CN110725736A

CN110725736A - Method for operating an exhaust gas aftertreatment device, control unit for an internal combustion engine and internal combustion engine

Info

Publication number: CN110725736A
Application number: CN201910628966.2A
Authority: CN
Inventors: 托马斯·维特卡; 亚历山大·沃夫克; 迈克尔·菲比希
Original assignee: FEV Europe GmbH
Current assignee: FEV Europe GmbH
Priority date: 2018-07-16
Filing date: 2019-07-12
Publication date: 2020-01-24
Also published as: DE102018117187A1; DE102019116776A1

Abstract

A method for operating an exhaust gas aftertreatment device of an internal combustion engine is described, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst; a control unit for an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein the control unit is designed to occasionally carry out a nitrate regeneration of the nitrogen oxide storage catalyst in that the internal combustion engine generates an exhaust gas with a reducing composition during the nitrate regeneration; and an internal combustion engine having such a control unit.

Description

Method for operating an exhaust gas aftertreatment device, control unit for an internal combustion engine and internal combustion engine

Technical Field

The invention relates to a method for operating an exhaust gas aftertreatment device of an internal combustion engine, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst. In the case of an oxidizing composition of the exhaust gas of an internal combustion engine, nitrogen oxides and sulfur oxides are extracted from the exhaust gas in a nitrogen oxide storage catalyst and stored therein. The nitrate regeneration of the nitrogen oxide storage catalyst is carried out by: the reducing composition of the exhaust gas is set. The invention further relates to a control unit for an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein the control unit is designed to sometimes carry out a nitrate regeneration of the nitrogen oxide storage catalyst in that the internal combustion engine generates an exhaust gas with a reducing composition during the nitrate regeneration. The invention also relates to an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein a control unit is provided.

Background

In the aftertreatment of the exhaust gases of internal combustion engines, it is known to use a plurality of different systems in order to reduce the emissions of undesirable constituents of the exhaust gases. These systems furthermore comprise a nitrogen oxide storage catalyst and an SCR catalyst, by means of which the proportion of nitrogen oxides (NOx) in the exhaust gas is reduced. In a Selective Catalytic Reduction (SCR) method, a urea-water solution is introduced into an oxygen-rich exhaust gas. In the SCR catalyst, the urea-water solution reacts to form ammonia, which is subsequently combined with nitrogen oxides, thereby producing water and nitrogen. Nitrogen oxides are stored in the nitrogen storage catalyst in the case of lean-burn, i.e. likewise oxygen-rich, exhaust gases. The operating conditions of the internal combustion engine are temporarily changed so that there is a lack of oxygen in the exhaust gas and, therefore, a rich exhaust gas. The stored nitrogen oxide can now be reduced to harmless nitrogen, which is subsequently discharged. The systems are operated independently of one another, for example, in each case according to a characteristic map which describes the operating state of the catalytic converter, the operating point of the exhaust gas sensor system and the internal combustion engine.

DE 102013021156 a1 discloses a method for operating an engine in a lean combustion mode and a rich combustion mode, wherein the engine is operated in the rich combustion mode with an early injection in order to generate ammonia for storage in an SCR in a nitrogen-storage catalyst, also referred to as LNT representing a lean NOx trap, which SCR is located downstream of the LNT. In SCR, when the engine is operating in a lean combustion mode, the stored ammonia reacts with NOx escaping from the LNT to produce diatomic nitrogen. Using a rich combustion mode with an earlier injection reduces the amount of soot that is produced when the engine is operating rich, which allows the engine to operate in a rich, early combustion mode for a longer period of time than when using conventional rich combustion. The longer period of rich operation offers the potential to use less PGM materials in the LNT while proposing the feasibility of producing more ammonia that is necessary for subsequent use as a reductant in the SCR during lean burn operation.

Disclosure of Invention

The object of the invention is to operate a nitrogen oxide storage catalyst and at least one SCR catalyst in an exhaust gas aftertreatment device when the exhaust gas of an internal combustion engine is being treated, wherein the regulation of the exhaust gas aftertreatment device takes into account a plurality of systems.

