amount of exhaust gas flowing through the catalyst 6b (including complete shutoff) (including positive cooling by the catalyst cooling device 16). As a result, the lean NOx catalyst 6b is cooled to a temperature lower than the activation temperature and considerably lower than T0. Lean NO with a small amount of exhaust gas
x When the HC is flowing to the catalyst 6b, the HC is lean N while cooling.
It is adsorbed on the Ox catalyst 6b.
【００３３】内燃機関の運転状態が加速時に変わると、
排気ガス中のＮＯｘ量が増えるとともに、排気ガス温度
も急激に昇温する。この時、弁８ｂが開とされるか開度
が増大され、弁８ａは閉とされるか開度が減少される。
今まで冷却されていたリーンＮＯｘ触媒６ｂに排気ガス
が流れてくるが、触媒床が十分に冷却されており、熱容
量があるためすぐには触媒床温が高温にならず、一定時
間ＣＴ０の間は排気ガスが低温の触媒床に触れて低温に
なり、排気ガス中のＨＣは直接酸化することを抑えられ
て、部分酸化が促進され、多量の活性種が生成される。
この活性種が排気ガス中のＮＯｘと反応するので、ＮＯ
ｘは十分に浄化される。また、リーンＮＯｘ触媒６ｂに
ＨＣが吸着されていた場合は、そのＨＣもＮＯｘ浄化に
寄与する。When the operating state of the internal combustion engine changes during acceleration,
As the amount of NOx in the exhaust gas increases, the exhaust gas temperature also rises sharply. At this time, the valve 8b is opened or the opening is increased, and the valve 8a is closed or the opening is decreased.
Exhaust gas flows into the lean NOx catalyst 6b, which has been cooled until now, but the catalyst bed is not cooled to a high temperature immediately because the catalyst bed is sufficiently cooled and has a heat capacity, and during a certain time CT0. The exhaust gas comes into contact with the low temperature catalyst bed to become a low temperature, and the HC in the exhaust gas is suppressed from being directly oxidized, partial oxidation is promoted, and a large amount of active species is generated.
Since this active species reacts with NOx in the exhaust gas, NO
x is sufficiently purified. When HC is adsorbed on the lean NOx catalyst 6b, the HC also contributes to NOx purification.
【００３４】加速状態に変った後一定時間ＣＴ０が経過
すると、冷却してあったリーンＮＯｘ触媒６ｂもついに
は高温になってしまうので、すべての弁８ａ、８ｂを開
いて、通常の状態に戻し、低空間速度下でのＮＯｘ浄化
を行う。When CT0 elapses for a certain time after changing to the acceleration state, the cooled lean NOx catalyst 6b finally becomes high temperature, so all the valves 8a and 8b are opened to return to the normal state. , Perform NOx purification under low space velocity.
【００３５】[0035]
【発明の効果】本発明によれば、排気系に並列に複数の
リーンＮＯｘ触媒を設け、触媒床温が所定温度より低い
ときに触媒床温を降温させ、かつ機関運転状態が加速状
態になったときには前記一部のリーンＮＯｘ触媒の降温
を解除するようにしたので、加速時になったときに今ま
で冷却していたリーンＮＯｘ触媒でのＨＣの完全酸化を
抑えることができ、ＨＣの部分酸化を促進して、加速時
に増えたＮＯｘの浄化を促進することができる。According to the present invention, a plurality of lean NOx catalysts are provided in parallel in the exhaust system, the catalyst bed temperature is lowered when the catalyst bed temperature is lower than the predetermined temperature, and the engine operating state becomes the accelerating state. In this case, the temperature decrease of the part of the lean NOx catalyst is released, so that the complete oxidation of HC in the lean NOx catalyst which has been cooled until the time of acceleration can be suppressed, and the partial oxidation of HC can be suppressed. Can be promoted to promote purification of NOx increased during acceleration.
【図１】本発明の実施例に係る内燃機関の排気浄化装置
の系統図である。FIG. 1 is a system diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.
