DE102019116775A1 - Method for operating an exhaust aftertreatment device, control unit for an internal combustion engine and internal combustion engine - Google Patents

Abstract

A method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalyst and at least one downstream of the nitrogen oxide storage catalytic converter arranged SCR catalytic converter, wherein in an oxidizing composition of an exhaust gas of the internal combustion engine in the nitrogen oxide storage catalytic converter nitrogen oxides and sulfur oxides are withdrawn and stored, wherein the SCR catalyst has a loading of ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen, and control unit for an internal combustion engine with an exhaust aftertreatment device, wherein the exhaust aftertreatment device is a nitrogen oxide storage catalyst and at least one arranged downstream of the nitrogen oxide storage catalytic converter SCR catalyst, wherein the SCR catalyst has a loading with ammonia, so that in the oxidizing Zusammens tion of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen, and internal combustion engine with an exhaust aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide storage catalyst and at least one downstream of the nitrogen oxide storage catalytic converter arranged SCR catalyst, further comprising a control unit is provided.

Description

The invention relates to a method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalyst and at least one downstream of the nitrogen oxide storage catalytic converter arranged SCR catalytic converter, wherein withdrawn in an oxidizing composition of an exhaust gas of the internal combustion engine in the nitrogen oxide storage catalyst the exhaust gas oxides and sulfur oxides and stored, wherein the SCR catalyst has a loading of ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen. The invention further relates to a control unit for an internal combustion engine having an exhaust aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide storage catalyst and at least one arranged downstream of the nitrogen oxide storage catalytic converter SCR catalyst, wherein the SCR catalyst has a loading with ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to form water and nitrogen. The invention further relates to an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalytic converter and at least one SCR catalytic converter arranged downstream of the nitrogen oxide catalytic converter, wherein a control unit is also provided.

In the after-treatment of exhaust gases of internal combustion engines, it is known to use several different systems to reduce the emission of undesirable components of the exhaust gas. These systems include, among others, nitrogen oxide storage catalysts and SCR catalysts, which reduce the proportion of nitrogen oxides (NOx) in the exhaust gas. In the Selective Catalytic Reduction (SCR) process, a urea-water solution is introduced into the oxygen-rich offgas. In the SCR catalyst, the urea-water solution reacts to ammonia, which then combines with the nitrogen oxides, resulting in water and nitrogen. In a nitrogen storage catalytic converter, nitrogen oxides are stored in lean, that is also oxygen-rich, exhaust gas. The operating conditions of the internal combustion engine are briefly changed so that a lack of air in the exhaust gas, therefore rich exhaust prevails. Now, the stored nitrogen oxides can be reduced to harmless nitrogen, which is then ejected. In NOx storage catalysts, a certain amount of sulfur oxides is regularly stored in addition to the nitrogen oxides. Since these stored sulfur compounds, which are also called sulfates, have a higher stability than the corresponding nitrogen compounds, the so-called nitrates, they accumulate continuously in the nitrogen oxide storage catalyst. From time to time, therefore, the nitrogen oxide storage catalyst must be freed from sulfates. This desulfurization requires an elevated temperature in combination with a substoichiometric, ie rich exhaust gas composition in the nitrogen oxide storage catalyst. The systems are operated independently of one another, for example in each case on the basis of characteristic maps which map a catalytic converter operating state, an exhaust gas sensor system and operating points of the internal combustion engine.

In the publication DE 10 2007 041 501 B4 For example, a method for purifying exhaust gases for an internal combustion engine is described, wherein an exhaust system comprises a NOX storage catalytic converter device and an SCR catalytic converter device. The NOX storage catalytic converter device and the SCR catalytic converter device are arranged in partial exhaust gas strands assigned to different cylinder groups, a substoichiometric exhaust gas composition being present in the NOX storage catalytic device for desulfating the same, and a predetermined amount of the sulfur compounds released thereby together with an exhaust gas flow having a lean exhaust gas composition to the SCR catalytic converter device flows, in which the present in the sulfur compounds hydrogen sulfide is oxidized.

