EP1138898B1 - Method and device for purification of exhaust gases - Google Patents

Method and device for purification of exhaust gases Download PDF

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Publication number
EP1138898B1
EP1138898B1 EP01250100A EP01250100A EP1138898B1 EP 1138898 B1 EP1138898 B1 EP 1138898B1 EP 01250100 A EP01250100 A EP 01250100A EP 01250100 A EP01250100 A EP 01250100A EP 1138898 B1 EP1138898 B1 EP 1138898B1
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EP
European Patent Office
Prior art keywords
storage
exhaust
downstream
storage catalysts
catalyst
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EP01250100A
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German (de)
French (fr)
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EP1138898A3 (en
EP1138898A2 (en
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Ekkehard Dr. Pott
Achim Donnerstag
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Volkswagen AG
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Volkswagen AG
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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
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • 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
    • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/1441—Plural sensors
    • 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
    • F02D41/1454—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 oxygen content or concentration or the air-fuel ratio
    • 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

Definitions

  • the invention relates to a method and a device for exhaust gas purification in a Internal combustion engine with the mentioned in the preamble of the independent claims Features.
  • NO x storage catalysts are operated in a storage cycle that includes at least one usually long absorption mode and a relatively short regeneration mode.
  • a single-pipe exhaust system in which a NO x storage catalyst is arranged between two 3-way catalysts.
  • Desulphurization (SO x regeneration) of the NO x storage catalytic converter is detected as a function of a NO x storage capability of the storage catalytic converter, which is determined by means of a downstream NO x sensor or by means of a pre and a downstream lambda probe.
  • NO x storage catalysts are mainly used in direct injection systems, which make significant fuel savings possible in the so-called stratified charge mode. This enables safe combustion of extremely lean mixtures at idle and part load with fuel savings of> 40% at idle and approximately 15% over the entire Eurotest cycle MVEG.
  • the fuel is injected via electromagnetic nozzle valves directly into the combustion chamber. In this case, the engine is operated with almost fully open throttle, which in addition charge exchange losses are avoided. Only after a certain demanded power, the engine must be operated again in conventional operation, in which the throttle position determines the amount of air / fuel mixture sucked.
  • the NO x storage catalyst is operated in the absorption mode. In homogeneous operation of the engine, however, a stoichiometric or for the regeneration of the NO x storage catalytic converter fed to a rich air / fuel mixture.
  • NO x storage catalytic converter When more than one NO x storage catalytic converter is used, its uniform application of NO x can not be assumed since the function and efficiency of an NO x storage catalytic converter depend on a multiplicity of influencing factors. However, a detection of the operating state, for example, the NO x -BleadungsSches or the end of the NO x regeneration of the individual NO x storage catalytic converters arranged in the mixed exhaust gas downstream of the NO x storage sensor means, such as a downstream NO x sensor or a Lambda Probe, not possible.
  • the object of the invention is therefore to provide a method and a device for exhaust gas purification in an internal combustion engine with at least two parallel downstream of a branch of an exhaust line arranged regenerable NO x storage catalytic converters, which allow a complete regeneration of all NO x storage catalysts and at the same time a high degree to exhaust purification afford.
  • the invention is based on the idea of terminating a currently performed NO x regeneration measure as a function of a later (in particular the latest) point in time at which a state parameter value characteristic of the termination of an NO x regeneration measure at one of the NO x - Storage catalysts is measured.
  • This procedure makes it possible to regenerate all NO x storage catalytic converters until even at the last of the NO x storage catalytic converters an operating state that is characteristic for the termination of a regeneration measure occurs, so that the NO x storage capacity of all NO x storage catalytic converters can be used without restriction.
  • reducing agent breakthroughs are oxidized at the time first regenerated NO x storage catalysts and thus rendered harmless.
  • a 3-way catalyst with Rh and Pt and / or Pd as essential noble metal components preferably a 3-way catalyst with Rh and Pt and / or Pd as essential noble metal components, but also conceivable is the use of a pure oxidation catalyst with Pt and / or Pd as essential noble metal components.
  • FIG. 1 shows an internal combustion engine 1 of a motor vehicle with a downstream exhaust line 2, which is shown only schematically, preferably in stratified charge mode, and with an engine control unit 5 for evaluating and influencing operating parameters of the internal combustion engine 1.
  • the exhaust line 2 has two regenerable NO x storage catalysts 3 and 4 , which are arranged downstream of a branch 7 in the exhaust line 2. Upstream of the branch 7, a precatalyst 15 is arranged in the exhaust gas line 2.
  • the exhaust gas line 2 also has a junction 8 downstream of the NO x storage catalysts 3 and 4, as well as a downstream catalyst 9, preferably a conventional 3-way catalyst.
  • a downstream catalyst 9 preferably a conventional 3-way catalyst.
  • lambda probes 10, 11, 12 are arranged upstream or downstream of the NO x storage catalytic converters 3 and 4, respectively.
  • the sensors 11, 12 downstream of the NO x storage catalysts 3 and 4 may also be designed as NO x sensors and provide in this case a selectively the NO x concentration in the exhaust gas representing NO x signal, and a corresponding signal for the oxygen concentration ,
  • the engine control unit 5 detects in a conventional manner via a temperature sensor 14th and other sensors, not shown, operating parameters of the internal combustion engine 1 as Exhaust temperature, load, speed, raw emission or the like and the like not shown actuators, such as electromagnetic nozzle valves or a throttle valve in the air supply of the internal combustion engine 1, if necessary influence.
  • actuators such as electromagnetic nozzle valves or a throttle valve in the air supply of the internal combustion engine 1, if necessary influence.
  • a cable system 16 intended for communication between the engine control unit 5 and the Internal combustion engine 1 or the actuators.
  • the engine control unit 5 comprises in particular a lambda control, which signals the Lambda probe 10 and the sensors 11 and 12 evaluates and depending on Operating state of the catalysts 3, 4 and 15, a change in the operating parameters of the Internal combustion engine 1 performs the exhaust gas control.
  • the sensors 11 and 12 Due to their arrangement in the exhaust line 2 before the merger 8, it is possible with the sensors 11 and 12 to detect the state parameter values of the NO x storage catalysts 3 and 4 individually.
  • NO x sensors for each of the NO x storage catalysts 3 and 4, in particular the loading of NO x and the NO x reduction performance can be determined in a manner known per se.
  • a regeneration measure can be initiated by switching from a lean to a rich air / fuel mixture. This can be triggered for example by the higher-loaded catalyst or catalyst with faster occurring and / or higher NO x breakthroughs.
  • a currently performed NO x regeneration action is terminated in response to the latest time point at which a state parameter value characteristic of the completion of an NO x regeneration measure is measured on one of the NO x storage catalysts.
  • a state parameter value characteristic of the completion of an NO x regeneration measure is measured on one of the NO x storage catalysts.
  • Such operating conditions are, for example, a reducing agent breakthrough at one of the NO x storage catalysts 3 and 4, a minimum in the NO x concentration after switching to a rich air / fuel mixture or a short-term NO x desorption peak. Since the completion of the regeneration measure necessarily affects all NO x storage catalysts 3 and 4 by design, the termination of the regeneration measure according to the invention ensures that each of the NO x storage catalysts 3 and 4 is completely regenerated.
  • the engine control unit 5 has a control device 6, by means of which the signals of the sensors 11, 12 are evaluated.
  • the control device 6, which may also be designed as a separate component, determines the latest point in time at which a state parameter value characteristic of the termination of the regeneration measure occurs at one of the NO x storage catalytic converters 3 and 4.
  • the NO x control device 6 can be realized for example by a microcontroller with a CPU, a program memory, a data memory and input and output interfaces. In order to determine the latest time for the completion of the regeneration measure 6 known per se sorting algorithm are used by the control device.
  • the catalytic converter 9 is arranged in the exhaust gas line 2 downstream of the convergence 8 for the effective exhaust gas purification.
  • a partially damaged NO x storage catalyst 3, 4 generally occurs because of a lower NO x storage capacity less reducing agent requirement during a regeneration measure.
  • the oxygen storage capacity of the downstream catalytic converter 9 is therefore sufficient to be dimensioned so that even with partially damaged NO x storage catalysts 3, 4, the correspondingly higher amounts of reducing agents can be catalytically converted. This avoids additional pollution of the environment with hydrocarbons and carbon monoxide.
  • the catalyst 9 is designed so that about 30% of the total through the exhaust line 2 to the NO x storage catalysts 3 and 4 supplied reducing agent can be reduced.
  • a sensor 13 preferably a Lambda probe, downstream of the catalyst 9 for monitoring the functionality intended.
  • the signal of the sensor 13 is the control device 6 or the Engine control unit 5 supplied.
  • FIG. 2 shows an alternative embodiment of the invention, in which no merging of the exhaust line 2 downstream of the NO x storage catalysts 3, 4 is provided. This is necessary, for example, even if the downstream catalyst has to be divided for packing reasons. Accordingly, an exhaust gas branch 2 with a downstream catalytic converter 9 is connected to the NO x storage catalytic converter 3, and an exhaust gas branch 2 a to a further catalytic converter 9 a is connected to the NO x storage catalytic converter 4.
  • the design of the preferably realized as a 3-way catalysts catalysts 9, 9a is again sized so that a safe implementation of erupted reducing agent is possible.
  • a monitoring of the catalysts 9, 9a can be done by downstream sensors 13, 13a. Preferably lambda probes are provided for this purpose.
  • the signal of the sensors 13, 13a of the control device 6 or the engine controller 5 is supplied and causes a termination of an NO x -Regenerationsggiookie if a reducing agent breakdown predetermined height is detected.
  • the inventive termination of a NO x -Regenerationsterrorismtung allows safe and efficient exhaust gas purification in an internal combustion engine with at least two parallel arranged after a diversion in the exhaust line regenerable NO x storage catalytic converters.

