DE102019100384A1 - Exhaust gas aftertreatment system and method for exhaust gas aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine (10). The internal combustion engine (10) has at least one combustion chamber (12) and its outlet (16) can be connected to an exhaust system (20). At least one SCR catalytic converter (26, 30) is arranged in the exhaust system (20), which is preceded by a metering element (32) for metering in a reducing agent for the selective, catalytic reduction of nitrogen oxides. It is provided that an exhaust gas flow from the internal combustion engine is passed at least in part through an exhaust gas cooler (46) in order to cool the exhaust gas flow before entering the SCR catalytic converter (26, 30) and thus thermal decomposition of ammonia or increased discharge of ammonia from the SCR catalytic converter (26, 30). The invention further relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with such an exhaust gas aftertreatment system, wherein the exhaust gas of the internal combustion engine (10) is cooled if thermal decomposition or increased discharge of ammonia from the SCR catalytic converter (26, 30) is to be expected. Exhaust aftertreatment system for performing such a method.

Description

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine and an exhaust gas aftertreatment system for carrying out such a method according to the preamble of the independent patent claim.

The current exhaust gas legislation, which will become increasingly stringent in the future, places high demands on raw engine emissions and exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for the engine developers. In gasoline engines, exhaust gas cleaning takes place in a known manner using a three-way catalytic converter and the three-way Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for the separation of soot particles and, if appropriate, further catalytic converters. Ammonia is preferably used as the reducing agent. Because the use of pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas stream in a mixing device upstream of the SCR catalytic converter. This mixing heats the aqueous urea solution, the aqueous urea solution releasing ammonia in the exhaust duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

From the DE 195 29 835 A1 a gasoline engine with an exhaust gas aftertreatment system is known. An SCR catalytic converter is arranged upstream of a three-way catalytic converter in the exhaust system, a bypass being provided for the SCR catalytic converter in which a starting catalytic converter is arranged. The catalytic converter in the bypass allows a catalytic converter to be heated to its operating temperature immediately after a cold start, in order to enable efficient exhaust gas aftertreatment of the gasoline engine shortly after the cold start. During further operation, the SCR catalytic converter converts the nitrogen oxides particularly efficiently if the gasoline engine is operated in a lean mode and there is therefore no reducing agent for reducing the nitrogen oxides through the three-way catalytic converter.

From the DE 10 2005 015 479 A1 an internal combustion engine is known, which is designed as a self-igniting diesel engine. An oxidation catalytic converter is arranged in the exhaust gas system in the direction of flow of an exhaust gas through the exhaust gas system, a particle filter downstream of the oxidation catalytic converter and an SCR catalytic converter further downstream. In order to prevent the SCR catalytic converter from overheating and to prevent the nitrogen oxides retained in the SCR catalytic converter from thermally dissipating, a bypass is provided for the SCR catalytic converter in order to prevent particularly hot exhaust gas, in particular during regeneration of the particle filter, Guide catalyst over. Alternatively, a cooling air system is provided with which the SCR catalytic converter is cooled externally in order to prevent thermal dissipation of the nitrogen oxides.

The EP 2 055 909 A1 discloses an internal combustion engine with an exhaust system. The internal combustion engine is designed as a gasoline engine, which can be operated in a stratified charge mode with an over-stoichiometric combustion air ratio. An SCR catalytic converter is arranged upstream of a three-way catalytic converter in the exhaust system. A bypass is provided for the SCR catalytic converter. In stratified charge mode, the exhaust gas is passed through the SCR catalytic converter. At a stoichiometric operating point of the internal combustion engine, the exhaust gas is passed through the bypass, the nitrogen oxides being reduced by the three-way catalytic converter.

The invention is based on the object of preventing the discharge of ammonia from the SCR catalytic converter in an exhaust gas aftertreatment system with an SCR catalytic converter and thus being able to use the complete catalytic converter volume for converting nitrogen oxides.