The object is achieved according to the invention by a method and a control unit for operating an exhaust gas aftertreatment device of an internal combustion engine. Preferred embodiments and advantageous refinements are given in the following description.

The method according to the invention is used for operating an exhaust gas aftertreatment device of an internal combustion engine, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst. In the case of an oxidizing composition of the exhaust gas of an internal combustion engine, nitrogen oxides and sulfur oxides are extracted from the exhaust gas in a nitrogen oxide storage catalyst and stored therein. Nitrate regeneration of the nox storage catalyst is carried out by setting a reducing composition of the exhaust gas, wherein the temperature of the nox storage catalyst is determined and nitrate regeneration is carried out only when the temperature of the nox storage catalyst exceeds a temperature limit value. According to the invention, the temperature limit value for the nitrate regeneration is determined taking into account the state of the SCR catalyst.

The method according to the invention has the advantage that, depending on the state of the SCR catalyst, nitrate production can already be started when the temperature of the nox storage catalyst is low. If the state of the SCR catalyst allows nitrate regeneration when the temperature of the nox storage catalyst is low, the heating of the nox storage catalyst can advantageously be dispensed with. The following requirements are also less necessary: the regeneration is delayed until the nitrogen oxide storage catalyst has reached a sufficiently high temperature.

Nitrogen oxide storage catalysts are known from the prior art. The nitrogen oxide storage catalyst is also referred to as a NOx storage catalyst (NSK), a NOx trap or a Lean NOx Trap (LNT). NOx here means not only nitric oxide NO, but also nitrogen dioxide NO 2. When using a nitrogen oxide storage catalyst, the internal combustion engine is usually operated lean, which enables low fuel consumption. The exhaust gas thus has an oxidizing composition with excess air. The exhaust gas containing nitrogen oxides is fed to a nitrogen oxide storage catalyst, which extracts nitrogen oxides from the exhaust gas by storage, currently as nitrate storage. Depending on the amount of stored nitrogen oxides, nitrate regeneration of the storage catalyst is sometimes performed. For this purpose, the internal combustion engine is switched over in a short time to rich operation, whereby a rich exhaust gas is produced, which has an excess of reducing agents, such as carbon monoxide, hydrogen or hydrocarbons, i.e. a reducing composition. This causes the release of the nitrogen oxides stored in the nitrogen oxide storage catalyst.

The term SCR catalyst for the purposes of the present invention generally includes catalyst systems which apply the principle of selective catalytic reactions and otherwise function without limitation. The term includes, in particular, so-called SCRF or SDPF catalysts, in which the SCR coating on the particle filter is functionally integrated.

Preferably, an aqueous urea solution or a urea-water solution is injected into the exhaust gas line upstream of the SCR catalytic converter, for example by means of a dosing pump or an injector. Ammonia and CO2 are produced from the urea-water solution by a hydrolysis reaction. The ammonia (NH3) thus produced reacts with the nitrogen oxides in the exhaust gas at a corresponding temperature substantially in the SCR catalyst. Ammonia is also produced in the nitrogen oxide storage catalyst during the nitrate regeneration, which is trapped in the SCR catalyst and is converted together.

The combustion air ratio is also synonymously referred to herein as the air-fuel ratio, abbreviated as Lambda (Lambda). The designations air ratio or air number are also common for dimensionless characteristic numbers which describe the mass ratio of air to fuel in the combustion process. A combustion air ratio of less than 1(λ <1) indicates a lack of air, which in the case of internal combustion engines refers to a rich or rich mixture (reiche Gemisch), which produces exhaust gases with a reducing composition. Combustion air ratios greater than 1(λ >1) indicate excess air, which in the case of internal combustion engines is referred to as lean mixtures or lean mixtures (armen Gemisch), which produces exhaust gases with a reducing composition. The regulation, also referred to as lambda regulation, is preferably carried out in gasoline engines by direct intervention of the injected fuel quantity, and in diesel engines by adjusting the exhaust gas recirculation rate via an exhaust gas recirculation device, preferably via an air system.

According to the invention, the temperature limit value for the nitrate regeneration is determined taking into account the state of the SCR catalyst. Preferably, the state of the SCR catalyst is evaluated here on the basis of one or more of the following features of the SCR catalyst:

-the efficiency of the conversion of nitrogen oxides,

-a thermal life time,

-a temperature of the liquid to be heated,

-ammonia filling degree.