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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)

Abstract

Process for purifying IC engine exhaust gases comprises terminating a NOx regeneration depending on one of the NOx storage catalysts (3, 4); and measuring a condition parameter value characteristic for the termination of the NOx regeneration. An Independent claim is also included for an apparatus for purifying IC engine exhaust gases comprising an engine control unit (5) having a controller (6) for terminating the NOx regeneration. Preferred Features: The exhaust gas branches are brought together at a connecting point downstream of the NOx storage catalysts and upstream of a connected oxidation catalyst.

Description

Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Abgasreinigung bei einem Verbrennungsmotor mit den im Oberbegriff der unabhängigen Ansprüche genannten Merkmalen.The invention relates to a method and a device for exhaust gas purification in a Internal combustion engine with the mentioned in the preamble of the independent claims Features.

Üblicherweise bestehen moderne Abgasreinigungssysteme aus einem Vorkatalysator mit einem nachgeschalteten NOx-Speicherkatalysator. Hiermit wird berücksichtigt, dass mit dem bisher üblichen 3-Wege-Katalysator allein das Problem, leistungsfähige und zugleich umweltfreundliche Verbrennungsmotoren für Kraftfahrzeuge zu entwickeln, nicht zu lösen ist. Nur wenn Luft und Kraftstoff im genau definierten stöchiometrischen Verhältnis dem Motor zugeführt werden, können die beim Betrieb des Motors entstehenden Abgase zu unschädlichen Gaskomponenten reduziert werden. Die stöchiometrische Betriebsart mit einem so genannten Lambda-Wert = 1 des Luft/Kraftstoffgemischs ist jedoch nicht die verbrauchsgünstigste. Ein wesentlich geringerer Kraftstoffverbrauch kann bei etwa zweifachem Luftüberschuss im Luft/Kraftstoffgemisch, das heißt bei einem Lambda-Wert von zirka 2, erreicht werden.Conventionally, modern exhaust gas purification systems consist of a pre-catalyst with a downstream NO x storage catalytic converter. This takes into account that with the usual 3-way catalyst alone, the problem of developing powerful and environmentally friendly internal combustion engines for motor vehicles, can not be solved. Only when air and fuel are supplied to the engine in the well-defined stoichiometric ratio can the exhaust gases produced during operation of the engine be reduced to harmless gas components. However, the stoichiometric mode with a so-called lambda value = 1 of the air / fuel mixture is not the most fuel-efficient. A much lower fuel consumption can be achieved at about twice the excess air in the air / fuel mixture, that is at a lambda value of about 2.