It is an object of the invention to operate a nitrogen oxide storage catalytic converter and at least one SCR catalytic converter in an exhaust aftertreatment device in the after-treatment of exhaust gases of an internal combustion engine, wherein a regulation of the exhaust gas aftertreatment device takes into account a plurality of systems.

The object is achieved by a method and a control unit according to the independent claims. In the respective subclaims preferred embodiments and advantageous developments are given.

The method according to the invention serves to operate an exhaust gas aftertreatment device of an internal combustion engine, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalytic converter and at least one SCR catalytic converter arranged downstream of the nitrogen oxide storage catalytic converter. In an oxidizing composition of an exhaust gas of the internal combustion engine, nitrogen oxides and sulfur oxides are removed from the exhaust gas in the nitrogen oxide storage catalyst and stored therein. According to the invention, the SCR catalyst has a loading of ammonia, so that at the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen, wherein the loading of the SCR catalyst is controlled with ammonia, taking into account a state of the nitrogen oxide storage catalyst.

An advantage of the method according to the invention is that depending on the state of the nitrogen oxide storage catalyst, the loading of the SCR catalyst with ammonia can be kept low, so that hatching, ie, escape of ammonia, is avoided. Furthermore, in the case of a high sulfur loading of the nitrogen oxide storage catalyst, the loading of the SCR catalyst with ammonia can advantageously be increased in order to compensate for a collapse of the nitrogen oxide conversion of the nitrogen oxide storage catalyst.

Nitrogen storage catalysts are known in the art. These are also referred to as NOx Storage Catalyst (NSK), NOx Trap or Lean NOx Trap (LNT). NOx designates both nitrogen monoxide NO and nitrogen dioxide NO2. When using a nitrogen oxide storage catalytic converter, the internal combustion engine is usually operated lean, which allows low fuel consumption. As a result, the exhaust gas has an oxidizing composition with an excess of air. The nitrogen oxide-containing exhaust gas is fed to the nitrogen oxide storage catalyst, which removes the nitrogen oxides by storing, mainly as nitrate, the exhaust gas. Depending on the amount of nitrogen oxides stored, the nitrate regeneration of the storage catalytic converter is carried out from time to time. For this purpose, the internal combustion engine is reversed for a short time to rich operation, whereby a rich exhaust gas is generated, which has an excess of reduction agents such as carbon monoxide, hydrogen or hydrocarbons, ie a reducing composition. This results in a release of the nitrogen oxides stored in the nitrogen oxide storage catalyst.

For the purposes of the invention, the term SCR catalyst generally comprises catalyst systems which use the principle of the selective catalytic reaction and moreover has no restrictive effect. The term includes in particular so-called SCRF or SDPF catalysts, in which an SCR coating is functionally integrated on a particle filter.

Preferably, an aqueous urea solution or urea-water solution before the SCR catalyst in the exhaust line, z. B. by means of metering pump or injector, sprayed. The urea-water solution produces ammonia and CO2 through a hydrolysis reaction. The ammonia (NH3) thus produced reacts essentially in the SCR catalyst at the appropriate temperature with the nitrogen oxides in the exhaust gas. Also in the nitrogen oxide storage catalyst, ammonia is formed in the nitrate regeneration, which is collected in the SCR catalyst and reacted with it.

The combustion air ratio is here also synonymously referred to as air-fuel ratio with the abbreviation lambda (λ). Also, the terms air ratio or air ratio are common for the dimensionless number that indicates the mass ratio of air and fuel in a combustion process. A combustion air ratio less than 1 (λ <1) means lack of air, in internal combustion engines is called a rich or rich mixture, it produces exhaust gas with a reducing composition. A combustion air ratio greater than 1 (λ> 1) means excess air, in internal combustion engines is called a lean or poor mixture, it produces exhaust gas with a reducing composition. The control, which is also referred to as lambda control, preferably takes place in a gasoline engine by a direct intervention on the injected fuel quantity, in the case of a diesel engine preferably via the air system by regulating an exhaust gas recirculation rate via exhaust gas recirculation.