That is, the temperature limit for nitrate regeneration (LNT NOx regeneration) is preferably determined by means of the following function: the function takes into account the current SCR efficiency and/or the current SCR temperature and/or the current SCR-NH3 filling level and/or the thermal life of the SCR catalyst. Particularly preferably, the state of the SCR catalyst is evaluated here on the basis of all the previously mentioned features of the SCR catalyst.

According to a preferred embodiment, it is provided that the temperature limit value is reduced in the case of a high efficiency of the nox conversion of the SCR catalyst. With a low temperature start for nitrate regeneration, the nitrogen oxide storage catalyst is advantageously already regenerated at a lower temperature. Otherwise the nitrogen oxide storage catalyst must first be heated, or regeneration must be delayed until the nitrogen oxide storage catalyst has reached a sufficiently high temperature. In contrast, especially in the case of a low efficiency of the NOx conversion of the SCR catalyst, the temperature limit value is increased to a typical value from which the NOx reduction is sufficiently high during regeneration of the NOx storage catalyst.

According to a further preferred embodiment, it is provided that the temperature limit value is increased at higher thermal lives of the SCR catalytic converter. The efficiency reduction due to the higher thermal life of the SCR catalyst is advantageously compensated by the higher temperature during the nitrate regeneration. In contrast, the temperature limit value is reduced, in particular in the case of a low thermal life of the SCR catalyst, in order to advantageously reduce the thermal load on the nitrogen oxide storage catalyst during the regeneration of nitrates.

According to a further preferred embodiment, it is provided that the temperature limit value is reduced when the temperature of the SCR catalytic converter is high. The increased conversion of the SCR catalyst at higher temperatures is advantageously used to carry out nitrate regeneration of the nox storage catalyst at lower temperatures and to advantageously dispense with heating of the nox storage catalyst.

According to a further preferred embodiment, it is provided that the temperature limit value is reduced in the case of a high ammonia filling level in the SCR catalytic converter. When the ammonia filling level in the SCR catalytic converter is high, nitrate regeneration of the nitrogen oxide storage catalytic converter is carried out at a lower temperature and the heating of the nitrogen oxide storage catalytic converter is advantageously dispensed with. If necessary, the formation of additional ammonia during nitrate regeneration can be reduced by the lower temperature, so that the escape of excess ammonia (NH3), i.e. undesirable emissions, is advantageously avoided.

A further subject matter of the invention relates to a control unit for an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst. The control unit is designed to sometimes carry out a nitrate regeneration of the nitrogen oxide storage catalyst in that the internal combustion engine generates exhaust gas with a reducing composition during the nitrate regeneration, wherein a sensor is provided in order to determine the temperature of the nitrogen oxide storage catalyst, and wherein the control unit is designed to carry out the nitrate regeneration only when the temperature of the nitrogen oxide storage catalyst exceeds a temperature limit value. The control unit is also designed to determine a temperature limit value for nitrate regeneration taking into account the state of the SCR catalytic converter.

Preferably, the state of the SCR catalyst is characterized here by one or more of the following features:

-the efficiency of the conversion of nitrogen oxides,

-a thermal life time,

-a temperature of the liquid to be heated,

-ammonia filling degree.

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

A further subject matter of the invention relates to an internal combustion engine having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst and at least one SCR catalyst arranged downstream of the nitrogen oxide storage catalyst, wherein a control unit as described above is also provided.

Drawings

The invention is explained in detail below with reference to the figures according to embodiments. The embodiments are equally related to the overall inventive subject matter, which is only exemplary and does not limit the general inventive concept.

The figures show:

figure 1 shows a schematic block diagram of an internal combustion engine with an associated exhaust gas aftertreatment device according to an embodiment of the invention,

figure 2 shows a schematic block diagram of a variant of an exhaust gas aftertreatment device according to another embodiment of the invention,

fig. 3 shows a schematic block diagram of a further variant of an exhaust gas aftertreatment device according to a further embodiment of the invention.