Da die herkömmlichen Katalysatoren bei Luftüberschuss die entstehenden Stickoxyde (NOx) nicht mehr reduzieren können, ist diese Betriebsart ohne weitere Maßnahmen unter dem Gesichtspunkt der Umweltbelastung nicht zu vertreten.Since the conventional catalysts can no longer reduce the resulting nitrogen oxides (NO x ) in the presence of excess air, this mode of operation can not be justified without further measures from the point of view of environmental pollution.

Stickoxyde können durch einen Speicherkatalysator unter bestimmten Randbedingungen bei einem Lambda-Wert > 1 einen begrenzten Zeitraum absorptiv gespeichert und zu einem späteren Zeitpunkt bei einem Lambda-Wert < 1 oder = 1 wieder ausgespeichert und dann durch im Abgas enthaltene, als Reduktionsmittel wirkende, Kohlenwasserstoff- und Kohlenmonoxydbestandteile katalytisch zu unschädlichen Gasen reduziert werden.Nitrogen oxides can be added by a storage catalyst under certain conditions a lambda value> 1 absorptively stored for a limited period and to a later stored at a lambda value <1 or = 1 again and then by contained in the exhaust, acting as a reducing agent, hydrocarbon and Carbon monoxide components are catalytically reduced to harmless gases.

Üblicherweise werden NOx-Speicherkatalysatoren in einem Speicherzyklus betrieben, der zumindest einen üblicherweise langen Absorptionsmodus und einen relativ kurzen Regenerationsmodus umfasst. Typically, NO x storage catalysts are operated in a storage cycle that includes at least one usually long absorption mode and a relatively short regeneration mode.

Aus DE 198 16 276 A ist beispielsweise eine einsträngige Abgasanlage bekannt, bei der ein NOx-Speicherkatalysator zwischen zwei 3-Wege-Katalysatoren angeordnet ist. Eine Entschwefelung (SOx-Regeneration) des NOx-Speicherkatalysators wird in Abhängigkeit einer NOx-Speicherfähigkeit des Speicherkatalysators erkannt, welche mittels eines nachgeschalteten NOx-Sensors oder mittels einer vor- und einer nachgeschalteten Lambda-Sonde ermittelt wird.From DE 198 16 276 A, for example, a single-pipe exhaust system is known, in which a NO x storage catalyst is arranged between two 3-way catalysts. Desulphurization (SO x regeneration) of the NO x storage catalytic converter is detected as a function of a NO x storage capability of the storage catalytic converter, which is determined by means of a downstream NO x sensor or by means of a pre and a downstream lambda probe.

Ist aus Packungsgründen der Einsatz eines einzelnen NOx-Speicherkatalysators nicht möglich, wird ein Abgasstrang geteilt und das Abgas zwei parallel geschalteten NOx-Speicherkatalysatoren zugeleitet.If, for reasons of packaging, the use of a single NO x storage catalytic converter is not possible, an exhaust gas line is divided and the exhaust gas is fed to two NO x storage catalytic converters connected in parallel.

Eine solche Lösung wird zum Beispiel bei allradgetriebenen Fahrzeugen verwendet, bei denen die Kardanwelle die Anordnung eines einzelnen zylindrischen NOx-Katalysators unmöglich macht. Andererseits ist bei turboaufgeladenen Motoren mit einem einzelnen Turbolader die Anordnung von zwei vollkommen autarken Abgassträngen aus zwei Vorkatalysatoren und zwei NOx-Speicherkatalysatoren nicht möglich.Such a solution is used, for example, in all-wheel drive vehicles in which the propeller shaft makes the arrangement of a single cylindrical NO x catalyst impossible. On the other hand, in turbocharged engines with a single turbocharger, the arrangement of two completely self-sufficient exhaust strands from two pre-catalysts and two NO x storage catalysts is not possible.

NOx-Speicherkatalysatoren finden vorwiegend Anwendung bei Direkteinspritzsystemen, die im so genannten Schichtladbetrieb bedeutende Kraftstoffeinsparungen möglich machen. Hiermit ist eine sichere Verbrennung äußerst magerer Gemische im Leerlauf- und Teillastbereich mit Kraftstoffeinsparungen von > 40 % im Leerlauf und zirka 15 % über den gesamten Eurotestzyklus MVEG möglich. Der Kraftstoff wird über elektromagnetische Düsenventile direkt in den Brennraum eingespritzt. Dabei wird der Motor mit nahezu vollständig geöffneter Drosselklappe betrieben, womit zusätzlich Ladungswechselverluste vermieden werden. Erst ab einer gewissen abverlangten Leistung muss der Motor wieder im konventionellen Betrieb, bei dem die Drosselklappenstellung die Menge des angesaugten Luft/Kraftstoffgemischs bestimmt, betrieben werden. Während des Schichtladebetriebs wird der NOx-Speicherkatalysator im Absorptionsmodus betrieben. Im Homogenbetrieb des Motors wird dagegen ein stöchiometrisches oder für die Regeneration des NOx-Speicherkatalysators ein fettes Luft/Kraftstoffgemisch zugeführt.NO x storage catalysts are mainly used in direct injection systems, which make significant fuel savings possible in the so-called stratified charge mode. This enables safe combustion of extremely lean mixtures at idle and part load with fuel savings of> 40% at idle and approximately 15% over the entire Eurotest cycle MVEG. The fuel is injected via electromagnetic nozzle valves directly into the combustion chamber. In this case, the engine is operated with almost fully open throttle, which in addition charge exchange losses are avoided. Only after a certain demanded power, the engine must be operated again in conventional operation, in which the throttle position determines the amount of air / fuel mixture sucked. During the stratified charge mode, the NO x storage catalyst is operated in the absorption mode. In homogeneous operation of the engine, however, a stoichiometric or for the regeneration of the NO x storage catalytic converter fed to a rich air / fuel mixture.