Desulfurization of the nitrogen oxide storage catalyst is preferably carried out by adjusting a reducing composition of the exhaust gas and increasing an exhaust gas temperature, so that sulfur oxides stored in the nitrogen oxide storage catalyst are released with formation of hydrogen sulfide. Hydrogen sulfide released from the nitrogen oxide storage catalyst during desulfurization is fed to the SCR catalyst and oxidized to sulfur dioxide under the reducing composition of the exhaust gas in the SCR catalyst. The desulfurization of the nitrogen oxide storage catalyst is preferably carried out as soon as a sulfur oxide loading of the nitrogen oxide storage catalyst reaches a loading limit value, the loading limit value being determined in particular taking into account a state of the SCR catalytic converter.

According to the invention, the state of the nitrogen oxide storage catalyst is evaluated according to the thermal age and / or after the sulfur oxide loading of the nitrogen oxide storage catalyst.

According to a preferred embodiment, it is provided that with increasing thermal age of the nitrogen oxide storage catalyst, the loading of the SCR catalyst with ammonia is increased.

According to a preferred embodiment, it is provided that with a rising Sulfur oxide loading of the nitrogen oxide storage catalyst, the loading of the SCR catalyst is increased with ammonia. Particular preference is given to desulfurization of the nitrogen oxide storage catalyst from time to time, wherein the charge of the SCR catalyst with ammonia is lowered again after desulfurization.

Another object of the invention relates to a control unit for an internal combustion engine with an exhaust gas aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide storage catalyst and at least one arranged downstream of the nitrogen oxide storage catalytic converter SCR catalyst. The SCR catalyst has a loading of ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen. The control unit according to the invention is designed to control the loading of the SCR catalyst with ammonia, taking into account a state of the nitrogen oxide storage catalytic converter.

Preferably, the control unit is designed to evaluate the state of the nitrogen oxide storage catalytic converter after a thermal age and a sulfur oxide loading of the nitrogen oxide storage catalytic converter.

The control unit is furthermore preferably designed to carry out a desulfurization of the nitrogen oxide storage catalyst from time to time by the exhaust gas during desulfurization exhaust gas with a reducing composition and at an elevated temperature, so that stored in the nitrogen oxide storage catalyst sulfur oxides released to form hydrogen sulfide oxidize in the SCR catalyst under the reducing composition of the exhaust gas to sulfur dioxide. The control unit is furthermore preferably designed to carry out the desulfurization of the nitrogen oxide storage catalytic converter as soon as a sulfur oxide loading of the nitrogen oxide storage catalytic converter reaches a loading limit value, wherein the control unit is in particular designed to variably determine the loading limit value taking into account a state of the SCR catalytic converter

Further preferably, the control unit is designed to carry out the method described above.

Another object of the invention relates to an internal combustion engine with an exhaust gas aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide storage catalyst and at least one arranged downstream of the nitrogen oxide storage catalytic converter SCR catalyst, wherein a control unit, as described above, is also provided.

The invention will be explained in more detail below with reference to an embodiment with reference to the accompanying drawings. The statements relate to all subjects of the invention equally, are merely exemplary and do not limit the general inventive concept.

• 1 ein schematisches Blockbild einer Brennkraftmaschine mit zugehöriger Abgasnachbehandlungseinrichtung gemäß einer Ausführungsform der Erfindung,
• 2 ein schematisches Blockbild einer Variante der Abgasnachbehandlungseinrichtung gemäß einer weiteren Ausführungsform der Erfindung,
• 3 ein schematisches Blockbild einer weiteren Variante der Abgasnachbehandlungseinrichtung gemäß einer weiteren Ausführungsform der Erfindung.

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• 1 1 is a schematic block diagram of an internal combustion engine with associated exhaust gas aftertreatment device according to an embodiment of the invention,
• 2 1 is a schematic block diagram of a variant of the exhaust gas aftertreatment device according to a further embodiment of the invention,
• 3 a schematic block diagram of another variant of the exhaust aftertreatment device according to another embodiment of the invention.