Detailed Description

In the embodiment shown in fig. 1, a diesel engine is used as the internal combustion engine 1. Combustion air is supplied to the internal combustion engine 1 via the intake air line 3. An exhaust gas aftertreatment device 2 is associated with the internal combustion engine 1, which exhaust gas aftertreatment device has an oxidation catalyst 5, a particle filter 6, a nitrogen oxide storage catalyst 7 and an SCR catalyst 8 in an exhaust gas line 4. In the present case, on the one hand, the particle filter 6 is connected directly downstream of the oxidation catalytic converter 5, and on the other hand, the SCR catalytic converter 8 is connected directly downstream of the nitrogen oxide storage catalytic converter 7. The temperature of the nitrogen oxide storage catalyst 7 is measured by means of a sensor 15. Upstream of the oxidation catalytic converter 5, an exhaust gas turbocharger 12 is installed in the exhaust gas line 4 for compressing the combustion air, which after compression is cooled by a charge air cooler 14 arranged in the intake air line 3. Furthermore, a control unit 9 is associated with the internal combustion engine 1, which control unit is also used to control the combustion. In order to transmit the control signals necessary for this, a control or signal line 10 is present. Other components for measuring and controlling operating parameters, such as oxygen probes, temperature sensors, throttle valves, other signal lines, etc., are not shown in the figures for the sake of overview.

The internal combustion engine 1 is initially operated lean. The particulates contained in the exhaust gas are intercepted in the particulate filter 6. As the exhaust gas passes through the oxidation catalytic converter 5, NO contained in the exhaust gas is oxidized to NO2 and can subsequently oxidize the carbonaceous particles accumulated there in the downstream connected particulate filter 6, as a result of which a continuous regeneration of the particulate filter 6 takes place. The exhaust gas flowing out of the particle filter, which additionally contains nitrogen oxides, is fed to a nitrogen oxide storage catalytic converter 7, which catalytic converter 7 extracts nitrogen oxides from the exhaust gas by storage, currently as nitrate storage. Depending on the amount of stored nitrogen oxides, nitrate regeneration of the storage catalyst 7 is sometimes performed. For this purpose, the internal combustion engine 1 is switched to a rich operation in a short time, thereby generating a rich exhaust gas which has an excess of reducing agent, such as carbon monoxide, hydrogen or hydrocarbons. This causes the release of nitrogen oxides stored in the nitrogen oxide storage catalyst 7, which are reduced by the reducing agent of the exhaust gas at the centers of the precious metals present in the catalytic layer of the nitrogen oxide storage catalyst 7. The temperature of the nox storage catalyst 7 is determined by means of the sensor 15, since the nitrate regeneration is only carried out if the temperature of the nox storage catalyst 7 exceeds a temperature limit value. According to the invention, the temperature limit value for the nitrate regeneration is variably determined taking into account the state of the SCR catalyst 8.

The combustion air ratio is also synonymously referred to herein as the air-fuel ratio, abbreviated as λ. In the case of gasoline engines, the control, also referred to as lambda control, is therefore carried out by direct intervention of the injected fuel quantity, which is not usual in diesel engines, since in diesel engines the engine torque is controlled via a change in the fuel quantity. Instead, lambda regulation in diesel engines takes place via an air system by adjusting the exhaust gas recirculation rate via the exhaust gas recirculation device 11.

Nitrogen gas is mainly produced as a reduction product of the reduction of nitrogen oxide. Additionally, depending on the conditions under which the nitrate regeneration is carried out, a greater or lesser amount of the reduction product ammonia (NH3) is also formed, the release of which into the environment is undesirable. By means of the SCR catalyst 8 according to the invention, which is arranged downstream of the nitrogen oxide storage catalyst 7, ammonia is trapped by the storage. The stored NH3 is supplied as an additional reducing agent to the selective nitrogen oxide reduction in the SCR catalytic converter 8 during lean internal combustion engine operation following nitrate regeneration. The efficiency of the nitrogen oxide removal in the exhaust gas aftertreatment device 2 is thereby additionally increased in an advantageous manner.

The temperature limit value for the nitrate regeneration during the nitrate regeneration (LNT NOx regeneration) is preferably determined by means of a function which takes into account the current SCR efficiency and/or the current SCR temperature and/or the current SCR-NH3 filling level and/or the thermal life of the SCR catalyst.