Beim Einsatz von mehr als einem NOx-Speicherkatalysator kann deren gleichmäßige Beaufschlagung mit NOx nicht unterstellt werden, da Funktion und Wirkungsgrad eines NOx-Speicherkatalysators von einer Vielzahl von Einflussfaktoren abhängig sind. Jedoch ist eine Erfassung des Betriebszustandes, beispielsweise des NOx-Beladungszustandes beziehungsweise des Endes der NOx-Regeneration der einzelnen NOx-Speicherkatalysatoren über im Mischabgas hinter den NOx-Speicherkatalysatoren angeordnete Sensormittel, beispielsweise eines nachgeschalteten NOx-Sensors oder einer Lambda-Sonde, nicht möglich.When more than one NO x storage catalytic converter is used, its uniform application of NO x can not be assumed since the function and efficiency of an NO x storage catalytic converter depend on a multiplicity of influencing factors. However, a detection of the operating state, for example, the NO x -Bleadungszustandes or the end of the NO x regeneration of the individual NO x storage catalytic converters arranged in the mixed exhaust gas downstream of the NO x storage sensor means, such as a downstream NO x sensor or a Lambda Probe, not possible.

Günstiger ist daher die Anordnung von Sensormitteln stromabwärts jedes NOx-Speicherkatalysators. Bei der Steuerung der NOx-Regeneration stellt sich dabei das Problem, den Endzeitpunkt des Regenerationsmodus unter der Bedingung festzulegen, dass die NOx-Regeneration durch das Abgas bei mehreren parallel geschalteten NOx-Speicherkatalysatoren zwangsweise zeitgleich geschieht. Insbesondere muss hier vermieden werden, dass einer oder mehrere der Katalysatoren permanent nur teilregeneriert werden, wodurch ihr NOx-Speicherkapazität zunehmend eingeschränkt würde.Cheaper is therefore the arrangement of sensor means downstream of each NO x storage catalytic converter. The control of the NO x regeneration poses the problem of specifying the end time of the regeneration mode under the condition that the NO x regeneration by the exhaust gas in the case of several NO x storage catalytic converters connected in parallel forcibly takes place at the same time. In particular, it must be avoided here that one or more of the catalysts are permanently only partially regenerated, which would increasingly limit their NO x storage capacity.

Andererseits besteht die Gefahr, dass ein relativ zu den anderen NOx-Speicherkatalysatoren schnell regenerierter Katalysator einen Reduktionsmitteldurchbruch erleidet, mit der Folge einer Freisetzung von Kohlenwasserstoffen in die Umwelt.On the other hand, there is the danger that a catalyst regenerated rapidly relative to the other NO x storage catalysts suffers a reductant breakdown, with consequent release of hydrocarbons into the environment.

Die Aufgabe der Erfindung besteht daher in der Angabe eines Verfahrens und einer Vorrichtung zur Abgasreinigung bei einem Verbrennungsmotor mit mindestens zwei parallel stromabwärts einer Abzweigung eines Abgasstrangs angeordneten regenerierbaren NOx-Speicherkatalysatoren, die eine vollständige Regeneration aller NOx-Speicherkatalysatoren ermöglichen und gleichzeitig einen hohen Grad an Abgasreinigung leisten.The object of the invention is therefore to provide a method and a device for exhaust gas purification in an internal combustion engine with at least two parallel downstream of a branch of an exhaust line arranged regenerable NO x storage catalytic converters, which allow a complete regeneration of all NO x storage catalysts and at the same time a high degree to exhaust purification afford.

Diese Aufgabe wird jeweils mit den Merkmalen der unabhängigen Ansprüche gelöst.This object is achieved in each case with the features of the independent claims.

Die Erfindung geht von der Idee aus, eine gerade durchgeführte NOx-Regenerationsmaßnahme in Abhängigkeit von einem späteren (insbesondere dem spätesten) Zeitpunkt zu beenden, an dem ein für die Beendigung einer NOx-Regenerationsmaßnahme charakteristischer Zustandsparameter-Wert an einem der NOx-Speicherkatalysatoren gemessen wird. Dieses Vorgehen ermöglicht es, sämtliche NOx-Speicherkatalysatoren zu regenerieren, bis auch am zeitlich letzten der NOx-Speicherkatalysatoren ein für eine Beendigung einer Regenerationsmaßnahme charakteristischer Betriebszustand auftritt, so dass das NOx-Speichervermögen aller NOx-Speicherkatalysatoren uneingeschränkt genutzt werden kann. Wenn das Abgas zumindest einem stromabwärts der NOx-Speicherkatalysatoren im Abgasstrang angeordneten Katalysator zugeführt wird, werden Reduktionsmitteldurchbrüche bei den zeitlich zuerst regenerierten NOx-Speicherkatalysatoren oxidiert und damit unschädlich gemacht. Hierzu eignet sich vorzugsweise ein 3-Wege-Katalysator mit Rh und Pt und/oder Pd als wesentlich Edelmetallkomponenten, denkbar ist jedoch auch der Einsatz eines reinen Oxydationskatalysators mit Pt und/oder Pd als wesentliche Edelmetallkomponenten.The invention is based on the idea of terminating a currently performed NO x regeneration measure as a function of a later (in particular the latest) point in time at which a state parameter value characteristic of the termination of an NO x regeneration measure at one of the NO x - Storage catalysts is measured. This procedure makes it possible to regenerate all NO x storage catalytic converters until even at the last of the NO x storage catalytic converters an operating state that is characteristic for the termination of a regeneration measure occurs, so that the NO x storage capacity of all NO x storage catalytic converters can be used without restriction. If the exhaust gas is supplied to at least one downstream of the NO x storage catalysts arranged in the exhaust gas catalyst, reducing agent breakthroughs are oxidized at the time first regenerated NO x storage catalysts and thus rendered harmless. For this purpose, preferably a 3-way catalyst with Rh and Pt and / or Pd as essential noble metal components, but also conceivable is the use of a pure oxidation catalyst with Pt and / or Pd as essential noble metal components.

Weitere Merkmale und Vorteile der vorliegenden Erfindung ergeben sich aus den abhängigen Ansprüchen sowie unabhängig von ihrer Zusammenfassung in den Ansprüchen aus der nachfolgenden Beschreibung bevorzugter, erfindungsgemäßer Ausführungsbeispiele in Verbindung mit den zugehörigen Zeichnungen. Other features and advantages of the present invention will become apparent from the dependent claims and regardless of their summary in the claims from the following description of preferred, inventive Embodiments in conjunction with the accompanying drawings.