According to the invention, this object is achieved by an exhaust gas aftertreatment system for an internal combustion engine, the outlet of which can be connected to an exhaust gas system, wherein at least one SCR catalytic converter is arranged in the exhaust gas system downstream of a turbine of an exhaust gas turbocharger. The exhaust system includes a metering element with which a reducing agent can be metered upstream of the SCR catalytic converter into an exhaust duct of the exhaust system. It is provided that an exhaust gas cooler is arranged in the exhaust system, with which an exhaust gas flow of the internal combustion engine can be cooled before it enters the SCR catalytic converter. An exhaust gas aftertreatment system according to the invention makes it possible to fully load the SCR catalytic converter with ammonia and to avoid an increase in tailpipe emissions. A discharge of ammonia from the SCR catalytic converter is completely avoided by cooling the exhaust gas flow guide of the internal combustion engine.

The features listed in the dependent claims enable advantageous improvements and non-trivial further developments of the exhaust gas aftertreatment system listed in the independent claim.

In a preferred embodiment of the invention, it is provided that the exhaust duct branches downstream of the turbine and upstream of the SCR catalytic converter into a main duct and a bypass, the exhaust gas cooler being arranged in the bypass. As a result, depending on the operating situation of the internal combustion engine, the exhaust gas temperature and the temperature of the exhaust gas aftertreatment components, the exhaust gas flow can optionally be passed through the main duct or the bypass. There is thus the option of optionally switching the cooling of the exhaust gas flow on or off, or passing a partial flow of the exhaust gas through the exhaust gas cooler in order to operate the SCR catalytic converter at a temperature at which the most efficient conversion of nitrogen oxides can be expected.

In a preferred embodiment of the exhaust gas aftertreatment system, it is provided that the bypass upstream of the SCR catalytic converter re-opens into the main duct of the exhaust system. With the help of a calculated or measured exhaust gas temperature, a model can be created to ensure optimal operation of the SCR system with high efficiencies with regard to the selective, catalytic reduction of nitrogen oxides. In addition, an exhaust gas cooler upstream of the metering element offers the possibility of cooling the metering element and the mixing section. In this way, premature thermal decomposition of the metered reducing agent, in particular the ammonia obtained therefrom, can be avoided.

In an alternative embodiment of the exhaust gas aftertreatment system, it is provided that the bypass opens into the main duct of the exhaust system downstream of the SCR catalytic converter and upstream of a blocking catalytic converter, in particular another SCR catalytic converter. High exhaust gas temperatures can lead to ammonia being discharged from the SCR catalytic converter. The exhaust gas cooler in the bypass can be used to set an optimum temperature for high efficiencies of the blocking catalytic converter using a temperature sensor or a model for determining the exhaust gas temperature. An additional blocking catalytic converter makes it particularly easy to load the SCR catalytic converter up to its storage limit. Excess ammonia is stored in the second SCR catalytic converter and can be used there for selective, catalytic reduction of nitrogen oxides. At the same time, the amount of reducing agent metered in is reduced in order to be able to adapt the amount of reducing agent introduced to the ammonia requirement required for the selective, catalytic reduction of nitrogen oxides. Alternatively, the blocking catalytic converter can also be designed as an oxidation catalytic converter. This enables additional oxidation of unburned hydrocarbons or carbon monoxide. It is particularly preferred if the blocking catalytic converter is designed as a further SCR catalytic converter.

In a preferred embodiment of the exhaust gas aftertreatment system it is provided that a control element, in particular an electrically switchable exhaust gas flap, is arranged at the junction of the main duct and the bypass, at the junction of the bypass into the main duct or in the bypass. An electrical exhaust flap allows the exhaust gas flow of the internal combustion engine to be divided into the exhaust duct and the bypass in a simple and reliable manner. Furthermore, the flow velocity of the exhaust gas through the SCR catalytic converter can be reduced by means of the exhaust gas flap in order to increase the conversion line of the SCR catalytic converter and / or to avoid the discharge of ammonia.

In a preferred embodiment of the method it is provided that the flow rate through the SCR catalytic converter is reduced in order to prevent ammonia discharge from the SCR catalytic converter and to increase the residence time of the exhaust gas when it flows through the SCR catalytic converter. A reduced flow rate increases the duration of the exhaust gas in the SCR catalytic converter, which increases the conversion rate of the nitrogen oxide emissions.