The lower temperature turn-on for LNT NOx regeneration is f (current SCR efficiency and/or current SCR temperature and/or current SCR-NH3 fill and/or thermal life of the SCR).

Preferably, the temperature limit is lowered in case the efficiency of the nitrogen oxide conversion of the SCR catalyst 8 is high. With a low temperature start for the nitrate regeneration, the nitrogen oxide storage catalyst 7 is advantageously already regenerated at a lower temperature. Otherwise the nitrogen oxide storage catalyst 7 must first be heated, or regeneration must be delayed until the nitrogen oxide storage catalyst 7 has reached a sufficiently high temperature. In contrast, especially in the case of a low efficiency of the NOx conversion of the SCR catalyst 8, the temperature limit value is increased to a typical value from which the NOx reduction is sufficiently high during the regeneration of the NOx storage catalyst 7.

When using sulfur-containing fuels, the exhaust gases of the internal combustion engine 1 contain sulfur dioxide, which is absorbed by the catalyst material of the nitrogen oxide storage catalyst 7 to form stable sulfates, which over time reduce its nitrogen oxide storage capacity more and more. The nitrogen oxide storage catalyst 7 thus repeatedly removes the accumulated sulfur during the desulfurization, i.e., regenerates. For this purpose, the internal combustion engine 1 is operated in the desulfurization operation mode. The desulfurization operation mode includes causing the exhaust gas temperature to increase to over 500 c, for example, by fuel reinjection and setting the reducing exhaust gas component to a value of about 0.95 or less for the air-fuel ratio (λ), similar to that for the purpose of nitrate regeneration. Under these conditions: the relatively stable sulfates are reductively decomposed in the nitrogen oxide storage catalyst 7. Depending on the temperature, the magnitude of the concentration increase and the amount of sulfur stored in the nitrogen oxide storage catalyst 7, a greater or lesser amount of hydrogen sulfide is produced (H2S). However, this hydrogen sulfide H2S is converted into sulfur dioxide with a lower odor (SO2) under the reducing conditions of desulfurization at the SCR catalyst 8, which is arranged downstream of the nitrogen oxide storage catalyst 7 according to the invention. This avoids the odor problems normally associated with the desulfurization of nitrogen oxide storage catalysts, which is also referred to herein as desulfurating. A particular advantage of using the SCR catalyst 8 downstream of the nitrogen oxide storage catalyst 7 for the purpose of converting H2S to SO2 under reducing conditions is that the process control of the desulfation can thereby be simplified, since it is not necessary for the process control to achieve a minimization of the undesirable desulfation product H2S. For example, the desulfates can be significantly shortened by a stronger enrichment with a lambda value of less than 0.95 and a stronger and faster H2S release from the nox storage catalyst 7 associated therewith.

The feasibility of using the SCR catalyst 8 downstream of the nox storage catalyst 7 for converting H2S into SO2 under reducing conditions is independent of the presence of cleaning components connected upstream, such as the particle filter 6 and the oxidation catalyst 5.

Fig. 2 and 3 show a variant of an exhaust gas aftertreatment device 2, which is typically used with an internal combustion engine according to the invention. Reference is made to fig. 1 with regard to an embodiment of elements of the internal combustion engine which are not shown.

Fig. 2 shows a schematic block diagram of a variant of an exhaust gas aftertreatment device 2, in which a nitrogen oxide storage catalytic converter 7 and an SCR catalytic converter 8 with a first combination of filters 6 are arranged in succession in the flow direction of the exhaust gas. The reference numeral 6+8 denotes a so-called SCRF (Selective Catalytic Reduction/filtration), in which the SCR coating on the particle Filter is functionally integrated and which, for the purposes of the present invention, belongs to the SCR Catalytic converter. A second SCR catalyst 8 can optionally also be arranged downstream. An inlet line for the aqueous urea solution 16 is provided upstream of the SCRF6+8 and upstream of the SCR catalyst 8, respectively. The second supply line for the downstream aqueous urea solution 16 and the second SCR catalyst are optional. The temperature of the nox storage catalyst 7 is determined by means of a sensor (15, see fig. 1), since the nitrate regeneration is only carried out if the temperature of the nox storage catalyst 7 exceeds a temperature limit value. According to the invention, the temperature limit value for the nitrate regeneration is variably determined taking into account the state of the SCR catalyst 8.