In den Zeichnungen zeigen in schematischer Darstellung

Figur 1
einen Verbrennungsmotor mit einer erfindungsgemäßen Vorrichtung zur Abgasreinigung mit zwei NOx-Speicherkatalysatoren und einem stromabwärts der NOx-Speicherkatalysatoren im Abgasstrang angeordneten Katalysator und
Figur 2
einen Verbrennungsmotor mit einer erfindungsgemäßen Vorrichtung zur Abgasreinigung mit zwei NOx-Speicherkatalysatoren und zwei stromabwärts der NOx-Speicherkatalysatoren im Abgasstrang angeordneten Katalysatoren.
In the drawings show in schematic representation
FIG. 1
an internal combustion engine with a device according to the invention for exhaust gas purification with two NO x storage catalytic converters and a downstream of the NO x storage catalytic converter arranged in the exhaust system and catalyst
FIG. 2
an internal combustion engine with a device according to the invention for exhaust gas purification with two NO x storage catalysts and two downstream of the NO x storage catalysts arranged in the exhaust system catalysts.

Figur 1 zeigt einen nur schematisch dargestellten, vorzugsweise im Schichtladebetrieb betreibbaren Verbrennungsmotor 1 eines Kraftfahrzeugs mit einem nachgeschalteten Abgasstrang 2 sowie mit einem Motorsteuergerät 5 zur Auswertung und Beeinflussung von Betriebsparametern des Verbrennungsmotors 1. Der Abgasstrang 2 weist zwei regenerierbare NOx-Speicherkatalysatoren 3 und 4 auf, die stromabwärts einer Abzweigung 7 im Abgasstrang 2 angeordnet sind. Stromaufwärts der Abzweigung 7 ist ein Vorkatalysator 15 im Abgasstrang 2 angeordnet.FIG. 1 shows an internal combustion engine 1 of a motor vehicle with a downstream exhaust line 2, which is shown only schematically, preferably in stratified charge mode, and with an engine control unit 5 for evaluating and influencing operating parameters of the internal combustion engine 1. The exhaust line 2 has two regenerable NO x storage catalysts 3 and 4 , which are arranged downstream of a branch 7 in the exhaust line 2. Upstream of the branch 7, a precatalyst 15 is arranged in the exhaust gas line 2.

Der Abgasstrang 2 weist ferner eine Zusammenführung 8 stromabwärts der NOx-Speicherkatalysatoren 3 und 4 auf sowie einen der Zusammenfügung nachgeschalteten Katalysator 9, vorzugsweise einen konventionellen 3-Wege-Katalysator. Zur Erfassung des Lambda-Wertes des Abgases im Bereich des Vorkatalysators 15 beziehungsweise der NOx-Speicherkatalysatoren 3 und 4 sind Lambda-Sonden 10, 11, 12 stromaufwärts beziehungsweise stromabwärts der NOx-Speicherkatalysatoren 3 und 4 angeordnet. Die Sensoren 11, 12 stromabwärts der NOx-Speicherkatalysatoren 3 und 4 können auch als NOx-Sensoren ausgeführt sein und liefern in diesem Fall ein selektiv die NOx-Konzentration im Abgas repräsentierendes NOx-Signal, sowie ein entsprechendes Signal für die Sauerstoffkonzentration.The exhaust gas line 2 also has a junction 8 downstream of the NO x storage catalysts 3 and 4, as well as a downstream catalyst 9, preferably a conventional 3-way catalyst. For detecting the lambda value of the exhaust gas in the region of the primary catalytic converter 15 or the NO x storage catalytic converters 3 and 4, lambda probes 10, 11, 12 are arranged upstream or downstream of the NO x storage catalytic converters 3 and 4, respectively. The sensors 11, 12 downstream of the NO x storage catalysts 3 and 4 may also be designed as NO x sensors and provide in this case a selectively the NO x concentration in the exhaust gas representing NO x signal, and a corresponding signal for the oxygen concentration ,

Das Motorsteuergerät 5 erfasst in an sich bekannter Weise über einen Temperatursensor 14 und weitere nicht dargestellte Sensoren Betriebsparameter des Verbrennungsmotors 1 wie Abgastemperatur, Last, Drehzahl, Rohemissionsverlauf oder dergleichen und kann diese über nicht dargestellte Stellglieder, wie beispielsweise elektromagnetische Düsenventile oder eine Drosselklappe in der Luftzuführung des Verbrennungsmotors 1 gegebenenfalls beeinflussen. Zur Kommunikation zwischen dem Motorsteuergerät 5 und dem Verbrennungsmotor 1 beziehungsweise den Stellgliedern ist ein Kabelsystem 16 vorgesehen.The engine control unit 5 detects in a conventional manner via a temperature sensor 14th and other sensors, not shown, operating parameters of the internal combustion engine 1 as Exhaust temperature, load, speed, raw emission or the like and the like not shown actuators, such as electromagnetic nozzle valves or a throttle valve in the air supply of the internal combustion engine 1, if necessary influence. For communication between the engine control unit 5 and the Internal combustion engine 1 or the actuators is a cable system 16 intended.

Das Motorsteuergerät 5 umfasst insbesondere eine Lambda-Regelung, die die Signale der Lambda-Sonde 10 sowie der Sensoren 11 und 12 auswertet und in Abhängigkeit vom Betriebszustand der Katalysatoren 3, 4 und 15 eine Veränderung der Betriebsparameter des Verbrennungsmotors 1 zur Abgasregelung vornimmt.The engine control unit 5 comprises in particular a lambda control, which signals the Lambda probe 10 and the sensors 11 and 12 evaluates and depending on Operating state of the catalysts 3, 4 and 15, a change in the operating parameters of the Internal combustion engine 1 performs the exhaust gas control.