In the in 1 illustrated embodiment, a diesel engine is used as an internal combustion engine 1 , The internal combustion engine 1 is via the intake air line 3 Combustion air supplied. The internal combustion engine 1 is the exhaust aftertreatment device 2 assigned, which in the exhaust pipe 4 an oxidation catalyst 5 , a particle filter 6 , a nitrogen oxide storage catalyst 7 and an SCR catalyst 8th having. In the present case, on the one hand, the particulate filter 6 directly to the oxidation catalyst 5 downstream and on the other hand, the SCR catalyst 8th directly to the nitrogen oxide storage catalyst 7 downstream. A temperature of the nitrogen oxide storage catalyst 7 is by means of a sensor 15 measured. Upstream of the oxidation catalyst 5 is in the exhaust pipe 4 an exhaust gas turbocharger 12 housed, which serves for the compression of the combustion air, which after the compression of one in the intake air line 3 arranged intercooler 14 is cooled. The internal combustion engine 1 is also a control unit 9 assigned, which among other things serves to control the combustion. To transfer the necessary control signals are control or signal lines 10 available. Other components of the measurement and control of operating parameters such as oxygen probes, temperature sensors, throttle valves, other signal lines and the like are not shown in the drawing for the sake of clarity.

The internal combustion engine 1 is primarily operated lean. Particles contained in the exhaust gas are in the particle filter 6 retained. During the passage of the exhaust gas through the oxidation catalyst 5 NO in the exhaust gas is oxidized to NO2 and can then in the downstream particle filter 6 For its part, carbonaceous particles deposited there oxidize, which results in continuous regeneration of the particulate filter 6 he follows. The effluent from the particulate filter, further nitrogen oxide-containing exhaust gas is the nitrogen oxide storage catalyst 7 supplied to the exhaust gas, the nitrogen oxides by storage, mainly as nitrate, withdraws. Depending on the amount of stored nitrogen oxides is from time to time a nitrate regeneration of the storage catalyst 7 carried out. For this purpose, the internal combustion engine 1 reversed for a short time to rich operation, whereby a rich exhaust gas is generated, which has an excess of reduction agents such as carbon monoxide, hydrogen or hydrocarbons. This has a release in the nitrogen oxide storage catalyst 7 stored nitrogen oxides result, which in the catalytic layer of the nitrogen oxide storage catalyst 7 existing noble metal centers are reduced by the reducing agents of the exhaust gas. A temperature of the nitrogen oxide storage catalyst 7 is done by means of the sensor 15 determined since the nitrate regeneration is performed only when the temperature of the nitrogen oxide storage catalyst 7 exceeds a temperature limit.

The combustion air ratio is here also synonymously referred to as air-fuel ratio with the abbreviation lambda (λ). The therefore also referred to lambda control takes place in a gasoline engine by a direct intervention on the injected fuel amount, which is not common in the diesel engine, since the diesel engine, the engine torque is controlled by the change in fuel quantity. The lambda control in the diesel engine instead takes place via the air system by regulating the exhaust gas recirculation rate via exhaust gas recirculation 11 ,

The reduction product of nitrogen oxide reduction is mainly nitrogen. In addition, depending on the conditions under which the nitrate regeneration is carried out, more or less large amounts of the reduction product ammonia (NH3) are formed, the release of which is undesirable in the environment. With the help of the present invention downstream of the nitrogen oxide storage catalyst 7 arranged SCR catalyst 8th the ammonia is intercepted by storage. This stored NH3 is in the following on the nitrate regeneration lean engine operation as an additional reducing agent for selective reduction of nitrogen oxides in the SCR catalyst 8th to disposal. Thereby, the efficiency of the nitrogen oxide removal in the exhaust gas aftertreatment device becomes 2 additionally increased in an advantageous manner.