【図２】図１の装置のＥＣＵに格納された制御ルーチン
のフローチャートである。FIG. 2 is a flowchart of a control routine stored in an ECU of the device shown in FIG.
２ 内燃機関 ４ 排気系 ４ａ 通路 ４ｂ 通路 ６ａ リーンＮＯｘ触媒 ６ｂ リーンＮＯｘ触媒 ８ａ 弁 ８ｂ 弁 １０ 温度センサ １２ ＥＣＵ １４ センサ １６ 触媒冷却装置 2 internal combustion engine 4 exhaust system 4a passage 4b passage 6a lean NOx catalyst 6b lean NOx catalyst 8a valve 8b valve 10 temperature sensor 12 ECU 14 sensor 16 catalyst cooling device
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.5 識別記号 庁内整理番号 ＦＩ 技術表示箇所 Ｆ０１Ｎ 3/24 Ｒ ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 5 Identification code Internal reference number FI technical display location F01N 3/24 R
Claims (1)
数のリーンＮＯｘ触媒と、 前記リーンＮＯｘ触媒の触媒床温を代表する温度を検出
する温度検出手段と、 前記内燃機関の運転状態を検出する運転状態検出手段
と、 前記温度検出手段によって検出された前記触媒床温を代
表する温度が所定温度より低いと判定したときに前記複
数のリーンＮＯｘ触媒のうち一部のリーンＮＯｘ触媒の
触媒床温を降温させ、かつ前記運転状態検出手段によっ
て検出された機関運転状態が加速状態にあると判定した
ときに前記一部のリーンＮＯｘ触媒の触媒床温の降温を
解除する触媒床温制御手段と、を備えたことを特徴とす
る内燃機関の排気浄化装置。1. A plurality of lean NOx catalysts arranged in parallel with an exhaust system of an internal combustion engine, temperature detecting means for detecting a temperature representative of a catalyst bed temperature of the lean NOx catalyst, and an operating state of the internal combustion engine. An operating state detecting means for detecting, and a catalyst of a part of the lean NOx catalysts of the plurality of lean NOx catalysts when it is determined that the temperature representative of the catalyst bed temperature detected by the temperature detecting means is lower than a predetermined temperature. Catalyst bed temperature control means for lowering the bed temperature and releasing the catalyst bed temperature decrease of the part of the lean NOx catalyst when it is determined that the engine operating state detected by the operating state detecting means is in an accelerating state An exhaust emission control device for an internal combustion engine, comprising:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9234692A JP2867788B2 (en) | 1992-03-19 | 1992-03-19 | Exhaust gas purification device for internal combustion engine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9234692A JP2867788B2 (en) | 1992-03-19 | 1992-03-19 | Exhaust gas purification device for internal combustion engine |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH05263633A true JPH05263633A (en) | 1993-10-12 |
| JP2867788B2 JP2867788B2 (en) | 1999-03-10 |
Family
ID=14051846
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9234692A Expired - Fee Related JP2867788B2 (en) | 1992-03-19 | 1992-03-19 | Exhaust gas purification device for internal combustion engine |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2867788B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0838579A3 (en) * | 1996-10-23 | 2000-08-30 | Toyota Jidosha Kabushiki Kaisha | An exhaust gas purification device for an engine |
| US6502391B1 (en) * | 1999-01-25 | 2003-01-07 | Toyota Jidosha Kabushiki Kaisha | Exhaust emission control device of internal combustion engine |
-
1992
- 1992-03-19 JP JP9234692A patent/JP2867788B2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0838579A3 (en) * | 1996-10-23 | 2000-08-30 | Toyota Jidosha Kabushiki Kaisha | An exhaust gas purification device for an engine |
| US6502391B1 (en) * | 1999-01-25 | 2003-01-07 | Toyota Jidosha Kabushiki Kaisha | Exhaust emission control device of internal combustion engine |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2867788B2 (en) | 1999-03-10 |
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