Aufgrund ihrer Anordnung im Abgasstrang 2 vor der Zusammenführung 8 ist es möglich, mit den Sensoren 11 und 12 die Zustandsparameter-Werte der NOx-Speicherkatalysatoren 3 und 4 individuell zu erfassen. Mit NOx-Sensoren kann für jeden der NOx-Speicherkatalysatoren 3 und 4 insbesondere die Beladung mit NOx sowie die NOx-Reduktionsleistung in an sich bekannter Weise bestimmt werden. In ebenfalls an sich bekannter Weise kann beispielsweise in Abhängigkeit von der NOx-Beladung der NOx-Speicherkatalysatoren 3 und 4 eine Regenerationsmaßnahme durch Umschalten von einem mageren auf ein fettes Luft/Kraftstoffgemisch eingeleitet werden. Dies kann beispielsweise durch den höher beladenen Katalysator beziehungsweise den Katalysator mit schneller auftretenden und/oder höheren NOx-Durchbrüchen ausgelöst werden. Bei Verwendung von Lambda-Sonden erfolgt in an sich bekannter Weise eine Auswertung des Lambda-Signals um eine Regenerationsmaßnahme einzuleiten. Darüber hinaus erfolgt eine Regeneration der NOx-Speicherkatalysatoren 3 und 4, falls der Betriebszustand des Verbrennungsmotors es ohnehin erfordert, wie beispielsweise in der Warmlaufphase bei Beschleunigung und Volllast, wenn ein fettes Luft/Kraftstoffgemisch eingesetzt wird.Due to their arrangement in the exhaust line 2 before the merger 8, it is possible with the sensors 11 and 12 to detect the state parameter values of the NO x storage catalysts 3 and 4 individually. With NO x sensors, for each of the NO x storage catalysts 3 and 4, in particular the loading of NO x and the NO x reduction performance can be determined in a manner known per se. In a manner also known per se, for example, depending on the NO x charge of the NO x storage catalysts 3 and 4, a regeneration measure can be initiated by switching from a lean to a rich air / fuel mixture. This can be triggered for example by the higher-loaded catalyst or catalyst with faster occurring and / or higher NO x breakthroughs. When lambda probes are used, an evaluation of the lambda signal by a regeneration measure is initiated in a manner known per se. In addition, there is a regeneration of the NO x storage catalysts 3 and 4, if the operating condition of the internal combustion engine requires it anyway, such as in the warm-up phase during acceleration and full load when a rich air / fuel mixture is used.

Eine gerade durchgeführte NOx-Regenerationsmaßnahme wird in Abhängigkeit von dem spätesten Zeitpunkt beendet, an dem ein für die Beendigung einer NOx-Regenerationsmaßnahme charakteristischer Zustandsparameter-Wert an einem der NOx-Speicherkatalysatoren gemessen wird. Erfindungsgemäß wird bei der Beendigung der Regenerationsmaßnahme berücksichtigt, dass im Allgemeinen jeder der NOx-Speicherkatalysatoren 3 und 4 zu einem unterschiedlichen Zeitpunkt einen Betriebszustand erreicht, der eine Beendigung der Regenerationsmaßnahme erfordert. Solche Betriebszustände sind beispielsweise ein Reduktionsmitteldurchbruch an einem der NOx-Speicherkatalysatoren 3 und 4, ein Minimum in der NOx-Konzentration nach dem Umschalten auf ein fettes Luft/Kraftstoffgemisch oder ein kurzzeitiger NOx-Desorptionspeak. Da die Beendigung der Regenerationsmaßnahme sich konstruktionsbedingt zwangsweise auf sämtliche NOx-Speicherkatalysatoren 3 und 4 auswirkt, ist durch die erfindungsgemäße Beendigung der Regenerationsmaßnahme gewährleistet, dass jeder der NOx-Speicherkatalysatoren 3 und 4 vollständig regeneriert wird.A currently performed NO x regeneration action is terminated in response to the latest time point at which a state parameter value characteristic of the completion of an NO x regeneration measure is measured on one of the NO x storage catalysts. According to the invention, at the completion of the regeneration measure, it is considered that in general each of the NO x storage catalysts 3 and 4 reaches an operating state at a different time, which requires a termination of the regeneration measure. Such operating conditions are, for example, a reducing agent breakthrough at one of the NO x storage catalysts 3 and 4, a minimum in the NO x concentration after switching to a rich air / fuel mixture or a short-term NO x desorption peak. Since the completion of the regeneration measure necessarily affects all NO x storage catalysts 3 and 4 by design, the termination of the regeneration measure according to the invention ensures that each of the NO x storage catalysts 3 and 4 is completely regenerated.

Um eine Regenerationsmaßnahme erfindungsgemäß zu beenden, weist das Motorsteuergerät 5 eine Kontrolleinrichtung 6 auf, mit deren Hilfe die Signale der Sensoren 11, 12 ausgewertet werden. Die gegebenenfalls auch als separates Bauteil ausgeführte Kontrolleinrichtung 6 ermittelt hierfür den spätesten Zeitpunkt, zu dem ein für die Beendigung der Regenerationsmaßnahme charakteristischer Zustandsparameter-Wert an einem der NOx-Speicherkatalysatoren 3 und 4 auftritt.In order to terminate a regeneration measure according to the invention, the engine control unit 5 has a control device 6, by means of which the signals of the sensors 11, 12 are evaluated. The control device 6, which may also be designed as a separate component, determines the latest point in time at which a state parameter value characteristic of the termination of the regeneration measure occurs at one of the NO x storage catalytic converters 3 and 4.

Daraufhin wird von der Kontrolleinrichtung 6 der Motorsteuerung 5 ein Kontrollsignal zugeführt und von der Motorsteuerung 5 die NOx-Regenerationsmaßnahme über die Aktivierung entsprechender Stellglieder am Verbrennungsmotor 1 beendet. Die NOx-Kontrolleinrichtung 6 kann beispielsweise durch einen Mikrocontroller mit einer CPU, einem Programmspeicher, einem Datenspeicher und Eingabe- und Ausgabeschnittstellen realisiert sein. Zur Ermittlung des spätesten Zeitpunkts für die Beendigung der Regenerationsmaßnahme werden von der Kontrolleinrichtung 6 an sich bekannte Sortieralgorithmus eingesetzt.Subsequently, a control signal is supplied from the control device 6 to the engine control 5 and the engine control 5 terminates the NO x regeneration measure via the activation of corresponding actuators on the internal combustion engine 1. The NO x control device 6 can be realized for example by a microcontroller with a CPU, a program memory, a data memory and input and output interfaces. In order to determine the latest time for the completion of the regeneration measure 6 known per se sorting algorithm are used by the control device.