When sulfur-containing fuel is used, the exhaust gas of the internal combustion engine contains 1 Sulfur dioxide, that of the catalyst material of the nitrogen oxide storage catalyst 7 is formed with the formation of stable sulfates, which increasingly reduces its nitrogen oxide storage capacity over time. The nitrogen oxide storage catalyst 7 is therefore repeatedly freed of stored sulfur in a desulfurization (desulfurization), ie regenerated. This is the internal combustion engine 1 operated in a desulfurization mode. This desulfurization mode includes, for example, fuel post-injection raising the exhaust gas temperature to over 500 ° C and setting a reducing exhaust gas composition to values of about 0.95 or less for the air-fuel ratio (FIG. A ), similar to the purpose of nitrate regeneration. Under these conditions, the relatively stable sulfates in the nitrogen oxide storage catalyst succeed 7 to decompose reductively. Depending on the temperature, the strength of the enrichment and the amount of sulfur stored in the nitrogen oxide storage catalyst, more or less large amounts of hydrogen sulfide (H2S) are formed. This H2S is in the nitrogen oxide storage catalyst 7 and in the SCR catalyst 8th converted to less odorous nitrogen dioxide (SO2) under the reducing conditions of desulfurization. As a result, the odor problem usually associated with desulfurization, also referred to herein as desulfation, is avoided by nitrogen oxide storage catalysts. An advantage of using the SCR catalyst 8th downstream of the nitrogen oxide storage catalyst 7 This is because the process of desulfation can be simplified because it does not have to be oriented towards minimizing the undesired desulfurization product H2S. For example, desulfation can be achieved by a stronger enrichment with λ values below 0.95 and thus associated stronger and faster H2S release from the nitrogen oxide storage catalyst 7 shorten significantly.

The SCR catalyst 8th has a loading of ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst 8th the ammonia reacts with the nitrogen oxides to form water and nitrogen, with the loading of the SCR catalyst 8th with ammonia, taking into account a state of the nitrogen oxide storage catalyst 7 is regulated, in particular taking into account the thermal age and / or the sulfur oxide loading of the nitrogen oxide storage catalyst 7 , An advantage of the method according to the invention is that, depending on the state of the nitrogen oxide storage catalyst 7 the loading of the SCR catalyst 8th can be kept low with ammonia, so that hatching, ie escape of ammonia is avoided.

Before the SCR catalyst 8th is an introduction of aqueous urea solution 16 intended. In the SCR catalyst 8th reacts the urea-water Solution to ammonia, which then combines with the nitrogen oxides, resulting in water and nitrogen. The regulation of the loading of the SCR catalyst 8th with ammonia is preferably carried out by the amount of added urea-water solution.

The control unit 9 the internal combustion engine 1 is preferably designed from time to time to desulfate the nitrogen oxide storage catalyst 7 perform by the internal combustion engine 1 during desulfurization produces exhaust gas with a reducing composition and at an elevated temperature, so that in the nitrogen oxide storage catalyst 7 stored sulfur oxides are released to form hydrogen sulfide. The control unit 9 is designed to the desulfation of the nitrogen oxide storage catalyst 7 as soon as a sulfur oxide loading of the nitrogen oxide storage catalyst reaches a loading limit, the control unit 9 is designed in particular to the loading limit taking into account a state of the SCR catalyst 8th to determine, in particular the loading limit taking into account a thermal age of the SCR catalyst 8th to determine.

The possibility of using the SCR catalyst 8th downstream of the nitrogen oxide storage catalyst 7 is not due to the presence of upstream cleaning components such as particle filters 6 and oxidation catalyst 5 dependent. H2S can also be used in the nitrogen oxide storage catalytic converter 7 be oxidized. An SCR catalyst 8th This is not mandatory.

In the 2 and 3 are variants of the exhaust aftertreatment device 2 shown, which are typically used with an internal combustion engine according to the invention. The statements relating to the elements of the internal combustion engine, not shown, relate to the 1 ,

In the 2 is a schematic block diagram of a variant of the exhaust aftertreatment device 2 shown, wherein in the flow direction of the exhaust gas behind one another, the nitrogen oxide storage catalyst 7 a first combined SCR catalyst 6 . 8th with filter, a so-called SCRF (Selective Catalytic Reduction Filter) and a second SCR catalyst 8th are arranged. The SCRF is a combination of SCR catalyst 8th and particle filters 6 , which is to be counted among the SCR catalysts in the context of the invention. Each before the SCR catalysts 8th is an introduction of aqueous urea solution 16 intended. The downstream second discharge of aqueous urea solution 16 and the second SCR catalyst are optional.