In a further improvement of the invention it is provided that an exhaust gas mixer is arranged in the exhaust gas duct downstream of the metering element and upstream of the SCR catalytic converter. An exhaust gas mixer can achieve a homogeneous distribution of the reducing agent in the exhaust gas stream before it enters the SCR catalytic converter. The length of the mixing section can be shortened by the exhaust gas mixer in order to achieve such a homogeneous distribution. As a result, the SCR catalytic converter can be arranged closer to the outlet of the internal combustion engine, which promotes heating of the SCR catalytic converter after a cold start of the internal combustion engine.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that the exhaust gas cooler comprises a heat exchanger, the heat exchanger being connected to a coolant circuit of the internal combustion engine. A water-cooled exhaust gas cooler enables particularly efficient cooling of the exhaust gas flow can be achieved. A correspondingly high cooling capacity for the exhaust gas flow can be achieved even at high loads and low speed, for example when driving uphill.

Alternatively, it is advantageously provided that the exhaust gas cooler comprises a heat exchanger, wherein the exhaust gas is cooled in the heat exchanger by means of a gaseous cooling medium, in particular by means of the headwind of a motor vehicle in which the exhaust gas aftertreatment system is installed. An exhaust gas cooler, which cools the exhaust gas with the wind of the motor vehicle, enables a particularly simple and inexpensive solution for an exhaust gas cooler. The cooling power increases with the speed of the motor vehicle, which has the desired effect of implementing particularly efficient cooling of the exhaust gas flow with high engine power and the resulting high speed.

In a preferred embodiment of the invention it is provided that a temperature sensor or an exhaust gas sensor is arranged in the exhaust system. The temperature sensor is preferably arranged immediately upstream of the metering element in order to measure the exhaust gas temperature and to compare the measured exhaust gas temperature with a threshold value above which thermal decomposition of the ammonia obtained from the reducing agent is to be avoided. Alternatively, it is advantageously provided that the temperature sensor is arranged immediately before entering the SCR catalytic converter in order to estimate the conversion performance of the SCR catalytic converter and to avoid the risk of ammonia breakthrough by the SCR catalytic converter. The concentration of the respective gas in the exhaust gas duct can be determined by an exhaust gas sensor, in particular a NOx sensor or an ammonia sensor. The exhaust gas sensor is preferably arranged immediately downstream of the SCR catalytic converter in order to be able to detect a NOx or ammonia breakthrough through the SCR catalytic converter.

• - Ermitteln einer Abgastemperatur in der Abgasanlage des Verbrennungsmotors,
• - Leiten zumindest einer Teilmenge des Abgasstroms des Verbrennungsmotors durch den Abgaskühler, wenn die Abgastemperatur eine Schwellentemperatur, insbesondere eine Temperatur von 530°C, bevorzugt von 500°C, besonders bevorzugt von 450°C, überschritten hat, ab welcher eine thermische Zersetzung von Ammoniak oder ein erhöhter Austrag von Ammoniak aus dem SCR-Katalysator zu erwarten ist.

Durch ein erfindungsgemäßes Verfahren können die Stickoxid-Emissionen eines Kraftfahrzeuges reduziert werden, da die Konvertierungsleistung des SCR-Katalysators bei hohen Abgastemperaturen verbessert wird. Ferner kann der Füllstand des SCR-Katalysators bedarfsweise reduziert werden, sobald die Gefahr von zu hohen Abgastemperaturen droht, um einen Anstieg von Ammoniakemissionen zu verhindern.According to the invention, a method for exhaust gas aftertreatment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention is proposed, which comprises the following steps:

• Determining an exhaust gas temperature in the exhaust system of the internal combustion engine,
• - Passing at least a portion of the exhaust gas flow of the internal combustion engine through the exhaust gas cooler when the exhaust gas temperature has exceeded a threshold temperature, in particular a temperature of 530 ° C, preferably 500 ° C, particularly preferably 450 ° C, above which a thermal decomposition of ammonia or an increased discharge of ammonia from the SCR catalytic converter is to be expected.

The method according to the invention can reduce the nitrogen oxide emissions of a motor vehicle, since the conversion performance of the SCR catalytic converter is improved at high exhaust gas temperatures. Furthermore, the fill level of the SCR catalytic converter can be reduced if necessary as soon as there is a risk of excessive exhaust gas temperatures in order to prevent an increase in ammonia emissions.