Da an einem bereits regenerierten NOx-Speicherkatalysator Reduktionsmitteldurchbrüche mit einer gewissen Menge nicht verbrauchter Kohlenwasserstoff- und Kohlenmonoxydbestandteile auftreten, ist für die wirksame Abgasreinigung der Katalysator 9 im Abgasstrang 2 stromabwärts der Zusammenführung 8 angeordnet. Bei einem teilgeschädigten NOx-Speicherkatalysator 3, 4 tritt im Allgemeinen wegen einer geringeren NOx-Speicherfähigkeit ein geringerer Reduktionsmittelbedarf während einer Regenerationsmaßnahme auf. Die Sauerstoff-Speicherkapazität des nachgeschalteten Katalysators 9 ist daher so ausreichend zu bemessen, dass auch bei teilgeschädigten NOx-Speicherkatalysatoren 3, 4 die entsprechend höheren Mengen an Reduktionsmitteln katalytisch umgesetzt werden können. Damit wird eine zusätzliche Belastung der Umwelt mit Kohlenwasserstoffen und Kohlenmonoxyd vermieden. Vorzugsweise ist der Katalysator 9 so ausgelegt, dass zirka 30 % des gesamten durch den Abgasstrang 2 den NOx-Speicherkatalysatoren 3 und 4 zugeführten Reduktionsmittels abgebaut werden können. Dies entspricht einer Auslegung des Katalysators 9, bei der pro Gramm speicherbares NO2 vor Einleitung des NOx-Regenerationsmodus für die NOx-Speicherkatalysatoren 3, 4 zirka 0,1 Gramm O2-Speicherfähigkeit vorgehalten wird. Since reducing agent breakthroughs with a certain amount of unused hydrocarbon and carbon monoxide constituents occur at an already regenerated NO x storage catalytic converter, the catalytic converter 9 is arranged in the exhaust gas line 2 downstream of the convergence 8 for the effective exhaust gas purification. In a partially damaged NO x storage catalyst 3, 4 generally occurs because of a lower NO x storage capacity less reducing agent requirement during a regeneration measure. The oxygen storage capacity of the downstream catalytic converter 9 is therefore sufficient to be dimensioned so that even with partially damaged NO x storage catalysts 3, 4, the correspondingly higher amounts of reducing agents can be catalytically converted. This avoids additional pollution of the environment with hydrocarbons and carbon monoxide. Preferably, the catalyst 9 is designed so that about 30% of the total through the exhaust line 2 to the NO x storage catalysts 3 and 4 supplied reducing agent can be reduced. This corresponds to a design of the catalytic converter 9 in which about 0.1 grams of O 2 storage capacity is stored per gram of storable NO 2 before the initiation of the NO x regeneration mode for the NO x storage catalysts 3, 4.

Bei einer bevorzugten Ausführungsform der Erfindung ist ein Sensor 13, vorzugsweise eine Lambda-Sonde, stromabwärts des Katalysators 9 zur Überwachung der Funktionsfähigkeit vorgesehen. Das Signal des Sensors 13 wird der Kontrolleinrichtung 6 oder dem Motorsteuergerät 5 zugeführt.In a preferred embodiment of the invention is a sensor 13, preferably a Lambda probe, downstream of the catalyst 9 for monitoring the functionality intended. The signal of the sensor 13 is the control device 6 or the Engine control unit 5 supplied.

Bei Auftreten von Reduktionsmitteldurchbrüchen an dem Katalysator 9 vor Beendigung einer NOx-Regenerationsmaßnahme an den NOx-Speicherkatalysatoren 3 und 4, wird die NOx-Regeneration auch bei nicht vollständig regenerierten NOx-Speicherkatalysatoren 3, 4 beendet, um eine hohe Qualität der Abgasreinigung zu gewährleisten.Upon occurrence of reductant breakthroughs on the catalyst 9 before completion of a NO x regeneration measure on the NO x storage catalysts 3 and 4, the NO x regeneration is terminated even with incompletely regenerated NO x storage catalysts 3, 4, to a high quality To ensure exhaust gas purification.

Figur 2 zeigt eine alternative Ausführung der Erfindung, bei der keine Zusammenführung des Abgasstrangs 2 stromabwärts der NOx-Speicherkatalysatoren 3, 4 vorgesehen ist. Dies ist beispielsweise erforderlich, wenn auch der nachgeschaltete Katalysator aus Packungsgrunden geteilt werden muss. Dementsprechend ist an dem NOx-Speicherkatalysator 3 ein Abgasstrangzweig 2 mit einem nachgeschalteten Katalysator 9 und an den NOx-Speicherkatalysator 4 ein Abgasstrangzweig 2a mit einem weiteren Katalysator 9a angeschlossen. Die Auslegung der vorzugsweise als 3-Wege-Katalysatoren realisierten Katalysatoren 9, 9a ist wieder so zu bemessen, dass eine sichere Umsetzung von durchgebrochenem Reduktionsmittel möglich ist. Eine Überwachung der Katalysatoren 9, 9a kann durch nachgeschaltete Sensoren 13, 13a erfolgen. Vorzugsweise sind hierfür Lambda-Sonden vorgesehen. Das Signal der Sensoren 13, 13a wird der Kontrolleinrichtung 6 oder der Motorsteuerung 5 zugeführt und veranlasst eine Beendigung einer NOx-Regenerationsmaßnahme, falls ein Reduktionsmitteldurchbruch vorgegebener Höhe detektiert wird.Figure 2 shows an alternative embodiment of the invention, in which no merging of the exhaust line 2 downstream of the NO x storage catalysts 3, 4 is provided. This is necessary, for example, even if the downstream catalyst has to be divided for packing reasons. Accordingly, an exhaust gas branch 2 with a downstream catalytic converter 9 is connected to the NO x storage catalytic converter 3, and an exhaust gas branch 2 a to a further catalytic converter 9 a is connected to the NO x storage catalytic converter 4. The design of the preferably realized as a 3-way catalysts catalysts 9, 9a is again sized so that a safe implementation of erupted reducing agent is possible. A monitoring of the catalysts 9, 9a can be done by downstream sensors 13, 13a. Preferably lambda probes are provided for this purpose. The signal of the sensors 13, 13a of the control device 6 or the engine controller 5 is supplied and causes a termination of an NO x -Regenerationsmaßnahme if a reducing agent breakdown predetermined height is detected.