In the 3 is a schematic block diagram of another variant of the exhaust aftertreatment device 2 shown, wherein in the flow direction of the exhaust gas behind one another, the nitrogen oxide storage catalyst 7 , the particle filter 6 and the SCR catalyst 8th are arranged. Before the SCR catalyst 8th is an introduction of aqueous urea solution 16 intended.

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

exhaust treatment device

3

intake air line

4

exhaust pipe

5

oxidation catalyst

6

particulate Filter

7

Nitrogen oxide storage catalyst

8th

SCR catalyst

6, 8

SCRF, combined SCR catalytic converter with particulate filter

9

control unit

10

signal line

11

Exhaust gas recirculation

12

turbocharger

14

Intercooler

15

sensor

16

Introduction of the aqueous urea solution

A

Arrow, flow direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007041501 B4 [0003]

Claims (10)

Method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalytic converter (7) and at least one SCR catalytic converter (8) arranged downstream of the nitrogen oxide storage catalytic converter (7), wherein in an oxidizing composition of an exhaust gas of the internal combustion engine in the nitrogen oxide storage catalyst (7) the exhaust gas nitrogen oxides and sulfur oxides are removed and stored, wherein the SCR catalyst (8) has a loading of ammonia, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen, wherein the loading of the SCR catalyst (8) with ammonia is controlled in consideration of a state of the nitrogen oxide storage catalyst (7). Method according to Claim 1 , characterized in that the state of the nitrogen oxide storage catalyst (7) is evaluated according to one or more of the following features: thermal age and sulfur oxide loading of the nitrogen oxide storage catalyst. Method according to one of the preceding claims, characterized in that with increasing thermal age of the nitrogen oxide storage catalyst, the loading of the SCR catalyst (8) is increased with ammonia. Method according to one of the preceding claims, characterized in that with an increasing sulfur oxide loading of the nitrogen oxide storage catalyst, the loading of the SCR catalyst (8) is increased with ammonia. Method according to Claim 3 , characterized in that from time to time desulfation of the nitrogen oxide storage catalyst (7) is carried out, wherein the loading of the SCR catalyst (8) with ammonia is lowered again after desulfurization. Method according to one of the preceding claims, characterized in that upstream of the SCR catalyst (8), a urea-water solution (16) is added to the exhaust gas, wherein the urea-water solution in the SCR catalyst (8) to ammonia reacts, wherein the loading of the SCR catalyst is controlled with ammonia on the amount of added urea-water solution. Control unit (9) for an internal combustion engine (1) with an exhaust aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide storage catalyst (7) and at least one downstream of the nitrogen oxide storage catalytic converter arranged SCR catalyst (8), wherein the SCR catalyst (8) a Containing ammonia loading, so that in the oxidizing composition of the exhaust gas in the SCR catalyst, the ammonia reacts with the nitrogen oxides to water and nitrogen, wherein the control unit (9) is adapted to the loading of the SCR catalyst (8) with ammonia under Considering a state of the nitrogen oxide storage catalyst (7) to regulate. Control unit after Claim 7 , Characterized in characterized in that the control unit (9) is designed to evaluate the condition of the nitrogen oxide storage catalyst (7) according to one or more of the following characteristics: thermally age and Schwefeloxidbeladung the nitrogen oxide storage catalyst. Control unit according to one of Claims 7 or 8th , characterized in that the control unit (9) is adapted to the method according to one of Claims 1 to 6 perform. Internal combustion engine (1) having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device comprises a nitrogen oxide storage catalytic converter (7) and at least one SCR catalytic converter (8) arranged downstream of the nitrogen oxide storage catalytic converter, wherein furthermore a control unit (9) according to any one of Claims 7 to 9 is provided.

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