In a further improvement of the method, it is provided that an ammonia concentration and / or a nitrogen oxide concentration is determined in the exhaust system downstream of the first SCR catalytic converter, the partial amount of the exhaust gas flow which is caused by an increase in the ammonia or nitrogen oxide concentration determined the exhaust gas cooler is directed, is increased. As a result, the amount of exhaust gas flow which is passed through the exhaust gas cooler can be regulated in a simple manner in order to ensure the most efficient conversion of the nitrogen oxides in the exhaust gas. The temperature inertia of the long exhaust gas section complies with this regulation.

Unless otherwise stated in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 ein erstes Ausführungsbeispiel für einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem, wobei im Abgaskanal stromaufwärts eines SCR-Katalysators ein Abgaskühler vorgesehen ist;
• 2 ein zweites Ausführungsbeispiel für einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem, wobei ein Bypass für den SCR-Katalysator vorgesehen ist, wobei in dem Bypass ein Abgaskühler angeordnet ist; und
• 3 ein weiteres Ausführungsbeispiel für einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem, welches die Komponenten der beiden vorhergehenden Ausführungsbeispiele kombiniert.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components with the same function are identified in the different figures with the same reference numbers. Show it:

• 1 a first embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention, wherein an exhaust gas cooler is provided in the exhaust duct upstream of an SCR catalytic converter;
• 2nd a second embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention, wherein a bypass is provided for the SCR catalytic converter, an exhaust gas cooler being arranged in the bypass; and
• 3rd a further embodiment for an internal combustion engine with an exhaust gas aftertreatment system according to the invention, which combines the components of the two previous embodiments.

1 shows the schematic representation of an internal combustion engine 10th which with its outlet 16 with an exhaust system 20 connected is. The internal combustion engine 10th is a direct injection diesel engine in this embodiment and has several combustion chambers 12th on. At the combustion chambers 12th is a fuel injector 14 for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10th may further comprise a high-pressure exhaust gas recirculation, via which an exhaust gas of the internal combustion engine 10th from the outlet 16 to an inlet of the internal combustion engine 10th can be traced back. At the combustion chambers 12th Inlet valves and outlet valves are arranged, with which a fluid connection from the intake tract to the combustion chambers 12th or from the combustion chambers 12th to the exhaust system 20 can be opened or closed.

The exhaust system 20 includes an exhaust duct 22 , in which in the flow direction of an exhaust gas of the internal combustion engine 10th through the exhaust duct 22 a turbine 24th of an exhaust gas turbocharger 18th and downstream of the turbine 24th an SCR catalyst 26 are arranged. The exhaust gas turbocharger 18th is preferably used as an exhaust gas turbocharger 18th designed with variable turbine geometry. For this are a turbine wheel of the turbine 24th adjustable guide blades connected upstream, through which the flow of the exhaust gas onto the blades of the turbine 24th can be varied. Downstream of the turbine 24th of the exhaust gas turbocharger 18th and upstream of the SCR catalyst 26 the exhaust duct branches 22 on a branch 36 into a main channel 60 and a bypass 40 . It is at the junction 36 a control 42 in the form of an electrically switchable exhaust flap 44 provided with which the exhaust gas flow of the internal combustion engine 10th optionally through the main channel 60 through the bypass 40 or proportionately through both exhaust duct segments 40 , 60 can be directed. In the bypass 40 is an exhaust gas cooler 46 arranged, which is preferably a heat exchanger 48 comprises, which is flowed through by a gaseous or liquid cooling medium and by the exhaust gas, the heat being transferred from the exhaust gas to the cooling medium. Downstream of the exhaust gas cooler 46 is a confluence 38 provided on which the bypass 40 back into the main channel 60 of the exhaust duct 22 flows into. Downstream of the confluence 38 and upstream of the SCR catalyst 26 is a dosing element 32 arranged with which a reducing agent, in particular aqueous urea solution, in the exhaust duct 22 can be dosed. The dosing element 32 is an exhaust gas mixer 34 downstream, for better mixing of the reducing agent and the exhaust gas before entering the SCR catalytic converter 26 to reach. Ammonia is obtained from the aqueous urea solution, with which the nitrogen oxides are reduced to molecular nitrogen. Furthermore, is in the exhaust duct 22 , preferably downstream of the confluence 38 and upstream of the metering element 32 a temperature sensor 56 provided with which an exhaust gas temperature T _{EG of} the internal combustion engine 10th can be recorded. The internal combustion engine 10th is with an engine control unit 70 connected, via which the fuel is injected into the combustion chambers 12th of the internal combustion engine 10th , the metering of the reducing agent into the exhaust duct 22 as well as the position of the control element 42 being controlled. In this embodiment, the exhaust gas flow through the exhaust gas cooler 46 in the bypass 40 using the control 42 set to discharge ammonia from the SCR catalyst 26 is avoided. In addition, the in 1 arrangement shown the possibility of the metering element 32 and the mixing section between the metering element 32 and entry into the SCR catalyst 26 to cool. In this way, premature thermal decomposition of the ammonia obtained from the metered-in reducing agent can be prevented.