Insgesamt ermöglicht die erfindungsgemäße Beendigung einer NOx-Regenerationsmaßnahme eine sichere und effiziente Abgasreinigung bei einem Verbrennungsmotor mit mindestens zwei parallel nach einer Abzweigung im Abgasstrang angeordneten regenerierbaren NOx-Speicherkatalysatoren.Overall, the inventive termination of a NO x -Regenerationsmaßnahme allows safe and efficient exhaust gas purification in an internal combustion engine with at least two parallel arranged after a diversion in the exhaust line regenerable NO x storage catalytic converters.

Claims (14)

  1. Method for cleaning an exhaust gas of a combustion engine (1) with at least two NOx storage catalysts (3,4) regenerable by a reducing agent contained in the exhaust gas, which are arranged in parallel downstream of a branch (7) of an exhaust-gas duct (2), and to each of which a sensor (11,12), for example, an NOx sensor and/or a lambda probe, is allocated downstream, for the individual measurement of status parameters, wherein the exhaust gas is supplied to at least one oxidation catalyst (9), preferably a 3-way catalyst, arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2), and wherein NOx regeneration measures are implemented in dependence upon the status-parameter values of the NOx storage catalysts (3,4), characterised in that an NOx regeneration measure just implemented is terminated in dependence upon a later, especially the latest, point in time, at which a status-parameter value characteristic for the termination of the NOx regeneration measure is measured in one of the NOx storage catalysts (3,4).
  2. Method according to claim 1, characterised in that a predetermined lambda value of the exhaust gas downstream of an NOx storage catalyst (3,4) is selected as the status-parameter value characteristic for the termination of an NOx regeneration measure.
  3. Method according to at least one of claims 1 or 2, characterised in that the oxygen storage capacity of the oxidation catalyst (9) arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2) is dimensioned sufficiently high to break down the quantity of reducing agent breaking through in the event of a partially damaged NOx storage catalyst (3,4) by at least 50%, especially at least 90%.
  4. Method according to at least one of the preceding claims, characterised in that the oxygen storage capacity of the oxidation catalyst (9) arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2) is dimensioned sufficiently high to break down at least 20%, preferably at least 30% of the reducing agent flowing towards the NOx storage catalysts (3,4) during an NOx regeneration.
  5. Method according to at least one of the preceding claims, characterised in that, for each gram of NOx storable in the NOx storage catalysts (3,4), at least 0.07 g, especially 0.1 g oxygen is reserved in the oxidation catalyst(s) (9) arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2).
  6. Method according to at least one of the preceding claims, characterised in that the operating status of the oxidation catalyst (9) arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2) is determined by means of a downstream sensor (13), for example, a lambda probe.
  7. Method according to at least one of the preceding claims, characterised in that the oxidation catalyst (9) arranged downstream of the NOx storage catalysts (3,4) in the exhaust-gas duct (2) is monitored for the occurrence of a breakthrough of reducing agent and, in the event of a breakthrough of reducing agent of a predetermined level, an NOx regeneration measure, which has just been implemented, is terminated.
  8. Method according to at least one of claims 1 to 7, characterised in that the NOx regeneration measure is introduced in dependence upon the NOx charging of the NOx storage catalysts (3,4).
  9. Method according to claim 8, characterised in that the NOx regeneration measure is introduced in dependence upon the first point in time, at which an NOx breakthrough of a predetermined level occurs in one of the NOx storage catalysts (3,4).
  10. Method according to at least one of claims 1 to 9, characterised in that the exhaust gas is supplied to at least one pre-catalyst (15) upstream of the NOx storage catalysts (3,4).
  11. Device for cleaning the exhaust gas of a combustion engine (1) with at least two NOx storage catalysts (3,4), which are arranged in parallel in the exhaust-gas duct (2) downstream of a branch (7) and which are regenerable by means of reducing agents contained in the exhaust gas, and with at least one oxidation catalyst (9), preferably a 3-way catalyst, arranged downstream of the NOx storage catalysts (3,4), wherein sensors (11, 12) are provided downstream of the NOx storage catalysts (3,4) for the individual registration of status-parameter values of the NOx storage catalyst (3,4), which can be supplied to an engine-control device (5) in order to evaluate and influence operational parameters of the combustion engine (1), characterised in that the engine-control device (5) provides a control unit (6) for the termination of an NOx regeneration measure, which has just been implemented, in dependence upon a later, especially the latest, point in time, at which a status-parameter value characteristic for the termination of the NOx regeneration measure is measured in one of the NOx storage catalysts (3,4).
  12. Device according to claim 11, characterised in that the branches of the exhaust-gas duct are recombined at a connecting position (8) downstream of the NOx storage catalysts (3,4) and upstream of the oxidation catalyst (9), which is connected downstream.
  13. Device according to claim 11, characterised in that the branches (2,2a) of the exhaust-gas duct remain divided downstream of the NOx storage catalysts (3,4), and that at least one oxidation catalyst (9,9a), preferably a 3-way catalyst, is arranged downstream in each branch (2,2a) of the exhaust-gas duct.
  14. Device according to at least one of claims 11 to 13, characterised in that sensor means (13,13a) for monitoring the operational status of the relevant oxidation catalyst (9,9a) are arranged downstream of each oxidation catalyst (9,9a), which is connected downstream of the NOx storage catalyst (3,4).
EP01250100A 2000-03-28 2001-03-21 Method and device for purification of exhaust gases Expired - Lifetime EP1138898B1 (en)

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DE102004015129A1 (en) * 2004-03-27 2005-10-13 Robert Bosch Gmbh Management of an internal combustion engine comprising two banks of cylinders comprises controlled regeneration of downstream nitrogen oxide storage catalysts
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