Fig. 3 shows a schematic block diagram of a further variant of an exhaust gas aftertreatment device 2, in which a nitrogen oxide storage catalytic converter 7, a particle filter 6 and an SCR catalytic converter 8 are arranged in succession in the flow direction of the exhaust gas. Upstream of the SCR catalytic converter 8, a feed line 16 for the aqueous urea solution is provided. The temperature of the nox storage catalyst 7 is determined by means of a sensor (15, see fig. 1), since the nitrate regeneration is only carried out if the temperature of the nox storage catalyst 7 exceeds a temperature limit value. According to the invention, the temperature limit value for the nitrate regeneration is variably determined taking into account the state of the SCR catalyst 8.

List of reference numerals

1 internal combustion engine

2 exhaust gas aftertreatment device

3 suction air line

4 waste gas line

5 Oxidation catalyst

6 particulate filter

7 nitric oxide storage catalyst

8 SCR catalyst converter

9 control unit

10 signal line

11 exhaust gas return device

12 exhaust gas turbocharger

14 charge air cooler

15 sensor

16 water-urea solution leading-in pipeline

Arrow A, flow direction

Claims

1. Method for operating an exhaust gas aftertreatment device of an internal combustion engine, comprising a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7),

wherein nitrogen oxides and sulfur oxides are extracted and stored from the exhaust gas of the internal combustion engine in the nitrogen oxide storage catalyst (7) in the case of an oxidizing composition of the exhaust gas,

wherein nitrate regeneration of the nitrogen oxide storage catalyst (7) is performed by setting the reducing component of the exhaust gas,

wherein the temperature of the nitrogen oxide storage catalyst is determined and nitrate regeneration is performed only if the temperature of the nitrogen oxide storage catalyst exceeds a temperature limit value,

wherein a temperature limit value for the nitrate regeneration is determined taking into account the state of the SCR catalyst (8).

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

evaluating the state on the basis of one or more of the following characteristics of the SCR catalyst (8): efficiency of nitrogen oxide conversion, thermal life, temperature, ammonia fill level.

3. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the temperature limit value is reduced when the efficiency of the SCR catalyst (8) for converting nitrogen oxides is high.

4. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the temperature limit value is increased when the thermal life of the SCR catalyst (8) is high.

5. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

in the case of a higher temperature of the SCR catalyst (8), the temperature limit value is reduced.

6. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the temperature limit value is reduced when the ammonia filling degree in the SCR catalyst (8) is high.

7. A control unit (9) for an internal combustion engine (1) having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7), wherein the control unit (9) is designed to perform a nitrate regeneration of the nitrogen oxide storage catalyst (7) at times in such a way that the internal combustion engine (1) generates exhaust gas with a reducing composition during the nitrate regeneration, wherein a sensor (15) is provided in order to determine a temperature of the nitrogen oxide storage catalyst (7), and wherein the control unit (9) is designed to perform a nitrate regeneration only when the temperature of the nitrogen oxide storage catalyst exceeds a temperature limit value, wherein the control unit (9) is also designed to determine a temperature limit value for the nitrate regeneration taking into account the state of the SCR catalyst (8).

8. The control unit of claim 7, wherein,

it is characterized in that the preparation method is characterized in that,

the state is characterized by one or more of the following characteristics of the SCR catalyst (8): efficiency of nitrogen oxide conversion, thermal life, temperature, ammonia fill level.

9. The control unit of claim 7 or 8,

it is characterized in that the preparation method is characterized in that,

the control unit (9) is designed to carry out the method according to any one of claims 1 to 6.

10. An internal combustion engine (1) having an exhaust gas aftertreatment device, wherein the exhaust gas aftertreatment device has a nitrogen oxide storage catalyst (7) and at least one SCR catalyst (8) arranged downstream of the nitrogen oxide storage catalyst (7), wherein a control unit (9) according to one of claims 7 to 9 is also provided.