In 2nd is an alternative embodiment for an internal combustion engine 10th with an exhaust system 20 shown. The exhaust system differs 20 downstream of the turbine 24th of the exhaust gas turbocharger 18th from that in 1 illustrated embodiment. Downstream of the turbine 24th of the exhaust gas turbocharger 18th and upstream of the SCR catalyst 26 the exhaust duct branches 22 on a branch 36 into a main channel 60 and a bypass 40 . Here is the SCR catalytic converter 26 in the main channel 60 of the exhaust duct 22 arranged. Downstream of the turbine 24th and upstream of a branch 36 from the main channel 60 and the bypass 40 is a dosing element 32 provided which an exhaust gas mixer 34 is connected downstream for better mixing of the reducing agent and the exhaust gas before entering the SCR catalytic converter 26 to reach. In the bypass 40 are an exhaust flap 44 as a control 42 and downstream of the exhaust flap 44 an exhaust gas cooler 46 arranged. The bypass 40 ends at a junction 38 downstream of the SCR catalyst 26 and upstream of a second SCR catalyst 30th , which is also used as a blocking catalyst 28 regarding that from the first SCR catalyst 26 released ammonia serves again in the main channel 60 of the exhaust duct 22 a. Downstream of the confluence 38 and upstream of the second SCR catalyst 30th is a temperature sensor 56 arranged to determine an exhaust gas temperature in the exhaust system. Downstream of the first SCR catalytic converter 26 and upstream of the second SCR catalyst 30th is an exhaust gas sensor 58 provided with which the nitrogen oxide concentration and / or the ammonia concentration downstream of the first SCR catalyst can be determined. Because high Exhaust gas temperatures to discharge ammonia from the first SCR catalytic converter 26 In this embodiment variant, hot exhaust gas can lead to the first SCR catalytic converter 26 be passed and is through the exhaust gas cooler 46 in the bypass 40 cooled down. With the help of the exhaust gas cooler and the metering of the reducing agent through the metering element 32 an exhaust gas temperature can be adjusted at which an optimal conversion of nitrogen oxides by the second SCR catalytic converter 30th can be done.

In 3rd Another embodiment of an exhaust gas aftertreatment system according to the invention is shown. The combined in 3rd illustrated embodiment the advantages of in 1 and 2nd presented exhaust aftertreatment systems. At essentially how to 1 in this exemplary embodiment, the construction is downstream of the metering element 32 and upstream of the SCR catalyst 60 another branch 50 provided on which a second bypass 52 from the main channel 60 of the exhaust duct 22 branches. Here is the SCR catalytic converter 26 in the main channel 60 arranged. In the second bypass 52 are a second control 62 in the form of a second exhaust flap 64 and a second exhaust gas cooler 66 , which is preferably also used as a heat exchanger 68 is arranged. Downstream of the first SCR catalytic converter 26 is a second SCR catalytic converter 30th as a blocking catalyst 28 intended. The second bypass 52 flows into a second junction 54 downstream of the first SCR catalytic converter 26 and upstream of the second SCR catalyst 30th back into the main channel 60 of the exhaust duct 22 . Through the second bypass 52 it is possible to reduce the exhaust gas flow of the internal combustion engine 10th on the first SCR catalytic converter 26 pass and cool again when the cooling capacity of the first exhaust gas cooler 46 is not sufficient to meet the requested temperature level for the first SCR catalytic converter 26 to reach. In this case, the nitrogen oxide can be converted by the second SCR catalytic converter 30th respectively. Furthermore, it is possible to divide the exhaust gas flow in order to achieve the catalyst volume of both SCR catalysts in the case of large exhaust gas volumes 26 , 30th to use and thus improve the performance of the SCR system with regard to the conversion of nitrogen oxides into molecular nitrogen. Furthermore, ammonia breakthroughs through the first SCR catalytic converter can also occur in this embodiment variant 26 are collected, with the ammonia in the second SCR catalyst 30th is recorded and is available there for the selective, catalytic reduction of nitrogen oxides.

Reference list

10th

Internal combustion engine

12th

Combustion chamber

14

Fuel injector

16

Outlet

18th

Exhaust gas turbocharger

20

Exhaust system

22

Exhaust duct

24th

turbine

26

first SCR catalytic converter

28

Blocking catalyst

30th

second SCR catalytic converter

32

Dosing element

34

Exhaust mixer

36

first branch

38

first junction

40

first bypass

42

Control

44

Exhaust flap

46

Exhaust gas cooler

48

Heat exchanger

50

second branch

52

second bypass

54

second junction

56

Temperature sensor

58

Exhaust gas sensor

60

Main channel

62

second control

64

second exhaust flap

66

second exhaust gas cooler

68

second heat exchanger

70

Engine control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 19529835 A1 [0003]
• DE 102005015479 A1 [0004]
• EP 2055909 A1 [0005]

Claims (10)

Exhaust gas aftertreatment system for an internal combustion engine (10), the outlet (16) of which can be connected to an exhaust gas system (20), with at least one SCR catalytic converter (26, 30), the exhaust system (20) comprising a metering element (32) with which a reducing agent can be metered upstream of the SCR catalytic converter (26, 30) into the exhaust duct (22), characterized in that in the exhaust system (20 ) an exhaust gas cooler (46) is arranged, with which an exhaust gas flow of the internal combustion engine (10) can be cooled before entering the SCR catalytic converter (26, 30). Exhaust aftertreatment system after Claim 1 , characterized in that the exhaust duct (22) branches downstream of the turbine (24) and upstream of the SCR catalytic converter (26) into a main duct (60) and a bypass (40), the exhaust gas cooler (46) in the bypass ( 40) is arranged. Exhaust aftertreatment system after Claim 2 , characterized in that the bypass (40) upstream of the SCR catalytic converter (26, 30) re-opens into the main channel (60). Exhaust aftertreatment system after Claim 2 , characterized in that the SCR catalytic converter (26) is arranged in the main channel (60), the bypass (40) downstream of the SCR catalytic converter (26) and upstream of a blocking catalytic converter (28, 30) back into the main channel (60 ) flows into. Exhaust aftertreatment system after Claim 4 , characterized in that the blocking catalytic converter (28) is a further SCR catalytic converter (30). Exhaust aftertreatment system according to one of the Claims 1 to 5 , characterized in that the exhaust gas cooler (46) is a heat exchanger (48), the heat exchanger (48) being connected to a coolant circuit of the internal combustion engine (10). Exhaust aftertreatment system according to one of the Claims 1 to 5 , characterized in that the exhaust gas cooler (46) is a heat exchanger (48), the cooling of the exhaust gas in the heat exchanger (48) being carried out by means of a gaseous cooling medium. Exhaust aftertreatment system according to one of the Claims 1 to 7 , characterized in that a temperature sensor (56) or an exhaust gas sensor (58) is arranged in the exhaust system (20). Method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust gas aftertreatment system according to one of the Claims 1 to 8th , comprising the following steps: - determining an exhaust gas temperature (T _EG ) in the exhaust system (20) of the internal combustion engine (10), - passing at least a portion of the exhaust gas flow of the internal combustion engine (10) through the exhaust gas cooler (46) when the exhaust gas temperature (T _EG ) exceeds a threshold temperature (T _S ), above which thermal decomposition of ammonia or increased discharge of ammonia from the SCR catalytic converter (26, 30) can be expected. Exhaust gas aftertreatment process after Claim 9 , characterized in that an ammonia concentration and / or a nitrogen oxide concentration is determined in the exhaust system (20) downstream of the first SCR catalytic converter (26), the partial amount which is increased by the exhaust gas cooler () when the ammonia or nitrogen oxide concentration ( 46) is directed, is increased.

Images